Sedimentary Environment and Organic Matter Accumulation of Black Rock Series of Wufeng-Longmaxi Formations in Foreland Depression, Western Hunan Province: An Example from Well TD2 in Changde Area
-
摘要: 受地层剥蚀和强烈构造活动的影响,对中扬子东南缘前陆坳陷区五峰‒龙马溪组黑色岩系关注较少,该区黑色岩系沉积特征与有机质富集规律尚不清楚.利用近年来新获取的常德TD2井岩心资料,基于岩石学、沉积学以及地球化学分析,对湘西前陆坳陷区五峰‒龙马溪组黑色岩系的发育特征、沉积环境及有机质富集机制开展了深入研究.结果表明,湘西前陆坳陷区TD2井五峰‒龙马溪组黑色岩系厚度较大,TOC > 2%的富有机质页岩厚约21 m,岩性以硅质页岩与碳质页岩为主,基于岩性差异自下而上可划分为四个沉积单元,富有机质页岩主要集中凯迪阶至鲁丹阶下部,而鲁丹阶上部‒埃隆阶下部黑色岩系TOC含量普遍偏低且呈间断发育.综合研究认为,前陆坳陷区五峰‒龙马溪组黑色岩系的形成主要受构造、海平面以及陆源碎屑供给等因素的综合控制.凯迪晚期‒鲁丹早期,受区域构造挤压和全球海平面上升的影响,湘西地区经历了显著的构造沉降及相对海平面上升等事件,极大地促进了坳陷区强还原条件的形成以及古生产力的提高,使得该时期研究区黑色岩系中的有机质大量富集.然而,随着鲁丹晚期区域构造挤压活动的加剧,研究区由构造沉降向构造隆升转变,持续的构造抬升与风化作用增强,导致了研究区陆源碎屑供给大量增加和相对海平面不断下降,并最终使得研究区富有机质页岩的形成发育在埃隆早期被终结.值得注意的是,埃隆早期的全球冰川型海平面上升在研究区也有响应,促进了龙马溪组黑色页岩的二次发育.据此,提出了湘西前陆坳陷区奥陶‒志留纪之交富有机质页岩的发育模式,以期为该区五峰‒龙马溪组页岩气勘探及奥陶‒志留纪之交重大地质事件沉积响应研究提供参考.Abstract: As the main sediments across the Yangtze area during the Ordovician-Silurian (O-S) transition, the Upper Ordovician Wufeng Formation and Lower Longmaxi Formation are widely distributed in the Yangtze Sea, and they are also the main targets for marine shale gas exploration in the South China. However, little attention has been paid to the Wufeng-Longmaxi black rock series in the foreland basin, southeastern Yangtze Block, due to the lack of complete and fresh outcrops caused by intensive erosion and tectonic damage. In this paper, by utilizing the newly obtained drilling cores of the Well TD2 located in the Hunan Province, the sedimentary environment and organic matter accumulation of the Wufeng-Longmaxi black rock series in the foreland basin were investigated based on the systematically petrological and geochemical analysis. The organic-rich shale of the Wufeng-Longmaxi formations is dominated by siliceous shale and carbonaceous shale, in which plenty of terrigenous clast and even thin sandstone can be observed. The black shale with TOC > 2% is about 21 m in thickness. Four sedimentary cycles can be recognized from the O-S black series and they exhibit different lithological and geochemical variation characteristics. The organic shale generally developed in the Late Katian to the Early Rhuddanian, while the black rock series developed during the Late Rhuddanian to Early Aeronian have low TOC content and are discontinuous. Based on the analyses of lithology, mineral composition and geochemistry, tectonism, sea-level and terrigenous supply should be the primary controlling factors for the deposition of the O-S black shale in the foreland basin, Yangtze area. During the Late Katian to Early Rhuddanian, the study area experienced significantly tectonic subsidence and sea-level rise caused by regional tectonic compression and global sea-level rise, then strongly reducing conditions were formed and paleoproductivity was improved in the deep-depression area, which promoted the enrichment of organic matter in black rock series during this stage. Nevertheless, with intensifying tectonic collision between the Yangtze and Cathaysia blocks since Late Rhuddanian, the tectonism in the study area changed from tectonic subsidence to uplift. Persistent tectonic uplift and intensive weathering conditions led to the noticeable increase of terrigenous supply in the foreland depression, as well as gradual sea-level fall, and then, the development of black organic-rich shale in the foreland basin was terminated at the Early Aeronian. It should be noted that during the earliest Aeronian stage, global glacial sea-level rise promotes the development of black shale in the study area again. Finally, a sedimentary model for the O-S black shale in the foreland depression, western Hunan area was proposed. This study is not only beneficial for gaining more geological knowledge about the black shale formation in a marine foreland basin, but also helpful for understanding the sedimentary responses to major geological events occurred in Yangtze area during the O-S transition.
