Amplitude (Seismic reflection)................................................................................................................................Amplitude (réflexion sismique)

Amplitude/ Amplitud (reflexión sísmica) / Amplitude (reflexionsseismischen) / 地震反射的幅度 / Амплитуда (сейсмическое отражение) / Ampiezza (riflessione sismica) /

Half the wave-height measured perpendicular to the seismic trace between two consecutive trough or crest (for asymmetric and non-periodic systems).

See: « Lateral Reflection »
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« Negative Reflection »
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« Positive Reflection »

When a seismic wave reaches the Earth's surface, the amplitude of the signal decreases rapidly with time. The value of the amplitude of seismic waves can be within a range of 1 million (or more) to 1. In such a context, values within the range of 1 mm/1 km, although perceived by the naked eye, are impossible to record in a functional mode. In contrast, amplitude values within a range of 10 to 1 (0.1 mm/1 mm), which are not detected by our view, are represented, usually, on seismic lines by automatic processes (data function) or changes, merely, functional. As shown in this figure, according to the polarity convention proposed by the European Geophysical Society (SEG), for a positive reflection coefficient (interface defined by a low on a high acoustic impedance), the polarity is expressed by a deflection to the right of the baseline, coloured in black and one to the left, coloured in white, for a negative polarity. The reflection coefficient can be measured by the ratio of the amplitude of the reflected wave to the amplitude of the incident wave. The acoustical impedance of a given interval, such as a sandstone layer, is the product of the acoustic velocity (velocity of the sound waves through the sandstone) and the density of the sandstone. The acoustic velocity of the waves depends on the composition (constants of elastic and density). Theoretically, when two sedimentary intervals, with the same structural behaviour and the same acoustical impedance overlap, theoretically, there is no seismic reflection associated with the interface defined by the two intervals. However, if the structural behaviour of the two intervals defining the interface is not the same or when the interface is separated by a tectonically enhanced unconformity, there is, almost always, a seismic reflector between them, even if the acoustical impedance of the intervals is the same. However, several times, throughout our professional career, we found a, more or less, continuous seismic reflector between two sedimentary intervals A and B with the same acoustical impedance calibrated by two exploration wells P1 and P2 not far apart from each other. The conventional electric logs* of these two wells (P1 and P2) exhibit, practically, the same response since the intervals A and B, which define the reflective interface, have the same acoustical impedance. However, the HDT (High Dipmeter Tool) diagrams of the wells P1 and P2 are, totally, different, suggesting an important shortening of the lower interval A, which does not exist in the upper range B. This probably means that unconformity, between the two intervals, induces a seismic reflection even if it does not correspond to an acoustic impedance contrast**. Likewise, there is not a single continuous seismic reflection associated with an tectonically enhanced unconformity (erosional surface, induced by a significant relative sea level fall), since the reflection coefficient varies laterally. To follow or picking a tectonically enhanced unconformity (n angular unconformity) on a seismic line, the geoscientist has to jump from one peak to a trough or the opposite, since the reflection coefficient changes, laterally, along the unconformity.

(*) The main conventional electric logs are: Gamma Ray (GR), Sonic (S), Neutron (N), Spontaneous Potential (SP), Short Normal Resistivity (SNR) and Large (LNR), Lateral Resistivity (LR), Temperature Diagram (T), Laterolog (L), Magnetic Resonance (MR), etc. The "GR" is probably the most important and gives information about the boundaries between the groups of sedimentary layers and the clay content (response is high for shale and weak for limestone and coal). The "S" (sonic) reports on fracturing and lithology, especially in carbonate aquifers, eruptive or metamorphic rocks (shows the contrast between the more elastic layers such as limestones and less elastic strata such as shales for example). The (N) uses a source that emits neutrons and a corresponding detector, allows to obtain the neutron porosity. The "SP" is used in a punctual way to solve the limits of the aquifers and the movement of the water ; it gives informations in the conductivity of the formations. The "SNR" and "LNR" indicate the water conductivity and the deformation and boundaries of the layers. The "RL" detects the differences in the resistivity or conductivity of the strata (limestones have a low conductivity, while shales have a high conductivity). The "T" identifies the thermal gradient, aquifers and water inputs with different geological temperatures.

(**) A similar but opposite phenomenon is observed with facies lines, which are characterized by a significant lateral change of the acoustic impedance, but which, rarely, have an associated seismic reflector. On the contrary, chronostratigraphic lines, which, almost always, cut facies lines, are characterized by more or less continuous seismic reflectors, although, in general, they do not present a large contrasts (vertical) of the acoustic impedance.

Anaerobic (Environment)........................................................................................................................................................................Anaérobie (milieu)

Anaeróbico / Anaeróbico (ambiente) / Anaerobisch / 厌氧 / Анаэробный (не содержащий атмосферного кислорода) / Anaerobica /

Environment characterized by an absence of oxygen. The term anaerobic is mostly used to denote an aquatic system without dissolved oxygen (0% saturation). An anaerobic environment can be natural or anthropogenic (resulting from the influence of humans). The opposite of an anaerobic environment, sometimes referred to as reducing or anoxic, is an aerobic (oxygen rich) environment.

See: " Source-Rock "
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" Criptozoic "
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" Sedimentary Environment "

In this figure, two aquatic environments, with different dissolved oxygen saturations and with a lethal level between them are, easily, recognized. The existence of anaerobic environments, under aerobic environments, flavours and allows the formation of sedimentary intervals rich in organic matter, which is the sine qua non condition for the formation of potential source-rocks. These environmental conditions are very frequent in, more or less, closed slater-bodies and in certain shelves, especially when they are invaded by upwelling currents. In highstand geological conditions*, the invasion of cold upwelling currents (rich in oxygen and nutrients) allows a great development of fauna and flora in the photic zone, especially, in the distal part of the platform. The colder it is an upwelling current, the richer it is in oxygen and nutrients, which favours the food chain: (i) Phytoplankton ☛ (ii) Zooplankton ☛ (iii) Predator zooplankton ☛ (iv) Filter-feeding animals (e.g., sponges, whales, etc.)☛ (v) Predatory Fish and Animals ☛ (vi) Man. Remember that an upwelling current is a process by which cold deep-water from the ocean comes to the surface. When the wind blows under an area of the ocean, the wind pushes the ocean water in the direction of the wind causing a rise of the deep-water to the surface in order to replace the water displaced by the wind. The appearance of these upwelling currents occurs in the open ocean and along the coasts. The reverse process, that is to say. the formation of downwelling currents, occurs when the wind causes surface water to accumulate along a shoreline and the surface water plunges towards the sea-floor. In the world, there are five major upwelling currents: (a) Canary Current ; (b) Benguela current ; (c) California Current ; (d) Humboldt Current (Peru and Chile) and (e) Somali Current. Upwelling water is, generally, colder and is rich in nutrients. It fertilizes surface waters that generally have high biological productivity. Very low sedimentation rates occur in the distal part of the continental shelves, during relative sea level rises in acceleration, i.e., during increasingly important marine ingressions, among which are deposited increasingly smaller sedimentary regressions. Collectively, increasingly important marine ingressions and increasingly smaller sedimentary regressions form the transgressive interval (TI) of sequence-cycle**. The great explosion of flora and fauna, which occurs in the distal part of the shelf affected by an upwelling current, consumes a lot of oxygen, which, progressively, impoverishes the lower part of the water-column in oxygen making it anaerobic. The formation of a lower anaerobic zone allows the preservation of the dead organic matter deposited in the sea-floor before it is fossilized by the deposition of regressive systems (progradational systems).

(*) When the relative sea level (local and referenced to the top the continental crust or to sea floor and which is the result of the combined action of absolute or eustatic sea level and tectonics) is higher than the basin edge. Under these conditions, the sedimentary basin has a shelf. The shoreline, which corresponds, more or less, to the depositional coastal break of the depositional surface, is located continentward of the basin edge (here, it is, also, the continental edge) except during the 2^nd phase of development of the highstand prograding wedge (HPW). During the 2^nd phase of the highstand prograding wedge (HPW) of a sequence-cycle, the basin has no more continental shelf: the shoreline matches , roughly, with the continental edge (particularly on seismic lines due to the seismic resolution).

(**) Within a sequence-cycle, the sequence-paracycles forming the different groups of sedimentary systems tracts (except for the submarine basin and floor fans), are deposited during stability periods of the relative sea level occurring after each marine ingression and not during the marine ingressions. Only, ravinment surfaces, induced by the action of the waves, form on the pre-existent topography when the relative sea level rises, especially, when the rising is in acceleration.

Anamorphosed (Seismic data).....................................................................................................................................................................Anamorphosée

Anamorfizado / Anamorfizados (dados sísmicos) / Anamorphosiertem / 变形 / Анаморфотный / Anamorfico /

When the vertical and horizontal scale of a document are different. A perfectly concentric and isopach anticline (constant thickness) in the field (1:1 scale) when represented in a geological cross-section with a vertical scale 5x larger than the horizontal scale, it will appear, substantially, elongated and with a thickness in the apex greater than on the flanks. Its image is no longer isopach. A naive geoscientist, i.e., an inductivist geoscientist* may even think that the apex represents the most subsident part of the sedimentary basin. Conventional seismic lines have a metric horizontal scale. The vertical scale is in time (seconds). They can be considered as anamorphized profiles, what has important implications in their tentative geological interpretations.

See : " Scale "

(*) One that advocates  the practice of using an inductive method or stressing induction in one's methods. According to K. Popper, induction, i.e., inference based on many observations, is a myth. It is neither a psychological fact, nor a fact of ordinary life, nor one of scientific procedure.

Ancestry Zone..............................................................................................................................................................................................Zone de lignage

Zona de Linhagem / Zona de linaje / Lineage Zone, Ancestry-Zone / 天堂区 / Зона преемственности / Zona di Discendenza /

Zone of transition between two taxonomic groups supposed derived from the same common ancestor. The Australopithecus afarensis, for instance, has mandibular features suggesting its ancestry zone is associated with a human ancestor.

See: « Theory of Evolution »
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« Paleontology »
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« Universe (age) »

In paleontology*, lineage zones just exist if the theory of evolution is true, which seems to be more than likely. Though creationists and, particularly, the YEC (Young Create Macintosh, who continue to claim that the age of the Earth is between 6,000 and 10,000 years) continue to deny it. Charles Darwin, in the Origin of Species, says: "Probably all organic beings which have ever lived on this Earth have descended from some one primordial form, into which life was first breathed ... There is grandeur in this view of life ... that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved." In paleoanthropology (study of hominid fossils), taxonomic confusion between ancestry zones increases as more fossils are discovered. In ancestry zones associated with the transition between reptiles and mammals, the decision to consider a specimen as a reptile or a mammal is, sometimes, very difficult. Reptile-like mammals and mammals are members of Synapsida ( a group of animals including mammals and animals which are more related to mammals than to any other type live amniotes**, i.e., to any another group of vertebrates with four legs and a vertebral column that has an egg adapted to the terrestrial environment). Technically, reptile-like mammals are called non-mammalian synapsids. They have primitive characteristics with the common ancestors of reptiles and synapsids (***). Essentially, reptiles and synapsids have a sister group relationship rather than an ancestral-descendant relationship. As the hominids family tree proliferates, scientists observe a wide variety of fossils with features that erase the barriers not only between Australopithecus and Man, but also within these taxonomic categories where ancestry zones are less and less refutable. Creationism attempts to destroy the culture of evolution: (i) Defeat scientific materialism and its destructive moral, cultural, and political legacies; and (ii) Replace scientific explanations with theistic solutions where humans and nature are created by God.

(*) Paleontology or palaeontology is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene Epoch (roughly 11,700 years before present ). It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments (their paleoecology). (https://en.wikipedia.org/wiki/Paleontology) 

(**) Clade of tetrapod vertebrates comprising the reptiles, birds and mammals.

(***) Synonymous with therapsids, are a group of animals including mammals and every animal more, closely, related to mammals than to other living amniotes.

Andes..................................................................................................................................................................................................................................................................................................Andes

Andes / Andes / Anden / 安第斯山脉 / Анды / Andes /

The longest continental mountains chain. They form a continuous mountain range along the western part of South America. They are over 7,000 km long and, in certain areas (between 18° to 20° S), about 500 km wide. The average altitude of the Andes is around 4,000 meters. Nevertheless, when compared to the Mid-Atlantic Ridge (perhaps the longest Earth mountain range) it is, relatively, small.

See: « Continental Collision »
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« B-Type Subduction (Benioff) »
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« Pangea »

In this figure one can recognize one of the best known peaks of the Andes, i.e., the Machu Pichus, as well as the vestiges of the ancient Inca city of Cusco, and probably the most famous Incas roadway. Geologically, the Andes are part of the Meso-Cenozoic megasuture within which episutural sedimentary basins are located. The perisutural basins (forearc and others) are adjacent to the megasuture. The Andes mountain chain is associated with a B-type subduction zone (Benioff), in which the Pacific lithospheric plate (oceanic crust) plunges under the South American lithospheric plate (continental crust). The subduction of the oceanic plate induces, on the overriding plate a, more or less continuous, volcanic arc that can be followed from Venezuela to the Land of Magellan (Southern Chile). However, as shown in the map on the right, the distance between the oceanic trench (relatively narrow topographic depression of the Pacific sea floor all along the western margin of the South America) and the volcanic arc (chain of volcanoes formed on an overriding plate, often, with an arc shape as seen from above) varies, significantly, between the north and south (the arrow indicates, roughly, the area of change). In the Central and South areas, the distance between the oceanic trench and the volcanic arc is greater than the North. Such a fact is explained by geoscientists as the direct consequence of the change of the subduction angle: the greater the subduction angle, the faster the rocks of the plunging lithospheric plate are digested by the asthenosphere and transformed into magma (mixture of molten or semi-molten rock, volatiles and solids found, locally, beneath Earth's surface). The vertical rising of the magma thus formed creates on the surface of the overriding lithospheric plate an volcanic arc not far from the ocean trench, as is the case in the northern part of South America. Eastward of the Andes, the South America continental lithospheric plate seems plunges under the Andes (A-type subduction or Ampferer subduction), inducing a significant shortening (folds, reverse faults and tectonic inversions) of the rocks forming the Andes. However, the mechanism of this subduction is very different of the Benioff or B-type subduction bordering the westward the Andes.

(*) At the time of the Inca empire (1438-1533), all the routes of South America went to Cusco, which at that time was the main South American metropolis.

(**) Earth's mobile region (folded and faulted mountain belt) which testifies to the complexity of the accretion and deformation phases undergone by the geological bodies in the regions where the compressive tectonic regimes (ellipsoid of the effective stresses characterized by having the major axis i.e., σ₁ horizontal). Although the compressive tectonic regimes associated with the subduction zones are predominant in the formation of a megasuture. The extensional tectonic regimes and the formation of sedimentary basins also play an important role. (Bally, A. W.,1980)

Anemometer.....................................................................................................................................................................................................................................Anémomètre

Anemómetro / Anemómetro / Anemometer, Windgeschwindigkeitsmesser / 风速表 / Анемометр / Anemometro /

Apparatus that measures wind speed. There are two types of anemometers: (i) Those that directly measure wind speed and (ii) Anemometers that, also, measure wind pressure.

See: « Atmosphere »
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« Fetch »
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« Dune »

Cup anemometers, as shown in the figure, on the left, are the most common type of anemometer. This type, which contrasts with more recent electrical anemometers (figure on the right), indicates the speed of the wind by the rate at which the wind rotates the cups, placed in horizontal arms, around the vertical axis. Some of these anemometers are coupled to aneroid barometers that measure atmospheric pressure. The determination of the amplitude, speed and direction of the wind is important in meteorology, but also in geology, since the wind is an agent of erosion. We must not forget that it is a system of winds that distributes the heat of the Sun through the Earth's surface. The wind has an important kinetic energy*. The kinetic energy of the wind can be exploited by aero-generators to produce electricity and work. In the United States, at least 20% of the energy consumed in heating of the buildings, and in the colder regions, heating is usually associated with wind power. Electricity aero-generators combined with photovoltaics (conversion of light into electricity using semiconducting materials exhibit the photovoltaic effet**), i.e., intermittent processes producing electricity, can reduce the consumption of fossil fuels. Wind is an important factor in erosion. The first effect of the wind is the sorting (separation) of the small sedimentary particles. Wind erosion (type of wind erosion with the removal of thinner fragments) is very selective and can transport the finest particles (clay, organic matter, mud, etc.) several kilometers away. The accumulation of alluvial matter deposited by the wind in the periglacial*** steppes has created loess, which cover large areas of Europe and North America, where highly productive agriculture has developed. The wind is responsible for the formation of dunes (mounds, more or less, sterile of sand) and their displacement, which can produce burial of oasis and agglomerations. The wind produces the degradation of the sedimentary crusts of the surface of the soils and the wear of the rocky substrate. Slabs or sand sheets, moving at high speed near the Earth's surface (30-50 meters), can degrade crops, particularly maize and cotton, in semi-arid areas. Wind erosion can be said to reduce a soil's ability to store nutrients and water, making the environment very dry.

(*) Kinetic energy of an object is the energy  that it possesses due to its motion. Kinetic energy is defined as the work (a force is said to do work if, when acting, there is a displacement of the point of application in the direction of the force) needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. The same amount of work is done by the body when decelerating from its current speed to a state of rest. (https://en.wikipedia.org/wiki/Work_(physics)

 (**) Process in which two dissimilar materials in close contact produce an electrical voltage when struck by light. Light striking crystals such as silicon or germanium , in which electrons are usually not free to move from atom to atom within the crystal, provides the energy needed to free some electrons from their bound condition. The photovoltaic effect is obtained by absorption of photons in a semiconductor material which then generates electron-hole pairs (excitation of an electron from the valence band to the conduction band) creating a voltage or an electric current.

