Gill Benjamin C.

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Gill
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Benjamin C.
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  • Preprint
    Trace elements at the intersection of marine biological and geochemical evolution
    ( 2016-10) Robbins, Leslie J. ; Lalonde, Stefan V. ; Planavsky, Noah J. ; Partin, Camille A. ; Reinhard, Christopher T. ; Kendall, Brian ; Scott, Clint ; Hardisty, Dalton S. ; Gill, Benjamin C. ; Alessi, Daniel S. ; Dupont, Christopher L. ; Saito, Mak A. ; Crowe, Sean A. ; Poulton, Simon W. ; Bekker, Andrey ; Lyons, Timothy W. ; Konhauser, Kurt O.
    Life requires a wide variety of bioessential trace elements to act as structural components and reactive centers in metalloenzymes. These requirements differ between organisms and have evolved over geological time, likely guided in some part by environmental conditions. Until recently, most of what was understood regarding trace element concentrations in the Precambrian oceans was inferred by extrapolation, geochemical modeling, and/or genomic studies. However, in the past decade, the increasing availability of trace element and isotopic data for sedimentary rocks of all ages have yielded new, and potentially more direct, insights into secular changes in seawater composition – and ultimately the evolution of the marine biosphere. Compiled records of many bioessential trace elements (including Ni, Mo, P, Zn, Co, Cr, Se, and I) provide new insight into how trace element abundance in Earth’s ancient oceans may have been linked to biological evolution. Several of these trace elements display redox-sensitive behavior, while others are redox-sensitive but not bioessential (e.g., Cr, U). Their temporal trends in sedimentary archives provide useful constraints on changes in atmosphere-ocean redox conditions that are linked to biological evolution, for example, the activity of oxygen-producing, photosynthetic cyanobacteria. In this review, we summarize available Precambrian trace element proxy data, and discuss how temporal trends in the seawater concentrations of specific trace elements may be linked to the evolution of both simple and complex life. We also examine several biologically relevant and/or redox-sensitive trace elements that have yet to be fully examined in the sedimentary rock record (e.g., Cu, Cd, W) and suggest several directions for future studies.
  • Preprint
    An evaluation of sedimentary molybdenum and iron as proxies for pore fluid paleoredox conditions
    ( 2018-04) Hardisty, Dalton S. ; Lyons, Timothy W. ; Riedinger, Natascha ; Isson, Terry T. ; Owens, Jeremy D. ; Aller, Robert C. ; Rye, Danny ; Planavsky, Noah J. ; Reinhard, Christopher T. ; Gill, Benjamin C. ; Masterson, Andrew L. ; Asael, Dan ; Johnston, David T.
    Iron speciation and trace metal proxies are commonly applied together in efforts to identify anoxic settings marked by the presence of free sulfide (euxinia) or dissolved iron (ferruginous) in the water column. Here, we use a literature compilation from modern localities to provide a new empirical evaluation of coupled Fe speciation and Mo concentrations as a proxy for pore water sulfide accumulation at non-euxinic localities. We also present new Fe speciation, Mo concentration, and S isotope data from the Friends of Anoxic Mud (FOAM) site in Long Island Sound, which is marked by pore water sulfide accumulation of up to 3 mM beneath oxygen-containing bottom waters. For the operationally defined Fe speciation scheme, ‘highly reactive’ Fe (FeHR) is the sum of pyritized Fe (Fepy) and Fe dominantly present in oxide phases that is available to react with pore water sulfide to form pyrite. Observations from FOAM and elsewhere confirm that Fepy/FeHR from non-euxinic sites is a generally reliable indicator of pore fluid redox, particularly the presence of pore water sulfide. Molybdenum (Mo) concentration data for anoxic continental margin sediments underlying oxic waters but with sulfidic pore fluids typically show authigenic Mo enrichments (2-25 ppm) that are elevated relative to the upper crust (1-2 ppm). However, compilations of Mo concentrations comparing sediments with and without sulfidic pore fluids underlying oxic and low oxygen (non-euxinic) water columns expose non-unique ranges for each, exposing false positives and false negatives. False positives are most frequently found in sediments from low oxygen water columns (for example, Peru Margin), where Mo concentration ranges can also overlap with values commonly found in modern euxinic settings. FOAM represents an example of a false negative, where, despite elevated pore water sulfide concentrations and evidence for active Fe and Mn redox cycling in FOAM sediments, sedimentary Mo concentrations show a homogenous vertical profile across 50 cm depth at 1-2 ppm. A diagenetic model for Mo provides evidence that muted authigenic enrichments are derived from elevated sedimentation rates. Consideration of a range of additional parameters, most prominently pore water Mo concentration, can replicate the ranges of most sedimentary Mo concentrations observed in modern non-euxinic settings. Together, the modern Mo and Fe data compilations and diagenetic model provide a framework for identifying paleo-pore water sulfide accumulation in ancient settings and linked processes regulating seawater Mo and sulfate concentrations and delivery to sediments. Among other utilities, identifying ancient accumulation of sulfide in pore waters, particularly beneath oxic bottom waters, constrains the likelihood that those settings could have hosted organisms and ecosystems with thiotrophy at their foundations.
