The Structural Evolution of Thin Shale Detached Deepwater Fold and Thrust Belts

Deepwater fold and thrust belts (DWFTBs) have been recognized on most the world’s passive margins. They play a key role in the redistribution of gravitationally induced strain from the continental margin into the abyssal plain. Commonly they form tripartite systems linked by a detachment or detachments, containing: an updip extensional domain dominated by normal faulting, a downdip contractional domain dominated by folding and thrusts, and a transitional domain between. Typically they are commonly classified based upon their driving forces, geometry and detachment lithology. Systems concentrated on active margins and those detaching onto salt detachments are well described and modelled, but do not provide models applicable to other margin types. The geometry of thin shale detached DWFTBs on passive margins are poorly constrained. A wide variety of geometric arrangements are observable that do not conform to our current understanding of their formation. Through observation, interpretation and restoration of interpreted seismic profiles this study proposes new models for their formation and growth in both two and three dimensions. A consistent deficit of extensional versus compressional displacement in favour of extension has been observed in DWFTB systems. This study reveals this to be a consistent feature across DWFTBs and relates it to an early compactional phase of deformation in their development. This study then further investigates this phenomenon through field studies, seismic interpretation and the restoration of DWFTB structures at a range of scales. This study proposes this missing strain component is compensated for by the internal deformation, through folding and thrusting, of sediments within the DWFTB itself. Finally this thesis draws on the understanding gained from the entire margin to discuss what DWFTB development reveals about wider margin and tectonic scale processes.