During the Miocene, several reefs formed in the Beikang Basin, South China Sea, which may be potential targets for hydrocarbon exploration. This is due to the environment that developed as a result of the collision, splitting, and splicing of the Nansha Block, which was influenced by the Neogene expansion of the area. However, studies on the types, distribution, controlling factors, and evolution stages of these reefs are scarce. In this study, we used high-resolution seismic data and extensive well-drilling records to gain insights into the evolution of reefs in this particular area. Six distinct types of reefs, namely, the point reef, the platform-edge reef, the block reef, the bedded reef, the pinnacle reef, and the atoll reef, were identified based on our data. These reefs underwent four stages of development. During the initial stage, a few small-sized point reefs emerged in the basin and experienced significant growth during the early Middle Miocene. In the flourishing stage, the reefs predominantly thrived around the Central Uplift and Eastern Uplift areas. In the recession stage, the reefs began to deteriorate during the late Middle Miocene period as a result of the rapid increase in relative sea level caused by tectonic subsidence. In the submerged stage, since the Late Miocene, as the relative sea level continued to rise steadily over time, many reefs that had previously flourished surrounding the Central Uplift and Eastern Uplift areas became submerged underwater, with only a handful of atoll reefs surviving near islands located on the Eastern Uplift. This study indicated the presence of a significant number of well-preserved reefs in the Beikang Basin that have experienced minimal subsequent diagenesis and therefore exhibit high potential as reservoirs for oil and gas exploration.

The southwestern margin of the South China Sea (SCS) features a well-developed strike-slip fault system. The Zengmu Basin and its adjacent areas, bounded by the Wan’an, Lupar and Tinjar strike-slip faults, exhibit prominent high heat flow anomalies that substantially exceed the regional average geothermal value of the SCS, with a maximum heat flow of 140 mW/m². Nevertheless, the genetic mechanism governing these extreme geothermal anomalies remains poorly constrained, representing a key scientific issue in regional geothermal research. Based on integrated geological and geophysical datasets, this study conducts numerical thermal modeling to explore the effect of shear frictional heat on regional high heat flow anomalies under variable slip rates and thermophysical conditions. The results show that, under the assumed model conditions, shear frictional heating generates heat flow of 24.5–47.5 mW/m² and accounts for approximately 22–35% of the total surface heat flow, indicating that it is a significant heat source in this region. The high heat flow anomalies on the southwestern margin of the SCS originate from the superposition of three dominant heat sources: mantle heat input driven by mantle upwelling along deep-seated faults, persistent shear frictional heat generated by continuous strike-slip activity, and crustal radioactive heat production from abundant heat-producing elements. The findings provide a robust theoretical basis for understanding the thermal evolution and maturity assessment of source rocks in sedimentary basins of the SCS.

A notable feature of volcanic activity in the Halmahera arc since the Middle Miocene is that eruptions have occurred episodically from south to north, rather than simultaneously. However, the dynamic cause of the volcanic age disparity between the northern and southern regions remains unresolved. To investigate this, thermal simulation methods were employed to calculate the temperature structures of the subducted slab and mantle wedge under varying movement rates of subduction and overriding plates. Simulation results indicate that arc magmatism is favored at lower subduction rates or higher overriding plate movement rates. During the Middle Miocene, the northward drift of the Australian plate propelled the Obi microplate southward via left-lateral strike-slip faults, accelerating its movement rate. In contrast, the movement rate of the Halmahera microplate in the north remained lower, unaffected by the Australian plate. The accelerated movement of the Obi microplate resulted in the rapid generation of a higher temperature zone, facilitating arc volcanism on Obi Island in the late Middle Miocene. Meanwhile, the lower movement rate of the Halmahera microplate delayed the formation of a favorable high-temperature zone for arc volcanism, leading to the emergence of volcanism on Halmahera Island in the late Pliocene.