Formation of glaciolacustrine Late Pleistocene end moraines in the Tasman Valley,New Zealand |
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| Institution: | 1. Department of Geography, University of Canterbury, Private Bag 4800, Christchurch, New Zealand;2. Antarctic Research Centre, Victoria University of Wellington, PO Box 600, Wellington, New Zealand;3. Lake Hawea Institute of Cryodynamics, 20 Muir Rd., LGM Hawea, RD2 Wanaka, New Zealand;1. School of Geography, University of Leeds, Leeds LS2 9JT, UK;2. School of Geography, Archaeology and Palaeoecology, Queen''s University Belfast, Belfast BT7 1NN, UK |
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| Abstract: | Detailed examination of the Tekapo Formation in the Tasman Valley, New Zealand has identified 20 facies, and five facies associations. These associations are delta foresets and bottomsets, sediment density flows, ice-contact lake sediments with ice-rafted debris and resedimentation deposits, and outwash gravels. Interpretation of the sediment-landform associations informed by observations at modern glacier termini suggests that the Late Pleistocene Tekapo Formation moraines have been formed by downwasting of a more expanded Tasman Glacier. During the early stages of glacier retreat, ponds on the glacier surface develop into thermokarst lakes which enlarge and coalesce to form a large supraglacial lake. Continued downwasting causes the lake outlet river to entrench into the impounding latero-frontal ice-cored moraine, lowering the lake level. This exposes lake-bottom sediments and forms shorelines on the proximal slopes of the ice-cored moraine. As the ice-cored moraine melts, these lake sediments are deformed and deposited against the Mt. John moraine. The observations and interpretations reported here suggest the Late Pleistocene end moraine is a constructional feature not a structural (glaciotectonic) feature as suggested by previous studies. |
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