Analysis Of Cyclostratigraphy In The Third Series Zhangxia Formation Of Cambrian In The Western Of Henan Province

The Third Series Zhangxia Formation of Cambrian in the western of Henanprovince, display the continuous and abundant depositional and palaeoichnologicalrecords which can be better used for the study of cyclostratigraphy. Based on thecharacteristics of sedimentology and ichnology, six kinds of trace fossils and fourmicrobiolites were distinguished, the trace fossils from the bottom to the top namely are:Planolites montanus; Palaeophycus tubularis; Thalassinoides horizontalis; Skolithoslinearis; Blurry bioturbation; Macaronichnus and Palaeophycus heberti. Themicrobiolites include stromatolites, trombo1ites, dendrolites and oncolites.Based on the palaeoichnological features in the Zhangxia Formation in the westernof Henan province, there are two kinds of meter-scale cyclic sequences in Dengfengarea, respectively dominated by microbiolites and by metazoan bioturbated limestones,however, there is only one kind of meter-scale cyclic sequence in the Luoyang area,dominated by metazoan bioturbated limestones. Study on palaeoichnology andmicrobiolites shows that the boundary features of meter-scale cyclic sequencesdominated by microbiolites display either the microflora change one to another or theshape of microbiolites limestones occur change across cyclic sequences boundaries;the boundaries of meter-scale cyclic sequences dominated by metazoan bioturbatedlimestones are mainly marked by the changes of bioturbation index and ichnospecies;the boundaries of fourth-order or fifth-order cyclic sequences are mainly based on thechanges of ichnofabrics. The cyclic sequences dominated by microbiolites give ways tothe cyclic sequences dominated by metazoan bioturbated limestones from bottom to topin the Zhangxia Formation of Dengfeng area.Based on Fischer diagram, the72meter-scale cyclic sequences in the ZhangxiaFormation of western Henan province constitute one third-order cyclic sequence andfour fourth-order cyclic sequences. The depositional system in the Zhangxia Formationof Dengfeng area evolves from the carbonate platform without oolitic shoals into theplatform developed oolitic shoals; the sedimentary environments develop from lowenergy deep subtidal zone to open platform zone, and gradually become shallower intooolitic shoals and eventually end up with restricted platform.