Acta Petrolei Sinica ›› 2019, Vol. 40 ›› Issue (s1): 188-196.DOI: 10.7623/syxb2019S1016

• Petroleum Exploration • Previous Articles     Next Articles

Radiolarian assemblage,geochemical characteristics and tectonic paleo-geographic significance of silicite in Well MZ-1,Chaoshan depression of the northern South China Sea

Lin Heming1, Zhang Qinglin1, Zhang Xiangtao1, Shao Lei2, Zheng Jinyun1   

  1. 1. CNOOC Deepwater Development Limited, Guangdong Shenzhen 518000, China;
    2. State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China
  • Received:2018-07-16 Revised:2018-10-23 Online:2019-07-25 Published:2019-07-15

南海北部潮汕坳陷MZ-1井硅质岩放射虫组合、地球化学特征及构造古地理意义

林鹤鸣1, 张青林1, 张向涛1, 邵磊2, 郑金云1   

  1. 1. 中海石油深海开发有限公司 广东深圳 518000;
    2. 同济大学海洋地质国家重点实验室 上海 200092
  • 通讯作者: 张青林,男,1981年1月生,2002年获中国地质大学(武汉)学士学位,2008年获同济大学博士学位,现为中海石油深海开发有限公司工程师,主要从事石油地质综合研究及勘探工作。Email:zhangql7@cnooc.com.cn
  • 作者简介:林鹤鸣,男,1972年11月生,1994年获南京大学学士学位,1997年获南京大学硕士学位,现为中海石油深海开发有限公司高级工程师,主要从事石油地质研究和勘探管理工作。Email:linhm_sk@cnooc.com.cn
  • 基金资助:

    国家科技重大专项(2016ZX05026-003-006,2016ZX05026-003-002)、中海石油(中国)有限公司科研项目(YXKY-2018-SHENHAI-01)资助。

Abstract:

Multi-layer radiolarian silicite is developed in Well MZ-1 of Chaoshan depression, the northern South China Sea, where the radiolarian fauna containing Loopus primitivus, Pantanellium philippinense, Praeconosphaera sphaeraconus and Spongocapsula sp. cf. S. palmerae is found in the 1 725-1 887 m layer as the Pseudodictyomitra primitive zone of Pacific biotic province at the Late Jurassic Tithonian age. In the 1 725-1 785 m layer of silicite, the content of SiO2 is 68.36% -74.53%, the content of Al2O3 is 12.29% -16.05%, w(Si)/w(Al)=3.86-5.35, w(Al)/w(Al+Fe+Mn)=0.65-0.74, w(Si)/w(Si+Al+Fe)=0.72-0.79, the high ∑REE is (127.61-182.08)×10-6, and the content of Ba is (722.42-1 812.12)×10-6 which is negatively correlated with the content of SiO2. These characteristic parameters all indicate that bio-action is dominant; a great number of terrigenous materials were mixed with some volcanic materials, thus forming silicite. w(Al2O3)/w(Al2O3+Fe2O3)=0.71-0.81, w(MnO)/w(TiO2)=0.09-0.21, (La)N/(Yb)N=0.75-1.35, δCe=1.05-1.09, and (La)N/(Ce)N=0.94-0.99. All these indicate that the silicite from Well MZ-1 is formed in the continental margin environment. MORB-normalized multielement spider diagrams show the silicite loss of P, Ti, Nb and Ta in high field-strength elements in Well MZ-1, reflecting the genetic relationships between the silicite and island arc volcanic rocks. The comprehensive analysis proves that the Late Jurassic Chaoshan depression is a fore-arc basin related to the subduction of the paleo-Pacific plate in the northern South China Sea.

Key words: silicite, radiolarian assemblage, geochemical characteristics, Mesozoic, tectonic paleo-geography, fore-arc basin, northern South China Sea

摘要:

中国南海北部潮汕坳陷MZ-1井发育多层放射虫硅质岩,其中1 725~1 887 m层段发现含Loopus primitivus、Pantanellium philippinense、Praeconosphaera sphaeraconusSpongocapsula sp.cf.S.palmerae等重要分子的放射虫动物群,属于太平洋生物区系的放射虫Pseudodictyomitra primitiva带,对应的时代为晚侏罗世提塘期。1 725~1 785 m层段硅质岩SiO2质量分数为68.36%~74.53%,Al2O3质量分数为12.29%~16.05%,Si/Al质量比为3.86~5.35,Al/(Al+Fe+Mn)质量比为0.65~0.74,Si/(Si+Al+Fe)质量比为0.72~0.79,以及高的∑REE[(127.61~182.08)×10-6],Ba质量分数为(722.42~1 812.12)×10-6且与SiO2质量分数呈负相关,这些特征共同指示其是以生物作用为主,并有大量陆源物质混入,还有火山物质加入形成的硅质岩。Al2O3/(Al2O3+Fe2O3)质量比为0.71~0.81、MnO/TiO2质量比为0.09~0.21、(La)N/(Yb)N比值为0.75~1.35、δCe为1.05~1.09、(La)N/(Ce)N比值为0.94~0.99指示,MZ-1井硅质岩形成于大陆边缘环境。N-MORB标准化多元素蛛网图显示,MZ-1井硅质岩高场强元素P、Ti、Nb、Ta亏损,这表明其与岛弧火山岩有成因联系。综合分析表明,南海北部潮汕坳陷晚侏罗世盆地为与古太平洋板块俯冲相关的弧前盆地。

关键词: 硅质岩, 放射虫组合, 地球化学特征, 中生界, 构造古地理, 弧前盆地, 南海北部

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