Evolution of clay mineral assemblages and organic matte, in the Late glacial-Holocene sedimentary infill of Lake Annecy (northwestern Alps): paleoenvironmental implications

Citation
F. Manalt et al., Evolution of clay mineral assemblages and organic matte, in the Late glacial-Holocene sedimentary infill of Lake Annecy (northwestern Alps): paleoenvironmental implications, J PALEOLIMN, 25(2), 2001, pp. 179-192
Citations number
49
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Environment/Ecology
Journal title
JOURNAL OF PALEOLIMNOLOGY
ISSN journal
0921-2728 → ACNP
Volume
25
Issue
2
Year of publication
2001
Pages
179 - 192
Database
ISI
SICI code
0921-2728(200102)25:2<179:EOCMAA>2.0.ZU;2-6
Abstract
The basin fill of Lake Annecy was investigated from a 44 m core which reach ed down to glacial sediments of the last glaciation (called Wurm in the alp ine areas). We analyzed three main parameters: sediment texture (optical mi croscopy and laser microgranulometry), clay mineral assemblages (CMA by XRD ), and organic matter (OM by Rock-Eval pyrolysis). Settling of suspended lo ad, under variable hydrodynamic conditions is the main depositional process . Both CMA and OM provenances can be recognized for the different sedimenta ry and igneous-metamorphic formations (Carboniferous to Quaternary, and old er crystalline basement) and corresponding areas, in the surrounding region of Lake Annecy. Oligocene-Miocene molasses, Early Cretaceous marls, and Ea rly-Middle Jurassic marls and shales are the main sedimentary sources. Two distinct processes were operating: destruction of glacial sediments (till s ensu largo) and reworking, or direct erosion and run-off from ice-free catc hment areas. Clay minerals related to pedogenesis, and non-reworked terrest rial and lacustrine OM, were progressively added to these primary sources d uring the Late Wurmian/Holocene transition to wanner climatic conditions. R apid modifications of CMA and OM sources during the earlier phase of sedime ntary infilling (Unit 2) suggest that valley glaciers connected to the lake basin almost completely disappeared within a few centuries.