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Tectonic-depositional environment and prototype basin evolution of the Permian-Triassic in southern Junggar Basin
Author(s): 
Pages: 643-660
Year: Issue:  4
Journal: Journal of Palaeogeography

Keyword:  Junggar BasinPermianTriassicdepositional environmentprototype basintec-tonic evolution;
Abstract: The tectonic-depositional environment and prototype basin evolution of the Permian-Trias-sic in the southern Junggar Basin have long been debated.Detailed sedimentary environment,stratigraphic correlation and sedimentary evolution analyses,combined with collection and sorting out of relevant data, have been carried out on the Permian-Triassic strata.Hereby,we discussed a multicycle of compressional and extensional transformation in the Permian-Triassic,and proposed the prototype of the sedimentary ba-sin.In the Late Carboniferous,the west segment of the southern Junggar Basin situated at the end of the North Tianshan Ocean crust subducted southward below the Yili Block,and dominated by littoral and ne-ritic facies,showing the characteristic of a remnant ocean basin.However,the east segment of the south-ern Junggar Basin is mainly composed of bathyal carbonate deposits and a set of bimodal volcanic rocks, implying that it formed under an extensional environment.In the Early Permian,they both primarily con-tain fine grained clastic rocks of the littoral-shallow facies.Moreover,syn-depositional faults and collapse deformations can be observed,indicating an intracontinental rift basin.Later on,the deposition rates is faster and the thickness is thicker.Thus,the prototype basin has been transformed into the depression ba-sin in the Middle Permian.Until the Late Permian,the depositional environments were characterized by the alluvial fan or fan delta deposits in the North Tianshan and Bogda area.Also,the Upper Permian Quanzijie Formation is in unconformity relation with the Middle Permian Hongyanchi Formation.Hence,it implied the rapid uplift of the North Tianshan,formed an intracontinental compressional basin.In the Early Triassic,because of the end of the uplift,the basin entered into a relatively stable stage,which formed a weak intracontinental compressional basin dominated by a series of fine grained sediments of coastal shal-low-lake facies.In the Middle-Late Triassic,with the occurrence of continuously transgress of the basin, the North Tianshan have been eroded,which was consistent with the expansion of the lacustrine basin and the widespread fine-grained shallow-deep lacustrine sediments.Taken together,we suggested that the ba-sin of the Late Carboniferous to Middle Permian belongs to post-collision extensional depression stage.Nev-ertheless,a short thrust stage happened in the Late Permian.In the Triassic,the plate squeezing action weakened and Junggar Basin gradually entered a depression-subsidence stage from the intense compressive stage.The Early Triassic is a weak compression and denudation stage,and the Middle-Late Triassic is a stable depression and peneplanation stage.
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