The Manihiki Plateau in the western equatorial Pacific Ocean is a Cretaceous Large Igneous Province. Several studies have proposed that the Manihiki Plateau was formed by the same mantle plume that formed the Ontong Java and Hikurangi plateaus ca. 125 Ma. Recent multibeam bathymetric surveys of the Manihiki Plateau reveal the morphology of the Danger Islands Troughs (DIT), Suvarov Trough, which are systems of deep troughs within the plateau. The troughs divide the Manihiki Plateau into three distinct provinces, the North Plateau, the Western Plateaus, and the High Plateau. The DIT between the High Plateau and Western Plateaus comprises four en echelon troughs. With one exception, all segments of the DIT are bordered by steep escarpments, to 1500 m high. The basins of the DIT are smooth. Elongated northeast-southwest–striking scarps are common in the southernmost DIT and at the junction between the DIT and Suvarov Trough. The features revealed by the new bathymetric data indicate that a sinistral strike-slip tectonic environment formed the DIT during the break-up into the Manihiki and Hikurangi plateaus, whereas the Suvarov Trough developed after the formation of the DIT.

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ABSTRACT The continental margin of East Africa began forming in the Permo-Carboniferous with the development of rift basins, and extension occurred intermittently over 150 million years until the Late Jurassic initiation of sea floor spreading. The margin developed by a combination of extensional and transform tectonics that separated plates containing Africa, Madagascar-Greater India, South America, and Antarctica. A salient aspect of the pre-breakup stratigraphy of the rift basins is salt in isolated Tanzanian grabens, in the Somali Coastal Basin, and in offshore Madagascan basins. At the initiation of sea floor spreading, sedimentary facies changed throughout the rift and pull-apart basins from dominantly continental to marine. Volcanic activity and faulting occurred at the same time. Sea floor spreading ceased in the Western Somali Basin in the Early Cretaceous. Vigorous abyssal circulation along the East African margin probably commenced in the mid-Cretaceous, and widespread regional volcanism occurred in the Late Cretaceous. Middle Jurassic through Holocene sediment thicknesses exceed 8 km in places along the margin.

The geologic evolution of the conjugate sedimentary basins and margins produced during the early breakup of Gondwanaland by the relative motion between Madagascar and Africa is reconstructed utilizing interpretations drawn from outcrop, industrial onshore drilling, Deep Sea Drilling Project (DSDP) offshore drilling, Lamont-Doherty multichannel seismic (MCS) data, and single-channel seismic data. Herein we present (1) maps displaying lithological columnar sections for Karroo (Permo-Carboniferous through Early Jurassic) to Quaternary time slices, (2) depth-to-basement and sediment isopach maps, and (3) acoustic stratigraphy studies based on MCS data. Formation of the conjugate sedimentary basins began in Permo-Carboniferous time, and extension recurred intermittently over a 150-m.y. span until the initiation of sea-floor spreading between Madagascar and Africa in Middle Jurassic time. Occasional marine incursions and the resulting deposition of salt in isolated Tanzanian grabens, and in the conjugate Somali Coastal and Majunga basins, highlight the pre-breakup stratigraphy. At the initiation of sea-floor spreading, facies changed throughout the basins from dominantly continental to overwhelmingly marine, and volcanic activity and faulting occurred. The mid-Cretaceous was marked by the beginning of vigorous abyssal circulation in the Western Somali Basin, and the Late Cretaceous was a time of widespread regional volcanism. During the Paleogene, rifting was renewed in the Tanzanian Coastal Basins, extending to the Davie Fracture Zone, and all of the basins record numerous hiatuses in the Paleocene and Oligocene sections. A vast sediment slide offshore Somalia and Kenya occurred in mid-Tertiary time, demonstrating that the formation of olistostromes characterized by significant internal deformation (including thrust faults) may occur in passive margin settings. An intense erosional event in the Western Somali Basin marked the end of Paleogene time. Frequent volcanism affected the Diego Basin throughout the Cenozoic Era and the Comoros Islands during Neogene and Quaternary time. Folding and faulting of onshore and offshore strata of the Tanzanian margin continued through Neogene and Quaternary time to the present. We observed a major network of late Cenozoic canyons and channels on both the East African and Madagascan margins and in the Western Somali Basin. Accumulations of sediment on the Madagascan and East African margins total 5+ and 8+ km, respectively, for Middle Jurassic to Holocene time.