Study On The Sedimentary Systems Of Neogene Of Chepaizi Area In The Northwest Edge Of Junggar Basin

Chepaizi salient is one of the important exploration blocks in Junggar Basin,the exploration and practice data show that there's potentiality to find oil and gas fields in the Neogene Shawan Formation. This paper proposes the research of the depositional systems of the Neogene strata in Chepaizi area,and take the Shawan Fm and Taxihe Fm as the major target layer. Considering the guidance of theories of sequence stratigraphy, sedimentology, geology of petroleum and so on, including the information of field outcrop,rock core,seismic,well logging,mud logging and so on, we did a systematic research on sequence stratigraphy, sediment sources,depositional systems for Neogene strata in Chepaizi area. By the methods of structural geology and tectonics,geology,logging,seismic,sequence stratigraphy,sedimentology etc..The Neogene Shawan Formation and Taxihe Formation in Chepaizi area was recognized four third order sequences interfaces and divided into three third order sequences,and the SQ1 corresponding to N1s1,the SQ2 corresponding to upper N1s2 and N1s3,the SQ3 corresponding to Taxihe Formation;On the basis of the sequence division,combined with sequence boundaries and systems tract boundaries characters,we recognized three systems tracts in every sequence,the result as follows:lowstand systems tract,transgressive systems tract,high systems tract. Then we established isochronous stratigraphic framework of N1s and N1t in Chepaizi area.By using sedimentary tectonic features,maturity analysis of sandstone composition etc.,we found that the source area of northern foot of Mt Zaire is the source supply area of Neogene. Guiding with the theory of modern sedimentology,considering single well facies analysis,across-well analyses,seismic facies analysis,synthetic analyses of sedimentary facies and combined with provenance analysis,tectonic background ect., braided delta depositional system and lake system are recognized from Chepaizi area. At the period of lowstand systems tract and transgressive systems tract of the SQ1 and SQ2 of Braided Delta Depositional System,braided fluvial delta front were developed ,among which the underwater distributary channel and mouth bar are the main facies belts; and at the period of high systems tract of SQ2 and SQ3,there is a chief subfacies and several microfacies,such as braided river delta plain subfacie, braided distributary channel and flood plain microfacies. For the lacustrine system, the chief subfacies is coastal and shallow lake which mainly produce the mud in offshore-shallow lake microfacies,and there is also sand bar microfacies. The planar distribution of the two Depositional systems in every periods of system tract was discussed in details, and the evolution model of Neogene sedimentary facies are built.