Discontinuidad sedimentaria del Ordovícico terminal en los Pirineos Centrales

Resumen

The Upper Ordovician stratigraphic sequence from the Pyrenean Axial Zone starts at a basal conglomerate, known as the Rabassa Fm in the Central and Eastern Pyrenees, that overlays unconformably an undated silicidastic sequence. The vertical stacked fades of that sequence include, over the basal conglomerate layer, greywackes, siltstones and claystones with brachiopod and briozoan fauna of the Upper Caradoc to Lower Ashgill age, reported in the Cava Fm from the Central Pyrenees; micritic and crinoidal limestones dated as Ashgill, the Estana Fm; and, finally, slates with a poorly fossil contends attributed to the Ashgill, the Ansovell Fm. The sequence ends at an unconformity, described in this work, that is overlaid by a discontinuous conglomerate including pebbles of previous Upper Ordovician stratigraphic units. That unconformity and the conglomerate layer are attributed to the erosion of the top of the Upper Ordovician sequence caused by the sea level fall of the glacial Hirnantian stage. The overlain transgressive quarzite, Bar Fm, preludes the well dated black carbonaceous slates of Silurian age and it is attributed to the sea level rise that mark the end of the glacial Hirnantian event