Source-to-Sink Comparative Study between Gas Reservoirs of the Ledong Submarine Channel and the Dongfang Submarine Fan in the Yinggehai Basin, South China Sea

Abstract

The Ledong submarine channel and the Dongfang submarine fan, two remarkable sedimentary systems developed during the late Miocene, are considered promising hydrocarbon reservoirs in the Yinggehai Basin of the South China Sea. A comparative study was conducted to reveal the differences between the source-to-sink characteristics of the two gas-bearing and gravity-driven depositional systems to determine their provenances, formation mechanisms and migration paths as well as their key controlling factors. The heavy mineral assemblages and detrital zircon U-Pb dating results suggest that the Ledong channel was fed by the Hainan provenance from the eastern margin, whereas the Dongfang fan was supplied by northwestern terrigenous sources. The relative sea level transgression and sufficient sediment supply triggered the delivery of deltaic loads toward the continental shelves. Seismic data show that fracture activity had a great impact on the tectono-morphologic features of the margins. During downward flow, the gravity flow along the Yingdong Slope encountered steeply falling faulted slope break belts and formed the Ledong incised channel, and the gravity flow of the Yingxi Slope moved through the gently dipping flexural break slope zone and formed the Dongfang dispersed lobe deposits. Since ca. 30 Ma, the sedimentary center has been migrating from the north to the southeast, which produced a clear control of the southeastward distribution pattern of these two sedimentary systems. Observations of cores and thin sections indicate that the rock structures and their compositions are more mature in the Dongfang channel than in the Ledong fan. This study documents significant differences and similarities by comparing the source-to-sink processes of the two gravity-driven systems that developed in the Yinggehai Basin and provides analogies for understanding similar submarine sedimentary systems that developed under similar geological contexts worldwide.