Brachiopod Fauna Of Early Devonian Heitai Formation In Baoqing Area, Heilongjiang Province And Its Palaeobiogeography

Heitai Formation develops in Baoqing-Mishan area of Heilongjiang Province, Northeast China. It contains extremely abundant fossils, including brachiopods, corals, trilobites, bryozoans, blastoids, crinoids, bivalvias and so on, we call it "Baoqing Fauna", which contains abundant fossis and preserved well, the fauna like this is unusual in Northeast China. This paper according to modern paleobiology, identified systematically and described the brachiopod fauna from Heitai Formation; discussed the assemblage character, biostratigraphy and chronostratigraphy; determined the attribution of brachiopod palaeobiogeography of Baoqing-Mishan area, and preliminary studied the tectonic significance of Baoqing Fauna.The study to the brachiopods in this area has made some achievements before 80s, seeing in Yabe (1940), Yabe and Sugiyama (1942), Wang Yu (1955), Hou Hongfei (1959) and Su Yangzheng (1980). There is no reports after 80s. Moreover, these studies concentrated in Mishan, the fossils from Baoqing is discoveried for first time, Baoqing-Mishan is the perfect region to study the brachiopods, paleobiogeography and tectonic of Northeast China. The brachiopods of previous reports from Heitai formation is totally 8 genus 8 species, and lack of detailed and systematic classified description. Basing on the formers' research materials and the fossils first collected from Baoqing, the paper describe Baoqing-Mishan brachiopods 18 genus and 21 species, including 2 new species, taking the newest scheme of brachiopod classification. They are Leptaena {Leptaena) rhomboidalis, Leptagonia zlichovensis, Leptostrophia {Leptostrophia) heitaiensis, L. {Leptostrophia) mishanensis sp.nov, Protoleptostrophia sp., Systostrophia semicircularis sp.nov., Dalejina sp., Discomyorthis kinsuiensis, Schizophoria (Schizophoria) sp., Leptocoelia sinica, Atrypa {Atrypa) reticularis, A. {Atrypa) bodini, Spinatrypa subspinosa, Howellella {Howellella) amurensis, H. (Howellella) elegans, Euryspirifer grabaui, Fimbrispirifer divaricatus, Acrospirifer pseudocheechiel, Costispirifer heitaiensis, Kymatothyris pseudofallax, Deltospirifer transverses. This fauna is mainly spiriferidea with thick shell, small atrypidea and large strophomenoidea. The found and description of the brachiopod fauna extremely enriched the brachiopod materials and improved the study level of this area.Through discussing the compose character of the brachiopod fauna, the paper fistly setting up 2 Brachiopod Assemblages. The lower Assemblage is Costspirifer heitaiensis Assemblage; the upper Assemblage is Euryspirifer grabaui Assemblage. These assemblages include corals, trilobites, bryozoans, blastoids, crinoids, bivalvias and fossil fish, especially Costspirifer heitaiensis Assemblage, abundant brachiopods and multitudinous paleontology showing that Baoqing-Mishan was in shallow water, oxygen and light rich, and strong hydrodynamics environment during late Early Devonian.So far the age of Heitai Formation is in a state of controversy. Majority researchers think it should be Middle Devonian. Most of the brachiopods can be contrasted with Emsian brachiopods in Xinjiang Zhunggar, Gansu Beishan, Innermogolia Dongwuzhumuqinqi, northern Xiaoxing'anling, and contained some Lower Devonian brachiopods from Western Europe, North America and Russia. In addition, there are some brachiopods only developed during Emsian. Such as, Spinatrypa subspinosa and Kymatothyris pseudofallax produced in Russia Altai Lower DevonianМедведевскиеслои(Emsian); Euryspirifer was considered in Early Devonian late Emsian, Euryspirifer grabaui is similary with Euryspirifer paradoxus, distributed in Europe late Emsian; Fimbrispirifer divaricatus was found in North America Schoharie age of Lower Devonian (Emsian). These brachiopods are lack of characteristic species of Middle Devonian, so can eliminate Middle Devonian of Heitai Formation. These brachiopods in the paper all collected from middle stage of Heitai Fm. Therefore, The middle stage of Heitai Formation should be correspond with late Emsian.The study about brachiopod palaeobiogeography of Baoqing-Mishan is weak, without special discussion. Most researchers, such as Hou Hongfei et. al.(1981, 1988), Zhao Xiwen (1988), Guo Shengzhe et.al.(1992), fell the Baoqing-Mishan under Boreal Realm Zhunggar-Xing'an Province with northern Xinjiang, Gansu Beishan, Innermongolia and north Northeastern China. The paper preliminary study the brachiopod Palaeobiogeography of Baoqing-Mishan based on the lots of fossil materials. In the 18 genus brachiopods, there are 9 genus distributed cosmopolitan, including Leptaena {Leptaena), Leptagonia, Leptostrophia (Leptostrophia), Protoleptostrophia, Dalejina, Schizophoria (Schizophoria), Atrypa (Atrypa), Spinatrypa, Howellella (Howellella). The other 9 genus distributed in North America, Europe or North Africa, where all belonged to Tethyan Realm. The brachiopods distributed in Boreal Reaml disappeared in the area. Therefore, Baoqing-Mishan should belong to Tethyan Realm. And it approach with the brachiopods in Zhunggar-Xing'an province which we think belong to Tethyan Realm, they should belong to the same province because of 14 same gunus and 6 same species. According to 19% endemic species of Baoqing-Mishan, we set up the Baoqing-Mishan subprovince.Recent years, Wang Chengwen et. al.(2003, 2008) proposed a new conception about the tectonics of Northeastern China, he thinks that the northeastern China and adjacent areas are bounded by Mongolia-Okhotsk suture belt to the north, Xilamulun-Yanji suture belt to the south and Middle Sikhote subduction belt to the east, are a stable Late Paleozoic tectonic unit, which consists of a huge Late Paleozoic block, named as Jiamusi-Mongolia Block. Baoqing-Mishan area stand in the eastern margin of Jiamusi-Mongolia Block. The paper throught studying the distribution character of the brachiopod fauna from Heitai Formation, indicate Baoqing-Mishan belong to Tethyan Realm, located in low latitude. According to the development of cora reefs and fish fossil, who are sensitive to climate and latitude, and referencing some paleomagnetism data, showing that Jiamusi-Mongolia Block maybe placed in low latitude area between equator and tropic of cancer in late Early Devonian. Wang Chengwen and Zhang Songmei (2003) have obtained the palaeogeographic map of Jiamusi-Mongolia Block, placed it at Boreal Realm in high latitude. Therefore, Jiamusi-Mongolia Block should movement from low to high latitude from Early Devonian to Middle Permian.