Oliver B. Duffy, Naiara Fernandez , Frank Peel, Michael Hudec, Timothy Dooley, Christopher Aiden-Lee Jackson 

Salt-detached gravity-gliding/spreading systems having a rugose base-of-salt display complex strain patterns. However, little was previously known about how welding of supra-salt minibasins to the sub-salt may influence both the downslope translation of minibasins on salt-detached slopes and the regional pattern of supra-salt strain. Using a regional 3D seismic reflection data set, we examine a large salt-stock canopy system with a rugose base on the northern Gulf of Mexico slope, on which minibasins both subside and translate downslope. Some minibasins are welded at their bases, and others are not. We suggest that basal welds obstruct downslope translation of minibasins and control regional patterns of supra-canopy strain.
The distribution of strain above the canopy is complex and variable. Each minibasin that becomes obstructed modifies the local strain field, typically developing a zone of shortening immediately updip and an extensional breakaway zone immediately downdip. This finding is corroborated by observations from a physical sandbox model of minibasin obstruction. We also find in our natural example that minibasins can be obstructed to different degrees, ranging from severe (e.g. caught in a feeder) to mild (e.g. welded to a flat or gently-dipping base-of-salt). By mapping both the presence of obstructed minibasins, and the relative degree of minibasin obstruction, we provide an explanation for the origin of complex 3-D strain fields on a salt-detached slope and, potentially, a mechanism that explains differential downslope translation of minibasins. In minibasin-rich salt-detached slope settings, our results may aid: i) structural restorations and regional strain analyses; ii) prediction of subsalt relief in areas of poor seismic imaging; and iii) prediction of stress fields and borehole stability. Our findings are applicable to other systems detached on allochthonous salt sheets (e.g. Gulf of Mexico; Scotian Margin, offshore eastern Canada), as well as systems where the salt is autochthonous but has significant local basal relief (e.g. Santos Basin, offshore Brazil; Kwanza Basin, Angola).