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Journal of Cultural Heritage 12 (2011) 88–97

ase study

S-based geomorphic analysis of Zhangjiajie Sandstoneeak Forest Geopark, China

uifang Yanga,∗, Zhen Yanga, Xujiao Zhanga, Mingzhong Tiana, Anze Chenb, Zhiliang Gea,amin Pinga, Zhiyun Nia

School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, ChinaChinese Academy of Geological Sciences, Beijing 100037, China

r t i c l e i n f o

rticle history:eceived 4 February 2010ccepted 31 July 2010vailable online 23 October 2010

eywords:R remote sensingandstone landformerrain analysiseomorphic formation

a b s t r a c t

This study aims to characterize the regional geomorphic features of Zhangjiajie Sandstone Peak ForestGeopark in northwest Hunan, China. High-resolution French SPOT-5 HRG data (red, green and NIR-10 m,SWIR-20 m and Pan-2.5 m ground resolution), in conjunction with topographic mapping and field surveys,were utilized for systematic analysis of various morphometric landforms and their possible constraints.Four major types of landforms were discriminated in the study area based on visual interpretation of satel-lite sensor data. A high diversity of sandstone landforms is in the west and southeast geopark, involvingmesa, square mountain, peak wall, peak cluster, peak forest, single peak, remnant peak. Surroundingthe sandstones is the widely distributed denudation terrain, occupying 44% of the region. The alluviumlocally scatters in the middle Suoxi River, whilst the karst landscapes preferably emerge in the limestonearea, covering an area of about 82 km2. Our study indicates that the distribution of various landscapes is

primarily controlled by the distinct linear features and river system, which is of significance to increaseunderstanding the landform evolutionary processes. The remote sensing approach described in this papercan quickly and accurately map terrain at coarse approximation and semi-detailed levels. This method,in combination with appropriate conventional methods, can associate diverse landforms with their pos-sible controls, thus allowing further scientific geomorphic evaluation and sustainable management at river basin level.

. Introduction

The idea that geomorphic evolution in different parts of thelobe has been largely attributed to the interactions of factorsf regional tectonics, climatic variations and associated surfacerocesses superseded a vast earlier literature [1–3]. Numerousrevious studies have considerably addressed the topographiceatures to increase understanding the influence of internal andxternal factors on relief production, although the requisiteetailed information to properly model the relief-constructing andhape-making processes is still poorly understood in some previ-usly inaccessible areas. The conventional methods, however, arencapable of accurate estimating landform formation and morpho-ectonic evolution in the region. Difficulties arise when extensive

arge-scale geomorphologic surveys are impossible, as it is oftenhe case in many mountainous hinterlands [4–7]. Detailed descrip-ion and classification of regional geomorphometry also requireshe synthesis of areal, linear or even point information, which

∗ Corresponding author.E-mail address: yangguifang@cugb.edu.cn (G. Yang).

296-2074/$ – see front matter © 2010 Elsevier Masson SAS. All rights reserved.oi:10.1016/j.culher.2010.07.001

© 2010 Elsevier Masson SAS. All rights reserved.

is of great help in understanding the topographic patterns andtheir controls. Since access of some mountainous areas is difficult,remote sensing (RS), from aerial photography to satellite imagery,constitutes a powerful alternative tool to improve accuracy andprecision of large-scale geomorphologic surveys, making it possi-ble to investigate previously inaccessible regions [5,7–9]. It can alsoconsiderably facilitate the analysis of geomorphometric propertiesand their spatial distribution [10–12]. The further developmentstowards improvement of spatial resolution resulted in the SPOT-5(with 10 m ground resolution in a three-band multispectral modeand 2.5 m ground resolution in a panchromatic mode), Quickbird(with 0.6 m ground resolution in a panchromatic mode) and otherRS imageries, allowing detailed understanding the various land-scapes in response to their controls.

