Environ Earth Sci (2012) 65:1877–1894 DOI 10.1007/s12665-011-1170-1

ORIGINAL ARTICLE

Quartz sandstone peak forest of Geopark, northwest Province, : pattern, constraints and comparison

Guifang Yang • Mingzhong Tian • Xujiao Zhang • Zhenghong Chen • Robert A. L. Wray • Zhiliang Ge • Yamin Ping • Zhiyun Ni • Zhen Yang

Received: 13 July 2010 / Accepted: 24 June 2011 / Published online: 10 July 2011 Ó Springer-Verlag 2011

Abstract The Zhangjiajie Sandstone Peak Forest Geo- forests and peak pillars to remnant peaks in the lower park in northwest Hunan Province, China, is a compre- valley bottoms. The form and distribution of the Zhang- hensive geopark containing many spectacular quartz jiajie sandstone landforms are primarily dominated by the sandstone landforms, limestone landscapes and vari- geological setting, particularly the presence of brittle ous other important geoheritage resources. It is listed as a structures (fractures and joint sets) trending NNW, ENE UNESCO World Geopark and is also part of the World and NE. Triggered by the episodic tectonic movements, Heritage Scenic and Historic Interest Area for major streams and escarpments frequently occur along its important landscape features. Many of the sandstone these structural directions, while some of the peak walls, landforms, particularly the vast number of thin pillars or peak clusters and peak forests have their longer elongated spires, are very unusual and serve as the core landscapes of axes corresponding to NE or NNW directions, with an the geopark. But Zhangjiajie displays a diverse range of increased density of peak forms at the intersection of these types, exhibiting spectacular patterns and regular fractures and joints. The geometry of the diverse sandstone distributions. In this paper, the geomorphic traits, distri- landforms is also influenced to a certain degree by the bution pattern and constraints of the sandstone landforms climatic, water system distribution, lithologic properties, of the Zhangjiajie Geopark are examined. Our study indi- biological process, meteorological features and denudation cates that in the outcropping areas, the sandstones display processes. The suite of quartz sandstone landforms in four distinctive levels from 300 to 1,000 m above sea level, Zhangjiajie can be compared with other sandstone land- and these extend clearly from the highest sandstone plateau scapes regionally, and our interpretation of the sandstone platform to the center of the valleys. The high sandstone peak forest formation processes offers a significant con- platforms developed close to a flat high-level erosional tribution to the study of topographic features and the surface, and subsequent erosion into this plateau has geomorphic evolution of sandstone landscapes. resulted in successively lower levels of landforms that transition gradually from peak walls, peak clusters, peak Keywords Sandstone landform Topographic diversity Tectonic constraints Climatic variation

G. Yang (&) M. Tian X. Zhang Z. Ge Y. Ping Z. Ni Z. Yang School of Earth Sciences and Resources, Introduction China University of Geosciences, Beijing 100083, China e-mail: [email protected] Quartz arenites have been described as practically immune Z. Chen to chemical (Tricart 1972) and form the back- Development Research Centre, China Meteorological drop to some of the world’s most spectacular scenery Administration, Beijing 100081, China (Wray 1997a; Young et al. 2009). In recent decades, interest in quartz sandstone landforms worldwide has dis- R. A. L. Wray UOW College and School of Earth and Environmental Sciences, tinctly increased (e.g., White et al. 1966; Chalcraft and Pye University of Wollongong, Wollongong 2522, Australia 1984; Young 1986a, b, 1988; George 1989; Bricen˜o and 123 1878 Environ Earth Sci (2012) 65:1877–1894

