Obstructed minibasins on a salt‐detached slope: An example from above the Sigsbee canopy, northern Gulf of Mexico. (29th June 2019)

• Record Type: Journal Article
• Authors: Duffy, Oliver B.; Fernandez, Naiara; Peel, Frank J.; Hudec, Michael R.; Dooley, Tim P.; Jackson, Christopher A.‐L.
• Is Part Of: Basin research. Volume 32:Number 3(2020)
• Page Start: 505
• Page End: 524
• Publication Date: 2019-06-29
• Subjects: base‐of‐salt relief -- extension -- salt tectonics -- salt‐detached slopes -- shortening -- supra‐salt strain -- welding; Sedimentation and deposition -- Periodicals; Sedimentary basins -- Periodicals; 551
• DOI: 10.1111/bre.12380
• Languages: English
• ISSNs: 0950-091X

Abstract

Abstract: 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 of the obstructed minibasin. 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 example is detached on allochthonous salt and where the base‐of‐salt is rugose, with the findings applicable to other such systems worldwide (e.g., Gulf of Mexico; Scotian Margin, offshore eastern Canada). However, our findings are also applicable to systems where the salt is autochthonous but has significant local basal relief (e.g., Santos Basin, Brazil; Kwanza Basin, Angola). Abstract : In the early stages of margin development when minibasins are relatively thin and do not interact with the base‐of‐salt relief, the strain pattern on the salt‐detached slope is expected to be relatively simple. In contrast, later in margin development, when minibasins are thick enough such that their bases weld to the rugose base‐of‐salt, they become obstructed. During the latter stage a more complex strain pattern develops, with shortening strains typically developed immediately upslope of each obstructed minibasin and an extensional breakaway developed immediately downslope. In this paper, we propose that minibasin obstruction exerts a first‐order control on the mobility of minibasins and the pattern of supra‐salt strain.