Strain analysis of a seismically-imaged mass-transport complex (MTC), offshore Uruguay
Author(s)
Steventon, Michael
Jackson, Christopher
Hodgson, David
Johnson, Howard
Type
Journal Article
Abstract
Strain style, magnitude, and distribution within mass-transport complexes (MTCs) is important for understanding the process evolution of submarine mass flows and for estimating their runout distances. Structural restoration and quantification of strain in gravitationally-driven passive margins have been shown to approximately balance between updip extensional and downdip compressional domains; such an exercise has not yet been attempted for MTCs. We here interpret and structurally restore a shallowly buried (c. 1500 mbsf) and well-imaged MTC, offshore Uruguay using a high-resolution (12.5 m vertical and 15x12.5 m horizontal resolution) 3D seismic-reflection survey. This allows us to characterise and quantify vertical and lateral strain distribution within the deposit. Detailed seismic mapping and attribute analysis shows that the MTC is characterised by a complicated array of kinematic indicators, which vary spatially in style and concentration. Seismic-attribute extractions reveal several previously undocumented fabrics preserved in the MTC, including internal shearing in the form of sub-orthogonal shear zones, and fold-thrust systems within the basal shear zone beneath rafted-blocks. These features suggest multiple phases of flow and transport directions during emplacement. The MTC is characterised by a broadly tripartite strain distribution, with extensional (e.g. normal faults), translational and compressional (e.g. folds and thrusts) domains, along with a radial frontally emergent zone. We also show how strain is preferentially concentrated around intra-MTC rafted-blocks due to kinematic interaction between these features and the underlying basal shear zone. Overall, and even when volume loss within the frontally emergent zone is included, a strain deficit between the extensional and compressional domains (c. 3-14%) is calculated, which we attribute to a combination of distributed, sub-seismic, ‘cryptic’ strain, likely related to de-watering, grain-scale deformation, and related changes in bulk sediment volume. This work has implications for assessing MTCs strain distribution and provides a practical approach for evaluating structural interpretations within such deposits.
Date Issued
2019-06
Date Acceptance
2019-01-06
Citation
Basin Research, 2019, 31 (3), pp.600-620
ISSN
0950-091X
Publisher
Wiley
Start Page
600
End Page
620
Journal / Book Title
Basin Research
Volume
31
Issue
3
Copyright Statement
© 2019 The Authors. Basin Research © 2019 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists
Sponsor
Statoil ASA
Equinor ASA
Identifier
https://onlinelibrary.wiley.com/doi/abs/10.1111/bre.12337
Grant Number
PO# 4502563053
Laila Roen
Subjects
Science & Technology
Physical Sciences
Geosciences, Multidisciplinary
Geology
deep-water depositional systems
kinematic indicators
mass-transport deposit (MTD)
Oriential del Plata
Punta del Este
seismic geomorphology
submarine landslide
SOFT-SEDIMENT DEFORMATION
INTERNAL DEFORMATION
SUBMARINE LANDSLIDES
VISCHKUIL FORMATION
SOUTH-ATLANTIC
COUNTY CLARE
KAROO BASIN
NORTH-SEA
EVOLUTION
DEPOSIT
04 Earth Sciences
Geology
Publication Status
Published
Date Publish Online
2019-01-10