Basic Principles in Tectonics

5- Tectonic Regimes in Sedimentary Basins

Contents:
5.3- Surface Phenomena
       5.3.1- Landslide and Extrados Fractures
       5.3.2- Folds and Faults associated with Gravity

5.3- Surface Phenomena (Traction, 3 negative)

5.3.1 - Landslide and Extrados Fractures

Landslides and extrados fractures are created by an extensional tectonic regime (1 vertical), but with a 3 negative, that is to say by traction) as illustrated in fig. 300.

Fig. 300- Extrados fractures should not be confounded with normal faults associated with anticlines. Indeed, they with a single bed and above the neutral surface, i.e. the area extended. Normal faults affect several beds and are not contemporaneous of compressional structures.

5.3.2- Folds and Faults associated with Gravity

Folds and faults can be associated with slumping (gravity) as illustrated in fig. 301.

Fig. 301- These faults, which are normal updip and reverse downdip, have been labeled listric (Selley), term coming from the Greek listron, which means shovels. Indeed, in the toe of a slumping, there is development of a local compressional tectonic regime responsible by the shortening of the sediments to be accommodate to the new volume conditions (see fig. 302).

The next seismic line illustrates a reverse fault associated to gravity sliding. The reverse faults are associated with local tectonic stresses; they are the seaward continuation of normal faults.

Fig. 302- The sedimentary gliding, probably due to a slope instability, created a curvilinear fault plane with a normal geometry (extension updip) and a reverse geometry (compression) downdip. This kind of faulting develops in areas where the confinement pressure is relatively small, i.e. and near the surface.

Additional reading:

Arbenz, J.K., 1968- Shell Documents

Bally, A. W. , R. Catalano, J. Oldow, 1985- Elementi di Tettonica Regionale, Pitagora Editrice, Bologna.

Berest, P., 1988- La thermomécanique des roches, Manuels et Methodes nû16, BRGM.

Canadian Society of Petroleum Geologists, 1982, Special reprinting, Series 3.

Goguel , J. 1965- Traité de Tectonique, Masson et Cie, Editeurs.

Goguel J., 1983- Etude mécanique des déformations géologiques. Mauels et Methodes n°6, BRGM.

Guidon, M., 1987- Les Structures Tectoniques, Manuels et Méthodes, n° 15, BRGM.

Martin, J., 1950- Marathon Document

Price, N. J. and J.W. Copsgrove, 1990- Analysis of Geological Structures. Cambridge University Press.