Boletín de la RSEHN. Sección Geológica

El presente trabajo se localiza en el Macizo de Los Pelados-El Nevero y tiene como objetivos el inventario, cartografía, cronología e interpretación de la secuencia evolutiva de sus paleoglaciares. La altura media de este macizo es de 2100 m (Pico del Nevero, 2209 m) y su litología (orto, para y leuco-gneises) y ambiente climático (mediterráneo de montaña continentalizado) son los propios del Guadarrama Central. En el contexto fisiográfico, este macizo destaca por su trazado casi E-W frente a la dirección general NE-SW del conjunto de los Montes Carpetanos y por su morfoestructura de bloque disimétrico basculado (laderas meridionales escarpadas-laderas septentrionales tendidas). Esa dismetría, junto a los escalones oriental y occidental debidos a sistemas de fallas de tendencia N-S (los de los puertos de Navafría y Malagosto), dieron origen a una pequeña meseta topográfica en la planicie de cumbres que posibilitó el desarrollo de un glaciarismo distintivo en estas áreas, caracterizados por: una tendencia centrífuga de las lenguas glaciares a partir de las cimas; una relativa abundancia de glaciares con localización septentrional y la presencia de un pequeño glaciar de meseta. Los datos obtenidos mediante datación absoluta 10Be-TCN en el paleoglaciar de Hoyo Grande, muestran que la MIE local (~26 ka BP; MIS2) ocurrió sincrónicamente con el LGM.

The studies on glacial geomorphology of the Sierra de Guadarrama have been focused mainly on the Peñalara Massif and, in general, the cartographies provided have little detail and in many cases are imprecise. In fact, in this mountain range there are areas with paleoglaciares that were described for the first time in the second half of the last century and the cartographies are only schematic. One of these areas is Los Pelados-El Nevero Massif, which is where this work is located. The main objectives are the inventorying, describing and mapping in detail its glacial morphology and establishing the absolute chronology of some evolutionary reference stages.

Los Pelados-El Nevero Massif has an average height of 2100 m asl and its culmination is the peak of Nevero (2209 m). Its lithology (ortho, para and leuco-gneises) and climatic environment (Continentalized Mediterranean mountain climate) are the generals corresponding to central Guadarrama sector (Fig. 1). However, its morphology has some distinctive features such as its E-W tendency versus the NW-SW general direction of the whole of the Montes Carpetanos range, or the dissymmetric morphostructure of its mountain-block (tilted block: steep southern-face and gentle northern-slopes). This dissymmetry, together with the eastern and western steps due to N-S trend faults systems (those of the Navafría and Malagosto ports), gave rise to a small plateau type summit surface that enabled the development of a distinctive glaciarism in this massif (Fig. 2, Fig. 3).

In the other massifs of the Sierra de Guadarrama (Peñalara, Cabezas de Hierro) the glaciers were developed on double slope (southeast-northwestern; northern-southern) predominating those of southern location. However, in the case of the Los Pelados-El Nevero Massif the glaciers had a centrifugal tendency from the topographic plateau with of the glaciarism of this massif are, as much the relative abundance of glaciers in northern slopes as the existence of a small plateau-type glacier. All this configures a massif with remarkable development of the glaciers (Fig. 3, Table I). The maximum length reached by a glacier in this area was 2294 m and the lower topographic elevation reached by the ice during its maximum extension (local MIE) was 1560 m asl, parameters that corresponds to the paleoglacier of Porrinoso-Peñacabra. With the data available so far, obtained by means of 10Be-TCN absolute dating in the paleoglacier of Hoyo Grande (Table II), the local MIE is synchronous with the LGM (~26 ka Bp; MIS2). This age is in agreement with the chronology obtained for the MIE of the Peñalara paleoglacier (18 km to the SW), but it is in disagreement with chronology obtained for the MIE of the La Mujer Muerta paleoglacier (30 km to the SW), given that it is attributed an age corresponding to the MIS3 and, therefore, prior to the LGM.