(***) In geomorphology, originally the term periglacial referred to geomorphic processes created by the freezing of the water in ice and the areas where these processes occur. Today, the term periglacial is used in certain geoforms associated with freezing water or a cold climate regime, although many of these geoforms have been found in places where water does not freeze, which means that the role of ice in the production of such forms in cold places has been called into question. Some geoscientists estimate that about a quarter of the Earth's surface sea level has peri-glacial conditions.

Angle of Incidence..........................................................................................................................................................................................Angle d'incidence

Ângulo de Incidência / Ángulo de incidencia / Einfallswinkel / 入射角 / Угол падения / Angolo di incidenza /

Angle that a ray or wave of energy (seismic or other) does with a given surface. The angle of incidence is measured in relation to the vertical of the surface. An incident ray (or wave) in a direction that is not perpendicular to a given surface is divided into a reflected ray and a refracted radius.

See: « Angle of Reflection »
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« Angle of Refraction »
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« Reflection Coefficient »

According to classical physics, a mirror an interface reflects light* so that the angle of reflection is equal to the angle of incidence even if the light source and the observer (detector) are not at the same level. In quantum physics, the light is reflected on all parts of the mirror or of the interfacer with the same probability amplitude (the absolute value, i.e., its distance to zero, or modulus square of this quantity represents a probability or a probability density), in other words,  the light when reflected can follow different trajectories with the same probability. The length of the trajectories is the same. However their directions are very different because the travel time depends very much on the trajectory. The point on the mirror or on the interface where the travel time is minimal is also where the travel time does not vary from one track to another. It is the reason why we can be content with this crude view of the world that the light follows the trajectory corresponding to a minimal time (trajectory of lesser time). It is easy to show that the trajectory corresponding to a minimal travel time corresponds to the equality of the angles of incidence and reflection. So, when an incident ray of light reaches a interface between two mediums with different characteristics, one part of the energy is reflected and the other is refracted. The angle of reflection is equal to the angle of reflection. The angle of refraction is given by the Snell’s Law or Descartes’s Law or simply the Refraction Law, which says that the product of the sine of the angle of incidence by the value of the refractive index of the medium in which the incident wave propagates is equal to the product of the sine of the refraction index by the refractive index of the medium where the refracted wave propagates (see Angle of Refraction). Assuming two consecutive sedimentary intervals (one on the other) with velocities v₁ and v₂ and different densities d₁ and d₂, i.e., with different acoustic impedances (v₁ x d₁), the reflection coefficient of the interface defined by these intervals is given by the quotient between the difference and the sum of the acoustic impedances of the intervals. Theoretically, the reflection coefficient is responsible for the seismic reflection between two sedimentary intervals. When the impedance of the upper range is greater than the impedance of the lower range, the associated reflection is positive (according to the polarity convention proposed by the European Geophysical Society). It is represented on a seismic line by a deflection (coloured in black) to the right of the baseline of the seismic trace. When the acoustic impedance of the upper interval is smaller than that of the lower interval, the reflection is considered negative. However, all geoscientists have often found the presence of magnificent seismic reflections between intervals with equal acoustic impedances. This fact seems to be regularly observed when the electrical logs of the intervals that characterize the sedimentary packages defining the interface do not show important variations except for the dipmeter log. In other terms, seismic reflections induced by a different structural behaviour of the chronostratigraphic surfaces, which compose the intervals that define an interface, may be observed, whether it is associated with a tectonically enhanced unconformity (angular discordance) or a tectonic disharmony created by the partial or total flow of a mobile interval (salt or clay). Through a tectonically enhanced unconformity (angular discordance), the reflection coefficient varies laterally. Theoretically, there can not be a single continuous seismic reflection associated with such an unconformity, but several reflections (function of the impedance contrast). that is to say, the interpreter is obliged to jump from the crests to the trough waves, or vice versa, to get an idea of the geometry of unconformity.

(*) Do not forget light is just visible if an object intercepts its trajectory. When light is projected in a closed container and take care that it does not fall on any object or any surface we see just darkness ; it is only when we introduce an object across the light trajectory that we realize that the container is filled with light. That is why an astronaut looking through the porthole of the space nave cabin sees only black, although the sunlight reigns around him: light falling on nothing, can not be seen.

Angle of Reflection......................................................................................................................................................................................Angle de réflexion

Ângulo de Reflexão / Ángulo de reflexión / Reflexionswinkel /反射角 / Угол отражения / Angolo di riflessione /

Angle that a reflected energy ray (seismic or other) forms with a reflection surface. The angle of reflection is measured relative to the perpendicular of the reflecting surface. A reflected or refracted ray (or wave) results from the division of an incident ray which is not perpendicular to the reflecting surface.

See: « Angle of Incidence »
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« Angle of Refraction »
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« Reflection Seismic »

According to the classic conception, the interface between two medium reflects the incident wave so that the angle of reflection is equal to the angle of incidence. According to the quantum conception, the incident wave is reflected by all the parts of the interface, with the same amplitude of probability, but with very different time trajectories which depend on the followed track. The trajectories with, more or less, the same travel times are roughly around of the trajectory of lesser time (principle of the least time or Fermat's principle). Approximately, it can be said that the incident wave follows the trajectory which corresponds to a minimum time (path of the lesser travel time), which corresponds to the equality of angles of incidence and reflection. The sound behaviour, as well as that of light*, is easy to predict. If a ray** of a sound wave could be observed as it approaches an interface between two more or less smooth and flat sedimentary layers, it would appear that the behaviour of the ray of the reflected wave follows a law called the law of reflection, which is illustrated in this diagram. The ray that approaches the interface between the two sedimentary layers is called the incident ray. The ray of the wave, which departs from the sedimentary interface is the reflected ray. The line perpendicular to the sedimentary interface, at the point where the incident ray reaches the interface, is called the normal line. This line divides the angle between the incident ray and the normal ray at two equal angles. As shown above, the angle between the incident ray and the normal line is called the angle of incidence. The law of reflection illustrated in this figure stipulates that when a wave reaches a sedimentary interface, the angle of incidence is equal to the angle of reflection. Assuming that the velocity of a sound wave moves in the upper sedimentary layer (interval 1) at velocity v₁ and velocity v₂ in the lower layer and that the layers have densities of d₁ and d₁it can be said that the acoustic impedance of the upper layer is v₁ x d₁ and that of the lower layer is v₂ x d₂. The acoustic impedances allow us to easily calculate the reflection coefficient by the formula R = {(v₂ x d₂) - (v₁ x d₁)} / {v₂ x d₂) + (v₁ x d₁)}. Note that the reflection coefficient can describe either the amplitude (amount of change) or the intensity (measured, in time, of the wave flux) of the reflected wave relative to the incident wave. A ray, whether it be incident, reflected, or refracted, is a mental construct that serves, solely, to model the waves. Each ray represents the wavefront propagation of a hypocenter*** (source). On the other hand, as in sea waves, the velocity of the wave represents, in reality, a phase velocity, that is to say, that which moves is not matter (water, in the case of waves of the sea), but rather the crests and trough of the wave, that is, the phase of the surface of the sea.

(*) Do not forget light is just visible if an object intercepts its trajectory. When light is projected in a closed container and take care that it does not fall on any object or any surface we see just darkness ; it is only when we introduce an object across the light trajectory that we realize that the container is filled with light. That is why an astronaut looking through the porthole of the space nave cabin sees only black, although the sunlight reigns around him: light falling on nothing, can not be seen.

(**) In optics  a ray is an idealized model of light, obtained by choosing a line that is perpendicular to the wave-fronts of the actual light, and that points in the direction of energy flow Rays are used to model the propagation of light  through an optical system, by dividing the real light field up into discrete rays that can be computationally propagated through the system by the techniques of ray tracing. https://en.wikipedia.org/wiki/Ray_(optics)

(**) In general, the term hypocenter is used to designate the focus of an earthquake or seismic focus, which is the point within the Earth where a seismic displacement or earthquake begins. In the same way, the term epicentre is the vertical projection of the hypocenter on the earth's surface and corresponds to the area where the earthquake feels most strongly.

Angle of Refraction....................................................................................................................................................................Angle de de Refraction

Ângulo de refracção/ Ángulo de refracción / Brechungswinkel /  折射角 / Угол преломления / Angolo di rifrazione /

Angle that a refracted ray of seismic energy (or other type) does with refractive surface (sedimentary interface, for instance) after it has crossed it. The angle of refraction is measured in relation to the perpendicular of the surface. Refracted and reflected rays (or waves) result from the division of incident rays (or waves) that are not perpendicular to the surface.

See: « Angle of Incidence »
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« Angle of Reflection »
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« Reflection Seismic »

In quantum theory, light can take several paths to go from the source, in the upper medium to a detector in the lower medium. However, the trajectories with, more or less, the same travel times are roughly around of the trajectory of lesser time (principle of the least time or Fermat's principle). Snell's Law states that during refraction (in this example, light), the ratio of sine* of the angles of incidence (i₁) and refraction (i₂) is constant and equal to the refractive index of the refractory medium, in this case the water. Each material (medium) that the light can traverse has an absolute refractive index (or simply refractive index), which is equal to the speed of light in space divided by the speed of light in the material. The terms used in the diagram illustrated above may be summarized as follows: (i) The light ray** travelling through the upper medium and reaching the interface is called the incident ray ; (ii) The light ray in the lower medium, from the interface is called refracted ray ; (iii) The line perpendicular to the interface between the two media and imagined at the refraction point (dashed line) is called normal ; (iv) The angle between the incident ray and the normal ray is called the angle of incidence ; (v) The angle between the refracted ray and the normal ray is called the refracted angle. Under certain conditions, the refracted ray approaches the normal, which means that the angle of incidence is greater than the angle of refraction. Situations in which a refracted ray of light moves away from normal become very complicated when the angle of incidence increases. This implies that from a certain angle, the angle of refraction is greater than 90°, which prevents the ray from entering the lower interface medium, i.e., in the water. The angle of incidence from which a ray of light does not enter the lower medium (water) is called the critical angle. When the incident ray is perpendicular to the interface, the direction of the refracted ray is the same as that of the incident angle. When the two media have the same index of refraction the light does not deviate since the incident angle and the angle of refraction are equal. Note that light: (i) Corresponds to electrical and magnetic changes and to vibration of particles: (ii) Propagates through transverse electromagnetic waves ; (iii) It does not need any means to propagate ; (iv) Propagate in any medium as well as in vacuum ; (v) It spreads in a vacuum at the speed of 300,000 km / s through the route that takes less time and not in a straight line.

(*) One of the best ways to recall what is the sine, cosine, and tangent of an angle φ is to consider a point on a circle of radius r and the horizontal and vertical axes passing through the centre of the circle as Cartesian coordinates. The point x on the horizontal axis that is generally known is the variable y the point y on the vertical axis which, in general depends on the point x, is the function (the opposite is also possible). Thus any point 'P' located in the circle can be characterized by the coordinates x and y. The x-coordinate is the cosine of the angle φ defined by the radius «r» of the circle passing through P and the horizontal axis (x-axis), while the y-coordinate is the sine of the same angle φ. In fact, x, y and the radius r define a right triangle in which x and y are the  cathetus and r the hypotenuse, which means that if the radius of the circle equals 1, Pythagoras' theorem says that (sin φ)²+ (cos φ)² = 1. If the point P is moved in the opposite direction of the hands of a clock, it is easy to see that sin φ (i.e., the y coordinate) will vary from 0 (φ = 0) to 1 (φ = 90 °), then to 1 for 0 (φ = 180°) and then to -1 (φ = 270°) and again to 0 after a full rotation (φ = 360°). Obviously, the same is true for the cosine of φ which varies from 1 to 0, -1, 0 for the end of a turn again to 1 (φ = 0). The tangent of φ (tan φ) emphasizes the slope of the radius passing through the point P and is given by the ratio sin φ / cos φ, which means that when φ = 45° the tangent equals 1, since sin φ = cos φ and that for φ = 90° (vertical radius) the tangent equals infinity, since tan 90° = sin 90° / cos 90° = 1/0 = infinity. straight line.

(**) A ray of light is the imaginary line representing the direction along which light propagates. The use of light rays greatly simplifies calculations, particularly in Optics. However, light rays are waveforms that indicate the propagation orientation of light waves in the medium in which energy is propagated. A wavefront is the region of space that collects all points of the medium simultaneously reached by a pulse (all points of a wavefront have the same phase).

Angle of Repose (Critical angle)................................................................................................................................................Angle de Repos

Ângulo de repouso / Ángulo de rozamiento interno/ Reibungswinkel (Winkel der inneren Reibung )/ 休止角 / Угол естественного откоса / Angolo di resistenza al taglio (angolo di attrito interno) /

Maximum slope angle (measured from the horizontal) whereby an unconsolidated material will be resting when added to a stack of similar material. Maximum slope from which a poorly consolidated material collapses due to gliding faults.

See : « Turbidite »

« Talus, Slope »
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« Highstand »

As and when a delta progresses seaward, the angle of the prodelta increases until reaching the angle of repose (critical angle), which varies with the water-depth. If the angle of repose is exceeded, the delta front collapses creating turbidite currents, which deposit the material transported since they lose the competence to carry them. Similarly, under highstand geological conditions (sea level above the basin edge), the rupture of the critical angle of a continental slope can produce important turbidite currents responsible for the deposition of thick submarine fans (Emiliano Mutti's model). The gravitational movements of mass, that mobilize the soil, the rock or both, occur when the tensile forces, induced by gravity, especially on the slopes, overcome the forces of resistances, mainly, the forces of friction. According to Montgomery (1992), such movements (since the shear force exceeds the friction) are determined by the angle of repose, which is the maximum slope angle, with which all material is in a stable situation. The angle of repose varies function of the nature of the material under consideration. The spherical and rounded sedimentary particles support a very low angle, i.e., a heap of spherical and rounded sedimentary particles has, in the absence of any cement between them, a relatively flattened morphology (small angle of slope). In contrast, irregular and angular sedimentary particles may constitute a much steeper pile or heap, without the particles becoming unstable. The coarser the sedimentary particles, the greater the slope angle, that is to say, the greater the resistance of the material to slipping. The model (a very useful way of making a little light of a world, very imperfectly known), proposed by Pier Bak (1947) to study the sedimentary systems that self-organize, when in a critical state, is, often, used to better understand turbidite deposition systems. This is true both for the turbidite systems of P. Vail (associated with significant relative sea level falls, which put the sea level lower than the basin edge, exhuming the shelf and upper continental slope), and for the E. Mutti turbidite systems, where river floods and landslides, induced by instabilities of the continental edge, are decisive (in high or lowstand geological conditions). In the P. Bak model shown in this figure, when the sand heap is stable, the slope corresponds to the angle of repose. However, each time more grains are added, the balance of the sand pile is broken and collapses occur until the angle of rest is restored again. The systems theory ** is, perfectly, explained by this model. The characteristics of a "whole" (which in this case is a heap of sand and in the case of sequential stratigraphy may be, for instance, a submarine basin floor fan) can not be determined by studying each grain of sand, i.e. a "Part. In other words, the characteristics of the sand heap do not correspond to the sum of the characteristics of the grains or, more simply, the heap has characteristics which do not correspond to the sum of the characteristics of the grains. This is often overlooked by certain geoscientists, particularly by those working in the field, who focus too much on the details of the outcrops and, often, lose the regional and global geological perspective. With P. Bak, the study of details, in this example, the study of each of the sand grains, is perhaps very interesting and may even be fascinating, but geoscientists do not grasp from details, but from generalities. That is why in Sequential Stratigraphy, geoscientists go from the general to the particular and not from the particular to the general. This explains, in part, the reason why sequential stratigraphy was discovered in oil companies, especially in Exxon's Exploration Production Research (EPR), which had regional seismic lines (macroscopic scale) across all types of sedimentary basins, with which the geological context is easier to refute than from field observations. In most doctoral theses prior to the 1980s, doctoral students have almost always forgotten that "Theory precedes Observation" (K. Popper, 1934). Stratigraphic studies, for example, were often limited to simple lithological descriptions of outcrops, which is far from being the objective of stratigraphy. Similarly, in the oil industry, the purpose of seismic lines is not, or should not be, to determine the geological history of the region where the seismic lines were drawn, but to test (refute) the conjectures or hypotheses advanced, a priori, by geoscientists.

(*) Many geoscientists oppose Emiliano Mutti's turbidite systems to Peter Vail's turbidite systems, which is a mistake. Mutti just believes and probably with rightly that in addition to turbidites deposited under lowstand geological conditions (P. Vail) there are turbidite systems deposited under highstand geological conditions.

(**) Theory that studies, in an inter-disciplinary way, the abstract organization of phenomena, regardless of their formation and present configuration, in which a system is a set of interacting and interdependent parts that together form a unitary whole with a certain objective and that perform a function.

Angular Unconformity (Tectonically enhanced unconformity)........................Discordance angulaire

Discordância Angular / Discordancia angular / Schräg-Diskordanz / 角度不整合 / Угловое несогласие / Discordanza angolare /

Unconformity in which the overlying and underlying layers have different tectonic behaviours (dips). A tectonic phase (relative sea level fall) exists between the two stratigraphic cycles limited by an unconformit. Synonym with Tectonically Enhanced Unconformity.

