THE EDIACARAN-CAMBRIAN TRANSITION IN THE CAROLINA TERRANE

The Cambrian Explosion saw one of the greatest diversifications of life in the history of the planet, and marked the transition between the Precambrian and Phanerozoic eons. During this time, increasing atmospheric oxygen led to an influx of trace metals and other ions to the global ocean, as well as an increasing ability for the oceans to store these metals in oxygenated seawater. The relationship between oxygenation, increasing trace metal inventories, nutrient cycling, and diversification remains an active area of study. The goal of this study is to determine when oxygenation of the global ocean occurred relative to the diversification of animals. To do this, we collected samples from the New London Syncline, near Albemarle, NC.

The metasediments of the Albemarle Group are associated with the Carolina Terrane, a peri-Gondwanan volcanic arc that began forming during the late Ediacaran before accreting to Laurentia in the Early Paleozoic. Field observations of sediments show hummocky cross stratification and soft sediment deformation, suggesting deposition in a tectonically active setting at or near storm wave base. Preliminary geochemical measurements indicate a consistent provenance of sediments from the exposed Carolina arc, punctuated by more volcanically influenced deposition events. 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. Additional work is being done to determine the degree of local oxygenation using pyrite petrography. Measurements of nitrogen isotopes will indicate whether low trace metal inventories may have inhibited nitrogen fixation in the early Cambrian.