Preliminary Study On The Development Model Of The Planation Surface And Karst Weathering Crust In The Liaodong Peninsula

Planation surface is a large-scale geomorphic landscape associated with long-term stable tectonic environment.The study of planation surface and weathering crust as a whole is the mainstream of modern planation surface research.The weathering crust is the surface of lithosphere composed of residual matter and new matter after the surface of the earth is weathered by physical,chemical and biological effects.Climate factors are the main factors affecting the development of weathering crusts.Red weathering crusts generally represent hot and humid climatic conditions.The climate is humid and hot in southern China,and various types of weathering crusts are widely developed.Compared with the northern part less exposed and mostly ancient weathered shells,the study of red karst weathering crust in southern Liaoning is helpful to understand the development patterns,the development characteristics,the development and profile structure of ancient planation surface of red karst weathering crust in northern China.,and have a certain significance for the prediction of the uplifting speed of the Liaodong Peninsula from the Neogene to the present.In this paper,based on the Lashufang profile and the red karst weathering crust in Jinshiyuan area a total of 41 samples of red karst weathering crust in southern Liaoning were taken,including 21 samples from the eastern side of Liaodong peninsula and 3 samples from the bedrock;20 samples from the west side of the peninsula and 3 samples from the bedrock.By means of geomorphology,geochemistry,particle size analysis and other means,the development characteristics,the development patterns,the development and profile structure of ancient planation surface of red karst weathering crust in Liaodong peninsula were preliminarily studied,and the following understandings were obtained:The six red karst weathering crusts discovered so far are all located in the Fuzhou-Dalian sag,and the strata are Sinian strata.The Binhai Garden and the Qidingshan bedrock are Sinian carbonate rocks,the Lashufang and Jinshiyuan bedrocks are the interbeds of the Sinian claystone and carbonate rocks,and the Shicao and Chengshantou are the interbeds of the Sinian quartzite and carbonate rocks.The red karst weathering crust on the Liaodong peninsula is usually around 4m thick.The weathering crust on the west side of the peninsula is usually covered by a thick layer of loess,while the weathering crust on the east side is only covered by a thin layer of soil.The mass of acid insolubles prepared from the bedrock of Lashufang section is 91.4%lower than that of bedrock,indicating that the formation of carbonate weathering crust requires the dissolution of a large amount of bedrock.The weathering crust samples of Lashufang section are mainly silt,the silt content is between 43.1%and 75.2%,the average value is 59.4%,the clay content is between 2.2%and 3.9%,and the average value is 3%.The silt-clay ratio is between 15.5 and 29.77,with an average of 20.3.The above indicators indicate that the red weathering crust of the Lashufang is poorly developed.In the scatterplot of the particle size parameter of the weathering crust sample,the sample points are clustered in two obviously distinct parts,indicating the heterogeneity of the parent rocks of the weathered crust.The content of macro elements in Lashufang section and Jinshiyuan red karst weathering crust is very close.The content of SiO₂ and MgO in the weathering crust of Jinshiyuan is slightly lower than that in Lashufang;the content of Al₂O₃,Na₂O,K₂O,TiO₂ and CaO is slightly higher than that of Lashufang,and the content of Na₂O and Fe₂O₃ is basically the same in the tree house section;the comparison of SiO₂,Al₂O₃ and Fe₂O₃ content indicates that the development degree of the weathering crust of Jinshiyuan is slightly higher than that of Lashufang profile.From the standard deviation,the overall fluctuation of the profile of Lashufang is large and the sample of the weathering crust of the Jinshiyuan is taken from the same layer,so the fluctuation range is small.And Ti acts as a stable element,and its content is stable for both.The chemical alteration index?CIA?of the red karst weathering crust in the Liaodong peninsula been found indicates that the weathering crust in this area is formed in warm and humid climate conditions,and the chemical weathering is at moderate weathering level.The migration coefficient?_j of Lashufang red weathering crusts indicates that SiO₂,Al₂O₃,K₂O and Fe₂O₃ are enriched,and Na₂O,MgO and CaO have sustained loss characteristics.The pH,geochemical analysis and silt-clay ratio indicate that the overall maturity of the red weathering crust in Lashufang is low,and the maturity of the lower red weathering crust is relatively higher than that in the upper part.Geochemical analysis shows that the development strength of the weathering crust of the Jinshiyuan is relatively higher than that of Lashufang.The author defines the red karst weathering crust with the bedrock as limestone and the native weathered crust overlying the loess on the west side of the Liaodong peninsula as a loess-covered weathering crust.Geochemical analysis and grain size characteristics indicate that the development intensity of red karst weathering crust on the eastern side of the Liaodong peninsula is relatively better than that of the west.This reason may be higher than that in the central Liaodong peninsula during the Pliocene?now all is denuded?.On the east side,there is more precipitation on the windward side than on the west side.Under similar climatic conditions,the more precipitation,the stronger the leaching effect,so the development strength of the weathering crust in the east is relatively stronger than that on the west.The development pattern of the red karst weathering crust in the Liaodong peninsula is in line with the similar weathering crust in the south,but it has regional characteristics.Before the Quaternary period,it was a two-stage mode,and the flattening-shelling period-cutting-redening period.There has only been one stage in the Quaternary to this day-the cutting-redening period.The full-section clay content,clayey change trend,geochemical characteristics and geomorphological evolution of the red karst weathering crust in the Liaodong peninsula indicate that the weathering crust in this area is formed in an environment that is not conducive to viscosification and leaching.From the large scale,this developmental condition can only be met by the low-altitude planation surface under the hot and humid conditions in the middle and low latitudes.Geological profile,grain size,and geochemical analysis indicate that there are two different planations in the area.The structure of the ancient planation on the west side of the Liaodong peninsula consists of two parts:The subsurface action surface?the weathered crust buried under the loess?;The covered karst.The east side of the ancient planation has the same profile structure as the south.