| 西藏北部石炭纪冰川-海洋相地层的发现 |
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| CARBONIFEROUS GLACIAL-MARINE DEPOSITS IN NORTHERN XIZANG |
| The Himalayan Carboniferous glacial-marine deposits have been already studied and confirmed by both Chinese and foreign geologists and, therefore, the Himalayas are usually accepted to be an indivisible northern member of the Indian Shield, where the Permo-Carboniferous Gondwana series is well developed and was investigated long ago. From this point, the Yarlung Zang-bo-Indus line is presumed to be the suture between the Gondwana and Eurasia. The results of our investigations of 1980, however, have shown that in Northern Xizang there are also well-developed Carboniferous glacial-marine deposits throughout the broad territory including the Lhasa area.The Carboniferous strata are widely distributed and the most complete Upper Palaeozoic sections occur in the Xainza district,where they are continuous from the top of the Devonian to the base of the Permian dominated by slightly metamorphosed rocks that are well-exposed and dated by fossils. Directly above the fine sandstones and shales with a few intercalations of limestones yielding Late Visean ammonites, the glacial-marine deposits begin to appear. They are represented by slates and fine sandstones with glacial debris of granite, granite gneiss, variously coloured quartzite, dark-red chert and gray limestone. The debris of granite and quartzite are angular, suban-gular or subrounded, either large or small (from one meter to microscopic) and disperse chaotically in the matrix of green clay slate and fine-grained sandstone. The debris with pressure pits are common (reaching 1/3 of the total amount of the debris) and some ice-striated fragments also occur. A large amount of debris are fractured and their fracture surface, as a rule, is very fresh. This clearly indicates that they had not been significantly weathered and were buried shortly after being released from the carrier-the floating ice masses-into the water and then fell to the bottom of the sea.The debris-bearing strata, corresponding to the glacial stages, and the normal slates and sandstones without them, corresponding to the interglacial stages, are distributed alternately every few tens of meters. The rocks become coarser and coarser upward along the section and the Mid-Upper Carboniferous is predominated by the glacial-marine sediments. The section is 1600 meters thick.Except cosmopolitan forms,there are cold-water brachiopods of the Australian type, for example, Alispirifer. The Stepanoviella fauna of Late Carboniferous was already known for several years from the glacial-marine debris-bearing slates of the Lhasa area. The cold-water nature of the fauna will be even more obvious if we take the Permian into account, the limestones of which contain also cold-water brachiopods, for instance, Costiferina, associated with warm-water forms. The Carboniferous of such a type also occurs at the western end of the Changtang-San Jiang block.All the above mentioned shows that the Qinghai-Xizang land, as well as the Indian Shield, was united as a single palaeocontinent and is an indivisible element of the great Gondwanaland. Hence it follows that the Yarlung Zang-bo-Indus line is unlikely to be the suture between the Gondwana and the Eurasia. The real suture between the two continents has to be traced much farther to the north and the Jinsha River-Tongtian River zone may be the proper one. |
| HAN Tong-lin,WANG Nai-wen.1983.CARBONIFEROUS GLACIAL-MARINE DEPOSITS IN NORTHERN XIZANG[J].Acta Geoscientica Sinica,5(3):41-56. |
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