Sedimentary Geology Of The Wufoshan Group In The Southern Margin Of North China Block And Its Tectonic Implications

The Wufoshan Group,developed in Songshan area of western Henan province,is a set of terrigenous clastic rocks and carbonate sedimentary rocks,which are in unconformable contact with the Dengfeng Group and the Songshan Group at lower angles and Cambrian unconformable contact at higher angles,and belongs to late Precambrian stratigraphic unit.This group is the northernmost late-precambrian sedimentary rock series on the southern margin of the north China continent,the birthplace of the study of "Sliding Structure" in China,and the first set of "sedimentary cover" with regional significance after the formation of crystalline basement on the southern margin of the north China block,which has important tectonic significance.In this paper,a comprehensive study of stratigraphy,sedimentary geology and seismolites was carried out in Wufoshan Group in Songshan area,aiming at revealing the chronostratigraphic sequence,sedimentary and tectonic characteristics,geodynamic environment of the Wufoshan group and its genetic relationship with the ancient Qinling orogenic belt.Through comprehensive research in the field and indoor,the following major new progress has been made:1)The study on the rock assemblage,sedimentary facies and their changes of the Wufoshan Group shows that the group can be divided into two sedimentary cycles: the Ma'anshan Formation + the Puyu Formation,the Luotuopan Formation + the Hejiazhai Formation.The former is characterized by Marine terrigenous clastic rock type sedimentary formations with good developmental component maturity and structural maturity,while the latter is characterized by continental terrigenous clastic rock type sedimentary formations with low developmental component maturity and structural maturity.2)The study on sedimentary facies and sequence of the Luotuopan Formation reveals that the main body is braided river sedimentary sequence.3)The field survey of 67 groups of large trough-like,plate-like and wedge-shaped oblique bedding predeposit rose-shaped illustration confirmed that the main development of the Ma'anshan Formation is a two-way cross-bedding,the main sediment diffusion direction points to the south;The dominant direction of the foreset stratum inclination of the Luotuopan Formation inclined bedding is north,indicating that the source area of the terrigenous clastic rock series of the Luotuopan Formation is located in the south of the study area.4)It is the first time that fluidized conglomerate,ball-pillow structure,liquefied vein,hydroplastic fold and seismogenic fault are found in the carbonate depositional system of the Hejiazhai Formation,indicating that the Hejiazhai Formation was formed in a geodynamic environment with strong basement activities.5)The statistical results of sandstone skeleton grain show that the source area of the Luotuopan Formation is an ancient basement formed by fault uplift.Combined with the spatial and temporal development characteristics of neoproterozoic orogeny in Qinling mountains,it is speculated that the Songshan area at that time should be a peripheral foreland basin extending in the near east-west direction.6)Based on the above new development and the previous research results,this paper further discusses the regional stratigraphic correlation of the Wufoshan Group,the neoproterozoic basin structure and its connection with the neoproterozoic orogeny of Qinling mountains,and puts forward the basin-mountain coupling model of the south margin of north China ancient continent and north Qinling mountains.