Showing papers by "Grant M. Raisbeck published in 2005"

Cosmogenic 10 Be ages on the Pomeranian Moraine, Poland

Abstract: Rinterknecht, V R, Marks, L, Piotrowski, J A, Raisbeck, G M, Yiou, F, Brook, E J & Clark, P U 2005 (May): Cosmogenic 10Be ages on the Pomeranian Moraine, Poland Boreas, Vol 34, pp 186–191 Oslo ISSN 0300–9483 We measured the 10Be concentrations in boulders collected from the Pomeranian Moraine in Poland, providing the first direct dating of the southern margin of the Scandinavian Ice Sheet (SIS) in the Polish Lowland The mean age of 8 10Be ages of the Pomeranian Moraine in northwestern Poland is 14308 10Be ka, while in northeastern Poland the mean age of 19 10Be ages of the moraine is 15005 10Be ka Given the excellent agreement between the two age groups, we calculate a mean age of 14804 10Be ka for final deposition of the Pomeranian Moraine of northern Poland The age of the Pomeranian Moraine suggests that the southern margin of the SIS was near its maximum extent in Poland at a younger time than previously inferred, and that retreat from the moraine at 14804 10Be ka probably occurred in response to the onset of the Bolling interstade

Growth of South Rough Ridge, Central Otago, New Zealand: using in situ cosmogenic isotopes and geomorphology to study an active, blind reverse fault

Abstract: [1] In situ cosmogenic 10Be and 26Al measurements on sedimentary quartzites, together with analysis of abandoned river terraces, can be used to show how drainage responded to the lateral propagation of a late Quaternary anticline forming above a blind reverse fault in Central Otago, New Zealand. A close link between the progression of cosmogenic ages and the tectonic geomorphology allows us to confirm that uplift and propagation rates on the anticline are in the ranges 0.08–0.12 mm yr−1 and 0.8–1.5 mm yr−1, respectively, over the last 550,000 years. The agreement between the isotopic and geomorphological evidence in turn requires that minimum 10Be exposure ages as great as 660 ka are not in steady state with respect to erosion. This is a geochemical result of significance, as it opens the possibility of a more regional analysis of landscape evolution in this region, using the same rocks. On an adjacent anticline, thought to be even older on geomorphological arguments, 10Be concentrations give minimum exposure ages in the range 750–1400 ka. These extremely old minimum ages are rare worldwide, as they are usually limited to smaller values by erosion. They are attributable to the very resistant nature of the quartz-rich boulders in which the measurements were made, which in places are shown to have erosion rates lower than 0.5 mm kyr−1.

“Sarsen Stones” at German Hill, Central Otago, New Zealand, and Their Potential for In Situ Cosmogenic Isotope Dating of Landscape Evolution

Abstract: 10Be concentrations measured in silica‐cemented Tertiary sandstones in Central Otago have yielded minimum exposure ages of up to 1400 ka, some of the oldest ever recorded outside the dry valleys of Antarctica and some arid deserts The silica‐cemented sandstones outcrop as boulders in a region where their exposure is caused by the growth of anticlinal ridges above blind reverse faults Initial studies using a combination of in situ cosmogenic isotope measurements and geomorphological observations on one range have demonstrated the potential of this technique to investigate Late Cenozoic fault growth and erosion rates The best‐exposed and preserved occurrence of the quartz‐rich boulders is at German Hill on North Rough Ridge, where their stratigraphic context and their sedimentary and diagenetic origin, together with their method of emplacement and preservation on the modern land surface, can be studied in detail These are all features that affect their suitability for cosmogenic isotope studies