--> Evolution of Basin Brines in the Paradox Formation, Western United States: Evidence From Sedimentary Textures, Fluid Inclusions and Stable Isotopes, by S. C. Williams-Stroud and T. K. Kyser; #90986 (1994).

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Abstract: Evolution of Basin Brines in the Paradox Formation, Western United States: Evidence From Sedimentary Textures, Fluid Inclusions and Stable Isotopes

Sherilyn C. Williams-Stroud, T. Kurtis Kyser

Identification of primary depositional textures in halite rocks is usually based on euhedral crystals of halite with anhydrite or clay drapes, halite cube cumulate layers, erosional surfaces separating successive layers of halite crust growth, and chevron fluid inclusion banding. Interactions of the rocks with early diagenetic and later post-burial brines can cause recrystallization of the halites and/or formation of pseudomorphs, or complete obliteration of the original sedimentary textures. Some halite beds in the Paradox Formation show excellent preservation of sedimentary textures in several cored intervals, while other beds display textures that suggest significant recrystallization and tectonic deformation. Fluid inclusion homogenization temperatures were measured in halite crys als which appear to be primary (crystals which have chevron fluid inclusion banding, or fluid inclusion-rich halite cumulate cubes), in diagenetic halite (void fills or replacements of euhedral crystals which are fluid inclusion-poor), and halite of post-burial origin (anhedral crystals or crystals from tectonically deformed zones). Fluid inclusion homogenization temperatures for all samples ranged from 25°C to more than 100°C, with the lower temperatures generally associated with the primary textures. Somewhat enigmatic are the very high homogenization temperatures (90°-100°C) associated with bottom-growth halite crusts in crystals with well-developed chevron fluid inclusion banding. Although the geology of rocks associated with the Paradox Formation indicates a majo source of brines was seawater, stable isotope data for brines extracted from the fluid inclusions and the geochemistry of the soluble salt minerals in the halite indicate that meteoric water and groundwater were as important as seawater in supplying solutes to the basin. Even though the Paradox Formation has undergone considerable post-burial interactions with brines, and suffered the effects of tectonic deformation, some parts of the Formation still retain information about the original depositional environment. By separating the brine composition data on the basis of sedimentary and post-depositional textures, the halite rocks provide a detailed record of the brine evolution of the basin during deposition and after burial.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994