Geological and seismic characteristics of the organic reefs on the Dongsha uplift, Zhujiangkou Basin

The reef limestones in the Zhujiang Formation on the Dongsha uplift may be classified into three types:framestone, bindstone and bafflestone developed in the open platform, platform-margin and foreslope facies, and composed of the intraplatform patch reefs, platform-margin barrier reefs and foreslope pinnacle reefs, respectively. During the early stages of the deposition of the Zhujiang Formation, the littoral sandy deposits were initiated on the Dongsha uplift, followed by the rimmed shallow-water carbonate platforms during the middle stages. During the late stages, the carbonate platforms were gradually drowned and consumed by trangressions, and then the shallow shelf muddy deposits were accentuated. Among the carbonate platforms, the Liuhua platform has a maximum thickness of 563 m, and displays strongly seismic reflection on the topmost part while moderate-weak amplitudes and reflection and poor continuity in the interior of the platforms. The Huizhou platform with a thickness of more than 100 also displays strongly seismic reflection on the topmost part while strong-moderate amplitudes, high-moderate continuity and moderate-low frequency and locally blank reflection in the interior of the platforms. The Lufeng platform only with a thickness of about 30 m exhibits highly continuous strong amplitudes. The seismic reflection configurations generally display the mound, box, low hills-lenticular forms. The onlapping and draping can be observed as well.