Résumé -Abstract - Zusammenfassung -:The karst deposits studied are concretions (speleothems and
travertines), lithified detritic deposits (conglomerates) and
the large underground detritic series of Dadong (Wufeng/Hubei).
The speleothems of the subtropical karsts of China are very important
in the stepped fossil systems. They are the environment recorders.
Morphologies (e.g. columnar, meshed saccharoid, mosaic calcites)
and crystalline structures (e.g. microstromatolitic, balled, oncolitic)
especially provide information about the infiltration conditions.
The detritic contaminations (grains of soil, hydroxides, eolian
dusts) provide information about the soil withdrawings, i.e.
the unsteadying of the pedologic and vegetal cover ("rhexistasie").
The distribution diagram of 58 U/Th isotopic datations shows an
important concretion phase during the upper Pleistocene, especially
during the Eemian. However, it seems that the speleothems formation
has been relatively unceasing.
Some cave sediments are preserved by the consolidation of the
detritic fillings (breccia, pudding stone). The petrographic study
of the skeleton parts provides information about the origin of
the deposits and about the original watershed. The calcitic cements
are varied, e.g. travertinous (tuffs of acicular crystals), meshed,
micritic saccharoid, etc. The fluviatile conglomerates, located
on several levels (e.g. Daxiaocaokou/Zhijin-Guizhou), provide
information about the karstification hollow during the Tertiary
uplift.
The rhythmic series of Dadong (Wufeng county), 20 to 25 m thick,
is located in the fossil level of the Dadong sinkhole-cave (+
100 m). It shows an alternation of gravel beds and layers of
varved loams. This sedimentary site is a record of the regional
hydroclimatic regime and testifies to climatic alterations lasting
several centuries or millenias. The important red colouring of
the gravels and varved seams (hydroxides resulting from the pedologic
alteration of the schistous Ordovician) testifies to soil erosion
and withdrawing. This process must have been triggered off by
a climate with very contrasted dry and wet seasons.
Keywords : Karst fillings, speleothem, travertine, U/Th dating, detrital deposit, conglomerate, breccia, loam, clay, rhythmic sedimentation, recorder, indicator, soil, alteration, erosion, climatic change, paleoclimate.