Continental margin molybdenum isotope signatures from the early Eocene

Dickson, Alexander J.; Cohen, Anthony S. and Coe, Angela L. (2014). Continental margin molybdenum isotope signatures from the early Eocene. Earth and Planetary Science Letters, 404 pp. 389–395.

DOI: https://doi.org/10.1016/j.epsl.2014.08.004

Abstract

Molybdenum (Mo) isotope compositions of marine sedimentary deposits that span the Paleocene–Eocene Thermal Maximum (PETM, approximately 56 Ma) are presented from two Tethys Ocean sites (Guru Fatima, Tajikistan and Kheu River, Georgia). Local redox indicators suggest that both locations experienced anoxia and intervals of euxinia (with hydrogen sulphide present in seawater) during the early part of the PETM. However, the Mo-isotope compositions (expressed as δ^98/95Mo) for each site differ significantly. Local redox conditions were very stable at Guru Fatima, where δ^98/95Mo reached a maximum of 0.96‰, which is ∼0.7‰ lower than for early Eocene seawater as recently inferred from euxinic Arctic Ocean deposits. This observation supports the argument that a ∼0.7‰ difference between seawater and anoxic continental margin marine sediments documented at the present day might also be found in the paleo-record. In contrast, local redox conditions at Kheu River were not stable over the study interval, and δ^98/95Mo were much lower than at Guru Fatima. The low δ^98/95Mo values at Kheu River are attributed to the influence of post-depositional remobilization of Mo by repeated adsorption and dissolution of Fe–Mn oxides during brief intervals of bottom water oxidation. The data highlight the importance of obtaining multi-proxy constraints on both local redox and paleoceanographic setting before the Mo-isotope compositions of sedimentary deposits can be interpreted accurately.

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About

• Item ORO ID
• 52810
• Item Type
• Journal Item
• ISSN
• 0012-821X
• Project Funding Details

• Funded Project Name	Project ID	Funding Body
  Quantifying seawater redox variations and continental weathering rates through the Paleocene-Eocene Thermal Maximum	NE/F021313/1	NERC (Natural Environment Research Council)

• Keywords
• molybdenum isotopes; Paleocene–Eocene Thermal Maximum; Tethys; redox
• Academic Unit or School
• Faculty of Science, Technology, Engineering and Mathematics (STEM) > Environment, Earth and Ecosystem Sciences
  Faculty of Science, Technology, Engineering and Mathematics (STEM)
• Copyright Holders
• © 2014 Elsevier B.V.
• Depositing User
• Angela L. Coe