Quaternary Science Reviews 89 (2014) 70e84

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Quaternary Science Reviews

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Late Quaternary tephrostratigraphy of southern Chile and Argentina

Karen Fontijn a,*, Stefan M. Lachowycz a, Harriet Rawson a, David M. Pyle a, Tamsin A. Mather a, José A. Naranjo b, Hugo Moreno-Roa c a Department of Earth Sciences, University of Oxford, South Parks Road, Oxford, Oxfordshire OX1 3AN, United Kingdom b Servicio Nacional de Geología y Minería, Avenida Santa María 0104, Santiago, Chile c Observatorio Volcanológico de Los Andes del Sur, Servicio Nacional de Geología y Minería, Dinamarca 691, Temuco, Chile article info abstract

Article history: The Southern and Austral Volcanic Zones of the Andes comprise 74 volcanic centres with known post- Received 6 November 2013 glacial activity. At least 21 of these have had one or more large explosive eruptions in the late Quater- Received in revised form nary, dispersing tephra over vast areas. These tephra layers therefore have great potential as teph- 28 January 2014 rochronological marker horizons in palaeoenvironmental studies in southern Chile and Argentina, a Accepted 7 February 2014 region that is particularly useful to study climate dynamics of the southern hemisphere. However, to date Available online 5 March 2014 tephrochronology has rarely been fully utilised in this region as a correlation and dating tool. Here we review the existing post-glacial tephrostratigraphic record of the Southern and Austral Volcanic Zones, Keywords: Tephra and compile a database of known occurrences of tephra from these volcanoes in ice and lacustrine, Tephrostratigraphy marine, peat, and cave sediment records. We address the inconsistencies in and revisions of the teph- Tephrochronology rostratigraphies presented in prior literature, and discuss the challenges in correlating tephras and the Southern Volcanic Zone limitations of the tephrostratigraphic record in this area. This study highlights the many gaps that still Austral Volcanic Zone exist in our knowledge of the eruptive histories of these volcanoes, but also reveals the largely under- Andes utilised potential of tephra as a correlation tool in this region. This is exemplified by the severe lack of Patagonia adequate geochemical analysis of tephra layers preserved in many lacustrine and peat sediment sections, Lake sediment core which are particularly important tephrostratigraphic records in southern Chile and Argentina due to the Peat core paucity of surface preservation. Tephra correlation Ó Tephra preservation 2014 The Authors. Published by Elsevier Ltd. Open access under CC BY license.

1. Introduction geographical area and in different environmental settings, e.g., terrestrial outcrops and lacustrine and marine sediment cores, has Tephrochronology is widely employed as a stratigraphic corre- great potential for synchronising and dating sequences of events lation tool in a broad range of disciplines, including (but not limited recorded in diverse locations (cf. review by Lowe (2011)). to) archaeology (e.g., Prieto et al., 2013; Riede and Thastrup, 2013), In volcanology, characterisation of tephra deposits from a spe- palaeoclimatology (e.g., Davies et al., 2012; Elbert et al., 2013), cific source (either a known volcano or particular eruptive event) palaeoecology (e.g., Buckland et al., 1980; McCulloch and Davies, over a wide area helps constraining the frequencyemagnitude re- 2001), palaeogeomorphology (e.g., Stern et al., 2011; Dugmore lationships of explosive eruptions from the source volcanoes. and Newton, 2012), and volcanology (e.g., Shane, 2000; Watt Constraints on eruptive frequency and magnitude are crucial for et al., 2011). This technique is based on the principle that tephra volcanic hazard assessment and for understanding the moderate- layers represent (quasi-)isochronous marker horizons, because to long-term evolution of volcanic systems in relation to their they are the result of direct fallout of volcanic ash from the atmo- tectonic setting. Study of distal volcanic ash from large explosive sphere during and immediately after volcanic eruptions, which are eruptions is important in the reconstruction of eruptive parameters generally short-lived in geological terms. The identification and (e.g., erupted volume and eruption column height), as well as in correlation of synchronous volcanic ash (tephra) layers over a vast understanding the potential environmental impacts of explosive eruptions beyond the local scale. In other disciplines, such as archaeology and palaeoclimatology, tephra layers are invaluable geochronological markers, sometimes helping to date sequences * Corresponding author. Tel.: þ44 (0)1865 272044. where other geochronological methods might fail. In lacustrine and E-mail addresses: [email protected], [email protected] marine settings, age models for sediment cores spanning several (K. Fontijn). http://dx.doi.org/10.1016/j.quascirev.2014.02.007 0277-3791/Ó 2014 The Authors. Published by Elsevier Ltd. Open access under CC BY license. K. Fontijn et al. / Quaternary Science Reviews 89 (2014) 70e84 71

(or tens of) millennia often rely heavily on a set of radiocarbon ages, which can be difficult to calibrate due to reservoir effects (e.g., Yu et al., 2007). Such cores require well-constrained age models as they are commonly used to investigate the palaeoenvironmental record (e.g., Kilian and Lamy, 2012), regional earthquake history (e.g., Bertrand et al., 2008a), etc. If tephra horizons are found and assigned to a particular well-dated volcanic event, these can enable more accurate age models of the sediment cores. For tephrochronology to be used to its maximum potential and to validate the correlation of tephra layers in different settings as geochronological markers, a thorough characterisation of tephra layers encountered in different locations is essential. Tephra layers are preferably characterised in terms of glass (or sometimes whole- rock) chemical composition, mineral assemblage and composition, componentry, and physical characteristics such as colour, grain size, and texture, to aid correlations (Lowe, 2011). However, correlations sometimes only rely on a rough age correspondence between distinctive tephra layers in different sections (e.g., Abarzúa et al., 2004; Lamy et al., 2004). This may be problematic where signifi- cant age uncertainties exist and/or where multiple tephra layers occur in rather narrow time windows. Inadequate characterisation of tephra layers may lead to erroneous correlations, especially in areas with many active and thus potential source volcanoes. Mis- correlations can have serious implications for derived age models, e.g., in palaeoenvironment reconstructions. In this paper, we present a critical review of the late Quaternary tephrostratigraphic record as it is known from scientific literature for the Andean Southern and Austral Volcanic Zones, which span the approximate latitude range 33e55S(Fig. 1). They comprise 74 volcanic centres thought to have been active during post-glacial times (Global Volcanism Program, GVP, http://volcano.si.edu/; Large Magnitude Explosive Eruptions database (LaMEVE), http:// www.bgs.ac.uk/vogripa; Crosweller et al., 2012; Siebert et al., 2010), ranging from clusters of (monogenetic) cones to central stratovolcanoes and large volcanic complexes. They include some of the most historically active volcanoes of the Andes, such as Vil- larrica and Llaima, both of which have erupted several times per decade in recent history, with relatively limited regional impact (Dzierma and Wehrmann, 2010; Van Daele et al., in press). They also include several volcanoes that have had historical Plinian-style eruptions with significant regional or even hemispheric impact, e.g., the 1932 Cerro Azul (Quizapu; Hildreth and Drake, 1992), 1991 Cerro Hudson (Wilson et al., 2012), 2008 Chaitén (Watt et al., 2009) and 2011 PuyehueeCordón Caulle (Collini et al., 2013) events. This region is of particular interest not only for its frequent volcanic activity, but also because of the potential for investigating the (pre-)historical regional record of large earthquakes (similar to the 1960 Mw 9.5 Valdivia earthquake) using turbidite deposits in lakes (Arnaud et al., 2006; Moernaut et al., 2007; Bertrand et al., 2008a). In addition to being volcanically and tectonically active, southern South America is the only landmass to cross the southern Fig. 1. Map of southern Chile and Argentina showing the volcanoes of the Andean westerly wind belt, which is a significant control on global ocean Southern Volcanic Zone (SVZ) and Austral Volcanic Zone (AVZ) for which there is clear evidence of post-glacial activity (listed in Table 1: Stern, 2004; Siebert et al., 2010), and circulation and so climate (Kilian and Lamy, 2012). High-resolution some regional tectonic features (Bird, 2003; Stern, 2004; Stern et al., 2007; Matthews palaeoenvironmental archives have therefore been sought from the et al., 2011). The geographical data are from Natural Earth (natrualearthdata.com). many fjords, lakes, and areas of peatland in southern Chile and Argentina (Kilian and Lamy, 2012). The predominantly post-glacial records obtained have provided significant insights into, for rates during deglaciation and early post-glacial times (Huybers and example, interhemispheric climatic linkages and the dynamics of Langmuir, 2009; Watt et al., 2013a). both Holocene climate and the regional deglaciation (e.g., Lamy We present the known eruptive histories of the individual vol- et al., 2010; Moreno et al., 2012; Hall et al., 2013). At the Last canic centres in the study area, and we list all the known tephra Glacial Maximum (LGM; ca 25e16 ka in the study region; Hulton occurrences in published palaeoenvironment records, attributed to fi et al., 2002; Glasser et al., 2008; Kaplan et al., 2008) the Southern speci c eruptive events wherever possible. The aim is to provide a and Austral Volcanic Zones were largely glaciated, so this region is a regional stratigraphic framework (in the Supplementary good case study to investigate the potential coupling between Information) that can be used as a reference for tephrochrono- deglaciation and volcanism, namely a possible increase in eruption logical correlations in southern Chile and Argentina. It is important 72 K. Fontijn et al. / Quaternary Science Reviews 89 (2014) 70e84

