HIGH-PRECISION SEQUENCE STRATIGRAPHY IN QIONGDONGNAN BASIN

The principle of and method for the contemporary sequence stratigraphy are both employed to analyze comprehensively the references on seismology, logging, and cores. This comprehensive analysis shows that the Qiongdongnan basin may have experienced two major growth stages: the early rift stage and the late depression stage, corresponding to the two supersequence sets: Tejas A and Tejas B. In addition, five supersequences were formed that corresponded to the five evolutionary stages in the basin: nonmarine facies, marine transitional facies, growth fault, ramp, and passive continental setting. The unconformity and its counterpart, the conformity, both serving as the third-order sequence boundaries are employed to identify 19 sequences containing 57 systems tracts, over 54 parasequence sets and over 196 parasequences. The major differences between different evolutionary stages and between different sedimentary sequences in the basin are both attributed to the different sedimentary system contained in the lowstand systems tract. On the basis of the reconstruction of the paleo-environment settings, have been established the models of depositional sequences. The accomodation analysis is applied to the compilation of the sea-level change curve of the Qiongdongnan basin, resulting in the discovery of the perfect matching between the three major marine floods that occurred in the middle Lingshui, early Meishan and early Yinggehai stages, and the corresponding globe changes. The best potential hydrocarbon resources are located vertically in the section between the marine transgressive systems tract and the condensed section, but laterally between the outer-shelf to the continental slope. The next best potential hydrocarbon resources are located in the littoral-aquamarsh deposits or in the marine-continental transitional facies. This paper suggests that the lowstand wedge and the slope fan near the continental-shelf slope break should serve as the petroleum exploration target of the hidden traps worthy of attention.