Recurrent Community Patterns in Epeiric Seas: The Lower Silurian of Eastern Iowa

Authors

Markes E. Johnson, University of ChicagoFollow

Document Type

Research

Keywords

Community Patterns; Sea Level Fluctuations; Silurian, Llandovery Series, of Iowa

Abstract

In eastern Iowa, the Llandovery Series (Lower Silurian) consists of the Edgewood and Kankakee formations as well as much of the Hopkinton Dolomite. Outcrops of these rocks provide fossil assemblages of marine benthic invertebrates well suited for reconstructing epeiric sea communities. Results of preliminary field studies in Dubuque, Jackson. Jones, and Delaware counties indicate that an initial Lingula Community at the base of the section is succeeded by recurrent patterns of Coral, Pentamerid, and Stricklandid communities. The patterns are interpreted as community response to fluctuations in sea level, estimated to vary between a few and 60 m. At least two repetitions of deepening to shallowing seas are represented, possibly linked to eustatic causes. The orderly sequence of communities, symmetric with respect to reversals in changing water depth, suggests that the local geologic record is reasonably complete. Beds of the Hopkinton Dolomite previously unrecognized as distinct units are described and the first occurrences of the brachiopods, Cyrtia and Ferganella, from the Lower Silurian of Iowa are reported

Publication Date

July 1975

Journal Title

Proceedings of the Iowa Academy of Science

Volume

82

Issue

2

First Page

130

Last Page

139

Copyright

©1975 Iowa Academy of Science, Inc.

Language

en

File Format

application/pdf

Recommended Citation

Johnson, Markes E. (1975) "Recurrent Community Patterns in Epeiric Seas: The Lower Silurian of Eastern Iowa," Proceedings of the Iowa Academy of Science, 82(2), 130-139.
Available at: https://scholarworks.uni.edu/pias/vol82/iss2/15