Schubert 1990; Wray 1995, 1997a, b; McNally and Previous works on Zhangjiajie have primarily focused McQueen 2000; Netoff and Shroba 2001; Turkington on the physical properties and esthetic features of the and Paradise 2005; Turkington et al. 2005; de Melo and sandstones, with particular interest in the small-scale ana- Giannini 2007; Yang et al. 2009; Young et al. 2009; Siedel logs of sandstone megapillars and cliffs. However, detailed et al. 2010), with particular focus on the susceptibility of knowledge needed to properly model the evolution process quartz sandstones to weathering and erosion in a number of of such a distinct sandstone landscape is still poor, par- tropical, subtropical and even some arid or semiarid areas. ticularly compared with our understanding of widespread Many of these sandstones exhibit an almost identical size, sandstone landscapes elsewhere (Wray 1997a; Young et al. form and genetic formative process to those of their car- 2009). bonate relatives (Wray 1995, 1997a, b; Doerr 1999; Doerr Despite a growing consensus that the development of and Wray 2004; de Melo and Giannini 2007; Young et al. the Zhangjiajie sandstone landforms can be attributed to 2009). Among these, the quartz sandstone peak forest several factors including intermittent tectonic uplift, river landforms in Zhangjiajie, in northwest Hunan Province of incision, climatic variation and change of base level (Wu China, are becoming increasingly difficult to ignore due to and Zhang 2002; Hunan Province State Land and their spectacular geomorphology and unusual physicogeo- Resources Department 2003; Zhou et al. 2004; Tang et al. graphical features. However, little worldwide attention has 2005; Huang et al. 2006), the formation mechanisms and yet been given to the systematic study of these striking evolutionary processes at Zhangjiajie require a more landforms and the processes responsible. appropriate and universally accepted interpretation (Deng The extensive quartz sandstone landforms in the 1989; Tang et al. 2005). However, the absence of detailed Zhangjiajie Sandstone Peak Forest Geopark (also known geological records has largely hampered the understanding as the Zhangjiajie World Geopark) occur across an area of the development pattern and morphotectonic genesis of of 86 km2 in Upper and Middle Devonian sedimentary the Zhangjiajie region (Zhou et al. 2004; Tang et al. 2005; units. Many of these sandstone landforms bear a striking Yang et al. 2009). visual resemblance to the limestone peak forest karst In 2008 and 2009, two comprehensive field studies were elsewhere in China. At Zhangjiajie, the geomorphic undertaken as part of the analysis of geological heritage assemblage of sandstone peak forest landforms constitutes protection of the Zhangjiajie Sandstone Peak Forest Geo- a rare natural museum and a world-class tourist attraction park. During these field surveys, detailed observations of (Deng 1989; Chen 1993). Notably, the large number of various sandstone topographies were performed in an sandstone pillars and cliffs are characterized by great attempt to characterize the exceptional sandstone peak height differences, large height-to-width ratios and high forest landforms of this region, with specific references to peak densities, displaying a wide variety of topographic their development characteristics, distribution patterns and patterns. In 1992, the spectacular landforms of the formation mechanism. These region-wide analyses are Zhangjiajie sandstone area (Hunan Geo-environmental among the first in this area to advance beyond simple Monitoring Center 1988) were inscribed on the UNESCO descriptions of topographic classification in an attempt to World Heritage List as part of the Wulingyuan Scenic and examine the possible processes responsible for the land- Historic Interest Area for its important scientific value, form evolution of the region. These works also provide the superlative natural phenomena, exceptional natural beauty key to improving the area’s scientific management of and esthetic importance (UNESCO 2010). In 2004, the sustainable tourism and scientific geo-heritage protection. sandstone areas of Zhangjiajie were listed as a UNESCO global geopark. Since the early 1980s when the sandstone peak forest Characteristics of the study area landform was named by Guo (1982), it has received increasingly significant scenic and scientific attention in The Zhangjiajie Sandstone Peak Forest Geopark covers a China (Zhai and Xiong 1988; Deng 1989; Chen and Liu total area of approximately 398 km2 (Fig. 1) and is situ- 1991; Chen 1993; Su and Li 1993; Zhou et al. 2004). Many ated near the junction of the southwest Yunnan- notable studies have been made of this impressive sand- Plateau and the in China’s northwest stone landscape in terms of geomorphic character and Hunan Province (29°1301800–29°2702700N, 110°1800000– geological genesis (Liu 1988; Deng 1989; Chen 1993; 110°4101500E). The mean elevations primarily range from Tang et al. 2005), and recently the question of a relation- valley bottoms at 200–300 m above sea level (a.s.l.) to ship between lithologic traits and sandstone landform for- mountain peaks at 1,300 m a.s.l. The present day climate mation has been revisited (Zhou et al. 2004; Huang et al. is relatively temperate, predominately subtropical humid 2006). However, very little detailed analysis of this monsoon, with an annual average temperature of 16°C and remarkable area has been published in English. 1,200–1,600 mm precipitation. 123 Environ Earth Sci (2012) 65:1877–1894 1879

Fig. 1 a Location of the Hunan Province in relation to the middle geographical map of the Zhangjiajie World Geopark showing the water system; b Sketch map of Zhangjiajie with specific major sandstone peak forest landforms references to the Zhangjiajie World Geopark; c Compiled

Regional geological context framework of this region and initiated major faults and joint systems in the NE, NW and WNW directions. During the Standing across the Jiangnan ancient land and Yangtze para- recent Himalayan and neo-tectonic movements, intermittent platform, this area has undergone several tectonic movements, uplift and tilting re-activated these large-scale joints and which established the basement structure and influenced the fractures and these have been exploited by modern landform- later geomorphic configuration. The earlier Wuling-xuefeng making processes, directly influencing these imposing sand- Movement (approximately 1,000 * 850 Ma) formed the stone landforms. regional basement, and the Indosinian and Yanshanian Physiographically the Zhangjiajie area, and particularly Movements (around 250–205 and 160–68 Ma, respectively) the main areas of densely distributed peaks and spires, is caused the pre-Mesozoic strata to fold and fracture. These characterized by a low-obliquity flat to slightly undulating movements determined, to a large extent, the basic structural terrain, with a general slope of 5–8° toward NE–NNE. The

123 1880 Environ Earth Sci (2012) 65:1877–1894 eastward-flowing Suoxi River, a second-order tributary of Geomorphological regional context the , has incised the quartz sandstone to form various peak forest landscapes at different heights varying At Zhangjiajie, there is a great diversity of sandstone from 1,000 m a.s.l. down to the present day riverbed topography, including giant mesa, square mountains, peak (Fig. 2). walls, peak clusters, peak forests, stone gates, natural Stratigraphic deposits range from youngest Holocene bridges, valley, etc. The various sandstone landforms are alluvium to the extensive outcrops of Silurian and Devo- mostly developed in the areas of Devonian sandstone and nian sedimentary rocks that are representative of the region concentrated around the edges of the and (Fig. 1). Strata of the Middle Silurian Xiushan Formation along the Suoxi River in the areas between Wangjia Valley

(S2xs) and Xiaoxi Formation (S2x) occur in the south, north and Heicao Valley (Fig. 1c). and west of the geopark and constitute the bedrock foun- The major characteristics of Zhangjiajie are the more dation underlying the sandstone. The Xiaoxi Formation is than 3,100 sandstone rock peaks or pillars that are found disconformably overlain by approximately 520 m thick within the 86-km2 study area. Of these, 1,000 are more than

Middle Devonian Yuntaiguan Formation (D2yn), which is a 120 m in height (Table 1; Figs. 3, 4), and the Jinbian Rock chiefly gray-white, fresh pink, thick or medium-thick fine- exceeds 350 m (Fig. 3g). This gives a remarkable average grained quartz sandstone with a series of interbedded density of 37.5 peaks per/km2 (Table 1). Based on our thin-layer siltstones and muddy siltstones. The overlying remote sensing (RS) interpretations and field investiga-

