湖南崀山临水型丹霞地貌危岩体景观岩性分析

Analysis on Lithology of Facing-water Danxia Landform Dangerous Rock Landscape in Langshan,Hunan Province

以砂砾岩为主的丹霞地貌区因地势复杂、崖壁险峻、节理发育而形成了独特的危岩体景观。研究表明,崀山丹霞危岩体景观发育于区域性多期次活动大断裂及其不同方向的节理裂隙发育的构造背景、物质基础为巨厚的陆相紫红色磨拉石碎屑岩,在流水侵蚀溶蚀为主的外动力共同作用下形成。对岩矿薄片的鉴定结果表明,砂砾岩种类丰富,主要有泥晶或结晶灰岩、含白云母长石砂岩、含长石石英砂岩和石英砂岩。所有砂砾岩的微量元素含量均很低,主要元素的氧化物含量在不同岩石中差别较大。但所有岩石的SiO2、Al2O3和CaO含量均较高,尤其是灰岩角砾发育的下部层位,其CaO含量明显增高、K2O和Na2O含量较低。说明崀山红层的抗风化能力强。从抗压实验来看,所有岩石的抗压强度较大但不同类型砂砾岩的抗压强度略有差异,含砾砂岩的抗压强度为52.15MPa,砾岩的抗压强度为60.8MPa,粉砂质泥岩的抗压强度为41.4MPa。抗压强度较大的砾岩和含砾砂岩有利于丹霞地貌景观本身的稳定。

There are unique dangerous rock landscapes in Danxia landform area dominated by sandy conglomerate due to complex terrain,steep cliffs and joint development.The research shows that the formation mechanism of dangerous rock landscape mainly includes the structural background of regional multi-stage active large faults and joint fissure development in different directions,the extremely thick continental purplish red molasse clastic rock and the external dynamic conditions dominated by water erosion in Langshan Mountain.The water erosion is the most important and active external dynamic for shaping Danxia landform and forming dangerous rock landscape.The identification results of rock and mineral thin sections show that there are various types of glutenite,mainly including Muscovite feldspathic sandstone,argillaceous or crystalline limestone,feldspathic quartz sandstone and quartz sandstone.From the analysis of rock chemical composition,the content of trace elements in all rocks is very low,and the oxide content of main elements varies greatly in different rocks.However,the contents of SiO2,Al2 O3 and Cao of various types of rocks are high,especially at the bottom of the lower horizon.Due to the development of limestone breccia,the CaO content is significantly increased and the K2 O and Na2 O contents are low.It shows that Langshan red bed has strong weathering resistance.From the compressive test,the compressive strength of all rock is large,but the compressive strength of rock with different lithology is slightly different.The compressive strength of pebbly sandstone is 52.15 mpa,conglomerate is60.8 mpa,and silty mudstone is 41.4 mpa.The conglomerate and pebbly sandstone with high compressive strength are conducive to the stability of Danxia landform.