Foraminifera, Stratigraphy and Paleoecology of the Aquia Formation of Maryland and Virginia

By: Donald S. Nogan, 50 pages, 16 figures, 7 plates, 3 tables. July 1964.

Abstract - Twenty-two species of Planktonic Foraminifera and 89 species of benthonic Foraminifera are recognized in the Aquia Formation. The following 10 species are new: Lagenammina pseudodifflugiformis, Haplophragmoides aquiensis, Rectoglandulina aquiensis, Oolina virginiana, Nonionella aquiensis, Aeolostreptis marvlandica, Buliminella marylandica, Fissurina aquiensis, Fissurina marylandica, and Fursenkoina aquiensis.

The Aquia Formation contains three planktonic foraminiferal assemblage zones that are useful in correlating outcrop sections within the Aquia and in correlating the Aquia with equivalent units in the Atlantic and Gulf Coastal Plains. The early Paleocene Globigerinoides daubjergensis - Globorotalia compressa Assemblage Zone occurs in the basal part of the Aquia. The Globorotalia pseudobulloides Assemblage Zone of late Paleocene age is present in the middle portion of the Aquia. The Globigerina spiralis - Globorotalia acuta Assemblage Zone, early Eocene in age, is found in the upper fossiliferous section of the Aquia. The Globorotalia pseudobulloides and Globigerina spiralis - Globorotalia acuta zones are elevated to zone rank from subzones since they are distinctive and stratigraphically valid.

Paleoecologic analyses indicate that the underlying Brightseat Formation, the Aquia Formation, and the basal clay member of the overlying Nanjemoy Formation were deposited in a gradually shoaling sea. The Brightseat was deposited in water not exceeding 300 feet in depth, the Aquia in progressively shallower water, and the clay member in shallow brackish water. In highly glauconitic parts of the Aquia the foraminiferal fauna is characterized by a high foraminiferal number, dominance of one species- Anomalinoides umboniferus. low numbers of benthonic species, and a high percentage of planktonic specimens. These facts suggest that the environmental factors important in the formation of glauconite (rate of sedimentation and oxygen content) affected the composition of the foraminiferal fauna.