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Geological Society, London, Special Publications; 2009; v. 326; p. 193-210;
DOI: 10.1144/SP326.10
© 2009 Geological Society of London

Articles

Field-based investigations of an ‘Infracambrian’ clastic succession in SE Libya and its bearing on the evolution of the Al Kufrah Basin

Daniel Paul Le Heron1,*, James P. Howard2, Aiyad Mohamed Alhassi3, Lester Anderson2, Andrew Morton2 & C. Mark Fanning4

1 Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK
2 CASP (Cambridge Arctic Shelf Programme), Department of Earth Sciences, 181A Huntingdon Road, Cambridge CB3 0DH, UK
3 Arabian Gulf Oil Company, Exploration Division, P.O. Box 263, Benghazi, Libya
4 Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia

* Corresponding author (e-mail: d.leheron{at}es.rhul.ac.uk)

Field-based investigation of ‘Infracambrian’ rocks cropping out on the eastern flank of Al Kufrah Basin (area 500 000 km2) reveals a an approximately 500 m-thick clastic succession of massive and cross-bedded sandstones, separated by 60 m-thick mudrock intervals. New zircon age data indicate a maximum age of deposition of approximately 950 Ma; furthermore, the absence of zircons of Pan-African age suggests a minimum depositional age older than the Pan-African Orogeny. Previously unreported folding and spaced cleavage affects these deposits to produce a pronounced NE–SW-striking tectonic grain that is interpreted to result from NW–SE-directed orthogonal compression during the Pan-African Orogeny. These Infracambrian rocks are therefore unlikely to be suitable analogues for weakly deformed strata shown to exist beneath the Cambro-Ordovician strata of the Al Kufrah Basin. Earlier work mapped a series of Infracambrian marble outcrops along strike of the clastic deposits; thin section petrography reveals that some of these are basic igneous rocks metamorphosed to greenschist facies. Interpretation of gravity data over the Al Kufrah Basin shows NE–SW-striking faults, parallel to outcrop structures, and secondary NW–SE faults. The data do not support earlier interpretations of a rhomboidal geometry in the deep subsurface of the basin, which has previously been attributed to strike-slip (pull-apart) processes. This research impacts on earlier suggestions that the Al Kufrah Basin opened as one of a series of en echelon pull-apart basins situated along a 6000 km-long shear zone known as the Transafrican Lineament, stretching from the Nile to the Niger Delta.





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