摘要
珠穆朗玛峰北坡下侏罗统由乌垅组、康堆组和永佳组三个岩石地层单位组成。它们分别形成于碳酸盐缓坡、断陷盆地和碳酸盐台地三种不同的沉积环境,共包括6个沉积相。本区在早侏罗世经历了强烈的断陷下沉,属成熟裂谷盆地。下侏罗统含11个三级层序,3个二级层序,构成一个大的海进-海退旋回。三级层序在特提斯区具有良好的可比性,与全球海平面变化有密切联系;而二级层序与基底沉降及沉积速率变化直接相关,反映了新特提斯的演化及其两侧的板块活动。
The Lower Jurassic on the north slope of the Mt. Qomolongma is dominated by lithic sandstone of gravity flow origin alternating with dark shales, with a total thickness of 1362 m. From the bottom upwards, three new subdivisions, the Wulong (227 m), Kangdui (865 m) and Yongjia (220 m) Formations, are set up. They are thought to have been deposited respectively in environments of carbonate ramp, fault-bounded basin and carbonate platform. Six sedimentary facies and six sub-facies are recognized in the Lawer Jurassic, and two sedimentary models, the carbonate ramp to fault-bounded basin and the basin to carbonate platform, have been suggested respectively for the early and late Early Jurassic.The Lower Jurassic consists of eleven 3rd-order sequences, which can be further grouped into three clearly defined 2nd-order sequences and constitute a large transgressive-regressive cycle. The study indicates that, during the Early Jurassic, the Qomolongma area had experienced sea-level drop with large amplitude several times, resulting in exposure of sedimentary basement (in the early and late portion) and the development of slump and gravity flow deposits (in the mid portion). The recognized 3rd-order sequences may have been mainly caused by the eustacy, while the 2nd-order sequences seem to be more closely related to the changes in the rates of the basement subsidence and sedimentary influx, reflecting mainly the evolution of the Neotethys and the movements of the plates on its two sides.In the Early Jurassic, the Qomolongma area underwent strong rifting and subsidence, giving rise to a matured rift basin. At 177 Ma B. P. , the tectonic activity in the region was subdued rather evidently, thus a new stage- the inter-continental sea period-started.
出处
《地质学报》
EI
CAS
CSCD
北大核心
1996年第1期73-83,T001,共12页
Acta Geologica Sinica
基金
国家重大基础性研究项目<中国东部古大陆及其边缘层序地层及海平面变化研究>
关键词
下侏罗世
沉积相
层序地层
珠穆朗玛峰
Lower Jurassic, sedimentary facies, sequence stratigraphy, sea-level change, Mt. Qomblongma
