Late Quaternary climatic history of NW Romania: results from Th/U dating of speleothems

Abstract

Speleothems are secondary minerals that precipitate in caves, most commonly as stalagmites, stalactites and flowstones. They are primarily composed of calcium carbonate, precipitated by slow degassing of carbon dioxide from supersaturated waters entering the cave gallery. Trace elements may be transported in solution and co-precipitated in calcite. One of these, uranium, when in concentration that exceeds 0.01 ppm allows precise age determination by U-series dating methods. Speleothem growth is a sensitive indicator of both temperature and humidity, and changes in either one or both of these can cause periods of enhanced or reduced growth. Furthermore, the worldwide karst landscape distribution and the study of speleothems growth interval enable regional chronologies to be drawn up. Uranium concentration in speleothems depends on several factors: uranium content of the host rock, residence time in the underground water, HCO₃^- availability etc., and thus is highly variable from one speleothem to another or even in the same speleothem