Sequences, discontinuities and water stratification in a low-energy ramp: the Early Albian sedimentation in central Tunisia

Abstract

Based on a precise biostratigraphic framework stated previously, the detailed sedimentological study of eight sections of the early Albian succession of Central Tunisia made possible to refine the modalities of the Albian transgression and the related behavior of sedimentary system on the Tunisian margin. Major early Albian transgressive pulses occurred (i) at the base of the L. tardefurcata standard ammonite zone, (ii) around the top of the same zone, (iii) during the D. mammillatum standard zone, and (iv) near the top of the latter ammonite zone. They resulted in the progressive flooding of the Tunisian margin emergent since the Aptian boundary, in the disappearance of emergence evidences through time, in the southward backstepping of the carbonate shelf facies, and eventually in the homogeneization of the outer shelf marly sedimentation in the study area. The low energy of deposition of the early Albian sediments in this part of the South-Tethyan margin may be due to the deflection of winds and storms by the Coriolis forces toward the North-Tethyan margin, creating a clockwise gyre in this part of the ocean. This circulation may have enhanced upwelling currents likely responsible for phosphate mineralization, and for the oxygen depletion of deep waters, which progressively invaded the Tunisian margin, giving way to organic-rich deposits of late early Albian age. The early Albian sedimentation is then interrupted by a major hiatus of middle Albian to early late Albian age.