See: " Relative Sea level Fall "
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" Truncation "
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" Disconformity "

Two angular unconformities are easily recognized on this tentative geological interpretation of a Canvas auto-trace of a detail of a China offshore seismic line. This offshore corresponds to the stacking of four types of sedimentary basins of Bally and Snelson (1980) basin classification. From bottom to top, one can recognize: (i) Basement, which corresponds,probably, to a large extent, to a pre-Cambrian folded belt ; (ii) Paleozoic f,flattened folded belt ; (iii) A Mesozoic-Cenozoic back-arc basin, within which, theoretically, is, often, possible to distinguish half-grabens, developed during a rifting phase, covered by sediment deposited during the sag or thermal phase and (iv) A Cenozoic non-Atlantic type divergent margin.  Above the basement, which is, probably, composed by pre-Cambrian rocks, a large Paleozoic sedimentary package was deposited. Later, due to compressional tectonic regimes, this sedimentary package became a folded mountains range that, at the end of Paleozoic Era, became a peneplain (low-relief plain formed by protracted erosion). This Paleozoic interval is limited at the top by an angular unconformity, i.e., an unconformity, induced by a relative sea level fall*, which was enhanced by tectonics. Such a tectonically enhanced unconformity is, easily, recognized by the terminations (lapouts) of the seismic reflectors (toplaps by truncation). Above this unconformity, sediments of a back-arc basin were deposited. They exhibit a slightly different tectonic behaviour of the underlying package. A compressional tectonic regime shortened the rocks that were uplift and eroded. The erosional surface emphasises a new peneplain that was covered, during Cenozoic, by a non-Atlantic type divergent margin. The upper unconformity between the Paleozoic/Mesozoic and Cenozoic margin sediments is, also, an angular unconformity, although the sediments of the overlying interval are parallel to the unconformity. They have a parallel internal configuration. These unconformities, on the contrary, to the unconformity not enhanced by tectonics (cryptic unconformities), are not underlined by a homogeneous seismic reflector (more or less constant amplitude) and continuous, but by a lateral association of discontinuous reflectors with different characteristics, function of the acoustical impedance profiles**. This type of unconformity (tectonically enhanced) can not be followed or picked in continuity. The geoscientist is forced to jump from peaks to troughs of the reflections or the opposite, every time the acoustical impedance contrast changes. It is in the interpretation of unconformities and, particularly, in the interpretation of tectonically enhanced unconformities, that the qualities of interpreters can be tested. On a seismic line, and particularly within a sequence-cycle, the only seismic surface (defined by reflection terminations) which can be followed, more or less, in continuity and over a distance, relatively, important, is the downlap surface separating the highstand prograding wedge (HPW) from the transgressive interval (TI). A downlap surface is not a chronostratigraphic but diachronic. The hiatus between the underlying interval (transgressive interval, TI) and the overlapping interval (highstand prograding wedge, HPW) increases seaward. It was for these reasons that a few years ago certain American geoscientists said, somewhat unhappily, that the picking  of a tectonically enhanced unconformity is for men. In reality, all they wanted to say was that the picking of an angular unconformity requires a certain amount of knowledge and a certain experience which, in general, beginner or novice geoscientists do not have yet. In conclusion, tectonically enhanced unconformities, although they are the easiest to recognize on field or seismic lines (taking into account the reflector terminations of the intervals they separate) are, relatively, rare and local. The most frequent unconformity are cryptic. Their identification is made, mainly, from the recognition submarine canyon fills and incised valleys fills.

(*) Sea level, local, referenced to any point of the Earth's surface, that can be the seafloor or the top of the continental crust. The relative sea level is the result of the combined action of the absolute (eustatic) sea level (supposed global and referenced to the Earth's centre) and tectonics (subsidence or uplift of the sea-floor).

(**) On seismic terms, the acoustical impedance profiles, associated with all angular unconformities, vary, laterally, since the interfaces that define them change laterally.

Animalia.................................................................................................................................................................................................................................Animal (règne)

Reino animal / Reino animal / Tierreich, Animal Kingdom /  动物界 / Животное царство / Regni animale /

The highest classification of living organisms (in contrast to plants, fungi and others), which encompasses all animals. The Animalia Kingdom also called Metazoa does not contain prokaryotes* and protists**. All members of the Animalia Kingdom are multicellular and heterotrophic (directly or indirectly dependent on other organisms for their food).

See: « Eukaryota »
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« Protokaryota »
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« Phanerozoic »

The animal kingdom is one of the five taxonomic kingdoms of living beings: (i) Monera or Prokaryotae (includes many organisms with a prokaryote cellular organization, i.e., no nucleus) ; (ii) Protists or Protoctista (protozoa with animal affinities, protozoa with plant affinities and micetozoa that have affinities with mushrooms) ; (iii) Fungi (or Micota, a taxon that groups the mushrooms) ; (iv) Plantae ; (v) Animalia. The kingdom characteristics-can be summarized as follows ( https://www.ruf.rice.edu/~bioslabs/studies/invertebrates/ kingdoms.html): Monera - a) Individuals are single-celled ; b) May or may not move ; c) Have a cell wall ; d) Have no chloroplasts or other organelles ;  e) Have no nucleus; f) Are usually very tiny, although one type, namely the blue-green bacteria, look like algae ; g) They are filamentous and quite long, green, but have no visible structure inside the cells ; h) No visible feeding mechanism ; i) They absorb nutrients through the cell wall or produce their own by photosynthesis. Protists - a) Are single-celled and usually move by cilia, flagella, or by amoeboid mechanisms ; b) Usually, they do not have cell wall, although some forms may have a cell wall ; c) They have organelles including a nucleus and may have chloroplasts, so some will be green and others won't be ; d) They are small, although many are big enough to be recognized in a dissecting microscope or even with a magnifying glass e) Nutrients are acquired by photosynthesis, ingestion of other organisms, or both. Fungi - a) Are multicellular, with a cell wall, organelles including a nucleus, but no chloroplasts ; b) They have no mechanisms for locomotion ; c) They range in size from microscopic to very large (such as mushrooms) ; d) Nutrients are acquired by absorption ; e) For the most part, fungi acquire nutrients from decaying material. Plants - a) Are multicellular ; b) Most don't move, although gametes of some plants move using cilia or flagella ; c) Organelles including nucleus, chloroplasts are present, and cell walls are present ; d) Nutrients are acquired by photosynthesis (they all require sunlight). Animals - a) Are multicellular ; b) Move with the aid of cilia, flagella, or muscular organs based on contractile proteins ; c) They have organelles including a nucleus, but no chloroplasts or cell walls ; d) Acquire nutrients by ingestion. By definition, as an animal can not generate its own food it is dependent on plants or other animals for their sustenance. The animal kingdom, also called Metazoa, is formed by multicellular eukaryotic organisms. The body plane of the animals becomes, eventually, fixed as they develop, although some of them go through a late metamorphosis process. Most animals are mobile, which means that they can move, spontaneously, and independently. On the other hand, as stated earlier, all animals are heterotrophic, that is to say, they must ingest other organisms to feed themselves, but they adapt easily to the changes that occur in their environment. Many of the known animal phyla appeared in the fossil record as marine species during the Cambrian explosion about 540 million years ago. Animals can be classified into: (i) Vertebrates and (ii) Invertebrates. The first, which are characterized by having an internal skeleton, which supports the body and allows movement, are subdivided into 5 groups: (a) Mammals; (b) Birds; (c) Fish; (d) Amphibians and (e) Reptiles. The invertebrates, which are the most numerous, lack a vertebral column and articulated internal skeleton, but most of them have external protection, they are classified into several groups among which: 1) Arthropods ; (2) Molluscs ; 3) Worms ; 4) Echinoderms ; 5) Jellyfish ; 6) Sponges, etc. There are about 36 phyla in the animal kingdom.

(*) In scientific classification (biological taxonomy), the Prokaryotes are one of the three domain (Archae, Bacteria and Eukarya) of the cellular life (life➛domain➛kingdom➛phylum➛ class➛order➛family➛genus➛ species). They are unicellular organism without a membrane bounding the nucleus.

(**) Protists includes primarily unicellular eukaryotic organisms (Eukarya domain, super-kingdom or empire). The cells of protists are highly organized with a nucleus and specialized cellular machinery called organelles. 

Anomalistic Period (Moon).............................................................................................................Période anomalistique (De la Lune)

Período Anomalístico / Período anomalístico (de la Luna) / Anomalistisches Zeitraum / 不规则的时期 / Aномалистический период (Луна) / Periodo anomalistico /

Time that elapses between two passes of an object in orbit by its perihelion (the point that is closest to the centre of attraction). In the case of the Moon, the anomalistic period or anomalistic month differs from the sidereal period (or month). This is due to regression of the Moon's orbit. The "long" dimension of the elliptical orbit and hence the points of apogee and perigee, circle around the Earth about once every 9 years. The time it takes the Moon to travel from apogee to perigee and back again is slightly longer than its orbital period. The anomalistic lunar month is 27.554549 days. Synonym with Anomalistic Month.

See: « Sidereal Period (Moon) »
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« Synodic Period (Moon) »
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« Orbit »

The apogee and perigee are not relatively fixed points to Earth. This is due to regression of the Moon's orbit. The major axis of the elliptical orbit, and thus the points known as apogee and perigee, circulate around the Earth about once every nine years. In this way, the time that Moon spends to travel from apogee to perigee is, slightly, longer than its orbital period (Sidereal Month). This time period is called anomalistic month and lasts 27.5554549 days. The anomalistic month is very important for solar eclipses*. The size of a solar eclipse that we see and the type of eclipse (partial, total, annular or hybrid) depends on the distance from the Earth to the Moon during the eclipse and this distance depends on the point during the anomalistic month when the eclipse occurs. In the same way, the duration and appearance of the solar eclipse are affected too. Beyond the anomalistic month, there are other ways to consider how long it takes the Moon to complete an orbit: (i) Sidereal month, which is the time the Moon takes to make a complete return to Earth in relation to the fixed stars, which lasts about 27.3 days ; (ii) Synodic month, which is the time the Moon spends between two phases (between two consecutive New Moons), which lasts about 29.5 days ; (iii) Draconic month, which is the time that the Moon spends between two consecutive ascending nodes (point where the orbit of a satellite crosses the plane of the ecliptic and where the third coordinate of the satellite is increasing) ; (iv) Tropic month, which is the time between two consecutive phases of the Moon (same ecliptic longitude). The synodic month is longer than the sidereal month because the Earth-Moon system shifts a finite distance in its orbit around the Sun during each sidereal month and more time is needed to find the same relative geometry. As a result of the slow precession of the moon's orbit, the month anomalistic, tropic, and draconic period are different from the sidereal month. The average time of a calendar month (1/12 of a year) is about 30.4 days.

(*) An eclipse is an astronomical event occurring when an astronomical object  is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer. A solar eclipse occurs when a terrestrial observer passes through the shadow cast by the Moon,which fully or partially occults the Sun. This can only happen when the Sun, Moon and Earth are nearly aligned on a straight line in three dimensions during a new moon when the Moon is close to the ecliptic plane. In a total eclipse , the disk of the Sun is fully obscured by the Moon. In partial and annular eclipses, only part of the Sun is obscured. (https://en.wikipedia.org/wiki/Solar_eclipse).

Anomalous Accumulation (Poor sedimentation).............................Accumulation anormale faible

Acumulação Anómala Pobre / Acumulación anómala (sedimentos) / Anomale Akkumulation / 异常加积accumulation / Аномальное накопление / Accumulazione anomalo /

Accumulation, generally, very thin characterized by a very small sedimentation rate (such as 1-10 mm of sediments per 1,000 years) of hemipelagic and pelagic sediments (almost without terrigeneous influence). Often, synonymous with Condensed Stratigraphic Section. A condensed stratigraphic section is deposited in the distal part of a shelf, slope or abyssal plain, during periods of highstand (sea level higher than the basin edge) and of maximum marine ingression (landward displacement of the shoreline induced, generally, by a relative sea level rise). Within a sequence-cycle, this type of stratigraphic section is almost always associated with the downlap surface limiting the transgressive interval (TI) from the highstand prograding wedge (HPW). Poor anomalous accumulations contrast with rich, abnormally, thick accumulations such as carbonate build-ups and turbidite lobes.

See « Condensed Section »

Anoxic (Environment)..........................................................................................................................................................................................................Anoxique

Anóxico / Anóxico / Anoxischen / 缺氧 / Бескислородный / Anossico /

Environment characterized by a very weak oxygen content, (no oxidation), in which most of the paleoenvironmental indications are, often, removed. Anoxic events occur in lowstand geological conditions, when the oxygen content is very low. Global anoxic events have not occurred for many millions of years. However, geological records show that they have occurred many times in the past and that some of them have caused mass extinctions*.

See: « Sedimentary Environment »
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« Source-Rock »
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« Euxinic (environment) »

Anoxic is an adjective that means without oxygen. An anoxic water is an underground water, which does not contain dissolved oxygen. The terms anoxic and anaerobic (with little oxygen) are, practically, synonymous. In an aquatic environment, whether marine, freshwater or groundwater, contamination by organic substances favours the development of bacteria that consume dissolved oxygen in water, transforming it into an anoxic water environment (the oxidation rate of organic matter bacteria is greater than the supply of oxygen). Thus anoxic waters are those in which dissolved oxygen is depleted. This type of water is, generally, found in areas with processes of eutrophication** in progress or in areas where oxygen can not reach the deepest levels either due to a physical barrier or a pronounced density stratification. The heavier hyper-saline waters move in the bottom of a basin. In a more or less isolated basin there are two possibilities for invasion of water with a lot of oxygen: (i) When the water entering the basin is denser than the basin water; in this case  the entering water flows into the bottom pushing and displacing upward the less oxygenated water, which allows the deposition of gray and green mud since the conditions are not anoxic ; (ii) When water entering the basin (isolated) is denser than the surface water but less denser than bottom water ; in this case, it creates anoxic conditions at the bottom of the basin allowing the deposition of black mud rich in organic matter underneath the euxinic water (restricted or stagnant water with little oxygen). This possibility may explain the formation of certain oil or gas source-rocks, especially, those associated with transgressive episodes ,i.e., source-rocks deposited on the distal parts of shelf. In fact, within a sequence-cycle, during the transgressive interval (TI), at each relative sea level rise (marine ingressions in acceleration), the depositional coastal break of the depositional surface (more or less, the shoreline) moves landward before the deposition of the associated coastal deposits (during the stability period of the relative sea level occurring after each ingression or eustatic paracycle). This landward displacement creates, in the distal part of the shelf, geological conditions of low deposition rate (starved conditions). If at the same time, there is an invasion of cold water rich in oxygen and nutrients from, for instance, an upwelling current, production and preservation of organic matter is possible, which favours the development of potential source-rocks. The vast majority of marine source-rocks (organic matter type II) were, probably, formed in this way (areas of strong organic matter production with anoxic conditions at the bottom layer of water). The formation of anoxic environments is a natural phenomenon that has occurred throughout the geological history. At present, there are anoxic basins in Baltic Sea, Eastern Mediterranean Sea (Bannock Geographic Basin), Eastern Europe (in Black Sea geographic basin below 50 meters and in the Caspian geographic basin below 100 meters) in the Gulf of Mexico (Orca geographic basin), Argentina (San Roque), etc., etc.

(*) The extinction of a single species or group of related species, or even that of a family, is not regarded as a mass extinction. A mass extinction is characterized by the extinction of a large number of species belonging to different genera and families and living in different environments. Such extinction can only occur following a major, global, rapid environmental change affecting a large number of environments. To date there have been five major mass extinctions: (i) In the Ordovician, about 450 Ma, which seems to have wiped out more than 60% of life on Earth ; (ii) In the Devonian, about 360 Ma, when a series of extinctions exterminated about three quarters of the terrestrial species ; (iii) In the Permo-Triassic period, probably about 250 Ma, probably due to an increase in temperature following a gigantic volcanic eruption in Siberia, which would also have affected the oxygen content of the atmosphere (this mass extinction is considered the largest of all, since about 96% of the species disappear) ; (iv) In the Triassic-Jurassic period, approximately 200 Ma, which destroyed several species (about 20% of all marine families would have been exterminated by volcanic eruptions and climatic changes associated with the rupture of the supercontinent Pangea) ; (v) In the Cretaceous-Tertiary, about 65 Ma, for which two explanations have been advanced: (i) The impact of an asteroid over 10 km in diameter, which created the Chicxulub crater in the Yucatan peninsula and (ii) Strong volcanic activity. The last extinction is by far the best known not because it is the most important but because it has triggered or accelerated the extinction of dinosaurs.

(**) Increase of nutrients, generally, nitrogen and phosphorus, occurring either on land or at sea and which translates an increased productivity of an ecosystem.

Anoxic Conditions................................................................................................................................................................Conditions d'anoxie

Condições de Anoxia / Condiciones de anoxia / Anoxischen Bedingungen / 缺氧条件下 / Бескислородные условия / Condizioni anossiche /

When a water-body has a very low oxygen content. These conditions are, generally, found in areas of restricted water circulation or in communication with restricted water. In most of these cases, oxygen does not reach the deeper part of the water-body due to the formation of a horizontal physical barrier, as well as, a density barrier. It can be said that when the oxidation rate of the bacteria is higher than the oxygen source, the environmental conditions are anoxic.

