摘要
海陆交互相侏罗、白垩系,在中国只有西藏北部(南以雅鲁藏布江、北以怒江、班公湖线为界)系统发育,并以拉萨地区发育最好。拉萨地区的侏罗白垩系的研究,是从六十年代初开始的。在我们研究之前,已建立了属白垩系的林布宗组、楚木龙组与塔克拉组(但组段划分与时代确定方面尚有不少问题);属侏罗系的只有多底沟组。以上四组皆属拉萨北部岩相带。拉萨南部岩相带原只知有一组,即曾归于三叠系的叶巴组,我们认为应归属于上白垩统。
The present paper includes the following parts:a brief history of study,stratig-raphy of different zones,ages of the formations,sedimentary cycles and paleoenviron-ments.There are two(northern and southern)facies zones of the Juro-Cretaceous inLhasa Area,consisting of twelve formations,of which eight occur in the northern zone,four-in the southern one with seven newly erected.The northern zone:Jialapu Formation(Rhaetic-Lias)is represented by blackshale and limestone with thin coal seams,containing plant remains,such as Equisetumcf.sarrani,pollen and spores;Quosang Hot Spring Formation(Uppermost Middle tothe basal Upper Jurassic)is composed of sandstone and shale,containing bivalves,suchas Astartoides dingriensis;Duodigou Formation(Upper Jurassic)is represented bylimestone,containing Pseudocyclammina ex.gr.lituus(foraminifer)and Salpingoporella annulata(calcareous algae)etc.;Linbuzong Formation(Tithonian to Neocomian)iscomposed of shale intercalated with sandstone,containing the ammonite Virgatosphin-ctes at the base and plant remains(chiefly the Wealden Flora)throughout the forma-tion;Chumulong Formation(Upper Neocomian)is composed of sandstone,containingfossil plants;Langba Formation(Uppermost Neocomian to Lower Aptian)is repre-sented by the alternations of sandstone and shale,intercalated with tuff,Takla Forma-tion(Upper Aptian to Albian)is composed of limestone,marl and shale,containingOrbitolina texana(foraminifer)etc.;Shexing Formation(Upper Cretaceous)is repre-sented by variegated and red beds with volcanics in the upper part,containing Am-phidonte astracina(bivalve)and Homacephale cf.calathoceros(dinosaur)etc.Thissuccession is limited from below by the Upper Triassic Mailonggung Formation(orGroup)and from above by the Tertiary Linzizong Formation.The southern zone:Budala Formation(Upper Jurassic to basal Cretaceous)iscomposed of calcareous-clayish flysch-like series,containing small brachiopod Acantho-thyris aff.sentosa and belemnites etc.;Niedang Formation(Neocomian)is representedby sandy-clayish flysch-like series,containing fragmented bivalves,ammonites and plantremains;Liuwu Formation(Aptian to Albian)is characterized by limestone withsiliceous nodules,andesite and sandy-clayish deposits,containing Orbitolina texana(foraminifer);Yeba Formation(Upper Cretaceous)is composed of variegated ande-site,tuff and slate.So far,no strata have found to be earlier than the Budala For-mation in the southern zone and the overlying strata may be a series of massivevolcanics,equivalent to the Linzizong Formation.The main results of this study are as follows:1.The Juro-Cretaceous stratigraphic succession have been founded,includingtwelve formations,of which seven-Jialapu,Quosang Hot Spring,Langba,Shexing,Budala,Niedang and Liuwu Formations-are newly named.2.A large number of fossils have been collected.Except the"Wealden Flora"from the Linbuzong Formation,most fossils are newly discovered or restudied.3.Two facies zones have been found out,i.e.the northern and the southern facieszones.Besides,the southern one has not been recognised previously and its Stratigrap-hic succession is now founded for the first time.4.In the northern zone three regressional and two transgressional stages havebeen detected and,in the southern zone,only a Neocomian regression has been traced.5.The northern zone was predominated by a continental enviroment,hence,as-signed to the inner position of the North Tibet Continent;quite differently,the south-ern zone was characterized by a flysch-like sedimentation and an under-water volcaniceruption and,thus,assigned to an active continental margin.
出处
《地质学报》
1983年第1期83-95,共13页
Acta Geologica Sinica
