西藏南部羊卓雍措地区晚侏罗世维美组沉积特征及环境演化
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摘要
通过沉积岩石学、岩相学、粒度分析等研究方法,对维美组沉积特征、沉积环境及演化提出新的认识和探讨。晚侏罗世维美组主要为一套陆源碎屑物质沉积,沉积期共经历4个沉积旋回,每个沉积旋回的岩石组合大致为含砾石英砂岩-中、粗粒石英砂岩-细粒石英砂岩(长石石英砂岩)-粉砂岩(泥岩、页岩),由底到顶粒度变细,层厚减薄。识别出6种岩相类别:含砾石英砂岩、石英砂岩、长石石英砂岩、泥质粉砂岩、薄层页岩-泥岩互层;发现平行层理、水平层理、粒序层理和重荷模等沉积构造;识别出陆棚、滨岸和陆棚下切河道3类沉积相,其中陆棚相包括内陆棚和外陆棚亚相,滨岸相包括近滨上部和近滨下部亚相;陆棚下切河道充填结构大致为:下部河道砂砾岩层,中部不等粒长石砂岩、杂砂岩层,上部细粒石英砂岩、泥岩层。综合来看,维美组沉积环境为位于克拉通边缘上浅海环境,沉积物质及沉积序列受海平面升降变化影响显著,主要形成于全球海平面下降之后上升的阶段。
In this paper,the sedimentary characteristics,environment and evolution of Weimei Formation are studied by means of sedimentary petrology,petrography and particle size analysis.The Late Jurassic Weimei Formation(J3 w) was mainly composed of a set of terrigenous clastic sediments.The sedimentary period has experienced four sedimentary cycles,the rock assemblage of each sedimentary cycle is pebbly sandstone(breccia)-medium,coarse quartz sandstone-fine grained quartz sandstone(feldspathic quartz sandstone)-siltstone(mudstone,shale),the size of the bottom to the top is finer and the thickness is thinner.There are 6 major types of lithofacies were identified:pebbly sandstone,quartz sandstone,feldspar quartz sandstone,clayey siltstone,shale-mudstone interlayer,shale.It is found that parallel bedding,horizontal bedding,grain sequence stratification structure,load casts deformation structure.Three types of sedimentary facies are identified:shelf facies,shoreline and incised valley,among which shelf facies include inner shelf and outer shelf subfacies, and shoreline facies include backshore,foreshore and nearshore subfacies.The filling structure of the incised valley is roughly as follows:sand and gravel strata in the lower channel,arkose and miscellaneous sandstone layers of unequal grains in the middle,quartz sandstone and mudstone layers of fine grains in the upper part.On the whole,the sedimentary environment of Weimei Formation is located in the shallow sea environment on the edge of craton, and the sedimentary material and sequence are significantly affected by the change of sea level rise and fall, mainly forming the rising stage after the global sea level drop.
In this paper,the sedimentary characteristics,environment and evolution of Weimei Formation are studied by means of sedimentary petrology,petrography and particle size analysis.The Late Jurassic Weimei Formation(J3 w) was mainly composed of a set of terrigenous clastic sediments.The sedimentary period has experienced four sedimentary cycles,the rock assemblage of each sedimentary cycle is pebbly sandstone(breccia)-medium,coarse quartz sandstone-fine grained quartz sandstone(feldspathic quartz sandstone)-siltstone(mudstone,shale),the size of the bottom to the top is finer and the thickness is thinner.There are 6 major types of lithofacies were identified:pebbly sandstone,quartz sandstone,feldspar quartz sandstone,clayey siltstone,shale-mudstone interlayer,shale.It is found that parallel bedding,horizontal bedding,grain sequence stratification structure,load casts deformation structure.Three types of sedimentary facies are identified:shelf facies,shoreline and incised valley,among which shelf facies include inner shelf and outer shelf subfacies, and shoreline facies include backshore,foreshore and nearshore subfacies.The filling structure of the incised valley is roughly as follows:sand and gravel strata in the lower channel,arkose and miscellaneous sandstone layers of unequal grains in the middle,quartz sandstone and mudstone layers of fine grains in the upper part.On the whole,the sedimentary environment of Weimei Formation is located in the shallow sea environment on the edge of craton, and the sedimentary material and sequence are significantly affected by the change of sea level rise and fall, mainly forming the rising stage after the global sea level drop.
引文
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[16]胡修棉.藏南白至系沉积地质与上白至统海相红层——大洋富氧事件[D].成都理工大学,2002:76-83.
[2]西藏自治区地质矿产局.西藏自治区区域地质志[M].北京:地质出版社,1993,1-107.
[3]李廷栋,潘桂堂,肖序常,等.青藏高原隆升的地质记录及机制[M].广东省出版集团,2013,15-29.
[4]聂凤军,胡朋,江思宏,等.藏南地区金和锑矿床(点)类型及其时空分布特征[J].地质学报,2005,79(03):373-385.
[5]余光明,王成善.西藏特提斯沉积地质[M].北京:地质出版社,1990,1-185.
[6]李祥辉,王成善,胡修棉.深海相中的砂质碎屑流沉积——以西藏特提斯喜马拉雅侏罗—白垩纪为例[J].矿物岩石,2000,20(1):45-51.
[7]夏军,钟华明,童劲松,等.藏南洛扎地区侏罗、白垩纪岩相古地理特征[J].沉积与特提斯地质,2005,25(3):8-17.
[8]江新胜,颜仰基,潘桂棠,等.藏南特提斯晚侏罗世维美组的沉积环境[J].地质通报,2003,22:900-907.
[9]高莲凤,周巍,张盈,等.藏南贡嘎晚侏罗世—早白垩世海相地层地球化学特征与古海洋环境演化[J].2017,24(1):195-204.
[10]王义刚,孙东立,何国雄.喜马拉雅地区(我国境内)地层研究的新认识[J].地层学杂志,1980,4(1):55-59.
[11] Folk R L,Ward W C.Brazos River bar:a study in the significance of grain size parameters[J].Journal of Sedimentary Research,1957, 27(1):3-26.
[12] Garzanti E.,Straigraphy and sedimentary history of the Nepal Tethys Himalaya passive margin[J].Journal of Asian Earth Science.1999,17:805-827.
[13]杨明春,郑常青,张梅生,等.辽宁兴城地区中元古界长城系大红峪组石英砂岩质砾岩古沉积环境研究[J].矿物岩石,2012,32(3):103-109.
[14] Garzanti E..Stratigraphy of the Early Cretaceous Giumal Group(Zanskar Range. Northern India)[J].Rivista Italiana Paleontologia Stratigrafia,1991,97:485-509.
[15] Gibling M.R.,et al.Early Cretaceous strata of the NePal Himalayas:conjugate margins and rift volcanism during Gondwanan breakup[J].Journal of Geological Society, London.1994,151:269-290.
[16]胡修棉.藏南白至系沉积地质与上白至统海相红层——大洋富氧事件[D].成都理工大学,2002:76-83.
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