On the Permo-Triassic Boundary: New Radiometric Age Data from the Karoo Basin, South Africa
Nicholas Drinkwater1, Andrea Fildani2, Amy Weislogel3, Tim McHargue2, Julie Fosdick4, David Hodgson5, and Steve Flint5
1ETC, Chevron, Houston, TX
2ETC, Chevron, San Ramon, CA
3Geology, University of Alabama, Tuscaloosa, AL
4Earth Sciences, Stanford University, Stanford, CA
5Earth & Oceanagraphic Sciences, Liverpool University, Liverpool, United Kingdom.
U-Pb ages on single grain zircons were determined using the Sensitive High Resolution Ion Microprobe Reverse Geometry (SHRIMP-RG) for samples recovered from 12 ash beds exposed in the southwestern part of the Karoo basin of South Africa. Samples were collected within the siliciclastic submarine succession of the Permian-aged Ecca Group in the SW sector of the basin. We have determined distinct age populations at 272-277, 266 and a 255-257 Ma, with the youngest recorded ages (from submarine slope deposits of the upper Skoorsteenberg and Laingsburg Formations) straddling the latest Permian to the earliest Triassic. Contrary to previous studies, these new data suggest that submarine slope deposition was still ongoing in the southwestern basin at a time when fluvial floodplain conditions have been interpreted elsewhere in the Karoo basin. In addition, these data suggest the presence of an arc of solely Permian age, with implications on the convergent setting of this sector of the paleo-Gondwana margin. This new research has significant implications on the diachronous sedimentary fill history of the basin, its evolution and mechanism, and to the current understanding of the nature of deposition at the time of the Permian to Triassic boundary in the Karoo basin.
AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery