Penultimate Glacial Cycle Glacier Extent in the Iberian Peninsula: New Evidence from the Serra Da Estrela (Central System, Portugal)

Geomorphology 388 (2021) 107781 Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph Penultimate Glacial Cycle glacier extent in the Iberian Peninsula: New evidence from the Serra da Estrela (Central System, Portugal) Gonçalo Vieira a,⁎, David Palacios b, Nuria Andrés b, Carla Mora a, Lorenzo Vázquez Selem c, Barbara Woronko d, Carmen Soncco a, Jose Úbeda b, Gabriel Goyanes e a Centre of Geographical Studies, Institute of Geography and Spatial Planning, University of Lisbon, Rua Branca Edmée Marques, 1600-276 Lisboa, Portugal b High Mountain Physical Geography Research Group, Department of Geography, Universidad Complutense de Madrid, 28040 Madrid, Spain. c Institute of Geography, Universidad Nacional Autónoma de México, México DF, Mexico d Faculty of Geology, University of Warsaw, Żwirki i Wigury 92, 02-089 Warsaw, Poland e Centre of Natural Resources and Environment, Instituto Superior Técnico, University of Lisbon, Portugal article info abstract Article history: The objective of this work is to present a first assessment on the age of the glacial features of the Serra da Estrela, Received 14 April 2021 in the central Portugal, Iberian Peninsula (40°19′ N, 7°37′ W, 1993 m), using Cosmic-Ray Exposure dating (in situ Received in revised form 10 May 2021 cosmogenic 36Cl). A total of 6 samples were dated, 4 extracted from exposed moraine boulders and 2 from gla- Accepted 11 May 2021 cially polished bedrock surfaces. Despite the low number of samples, the results are consistent, reinforcing pre- Available online 14 May 2021 vious dating obtained by other methods and geomorphological and paleoclimatic information. The maximum Keywords: extension of the glaciers occurred at the end of the Penultimate Glacial Cycle (Marine Isotope Stage 6), during Penultimate Glacial Cycle Heinrich Stadial 11, around 140 ka. At the end of the Last Glacial Cycle, slightly before the Last Glacial Maximum, Last Glacial Cycle at around 30 ka, the Estrela glaciers reached again a similar extent. Finally, the glaciers disappeared from the Serra Deglaciation da Estrela at the beginning of the Bølling-Allerød Interstadial, at around 14.2 ka. These data confirm a certain syn- 36Cl cosmogenic isotope chronicity in the major glacial phases in most the Mediterranean and also European mountains, although there Serra da Estrela are notable differences in the maximum extent in the two cycles. Portugal © 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 1. Introduction (Gómez-Ortiz et al., 2012, 2015), it took place closer to the LGM at 35 to 31 ka. Recent research has contributed to significant advances on the under- The LGM is marked by an important and long glacial advance in all standing of the glacial chronology of the Iberian mountains, but it has fo- the mountains of the Iberian Peninsula and is responsible for the largest cussed mainly in the end of the last glacial cycle and Holocene. However, and best-preserved moraines (Delmas, 2015). Their ages have been the period when the glaciers reached their Maximum Ice Extent (MIE) in mainly obtained by Cosmic-Ray Exposure (CRE) dating and show mul- the Iberian Peninsula is still poorly known (Oliva et al., 2019). tiple small glacial advances and recession episodes between 26 and 21 TheMaximumIceExtent(MIE)wasnotcontemporaneouswith ka. Large polygenetic moraines formed in narrow glacial valleys, while the Last Glacial Maximum (LGM) in all the mountain ranges of Iberia. in unconstrained conditions, the glaciers gave origin to multiple mo- According to Clark et al. (2009),theLGMoccurredfrom26.5to19ka, raine ridges (Palacios et al., 2015). This situation occurs in the Pyrenees when the sea reached its last lowest level, although in fact the con- (Delmas, 2015; Turu et al., 2016), in the Cantabrian and northwest Ibe- cept of “global” for this period is in question in relation to glacial ex- rian mountains (Rodríguez-Rodríguez et al., 2014, 2015, 2016; Serrano pansion (Hughes et al., 2013). In the Pyrenees, the MIE during Last et al., 2015, 2017), in the Central System (Palacios et al., 2012a and Glacial Cycle (115–11.7 ka; LGC) occurred at 60 ka (García-Ruiz 2012b; Andrés and Palacios, 2014; Carrasco et al., 2015) and in the Si- et al., 2003, 2010, 2013; Lewis et al., 2009; Delmas, 2015), while in erra Nevada (Gómez-Ortiz et al., 2012, 2015; Oliva et al., 2014, the Cantabrian mountains (Rodríguez-Rodríguez et al., 2015, Palacios et al., 2016). 