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Miocene stratigraphy and paleoenvironments of the Calvert Cliffs, Maryland

By
Susan M. Kidwell
Susan M. Kidwell
Department of Geophysical Sciences, University of Chicago, 5734 S. Ellis Avenue, Chicago, Illinois 60637, USA
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David S. Powars
David S. Powars
926A National Center, U.S. Geological Survey, Reston, Virginia 20192, USA
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Lucy E. Edwards
Lucy E. Edwards
926A National Center, U.S. Geological Survey, Reston, Virginia 20192, USA
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Peter R. Vogt
Peter R. Vogt
Marine Science Institute, University of California, Santa Barbara, California, USA
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Published:
January 01, 2015

Abstract

Miocene strata exposed in the Calvert Cliffs, along the western shore of the Chesapeake Bay, Maryland, have a long history of study owing to their rich fossil record, including a series of spectacular shell and bone beds. Owing to increasingly refined biostratigraphic age control, these outcrops continue to serve as important references for geological and paleontological analyses. The canonical Calvert, Choptank, and St. Marys Formations, first described by Shattuck (1904), are generally interpreted as shallowing-up, from a fully marine open shelf to a variety of marginal marine, coastal environments. More detailed paleoenvironmental interpretation is challenging, however, owing to pervasive bioturbation, which largely obliterates diagnostic physical sedimentary structures and mixes grain populations; most lithologic contacts, including regional unconformities, are burrowed firmgrounds at the scale of a single outcrop. This field trip will visit a series of classic localities in the Calvert Cliffs to discuss the use of sedimentologic, ichnologic, taphonomic, and faunal evidence to infer environments under these challenging conditions, which are common to Cretaceous and Cenozoic strata throughout the U.S. Gulf and Atlantic Coastal Plains. We will examine all of Shattuck‚s (1904) original lithologic “zones” within the Plum Point Member of the Calvert Formation, the Choptank Formation, and the Little Cove Point Member of the St. Marys Formation, as well as view the channelized “upland gravel” that are probably the estuarine and fluvial equivalents of the marine upper Miocene Eastover Formation in Virginia. The physical stratigraphic discussion will focus on the most controversial intervals within the succession, namely the unconformities that define the bases of the Choptank and St. Marys Formations, where misunderstanding would mislead historical analysis.

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GSA Field Guide

Tripping from the Fall Line: Field Excursions for the GSA Annual Meeting, Baltimore, 2015

David K. Brezinski
David K. Brezinski
Maryland Geological Survey 2300 St. Paul Street Baltimore, Maryland 21218, USA
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Jeffrey P. Halka
Jeffrey P. Halka
Maryland Geological Survey 2300 St. Paul Street Baltimore, Maryland 21218, USA
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Richard A. Ortt, Jr.
Richard A. Ortt, Jr.
Maryland Geological Survey 2300 St. Paul Street Baltimore, Maryland 21218, USA
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Geological Society of America
Volume
40
ISBN electronic:
9780813756400
Publication date:
January 01, 2015

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