Table 1 List of volcanic centres in southern Chile and Argentina with strong evidence for late Quaternary (post-glacial) activity, modified from Siebert et al. (2010). Arc segments: SVZ ¼ Southern Volcanic Zone (N ¼ North, T ¼ Transitional, C ¼ Central, S ¼ South), AVZ ¼ Austral Volcanic Zone, BA ¼ back-arc volcanoes, after Stern (2004). Old GVP number refers to the indexing used by Siebert et al. (2010); VNum refers to the updated indexing introduced by GVP online (http://volcano.si.edu). Additional information on largest eruptions can be found in Supplementary Table 1.

Volcano Arc segment Latitude (N) Longitude (E) Maximum Old GVP number VNum Last eruption Large eruptions (VEI/M > 5) elevation (m)

Tupungatito NSVZ 33.40 69.80 6000 1507-01¼ 357,010 1987 San José NSVZ 33.78 69.90 5856 1507-02¼ 357,020 1960 Maipo NSVZ 34.16 69.83 5264 1507-021 357,021 1912 Palomo TSVZ 34.61 70.30 4860 1507-022 357,022 Holocene Caldera del Atuel TSVZ 34.65 70.05 5189 1507-023 357,023 Holocene Tinguiririca TSVZ 34.81 70.35 4280 1507-03¼ 357,030 1994 Risco Plateadoa TSVZ 34.93 70.00 4999 1507-024 357,024 Holocene Infiernillo TSVZ 35.14 69.83 2045 1507-041 357,041 Holocene Planchón-Peteroa TSVZ 35.24 70.57 4107 1507-04¼ 357,040 2010 Calabozos TSVZ 35.56 70.50 3508 1507-042 357,042 Holocene Descabezado Grande TSVZ 35.58 70.75 3953 1507-05¼ 357,050 1933 Cerro Azul TSVZ 35.65 70.76 3788 1507-06¼ 357,060 1967 1932 San Pedro-Pellado TSVZ 35.99 70.85 3621 1507-062 357,062 Holocene Laguna del Maule TSVZ 36.02 70.58 3092 1507-061 357,061 Holocene Nevado de Longaví TSVZ 36.19 71.16 3242 1507-063 357,063 Holocene Lomas Blancas TSVZ 36.29 71.01 2268 1507-064 357,064 Holocene Payún Matru BA 36.42 69.20 3680 1507-066 357,066 Holocene Resago TSVZ 36.45 70.92 1890 1507-065 357,065 Holocene Domuyoa TSVZ 36.58 70.42 4709 1507-067 357,067 Holocene Cochiquito Volcanic Group BA 36.77 69.82 1435 1507-071 357,071 Holocene Nevados de Chillán TSVZ 36.86 71.38 3212 1507-07¼ 357,070 2009 Tromen BA 37.14 70.03 3978 1507-072 357,072 1822 Antuco CSVZ 37.41 71.35 2979 1507-08¼ 357,080 1869 Puesto Cortaderasa BA 37.57 69.62 970 1507-073 357,073 Holocene Trocona CSVZ 37.73 70.90 2500 1507-081 357,081 Holocene Copahue CSVZ 37.85 71.17 2997 1507-09¼ 357,090 2013 Callaqui CSVZ 37.92 71.45 3164 1507-091 357,091 1980 Laguna Mariñaqui CSVZ 38.27 71.10 2143 1507-092 357,092 Holocene Tolguaca CSVZ 38.31 71.65 2806 1507-093 357,093 Holocene Lonquimay CSVZ 38.38 71.58 2865 1507-10¼ 357,100 1990 Tralihuea BA 38.52 70.90 2345 1507-101 357,101 Post-glacial Llaima CSVZ 38.69 71.73 3125 1507-11¼ 357,110 2009 Llaima Pumice; Curacautín 1,2 Sollipulli CSVZ 38.97 71.52 2282 1507-111 357,111 1240 Alpehué Pumice Laguna Blancaa BA 39.02 70.37 1700 1507-102 357,102 Holocene Caburgua-Huelemolle CSVZ 39.25 71.70 1496 1507-112 357,112 Holocene Villarrica CSVZ 39.42 71.93 2847 1507-12¼ 357,120 2011 Pucón Ignimbrite; Licán Ignimbrite Quetrupillan CSVZ 39.50 71.70 2360 1507-121 357,121 1872 Lanín CSVZ 39.63 71.50 3747 1507-122 357,122 560 Huanquihue Group CSVZ 39.88 71.58 2139 1507-123 357,123 1750 Mocho-Choshuenco CSVZ 39.93 72.03 2422 1507-13¼ 357,130 1937 Pirehueico; Neltume Pumice Carrán-Los Venados CSVZ 40.35 72.07 1114 1507-14¼ 357,140 1979 Puyehue-Cordón Caulle CSVZ 40.59 72.12 2236 1507-15¼ 357,150 2011 Mil Hojas; Pr2/Pht Cerro Pantoja CSVZ 40.77 71.95 2024 1507-152 357,152 Holocene Antillanca Group CSVZ 40.77 72.15 1990 1507-153 357,153 Holocene An-A/RA; Nahuel Huapi Tephra Puntiagudo-Cordón Cenizos CSVZ 40.97 72.26 2493 1507-16- 357,160 1850 Osorno SSVZ 41.10 72.49 2652 1508-01¼ 358,010 1869 Tronadora SSVZ 41.16 71.89 3491 1508-011 358,011 Post-glacial Cayutué - La Viguería SSVZ 41.25 72.27 506 1508-012 358,012 1050 Calbuco SSVZ 41.33 72.61 2003 1508-02¼ 358,020 1972 Ca8; Ca1 Cuernos del Diablo SSVZ 41.40 72.00 1862 1508-021 358,021 Holocene Yate SSVZ 41.76 72.40 2187 1508-022 358,022 Holocene Hornopirén SSVZ 41.87 72.43 1572 1508-023 358,023 Holocene Apagado SSVZ 41.88 72.58 1210 1508-024 358,024 Holocene Ap1 Crater Basalt Volcanic Field BA 42.02 70.18 1359 1508-025 358,025 Holocene Huequi SSVZ 42.38 72.58 1318 1508-03¼ 358,030 1907 Minchinmávida SSVZ 42.79 72.44 2404 1508-04¼ 358,040 1835 MIC1; Amarillo Ignimbrite Chaitén SSVZ 42.83 72.65 1122 1508-041 358,041 2010 Cha2; Cha1 Corcovado SSVZ 43.18 72.80 2300 1508-05¼ 358,050 Holocene COR3 Yanteles SSVZ 43.50 72.80 2042 1508-050 358,049 Holocene YAN1 Palena Volcanic Group SSVZ 43.78 72.47 1449 1508-051 358,051 Holocene PalRF Melimoyu SSVZ 44.08 72.88 2400 1508-052 358,052 Holocene MEL1 Puyuhuapi SSVZ 44.30 72.53 524 1508-053 358,053 Holocene Mentolat SSVZ 44.70 73.08 1660 1508-054 358,054 1710 MEN1 Caya SSVZ 45.06 72.98 2090 1508-055 358,055 Post-glacial Macá SSVZ 45.10 73.17 2960 1508-056 358,056 Holocene MAC1 Cerro Hudson SSVZ 45.90 72.97 1905 1508-057 358,057 2011 1991; H2/T5; H1/T2; Ho Río Murtaa SSVZ 46.17 72.67 270 1508-058 358,058 Holocene Lautaro AVZ 49.02 73.55 3607 1508-06¼ 358,060 1979 Viedma AVZ 49.36 73.28 1500 1508-061 358,061 1988 K. Fontijn et al. / Quaternary Science Reviews 89 (2014) 70e84 73

