Dating method glaciation


16-Oct-2019 11:42

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Absolute age limits were obtained for two of the Pleistocene glaciations by radiometric dating of basalt flows interfingered with the moraines.Three of the recognized glaciations, probably corresponding to the Matthes, Recess Peak, and Hilgard neoglaciations found by J. Birman in the central Sierra Nevada, occurred during the Holocene Epoch.The youngest glaciers (Matthes glaciation) left unconsolidated and unvegetated till in stagnant rock glaciers and moraines in cirques on high peaks. Extending out from the cirques and into the upper reaches of the canyons are moraines correlating to the Recess Peak glaciation.Till is generally consolidated and supports heavy lichen growth and bushes but few trees.These sediments have been shown in geophysical studies to mask a second escarpment as high as the one of the range front, and the total bedrock relief from the Sierra crest to the floor of the graben is as much as 6 km.During the Quaternary Period the southeastern Sierra Nevada was characterized by the down-faulting of Owens Valley along two zones, one a series of normal faults along the range front (Independence Fault) and the other a series of faults along the center of the valley (Owens Valley fault zone).The southeastern Sierra Nevada consists of three geographic regions.

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It included the southern part of the Big Pine volcanic field, an eruptive center for basaltic lavas for most of the Pleistocene Epoch.

Traces of at least seven glaciations were found during this study.

Moraines and other deposits left during these glaciations could be distinguished based on the degree of weathering of granitic clasts, vegetative cover, and morphologic characteristics.

These rocks, originally ranging in composition from basalt to rhyolite, are most common near the Sierra crest.

In the northern canyons of the study area, Paleozoic metasedimentary rocks including sandy marbles and biotite schist replace the metavolcanic pendants.

In each case, moraine morphology has been well preserved.