The Neoproterozoic Xiuning Formation and the underlying Shangshu Formation, located on the northern side of the Jiangshan- Shaoxing fault, represent significant stratigraphic units in the eastern Jiangnan Orogen, South China. They record valuable information about Neoproterozoic tectonic evolution and provide crucial evidence for regional stratigraphic correlation and tectonic reconstruction. This study presents microscopic characteristics, zircon CL images, and LA- ICP- MS U- Pb geochronological data for sandstone and tuff samples from the Xiuning and Shangshu formations, respectively. The microscopic analysis of the sandstone and the CL images of the zircons show that the detrital particles and zircons are mainly angular and subangular, revealing short- range sediment transport. In contrast, the Shangshu Formation tuff exhibits plagioclase phenocrysts and zircons with zonal and rhythmic structures, consistent with a magmatic origin. The detrital zircon U- Pb ages from the Xiuning Formation are primarily clustered between 843 Ma and 718 Ma, with six ages ranging from the Mesoproterozoic to Paleoproterozoic. The weighted mean U- Pb age of zircons from the Shangshu Formation tuff is 847±6. 7 Ma (n=18，MSWD=1. 8). Integrating these findings with previously published data from the eastern Jiangnan Orogen, we infer that the deposition of the Xiuning Formation began at ~785 and ended at ~725 Ma, while the underlying Shangshu Formation was formed between 845 Ma and 785 Ma. The Shangshu Formation records magmatic activities at approximately 845 Ma, 825 Ma, and 800~785 Ma, reflecting multiple volcanic- depositional cycles in the study area. During the period of 850~785 Ma, the Yangtze and Cathaysian blocks underwent a series of tectonic processes, including subduction, collision, and post- collisional extension, with the rift basin gradually opening after ~785 Ma.