Xihu Basin is one of the Cenozoic sedimentary basins within the continental shelf of the East China Sea, within which eight oil and gas fields and four hydrocarbon-bearing structures have been found. Our systematic analysis of potential petroleum systems in the basin has identified the Eocene Pinghu Formation as the most important source rock in the basin. The Eocene Pinghu Formation consists of mudstone and coal deposited in an embayment and tidal-flat environment and is characterized as containing type III kerogen. The Pinghu Formation is mature and, at the present time, is within the oil and wet-gas windows with determined vitrinite reflectance values in the range of 0.55–2.2% measured vitrinite reflectance (Rom). Modeling results suggest that the main stage of hydrocarbon expulsion occurred during the Miocene. The main reservoir consists of fine-grained sandstones of the Huagang and Pinghu formations deposited within shallow lacustrine and estuarine environments. The measured porosity from core samples of reservoir rock ranges from 10 to 35%, whereas permeability values range from 1 to 4000 md; both porosity and permeability decrease with depth. The mudstones of the upper Huagang and Longjing formations also occur as regional seals, which developed overpressure zones as determined by two-way sonic transit times. The overburden includes all the Oligocene, Miocene, Pliocene, and Quaternary strata. The hydrocarbon traps in the basin are mainly structural traps, including faulted blocks, faulted structural noses, and anticlines. Most traps were developed at the ends of the Eocene or Oligocene. Hydrocarbons produced from the Xihu Basin are predominantly natural gases with minor amounts of crude oil. The crude oil in the basin is characterized by a low density, low sulfur, low wax, low vanadium/nickel ratio, a low resin and asphaltene content, and a high proportion of saturated hydrocarbons. The natural gas in the basin is composed predominantly of methane, with an average C1/∑C1–5 ratio of 0.89 and a C1/∑C2–5 ratio of 8.6. Two petroleum systems have been identified in the basin: the known Pinghu-Huagang and the hypothetical Huagang-Huagang systems. The Pinghu-Huagang is the major petroleum system and most important for oil and natural gas exploration in the basin.

Paleogene syn‐rift successions in the South China Sea are poorly understood and systematic provenance analysis, which could provide clues to their history, is lacking. Here we report 409 new concordant U‐Pb ages from detrital zircons separated from the Paleogene Wenchang, Enping, and Zhuhai formations in the Zhu 1 depression, Pearl River Mouth Basin. The new data, combined with the published age data from the region, document changes in the provenance of syn‐rift successions. Detrital zircons from the Eocene Wenchang Formation are unimodal, with Jurassic‐Cretaceous (180–80 Ma) ages making up >80% of grains. The ages are consistent with the geochronology of intrabasinal highs, dominated by igneous rocks emplaced during the Yanshanian orogeny, and suggest local provenance. By contrast, detrital zircons from the upper Eocene to lower Oligocene Enping Formation form three well‐recognized age‐clusters, with peaks at 150, 254, and 438 Ma that match documented tectonomagmatism in South China Block (SCB). Combined with increasing numbers of Precambrian zircons, the data suggest increasing influence of regional provenance of the SCB. Similar age peaks are also recognized from the limited number of zircons analyzed from the upper Oligocene Zhuhai Formation and comparability with modern shelf and river sediment indicates the unit was mainly sourced from the SCB and likely transported by a paleo‐Pearl River. We infer that the change in provenance, from local uplifts within the Zhu 1 to the SCB, is related to distinct phases of PRMB rift development; however, later changes are best explained by SCB drainage evolution.

Researchers have long suspected a source‐to‐sink link between the Yangtze Block (and/or North China Block) and Eocene‐Miocene passive margin strata in Taiwan, and various models have been proposed to explain similarities in provenance and the presence of Archean grains. The East China Sea Shelf Basin, whose evolution has been neglected in most models, resides between potential mainland China source regions and the sediment sink in Taiwan, and occupies the corridor through which sediment would have been transported. Here we present 378 new concordant detrital zircon U–Pb ages from the Oligocene Huagang formation in the Xihu Sag, eastern East China Sea Shelf Basin. We also present a compilation of published detrital zircon data from major rivers across mainland China to evaluate potential sediment source regions. Detrital zircons in the Huagang formation range in age from 33 ± 0.4 to 2842 ± 43 Ma, with major clusters at 100–300 and 1,600–2,200 Ma and small early‐middle Paleozoic, Neoproterozoic, and Paleoproterozoic to Archean peaks. Visual and statistical comparison of age distributions suggest close relationships between the Min River and Eocene–Oligocene samples from western Taiwan and between the Oligocene Huagang formation and Miocene strata in western Taiwan. Combined with the tectonic and depositional evolution of the region, these observations suggest that Eocene–Oligocene sediments in Taiwan were mainly sourced from the Min River or similar drainage in the Cathaysia Block. However, the similarities between the Huagang formation and Miocene strata are best explained by reworking of the Oligocene sediment in the Xihu Sag and transportation to western Taiwain during Miocene tectonic inversion of the East China Sea Shelf Basin.