13We performed an interlaboratory comparison study with the aim to determine the accuracy of cosmogenic 21 Ne measurements in quartz. CREU-1 is a natural quartz standard prepared from amalgamated vein clasts which were crushed, thoroughly mixed, and sieved into 125-250 µm and 250-500µm size fractions. 50 aliquots of CREU-1 were analyzed by five laboratories employing six different noble gas mass spectrometers. The released gas contained a mixture of 16-30% atmospheric and 70-84% non-atmospheric (predominantly cosmogenic) ], and suggest that the 7.1% (2σ) overdispersion of our measurements may be representative of the current accuracy of cosmogenic 21 Ne in quartz. CREU-1 was tied to CRONUS-A, which is a second reference material prepared from a sample of Antarctic sandstone. We propose a reference value of 320±11×10 6 at/g for CRONUS-A. The CREU-1 and CRONUS-A intercalibration materials may be used to improve the consistency of cosmogenic 21 N e to the level of the analytical precision.
Geomorphological and glacial geological surveys and multiple cosmogenic nuclide analyses ((10)Be, (26)Al, and (21)Ne) allowed Lis to reconstruct the chronology of variations prior to the last glacial maximum of the East Antarctic Ice Sheet (EAIS) and valley glaciers in the Terra Nova Bay region. Glacially scoured coastal piedmonts with round-topped mountains occur below the highest local erosional trimline. They represent relict landscape features eroded by extensive ice overriding the whole coastal area before at least 6 Ma (predating the build-Lip of the Mt. Melbourne volcanic field). Since then, summit surfaces were continuously exposed and well preserved under polar condition with negligible erosion rates on the order of 17 cm/Ma. Complex older drifts rest on deglaciated areas above the younger late-Pleistocene glacial drift and below the previously overridden summits. The combination of stable and radionuclide isotopes documents complex exposure histories with Substantial periods of burial combined with minimal erosion. The areas below rounded summits were repeatedly exposed and buried by ice from local and outlet glaciers. The exposure ages of the older drift(s) indicate multiple Pleistocene glacial cycles, which did not significantly modify the pre-existing landscape. (C) 2008 University of Washington. All rights reserved
To reconstruct the timing of Alpine glacier advances onto the Jura Mountains, we sampled 17 Alpine erratic boulders within and beyond the LGM (Last Glacial Maximum) extent of the Valais Glacier along three transect for the analysis of cosmogenic 10 Be. Our results indicate at least two advances into the study area in Northwestern Switzerland; one during the LGM and one beforehand. Reaching of the maximum extent of by the Valais Glacier into the Jura mountains during the LGM occurred at 21.9 ± 1.8 ka based on erratic boulders exposure ages. Ages of boulders located beyond the LGM extent of the Valais Glacier vary from 19.9 ± 1.6 to 144.0 ± 9.6 ka. These ages indicate that many of the boulders were displaced and re-deposited by local ice in the Jura Mountains both during and perhaps even prior to the LGM. Therefore, the chronology of the pre-LGM advance(s) of Alpine glaciers into the Jura Mountains remains still to be elaborated.
The Jura Mountains are a perialpine chain bending from the SW to the NW of Switzerland. Alpine ice reached only marginal areas of this chain during the Last Glacial Maximum (LGM) but remaining erratic boulders of alpine origin indicate older glaciations of unknown age, tentatively correlated either with the classical Rissian or with the Most Extensive Glaciation. Presented here are the first results of dating these pre-LGM boulders by using cosmogenic radionuclides ( 10 Be) and noble gases ( 21 Ne). Both data sets are in good agreement within 1s error, with radionuclide apparent exposure ages ranging from 60 to 107 ka, and noble gas apparent ages from 73 to 123 ka. Considering the importance of erosion on older boulders, the age of the erratics corresponds most probably to Marine Isotope Stage 6. These results are encouraging for further studies on pre-LGM erratic boulders in the mid-latitudes.
One of the major issues in (palaeo-) climatology is the response of Antarctic ice sheets to global climate changes. Antarctic ice volume has varied in the past but the extent and timing of these fluctuations are not well known. In this study, we address the question of amplitude and timing of past Antarctic ice level changes by surface exposure dating using in situ produced cosmogenic nuclides ( 10 Be and 21 Ne). The study area lies in the Ricker Hills, a nunatak at the boundary of the East Antarctic Ice Sheet in southern Victoria Land. By determining exposure ages of erratic boulders from glacial drifts we directly date East Antarctic Ice Sheet variations. Erosion-corrected neon and beryllium exposure ages indicate that a major ice advance reaching elevations of about 500 m above present ice levels occurred between 1.125 and 1.375 million years before present. Subsequent ice fluctuations were of lesser extent but timing is difficult as all erratic boulders from related deposits show complex exposure histories. Sample-specific erosion rates were on the order of 20-45 cm Ma -1 for a quartzite and 10-65 cm Ma -1 for a sandstone boulder and imply that the modern cold, arid climate has persisted since at least the early Pleistocene.
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