Cenozoic Subsidence and Lithospheric Stretching Deformation of the Ajdabiya Trough Area, Northeast Sirt Basin, Libya*

The Ajdabiya Trough is a failed rift that represents the deepest part of the Sirt Basin, Libya (Figure 1). It is postulated that more than 7000 m of Mesozoic-Cenozoic sediments accumulated in this depocenter (Rusk, 2001; Hallett, 2002). The Ajdabiya Trough has significant petroleum potential. However, most exploration activity has focused on the relatively shallow basin flanks and adjacent platforms. As a result, the structural and stratigraphic development of the central Adjabiya Trough is poorly known. The aim of this study is to use 2D seismic reflection profiles, potential field data and information from exploration wells to illustrate key features of the tectonic evolution across the Ajdabiya Trough. In particular, these data are used to determine the tectonic subsidence during the latest syn-rift (Cretaceous to Palaeocene) to post-rift periods, and to estimate syn-rift crustal stretching. Our study builds on previous research by Gumati (1981), Gumati and Kanes (1985), van der Meer and Cloetingh (1993) and Abadi et al. (2008). Subsidence is calculated by assuming 1D Airy isostatic equilibrium, which allows backstripping based on sedimentary thicknesses, horizon ages, lithologies, and paleo-water depths obtained from well information and crosschecked against sediment isopach and structural maps. The combination of these two approaches allows quantification of tectonic and total subsidence and their relationship to fault activity during the syn- to post-rift stages. The syn-rift sedimentary package has not been encountered or entirely drilled in most of the wells. For this reason, a pseudo (synthetic) well derived from 2D seismic interpretation has also been modeled. In addition to the syn-rift package, the location of the pseudo-well was chosen in order to evaluate the history of the deepest parts of the basin, which are not yet drilled.