AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Open-System Chemical Behavior in Deep Wilcox Group Mudstones, Texas Gulf Coast, USA
(1) Bureau of Economic Geology, University of Texas, Austin, TX.
(2) Macaulay LURI, Aberdeen, United Kingdom.
(3) Newcastle University, Newcastle, United Kingdom.
(4) University of Michigan, Ann Arbor, MI.
Wilcox Group mudstones have been massively, mechanically, and geochemically transformed over a temperature range of 20 to 200°C. Our research controlled Wilcox Group provenance and age by sampling from five wells parallel to the paleodepositional axis to produce a synthetic Wilcox Group profile. Mudstone physical properties have undergone significant change, porosity has been reduced from ~25 to <10%, and clay mineral fabric, quantified by high-resolution X-ray texture goniometry (HRXTG), has been enhanced in clay-rich mudstones and inhibited in more silt-prone samples. Bulk mineral change dominates the system, and we document it using quantitative X-ray diffraction, quartz, K-feldspar and kaolinite decrease, and illite + illite-smectite, chlorite, and plagioclase increase. These mineral transformations move elements from one mineralogical form to another; however, only Al2O3 and TiO2 are conserved within the system (trace-element ZrO2 is also conserved). Additional X-ray fluorescence data point toward K2O being added to and SiO2 released from the Wilcox Group. Cathodoluminescence and secondary electron imaging did not find this SiO2 locally precipitated. We, therefore, document an open-system geochemical behavior.