Proxies from ancient rocks can be inaccurate if their chemistry is not completely understood or if they do not reflect their original environment. (Bio)geochemically-precipitated sediments initially reflect their current environment, but sediments then undergo a series of chemical alterations into different minerals in a process known as ‘diagenesis’. In addition, some rocks are subsequently altered even further by high pressures, heat, high-temperature fluids, or oxidative weathering. We make detailed investigations into the extent of diagenesis and alteration, especially for elements that may signal the presence of oxygen. More recently, we have also begun to perform simulated diagenesis experiments to advance our understanding of mineral diagenesis and alteration, improving our interpretation of how rocks and minerals record ancient environments.
Relevant publications:
Koshurba K, Johnson JE, (in revision) Braunite synthesized under simulated diagenetic conditions: Implications for the ancient manganese cycle.
Hinz IL, Rossi L, Ma C, Johnson JE (2023), Simulated Diagenesis of the Iron-Silica Precipitates in Banded Iron Formations, American Mineralogist 108 (9): 1732–1753. doi: 10.2138/am-2022-8758.
Slotznick SP, Johnson JE, Rasmussen B, Raub TD, Webb SM, Kirschvink JL, Fischer WW (2022) Re-examination of 2.5 Ga “Whiff” of Oxygen Interval Points to Anoxic Ocean Before GOE, Science Advances 8 (1), 1-10. doi: 10.1126/sciadv.abj7190
Guillaume Paris G, Fischer WW, Johnson JE, Webb SM, Present TM, Sessions AL, Adkins JF (2020) Deposition of sulfate aerosols with positive Δ33S in the Neoarchean, Geochimica et Cosmochimica Acta, 285, 1-20, doi: https://doi.org/10.1016/j.gca.2020.06.028.
Johnson JE, Savalia P, Davis R, Kocar BD, Webb SM, Nealson KH, Fischer WW (2016) Real-time Manganese Phase Dynamics during Biological and Abiotic Manganese Oxide Reduction, Environmental Science and Technology, 50 (8), 4248-4258.
Johnson JE, Webb SM, Ma C, Fischer WW (2016) Manganese mineralogy and diagenesis in the sedimentary rock record, Geochimica et Cosmochimica Acta, 173, 210-231.
Johnson JE, Gerpheide A, Lamb MP, Fischer WW (2014) O2 constraints from Paleoproterozoic detrital pyrite and uraninite, Geological Society of America Bulletin, 126 (5-6), 813-830.
Fischer WW, Fike DA, Johnson JE, Raub TD, Guan Y, Kirschvink JL, Eiler JM (2014) SQUID-SIMS, a useful approach to uncover primary signals in the Archean sulfur cycle, Proceedings of the National Academy of Sciences, 111, 5468-5473.
Johnson JE, Webb SM, Thomas K, Ono S, Kirschvink JL, Fischer WW (2013) Manganese-oxidizing photosynthesis before the rise of cyanobacteria, Proceedings of the National Academy of Sciences 110 (28), 11238-11243.