Description: Submarine fans and turbidite systems are important and sensitive features located offshore from river deltas that archive tectonic events, regional climate, sea level variations and erosional process. Very little is known about the sedimentary structure of the 1800 km long and 400 km wide Mozambique Fan, which is fed by the Zambezi and spreads out into the Mozambique Channel. New multichannel seismic profiles in the Mozambique Basin reveal multiple feeder systems of the upper fan that have been active concurrently or consecutively since Late Cretaceous. We identify two buried, ancient turbidite systems off Mozambique in addition to the previously known Zambezi-Channel system and another hypothesized active system. The oldest part of the upper fan, located north of the present-day mouth of the Zambezi, was active from Late Cretaceous to Eocene times. Regional uplift caused an increased sediment flux that continued until Eocene times, allowing the fan to migrate southwards under the influence of bottom currents. Following the mid-Oligocene marine regression, the Beira High Channel-levee complex fed the Mozambique Fan from the southwest until Miocene times, reworking sediments from the shelf and continental slope into the distal abyssal fan. Since the Miocene, sediments have bypassed the shelf and upper fan region through the Zambezi Valley system directly into the Zambezi Channel. The morphology of the turbidite system off Mozambique is strongly linked to onshore tectonic events and the variations in sea level and sediment flux.

Description: Continental break-up and collision and the opening and closing of ocean basin constitute the integral part of the Wilson cycle that constantly recycles the Earth’s crust. The initial dispersal of the last supercontinent Gondwana into east and west Gondwana resulted in the formation of the several ocean basins along the margins. The oldest amongst the basins along the West Gondwana margin -- presently the Eastern Africa passive margin -- are the Somali and Mozambique basins. The submarine morphological features of passive margins are dominated by downslope and along slope processes that are directly or indirectly controlled by tectonic, oceanic and climatic settings. The Mozambique Basin hosts a thick and continuous sequence of sediment archive from the Jurassic separation of Antarctica from Africa but despite its economic and geological significance, the region continues to remain poorly studied. This cumulative dissertation focuses on the evolution of the Mozambique Basin and its transition from a rift basin to a passive margin basin. 2200 km of seismic profiles and bathymetry data acquired in 2007 have been used to study the controls on sediment architecture and dispersal of sediments in the basin along the Mozambican continental margin. Additionally, palaeobathymetry models of the Africa-Antarctic Corridor using “backstripping” technique and plate kinematics augment our knowledge of the basin. The palaeobathymetry models show topographic highs along the edge of the basin namely, the continental margins, Mozambique, Gunnerus, Astrid ridges enclosed the basin preventing any bottom circulation until the Late Cretaceous. High sediment accumulation rates coupled with a euxinic setting in a rapidly subsiding basin results the formation of shale layers interbedded with turbidite layers. The present-day 1800 km long and 400 km wide Mozambique Fan is spread out in the Mozambique Channel. Local sea-level change and increased sediment influx due to tectonic activity into the basin from the Zambezi in Late Cretaceous times resulted in the formation of an elongated submarine fan lobe into the Mozambique Channel north of Beira High. Strong north-south bottom currents commenced within the channel in Late Cretaceous times, forcing the aggradation of sediments on the southern flank of the lobe until the Eocene. In addition, we observe several current-controlled sediment deposits in the deeper basin that are influenced by north-south bottom currents. The taphrogenesis along the Mozambique margin ensured that turbidite systems continued to feed the basin after the mid-Oligocene marine regression with a large Channel-levee complex over Beira High supplying sediments from the southwest until Miocene times. Since the Miocene, sediments bypassed the shelf and upper fan region through the Zambezi Valley system directly into the Zambezi Channel. The palaeobathymetry models reveal a previously undocumented uplift in the Mozambique Basin ranging up to 1300 m, that cannot be explained by mantle convection or plumes alone as on the neighbouring African continent. Instead thickening of the oceanic crust due to underplating is a more reasonable assumption when the basin passed over the Quathlamba Hotspot during Early Paleogene that also produced Bassas Da India and Isle de Europa. Both conjugate margins display flexure over halfwavelengths of ~60-80 km landwards and an amplitudes of 1500 m. Isolated crustal fragments of transitional or continental composition near the margin, including Beira High and Gunnerus Ridge subside in similar to adjoining oceanic crust. Overall, the new discoveries in this thesis make significant contributions to the understanding of passive margin development off Mozambique.

Description: An extensive database of geophysical data in the Riiser-Larsen Sea and Mozambique Basin conjugate margins indicates a dynamic evolution that was actively influenced by different events. However, analyses of individual datasets are not sufficient to reconstruct the complete structural evolution of the rifted margins during Gondwana break-up and thereon. We use crustal age models and chronology of interpreted horizons from extensive seismic datasets in the Riiser-Larsen Sea and off Mozambique to create the palaeobathymetric reconstruction of the conjugate margins. We also incorporate the effects of different models for sediment decompaction, thermal subsidence and lithospheric flexure from sediment loading and sea level variation into our calculations. The geodynamics of the two passive margins is reconstructed on a 0.5° x 0.5° grid resolution. Plate kinematic model of Antarctic plate with respect to Africa controls palaeogeography of the break-up. The model shows the initial period of common phases of the geodynamic evolution of the two margins. The results provide new boundary conditions for palaeoenvironment settings, palaeoceanographic models and sediment deposition architecture in the Africa-Antarctic corridor.

