Comparison of basin types in active and ancient strike-slip zones

Hydrocarbon exploration in strike-slip zones requires awareness of several distinct basin types, traditionally defined on the basis of bounding fault geometry: pull-aparts (P), fault-wedge basins (W), fault-angle basins (A), fault-flank basins (F), and ramp valleys (R). We compare the characteristics and frequency of these basin types in an active (40 post-Eocene basins of the northern and southern Caribbean) and ancient (19 Late Devonian-Carboniferous basins of the northern Appalachians) strike-slip setting. Pull-apart basins, which lengthen and deepen at fault discontinuities with increased strike-slip offset, constitute the best studied and most numerous basin type. Other recognizable basin types are less numerous and often shorter lived than pull-aparts, and this may reflect: (1) their role as precursory structures prior to concentration of strike-slip displacement on a single fault; (2) their role as interference structures at random fault junctures; and (3) the unlikelihood of preservation because of thinner sedimentary fill. Several disrupted basins of complex or unknown origin (D) appear to have initiated as pull-aparts and subsequently to have been offset into halves or modified into compressional ramp valleys. Using observations from active basins, several geologic criteria for distinguishing compressional vs. extensional origin of reactivated ancient basins are discussed.