Pyrite mega-analysis reveals modes of anoxia through geological time

Abstract

The redox structure of the water column in anoxic basins through geological time remains poorly resolved despite its importance to biological evolution/extinction and biogeochemical cycling. Here, we provide a temporal record of bottom and pore water redox conditions by analyzing the temporal distribution and chemistry of sedimentary pyrite. We combine machine-reading techniques, applied over a large library of published literature, with statistical analysis of element concentrations in databases of sedimentary pyrite and bulk sedimentary rocks to generate a scaled analysis spanning the majority of Earth’s history. This analysis delineates the prevalent anoxic basin states from the Archaean to present day, which are associated with diagnostic combinations of five types of syngenetic pyrite. The underlying driver(s) for the pyrite types are unresolved but plausibly includes the ambient seawater inventory, precipitation kinetics, and the (co)location of organic matter degradation coupled to sulfate reduction, iron (oxyhydr)oxide dissolution, and pyrite precipitation.

Microbially-mediated aerobic oxidation of trace element-bearing pyrite in neutral-pH sandstone aquifer sediments

“…A recent compilation of the temporal distribution of pyrite in sedimentary rocks 59 suggests that the majority (83%) of pyrite-bearing geological strata are siliciclastic and dominantly fine-grained, i.e. the types of materials that would typically represent confining units in intermediate and regional groundwater flow systems.…”

Intrashelf Basin Record of Redox and Productivity Changes Along the Arabian Margin of Neo-Tethys During Oceanic Anoxic Event 1a

“…The latter is also suggested by the contemporaneous enrichment in Ni and Cu, both of which occur in organic phases and may contribute to pyrite formation (Tribovillard et al, 2006). Given that pyrite framboids precipitate relatively quickly under diffusion-limited conditions and from waters at the supersaturation limit with respect to FeS or FeS2 (Emmings et al, 2022), the local presence of pyrite framboids (~2-8 μm; Jafarian et al, 2023) suggests that euxinic conditions may have existed for limited periods of time within microenvironments, ambient bottom waters or porewaters. The majority of trace metals enriched in this succession can form sulfides, leading to the assumption that sulfidic (euxinic) conditions could have been present at or near the sediment-water interface in some short periods, and that reductive mobilization trapped these trace metals in the sediments (e.g., Hetzel et al, 2011;Sanchez-Hernandez and Maurrasse, 2015).…”

Primary Controlling Factors of Apatite Trace Element Composition and Implications for Exploration in Orogenic Gold Deposits

“…J. Zhou et al, 2023). The Z-score scaling represents the distance between the raw values and the overall mean and is measured in units of standard deviation (Emmings et al, 2022). When the Haoyaoerhudong (biotite Ar-Ar, J. P. Wang et al, 2014), Hatu (whole rock Rb-Sr, H. Q.…”

“…Initially, each observation is initially considered as an isolated group, and then an iterative agglomeration process is applied to merge the two most similar observations until all observations are pooled in a single group (Filzmoser et al., 2018; Reimann et al., 2008; Z. J. Zhou et al., 2023). The Z‐score scaling represents the distance between the raw values and the overall mean and is measured in units of standard deviation (Emmings et al., 2022). When the raw values are below the mean, Z is negative, and conversely, it is positive when they exceed the mean.…”