Abstract
Speleothem from West Virginia, ranging in age from 2000 to 200,000 yr B.P. contains uranium with U 234 U 238 ratios significantly greater than unity. This ratio varies from one speleothem to another, as does average U content. Initial ratios, corrected for age, are remarkably constant for a given speleothem. By contrast, U 234 U 238 ratios in seepage waters vary significantly from month to month at a given drip site, and their average values differ from that of the speleothem which they are depositing. This discrepancy is attributed either to long-term averaging-out of fluctuations, or fractional precipitation on the speleothem of a chemical species of uranium with a more constant ratio. Constancy of initial U 234 U 238 ratios from Th 230 U 234 . datable portions of speleothems should permit U 234 U 238 -dating of older portions of the same speleothem, back to about 10 6 yr B.P., with estimated precision of ±5 per cent.
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