Abstract
Sirt Basin, situated in the north-central part of Libya, is the largest oil producer in Africa. Present asymmetrical configuration of the Sirt Basin with southwestern flank being about 400km wide and northeastern flank about 120km wide, is a result of a single, broad, large scale, post Eocene subsidence. The axial position of deep Ajdabiya Trough represents the present axis of the Sirt Basin. All the structural features in the western flank of the basin (Hun Graben, Waddan Uplift, Zallah Trough, Az Zahrah-Al Hufrah Platform, Maradah Trough, Zaltan Platform) and eastern Sirt Basin (Amal Platform, Maragh Low, Ar Rakb High) are tilted and have moved progressively deeper towards the axis of the Ajdabiya Trough.
These major late Tertiary subsidence and tiltings are considered as one of the most important tectonic events of the Sirt Basin. The
peak of the oil generation from the Upper Cretaceous Campanian-Turonian shales as the principal petroleum source rocks in the Sirt Basin was mainly during the Oligocene-Miocene time when the burial depth of these source rocks was below a depth of 4000m. Therefore, generation, migration, and accumulations occurred mainly after the huge post Eocene subsidence, at a time when the present structural configuration of the basin had already been established.
Seismic signatures such as reversal block movements associated with larger fault displacements in the shallower horizons (some deeper pre-Upper Cretaceous blocks have thinner overlying Upper Cretaceous formations); scissor faults and/or strike slip faults as a result of differential block tiltings; localized lateral compressional forces in the shallow horizons of the trough areas (generating complicated structural pictures); and NW-SE and NE-SW trending late Tertiary structural lineaments are thought to be mainly due to the late Tertiary major subsidence and tiltings.