Stratigraphy and Sedimentology of Upper Cretaceous to Upper Palaeocene Succession in Zimam Formation Along Wadi Tar al Kabir, NW Libya

Abstract

The Upper Cretaceous to Upper Palaeocene rocks of the Zimam Formation along the southwestern escarpment of the Hun Graben of NW Libya have been stratigraphically investigated from two stratigraphical sections in wadi Tar al Kabir. The field investigations led to the recognition of three members, from the oldest to the youngest, the Lower Tar Member, the Upper Tar Member and the Had Member. Eight sedimentary facies were distinguished at outcrop-scale and several microfacies were recognized and the outcome indicates that the depositions of the Zimam Formation are corresponding to two transgressive-regressive sedimentary cycles. The first cycle is attributed to the Lower Tar Member in which small planktonic foraminifera is quite common in the Campanian whereas the larger benthic foraminifera, namely, Omphalocyclus macroporus and Siderolites calcitrapoides are abundant in the Maastrichtian. The last occurrence of the latter two taxa, however, was used to delineate the contact between the Maastrichtian and Danian stages in the studied sequence. Up-sequence the sediments of the Upper Tar Member along with the overlying Had Member correspond to the second transgressive-regressive sedimentary cycle. Herein, the Upper Tar Member is enriched by small benthic foraminifera; Neoeponides duwi and Cibicides cf. libycus, and has been ascribed to the Danian (Lower Palaeocene). The reaming sediments of Zimam Formation, however, are belonging to the overlying Had Member and is tentatively ascribed to the Selandian (Upper Palaeocene) based on the last occurrence of the Danian fauna and the total range of the codiacean algae Ovulites morelleti.