摘要
志留纪是晚加里东运动对塔里木盆地古地理和古构造格局产生重要影响的构造变格阶段,以全盆地规模的不整合面为界,前志留纪以海相碳酸盐岩沉积为主的古环境转变为志留纪以海相碎屑岩沉积为主的古环境.开展志留纪沉积充填序列及岩矿特征研究,有助于进一步认识塔里木盆地该变格阶段构造运动特征及其沉积充填响应.为此,精选柯坪露头区志留系出露连续、完整的大湾沟及四石场剖面,进行了露头精细沉积学观察采样及室内分析测试工作,描述和重建了早、中志留世沉积环境、沉积序列及其所反映的海平面变化,在此基础上划分了层序地层单元.下、中志留统可识别出陆棚、三角洲和潮汐影响的海岸等沉积体系类型,大型三角洲的存在则是柯坪露头区的特色.通过砂岩碎屑组分构成研究,并与Dickinson的砂岩组构大地构造背景模式图解对比,揭示该区早、中志留世砂岩沉积物主要来自碰撞造山带和前陆隆起区以及大陆块的物源区,该结果反映了志留纪早期,受晚加里东运动影响,塔里木周缘发生汇聚碰撞,并由此造成塔里木地块南部和北部构造抬升并形成剥蚀区的背景.综合分析揭示早、中志留世沉积序列对构造和海平面变化响应特征.受晚加里东运动影响,早期(柯坪塔格组沉积期)构造活动较强,海平面波动明显,在陆棚基础上发育有大型三角洲沉积.其砂岩岩屑含量高、成分成熟度低,总体反映了构造活动期快速抬升导致大量物源注入的特点;后期(柯坪塔格组上部-依木干他乌组沉积期)构造活动逐渐减弱并趋于稳定,海平面低幅度波动,主要以潮坪、潮道、小型三角洲和泻湖沉积为主,砂岩成分成熟度高,细粒沉积物比例加大.总体上,早、中志留世沉积序列反映了构造活动由强逐渐减弱并对凹陷区逐渐填平补齐的演化特征.
The Silurian,influenced by the Late Caledonian movement,is a significant change stage of palaeoenvironments and palaeotectonics in Tarim basin.The transformation from Pre-Silurian marine carbonate dominant deposits into Silurian marine clastic dominant deposits is bounded by the basin-scale unconformity surface at the bottom of Silurian.It is important to recognize the character of the tectonic movement and its depositional response by studying the sedimentary successions and mineral and lithological feature of sandstone in this period.Therefore,the outcrops in Keping area,where the Silurian depositional sequence is continuous and of perfect exposure,were selected for this study.Based on the detailed outcrop observation,sampling and laboratory tests,the sedimentary environments and successions of the Early-Middle Silurian,and its responses to sea-level changes are reconstructed,and then sequence stratigraphy units are divided.Continental shelf,deltas and tidal influenced shoreline etc.are recognized from the Lower-Middle Silurian in Keping area.Large scale deltas deposits have been founded in the Lower Silurian.The study results of sandstone framework mineralogy composition,compared with Dickinson’s framework modes,reveal that the Early-Middle Silurian sandstone were mainly derived from the provenance of collision orogenes,forebulge,and continental block.It directly reflects that the orogene around the Tarim plate’s impact was due to the Late Caledonian compression during the Early Silurian.As a result,the north and the south of the Tarim plate were uplifted and a large denudation area was formed.Sedimentary successions analysis reveals the tectonics and eustatic fluctuation in the period of the Early-Middle Silurian.During the early stage（Kepingtage stage） of the Early-Middle Silurian,tectonic activity was intensive and eustatic fluctuation was obvious under the influence of the Late Caledonian movement.As a result,large scale delta systems with lower maturity and higher lithic content sandstone on the b
出处
《地球科学（中国地质大学学报）》
EI
CAS
CSCD
北大核心
2011年第3期541-554,共14页
Earth Science-Journal of China University of Geosciences
基金
中石化前瞻性项目"塔里木盆地台盆区古构造古环境及其动态演化"(No.YPH08114)
关键词
塔里木盆地
志留系沉积序列
砂岩组构
构造
Tarim basin； Silurian sedimentary successions； sandstone fabric； tectonics；
