| Description |
Diagenetic variables (e.g., microbial influence, sediment composition and fluid chemistry) are investigated to determine the effects on iron redox reactions and iron (oxyhydr)oxide nucleation, cement textures, mineralogy and chemistry. Three individual examinations are conducted in the Colorado Plateau, USA: 1. reservoir fluid chemistry in a natural fossil CO2 reservoir in the Jurassic Navajo Sandstone exposed in Justensen Flats in the northern San Rafael Swell, 2. concretion formation in the reactive, volcaniclastic Jurassic Brushy Basin Member of the Morrison Formation, and 3. comparative microbial influences in the precipitation of iron (oxyhydroxides) in a modern Ten Mile Graben spring system and the Brushy Basin Member. Bulk geochemistry in a lithologically controlled, iron (oxyhydr)oxide reaction front in Justensen Flats shows that the precipitating fluid in the reservoir was likely a CO2- and hydrocarbon-charged fluid and that CO2 injection into a saline reservoir would result in dolomite precipitation and significantly reduce porosity. Chemical and physical concretion comparisons in the Brushy Basin Member show that reactants are moving via fluid flow in porous host rocks and producing uniform concretion morphologies and mineralogies. In reactive Brushy Basin Member claystone and siltstone lithofacies, reactants are being sourced from abundant ashes reacting with groundwater to create localized diagenetic microenvironments and produce variable concretion mineralogies and morphologies. Variability of fluids on regional to outcrop scales and lithologically controlled fluid flow and cement precipitation in permeable reservoirs furthers the science of carbon capture and sequestration. Comparison of modern and 100ka microbial iron (oxyhydr)oxides in tufas at the Ten Mile Graben spring system shows that biosignatures exhibit some degradation and recrystallization on millennial time scales, although biotic features are clearly recognizable. Microbial fossils in the Brushy Basin Member are associated with macroscopic biotic features such as charophyte molds. Biogenic iron (oxyhydr)oxides in modern tufas and Jurassic rocks exhibit two distinct elemental suites that function as biosignatures: 1. C, Fe, and As, and 2. C, S, Se. Biogeochemical markers provide diagnostics for depositional environment, fluid chemistry and potential microbial fossils and/or biosignatures to aid in the exploration of similar iron- and clay-rich sediments on Mars in Gale Crater. |
