沁水盆地晚古生代含煤地层物源转换关键时期及其对盆山耦合的响应

The sedimentary sequence and sequence stratigraphic framework of coal-bearing strata have established the material and physical basis of the superposed gas-bearing system, and they are the precondition for identifying the system. The detrital zircon isotopic results of the coal-cearing strata of Qinshui basin record a dramatic provenance shift. This proposed study systematically carries out the research on sedimentology, mineralogy, geochemistry, geochronology and zircon morphology to sedimentary rocks of Benxi-Taiyuan-Shanxi Formations in different sections (Shouyang-Yangquan, Yushe-Wuxiang, and Jincheng-Yangcheng), Qinshui basin. Based on the sedimentary structure, Zircon-Tourmqline-Rutile (ZTR) maturity index and paleocurrent characteristics, the provenance orientation will be analyzed. Combined with fragmentary minerals and heavy minerals composition, rare trace element characteristics and cathodoluminescence of minerals, we will analyse the parent rock types and tectonic environment. Combined with zircon U-Pb geochronology, Lu-Hf isotopic, geochemical and morphological features, we will conclude the space-time distribution characteristic of zircons, confirm provenance and the accurate layer of dramatic provenance shift occurred. According to the recognized sequence boundaries, we discuss the relationship between the accurate layer and sequence boundary, and then construct a high-resolution sequence framework. Moreover, we initially built source-to-sink community, and systematically discuss the relationship between provenance shift and tectonic evolution process of provenance area, which is helpful to predict the rich accumulation area of coal-bearing gas.

含煤地层的沉积序列和层序地层格架奠定了煤系叠置含气系统的物质和物性基础，是识别叠置含气系统的前提。基于沁水盆地晚古生代含煤地层物源区由南向北发生转换这一事实，本项目拟以沁水盆地北部寿阳-阳泉、中部榆社-武乡和南部晋城-阳城三个典型剖面的本溪组、太原组和山西组为研究对象，综合运用沉积学、矿物学、地球化学和同位素年代学等理论与方法，以沉积构造、重矿物ZTR指数和古流向特征为基础，限定物源方向；以碎屑组分、重矿物组合、微量/稀土元素和矿物的阴极发光特征为约束，分析物源区母岩类型和构造环境；以碎屑锆石年代学、同位素和稀土元素特征为基础，揭示碎屑锆石的时空分布特征，限定物源区及物源转换的关键层位；以层序界面的识别为基础，明确物源转换关键层位与层序界面的关系，构建高分辨层序地层格架；在此基础上，初步建立源-汇体系，系统探讨物源转换与物源区构造演化的耦合关系，为盆地内煤系气富集区预测提供地质依据。

含煤地层的沉积序列和层序地层格架奠定了煤系叠置含气系统的物质和物性基础，是识别叠置含气系统的前提。基于沁水盆地华北石炭—二叠系标准煤系地层剖面的岩性组合、沉积构造特征，将该区域晚古生代含煤地层划分20个短期基准面旋回、7个中期基准面旋回和3个长期基准面旋回。层序界面相邻地层的地球化学和碎屑锆石形态学研究结果显示Mn/Fe、Mn/Ti、V/Ni、Th/U比值与∑REE和δEu等地球化学指标在中期基准面沉积旋回内变化趋势一致，对不同级别的基准面旋回均有良好的对应关系，锆石长轴平均值和锆石的长宽比值对中期和长期基准面旋回有较好的响应。沁水盆地北部晚古生代本溪组地层中碎屑锆石的年龄以早古生代和晚古生代为主，太原组地层中碎屑锆石年龄主要分布以晚古生代晚石炭-早二叠世为主，未发现早古生代年龄的碎屑锆石，山西组和下石盒子组样品的碎屑锆石年龄均以晚石炭-早二叠世为主，但山西组顶部样品中发现少量早古生代碎屑锆石。本溪组沉积时，沁水盆地整体受控于南部北秦岭的阶段性隆升，随着古亚洲洋的持续俯冲，华北北缘的内蒙古隆起发生剧烈抬升，沁水盆地北部的物源区发生变化；山西组沉积时，内蒙古隆起再次剧烈抬升，南部开始接受来自内蒙古隆起的碎屑物质；北部山西组顶部地层中的早古生代碎屑锆石来源于华北北部的岛弧，但在南部山西组地层中并未发现，表明其影响范围有限。这一研究成果为研究区内叠置含气系统的开发提供了地质基础。