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