-
图 1 扬子地区奥陶‒志留纪之交构造‒沉积古地理(a)与湘西前陆盆地区五峰‒龙马溪组黑色岩系地层特征(b)
图a修自Chen et al.,2004;图b中全球海平面数据来自Haq and Schutter(2008),扬子地区海平面来自Cai et al.(2022a)
Fig. 1. The Ordovician-Silurian paleogeography of the Yangtze Block (a) and stratigraphic characteristics (b) of the Wufeng- Longmaxi black shale in the foreland basin located in western Hunan Province
图 3 五峰‒龙马溪组黑色岩系主要岩石类型及特征图版
a. 黑色硅质页岩,裂缝发育,被方解石充填,1 558.1 m;b. 硅质页岩,见大量陆源碎屑及少量硅质放射虫,1 561.0 m;c. 硅质页岩,发育多期裂缝,硅质充填,1 554.5 m;d. 黑色碳质页岩,见笔石化石,含陆源碎屑,1 566.7 m;e. 灰黑色碳质页岩,笔石具定向排列特征,1 537.7 m;f. 大量陆源碎屑与有机质分散分布,陆源碎屑石英具棱角状,1 524.3 m;g. 灰色粉砂质泥岩夹薄层粉砂岩,可见岩性突变面和波状层理,1 539.6 m;h. 粉砂质泥岩夹黑色碳质纹层与灰白色砂质纹层,1 513.5 m;i. 灰白色粉细砂岩,底部见明显的冲刷侵蚀面,1 508.7 m
Fig. 3. Rock type of the black shale in the Wufeng-Longmaxi formations, Well TD2
表 1 五峰‒龙马溪组黑色岩系干酪根镜检结果统计分析
Table 1. Types of kerogens in the Wufeng-Longmaxi black shale
样品编号 腐泥组(%) 壳质组(%) 镜质组(%) 惰性组(%) TI 类型 B1 97 0 3 0 94.8 Ⅰ B2 98 0 2 0 96.5 Ⅰ B3 95 0 5 0 91.3 Ⅰ B4 97 0 3 0 94.8 Ⅰ B5 96 0 4 0 93.0 Ⅰ B6 97 0 3 0 94.8 Ⅰ B7 94 0 6 0 89.5 Ⅰ B8 98 0 2 0 96.5 Ⅰ B9 95 0 5 0 91.3 Ⅰ B10 97 0 3 0 94.8 Ⅰ -
Algeo, T. J., Liu, J. S., 2020. A Re-Assessment of Elemental Proxies for Paleoredox Analysis. Chemical Geology, 540: 119549. https://doi.org/10.1016/j.chemgeo.2020.119549 Algeo, T. J., Lyons, T. W., 2006. Mo-Total Organic Carbon Covariation in Modern Anoxic Marine Environments: Implications for Analysis of Paleoredox and Paleohydrographic Conditions. Paleoceanography, 21(1): PA1016. https://doi.org/10.1029/2004PA001112 Algeo, T. J., Maynard, J. B., 2004. Trace-Element Behavior and Redox Facies in Core Shales of Upper Pennsylvanian Kansas-Type Cyclothems. Chemical Geology, 206(3-4): 289-318. https://doi.org/10.1016/j.chemgeo.2003.12.009 Algeo, T. J., Tribovillard, N., 2009. Environmental Analysis of Paleoceanographic Systems Based on Molybdenum-Uranium Covariation. Chemical Geology, 268(3-4): 211-225. https://doi.org/10.1016/j.chemgeo.2009.09.001 Cai, Q. S., Chen, X. H., Zhang, G. T., et al., 2021. Characteristics and Exploration Potential of the Wufeng-Longmaxi Shale Gas Reservoirs of Lower Paleozoic in Yichang Area, Western Hubei Province, China. Oil & Gas Geology, 42(1): 107-123 (in Chinese with English abstract). Cai, Q. S., Hu, M. Y., Kane, O. I., et al., 2022a. Cyclic Variations in Paleoenvironment and Organic Matter Accumulation of the Upper Ordovician-Lower Silurian Black Shale in the Middle Yangtze Region, South China: Implications for Tectonic Setting, Paleoclimate, and Sea-Level Change. Marine and Petroleum Geology, 136: 105477. https://doi.org/10.1016/j.marpetgeo.2021.105477 Cai, Q. S., Hu, M. Y., Zhang, B. M., et al., 2022b. Source of Silica and Its Implications for Organic Matter Enrichment in the Upper