贵州七星关地区含煤岩系龙潭组沉积微相特征及沉积环境

Sedimentary Micro Phase Characteristics and Sedimentary Environment of Longtan Formation Coal Bearing Rock Series in Qixingguan Area of Guizhou

二叠系龙潭组是贵州中-西部地区重要产煤层位,在特定的地质条件下富集REE、铀(U)、钪(Sc)、铌(Nb)等关键金属元素,是潜在的稀有金属矿产资源。开展毕节七星关区二叠纪龙潭组沉积微相和沉积环境分析,对研究REE、Li、Nb、Ti等关键金属元素的时空分布特征和富集规律具有重要意义。本文以野外实测剖面为基础,结合岩矿鉴定、古生物化石等,对龙潭组岩石组合关系和沉积微相特征进行分析研究。根据岩石组合特征将研究区龙潭组分为三段,其岩性主要以灰色-深灰色粉砂岩、砂岩、炭质粘土岩夹煤层组成,夹6-45层煤,发育海相介壳化石及陆相植物化石Pecopteris sp.等,厚150210 m。同时,确定研究区龙潭组属海陆过渡相之三角洲沉积,划分了三角洲平原、三角洲前缘和前三角洲3种亚相以及分流河道、决口堤等9种沉积微相,并分析探讨该时期龙潭组三个岩性段的沉积环境,认为三角洲平原亚相中分流间湾(IB)和沼泽(SW)微相等有利于粘土矿物和有机质沉积的环境为稀土REE、Li等金属元素的富集提供了有利条件。

Longtan formation of Permian is an important coal seam in the middle and west Guizhou,REE,U,Sc,Nb and other key element concentrated in some special geologic condition,so it’s a potential are for rare mineral resource.The analyses on the sedimentary phase and sedimentary environment of Lontan formation,Permian in Qixingguan district of Bijie has important significance for study the time-space distribution of REE,U,Sc,Nb and other key metallic element.In this paper,base on the field measured section,combine with rock indentify,paleontological fossil and so on,the rock association relation of Longtan formation and sedimentary microfacies characteristics are studied and analyzed.According the rock association characteristics,the Longtan formation in the study area is divided into 3 sections,their lithology include gray-deep gray siltite,sandstone,carbonaceous claystone with coal seam 6 to 45 seams,marine shell fossil and continental plant fossil Pecopteris sp.developed which the thickness is 150 to 210 m.Meanwhile,the Longtan formation in the study area is ensured to be sea-land transient phase delta deposit,3 secondary phase(delta plain,delta edge and delta)and 9 sedimentary micro phase(distributary channel,breached dike and so on)are divided.The sedimentary environment of three lithologic members in Longtan formation of this period are discussed and analyzed,it’s thought that the diversion bay and swamp micro phase in the delta plain secondary phase are favorable for the sedimentary environment of clay mineral and organic matter,it affords beneficial condition for the concentration of REE,Li and other metal elements.