See: « Depositional Environment »
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« Starvation Interval »
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« Lowstand (sea level) »

In Earth's history, the time intervals during which certain areas, more or less, deep of the oceans have become oxygen-poor (O₂) correspond to what geoscientists call oceanic anoxic events. Although, globally, no anoxic events have occurred in the last millions of years. The geological records show that they have occurred many times in the past. Geoscientists think that anoxic events may be associated with the deceleration of the circulation of ocean currents. The concept of anoxic oceanic events is associated with the discovery of carbon-rich black shales in Cretaceous sediments found in the DSDP (acronym of "Deep Sea Drilling Project" ), which are similar, not only in facies but also in age, to shales outcropping in several areas of the world. That suggested that such a rocks were deposited in environments quite poor in oxygen. Similarly, the study, of such a rocks, rich in organic matter, show the presence of thin laminations of deep fauna, which corroborates the presence of anoxic conditions in the sea-floor, which are thought to be correlated with the poisonous layer of hydrogen sulphide (called hydrogen sulphide when in aqueous solution). Geochemical studies revealed the presence of particular molecules (biomarkers) that are derived from the purple sulphurous bacteria and green bacteria of sulphur (Chlorobi), which are organisms that require not only light, but also the presence of free hydrogen sulphide (H₂S), which suggests that the anoxic conditions can extend to the photic zone. At present there are anoxic conditions: (i) In Black Sea, below 50 m depth ; (ii) in Caspian Sea, below 100 m depth ; (iii) in Eastern Mediterranean Sea (Bannock geographic Basin, 34 ° 21'64 "N, 20 ° 02'26" E) and (iv) in many other more or less closed seas. There are indications that eutrophication (increased nutrients, that is, foods that an organism needs to live and grow, which are withdrawn from the environment) has been responsible for increasing the extent of anoxic conditions, such as in the Gulf of Mexico and Baltic Sea, where anoxic conditions appear to have varied throughout the geological history. The anoxic conditions can result from several factors: (a) Stagnation (state of a liquid that does not flow) ; (b) Water stratification by density (formation of horizontal layers of water with different stable densities, arranged so that the less dense ones float over the denser ones, with a minimum degree of mixing between them) ; (c) Organic Material Supply ; (d) Strong thermoclines (abrupt temperature variations at particular depths of the sea in freshwater environments), etc. The production of sulphites (salt or sulphuric acid ester) by bacteria begins in the sediments, where they find suitable substrates and then in the water. When in a basin the oxygen content is very low, the bacteria use nitrates (good electron acceptors) and a denitrification occurs (a process of dissimulatory reduction of the nitrate producing nitrogen, N₂), which means that nitrates are consumed very quickly. After reducing some of the minor elements, the bacteria begin to reduce nitrate. If, by chance, the water is re-oxygenated, the sulphites will be oxidized to sulphates (HS + 2O₂ in HSO₄). When anoxic conditions are created in the oceans, oxygen levels become weak even at small depth. Such conditions have not occurred in the last few million years. However, geological records suggest several occurrences in the past that have caused major mass extinctions. Anoxic conditions are fundamental to the formation of source-rocks, since the organic matter of the sediments has to be preserved. If dead organic matter accumulates in an oxygen-rich environment, it is rapidly oxidized. In order for it to be preserved, it has to accumulate in an anoxic environment. Later, the organic matter may, eventually, turn into oil or gas. For the formation of organic matter, the presence of oxygen and nutrients is indispensable. That is why the distal sectors of the continental shelf are ideal environments for the formation of potential marine source-rocks, since the formation of organic matter is, there, abundant, which produces a depletion in oxygen, allowing the preservation of its dead organic matter, accumulated in the sea bottom.

Anticline........................................................................................................................................................................................................................................Anticlinal

Anticlinal / Anticlinal / Anticline / 背斜 / Антиклиналь / Anticline /

Compressive structure with the form of a bell resulting from the shortening of the strata when subjected to a compressional tectonic regime characterized by an ellipsoid of the effective stresses* with the major axis (σ₁) horizontal. In association with the anticlines, reverse faults can be formed. Anticlines and reverse faults are the only structures that can shorten strata (normal faults lengthen the strata). Do not confuse anticline (shortening) and antiform (lengthening). In the field, taken into account the erosion, in an anticline structure the oldest rocks are always located in the central part of the structure.

See: « Antiform »
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« Syncline »
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« Relative Sea level Rise »

On the tentative geological interpretation of a Canvas auto-trace of the Angola deep offshore seismic line, several anticline structures are visible. The seismic intervals (salt interval, coloured in red, included) were shortened by cylindrical folds (anticlines) and reverse faults. The faults located near the crests of the structures are contemporaneous with the deformation and, therefore, they are not normal faults. They developed during a compressional tectonic regime and correspond to small strike slip faults**. They lengthen the anticline along the axial direction. Such a lengthening is, also, perfectly visible in the geological map of the Bavush anticline (Southern Iran onshore) illustrated at the top of this figure. An anticline correspond, always, to a shortening of the sediments in response to a compressional tectonic regime, i.e., to a tectonic regime in which the maximum effective stress (σ₁) is horizontal. It is impossible to have formation of normal faults (extensive structures), in the same place and at same time, when the sediments are shortened in an anticline fold, particularly, near the top of the structure. If, in the field or on a seismic line, there are normal faults associated with an anticline, the normal faults are either more recent than the anticline or are older. If they are younger, they are not reactivated by the compressional tectonic regime. If they are older, they are, probably, reactivated, into reverse faults. The reactivation is function of the angle between the direction of the fault planes and the direction of maximum effective stress (σ₁). The larger the angle the greater the reactivation in reverse fault along the σ₂ of an older extensional tectonic regime. Another criterion for reactivation of normal faults predating the shortening is the angle between the maximum effective stress direction (σ₁) and the dip of the fault planes. In the field and, especially, in the geological maps, contrary to what happens in a syncline, in an anticline structure, the oldest sediments are always in the central part of the structure.

(*) The effective stresses are those which deform the sediments. They are the main axis of the effective stresses ellipsoid, which is the result of the combined action of the geostatic or lithostatic pressure (σ_g), pore pressure or hydrostatic pressure (σ_p) and the tectonic vector (σ_t). Mathematically, the geostatic pressure is a biaxial ellipsoid, the pore pressure is a sphere and the tectonic pressure is a vector, i.e., a mathematical object, that has a length (magnitude) and a direction in space.

(**) Strike-slip faults are vertical (or nearly vertical) fractures where the faulted blocks have, mostly, moved horizontally. If the block opposite an observer looking across the fault moves to the right, the slip style is termed right lateral ; if the block moves to the left, the motion is termed left lateral (https:// earthquake.usgs.gov/learn/glossary/?term=strike-slip).

Anthropic Principle....................................................................................................................................................................Principe anthropique

Princípio Antrópico / Principio antrópico / Anthropisches Prinzip / 人择原理 / Антропный принцип / Principio antropico /

Hypothesis assuming observations of the physical Universe must be compatible with the life that is observed there, or, in other words, the principle that tries to deduce certain facts about the Universe function of the fact that we exist and can perceive it. There are two forms of anthropic principle : (i) Weak form and (ii) Strong form.

See: « Early Universe »
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« Natural Greehouse Effect »
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« Geological Principle »

In Physics and Cosmology*, the anthropic principle establishes that any valid theory about Universe has to be consistent with the existence of the human being. In other words, the only Universe we can see is Universe that has life. If there is another kind of Universe, we can not exist to see it. The anthropic principle has given rise to some confusion and controversy, in part because this expression has been applied to different ideas. All versions of the principle have been accused of discouraging the search for a deeper understanding of the physical Universe. Those who attempt to explain the anthropic principle often invoke ideas from multiple Universes or an Intelligent Designer. However, since the advanced hypotheses are not testable, some geoscientists think that the anthropic principle is more a philosophical concept than a scientific theory. The anthropic principle is divided into strong anthropic principle and weak anthropic principle. The strong anthropic principle states, in general, that Universe behaved in such a way as to adapt itself to Man. The weak principle says that the Universe behaved in a way that man appeared, without a pre-defined demand. "Nature is exquisitely tuned for the possibility of life on planet Earth": "If the gravitational force were reduced or increased by 1%, the Universe would not form" ; "A tiny change in the electromagnetic force, the organic molecules would not unite" ; "We see Universe the way it is because if it were different, we would not be here to see it". Stephen Hawking works with the hypothesis that nature continually generates universes different from each other. Few of these universes generate intelligent life. Our Universe has generated intelligent life, at random, but when we admire ourselves of our Universe, we must take into account that it is admirable because we are here, alive and intelligent to admire it, while a number of universes we do not see are hostile to life, smart or not.

(*) Branch of astronomy  concerned with the studies of the origin and evolution of the Universe,  from the Big Bang  to today and on into the future.

Anthropogenic (Anthropogeneous, principle)..................................................................................................................Anthropique

Antropogénico / Antrópico / Antropogeneous / 人为 的 / Антропогенный / Antropico /

Conjecture that the laws of nature and the fundamental physical constants have values that are consistent with living conditions as we know them, rather than having values that would not be consistent with life as observed on Earth. A typical star, like the Sun, is surrounded by a favourable zone ("Goldlilocks"), which is neither too hot nor too cold, in which planets can contain liquid water indispensable to life as we know it.

See: « Earth »
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« Life »
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« Uniformitarianism (Principle) »

The fact that Universe can be so hospitable to the development of life is a great puzzle, since it is dependent on a large number of factors, more or less, accidental. Attempts to solve this great enigma have naturally provided a great number of speculations, some of which have a more philosophical rather than scientific character. The anthropic principle emphasizes that we live in a Universe that allows the existence of life as we know it. This means that if at the Universe's birth one or more fundamental physical constants* had a different value, there would be no stars, galaxies, planets, and life as we know it would not have been possible. Consequently, in formulating scientific theories, scientists must be careful that they are compatible with our existence. This principle, simple in itself but not trivial, has been interpreted differently, to be used to justify visions of opposite meaning. Several texts argue that the anthropic principle could explain the physical constants. In itself, the principle, in its weak formulation, as announced by Brandon Carter (1974) does not explain, but restricts the scope of possible theories and justifies some. In fact, the anthropic principle can be presented in two forms: (i) Weak Anthropic Principle and (ii) Strong Anthropic Principle. The weak anthropic principle says that we must be prepared to take into account the fact that our location (time and space) in Universe is, necessarily, privileged to the point of being compatible with our existence as observers. Universe behaved in such a way that it can contain us, that is, the physical and cosmological quantities we observe have values compatible with the emergence of life based on carbon. The strong anthropic principle says that Universe, as well as the fundamental parameters on which it depends, must be such that it admits the creation of observers within it at a given moment. These forms, and in particular the weak anthropic principle which says, fundamentally, that if Universe did not have a certain number of characteristics, we would not be here to see it, they are not scientific hypotheses, since they can not be falsified. Just as the "God exists" hypothesis may or may not be true. But true or not, it is not a scientific hypothesis because it is not susceptible of refutation. On the contrary, Einstein's general theory of relativity is a scientific theory because it announces a number of predictions that can be tested by experiments. Note that the refutation criterion of Karl Popper (1934) is not a criterion of truth, but of scientificity. For example, the statement "The earth is flat" is, according to Popper, a scientific statement since it can be tested by an experience, which can refute it, that is, show that it is not a true statement.

(*) The evolution of the Universe is determined by the initial conditions (such as the initial rate of expansion or the initial mass of matter) and by a fortnight of numbers called physical constants (such as the speed of light, the electron mass, which depends on the gravitational constant, etc.). Scientists have accurately measured the value of these constants, but for now, they have no theory to explain them (T. Xuan Thuan, 1988).

(**) Two other variations of the anthropic principle are advanced by certain scientists: (i) Final Anthropic Principle, in which the Universe aims to produce living beings, or humans and (ii) Participative Anthropic Principle, which says that the existence of observers gives existence to the Universe.

Antiform........................................................................................................................................................................................................................................Antiforme

Antiforma / Antiforma / Antiform / 背斜 / Антиформа / Antiforma /

Non-genetic term used to describe geological structures with the bell-shape geometry. Most geoscientists working on hydrocarbon exploration reserve the term antiform to describe an extensive bell-shaped structure resulting from the lengthening of the strata when they undergo an extensive tectonic regime, i.e., a tectonic regime characterized by a ellipsoid of the effective stresses with the major axis (σ₁) vertical. Antiforms are, sometimes, interpreted, erroneously, as anticlines (compressive structures). In a purely descriptive and non-generic terminology, it may be said that all anticlines are antiforms, but not all antiforms are anticlines.

See: « Anticline »
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« Synform »
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« Goguel's Law »

On the tentative geological interpretation of a Canvas auto-trace of a North Sea seismic line, it is evident the salt sediments (in red) were elongated by an extensional local tectonic regime (ellipsoid of effective stresses with the maximum effective stress, σ₁, vertical) induced by the upward and basinward movement of the salt) and not shortened by a compressional tectonic regime (major axis of the ellipsoid of the effective stresses, σ₁, horizontal). The normal faults that extend the sediments and that, generally, are formed at the apex of the antiform structures, have, in most cases, a vertical displacement lower than the seismic resolution (20-40 meters). That is why they can not be visible on this tentative interpretation. It is possible that after the deformation in extension, a compressional tectonic regime may have, slightly, shortened the sediments. In fact, on certain seismic lines, parallel to the seismic line of this Canvas auto-trace, small tectonic inversions* are visible. This tentative interpretation, clearly, shows the presence of a salt horizon in a stratigraphic series can produce a tectonic disharmony** between the supra-saliferous and the infra-salt sediments. In this particular case, both intervals (supra and infrasalt) were lengthened, but by different tectonic regimes. The infrasalt sediments were extended by a tectonic regime with a vertical σ₁ and σ₂ and σ₃ different and perpendicular between them, whereas the suprasalt sediments were extended by a tectonic regime with a vertical σ₁ and σ₂ = σ₃ (halokinesis or tectonic of the salt). In the infra-salts sediments, the normal faults are parallel to the direction of σ₂, whereas in the supra-salts sediments, they are oriented in all directions (radial faults), since σ₂ = σ₃. Locally, the salt interval may disappear by lateral flowage or have a thickness lower than the seismic resolution, but the disharmonic surface (salt weld) will always be present. On the auto-traces illustrated at the top of this figure, it is obvious that the antiform structures are associated with an lengthening of the suprasalt sediments induced by the formation of the salt diapiric structures. To test the lengthening deformation of the supra-salts sediments induced with the salt domes, put a finger under a your pullover with a wide knit exercising an upward movement with finger. You will, easily, notice that the knit of your pullover opens, as the sediments do above a salt dome.

(*) Inversion of vertical movement of faulted blocks recorded by thickening or thinning stratigraphic of strata contemporaneous of the deformation, i.e., that a normal fault can later be reactivated as an reverse fault. In other words, in a tectonic inversion, the structural low points become high and the structural high points become low.

(**) A tectonic disharmony is a geological surface that separates two domains of deformation. Disharmonies are, often, associated with a mobile sedimentary interval, usually, evaporitic or shaly.

Antinodal Point (Wave)....................................................................................................................................................Point antinodal (Onde)

Ponto Antinodal / Punto antinodal (onda) / Schwingungsbauchzone Punkt (Welle) / Antinodal 点(波） / Пучность (волна) / Punto antinodal (onda) /

Point where waves interfere constructively. The point on a standing wave where the vertical motion is the largest and the horizontal velocity is the smallest.

See: « Wave »
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« Crest (Wave) »
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« Trough, Hollow (Wave) »

In physics, as shown in this figure, an antinodal point is the point at which the amplitude of one of the two displacements in a standing wave has the maximum value. Generally, the other type of displacement has its minimum value at this time. A wave is a disturbance that propagates through space and time, transferring energy. A stationary wave is a combination of two waves that move in opposite directions, each with the same amplitude and frequency, which implies an interference. When the waves overlap, their energies are added or cancelled (the vibration of a rope tied at one end produces a standing wave, that is, a pattern characterized by sites, nodes, where there is no motion). In the case of waves moving in the same direction, interference produces a displacement wave (when the wave appears to travel through a medium, i.e., when a crest is followed by a hollow which in turn is followed by another crest and so next). On the contrary, when the waves are moving in the opposite direction, the interference produces a fixed oscillation wave in space. This figure illustrates the pattern resulting from the propagation of water-waves across the surface of a water-body. The waves propagate from the sources of vibration, forming a series of concentric circles around each source. The thicker lines represent the crests of the waves and the fine lines represent the hollows. The crests and hollows of the two sources interfere with each other at a more or less regular rhythm producing nodes and antinodes along the surface of the water. Nodal positions are located where the water is not disturbed, while the antinodal positions are places where the water suffers a maximum of disturbances above and below the water level in the neighbouring regions. One of the characteristics of the two point source interference pattern is that the antinodal and nodal positions are arranged in separate lines. Each line can be described as a hyperbola and the spatial separation between the antinodal and nodal lines is related to the wavelength of the waves.

Aphelion.................................................................................................................................................................................................................................................Aphélie

Afélio / Afelio / Aphelion, Aphel / 远日点 / Афелий / Afelio /

Point of the orbit of a planet or comet that is farthest from the Sun. The aphelion is the opposite of the perihelion. Aphelion is not to be confused with the apsis, which is the name of each of the extreme points of the orbit of a celestial body (planet or comet).

