THE LAC PAVIN SEDIMENT CORES (MASSIF CENTRAL, FRANCE) - CHRONOLOGICAL AND PALEOENVIRONMENTAL INFORMATION FROM VARVED SEDIMENTS

Proxy data derived from annually laminated lake sediments provide a great potential for analysing climatic and human response signals in association with an absolute chronology. Lake sediments, from Lac Pavin (45°55’N; 2°54’E) (Massif Central, France), provide valuable proxy data for the reconstruction of the late Quaternary environmental history in this region.

The Pavin maar is the youngest volcano of the Chaîne des Puys with an age of the volcano still a matter of debate (Camus et al. 1973; Guenet 1986; Juvigné & Gilot 1986). Lac Pavin is located in a mountain range about 1200 m asl. The lake is circular in shape with a mean diameter of 750 m and a max. depth of 96 m. The water column is characterised by a permanently anoxic monimolimnion. Never before was a complete sediment core drilled in the lake.

During a field trip in December 1999 a 180 cm long surface core was drilled (Brüchmann et al. 2003). Distinct silty laminae contain diatoms, vivianite and siderite. The laminae comprise several diatom species with distinct layers consisting mainly of one or two planktonic species. These mono- or duospecific layers alternate with layers mostly comprising benthic species, such as Epithemia spp., Fragilaria spp., Rhopalodia spp. and others, in addition to siderite, vivianite and organic particles. The seasonal variations in these diatom blooms indicate that the laminations represent annual layers. On the basis of preliminary varve chronology, the analysed sediment sequence covers the last 600-700 years.

In 2001 a ~1100 cm long core was recovered from the lake to enable the reconstruction of the paleoclimate for the last ~ 6,000 yrs. on an annual scale. A composite profile from the laminated olive green up to black sediment was made from two parallel cores. Thin section investigations using a light microscope allowed counting of the varves and produce, in combination with the biological investigations, a chronology. For the first time we present the results of analyses of chronology, sedimentology, geochemistry, diatoms and pollen.

References:

Camus, G. et al., 1973: C. R. Acad. Sci. Paris 277, 1121-1124.

Guenet, P., 1986: 11e réunion des Sciences de la Terre, Clermont Ferrand, Soc. géol. France (éd), 86.

Juvigné, E. & Gilot, E., 1986: Z. d. DGG 137, 613-623.

Brüchmann, C. et al. (2003): 3rd Int. Limnogeology Congr. (ILIC 3).