西藏南部洛扎地区中生代遗迹化石及其环境意义

MESOZOIC TRACE FOSSILS FROM LHOZHAG AREA OF SOUTHERN TIBET AND THEIR ENVIRONMENTAL SIGNIFICANCE

详细描述了西藏南部洛扎地区中生代地层中所含的遗迹化石Arenicolitessp .,Beaconitesantarcticus,Chondritessp .A ,C .sp .B ,C .sp .C ,C .sp .D ,?Cruzianasemiplicata ,Palaeophycustubularis,Phycodescircina tum ,Protovirgulariadichotoma ,Skolithosverticalis,Teichichnusrectus和Unaritessuleki计 1 0遗迹属 1 3遗迹种 。

According to Gansser (1964), the Tethyan Himalayas is a tectonic unit which is borded by the central Crystallines of the High Himalayas to the south and the Indus Yarlung Zangpo suture zone to the north. The Tethyan Himalayas can be subdivided into two subzones of different lithological compositions by the Kyen La Kangmar intracrustal thrust. The northern Tethyan depositional zone is dominated by slightly metamorphosed deposits of the outer shelf, continental slope and deep sea environments. The southern Tethyan zone is characterized by non metamophic shallow water deposits (Yin, 1988; Liu and Einsele, 1994; Willems et al ., 1996). On the basis of the depositional features, the northern subzone can further be divided into two areas: Lhagu Kangri area and the Yarlung Zangpo area. The Mesozoic deposits in the Yarlung Zangpo area were deposited in a more active tectonic background than that in the Lhagu Kangri area. The Lhozhag area is located to the east of Gyangze Kagmar and can be acted as the east part of Lhagu Kangri area. More than ten thousand meters of Mesozoic deep sea and shelf terrigenous detrital sediments are piled on the Kangmar Fm. aged Permian of passive margin base. Yang Shi pu et al. described Middle Upper Triassic trace fossis from Zanda area and Middle Jurassic to Early Cretaceous trace fossils from Shiquanhe Domar area of Ngari of western Tibet (1985, 1982). Zhou Zhi cheng (1997), Zhou Zhi cheng et al. (1997), and Zhou Zhi cheng et al. (2000) studied the Cretaceous Tertiary trace fossils from Gangba and Tüna areas of southern Tibet and discussed their environmental significance. The trace fossils from Lhozhag area describeded and discussed in this paper can reflect the basic aspects of Mesozoic trace fossils of Lhagu Kangri area. This is also an important evidence of the great changes in the tectonic background which resulted in the changes of sedimentary environments in these areas during Mesozoic Era.