Two Kinds of Sequence Hierarchy Classification Systems： A difficult Problem with Scientific Significance

Sequence hierarchy has fundamental effects on establishing sequence stratigraphic architecture.There are mainly two kinds of sequence hierarchy classification systems:one is the hierarchy system based on cycle duration or boundary frequency(time),and the other is based on the physical attributes of boundary.The former has a historical priority and is propitious to correlate in world scale.Having been proposed at the dawn of sequence stratigraphy,it emphasizes eustasy as the main driving force behind stratigraphic cyclicity,but the validity of the global cycle chart is under intense scrutiny currently.The latter depends on the physical attributes of boundary and independent of cycle duration/time,which is much more convenient for Precambrian stratigraphic division because of the serious lack of time control.However,this classification system also has two obviously questions,i.e.basing on different attributes of boundary may obtain contradictory results but it has a strict requirement to the preservation of basin margin.By extensively reading and analyzing a variety of references,this paper systemically introduces and assesses the relative merits of the two sequence hierarchy classification systems.Tracing the important significance of the basic problems of sequence stratigraphy,we can not only understand the persistent efforts of former scholars,but also provide significant clues for the future research.