Volumetric Relations Between Dissolved Plagioclase and Kaolinite in Sandstones: Implications for Aluminum Mass Transfer in the San Joaquin Basin, California
Michael J. Hayes, James R. Boles, 1992. "Volumetric Relations Between Dissolved Plagioclase and Kaolinite in Sandstones: Implications for Aluminum Mass Transfer in the San Joaquin Basin, California", Origin, Diagenesis, and Petrophysics of Clay Minerals in Sandstones, David W. Houseknecht, Edward D. Pittman
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Mass transfer of aluminum is investigated on a thin-section scale by comparing volumes of dissolved plagioclase and authigenic kaolinite in quartzofeldspathic sandstones from the San Joaquin Basin. Samples include Oligocene marine-shelf sandstones, which have been infiltrated by meteoric water, and Late Miocene turbidite sandstones, which contain diluted sea water. Other aluminum sources and sinks are volumetrically minor in these sandstones.
Dissolved plagioclase and kaolinite presently appear from 600 m to depth of sample control (30–70°C present temperature) in the meteoric zone and from 2,100 m to depth of sample control (75–130°C present temperature) in the marine zone. Leached plagioclase and kaolinite are rare in the matrix-rich or carbonate-cemented sandstones, but appear in more than 80% of the uncemented turbidite sandstones and in up to 60% of the uncemented sandstones in some meteoric-zone reservoirs.
Point-counted volumes of plagioclase porosity and kaolinite in all sandstones are compared with relative volumes calculated from a mass-balance reaction in which aluminum is conserved between An30 plagioclase and kaolinite (25 to 50% microporosity). Aluminum is conserved on a centimeter scale in shale-encased turbidite sandstones exposed to limited fluxes of marine pore water, despite enrichment in organic-acid anions, which potentially may mobilize aluminum in soluble complexes. The average marine-zone sandstone has a volume of kaolinite approximately equal to that calculated for plagioclase porosity, based on relative volumes of the mass-balance reaction.
In contrast, the average sandstone with meteoric pore water has a kaolinite shortfall of 0.4 ± 0.3 volume percent of total rock relative to plagioclase porosity. This average aluminum loss is 0.2 ± 0.1 gm/100 cm3 rock volume. Complementary zones of aluminum import are not found in the meteoric zone. A small amount of aluminum is mobilized beyond a centimeter scale in shelf sandstones flushed by low-temperature, dilute waters.
Plagioclase dissolution and kaolinite precipitation in sandstones from both porewater settings result in compositional shifts of less than 0.4 weight percent Al2O3, too small to discriminate from the natural bulk chemical variation of 1 to 2 weight percent Al2O3. Data from this study do not support models proposed for transfer of large masses of aluminum over significant distances.
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Origin, Diagenesis, and Petrophysics of Clay Minerals in Sandstone–This volume grew out of a symposium held at the 27th Annual Meeting of the Clay Minerals Society in Columbia, Missouri on October, 1990. The symposium was designed to present a current synthesis of research devoted to the origin, diagenesis and petrophysics of clay minerals in sandstones. International authors demonstrate a multidisciplinary approach to interpreting the origin and diagenesis of clay minerals in sandstones and to evaluating their influence on reservoir quality. This volume bridges a gap between petrographic and geochemical researchers and reservoir geologists and engineers.