摘要
Abstract
The term peritidal coined by Folk is a useful general name for the spectrum of nearshore and shoreline deposi-tional environments and facies. Ancient peritidal carbonate lithofacies are characteristically organized stratigraphi-cally into meter - to decameter - thick, shallowing - upward successions; their vertical stacking is a valuablerecord of the dynamics of carbonate platform development. There are currently three models used to explain how ashallowing-upward succession forms, 1) as a prograding wedge, 2) as a simultaneously aggrading sheet or, 3) asa mosaic of tidal flat islands. A prograding wedge is generated by the tidal flats prograding in two styles, simple of-flap and staggered offiap. A simultaneously aggrading sheet accretes vertically to sea level and the whole platformbecomes sequentially intertidal and then supratidal. Tidal flat islands nucleate and accrete by aggradation andprogradation and shift in response to hydrographic forces. Much discussion exists currently as to what causes therhythmic stacking into thick stratigraphic packages of ancient shallowing - upward successions. Two possiblemechanisms are suggested, i, e., allocyclic and autocyclic mechanisms. The driving force behind the autocyclicity isthe dynamics of sedimentation on the platform, while the allocyclicity emphasizes the factors of subsidence and eu-stacy that cause relative sea level change. However, the two mechanisms are not necessarily mutually exclusive.The Ordovician M5 section in central Ordos basin consists of a rhythmic repetition of several shallowing- upwardperitidal carbonate successions deposited in epeiric sea. Based on the sedimentary structure and lithologic features ofstudied area, with the consideration of paleotectonics and paleogeography of the central basin, thirteen carbonatesedimentary - diagenetic microfacies are recognized that make up six sedimentary facies. The facies changes verti-cally and laterally. The paper presents the possible mechanism of the rhythmic package. Considering the geologicalsettings of the studied area, Autocyclicity may interpret the formation of the repetition of peritidal carbonate shal-lowing - upward successions as the result of the peritidal prograding through simple offlap and staggered offlap.关键词
潮缘碳酸盐岩沉积简单退覆阶段退覆自旋回Key words
peritidal carbonate sedimentation simple offlap staggered offlap autocyclicity分类
天文与地球科学
