关于夷平面的科学问题——兼论青藏高原夷平面

长期地貌演化研究表明,夷平面的形成有4种基本方式：准平原、山麓剥蚀平原、双层水平面和冻融剥夷平原。它们的形成都需要上千万年至数亿年的构造相对稳定时期。青藏高原上的层状地貌面可以划分为两级夷平面和一级剥蚀面。山顶面形成于渐新世至中新世早期;主夷平面是以双层水平面或山麓剥蚀平原形式发育的,大致形成于20-3.6Ma B.P.期间,完成时的高度低于1000m;剥蚀面形成于3.6-1.7MaB.P.期间。     

夷平面研究综述

夷平面100多年的研究已经取得了一定的进展。文章从定义、识别、分类、形成和测年等方面论述了夷平面的研究情况,完善了夷平面的定义,加强了对影响夷平面形成和保存的自然因素的探讨,提出了未来夷平面研究的方向。     

青藏高原东北缘马衔山夷平面特征指标的提取与分析

夷平面研究在地貌演化和新构造运动,特别是青藏高原隆升过程研究中占有极其重要的地位,准确界定夷平面分布范围是开展夷平面定量--半定量研究的重要基础.截至目前,前人已利用计算机图像处理技术和目视解译等方法开展了相关工作,并取得重要研究进展.然而,以往利用坡度高程指标提取夷平面时存在一定的随意性和主观性.青藏高原内部及其周边地区发育系列夷平面,其中高原东北缘马衔山地区较好的保存了两级夷平面.被夷平的地层为前寒武系马衔山群混合岩,山顶面上发育冰缘地貌,主夷平面波状起伏,上有岛山和晚新生代沉积,局部覆盖有40 m左右红粘土和30 m以上更新世黄土,并在局地残留3 m以上风化壳,是开展夷平面研究的理想地区.为探讨如何确定提取夷平面的最佳坡度高程指标,本文基于夷平面的特殊地貌几何形态,利用均值变点分析法和最小误差法确定了提取夷平面的最佳高程和坡度指标,并据此对马衔山地区的两级夷平面的分布范围进行提取和统计分析.最后结合剖面线,坡向分布图和区域地质资料探讨了夷平面的构造变形特征.研究发现马衔山地区两级夷平面最佳坡度指标均为12°,山顶面和主夷平面高程主要分布在3470~3640 m和2670~2870 m;统计分析表明山顶面面积约为6.4 km²,平均高程为3559 m,主夷平面面积约为15.5 km²,平均高程为2771 m;而夷平面的变形特征主要受控于区域断层.     

Simulating the development of Martian highland landscapes through the interaction of impact cratering, fluvial erosion, and variable hydrologic forcing

On the highlands of Mars early in the history of the planet precipitation-driven fluvial erosion competed with ongoing impact cratering. This disruption, and the multiple enclosed basins produced by impacts, is partially responsible for a long debate concerning the processes and effectiveness of fluvial erosion. The role of fluvial erosion in sculpting the early Martian landscape is explored here using a simulation model that incorporates formation of impact craters, erosion by fluvial and slope processes, deposition in basins, and flow routing through depressions. Under assumed arid hydrologic conditions, enclosed basins created by cratering do not overflow, drainage networks are short, and fluvial bajadas infill crater basins with sediment supplied from erosion of interior crater slopes and, occasionally from adjacent steep slopes. Even under arid conditions adjacent crater basins can become integrated into larger basins through lateral erosion of crater rims or by rim burial by sediment infilling. Fluvial erosion on early Mars was sufficient to infill craters of 10 km or more in diameter with 500–1500 m of sediment. When the amount of runoff relative to evaporation is assumed to be larger, enclosed basins overflow and deeply incised valleys interconnect basins. Examples of such overflow and interconnection on the Martian highlands suggest an active hydrological cycle on early Mars, at least episodically. When fluvial erosion and cratering occur together, the drainage network is often disrupted and fragmented, but it reintegrates quickly from smaller impacts. Even when rates of impact are high, a subtle fluvial signature is retained on the landscape as broad, smooth intercrater plains that feature craters with variable amounts of infilling and rim erosion, including nearly buried “ghost” craters. The widespread occurrence of such intercrater plains on Mars suggests a strong fluvial imprint on the landscape despite the absence of deep, integrated valley networks. Indisputable deltas and alluvial fans are rare in the crater basins on Mars, in part because of subsequent destruction of surficial fluvial features by impact gardening and eolian processes. Simulations, however, suggest that temporally-varying lake levels and a high percentage of suspended to bedload supplied to the basins could also result in poor definition of fan–delta complexes.     

