A luminescence method for dating 'dirty' pedogenic carbonates for paleoenvironmental reconstruction

Abstract

Pedogenic carbonates are sensitive paleoclimatic and paleomonsoonal indicators, stratigraphic markers and important sources and sinks in the global CO budget. Establishing a chronology of such carbonates has been difficult due to their open-system behaviour with respect to the radioisotopes used for dating. A luminescence method for chronometric dating of carbonates is proposed which is less susceptible to post-depositional changes and uses subtle changes in the radiation flux to a mineral grain on being carbonated. This change is estimated by measuring luminescence signals of carbonated and uncarbonated mineral separates from the sediment strata and can be related to the age of the carbonate formation. Such ages of pedogenic carbonates from Thar Desert, India conform with paleoclimatic and stable isotopic data and show that they formed in Thar ca. 17 ka, 5 ka and 2 ka ago, since the last glacial epoch.