Quantitative Color Analysis of Evaporites from the Middle Pennsylvanian Paradox Formation, Paradox Basin, Utah
Ofori Pearson, Russell Dubiel, Jennifer Eoff, Sarah Hawkins, Kristen Marra, Janet Pitman, and Katherine Whidden
The Paradox Basin is an asymmetric basin that formed along the southwestern edge of the Uncompahgre uplift during the Pennsylvanian – Permian Ancestral Rocky Mountain orogeny. The modern basin is located in the Four Corners region of the United States, mainly in southeastern Utah and southwestern Colorado. The Paradox Basin has a long history of geologic research due to excellent outcrop exposures combined with abundant natural resources. The U.S. Geological Survey completed a geologic assessment of undiscovered technically recoverable oil and gas resources in the Paradox Basin. As part of that effort, a detailed examination is being undertaken of the Delhi-Taylor Oil Company's Shafer-1 core, which was drilled on the crest of the Shafer anticline, about 20 km southwest of Moab, Utah. The core contains about 2,000 ft of the Middle Pennsylvanian Paradox Formation, which is a thick succession of halite and sylvite, anhydrite, siltstone, and black shale. Analysis of the core indicates that at least five different scales of nested cyclicity are represented. This cyclicity is likely due to changes in local and regional paleoclimate, which affected temperatures and the salinity of basin waters. The core contains several thick intervals of halite, commonly with variable amounts of red sylvite that is present either as discrete lamina or as disseminated fine crystals within the halite. Sylvite is one of the last evaporite minerals to precipitate out of solution, most likely during the driest periods. A preliminary quantitative color analysis of one of the thick halite intervals indicates that the amount of sylvite increases towards the upper-middle portion of the halite interval before abruptly decreasing. The color analysis was done with high-resolution core photographs taken under consistent lighting conditions. Color distributions within the photographs were analyzed using a Perl script. An increase in the amount of sylvite within the halite interval is consistent with the idea that already dry-climate conditions became even more arid during precipitation of the middle interval.
AAPG Search and Discovery Article #90156©2012 AAPG Rocky Mountain Section Meeting, Grand Junction, Colorado, 9-12 September 2012