【作者】 胡修棉；

【导师】 王成善；

【作者基本信息】 成都理工大学 ， 古生物学与地层学， 2002， 博士

【摘要】 特提斯洋的形成与演化一直是地学界长期讨论的焦点，尤其是印度与欧亚板块碰撞之前的白垩纪东特提斯洋更是科学家们努力追寻的目标，而揭开东特提斯神秘面纱的记录就保存在现今世界屋脊的特提斯喜马拉雅地区。白垩纪是地质历史中的一个极其特殊的时期，其全球性海平面变化、全球性分布的富有机质的黑色页岩、全球性的碳酸盐台地的沉没以及全球性火山作用和与之有关的极端温室气候、碳旋回等地学现象一直是近几十年来地学界关注的热点。本文围绕着以上两个热点，选择特提斯喜马拉雅白垩系为研究对象，对藏南白垩系沉积地质以及上白垩统海相红层两个科学问题进行深入而全面的研究。 长期以来，西藏特提斯喜马拉雅白垩系地层格架没有达成共识，对于沉积环境和沉积相研究更是重视不够，而且，地层划分多是基于藏南白垩系本身研究所提出的，对境外特提斯喜马拉雅地区白垩系缺乏系统的对比和分析。本文根据实际资料和前人成果，重新厘定研究区白垩系地层系统。特提斯喜马拉雅南带自下而上地层系统为：古错组(? Berriasian早期～?Aptian)、岗巴东山组(?—Aptian)、察且拉组(Albian期)、冷青热组(Cenomanian期～Turonian早期)、岗巴村口组(Turonian～Santonian期)、宗山组(Campanian～Maastrichtian)和遮普惹山坡组(Maastrichtian中晚期～Danian期)：特提斯喜马拉雅北带加不拉组包括整个早白垩世和晚白垩世早期，最晚可达Coniacian期，其中黑层段构成了整个下白垩统，底界应低于Valanginian阶，顶界可到上白垩统Cenomanian底部，白层段相当于Cenomanian至Turonian，而硅质岩段时代大致为Coniacian期。床得组为Santonian-Campanian期，宗卓组时代可跨整个晚白垩世，并穿时到古新世。 岩石学研究表明，特提斯喜马拉雅南带白垩系岩石类型有泥质岩、陆源碎屑砂岩、碳酸盐岩以及碳酸盐岩与陆源碎屑砂岩混积岩等四大类：北带江孜白垩系岩石有碳酸盐岩、泥质岩、硅质岩和碎屑岩类；羊湖地区床得组红层岩石类型可划分为四大类：碳酸盐岩、泥质岩、硅质岩和碎屑岩类。南带白垩系沉积相分为陆源碎屑陆棚相、碳酸盐与陆源碎屑混积的陆棚相、碳酸盐陆棚相、生物礁相、(半)远洋相、大陆斜坡相等六大类；北带江孜地区为斜坡—远洋相带，并见火山沉积建造，主体环境位于斜坡带以下的半远洋和远洋地带，并划分上斜坡、下斜坡、(半)远洋和海相火山沉积相四种类型。 根据岩石学、沉积相及其演化特征，本文将西藏特提斯喜马拉雅白垩纪沉积历史划分为六个阶段：A侏罗纪末期—白垩纪早期(Tithonian～Berriasian)石英砂岩沉积；B早白圣世旧e巾asian－APtian）火山岩屑沉积。C中白要世（Abian－Coniacia n）黑色页岩 A沉积；D晚白要世早期（S。山巾—～＊一p—I二 ）深水红色沉积：E晚白圣世晚期 （＊一p咖。晚期－＊删d＊M。早期）碳酸盐沉积和滑塌沉积：r白晋纪末期－古新世早期（Maastrichtian晚期～Danian早期）混积沉积和滑塌沉积。 在对藏南白圣纪沉积地质详细研究基础上，本文对尼泊尔喜马拉雅和LhadAn喜马拉雅白圣系进行了对比。结果发现，从白要系底部石英砂岩开始到火山碎屑岩出现，喜马拉雅东部地区比西部地区要早 15—20Ma。SPih页岩在 Zanskar地区结束历史比藏南地区晚将近15Ma，而石英砂岩结束的历史藏南地区要比 Zanskar地区晚 18Ma；在藏南地区早白碧世火山岩屑砂岩时代大致为？Be巾asian～Albian早期，延续时间超过30Ma；而在Thakkhola地区时代为Hauterivian晚期－Albian早期，延续时间约20Ma，在Zanskar地区火山岩屑砂岩仅仅出现在Albian期，延续时间小于10Ma。对比研究还发现，火山岩屑砂岩结束的时间均在Albian中晚期，随后整个特提斯喜马拉雅地区Albian晚期出现典型暗色－黑色泥质岩并以含海绿石和磷酸盐层为特征，代表着最大海泛面时期；晚白要世藏南陆棚相地区相对于 Zanskar地区细碎屑沉积更发育，在 Zanskar地区则直接过渡到 Chikkim组／Fain La组远洋灰岩。Carnnanian－Maastrichtian期Zanskar地区大体与藏南相当，整体为一个海平面 炳下降的过程。特提斯喜马拉雅斜坡相对比研究表明，从构造属性来看，Lamnyuru－Karamba构造带和江孜地区分别为活动的受火山作用影响的斜坡环境和稳定的斜坡环境，并一致性地出现稳定的晚白翌世红色远洋灰岩、红色页岩，但江孜地区晚白要世出现滑塌堆积，而Zanskar地区地层缺失，发生构造侵位。 基于以上研究，本文初步恢复了特提斯喜马拉雅沉积一构造演化历史。诛罗纪末－白坚纪初印度大陆的北缘同时期存在大陆向上挠曲，导致陆源碎屑输入量的快速增加，石英砂岩广泛存在：早白圣世火山岩屑砂岩对应着的印度大陆北缘地层侵蚀加深，使得较深部的深成火山岩暴露并遭受侵蚀；石英砂岩和早白要世岩屑砂岩所代表的印度大陆剥露时间在空间上的“东早西晚”，说明构造运动首先是从特提斯喜马拉雅的东部开始（大印度（GreatIndia）与澳大利亚的彻底分离），然后逐渐波及西部的，东西时间差为15—20Ma；由于地壳均衡作用，大陆分离后原先地壳挠曲转变为地壳下更多还原

