Research On Tectonic Activity And Sedimentary Response In Jianmenguan Area

Jianmenguan area is located in Jiange County of Guangyuan city of Sichuan province.It is an important tourist attraction in our country.It is cultural relics protection units,national Forest Park,national natural and cultural heritage,especially the geological landscapes and relics,characterized by Danxia landforms,are deeply loved by tourists.In recent years,the rise of geological tourism has set off a hot wind in Jianmenguan area to explore the process of its formation,which has attracted many domestic and foreign scholars.The tectonic activities of the Jianmenguan area are mainly influenced by the nappe and uplift of the Longmen mountain tectonic belt from the northwest direction,resulting in the deposition of a huge thick sand and gravel layer.The lithologic characteristics and distribution of the rock strata are controlled by the strong and weak tectonic activity.The characteristics of the sedimentary system mark the strength of tectonic activity.By analyzing the lithologic characteristics of the sedimentary system in the Jianmenguan area,the characteristics of sedimentary rhythms can be summed up,and the characteristics of the sedimentary dynamic can be determined,which reflect the characteristics of tectonic activity,the place of sedimentary dynamic and the law of the change of strength and weakness.The Jianmenguan area belongs to the foreland part of the Longmen mountain tectonic belt,and its tectonic activity is affected by the Longmen mountain tectonic belt.During the geological history,the Longmen mountain tectonic belt had many thrusting and nappe activities.In the process of nappe and uplift,the Longmen mountain tectonic belt played the role of the transfer zone,and transferred the compressive stress from the northwest to the Jianmenguan area,which made the tectonic activities in the Jianmenguan area change correspondingly,and formed a series of small fracture zones.During the continuous uplift of the Longmen mountain tectonic belt,a large number of rock debris were produced.Through the transfer zone and the external dynamic handling,the debris was transported to the Jianmenguan area of the foreland area.After a long time,a large and thick sedimentary system was formed.The formation,development,and evolution of sedimentary system in Jianmenguan area was controlled by Longmen mountain tectonic belt,the clastic sediments that from Longmen mountain tectonic belt form sedimentary rock by deposition,cementation,compaction.The Jianmenguan area is characterized by the red Danxia Landform,through the long-term evolution of geological history and the joint action of internal and external forces,it is formed the unique landscape,and because the area is located in the humid climate area,thechemical reaction of the diagenetic process is formed the unique red rock formation.The red bed mainly including Jianmenguan group,Lianhuakou group,Suining group and Shaximiao group.The characteristics of each layer are remarkable,and the development is parallel and interlaced.The area of Jianmenguan distributes numerous geological remains of Danxia landform,there are clear boundary of rock and kinds of typical geological outcrops,it has being the important research areas on the our country.According to the dynamics of into landscape and the characters of modeling,this article divide landscape into Fracture uplift cliff,Water erosion valleys and Karst caves,Wind erosion column and hoodoo and Trace the collapse,and discussed classify characteristics.Through analyzing the structure characteristics,rocks provenance and joint occurrence etc.,the mechanism into landscape can be divided into process mechanism and motivation mechanism,determine the developmental stage of Danxia Landform belongs to the adolescence stage.Joint rose show that the Rock trend consistent with the Longmenshan tectonic belt,within the fracture,joint controlled by the Longmenshan nappe fold belt.The sedimentary system of thick sand breccia and sand mudstone in Jianmen area has obvious vertical rhythm and NW-NW denaturation.The Longmen mountain tectonic belt controls the characteristics of distribution and the hydrodynamics control the vertical rhythmic characteristics of strata.Triassic period is an important period of sea — land conversion in the Sichuan basin.According to the characteristics of progradation and reprogradation of sediment,the characteristics of river evolution process and the characteristics of sediment change in water and land transition zone,the sedimentary facies of Middle Jurassic and lower Cretaceous in Jianmenguan area are divided into alluvial fan facies,fluvial facies,delta facies and lacustrine facies,and extend to South East.The tectonic activity in the Jianmenguan area controls the development trend of the sedimentary system,and the variation rule of the sedimentary system reflects the strong and weak order of the tectonic activity.Through the analysis of the tectonic activities and depositional systems in the Jianmenguan area,the coupling relationship between the two is established in three aspects: the sedimentary rhythm,the deposition process and the dynamic mechanism,respectively,in the coupling relationship of the tectonic activity.(1)the coupling of sedimentary rhythm and tectonic activity in the Jianmenguan area is summarized as follows:in the early Late Jurassic,the Longmen mountain was in the uplift stage,the surface debris was broken and the alluvial fan phase was formed with the flood flow out of the mountain.In the middle and late Late Jurassic,the Longmen mountain structural belt was more active,the river facies developed in the front of the mountain,the river finally flowed to lakes and formed lakes.In the early Cretaceous,the Longmen mountain tectonic belt is relatively stable,and various sedimentary facies are well developed.(2)the coupling of sedimentary process and tectonic activity in the Jianmenguan area is summarized as follows: the deposition process is formed on the basis of millions of years of geological time units,and in the depositional system,the sedimentary sequence is centigrade or even millimeter.Tectonic activity controls the evolution of sedimentary systems,and the sedimentary system affects the strength of tectonic activities.The change of grain size of sedimentary material is the most direct evidence of the intensity of tectonic activity.Coarse to fine grain size is a manifestation of strong and weak tectonic activity,and vice versa.The level and scale of tectonic activities in the lithosphere are also affected by the sedimentary system.The main manifestations are that the composition of sediment,the degree of cementation,and the lithology can affect the strength of the tectonic activity.For example,the strong cementation degree and the strong lithology can weaken the tectonic activity strength.(3)the coupling of dynamic mechanism and tectonic activity in Jianmenguan area is summarized as follows: the dynamic mechanism mainly includes two types of internal power and external power,the inner power makes the earth surface undulating,and the external power mainly plays the flattening effect.The internal force controls the macroscopic pattern of landform and topography,and the external force shapes the landscape type.The depositional system also reacts on the dynamic mechanism,mainly in the aspects of the composition,structure and structure of the sedimentary rock,the weakening of the dynamic force of the tectonic activity,the obstruction of the internal dynamic by the tight rock layer and the uneven mechanical properties of the surface of the rock layer.With the appearance of digital earth and digital geology,it is a certain trend to study deeply-underground sedimentary system with mathematical method.The development of Markoff chain method provides a mathematical basis for quantitative discussion of sedimentary rhythm and sedimentary cycle.The principle of Markoff theory method: the total number of all the lithologic states measured in the rock layer section is calculated by simple addition,and the threshold value is established by transfer matrix method,and the Markoff chain diagram is established.In this paper,the Markoff chain mathematical model is used to analyze the change regulation of sedimentary system in Jianmenguan area,combining future of tectonic activity,building the coupling relationship between tectonic activity and sedimentary system,further reveal the process of formation and evolution of sedimentary system in Jianmenguan area,and explain the relationship between the process and tectonic activity in Longmen mountain.The sedimentary facies model is a combination of various characteristics such as lithology,formation,structure and structure of sedimentary facies.The complex sedimentary system is reacted in a simple sedimentary model by mathematicalmethod.The Markoff chain method is used to study the sedimentary sequence of the rock strata,to establish sedimentary facies model,to analyze the change law of the sedimentary system in the Jianmenguan area,and to reflect the activity process of the Longmen mountain tectonic belt.