Owing to its spectacular sandstone peak forest landform,Zhangjiajie Sandstone Peak Forest Geopark (Zhangjiajie WorldGeopark) has received a growing attention [9,13–16], yet little is

known about the evolution process of such spectacular landscapeand its controls, as compared with the widespread karst landscapeselsewhere in China [17]. Previous work at Zhangjiajie has primarilyfocused on the physical properties and aesthetic features of thesandstone, with particular interest in the small-scale analogs of

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G. Yang et al. / Journal of Cu

andstone megapillars and cliffs [13,18–19]. The detailed knowl-dge, however, to properly model the evolution process of distinctandstone landscape is still poorly understood. The absence ofetailed geological records and inaccessibility of extensive geolog-

cal surveys due principally to the extremely complex terrains haveampered to a large degree the understanding of the developmentattern and morphotectonic genesis of the region. In addition, aather pragmatic approach is recommendable for surveying such

large area, allowing the integration of geomorphic data andomprehensive analysis of topographic process. The RS-based geo-orphic analysis thus serves as a powerful alternative method for

xtensive large-scale geomorphologic surveys, making it possibleo macroscopically investigate previously inaccessible spectacularandforms in this region [20].

The aim of the study, combined with previous work, is attempt-ng to characterize the various types of landforms appeared in thehangjiajie World Geopark by the aid of RS approach. With themproved spatial resolution of SPOT-5 data (red, green and NIR-0 m, SWIR-20 and Pan-2.5 m), the distribution of topography isnalyzed for further exploring the inherent formation mechanismf sandstone peak forest landform as well as other geo-heritagesf the region, enabling more intuitive access to specific perceivedcenic terrain. Our results will facilitate the prompt terrain mappingnd detail study of the geomorphic evolution history and sustain-ble management of the geo-heritages of this region.

. Study area

The Zhangjiajie World Geopark (also referring to Wul-ngyuan) of northwest Hunan (29◦13′18′′–29◦27′27′′N,

10◦18′00′′–110◦41′15′′E), is in the junction of southwest Yunnan-uizhou Plateau and Wuling low mountains of northwest Hunan.s reported by previous documents, it covers a total area ofpproximately 398 km2 (Fig. 1). The plateau monsoon climates typical of the area, with an annual average precipitation of

Fig. 1. Map of Zhangjiajie World Geopark showing the localities discussed in the

Heritage 12 (2011) 88–97 89

1400 mm and an annual mean temperature of 16 ◦C. Elevationranges from ∼ 200–300 m above sea level (a.s.l.) in the valleybottom to 1300 m a.s.l. in the mountain peaks.

Episodic tectonic movements have shaped the basement struc-ture and following geomorphic configuration. Presently, the areais drained by the Suoxi River, second-order tributary of the LishuiRiver, which flows eastward through the region. It has incised thequartz sandstone landform to form various peak forest landscapesat different heights varying from 1000 m to the present-day riverbed (Fig. 1). Bedrock sequence predominantly ranges from Silurianto Holocene, with extensive outcrops of Silurian and Devonianstrata prevailing in the region [9]. Quaternary stratigraphic distri-bution is very limited, usually with locally distributed alluvium.

More than 3000 rock peaks stand aloft within the study area,of which 1000 peaks exceed 200 m in height. The Jinbian Peak,in particular, even has a height exceeding 350 m. The individualmicrotopography is of great diversity, generally including mesa,square mountain, peak wall, peak cluster, peak forest, crosscut,stone door, natural bridge and river valley, etc. [17]. The geopark iscentralized by its unparalleled sandstone peak forest landforms, inline with the karst landscapes and many other geological heritages.These different landforms comprise the remarkable geomorphicassembly of Zhangjiajie World Geopark with particular character-istics.

3. Methodology

To meet the primary objectives of our present study, the ortho-corrected French SPOT-5 images of September 2007 at 1:10000scale (2.5 m panchromatic and red-10, green-10, NIR-10 and SWIR-

20 m multispectral imagery) are mainly employed for the mappingof geomorphological units (Table 1). The nominal revisit inter-val is 26 days. The images cover the area between 110◦22′42′′ to110◦37′09′′ North latitudes and 29◦25′00′′ to 29◦17′36′′ East longi-tudes. RS imageries are preserved with a format of GEOTIFF.

context, inlet is the map of China showing the location of our study area.

90 G. Yang et al. / Journal of Cultural Heritage 12 (2011) 88–97

Table 1Satellite data used in our study.

