Long-term cooling/drying record of North China since the middle Pleistocene from geochemical evidence of a 150 m deep drill core, Beijing plain, China

Abstract

The Quaternary strata in North China primarily consist of fluvial sediments, which react strongly to East Asian Monsoon circulation. However, the records of the Quaternary climate change history in terms of these fluvial sedimentations were limited which impeded understanding the East Asian Monsoon evolution in North China. Thus, a 150 m deep drill core was collected from Changping in the Beijing plain to reconstruct the Quaternary palaeoenvironmental changes. The core was chronologically well constrained using palaeomagnetic and thermoluminescence dating. The magnetostratigraphic result indicated that the Brunhes/Matuyama boundary is at 134.2 m (0.78 Ma) and the age at the bottom of the core is 1.07 Ma. The thermoluminescence (TL) dating of the upper sand at ∼2 m was 10.4 ka. The chemical weathering history since the middle Pleistocene in Beijing plain was reconstructed by using geochemical proxies including selected major element pairs, chemical index of alteration and Al2O3–CaO*–(Na2O + K2O) diagrams. The CIA value of the Changping core ranged from 50.3 to 69.4 (average 59.2), which indicated that the sediment has experienced incipient to intermediate chemical weathering during the middle Pleistocene. The result of A–CN–K figure shows a high plagioclase to K-feldspar ratio in the source, which would be indicative of a granodiorite (Gd) source from Jundu Mountains north of the Beijing plain. All the geochemical results revealed a long-term gradual decrease of weathering since the middle Pleistocene, which implied a long-term increasing aridification/cooling in the Beijing plain.