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Nature and stratigraphic architecture of the Devonian succession in the Ghadamis basin of western Libya

Abstract : During Palaeozoic times, the structuring of North Gondwana induced the formation large epicratonic platforms in North Africa. These platforms are comprised of extensive, shallow sub-basins or swales separated by smooth tectonic arches. The sub-basins were slowly subsiding whereas the arches were periodically eroded by tectonic uplift or eustatic sea-level drops. The resulting architecture of sedimentary rocks into these basins is characterized by thin, laterally extensive, sediment wedges truncated by large unconformities representing long time gaps. The aim is here to illustrate this architecture from the example of the Devonian rocks preserved in the Ghadamis basin and along the Gargaf Arch in NW Libya, and to discuss the origin and the influence of the parameters that control both the sequence architecture and the reservoir distribution on such large cratonic areas. The Devonian rocks exposed along the Gargaf arch in Awaynat Wanin area are characterized by the intercalation of sandstones, claystones and shales interbedded with few carbonate beds. They represent a broad range of depositional environments from proximal fluvial to offshore marine shelf organized into a complex stack of six 30 to 80m-thick, unconformity-bounded, transgressive-regressive sequences. The overall architecture of the sedimentary units and depositional environments in the Ghadames basin is reconstructed from the correlation of field observations and subsurface data (wells and seismic data). They show an overall thinning out of the sandstone units in the shale units, northwestward, in a dip direction along hundreds of kilometres, but a better consistency across strike (except for the Frasnian-Famennian sandstones). Offshore marine, organic-rich shale units are prominent marker beds into the whole basin. The most important are the Eifelian Emgayet shales and the Frasnian radioactive shales and limestones. These units are both seal and secondary source rocks units.
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Conference papers
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Submitted on : Thursday, April 16, 2009 - 1:49:57 PM
Last modification on : Tuesday, December 3, 2019 - 5:24:10 PM

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M. Ben Rahuma, Jean-Noël Proust, R. Eschard. Nature and stratigraphic architecture of the Devonian succession in the Ghadamis basin of western Libya. Sedimentary Basin of Libya, 4th Symposium, The Geology of southern Libya, Nov 2008, Tripoli, Libya. ⟨insu-00375938⟩

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