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3 results

The Iron Speciation Paleoredox Proxy

The Iron Speciation Paleoredox Proxy
  • Simon W. Poulton
  • Published online:
    02 February 2021
    Print publication:
    04 March 2021
  • In one form or another, iron speciation has had a long history as a paleoredox proxy. The technique has been refined considerably over the years, and the most recent scheme is unique in its potential to distinguish three major oceanic redox states - oxygenated, ferruginous and euxinic. This Element covers the theory behind the proxy, methods involved in applying the technique, and potential complications in interpreting Fe speciation data. A series of case studies are also provided, which highlight how more advanced consideration of the data, often in concert with other techniques, can provide unprecedented insight into the redox state of ancient oceans.
The Pyrite Trace Element Paleo-Ocean Chemistry Proxy

The Pyrite Trace Element Paleo-Ocean Chemistry Proxy
  • Daniel D. Gregory
  • Published online:
    28 November 2020
    Print publication:
    24 December 2020
  • The use of the trace element content of sedimentary pyrite as a proxy for the trace element composition of past oceans has recently emerged. The pyrite proxy has several potential advantages over bulk sample analysis: preservation through metamorphism; little dilution during analysis (samples are ablated not dissolved, allowing for the less abundant elements commonly held in the sulfide fraction to be investigated as proxies); accurate measurement of several elements simultaneously; the ability to screen sediments for hydrothermal overprint; and the technique can give information regarding trace element availably at multiple stages of diagenesis. Because of these multiple strengths, the pyrite trace element proxy is a valuable potential addition to the paleo-ocean chemistry tool kit.
The Uranium Isotope Paleoredox Proxy

The Uranium Isotope Paleoredox Proxy
  • Kimberly V. Lau, Stephen J. Romaniello, Feifei Zhang
  • Published online:
    12 August 2019
    Print publication:
    29 August 2019
  • Uranium isotopes (238U/235U) have emerged as a proxy to reconstruct the redox conditions of the Earth's oceans and atmosphere based upon the large isotopic fractionation between reduced U(IV) and oxidized U(VI). Variations in 238U/235U, particularly when recorded in carbonate sediments, can track global trends in marine oxygenation and de-oxygenation. It is unique from other proxies because reduction primarily occurs at the sediment-water interface, and this sensitivity makes U isotopes especially relevant for the habitability of benthic animals. This Element covers the background, methods, and case studies of this promising tool for understanding Earth's environmental transitions, as rapid development continues to refine the accuracy of interpretations of 238U/235U records.