HOW QUICKLY DID PRIMARY PRODUCERS RECOVER FROM THE PERMIAN-TRIASSIC MASS EXTINCTION? EARLIEST TRIASSIC (GRIESBACHIAN) PRODUCTIVITY ESTIMATES FROM THE PEDIGREE-RING BORDER-KAHNTAH RIVER AREA (WESTERN CANADA SEDIMENTARY BASIN) NORTHWESTERN ALBERTA AND NORTHEASTERN BRITISH COLUMBIA

The Permian-Triassic extinction was the most devastating biotic crisis in Earth history. The timing and shape of recovery from this event is still poorly understood, although it appears to have been strongly controlled by paleoenvironmental factors. Relatively little is known about the recovery of primary producers, which is crucial, since the base of the food web must recover before any macrofaunal rebound can occur. The Western Canadian Sedimentary Basin (WCSB) contains a variety of sedimentary depositional environments ranging from shoreface to basin and was deposited across the entire Early Triassic recovery interval, making it ideal for paleoenvironmental and paleoproductivity reconstructions. Five cores (16-8-86/20W6, 16-33-84/18W6m, B-24-B/9-H-16, C-74-E/94-H-16, and C-78-I/94-H-9) from the Pedigree-Ring Border-Kahntah River area, located northwestern Alberta and northeastern British Columbia, were examined to determine palaeoproductivity during the earliest Triassic (Griesbachian). Paleoproductivity was estimated by measuring %TOC (total organic carbon) and %TIC (total inorganic carbon, or carbonate carbon) using the loss on ignition method of Dean (1974); while many factors control the accumulation of organic matter, we assume that organic matter enrichment has to be at least partially due to the reestablishment of primary productivity.

A total of 241 Samples were analyzed. Results indicate %TOC contents for the cores range from 3-5% suggesting a rapid and sustained recovery of primary producers during the Griesbachian. %TIC values typically range from 5-15%, although spikes in %TIC can reach nearly 90% in some cores. Much of the carbonate within the WCSB is thought to be detrital in nature (Davies, 1997), and therefore %TIC values reflect detrital (i.e., sand) input as opposed to skeletal input; spikes in %TIC correspond to sandy units, and represent turbidites. The results of this study imply that primary producers were relatively unaffected by the extinction and subsequent environmental stress. However, since many factors can affect TOC values, future research will estimate primary productivity using trace elements (Ba, Cu Zn), as well as paleoxygenation (Mo, U, V) to determine the robustness of post-extinction recovery and its relationship to environmental conditions.