A Model for the Oceanic Mass Balance of Rhenium and Implications for the Extent of Proterozoic Ocean Anoxia

UC Riverside UC Riverside Previously Published Works Title A model for the oceanic mass balance of rhenium and implications for the extent of Proterozoic ocean anoxia Permalink https://escholarship.org/uc/item/1gh1h920 Journal GEOCHIMICA ET COSMOCHIMICA ACTA, 227 ISSN 0016-7037 Authors Sheen, Alex I Kendall, Brian Reinhard, Christopher T et al. Publication Date 2018-04-15 DOI 10.1016/j.gca.2018.01.036 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Available online at www.sciencedirect.com ScienceDirect Geochimica et Cosmochimica Acta 227 (2018) 75–95 www.elsevier.com/locate/gca A model for the oceanic mass balance of rhenium and implications for the extent of Proterozoic ocean anoxia Alex I. Sheen a,b,⇑, Brian Kendall a, Christopher T. Reinhard c, Robert A. Creaser b, Timothy W. Lyons d, Andrey Bekker d, Simon W. Poulton e, Ariel D. Anbar f,g a Department of Earth and Environmental Sciences, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada b Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada c School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA d Department of Earth Sciences, University of California, Riverside, CA 92521, USA e School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK f School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA g School of Molecular Sciences, Arizona State University, Tempe, AZ 85287, USA Received 13 July 2017; accepted in revised form 30 January 2018; available online 8 February 2018 Abstract Emerging geochemical evidence suggests that the atmosphere-ocean system underwent a significant decrease in O2 content following the Great Oxidation Event (GOE), leading to a mid-Proterozoic ocean (ca. 2.0–0.8 Ga) with oxygenated surface waters and predominantly anoxic deep waters. The extent of mid-Proterozoic seafloor anoxia has been recently estimated using mass-balance models based on molybdenum (Mo), uranium (U), and chromium (Cr) enrichments in organic-rich mudrocks (ORM). Here, we use a temporal compilation of concentrations for the redox-sensitive trace metal rhenium (Re) in ORM to provide an independent constraint on the global extent of mid-Proterozoic ocean anoxia and as a tool for more generally exploring how the marine geochemical cycle of Re has changed through time. The compilation reveals that mid-Proterozoic ORM are dominated by low Re concentrations that overall are only mildly higher than those of Archean ORM and significantly lower than many ORM deposited during the ca. 2.22–2.06 Ga Lomagundi Event and during the Phanerozoic Eon. These temporal trends are consistent with a decrease in the oceanic Re inventory in response to an expan- sion of anoxia after an interval of increased oxygenation during the Lomagundi Event. Mass-balance modeling of the marine Re geochemical cycle indicates that the mid-Proterozoic ORM with low Re enrichments are consistent with extensive seafloor anoxia. Beyond this agreement, these new data bring added value because Re, like the other metals, responds generally to low- oxygen conditions but has its own distinct sensitivity to the varying environmental controls. Thus, we can broaden our capac- ity to infer nuanced spatiotemporal patterns in ancient redox landscapes. For example, despite the still small number of data, some mid-Proterozoic ORM units have higher Re enrichments that may reflect a larger oceanic Re inventory during transient episodes of ocean oxygenation. An improved understanding of the modern oceanic Re cycle and a higher temporal resolution for the Re compilation will enable further tests of these hypotheses regarding changes in the surficial Re geochemical cycle in response to variations in atmosphere-ocean oxygenation. Nevertheless, the existing Re compilation and model results are in agreement with previous Cr, Mo, and U evidence for pervasively anoxic and ferruginous conditions in mid-Proterozoic oceans. Ó 2018 Elsevier Ltd. All rights reserved. Keywords: Rhenium; Anoxia; Proterozoic; Organic-rich mudrocks; Ocean; Oxygen ⇑ Corresponding author at: Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada. E-mail address: [email protected] (A.I. Sheen). https://doi.org/10.1016/j.gca.2018.01.036 0016-7037/Ó 2018 Elsevier Ltd. All rights reserved. 