High-precision temporal calibration of Late Permian vertebrate biostratigraphy: U-Pb zircon constraints from the Karoo Supergroup, South Africa
Bruce S. Rubidge et al. (Jahandar Ramezani, corresponding), Bernard Price Institute for Palaeontological Research, School of Geosciences, University of the Witwatersrand, PO Wits, Johannesburg 2050, South Africa; and Dept. of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. Posted online 4 Jan. 2013; http://dx.doi.org/10.1130/G33622.1.
The continental sedimentary rocks deposited in the Karoo Basin of South Africa preserve a remarkable fossil record of reptile and mammal ancestors that elucidate the evolutionary and biodiversity changes in the crucial geologic period between the Permian and the Jurassic (270-180 million years ago). Stratigraphic zonations based on the South African tetrapod fossils have global applicability in correlating continental deposits throughout the Pangean supercontinent. A major limiting factor, however, has been a lack of independent and reliable age constraints for the Karoo biozones. Bruce S. Rubidge and colleagues report on the discovery of volcanic ash deposits interbedded with four lower Permian biozones of the Karoo Supergroup and their geochronology based on high-precision U-Pb analyses by the CA-TIM method. The calibrated biostratigraphy improves understanding of basin development, as well as rates of vertebrate evolution at a time when the earliest reptile lineages were being established. It also allows correlation to the marine realm with enormous implications for global patterns of faunal evolution, including mass extinction events of the Permian Period and their possible driving mechanisms.
Oxygen isotope composition of meltwater from a Neoproterozoic glaciation in South Ch
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