The Geochemical Records of the Mid-Cretaceous in Tibet and Their Implications to the OAEs

It is well known that a few Oceanic Anoxic Events（OAEs）occurred with extreme warming climates during the Middle Cretaceous. Although many models have been proposed[ e.g. reference 1-4], the mechanisms for the occurrences of the OAEs with extreme climates remain unclear. Here, we provide inorganic carbon isotope (δ¹³C), iron speciation chemistry and trace element records for the later Aptian and the Cenomannian OAEs in the Southern Tibet. Our results indicate that these OAEs in the Tibet were featured by extremely negative δ¹³Canomalies(-15‰~-35‰),rich LREE with Eu positive anomalies and low iron ratios which suggest oxic bottom water conditions for the depositions .Accordingly, we propose that large-scale releases of methane may have greatly consumed dissolved oxygen and other oxidants in the water columns with increasing carbon emissions, which may at least partially contributed to the multiple developments of the oceanic anoxia and extreme warming in the middle Cretaceous.

Reference:

1. Larson, R.L. and E. Erba, Onset of the Mid‐Cretaceous greenhouse in the Barremian‐Aptian: Igneous events and the biological, sedimentary, and geochemical responses. Paleoceanography, 1999. 14(6): p. 663-678.

2. Weissert, H., et al., Correlation of Early Cretaceous carbon isotope stratigraphy and platform drowning events: a possible link? Palaeogeography, Palaeoclimatology, Palaeoecology, 1998. 137(3): p. 189-203.

3. Erbacher, J., et al., Increased thermohaline stratification as a possible cause for an ocean anoxic event in the Cretaceous period. Nature, 2001. 409(6818): p. 325-327.

4. Wilson, P.A. and R.D. Norris, Warm tropical ocean surface and global anoxia during the mid-Cretaceous period. Nature, 2001. 412(6845): p. 425-429.