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

Farrell, Una C.; Briggs, Derek E G; Hammarlund, Emma U. LU ; Sperling, Erik A. and Gaines, Robert R. (2013) In American Journal of Science 313(5). p.452-489
Abstract

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... (More)

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.

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author
publishing date
type
Contribution to journal
publication status
published
keywords
Distal turbidite, Dysoxia, Iron paleoredox proxy, Konservat Lagerstatte, Paleoenvironment, Sulfur isotopes, Taphonomy, Trace elements
in
American Journal of Science
volume
313
issue
5
pages
38 pages
publisher
Amer Journal Science
external identifiers
  • scopus:84894498271
ISSN
0002-9599
DOI
10.2475/05.2013.02
language
English
LU publication?
no
id
27cc7be0-b458-434e-86f9-8e101a417b60
date added to LUP
2017-05-17 11:25:45
date last changed
2018-10-07 04:56:12
@article{27cc7be0-b458-434e-86f9-8e101a417b60,
  abstract     = {<p>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.</p>},
  author       = {Farrell, Una C. and Briggs, Derek E G and Hammarlund, Emma U. and Sperling, Erik A. and Gaines, Robert R.},
  issn         = {0002-9599},
  keyword      = {Distal turbidite,Dysoxia,Iron paleoredox proxy,Konservat Lagerstatte,Paleoenvironment,Sulfur isotopes,Taphonomy,Trace elements},
  language     = {eng},
  number       = {5},
  pages        = {452--489},
  publisher    = {Amer Journal Science},
  series       = {American Journal of Science},
  title        = {Paleoredox and pyritization of soft-bodied fossils in the ordovician frankfort shale of New York},
  url          = {http://dx.doi.org/10.2475/05.2013.02},
  volume       = {313},
  year         = {2013},
}