Reconstruction of environmental and climatic dynamics during the Eemian (MIS 5e, 130-115 ka) in temperate Europe through malacological and isotopic analysis of calcareous tufas

Reconstruction of the Eemian interglacial environmental dynamics (MIS 5e, 130-115 ka) is essentially based on the study of long palynological sequences but remains limited in Western Europe due to the scarcity of lacustrine deposits. Therefore, calcareous tufas have been favoured in recent years as they are widely distributed on the continent and are particularly useful for the study of Pleistocene interglacials. These carbonate deposits identified in alluvial valleys with calcareous substratum are formed in temperate climates and in waters at ambient temperature. An approach combining malacology and isotopic geochemistry (δ¹⁸O and δ¹³C of tufa calcite) used on several Pleistocene calcareous tufas has demonstrated its effectiveness for the detailed reconstruction of environments and climates of past interglacials.

This study mainly focuses on the malacological contribution. Mollusc carbonated shells are particularly well-preserved in calcareous sediments such as tufas and are powerful bioindicators for palaeoenvironmental studies. Indeed, these small organisms are very dependent on their environment and have reduced mobility and thus provide a strong local signal of plant cover. In addition, identification to the species rank allows deeper palaeoenvironmental interpretations.

This study of Eemian calcareous tufas along an east-west transect in temperate Europe aims to report on the evolution of malacofaunas and associated environments during this period. Similar data obtained for the Holocene show a decrease in biodiversity towards the west, linked to a distancing from the main European refuge area, the Carpathian Mountains. Since the current distributions of species on the continent are intrinsically linked to Quaternary climate fluctuations, the existence of a similar gradient remains to be demonstrated for Pleistocene interglacials. This study will ultimately improve knowledge on the chronology of the Eemian interglacial in Europe (palaeoenvironmental axis), on the current and fossil distribution of molluscs (biodiversity/palaeobiogeography axis) and will establish the palaeoenvironmental context of associated archaeological sites. Two Eemian tufas form the core of this project: Resson (France) and Burgtonna (Germany). This communication will present the preliminary results obtained at both sites.

At Resson, the malacological analysis highlights the importance of this site as a new reference sequence of the Eemian in northwestern Europe by uncovering several diagnostic species of the period and identifying the maximum forest development at the top of the sequence, in agreement with the results of isotopic geochemistry for the climatic optimum.

Burgtonna tufa, formerly known through the work of Mania (1978), has been selected for its impressive malacological content (more than 50 species and 8 phases of forest cover development) and the accuracy of the chronological attribution to the Eemian. Field observations and preliminary results confirm the excellent preservation of shells and the richness of the malacological cortege.