藏南萨噶—江孜地区中生代遗迹化石及其行为习性分析

MESOZOIC TRACE FOSSILS FROM SAGE-JIANGZI REGION IN SOUTHERN XIZANG(TIBET) AND THEIR ETHOLOGICAL ANALYSIS

文中描述的遗迹化石是河北区调队 1 2 5万萨噶幅 (2 0 0 1年 )和中国地质大学 1 2 5万江孜幅、亚东幅 (2 0 0 2年 )野外地质调查过程中分别采集的。遗迹化石的产地和层位是 :萨噶和吉隆附近的上白垩统 ,冈底斯弧前盆地日喀则群昂仁组复理石(化石点 1 ) ,和康马地区北喜马拉雅拉轨岗日带上三叠统涅如组 ,下、中侏罗统田巴群 ,下白垩统加不拉组和上白垩统宗卓组复理石 (化石点 2 ) ,少量标本产自北喜马拉雅南带岗巴—定日上白垩统岗巴村口组 (化石点 3)。文内共计描述上述地区中生代遗迹化石 1 2个遗迹属 ,1 4个遗迹种 (包含 4个未定遗迹种 ) ,其中多数 (5个遗迹属 ,7个遗迹种 )为首次在中国被发现和描述 (包含有两个新遗迹种 )。文中详细研究了各遗迹属的行为习性特征 ,其中多数 (有 9个遗迹属 )过去经常产于世界各地中、新生代深海复理石内。根据不同的埋藏和保存环境它们又可分为两大类 ,第一类为浊流形成后形成的遗迹 ,它们都是深海食沉积物动物的觅食迹 (fodinichnia)和游动的牧食迹 (pascichnia)如 :Gyrophyl lites,Phymatoderma,Helminthoida和Phycosiphon ,它们的主要特征是都具有主动回填构造 (activebackfill) ;另一类为浊流形成前形成的雕画迹 ,它们的主要特征是生活时期形成复杂的多孔的水?

The authors describe Mesozoic trace fossils collected by the Hebei Geological Survey during mapping of the Sage region in 2001 and by China University of Geosciences during mapping of Jiangzi and Yadong regions in 2002.These trace fossils occurred in the following locations and geological ages: Fossil site 1:Late Cretaceous rocks of fore-arc basins in Gangdisi and flysch deposits in the Angren Formation (Shigatse Group) in Sage and Jilong areas; Fossil site 2:Late Triassic Nierw Formation, Early-Middle Jurassic Tianba Group, Early Cretaceous Jiabula Formation, and Late Cretaceous Zongzhuo Formation flysch deposits in Laguigangri belt of Kangma region in the northern Himalayas;Fossil site 3: (small amount) Late Cretaceous Gangbacunkou Formation in the southern part of north Himalayas.Twelve ichnogenera and fourteen ichnospecies are described. Most of these trace fossils (5 ichnogenera and 7 ichnospecies ) have been reported in China firstly, including two new ichnospecies. Ethological characteristics of these trace fossils, including 9 common Mesozoic and Cenozoic ichnogenera occurred in flysch deposits around the world, are analyzed. According to their taphonomic environment and preservational style, these trace fossils can be divided into two categories. The first type is known as post-turbidite traces predominated by feeding and grazing trails in the deep sea, for example, Gyrophyllites, Phymatoderma, Helminthoida and Phycosiphon. These traces were characterized by the active backfills. The second type is pre-turbidite graphoglyptida which were characterized by a complex tunneling system that was filmed by bacteria and gardening (agrichnia). Representatives of this type are Megagrapton, Rhabdoglyphus and Helicorhaphe. This group also includes animals with chemosymbiosis that had adopted low oxygen conditions, such as Chondrites and Cladichnus.The described trace fossils also include the dwelling and feeding structures, such as Schaubcylindrichnus, Syringomorpha, and cubichnia, which were aligned with water currents such as Sagittichnus.Except for Tibet area, Mesozoic deep sea flych strata (especially the Late Triassic and Jurassic-Cretaceous rocks) were rarely developed in other parts of China. Thus, these trace fossils can provide some unique valuable materials for further understanding the sedimentology, stratigraphy, and palaeogeography in Tibet area.