| 柴北缘西大滩地区下—中侏罗统层序—古地理及聚煤特征 |
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| 引用本文： | 黄献好,孙玉琦,王伟超,刘炳强,张少林,张语涛,邵龙义.柴北缘西大滩地区下—中侏罗统层序—古地理及聚煤特征[J].沉积学报,2020,38(2):266-283. |
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| 作者姓名： | 黄献好 孙玉琦 王伟超 刘炳强 张少林 张语涛 邵龙义 |
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| 作者单位： | 1.中国矿业大学(北京)地球科学与测绘工程学院, 北京 100083 |
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| 基金项目： | 青海省地质勘查基金项目2017042109kc059中央高校基本科研业务费专项资金资助2010YD09 |
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| 摘 要： | 柴达木盆地北缘西大滩地区是近年来新发现的煤炭资源有利勘探区，含煤岩系以早侏罗世小煤沟组和中侏罗世早期的大煤沟组及石门沟组为代表。根据露头剖面、钻孔岩芯及测井曲线对该含煤岩系的沉积相、层序地层格架、聚煤模式及岩相古地理进行研究，并对该区聚煤规律进行了分析。研究结果表明:区内含煤岩系由砾岩、砂岩、粉砂岩、泥岩、油页岩及煤组成，可识别出16种岩相类型以及冲积扇、辫状河三角洲与湖泊等3种沉积相类型。以区域不整合面、沉积相转换面、下切谷砂体底部冲刷面、岩性及颜色突变面等为层序界面，共识别出6个层序界面，划分出5个三级层序和相应的低位、湖侵及高位体系域。恢复出各个层序的岩相古地理，主要古地理单元为冲积扇、辫状河三角洲、滨浅湖及半深湖。研究区厚煤层主要发育于湖侵体系域上部靠近最大湖泛面处的下三角洲平原环境，这里作为低可容空间背景，较高的可容空间增加速率与较高的泥炭聚集速率相平衡，有利于泥炭/煤的聚集。煤层主要在层序SIII1、层序SIII2及层序SIII3中发育，由于古气候逐渐变得干燥，层序SIII4和SIII5聚煤作用变弱直至终止。
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| 关 键 词： | 下-中侏罗统 层序地层 河湖相 岩相古地理 聚煤规律 |
| 收稿时间： | 2019-01-28 |
Sequence-palaeogeography and Coal Accumulation from the Early and Middle Jurassic in the Xidatan Area of the Northern Qaidam Basin |
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| Institution: | 1.College of Geosciences and Survey Engineering, China University of Mining & Technology(Beijing), Beijing 100083, China2.No. 105 Exploration Team, Qinghai Administration of Coal Geology, Xining 810007, China |
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| Abstract: | The Xidatan area has become a new area of exploration for coal resources in recent years, and the coal measures are represented by the Early Jurassic Xiaomeigou Formation and the Middle Jurassic Dameigou and Shimenggou Formations. In order to unveil the coal distribution in this area, we studied the sedimentary facies, sequence stratigraphy, coal accumulation, and lithofacies palaeogeography and analyzed the regional coal accumulation by using data from outcrop sections, borehole cores, and logging curves. The coal measures are composed of conglomerates, sandstones, siltstones, mudstones, oil shales, and coals. A total of 16 lithofacies types were identified, and three types of sedimentary facies were recognized, including alluvial fan, braided fluvial delta, and lacustrine, which constitute an overall fluvio-lacustrine setting. According to recognition of the regional unconformities, sedimentary facies reversal surface, base of incised valley fill sandstones, and abrupt changes in color and lithology, we have identified 6 sequence boundaries and have subdivided the coal-bearing strata into 6 third-order sequences and related low-stand, transgressive, high-stand systems tracts.The lithological data of each third-order sequence were statistically counted, and the stratal thickness contours and the sandstone/mudstone ratios were drawn. Based on these contours, lithofacies paleogeography maps of each sequence were reconstructed. The major paleogeographic units include an alluvial fan, braided river delta, littoral-sublittoral lake, and profundal lake. The thick coals were formed in the lower delta plain environment, which is typical for a low accommodation setting, around the maximum flooding surfaces where the higher rates of peat accumulation were balanced by the higher rates of accommodation creation. The coal accumulation mainly took place in sequence III1, sequence III2, and sequence III3, and due to the occurrence of relatively arid palaeoclimates, the coal accumulation weakened and even ceased during sequence III4 and sequence III5. |
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