The filament event, sequence stratigraphy and correlation of recorded bioevents near the Cenomanian–Turonian boundary: Implications in Central Tunisia

Abstract

Near the Cenomanian–Turonian boundary, the filament event has been identified worldwide. In Tunisia, filaments are well represented in the laminated black shales of the Bahloul Formation. These black shales were deposited under anoxic conditions in an outer ramp environment. Filaments are particularly abundant in the upper part of the Bahloul Formation, and within the W. archaeocretacea Zone; these correspond to the massive occurrence of fragments of thin-shelled bivalves, whether planktic or nektonic. In terms of sequence stratigraphy, two sampled sections in Central and Central-West Tunisia have led to the interpretation of these deposits as a transgressive interval (TST). In the Oued Ettalla area, the organic-rich laminated limestone and the interbedded dark grey marly claystone constitute the Bahloul Member. The transgressive interval ends with a maximum flooding surface (MFS) included within the lower part of the Kef Formation (Annaba Member) which consists of yellowish-grey marly claystone and marly limestone intercalations, rich in filaments. Whilst in the Oued Sfala section the maximum flooding surface (MFS) is characterised by a thin layer of pebbles (approximate centimetric scale) occurring between Unit 4 and Unit 5. Through the analysis of both oxic and anoxic facies from the Cenomanian–Turonian transition, five bioevent markers have been identified in our sections and in other regions within the Tethyan domain: the extinction of the genus Rotalipora, the Heterohelix shift, the proliferation of globular planktic foraminifera, the filament event, and the first occurrence of Helvetoglobotruncana helvetica. These bioevents are important for establishing high-resolution correlations both regionally and worldwide.