Stratigraphic Framework Of Late Paleozoic In Northeastern China

Stratigraphic framework refers to the distribution or arrangement of various stratigraphy or rock units in time and space. The stratigraphy framework of Late Paleozoic in northeastern China mainly incudes continetal margin deposits, stratigraphic provincialism and stratigraphic division and correlation.The recognition of continental margin deposits, belonged to the the category of stratigraphic distribution research, is one of the key issues of studying the Late Paleozoic stratigraphic framework in northeastern China and make an significant role in the basic geology and application basic geology. The confirmation of continental margin deposits as one of the important theoretical bases of stratigraphic provincialism, division and correlation, and stratigraphic framework, supported the establishment of Jiamusi-Mongolia Block and laid solid foundation of stratigraphy to the exploration and exploitation of mineral deposits. Meanwhile, chart of stratigraphic correlation is the manifestation of stratigraphic framework.1. The confirmation of continental margin depositsThe viewpoint of continental margin deposits derives form the Jiamusi-Mongolia Block. Wang et al. (2008a) put forward that the northeastern China and adjacent areas, bounded by Mongolia-Okhotsk suture belt to the north, Xar Moron River-Yanji suture belt to the south and Middle Sikhote subduction belt to the east, are a stable Late Paleozoic tectonic unit which was named Jiamusi-Mongolia Block. There would be the continental margin and corresponding deposits when esisting a continent.Late Paleozoic strata in northeastern China are distributed in a zonal pattern around the old-land on the Jiamusi-Mongolia Block. They are composed of active deposits in the regular distributed tectonic lithofacies zones. This indicates that the Late Paleozoic strata are of continental margin deposits.The phenomenon that Late Paleozoic strata in northeastern China reveal a zonal distribution around the core of Jiamusi-Mongolia Block was discovered by analysing geological maps of all the provinces of northeastern China and the adjacent regions, including southern Russian Far East and Mongolia (Wang, et al,2009). It is one of the distinct features for continental margin deposits.The paper reached the conclusion that the Late Paleozoic strata of northeastern China belong to active deposition through the field work, showing the following remarkable characteristics. First, lithic sandstone and debris-feldspar are more developed in most of lithostratigraphic units. Second, the lateral variation of formation thickness, lithology and lithofacies is obvious. Third, volcanic rocks developed in each margin, such as Daminshan Fm. and Moergenhe Fm. in northern margin, Laotudingzi Fm. and Erlongshan Fm. in eastern margin, and Dashizhai Fm. in southern margin, and so on.The lithofacic variation from old land (denudation or continental sedimentary)-marine-rerrigenous facies deposit -- neritic facies (mainly the continental shelf sedimentary)-abyssal facies (oceanic crust sedimentary or the sedimentary of closely related with it) from the inner to these sutures can be found on the Jiamusi-Mongolia Block. This lithofacies regularity consist with the ideal model of the continental margin facies basically, and is the significant corroboration evidence of the continental margin deposit.Paleobiogeographically, Tuvaella fauna are the aboriginal brachiopod fauna, which are characterized by Tuvaella and Tanguspirifer. They are mainly developed in Middle-Late Silurian and formed the Mongolia-Okhotsk paleobiogeographic province independently. Tuvaella fauna are distributed not only in the southwestern margin of the Siberia Plate (moden position), but also in the northern margin of the Jiamusi-Mongolia Block and the northeastern margin of Kazakhstan Plate. In Middle-Late Silurian, the Siberia Plate, the Jiamusi-Mongolia Block and the Kazakhstan Plate might be united in an arc. Tuvaella fauna developed in northeastern margin of Siberia Plate (the original state), northern margin of Jiamusi-Mongolia Block and northeastern margin of Kazakhstan Plate during Middle-Late Silurian. The corresponding ocean basin could be called Irtysh Mid-Mongolia-Okhotsk Ocean. The above showed that Tuvaella fauna developed in the Heihe-Dongwujimqinqi area of China can not prove this area belong to the Siberia Plate, and this area should be in the northern margin of Jiamusi-Mongolia block.Zhesi brachiopod fauna, a cold-water type brachiopods, belongs to the Borael Raelm. Mongolian provice is recognized because of 75% endemic species in the Zhesi brachiopods. It is self-grouped as a geographic province. This suggests that there exists a geographic isolation to the north, and implies the existing of a large paleo-continent (block). The cold-water feature of the brachiopods suggests that there is an enough wide deep ocean, i.e. the southern branch of Paleo-Asian Ocean, between the block and North China Plate during Middle Permian. Therefore, the area Gansu Beishan-Zhesi Xiujimqinqi-Suolun-eastern Harbin-central Jilin-Ussuriysk developed Middle Permian strata with Zhesi brachiopod fauna should belong to the southern margin of Jiamusi-Mongolia Block. The southern boundary of Zhesi brachiopod fauna accord with the Xar Moron River-Yanji suture.To sum up, the continental margin deposits refered in this paper are the active deposition, which mainly the marine strata based on the continental crust or transitional crust, arounding the margin of old continent. Continental margin deposit is similar with the miogeosyncline of Geosyncline-Geoanticline. It should be explained that "miogeosyncline is neither the depression zone in continental interior nor the active zone between two continents, it is the sedimentary zone of continental margin" (Li et al. 1982).2. Stratigraphic provincialismThe Jiamusi--Mongolia Stratigraphical Province derives form Jiamusi-Mongolia Block. According to that "tectonic domain is used as the higher tectonic unit" and "junction belt is the better boundary of the stratigraphic provinces", proposed by Wang Hongzhen et al. (1985,1990), we divided the Jiamusi -- Mongolia Block, bounded by Mongolia -- Okhotsk suture belt and Xar Moron River --Yanji suture belt, as a stratigraphic province, named Jiamusi--Mongolia Stratigraphical Province.According to the distinct conformity in each margin strata and obvious difference between three margins of Jiamusi--Mongolia Block. Thus, three stratigraphical regions of the Jiamusi-Mongolia Stratigraphical Province are recognized along the northern, southern and eastern margins of the Jiamusi-Mongolia Block, named respectively as Xing'an Stratigraphical Region, Inner Mongolia grass--Songhua River Stratigraphical Region, and Baoqing-Hunchun Stratigraphical Region.3. Chart of stratigraphic correlationIn this area, it is impossible to contrast layer with layer among the different strata sections of the same lithostratigraphic unit like on the epicontinental sea of a large craton, resulting from the different between stable sedimentary and active sedimentary. According to the attribute of continental margin deposits and active sedimentary, the paper discussed the Late Paleozoic strata of the three regions in detail. It is feasible to make the rock combination comparison of group level, and the maker beds of volcanic rocks or volcanic events have distinctive effect in researching the active sedimentary. It is can be found that lots of lithostratigraphic units in group level can be used universally in the same region through analysis of rock combination. Thereby, the lithostratigraphic units were sorted out. Such as Niqiuhe Fm., Hongshuiquan Fm. in northern margin of Jiamusi-Mongolia Block, Xibiehe Fm. and Zhesi Fm. in sorthern margin. This is the result of the continental margin deposit characteristic.The present stratigraphic framework is setting on the International Stratigraphic Chart on the level of stage, after comprehensive researches to lithostratigraphy, biostratigraphy and chronostratigraphy, especially the conodont biostratigraphy and isotopic ages of volcanic rocks obtained in recent years.