3-D Salt Walls and Associated Fault Systems: Animations

FAULT SURFACES

Animation showing fault surfaces (various colors) and the salt layer (gray). Grabens form curved, relay, parallel or branching patterns, but their mean trend is roughly perpendicular to the direction of seaward extension and progradation. Fault patterns combine with salt walls to form complex partial barriers that could influence the flow of hydrocarbons. The advantage of using 3-D visualization to help grasping of the geometry of these faults and their relations to the salt structures is evident. (358 K)

RAFT LINKAGE

This animation shows the progressive peeling of strata revealing subsurface 3-D structures in the model. Removing the upper two layers exposes the crests of the tallest diapirs (pale gray) and fault scarps seaward. Peeling another layer shows how rafts, which are separated in the dip section, connect between stocks rising from a salt wall; the rafts have been gently flexed to form turtle structures. Further peeling exposes deep levels where rafts are increasingly more isolated because of the greater extension of older strata. Completely exposed salt layer. Horizontal grooves (parallel to the red arrows) are the actual impressions of sand layers against the steeply dipping flanks of diapirs. These bedding traces illustrate the fidelity of the computer-rendered surfaces. (520 K)

SALT LAYER

This animation shows structure contours on top of the salt. Warm colors represent structural highs; cold colors, structural lows. The map view is lit from the left. Landward, slow aggradation rates (relative to extension rates) favor shallowly buried, steep-sided, overhanging salt walls. Salt walls change markedly along strike, including reactive diapirs with triangular sections, passive stocks, immature salt rollers or ridges, and mature passive walls with overhangs. Although deeply buried salt rollers having gently dipping flanks may form throughout the model, they are more common seaward where aggradation rates rise faster than extension rates. The tallest walls and stocks have flat crests because they reached the surface as passive diapirs. Conversely, lower salt ridges and rollers never reached the surface so retain the pointed crest of a reactive diapir. The mean trend of the salt walls and rollers is roughly perpendicular to the direction of extension. However, their trends vary considerably (red lines in map view), and the salt walls form branching and relay patterns. High stocks curve and decline along strike to form low salt ridges. Branching patterns may connect to form polygons. (423 K)

IRREGULAR TURTLE-STRUCTURES

This animation shows structure contours on top of layer 3. Salt walls (gray) drain salt from beneath adjacent strata producing irregular turtle-structure highs (warm colors) and adjoining irregular regions of salt subsidence (blue and purple). These structures evolve unevenly in time and space. (423 K)

SALT WITHDRAWAL

This animation shows an overhanging, passive stock that efficiently withdraws salt from the reactive diapir along strike. Adjacent strata subside below the regional datum. (455 K)

CLOSURES AT CURVED WALL, MAP VIEW

At depth, along-strike curvature of the salt wall strongly controls trap area and closure. In the outer (west) arc, contact drag is dispersed to produce a trap of large area but small closure. Conversely, in the inner arc, contact drag is focused, which creates a trap of small area but large closure. (195 K)

CLOSURES AT CURVED WALL, OBLIQUE VIEW

At depth, along-strike curvature of the salt wall strongly controls trap area and closure. In the outer (west) arc, contact drag is dispersed to produce a trap of large area but small closure. Conversely, in the inner arc, contact drag is focused, which creates a trap of small area but large closure. (520 K)

CLOSURE AT FAULT-DISPLACEMENT HALF-DOME

This animation shows a three-way anticlinal closure in the upthrown block of a normal fault in layer 6 is produced by variation of slip along the strike of the fault. This fault-displacement half-dome contrasts with the opposing half-basin on the downthrown side, which would be drained of hydrocarbons. (423 K)

CLOSURE AT CANOE-SHAPED GRABEN TERMINATION

Canoe-shaped graben termination at the base of a stock. The sides of the canoe are represented by curved (listric) fault surfaces showing curved bedding traces. The crestline of a stock (gray) raises the bow of the canoe, creating a structural high that could trap hydrocarbons that migrate laterally from deeper parts of the graben. (163 K)