Fracture-controlled paleohydrogeology in a basement-cored, fault-related fold: Sheep Mountain Anticline, Wyoming, United States

Abstract

[1] New geochemical and microstructural data constrain the origins and pathways of paleofluids during the growth of Sheep Mountain Anticline, Wyoming, United States. Oxygen, carbon, and strontium isotope studies were performed on prefolding and fold-related calcite veins and their sedimentary host rocks and combined to fluid inclusion microthermometry results. We show that most of the cements precipitated from Paleogene meteoric fluid. Stable isotopes and fluid inclusion homogenization temperatures further indicate that most veins were mineralized from upward moving fluids after these fluids were heated at depth (T > 110°C). This implies that fluids migrated along the basement thrust underlying the fold and/or at the base of the cover. Above the fault tip, the fluids circulated rapidly in the diffuse synfolding (and early folding) fracture network. The zone of preferential migration of the warm fluids is currently located in the backlimb of the fold, which supports some of the previously published structural interpretation of the subsurface. This study also highlights the potential of combined fracture analysis and geochemical analyses of paleofluid flows in fractures to constrain both the deformation history and the fluid flow during basement-involved shortening in Laramide-style forelands.

Crustal‐scale fluid flow during the tectonic evolution of the Bighorn Basin (Wyoming, USA)

“…Data set from Sheep Mountain Anticline is after Beaudoin et al . (). (b) δ 13 C vein calcite vs the δ 13 C limestone host‐rock and δ 18 O vein calcite vs δ 18 O limestone host‐rock in the same studied structures.…”

“…(c) Cross‐section of Rattlesnake Mountain Anticline (after Beaudoin et al ., ). (d) Cross‐section of Sheep Mountain Anticline (after Amrouch et al ., ; Beaudoin et al ., ).…”

“…130° E), being mainly located at their hinges. This set appears to have a high vertical persistence at SMA (Beaudoin et al ., ; Barbier et al ., , b) and is interpreted as related to layer curvature during folding. A third fracture set (set L‐III) comprises small‐scale newly formed strike‐faults and reverse faults and reactivated joints/veins witnessing a NE–SW‐directed compression during a late stage fold tightening in both folds (Amrouch et al ., ; Beaudoin et al ., ).…”

“…First, petrological and geochemical (oxygen, carbon and strontium isotope composition) analyses of calcite veins and of their host sedimentary rocks were performed along with fluid inclusion microthermometry and RAMAN microspectrometry to constrain the palaeohydrological systems at the fold scale. Second, the palaeohydrological evolution of the entire basin during its late Cretaceous‐early Tertiary tectonic evolution was reconstructed based on each of the individual fluid systems, including the one previously reconstructed at SMA (Beaudoin et al ., ).…”

Possible Involvement of Permian Phosphoria Formation Oil as a Source of REE and Other Metals Associated with Complex U-V Mineralization in the Northern Bighorn Basin?

“…Tectonic hydrothermal brecciation with associated hydrothermal dolomite [46] and calcite has been documented in the Madison Group in the Bighorn Basin and nearby Wind River Basin in oil reservoir characterization studies [47][48][49][50][51]. The silicic THB, in this district are the first reported in the Bighorn Basin.…”