Abstract

Extensive low-lying marine deposits border the southeastern United States Atlantic Coastal Plain. Some units are fossiliferous and contain corals as isolated fragments in sediments of a detrital character. These corals are subject to alteration processes such that suites of related samples must be examined to determine the suitability of these coral samples for reliable uranium-series dating. With the exception of those from one location, most samples appear to have remained closed systems with respect to the isotopes of uranium and thorium throughout their geologic history. Extraneous 230Th has been detected in some of the corals due to incorporation of some detrital materials into their skeletons. For these samples, different methods are applied to correct for the initial 230Th contamination. Continued sampling and analyses have resulted in 55 individual uranium-thorium determinations.

The average 230Th ages of samples from the Norfolk Formation, and from later- and earlier-deposited sediments of the Wando Formation are ∼71,000, 87,000, and 129,000 yr, and they appear to correlate with oxygen isotope substages 5a, 5c, and 5e, respectively. The average 230Th age of samples from beds of the Rappahannock River, Ponzer, and Ten Mile Hill localities is ∼212,000 yr, and they correlate with oxygen isotope stage 7. The sediment of the Canepatch Formation is ∼460,000, yr old, and it is tentatively correlated with oxygen isotope stage 11.

There is general agreement between uranium-series and uranium-trend dates and between the quantitative trends of the amino acid data and uranium-series dates. The amino acid values, however, ure unacceptably high in at least two groups of samples, those from localities near Charleston, South Carolina, and from central Virginia.

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