Martha Oliver Withjack¹, Roy W. Schlische¹

(1) Rutgers University, Piscataway, NJ

ABSTRACT: Structural Styles of Rift Basins

Structural geometries of rift basins vary significantly, depending on the mechanical behavior of prerift and synrift packages, tectonic activity before and after rifting, and obliquity of rifting. The following rift-basin classification is based on these factors. Type 1 basins (e.g., southern Suez rift; Jeanne d'Arc basin, SE Canada) have salt or thick shale in the prerift or synrift packages. They are characterized by forced folds above basement-involved normal faults, diapiric structures, and detached normal faults and associated fault-bend folds. In Type 2 basins (e.g., Fundy basin, SE Canada; Jeanne d'Arc basin), one or more major contractional events preceded rifting. Many of the normal faults in Type 2 basins are reactivated basement-involved thrust faults. These faults are commonly low angle and have large displacements. In Type 3 basins (e.g., Fundy basin; Vøring basin, offshore Norway; Exmouth basin, NW Australia), one or more contractional events followed rifting. These inverted rift basins are affected by late-formed contractional structures including normal faults reactivated as reverse faults, newly formed reverse faults, and contractional fault-bend and fault-propagation folds. Type 4 basins (e.g., Dampier basin, NW Australia) are produced by oblique rifting. They are characterized by faults with strike-slip, normal, and oblique-slip displacement and with multiple trends (i.e., parallel and oblique to the rift trend). Rift-basin type strongly affects petroleum potential. The timing and geometry of potential structural traps differ for the rift-basin types. Also, the distinct structural geometries in the rift-basin types influences depositional patterns and, thus, the distribution of potential reservoir and source rocks.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado