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Abstract: Interaction of Folding, Sedimentation, and Erosion in Three Dimensions: A Study of the Sant Llorenc de Morunys Fault Propagation Fold, Southeast Pyrenees Using gOcad: Initial Results

FORD, MARY, Ecole Nationale Superierure de Geologie, Nancy, France 

Modeling of structures in three dimensions is an area of intense research activity both within the hydrocarbon industry and within academia. Initial results of a new project involving the three-dimensional modeling of a fault propagation fold using gOcad will be presented. The project focuses on the Sant Llorenc de Morunys growth fold pair that lies on the northern border of the Tertiary foreland basin of the Southeast Pyrenees (Elbro Basin). This fold pair represents one of the best preserved, best exposed, and best study examples in the world of fault propagation folding associated with growth strata. The folds, formed within alluvial conglomerates, are exposed for 15 km in a series of deeply incised river valleys with topography of more than 1000 m, and have been mapped at a scale of 1:5000. Four sequentially restored cross sections reveal remarkable structural and stratigraphic variations across strike. The mechanism of fold development is controversial. Suppe et al. (Suppe, J. Sábat, F., Munoz, J. A., Poblet. J., Roca, E., and Verges, J., 1997, Bed-by-bed fold growth by kink-band migration: Sant Llorenç de Morunys, eastern Pyrenees: Journal of Structural Geology, v. 19, p. 443-461) have proposed a model of hinge zone migration whereas Ford et al. (Ford, M., Williams, E. A., Artoni, A., Verges, J., and Hardy, S., 1997, Progressive evolution of a fault-related fold pair from growth strata geometries, Sant Llorenc de Morunys, southeast Pyrenees: Journal of Structural Geology, v. 19, p. 413-441) have proposed a limb rotation model with minor hinge migration as a necessary process due to the synsedimentary nature of folding. The area therefore represents an ideal natural laboratory for the development of three-dimensional modeling procedures for fault propagation folds.

A three-dimensional image of the fold pair is constructed on a digital elevation model within gOcad. The aims of this project are to sequentially restore each of nine stratigraphic levels in three dimensions using surface and volume restoration procedures currently being developed within the gOcad group. A three-dimensional forward model or models of fold elevation incorporating processes of erosion and sedimentation are being developed. 

AAPG Search and Discovery Article #90912©1999-2000 AAPG International Distinguished Lectures