Study on the base-level cycle and the sedimentology of Permian in Jiyang area

摘要

The identification of sequence boundaries is the key point for sequence stratigraphicclassification.Both the higher-order sequences and the units within the sequencesare bounded with the key sediments or isochronous surfaces.Eight sequences can be dividedin the whole Permo-Carboniferous strata (the Shiqianfeng Formation is not included)which is from the Benxi Formation,Taiyuan Formation,Shanxi Formation,Xiashihezi Formation,Wanshan Section,and Kuishan Section to the Xiaofuhe Section.Also,differentsystem tracts (lowstand system tract,transgression system tract and highstand systemtract) and some parasequences can be recognized in each sequence.Parasequenceanalysis was on the basis of the division of the base-level cycle.The base-level cycle wasmainly identified according to the change of the water area,which was reflected by thedepositional sequence.The physical characteristic of the strata was reflected by the welllog.It was supplied by the test of the minerals and rocks and the analysis of the microelementin the lab.The paleogeographic characteristic of the lowstand system tract in thesequence Ⅵ is that the east-north part takes the river system as its feature;the south partis the lake system,the river channel spreads from north to south,and the area of theflooding plain is great.The paleogeographic characteristic of the water-transgressive systemtract is that the range of the lake in the south extended distinctively,the range of theriver channel in the east reduced.The coastal shallow lake deposit is the main characteristicin the water-transgressive system tract.The paleogeographic characteristic of thehighstand system tract is similar to the one of the lowstand system tract.