中扬子区震旦-三叠纪沉积体系划分及影响因素

在进行沉积体系恢复时,必须综合考虑4方面因素:①中场子区盆山转换及海陆变迁主要受控于三大板场,即华北板块、扬子板块和华夏板块的拼合和分离,盆山转换包括四个阶段;②古气候演变可能出现冷、热、干的变化周期,这种变化周期明显控制了沉积体系的物质组成;③根据露头层序地层学的研究和部分年代地层、生物地层资料,可划分出3个不同级别的周期,与全球海平面变化相对应的一级周期有2个,超周期13个,三级周期75个,海平面升降变化直接影响着古地理海陆分布和沉积格局,并控制着沉积体系的发育状况及相带的展布。④发生在分地中的事件对岩相和古地理景观起着决定性的作用,每一个重大的事件常强烈地改变了正常的渐变的相序以及地貌和海底的古地理,因此,重大的地质事件和事件记录的研究在岩相古地理分析中,将发挥重大的作用和影响。

Depositional system and influence factors of Middle Yangtze Sinian-Triassic

The four factors must be considered synthetically while depositional systems are rebuilt:① the convergence and divergence of northern China plate、Yangtze plate and Cathaysian plate control basin-mountain transform and marine-continent change of Middle Yangtze;② the palaeoclimate cycles with temperature and humidity have effects on buildup of depositional systems;③ in the light of the study of outcrop sequence stratigraphy,chronostratigraphy and biostratigraphy,three different order cycles which include two first-order、thirteen second-order and seventy-five third-order cycles are divided,which are corresponding with worldwide sea-level changes. The sea-level changes control the palaeogeographic distribution and depositional pattern,and control the development situation of depositional system and facies-expending;④ the geologic events occurring in basin have crucial effects on lithofacies and palaeogeographic features. Every fatal event usually remolds normal gradual-change facies orders,topography and sea floor palaeogeographic intensively. So study of fatal geologic events and records will be very important for analyzing lithofacies and palaeogeography.