宁夏同心地区古近纪-新近纪沉积岩地球化学特征及意义

Geochemical Characteristics and their Significances of the Paleogene-Neogene Sedimentary Rocks in the Tongxin Area, Ningxia, China

为研究宁南盆地北部同心地区古近纪-新近纪时期的沉积环境、构造背景及古气候特征,采集了该区的砂岩、泥岩地层样品进行主、微量和稀土元素分析。结果显示,研究区古近系-新近系均为初次旋回的沉积物,其物源区具有较弱的风化作用,物源为长英质或富含石英质沉积岩,源岩的大地构造背景为被动大陆边缘。整个古近纪-新近纪期间,该区沉积环境均为氧化环境,沉积水体为较高盐度的半咸水-咸水;寺口子组及干河沟组时期为湿润气候区域,清水营组和彰恩堡组时期为干旱气候区域。

In order to study characteristics of sedimentary environment, tectonic setting, and paleoclimate of the Paleogene-Neogene strata in the Tongxin area of the northern Ningnan Basin, we have comprehensively analyzed the weathering degree, property and tectonic setting of source materials, sedimentary environment and paleoclimate of the strata based on data obtained using geochemical methods in this paper. The results show that the Paleogene-Neogene strata are composed of primary cycle sediments, whose source materials could be weakly weathered felsic rocks or quartz-rich sedimentary rocks formed in the tectonic setting of passive continental margin. The Paleogene-Neogene sediments were deposited in an oxidized brackish-saline water environment during the Paleogene-Neogene period. The paleoclimate for deposition of the Sikouzi and Ganhegou Formation was humid while that of the Qingshuiying and Zhangenbao Formation was arid.