2016), the northwest Iberian mountains (Rodríguez-Rodríguez Contrasting with the knowledge on the MIE during the LGC, the un- et al., 2014), the Central System (Palacios et al., 2012a; Domínguez- derstanding of pre-LGC glacial events in the Iberian Peninsula remains Villar et al., 2013; Pedraza et al., 2013) and the Sierra Nevada poor. Glacial landforms older than LGC have been dated only in very few locations of the central Pyrenees, the central Cantabrian Mountains, ⁎ Corresponding author. mountain ranges of NW Iberia and Sierra Nevada. In the south of the E-mail address: [email protected] (G. Vieira). central Pyrenees, Lewis et al. (2009) applied optically stimulated https://doi.org/10.1016/j.geomorph.2021.107781 0169-555X/© 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). G. Vieira, D. Palacios, N. Andrés et al. Geomorphology 388 (2021) 107781 luminescence (OSL) techniques to fluvioglacial terraces and on overly- out to result from pulses within the LGC (Oliva et al., 2019).Thescarceev- ing aeolian silt, with results indicating glacial periods at 151 ± 11 ka idence of MIE of pre-LGC ages in Iberia contrasts with the data from other in the Gállego valley, and at 178 ± 21 ka in the Cinca valley. Elsewhere Mediterranean mountains, such as the Apennines (Kotarba et al., 2001; in the Pyrenees, García-Ruiz et al. (2013) also applied OSL dating Giraudi et al., 2011; Giraudi and Giaccio, 2017)andtheBalkans(Hughes methods in the Aragón valley fluvioglacial terraces, with results show- et al., 2006a, 2006b, 2007, 2010, 2011; Žebre and Stepišnik, 2014, 2015; ing two glacial phases at 171 ± 22 and 263 ± 21 ka. Moreover, Adamson et al., 2017; Leontaritis et al., 2020). Rodríguez-Rodríguez et al. (2016) applied CRE (10Be) dating to erratic The Serra da Estrela, the highest mountain of the western and moister and moraine boulders in the Porma valley (central Cantabrian Moun- sector of the Central System, shows extremely well-preserved glacial tains) and yielded ages of 134 ± 4 ka and 169 ± 6 ka. In adition, an landforms and deposits, but with a still very poorly constrained chronol- age of 286 ± 6 ka from an erratic was considered an outlier. Villa et al. ogy (Fig. 1). The glacial geomorphology of the area was studied in detail (2013) applied U/Th dating to the limestone of cemented calcareous by Lautensach (1929; 1932), Daveau (1971) and Vieira (2004). Daveau breccias in Duje valley, in Picos de Europa, also in the central Cantabrian (1971) suggested the possibility for a pre-LGC glaciation following the mountains. These breccias are resting on glacially abraded surfaces and identification of sparse boulders in the Lagoa Seca site, which contrasted are covered by moraines. The oldest dates obtained for the base of the with other moraine deposist of the mountain. Based on geomorphological breccias are between 276 ± 23 ka and 394 ± 50 ka. Vidal-Romaní and analysis, Vieira (2004) identified four general stages in the Estrela glacia- Fernández-Mosquera (2006), Vidal-Romaní et al. (2015) applied CRE tion, including one probably pre-LGC with evidence in several areas in the (21N) dating in two ranges of the NW of the Peninsula: in the Sierra plateaus. Using preliminary thermoluminescence (TL) dating from de Queixa, a maximum advance was dated at 155 ± 30 ka, and in the fluvioglacial sediments, he placed the MIE in the LGC at ca. 33 to 30 ka, Serra de Gerês/Xurez, polished bedrock outcrops were dated at 231 ± a value in agreement with other Iberian mountains, but no further ages 48 ka and 131 ± 31 ka. Palacios et al. (2019) applied CRE (10Be) dating existed up to the present work on pre-LGC or LGC evidence. to the most external moraine boulders in the Mulhacen valley (Sierra The objective of this work is to present a first assessment on the age Nevada) and obtained ages of 134.8 ± 10 ka and 129.2 ± 8.9 ka. of the glacial features in Serra da Estrela using CRE methods (36Cl). The identification of pre-LGC glacial landforms is still lacking in the Aiming at identifying the age of the MIE during the LGC, or earlier, gla- Iberian Range and in the Central System, although its existence has long cial boulders and polished surfaces, have been selected from key sites been postulated (Lotze, 1962; Obermaier and Carandell-Pericay, 1917). identified in previous studies. Vieira (2004, 2008) mentions the signifi- However, after the application of modern dating methods, many of the cance of the Estrela plateau for paleoenvironmental reconstruction landforms thought to be pre-LGC in most of the Iberian mountains turned based on its flat top morphology and elevation just above the Fig. 1. Location and general characteristics of the Serra da Estrela. The Maximum Ice Extent is derived from Vieira (2004). 2 G. Vieira, D. Palacios, N. Andrés et al. Geomorphology 388 (2021) 107781 Fig. 2. Distribution of moraines and glacial erosion features in the Serra da Estrela and location of Fig. 5. The map is based in Vieira (2004). equilibrium line altitude (ELA) at the MIE. This would have generated highest elevation in mainland Portugal (Fig.

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