Fabric ............................................................................................................................................................................................................................................................Texture

Textura / Textura / Textur, Struktur / 质地, 布 / Текстура (структура) / Trama, Tessuto /

Pattern (organization) or absence of pattern of crystals or grains that form a rock. Genetically, there are two types of texture: (i) Primary or Depositional and (ii) Secondary or Postdepositional (deformation).

See: « Facies »
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« Granulometry »
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« Lithification »

Most of the texture (fabric) of a rock that it be igneous (as in this figure, representing the evolution of the texture of a granite slightly deformed into a milonite) or sedimentary, is mainly function of three parameters: (i) Shape and contours of the grains that constitute it ; (ii) Relative sizes of grains and (iii) Spatial relationships between grains. The texture of a sedimentary rock controls the porosity and permeability, i.e., it controls the possibility of the rock containing and being able to transmit fluids. The orientation or absence of orientation of the crystals or grains forming a sedimentary rock is one of the important parameters of the texture. Genetically, the texture may be contemporaneous with deposition (primary) or posterior to the deposition (secondary). Examples of the first type are frequent in certain fluvial and turbiditic deposits in which the elongated particles are oriented parallel to the flow. As an example of secondary textures, in a sedimentary rock, we can mention the rotation of certain grains produced by the effective stresses (σ₁, σ₂, σ₃) or due to the growth of new elements during the diagenesis. The texture of coarse clastic sedimentary rocks such as conglomerates can be determined by measuring and projecting the dimensions (axes) of the grains. In clayey rocks, the texture can be determined by studying the orientation of clay minerals and micas. In addition, to the orientation of the grains, another important parameter of the texture of the sedimentary rocks is the packing, i.e., the distribution of the grains and intergranular spaces, whether these spaces are empty or filled by cement or a fine matrix. It can be said the compaction of a sedimentary rock, which determines the apparent density (density of the total fraction), is controlled by the size, shape and packaging of the sedimentary grains. The description of the packaging is, generally, based on the microscopic study of the thin sections.

Facies..................................................................................................................................................................................................................................................................................................Faciès

Fàcies / Facies / Fazies / 相 / Фации / Facies /

Term used by Gressly, in 1838, to express a lithology and the associated fauna. This term has lost much of its original meaning. Frequently, certain geoscientists, particularly American geoscientists use the term facies to express the shape, appearance, and deposit conditions, that is, more or less, synonymous with sedimentary environment. For intsnace, they say, "an interval of deltaic facies sand," while a European geoscientist says "a sand facies interval from a deltaic environment" (see Facies vs. Sedimentary Environment).

See: « Sedimentary Environment »
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« Sedimentary Facies »
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« Lithostratigraphy »

One facies, as illustrated in this figure, corresponds to a restricted part of a lithostratigraphic unit. It can be mapped. It differs from the other parts, deposited at the same time, in continuity of sedimentation, by the lithology and fossils and, sometimes, by the depositional environment. The texture, composition and structural characteristics of a sedimentary deposit result mainly from the accumulation and modification of a particular environment. The concept of facies refers to the sum of the characteristics (usually on a small scale, centimeters or meter) of a sedimentary unit, i.e.: (i) Lithology ; (ii) Granulometry ; (iii) Sedimentary structures ; (iv) Colour ; (v) Composition; (vi) Biogenic content, etc. The lithofacies concern the physical and chemical characteristics, whereas the biofacies refers to the content of macrofossils and ichnofacies*, which are the work of live organisms in the form of: 1) Traces stricto sensu ; 2) Tracks ; 3) Trails ; 4) Burrows ; 5) Holes, etc). For most American geoscientists, facies analysis is the interpretation of the strata in terms of depositional environments (or depositional systems) on the basis of a certain number of observations. Facies associations form several facies that occur in combination and typically represent a depositional environment (note that many individual facies are characteristic of a particular context). Facies successions (or sequence of facies) are associations of facies with a characteristic vertical order. Walther's law** says different facies, laterally synchronous, overlap, vertically, each other without unconformity (erosional surface) between them. As illustrated, a lateral succession of facies as: sand (Facies I), shales (Facies II) and carbonates (Facies III), in continuity of sedimentation, is also recognized vertically (carbonates, clay, sand) as facies prograde seaward. In the same way, when on a seismic line, a geoscientists recognize, in continuity of sedimentation (absence of unconformities, i.e., erosional surfaces and significant hiatus): (i) Sub-horizontal reflectors (platform sediments) ; (ii) Inclined reflectors dipping seaward sea (continental slope sediments) and (iii) sub-horizontal reflectors downstream of the inclined reflectors (abyssal plain sediments) an inverted succession (ii), (ii) and (i) is found vertically. it fact, it can be said each chronostratigraphic line consists of three segments : horizontal shallow, dipping seaward and horizontal deep. The inverted succession: horizontal shallow, dipping seaward and horizontal deep, is find, vertically, as the chronostratigraphic lines prograde seaward. An interval with a subhorizontal interval configuration correspond to deep-water sediments if it is downdip and in continuity of sedimentation of an interval with an oblique internal configuration. Otherwise, if the interval with a sub-horizontal internal configuration is updip of an interval with an oblique internal configuration dipping seaward, the interval with a sub-horizontal internal configuration correspond, likely, to platform sediments. So, geoscientists, have all interest to start the tentative geological interpretation of the seismic lines by locating, on the seismic lines, the reflectors associated with the continental slopes. This approach is, relatively, more difficult in the carbonate environments but sometimes the results are excellent as illustrated in the outcrop of the Canning cratonic basin (Australia) illustrated in this figure. In fact, since a geoscientist recognizes, in the field or on a seismic line, front slope sediments of the reef (sediments inclined seaward, mainly, micro-breccias or packstones with bioclastic lithoclasts), he deduces that upstream reef construction (boundstones and grainstones with embedded bioclasts) will be find with mounded geometry and that upstream of these the sub-horizontal sediments of the internal carbonate platform (grainstones with foraminifera, packstones / wackestones with bioclasts) will be find.

(*) Association of preserved fossil features reflecting the environmental conditions (bathymetry, hydrodynamics, substrate, etc.).

(**) For American geoscientists facies is, above all, a sedimentary environment. Walther's facies law implies a vertical sequence of facies is the product of a series of depositional environments which are, laterally, adjacent to one another and is applicable only in situations where there is no interruption of sedimentation. For most European geoscientists, Walther's law says in continuity of sedimentation, the lateral succession of depositional systems (a lithology with associated fauna deposited in a given environment) is, also, found vertically, i.e., if laterally (seaward), we find succession a, b, c, vertically, and from bottom to top, we will find c, b, a.

Facies Change...........................................................................................................................................................................Changement de faciès

Mudança de Fácies / Cambio de facies / Fazies ändern / 相变 / Фациальное изменение / Cambio di facies /

Lateral or vertical change of lithology and/or paleontological characteristics in contemporary sedimentary deposits, caused by, or reflecting, a change in the depositional environment.

See: « Sedimentary Environment »
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« Sedimentary Facies »
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" Systems Tract "

The term facies was defined by Gressly, in 1835, as a lithology with an associated fauna. A sedimentary environment is not a sedimentary facies. The former is a part of the Earth's surface physically, chemically, and biologically distinct from adjacent land. A sedimentary facies is a rock mass, which can be defined and distinguished from the others by its lithology, geometry, sedimentary structures and fossils. It is always very important to distinguish a sedimentary environment from a sedimentary facies. There is no problem in identifying a sediment environment in recent sediments. If you go to the beach and take a sample of the sand from the (shoreface), by definition, it is a shoreface sand. However, when studying ancient sediments, both in the field and on seismic data, it is preferable to begin by classifying them in facies, on a purely descriptive basis. One should speak of a facies of coarse sand, shaly facies and not of a fluvial facies or turbiditic facies. It should be avoided, for instance, "this interval corresponds to sands of deltaic facies". It is better and far more correct to say: "this interval corresponds to a sandy facies deposited in a deltaic environment". And above all never said, as do a large part of American geoscientists, "a map in facies" when sedimentary environments are mapped. This means that when American geoscientists consider a vertical facies sequence (Walther's facies law) is the product of a series of depositional environments that are, laterally, adjacent to one another (in situations where there is no interruption of sedimentation), they deviate much from the original definition of Armanz Gressly and J. Walther. In 1898, J. Walther proposed the law or the correlation of facies saying that the deposits of a region with the same facies ("faciesbezirk" , which in German literally means "facies of the region"), as well as, a set of rocks of the same region with different facies are formed, side by side. Although in a cross section, they are seen one on top of the other. In 1907, E. Haug standardized the meaning of facies as the sum of the lithological and paleontological characteristics of a given deposit in a given place. In 1970, Selley emphasized that all proposed facies definitions are, merely, descriptive and therefore expressions such as fluvial facies or turbiditic facies are not relevant. In 1971, Busch applied Walther's concept of "faciesbezirk" to a whole rocky body and not only to a vertical succession considering the "genetic increment of strata" (GIS) and the "genetic sequence of strata" (GSS), i.e., a set of increments involving more than one increment of the same genetic type (a delta is a genetic increment of strata, whereas a deltaic building is a genetic sequence of strata). In 1977, Brown and Fischer used the same concept ( Walther's "faciesbezik") in the analysis of facies and renamed as systems tract. In this tentative geological interpretation of an Indonesia seismic line, it is not difficult to identify a facies change in the highstand prograding wedge (HPW) of sequence-cyle, limited between two unconformities, i.e., by two significant relative sea level falls defining a 3^rd order eustatic cycle (time-duration between 0.5 and 3/5 My). This sequence-cycle is incomplete. Just the highstand systems tracts group was deposited. The transgressive interval TI (systems tract sub-group) is, easily, recognized. Its internal configuration is, more or less, parallel but, globally, it has a retrogradational. Similarly, the highstand prograding wedge (HPW), whose internal configuration and geometry are progradational, is, easily, recognized. In this example, it is along the progradations of the highstand prograding wedge, which are chronostratigraphic lines, that the facies change is observed. This change corresponds to the passage of the upstream (SE) shallow-water carbonates (lagoon) to deep carbonated shales of the open platform and reef slope. This tentative geological interpretation does not refute the hypothesis advanced in the early days of Sequential Stratigraphy that facies lines (lithology) cut chronostratigraphic lines (time). However, almost all reflectors underline chronostratigraphic lines (time lines).

Facies vs Environment.......................................................................................Faciès vs environment sédimentaire

Fácies vs ambiente sedimentar / Facies vs ambiente sedimentario / Facies kontra Umwelt / 环境相对 / Фации по сравнению с осадочной средой / Facies rispetto ambiente /

According to Teichert (1958), it seems it was Nicolas Steno (1669), who for the first time used the term facies (from the Latin Facies "appearance" or "appearance") to designate all or a part of the surface aspect of the Earth during a certain geological time interval. Gressly, in 1838, went further than other geoscientists because, on the basis of local and isolated observations, he considered rocky units and used the term facies to express the lateral changes of appearance and to underline the fact that the rocky units are not lithologically uniform since they change since depositional environments change (R. Prothero, 1989). The term seismofacies is, often, used by American geoscientists to designate charts of sedimentary environments constructed from seismic data. The term seismofacies, when used, should be limited to lithological assemblages within a cycle-sequence or GIS (genetic increment strata).

See: « Fácies »
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« Sedimentary Environment »
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« Genetic Increment Strata (GIS) »

Two main factors characterize the total sum of the changes that Armanz Gressly (1838) called facies of a stratigraphic unit: (i) The lithological aspect of the stratigraphic unit, which is connected to a paleontological group and (ii) The set of fossils that excluded, invariably, other facies. Haug (1907) standardized the meaning of facies as the sum of the lithological and paleontological characteristics of a particular deposit in a given place. Selley (1970) emphasized that all proposed facies definitions are, merely, descriptive and therefore expressions such as fluvial facies or turbiditic facies are not relevant. Thus, it is more correct to say: a sandy facies associated with a fluvial environment, than a sand of fluvial facies. This means that when American geoscientists consider a vertical facies sequence (Walther's facies law) is the product of a series of depositional environments that are, laterally, adjacent to each other (in situations where there is no interruption of sedimentation), they deviate much from the original definition of A. Gressly and J. Walther. Walther's conception of " faciesbezirk", an idea, partially, taken from Gressly, was adopted by Busch* (1971) for a whole rocky body and not only for a vertical succession. Busch called it "genetic increment of strata "(GIS). In 1977, Brown and Fischer ** used the same concept ("faciesbezik" of Walther) in facies analysis and renamed it "systems tract". A genetic increment of strata (GIS) is a set of sedimentary rocks in which the facies or subb-facies are, genetically, related. The typical example of a genetic increment of strata is a delta, which consists of four facies or depositional systems: (i) Delta plain silts ; (ii) Delta front sands ; (iii) Prodelta shales and (iv) Shales and, sometimes, sands at the base of the prodelta. A genetic sequence of the strata involves more than an genetic increment of strata of the same type, as an delta building. According to Selley (2000, ISBN: 0-12-636375-7), these terms were created, primarily, to help the subsurface mapping of delta deposits. So an isochron map of a genetic increment of strata defines a delta lobe (a delta), while an isochron map o of a genetic sequence of strata (set of increments) defines a delta building (stacking of deltas). This scheme illustrates the differences between facies, environment and genetic increment of strata. A GIS (genetic increment of strata) is a sedimentary unit in which facies are genetically associated. As illustrated, three GIS are readily recognizable (3, 2, 1). Within each IGS, three contemporary sedimentary environments A, B and C are identified. The A sedimentary environment, which is, practically, sub-aerial or covered with a small water column, is characterized by the sediments deposited, more or less, horizontally. Their facies is, probably, shaly siltstones (a). The B sedimentary environment is marine (the water-depth increases, progressively, basinward). It is located downstream of the environment A and is characterized by shales with a seaward depositional dip (b). The C depositional environment, located downstream of environment B, is a deep water environment. It is characterized by sediments, probably sands, deposited, more or less, sub-horizontally (submarine basin floor and slope fans). In other words, within each increment of facies, depositional surfaces (chronostratigraphic lines) are formed by three segments, which from the continent seaward different geometries: (i) Proximal sub-horizontal ; (ii) Dipping seaward and (iii) Distal subhorizontal. On the other hand, it is easy to see that the depositional surfaces, i.e., the stratification planes or time lines (reflectors on the seismic lines) cut the facies lines. A genetic increment of strata corresponds, more or less, to a stratigraphic cycle called the sequence-cycle in sequential stratigraphy, which is formed by a set of sedimentary systems tracts that are lateral associations of contemporary and genetically related depositional systems that form a sequence-paracycle. Two main factors characterize the sum total of the modifications that Gressly (1838) called facies of a stratigraphic unit: (i) The lithological aspect of the stratigraphic unit, which is connected to a paleontological complex and (ii) Such a set of fossils invariably excludes, other facies. Haug (1907) standardized the meaning of facies as the sum of the lithological and paleontological characteristics of a particular deposit in a given place. Selley (1970) emphasized that all proposed facies definitions are merely descriptive and therefore, expressions such as fluvial facies or turbidite facies are not relevant. Thus, it is more correct to say: a sandy facies associated with a fluvial environment, than a sand of fluvial facies.

(*) Busch, D. A. (1971) - Genetic units in delta prospecting. Am. Assoc. Pet. Geol. Bull. 55, 1137-1154.

(**) Brown, L. F., and Fischer, W. L. (1977) - Seismic-stratigraphy interpretation of depositional Systems: Examples from Brazilian rift and pull-apart basins. In “Seismic Stratigraphy Applications to Hydrocarbon Exploration” (C. E. Payton, ed.). Am. Assoc. Petrol. Geol. 26, 213-248.

Facies Line................................................................................................................................................................................................................Ligne de faciès

Linha de fácies / Línea facies / Facies Linie / 相线 / Линия фаций / Linea di facies /

Imaginary line limiting different lithologies (facies). Within each of the sedimentary systems tracts that make up a sequence-cycle, along the time lines (chronostratigraphic lines), several facies (lithologies) are recognized, so that facies lines cross time lines.

See : " Systems Tract "

Facies Sequence............................................................................................................................................................................Séquence de faciès

Sequência de Fácies / Secuencia de facies / Facies Sequenz / 序列的相 / Последовательность фаций / Facies sequenza /

Facies association with a characteristic vertical order. Walther's law says in continuity of sedimentation, different facies, that overlap one another, were depoisted next to each other (adjacent) and at the same time. In other words, in absence of unconformities (erosionl surfaces), a lateral succession of a, b, c facies, is also found, vertically, but from the most distal to the most proximal, i. e., c, b, a facies.

See: « Fácies »

Facies Tract ............................................................................................................................................................................................................................Cortège de faciès

Cortejo de Fácies / Cortejo de facies / Prozession der Fazies, facies-Darm-Trakt / 游行的相, 相道 / Фациальный интервал / Processione di facies, Zona di facies /

Lateral and synchronous association of different lithologies, genetically associated, with a characteristic fauna. Synonym with Depositional Systems Tract or Sedimentary Tract.

See: " Systems Tract "
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" Sequential Stratigraphy "
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" Depositional System "

In geology, the term facies means more lithology than a sedimentary environment, as it is often used, especially in American publications. This term was first used by the Swiss geoscientist Amanz Gressly (circa 1835) to define a lithological complex accompanied by a more or less characteristic fauna deposited in a particular environment. Thus, one should not say a sand of deltaic facies. It is preferable to say a sandy facies of a deltaic environment. Similarly, do not say, "A tentative geological interpretation of a seismic line in facies" as many American geoscientists say to designate a tentative geological interpretation in sedimentary environments. Simply say, "A tentative geological interpretation of a seismic line in sedimentary environments" when attempting to interpret the different sedimentary environments that make up the intervals of a seismic line, whether they are determined within a sequence-cycle, a continental encroachment subcycle, a continental encroachment cycle, or even within a sequence-paracycle. In this way, i.e., etymologically, a facies tract (synonymous with sedimentary systems tract), in the field or seismic lines, corresponds to a lateral and synchronous association of different lithologies, genetically, linked. That means if a lithology disappears or was not deposited) the others, usually, also disappear (or do not deposit). A delta is a typical example of a facies tract (do not confuse a delta that, in general, has a thickness between 10 and 50 meters, with a delta building, i.e., with a, more or less, vertical stacking of deltas, whose thickness can, easily, surpass several thousands of meters. In a delta, in the field or on a seismic line (between two chronostratigraphic lines) there are, mainly, three different lithologies forming a facies tract (systems tract) : (i) Delta plain silts and delta front sandstones ; (iii) Prodelta shales and (iii) Shales at the bottom of the prodelta with, sometimes, turbidite sands associated. The delta plain silts are sedimentary rocks formed, mainly, of quartz, mica and clay, with a intermediate grain size between sand and clay sedimentary particles. The delta front sandstones are composed of quartz, feldspars, micas and miscellaneous impurities with sand-sized grains. The prodelta shales are clastic rock composed of phyllosilicates* (the micas group, the chlorite group, the coil group and the group of clay minerals with a grain size <0.004 mm). The sands of the delta base have a turbiditic nature. They are deposited in association with failures and landslides of the delta front, whose facies control the facies of these proximal turbidites as many geoscientists call them. In sequential stratigraphy, as illustrated in this sketch, based on Mahakam offshore (Indonesia) seismic lines, sequence-cycles, which are associated with 3^rd order eustatic cycles (characterized by a time-duration time between 0.5 and 3-5 My), are composed of two groups systems tracts (facies tracts), which are constituted by the superposition of several systems tracts subgroups. Each systems tracts subgroup can be formed by one or more systems tracts. When a sequence-cycle is complete, from the bottom to top we recognize the following systems tracts subgroups: (a₁) Submarine Basin Floor Fans (SBFF) ; (a₂) Slope Submarine Cones (CST) ; (a₃) Lowstand Prograding Wedge (LPW) ; (b₁) Transgressive Interval (TI) and (b₂) Highstand Prograding wedge (HPW). The subgroups a1, a₂, et a₃ form the Lowstand Systems Tracts Group (LSTG). The sub-groups b₁ and b₂ form the Highstand Systems Tracts Group (HSTG). Within each sedimentary systems, one or more chronostratigraphic lines can be recognized and along these time lines several facies (lithologies) can be identified so that, in general, the facies lines same lithology) cut the time or chronostratigraphic lines (depositional surfaces).

