Tectono-Stratigraphic Evolution associated with Salt Tectonics along Atlantic Margins: Effects of Pre-Salt Relief and Regional Events

Abstract

The inherent complexity of salt tectonics, the complications encountered when imaging structures adjacent to salt and the lack of outcrop analogues, coupled with its importance to petroleum systems, makes salt tectonics one of the most interesting and debated topics in basin studies. This thesis investigates the mechanisms and dynamics of salt tectonics, ultimately analysing the impacts of lateral and vertical salt flow on the supra-salt tectono-stratigraphic architecture along passive margins. To achieve this, the thesis utilises a wealth of 2D and a total of c. 25,000 km2 of 3D seismic data from two distinct Atlantic-type salt basins formed at different passive margins settings, the syn-rift Essaouira-Agadir salt basin (EAB) offshore Morocco, and the late syn- to post-rift salt basin of Santos, Brazil. The analysis of seismic data is integrated with novel numerical modelling techniques that help constrain the kinematics and, thus, dynamics of salt-related deformation; and to understand their geometries and structural style variation along different basins. A novel numerical modelling approach involving Discrete-Element Modelling (DEM) of salt tectonics is developed here, which affords fast, fully reproducible models simulating complex salt flow kinematics, realistic overburden deformation patterns, diapirism and sedimentation. This technique is applied here, firstly, to analyse aspects of active diapirism at local-scale, being further extended to more complex, regional scenarios of salt-detached translation, diapirism and overburden deformation. The effects of complex base-salt topography on salt tectonics at both post- and syn-rift salt settings are, then, investigated by combining seismic interpretation with different numerical modelling techniques, DEM and SaltDragOn, the latter being used to simulate stratal architecture of minibasins formed by translation over base-salt ramps. This integrated approach allows higher confidence in the interpretation of complex salt-related geometries and kinematics, ultimately improving their comprehension. A series of ramp-syncline basins (RSBs) is identified and modelled for the first time above thick salt and in the Santos Basin, Brazil, as well as above allochthonous salt offshore Morocco. These minibasins form by translation above basinward-dipping and landward-dipping base-salt ramps, being secondarily affected by other salt-related processes. They provide confident estimates of translation magnitudes, rates and kinematics along passive margins, and work as a guide to the identification of pre-salt structures, being relevant not just to academia but also to hydrocarbon exploration. This work contributes to solving a long-standing debate of the kinematics of salt-related deformation in the São Paulo Plateau and the adjacent Albian Gap, in the Santos Basin, Brazil; and also helps explain the complex structural variation and salt tectonics mechanisms offshore Morocco. Results presented here improve our knowledge of complex salt deformation and the often neglected aspects of translation and associated effects of base-salt relief on salt flow, diapirism and supra-salt architecture. This ultimately contributes to the understanding of regional salt tectonics and the ongoing deep-water exploration efforts in the Santos and Essaouira-Agadir Basins, with applications to many other continental margins affected by salt tectonics.

Date of Award	31 Dec 2018
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Emma Finch (Supervisor) & Mads Huuse (Supervisor)