Abstract:

There was a topographic break in the northeast edge of Junggar basin during Jurassic Period.Middle-Lower parts of Jurassic can be divided into 4 sequences according to sequence boundaries,such as unconformity and thick coal bed.Lowstand system tract,lacustrine transgression and highstand system tracts in the interest area can be subdivided by the repeated pattern of stratigraphy,locally distribution of coal-bearing measure and the location of topographic break in sedimentary sequence.Lowstand system tract is characterized by the incised valley(braided river) sediment,lacustrine transgression system tract is represented in nature by the widespread of lacustrine sediment and highstand system tract is featured by the prograding delta.It is predicated that,on the basis of establishing a model of sequence stratigraphy of coal-bearing measure in lacustrine basin with a topographic break belt and analyzing the conditions of hydrocarbon accumulation,the incised valley in Lowstand system tract and distant lenticular sandbody in front of the delta in highstand system tract is the area where subtle trap formed.

Key words: lacustrine basin, coal-bearing formation sequence stratigraphy, subtle trap, Jurassic Junggar basin