Ordovician-Lower Silurian Black Shale in Western Hubei Province, China: Insights from Geochemical and Petrological Analysis. Petroleum Science, 19(1): 74-90. https://doi.org/10.1016/j.petsci.2021.10.012 Chen, Q., Fan, J. X., Zhang, L. N., et al., 2018. Paleogeographic Evolution of the Lower Yangtze Region and the Break of the "Platform-Slope-Basin" Pattern during the Late Ordovician. Scientia Sinica Terrae, 48(6): 767-777 (in Chinese). doi: 10.1360/N072018-00002 Chen, X., Chen, Q., Zhen, Y. Y., et al., 2018. Circumjacent Distribution Pattern of the Lungmachian Graptolitic Black Shale (Early Silurian) on the Yichang Uplift and Its Peripheral Region. Scientia Sinica Terrae, 48(9): 1198-1206 (in Chinese). doi: 10.1360/N072017-00445 Chen, X., Rong, J. Y., Li, Y., et al., 2004. Facies Patterns and Geography of the Yangtze Region, South China, through the Ordovician and Silurian Transition. Palaeogeography, Palaeoclimatology, Palaeoecology, 204(3-4): 353-372. https://doi.org/10.1016/s0031-0182(03)00736-3 Dong, D. Z., Shi, Z. S., Guan, Q. Z., et al., 2018. Progress, Challenges and Prospects of Shale Gas Exploration in the Wufeng-Longmaxi Reservoirs in the Sichuan Basin. Natural Gas Industry B, 5(5): 415-424. https://doi.org/10.1016/j.ngib.2018.04.011 Fan, J. X., Melchin, M. J., Chen, X., et al., 2011. Biostratigraphy and Geography of the Ordovician-Silurian Lungmachi Black Shales in South China. Science China Earth Sciences, 54(12): 1854-1863. https://doi.org/10.1007/s11430-011-4301-3 Haq, B. U., Schutter, S. R., 2008. A Chronology of Paleozoic Sea-Level Changes. Science, 322(5898): 64-68. https://doi.org/10.1126/science.1161648 Huang, H. Y., He, D. F., Li, D., et al., 2020. Geochemical Characteristics of Organic-Rich Shale, Upper Yangtze Basin: Implications for the Late Ordovician-Early Silurian Orogeny in South China. Palaeogeography, Palaeoclimatology, Palaeoecology, 554: 109822. https://doi.org/10.1016/j.palaeo.2020.109822 Huang, H. Y., He, D. F., Li, Y. Q., et al., 2018. Silurian Tectonic-Sedimentary Setting and Basin Evolution in the Sichuan Area, Southwest China: Implications for Palaeogeographic Reconstructions. Marine and Petroleum Geology, 92: 403-423. https://doi.org/10.1016/j.marpetgeo.2017.11.006 Li, Q. Q., Lan, B. F., Li, G. Q., et al., 2021. Element Geochemical Characteristics and Their Geological Significance of Wufeng-Longmaxi Formation Shales in North Margin of the Central Guizhou Uplift. Earth Science, 46(9): 3172-3188 (in Chinese with English abstract). Liu, C. S., Guo, J. H., Wang, Z. X., 2019. Potential for Shale Gas Exploration of Xuefengshan Foreland Basin of Lower Silurian. Earth Science, 44(11): 3678-3691 (in Chinese with English