Early Permian to Middle Jurassic rifting and sedimentation in East Africa and Madagascar

Abstract

Pre-drift sediments of Madagascar (Early Permian-Middle Jurassic) have been studied palynologically. These studies resulted in a more precise dating of individual stratigraphic units and the recognition of minor and major breaks in the succession. Palynostratigraphic and physical evidence of unconformities have been used to subdivide the pre-drift sediments into depositional cycles and to infer rifting events. A comparison with equivalent strata of Mozambique, Tanzania, Kenya, Ethiopia and Somalia shows a general correspondence and provides additional information for the construction of a generalized framework for the East African/Madagascan region which demonstrates the relationships between rifting and sedimentation and elucidates the prehistory of the break-up of Gondwana into a western and eastern fragment during the Middle Jurassic. The predrift succession of East Africa/Madagascar can be subdivided into two major sequences, a Karoo sequence (cycles 1–5, Asselian-early Smithian) and a transitional sequence (cycles 6–9, Ladinian-early Bajocian). The two sequences are separeted by a late Scythian to Anisian hiatus which indicates extensive uplift and erosion before a major rifting event initiated the resumption of sedimentation in the Ladinian. This Middle Triassic event marks the transition from the intracratonic rift stage to the pericratonic basin stage and correlates with a significant event in the Pangaean history, the transition from final coalescence to initial dispersal. The onset of the southward drift of Madagascar is believed to have occurred about 60 Ma later near the Aalenian-Bajocian boundary, contemporaneous with or immediately after the deposition of syntectonic sediments of cycle 9.