Samples of visualization and interpretation of rising and falling salt diapirs (see 2-D animation ). Hot colors represent structural highs.

Figure 1 Structure contours on top of the salt.  Regional extension produced listric faults that triggered the rise of continuous reactive salt walls (A and B) and intervening salt-wall relay systems. Active diapirs emerged and evolved into flat-topped passive diapirs that were later buried. Extensional rejuvenation then produced a central spinelike reactive crest (B and Figure 4). Diapir sagging and indentation of crestal grabens into the salt produced a double-crested salt wall (B), where diapirs widened faster than they could import salt from their depleted source layer.

Figure 2 Hydrocarbon migration patterns. Early regional extension produces rotational faulting in prekinematic blocks so that the landward edges of each block (purple) subside the most into the salt. At this stage, hydrocarbon migration (white arrows) tends to be seaward (to the right).

Figure 3 Late diapir sagging and grounding of the underlying fault block reverses the rotation and causes the seaward edge (A) of synkinematic fault blocks to subside. Regional hydrocarbon migration (black arrows) tends to be landward, opposite to that in the prekinematic layers (Figure 2). Farther landward, extension was much less and created several en-echelon grabens. There, within the soft-linked zone of relay ramps (B), subsidence was minimal because total regional extension was distributed among more grabens than elsewhere (C and D). Within each graben, hydrocarbons would migrate up the relay ramps (blue arrows). This local migration would be orthogonal to regional migration elsewhere in prekinematic or synkinematic strata.

Figure 4 Early extension creates faults (A) flanking the base of a reactive salt wall. The crest of this wall was flat (yellow) because the diapir emerged and became passive before being buried by the blue-gray layer. Later extension created a graben (B) in the new sedimentary roof, which triggered rise of a narrow second-generation reactive diapir (red) above the broad crest of the passive diapiric wall.

Figures 5 and 6 In a soft-linked zone, gray salt walls enhance deformation of older prekinematic layers (brown, green, and blue). The map shows the structure of the brown layer, which pinched out (B) as an apparent downlap against the underlying green layer. Horsts (bounded by faults C) warped along strike to form an anticline (most apparent in the oblique view). Arrows show potential hydrocarbon migration paths toward the anticlinal culmination of this fault-bounded turtle structure.


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