The microfacies of the eemian caours tufa (Somme, France, MIS 5e): Data to A palaeoecological analysis of the last interglacial [Les microfaciès du tuf calcaire éemien (sim 5e) de caours (somme, france): éléments d'analyse paléoécologique du dernier interglaciaire]

摘要

Calcareous tufa deposits are essential record of the climatic evolution and its environmental responses during Pleistocene Interglacial in Western Europe. A petrographical study of 34 thin sections from Caours tufa deposit was compared to other palaeo-ecological data, such as mollusk and ostracod fauna and to the results of sedimentological analyses. In the lowest part, fine detritical alluvial deposits show the transition to interglacial conditions. Above, the tufa deposit is precipitated by cyanobacteria of the fossil genus Broutinella, Ponsella and Ponsinella. Broutinella and Ponsella built well crystallized stromatolites in and at the top of channels. Broutinella also builts a massive tufa qualified as "cauliflower". This facies precipitates in places always in water and associated to aquatic mollusks and ostracods. In massive tufa, Ponsinella dominates the "mille-feuilles" facies associated to dry phases and mainly terrestrial malacofauna. Consequently, the facies diversity compared to malacological data shows palaeoecological variations during the 5e interglacial.