Description: An extensive database of geophysical data in the Riiser-Larsen Sea and Mozambique Basin conjugate margins indicates a dynamic evolution that was actively influenced by different events. However, analyses of individual datasets are not sufficient to reconstruct the complete structural evolution of the rifted margins during Gondwana break-up and thereon. We use crustal age models and chronology of interpreted horizons from extensive seismic datasets in the Riiser-Larsen Sea and off Mozambique to create the palaeobathymetric reconstruction of the conjugate margins. We also incorporate the effects of different models for sediment decompaction, thermal subsidence and lithospheric flexure from sediment loading and sea level variation into our calculations. The geodynamics of the two passive margins is reconstructed on a 0.5° x 0.5° grid resolution. Plate kinematic model of Antarctic plate with respect to Africa controls palaeogeography of the break-up. The model shows the initial period of common phases of the geodynamic evolution of the two margins. The results provide new boundary conditions for palaeoenvironment settings, palaeoceanographic models and sediment deposition architecture in the Africa-Antarctic corridor.

Description: In this study we introduce a palaeobathymetric model for the conjugate Mozambique Basin and Riiser-Larsen Sea built by employing backstripping techniques, compensating for dynamic topography and plate motions. The model is presented at 0.2◦×0.2◦grid resolution, making it suitable for future oceanographic and climate simulation model experiments aimed at a better understanding of the climatic and oceanographic relevance of oceanic gateways in the southern ocean. At the present day, the seafloor next to the Mozambican continental margin is around 300m shallower, and that in the central Mozambique Channel is almost 1300m shallower, than their conjugate areas or the predictions of oceanic thermal subsidence models. The cause of this anomalous depth is difficult to determine confidently because of sparse data, in particular concerning sediment thickness, and because of the wide range of amplitudes in modelled present-day dynamic topography. The distribution of shallow seafloor suggests that it might be attributed to the presence of thicker-than-usual oceanic crust, which in turn can be attributed to the Paleogene passage of the Quathlamba plume beneath the basin. We portray these effects in our palaeobathymetric models. In contrast, the Riiser-Larsen Sea has experienced fairly stable subsidence since its formation in Jurassic times, with only slight observable changes attributable to the onset of Antarctic glaciation and during the middle Miocene climate transition. Both basins display flexure over half-wavelengths of ∼60–80 km with amplitudes of 1500 m towards their continental margins. This plays an important role in models of palaeobathymetry for times older than 100 Ma. Near the margins, isolated areas of transitional or debatable crustal composition, including Beira High and Gunnerus Ridge, are depicted to subside in a similar fashion to oceanic crust. Further into the Indian Ocean, oceanic lithosphere younger than 100 Ma on both plates has subsided to depths that are typical of thermal subsidence models. Finally, the new palaeobathymetry had distinct consequences for the current systems in the young Southern Ocean during the time periods. The onset of coast-parallel bottom currents and associated contourite deposition in the Mozambique Channel at palaeo water depths of 3500–4000 m may be a consequence of either an opening of a deep-water passage into the South Atlantic between Southwest Indian Ridge and Agulhas plateau or into the Tethys Ocean in the Late Cretaceous.

Description: Mozambique Basin is one of the oldest rifted sedimentary basins developed along the eastern African margin in Jurassic times. The basin has a continuous record of sediments since Jurassic when Antarctica separated from Africa. The primary objectives of this study were to extend the regional stratigraphic framework north of the Zambezi Delta and review early developments in the Mozambique basin. Nine Multi-Channel seismic reflection profiles are used to extend the regional stratigraphy in to deeper basin. We identify six major stratigraphic units that correlate to Jurassic, Early Cretaceous, Late Cretaceous, Paleogene, Neogene and Quaternary. Mesozoic sedimentation rates of 3-5 cm/kyr are observed in the deeper basin and 1-2 cm /kyr during Paleogene (neither compensated for compaction). Presence of shale from neighbouring wells imply a restricted circulation in the basin until mid-Cretaceous. Mesozoic sediments have a high velocity that exceed 4.5 km/s with an exception of a distinct low-velocity zone of 3.7 km/s in mid-Cretaceous that may indicate undercompacted overpressured shales. Albeit a smaller catchment area of the proto-Zambezi until Miocene, higher sedimentation rate in Late Cretaceous can be attributed to rapid denudation of the African continent after a major tectonic uplift episode at approximately 90 Ma. Increased sediment influx into the basin from the Zambezi in Late Cretaceous resulted in the formation a submarine delta fan lobe progressing into the Mozambique Channel around the northern periphery of Beira High. Strong north-south bottom currents commenced within the channel in Late Cretaceous that forced the aggradation of sediments of the submarine fan lobe on the southern flank. In addition, we observe several current-controlled drift bodies in the deeper basin that are influenced by the north-south bottom current. Low sedimentation rate in Paleogene is attributed to relative quiet tectonic phase onshore and erosion during global marine regression in mid-Oligocene.