The evolution of the Sinian–Early Cambrian E’xi Trough in the Central Yangtze region and its geological significance for natural gas
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摘要: 新元古代震旦纪—早寒武世华南断陷盆地沉积了大量富有机质页岩和碳酸盐岩，优质烃源岩与储层发育，是油气勘探的重点领域。中扬子地区震旦纪—早寒武世发育鄂西海槽，但其形成与演化过程尚需进一步研究。基于钻井、野外露头和地震剖面等资料的综合分析，揭示出南北向鄂西海槽的形成与演化历史。研究结果表明，鄂西海槽经历了4个不同的阶段：南沱组沉积时期，鄂西地区初步形成沉降中心，但冰碛岩沉积厚度较小；陡山沱组沉积时期，雪球地球结束，气候转为温暖湿润，在鄂西海槽东侧形成了具有同沉积断裂的半地堑盆地；灯影组沉积时期，中—上扬子地区整体上形成2个台地和1个盆地的台−盆结构，鄂西地区发育完整的地堑盆地，呈现出碳酸盐台地的特征；牛蹄塘组沉积末期，鄂西海槽填充并消亡。其中陡山沱组二段和四段、牛蹄塘组二段发育富有机质页岩，是页岩气勘探的主要层系。同时鄂西海槽自下而上发育陡山沱组烃源岩、灯影组储层、牛蹄塘组烃源岩和盖层，具有“三明治”式的常规油气成藏模式。但多期次的构造活动导致部分油气封闭系统遭到破坏；此外，局部地区烃源岩埋藏深度大，致使有机质成熟度偏高。因此，寻找构造稳定区和成熟度适中地区是鄂西海槽页岩气勘探的关键，而优选有效成藏条件和良好保存地区是常规天然气勘探的重点方向。Abstract:
Objective From the Neoproterozoic Sinian to the Early Cambrian periods, extensive basins in South China accumulated substantial volumes of organic-rich shale and carbonate rocks, providing high-quality source rocks and reservoirs. These basins constitute key targets for petroleum exploration. The Central Yangtze Region hosts the Sinian–Early Cambrian E’Xi trough, whose formation and evolutionary processes require further investigation. Methods Comprehensive analyses integrating drilling data, outcrop sections, and seismic profiles reveal the evolution history of this north-south-trending trough. Results Research indicates four distinct developmental stages: (1) During the deposition of the Nantuo Formation, an initial subsidence center emerged in western Hubei with limited tillite thickness; (2) The Doushantuo Formation developed in a half-graben basin system, coinciding with the post-Snowball Earth warming and humidification, which fostered syn-depositional faulting along the eastern trough margin; (3) The deposition of the Dengying Formation was characterized by carbonate platform with the establishment of a "two-platform, one-basin" architecture across the Central–Upper Yangtze region and the development of a complete graben basin in western Hubei; (4) The Niutitang Formation, dominated by clastic sediments, exhibits thickness complementarity with the underlying Dengying dolomites, marking trough filling and termination. Conclusions Members II and IV of Doushantuo Formation, together with Member II of the Niutitang Formation, host organic-rich shales, which constitute the primary targets for shale gas exploration. Conventional hydrocarbon systems display a "sandwich-style" accumulation model comprising Doushantuo source rocks, Dengying reservoirs, and Niutitang seal/source couples. Multiphase tectonic activities have disrupted some oil and gas closed systems, while excessive burial depths locally induced overmatured organic matter. Therefore, the key to shale gas exploration is identifying tectonically stable areas with moderate maturity levels, while the strategic focus for conventional natural gas exploration is prioritizing regions characterized by effective hydrocarbon accumulation and favorable preservation conditions. -
Key words:
- E’xi trough /
- Sinian–Early Cambrian /
- basin evolution /
- shale gas /
- natural gas exploration
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图 1 扬子地区震旦纪—早寒武世沉积古地理特征和鄂西地区地层综合特征（据王剑等，2024；丁一等，2025修改；地质年龄据Condon et al.，2005；Chen et al.，2015）
a—扬子地区震旦纪—早寒武世沉积古地理图；b—鄂西地区震旦系—下寒武统综合地层特征
Figure 1. Sinian–Early Cambrian paleogeographic map and comprehensive log in the Yangtze region (modified after Wang et al., 2024; Ding et al., 2025; geological ages from Condon et al., 2005; Chen et al., 2015)
(a) Sinian–Early Cambrian paleogeographic map in the Yangtze region; (b) Comprehensive log of the Sinian–Lower Cambrian in western Hubei
图 2 南沱组野外露头特征（据胡军等，2021；胡军，2021修改；具体位置见图1）
a—湘西北三叉乡冰碛岩；b—湘西北三叉乡含砾砂岩；c—鄂西神农架地区砾石擦痕；d—鄂西神农架地区碳酸盐岩砾石擦痕
