Late Aptian carbonate platform evolution and controls (south Tethys, Tunisia): response to sea-level oscillations, palaeo-environmental changes and climate

Abstract

The late Aptian Lower Serdj Formation (LSF) in the Northern Atlas of Tunisia records a mixed carbonate–siliciclastic system from the southern margin of Tethys. Sedimentological investigations of key sections in the Serdj-Bargou area along a NE–SW-platform-to-basin profile reveal five shallow-marine carbonate units (Cu1, Cu2, Cu3, Cu4a and Cu4b), dominated by subtidal deposits, separated by four terrigenous units (T1, T2, T3, T3a). Twelve basic facies are grouped into six facies associations or zones (FZA to FZF), representing particular palaeo-environments from proximal to distal settings. Carbonate units Cu1, Cu2 and Cu4a are dominated by coral algal-Orbitolina facies representative of a homoclinal ramp. However, units Cu3 and Cu4b are dominated by high-energy oolitic facies of a shoaled ramp. The terrigenous deposits (T1 to T4) are dominated by siliciclastics with shale, sandstone/siltstone and marl and have mostly been assigned to off-platform to basinal environments (FZF). The vertical facies changes are closely related to amplitudes of sea-level fluctuations and late Aptian Tethyan climatic perturbations. The terrigenous units were the result of short cooling periods and a humid climate. Moreover, this climate favoured the development of tide-influenced oolitic shoals, with the nuclei of ooids formed by fine quartz grains. Both the oolitic and siliciclastic deposits reflect episodes of maximum platform progradation basin-ward at a time of low accommodation space through the late Aptian period. Overall the new stratigraphic dataset from the southern Tethys margin is interpreted as reflecting the global Late Aptian cooling episode and sea-level lowstand.