A peak-cluster assessment method for the identification of upland planation surfaces

Residual upland planation surfaces serve as strong evidence of peneplains during long intervals of base-level stability in the peneplanation process. Multi-stage planation surfaces could aid the calculation of uplift rates and the reconstruction of upland plateau evolution. However, most planation surfaces have been damaged by crustal uplift, tectonic deformation, and surface erosion, thus increasing the difficulty in automatically identifying residual planation surfaces. This study proposes a peak-cluster assessment method for the automatic identification of potential upland planation surfaces. It consists of two steps: peak extraction and peak-cluster characterization. Three critical parameters, namely, landform planation index (LPI), peak elevation standard deviation, and peak density, are employed to assess peak clusters. The proposed method is applied and validated in five case areas in the Tibetan Plateau using a Shuttle Radar Topography Mission digital elevation model (SRTM DEM) with 3 arc-second resolution. Results show that the proposed method can effectively extract potential planation surfaces, which are found to be stable with different resolutions of DEM data. A significant planation characteristic can be obtained in the relatively flat areas of the Gangdise–Nyainqentanglha Mountains and Qaidam Basin. Several vestiges of potential former planation areas are also extracted in the hilly-gully areas of the western part of the Himalaya Mountains, the northern part of the Tangula–Hengduan Mountains, and the northeastern part of the Kunlun–Qinling Mountains despite the absence of significant topographical features characterized by low slope angles or low terrain reliefs. Vestiges of planation surfaces are also identified in these hilly-gully upland areas. Hence, the proposed method can be effectively used to extract potential upland planation surfaces not only in flat areas but also in hilly-gully areas.     

夷平面的三维显示与定量分析方法初探

夷平面是当代地貌学研究的一个重要课题之一,对于重建一个地区的地貌演化的历史具有重要的意义,中利用遥感与地理信息系统建立了位兰州以南、青藏高原东北部边缘的美武高 程工与陆地卫星影像结合起来集成分析,论述了美武高原三维地貌影像图的信息特点,提取了若干区段的地形剖面,进而在分析了高原夷平面地貌参数体系的基础上运用遥感图像监督分类技术自动提出高原夷平面的具体分布区域,揭示了此项对于夷平面分析的巨大潜力。     

夷平面研究评述

全球构造与地球大尺度地形特征之间的关系研究重新成为一个地学研究热点。在国内,夷平面研究的“回春”是其一个主要的表现形式。但在研究中,一些基本的理论与问题有待明确、探讨和解决。在夷平面理论的研究中,地貌演化的历史研究和演化的机制研究仍是最基本的问题。“夷平面”定义的混乱严重阻碍了相关研究的发展。不同气候和构造环境下,夷平面的形成和演化过程仍需科学地概括和抽象。在研究实践中,时间和空间尺度的精确解释成为关键的问题。一方面,不同类型夷平面的地貌特征(海拔高度、地面坡度、相对高度和面积)仍待明确或半定量、定量表示;而另一方面,夷平面的定年仍是一个棘手的问题。在夷平面的确认过程中,一些地貌学原则和规律应当遵循,如齐一山顶面地貌学成因的不确定性;以及同一地貌单元内,准平原型夷平面的出露具有唯一性等。夷平面的相关堆积是夷平面定年和古地貌重建的基础,但是我们必须明确相关堆积与夷平面的关系,如夷平面的原地相关堆积——风化壳的年龄只能够对夷平面的形成时代给予约束,而不能指示其确切的形成时间。更为困难的是,在古地貌的重建过程中,起始时刻某一区域的地貌特征参数仍然无法精确的确定。     

湘桂黔滇藏一线覆盖型岩溶地貌特征与岩溶(双层)夷平面

根据岩溶风化壳的发育条件及研究覆盖型岩溶特征,提出岩溶（双层）夷平面概念,认为研究区覆盖型岩溶是一个统一的岩溶（双层）夷平面的组成部分。其现阶段的存在形式如石林、岩墙等为后期不同程序风化－刻蚀作用的结果;其地貌形态多为土下成因,并随剥蚀程度、裸露时间环境的差异而叠加各种后期气下改造特征。     

