Factors controlling the distribution of oil shale layers in the Eocene Fushun Basin, NE China
Factors controlling the distribution of oil shale layers in the Eocene Fushun Basin, NE China
复制标题
抚顺盆地始新世油页岩层分布控制因素
DOI：
10.1016/j.marpetgeo.2021.105350
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发表时间：
2021-10-01
影响因子：
4.2
通讯作者：
Ma, Lin
中科院分区：
文献类型：
--
作者：
Li, Yuanji;Sun, Pingchang;Ma, Lin
抚顺盆地是一个典型的陆相盆地，沉积岩以煤、油页岩和灰绿色泥岩为主，富含有机质。目前，对该盆地的研究主要集中在煤和油页岩中有机质的富集机理以及煤层转化为油页岩的控制因素。但在转化阶段，油页岩沉积停止，转化为灰色绿色泥岩与油页岩薄层互层。这种沉积序列的控制机制尚不清楚。本文以吉军屯组上部（Ⅰ单元）厚层油页岩和西楼田组（Ⅱ、Ⅲ单元）高频互层泥岩和薄油页岩为关键层进行了分析。有机和无机地球化学数据进行了分析，重建的各种类型和来源的有机质和控制因素，包括古气候，古风化，生物生产力，陆源碎屑输入，古盐度和氧化还原条件的转换。其中，I单元主要受潮湿气候影响。水深、水量大，陆源碎屑输入量少。淡水藻类大量繁殖和缺氧条件导致了有机物的供应，这些有机物被保存得很好。这进一步导致了沉积岩中有机质的高丰度。第二单元受半湿润-半干旱和干旱气候条件的影响。湖泊变浅，陆源碎屑物质输入和湖泊古盐度增加，这些变化代表了从淡水到微咸水的过渡阶段。该湖仍然呈现亚氧/缺氧条件，但生物生存空间减少，导致有机质供应有限，沉积物中有机质丰度低。单元III受半湿润-半干旱气候条件的影响，古盐度持续升高。湖水微咸，生物生产力高，水量减少，有机物供应有限。但由于湖水呈微咸水分层，形成了强缺氧环境和良好的保存条件，导致有机质丰度较高。综合分析认为，古气候引起的环境变化是促使抚顺盆地油页岩沉积停止并开始存款灰色绿色泥岩和薄层油页岩的主要因素。
The Fushun Basin is a typical continental basin filled with organic-rich fine-grained sedimentary rocks, such as coal, oil shale and greyish green mudstone. Currently, research on this basin predominantly focuses on the enrichment mechanisms of organic matter in coal and oil shale and the controlling factors of coal seam trans-formation to oil shale. However, during the transformation stage, the deposition of oil shale ceased and was converted to interbeds of grey green mudstone and thin oil shale layers. The control mechanism of this type of sedimentary succession is still not clear. In this study, the thick oil shale in the upper part of the Jijuntun For-mation (Unit I) and the high-frequency interbedded mudstone and thin oil shale in the Xiloutian Formation (Units II and III) were analysed as key strata. Organic and inorganic geochemical data were analysed to reconstruct the transformation of the various types and sources of organic matter and controlling factors including the palaeoclimate, palaeoweathering, bioproductivity, terrigenous clastic input, palaeosalinity, and redox conditions. Among these, Unit I was affected by humid climate conditions predominantly. The water depth and volume were large, and the input of terrigenous debris was low. Freshwater algae blooms and anoxic conditions led to a supply of organic matter and that was well preserved. This further resulted in a high abundance of organic matter in the sedimentary rocks. Unit II was affected by semihumid-semiarid and arid climate conditions. The lake became shallower while terrigenous clastic input and lake palaeosalinity increased; these changes represented the transition stage from freshwater to brackish water. The lake still exhibited sub-oxic/anoxic conditions, but the biological living space decreased, resulting in a limited organic matter supply and a low abundance of organic matter in the sediment. Unit III was affected by semihumid-semiarid climate con-ditions, and the palaeosalinity continued to increase. The lake had brackish water, with a high bioproductivity, a decreased water volume and a limited supply of organic matter. However, brackish water stratification occurred in the lake, which created a strongly anoxic environment and good preservation conditions, resulting in a sec-ondary high abundance of organic matter. A comprehensive analysis indicates that the environmental change caused by the palaeoclimate was the main factor driving the oil shale deposition to cease and the onset to deposit grey green mudstone and thin oil shale in the Fushun Basin, Northeast Asia.