This study aims to investigate the sedimentary characteristics and evolution of Mesoproterozoic Changcheng System in Ordos region, providing fundamental data and theoretical support for geological research and hydrocarbon exploration in this area.
Through comprehensive multidisciplinary approaches including geological surveys, drilling data analysis, petrological and sedimentological studies, geochemical analysis, and structural geology investigations, we conducted stratigraphic division, sedimentary facies characterization, depositional environment analysis, and lithofacies paleogeographic reconstruction of Changcheng System in Ordos region and its periphery.
The research reveals vertical lithological differentiation in Changcheng System: The lower section predominantly consists of purplish-red and grayish-white quartz sandstone and feldspathic quartz sandstone, with several-meter-thick quartz pebbly conglomerate at the base. The middle section shows an assemblage of quartz sandstone, siliceous siltstone, and micritic-dolomicrite dolomite. The upper section contains quartz sandstone interbedded with minor dolomite. Thickness distribution is controlled by basement structures: The Huangqikou Formation in the northwestern Helan Mountains reaches maximum thickness of 340 m, gradually thinning northward; the Agulugou Formation along the northern margin attains 1800 m; the Gaoshanhe Group in the southwestern-southern margin reaches 3990 m, sharply decreasing westward to 400 m; while the eastern margin maintains relatively stable thickness.
The northwestern margin developed in a warm-humid oxidizing terrestrial-marine transitional environment. The southern and southeastern margins evolved a tidal flat-lagoon system within an intracontinental rift setting, characterized by climatic transition from arid to temperate-humid conditions under tidal-fluvial interactions. The eastern margin features an oxidizing shallow marine environment dominated by arid climate. Provenance analysis indicates northwestern materials derived from Archean Helanshan Group metamorphic basement, while the eastern margin shows affinity with Precambrian felsic source areas along the southern North China Craton.
The transgression of Changcheng System initiated from high-energy non-barrier beaches (oxidizing environment) along the southwestern margin, transitioning eastward to moderate-energy tidal flats and lagoonal transitional zones (alternating oxic-anoxic conditions). Laterally, the system demonstrates a systematic facies zone migration from continental braided rivers to tidal flats, shallow coastal seas, and shallow marine carbonate platforms. Vertically, the sedimentary sequence records a southwest-to-northeast progression of marine transgression, manifested as an evolutionary shift from high-energy beaches to low-energy tidal flats. This reflects the gradual expansion of the transgression scope and the dynamic transformation of depositional environments from continental to marine settings.