The effects of geopressuring and kerogen decomposition on mineral-fluid equilibria were calculated in order to predict the diagenetic-alteration mineralogy produced in equilibrium with kerogen-rich, geopressured sediments. These calculations indicate that several processes specific to kerogen-rich geopressured sediments contribute to the development of a characteristic alteration mineralogy. These processes are: (1) the upward flow of fluids in geopressured sediments, in contrast to the generally downward flow of fluids in normally-pressured sediments; (2) the coincidence of the depths of geopressuring (2-3 km; Fertl et al., 1976), with the geothermal temperatures necessary for CO₂ release (100°-135°C; Hunt, 1979), and CH₄ release (>90°C; Hunt, 1979); and (3) the opposing rates of sediment burial and CO₂ and CH₄ transfer into the upward-flowing fluids, which result in the geopressured pore fluids becoming enriched, and in some cases saturated, with respect to CO₂ and CH₄. Three patterns of mineral deposition during diagenesis of kerogen-rich geopressured sediments are predicted. Quartz deposition should occur at the top of the geopressured zone and decrease rapidly with increased depth as a result of the decreased flux of upward fluid flow with increased depth. Carbonate deposition should occur above the zone of CO₂ release from kerogen degradation as a result of the upward flux of CO₂ saturated fluids and subsequent decreases in fluid temperature, pressure and CO₂ solubility. Kaolinite-carbonate could deposit within and above the zone of CO₂ release from kerogen as a result of silicate dissolution by CO₂-rich acid pore fluids, followed by the potential for albite-carbonate deposition upon CO₂ depletion. In contrast, laumontite and anhydrite should not deposit during diagenesis of kerogen-rich geopressured sediments, but could deposit during diagenesis of normally-pressured or kerogen-poor geopressured sediments. An additional difference between these diagenetic environments is that quartz deposition would not be expected in normally-pressured sediments in which fluids are expected to be flowing downward. These mineralogic relationships compare favorably with observed relationships in the kerogen-rich geopressured sandstones of the Frio formation from the Texas Gulf Coast.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/184351 |
| Date | January 1988 |
| Creators | Capuano, Regina Marie. |
| Contributors | Norton, Denis, Long, Austin, Titley, Spencer, Ince, Simon |
| Publisher | The University of Arizona. |
| Source Sets | University of Arizona |
| Language | English |
| Detected Language | English |
| Type | text, Dissertation-Reproduction (electronic) |
| Rights | Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. |
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