Amelioration of marine environments at the Smithian–Spathian boundary, Early Triassic

[摘要] The protracted recovery of marine ecosystems followingthe Permian–Triassic mass extinction may have been caused, in part, byepisodic environmental and climatic crises during the Early Triassic, amongwhich the Smithian–Spathian boundary (SSB) event is conspicuous. Here, weinvestigate the SSB event in the Shitouzhai section, Guizhou Province, SouthChina, using a combination of carbonate carbon (δ¹³C_carb)and carbonate-associated sulfate sulfur isotopes (δ³⁴S_CAS), rare earth elements, and elemental paleoredox andpaleoproductivity proxies. The SSB at Shitouzhai is characterized by a+4‰ shift in δ¹³C_carb and a −10 to−15‰ shift in δ³⁴S_CAS, recordingnegative covariation that diverges from the positive δ¹³C_carb−δ³⁴S_CAS covariation that characterizes most of the Early Triassic. This pattern is inferred to reflect an increasein organic carbon burial (e.g., due to elevated marine productivity)concurrently with the oxidation of isotopically light H₂S, as the result ofenhanced vertical advection of nutrient- and sulfide-rich deep waters to theocean-surface layer. Enhanced upwelling was likely a response to climaticcooling and the reinvigoration of global-ocean overturning circulation at theSSB. Coeval decreases in chemical weathering intensity and detrital sedimentflux at Shitouzhai are also consistent with climatic cooling. A decline inmarine biodiversity was probably associated with the late Smithian thermalmaximum (LSTM) rather than with the SSB per se. The SSB thus marked thetermination of the extreme hothouse conditions of the Griesbachian–Smithiansubstages of the Early Triassic and is significant as a record ofaccompanying climatic, environmental, and biotic changes. The ultimate causeof the SSB event is uncertain but may have been related to a reduction inintrusive magmatic activity in the Siberian Traps large igneous province.

[学科分类] 地球化学与岩石