Résumé
PALAEOENVIRONMENTAL CONTEXT INFERRED FROM HOLOCENE DEPOSITS OF LAKE IFFER (MIDDLE ATLAS, MOROCCO) Moroccan middle Atlas is a climatically sensitive area to the influence of Mediterranean sea, Saharan desert and Atlantic ocean air masses. It encloses several natural small lakes preserved from anthropogenic perturbations. A ten-meter-long core from lifer lake provided a record of palaeoclimatic and paleohydrologic conditions in the Middle Atlas during the last 6 500 years. Magnetic susceptibility, organic and inorganic geochemistry and granulometry show that lake sediments contain detrital silt layers rich in organic matter alternating with marl layers rich in authigenic carbonates linked to the regional climatic variability. The main results are:
- lacustrine records started at about 6 500 years BP with yellowish carbonate-rich sands corresponding to the lake settlement. This period was characterized by warm and dry climate,
- the 4600-2 000 years BP period is characterized by the establishment of wetter climatic conditions with high lake level levels interspersed by relatively abrupt dry events,
- during the last 2 000 years, the human impact due to increasing pastoral and agricultural activities caused the decline of forest. This deforestation is indicated by a strong disequilibrium of pedological profiles (erosion of soils) and high detrital inputs in the lake.