Late Quaternary terrigenous sediments from the Murray Canyons area, offshore South Australia and their implications for sea level change, palaeoclimate and palaeodrainage of the Murray-Darling Basin

摘要

Two sediment cores from the deep-sea Murray Canyons area, south of Kangaroo Island, Australia were investigated for quantity and composition of terrigenous material. Spanning the last 175 ka, terrigenous matter from these cores provides evidence for changes in sea level and palaeoclimate of the adjacent Australian continent. Located offshore Australia's major river system, the Murray-Darling, the sediment cores record varying inputs of suspended river clays. High input prevails during glacial periods, when sea level is low and the river discharges directly at the edge of the continental shelf. Today, and during previous periods of high sea level, the Mouth of the River Murray is more than 200 km away from the core sites, sedimentation of terrigenous matter is reduced and consists primarily of aeolian dust. However, even during periods of high sea level in the early Holocene (11-6 ka), river clays reached the core site, indicating a stronger discharge from the Murray and more humid conditions in the catchment area. The present mode of low-input aeolian sedimentation over the core sites was only established 4 ka ago. Differences in composition of the river clays between the penultimate glacial (isotope stage 6) and the last glacial maximum (isotope stage 2; LGM), as well as different clay mineral assemblages between the two cores during the LGM suggest that palaeodrainage on the exposed shelf varied between sea level lowstands. Minute changes in shelf morphology could have prevented the "Palaeo-River Vincent", a river which drained the glacially dry Gulf St. Vincent, from joining the course of the Murray during the LGM. Clay mineral evidence suggests that this palaeo-river did join the Murray during the penultimate glacial and significantly altered the clay mineral signature from the Murray-Darling catchment area.