Titel: Tectonic and environmental perturbations at the Permian-Triassic boundary: insights from the Blue Nile River Basin in central Ethiopia
Maryam Mansouri1, Matthias Hinderer1, Laura Stutenbecker1, Guido Meinhold2, Enkurie L. Dawit3, Jasper Berndt4, Robert Bussert5
1Institute of Applied Geosciences, Technische Universität Darmstadt, Darmstadt, Germany; 2School of Geography, Geology and the Environment, Keele University, Keele, UK; 3Department of Geology, University of Gondar, Gondar, Ethiopia; 4Institut für Mineralogie, Westfälische Wilhelms-Universität, Münster, Germany; 5Institut für Angewandte Geowissenschaften, Technische Universität Berlin, Berlin, Germany
Veranstaltung: GeoKarlsruhe 2021
The Blue Nile River Basin contains a thick fluvio-lacustrine sediment succession of Permian to Jurassic age. Its evolution is linked to extensional tectonics during break-up of Pangea in the aftermath of the Carboniferous-Permian glaciation. We collected sandstone samples from several sections in order to study the tectonic evolution and possible impacts of environmental perturbation around the Permian-Triassic boundary. Based on thin-section petrography, bulk-rock geochemistry, heavy mineral spectra, and detrital zircon U-Pb ages we are able to establish a provenance model for the Permian-Triassic basin-fill evolution. The results reveal distinct differences between Lower Permian and Upper Permian to Upper Triassic sediments. The Lower Permian sandstones are rich in feldspar, carbonate cement, and relatively unstable heavy minerals like apatite and garnet. The chemical index of alteration and trace elements suggest little chemical weathering and proximity to the source area. Upper Permian to Upper Triassic sandstones, however, contain a large amount of ultra-stable heavy minerals, and geochemical data point to intense chemical weathering, reworking and/or recycling. In the Lower Permian, detrital zircon U-Pb age spectra are dominated by Pan-African and Tonian ages, whereas Upper Permian and Upper Triassic samples show a higher proportion of old zircons and young zircons (c. 1 Ga and c. <541 Ma) probably from intraplate magmatic rocks. The results show that during the Upper Permian and Triassic, uplift and unroofing was happening accompanied by climate change.
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