Uranium-series dating of speleothems.

Uranium and thorium geochemistry is described in application to U-series dating of speleothems by the ²³⁰Th/²³⁴U, ²³¹Pb/²³⁵U, and ²³⁴U/²³⁸U methods. The principles and limitations of each dating method are discussed, followed by a description of the analytical techniques used in obtaining sources for alpha spectrometry. Previous results on speleothem dating are summarized. Age data for 125 speleothems from several limestone regions in North America are presented and the various factors influencing U content and ²³⁴U/²³⁸U ratio in speleothem calcite are discussed. Average growth rates are calculated from age data and are found to range between 0.4 and 4.1 cm/1000 yr depending on climate, precipitation, soil cover, and depositional conditions. The ages are used to infer rates of karst geomorphic processes, and ages from submerged speleothems in Bermudan caves are used to infer the position of past sea-levels. All results are then used to define the timing and duration of past glacial/interglacial cycles in North America from the abundance frequency of speleothem ages. -M.Gy.