abstract). Liu, Z. H., Algeo, T. J., Guo, X. S., et al., 2017. Paleo-Environmental Cyclicity in the Early Silurian Yangtze Sea (South China): Tectonic or Glacio-Eustatic Control? Palaeogeography, Palaeoclimatology, Palaeoecology, 466(6): 59-76. https://doi.org/10.1016/j.palaeo.2016.11.007 Lu, X. Z., Shen, J., Guo, W., et al., 2021. Influence of Mercury Geochemistry and Volcanism on the Enrichment of Organic Matter near the Ordovician Silurian Transition in the Middle and Upper Yangtze. Earth Science, 46(7): 2329-2340 (in Chinese with English abstract). Malekzadeh, M., Hosseini-Barzi, M., Sadeghi, A., et al., 2020. Geochemistry of Asara Shale Member of Karaj Formation, Central Alborz, Iran: Provenance, Source Weathering and Tectonic Setting. Marine and Petroleum Geology, 121: 104584. https://doi.org/10.1016/j.marpetgeo.2020.104584 McLennan, S. M., 1993. Weathering and Global Denudation. The Journal of Geology, 101(2): 295-303. https://doi.org/10.1086/648222 Munnecke, A., Calner, M., Harper, D. A. T., et al., 2010. Ordovician and Silurian Sea-Water Chemistry, Sea Level, and Climate: A Synopsis. Palaeogeography, Palaeoclimatology, Palaeoecology, 296(3-4): 389-413. https://doi.org/10.1016/j.palaeo.2010.08.001 Nesbitt, H. W., Young, G. M., 1982. Early Proterozoic Climates and Plate Motions Inferred from Major Element Chemistry of Lutites. Nature, 299: 715-717. https://doi.org/10.1038/299715a0 Nie, H. K., Li, P., Dang, W., et al., 2022. Enrichment Characteristics and Exploration Directions of Deep Shale Gas of Ordovician-Silurian in the Sichuan Basin and Its Surrounding Areas, China. Petroleum Exploration and Development, 49(4): 648-659 (in Chinese with English abstract). Price, J. R., Velbel, M. A., 2003. Chemical Weathering Indices Applied to Weathering Profiles Developed on Heterogeneous Felsic Metamorphic Parent Rocks. Chemical Geology, 202(3-4): 397-416. https://doi.org/10.1016/j.chemgeo.2002.11.001 Qin, M. Y., Guo, J. H., He, H. S., et al., 2018. Geological Conditions and Gas-Bearing Characteristics of Shale Gas in Complex Structure Area out of Sichuan Basin: A Case of Wufeng-Longmaxi Formation in Northwestern Hunan, China. Journal of Central South University (Science and Technology), 49(8): 1979-1990 (in Chinese with English abstract). Qiu, Z., Zou, C. N., 2020. Unconventional Petroleum Sedimentology: Connotation and Prospect. Acta Sedimentologica Sinica, 38(1): 1-29 (in Chinese with English abstract). Rimmer, S. M., 2004. Geochemical Paleoredox Indicators in Devonian-Mississippian Black Shales, Central Appalachian Basin (USA). Chemical Geology, 206(3-4): 373-391. https://doi.org/10.1016/j.chemgeo.2003.12.029 Sageman, B. B., Murphy, A. E., Werne, J. P., et al., 2003. A Tale of Shales: The