Jeffrey U. Kraus2
(1) University of Houston, Houston, TX
(2) Mobil New Exploration and Producing Ventures, Dallas, TX
Abstract: Tectonic significance of the voluminous Lower Paleozoic quartz-rich sandstones of North Africa and the Arabian Peninsula
Well known Cambro-Ordovician reservoirs of North Africa and Arabia are part of an extensive and unusually thick sequence of dominantly siliciclastic rock deposited during the extensional collapse of the Panafrican mountain range. Between 10 and 20 million cubic kilometers of quartz-rich sandstones were deposited in a variety of environments slightly above and slightly below sea level over an area of approximately 10 million square kilometers. These sandstones have an average thickness of about 1500 meters, except in areas where significant erosion has occurred and in the Oman Salt Basin where their thickness is anomalous.
We address two fundamental aspects of this extensive sand-rich system; the processes responsible for depositing such a large volume of sand, and the mechanisms necessary to create basins in to which those sediments were deposited. Sands were derived from mountains and orogenic plateaus uplifted by the Panafrican assembly of Gondwana and were transported northward by fluvial systems. Cambro-Ordovician strata record these fluvial systems and the shallow marine environments in to which they flowed. The quartz-rich nature of the sands is considered to be the result of provenance, transport mechanism, and the pre-land plant weathering regime. The "steer's horns" geometry of the Cambro-Ordovician reflects its origin as part of the rift development processes associated with large-scale tectonic escape along regional NNE-oriented strike-slip faults. The formation of large rifts thinned the tectonically thickened Panafrican lithosphere by roughly a factor of two. The newly thinned lithosphere then began to thermally subside creating space for thick Cambro-Ordovician sandstones to accumulate.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana