High-resolution carbonate spurious thermoluminescence records during the Permian-Triassic transition from Meishan section: implication for sea-level change

The Permian-Triassic (P-Tr) crisis was the largest mass extinction of the Phanerozoic and eliminated over 90% of marine species. Widespread regression took place in whole South China during the P-Tr transition. Timing of the low ebb of this regression was pinpointed to the mass extinction interval. However, how sea-level changed on the orbital time scale during the P-Tr transition remains unknown. Here, we present high-resolution carbonate spurious thermoluminescence records across the P-Tr boundary from Meishan section. Carbonate spurious thermoluminescence is probably associated with chromophoric dissolved organic matter (CDOM) absorbed in carbonate crystals during the depositional stage. The distribution of CDOM in modern ocean exhibits a maximum in lower euphotic zone (~80 m in depth) which co-varies with the sea-level. The carbonate succession in the Meishan section is generally considered to have accumulated on a carbonate slope in a depth about 100-200 meters. When sea-level drops, the decreasing maximum zone of CDOM gradually approaches the depositional location of Meishan section, which finally increase carbonate spurious thermoluminescence. In contrast, when seal-level rises, carbonate spurious thermoluminescence will decrease. Therefore, sea-level oscillation can influence contemporary carbonate spurious thermoluminescence. Carbonate spurious thermoluminescence in Meishan section shows low values in the uppermost interval of Bed 23 and the lower and middle part of Bed 24 and begins rising up at the uppermost interval of Bed 24. It keeps high levels in Beds 27 and 29, and finally drops in Bed 30. This overall variation possibly accords with the widespread regression happened in whole South China during the P-Tr transition. Moreover, carbonate spurious thermoluminescence is characterized by prominent periodic variations, co-varing with magnetic susceptibility, which possibly reflects sea-level changes on the orbital time scale.