Table 1 (continued )

Volcano Arc segment Latitude (N) Longitude (E) Maximum Old GVP number VNum Last eruption Large eruptions (VEI/M > 5) elevation (m)

Aguilera AVZ 50.33 73.75 2546 1508-062 358,062 Holocene A1 Reclus AVZ 50.96 73.59 1000 1508-063 358,063 1908 R1 Palei-Aike Volcanic Field BA 52.00 70.00 282 1508-08- 358,080 Holocene Monte Burney AVZ 52.33 73.40 1758 1508-07¼ 358,070 1910 MB2; MB1 Fueguino AVZ 54.95 70.25 150 1508-09- 358,090 1820

a Volcanic centres for which the only evidence for post-glacial activity exists in the presence of morphologically youthful-looking lava flows, lava domes and/or pyroclastic cones, but for which no radiometric data are available.

to note that the record presented here is incomplete, because the of the Chile Rise, an oceanic ridge separating the Nazca and Ant- majority of the volcanoes in the study area are still poorly studied, arctic plates. There is no evidence of arc volcanism in this area for or results from existing field studies are difficult to access. As the the last 12 Ma; however, there has been back-arc volcanic activity eruptive histories of specific volcanoes become better known, or (Gorring et al., 1997; Stern, 2004; Espinoza et al., 2005). Late Qua- additional lithological data from sediment cores becomes available, ternary back-arc volcanism occurs up to 250 km east of the main new information could easily be integrated into this record. volcanic arc, principally in Argentina, between 34 and 52S. This back-arc activity is dominated by alkaline basaltic volcanism from small monogenetic spatter and scoria cones with associated lava 2. The Andean Southern and Austral Volcanic Zones flows. Examples include the Palei-Aike volcanic field (w52S; D’Orazio et al., 2000) and the Payenia volcanic province (w34.5e 2.1. Geological setting 37.5S; Søager et al., 2013).

