The low-temperature geochemical cycle of iron: From continental fluxes to marine sediment deposition

Poulton, Simon W.; Raiswell, R.

doi:10.2475/ajs.302.9.774

Cited by 446 publications

(333 citation statements)

References 75 publications

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“…Specifically, we calculated the mean [Re] sed values for those stage 3 ORM that have independent Fe speciation evidence for deposition from anoxic bottom waters-specifically ratios of biogeochemically highly reactive Fe to total Fe (Fe HR / Fe T ) greater than 0.38 or degree-of-pyritization (DOP) values greater than 0.45 (Table S5 in the supplementary database; Raiswell and Canfield, 1998;Poulton and Raiswell, 2002;reviewed in Lyons and Severmann, 2006). These filters should largely exclude any ORM deposited under suboxic bottom waters.…”

Section: Constraints On the Extent Of Mid-proterozoic Ocean Anoxiamentioning

confidence: 99%

A model for the oceanic mass balance of rhenium and implications for the extent of Proterozoic ocean anoxia

Sheen

Kendall

Reinhard

et al. 2018

Geochimica et Cosmochimica Acta

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Emerging geochemical evidence suggests that the atmosphere-ocean system underwent a significant decrease in O 2 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 expansion 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 lowoxygen conditions but has its own distinct sensitivity to the varying environmental controls. Thus, we can broaden our capacity 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.

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Section: Constraints On the Extent Of Mid-proterozoic Ocean Anoxiamentioning

confidence: 99%

A model for the oceanic mass balance of rhenium and implications for the extent of Proterozoic ocean anoxia

Sheen

Kendall

Reinhard

et al. 2018

Geochimica et Cosmochimica Acta

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“…Values between 0.22-0.38, however, are somewhat equivocal, and care needs to be taken to determine if such values are a consequence of masking of the additional anoxic water column flux of Fe HR , either due to rapid sedimentation (Raiswell and Canfield, 1998;Poulton et al, 2004a) or due to post-depositional transformation of unsulfidized Fe HR minerals to less reactive sheet silicate minerals (Cumming et al, 2013;Poulton and Raiswell, 2002;Poulton et al, 2010). Additional examination of the Fe py /Fe HR ratio has the unique advantage in that it allows the separation of anoxic settings into euxinic (sulfidic) environments (Fe py /Fe HR >0.7-0.8) and non-sulfidic (Fe-rich; ferruginous) environments (Fe py /Fe HR <0.7) (Poulton and Canfield, 2011;Poulton et al, 2004a).…”

Section: Fe-speciationmentioning

confidence: 99%

“…The technique allows identification of oxic and anoxic water column conditions (Raiswell and Canfield, 1998;Poulton and Raiswell, 2002;Poulton and Canfield, 2011), where anoxia may be separated into euxinic (H 2 S-bearing) and ferruginous (Fe(II)-containing) (Poulton et al, 2004a). However, the technique lacks the sensitivity to more precisely identify changes in the extent of ocean oxygenation (i.e.…”

Section: Fe-speciationmentioning

confidence: 99%

“…These processes have the consequence that Fe HR /Fe T ratios provide a particularly sensitive means to determine whether a depositional setting was oxic or anoxic. Calibration in modern and ancient marine environments suggests that Fe HR /Fe T <0.22 provides a robust indication of oxic conditions, while Fe HR /Fe T >0.38 suggests deposition from an anoxic water column (Poulton and Canfield, 2011;Raiswell and Canfield, 1998;Poulton and Raiswell, 2002).…”

Section: Fe-speciationmentioning

confidence: 99%

Section: Fe-speciationmentioning

confidence: 99%

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Dynamic redox conditions control late Ediacaran metazoan ecosystems in the Nama Group, Namibia

