Roger M.H. Smith, Peter D. Ward; Pattern of vertebrate extinctions across an event bed at the Permian-Triassic boundary in the Karoo Basin of South Africa. Geology ; 29 (12): 1147–1150. doi: https://doi.org/10.1130/0091-7613(2001)029<1147:POVEAA>2.0.CO;2
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The extinction of vertebrates around the time of the Permian-Triassic boundary has long been regarded as a gradual event occurring over millions of years. Our new field investigations of fluvial strata in the central and southern Karoo Basin of South Africa have revealed the presence of an event bed coinciding with a mass extinction of terrestrial fauna and flora. The bed is in a sedimentary sequence that is marked by a reddening of flood-plain mud rocks and a change from high- to low-sinuosity river channel systems. Here we show that the pattern of vertebrate taxa disappearing below this boundary and the subsequent appearance of new taxa above the boundary are consistent with a relatively sudden, possibly catastrophic event, perhaps of 50 000 yr duration or less.