The influence of fold and salt-wall growth on deepwater sedimentary systems in an active salt mini-basin, offshore Angola
File(s)
Author(s)
Doughty-Jones, Gemma
Type
Thesis
Abstract
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.
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.
Version
Open Access
Date Issued
2014-06
Date Awarded
2015-07
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Lonergan, Lidia
Sponsor
Natural Environment Research Council (Great Britain); British Petroleum Company
Grant Number
NE/H017682/1
Publisher Department
Department of Earth Science and Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)