--> ABSTRACT: Geomechanical Implications and Structural Interaction between Allochthonous and Autochthonous Salts and in the Southern Pyrenean Central Unit, Spanish Pyrenees, by Backe, Guillaume; Brealey, Simon; O'Brian, Sean; #90135 (2011)

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Geomechanical Implications and Structural Interaction between Allochthonous and Autochthonous Salts and in the Southern Pyrenean Central Unit, Spanish Pyrenees

Backe, Guillaume 1; Brealey, Simon 2; O'Brian, Sean 2
(1)ASP, University of Adelaide, Adelaide, SA, Australia. (2) Beach Energy, Adelaide, SA, Australia.

The Southern Pyrenean Central Unit in the Spanish Pyrenees represents a series of thrust stacks accommodating the convergence between the European and the Iberian plates during the Pyrenean orogeny. The presence of various levels of salt in the stratigraphy of the SPCU played a major role in the development of the structure in the Pyrenean Foreland basins, and in the SPCU. Salt is a weak material, which can accommodate very large amount of strain and displacement following visco-plastic rock behaviour. Amongst these possible detachments in the SPCU, the Triassic salt Fm., present throughout the Pyrenan forelands basins, and the Oligocene evaporites of the Barbastro Fm. have held a major influence in the development of the structures in the SPCU.

In this work, a new series of structural cross-sections across the SPCU and foreland basin of the Pyrenees are proposed. These sections have been constructed using a combination of satellite imagery interpretation, field data, seismic data of different vintage including recent acquisition programs, and well data. These sections highlight the structural relationships between the different levels. In particular, the south-verging thrust stacks detached above the Triassic evaporites in the SPCU are limited to the south by a major autochtonous detachment anticline cored by the Oligocene Barbastro evaporite. Furthermore, finite and boundary element geomechanical modelling, using state of the art numerical codes, shows that the variation of the in-situ stress as well as the distribution of fault slip and reactivation risk is highly controlled by the geometries and thicknesses of the salt bodies at depth.

This study brings forward new clues to understand the tectonics of the salt-bearing Pyrenean foreland basins. The methodology presented here could potentially be applied to similar basins around the Alpine-Himalayan belt, but also in other foreland basins around the world.

 

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.