Evolution of paleofluids and hydrochemical processes in the Paradox Basin

Jihyun Kim, Ambria Dell'Oro, Chandler Noyes, Jennifer McIntosh, Lin Ma1, and Zheng-Tian Lu2

Hydrology and Atmospheric Sciences
The University of Arizona

The Paradox Basin in the Colorado Plateau has diverse manifestations of paleofluid flow, including widespread sandstone bleaching and ore mineralization, distinctive salt deposits and abundant hydrocarbon accumulations. Forty-six fluid samples were collected in 2018 to evaluate the hydrochemical distribution and sources of modern fluids as an indicator of the long-term evolution of paleofluids in the Paradox Basin. Surface waters and shallow groundwater in the Paradox and Sinbad salt valleys contain Na-Cl type brines from meteoric water dissolution of halite and gypsum. Sr and S isotopic signatures of the Na-Cl type brines confirm that dissolution of evaporites is the dominant source of solutes. Holocene to Pleistocene age shallow groundwaters outside the salt valleys are Na-Ca-HCO3 type dilute meteoric waters with S and Sr isotope ratios indicative of interaction with sulfides and carbonates. Deeper Ca-Cl type basinal fluids come from remnant paleo-evaporated seawater that has dissolved evaporites, reacted with radiogenic minerals, and oxidized sulfides. The distribution of trace metals in fluids is being interpreted with the concomitant sedimentary record. Radio-krypton (81Kr) is also being analyzed to date relatively old (0.05 to 1.3 Ma) formation water.

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

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