喀喇昆仑山地区三叠纪双壳类

OCCURRENCE OF TRIASSIC BIVALVES IN THE KARAKORUM MOUNTAIN AREA

本文描述的双壳类化石共5属13种,分别采自喀喇昆仑山地区9个地点,分别采目下三叠统下河尾滩群、中三叠统上河尾滩群、上三叠统克勒青河组.所描述的该区化石绝大多数为首次报道.早三叠世双壳类动物群无疑地属于南特提斯区,中晚三叠世的双壳类及沉积具有浊流沉积特征,并根据构造研究结果,处于南特提斯区.

13 soecies of Triassic marine bivalves are described here belonging to 5 genera respectively from nine localities(see textfig.l). They are, Claraia concentrica Yabe and Eumorphotis ? sp. of the Lower Heweitan Group, Lower Triassis, the Middle Triassic( Ladinian )Daonella indica Bittner and D. cf. bulogensis kittl of the Upper Heweitan Group, Middle Triassic and Halobia comata Bittner, H. styriaca (Moj. ) , H. austriaca Moj., H. sp. cf. H. sirii Kittl,H. aff. bukovinensis Kittl, H. arthaberi Kittl, H. cordillerana Smith, H. sp. and Parahalobia qinghaiensis Chen ef Lu of the Keleqinghe Group, Upper Triassic ( Carnian ) . Among them the Lower and Middle Triassic fossils are the first record in the Karakorum mountain area, and of all the Upper Triassic abundant fossils only one species, Halobia cordillerana Smith was formerly reported by Renz ( 1940 ) from the west margin of the area. The faunal features of the Lower Triassic bivalves show that it undoubtedly belongs to the South Tethyan province which bears Claraia concentrica-C. decidens species group to the contrast with the North Tethyan Claraia stachei species group ( see Yin and Lin, 1986) . Both of the two places bearing the Middle Triassic Daonella and the Upper Triassic Halobia are reserved in flysch rocks which are usually considered to be deposited under a turbidite environment. The authors believe that the-Middle and Upper Triassic flysch may be formed near the active belts which were located in the south Tethyan province during that time according to the tectonic study ( Argyriadis et al., 1980) .The features of the present bivalve fauna are just corresponding to that of the Upper Paleozoic Eurydesma-fauna in such adjacent regions as Kashmir, Salt Range and Ruto region of northwest Tibet. The latter regions were far away at that time and are considered to belong to Indian Plate. The zonal significance and the geological distribution of Claraia, Daonella and Halobia in China will be discussed. We believe that the' Lower Triassic'genus Claraia ranges from uppermost Permian upto Dienerian and the C. concentrica-zone may be limited within Griesbachian.