The Andean arc is a segmented volcanic arc along the western margin of South America (Stern, 2004). It is divided into four main 2.2. Geochemistry volcanic zones; the Northern Volcanic Zone (NVZ; 5Ne2S), Cen- tral Volcanic Zone (CVZ; 14e27S), Southern Volcanic Zone (SVZ; The geochemistry of tephra is invaluable for fingerprinting and 33e47S), and Austral Volcanic Zone (AVZ; 49e55S). The latter correlating past deposits, as the volcanic products from each vol- two are the focus of this study, because they are the scene of cano and eruption typically have a distinct glass and/or mineral frequent volcanic (Stern, 2008; Watt et al., 2013a) and tectonic chemistry (e.g., Lowe, 2011; Gilbert et al., in press). The petrology (Moernaut et al., 2007; Bertrand et al., 2008a) activity, they have and geochemistry of the SVZ and AVZ is diverse as a result of been subjected to extensive glaciation in the past, and the regions varying subduction geometry and crustal thickness along the arc in which they are located are sensitive recorders of late Quaternary (Lowrie and Hey, 1981; Lüth and Wigger, 2003; Watt et al., 2013b), palaeoenvironmental conditions (De Batist et al., 2008; Kilian and with erupted magmas ranging in composition from picrites and Lamy, 2012). tholeiitic basalts through to rhyolites and andesitic adakites (Stern The Southern Volcanic Zone (SVZ) is a 1400 km long, continuous and Kilian, 1996; Stern et al., 2007). volcanic arc segment that arises from the subduction of the oceanic The volcanoes of the NSVZ (33.3e34.4S) have erupted magmas Nazca Plate beneath the continental South American Plate (Fig. 1). It ranging from basaltic andesite to dacite. The predominant rock comprises 60 volcanic centres that have been active during the late types are 2-pyroxene and olivine-clinopyroxene andesites, Quaternary (see Table 1 and Section 3.1), in four sub-zones distin- although the more silicic rocks (>57% SiO2) commonly contain guished by along-arc changes in geochemical characteristics (e.g., hornblende and rare biotite (e.g., at Tupungatito volcano: Hildreth Hildreth and Moorbath, 1988; Stern, 2004; Stern et al., 1984a, and Moorbath, 1988). Magmas erupted from the NSVZ have rela- 2007), called the Northern (NSVZ; 33.3e34.4S), Transitional tively high K, Rb, Sr, La/Yb, and 87Sr/86Sr, and lower 143Nd/144Nd, (TSVZ; 34.4e37S), Central (CSVZ; 37e42S) and Southern (SSVZ; compared to similarly evolved rocks from other parts of the SVZ 42e46S) zones (Table 1; Fig. 1). The Austral Volcanic Zone (AVZ), to (Stern et al., 2007). There are two main theories on the cause of this the south of the SVZ, is an 800 km long volcanic arc segment that signature: (1) crustal contamination, as a result of the thicker arises from the subduction of the oceanic Antarctic Plate beneath continental crust, and (2) higher rates of subduction erosion due to the South American continent (w49e53S) and Scotia microplate the subduction of the Juan Fernández Ridge (Hildreth and (w53e55S) (Fig. 1). It is thought to comprise six volcanic centres Moorbath, 1988; Stern, 1991). that have been active during the late Quaternary (see Table 1 and In the TSVZ (34.4e37S), andesites and dacites dominate, Section 3.1) and may be divided into two sub-zones, Northern although basalts through to rhyolites are erupted. This large (NAVZ; 49e50.3S) and Southern (SAVZ; 50.3e52S) (Table 1), on compositional range has been observed within individual com- the basis of geochemistry (Stern and Kilian, 1996; Stern, 2008). plexes, such as Laguna del Maule (basalts to rhyolites: Hildreth The major zones of arc volcanism in Chile and Argentina are et al., 2010) and Planchón-Peteroa (basalts to dacites: Tormey separated by significant gaps. The SVZ is bounded north of 33Sby et al., 1995). Isotopic and trace element studies indicate that rhy- the Pampean flat-slab segment and south of 46S by the Patagonian olites from the TSVZ have a significant contribution from crustal volcanic gap, which also marks the northern limit of the AVZ (e.g., partial melts, whilst the more mafic magmas are dominated by a Stern, 2004; Espinoza et al., 2005). The Pampean flat-slab segment slab-derived component (Hildreth et al., 1999). The source of back- (27e33S) is a region of shallow subduction (<10), thought to arise arc magmas is predominately the sub-continental lithospheric from the subduction of the Juan Fernández Ridge. This slab ge- mantle (Jacques et al., 2013). This complexity in magma sources is ometry is thought to have prevailed for the last 5e6 Ma; conse- reflected in the large geochemical range of the volcanic products. quently, no Pleistocene or Holocene magmatic activity has been In the CSVZ (37e42S) and SSVZ (42e46S), basalts through to recognised in this area (Kay and Mpodozis, 2002; Kay et al., 2005). rhyolites are erupted, with a predominance of basalts and basaltic The Patagonian volcanic gap (46e49S) arises from the subduction andesites. An important difference between the two segments is 74 K. Fontijn et al. / Quaternary Science Reviews 89 (2014) 70e84 the relative lack of hydrous phases in the CSVZ: in evolved rocks explosive eruptions in recent history, most notably the 1932 Qui- 3 (>59% SiO2) from the SSVZ, amphibole is commonly found and zapu (Cerro Azul; M 6.0, >9.5 km tephra; Hildreth and Drake, biotite may be present (although it has only been reported in 1992) and 1991 Cerro Hudson (M 5.8, 4e7km3 tephra; Naranjo rhyolites from Chaitén: Amigo et al., 2013), whereas amphibole is et al., 1993a) eruptions. Even larger eruptions are known to have rare and biotite is absent in the CSVZ (Stern et al., 2007; Gilbert occurred in the SVZ during the Pleistocene (e.g., the Diamante et al., in press). Isotopic and trace element studies suggest that caldera-forming event, Maipo; M 7.7, w270e350 km3 tephra: the mantle is the primary source of melts, but that there is also a Sruoga et al., 2005; Stern et al., 1984b). In the late Quaternary (relatively minor) slab-derived component (e.g., Hickey-Vargas (ca the last 25 ka, i.e., the period for which terrestrial tephros- et al., 1989; Stern, 2004). The evolved melts typically have a tratigraphic records exist), there have been at least 25 large similar isotopic signature to more primitive melts; therefore only a (1km3 of tephra) explosive eruptions generating widespread fall minor crustal contribution, or a contribution from young, isotopi- deposits from 18 different SVZ volcanoes (Table 1; Supplementary cally similar crust, is inferred (McMillan et al., 1989; Singer et al., Table 1; Fig. 2). An additional 4 large ignimbrite-forming erup- 2008). The degree of differentiation, i.e., how evolved the melts tions have been recognised. Some of these volcanoes are thought to become, appears to be strongly controlled by tectonics. Volcanic be the source of multiple such events including (but not limited to) centres controlled by NE-trending fractures and faults, for example Calbuco (Watt et al., 2011), Chaitén (Watt et al., 2013c), and Cerro the volcanic chain of OsornoePuntiagudoeCordón Cenizos, Hudson (Naranjo and Stern, 1998; Weller et al., 2013). Such an commonly erupt more mafic rocks than centres controlled by NW- abundance of large eruptions suggests there is significant potential trending fractures and faults, for example PuyehueeCordón Caulle for tephrostratigraphic correlations in southern Chile and (Lopez-Escobar et al., 1995; Lara et al., 2006; Cembrano and Lara, Argentina. Since there are several large population centres, trans- 2009). Furthermore, across-arc geochemical trends have been port hubs (e.g., airports), and economically significant infrastruc- identified: more easterly centres typically have lower Ba/La, La/Nb, ture (e.g., agriculture and tourist centres) both in Chile and and Ba/Nb ratios, and a higher concentration of K, compared to Argentina at these latitudes, explosive eruptions from the SVZ also similarly evolved rocks erupted at more westerly centres (Hickey- pose significant risks. Considerable impact is possible many hun- Vargas et al., 1989; Jacques et al., 2013). This trend has been inter- dreds of kilometres downwind, as exemplified by the effects of the preted to reflect smaller degrees of partial melting in the mantle mid-Holocene (Prieto et al., 2013) and 1991 (Inbar et al., 1995; wedge, and a decreasing slab-derived contribution towards the east Wilson et al., 2012) eruptions of Cerro Hudson, and even on a (Hickey-Vargas et al., 1989; Jacques et al., 2013). Watt et al. (2013b), hemispheric scale, as was the case in the 2011 PuyehueeCordón however, infer that increasing slab-surface temperatures result in Caulle eruption (Collini et al., 2013). Although similar eruptions less hydrous parental melts further eastward in the arc, giving rise from the AVZ may have comparable distal impacts, these volcanoes to the observed geochemical variations. are further from large population centres and critical infrastructure. Volcanic rocks from the AVZ (49e55S) have a narrow compo- Four large explosive events are known to have occurred in this arc sitional range compared to the SVZ, as only andesites and dacites segment in the past 12 ka: A1 from Aguilera, R1 from Reclus and are found (Stern and Kilian, 1996). However, this more restricted MB1 and MB2 from Monte Burney (Stern, 2008; Supplementary range may simply reflect the limited samples analysed from this arc Table 1). segment, due to the remote location of these volcanoes. The rocks Eruptive explosivity and hazards are also elevated in this region typically contain pyroxenes, amphibole, plagioclase and biotite, by the presence of substantial ice and snowpack. Approximately though the latter is only noted at the three northernmost volcanoes half of the SVZ volcanoes active in post-glacial times host summit (comprising the NAVZ; 49e50.3S: Stern and Kilian, 1996) and less glaciers, or ice-filled summit craters or calderas (Siebert et al., 2010; abundantly at Reclus (Stern et al., 2011). In addition, crustal xeno- Rivera and Bown, 2013). Ice cover is extensive in the AVZ, with four liths, such as granite from the Patagonian batholith, are found in all of the six volcanoes lying within or adjacent to the southern six volcanoes, though more abundantly further north. At Monte Patagonian ice field (Stern, 2008; Siebert et al., 2010). At the peak of Burney, xenocrysts of clinopyroxene and/or olivine are also found; the LGM, at ca 25e16 ka in this region (Hulton et al., 2002; Glasser these are inferred to be mantle-derived (Stern and Kilian, 1996). et al., 2008; Kaplan et al., 2008), all the edifices in the SVZ and AVZ The erupted products in the AVZ have an adakitic signature: low south of w38S were covered by ice, possibly >1 km thick (Hulton heavy rare earth