Stratigraphy, Paleomagnetic Results, and Preliminary Palynology across the Permian-Triassic (P-Tr) Boundary at Carlton Heights, Southern Karoo Basin (South Africa)
The most severe mass extinction of marine species and terrestrial vertebrates and plants is associated with the Permian-Triassic (P-Tr) boundary (~253 Ma). In order to investigate the relative timing of the biotic crises in terrestrial and marine environments, we studied the stratigraphy, paleomagnetism, and palynology of the Carlton Heights section in the southern Karoo Basin, South Africa. Stratigraphic and palynological study at Carlton Heights revealed the abrupt disappearance of Late Permian gymnosperm taxa and replacement by Triassic palynomorphs just below the boundary between the Balfour Formation and the Katberg sandstone, at a layer characterized by abundant remains of fungi. This “fungal spike” occurs globally in marine and terrestrial P-Tr boundary sections, and thus can be used to correlate the extinctions of marine fauna and terrestrial land plants and vertebrates in the P-Tr boundary interval. Our results suggest that the extinction of mammal-like reptiles at the end of the Permian may have preceded the fungal event and land-plant extinction within an interval of less than ~100,000 years, and possibly less than ~25,000 years.
Paleomagnetic data confirm multiple magnetizations of Karoo Basin P-Tr strata during Jurassic intrusive events. Mildly altered sedimentary strata, more altered sediments, and an intrusive dike all showed normal polarity magnetization stable to about 500-575°C and 60 mT; reversed polarity was exhibited primarily as trends at high demagnetization temperatures and field strengths. The normal polarity directions in the sedimentary and igneous rocks are statistically identical to the mean Jurassic direction during Karoo igneous activity. A Permian-Triassic magnetic signature is no longer identifiable.
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