Date Thesis Awarded

5-2017

Document Type

Honors Thesis

Degree Name

Bachelors of Science (BS)

Department

Geology

Advisor

Rowan Lockwood

Committee Member

Christopher Bailey

Committee Member

Paul Heideman

Abstract

The Calvert Cliffs (Maryland, USA) is a classic condensed Miocene sequence that has attracted much scientific attention for its laterally extensive and highly condensed fossil beds (Kidwell, 1982a). Several meters thick and up to 70% shell material, the period of formation of these major complex shell beds has been debated for decades. Kidwell (1989) and associated studies have demonstrated that the major complex shell beds possess certain characteristics that suggest the beds formed as a succession of condensed parasequences during a transgressive systems tract. However, no quantitative analysis has calculated the period of formation of the major complex shell beds in order to assess this interpretation.

Using strontium isotope stratigraphy, the period of formation of the Camp Roosevelt shell bed was demonstrated to be on the order of ~600 kyr. This same period of formation, on the order of 105 years, was consistent across all three localities studied. These findings provide the first geochemical evidence to support the hypothesis that the major complex shell beds formed as a series of condensed parasequences. Combining existing data from Kidwell (1982a) with more recent fieldwork allowed for a comparison of ecology among three of the four major complex shell beds. Characterizing the ecology of the major complex shell beds revealed a striking difference between the community composition of the shell beds from the Calvert Formation and those of the Choptank Formation, with higher levels of diversity seen in the Late Miocene when compared to the Early Miocene. However, future work must focus on more intensive sampling of the biostratigraphic intervals within the shell beds to determine the probable biological or geological cause of this long-term increase in diversity seen during the Miocene.

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