--> Abstract: Geologic Setting for Hydrocarbons in the Gafsa Trough of Central Tunisia, by M. Traut, J. K. Reed, S. Schamel, and K. B. Hassine; #91004 (1991)

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Geologic Setting for Hydrocarbons in the Gafsa Trough of Central Tunisia

TRAUT, M., Occidental International, Bakersfield, CA, J. K. REED and S. SCHAMEL,* Earth Sciences & Resources Institute, University of South Carolina, Columbia, SC, and K. BEN HASSINE, ETAP, Tunis, Tunisia

The Gafsa trough of onshore central Tunisia is one of the more interesting and underexplored features of North Africa. It is a 5-12-km deep, east-west-trending depression bounded by the Saharan flexure on the south and the Kasserine platform on the north. The geology of the Gafsa trough has been characterized with a series of regional stratigraphic and structural cross sections prepared from well data, and a set of depth and time structure maps prepared from an array of regional seismic lines.

The southern margin of the basin is a simple north- and northwest-dipping homocline broken by small down-to-basin normal faults. The northern margin against the Kasserine platform has considerably lower structural relief but is marked by a complex system of normal and reverse faults. The axis of the trough deepens to the east and west away from a broad saddle between Tozeur and Kebili. Late Cretaceous-Tertiary compression has further modified the configuration of the basin.

The Gafsa trough is developed on the erosionally beveled and rifted northern flank of the late Paleozoic Talamzane arch. Middle Paleozoic sediments, including organic-rich Lower Silurian shales, appear to underlie the basin. The trough is filled with several distinct successions of sediments: Permo-Carboniferous carbonates and clastics locally exceeding 3000 m in thickness; 100-2000 m of Triassic-Liassic basal sands and evaporites; and a 6000-8000-m-thick succession of Middle Jurassic-lower Tertiary marine to paralic carbonates and clastics. Basal Triassic and underlying Paleozoic strata are considered too deeply buried in the Gafsa trough to be reasonable exploration targets. The most prospective target is sand lenses within the Middle-Upper Jurassic clastic/carbonate basin fill. In he extreme eastern part of the basin, commercial quantities of hydrocarbons have recently been discovered in these sands.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)