Paleoclimatic significance of rare earth element record of the calcareous lacustrine sediments from a long core (SG-1) in the western Qaidam Basin, NE Tibetan Plateau

Rare earth elements (REEs) have been widely applied as provenance tracer, but few studies focus on the potential paleoclimatic implications in long-term sedimentary sequences. This study analyzed REEs in the calcareous lacustrine sediments from a 938.5 m long core (SG-1) in the western Qaidam Basin in order to evaluate the usefulness of their abundance and fractionation in understanding the paleoclimatic evolution in the drainage area. We used acetic acid (HOAc) to leach the labile fraction of REEs, and citrate-bicarbonate-dithionite (CBD) to extract REEs associated with Fe-Mn oxides/oxyhydroxides. Four REE phases in the core sediments were identified, including HOAc leachate, HOAc residue, CBD extraction, and the bulk phase. On average, portion of REEs in HOAc residue constitutes about 80% of the bulk phase, while those portions from HOAc leachate and CBD extraction make up 18% and 3%, respectively. The REE's characteristics in the HOAc residue phase, and to a lesser extent in the bulk phase, remain stable along the core, while those in HOAc leachate and CBD extraction vary dramatically. REE abundance and fractionation in HOAc leachate and the CBD extraction phases with other well studied climatic proxies in the core are compared. The REE abundance and the degree of fractionation of HOAc leachate and CBD extraction phases provide sensitive proxies for the intensity of chemical weathering in the source area, which relate to climate change in the drainage area. The REE records in the core SG-1 reveal a long-term weakening of chemical weathering since 2.77 Ma in the western Qaidam Basin.