The Study On The Geological Causes And Ages Of The Luoquan And Dongpo Formations In Ruzhou,western Of Henan

On southern margin of the North China Platform, the Luoquan Formation is characterized by the diamicton,has attract the attention of the geological field since it’s been named. There has been no unified opinion about whether it’s deposited by the glacier or when it’s been formed. The overlying stratum of Luoquan Formation is Dongpo Formation,which is generally consists mainly of microclastic rock in higher maturity. And the dongpo Formation has a unconformity contact relationship with its upper formation that at the bottom of the Cambrian also has biological evidence in it.This paper based on the geological survey of the profiles and the statistical analysis of the gravels’ data, could indicates the deformation of the bedding that surround the gravels was a sedimentary dropstone-structure caused by ice-rafted deposits. In particular,we found the sand-size clast can also cause the microscopic dropstone-structure, might reflect for the cold glacial environment at that time.Combined with the other evidences of glaciation in Luoquan diamictite,like the existence of the boulders,the gravels’ morphological characteristics,also considering the regularity of its stratigraphic horizon and distributing,can prove the Luoquan Formation should be formed by glaciation.The discovery of ichnofossils in Dongpo Formation, including Skolithos,Arenicolites,Treptichnus,Palaeophycus and Planolites,indicates that the Dongpo Formation was deposited at least after the Treptichnus(Phycodes) pedium Biozone,which is the earliest Biozone of Cambrian. So the Dongpo Formation was formed in the early Cambrian, later than the Sinian. Conformably underlying the DongpoFormation,the Luoquan Formation should belong to the early Cambrian or the late Sinian(the terminal Ediacaran or later).