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LU

Emma Hammarlund

Research team manager

LU

Paleoredox and pyritization of soft-bodied fossils in the ordovician frankfort shale of New York

Author

  • Una C. Farrell
  • Derek E G Briggs
  • Emma U. Hammarlund
  • Erik A. Sperling
  • Robert R. Gaines

Summary, in English

Multiple beds in the Frankfort Shale (Upper Ordovician, New York State), including the original "Beecher's Trilobite Bed," yield fossils with pyritized soft-tissues. A bed-by-bed geochemical and sedimentological analysis was carried out to test previous models of soft-tissue pyritization by investigating environmental, depositional and diagenetic conditions in beds with and without soft-tissue preservation. Highly-reactive iron (FeHR), total iron (FeT), δ34S, organic carbon and redox-sensitive trace elements were measured. In particular, the partitioning of highly-reactive iron between iron-carbonates (Fe-carb), iron-oxides (Fe-ox), magnetite (Fe-mag), and pyrite (FeP) was examined. Overall, the multi-proxy sedimentary geochemical data suggest that the succession containing pyritized trilobite beds was deposited under a dysoxic water-column, in agreement with the paleontological data. The data do not exclude brief episodes of water-column anoxia characterized by a ferruginous rather than an euxinic state. However, the highest FeHR/FeT values and redox-sensitive trace element enrichments occur in siltstone portions of turbidite beds and in concretions, suggesting that subsequent diagenesis had a significant effect on the distribution of redox-sensitive elements in this succession. Moderately high FeHR/FeT and FeP/FeHR, low organic carbon, enriched δ34S, and the frequent presence of iron-rich carbonate concretions in beds with soft tissue preservation confirm that pyritization was favored where porewaters were iron-dominated in sediments relatively poor in organic carbon.

Publishing year

2013-05

Language

English

Pages

452-489

Publication/Series

American Journal of Science

Volume

313

Issue

5

Document type

Journal article

Publisher

American Journal of Science

Keywords

  • Distal turbidite
  • Dysoxia
  • Iron paleoredox proxy
  • Konservat Lagerstatte
  • Paleoenvironment
  • Sulfur isotopes
  • Taphonomy
  • Trace elements

Status

Published

ISBN/ISSN/Other

  • ISSN: 0002-9599