76 A.I. Sheen et al. / Geochimica et Cosmochimica Acta 227 (2018) 75–95 1. INTRODUCTION 2017), such conditions imply poorly buffered surface O2 inventories and the potential for significant spatiotemporal The progressive oxygenation of the early Earth’s surface variability (Planavsky et al., 2014; Cole et al., 2016; had a profound impact on Earth’s biological and geochem- Reinhard et al., 2016; Daines et al., 2017; Hardisty et al., ical evolution (Lyons et al., 2014). A poorly oxygenated 2017). Indeed, there has been much recent interest in the atmosphere-ocean system in the Archean is indicated by possibility of dynamic spatiotemporal variations in several lines of evidence in the sedimentary record atmosphere-ocean redox conditions during this time (e.g., (Farquhar et al., 2000; Bekker et al., 2010; Sverjensky Sperling et al., 2014; Gilleaudeau and Kah, 2015; and Lee, 2010; Lyons et al., 2014), such as abundant Gilleaudeau et al., 2016; Mukherjee and Large, 2016; banded iron formations (BIF), common occurrence of Planavsky et al., 2016; Reinhard et al., 2016; Zhang et al., redox-sensitive detrital minerals, and preservation of sulfur 2016) against a background of lower atmospheric pO2 com- mass-independent fractionation (S-MIF). In addition, the pared with today (e.g., Cole et al., 2016). Hence, additional low concentrations of some redox-sensitive elements (e.g., data and proxies sensitive to global redox conditions are Mo, U) in sedimentary archives suggest low seawater con- needed to better understand the spatiotemporal evolution centrations of these elements because of their limited oxida- and the dominant redox state of the mid-Proterozoic tive mobilization from the Archean continental crust (Scott oceans. Such information is critical to a full understanding et al., 2008; Partin et al., 2013). The Great Oxidation Event of the relationship between Earth’s surface oxygenation (GOE) is marked by a permanent increase of atmospheric and the evolution of both eukaryotic organisms and com- O2 content to >0.001% present atmospheric level (PAL), plex metazoan life. The integrated use of diverse metals starting between 2.45 and 2.32 Ga (Pavlov and Kasting, spanning a broad range of redox sensitivity (e.g., 2002; Bekker et al., 2004; Bekker, 2014; Gumsley et al., Reinhard et al., 2013a), detrital backgrounds, uptake path- 2017). This transition was accompanied by the appearance ways, and crustal sources will strengthen our conclusions. of new mineral species containing redox-sensitive elements The concentrations of some redox-sensitive trace metals in their highest oxidation states, reduction in BIF deposi- in marine organic-rich mudrocks (ORM) can provide tion, disappearance of S-MIF, and an increase in seawater insight into global ocean redox conditions. Behaving largely Mo, U, and sulfate concentrations (Bekker et al., 2004, conservatively in oxygenated seawater, trace metals such as 2010, 2013; Schro¨der et al., 2008; Scott et al., 2008, 2014; Mo, Cr, Re, and U are removed to anoxic sediments at Sverjensky and Lee, 2010; Hazen et al., 2011; Planavsky higher rates compared with oxygenated sediments, with et al., 2012; Reuschel et al., 2012; Partin et al., 2013; removal rates dependent on the specific chemistry of the Reinhard et al., 2013a). The latter part of the GOE was water column and underlying sediment pore fluids (e.g., marked by a protracted episode of elevated organic carbon Morford and Emerson, 1999; Tribovillard et al., 2006). burial (Lomagundi Event) between ca. 2.22 and 2.06 Ga, Chromium, U, and Re become authigenically enriched in which suggests a long-lasting, but transient increase in sediments overlain by an anoxic water column (at both high atmosphere-ocean O2 contents to levels that may not have and low levels of dissolved H2S) and, to a lesser extent, in occurred again until the Neoproterozoic Oxidation Event anoxic sediments overlain by mildly oxygenated bottom (NOE) (Karhu and Holland, 1996; Scott et al., 2008, waters (Crusius et al., 1996; Morford and Emerson, 1999; 2014; Kump et al., 2011; Planavsky et al., 2011, 2012, Morford et al., 2005; Partin et al., 2013; Reinhard et al., 2014; Bekker and Holland, 2012; Partin et al., 2013). 2013a). By contrast, high authigenic Mo enrichments in Although dramatic swings in the extent of atmosphere- sediments require the accumulation of dissolved H2Sin ocean oxygenation are recognized in the early and late the water column. Anoxic sediments beneath mildly oxy- Proterozoic, surficial redox dynamics during the interven- genated bottom waters display mild Mo enrichments if dis- ing period were likely muted. Recent geochemical data solved H2S is present in sediment pore fluids at shallow (e.g., redox-sensitive trace metals and Fe speciation) suggest depths below the sediment-water interface (Crusius et al., stratified ocean redox conditions for the middle portion of 1996; Morford and Emerson, 1999; Morford et al., 2005). the Proterozoic (ca. 1.8–0.8 Ga; hereafter referred to as the Because these trace metals have a long seawater resi- mid-Proterozoic), wherein oxygenated surface waters were dence time relative to the average ocean turnover time underlain by euxinic (anoxic and sulfidic) waters in highly (1–2 kyr), their enrichment record in open-marine anoxic productive marginal settings, and ferrous iron (Fe2+) accu- sediments reflects, in principle, the global marine redox mulated in suboxic to anoxic deep waters in offshore set- state. Once an environment becomes authigenically active tings (ferruginous anoxia; Poulton et al., 2010; Planavsky for a particular redox-sensitive trace metal, the degree of et al., 2011; Reinhard et al., 2013a; Sperling et al., 2015).

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