The Cenomanian—Turonian Boundary Event (CTBE) in north-central Tunisia (Jebels Serj and Bargou) integrated into regional data (Algeria to Tunisia)

Abstract Two new sections covering the Cenomanian—Turonian transition have been studied at the foot of the Kasserine platform in the northeastern Mellegue basin (Jebels Serj and Bargou). They show, in the uppermost part of the Cenomanian Fahdene Formation, a Pre-Bahloul unit overlain by the well-known Bahloul black shale. Combined foraminiferal and isotope data of the sections complement other published results: (1) extinction of rotaliporids atop of the Pre-Bahloul bed during the build-up of the Cenomanian—Turonian Boundary Event (CTBE) δ 13 C positive shift, (2) Heterohelix bloom during the deposition of the Bahloul black shale, (3) filament event during δ 13 C return to normal values, and (4) first occurrence of Helvetoglobotruncana helvetica during the transition to the marlstone of the Annaba Formation. The Bahloul black shale is here divided into three units, U1 to U3 which are compared with the other sections of the Mellegue basin. The bulk of this paper is a comparison of the two new sections with revisited nearby sections of the Mellegue basin, as well as with those published from the south Tunisian Gafsa trough and Saharan Atlas of Algeria. The comparison suggests that the pre-Bahloul of the Mellegue basin is correlatable with the transgressive fine-grained limestone bed underlying the CTB black shale in the corridors between isolated, keep-up platform carbonates of the Ouled Nail in Algeria, as well as the fine-grained limestone bed overlying upper Cenomanian shallow-water deposits of southern Tunisia. Its sequence stratigraphic significance in the Mellegue basin should therefore be recognized as a deeper-water equivalent of a transgressive systems tract, instead of being interpreted as a lowstand or highstand as it is by other authors. If correct, the inception of the CTBE δ 13 C shift would correspond to a transgression over most of Algeria and Tunisia, as observed in the North American Western Interior.