High-resolution sedimentary record of the last deglaciation from a high-altitude lake in Ethiopia

Abstract

Sedimentological and geochemical studies conducted on a 15.82-m long core collected from Lake Garba Guracha (Ethiopia) associated with a precise AMS- 14C time-scale document a unique record of the sedimentary processes linked to the progressive retreat of a high-altitude glacier in the Bale Mountains since 17,000 yr cal BP. Lake sedimentation is interpreted as the result of discharges of meltwater and glaciogenic sediment which progressively filled the accommodation space generated by glacier retreat within the basin. Monogenic sediment originated from glacial erosion of the trachytic tuff forming the cirque floor. Ice melting ended progressively between 12,600 and 11,800 cal BP, as suggested by the decrease in sedimentation energy followed by a sharp change in sedimentary facies. From 11,800 cal BP, the lake reached its maximum development and clastic input was replaced by organic-rich sedimentation. This relates to a major increase of lake productivity, which lasted up to 4500 cal BP. From this period, a lowering in productivity reflects the widespread dryness which occurred throughout the East African tropics.