Strat?graph?c and Structural Controls on the D?str?but?on of S?lur?an Source Rocks in Northern Gondwana: Results of a F?eld Based Study in Southern L?bya

Rhuddanian transgressive black shales deposited across northern Gondwana include world class hydrocarbon source intervals in North Africa, Arabia and southern Turkey. The highest TOC values are usually concentrated in one (or more) layers in the lower part of the Silurian succession. These source units are commonly referred to as hot shales because high TOC values are often coincident with elevated uranium contents. Hot shales were deposited during the early stages of the Silurian marine transgression and their distribution was controlled by relief on the underlying depositional surface (Lüning et al., 2003). Understanding how glacial and tectonic processes influenced topography on the pre-Silurian depositional surface and how such topography influenced the deposition of hot shales can therefore reduce risk during hydrocarbon exploration.

Southern Libya contains part of two large sedimentary basins, the Murzuq and Kufra basins which are separated by a basement uplift. The northern part of the Murzuq basin contains a proven hydrocarbon system sourced from Silurian shales (the Tanezzuft Formation) and produced from sandstone reservoirs in the glacial Mamouniyat Formation and shallow marine/fluvial Hawaz Formation. Both the southern Murzuq Basin and Kufra Basin contain similar sediments to those in the northern Murzuq Basin and they are therefore considered prospective for hydrocarbons. The presence, distribution and quality of Silurian source rocks is the major risk factor during exploration within these basins.

CASP has completed a field-based research project in the southern basins of Libya. The objectives of this project were 1) to identify Silurian source rocks, 2) to quantify their source potential and, 3) to understand the structural and sedimentological controls on their distribution. Fieldwork was undertaken on Paleozoic outcrops on the margins of the Kufra Basin (Jebel Dalma, Jebel Asba and Jebel Eghei) and the Murzuq Basin (Dor el Gussa and Mourizidie).