COWARD, MIKE and ALISON RIES, Ries-Coward Associates Limited, Reading, UK

Abstract: Thick-skinned Versus Thin-skinned Fold and Thrust belts, Alternative Models for the Interpretation of Structures in the Sub-Andean Basins and their Significance in Terms of Basin Modelling

Hydrocarbon plays in many fold and thrust belts often have been interpreted in terms of thin-skinned tectonics, where the thrusts are linked to a basal detachment, usually within the cover sequence. However faults and folds related to thick-skinned, basement-involved deformation have been recognised in the frontal regions of many orogenic belts, from the Andes to Himalayas. They form the main types of structures within many intra-continental fold belts. Often thin-skinned structures hide thrust geometries and associated sub-thrust hydrocarbon plays related to basin inversion at depth. In many regions it is the thick-skinned structures, sometimes associated with basin inversion, sometimes with reworking of early basement fabrics, which form the best hydrocarbon traps, particularly in the frontal regions of the fold and thrust belts.Thick-skinned structures generally initiate before adjacent thin-skinned thrusts, blocking hydrocarbon migration across the foreland basin. Recognition of these structures therefore is critical for modelling hydrocarbon maturation and migration within a basin.

This paper will describe some of the geometrical techniques which can be used to help distinguish between thin-skinned thrusts and their associated folds and those structures developed by reactivation of steeper basement faults.

Examples will include the fold/thrust belts and their associated hydrocarbon fields from different basins along the length of the Andes, including the East Venezuela Basin, the Magdalena basins and the frontal belts of Peru and Bolivia. Emphasis will be made of the importance of thick-skinned fault recognition in terms of 2D and 3D basin modelling.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England