Introduction :  Karsts of Hunan/Hubei

Résumé - Abstract - Zusammenfassung :We visited regions located between 29 and 31 °N, in the Hubei and the Hunan Provinces. The landscape is a subtropical karst with cones, developed in mountains ranging from 200 to 2 000 m a.s.l. The main caves are tunnels and sinkholes where the galleries and the shafts are very wide. They are crossed by big underground rivers, flowing from impervious outcrops. The karsts are developed in a very wide geotectonic unit covering most of the Yangtse basin : the Yangtse folded paraplatform. The carbonate rocks range from the Sinian (Upper Precambrian) to Middle Triassic and are very thick (more than five thousand meters). Cenozoic exists only as continental sediments : conglomerates and red beds filling inter mountainous basins. The whole Upper Proterozoïc and Lower Palaeozoic has been lift up during the end of the Lower Palaeozoic (Upper Caledonian uplift). During Devonian, most of the Yangtse paraplatform was above sea level (and some parts during Lower Carboniferous). It was lift up during Permian and Lower Triassic (Hercynian orogenesis in Europe). During Permian and Trias, the sea came back and deposited some of the most thick carbonate beds of the Earth. The sea withdraws during Middle Triassic, with the beginning of the Yangshan orogenesis. It is divided in three stages (Jurassic, Cretaceous and Eocene) and is very important for us because it is responsible for the present folded structure of the development of the main karsts in Central and Southern China. During Cenozoic (Oligocene to Quaternary), the Himalayan orogenesis produced a general uplift and consequently the valleys deepened and the caves developed new gallery levels. Today, the climate of these regions is subtropical and humid with contrasted seasons (monsoon rains and continental influence). Annual rainfalls range from 1 500 to 1 800 mm/year. Summer is hot and wet and winter is cold and quite dry.

Keywords: Karst, cave, geography, geology, orogenesis, climate, Central China, Hubei, Hunan.