  • Article
    The Sedimentary Geochemistry and Paleoenvironments Project
    (Wiley, 2021-07-05) Farrell, Úna C. ; Samawi, Rifaat ; Anjanappa, Savitha ; Klykov, Roman ; Adeboye, Oyeleye O. ; Agic, Heda ; Ahm, Anne-Sofie C. ; Boag, Thomas H. ; Bowyer, Fred ; Brocks, Jochen J. ; Brunoir, Tessa N. ; Canfield, Donald E. ; Chen, Xiaoyan ; Cheng, Meng ; Clarkson, Matthew O. ; Cole, Devon B. ; Cordie, David R. ; Crockford, Peter W. ; Cui, Huan ; Dahl, Tais W. ; Mouro, Lucas D. ; Dewing, Keith ; Dornbos, Stephen Q. ; Drabon, Nadja ; Dumoulin, Julie A. ; Emmings, Joseph F. ; Endriga, Cecilia R. ; Fraser, Tiffani A. ; Gaines, Robert R. ; Gaschnig, Richard M. ; Gibson, Timothy M. ; Gilleaudeau, Geoffrey J. ; Gill, Benjamin C. ; Goldberg, Karin ; Guilbaud, Romain ; Halverson, Galen P. ; Hammarlund, Emma U. ; Hantsoo, Kalev G. ; Henderson, Miles A. ; Hodgskiss, Malcolm S. W. ; Horner, Tristan J. ; Husson, Jon M. ; Johnson, Benjamin ; Kabanov, Pavel ; Keller, C. Brenhin ; Kimmig, Julien ; Kipp, Michael A. ; Knoll, Andrew H. ; Kreitsmann, Timmu ; Kunzmann, Marcus ; Kurzweil, Florian ; LeRoy, Matthew A. ; Li, Chao ; Lipp, Alex G. ; Loydell, David K. ; Lu, Xinze ; Macdonald, Francis A. ; Magnall, Joseph M. ; Mänd, Kaarel ; Mehra, Akshay ; Melchin, Michael J. ; Miller, Austin J. ; Mills, N. Tanner ; Mwinde, Chiza N. ; O'Connell, Brennan ; Och, Lawrence M. ; Ossa Ossa, Frantz ; Pagès, Anais ; Paiste, Kärt ; Partin, Camille A. ; Peters, Shanan E. ; Petrov, Peter ; Playter, Tiffany L. ; Plaza-Torres, Stephanie ; Porter, Susannah M. ; Poulton, Simon W. ; Pruss, Sara ; Richoz, Sylvain ; Ritzer, Samantha R. ; Rooney, Alan D. ; Sahoo, Swapan K. ; Schoepfer, Shane D. ; Sclafani, Judith A. ; Shen, Yanan ; Shorttle, Oliver ; Slotznick, Sarah P. ; Smith, Emily F. ; Spinks, Sam ; Stockey, Richard G. ; Strauss, Justin V. ; Stüeken, Eva E. ; Tecklenburg, Sabrina ; Thomson, Danielle ; Tosca, Nicholas J. ; Uhlein, Gabriel J. ; Vizcaíno, Maoli N. ; Wang, Huajian ; White, Tristan ; Wilby, Philip R. ; Woltz, Christina R. ; Wood, Rachel A. ; Xiang, Lei ; Yurchenko, Inessa A. ; Zhang, Tianran ; Planavsky, Noah J. ; Lau, Kimberly V. ; Johnston, David T. ; Sperling, Erik A.
