The aims of this investigation were to determine the geological provenance of the lake sediments, as well as to identify storm-induced deposits in order to reconstruct the sedimentation history within the Moeraki catchment. Trace-element geochemistry of deposits from Lake Moeraki, south Westland, New Zealand, recorded the chemical signature of the two lithologies. Sediment derived from the schist terrane was distinguished by higher concentrations of strontium and vanadium. In contrast, greywacke-derived sediment was characterised by higher concentrations of rubidium. Particle size analysis, using the pipette method, identified coarse storm deposits within the lake sediments. These coarse particle layers consisted of sediment characteristics of both geological terranes. Deposits which represented material from the greywacke tributary Boulder Creek, consisted of finer silt and clay particles eroded from the exposed slopes following landsliding within the tributary. A comparison between the magnetic susceptibility and geochemistry records suggest that troughs in the susceptibility record correspond with schist-derived deposits, whereas peaks in the record may relate to sediment derived from the greywacke terrane. However, there is some uncertainty in these results. An attempt to construct a chronology of lake sedimentation based on radiocarbon dating, could not be established because of contamination problems from old soil carbon. Results suggest that careful radiocarbon dating of organic macrofossils within the lake sediment should be undertaken, in order to obtain an accurate chronology of the erosion and sedimentation processes occurring within the Moeraki catchment.
Dow, M. 1998. Lake Sediment Geochemistry and Provenance. Unpublished MSc thesis in Geography, University of Otago, Dunedin, New Zealand. 99pp.