Seismic Responses and Sedimentary Characteristics of the Miocene Wan'an Carbonate Platform in the Southern South China Sea
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摘要: 利用反射地震并结合部分钻井资料, 通过对万安盆地大量地震资料的详细解释, 对研究区内碳酸盐台地进行地震识别, 进而探讨台地的沉积特征与时空分布.万安盆地碳酸盐台地最初发育于早中新世, 并于中中新世时达顶盛时期, 呈南北向展布, 主要分布在盆地中部走滑断块构造高部位及盆地南部边缘.东西两带台地具有不同的构造沉积背景, 西带为被断层复杂化的东倾斜坡, 离物源较近, 为碳酸盐岩与碎屑岩互层沉积; 东带濒临南海海盆, 离物源较远, 碳酸盐岩厚度大、岩性较纯.层序地层分析表明, 万安盆地碳酸盐台地主要发育于海侵体系域和高水位体系域.单个台地沉积相在平面上呈圈层结构展布, 相带窄但较规则, 可能包括: 台内相、台缘相、前缘斜坡相(缓坡与陡坡) 和盆底相, 但只在台地东侧发育盆底相, 这与盆地东侧靠近南海海盆的地质环境有关.Abstract: Based on a large quantity of seismic data interpretation and some drilling data in Wan'an basin, the Miocene Wan'an carbonate platforms are identified from seismic reflection profiles and their sedimentary characteristics as well as spatial and temporal distributions are documented in detail.The Wan'an carbonate platforms developed initially during the Early Miocene and reached its prosperous period during the Middle Miocene, showing north-south orientation, and mainly occurring on the hanging wall of the strike-slip fault block in the centre of the basin and the southern basin margin.The Miocene Wan'an carbonate platform can be divided into the east band and the west band according to two different sedimentary tectonic forming backgrounds, where the west side is the slope dipping towards the east fractured by faults and approaches land-source areas resulting in alternating clastic and carbonate rocks, while the east side is close to the South China Sea basin and far from terrigenous areas showing thick and pure carbonate rocks.The sequence stratigraphic analyses show that the Wan'an carbonate platform exists mainly in transgressive and highstand system tracts.The sedimentary facies of single carbonate platform show ring construction in the plane view, and they are relatively narrow but regular, which may be divided into inner platform facies, fringing platform facies, foreslope facies (ramp and steep slope) and basin floor facies.However, the basin floor facies are found only in the eastern side of carbonate platform which may be related to the geological settings near the South China Sea.
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Key words:
- marine geology /
- carbonate platform /
- sedimentation /
- Wan'an basin /
- South China Sea
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图 1 万安盆地构造区划与中新世万安盆地碳酸盐台地分布(左上图方框表示万安盆地位置)
1.盆地轮廓; 2.二级构造单元界线; 3.水深线(m); 4.断裂; 5.钻井; 6.碳酸盐台地分布区; 7.地震测线; 8.文中地震剖面位置; Ⅰ.西北断阶带; Ⅱ.北部坳陷; Ⅲ.北部隆起; Ⅳ.中部坳陷; Ⅴ.中部隆起; Ⅵ.南部坳陷; Ⅶ.东部隆起; Ⅷ.东部坳陷; Ⅸ.西南斜坡; Ⅹ.西部坳陷
Fig. 1. Geotectonic map of the Wan'an basin illustrating the distribution of the Miocene Wan'an carbonate platform
图 2 万安盆地地层层序划分(据杨木壮等, 2003修改; 其中, 全球海平面升降曲线据Haq et al., 1987)
Fig. 2. Chronostratigraphic chart illustrating the stratigraphic divisions in Wan'an basin
图 3 穿过东西侧2个碳酸盐台地的地震解释剖面(测线位置见图 1中AA')
Fig. 3. Interpreted seismic profile transecting both the western carbonate platform and the eastern one
图 4 盆地西(a)、东(b) 两侧碳酸盐台地地震响应特征(测线位置见图 1中BB'、CC')
Fig. 4. Seismic response characteristics in the western (a) and eastern (b) carbonate platforms
图 5 上中新统万安盆地碳酸盐台地层序地层分析(测线位置见图 1中DD')
a.原始地震剖面; b.地震解释剖面; c.岩性推测; 1.低水位体系域; 2.海侵体系域; 3.高水位体系域; 4.碳酸盐岩碎屑(异地低位楔); 5.含泥晶碳酸盐岩(原地低位楔); 6.泥晶灰岩与灰岩互层(海侵体系域); 7.致密泥晶灰岩(高水位体系域, 滞后型); 8.泥晶灰岩与粒状灰岩(高水位体系域, 平衡型); 9.生物礁与礁灰岩; 10.碳酸盐岩斜坡裙(高水位体系域)
Fig. 5. Sequence stratigraphic analysis in the Upper Miocene Wan'an carbonate platform
图 6 地震剖面上万安盆地碳酸盐台地的沉积相划分(测线位置见图 1中EE')
Fig. 6. Sedimentary facies of the Wan'an carbonate platform in the seismic section
图 7 万安盆地碳酸盐台地沉积相的平面分布(位置见图 1)
a.早中新世; b.中中新世; c.晚中新世
Fig. 7. Sedimentary facies layout of the Wan'an carbonate platform in the plane view
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