element (HREE), Y, and high field strength element et al., 2002; Glasser et al., 2008). The lateral extent of the ice sheet, (HFSE) concentrations, and high Sr concentrations, as well as pos- w100e150 km and w250e300 km wide north and south of w42S itive Sr and Eu anomalies and a high Mg# (Stern and Kilian, 1996). respectively (Hulton et al., 2002), greatly restricted terrestrial This suggests a source region with residual garnet, amphibole, and preservation of tephra from eruptions during glacial periods in the pyroxene, with little or no plagioclase or olivine. Therefore, the Pleistocene (Section 4.1). It has been proposed that ice retreat after chemical signature is attributed to partial melting of the unusually the LGM caused a significant increase in global volcanic activity in hot subducting Antarctic slab (potentially several hundred degrees previously glaciated regions (Huybers and Langmuir, 2009), but higher than ‘normal’), as a result of the very slow convergence rate evaluation of the post-glacial explosive eruption history of the (2e3 cm/year) and relatively young (and hot) oceanic crust (0e central and southern sectors of the SVZ by Watt et al. (2013a) found 24 Ma, younger to the north) (Stern et al., 1984a; Peacock et al., no statistically significant increase in the early post-glacial period 1994; Stern and Kilian, 1996). here compared to the later Holocene. However, recognition and accurate quantification of such potential changes in eruption rate in 2.3. Large explosive eruptions the southern Andes are difficult without a more comprehensive tephrostratigraphic record. Large explosive eruptions, erupting 1km3 of tephra (Volcanic Explosivity Index, VEI 5(Newhall and Self, 1982), roughly corre- 3. Tephrostratigraphic record of major explosive eruptions sponding to magnitude, M 5(Pyle, 2000)), will typically deposit >1e10 cm thickness of tephra over an area exceeding 103e104 km2 3.1. Volcanoes active in the late Quaternary (e.g., Pyle, 1999). Therefore, they have significant potential for tephrostratigraphic correlation, and so these large events are the Table 1 lists all of the volcanic centres in southern Chile and focus of this study. The SVZ has produced some of the largest Argentina thought to have had post-glacial activity, for which we K. Fontijn et al. / Quaternary Science Reviews 89 (2014) 70e84 75 have compiled all the available information on their post-glacial The most important documented eruptions for each volcano, eruptive history. All the centres in the GVP (http://volcano.si.edu) which are likely to have left traceable deposits over a large area (i.e., database of Holocene active volcanoes are included, except for in multiple lakes, peat bogs, etc.) are highlighted in blue in Arenales (47.20S, 73.48W), in the Patagonian volcanic gap. The Supplementary Table 1. Eruptions with estimated tephra fall vol- only eruption attributed to this edifice by Siebert et al. (2010) is one umes >1km3 and for which dispersal data in the form of isopach in 1979, based on the observation of a thin tephra deposit on the maps are available from literature, are highlighted in red in Arenales glacier in a March 1979 Landsat image (Lliboutry, 1999). Supplementary Table 1. Their dispersal patterns are indicated on However, this deposit may have been from a VEI 2 eruption of Fig. 2. Lautaro volcano, 200 km to the south, in June 1978 (Lliboutry, A careful screening of the available literature on certain major 1999): a March 1979 Landsat image indeed shows a fresh tephra eruptions has highlighted a number of inconsistencies. The deposit on Lautaro, as well as three older tephra horizons in nearby compositionally zoned pumice fall and pyroclastic density current glaciers (Lliboutry, 1999), which have been attributed to Lautaro on deposits associated with the Llaima Pumice eruption, for example, the basis of their chemistry (Motoki et al., 2006). Other volcanic have previously been treated as separate eruptions (Watt et al., centres, such as Risco Plateado (34.93S, 70.00W) and Trocon 2013a), although there is no palaeosol or any other evidence for a (37.73S, 70.90W), have been assigned a late Quaternary/Holocene significant time break between the different phases (Naranjo and age only on the basis of morphologically youthful-looking cinder Moreno, 1991, 2005). On the contrary, this eruption appears to and scoria cones or lava flows (e.g., González-Ferrán, 1995). have been characterised by a sustained Plinian eruption column (Ll- Therefore, their presence in Table 1 should be treated with caution pl) which experienced a fountain collapse generating pyroclastic until conclusive radiometric dates have been published. density currents (Ll-s1, Ll-s2; Naranjo and Moreno, 1991, 2005; There is some confusion regarding the historical record of ac- Supplementary Table 1). It should therefore be considered as one tivity of a number of these volcanic centres as few written accounts eruption characterised by multiple eruptive phases. exist, and those that do are mostly secondary sources (e.g., Supplementary Table 2 summarises all of the known tephra Martinic, 1988, 2008; Petit-Breuilh Sepúlveda, 2004). This confu- occurrences in sediment sections in southern Chile and Argentina, sion is exacerbated by the fact that some of the volcanoes have had predominantly in lacustrine, marine and peat cores. The lacustrine multiple names, which in some cases may be shared with neigh- and peat cores are almost all restricted to post-glacial times (the bouring volcanoes, making determination of historical activity from most notable exception being the Laguna Potrok Aike record; written sources problematic (Martinic, 1988; Petit-Breuilh Sepúl- Wastegård et al., 2013), but the marine cores may span up to 2e veda, 2004; LaMEVE database: http://www.bgs.ac.uk/vogripa). As 3 Ma (e.g., ODP Sites 859e862; Behrmann et al., 1992). The latter well as this ambiguity concerning the source of eruptions, there is are merely given for completeness. Unless a name was already also potential for confusion from the existence of multiple names given to a specific tephra horizon, all tephra horizons are given a for single events (examples in Supplementary Table 1). unique name consisting of the (abbreviated) core or location name followed by the central depth of the tephra in the sediment core. 3.2. Explosive eruptions in the late Quaternary This method of labelling tephra was suggested by Bertrand et al. (2008b), who presented one of the few studies on lake cores in Supplementary Table 1 lists all the known (and dated) post- the region specifically dedicated to tephrostratigraphy. In glacial eruptions of all the volcanoes listed in Table 1, from both Supplementary Table 2 we list as much information as possible on historical and geological records. Our critical review of the available the tephra horizons, e.g., thickness, colour, grain size, composition literature on the tephrostratigraphic record in southern Chile and and age, and, if known, the inferred source volcano or eruption. The Argentina has highlighted several ambiguities, which we attempt missing information in Supplementary Table 2 indicates that the to address in Supplementary Table 1 (see the “Remarks” column). vast majority of tephra layers encountered in sediment sections For a number of historical eruptions listed as “uncertain” by Siebert lack published chemical analyses. In many cases even basic infor- et al. (2010), no reference could be found: these entries are not mation such as tephra thickness, colour or grain size is lacking. This included in our database. makes it very difficult to try to assign a source volcano to these The vast majority of the events listed in Supplementary Table 1 tephras. were rather small (M 1e2) eruptions, e.g., the tens of historical eruptions of Villarrica and Llaima volcanoes. Such eruptions are 4. Discussion unlikely to have left distinct regional marker beds, and are there- fore of limited use in a regional-scale (>104 km2) tephrostrati- 4.1. Preservation potential of tephra in southern Chile and graphic framework. For example, most visible tephra layers found Argentina in short cores in the Villarrica and Calafquén lakes originate from VEI/M 2 eruptions of nearby Villarrica volcano, and are difficult to Large explosive eruptions with estimated tephra fall volumes characterise chemically due to an abundance of microphenocrysts >1km3 have been recognised from 21 individual volcanic centres, and non-distinct chemical compositions (Van Daele et al., in press). most of them located in the SSVZ and AVZ. At least 9 of these have Though useful to unravel the detailed eruptive history of Villarrica also had multiple moderate (V > 0.1 km3) to large explosive volcano, these tephras cannot be used as well-defined time eruptions in their post-glacial history (Supplementary Table 1). markers on a broader scale and thus only have very limited teph- From the tephra dispersal patterns presented in Fig. 2 it is clear that rochronological potential. In some specific cases however, tephra tephra from the majority of the large eruptions is dispersed east- layers resulting from relatively small eruptions, and with a distinct ward. Because of poor preservation and/or accessibility however geochemical signature, may be very useful to correlate high- (discussed below), precise tephra fall volume estimates are often resolution lacustrine records. This was nicely demonstrated, for difficult to obtain. This is especially obvious when comparing the example, by Van Daele et al. (in press), who identified the area encompassed by 1 cm isopach contours for recent eruptions ca 200 100 14C yr BP Achen Ñiyeu tephra from the Huanquihue (1932 Quizapu; 1991 Hudson; 2008 Chaitén) with the dispersal Group (Supplementary Table 1; Siebert et al., 2010) in short cores patterns for prehistoric deposits (for which 1 cm isopach contours from Lakes Calafquén and Villarrica, ca 60e80 km from source, and are usually not available; Fig. 2). For many prehistoric deposits refined the eruption age using varve chronologies to 1591 varve AD. listed in Supplementary Table 1, no volume estimates exist at all. Fig. 2. Maps of a) south-central and b) southernmost Chile and Argentina, showing the locations of volcanoes (listed in Table 1) and the archeological and palaeoenvironmental records in which tephra has been recognised (listed in Supplementary Table 2), as well as the distributions of the tephra deposits from each post-glacial large (1km3 tephra; VEI/ M 5) explosive eruption (listed in Supplementary Table 1), and of some of the environments amenable to tephra unit preservation. The legend for Fig. 2a also applies to Fig. 2b. K. Fontijn et al. / Quaternary Science Reviews 89 (2014) 70e84 77

