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The Paradox Basin in the Colorado Plateau (USA) has some of the most iconic records of paleofluid flow, including sandstone bleaching and ore mineralization, and hydrocarbon, CO2, and He reservoirs, yet the sources of fluids responsible for these extensive fluid-rock reactions are highly debated. This study, for the first time, characterizes fluids within the basin to constrain the sources and emergent behavior of paleofluid flow resulting in the iconic rock records. Major ion and isotopic (δ18Owater; δDwater; δ18OSO4; δ34SSO4; δ34SH2S; 87Sr/86Sr) signatures of formation waters were used to evaluate the distribution and sources of fluids and water-rock interactions by comparison with the rock record. There are two sources of salinity in basinal fluids: (1) diagenetically altered highly evaporated paleo-seawater-derived brines associated with the Pennsylvanian Paradox Formation evaporites; and (2) dissolution of evaporites by topographically driven meteoric circulation. Fresh to brackish groundwater in the shallow Cretaceous Burro Canyon Formation contains low Cu and high SO4 concentrations and shows oxidation of sulfides by meteoric water, while U concentrations are higher than within other formation waters. Deeper brines in the Pennsylvanian Honaker Trail Formation were derived from evaporated paleo-seawater mixed with meteoric water that oxidized sulfides and dissolved gypsum and have high 87Sr/86Sr indicating interaction with radiogenic siliciclastic minerals. Upward migration of reduced (hydrocarbon- and H2S-bearing) saline fluids from the Pennsylvanian Paradox Formation along faults likely bleached sandstones in shallower sediments and provided a reduced trap for later Cu and U deposition. The distribution of existing fluids in the Paradox Basin provides important constraints to understand the rock record over geological time.
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Paleofluid Flow in the Paradox Basin: Introduction
This field trip focuses on several of the classic Cu and U(-V) ore systems of the Colorado Plateau in the context of diverse geologic environments, processes, and consequences of fluid flow of the Paradox Basin. The Paradox Basin contains a >300-m.y. history of fluid flow and resource generation. Late Paleozoic development of a K-rich evaporitic foreland basin created a setting upon which later fluid-dominated processes generated economically significant accumulations of hydrocarbons, K-rich brines, CO2, and—most notably—metals including, significant deposits of Cu and some of the largest U and V resources of the United States. The sourcing and movement of fluids of diverse types and the resulting multiplicity of metasomatic features reflect a complex history starting with salt movement beginning in the Permian, sedimentation continuing intermittently into the Paleogene, distal manifestations of Cretaceous to Paleocene orogenesis, Cenozoic magmatism and, most recently, Neogene exhumation. In light of this broader context, we will examine Cu(-Ag) systems associated with salt anticlines at Paradox Valley (Cashin mine) and Lisbon Valley (Lisbon Valley mine), superimposed modern and ancient systems at Sinbad Valley, and contrasting U-V systems in the Jurassic Morrison Formation at Monogram Mesa (Uravan district) and Triassic Chinle Formation at Lisbon Valley (Big Indian district). In these areas, we consider the types and sources of various fluids (brines, hydrocarbons, meteoric), their solutes, the sequence of events, and links to overall basin evolution. A key objective of the trip is to use these examples and current interpretations to stimulate discussion and research about fluid flow and mass transfer in basinal settings.
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- Award ID(s):
- 1725338
- PAR ID:
- 10113160
- Date Published:
- Journal Name:
- Guidebook series
- Volume:
- 59
- ISSN:
- 2374-6955
- Page Range / eLocation ID:
- 1-12
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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