摘要
江孜盆地紧邻雅鲁藏布江缝合带,随着特提斯洋的演化及最终消亡,盆地必然随之经历一系列演化,分析其沉积响应是了解盆地演化的一个重要手段。因而,本文以分布于江孜地区的晚侏罗世至古近纪海相沉积地层为研究对象,在前人建立的地层格架基础上,基于野外露头和镜下观察,仔细分析了其沉积岩石学特征。江孜地区晚侏罗世至古近纪沉积序列为:石英砂岩(上侏罗统维美组)-页岩夹火山岩屑砂岩(下白垩统日朗组)-黑色硅质/钙质页岩(中白垩统加不拉组黑层段、白层段)-黑色硅质岩(上白垩统加不拉纽硅质岩段)-红色硅质页岩、泥灰岩夹滑塌灰岩(上白垩统床得组)-灰绿色页岩夹外来岩块(上白垩统宗卓组)-砂/页岩互层(古近系甲查拉组)。从中可以看出海水从维关组至加不拉组硅质岩段为逐渐加深的过程,而至甲查拉组海水再次浅于硅质岩段沉积水深。生物沉积、悬浮沉积及块体搬运作用沉积常见,其中块体搬运作用包括砂质碎屑流、浊流、滑塌和岩崩等,沉积环境为大陆斜坡至深水洋盆。通过沉积学与沉积地球化学分析可知,底层水经历了缺氧、氧化再到缺氧的过程。根据沉积岩石学特征结合沉积环境分析,从较长的时间尺度上将盆地的演化历史划分为四个阶段:晚侏罗世至早白垩世被动大陆边缘盆地稳定发育阶段,白垩纪中期被动大陆边缘盆地持续沉降阶段,晚白垩世残留被动大陆边缘盆地阶段,白垩世末期至始新世初期为残留洋盆地阶段。
Gyangze basin located immediately on the south of the Indus-Yalung Zangbo Suture （IYZS） evolved along with the evolution of the Tethyan Ocean. The evidences of the evolution history of a basin generally recorded well in the sediments. Based on the published stratigraphy framework of Upper Jurassic to Paleogene in Gyangze basin, this paper studied the petrology of the strata with observation on the sedimentary rocks in the field and under the microscope. The sediments of Upper Jurassic to Lower Paleogene in Gyangze Basin is a sequence of quartz arenites （Weimei Fm）, shales intercalated with sublitharenites （Rilang Fm）, black siliceous and calcareous shales （ black unit and white unit, Gyabula Fm）, chert （ chert unit, Gyabula Fm）, red shales intercalated with limestones （Chuangde Fm）, shales with olistoliths （Zongzhuo Fro）, and sandstones interbedded with shalds （Gyachala Fm）. This sequence indicates that the water was deepened from Weimei Fm to Gyabula Fm, while the Gyachala Fm records the shallower water sediments than Gyabula Fm to Zongzhuo Fm. Biogenic sediments, suspended sedimentation and mass flow including sandy debris-flow, turbidity current, slump and rock slide were common in the sections. The depositional environments of the strata are of deep water, most likely slope to oceanic basin. Based on the distribution of major element, we suggested that the bottom water of Gyangze basin was mainly anoxic or dysoxic during late Jurassic to early Paleogene, but the late Cretaceous red unit was deposited under an oxic condition. According to the petrology and depositional environments of sedimentary rocks, we divided the evolution history of Gyangze basin into four stages from late Jurassic to early Paleogene： stable basin stage during late Jurassic to early Cretaceous, subsiding basin of mid- Cretaceous, residual basin of passive continental margin late Cretaceous, and remnant ocean basin of latest Cretaceous to early Eocene.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2008年第3期616-624,共9页
Acta Petrologica Sinica
基金
国家重点基础研究发展计划项目(编号2006CB701400)资助
关键词
沉积岩石学特征
沉积环境
盆地演化
江孜
西藏
Petrology
Depositional environment
Evolution of Gyangze basin
Southern Tibet
