鄂尔多斯盆地东部石盒子组盒8沉积环境的地球化学表征

Geochemical characteristics of sedimentary environment on He 8 Member of Shihezi Formation in eastern Ordos Basin

采用Sr、Sr／Ba、Rb、Rb／K、K＋Na质量分数、K／Na、B／Ga、B元素法、V／Cr、Ni／Co、U／Th、V／（V＋Ni）、铈异常（Ceanom）值、Fe2＋／Fe3＋、Cu／Zn、Sr／Cu、Fe／Mn、Mg／Ca、Mg／Sr和Al2O，／MgO等微量元素和常量元素等地球化学方法对鄂尔多斯盆地东部盒8期沉积环境的古盐度、氧化还原态和古气候进行综合判断。结果表明：古盐度介于2．76％0～14．32％0之间，平均值为8．62％0，显示沉积水介质以淡水一微咸水为主；铈异常（Ceanom）值主要集中在-0．05～0．1之间，整体表现为ce富集，指示缺氧弱还原的古水体环境；Sr／Cu比值为1．66—9．41，平均值为4．60，环境为温湿气候。纵向上盒8_F古盐度高于盒8上，盒8下比盒8上气候略微干旱。平面上研究区南部米脂榆79井一榆28井一带和研究区北部通岗浪沟一什汗水利一带古盐度较大，大于10％o，属半咸水一咸水沉积，相对应地这两个区块古气候比其它区块较为干旱，这一规律和沉积体系在研究区的分布高度吻合。分析认为：盒8期研究区湖岸线分布于南部米脂榆79井一榆28井一带，受湖水和干旱气候的影响，造成古盐度较高；北部通岗浪沟一什汗水利一带发育辫状河沉积，受干燥气候、蒸发环境的影响，古盐度增大。研究区微咸水一半咸水一咸水的沉积环境有利于绿泥石膜胶结发育，也有利于储层的发育。该认识对鄂尔多斯盆地盒8沉积环境研究起到一定的补充作用，同时也对该区盒8段天然气勘探具有重要意义。

This study comprehensively analyzed about the salinity of ancient sedimentary environment, redox state and paleoclimate of He 8 Member of Shihezi Formation in east part of Ordos Basin. Various methods were used in the study such as the mass fraction of Sr, Sr/Ba, Rb, Rb/K, K＋Na, element method of K/Na, B/Ga, B, Ce anomaly（Ce ） value, trace element and macroelement, etc. The results show that the paleosalinity of study area is between 2.76‰ to 14.32‰ with an average of 8.62‰, which reflects fresh water to brackish water sediments; The Ce is mainly concentrated in the -0.05 to 0.1. The enrichment of Ce as a whole indicates a weak reductive water environment; Sr/Cu ratio ranges from 1.66 to 9.41 with an average of 4.60, which indicates humid climate. The paleosalinity of upper He 8 is higher than lower He 8 Member on vertical, and its climate is slightly arid than lower He 8 Member. The paleosalinity of well 79 and well 28 of Mizhi in the southern study area and Tongganglanggou-Shihanshuili on the northern study area is higher than 10‰ in a plane, which indicates brackish-saline water deposits. Correspondingly, the ancient climate of the two blocks is relatively more droughtier than other blocks. This achieves high conformity with the distribution characteristics of depositional system. The analysis suggests that the lake shoreline during He 8 period in study area is located in well 79 and well 28 of Mizhi area. Therefore the paleosalinity is higher on the affects by the lake and the arid climate. And braided river sedimentary was developed in Tongganglanggou-Shihanshuili on the northern part. The paleosalinity increased under the influence of arid climate and evaporation environmental. The brackish-salt water depositional environment of the study area is conducive to the development of chlorite cementation, and also to the development of reservoir. The conclusion not only plays a complementary role in the research of sedimentary environment on He 8 Member in Ordos Basin, but also has an important meaning for gas exploration in He 8 Member.