Relative Roles of Production, Decomposition, and Dilution in the Accumulation of Organic-Rich Strata, Middle-Upper Devonian, Appalachian Basin. Chemical Geology, 195(1-4): 229-273. https://doi.org/10.1016/s0009-2541(02)00397-2 Shao, J. Q., Yang, S. Y., Li, C., 2012. Chemical Indices (CIA and WIP) as Proxies for Integrated Chemical Weathering in China: Inferences from Analysis of Fluvial Sediments. Sedimentary Geology, 265-266: 110-120. https://doi.org/10.1016/j.sedgeo.2012.03.020 Sweere, T., van den Boorn, S., Dickson, A. J., et al., 2016. Definition of New Trace-Metal Proxies for the Controls on Organic Matter Enrichment in Marine Sediments Based on Mn, Co, Mo and Cd Concentrations. Chemical Geology, 441: 235-245. https://doi.org/10.1016/j.chemgeo.2016.08.028 Su, W. B., Li, Z. M., Shi, X. Y., et al., 2006. K-Bentonites and Black Shales from the Wufeng-Longmaxi Formations (Early Paleozoic, South China) and Xiamaling Formation (Early Neoproterozoic, North China)-Implications for Tectonic Processes during Two Important Transitions. Earth Science Frontiers, 13(6): 82-95 (in Chinese with English abstract). Taylor, S., McLennan, S., 1985. The Continental Crust: Its Composition and Evolution. Blackwell Scientific Publications, Oxford. Tribovillard, N., Algeo, T. J., Lyons, T., et al., 2006. Trace Metals as Paleoredox and Paleoproductivity Proxies: An Update. Chemical Geology, 232(1-2): 12-32. https://doi.org/10.1016/j.chemgeo.2006.02.012 Wang, G. X., Zhan, R. B., Percival, I. G., 2019. The End-Ordovician Mass Extinction: A Single-Pulse Event? Earth-Science Reviews, 192: 15-33. https://doi.org/10.1016/j.earscirev.2019.01.023 Wang, H. Y., Shi, Z. S., Sun, S. S., 2021. Biostratigraphy and Reservoir Characteristics of the Ordovician Wufeng Formation-Silurian Longmaxi Formation Shale in the Sichuan Basin and Its Surrounding Areas, China. Petroleum Exploration and Development, 48(5): 1019-1032. https://doi.org/10.1016/s1876-3804(21)60088-5 Wang, P., Du, Y. S., Yu, W. C., et al., 2020. The Chemical Index of Alteration (CIA) as a Proxy for Climate Change during Glacial-Interglacial Transitions in Earth History. Earth-Science Reviews, 201: 103032. https://doi.org/10.1016/j.earscirev.2019.103032 Wang, Y., Rong, J. Y., Zhan, R. B., et al., 2013. On the Ordovician-Silurian Boundary Strata in Southwestern Hubei, and the Yichang Uplift. Journal of Stratigraphy, 37(3): 264-274 (in Chinese with English abstract). Wang, Y. M., Dong, D. Z., Li, X. J., et al., 2015. Stratigraphic Sequence and Sedimentary Characteristics of Lower Silurian Longmaxi Formation in Sichuan Basin and Its Peripheral Areas. Natural Gas Industry B, 2(2-3): 222-232. https://doi.org/10.1016/j.ngib.2015.07.014 Xiao, B., Liu, S. G., Ran, B., et