Satellite Date Mode Spectral resolution (�m) Spatial resolution (m) Digitization (bits)

9985

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tsdsbamdwtfdtso

acvcsfmtt

4

4

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SPOT 5 Sep 2007 Pan 0.49–0.6SPOT 5 Sep 2007 B1 (green) 0.50–0.5SPOT 5 Sep 2007 B2 (red) 0.61–0.6SPOT 5 Sep 2007 B4 (SWIR) 1.58–1.7

The processing of SPOT-5 data follows the generalized pro-edures [21–22]. Geometric and radiometric distortions in theatellite data have been removed and satellite digital data haveeen enhanced and classified to better discriminate between land-cape features. The SPOT-5 multispectral data (red, green andWIR) and the panchromatic data (taken in September 2007) haveeen collected for image fusion by using the Hue, Saturation, and

ntensity (HSI) fusion technique [22], the linear, relief, and arealeatures are enhanced and boundaries of gemological units areepicted. In this study, SPOT-5 Pan is merged as an intensity mod-lator due to its higher spatial resolution. On the contrary, bands 1,and 4 (red, green, and SWIR) were selected based on their spec-

ral superiority in accumulating most of the variance of geologicalnformation. Of note, the processing of geometric and radiometricistortions, as well as the image fusion were conducted by Remoteensing Center of Hunan Province, China.

With the orthocorrected image, we established the RS interpre-ation symbols (as indicated in Table 2) and delineate the Suoxi riverystem and major geomorphic units in the study area based on theivide line and boundary concept. The ancillary and collateral data,uch as contemporary topographic maps (at 1:50000 scale) haveeen used in order to improve the accuracy of visual interpretationnd identification of representative relief types for different geo-orphologic units during the field investigation. A few of subriver

rainage network lines were extended through some water bodiesith the help of collateral data and field investigation to facilitate

he geomorphic and tectonic analysis. The evaluated geomorphiceatures were grouped as linear, relief and areal dimensions. Theigital elevation model (DEM) was generated based on the con-our values of 10 m interval from high resolution SPOT-5 images tohow the height and terrain features. Ground control points werebtained from a 1:50000 topographic map.

Selected localities were studied on different geomorphic unitss complementarities to further verify the reliability of our researchonsidering the heterogeneity of topography, geology settings andegetation conditions. GIS was simultaneously employed to cal-ulate and estimate the area, length, height, slope gradient, andcale to associate the basin tectonic features with different land-orms. Two field surveys have been conducted in 2008 and 2009,

ainly in some preselected random sample sites in order to inves-igate and check the derived results from RS images as a groundruth.

. Remote sensing image processing

.1. Visual interpretation

As noted prior, the information in the SPOT-5 image gives anbjective, reliable picture of the geological and geomorphic unitsn the Earth’s surface, as well as the “perspective information” ofhe loose sediment deeply below the geological bodies [21–22]. TheS interpretation symbols, no matter direct or indirect ones, can

reatly help to distinguish and interpret the image characteristicsf real objects and associated phenomena. The direct interpretationogos are the intuitive reflection of geomorphic or geological prop-rties in the image, usually referring to various natures of imagesn terms of shape, size, tone and color, shadows, texture, image

2.5 810 810 820 8

structure, design patterns, and so on. Indirect interpretations aredeveloped based on linkages of objects with their surrounding unitsby the aid of observation, analysis and reasoning. For instance, mostfractures are supposed to be found adjacent to water body or riversystem, thus allowing an effective detection of fracture within theriver catchment.

Visual interpretation techniques have been followed in thedelineation of geology, landforms, strata boundaries based on thetone, texture, shape, drainage pattern, color and differential ero-sion characteristics of the satellite imagery in combination withdrainage morphometry and collateral data. Subsequently detailedlandform analysis has been implemented based on their genesis,relief and their morphometric features. The linear structures weredepicted and identified according to the traits of satellite imagery,satellite sensor data in conjunction with available drainage mor-phometry, vegetation cover, ground data and the correlation withthe surrounding objectives in the geopark.

Before arriving at a prompt and accurate interpretation, thestudy area was divided into two groups of major landforms, withand without spectacular sandstone relief. Dominant denudationlandforms, karst reliefs and Quaternary alluvium were visuallyinterpreted from the coarse approximation of improved color com-position of the SPOT-5 images, coupled with rock type and relief.Field verification consists of stratigraphic profiles following riversor streams that intersected major geomorphic units. At this scale,ambiguous geomorphic entities and boundaries can be basicallydiscriminated.

