Lower Ordovician unconformities and the Ollo de Sapo magmatic event: coeval 478 Ma pyroclastic base-surge deposits and subvolcanic granite intrusion in the Hiendelaencina Antiform

Ordovician geodynamics: The Sardic Phase in the Pyrenees, Mouthoumet and Montagne Noire massifs International Meeting (2017. Figueras, España)The Cambro-Ordovician Ollo de Sapo volcanic event in the Central Iberian Zone has different stratigraphic unconformities associated with it. In the Ollo de Sapo antiform of northwest Iberia and its continuation in the Hiendelaencina antiform of Central Spain, there is not clear evidence of an angular unconformity at its base. However, an erosive unconformity is mentioned in the literature separating the coarse Ollo de Sapo from the overlying Ordovician sequence in the Hiendelaencina Antiform. The Bornova conglomerate of Soers (1972) was interpreted as a product of the erosion of the underlaying felsic tuffs and ignimbrites of the Hiendelaencina gneiss of Schäfer (1969). Closer examination of this unit, along new clean road cuts near the village of La Bodera indicates that these “microconglomerates” are part of metric-scale pyroclastic base surge deposits. These base surge deposits are approximately 1 m thick with a felsic volcanic breccia at the base, a coarse unit with well-developed cross bedding and abundant rounded volcanic quartz and thin 1-2 cm thick siltstone at the top. The deposits are locally truncated by successive surges and intercalated with quartzite beds, suggesting that they might be the product of phreatomagmatic eruptions in a near-shore environment.Instituto Geológico y Minero de España, EspañaGeological Survey of Canada, CanadáPeer reviewe