Paleoredox and pyritization of soft-bodied fossils in the ordovician frankfort shale of New York
(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.
(Less)
- author
- Farrell, Una C. ; Briggs, Derek E G ; Hammarlund, Emma U. LU ; Sperling, Erik A. and Gaines, Robert R.
- publishing date
- 2013-05
- 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
- American Journal of 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
- 2022-03-24 18:31:07
@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}},
keywords = {{Distal turbidite; Dysoxia; Iron paleoredox proxy; Konservat Lagerstatte; Paleoenvironment; Sulfur isotopes; Taphonomy; Trace elements}},
language = {{eng}},
number = {{5}},
pages = {{452--489}},
publisher = {{American Journal of 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}},
doi = {{10.2475/05.2013.02}},
volume = {{313}},
year = {{2013}},
}