Organic-Rich Sedimentation During the Late Lias in the Mediterranean Tethys

J. P. Bassoulet, F. Baudin, J. Dercourt, J. P. Herbin, G. Lachkar

The paleogeographic distribution of the organic matter (OM) in the Tethys during very specific periods of time is one of the topics addressed by the Tethys Project. The aim of such a study is to lead to a better knowledge of the global anoxic events based on a study of the OM (age, TOC, petroleum potential, type of OM, thickness of the organogenic sequences), which remains one of the most important stages in a geological approach.

A particular interest has been devoted to the Toarcian, which corresponds to a period of opening of the Tethys and to a transgressive stage within the Jurassic. Since 1986, field studies with pluridisciplinary geological teams composed of stratigraphers, sedimentologists, structuralists, and organic geochemists have been engaged to collect samples of Toarcian age all around the Mediterranean Tethys. All samples are studied using the same procedure. The organic geochemistry study is mainly based on Rock-Eval pyrolysis and kerogen analysis. Sections in Morocco, Spain, and the Ionian Zone (Greece) have not yet been sampled; outcrops and boreholes in Turkey and Saudi Arabia will be sampled in 1988.

According to the type of environment, the OM is more or less well preserved. Completely oxidized within the carbonate platform, the accumulations of OM occur mainly at the bottom of strait basins, as those of the Ionian Zone where the TOC can reach up to 5%.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.