Browsing by Author "Thackray, GD"
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- ItemThe chronology of the last deglaciation from two New Zealand valleys and some climatic implications(18th INQUA Congress, 2011-07-21) Shulmeister, J; Fink, D; Rother, H; Thackray, GDWe present Be-10 and Al-26 chronologies from the paleo-Rakaia glacier and the Clearwater lobe of the Rangitata glacier focussing on the transition from the last glaciation maximum (LGM) to the Holocene. From the Rakaia we demonstrate that the local glacial maximum preceded the global LGM by several thousand years at c. 25 ka. Over the succeeding 12,000 years the glacier retreated only about 10 km and although undated, geomorphic evidence suggests a continued steady retreat after this time. The Clearwater lobe of the Rangitata glacier provides the most detailed LGIT record from any New Zealand glacier because it the valley was protected from significant meltwater flow during the deglaciation. Between 16.4 ka and 13.7 ka the Clearwater ice lobe retreated only 12 km producing 23 closely spaced recessional ice positions. The geomorphology and chronology are categorical in demonstrating that no significant re-advance can have occurred during this period. The inboard termination of the record occurs where the Clearwater valley drops into the main Rangitata Valley and should not be interpreted as the start of the more significant retreat. We highlight that uncertainties in isotope production rates and other elements of cosmogenic age determination (e.g. geomagnetic corrections) means that while we have millenial scale precision on ages during the LGIT, the accuracy of the ages is not as high. Nevertheless, our data clearly demonstrate that the evacuation of ice from these east coast valleys in New Zealand was remarkably slow with glaciers extending to ~60% of their LGM extents at 14 kyr (or younger). There is no evidence for either an early LGIT ice collapse or rapid retreat and consequently no late LGIT major readvance. We contrast our findings with the interpretations of chronologies coming from the Mackenzie Basin and we conclude that the records are compatible, with the chronological differences created by the morphometry of the respective ice catchments.Copyright (c) 2011 INQUA 18
- ItemComment on Barrell et al. “Reconciling the onset of deglaciation in the Upper Rangitata valley, Southern Alps, New Zealand” (Quaternary Science Reviews 203 (2019), 141–150.)(Elsevier, 2019-09-01) Shulmeister, J; Fink, D; Winkler, S; Thackray, GD; Borsellino, R; Hemmingsen, M; Rittenour, TMRecently, Barrell et al. (2019) published an article that responded to our article (Shulmeister et al., 2018a) on gradual evacuation of ice from the Upper Rangitata Valley, South Island, New Zealand, during the last glaciation. They base their contrasting interpretation of substantial and rapid ice-lowering of Rangitata glacier shortly after 18 ka on a revision of our 10Be cosmogenic radionuclide (CRN) chronology and by reference to published sources (e.g. Mabin, 1980, 1987). Their interpretation relies on glacial landform features extracted from a geomorphology map of the central Southern Alps by Barrell et al. (2011). Barrell et al. (2019) highlight that rapid ice recession of the Rangitata glacier is compatible to their results from Mackenzie Basin and Rakaia Valley (Putnam et al., 2013a, b). We highlight four points in response to Barrell et al. (2019). © 2019 Elsevier Ltd.
- ItemCorrigendum to “Evidence for slow late-glacial ice retreat in the upper Rangitata Valley, South Island, New Zealand” [Quat. Sci. Rev. 185 (2018) 102–112](Elsevier, 2019-09-01) Shulmeister, J; Fink, D; Winkler, S; Thackray, GD; Borsellino, R; Hemmingsen, M; Rittenour, TMIt has been brought to our attention, following a recent publication by Barrell et al. (2019), that the elevations for 12 of 23 boulders reported in our publication, Shulmeister et al., v185, 102–112 (2018) are incorrect. For these 12 samples, the true elevations are higher and hence all exposure ages based on their respective 10Be concentration measurements require a downward correction of between 10 and 15%. This change in age does not alter our main conclusions but does have some implication for the initiation and pace of deglaciation. © 2019 Elsevier Ltd.
- ItemCosmogenic 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, HNew 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.