Huangjiadeng Formation (D3h) of the Upper Devonian has tions, many of these peaks display relatively high height- a regional thickness of 5.3–40.6 m and is a fine-grained to-width radios, although the diameter and height ratios for ferruginous quartz sandstone, with 1–3 layers of oolitic all the peaks cannot be individually measured. For exam- hematite on the top, making the resistant red caps on some ple, the Imperial Brush Peak has a height of[100 m and a sandstone peaks. diameter of only *2–3 m, revealing a very high height-to- Carboniferous strata are normally absent and mark the width ratio of around 30–40:1. Zhangjiajie has the largest Hercynian tectonic movements that occurred during this area, maximum density and highest quality of such sand- period. The Huangjiadeng Formation sandstone is uncon- stone peaks in China, and possibly even the world. formably overlain by thick Permian limestone, but this The relative heights of the various quartz sandstone approaches conformity with the younger limestone and landforms range from tens of meters to a maximum of dolomitized limestone Triassic strata. 350 m, with the majority less than 100 m (Table 1), and In the geopark, the sandstone peak forest landforms are are found concentrated at four distinct elevation levels mostly developed in the Upper and Middle Devonian units between 300 and 1,000 m a.s.l (Fig. 2). The highest peak

(D2?3), whilst limestone karst landforms appear in the level is at 900–1,000 m a.s.l. and these are at the top of the Permian or Triassic strata (majorly P1q and T1j), and along sandstone surface; this relatively flat surface (Fig. 2) was the Suoxi Valley as well as the northeast Tianzi Mountain. the initial top surface of the sandstone before the river A Quaternary stratigraphic distribution is very limited, incised deeply into the quartz sandstone. A second level of usually with dominant fluvial and diluvial deposits. pillars at 700–750 m a.s.l. largely owes its formation to the

Fig. 2 Development patterns at different levels (L1–L4) for sandstone landforms at the Zhangjiajie World Geopark

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Table 1 Statistical numbers of sandstone peaks in Zhangjiajie World Geopark Types of peak forest Relative height (\100 m) Relative height (100–200 m) Relative height (200–300 m) Relative height ([300 m)

Number 2,061 799 198 45

Fig. 3 Diverse sandstone landforms at the Zhangjiajie World Geopark. a Mesa; b square mountain; c peak wall; d peak cluster; e natural sandstone bridge; f South Natural Gate; g Jinbian Peak; h peak forests at different levels; i mesa, peak cluster, peak forest and remnant peak

collapse of interbedded thin and soft rocks. Some low carved by water erosion and mass failure exploiting the sandstone pillars have developed in the third level at an densely developed joint and fracture systems. Residual altitude of approximately 500–550 m a.s.l., and these were sandstone peaks, mostly less than 10-m high, are found

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Fig. 4 Spectacular sandstone landforms in the Zhangjiajie Geopark Peak; g Beetles in the Foggy Sea; h Three Sisters; i Fairy Scattering discussed in the text: a Garden in the Air; b Huangshizhai Palm Peak; Flowers c South Sky Pole; d Palm Peak; e Thin Strip of Sky; f Imperial Brush along the base of the Suoxi River valley and these comprise landforms are closely associated with topographic position, the lowest level at around 300 m of elevation (Fig. 2). the lithologic and fracture characteristics of the bedrock, river system features, and with hydrological and meteoro- Distribution pattern of sandstone landforms logical controls. The large-scale topography including the mesa, square The geomorphic characteristics and landscape evolution mountains, peak walls and peak clusters are usually con- of the remarkable Zhangjiajie sandstone peak forest trolled by the major structure-controlled jointing and

123 Environ Earth Sci (2012) 65:1877–1894 1883 bedding. They are most developed near the escarpment or square mountains, and summits are usually in the order of plateau edges where the joint and major fractures are most 700–800 m a.s.l. open. Further away from the platform and near the outer zone The sandstone terrains at smaller scales, including the are the typical quartz sandstone peak forest landforms at peak forests and singular peaks, are generally found near different levels. More than 3,100 sandstone pillars and the river valleys. In the central Suoxi catchment, for peaks have developed in the geopark, many of which are example, the continuous downcutting and convergence of over 120 m in height (Fig. 1; Table 1). The diverse natural rivers has gradually carved a range of diverse sandstone shapes of these landscapes have strongly inspired the ideas landforms ranging from the larger mesa/square mountains of Chinese esthetic beauty. along the edge of Tianzi Mountain to remnant sandstone At the lower levels, many small isolated remnant peaks, peaks near the river valley (Table 2; Fig. 1). From the side usually less than 10-m high, border the lower-level central hill to the center of the valley, the cutting depth gradually rivers or streams. These peaks have suffered from long- increases and can attain 500 m or more. term denudation, erosion and mass failure, and are often The marginal zone, the outer edge of the Tianzi Moun- only weakly preserved (Fig. 2; Table 2). tain, is characterized by a relatively gentle relief (Table 2). River valleys and canyons at all levels owe their primary

The Upper Permian limestone karst platform (P1q) is found alignments to well-developed joint and fracture systems primarily on top of the Tianzi Mountain. It displays typi- (Figs. 5, 6). cally small relief of about 200 m and atop of it are well- developed paleo-weathering crust and loose sediment layers (Fig. 1). The original topography of the Tianzi Mountain Diversity of sandstone landscapes remains unspoiled and constitutes a residual planation sur- face at an elevation between 1,300 and 1,000 m a.s.l. Under The types of sandstone landforms in Zhangjiajie World the remnant limestone planation surface is the well-pre- Geopark range progressively from giant mesa/square served sandstone top surface with an elevation of around mountains, peak walls, peak clusters, peak forests, single 850–1,000 m a.s.l. Streams have incised deeply into the peaks or pillars and finally to remnant peaks. This diverse sandstone to form the platform, mesa or square mountains. topography at a range of scales suggests a model of sand- Close to these flat residual platforms is the outer zone of stone formative processes, from the early stages following the mountain where numerous peak walls and peak clusters plateau dissection (mesa or square mountains) right through have developed, due chiefly to generally weak downcutting to late period erosion (remnant peaks). They therefore dis- processes but much more rapid excavation of the intense play an integrated process of geomorphic evolution. joint systems (Fig. 1). These landforms are primarily sep- arated from the platforms and show elongated platforms Mesas and square mountains with narrow, flat but irregular tops (the first sandstone level shown in Fig. 2). Overall, the height difference is not big Mesa and square mountains are the primitive forms of peak between the peak walls, peak clusters and the flat mesas or development and signify early erosion of a plateau surface.

