南海中建南盆地地质构造特征与油气远景
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摘要
本文在综合解释中建南盆地重、磁、地震资料的基础上,阐明盆地的地质构造特征,划分对比地震层序,应用地震相解释等手段分析新生代沉积特征,利用实际资料讨论南海西缘断裂以及盆地的断裂系统与基底属性,初步探讨盆地的成因及构造演化,进而阐述其油气远景。根据界面的不整合标志,划分对比了T_1、T_2、T_6、T_g四个反射界面,相应地分为T_6-T_g(早第三纪)、T_2-T_6(晚渐新世末-中中新世)和T_0(海底)-T_2(晚中新世-第四纪)三套沉积层序。新生代沉积层具有从老到新由河湖相发展到海陆过渡相并逐渐海侵为广海相的沉积特征。盆地位于南海西部的走滑断裂带以东、在南海北部陆缘拉张和西缘剪切活动的构造背景下形成。主要发育北东、北西、南北向等几组断裂系,不同方向的断裂互相截切、错断。南北向断裂系是南海西缘断裂的一部分,在地形、地貌和重磁异常特征上都有明显标志,地震剖面显示其具有走滑断裂的特征。盆内划分出一隆两坳和一个断阶带等次级构造单元。油气地质条件的分析展示了盆地潜在的含油气远景。
The Zhong Jian Nan (Z.J.N.) Basin was found by Guangzhou Marine Geological Survey, MGMR, in 1993. Based on the 2 000 km geophysical survey lines and other geological data, the geologic and tectonic features of the basin are identified and its hydrocarbon poten- tial is discussed in this paper. TheZ. J. N. Basin of ca.40000 km~2 is situated in 109°-112°E, 11°-14°N, to the south of Zhong Jian Island, and extends in NE. The basin formed during end Mesozoic and early Cenozoic, when the extension of northern continental margin of South China Sea was taking place, and was influenced later by the western margin strike-slip fracture there. Seismic pro- files show that there are a set of Cenozoic deposits of 9 000 m thick. According to the uncon- formity marks such as onlap, downlap, truncation, etc., four reflective surfaces named T_1, T_2, T_6 and T_g are distinguished, in which T_2 and T_6 are angular unconformity, T_1 pseudocon- formity and T_g the reflection of the acoustic basement. The geological ages of these reflective surfaces are defined by contrasting the data of adjacent regions. Correspondingly, three depo- sitional sequences including T_6-T_g (Paleogence), T_2-T_6 (late Oligocene-mid Miocene), T_0 (submarine reflection) -T_2 (late Miocene-Quatermary) are separated and using those uncon- fimity surfaces as the sequence boundaries. By using the seismic-stratigraphy to the environ- ment of the sequences, the authors suggest that the Paleogene sediments are fluvio-lacustrine and swamp fades. Because of the gradually transgression, the environment of the late Oligocene-mid Miocene sequence changed from paralic fades into littoral and neritic fades. Successively, a set of large thickness of marine deposits of late Miocene-Quaternary overlay unconformably the older deposits. There are mainly several fracture systems trending NE, NW or S - N. The S - N trend fracture system in this region is a segment of the western Marginal Fracture Zone of the South China Sea and is distinctive in topography contour, morphologic landscape, gravity and mag- netic anomalies. The NW trend fracture system is also evident on maps of gravity and magnetic anomalies. These two fracture systems may be so inferred as deep fracture zones. The NE trend fracture system mainly consists of normal faults and basically controls the subsidence and depositional centres resulting in the formation of grabens and semi-grabens. The fact that it is not manifested on maps of gravity and magnetic anomalies suggests that the NE trend fracture only controlled the development of the depositional cover of this basin. The NE trend faults are obviously offeetted or obstructed by the NW and S N trend fractures causing the partial ex- tending stress and forming depressions at the intersections. The four sub-structure units of one uplift, two depressions and one step-fault zone in the sedimentary cover are determined on the basis of the depositional thickness and major fractures. This basin is of good geological conditions of resources, reservoir, structure trap and cover and is prospecting in hydrocarbon potential.
