Study On Genesis Of Tafoni Along Sandstone Cliffs Of The Mt. Danxiashan In Guangdong Province

The Mt.Danxiashan is located in Renhua County of Shaoguan City in northern Guangdong Province.It is representative of Danxia landforms of the mid-late cluster of the peak clusters.The type of Danxiashan landform is famous for its various kinds of strange shapes like honeycomb walls.In the past ten years,it has attracted experts and scholars from various fields to study tafoni.This paper takes the Mt.Zhanglao Peak Jinshiyan Temple and Mengjueguan tafoni of the Mt.Danxiashan as the research objects to detailed field observation,meteorological monitoring,and rock sample microscope and scanning electron microscope analysis.The formation process of honeycomb cavity is discussed.The tafone of the Mt.Danxiashan are mainly produced on the cliff of the wind-forming sandstone of the second member of the Danxia Formation(Jinshiyan section)of the Late Cretaceous,with large plate-like and wedge-shaped interlaced layers,with good roundness,sorting and permeability.Using the statistical principle to analyze the cavity shape,opening direction and wind direction,it is found that its morphological characteristics are consistent with the distribution of Tyson's polygon.The opening direction and the opposite direction of the wind indicate that the cave has been exposed to wind for a long time,and the wet water vapor of the Jinjiang River is brought inside the cave,which speeds up.The weathering and erosion of the cavities,the cavity is continuously enlarged and deepened towards the interior.With the gradually unbalanced of gravity and weathering erosion,the inner wall of the tafoni is thickened and thinned,eventually die out due to instability.The meteorological monitoring data show that the external temperature of the cavity is always higher than the internal temperature,which is opposite to the change of humidity,indicating different microclimate changes inside and outside the cavity;the measurement results of wind speed,interpretation The residue inside the cavity is weathered by the wind on the rock surface of the cavity.Because the weak wind can not take away the weathering products,it slowly accumulates in the cavity.Both the scanning electron microscopy and major element analysis of sandstone samples show that the severe weathering and dissolution of mineral particles and the increase of Na and kaolinite contents in salt minerals are the most obvious evidence of salt weathering.In addition,by comparing the element content of the top,back and bottom of the cavity,the development direction of the cave is inward and upward.Therefore,the macroscopic research in the macroscopic research mainly includes the geographical location of the cavity,the development of environmental conditions,lithologic features and sedimentary structures,and the microclimatic effect of the tafoni itself.Salt weathering at the micro level is an important factor in the formation-development-depletion process of the honeycomb cavities in the Mt.Danxiashan.