米级旋回层序的成因类型及其相序组构特征

Genetic Types of Meter-Scale Cyclic Sequences and Their Fabric Features of Facies-Succession

与米兰柯维奇旋回存在成因联系的幕式地层堆积作用的结果 ,是在地层记录中形成各种类型的米级旋回层序。在不同的古地理背景中 ,受物质来源及沉积动力学背景的控制 ,故发育具有不同相序组构的不同类型的米级旋回层序。因此 ,相序组构特征就成为米级旋回层序类型划分的基本准则。地层记录中米级旋回层序的广泛发育 ,以及它们在长周期层序中的有序垂直叠加形式和地史演化特征 ,由不同相序组构所反映的成因类型以及由不同类型所指示的沉积动力背景等等 ,不但表明了米级旋回层序是描述地层结构的基本工作单元 ,而且是对“准层序”的延展和补充。在海相地层中 ,不管是碳酸盐岩还是陆源碎屑岩地层 ,这种厚几厘米至几米的米级旋回层序 ,大致都可以划分为正粒序和反粒序两种相序组构 ,正粒序组构主要是潮汐作用的结果 ,而反粒序主要是以波浪作用为主的浅海环境的产物 ;不管是正粒序还是反粒序序列 ,均构成总体向上变浅序列。由此 ,碳酸盐岩米级旋回层序可划分为L—M型、深水非对称型、潮下型及环潮坪型 ;碎屑岩米级旋回层序可划分为潮汐动力型及波浪动力型。米级旋回层序的界面是由高频率海平面变化所产生的非沉积作用面 ,包括瞬时暴露间断面和瞬时加深淹没间断面乃至它们的相关面 ,这些在区域上延伸较远 ,甚至?

Different types of meter-scale cyclic sequences in stratigraphical records are the outcomes of episodic accumulation of strata related to Milankovitch cycles. They are marked by particular features of facies-successions resulted from different sediment source and sedimentary dynamics in different paleogeographic background, which become the fundmental rule on the division of meter-scale cyclic sequences. The widespread development in stratigraphic records and the regularly vertical stacking-patterns in long-term sequence, the evolution characters of earth-history and the genetic types reflected by particular fabric features of facies-succession in different paleogeography background, all of these features shows that meter-scale cyclic sequences are not only the fundmental working-unit on stratigraphy and sedimentology but also the replenish and extention of parasequence in sequence stratigraphy.There are generally two kinds of facies-succession for meter-scale cyclic sequcence in neretic-facies strata of carbonates as well as clastic rock, which are normal grading succession mainly formed by tidal sedimentation and inverse grading succession mainly made by wave sedimentation, both of them constitutes generally upward shallowing succession, the thickness of succession is from several tens centimeters to several meters. In terms of fabric features of facies-succession,it can be made the division of genetic types for meter-scale cyclic sequences. Carbonate meter-scale cyclic sequences could be divided into four types,which are L-M type, deep-water asymmetrical type, subtidal type and peritidal type. Clastic meter-scale cyclic sequences could be divided into two types, which are tidal-dynamic type and wave-dynamic type. The boundaries of meter-scale cyclic sequence are marked by instantaneous punctuated surface formed by non-deposition resulted from high-frequence sea-level changes, which include instantaneous exposed punctuated surface and drowned punatuated surface as well as their correlative surface. The development of instantaneous punctuated surface used as the boundary of meter-scale cyclic sequence lead to the limiting of Walthers Law that is used to explain facies distribution in time and space, and reaffirm the importance of Sander's Rule on analysis of stratigraphical records. These noncontinue surfaces could be traced in long distance and some be correlative in same basin range. The study on meter-scale cyclic sequences and their regularly vertical stacking patterns in long-term sequence indicate that the research on cyclicity of stratigraphic records is a useful way to get more regularity from stratigraphic records that are frequently complex as well as non-integratd.