For the semi-detailed analysis of sandstones, we primarilyfocus on the area around the Tianzi Mountain. We interpretedthe 1:10000 SPOT-5 images for sandstone landform delineation.Within some small-scale local units, sandstone landforms werediscriminated primarily according to morphogenesis and ancillarydata including altitude and slope characteristics from the DEM.Interpretations were manually digitized directly from RS imagesand geometrically corrected using the monoresititution capabil-ity of the GIS. This method allows the rectification of RS imageriesthrough ground control points and digital elevation data.

Overall, four geomorphic units have been grouped based ontheir shape, texture, color, and connection with their surround-ing units (Table 3). The water bodies, river system, inferred linearfeatures, different denudation terrains and karst landscapes areidentified at the coarse approximation of the 1:10000 scale images,and the special sandstone elements are emphasized a more phys-iognomic approach in combination with semi-detailed criteria.

4.2. Field check

The interpretation symbols should be verified based on the traitsto which degree they match the real existing data. The field inves-tigations are also needed to compare the actual objects with theinterpretation symbols with specific references to the representa-tive or ambiguous points in RS images. Repeated observations and

comprehensive verifications would be implemented for arriving ata set of highly reliable interpretation marks. According to the highreliability of the interpretation symbols, GIS software is employedto redraw the initial mapping. The typical field verification linesand points are determined and the field validation is carried out

G. Yang et al. / Journal of Cultural Heritage 12 (2011) 88–97 91

Table 2Major visual interpretation logos on the basis of remote sensing image.

Type Direct interpretation symbols Indirect interpretationsymbols

Description of RS image

Color Shape Structure

Water body Dark blue Stripped, massive Single color,smooth surface

Connected with riversystem

River system White or gray withwater; dark blackwithout water

Irregular strippedor slenderstreamlined

Single color withnumerousbranched, networkor scatteringstructure

Usually close to the roads

Single peak Dark green withwhite or light colortop

Irregularcylindrical, smoothtopped

Single color withup-and-downsurface

Shadow existed, longershadow indicating greaterheight

Peak forest Dark green,White-spot top

Narrow-striped,smooth margin

Single color,up-and-downsurface

White-spot line usuallyrefers to peak cluster

Peak wall Dark green Narrow stripped,smooth margin

Single color, slightup-and-downsurface

Mostly close to mesa orsquare mountain

Square mountain Light green Irregular massive,flaky

Single color, withrelative flat surface

Usually in the end of broadand flat area

Fracture Light green,differing from thesurroundingobjects

Slender bar, linear Single color,relatively flatsurface

Mostly occurs in close toriver system or peak forest

Sandstone Dark green, usuallywith shadow

Convex-shape,blocky

Spotted structure Densely, sheeteddistributed

Limestone Light green, with Smooth surface Areal structureflat su

Widely distributed and

toio

brighter color with

o obtain more accurate information for the later study. Duringur field investigations, a total of 33 RS locations were observedn detail, including a variety of landscape, structural and lithologicbservation localities.

rface connected each other

5. Interpretation results

The results of visual interpretation are presented in a gener-alized manner (as indicated in Figs. 2 to 6). Quantitative data are

92 G. Yang et al. / Journal of Cultural Heritage 12 (2011) 88–97

Table 3Details of geomorphic and geologic units in this study.

Geomorphic/geologic units Number Area/km2 Description

Sandstone landform 3103 86 Mesa, square mountain, peak wall, peak cluster, peak forest, single peak, and remnant peakKarst landscape 82 Karst cave, karst funnel, sinkhole, depression, karst dome, clint, and so onAlluvium 9 Alluvial terracesDenudation terrain 140 Low hillsFold 4 2 synclines and 2 anticlines tracking NNE and NEE directions

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Fractures 1031 PredSandstone DensLimestone Wide

ummarized in Table 3. Results at the reconnaissance level overallisplay the major linear features and dominant landforms, suggest-

ng the spatial distribution of various topographies in relation to theinear features. Areas of big-scale fractures and overall geomorpho-ogical characteristics are easily detected at this rough scale. Theesults at semi-detailed level discriminate the individual sandstoneandforms according to the morphogenetic criteria. The method at:10000 scale can be further combined with ancillary topographicaps and field validation for a more detailed spatial and genetic

nalysis.

