Uranium series dating of quaternary deposits
Uranium-series dating of dense tufa deposited in a small cave, at former lake margins, and in large tufa mounds clarifies the timing of lake-level variation during the past 400,000 yr in the Pyramid Lake basin. P., as shown by Th-excess ages of tubular tufas, and average isochron-plot ages of shoreline-deposited tufas.
A moderate-sized lake occasionally overflowed the Emerson Pass sill at elevation of ∼1207 m between ca. (By comparison, modern Pyramid Lake is ∼50 m below this sill).
Correction for detrital contaminant is demonstrated in the dating of speleothem from a cave in Italy.
U at the time of sample formation must be known or calculated.
Thorium is not soluble in natural waters under conditions found at or near the surface of the earth, so materials grown in or from these waters do not usually contain thorium.
In contrast, uranium is soluble to some extent in all natural waters, so any material that precipitates or is grown from such waters also contains trace uranium, typically at levels of between a few parts per billion and few parts per million by weight.
230Th/234U and 14C dating of a late Pleistocene stalagmite in Lobatse II cave, Botswana.
Alpha-counting techniques allow the dating of carbonates and phosphates with a precision of ± 5 to 10% over the time range from 1 ka to 350 ka.
Ages between 1000 and 300,000 years have been reported.
Uranium/Thorium dating of ferricretes from mid- to late Pleistocene glacial sediments, western Tasmania, Australia.
Atom counting methods (mass spectrometry and AMS) substantially increase precision and may increase the range.
Problems of contamination and open-system behavior are discussed.
There is a lack of tufa record during the intervening period from ca.