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Lithology, mineralogy, and paleontology of Quaternary lake deposits in Long Valley Caldera, California

Open-File Report 89-413

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Abstract

Drill cores and cuttings from two drill holes, about 3 km apart, in Long Valley caldera, Mono County, California, were studied using x-ray diffraction and optical methods. A thick sequence of tuffs and lake sediments was encountered in LVCH-1 (1,000 ft deep) and Republic well 66-29 (6,920 ft deep), drilled in the southeast part of the Long Valley caldera. Ostracods, diatoms, and isotopic data indicate that the sediments and tuffs were deposited in a shallow caldera lake which changed in salinity over time. Conditions ranged from very saline in the older lake to fresh in the youngest. The sequence of secondary minerals from top to bottom is: clinoptilolite, mordenite, analcime, K-feldspar (and albite). In some geothermal systems, this sequence of secondary minerals is a function of temperature; however, the paleontological and isotopic data indicate that the change in secondary minerals with increasing depth is due to the older strata being deposited in a more saline environment. No mineralogical evidence of hydrothermal alteration is present, although the high lithium content of some clays and feldspars and the isotopic composition of some sulfate (gypsum) seems to require a hydrothermal source. (Lantz-PTT)

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Lithology, mineralogy, and paleontology of Quaternary lake deposits in Long Valley Caldera, California
Series title:
Open-File Report
Series number:
89-413
Edition:
-
Year Published:
1989
Language:
ENGLISH
Publisher:
U.S. Geological Survey,
Description:
v, 97 p. :ill., maps ;28 cm.