(*) The word phyllosilicate comes from the Greek phylon, meaning sheet. All members of this group of minerals have a flat or flaked habit and a basal cleavage whose lamellae are flexible elastic or plastic, but rarely brittle. The phyllosilicates have a low hardness, usually less than 3.5, on the Mohs scale, and a relatively low density relative to other silicates. The most striking features of the phyllosilicates (divisibility, hardness and habit) are associated with their structure consisting of two-dimensional shared silicon tetrahedra forming a leaf, where three of the four oxygen atoms of the SiO₄ tetrahedra are shared with the neighbouring tetrahedra ( ratio Si: O = 2: 5). For the constitution of the minerals of this class the tetrahedral leaves are attached to octahedral leaves, constituted by brucite [Mg(OH)₂] or gibbsite [Al(OH)₃], giving rise to two families, called respectively trioctahedral and dioctahedral. (http://www.rc.unesp.br/ museudpm/banco/silicatos/filossilicatos/ filossilicatos.html)

Fair Weather Wave Base.............................................................Limite d'action des vagues de beau temps

Acção da vagas (mar calmo) / Acción de olas (mar calmo) / Aktion der Wellen (ruhige See) / 波行动的限制（宁静的海）/ Предел волнового воздействия (спокойное море) / Limite di azione delle onde (mare calmo) /

When the erosive action of the sea-waves reaches, more or less, the depth of 10 meters. This water-depth corresponds, approximately, to the position of the depositional coastal break.

See: « Major Storm Wave Base »
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« Depositional Coastal Break »
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« Average Storm Wave Base »

When the sea is calm, as illustrated in this picture of Bells beach near Melbourne, Australia, it is, slightly, undulating with the base level (erosive action of the waves) reaches just 5-10 m depth. Under these conditions, the sea is, generally, relatively limpid. The band of the sea floor affected by the action of the waves is, generally, more or less, formed by coarse sand. In his photograph, in the cliff or in the beach cliff different levels can be highlighted on the beach itself (shoreface and nearshore). The swash currents (set of the uprush and backwash t for certain geoscientists) are very visible. The promontory or cliff, i.e., the steep escarpment, at the seaside, formed by the action of the marine erosion, and the abrasion platform (region, more or less, flattened by the waves action) are, easily, recognized in the northern part of the coast. Although it is more evident in the photography of the Algarve coast (Portugal). The speed of the sea waves is a function of the wave-length of the waves (L). When the depth of the sea floor is greater than the wave-length, the velocity is given by v = (gL / 2π) 1/2 = 1.56 L 1/2. If the depth of the sea (h) is smaller than the wave-length, the velocity of the waves is given by v = (g x h) 1/2. When the sea is calm, as in this example, the action of the waves corresponds, mainly, to a washing of the sandy and coarse sediments of the sea floor without formation of a ravinement surface. Ravinement surfaces a submarine erosional surfaces induced, on the shelf, by minute erosion. Unlike other erosional surfaces, ravinement surfaces are not associated with relative sea level falls, as the unconformities, but with relative sea level rises (marine ingressions). They are, mainly, associated with the eustatic-paracycles, that induce the deposit of the transgressive interval (TI) of a sequence-cycle. Each eustatic-paracycle (marine ingression) moves continentward the successive depositional coastal breaks of the depositional surface. In any case, ravinement surfaces can be interpreted as unconformities. In sequential stratigraphy, unconformities limit sedimentary packages deposited during eustatic cycles. The ravinement surfaces can, easily, become evident in the field studying the geometric relationships between the bedding planes. On seismic lines, they are impossible to recognize directly. They can just be predicted within a sequence-cycle. They correspond to the boundaries between the different sedimentary systems tracts. Only unconformities (erosional surfaces induced by significant relative sea level falls) are visible on seismic data. This is particularly true at the top of the continental slope (submarine canyons fills) and upstream of the basin edge (incised valleys fills). In the absence of a tectonic reinforcement of the geometric relations (development of angular unconformities) and submarine canyons and incised valleys fillings, only the recognition of onlaps (coastal or marine) allows the identification of the stratigraphic cycles boundaries. Therefore, in the sequential stratigraphy, the tentative geological interpretation of regional seismic lines, which illustrate the different physiographic provinces (coastal plain, continental shelf, continental slope and abyssal plain) are fundamental. When geoscientist speaks in sea level, he must always specify is is the absolute sea level (also called eustatic sea level) or the relative sea level. The first is supposed to be global and referenced to a fixed land point, usually, the Earth's centre (absolute sea level measurements are now, mainly, determined from satellites). The second, i.e., the relative sea level is local and referenced either to the top of the continental crust (usually the base of the sediments) or to the sea floor. The absolute sea level rises or falls as a function of: i) Tectono-Eustasy (variation of the volume of ocean basins in association with oceanic expansion following the break-up of supercontinents) ; (ii) Glacio-Eustasy (variation of water volume of the oceans as a function of the amount of ice, assuming that the amount of water in all its forms is constant since the Earth formation around 4.5 Ga) ; (iii) Geoidal-Eustasy (distribution of ocean water caused by variations in the Earth gravity field and (iv) Steric sea level rise or thermal expansion of the oceans, which is controlled by rising ocean temperatures. The relative sea level falls or rises as a function of the combined action of absolute sea level (eustatic sea level) and tectonics (uplift or subsidence of the sea floor).

Falling Stage Systems Tract..........................................................................Cortège sédimentaire descendant

Cortejo sedimentar descendente / Cortejo sedimentario descendente / Sedimentary Prozession nach unten, Falling Stage Systems-Darm-Trakt / 沉积游行下降 / Снижающийся уровень цикла осадконакопления / Processione sedimentario discendente /

One of the systems tracts that form the set of sediments deposited during a relative sea level fall. A descending systems tract exists in association with a forced regression. It has a progradational geometry and is deposited lower than the highstand prograding wedge. Synonym with Descending Prograding Wedge.

See:« Systems Tract »
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« Sequential Stratigraphy »
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« Forced Regression »

These sedimentary systems tracts develop when the shoreline moves seaward and downward, due to a relative sea level fall but does not exhumes the totality of the shelf. The associated erosional surface, that is, the unconformity limiting the bottom of the falling systems tracts is difficult to locate. Since a few years ago, there has been and still is a debate regarding the position of erosional surface (unconformity) in transitions from marine to non-marine environments. This problem is expressed by certain geoscientists as the problem of forced regression of the shoreline. The deposits of a forced regression (deep and shallow-water) accumulate, at the same time, developing a sub-aerial erosion surface in non-marine part of the basin. Theoretically, the falling systems tracts are associated with: (i) Fluvial incisions in the exhumed coastal plain ; (ii) Progressive sub-aerial exposure of the platform ; (iii) Transport of the sedimentary particles along the continental slope and formation of submarine canyons and (iv) Deposition of submarine basin floor fans (SBFF). On the other hand, the falling sedimentary systems tracts can be characterized by: (a) An abundance of microfossils ; (b) Strong values of δ¹⁸O* ; (c) Erosion of the continent ; (d) Absence of contemporary deposition on the coastal plain ; (e) Progradations thin basinward ; (f) Myopic or abbreviated stratigraphy (thickness of the sequence-paracycles below the depositional water paleodepth determined by the biostratigraphy). As illustrated in these sketches, the problem of the falling sedimentary systems tracts (FSST), which correspond, more or less, to Exxon's disused Bordering Prograding Wedge (BPW), is whether the unconformity that limits the sequence-cycle should be placed above them or if the falling systems tracts settle over the unconformity. For Vail, at least at the beginning of the sequential stratigraphy vulgarisation, the falling systems tracts (bordering prograding wedge) deposited above an unconformity that he called type II. Such erosional surface develops in in association with a small relative sea level* fall that did not the put the sea level under the basin edge. It is only later that the relative sea level fall is sufficient to displace sedimentation to the deep-water environments. Hunt and Tucker (1995), incorporate the falling systems tracts at the top of the sequence-cycle, under the unconformity. it is initiated at the beginning of the falling phase, but the erosion and incision continue until the end of the falling phase of the sea level. At present, the differentiation between type I and type II unconformities seems to have disappeared and, practically, any geoscientist recognizes, at least on seismic lines, type II unconformities. On the other hand, the falling systems tracts correspond, more or less, to what is now called forced regressions. They are independent of the variations of the terrigeneous influx and move the shoreline basinward and downward. Sediment deposition, particularly, in siliciclastic environments, can be very important during a forced regression. Independently of the rivers that carry the sedimentary particles to the basin, additional sediments can be obtained by sub-aerial erosion and fluvial incision in the sediments, previously, deposited. All this means, more or less, that when a relative sea level falls, the shoreline moves seaward, the depositional base level decreases and accommodation decreases, so that there is no more space available for the sediments. Coastal and marine regions are exposed to erosion, while the paralic systems migrate towards the shoreline, overlapping continental sediments with the coastal and marine sediments deposited earlier.

(*) δ ¹⁸O or delta O₁₈ is the rate of the stable isotopes of oxygen-18 (¹⁸O) and oxygen-16 (¹⁶O), which is used as a measure of precipitation temperature, the interactions between groundwater and minerals. The rate of ¹⁸O: ¹⁶O of the corals, foraminifera and ice cores are used as a proxy for temperature (measuring parameters, which correlate with paleoclimate variables and then infer the values of paleoclimate variables, since they can not be measured directly) .

(**) Sea, local, referenced to any point on the Earth's surface whether it is the sea floor or the base of the sediments and which is the result of the combined action of the tectonics and the absolute (eustatic) sea level, which is supposed to be global and referenced to the Earth's centre.

Falling Tide (Ebb, downward current).......................................................................................................Descendante (Courant de maré)

Vazante (corrente de maré) / Bajante (corriente) / Flut / 落潮 / Отлив (понижение уровня воды) / Caduta di marea /

Return current of the tide, once the water returns to the sea.

See : « Tide »
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« High Tide »
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« Oposition (astronomy) »

Tides are the sea level changes caused by the gravitational interference of the Moon and the Sun (the latter with less intensity due to its great distance from Earth) over the gravity Earth field. In an ideal Earth gravitational field, i.e., without interference, the Earth surface waters would suffer an identical acceleration towards the Earth's centre mass, thus being in an isopotential situation. Due to the existence of bodies with significant gravitational fields interfering with that of the Earth, such as the Moon and the Sun, they cause accelerations that act on the Earth mass with different intensities. As the gravitational fields act with an intensity, inversely, proportional to the square of the distance, the accelerations felt in the different points of the Earth are not the same. The acceleration caused by the Moon has, significantly, different intensities between the points closest to and farther from the Moon. The oceanic masses that are closest to the Moon undergo an acceleration of intensity higher than the ocean masses further away from the Moon. It this differential that causes changes in the height of water-bodies to the Earth. When the tide is at its apex, it is called high-tide or full tide. When sea level is at its lowest level it is called low-tide or ebb tide. On average, the tides oscillate in a period of 12 hours and 24 minutes. Twelve hours due to Earth rotation and 24 minutes due to lunar orbit. (http://en.wikipedia.org/wiki/Maré). As the rise of the tide in an estuary, usually, causes a flood (tide flood) and a fall of the tide causes a ebb flow (ebb tide). Tide currents are, practically, null near the high-tide and low-tide. When this occurs, many geoscientists say that the tidal wave is in phase with the variation of the currents and the tidal wave is said to be stationary. However, this is not a rule. In long and low-converging estuaries, or in channels leading to internal lagoons, vertical tide (rise and fall) may be associated in a different way with the horizontal tide (tidal currents).

False Downlap....................................................................................................................................................................Biseau de progradation faux

Bisel de progradação falso / Bisel de progradación falso / Falsch downlap, Bevel Progradation Falsch, Progradierender Keil falsch / 假downlap, Progradational楔假 / Ложное подошвенное прилегание / False downlap, Bisello progradazionale falso /

Seaward tangential termination of the strata (or seismic reflectors), in which strata become, more or less, horizontal and continue seaward as independent stratigraphic units that are, often, so thin that they are not visible on the seismic lines (thickness under seismic resolution). This type of downlap is, mainly, observed on seismic lines due to seismic resolution.

See: « Downlap »
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" Geometric Relationship (reflector, stratum) "
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" Distal Downlap "

The geographic basin of the Adriatic (Italy) corresponds to a marginal sea opened in association with the oceanic expansion (sea floor spreading) induced by the lengthening and break-up of continent (folded mountain belt), which characterizes the Mediterranean-type perisutural basins associated with an A-type subduction (Ampferer). The Po geographic basin, located at the NW of the Adriatic geographic basin, is a Pannonian-type perisutural basin associated with an A-type subduction. However, the lengthening of the folded mountain belt was insufficient to develop an oceanization. In a succinct way, it can be said that the Panonian-type sedimentary basins, as well as those of the Mediterranean type, are associated with the lengthening (extension) induced by the continental collisions located in the concave part of the Ampferer subduction arcs, i.e., an A-type subduction. The Panonian-type basins develop over a thin continental crust, but not enough to open an ocean basin. On the contrary, in the Mediterranean-type basins, the lengthening is sufficient for the central part of the basin rest on the oceanic crust*. The mouth area of the Po river corresponds to the stacking of two types of basins of the classification of the sedimentary basins of Bally and Snelson (1980). From the bottom to top, as illustrated on this tentative geological interpretation of a Canvas auto-trace of a detail of an offshore seismic line, one can recognize: (i) A Cenozoic folded mountains belt and (ii) A non Atlantic-type divergent margin. The tectonically enhanced unconformity (angular discordance for many geoscientists) separates these two sedimentary basins. As illustrated, in a false downlap, the reflectors became, progressively, sub-horizontal in depth and continue basinward as, relatively, thin sedimentary units (see Onlap, in the auto-trace of an offshore seismic line of the Maluinas). Almost all bodies and sedimentary intervals have a fusiform geometry. Seaward, a sedimentary body or rather the thickness between two successive chronostratigraphic reflectors, increases, reaches a maximum of thickness and then decreases progressively. In a tentative geological interpretation of a seismic line, the interpreter has to have an idea of the seismic resolution before considering a downlap as a false downlap or not. Often and especially in the old 2D seismic lines, the reflector terminations seem obvious but, in reality, they are sometimes apparent due to a weak seismic resolution (ability to separate two seismic events that are adjacent each other). If the seismic resolution is 20-30 meters, a progradational stratigraphic unit extending outward with a thickness of 10-15 meters is, seismically, invisible and the false downlap can not be easily recognized. Most interpreters use an indirect criterion to determine whether a downlap is false or true. They use the geometry of the downlap surface base. When this is, more or less, horizontal and the thickness of the progradating range is, relatively, constant, most likely the downlap is true downlap. When the geometry of the downlap surface is, poorly, marked (slightly inclined continentward) and the thickness of the progradational interval decreases seaward, as is the case, in this tentative interpretation, the most probable is a false downlap. If an interpreter considers that the downlaps are false, the distal aggradational deposits can not be considered as submarine basin floor fans. There is any unconformity. The sub-horizontal distal aggradational deposits are not associated with significant relative sea level fall. At the top of this tentative interpretation, the violet horizon is considered as a multiple of the sea floor, i.e., a reflector with no geological value, suggesting that seismic energy has been reflected more than once on the sea floor.

(*) Examples of Pannonian-type basins are the geographical basins of Transylvania, Pannonian (Hungary), Vienna, Po, Guadalquivir, Bowser, Hope Quesnell, Chiriqui, etc. Examples of Mediterranean-type basins are the geographical basins of the Balearic Islands, Sardinia, Salonica, Tirrenean, Adriatic, Gulf of Mexico, Big Horn, Ana Maria, Cochinos, Adana (Cyprus), Black Sea, Teshio (Japan), Cayman, Alboran, Melawi, Gulf of St. Lawrence, etc.

Fan Delta (Alluvial fan).........................................................................................................................................Cône alluvial (Aboutissant à la mer )

(Coine Aluvial (terminando num corpo de água) / Abanico aluvial (que termina en el mar o lago) / Fan - Delta, Schwemmkegel (zum Meer, See) / 扇三角洲 / Аллювиальный конус выноса / Conoide alluvionale (che porta al mare, lago) /

Non-marine sedimentary lobe, composed of a relatively heterogeneous rock mass, slightly, dipping and deposited by a torrent (especially in semi-arid regions). An alluvial fan is deposited when: (i) A stream flows out of a narrow valley upstream of a much wider valley ; (ii) A current is tributary and flows into the main stream ; (iii) The constraint of the valley disappears abruptly or (iv) The gradient of the current decreases rapidly. An alluvial fan is steeper near the mouth of the valley. Its highest point is upstream and plunges convexly downstream, as the gradient decreases.

See: " Alluvial "
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" Bayline "
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“ Depositional Environment”

As shown on this tentative geological interpretation of an Angola offshore seismic line, the influence of river deposits in deep-water deposits is suggested by the configuration of certain seismic reflectors from which most geoscientists recognize an alluvial or Gilbert-type fan delta*. Gilbert-type deltas are, often, formed in lakes, particularly, when the water density of the river is, more or less, equal to the density of the lake water. They can, also, develop at sea when the bay ** is not far from the shoreline. Certain incised valleys from the coast of Liguria (NE Italy), connected with the submarine canyons, induced by the deep river erosion caused by a fall of the absolute (eustatic) sea level (supposed global sea referenced to the Earth's centre) during the Messinian. They were flooded by the sea in the Pliocene and transformed into estuaries. The filling of these incised-valleys reached about 500 m. The bottom of the incised valleys fills is, locally, paved by thin remains of thin sub-aerial deposits, abruptly, covered by marls (up to 150 m thick), above which a number of Gilbert-type deltas (rich in conglomerates) have been deposited filling a large part of the valleys valleys. The thickness of these deltas, which alternate with marl intervals (20-30 meters), ranges between 50 and 250 meters. The inclined layers reach 15°-25° of dip. These deltas are characterized by a high rate of absolute sea level rise, after the incision phase. Processes of mass flow and debris avalanches are, by far, the more predominant, in the first stage of progradation. In the later stages of delta progradation (deposit of inclined and stratified layers along the slope of the delta), flows by inertia and turbidity predominate. On the tentative geological interpretation illustrated in this figure, the erosional surface (dashed red line) i.e., the unconformity marks the limit between two stratigraphic cycles. This erosional surface, which is recognized by the truncation of the underlying reflectors and, also, by the onlaps and downlaps that characterize the reflections terminations of the overlying reflectors, was induced by a fall of the relative sea level (local sea level referenced to any point of the Earth's surface which can be the sea floor or the base of the sediments), which put the sea level lower than the basin's edge (lowstand geological conditions). This relative sea level fall was, probably, exaggerated by the uplift of South-West Africa during the Late Tertiary. In the geographic Congo basin, where the original seismic line was shot, seismic data suggest an uplift between 1,500 and 2,000 meters. This relative sea level fall (result of the combined action of absolute sea level and tectonics) exhumed the old platform (if it existed) and, partially, the submarine canyon fills present in the upper continental slope. This suggest that a large part of the erosion, visible in the central part of this tentative interpretation, pre-dated the relative sea level fall. It would have been made by the erosive action of a submarine canyon, probably, associated with a predecessor of the Congo River. The upper limit of this canyon and the orientation of the seismic line of this tentative interpretation is shown on the right of the figure. It may be assumed that during the relative sea level fall, when the shoreline (more or less the depositional coastal break of the depositional surface) was lower than the basin edge. Alluvial sediments entered, directly, into the submerged part of the canyon depositing, under a water-depth, a relatively, important, alluvial delta ending in the sea or Gilbert-type delta (coarsening and thickening upward alluvial fan prograding into a deep-water body with relatively weak energy). The geometry of the reflectors, which fossilize the submarine canyon (sigmoid geometry or S upside down) is characteristic of the chronostratigraphic lines of delta bodies, which are composed of basal beds (prodelta base and proximal turbidites), frontal beds (prodelta) and upper beds (delta plain and delta front). In this type of alluvial fan terminating at sea, the reflection terminations (downlaps) are obvious at the lower limit, as well as the onlaps. Toplaps by non-deposition and by truncation characterize a filling of the canyon by sigmoid and oblique progradations.

(*) River Delta, formed by a wedge-shaped sedimentary body, whose upper layers are, relatively, thin and sub-horizontal, with long frontal beds that prograde from the river's mouth and thin, sub-horizontal lower beds.

