珠江口盆地深水区伸展陆缘地壳减薄背景下的沉积体系响应过程及油气勘探意义
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摘要
珠江口盆地白云深水区(包括白云凹陷和荔湾凹陷)位于南海北部陆缘地壳薄化带上,地壳厚度从北侧的29km迅速减薄至17～18km。地壳岩石圈强烈伸展薄化使得陆缘深水区具有特殊的断裂结构样式与沉降特征,对沉积体系产生重要的控制作用,并导致深水区成藏组合特征的差异性。通过调研全球典型伸展陆缘盆地的伸展破裂过程、断裂结构样式对沉积体系的控制作用,开展了对白云深水区凹陷结构、断裂构造样式、构造沉降史与沉积体系的耦合分析,揭示出珠江口盆地深水区特殊的沉积体系响应特征与发育机制。研究结果显示:地壳内脆韧性变形过程产生的大型低角度拆离断裂活动是裂陷期陆缘岩石圈伸展、薄化、破裂的主要机制,裂陷期地壳的均衡抬升、断裂带上盘块体的旋转和大型低角度主控断裂转换带的发育导致始新世文昌组—恩平组沉积期深水区具有宽深断陷结构与大型三角洲—湖相沉积响应体系;裂解期的缓慢沉降和丰富的单边物源供给导致渐新世珠海组沉积期陆架坡折带的发育,并形成海退型进积层序组合,大型海相陆架边缘三角洲和陆坡深水峡谷/深水扇体系分别发育在白云凹陷及其南部凹陷区;裂后热沉降期,台阶式沉降和充足的北侧单边物源体系控制了陆架坡折带由南往北的迁移,并使得陆架坡折带稳定分布在白云北坡,形成海侵加积型层序组合,陆架边缘三角洲和深水扇体系呈现垂向叠置分布特征。在新生代陆缘地壳拆离薄化背景下,裂陷期宽深断陷结构、裂陷后期台阶式沉降和单边物源体系供给等特征使得陆缘深水区发育裂陷期大型三角洲—湖相沉积体系到裂后期大型陆架坡折带的古珠江陆架边缘三角洲和陆坡深水重力流响应体系,最终导致规模烃源岩集中分布、纵向台阶式储-盖组合和两大陆架坡折带控制大型有利油气聚集带的分布格局。
The Baiyun deep water area(including Baiyun depression and Liwan depression)in the Pearl River Mouth Basin is located on the continental margin crust thinning zone in the northern South China Sea.The thickness of the crust is rapidly reduced from 29 km on the north side to 17-18 km.Due to the strong extension and thinning of the crustal lithosphere,the deep water area at the continental margin is characterized with special fracture structure and sedimentation characteristics,which has an important control effect on the sedimentary system and leads to differences in the characteristics of hydrocarbon play in the deep water area.By investigating the extension and rupture process of the global typical extensional continental margin basin and the control of fault structure pattern on sedimentary system,a coupling analysis was conducted between the depression structure,fault structure pattern,tectonic subsidence history and sedimentary system in the Baiyun deep water area,revealing the response characteristics and developmental mechanisms of special sedimentary systems in the deep waters of the Pearl River Mouth Basin.The results show that the large-scale low-angle detachment fault activity generated by the brittle-ductile deformation process in the crust is the main mechanism for extension,thinning and rupture of the crustal margin lithosphere during rifting period.The balanced lifting of the crust during rifting period,the rotation of hanging wall blocks on the fault zone and the development of the large low-angle major fracture transition zone led to the deep-water fault zone of Eocene Wenchang Formation-Enping Formation with wide deep faulted depression structure,and the large delta-lake sedimentary response system during sedimentary period.The slow sedimentation during pyrolysis period and the abundant unilateral source supply resulted in the development of the continental shelf slope-break zone during the sedimentary period of Oligocene Zhuhai Formation,thus forming the regressive prograding sequence combination.The large-scale marine shelf margin delta and the continental slope deepwater canyon/deep water fan system were developed in Baiyun depression and its southern sags separately.During the post-crack thermal subsidence period,stepped settlement and sufficient north unilateral provenance system controlled the migration of the shelf slope breaks from south to north.Thus,the shelf slope breaks stably distributed on the north slope of Baiyun,thus forming a transgressive aggradated sequence combination.The continental shelf margin delta and deep water fan systems are vertically stacked.Under the background of the Cenozoic continental marginal crust detachment and thinning,the wide and deep faulted depression structure in the rifting period,the stepped subsidence in the late stage of rifting and the supply of unilateral provenance system resulted in the development of a large delta-lake sedimentary system in the continental margin deep water areas during rifting period,as well as a deep water gravity flow response system in the continental shelf margin delta and continental slope of large continental slope breaks during the late period of rifting.Eventually,a distribution pattern was developed as the concentrated distribution of large-scale source rocks,a longitudinal stepped reservoir-cap assemblage and two continental slope breaks controlling large-scale favorable oil and gas accumulation.
