Chronology and depositional processes of the laminated sediment record from Lac d'Annecy, French Alps

A high resolution sediment record spanning the entire time since the ice re treat after the Last Glacial Maximum has been recovered from Lac d'Annecy. The main focus of this study is to develop a reliable chronology of the rec ord and to evaluate the environmental variability during the period of Late Wurmian ice retreat. Most of the record is laminated. These laminations ar e of different structure, composition, and thickness. On the basis of varve stratigraphy five sedimentation units were identified which correspond to particular stages in the deglaciation of the region. Except for one each fa cies type has been related to an annual cycle of deposition. Varve counting in combination with radiocarbon dating provides the time control of the re cord and dates the base of lacustrine deposits to 16,600 varve yrs BP. The beginnings of the Late Glacial is marked by a shift from elastic to endogen ic carbonate varves caused by the climatic warming. Clastic varves have bee n further subdivided into a succession of complex and standard varve types. These variations of elastic varve formation are triggered by the ice retre at and related hydrological variations in the watershed of the lake. Sedime ntological, mineralogical and isotopic data help identify different sedimen t sources of the sub-layers. Proximal sediments originate from local carbon aceous bedrock whereas distal sediments have characteristics of the molassi c complex of the outer Alps. The alternation of proximal and distal sedimen ts in the varve sequence reflects the deglaciation of the Annecy area with a changing influence of local and regional glaciers. The melting of the Alp ine ice sheet is the driving force for regional environmental changes which in turn control the sediment transport and deposition processes in Lac d'A nnecy.