中国南方岩溶区土地石漠化的成因与过程

中国南方岩溶区是石漠化广为发展的脆弱生态区域。南方岩溶区土地石漠化的起因既有自然因素,也有人为因素。在地质历史时期其自身环境孕育和存在着自然石漠化过程,在历史时期—现代自然石漠化过程又叠加了人为石漠化过程,人为活动加速、加剧了石漠化的发展。清朝初、中期是人为活动影响石漠化的重要转折时期,此后人为因素作用比重逐渐超过自然因素的作用比重。岩溶区土地石漠化过程是由植被退化丧失过程、土壤侵蚀过程、地表水流失过程、基岩溶蚀侵蚀过程、土地生物生产力退化过程合成的地表生态过程,其实质是形成石质荒漠的土地退化过程。     

Planation of the relief of terrestrial surface

Some problems related to the evolution of relief with the formation of planed surfaces are considered. Target-oriented classifications of planed surfaces are suggested. The paper raises the question concerning tectonic planation of relief, and the relationship of the processes of planation and formation of weathering crusts. The distinctive features of equiplanation in the Earth's northern and southern hemispheres, and the importance of aeolian processes in them are discussed. Attention is drawn to the studies of the planation processes of the relief in the regions under the ice and of the bottom of the World Ocean. The article underlies the need for perfection of the conceptual-terminological body of the theory of planation surfaces.     

King of the plains: Lester King's contributions to geomorphology

Lester King was one of the most influential geomorphologists of the twentieth century. He based his interpretations of landforms and landscapes firmly in the concept of parallel scarp retreat, for although he acknowledged the possibility of slope decline in certain lithological and vegetational environments, he used the mechanism little, if at all, in understanding landscape. Rather, pediments and inselbergs, for instance, as well as entire landscapes, were construed in terms of scarp recession.King appreciated and emphasised the evidence provided by plains for the interpretation of landscape. He considered pediplanation (scarp retreat and pedimentation) to be active in all regions where running water is responsible for shaping the land surface. King's studies in denudation chronology are consistent with his commitment to scarp retreat, implicit in which is the possibility of the survival of very old surfaces; though whether old enough to match the realities of landscape is doubtful.King challenged the Davisian scheme of landscape evolution and offered an alternative model that has proved viable in many parts of the world. Whether pedimentation and scarp retreat are necessarily related is however questionable. King devised original explanations for several well known landforms, and though many of his ideas and interpretations have fallen by the wayside he stimulated many of his contemporaries critically to review their assumptions and explanations.     

云南东川地区层状地貌面的成因

在东川地区的山地及小江河谷的两侧山麓上部，分布着不同高度和不同规模的层状地貌面，对其成因仍有不同的认识。分歧主要表现在两个方面：一是高原隆升之前的初始地貌面是否是准平原型夷平面；二是山顶面之下的梯级层状地貌面的成因。本文从以下几个方面对上述问题进行讨论：(1)层状地貌面的地貌特征及其与侵蚀河谷体系的关系；(2)层状地貌面上堆积物的性质；(3)层状地貌面与断裂构造水平展布的关系；(4)相邻层状地貌面的空间过渡关系；(5)区域构造演化背景。作者认为在云贵高原抬升过程中，东川地区以挤压穹起隆升变形为主。不同海拔高度的层状地貌面具有多成因特性。山顶面及局部高原面是高原隆升之前古夷平面的残留。并遭到后期强烈的侵蚀改造。目前，尚缺乏足够证据证明高原隆升之前的古夷平面为准平原型夷平面。小江河谷两侧的梯级层状地貌面是侵蚀或剥蚀面，它们形成于高原隆升及初始地貌面解体之后，其梯级空间分布特征与区域性的阶段隆升有关。     

祁连山北麓地貌信息熵与山体演化阶段分析

利用定量化的手段分析地貌演化的阶段和趋势,是地貌学研究领域的一个重大的理论课题。在地理信息系统软件ArcGIS和ArcView的支持下,利用数字高程模型提取祁连山北麓的河网和流域。利用Strahler积分计算了各个流域的地貌信息熵,按照主夷平面的高度将祁连山北麓的各个流域分为不同的部分,它们具有不同的地貌信息熵值。结果显示,祁连山地区正在进入戴维斯侵蚀旋回的幼年期阶段。     

The development of talus slopes around Lord Howe island and implications for the history of island planation

