ROCK-MAGNETIC RECORD OF TWO GLACIAL LAKES REFLECTS HISTORY OF GLACIAL RETREAT AND LANDSCAPE STABILIZATION IN THE EASTERN WIND RIVER RANGE AT THE PLEISTOCENE-HOLOCENE TRANSITION

Analysis of four sediment cores from Louis Lake (lat. 42°35'44.28"N, long. 108°50'50.33"W, elev. 2610m) and Fiddler Lake (lat. 42°37'54.20"N, long., 108°52'45.57"W, elev. 2868m) reveals a record of deglaciation and landscape stabilization for the eastern Wind River Range during the late Pleistocene. Cores have been dated by a combination of radicarbon dates (six macrofossil-based dates for Fiddler lake) and paleomagnetic analyses (to correlate between the two lakes), and both records span the late-Pleistocene - Holocene transition. The earliest depositional period of both lakes (19.5 - 17,5 ka B.P. for Louis Lake, 19.5 -16.0 ka B.P. for Fiddler Lake) is characterized by extremely rapid infilling of highly magnetic sediment. Low-ARM ratios and Curie-point determinations show that the magnetic component consists of coarse-grained magnetite. During a transitional period (17.5 - 16.0 ka B.P. at Louis Lake, 15.5 - 11.0 ka B.P.) clastic input decreases and the abundance of magnetic minerals drops due to dilution with organic material and dissolution associated with reducing sedimentary conditions. Increasing ARM-ratios suggest that biogenic SD magnetite gains importance as the main carrier of the sediment-magnetic signal. Holocene sediments in both lakes are characterized by weakly magnetic organic sediment. Neither lake reflects cooling during the Younger Dryas, indicating that any glacial readvances and associated landscape instabilities were limited to areas up-valley from both sites.