Soil reactions to extreme environmental stress: lessons from the past records

摘要

Two paleosol sequences of the Late (South France) and Middle Pleistocene (South China) were investigated using a high resolution approach associated with SEM-EDS and XRD analysis oh selected grains. This approach has enabled us to distinguish the repetitive succession of an initial pedogenic phase, ending by a soil disruption in response to an abrupt event. In South France, the sequence is terminated by a cryogenic episode associated with poor drainage as indicated by the hydromorphic characters thatare superimposed on the earlier pedogenic events. In South China, the disruption episode is associated with the presence of macro and micro-tektites which leads to interpret this disruption as due to a cosmic airburst. The clear signatures of exceptional events in these Pleistocene paleosols have at present no analogue in modern soils. Their considerable high amplitude in comparison to the gentle stress that is generated by the global warming suggests that paleosols are of limited use for predicting effects on soils of the ongoing atmospheric change.