Lord Howe Island is a small eroded remnant of a Late Miocene shield volcano. A fringing coral reef dissipates wave energy along a portion of the shoreline, but the remainder of the coast is rugged with spectacular high basaltic sea cliffs. This paper investigates the evolution of talus slopes that occur beneath the loftiest cliffs, and places this analysis within the context of a longer history of island planation that has resulted in a wide truncated shelf around the island. During the Last Glacial, when the sea level was lower than at present, talus slopes accumulated around the extent of the island's cliffed coast because material eroded from cliffs by subaerial processes could not be removed by marine processes. The survival of these slopes during the Holocene has depended on a balance achieved between rates of subaerial and marine erosion. This balance is fundamentally influenced by cliff height, as cliffs higher than 200 m are plunging or veneered by talus slopes, whereas lower cliffs have erosional shore platforms. On comparison with published erosion rates from inland basalt scarps it appears that marine processes may account for over 90 per cent of the total cliff retreat that has occurred at Lord Howe Island, yet contemporary coastal morphology attests to the significance of subaerial processes in recent times. It is likely that marine cliffing was very rapid soon after volcanism ceased, but rates of erosion decreased through time as wave energy became increasingly attenuated across a widening planation surface, and as increasing cliff heights yielded greater quantities of talus that provided protection from rapid marine erosion.     

LiDAR-derived DEM evaluation of deep-seated landslides in a steep and rocky region of Japan

In steep and rocky terrains, their rough surfaces make it difficult to create landslide inventories even with detailed maps/images produced from airborne LiDAR data. To provide objective clues in locating deep-seated landslides, the surface textures of a 5 km² steepland area in Japan was investigated using the eigenvalue ratio and slope filters calculated from a very high resolution LiDAR-derived DEM. The range of filter values was determined for each of a number of surface features mapped in the field and these included: cracked bedrock outcrops, coarse colluvial deposits, gently undulating surfaces, and smooth surfaces. Recently active slides commonly contained patches of ground in which deposition and erosion occurred together near the erosion front, or where cracked bedrock outcrops and coarse colluvial deposits coexisted under a gently undulating surface. The characteristic eigenvalue and slope filter values representing this sliding process were applied to maps of the DEM derived filter values to extract potential sites of recent landslide activity. In addition, the relationships between the filter values of deep-seated landslides at various stages of evolution within the field mapped area were extended to the entire study area, to assess the contribution that landslide evolution makes to change in the landscape as a whole. While landslide components made up the steepest as well as the gentlest parts of the landscape depending on their evolutionary stage, landslides were constantly coarsened and steepened by progressive erosion, probably initiated by river bank erosion at the foot of slopes.     

渭河三阳川盆地最高级阶地的年代厘定及其对河谷发育的指示意义

青藏高原东缘水系的演化历史长期存在着重大争议,鉴于任一水系的形成演化都是通过主要河谷的发育及其不断延展与整合完成的,因此确定河谷发育的起始时代是研究水系演化的关键。本文针对渭河上游三阳川盆地最高级阶地形成时代的研究,发现李家小湾河流阶地砾石层的ESR年代为1.26±0.15 Ma和1.32±0.19 Ma,26Al/10Be埋藏年代为1.45±0.70 Ma和1.04±0.43 Ma,说明该段河谷形成于早更新世晚期。综合青藏高原东缘夷平面、剥蚀面与河流阶地的研究成果,推断该区现代河谷系列主要形成于1.2 Ma以后,河流平均下切速率较高,为0.1~0.32 m/ka,指示了中更新世以来该区快速的地表抬升与河谷发育过程;而其前少数地段的先成河谷下切速率介于0.04~0.29 m/ka之间,说明区域地势总体低平,地表过程以剥蚀夷平为主,即高原东缘的现今水系格局主要是第四纪期间构造和气候共同作用下河流侵蚀的产物。     

Cosmogenic nuclide measurements in southernmost South America and implications for landscape change

We measured in situ ¹⁰Be, ²⁶Al and³⁶Cl on glacial deposits as old as 1.1 Myr in the southernmost part of Patagonia and on northern Tierra del Fuego to understand boulder and moraine and, by inference, landscape changes. Nuclide concentrations indicate that surface boulders have been exposed for far less time than the ages of moraines they sit upon. The moraine ages are themselves constrained by previously obtained ⁴⁰Ar/³⁹Ar ages on interbedded lava flows or U-series and amino acid measurements on related (non-glacial) marine deposits. We suggest that a combination of boulder erosion and their exhumation from the moraine matrix could cause the erratics to have a large age variance and often short exposure histories, despite the fact that some moraine landforms are demonstrably 1 Myr old. We hypothesize that fast or episodic rates of landscape change occurred during glacial times or near the sea during interglacials. Comparison with boulder erosion rates and exhumation histories derived for the middle latitudes of semi-arid Patagonia imply different geomorphic processes operating in southernmost South America. We infer a faster rate of landscape degradation towards the higher latitudes where conditions have been colder and wetter.     

