Carbonate Microfacies And Reefs Of Amushan Formation In The Damao Area, Inner Mongolia

Since Outcrop has the property of visibility, measurability, ccuracy and being researched by various scales and precision, the outcrop is the most ideal place of establishing diverse geological models. As the development of Sedimentary Geology theories and extension of Oil-Gas Exploration, the study of the Outcrop should be emphasized again.In eastern Inner Mongolia, degree of Upper Paleozoic oil and gas exploration is low, evaluation is still in the early stages, the main work of initial stage is outcrop of measure, stratigraphic correlation, and finally establish the Upper Paleozoic stratigraphic framework, restore ancient environment. The Ancient and modern reefs mainly distributed carbonate platform margin and island front slope. Distribution of reefs usually indicates the plate egde slope break belt,throuth detailed study on the sedimentrary characterisitic of reefs,it is important significance tectonic environment.Amushan Formation geological age is Late Carboniferous-Early Carboniferous, characteristics of the rocks are mainly carbonate rock.Because distribution of Amushanzu Formation are wide,the transverse difference of lithology and thickness is great, rocks boundary is not clear.Through the division of age in favor Amushan Formation on regional contrast.The paper is guided by theories of paleontology, palaeoecology,sedimentary, and so on.Throuth distribution of fusulinid fossil zones,make division of Amushan Formation geological age.According to the study of the measured section,observed sections and indoor reaserch,conduct in-depth reaserch on carbonate microfacies and reefs The following results has been acquired.1.According to sampling and identification of DaMaoqi Shan Da Amushan Formation profile fusulinid fossils, divided into three fusulinid fossil assemblage, and according to the fusulinid fossil zone, AMushan time is accurately divided.section6layer below the Late Carboniferous Xiaodushan stge section6layer above for the Early Carboniferous Zisongian Stage.2. Amushan Formation carbonate are divided into11types of microfacies,.They are respectively microfacis1(MF1) plaster homo-spherules limestone, microfacis,2(MF2) dasycladacean plaster limestone, microfacis3(MF3) plaster phylloid algal limestone,microfacies4(MF4) plaster bioclastic limestone, microfacies5(MF5) plaster limestone, microfacies6(MF6) containing bioclastic plaster limestone, microfacis7(MF7)bioclastic plaster limestone, microfacies8(MF8) containing plaster sand cutting limestone, microfacis9(MF9) plaster intra-clastic grain limestone, microfacis10(MF10) phylloid algal reef limestone, microfacis11(MF11) coral framework limestone,Through the carbonate microfacies combination, four sedimentary facies can identified in profile,they are restricted platform facies, open platform facies, platform margin shoal facies, platform edge reef and platform foreslope.3. According to biology and rock type.Reef facies of Amushan Formation from DaMaoqi region is divided into reef behind, reef core,fore-reef subfacies. Sea level due to frequent lifting,two reef forming cycle can be identified in profile. the first cycle of reef, reef building organisms is phylloid algal, the second cycle, most reef building organisms are corals.4. The growth process of the reef is divided into3separate stages, they are respectively foundation stage, growth stage, perdition stage.Each stage has its own features, mainly in the limestone type, relative diversity and morphological aspects of reef building organism. According to the stage of reef formation,establish the Amushan Formation reef-forming model.5. According to carbonate microfacies study, combined with the features of reef.The Late Carboniferous period occurred in the early stage of Xiaodushan stge, sea level rise in the study area.During the early stage,water is cloudy, the shale content is high, is not conducive to the development and growth of reef building organisms, until the Early Carboniferous Zisongian Stage early, the sea level dropped, the platform edge water suitable for a lot of biological growth and development, phylloid algal amassed plaster and bioclastic forming reef. With the transgression speed increasing, result to the biological growth base becomes deeper, eventually lead to reef building organisms were drowned, and was covered with deep water sediments. Zisongian term, rapid sea level drops, the water turbidity, unfavorable reef building organism growth, along with the further fall, species and content is increased, the coral framework reef forming again, and finally into platform foreslope. In summary,the late Late Carboniferous-early Early Permian in the area,experienced multiple transgression-regression cycles.6. Through the research of island margin reefs in Damaoqi area, that existe middle terrane collision of paleo Asian Ocean in Carboniferous-Permian. There are three terrane in study area. In this paper, the reefs are mainly developed in the terrane I edge.Inside, similar reefs are found in terrane blocks II and III edge, reefs distributed in three middle land splicing,The boundary of terrane is fine-grained sediments of Amushan group Four section.Reason of terrane collision probaly is the North China plate and Siberia plate during the closure, terrane close to the North China plate,finally they are together.