The Permian-Triassic boundary sections in northern Vietnam (Nhi Tao and Lung Cam sections): Carbon-isotope excursion and elemental variations indicate major anoxic event

The shape of the Ce/Ce* curve suggests that the redox conditions of depositional environments in both sections fluctuated, but that there was a decline in oxygenation with time, possibly into the anoxic range. Distinct negative anomalies coincide with the onset of the carbon isotope shifts, which might indicate additional influx of anoxic waters. The Th/U ratios in both sections are mainly less than 2, reinforcing this possibility. Upwelling of anoxic deep-ocean water onto the shallow carbonate platform at Nhi Tao and Lung Cam at the end of the Permian, with related disastrous consequences for the biosphere, is indicated by our data.