Basis of Comparative Analysis

It is important that any comparative analysis should compare like with like. It is clear that Danxia sites can be compared on the basis of geology (continental red bed lithology), although the geomorphology is rather more problematic. The Danxia landscape is a product of dissection by fluvial action of greatly fractured, usually near-horizontally bedded (sometimes with low dip) terrigenous sediments (not solely sandstones, but also conglomerates, siltstones and some evaporites). Logically this process would lead to the production firstly of plateaus dissected by river-cut canyons and gorges, then to valley widening and valley-side collapse, to produce more isolated table lands, and ultimately to a more open landscape with mesa and buttes representing the remnants of the former plateau. Theoretically such a process would lead to angular or rectilinear landscape forms, particularly in arid and semi-arid climates, but in the warm humid climate of SE China many Danxia sites have rounded and fluted slopes, with groups of bell-shaped hills, indicating a very active surface weathering regime. Thus it appears that the process of tectonically-controlled fluvial dissection of plateaus described above is supplemented or overprinted by significant surface weathering, in some sites producing a landscape visually analagous to cone karst (but it is not correct to call Danxia sandstone karst or 'psuedokarst').

A fundamental geomorphological question is the nature of the weathering that causes slopes to become rounded and fluted. The Danxia sediments are relatively young (Cretaceous), mainly sandstones, siltstones and conglomerates. While some quartz dissolution of the sandstones may occur, some of the Danxia rocks may have a carbonate cement, which is more susceptible to dissolution than quartz. However, dissolution is not thought to be the most important weathering process, and the rounding and fluting of slopes is more likely to be an effect of weakening of the shear strength of the clayey sedimentary rocks due to poor mineral overgrowths and saturation with water.

The particular values of this serial nomination and the bases upon which it should be compared with other similar sites therefore are:

1) Danxia geomorphology is more extensively developed and diverse in China than anywhere else in the world
2) The serial nomination illustrates a complete geomorphic system and evolutionary equence
3) The serial nomination embraces a unique assemblage of landforms, as a group not replicated with the same quality or as complete in any other world location
4) The China Danxia's red bed geology signifies a particular geological climatic period and environment not well represented in the World Heritage List
5) The Danxia landscapes of SE China have formed in one particular group of rocks, under a particular morphoclimate regime, and under particular tectonic conditions
6) The China Danxia harbours largely untouched forest, of high biodiversity and with important protected species
7) The Danxia landscapes of SE China have unrivalled, majestic and colourful scenic beauty,. Each landscape is a combination of imposing vistas of table mountains and peak forest, abundant exposed red rock in cliffs and ravines, extensive forest cover, superb and highly visible wildlife, and abundant water courses (as large rivers , mountain streams and lakes)
8) The serial nomination claims Outstanding Universal Value under scenic, geomorphological and biological criteria (vii, viii, ix, x)

Technical note on the difficulties of comparative analysis and on the titles of the columns in the following tables.

Danxia-type landscapes are present throughout the world, but very little research has been undertake on any of them, in particular of their biological and geomorphological values. However, both of these values are heavily influenced by climate. Climate therefore is an important comparator.

Nevertheless, while biology responds relatively rapidly to climate change, modification of landscape form (geomorphology) is much slower, and it is suspected that some Danxia-type landscapes throughout the world may still exhibits forms that were developed in a previous climatic regime. There is also some evidence that the length of time that Danxia-type rocks have been exposed to the atmosphere (ie.,weathering and erosion) may have influence on the landforms we see today. Thus, when considering the evolution of any Danxia-type landscape in any part of the world, it is essential to know the length of time the rocks have been exposed to exogenetic processes, and how these processes might have changed (for example from humid to arid-type processes, or vice versa) over that period of exposure. What we observe in any physical landscape may therefore be an illusion of the truth. It is therefore necessary to ask the question: to what extend are the landscapes we see today fossil landscapes, fossil landscapes undergoing modification in the contemporary climate, or wholely the product of the contemporary climate The answers to this question is not known in any Danxia-type landscape in the world, It is therefore not possible with the current state of knowledge to compare Danxia geomorphological landscapes on the basis of their morphogenesis, which means that comparison is only possible on the basis of the visual appearance, or form, of the landscape.

A simple grouping of the different types of landscape is therefore necessary. As noted above, some Danxia landscapes contain rounded slopes, while others are angular or rectilinear, and still others have combinations of these land forms. While we may speculate on possible causes for these different landscape forms (e.g., angular forms from mechanical weathering in arid or cold climatic conditions, rounded forms caused by mixtures of physical and chemical weathering in warm, humid climatic conditions), the determining processes are not known definitively, and so any classification must be solely descriptive. Even here, the 'types' of Danxia landscapes are not clear-cut, because some (as in this serial nomination) have formed discrete mountainous area, while others occur because sedimentary red beds have become exposed and eroded through the widening of major river valleys (e.g., the Grand Canyon, or Three Parallel Rivers) or previously glaciated valleys (e.g., Pyrenees - Mont Perdu, or Canadian Rocky Mountains).

Another problem in identifying like for like is the degree of completeness, or integrity, of the geomorphological landscapes. As a first base to identifying Danxia world-wide it is possible to locate important outcrops of continental red sedimentary beds, but these do not always form complete, discrete (closed) geomorphic landscapes. The places where such landscapes are known in the world are very few and in any case on the basis of our present scientific knowledge are difficult to identify.

In summary, Danxis can only be compared around the world by description of form and not by origin. Furthermore, while climate is an important controlling factors, climatic information is only of sufficient to be able to use it at the macro (world) scale, rather than at the local or site level. Geology, geomorphology and climate are also controls on biology, but again a lack of information from sites across the world precludes any attempt to produce a deep, meaningful comparison, other than in world climatic zones.