Stages in Evolution of Jurassic Carbonate Platforms and Their Relations to Basins Around Western Mediterranean: Example of Southern France
Comparative sedimentological, paleontological, and structural studies document different kinds of controls on the origin, development, and termination of carbonate platforms and adjacent basins.
The Vivarais-Cevennes area belongs to the French Subalpine basin where the Jurassic sedimentation was controlled by local tectonics, Tethyan structural evolution, and climates. The environment changed through time from (1) sandy alluvial plains to (2) shallow proximal platform, (3) distal platform, (4) split small subbasins (umbilicus), and (5) slope of a larger basin. The evolution is illustrated by palinspastic reconstructions, isopach maps, and facies analyses of both field and well data.
A tentative model is given using the rhythmic sequential succession: opposition between "escarpment" and "hinge-ridge" evolution. Their vertical distribution was independent in the contiguous blocks when the sedimentation was mainly controlled by local tectonics. However, the successions were similar where regional controls were involved. Events of the first model are contemporaneous with a stage of rifting. The second corresponds to more global processes (spreading, sea level variations, climatic changes). The different types of lithoclines are documented from both holes and outcrops.
At the end of the Jurassic, physiographic, chemical, and probably climatic conditions had strongly changed. Afterward, some carbonate (or associated) facies disappeared from the region (and from the Tethys), e.g., iron ore, "grumeleux" lumpy facies, and ammonitico-rosso suite. Some of these changes could be related to modification in the balance of the oceanic water circulation.
These data are confronted to the results gathered in similar settings in North Africa and the Apennines.
AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.