Fig. 2. (continued).

Coloured lines are isopach contours, indicating the area in which the deposits of an eruption are inferred to be 10 cm, unless an otherwise labelled (number of centimetres) dashed line. These data are from the articles cited for the corresponding eruptions in Supplementary Table 1; the source volcanoes of these eruptions are named. Tephra-bearing core/ exposure location labels refer to reference numbers in Supplementary Table 2; only distal exposure locations are plotted. The geographical data are from Natural Earth (natrualearthdata.com), except the peatland extent, which is from Yu et al. (2010). 78 K. Fontijn et al. / Quaternary Science Reviews 89 (2014) 70e84

For these reasons it is highly likely that the number of large so rapid soil accrual, appear to be most amenable to relatively high- explosive eruptions in Supplementary Table 1 is severely quality preservation of tephra and dateable material. However, the underestimated. rugged topography in this region often results in variable and The completeness and accuracy of the tephrostratigraphic re- sporadic preservation of any single tephra unit, complicating cord presented here is restricted by the limited extent and rela- stratigraphic correlation in the field. Furthermore, tephra is tively poor quality of preservation of tephra on land. Poor terrestrial extremely prone to erosion and remobilisation from/on slopes, preservation is partly related to the humid temperate conditions which inhibits accurate inference of the eruptive sequence and characterised by high rainfall across much of southern Chile (Miller, parameters (Engwell et al., 2013). Note that when unit thickness 1976). Across the region, tephra is preserved in a wide variety of measurements can only be made on these steep slopes, the slope environments (Fig. 3), but often either preservation of an isochro- angle should be taken into consideration to obtain an estimate of nous tephra unit is rare (e.g., in caves) or the record is difficult to the primary depositional thickness. obtain (e.g., from lake sediments). Furthermore, just like in other Stratigraphic correlation and accurate characterisation are previously glaciated arcs, the time period in which preservation has confounded further by physicochemical alteration of tephra de- been possible is generally restricted in southern Chile and posits in the areas of the southern Andes with high rainfall. Argentina to since glacial retreat (Watt et al., 2013c). In many en- Weathering can modify or even remove the diagnostic feature(s) vironments, post-depositional processes can significantly modify of some tephra units, making them difficult to distinguish and so the record (discussed below), complicating tephra identification, correlate. Accurate inference of eruption parameters is also characterisation, and correlations. The best picture of the teph- compromised, as alteration and compaction of the tephra pile rostratigraphic record therefore is drawn from a combination of reduces unit thickness, and that of individual tephra clasts makes sedimentary sequences in a range of depositional environments. accurate measurement of maximum clast size difficult. Accurate As shown in Fig. 2, distal tephra fallout from most of the large clast size measurement is thwarted further (especially close to the explosive eruptions in the late Quaternary has occurred on the source volcano) by the deposition of clasts that are outliers to the (largely Argentine) Patagonian steppe, due to the prevailing west- main size distribution (Bonadonna et al., 2013), such as ballistic erly winds. This environment predominantly comprises sparsely bombs, which can be problematic to distinguish from pumices, vegetated, terraced outwash plains, and has a continental semi-arid especially when both are degraded. Alteration also inhibits climate, making it susceptible to strong wind erosion (Peri and chemical characterisation, which is critical for rigorous strati- Bloomberg, 2002; Villa-Martínez and Moreno, 2007), including of graphic correlation. Breakdown of glass can make it difficult to tephra, as seen after the 1991 Cerro Hudson eruption (Wilson et al., find large enough glass fragments to analyse, and alkali elements 2011). Surface accumulations of tephra are therefore almost (most notably sodium and potassium) are readily leached (e.g., exclusively preserved thanks to the presence of vegetation in or Cerling et al., 1985; Amigo et al., 2013). Although this effect can be near the Andes, where tephra accumulation has only been possible recognised, it is not possible to fully correct for this by normalising since the time at which the ice sheet last retreated from the loca- the altered compositions, hindering effective comparison of tion (e.g., Menounos et al., 2013). Areas with thick vegetation, and samples.

Fig. 3. Schematic representation of preservation environments for tephra in southern Chile and Argentina. Most preservation is restricted to vegetated areas (i.e., the Andes), lakes (6) and peatland (2). In addition to lake and peat cores, marine cores (1) can also provide important tephrostratigraphic records. Distal tephra deposits (5, 7) are easily eroded away due to prevailing westerly winds over the Argentine steppe. Strong winds may also result in complex dispersal patterns reflected in the architecture of the deposits (5, 7). Tephra in lakes may not always result from primary fallout, and can instead be remobilised into the lake from the river catchment (3, 4). K. Fontijn et al. / Quaternary Science Reviews 89 (2014) 70e84 79