See: « Apside »
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« Perihelie, Perihelion »
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« Astronomic Theory of Paleoclimate »

In this scheme of the orbit of a star, around the Sun, the aphelion corresponds to the point of the orbital trajectory farthest from the Sun, which occupies one of the foci of the ellipsoid of the orbit. The notion of aphelion and perihelion (orbit point closest to the Sun) from Earth's orbit is a very important factor in understanding modern climatology, but not in past climatic changes (paleoclimatology). When the Earth is in the aphelion, the insolation (amount of energy received from the Sun) is lower than when it is in perihelion. Modern climatology, which is based on a large number of observations made over a short period of time, which correspond, often, to direct measurements of the properties and characteristics of the atmosphere, oceans and ice, badly explain climate change (paleoclimatology). The history of geology suggests that the temperature and amount of CO₂ in the atmosphere varied, more or less, cyclically and that we are now in a similar condition as those reigned at about 300 Ma (Carboniferous and Permian): (i) Average global temperature about 12° C and (ii) CO₂ content about 300 ppm. Cretaceous appears to have been the hottest geological period with an average global temperature of 22° C and a CO₂ content, progressively, decreasing from 2,300 to 800 ppm (part per million, 1 gram equivalent per ton). Current temperature variations (after the industrial age) are insignificant in relation to past variations (Deconinck, 2001). The climatic changes, which influenced stratigraphy, are now well explained by the astronomical theory of paleoclimates (Milankovitch's theory), which is now accepted, practically, by almost all geoscientists. The basic hypothesis of this theory is that terrestrial temperature depends, mainly, on the amount of solar energy captured by Earth, which is controlled by: (i) Precession of the Earth's rotational axis* (cycles of 25 and 19 ky) ; (ii) Obliquity of the axis of rotation of the Earth** (41 ky cycle) ; (iii) Eccentricity of the Earth's orbit ellipse (cycles of 100 and 413 ky) and (iv) Position of the Earth in orbit (1-year cycle). Obviously, these three factors have a significant influence on the relative variations of the mean sea level, since they influence eustasy. The eccentricity of Earth's orbit emphasizes how much the Earth's orbit, which is an ellipse, moves away from the circular shape. The eccentricity, which varies between 0 and 1, can be determined by the relation between the smallest and largest half-axis of the orbit or, directly, by the distance from the Sun, which occupies one of the foci of the ellipse, to the geometric centre of the orbit. An increase in eccentricity changes the relationship between the smallest and the longest distance from the Sun, which increases the difference in summer and winter temperatures.

(*) Earth rotates about an axis of rotation. The axis is not align with the ecliptic axis (projection on the celestial sphere of the apparent trajectory of the Sun observed from the Earth) but precesses around it, in the same way as a top rotates precesses around the vertical axis to the ground. Thus, the precession of the axis of rotation of the Earth is the gyroscopic motion of its axis of rotation (Earth moves about one axis, but it belongs to another rotating system). The cycle length of precession of the axis of rotation of the Earth effecting cycle is 25,770 years.

(**) The obliquity of the axis of rotation of the Earth or axial inclination is the angle between the axis of rotation and the plane of the orbit. This angle varies between 21.8° and 24.4° in periods of about 41 ky. The stability of the inclination is maintained by the torque (moment of a force in relation to a certain point or is a vectorial physical quantity that indicates ability of that force to rotate a mechanical system around that point, often called pivot) exerted by the Moon, which acts as a stabilizer on the Earth's equatorial protuberance. The variations of the axial inclination (within the range of 21.8° and 24.4°) can produce changes of about 10% in the sunshine, especially in the highs at latitudes. The increase in the inclination of the axis of rotation of the Earth relative to the plane of the orbit increases the temperature differences between winter and summer. Geoscientists think that the inclination of Earth's axis of rotation is the result of a collision with an asteroid. It is the domain of contingency. Such inclination was not fundamentally inscribed in the laws of Nature. No physical law predestined the Earth to be inclined more or less 23.5° (T. Xuan, Thuan, 1998).

Apatite.........................................................................................................................................................................................................................................................Apatite

Apatite / Apatita / Apatit / 磷灰石 / Апатит / Apatite /

Group of phosphate minerals such as hydroxylapatite, fluorapatite and chlorapatite, so called because of the high concentrations of ions, respectively, OH-, F-, and Cl- in the crystals. Apatite is one of the few minerals that is produced and used in microenvironmental systems.

See: « Fission Track »
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« Radiometric Dating »
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« Authigenesis »

Apatite appears in almost all types of rocks (igneous, sedimentary and metamorphic). However, it appears, above all, disseminated in crypto-crystalline grains or fragments. The most well developed forms are found in rocks associated with a contact metamorphism*. Apatite is one of the few minerals that is produced and used by the biological systems of the micro-,environment. Hydroxylapatite is the major component of tooth enamel and one of the important components of bones. Hydroxylapatite is a relatively rare form of apatite in which many of the OH groups are absent and contain many carbonate and phosphate acid substitutions. Because fluoroapatite resists acid attack much better than hydroxylapatite, fluoroapatite is used in toothpastes, which almost always contain a source of fluoride anions. Also, fluoridated water allows an exchange in the teeth of fluoride ions by hydroxyl groups in apatite. Apatite is also used to fertilize tobacco. The apatite deprives the plants of the tobacco of nitrogen, which gives the tobacco a very particular taste and appreciated by certain smokers. Apatite is rarely, used as a precious stone. Transparent apatite of limpid colour is sometimes lapidated, and certain specimens are carved in cabochon (polished, but not faceted). The apatite with various reflexes is known as cat's eye. When rusty crystals are present inside the crystals of apatite, these, when carved in cabochon and illuminated under certain angles, have a similar effect to that observed in the eyes of cats. The transparent green apatite is known as asparagus stone and the blue as moroxite. The apatite fission traces are widely used to determine the thermal history of a mountain chain or system and the sediments deposited in the buried sedimentary basins. The apatite (U-Th) / He dating is often used for the determination of less well-known thermal and other geological histories, such as paleo-fire dating.

(*) Set of mineralogical and structural changes induced in rocks, in particular, in sedimentary rocks, due to the proximity or contact with intrusive bodies of igneous rocks, which turns them into metamorphic rocks, whose degree of metamorphism increases as the distance to the igneous rocks decreases.

Aphotic Zone...................................................................................................................................................................................................Zone aphotique

Zona afótica / Zona afótica / Aphotische Zone / 无光区 / Афотическая зона / Zona afotica /

Portion of an ocean or lake where the light of the Sun is very little intense or non-existent. The aphotic zone is, formally, defined as the water-depth beyond which only 1% of sunlight is present. The light from this zone is, essentially. of biological origin (bioluminescence*).

See: « Shelfal Accommodation »
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« Photic Zone »
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« Relative Sea Level Rise »

The depth of the aphotic zone is, greatly, affected by the turbidity of the water and the seasons. As shown in this figure, the aphotic zone underlies the photic zone (certain geoscientists do not distinguish the dysphotic zone), which is the portion of the oceans directly affected by sunlight**. The upper boundary of the aphotic zone varies greatly, but it is, rarely, less than 1,000 m. In certain cases, the upper limit may be deeper and certain authors advance even depths of the order of 5,000 meters. The temperature at the top of the aphotic zone may be slightly positive. The aphotic zone is the realm of particular creatures such as the giant squid, pelican eel (so called because its mouth is similar to that of a pelican), vampire squid, etc. Many of the organisms that live in the oceans depend on sunlight. Plants and bacteria, such as the vareque (generic name of all seaweed family of the algae family, such as the sargasso), plant plankton and photosynthetic, use sunlight to obtain energy through photosynthesis. Then these organisms are eaten by larger animals, which in turn are eaten by more larger animals and so on. In other words, sunlight is the basis or beginning of the food chain. Sunlight, too, not only warms the water of the oceans, which is very important, since it makes the water warm enough for animals to live there, but it also induces the formation of marine currents, which many animals use to move. When the sunlight penetrates the oceans, it is absorbed which allows to consider three zones, as a function of the amount of sunlight they receive: (i) Euphotic Zone, (ii) Dysphotic Zone and (iii) Aphotic Zone. In the aphotic zone, there is no sunlight. It starts at about 1,000 m of water-depth (depends on the region considered) and ends at the bottom of the sea. The animals that live there are rare, but certain communities find near the deep hydrothermal vents*** the energy needed to survive. Hydrothermal vent communities are able to sustain such vast amounts of life because vent organisms depend on chemosynthetic bacteria for food. The water from the hydrothermal vent is rich in dissolved minerals and supports a large population of chemoautotrophic bacteria. These bacteria use sulphur compounds, particularly hydrogen sulfide, a chemical highly toxic to most known organisms, to produce organic material through the process of chemosynthesis.

(*) Bioluminescence is the production and emission of light by a living organism via a chemical reaction in which chemical energy is converted into light energy.

(**) "Sunlight" does not just mean visible light, ranging from red to blue. The light we can see is only a small part of a much larger spectrum. The range of lights can be spotted by numbers called frequencies. As the number representing the frequency increases, we go, successively, from red to blue, then from blue to violet and to ultraviolet. Increasing more the frequency we arrive in the X-ray domain, then gamma rays. If we decrease the frequency from blue, we successively, switch from blue to red, then to infrared, then to television and radio waves.

(***) A hydrothermal vent is a fissure in a planet's surface from which geothermally heated water issues. Hydrothermal vents are commonly found near volcanically active places, areas where tectonic are moving apart at spreading centres, ocean basins, and hotspot . Hydrothermal vents exist because the earth is both geologically active and has large amounts of water on its surface and within its crust.  (https://en.wikipedia.org/wiki/Hydrothermal_vent)

Apocynthian (Moon).........................................................................................................................................................................................Apocynthian

Apocintião / Apocynthiano / Apocynthion/ Apocynthian（天文）/ Апоселений / Apocynthian (astronomia) /

Point in the Moon's orbit farthest from the centre of the Moon. The farthest point of the Moon in the orbit of a lunar satellite. The terms apocynthian and pericynthian (the closest point to the centre of the Moon) were used by the American astronauts during the Apollo program.

See: « Moon »
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« Apogee »
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« Apside »

The most used terms to identify an object in orbit are: (i) Apogee and Perigee, to the orbits around the Earth ; (ii) Aphelion and Perihelion for the orbits around the Sun and (iii) Apocynthian and Pericynthian for the orbits around the Moon. In the scheme illustrated above, during the NASA Apollo program, the terms "pericynthian" and "apocynthian" were used by the crew to to designate the points of the spacecraft's orbits, respectively, closer and further away around the Moon, since several orbits were required before landing and after take-off. In celestial mechanics, an apsis is the farthest point or the farthest point of the orbit of an object from its centre of attraction, which is, usually, the centre of mass of a system (theoretical point, to facilitate calculations, in which the whole mass of the system is supposed to be concentrated). The point at which two bodies are closest to each other is called periapsis or pericentre. The point in the orbit where they are further apart is called apoapside or apocentre. The straight line between the periapsis and the apoapside is the apsides line. This line is the largest axis of the ellipse that underlines the orbit. For the orbits around the Sun, the apside moment is much more relevant when expressed, relatively, to the seasons because it determines the contribution of the orbit in the annual variation of the insolation of the atmosphere. Such a variation is mainly controlled by the annual cycle of the declination* of the Sun due to the inclination of the axis of rotation of the Earth relative to the plane of the orbit. The inclination of the axis of rotation of the Earth (at the equator, the average speed of rotation of the Earth around its canter is 1,670 km/h (0.46 km/s), which is responsible for the terrestrial stations. Orbit around the Sun is another responsible one), seems to be the consequence of the shock with an asteroid**. Note that Earth is also in orbit around the Sun, travelling at a speed of 107,280 km/h (30 km/s). Sun itself rotates in the Milky Way (our galaxy), in relation to its centre, with a speed of 700,000 km/h (194 km/s). At present, in the northern hemisphere, perihelion occurs about 14 days after the winter solstice (21 December), which means that perihelion is on 4 January. In perihelion, the Earth is at a distance from the Sun of 147.098074 million km, or 0.98328989 AU (astronomical units) and in the aphelion at about 152.097701 Mkm (million kilometers) or 1.01671033 AU. The time (time) of the perihelion advances with the seasons and runs a complete revolution between 22 and 26 k years. This movement, which is an important contribution to the Milankovitch cycles, is known as precession.

(*) In astronomy, the declination is the angle formed by a star with the celestial equator, i.e., one of the two coordinates of the equatorial coordinate system, the other coordinate being the right ascension. The declination, which is measured in degrees. It is positive if it is to the north of the celestial equator and negative if it is to the south. The declination is comparable to the geographical latitude (measured against the terrestrial equator).

(**) This same explanation (impact with an asteroid) is advanced to explain the formation of the Moon there is about 4.6 Ga. However, no one has the least idea of the conditions of such collisions and in particular that which inclined the axis of rotation of the Earth of about 23 ° and did not lay it down completely, as is the case with Uranus, or only 3° as in the case of Jupiter.

Apogee.........................................................................................................................................................................................................................................................Apogée

Apogeu / Apogeo / Höhepunkt / 远地点 / Апогей (наивысшая точка) / Apogeo /

The farthest point of Earth from a body that gravitates (orbits) around it. The apogee is the opposite of perigee.

See: « Perigee »
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« Milankocitch Cycle »
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« Orbit »

The apogee and its opposite, that is, the perigee, should not be confused with aphelion and perihelion or perihelie. The apogee and perigee are terms related to the orbit of an Earth satellite, whether natural or artificial. The aphelion and perihelion are characteristics of the orbit of a planet orbiting the Earth. Periastre and apoastre are the equivalent points of an orbit around the Sun. Thus periastre is the position in which the smaller component of a binary star*, in its orbit around the main star, is closer to it. One can speak of the apogee and perigee of the Moon, which gravitates around the Earth, or of the apogee and perigee of any asteroid like the Ida that gravitate around the Earth. The apogee and perigee of the Moon, evidently, have a very significant influence on the tides, which may be further reinforced by the influence of the position of the Sun, which may be added to or subtracted from the influence of the Moon. The limits of the inter-tidal beach (littoral area defined by high and low tides), located downstream of the backshore, are conditioned, indirectly, by the distance from the Moon to the Earth and by the position of the Moon in its orbit relative to the apogee (point at which Moon is further from the Earth) and perigee, that is, to the point where Moon is closest to Earth. Likewise, the depth of the wave action, i.e., the depth to which the sea-waves induce, more or less, erosive movement of the water, which is, generally, equal to half the wave-length (distance between two consecutive crests), is most important when the Earth is in perihelion and the Moon in the perigee. The term apogee is, in common parlance, used to designate the highest point or culmination of a geological event or not. Thus, it can be said that a certain civilization reached its apogee at a certain time or that the Cretaceous transgression reached its apogee during Cenomanian-Turonian, when the maximum flooding surface (MFS 91.5 Ma) was formed with the which are associated with the main post-Pangea marine source-rocks, which were later fossilized by overlapping regressive sediments.

(*) Stellar system formed by two stars (primary brighter and secondary or companion star less bright) gravitically connected to each other and orbiting a common centre of mass or barycenter. According to some astrophysicists, about one-third of our galaxy's star systems, that is to say, of the Milky Way are binary systems that view unarmed or observed with small magnification are considered as stellar unitary systems.

Apparent Onlap..................................................................................................................................................Biseau d'aggradation apparent

Bisel de Agradação Aparente / Bisel de agradación aparente / Scheinbare Onlap, Bevel Verlandung Schein / 表观上超 / Видимое подошвенное налегание / Onlap apparente, Bisello d’aggradazione apparente /

Onlap observed, in the field or on a seismic line, in a direction that is not, necessarily, parallel to the orientation* and sense of the regional terrigeneous influx. A true onlap is the one that is observed, parallelly, to the direction and sense of depositional slope. When two apparent onlaps are observed in two ortogonal geological cross-sections or seismic lines, there is, necessarily, a true onlap between them.

See: « True Onlap »
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« Downlap »
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« Aggradation »

This figure illustrates a tentative geological interpretation of a Canvas auto-trace of a detail of the Labrador offshore (Canada) seismic line, which corresponds to the stacking of three types of basins of the classification of the sedimentary basins of Bally and Snelson (1980), which, from bottom to top, are: (i) Basement or a folded mountain belt (Precambrian supracrustal rocks) ; (ii) Rift-type basins (Early Jurassic/Early Cretaceous) and (iii) Atlantic-type divergent Margin (Mesozoic/Cenozoic). If the geoscientist in charge of tentative interpretations does not know the orientation and sense (direction) of the terrigeneous influx, the onlapping of the sediments of the rift-type basins and the divergent margin sediments, should be considered, in the first stage of the interpretation, as apparent. Sometimes, the dip seismic lines (parallel to the direction of the terrigeneous influx) show that what looks like a real or true onlap is, in fact, on a strike seismic line (oriented perpendicular to the terrigeneous influx), an apparent downlap. In this particular case and although, regionally, the sea-floor is deeper westward (iceberg passage zone and erosion of the icebergs), which is not evident in this auto-trace, the prevailing terrigeneous influx comes from the West (continent). This is true, during the filling of the rift-type basins and during the development of the Atlantic-type divergent margin. In the rift-type basin, at the centre of this tentative interpretation, proximal onlaps (looking westward) can be observed. They fossilize the fault plane* bordering the basin. Distal onlaps (looking eastward) fossilize the basement. The onlaps that fossilize the fault plane define a seismic surface that corresponds to a mechanical discontinuity **. In the other rift-type basin, as well as, at the base of the divergent margin, only proximal onlaps are visible (facing or looking to the continent). The internal configuration of the reflectors of the main rift-type basin suggests the presence of clay sediments rich in organic matter. Theoretically, a more or less, parallel internal configuration suggests not only a significant water depth (formation of a relatively deep lake), where the fauna and flora can develop, but also a filling, by decantation (separation of solid and liquid mixtures by allowing gravity to pull the solid fragments to settle at the bottom of the shaly particles deposits and dead organic matter as and when the water column progressively decreases. This means, that during filling, the accommodation rate was greater than the deposition rate or, in other words, that the lengthening of the substratum (supracrustal rocks) was not compensated for by the terrigeneous influx. On the contrary, a divergent filling configuration, toward the bordering fault, suggests that the accommodation rate and deposition rate were balanced. Such a balance prevents the formation of a water-column. In this case, the facies of the filling is, mainly, sandy, toward the fault plane, where subsidence is more important. Aggradation and continental encroachment of the onlaps underline marine ingressions, i.e., relative sea level rises. At each increment of the relative sea level rise (eustatic paracycles), the shoreline moves continentward (marine ingression). Then, during the stability period of the relative sea level occurring after each eustatic paracycle, as the sedimentary particles (terrigeneous influx) coming from the continent become sediments (when they are deposited), the shoreline progrades seaward (usually without significant aggradation). If there is not a fall of the relative sea level, between the eustatic paracycles, two cases are possible: (i) The marine ingressions are increasingly important or (ii) Marine ingression are, each time, smaller. If the rate of terrigeneous influx is constant, in the former case there is retrogradation (rate of accommodation > deposition rate), while in the second case there is progradation (rate of accommodation < deposition rate).

