华北晚古生代陆表海盆地海侵事件微观沉积特征及成煤探讨

采用沉积学、煤地质学、古生物学、地层学及地球化学等多技术手段,结合比较分析法的思路,分析了事件型海侵的特点和海侵事件沉积组合特征,研究发现:海侵事件沉积组合为区域对比性强、具沉积时间连续性与相序间断性的暴露沉积-煤层-灰岩组合,其关键沉积学特征是煤层底板的暴露沉积.海侵事件组合灰岩的古生化石个体小、破碎强烈等特征表现为高能量水体运动等环境,孢粉表现为低含量的单缝孢和裸子植物及高含量的三缝孢.地球化学分析表明暴露沉积为陆相环境,煤层中的微量元素表现为海相主要原因是由于泥炭沼泽覆于深水后受海水影响所致.海侵事件成煤与海侵过程成煤差异体现在两个方面:第一,盆地属性差异,即海侵事件成煤形成于陆表海盆地之中,而海侵过程成煤则形成于具有缓坡的边缘海盆地,第二,成煤原理存在着差异,海侵事件成煤强调的是成煤前海侵未发生前的碎屑体系废弃而发育大量泥炭沼泽且被后期突发性海侵终止,而海侵过程成煤则强调的是泥炭沼泽发育于滨海的活动碎屑体系并终止于后期的缓慢海平面上升.

Discussion on Micro-characteristics of Transgressive Event Deposition and Its Coal-forming Mechanism in the Late Paleozoic Epicontinental Sea Basin of North China

The characteristics of the event transgression and its depositions have been studied by ways of sedimentology, coal geology, paleontology, and geochemistry association with comparative analysis. The results are as follows. The sedimentary assemblage (exposure deposition, coal seam and limestone) have characteristics of regionally correlative, the successive deposition, and facies gap. The key identification mark is the exposure deposition under coal seams. The paleontology has small size and is broken into some fragments. All the characteristics can proof paleontology the depositional environment of high energy water. And there are lower content of monolete spore and Gymnosperm with higher content of trilete spore in the transgressive event deposition. The author found the depositional environment of different beds. The exposure deposition formed in terrestrial environment. Coal beds were formed in the peat moor and preserved under the sea water. Then the differences between transgressive event coal and transgressive process coal can be concluded. Firstly, there are differences in basin characteristics. The transgressive event coals are often found in epicontinental basin while the transgressive progressive coals are found in marginal basins. Secondly, there are differences in coal-forming principle. The former theory emphasis that the peat moor were formed in the abandon stage of the clastic system and then were stopped by the event transgression, the later think that the peat moor were formed in the coast of activity system and were stopped by the slow transgression.