TRIANGLE ZONE AND THRUST WEDGE GEOMETRIES RELATED TO EVAPORITIC HORIZONS (SOUTHERN PYRENEES)

The South Pyrenean fold-and-thrust belt triangle zone developed above Eocene to Oligocene foreland evaporitic levels, The triangle zone, Oli gocene in age, dies eastwards and westwards where the thrust front bec omes south-directed and emergent. The eastern and western terminations of the triangle zone coincide with the edges of the evaporitic basins . The frontal thrust wedge defines abrupt changes in trend related to the depositional orientation of evaporitic limits: the NE-SW Suria Ant icline, the NW-SE Sanaiija Anticline and the E-W Barbastro-Balaguer An ticline. The thrust wedge is formed commonly at pinch-outs of salt wit hout changes in structural level, although in some localities the thru st wedge developed above a thrust ramp geometry. Constrained timing an d structural evolution of the foreland fold-and-thrust belt indicate t he existence of northern and previous thrust wedges located at the Oli ana and Puig-reig anticlines and the Sanaiija Anticline that have been abandoned as deformation progressed southward. Frontal thrust wedges were incorporated into the triangle zone which widened as new frontal thrust wedges developed forwards, at the southern edge of higher evapo ritic levels. The exposed example is well understood because of contin uous field exposures, syntectonic sedimentary relationships and new, g ood quality seismic profiles as well as subsurface control from oil an d potash exploration wells.