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Mid-Paleozoic trilobite Lagerstaetten; models of diagenetically enhanced obrution deposits

Carlton E. Brett, James J. Zambito, Brenda R. Hunda and Eberhard Schindler
Mid-Paleozoic trilobite Lagerstaetten; models of diagenetically enhanced obrution deposits (in Lagerstaetten through time; a collection of exceptional preservational pathways from the terminal Neoproterozoic through today, James D. Schiffbauer (editor) and Marc Laflamme (editor))
Palaios (May 2012) 27 (5): 326-345

Abstract

Spectacular trilobite Lagerstatten occur in distinctive offshore calcareous mudstone facies through the Late Ordovician to Devonian, and reflect a combination of mass mortality or molting and burial, coupled with early diagenetic enhancement. Evidence indicates two distinct modes of burial, Type I and II assemblages, which show evidence for burial without or with seafloor disturbance, respectively. Type I assemblages suggest rapid (hours to days), but not instantaneous burial, without bottom disruption, enabling preservation of in situ behavior, including mass aggregations and molt ensembles. Most occurrences contain bedding planes in which trilobites exhibit incipient disarticulation. These assemblages were buried by cascades of flocculated sediment from hypopycnal, detached flows. Type II assemblages show well-articulated, enrolled, semi-enrolled, and outstretched trilobites in varied orientations relative to bedding. In such cases, bottom flows and seafloor disruption by storm or seismic disturbances in shallow waters suspended large amounts of flocculated muds as viscous slurries, which developed into hyperpycnal flows that entrained carcasses of trilobites and other organisms. In many cases, both Type I and II obrution was followed by additional sedimentation, geochemical zones moved upward through the sediment column, and there was little tendency to form diagenetic overprints. Alternatively, if burial was followed by an interval of sediment starvation, the sediments were bioturbated and very early diagenetic mineralization was superimposed, first, in rare cases, as mineralized soft parts in entombed carcasses, and later as pyritization of burrow linings. Development of the concretionary layers required more prolonged periods of stability of the sulfate reduction zone. Cementation of sediment shielded organism bodies from most or all effects of compaction. Thus, ironically, the best preservation of delicate remains required rapid burial, associated with mass mortality, and very low rates of background sedimentation following the event.


ISSN: 0883-1351
Serial Title: Palaios
Serial Volume: 27
Serial Issue: 5
Title: Mid-Paleozoic trilobite Lagerstaetten; models of diagenetically enhanced obrution deposits
Title: Lagerstaetten through time; a collection of exceptional preservational pathways from the terminal Neoproterozoic through today
Author(s): Brett, Carlton E.Zambito, James J., IVHunda, Brenda R.Schindler, Eberhard
Author(s): Schiffbauer, James D.editor
Author(s): Laflamme, Marceditor
Affiliation: University of Cincinnati, Department of Geology, Cincinnati, OH, United States
Affiliation: Virginia Polytechnic Institute and State Univesity, Nanoscale Characterization and Fabrication Laboratory, Blacksburg, VA, United States
Pages: 326-345
Published: 201205
Text Language: English
Publisher: Society for Sedimentary Geology, Tulsa, OK, United States
Meeting name: Geological Society of America annual meeting
Meeting location: Denver, CO, USA, United States
Meeting date: 20101031Oct. 31-Nov. 3, 2010
References: 73
Accession Number: 2012-065525
Categories: Invertebrate paleontology
Document Type: Serial Conference document
Bibliographic Level: Analytic
Annotation: NSF Grant 0819715
Illustration Description: illus. incl. 1 table, strat. col.
N27°40'00" - N36°00'00", W13°15'00" - W01°00'00"
Secondary Affiliation: Smithsonian Institution National Museum of Natural History, USA, United StatesCincinnati Museum Center, USA, United StatesSenckenberg Forschungsinstitut und Naturmuseum Frankfurt, DEU, Germany
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 201234
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