--> ABSTRACT: Physical (Centrifuge) Modelling of the Influence of Lateral Fades Boundaries on Folding and Thrusting, and Implications for Hydrocarbon Trapping, by J. M. Dixon; #91021 (2010)

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Physical (Centrifuge) Modelling of the Influence of Lateral Fades Boundaries on Folding and Thrusting, and Implications for Hydrocarbon Trapping

DIXON, JOHN M.

Lateral facies boundaries are shown by scaled physical (centrifuge) modelling to affect the location and timing of nucleation of folds and thrusts. Model stratigraphic units consist of interlayered plasticine (simulating carbonates) and silicone putty (shale). A facies change, simulating a carbonate bank margin, is marked by a lateral change in the ratio between competent and incompetent laminae ("lime-shale" ratio) in one stratigraphic unit. The margin may have any plan configuration and orientation (strike and dip) relative to the shortening direction. The models have a length ratio of 10{-6} (1mm=1km) and are run at 2500-4000g.

The models indicate that bank margins are significant mechanical heterogeneities which have strong influence on superimposed fold-thrust structures. If shortening propagates from off-reef to reef, the off-reef strata undergo significant shortening before the reefal facies begins to deform. Folding dominates over thrusting in the off-reef. The bank margin can localize a prominent fold ahead of the advancing fold-thrust deformation front. A massive reefal facies (simulating massive carbonate) tends to resist shortening and then to deform by thrusting rather than by folding. This type of margin can localize a prominent thrust dislocation that propagates upwards into the overlying strata. A laminated reefal facies (simulating bedded carbonate or interbedded carbonate and shale) tends to deform by folding rather than thrusting, but the wave-length is longer than in the off-reef. in this situation the margin does not tend to nucleate a major thrust dislocation. Structures localized by a bank margin in a fold-thrust belt may be significant exploration targets because they may have formed sufficiently early in the generation-migration sequence to have trapped an early hydrocarbon charge. 

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.