The Quaternary stratigraphy and sedimentology of the King River Valley, Western Tasmania

This thesis is concerned with the Quaternary deposits of the King Valley in western Tasmania, Australia. The aims of the study were to describe the character and map the extent of the glacial deposits, to determine the stratigraphy and age of the deposits associated with each glacial advance, to compare the inferred processes and patterns of sediment genesis with the depositional processes observed at the margins of modern glaciers, and to formulate a model of environmental changes associated with the glaciations. Deposits were mapped at a scale 1: 25,000 using morphostratigraphic, lithostratigraphic and biostratigraphic units. The stratigraphic classification and mapping defined thirteen formations from four glaciations. The last or Margaret Glaciation consisted of two main ice advances. The first appears to have occurred before 48ka; the second culminated after 191ca and had ended by 12ka. The Henty Glaciation, of middle Pleistocene age consisted of three ice advances. Two of the advances are separated by a long interval of lake sedimentation. The preceding Governor Glaciation, also of middle Pleistocene age, consisted of two ice advances. The glacial sediments are separated by organic sediments that record an interstadial climate. The Linda Glaciation is probably early Pleistocene in age. Its deposits are separated from younger glacial sediments by organic sediments that record the sucessional development of temperate rainforest during the Regency Interglacial. Linda Glaciation deposits are underlain by non-glacial sediments that are probably of late Pliocene age. Detailed descriptions of the glacial sediments on which the stratigraphy was based have enabled elements of the dynamics and debris paths of the King Glacier to be reconstructed. These reconstructions suggest that the dominant sedimentary environment was supraglacial and that the debris was derived from the basal transport zone. Two of the more unusual patterns in the sediments are lithological stratification of erratic clasts in some tills and a widespread series of sedimentary wedges that resemble but differ from ice-wedge casts. The chronology of the King Valley glaciations is estimated using a variety of relative dating methods that were applied to the deposits in their stratigraphic setting. The absence of reliable dating methods has meant that correlation of glacial events in Tasmania is largely based on comparing weathering characteristics. Wider correlation with glacial events in other Southern Hemisphere mid-latitude areas is not possible without accurate dating of the events.