从正常海退与强迫型海退的辨别进行层序界面对比:层序地层学进展之一

Correlation of sequence boundaries according to discerning between normal and forced regressions:The first advance in sequence stratigraphy

针对类型1和类型2层序定义过程之中所存在的概念体系的不协调,1988年以后的层序地层学发生了较多的变化,这些变化代表了层序地层学的重要进展之一。这些变化包括:(1)成因地层层序的提出,表明了一个"水下不整合面"——最大海泛面也可以作为层序界面;(2)将强迫型海退沉积的顶面作为层序界面,是为了始终将层序界面置于海平面变化的最低点,从而与全球海平面变化曲线保持一致;(3)海侵—海退层序模式,似乎代表了层序地层学的简单化;(4)淹没不整合型层序,代表了快速海侵事件的产物。这些变化的基础是将强迫型海退与正常海退区分开,以便能更准确地将暴露不整合面(subaerial unconformity,也有学者译为陆上不整合面)所形成的层序界面与"可以对比的整合面"进行对比。也就是说,层序内部地层的叠加形式是对沉积作用速率变化与基准面变化相互作用的响应,而且每一种叠加形式还代表了独特沉积的成因类型(即"海侵的"、"正常海退的"以及"强迫型海退的沉积"),对这些过程的研究即为层序地层学研究的核心内容。因此,从正常海退与强迫型海退的区别去追索不整合面所构成的层序界面的水下整合部分——"可以对比的整合面",产生了不同的认识及其所代表的不同的层序地层模式,最终代表了层序地层学从1988年以来的重要进展之一。追索这个重要进展,对于深入理解层序地层学的发展具有重要意义。

The cognition on the inconsistence of conceptual system between type 1 and type 2 sequences results in many advances in sequence stratigraphy after 1988.These advances include： （1）the establishment of the generic stratigraphic sequence,which demonstrates that a subaqueous unconformity that is a maximum flooding surface can be used as a sequence boundary;（2）the using of the top boundary of the forced regressive deposit as a sequence boundary,which makes a sequence boundary always be positional at the lowest point on the curve of sea-level changes and becomes consistent with the establishment of sea-level curves;（3）the transgressive-regressive sequence model is useful to make sequence stratigraphy towards simplification;（4）sequence of the drowning unconformity type represents the product of the rapid transgressive event.Thus,the discerning between the normal and the forced regressions is the basis to correlate the subaerial unconformity that makes up a sequence boundary with the correlative conformity. Further,stratal stacking patterns within a sequence are the respond to the interplay of changes in rates of sedimentation and base level,and each stratal stacking pattern defines a particular genetic type of deposit（i.e.,＂transgressive＂,＂normal regressive＂ and ＂forced regressive＂）,which are the key in the study of sequence stratigraphy.Therefore,studies from the discerning between the normal and the forced regressions to tracing the subaqueous conformity part（the correlative conformity）of a sequence boundary that is made of the unconformity lead to different cognitions and several sequence stratigraphic models,which reflect one of the advances in sequence stratigraphy since 1988.Seeking this important advancement will be very meaningful to further understand the progresses of sequence stratigraphy.