浅谈内蒙古大兴安岭地区中南部侏罗系与白垩系之界线

DISCUSSION ON THE BOUNDARY BETWEEN JURASSIC AND CRETACEOUS IN SOUTH-CENTRAL DAXINGANLING REGION,INNER MONGOLIA

通过对大兴安岭地区侏罗系与白垩系之间不整合面的讨论,以地层区域对比及同位素测年数据等信息确定其界线,达到本区侏罗系与白垩系界线的可识别性、客观性和稳定性之目的.同时,对该区主要地层形成的大地构造环境的研究,认为土城子组是碰撞造山后伸展阶段形成的一套陆相红层,也是侏罗纪结束的标准层;而满克头鄂博组、玛尼吐组和白音高老组则是碰撞造山后垮塌阶段形成的火山地层.以大规模火山爆发为特征,本区开始了白垩纪地壳演化阶段.侏罗系与白垩系界线位于土城子组与满克头鄂博组之间,二者界线以区域不整合(假整合)为特征,不整合面形成于碰撞造山后伸展与垮塌的转换时期.

By discussion on the unconformity between Jurassic and Cretaceous in the south-central Daxinganling region, combining with regional stratigraphic correlation and isotope data, the boundary with identifiablity,objectivity and stability is determined. With study on the geotectonic setting for the forming of major strata, it is believed that the Tuchengzi Formation is a set of continental redbeds formed in the collision of post-orogenic extensional tectonic stage and is also the marker bed of the end of Jurassic, while Manketouebo Formation,Manitu Formation and Baiyingaolao Formation are volcanic strata formed in the post-collisional orogenic collapse tectonic stage. The Cretaceous crustal evolution begins with massive volcanic eruptions. The boundary of Jurassic and Cretaceous is between the Tuchengzi Formation and Manketouebo Formation, which is characterized by regional unconformity or disconformity. The unconformity surface is formed in the transition period from extension to collapse of post-collisional orogeny tectonic background.