层序级别划分的两种途径：具有重要科学意义的难题

层序级别的合理划分是层序地层学面临的基本问题之一,根据多年的探索,前辈学者提出了两种方案：以层序界面出现的频率（时间）和以层序界面物理属性为基础的两种划分方案。第一种方案具有历史优先性的特点,伴随着层序地层学的诞生而出现,这种以时间为基础的划分方案强调全球海平面变化是地层旋回的主要驱动力,为研究全球变化提供了一个有益线索,但是由此而产生的全球旋回曲线图的有效性正在经受严峻的考验。第二种划分方案不受时间跨度的限制,而是按层序界面的特征和属性对层序进行级别划分,该方案实践性较强,有利于单个盆地的层序划分,尤其对年代地层分辨率普遍较低的前寒武纪地层研究十分有用。但是该方案也存在两个明显的缺陷：即以不同的界面属性进行划分可能会得出相互矛盾的结论,并且对盆地边缘地层的保存程度要求很高。追踪这一具有重要意义的层序地层学基本问题,不但有助于深入理解前辈学者们持续不懈的艰苦努力,而且也为今后对复杂地质作用过程的进一步研究提供了重要的思考线索。

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.