[1] Univ Utrecht, Dept Earth Sci, NL-3584 CB Utrecht, Netherlands
[2] Univ Utrecht, Dept Phys Geog, NL-3584 CB Utrecht, Netherlands
[3] Catholic Univ Louvain, Earth & Life Inst, Earth & Climate Res Ctr, Louvain la Neuve, Belgium
[4] Chinese Acad Sci, Inst Earth Environm, State Key Lab Loess & Quaternary Geol, Xian 710061, Peoples R China
[5] Univ Bristol, Sch Chem, Organ Geochem Unit, Bristol, England