上扬子区下寒武统海相页岩岩相类型及沉积模式

摘要/Abstract

摘要：

上扬子区下寒武统牛蹄塘组页岩是我国南方地区页岩气重要勘探层系之一。通过露头、岩心、薄片、实验测试等资料综合分析,识别了该套页岩岩相类型及相关沉积作用方式,在水体氧化还原条件演变规律分析基础上总结了其沉积演化模式。牛蹄塘组页岩共包含6类岩相:富有机质硅质页岩、含粉砂硅质页岩、粉砂质页岩、黏土质页岩、泥质钙质页岩及粉砂质钙质页岩,主要体现为5种沉积作用方式:砂质机械沉积、钙质化学沉积、硅质生物沉积、泥质絮凝沉积及底流改造沉积。从底到顶,该套页岩表现为一套水体变浅的进积型演化序列,水体还原程度减弱,有机质保存条件变差。牛蹄塘组下段沉积期,盆地相区和陆棚相区分别以硅质生物沉积和钙质化学沉积为主,主体岩相类型为硅质页岩和钙质页岩;上段沉积期,盆地相区和陆棚相区分别以泥质絮凝沉积和砂质机械沉积为主,主体岩相类型为黏土质页岩和粉砂质混合质页岩。提出的牛蹄塘组页岩岩相发育模式及沉积演化规律能为研究区优质页岩的分布预测及页岩气勘探选区评价提供理论依据。

关键词: 海相页岩, 岩相类型, 沉积环境, 牛蹄塘组, 上扬子

Abstract:

On the basis of comprehensive analysis of outcrops, cores, thin-section, mineral X-ray diffraction, and drilling material, the lithfacies and sedimentary processes for the Lower Cambrian Niutitang shale in the upper Yangtze Platform are identified. Furthermore, the depositional conditions and sedimentary evolutional patterns for this shale are also analyzed. According to organic matter content, mineral composition, mineral texture and rock fabric, six lithofacies are identified, including organic-rich siliceous shale, silty siliceous shale, argillaceous shale, argillaceous calcareous shale, silty calcareous shale and silty mixed shale. These lithofacies are mainly deposited in the ways of clastic mechanical deposition, carbonate chemical deposition, silica biological deposition, argillaceous flocculation deposition, and bottom current rework deposition. Trace elements analysis reveals that the predominated redox conditions for the Niutitang shale deposition are anoxic to dysoxic environments. The degree of anoxia gradually decreases with the sea level fall upwards. During the lower member shale depositional period, the basinal environment is occupied by siliceous shale, and the shelf region is occupied by calcareous shale. During the upper member shale depositional period, the basinal environment is covered by argillaceous shale, and the shelf region is covered by silty mixed shale. The Niutitang shale generally shows a shallowing-upward prograding depositional sequence. From bottom to top, the organic matter content and anoxic degree decreases largely with the sea level fall. The average content of quartz decreases, but the average content of clay mineral increases.

Key words: marine shale, lithofacies type, sedimentary environment, Niutitang Formation, Upper YangtzePlatform

中图分类号:

TE121.3

伍岳, 樊太亮, 丁怀宇. 上扬子区下寒武统海相页岩岩相类型及沉积模式[J]. 现代地质, 2017, 31(06): 1222-1221.

WU Yue, FAN Tailiang, DING Huaiyu. Lithofacies and Sedimentary Model of the Lower Cambrian Marine Shale in the Upper Yangtze Platform[J]. Geoscience, 2017, 31(06): 1222-1221.

图/表 9

图1 扬子板块早寒武世沉积古地理图(改自文献[12])

Fig. 1 Sedimentary paleo-geographic map of the Yangtze Platform in the Early Cambrian stage

图2 上扬子地区下寒武统区域地层对比(据文献 [19])

Fig.2 Regional stratigraphic correlation of the Lower Cambrian strata in the Upper Yangtze Platform

图3 牛蹄塘组页岩矿物三角图(剖面位置见图1)

Fig.3 Ternary diagrams of mineralogy for the Lower Cambrian Niutitang shale

图4 不同类型页岩岩相露头照片 (a)富有机质硅质页岩,含磷结核,染手,南皋剖面;(b)富有机质硅质页岩,薄层加积样式,南皋剖面;(c)含粉砂硅质页岩,粉砂呈薄纹层状,南皋剖面;(d)含粉砂硅质页岩,厚层加积样式,南皋剖面;(e)黏土质页岩,球形风化发育,龙鼻嘴剖面;(f)黏土质页岩,发育溶蚀孔缝,龙鼻嘴剖面;(g)粉砂质混合质页岩,粉砂条纹发育,龙鼻嘴剖面;(h)泥质钙质页岩,劈理化严重,肖滩剖面;(i)粉砂质钙质页岩(下部)与泥质钙质页岩(上部)突变接触,肖滩剖面

