The Lukeino Formation is one of a series of volcanic and sedimentary units in Baringo District, Kenya, which together span much of the Neogene and Quaternary periods. Outcrops of the Formation occur over an area of about 450 km2 to the west and north-west of Lake Baringo, and east of the Tugen Hills range.
The Formation contains an abundant and varied fauna, including Hominidae and Cercopithecidae, dated as upper Miocene on both radiometric and faunal evidence. It is equivalent to the upper parts of the Turolian Land Mammal Age, and is the only known fossiliferous unit of its age in sub-Saharan Africa.
Over 140 metres of sediment, exposed in the type section, comprise principally diatomaceous silty tuffs and shales which are considered to have accumulated slowly under lacustrine conditions. However, there are substantial piedmont and fluviatile facies as well as some primary volcanic material in the sequence.
It has been possible to reconstruct details of the palaeogeomorphology of the basin as well as the palaeoenvironmental, sedimentary and structural history of the area. The climate is considered to have been dominated by seasonal variation in rainfall in an area with both large trees and bushland/grassland. The lake was probably fresh throughout its existence, although the presence of algal mats in lake margin sediments might indicate slightly saline conditions for part of the time.
The general conditions of basin formation, sedimentation, volcanicity, burial and subsequent exposure of the Lukeino succession have parallels in several other units in the Baringo area and elsewhere
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