关键词: 震旦纪, 早寒武世, 隆坳格局, 裂陷作用, 油气勘探, 四川盆地, 扬子克拉通

Abstract: 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.

Key words: Sinian, Early Cambrian, uplift-depression framework, rifting, hydrocarbon exploration, Sichuan Basin, Yangtze Craton