Biotic and abiotic chemical weathering of siliciclastic sediments in cold environments

Dissertation Summary Chemical weathering of silicate minerals is one of the most important Earth processes, moderating atmospheric carbon dioxide levels by consumption of carbon dioxide during hydrolysis of silicates (Nesbitt and Young, 1982; White and Peterson, 1990; Velbel, 1993; White and Blum, 1995; White et al., 1996; White and Brantley, 2003; White and Buss, 2014). Owing to its significance to the carbon cycle, and sensitivity to climatic conditions, chemical weathering and indices developed to determine the extent of weathering (i.e., Chemical Index of Alteration- CIA) have been the focus of significant studies aimed at investigating implications for paleoclimate in both terrestrial and extraterrestrial settings (i.e., Nesbitt and Young, 1982; Nesbitt and Young, 1989; Soreghan and Soreghan, 2007; Yang et al., 2016; Siebach et al., 2017; Deng et al., 2022). Chemical weathering leaves physical, chemical, and mineralogical signatures on rocks, sediments, and the aquatic environment, both via abiotic and biotic pathways. Therefore, weathering signatures studied on Earth are analogs for extraterrestrial signatures of surface alteration processes (i.e., Cannon et al., 2015; Olsson-Francis et al., 2017). However, abiotic and biotic weathering pathways in cold environments (i.e., within glacial settings) and subsequent weathering signatures remain poorly understood. This dissertation investigates biotic and abiotic weathering signatures and pathways within various glaciated settings, with the focus on Antarctica and Iceland as climatic and mineralogical analogs of Mars. Non-glaciated settings are also investigated to compare weathering signatures generated within cold and hot climates. Chapters within this dissertation are formatted as peer-reviewed journal publications (in prep. or published). The Chemical Index of Alteration (CIA) was developed to quantify the extent of weathering based on major oxides within silicates that are significantly associated with weathering: Al2O3, CaO, Na2O and K2O (Nesbitt and Young, 1982). CIA has been largely used to interpret paleoclimate, and correlated with climate parameters (mean annual temperature, MAT, and mean annual precipitation, MAP), especially with MAT within tropical soil profiles and watersheds on felsic bedrock (i.e., Nesbitt and Young, 1989, Rasmussen et al., 2011; Yang et al., 2016; Joo et al., 2018a). However, these correlations don’t seem to apply to glaciated settings (Deng et al., 2022), and various studies discuss shortcomings of applying CIA when mafic rock types are involved, as mafic major oxide components (such as FeO and MgO) are not incorporated within CIA calculations, and CIA is highly dependent on CaO that can result in artificially underestimated CIA values when the source rock contains high CaO (Nesbitt et al., 1996; Siebach et al., 2017; Mangold et al., 2019; Berger et al., 2020). Despite these documented issues, CIA remains widely utilized for various depositional settings, including potentially glaciated environments on Earth and Mars (i.e., Nesbitt and Young, 1982; Balburg and Dobrzinski 2011; Marra et al., 2017; Hurrowitz et al., 2017; Wang et al., 2020). In Chapter 1, I investigate and compare weathering signatures (mineralogy, chemistry, grain size, and surface area) within mud-sized (