Environmental instability prior to end-Permian mass extinction reflected in biotic and facies changes on shallow carbonate platforms of the Nanpanjiang Basin (South China)

Shallow carbonate platforms exhibit major changes in faunal composition and facies types during the latest Permian and earliest Triassic. Although the microbialites that developed following the latest Permian mass extinction (LPME) have attracted wide attention, temporal variations in shallow-platform facies and faunas prior to the LPME have been less thoroughly studied. Here, we analyze diversity patterns and variation in skeletal composition in three Upper Permian sections from isolated carbonate platforms of the Nanpanjiang Basin. In addition to the well-known transition from fossil-rich Upper Permian limestones to fossil-poor Permian-Triassic boundary (PTB) microbialites, these sections exhibit several distinct changes that predate the LPME. First, foram faunas show a shift from non-fusulinid-dominated to fusulinid-dominated communities in the <1-m interval below the LPME horizon of each section, reflecting a shallowing trend over ~20–30 kyr preceding the mass extinction. Second, a “foram gap” and concurrent “detrital event” are observed below the LPME in all three sections, recording a rapid influx of detrital siliciclastics that predated the mass extinction by <60 kyr. These features reflect a degree of marine environmental instability prior to the end-Permian mass extinction. The sudden influx of siliciclastics may represent an early perturbation to terrestrial ecosystems linked to incipient Siberian Traps magmatism, resulting in secondary effects in marine environments through increased sediment yields.