Iron-rich carbonate tidal deposits, Angepena Formation, South Australia: A redox-stratified Cryogenian basin
Introduction
The Neoproterozoic Era is characterized by some of the most dramatic environmental changes in Earth’s evolutionary history, encompassing 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 pO2 during this time, which is referred to as the Neoproterozoic Oxygenation Event (e.g. Canfield et al., 2007, Fike et al., 2006, Scott et al., 2008, Och and Shields-Zhou, 2012, Lyons et al., 2014). However, the timing and magnitude of this oxygenation event remains poorly constrained. Recent evidence suggests that while the oxygenation of the atmosphere and surface ocean environments 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 sedimentological 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 sediments—can serve as robust archives for paleoredox proxies when coupled with sedimentological and petrographic work. Nearshore depositional settings such as tidal flats record deposition at the interface of the atmosphere and marine settings and can therefore provide insights into both systems. The Cryogenian Angepena Formation (northern Adelaide Fold Belt, South Australia; Fig. 1) provides an opportunity to study a Neoproterozoic intertidal environment (Giddings et al., 2009, Wallace et al., 2015, Hood and Wallace, 2012). The Angepena Formation represents the peritidal facies of the Balcanoona reef complex, which developed during the nonglacial period between the Cryogenian ‘Snowball Earth’ ice ages (Giddings et al., 2009, Wallace et al., 2015). Peritidal sediments of the Angepena Formation, as well as laterally equivalent Balcanoona Formation back reef and reef margin facies, contain well-preserved marine cements that are ideally suited for tracking the chemical composition of Neoproterozoic seawater.
The shales and carbonates of the Angepena Formation are strongly enriched in disseminated iron oxides, and represent the oldest marine red bed succession of the Adelaide Fold Belt. Marine red beds (iron-rich strata) are marine sedimentary strata containing iron (oxyhydr)oxides that impart a characteristic red weathering color (Wagreich, 2009, Wang et al., 2011, Cai et al., 2012, Hu et al., 2012). As iron is highly insoluble in its oxidized (ferric) form under circumneutral conditions, marine iron-rich strata have been used to draw important inferences about marine redox evolution throughout Earth’s history (e.g. Song et al., 2017). However, diagenetic iron enrichment or remobilization can potentially complicate the interpretation of the paleoredox significance of marine iron-rich strata. This paper presents a combined process-based sedimentologic and geochemical analysis of the Angepena Formation to constrain the redox state and depositional setting of this iron-rich Cryogenian tidal flat system.
Section snippets
Geological setting
The Angepena Formation forms part of the Cryogenian Umberatana Group in the northern Adelaide Fold Belt, South Australia (Fig. 1, Fig. 2). The Umberatana Group comprises strata deposited during the Sturtian glaciation, the Marinoan glaciation, and the intervening nonglacial period (Coats and Preiss, 1987), and therefore includes all strata of Cryogenian age in the Adelaide Fold Belt. Age constraints for the Umberatana Group are few, but include U-Pb zircon dates from a tuffaceous horizon in the
Methods
Stratigraphic sections were measured using a Jacob’s staff. Stratigraphic sections were correlated by walking out contacts and by using high-resolution air photos coupled with stratigraphic logs to trace distinctive stratigraphic beds. Samples collected from within measured sections and in laterally equivalent beds include marine cements, depositional micrites, dolomitic shales, ooid grainstones and ferruginous mudstones and siltstones. Transmitted light and cathodoluminescence (CL) petrography
Angepena Formation
The Angepena Formation in the Balcanoona reef complex features a thick and laterally extensive marine iron-rich succession. The Angepena Formation can be divided into four main facies, including: red dolomitic mudcracked shale (referred to herein as F1); laminated dolostone with tepees (F2); carbonate-rich facies with oolitic and intraclastic grainstones (F3); and carbonate sheet cavity facies (F4).
