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1. Mineral Weathering and Bedrock Weakening: Modeling Microscale Bedrock Damage Under Biotite Weathering

   https://doi.org/10.1029/2019JF005068  

   Shen, Xianda; Arson, Chloe; Ferrier, Ken L.; West, Nicole; Dai, Sheng (November 2019, Journal of Geophysical Research: Earth Surface)

   Bedrock weakening is of wide interest because it influences landscape evolution, chemical weathering, and subsurface hydrology. A longstanding hypothesis states that bedrock weakening is driven by chemical weathering of minerals like biotite, which expand as they weather and create stresses sufficient to fracture rock. We build on recent advances in rock damage mechanics to develop a model for the influence of multimineral chemical weathering on bedrock damage, which is defined as the reduction in bedrock stiffness. We use biotite chemical weathering as an example application of this model to explore how the abundance, aspect ratio, and orientation affect the time‐dependent evolution of bedrock damage during biotite chemical weathering. Our simulations suggest that biotite abundance and aspect ratio have a profound effect on the evolution of bedrock damage during biotite chemical weathering. These characteristics exert particularly strong influences on the timing of the onset of damage, which occurs earlier under higher biotite abundances and smaller biotite aspect ratios. Biotite orientation, by contrast, exerts a relatively weak influence on damage. Our simulations further show that damage development is strongly influenced by the boundary conditions, with damage initiating earlier under laterally confined boundaries than under unconfined boundaries. These simulations suggest that relatively minor differences in biotite populations can drive significant differences in the progression of rock weakening. This highlights the need for observations of biotite abundance, aspect ratio, and orientation at the mineral and field scales and motivates efforts to upscale this microscale model to investigate the evolution of the macroscale fracture network. 

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2. Mineral surface area in deep weathering profiles reveals the interrelationship of iron oxidation and silicate weathering

   https://doi.org/10.5194/esurf-11-51-2023  

   Fisher, Beth A.; Yoo, Kyungsoo; Aufdenkampe, Anthony K.; Nater, Edward A.; Feinberg, Joshua M.; Nyquist, Jonathan E. (January 2023, Earth Surface Dynamics)

   Abstract. Mineral specific surface area (SSA) increases as primaryminerals weather and restructure into secondary phyllosilicate, oxide, andoxyhydroxide minerals. SSA is a measurable property that captures cumulativeeffects of many physical and chemical weathering processes in a singlemeasurement and has meaningful implications for many soil processes,including water-holding capacity and nutrient availability. Here we reportour measurements of SSA and mineralogy of two 21 m deep SSA profiles attwo landscape positions, in which the emergence of a very small mass percent(<0.1 %) of secondary oxide generated 36 %–81 % of the total SSAin both drill cores. The SSA transition occurred near 3 m at bothlocations and did not coincide with the boundary of soil to weathered rock. The3 m boundary in each weathering profile coincides with the depth extentof secondary iron oxide minerals and secondary phyllosilicates. Althoughelemental depletions in both profiles extend to 7 and 10 m depth, themineralogical changes did not result in SSA increase until 3 m depth. Theemergence of secondary oxide minerals at 3 m suggests that this boundary may bethe depth extent of oxidation weathering reactions. Our results suggest thatoxidation weathering reactions may be the primary limitation in thecoevolution of both secondary silicate and secondary oxide minerals. Wevalue element depletion profiles to understand weathering, but our findingof nested weathering fronts driven by different chemical processes (e.g.,oxidation to 3 m and acid dissolution to 10 m) warrants the recognition thatelement depletion profiles are not able to identify the full set ofprocesses that occur in weathering profiles. 

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3. Deep abiotic weathering of pyrite

   https://doi.org/10.1126/science.abb8092  

   Gu, Xin; Heaney, Peter J.; Reis, Fabio D. A. Aarão; Brantley, Susan L. (October 2020, Science)

   Pyrite is a ubiquitous iron sulfide mineral that is oxidized by trace oxygen. The mineral has been largely absent from global sediments since the rise in oxygen concentration in Earth’s early atmosphere. We analyzed weathering in shale, the most common rock exposed at Earth’s surface, with chemical and microscopic analysis. By looking across scales from 10⁻⁹to 10²meters, we determined the factors that control pyrite oxidation. Under the atmosphere today, pyrite oxidation is rate-limited by diffusion of oxygen to the grain surface and regulated by large-scale erosion and clast-scale fracturing. We determined that neither iron- nor sulfur-oxidizing microorganisms control global pyrite weathering fluxes despite their ability to catalyze the reaction. This multiscale picture emphasizes that fracturing and erosion are as important as atmospheric oxygen in limiting pyrite reactivity over Earth’s history. 

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4. Using a mathematical model of a weathering clast to explore the effects of curvature on weathering

   https://doi.org/10.1016/j.chemgeo.2015.03.027  

   Lebedeva, M.I.; Sak, P.B.; Ma, L.; Brantley, S.L. (May 2015, Chemical Geology)
5. Lithium isotopic fractionation during weathering and erosion of shale

   https://doi.org/10.1016/j.gca.2020.12.006  

   Steinhoefel, Grit; Brantley, Susan L.; Fantle, Matthew S. (February 2021, Geochimica et Cosmochimica Acta)