Hydrological Changes in West Amazonia over the Past 6 Ka Inferred from Geochemical Proxies in the Sediment Record of a Floodplain Lake

The Amazon is responsible for the higher discharge of water and sediment from continent to ocean in the world, but the Amazon basin embodies a large variety of regions with different seasonal climate, hydrological regimes and vegetation. Some of these compartments may be considered as the most critical zones because they encompass severe changes in the recent past and one of the geomorphological features mostly impacted by these changes are the Amazon floodplains. In this study we report data from a floodplain lake, Quistococha, in Peru. The sediment was dated, radiographed, described and bulk density, granulometry, mineral composition, and total organic carbon were determined. Two distinctive sedimentary depositional phases were identified. During the first one, between 6100 and 5600 cal years BP, Quistococha Lake was strongly influenced by the Amazon River constraining high sediment accumulation rates. The influence of Amazon River decreased and ceased around 5600 cal years BP, due to an avulsion of the River toward its present-day position. Between 5600 and 2600 cal years BP a gap in sedimentation is observed, probably related to the dry mid-Holocene climate conditions. The sedimentation re-started about 2600 cal years BP, now the lake is an isolated lake.