TOTAL ORGANIC CARBON AND GEOCHEMICAL ANALYSIS OF A PALEOARCHEAN SPHERULE LAYER

The S3 spherule layer of the Barberton Greenstone belt in South Africa was formed by a bolide impact that occurred around 3.24 billion years ago during the Paleoarchean. This layer is well-characterized and deposited in a range of environments. Trace element chemistry was analysed below, within, and above the layer in both a shallow water and moderately deep water deposit in order to provide insight into localized conditions associated with the impact event within these different depositional environments. Barium concentrations within the S3 layer spike compared to overlying and underlying deposits. This trend is observed other spherule beds, including the 2.47 Ga Paraburdoo spherule layer and in the K-Pg spherule layer. We observe a positive correlation between the Ba content and the Total Organic Carbon (TOC) concentration within the spherule bed. Two possible explanations for high TOC within and above the spherule layers include: (1) a large die-off of organisms during the impact, leading to accumulated organic material. This is consistent with an accumulation of barite if sulfate is not scavenged by microbal activity; or (2) microbal feeding on the spherule glass. This is consistent with the graphite observed petrographically along spherule rims. Increased barite accumulation may also be caused by the release of SOx into the atmosphere during impact.