Abstract: Hydrocarbon Prospectivity and Classification of Extensional Basins

Charles W. Harris, Emery D. Goodman

Based on studies of 125 basins, we subdivide extensional basins into four classes: (1) core complex (e.g., Betic basin), (2) orogenic collapse (Newark basin), (3) narrow rift (Gulf of Suez), and (4) wide rift (Viking Graben). The hydrocarbon potential of core complex and orogenic collapse basins generally is poor, while that of narrow- and wide-rift basins can be fair to excellent. Narrow-rift and wide-rift basins are more hydrocarbon prone because multiphase extension and thermal subsidence improve source, reservoir, and trap potential and lead to favorable maturation-migration histories. A generalized pattern of evolution leads from basins formed on overthickened crust (>45 km, core complex and orogenic collapse basins) to those formed on normal thickness crust (approx. 30 to 40 m, narrow- and wide-rift basins). Core complex and orogenic collapse basins that are generated by simple shear commonly owe their internal geometry and low-angle fault dips to structures formed during compression or duplication of continental crust. Extension on low-angle faults occurs within 50 m.y. of the last compressional event and is attributed to isostatic and gravitational instabilities. Either these early faults are reactivated, or new faults supersede and overprint existing structures. Narrow- and wide-rift basins develop on crust <40 km thick, with average to elevated regional heat flow. Their formation postdates by >50 m.y. any previous crustal thickening. High-angle normal faults are prevalent in narrow- and wide-rift basins.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994