Chemical alteration is a particularly significant issue with tephra been reported in the sparse offshore sediment cores from the re- preservation in peat bogs, cores or sections through which are the gion (Supplementary Table 2): this is perhaps in part due to a lack of most common source of tephra samples in southernmost Patago- recognition rather than absence, but also because with the pre- nia/from the AVZ (Supplementary Table 2; Stern, 2008). vailing westerly winds, deposition of macrotephra (visible tephra) Aluminium, iron, and the common alkali and alkali earth metals are layers in either the Pacific or Atlantic is unlikely except during the all readily leached from volcanic ash by dissolved organic com- largest of eruptions. Offshore marine preservation is more likely for pounds (Antweiler and Drever, 1983). Particularly rapid rates of tephra from the SSVZ or AVZ, where the transport distances dissolution of (ferromagnesian) minerals are possible in low pH required to the Atlantic are shorter. (<4) conditions: for example, complete loss of biotite has been SVZ and/or AVZ tephra units have also been reported in sedi- observed from the 770 yr rhyolitic Kaharoa tephra in a New Zealand ments in caves (Supplementary Table 2), but the tephra preserved bog (Hodder et al., 1991). Complete alteration of the original here is likely to be predominantly remobilised, complicating cor- chemistry is possible: e.g., some thin tephra layers in an Austral relation and making thickness, componentry and clast size mea- Andean peat core are reported to have been partly transformed to surements prone to uncertainty (e.g., Lundberg and McFarlane, siderite and rhodochrosite (Kilian et al., 2003). Theoretical model- 2012). Considerable sampling bias is also likely, determined by ling and experimental studies by Pollard et al. (2003) indicate that the orientation of the cave opening relative to potential source glass shard composition is a major factor in the resistance of distal volcanoes and the prevailing wind direction (e.g., Morley and tephra to chemical alteration: more mafic glasses are more prone to Woodward, 2011). SVZ and AVZ cryptotephra units have also been alteration. Although the resulting deviations from the ‘true’ reported in Antarctic ice cores (Supplementary Table 2), demon- chemical composition have not been quantified, chemical alter- strating the potential utility of tephra from this region for strati- ation should be considered in tephrostratigraphical studies in peat graphic correlation between multiple environments and over a sequences. wide area. This also implies that more proximal areas of permanent The physical preservation of tephra in peat bogs is also prob- ice, such as intra-caldera ice caps (Rivera and Bown, 2013) and the lematic, as peat accumulation rates are highly spatially and northern and southern Patagonian ice fields, could contain signif- temporally variable, even within a single bog. For example, two icant tephra records. cores of a bog at Puerto del Hambre (south of Punta Arenas) taken There are significant spatial and temporal biases in the preser- only one metre apart had identical basal depths, but the H1 tephra vation and sampling of tephra from the SVZ and AVZ: preservation (Stern, 2008; Supplementary Table 2) was missing from one of the is much more likely in or close to the Andes, where the majority of cores, and the basal depths of the MB2 and R1 tephras (Stern, 2008; lakes, fjords, peat bogs, ice, and significant soil accumulations are Supplementary Table 2) in the two cores differed by 15 and 40 cm, all located (Fig. 2). Preservation is likely to be more frequent at respectively; the MB2 tephra was also found to vary in thickness southern latitudes for the same reason, but sampling here (of from 2 to 5 cm in a single excavation at this site (McCulloch and tephra from the SSVZ and AVZ) is hampered by the relatively poor Davies, 2001; Supplementary Table 2). Thin tephra layers are accessibility of the southernmost Andes. Accessibility is just as readily dispersed by root growth, confounding accurate thickness significant a contributor to spatial sampling bias as preservation; estimation, or even recognition; less disruption has been reported this bias can have a significant effect on the inferred eruption pa- in ombrogenic compared to minerogenic core sections (Kilian et al., rameters, as these are highly sensitive to sample location distri- 2003). Tephra deposition itself may have adverse effects on the peat bution (Alfano et al., 2011; Longchamp et al., 2011). The age of the accumulation rate, as well as the microbiological communities and oldest post-glacial tephra units reported here (in Supplementary pore water chemistry (De Vleeschouwer et al., 2008; Payne and Table 1) generally decreases with increasing latitude, reflecting Blackford, 2008; Hughes et al., 2013). Cryptotephra layers (i.e., the timing of ice retreat, as previously noted for part of the SVZ by tephra deposits hidden from view, due to very small grain sizes Watt et al. (2013a). The temporal bias resulting from the lack of (<0.1 mm) and/or deposit volumes (Lowe and Hunt, 2001; Lowe, environments during the LGM in which preservation to the present 2011)) are readily preserved in peat (although they are particu- day was possible hinders correlations prior to deglaciation (25e larly prone to alteration and physical disturbance), but to date have 16 ka; Glasser et al., 2008; Hulton et al., 2002; Kaplan et al., 2008), rarely been searched for or examined in Patagonian bog cores. and investigation of long-term eruption frequency. Although Some care is required to distinguish peaks in cryptotephra con- tephra stratigraphies spanning multiple glacial cycles have been centration representing primary fallout from those reflecting found in lakes beyond the maximum ice extent (e.g., Potrok Aike: tephra remobilisation (Swindles et al., 2013), which is possible even Wastegård et al., 2013) and in the Pacific Ocean (e.g., Carel et al., in distal locations, where the tephra can be sourced from erosion of 2011), considerable further work would be necessary to acquire the peat bogs themselves (e.g., Swindles et al., 2013). sufficient data to establish a regional tephrochronology prior to Some of the best preserved tephra can be found in lake and deglaciation. marine sediment cores: significant chemical alteration and erosion of deposited tephra is uncommon in these environments, but the 4.2. Challenges in dating and correlation of tephra units thickness of and grain size in tephra layers may not be represen- tative of primary fallout. This is particularly the case for lakes and An in-depth discussion on the different techniques used and fjords, where it is more likely that terrestrial deposits will be existing challenges in tephrochronology is beyond the scope of this remobilised into the water and pumice will be rafted to the paper; the reader is referred to the review paper by Lowe (2011). downwind side of the water body. Remobilisation of tephra layers Instead we highlight a few issues that we consider most relevant by turbidites (Moernaut et al., 2007; Bertrand et al., 2008a)is for tephrochronological studies in southern Chile. The tephros- common; reworked layers can be difficult to distinguish from pri- tratigraphic record presented in Supplementary Table 1 highlights mary fallout, with implications for correlation and constraints of the many gaps that still exist in our knowledge of the eruptive eruption frequency (Wastegård et al., 2013; Van Daele et al., in history of individual SVZ and AVZ volcanoes. In addition to detailed press). Tephra layer dispersal has been reported in lake cores geological field studies, high-resolution sediment cores provide without associated sediment mixing, attributed to reworking into crucial information on regional eruptive frequency in the form of desiccation cracks or post-depositional intrusion into other levels preserved tephra layers. This is especially the case in areas like (Markgraf et al., 2003). Few tephra units from the SVZ and AVZ have Patagonia where tephra preservation on land is limited due to 80 K. Fontijn et al. / Quaternary Science Reviews 89 (2014) 70e84 strong winds and limited vegetation (Section 4.1). The tephra layers tephra layers from the same source might exist in a narrow time in sediment cores in turn form excellent synchronous tie-points for window, e.g., the 20the21st Century eruptions at PuyehueeCordón core age models if recognised in multiple locations. However, the Caulle. In these cases, compositional data of FeeTi oxide minerals compilation of tephra records in palaeoenvironmental archives of might prove to be more useful, as documented by Fierstein (2007) southern Chile and Argentina (Supplementary Table 2) shows that for the Katmai region on the Alaskan Peninsula. the vast majority of tephra layers are insufficiently characterised to Other difficulties in tephra fingerprinting exist in the analysis of allow the source to be identified. tephra compositions in the basalt to andesite range, which is the Inter-core correlations sometimes rely on the mere presence of a modal erupted composition in both this region and for two of the distinct marker bed showing a rough age correspondence, but for most active Andean volcanoes, Llaima and Villarrica. Apart from which no, or hardly any, chemical analyses or physical descriptions being relatively more prone to chemical alteration in their post- (e.g., colour, grain size, and mineral content) are available. This is depositional environment than rhyolitic glasses (e.g., Pollard the case for a regional marker bed dated by interpolation at ca 9600 et al., 2003), basalticeandesitic glasses are often characterised by 14C yr BP (ca 11 ka cal BP), which has been recognised in cores at the presence of abundant microphenocrysts in the groundmass, ODP Site 1233 and correlated with a tephra layer in cores on Chiloé which can obstruct valuable analyses of a glass phase and result in Island and the Chilean Lake District (Heusser et al., 1999; Moreno apparent chemical heterogeneity (Platz et al., 2007; Lowe, 2011). and León, 2003; Abarzúa et al., 2004; Lamy et al., 2004; Moreno, This is the case for the Chaimilla deposit from Villarrica (Costantini 2004; Abarzúa and Moreno, 2008; Supplementary Table 2). et al., 2011) and historical tephras from Llaima (Bouvet de Amigo et al. (2013) found that this tephra in the cores of ODP Site Maisonneuve et al., 2013). Chemical similarity between mafic 1233 consists of two populations of shards, rhyodacitic and basaltic products from different, but geographically nearby, volcanoes may andesitic, but could not identify a source volcano for this tephra. also make it very difficult to assign a source to tephra layers in Although the inter-core correlations for this specific horizon seem sediment cores. Where different tephras are indistinguishable in reasonable given the relative geographical proximity of the terms of their glass major element chemical composition, alterna- different cores and the consistent interpolated age values, they tive methods should be explored, such as analysis of mineral should be treated with caution because several regional tephra compositions or the trace elements of glass shards (Lowe, 2011). horizons are known in this section of the arc around the start of the Silicic pumice and mafic scoria particles have been reported to Holocene (e.g., Cha1 from Chaitén and several horizons from Cal- occur together in the same tephra layers in cores taken from lakes buco: Supplementary Table 1; Watt et al., 2013a). in the Nahuel Huapi National Park in