(**) The bay-line was, more or less, defined as follows by Posamentier and Vail (1988): (a) The coastal plain is formed by processes of sea floor progradation, rather than by exhumation ; (b) The sediments that accumulate on the coastal plain during the progradations of the shoreline are part of what is called the coastal wedge, which includes river and shallow-water deposits ; (c) The coastal wedge is wedge-shaped and extends continentward by onlaps over the pre-existing topography ; (d) The upstream boundary of the coastal wedge is the bay-line, which may move upstream when the progradation of the shoreline is accompanied by aggradation ; (e) The bay-line is the boundary between the coastal wedge and the alluvial plain ; (f) Upstream of the bay-line, relative sea level changes have, practically, no influence on depositional systems.

Fan-Delta System.............................................................................................................................................Système deltaïque-alluvial

Sistema deltaico-aluvial / Sistema deltaico-aluvial / Delta-alluvialen-System / 扇三角洲系统 - / Дельтово-аллювиальная система / Sistema delta-alluvionale /

Sedimentary system, usually, ancient, deposited in tectonically active basins and built, essentially, by systems of alluvial deltas and delta rivers dominated by catastrophic floods. These systems and the depositional elements composing them, can not be described by the current sedimentary models, i.e., by: (i) "Normal" fluvial and deltaic processes; (ii) Lithologies and (iii) Geomorphological contexts derived from the study of modern marine environments (Mutti, 1996).

See: " Alluvial "
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« Delta »
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“ Depositional Environment”

Generally, alluvial delta systems prograde from an important failure on a chronostratigraphic line, such as the foothills of a mountain, as can be seen in the geological model, proposed by E. Mutti, for alluvial delta systems, illustrated in this figure. In the simulation illustrated in the upper left part of this figure, the small sedimentary lobes formed under a very small water column in the margin of a more important sedimentary fan behave like a finger delta delta. They simulate an alluvial delta system. In the Mutti model, the lobes associated with floods, which are, easily, differentiated from the submarine slope fans (SSF), induced by turbidite currents and deposited in the deep parts of the basin. In highstand geological conditions, they may extend beyond the border of the basin (basin edge). Mutti's alluvial delta system develops in the vicinity of what P. Vail and Posamentier (1988) called, in sequential stratigraphy, the bay-line. The concept of the bay-line was defined on the basis of the conjecture that delta deposits occur when a water-course encounters a water-body, almost immobile, and the velocity of the stream decreases almost instantaneously: (i) The coastal plain is formed by processes of sea floor progradation, rather than by exhumation ; (b) The sediments that accumulate on the coastal plain during the seaward shoreline progradation are part of coastal wedge, which includes fluvial and shallow-water deposits ; (c) The coastal wedge or coastal prism is wedge-shaped and extends continentward by coastal onlaps on the preexisting topography ; (d) The upstream limit of the coastal edge is the bay-line, which may move updip when the shoreline progradation is accompanied by aggradation (vertical deposition) ; (e) The bayline is the limit between the coastal and the alluvial plain ; (f) Upstream of the bay-line, relative sea level changes have, practically, no influence on depositional systems. Certain geoscientists consider that the basic idea of Posamentier and Vail, that is to say, that the deltaic deposition occurs when a water-course encounters an almost immobile water-body, which controls its provisional equilibrium profile, is not the bayline, but the water-course mouth. For them the head or apex of a delta is not the bayline but the stream mouth. In such conditions, in the sequential stratigraphy terminology of P. Vail Under, the differentiation between a delta lobe and a submarine fan, when possible, is very subtle. Mutti admits that the deposit of submarine fans, whether basin floor fans or or slope fans, does not, always, occur under lowstand geological conditions (sea level lower than the basin edge) in association with a significant relative sea level fall (P. Vail hypothesis). Sea level can be of two types: (i) Relative sea level, which is the local and referenced to any fixed point on the Earth's surface, whether the base of the sediments (top of the continental crust) or the sea floor and (ii ) Absolute (eustatic) sea level, which is supposed to be global and referenced to the Earth's centre. The relative sea level is the result of the combined action of absolute (eustatic) sea level and tectonics (subsidence or uplift of the sea floor). The absolute sea level is the result of the combination of : i) Tectono-Eustasy, which is controlled by the volume variation of the ocean basins in association with oceanic expansion following the breakup of the supercontinents; (ii) Glacio-Eustasy, which is controlled by the volume of water in the oceans as a function of the amount of ice (assuming that the amount of water in all its forms is constant since the Earth formation around 4.5 Ga) ; (iii) Geoidal-Eustasy, which is controlled by the distribution of ocean water caused by variations in the Earth's gravity field (where gravity is stronger than normal, sea level is pulled to the Earth's centre) and (iv) Steric sea level rise or thermal dilatation of the oceans (if the temperature of the oceans increases, the density of the water decreases and, for a constant mass, the volume increases). During the floods, the river load is so great that when they enter the sea they can induce turbiditic currents. The sedimentary particles are transported to the deeper parts of the basin and deposited since the turbidite currents lose the ability to carry. They form depositional turbidite systems: submarine basin floor fans and/or submarine slope fans. When in lowstand geological conditions (sea level lower than the basin edge), the bayline is close to the continental edge (not to be confused with the basin edge, although, in certain settings they may be coincident), it is possible that an alluvial delta system enters, directly, into deep-water creating what many geoscientists call an alluvial delta or a Gilbert-type delta.

Faro (Atollon)...............................................................................................................................................................................................................................Atollon (Faro)

Atolon, Faro / Atolón / Atollen / 法鲁 / Небольшой атоллоподобный риф / Faro /

Set of small chained atolls.

See: « Atoll »
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« Faro (reef) »
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« Reef »

The large image recognizes, clearly, the different chained atolls that form the atollon of the Maldives. Each atoll corresponds to a low island, formed by an annular coral reef, continuous or interrupted by small channels, involving a shallow central lagoon. At the bottom of the lagoon grow corals, in the form of pinnacles or spheres of spherical geometry. At the outer margin, on the shelf of the reef, there are banks of coral sand, that constitute islets or are arranged in steps of beach due to the surfing of the waves. In the morphology of the atoll platform there are sometimes blocks of reef limestone cut into mushrooms or head-shaped. When the channels between the reef islands are deep they allow navigation and constitute the channels of passage (channel of Kardiva and Suvadiva). In geological history, many atolls die during rises of the relative sea level. In fact, the survival of the atolls and, consequently, of an atoll implies that coral growth counterbalances relative sea level rise (eustasy more tectonics, i.e., uplift or subsidence) in order that the water-depth, in which the corals are, is more or less constant. Otherwise, corals will be found under a large water-depth and, progressively, they will die, especially if the rising of the relative sea level is controlled more by subsidence than by eustasy (in this case, the rate of subsidence seems to be faster than the rate of eustasy). The same happens with the carbonated platforms, which created in the sequential analysis a great subject of discord between the Vail's scholl and Schlager's school. Vail considers that an unconformity (erosional surface) is always associated with a fall of the relative sea level, that causes the exhumation of the calcareous platforms and thus the death of the corals since these can be put under the photic zone. W. Schlager considers that certain Vail's unconformities, particularly, on carbonated platforms, do not correspond to significant falls of the relative sea level but rather to significant rises of the relative sea level that have placed the carbonate platform below the photic zone preventing the formation of carbonate. Thus, in this case, there is no erosion surface, which, in sequential analysis, limits stratigraphic cycles, but rather a drowning surface.

(*) Do not forget that sea level can be absolute (eustatic) or relative. The absolute or eustatic level is the supposed to be global and referenced to the Earth's centre. The absolute sea level is dependent on glacio-eustasy, tectono-eustasy, geoidal-eustasy, and the temperature of the oceans. The relative sea level is local and referenced either to the top of the continental crust (base of the sediments) or to the sea floor. The relative sea level is the result of the combination of absolute or eustatic level and tectonic (subsidence or survey of the sea floor).

Faro (Reef)...........................................................................................................................................................................................................................................Faro (Atolon)

Faro (atolon) / Faro (recife) / Faro (Riff) / 法鲁（礁） / Небольшой атоллоподобный риф / Faro (scoglio)/

Ring-shaped reefs delimiting lagoons.

See: « Atoll »
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« Faro (atollon) »
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« Reef »

In general, there are three main types of reefs: (A) Bioclastics, i.e., reefs constructed by the accumulation of organisms, especially, metazoans, which have a rigid carbonate shell ; (B) Biogenic, corresponding to carbonate biogenic constructions without accumulation of bioclasts and (C) Complexes, which correspond to reef constructions, sufficiently, large and resistant to the sea-waves to be able to form important reliefs and create a reef core with an internal margin and an outer reef. All of these reefs are complex systems in which biological, physical and chemical factors interact. There are, mainly, four processes that operate in the formation of reefs: (a) Constructive processes, i.e., biological processes, such as the growth of carbonate organisms ; (b) Destructive processes, i.e., all processes that can destroy or cause damage to reef growth, such as the action of sea waves and bioerosion (biological destruction) ; (c) Sedimentation, i.e., the accumulation of biogenic matter, created by the intense biological activity around the reef and the debris of the reef itself ; (d) Cementation, which has a great influence on the shape of the reef and which can be early and important, as is the case in many ancient and recent reefs. Of these four processes (constructive, destructive, sedimentation and cementation), a great variety of morphologies and internal structures can be recognized in reefs. In this figure a classification of the reefs is plotted taking into account the location and the form. From the continent seaward we can find: (i) Fringing reefs, more or less, connected to the shoreline; (ii) Faros (atoll within the lagoon), which has a ring- shape ; (iii) Patches or solitary reefs, which typically have a relatively important platform ; (iv) A barrier reef limiting the coastal zone ; (v) Reef mounds (a poorly used term) that are isolated reefs in deep-water, often, associated with landslides or barrier reefs instabilities ; (vi) Atolls, which area ring-shaped structure with a central lagoon, which develop in relatively deep-water and (vii) Tabular reef, such as atoll forms in deep water but without lagoon.

Fault.........................................................................................................................................................................................................................................................................Faille

Falha / Falla / Verwerfung (Geologie) / 斷層 / Разлом (сброс) / Faglia /

In geology, a fault is a fracture, more or less, planar in a rock in which the rocks on one side of the fracture (faulted block) is shifted relative to the rocks on the other side. There are three major types of faults: (i) Normal ; (ii) Reverse and (iii) Strike-Slip.

See : « Footwall »
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« Transform Fault »
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« Rift-Type (basin) »

Normal faults are formed during extensional tectonic regimes (σ₁ vertical). Reverse faults and strike-slip faults are formed during compressional tectonic regimes (σ₁ horizontal). The reverse faults are formed when σ₃ is vertical. The slip faults are formed when σ₃ is horizontal. The main axes of the effective stress ellipsoid are σ₁, σ₂ and σ₃ axes. The effective stress ellipsoid results from the combined action of : (i) Lithostatic pressure (σ_g), i.e., the sedimentary column weight ; (ii) Hydrostatic pressure (σ_p) , i.e., the water column weight and (iii) Tectonic vector (σ_t). Many failure theories have been proposed. The Mohr's theory seems to be the more difficult to refute. It describe the influence of pressure on failure. This theory postulates that in a general state of effective stresses σ₁> σ₂> σ₃, the effective intermediate stress σ₂ has no effect on failure. All faults form parallel to σ₂. However, it assumes that normal stresses, whether tension or compression, play a role in failure. Normal faults lengthen the sediments. Reverse faults shorten the sediments. Strike-slip faults displace the fault blocks horizontally relative to each other. Strike-slip faults do not lengthen or shorten the sediments. They just displace horizontally, the faulted blocks. Strike-slip faults have a, more or less, vertical fault plane. Fault planes of normal and reverse faults may be, locally, vertical. However, at the macroscopic scale (scale of seismic lines and geological maps), they are always inclined. In addition, in depth, they become, more or less, horizontal, as pressure increases. As illustrated, the faults (normal and inverse) are grouped in fault systems in order to lengthen or shorten the sediments homogeneously over a large extent. Individually, in a map, a fault is limited between two points where there is no displacement. Along the fault trace, the displacement increases, progressively, away from these end points, reaching the maximum value, more or less, midway between the endpoints. In order to respect the Goguel's law (during deformation the volume of sediments must be more or less constant) and to get an homogeneous shortening or lengthening, the faults are grouped like the sardines in a can: the end of a fault trace, where the displacement is zero, is relayed with the adjacent fault at the point where the displacement is maximum (more or less in the middle of the fault trace). In this way, it is possible to lengthen or shorten a large area without wrenching.

Feedback.................................................................................................................................................................................................................................Rétroaction

Feedback(retroalimentação) / Retroalimentación / Rückkopplung / 反馈 / Обратная связь / Retroazione /

When the result of a process returns to the system and modifies the next behaviour of the same process. Feedback may result in amplification or suppression of the process and therefore change the equilibrium conditions of the system. Feedback occurs in living and non-living systems. Positive feedback or positive retroaction amplifies the process, while a negative feedback reduces it, i.e., it causes decreasing. A feedback can have a variable effect according to the conditions, namely, the period of transformation and inertia of the system. Synonym with Retroaction.

See : « Hydrologic Cycle »

Feedback (Retroaction)....................................................................................................................................................Rétroaction, Feeedback

Retroacção / Retroalimentación / Rückkopplung / 反馈 / Обратная связь / Retroazione /

When the result of a process returns to the system and modifies the next behaviour of the same process. Feedback may result in amplification or suppression of the process and therefore change the equilibrium conditions of the system. Feedback occurs in living and non-living systems. Positive feedback or positive fretroaction amplifies the process, while a negative feedback reduces it, i.e., it causes decreasing. A feedback can have a variable effect according to the conditions, namely, the period of transformation and inertia of the system. Synonym with Retroaction.

See : «Albedo »
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« Global Warming »
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« Systems' Theory »

This sketch illustrates an ideal feedback or retroaction model. When B < 0, feedback is negative. When B> 0, feedback is positive. In biological systems, for instance in organisms, ecosystems or biosphere (ideal layer that forms around the Earth's crust the set of living beings), many parameters are just controlled within a relatively small range around an optimal value (under certain environmental conditions). A deviation from the optimal value of a parameter can result in internal and external environmental changes. A bipolar feedback is present in most natural and human systems. In natural environments, feedback is, usually, bipolar. It is positive or negative, which, in its diversity, provides synergistic and antagonistic responses to the output of the whole system. Climate, for instance, is characterized by important feedbacks between processes that affect the state of the atmosphere, oceans and continent. One of the best known examples of feedback is the ice and the albedo (the ratio of the amount of electromagnetic energy reflected by a surface to the amount of reflected energy). In the particular case of solar energy received by the Earth, the albedo is the ratio between the solar energy reflected and received by the Earth's surface. It ranges from 0 to 1. It is zero for a very black terrestrial surface and 1 for an ideal mirror type terrestrial surface. When the temperature rises, as when the Earth is in the perihelion, the melting of a part of the ice exposes the underlying ground which, having a smaller albedo, absorbs more heat and causes the melting of more ice, which reveals more terrain (smaller albedo), which warming melts more ice and so on.

Feedback (Example)..............................................................................................................................................................................Rétroaction (Exemple)

Retroacção / Retroacción (retroaliomentación) / Rückkopplung / 反馈 / Обратная связь (регенерация) / Retroazione /

Modification of the behaviour of a process by the result of the process that returns to the system, i.e., when the result of a process returns to the system and modifies the next behaviour of the same process. A feedback can produce an amplification or suppression of the process and, therefore, it changes the equilibrium conditions in the system. Feedback occurs in living and non-living systems. A positive feedback amplifies the process, whereas a negative feedback reduces it, that is to say, it causes a depreciation. A feedback can have a variable effect according to the conditions, namely, the period of transformation and inertia of the system. Synonym with retroaction.

See : «Albedo »
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« Global Warming »
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« Glacier »

One of the typical examples of negative feedback is the thinning of glaciers. When a glacier becomes thin, it abandons, gradually, the ablation zone, and therefore the rate of thinning decreases progressively. When ablation is greater than accumulation, the glacier does not shrink, it continues to flow, but thinning. In the ablation zone, which corresponds to the distal part of a glacier, below the snow-line, the ice disappears, mainly, by evaporation and fusion. When a glacier is thinning, it approaches the accumulation zone, which is the area where snowfall exceeds melting ice, evaporation, and sublimation losses. An example of positive feedback is the accumulation of snow and ice of a glacier, which by increasing the albedo decreases the temperature of the region, which favours the precipitation of more snow and ice, thus accelerating the growth of the glacier. The albedo is the ratio of the amount of electromagnetic energy reflected by a surface to the reflected energy. In the case of solar energy received by the Earth, the albedo is the ratio between the solar energy reflected and received by the Earth's surface. It ranges from 0 to 1, with zero for a black terrestrial surface and 1 for an ideal mirror-like terrestrial surface, from which the surface of a glacier approaches. The images of the Icelandic Breidamerkurjölkull (shown above), which is part of Vatnajökull (the largest ice cap in Europe), suggest a thinning of the 2 km glacier in 27 years which corresponds to a rate of 74 m/year. The image of 2009 suggests that the thinning seems to have increased strongly (do not confuse retreat with thinning). A glacier is a current of ice that flows downdip. It does not has reverse like a car, that has a back gear. When ablation exceeds ice deposition, a glacier continues to flow downdip, but thinning.

Feeding (Coastal area)....................................................................................................................................................................Alimentation (De la côte)

Alimentação (da costa) / Alimentación (de la costa) / (Küsten) Sammlung / 功率（海岸）/ Мощность (побережье) / Potenza (costa) /

Quantity of material (solid inorganic and organic particles, i.e., a sedimentary particle*) brought to the coast by marine, wind and continental morphogenic agents contribute to the maintenance or growth of coastal landforms. All the primeval clastic sedimentary particles comes from the continent. Progradations suggest the sense (direction) of the regional terrigeneous influx. In certain cases, as in the "gull wings" (P. Vail) structures observed in submarine slope fans (SSF), the development of the natural turbidite levees indicates the direction of a local terrigeneous influx (usually perpendicular to the regional influx). There is no original sedimentary particles coming from the sea. When the geometry of a sedimentary interval is retrogradational, as that of the sedimentary transgressions (set of increasingly important marine ingressions and increasingly smaller sedimentary regressions) forming the transgressive interval (TI) of a sequence-cycle, the sediments come from the mainland. They prograde during the periods of stability of relative sea level occurring between the eustatic paracycles. In the field and drilling cores, every sedimentary interval (shallow-water) exhibits progradations indicating a terrigeneous influx coming from the continent.

Sea: " Shoreline "

(*) In spite of the fact that many geoscientits consider a sedimentary particle as synonym of sediment, in geology, a sedimentary particle (solid, inorganic and organic particulate matter) becomes a sediment when settles on the bottom of the sea or other water-body, by sedimentation, when the hydrological conditions no longer carry it or keep it suspended.

Femtoplankton...........................................................................................................................................................................................Femtoplancton

Femtoplâncton / Femtoplancton / Femtoplankton (Sache) / Femtoplankton (的事) / Фитопланктон / Femtoplankton (cosa) /

Plankton less than 0.2 microns (10^-6) in diameter. The term femtoplankton is misused. The prefix femto designates 10^-15 (1 fentometer* is, more or less, the radius of a proton).

See: « Plankton »
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« Meroplankton »
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« Epipelagic »

The importance of size and shape in free-floating organisms (planktonic organisms), in which the maximum linear dimension varies between <0.2 μm and> 200 μm, allows to separate the biota into five size categories. From the small femto-planktonic to large to the macroplankton, we can individualize: (i) Femto-plankton ; (ii) Pico-plankton ; (iii) Nanoplankton ; (iv) Microplankton and (v) Macroplankton. The distinction between non-particles (soluble) and non-soluble particles in fresh-water systems is, usually, defined in terms of retention in a 0.2 μm mesh network. On this basis, the smallest group, i.e., the femtoplankton (<0.2 μm) falls within the category of non-particles, i.e., viruses and small bacteria that are an integral part of dissolved organic material in the freshwater environment . For Homer, the term plankton designated the animals that erred to the surface of the waves. In 1887, Hensen defined plankton as small organisms that live in fresh, brackish and salty water, often suspended such as: gametes, larvae, unfit animals to fight against the current (small crustaceans, plankton and jellyfish), plants and microscopic algae. Plankton is the first link in a marine food chain. Phyto-plankton is consumed by zooplankton and a myriad of marine organisms. They are the prey of small predators, which are themselves hunted by larger predators. Plant plankton or phytoplankton are autotrophic vis-à-vis carbon. They are able to grow in environments containing only inorganic carbon. Nanoplankton and phytoplankton are present in the superficial layers of the sea (0-15 m deep), where photosynthesis occurs. They absorb minerals and carbon dioxide (CO₂) and reject oxygen under the effect of light. As examples of phyto-plankton we can mention: cyanobacteria, diatoms, dinoflagellates, etc. Phytoplankton represents just 1% of the biomass of photosynthetic organisms on the planet, but 45% of the primary production (fixation of inorganic carbon, CO₂, in organic carbon, C₆H₁₂O₂).

