The role of structural growth in controlling the facies and distribution of mass transport deposits in a deep-water salt minibasin
File(s)
Accepted version
Author(s)
Doughty-Jones, Gemma
Lonergan, Lidia
Mayall, Mike
Dee, Stephen
Type
Journal Article
Abstract
We distinguish two types of mass-transport deposits (MTDs) within a salt-related slope minbasin. The locally-derived MTDs are sourced from growing structures bounding the minbasin, and the more extensive, regional, MTDs are sourced from the shelf of the continental margin, at least 100 km east of the study area. The two types of MTDs have different internal characteristics, distribution within the basin and depositional mechanisms. Using a high-resolution 3D seismic dataset we characterise the internal structures and dimensions of the MTDs, and also quantify the deformation history of the salt structures. Through these analyses we demonstrate that the ‘local’ and ‘regional’ MTDs react in different ways to growth on the structures within, and bounding, the slope minbasin.
The regionally derived MTDs are debris flows, with individual deposits up to 300 m thick and covering an area of up to 1300 km2 within the minbasin. Seismic facies analysis suggests they are mostly composed of chaotic material but in some places contain discrete blocks of sediment ranging from 50 m to 250 m in length. In contrast, the more locally derived MTDs are submarine slides consisting of translated material from the flanks of salt structures. Each slide has an up-dip extensional domain with normal faults and a down-dip contractional domain with thrusts and folds. They cover areas between 11 and 28 km2 with frontal and lateral ramps up to 200 m high. Relict topography on the top surface of the MTDs is infilled with younger sediment.
Shortening analysis of the intra-slope salt structures within and bounding the minbasin is used as a proxy for the growth rate of the structures. This novel approach of combining shortening with the detailed observations of the local and regional MTDs has allowed us to draw new conclusions on the relationship between structural growth and MTD initiation. Local MTDs either form during periods of high structural growth (10–30 m/ma) or in a period of quiescence (<10 m/ma) immediately following a period of high growth rate. In contrast, the regional MTDs infill existing topography in the basin, thinning and terminating against the flanks of the growing structures with thicker deposits extending further up the slope of the salt structures. Closely spaced, imbricate thrust faults are developed as the deposit impinges on the flanks of the structures and in narrow areas between anticlines, flow structures are developed defined by the alignment of isolated blocks.
The regionally derived MTDs are debris flows, with individual deposits up to 300 m thick and covering an area of up to 1300 km2 within the minbasin. Seismic facies analysis suggests they are mostly composed of chaotic material but in some places contain discrete blocks of sediment ranging from 50 m to 250 m in length. In contrast, the more locally derived MTDs are submarine slides consisting of translated material from the flanks of salt structures. Each slide has an up-dip extensional domain with normal faults and a down-dip contractional domain with thrusts and folds. They cover areas between 11 and 28 km2 with frontal and lateral ramps up to 200 m high. Relict topography on the top surface of the MTDs is infilled with younger sediment.
Shortening analysis of the intra-slope salt structures within and bounding the minbasin is used as a proxy for the growth rate of the structures. This novel approach of combining shortening with the detailed observations of the local and regional MTDs has allowed us to draw new conclusions on the relationship between structural growth and MTD initiation. Local MTDs either form during periods of high structural growth (10–30 m/ma) or in a period of quiescence (<10 m/ma) immediately following a period of high growth rate. In contrast, the regional MTDs infill existing topography in the basin, thinning and terminating against the flanks of the growing structures with thicker deposits extending further up the slope of the salt structures. Closely spaced, imbricate thrust faults are developed as the deposit impinges on the flanks of the structures and in narrow areas between anticlines, flow structures are developed defined by the alignment of isolated blocks.
Date Issued
2019-06-01
Date Acceptance
2019-03-11
Citation
Marine and Petroleum Geology, 2019, 104 (1), pp.106-124
ISSN
0264-8172
Publisher
Elsevier
Start Page
106
End Page
124
Journal / Book Title
Marine and Petroleum Geology
Volume
104
Issue
1
Copyright Statement
© 2019 Published by Elsevier Ltd. All rights reserved. This manuscript is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Licence http://creativecommons.org/licenses/by-nc-nd/4.0/
Sponsor
Natural Environment Research Council–Collaborative Awards in Science and Engineering award with BP
Identifier
https://www.sciencedirect.com/science/article/abs/pii/S0264817219301059
Grant Number
NE/H017682/1
Subjects
Science & Technology
Physical Sciences
Geosciences, Multidisciplinary
Geology
Mass transport deposit (MTD)
Debris flow
Debrite
Slump
Minibasin
Salt
Lower Congo basin
Angola
Tectonics
SAHARAN DEBRIS FLOW
SUBMARINE LANDSLIDES
SEA-FLOOR
COMPLEXES
SLOPE
STRATIGRAPHY
EVOLUTION
EXAMPLES
MARGIN
CLASSIFICATION
0403 Geology
0404 Geophysics
Geology
Publication Status
Published
Date Publish Online
2019-03-19