鄂尔多斯盆地东南部本溪组—下石盒子组泥岩元素地球化学特征

Elemental Geochemistry Characteristics of Mudstones from Benxi Formation to Lower Shihezi Formation in Southeastern Ordos Basin

以鄂尔多斯东南部取心资料为基础,对不同层位泥岩的微量元素及稀土元素等测试结果进行分析,研究了本溪组至下石盒子组的沉积环境演化规律及物源特征。岩性资料分析结果表明,本溪组至下石盒子组,泥岩颜色由深及浅,表明沉积环境的还原性由强至弱;对环境敏感的微量元素(V、Ni、Sr和Cu等)及Ceanom值分析结果表明,本溪组至下石盒子组沉积环境总体属于弱还原-还原环境且还原性有逐渐减弱的趋势;气候总体为温暖湿润环境,自下而上,气候的温湿性变弱;本溪组为海相咸水沉积,山西组及下石盒子组以陆相淡水沉积为主;本溪组水体较浅,山西组水体较深,下石盒子组水体较山西组浅。δEu、(La/Yb)N及Gd/Yb等稀土元素指标分析表明,研究区沉积母岩以上地壳岩石为主,存在南北两个物源,北部物源为盆地北部阿拉善—阴山古陆造山带,南部物源为北秦岭造山带;受南北物源控制,研究区南部近源沉积的Al2O3/Ca O值普遍高于北部的远源搬运沉积。

Based on the coring samples of mudstones in the southeastern Ordos Basin,this article focuses on the analysis of trace elements and rare earth elements in different horizons and studies the evolution of sedimentary environment and provenance from Benxi Formation to Lower Shihezi Formation. Core data show that from Benxi Formation to Lower Shihezi Formation the color of mudstones varies from deep to shallow and the reducibility of sedimentary environment changes from strong to weak. According to the analysis of environmental sensitive trace elements（ such as V,Ni,Sr,Cu,etc.） and Ceanom,from the Benxi Formation to the Lower Shihezi Formation,the sedimentary environment is generally the weak reducing-reducing environment,and the reducibility tends to decrease gradually; the climate is generally warm and humid with the wettability of climate gradually decreasing from bottom to top. The Benxi Formation is marine saline deposits,and the Shanxi Formation and Lower Shihezi Formation are dominated by continental fresh water deposits. The depth of water is shallow in Benxi Formation,more deeper in Shanxi Formation,which is more deeper than in Lower Shihezi Formation. The REE indexes analyses,such as δEu,（ La/Yb）N,Gd/Yb and so on,show that the sediments in the study area are mainly from upper crust rocks and there are two sources respectively from south and north. The northern provenance is from Alanshan-Yinshan ancient continent in the northern basin and the southern provenance is from the northern Qinling orogenic belt. Under the control of the south and north sedimentary origins,the value of Al2 O3/Ca O of the proximal sediments in the southern area is generally higher than that of the far-source sediment in the northern area.