第八届青年地学论坛

The early Toarcian of the Early Jurassic was characterized by an interval of global warming, enhanced continental weathering, and oceanic anoxic events (T-OAE, ∼183 Ma). However, the changes in continental weathering intensity in low latitude and its direct relationship with oceanic deoxygenation remains poorly constrained. Here, we present strontium isotope (⁸⁷Sr/⁸⁶Sr) data of the Toarcian interval from the Tibetan Himalaya, which was formerly located in the tropical/subtropical zone of the southeastern Tethys. The ⁸⁷Sr/⁸⁶Sr ratios of Nianduo display an abrupt positive shift beginning around the Pliensbachian–Toarcian (Pl–To) boundary and reach maximum values (~ 0.70782) in the negative interval of the T-OAE CIE (~ −5.6 to 20.4 m), suggesting enhanced continental weathering and terrigenous influx in the Tethys Himalaya. Stratigraphically higher, the ⁸⁷Sr/⁸⁶Sr of Nianduo gradually decrease to background ratios during the recovery phase of the T-OAE CIE, suggesting decline in continental weathering. These observations have a great corresponded with δ^44/40Ca records from Peniche and ¹⁸⁷Os/¹⁸⁸Os records from Bighorn Creek. Notably, the ⁸⁷Sr/⁸⁶Sr curves of the Europe shelf and western Tethys increase gradually during the T-OAE CIE and maintain persistent positive values. These distinctions are probably due to differing degrees of hydrographic restriction. Additionally, the discrepancy in absolute ⁸⁷Sr/⁸⁶Sr values is due to the possibility that the Tethys Himalaya, Europe Shelf, and western Tethys could have suffered different intensities of continental weathering during the early Toarcian.
The coupled relationship between ⁸⁷Sr/⁸⁶Sr ratios and geochemical data suggest that: the ⁸⁷Sr/⁸⁶Sr from the European shelf, western Tethys, and Tethys Himalaya all represent the global seawater signal. Continental weathering increases the inflow of terrigenous influx into the ocean, causing high ⁸⁷Sr/⁸⁶Sr ratios and possibly elevating primary production, which consumes the dissolved oxygen and then triggers global oceanic anoxia.

Toarcian Oceanic Anoxic Event,Strontium isotopes,Continental weathering,Tibetan Himalaya