Petroleum Systems of East African Margin Constrained by Paleogeographical and Tectonostratigraphic Analyses

Abstract

East African margin evolved from the assembly and fragmentation of Gondwana and thus shares a multi-phase rift-drift history with Madagascar, Seychelles and West Indian margin. Through the construction of 19 paleofacies maps spanning Carboniferous-Pliocene periods and 24 integrated stratigraphic charts for both onshore and offshore East African basins, this study suggests six tectonostratigraphic megasequences with implications for a stack of source rocks and reservoirs in the region: (1) Late Carboniferous-Early Triassic, (2) Late Triassic-Early Jurassic, (3) Middle Jurassic-Cenomonian, (4) Turonian-Maastrichtian, (5) Paleocene-Eocene, and (6) Late Oligocene-Miocene megasequences. In this interpretation, the so-called “Karoo Group” is divided into two distinct groups: Karoo-1 corresponds to purely continental gas-prone plays of Late Carboniferous-Early Triassic age well preserved in the interior basins such as Anza and Rufiji, while Karoo-2 represents fluvial-lacustrine sediments related to initial continental rifts between East Gondwana and West Gondwana and thus associated with Karoo volcanics (185–175 Ma). The Jurassic-Recent tectonostratigraphy is marked by a succession of rift events: (1) opening of the Somali oceanic basin and Mozambique Channel (165–100 Ma) resulting in the separation of Madagascar from East African margin; (2) opening of the Mascarene oceanic basin (90–60 Ma) beginning with separation of Seychelles-India from Madagascar; (3) opening of the SW Indian ocean (70 Ma to present) associated with separation of Seychelles from West India; and (4) the Afar triangle at the junction of Red Sea, Gulf of Aden, Kenya-Mozambique rift systems (Oligocene-Recent). Although recent discoveries of East African deepwater basins have been major gas fields, regional geological analysis is suggestive of oil plays as well.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015