.1. Linear features

Folds are typical of the region and well-preserved (Fig. 2). Theyncline is more open and gentle, with the Triassic strata constitut-ng the core part, while the anticline is tightly closed. By combininghe direct and indirect interpretation process, two groups of folds

ere identified in the study area, as evidenced by the strips of dif-

erent reflectance but with symmetrical distribution and round,val and irregular zonal characteristics in the SPOT-5 HRG images.ne group tracks NEE direction as shown in Sinanyu anticline anduoxiyu syncline, whilst the other group fold is predominated by

Fig. 2. Major folds and big-scale faults derived f

ntly distributed in the directions of NE, NNE, NNW, NW, NWW, NEE, EW and SNstributed with sheeted-like shapetributed and usually connected with each other

NNE direction as seen in Tianzishan syncline and Caijiayu anticline(Fig. 2).

Linear features which were distinguished in Zhangjiajie geoparkinclude mainly fractures and joints, showing remarkably differentreflectance from those of the surrounding objects in RS map (Fig. 3).In the higher spatial resolution SPOT-5 data, the narrower linearfeatures such as fractures are preferably shown as lighter greencolor, slender bar or linear nature, primarily occurring near theriver system or parallel to the extension of peak forests/clusters(as shown in Fig. 3). In practice, it is difficult to identify small-scale linear features from SPOT-5 imagery reliably, which, however,often can be inferred from differential sandstone peak clusters orremnant peak patterns associated with areas adjacent to rivers orvalleys. The presence of relatively straight river associated with thegeological conditions specified above may give additional evidenceto the presence of fractures. For instance, a distinctive fracture inNNE-direction can be identified near the famous Bailong Bridge

in Zhangjiajie (Fig. 4a, b). This feature is extremely evident in theRS imageries, showing as linear elongated strip, darker reflectance,occurring simultaneously with the rivers.

Approximately 1031 linear features at various scales involv-ing faults, fractures and joints were distinctively identified from

rom remote sensing visual interpretation.

G. Yang et al. / Journal of Cultural Heritage 12 (2011) 88–97 93

r featu

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Fig. 3. RS-based linea

POT-2.5 m imagery in the Zhangjiajie World Geopark, occurringredominantly in the directions of NE, NNE, NNW, NW, NWW,EE, EW and SN (Fig. 5; Table 3), with the NE, NNE, NNW and NWrevailing in the study area.

.2. Landform interpretation

The visual interpretation of satellite image symbols as well as

he field investigations enables the delineation of at least four dis-inct geomorphic units and their associated landforms, involvinghe denudation landforms, karst reliefs, Quaternary alluvium andandstone landscapes (Fig. 6). Quantitative data are summarized inable 3.

res in the study area.

5.2.1. Denudation terrainsThe denudation terrains, as largely affected by the episodic tec-

tonic movements, actively involved in the shape-producing andlandscape constructing processes in the Zhangjiajie geopark. Theseterrains reflect local geological conditions such as fold distributionand stratigraphic properties. The RS-based geomorphic analysisreveals that denudation terrains are excessive in the wings of foldsor fractures with a total area of 140 km2 (Fig. 6; Table 3). Typically,they are primarily scattered in the south, north and west parts

of map area or the external zone of other landforms, occupyingnearly 44% of the Suoxi catchment (Fig. 6; Table 3). These units arenoticed as alternative light green and dark green colors, significantdropshadow, and relatively undulating surface with clear dendriticradiated texture showing the distinct fluvial erosion on the satellite

94 G. Yang et al. / Journal of Cultural Heritage 12 (2011) 88–97

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ig. 4. Peak wall of Wulongzhai interpreted in remote sensing image (a) and real pd).

magery. They are generally mapped as a broad areal nature formedy the intermittent tectonic movement and stream incision.

.2.2. Karst landformsKarst landforms in remote-sensing images are characterized by

he brighter green color, areal smooth surface, rough or wavy tex-ures, and extensive distribution, distinctively differing from theandstones (Table 2). They are mainly distributed in the middlend northeastern parts of the study area, covering an area of about2 km2 (Fig. 6; Table 3). To date, more than 100 caves are detected inhe geopark based on visual interpretation and field investigation,ut most of them are still unexplored [23–24]. These karst cavesre distributed mainly at four different levels, of which 200∼400 mnd > 900 m are most favorable for cave development (Fig. 6). For

nstance, Huanglong Cave, Longwang Cave, Guanyin Cave, and Jiu-ian Cave are the primary caves which are developed in the thickolomitic limestone of Jialingjiang Formation (T1j) from Lower Tri-ssic, usually lower than 400 m a.s.l. As compared, almost all ofaves in Tianzishan area are present in the interface between Per-

Fig. 5. Direction of fractures in geopark in rela

(b); fracture close to Bailong bridge in remote sensing image (c) and its real photo

mian limestone and Devonian sandstone, with an elevation of about900–1100 m a.s.l. (Fig. 6).