(*) fem-to (symbol f) is the prefix of the International System of Units (SI) which represents 10 ^-15 times this unit (one millionth of a billionth). Adopted in 1964, it comes from the Danish word fem-ten, meaning "fifteen".

Fetch.........................................................................................................................................................................................................................................................................Fetch

Varrido / Fetch, Barrido / Fetch / 取 / Нагон воды / Fetch /

Area of the ocean open above the surface from which the wind blows with a constant speed and direction creating a system of waves. Extension of the surface of the ocean over which the wind blows for some time to generate a wave or wave system (Moreira, 1984).

See: « Littoral »
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« Wave Action Level »
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« Continental Platform »

The growth of the sea-waves depends, fundamentally, on three major factors: (i) Wind speed , (ii) Fetch and (iii) Wind duration. Fetch is the distance over which the wind blows in a certain direction with, a more or less, constant velocity. The duration of the wind is, of course, the time during which the wind affects that distance. Winds that abruptly accelerate or decelerate or change direction, significantly, create conditions for a new fetch to form in an area where there were already waves. With the wave monograms (graph used to represent in a plan, equations with several variables, such that the calculation of their solutions is reduced to a simple reading made in this graph also called abacus) or other methods is possible to predict the maximum height that the waves reached in the new fetch. However, the time at which this maximum height occurs will depend on the height of the waves that incorporate the new fetch. The higher the fetch, the higher the wind speed and the stronger and higher the waves. Understanding how the fetch of a region changes or knowing how many different regions of fetch exist in a particular area, it is very helpful for meteorologists to construct the numerical models of the swell and the value of their predictions. In the example illustrated in this figure, several fetches can be observed. The ovals underline just the possibility of fetching. When evaluating a fetch, the interpreter needs just to worry about fetches that have created waves. There are no rules to determine the boundaries between the fetches. The changes of speed and direction of the wind are, in the high sea (open sea), very subtle. Since the wind speed slows or the direction begins to change, the waves do not grow anymore. It is the fetch, which produces the swell and it is, also, responsible for a part of the coastal erosion, since it influences the coastal currents.

Fibonacci Sequence................................................................................................................................................Séquence de Fibonacci

Números de Fibonacci / Números de Fibonacci / Fibonacci-Folge / 斐波那契数列 / Чи́сла Фибона́ччи / Successione di Fibonacci /

Sequence of numbers with very interesting properties, in which a given number is the sum of the two preceding numbers.

See: « Theory of Evolution »
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« Law of Sigmoid Growth (carbonates) »
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« System (theory) »

The numerical sequence that today has the name of Leonardo of Pisa or Fibonacci arose from a problem of rabbits, that Fibonacci treated in its book Liber abbaci published in 1220: "A certain man put a pair of rabbits in a place surrounded on all sides. How many pairs of rabbits can be produced from this pair in a year, assuming that each pair generates a new pair, which becomes productive since the second month? "It is easy to see that the number of pairs of rabbits in each of the 12 successive months will be: 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, ... etc. In other words, the number of pairs of rabbits will create a series in which each term is the sum of the two previous ones. This is known as a Fibonacci sequence and the numbers are known as Fibonacci numbers. This kind of sequence has interesting mathematical properties. A line can divided in two segments so that the ratio of the larger to the smaller segment is the same as the ratio of the line to the larger segment. This ratio, which is approximately 1,618, is known as the Golden Ratio. It was used during the Renaissance as a basic proportion in architecture. The Fibonacci sequence also appears in plants, particularly with respect to growth points. Take the time that a plant takes puts out a new sprout (it grows two months before it is strong enough to withstand the branching). If the plant branches out every month, the number of growth points (sprouts) follows a Fibonacci sequence. In many plants, the number of petals is a Fibonacci number. Ranunculus plants have 5 petals, lilies and irises have 3 petals, some delphiniums have 8, maize marigolds have 13 petals, some asters have 21. Daisies can have 34, 55 or even 89 petals. Also, as illustrated in this figure the Fibonacci numbers can also be recognized in the arrangement of the seeds at the head of the flowers. In the same way the Fibonacci numbers are in the structures of the shells and, particularly, in the nautical shells (as illustrated in the diagram of this figure).

Fifth Order Eustatic Cycle.........................................................................................Cycle eustatique de 5 ^ème ordre

Ciclo eustático de 5^a ordem / Ciclo eustático de 5° orden / Fünfte Ordnung eustatischen Zyklus / 第五秩序海平面周期 / Эвстатический цикл пятого порядка / Ciclo eustatiche (5°ordine) /

Expression to avoid since it does not correspond to a cycle but a eustatic paracycle limited between two flooding surfaces, with a duration between 0.1 and 0.5 My (as in the 4^th order eustatic cycles) and boundary by unconformities. Between the eustatic paracycles (marine ingressions), which form the different systems tracts of a sequence-cycle, there are no relative sea level fall (hence the name of the paracycle), but only a stability period of the relative sea level during which there is deposition.

See: « Eustatic Cycle »
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« Supercontinent »
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« Stratigraphic Cycle »

Many geoscientists have considered the 5^th order eustatic cycles induce parasequences, which we consider abusive, since a parasequence does not exhibit any cyclicity. We prefer to use the terms eustatic cycle and sequence-paracycle. The use of the term cycle is abusive, since it corresponds to the period in which a series of events or phenomena occur until it reaches a point from which the events repeat themselves in the same order. In scientific language it is said a cycle is a set of phenomena occurring in an ordered and repeated way indefinitely, as for instance the water cycle, the nitrogen cycle or a sequence-sequence, to indicate the successive transformations of the physical state or combining water, nitrogen or sediment deposition in nature. In sequence stratigraphy, a set of eustatic paracycles, which are bounded by flooding surfaces, form an eustatic cycle, which is limited between significant relative sea level falls. Similarly, a set of sequence-paracycles form different sub-groups of sedimentary systems tracts that constitute a sequence-cyle. Sequence-paracycles are induced by eustatic paracycles that create the necessary space available for sedimentation. A paracycle sequence corresponds to one, or several (stacked), lateral succession of synchronous and genetically linked depositional systems that fill the available space created by eustatic paracycles which are limited by ravinement surfaces produced by the marine ingressions. Between successive eustatic paracycles there are no relative sea level falls, just stability periods of relative sea level during which deposition occurs as shorelines prograde seaward. There are two types of sequence-paracycles: (i) Periodic and (ii) Episodic. The first are linked to the Milankovitch orbital cycles, especially, in the transgressive intervals of the sequence-cycles. Milankovitch cycles are climatic cycles with periods of 19, 23, 41 and 100 ky, induced by insolation, which creates important changes in the cryosphere and, therefore, produces important eustatic changes. The episodic sequence-paracycles, called sub-sequences by certain geoscientists, are deposited in lowstand and highstand prograding wedges. They are created, mainly, by lateral displacements of the delta lobes (formed by a, more or less, vertical accretion of a number of deltas, which form the delta buildings). They are magnificent examples of the pendulum effect. In the same way that eustatic paracycles form the eustatic cycles of 4^th and 3^rd order, the sequence-paracycles are sedimentary intervals that compose the systems tracts groups of the sequence-cycles. Eustatic cycles of the 3^th order induce the sequence-cycles. They are bounded by unconformities or by their associated correlative paraconformities in deep-water. On this subject it is interesting to understand how, in the transgressive interval (TI) of a cycle-sequence, a clastic sedimentation is made: (i) A small relative sea level rise (marine ingression or eustatic paracycle) moves the shoreline continentward; (ii) The marine ingression cover the sediments, already, deposited by certain water column, creating not only available space for the sediments (accommodation), but also a ravinement surface at the the sea floor ; (iii) A period of stability of relative sea-level* occurs after the marine ingression ; (iv) During this period of stability, deposition takes place as the shoreline is displaced seaward (sequence-paracycle, i.e., a sedimentary regression) without reaching the position it had before of the marine ingression ; (v) A new relative sea level rise, more important that the previous one, displaces, again, the shoreline continentward (marine ingression in acceleration) ; (vi) New stability period of the relative sea-level with the deposition of a new sequence-paracycle (sedimentary regression), which again displaced the shoreline, which did not reach the position it had before. This process is repeated until the new marine ingression is smaller than the previous one (marine ingress in deceleration). It is these successive incremental rise of relative sea level, which are called eustatic paracycles (duration between 100-500 ky), that allow the deposition of the sequence-paracycles. That is why it is said that within a sequence-cycle (siliciclastic intervals) the "transgressions" (and not transgression) correspond to the set marine ingressions increasingly important and sedimentary regressions increasingly smaller, characterized by a global retrogradational geometry.

(*) Local sea level referenced at any point on the Earth's surface which can be the sea floor or the top of the continental crust (base of the sediments). It is the result of the combined action of tectonic (subsidence or uplift of the sea floor) and absolute (eustatic) sea level referenced to the Earth's centre.

Fill Seismic Reflection Configuration.............................................Configuration de remplissage

Configuração de preenchimento / Configuración de relleno / Füllen Sie reflexionsseismischen Konfiguration / 填写地震反射结构 / Картина осадочного заполнения на разрезах МОВ / Configurazione di riempimento (riflettori) /

Set of seismic reflectors, interpreted as strata, that fill negative topographic anomalies of the underlying strata. The underlying reflectors may be truncated or concordant with the fill, which may be classified in relation to the underlying layers or relative to their own geometry.

See: « Stratal Patterns »
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« Reflections Configuration »
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« Incised Valley »

On this tentative geological interpretation of a Canvas auto-trace of a detail of a North of Angola offshore seismic line, the filling of the erosional anomalies created by old submarine canyon is well visible. The successive onlaps, in NW-SE direction fossilizing the erosional surfaces are evident. These reflection terminations, in a first phase, have to be considered as apparent. Nothing says they exist in the perpendicular direction. On NW-SE seismic lines, i.e., roughly perpendicular to the shoreline, the internal reflection configuration of the fillings diverges towards the central part of the anomalies. However, it is apparent. The seismic line is, more or less, parallel to the terrigeneous influx. The geometric relationships and the internal reflection configuration of the fillings observed on this line do not occur on the perpendicular lines, which are, practically, parallel to the terrigeneous influx. On the parallel lines to the terrigeneous influx, it is easy to see that the lower terminations of the seismic reflectors filling the anomalies, are downlaps. This corroborates the a priori hypothesis, that the geometric relationships suggested on this tentative interpretation are not real, but apparent. Likewise, the internal divergent reflection configuration is also apparent. According to the transport direction of the sedimentary particles (along which the geometrical relationships and the reflector terminations are true), the internal reflection configuration of the fills is, practically, parallel. Such a configuration suggests the filling was done in retrogradation (in the reverse direction of a natural filling), i.e., from the bottom upwards and backwards, by onlapping as the continental slope was fossilized by lowstand or highstand deposits. The filling by marine or coastal onlaps underline a relative sea level rise. The normal faults with opposite dips, visible in the sedimentary substrate, suggest the location of the submarine canyon seems to have been, at least, partially, induced by an extensional tectonic regime (lengthening). It is important to take into account that during the Late Tertiary this area underwent a significant tectonic uplift. The amplitude of such a tectonic uplift exceeded, locally, 1,500 meters. This uplift was not induced by a compressional tectonic regime, i.e., by a shortening of the sediments. The sediments were rather lengthened (σ₁ vertical). The westward dip of the reflectors of the sedimentary substrate does not refute the conjecture of such tectonic uplift. On the contrary, it seems to corroborate it. The most common types of internal reflection configurations of the seismic intervals are, schematically, illustrated in the lower right-hand corner of figure. Different types of internal configurations are schematically illustrated : (i) Parallel, set of seismic reflectors interpreted as parallel deposited strata ; (ii) Sub-parallel, when undulations of the reflectors are visible within a parallel internal configuration ; (iii) Oblique Tangent, the seismic reflectors or associated strata, have a decreasing dip to the base; (iv) Parallel Wavy, set of wavy seismic reflectors, more parallel to each other ; (v) Divergent, set of seismic reflectors, interpreted as strata, which thicken laterally basinward ; (vi) Parallel Oblique, set of seismic reflectors with a parallel/oblique pattern, i.e., a set in which the strata end up downstream with a relatively large dip ; (vii) Convergent, set of seismic reflectors, interpreted as strata, that thin laterally basinward ; (viii) Sigmoid, progradations with an upside-down S geometry, i.e., the dip in the upper and lower parts is relatively small, whereas in the medial part it is much higher ; (ix) Sigmoid/Oblique Complex, a particular case of the sigmoid configuration, in which the inclination of the median parts of the progradations is quite high with a frequent presence of toplaps by truncation ; (x) No reflections, i.e., an absence of seismic reflections, which translates homogeneous seismic intervals without bedding or very deformed or even intervals with a very strong dip ; (xi) Hummocky, when the sediments form topographic anomalies or sedimentary build-ups above the base level, as in organic or volcanic constructions ; (xii) Shingled, when the progradations are obliques, almost lying down that take turns one after the other ; (xiii) Chaotic, with disordered reflectors ; (xiv) Filling, set of seismic reflectors, interpreted as strata, that fill negative topographic anomalies of the underlying strata.

Finger Delta (Digitated delta)......................................................................................................................................................................Delta digité

Delta digitado / Delta digitado / fingert Delta / 手指三角洲 / Пальчатая дельта / Delta dita /

When the delta plain extends through several narrow, long, finger-shaped lobes or with a bird-like morphology.

See: « Delta »
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« Cuspate Delta »
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« Delta PLain »

The deltas of  the Mississippi Delta building are typical example of finger deltas. The deltas, themselves, were constructed, mainly, by alluvium deposited by the river when it lost competence entering the Gulf of Mexico. The Mississippi delta building corresponds to a prograding stacking of a large number of deltas of average thickness between 30-50 meters, in the same way that a skyscraper (delta building) is a stacking of flats with a height of more or less, 2.4 m. A delta slope, i.e., a prodelta should not be confused with a continental slope, which in the case of a delta building, may correspond to a, more or less, vertical stacking of several prodeltas. This is the case when, within a sequence-cycle, the basin has no platform, i.e., when the lowstand prograding wedge, for instance, is an outbuilding of deltas. In these conditions, the shoreline corresponds,roughly, to the continental edge that is, also, the basin edge. In the same way, during the 2^nd stage of development of the highstand prograding wedge, the continental slope may be the result of the construction of a delta building. Another case in which the continental slope may be the result of a more or less vertical accumulation of small prodeltas is the overlapping of a series of incomplete sequence-cycles formed just by lowstand prograding wedges. In this case, it can, also, be said, collectively, the continental slope corresponds to a, more or less, progradational stacking of delta slopes. A continental slope may be hundreds to thousands of meters thick. A delta slope is just few tens of meters height. The deltas that make up the Mississippi Delta building have developed in an area characterized by: (i) Wave action so weak that the amount of sand that is transported to the beach is less than the sand scattered offshore by storms ; (ii) A difference between low tide and high tide of about 30 cm, which is seems sufficient to play an important role in sedimentation (the delta gradient is very small) ; (iii) Strong subsidence, induced by compaction of recent sediments, which is about 30-60 cm per 100 years. Recent sedimentation processes, that is, from 7,000/5,000 years ago, displaced the shoreline seaward, between 30 and 80 km*. Several times, more or less, every 1,000 years, the main stream changed bed creating different sets of delta lobes. Each set appears to have been initiated by the gradual capture of the main current by one of its distributaries. During the construction of the delta building, six main lobes were highlighted: (a) Maringoiun ; (b) Teche ; (c) St. Bernard ; (d) Lafourche ; (e) Achafalaya and (vi) The Present-time lobe. The lateral displacement of these lobes, probably, associated with a pendulum effect, created, locally, transgressive episodes, which should not be confused with the two global transgressive episodes created in this area by glacio-eustasy: (1) Brackish Ingression, when lakes, bays and lagoons covered the alluvial delta plain and (2) Marine Ingression, when the longshore of the barrier-bars advanced continentward. The first was done, practically, without ravinement, which, in the marine ingression is quite important. When the relative sea level rises, the shoreline is shifted continentward. It is what the geoscientists call marine ingression. However, a marine ingression may be in acceleration or deceleration. When the sea level accelerates, collectively, i.e, with the associated sedimentary regressions, the shoreline moves continentward: this is what the geoscientists call sedimentary transgressions. Indeed, a set of increasingly large marine ingressions and the associated increasingly smaller sedimentary regressions create, globally, a retrogradational geometry, which were collectively called "transgressions" by C. Emiliani  in 1992. The term transgression to designate the displacement of the coastal deposits to the continent is inappropriate, since, in isolation, all the sequence-paracycles prograde seaward. There is no clastic sediments coming from the sea (remobilized sediments excluded).

(*) A displacement of the shoreline seaward, generally, corresponds to what the geoscientists call a sedimentary regression when, at the hierarchical level of a sequence-sequence, it is the result of the gradual seaward progradation of coastal onlaps during stability periods of relative sea level that occur after each marine ingression in deceleration (marine ingression smaller than the previous one).

(**) The capture of a water-course is a hydrographic phenomenon in which the upstream erosion of a river opens a breach in the bed of another stream, more or less, perpendicular, capturing its waters, leaving it without flow. Different types of catch were proposed by Christofoletti (1975): (i) By absorption; (ii) By retreat of headwaters ; (iii) By lateral flattening ; (iv) By overbanking ; (v) Underground erosion, etc.

Firn (Snow-field)........................................................................................................................................................................................................Champ de neige

Campo de neve / Campo de nieve / Schnee - Bereich / 雪原 / Фирновое поле / Nevaio /

Glacial environment encompassing the volume of snow above the snow line. It, usually, corresponds to the mountainous terrain covered, permanently, by a layer of snow, more or less, smooth.

See: « Glacier »
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« Snowline »
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« Glaciation »

In glacial environments it is important to distinguish: (i) Accumulation zone ; (ii) Melting and evaporation zone ; (iii) Snow line ; (iv) Crevasses ; (v) Moraines and (vi) Out-wash plain. During glaciations, glaciers are very important geological bodies. The accumulation zones are, extremely, large and the snow lines are very low. The snow * that forms the glaciers undergoes repeated fusions and freezes that transform it into granular snow ("névée" in French). Under the action of the weight of the snow layers and the upper horizons of granular snow, the deeper horizons become firn. Later (which can mean thousands of years, which is, systematically, forgotten by the geoscientists who work for the IPPC), the firn under the action of compaction, turn into ice. In addition, a few hours after deposition, snow is metamorphosed by the presence of temperature gradients. The blue ice matrix of the glaciers is, often, but erroneously, attributed to the Rayleigh scattering** is, probably, induced by the presence of air bubbles in the ice. The blue colour may, actually, be induced for the same reason that the water is blue. As water is blue due to a slight absorption of red light caused by a resonance (stretching) of the water molecules, the blue ice matrix may have a similar origin. The lower ice levels of a glacier deform, plastically, and flow under pressure. This allows the glacier to move, slowly, as a viscous liquid. Glaciers, generally, flow downdip, although they do not require a sloped surface to flow. The flowing may be motivated, just, by the, more or less, continuous deposition of the snow in the updip area with higher slope. As suggested by crevasses (fractures caused by a local extensional tectonic regimes) developed on the surface of a glacier. The upper horizons of a glacier are more fragile. A glacier is like any other current. It exists, just, as it flows (while accumulation equals ablation). Since ablation exceeds accumulation, the glacier does not shrink (retreat as certain media say), it continues to flow, but become thinner.

(*) Snow forms from raindrops when the air temperature is negative and when the thickness of the layer with positive temperature, immediately, above the Earth's surface is too small to melting the snow. Colder is the air, more the snowflakes are evident: (i) In flakes for very low temperatures ; (ii) In powder (density 0.1) at temperatures above -10° C. The heavy snow (density 0.5) with flakes loaded with liquid water is explained by the blocking of the melting (initiated at several hundred meters of altitude) by the presence of a low altitude layer of air with a temperature near 0° C .

