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Ammobaculites, Foraminiferal Proprietor of Chesapeake Bay Estuaries

By
Robert L. Ellison
Robert L. Ellison
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Published:
January 01, 1972

In the central parts of Virginia estuaries that are tributaries of Chesapeake Bay a foraminiferal facies characterized by Ammobaculites is replaced seaward by an Elphidium facies, upstream by a Difflugia facies, and laterally in the marshes by a Miliammina and Ammoastuta facies. Within the area where Ammobaculites is most abundant, foraminiferal tests commonly number between one and ten thousand per 20 cubic centimeters, and Ammobaculites comprises nearly 100 percent of the total. Locally, empty tests and living specimens aggregate in clumps 15 to 150 meters in diameter. The genus is distributed vertically from 100 centimeters above the estuary floor, where it lives in eelgrass, to at least 9 centimeters below the bottom, where it subsists in organic-rich muds. Concentrations of empty tests in estuarine samples from Virginia and Maryland suggest that Ammobaculites must have a moderately high annual turnover while thriving on the “vegetable soup” of the estuaries.

Ammobaculites crassus Warren dominates foraminiferal communities in the Chesapeake Bay area wherever salinities are between 1 and 15 °/°°. The Ammobaculites and contiguous facies shift along the estuary in response to seasonal salinity changes, and faunal patterns across the estuary conform to the asymmetrical distribution of salinity induced by Coriolis effects. High temperatures, up to 14°C above the normal in thermally polluted waters, have only limited effect on Ammobaculites. Comparison with other estuaries suggests that the dominance of Ammobaculites depends on salinity, geographic location or physiographic setting, and the presence of organic detritus.

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Contents

GSA Memoirs

Environmental Framework of Coastal Plain Estuaries

Bruce W. Nelson
Bruce W. Nelson
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Geological Society of America
Volume
133
ISBN print:
9780813711331
Publication date:
January 01, 1972

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