Apport de l’analyse factorielle dans l’étude de la biostratigraphie et la biodiversité des associations de foraminifères planctoniques du Cénozoïque de Casamance (Sénégal)

Abstract

Multidisciplinary approach based on biostratigraphy and detrended correspondance analysis was applied to study the planktonic foraminifera associations from seven boreholes located in the Casamance sub-basin. The westernmost part of the transect contains abundant planktonic foraminifera, which allows correlation with global biozonation. Further to the East, the transect becomes progressively shallower, but the high spatial resolution of this study permit to link the standard planktonic foraminifera zones with local ecozones. Biostratigraphy of planktonic foraminifera allowed us to assign the studied section to the Late Paleocene (P4a) through Late Eocene (E16). Detrended correspondence analysis allows correlations between planktonic foraminiferal assemblages and samples. Based on lithologicals analysis the Paleocene was characterized by clastic sediments (sand, clayey sand), relayed by carbonate sediments (calcareous marls) during the Eocene. The calcareous sequence is terminated by a large regional hiatus encompassing the planktonic foraminifera zones E16 to O3. The Paleogene planktonic foraminifera assemblages are dominated by generas Morozovella, Pseudohastigerina and Parasubbotina. The Eocene deposits are dominated by Subbotina, Acarinina, Turborotalia, Paragloborotalia, Globoturborotalita and Globigerina. Significant correlations were recorded between the percentage of planktonics, used as proxy for paleodepth, and both the diversity index (measured control on the depositional environment). This is also reflected in quantitative analysis of the faunas in individual cores.