摘要
西藏吉隆县宗卓组顶部发现了丰富的浮游有孔虫动物群 ,其时代为晚白垩世马斯特里赫特期G .gansseri带的上部至A .mayaroensis带的下部 ,年龄值在 6 8— 70Ma之间。据江孜至吉隆一带地层和古生物学的研究与对比 ,认为特提斯 喜马拉雅北亚带的半深水至远洋环境是在康潘晚期至白垩纪末期由东向西逐步结束的 。
Marine Cretaceous is widespread in the Tethys Himalaya region. It has been accepted that the Himalayas was formed by collision of the Indian Plate with the south Asian margin. The northward shifting of the Indian Plate closed the Neothethys Ocean which lay to the north of the former. Suturing is thought to have occurred scissor like, with first contact in the western Himalayas as early as perhaps the latest Cretaceous (Beck et al ., 1995), and afterwards prograding eastwards. The collision in southern Tibet, by the recent study, started around the Cretaceous Tertiary boundary time (Wan et al ., in press). Prior to the collision, a pelagic ocean existed along the Yarlung Zangbo suture. The north margin of the Indian Plate was in continental slop and shelf positions. That part of sea in Cretaceous is called the Tethys Himalaya. This region is sedimentologically subdivided into the south Tethys Himalaya sub belt and north Tethys Himalaya sub belt. During the Latest Cretaceous, the south sub belt was a carbonate platform sedimentary belt that has been studied by many authors (Wen Shixuan, 1974; Wang Yigang, 1980; Wan Xiaoqiao, 1985,1991; Hao Yichun et al ., 1985; Willems, 1993). The north sub belt, however, was a semi pelagic to pelagic sedimentary belt. Due to the tectonic deformation and rare fossil preservation in the north sub belt, the stratigraphic sequence and dating were obscure. Recently, the authors found a rich planktonic foraminiferal fauna from the Gyirong region. The discovery of the fauna give an age to the stratigraphy of the northern sub belt, and also make a better understanding to the shifting progress of the Indian Plate to the north. The Cretaceous is distributed along the south sside of the Yarlung Zangbo suture zone and represented by a set of sandy and pelagic sediments intercalated with volcanic rocks and silicalites. The entire sequence of strata has been strongly deformed, especially near the Yarlung Zangbo opiolites. Tectonic mélanges and high pressure/low temperature metamorphism of greenschist facies are common. The lower Cretaceous is widely distributed in the northern sub belt, but locally extended into the upper Cretaceous. The strata of hemipelagic to pelagic facies in the north sub belt were named the Zongzuo Formation by Yang Zuyi et al. (1964). Wu Haoruo et al. described this formation in the Gyangze region as “the Beijia Mélange”. Li Xianghui et al. (1999) and Wang Chengshan et al. (2000) re studied the strata in Gyangze and roughly dated an age from late Early Cretaceous to Late Cretaceous for the Zongzuo Formation. The Zongzuo Formation also occurs in the Gyirong region, but has not been studied in detail in the previous work. The strata in the north part of the Gyirong region was found by scientists of the Chinese Academy of Science in 1966, and roughly refered to “Triassic”. Chen Guoming et al. (1980) and Qian Dingyu(1982) described the mélange feature of these strata. Wang Liancheng (1982) correlated the mélange in Gyirong with the Zongzuo Formation in Gyangze and supposed that the strata from both regions were late Cretaceous in age. Based on limited fossils of bivalves and foraminifera, Yin Jixiang et al.( 1988) suggested that the age of the strata in Gyirong is early Late Cretaceous. They put the strata in lower part of the Zongzuo Formation in Gyangze. As the fossil constrain is low, the age of the strata was not clear. The Upper Cretaceous strata crop out in the area from Sangdanlin to Dangla of the north part of the Gyirong region, where the strata were called the Zongzuo Formation after correlationg with those in the Gyangze region (Yin Jixiang et al. , 1988). The Sangdanlin section was measured by the present authors and studied in more detail. It is composed of the Zongzuo Formation and 584 m in thickness. In this work, an abundant planktonic foraminiferal fauna has been found from the top of the Zongzuo Formation. It is composed of 7 species of 4 genera: Globotruncana aegyptiaca Nakkady, G.arca (Cushman
出处
《古生物学报》
CAS
CSCD
北大核心
2002年第1期89-95,共7页
Acta Palaeontologica Sinica
基金
国家重点基础研究发展规划项目 (G19980 40 80 0 )
国家自然科学基金 (No .49872 0 0 3)资助课题
关键词
浮游有孔虫
白垩纪末期
西藏吉隆
时代
Planktonic foraminifera, Latest Cretaceous, Gyirong, Tibet
