ABSTRACT: New Models of Thrust Kinematics and Implications for the Generation, Migration, and Entrapment of Hydrocarbons in Fold and Thrust Belts

Steven E. Boyer

The sequential development of thrusts is often more complicated than models commonly used in predicting the relative timing of hydrocarbon generation and entrapment in thrust belts and adjacent synorogenic foredeeps. Consequently, existing models may inadequately evaluate the potential of an unexplored basin or lead to missed opportunities in mature basins.

In a common approach to burial history profiling, thrusts are modeled as advancing singly in a simple hinterland-to-foreland (piggyback) sequence. Such models will often predict that hydrocarbons are generated and migrate updip toward the basin margins at rates faster than the advance of the thrust front. However, a more detailed study of the stratigraphic and structural evidence in some basins reveals that two or more thrusts experienced major movements simultaneously. Subsidence profiling that incorporates simultaneous thrusting suggests that hydrocarbon traps will develop synchronously with hydrocarbon generation and migration. A thrust load toward the hinterland will push its footwall into the generating window, and accompanying movement on an adjacent up-dip thrust provides the n cessary trap. During simultaneous thrusting, hydrocarbons may be trapped at depth within the basin, but an explorationist applying the piggyback thrust model would concentrate most of his or her effort on stratigraphic and structural traps on the basin margins.

Burial history modeling incorporating sequential thrusting suggests that hydrocarbons usually will migrate into an existing trap, which would be expected to exhibit planar oil-water contacts. In contrast, simultaneous thrusting should lead to tilted or folded oil-water contacts because hydrocarbon generation and thrusting occur concurrently in simultaneous thrusting.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990