Biodiversity across the Guadalupian-Lopingian Boundary: first results on the ostracod (Crustacea) fauna, Chaotian section (Sichuan Province, South China)

The Middle Permian-Late Permian boundary (Guadalupian-Lopingian boundary, GLB) interval is characterised by important faunal assemblage changes. This extinction-turnover episode is considered by some authors to be the first step of the end-Permian biodiversity drop. The forty-five meters thickness of sediment encompassing the GLB in Chaotian section (Sichuan Province, South China) was sampled and processed for ostracod study. This study presents the first analysis of ostracod faunas in the GLB interval. A total of 154 species belonging to 29 genera are identified. Three species are described as new: Bairdia chaotianensis Zazzali, n. sp., Microcheilinella wujiapingensis Zazzali, n. sp., Microcheilinella pagodaensis Zazzali, n. sp. All the ostracods discovered in the section belong to shallow marine taxa. So these results are not consistent with previous interpretations (lagoonal environment or deep water setting) based on other evidences. Abundance and diversity present a rapid and noticeable decline in the Early Capitanian. Recovery is then recorded about three meters above the GLB. At specific level, a 93% extinction rate and a 96% turnover rate are recorded at the GLB. Moreover, Palaeocopida, straight dorsal border ostracods known to progressively disappear from the Late Permian to the basal Middle-Triassic, are here less abundant and diversified after the GLB. This could reflect the first step of their disappearance at the end of the Palaeozoic.