摘要:
中卫及周缘地区位于阿拉善地块、华北板块、北祁连加里东造山带之间,该区上古生代受区域构造和全球海平面变化影响,地层发育与华北地区有较大差异。通过收集整理3条野外实测地质剖面及19条剖面资料,根据剖面岩性、沉积结构、构造、沉积旋回等,对中卫及周缘地区石炭纪岸线变迁、沉积范围、主要海泛期沉积体系及沉积相的纵向演变规律进行了研究。将研究区石炭系地层划分为三角洲、堡岛、碳酸盐岩台地、浅海4类沉积体系。早石炭世早期,南秦岭洋的海水开始入侵研究区南部,沉积范围呈狭长带东西向展布;早石炭世晚期海侵范围逐步向北、向东扩大,于早石炭世形成由阿拉善古陆、鄂尔多斯、北祁连围成的祁连海沉积区。早石炭世海水较深,沉积物以厚层灰岩为主,碳酸盐岩台地和堡岛沉积体系较为发育。晚石炭世海侵继续向北、向东扩大,晚石炭世晚期研究区祁连海与华北陆表海在中央古隆起北部汇合;早二叠世早期,中央古隆起没于水下,祁连海与华北海已广泛连通。晚石炭世至早二叠世早期海平面变化频繁,海水较浅,沉积物以碎屑岩为主并夹有灰岩,主要发育三角洲沉积体系、堡岛沉积体系以及浅海沉积体系。
关键词:
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中卫
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石炭纪
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最大海泛期
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沉积相
Abstract:
The Zhongwei area and adjacent regions are surrounded by the Alxan block, North China Plate and North Qilian. Stratigraphic classification in the study area is different from the North China Plate because of regional tectonic and eustatic sea level changes. Field investigations,in addition to previous studies, were carried out in order to study the depositional systems during the maximum flooding period. According to lithology, depositional fabric, sedimentary structures, sedimentary cyclicity of the deposits. a detailed sedimentary facies division for Carboniferous has been made for the research area. They are grouped into 4 depositional systems, i.e. the deltaic system, barrier-tidal flat-lagoon system, carbonate platform system, and shallow sea system. In the early period of early Carboniferous, seawater invaded into the study area surrounded by the Alxa, Erdos, and Northern Qilian, and formed the carbonate platform and the barrier-tidal flat-lagoon systems. In the period of late Carboniferous, transgression was extended and the research area was then connected with the seawater from North China in Otog and Otog Front. In the early period of early Permian, the sea was further expanded to be an epicontinental sea. Sea level frequently changed in the period of late Carboniferous, and the barrier-tidal flat-lagoon, deltaic and shallow sea depositional systems were developed in the study region
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