Provenance constraints for the evolution of a multibranch submarine channel system across the Ledong gas field, eastern margin of the Yinggehai Basin

Abstract

Provenance identification and evolving process restoration for submarine sedimentary systems are crucial for understanding the deposition process of gravity flows and for future evaluations of oil and gas reservoirs. This paper targets a newly discovered late Miocene multibranch submarine channel developed in the Ledong gas field, eastern margin of the Yinggehai Basin, South China Sea. The natural gas sweet spot, Ledong block, located in the intersection area of the channel's three branches, was systematically studied via zircon U–Pb dating, heavy minerals, seismic and well logging approaches, and structure analysis to obtain information about the characteristics of provenance and the process of sedimentation. Detrital zircon U–Pb age distribution and heavy mineral assemblage results indicate that the channel shares similar geochronological signatures of sediment from the rivers in western Hainan Island. The seismic interpretation suggests that the East Branch bifurcates at the intersection area, meeting the North Branch in the northwest and extending southeast to form the South Branch. Active fault movement during the early Miocene provides negative topography for the formation of the gravity flow channel, while the later sea level fall facilitates the transport and deposition of the river sediments. This study finally reconstructs a time series-based sedimentary model to better illustrate the channel evolution process. The development of channel reservoirs in the southeast Yinggehai Basin could be mainly constrained by the fault's activation as well as the Hainan sediment supply. The findings reveal the major provenance constraints for the evolution of a multibranch submarine channel system across the Ledong gas field and are of great significance for future natural gas resource exploration.