Characteristics of Lithofacies Paleogeography of the Taiyuan Formation Sedimentary Period, Henan Province

Key words: 
• sedimentary facies

Abstract: The sedimentary area of the Early Permian Taiyuan Formation in Henan Province is located in the south of north China basin and to the north of LuanchuanGushi deep fault in the North Qingling fold belt, at that time, this sedimentary basin was controlled by the tectonopaleogeographic features of the west uplift in the North China platform block. The Taiyuan Formation was a part of deposits of the NorthChina epicontinental sea or carbonate platform in the Late Paleozoic, and developed a set of deposits of the epicontinental sea characterized by the carbonate rocks intercalated some clastic rocks and coal. This section is mainly composed of gray, dark gray, thinmedium bedded bioclastic limestones, intercalated with thinmedium bedded mudstone, micritic limestone, fine sandstone, siltstones and thin coals, locally appeared light gray thick beded moderatefine grained sandstone, coarse sandstone or graywhite quartz sandstone, with very abundant body fossils, such as fusulinids, conodonts, brachiopods, corals, crinoids, bivalves and plants fossils and so on. According to the analysis of sedimentary sequence, the Taiyuan Formation can be divided into three units from bottom to top: the lower limestone unit, mainly containing 4 ~ 5 limestone layers; the middle clastic unit, dominated by sandstone and mudstone, intercalated with 1~3 layers of limestone, unstable bioclastic microcrystalline limestone; the upper limestone unit, composed of 2 ~ 3 layers of limestone, locally, 4 ~ 5 layers. Based on the isoline trend analysis including the thickness of the formation and carbonate rock and the ratio of sand to mudstone, along with the composition and distribution features of ichnofossils, facies fossils and sedimentary assemblage types, 5 sedimentary facies (tidalflat, lagoon , barrier island or sand bar, restricted carbonate platform and open carbonate platform facies) , 12 kinds of sedimentary types, 3 sedimentary assemblage types and 3 types of lithofacies areas as the micritic limestone and mudstone lithofacies area of restricted flatformtidal flat setting, limestone and clastic lithofacies area of open platformtidallagoon setting and limestone and clastic lithofacies area of open platformbarrier islandtidal flat setting can be suggested. The Lithofacies palaeogeographic characteristics of Henan province during the deposit of the Taiyuan Formation display：(1) The marine invasion is widespread and limestone of shallow sea facies is almost throughout the whole sedimentary region；(2)Sealine extended eastward and southward to LingbaoLuoningSongxianFangchengBiyang zone；(3)Old land areas are situated the Funiu mountain to sorthwest of this basin and Zhongtiao Mountain to west of this basin；(4)Paleotopography shows steep in the west, gentle in the east, high relief in the northwest, and low relief in the southeast；(5)The sedimentary zone of largest thickness of this formation is in the northeast and east of this basin；(6)Seawater invasion was from the east and northeast, and regression from northwest to southeast. In the Taiyuan Formation sedimentary period, the basement terrain of this sedimentary basin was relatively gentle and sea water was frequently progressive and regressive, thereby, the interbeds of carbonate rocks of the restricted epicontinental sedimentary environment and coalbearing clastic rock of tidal flat sedimentary setting were generated, and the larger area peat flat were developed in the coastal plain in Henan Province, and the coal layers with industrial value were formed in many parts.