Keywords: 
• Youjiang Basin /
• Late Paleozoic Ice Age /
• Sedimentary microfacies /
• Transgressive-regressive sequence /
• Foraminiferal zone

Abstract: [Objectives] The middle to late Early Carboniferous witnessed profound reorganization of Earth’s tectonic paleogeography, climate systems, marine environments, and ecosystems. To refine the initiation timing of the main-phase of the Late Paleozoic Ice Age (LPIA), [Methods] this study integrates high-resolution sedimentary facies and their stacking patterns analyses of the Du’an Formation in the Shuidong Section, Youjiang Basin, South China. A robust transgressive–regressive (T-R) sequence framework was established, enabling quantitative reconstruction of relative sea-level history for the basin during the middle-late Early Carboniferous. [Results] Twelve microfacies were identified across the section, spanning the middle Visean to upper Serpukhovian. These are grouped into four distinct facies associations: restricted platform, open platform, platform-margin shoal, and upper slope. Seven third-order sequences and at least twenty-six fourth-order T-R cycles were resolved within the upper Visean and Serpukhovian. [Conclusions] The onset of high-frequency, high-amplitude relative sea-level fluctuations in the Youjiang Basin coincides with the Aleksinian-Mikhailovian boundary. This is independently corroborated by other low-latitude far-field proxies, thereby providing robust stratigraphic evidence that the main-phase of the LPIA initiated during this interval.