The Cenozoic sedimentary environment and sedimentary filling evolution of Wan'an Basin in the western South China Sea

Abstract

As one of the basins with extremely abundant oil and gas resources in South China Sea, the Wan'an Basin has attracted great attention from domestic and international geologists and hydrocarbon explorers. Currently, the sequence stratigraphic framework, distribution of sedimentary systems and sedimentary filling evolution of the Wan'an Basin are still not clear, consequently, it bring some difficulties for hydrocarbon exploration. Based on the palaeobios, well drilling, well logging, and seismic and other data, the sequence stratigraphic framework of the Wan'an Basin is established, and the sequence interfaces of T100, T60, T50, T40 and T30 in this study are identified. On this basis, the sedimentary environment and sedimentary filling evolution of the Wan'an Basin are systematically analyzed. The results show that the basin had experienced three tectonic evolution periods since Cenozoic, i.e., the Oligocene–Early Miocene extensional fault-depression period, Middle Miocene strike-slip reformation period and Late Miocene–Quaternary regional depression period. Thereinto, the provenance in the extensional fault-depression period (Oligocene–Early Miocene) was mainly from the western uplift of the basin, where the delta–shore-shallow lacustrine–bathylimnetic sedimentary system during Early Oligocene and delta–littoral-neritic sedimentary system during Late Oligocene–Early Miocene were developed respectively. The provenance during the strike-slip reformation period (Middle Miocene) was still mainly from the western uplift of the basin, where the delta–littoral-neritic–carbonate platform sedimentary system was developed, and the carbonate platform began to develop abundantly. The provenance during the regional depression period (Late Miocene–Quaternary) is mainly supplied by input of the western distal large rivers, the delta–littoral-shallow sea–carbonate platform–bathyal sea sedimentary system was developed in the Late Miocene, and the shelf-margin delta–continental slope–bathyal sea sedimentary system was developed during Pliocene-Quaternary. Therefore, the Wan'an Basin has a favorable hydrocarbon resource potential.