Analysis Of Sedimentary Environment On Boli Coal Basin Of Cretaceous Coal Series

Boli Basin, in the east of Heilongjiang Province, is the largest fault basin in mesozoic. The denudation boundary located in north of the basin, the Yilan ~ Boli fracture in the southwest, the Xingnong~ Xingkai fracture in the south and the Feide fracture in the southeast. The faults in the basin are very developed and geological structures are complicated.Located in the eastern of Heilongjiang Province in Northeast China, Boli Basin is the unique area contained the marine sedimentary in Mesozoic. Complex and complete sedimentary facies--marine, continental and transitional were frequently alternating. Boli Basin's development can be divided into four stages: early chasmic stage, expansion chasmic stage, expansion sedimentary stage and depression dwindling stage.Coal measure strata of Boli Basin include Jixi group and Longzhaogou group. The coal-bearing strata's main features are large thickness, wide distribution, multiple coal seams and complete coal type. Jixi group located in western Huanan depression and central Qitaihe depression. Longzhaogou group mainly located in Baomi depression. All of petrofabric contains coal, but the best is Chengzihe formation.It is the characteristics of Boli Basin in the eastern part of Heilongjiang Province's various basins that settlement earlier and sediment thickness, multi-transgression, transgressive wide range, intense volcanic activity ect. Sedimentary basin evolution is obviously controlled by the tectonic evolution.Boli basin basement is constituted by Proterozoic, together with upper Paleozoic, upper Triassic and Indo-Proterozoic granite. The major strata filling in the basin are Longzhaogou Group and Jixi group of Lower Cretaceous, Hua shan group of Cretaceous, Upper Cretaceous, Tertiary and Quaternary. Lower Cretaceous in the southern Basin is developed, but the northern missing seven Hulin formation and eastern missing Muling formation.The stratigraphic framework which is made up of thickness, and geometry, accumulation of the nature, relationship in Boli Basin shows faulted-depressed basin sedimentary filling characteristics. Overall thickness features of sedimentary strata in the east, south are thicker than north and west.Belts of coal bed accumulated in Boli Basin are offshore water. The regressive~ transgressive sedimentary cycle that formed by sea level uplift and sag controled deposition of coal seams, formed poly sea coal deposits alternating sequence. Basin-fill sequence is Didao (transgression period), Chengzihe (regression period) that contained coal from the interior plains and coastal plains, formed a large coal basin. Muling formation is clastic deposition form inland basin.In Boli Faulted Basin coal-accumulating belt and rich coal center is affected by basin in subprime homozygous uplift and sag control. So in the same period it is not the whole basin all coal-accumulating, but only in a part basin coal-accumulating. Coal-accumulating belt have coal center difference with the poverty. Therefore, from the perspective of the whole basin Boli Basin coal seam layers are locally.