Does sedimentary facies transformation modulate the recording of orbital forcing? Insights from environmental magnetism and multi-proxy data in the Songnen Basin (NE China)

The question of which orbital parameters (eccentricity, obliquity, and precession) drove Pleistocene variability in East Asian monsoon precipitation has become one of the enduring problems in paleoclimatology, yet a consensus remains elusive. Here, we test whether major sedimentary facies transformations can modify the orbital imprint preserved in climate archives by integrating environmental magnetic and non-magnetic proxies from a 954 kyr borehole (47°25′42″N, 125°55′00″E) in the Songnen Basin, NE China. We analyze magnetic susceptibility together with elemental contents and grain-size indices across intervals characterized by pronounced facies transitions. The χ_lf, χ_fd, Mn/Fe, Rb/Sr, Fe content, and the percentage of >32 μm (%) show significant correlations with lithological transitions over time. The shift from swamp/peat to lacustrine facies is marked by a notable decline in χ_lf, Rb/Sr, and Fe flux, while χ_fd, Mn/Fe, and the percentage of >32 μm (%) exhibit a clear increase. The transition from lacustrine to marginal lacustrine facies shows relatively minor but still distinct changes, with χ_fd, Mn/Fe, Fe flux, and the percentage of >32 μm (%) increasing significantly. The most pronounced transition occurs around 200 ka, changing aqueous to eolian deposition. During this period, χ_lf, χ_fd, and Mn/Fe rise sharply, the Rb/Sr ratio continues to decline, and Fe flux and the percentage of >32 μm (%) display a stable trend with weaker amplitude fluctuations compared to before 200 ka. Spectral and evolutionary spectral analyses show that the dominant orbital periodicity is consistently expressed across facies changes, indicating that facies transformation does not fundamentally reorganize the primary orbital pacing recorded in this sequence. In contrast, the relative power and temporal stability of specific orbital bands vary among proxies, implying proxy-dependent sensitivity rather than archive-dependent forcing. We attribute these differences to differential responses of regional climate components (i.e., temperature, effective moisture, and lake-level variability) to orbital forcing, which in turn regulate magnetic mineral concentration and grain size, detrital input, and chemical transport pathways. Our results highlight that discrepancies among orbital-forcing reconstructions of East Asian rainfall arise mainly from how individual proxies encode climate conditions, rather than from changes in the geological archive itself.