The distribution of coarse-grained sediments in modern Lake Turkana, Kenya: Implications for clastic sedimentation models of rift lakes

The nearshore environment of Lake Turkana, Kenya was studied to determine how coarse clastic sediments are being distributed in the modern lake. Four lake margin study localities were examined in detail: (1) an area of basaltic colluvial headlands; (2) an area of sand, sandy silt and silty mud substrates; (3) an area of highly variable substrate conditions; and (4) an area of alternating basaltic headlands and gravel/shingle terraces. Based upon quantitative observations in these areas and qualitative observations elsewhere in the lake, we believe that two interacting factors have the greatest influence on the distribution of nearshore clastics. The first is a sediment distribution system which is primarily dependent on localized supply, via rockfall and intermittent streams. The second is the presence of physiographic barriers, principally faulted and eroded volcanic flows, which border on local coarse sediment delivery systems and isolate them from adjacent systems. Volcanic barriers may operate at various scales in regulating the delivery systems of clastic sediments in rift lakes, from localized facies disruption, as observed in Lake Turkana, to the isolation of entire sedimentary basins. At the largest levels the presence or absence of volcanic activity may have an important bearing on the controversy of hydrocarbon accumulation in rift lakes.