山西平朔矿区上石炭统太原组11号煤层沉积地球化学特征及成煤微环境

Geochemistry characteristics and sedimentary micro-environments of No.11 coal seam of the Taiyuan Formation of Upper Carboniferous in Pingshuo Mining District,Shanxi Province

山西平朔矿区上石炭统太原组11号煤层具有中硫、高灰、较高有机硫的特征,但其中各煤分层的基本性质差异较大,指示其成煤微环境显著变化。地球化学研究表明,Ca/ (Ca +Fe)、Th/U、Al/Ti、V/Zn、δEu、δCe可作为指示11号煤层沉积水介质盐度的标志,St,d、So ,d/Sp,d可分别作为指示水介质氧化还原程度和酸碱度的标志,Ad、V/I、ΣREE可作为指示水介质动力条件的标志。在此基础上,分析了该煤层成煤微环境特征及其演化历程,认为11号煤层形成于波动式海进的半咸水—咸水沉积环境。在此过程中,海水对泥炭沼泽的影响经历了3个发展阶段:第1阶段,泥炭形成于微咸—半咸水条件,水动力条件逐渐增强;第2阶段,泥炭形成于半咸水—咸水条件,水动力条件总体上相对较强,沼泽水体从逐渐加深演化为显著变浅;第3阶段,泥炭形成于半咸水环境,海水影响再次逐渐增强,在泥炭沼泽演化末期水体显著变深,动力条件明显减弱,还原性显著增强。

The No.11 coal seam of the Taiyuan Format ion of Upper Carboniferous in the Pingshuo Mining District is generally characteristic of the medium-s ulfur, high-ash and high-organic sulfur,but there are great differences in the ess en tial identifications among the coal layers,which might imply the remarkable div ersification of the coal-forming micro-environments.The results show that th e C a/?(Ca+Fe),Th/?U,Al/?Ti,V/?Zn,δEu and δCe could be used as the sa linity indica tors,the S t,d and S o,d/?S p,d respectively as the Eh and pH ind icators,and the A d,V/?I and ΣREE as the water-dynamic indicato rs.Based on the indicators,the coal-forming micro-environments and the evolution of th e seam were analyzed.It was considered that the seam was formed under the bracki s h-saline water micro-environments with the fluctuant transgression and the e ffect of the paleo-seawater on the peat swamp experienced three stages.The pea t wa s formed in the slightly brackish-brackish micro-environment with the gradua l ly reinforced water-dynamic condition during the first stage,in the brackish- salt water micro-environment with the rather strong water-dynamic condition d ur ing the second stage,and in the brackish micro-environment with the distinctly weakened water-dynamic condition during the third stage.