Argentina (Daga et al., 2006, For late Quaternary records, most tephra horizons in sediment 2008, 2010). In the case of large explosive eruptions, it is conceiv- cores are dated by (linear) interpolation of 14C dates of carbonates, able that such tephra layers result from tapping of a chemically bulk sediment or organic remains. However, lakes are especially zoned magma chamber, or mafi c magma batches intruding into a prone to a reservoir effect, due to dissolution of ancient carbonates more evolved magma body. Eruptions of mixed and mingled and/or old organic matter that is washed into the lake from the magmas have been recognised worldwide (Woods and Cowan, catchment and incorporated into the sediment. Both phenomena 2009). In these cases, the distal deposits could indeed consist of can result in anomalous 14C ages and an offset from the real age of several populations of chemically distinct particles, as seen for the the dated material, which is not necessarily constant through time Nahuel Huapi Tephra (Villarosa et al., 2006), corresponding to a in the sediment section (Geyh et al., 1998; Yu et al., 2007). This ca 2.2e2.8 ka cal BP dacitic pumice fall overlain by basaltic andesitic offset from the real age can be of the order of several hundred or scoria from the Antillanca Group (Supplementary Table 1; Singer even more than a thousand years if bulk sediment or carbonates are et al., 2008). Similarly, multiple populations of clasts in distal dated, and can thus lead to misleading or erroneous age models if it tephra layers could be expected for other chemically zoned tephra is not taken into account (Geyh et al., 1998; Bertrand et al., 2012). fall deposits, e.g., the Llaima Pumice, still relatively poorly dated at Sediment sections spanning time intervals with multiple tephra ca 8.2e10.2 ka cal BP (Ll-pl, Supplementary Table 1; Naranjo and layers could therefore easily be miscorrelated if the tephra is not Moreno, 1991, 2005). If the end-members of a chemically zoned adequately characterised to back up correlations. Appropriate deposit are well-defined, fingerprinting a distal tephra should be tephra characterisation can potentially also help in evaluating the relatively straightforward as long as both end-members are found. reservoir effect in a sediment section by providing a tie-point in the However, the tephra layers in the short cores in the Nahuel Huapi age model, provided the age of the tephra is well known from one National Park have been assigned to the PuyehueeCordón Caulle, or more independent sources (e.g., 14C dating on charcoal incor- Calbuco and Osorno volcanoes (Daga et al., 2008, 2010), none of porated in terrestrial deposits, for example the well-constrained which are thought to have erupted chemically diverse magmas in a 3.00e3.05 ka cal BP Alpehué Pumice (So-A) eruption from Sol- single event in the last 600 years, the time span of the cores. It is lipulli; Supplementary Table 1; Naranjo et al., 1993b). therefore possible that the scoria component in otherwise pumi- The most widely used (and arguably most straightforward) ceous tephra layers results from contamination from the back- method to fingerprint and correlate tephra layers between different ground sediment, either washed in or remobilised within the lake sites is major element composition analysis of individual glass sediments. Alternatively, in some cases pieces of shattered brown shards by electron microprobe (Lowe, 2011). Although this tech- glassy bombs of the same composition as light grey pumice from nique has proven its value in many areas worldwide (for references PuyehueeCordón Caulle (Castro et al., 2013) might have been to relevant case studies, see Lowe (2011)), some complications exist mistaken for moderately vesicular scoria clasts. that are particularly relevant for southern Chile and Argentina. The Peat deposits are important environmental archives, and as two most recent significant explosive eruptions in this region were discussed above (Section 4.1), are prevalent in southern Chile. Some both of highly evolved magma compositions, i.e., the rhyolitic 2008 specific difficulties have to be considered when studying tephra in Chaitén (Watt et al., 2009; Alfano et al., 2011) and rhyodacitic 2011 peat sequences. Peat deposits are known to be difficult to date PuyehueeCordón Caulle (Castro et al., 2013) events. In both cases, using 14C because they consist of organic matter of different origins. the major element chemical composition of the glass was almost In some case studies, humin versus humic acid fractions extracted indistinguishable from that of previous eruptions at the same vol- from peat have been found to result in significantly different 14C cano (Castro et al., 2013; Watt et al., 2013c). This raises concerns ages, in some cases differing by up to more than a thousand years about miscorrelation, especially where a sequence of highly similar (e.g., Shore et al., 1995; Brock et al., 2011). These uncertainties K. Fontijn et al. / Quaternary Science Reviews 89 (2014) 70e84 81 clearly have to be taken into account when tephras in different Charles Stern and an anonymous reviewer were greatly sections are correlated on age-equivalence alone. Correlation based appreciated. on the mineralogy and/or chemistry of tephra preserved in peat is also hampered by dissolution and alteration, as discussed in Section Appendix A. Supplementary data 4.1. Additional complications in tephrochronological studies in Supplementary data related to this article can be found at http:// peatland may exist in the possible post-depositional movement of dx.doi.org/10.1016/j.quascirev.2014.02.007. tephra through the peat, which may make it difficult to define the exact position of the isochron that represents the timing of tephra References deposition in the peat sequence. Experiments by Payne and Gehrels (2010) in both laboratory and natural environments have shown Abarzúa, A.M., Moreno, P.I., 2008. Changing fire regimes in the temperate rainforest e that most tephra remains trapped at the surface of peatland after region of southern Chile over the last 16,000 yr. Quat. Res. 69, 62 71. http://dx. fi doi.org/10.1016/j.yqres.2007.09.004. deposition, and thus forms a relatively stable and easily identi able Abarzúa, A.M., Villagrán, C., Moreno, P.I., 2004. Deglacial and postglacial climate isochron. However, some tephra particles can easily move more history in east-central Isla Grande de Chiloé, southern Chile (43S). Quat. Res. than 10 cm downward (possibly as a function of their grain size), as 62, 49e59. http://dx.doi.org/10.1016/j.yqres.2004.04.005. Alfano, F., Bonadonna, C., Volentik, A.C.M., Connor, C.B., Watt, S.F.L., Pyle, D.M., well as upward, in accumulating peat. The scale of this movement Connor, L.J., 2011. Tephra stratigraphy and eruptive volume of the May, 2008, may span several hundreds of years of peat accumulation and so is Chaitén eruption, Chile. Bull. Volcanol. 73, 613e630. http://dx.doi.org/10.1007/ significant when dating tephra deposition in peat sequences (Payne s00445-010-0428-x. fi Amigo, A., Lara, L.E., Smith, V.C., 2013. Holocene record of large explosive eruptions and Gehrels, 2010). Concentration pro les of tephra are therefore from Chaitén and Michinmahuida Volcanoes, Chile. Andean Geol. 40, 227e248. essential in evaluating the position of the isochron, especially when http://dx.doi.org/10.5027/andgeoV40n2-a03. studying (crypto)tephra horizons at high temporal resolution. Antweiler, R.C., Drever, J.I., 1983. The weathering of a late Tertiary volcanic ash e importance of organic solutes. Geochim. Cosmochim. Acta 47, 623e629. http:// dx.doi.org/10.1016/0016-7037(83)90283-1. 5. Conclusions Arnaud, F., Magand, O., Chapron, E., Bertrand, S., Boés, X., Charlet, F., Mélières, M.A., 2006. Radionuclide dating (210Pb, 137Cs, 241Am) of recent lake sediments in a e A critical review of the post-glacial tephrostratigraphic record in highly active geodynamic setting (Lakes Puyehue and Icalma Chilean Lake District). Sci. Tot. Environ. 366, 837e850. http://dx.doi.org/10.1016/j.scitotenv. southern Chile and Argentina reveals that at least 21 of the 74 2005.08.013. known volcanic centres have had large explosive eruptions that Behrmann, J.H., Lewis, S.D., Musgrave, R.J., Shipboard Scientific Party, 1992. Proc. have dispersed tephra over vast areas. At least 9 of them have had Ocean Drill. Prog. Initial Rep. 141. Ocean Drilling Program, College Station TX. In: http://dx.doi.org/10.2973/odp.proc.ir.141.1992. multiple moderate to large explosive eruptions in their post-glacial Bertrand, S., Araneda, A., Vargas, P., Jana, P., Fagel, N., Urrutia, R., 2012. Using the N/C history. Tephra from these eruptions was predominantly dispersed ratio to correct bulk radiocarbon ages from lake sediments: insights from eastward over the Patagonian steppe. However, the estimated fre- Chilean Patagonia. Quat. Geochron. 12, 23e29. http://dx.doi.org/10.1016/j. quageo.2012.06.003. quency of large explosive eruptions in this part of the Andes is likely Bertrand, S., Castiaux, J., Juvigne, E., 2008b. Tephrostratigraphy of the late glacial to be significantly underestimated, because of limited knowledge of and Holocene sediments of Puyehue Lake (Southern Volcanic Zone, Chile, 40 the eruptive histories of individual volcanoes and the poor pres- degrees S). Quat. Res. 70, 343e357. http://dx.doi.org/10.1016/j.yqres.2008.06. 001. ervation and/or accessibility of tephra deposits. Inadequate char- Bertrand, S., Charlet, F., Chapron, E., Fagel, N., De Batist, M., 2008a. Reconstruction of acterisation of individual eruptions and deposits not only leads to the Holocene seismotectonic activity of the Southern Andes from seismites underestimates in the tephrostratigraphic record, but also to recorded in Lago Icalma, Chile, 39 S. Palaeogeogr. Palaeoclimatol. Palaeoecol. 259, 301e322. http://dx.doi.org/10.1016/j.palaeo.2007.10.013. ambiguities. Bird, P., 2003. An updated digital model of plate boundaries. Geophys. Geochem. Most tephra horizons from large explosive eruptions form Geosyst. 4, 1027e1079. http://dx.doi.org/10.1029/2001GC000252. excellent marker beds in palaeoenvironmental archives, of which Bonadonna, C., Cioni, R., Pistolesi, M., Connor, C., Scollo, S., Pioli, L., Rosi, M., 2013. many exist in southern Chile and Argentina. These archives are Determination of the largest clast sizes of tephra deposits for the character- ization of explosive eruptions: a study of the IAVCEI commission on tephra especially useful to study climate dynamics of the southern hemi- hazard modelling. Bull. Volcanol. 75, 680. http://dx.doi.org/10.1007/s00445- sphere. However, to date the tephrochronological potential of these 012-0680-3. archives is severely under-utilised, as exemplified by the acute lack Bouvet De Maisonneuve, C., Dungan, M.A., Bachmann, O., Burgisser, A., 2013. Petrological insights into shifts in eruptive styles at Volcán Llaima (Chile). of geochemical data on tephra horizons encountered in lacustrine, J. Petrol. 54, 393e420. http://dx.doi.org/10.1093/petrology/egs073. marine, and peat sediment cores (Supplementary Table 2). A more Brock, F., Lee, S., Housley, R.A., Bronk Ramsey, C., 2011. Variation in the radiocarbon rigorous use of the tephra record to correlate sediment sections age of different fractions of peat: a case study from Ahrenshöft, northern Germany. Quat. Geochron. 6, 550e555. http://dx.doi.org/10.1016/j.quageo.2011. from different environments is highly recommended, by means of 08.003. adequate geochemical, mineralogical, and physical characterisation Bronk Ramsey, C., 2009. 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