梅河盆地古近系梅河组下部含煤岩系有机质富集模式

Organic matter accumulation pattern of coal bearing layers in the lower part of Meihe Formtion in Paleogene,Meihe Basin

揭示控制梅河盆地煤层分布和质量的因素以及不同环境下煤层的聚集规律,可进一步丰富梅河盆地的能源资料。梅河盆地为古近系富含煤层的断陷盆地,梅河组下含煤段为主要含煤层,在岩芯观察等相分析的基础上,下含煤段以扇三角洲和湖泊沉积为主,其中扇三角洲平原河道间沼泽和湖沼为主要聚煤场所。通过系统的有机地球化学分析,浅湖泥岩有机质类型主要为II1型,湖泊生物来源为主;扇三角洲前缘泥岩有机质类型主要为III型,陆源高等植物来源为主;扇三角洲平原河道间沼泽和湖沼煤有机质类型主要为II2型,陆源高等植物为主,含少量湖泊生物。生物标志化合物参数表明煤层形成于淡水还原环境中。湖沼成煤区域主要有3个,分布于盆地东南侧,厚度大且层数多,平原成煤区仅一个,位于盆地西南侧,厚度小且层数少。保存条件较好的浅湖沉积物中有机质丰度较高,保存条件较差的扇三角洲前缘泥岩有机质丰度最低,扇三角洲平原沼泽因保存条件不稳定而形成厚度较小的煤层;而在静水还原的湖沼环境中则沉积了稳定的工业可采厚煤层。

The aim of this study is to reveal the factors controlling the distribution and quality of coals as well as the accumulating regulations of coal seams in various sedimentary facies,which will further enrich the data of energy resources in Meihe Basin. Meihe Basin is a Paleogene fault basin where is rich in coal seams,and the lower coal-bearing member is the main layer. Based on sedimentary facies analyses,this member is mainly filled with fan delta and lacustrine sediments,and the fan delta plain and limnetic subfacies are main coal-accumulation environment. According to systematical organic geochemical analysis,the type of organic matter from shallow lake mudstone is II1 and the sources are mainly aquatic organisms; the type of organic matter in fan delta mudstones is III,the sources are mainly higher plants; the type of fan delta plain inter-channel swamp and limnetic mudstones is II2,the sources are mainly higher plants while a small amount of aquatic organisms are included. Biomarker characteristics show that the coal layers areformed in a freshwater reduction environment. There are three coal-accumulating areas of limnetic parts and they are all distributed in the southeast of the basin with huge thickness and multi-layers. There is only one fan delta plain coalaccumulating area,which is located in the southwest of the basin and the coal has a smaller thickness and fewer layers. The shallow lake mudstones having well preservation conditions are high in organic matter abundance,while the fan delta front mudstones owing poor preservation conditions have the lowest organic matter abundance. The fan delta plain swamp has unstable preservation conditions,thus forms smaller thickness coal seams,the limnetic reduction environment with standing water deposits industrial minable thickness seams.