摘要： 加里东早期的怀远运动是早古生代的重要构造运动,它在华北古陆主要表现为区域性不整合。基于野外露头、地质图、钻井与最新的地震资料,研究鄂尔多斯盆地怀远运动期不整合的标志、类型及其时空分布。结果表明: (1)鄂尔多斯盆地怀远运动不整合面附近发育砂砾岩、风化壳, 测井曲线具高声波时差、高伽马、高微量元素(U、Th、K)含量、高钍铀比值及低电阻率、低密度特征,地震响应特征为强相位,表现为不整合面上、下波组振幅强度,频率、连续性存在明显差异,局部可见削截点反射。(2)怀远运动期鄂尔多斯盆地形成平行、低角度削截2种不整合,前者广泛分布于盆地及周缘,后者分布于盆内古隆起附近。(3)鄂尔多斯盆地及周缘受到怀远运动3幕活动影响,依次表现为: 中寒武世张夏组沉积期盆地东南部最先发生抬升,而后向西北部推进; 晚寒武世三山子组沉积末期,盆内古隆起发育并遭受剥蚀; 晚寒武世末期—奥陶纪马家沟组沉积前, 受全球海平面下降的影响,盆内马家沟组底部的碳同位素呈负漂。上述认识可为鄂尔多斯盆地下古生界油气勘探新领域研究提供参考依据。

关键词: 鄂尔多斯盆地, 奥陶系, 削截, 不整合, 怀远运动

Abstract: The Huaiyuan Movement is an important tectonic event in the early Paleozoic of the North China Platform,resulting in a regional unconformity. Based on outcrop data,geological maps,drilling data and new seismic data,the identification marks,types and distributions of unconformities formed during the Huaiyuan movement in the Ordos Basin were analyzed. The results show that(1)sandy conglomerate and weathered crust developed near the unconformity surface;additionally,high acoustic time,high gamma values,high content of trace elements(U,Th and K),high thorium-uranium ratios,low resistivity,and low density of logging curves occurred near the unconformity surface. The seismic response of the unconformity is characterized by a strong phase,and there are obvious differences in amplitude intensity,frequency and continuity in the wave groups on both sides of the unconformity. In addition,the truncation point reflections can be observed in local domain. (2)The Huaiyuan movement caused both parallel-unconformity and low-angle cutting unconformity in the basin. The former was widely distributed in the basin and its periphery areas,and the latter was distributed near the paleo-uplift in the basin. (3)The Ordos Basin and its periphery areas were affected by three stages of the Huaiyuan tectonic movement: during the depositional period of the Zhangxia Formation in the Middle Cambrian,uplift first occurred in the southeast region of the basin and then moved to the northwest direction;at the end of the Sanshanzi Formation deposition period in the late Cambrian,paleo-uplifts developed in the basin,and they were subjected to erosion; at the end of the late Cambrian, before the Ordovician Majiagou Formation was deposited,the negative drift of carbon isotopes first occurred in the bottom layer of Majiagou Formation due to the influence of global sea level decline. These results provides a reference for the research of new fields of oil and gas exploration in Lower Paleozoic in the Ordos Basin.

Key words: Ordos Basin, Ordovician, truncation, unconformity, Huaiyuan movement

中图分类号: 

• P542.3+4