The lower Maastrichtian chalk in the Ghezala-Mateur area, northern Tunisian domain: Sedimentary environments and early diagenetic features

Abstract

The lower Maastrichtian chalks of the Ghezala-Mateur area, northern Tunisian domain, were investigated with regard to their palaeogeographic implications. Two lateral facies have been identified (i) the white chalk facies occurs to the NW, NE and SE strikethrough of the late Cretaceous synsedimentary El Aouana Graben and, (ii) the chalky limestone facies occupied the central part of the Graben.Sedimentary features, fossil content and trace fossils distribution reveal that sedimentation occurred in a slightly reducing shallow-water environment, probably corresponding to an outer platform setting, characterized by frequently interrupted sedimentation and conspicuous activity of erosional currents. Both features seemingly contributed to the genesis of numerous hiatal surfaces marked by the widespread activities of Thalassinoides trace fossils. The genesis of hiatal surfaces was probably promoted by recurrent burial-early diagenesis-exhumation cycles in which Thalassinoides burrows were preferentially affected by early diagenetic processes. Nodular chalky limestone, intraformational conglomeratic chalky limestone and knoby chalky limestone are the most common lithologies resulted from the early diagenesis of Thalassinoides-omission surfaces.