(**) Dispersion of light or any other electromagnetic radiation by particles much smaller than the wave-length of the dispersed photons, which occurs when light travels through solids and transparent liquids, but which is also observed in gases, albeit less frequently. It is Rayleigh scattering of sunlight into the atmosphere which induces the blue sky.

First Order Eustatic Cycle.............................................................................................Cycle eustatique de 1 ^ère ordre

Ciclo eustático de 1^a ordem / Ciclo eustático de 1er orden / Erster Auftrag eustatischen Zyklus / 一阶海平面周期 / Эвстатический цикл первого порядка / Ciclo eustatiche (1°ordine) /

Eustatic cycle lasting more than 50.0 My (millions of years).

See: « Eustatic Cycle »
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« Supercontinent »
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« Stratigraphic Cycle »

Phanerozoic first order eustatic cycles are directly connected with the aggregation and break-up of supercontinents: (i) Proto-Pangea or Rodhinia, at the end of the Precambrian and (ii) Pangea, at the end of the Paleozoic. The great majority of geoscientists admit that the amount of water (in all its forms, i.e., solid liquid and gaseous) is constant, since the Earth's formation, around 4.5 Ga. The first order eustatic cycles can be explained as follows: (A) When a supercontinent forms, the volume of the ocean basins is maximal, since the volume of the oceanic ridges is minimal (little or no oceanic expansion) ; (b) When a supercontinent breaks-up in several continental masses, they begin to move away from each other, due to the new oceanic crust formation ; the volume of the oceanic basins decreases, progressively, what for a quantity of water, more or less constant, implies an absolute (eustatic) sea level* rises ; (c) When the dispersion of the continents is maximum, the volume of the ocean ridges is maximum and the absolute sea level is maximum ; (d) The continents begin to approach one another ; the rate of the oceanic crust formation is lower than the rate of its disappearance along the subduction zones (B- and A-type) ; the volume of the ocean basins begins to increase (oceanic crust and oceanic ridges disappear along the subduction zones) forcing the absolute sea level to fall (for the same amount of water). In this way, the diagrams of this figure are understood without great difficulty. When the number of lithospheric plates is very large (maximum dispersion of the continents), the absolute sea level is high. When the number of lithospheric plates is small, what happens when supercontinents form, absolute sea level is low (the volume of the ocean basins is too large for a constant volume of water). During the Phanerozoic*, eustacy is, easy, to reconstitute. The break-up of the supercontinents is well known. The absolute sea level was low during the Proto-Pangea. Within each sequence-cycle, the sea level was lower than the basin edge . During the Cambrian and Lower Ordovician (dispersion of the continents resulting from the break-up of the supercontinent Proto-Pangea), the absolute sea level rose to the maximum height during the Ordovician. From the Ordovician to the Permian (aggregation of continents to form a new supercontinent - Pangea), the absolute sea level fell. The absolute sea level reached the lowest point with formation of the Pangea supercontinent. The volume of the ocean basins was very large. The quantity and volume of the oceanic ridges was very small. With the break-up of the Pangea supercontinent and the associated oceanic expansion (sea floor spreading), the absolute sea level rose until reaching its acme during the Cenomanian/Turonian (maximum dispersion of the continents). Then, as the old oceanic crust disappears along the B-type and A-type subduction zones, the absolute sea level declined, globally, to the present-day (aggregation of continents for formation, in a few million years, of a new supercontinent). At the scale of first order eustatic cycles, the glaciations that occurred during the Quaternary (Pleistocene), probably, due to the variation of the position of the Earth relative to the Sun (alteration of the solar energy received by the Earth), covered with ice (glaciers and ice caps) a large part of North America and Northern Europe, the Arctic and the Antarctic. During this time-interval there was alternation of periods of glacial thickening ** (absolute sea level fall) and glacial thinning (absolute sea level rise).

(*) The absolute (eustatic) sea level, which depends on Glacio-Eustasy, Geoidal-Eustasy, Tectono-Eustasy and the Thermal Dilatation of the oceans (Steric sea level rise), is the sea level referenced to a fixed point, which is usually the Earth's centre, which combined with tectonics (subsidence or uplift of the sea floor) controls the relative sea level, which is local and referenced to the sea floor or to the top of the continental crust (base of the sediments).

(**) From the Greek phaneros = visible and zoikos = life). Phanerozoic begins in the Cambrian (Paleozoic Era) with the appearance of several animals with shell. Phanerozoic is the Eon along which the abundance of life is greater.

(***) We avoid the expressions, much used by certain geoscientists, of advancing and retreating the ice, since a glacier is a current of ice and so, by definition, it advances down-dip. A glacier does not retreat (it does not have reverse gear). It becomes slim what is quite different. When moving down-dip, it move,s slowly, due to gravity, causing erosion and sedimentation.

First Transgressive Surface................................................................................Première surface transgressive

Primeira superfície transgressiva / Primera superficie transgresiva / Erste transgressive Oberfläche / 第一次海侵面 / Первая трансгрессивная поверхность / Prima superficie trasgressiva /

Surface that marks the beginning of the transgressive interval (TI) within a sequence-cycle. Upstream of the last onlap of the lowstand prograding wedge (LPW) and in the absence of incised valley (Iv) fills, the first flooding surface (1^st FS) coincides with the lower unconformity limiting the stratigraphic cycle referred as sequence-cycle (SC).

See: « Transgressive Interval »
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« Flooding Surface »
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« Sequence-Cycle »

A unconformity (E), i.e., an erosional surface induced by a fall of the relative sea level* is, easily, recognized on this tentative interpretation of a detail of Gulf of Mexico seismic line, by the river incision that created an incised valley. The relative sea level fall responsible for the unconformity, displaced basinward and downward, the coastal onlaps outcropping the shelf (if the basin had a platform), rising, even more, the coastal wedge in relation to the sea level, The coastal wedge or coastal prism is the set of fluvial and shallow-water deposits accumulated in the coastal plain during the seaward progradation of the shoreline. It extends continentward onlapping the pre-existing topography. The seaward displacement of the shoreline broke the provisional equilibrium profiles of the rivers (the definitive equilibrium profile of a water-course is a utopia ; it is never reached), which forced the water-courses to dig (erode) their beds, even more, in order to reach a new provisional equilibrium profile. The incised valley recognized on this tentative interpretation (negative anomaly on the E unconformity) was, probably, form in such a way. On a seismic line, far up-dip of the depositional coastal break ( roughly the shoreline) of the chronostratigraphic lines (depositional surfaces), where the unconformities are more difficult to recognize by onlapping, the identification of a incised valley highlights the its associated discordance, which can be then inferred, more or less, in continuity landward. During the relative sea level fall, in the new sequence-cycle, the lower sub-groups of the lowstand systems tracts group are deposited, i.e., the submarine basin floor fans (SBFF) and the submarine slope fans (SSF), which are not visible in this auto-trace, but are present eastward of this auto-trace. During the deposition of the upper part of the lowstand prograding wedge (LPW), which is also not visible in this auto-trace, but present more to the east, the relative sea level began to rise. In the final part of lowstand prograding wedge deposition, the sea, progressively, invaded the incised valleys that began to be more and more filled (yellow colored range). When the relative level of the sea, completely, flooded the coastal plain of the lowstand prograding wedge, the first transgressive surface (base of the transgressive interval, TI, green coloured) covered and fossilized the filling of the incised valley, initiating the deposition of the highstand systems tracts group: Transgressive interval (TI) sub-group and Highstand prograding wedge (HPW) sub-group. On seismic lines, it can be said that the transgressive surface is, in the great majority of cases, the upper limit of the incised valleys fills, particularly, the incised valleys closer to the continental edge (edge of the lowstand prograding wedge). The continental edge that has become the new basin edge, once the basin has now a continental shelf. During the deposition of the lowstand systems tracts group (LSTG) of a sequence-cycle, the geological conditions are lowstand. The continental edge does not correspond to the basin edge, which remains the last edge of the preceding sequence-cycle. On the contrary, during the deposition of the highstand sedimentary systems tracts group (HSTG), the basin has, in general, a continental shelf. The continental edge is the basin edge. Throughout the deposition of the transgressive interval (TI) of a sequence-cycle, the basin has, always, a platform. The marine ingressions are increasingly important and the sedimentary regressions becoming increasingly smaller. Globally, the shoreline is always located upstream of the continental edge. At the beginning of the deposition of the highstand prograding wedge (HPW), the basin does not have a continental shelf. As the relative sea level rises in deceleration (marine ingression increasingly smaller and increasing important sedimentary regressions) at a certain moment (beginning of 2^nd phase of the highstand prograding wedge), the progradations of highstand prograding wedge fossilize the continental shelf. The basin no longer has a continental platform (shelf) and the shoreline coincides as the continental edge which is also the basin edge.

(*) Local sea level, referenced to any point on the Earth's surface, as for instance, the base of the sediments (top of the continental crust) or the sea floor, which is the result of the combined action of the tectonics (subsidence or uplift of the sea floor) and absolute eustatic sea level (supposed global and referenced to the Earth's centre).

Fischer-Tropsch Reaction...................................................................................................Réaction de Fischer-Tropsch

Reacção de Fischer-Tropsch / Reacción de Fischer-Tropsch / Reaktion von Fischer-Tropsch / 费 - 托反应 / Реакция Фишера-Тропша / Reazione di Fischer-Tropsch /

Reaction using a catalytic, rich in iron, to convert gases (CO₂ and H₂) into liquid hydrocarbons. During World War II, Germany, which had no access to oil, produced gasoline and diesel from gasification of coal by the Fischer-Tropsch reaction.

See: « Sinthetic Natural Gas (SNG) »
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« Hydrocarbon »
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« Coal Oil »

This photograph illustrates the Gussing pilot gasification plant, in Austria, which uses the reaction of Fischer-Tropsch (FT reaction). The Fischer-Tropsch process is a well-established and widely applied technology on a large scale. Although its popularity is affected by the heavy investment it requires and the high cost of operations and maintenance. The current volatility of the price of a barrel of oil and any environmental problems that the technology may create are negative factors for its use. The use of natural gas as feedstock is just valid when using non-economic gas (discovered gas but not usable for physical or economic reasons), i.e., natural gas resources located away from major cities and which are not sufficiently important to be transported by pipelines or to power a LNG project, where natural gas, mainly, methane (CH₄) is temporarily converted into liquid form to facilitate storage or transport. Otherwise, the direct sale of gas to consumers would be more profitable. Several companies are looking at ways to produce non-economical gas resources in a profitably way. The great majority of oil company geoscientists think if current energy consumption (2008) is maintained, the natural gas production peak will be reached in 5 to 15 years after peak oil. For certain geoscientists, especially those retired for oil companies (who can, mow, say what they really think), the peak of oil has, already, been reached. There are large reserves of coal that can be, progressively, used as a energy source during the oil depletion. The Fischer-Tropsch process can use coal to produce an alternative fuel if the price of oil becomes too high.

Fission Track..................................................................................................................................................................................................Trace de fission

Traço de fissão / Trazas de Fisión / Fission Track Dating / 裂变径迹 / След осколков деления / Fissione traccia /

Visible imperfection in certain minerals and volcanic glass produced by the spontaneous fission of an unstable atomic nucleus, which sends particles of energy through matter. The density of the fission traces is a function of the number of atoms that have undergone the fission and, therefore, of the age of the minerals or of the volcanic glass.

See: « Apatite »
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« Chronostratigraphy »
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« Radiometric Dating (radiochronology) »

The dating of a rock by fission traces is a radio-isotopic synchronization method based on the natural, but statistically constant, fission of uranium (U²³⁸), which is present in trace form in certain minerals such as apatite, zircon , titanium, etc. The energy released by the fission ejects nuclear fragments into the confining material causing damage trajectories that are the fission tracks. The number of tracks, of length between 10 and 20 μ (micron), depends on the initial amount of uranium contained in the sample and the time. These tracks can be observed under the microscope after the sample is attacked by an acidic solution so that the tracks are highlighted. The usefulness of this dating method lies in the fact that certain materials lose their fission tracks when heated (70-110° C as, for instance, to apatite). The useful time interval of this method is between 100 and 100,000 years, although the method error is difficult to determine. Most geoscientists think the dating interval with a relatively small error is between 30,000 and 100,000 years. The number of fission tracks per unit area when counted under a microscope depends on several factors: (i) The time during which the tracks are accumulated ; (ii) The amount of uranium in the crystal and (iii) The length of the fission tracks. In the case where the mineral used is apatite, its age can be determined by the population method, i.e.: (a) The apatite grains are separated into two populations ; (b) A population is heated to about 600° C during 6 hours, which removes all fossil fission tracks ; (c) This population is subjected to a certain fluence of neutrons and, thus, new fission traces are formed ; (d) The two populations are mounted on thin sections ; (e) The grains are polished and then corroded during 20/30 seconds by 10% NO₃H (nitric acid) so that the fission tracks become optically visible ; (f) The grains of each population are counted, which gives the density of the fossil tracks induced (annealed population) and from which age is calculated, since the decomposition rate of U²³⁸ is known.

Fjord.........................................................................................................................................................................................................................................................................Fjord

Fiorde / Fiordo / Fjord / 峡湾 / Фьорд / Fiordo /

Long and narrow entrance of the water of the sea in a valley with very steep walls, created by the action glacier. The origin of the fjords is due to the movement of the glaciers that create valleys in the form of a "U" due not only to the erosion of the substrate by the ice, but also to the sedimentary particles that they carry.

See: « Glacier »
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« U-Shaped Valley »
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« Glaciation »

This photograph illustrates the proximal (upstream) part of the Geiranger Fjord Sunnmore region in Norway. This fjord is, simply, a small branch (about 15 km) from the Storfjord (Grand Fjord). The Geiranger fjord is under threat of the vertical walls of the Sauternes mountain (a few kilometers from where the photograph was taken). Sooner or later, the walls collapse producing, probably, a tsunami that in less than 10 minutes, will reach, the nearest cities with all the consequences that such an event may entail. Throughout the fjord a whole series of farms have been abandoned, but unconsciously, or for purely economic reasons, every year, in the summer, tens of thousands of tourists are carried by hundreds of boats (as can be seen in this photograph ) along the fjord to admire the waterfalls on the fjord walls. There is great confusion associated with the term fjord. The water-bodies that the Scandinavians designate fjords are not fjords to the English. In the same way, the water-bodies that the Scandinavians do not consider fjords are for the English fjords. For example, the Koror bay (Montenegro), considered by some geoscientist as a fjord, corresponds, in fact, just to the flooding of the river canyon. For most of the geoscientists the Bay of Kotor is a ria landform, often, referred as a drowned river valley). In Croatia, the Lim bay, which is called the Lim fjord, also, does not correspond to a fjord carved by glacial erosion, but to a river excavated by the Pazincica river. In northern Denmark, the Scandinavian term, Lim fjord (which has nothing to do with the Lim fjord of Croatia), is for the English geoscientists the channel that separates the north of the island of Jutland (Vendsyssel /Thy) of the rest of Jutland. Of all the recesses along the New England (USA) coastline, which are designated fiords (sometimes fiardes), just the Somes Sound (Maine), seems to have a glacial origin.

Flame Test....................................................................................................................................................................................................Teste de la flamme

Teste da chama / Teste de llama / Prüfflammen / 试验火焰 / Испытания на воспламеняемость / Test di fiamme /

Identification of the presence of metals by the color of the flames they produce.

See: « Spectroscopy »
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« Kirchhoff-Bunsen Theory»
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« Atom »

The flame test is a procedure used in chemistry to detect the presence of some metal ions, based on the characteristic emission spectrum for each element. The test involves the introduction of a sample into a flame and observing the resulting colour. Samples are, generally, handled with a platinum wire, previously, cleaned with hydrochloric acid to remove residues of previous analysis. The flame test is based on the fact that when a certain amount of energy is supplied to a particular chemical element (in the case of the flame, energy* in the form of heat**), some electrons from the last valence layer absorb this energy passing to a level of higher energy, producing what we call an excited state. When one of these excited electrons returns to the fundamental state, it releases previously received energy in the form of radiation. Each element releases the radiation at a characteristic wave-length. The amount of energy required to excite an electron is unique to each element. The radiation released by some elements has wave-lengths in the range of the visible spectrum, i.e., the human eye is able to see them through colours. Thus, it is possible to identify the presence of certain elements due to the characteristic colour they emit when heated in a flame. The flame temperature of the Bünsen burner is sufficient to excite an electron quantity of certain light emitting elements as they return to the fundamental state of colour and intensity, which can be detected with considerable certainty and sensitivity by visual observation of the flame. Flame testing is quick and easy to do, and requires no equipment that is not normally found in a chemistry lab. However, the amount of detectable elements is small and there is a difficulty in detecting low concentrations of some elements, while other elements produce very strong colours that tend to mask weaker signals. Sodium, which is a common constituent or contaminant in many compounds, produces an intense yellow colour in the flame test that tends to dominate over other colours. The colour of the flame is, usually, observed through a blue cobalt glass to filter the yellow produced by the sodium and allow the visualization of colours produced by other metallic ions.

(*) Energy is the ability to do a work.

(**) Neither the heat nor the work is energy forms. Both are methods to transfer energy from one place to another... work is a method, heat is another. The energy can be transferred either through work or heat.

Flexural Subsidence............................................................................................................................................Subsidence par flexure

Subsidência por flexura / Subsidencia por flexura / Subsidenz durch Biegung / 弯曲的沉降 / Искривленное оседание / Subsidenza per flessione /

Subsidence created by the overlapping of the thrust faults associated with the formation of mountain ranges. In foreland basins, flexural subsidence or subsidence by flexure is probably the main responsible for creating available space for sediments (accommodation).

See: « Continental Collision »
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« Subsidence »
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« Tectonic Subsidence »

The correlation between the exploration wells in the foothills of the Cordillera Colombian, illustrated in this figure, suggests the subsidence during post-Cretaceous was, mainly, induced by overloading of the thrusts (low angle reverse faults with a dips lower 15°) which caused a lithosphere flexure. The isostasy principle results from the flotation of lithospheric plates on the densest material of the asthenosphere, whose equilibrium depends on their relative densities and the weight of the lithospheric plates. Such equilibrium implies an increase in the weight of the plates (by thickening or deposition of sediments, water or ice on its surface) leads to its sinking. Conversely, an isostatic rise or rebound, occurs when the weight of the plates decreases. This implies the existence in the mantle of a compensation depth, where the pressure, in a charged area or not, is the same. Such an equilibrium corresponds to the Archimedes principle when applied to a boat, iceberg or to the crust floating in a dense mantle. When the sediments displace the water, they apply a load on the crust and lithosphere (crust and upper mantle, above the isotherm 1350° C) that lower it under the action of weight. Assuming that "Wd" is the height of the water column, "ρs" the density of the sediments (plus or minus 2,500 kgm³), "ρm" the mantle density (plus or minus 3,300 kgm³), "ρw" the water density (about 1,030 kgm³), "ρc" the density of the crust (plus or minus 2,500 / 2,900 kgm³), "Tc" the average thickness of the crust and "r" the distance from the base of the crust to the compensation surface , it is easy to calculate the depth of the compensation surface (Wd. ρw xg + Tc. ρs xg + r. ρm. g) and the thickness of the sediments S = Wd {(ρm-rw)/(ρm-rs)}. If the compensation surface is located, for instance, at the base of the crust with an initial water height of 2 km, theoretically, it is possible to accumulate about 5 km of sediment due just to the subsidence induced by the weight of the sediments. If water-depth and the terrigeneous influx are adequate, it is possible to accumulate around 2.5 times the height of water without any tectonic subsidence or sea level variation, whether absolute (eustatic) or relative. The subsidence of foreland basins** is mainly , controlled by mechanical, rather than thermal, geological events. The loading of the thrusts induces, mainly, the subsidence of the substratum. The consequences of such loading, which is enhanced by the weight of the sediments, appear to be controlled by the flexural strength of the substrate, which influences the elastic thickness of the underlying lithosphere. In the upper part of this figure, the auto-trace of an offshore seismic line from southern Argentina illustrates a time profile (take into account the seismic artefact induced by the water-depth changes) from a back arc basin and associated mountain folded basin. The origin of responsible loading of tectonic subsidence is not always so obvious. The gravimetric anomalies found in certain folded mountain belts, such as in the Himalayas, suggest the present-time topography is sufficient to explain the subsidence of the Australian-Indian lithospheric plate. On the contrary, gravimetric anomalies in the Alps or in the Appalachians folded belts, suggest the present-time topography is insufficient to explain the sinking of the associated foredeep. In these cases, certain geoscientists invoked buried loads*** within the crust. However, the temporal distribution of these buried loads is, practically, unknown. The recognition and study of foreland basins without associated folded belts has led certain geoscientists to think that "buried loads" are responsible for the main mechanism of the creation and preservation of foreland basins. The a priori advanced conjectures can be formulated as follows:   (i) If a folded mountain belt is exposed to erosional agents and if it is responsible for the loading of foreland basins, the loading disappears as erosion occurs ; (ii) The foreland basins will be, partially, eroded due to the erosion induced by the decrease of the tectonic loading (weight of the thrusts) ; (iii) Conversely, the buried loads are protected from erosion and, therefore, will survive long time within the continental crust".