    Geobiology explores how Earth's system has changed over the course of geologic history and how living organisms on this planet are impacted by or are indeed causing these changes. For decades, geologists, paleontologists, and geochemists have generated data to investigate these topics. Foundational efforts in sedimentary geochemistry utilized spreadsheets for data storage and analysis, suitable for several thousand samples, but not practical or scalable for larger, more complex datasets. As results have accumulated, researchers have increasingly gravitated toward larger compilations and statistical tools. New data frameworks have become necessary to handle larger sample sets and encourage more sophisticated or even standardized statistical analyses. In this paper, we describe the Sedimentary Geochemistry and Paleoenvironments Project (SGP; Figure 1), which is an open, community-oriented, database-driven research consortium. The goals of SGP are to (1) create a relational database tailored to the needs of the deep-time (millions to billions of years) sedimentary geochemical research community, including assembling and curating published and associated unpublished data; (2) create a website where data can be retrieved in a flexible way; and (3) build a collaborative consortium where researchers are incentivized to contribute data by giving them priority access and the opportunity to work on exciting questions in group papers. Finally, and more idealistically, the goal was to establish a culture of modern data management and data analysis in sedimentary geochemistry. Relative to many other fields, the main emphasis in our field has been on instrument measurement of sedimentary geochemical data rather than data analysis (compared with fields like ecology, for instance, where the post-experiment ANOVA (analysis of variance) is customary). Thus, the longer-term goal was to build a collaborative environment where geobiologists and geologists can work and learn together to assess changes in geochemical signatures through Earth history.
  • Preprint
    Chromium isotope fractionation during subduction-related metamorphism, black shale weathering, and hydrothermal alteration
    ( 2016-01) Wang, Xiangli ; Planavsky, Noah J. ; Reinhard, Christopher T. ; Zou, Huijuan ; Ague, Jay J. ; Wu, Yuanbao ; Gill, Benjamin C. ; Schwarzenbach, Esther M. ; Peucker-Ehrenbrink, Bernhard
    Chromium (Cr) isotopes are an emerging proxy for redox processes at Earth’s surface. However, many geological reservoirs and isotope fractionation processes are still not well understood. The purpose of this contribution is to move forward our understanding of (1) Earth’s high temperature Cr isotope inventory and (2) Cr isotope fractionations during subduction-related metamorphism, black shale weathering and hydrothermal alteration. The examined basalts and their metamorphosed equivalents yielded δ53Cr values falling within a narrow range of -0.12±0.13‰ (2SD, n=30), consistent with the previously reported range for the bulk silicate Earth (BSE). Compilations of currently available data for fresh silicate rocks (43 samples), metamorphosed silicate rocks (50 samples), and mantle chromites (39 samples) give δ53Cr values of -0.13±0.13‰, -0.11±0.13‰, and -0.07±0.13‰, respectively. Although the number of high-temperature samples analyzed has tripled, the originally proposed BSE range appears robust. This suggests very limited Cr isotope fractionation under high temperature conditions. Additionally, in a highly altered metacarbonate transect that is representative of fluid-rich regional metamorphism, we did not find resolvable variations in δ53Cr, despite significant loss of Cr. This work suggests that primary Cr isotope signatures may be preserved even in instances of intense metamorphic alteration at relatively high fluid-rock ratios. Oxidative weathering of black shale at low pH creates isotopically heavy mobile Cr(VI). However, a significant proportion of the Cr(VI) is apparently immobilized near the weathering surface, leading to local enrichment of isotopically heavy Cr (δ53Cr values up to ~0.5‰). The observed large Cr isotope variation in the black shale weathering profile provides indirect evidence for active manganese oxide formation, which is primarily controlled by microbial activity. Lastly, we found widely variable δ53Cr (-0.2‰ to 0.6‰) values in highly serpentinized peridotites from ocean drilling program drill cores and outcropping ophiolite sequences. The isotopically heavy serpentinites are most easily explained through a multi-stage alteration processes: Cr loss from the host rock under oxidizing conditions, followed by Cr enrichment under sulfate reducing conditions. In contrast, Cr isotope variability is limited in mildly altered mafic oceanic crust.
