Reactive Transport Modeling Of Fluid-Rock-Microbial Interactions In The Deep Critical Zone
Presenter: Tong Guo P61
Co-Author(s): Grant Ferguson, Coleman Hiett, Peter Reiner, and Jennifer McIntosh
Advisor(s): Jennifer McIntosh
1Hydrology & Atmospheric Sciences
Iron cycling is a common process from the land-surface to the bottom of the meters- to kilometers-deep Critical Zone. Microorganisms help facilitate and gain energy from iron oxidation-reduction reactions, which can sustain deep subsurface microbial communities over geologic timescales. In the Colorado Plateau, bleaching of former red bed sandstones by reduced fluids mobilized iron and deposited it downgradient, potentially creating ‘hot spots’ for microbial activity. However, it is unclear the compositions of the fluids involved in iron cycling and their impacts on the mineralogy and physical properties of joint systems in sandstones that may have influenced fluid transport and microbial communities. We hypothesize iron mineralization along joint systems is the result of mixing of oxygenated fresh meteoric water and deeper, hydrocarbon-bearing reduced fluids. To test this hypothesis, we use a geochemical modeling code (PHREEQC) to investigate the extent, mechanisms, and timescales of fluid mixing and fluid-rock-microbe reactions in the Navajo Sandstone. Preliminary one-dimensional modeling results show that mixing of reduced, CH4 and CO2-bearing deep groundwater with oxygenated recharge waters dissolves albite, anorthite and siderite and precipitates quartz, kaolinite and hematite. Moving forward, we will develop two-dimensional models using PFLOTRAN to investigate the behavior of mixing fluids and the spatial extent of physical and chemical changes in joint systems.