(*) The Archimedes principle states than every body immersed in a fluid undergoes the action of a, vertically, upward force whose intensity is equal to the weight of the fluid displaced by the body.

(**) Sedimentary basins that lie on the edge of mountain ranges which, generally, have a wedge shape and a depth that decreases, gradually, towards the craton or older adjacent basins.

(***) May correspond to a relic of oceanic crust or mantle material pushing to continental crust implemented during the convergence of lithospheric plates.

Flocculation......................................................................................................................................................................................................................Floculation

Floculação / Floculación / Flockulation / 絮凝 / Флокуляция (коагуляция) / Flocculazione /

Physicochemical phenomenon during which the micelles (set of molecules that constitute one of the phases of the colloids) and particles in suspension form flakes or aggregate in a flake, which destroys the stability of the solution and favors the deposition.

See: « Deposition (clastics) »
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« Transportation (sedimentary particles) »
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« Leaching »

In chemistry, flocculation is a process where colloids* come out of suspension in the form of flakes. Flocculation differs from precipitation since, prior to flocculation, the colloids are, simply, suspended in a liquid and not actually dissolved in the solution. Flocculation is synonymous with coagulation, i.e., process in which dispersed colloidal particles agglomerate. As illustrated in this figure, in some cases flocculation corresponds to the beginning of deposition. The micelles and sedimentary particles suspended by flocculation form, more or less, heavy aggregates which, sooner or later, as a function of the flow velocity, are deposited in the bed of the stream. Flocculation and sedimentation are, widel, used in the purification of drinking water, as well as, in the treatment of sewage, rainwater and industrial effluents. In water, particles smaller than 0.1 μm (10^-7 m) remain, continuously, moving due to the (often negative) electrostatic charge, which causes them to repel. Since its electrostatic charge is neutralized by the use of chemical coagulants, the finer particles begin to collide and clump together under the influence of Van der Waals forces (intermolecular forces resulting from the polarization of molecules). These larger and heavier particles are called flakes. Flocculants or flocculation agents, are chemicals substances that promote flocculation by forcing the colloids, and other particles in suspension into a liquid, to aggregate and form a flake. Flocculants are used in the treatment of water to improve the sedimentation or filtrability processes of small particles. Flocculants are used in pools to aid in the removal of microscopic particles, which could make the water turbid and that would be difficult to remove by filtration.

(*) Systems in which one or more components have at least one of their dimensions within the range of 1nm (1×10⁻⁹ meter or 0.000000001 meter) at 1μm (10⁻⁶ m = 0,000 001 meter).

Flood (Rising tide, flow)..............................................................................................................................................Marée montante, Flux, Flôt

Enchente / Flujo, Marea creciente / Flut, Steigen / 涨潮 / Приливная волна / Marea montante /

Part of the tidal cycle during which the sea level rises. Synonym with Rising Tide and Flow.

See: « Flow »
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« Intertidal Beach »
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« Shoreface »

In this figure, at the maximum of the tidal current (rising tide) or, in other words, in the high-tide, the sea level is, more or less, three meters from the top of the quay. The boat no longer rests at the exhumed sea floor since almost the whole area was covered by the sea (compare with the figure, which represents the same area during the low tide). The tide is an oscillation wave* of low amplitude and with a large wavelength, which forms in the high sea, due to the luni-solar attraction on the surface of the water. There are two current tides: (i) Flood, or rising tide current, which runs from the open sea to the coast, where it causes an accumulation of water whose maximum is flood or rising-tide and (ii) Ebb or falling tide that goes towards the open sea, draining the water accumulated next to the coast during the flood. The lowest water level reached by the downward tide is low-tide or empty tide. It can be said that the tides are sea level falls or rises rises with a period of about 12 and a half hours, caused by the combination of the effects of the Earth's rotation and the gravitational attraction of the Moon and the Sun. When the Sun and Moon are in conjunction or opposition the tides are with great amplitude. When the Moon is in waning or crescent (quadrature), the tides have the minimum amplitudes. The circulation of the tidal currents induces formation of more or less symmetrical submarine deltas which, generally, form in the openings of the lagoons or in the straits. The delta formed on the inner side is the flood delta and the one formed on the outer side is the ebb delta. The presence of the tide deltas, as well as, their shape and dimensions depend on three main factors: (i) Sedimentation; (ii) Wave interaction and tidal processes; and (iii) Tidal flow during the tide cycle. Tidal deltas are excellent reservoirs of substitute sandy material that is used to restore the size of beaches subject to erosion of coastal currents.

(*) Wave composed of particles of water, each of which oscillates around a point with little, if any, permanent change of position, which means that the water particles move in a orbital.

Flood-Plain Deposit......................................................................................................................Dépôt de plaine de inondation

Depósito de planície de inundação / Depósito de planicie de inundación / Ablagerung von Aue / 漫滩存款 / Пойменные отложения / Deposito della golena /

Sandy and clay deposit deposited by the water of a river that overflowed over the flood-plain.

See: « Overbank Deposit »
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« Meander Belt »
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« Flooding Plain »

Although the deposits at the base of the valleys result from a series of sedimentary processes of various environments, the most important flood-plain deposits are those formed near the river channels. These deposits normally refer to: (i) Lateral Accretion Deposits, which form within the channels, as the river migrates back and forth at the base of the valley and (ii) Vertical Accretion Deposits, which accumulate in the flood-plain when the rivers overflow the banks of the channel. Vertical accretion or flood-plain deposits occur when rivers leave the channels, where they flow, normally, during flood seasons. and deposit the transported sedimentary particles on the top of flood-plain surfaces. The altitude of flood surfaces increases during floods, as illustrated in this figure. The deposition by overbanking varies from one flood to another. When deposition is poor, the maximum concentration of suspended material occurred during the rise of the flood level since much of the potential of the overbanking sediments is removed from the system before the level reaches the maximum point. Lateral and vertical accretion processes occur at the same time. The alluvium beneath the flood-plain surfacer is, usually, formed by these two deposit types. Their granulometry is, fundamentally, different. Lateral accretion deposits are coarser. Flood-plain deposits are, also, formed in association with braided rivers. The associated river processes are more dynamic and less regular. Braided water-courses have numerous channels, that separated and rejoin, creating an anastomosing geometry. Bank and bar erosion is not confined to a particular side of the channel. The river changes, often, its position without eroding. Typically, they carry coarse sedimentary particles along a fairly steep slope. The water discharge tends to be highly variable. Braided or anastomosing rivers are, usually, located near mountainous regions, especially those associated with glaciers. In the photograph, taken by J. S. Shelton, the different terraces of the San Juan River (New Mexico) are, perfectly, visible. Each of these terraces corresponds to abandoned flood deposits where, later, the river dug deep channels. These river terraces are an exception to the superposition principle (Steno's principles). Over time, the river decreases the flow and that excavates the geological formation that a given time formed its own bed. The sediments found on the upper terraces are older than those on the lower terraces. In the diagram illustrated in this figure, it is easy to recognize: (a) The abandoned flood-plain deposits ; (b) The flood-plain deposits and (c) The natural marginal dikes (fluvial levees) associated with the active channel. Fluvial natural marginal dikes are always far above the base of the river bed, what is not the case for the turbidite natural marginal dikes. Marginal deposits developed on the banks of the river channels during floods, include: (i) Natural marginal dikes (also named levees) and (ii) Crevasse-splays associated with the breaking of natural marginal dikes. The formers form sinuous bars bordering the river channels making difficult to drain the flood plains and favouring marshes and lagoons development. Natural marginal dikes pass, gradually, to flood-plain deposits. Crevasses splay are formed when an flood-water excess breaks the natural marginal dikes and excavates a channel (rupture bed) through the dike allowing the deposition of sinuous or lobed fans in the flood-plain. Flood-plain deposits are, obviously, formed by fine sedimentary particles deposited by decantation. The flood-plain functions as a sedimentary basin. Out-wash deposits of the pro-glacial margin (located, immediately, at the front of a glacier) are, strongly, reworked by the thawing action. Due flow changes of pro-glacial waters and quantity of sediments, the streams are, generally, braided and often incised. This implies the formation of terraces, which should not be confused with terraces associated with flood-plain (San Juan river). The same goes further downstream, in the valley. The initial post-glacial filling is, generally, eroded forming secondary out-wash terraces, often called nested alluvial terraces*.

(*) Nested alluvial terraces or nested fill terraces are the result of the valley filling with alluvium, the alluvium being incised, and the valley filling again with material but to a lower level than before. The terrace that results for the second filling is a nested terrace because it has been “nested” into the original alluvium and created a terrace. (https://en.wikipedia.org/wiki/Fluvial_terrace)

Flood-Tide (High-tide)........................................................................................................................................................................................Mareé haute

Maré cheia (preiamar, maré alta) / Marea alta / Hochwasser / 高-潮 / Верхняя точка прилива / Marea alta /

The part of the tidal cycle during which the sea level rises. Synonym with High-Tide and Ascending Tide.

See: « Tide »
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« Intertidal Beach »
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« Foreshore »

A tide is caused by the gravitational pull of the Sun and Moon. The influence of the Moon is much higher. The Moon's mass is much smaller than the Sun, but it is a smaller distance to Earth. Mathematically, the tide is a sum of sinusoids (constituent waves) whose periodicity is known and depends, exclusively, on astronomical factors. It can be said the tide rises when the upper and lower meridian passages of the Moon. There is an high-tide when the Moon passes over us and when the Moon passes beneath us, that is, over our antipodes. High-tides are, regularly, repeated with an average interval of half lunar day (approx. 12h 25m) corresponding, mathematically, to the semi-diurnal lunar constituent (M2). This is expressed by the people who said that "the tide of the next day is one hour later" (in reality, more or less, 50 minutes later). The time interval between an high-tide and the next low-tide is, on average, 6 h 13 m. The sea does not react, instantaneously, to the passage of the Moon. There is, for each place, a greater or lesser delay of the high-tides and low-tides. The time interval between the meridian passage of the Moon and the next high-tide is the so-called lunitidal interval. Watches are currently being marketed at which this value is requested, so they can provide a rough tide forecast. Although this value varies over time, in average terms this delay is, for instance, around 2 hours in Portugal and less than 30 minutes in Madeira and Azores. Another important aspect to take into account is the bi-weekly phenomenon of alternation between spring tides and neap (apogean) tides. This phenomenon, mathematically, is explained by the constituent S2 (semi-diurnal solar), which derives from the effect of the Sun as a "disturbing" element. When the Sun and Moon are in opposition (full moon) or conjunction (new moon), the influence of the Sun reinforces that of the Moon and the spring tides occur (mathematically, the constituents add up). When the Sun and Moon are in quadrature (crescent and waning quarter), the influence of the Sun contravenes that of the Moon and the neap tides occur (http://www.hidrografico.pt /glossario-cientifico-mares.php.)

Flooding......................................................................................................................................................................................................................................Inondation

Inondação / Inundación / Überschwemmung (Flüsse) /洪水（河流）/ Наводнение (реки) / Inondazioni (fiumi) /

Coverage of more or less horizontal land by sea or river water.

See : « Relative Sea Level »
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« Transgressive Interval »
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« Transgression »

Floods are natural events. They occur, above all, when the catchment area of the river, i.e., the land surface area and currents that feed the river, receives much more water than is normal. Under such conditions, the river can not contain the excess water. The water overflows into the flood-plain. A flood can occur at any point along a river's path and not, necessarily, where excess water has entered. Regularly, during the monsoon* catastrophic floods occur in eastern India, Nepal and Bangladesh, killing hundreds of people and leaving millions of people homeless. The main causes of flooding in these region are: (i) The monsoon, which annually brings heavy rains and snow in such a way that the soils are leached producing a very strong flow causing a very large soil erosion ; (ii) Snow melting, which causes soil erosion and a very rapid increase in river discharge ; (iii) Deforestation of the foreland (a consequence of population growth in Nepal and Tibet) ; a large number of trees are felled for use as fuel and to increase pasture areas, reducing evapotranspiration, increasing water runoff, and producing frequent landslides ; (iv) River load increasing (due to soil erosion), particularly, in silt material, uplifts river beds, which reduces, greatly, channel capacity and increases the likelihood of flooding ; (v) Topography, indeed, the vast majority of this area is located on a delta-plain, whose altitudes rarely exceed 1 m (above sea level) ; (vi) Irrigation, since in many places the Ganges River has been diverted to irrigation, which retains much of the silt material and prevents the construction of the flood-plain downstream ; (vii) Cyclones, which are very frequent in this region, increase the probability of occurrence of floods and (viii) Subsidence induce by the sedimentary overload. The two photographs shown above, of the Mississippi River and its tributaries (Missouri and Illinois), taken August 14, 1991 and August 19, 1991, illustrate the extent of one of the many floods in the Mississippi Valley.

(*) Seasonal change of wind direction accompanied by a change in precipitation ti.e., currently, used to describe seasonal changes in circulation and atmospheric precipitation.

Flooding-Forestepping.................................................................................................................................Inondation-Régression

Inundação-regressão sedimentar/ Iundación-regresión / Überschwemmungen - Rückbildung / 洪水 - 回归 / Наводнение-регрессия / Inondazioni-Regressione /

Sedimentary interval formed by an alternation of regressive deposits (progradational geometry) and flooding surfaces (ravinment surfaces, associated to ingressions). These intervals when associated with a transgressive interval (IT) of a sequence-cycle, imply relative sea level rises in acceleration (increasingly important marine ingressions, without relative sea level falls between them). In this case the sedimentary regressions are increasingly smaller and, in general, the shoreline moves to the mainland. Collectively, the increasingly important marine ingressions and increasingly smaller sedimentary regressions define what geoscientists call, or should call, sedimentary transgressions and not transgression. When the flooding/regression intervals are associated with a highstand prograding wedge (HPW) of a sequence-cycle, they imply decelerating relative sea level rises (marine ingressions smaller and smaller). In this case, the sedimentary regressions are increasingly important and the shoreline, globally, progresses seaward. Collectively, the increasingly smaller marine ingressions and the sedimentary regressions are what geoscientists call a sedimentary regression. Obviously, there are no relative sea level falls between the marine ingressions (eustatic paracycle) and all sediments are deposited, forming the paracycles-sequence, during the stability periods of relative sea level between the marine ingressions.

See: « Relative Sea Level Change »
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« Transgressive Interval »
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« Sequence-Cycle »

The sedimentary intervals bounded by flooding surfaces (paracycles-sequence), induced by marine ingressions, which form all sub-groups of sedimentary systems tracts of a sequence-cycle (submarine floor fans, submarine slope fans, lowstand prograding wedge, transgressive interval, highstand prograding wedge and sometimes bordering prograding wedge) correspond to sedimentary regressions. During their deposition (submarine fans excepted), the shoreline, progressively, moves seaward, before a new marine ingression displace it, again, continentward. In this sketch, two large groups of sedimentary regressions, underlined by two marine ingressions. Each marine ingressions is formed by several increments, in acceleration, of the relative sea level. These two marine ingressions are in acceleration. The second is more important than the first. They form an incomplete sequence-cycle. The set of these sequence-paracycles are limited by two unconformities (erosional surfaces) whose age difference is less than 3-5 My. In this example, the geological conditions are of highstand sea level. The lower unconformity (SB 5.5 Ma) has a large slope break downstream of the area illustrated in this sketch. Such a break emphasizes the basin edge at the beginning of the deposition of the sequence SB. 5.5 Ma / SB. 4.2 Ma. The relative sea level is the local sea level, referenced to any point on the Earth's surface as for instance the sea floor or the base of the sediments (top of the continental crust). The relative sea level (RSL) is the result of the combined action of the tectonics (subsidence or uplift of the sea floor) and the absolute (eustatic) sea level, which is supposed to be global and referenced to the Earth's centre. The sediments deposited when the sea level was lower than the basin edge, i.e., the sediments of the lowstand systems tracts group (LSTG) formed by submarine basin floor fans, submarine slope fans and lowstand prograding wedges sub-groups, were deposited downstream (rightward) of this sketch. Just the sequence-paracycles (sedimentary systems tracts sub-groups) composing the transgressive interval are illustrated in this sketch. The sequence-paracycles are deposited during the stability periods of relative sea level (RSL) occurring after each increment of a marine ingression. The geological evolution of this transgressive interval may have been as follows: (i) Marine ingression, i.e., relative sea level rise, which puts the sea level higher than the basin edge (outside of this scheme) ; (ii) Flooding of the coastal plain with the formation of a ravinement surface due to the continentward displacement of the shoreline, which created a shelf (first vertical arrow) ; (iii) Stability period of relative sea level with sediment deposition and seaward displacement of the shoreline ; (iv) Relative sea level rise (second arrow), i.e., a new marine ingression (usually, more important than the first one) and new displacement of the shoreline upstream ; (v) Deposition and seaward displacement of the shoreline (circles with white interior) that surpassed the previous position (progradation) ; (vi) Relative sea level rise and shoreline displacement upstream and new sediment deposition with a shorter seaward displacement shoreline than the former ; (vii) New relative new sea level rise, but this time more important than the last two, which moves the shoreline much more upstream (increasing the water-depth) and history repeats itself, until a significant relative sea level fall moves the shoreline seaward and downwards to bring the sea level lower than the basin edge (low-level geological conditions) and creating an erosional surface (unconformity, i.e., sequence-cycle boundary). As there are no relative sea level fall between successive sea level rises, each increment marks an eustatic-paracycle during which a sequence-paracycle is deposited. Sediments come from the continent. A sequence-paracycle has, always, a progradational geometry, whether it belongs to the lowstand prograding wedge (LPW), transgressive interval (IT) or highstand prograding wedge (HPW). A set of increasingly important marine ingressions and increasingly smaller sedimentary regressions deposited during the stability periods of relative sea-level, are what Emiliani (1992) called "transgressions." In fact, what many geoscientists call "transgression" (without specifying whether they are speaking of the sea or of the sediments) is nothing more than a succession of less extensive sedimentary regressions which, collectively, have a retrogradational geometry: a) The terrigeneous influx decreases with a platform increasing and b) The relative sea level rises in acceleration.

Flooding Plain...............................................................................................................................................................................Plaine d'inondation

Planície de inundação / Planicie de inundación / Flussaue / 泛平原 / Аллювиальная равнина / Pianura di inondazioni /

Relatively flat surface or land band adjacent to a river bed, which is built during the normal river system and which is covered with water when the river water overflows its banks.

