PETM effects in a shallow marine environment : benthic foraminiferal turnover and echinoid bloom (Sidi Nasseur, Tunisia)

Despite a large number of studies on the Paleocene/Eocene thermal maximum (PETM) in continental margin sections, our knowledge of the PETM in inner to middle neritic environments remains quite poor. In order to unravel faunal and paleoenvironmental changes in shallow marine settings during the PETM, we investigated the Sidi Nasseur (NAS) section in Tunisia. The section exposes upper Paleocene to lower Eocene shales and marls of the El Haria Formation. The lower 9 m of the NAS section is marked by moderately rich, fairly diversified nannofossil associations, containing the typical pre-PETM taxa of the middle part of NP9 (Discoaster multiradiatus, D. falcatus, Rhomboaster cuspis, Fasciculithus alanii, F. schaubii, etc.). The upper half of the section (10.50 17.50 m) is very poor in nannofossils (Coccolithus pelagicus and a few D. multiradiatus are present), partly because of selective decalcification, excluding refined age attributions. The lower 9m of the NAS section contain a benthic foraminiferal assemblage with numerous large Frondicularia, Nodosaria, Lenticulina, many small calcareous and arenaceous species, but only rare planktic foraminifera, pointing to inner to middle neritic deposition (~ 50 m paleodepth). A faunal turnover is situated within a carbonate-poor interval interpreted as a decalcified zone, rich in arenaceous foraminifera. From 10.50 to 17.50 m the foraminiferal assemblages consist of many minute trochospiral and bi-/triserial benthic taxa. Frondicularia and Nodosaria do not reappear above the carbonate-poor interval. Planktic foraminifera become frequent above the carbonate-poor interval and consist to a large extent of flat-spired species of Acarinina, including the multichambered variety of Acarinina sibaiyaensis. This planktic assemblage typifies Anuar io do Inst i tu to de Geociencias UFRJ ISSN 0101-9759 Vol. 29 1 / 2006 p. 509-510