Contents lists available at ScienceDirect Precambrian Research journal homepage: www.elsevier.com/locate/precamres Iron-rich carbonate tidal deposits, Angepena Formation, South Australia: A redox-stratified Cryogenian basin Brennan O'Connell a, ⁎ , Malcolm W. Wallace a , Ashleigh v.S. Hood a , Maxwell A. Lechte a,b , Noah J. Planavsky c a School of Earth Sciences, University of Melbourne, Parkville, Victoria 3010, Australia b Department of Earth and Planetary Science, McGill University, Montréal, Québec H3A 0E8, Canada c Department Geology and Geophysics, Yale University, New Haven, CT 06520-8109, USA ARTICLE INFO Keywords: Ocean oxygenation Marine red beds Back reef Tidal flat Neoproterozoic reefs Precambrian reefs REE+Y Marine cements ABSTRACT The Cryogenian Angepena Formation (ca. 650 Ma) of South Australia records deposition in a peritidal en- vironment equivalent to, and landward of the Balcanoona reef complex, and offers valuable insights into shallow marine chemistry during the nonglacial interlude between two global ice ages. The sedimentary facies comprise an iron-rich marine red bed succession and include red mudcracked dolomitic shales, tepee dolostone, cross- bedded intraclastic ooid grainstone, and tepee-related sheet cavities with marine cements. These facies are in- terpreted to have been deposited in a Cryogenian tidal flat to subtidal setting that is laterally equivalent to the reefal and back reef environments of the Balcanoona Formation. Marine cements from this environment are characterized by well-preserved, non- and bright-cathodoluminescent zoning, and strong negative to slightly positive cerium (Ce) anomalies (Ce/Ce*). We suggest that the Angepena Formation is indicative of intermittent synsedimentary iron oxide precipitation in an oxidized peritidal environment in an otherwise strongly ferrugi- nous and anoxic oceanic setting. Large negative Ce anomalies develop over a narrower depth range when compared to modern oxic marine settings, highlighting the importance of dissolved Mn and Fe concentrations in controlling the magnitude of the negative Ce anomalies. Overall, coupled sedimentological and geochemical evidence suggest a Neoproterozoic shallow marine system at the interface of an oxidizing atmosphere and an anoxic ferruginous marine system. 1. Introduction The Neoproterozoic Era is characterized by some of the most dra- matic environmental changes in Earth’s evolutionary history, encom- passing global glaciation (e.g. Harland, 1964; Hoffman et al., 2017), the accumulation of significant atmospheric oxygen (e.g. Och and Shields- Zhou, 2012; Lyons et al., 2014) and the radiation of complex life (e.g. Narbonne, 2005; Love et al., 2009; Knoll and Sperling, 2014). Several independent geochemical proxies have been used to support the idea of a stepwise increase in atmospheric pO 2 during this time, which is re- ferred to as the Neoproterozoic Oxygenation Event (e.g. Canfield et al., 2007; Fike et al., 2006; Scott et al., 2008; Och & Shields-Zhou, 2012; Lyons et al., 2014). However, the timing and magnitude of this oxy- genation event remains poorly constrained. Recent evidence suggests that while the oxygenation of the atmosphere and surface ocean en- vironments may have been underway by ~800 Ma (Thomson et al., 2015; Turner and Bekker, 2016; Cole et al., 2016), the deep oceans may not have become pervasively oxygenated until the Ediacaran (e.g. Canfield et al., 2007) or as late as the middle Paleozoic (e.g. Sperling et al., 2015; Wallace et al., 2017). Our understanding of the redox state of Neoproterozoic surface environments is complicated by spatial and temporal variability in marine conditions during this dynamic interval (e.g. Li et al., 2015; Jin et al., 2018), necessitating robust sedimento- logical constraints on geochemical proxy data in order to constrain the environment specific redox state. Given strong spatial variability, a detailed facies analysis coupled with paleoredox proxy work is essential to move forward our understanding of Neoproterozoic environmental evolution. Marine chemical sediments—carbonates and ferruginous sedi- ments—can serve as robust archives for paleoredox proxies when coupled with sedimentological and petrographic work. Nearshore de- positional settings such as tidal flats record deposition at the interface of the atmosphere and marine settings and can therefore provide in- sights into both systems. The Cryogenian Angepena Formation https://doi.org/10.1016/j.precamres.2020.105668 Received 3 January 2020; Received in revised form 13 February 2020; Accepted 19 February 2020 ⁎ Corresponding author. E-mail address: oconnellb@student.unimelb.edu.au (B. O'Connell). Precambrian Research 342 (2020) 105668 Available online 22 February 2020 0301-9268/ © 2020 Published by Elsevier B.V. T