The Zhong Jian Nan (Z.J.N.) Basin was found by Guangzhou Marine Geological Survey, MGMR, in 1993. Based on the 2 000 km geophysical survey lines and other geological data, the geologic and tectonic features of the basin are identified and its hydrocarbon poten- tial is discussed in this paper. TheZ. J. N. Basin of ca.40000 km~2 is situated in 109°-112°E, 11°-14°N, to the south of Zhong Jian Island, and extends in NE. The basin formed during end Mesozoic and early Cenozoic, when the extension of northern continental margin of South China Sea was taking place, and was influenced later by the western margin strike-slip fracture there. Seismic pro- files show that there are a set of Cenozoic deposits of 9 000 m thick. According to the uncon- formity marks such as onlap, downlap, truncation, etc., four reflective surfaces named T_1, T_2, T_6 and T_g are distinguished, in which T_2 and T_6 are angular unconformity, T_1 pseudocon- formity and T_g the reflection of the acoustic basement. The geological ages of these reflective surfaces are defined by contrasting the data of adjacent regions. Correspondingly, three depo- sitional sequences including T_6-T_g (Paleogence), T_2-T_6 (late Oligocene-mid Miocene), T_0 (submarine reflection) -T_2 (late Miocene-Quatermary) are separated and using those uncon- fimity surfaces as the sequence boundaries. By using the seismic-stratigraphy to the environ- ment of the sequences, the authors suggest that the Paleogene sediments are fluvio-lacustrine and swamp fades. Because of the gradually transgression, the environment of the late Oligocene-mid Miocene sequence changed from paralic fades into littoral and neritic fades. Successively, a set of large thickness of marine deposits of late Miocene-Quaternary overlay unconformably the older deposits. There are mainly several fracture systems trending NE, NW or S - N. The S - N trend fracture system in this region is a segment of the western Marginal Fracture Zone of the South China Sea and is distinctive in topography contour, morphologic landscape, gravity and mag- netic anomalies. The NW trend fracture system is also evident on maps of gravity and magnetic anomalies. These two fracture systems may be so inferred as deep fracture zones. The NE trend fracture system mainly consists of normal faults and basically controls the subsidence and depositional centres resulting in the formation of grabens and semi-grabens. The fact that it is not manifested on maps of gravity and magnetic anomalies suggests that the NE trend fracture only controlled the development of the depositional cover of this basin. The NE trend faults are obviously offeetted or obstructed by the NW and S N trend fractures causing the partial ex- tending stress and forming depressions at the intersections. The four sub-structure units of one uplift, two depressions and one step-fault zone in the sedimentary cover are determined on the basis of the depositional thickness and major fractures. This basin is of good geological conditions of resources, reservoir, structure trap and cover and is prospecting in hydrocarbon potential.
引文
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[3] 邱燕,1990;地震地层学解释法在珠江口盆地的应用;地质论评,第36卷,第6期,540-549。
[4] 吴进民,1991;南海群岛地质构造特征与油气远景展望;南海地质研究(3) 24-38;广州:广东科技出版社。
[5] 姚伯初,1991;南海海盆在新生代的构造演化;南海地质研究(3) 9-23;广州:广东科技出版社。
[6] 姚伯初、曾维军等,1994;中美合作调研南海地质专报;武汉:中国地质大学出版社。
[7] 鲍才旺、薛万俊,1990;南海主要海山海槽的地形地貌特征;广州:广东省地图出版社。
[8] 曾维军,1991;广州-巴拉望地学断面综合研究;南海地质研究(3) 39-64;广州:广东科技出版社。
[9] CCOP, 1994; Magnetic anomaly map of east Asia, 1:4000000; Geological Survey of Japan.
[10] Taylor, B.and Hayes, D.E., 1980; Tectonic evolution of South China Sea Basin, In D.E.Hayes (ed.) The teclonic and geologic evolution of southeast Asian seas and islands; Geophys.Monogr.23, 89-104． Geophys. Union, Washington.
[11] Taylor, D.andHays, D.E., 1983; The formation and histry of South China Sea Basin, In D.E. Hays (ed.) The tectonic and geologic evolution of southeast Asian seas and Islands, Part 2, Geophys Monogr.27, 23-56．
[12] Qiu Yan, Li Tanggen, 1993; Tectonic features and evolution of the China seas and adjacent regions, Geol. Soc.Malagsia, Bulletin 33, 33-41．
[13] Tung-Yi Lee, Lawrence A.Lawrer, 1994; Cenozic plate reconstruction of the South China Sea region; Tectonophsics,(235) 1-2, 149-180．
[2] 李唐根,1987;南海北部沿海陆地及岛屿岩石密度、磁性的测定和研究;海洋地质与第四纪地质,第7卷,第3期。
[3] 邱燕,1990;地震地层学解释法在珠江口盆地的应用;地质论评,第36卷,第6期,540-549。
[4] 吴进民,1991;南海群岛地质构造特征与油气远景展望;南海地质研究(3) 24-38;广州:广东科技出版社。
[5] 姚伯初,1991;南海海盆在新生代的构造演化;南海地质研究(3) 9-23;广州:广东科技出版社。
[6] 姚伯初、曾维军等,1994;中美合作调研南海地质专报;武汉:中国地质大学出版社。
[7] 鲍才旺、薛万俊,1990;南海主要海山海槽的地形地貌特征;广州:广东省地图出版社。
[8] 曾维军,1991;广州-巴拉望地学断面综合研究;南海地质研究(3) 39-64;广州:广东科技出版社。
[9] CCOP, 1994; Magnetic anomaly map of east Asia, 1:4000000; Geological Survey of Japan.
[10] Taylor, B.and Hayes, D.E., 1980; Tectonic evolution of South China Sea Basin, In D.E.Hayes (ed.) The teclonic and geologic evolution of southeast Asian seas and islands; Geophys.Monogr.23, 89-104． Geophys. Union, Washington.
[11] Taylor, D.andHays, D.E., 1983; The formation and histry of South China Sea Basin, In D.E. Hays (ed.) The tectonic and geologic evolution of southeast Asian seas and Islands, Part 2, Geophys Monogr.27, 23-56．
[12] Qiu Yan, Li Tanggen, 1993; Tectonic features and evolution of the China seas and adjacent regions, Geol. Soc.Malagsia, Bulletin 33, 33-41．
[13] Tung-Yi Lee, Lawrence A.Lawrer, 1994; Cenozic plate reconstruction of the South China Sea region; Tectonophsics,(235) 1-2, 149-180．
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