<p>The Qiangtang Basin, the largest Mesozoic marine hydrocarbon-bearing basin in China, has long been at the center of debate regarding the formation age of its principal source rocks. In this study, we apply <i>in situ</i> LA-ICP-MS calcite U-Pb geochronology for the first time, integrated with cathodoluminescence imaging and geochemical analyses, to provide precise chronological constraints on their formation. The results indicate that the limestone interbeds within the Xichangliang-Shenglihe oil shale of the Northern Qiangtang Depression yield ages of 164–163 Ma (Callovian, Middle Jurassic), revising the previously inferred Late Jurassic-Early Cretaceous age based on Re-Os data. In contrast, the Amdo 114 Station source rock in the Southern Qiangtang Depression yields ages of 168–165 Ma (late Bathonian to Callovian, Middle Jurassic), consistent with calcareous nannofossil evidence and published U-Pb ages (166–164 Ma) from the Biluo Co oil shale. Collectively, these results together with seismic reflection and paleogeography demonstrate that these three major source rocks were deposited contemporaneously during the late Bathonian-Callovian, indicating a widespread, high-quality Middle Jurassic source rock system developed across the Northern Qiangtang Depression. This study establishes a robust, high-precision geochronological framework that resolves the long-standing controversy over the timing of source-rock formation. We propose that these high-quality source rocks were developed under warm, semi-arid paleoclimatic conditions, where regional evaporitic restriction and elevated salinity likely enhanced organic matter preservation within a stratified water column.</p>