The Ordovician Seas of Central Pennsylvania: Analyzing environmental affinities and faunal gradients in the Taconic Foreland Basin

Open Access
Whitaker, Anna Friendly
Area of Honors:
Bachelor of Science
Document Type:
Thesis Supervisors:
  • Mark E Patzkowsky, Thesis Supervisor
  • Mark E Patzkowsky, Honors Advisor
  • Maureen Feineman, Faculty Reader
  • paleontology
  • Ordovician
  • faunal gradient
Middle and Upper Ordovician strata of the Appalachian foreland basin have served as a model system for understanding the structure of marine ecosystems on multiple scales (Bretsky, 1970; Springer and Bambach, 1985). A primary finding of these studies is that marine fossil assemblages are related to gradients in water depth and sediment carbonate content. Bretsky (1970) identified Peterson-type communities related to water depth and a siliclastic-carbonate gradient based on the abundant taxa. Springer and Bambach (1985) performed gradient analysis of fossil assemblages in Virginia and identified water depth (or factors related to water depth) as the primary control on fossil distributions. Multivariate analysis of new collections from the Reedsville shale in central Pennsylvania revealed a water-depth gradient in faunal composition that ranges from shoreface to offshore (below storm wavebase) environments. Fossil assemblages are associated with Bretsky’s deep-water Sowerbyella-Onniella community and the shallower Orthorhynchula-Ambonychia association. The faunal gradient in central Pennsylvania shares many characteristics with the depth gradient in Virginia. However, there are some significant differences in the shoreface environments, with the abundant brachiopod Orthorhynchula in central Pennsylvania, rather than abundant brachiopods Hebertella and Zygospira and the bivalve Ambonychia in Virginia. Differences in taxonomic composition in shoreface environments may reflect the increasing carbonate content of these environments, as the species uniquely present in south-west Virginia are located in a more carbonate-rich region of the Taconic Foreland Basin than the central Pennsylvania samples.