Effective use of cerium anomalies as a redox proxy in carbonate-dominated marine settings

Effective use of cerium anomalies as a redox proxy in carbonate-dominated marine settingsEffective use of cerium anomalies as a redox proxy in carbonate-dominated marine settings' Chemical Geology, vol 438, pp. 146-General rights Copyright for the publications made accessible via the Edinburgh Research Explorer is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights. Take down policy The University of Edinburgh has made every reasonable effort to ensure that Edinburgh Research Explorer content complies with UK legislation. If you believe that the public display of this file breaches copyright please contact [email protected] providing details, and we will remove access to the work immediately and investigate your claim. a b s t r a c t a r t i c l e i n f o Rare earth elements and yttrium (REY) have a distinct distribution pattern in seawater, and this pattern may be faithfully preserved in carbonate sediments and rocks. Anomalous concentrations of redox-sensitive cerium (Ce) compared with neighbouring REY originate in oxic water column conditions, and as such, Ce anomalies can provide a potentially useful redox proxy in carbonate-dominated marine settings. The methods used to extract REY from car-bonates vary widely, and may suffer from widespread leaching of REY from accessory non-carbonate minerals and organic matter, limiting the application of Ce anomalies for palaeo-redox reconstruction. We have systematically compared different methods on 195 carbonate samples with varying purity (% carbonate) from both modern and ancient environments. We used sequential leaching experiments in nitric acid to identify the most 'seawater-like' portion of the carbonate sample where contributions from non-carbonate minerals and organic matter are minimised. We also compared the results of sample dissolution in different types and strengths of acid. Our results confirm that REY concentrations can be inadvertently contaminated by partial leaching of clays and Fe (oxyhydr)oxides during a single-step digestion, and we suggest a pre-leach of 20% of the sample, followed by a partial leach of 40% of the sample to selectively dissolve carbonate. We suggest that REY studies are optimised in carbonates with N 85% CaCO 3 , and show that dolomites behave differently during the leaching process and must be treated separately. We present REY patterns for modern carbonate-rich sediments from a range of environments, and show that seawater REY are faithfully preserved …