Seismic analysis of early-mid Miocene carbonate platform in the southern Qiongdongnan Basin, South China Sea
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Seismic analysis of early-mid Miocene carbonate platform in the southern Qiongdongnan Basin, South China Sea WU Xiaochuan1, PU Renhai1*, CHEN Ying2, QU Hongjun1, SHEN Huailei2 1 State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an 710069, China 2 CNNOOC Research Institute, Beijing 100028, China
Received 30 October 2016; accepted 31 May 2017 ©The Chinese Society of Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract
The southern uplift of the Qiongdongnan Basin is a deepwater area in which no wells have beens drilled. The Miocene-Quaternary strata in the Xisha Islands, which are located 40–100 km to the south, are composed of carbonate reef formations. Paleotectonic and paleogeographic analyses of the basin suggest that the southern uplift experienced favorable geological conditions for the development of carbonate reefs during the Miocene. The high-impedance carbonates have high amplitudes and low frequencies on seismic profiles. The reefs are distributed on paleotectonic highs and are thicker than the contemporaneous formations. A forward model of the variation in carbonate thickness based on lithological and velocity information from wells in nearby regions can simulate the seismic response of carbonates with different thicknesses. We identified several important controlling points for determining the thickness of carbonates from seismic profiles, including the pinchout point, the λ/4 thickness point, and the λ/2 thickness point. We depict a carbonate thickness map in the deepwater area of the southern Qiongdongnan Basin based on this model. The carbonate thickness map, the paleotectonic and paleogeographic background, and the seismic response characteristics of reefs suggest that the carbonates that developed on the southern uplift of the Qiongdongnan Basin during the Miocene were mainly an isolated carbonate platform peninsula and ramp deposits. It consisted of gentle ramp platform, steep slope platform, platform depression, gravity flow, and reef bank facies. Key words: forward model, carbonate rock, thickness, facies distribution, Qiongdongnan Basin Citation: Wu Xiaochuan, Pu Renhai, Chen Ying, Qu Hongjun, Shen Huailei. 2018. Seismic analysis of early-mid Miocene carbonate platform in the southern Qiongdongnan Basin, South China Sea. Acta Oceanologica Sinica, 37(2): 54–65, doi: 10.1007/s13131-017-1128-6
1 Introduction Carbonate rocks are both source and reservoir rocks and important in oil and gas exploration. Analysis of seismic data is the major method of studying deepwater areas with no wells. However, identifying carbonate platforms solely based on seismic data is risky. Carbonate platforms, folds, tilted fault blocks, volcanoes, and basement uplifts may all show similar seismic responses (Burgess et al., 2013). Especially it is more difficult if we attempt to identify an isolated carbonate platform by means of seismic interpretation. The deepwater area of the southern uplift of the Qiongdongnan Basin has favorable growth cond