- ItemA cosmogenic glacial chronology of Lake Judd, southwest Tasmania and latitudinal shifts in the Roaring Forties(International Union for Quaternary Research (INQUA), 2019-07-27) Fink, D; Wilcken, KM; Simon, KJ; Schulmeister, J; Thackray, GDLimited attention has been paid to the glacial history of Tasmania (40-44 S). At the northern limits of today’s Westerly storm track (the Roaring Forties), it experiences precipitation changes due to shifts in the Southern Annular Mode and ITCZ. Cosmogenic dating in southwest Tasmania (Kiernan 2010) highlights the marginal nature of its glaciation where small precipitation or temperature changes cause large changes in mass balance. This makes southwestern Tasmania an excellent location to study Westerly flow through the Last Glacial Cycle. The prevailing idea is that during glacial times, Westerlies expand northward to lower Southern Ocean latitudes, delivering increased rainfall to Tasmania, whilst during interglacials, their migration polewards reduces precipitation. Somewhat counterintuitively, from a Tasmanian perspective of increased Westerly circulation and wind strength, maxima glaciation should coincide with peak global glacials. Although well preserved, extensive last glacial cycle moraine sequences are not common, a series of more than 20 terminal moraine ridges have been mapped over 3 km concentric with the southern margin of Lake Judd, in the SW wilderness corner of Tasmania. Morphologically, the Lake Judd sequence is believed to represent three phases; pre MIS-6, MIS 5-3 and MIS 2 (LGM), representing substantially different volumes of ice accumulation. Our first field campaign collected 16 dolerite samples (36Cl) from the three innermost concentric moraines adjacent to lake edge and 4 quartzite (10Be, 26Al) samples from the most distal moraines. Our aim is to test correlation of the long-term glacial history with records of westerly fluctuations from NZ speleothems (Whittaker et al., 2011) to determine whether the latitudinal variation in Westerly winds in the Australasian region are zonal during glacial times as they are demonstrated to be in interglacial intervals (Fletcher and Moreno, 2012). Preliminary exposure age calculations on the full set of 20 samples are in poor agreement with Kiernan’s age associations. The 10Be (and 26Al) ages on the distal moraine indicate a most probable MIS 4/5 affiliation (>50 ka), significantly younger than expected. In contrast, the 16 dolerite samples from the 3 innermost proximal moraines at lake edge gave a complex set of ages that ranged from MIS 3 to MIS 4 affiliation (45-25ka), somewhat older than predicted. To add further complexity, these 16 ages show no intra or inter moraine age trends with respect to their morphologic positions and ice flow direction. These results contrast with those from other Tasmanian glacial records and reveal the need for a concretive effort to apply cosmogenic exposure dating to the numerus glacial deposits already mapped throughout Tasmania.
- ItemEvidence for expanded Middle and Late Pleistocene glacier extent in northwest Nelson, New Zealand.(Wiley-Blackwell, 2009-12) Thackray, GD; Shulmeister, J; Fink, DThe extent of Late Quaternary glaciation in the northwest Nelson region of New Zealand has traditionally been regarded as minor, with small-scale valley glaciation in confined upland reaches. New geomorphological evidence, including moraines, kame terraces, till-mantled bedrock and outwash terraces, indicate that greatly expanded valley glaciers flowed into the lowland valley system at the mouths of the Cobb-Takaka and Anatoki drainages. The timing for this ice advance into lowland valleys is constrained by lowland landform characteristics and a single cosmogenic exposure age, suggesting Late and Middle Pleistocene ice expansion, respectively. Evidence for expanded upland ice on the Mount Arthur Tableland and adjacent areas includes trimlines, boulder trains and roche moutonées. Two cosmogenic exposure ages on upland bedrock surfaces suggest that major ice expansion occurred during MIS 3 and/or 4, while previously published exposure dating from Cobb Valley suggests large MIS 2 ice expansion as well. The inferred, markedly expanded ice left little or no clear geomorphic imprint on the Cobb–Takaka Gorge, and required temperature depression of 4–6°C with near-modern precipitation levels. © 2009, Wiley-Blackwell.
