Open-system chemical behavior in deep Wilcox Group mudstones,Texas Gulf Coast,USA |
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| Authors: | Ruarri J Day-Stirrat Kitty L Milliken Shirley P Dutton Robert G Loucks Stephen Hillier Andrew C Aplin Anja M Schleicher |
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| Institution: | 1. Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, University Station, Box X, Austin, TX 78713, USA;2. Macaulay Institute, Craigiebuckler, Aberdeen, AB15 8QH, UK;3. School of Civil Engineering and Geosciences, Drummond Building, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK;4. Department of Geological Sciences, University of Michigan, C.C. Little Building, 425 E. University Ave., Ann Arbor, MI 48109, USA |
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| Abstract: | Wilcox Group mudstones have been mechanically and geochemically transformed over a temperature range of 20–200 °C. Our research controlled for provenance and age by sampling from five wells, parallel to the paleodepositional axis, all within the Houston delta system. Across the sampled depths, mudstone porosity has been reduced from ∼25 to <10% and bulk mineralogical change as documented by quantitative X-ray diffraction includes decreases in quartz, K-feldspar and kaolinite content whereas illite + illite − smectite, chlorite, and plagioclase increase. These mineral transformations transfer elements at a scale of less than 1 mm from one mineralogical form to another, however, X-ray fluorescence data suggest that among major elements only Al2O3 and TiO2 are fully conserved within the system (trace-element ZrO2 is also conserved). K2O has been added to and SiO2 released from the Wilcox Group mudstones. Cathodoluminescence and secondary electron imaging did not find this SiO2 locally precipitated. We, therefore, document an open-system geochemical behavior. |
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| Keywords: | Mudstone Wilcox Group Illite&ndash smectite Element mobility |
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