Late Holocene sedimentation rates and geomorphological significance of the Ncamasere Valley, Okavango Delta, Botswana

This paper presents the preliminary results of geomorphological and sedimentological investigations in the Ncamasere Valley, a seasonally back-flooded tributary of the Okavango River in northwestern Botswana. Geomorphological studies indicate the importance of the Okavango River flood regime for determining the past and present hydrology of the Ncamasere, and suggest that water levels in the Okavango have been up to 1.5 m higher at times during the Holocene compared to maximum historical flood levels. A series of cores supported by four radiocarbon dates, taken in a transect along the valley, indicate the chronology of mid- to late-Holocene sedimentation since c. 3850 yrs BP. Analyses reveal that much of the sedimentary fill within the valley is derived from Okavango back-flooding as opposed to down-valley transportation. Studies of organic horizons within cores indicate the differences in organic material generated within different ecological habitats within the Okavango system and confirm the highly dynamic nature of organic cycling within this wetland environment.