Rock mechanical characteristics and landscape evolutionary mechanism of the slit-type Danxia landform on the Chinese Loess Plateau

Since 2015,the newly discovered slit-type Danxia landform on the Chinese Loess Plateau has become a hot topic in the field of geomorphology worldwide.However,the relationships among its formation,evolutionary mechanism,and mechanical characteristics of its strata and rocks are not clear.In this paper,the Ganquan canyon group is used as the research object.Basic physical and mechanical indices of sandstone in the Ganquan canyon group were measured through field investigation and indoor experiments,and the deterioration trends for the mechanical parameters of sandstone in this area under the action of infiltration,acid dry-wet cycles,and freeze-thaw cycles were revealed.Lastly,the formation and evolutionary mechanism of the slit-type Danxia landform were discussed.The results showed that:(1)The sandstone in the canyon group had a low cementation degree and weak cohesive force,which was easily weakened under the action of water,resulting in a decrease in compressive strength and elastic modulus.(2)Acidic dry-wet cycles caused the mineral composition of the sandstone to be dissolved,and the micropores continued to grow and develop until new cracks were produced.Macroscopically,the compressive strength and elastic modulus of sandstone were greatly reduced,and this damage was cumulative and staged.The greater the acidity,the greater the damage.(3)As the number of freeze-thaw cycles increased,the uniaxial compressive strength and elastic modulus of the sandstone decreased continuously.During the freeze-thaw cycle process,the growth and development of cracks were primarily in fracture mode and usually developed along parallel bedding positions.(4)The interaction of tectonic activity and lithology with different weathering processes was a key factor in the formation and evolution of the slit-type Danxia landform.In conclusion,the intricate process of weathering influenced by historical climatic fluctuations has been pivotal in shaping the topography of Danxia landform.

Age and genesis of the Danxia landform on Jianglang Mountain, Zhejiang Province

Jianglang Mountain is situated at the transitional zone of South China fold-system, Jiangshan-Shaoxing deep fracture zone and Baoan-Xiakou-Zhangcun fracture zone. The forming of the Xiakou basin was attributed to the pull-apart fault depression by the above fractures in earlier Cretaceous, afterward, series deposits such as Guantou formation （K1g）, Chaochuan formation （K1c） and Fangyan formation （K1f） which belong to Yongkang group, the lower Cretaceous layer accumulated in the Xiakou basin. In late Cretaceous, the above fractures occurred to extrude and the basin began to uplift, meanwhile, amounts of tension fissures and joints were produced since Cenozoic, which accelerated water-dicing into bed-rock. Consequently, landform-building processing： weathering, eroding and collapsing etc. were prevalent as finally to develop the so-called Danxia landform. The Jianglang Mountain landscape zone of the Danxia landform to apply for world natural relics are relying on unique and unparalleled peak, sky-split valley with vivid stones and reviving of platform. What is more, there is significance of study at lithology, stratigraphy and paleo-biology. According to dating for specimen of ophitic vein through-crossing the Yongkang group of Yafeng Peak by K-Ar method, this article revealed the uplift age of red-bed basin to be 77.89±2.6 MaBP （K2） i.e. late Cretaceous, and it is the first chronological datum of Danxia landform research in China.

Upper Cretaceous alluvial fan deposits in the Jianglangshan Geopark of Southeast China:implications for bedrock control on Danxia landform evolution

The Jianglangshan Geopark in the western Zhejiang Province of Southeast China is well-known for its spectacular red-colored sandstone landforms. Little is known about the depositional processes of the conglomerate-dominated Fangyan Formation, the lithologic base of the Danxia landforms in this geopark. Based on detailed field investigation of lithology, sedimentary structures, bed thickness and geometry, five facies are recognized: facies A(matrixsupported cobble conglomerate), facies B(pebble conglomerate), facies C(pebbly sandstone), facies D(fine-grained sandstone) and facies E(mudstone). The results show that streamflow-dominated fans were the main depositional processes responsible for the accumulation of the Fangyan Formation along the mountain fronts. These fan conglomerates form the base for the evolution of the Danxia landscapes owing to the uplift and erosion of the study area. In contrast, the fine-grained sedimentary successions produced by fluvial floodplains in the distal part of the fans were thinner and more easily weathered. Such sedimentary facies distribution patterns were thought to be similar during Late Cretaceous across Southeast China. The Danxia landforms are largely the geographical expressions of the conglomerate-dominated redbeds in the proximal-middle fans.

