Chapter 11: Morphogenesis of subtropical karst in south China

Résumé -Abstract - Zusammenfassung -:The actual karstification is controlled by a subtropical humid monsoon climate of contrasting seasons. The deteriorated forest cover is no longer able to serve as a filter and the denuded soils are washed into and from the karst. The specific dissolution-40 m3/km2/year-is moderate, e.g. when compared with the superhumid equatorial karsts of Borneo or New Guinea. Two main types of karst relief can be observed after the chinese terminology :
- fenglin-polje  (tower and cone-karst with poljes), which is the prevalent type in the south (Guangdong, Guangxi provinces), which corresponds to the moderately folded limestone platform of the "geosynclinal zone of south China" (max. altitude 700 to 800 m).
- fenglin-ouvala (tower and cone-karst with ouvalas) examples of which can be found further to the north (Yunnan, Guizhou, Hubei, etc.) and which is associated with the "Yangtse paraplatform", which was folded and karstified in the Jurassic-Cretaceous during the Yanshan tectogenesis and uplifted considerably along with the Himalayan uplift during the Tertiary (plateaus : 1200 /1500 m ; summits :  2000 to 2300 m).
 These two types of relief depend on perenial dissolution under soils,  morphotectonic conditions and their relative location to the base level (role of uplift). These reliefs have developed in all kinds of limestones and dolomitic limestones of Upper Paleozoic to Triassic. Calcite predominates dolomite and the latter contributes few to fenglin.
 The Cretaceous to Eocene red formations are detritic deposits (conglomerates, sands, silts) derived by the erosion of red soils and reliefs in the course of the Yanshan orogenesis. Intermontane and piedmont red formations can be distinguished. The series can exceed a thickness of 500 m. The old alterations, transportations and sedimentations downvalley in the geosystem took place at the end of the Cretaceous and at the beginning of the Eocene with lofty reliefs. Quarternary erosion of this cover laid open and thus revealed a crypto-karst. Now, in the "stone forest", the morphology of wallkarren is only the result of susbsequent external dissolution. The recent decapitation of soilcover is a result of deforestation and reveals subsoil karren of several metres of depth which represent a stage of "stone forest". Red formations and revealed crypto-karst suggest that the Cretaceous period was characterized by strong alterations of relief accompanied by a crypto-karstification varied only by the disposition of limestone strata.
 The reliefs of fenglin and qiufeng are pierced at several levels by fossil caves subsequently cut by erosion. These cave levels relate to ancient tunnel-caves abandoned by their rivers in the course of the Tertiary to Quarternary uplift which still continues today. The upper levels have disappeared as a result of karstic erosion. The superposition of the cutting of the tunnel-caves is also affirmed by old perched fluvial deposits found, for example, in Daxiaocaokou in Zhijin, Guizhou (see chapter 9).

Keywords: Geomorphology, karstogenesis, speleogenesis, dissolution, tectonics, fenglin-polje, fenglin-ouvala, tower-karst, cone-karst, red soil, red basin, crypto-karst, tunnel-cave, cave level, South China.