Palaeclimatic significance of the Xiantai fluvio-lacustrine sequence in the Nihewan Basin (North China), based on rock magnetic properties and clay mineralogy

Here, we report an increased cooling coupled with an intensified aridification for the Xiantai fluvio-lacustrine sequence of Pleistocene age (1.9-0.1 Ma) in the Nihewan Basin (North China), known for the occurrence of several hominin sites. The cooling is related to an up-section decrease in propensity to chemical weathering as inferred from an increase in low-field susceptibility after cycling to 700 degrees C. Close to 700 degrees C, reacting chlorite is providing the iron source for newly formed very fine-grained ferrimagnetic minerals which enhances the susceptibility signal. The reactivity of chlorite after annealing at temperatures above 600 degrees C is documented with X-ray diffraction and the up-section decrease in propensity to chemical weathering is confirmed by the up-section declining illite/chlorite ratios and increasing chlorite and illite contents based on X-ray diffraction analysis on selected samples.