(*) The characteristics of a vector as, for instance, the terrigeneous influx, are: (i) The magnitude; (ii) The orientation and  (iii) The sense. The orientation of the terrigeneous influx is specified by the relationship between the terrigeneous influx and a given reference lines (North-South, for instance). The sense of a terrigeneous influx is specified by the order of two points on a line parallel to the terrigeneous influx. Orientation and sense together determine the direction of terrigeneous influx. The orientation tells us what angle the terrigeneous influx  do with the reference line (N-S) and the sense tells you which way it is pointing.

(**) On seismic lines, fault planes are rarely underlined by seismic reflectors. There are some exceptions to this conjecture: (i) When the fault zone is filled either by salt, clay or volcanic rocks ; (ii) When the fault zone coincides with an interface basement / sediments ; (iii) When the fault zone is slightly dipping.

(***) Within the lithological discontinuities, which are the most important in the sequential stratigraphy, we can recognize the following: (i) Concordant Discontinuities, when there is continuity between successive intervals ; (ii) Paraconform Discontinuities or Paraconformities, when there is no difference in attitude between the overlapping intervals, but there is a gap due to the absence of significant deposition between them ; (iii) Non-Conform Discontinuities or Non-Conformities, when there is a contact between a sedimentary interval and an older igneous body ; (iv) Disconform Discontinuities or Disconformities, when the layers of the intervals are parallel on one side and the other side of the contact surface, which does not conform to regional stratification ; (v) Discordant Discontinuities or Unconformities when the two intervals are separated by an erosion surface induced by a relative sea level fall ; (vi) Enhanced Discontinuities or Tectonically Enhanced Unconformities, when the sediments of the interval underlying an unconformity were deformed by tectonics ; (vii) Intrusive Discontinuities, when an igneous body traverses a sedimentary series ; (viii) Mechanics discontinuities, when they are induced by faults, etc. (https: // estpal13.wordpress.com / 2013/06/04 / discontinuities-sedimentary-and-stratigraphic /).

Apparent Truncation.........................................................................................................................................Troncature apparente

Truncatura Aparente / Truncación aparente / Scheinbare Trunkierung / 明显的截断 / Явное усечение / Troncamento apparente /

Geometric relationship between strata or terminations of seismic reflectors in the transgressive interval (TI) and in the lowstand prograding wedge (LPW) of a sequence-cycle. The sequence-paracycles retrogradation of the transgressive interval and the sequence-paracycles progradation of the highstand and lowstand prograding wedges induce an apparent truncation geometry which, in majority of the cases, does not correspond to any erosion. The apparent truncation geometry is, easily, recognized on seismic lines, either above downlap surfaces (peak of marine ingressions) or in the upper part of the progradational intervals (sedimentary regressions).

See: « Unconformity »
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« Erosion »
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« Stratal Termination »

On this Canvas auto-trace of a detail of seismic line of China offshore, which corresponds to the stacking of a non-Atlantic divergent margin over a back-arc basin within the Meso-Cenozoic megasuture, i.e., in a geological setting, globally, compressive, the upper reflection terminations of the progradational interval (between 1.1 and 1.3 seconds) underline, what many geoscientists consider as an apparent truncation. For them, in this area, the sediments deposited downdip of the depositional coastal break of the depositional surface (more or less coincident with the shoreline), usually, on a delta slope, since the space available for the sediments (accommodation) is not enough upstream. For these geoscientists, the sediments prograde seaward with very little or even, in certain places, without any aggradation (no upbuilding). Other geoscientists think that the sediments were deposited not only in outbuilding but also in upbuilding. However, the upbuilding part was, immediately, eroded by the sedimentary processes themselves. As illustrated on this tentative interpretation and in the geological model (upper right corner of the figure), in delta buildings (not confuse delta building, whose thickness can reach thousands of meters, with a delta, whose thickness, rarely, exceeds 50 meters), this type of geometry can also be interpreted as a consequence of the pendulum effect. In fact, after a marine ingression, which displaces landward the shoreline creating available space for sediments (accommodation) which is filling-up during the stability period of relative sea level occurring after the marine ingression. In fact, a delta may deposit as and when the shoreline moves seaward. A delta, which is nothing more than a sedimentary systems tract formed by the lateral association of synchronous and genetically associated depositional systems, may be deposited at the mouth of a river: a) Silt and sand of the delta plain and delta front (upper sub-horizontal delta beds) ; b) Deltaic slope shales (seaward dipping delta beds) and c) Shales and silts of the base of the prodelta (lower sub-horizontal delta beds). However, as the shoreline moves seaward and the depositional systems that make up the delta settle, the available space for the sediments decreases. The sedimentary systems tract(s) is deposited laterally, relative to the former, where the available space for the sediments is sufficient and so on, as illustrated in the geological scheme, with no significant relative sea level fall occurring, i.e., without significant erosion (unconformity) occurring between the relative sea level rises. Such a lateral displacement of delta systems tracts, function of the available space, creates an apparent truncation geometry on the seismic data. Such a mechanism was very well described by the French geoscientists (G. Dailly) of the petroleum company Elf, who called it a pendulum effect. Obviously, such a pendular displacement of the delta depocenters or lobes is the main responsible for the overlapping of sandy (front of delta) and shaly facies (shale moats surrounding the delta lobes are, sometimes, quite rich in organic matter) favouring the formation and development of petroleum systems (generating petroleum subsystems, i.e., potential source-rocks). However, the overall geometry of the delta lobes depends, mainly, if marine ingressions are increasingly important (relative sea level rises in acceleration) or if they become smaller (relative sea level rise in deceleration). In the first case (illustrated in the transgressive episode), as the sedimentary regressions. The delta lobes are smaller and smaller. Globally, the geometry becomes retrogradational. On the contrary, in the second case (regressive episode), as associated sedimentary regressions. The delta lobes are increasingly important and the geometry is, globally, progradational.

Apron (Turbidite systems).......................................................................................................................................................................................................Tablier

Apron / Apron / Schürze (Geologie) / 围裙（地质） / Фартук (геология) / Apron (geologia)/

A clay deposit located at the base of the continental slope forming the substratum of submarine slope fan (SSF). The apron is fossilized by overbanking deposits (turbidite levees, i.e., turbidite natural marginal dikes) or by the filling of turbidite channels or depressions (negative bathymetric anomalies between turbidite lobes). The distal part of the apron may be covered by the submarine basin floor fan (SBFF). Often, synonym with Basal Slope Deposit.

See : « Slope Fan »
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« Basin Floor Fan »
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« Turbidite »

The apron is part of a submarine slope fan (SSF) which, according to EPR ("Exploration Production Research" of Exxon) model referred almost, always, as P. Vail model, is deposited within a sequence-cycle when geological conditions are of lowstand (sea level lower than the basin edge.) This is not always the case in the Mutti's model (large floods, continental edge and slope failures, etc., which may occur in highstand geological conditions). The apron supports the turbidite natural marginal dikes (turbidite levees) and the depression or channel (when there is erosion) between the lobes (turbidite fans), which is later filled, in retrogradation, by sandy or clayey sediments. The apron can be deposited, directly, on the submarine basin floor fan (SBFF), when this is connected to the base of the continental slope. As illustrated in this figure, a submarine slope fan (SSF) is, generally, composed by : (i) Apron ; (ii) Overbanking deposits ; (iii) Fillings of depressions (between turbidite lobes) or turbidite channels ; (iv) Turbidite levees or turbidite natural marginal dikes ; (v) Distal shales and (vi) Abandonment shales. Abandonment shales are deposited on the upper part of the channel fillings or depressions fillings (between the lateral turbidite lobes when they become inactive). The morphology of electrical logs of submarine fans is characteristic. As can be seen above, the submarine basin floor fan (CSB), in the gamma ray (GR) log and in SP log (spontaneous potential) is characterized by a cylindrical geometry (abrupt boundaries). Gamma ray log measure the total natural radioactivity, related to the presence of radioactive isotopes emitting gamma rays, such as potassium, thorium, etc. It allows the detection of fine radioactive beds. The SP log measures the difference between the potential of a fixed electrode on the surface and the potential of the electrode moving in the drill hole. It gives us an idea of the clay components, porosity and permeability, which allows determining the resistivity of the formation water* (water naturally occurring within the pores of the rock) and its salinity. The submarine slope fan (SSF) has gamma ray (GR) and spontaneous potential (SP) logs, globally, nervous (alternation of high and low peaks). The apron has a, more or less, linear spontaneous potential and gamma ray logs of low amplitude, with a geometry, globally, coarsening and thickening upwards. The SP and GR logs in overbank deposits have oscillating geometries. The depressions or channels filings have a geometry, globally, thinning upward. In geological sections and dip seismic lines oriented, more or less, perpendicular to the continental slope along the direction (orientation and sense of the terrigeneous influx), the apron, generally, rests against a continental rise by onlapping. On the other hand, it can rest, directly, on the submarine basin floor fan (SBFF). However, when the submarine basin floor fan is disconnected from the base of the continental slope, the submarine slope fan (SSF) and, particularly, the apron, rest directly on the lower limit of the stratigraphic cycle to which it belongs, which, on the abyssal plain, is a paraconformity that correlates updip with the unconformity of the base of the stratigraphic-cycle. What many geoscientists call the turbidite channel corresponds, most often, to a filling (geological body) of a negative topographic anomaly (without erosion) formed between the first natural turbidite marginal dykes and not to the depression on the pre-existent topography along which the turbidite currents flow. This depression, which is increasingly, accentuated by the deposition of the successive natural marginal dikes, is fossilized, later, by retrogradational sediments when, within the associated eustatic cycle, the relative sea level begins to rise. Abandonment shales and the pelagic drape, that fossilize the submarine slope fan, are deposited in a period of time that far exceeds the time of deposition of the submarine cones (CSB). In geological terms, however, it can be considered as instantaneous deposit. The submarine basin floor fan (SBFF) and the submarine slope fan (SSF), as well as, the lowstand prograding wedge (LPW) are sub-groups of systems tracts that form the lowstand systems tract group (LSTG). In the same way, the transgressive interval (TI) and the highstand prograding wedge (HPW) are sub-groups of sedimentary systems tracts that make up the highstand systems tracts group (HSTG).

(*) Water from fluids introduced into a formation by drilling or other interferences, such as mud and water, is not part of the formation water. Water formation or interstitial water, may not have been present when the rock was originally formed. Connate water is trapped in the pores of a rock during its formation. It can be, also, called fossil water.

Apside..............................................................................................................................................................................................................................................................Apside

Apside / Apside / Apsis / 拱点 / Апсида / Apside /

Each of the points of the orbit of a celestial body that determine the great axis of the ellipse. The upper apside is the farthest point of the central body. The lower apside is the closest point of the central body. In the case of Earth, due to the eccentricity* of the ellipse of the Earth's orbit, this differentiation is relatively easy. Some geoscientists consider the upper apside as synonymous with aphelion (point of the Earth's orbit farthest from the Sun) and lower apside as the perihelion (nearest point).

See: « Aphelion »
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« Perihelie »
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« Milankocitch Cycle »

Although certain geoscientists consider the upper apside as synonymous with aphelion and the lower apside as synonymous with perihelion, we do not use this terminology, which generates confusion. As illustrated in this figure, two possible orbits, with different eccentricities, are represented, there have very different apsides. In astronomy, the apside is one of the points, more or less distant, in an elliptical orbit of an astronomical object, of its centre of attraction, which is, in general, the centre of mass of the system. The nearest point is often called periapsis or pericentre, and the farthest point apoapside, apocentre or apoapside. The straight line between the periapsis and apoapside is the apside line. It is the major axis of the ellipse. Other terms are, also, used to locate and identify objects in orbit. The most common are perigee, the nearest and apogee, which is the farthest point, when the objects orbit around the Earth and perihelion (the closest point) and aphelion (more distant) when the objects orbit the Sun. The terms pericynthian (the nearest point) and apocynthian (the farthest point) were used by NASA scientists at the time of the Apollo program to characterize the spacecraft's orbit when it orbited the Moon. The moment (time) of the perihelion advances with the stations, making a complete cycle between 22 and 26 thousand years. This cycle is known as precession and is a significant contribution to the Milankovitch cycles and therefore an important factor in the triggering event of  ice ages**.

(*) Relation between the focal semidistance and the larger half-axis of the ellipse.

(**) In the geological history were detected at least five glacial ages or ice ages: (i) Huronian ; (ii) Cryogenic; (iii) Andean-Saharan; (iv) Karoo and (v) Quaternary. The Huronian glacial age occurred about 2.4 to 2.1 Ga (10⁹ years ago) during the Early Proterozoic. The Cryogenic ice age occurred between 850 and 630 million years ago and appears to have produced the so-called Terrestrial Snowball, once the ice caps have reached the equator. The Andean-Saharan glacial age occurred between 460 and 420 million years ago, during the Late Ordovician and the Silurian. The Karoo ice age occurred between 360 and 260 Ma, particularly in South Africa (where evidence of this ice age was clearly identified) and in Argentina during the Carboniferous and Permian. The Quaternary glacial age corresponds to a glaciation, which began about 2.5 Ma during the late Pliocene when the glacial caps began to extend in the Northern Hemisphere. At present, Earth is in a interglacial period. The last glacial period ended about 10,000 years ago.

Aquifer...................................................................................................................................................................................................................................................Aquifère

Aquífero / Acuífero / Aquifer / 含水层 / Водоносный горизонт / Acquifero /

Stratum of permeable layers or area underneath the terrestrial surface that store underground water through which it flows, eventually, into production wells.

See : « Reservoir »
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« Formation Water  »
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« Juvenile Water »

In the morphological and non-structural trap (the top and bottom of the rock-reservoir are not parallel, which means that the reservoir was not shortened), probably a reef, illustrated in the right part of this figure, three saturants can fill the porosity of the rock-reservoir: (i) Oil ; (ii) Water, which replaced the oil produced and (iii) Water from the aquifer. As oil enters the production well, it rises to the surface (if the pressure is large enough) aided by the activity of the aquifer. The space left free is, immediately, occupied by the water of the aquifer (nature has a horror of emptiness), which brings up the initial contact plane between oil and water, which is, sometimes, visible on seismic data. When the rock-reservoir porosity is significant, the initial oil/water contact plane limits two diagenesis domains. Above the water plane, the initial porosity of the rock-reservoir remains, more or less, constant, since oil prevents diagenesis. This does not happen under the plane of contact, since, the water favours the diagenesis decreasing the porosity. In this way, an interface is formed between two intervals with different acoustic impedances (weak above strong), which produces a diachronic (non-chronostratigraphic) seismic reflection, which underlines a diagenesis line which, in certain cases, may suggest the presence of hydrocarbons in the rock-reservoir *. If for various reasons, such as the tilting of the trap or breaking in the resrvoir-rocks cover, the oil escapes the trap. In addition, if the residence time of the replacement water is not sufficient for a diagenesis of the part of the reservoir rock abandoned by the oil, the initial diagenesis line is not destroyed. It produces the same diachronic reflection (like the one prior to tertiary migration or the dismigration** of oil) but the hydrocarbons are no longer there. They migrated to another trap (tertiary migration) or to the surface (dismigration), where they form important exudations. When the aquifer is active and flows from the initially lower to the higher points (tectonic inversion), hydrodynamism*** favours retention of the hydrocarbons in the traps and may, in certain cases, create hydrodynamic traps (prevailing hydrodynamic component).

(*) The transformation of kerogene (insoluble part of the organic matter, more or less, modified by the geological agents) into hydrocarbons is accompanied by a volume increase that fractures the rock allowing the migration of the hydrocarbons to lower pressure regions. The movement of hydrocarbons from the source-rock to a porous site of lower pressure where they can be accumulated is called migration. However, the process of migration of the hydrocarbons within a source-rock is called the primary migration, whereas the movement toward a rock-reservoir, is considered as secondary migration (hydrocarbon displacement pressure greater than the pressure capillary porosity of the porous system through which they migrate), which ceases as long as the capillary pressure of the porous system exceeds the displacement pressure of the hydrocarbons.

(**) The loss of hydrocarbons out of a trap is frequently called dismigration.

(**) Hydrodynamism is a natural phenomenon that occurs in oil fields that have a natural active aquifer that acts as an energy of it. The water pushes the crude oil, through the rock-reservoir, into the wells. Hydrodynamism can significantly impede the movement of hydrocarbons and create, even, a non-structural trap. On the other hand, a reservoir-rock, in lateral continuity to the surface, is recharged in water. When the production of fresh water in the production wells of an oil field increases over time, while the pressure of the rock-reservoir remains constant or decreases, the hypothesis of an inflow of water or recharge from a point on the earth's surface is likely.

