ABSTRACT: Compartmentalisation of an Inverted Lower Cretaceous extensional basin, south central Pyrenees, Spain

Bond, Robert M.G.¹, and Ken R. McClay²
(1) Paradigm Geophysical (UK) Ltd, Slough, Berkshire, United Kingdom
(2) Department of Geology

The Boixols thrust sheet is the uppermost structural unit of the south-vergent upper cover thrust sheets in the South Central Spanish Pyrenees. It is composed of kilometric-scale folds. Five sedimentary megasequences identified within the thrust sheet can be related to phases of extension, tectonic quiescence and phases of inversion. At the leading edge of the thrust sheet the Sant Corneli - Boixols - Avets - Nargo - Narieda chain of anticlines exhibit evidence of synsedimentary growth due to fault-propagation.

Abrupt lateral and longitudinal variations in the thickness of the Lower Cretaceous deposits are interpreted as being due to an oblique extensional event which generated en-echelon extensional faults. These segmented the basin and produced offsets in the bounding extensional margin fault. During Uppermost Cretaceous contraction, the locations and geometries of the leading-edge folds and thrusts were strongly controlled by this initial segmentation. Folds cored by large thicknesses of Lower Cretaceous marls and limestones have longer wavelengths and more rounded geometries than folds cored by thinner Lower Cretaceous and Jurassic successions. Variations in the original structural linkage of the basin segments and in the fold shapes caused complex interactions along strike between each member of the fold chain and its neighbours.

This study has investigated the nature of the compartmentalisation of the leading edge thrusts, through forward modelling of growth structures, and structural reconstruction of the thrust sheet in a number of balanced sections.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia