鄂尔多斯盆地子洲地区上古生界沉积相及演化特征

Sedimentary facies and its evolution of the Upper Palaeozoic in Zizhou area of Ordos Basin

在对大量钻井岩心观察分析的基础上,结合鄂尔多斯盆地区域地质背景,利用岩性、古生物、沉积构造、粒度分析、地球化学特征等鉴别沉积标志特征,分析鄂尔多斯盆地子洲地区晚古生代各时期沉积相特征,总结其演化规律。晚古生代研究区共发育5种沉积体系,分别是障壁海岸沉积体系、浅海陆棚沉积体系、曲流河三角洲沉积体系、辫状河三角洲沉积体系以及湖泊沉积体系。研究区晚古生代沉积演化经历两大阶段。重点分析山西期与石盒子早期盒8期沉积环境,子洲地区山西组沉积为水下还原环境,受河流三角洲作用控制,仅在山西组早期研究区南部受到短期海泛的影响;石盒子早期研究区处于完全的淡水环境,受辫状河三角洲作用控制。晚古生代沉积时气候特点体现出由温暖潮湿气候向半干旱—干旱气候转变,沉积体系表现为由海相、海陆过渡相向陆相过渡转变的特点。

On the basis of the analysis on a large number of drilling core observation,combined with regional geological background of Ordos Basin,the study uses the signal features such as lithology,palaeontology,sedimentary structure,grain size analysis,the geochemical characteristics to identify the sedimentary environment of each periods of Late Paleozoic in Zizhou area of Ordos Basin and summarize the evolution rules.There are five sedimentary systems in the study area of Late Paleozoic which are barrier coast system,shelf sedimentary system,meandering river delta sedimentary system,braided river delta sedimentary system and lacustrine sedimentary system.The sedimentary evolution is divided into two stages.The study focuses on sedimentary environment of Shanxi Formation and He 8 Member of Shihezi Formation.Shanxi Formation in Zizhou area deposits on the underwater environment.It is controlled by meandering river delta.There is short-term sea flooding only in the south part of study area.The study area is in fresh water environment in the early stage of Shihezi.It is controlled by braided river delta.The climate is changed from warm and humid to semi-arid and arid during Late Paleozoic.Sedimentary system is from marine and transitional to continental.