Guilbaud, RomainSlater, BenPoulton, SimonHarvey, TomBrocks, JochenBruisten, BenjaminButterfield, Nicholas J2020-04-202020-04-202410-339Xhttp://hdl.handle.net/1885/203299The relationship between the evolution of early animal communities and oceanic oxygen levels remains unclear. In particular, uncertainty persists in reconstructions of redox conditions during the pivotal early Cambrian (541-510 million years ago, Ma), where conflicting datasets from deeper marine settings suggest either ocean anoxia or fully oxygenated conditions. By coupling geochemical palaeoredox proxies with a record of organic-walled fossils from exceptionally well-defined successions of the early Cambrian Baltic Basin, we provide evidence for the early establishment of modern-type oxygen minimum zones (OMZs). Both inner-and outer-shelf environments were pervasively oxygenated, whereas mid-depth settings were characterised by spatially oscillating anoxia. As such, conflicting redox signatures recovered from individual sites most likely derive from sampling bias, whereby anoxic conditions represent mid-shelf environments with higher productivity. This picture of a spatially restricted anoxic wedge contrasts with prevailing models of globally stratified oceans, offering a more nuanced and realistic account of the Proterozoic-Phanerozoic ocean transition.This work was funded by NERC (NE/K005251/1). SWP acknowledges support from a Royal Society Wolfson Research Merit Award.application/pdfen-AU© 2018 The Authors Published by the European Association of Geochemistryhttp://creativecommons.org/licenses/by/4.0/201810.7185/geochemlet.18062023-11-26Creative Commons Attribution 4.0 License