Publication: Sedimentary evolution of tectonically-controlled Cenozoic shallow marine glaucony, fluviatile and lacustrine-palustrine deposits at Bahariya region, Egypt
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2022-06
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Elsevier Science
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Abstract
The Cenozoic basin of the tectonically-active Bahariya region (Western Desert, Egypt) contains a unique paleoenvironmental, paleotectonic and paleoclimatic record displaying a large variety of sedimentary facies, stratigraphic discontinuities, and geochemical changes. This study deals with the sedimentary evolution and tectono-stratigraphic modelling of shallow marine Upper Eocene glaucony facies (Upper Hamra Formation) that changes upward into a sequence of Oligocene continental fluviatile sandstone-calcrete (Radwan Formation) and then into Miocene lacustrine-palustrine deposits (Continental Carbonate Unit). The tectonic instability of the Bahariya basin can be deduced from occurrence of sedimentary discontinuities, development of pedogenic features, and unconformable relations among rock units. Both sedimentation pattern and facies distribution seem to have been controlled by fault activity through time. Two types of glaucony facies (pelloidal and massive smectitic glaucony) were deposited in a narrow sub-basin along main faults reaching the basin center. These faults also conditioned the deposition of the Oligocene fluviatile sandstone and Miocene lacustrine-palustrine carbonates. A transition from greenhouse (global warming event of the Middle Eocene Climatic Optimum) to icehouse climatic conditions (Eocene-Oligocene climatic cooling) is probably represented by the deposition of the shallow marine glaucony facies during the Priabonian. Semi-arid to sub-humid conditions were dominant during the formation of the Oligocene calcretes and the Miocene lacustrine-palustrine carbonates. The latter carbonate deposits consist of basal thin-bedded chert deposits displaying hydro-plastic sedimentary structures that are possibly coeval with the Miocene basaltic extrusions along faulted and low-lying areas. We conclude that both paleoclimate and intraplate tectonic activity related to the Red Sea rifting influenced the pattern of sea level, continental drainage, sedimentation rate and clastic supply since the Priabonian up to the middle Miocene in the Bahariya basin.