萍乡坳陷安源组沉积环境与成煤模式分析

Analysis of Sedimentary Environment and Coal-forming Pattern of Anyuan Formation in Pingxiang Depression

萍乡地区位于萍乐坳陷西部,其安源煤系(安源组分为紫家冲段、三家冲段、三丘田段)储量丰富。不同层段煤层发育特征差异显著,对于不同层段的成煤环境的认识不一。以安源组野外露头剖面和煤田地质资料为基础,开展了安源组3个段的沉积环境和岩相古地理分析。结果表明,安源组紫家冲段和三家冲段的沉积环境主要为海陆交互环境中的有障壁海岸堡岛体系,三丘田段为浅水三角洲沉积体系;煤系的发育分布受沉积微环境控制,泥炭沼泽微相为主要聚煤场所;紫家冲段沉积期为主要成煤期,为海进背景下的海湾泻湖-潮坪成煤模式,滨海平原的泥炭沼泽是主要成煤环境,形成的煤层分布广、厚度大、结构单一;三丘田段沉积期为海退背景下的为浅水三角洲成煤模式,煤层主要产出于三角洲平原分流河道间泥炭沼泽,形成的煤层较薄、灰分较高。

Pingxiang area is located in the West of Pingle depression and the Anyuan coal reserves( which divided into Zijiachong Member,Sanjiachong Member,Sanqiutian Member) are abundant. The development characteristics of different layers of coal seams were significantly different and the understanding of the coal forming environment of each layers is different too. Based on coalfield outcrop and group geological data,analysis of sedimentary environment and lithofacies paleogeography of Anyuan formation were carried out. The results show that the sedimentary environment of Zijiachong member and Sanjiachong member is fort island system,; the sedimentary environment of Sanqiutian member is shallow water delta system. The development and distribution of coal seam are controlled by the sedimentary environment. Peat bog microfacies and delta plain distributary channel between swamp microfacies are the main coal accumulating places. Zijiachong sedimentary period is the main coal forming period,as the gulf lagoontidal flat coal forming pattern under the background of transgression,and peat swamp is the main coal forming environment and coal forming has a wide distribution,big thickness and a single structure; the coal forming pattern of Sanqiutian member is shallow water delta under the background of regressive and coal is mainly produced in delta plain distributary interchannel swamp,and coal forming has a thin thickness and a high ash content.