TECTONIC SUBSIDENCE OF THE SIRTE BASIN, LIBYA

Abstract

The Sirte Basin of Libya has a history of faulting and differential subsidence brought about by lithospheric extension during a 25 MM (million) year period beginning in the Late Cretaceous. The first phase of extension and initial subsidence, with faulting and graben formation, occurred from Cenomanian to Campanian times. Following extension. there occurred widespread thermally‐driven subsidence from Maastrichtian through Eocene and Oligocene times, accounting for about half of the total subsidence. Details of basin subsidence, sediment accumulation rates. and facies variations have been reconstructed for the northern Sirte Basin from a suite of approximately 100 completion well logs and numerous seismic lines. These show that at various times in the Late Cretaceous and Paleocene‐Eocene, renewed differential subsidence followed fault reactivation. Tectonic subsidence maps show a sysrematic SE to NW shift in the loci of maximum and minimum subsidence, which parallels the structural trend of the basin. The greatest subsidence observed in the Sirte Trough is 2,085 meters, whereas subsidence of the horsts is generally less than 1,000 meters. The stretching factor (β: in the range of 1.1 to 1.75). corresponds to an extension of 10–75%. with an average of less than 50%. The greatest stretching is associated with the central graben.