A study of late quaternary environment and man from four sites in Southeastern Tasmania.
Creators: name: Sigleo, Wayne Richard
Publisher: name: University Of Tasmania
Year: 2023

description: A study of the geomorphic and stratigraphic relations of selected sandsheets, lunettes and associated landforms in southeastern Tasmania revealed a complex sequence of aeolian, slope and alluvial deposits including buried soils that were developed during the late Quaternary period. In addition, several of the aeolian deposits contained evidence of Aboriginal occupation, and provided information on the antiquity of Man in southeastern Tasmania and his role in locally modifying the landscape. At least two major phases of aeolian activity are recorded from the late Quaternary period, each related to relatively cold, and seasonally arid conditions that occurred during and/or immediately following episodes of periglacial activity in the lowlands of Tasmania. The age of the initial phase of deflation is yet to-be determined; however, aeolian activity could have occurred during either the Penultimate Glaciation or an early stadial of the Last Glacial Stage. The aeolian sediments of this phase unconformably overlie still older alluvial fan and lacustrine deposits. These were formed during cold climatic conditions when geomorphic processes causing slope instability and alluviation of small catchments operated with greater intensity than during warmer and moister intervals. Reduced precipitation was more than counter-balanced by reduced evaporation to maintain high lake levels in the Midlands. Truncated paleosols on the older sandsheets and dunes indicate that a period of climatic warming of unknown duration and intensity occurred between the two major colder and drier episodes. Renewed deflation, resulting in the accumulation of younger sandsheets and lunettes, occurred during the later part of the Last Glacial Stage, and was broadly synchronous with a second period of fan deposition and high lake levels. An approximate age for this phase of aeolian activity is indicated by a radiocarbon date of 15,740 BP from a sand dune at Malcolms Hut. Pollen evidence from lake sediments in the Midlands suggests a considerably colder climate throughout much of this period. Archeological material from the base of a sandsheet in the lower Derwent Valley demonstrates the presence of Aboriginal Man in southeastern Tasmania by at least the later part of the Last Glacial Stage. Towards the end of the Last Glacial Stage, increased summer temperatures and evaporation rates resulted in intermittent or seasonal drying of the lake basins in the Midlands and clay dune formation. This later phase of aeolian activity was followed by soil development on the various sandsheets and lunettes, and weathering occurred during the general climatic amelioration beginning at the end of the Last Glacial Stage. Relative land surface stability continued during the Holocene until profile truncation occurred locally through Aboriginal occupation, and the site-intensive activities of Man were responsible for the generation of secondary, anthropogenic coversand deposits at some of the sites. Radiocarbon dates indicate the profile truncation caused by Aboriginal occupation occurred by at least 5,800 BP in the lower Derwent Valley and by 4,800 BP in the Midlands. European land use and quarrying activities after 1803 resulted in the disturbance of the Aboriginal occupation units and initiated the deposition of tertiary aeolian deposits. A reasonable framework exists for correlation of the major late Quaternary events in southeastern Tasmania presented in this study with similar sequences recorded from adjacent parts of the Australian mainland.