  • Article
    Sulphur and carbon cycling in the subduction zone mélange
    (Nature Publishing Group, 2018-10-19) Schwarzenbach, Esther M. ; Caddick, Mark J. ; Petroff, Matthew ; Gill, Benjamin C. ; Cooperdock, Emily H. G. ; Barnes, Jaime D.
    Subduction zones impose an important control on the geochemical cycling between the surficial and internal reservoirs of the Earth. Sulphur and carbon are transferred into Earth’s mantle by subduction of pelagic sediments and altered oceanic lithosphere. Release of oxidizing sulphate- and carbonate-bearing fluids modifies the redox state of the mantle and the chemical budget of subduction zones. Yet, the mechanisms of sulphur and carbon cycling within subduction zones are still unclear, in part because data are typically derived from arc volcanoes where fluid compositions are modified during transport through the mantle wedge. We determined the bulk rock elemental, and sulphur and carbon isotope compositions of exhumed ultramafic and metabasic rocks from Syros, Greece. Comparison of isotopic data with major and trace element compositions indicates seawater alteration and chemical exchange with sediment-derived fluids within the subduction zone channel. We show that small bodies of detached slab material are subject to metasomatic processes during exhumation, in contrast to large sequences of obducted ophiolitic sections that retain their seafloor alteration signatures. In particular, fluids circulating along the plate interface can cause sulphur mobilization during several stages of exhumation within high-pressure rocks. This takes place more pervasively in serpentinites compared to mafic rocks.
  • Preprint
    Perspectives on Proterozoic surface ocean redox from iodine contents in ancient and recent carbonate
    ( 2017-01) Hardisty, Dalton S. ; Lu, Zunli ; Bekker, Andrey ; Diamond, Charles W. ; Gill, Benjamin C. ; Jiang, Ganqing ; Kah, Linda ; Knoll, Andrew H. ; Loyd, Sean ; Osburn, Magdalena ; Planavsky, Noah J.
    The Proterozoic Eon hosted the emergence and initial recorded diversification of eukaryotes. Oxygen levels in the shallow marine settings critical to these events were lower than today’s, although how much lower is debated. Here, we use concentrations of iodate (the oxidized iodine species) in shallow-marine limestones and dolostones to generate the first comprehensive record of Proterozoic near-surface marine redox conditions. The iodine proxy is sensitive to both local oxygen availability and the relative proximity to anoxic waters. To assess the validity of our approach, Neogene-Quaternary carbonates are used to demonstrate that diagenesis most often decreases and is unlikely to increase carbonate-iodine contents. Despite the potential for diagenetic loss, maximum Proterozoic carbonate iodine levels are elevated relative to those of the Archean, particularly during the Lomagundi and Shuram carbon isotope excursions of the Paleo- and Neoproterozoic, respectively. For the Shuram anomaly, comparisons to Neogene-Quaternary carbonates suggest that diagenesis is not responsible for the observed iodine trends. The baseline low iodine levels in Proterozoic carbonates, relative to the Phanerozoic, are linked to a shallow oxic-anoxic interface. Oxygen concentrations in surface waters would have at least intermittently been above the threshold required to support eukaryotes. However, the diagnostically low iodine data from mid-Proterozoic shallow-water carbonates, relative to those of the bracketing time intervals, are consistent with a dynamic chemocline and anoxic waters that would have episodically mixed upward and laterally into the shallow oceans. This redox instability may have challenged early eukaryotic diversification and expansion, creating an evolutionary landscape unfavorable for the emergence of animals.