Lalonde Stefan V.

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Stefan V.

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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
    Iron formations: A global record of Neoarchaean to Palaeoproterozoic environmental history
    ( 2017-06-25) Konhauser, Kurt O. ; Planavsky, Noah J. ; Hardisty, Dalton S. ; Robbins, Leslie J. ; Warchola, Tyler J. ; Haugaard, Rasmus ; Lalonde, Stefan V. ; Partin, Camille A. ; Oonk, Paul B. H. ; Tsikos, Harilaos ; Lyons, Timothy W. ; Bekker, Andrey ; Johnson, Clark M.
    Iron formations (IF) represent an iron-rich rock type that typifies many Archaean and Proterozoic supracrustal successions and are chemical archives of Precambrian seawater chemistry and postdepositional iron cycling. Given that IF accumulated on the seafloor for over two billion years of Earth’s early history, changes in their chemical, mineralogical, and isotopic compositions offer a unique glimpse into environmental changes that took place on the evolving Earth. Perhaps one of the most significant events was the transition from an anoxic planet to one where oxygen was persistently present within the marine water column and atmosphere. Linked to this progressive global oxygenation was the evolution of aerobic microbial metabolisms that fundamentally influenced continental weathering processes, the supply of nutrients to the oceans, and, ultimately, diversification of the biosphere and complex life forms. Many of the key recent innovations in understanding IF genesis are linked to geobiology, since biologically assisted Fe(II) oxidation, either directly through photoferrotrophy, or indirectly through oxygenic photosynthesis, provides a process for IF deposition from mineral precursors. The abundance and isotope composition of Fe(II)-bearing minerals in IF additionally suggests microbial Fe(III) reduction, a metabolism that is deeply rooted in the Archaea and Bacteria. Linkages among geobiology, hydrothermal systems, and deposition of IF have been traditionally overlooked, but now form a coherent model for this unique rock type. This paper reviews the defining features of IF and their distribution through the Neoarchaean and Palaeoproterozoic. This paper is an update of previous reviews by Bekker et al. (2010, 2014) that will improve the quantitative framework we use to interpret IF deposition. In this work, we also discuss how recent discoveries have provided new insights into the processes underpinning the global rise in atmospheric oxygen and the geochemical evolution of the oceans.