The Baiyun deep water area(including Baiyun depression and Liwan depression)in the Pearl River Mouth Basin is located on the continental margin crust thinning zone in the northern South China Sea.The thickness of the crust is rapidly reduced from 29 km on the north side to 17-18 km.Due to the strong extension and thinning of the crustal lithosphere,the deep water area at the continental margin is characterized with special fracture structure and sedimentation characteristics,which has an important control effect on the sedimentary system and leads to differences in the characteristics of hydrocarbon play in the deep water area.By investigating the extension and rupture process of the global typical extensional continental margin basin and the control of fault structure pattern on sedimentary system,a coupling analysis was conducted between the depression structure,fault structure pattern,tectonic subsidence history and sedimentary system in the Baiyun deep water area,revealing the response characteristics and developmental mechanisms of special sedimentary systems in the deep waters of the Pearl River Mouth Basin.The results show that the large-scale low-angle detachment fault activity generated by the brittle-ductile deformation process in the crust is the main mechanism for extension,thinning and rupture of the crustal margin lithosphere during rifting period.The balanced lifting of the crust during rifting period,the rotation of hanging wall blocks on the fault zone and the development of the large low-angle major fracture transition zone led to the deep-water fault zone of Eocene Wenchang Formation-Enping Formation with wide deep faulted depression structure,and the large delta-lake sedimentary response system during sedimentary period.The slow sedimentation during pyrolysis period and the abundant unilateral source supply resulted in the development of the continental shelf slope-break zone during the sedimentary period of Oligocene Zhuhai Formation,thus forming the regressive prograding sequence combination.The large-scale marine shelf margin delta and the continental slope deepwater canyon/deep water fan system were developed in Baiyun depression and its southern sags separately.During the post-crack thermal subsidence period,stepped settlement and sufficient north unilateral provenance system controlled the migration of the shelf slope breaks from south to north.Thus,the shelf slope breaks stably distributed on the north slope of Baiyun,thus forming a transgressive aggradated sequence combination.The continental shelf margin delta and deep water fan systems are vertically stacked.Under the background of the Cenozoic continental marginal crust detachment and thinning,the wide and deep faulted depression structure in the rifting period,the stepped subsidence in the late stage of rifting and the supply of unilateral provenance system resulted in the development of a large delta-lake sedimentary system in the continental margin deep water areas during rifting period,as well as a deep water gravity flow response system in the continental shelf margin delta and continental slope of large continental slope breaks during the late period of rifting.Eventually,a distribution pattern was developed as the concentrated distribution of large-scale source rocks,a longitudinal stepped reservoir-cap assemblage and two continental slope breaks controlling large-scale favorable oil and gas accumulation.
引文
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[2]孙珍,刘思青,庞雄,姜建群,毛爽.被动大陆边缘伸展-破裂过程研究进展[J].热带海洋学报,2016,35(1):1-16.SUN Zhen,LIU Siqing,PANG Xiong,et al.Recent research progress on the rifting-breakup process in passive continental margins[J].Journal of Tropical Oceanography,2016,35(1):1-16.
[3]任建业,庞雄,雷超,等.被动陆缘洋陆转换带和岩石圈伸展破裂过程分析及其对南海陆缘深水盆地研究的启示[J].地学前缘,2015,22(1):102-114.REN Jianye,PANG Xiong,LEI Chao,et al.Ocean and continent transition in passive continental margins and analysis of lithospheric extension and breakup process:Implication for research of the deepwater basins in the continental margins of South China Sea[J].Earth Science Frontiers,2015,22(1):102-114.
[4]陈长民,施和生,许仕策,等.珠江口盆地(东部)第三系油气藏形成条件[M].北京:科学出版社,2003:1-121.CHEN Changmin,SHI Hesheng,XU Shice,et al.The conditions of hydrocarbon accumulation of the tertiary petroleum system in the Pearl River mouth basin[M].Beijing:Science Press,2003:1-121.
[5]庞雄,任建业,郑金云,等.陆缘地壳强烈拆离薄化作用下的油气地质特征:以南海北部陆缘深水区白云凹陷为例[J].石油勘探与开发,2018,45(1):27-39.PANG Xiong,REN Jianye,ZHENG Jinyun,et al.Petroleum geology controlled by extensive detachment thinning of continental margin crust:A case study of Baiyun sag in the deep-water area of northern South China Sea[J].Petroleum Exploration and Development,2018,45(1):27-39.
[6]施和生,柳保军,颜承志,等.珠江口盆地白云-荔湾深水区油气成藏条件与勘探潜力[J].中国海上油气,2010,22(6):369-374.SHI Hesheng,LIU Baojun,YAN Chengzhi,et al.Hydrocarbon accumulation conditions and exploration potential in Baiyun-Liwan deepwater area,Pearl River Month basin[J].China Offshore Oil and Gas,2010,22(6):369-374.
