Soil Relative Dating of Moraine and Outwash-Terrace Sequences in the Northern Part of the Upper Arkansas Valley, Central Colorado, U.S.A.

Abstract

Profile development indices for soils developed in moraines and outwash near Twin Lakes and in outwash near Leadville support the correlation of moraines with subdued morphology and two high outwash terraces with the Bull Lake glaciation (ca. 130-160 ka) and the correlation of hummocky moraines and two low outwash terraces with the Pinedale glaciation (ca. 14-47 ka). Elsewhere in the northern part of the upper Arkansas Valley, glacial sequences are correlated by mapping outwash terraces near the mouths of major tributaries of the Arkansas River. Near Twin Lakes, indices for soils on low, outer lateral moraines suggest that the older Pinedale glaciers extended beyond the margin of high, younger Pinedale lateral moraines with hummocky topography. A few subdued moraines near Twin Lakes and Leadville probably record one or more glaciations significantly older than the Bull Lake. The downvalley extent of Pinedale glaciers in the Mosquito Range on the east side of the Arkansas Valley is uncertain: most likely, Pinedale glaciers were almost as extensive as Bull Lake glaciers but built no prominent terminal moraines at their maximum positions.

Assessing climatic and nonclimatic forcing of Pinedale glaciation and deglaciation in the western United States

“…The Clear Creek, Pine Creek, and Lake Creek valleys are all east facing, and at their Pinedale maximum extent glaciers emanating from Clear Creek and Pine Creek valleys dammed the Arkansas River (Scott, 1984;Nelson and Shroba, 1998;Lee, 2010). Clear Creek and Pine Creek valleys each host a pair of sharp, singlecrested lateral moraines that are >150 m high.…”

“…Clear Creek and Pine Creek valleys each host a pair of sharp, singlecrested lateral moraines that are >150 m high. These moraines are easily distinguishable from more extensive Bull Lake (MIS 6) moraines that are characterized by a more subdued surface topography and higher degrees of weathering on boulder surfaces (Nelson and Shroba, 1998). Unlike Clear Creek and Pine Creek valleys, where single Pinedale moraines are preserved, the Lake Creek valley contains numerous Pinedale end moraines ( Fig.…”

“…Unlike Clear Creek and Pine Creek valleys, where single Pinedale moraines are preserved, the Lake Creek valley contains numerous Pinedale end moraines ( Fig. 2; Nelson and Shroba, 1984). Glacier retreat from the terminal moraines in the Clear Creek and Pine Creek valleys likely led to a series of outburst fl oods that deposited two boulder-rich terraces downstream of Pine Creek, ~15 and 6 m above the modern-day Arkansas River (Scott, 1984;Lee, 2010;Fig.…”

Coarse sediment transport in mountain streams in Colorado and Wyoming, USA

“…Nearly all of the sites have been glaciated and are mantled by till and glacial outwash correlative of Bull Lake and Pinedale aged deposits (e.g. Nelson and Shroba, 1998). At most sites, hillslopes are relatively stable under the current climatic regime and vegetative cover, though there is evidence of active mass wasting in the past (Caine, 1986).…”

Geologic map of the Leadville North 7.5’ quadrangle, Eagle and Lake Counties, Colorado

“…Al cosmogenic nuclide ages on exposed surface boulders that generally range from approximately 22 to 16 ka within the quadrangle (table 1). Other studies within the region indicate Pinedale glaciation occurred between 30 and 12 ka (Madole, 1986;Nelson and Shroba, 1998;others, 2004, 2005) with the LGM being about 22 ka and a possible ice advance or stagnation at approximately 15.5-14.5 ka (Brugger, 2007;Briner, 2009;Mason and others, 2011;Young and others, 2011;Ruleman and others, 2013). Complete deglaciation of the northern Sawatch Range occurred by approximately 14-13 ka (table 1) (Ruleman and others, 2013 Be and 26 Al cosmogenic radionuclide exposure minimum age estimates of 101±21 ka and 122±26 ka (Schildgen and others, 2002).…”