Types and spatial combinations of Danxia landform of Fangyan in Zhejiang Province

The prominent types of Danxia landform in Fangyan include enclosed valleys, mesas, peaks, stone columns and grooves etc. Their spatial combinations have regular configurations along the northwest–southeast direction: typical grooves and caves are located in the northwestern Wufengshuyuan mainly; abundant fresh collapsed stones may be observed in central Jimingfeng and Taohuafeng; stone drums and stone columns are in the southeastern Shiguliao particularly; enclosed valleys are encircling joints of peaks and plains from three directions east, west, and south. Their spatial combinations reflect that the developments of Danxia landform have undergone stages of geomorphic cyclical erosion in the form of weathering, collapse, transportation, sedimentation and other processes, together with the "sculpture" of external forces mainly as tectonic uplift. The picturesque Danxia landform began its formation at that point. Danxia landform developed mainly in the strata of Fangyan Formation (K1f) caused by the alluvial fan-braided river phase of anterior fan in the late period of the Early Cretaceous. Regular patterns of weathering of stones and features of braided alluvial phase sediments may be verified by the analysis of three groups of experimental data. Danxia landform of Fangyan is a unique representative of the "adolescent" development type in the application of the World Natural Heritages status in China, by virtue of its outstanding universal aesthetic and scientific value.

Danxia landform genesis of the Qiyun Mountain, Anhui Province

The Danxia landform of Qiyun Mountain is mainly developed on the red granule conglomerates named Xiaoyan Group （K2x^1） of middle Cretaceous series, which is controlled mainly by three faulted zones, namely, Jingdezhen-Qimen faulted zone, Jiangwan-Jiekou compressional faulted zone and Kaihua-Chun＇an folding faulted zone. During the Cretaceous period, this area firstly experienced massif subsidence to become a continental faulted basin, then having thick Cretaceous red sediments accumulated on it. In the supervened neotectonism, this area experienced an uplifting process, which made the thick Cretaceous sediments into a mountain with an altitude of 500-600 m. After undergoing the processes of vertical joint development, weathering, denudation and transportation, as well as evidently differential weathering and denudation influenced by lithology and structure between sandstone and conglomerate, the grand Danxia landscape consisting of peak forests, steep cliffs, caves, mesas, castellated peaks, natural bridges and so on formed. The three nick points located respectively at 585 m, 400 m and 150 m generally reflect the three dominated uplifting processes during the neotectonism.

Comparative studies of Danxia landforms in China

Danxia geomorphology originates fi＇om China. This paper studies the spatial distribution and differences in characteristics of Danxia landforms. Based on relevant research and investigations, three congregated areas of Danxia landform in China are discussed in this paper. They are the southeast area （including Jiangxi, Fujian, Zhejiang, Hunan and Guangxi provinces）, the southwest area （the transitional zone of Yunnan-Guizhou Plateau and Sichuan Basin） and the northwest area （including Longshan mountain and along the banks of the Huanghe River and its anabranches）. Not only the conditions of geology and geography of the three areas but also the differences of Danxia landforms of the three areas are analyzed. The Danxia landscape, characterized by upright-shaped peaks, Danxia mesa, stone wall, cave and vertical cave, ＂Danxia natural bridge＂, ＂a narrow strip of sky＂ and so on, often presents in the southeast area. The landscape of southwest area is characterized by Danxia escarpment faces and waterfalls. In the northwest area, the Danxia landscape has the traits of arid areas simultaneously, for example, mud-coating type, columniation type, board type, moreover, it is greatly different between these environmental factors such as the microclimate, water, wind, and the loess cover. Finally it explores the causes which lead differences in landform and also explains the landform formation process and its mechanism with reference to the rates of crustal uplift, the tectonic red-basin, and the external processes including working of running water, weathering, biogenic, gravity in each area of Danxia Landforms in China.

Species Diversity of Rock Plant Community in Danxia Landform of Zhejiang Province

In order to provide scientific basis for vegetation and biodiversity conservation,species diversity of rock plant in Danxia landform of Zhejiang Province was analyzed in this study.According to the results,there were 195 species belonging to 143 genera and 82 families.The changing trend in Margalef index,Simpson index and Shannon-Wiener index of the same community in different layers was the same,namely herb layer>shrub layer>moss layer>liana layer;the order of Pielou index was moss layer>liana layer>herb layer>shrub layer.Comparing species diversity in different regions,we found that the index of all layers on Jianglang Mountain was higher except the moss layer.

