Oxidative weathering and the genesis of continental red beds in the Huronian supergroup, Canada: new perspectives on continental paleoredox archives

The first appearance of oxidized paleosols and continental red beds in the Paleoproterozoic rock record is an important Fe-based proxy marker of newly oxidizing surface conditions accompanying Earth’s Great Oxidation/Oxygenation Event (GOE). However, there has been little attempt to bridge the independent records of these metasomatically overprinted rocks with a more unified understanding of Fe surface-cycling, from its source in weathering profiles to its sink in continental siliciclastic sedimentary deposits. This thesis contributes to this unification through 3 studies focused on rocks of the Gowganda and Lorrain formations of the ca. 2.45–2.22 Ga Huronian Supergroup (Ontario/Quebec, Canada) deposited during the GOE and across an interval of significant glacial-to-deglacial climate change. First, the metasomatic origin of alkali-element enrichments in paleosols is reviewed with literature data, and used to develop a new, integrated geochemical-petrographical approach to correction for excess K in paleosols formed on different rock types capturing redox-variable Fe weathering behavior. Second, a targeted field, mineralogical, and geochemical study revisiting the basement granite-hosted Ville-Marie paleosol and its capping polymictic breccia (Lorrain Formation) provides new evidence for lithology- and environment-dependent Fe behavior during in situ weathering and near-source transport, akin to modern redox-variable systems. Third, a broad-sampling, geochemical-mineralogical study of red beds across the Gowganda and Lorrain formations examines sedimentary Fe behavior across wider continental environments and into the shallow-marine realm, finding new robust evidence in hematite micromorphologies for syn- to early post-depositional Fe oxidation. The latter two studies better resolve Huronian red beds as a sedimentary product preferentially formed in: 1) catchments proximal to high-Fe mafic rocks; 2) source-distal environments only where fine-grained detritus could deposit; and 3) environments favoring in situ Fe oxidation during early sediment burial.