GLACIATION IN THE TAYLOR RIVER VALLEY, COLORADO: NEW MORAINE AGES, RETREAT RATES, GLACIER RECONSTRUCTIONS, AND PALEOCLIMATE

Late Pleistocene glaciation in the Taylor River drainage was dominated by a glacier complex that supported large valley glaciers and multiple smaller ice lobes. In the headwaters of the Taylor valley proper, at least 9 recessional moraines document punctuated retreat, a result of either stillstands or re-advances. Ages of 5 of these moraines were determined using cosmogenic nuclide exposure dating as well as providing addition ages of the terminal moraine complex. The latter confirm an age of 20.5 ± 0.8 ka corresponding to the Last Glacial Maximum (LGM). Ages of the recessional span an interval of 18.0 ± 0.1 to 15.1 ± 0.7 ka, thus recording ice retreat during the early phase of the LGM-interglacial transition. Base on these ages, retreat rates and intervals of quasi-stability of the glacier’s terminus broadly correlate in some instances with known climatic events (e.g. Heinrich Stadial 1). Other correlations are equivocal owing to uncertainties in interpretation and glacier dynamics. For example, one recessional moraine might have been constructed solely by a tributary glacier after ice in the main valley had by this time retreated upvalley from this position.

New field and lidar-based mapping combined with a set of GIS-based glaciological tools facilitated the reconstruction of the full extent of ice in the Taylor Valley. This reconstruction of glacier shape and thickness compares favorably with that based on older, pre-lidar field mapping and, when combined with temperature-index modeling, suggests an LGM temperature depression of ~7 to 8.5 °C.