Quaternary Sedimentary Sequence and Paleoclimatic Evolution in the Southern Yinchuan Basin: Evidence from Sedimentology, Geochemistry, and Detrital Zircon U–Pb Geochronology of ZK01 Borehole

The Yinchuan Basin is situated at the leading edge of the latest northeastward expansion of the northeastern Tibetan Plateau. Sedimentary sequences at basin margins are crucial for understanding basin–mountain coupling relationships, yet systematic studies remain scarce. Here, we present a comprehensive sedimentological, paleomagnetic, whole-rock major and trace element, carbon–oxygen isotope, and detrital zircon U–Pb geochronological analysis of ZK01 Borehole (203 m) from the Kushui River area in the southern basin. Multi-proxy reconstruction reveals that Quaternary climate evolution can be divided into five stages: (1) Early Pleistocene (~2.58–1.77 Ma) alluvial fan-lacustrine alternations with high-amplitude climatic fluctuations, responding to orbitally-driven monsoon precipitation changes; (2) late Early Pleistocene (~1.77–0.78 Ma) stable lacustrine environment with sustained warm–humid conditions and subdued wet–dry oscillations; (3) Middle Pleistocene Climate Transition (MPT, ~0.9–0.6 Ma), marked by positive δ13C shifts, heavier δ18O values, and peak CIA values, indicating intensified chemical weathering in the catchment despite regional warming–drying; (4) Late Pleistocene (~0.16–0.12 Ma) extreme arid alluvial fan phase, with decreased CIA, recording a major dry event; and (5) post-last interglacial (~0.12 Ma–present) shallow lake recovery, with gradual enrichment of all proxies. Detrital zircon U–Pb age spectra show multi-peak characteristics (200–300 Ma, 400–500 Ma, etc.), consistent with upper Yellow River sediments. From the Late Pliocene to the Quaternary, the 200–300 Ma component increased while Precambrian components decreased. Provenance evolution indicates the Yellow River has been the primary sediment carrier, with increasing young components linked to the far-field effects of the Kunlun-Huanghe Movement, revealing tectonic uplift-driven headward erosion and provenance changes. We conclude that Quaternary environmental evolution of the Yinchuan Basin was jointly controlled by orbital-scale monsoon climate and episodic tectonic uplift of the northeastern Tibetan Plateau margin, with Yellow River integration further reshaping the basin’s drainage pattern.