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Title: The influence of fold and salt-wall growth on deepwater sedimentary systems in an active salt mini-basin, offshore Angola
Author: Doughty-Jones, Gemma
ISNI:       0000 0004 6420 9479
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2014
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Interactions between deepwater sedimentary systems and growing coeval salt structures result in the development of unique morphological features. This thesis focuses on controls on the formation and development of these features in a deforming deepwater passive margin setting, offshore Angola. Using 3D seismic datasets and well data, the evolution of basin-bounding structures and infill history of a salt withdrawal mini-basin are investigated, focusing on fan lobe complexes and mass transport complexes (MTCs). Structural restoration, isopachs and sediment accumulation rate maps are used to describe the basin evolution, with rates of change of bed length of individual structures calculated using biostratigraphic data. Early sedimentation on the slope was dominated by erosional channel complexes (33.9 - 18.26 Ma). Subsequently, salt movement and a concomitant increase in the growth rate of the basin-bounding anticlines, led to the formation of MTCs (18.26 - 8.29 Ma). Two types of MTC are examined: 1. laterally extensive deposits which thin onto structures and were sourced from the contemporaneous shelf; 2. small-scale MTCs sourced from basin-bounding structures. As salt movement continued, the basin became largely enclosed and ponded fans developed (8.29 - 5.58 Ma). Four lobe complexes imaged in unprecedented detail are investigated, revealing systematic changes in sediment entry point, fan shape and orientation through time. Combining observations on spatial distribution of sedimentary systems with maps showing the rate of growth of structures within the mini-basin and observations of the variations in stratal relationships through time, the following can be concluded: • ponded fan deposition occurred during low growth rate intervals (rate of change of bed length < 10 mMa-1). The lobe complex shape resulted from their passive response to relict topography from preceding high rate of change of bed length periods, • regional MTC deposits respond passively to structural growth and relict topography, being preferentially deposited in bathymetric lows, whilst • channels and local MTCs respond actively to medium and high growth rate structures; channel pathways change in response to structures with bed length change rates > 15 mMa-1.
Supervisor: Lonergan, Lidia Sponsor: Natural Environment Research Council ; British Petroleum Company
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral