Orbital forcing of Middle Miocene East Asian summer monsoon variability recorded by aeolian sediments on NE Tibetan Plateau
Akemu Saimaiti , Chaofeng Fu , Xiaoke Qiang , Yougui Song , Rui Zhang , Peng Jia , Beibei Zhang
Geoscience Frontiers ›› 2025, Vol. 16 ›› Issue (6) : 102130
An accurate chrono-stratigraphy of aeolian sediments is crucial for understanding East Asian Summer Monsoon (EASM) variability. However, there are few studies of EASM variability recorded in aeolian sed-iments on the northeastern margin of the Tibetan Plateau, especially high-resolution aeolian sedimentary sequences spanning the period of 15-10 Ma. We studied an aeolian red clay section (89.1 m) with interbedded fluvial sediments, in the Jianzha Basin, northeastern Tibetan Plateau, using the integration of magneto stratigraphy, cyclo-stratigraphy, and detrital zircon provenance analysis. Magneto stratigra-phy revealed 12 normal and 11 reverse polarity zones that are well correlated with chrons C5n.2n to C5Bn.2n of the Geomagnetic Polarity Time Scale (GPTS); this constrains the age of the section to the Middle Miocene. Subsequently, we use the frequency-dependent magnetic susceptibility as an EASM proxy, combined with spectral analysis in the depth domain, to identify Earth orbital periodicities. Gaussian band-pass filtering enabled us to extract the 405-kyr eccentricity signal, which provided a high-resolution astronomical time scale for the interval of 15.231-10.439 Ma. Detrital zircon U-Pb prove-nance tracing and sediment accumulation rate analysis revealed a provenance shift between 14.08 Ma and 10.2 Ma, which we attribute to the rapid uplift of the West Qinling Mountains at ∼ 13-12 Ma. The relationship between the variation of monsoon proxy indicators in the section and the global marine oxy-gen isotope (d18O) record indicates that EASM evolution during the Middle Miocene was primarily a response to global temperature changes. On an orbital time scale, the frequency-dependent magnetic susceptibility record shows a significant long-eccentricity (∼405 kyr) periodicity component, indicating that EASM variations during the Middle Miocene were forced mainly by eccentricity. We conclude that a combination of eccentricity-modulated low-latitude summer insolation and Antarctic Ice Sheet fluctu-ations drove the eccentricity-paced precipitation variability on the northeastern Tibetan Plateau during the Middle Miocene.
Middle Miocene / East Asian summer monsoon / Aeolian sediments / Tibetan Plateau
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