Climate shift recorded at around 10 Ma in Miocene succession of Samburu Hills, northern Kenya Rift, and its significance

Abstract

Abstract A significant climate shift around 9.6 Ma has been detected from the Middle to Upper Miocene Aka Aiteputh and Namurungule Formations exposed in the Samburu Hills, northern Kenya. Around 9.6 Ma, changes in sediments are recorded from the red soil-dominated interval of the upper Aka Aiteputh Formation to the lacustrine and deltaic facies of the lower Namurungule Formation, containing open woodland/savanna mammalian fauna. These reveal a shift from a dry climate with seasonal precipitation to a climate with strong seasonality. In particular, an increase in precipitation was recorded by the predominance of lacustrine facies. This shift happened at around the same time as the intensification of the Indian summer monsoon that has been detected in the Himalayas and some of surrounding regions. There are two scenarios that could explain the increased precipitation at the beginning of the deposition of the Namurungule Formation: (1) enhanced moisture transport by the Intertropical Convergence Zone (ITCZ), synchronized with Indian summer monsoon intensification, or (2) intensification of the Indian summer monsoon itself, permitting moisture to penetrate deep into East Africa if the altitude of the rifted area was lower than it is now. Presently, the former is considered to be the more plausible explanation for the climate shift detected in the Samburu Hills.