Early Carboniferous To Early Triassic Stratigraphic Sequence And Tectonic Evolution In Central And Eastern Jilin

The Carboniferous and Permian are very important period in the history of the Earth evolution; and the super continent, Pangea was formed in this time. Carboniferous and Permian strata were developed well in the margin of Siberia Plate, especially in Ural region, and attract great attention on them, such as Lower Permian (Ural Series), for a long time. The International Union of Geological Sciences and International Commission on Stratigraphy had approved formally the Aidaralash section in Kazakhstan (southern Ural) to be Global Standard Section and Point (GSSP) of the Carboniferous and Permian boundary. And some stage boundaries selecting GSSP, such as Asselian/Sakmarian, Sakmarian/Artinskian, and Artinskian/Kungurian, located in the Ural region also.In northern China, besides the terrestrial Carboniferous and Permian in the North China Plate, the Permo-Carboniferous strata in the Tianshan - Xing'an Orogen between North China Plate and Siberia Plate are poorly studied. The stratigraphic provinces are complex, Stratigraphic classification and correlation are confused. The present researching area is located in the eastern parts of the Tianshan - Xingan Orogen.It is still argued how and when the two plates collided and where the suture is. Some researchers think that it is at the end of Permian the two plates collided together, others agree with that the orogenic event took place in Early Triassic, companied with magma events and sedimentary events. Since the Carboniferous and Permian strata were faulted and reformed by the Paleo-asia muti-stages orogenic movements and the Pacific tectonic movements later, their stratigraphic sequences are interpreted in different opinions.Based on the systematic investigation in Jilin and Yanji area, including the measurement of typical stratigraphic sections, the Early Carboniferous to Early Triassic stratigraphic sequences in the eastern part of Tianshan - Xing'an Orogen are discussed. The new achievements are as fellows:1. As a whole, the Carboniferous and Permian stratigraphic sequence, sedimentary setting, fossil assemblages, tectonic and magma events in the two regions, i. e. central Jilin and Yanji are almost the same, and can be correlated with those in Chifeng - Ulanhot region, Inner Mongolia and eastern parts of Heilongjiang. The Changchun-Jilin-Dunhua-Yanji suture is inexistence. Two stratigraphic subprovinces, Central Jilin Subprovine and Yanbian Subprovince, belonging the Central Jilin-Yanbian Province, Inner Mongolia - Songhuajiang Region, Northern Xinjiang - Xing,an Realm, are put forward by the present author.2. Based on the synthetic researches of the sedimentology, depositonal environments and stratigraphic sequences on the holotype section of Kedao Formation at Kaishantun Town, Yanji City, and other typical sections in Daxinggou-Tianqiaoling of Wangqin County, Mijiang of Hunchun City, the Kedao Formation is assigned to terrestrial clastic sedimentary deposits for the first time. It is composed of alluvial fan, river and lacustrine sediments. A tectonic schist zone, 40 meter wide, was found between the Kaishantun Formation and the Kedao Formation on the Kedao Section of Kaishantun Town; and the Late Permian Kaishantun Formation is faulted reversely on the Kedao Formation. There are some bivalve fossils founded in the Kedao Formation near Tianqiaoling railway station, namely: Shaanxiconchan cf. ellptica, Shaanxiconchan sp., Lilingella cf. liuyangensis, Modious?sp. This indicates that the age of Kedao Formation might be Early Triassic.3. Owing to the Miaoling Formation covered by Kedao Formation near the holotype section, and the Kedao Formation correlated to Guanmenzuizi Formation, so for long time geologists located the Miaoling Formation under the Guanmenzuizi Formation, and causing the chaotic situation of the correlation of Permian in Yanbian region. We found that under the Guanmenzuizi Formation there are a series of sandstone, quartz sandstone interbeded with siltstone and limestone, but in the holotype section of Miaoling Formation, Companying with limestone are black siltstone and slate which may correlate to Jiefangcun Formation. So we re-ordered the strata sequence from Permian to Early Triassic in Yanbian region as follow (in ascending order): Dasuangou Formation, Shidonggou Formation, Guanmenzuizi Formation, Miaoling Formation (or Jiefangcun Formation) and Kedao Formation.4. The Fusulinid fossils of Laohudong-Huangyu section at Yongji County, central Jilin and Guangpigushan-Houjiacaozi section at Shuangyang can correlated to those near the boundary of Carboniferous and Permian in China and other countries. The Pseudoschwagerina uddeni fusulinid zone as the Permian base boundary covers on the Carboniferou Triticites fusulinid zone. At Laohudong-Huangyu section at Yongji, central Jilin, the species Triticites noinsky plicatus are very common in the Triticites Fusulinid zone, which are similar with that of section at Yishan, Guangxi. At Guangpigushan-Houjiacaozi section at Shuangyang, besides the typical elements of Pseudoschwagerina uddeni zone, such as: P. borealis,P. sp.,Rugosofusulina cf. vacuta,Schwagerina anderssoni,S. cf. longissimodes,S. sp.,Eoparafusulina sp., there are also found the typical elements in Triticites zone, such as, Triticites schwageriniformis, T. mogutouensis, T. variabillis, T. paramontiparus, T. noinsky plicatus, T. ferganensis, Schwagerina cf. longissimoides, S. nathorsti, Montiparus confertus, M. sp., Pseudofusulina sp. This is quite similar to that of sections in western Geizhou, China. These two sections can be regarded as reference sections around C/P boundary in northeastern China.5. Field investigation shows that there exist basal conglomerate of river and alluvial fan facies in the Shoushangou Formation at central Jilin and Dasuangou Formation at Yanbian. The underlying strata develop some Pseudoschwagerina zone Fusulinid fossls, indicate Asselian in age. And there develop Pseudofusulina - Parafusulina assemblage in these two formations indicate their age may be Roadian or later. There is a long time gap between the two formations and their underlying strata, so there should be a disconformity. There also develop Early Permian synorogenic granite (Jishuitong granite of Helong, 285Ma)and Middle Permian Postorogenic intrusion (Xiaoxinancha corsilite, 270Ma; Dakangshan quartz-syenite, 267Ma). So we concluded that there develop a regional unconformity between Lower and Middle Permian.6. Three orogenic events, in Early Permian, Late Permian and Early Triassic, were recognized in the present research area, based on the investigation of lithostratigraphic units and regional tectono-magmatic movements. The Early Permian event is characterized by the unconformity between the Shoushangou Formation and Shizuizi Formation in central Jilin, and by the unconformity between the Dasuangou Formation and Shanxiuling Formation in Yanbian area, accompanied by the Jishuidong synorogenic granite intrusion (285Ma). The Late Permian orogenic event is characterized by the unconformity between the Yangjiagou Formation and Fanjiatun Formation in central Jilin, and by the unconformity between the unconformity between Kaishantun Formation and Jiefangcun Formation in Yanbian area, and also accompanied by the Liukesong synorogenic granite intrusion (262Ma). The Early Triassic orogenic event is characterized by the unconformities between the Lujiatun Formation and Kedao Group, and their underlying strata, and accompanied by the synorogenic granite intrusions of 242-248Ma (Dayushan intrussion, Xiaosiping intrussion, Bailiping intrussion, etc.).