Print this pagePull-Apart Basin Evolution Based on Physical Analog Modeling and Natural Examples: Implications for Hydrocarbon Trapping
FERRILL, DAVID A., BRET RAHE, and ALAN P. MORRIS
Comparing experimental results with natural prototypes (Death Valley region, CA) allows insight into pull-apart basin evolution, geometry and topology with emphasis upon hydrocarbon trapping potential. Based upon experimental results, basin evolution is separated into three stages: incipient, early, and mature: Incipient basins are characterized by normal fault bounded grabens or half-grabens parallel to the oblique step between main strike-slip zones. In early stage, new normal faults form toward the basin interior and cross-basin strike-slip faults cut diagonally across the basin; basin-bounding normal faults are characterized by lateral variations of throw and localized relay ramps. In mature stage, strike-slip and normal faults join to completely bound the basin while cross-basin faulting develops into a through-going strike-slip fault which links the two main strike- slip zones ultimately resulting in a decline in normal fault activity. Modeling indicates that end-member symmetric and asymmetric and intermediate hybrid pull-apart basins follow the sequence described above. Basin symmetry is controlled by the relative displacement of opposing basin sides. Models with one fixed side form asymmetric basins defined by a half-graben with the master fault on the mobile side. Symmetric basins form where rates for opposing sides are equal and are defined by horst and graben structure with master fault dominance switching sides along basin length. Experimental results indicate that trapping potential exists in each basin type but that prime target areas are basin-type and developmental-stage dependent: Examples include the horst and complex hanging-wall structures of symmetric basins, antithetic rollover in asymmetric basins, and dissected hanging wall in hybrid basins. Developmental effects include the degree of fault linking or separation via relay ramps and the development of cross-basin strike-slip faults serving as barriers or conduits for fluid flow.