陕西靖边龙洲波浪式丹霞地貌成因机理初探

近期,通过对陕西靖边龙洲地区的丹霞地貌进行详细调查,查明了该地区丹霞地貌类型为丹霞正-负地貌的过渡类型——波浪式丹霞地貌。为了科学评价其价值和意义,本文主要从成景地层岩石特征、地质构造特征以及外动力因素等方面来初步探讨龙洲波浪式丹霞地貌的成因机理。研究表明:首先,研究区洛河组砂岩平行层理、大型风成交错层理对波浪式丹霞景观的形成具有很好的塑造作用;成景地层洛河组紫红色砂岩,为一套风成沙漠相沉积,岩石胶结程度较差,硬度低易碎,是波浪式丹霞地貌形成的物质基础;晚白垩世以来,鄂尔多斯盆地掀斜,区内地壳普遍隆起,表现为靖边龙洲地区发育多级古夷平面和河流阶地,对波浪式丹霞地貌的形成起基础性控制作用;该区洛河组砂岩中发育多组节理、裂隙构造,将洛河组砂岩切割成块状,其对波浪式丹霞地貌的形成和改造起着关键性控制作用;外动力因素上,靖边为半干旱内陆性季风气候,受西北风改造作用非常明显,是波浪式丹霞微地貌形成的主导外动力因素,此外,夏秋季的暴雨强烈冲刷侵蚀地表岩层,春秋季的寒潮霜冻,岩石发生冻融和崩落,对龙洲波浪式丹霞地貌的形成也有重要改造作用;靖边龙洲波浪式丹霞地貌除了受到地质构造和流水侵蚀的约束外,风力吹蚀对微地貌的改造非常明显,这是该地区丹霞地貌形成的主导外动力因素和特色所在;该地区波浪式丹霞地貌的发育阶段可分为两期。

A Preliminary Study on the Genetic Mechanism of Wavy Danxia Landform in Longzhou, Jingbian, Shaanxi Province

Recently,based on the detailed investigation of Danxia landform in Longzhou,the authors found that the type of Danxia Landform in this area is the transitional type of positive-negative landform—wavy Danxia landform.In order to evaluate its value and significance scientifically,the authors mainly discussed the genetic mechanism of the wavy Danxia landform in Longzhou in the aspects of rock characteristics,geological structure characteristics and external dynamic factors.Some phenomena have been found:First,parallel bedding and large-scale wind-staggered bedding of sandstone of Luohe Formation in the study area have a good shaping effect on the formation of wavy Danxia landscape;The purple-red sandstone of Luohe Formation is a set of aeolian desert facies deposits,rocks with poor cementation,low hardness and fragility,which constitutes the material basis for the formation of wavy Danxia landform;Since the late Cretaceous,the Ordos Basin has been tilted and the crust in the area has been generally uplifted,which shows that the Longzhou area in Jingbian has developed multi-level palaeoplanation planes and river terraces,which play a basic role in controlling the formation of wavy Danxia landform;There are many sets of joints and fissures in the sandstones of the Luohe Formation in this area,and the sandstones of the Luohe Formation are cut into blocks,which play a key role in controlling the formation and transformation of the wavy Danxia landform;In terms of the external dynamic factors,Jingbian has a semi-arid inland monsoon climate,obviously transformed by the northwest wind,which is the main external dynamic factor for the formation of wavy Danxia landform.In addition,the rainstorm in summer and autumn which has strongly eroded the surface strata,the cold wave and frost in spring and autumn,and the freezing,melting and collapsing of the rocks have also played an important role in the formation of Longzhou wavy Danxia landform.In addition to the constraints of geological structure and water erosion,the transformation of micro landform by wind is very obvious,which is the main external dynamic factor and feature of the formation of Danxia landform in Longzhou,Jingbian.The development stage of wavy Danxia landform in this area can be divided into two stages.