Sedimentary Characteristics And Tectonic Significance Of The Early Cretaceous In The Shuangling Basin,Chifeng,inner Mongolia

The Late Mesozoic era is a crucial period for the structural transition in mainland China.More and more research results show that before and after the late Jurassic,the tectonic deformation system in East Asia has undergone a major transformation,and the tectonic has shifted from the late Jurassic extrusion system to the stretch system in the Early Cretaceous.As a result of the intense intracontinental stretch cracking since the Early Cretaceous,a series of Early Cretaceous basins have formed in eastern China and its neighboring regions,and a series of Early Cretaceous volcanic-sedimentary basins have been developed in the Chifeng area of central eastern Inner Mongolia.These basins are distributed in the northeast direction.The basin is dominated by a semi-marine mantle,controlled by a single boundary main fault.The margins of the basin are dominated by alluvial fan conglomerates,and the center of the basin is mainly lake fine-grained sediments.However,due to the basalts of the Cenozoic Hanuoba Formation,rivers,lacustrine facies,and desert deposits,the Early Cretaceous basins were extensively covered,which caused great difficulties for the restoration of the basin prototypes and basin analysis.Therefore,on the basis of traditional basin analysis methods,combined with geophysical exploration and drilling methods,basins were analyzed and prototypes were restored and to the formation mechanism of the basin can be studied.The Shuangling Basin is located in the southern Wengniute County,Chifeng City,and is located on the northern margin of the North China Plate and the southern edge of the Xingmeng Orogenic Belt.The basin is mainly composed of the Early Cretaceous Jiufotang Formation strata.The depositional characteristics of the Jiufotang Formation in the basin show that there are two stages in the basin deposition.In the early stages of the deposition of the Jiufotang Formation,basins developed fluvial and lacustrine deposits in turn,forming an upwardly tapering sedimentary sequence.The gravel constituents in the river facies mainly consisted of andesite,and the ancient water flow from the southeast to the northwest;in the late stage of basin deposition,the basin fills from bottom to top has a gradually thickening sequence,showing the sedimentary environment of the lacustrine facies,delta facies,braided facies,alluvial fans,respectively.The paleocurrent direction is from the southeast to the northwest.The gravel composition is mainly composed of metamorphic rhyolite and andesite.Among them,the metamorphic rhyolite is the Silurian Badangshan Formation;the isotope chronology tests show that the andesite zircon U-Pb.The isotope test result is 152.4Ma,which is dominated by Late Jurassic and is presumed to be the Manitu group.Based on the changes of paleocurrent and gravel composition,it is speculated that the control basin fault is located in the southeastern part of the basin,and it is near the NE-SW trend.According to the sedimentary and tectonic features of the northwestern margin of the basin,it is assumed that a northwest-southeast compression occurred after the basin deposition,ie,and the structural transformation occurred.By studying the relationship between basin sediments and basin-edge structures,the sedimentary environment of the Early Cretaceous in the Shuangling Basin can be restored,and the tectonic setting of the basin filling can be restored.Then,we can know the discussion of the structural systems of the Early Cretaceous Yanshan Movement significance.With the help of provenance analysis methods in the basin,combined with geophysical exploration and drilling methods,the restoration and verification can provide support for the mapping of detrital sedimentary bedrock in the covered area.