羌塘盆地晚三叠世构造属性与层序地层格架下聚煤特征

依据近年来最新资料,通过对羌塘盆地南、北边界构造带构造属性、地球动力学机制及构造演化历程的讨论,剖析了羌塘盆地晚三叠世构造属性与盆地演化历程;在对盆地内部不同位置上三叠统岩性、岩相研究的基础上,通过不同古地理背景下层序界面与体系域界面的识别,建立了羌塘盆地晚三叠世层序地层格架,讨论了煤层在层序格架下的位置、聚煤特征及空间分布规律。研究表明,羌塘盆地晚三叠世为一复杂叠合盆地,经历了晚三叠世早、中期被动陆缘盆地,晚三叠世晚期羌北前陆盆地和羌南被动陆缘裂陷-坳陷盆地等不同的盆地演化历程;上三叠统构成一个完整的构造层序和两个三级层序,煤层位于高位体系域中上部,主要受控于高频率低级次海平面变化。具含煤岩系厚度大,煤层层数多,单层厚度小的特征;三角洲平原地带有利于煤层发育,三角洲沉积体系沿分割羌南、羌北盆地的中央隆起带发育,进一步指出该带是羌塘盆地内今后重要的找煤方向,并得到新发现的赛包玛煤点验证。

The Structure Characteristics and Coal-Accumulating Features Under Sequence Framework in the Late Triassic of Qiangtang Basin

Based on the geological data in recent years, by discussing the structural attribute, geodynamic mechanism, structural evolution course of the south and north boundary structural belts of Qiangtang Basin, we analyzed the evolution and structural attributes in the late Triassic of Qiangtang Basin. On the basis of researching the Upper Triassic lithology, lithofacies in different locations within the basin, we established sequence stratigraphic framework in the Upper Triassic by Identifying Sequence interface and systems tract interface under the different ancient geographical backgrounds, and discussed the location of coal-bed in the sequence stratigraphic framework, the coal accumulation characteristics and spatial distribution law. The results show that the Qiangtang basin was a complex superposition basin in the Upper Triassic, and experienced the passive continental margin basin at the early and mid-stage in Late Triassic, the Foreland Basin in the northern Qiangtang and the passive continental margin rifting- depression basin in the southern Qiangtang at the late-stage in Irate Triassic. The coal-bed was located in the middle-upside of the highstand systems tract, which was mainly controlled by high-frequency and low-grade seadevel changes. There are the characteristics of the big thickness of coal-bearing formation, the muti-layer of coal-bed, small thickness of the single coal-bed. The belt of delta-plain was conducive to coal accumulation. The delta depositional system had developed along the basin central uplift belt. It is an important direction to search for coal in the Qiangtang basin. This view has been proved by the newly discovered Saibaoma coal-points.