燕山地区冀北坳陷元古界下马岭组沥青砂岩岩石学特征和沉积环境

通过对冀北坳陷中新元古界下马岭组进行剖面实测,对下马岭组底部的沥青砂岩进行室内薄片鉴定和扫描电镜分析,观察与分析了下马岭组沥青砂岩的出露分布特征,镜下研究了此砂岩的碎屑颗粒和填隙物的组分特征和磨圆、分选、粒度等结构特征,依据岩石学特征、粒度分析系列参数等研究了沥青砂岩的沉积环境。结果表明此砂岩为成分与结构成熟度均高的纯石英砂岩和石英砂岩,硅质与沥青质填隙、沥青含量达5%~15%,细粒为主,分选好到极好。粒度分析是本段松散状沥青砂有效环境判别标志。综合分析认为下马岭沥青砂岩形成于无障壁海岸体系的滨浅海环境,形成于前滨到临滨的海相高能环境,可能的沉积位置是前滨下部到中上临滨;此砂岩主要来自临滨潮下高能带的沉积物、含部分前滨下部沉积物、也夹少量潮汐水道沉积物。不同剖面位置所处的沉积环境不同,凌源地区和平泉地区为临滨带的中上部的水下高能带沉积为主,宽城地区为临滨带上部沉积和前滨下部沉积,凌源地区和宽城地区也包含少量的潮汐水道沉积。

Petrologic characteristics and sedimentary environments of bituminous sandstone in the Proterozoic Xiamaling Formation of Jibei Depression,Yanshan region

We detail measured the Xiamaling Formation outcrops in Jibei Depression and carried thin section analysis and SEM observation on the bottom section of massive bituminous sandstone. A sedimentary environment analysis was carried by studying the distribution of bituminous sandstone,composition of the rock such as ratio of the clastic grain and interstitial materials,structure such as sorting, rounding, grain size,and petrological features. The outcome indicates the bituminous sandstone was composed mainly by high maturity quartz sandstone with 5%~15% bitumen filled within the intergranular pores. The sandstone was mainly fine grain sandstone and was well or extremely well sorted. The comprehensive analysis shows that the sedimentary environment of the bituminous sandstone in the Xiamaling formation was high energy foreshore to shoreface with no barriers. The probably depositional position of the bituminous sandstone was located between the lower foreshore to middle-upper shoreface. Besides,tidal channels also contribute sediments to the bituminous sandstone. The sedimentary environments in each measured outcrop profile was varies. The Lingyuan and Pingquan profiles mainly are high energy middle-up shoreface environments,while the Kuangcheng profile mainly are upper shoreface and lower foreshore environments. The Lingyuan and Kuangcheng profiles contain a few tidal channel deposits.