SALT FLOW AROUND MINIBASINS: INSIGHT FROM THE INTERACTION OF SALT WALLS AND FAULTS SURROUNDING THE LYONS MINIBASIN, GULF OF MEXICO

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. The analysis shows that the geometry of salt walls varies. Salt walls are narrower in the south than in the east and north of the Lyons Basin. Additionally, salt is very limited at the Lyons Basin center, suggesting that this basin is now partially welded or moved relatively slowly. Faults that are bounding the Lyons Basin are mostly normal faults that form grabens around the basin. The narrow walls are associated with many fewer faults than the wider salt walls. Faults in each zone around the Lyons Basin have two dominant orientations, one striking parallel to the boundary faults, and the second striking about 20º oblique to the first. The calculated total heave across these zones shows that the eastern zone extended on average about 1800 m, and the southern zone extended by approximately 500 m. However, the percentage of extension suggests that the eastern zone strained the least with about 29%, whereas the southern zone strain may be as much as 69%. We argue that the geometry of the salt walls constrains the size of the faults and fault zones, and the complex fault geometries result from two phases of extension during the development of the Lyons Basin. The first phase of extension is perpendicular to the boundary faults forming faults dominated by dip-slip motion. The second phase of extension is oblique to the first, suggesting that there is also a strike-slip component.