Trilobitas foram 'subitamente' soterrados, diz estudo

quarta-feira, outubro 28, 2009

Beyond Beecher's Trilobite Bed: Widespread pyritization of soft tissues in the Late Ordovician Taconic foreland basin

Úna C. Farrell1, Markus J. Martin2, James W. Hagadorn3, Thomas Whiteley4 and Derek E.G. Briggs1,5

+ Author Affiliations

1Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06520, USA

2371 Pawling Street, Watertown, New York 13601, USA

3Department of Geology, Amherst College, Amherst, Massachusetts 01002, USA

4105 White Village Drive, Rochester, New York 14625, USA

5Yale Peabody Museum of Natural History, Yale University, New Haven, Connecticut 06520, USA



Pyritization of soft tissues is extremely rare. Pyritized fossils have been discovered at six new localities spanning 54 km of outcrop of the Ordovician Lorraine Group of New York State, suggesting that soft-tissue pyritization is widespread in the Taconic basin. Notable new taxa with soft-tissue preservation include ostracods and other arthropods. Such fossils are rare and occur within 4–9-cm-thick mudstones representing single rapid depositional events. High ratios of reactive iron to total iron and high values of δ34S, together with a near-absence of disarticulated and fragmented skeletal material, suggest that organisms in these pyritic horizons were buried rapidly and underwent bacterial sulfate reduction in porewaters rich in highly reactive iron and low in organic carbon. These conditions facilitated iron sulfide precipitation within and on decaying carcasses. Such conditions occur repeatedly in some fine-grained distal turbiditic facies of the Taconic foreland basin. Pyritized soft-bodied fossils await discovery elsewhere in the Lorraine Group.

Received 25 February 2009.
Revision received 15 May 2009.
Accepted 17 May 2009.
© 2009 Geological Society of America



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