Eustatic and palaeogeographic control of the western Aurès Upper Cretaceous sedimentation (Algeria)

The Upper Cretaceous sedimentation in the Aurès Mountains occurred in a subsident basin delimited to the south by the Saharan platform and by the Preatlasic high zone to the north. In these series 4 transgressive-regressive megasequences are distinguished, the first one (I) in the late Albian-Cenomanian, the second one (II) in the Turonian, the third one (III) in the Coniacian - Santonian and the fourth one (IV) in the Campanian - Maastrichtian. Each megasequence is made up of three or four sequences, which correspond to third order cycles identified in the eustatic chart of Haq et al. [1987]. In late Albian and lower Turonian periods, during the deposition of basal sequences of the megasequences I and II, the reactivation of basement faults in the Aurès basin occurs consecutively to distension phases, resulting in the formation of rotated blocks. At the same time high eustatic levels are reached according to the global eustatic curve. These processes control the drowning of the carbonate platforms pre-existing to these sequences, and deep ramps progressively form on the tilted block tops. This sedimentary setting generates in the late Albian and lower Turonian series anoxic sequences made up of calcareous and shaly transgressive pelagic intervals. The succeeding sequences lack pelagic facies and are composed of alternate marls / carbonate beds deposited on a homoclinal ramp, indicating a gradual development of shallow open marine conditions, which became progressively restricted upwards. Toward the top of these megasequences, lagunal muds and isolated rudists mounds, surrounded by bioclastic and ooid / pellet banks occur. The Coniacian-Santonian and Campanian-Maastrichtian megasequences are characterized by a shallow ramp sedimentation, essentially marly during the Coniacian, Santonian and Campanian periods, interlayered with some bioclastic / ooid carbonate banks and upwards by sequences mostly homogeneous. The Maastrichtian platform carbonates are composed of bioclastic / ooid sands and were deposited in a ramp-barrier-bank system. Some sequences in the Campanian-Maastrichtian megasequence are condensed or absent due to the accommodation reduction related to a weak subsidence rate period.