Obliquity-modulated poleward rain-belt shifts recorded in the Pliocene-Pleistocene sequence, northern Chinese Loess Plateau

Earth’s axial tilt modulates meridional insolation gradients and, in turn, the latitude of the tropical rainbelt/Intertropical Convergence Zone (ITCZ). We test this mechanism at the northern limit of the Asian summer monsoon using a 63.5-m red clay–loess succession on the northern Chinese Loess Plateau (CLP). New magnetic susceptibility (χ) and grain-size (< 5 μm) series, anchored by magnetostratigraphy and refined by astronomical tuning, reveal statistically significant 405 kyr eccentricity, ~173 kyr obliquity modulation, and ~1.2 Myr bands. We iteratively tuned the χ series to the astronomical solution using the ~173 kyr obliquity-modulation filter, and independently validated the chronology against the 405 kyr eccentricity band; evolutive spectral analysis further verifies the cyclic pacing and phase relationships. Band-pass reconstructions show that χ maxima broadly coincide with obliquity amplitude highs, consistent with strengthened summer monsoon and northward rainbelt displacement. Coherence with χ from nearby CLP sections (Wujiamao, Lingtai) and with benthic δ18O–δ13C further supports regional to global controls. We interpret the CLP record as an obliquity-gated archive of ITCZ poleward pulses during the Pliocene-Pleistocene, modulated by 173 kyr (Earth-Saturn) and ~1.2 Myr (Earth-Mars) beats, superposed on the long-eccentricity metronome. The tuned framework provides a physically grounded chronology for future multi-proxy work and a benchmark for testing monsoon-ITCZ dynamics in warm-climate simulations.