Donghe 92 Summary

Chapter 9: Morphological Evolution of the Hubei karst


Résumé - Abstract - Zusammenfassung :  The genesis of the Chinese tropical karsts is complex because it was very long and linked to many parameters. The most developed karsts combine a strong hydraulic potential, a vegetal and pedologic cover (biogenic CO2 and organic acids) and high rainfalls. These conditions occur in the equatorial humid mountains. The bio-climatic and tectonic parameters are thus very important and influence simultaneously the karst genesis.
The karsts in Central and South China belong to ancient carbonate platforms (Palaeozoic and Trias) who emerged from the sea during the end of Trias. So, they evolued in continental conditions during 200 millions of years, with orogenis stages separated by long erosion periods after which the reliefs were sometimes completely eroded (karstic peneplain). These peneplain stages occurred partially or totally during Jurassic and Cretaceous, between the tectonic stages Yanshan 1 (Jurassic), Yanshan 2 (Cretaceous) and Yanshan 3 (Eocenous). The Himalayan orogenesis began during Oligo-Miocene, with a strong epirogenesis and is still continuing.
In this paper, we discuss about the fluvio-karst and the evolution from cone karst to tower karst with corrosion plains. The shaping of a cone karst by erosion of a flysch cover is proved in Wufeng county. Fluvio-karst is very frequent in the South China's tropical karsts and has been quoted by many authors. So, in the tower karsts of the Guizhou and Guangxi Province, you can see semi-karstic basins ( largely impervious ) bordering completely karstic areas. That explains the great number of tunnel caves, trough which residual hills are crossed by surface rivers. During the genesis of such a relief, there is a competition between uplift and erosion down to the base level. When the negative forms reach the regional base level, lateral corrosion occurs, giving depressions and poljes with a flat bottom drowned during the rainy season. This lateral evolution transforms cones into towers. Gravity is a major factor, leading to the collapse of the cone walls. The Central China's karsts are less developed than the Guangxi tower karsts. This is linked with the quick uplift and folding since Middle Cenozoic. After a long quiet period, the evolution should give the same tower landscape.

Key-words: tropical karst, geomorphology, pedology, tectonics, fluvio-karst.


Karstologia Mémoires N° 6 Année 1995 DONGHE 92 - ISBN : 2-7417-0162-8