See: « Alluvial Plain »
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« Point Bar »
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« Overbank Deposit »

Whenever the amount of water exceeds the maximum water level that a stream bed may contain, a portion of the stream and the sedimentary particles it transports overflow the natural marginal dikes (levees) covering the floodplain sediments. Downstream of the bay-line (demarcation line between the fluvial and paralic-deltaic deposits), the floodplain develops, particularly, in association with the exaggeration of the meander geometry. The concept of the bayline was defined, more or less, as follows: (i) The coastal plain is formed mainly by sea bottom progradation rather than by exhumation ; (ii) Sediments that accumulate on the coastal plain during the progradation of the shoreline are part of what Vail and Posamentier (1988) called "coastal wedge" or "coastal prism" which includes fluvial and shallow water deposits ; (iii) The coastal prism has wedge-shaped and extends continentward by onlapping on the pre-existing topography ; (iv) The updip limit of the coastal edge is the bay-line, which moves upward, when the progradation (outbuilding) of the shoreline is accompanied by a significant aggradation (upbuilding) ; (v) The bayline is the limit between the coastal plain and the alluvial plain ; (vi) Upstream of the bayline, relative sea level changes have no influence on depositional systems. Conventionally, the boundaries between stratigraphic cycles, irrespective of their hierarchy (sequence-paracycles excluded), are unconformities or/and their correlative deep-water paraconformities. Unconformities are induced by significant relative sea level falls, that put the sea level lower than the basin edge. Each stratigraphic cycle, when complete, begins with the deposition of deep turbidite depositional systems, that allow to date discordances. On the seismic lines, the onlapping of turbidite deposits are used to identify the deep-water paraconformities that correlate with the unconformities. Mutti, thinks that turbidite systems do not settle down, exclusively, during lowstand geological conditions. They can also be deposited under highstand conditions, particularly during river floods. Indeed, during a flood, a water-course carries such an amount of sedimentary particles that when they reach the mouth, they creates, often, gravity currents along the continental slope. When the turbiditic currents reach the deeper parts of the basin, the transported sedimentary particles are deposited in the form of submarine fans (basin or slope fans). The presence of submarine turbidite fans on seismic or field data does not, necessarily imply, that they underline a significant relative sea level fall. In other words, submarine basin floor fans do not, necessarily, lie on a sequence-cycle boundary. One of the most classic examples of flood-plain is the Nile Delta flood-plain, particularly, before the construction of the Aswan dam. During the annual floods a layer of humus, was deposited on the banks of water-courses. Such a humus layer was a precious natural fertilizer allowing the cultivation with high fertility and the maintenance of the ancient Egyptian civilization. Unfortunately, after the dam construction (1970), the river level was regulated, avoiding floods in Egypt. This caused not only the salinization of many areas downstream of the dam, but also the destruction of most of the arable land. Another typical example of a flood-plain is the Tagus River flood-plain, which extends (NE-SW) between Constancia and Lisbon (around 80 km) with a width ranging between 3 and 13 kilometers. During floods, the floodplain is completely submerged, creating a 870 km² water-plane. Hydrological analysis has shown that larger centennial floods form the highest natural marginal dikes (± 12 m). Floods with a return period of less than 5 years shape the majority of marginal dikes, which height does not exceed 10 m. All studies show a great dynamism of the Tagus river and its floodplain, translated by the lateral migration of channels and the progressive elevation of the plain, with stacking of correlative forms of accumulation (natural marginal dikes and and low flooding reliefs) or erosion (abandoned channels).

Flooding Surface.................................................................................................................................................................Surface d'inondation

Superfície de inundação / Superficie de inundación / Hochwasser Oberfläche / 泛面 / Поверхность затопления / Superficie di Inondazioni /

Area associated with relative sea level rises (marine ingressions). Within a sequence-cycle, they are well visible, particularly, in the transgressive intervals (TI) since they are emphasized by the ravinment surfaces. The maximum flood surface of a transgressive interval is fossilized by a downlap surface defined by the progradations of the highstand prograding wedge.

See: « Transgressive Interval »
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« Hiatus »
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« Relative Sea Level Rise »

Within a stratigraphic cycle said sequence-cycle (induced by a 3^rd order eustatic cycle, i.e., with a time-duration between 0.5 and 3/5 M), the boundary between the lowstand prograding wedge (LPW) or the associated incised valley fills (Ivf) and the transgressive interval (TI) is marked by the first flooding surface. Transgressive surfaces are, particularly, well marked in highstand systems tracts, during which the sea level is higher than the basin edge (continental edge when the basin has a shelf). On this tentative geological interpretation of a Canvas auto-trace of a detail of a Gulf of Mexico seismic line, the unconformity (D), which separates two sequence-cycles is, easily, recognized by toplaps by truncation. The toplaps formed by the relative sea level fall that originated an erosional surface in which an incised valleys is recognized without great difficulty. The relative sea level* fall put the sea level lower than the basin edge. It exhumed the coastal plain of the highstand prograding wedge of the underlying sequence-cycle and, at the same time, formed incised valleys on the the coastal plain. During this relative sea level fall, in the deepest part of the basin (eastward of the seismic line of this auto-trace), submarine basin floor fans basins (SBFF) and submarine slope fans (SSF) were, certainly, deposited. Since the relative sea level began to rise, a lowstand prograding wedge (LPW) was deposited downstream of the basin edge. The incised valley was filled, under lowstand geological conditions, during the deposit of the terminal part of the lowstand prograding wedge. When the relative sea level covered the edge (continental border) of the lowstand prograding wedge (LPW), it flooded the coastal plain and the pre-existing topography (preceding sequence-cycle). The incised valley fill was fossilized by the regressive sediments, induced by the first marine ingression which begins the deposition of the transgressive interval (coloured in dark green in this tentative interpretation). In highstand geological conditions, the first marine ingression, displaced then shoreline continentward flooding the pre-existing topography and creating a ravinment surface on the sea floor. Following this marine ingression, the relative sea level remains stable for a certain, more or less, long period of time. During this stability period of relative sea level, the shoreline begins to move seaward as the systems tracts deposit, more or less by progradations. During the deposition of the transgressive interval (TI), each increment of relative sea level rise (**), i.e., each eustatic paracycle (or marine ingression), a flooding surface is formed. It is fossilized by the deposit of a sequence-paracycle, during the stability period of relative sea level occurring after each eustatic paracycle. Individually, each sequence-paracycle has a progradational geometry (systems tracts are progradational units). However, collectively, a set of sequence-paracycles has a retrogradational geometry (the shoreline, globally, is displaced landward). The marine ingressions, responsible for the accommodation, become increasingly important (acceleration) and the associated sedimentary regression, increasingly smaller. When marine ingressions become less important (deceleration) the associated sedimentary regressions are increasingly important, i.e., the sequence-paracycles has, globally, a progradational geometry and the shoreline, globally, moves seaward.

(*) Local sea level, referenced to any fixed point on the Earth's surface, whether the base of sediments or the seabed and which is the result of the combined action of tectonics and the absolute (eustatic sea level), which is global and referenced to the Earth's centre.

(**) A relative sea level rise, i.e., a marine ingression is made by increments followed by stability periods of relative sea level such as: (i) Relative sea level rises 3 m ; (ii) Relative sea-level stability period ; (iii) Relative sea level rises 5 m ; (iv) Relative sea-level stability period ; (v) Relative sea level rises 7 m ; (vi) Relative sea-level stability period ; (vii) Relative sea level falls 10 m. In this case, overall, the relative sea level rose 15 meters acceleration, as marine ingression steps are increasingly important. Certain geoscientists consider simple marine ingressions (increment of relative sea level rise) and composite marine ingressions (total relative sea level rise).

Flow (Flood tide, rising tide, flood)...................................................................................................................Marée montante, Flux, Flôt

Enchente / Flujo, Marea creciente / Flut, Steigen / 涨潮 / Приливная волна / Marea montante /

Part of the tidal cycle during which the sea level rises. Synonym with Rising Tide, Flood-Tide and Flood.

See: « Opposition (astronomy) »
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« Intertidal Beach »
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« Shoreface »

In this figure, at the maximum of the tidal current (rising tide) or, in other words, in the high-tide, the sea level is, more or less, three meters from the top of the quay. The boat no longer rests at the exhumed sea floor since almost the whole area was covered by the sea (compare with the figure, which represents the same area during the low tide). The tide is an oscillation wave* of low amplitude and with a large wavelength, which forms in the high sea, due to the luni-solar attraction on the surface of the water. There are two current tides: (i) Flood, or rising tide current, which runs from the open sea to the coast, where it causes an accumulation of water whose maximum is flood or rising-tide and (ii) Ebb or falling tide that goes towards the open sea, draining the water accumulated next to the coast during the flood. The lowest water level reached by the downward tide is low-tide or empty tide. It can be said the tides are sea level falls or rises rises with a period of about 12 and a half hours, caused by the combination of the effects of the Earth's rotation and the gravitational attraction of the Moon and the Sun. When the Sun and Moon are in conjunction or opposition the tides are with great amplitude. When the Moon is in waning or crescent (quadrature), the tides have the minimum amplitudes. The circulation of the tidal currents induces formation of more or less symmetrical submarine deltas which, generally, form in the openings of the lagoons or in the straits. The delta formed on the inner side is the flood delta and the one formed on the outer side is the ebb delta. The presence of the tide deltas, as well as, their shape and dimensions depend on three main factors: (i) Terrigeneous influx ; (ii) Wave interaction and tidal processes ; and (iii) Tidal flow during the tide cycle. Tidal deltas are excellent reservoirs of substitute sandy material that is used to restore the size of beaches subject to erosion of coastal currents.

(*) Wave composed of particles of water, each of which oscillates around a point with little, if any, permanent change of position, which means that the water particles move in a orbital way.

Flow Delta (Tidal delta)..............................................................................................................................Delta de Flôt, Delta de marée

Delta de enchente / Delta de inundación / Flutdelta / 流三角 / Дельта потока / Delta del flusso, Delta alta marea /

Small delta formed on the inner side of the lagoon openings or barrier beaches due to high tidal current. The delta that forms on the outer side is the ebb delta.

See: « Delta »
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« Tidal Delta »
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« Ebb Delta »

In the geological model of a flow delta, illustrated in this figure, we recognize: (A) The barrier bars or spits (coastal structures constructed by the combined action of the transport of materials by the great rivers and by the sea), that replace the contours of the coast and in which we can identify: 1) Beaches ; 2) Dunes and 3) Overbanking deposits ; (B) The tidal channel, which individualizes two barrier bars ; (C) The flow delta ; (D) The ebb delta; (E) The tidal flat or tidal plain ; (F) The swamp and (G) A secondary tidal channel. Along the barriers bars, which are forms of accumulation of sand and pebbles and developed in the backshore, due to the accumulation of sediments by the waves. In association with the tides, small sets of submarine deltas that form in symmetrical position can be formed in the openings of the lagoons or narrow. The deltas, which form on the inner side are the flow deltas, as illustrated in this photograph. The deltas, which develop outwardly and are, generally, smaller in size and more irregular (due to wave ripple) are the ebb deltas. The presence and size of these deltas are determined by several factors: (i) Sedimentary particles influx (the amount of solid sedimentary particles transported, in general, by a combination of gravity force and / or flow of a fluid, to the deposition environments) ; (ii) Interaction between waves and tides and (iii) Stream flow during a tide cycle. These deltas form a large part of the sand bodies, which constitute the Atlantic coasts and the Gulf of Mexico. Along the United States coast, for instance, flow deltas, generally, have a sandy facies and, usually, develop with two different, very characteristic morphologies: (a) Fan-shaped (usually in groups) and (b) Horseshoe-shaped, with the open side facing the sea. Fan-shape deltas are, mainly, in areas where the difference between tides (tidal coefficient **) does not exceed 1.5 meters. The tidal coefficients are the same for the whole Earth, but they affect very differently the amplitude of the tides according to the place considered. This amplitude variation is, practically, zero in the closed seas ***, except for local resonances, weak in the middle of the oceans, but it amplifies, greatly, when it propagates to the continental coasts. In addition, the amplitude of the tides varies spatially and temporally. There are low tides (tens of centimeters) near the equator, while in other places it may exceed 10 meters (17 m in the Bay of Fundy in Canada and 15.5 m in the Bay of Monte de Saint-Michel in France ). The coefficient and as consequence the amplitude of the tides follow the phases of the moon with soft waxing and waning crescents and great differences at the time of new moon and the full moon The differences in amplitude between low and high tides show great contrasts. In Saint Malo (France) the difference of level enters the high-tide and the low-tide diminishes until three meters in periods of low-tides and reaches thirteen meters in period of high-tides. The deposits associated with the flow deltas are typically infra-tidal, the flow tide passes back and forth and over the delta, practically, without influencing it. This type of flow delta has, in general, 1/2 meters thick. It is formed by mud, that is, typically, a combination of clay minerals and fine organic particles. Horseshoe-shaped flow deltas are always found in areas where the difference between tides is greater than 1.5 meters. The associated sandy deposits are modelled by the combination of tidal currents, which is not the case for the fan-shape flow deltas. When the tide goes down, the downstream currents are deflected around the accumulations of sand, emerging the delta. This type of delta may contain hundreds of thousands of cubic meters of sediments.

(*) Coastal zone, usually, dry and, relatively, narrow between the highest line of equinoctial tides, which forms the lower bound and the upper of the coastal processes zone, that is, the base of the cliff.

(**) The tide coefficient is a dimensionless number ranging from 0.2 to 1.2. It is, usually, expressed as hundredths. For instance, a coefficient 20 corresponds to an extraordinary neap tidal, when Earth, Moon and Sun are in quadrature) and a coefficient 120 indicates an-extraordinary spring tidal due to the attraction of the Moon and the Sun, whose influences combine in a way extremely variable from one day to the next).

(***) Sea and ocean are not synonymous. The territorial extension is not the same. Oceans occupy great extensions that delimits continents. Seas are smaller and are delimited by the continents, mainly, its entrances, The depth is, also, different. The oceans are thousands of meters deep. The seas are deep in the order of hundreds of meters.

Flow-Stripping ....................................................................................................................................Courant de débordement (Turbidites)

Corrente de escape (remoção) / Corriente de desborde (turbiditas) / Überlauf Strom (Turbiditen) / 当前的溢出 (浊流） / Приливное течение / Corrente di traboccamento, Corrente di straripamento (torbiditi) /

Current formed by the most diluted part (loaded with fine material) of a turbidite current that escapes from the topographic confinement where it flows. The material carried by this type of current, usually, deposits not far from the deviation point. When this current forms, it causes an increase in the sand/clay ratio of the main turbidite current.

See: « Avulsion »
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« Overbank Deposit »
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« Submarine Slope Fan »

A turbiditic or turbidity stream is a turbulent subaquatic density current. Its density is primarily a function of the sediments it carries. The sedimentary particles are transported by traction (near or at the bottom of a stream, whether by rolling, jumping or slipping) and by suspension. Suspension transport occurs when the turbulence intensity and velocity are greater than the deposition velocity. The higher the velocity of a stream, the greater its ability to hold and transport particles in suspension. The particles transported by suspension are the least dense, the smallest and the least spherical. The great majority of geoscientists admit that a turbidite current carries the grains in a solution composed of water and dispersed sediments, kept in suspension by turbulence (when the particles mix non-linearly, as opposed to laminar flow). Turbidity currents can be caused by significant relative sea level* falls, earthquakes, storms, ruptures or failures of the continental slope, submarine avalanches, river discharges, etc. Once set in motion, these currents drain down slope by gravity**. They can, significantly, affect the morphology of the sea floor, either by eroding important areas or by creating submarine canyons. They can also deposit huge amounts of sediment, usually, in a fan form, which the geoscientists subdivide in: (i) Submarine Basin Floor Fans (SBFF) and submarine Slope Fans (SSF). The geological sketch illustrated in this figure attempts to explain how a turbidite flow-stripping current induces avulsion. Avulsion is, an abrupt and violent change in the current trajectory when it leaves the anomaly where it flows (turbiditic channel or depression between the lobes), to take another route. This type of current is mainly formed in the submarine slope fans (SSF), which, normally, overlap with the submarine basin floor fans (SBFF). This is particularly true when the main turbiditic current is, more or less, channelized by the deposit of the natural marginal dikes (levees). As overbank deposits (levees) settle down, they channelize, gradually, the turbidite currents, since between the levees a central depression by non-deposition forms. The following turbidite currents will use such a depression to flow into the deepest parts of the basin. With time and overbanking deposition, the central depression becomes sinuous, as the amount of sedimentary particles transported by the current decreases. Sometimes, in the most sinuous part of the depression, due to the high density and velocity of the turbiditic currents, the more dilute part of the current escapes over the topography (flow-stripping). The the clay material that the flow-stripping current transports will be deposited in the deep parts of the submarine slope fans. When a turbiditic flow-stripping occurs, the principal current becomes enriched in sand. The terminal lobes will be more sandy. Deposits associated with flow-stripping currents are very common, for instance, in offshore Monterey (California), but also in Brazil offshore (particularly in the Campos geographic basin). The associated terminal lobes form quite important morphological traps for hydrocarbons. in additional, they have thick intervals with good reservoirs-rocks characteristics. On this subject it is important to remember that for P. Vail submarine fans are associated with turbidite currents induced by significant relative sea level falls that originated unconformities. Emilano Mutti is less restrictive. He considers that turbidite fans can, also, be formed when the level of the sea is higher the basin edge (highstand geological conditions) in association with river floods or with failures of the basin edge. As shown on these seismic lines, avulsion is, also, frequent in fluvial depositional systems. Unlike a turbidite current, a fluvial current needs to have a bed to flow The first fluvial natural marginal dikes (levees) is above the bed where the current flows. The first turbidite levees is deposited at the same level that the current.

(*) Local sea level referenced to any point on the Earth's surface such as the sea floor or the base of the sediments (top of the continental crust). It is the result of the combined action of the tectonics (subsidence or uplift of the sea floor) and  the absolute (eustatic) sea level, which is the global and referred to the Earth’s centre.

(**) All materials originated by weathering and erosion of rocks and soils that are transported by geological agents such as a river, wind, ice, currents and that accumulates in low places (base of foothills, alluvial plains or even large sedimentary basins).

Flutecast...............................................................................................................................................................................................................Moulage en flûtes

Turboglifo / Moldeado en flauta / Form Flöte, Strömungsmarke / 成型笛 / литье флейта / Stampaggio flauto /

Fluting dug in clay sediments by water runoff and filled by the sediments of the overlying layer. The concavity of the flutes indicates the top of the layer. The elongation of the turboglyphs (erosion path footprint) gives the direction of flow and the conical end points the direction, downstream, of the flow. Synonym of Fluting Mark.

See : « Gilbert Delta»

Fluvial............................................................................................................................................................................................................................................................Fluvial

Fluvial / Fluvial / Fluvialen / 河流 / Речной / Fluviale /

Which belongs, or which is associated or which refers to one or more rivers.

See: « River »
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« Meander »
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« Distributary »

The fluvial term is used in geology and geography to designate deposits or morphologies, which were created by the action of the rivers or other watercourses and the depositional processes associated with them. When rivers or water-courses are associated with glaciers or ice caps, it is preferable to use the term fluvio-glacial or out-wash. Along rivers or any other watercourse, erosion (disintegration and transport of solid particles downstream in response to gravity, which should not to be confused with weathering) is always present. Erosion can act in two different ways: (i) Friction (hydraulic action), i.e., the erosive action of water movement on the rocks and (ii) Abrasion and Friction, i.e., wear of the rocks by the sedimentary particles that the current carries and the decrease of size and sorting of the grains as they move. The sedimentary particles are transported along the bottom of the river (basal charge), suspended or dissolved. According to the Hjulstrøm* curve, when velocity falls below a certain value (critical velocity) the particles are deposited or transported instead of being eroded. Particles less than 1 mm in diameter require less energy to be eroded. The finer particles, such as the clay, require a higher velocity of the current to produce the energy required to separate the particles that have coagulated. Larger particles such as gravel and pebble are eroded at high speeds. Point bars and natural marginal dikes (associated with overbank deposits) are perhaps the most typical fluvial deposits. Many of the deposits near the river mouths are, sometimes, mistakenly regarded as fluvial deposits. They are, fundamentally, associated with the marine currents and, especially, with littoral currents or longshore drifts (zigzag currents with longitudinal resultants, when the surf is oblique to the coast), as is the case of the Douro River illustrated in this photograph, where the obliquity of the waves is, local, slightly oblique to the shoreline.

(*) Graph that takes into account the size of the sedimentary particles and the velocity of the current and that determines if the current erodes, transports or deposits the sediments.

Fluvial Deposition..................................................................................................................................................................Déposition fluviale

Deposição Fluvial / Depositación fluvial / Fluvial Ablagerung / 河流沉积 / Речные отложения / Deposizione fluviale /

The process by which sedimentary particles deposit upstream of the bay line (upstream limit of the Posamentier/Vail coastal prism or coastal wedge). The processes that allow the deposition of the coastal sediments and deltaic plain are excluded from the fluvial deposition, since marine influence is preponderant. In fluvial deposition, relative sea level changes have no influence at all.

