在Exxon层序地层学概念体系中,由不整合面及其可以对比的整合面所限定的地层单位被定义为层序,即三级沉积层序;构成三级层序的单元为体系域,体系域由若干准层序和准层序组所组成.基于海岸沉积的层序地层模式,准层序被定义为"由海泛面所限定的层或层组组成的一个相对整合的序列";作为准层序界面的海泛面被进一步定义为:一个将老地层与新地层分开的面,穿过该面存在一个突然的"水深加深".因此,从海泛面到准层序,其定义由于不具有普遍性而表现出欠完整性.虽然类似级别的地层单元后来又被Exxon的科学家修改为"高频层序",但是,准层序这个欠完整的概念一直被广泛使用着.与层序地层学的Exxon时代大致同步,或者在更早的时期,地质学家就已经注意到那些由岩层所构成的沉积旋回,以"洛非尔旋回层"为典型代表;这种类似的旋回性沉积记录,后来被进一步定义为"米级旋回",而且将米级旋回进一步解释为异成因机制控制下的自旋回沉积过程(间断-加积-旋回机制;PAC机制)的产物,这种异成因机制是与米兰柯维奇旋回相关的极地冰盖的消长所造成的海水体积变化,以及由这种数万年至数十万年级别的海水体积变化所产生的高频海平面变化旋回.这些厚度为数厘米至数米的沉积旋回,在长周期三级层序中常常构成有序的叠加形式,这种叠加形式成为研究三级层序内沉积趋势变化的主要标志.再者,对与米兰柯维奇旋回存在成因关联的沉积旋回的研究,成为另一个地层学分支--旋回地层学的主要内容.如果说对Exxon层序地层学概念体系不协调的研究是第1个进展、对长周期层序的形成机制的探索为层序地层学的第2个进展,那么,从旋回的有序叠加形式到层序的识别与划分,不但表现出了旋回地层学和层序地层学的交融,而且也代表了层序地层学的第3个重要进展.%In the conceptual system of the Exxon sequence stratigraphy, stratal units bounded by unconformities and their correlative conformities are defined as the depositional sequence. The depositional sequence is made up of systems tract, and the systems tract is composed of many parasequences or parasequence sets. In term of the sequence stratigraphic model that is based on the coastal sedimentology, the parasequence can be defined as a relative conformity succession of strata that is bounded by flooding surface; Further, the flooding surface, that is used as the bound surface of parasequence, is defined as a stratigraphic surface that divides the older strata from the young strata through which exists an abrupt rapid deepening of water depth. Thus, there is no universalism for the flooding surface that can be used as the bound surface of parasequence, which leads to the lacking of the integrality for parasequence. The term of the parasequence has subsequently been modified as high-frequency sequence by Exxon scientists, but this term that is lack of integrality has widely been used up to the present. In the same time or the time that is earlier than that of the Exxon age for sequence stratigraphy, the sedimentary cycle that is made up of lithofacies successions had been described by geologists, such as Lofer Cyclothem. This similar type of cyclic sedimentary records has been further defined as meter-scale cycle, and the meter-scale cycle has been interpreted as the product of autocyclic depositional process (the puncatuated aggradational cyclic mechanism; the PAC mechanism) which is controlled by allocyclic mechanism; Further, the allocyclic mechanism was explained as high frequency sea level change that is genetically related to the volume change of sea water due to the increasing and decreasing of ice cap in the polar region resulting from the Milankovitch cycle. These meter-scale cycles with thickness from several centimetem to several meters generally form a vertical stacking pattern in the third-order sequence, and this vertically stacking pattern of meter-scale cycle becomes a main marker to study the change of sedimentary trends within the third-order sequence. Importantly, studies on sedimentary cycles that are genetically related to the Milankovitch cycles are grouped into the main content of other stratigraphic discipline, i.e. the cyclostratigraphy. Therefore, if the study on inconsistence of conceptual system for the Exxon sequence stratigraphic model represents the first ad vance, while the research on the forming mechanism of those long-term sequences is the second advance in sequence stratigraphy, the study on the discerning and division on the basis of regular vertical stacking patterns of cycles can delegate the third advance in sequence stratigraphy, which is marked by the mingling of both sequence stratigraphy and cyclostratigraphy.
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