5.2.3. AlluviumSediments, transported from upland area, are responsible

for the development of alluvial deposits on river valleys or lowland areas. Alluvium was noticed in the middle Suoxi river basin,with a limit area of approximately 9 km2 (Fig. 6 and Table 3).Predominantly, it is featured by the deposits available with sortedcobbles and pebbles transported by the tributary streamlets.Terrace sequences are also observed partially in the north part ofmap, with a locally restricted distribution in the geopark. Narrowvalleys have been identified in almost all the subcatchment andare delineated based on the image features viz., smooth texture,

drainage patterns and land use. These units have unequal widthand moderate to steep valley floors along the Suoxi River. Minorvalleys, generally dentritic in drainage pattern are typical of theregion. Main valley floor, the Suoxi Valley, is noticed as irregularshape and white or gray tone with fine texture on the satellite

tion with peak clusters and peak walls.

G. Yang et al. / Journal of Cultural Heritage 12 (2011) 88–97 95

iajie W

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Fig. 6. RS-based geomorphic map of Zhangj

magery. It was mapped as a narrow strip primarily in west-eastlongated zone formed by the fluvial behaviors on both flanksf river course. This kind of landform, as well as karst landscape,rovides an important source of evidence for Quaternary climatic,ectonic and geomorphic evolution. Quaternary alluvium andlongated narrow zone occupies nearly 3% of the area under study.

.2.4. Sandstone landformsThe extensive quartz sandstone landforms are mostly developed

n the areas of Devonian sandstone and concentrated around thedges of the Tianzi Mountain and along the Suoxi River in the areasetween Wangjia Valley and Heicao Valley (Fig. 6). In the area of6 km2, a total of more than 3100 sandstone peaks appeared, withhigh average density of 37.5/km2 (Table 3). The sandstone peak

orest landform in Zhangjiajie represents a unique geomorphic andhysicogeographical sandstone assemblage with particular char-cteristics, occupying nearly 27% of Zhangjiajie World GeoparkTable 3).

Various types of sandstone landforms ranging progressivelyrom giant mesa/square mountains, peak walls, peak clusters, peakorests, single peaks or pillars, and finally remnant peaks can bedentified in Zhangjiajie World Geopark (Table 3). For instance,he single peaks are found as irregular shapes and darker greenolor on the satellite imagery, with longer shadow indicating thereater height. The peak forests and peak clusters are shown asarrow-striped, with smooth margin and intermittent white-spot

ine showing the isolated peaks and continuous white-spot lineeflecting the groups of columnar peaks connected by the same baseTable 2). The clusters of peaks are noticed with darker green sinu-us hilltops on the satellite imagery, usually distributing closely tohe irregular massive, flat square mountain or mesa. These diverseandstone landforms therefore display an integrated process of

eomorphic evolution, from the early stages following plateau dis-ection (mesa or square mountains) through to late period erosionremnant peaks).

Notwithstanding their importance, it is difficult to successfullyutomate the recognition of peak walls solely based on shape

orld Geopark showing different landforms.

and texture features. Using them in combination with correla-tion with surrounding geomorphic units might result in a betterdiscrimination of this linear peak walls. Hence, based on a prioriknowledge of peak walls, we screen out shape and textural fea-tures that most likely characterize peak walls in a unique way. Peakwall were well identified in SPOT-5 2.5 m data, provided superioridentification and delineation of valleys and linear feature align-ments. Aligned parallel to linear features or close to mesa or squaremountain, there are some narrower and elongated geomorphicunits, with longer shadow indicating the greater height. Signifi-cant information for peak walls could be extracted from the darkergreen color, larger length to width ratio, an irregular and compactshape, linear texture, and limited striped distribution (Fig. 4 andTable 2).

6. Discussion

The various landforms within the geopark are considerablyinfluenced by the underlying geology, exogenic and endogenicactivities, drainage morphometry, and considerable climatic vari-ations [17,25–27]. In the study area, the denudation terrain,sandstone relief, karst landscape and alluvium are identified andmapped as the four major landforms. These landforms are closeassociated with the tectonic uplift and large-scale linear features,constituting the basic geomorphic configuration of ZhangjiajieSandstone Peak Forest Geopark.

