Foraminifers of the Late Cretaceous- Early Eocene in central Tunisia: Biostratigraphy and paleoenvironment


Biostratigraphic and statistical studies were carried out on the Late Cretaceous- Early Eocene succession of Khanguet Zalga in Jebel Serj area, central Tunisia. Paleontological analysis shows the occurrence of about 300 species (200 benthic foraminifera and 48 planktonic foraminifera). The most significant foraminifera (relative abundance more than 5%) are indicated in the vertical charts of distribution. Based on the vertical stratigraphic distribution of the planktonic foraminiferal species, six zones and subzones are recognized: Gansserina gansseri zone of Late Cretaceous (lower Maastrichtian), Igorina albeari (P3b) zone of Middle Paleocene (Selandian), Acarinina soldadoensis (P4c) subzone of the upper Paleocene, Morozovella velascoensis (P5) zones of Late Palaeocene (Thanetian), Morozovella edgari (E3) and Morozovella subbotinae (E5) zones of Early Eocene (Lower Ypresian). Biotic parameters and benthic assemblages from Late Cretaceous- Early Eocene Serj section allow the reconstruction of paleoenvironment and paleoecological fluctuations. In fact, our records indicate that the environment evolved from an initially oligotrophic, middle bathyal depositional environment for Gansserina gansseri, and P4c zone to upper bathyal setting for P3b and P5 towards a more eutrophic inner neritic setting for E3 and E5. The high abundance and the low diversity in this section are related to the sedimentological, the minimum of dissolved oxygen and the paleodepth conditions.  The ecosystem is unbalanced for middle bathyal environments (hyaline shell-groups), balanced for shallow environment and upper bathyal (agglutinated and calcareous shell-groups).