Abstract:

Comprehensively using the lithologic association, drilling core, logging, geochemistry and palaeontology data, combining structural evolution and seismic reflection feature, 7 third-order sequence boundaries are identified and 6 sequences，16 system tracts are classified in Lower Cretaceous of Chagan depression. In the early phase, sequences in the south and west were thicker. Lately, the depocencer migrated to the north, and the sequences of the west and north were thicker. The sedimentary framework was different between the west and east in early phase because of the Maodun sub-arch, but subsea apron, fan delta and braid river delta were the main depositional system totally. Lately, Maodun sub-arch deposited to alluvial plain, bet lands, and fluvial facies. Three source rock-reservoir-cap rock assemblages in Lower Cretaceous  were developed. In the lower part, the reservoir of the LST was covered by the mudstone of the TST and the selfgeneration; selfreservation source rock-reservoir-cap rock assemblage was formed. In the middle part, the reservoir developed in the HST of the SQ2 and the LST of the SQ3. The reservoir  in the upper part consists of clastic rock of SQ4-SQ6 and volcanic rocks.

Key words: Chagan depression, Lower Cretaceous, sequence stratigraphy, depositional system