| The Junggar Basin is located in the central part of the Central Asian Orogenic Belt(CAOB).It is not only an ideal place to study Paleozoic accretionary orogeny in Central Asia,but also an important petroliferous basin for deep oil and gas exploration.Therefore,carrying out a study of geological architecture and tectonic framework of the Carboniferous in the Junggar area is both with great scientific and petroleum industrial significance.In this thesis,based on a combination of outcrop,deep borehole,and seismic data,the distribution characteristics of the Carboniferous basin has been achieved.Combined with logging analysis,core observation,seismic facies,and other techniques,this paper finally revealed the filling process of the Carboniferous basin.Through quantitative analysis of geometric and kinematic characteristics of typical Carboniferous fault depressions,a structural model of two stages of"fault depression" is unveiled.On this basis,considering the tectonic evolution background in Central Asia,a comprehensive model of the evolution of the Carboniferous tectonic framework in the Junggar Basin and adjacent areas is proposed.Based on the analysis of petrology,geochronology,palaeontology stratigraphy and seismic stratigraphy,the Carboniferous can be re-divided from bottom to top into:the Dishuiquan Formation(C1d),the Songkaersu Formation(C1s),the Shuangjingzi Formation(C1-2s),the Batamayineishan Formation(C2b)and the Shiqiantan Formation(C2sq).Among them,the Dishuiquan Formation is a pre-rift sequence,which is mainly comprised of a set of marine coarse clastic rocks;The Songkaersu Formation is a synrift strata which is mainly composed of a set of subaqueous volcanic rocks intercalated with pyroclastic rocks;The Shuangjingzi Formation is a postrift sequence with a set of marine-continental transitional sedimentary rocks;The Batamayineishan Formation is a synrift sequence,which is mainly a set of subaerial volcanic rocks;The Shiqiantan Formation is a postrift sequence with a set of lacustrine and shallow marine clastic deposits.The Carboniferous structural layers are distributed in NW-SE direction,and could be roughly divided into 4 rows of sedimentary distribution belts as a whole.Among them,the second and third belts preserves the most Carboniferous,while only a few developed in the first and fourth belts.Specifically,the Songkaersu Formation is widely developed,and the Shuangjingzi Formation has a even larger distribution range.However,the distribution of the Batamayineishan Formation is relatively limited.The development of the Carboniferous strata is controlled by extensional faults,noticeably,forming two stages of typical "fault depression" structure feature.C1s and C1-2s are the rift and depression sequence of the first stage,while C2b and C2sq are the rift and depression sequence of the second,respectively.On the plane,there are total 114 faults in the Lower Carboniferous,which are distributed in NW-SE direction as a whole.In contrast,the Upper Carboniferous is only 58 faults,which in NWW-SEE direction.Compared with the former one,the number of faults in the Upper Carboniferous is dramatically reduced,and a counterclockwise rotation of about 15°occurred.The Carboniferous fault depressions in Junggar area are mainly developed on the Luliang and Junggar-Qitai island arcs,and most of them are characterized as intra-arc basins or fore-arc basins.It is widely considered that their formation and evolution are mainly controlled by the subduction and roll back process of the Karamaili ocean and the North Tianshan ocean.During the clockwise rotation of the oceanic island arc system,the Karamaili ocean and the Northern Tianshan ocean rotated anticlockwise by 15° relative to the overlying thrust island arc,and resulting in the change of fault depression orientations between the Early and Late Carboniferous. |
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