Fate of the preglacial regolith beneath the Laurentide Ice Sheet
Subglacial erosion and transport of deformable sediment influence the size, stability, and sensitvity to climate of large ice sheets. These processes may cause or sustain ice-sheet in-stabilities [1], and may have dictated the periodicity of the Cenozoic ice ages, in particular the enigmatic mid-Ple...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.506.6554 http://depts.washington.edu/cosmolab/preprints/new_regolith_paper.pdf |
| Summary: | Subglacial erosion and transport of deformable sediment influence the size, stability, and sensitvity to climate of large ice sheets. These processes may cause or sustain ice-sheet in-stabilities [1], and may have dictated the periodicity of the Cenozoic ice ages, in particular the enigmatic mid-Pleistocene transition from small and frequent to large and infrequent glaciations [2,3]. Subglacial erosion, however, is difficult to study. Where active at present, it is hard to observe, and, like other erosional processes, it continuously removes the ev-idence of its previous actions. Here we use the cosmic-ray-produced radionuclide 10Be, which is abundant in deeply weathered soils but absent in fresh bedrock, to investigate the sources of subglacial sediment eroded from the Canadian Shield by the Laurentide Ice Sheet (LIS) and deposited as till in the north-central U.S. Some tills have extraordinarily high 10Be concentrations, as high as those in deeply weathered regolith in unglaciated areas that has accumulated 10Be over millions of years. In general, the lowermost tills have high 10Be concentrations, tills directly overlying them have 10Be concentrations that are lower by an order of magnitude, and Wisconsinan tills have the lowest 10Be concentrations. There |
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