What Controls Contraction in the Translation Domain of the Outer Kwanza Basin, Offshore Angola?

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Authors

Aurio Erdi , Christopher Aiden-Lee Jackson 

Abstract

It is now well-established that base-salt relief drives complex deformation in the mid-slope domain of salt-bearing passive margins, in a location classically thought to be dominated purely by horizontal translation. However, due to a lack of detailed studies drawing on high-quality, 3D seismic reflection data, our understanding of how base-salt relief controls four-dimensional patterns of salt-related deformation in natural systems remains poor. We here use 3D seismic reflection data from, and structural restorations of the Outer Kwanza Basin, offshore Angola to examine the controls on the evolution of variably oriented salt anticlines, rollers, and walls, and related normal and reverse faults. We show that the complex geometries and kinematics of predominantly contractional salt structures reflect up to 22 km of seaward flow of salt and its overburden across prominent base-salt relief. More specifically, contractional deformation occurs where seaward salt flow: (i) is retarded, and salt thickens and overburden buckles above landward-dipping ramps; (ii) encounters thick, slower-moving salt at the base of seaward-dipping ramp; (iii) translates across an array of concave-into-the-basin ramps; (iv) is retarded due to the formation of primary salt welds at the upper hinge of seaward-dipping ramps. The rate at which salt and its overburden translates seaward varies along strike due to corresponding variations in the magnitude of base-salt relief and, at a larger scale, primary salt thickness. As a result, overburden rotation accompanies bulk contraction. Our study improves our understanding of salt-related deformation on passive margins, highlighting the key role of base-salt relief, and showing contraction and rotation are fundamental processes in mid-slope translational domains of salt basins.

DOI

https://doi.org/10.31223/osf.io/27p5w

Subjects

Earth Sciences, Engineering, Geology, Life Sciences, Physical Sciences and Mathematics, Tectonics and Structure

Keywords

salt tectonics, base-salt relief, passive margin, salt weld, section restoration, shortening, structural geology

Dates

Published: 2020-07-12 19:31

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License

Academic Free License (AFL) 3.0

Additional Metadata

Conflict of interest statement:
Indonesia Education Scholarship (BPI), Indonesia Endowment Fund for Education (LPDP), Grant/Award Number: 201712220212151

Data Availability (Reason not available):
The seismic data supporting the findings of this study are available from CGG. However, restrictions apply to the availability of these data, which were used under license for this study.

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