Fig.4 Outcrops for different lithofacies

图5 不同类型页岩岩相显微照片 (a)富有机质硅质页岩,硅质斑块大小不一,聚集分布,龙鼻嘴剖面;(b)富有机质硅质页岩,硅质纹层呈断续状定向平行分布,南皋剖面;(c)含粉砂硅质页岩,粉砂均匀分布,绢云母定向排列,见少量生物化石碎片,龙鼻嘴剖面;(d)含粉砂硅质页岩,粉砂均匀分布,裂缝呈斜交层理分布,硅质充填,南皋剖面;(e)黏土质页岩,部分黏土因重结晶呈斑块状分布,富含生物化石, 南皋剖面;(f)黏土质页岩,发育断续硅质纹层,见硅质海绵生物, 南皋剖面;(g)粉砂质混合质页岩,暗色纹层为含有机质黏土层,亮色纹层为粉砂层,突变接触,龙鼻嘴剖面;(h)泥质钙质页岩,发育两期裂缝,钙质充填,肖滩剖面;(i)粉砂质钙质页岩,钙质与粉砂混杂堆积,肖滩剖面

Fig.5 Thin-sections for different lithofacies

表1 南皋剖面牛蹄塘组硅质页岩岩相主量元素分析结果

Table 1 Major element contents of the siliceous shale in the Niutitang Formation at Nangao outcrop

样品号	元素含量/%											Al/(Al+ Fe+Mn)	Si/(Al+ Fe+Si)
样品号	Si	Al	Fe	MgO	CaO	Na	K	MnO	Ti	P	FeO	Al/(Al+ Fe+Mn)	Si/(Al+ Fe+Si)
NG-01	43.93	6.66	6.97	1.47	10.7	0.07	2.18	0.07	0.4	7.69	2.41	0.49	0.76
NG-02	45.14	9.64	7.88	1.7	4.78	0.04	3.23	0.03	0.57	3.17	2.21	0.55	0.72
NG-03	39.34	7.33	5.05	1.7	11.98	0.13	2.44	0	0.83	8.43	2.3	0.59	0.76
NG-04	43.47	8.41	15.18	0.85	0.49	0.08	4.51	0	0.68	0.19	1.51	0.36	0.65
NG-05	56.27	10.99	3.81	0.92	0.2	0.09	5.81	<0.004	1	0.08	1.43	0.74	0.79
NG-06	54.6	10.06	3.5	0.86	0.13	0.1	5.08	<0.004	1.46	0.06	1.34	0.74	0.80
NG-07	54.81	10.37	3.21	0.92	0.21	0.08	5.33	<0.004	1.31	0.07	1.57	0.76	0.80
NG-08	51.1	8.59	5.06	0.75	1.26	0.09	4.36	<0.004	1.41	0.16	1.66	0.63	0.79
NG-09	55.73	8.6	5.22	0.65	1.04	0.12	4.36	<0.004	0.73	0.14	2.23	0.62	0.80
NG-10	60.97	8.46	3.46	0.62	0.87	0.29	4.27	0.01	0.5	0.16	2.14	0.71	0.84
NG-11	63.83	9.36	2.84	1.03	0.5	0.15	4.02	<0.004	0.63	0.17	1.42	0.77	0.84
NG-12	66.81	8.5	4.43	0.69	0.8	0.43	4.06	0.01	0.52	0.3	1.11	0.66	0.84
NG-13	64.3	10.67	4.03	1.86	2.26	0.31	4.73	0.03	0.66	0.23	1.79	0.73	0.81
NG-14	67	12.74	1.61	1.01	0.11	0.51	5.64	<0.004	0.92	0.06	1.26	0.89	0.82
NG-15	67.48	12.97	1.45	0.93	0.12	0.61	5.95	<0.004	0.9	0.04	1.14	0.90	0.82
NG-16	64.51	10.98	2.62	0.65	0.12	0.67	5.47	<0.004	1.05	0.04	0.87	0.81	0.83
NG-17	67.35	11.87	1.35	0.76	0.15	0.27	5.67	<0.004	1.12	0.06	0.68	0.90	0.84

图6 南皋剖面牛蹄塘组页岩微量元素垂向变化图

Fig.6 Vertical variations in the content of Mo and the ratios of V/Cr, V/(V+Ni) and Ni/Co at Nangao outcrop

图7 南皋剖面牛蹄塘组页岩V/Cr、V/(V+Ni)及Ni/Co比值交汇图 (改自文献[28]和[29])

Fig.7 The cross-plots of trace elements ratios for the Lower and Upper members of the Niutitang Formation shale at Nangao outcrop

图8 上扬子下寒武统牛蹄塘组页岩岩相组合及沉积演化模式(剖面位置见图1)

Fig.8 Lithofacies associations and sedimentary evolution model of the Niutitang shale in the Upper Yangtze Platform

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