鄂尔多斯盆地西北部延长组中下部古物源与沉积体空间配置

Spatial Combination of Paleoprovenance and Depositional Lobe of Mid-Lower Yanchang Formation in the Northwest of Ordos Basin

为了查明鄂尔多斯盆地西北部延长组沉积体系的分布格局等问题,以上三叠统延长组中下部为目标,通过常规矿物成分分析、重矿物特征研究、古水流测量、砂分散体系制图和古地貌恢复等方法,对鄂尔多斯盆地西北部的物源及源区母岩性质等进行了系统研究.结果表明,研究区主要受到4个物源的影响,古物源与沉积体系具有良好的空间配置关系:西北部的汝箕沟朵体受阿拉善古陆物源区控制,它对研究区影响最大;石沟驿朵体的物源来自大罗山逆冲席隆起;东部的鄂托克旗朵体和定边朵体则受到鄂尔多斯盆地东北部物源的控制.四大物源区的母岩性质具有差异,其中西部的阿拉善古陆物源区和大罗山逆冲席物源区的母岩以变质岩为主,还有一定量的花岗岩和沉积岩;而鄂尔多斯盆地东北部物源则以花岗岩和变质岩为主.沉积物源的研究有助于油气勘探的部署.

For determining the distribution pattern of the depositional system of Yanchang Formation in the northwest of Ordos basin, the authors chose mid-lower Yanchang Formation and did a systematic research on the provenance and the characteristics of the mother rock by methods such as the analysis of rocks and minerals, heavy mineral analysis, paleocurrent survey, sand distribution system drawing and paleo-topogrphy reconstruction etc.. The results indicate that the study area is mainly affected by four sediment sources, which have favorable spatial combination with depositional system： Rujigou lobe which has the largest influence on the study area is controlled by the Alxa Ancient Land; Shigouyi lobe develops from the overthrust sheet of Daluo Mountain; Otog Qi lobe and Dingbian lobe are controlled by the sedimentary sources in the northeast of Ordos basin. The mother-rock properties of the four provenances are very different. The ones in the Alxa Ancient Land and in the overthrust sheet of Daluo Mountain mainly consist of metamorphic rocks, including some granite and sedimentary rocks. However, the ones in the northeast of Ordos basin are mianly made up of granite and metamorphic rocks. Provenance analysis is useful to reasonable deployment of oil and gas exploration.