Banded iron formation deposition through photoferrotrophy and the evolution of earth surface chemistry and climate

Abstract

Banded Iron Formations (BIFs) are chemical sedimentary deposits composed of alternating iron- and silica-rich layers that are conspicuously abundant in the Precambrian rock record. The iron-rich bands likely form through the oxidation of dissolved ferrous iron [Fe(II)] and the subsequent precipitation of iron oxyhydroxides from ferruginous early oceans. Available evidence suggests that microbial activities may have played a key role in iron oxidation and BIF deposition. Proposed mechanisms include abiotic reactions with photosynthetic oxygen, reaction with oxygen catalyzed by iron- oxidizing bacteria (IOB), and anoxic oxidation by photoferrotrophs. These iron oxidation processes and the corresponding microbes may have existed concurrently, but their relative contributions to BIF deposition have not been considered. At the same time, the effects of Archean ocean pH on the growth and competition between different modes of primary production, i.e., photoferrotrophy and oxygenic photosynthesis, have not been quantitatively assessed. Furthermore, the potential microbial nature of BIF deposition implies that its rhythmic banding may offer an unexplored record of early marine productivity dynamics and their connection to climatic oscillations. In this dissertation, I develop new knowledge on photoferrotroph physiology under laboratory conditions. I subsequently integrate this new knowledge, together with literature-gathered microbial physiology, into models that examine the possible role of various Fe(II) oxidation pathways in BIF deposition and the competition among primary producers in early oceans. These models demonstrate the dominant role of photoferrotrophs in BIF de- position and suggest that increases in ocean pH rise acted in concert with enhanced nutrient flux to initiate the Great Oxidation Event. Additionally, I generate new data from a microbanded BIF sample and reveal stable solar cycles during the earliest Paleoproterozoic Era.