Research on the Genesis and Development of Danxia Landform in the South Sichuan

The South Sichuan is one of the areas in China famous for Danxia Landform. Danxia Landform in the South Sichuan is characterized by wide distribution and square shaped hills. However, there is no systematic research on the genesis of those Danxia Landforms at present. Based on the study of spatial distribution and the genesis of the Danxia Landforms in the South Sichuan, we discovered that the lithostratigraphy, regional tectonic, crustal uplift and external forces contribute together to the formation of the Danxia Landform. On the basis of learning the development experiences from famous scenic spots and the updated national policies and regulations, proposals were made to boost the development of Danxia Landform resources in the South Sichuan by excavating its historic, cultural, natural and scientific connotation in the form of educational tourism.

Danxia Landforms: Rosy Clouds on Earth

A Danxia landform is a red-bed landform characterized by steep cliffs. It was initially discovered and named by Chinese scholars. Although there are red-bed landforms in many parts of the world, China, with a special fondness for the color red, boasts the most widely distributed Danxia possessing unique characteristics. This is a mesmerizing natural formation and a special gift that nature has bestowed upon this country.

江西丹霞地貌演化阶段与分布及其构造控制探讨

晚白垩世至古近纪期间,江西省内沿区域性断裂构造发育30余个断陷盆地,沉积了巨厚的红色陆相碎屑岩,为丹霞地貌的形成提供了物质基础。已发现的228处丹霞地貌点主要分布于江西东部武夷山北麓和西麓的红层盆地内。利用面积—高程积分法,对江西省9个盆地的丹霞地貌演化阶段进行了定量分析,结果表明省内丹霞地貌景区的面积—高程HI为0.17~0.52,平均为0.38,即其演化阶段处于壮年晚期至老年早期,在空间分布上具有由南向北,由壮年期转为老年期的趋势。该趋势可能与武夷山的构造隆升有关。构造分析显示,节理与武夷山的隆升对江西丹霞地貌演化起控制作用,具体表现为:(1)龙虎山、九仙湖、仙岩、蛤蟆坞、赭亭山、龟峰等地发育的崖壁、一线天、巷谷、石墙、石寨、峰丛、峰林等丹霞典型景观均与节理有关。(2)流水侵蚀等外营力的作用对丹霞地貌的剥露、削平起重要作用,统计表明距离武夷山越近,丹霞地貌山峰越密集、崖壁越陡峻,指示武夷山的隆升与丹霞地貌的发育有直接关系。总体来看,江西省内的红层为丹霞地貌的发育提供了物质基础,武夷山的隆升控制了丹霞地貌的分布。值得注意的是,丹霞地貌区的节理构造是否与武夷山的隆升存在直接因果关系还需进一步研究。

广东韶关丹霞山生态系统多样性及其空间定位

丹霞山复杂地形地貌塑造了很高的生态系统多样性和复杂的景观多样性,全面的系统分类、空间定位和生态系统类型描述对该区域的生态特征研究具有重要意义。本研究基于IUCN全球生态系统分类框架,结合植被类型和特殊地形地貌特征,对韶关丹霞山国家级自然保护区全境的生态系统类型进行研究,并利用遥感数据与实地调查数据,对各级生态系统进行空间定位和可视化制图。结果显示:(1)该保护区生态系统类型可划分为81类,包括3个I级类型、6个Ⅱ级类型、12个Ⅲ级类型、28个Ⅳ级类型和81个Ⅴ级类型;(2)除空间定位与格局分析外,特别对丹霞山的4个大类的特色生态系统进行了单独的空间展示,包括用面来展示的山顶生态系统23类和沟谷生态系统13类,用点来代表的洞穴生态系统4类,用线来代表崖壁生态系统4类。本研究关于生态系统类型的划分及空间定位,揭示了丹霞山地区的独特地形地貌特征和生态系统多样性特征,深化了丹霞山生态系统多样性和形成机制的理解,结果可为开展生态系统保护和管理提供重要的参考。

韶关丹霞地貌铁皮石斛野生资源调查与生境分析

目的:调查广东韶关丹霞地貌现存铁皮石斛野生资源的生存现状,为野生铁皮石斛就地保护、回归保育及仿野生栽培提供参考。方法:对国内铁皮石斛野生资源情况进行整理,基于本课题组近10年来对广东韶关丹霞地貌野生铁皮石斛资源分布和生境开展的跟踪调查,对11个调查地点的海拔、朝向、铁皮石斛数量、坡位、坡向进行分析,探讨丹霞地貌野生铁皮石斛植物形态和生境特点。结果:调查记录了广东韶关丹霞地貌中的野生铁皮石斛300余丛,约3000 g,处于极度濒危状态;实地观察发现,野生铁皮石斛茎多呈紫红色,长5~10 cm,有“形似蚱蜢髀”的茎条,叶铁锈色斑点明显;丹霞地貌的野生铁皮石斛大多生长在海拔100~500 m的丹霞崖壁中部或近坡顶处,常与苔藓和地衣伴生,一般生长在东南至西南朝向、通风良好、傍水潮湿的丹霞岩壁上,且半阳偏阴、温凉高湿环境下长势较好。结论:野外考察证实,《本草经集注》中记载的“今用石斛出始兴”的石斛为铁皮石斛,其药用历史在1500年以上;丹霞地貌的铁皮石斛为目前国内铁皮石斛的主要种源之一;野生丹霞铁皮石斛因自身繁殖率低、人为长期采摘等原因,现已极度濒危,亟须开展铁皮石斛野生资源的调查与保护工作。

