WORKING TOWARDS A COMPREHENSIVE DIAGENETIC MODEL FOR IRON-RICH SEDIMENTARY ROCKS

Some geochemical proxies hint at a prolonged interval of low or unstable surface oxygen levels across the Proterozoic following the Great Oxidation Event. Primary mineral phases in chemical sedimentary rocks archive seawater geochemistry across these critical geologic intervals. However, uncertainties in the effects of diagenesis and other post-depositional changes on proxy records complicate the reconstruction of geochemical attributes of evolving Proterozoic environments. A mineral reaction database that catalogs depositional vs. post-depositional mineral associations in Precambrian iron-rich chemical sedimentary units may aid in the deconvolution of the redox record. Here, we present a case study and proposed workflow to decipher texturally early minerals from diagenetic indicators through the development of paragenetic sequence sets paired with texture-specific mineral and geochemical data. The focus will be on historic drill cores that transect Paleoproterozoic assemblages of Minnesota and Wisconsin (USA). Such units offer the opportunity to systematically decipher diagenetic heterogeneity. Key results include: (1) silicified horizons preserve multiple incomplete reaction sequences that can be deciphered into a relative order of events; (2) geochemical data separated from co-occurring banded and granular couplets record the same redox information for any given depth interval; and (3) iron-rich chemical sedimentary rocks may be reactive post-deposition, and so a full accounting of heterogeneity and local element mobility may need to be built into the larger diagenetic framework.