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Deuterium and oxygen isotopes, paleoelevations of the Sierra Nevada, and Cenozoic climate

Peter Molnar
Deuterium and oxygen isotopes, paleoelevations of the Sierra Nevada, and Cenozoic climate
Geological Society of America Bulletin (July 2010) 122 (7-8): 1106-1115


Although geomorphic observations suggest that the Sierra Nevada has tilted so that the crest has risen 1-2 km since late Miocene time, deuterium and oxygen-18 isotope concentrations in Cenozoic geologic materials decrease eastward across California and Nevada similarly to those in modern, orographically induced precipitation, as if little change in Sierra Nevadan elevations has occurred since Eocene time. Orographic precipitation, however, depends on the amount of moisture in the atmosphere, which in turn can be much larger in warm air, as in Eocene or Oligocene time and in summer, than in the cooler air characteristic of present-day, dominantly winter, precipitation. Moreover, the integrated rainout of vapor, and hence presumably in stable isotope concentrations in the remaining vapor, depends largely on the difference in heights traversed by air masses, not slopes of mountain ranges. Thus, if due simply to orographically induced rainout, both Eocene and Oligocene variations in deuterium isotopes across the Sierra Nevada and Miocene-Quaternary differences in deuterium and oxygen isotopes between the Great Valley of California and the Basin and Range place only weak constraints on the slope or past elevations of the Sierra Nevada. They do not necessarily contradict the inference that the crest of the Sierra Nevada has risen 1000 m or more since late Miocene time.

ISSN: 0016-7606
EISSN: 1943-2674
Serial Title: Geological Society of America Bulletin
Serial Volume: 122
Serial Issue: 7-8
Title: Deuterium and oxygen isotopes, paleoelevations of the Sierra Nevada, and Cenozoic climate
Author(s): Molnar, Peter
Affiliation: University of Colorado, Department of Geological Sciences, Boulder, CO, United States
Pages: 1106-1115
Published: 201007
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 59
Accession Number: 2010-050189
Categories: StratigraphyIsotope geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Includes appendices
Illustration Description: illus. incl. 1 table, sketch map
N32°30'00" - N42°00'00", W124°30'00" - W114°15'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201027
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