NEW EVIDENCE FROM THE CAMBRIAN EXPLOSION IN THE CAROLINA TERRANE

The Cambrian Explosion was a geologically rapid diversification of animal life that marked the transition between the Precambrian and Phanerozoic eons. Increasing atmospheric oxygen both a) led to an influx of trace metals and other ions into the global ocean, and b) allowed oxygenated seawater to store these metals at higher concentrations. The relationship between oxygenation, increasing trace metal inventories, nutrient cycling, and early animal diversification remains an active area of research. The goal of this study is to determine when oxygenation of the Iapetus Ocean occurred relative to the diversification of animals. To do this, we collected samples from the metasediments of the Albemarle Group. These strata are associated with the Carolina Terrane, a peri-Gondwanan volcanic arc that formed during the late Ediacaran and accreted to the margin of Laurentia in the Early Paleozoic. Samples were collected from the New London Syncline, near Albemarle, NC, spanning from the Ediacaran into the Early Cambrian. These were supplemented by Middle Cambrian samples collected from the Asbill Pond Formation in South Carolina.

Field observations of Ediacaran metasediments show hummocky cross stratification and soft sediment deformation, suggesting deposition at or near storm wave base. Early Cambrian samples from the central syncline show stromatolitic layering. Redox sensitive transition metals are consistently depleted below typical crustal levels, suggesting minimal oceanic trace element inventories in the terminal Ediacaran and Cambrian Stages 1 and 2. Nitrogen isotopes show a minor shift toward more negative values in the Early Cambrian, which may reflect an increased role of nitrogen fixation. Additional work is being done to determine the degree of local oxygenation using iron speciation and pyrite petrography.