A thermochronological history of burial and exhumation at Kevin Dome, Northwest Montana including the origin of CO2 in Upper Devonian Duperow Formation and the Bakken Petroleum system at the Dome

Abstract

Kevin Dome is a geologic structure and historic hydrocarbon producer in northwest Montana. This structure is also a known CO 2 reservoir, yet its development has not been constrained with thermochronological techniques and the origin of the natural (~ 283 x 109 m 3) CO 2, of the Upper Devonian Duperow Formation, is not well understood. This work seeks to create a temporal understanding of the burial and exhumation history of Kevin Dome including the hydrocarbon generation and CO 2 emplacement. I constrained the burial and exhumation history at Kevin Dome with low-temperature thermochronology, carbonate clumped isotope thermometry, and thermobarometric proxies. I also tested for microbial, thermogenic, and magmatic CO 2 source(s) as well as CH 4 and N 2 gas sources at the dome with major gas composition, stable and noble gas isotopic geochemistry methods. I found that Kevin Dome rocks were buried to oil and gas generation windows before exhumation during the Late Cretaceous-Paleocene (~65 - 72Ma) and the Oligocene-Miocene (~ 15 - 26Ma) at an average rate of ~ 0.27 mm/yr. My study supports an evolved forebulge-dome origination model for Kevin Dome that is driven by the Late Cretaceous-Paleocene emplacement of the Rocky Mountain overthrust in a Foreland Basin setting in northwestern Montana (and proximal Canada) and an Oligocene-Miocene erosional or epeirogenic event not previously recognized in northwest Montana. I estimated ~4 - 5 km more overburden erosion than was previously thought in the region and suggest that the Oligocene-Miocene exhumation terminated hydrocarbon generation at Kevin Dome. In terms of CO 2 origin, my data supports a magmatic origin for the Duperow CO 2, with emplacement during the Sweetgrass Hills igneous complex intrusion(~52 Ma). I also found that the CH4 and N2 gases at Kevin Dome were mainly thermogenic in origin. A CO 2 solubility model showed that ~98% of the CO 2 has been dissolved into the groundwater in the Bakken petroleum system's hydrocarbon-bearing reservoirs at Kevin Dome during migration. I present a novel approach of integrating modern t-T sensitive techniques, stratigraphy, thermal maturity data, and isotopic geochemistry to address the structural development of sedimentary basins/domes, hydrocarbon generation, and magmatic CO 2 emplacement and subsequent evolution.