Contrasting Deep-water Records from the Upper Permian and Lower Triassic of South Tibet and British Columbia: Evidence for a Diachronous Mass Extinction

Remarkably different Late Permian–Early Triassic marine records are seen in sections from the western deep-water mar-gin of Pangea (Ursula Creek, British Columbia) and the high paleolatitude, southern margin of the Neotethyan Ocean (Se-long, South Tibet). The Ursula Creek section reveals the pro-gressive decline of seafloor oxygen values in the Changxingian Stage (loss of bioturbation, authigenic U enrichment, appear-ance of pyrite framboid populations), followed by the persistent development of euxinic conditions in the latest Changxingian and throughout the Early Triassic; an event that coincides with the disappearance of a siliceous sponge fauna and the loss of diverse radiolarian populations. The Selong section, which was located on a distal passive margin, records regres-sion and erosion in the mid-Changxingian, followed by a phase of deepening that began in the late Changxingian. The boundary interval is associated with a marked diversity in-crease due to the appearance of equatorial taxa (foraminifera, brachiopods, and sponges), suggesting warming without ex-tinction in marine waters at high southern paleolatitudes. Only in the late Griesbachian Stage are the diverse Permian holdovers eliminated, again at a level showing evidence for dy-soxia (thinly-bedded, authigenic U-enriched, pyrite-rich lime-stone). Thus, the end-Permian mass extinction is seen to be diachronous by half a million years or more, with late Chang-xingian extinction in Panathalassa coinciding with diversity increase associated the migration of warm-water taxa into the high southerly paleolatitudes regions of Neotethys.