New interpretation on the provenance changes of the upper Pinghu-lower Huagang Formation within Xihu Depression, East China Sea Shelf Basin

Both Pinghu and Huagang formations are important hydrocarbon reservoirs of the Xihu Depression in the East China Sea Shelf Basin. Clarifying the source suppliers and restoring source-to-sink transport routes are of great significance to the future petroleum and gas undertakings. Previous researchers were largely confined by either limitation of geological records, highly dependence on a singular method or low-precision dating techniques. Our study integrated heavy mineral assemblages, geochemical analyses and detrital zircon U-Pb dating to reconstruct multiple source-to-sink pathways, and to provide a better understanding on the provenance evolution for the upper Pinghu-lower Huagang depositions of the Xihu Depression. At least three major provenances have been confirmed and systematically investigated for their separate compositional features. The Hupijiao Uplift (or even farther northern area) was dominated by a major Paleoproterozoic population peaked at ca. 1 830 Ma along with minor Mesozoic clusters. The Haijiao Uplift to the west and the Yushan Low Uplift to the southwest, on the other hand, generate opposite U-Pb age spectra with apparently larger peaks of Indosinian and Yanshanian-aged zircons. To be noted, both Indosinian and Paleoproterozoic peaks are almost identical in proportion for the Haijiao Uplift. The overall sedimentary pattern of late Eocene-early Oligocene was featured by both spatial and temporal distinction. The Hupijiao Uplift was likely to cast limited impact during the late Eocene, whereas the broad southern Xihu Depression was transported by a large abundance of materials from the nearby Haijiao and Yushan Low Uplifts. The northern source substantially extended its influence to the farther south during the early Oligocene by delivering plentiful sediments of higher-degree metamorphic parent rocks. Combined with the proximal western and southwestern suppliers, the overall Xihu Depression was under control from both distant and local provenances.