THE EDIACARAN-CAMBRIAN TRANSITION IN THE CAROLINA TERRANE: PRELIMINARY RESULTS AND NEW DIRECTIONS

The Ediacaran-Cambrian transition represents an interval of rapidly increasing animal diversity, coupled with global biogeochemical changes. The oxygenation of the atmosphere and oceans, the increased flux of trace metals and other ions to the ocean, and the increasingly ability of the ocean to serve as a reservoir for key metal cofactors in nutrient cycling may have interacted to drive the timing and tempo of the Cambrian Explosion. Much of what is known about these changes, and their timing relative to the diversification of animal life, comes from a limited number of sites, with a focus in southern China. An expansion of the Ediacaran-Cambrian map into new areas will allow us to better assess the degree to which changes in oceanic trace element cycles were global in scale.

Here we report preliminary geochemical measurements from the Albemarle Group, sampled from a number of sites on the limbs of the New London Syncline, near Albemarle, NC. This succession of fine-grained, low- to medium-grade metasediments ranges from the latest Ediacaran to the late Cambrian, and is associated with the Carolina Terrane, an arc accreted to the Laurentian margin in the Paleozoic. The sediments display little to no axial-planar foliation, and preserve primary sedimentary structures suggesting deposition at or near storm wave base. They include extensive evidence of local volcanism, including pumice clasts, fiamme structures, and laminated ash horizons, as well as evidence of syndepositional tectonic activity in the form of soft-sediment deformation.

This succession may have been deposited in a restricted back-arc basin, which in Ediacaran time is likely to have been a semi-permanently anoxic environment. We would thus expect these sediments to accumulate redox-sensitive trace metals, to the extent that these metals were available in the global ocean. Global trace element inventories are expected to reflect both oxidative continental weathering and the volume of oxygenated seawater available to serve as a trace element reservoir, both of which will track the progressive oxygenation of the oceans and atmosphere.