Figure 2. Outcrop characteristics of the Nantuo Formation (modified after Hu et al., 2021; Hu, 2021; locations are shown in Figure 1)
(a) Glacial deposits in Sanchaxiang, northwest Hunan; (b) Conglomeratic sandstone in Sanchaxiang, northwest Hunan; (c) Striations on conglomerates in the Shennongjia area; (d) Striations on carbonate clasts in the Shennongjia area
图 3 鄂西地区南沱组厚度等值线及沉积相特征（据王剑，2000修改）
Figure 3. Isopach and sedimentary facies map of the Nantuo Formation in western Hubei (modified after Wang, 2000; location is shown in Fig. 1)
图 4 宜昌三斗坪地区陡山沱组沉积特征（具体位置见图1）
a—陡二段黑色页岩；b—陡四段黑色页岩；c—陡三段浅灰色含泥质条带灰岩；d—陡三段中白云质泥岩中燧石结核
Figure 4. Sedimentary characteristics of the Doushantuo Formation in the Sandouping area, Yichang (Location is shown in Figure 1)
(a) Black shale from the second member of the Doushantuo Formation; (b) Black shale from the fourth member of the Doushantuo Formation; (c) Light gray, argillaceous ribbon limestone from the third member of the Doushantuo Formation; (d) Chert nodules within dolomitic mudstones from the third member of the Doushantuo Formation
图 5 鄂西地区陡山沱组厚度等值线图（陈科等，2024）
Figure 5. Isopach map of the Doushantuo Formation in western Hubei (Chen et al., 2024）
图 6 灯影组沉积特征（具体位置见图1）
a—鹤峰白果坪剖面台地边缘浅滩鲕粒；b—鹤峰白果坪剖面水平层理；c—秭归九龙湾水平层理和滑塌构造；d—秭归头顶石丘状交错层理
Figure 6. Sedimentary characteristics of the Dengying Formation (Locations are shown in Fig. 1)
(a) Shoal ooids from the platform margin of the Baiguoping section, Hefeng; (b) Horizontal bedding in the Baiguoping section, Hefeng; (c) Horizontal bedding and slump structures in the Jiulongwan section, Zigui; (d) Hummocky cross-bedding in the Toudingshi section, Zigui
图 8 鄂西地区灯影组厚度等值线图（据汪泽成等，2014修改）
Figure 8. Isopach map of the Dengying Formation in western Hubei (modified after Wang et al., 2014）
图 9 牛蹄塘组沉积特征（具体位置见图1）
a—深灰色中层含炭粉晶灰岩夹黑色薄层含炭粉砂质泥岩；b—薄层含炭钙质泥岩夹灰岩透镜体；c—含炭钙质泥页岩夹灰岩透镜体；d—鄂阳页1井牛蹄塘组二段层状黄铁矿
Figure 9. Sedimentary characteristics of the Niutitang Formation (Location is shown in Fig. 1)
(a) Dark gray medium-bedded micrite limestone interlayered with thin beds of carbon-bearing silty mudstone; (b) Thin-bedded calcareous mudstone intercalated with lenses of limestone; (c) Calcareous mud shale intercalated with lenses of limestone; (d) Layered pyrite from the second member of the Niutitang Formation in well EYY1
图 10 鄂西地区牛蹄塘组厚度等值线图（据陈科等，2025修改）
Figure 10. Isopach map of the Niutitang Formation in western Hubei (modified after Chen et al., 2025)
图 11 鄂西震旦系—下寒武统关键地层界面特征
a—陡一段盖帽白云岩，与下伏南沱组呈不整合接触；b—灯影组与陡山沱组整合接触；c—灯影组与牛蹄塘组之间平行不整合接触；d—牛蹄塘组一段（岩家河组）与二段（水井沱组）界面
Figure 11. Photographs of key stratigraphic interfaces in the Sinian–Lower Cambrian in western Hubei
(a) Cap dolomite of the first member of the Doushantuo Formation, in conformable contact with the underlying Nantuo Formation; (b) The Dengying Formation is in conformable contact with the Doushantuo Formation; (c) The Dengying Formation has a parallel unconformity contact with the Niutitang formation; (d) The interface between the first member (Yanjiahe Formation) and the second member (Shuijingtuo Formation) of the Niutitang Formation
图 12 鄂西地区震旦系—下寒武统层序地层划分（据王剑，2000修改）
Figure 12. Sequence stratigraphy of the Sinian–Lower Cambrian in western Hubei (modified after Wang, 2000)
图 14 横穿鄂西海槽地层厚度剖面图（剖面位置见图10）
a—牛蹄塘组沉积厚度剖面；b—灯影组沉积厚度剖面；c—陡山沱组沉积厚度剖面；d—南沱组沉积厚度剖面
Figure 14. Cross section of stratigraphic thickness across the E’xi trough (Location is shown in Fig. 10)
(a) Sedimentary thickness section of the Niutitang Formation; (b) Sedimentary thickness section of the Dengying Formation; (c) Sedimentary thickness section of the Doushantuo Formation; (d) Sedimentary thickness section of the Nantuo Formation
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