DEPOSITIONAL ARCHITECTURE AND PROCESSES OF SEDIMENT GRAVITY FLOWS: A 3D SEISMIC CASE STUDY FROM OFFSHORE ANGOLA Kehinde Olafiranye Department of Earth Science and Engineering Imperial College London Thesis submitted in accordance with the requirements for the degree of Master of Philosophy of Imperial College London October 2013 Declaration of originality I declare that this thesis is entirely my own work carried out in the Department of Earth Science and Engineering at Imperial College London under the supervision of Drs Christopher Jackson (Imperial College), David Hodgson (University of Leeds), and Gary Hampson (Imperial College). Full citation and adequate referencing have been made where any material could be construed as the work of others. No part of this work has been previously submitted to this or any other academic institution for a degree or diploma, or any other qualification. Kehinde Olafiranye Department of Earth Science and Engineering Imperial College London 2 Copyright Declaration ‘The copyright of this thesis rests with the author and is made available under a Creative Commons Attribution Non-Commercial No Derivatives licence. Researchers are free to copy, distribute or transmit the thesis on the condition that they attribute it, that they do not use it for commercial purposes and that they do not alter, transform or build upon it. For any reuse or redistribution, researchers must make clear to others the licence terms of this work’ 3 Abstract Deepwater environments are characterised by the deposits of mass flows (e.g. debrites, slumps, slides), sediment density flows (turbidites), and background hemipelagic and pelagic suspension fallout. ‘Mass transport’ is a general term used for the failure and downslope movement of sediment under the influence of gravity in both subaerial and subaqueous environments, the products of which are called Mass Transport Deposits (MTDs). The aims of this study are: (i) to investigate the temporal and spatial development of sediment gravity flows, particularly the coupling of MTDs, turbidites and hemipelagites (ii) to characterise and interpret the seismic facies present within a well-imaged deep-water succession, offshore Angola, with particular focus on the external morphology and distribution of MTDs and associated sediment gravity flows; (iii) to document the geometry, scale, distribution and kinematic importance of structures within the MTDs and relate these to the emplacement of these deposits, in order to understand the impact of seafloor bathymetry on the distribution of the deep-water deposits; and (iv) to characterise and classify the development of pockmarks that are formed contemporaneously or successive to the emplacement of the MTDs. Key results of this study are that: (1) the grade of the submarine slope is a primary intra-basinal control on the emplacement and depositional patterns of MTDs and associated sediment gravity flows, (2) the emplacement of MTDs in upper slope environments promotes the capturing and trapping of sediments, (3) strain indicators genetically linked to MTDs record kinematic information related to the initiation, translation and ultimate deposition of the MTDs, (4) pockmarks may develop from the dewatering of MTDs due to their rapid transportation and consequent entrapment of fluid, and (5) the distribution of pockmarks in slope sediments may be haphazard, but pockmarks may also form preferentially along fault traces and along the evacuation planes of MTDs. 4 Table of contents Declaration of originality ........................................................................................................................... 2 Copyright Declaration ................................................................................................................................ 3 Abstract ........................................................................................................................................................ 4 Table of contents ......................................................................................................................................... 5 List of figures ............................................................................................................................................... 9 Chapter One .............................................................................................................................................. 14 Introduction ............................................................................................................................................... 14 1.1 Rationale and motivation ............................................................................................................ 14 1.2 Aims and objectives .................................................................................................................... 16 1.3 Study area ................................................................................................................................... 17 1.3.1 Tectono-stratigraphic evolution ................................................................................................. 17 1.4 Research methodology ............................................................................................................... 20 1.5 Structure of the thesis ................................................................................................................ 20 Chapter Two. ............................................................................................................................................. 22 Overview of sedimentation on submarine slopes and gravity-flow deposition .................................... 22 2.1 Introduction ................................................................................................................................. 22 2.2 Triggering of gravity flows ......................................................................................................... 23 2.3 Forms and characteristics of gravity flows ................................................................................. 24 2.3.1 Mass Transport Deposits (MTDs) ....................................................................................... 24 2.3.2 Sediment gravity flows ....................................................................................................... 27 2.3.3 Flow translation and transformation ................................................................................... 28 2.4 Rheological behaviour and the classification of sediment gravity flows .................................... 30 2.5 Impact of active structures on slope sedimentation .................................................................... 31 2.5.1 The concept of slope grade and associated processes ......................................................... 31 2.5.2 Type and impact of bathymetry on slope depositional patterns .......................................... 33 5 2.6 Internal architecture and strain indicators within MTDs ............................................................ 36 2.6.1 Headwall Domain ............................................................................................................... 37 2.6.2 Translational Domain .......................................................................................................... 38 2.6.3 Toe Domain ........................................................................................................................ 40 2.7 Seismic facies analysis ................................................................................................................ 40 2.8 Impact of MTDs and sediment gravity flows on fluid movement and pockmarks ..................... 47 2.8.1 Generation and transfer of overpressure ............................................................................. 48 Chapter Three ........................................................................................................................................... 52 The role of tectonics and mass-transport complex emplacement on upper slope stratigraphic evolution: a 3D seismic case study from offshore Angola ..................................................................... 52 3.1 Abstract ....................................................................................................................................... 52 3.2 Introduction ................................................................................................................................. 53 3.3 Geological setting ....................................................................................................................... 57 3.4 Dataset and methodology ............................................................................................................ 61 3.5 3D seismic interpretation ............................................................................................................ 65 3.5.1 The Lower Seismic Package (LSP) .................................................................................... 65 3.5.2 Middle Seismic Package (MSP) ......................................................................................... 74 3.5.2.1 Seismic Unit 3 (SU3) .......................................................................................................... 74 3.5.2.2 Seismic Unit 4 (SU4) 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