Lake Devlin and Pinedale Glacial History, front Range, Colorado

Abstract

Glacial Lake Devlin was an ice-margin lake that formed during Pinedale time when the North Boulder Creek valley glacier blocked the mouth of a tributary near the downvalley limit of glaciation. The lake was about 2 km long and as much as 60 m deep, and was fed by meltwater from small valley glaciers. It accumulated sediment, apparently without interruption, for about 10,000 yr. The inception of Lake Devlin between 23,500 and 21,000 yr B.P. provides a limiting date for the maximum expansion of Pinedale ice, because the lake could not form until the North Boulder Creek glacier had advanced to within 2 km of its downvalley limit. The maximum lowering of timberline, which occurred about 19,000 yr B.P., is assumed to coincide with the Pinedale glacial maximum. Apparent timberline elevations determined from Picea/Pinus pollen ratios suggest that ice-front positions during the time between 23,000 and 19,000 yr B.P. may have been only slightly less extensive than at the Pinedale maximum. Lake Devlin drained catastrophically about 13,000 yr B.P., which was after ice had receded from the outlet area. Pinedale glaciation in the Front Range began about or after 30,000 yr B.P. and final deglaciation occurred between 15,000 and 12,000 yr B.P.

A climatic record from l4C‐dated wood fragments from southwestern Colorado

“…The last major glaciation in Colorado is estimated to have reached its height about 22,000 "B.P." [Madole, 1986]. However, the glaciation disappeared prior to 10,000 "B.P.…”

Geologic map of the Harvard Lakes 7.5' quadrangle, Park and Chaffee Counties, Colorado

“…Bull Lake glacial deposits, approximately 165-120 ka (Licciardi and Pierce, 2008;Schildgen and others, 2002;Shroba and others, 1983), are mapped in a few places. Most glacial deposits are from the Pinedale glaciation (about 30-12 ka; Nelson and others, 1979;Madole, 1986;others, 2004, 2005; and additional references listed under description for till of Pinedale glaciation, Qtp); compared to older till deposits, Pinedale-age moraines have sharper crests and more hummocky topography.…”

Geologic map of the Fraser 7.5-minute quadrangle, Grand County, Colorado

“…Artificial Fill Deposits (Nelson and others, 1979;Madole, 1986;others, 2004, 2005). Cosmogenic dating of Pinedale outwash, 4-14 m above stream level in Boulder Canyon east of Nederland, Colorado, yielded surface-exposure ages of 10-32 ka (Schildgen and others, 2002 fig.…”

“…Unit locally includes deposits of stratified drift, mass-movement deposits, till of Bull Lake age (Qtb), and locally may include till of pre-Bull Lake age. Radiocarbon ( 14 C) and cosmogenic surfaceexposure ages, some for deposits in nearby areas, indicate that till of unit Qtp is about 12-30 ka (Nelson and others, 1979;Madole, 1986;Schildgen and Dethier, 2000;others, 2004, 2005;2007). Subsurface deposits and locally some surface deposits of unit Qtp may be older than 30 ka, because uranium-series ages of travertine in the northern Yellowstone area suggest an advance of Pinedale ice occurred about 34-47 ka (Sturchio and others, 1994).…”

“…Till and minor stratified drift of the Pinedale glaciation form well preserved moraines in glaciated valleys in and near the Fraser quadrangle. Pinedale glacial deposits in Colorado are about 30-12 ka (Nelson and others, 1979;Madole, 1986;Schildgen and Dethier, 2000;others, 2004, 2005). They accumulated during a major cold climatic episode during MIS 2 (35-14 ka; Lisiecki and Raymo, 2005).…”