Details

Autor(en) / Beteiligte

• McIntosh, Jennifer
• Kim, Ji‐Hyun
• Bailey, Lydia
• Osburn, Magdalena
• Drake, Henrik
• Martini, Anna
• Reiners, Peter
• Stevenson, Bradley
• Ferguson, Grant

Titel

Burial and Denudation Alter Microbial Life at the Bottom of the Hypo‐Critical Zone

Ist Teil von

• Geochemistry, geophysics, geosystems : G3, 2023-06, Vol.24 (6), p.n/a

Ort / Verlag

Washington: John Wiley & Sons, Inc

Erscheinungsjahr

2023

Quelle

Wiley-Blackwell Full Collection

Beschreibungen/Notizen

• How subsurface microbial life changed at the bottom of the kilometers‐deep (hypo) Critical Zone in response to evolving surface conditions over geologic time is an open question. This study investigates the burial and exhumation, biodegradation, and fluid circulation history of hydrocarbon reservoirs across the Colorado Plateau as a window into the hypo‐Critical Zone. Hydrocarbon reservoirs, in the Paradox and Uinta basins, were deeply buried starting ca. 100 to 60 Ma, reaching temperatures >80–140°C, likely sterilizing microbial communities present since the deposition of sediments. High salinities associated with evaporites may have further limited microbial activity. Upward migration of hydrocarbons from shale source rocks into shallower reservoirs during maximum burial set the stage for microbial re‐introduction by creating organic‐rich “hot spots.” Denudation related to the incision of the Colorado River over the past few million years brought reservoirs closer to the surface under cooler temperatures, enhanced deep meteoric water circulation and flushing of saline fluids, and likely re‐inoculated more permeable sediments up to several km depth. Modern‐ to paleo‐hydrocarbon reservoirs show molecular and isotopic evidence of anaerobic oxidation of hydrocarbons coupled to bacterial sulfate reduction in areas with relatively high SO4‐fluxes. Anaerobic oil biodegradation rates are high enough to explain the removal of at least some portion of postulated “supergiant oil fields” across the Colorado Plateau by microbial activity over the past several million years. Results from this study help constrain the lower limits of the hypo‐Critical Zone and how it evolved over geologic time, in response to changing geologic, hydrologic, and biologic forcings. Plain Language Summary This study investigates the dynamic geologic, hydrologic, and biological history of hydrocarbon reservoirs across the Colorado Plateau to gain insights into how the lower boundaries for microbial life evolved in response to changes in earth surface conditions. Microbial communities at depth were likely sterilized in the geologic past when sediments were deeply buried, reaching temperatures beyond the limits for microbial life. Generation and upward migration of oil and gas, during this time, set the stage for later re‐introduction of microbial communities that degrade hydrocarbons. Recent down‐cutting of the Colorado River and erosion of the Colorado Plateau, over the past few million years, brought hydrocarbon reservoirs closer to the surface, at lower temperatures and in contact with circulating groundwater. Associated transport of microbial communities and solutes drove the biodegradation of oil in more permeable reservoirs. This type of biological activity could have been responsible for the removal of ancient oil fields across the Colorado Plateau. The integrated approach used in this study could be applied to other crustal environments to unravel the co‐evolution of microbe‐rock‐fluid systems at the bottom of the deep biosphere. Key Points Sediments at depth across the Colorado Plateau were likely sterilized during maximum burial and hydrocarbon generation Hydrocarbon‐containing sediments were re‐inoculated during recent denudation, meteoric water circulation, and flushing of saline fluids Some portion of hydrocarbons were removed via anaerobic oxidation coupled to bacterial sulfate reduction in areas of sulfate influx