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Morphology and Time/Depth Distribution of Uvigerina peregrina: Continental Slope, Eastern Margin, United States

William L. Balsam, Anthony C. Gary, N. Healy-Williams, Douglas F. Williams

Uvigerina is one of the most important genera of benthic foraminifera for biostratigraphic and paleoenvironmental investigations of continental margin sediments from bathyal water depths. We present morphological and distributional evidence for distinct subpopulations within Uvigerina peregrina from the continental slope of the eastern United States. A detailed record of U. peregrina distribution in the western North Atlantic over water depths from 700 to 4,400 m was determined for the last 25 k.y. Modern U. peregrina is found in core tops from water depths of 700-3,000 m, reaching its acme between 1,300 and 1,800 m. During the glacial maximum (18 k.y.B.P.), this species occupied depths from at least 2,800 to 4,350 m. Beginning 16 k.y.B.P., Uvigerina disappeared from both the shallow and deep parts of its range, until the last remnants of this glacial-age population disappeared 7.6 k.y.B.P. from a depth of 3,600 m. Fourier shape analysis shows that the modern and glacial-age U. peregrina are morphologically distinct. These observations indicate the following. (1) Modern Uvigerina has occupied depths below 1,800 m only during the last 4 k.y. (2) The lack of continuity between modern and glacial-age specimens suggests that separate subpopulations or morphotypes of this species existed. (3) Water mass properties in the western North Atlantic are a major control on the distribution of Uvigerina. (4) Paleobathymetric reconstructions using Uvigerina should consider what morphotypes are the basis for the depth zonation.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.