The Role of Hanging Wall Structure in Thrust Systems

N. J. Banbury
University of Edinburgh, Dept. of Geology and Geophysics, Edinburgh, Scotland

Thrust-related anticlines provide important petroleum exploration targets in prospective sedimentary basins. Analysis of the folds in these areas show that they are commonly characterized by subsidiary structures which can enhance or destroy their prospective potential and are frequently beyond seismic resolution. Well-exposed thrust systems such as the south Pyrenean foreland fold and thrust belt provide invaluable analogs for these structures and allow structural styles to be analyzed at the outcrop scale.

Detailed field investigations of two regionally significant thrust settings in the southern Pyrenees has revealed several important mesoscale structures. A fault-propagation anticline at the leading edge of the Boixols thrust contains an extensive system of extensional faulting all of which is superimposed on the structure and is a function of the hanging-wall fold geometry. Faults have two dominant orientations, axis parallel and axis perpendicular and range in offset from one to eighty meters with axis parallel faults generally having the greatest throw. A further study area in the Aguero area of the western External Sierras consists of a triangle zone thrust geometry with a pair of foreland dipping backthrusts converging to a single point. In both cases synsedimentary and posttectonic sediment entry points have been controlled by the structural configuration of the thrust front. This has led to localized coarse clastic deposition.

The clear implication of the field studies is that petroleum prospectivity of structural closures and reservoir distribution can be improved through detailed analysis of exposed thrust systems.

AAPG Search and Discovery Article #90902©2001 AAPG Foundation Grants-in-Aid