The ca. 1.4 Ga Roper Group of northern Australia comprises the sedimentary fill of one of the most extensive Precambrian hydrocarbon-bearing basins preserved in the geological record. It is interpreted to have been deposited in a large epeiric sea known as the Roper Seaway. Trace element data suggest that the redox structure of the basin was a shallow oxic layer overlying deeper anoxic to intermittently euxinic waters. These anoxic and sulfidic conditions, as inferred by trace element abundances (molybdenum, vanadium, uranium), developed due to high organic carbon loading consistent with models that suggest that euxinic conditions cannot develop until the flux of organic matter is significantly greater than the flux of bioavailable Fe3+, which permits sulphate reduction to proceed. We propose that the high organic matter flux was the result of increased nutrient loading to the Roper Seaway from weathering of the continental hinterland. Data from both major and high field strength elements (niobium, tantalum, zirconium, hafnium) together with neodymium isotopes(143Nd/144Nd) indicate that a likely source for this enhanced nutrient delivery was a shift in sedimentary provenance to a more primitive (mafic) precursor lithology. This switch in provenance would have increased phosphorus delivery to the Roper Seaway, contributing to high primary productivity and the onset of euxinia. This dataset and model serve as a basis for understanding the temporal evolution of the deepest sections of the Roper Seaway and finer scale changes in the palaeo-environment at this time.

Presentation given to the Flood Management Australia Flood Data and Insurance Workshop on 25 November 2015 on the copyright assignmnet issue preventing the sharing of flood risk information to the Australian community.

This presentation was given to a group of flood consultants on 20 November to provide them information on the copyright assigment issue preventing the communcation of flood risk information to the Australain community and proposing a strategy to resolve the issue.