Emma Hammarlund
Research team manager
Paleoredox and pyritization of soft-bodied fossils in the ordovician frankfort shale of New York
Author
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