Une biocénose remarquable dans la mare temporaire méditerranéenne de Lanau en Crau (Bouches-du-Rhône, sud-est de la France)

International audienc

Une biocénose remarquable dans la mare temporaire méditerranéenne de Lanau en Crau (Bouches-du-Rhône, sud-est de la France)

International audienc

Late Holocene water level fluctuations of Lake Afourgagh (Middle-Atlas Mountains, Morocco) inferred from charophyte remains

International audienceWater level fluctuations of Lake Afourgagh (Middle-Atlas Mountains, Morocco) over the last 2500 years (Late Holocene) have been reconstructed using charophyte remains in the lake sediment archives. The study involved 22 pits (1-3 m deep) dug along a transect across the lake shore terrace. Biogenic activity appears to be a dominant contributor to the accumulation of the lake sediments, as the thickest deposits are tufas composed of charophyte-encrusted stems with numerous gyrogonites (termed "charophyte tufas"). The gyrogonites were identified as Chara aspera and Chara hispida remains. The spatial distribution of these two species, measured vertically within a single core and horizontally along the shore terrace, varies according to bathymetry. Shallow proximal environments are characterized by the development of C. aspera, whereas C. hispida remains are mostly observed in distal sediments. Moreover, according to their ecological characteristics, the C. hispida belt migrated proximally when the water level rose, whereas the C. aspera belt migrated distally when the water level fell. These trends were observed successively in a single charophyte tufa layer which records the rise, highstand, and fall of lake level in a single depositional sequence. The late Holocene palaeobathymetry of Lake Afourgagh was inferred by comparing data on charophyte remains and deposit geometry. Data provide evidence for four major low lake level phases (estimated in terms of amplitude) which induced the development of palaeosols in proximal settings at 2191 cal. BP, 1769 BP, 1515 cal. BP and 1062 cal. BP. These results confirm the accuracy of charophyte-based palaeobathymetry studies

A 4500-YEAR OSTRACOD RECORD FROM LAKE SHKODRA (ALBANIA): PALAEOENVIRONMENTAL AND PALAEOCLIMATIC RECONSTRUCTION USING A MULTI PROXY APPROACH

During September 2003 several cores were drilled from the Albanian side of Lake Shkodra. Among them, a 7,8 m long composite core (SK13), drilled at a lake bottom depth of 7 m in the central southern part of the lake (42°6’11.65”N, 19°25’18.96”E) has been selected for multidisciplinary analysis. Ostracods, characeae, pollen, CaCO3 content and stable isotopes were studied with the aim to reconstruct the palaeoenvironmental and palaeoclimatic changes occurred during the Late Holocene. The chronological framework of SK13 was established through the recognition of four well-dated tephra layers and four 14C accelerator mass spectrometry measurements; the sedimentation rate has been calculated as spanning between 1.1 and 3.0 mm/yr in the different portions of the composite sediment core (SULPIZIO et al., 2010, VAN WELDEN et al., 2008)