Stepwise formation of seven Al-rich series in the upper Paleozoic, North China Craton: Tectonic uplift and glacial−interglacial controls

The North China Craton experienced pronounced climatic fluctuations and episodic tectonic uplift during the late Paleozoic in response to glacial−interglacial cycles and the progressive closure of the Paleo-Asian Ocean. Seven stratigraphically discrete Al-rich sedimentary series were deposited between the Late Carboniferous Benxi Formation and the Early Permian Shangshihezi Formation; however, their links to tectonic and climatic forcing have remained poorly constrained. This study integrates multiproxy geochemical data and zircon U-Pb geochronology to demonstrate that the seven Al-rich series (Series A−G) are temporally consistent with seven discrete tectonic uplift events along the northern margin of the craton, indicating a close association between pulsed uplift and Al-rich sedimentation. Rare earth element patterns and zircon age spectra further suggest a stepwise sediment supply from basement and contemporaneous magmatic sources during Paleo-Asian Ocean closure. Al enrichment operated through contrasting mechanisms during glacial (Series G, C, and A) and interglacial intervals (Series F, E, D, and B). Glacial conditions likely enhanced hydrological flux and leaching under relatively reducing environments, favoring Al enrichment but commonly producing low-grade deposits owing to limited effective drainage. In contrast, interglacial intervals were characterized by aridification, sea-level rise, and more oxidizing conditions that restricted prolonged leaching and promoted Fe retention, resulting predominantly in low-grade, Al-rich deposits despite continued tectonic sediment supply. These results indicate that tectonic uplift modulated sediment supply, whereas climate-driven hydrological efficiency exerted a primary control on the intensity of chemical weathering and Al enrichment, providing new insights into bauxite formation during the Carboniferous−Permian transition.