Division of the Cambrian sequences in the Xichuan stratigraphic microprovince,Henan

The Cambrian stratigraphic sequences in the Xichuan stratigraphic microprovince,Henan consist of the Shuikougou,Yuejiaping and Wugongya Formations,which are in parallel unconformable contact with the underlying Sinian strata and in conformable contact or in parallel unconformable contact with the overlying Ordovician strata,characteristic of the type II boundary for both the top and basal boundaries.These stratigraphic sequences are involved in 46 basic sequences,and examined in detail in vertical and horizontal variations,stratal architectures and division of systems tracts.The maximum marine flooding phase occurred during the early Cambrian when the rapid transgressions took place.There are big gaps in lithology of the lower part and upper part of the Cambrian strata,indicating the inhomogeneous uplifting of the crust during the early and latest Cambrian.