Age dating of Paleocene Meirenfeng Formation and its significance for the hydrocarbon source rocks in the East China Sea basin

Abstract

The Meirenfeng Formation, a critical Paleogene stratigraphic unit within the Yangtze Sag in the East China Sea Basin, has long suffered from uncertain age estimation due to limited paleontological evidence, which has consequently hindered regional stratigraphic correlation. This study employed zircon U–Pb age dating through the LA-ICP-MS method to two tuff samples extracted from the CJ-2 well. The obtained ages are approximately 61.0 ± 1 Ma and 62.25±1 Ma, respectively, which confirms the sedimentary age of the Meirenfeng Formation as Paleocene Danian-Selandian. This age directly correlates it to the Paleocene Yueguifeng Formation in the Lishui-Jiaojiang Sag, a confirmed source of hydrocarbons. In addition, geochemical investigations conducted on the shale samples from the Meirenfeng Formation indicate a medium to good abundance of organic matter and a kerogen type of III. The regional seismic profile further reveals that the Meirenfeng Formation in the Yangtze Sag extends continuously to the Zhedong Depression, boasting a maximum residual thickness of up to 2000m. This suggests a similar Paleocene period of extensive stretching and rifting in the Zhedong Depression. This research offers the first robust age estimation for the Meirenfeng Formation in the Yangtze Sag, providing an essential geological foundation for accurate tectonic history reconstruction, Paleocene stratigraphic subdivision, regional correlation, and hydrocarbon prospectivity assessment within the East China Sea Basin.