Chapter 5 - Stratigraphy Part Three: Cainozoic

Abstract

This chapter focuses on the rift grabens in the Sirt Basin that played a part in late Cretaceous sedimentation, and had been largely in filled by the end of the Maastrichtian, with the topography of the intervening horsts that have been leveled to the extent that only very small islands are left. Nevertheless, gentle tectonic forces during Palaeocene time resulted in the gradual tilting of northern-western Libya towards the east. The Hamadah al Hamra became emergent by the end of the Palaeocene whilst subsidence continued in the Sirt Basin. This regional tilting became one of the most persistent features of Cainozoic deposition in Libya. Cainozoic outcrops are widespread in Libya, and shows predominently shallow-water marine lithologies. These same rocks contain major oil and gas accumulations in the subsurface in a variety of different facies including reefs, bioherms and nearshore sands. They contain excellent shale and evaporite seals, but source rock quality is generally poor. Most of the potential Cainozoic source rocks are lean, and they are usually immature.