Cerium negative anomaly just before the Permian and Triassic boundary event — The upward expansion of anoxia in the water column

A negative excursion of Ce and a succeeding steep decline in δ13C found just before the Permian and Triassic boundary (PTB) of Julfa area offer a geochemical constraint on the cause of the mass extinction event of PTB. The geochemical studies of recent anoxic basins like the Black Sea strongly suggest that the Ce negative excursion of these carbonate platform sequence indicates the buildup of anoxic water in the offshore realm. The suboxic water mass associated with the Ce negative anomaly zone migrated and invaded into shallow carbonate shelf around 600 thousand years before the PTB. This was followed by an anoxic water mass without Ce anomaly, and resulted in a steep decline in δ13C and then mass extinction of marine shelf biota.