Abstract

Pliocene deposits assignable to the Yorktown Formation (Sunken Meadow, Rushmere, and Morgarts Beach Members) and Chowan River Formation (Edenhouse Member) yielded 129 species and subspecies of benthic foraminifera. Twenty-six taxa, selected on the basis of consistent occurrence (present in 50% or more of the samples) and relative abundance (3% or more of the benthic assemblage in at least one sample), account for 88% of the identifiable specimens. From among these 26, principal components analysis identified 14 species that account for nearly 90% of the faunal variation, and cluster analyses revealed distinct stratigraphic assemblages that in general conform to the lithologic subdivisions. The most dramatic faunal change corresponds to the boundary between the Sunken Meadow and Rushmere Members. Based upon the benthic foraminiferal faunas, the Sunken Meadow, Rushmere, and Morgarts Beach Members of the Yorktown Formation were deposited in middle to outer neritic, outer neritic, and middle neritic environments, respectively. The Edenhouse Member of the Chowan River Formation was deposited in an inner to middle neritic environment. Paleobathymetric interpretations based on benthic foraminifera are consistent with those based on other fossil groups.

Paleotemperature implications of the benthic foraminiferal assemblages are not entirely consistent with previous studies. Whereas numerous studies have concluded that Pliocene temperatures at middle and high latitudes were significantly warmer than modern temperatures, the benthic foraminiferal faunas encountered in our study suggest paleotemperatures comparable to those of today. Evidence from benthic foraminifera at the Lee Creek Mine is not sufficient basis to question studies indicating warmer mid-latitude Pliocene seas. Rather, it is likely that localized conditions have overprinted the larger-scale climatic signal.

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