Abstract
A study of benthic Foraminifera from the Toarcian in Quercy (Aquitaine Basin, France) shows that micropaleontological assemblages are influenced by sea level changes. The percentages of coiled, and straight Nodosarridae ( Lenticulina, Citharina) differ during periods of low sea level to high sea level. Statistical analysis of all the taxa in the successive levels of a section (Multiple factorial Analysis of Correspondences, methods of automatic clustering) show that there is a perfect distribution of the samples into groups corresponding to the type of systems tract: differences within the foraminiferal benthic biocoenosis allow the successive systems tracts to be separated. The first axis in the Multiple Analysis of Correspondences coincides with a gradient of biotic capacity and seems to be connected with the sea level changes. The second axis could be linked with depth. The renewal rate of taxa and the factorial diversity of the sampling levels show fluctuations associated with 4th, 3rd and 2nd order variations of the sea level. These connections are caused by intricate processes with ecological, biogeographical and bioevolutionary influence. However, the micropaleontological assemblages can be good indicators of systems tracts and unconformities. This is particularly important within deposits that have homogeneous lithology.
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