6.1. Tectonic constraints on landform developments

The overlay analysis of landform pattern and geological set-tings shows that the specific geological settings influence greatlythe shape-making and topographic constructing process, as evi-

dently observed in the sandstone area (Figs. 2 and 3). The geoparkis located in the wings of Tianzishan short-axis syncline and south-west part of Sanguansi syncline. The uplifting of Caijiayu anticlinehas produced the relatively flat strata (with a general occurrence of< 8◦), remarkably facilitating the stability of sandstone peak forest

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6 G. Yang et al. / Journal of Cu

andforms (Fig. 2). The sandstone peak forest landforms are pri-arily concentrated on Tianzi Mountain, Sanguansi syncline rising

art, and Sangzhi syncline rising part (Fig. 2), in close associationith the high density of fractures and joints (Figs. 2 and 3).

The study area has been the southeast edge of the Yangtze plat-orm, bordering on the Jiangnan Oldland in the south. Episodicectonic movements constrained the regional folds and fractures,rominently controlled the development of river valleys, water sys-ems and their base levels. River water eventually cuts throughhe high-angle joints or structural weak zones where mass wast-ng appears, therefore forming the present quartz sandstone peakorest landscapes. Overall, the larger lineaments typically con-rol the alignment of the major streams and escarpments, whilemaller fractures/joints usually break the rock mass into smaller-ize blocks. Some of the peak walls, peak clusters and peak forestsave larger elongated axes in a NE or NNW direction or even at therossing of these fractures and joints (Figs. 3 and 5), or are placedlose to some river valley tracking these structures (Fig. 3).

Like much of central China, the region around Zhangjiajie hasndergone a long and complex uplift and fracture history. Weelieve that the landform process in the study area have been con-trained by at least two stages of intensive tectonic movements, asvidenced by the earlier fracture systems tracking NNW (340◦±)nd NEE (60◦∼70◦) directions superposed by small-scale joints inhe SPOT-5 imagery. These structures created as response to theectonic activities remarkably influenced the landform distribution,andstone landscapes in particular, of this region.

.2. Water system distribution and its controls on landforms

It is clear from the results considered here that water systemistribution does exert an important influence on the shaping ofhe sandstone terrain. RS-based visual interpretation provide addi-ional insight into the nature of tectonic-induced water systemhat models the diverse landforms, as it is distinctively showns the good agreement of water system with the primary lineareatures and topographic patterns (Fig. 2). The wide distributionf surface water and groundwater due to the abundant rainfallaround 1400 mm per year) would have been favorable for theenudation process, karstification and sandstone development inost parts of study area. The seasonal linear flow, surface flow,

mall streams, and groundwater systems are focused along theoints, fractures, and other zones of broken rock, often becom-ng the one of the dominant controls on the expansive sandstoneandscapes with widespread distribution and unique topographiesFigs. 2 and 3).

The geopark is currently drained by the Suoxi River, the second-rder tributary of the upper Lishui catchment. The Suoxi River is aentral area of heavy rain, resulting in the intensive river system.he mainly radial drainage pattern around the Tianzi Mountain sig-ifies intense headward stream erosion due to joint and factures,

eading to peculiar peaks of various shapes in the margin of thelatform (mesa or square mountain) (Fig. 6). The intensive wateretwork continuously incises the “checkerboard-like” joint system

nto the strong, thick sandstone, accelerating the formation of thenique landscape of sandstone peaks in the river valleys, as evi-enced by the Jinbian brook, Pipa brook, Hua brook, Shadao brooknd Suoxi river valley.

.3. Lithologic features in relation to sandstone landforms

The sandstone peak forest landforms have been developedainly in the middle Devonian Yuntaiguan formation (D2yn) and

he upper Devonian Huangjiadeng formation (D3h) (as shown inig. 2). It is highly probable that the existing sandstone land-capes have differential lithologic features, though most of them

Heritage 12 (2011) 88–97

were composed of thick-layer quartz sandstone or thin-layerquartz siltstone, with a total quartz content of more than 90%[25].

