University of Vermont

Virtual Field Study


Stratigraphy / Sedimentology

strat   The study of rock layers is called "stratigraphy."  When you study layers of rock you're not only studying periods of time, but also environments and how they have changed.  The material that comprises the cliffs is 8 to 17 million years old and consists of thick deposits of clay and sand that have not yet been hardened into rock (lithified).   Geologists have grouped these layers into formations.  Each formation records conditions in an environment on the ancient shoreline, such as a beach or lagoon.  Changes from one formation to another records changes in the environment in which the sediment accumulated.  There are three formations exposed in the cliffs of Calvert County: the St. Mary's, the Choptank, and the Calvert.  A diagram identifiying the formations, their representative thickness, and relative age at a shoreline location called "Scientists Cliffs" can be seen on the right.  The sand and clay deposited in this location offer geologists a window into the past, and indicate that a near shore sedimentary environment once existed where dry land is exposed today.  Along the east coast of Calvert County these formations dip to the southeast at about 11 feet/mile, with the older formations dipping below sea level to the south.  This means that as one travels south along the western shore of Calvert County (down Bay), the beds become progressively younger in age (see figure below).
(Drawing courtesy of Rasmussen, 1999)                                             

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Last modified October 06 2008 02:32 PM

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