[7]张功成,米立军,屈红军,等.全球深水盆地群分布格局与油气特征[J].石油学报,2011,32(3):369-378.ZHANG Gongcheng,MI Lijun,QU Hongjun,et al.A basic distributional framework of global deepwater basins and hydrocarbon characteristics[J].Acta Petrolei Sinica,2011,32(3):369-378.
[8]孙珍,庞雄,钟志洪,等.珠江口盆地白云凹陷新生代构造演化动力学[J].地学前缘,2005,12(4):489-498.SUN Zhen,PANG Xiong,ZHONG Zhihong,et al.Dynamics of tertiary tectonic evolution of the Baiyun Sag in the Pearl River Mouth Basin[J].Earth Science Frontiers,2005,12(4):489-498.
[9]龚再升,李思田,谢泰俊,等.南海北部大陆边缘盆地分析与油气聚集[M].北京:科学出版社,1997:1-510.GONG Zaisheng,LI Sitian,XIE Taijun,et al.Continental margin basin analysis and hydrocarbon accumulation of the northern South China Sea[M].Beijing:Science Press,1997:1-510.
[10]柳保军,庞雄,颜承志,等.珠江口盆地白云深水区渐新世-中新世陆架坡折带演化及油气勘探意义[J].石油学报,2011,32(2):234-242.LIU Baojun,PANG Xiong,YAN Chengzhi,et al.Evolution of the O-ligocene-Miocene shelf slope-break zone in the Baiyun deep-water area of the Pearl River Mouth Basin and its significance in oil-gas exploration[J].Acta Petrolei Sinica,2011,32(2):234-242.
[11]彭大钧,陈长民,庞雄,等.南海珠江口盆地深水扇系统的发现[J].石油学报,2004,25(5):17-23.PENG Dajun,CHEN Changmin,PANG Xiong,et al.Discovery of deep-water fan system in South China Sea[J].Acta Petrolei Sinica,2004,25(5):17-23.
[12]MCKENZIE D.Some remarks on the development of sedimentary basins[J].Earth and Planetary Science Letters,1978,40(1):25-32.
[13]WERNICKE B.Low-angle normal faults in the Basin and Range province:nappe tectonics in an extending orogen[J].Nature,1981,291(5817):645-648.
[14]UNTERNEHR P,PRON-PINVIDIC G,MANATSCHAL G,et al.Hyper-extended crust in the South Atlantic:in search of a model[J].Petroleum Geoscience,2010,16(3):207-215.
[15]李友川,邓运华,张功成,等.南海北部第三系海相烃源岩[J].石油学报,2011,32(2):219-225.LI Youchuan,DENG Yunhua,ZHANG Gongcheng,et al.Tertiary marine source rocks in the northern South China Sea[J].Acta Petrolei Sinica,2011,32(2):219-225.
[16]吴时国,袁圣强.世界深水油气勘探进展与我国南海深水油气前景[J].天然气地球科学,2005,16(6):693-699.WU Shiguo,YUAN Shengqiang.Advance of exploration and petroleum geological features of deep-water hydrocarbon in the world[J].Natural Gas Geoscience,2005,16(6):693-699.
[17]朱俊章,施和生,庞雄,等.珠江口盆地番禺低隆起凝析油地球化学特征及油源分析[J].中国海上油气,2006,18(2):103-106.ZHU Junzhang,SHI Hesheng,PANG Xiong,et al.Geochemical characteristics and oil sources of condensates in Panyu Low Uplift,Pearl River Mouth basin[J].China Offshore Oil and Gas,2006,18(2):103-106.
[18]张云帆,孙珍,庞雄.珠江口盆地白云凹陷下地壳伸展与陆架坡折的关系[J].中国科学:地球科学,2014,44(3):488-496.ZHANG Yunfan,SUN Zhen,PANG Xiong.The relationship between extension of lower crust and displacement of the shelf break[J].Science China Earth Sciences,2014,57(3):550-557,doi:10.1007/s11430-013-4676-4.
[19]MASINI E,MANATSCHAL G,MOHN G.The Alpine Tethys rifted margins:Reconciling old and new ideas to understand the stratigraphic architecture of magma-poor rifted margins[J].Sedimentology,2013,60(1):174-196.
[20]HUISMANS R,BEAUMONT C.Depth-dependent extension,two-stage breakup and cratonic underplating at rifted margins[J].Nature,2011,473(7345):74-78.
[21]ROBERTS A W,WHITE R S,LUNNON Z C,et al.Imaging magmatic rocks on the Faroes margin,2005[C].Geological Society of London.
[22]BOILLOT G,WINTERER E L,MEYER A W.Leg 103[J].Proceeding ODP Initial Reports,1987,103:663.
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