On the other hand, the lithologic component, essentiallyimmune to chemical erosion and higher compressive strength, con-stitutes the solid base of the peak column, with the purple thicksiliceous-cemented quartz sandstone of Huangjiadeng group (D3h)as the peak column cap. The gentle rock occurrence, usually atslopes 5 ∼ 8◦, is conducive to the structural stability of peak columnformation. Even for the separated sandstone peaks, the skyscrap-ing sandstone column can be maintained for a longer time becauseof the low dips allowing the center of mass of the columns to bemaintained vertically within column base area and thus geome-chanically stable and resistant to toppling and collapse. If there are anumber of weak thin-layer siltstones among the thick-layer quartzsandstone, they would be subjected to the weathering erosion dueto the weak resistance to the weathering process. In addition, theweakened mechanical properties are prone to produce the sin-gle spectacular peak pillar landform, shaping a diversity of visualtopographies.

6.4. RS-revealed geomorphic evolution

The detailed geomorphological and geological analysis of vari-ous landforms in the entire Suoxi River basin based on RS approachhelps considerably in the understanding of the geomorphic evo-lution history. The systematic delineation and identification ofvarious landforms with different scale, pattern and distribution alsogive the clues for geomorphic history. The comparability of land-scapes and structural lines should serve as the significant evidencefor terrain evolution process. Visual interpretation reveals that atleast two episodic tectonic movements occurred in the study area,as indicated in the linear structures tracking two major directions(Fig. 5). The earlier NE and NW fractures should be possibly favor-able for initial topographic prototype, which was overlain by theadditional NNE, NE and NNW joints and fractures. These, therefore,significantly controlled the basic geomorphic configuration of theregion (Figs. 2–4).

The well-recognized river network in Zhangjiajie World Geop-ark, obviously in agreement with the extension of structural line,was principally controlled by the fractures and joints (Fig. 3).Following the well-developed joints, the sandstone landformspreferably developed along the Tianzi Mountain and part of south-west area with a high dense distribution. The structural-inducedriver system begun to develop and incised the sandstone landformat a relatively prompt rate, as remarkably affected by the later masswasting in the region. Possibly, several distinctive rapid incisionstages occurred in the study area, shaping the stepped landformsincluding the striking sandstone landscape at different levels aswell as terrace sequences and karst caves.

7. Conclusions

The present study is an attempt to deploy remotely senseddata to properly model the landscape features and their controlsin Zhangjiajie World Geopark. From RS analysis, in combinationwith field investigations and available topographic mapping, ourstudy was concentrated on the temporal and spatial geomor-phic nature within Zhangjiajie World Geopark. Direct and indirectinterpretation signs were established and various landforms were

exhumed as an important source of evidence for geomorphic study.The RS-based coarse approximation and semi-detailed geomorphicanalysis enhanced the possibility of accurate and prompt estima-tion of regional geomorphic configuration and sustainable resourcemanagement at the river basin level.

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Our study indicated that out of the core area of the geopark, 86,2, 9 and 140 km2 consist of sandstone relief, limestone landscape,lluvium and denudation terrain, respectively. The distributions ofifferent reliefs were obviously controlled by the distinct fracturesnd river system, in consistence with the results of our previoustudies [17,27]. The influence of geological settings and surface pro-esses on the drainage geomorphic units can quantitatively be usedo determine the landform formation. At least two episodic tectonic

ovements have largely altered these landforms and pre-existingandscapes. The structural-controlled river system and water dis-ribution began to incise the sandstone landform, resulting in theifferent stepped landforms at a relatively prompt rate. For this rea-on, the sandstone landforms begun to develop transitionally fromhe mesa, square mountain, peak wall, peak cluster, peak forest toingle peak or remnant peak, showing a clear model of peak forestormation. Analysis of these diverse landforms is evidently help-ul for classification of micro-landform types and unravelling theelative controls of geomorphic evolution of the study area.

cknowledgement

We would like to express profound gratitude to the coopera-ion of the staff at Zhangjiajie Geopark Management Department,nd the Bureau of Land Resource Management office in Zhangjia-ie, who made much of this work possible. Our deep appreciations offered to our project members, professors Zhijiu Cui, Naigongeng and Keyi Guo, for useful discussions throughout this work.e gratefully acknowledge Ms. Yan Yang and Mr. Wenqiang Shi

or their participation in parts of the field investigations and sam-le collections. This work is a contribution to the specific projectf “Formation age of sandstone peak forest landform and crustaltability in Zhangjiajie World Geopark” from Zhangjiajie Geoparkanagement Department.

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