Sulfur isotopic trends and iron speciation from the c. 2.0 Ga Pilgujärvi Sedimentary Formation, NW Russia

Reuschel, M.; Melezhik, Victor A.; Strauß, Harald

doi:10.1016/j.precamres.2011.12.009

Cited by 18 publications

(19 citation statements)

References 56 publications

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“…The presence of AVS/pyrrhotite could be highlighting differences in lithology or metamorphism between the cores that could skew the redox results; notably, most of the euxinic redox results occurred in these AVS-bearing cores. Taking the opposite approach, Reuschel et al (2012) added Fe AVS to the Fe py pool and did not include the Fe carb extraction in Fe HR ; this sulfide grouping was supported by analysis of iron speciation ratios and petrographic relations suggesting pyrrhotite formed from desulfurization of pyrite for the majority of their samples.…”

Section: Discussionmentioning

confidence: 99%

“…Tables 1, 2). Notably, because of its variable chemistry, pyrrhotite is entirely or partially dissolved during the Fe carb extraction (Poulton and Canfield, 2005;Reuschel et al, 2012), potentially with more extracted in the Fe ox or Fe mag extractions (e.g. Chang and Kirschvink, 1985), and can also be extracted in the Fe py pool (Partin et al, 2015;Praharaj and Fortin, 2004;Schumann et al, 2012); therefore additional extraction steps and calculations are often included when pyrrhotite may be present.…”

Section: Sequential Extraction Poolsmentioning

confidence: 99%

“…Pyrrhotite is typically grouped with the Fe py pool with the assumption that it formed either as a primary phase or from pyrite, and in either case marks euxinic depositional conditions (e.g. Asael et al, 2013;März et al, 2008;Reuschel et al, 2012).…”

Section: Sequential Extraction Poolsmentioning

confidence: 99%

“…There is lingering debate about the accuracy of various sequential extraction techniques in diagenetically stabilized sedimentary rocks (Praharaj and Fortin, 2004;Raiswell et al, 2011;Reinhard et al, 2009;Reuschel et al, 2012) and even in modern sediments and soil (Bacon and Davidson, 2008;Egger et al, 2014;Hanahan, 2004;Hsieh et al, 2002;La Force and Fendorf, 2000). Our approach in this study is to assume the chemical extractions accurately extract the targeted phases and instead probe a set of questions about the iron speciation proxy arising from changes in chemistry and mineralogy that occur during metamorphism of sedimentary rocks.…”

Section: Sequential Extraction Poolsmentioning

confidence: 99%

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The effects of metamorphism on iron mineralogy and the iron speciation redox proxy

Slotznick

Eiler

Fischer

2018

Geochimica et Cosmochimica Acta

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As the most abundant transition metal in the Earth's crust, iron is a key player in the planetary redox budget. Observations of iron minerals in the sedimentary record have been used to describe surface atmospheric and aqueous redox environments over the evolution of our planet; the most common method applied is iron speciation, a geochemical sequential extraction method in which proportions of different iron minerals are compared to calibrations from modern sediments to determine water-column redox state. Less is known about how this proxy records information through post-depositional processes, including diagenesis and metamorphism. To get insight into this, we examined how the iron mineral groups/pools (silicates, oxides, sulfides, etc.) and paleoredox proxy interpretations can be affected by known metamorphic processes. Well known metamorphic reactions occurring in sub-chlorite to kyanite rocks are able to move iron between different iron pools along a range of proxy vectors, potentially affecting paleoredox results. To quantify the effect strength of these reactions, we examined mineralogical and geochemical data from two classic localities where SilurianDevonian shales, sandstones, and carbonates deposited in a marine sedimentary basin with oxygenated seawater (based on global and local biological constraints) have been regionally metamorphosed from lower-greenschist facies to granulite facies: Waits River and Gile Mountain Formations, Vermont, USA and the Waterville and Sangerville-Vassalboro Formations, Maine, USA. Plotting iron speciation ratios determined for samples from these 2 localities revealed apparent paleoredox conditions of the depositional water column spanning the entire range from oxic to ferruginous (anoxic) to euxinic (anoxic and sulfidic). Pyrrhotite formation in samples highlighted problems within the proxy as iron pool assignment required assumptions about metamorphic reactions and pyrrhotite's identification depended on the extraction techniques utilized. The presence of diagenetic iron carbonates in many samples severely affected the proxy even at low grade, engendering an interpretation of ferruginous conditions in all lithologies, but particularly in carbonate-bearing rocks. Increasing metamorphic grades transformed iron in carbonates into iron in silicate minerals, which when combined with a slight increase in the amount of pyrrhotite, drove the proxy toward more oxic and more euxinic conditions. Broad-classes of metamorphic reactions (e.g. decarbonation, silicate formation) occurred at distinct temperatures-pressures in carbonates versus siliciclastics, and could be either abrupt between metamorphic facies or more gradual in nature. Notably, these analyses highlighted the importance of trace iron in phases like calcite, which otherwise might not be included in iron-focused research i.e. ore-system petrogenesis, metamorphic evolution, or normative calculations of mineral abundance. The observations show that iron is mobile and reactive during diagenesis and metamorphism, a...

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Section: Discussionmentioning

confidence: 99%

Section: Sequential Extraction Poolsmentioning

confidence: 99%

Section: Sequential Extraction Poolsmentioning

confidence: 99%

Section: Sequential Extraction Poolsmentioning

confidence: 99%

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The effects of metamorphism on iron mineralogy and the iron speciation redox proxy

Slotznick

Eiler

Fischer

2018

Geochimica et Cosmochimica Acta

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“…The Fuller test results indicated that the magnetite in these regions is detrital in origin (Fuller et al, 2002;Figure 4c). Magnetite abundance, calculated by comparing the massnormalized saturation magnetization with that of pure magnetite (Klein et al, 2014), in all lower Belt samples is approximately 1-8 ppm (Table S5); this is much lower than the 0.08 to 0.7 wt% magnetite inferred from the iron speciation extraction for magnetite in samples from the same formation (Planavsky et al, 2011;see supporting information;Algoe et al, 2012;Burton et al, 2006;Raiswell et al, 2011;Reinhard et al, 2009;Reuschel et al, 2012;Slotznick, Swanson-Hysell, & Sperling, 2018). We therefore interpret the magnetite as detrital grains that remained after incomplete reaction with porewater sulfide to form pyrite.…”

Section: Primary Mineralogy and Paleoredox Processesmentioning

confidence: 87%

Mid‐Proterozoic Ferruginous Conditions Reflect Postdepositional Processes

Slotznick

Webb

Kirschvink

et al. 2019

Geophysical Research Letters

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To evaluate the mechanics of mid‐Proterozoic environmental iron transport and deposition, we coupled microscale textural and bulk rock magnetic techniques to study the ~1.4‐Ga lower Belt group, Belt Supergroup, Montana and Idaho. We identified a pyrrhotite‐siderite isograd that marks metamorphic iron‐bearing mineral reactions beginning in subgreenschist facies samples. Even in the best‐preserved parts of the basin, secondary overprints were common including recrystallization of iron‐bearing sulfides, base metal sulfides, and nanophase pyrrhotite. Despite these overprints, a record of redox chemistry was preserved in the early diagenetic framboidal pyrite and detrital iron oxides including trace nanoscale magnetite that remained after sulfidization in anoxic and sulfidic sedimentary pore fluids. Based on these results, we interpret the Belt Basin as having oxic waters, at least in shallow‐water environments, with no indication of abundant ferrous iron in the water column; this is consistent with the cooccurrence of early eukaryotic fossils within the same strata.

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