Relict colluvial boulder deposits as paleoclimatic indicators in the Yucca Mountain region, southern Nevada

Geological Society of America Bulletin
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Early to middle Pleistocene boulder deposits are common features on southern Nevada hillslopes. These darkly varnished, ancient colluvial deposits stand out in stark contrast to the underlying light-colored bedrock of volcanic tuffs, and they serve as minor divides between drainage channels on modern hillslopes. To demonstrate the antiquity of these stable hillslope features, six colluvial boulder deposits from Yucca Mountain, Nye County, Nevada, were dated by cation-ratio dating of rock varnish accreted on boulder surfaces. Estimated minimum ages of these boulder deposits range from 760 to 170 ka. Five additional older deposits on nearby Skull and Little Skull Mountains and Buckboard Mesa yielded cation-ratio minimum-age estimates of 1.38 Ma to 800 ka. An independent cosmogenic chlorine-36 surface exposure date was obtained on one deposit, which confirms an estimated early to middle Quaternary age. These deposits have provided the oldest age estimates for unconsolidated hillslope deposits in the southwestern United States. We suggest that the colluvial boulder deposits were produced during early and middle Pleistocene glacial/pluvial episodes and were stabilized during the transition to drier interglacial climates. The preservation of old, thin hillslope deposits and the less-than-2-m incision by hillslope runoff adjacent to these deposits, indicate that extremely low denudation rates have occurred on resistant volcanic hillslopes in the southern Great Basin during Quaternary time. -from Authors

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Relict colluvial boulder deposits as paleoclimatic indicators in the Yucca Mountain region, southern Nevada
Series title Geological Society of America Bulletin
Volume 105
Issue 8
Year Published 1993
Language English
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Geological Society of America Bulletin
First page 1008
Last page 1018