Effects of Distinct Tectonic Evolutions on Hydrocarbon Accumulation in Northern and Southern Continental Marginal Basins of the South China Sea

Abstract

Three distinct continental marginal basin types developed in the South China Sea, i.e. divergence, transform‐extensional and flexural‐extensional complex types, due to different boundary conditions. Differences of tectonic evolution in these basins resulted in great variations in sedimentary fill and associated hydrocarbon accumulating conditions. Source rocks of lacustrine and marine mudstones mainly developed in northern diverging continental marginal basins in the northern South China Sea. Although there developed good lacustrine sources, limited hydrocarbon accumulation occurred in the adjacent areas around these separated depressions with a relative small scope distribution. In the southern flexural‐extensional complex continental marginal basins of the South China Sea, the Zengmu basin underwent the peripheral foreland tectonic stage earlier than other basins such as the Liyue, Beikang and Nanweixi basins. An available hydrocarbon accumulating condition occurred in those basins, where there are not only large areas and thicknesses of depressions with the sources of coal‐bearing and marine mudstones, but also formation of a broad carbonate and reef reservoirs resulted from slow subsidence during the terminating period of the South China Sea spreading (about 15.5 Ma). The transform‐extensional basins in western continental margins of the South China Sea are characterized by natural gas accumulation due to very thick sediments and high heat flow values. Considering all kinds of geological conditions mentioned above, we suggest that the hydrocarbon‐bearing prospects in southern continental marginal basins are superior to the northern continental marginal basins.

Oligocene–Miocene carbonates in the Reed Bank area, South China Sea, and their tectono-sedimentary evolution

“…The dominant role on the development of the carbonate platform and reef deposits is played by water depth, which is a response of the interplay of relative sea level changes and tectonic subsidence (Wilson 1999;Zampetti et al 2004;Sattler et al 2009;Wu et al 2008;Xie et al 2011). A 100 m high euphotic zone could have a large growth potential of reefs and carbonate platforms, while shallow water carbonates would be drowned when the rate of increase of water depth is greater than the rate of carbonate accumulation (Schlager and Camber 1986).…”

“…It also forms a regional unconformity truncating the sequence beneath (Ding et al 2013;Franke et al 2013). Most authors concluded that the carbonate platforms and patch reefs generally developed during the Early Miocene and their formation migrated from E to W and from S to N (Wu et al 2008;Ma et al 2011;Xie et al 2011;Franke et al 2013).…”

Dynamics of the Continental Margins in South China Sea: Scientific Experiments and Research Progresses

“…The western marginal basins are mainly with plays in syn-spreading and the early post-spreading stages, and the southern marginal basins are mainly with marine facies plays in the later post-spreading stage. Considering all kinds of geological conditions mentioned above, we believe that the hydrocarbon-bearing perspectives in southern continental marginal basins are superior to these northern continental marginal basins [17] .…”

“…The marginal basins in the northern margin were mainly affected by the sea floor spreading of the Eastern Sub-basin and Northwest Sub-basin, while the southern margin was generally related with the opening of the Southwest Sub-basin. The transition time between different stages are correspondent with the beginning and end of the sea floor spreading in different sub basins [17] .…”

“…Oil is distributed mainly in Beibuwan basin, Reed Bank basin, Pearl River Mouth basin, Wanan basin, Zengmu basin. While the basins with thick post-rifting sediments, such as Yinggehai basin, Qiongdongnan basin and Zengmu basin, are mostly with natural gas reservoirs [17] .…”