Accumulation And Potential Evaluation Of Jurassic Coal In Toksun Coalfield

Coal is the major energy sources of China. About 90% of the fossil energy resources are coal in China. In one hand, the exploitation of coal faces many crises in the east of China. In the other hand, the coal resource is much richer of Northwest China than that of in East China. Because of the good occurrence conditions, strong accumulations and wide distribution of rich coal, the coal resources in Northwest is top of China, and the potential of coal exploration and exploitation is huge. In this thesis, the date of drill samples, logs and seismic were collected, and the sedimentology, sequence stratigraphy, tectonic geology, coal geology and coal resources exploration theory were used to study the sedimentary boundaries, structure coal-control and the coal accumulations of Jurassic coal resources in Tokesun coalfield.Three third tectonic units and six fourth tectonic units were recognized based on the analysis of the structure characteristics of the basement, regional tectonic and coal bearing strata distribution. And the third tectonic units are consisted of Boluohuofu anticlinorium, Hami-Turpan fault depression and Bogeduo anticlinorium. The coalfield was deposited in the Small depression basin of Meso-Cenozoic which was superimposed on the marine-continental sedimentary basin of the late Paleozoic. The coalfield structures were mainly a series of synclines. The strata were steep in the edge of the basin but were smooth in the center of the basin.The tectonic evolution history of Toksun coalfield can be divided into four stages. The first stage was basin basement tectonics and evolution stage from Carboniferous to Late Triassic; the second stage was coal accumulating tectonic evolution during Jurassic; the third stage was post-coal tectonic evolution began in Yanshanian; and the fourth stage was rejuvenated foreland basin tectonic evolution during Neogene and Quaternary.Application of the date of drillings and outcrops, sequence stratigraphic framework was built. Based on second-order sequences whose boundaries were Kt1 and Jt1,4 pieces of third-order sequences were recognized. Furthermore, lowstand system tract, lacustrine transgressive system tract and highstand systems tract were also recognized. The SQ1 corresponded to the lower Badaowan Formation, SQ2 corresponded to the upper Badaowan Formation, SQ3 corresponded to the Sangonghe Formation, and SQ4 corresponded to the Xishanyao Formation, respectively.Coal accumulations mainly occurred in synsedimentary graben fault sags at east and west margins of the basin during Badaowan Formation and the coal-rich zones were located in Aiweiergou and Keerjian, the western of the basin. The coal accumulations were mainly developed in braided river, meandering stream overbank, river bend, and flood plain in Turpan, Hami and Qiatekaersu depressions in Early Xishanyao Formation.