| 广西象州中坪马鞍山剖面上泥盆统弗拉斯阶/法门阶(F/F)界线的研究 |
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| STUDY ON UPPER DEVONIAN FRASNIAN/FAMENNIAN BOUNDARY IN MA-ANSHAN,ZHONGPING, XIANGZHOU, GUANGXI |
| Since 1984 the author has systematically studied the conodont fauna of Upper Devonian in Ma-anshan, Zhongping, Xiangzhou, Guangxi. Especially in the middle ofRongxian Formation", the author first discovered the Frasnian/ Famennian boundary level where the beds are continuous, the lithology is same, and conodont zone are complete. This boundary level coincides with well the decision on the Frasnian/Famennian boundary made by SDS in 1983, and is generally identical with the conodont sequence of Schmidt section in W-Germany (SDS Newsl. 1986, no. 1, Doc. C). On the basis of detailed study of 23 samples (see figure 2) from 6m thick beds (i. e. upper part of Uppermost gigas zone to lower part of Middle triangularis zone) and the SDS decision, the author takes the first occurrence of primitive Pa. d. delicatula (in this paper, named Pa. d. delicatula Morphotype 1) as the indicator of the lower boundary of Middle triangularis zone and places the boundary level between samples F13 and F14 in D295 bed, middle part of "Rongxian Formation" in .Ma-anshan section.The Frasnian/Famennian boundary level in Ma-anshan section is characterized by thick, light grey limestone. Except the sample F13 immediatly underlying Frasnian/Famennian boundary level is light grey brachiopodous shell sparite, the rest is light grey pelmicrite. On short, no depositional gap and lithological change were found at the Frasnian/Famennian boundary level.Biostratigraphically, the Frasnian / Famennian boundary level has the following characters: ( 1 ) The deep water Palmatolepis fauna is recognized near the boundary. The conodonts occure continously, the Uppermost gigas Zone, the lower triangularis Zone, and the Middle triangularis Zone may be well divided. The distribution of important conodont species is basically identical to that of Schmidt section in W-Germmany.( 2 ) At the base of Lower trangularis Zone, shallow water Icriodus occurs abruptly, and it is as rich as Palmatolepis. This assemblage characteristic is only limited to Lower triangularis Zone, from the Middle triangularis Zone, Icriodus obviously decreases.( 3 ) The uppermost part (sample F13) of the Lower triangularis Zone is a brachiopodous shell bed, which is dominated by Rhynchonellida and Spiriferida, and with minor amount of Atrypida et al. they are all the common Frasnian elements.( 4 ) In the Uppermost gigas Zone, the samples F7 and F8 contains minor amount of Tentaculites:Homoctenus ultimis derkaouaensis Lardeux. Near the boundary level, there are also a few planktonic Ostracods, but no other fossils are found.On the basis of the present available data, the author will discuss the Frasnian/Famennian boundary level with new knowledge.The author notices that either in Schmidt section of W-Germmany or in the Ma-anshan section, the present Frasnian/Famennian boundary level all faces a serious problem: because of the influence of the global events, the Schmidt section is a barren black shale bed before the occurrence of primitive Pa. celicatula (i. e. between beds C and B) while Ma-anshan section is a brachiopodous shell bed without or with few conodonts. In both sections, the conodonts appear to be slightly discontinuous. In addition, the primitive Pa. delicatula has no reliable evolutionary lineage, its ancestor is not yet clear, so it is difficult to know its first occurrence level. Therefore, it should be noted that this organism boundary is not ideal.The author also notices that the Schmidt section has also a barren bed between the first occurrence of the primitive Pa. delicatula and typical Pa. delicatula, while the situation for Ma-anshan section is better, between the first occurrence of Pa. d. delicatula Morphotype 1 and Morphotype 2 (i. e. typical elemen Pa. d. delicatula,has continuous evolutionary relationship, and the stratigraphic interval is about 76cm(samples F14-F19), which is composed of same limestone, without lithological change and organism hiatus. The organism boundary with the first occurrence of Pa. d. delicatula Morphotype 2 as its indication is within a natural bed. |
| HAN Ying-jian.1987.STUDY ON UPPER DEVONIAN FRASNIAN/FAMENNIAN BOUNDARY IN MA-ANSHAN,ZHONGPING, XIANGZHOU, GUANGXI[J].Acta Geoscientica Sinica,9(3):171-197. |
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