Table 2 Primary sandstone landform types and typical landscapes

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Fig. 5 Structural lineaments and major anticlines and synclines of the Zhangjiajie World Geopark (after Yang et al. 2011a)

At Zhangjiajie, they are well preserved at an elevation of narrow (relative to height), elongated walls of rock (Fig. 3c). approximately 850–1,000 m a.s.l. because of the protection Peak clusters are groups of columnar peaks with conical or offered by the 40-m thick resistant oolitic hematite-rich cone-shaped top surfaces connected by the same base sandstone layers in the Upper Huangjiadeng Formation (Fig. 3d), whereas peak forests are characterized by a large

(D3h; Fig. 2). The top surfaces of these mesas are relatively variety of isolated irregular-cylindrical or oval-cylindrical flat and their rims are comparatively steep, usually with a peaks generally with smooth top surfaces (Fig. 3h). height difference of tens to a few hundred meters (Fig. 3a). In general, the long axis of peak walls and peak clusters They are primarily located on the extremely impressive and are usually aligned parallel to fractures, especially in the extensive 3.1-km2 Sonzigang platform around the southern NNE and NE direction, while the peak forests are chiefly edge of the Tianzi Mountain. Below this is the famous aligned parallel to the major joints (Table 3). As joints are Jinbian Stream. deepened and widened, both by stream erosion and mass Square mountains are separated from the mesa or plat- failure along joints, the remaining sandstone between the form and are surrounded on four sides by precipitous cliffs, joints is shaped into towers or pinnacles of various shapes often nearly a 100 m high (Fig. 3b), which are typically and sizes. Where fracturing is most intense, the sandstones nearly as high as the diameter of the mesa. The summits of may progressively develop into intricate collections of these almost inaccessible platforms are quite flat and cliff-bounded needle-like spires. commonly mist shrouded. The Yaozizhai (Fig. 3b), Garden in the Air (Fig. 4a) and Huangshizhai (Fig. 4b) are repre- Natural stone bridges sentative of this kind of landform. Natural stone bridges are another spectacular sandstone Peak walls, peak clusters and peak forests form well developed at Zhangjiajie World Geopark. One fine example is the very impressive ‘The First Bridge in the This series of landforms form the most remarkable landscapes World’ (Fig. 3e), which has a length of more than 40 m, a in the region. They principally exist in the vicinity of mesas or width of 2 m, a top thickness of 5 m and a vertical height square mountains, and can be clearly attributed to the deep of more than 350 m. downcutting of streams into the mesas and platforms. The The most basic constraints on the form and shapes of peak walls are mostly flat topped and are characteristically natural stone bridges are differences of strata thickness, and

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Fig. 6 Primary joint sets (a) (modified from Hunan Geo-environmental Monitoring Center 1988; Su and Li 1993) and rosette joint diagrams (b) of the Zhangjiajie Geopark the lithologic nature and continuity of the joint systems. Primary fractures or stress release joints then cause the Initially, weathering and water erosion will largely promote mass of interlayer soft rock to crack and vertically fall from collapse of interbedded thin and weak muddy siltstones. As the peak wall, leaving the recessed roof bounding a door- erosion continues, the overhanging thick and hard sand- shaped or arch-shaped form. With time, the size of the stone rock layers may undergo mass wasting along various stone gate increases, as does the relief of the suspended soft fracture planes leaving a bridge-shaped topography, with rock. This process is most clearly seen, for instance, in the broad openings extending right through a sandstone peak singular ‘South Natural Gate’ (Fig. 3f), which attains 15 m wall. In this regard, natural stone bridges also represent the of height with a base width of 10 m. remnants in the development process from square moun- tains to peak forest landforms. Peak pillars and remnant peaks

Stone gates The very large numbers of peak pillars and remnant peaks are other spectacular forms for which Zhangjiajie is most Stone gates also occur in the geopark (Fig. 3f) and appear famous. Peak pillars/columns are single towering columnar as if they are drawn on the smooth face of a peak wall. The bodies of sandstone with different widths, but tens of stone gate is usually door shaped and is believed to form meters to 100 m or more high. The form of peak pillars is from mass failure along two or more prominent intersect- constrained by both the joint patterns and sandstone ing fractures or joint sets. properties.

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Table 3 Orientation statistics of peak walls and peak clusters in Zhangjiajie World Geopark (after Hunan Geo-environmental Monitoring Center 1988) Direction NNE NE NS NNW NW ENE WNW EW In total

Numbers of peak clusters 90 81 25 12 8 7 5 1 229 and walls % 39.3 35.4 10.9 5.2 3.5 3.1 2.2 0.4 100