延安典型丹霞地貌景观特征及发育演化研究

本文是在延安典型丹霞地貌景观特征分析的基础上,采用宇宙成因核素^(10)Be和^(26)Al技术获得暴露年龄和侵蚀速率,研究“黄土覆盖型沟谷丹霞”地貌景观的演化历史。研究结果显示:延安典型丹霞地貌的类型有狭缝式、石蘑菇式、天生桥式,其中狭缝式丹霞的景观特征为“窄狭、多弯、韵律、多彩”,同时也是典型的“黄土覆盖型沟谷丹霞”,石蘑菇式丹霞造型奇特,天生桥式丹霞地貌整体规模宏大,这两者发育都严格受控于垂直节理和外力作用的侵蚀;运用宇宙成因核素^(10)Be和^(26)Al技术,计算获得志丹猫巷狭缝式丹霞地貌的暴露年代有两期,分别为(0.75±18)~(0.83±0.14)ka和(1.14±13)~(1.29±0.30)ka,安塞王家湾石蘑菇式丹霞地貌暴露年代为(1.76±0.45)~(1.77±0.15)ka,这两处丹霞地貌暴露地表的年代都在全新世(Qh),前者晚于后者,地貌较年青;运用宇宙成因核素^(10)Be-^(26)Al计算获得两处典型丹霞地貌侵蚀速率为(39±3.3)~(104±24.4)cm·ka~(-1),与目前国内外学者研究地表和基岩得到的侵蚀速率对比,这两处典型丹霞地貌的侵蚀速率较大,结果还有待进一步研究;延安典型丹霞地貌景观发育的演化始于白垩纪红层的堆积,大致都经历了四个演化阶段,初步揭示了地质构造、上覆黄土盖层以及流水等多种因素共同控制和影响延安典型丹霞地貌的形成,演化阶段总体都处于青年晚期。

贵州省丹霞地貌区工程边坡变形机制模拟分析

贵州省仁赤高速在修建时,对沿线丹霞工程边坡采取主动防护网的支护措施。经过几年的风化剥蚀,此段工程边坡岩体出现了卸荷松动、剥落掉块的现象,影响公路安全运营。为掌握丹霞工程边坡的变形机制,以旺隆匝道边坡为例,采用野外地质调查和底摩擦试验的方法开展贵州省丹霞地貌区工程边坡变形模拟分析。研究结果表明,贵州省丹霞地貌区的边坡岩层属于典型的泥岩和砂岩相间组合的红层边坡,由于泥岩和砂岩的岩性不同,造成了泥岩多发育成凹岩腔,而砂岩则会形成危岩体。新开挖的边坡坡面在卸荷裂隙、风化的单独作用或共同作用下发生浅层破坏。

安徽齐云山丹霞地貌成因

齐云山丹霞地貌主要发育于中白垩统小岩组K2x1红色砂砾岩层中,该区地貌发育主要受景德镇-祁门断裂带、江湾-街口挤压破裂带和开化-淳安褶断带三大断裂带控制。在白垩世该区经历了地块沉降,成为陆上的断陷湖盆,由此接受了巨厚的白垩系红层堆积。在新构造运动中,该区经历了隆升过程,巨厚的白垩系沉积物变成了海拔500￣600m的山体。白垩系红色砂砾岩在经历了垂直节理发育、风化破坏阶段及剥蚀搬运阶段后,同时受岩性本身砂岩与砾岩在组分和结构上的影响,差异性风化剥蚀显著,因此形成了壮观的峰林、崖、洞、方山、城堡及天生桥景观。该区585m、400m和150m处的三级裂点,大致反映了该区新构造运动中三次主要的抬升过程。

