ABSTRACT
The Choptank Formation differs from the Calvert Formation in that all its members contain well-preserved fossil mollusks. Having been deposited during the Mid-Miocene Cold Time, in a period of rapidly fluctuating sea levels and lowered water temperatures (Petuch, 2004:101, 261), the Choptank molluscan fauna is relatively impoverished. The three members of the Choptank Formation are each represented by a single Shattuck Zone, with Shattuck Zone 17 being the St. Leonard Member, Shattuck Zone 18 being the Drumcliff Member, and Shattuck Zone 19 being the Boston Cliffs Member (Ward, 1992). Of these members, the St. Leonard Member contains the most impoverished fauna, while the Drumcliff Member contains the richest fauna with the highest diversity.
