| The Danxia landform is a sort of unique geological resource with high scientific and aesthetic value.With the success of the joint application to join the UNESCO World Heritage List for the areas with the Danxia landform,the domestic researches on the Danxia landform gradually go to the world,which ushers in a new stage of development.The red bed is a kind of red terrestrial detrital sediment,which is widely distributed at home and abroad.As the material basis of the Danxia landform,its research is unavoidable.Although the red bed and the Danxia landform have been studied in China for about 90 years,there still exist some shortcomings,such as weak basic research,insufficient cross-disciplinary integration,uneven development of regional research,and lack of comparative research at home and abroad.The northwest region boasts a large number of red beds which play an important part of the red bed distribution in China.Gansu Province,situated in the northwest,as is the case,ranks third in the country.Under the framework of the “One Belt,One Road” cooperation initiative and the “Great West Development” strategy,study on the northwest red bed and Danxia landform greets a good opportunity.Therefore,the red bed and the Danxia landform of Gansu were selected as research objects,relevant data were collected,appropriate field investigation was carried out,and the spatial analysis software Arcgis was used to study the geologic historical background,lithologic facies and distribution of the red bed,and to analyse the influencing factors on its formation.At the same time,the distribution law,types,forming conditions and developmental evolution of the Danxia landform are studied.On this basis,relevant factors are selected to categorize the Danxia landforms in Gansu.The main conclusions are as follows:(1)The age of the red beds in Gansu ranges widely,but most of them came into being after the middle Mesozoic,among which the Cretaceous is the most densely distributed and the Devonian the least;the main distribution is in the east and central areas of Gansu,and the rest areas have a small mount of red bed development,basically consistent with the extension direction of structural lines such as deep and large fault zones.The lithology is mostly conglomerate,sandstone,glutenite and shale,and the sedimentary facies are all continental deposits,mainly composed of hawthorn facies and river-lake facies.There is a significant difference in the distribution of the red beds between the platform area and the fold belt.The lithologic facies vary greatly in lateral and longitudinal directions.The paleo-tectonic movement and its tectonic features(deep faults)and paleoclimate are the main influencing factors for the formation of the red beds in Gansu.(2)There are 116 Danxia landforms in Gansu Province distributed widely in all the cities except Jiayuguan;the distribution altitudes range from 1028 to 3468 m,and the vertical height differences are large;the distribution density shows a strip-like and flaky pattern;they are formed in the red beds from the Late Paleozoic to the Mesozoic and Cenozoic,concentrated in the Cretaceous-New Neogene strata;the distribution in geomorphic area is concentrated in the hilly areas of central Gansu Loess Plateau;the watershed distribution is the largest in the Yellow River system,and the number of Danxia landforms decreases with the distance from the river;the tectonic plates are distributed on the plates of Qaidam-Qilian,North China and Yangtze instead of other plates.Based on the material basis,structural factors,dominant dynamics and scales,the Danxia landforms in Gansu were initially classified.(3)The geological functions of internal and external forces jointly affect the formation and evolution of the Danxia landforms in Gansu.Among them,the red bed and lithology are basic material conditions,the neotectonic movement is the key dynamic condition,the fracture is the control condition,and the climate,flowing water and weathering are important external dynamic conditions for the formation and appearance.Gansu Danxia landform has experienced three important stages: red pot development and diagenesis,tectonic uplift and landscape formation.(4)Danxia landforms are divided into four development areas: super high,high,medium and low,by synthesizing elements such as stratigraphic,geological structure,water system,geomorphology and neotectonic movement,selecting red bed,distance from fracture,distance from river,landform types and new tectonic movement division as representative factors,and adopting frequency ratio model.Both theoretical and field verifications indicate that this partition is reasonable and has a good predictive effect on the development of Danxia landform.The results of researches on Gansu red bed features and on the distribution,classification,developmental evolution and developmental division of Gansu Danxia landform,provide a basis for further exploring the scientific and tourist value of the red bed and the Danxia landform,and display guiding significance for investigating,protecting and developing the red bed and its geomorphological resources. |
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