Residual peaks are the short remains of peak bodies that differing factors and scale, but mostly involving the internal have undergone long-term erosion and actually represent geodynamical controls of the bedrock and external water the late development stage of peak pillars (Fig. 3i). When erosion and mass failure (Wray 1997a, 2009; Young et al. the peak forest forms, erosion continues to cut down into 2009). They are also largely influenced by rock properties the base rock along the primary joint sets, resulting in the such as texture, cementation and sedimentary structures. collapse of forest peaks. This may eventually result in Each of these factors have been critical in the formation isolated remnant peak columns, showing the peak pillar of basic configuration of the dramatic Zhangjiajie sand- landscape (Fig. 3g). Cross-bedding, and the junction of soft stone peak forest landforms, but particularly the erosion of and brittle rocks, in particular, can produce irregularly large- and small-scale fault and joint fracturing resulting shaped pillars, and this is well seen at South Sky Pole, from neogenic tectonic uplift (Liu 1988; Zhou et al. 2004; Palm Peak and Imperial Brush Peak (Fig. 4c, d, f). A Yang et al. 2009). change from intersecting joints to a single dominant joint orientation is often reflected topographically in a change Tectonic constraints on sandstone landforms from towers or pillars to elongated strip or wall-like forms. It is very clear that mass wasting is actively involved in At Zhangjiajie, a correspondence exists between the sand- the continued formation of peak forests, peak walls and stone landforms and the geological setting (Figs. 1, 5, 6), and some single peaks. Many fallen sandstone blocks, some our investigations have found regional fracturing to exert a even showing the peak shape and near-vertical sides, litter prominent control on the sandstone peak forest landscapes. the base of most vertical cliffs. They are being destroyed Overall, the larger lineaments typically control the alignment by continued erosive processes, but have clearly collapsed of the major streams and escarpments, while secondary from the overlying cliffs down vertical joints revealing new fractures/joints usually break the rock mass into smaller-size vertical faces. Such landscapes are seen across the whole blocks. The surface features and vertical variations are geopark area, but are best seen in outlying areas of thereby intricately linked to the dynamic processes affecting Devonian sandstones. the widening of fractures and joint sets at all scales. Like much of central China, the region around Zhang- Canyons and valleys jiajie has undergone a long and complex uplift and fracture history. We believe that the landform processes in the River valleys and canyons with a depth of 200–500 m are study area have been constrained by at least three stages of densely developed in the Zhangjiajie World Geopark. intensive tectonic movements. The earlier tectonic move- Vertical cliffs generally line both sides of these rivers and ment during the Late Jurassic period (around 160–140 Ma) form box or V-shaped valleys. The best examples are the sculpted the topographic outlines and larger-scale fracture Jinbian Valley, Shadao Valley, Kuangdong Valley, Pipa systems tracking NNW (*340°) and ENE (60–70°) Valley and Yuanyang Valley. The direction and spatial (Figs. 5, 6; Table 3). Late Cretaceous tectonic movements distribution of these valleys and canyons suggest strong (around 130–68 Ma) helped to shape the small-scale joints control by the pattern and spacing of fault structures. For and reactivate already existing faults. example, the ‘‘Thin Strip of Sky’’ in Black-grass Valley Several periods of recent intermittent neo-tectonic uplifts (Fig. 4e) has developed in an NW direction and is crossed (the Xishanian movement in particular) were relatively weak. by the ‘‘Water winding 4 gates’’ that follows a vertical Comparison of terrace features with adjacent karst has fault, leading to a structure-controlled criss-cross valley. enabled the quantification of an average rate of surface uplift of *0.2 mm a-1 in the study area since 0.93 Ma (cf., Yang et al. 2011a, b). These intermittent uplifting processes may Discussion have triggered or contributed to the vertical spacing of the sandstone landforms and induced mass failure along the Worldwide, spectacular sandstone peak and tower land- dense joint systems, leading to minor irregular shapes as forms are commonly attributed to the interaction of shown in some individual peaks (Figs. 2, 4). 123 Environ Earth Sci (2012) 65:1877–1894 1887

