Ninth International Conference on Permafrost ... - IARC Research

Pleistocene and Holocene Periglacial Forms in the Cantabrian Mountains(Northwest Spain)Dario Trombotto LiaudatIANIGLA, CONICET, 5500 Mendoza, ArgentinaV. AlonsoDepartamento de Geología. Universidad de Oviedo. 33005, Oviedo, SpainDetailed geomorphological mapping of a deglaciatedarea in the Cantabrian Mountains (CM) has revealed agreat variety of periglacial forms that have been ascribed todifferent cryomeres during and following deglaciation.The CM, with frequent altitudes around 2000 m, showerosional and depositional glacial features related to thePleistocene last glacial cycle; distribution of till, erraticblocks and glacially abraded surfaces indicate ice thicknessesup to 400 m in some areas (Alonso & Suárez Rodríguez,2004), while glacier fronts reached altitudes around 900 ma.s.l. in many of the valleys.A geomorphological map, at a 1:5000 scale, was made fora sector to the south of the main watershed characterized bya homogeneous bedrock. The map has been analyzed in aregional context.This zone around El Miro peak, 1985 m, shows a strongasymmetry in processes and forms. Most of them are fossilfeatures. Rock glaciers (Fig. 1), felsenmeer, protalus, boulderlobes, solifluction forms, and talus deposits were developed,from glacially derived material or from cryosediment, oncold slopes.Warm slopes, slighter or even nonglaciated, developedgiant sorted stone stripes (Fig. 2), boulder lobes and stonebankedlobes from cryosediment.In relation to deglaciation, gravitational slope readjustmentstook place in cirque zones and mixed landslides partiallymodified warm slopes; paraglacial alluvial fans were formedin adjacent valleys.Deglaciation in this zone of the CM was dated to be before34,000 ± 1400 14 C yr BP in Laguna de Villaseca, at 1305 ma.s.l. (Jalut et al. 2004). But terminal moraine complexes atlower altitudes, formed when glaciers still were 11 km inlength in areas with calculated previous ice thicknesses upto 260 m, suggest a long evolution between the beginningof deglaciation and stabilization phases during retreat. Otherdata worth mentioning (Pallàs et al. 2006) about the closeregion of the Pyrenees, where an early maximum glacierextent during the last glacial cycle is not excluded, indicatean extensive glaciation at ca. 18–20 ka (MIS 2), coincidingwith the global LGM.Altitude, aspect, preservation degree, and soil developmentof cryogenic forms around El Miro indicate more than onecryomere, although the lack of datable material has notallowed us to determine a precise time for these cryomeres.A tongue-shaped rock glacier in a cold and low positionand giant sorted stripes on warm slopes, both proposed tobe coeval with cirque glaciers, suggest continuous mountainpermafrost in ice-free areas during deglaciation, when themost important indicators were cryogenic periglacial and notglacigenic. We propose that conditions during deglaciationwere probably similar to those of the Pyrenees, wherecontinuous permafrost and important cryogenic landformswith glacier ice at the same time are represented in theClimex Map of 2002 for the Last Glacial Maximum.The peak of the periglacial environment in the CM, however,must have occurred after the LGM, with predominantly muchdrier climatic conditions and benefitting from vaster areasuncovered by ice; discontinuous permafrost, expressed byrock glaciers during the Late Pleistocene or Early Holocene,is likely to have reached 1540 m a.s.l.Figure 1. Fossil rock glacier.Figure 2. Giant sorted stone stripes.319