Aragonite.....................................................................................................................................................................................................................................Aragonite

Aragonite / Aragonita / Aragonit / 文石 / Арагонит (волнистый известняк) / Aragonita /

One of two forms of occurrence of calcium carbonate (CaCO₃). The other form is calcite. The typical locality of the aragonite is "Molina de Aragon", about 25 km of the city of Aragon (Spain).

See: « Calcite »
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« Dolomitization  »
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« Limestone »

Aragonite is one of two polymorphs of calcium carbonate (CaCO₃). The other is calcite. Aragonite forms, of course, in the shells of almost all molluscs. However, the deposit of minerals in the shells is, heavily, biologically controlled. Some crystal forms are very different from those of inorganic aragonite. Although aragonite has the same chemical composition as calcite it has a different structure and, more importantly, it has a symmetry and forms of different crystals, as illustrated above in the atomic structures. The more compact structure of aragonite is composed of groups of triangular carbonate ions (CO₃), with carbon in the centre of the triangle and the three oxygen in each corner. Aragonite may be columnar or fibrous, occasionally, in branches with stalactitic forms. Massive deposits of oolitic aragonite are known on the sea-floor of the Bahamas. Aragonite is unstable at normal temperature and pressure. It is stable at high temperature, but not at high temperatures which require an increase in pressure to remain stable. Thus, aragonite when heated to 400° C, if the pressure does not increase, spontaneously transforms into calcite. Geoscientists and, in particular, sedimentologists always wonder why aragonite forms if calcite is the most stable mineral. In fact, it seems in certain formation conditions, the crystallization of aragonite is favoured in relation to calcite. The magnesium and salt content of the crystallizing fluids, the turbidity of the fluids and the crystallization time appear to be important factors for the crystallization of aragonite. In the same way, it seems certain sedimentary environments, such as sabkhas (supratidal sedimentary environment formed under arid or semi-arid climatic conditions in coastal plains, immediately above the normal level of high tide) and carbonated (oolitic), favour the formation of aragonite. Likewise, a metamorphism characterized by high pressures and relatively low temperatures seems to favour the formation of aragonite. However, what is important is that after a certain time of burial, aragonite changes in calcite and it is, therefore, that sedimentologists are interested in the fields of stability of calcite and aragonite.

Archaeocyatha, Archaeocyathid (Fossil)............................................................................................Archaeocyatha

Arqueociatídeo / Arqueociatídeo / Archaeocyatha / 古杯动物门 / Археоциаты / Archeociatide /

Marine organism sessile* of tropical and subtropical seas that lived during the Early Cambrian period.

See: « Fossil »
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« Cambrian »
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« Paleontology »

Archaeocyathids were fixed reef-building marine organisms that lived mainly during the Early Cambrian, i.e., about 500-600 Ma. During the Early Cambrian, the archaeocyathids allowed the construction of enormous mound structures, called bioherms, from the accumulation of their skeletons. However, around 520 Ma, they went into decline and, progressively, sponges and algae replaced them as reef builders. Finally, most species of archaeocyathids extinguished before the Ordovician, which is to say that they are just known by their fossils. Morphologically, the archaeocyathids make, more or less, hollow reefs. Each had a calcite skeleton with a conical or potted form, similar to that of certain current sponges. The structure of the skeleton resembled perforated ice cream cones. The skeleton consisted of a single porous wall or, more often, by two porous concentric walls, i.e., an inner and outer wall separated by a space. Inside the inner wall was a cavity, more or less, empty (like that of the interior of an empty ice cream cone). At the base, the archaeocyathids were attached to the rocky substratum (limestone or sandstone) by a kind of a clamp. The archaeocyathids inhabited shallow-seas located near the continent or epicontinental seas rich in nutrients. Their great distribution, since they are found practically in all parts of the world and the diversity of species, can in large part be explained by the fact that, like many sponges**, they had a planktonic larval phase (which derive with the currents). Although they have an uncertain phylogenetic history and have been interpreted in very different ways. There is currently some consensus to consider them as a variety of sponges. Although many geoscientists have included them in the extinct phylum Archaeocyatha. Recent experiments suggest that the morphology of the archaeocyathids allows them to use important gradients of water flow through the skeleton, as certain sponges do today.

(*) Organism that can not move, since it is directly connected to the rocky substratum by the base.

(**) The sponges are poriferous that form a phylum of the kingdom Animalia, subkingdom Parazoa. Sponges are very simple organisms, which can live in fresh or salt water, sessile and that are fed by filtration. The water is pumped through the walls of the body and the food particles retained in the cells.

Archean..................................................................................................................................................................................................................................................Archéen

Arcaico / Arcaico / Archaikum / 太古 / Архейский / Archeano /

Geological Eon, initially, denominated Arqueozoic, that refers to the geological time before the Proterozoic, more or less, 2,500 Ma (millions of years ago). This date was defined chronometrically and not from Stratigraphy. The lower boundary, which has not yet been recognized by the International Commission on Stratigraphy, is taken,usually, at 3,800 Ma (end of Hadean).

See: « Eon »
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« Geological Scale Time »
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« Geological Time »

Biostratigraphy allowed geoscientists to distinguish, on the geological scale, the concepts of (i) Time Unity and (ii) Stratigraphic Unit. The first concept concerns geological time*, while the second relates to space. Thus, taking into account geological time, the Earth's history is divided into four Eons (Hadean, Archaic, Proterozoic** and Phanerozoic), which are composed of Eras (mainly Proterozoic, Paleozoic, Mesozoic and Cenozoic). The Ages are composed of Periods (such as Silurian, Triassic, Neogene, etc.), which encompass several Epochs (e.g., Caradocian, Neocomian, Albian, etc.), which in turn are made up of several Ages (such as Valanginian, Hauterivian, Serravalian, etc.). Considering space, that is, stratigraphic units (i.e., rocks), the history of the Earth is divided into three or four Enothems, which are composed of several Erathems. Each Erathem consists of Systems, which include several Series, in which several Stages can be highlighted. In this way, the stratigraphic equivalents of Eon, Era, Period, Epoch and Age are, respectively, Enothem, Erathem, System, Series, and Stage. When a geoscientist speaks of the Upper Cretaceous, he is referring to a stratigraphic interval, i.e., to the rocks, which were deposited in the Late Cretaceous, which is a time interval. That is why geoscientists say: "These carbonate rocks belong to the Cretaceous System and were deposited during the Valanginian which is an Epoch of the Cretaceous Period." The suffix "Upper" is used for the rocks and "Late" for the time. Therefore, never confuse Upper Cretaceous (rocks) and Late Cretaceous (geological time). In the last column of the geological scale shown in the upper right corner of this figure, the time of each Period is indicated as a percentage. The time interval between the Paleogene and today, for example, represents only 1.7% of the total archaeological time (100%).

(*) Time elapsed since the formation of the Earth is about 4.5 Ga to date, which is subdivided into unequal time intervals that emphasize significant changes not only in the physical environment, but also biological: (i) Eons; (ii) Eras; (iii) Periods; (iv) Epochs and (v) Ages.

(**) The whole of Archaic or Archean and Proterozoic form what many geoscientists call the Precambrian.

Arcuate Delta...............................................................................................................................................................................................................................Delta Arrondi

Delta arredondado / Delta redondeado / gerundt Delta / 弓状三角洲 / Дугообразная дельта / Delta arrotondato /

When the distal limit of the delta plain, modeled by the coastal currents, has an arched geometry, which suggests a balance between deposition and erosion.

See: « Delta »
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« Delta Front »
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« Fluvial Depositionl »

Generally, an arcuate or rounded delta, as illustrated in this figure, is formed when a stream of water, in general, a river enters the sea in an area where the waves, currents and tides are very strong. One of the characteristics of this type of delta is that it is almost always crossed by numerous distributaries (stream that flow out of the main channel of the river). The delta illustrated in this figure is a sector of the Ganges delta, which is, also, known as the Bengal delta, Sunderban or Ganges/Bramaputra, and which results, actually, from the confluence of three major rivers: (i) Padma river (lower Ganges) ; (ii) Jamuna river (lower Bramaputra) and (iii) Meghna river. Rivers from Bhutan, China, and Nepal contribute, also, significantly, to the development and progradation of the Ganges/Bramaputra delta, which covers an area of more than 105,000 km², mainly in Bangladesh and India. The eastern part of this delta building is very active. However, the western part has already been abandoned or is not very active. Most of the deltas that make up the delta building are alluvial, which have a lot of minerals and nutrients, which makes the soil very suitable for agriculture. That is why two-thirds of Bangladesh's population (about 100 million people) live in agriculture in this area, which of course creates a major problem. In this region, as practically every day the media and politicized environmentalists tell us: "Sea level is rising due to the greenhouse effect* induced by the anthropogenic increase of CO₂ in the atmosphere." However, they never say what level of the sea is rising, whether it is the relative or the absolute (eustatic) sea level. The sea level can be absolute (eustatic) and relative. The absolute or eustatic sea level is supposed to be global and referenced to a fixed point that is, generally, the Earth's centre. The relative sea level is a local sea level, referenced to a point that may be the sea-floor, the base of the sediments (top of the continental crust) or any other point on the Earth's surface. This means that the relative sea level is the result of the combination of absolute or eustatic sea level and tectonic (subsidence of the sea-floor, when the predominant tectonic regime is in extensional or uplift when the predominant tectonic regime is compressional). Thus, with a constant absolute or eustatic sea level, the relative sea level may rise if the sea-floor falls. This is, exactly, what happens not only in the Ganges/Bramaputra delta but also in other deltas (Po Delta, Mahakam Delta, Bin Delta, etc.), when there is a sinking due to the weight of the sediments on a substratum, more or less, mobile. In other words, such a relative sea level rise is not due to any kind of global warming (an increase in average temperature measured at the surface of the earth and oceans since the mid-20th century, and particularly since 1990), as certain " alarmist " say, but just and simply brought about by the weight of the sediments that induces the subsidence of the sea-floor. Unfortunately, if the relative sea level rises in the next few years of about half a meter, which is very likely, more than six million people will lose their homes and agricultural land. However, certain geoscientists predict that in the next years the average global temperature will drop as we have entered solar cycle n° 24 (2009) and an increasing in the melting snow and ice of the Himalayan glaciers, which would cause huge floods and amplify the disastrous effect is unlikely. If there is an absolute rise of the sea level, it is enhanced by the subsidence of the sea-floor. On these issues concerning humanity, two attitudes are currently shared by the market of public opinion**: (i) Optimists who fight for growth and innovation against (ii) The pessimists who disclose psychological depression and moral supposed to ruin everything.

(*) On this subject it is important to remember that the earth's surface is, in average, warmer than the atmosphere. If heat passes from an atmosphere to a warmer Earth's surface, without an external energy influx, as the "Greenhouse Effect" supposes, such a flow violates the second principle of thermodynamics (the amount of entropy of any thermodynamically isolated system tends to increase with time until it reaches a maximum value ".

(**) L. Ferry., 2016- La Révolution transhumaniste, Plon, Paris. ISBN 9782259249157

Arenite............................................................................................................................................................................................................................................Grés prope

Arenito (Grés limpo) / Arena limpia / Saubere Sandstein, Arenit / 清洁砂岩 / Аренит / Arenaria limpida /

Sedimentary rock whose grains have a size between 0.0625 and 2 mm and a clay content less than 5%.

See: « Sandstone »
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« Reservoir-Rock »
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« Granulometry »

This sample (Oriskany clean sandstone, West Virginia, USA) is, practically, 99% pure quartz. This type of sandstone is used in the manufacture of glass containers and often in the manufacture of telescope lenses. The highest quality quartz crystals are the silica crystals which have optical and electronic properties*. According to USGS, about ten billion quartz crystals are used every year in the industry. Quartz crystals with electronic properties are used as filters, frequency controllers, timers, electronic circuits, which become indispensable in the components of cell phones, watches, games, television, computers, navigation instruments and other products. Quartz crystals with optical properties are used in the manufacture of lenses and windows for lasers and other specialized devices. At present, the vast majority of quartz crystals used in industry are not natural crystals, taken from clean sandstones, but manufactured crystals. This type of sandstone has excellent petrophysical characteristics. With a strong permeability, induced by the presence of large pores, perfectly connected to each other. The clean sandstones form excellent reservoir-rocks for the hydrocarbons, although, sometimes, the porosity is, relatively, small. Large pore size can create drilling problems, in particular important drilling mud losses. The Mirador formation in the Cusiana (Colombia) oilfield can be considered as a clean sandstone (very low clay content). The typical mineralogy of this formation is 78% quartz grains, 14% quartz cement and a porosity of about 8%. Despite the low porosity, the permeability is high. At a porosity of 8%, it corresponds to a permeability of 100 mD (or 100 millidarcies). For a porosity of 10%, the permeability is around 400 mD. The permeability is a function of granulometry. When the rock-reservoir is a clean sandstone with a porosity of 10%, the permeability is 800 m D. A fine clean sandstone of 10% porosity has a permeability of 90 mD.

(*) In the wikipedia on the properties of the crystals one can read: "The crystals present specific optical and electrical properties distinct from any other solids or fluids, which makes them extremely useful in electro-optic and electronic applications, which depend on their structure, the type of bonds and the impurities and defects in the crystalline mesh. Most of the materials have defects in their crystalline mesh, usually resulting from the presence of atoms or molecules of other substances or defects in the positioning of the mesh during crystallization. These defects give particular characteristics to the crystals, which are the basis of many technologies. They are defects in the crystalline mesh of silicon, induced, for example, by the presence of germanium or gallium atoms, which allow the appearance of semiconductors, the basis of current electronic technology. The most well-known effects of the crystalline structure are the piezoelectric ones, which are based on, among other things, quartz clocks and electronic scales, ferroelectrics used in various detectors, and the pyroelectric device used in heat detectors, thermometers and intrusion detectors, and, above all, training of semiconductors, which are at the base of all the electronics of the transistors and diodes to the computers ".

(**) 1 Darcy = 1 x 10⁻¹².m². Permeability measures the ability of fluids to flow through a rock (or other porous media). The darcy is defined using Darcy's law, which can be written as: Q = (A κ ΔP) ÷ (μ Δx), where: (i) Q = is the rate of fluid flow through the medium ; (ii) A is the middle area ; (iii) κ is the permeability of the medium ; (iv) μ is the viscosity of the fluid ; (v) ΔP is the pressure difference applied and (vi) Δx is the thickness of the medium. The darcy is referenced to a mixture of systems of units. A medium with a permeability of 1 darcy allows a flow of 1 cm³/s of a fluid with viscosity 1 cP (1 mPa.s) under a pressure gradient of 1 atm/cm acting in an area of 1 cm². Typical permeability values range up to 100 darcis for gravel, less than 0.01 microdarci for granite. Sand has a permeability of approximately 1 darcy. https://en.wikipedia.org/wiki/Darcy_(unit).

Argillite...................................................................................................................................................................................................................................................Argillite

Argilito / Arcilita / Argillit /泥质/ Аргиллит (глинистый сланец) / Argillite /

Rock composed of clayey sediments characterized by an absence of foliation  and, often, by irregular fracturing. An argillite does not correspond in any way to a clay. A clay is a sedimentary particle characterized by a certain granulometry. By the same token, it does not correspond to a slate, as certain geoscientists think. A slate is a shale, slightly, metamorphosed by illite recrystallization.

See: « Clay »
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« Compacted Clay »
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« Potential Source-Rock »

In 1953, Flawn named argillite a metamorphic clay a slightly metamorphic sedimentary rock intermediate between a compacted clay and a meta-argillite (metamorphic), in which, at least, half of the clayey constituents (diameter between 0.01 to 0, 05 mm), were recrystallized in sericite, chlorite, biotite and epidote. The English word "claystone" used to describe a nonlaminar sedimentary rock composed of clay-sized particles (<1/256 mm in diameter) does not correspond to what certain geoscientists call argillite. In English the term argillite is used for to describe an anchi-metamorphic clayey rock. An argillite, which many geoscientists call slate or shale, is not considered as a source-rock, although it has been rich in organic matter, since the maturation of its organic matter has exceeded the gas window. The index of crystallinity of the illite* (Kubler index) is in this crucial subject. At the beginning of the second phase of exploration of the geographic Kwanza basin (Angola), in the 1960s, geoscientists thought that the source-rock of the oil shows recognized in the field and in the exploration wells were the brownish clay of the substratum (Karoo formation), since Cretaceous clayey rocks, rich in organic matter, were little buried (500-1500 m). Samples from the alleged substratum rock of the Kwanza geographic basin were sent to the laboratory and the results of the X-ray analysis were conclusive. The illite and other clay minerals were recrystallized. Such a fact implied that these clayey rocks had been sufficiently buried in such a way that the maturation of the organic matter had passed the gas window. Later, the Cretaceous rocks, rich in organic matter, were also analyzed and the results were a surprise. The illite crystallinity suggested that they had been buried, sufficiently, so that the maturation of organic matter would reach the oil window. That is to say, that there was a significant tectonic uplift of the eastern part of the basin (between 1500-2000 m), since, at present time, they  are in a depth ranging between 500-1500 m.

