Browsing by Author "Hyatt, OM"

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    Cosmogenic 10Be and 26Al exposure ages of moraines in the Rakaia Valley, New Zealand and the nature of the last termination in New Zealand glacial systems
    (Elsevier, 2010-09-01) Shulmeister, J; Fink, D; Hyatt, OM; Thackray, GD; Rother, H
    New Zealand glaciers reached their last glacial maximum position at or before ~ 25 ka, and, as early as 23 ka, commenced a slow and continual retreat. New cosmogenic exposure ages and field mapping from the Rakaia Valley in the South Island suggest that extensive ice survived well into the latter half of the Last Glacial–Interglacial Transition (18–11 ka), with the post-15 ka period inferred to have near Holocene climate conditions based on ecological proxy data. By as late as ~ 15.5 ka, glacier termini had retreated as little as 5–10 km from glacial maximum positions. Numerous minor ice still-stand positions and oscillations are recognized, but the record specifically excludes evidence for either a major climatic amelioration at ~ 15–16 ka or a significant glacial re-advance during the Antarctic Cold Reversal (ACR) or the Younger Dryas (YD). We conclude that the currently widespread interpretation of an episodic New Zealand glacial record since the LGM is an artifact of valley-dependent retreat processes. Pro-glacial lake formation and local site conditions combined to give an apparent, but misleading, picture of glacial retreat punctuated by major, climatically driven, re-advances. © 2010, Elsevier Ltd.
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    Re-evaluating the deglacial sequence in New Zealand – part 2 - sudden ice collapse or gradual retreat?
    (GNS Science, 2009-05-15) Shulmeister, J; Fink, D; Hyatt, OM; Thackray, GD; Rother, H
    New data on moraine formation and glacial valley chronology challenges the existing understanding of the nature of deglaciation in New Zealand. When the glaciers retreat from glacial maximum limits they drop behind their fan heads and this creates accommodation space. This almost invariably leads to the formation of a pro-glacial lake system during retreat. Where the glacier trough is well developed deep lakes are formed. This results in an apparent collapse of the ice margin as floating ice leaves no terminal moraines. In contrast, if an over-deepened trough is not present, the glacier retreats in a stepwise fashion up valley with many terminal positions created (though not always preserved). At Rakaia Valley ice retreated less than 10 km in 10,000 years from its glacial maximum position. In dated east coast systems, the subsequent timing of ‘ice collapse’ differs from valley to valley. The chronology of deglaciation in New Zealand indicates that apparent ice collapse occurred at different times in different valleys during the deglaciation but this is largely an artifact of the timing of proglacial lake formation. Instead of ice collapse during the early part of the deglaciation followed by a significant very late glacial (ACR/YD) re-advance, we propose that extended ice remained in valleys with high elevation catchments until after ~15 ka. There is no major ice collapse prior to this time. Subsequently a minor ice re-advance occurred in these systems, which might relate in timing to either the ACR or YD. It may alternatively reflect a change from a calving terminus into a proglacial lake back to an outwash fan head system. In either case this event is of minor significance.
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    Stratigraphy, timing and climatic implications of glaciolacustrine deposits in the middle Rakaia Valley, South Island, New Zealand.
    (Elsevier, 2010-08) Shulmeister, J; Thackray, GD; Rieser, U; Hyatt, OM; Rother, H; Smart, CC; Evans, DJA
    Stratigraphic interpretations and infrared stimulated luminescence (IRSL) ages document the glacial history of the Middle Rakaia Gorge section of the Rakaia Valley, Canterbury, New Zealand, during the last two glacial cycles. Sheets of glaciolacustrine sediments several tens of metres in thickness can be traced at least 10 km upstream of the Rakaia Gorge. The stratigraphic package is capped by outwash gravels associated with the last glacial maximum (LGM) advances. The dominant inferred sedimentary environments in the sequence are 1) pro-glacial and paraglacial lake beds, 2) sub-aqueous ice-contact fans, 3) sub-aqueous mass flow deposits 4) supraglacial dump material and 5) outwash gravels. Syndepositional deformation, associated with glacitectonic deformation, is common. The stratigraphy records glacier margin oscillations, including six significant advances. These occurred in early MIS 6, mid-MIS 6, MIS 5b (c100–90 ka), MIS 5a/4 (c 80 ka), mid-MIS 3 (c 48 ka), and late MIS 3 (c 40ka). All the post-MIS 6 advances can be corroborated from other sites in New Zealand and the timings appear to coincide with both Southern Hemisphere insolation minima and maxima, suggesting variable combinations of climatic forcing in New Zealand glaciation. © 2010, Elsevier Ltd.