Sedimentation history and geodynamic evolution of the Mozambique Basin using seismic data

Jude.Castelino [ at ]


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.

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Castelino, J. A. (2016): Sedimentation history and geodynamic evolution of the Mozambique Basin using seismic data , PhD thesis, Universität Bremen.

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