Grottes et karsts de Chine
Sur les traces de Xu Xiake

L'eau goutte à goutte finit toujours par percer la pierre. Parcourir dix mille li, lire dix mille livres.

Climatic changes and human impact recorded in the karst infillings of central China (Hubei).

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Climatic changes and human impact recorded in the karst infillings of central China (Hubei). Grottes et karsts de Chine... Sur les traces de Xu Xiake

Climatic changes and human impact recorded in the karst infillings of central China (Hubei).

Résumé - Abstract - : In the mountainous subtropical karsts of central China, detritic fillings are formed from allogenic elements like soils. They are related to climatic breaking. In the giant Dadong cave (Wufeng county), two sections were studied. The older one, 25 m thick, is located in an old fossil gallery, 100 m above the sinkhole. This laminated deposit shows an important hydroclimatic change which could be Middle or Lower Quaternary. The other deposit is younger : a fossil wood (18 590 ± 160 y BP) lies on the bottom of 20 to 30 m of brown laminated deposits. These subtropical karsts, especially at medium altitude, are very good recorders of the climatic evolution since the end of Tertiary. In-situ neoformations certify the role of sulfo-bacteries and algae in the biosedimentation and registration of paleoclimate under the soil surface. Moreover, some cave fillings contain charcoal (Yanziping, Wufeng). These pieces of coal, like the polje fillings, are the proof of the destruction of the forests by man during the last millenaries. These deposits are subactual (beginning of the 20 th century and before 1950 by C14). Some are corresponding to a long period of destabilisation due to forest exploitation for metallurgy of steel. Others are witnesses of extensive cultivation of the Mao era.

Key-words : endokarst, infillings, varves, datings, environment, paleoclimate, deforestation, soil erosion.



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