西藏南部晚白垩世—古新世大洋红层的分布与时代

The distribution and ages of Late Cretaceous-Paleocene oceanic red beds in southern Tibet.

特提斯-喜马拉雅北沉积亚带沉积有一套大洋红色岩层,由东往西在羊卓雍错、江孜、萨迦、萨嘎、札达一带断续出露,并与宗卓组上部地层相关.这套海相红层,根据岩性特征和浮游有孔虫可以直接进行区域对比.其时代在江孜地区为Santonian晚期-Campanian中期,包括Dicarinella asymetrica, Globotruncanita elevata,Globotruncana ventricosa和Globotruncanita calcarata浮游有孔虫带;在萨迦地区限于Campanian期,鉴定有Globotruncanita elevata, Globotruncana ventricosa和G. linneiana等具时代意义的浮游有孔虫;在萨嘎-吉隆地区为Maastrichtian期,识别出Gansserina gansseri和Abthomphalus mayaroensis浮游有孔虫带;在札达地区为古新世早期,以Glibigerina eugubina-G. fringa化石带为代表.海相红层在西藏南部由东往西其时代逐渐变新,主要沉积时代分布在Santonian晚期-古新世早期.其总体时间跨度较大,大约长达20 Ma. 而事件在各个地点的延续时间有限,基本在3～8 Ma之内.根据对海相红层和沉积基质中浮游有孔虫的研究,该沉积带宗卓组的顶界时代已超出白垩纪,进入了古新世.

Oceanic red beds are deep marine sediments deposited under pelagic oxic conditions. They are widespread in southern Tibet, south of the Indus-Yarlung Zangbo suture. As a typical locality, the oceanic red beds in the Chuangde Section span an age from the late Santonian to the middle Campanian, and consist of the Dicarinella asymetrica, Globotruncanita elevata, Globotruncana ventricosa and Globotruncanita calcarata planktonic foraminiferal zones. Westward near Sagya, the red beds in the Saiqu section consist of Globotruncanita elevata, Globotruncana ventricosa and G. linneiana planktonic foraminifera, and are of Campanian age. Farther west in the Saga-Gyirong region, an abundant planktonic foraminiferal fauna was described from these red beds. The age of the microfauna is Maastrichtian and is correlated with Gansserina gansseri and Abthomphalus mayaroensis zones. In the Zanda region of the westernmost Tibet, the Longji section yields a large amount of planktonic foraminifera. They are referred to the Globigerina eugubina-G. fringa fauna of the early Paleocene. The red sequences, and the strata in southern Tibet tend to be younger from east to west.