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Université des géosciences de Chine (2018)

Analysis on Sand Source and Its Geological Origin of Desertification in Xilinguole Grassland, Inner Mongolia


Titre : Analysis on Sand Source and Its Geological Origin of Desertification in Xilinguole Grassland, Inner Mongolia

Auteur : 吴昕;

Grade : Doctoral Dissertation 2018

Université : Université des géosciences de Chine

Résumé partiel
The Xilinguole Grasslands is the less developed "resource-based regions",which have long relied on exploitation of mineral resources to implement the capital accumulation,economic development and people’s livelihood improvement.In recent years due to the development and utilization of mineral resources and global climate change,the grasslands in this area soon experienced serious environmental damage and ecological imbalances,and even caused ecological disasters—sandy desertifieation.In order to identify the potential hazards and the sand sources of desertification in the northern and central Xilinguole Grassland,and provide scientific basis for its treatment,this dissertation has carried out related research based on the national special research fund projects and referring to the results of a large number of studies on land desertification and grassland desertification in China.In this research,a technical route that combines the field macroscopic sedimentology analysis,grain size analysis of sediments,and historical analysis of basin structure-filling evolution from a geological perspective has been established to complete following research works :(1)Both.domestic and foreign research status and development trends of desertification were analyzed and reviewed,with particular emphasis on analysis and review of the current status,existing problems,and development trends of the intrinsic causes of desertification from a geological perspective.(2)A simple visualized macroscopic assessment method to evaluate the degree of grassland desertification marked by "wind erosion pit-dune combination" was established,and a rapid assessment of the desertification degrees in the 96,000 km2 area in the southern Hunshandake and Xilinguole grasslands has been conducted.(3)Based on remote sensing information,field observations of grassland degradation were conducted in typical depressions,and macroscopic sedimentary analysis of outcrop was carried out on 32 sites located in Quaternary Holocene section,Pleistocene section and Lower Cretaceous section.(4)Based on data collected from open-pit coal mines,Quaternary outcrop profiles and borehole cores,the sedimentary facies at the top of Saihantala Formation in Jiergalangtu Depression were analyzed and mapped to study the distribution of the sand bodies of Upper Saihantala Formation.(5)Accurate sampling and particle size analysis on the microfacies of the Quaternary Holocene chestnut soil were conducted,the particle size parameter model of the microfacies was constructed,and dynamic clustering analysis with initial points was carried out.(6)By utilizing a large number of drilling core data from coal geological exploration,petroleum and gas exploration and seismic exploration data,the analyses of the structural stratigraphic framework,sedimentary facies,and sedimentary environment of the Saihantala Formation were conducted.(7)The contact relationship between the Quaternary Pleistocene sand layer(Qp3)and the upper Saihantala sandstone body(K1bs)in the study area,the constrains and controls of basin tectonic-sedimentary evolution to grassland desertification were studied,and the intrinsic causes and geological background of grassland desertification were analyzed.The research results can be summarized as the following 5 points :(1)It was confirmed that in Jiergalangtu depression,extremely severe and severe grassland degradation appeared on the river beach grassland and the plain-grassland among the banks of the Xilin River,and moderate degradation appeared on sloped grassland ;The potential sand source comes from the thick and loose sand layer at the top of the Quaternary and Saihantala groups layed under the grasslands.(2)A simple macroscopic assessment method for visualizing the degree of grassland desertification marked by the form and spatial structure of ‘wind erosion pit-dune combination’ is established.By using this assessment method and the standard atlas,a rapid assessment on the degree and stage of desertification in the southern Hunshandake and Xilinguole grasslands was conducted.(3)The Holocene chestnutite was proved to be formed in a modern river environment.,and a particle size parameter model of six kinds of microfacies of chestnut soil was established(including : riverbed retention,point bar,natural levee,crevasse splay,flood-plain and backswamp).The unknown microfacies can be classified quickly and efficiently throuth the clustering method.(4)The ultra-thick and loose sand layer at the top of the Saihantala Formation was proved to be formed in the river-delta environment in the late Early Cretaceous.It was the product of the base decelerating subsidence of the Erlian Basin.Its unconsolidated state was due to regional tectonic inversion and continuing uplift.

Mots clés : Grassland desertification; Sand source; Sedimentary facies; Grain size analysis; Macro-evaluation index of desertification; Xilinguole-type grassland; Xilinguole-type desertification;

Présentation (CNKI)

Page publiée le 16 avril 2019