New insights into Cretaceous tectonic inversion events. Example of tectono-sedimentary framework of Central Eastern Tunisia

In Tunisia, the Atlas basin represents a key area to investigate sedimentation’s tectonic control from the Tethys Ocean’s final rifting stages to the onset of its closure. In this study, conducted in the Central Atlas, we aim to understand the regional rapid variations in thickness and facies of the Upper Cretaceous strata. Our study integrates both surface and subsurface data including lithostratigraphic sections of key outcrops, land gravity data, 2D seismic sections, and well data. The applied methodology successfully allowed us to determine the timing and duration of unconformities and highlight the subsidence migration within the basin. Cretaceous tectonics mainly consist of extensional deformations that created grabens and half grabens, where subsidence was active. 2D seismic sections interpretation and subsurface mapping reveal that sedimentary strata infilling grabens are expressed by divergent reflectors i.e. onlap terminations. However, pinch-outs and unconformities are marked by toplap terminations, suggesting non-deposition and/or erosion. Major unconformity (TGU) is identified on top of the Upper Cenomanian-Early Turonian shallow-water rudist-rich Gattar carbonates. It outlines a clear inversion creating local exposed paleohighs on subsiding domains prior to the event, and characterized in seismic with toplap and onlap reflector terminations. An important erosion occurred on the created high lands and the eroded material that formed ‘the Rouana polygenic breccias’ is resedimented in half-grabens and grabens. Breccias infilling grabens suggesting a structural inversion event was fundamentally, controlled by syn-depositional E-W and NW-SE-trending faults. The structural inversion caused locally, a long time (~60My) hiatus in stratigraphy which appears to be enhanced by other tectono-sedimentary events, particularly salt tectonics.