塞文煤盆地煤化作用研究

COALIFICATION STUDIES IN STEPHANIAN CEVENNES BASIN, FRANCE

本文以煤的挥发分百分含量为指标对法国斯蒂芬期塞文煤盆地的煤化作用和古地温进行了研究,综合考虑和比较等挥发分线与盆地基底表面、煤层和上覆中生代地层的几何形态之间的关系,可定性地识别对煤化作用起主导控制作用的3个基本条件:(1)基底的起伏性;(2)中生代地层的巨厚覆盖;(3)断裂作用。定量计算所得到的古地温梯度表明该盆地为一“热”盆地,结合盆地的沉积充填史和构造演化史,提出了多期煤化作用的演化模式。

The coalification of the Stephanian coal is studied based on the volatile matter percent (V %) ,and three main controls : 1. basement top relief ,2. the overlying thick Mesozoic series , 3. faulting, which are recognized according to the relation of isovol to the basement surface, to the coal seams , and to the geometry of Mesozoic base. The semiquantitative analysis results show that the coal basin was a 'heat' basin with a high geothermal paleogradient (4. 4 to 8 ℃/100m). The Cevennes coal basin shows a early pre-folding of Stephanian series and a post-folding coalification. The maturation of the oldest Stephanian coal was achieved prior to the folding and pre-Mesozoic deformation-erosion. Local anomalies in coalification have been caused by faulting role. The 4 main coalification stages are recognized by filling processes and tectonic evolution of basin. They are: 1. Stephanian: associated with a heterogeneous coalification, controlled by the dip of the basement surface; 2. between the end of Stephanian and the beginning of Mesozoic : folding of Stephanian series and their partial erosion .coalification stoped ; 3. deposition during Mesozoic period :progressive covering of Stephanian series under a thick overlying Mesozoic; reactivation of an homogeneous maturation throughout the basin; 4. after the end of Mesozoic (since 65 Ma) : deformation ,fracturation and erosion of the Mesozoic series, without increasing in coalification.