See: « Deposition (clastics) »
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« Bay-line »
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« Depositional Environment »

In current language, deposition corresponds to the phenomenon of depositing particles in a given location, usually suspended by the action of fluvial, marine or lacustrine waters, wind or ice, causing clastic sedimentary deposits. Deposition occurs when the energy of the transport current is not strong enough to support the transported particles. These particles are deposited by a process known as the null point hypothesis. This hypothesis explains how the sedimentary particles settle along the coast according to the granulometry of the grains. Everything happens as a consequence of the hydraulic energy influence, which induces a decrease in grain size. Deposition tale place where the force of the fluid equals gravity for each grain size. This concept may also explain why a particle* of a certain size can move to a position where it is in equilibrium with the flows acting on that particular grain. This sorting mechanism combines the influence of gravity force (induced by the slope of the bottom of the current) and the forces created by the asymmetry of the flow. The position where there is no transport is known as the null point (Cornaglia, 1889). Note that: (i) Fluvial means referent or belonging to rivers ; (ii) Fluvio-glacial or Out-wash, is said deposits associated with natural water currents, coming from the melting of the glaciers ; (iii) Fluvio-graphy is the descriptive study of rivers ; (iv) Fluvio-lacustrine refers at the same time to rivers and lakes ; (v) Fluviometer is the apparatus for measuring water height in rivers and lakes ; (vi) Fluvio-volcanic refers to both fluvial and volcanic activity. There is no consensus regarding the downstream limit of river deposits. Posamentier and Vail (1988) consider the bay-line as the downstream limit of these deposits. However, for certain geoscientists, as Miall (1997), the concept of the bayline is very questionable, as well as the upper limit (upstream) of the river deposits. For E. Mutti, as illustrated in this figure**, a fluvial and turbidite systems have many common features. Both depositional systems are composed of: (i) Source Zone (Sz) ; (ii) Transport or Transfer Zone (Tz) and (iii) Deposition Zone (Dz). In some cases, the two deposition systems are interconnected. Mutti considers three possibilities: a) Fluvial systems, which develop upstream of the bay-line, with important alluvial fans and fluvio-deltaic deposits (downstream of the bayline, generally between the shoreline and the basin edge) associated or not, but without turbiditic deposits ; b) Mixed systems, which form when the basin has almost no continental shelf, and when the bay line is very close to the shoreline, which implies the formation of alluvial deltas ; when the distal part of the alluvial delta or Gilbert type delta, reaches the basin edge, gravitational landslides produce turbidity currents that deposit the sediments transported in submarine fans ; (c) Turbidite systems, which form when instabilities of the basin edge produce large-scale gravitational slides, which put in motion large amounts of sediment, which are transported over large distances to the deeper parts of the basin and deposited under the form of submarine fans. For Mutti, in mixed and turbidite systems, geological conditions are almost highstand (sea level higher than the basin edge), meaning that these deposits are not associated with significant relative sea level falls. Relative sea level is a local, referenced to any point on the Earth's surface which is, generally, the sea floor or the base of the sediments. It is the result of the combined action of tectonics and the absolute (eustatic) sea level, which is global and referenced to the Earth's centre or to a satellite.

(*)  Since a particle is deposited it becomes a sediment, i.e., since a solid material accumulated on the Earth's surface, it becomes a sediment, which can remain stable for many years, even millions of years, until it will be consolidated as a sedimentary rock.

(**) In this model, the geological conditions are highstand. The sea level is above the basin edge. Under such conditions, if there are turbidite deposits in the deep part of the basin, they can not be explained by the geological model proposed by P. Vail. Do not forget that E. Mutti does not rule out the deposition of turbidites in association with significant relative sea level falls (model of P. Vail), as many adherents of sequential stratigraphy think.

Fluvial Fill.......................................................................................................................................Remplissage fluvial (Prisme de bas niveau tardif)

Preenchimento fluvial/ Relleno fluvial (prisma de bajo nivel tardío) / Füllung Fluss (Low-Level-Prisma spät) / 河道充填 / Заполнение рек / Riempimento del fiume (prisma di basso livello tardivo) /

Filling made by sandy bodies fill up channels, created just before the 1^st transgressive surface, when within a sequence-cycle, the rate of relative sea level rise is maximum.

See: « Lowstand Prograding Wedge»

Fluvial Plain..........................................................................................................................................................................................................Plaine fluviale

Planície fluvial / Planicie fluvial / Flussniederung / 冲积平原 / Намывная равнина / Pianura fluviale /

Area of deposit above sea level and upstream of the coastal plain. The line, which separates the coastal plain from the fluvial plain, is the bayline.

See: « Bayline »
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« Fluvial Deposition »
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« Coastal Plain »

On this tentative geological interpretation of a Canvas auto-trace of a North Sea regional seismic line, a fluvial plain can be proposed upstream of the bayline, which limit the paralic/delta deposits (downdip) from the fluvial deposits (updip). The concept of the bay-line, was defined by Posamentier and Vail (1988), more or less, as follows: (i) The coastal plain is formed by processes of seafloor progradation rather than by exhumation ; (ii) The sediments that accumulate on the coastal plain during the seaward progradation of the shoreline form part of what they called the coastal wedge (or coastal prism), which includes fluvial and shallow water deposits ; (iii) The coastal prism is wedge-shaped and extends continentward by coastal onlaps on the pre-existing topography ; (iv) The upstream boundary of the coastal wedge is the bay-line ; (v) The bay-line moves upstream, when the shoreline seaward progradation (outbuilding) is accompanied by a significant aggradation (upbuilding) ; (vi) The bay-line is the limit between the coastal and alluvial plain ; (vii) Upstream of the bayline, relative sea level changes have no influence on depositional systems. On this tentative geological interpretation is based on the following facts: (i) The North Sea, which is a sea of the Atlantic Ocean, situated between Norway and Denmark at the East, British Isles at West and Germany, The Netherlands, Belgium and France at south, for the most part, is on the European continental shelf ; (II) It has a maximum depth of 90 meters ; (iii) An exception must be made to the Norwegian trench, which extends parallel to the coast, between the Oslo and north of Bergen regions, with an average width of 25 km and a maximum depth of 725 meters ; (iv) Geologically, this offshore is constituted by several basins of the classification of the sedimentary basins of Bally and Snelson (1980), which from the bottom to bottom are: a) Precambrian Basement ; b) Paleozoic, more or less, flattened folded basin, (c) Mesozoic rift-type basins, developed in association with the lengthening of the Pangea supercontinent and, particularly, with the lengthening of the Laurasia small supercontinent ; (d) Mesozoic/Cenozoic cratonic basin formed in association with a thermal subsidence, mainly, induced by a cooling the lithosphere ; (iii) North Sea Cratonic basin, which rests, discordantly, on the sediments of the rift-type basins ; (iv) The sedimentary interval of the lower part of the cratonic basin has a slightly divergent internal configuration (against faults not represented on this tentative), which means the faults created during the rifting phase were still active during the beginning of the cratonic basin ; (v) The upper interval, colored in pink, has a parallel internal configuration; (vi) The overlapping interval (coloured in green) has a retrogradational geometry ; it corresponds to a transgressive episode ; (vii) This transgressive episode is fossilized by a regressive interval ; (vii) In the early stages of the regressive interval (colored in khaki), the sedimentary basin still had a continental platform (shelf) ; (viii) Due to the regressive interval outbuilding, the basin has no longer a platform; (ix) The basin edge became the outer limit of the coastal plain and, probably, equivalent to the delta front ; (x) The relative sea level is, more or less, stable and the delta front outbuilding is more important than the deltaic plain upbuilding (yellow-coloured depositional interval) ; (xi) The coastal plain aggradation (upbuilding) is less than 100 milliseconds, while the delta progradation (outbuilding) is about 30 km ; (xii) The coastal plain is separated from the fluvial plain by the bay-line, which underlines a slope break of the depositional surface between them. In the sequential stratigraphy, the deltaic plain, which is part of the coastal plain, is an fluviomarine accumulation plain. The fluvial plain, located upstream of the coastal wedge, is, exclusively, fluvial. The relative sea level changes (combination of tectonics and absolute sea level, i.e., the global sea level referenced to the Earth's centre) appear to have any influence on depositional. To conclude it can be said : (1) The fluvial plain is characterized by a flat topographic surface with very low slope ; (2) The fluvial plain is always situated at low altitude and dominated by the reliefs of its drainage basin ; (3) The fluvial plain consists of alluvial deposits (usually older sediments) deposited during river floods ; (4) The fluvial plain, theoretically, belongs to the floodplain of a watercourse, but often landfills reduce the possibility of flooding; (5) In the fluvial plain, rivers are, generally, sinuous and rich in meanders, with ecotones (areas of contact and transition between adjacent ecological communities).

Fluvial System...............................................................................................................................................................................................Système fluvial

Sistema Fluvial / Sistema fluvial / Fluss-System / 河流系统 / Речная система / Sistema fluviale /

Depositional system developed upstream of the bayline, with important alluvial fans. It is important not to forget that there is no consensus on the downstream limit of river deposits. Posamentier and Vail (1988) consider the bayline as the downstream limit, but for Miall (1997), the bayline concept is very questionable.

See: « Coastal Non-Marine Deposit »

Flux (Outflow)........................................................................................................................................................................................................................Flux (Écoulement)

Fluxo/ Flujo (escurimiento) / Durchfluss (Flow) / 流 （流场） / Поток (течение) / Flusso (flow) /

Constant movement of a fluid. There are many forms of flow (or flux) and each has its units of measure. In geology, the volumetric flow expresses, above all, the flow of terrestrial chemicals from one reservoir to another..

See: «Debris Flow »
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« Granular Flow »
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« Stream »

In geology, the flow that interests us most is the volumetric flow, although the thermal flow (maturation of the organic matter of the source-rocks) and the energy flow (tectonics) are also very used. The volumetric flow, as this figure suggests, is the rate of volume flow through a unit area. On the basis of the results of the water flow through sands with different permeabilities (the ability of a rock to be crossed by fluids), the French hydraulic engineer Henri Darcy has shown : (i) The rate at which a fluid flows through a permeable substance per unit of area is equal to the permeability (property of the substance through which the liquid flows) multiplied by the pressure per length unit of the flow divided by the viscosity of the fluid. Volumetric flow should not be confused with volumetric flow rate (fluid flow rate), which in fluid dynamics is the volume of fluid passing through a given surface per unit time. After Darcy, his law was deduced from the Navier-Stokes equation by homogenization. One of the main applications of Darcy's law is for the water flow through aquifers. Darcy's law and the mass conservation equation are equivalent to the groundwater flow equation, which is one of the basic equations of hydrogeology (part of the geology that studies the distribution and movement of groundwater in soil and surface rocks of Earth, synonym of geohydrology). Darcy's law is also used, in petroleum geology, to describe the oil, gas and water flows through the reservoir-rocks. Do not forget that: (i) If there is no pressure gradient over a certain distance, there is no flow (under hydrostatic conditions of resting fluids) ; (ii) If there is a pressure gradient, the flow is made from the highest pressure to the lowest pressure ; (iii) The higher the pressure gradient, the higher the discharge rate ; (iv) The rate of discharge of a fluid may vary, even if the pressure gradient is the same.

Flux (Lato sensu)..................................................................................................................................................................................................................Flux (Écoulement)

Fluxo / Flujo (escurimiento) / Fluss (Begriffsklärung) / 流 / Поток (течение) / Flusso /

General term, which expresses the more or less continuous movement of a current (especially of a fluid). In structural geology, flow designates the deformation of a rock that is not instantly recoverable without permanent loss of cohesion. In petroleum geology, this term designates the flow of saturates (oil, gas or water) within a rock-reservoir or from one rock-reservoir to another.

See: « Flux (outflow) »
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« Reservoir-Rock »
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« Turbidity Current »

There are basically two types of flow: (i) Laminar and (ii) Turbulent. These two types can be easily observed in the smoke of a cigarette. If you leave a cigarette burning in an ashtray, at first the smoke rises vertically, that is to say, that the lines of flow are distinct (do not mix) and parallel, then the smoke begins to rise in a more or less, chaotic way. The flow lines are confused, mixed and swirling (sometimes moving backwards). On this figure, the flow lines of oil around a virtual production well are illustrated. The exact determination of the recovery mechanisms of the oil in a reservoir-rock, directly, affects the efficiency of the recovery. To better understand a reservoir-rock, reservoir engineers use simulation processes ("softwares") to visualize the flow as shown in this figure. Notwithstanding the fact that the storage of the porosity data uses a two-dimensional representation of the flow, simulation of the three-dimensional reservoir is difficult to visualize. As the model illustrated above, uses three flow arrows (each representing one of three phases: oil, gas and water), in each block of the simulation grid, hundreds of thousands of flow arrows are obtained in a single image for one complete simulation. If the reservoir-rock is faulted, the three-dimensional flow is more difficult to understand. As production engineers are always asking for more scenarios or alternatives over shorter time periods, there is a need to find more efficient ways of interpreting the results of the simulations. You have to transform the results into images more easy to understand, which currently does not yet exist.

Flysch.............................................................................................................................................................................................................................................................Flysche

Fliche / Flish / Flysch / 理石（滑瓷） / Флиш (тонкослоистые песчано-глинистые отложения) / Flysch (china scivolosa) /

Geological formation consisting mainly of sandstone and clayey rocks extending from SW Switzerland eastward along the northern part of the Alps to the geographical basin of Vienna (Austria) and which can be traced along the northern flank from the Carpathians to the Balkan peninsula, but that do not have not always the same age. Flysch is, also, represented in the Pyrenees, Apennines, Caucasus and Asia, etc. Similar deposits to flysch are also found in the Himalayas.

See: « Turbidity Current »
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« Turbidite »
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« Submarine Basin Floor Fan »

A flysch is a geological formation consisting of a monotonous repetition of layers of metric to decametric thickness starting each layer by coarse material and ending with fine grain levels. Normally, a flysch consists of alternating layers of sandstone with a very clear base base passing, upwards, to shales. Flysches are induced by submarine avalanches of mud and sand from surface deposits. Each layer corresponds to an avalanche (turbiditic current). It goes, more or less, far along a slightly dip. When it lost energy (less speed), transported sedimentary particles settle down creating a vertical stacking of finning and thinning upward layers. Presently, these layers are considered as turbidites. Flysches are not of the same age in each place. They are known throughout all geological times. In the Alps, geoscientists thought, for a long time, they corresponded to Tertiary sediments (which is true for the outermost areas). In the western part of Switzerland, the oldest flysches are Eocene, but the majority are of Oligocene. In Vienna and Carpathian geographic basins, there is an Early Cretaceous flysch. In certain areas, it is possible that this type of deposit began to form since the Jurassic and lasted until the end of the Tertiary. The scarcity of fossils makes the flysch difficult to correlate with other geological formations. The flysch corresponds to a set of sedimentary rocks deposited in the deep parts of the foreland basins, in association with the first phase of an orogen. The flysch is a syn-orogenic deposit. It is deposited at the same time that a mountain chain is built . With the evolution of the orogen, the foreland basin becomes less deep and molassic deposits are deposited on top of the flysch Molassic deposits are, mainly, conglomeratic-type formations derived from detrital sedimentary rocks of post-orogenic origin that accumulate in the periphery of a mountain folded belts. The stratigraphic studies allowed a better understanding of the deposition of the flysch. It may be said that flysches are, in fact, the evidence of the instabilities of the shallow sea floors with a marked submarine depression. Predominant situation when a mountain range begins its resurrection from the deep ocean bottoms. As shown on this figure*, the flysch is a stacking of turbidite lobes deposited on the abyssal plain. However, these lobes can develop either under lowstand geological conditions (P. Vail's model) or during highstand geological conditions (E. Mutti's model). In the first case, the relative sea level ** falls and becomes lower than the basin edge. The upper limit of the continental slope is exhumed. The shoreline coincides, more or less, with the continental edge. Sedimentary particles reaching the sea lie on the continental slope. Under such conditions, the terrigeneous influx can, easily, trigger gravitational currents. The sedimentary particles are transported along the continental slope to the deep parts of the basin (abyssal plain). They are deposited in the form of turbidite fans, as long as the gravity currents begin to decelerate and lose transport competence. In the second case, E. Mutti admits that many turbidite deposits may, also, be deposited during highstand geological conditions, either in association with river floods, basin edge ruptures, or with landslides on the continental slope. Both models admit, but for different reasons, two types of fans. For P. Vail the submarine basin floor fans are deposited during relative sea level falls and the submarine slope fans since the sea level begins to rise. Mutti considers type-I turbidites (roughly equivalent of basin floor fans) when the turbidite currents load is very large and type -II turbidites when the load of the currents is much smaller (equivalent of slope fans).

(*) Navigating along the Basque Coast, from Zumaia Mutriku, through Deba, you can discover the spectacular cliffs which are over 60 million years old.

(**) Do not forget that there are two types of sea level: (i) Absolute or eustatic sea level, which is supposed to be global sea level, referenced to the Earth's centre and (ii) Relative sea level, which is a local sea level, referenced to the base of the sediment (top of the continental crust) or to the sea floor. The relative sea level is the result of the combined action of absolute ( eustatic) sea level and tectonics (subsidence or uplift of the sea floor).

Foehn (Wind).............................................................................................................................................................................................................................................Foehn

Foehn (vento) / Foehn (viento) / Föhn (Wind) / 焚風, 焚风（风） / Фён (сухой и тёплый ветер в Альпах) / Favonio, Foehn (vento) /

A type of dry alpine wind that occurs in the leeward (opposite side to where the wind blows) of the mountains.

See: « Flux (out-flow) »
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« Laminar Flow »
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« Climate »

Strictly speaking, the foehn refers to a warm wind coming from the south, through the Alps. The word foehn is now used to describe similar meteorological effects in all mountains around the world, for example in the Pyrenees. As illustrated, this wind lies in the mountains where he is bound to climb the windward slopes to reach the other side. During the ascent along the mountain slopes, in contact with the ground and by the cooling effect (adiabatic expansion: the highest and coolest), the wind becomes cold. Because cold air can not contain the same amount of moisture as warm air, rainfall occurs on the windward slopes. Rainfall becomes more intense as the current gains altitude. The first consequence is a bad weather on this side of the mountain. The air then reaches the top of the mountain, where, as might be expected, wind gusts occur (Venturi effect, i.e., reduction of the pressure of a fluid as it flows through a restricted section), which push the air down on the opposite side of the mountain (leeward side). The air, now dry. It compresses as it descends, heating more rapidly, than it cools during the ascent, which means the change in temperature of the dry air is faster than the moist air due to the difference in mass. When all the air humidity disappears on the leeward side of the mountain range, the air is hot and the weather is very pleasant. In this example, on the Pyrenees, it can be said that the foehn effect often means a fresh and moist wind on the Spanish southern side (windward side), especially on the higher parts, and a much better climate on the French side (up to a certain distance). This may seem paradoxical, since Spain is famous for its sunny weather. The effect described is most likely to occur during the winter. Snow cover is very vulnerable to the foehn effect. Layers are destabilized and very dangerous avalanches can occur. During the fall, this often means a wonderful Indian summer and a perfect walking time. The term foehn is also used to refer to winds created by the same phenomenon in other regions, or also uses local names, such as the Chinook on the eastern slopes of the Rocky Mountains in Canada and the United States of North America. In the Pyrenees, this phenomenon can also occur in the opposite direction (The Duster), when the cold wind comes from northern Europe (France has a more oceanic climate than Spain).

Fold Belt (Wilson's Cycle)......................................................................................................................................................Chaîne de montagnes

Cadeia de Montanhas / Cadena de montañas (Ciclo de Wilson) / Gebirgskette (Wilson-Zyklus) / 山脉 / Горный хребет / Catene montuose /

A chain of mountains formed during a Wilson's cycle, whose tectono-stratigraphic phases are: (i) Stable Continental Craton ; (2) Thermal anomaly (hot spot) and Lengthening (rifting), which induces the formation of rift-ype basins (usually half-grabens with opposite vergence on each side of the thermal anomaly) ; (3) Breakup of the Lithosphere, with creation of new oceanic crust and formation of two divergent margins ; (4) Sea-floor Spreading (oceanic expansion) that gradually transforms the young margins into mature margins due to the cooling and increasing density of the oceanic crust ; (5) Subduction, as the density of the oceanic crust becomes higher, it is divided into two parts and one of them enters in subduction (plunges under the other) creating a convergent margin, forming a volcanic arc and uplift of a mountain range on the overriding lithospheric plate ; (6) Divergent Margin/Volcanic Arc Collision with formation of a mountain range ; (7) Peneplanation and new subduction of the oceanic crust with the twin margin creating another convergent margin ; (8) Continent/Continent Collision and closure of the ocean created between the two primeval divergent margins and (9) New stable continental craton.

See: « Wilson's Cycle »