Superimposition of contractional structures is widely observed in different scales in the world. Superimposed structures form due to different processes: change in strain accommodation from one type of structure to another during a single progressive shortening; successive coaxial shortening phases separated by an unconformity; superimposition of different non-coaxial shortening phases. Using results of a series of systematic analogue models and detailed field structural mapping, this thesis focuses on the geometry and kinematics of such superimposed structures that are formed by these three processes. During a single progressive folding, thrusts develop within a fold to accommodate stain variations in different regime of the fold. Limited displacement along these thrusts does not significantly modify the geometry of the fold. However, during multiple shortening phases (coaxial or non-coaxial), early formed structures are modified by the later phase ones. The later thrusts can cut and displace the pre-existing structures. The early folds are tightened or interfered by the later folding phase. Pre-existing thrusts may be reactivated either in dip direction and/or along strike during the later shortening. The pre-existing structures in turn influence development of the later structures, which results in change in structure spacing. An angular unconformity between two shortening phases clearly truncates the early phase structures and separates structures of different levels. Unlike in the post-erosional layers, in the layers below the unconformity, complicated superimposed structures are visible. This thesis shows that geometry and sequence of structures formed during one progressive shortening or multiple shortening phases strongly depend on the mode of the superimposition (coaxial, orthogonal or oblique) and the orientation of pre-existing structures.

archives@tulane.edu / Minibasins, i.e., small basins that can be up to 8 km in depth and a few tens of km in diameter, often form in regional salt basins and on salt-rich passive margins. As salt walls grow through time, brittle strain localizes in zones directly above the salt walls leading to complex fault arrays surrounding the minibasins. These fault arrays provide insight into the relative movement of minibasins and the local deformation field, which influences the hydrocarbon exploration around them. Using high-resolution bathymetry and 2D reflection seismic data, we have examined fault systems and their interaction with salt walls around the Lyons minibasin in the Gulf of Mexico, offshore USA. This analysis shows that the geometry of salt walls varies and controls the development of faults form in the overlying sedimentary layer. The wide plateau-like salt wall creates a mechanical constraint that restricts the development of faults vertically and laterally. The narrow ridge of the salt wall has less mechanical restriction and allows faults to grow in displacement. Deformation is more localized above the narrow ridge of salt wall. This study suggests that the intricate fault patterns around minibasins result from multi-phase deformation caused by the variation of salt flow within the salt walls. Initially, minibasin subsidence expels salt upward and outward. After the minibasins is welded, the regional slope enhances the lateral flow and allows salt to flow around welded minibasins. During this stage, the lateral flow of salt is constrained by the salt wall orientation. Moreover, this study demonstrates a new approach that provides an additional perspective to understand the evolution of minibasins and their interaction, which is a limitation of 2D modeling studies. / 1 / Thi Quan H. Pham