Structural Development of the Western Margins of the Sirte Basin

J. M. Anketell, S. M. Kumati

The Sirte basin, situated in north-central Libya, is a broad, northwest-trending embayment comprising a complex of small horsts and grabens. The basin was initiated in the early Cretaceous by collapse of the Tibisti-Sirte arch and underwent further faulting, notably in Late Cretaceous to early Paleocene time and during the latter part of the Eocene. Throughout the greater part of the region, faults are obscured by Neogene cover; however, west of the Dahra-Hofra horst they are exposed. The last major phase of faulting in this region is late Lutetian to early Priabonian in age with minor reactivation during Oligocene and Miocene time. A phase of intra-Lutetian movement is also recognized. Following deposition of open marine limestones and chalks in the early Lutetian, the r gion was tilted toward the east-northeast with emergence and development of a complex system of east-flowing drainage channels which sculpted the emerging surface. The channels are wide but shallow, ranging up to 2 km wide and 10 m deep. This phase of movement and intraformational erosion was terminated by slow subsidence and/or transgression with development of restricted marine shales. The late Eocene faults which delineate the western margin of the Dahra horst throw down to the west and display a complex en echelon pattern. They are interpreted in terms of Riedel shear mechanics related to oblique-slip reactivation of basement shears. Counterclockwise orientation of the shears indicates they formed in response to sinistral slip.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.