Did the Late Ordovician African ice sheet reach Europe?

Abstract

ABSTRACTPaleovalleys and their infi lling successions are described from outcrops and drill cores of the Cantabrian Range (northern Spain). A Hirnantia fauna and associated diamictites with striated lonestones indicate that the paleovalleys are related to the Hirnantian (latest Ordovician) glacial event. Based on overall geometry, depositional facies, and associated deformation structures, the paleovalleys are interpreted as subglacial tunnel valleys. They were most likely related to the North Gondwana ice sheet. The ice sheet therefore reached the Ibero-Armorican domain that was still attached to the Gondwana landmass at least until the latest Ordovician.INTRODUCTION The Hirnantian glacial record documents one or several ice sheets throughout Africa, Arabia, and South America, the extents of which are still controversial (Ghienne et al., 2007; Schonian and Egenhoff, 2007). Although glaciomarine strata are widespread in European peri-Gondwa-nan terranes (Robardet and Dore, 1988; Brenchley et al., 1991), they do not precisely indicate the presence of glaciers at those localities. Because a number of these terranes would have been attached to the Gondwana land-mass during the Late Ordovician (e.g., Robardet, 2003), the Gondwanan ice sheet may have reached some of them. The Hirnantian paleovalleys of the Cantabrian Range (northwest Spain) are the fi rst glacial valleys to be recognized outside the Gondwana landmass. They may be related to a Gondwanan ice sheet lobe or to a peri-Gondwana satellite ice cap.