Date of Award

1990

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean & Earth Sciences

Program/Concentration

Geology

Committee Director

Randall S. Spencer

Committee Member

Stephen Culver

Committee Member

Carl F. Koch

Committee Member

Lauck W. Ward

Call Number for Print

Special Collections LD4331.G4J65

Abstract

This study examines the foraminiferal fauna, both benthic and planktonic, of the outcropping (45 samples) and subsurface (31 samples) middle Eocene Piney Point Formation in Virginia and Maryland. The primary objective of this study is to further refine the depositional history of the Salisbury Embayment which is represented by the middle Eocene Piney Point Formation. Ninety-six species of benthic and planktonic foraminifera were identified in this study. Of these, several are characteristic of the middle Eocene: Asterigerina texana, Hanzawaia danvillensis, Ceratobulimina exima, Cibicides westi, Chiloguembelitria columbiana, C. stavensis, Testacarinata inconspicua and Pseudohastigerina wilcoxensislmicra. While these were relatively abundant, diagnostic middle Eocene species such as Truncorotaloides topilensis, T. rohri and Acarinina bulbrooki were present, but quite rare. Based upon these characteristic middle Eocene foraminifera, the Piney Point Formation can be correlated with other middle Eocene Atlantic and Gulf Coastal Plain units. The benthic and planktonic foraminiferal faunas of the Piney Point Formation are most similiar to those described from the Lisbon Formation of Alabama, the Cook Mountain Formation of Louisiana and the Castle Hayne Formation of North Carolina.

Examination of the benthic foraminifera using Q-mode cluster analysis on both presence/absence and abundance data reveals two distinctly different open marine biofacies of regional extent. Biofacies A, which is composed of the most shoreward localities, is characterized by species generally associated with paleodepths of between 15 and 50 meters such as Asterigerina texana, Cibicidoides tallahattaensis and Hanzawaia danvillensis, while biofacies B, composed of the most basinward localities, is characterized by species associated with paleodepths of between 50 and 150 meters, such as Epistominella danvillensis and Pyramidina subrotundata. These analyses also allowed subdivision of each of these biofacies into two smaller, more localized biofacies. These local biofacies reflect slight variations in paleobathymetry within the larger, regional biofacies.

The benthic foraminiferal fauna of the Piney Point Formation represents inner, middle and outer neritic paleoenvironments resulting from the transgression of marine waters ranging in depth from 15 to 150 meters into the middle Eocene Salisbury Embayment. A regional variation in paleobathymetry across the Salisbury Embayment as indicated by the distribution of the benthic foraminiferal fauna shows a progressive deepening of the basin from the southwest to the northeast.

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DOI

10.25777/6m0w-x505

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