Platform collapse and pelagic seamount facies: Jurassic development of central Tunisia

Abstract

Abstract In central Tunisia, the Lower Liassic facies consists of peritidal carbonates deposited on a wide platform which has been broken into irregular tilted blocks in the Early Pliensbachian. Black shale was deposited in some of the down-faulted blocks during the Early Toarcian Oceanic Anoxic Event. The Bajocian–Bathonian deposits are represented by ironstones and hemipelagic ammonite and Zoophycos -rich marl-limestones. The upper Jurassic is composed by pelagic limestones and debris flow deposits. The middle Jurassic deep marine sedimentation was frequently associated with condensed sections, submarine erosion leading to stratigraphic hiatuses. The latter results from the interaction between global sea-level fluctuations and regional tectonic activity generating an uplifted block in Central Tunisia in relation with Early Mesozoic rifting and associated distensional drifting of the North-African Tethyan margin. This horst block has acted as a starved pelagic shoal on which sedimentation has been recorded especially during retrogradational and the aggradational phases.