Interaction of geomorphological processes on the north-eastern Tibetan Plateau during the Holocene, an example from a sub-catchment of Lake Donggi Cona

Abstract

Geomorphological landforms on a large alluvial fan and neighboring areas on the eastern side of the Donggi Cona show a complex spatial pattern. Sediment availability is an important factor in the formation of these archives and is partly associated with lake level fluctuation. Different sedimentary archives therefore show a similar geomorphological signal while in some cases similar archives are related to different forcing. The chronology of the processes is based on 22 optical stimulated luminescence (OSL) ages obtained from coarse-grained quartz or potassium-feldspar. The base of the alluvial fan formed during the late Pleistocene but deposition of cover sediments on the fan only started at around 7ka ago. Silty sediments form a thin cover on the uppermost terraces and have been available only during short timespans. Most of the sediments are sandy deposits which form an internal sediment cycle on the fan. They developed throughout the Holocene. Sandy deposits on the footslopes of the neighboring hills have been preserved since the Pleistocene-Holocene transition. Thicker eolian deposits accumulated during the late Holocene. These sediments were washed into the Donggi Cona and formed sandy lake sediments which were susceptible to remobilization during lower lake levels. In combination with drier climatic conditions during the late Holocene these sediments formed small dunes on the fan. Sediments on the alluvial fan are highly active, for which erosion and deposition vary in space and time. The interaction of fluvial and eolian processes is an important part of this dynamic high mountain system.