Contrasting hydrocarbon reservoirs in the North China Craton in relation to inhomogeneous craton destruction

The North China Craton (NCC) provides a world-class example for how the destruction of a cratonic root can significantly influence metal and energy resources. The Bohai Bay Basin and Ordos Basin are two super basins that developed in the eastern and western NCC, respectively. Both basins witnessed the decratonization of NCC. However, their dominant energy-producing layers are vastly different, with vast Paleozoic natural gas resources in the Ordos Basin but mostly Cenozoic oil resources in the Bohai Bay Basin. The distinct hydrocarbon evolution periods of the two basins since the late Paleozoic coincides with different stages of the NCC destruction. However, the direct association between the NCC destruction and hydrocarbon evolution has not been has not been explicitly revealed or studied in detail.

In this comprehensive review, a four-stage hydrocarbons accumulation model related to NCC destruction is presented: 1) Homogeneous late Paleozoic (ca. 299–252 Ma) source and reservoir rocks formation across the entire craton due to the activation of cratonic margins; 2) divergent evolution from the early Mesozoic (ca. 252–165 Ma) caused by the initiation of westward flat subduction of the Paleo-Pacific slab, where the west NCC formed thick sedimentary strata (marked by the Yanchang Formation in the late Triassic) while east NCC experienced a depositional hiatus; 3) NCC destruction peak in the mid-late Mesozoic (ca. 165–66 Ma) that contributed to the voluminous natural gas generation in the west, resulting from the thermal perturbation of delamination or slab rollback; 4) continuous Cenozoic extension and elevated geothermal field (ca. <66 Ma) related to mantle upwelling (ca. 35–20 Ma) caused by the present-day Pacific slab subduction, resulting in thick lacustrine deposition of Cenozoic and maturation of Upper Paleozoic source rocks. We thus conclude that both differences and similarities between the two super basins of North China can be explained by the shared Paleozoic depositional conditions and the inhomogeneous Mesozoic destruction state across the craton. This entire process was initiated by the westward subduction of the paleo-Pacific plate that resulted in the change of tectonic regime of eastern China. The intense decratonization in the eastern NCC resulted in the partial destruction of the Paleozoic reservoirs, while continuous Cenozoic extension facilitated the formation of significant oil resources in the Bohai Bay Basin. This study highlights the importance of investigating the more homogeneous Paleozoic strata for undiscovered hydrocarbon resources.