Abstract
We have analyzed two recently acquired multi-channel seismic profiles across the Reed Bank area, South China Sea. A detailed seismic interpretation coupled with drilling data has proved the occurrence of a wide carbonate platform, developed between the Late Oligocene and the Early Miocene (32–20 Ma). The top of these carbonates is an important regional unconformity, corresponding to a strong and continuous seismic reflector. An age of about 20 Ma is inferred for this reflector, acting as a regional unconformity marking the cessation of seafloor spreading with an erosional/non-depositional hiatus, spanning 3 or 4 m.y. The time interval during which the carbonate platforms formed is concurrent with the opening of the South China Sea. The reconstruction of the tectonic subsidence in this area has shown a decrease in rate of subsidence during the drifting stage (32–17 Ma), indicating that the whole Reed Bank area was in a tectonically stable and shallow water environment for more than 10 m.y., favoring the development of shallow water carbonates. With a sharply increased subsidence rate after the end of spreading (17 Ma) and a continuously increased sea level, the carbonate platforms were drowned and died, except some structural highs with reef buildups, where the carbonate sedimentation continued to Middle Miocene. We suggest that delayed tectonic subsidence in Reed Bank area might have been related to a secondary mantle convection under the rift lasting more than about 10 m.y.
Highlights
Shallow water carbonates, including carbonate platform and reefs, are widely distributed in the middle and low latitude passive margins worldwide (Bathurst 1971; Lees and Buller 1972; Wilson 1975; Reading 1978)
Due to geological and geophysical data acquired in the last decades, Cenozoic shallow water carbonates in the South China Sea have been well documented on its (1) detailed seismic features, stratigraphic architecture, and controlling factors in local regions, such as the northern rim of the Dongsha Islands (Tyrell and Christian 1992); the western Pearl River Mouth Basin (Sattler et al 2009); the Qiongdongnan Basin (Wu et al 2008; Ma et al 2011) in the northern continental margin of the South China Sea; the Phu Khanh Basin (Fyhn et al 2009), the offshore of central Vietnam (Fyhn et al 2013) in the western continental margin; the Dangerous Grounds (Ding et al 2013; Franke et al 2013) in the southern continental margin; and (2)
We present two high-resolution multi-channel seismic profiles across the Reed Bank area of South China Sea to document the seismic characteristics of carbonate platform and different types of carbonates, the interplay between tectonics, sea level change and depositional rates resulting in a complex platform geometry and the geologic evolution models
Summary
Shallow water carbonates, including carbonate platform and reefs, are widely distributed in the middle and low latitude passive margins worldwide (Bathurst 1971; Lees and Buller 1972; Wilson 1975; Reading 1978). As a feature in tropical and sub-tropical depositional settings, carbonate deposition could act as an indication of tectonic subsidence, sea level changes, environmental factors and terrigenous sediment input (Schlager and Camber 1986; Schlager 1989; Ma et al 2011; Franke et al 2013; Ding et al 2014) They can be important for hydrocarbon exploration, because some reefs and carbonate platforms are highly porous and host nearly one half of the world’s hydrocarbon reserves, containing some of the largest aquifers on the Earth (Sun and Esteban 1994; Groetsch et al 1998; Wu et al 2008; Sattler et al 2009). Well locations are reported from Taylor and Hayes (1983) and Schlueter et al (1996)
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