Disruption of playa–lacustrine depositional systems at the Permo-Triassic boundary: evidence from Vyazniki and Gorokhovets on the Russian Platform
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Permo-Triassic sections at Vyazniki and Gorokhovets provide evidence on terrestrial events at, or close to, the Permo-Triassic boundary, the time of the largest ever mass extinction. The sedimentary succession records the overrun of a muddy playa–lacustrine depositional system by major channel belts transporting sand-grade sediments. Biostratigraphy of sections at Vyazniki and Gorokhovets (Zhukov Ravine) shows that this event occurred either at the very end of the Permian or 8 m above in the sections. The timing and nature of this event, which records increased sediment flux from the Ural Mountains, is closely comparable with that from the Southern Uralian Foreland Basin. The Vyazniki and Gorokhovets sections are 800 km from the mountain front and in a separate depositional basin, which strengthens the case that increased sediment flux from the Urals at the Permo-Triassic boundary is related to devegetation of upland catchments (increasing sediment yield) and a switch toward low-frequency but high-magnitude discharge events (increasing sediment delivery). The interbedding of fluvial and aeolian deposits provides further evidence for climatic instability and extremes in the Early Triassic.