Planktonic foraminifera and stable isotopes of the upper Cenomanian–middle Turonian in central Tunisia: Implications for bioevents synchronicity and paleoenvironmental turnover

Abstract

The upper Cenomanian–middle Turonian planktonic foraminifers and stable isotopes analyses of the Oued Ettalla section (central Tunisia) were incorporated to establish the temporal framework and unveil the paleoenvironmental signal of the Oceanic Anoxic Event 2 (OAE2). Some bioevents were reported at a lower stratigraphic level compared to their worldwide records; such as the synchronous extinction of Rotalipora cushmani and Globigerinelloides bentonensis at the onset of the δ13C peak A, besides the Heterohelix shift between δ13C peaks A and B. Thus, an intensified surface-water eutrophism complemented by a local acceleration in the thermal stratification collapse of the upper water column had occurred by the OAE2 onset. The results assign the pre-OAE2 interval to stable, reasonably ventilated meso-oligotrophic surface-water conditions. The paleoenvironment had shifted toward stressed, highly eutrophic, less stratified circumstances by the OAE2 onset, as evidenced by eliminating the taxa that occupied deep and intermediate habitats. The planktonic foraminifers alongside oxygen isotopes data denote an extreme warm condition during the OAE2 with a brief cooling episode, slightly after the δ13C peak A, equivalent to the so-called Plenus Cold Event. The presence of whiteinellids and prevalence of dwarfism excluded each other among the planktonic foraminifers assemblage within the OAE2 interval, indicating minor shifts in the eutrophication. The environmental wakeup from the OAE2 was stepwise and initiated well within the topmost part of the Whiteinella archaeocretacea Zone, as reflected from the permanent existence of the whiteinellids and the associated reoccurrence of the keeled taxa.