The paleogeomorphology and its impact on overlying Wufeng-Longmaxi shale in southern Sichuan Basin of China are still controversial. Based on geophysical interpretation, chronostratigraphic division and transection correlation, shale isometric map compilation, and shale mineral composition analysis, the depositional paleogeomorphology and its impact on the overlying gas-bearing shale were clarified. The results show that: (1) During Late Ordovician and Early Silurian, the southern Sichuan Basin was located on the southeastern slope of the Leshan-Longnüsi paleo-uplift. The paleo-uplift, which was a syn-depositional one and had span distance reaching up to 85 km and topographical gradient ranging from 0 to 1 m/km, extended from Weiyuan area to Luzhou area southeastward. (2) During the depositional period of the Wufeng-Longmaxi shale, there existed three significant slope breaks which divided the southeastern slope into four geomorphological units, namely, sub⁃aqueous high, subaqueous slope, subaqueous plain, and subaqueous sag. (3) The Wufeng-Longmaxi shale, which onlaps the southeastern slope from southeast to northwest, is wholly developed in subaqueous plain and subaqueous sag but commonly losses the graptolite zones LM1-4 in subaqueous high and subaqueous slope. (4) There exist significant differences in shale grain size, mineral composition, and TOC content of shale upon different geomorphological units. Commonly, from the subaqueous high to the subaqueous sag, the shale grain size gradually becomes finer, the TOC content and carbonate mineral content gradually decrease, the silica content gradually increases, and the clay mineral content first decreases and then increases.
SHI Zhensheng, YUAN Yuan, ZHAO Qun, SUN Shasha, ZHOU Tianqi, CHENG Feng. Paleogeomorphology and oil-bearing shale characteristics of the Wufeng-Longmaxi shale in southern Sichuan Basin,China. Natural Gas Geoscience[J], 2022, 33(12): 1969-1985 doi:10.11764/j.issn.1672-1926.2022.08.013
Fig.1
Sedimentary background, data point distribution and stratigraphic comprehensive histogram of the Wufeng-Longmaxi shale in southern Sichuan Basin[28-31]
Fig.2
Three typical 2D seismic lines showing the paleogeomorphology during the depositional period of the Wufeng-Longmaxi shale in southern Sichuan Basin (the position of measuring line is shown in Fig.1)
Fig.3
Four typical 3D seismic lines showing the paleogeomorphology during the depositional period of the Wufeng-Longmaxi shale in southern Sichuan Basin (the position of measuring line is shown in Fig.1)
Fig.6
Thin section photos showing grain size of different sedimentary facies of the Wufeng-Longmaxi shale on the southeastern slope of the Leshan-Longnüsi paleo-uplift
Fig.7
Enlarged thin section photos showing bedding types of different sedimentary facies of the Wufeng-Longmaxi shale on the southeastern slope of the Leshan-Longnüsi paleo-uplift
Fig.8
Stratigraphic correlation profile of the Wufeng-Longmaxi shale crossing Wells Guohuang 204 and Wangjia 1 on the southeastern slope of the Leshan-Longnüsi paleo-uplift (the profile location is shown in Fig.5)
Fig.9
Stratigraphic correlation profile of the Wufeng-Longmaxi shale crossing Wells Zi 201 and Wei 210 on the southeaster slope of the Leshan-Longnüsi paleo-uplift (the profile location is shown in Fig.5)
(a)水下高地,威210井,3 228.7 m;(b)水下斜坡,威206井,3 753.86 m;(c)水下平原,泸207井,3 456.75 m;(d)水下洼地,泸202井,4 319.85 m
Fig.11
SEM photos showing the gas-bearing shale grain size in various paleogeomorphic units on the southeastern slope of the Leshan-Longnüsi paleo-uplift
Table 2
表2
表2乐山—龙女寺古隆起东南斜坡不同古地貌单元含气页岩组成
Table 2 Composition of gas-bearing shale in different paleogeomorphic units on the southeastern slope of the Leshan-Longnüsi paleo-uplift
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Sedimentary background, data point distribution and stratigraphic comprehensive histogram of the Wufeng-Longmaxi shale in southern Sichuan Basin[28-31]Fig.1
Sedimentary background, data point distribution and stratigraphic comprehensive histogram of the Wufeng-Longmaxi shale in southern Sichuan Basin[28-31]Fig.1
Sedimentary background, data point distribution and stratigraphic comprehensive histogram of the Wufeng-Longmaxi shale in southern Sichuan Basin[28-31]Fig.1
Sedimentary background, data point distribution and stratigraphic comprehensive histogram of the Wufeng-Longmaxi shale in southern Sichuan Basin[28-31]Fig.1
... 扬子台地五峰组—龙马溪组黑色页岩形成于华南盆地消亡和华南造山带形成时期.中奥陶世之前,中上扬子地区为一大型被动大陆边缘,以碳酸盐沉积为主.晚奥陶世—早志留世,华夏地块与扬子地块相互碰撞,上扬子地区进入前陆盆地演化阶段[32-33],陆源碎屑沉积占主导地位.该时期,上扬子地区西北部为乐山—龙女寺古隆起,南部为黔中隆起、雪峰隆起和武夷—云开隆起,中间为中上扬子隆后滞流海盆,以浅海深水盆地沉积为主[图1(a)].该时期川南地区处于半闭塞滞流状态,水体上下对流受限,水体多呈缺氧还原状态.由于华夏地块向北西方向挤压作用增强,扬子地块不断抬升,乐山—龙女寺古隆起隆升幅度也逐渐扩大.研究区位于中上扬子地区西南部[图1(b)],其北部位于乐山—龙女寺古隆起南缘,南部位于泸州市以南,西部位于屏山以东,东部位于重庆以西,分布面积约为3×104 km2. ...
