Study On Genesis Of Danxia Landforms In The Southwestern Margin Of Ordos Basin

Danxia landform as a geomorphology’s new field, has gone through 80 years of research history. Since the end of the 30’s of last century, Mr. Chen Guoda put forward the Danxia landform. The research has become increasingly mature now through the three stages of start-up, formation and development.But most of them are from the perspective of the landscape resources development point of view. A few scholars do the research on the causes,and from the angle of structural geology, sedimentology study of its formation mechanism has been a weak link. The basic elements of the formation of Danxia landform are not clear,and the basic elements of the formation of Danxia landform are not systematic.In this paper, the Danxia landform in the southwestern margin of Ordos Basin is selected as the research object in this paper. Through the interpretation of ETM+ remote sensing data and field investigation and verification in the southwestern margin of Ordos Basin, find and delineate three Danxia landforms concentrated area in the southwest margin of the basin.Also in the new theory of modern geomorphology development as a guide, take the field investigation and literature reading, rock field sampling and indoor analysis and identification,system research and special studies, to study the formation mechanism of Danxia Landform in southwestern margin of Ordos Basin. Emphatically for the elements of Ordos Basin in the southwest margin of Danxia tectonic background, sedimentary environment, lithology,tectonic movement, etc. A new view and understanding of the characteristics and formation mechanism of Danxia landform in the southwestern margin of Ordos Basin are presented.(1)Ordos Basin on the southwestern margin of the Danxia landform basin formation,sedimentary tectonic uplift, joint fissure development, collapse cause Wai Valley, peak cluster and cliff development, lead to differences in bedrock weathering collapse and weathering and denudation handling this a series of process. Danxia landform area where the settlement movement, it was generally accepted deposition, at the end of the basin was uplifted, different regional stratigraphic occurred a series of faults and folds, and joints is developed,accelerating the cutting of the geological body, but also accelerate the geological body is cut after the rock layers collapse process. Lithologic sheet identification shows that the main component of Danxia landform in the southwest margin of Ordos Basin is mainly composed of quartz, its hardness and anti weathering ability is high, and it has become the framework ofDanxia landform in this area.The three Danxia landform area have undergone several intermittent crustal uplift, the process of landform development clear and intact structure. In a dome of intensive maturity characteristics of the largest peak Danxia peak cluster. The landform development of Danxia is closely related to alluvial fan sedimentary facies.Its sub phase and micro phase type play an important role in the control of Danxia landform development.(2)Through field investigation and rock mineral identification, to constitute the according to golden hill Danxia landform red layer deposited product conglomerate gravel group and lithology, sedimentary characteristics and paleocurrent direction analysis, identified the conglomerate is arid environment down in piedmont alluvial fan fluvial phase coarse clastic sedimentary rocks, hydrodynamic conditions strong, gravel composition complex,dominated by granite, quartz rock and metamorphic volcanic rocks, gravel sorting is generally poor, rounded generally, a sub angular, sub rounded shape and low degree weathering.According to the direction of the ancient water flow, it is determined that the provenance is mainly from North Qinling Mountains. According to an analysis of the characteristics and sedimentary- tectonic evolution that Tongchuan area during the early Cretaceous deposition and Wei northern uplift of the development time was the end of the early Cretaceous later. In the early Cretaceous period, the Weihe area is a transition zone between Ordos basin and the Qinling Mountains mountains, then identification of Early Cretaceous sedimentary basin in South Erdos original circles at least in the Weihe region now even reached North Qinling Mountains. The Tongchuan Danxia landform reflects the relationship between the Ordos Basin and the Qinling Mountains orogenic belt.(3) Through the analysis on the composition of Pingliang Kongtong mountain Danxia landform red layer sedimentary conglomerate gravel group and lithology, petrology,sedimentary characteristics and paleocurrent direction. That shapes Pingliang Kongtong mountain area of Danxia landform, mainly include two sets, respectively, for the upper Triassic Series Kongtongshan formation and lower Cretaceous Bridge Group. According to the paleocurrent direction, indicating that the Kongtong mountain during Late Triassic sedimentary stage mainly in southwest and southern provenance.The main source in the Qinling Qilian orogenic belt. The Kongtong mountain area of Lower Cretaceous formation lithology is a single bridge, the accumulation phase. Gravel grinding roundness difference is larger, from the muddy garden to angular shape, separation range, Unequal diameter. Gravelcomposition statistics show that the gravel components are mainly dominated by limestone,sandstone and silty sandstone. According to these characteristics and sedimentary- tectonic evolution analysis determination of the early Cretaceous sedimentary period of six mountain in the east side of the basin there is a paleo uplift provenance to six Basin. It not only makes early Cretaceous Liupanshan Basin Deposition to the eastern boundary, and will be separated from the Liupanshan Basin and Ordos Basin.(4)Through to constitute the Guyuan Huoshizhai Danxia landform red layer sedimentary conglomerate product conglomerate gravel group and lithology, sedimentary characteristics and paleocurrent direction analysis, finds that the conglomerate is arid environment down in piedmont alluvial fan fluvial phase coarse clastic sedimentary rocks and pretty close to the source area, single lithologic formation, composed of grey purple, purple red massive conglomerate, gravel composition mainly K-feldspar granite, granite diorite and quartz rock flash, gravel bottom conglomerate particle diameter greater than that of the upper particle size, with finer positive cycle sedimentary characteristics, gravel disordered.According to the direction of the ancient water flow, it is determined that the provenance is mainly from the North Qilian orogenic belt. According to these characteristics and sedimentary- tectonic evolution analysis, it is concluded that in this period the fire Danzhai area is the depositional center of Liupanshan Basin.Research shows that the development of Danxia Landform in southwestern margin of Ordos Basin and the position of the tectonic background, red layer deposition thickness,lithology, rock composition, sedimentary facies, and development of paleoclimate and faults and joints strength were closely related, these factors in interrelated constraints in the process of the formation of the southwestern margin of the basin Dan Xia landforms, together constitute the Danxia Landform in this area the scenery control factors. Due to the elements with different characteristics, they work together to the unique Danxia landform landscape composition in different position of development. At the same time, this area is the transition zone of Danxia Landform Development Zone in Northwest and southeast of China, and it is a special region of Danxia landform development in China.