Wood

Poulton

Prave

et al. 2015

Precambrian Research

167

194

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A c c e p t e d M a n u s c r i p t 3 ABSTRACTThe first appearance of skeletal metazoans in the late Ediacaran (~550 million years ago; Ma) has been linked to the widespread development of oxygenated oceanic conditions, but a precise spatial and temporal reconstruction of their evolution has not been resolved. Here we consider the evolution of ocean chemistry from ~550 to ~541 Ma across shelf-to-basin transects in the Zaris and Witputs Sub-Basins of the Nama Group, Namibia. New carbon isotope data capture the final stages of the Shuram/Wonoka deep negative C-isotope excursion, and these are complemented with a reconstruction of water column redox dynamics utilizing Fe-S-C systematics and the distribution of skeletal and soft-bodied metazoans. Combined, these inter-basinal datasets provide insight into the potential role of ocean redox chemistry during this pivotal interval of major biological innovation.The strongly negative  13 C values in the lower parts of the sections reflect both a secular, global change in the C-isotopic composition of Ediacaran seawater, as well as the influence of 'local' basinal effects as shown by the most negative  13 C values occurring in the transition from distal to proximal ramp settings. Critical, though, is that the transition to positive  13 C values postdates the appearance of calcified metazoans, indicating that the onset of biomineralization did not occur under post-excursion conditions. Significantly, we find that anoxic and ferruginous deeper water column conditions were prevalent during and after the transition to positive  13 C that marks the end of the Shuram/Wonoka excursion. Thus, if the C isotope trend reflects the transition to global-scale oxygenation in the aftermath of the oxidation of a large-scale, isotopically light organic carbon pool, it was not sufficient to fully oxygenate the deep ocean. Page 4 of 74A c c e p t e d M a n u s c r i p t 4 Both sub-basins reveal highly dynamic redox structures, where shallow, inner ramp settings experienced transient oxygenation. Anoxic conditions were caused either by episodic upwelling of deeper anoxic waters or higher rates of productivity. These settings supported short-lived and monospecific skeletal metazoan communities. By contrast, microbial (thrombolite) reefs, found in deeper inner-and mid-ramp settings, supported more biodiverse communities with complex ecologies and large skeletal metazoans. These long-lived reef communities, as well as Ediacaran soft-bodied biotas, are found particularly within transgressive systems, where oxygenation was persistent. We suggest that a mid-ramp position enabled physical ventilation mechanisms for shallow water column oxygenation to operate during flooding and transgressive sea-level rise. Our data support a prominent role for oxygen, and for stable oxygenated conditions in particular, in controlling both the distribution and ecology of Ediacaran skeletal metazoan communities.Keywords: Oxygenation; Neoproterozoic; Biomineralisation; Metazoans; Ediacaran; Ecosystems Introductio...

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Re-Os age and depositional environment for black shales from the Cambrian-Ordovician boundary, Green Point, western Newfoundland

Tripathy

Hannah

Stein

et al. 2014

Geochem. Geophys. Geosyst.

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Chemical and isotopic signatures for black shales serve as potential proxies for reconstruction of paleoenvironmental conditions. Here we bring Rock-Eval, major and trace element and Re-Os isotopic data together to examine the environmental record at the Cambrian-Ordovician Global Stratotype Section and Point (GSSP) at Green Point in western Newfoundland, Canada. The Green Point shales are oil mature and contain Type II organic material of marine origin. A Re-Os isochron for the shales provides the first radiometric age for shale deposition at the GSSP at 484 6 16 Ma, with an initial 187 Os/ 188Os ratio of 0.74 6 0.05 (Model 3 age; MSWD 5 21; n 5 13; 2r uncertainties). Factor analysis of the geochemical data set shows association of most trace elements with total organic carbon (TOC) and S contents, ensuring an authigenic origin for most elements and hence, their validity for evaluating the paleo-redox state. Relatively high-enrichment factors for redox-sensitive elements (e.g., Re, U, and Mo) compared to average shale, but comparatively low enrichment compared to modern Black Sea sediments, suggest deposition in anoxic, but not euxinic waters. Comparison of Lower Ordovician shale geochemistry data sets at a global scale leads us to suggest that anoxic conditions and warm oceanic regimes were restricted to the margins of Laurentia and Baltica, whereas depositional basins with colder waters (e.g., Avalonia and Gondwana) were less reducing. These outcomes underscore the important role of paleogeography in regulating oceanic conditions and marine life.

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The low-temperature geochemical cycle of iron: From continental fluxes to marine sediment deposition

Cited by 446 publications

References 75 publications

A model for the oceanic mass balance of rhenium and implications for the extent of Proterozoic ocean anoxia

A model for the oceanic mass balance of rhenium and implications for the extent of Proterozoic ocean anoxia

Dynamic redox conditions control late Ediacaran metazoan ecosystems in the Nama Group, Namibia

Re-Os age and depositional environment for black shales from the Cambrian-Ordovician boundary, Green Point, western Newfoundland

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