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The Middle And Late Permian Plant Fossils From The Northern Margin Of The North China Plate

Posted on:2016-10-15Degree:MasterType:Thesis
Country:ChinaCandidate:H S DingFull Text:PDF
GTID:2180330467997317Subject:Paleontology and stratigraphy
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Four important floras, namely Cathaysia, Euramerica, Angara and Gondwana florashad been developed on the earth during Carboniferous and Permian. The northernmargin of North China Plate and the northeastern China belong to the Cathaysia andAngara floristic regions, respectively. The boundary between these two floristicregions is located along the Xar Moron River. Question about the closure time of theXar Moron suture zone is still debated. It is of great significance to discuss the closuretime of the Xar Moron suture zone based on the palaeontological data.The thesis herein focuses on the Middle Permian Yujiabeigou and Late PermianTieyingzi floras, especialy their compositions and ages. Combining with the floras inthis and adjacent areas, we discussed the mixed time of Cathaysian and Angaranfloras, and concluded the combination time of the North China Plate andJiamusi-Mongolia Block along the Xar Moron River.The Yujiabeigou and Tieyingzi floras are important part of the Ongniud Flora. Onepart of the fossils plants described herein was collected from the type section of theMiddle Permian Yujiabeigou Formation in Yujiabeigou, Guangxingyuan, Chifeng City,Inner Mongolia. They are identified as30species of11genera. Adding the formerdata, there are50species of19genera in total found in the type section of theGuadalupian Yujiabeigou Formation. In this flora, filicopsids and pteridospermopsidsabsolutely dominate, and there is still numerous sphenopsids. Noeggerathiopsids,cycadopsids, cordaitopsids and coniferopsids rare occurred. Among the Yujiabeigouflora, Fascipteris and Gigantonoclea are the typical species of the Cathaysia flora,while Annularia orientalis Kaw., Pecopteris taiyuanensis Halle and Pterophyllumerratum Gu et Zhi are all the endemic members of the Cathaysia flora. The features ofthe Yujiabeigou flora are similar to those of the Cathaysia flora in North, South andNorthwest China. Paleogeographically, this flora belongs to northern floristic regionof the Cathaysia floristic realm. The present flora is comparable to the Gigantonoclealagrelii-Lobatannularia ensifolia-Fascipteris hallei assemblage from thelower-middle part of Shihezi Formation in North China. Therefore, the age of theYujiabeigou flora should be Guadalupian (Middle Permian). Further more, the isotopicdating of the andesitic crystal lithic tuff form the Yujiabeigou Formation is carriedout for the first time, and the weighted mean age of zircon LA-ICPMS U-Pb is270.1+4.2Ma (MSWD=1.8, n=19), this also prove that the geological age of theYujiabeigou Formation is Middle Permian.In this thesis,25species of11genera are identified in the Tieyingzi flora collectedfrom the upper part of Tieyingzi Formation in the Tieyingzi Village, Hexigten Banner,Chifeng City, Inner Mongolia. Together with the previous research, there are68species of23genera of fossil plants in the Tieyingzi Formation in total. Among them,filicopsids and pteridospermopsids are dominated also, followed by sphenopsids. Cordaitopsids and coniferopsids are rare occurred. There are still a small number offossil seeds. In detail, Pecopteris accounts the most both in variety and in quantity,Gigantonoclea and Taeniopteris rank the second. Sphenophyllum is relativelyabundant, and there are numbers of Annularia and Lobatannularia. In the Tieyingziflora, the members of Cathaysia flora absolutely dominant, including those typicalspecies of the Cathaysia flora (Gigantonoclea, Gigantopteris, Taeniopteris,Lobatannularia). However, some common members of Angara flora are found in thisflora, such as Comia, Paracalamites and Callipteris. Thus, the Tieyingzi flora wouldbelong to the Cathaysian-Angaran mixed flora. Most species of Tieyingzi flora arecommon elements in Permian strata of China, and22species of12genera are peculiarto the Late Permian. Therefore, the Tieyingzi flora is equivalent to those in the upperpart of Shihezi Formation in North China, and the Linxi Formation in GreaterHinggan Moutains, and the Sunan, Hongquan and Fangshankou formations inNorthwest China. Its age would be Lopingian (Late Permian).According to the present research on the Middle Permian Yujiabeigou flora and theLate Permian Tieyingzi flora, no mixed elements of Cathaysian and Angaran florashas been found in Middle Permian floras in this area. However, in the Late Permianflora, there appeared some mixed elements of the Cathaysian and Angaran floras. Thisindicates that the Paleo-Asian Ocean still played as the geographical barrier in MiddlePermian, but closed till Late Permian.
Keywords/Search Tags:Early Permian, Late Permian, Cathaysia flora, Angara flora, Xar MoronSuture Zone, Chifeng, Inner Mongolia
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