The Evolution And Characteristics Of Miocene Carbonate Platforms And Reefs In The Xisha Area, Northwestern Continental Margin Of The South China Sea

The huge thickness of Cenozoic carbonate platforms is widely developed in the conjugate continental margins of South China Sea. During Miocene, large quantity of reefs and carbonate platforms developed in the northwestern margin of South China Sea, which can be a potential reservoir in the future. As the exploration in this area is inchoate and lack of enough well data, study about development of reefs and carbonate platforms in this area was weak. Therefore, the study about the evolution process and main controlling factors about the reefs and carbonate platforms in Xisha area based on seismic analysis and shallow well drilled in Xisha Islands is necessary, and these research have academic and practical importance.Combined with the pre-study, and the latest drilling and seismic data in this area, the paper focused on the reefs and carbonate platforms in Xisha area, summarized the seismic characteristics of reefs and carbonate platforms in study area, and proposed the development model of reefs and carbonate platforms. Some innovated results have achieved: 1) Identify the reefs based on analysis on seismic data in the study area, seismic characteristics show mounded reflections, apparent amplitude anomalies, intermittent internal reflections; five types of reefs were identified : patch reef, platform edge reef, pinnacle reef, atoll reef and lagoon reef; 2) The evolution of reefs experienced 5 stages: Early Miocene, early Middle Miocene, late Middle Miocene, Late Miocene and Pliocene to present; 3)The seismic characteristics of Guangle carbonate platform was difference between the upper and lower half: a wavy and discontinuous reflection pattern together with the often relatively high reflection amplitudes characterized much of the Lower to lower Middle Miocene succession and distinguished the lower half from the younger part; 4) Peculiar depressions formed up to a few hundred meters deep scars in the upper surface of Guangle carbonate platform, the features overly poorly to chaotically reflected columns of platform carbonates, the upper part of these columns frequently contained very strong reflections, concave upwards reflectors frequently signified the upper part of these columns whereas up-warping of deeper platform reflectors occured along the flanks of the deeper parts of the columns. 5) Studied the spatio-temporal distribution of Guangle carbonate platform then established the development model of carbonate platform in this area; the composition and development of Guangle carbonate platform experienced four main stages: start up within early carbonate Miocene, build up and build out during early, middle Miocene, back stepping to decrease its distribution scope in near top of middle Miocene, the platform carbonate stage transfers to downgrade stage and to drowning in the top of middle Miocene and covered then by younger sediment deposited from late Miocene to present.