Abstract
An analysis of the Koobi Fora Plateau Gravel, N Kenya, reveals clear-cut but contradictory patterns of sedimentary sorting. Basalt particles form the major constituent and decrease in diameter downstream at a rate of 3 mm km-1, while feldspar is virtually eliminated from the sediment within 30 km. But over the same ground, agate particles increase in size more than 4-fold while the sphericity of quartzite clasts decreases. These apparently conflicting sorting patterns are used to formulate a clearer understanding of the sedimentary processes that operate in widespread gravel deposits. The nature of the basalt particle size-gradient is contrasted with those published for alluvial fans and simple undivided channels to suggest diagnostic features that distinguish braided channel deposits.
