A two‐stage, fault‐controlled paleofluid system at the southern termination of the Gypsum Valley salt wall, Paradox Basin, Colorado, USA. (26th January 2022)

• Record Type: Journal Article
• Authors: Lueck, Lillian R.; Fischer, Mark P.; Williams, Nicholas J.; Drost, Kerstin; Dodd, Justin P.; Chew, David M.
• Is Part Of: Basin research. Volume 34:Number 3(2022)
• Page Start: 1020
• Page End: 1054
• Publication Date: 2022-01-26
• Subjects: fault -- fluid -- Gypsum Valley -- Paradox Basin -- salt -- U‐Pb carbonate dating; Sedimentation and deposition -- Periodicals; Sedimentary basins -- Periodicals; 551
• DOI: 10.1111/bre.12649
• Languages: English
• ISSNs: 0950-091X

Abstract

Abstract: This study combines field structural analysis with thin‐section petrography, U‐Pb dating, and strontium, carbon and oxygen isotopic analysis of calcite fracture fills to constrain the evolution of the 2‐5 km scale paleofluid system around the faulted, plunging fold nose comprising the southern termination of the Gypsum Valley salt wall in the Paradox Basin, U.S.A. Brittle deformation in this region began with the formation of a down‐to‐the‐northeast, counter‐regional fault and then progressed into jointing and faulting in a radial pattern, followed by jointing in a concentric pattern. Coupled with increases in fracture abundance toward the faults, multiple stages of mineralization suggest that the faults served as efficient and long‐lived conduits for vertical fluid migration. Although fracture cement textures and calcite colour are variable throughout the area, the distribution of these characteristics does not correlate with fracture orientation, relative age, stratigraphic or structural position. Irrespective of the type of calcite comprising the fracture cements, δ 13 C values average near −7‰ (VPDB), whereas δ 18 O values cluster into groups whose averages are roughly 6‰ apart, with the more negative grouping stratigraphically restricted to fracture cements in Jurassic rocks. The stratigraphic segregation of δ 18 O values suggests the paleofluid system contained two distinct paleofluids, a more recent one comprised of meteoric waters and an older one comprising brine that originated in Pennsylvanian strata. 87 Sr/ 86 Sr ratios in fracture‐filling calcite cements indicate that the older fluid underwent fluid‐rock interaction with Permian strata and that this evolved fluid migrated upwards along the faults until the Triassic or Jurassic. Thereafter, fluid migrating along the faults was more meteoric and appears to have migrated downward along the faults, where it interacted with Permian strata. Consistent U‐Pb dates from carbonates precipitated from the older fluid suggest this stage of the paleofluid system was active around 240 Ma. Local burial history models and published temperatures for fracture cements elsewhere in the basin suggest the younger stage of the paleofluid system occurred during the Latest Cretaceous to Oligocene. This study highlights the spatial and temporal complexity of fluid systems in the vicinity of salt structures and emphasises the need to interpret them through careful integration of high resolution stratigraphic and structural data in the context of evolving salt tectonics. Abstract : Schematic representation of the hypothetical, time‐varying paleofluid system at the southeastern termination of the Gypsum Valley salt wall. Different colored arrows indicate varying fluid sources or geochemistry. Circular arrows are intended to generally illustrate mixing over a certain scale, not precise flow paths. (a) Paleofluid system that existed at the end of the Pennsylvanian. (b) Paleofluid system that existed around the time of the middle Permian. (c) Paleofluid system that existed at some time after deposition of the Morrison Formation (ca. 147 Ma) and from which Group 2 fracture cements precipitated. (d) Possibly stratigraphically segregated and fault‐controlled paleofluid system that existed in the Latest Cretaceous. Note that unit thicknesses near the diapir are highly schematic because the cross section cuts through the plunging nose of the salt wall, geometries vary rapidly into and out of the plane of the section and there may have been substantial out of plane motion of material. See the stratigraphic column in Figure 2 for the unit names, ages and labels. The fundamentals of each cross‐section geometry are based on the present day geometry shown in Figure 4b as well as the regional cross section restoration of Rowan et al. (2016).