BASIN ARCHITECTURE DURING THE CAMBRIAN EXPLOSION, DEATH VALLEY AREA, CALIFORNIA

The Lower Wood Canyon Formation (LWC), located in the Death Valley region contains the Precambrian-Cambrian boundary in some sections. The regional architecture of the mixed siliciclastic-carbonate formation is complex, and it is not clear whether the boundary is preserved regionally. The LWC thins from several hundred meters in Boundary Canyon (Death Valley National Park) to only 10 meters in the Soda Mountains to the southeast, and is absent altogether further to the southeast. The Boundary Canyon section contains four distinct carbonate beds, with the Precambrian-Cambrian boundary (denoted by the first appearance of Treptichnus pedum) residing in the siliciclastics between the third and fourth carbonate beds. The Soda Mountains section contains only one carbonate bed, and it is not readily apparent if the PC-C boundary is preserved or how the thin section correlates to the much thicker sections to the northwest.

The Precambrian-Cambrian boundary is accompanied by a sharply negative global δ13C excursion that can be used as a marker to determine how the carbonate units in the LWC correlate across the region. The full excursion is recorded at Boundary Canyon (the lower carbonate units record the initial negative excursion and the upper carbonate bed records the return to positive δ13C values). Only the rising limb of the return to positive values is recorded at the Soda Mountains locality, suggesting that the carbonate unit in the Soda Mountains correlates to the uppermost part of the thicker deposits to the northwest. The δ13C signature reveals that the Precambrian-Cambrian boundary may be preserved in the Soda Mountains and deserves further investigation.