EVOLUTION OF A CARBONIFEROUS PIGGYBACK BASIN IN THE SOUTHERN CENTRAL IBERIAN ZONE (VARISCAN BELT, SW SPAIN)

Two tectonic units have been distinguished in the southern parr of the Central Iberian Zone, an allochthonous and a para-autochthonous one, separated by a thrust with hanging wall movement towards the NE. The C arboniferous sedimentation is different in the allochthonous and para- autochthonous units. The latter has a thick (6,000-7,000 m) deposition al sequence of <<Culm>> facies essentially continuous with the pre-Car boniferous sedimentation. The allochthonous unit contains three Carbon iferous depositional sequences, namely a lower <<Culm>> facies sequenc e, a middle paralic facies sequence, and an upper continental facies s equence. These three depositional sequences are arranged as wedges suc cessively cropping out towards the northeast and separated by unconfor mities. The age, geometry, unconformable relationships and shallowing- upward tendency of the Carboniferous sedimentation in the allochthonou s unit are related to the geometry and propagation towards the northea st of the thrust separating the two tectonic units.