四川盆地北缘震旦纪—早寒武世隆—坳格局及其油气勘探意义

四川盆地北部震旦系-下寒武统是继安岳气田发现和绵阳-长宁裂陷提出之后备受关注的另一重点勘探领域，但对其沉积构造格局的认识存在严重分歧。文中基于露头剖面、地震、钻井和地球化学分析资料并结合前人研究成果，提出四川盆地北缘震旦纪-早寒武世期间存在隆坳并存的格局。四川盆地北缘震旦系-下寒武统厚度、岩相、地震反射和地球化学等指标的详细分析表明：(1)沉积构造格局表现为隆坳相间的特点，即自西向东依次为绵阳-长宁裂陷→汉南-米仓山隆起→万源-通江裂坳陷→达州-开江隆起→城口-开县裂坳陷→东安-巫溪隆起→巴东-恩施裂陷→神农架-黄陵隆起；(2)发育台地、斜坡和盆地三种沉积环境，其中斜坡环境以发育大量风暴、重力流、滑塌角砾沉积及同沉积滑移变形等为主要识别标志；(3)经历了三个“隆坳”旋回，即陡二段末期-灯二段早期、灯二段晚期-灯四段早期、灯四段晚期-筇竹寺组晚期。四川盆地北缘震旦纪-早寒武世隆坳格局的形成受控于震旦纪基底构造薄弱带、南秦岭地幔上隆底侵和原特提斯洋壳板片拖拽三者的联合作用，与罗迪尼亚大陆裂解和冈瓦纳大陆聚合的全球构造背景密切相关。四川盆地北缘震旦纪-早寒武世隆坳并存格局的提出不仅有助于进一步认识该时期扬子克拉通区域沉积构造格局和演化，也为川东北地区下一步油气勘探决策提供了参考依据。川东北地区震旦纪-早寒武世隆坳格局控制了烃源岩和储集层的发育及源储配置关系，建议首先将裂坳陷边缘带作为下一步勘探的重点。

Sinian to Early Cambrian uplift-depression framework along the northern margin of the Sichuan Basin,central China and its implications for hydrocarbon exploration

The SinianLower Cambrian suite in northern Sichuan Basin is considered one of the key exploration fields following the discovery of the Anyue giant gas field and Mianyang-Changning introcratonic rift. However, different views have emerged regarding its depositional-tectonic pattern. Based on previous studies and recent outcrop, seismic, drilling and geochemical data, we propose in this paper that introcratonic rift-sags could coexist with uplifts during the SinianEarly Cambrian on the northern margin of the Sichuan Basin. Detailed analyses on the thickness, lithofacies, seismic reflection and geochemical indices of the SinianLower Cambrian on the northern margin of the Sichuan Basin indicate (1) the depositional-tectonic pattern is characterized by alternating rift-sags and uplifts which include, from west to east, the Mianyang-Changning rift, Hannan-Micangshan uplift, Wanyuan-Tongjiang rift-sag, Dazhou-Kaijiang uplift, Chengkou-Kaixian rift-sag, Dong'an-Wuxi uplift, Badong-Enshi rift, and Shennongjia-Huangling uplift; (2) three kinds of sedimentary environments-platform, slope and basin developed at the basin margin, where slope is dominated by a large number of tempestites, gravity flow deposits, slump breccias, syndepositional slip deformation, and so on; (3) the basin experienced three “uplift-depression” cycles, i.e. from the end of the second member of the Doushantuo Formation to the early stage of the second member of the Dengying Formation, from the late stage of the second member of the Dengying Formation to the early stage of the fourth member of the Dengying Formation, and from the late stage of the fourth member of the Dengying Formation to the late stage of the Qiongzhusi Formation. The formation of the uplift-depression framework is controlled in combination by the pre-Sinian basement weak zones, the mantle upwelling in southern Qinling and the slab pull of proto-Tethyan oceanic lithosphere, and all were closely related to the global tectonic setting during the breakup of Rodinia and assembly of Gondwanaland. Our proposed uplift-depression framework not only helps to fully understand the depositional-tectonic pattern and its evolution of the Yangtze Craton during this period, but also provides a reference for future oil-gas exploration in this region. The SinianEarly Cambrian uplift-depression pattern in northeastern Sichuan Basin controls the development of source rocks, reservoirs and source-reservoir configuration. It is therefore suggested that the rift-sag marginal zones should be the preferred targets in future exploration.