Zinc in Precambrian iron formations: The record, partitioning, diagenetic effects and implications for eukaryotic metallome evolution

Abstract

Zinc is amongst the most important trace elements for eukaryotes. Previous work has suggested it to have been at biolimiting concentrations for much of the Precambrian, thereby limiting eukaryotic evolution. Yet, the iron formation (IF) record, a critical proxy for paleomarine conditions, has remained unexplored. Here, we examine aspects of the IF record and its geochemistry, including: thermodynamic models for Zn in paleomarine conditions, the abundance of Zn through geological time, and hypothesized partitioning models. Further, experimental constraints such as, derived partitioning isotherms and an assessment of the mobility of Zn (and for comparison Ni) during IF diagenesis are presented. Taken together, these examinations inform our interpretation of the IF record, indicating a static Zn reservoir throughout geological time that was unlikely to have been biolimiting to early eukaryotes. Instead, the most parsimonious explanation for a delay in eukaryotic evolution is tied to biological development, rather than marine geochemistry. Supplemental files to this thesis can be found at https://doi.org/10.7939/r3-tjbp-ec42.