(*) Clay minerals can be used to identify diagenetic zones and low metamorphism. Bernard Kubler, in 1964, proposed the index of illite crystallinity, which today most geoscientists call the Kubler Index, which consists in measuring the width at half height (FWHM or full-width at half maximum) of the reflection (001) of the illite, in diffractograms of the clay fraction. The limit value for the diagenesis is >0.42, while the zone of anchi-metamorphic is limited between 0.42 and 0.25 process in which initial diagenesis overtaken by metamorphism) and the epizome <0.25. According to Grubenmann's classification of metamorphic rocks (1904), the uppermost depth zone of metamorphism, characterized by low to moderate temperatures (less than 300 degrees C) and hydrostatic pressures with low to high shearing stress. Modern usage stresses pressure-temperature conditions (low metamorphic grade) rather than the likely depth of zone.

Argument of Perihelion..............................................................................................................................Argument du périhélie

Argumento do Periélio / Argumento de perihelio / Argument des Perihels / 论据近日点 / Аргумент перигелия / Argomento del perielio /

Angle between the ascending node (Ω)* and the perihelion of the orbit. The associated value is the longitude of the perihelion, π, although the distinction between these two values is not very clear. The longitude of the perihelion is defined as: π = ω + Ω.

See : « Perihelie »
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« Aphelion »
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« Orbit »

The argument of perihelion is the angle between the ascending node (one of the two points where the orbit crosses the reference plane, where the minor orbiting body passes from the southern hemisphere to the north) and the perihelion of a orbit around the Sun, measured in the plane of the orbit and in the direction of the orbital movement. The perihelion argument characterizes the direction of the major axis of the orbit around the Sun and is one of the main elements of the orbits. The other elements are: a) Longitude of the ascending node (Ω) ; b) Inclination ; c) Argument of perihelion (ω) ; d) Larger semiaxe (a) ; e) Eccentricity (e) and f) The number that gives the position of the planet in the orbit at a certain moment. This can be the time of passage of the perihelion (T or τ), the length of the season (L) or the average anomaly of the time (M). For a comet, for instance, with a very eccentric orbit, the semi-axis is, normally , replaced by the distance of the perihelion (q). The orientation of an elliptical orbit can be characterized by three orbital elements: (i) Inclination; (ii) Node ascending and (iii) Argument of perihelion. Assuming a given celestial body has an elliptical orbit with a certain eccentricity (e) and a certain larger semicircle (a), the perihelion is the closest point between the celestial body orbiting (e.g., a planet) and the focus occupied. The Sun is located in a focus of the orbit of the solar planets, while the other focus is free. If we rotate the orbit around the occupied focus, the axis of rotation is the perihelion argument (ω), as schematised in this figure. For the elliptical orbits around other celestial bodies, the perihelion argument can be replaced by: (i) Argument of the periastron (orbits around the stars) ; (ii) Argument of the perigee (orbits around the Earth) or (iii) Argument of periapsis (orbits around anything else). In the left sketch, an elliptical orbit with a larger semi-axis (a) and a smaller semi-axis (b) and a focus (star) is shown. The upper right figure illustrates an orbit seen from above the Z axis, which rotated from a certain angle that underlines the perihelion's argument about the Z axis. In the lower right diagram, the same orbit is observed along the Y axis.

(*) An orbital node is either of the two points where an orbit intersect a plane of reference to which it is inclined. The ascending node is the point where the orbit of the object passes through the plane of reference. A noninclined orbit, which contained in the reference plane, has no nodes.  The longitude of the ascending node is the angle from a reference direction, called the origin of longitude to the direction of the ascending node, measured in a reference plane. (https://en.wikipedia.org/wiki/ Longitude_of_the_ascending_node)

Arheic (Hydrographic basin)...............................................................................................................................................................Aréique (hydrographie)

Arréica / Arréica   (hidrografía) / Arheic Hydrographie / arheic 水文 / Ареический (не имеющий гидрографической сети) / Aréique (idrografia) /

A river basin in which water-courses do not flow into the sea on a permanent basis and evaporate, often, even before. The most frequent river basins are: (i) Exorheic, when the streams flow into the sea ; (ii) Endorrheic, when the water-course flows into a lake or other river within the space and (iii) Arheic when the river basin is formed by rivers that do not flow, once they are lost or seep into the earth. Certain geoscientists consider, also, cryptorheic basins, in which rivers are absorbed by rocky structures (drainage by subterranean streams).

See: « River »
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« Endorheic »
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« Mouth of a River »

In this hydrographic chart of Angola, it is easy to verify that the river basins of the rivers Congo, Kwanza and Cunene are exorheic and that Okowaongo and Caito basins are endorheic. On the other hand, in this map, it is interesting to note that south of the Congo River, just two, relatively, important rivers: (i) Kwanza and (ii) Cunene reach the sea. The Congo River itself has to cross a coastal escarpment before draining into the Ocean. All others water-courses flow either to the south (endorheic basins) or to the north to feed the basin of the Congo River, which is an exorheic basin. The main reason for this morphology is of tectonic origin. It was induced by a Tertiary tectonic uplift of the SW border of the African divergent margin (Congo, Angola, Namibia). This uplift induced, , probably, by an important deep volcanic activity is, perfectly, visible on North Angola offshore regional seismic lines. The sea-floor is underlined, especially, in the southern Congo basin (between the Congo river and the Ambriz promontory, located to the north of the Kwanza basin) by toplaps by truncation. It had consequences not only in the hydrography of the region, but in the evolution of the organic matter of the source-rocks as well. It should be recalled that on the Angola onshore, particularly, in the Cabinda enclave, the main oil source-rocks rocks, which generated most of the hydrocarbons, are, currently, very shallow, i.e., largely above of the depth necessary for maturation of the organic matter. However, the crystallinity index of the illite of the source-rocks corroborates the hypothesis advanced by Bernard Kubler *, about 60 years ago, that the source-rocks were, sufficiently, buried, during Early Tertiary, for their organic matter reach mature. Later (Late Tertiary), they were uplifted to the position they currently occupy.

(*) Bernard Kubler, in 1964, proposed the index of illite crystallinity, which today most geoscientists call the Kubler Index consisting of measuring the width at half height (FWHM or full-width at half maximum) of the reflection (001) of the illite, in clay fraction diffractograms, to identify the diagenetic zones and low metamorphism. The limit value for diagenesis is> 0.42, while the anchi-metamorphic zone is limited between 0.42 and 0.25 and the epizome <0.25.

Arheism (Without rivers).....................................................................................................................................................................Aréisme (Sans rivières)

Arréismo / Areismo / Areism, Kein Fluss / 没有河流 / Ареизм /Areismo /

Hydrologic term that characterizes an area with a little surface runoff (weak rainfall) and without organized hydrographic network. The erosion may be due to excessive permeability of the terrain or to a poorly accentuated topography. There are two types of arheism: (i) Endoarheism, when the currents do not reach the sea and (ii) Exoarheism, when the currents reach the sea.

See: « Arheic (hydrography) »
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« River »
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« Exorheic (hydrography) »

An arheic river basin is a basin in which streams do not ingress into the sea permanently and, often, evaporate before. In an arheic basin when the streams do not reach the sea it is spoken of endorheism and exorheism when they reach the sea. There are other types of river basins, such as: (i) Exorheic (when streams flow into the sea); (ii) The endorheic basins (when the water-course never reaches the sea) and (iii) The cryptorheic basins (when the water-courses are absorbed by rocky structures). The picture shown in this figure (Atacama desert) exemplifies an arheic basin where the arheism is mainly induced by very weak rainfall*, which is not always the case in this type of river basin. The arheism is present in the volcanic islands of Flores and São Miguel (Azores), Madeira, Tenerife (Canaries) and São Tiago (Cape Verde). In these islands, a part of the surface does not have an organized drainage network and, thus, is conducive to the arheism. In areas, particularly, recent, the arheism is not always determined by thermal and evaporation conditions. The age of the rocky substratum, porosity and permeability of the eruptive material variably inhibit surface runoff. These factors explain the behaviour of storm areas during periods of rainfall. The intensity and concentration of the rains, which is very pronounced by the elevation of the relief, do not, usually, present great risks in the highlands. However, in sectors without organized drainage, they can produce catastrophic floods, as happened, recently, in Madeira Island. Mapping of areas without organized drainage is indispensable to predict the spatial distribution of the impact caused by torrential rains.

(*) Amount of rain that has fallen over a given period of time in a region. The rainfall index is the amount in millivoltmeters of the total precipitation of water / rain, snow, hail) in a given area over a given period of time.

Arkose.............................................................................................................................................................................................................................................................................Arcose

Arkose / Arcosa / Arkose / 长石砂岩 / Аркоз (полевошпатный песчаник) / Arcose /

Sedimentary rock formed by the cementation of feldspar and quartz grains.

See: « Granite  »
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« Quartz »
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« Arenite  »

Arkose is a sedimentary rock that corresponds, more or less, to a sandstone rich in feldspars. Ordinarily, the arkose has a relatively coarse granulometry and a pinkish or reddish colour (such as the Triassic arkose shown in this figure). Typically, the arkose consists of grains, angular or subangular, derived, directly, from a rapid disintegration of granite or granitic rocks. Grains may be slightly or moderately calibrated. Quartz is, usually, the dominant mineral. Feldspar accounts for about 25% of the constituents. Cement (silica or calcite) is, in general, rare. The matrix (generally less than 15%) includes clay minerals (kaolinite), mica, iron oxide and rock fragments. Certain geoscientists consider that an arkose has the following characteristics: (i) Similar to a sandstone rich in feldspars (micas may be more or less present) ; (ii) Stratification is sometimes very visible ; (iii) Rarely with fossils ; (iv) Slightly effervescent in dilute hydrochloric acid, indicating calcite-based cement; (v) Colour, usually polished, greyed brown or pink; (vi) Medium texture and granulometry (2 mm, 1/16 on average), but may be thinner ; (vii) Drift from a rapid alteration, transport and deposition of granite rock debris ; (viii) The granitic debris, which make up the arkoses, are deposited very quickly in cold or arid deposition environments so that feldspars do not undergo chemical alteration or significant decomposition (which is why arkose are considered as immature sedimentary rocks). Arkoses are, often, associated with the conglomeratic deposits formed from the granite terrains. Arkoses are, often, above the unconformties overlying granite terrains. Arkoses can, sometimes, be mistaken with greywackes. However, the environments of deposition of arkoses and greywackes are, totally, different. While greywackes form in a deep-water sedimentary environment, in association with gravity currents (turbidite depositional systems), arkoses are, generally, formed upstream or near the shoreline, i.e., in a nonmarine or shallow-water environment.

Arm (Distributary channel, fork)......................................................................................................................................................Défluent (Distributaire)

Distributário, Distributivo / Canal distributario, Brazos / abzweigender Arme / 分流河道 / Рукав (реки) / Canale emissario /

Any of the numerous branches in which a river divides to reach its delta.

See: « River »
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« Delta »
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« Stream »

An arm, distributary or distributive channel is a water-stream, which branches out or flows out of the main channel. This phenomenon is known as river-bifurcation. The distributives, as illustrated in this figure, are very common in the deltas associated with rivers. The opposite of a distributive (or arm) is a tributary or river-tributary. Distributions occur, usually, as streams near the lakes or the sea. They occur, also, on onshore, such as in closed or endorheic basins (closed drainage basin, which holds water and does not allow any flow to other water-bodies) or when a distributive chain branches as it approaches the confluence with a more important current. In some cases, a smaller distributive can steal so much water from the main channel that it can become the main path of the stream. The study of the deltas shows, clearly, distributary channels control the flow of the sedimentary particles (debris) into the ocean. A relationship exists, sometimes, between the number of distributary channels, the length of the river, and the delta gradient. These relationships are valid for deltas controlled or, heavily, influenced, by sea-waves, discharge of rivers, tides or ice. Often, the arms of a delta result from the pendulum effect of the delta lobes, meaning the currents are forced to move sideways, as long as, a lobe is formed. Naturally controlled deltas, in contrast to man-controlled deltas such as the Klinaklini (Canada, British Columbia), have distributive channels, which act as overbanking sources during flood periods. Anthropogenically controlled deltas, such as the Po Delta, have distributive channels that control floods and also low runoff. Anthropogenic controls, strongly, influence the rate of natural delta progradation induced by changes in the terrigeneous influx. They control the position of the distribution channels, but also the subsidence induced by the extraction of groundwater and, in certain cases, of natural gas*. Even under these control conditions, the Po delta retains about 16% of the sediments transported by the canals, which rise at an annual rate of 4/10 cm in relation to the flood-plain.

(*) Most man-made subsidence results from ground-water withdrawal but the earliest observation of subsidence resulting from human activity was from oil and gas field production. The Houston area (Texas) area has perhaps the best examples in the world of subsidence that results from both ground-water and petroleum withdrawal. The first documented instance of land subsidence due to fluid withdrawal was from the Goose Creek oil field near the city of Houston. In 1917 oil was discovered on the margin of Galveston Bay near the mouth of the present-day Houston Ship Channel. After production of several million barrels of oil, bay waters began to inundate the oil field. The subsidence also works the other way sometimes in the case of injection wells where they are injecting high volumes of water into formations. In that case, your house might rise up some (http://www.texassharon.com/2010/08/29/subsidence-from-oil-and-gas-development/)

Arrow of Time............................................................................................................................................................................................Flèche du temps

Flecha do Tempo / Flecha de tiempo / Zeitpfeil / 时间箭头 / Ось вре́мени / Freccia del tempo /

Particular sense of time given by entropy increasing. As time goes by, the second law of thermodynamics says that entropy of an isolated system* increases when there is no consumption of energy outside the system.

See: « Geological Time »
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« Relative Time »
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« System (theory) »

Scientists and philosophers have long tried to understand the nature of time. The laws of physics do not have a preferred direction for time, unless we take into account the concepts of quantum cosmology**. Time is in reality an integral part of the Universe. The linear concept of time is linked to the concept of the second Law of Thermodynamics *** which establishes the conditions for thermodynamic transformations to occur. Without time as a real estate of the Universe, the second law of thermodynamics would have no meaning. In the natural sciences, the term arrow of time was first used, in 1927, by Sir Arthur Eddington to say, basically, time flows in only one direction (unlike the dimensions of space which have no preferential orientation) and to emphasize that direction of time can be determined by the study of the organization of atoms, molecules, and bodies. In the twentieth century physicists were shocked to discover that the arrow of time can not be derived from the laws of physics. The laws of physics seem to be, perfectly, symmetrical. For every solution of time "t" there seems to be a solution, equally, valid for "-t" (except in certain situations invoking the weak force, whose scenario the symmetry is more complex, involving other entities like load, parity and time). At first glance this seemed very strange to us, but after a few years of reflection most physicists now agree that it is, perfectly, possible that there are symmetrical laws that give rise to asymmetric phenomena. Physicists have identified a collection of such asymmetrical phenomena representing the "arrows of time." There are several arrows of time: (i) The time arrow in quantum mechanics, in which the preferred direction of time is determined by quantum decoherence ; (ii) The gravitational arrow, in which the preferred direction is determined by gravitational collapse (collapse into a stellar body due to the effect of its own gravity to form a black hole) ; (iii) The time-axis of thermodynamics, in which the entropy, which characterizes the degree of disorganization or the lack of information of a system, always grows in a closed system, etc. The latter is, certainly, the one that interests us the most, although in some isolated individual systems one can choose conditions that invert the arrow of time. From the point of view of a macroscopic observer, entropy, translates in a, more or less, typical way, the microscopic state of the system. It tends to increase because there are many more ways to have a high entropy than a low entropy. As illustrated in this figure, if we consider a gas box, in which the molecules (by some means) are all together in the middle of the box, the entropy is in a low configuration. By letting the system evolve, the molecules will move, colliding with each other and with the walls of the box, ending (with overwhelming probability) in a configuration of much greater entropy (or disorder if you will). It is easy to convince ourselves that there are some configurations from which the entropy would spontaneously be smaller. Imagine the state of the gas box at any moment after it has already had a high entropy, and consider a state in which all molecules have, exactly, the same positions but with inverse velocities. Theoretically, the motion of the molecules would reproduce, precisely, the inverse path they perform from the earlier low-entropy state. An observer outside the system would observe the entropy would decrease spontaneously. However, we all know that in such a process a lot of work would have to be done to accurately reverse all these speeds, so that such a process would increase the entropy of the rest of the world in order to satisfy the Second Law of Thermodynamics. Certain scientists (E. Klein, 2009) clearly distinguish the arrow from time and the course of time. The course of time involves causality, since time passes in a single direction without ever reversing. The arrow of time presupposes the existence of a well-established course of time, in which certain phenomena are themselves temporally oriented, or irreversible (impossible to nullify the effects they have produced).

(*)  Like all living things, are an open system, meaning that you exchange both matter and energy with your environment.  All of the exchanges of energy that take place inside of you (such as your many metabolic reactions), and between you and your surroundings, can be described by physical laws. There are three types of systems in thermodynamics: open, closed, and isolated. An open system can exchange both energy and matter with its surroundings. A closed system, on the other hand, can exchange only energy with its surroundings, not matter. An isolated system is one that cannot exchange either matter or energy with its surroundings. (https://www.khanacademy.org-/science/biology/energy-and-enzymes/the-laws-of-thermodynamics/a/the-laws-of-thermodynamics)

(**) Theory that seeks to study the effect of quantum mechanics in the early moments of the Universe after the Big Bang, which despite many efforts, continues to be a very speculative branch of quantum gravity. The Big Bang / Big Crunch is replaced by a quantum jump thus eliminating the singularities.

(***) The amount of entropy of any thermodynamically isolated system tends to increase over time until it reaches a maximum value. In other words, when one part of a closed system interacts with another part, the energy tends to divide equally, until the system reaches a thermal equilibrium.