1 results for Armstrong, Martina Hellen

  • Glaciotectonic Deformation of the Hawea Moraine

    Armstrong, Martina Hellen (2011)

    Masters thesis
    University of Otago

    Environmental reconstruction of ancient glacial environments encompasses a variety of evidence sources that include morphology, sedimentology and structures within sedimentary deposits. The analysis of glaciotectonic deformation structures is one source of evidence that can be utilised, in tandem with other sources, in determining the glaciological scenario and foreland/bed characteristics present either at the time of deposition or during subsequent reworking. Interpreting evidence of glaciotectonic deformation requires guidance from modern analogues, where the majority of the literature is largely restricted to the Northern Hemisphere. Research on glaciotectonism has not been carried out on modern glacier margins in the South Island, and the range of investigations on Late Pleistocene deposits is very limited. This study focuses on the Hawea moraine and, based on a combination of geomorphological, sedimentological and geophysical techniques, evidence of glaciotectonic deformation in both the extensive glaciolacustrine sediments and glaciofluvial gravels was found. Deformation observed included normal faults and folds resulting from melt out and the removal of supporting ice following retreat, and thrusts, folds, and normal and reverse faults as products of ice advance into the deposit. Variation in the type and extent of deformation throughout the deposit was attributed to localised differences in the glacial stress field and sediment type and its associated properties, which influence its yield strength such as grain size distribution, pore-water content and structure. Based on the findings in the Hawea moraine and limited literature on glaciotectonic deformation in the eastern valleys of the Southern Alps, it is clear that, at this stage, one regional model of ice marginal deformation cannot be applied to Late Pleistocene deposits in the South Island. It was shown that modern analogues drawn from the Northern Hemisphere do not adequately account for the thermal controls on glaciotectonic processes in the South Island, and the relative importance of glaciodynamics and the paleoenvironment of the glacial foreland remains unclear.

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