POSTVOLCANIC PALEOZOIC OF THE IBERIAN PYRITE BELT - AN EXAMPLE OF BASIN MORPHOLOGIC CONTROL ON SEDIMENT DISTRIBUTION IN A TURBIDITE BASIN

The Iberian Pyrite Belt (South Portuguese Zone, Hercynian Chain), an i mportant metallogenic province, has a volcanic-sedimentary origin. Ove rlying this volcanic succession is a thick sedimentary unit, the Culm Group, which represents postvolcanic Paleozoic sediments of the Iberia n Pyrite Belt, It consists of three stratigraphic units: the Basal Sha ly Formation (BSF), the Culm Facies Turbiditic Formation (CFTF), and t he Shallow-platform Sandy Unit (SPSU). The BSF is represented by fine- grained sediments of volcanic to nonvolcanic origin that mark the end of volcanism in the region, the reworking of volcanic products in a sh allow-marine basin, and the beginning of autochthonous sedimentation o f pelagic clay. It constitutes a depositional sequence sensu Mitchum e t al. (1977). The distribution, facies, and facies associations of the turbidites of the CFTF are related to the configuration of the basin, which controlled the mechanisms of deposition and distribution of the detritus from different source areas. The SPSU represents sediments e roded from the volcanic upland and redistributed over the shelf. Detai led study of these three units and their relationships provides the me ans to define the geometry and evolution of the postvolcanic Carbonife rous basin of the Iberian Pyrite Belt. The basin was roughly subdivide d by the Paymogo and the Puebla de Guzman paleoridges. Together with t he allochthonous Ossa-Morena Zone, north of the study area, they forme d three topographic barriers that delineated two interconnected subbas ins. Sedimentation in the postvolcanic basin of the Iberian Pyrite Bel t can be related to a model of oscillating sea level. Synorogenic char acteristics of the Culm Group sediments support a tectonic origin for the sea-level oscillations, particularly since the sediments had alrea dy been affected by the first pulses of the Hercynian Orogeny.