These several periods of uplift have also presumably formation of the modern sandstone landforms probably influenced the rate of river downcutting, especially by the occurring in the Middle Pleistocene (Yang et al. 2011b). Suoxi River, and we suggest that these tectonic periods Therefore the deep incision of the Suoxi River and the are reflected in the four distinctive levels of sandstone associated mass failure have controlled the four distinct landforms that are evident within the Zhangjiajie Sand- topographic levels and the general form of the regional stone Peak Forest Geopark (Fig. 2; cf. Yang et al. landforms (Fig. 2). In comparison, the biology, climate and 2011b). lithology have served as secondary controls in the sculpting To assess the role of jointing, a detailed study of the of these spectacular sandstone landforms. joint patterns was undertaken. It was found that generally the joints are widely spaced and their surfaces are planar, Climatic variations and associated water erosion closed and rough. Visual examination shows that the joints have seldom been weathered and altered. Some authors suggest that climatic variations, by and large, A total of *1,000 joint orientations were measured at determine the style of denudation and morphology (Tricart 11 selected sites and plotted on a rosette diagram using a and Cailleux 1972; Louis and Fischer 1979; see discussion class interval of 10° (Fig. 6). Dominant joint sets along by Young et al. 2009), with humid tropical and subtropical the Suoxi River show a similar pattern, with major ori- areas favorable for chemical and biological weathering entations tracking ENE and NNW (as shown in Fig. 6b). giving landforms dominated by vertical clifflines, whilst in Although many joints within these sandstones are rela- arid and sub-arid regions mechanical weathering and ped- tively small, only tens of centimeters to a few meters iment cliffs are common (Slaymaker et al. 2009; Young wide, numerous measurements at different locations et al. 2009). In sandstones, the duration of humid weath- within the geopark show that in many instances these ering seems to be a major constraint on denudation, and joints are highly comparable to the main trends of the episodes of climatic variations should therefore be closely sandstone peaks or cliffs. associated with periods of geomorphic development. Cli- In general, the larger-scale sandstone landforms are matic variation may also impact to a large extent on water usually controlled by two intersecting joint sets, trending erosion, permitting the presence of various sandstone approximately 70 and 330°, respectively (as shown in landforms (Wray 1997a; Young et al. 2009). Fig. 6a, b). For instance, some square and prismatic peaks The Pliocene and Pleistocene (*5.3–1.8 Ma) in eastern forests are primarily controlled by two or multiple groups China was dominated by a warm climate (Hunan Bureau of of joint sets, such as Gold Chair and Stone Buddha. Geology and Mineral Resources 1988), but it is believed At the smaller scale, the spectacular topographies of that the sandstone peak forest landforms of Zhangjiajie did many peaks are shaped by mass wasting along the smaller not begin to develop until the mid-Pleistocene. However, but denser vertical joints trending in the 30–40, 70 and the frequent glacial–interglacial climate fluctuations during 330° directions. These give many of the individual land- the Quaternary (Duan et al. 1980; Liu 2002) initiated the forms regular rectangular planforms, clearly shown in formation of these sandstone peaks. Triggered by the cli- Figs. 3, 4 and 6. mate variations and affected by intermittent uplift, the The geological structure has also clearly controlled the Suoxi River began to develop its river system during the development of river valleys, canyons and their base levels. Middle Pleistocene, leading to the initial incising into Rivers have preferentially focused on the high-angle joints the sandstone during this period. Several rapid formation and structurally weak zones; the larger platforms of some stages possibly occurred from Middle Pleistocene to the valley walls and the cliffs of peak clusters and peak forests present, revealing the four different levels of sandstone have larger elongated axes in an NE or NNW direction or landforms that are consistent with the evidence for four formed at the crossing of these fractures and joints (Figs. 1, orders of alluvial terraces along the middle and lower 5, 6; Table 3). Some of these landforms are also formed Suoxi River (cf. Yang et al. 2011b). close to river valleys tracking these fracture zones (Figs. 5, Quaternary climate and related water erosion has been 6), distinctively indicating that the bedrock structures very important to the continued development of this land- formed in response to tectonic movements have played a scape. The Zhangjiajie Geopark is currently drained by the dominant role in the formation of sandstone landforms over Suoxi River and, as already noted, rainfall and seasonal the region. linear flow, surface flow, small streams and groundwater Former tectonic movements and fracturing have thus systems are focused along joints, fractures and other been critical to the formation of the sandstone landform weakness inherent within the rock. These exert a prominent configuration, with the recent intermittent neotectonic erosive control on the expansive sandstone landscapes movements resulting in the downcutting of Suoxi River (Fig. 6). The Suoxi River is in a central area of heavy rain into the sandstone during the Quaternary, with the initial and typically shows a converging river network. The radial 123 1888 Environ Earth Sci (2012) 65:1877–1894 drainage systems around the Tianzi Mountain continue to (Fig. 4f), Three Sisters (Fig. 4h) and Fairy Scattering erode into the high plateau headwaters, leading to the Flowers (Fig. 4i). cutting of the spectacular peaks of various morphologies This differential weathering can also be seen where the (mesa or square mountain) into the edge of the platform hard rock stands out slightly to form a small ridge on (Figs. 3, 6). There is also a densely incised network of vertical faces and the relatively soft rock is recessed into a ‘checkerboard-like’ streams along the joint systems and bedded groove (Wray 1997b; Turkington and Paradise consequent downcutting into the hard, thick sandstones. 2005). This ‘sawtooth’ shape is very evident on the top of These eroding joints are constantly widening and deepen- some rock columns. This weathering control, however, ing and give rise to the form of striking sandstone peaks in only has a secondary importance compared with the effects the various river valleys. of geological structure, lithologic features and climatic Water erosion must also increase the susceptibility of variations. the sandstone to other processes of weathering, associated with development of numerous sandstone topographies at Biological and other factors different scales. For example, the erosion along the fracture surfaces will largely induce instability leading to failure of Our studies have also revealed close linkages between rock mass and helping to create diverse quartz sandstone biological and other hydro-ecological processes and land- landforms. scape forms. The abundant rainfall and water resources, dense vegetation, and high biological diversity and integ- Lithologic features in relation to sandstone landforms rity of this area are favorable for ecological stability and balance. Plant roots and biological processes clearly and The Zhangjiajie peak forest landforms have mainly actively destroy and transform the rock, and seem to have developed in the gently dipping Middle and Upper Devo- drastically decreased the resistance of the sandstone to nian Yuantaiguan and Huangjiadeng Formations, with weathering processes. This is particularly expressed in the thick-layer quartz sandstone, interbedded with many thin vegetation coverage of the top weathered layer of most layers of siltstone, and a total quartz content of more than sandstone peaks, which has resulted in, to a certain extent, 90% (Huang et al. 2006; Table 4). Because of their strong the disintegration and destruction of peak summits and the cementation with iron and siliceous cement, these sand- change in the peak body shape. stones are very stable and strongly resistant to chemical The regulating role of biology on the micro-climate also weathering (Table 4). These have a high compressive often results in the spectacular views of the region, espe- strength and commonly constitute the solid bases of the cially as the area extends over many hundreds of meters. cliff walls and peak columns. The higher purple iron- The vertical spacing of micro-climate in the mountainous cemented quartz sandstone of the Huangjiadeng Formation area also indirectly affects some natural landscapes, mak- often forms the resistant cap of peak columns. ing the views esthetically colorful, charming and imposing The gentle dip of the sandstones (usually 5–8°) is also at Zhangjiajie throughout the year. conducive to the structural stability of the many peak Solution weathering is also an important process in column formations. Even for widely separated sandstone some sandstone landform assemblages (Hunan Geo-envi- peaks, tall stone columns can be maintained for long ronmental Monitoring Center 1988), especially in those periods, because the low dips allow the center of mass of dominantly shaped by stream erosion and mass failure. the columns to be maintained vertically within the column This process can result in some minor features, but it is base area, and thus these are geomechanically stable and accepted that it is certainly not uniformly developed over resistant to toppling and collapse (Young et al. 2009). the entire sandstone area. Analyses of solution weathering in connection with sandstone landscape formation at Selective weathering Zhangjiajie will be addressed in a forthcoming study.

However, the many thin siltstone layers within the thick- layer quartz sandstones tend to weaken the whole rock. The Regional comparison of diverse sandstone landforms siltstones are less resistant than the sandstones to weath- ering and erosion, and where siltstone interbeds are com- Sandstone landforms in China mon, mechanical properties favor the sculpting of individual peak pillars into a diverse range of different Sandstone landscapes are widely scattered in most parts of shapes such as man-like and object-like shaped peaks, as China (Huang 1991, 1999, 2003; Guo 1992; Yang 1999; evidenced by the Jinbian Rock (or Golden Whip Rock Peng 2000a, b, 2002, 2007; Chen 2004; Qi et al. 2005; Cui (Fig. 3g), Palm Peak (Fig. 4d), Imperial Brush Peak et al. 2007; Hou et al. 2008), and in recent years Chinese 123 Environ Earth Sci (2012) 65:1877–1894 1889

Table 4 Lithologic components of different Zhangjiajie sandstone landscapes (after Huang et al. 2006; unit %)

Location Lithology Stratigraphic SiO2 CaO Al2O3 TiO2 ZrO2 Fe2O3 SO3 units

Baofeng Lake White iron-siliceous quartz D2yn 97.20 0.00018 1.84 0.15 0.00099 0.00076 0.00051 sandstone

