Lower Paleozoic Depositional System And Paleogeographic Evolution In Helan Mountain Region

Helan Mountain is located in the hub between the east and west tectonic units innorth of China. It is surrounded by the triangle region that formed by North ChinaCraton (the Ordos block), Alxa block and central Qilian-Qaidam block. Because theregion is in complex and special tectonic background, the structure activity is strongand frequently since the Paleozoic, and it has the characteristic of multiple cycles. Inthe past20years, according to the research of petrology, structural geology,paleontology, geochronology and geophysics, Geologists give geology of HelanMountain based on the background of different study region(Northwestern China,Ordos Basin, Alxa block). Most of these research are in the peripheral areas of HelanMountain,but the research of Helan Mountain is little. The previous studies of HelanMountain focus on the local research or field study like stratigraphy, paleontology,petrology. Lacking of awareness of the helan mountain region sedimentary system inthe whole systematic. This paper focus on the study of sedimentary system,sedimentary model and paleogeographic evolution in lower Paleozoic.According to the stratum development characteristics in lower Paleozoic,combined with tectonic setting, palaeogeographic pattern, sediment types andpaleontology distribution characteristics of the study region, we divide the studyregion into three stratigraphic areas and8stratigraphicminorregions. The threestratigraphic areas are Helan Mountainstratigraphic area, Qilianstratigraphic area andNorth China stratigraphic area. The8stratigraphicminorregions are Zhuozishan-lingwu,Yinchuan-HelanMountain,Qinglongshan-Pingliang,Zhongwei, North qilian,Zoulang, Ordos and North China. Based on the stratum statistics, stratigraphiccorrelation and previous research achievements,comparing with the latestinternational stratigraphic chart; we systematic analyse the lithostratigraphy,biostratigraphy and time stratigraphic, using them to establish biostratigraphicclassification in lower Paleozoic, and summarize the characteristic of residual stratadistribution in Helan Mountainin lower Paleozoic.We systematically summarizes the helan mountain rock types in the region,finding that carbonate rock and clastic rock is the most widely distributed and coverthe hole Helan Mountain area. Carbonate rocks such as limestone, dolomite anddolomitic limestone and clastic rock including conglomerate, sandstone, siltstone andmudstone, shale and so on are distributed in the study region. Besides, evaporite,siliceous rocks, volcanic clastic rock, metamorphic rock and so on other kinds of rockin research area development.Based on geological outcrop of Helan Mountain,previous research achievementsand the research of petrography, rock slice, paleontology and sedimentary structureand geochemistry, we divide the Helan Mountain’s stratigraphy of lower Paleozoicinto coast deposit, the carbonate platform deposits, platform edge slope and deep water slope, and analysesthe distribution and lateral evolution of sedimentary facies.On this basis, established depositional framework and depositional evolvement modelof lower Paleozoic.Based on the above research, we discusses the longitudinal distribution ofdepositional system. Integrated all kinds of depositional system and its characteristics,making the method of the mapping and drawing the main stratigraphy’slithofacies-paleogeographic maps of lower Paleozoic. Also, we discussessea levelchange and sedimentary palaeogeographic evolution rule of Early Paleozoic in HelanMountain...