【Abstract】 Studies of the evolution and changes in the Tethys Ocean occurring during past 200 Ma may provide a model for future oceanic evolution and a key to the knowledge of our planet’s global behavior (Cadet, 1996).Particularly the Cretaceous time period is a time of major changes in the Earth Systems demonstrated by major plate tectonic processes, as is the dispersal of Pangea supercontinent, plaeoclimate and paleoceanography changes. Such changes are revealed for example by worldwide distribution of organic-rich black shales, occurrence of oceanic anoxic events, periods of carbonate platforms drowning, high oceanic production, and brief periods of an extreme hot climate. Causes of many such changes are poorly understood. Therefore studies of the Cretaceous strata in southern Tibet contribute to the understanding of above processes and particularly to the global carbon cycling.We may ask: what happened during Cretaceous in eastern Tethys? This question can only be answered from the stratigraphical records in Tethys Himalaya. That is the reason why 1 select the Cretaceous in Tibetan Tethys Himalayas as my thesis topic.Based on field studies by the author and research by previous workers the Cretaceous stratigraphy in southern Tibet is refined. The Cretaceous in the southern subzone of Tibetan Himalaya consists upward of Gucuo Formation (? early Berriasian ~?Aptian), Gangbadongshan Fm. (? -Aptian), Chaquiela Fm. (Albian), Lengqingre Fm. (Cenomanian -early Turanian), Gangbachunkou Fm. (Turanian -Santonian), Zongshan Fm. (Campanian -Maastrichtian), and Zhepure Shanpo Fm. (middle-late Maastrichtian ~Danian). In the northern subzone of Tibetan Himalaya, the Gyabula Fm. can be extended from pre-Valanginian to Coniacian. The Chuangde Fm. is of Santonian ~ Campanian according to studies of planktonic foraminifera and nannofossils, while the overlying Zongzhuo Fm. is of latest Cretaceous through Paleocene age.Study of sediment composition and sedimentary microfacies of Cretaceous sedimentary sequences in Tibetan Himalayas allow to separate six stages in their development: 1) latestJurassic to earliest Cretaceous (Tithonian ~Berriasian) widespread deposition of quartz arenitic sandstone; 2) Early Cretaceous (Berriasian ~Aptian) occurrence of volcanic sandstones; 3) Middle Cretaceous (Albian ~ Coniacian) black shales deposition; 4) early Late Cretaceous deposition of oceanic red beds (Santonian ~ Campanian) on a continental slope, while shale was deposited on a shelf; 5) late Late Cretaceous (late Campanian -Maastrichtian) carbonate-rich sediments were deposited on a shelf and olistoliths on the slope; 6) latest Cretaceous to earliest Tertiary (late Maastrichtian ~ early Danian) deposition of mixed carbonate and elastics on the shelf and olistoliths on continental slope.The sedimentary geology study of the Cretaceous in the southern Tibet allows correlation with the Cretaceous strata both in Nepal Himalaya and Lhadkh Himalaya. Results show that the Spiti shale in Zanskar terminated 15Ma later than that in southern Tibet, while the lowermost Cretaceous quartz sandstone in Zanskar appeared 18Ma later than that in southern Tibet. The age of volcanic sandstone in southern Tibet is very poorly time constraint and their deposition occurred somewhere within Berriasian -early Albian. In Thakkhola, the Chukh Group volcanic sandstone are of late Hauterivian -early Albian age (duration about 20Ma), while in Zanskar, the volcanic sandstones facies only appeared in Albian (duration of less than lOMa). Therefore, it can be concluded that the onsets of both quartz sandstone and volcanic sandstone occurred earlier in eastern Tethys Himalayas (southern Tibet) than in western Tethys Himalayas (Lhadkh). It implies that during early Cretaceous major geotectonic activity occurred earlier on the eastern side of the India continental plate than at its western part, perhaps 15~20 Ma earlier in east This is interpreted to be the result of separation of Australia from Greater India.The continental doming preceding the break-up of Gond更多还原