U234U238 Ratios in limestone cave seepage waters and speleothem from West Virginia

Speleothem from West Virginia, ranging in age from 2000 to 200,000 yr B.P. contains uranium with U234U238 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, U234U238 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 U234U238 ratios from Th230U234. datable portions of speleothems should permit U234U238-dating of older portions of the same speleothem, back to about 106 yr B.P., with estimated precision of ±5 per cent.