| 长江下游五通组研究的新进展 |
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| RECENT ADVANCES IN THE STUDY OF THE WUTONG FORMATION OF THE LOWER YANGTZE VALLEY |
| The Wutong Formation (formerly Wutong Series), considered as a set of clastic rocks of continental origin, is widely spread in the eastern part of South China. It consists mainly of quartzose sandstones and conglomerates intercalated with a few layers of shales or sandy shales and can be divided into two members, the lower the Huanshan, and the upper, the Leigutai members in Longtan, where the parastrato-type is located near Nanjing. Owing to the presence of Sublepidodendron mirabile (Nath.), sphenophyllum lungta-nense Goth. & Sze, etc. in the upper part of the Leigutai member, Gothan & Sze (1933) in their pioneer palaeobotanical study believed the Wutong Formation to be of Early Carboniferous. However since the discovery of a An-tiarchi fauna in its upper part (Liu and Pan, 1958, and Pan, 1964), the age of this formation has given rise to much controversy. They considered it of late Middle Devonian or early Upper Devonian. Based on a relatively synthetical study of the flora, fish fauna, lithological facies as well as the new finding of Leptophloeum rhombicum in the upper part of Leigutai member, Liu (1963,1964) holds that the Wutung Formation belongs to the Late Devonian. Since then, this opinion has been generally accepted by geologists-and palaeontologists in China.Yet in recent years some new findings concerning both palaeontology and stratigraphy were found from the upper part of the formation in the Lower Yangtze Valley, which add much to our knowledge of its biotic groups and lithofacies. This paper is intended to discuss again the age and other relevant problems of the formation based mainly on the evidence afforded by the new findings. 1. The newly-found megafossil plants in this area are Leptophloeum rhom-bicum Daws., Cyclostigma kiltorkense Haugh. and Archaeopteris spp., all of which are generally regarded as typical cosmopolitan forms of Late Devonian.2. In the study of a palynoflora found from a core material in the Jirong County, Jiangsu, two spore assemblages for the Leigutai member can be recognised. One is the lower, including Retispora lepidophyta var. minor-Apicu-liretusispora hunanensis-Cymbosporites spp. Assemblage and containing a few Acritachs.It can be roughly considered of the Late Famennian in age. The other is the upper,including Knoxisporites literatus-Reticulatisporites cancellatus Assemblage and associated with some Acritachs. It may be tentatively determined as the Late Famennian to the Etroungtian in age. The presence of Acritarchs in the polynoflora"is worthy of attention, because the Acritachs-bearing beds are most likely of marine origin.3. The age of the peculiar Antiarchi fauna characterized by Sinolepis macrocephala Liu & P'an, Asterolepis sinensis P'an, etc., though without significantly new findings, has been considered recently by some ichthyologists as Late Devonian rather than any earlier ages.4. A special Conchostracan fauna consisting of the leading elements Lioes-theria longtanensis Zhang, L. yuelushanensis Zhang, L. orbiculais Xi, L. ovata Xi,Qingxtestheria anhuiensis Xi together with some fossil plants commonly seen in the Wutong formation found from the Leigutai member is of particular significance. These elements are all new species and have little value in determining the age of the strata where they occur. Some of them, however, have also been recorded in the Late Devonian strata interbedded with a few marine layers in Hunan Province. Accordingly, incertain respects, the Conchostracan fauna of the Leigutai member suggests a Late Devonian age and the Conchostracans might live in a transitional environment varying from brackish to freshwater.5. It has long been known that the Wutong Formation is disconformably overlain by the late Tournasian Kingling Formation in the Lower Yangtze Valley. |
| LI Xing-xue,CAI Chong-yang,OU Yang-shu.1984.RECENT ADVANCES IN THE STUDY OF THE WUTONG FORMATION OF THE LOWER YANGTZE VALLEY[J].Acta Geoscientica Sinica,6(2):119-136. |
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