摘要
在藏北双湖地区发现中侏罗世早期腕足动物13属19种。建立了Aalenian至早Bajocian期Ptyctorhynchia duogecoensis-Tubithyris tibetica和中、晚Bajocian期Cymatorhynchia densecosta-Monsardithyris ventricosa两个腕足动物组合。认为特提斯北支的演化发展及两侧板块活动是控制青藏高原北部古地理的主要因素,并决定了腕足动物群的分布特征。
The brachiopods dealt with in this paper are from the area of Latitude Nortb 33皛35?and Longitude East 85?0'~87?0' in North Tibet, where a little work has been done on the Jurassic and its fauna.So far as the northern Qinghai-Tibe-tan Plateau is concerned,these brachiopods are of the lowest benthic faunas found in the Jurassic. The brachiopods studied include 19 species of 13 genera and bio-stratigraphically can be grouped into two assemblages: Ptyctorhynchia duo&e-coensis-Tubithyris tibetica Ass. (Aalenian-Lower Bajocian)occurring in the lower to middle part of the Sewa Fm., and Cymatorhynchia densecosta-Monsardithyris ventricosa Ass. (Middle-Upper Bajocian) being yielded in the upper part of the Sewa Fm. (or its equivalent, the Quemoco Fm.) to the bottom of the Matuo Fm. in which Burmirhynchichia-Holcothyris fauna has been found in abundance. Based on the distribution of the'brachiopods and other evidence, a general outline of the paleogeographic changes in the northern Qinghai-Tibetan Plateau as well as the movements of the Gangdese-Nianqeng Tanggula and the Qiangtang Tanggula ter-raines during Jurassic have been traced out.It is proposed that the north branch of the Eastern Tethys opened in the Early Jurassic along the Bangong Lake桸ujiang River, but the significant sea-water invasion did not happen until the Middle Ju-rassic. By the opening of the North Branch, sea-water invaded mainly from west to east and was also accompanied with the northwards directed transgression.Du-ring Bathonian, the transgression attained its largest extent, covering eastwards Eastern Yunnan and Northern Burma and reaching northwards to the north of Yanshiping-Suxian-Denqeng. Since Callovian, a regression had taken place gradu-ally from east to west with a sea-water retreating southwards. By the end of Jurassic, the Gangdese-Nianqeng Tanggula terraine collided with the Qiangtang-Tanggula terraine which had become the south margin of the China continent and the north branch of the Eastern Tethys vanished. Since Cretaceous, the north part of the plateau had gotten rid of sea-water, and the sea-waters were restricted to the south of Gangdese-Nianqeng Tanggula terraine.
出处
《地球科学（中国地质大学学报）》
EI
CAS
CSCD
北大核心
1990年第3期251-256,共6页
Earth Science-Journal of China University of Geosciences
关键词
腕足动物群
中侏罗世
石地理
Aalenian, Bajocian, brachiopods, biostratigraphy, paleogeography, plate-tectonics.
