Browsing by Author "Kiernan, K"
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- ItemCosmogenic 10Be and 26A1 exposure ages of glaciations in the Frankland Range, southwest Tasmania reveal a limited MIS-2 ice advance(Elsevier, 2017-02-01) Kiernan, K; Fink, D; McConnell, ANew mapping of the glacial geomorphology coupled with 10Be and 26Al exposure age dating of moraines on the flanks of the Frankland Range in south west Tasmania indicate that glacier extent during MIS-2 was far smaller than during earlier glaciations with the ice cover being confined to only the uppermost cirques of the range. Moraines further down the range flanks, ∼50–150 m lower in altitude than the MIS-2 dated advance, indicate that glaciers were only slightly larger during earlier glaciations and, depending on the interpretation of their exposure ages, may range from MIS 7 to MIS 12. These older moraines are nested inside the maximum ice limits of an even more ancient and extensive glaciation, defined by degraded valley floor moraines and coalescing glacio-fluvial fans that remain undated but appear no younger than MIS 12. Patterns of glacial erosion and moraine deposition on the Frankland Range suggest that the more recent glaciations were increasingly influenced by the erosional morphology initiated by earlier glaciers. Microclimatic differences resulting from this earlier glacial topography were particularly influential determinants of glaciation during MIS 2. These results are consistent with emerging evidence from studies of other ranges in southwest Tasmania. Crown Copyright © 2016 Published by Elsevier Ltd.
- ItemCosmogenic radionuclide chronology of pre-last glacial cycle moraines in the Western Arthur range, Southwest Tasmania(Elsevier, 2010-11) Kiernan, K; Fink, D; Greig, D; Mifsud, CCosmogenic 10Be and 26Al exposure ages of 12 boulders from two moraine complexes in the Western Arthur Range of southwest Tasmania, which previously were considered to have been deposited during the Last Glacial Maximum, predate the Last Glacial Cycle. Zero-erosion minimum exposure ages range from 95 ka to 232 ka based on weighted mean 10Be and 26Al ages per boulder. For a reasonable choice of erosion rates, 10Be boulder ages range from 105 to 326 ka, respectively. Although a direct association of moraine construction to a specific marine isotope stage (MIS) glaciation is not definitive, erosion-corrected exposure ages indicate glacial advances commensurate with MIS-6 and -10, although the latter advance may be attributable to MIS-8 if the erosion rate correction is an over-estimate. Given the relatively close proximity of the dated moraines to their source cirques, this new cosmogenic glacial chronology implies a very limited extent for any younger glacial advances that occurred in the Western Arthur Range during the Last Glacial Cycle (post MIS-5) including the global LGM. © 2010, Elsevier Ltd.
- ItemDeglaciation and weathering of Larsemann Hills, East Antarctica(Cambridge University Press, 2009-08) Kiernan, K; Gore, DB; Fink, D; White, DA; McConnell, A; Sigurdsson, IAIn situ cosmogenic Be-10 exposure dating, radiocarbon determinations, salt and sediment geochemistry, and rock weathering observations indicate that parts of Larsemann Hills, East Antarctica have been subaerially exposed throughout much of the last glacial cycle, with the last glaciation occurring prior to 100ka BP. Salt-enhanced subaerial weathering, coupled with a paucity of glacial erratics, made exposure age dating challenging. Rapid subaerial surface lowering in some places means that some exposure ages may underestimate the true age of deglaciation. Despite this uncertainty, the data are consistent with the absence of overriding by a thick ice sheet during the Last Glacial Maximum similar to 20-18 ka BP. © 2009, Cambridge University Press
- ItemGeomorphology and glacial history of Rauer Group, East Antarctica(University of Washington, 2009-07) White, DA; Bennike, O; Berg, S; Harley, SL; Fink, D; Kiernan, K; McConnell, A; Wagner, BThe presence of glacial sediments across the Rauer Group indicates that the East Antarctic ice sheet formerly covered the entire archipelago and has since retreated at least 15 km from its maximum extent. The degree of weathering of these glacial sediments suggests that ice retreat from this maximum position occurred sometime during the latter half of the last glacial cycle. Following this phase of retreat, the ice sheet margin has not expanded more than ~ 1 km seaward of its present position. This pattern of ice sheet change matches that recorded in Vestfold Hills, providing further evidence that the diminutive Marine Isotope Stage 2 ice sheet advance in the nearby Larsemann Hills may have been influenced by local factors rather than a regional ice-sheet response to climate and sea-level change. © 2009, University of Washington
- ItemLate pliocene age of glacial deposits at Heidemann Valley, East Antarctica: evidence for the last major glaciation in the Vestfold Hills(Cambridge University Press, 2010-02) Colhoun, EA; Kiernan, K; McConnell, A; Quilty, PG; Fink, D; Murray-Wallace, CV; Whitehead, JA Pliocene (2.6–3.5 Ma) age is determined from glacial sediments studied in a 20 m long, 4 m deep trench excavated in Heidemann Valley, Vestfold Hills, East Antarctica. The age determination is based on a combined study of amino acid racemization, diatoms, foraminifera, and magnetic polarity, and supports earlier estimates of the age of the sedimentary section; all are beyond 14C range. Four till units are recognized and documented, and 16 subunits are identified. All are ascribed to deposition during a Late Pliocene glaciation that was probably the last time the entire Vestfold Hills was covered by an enlarged East Antarctic Ice Sheet (EAIS). Evidence for other more recent glacial events of the ‘Vestfold Glaciation’ may have been due to lateral expansion of the Sørsdal Glacier and limited expansion of the icesheet margin during the Last Glacial Maximum rather than a major expansion of the EAIS. The deposit appears to correlate with a marine deposition event recorded in Ocean Drilling Program Site 1166 in Prydz Bay, possibly with the Bardin Bluffs Formation of the Prince Charles Mountains and with part of the time represented in the ANDRILL AND-1B core in the Ross Sea. © 2010, Cambridge University Press
- ItemTopographic and microclimatic impacts on glaciation of the Denison Range, southwest Tasmania(Elsevier, 2014-08) Kiernan, K; McMinn, MS; Fink, DMorphostratigraphic relationships between landforms and sediments, comparative boulder weathering status, and paired 10Be and 26Al exposure ages indicate the occurrence of at least three separate glaciations that are interpreted as dating from MIS 2, 6 and possibly 8. The Rhona Glacier remained at or close to its greatest LGM extent until ∼17.6 ka due to a very favourable micro-climate that resulted from local topography. That these factors were sufficient to over-power relatively subtle zonal temperature shifts that caused significant changes in more exposed Tasmanian glaciers implies a need for caution in correlating between glacier systems in markedly different topographic settings when environmental conditions are only marginally supportive of glaciation. No evidence was detected for any greater ice extent during MIS 3 or MIS 4 than during MIS 2, but much more extensive glaciations occurred during earlier glacial climatic cycles. Reduced local precipitation in parallel with increasing aridity of the Australian continent may account for the progressively diminishing maximum extent of glaciers during the latter part of the Pleistocene, and it would have emphasized the importance of local topography and microclimate for the glaciers of southwest Tasmania. © 2014 Published by Elsevier Ltd.