The most carbonate-rich facies (F3, F4) are proximal to, and interbedded with the Balcanoona reef
Geochemical results
Based on sedimentological analysis and stratigraphic sections of the Angepena Formation, the northernmost section (A1, Fig. 1) was selected for geochemical-sedimentological analysis to provide information on redox conditions in Cryogenian nonglacial nearshore settings. This stratigraphic section was selected based on its paleogeographic location (i.e. the most oceanward facies of the Angepena tidal red beds) as well as the comparative abundance of marine cemented lithologies, which are regarded
Discussion
The significant iron oxide enrichment of the Angepena Formation (shales 3–6%; up to 10%, Coats and Blissett, 1971; FeO concentrations in ooid laminae up to 46.5 wt%)—and the sedimentary and petrographic evidence for synsedimentary iron oxide deposition—is potentially indicative of marine oxidation processes. This stands in stark contrast to the deeper water equivalent Balcanoona Formation carbonates, in which iron is predominantly present as ferrous iron bound within the carbonate crystal
Conclusions
The Cryogenian Angepena Formation is an iron-rich peritidal sedimentary succession deposited during the Cryogenian nonglacial interval.
- 1.
This study provides evidence for the lateral equivalence of the Angepena Formation and the Balcanoona Formation in the Northern Flinders Ranges. This work develops the stratigraphic relationships documented in some previous studies (Coats and Blissett, 1971, Fromhold and Wallace, 2011, Wallace et al., 2015), and establishes four facies. Facies include F1) red
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
We thank constructive reviews from Lizzie Trower and an anonymous reviewer. This study benefitted from discussion with Maurice Tucker, Murray Gingras. This study also benefitted from assistance by Hayden Dalton and Eric Duda. Brennan O’Connell acknowledges funding from APPEA, AAPG, and IAS. Ashleigh Hood acknowledges funding from the Australian Research Council DECRA (DE190100988) and the Baragwanath Geology Research Fund. Maxwell Lechte acknowledges funding from the Fonds de Recherche du
Data availability
The model code (.m file) is available upon request. Geochemical data is provided in Supplemental Tables 1–3.
References (158)
- et al.
Diagenesis of Fe and S in Amazon inner shelf muds: apparent dominance of Fe reduction and implications for the genesis of ironstones
Cont. Shelf Res.
(1986) - et al.
Stratigraphic position of the Ediacaran Miaohe biota and its constrains on the age of the upper Doushantuo δ13C anomaly in the Yangtze Gorges area, South China
Precambr. Res.
(2015) Scavenging of dissolved yttrium and rare earths by precipitating iron oxyhydroxide: experimental evidence for Ce oxidation, Y-Ho fractionation, and lanthanide tetrad effect
Geochim. Cosmochim. Acta
(1999)- et al.
Distribution of yttrium and rare-earth elements in the Penge and Kuruman iron-formations, Transvaal Supergroup, South Africa
Precambr. Res.
(1996) - et al.
The stratigraphic expression of a large negative carbon isotope excursion from the Ediacaran Johnnie Formation, Death Valley
Precambr. Res.
(2011) Near-shore hypoxia in the Chesapeake Bay: patterns and relationships among physical factors
Estuar. Coast. Shelf Sci.
(1990)- et al.
Physico-chemical characteristics of a colloidal iron phosphate species formed at the oxic-anoxic interface of a eutrophic lake
Geochim. Cosmochim. Acta
(1989) - et al.
Marine chemistry and geochemistry of the lanthanides
Handbook on the Physics and Chemistry of Rare Earths
(1996) - et al.
Origin of the red colour in a red limestone from the Vispi Quarry section (central Italy): a high-resolution transmission electron microscopy analysis
Cretac. Res.
(2012) - et al.
Lithofacies, microfacies and depositional environments of Upper Cretaceous Oceanic red beds (Chuangde Formation) in southern Tibet
Sed. Geol.
(2011)
A new estimate of detrital redox-sensitive metal concentrations and variability in fluxes to marine sediments
Geochim. Cosmochim. Acta
South Australian U-Pb zircon (CA-ID-TIMS) age supports globally synchronous Sturtian deglaciation
Precambr. Res.
A sedimentary prelude to Marinoan glaciation, Cryogenian (Middle Neoproterozoic) Keele Formation, Mackenzie Mountains, northwestern Canada
Precambr. Res.
Rare earth elements in the Pacific and Atlantic Oceans
Geochim. Cosmochim. Acta
Rare-earth element geochemistry of ferromanganese crusts from the Hawaiian Archipelago, central Pacific
Chem. Geol.
Rare earth elements of carbonate rocks from the Bambuí Group, southern São Francisco Basin, Brazil, and their significance as paleoenvironmental proxies
Precambr. Res.
The Vendian succession of northeastern Spitsbergen: petrogenesis of a dolomite-tillite association
Precambr. Res.