Short and long term effects of bioturbation on soil erosion, water resources and soil development in an arid environment

The importance of vegetal cover on soil erosion processes has been recognized for a long time. However, the short and long term effects of faunal activity on soil erosion and soil development had been largely overlooked by geomorphologists. The study of runoff and erosion processes in the Negev desert indicated pronounced systematic differences in sediment concentration and soil erosion rates between rocky and colluvial surfaces. Erosion rates were always higher on the former than on the latter. Field observations drew attention to an intense burrowing and digging activity conducted mainly by Isopods and Porcupines. The monitoring of this activity, based on a grid system, which consists of rows 5 m wide, lasted ten consecutive years. Data obtained suggest the existence of a strong link between the spatial pattern of bioturbation and that of soil erosion. The study also examines, through feedback processes, the regulatory role of bioturbation on the spatial distribution of water availability; soil moisture and soil forming processes. Due to bioturbation two distinct environments were recognised. The rocky environment which is characterized by a positive feedback with a high water availability and low soil salinity; and the soil covered areas where a negative feedback results in low water availability and a high soil salinity.     

Planation, bauxites and epeirogeny: One or two paleosurfaces on the West African margin?

Mapping of lateritic bauxites over the West African rifted margin and analysis of the geomorphic properties of these bauxites, combined with available geological data lead to a discussion of the presence of either two Meso-Cenozoic planation surfaces or a single Eocene surface to account for the morphotectonic and paleoclimatic evolution of the Guinean landforms. At large scale, two stepped bauxitic levels are documented. Ongoing or episodic uplift following Gondwana breakup and Meso-Cenozoic climate change are proposed to have allowed the formation and abandonment of an Early mid-Cretaceous surface today preserved as the higher bauxitic level, and the setting of an Eocene planation surface bearing a second generation of bauxites, making the lower bauxitic level. The single Eocene surface hypothesis requires that Paleogene bauxitization preserved large pre-existing relief to explain two stepped bauxitic levels of the same age. The two-surface hypothesis is favored because it would explain rebauxitization of alluvial pebbles of bauxites under the lower lateritic level.     

Relations between denudation,glaciation, and sediment deposition: implications from the Plio‐Pleistocene Central Alps

Despite abundant data on the early evolution of the Central Alps, the latest stage exhumation history, potentially related to relief formation, is still poorly constrained. We aim for a better understanding of the relation between glaciation, erosion and sediment deposition. Addressing both topics, we analysed late Pliocene to recent deposits from the Upper Rhine Graben and two modern river sands by apatite fission‐track and (U‐Th‐Sm)/He thermochronology. From the observed age patterns we extracted the sediment provenance and paleo‐erosion history of the Alpine‐derived detritus. Due to their pollen and fossil record, the Rhine Graben deposits also provide information on climatic evolution, so that the erosion history can be related to glacial evolution during the Plio‐Pleistocene. Our data show that Rhine Graben deposits were derived from Variscan basement, Hegau volcanics, Swiss Molasse Basin, and the Central Alps. The relations between glaciation, Alpine erosion, and thermochronological age signals in sedimentary rocks are more complex than assumed. The first Alpine glaciation during the early Pleistocene did not disturb the long‐term exhumational equilibrium of the Alps. Recent findings indicate that main Alpine glaciation occurred at ca. 1 Ma. If true, then main Alpine glaciation was coeval with an apparent decrease of hinterland erosion rates, contrary to the expected trend. We suggest that glaciers effectively sealed the landscape, thus reducing the surface exposed to erosion and shifting the area of main erosion north toward the Molasse basin, causing sediment recycling. At around 0.4 Ma, erosion rates increased again, which seems to be a delayed response to main glaciation. The present‐day erosion regime seems to be dominated by mass‐wasting processes. Generally, glacial erosion rates did not exceed the pre‐glacial long‐term erosion rates of the Central Alps.