Abstract:

Multistage slope break zones which are well developed on the northwestern edge of Junggar basin significantly control the development of sequence stratigraphy, overlapping and superimposition of strata, vertical lithologic combinations and vertical and lateral distribution of sediments. The control of multistage slope break zones on non-structural traps are mainly represented as follows:1) Non-structural traps are developed closely near the multistages slope break zones, and distributed in beaded occurrence along the slope break zones. 2) The development of non-structural traps is vertically characterized by their inheritance. 3) The types of non-structural traps vary with the geographical positions of the slope break zones. Non-structural traps would mainly be developed as stratigraphic overlaps and truncations in the slope break zone near basin edges, stratigraphic traps would gradually decrease basinward and then mainly become stratigraphic-lithologic or lithologic traps. The existence of multistage slope break zones would correspondingly lead to various erosions and depositions at different geographical positions in the basin, and control the combination of reservoirs and seals in non-structural traps. In addition, fractures developed in faulted slope break zones and fissures developed in flexural slope break zones would act as migration pathways, and would be favorable to hydrocarbon migration and accumulation. The structures deeply buried in the slope break zones would often be advantageous to hydrocarbon accumulation, thus the slope break zones would also be the favorable sites for accumulation of hydrocarbons that migrate vertically upward and redistribute from the earlier hydrocarbon accumulations at depth.

Key words: Junggar basin, Jurassic, downwarped lake basin, slope break zone, non-structural trap