ASTRONOMICAL CYCLES OF CARBONATES IN THE PLIOCENE RED CLAY FORMATION, CHINESE LOESS PLATEAU

The Pliocene epoch is considered the most recent analog of the current global warming, a time when global mean temperatures and atmospheric carbon dioxide concentrations were similar to those projected for the near-term as a result of climate change. However, the fundamental climate characteristic of the Pliocene still remains controversial. The Red Clay, which underlies the well-known Quaternary loess sequence, extends the eolian deposits from 2.6 Ma through the late Miocene, and is potentially a good archive to reconstruct Pliocene climate. Here we present a high-resolution, quantitative record of Red Clay carbonate variations from 8.2 to 2.6 Ma B.P. in addition to other climatic proxy data including magnetic susceptibility(MS), Rb/Sr and Zr/Rb ratios from the Jiaxian Red Clay section, which located at the northern limit of present East Asian summer monsoon (EASM) on Chinese Loess Plateau (CLP). The carbonate content of the JX Red Clay section is characterized by high frequency variations as peaks and valleys, corresponding to couplets of carbonate leaching and accumulation horizons, with a total 86 leaching and accumulation cycles identified. MS values, Rb/Sr ratios were higher and Zr/Rb ratios were lower in the leaching horizons than in the accumulation horizons. These variations are similar as the overlying Quaternary paleosol-loess sequences, suggesting an active EAM similar as Quaternary glacial-interglacial cycles during late Miocene and Pliocene, and arguing against the hypothesis that past and future warm climate background conditions will lead to a permanent El Niño-like state.