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Chronostratigraphy of the late Ediacaran Urusis Formation, Nama Group, Namibia

The terminal Ediacaran Urusis Formation of the Nama Group (southern Namibia and northwestern South Africa) is a fossiliferous, mixed carbonate-siliciclastic succession with numerous silicified volcanic tuff interbeds. Studies of the Urusis Formation have historically focused on the Swartpunt area of southern Namibia, where post-depositional thrusting associated with the Gariep orogeny transported and emplaced the Formation as a series of thrust plates, which abut autochthonous Nama Group deposits to the east. Over thirty years of geochronological, chemostratigraphic and paleontological investigations have made the Swartpunt area a key reference section for terminal Ediacaran chronostratigraphy. Recent geochronological data from an expanded succession, exposed on the border between Namibia and South Africa, have cast doubt on the interpretation that ash beds in the vicinity of Swartpunt record depositional ages, possibly due to zircon reworking. The resulting implications for the temporal calibration of global terminal Ediacaran chemostratigraphy, as well as confidence in the maximum reported uncertainty of radioisotopic dates across geological time, are numerous. However, alternative regional structural complications that may resolve these issues have not yet been fully considered. Here, we build upon foundational observations of structural tectonics in the Swartpunt area, combining high resolution geological mapping, outcrop and drill core stratigraphy obtained through the ICDP GRIND-ECT project, carbonate carbon isotope (δ13Ccarb) chemostratigraphy, and new high precision radioisotope geochronology (zircon U-Pb chemical abrasion-isotope dilution-thermal ionization mass spectrometry, CA-ID-TIMS). We use these data to explore structural alternatives that may resolve the chronostratigraphy of the Urusis Formation without invoking insidious zircon reworking.

Details

Author
Fred Toby Bowyer1, Collen-Issia Uahengo2, Maria Ovtcharova3, Ulf Linnemann4, Dan Condon5, Bontle Mataboge6, Rachel Wood7
Institutionen
1University of Leeds, United Kingdom; 2University of Namibia, Namibia; 3University of Geneva, Switzerland; 4Senckenberg Naturhistorische Sammlungen Dresden, Germany; 5British Geological Survey, United Kingdom; 6University of Cape Town, South Africa; 7University of Edinburgh, United Kingdom
Veranstaltung
GeoSaxonia 2024
Datum
2024
DOI
10.48380/s6v4-b864
Geolocation
Namibia