Characteristics of lacustrine diagenetic iron oxyhydroxides
Geochim. Cosmochim. Acta
Dissolved rare earth elements in the Southern Ocean: cerium oxidation and the influence of hydrography
Geochim. Cosmochim. Acta
Synsedimentary diagenesis in a Cryogenian reef complex: ubiquitous marine dolomite precipitation
Sed. Geol.
Extreme ocean anoxia during the Late Cryogenian recorded in reefal carbonates of Southern Australia
Precambr. Res.
The effects of diagenesis on geochemical paleoredox proxies in sedimentary carbonates
Geochim. Cosmochim. Acta
Cretaceous oceanic red beds (CORBs): different time scales and models of origin
Earth Sci. Rev.
Highly heterogeneous “poikiloredox” conditions in the early Ediacaran Yangtze Sea
Precambr. Res.
Fine-scale LA-ICP-MS study of redox oscillations and REEY cycling during the latest Devonian Hangenberg Crisis (Moravian Karst, Czech Republic)
Palaeogeogr. Palaeoclimatol. Palaeoecol.
Archean mafic–ultramafic volcanic landmasses and their effect on ocean–atmosphere chemistry
Chem. Geol.
Stable isotope record of the terminal Neoproterozoic Krol platform in the Lesser Himalayas of northern India
Precambr. Res.
Origin of negative Ce anomalies in mixed hydrothermal–hydrogenetic Fe–Mn crusts from the Central Indian Ridge
Earth Planet. Sci. Lett.
Colloidal iron oxyhydroxy-phosphate: the sizing and morphology of an amorphous species in relation to partitioning phenomena
Sci. Total Environ.
Modern carbonate ooids preserve ambient aqueous REE signatures
Chem. Geol.
Paleo-seawater REE compositions and microbial signatures preserved in laminae of Lower Triassic ooids
Palaeogeogr. Palaeoclimatol. Palaeoecol.
Early Triassic oceanic red beds coupled with deep sea oxidation in South Tethys
Sed. Geol.
Cerium anomaly variations in Ediacaran–earliest Cambrian carbonates from the Yangtze Gorges area, South China: implications for oxygenation of coeval shallow seawater
Precambr. Res.
Upper Ordovician marine red limestones, Tarim Basin, NW China: a product of an oxygenated deep ocean and changing climate?
Global Planet. Change
A radiotracer study of cerium and manganese uptake onto suspended particles in Chesapeake Bay
Geochim. Cosmochim. Acta
Megapolygons in Ladinian limestones of Triassic of southern Alps; evidence of deformation by penecontemporaneous desiccation and cementation
J. Sediment. Res.
Nature, origin and classification of peritidal tepee structures and related breccias
Sedimentology
Rare earth element and Nd isotopic variations in regionally extensive dolomites from the Burlington-Keokuk Formation (Mississippian); implications for REE mobility during carbonate diagenesis
J. Sediment. Res.
Redox conditions of calcite cementation interpreted from Mn and Fe contents of authigenic calcites
Geol. Soc. Am. Bull.
Oxidative scavenging of cerium on hydrous Fe oxide: evidence from the distribution of rare earth elements and yttrium between Fe oxides and Mn oxides in hydrogenetic ferromanganese crusts
Geochem. J.
Constraints on Paleoproterozoic atmospheric oxygen levels
Proc. Natl. Acad. Sci.
Origin of ferriferous ooids; an SEM study of ironstone ooids and bauxite pisoids
J. Sediment. Res.
Oolitic stratabound iron ores in the Silurian of Argentina and Bolivia
Diagenesis of iron-rich rocks
Globally synchronous Marinoan deglaciation indicated by U-Pb geochronology of the Cottons Breccia, Tasmania, Australia
Geology
Highly fractionated chromium isotopes in Mesoproterozoic-aged shales and atmospheric oxygen
Nat. Commun.
Late-Neoproterozoic deep-ocean oxygenation and the rise of animal life
Science
Cited by (13)
Marine redox fluctuations during the Marinoan glaciation
2024, Global and Planetary ChangeDynamic evolution of marine productivity, redox, and biogeochemical cycling track local and global controls on Cryogenian sea-level change
2024, Geochimica et Cosmochimica ActaOxygen production and rapid iron oxidation in stromatolites immediately predating the Great Oxidation Event
2022, Earth and Planetary Science Letters