Biogenic Fe(III) minerals: From formation to diagenesis and preservation in the rock record

Fe-metabolizing bacteria are intimately linked to the cycling of Fe in modern environments and have likely been key players in the evolution of the Earth's biogeosphere. Fe minerals have also been suggested as a key preservative of cell organic matter in sediments, keeping otherwise labile phases conserved at least on time scales of 100,000 years. The interpretation of a biological influence on the Fe rock record is difficult without a deeper understanding of the mechanisms of biogenic Fe(III) and Fe(II) mineral formation, the character of these minerals, and their diagenesis over short and long time scales. Here, we present the recent advances in the study of abiogenic and biogenic Fe(III) minerals. In particular, we focus on the role of Fe(II)-oxidizing bacteria in the deposition of ancient banded iron formations (BIF). We discuss this work within the framework of the main challenge: separating biogenic from abiogenic processes over deep time. We describe how efforts in isotope geochemistry, biomarker research, mineral analysis and biogeochemistry are helping to establish a window to the past. Finally, we present some new approaches that help investigate the main processes leading to the formation and potential fate of Fe-organic matter aggregates.