Thrusting, Halotectonics, and Sedimentation in the Spanish Pyrenees

David J. Anastasio

The Spanish Pyrenees are a linked system of regional thrust sheets and intermontane basins which formed during the Tertiary collision of the European and Iberian plates. The structural evolution of the Pyrenees was controlled by Mesozoic extensional structures and evaporite-bearing strata which served as the regional decollement and produced widespread pre- to postthrusting halotectonic folds. Palinspastic restoration of Cretaceous strata from the Pyrenean realm delineates a large normal-faulted embayment in the northern Iberian margin. Thicker sediments within the bay, coupled with the southward emplacement of the Cotiella-Montsec thrust sheet, caused underlying evaporites to flow toward the basin margins, producing folds such as the Mediano anticline.

Contemporaneous with the thrusting, salt structures propagated westward along the depositional axis of the foreland basin in response to prograding Paleogene clastic systems, which included fluvial, deltaic, and marine slope environments. More easterly folds, including those of the Boltana region, formed prior to local thrusting and controlled the geometry of the developing Gavarnie thrust sheet. The more westerly folds, including those exposed in the External Sierra, developed atop the active Guarga thrust sheet within the transported Jaca basin. The folds of the External Sierra are transport parallel (N-S), tight symmetric anticlines and broad synclines distributed periodically along the frontal emergent imbrications of the Guarga thrust. In general, the map-scale folds of the Spani h Pyrenees become smaller in dimension and younger westward. Although some diapirs occur, most of the anticlines are nonpiercing yet evaporite or cornieule cored. The structural geometries and temporal constraints between the thrusting and halotectonics within the region are well preserved within the synorogenic foreland basin stratigraphy.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.