The Permian-Triassic (P-T) extinction is documented geochemically in a marine sequence deposited in a basinal setting at Williston Lake, northeastern British Columbia, by using elemental and isotopic organic geochemical data from well-preserved sedimentary rocks. The δ13C values of kerogens in the rocks exhibit a sudden shift at the P-T boundary from latest Permian values of -29‰ ± 1‰ (PDB) to a minimum of -32.6‰ 2 m above the P-T boundary and then back to the Permian value 4 m above the P-T boundary. After considering various factors, we conclude that reduced surface-water primary productivity following the P-T mass extinction is largely responsible for the observed δ13C shift. The abruptness of the δ13C shift in a sequence of continuous deposition argues that the strong pulse of extinction at the P-T boundary was sudden rather than gradual. Marine primary productivity did not recover until at least 50 to 100 ka after the time of the P-T boundary, so a higher atmospheric pCO2 in the earliest Triassic may have resulted from buildup of dissolved CO2 owing to reduced photosynthetic carbon demand in the surface water.

First Page Preview

First page PDF preview
You do not currently have access to this article.