Shore-zone sedimentation and facies in a closed rift lake: the Holocene beach deposits of Lake Bogoria, Kenya

Small beach bars, spits, and barriers, composed predominantly of coarse sand, granules, and pebbles, are present along much of the modern shoreline of Lake Bogoria, a perennial saline, alkaline lake in the Kenya Rift Valley. Study of their distribution and composition indicates that most of the sediments are derived from peripheral fan-deltas, including material brought down in flood, and that derived by erosion of older exposed fan-delta sediments. Much of the sediment is redistributed by longshore currents, induced by winds funnelled along the axis of the lake.

Surrounding the lake, a series of regressive littoral terraces, composed of angular gravels, record shoreline sedimentation associated with former higher lake levels during the Holocene. During terrace formation, many fan-delta platforms were drowned and shoaling effects reduced, thereby increasing wave energy around much of the shoreline. The terraces record a complex history of Holocene lake-level fluctuations.

Although small saline lakes are unfavourable locations for beach development, a combination of factors, including the elongate form, significant fluvial inflow, and steep margins to supply coarse debris to the shore zone, permit a narrow zone of littoral clastic accumulation.

In terms of resources, shoreline clastic sediments in rifts can host metalliferous placer deposits, and can be sources of lime and aggregate. Their potential as hydrocarbon reservoirs increases with lake size and the quartz content of the catchment rocks. Littoral sands in volcanic-rich catchments are unfavourable owing to their high reactivity during diagenesis.