从基本层序地层模式论地层穿时的本质--以滇黔桂盆地泥盆纪层序地层格架为例

On the Essence of Stratigraphic Diachronism from the Basic Sequence Stratigraphic Model——An example from the Devonian sequence stratigraphic framework of the Dianqiangui basin

Shaw于1964年提出的穿时普遍性原理是现代地层学的重要支柱之一。20世纪70年代末由地震地层学发展而来的层序地层学是在年代和海平面变化框架内研究沉积相迁移的有效手段,它改变了划分沉积岩的原则而成为沉积地质学和地层学的一次重要革命。基本层序地层模式中相对海平面变化产生的地层超覆和退覆明显地体现了地层穿时普遍性原理,同时也暗示了地层穿时的本质。地层记录中的两种相变面——动态相变面和静态相变面形成于侧向加积和纵向加积两种沉积作用,它们所代表的两种穿时性——间断面穿时和相变面穿时,构成了地层穿时的两种基本形式。滇黔桂地区的泥盆系总体上构成一个自南向北厚度逐渐减小的楔状体,这是泥盆纪早期海侵尖灭与晚期海退尖灭的结果,研究区层序地层格架清楚地体现了地层记录的不完整性和穿时普遍性,同时也表明地层记录中的两种相变面及其所代表的两种穿时性是正确建立层序地层格架的关键要素。

The principle of ubiquity of diachronism proposed by Shaw in 1964 is now one of the mainstays of modern stratigraphy. Since the end of 1970s, sequence stratigraphy which was based on seismic stratigraphy has been an effective methodology for studying facies transplant within the framework of chronostratigraphy and sea-level changes. It changed the principle of subdivision of sedimentary rocks and initiated one crucial revolution of sedimentary geology and stratigraphy. In the basic sequence stratigraphic model, stratigraphic overlap and offlap induced by relative sea-level fluctuations clearly suggest the principle of ubiquity of diachronism, and imply the essence of diachroneity. The two kinds of facies-change surfaces （dynamic and static facies-change surfaces） produced by two kinds of sedimentation （lateral and vertical aggradation） in stratigarphic record represent two types of diachroneity, the diachronism of facieschange and diachronism of punctuated surface. As a result, they together represent two basic forms of diachronism in stratigraphic record. The Devonian in the Dianqiangui Basin takes the shape of a large wedge, thinning laterally from south to north, which was resulted from the earlier transgressive pinch-out event and later regressive pinch-out event during the Devonian. The sequence stratigraphic framework of the studied area indicates imperfection and ubiquity of diachronism of stratigraphic records, and that recognition and study of the two kinds of facies-change surfaces and two types of diachronism are keys to the construction of sequence stratigraphic framework as well.