al., 2021. Study on Sedimentary Tectonic Pattern of Wufeng Formation and Longmaxi Formation in the Northern Margin of Sichuan Basin, South China. Earth Science, 46(7): 2449-2465 (in Chinese with English abstract). Zhang, L. N., Fan, J. X., Chen, Q., 2016. Geographic Distribution and Palaeogeographic Reconstruction of the Upper Ordovician Kuanyinchiao Bed in South China. Chinese Science Bulletin, 61(18): 2053-2063 (in Chinese). doi: 10.1360/N972015-00981 Yan, D. T., Chen, D. Z., Wang, Q. C., et al., 2010. Large-Scale Climatic Fluctuations in the Latest Ordovician on the Yangtze Block, South China. Geology, 38(7): 599-602. https://doi.org/10.1130/g30961.1 Yao, W. H., Li, Z. X., 2016. Tectonostratigraphic History of the Ediacaran-Silurian Nanhua Foreland Basin in South China. Tectonophysics, 674: 31-51. https://doi.org/10.1016/j.tecto.2016.02.012 Zou, C. N., Qiu, Z., Poulton, S. W., et al., 2018. Ocean Euxinia and Climate Change "Double Whammy" Drove the Late Ordovician Mass Extinction. Geology, 46(6): 535-538. https://doi.org/10.1130/g40121.1 蔡全升, 陈孝红, 张国涛, 等, 2021. 鄂西宜昌地区下古生界五峰组‒龙马溪组页岩气储层发育特征与勘探潜力. 石油与天然气地质, 42(1): 107-123. https://www.cnki.com.cn/Article/CJFDTOTAL-SYYT202101011.htm 陈清, 樊隽轩, 张琳娜, 等, 2018. 下扬子区奥陶纪晚期古地理演变及华南"台‒坡‒盆" 格局的打破. 中国科学: 地球科学, 48(6): 767-777. https://www.cnki.com.cn/Article/CJFDTOTAL-JDXK201806009.htm 陈旭, 陈清, 甄勇毅, 等, 2018. 志留纪初宜昌上升及其周缘龙马溪组黑色笔石页岩的圈层展布模式. 中国科学: 地球科学, 48(9): 1198-1206. https://www.cnki.com.cn/Article/CJFDTOTAL-JDXK201809006.htm 李琪琪, 蓝宝锋, 李刚权, 等, 2021. 黔中隆起北缘五峰‒龙马溪组页岩元素地球化学特征及其地质意义. 地球科学, 46(9): 3172-3188. doi: 10.3799/dqkx.2020.354 刘辰生, 郭建华, 王宗秀, 2019. 雪峰山前陆盆地下志留统页岩气勘探潜力. 地球科学, 44(11): 3678-3691. doi: 10.3799/dqkx.2019.208 卢贤志, 沈俊, 郭伟, 等, 2021. 中上扬子地区奥陶纪‒志留纪之交火山作用对有机质富集的影响. 地球科学, 46(7): 2329-2340. doi: 10.3799/dqkx.2020.258 聂海宽, 李沛, 党伟, 等, 2022. 四川盆地及周缘奥陶系‒志留系深层页岩气富集特征与勘探方向. 石油勘探与开发, 49(4): 648-659. https://www.cnki.com.cn/Article/CJFDTOTAL-SKYK202204003.htm 秦明阳, 郭建华, 何红生, 等, 2018. 四川盆地外复杂构造区页岩气地质条件及含气性特征: 以湘西北五峰组‒龙马溪组为例. 中南大学学报(自然科学版), 49(8): 1979-1990. https://www.cnki.com.cn/Article/CJFDTOTAL-ZNGD201808019.htm 邱振, 邹才能, 2020. 非常规油气沉积学: 内涵与展望. 沉积学报, 38(1): 1-29. https://www.cnki.com.cn/Article/CJFDTOTAL-CJXB202101001.htm 苏文博, 李志明, 史晓颖, 等, 2006. 华南五峰组‒龙马溪组与华北下马岭组的钾质斑脱岩及黑色岩系——两个地史转折期板块构造运动的沉积响应. 地学前缘, 13(6): 82-95. https://www.cnki.com.cn/Article/CJFDTOTAL-DXQY200606013.htm 王怿, 戎嘉余, 詹仁斌, 等, 2013. 鄂西南奥陶系‒志留系交界地层研究兼论宜昌上升. 地层学杂志, 37(3): 264-274. https://www.cnki.com.cn/Article/CJFDTOTAL-DCXZ201303003.htm 肖斌, 刘树根, 冉波, 等, 2021. 四川盆地北缘五峰组和龙马溪组沉积构造格局研究. 地球科学, 46(7): 2449-2465. doi: 10.3799/dqkx.2020.208 张琳娜, 樊隽轩, 陈清, 2016. 华南上奥陶统观音桥层的空间分布和古地理重建. 科学通报, 61(18): 2053-2063. https://www.cnki.com.cn/Article/CJFDTOTAL-KXTB201618009.htm -