--> ABSTRACT: Volumetric Relations between Dissolved Plagioclase and Kaolinite in San Joaquin Basin Sandstones: Implications for Aluminum Mobility, by Michael J. Hayes, James R. Boles; #91003 (1990).

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ABSTRACT: Volumetric Relations between Dissolved Plagioclase and Kaolinite in San Joaquin Basin Sandstones: Implications for Aluminum Mobility

Michael J. Hayes, James R. Boles

The conservation of aluminum has been documented on a thin-section scale by comparing volumes and character of dissolved plagioclase and authigenic kaolinite in quartzofeldspathic sandstones from the east-central San Joaquin basin. Samples include Eocene to Pliocene age marine deposits from burial depths of 1400-14,000 ft. Central basin pore fluids are slightly diluted seawater, whereas meteoric water has infiltrated to depths of 6000 ft along the eastern flank of the basin. Our data suggest that aluminum behavior is dependent on pore-fluid composition. Dissolved plagioclase grains typically appear without kaolinite in sandstones currently in meteoric zones. The maximum volume percent of plagioclase porosity is 2.5%, corresponding to 0.16 mg of aluminum mobilized. Volumes of plagioclase porosity and kaolinite are subequal in deep sandstones containing modified seawater, apparently reflecting aluminum mass-balance and possible import in some cases.

Central basin reservoirs contain high concentrations of organic acid anions capable of mobilizing aluminum in these sandstones. In contrast, aluminum may be exported from sandstones in zones of prolonged meteoric flushing. Mass transfer of aluminum beyond a thin section scale may occur in both pore-fluid settings, although this apparently is less likely to occur in deep sandstones. Dissolution of potassium feldspar, rock fragments, and heavy minerals, and precipitation of authigenic feldspar and clays are of minor importance volumetrically relative to dissolved plagioclase and kaolinite in the San Joaquin basin.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990