White siliceous quartz D2yn 94.20 0.00039 1.66 0.00063 0.00026 0.0004 0.00044 sandstone

Jinbian Stream White iron-siliceous quartz D2yn 95.90 0.71 2.18 0.13 0.00053 0.14 0.13 sandstone

White siliceous quartz D2yn 94.00 0.51 2.94 0.23 0.00058 1.25 0 sandstone

‘First Bridge in the Yellow siliceous quartz D2yn 92.90 0.00022 1.68 0.00088 0.0003 0.27 0.00065 World’ sandstone

Baizhang Valley Red iron quartz sandstone D2yn 83.60 0.00066 10.60 0.36 0.00052 2.67 0.00075

Red thin-layer silty mudstone D2yn 67.20 0.00011 22.00 0.92 0.00035 2.17 0.0002

Xianyao Bay Red siliceous quartz sandstone D2yn 79.40 0.12 4.77 0.39 0.00076 13.20 0.00056

White siltstone D2yn 66.80 0.00021 24.70 1.30 0.00075 0.27 0.00017

Koho Red thick-layer iron quartz D3h 92.20 0.00097 5.26 0.21 0.12 0.46 0.21 sandstone

Peak forest Red iron-siliceous quartz D3h 93.50 0.00062 0.88 0.21 0.24 3.96 0.00019 sandstone

D2yn Yuntaiguan formation of Middle Devonian, D3h Huangjiadeng formation of Upper Devonian geomorphologists have devised a classification of sand- 2005; Cui et al. 2007; Yang et al. 2009). In most parts of stone landforms over a wide range of sizes (including China, a higher precipitation and more intensive tectonic Danxia landforms) consisting of 38 subdivisions (Peng uplift have favored large-scale canyons, ring-shaped 2000a; Chen 2004). Chinese Danxia landforms look very escarpments and many large waterfalls (southwest area of much like karst topography, but are a unique type of China), while elsewhere plentiful rainfall, slow crustal red-colored sandstones and conglomerates of largely uplift and a relatively stable sedimentary environment have Cretaceous age and are loosely described as ‘‘landforms promoted peak-group and isolated peak-shape landforms consisting of red beds characterized by steep cliffs’’ (southeast area of China). However, mud-coating, colum- (Huang 1991). However, the sandstone landforms of niation and plate-like sandstone landforms principally Zhangjiajie are different from Danxia. occur in the arid and semiarid climatic areas (Peng 2000a; Based on the tectonic uplift rate, annual mean precipi- Peng et al. 2004; Qi et al. 2005; Cui et al. 2007). tation, vegetation cover and their distribution quantities The sandstone landforms of the Zhangjiajie Geopark are and scales, Qi et al. (2005) recognized three relatively located just on the northwestern margin of the southeast congregated areas of sandstone landforms in the southeast, area as defined by Qi et al. (2005) and it might be expected southwest and northwestern areas of China (Fig. 7). Cui that plentiful rainfall and episodic tectonic uplift in the et al. (2007) also distinguished four types of sandstone study area have accelerated the sandstone landscape-mak- landforms (indicating three differential development ing process. The diverse topographies would also reveal the stages) termed Bryce, Zhangjiajie, Zion and Grand Canyon primary constraints of tectonic uplifting and climatic types. variation. Like that noted by Qi et al. (2005) and Cui et al. (2007), Based on these morphologic evidences and their con- the striking sandstone landforms of the Zhangjiajie area trols, we thus propose that the Suoxi River began to incise may be primarily attributed to the plentiful regional pre- the sandstones along the well-developed fractures and joint cipitation (*1,400 mm per year), relatively weak tectonic systems in the region. This, as well as later mass failure, uplift (*0.2 mm a-1, Yang et al. 2011a) and weathering has largely promoted the topographic development pro- process. gressively from mesa, peak wall, peak cluster and peak These summary findings are considered to highlight our forest to natural bridge and remnant peak. poor understanding that the sandstone landforms of China Whilst the sandstone peak forest landforms at Zhang- have been fundamentally controlled by intermittent uplift jiajie share some similarities with the Chinese Danxia and considerable climatic variations of the region (cf., landforms, there are important differences. The quartz Huang 1999, 2003; Peng 2000a; Peng et al. 2004; Qi et al. sandstone landforms in Zhangjiajie Geopark are composed

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Fig. 7 Regional comparison of sandstone landforms in China (modified after Huang 1999; Qi et al. 2005; Cui et al. 2007) of Devonian sandstone or siltstone, much finer than the Young 1986a, b, 1988; Yanes and Briceiio 1993; Wray Jurassic–Cretaceous sandy conglomerates forming the 1996, 1997a, 1997b; Doerr 1999; Martini 2000; Netoff and Danxia landforms. The unique formation dynamics in this Shroba 2001; Doerr and Wray 2004; Adamovic 2005;de study area, possibly associated with the specific geographic Melo and Giannini 2007; Cui et al. 2007; Piccini and location and geological setting, has also led to various Mecchia 2009; Wray 2009; Young et al. 2009; Figs. 7, 8). topographies at a range of scales. This is also evidently Based on the morphologic variations or geomechanical different from the Danxia landforms, which are largely properties, the sandstone landforms (including Danxia, controlled by fluvial processes. conglomerate and other kinds of sandstone landforms) can In Zhangjiajie, the deep downcutting and lateral erosion thus be briefly grouped into varying scales and distinct of fluvial process have also often given rise to the forma- types from small etch pits to large ruinform assemblages or tion of horizontal topographies on vertical cliff surfaces, undulating plateau (Young et al. 2009). leaving the harder rock above to overhang promoting the The spatial variations of Zhangjiajie sandstone land- possibility for mass wasting. This long-term water erosion forms are broadly comparable with previous studies of and intensive mass failure have remarkably led to the regional dimension (Wray 1997a, 1997b; Peng 2000a; continual formation of sandstone landform with diverse Netoff and Shroba 2001; Yang et al. 2009; Young et al. patterns. 2009). These updated findings indicate that sandstone landforms thus actually reflect the considerable climatic Regional comparison variations and spectacular neotectonic settings of a given area. Climatic variations, however, may largely disrupt As described in many pioneering scientific documents, these overall trends, particularly in areas with predominant similar landscapes have been identified in a wide variety of dry or semidry climate (Wray 1997a; Peng 2000a; Qi et al. environments around the world (e.g., Jennings 1979, 1983; 2005; Cui et al. 2007; Yang et al. 2009; Young et al. 2009).

