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Title: Late Cretaceous and Tertiary evolution of the Zambezi Delta Basin, Mozambique
Author: Vieira, Francisco
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1998
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The Zambezi Delta Basin is situated in central Mozambique at the present day Zambezi River mouth and extends from onshore to the offshore in a NW-SE direction into the waters of the Mozambique Channel over an estimated area of about 350,000 square kilometres both on- and offshore to the 2500m isobath. The analyses of approximately 21,700km of 2D seismic reflexion profiles and a well log suite for nine exploration wells supplied by the state oil company of Mozambique (ENH) has enabled an improved seismic stratigraphic model of the late Cretaceous and Tertiary evolution of the Zambezi Delta Basin to be made. It is demonstrated in this work that sedimentation alternated along a SWNE zone between two main depocentres separated by the Beira Basement High during their Tertiary development. These depocentres are the Zambezi Delta southwestern depocentre which is bounded to the southeast by the Beira Basement High and the East African Rift Active Extension in the northeast also bounded to the southwest by the Beira Basement High. The latter is suspected to be an active E-W graben structure. This finding is supported by seismological data studied here. Generally, periods of sedimentation in one depocentre mean a period of nondeposition and erosion in the other depocentre with sediment bypass, reworking and redeposition in the deeper parts of the basin (not covered by seismic data used in this study). Moreover sedimention is controlled by onshore tectonics controlling sediment sources onshore with tectonics, eustatic sea level variations and sediment load controlling basin subsidence and accommodation space in the basin offshore. Sedimentation generally was restricted to small areas which with time become widespread in the depocentres and at times cover the whole basin. This was the case during the early stages of major depositional cycles. Lithofacics relationships are very complex in the basin due to the sedimentary architecture produced by the interplay between sea level variation, basin subsidence and sediment supply. The resulting along-strike variability mapped in the Zambezi Delta Basin in this work has the potential not only to impact upon existing sequence stratigraphic models for deltaic settings but also on existing interpretation methods, for example the implications for the recognition of depositional sequences and "systems tracts". There is evidence of listric growth faulting of Middle Eocene age affecting turbidite deposits in the southwestern part of the basin while long wavelength folding observed in the deeper part of the sedimentary succession raises questions over the possibilities of evaporites or mobile shales underneath the sediment pile. Deltaic sedimentation switched from one depocentre to the other via distributary channels producing marked along-strike variability in the NE-SW direction. Generally sedimentation was more active in the southwestern part of the basin in late Cretaceous until late Middle Miocene when deposition moved into channel deposition in the northeastern part of the basin. Prom early late Miocene to Recent times various basinward prograding, southwestward-migrating depositional cycles with relatively high sedimentation and basin subsidence rates have characterized the evolution of the basin. Gravity and magnetic data supplied by GETECH (Leeds University) are used to derive crustal structure and to estimate the depth to magnetic basement beneath the basin. The Free-Air gravity model achieved in this study is a variant of the usual model achieved when crustal thinning and accumulated sediments extend seaward from the coastal area at a rifted passive continental margin. In view of the fact that oceanic magnetic anomalies lie 300km away to the south, thin crust beneath the Zambezi Delta Basin sediments is thought to be continental in origin and stretched immediately prior to breakup in middle Jurassic times.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available