Stratigraphy, petrography and dispersion of the lower Permian syn-eruptive deposits in the Viar Basin, Spain

摘要

This paper presents a stratigraphic, petrographic and sedimentologic analysis of felsic syn-eruptive deposits of the southernmost Permian basin in Europe (Viar Basin), an inner-orogenic, transtensional half-graben located between two major geotectonic zones of the Iberian Variscan Belt, SW Spain. The syn-eruptive deposits of the Viar Basin represent a mappable lithostratigraphic unit, that is herein named the Los Canchales Formation. This unit forms a wedge-shaped body bounded by alluvial-fluvial deposits (red layers) that are in gradational contact. The stratigraphic architecture of the Los Canchales Formation is complex with frequent facies changes and interfingering among pyrodastic rocks, resedimented-volcaniclastic rocks and sedimentary rocks. Abundant fossil flora is also recorded.rnA wax-wane cycle of volcanic activity is recognized during the syn-eruptive period. Two short-lived volcanic episodes were recorded including ignimbrites and a possible phreatomagmatic event. Explosive volcanism generated pyrodastic flow, surge and ash-fall deposits, in cases collapsing the drainage network. They also modified the vegetation and created a new depositional setting with four successive sedimentary environments: vegetated floodplain, ephemeral sandy braidplain, palustrine environment and again vegetated floodplain. Input of pyroclasts followed a NW to SE longitudinal-axial dispersal pattern.