1
... 扬子台地五峰组—龙马溪组黑色页岩形成于华南盆地消亡和华南造山带形成时期.中奥陶世之前,中上扬子地区为一大型被动大陆边缘,以碳酸盐沉积为主.晚奥陶世—早志留世,华夏地块与扬子地块相互碰撞,上扬子地区进入前陆盆地演化阶段[32-33],陆源碎屑沉积占主导地位.该时期,上扬子地区西北部为乐山—龙女寺古隆起,南部为黔中隆起、雪峰隆起和武夷—云开隆起,中间为中上扬子隆后滞流海盆,以浅海深水盆地沉积为主[图1(a)].该时期川南地区处于半闭塞滞流状态,水体上下对流受限,水体多呈缺氧还原状态.由于华夏地块向北西方向挤压作用增强,扬子地块不断抬升,乐山—龙女寺古隆起隆升幅度也逐渐扩大.研究区位于中上扬子地区西南部[图1(b)],其北部位于乐山—龙女寺古隆起南缘,南部位于泸州市以南,西部位于屏山以东,东部位于重庆以西,分布面积约为3×104 km2. ...
1
... 扬子台地五峰组—龙马溪组黑色页岩形成于华南盆地消亡和华南造山带形成时期.中奥陶世之前,中上扬子地区为一大型被动大陆边缘,以碳酸盐沉积为主.晚奥陶世—早志留世,华夏地块与扬子地块相互碰撞,上扬子地区进入前陆盆地演化阶段[32-33],陆源碎屑沉积占主导地位.该时期,上扬子地区西北部为乐山—龙女寺古隆起,南部为黔中隆起、雪峰隆起和武夷—云开隆起,中间为中上扬子隆后滞流海盆,以浅海深水盆地沉积为主[图1(a)].该时期川南地区处于半闭塞滞流状态,水体上下对流受限,水体多呈缺氧还原状态.由于华夏地块向北西方向挤压作用增强,扬子地块不断抬升,乐山—龙女寺古隆起隆升幅度也逐渐扩大.研究区位于中上扬子地区西南部[图1(b)],其北部位于乐山—龙女寺古隆起南缘,南部位于泸州市以南,西部位于屏山以东,东部位于重庆以西,分布面积约为3×104 km2. ...
1
... 扬子台地五峰组—龙马溪组黑色页岩形成于华南盆地消亡和华南造山带形成时期.中奥陶世之前,中上扬子地区为一大型被动大陆边缘,以碳酸盐沉积为主.晚奥陶世—早志留世,华夏地块与扬子地块相互碰撞,上扬子地区进入前陆盆地演化阶段[32-33],陆源碎屑沉积占主导地位.该时期,上扬子地区西北部为乐山—龙女寺古隆起,南部为黔中隆起、雪峰隆起和武夷—云开隆起,中间为中上扬子隆后滞流海盆,以浅海深水盆地沉积为主[图1(a)].该时期川南地区处于半闭塞滞流状态,水体上下对流受限,水体多呈缺氧还原状态.由于华夏地块向北西方向挤压作用增强,扬子地块不断抬升,乐山—龙女寺古隆起隆升幅度也逐渐扩大.研究区位于中上扬子地区西南部[图1(b)],其北部位于乐山—龙女寺古隆起南缘,南部位于泸州市以南,西部位于屏山以东,东部位于重庆以西,分布面积约为3×104 km2. ...