Tectonically expelled seawater from the northern Coast Ranges, California

Conference · Thu Apr 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5436449

Davisson, M L ^[1]; Presser, T S ^[2]; Criss, R E ^[3]

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1. Lawrence Livermore National Lab., CA (United States)
2. Geological Survey, Menlo Park, CA (United States)
3. Univ. of California, Davis, CA (United States). Geology Dept.

Tectonically expelled saline fluids derived from connate seawater emerge at high elevations from Upper Cretaceous rock in the Rumsey Hills, eastern California Coast Ranges. The perennial spring waters are near-neutral in pH and range from [approximately]1,000 to 27,000 mg/L total dissolved solids. In detail, the Na deficit'', defined as the difference between the measured Na content and the Na concentration on a hypothetical seawater dilution line, is almost precisely balanced by the Ca excess'', similarly defined relative to a seawater dilution line. This relationship strongly suggests that the fluid is diluted seawater that is being modified by active albitization of plagioclase at different depths. Simultaneous boron and [sup 18]O enrichment of the fluids, accompanied by deuterium depletion, suggests that the seawater modification is also influenced by clay diagenesis. Bicarbonate (55 to 400 ppm) and SiO[sub 2] (2 to 25 ppm) concentrations show an inverse correlation with Cl, with most waters showing saturation or slight oversaturation with calcite and quartz at their sampling temperatures ([approximately]20 C). The highest silica and bicarbonate concentrations correspond to the most dilute spring waters, and these also emerge as perennial springs along the same structures as the saline fluids, indicating that the fresh spring waters may not be modern. Fresh-water recharge possibly was deeper in the geologic past and diluted the saline fluid at depth, as typically seen in many sedimentary basins. Chemical geothermometry suggests that these saline fluids originate in the core of an anticline under near-lithostatic fluid pressures created by the active internal deformation of an east-tapering wedge below the southwestern Sacramento Valley.

• OSTI ID: 5436449
• Report Number(s): CONF-9305259--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:5
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
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CHEMICAL COMPOSITION
CHEMISTRY
CONNATE WATER
DEVELOPED COUNTRIES
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GEOLOGIC DEPOSITS
GEOTHERMOMETRY
GROUND WATER
HYDROGEN COMPOUNDS
IGNEOUS ROCKS
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NORTH AMERICA
OXYGEN COMPOUNDS
PH VALUE
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WATER
WATER CHEMISTRY
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