Abstract
The early Toarcian of the Early Jurassic was characterized by an interval of global warming, enhanced continental weathering, and an oceanic anoxic event (T-OAE, ∼183 Ma). However, the changes in continental weathering intensity in low latitudes still remain poorly constrained. Here, we present strontium isotope (87Sr/86Sr) data of the Pliensbachian–Toarcian (Pl–To) interval from the Tibetan Himalaya, which was formerly located in the tropical/subtropical zone of the southeastern Tethys. An abrupt positive shift in 87Sr/86Sr starting around the Pl–To boundary and continuing during the interval of the negative carbon-isotope excursion (CIE) suggests enhanced continental weathering and increased terrigenous influx. Stratigraphically higher, the 87Sr/86Sr ratios gradually decrease during the recovery phase of the T-OAE CIE, suggesting a decline in continental weathering. Notably, the absolute values and positive-recovery pattern of 87Sr/86Sr data from bulk carbonate (pure micrite) of this study are not consistent with that from belemnites and brachiopods of Europe. Based on strong relationship between 87Sr/86Sr and diagenetic and silicate-derived Sr proxies, the absolute 87Sr/86Sr values here could have been affected to some extent by diagenesis and regional terrestrial input, and thus greatly amplified relative to those of Europe. However, the strontium-isotope positive-recovery pattern broadly corresponds with the pattern and interpretation of other weathering proxies (δ44/40Ca and 187Os/188Os) during the T-OAE. These observations suggest that the 87Sr/86Sr trend still likely reflects the real regional signal but was superimposed by global influence, although the data were biased by diagenesis. Taken together, the 87Sr/86Sr records from Tibetan Himalaya probably provide a useful insight into the regional weathering response, superimposed by the global weathering signal, to the events of the early Toarcian.
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