Deep-water dissolved iron cycling and reservoir size across the Ediacaran-Cambrian transition

Abstract The majority of the deep ocean was likely under ferruginous conditions during the first four billion years of Earth's history. As the atmosphere was gradually oxygenated, the sources, sinks, redox cycling, and reservoir size of dissolved iron in the deep ocean are likely to have changed dramatically. Whether deep water was thoroughly oxygenated by the time of the Ediacaran-Cambrian transition, and the relationship of this oxygenation to the Cambrian explosion, remains debated. To explore the degree of oceanic oxygenation and its effect on Cambrian explosion, we measured the iron isotopic composition (δ56Fe) of bulk rock (i.e., cherts and mudstones/shales) through the Piyuancun and Hetang formations, using samples collected from the Chunye-1 core, on the Lower Yangtze Block in western Zhejiang. The limited variation in δ56Fe values ( 0.55‰ during the end-Ediacaran and Cambrian Stages 1–3 to