Thallium isotopes in early diagenetic pyrite; a paleoredox proxy?

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doi: 10.1016/j.gca.2011.07.047
Author(s): Nielsen, Sune G.; Goff, Matt; Hesselbo, Stechen P.; Jenkyns, Hugh C.; LaRowe, Doug E.; Lee, Cin-Ty A.
Author Affiliation(s): Primary:
University of Oxford, Department of Earth Sciences, Oxford, United Kingdom
Other:
Georgia Institute of Technology, United States
Rice University, United States
Volume Title: Geochimica et Cosmochimica Acta
Source: Geochimica et Cosmochimica Acta, 75(21), p.6690-6704. Publisher: Elsevier, New York, NY, International. ISSN: 0016-7037 CODEN: GCACAK
Note: In English. 66 refs.; illus., incl. 4 tables
Summary: This paper presents the first study of Tl isotopes in early diagenetic pyrite. Measurements from two sections deposited during the Toarcian Ocean Anoxic Event (T-OAE, ∼183Ma) are compared with data from late Neogene (<10Ma) pyrite samples from ODP legs 165 and 167 that were deposited in relatively oxic marine environments. The Tl isotope compositions of late Neogene pyrites are all significantly heavier than seawater, which most likely indicates that Tl in diagenetic pyrite is partially sourced from ferromanganese oxy-hydroxides that are known to display relatively heavy Tl isotope signatures. One of the T-OAE sections from Peniche in Portugal displays pyrite thallium isotope compositions indistinguishable from late Neogene samples, whereas samples from Yorkshire in the UK are depleted in the heavy isotope of Tl. These lighter compositions are best explained by the lack of ferromanganese precipitation at the sediment-water interface due to the sulfidic (euxinic) conditions thought to be prevalent in the Cleveland Basin where the Yorkshire section was deposited. The heavier signatures in the Peniche samples appear to result from an oxic water column that enabled precipitation of ferromanganese oxy-hydroxides at the sediment-water interface. The Tl isotope profile from Yorkshire is also compared with previously published molybdenum isotope ratios determined on the same sedimentary succession. There is a suggestion of an anti-correlation between these two isotope systems, which is consistent with the expected isotope shifts that occur in seawater when marine oxic (ferromanganese minerals) fluxes fluctuate. The results outlined here represent the first evidence that Tl isotopes in early diagenetic pyrite have potential to reveal variations in past ocean oxygenation on a local scale and potentially also for global oceans. However, much more information about Tl isotopes in different marine environments, especially in anoxic/euxinic basins, is needed before Tl isotopes can be confidently utilized as a paleo-redox tracer. Abstract Copyright (2011) Elsevier, B.V.
Year of Publication: 2011
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; Atlantic Ocean; Caribbean Sea; Cenozoic; Chemical composition; Cleveland Basin; Crystal chemistry; Diagenesis; East Pacific; Eh; England; Europe; Geochemistry; Great Britain; ICP mass spectra; Iberian Peninsula; Isotopes; Jurassic; Leg 165; Leg 167; Lower Jurassic; Major elements; Mass spectra; Mesozoic; Metals; Neogene; North Atlantic; North Pacific; Northeast Pacific; Ocean Drilling Program; Oceanic anoxic events; Pacific Ocean; Paleo-oceanography; Paleoenvironment; Peniche Portugal; Pliocene; Portugal; Pyrite; Sea water; Southern Europe; Spectra; Sulfides; Tertiary; Thallium; Toarcian; Trace elements; United Kingdom; Upper Liassic; Western Europe; Yorkshire England
Coordinates: N280000 N420000 W1170000 W1280000
N103000 N193000 W0650000 W0830000
Record ID: 2012005329
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands