Sedimentary Environment And Geomorphologic Evolution Of Danxia Landscape Layer From Danxiashan,Guangdong Province

The Danxia Landscape was named for at the Danxiashan in Guangdong Province.Over recent nearly a century,many scholars have conducted carried out a lot of researches on work in landscape geomorphology,stratigraphy,structural geology,dynamic geology,etc.,and have got many achievements.However,the research on the sedimentary environment of the red beds is obviously insufficient.For a long time,due to the influence of the Davis Erosion Cycle Theory,the evolution of the Danxia Landscape has just only emphasized three main controlling factors: tectonic uplift,weathering and erosion,and time.Moreover,it is assumed that internal and external geological forces act on a flat and uniform geological body.The previous studies show found that the sedimentary facies play a very important controlling role in the evolution of the Danxia Landscape except for above-mentioned three main factors in Southeastern China,However,the control mode and contribution rate of sedimentary facies rocks to Danxia Landscape have not been systematically recognized.This paper takes the Danxia Basin in Guangdong province as an example,and study expound the lithofacies and paleogeographic features of the main formation strata in the Danxia Basin and their relationships with geomorphic genesis by means of field geological survey,gravel statistics,particle size analysis of sandstone,and petrogeochemistry.The tectonic setting and paleowind direction of the basin were analyzed by studying the regional value distribution of clastic zircon U-Pb ages and the characteristics of prestratigraphic stratification of staggered strata.Based on studying the chroma value of red sandstone and the its relationship between it and the abundance of geochemical elements,the coloration factors of red beds are discussed.Furthermore,through the numerical simulation of the Channel-Hillslope Integrated Landscape Development(CHILD),the evolution process of Danxia Landscape under different parameters(lithology,time,rainfall,etc.)were comprehensively discussed.The main bedrock of Danxia Landscape of the Danxia Basin is the Danxia Formation,and comprises Bazhai Member,Jinshiyan Member and the upper part of Baizhai Member.The Jinshiyan Member is the most special one,where large plate-shaped and wedge-shaped staggered strata are developed.It can be also observed seen that the hummocky cross-stratification and tear structure formed under the influence of transient storms in Jinshiyan Member.Furthermore,this member is composed of thick to huge-thick stratiform medium to coarse sandstones intercalated with intermediate-thin to quite-thin stratiform mudstones,silty mudstones and calcareous layers.By Under scanning electron microscopy,the dish-shaped impact crater with the characteristics of aeolian deposition can be observed on the surface of quartz particles,showing aeolian deposition characteristics.The U-Pb Ages of Detrital Zircon are mainly concentrated in 6 age groups,which are 100?165 Ma,212?270 Ma,411?443 Ma,726?1523 Ma,1742?1991 Ma,2482?3456 Ma.The source areas of the bedrock are is mainly located at from the eastern part of the Nanling,the northeast and southwestern areas of the Danxia Basin.The Yanshanian acid volcano-intrusive rock was the main source.There are mainly two sets of foreset beds with NEE and SW trend respectively NEE and SW trending pre-layers in the interlaced bedding of aeolian sandstones,which are consistent with the trend of foreset bed in the Late Cretaceous aeolian sandstones in Sichuan Basin,Ordos Basin and Xinjiang Basin.This indicates that China was located in the westerly and northeasterly zones of north hemisphere in Late Cretaceous.At that time,the northeasterly wind prevailed,and the southwesterly wind was secondary.Meanwhile,there might be the southeasterly ancient monsoon.The characteristics of trace elements and rare earth elements in the sandstone and mudstone of the Jinshiiyan Member section of the Danxia Formation indicate represent drought to and semi-drought and conditions.The study on of chroma value of the red bed shows that P,Ti,Fe and other elements in the matrix/cement composition formed during sedimentation and diagenesis are the main red-producing elements rocks.However,the color-controlling minerals are mainly Hematite and Phosphorous Hematite,followed by Titanium Oxide.Some minerals such as quartz particles in the detrital component and calcite particles in the cement promote the brightness of the rocks.During the deposition of the Changba Formation(Late Cretaceous),an initial rift occurred in the Danxia Basin,which triggered weaker volcanic activity.With the continued sag,the basin expanded and the alluvial fan-river-lake sedimentary environment was dominant.The basin underwent the stage of uplift and shrink during the the deposition of the Danxia Formation,and the alluvial fan-wadi-paleodesert sedimentary environment prevailed.During the Himalayan period of the Paleogene and Early Neogene,the Danxia Basin was uplifted and eroded again.The geomorphic landscape with multi-level planation levels of 400 m,300 m and 200 m was formed after three planation events,respectively.The geomorphic evolution of Danxia Landscape is reproduced in with the simulation experiment of geomorphic evolution on the CHILD software platform.The simulation results show that the peaks in the young stage are more continuous,the ridges of peak forests are more obvious in the early mature stage,the peak forests become sparse in the late mature stage,and the isolated peak on the low plain is dominate in the old stage.Currently,Danxiashan is situated at the stage of late mature.