An 11-Ma-old red clay sequence on the Eastern Chinese Loess Plateau

Abstract

Older red clay deposits on the Chinese Loess Plateau contain information of early paleomonsoon evolution and tectonic history of the Ordos platform and the Tibetan Plateau. A well-conserved eolian red clay sequence was recently discovered at Shilou, on the Eastern Chinese Loess Plateau. Paleomagnetic measurements demonstrate that polarity zones recorded in the Shilou red clay profile correspond well with polarity zones between C2An.1n and C5n.2n of the GPTS, and the basal age of the study profile is approximately 11.0 Ma. Field observation, grain-size frequency distribution and quartz grain morphology suggest a wind-blown origin for this sequence. This indicates that the Eastern Loess Plateau began to accumulate dust deposits at 11 Ma ago, implying earlier establishment of the East Asian paleomonsoon probably owing to uplifting of the Tibetan Plateau and ongoing global cooling. It also demonstrates that the Eastern Loess Plateau belonging to the Ordos platform was slowly uplifted and suffered from erosion in the early Neogene, and has no conserved eolian deposits older than 11 Ma as in the Western Chinese Loess Plateau.