- ItemEvidence for slow late-glacial ice retreat in the upper Rangitata Valley, South Island, New Zealand(Elsevier, 2018-04-01) Shulmeister, J; Fink, D; Winkler, S; Thackray, GD; Borsellino, R; Hemmingsen, M; Rittenour, TMA suite of cosmogenic radionuclide ages taken from boulders on lateral and latero-terminal moraines in the Rangitata Valley, eastern South Island, New Zealand demonstrates that relatively thick ice occupied valley reaches inland of the Rangitata Gorge until c. 21 ka. Thereafter ice began to thin, and by c. 17 ka it had retreated 33 km up-valley of the Rangitata Gorge to the Butler-Brabazon Downs, a structurally created basin in the upper Rangitata Valley. Despite its magnitude, this retreat represents a minor ice volume reduction from 21 ka to 17 ka, and numerous lateral moraines preserved suggest a relatively gradual retreat over that 4 ka period. In contrast to records from adjacent valleys, there is no evidence for an ice-collapse at c. 18 ka. We argue that the Rangitata record constitutes a more direct record of glacial response to deglacial climate than other records where glacial dynamics were influenced by proglacial lake development, such as the Rakaia Valley to the North and the major valleys in the Mackenzie Basin to the south-west. Our data supports the concept of a gradual warming during the early deglaciation in the South Island New Zealand. © 2018 Elsevier Ltd.
- ItemRe-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, HNew 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.
- ItemStratigraphy, 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, DJAStratigraphic 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.
- ItemTiming and causes of MIS 4 and MIS 3 glacial advances in South Island, New Zealand(International Union for Quaternary Research (INQUA), 2019-07-27) Schulmeister, J; Thackray, GD; Rittenour, TM; Fink, D; Patton, NRThis poster summarises information on the timing and possible causes of glaciation in New Zealand prior to the LGM (26.5-19 ka). We recognise five regionally identifiable advances in MIS 4 and MIS 3 in South Island, NZ, including one which may mark the start of the LGM, but may also precede it. These advances, all secured by CRN and/or luminescence chronologies, occurred at 65 ± 3 ka, 47.5 ± 3 ka, 38.5 ± 2 ka, 31.5 ± 3 ka, and at 26.5 ± 2 ka. Not all advances have clear linkages to climate but some are coincident with periods of Southern Hemisphere insolation minima (65ka, and 31.5 ka advances), while another occurs during a notably cold phase (38.5 ka) and precipitation may play a role (65 ka and 26.5 ka advances). The timing of greatest glacial extent in the last glacial cycle is not simultaneous across New Zealand. The MIS 4 advance was the greatest in the southern South Island, while the MIS 3/2 advances (26.5-25 ka) were greatest in the central South Island. We attribute these spatio-temporal changes in the timing of maximum glaciation to precipitation changes related to a northward shift in the track of the southern-hemisphere westerlies.
- ItemThe timing and nature of the last glacial cycle in New Zealand(Elsevier, 2019-02-15) Shulmeister, J; Thackray, GD; Rittenour, TM; Fink, D; Patton, NRThis paper constitutes a review of the last (Otiran) glaciation in New Zealand, spanning marine isotope stages (MIS) 4-2. We highlight the nature of glaciation, which is characterised by exceptional sedimentation, relatively mild maritime climatic conditions and the widespread presence of water associated with proglacial settings. These conditions produce glacial systems characterised by extensive outwash fans and relatively small terminal moraines. Extensive recent geochronological work allows us to recognise at least eight glacial advances during the Otiran. These occurred at 65 ± 3.25ka, 47.5 ± 3 ka, 38.5 ± 2 ka, 31.5 ± 3 ka, 26.5 ± 2 ka, 20.5 ± 2 ka, 17 ± 2 ka and 13 ± 1 ka, which we term the Otira 1 to 8 advances, respectively. Though the analytical uncertainty ranges for some of these advances overlap, all are independently distinguished through moraine morphologic relationships and/or stratigraphic relationships in outcrop. Major advances appear to be associated with climate influences such as periods of Southern Hemisphere insolation minima (65ka, and 31.5 ka advances), the last glacial maximum cooling (LGM) (20.5 ka) and periods of Antarctic cooling (13ka). The timing of greatest glacial extent in the last glacial cycle is not simultaneous across New Zealand. The MIS 4 advance was the greatest in the southern South Island, while the MIS 3/2 advances (26.5 ka) were greatest in the central South Island. In the northern South Island and the North Island, MIS 4, MIS 3/2, and the last glacial maximum appear to be equivalent in extent. We attribute these spatio-temporal variations in the timing of maximum glaciation to precipitation changes related to a northward shift in the track of the westerlies. © 2018 Elsevier Ltd.