Mesozoic History of the East Coast of Africa

Abstract

SEVERAL recent contributions on the history of the Indian Ocean and eastern coast of Africa^1–4 can be supplemented from other sources of information. Contrary to a general view which still persists⁴, the East African coast must have originated long before the postulated Cretaceous movements, for there is abundant evidence that a Mesozoic sea invaded the modern coastal area of Somalia, Kenya, Tanzania and Madagascar at least as early as Middle Jurassic, the dating varying within modest limits from place to place^5–7. The Jurassic sea (Fig. 1) transgressed locally across pre-existing faulted troughs filled with continental Karroo sediments; in coastal Tanzania one internal rift already contained 10,000 foot of halite which had accumulated chiefly through the Trias⁶. This is the first symptom of the oceanic connexion, although the Permian rifting marks the initial tensional breakdown of the continental margin. The marine regime continued from the Jurassic to the present day without important interruption. Facies changes and overlap features from the Middle Jurassic onwards are consistent with this marine phase in Kenya and Tanzania forming an east-facing oceanic margin, either the Indian Ocean or its precursor.