Biostratigraphic and chemostratigraphic record of the Cenomanian/Turonian boundary interval of the Tellian Atlas (Algeria)

Abstract

A multi-proxy approach integrating data on planktonic foraminifera, calcareous nannofossils, δ13Ccarb, δ18Ocarb and the coiling direction of Muricohedbergella delrioensis was carried out for two sections in the Tellian Atlas (Algeria) both to establish a precise stratigraphic scheme and to precise the climatic events.The Sour el Ghozlane section offers a good record of the Oceanic Anoxic Event 2 (OAE2) in the southern margin of the Tethys, with organic-rich sediments and the continuous presence of planktonic foraminifera, nannofossils and other microfossils. The Cenomanian/Turonian boundary (CTB) in the Sour el Ghozlane section lies in the interval limited at the base by the last occurrence of Helenea chiastia and the first occurrence of Quadrum gartneri respectively located immediately below and above the last peak (C) of the carbon isotope excursion. However, in the Sidi Nadji section, the CTB interval is extremely thin; the last occurrences of Rotalipora cushmani and Thalmanninella greenhornensis coincide with the last occurrences of Corollithion kennedyi, Helenea chiastia, Axopodorhabdus albianus and Rhagodiscus asper and occur in the same level, therefore a hiatus is suspected.Sour el Ghozlane and Sidi Nadji are so far the southernmost sections where the percentage of sinistral M. delrioensis has been investigated. High proportion of left-coiled morphotypes among M. delrioensis indicate transient cooling episodes, including the Plenus Cold Event at the onset of OAE2 and before the warm conditions at the CTB characterized by the dominance of dextral forms.