Chapter 1 – General Geology of Kenya

Abstract

The oldest supracrustal rocks in Kenya are the Archaean Nyanzian meta-volcanics and the Kavirondian meta-sediments. These rocks are found to the west of the country in the areas adjacent to Lake Victoria. The Neo-Proterozoic Mozambique belt rocks occupy the central parts of Kenya. These are in most parts separated from the Archaean rocks by the Tertiary volcanics associated with the East African Rift System. The eastern parts of Kenya from the north to the south are dominated by sedimentary rock sequences ranging in age from the Jurassic to Recent. Large volumes of sediments are also found within the rift floor. Faulting and rifting characterizes the Mesozoic and Quaternary rocks and sediments. Sedimentary deposits of the Permo-Triassic are as a consequence of faulting and subsequent rifting during the break-up of Gondwanaland leading to the distribution of Karoo-like sediments in an intracratonic basin to the east along the Kenyan coast. These sediments are extensively exposed in the south-eastern coastal region and are locally referred to as the Duruma Group, while the small exposures to the northeast are referred to as the Mansa Guda Formation. Notably, Jurassic shales and limestones associated with shallow to deep marine environments are present alongside the Permo-Triassic sediments. The development of the East African Rift System led to the distribution of the Quaternary volcanics and sediments on the floor of the tectonic rift valley trough. Evidence of the Cenozoic history that is characterized by relict erosion surfaces is seen on certain areas of the coastal zone. Quaternary sediments are widely distributed in the country with extensive deposits in the eastern region (east of the Rift Valley) with limited exposures to the northwest.