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Fig. 8 Regional comparison of sandstone landforms; the numbers location of major sandstone landforms included in the study of Wray and characters indicate the sandstone landforms around the world (1997a). Points 1–61 indicate the location of major sandstone with specific reference to Zhangjiajie sandstone landforms (modified landforms in the book ‘Sandstone Landforms’ (Young et al. 2009) from Wray 1997a and Young et al. 2009). Points a–z refer to the

The sandstone landforms in Zhangjiajie are unparalleled sandstone landforms in some national parks in the western in the world (Cui et al. 2007; Yang et al. 2009), but the USA (such as the Grand Canyon National Park, Zion primary comparable landscapes in terms of limestone karst National Park and Bryce Canyon National Park) chiefly landforms and Danxia terrains share similar feature many stone windows, natural bridges, natural arches, traits with the Zhangjiajie sandstone peak forest land- and mesa or square mountains similar to Danxia landforms. scapes. For instance, tectonically induced deformation These should be attributed to intense tectonic uplift and often occurs in limestone, sandstone or even conglomerate only a little weathering, as well as relatively dry climates at a range scale in different places (Wray 1997a; Young and low precipitation. As a consequence, there are deeply et al. 2009), and it is common that peak forest landforms downcut valleys (with a maximum depth of [1 mile) but are closely associated with faulting, fractures and even single, or at most a few, topographic types typically prevail jointing. Near active tectonic areas with densely developed in these regions (Cui et al. 2007; Young et al. 2009). Other fractures, but relatively weak uplifting movements, are samples are from western Europe or the Brecon Beacons in prone to producing peak forest landforms, and this is evi- England, where the sandstone landforms are relatively dently supported by the distribution of most sandstone simple but widely distributed (Yang 1999; Liu and Peng landforms around the world (Young et al. 2009; Fig. 8). 2006; Young et al. 2009; as indicated in Fig. 8). The single These similarities show that episodic tectoninc uplift must categories of sandstone landforms should largely result have largely altered these landforms and pre-existing from the regional climatic variations (Young et al. 2009). landscapes. Sandstone landforms in northern and western Australia have Within a broad grouping, most sandstone terrains similar a very wide range of geomorphic forms, but with a com- to these primarily occurred in tropical/subtropical or other paratively smaller coverage area and lower peak density areas with relatively high precipitation (Wray 1997a; (Wray 1997a; Young et al. 2009). Young et al. 2009). We argue that a humid climate should In comparison, the landscapes of the Zhangjiajie sand- accelerate chemical weathering and biological weathering, stone peak forest are remarkably imposing; with their huge allowing the presence and formation of these sandstone peak density and relative height difference, large height/ landforms. Tectonic and climatic control of river erosion is diameter ratio, alternating hard–soft layers of rocks, lush also a common appearance in sandstone areas, which in vegetation, rare plant and animal species and almost intact turn promotes the widening and erosion of landform-pro- ecosystems. The 3,100 sandstone peaks are heavily vege- ducing structural lineaments. tated and very closely spaced, with a high average density However, topographic effects vary in different places of 37.5/km2, and at least 1,000 peaks exceeding 120-m with the types and sequences of rocks. For instance, height. The Jinbian Rock, in particular, exceeds 350-m

123 1892 Environ Earth Sci (2012) 65:1877–1894 height and is an inspiring sight for visitors. Many of these In conclusion, although similar landscapes have been peaks display height-to-width radios ranging from 5–7:1 to identified elsewhere in the world, the spectacular quartz 20–40:1 or even higher. However, such narrow and dense sandstone landforms in Zhangjiajie reveal the exceptional sandstone peaks are incomparable, or practically non- traits in terms of singular peak shapes, huge height dif- existent, in most other places worldwide (Wray 1997a; ferences, large height-to-width ratios and high peak den- Young et al. 2009). sity. It displays a clear model of peak forest formation and A significant conclusion that can be reached is that the may have significant implications for the interpretation of sandstone landforms of Zhangjiajie offer a clear model of possible genesis regimes in eastern China. Our results are fracture-controlled peak forest formation, ranging from evidently helpful for categorizing sandstone landforms and larger mesa, square mountain, peak wall, peak clusters and unraveling the relative controls of geomorphic evolution of peak forests down to smaller singular and remnant peaks. this study area. These diverse topographies at a range of scales clearly elaborate the integrated process of sandstone landform Acknowledgments Financial support for this work was provided by evolution from early platforms to late remnant peaks. the special funding study of ‘Formation age of sandstone peak forest landforms and geological instability in Zhangjiajie World Geopark’ Therefore, the Zhangjiajie sandstones display a superior by the Zhangjiajie World Geopark Management Committee. We are and rare geological heritage and are justifiably deserving of greatly indebted to helpful discussion with Profs. Anze Chen, Zhijiu their World Heritage and World Geopark status in terms of Cui, Naigong Deng and Keyi Guo in our research group. We would scientific and esthetic values. like to acknowledge Ms. Yan Yang and Mr. Wenqiang Shi for their partial participation in our field investigations. Special thanks must go These investigations have also highlighted important to the staff of the Zhangjiajie World Geopark Management Com- consequences for the sustainable management of the mittee, Zhangjiajie Land Resources Bureau and other departments, sandstone landforms within the geopark. Further studies in who made most of the investigations possible. We thank anonymous terms of geomorphology, sedimentology and chronology reviewers, especially the Reviewer #1, for helpful critical comments. are underway to further address the potential formation mechanisms, evolutionary process and conservation man- agement of the region. References

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