The relationships between tectonics and sedimentation in the Late Cretaceous series of the eastern Atlasic Domain (Algeria)

Abstract

Our study of the Late Cretaceous series in the eastern Atlasic Domain of Algeria is intended to show the geometry of the sedimentary deposits and the sequential palaeogeographic evolution of the region’s basins. The Late Cretaceous series consist of four transgressive–regressive sedimentary megasequences corresponding to 2nd order cycles, noted as I–IV. Each megasequence is made up of three or four sequences that have been correlated with 3rd order cycles. The beginning of megasequences I and II mark a rapid tectonic deepening concomitant with an acceleration of sea-level rise which allowed the deposition of pelagic sediments at their initiation, during the latest Albian and early Turonian times. This tectonism reflects the reactivation of basement faults resulting in extension and block-tilting. The succeeding sequences, showing alternating marls and carbonate beds with benthic facies were deposited in a homoclinal ramp and are indicative of a gradual development of shallow marine conditions. In the megasequences III (Coniacian to Santonian) and IV (Campanian to Maastrichtian) the sequences were wholly deposited on a homoclinal ramp. The major basement faults are NE-SW trending transtensional strike-slip faults, which delimit the margins of the basins, and WNW-ESE and NW-SE trending normal faults that led to block tilting during the Late Cretaceous. Both types of faults strongly influenced palaeogeography and sedimentation. The evolution of the subsidence through the Late Cretaceous shows a progressive sagging of these basins, interrupted by short phases of extension highlighted by accelerations on the subsidence curves. These phases constitute, after the Jurassic extension, a new extensional episode occurring during the latest Albian and Early Turonian, which led to a tilting of basement blocks. The Late Cretaceous extension phases reflect reorientations of the stress in the African plate, during its northeastwardly directed drift, and rifting processes on its northeastern margin. A first compressive phase, which was relatively localized, is registered at the end of the Maastrichtian, leading to palaeogeographic reorganization of the Atlasic basins.