Determination and interpretation of sediment provenance in a sedimentary sequence affected by post-depositional changes

Abstract

Post-depositional alteration of floodplain sedimentary deposits is a problem for the interpretation of environmental change. In particular groundwater movement can alter the physical and chemical character of these deposits. This study considers the potential influence of post-depositional change on the geochemical character of sediments contained within the Narran floodplain, in semi-arid Australia, and the implications for interpreting environmental change. A series of 12 cores, ranging in length from 6-15 m, were collected from a number of different geomorphic regions across the floodplain. Stratigraphic analysis of the individual cores revealed extensive mottling and iron staining of sediments in all cores along with the presence of well developed carbonate nodules between 5 and 15 metres below the surface. At this level of resolution it would appear that post-depositional processes have significantly influenced the geochemical character sediments within this floodplain deposit. However, a statistical comparison of the low and high solubility elements noted only small differences in the geochemistry of sediment within and between the different stratigraphic units of the individual cores. It appears that although the floodplain deposit has experienced post-depositional influences, as evident through the stratigraphic analysis, this has had little overall influence on sediment geochemistry. This highlights the importance of being scale aware when interpreting the environmental history of floodplain environments. In addition the study demonstrates the utility of integrating standard sedimentological and numerical techniques in unravelling environmental histories, possible post depositional processes and groundwater influences in floodplain depositional environments.