Surface-exposure ages of Front Range moraines that may have formed during the Younger Dryas, 8.2 cal ka,and Little Ice Age events |
| |
| Institution: | 2. Middlebury College, Middlebury, VT, United States;1. Texas A&M University Department of Geography, College Station, TX 77843, United States;2. Texas A&M University Center for Geospatial Sciences, Applications & Technology, College Station, TX 77843, United States;3. Texas A&M University Department of Geology and Geophysics, College Station, TX 77843, United States;1. Instituto de Física, Universidade Federal Fluminense, Av. Gal. Milton Tavares de Souza, S/N, Niterói, 24210-346, RJ, Brazil;2. Núcleo de Estudos do Mar, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina, Florianópolis, 88040-900, SC, Brazil;3. Departamento de Ciências da Natureza, Universidade do Estado do Rio de Janeiro, Rua Santa Alexandrina, 288, Rio de Janeiro, 20261-232, RJ, Brazil;4. Instituto Superior de Tecnologías y Ciencias Aplicadas, InSTEC, Quinta de los Molinos, Ave. Salvador Allende y Luaces, Plaza de la Revolución, Ciudad de La Habana, Cuba;5. Departamento de Biologia Marinha, Instituto de Biologia Universidade Federal Fluminense, Niterói, RJ, Brazil |
| |
| Abstract: | Surface-exposure (10Be) ages have been obtained on boulders from three post-Pinedale end-moraine complexes in the Front Range, Colorado. Boulder rounding appears related to the cirque-to-moraine transport distance at each site with subrounded boulders being typical of the 2-km-long Chicago Lakes Glacier, subangular boulders being typical of the 1-km-long Butler Gulch Glacier, and angular boulders being typical of the few-hundred-m-long Isabelle Glacier. Surface-exposure ages of angular boulders from the Isabelle Glacier moraine, which formed during the Little Ice Age (LIA) according to previous lichenometric dating, indicate cosmogenic inheritance values ranging from 0 to ～3.0 10Be ka.1 Subangular boulders from the Butler Gulch end moraine yielded surface-exposure ages ranging from 5 to 10.2 10Be ka. We suggest that this moraine was deposited during the 8.2 cal ka event, which has been associated with outburst floods from Lake Agassiz and Lake Ojibway, and that the large age range associated with the Butler Gulch end moraine is caused by cosmogenic shielding of and(or) spalling from boulders that have ages in the younger part of the range and by cosmogenic inheritance in boulders that have ages in the older part of the range. The surface-exposure ages of eight of nine subrounded boulders from the Chicago Lakes area fall within the 13.0–11.7 10Be ka age range, and appear to have been deposited during the Younger Dryas interval. The general lack of inheritance in the eight samples probably stems from the fact that only a few thousand years intervened between the retreat of the Pinedale glacier and the advance of the Chicago Lakes glacier; in addition, bedrock in the Chicago Lakes cirque area may have remained covered with snow and ice during that interval, thus partially shielding the bedrock from cosmogenic radiation. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
