Un exemple de tectonique de plate-forme : les causses majeurs (sud du massif central, France)

Dans cet article sont présentés à titre d'exemple les différents types de déformations subies par une région de plate-forme, les Causses majeurs (France méridionale), lors de la phase de compression tectonique d'âge pyrénéen. Les conclusions tirées de cette étude peuvent en effet être appliquées aux bassins pétroliers de même type. On définit la géométrie et l'orientation des structures produites lors de cette phase, failles, plis associés aux failles, fracturation, stylolithes. On s'attache à montrer l'influence d'anciennes structures hercyniennes du soubassement sur la répartition et l'orientation des déformations affectant la couverture jurassique. On montre aussi que des structures présentant des orientations particulières se forment au voisinage des failles apparues lors des premiers stades de la compression : ces structures traduisent une modification locale du champ de contraintes due aux failles précoces, un essai de chronologie des différents types de structures est proposé

Annotated record of the detailed examination of Mn deposits from R/V "Le Suroit" GEOMANCHE75/1 stations

We report here preliminary results from the detailed sampling of granitic basement at a depth of 4.000 m at the lower edge of the Armorican continental margin near 48°N and 12°W. We consider that we have sampled here the extreme lateral limit of the continental crust where local exposures emerge from under a cover of Cainozoic,Mesozoic and probable Palaeozoic sediments

Annotated record of the detailed examination of Mn deposits from R/V "Jean Charcot" GEOMANCHE 76/2 stations

This report presents the preliminary results of the study of rocks and sediments obtained by dredging during four cruises of the R/V Jean Charcot and R/V Le Suroit during a cooperative program between CNEXO and CEPM (CH 58: April 1975; SU 01: December 1975; CH 66: February 1976; and CH 67: March 1976). Several dredges on the continental slope of the Goban Spur recovered "granitic" rocks on two morphological structures, Granite Cliff and "Menez Bihan" (Pautot et al., 1976), in water depths ranging from 3200 to 4200 meters. According to the radiometric age and petrology, the granodiorite appears to have a close affinity with similar igneous facies which have been described in Iberia (Capdevilla et al., 1973) and attributed to the Variscan intrusive episode which is also found in the nearby continental area (southwest Great Britain and Brittany, France). They often are coated by a centimeter-thick layer of ferromanganiferous deposits (Shaaf et al., 1977)

Dredged Rocks from the Armorican and Celtic Margins

This report presents the preliminary results of the study of rocks and sediments obtained by dredging during four cruises of the R/V Jean Charcot and R/V Le Suroît during a cooperative program between CNEXO and CEPM (CH 58 : April 1975 ; SU 01 : December 1975 ; CH 66 : February 1976 ; and CH 67 : March 1976). A bathymetric map of the margins under study, as well as the location of the 27 dredges considered in this report, are presented in Figures 1 and 2, respectively. [NOT CONTROLLED OCR

THE GULF OF LION - SUBSIDENCE OF A YOUNG CONTINENTAL-MARGIN

The origin of the subsidence of Atlantic-type continental margins is of much interest to geology and geophysics. The main problem at these margins is in explaining the substantial thicknesses of mainly shallow-water sediments which accumulate soon after rifting and plate separation. We have now used biostratigraphic data from commercial wells to study the subsidence history of a young Atlantic-type continental margin. Backstripping the sediment load reveals that the margin has been subsiding at nearly mid-ocean ridge rates. Geological data indicate that lithospheric stretching alone cannot account for this amount of subsidence and other processes must be involved. © 1980 Nature Publishing Group

TECTONIC SUBSIDENCE, FLEXURE AND GLOBAL CHANGES OF SEA-LEVEL

Tectonic models for the evolution of passive continental margins predict that following rifting, sediments should progressively onlap basement at the edge of a margin as the lithosphere cools and increases its flexural rigidity with age. The pattern of modelled onlap is strikingly similar to that used by Vail and colleagues to estimate sea-level rise through geological time. This similarity suggests that major portions of stratigraphical sequences at margins may have a tectonic, rather than eustatic, control. The patterns of onlap used by Vail and colleagues may be widespread, however, because several widely separated passive margins rifted at similar times, but they are unlikely to be worldwide. © 1982 Nature Publishing Group