Brachiopod Fauna Of Early Carboniferous Hongshuiquan Formation In Yimin Area, Inner Mongolia

Hongshuiquan Formation is a suit of Early Carboniferous marine normal clastic, limestone, cliped tuff locally strata. In this study on Hongshuiquan Formation, we observed the section in a mountain at eastern of Heishantou township Hongshuiquan farm of Ergun Right Banner, Inner Mongolia. This section mainly represent the lower segment deposition of Hongshuiquan formation, comprising fine conglomerate, gritstone containing gravel, fine sandstone, siltstone, silty mudstone and shale compose a postitive cycle from coarse to fine, 472.45m thick. Upper section is incomplete, only amount to underpart of the upper section, representing a reverse cycle from coarse to fine, composed of shale, siltstone, fine sandstone, midian-coarse feldspar-quartz sandstone and fine conglomerate, more than 196.52m thick, containing some marine animal fossils brachiopoda and crinoid and so on. Upper and middle defects developed in 753.5 upland south of the observed section, comprising midian-fine sandstone, silty mudstone and carbonate rocks as bioclastic limestone, is a postitive cycle becoming thin upward, 283m, including large amount brachiopods, along to littoral neritic facies. Therefrom, these strata compose an entire Hongshuiquan Formation, and can be divided four lithologic members: underpart is sandy conglomerate; middle part is siltstone, mudstone; upper is sandy conglomerate and top is limestone.Early Carboniferous Hongshuiquan Formation in Yimin developed argillaceous siltstone, silty sandstone and mudstone, intercalated by little midian-fine sandstone, this strata is equal to middle part, siltstone, mudstone, in Hongshuiquan area. We collected a large number of brachiopod fossils in the silty mudstone of Yimin area, it is the first discovered, we named it as"Yimin brachiopod fauna". The brachiopod fauna is charactered by Spiriferacea with thick shells, small Chonetoidea and large-scale Productoidea.Previous studies on the brachiopods of Hongshuiquan Formation is few, The earlest study is the identification of brachiopods from lower Carboniferous at the south of 753.5 upland in north of Dayinuogaigou byYu Jianzhang in 1956, those fossils preserved poorly, this study identified two genus, Spirifer sp. and Schellweinella sp., so he think the age of Hongshuiquan Formation belong to Devonian to Carboniferous. In 1957, when the 118 team worked in this area for 1:200000 scale regional geological survey, they found lots of fossils presserved well near 753.5 upland in north of Dayinuogaigou, mainly are brachiopods. These brachiopods were identified by a Russia paleontologist B.И.Устреский, including Camarotoechia cf. aschlariki Simorn, Spirifer aff. attenuatus Sow.,Pliticatifera kassini Nal.,Pictyoclostus sp.,Spirifer baiahi Nal.,Plicatifera aff. borukaeri Simorin,Spirifer cf. sibiricus Lebedev,Athyris aff. ahgelica Hall, he thought the strata containing these brachiopods along to lower Carboniferous Tournaisian, and considered Hongshuiquan Formation is the prime of Early Carboniferous.The paper has described 202 brachiopods from Hongshuiquan Formation systematicly, basing on population theory and referencing internationally latest brachiopod classification scheme, including 10 genera and 10 species, containing two new species. These species are: Neochonetes plicatiformis, Rugosochonetes hardrensis, Chonetes moelleri, Productellana yiminensis sp. nov., Plicatifera yiminensis sp. nov., Dictyoclostus crawfordswillensis, Stenoscisma sp., Fusella aschalensis Yang, Finospirifer taotangensis, Torynifer pseudolineatus asiaticus.We established Linoproductus yiminensis—Fusella aschalensis assemblage zone according to the composition character of Yimin brachiopod fauna. This assemblage mainly including elements such as Neochonetes plicatiformis,Rugosochonetes hardrensis,Chonetes moelleri,Productellana yiminensis sp. nov.,Linoproductus yiminensis sp. nov.,Dictyoclostus crawfordswillensis,Fusella aschalensis,Finospirifer taotangensis,Torynifer pseudolineatus asiaticus and so on. Symbiotic fossils including corals, blastoid, crinoids, etc. We established Linoproductus yiminensis-Fusella aschalensis assemblage zone. Because of this assemblage containing large number of Linoproductus yiminensis, a total of 120 samples, and incorporate the Early Carboniferous typical spirifer Fusella aschalensis,.In the Yimin brachiopod fauna, Neochonetes develop from Carboniferous to Permian wordwide; Rugosochonetes Sokolskaya produced during Carboniferous wordwide, the age of Fusella McCoy, Chonetes Fischer and Productellana Stainbrook is from Devonian to Early Carboniferous, mainly developed in Asia, Europe, North America and Russia. Dictyoclostus Muir-Wood distributed in Europe, Great Basin, Ireland, Belgium and Russia during Tournaisian-Visean of Early Carboniferous. Torynifer Hall developed in Asia and North America during Early Carboniferous, Torynifer pseudolineatus was founded in Kazakhstan, Altay and America during Early Carboniferous. Linoproductus cora, the type species of Linoproductus Chao, was found in Early Carboniferous of Caucasia. Finospirifer Yin produced in center of Hunan Provnince, China during Tournaisian of Early Carboniferous, Finospirifer taotangensis also is the typical spicies in Tournaisian. Rugosochonetes hardrensis distributed in South of Europe, Russia, Ural, Shinchi, Altay, Iran and Caucasia during Tournaisian. According to above analysis on the age of Yimin brachiopod fauna, the age of the fauna should be along to Tournaisian of Early Carboniferous. Therefore, the age of middle lower part of Hongshuiquan Formation is the Tournaisian.