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Glacial and periglacial sediments and landforms record the chronology of glaciation and amount of Pleistocene erosion during colder periods that added substantially to global sediment budgets and contributed to the global CO2 cycle. The now-drained glacial Lake Devlin, dammed in a Front Range tributary valley by a glacier in the North Branch of Boulder Creek (Colorado, USA) preserves an important sedimentary archive of the ca. 32-14 ka Pinedale glaciation, recording both paleoclimate information and an integrated measure of glacial and periglacial erosion rates over a full glacial cycle. Despite rapid erosion of fine-grained deposits after the lake drained, most sediment generated during Pinedale time remains as legacy deposits in the catchment. Geomorphic evidence and dating of glaciolacustrine sediment from surface exposures demonstrate that the ca. 30 ka Pinedale glacial advance was nearly as extensive as the local Late Glacial Maximum at ca. 20 ka. Sedimentary archives dated by 14C, optically stimulated luminescence, and cosmogenic nuclides extend earlier studies (Madole et al., 1973) of pollen and magnetic susceptibility (MS) in cores from the glaciolacustrine deposits of Lake Devlin and of Pinedale climate. Records suggest short-term warming and biotic change at ca. 15 ka after ~14 kyr of cold, dry conditions punctuated by MS peaks at ca. 26.5 ka, 20 ka, and 16.5 ka. Lake Devlin drained catastrophically after ca. 14 ka, millennia after ice had retreated upvalley from the lateral moraine that dammed the lake. Sediment production during the Pinedale was equivalent to a periglacial and glacial erosion rate of ~70 mm kyr1, several times higher than long-term rates in the adjacent Front Range, but much lower than rates measured where modern glaciers are eroding weak bedrock in zones of rapid rock uplift, such as SSE Alaska, USA. Data from the Lake Devlin basin contribute to contemporary discussions of how glacial erosion influences the global CO2 cycle. [ABSTRACT FROM AUTHOR]

We used measurements of cosmogenic 10Be in alluvium to estimate erosion rates on a 103-104 yr time scale for small (0.01-47 km²), unglaciated basins in northern Colorado, southern Wyoming, and adjacent western Nebraska (western United States). Basins formed in Proterozoic cores of Laramide ranges are eroding more slowly (23 ± 7 mm k.y. -1, n = 19) than adjacent basins draining weakly lithified Cenozoic sedimentary rocks (75 ± 36 mm k.y. -1, n = 20). Erosion rates show a relationship to rock resistance and, for granitic rocks, to basin slope, but not to mean annual precipitation. We estimated longer-term (>105 yr time scale) erosion rates for the granitic core of the Front Range by measuring the concentration of 10Be and 26Al produced mainly by muon interactions at depths 1.7-10 m below the surface. Concentrations imply erosion rates of 9-31 mm k.y. -1, similar to shorter-term erosion rates inferred from alluvial sediment. The spatial distribution of erosion rates and stratigraphic evidence imply that relief in the southern Rocky Mountains increased in the late Cenozoic; modern relief probably dates from post-middle Miocene time. [ABSTRACT FROM AUTHOR]