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Alonso, J. L., F. Colombo, and O. Riba, 2011, Folding mechanisms in a fault-propagation fold inferred from the analysis of unconformity angles: The Sant Llorenc growth structure (Pyrenees, Spain), in K. McClay, J. Shaw, and J. Suppe, eds., Thrust fault-related folding: AAPG Memoir 94, P. 137151.


Copyright copy2011 by The American Association of Petroleum Geologists.

Folding Mechanisms in a Fault-propagation Fold Inferred from the Analysis of Unconformity Angles: The Sant Llorenc Growth Structure (Pyrenees, Spain)

J. L. Alonso,1 F. Colombo,2 O. Riba3

1Departamento de Geologia, Universidad de Oviedo, Oviedo, Spain
2Departament d'Estratigrafia, Paleontologia i Geociences Marines, Universitat de Barcelona, Barcelona, Spain
3Departament d'Estratigrafia, Paleontologia i Geociences Marines, Universitat de Barcelona, Barcelona, Spain


We thank Josep Poblet and Mayte Bulnes for their encouragement and critical reading of a previous version of the manuscript. We are grateful to John Suppe and Josep Anton Munoz who suggested to us working in the lower growth wedge of the Sant Llorenc structure. Three anonymous referees helped to improve the manuscript. We also thank Ana Ojanguren for helping with the English translation. Projects BTE2002-04316-C0303 and CGL2006-12415-C03-02 of the Spanish Ministry of Science and Technology, and the Grup de Qualitat SRG2002-2004, Department d'Universitats Recerca y Societat de l'Informacio, Generalitat de Catalunya, partially funded this work.


This chapter shows, from the theoretical point of view, that growth strata geometries above angular unconformities depend on the modification of initial unconformity angles due to different folding mechanisms operating in underlying layers. This theory is applied to the Sant Llorenc de Morunys growth structure, where the analysis of the unconformity angles shows that classic folding mechanisms, such as layer-parallel simple shear in both angular and curved folds, and tangential-longitudinal strain operated in the forelimb of a fault-propagation fold. These folding mechanisms, inferred from changes in unconformity angles, are consistent with the minor structures and lithological features of the involved stratigraphic units. Forward modeling, including limb rotation, hinge migration, and the above-mentioned folding mechanisms, explains the main structural features of the syntectonic sediments in the Sant Llorenc de Morunys fault-propagation fold.

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