中国丹霞地貌空间格局

通过分析中国丹霞地貌的空间分布格局,把我国丹霞地貌划分东南、西南和西北三大集中分布区。主要研究了三大丹霞地貌集中分布区的景观异质性。东南区(包括浙、闽、赣、粤、湘、桂等省区)多发育临溪丹霞峰林、丹霞赤壁、一线天、天生桥等景观;西南区(云贵高原与四川盆地过渡带)以赤壁与急流瀑布相伴为主要景观特色;西北区(包括陇山周围、河湟谷地)则呈现出特有的干旱区丹霞地貌景观,区内由于自然条件的复杂性,如小气候及流水作用,黄土盖层成分及其存在与否的差异性,区内景观异质性显著。从三区的构造运动上升速度、降水强度、植被等生物作用、河川过程以及黄土作用等地质地理、气候条件、生物、理化等内外动力作用,分析了形成这种景观差异性的原因、形成机理和过程。

浙江江郎山丹霞地貌发育的年代与成因

江郎山位于华南褶皱系、江山—绍兴深断裂和保安—峡口—张村断裂带之间。白垩纪早期这两大断裂的拉张断陷导致峡口盆地的形成,随之主要有下白垩统永康群馆头组(K1g)、朝川组(K1c)和方岩组(K1f)在盆地中的沉积。白垩纪晚期上述两大断裂发生强烈挤压活动,峡口盆地逐渐隆升。新生代以来,峡口盆地在构造抬升中,产生大量张断裂和节理,加速了对岩体的切割,以及岩体被切割后的崩塌,导致了丹霞地貌的发育。江郎山丹霞地貌申报世界自然遗产的主要依据是其特有的壮观而独特的老年期孤峰—巷谷以及生动而逼真的象形石丹霞地貌特征、独特的地台活化现象与重要的岩石学科学研究意义以及该区特有的重要事件地层学和古生物学研究的科学意义。本文根据对江郎山亚峰垂直贯穿于丹霞地貌岩层永康群中辉绿岩脉标本K-Ar法的测年,揭示了当地峡口红层盆地抬升的时代为晚白垩世77.89±2.6MaBP(K2),这也是我国目前丹霞地貌研究中所测得的可靠年代学数据。

福建冠豸山丹霞地貌成因及旅游景观特色

福建冠豸山自晚侏罗世以来经历了山间盆地形成和侏罗、白垩系巨厚砂砾岩堆积成岩阶段 ,新构造运动中使盆地隆升和节理发育。自第三纪以来主要经历了 4次较大幅度具掀斜性质的抬升过程。从 4级夷平面的相对高差可知 ,第一、二次抬升之间幅度差为 34～ 78.8m,第二、三次抬升之间的幅度差为 81～ 1 0 0 m,第三、四次为 38～ 46m。在抬升过程中 ,受内力挤压和四周围岩压力逐渐消失造成的卸荷作用影响 ,岩层出现众多深大裂隙和多组垂直节理 ,发育有石墙、石堡 (寨 )、陡崖壁、柱峰、石梁、隙谷、嶂谷、峰林、峡谷、巷谷、天生桥等的丹霞地貌 。

浙江方岩丹霞地貌发育的年代、成因与特色研究

方岩丹霞地貌在大地构造上隶属于华南褶皱系构造单元,该单元在燕山运动时期,由于太平洋板块俯冲入欧亚板块之下,促使大陆边缘地壳重新活动。晚侏罗世末至早白垩世,本区构造应力场由晚侏罗世的北西-南东向挤压,转为早白垩世的北东-南西向挤压和北西-南东向的拉张,发育了永康早白垩世断坳盆地,在盆地中沉积了下白垩统永康群馆头组(K1g)、朝川组(K1c)和方岩组(K1f)地层。中生代晚期永康盆地逐渐隆升,结束了红层沉积,遭受侵蚀,方岩地区丹霞地貌密集围谷、密集方山和廊穴等青年期的地貌特点表明该区大规模的抬升发生在较近的地质年代。

江西信江盆地白垩系沉积体系及其与丹霞地貌的关系

根据野外沉积层序、岩石学特征、古生物资料和地貌景观特征,本文对江西信江盆地白垩系沉积相进行了初步分析,首次探讨了沉积体系与丹霞地貌发育特征之间的内在联系。信江盆地白垩系主要发育4种沉积体系,即冲(洪)积、三角洲、湖泊和扇三角洲。早白垩世主要发育半深湖—深湖、扇三角洲相沉积,晚白垩世从盆地南缘到北缘大致为洪冲积相→辫状河流→三角洲→滨浅湖→三角洲→辫状河流→洪冲积相的展布方式。研究表明,该区丹霞地貌形成的物质基础主要是上白垩统冲积扇、辫状河相沉积产物,丹霞地貌的空间分布与盆地冲积扇、辫状河沉积相的平面展布具有较好的一致性,同时,沉积亚相、微相类型对丹霞地貌的发育起到一定的控制作用。