The hydrogeochemical evolution of basinal fluids in the Paradox Basin: Implications for sources, flowpaths, and residence time

Jihyun Kim, Ambria Dell’Oro, Chandler Noyes, Jennifer McIntosh, Lin Ma1, and Zheng-Tian Lu2
Department of Hydrology and Atmospheric Sciences
The University of Arizona

The Paradox Basin in the Colorado Plateau has abundant manifestations of paleofluid flow, including sandstone bleaching and ore mineralization, salt tectonics, and hydrocarbon, CO2, and He reservoirs. Formation water and dissolved gas samples were collected to evaluate the hydrochemical composition, sources, and residence time of remnant fluids as an indicator of the long-term evolution of the Paradox Basin fluid-rock system, using major ion and isotopic (δ18O & δ2H –H2O; δ34S & δ18O-SO4; 87Sr/86Sr) signatures of fluids and preliminary radio-krypton (81Kr) dating results from produced gases. Shallow brines near salt anticlines are dominantly derived from dissolution of evaporites by meteoric water and minor mixing with paleo-evaporated seawater (PES). Pennsylvanian Honaker Trail Formation brines (~0.5 Ma; 81Kr water age) are a mixture of (1) Upper Paleozoic formation water from influx of meteoric water that oxidized sulfides and acquired radiogenic Sr from the overlying Permian Cutler siliclastic formations; (2) partially-evaporated seawater; and (3) PES (>1.5 Ma; 81Kr water age). Mississippian and Devonian formation waters (~0.8 Ma; 81Kr water age) were surprisingly young and likely represent PES that was diluted by meteoric recharge, which interacted with radiogenic basement rocks or arkosic sandstones, and dissolved evaporites at the base of the Paradox Formation.

1Department of Geological Sciences, University of Texas at El Paso, El Paso, TX
2University of Science and Technology of China, Hefei, China

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