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Redox conditions in the Late Cretaceous Chalk Sea: the possible use of cerium anomalies as palaeoredox indicators in the Cenomanian and Turonian Chalk of England

Redox conditions in the Late Cretaceous Chalk Sea: the possible use of cerium anomalies as palaeoredox indicators in the Cenomanian and Turonian Chalk of England

Jeans, Christopher V, Wray, David ORCID: 0000-0002-0799-2730 and Williams, C. Terry (2015) Redox conditions in the Late Cretaceous Chalk Sea: the possible use of cerium anomalies as palaeoredox indicators in the Cenomanian and Turonian Chalk of England. Acta Geologica Polonica, 65 (3). pp. 345-366. ISSN 2300-1887 (Online) (doi:10.1515/agp-2015-0015)

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Abstract

The cerium anomalies preserved in the Chalk have been investigated as possible palaeoredox indicators of the Late Cretaceous Sea and its sediment. This has been based upon over a hundred new rare earth element analyses of selected samples and grain size fractions from the Chalk. Particular attention has been given to the methodology of differentiating between the cerium anomalies preserved in the bioclastic calcite and those in carbonate-fluorapatite preserved in the acetic acid insoluble residues of chalks. Variations in the cerium anomaly of different particle size fractions of uncemented chalks suggest that fractionation of rare earth elements between the Chalk's seawater and the various organisms that contributed skeletal material to the bioclastic calcite of the Chalk may have occurred. Post-depositional processes of calcite cementation and late diagenetic sulphidisation have had no apparent effect on the cerium anomaly of the acetic acid insoluble residues. The cerium anomalies associated with the acetic acid insoluble residues from (1) an alternating sequence of chalks and marls from Ballard Cliff (Dorset, UK) typical of Milankovitch cyclicity show a marked diagenetic pattern, whereas those from (2) non-volcanic and volcanic marls display a pattern that is best explained by the variations in the availability of phosphorus and the timing of argillisation of volcanic glass during diagenesis. The general conclusion is drawn that the cerium anomalies preserved in the Chalk can provide an insight into the changing palaeoredox conditions in the Late Cretaceous Sea as well as in the pore fluids of its sediments.

Item Type: Article
Additional Information: © 2015 Acta Geologica Polonica. This chapter is distributed under the terms of the Creative Commons Attribution 4.0 Public License. (CC BY 4.0)
Uncontrolled Keywords: Chalk environments; Rare earth element (REE) anomalies; Methods; Palaeoredox indicators; Diagenesis; History.
Subjects: Q Science > QD Chemistry
Q Science > QE Geology
Faculty / Department / Research Group: Faculty of Engineering & Science > Department of Pharmaceutical, Chemical & Environmental Sciences
Last Modified: 29 Apr 2017 12:41
Selected for GREAT 2016: None
Selected for GREAT 2017: GREAT c
Selected for GREAT 2018: None
URI: http://gala.gre.ac.uk/id/eprint/14131

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