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Taphonomy and paleoecology of echinoderm Lagerstaetten from the Silurian (Wenlockian) Rochester Shale

Wendy L. Taylor and Carlton E. Brett
Taphonomy and paleoecology of echinoderm Lagerstaetten from the Silurian (Wenlockian) Rochester Shale
Palaios (April 1996) 11 (2): 118-140


The Lewiston Member of the Rochester Shale (Silurian, Wenlockian) of western New York and southern Ontario contains three intervals of echinoderm Lagerstaetten (Homocrinus beds). These intervals preserve moderate diversity level-bottom communities dominated by epibenthic suspension feeders. Taphonomic and sedimentologic evidence indicates that these communities, existed in low-energy environments below normal wave base but were episodically disrupted and smothered by distal mud tempestites or gradient current deposits. The most favorable conditions for the preservation of these communities existed at the lower end of storm wave base, where relatively thick distal mud flows were frequently generated but where energy conditions precluded later reworking. These tiered communities were strongly dominated by suspension feeders, including brachiopods, bryozoans and pelmatozoans, which together make up approximately 93% of the preserved fauna. Low-level benthic forms such as brachiopods, fistuliporoid bryozoans, short-stemmed crinoids and edrioasteroids were buried intact, directly attached to shell pavements representing the blanketed seafloor. Disturbance was minimal but included toppling and uprooting of echinoderms and shells and minor disarticulation prior to burial. In contrast, long-stemmed pelmatozoans were buried within sparsely fossiliferous mud layers (up to 5 cm thick) commonly with columns and splayed arms oblique within the burial layers. Preservation of vagrant organisms, such as the asteroid Paleaster, the ophiuroid Protaster and ten genera of trilobites, provides further evidence of rapid and deep burial. In addition, scanning electron microscopy of the mud layers directly overlying smothered assemblages indicates the presence of micrograding and flocculated microfabrics. The Homocrinus intervals record the short-term succession of communities mediated by episodic storm-related sedimentation in low-energy offshore shelf environments. Distinct successional stages or seres are recognized: a) a suite of infaunal deposit feeders, b) low diversity (25-30 species) pioneer Amphistrophia-Dalmanites sere, c) intermediate diversity (35-60 species) Striispirifer sere, and in some cases d) high diversity (60-100 species) bryozoan-pelmatozoan thicket sere. Early seres (a, b) resemble faunal assemblages that typify deeper, dysoxic muddy bottom communities. With increasing diversity, organism interactions and density of species within tiers increased significantly in the Striispirifer association and reached a peak in the bryozoan thickets. However, the absolute vertical height of upper tiers may be as great or greater in the low diversity assemblages. The Homocrinus-bearing Striispirifer-Amphistrophia community and associated communities tracked east-west trending lithofacies belts that shifted position in response to transgressive/regressive pulses during Rochester Shale deposition. Water depth and sedimentation rate appear to have exerted major controls on the level of community development.

ISSN: 0883-1351
Serial Title: Palaios
Serial Volume: 11
Serial Issue: 2
Title: Taphonomy and paleoecology of echinoderm Lagerstaetten from the Silurian (Wenlockian) Rochester Shale
Affiliation: University of Rochester, Department of Earth and Environmental Sciences, Rochester, NY, United States
Pages: 118-140
Published: 199604
Text Language: English
Publisher: Society of Economic Paleontologists and Mineralogists, Tulsa, OK, United States
References: 86
Accession Number: 2006-026577
Categories: Invertebrate paleontology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. strat. cols., 1 table, geol. sketch map
N43°00'00" - N43°30'00", W79°30'00" - W77°30'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 200614
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