安徽定远东部—明光地区古近—新近纪地层、沉积相特征及层序地层分析

PALEOGENE-NEOGENE STRATA,FEATURES OF SEDIMENTARY FACIES AND ANALYSIS OF SEQUENCE STRATIGRAPHY IN THE DINGYUAN-MINGGUANG AREA,ANHUI

安徽省定远东部—明光地区古近—新近系划分方案不一,通过地层剖面的测制和利用构造—岩性—岩相法进行1∶5万地质填图,系统采集了ESR测年样,并结合区域对比,自下而上划分古近纪定远组、明光组,新近纪下草湾组和桂五组。该区古近—新近纪沉积物以陆相红色磨拉石和陆相火山岩建造为主,陆相红色类磨拉石的建造分析表明其形成于冲积扇和扇前河湖环境,碎屑物质来源于沉积区东边扬子地层区的浅变质岩和沉积区西北侧华北地层区变质岩和未变质岩石。其陆相火山喷发岩形成于大陆边缘活动性环境,是区内火山活动最盛的时期。其盆地类型为箕状断陷型、迁徒型和坳陷型。根据盆地充填沉积序列划分出4个层序(2个二级和2个三级层序),层序Ⅰ和层序Ⅳ不完整,层序Ⅱ和层序Ⅲ皆由冲积沉积体系域、湖扩张体系域和湖萎缩体系域3个基本单位构成。层序界面主要有区域构造运动界面和盆地构造应力转换面—体系域转换界面两种类型。

There are different division schemes for the Paleogene Neogene System in the Dingyuan Mingguang area ,Anhui.In this paper the strata are classified into the Paleogene Dingyuan Formation and Mingguang Formation,the Neogene Xiacaowan Formation and Guiwu Formation from below based on stratigraphic profile measurement,1:50000 scale geological mapping by using structure-lithology-lithofacies method,systematic collection of samples for ESR dating as well as regional correlation. The Paleogene Neogene sediments in the area mainly consist of terrestrial facies of red molasse and volcanics formation.The analysis of red molasse formation indicates that it formed in alluvial fan ,fluvial and lacustrine environment and the clasts are sourced from the slightly metamorphic rocks of the Yangtze stratigraphic province in east and from the metamorphic and unmetamorphic rocks of the North China stratigraphic province in west.The terrestrial facies of volcanic eruptive rock formed in the active environment of land margin during the most active period of volcano in the area.The basins are of migration and skip-like rift faulting ones.According to basinal filling deposition series four sequences(2 second-grade and 2 third-grade sequences)are divided,of which sequenceⅠ and sequence Ⅳ are incomplete,both sequence Ⅱ and sequence Ⅲ consist of three basic units such as lowstand system tract,expanding system tract and contraction system tract.The sequence interfaces include regional tectonic movement one and basinal tectonic stress transform one(system tract transform one).