Quaternary Science Reviews 67 (2013) 121e137
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Quaternary Science Reviews
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Identification and correlation of visible tephras in the Lake Suigetsu SG06 sedimentary archive, Japan: chronostratigraphic markers for synchronising of east Asian/west Pacific palaeoclimatic records across the last 150 ka
Victoria C. Smith a,*, Richard A. Staff a, Simon P.E. Blockley b, Christopher Bronk Ramsey a, Takeshi Nakagawa c, Darren F. Mark d, Keiji Takemura e, Toru Danhara f, Suigetsu 2006 Project Members1 a Research Laboratory for Archaeology and the History of Art, University of Oxford, Oxford OX1 3QY, UK b Centre for Quaternary Research, Royal Holloway University of London, Egham TW20 0EX, UK c Department of Geography, University of Newcastle, Newcastle Upon Tyne NE1 7RU, UK d Scottish Universities Environmental Research Centre (SUERC), East Kilbride G75 0QF, UK e Beppu Geothermal Research Laboratory, Faculty of Science, Kyoto University, Beppu 874-0903, Japan f Kyoto Fission-track Co. Ltd., 44-4 Tajiri-cho, Ohmiya, Kita-ku, Kyoto 603-8838, Japan article info abstract
Article history: The Lake Suigetsu SG06 sedimentary archive from Honshu Island, central Japan, provides a high- Received 29 August 2012 resolution palaeoenvironmental record, including a detailed record of explosive volcanism from Japan Received in revised form and South Korea. Thirty visible tephra are recorded within the 73 m-long SG06 core, which spans the last 19 January 2013 w150 ka. Here we describe and characterise these tephras based on major element glass composition, Accepted 23 January 2013 which is useful for the identification and correlation of these tephras and the age models of the records Available online in which they are found. Utilising the large number of radiocarbon measurements (n > 600) from ter- restrial plant macrofossils in the Lake Suigetsu SG06 record, we are able to provide precise and accurate Keywords: Lake Suigetsu ages for the tephras from eruptions within the last 50 ka. Glass compositional data of some of the largest Tephrostratigraphy eruptions from Japan (K-Ah, AT, Aso-4, Aso-A, Aso-D, and Ata; sampled at proximal outcrops) are also Radiocarbon dates presented. These data show that the major element glass chemistry is distinctive for many of the visible Glass composition SG06 tephra units, and allows some of the layers to be correlated to known eruptions from volcanoes in Eruption history Japan and South Korea, namely K-Ah (SG06-0967), U-Oki (SG06-1288), AT (SG06-2650), Aso-4 (SG06- 4963/SG06-4979), K-Tz (SG06-5181), Aso-ABCD (SG06-5287) and Ata (SG06-5181). The following ages were obtained for the SG06 tephra units: 3.966e4.064 cal. ka BP (95.4% probability range) for the SG06- 0588 tephra, 10.242e10.329 cal. ka BP (95.4% probability range) for SG06-1293, 19.487 112 SG062012 ka BP (2 s) for SG06-1965, 28.425 194 SG062012 ka BP (2 s) for SG06-2504, 28.848 196 SG062012 ka BP (2 s) for SG06-2534, 29.765 190 SG062012 ka BP (2 s) for SG06-2601, 29.775 191 SG062012 ka BP (2 s) for SG06-2602, 43.713 156 SG062012 ka BP (2 s) for SG06-3485, 46.364 202 SG062012 ka BP (2 s) for SG06-3668, 49.974 337 SG062012 ka BP (2 s) for SG06-3912, 50.929 378 SG062012 ka BP (2 s) for SG06-3974, and improved ages for two of the most important tephra markers across Japan, the K-Ah (7.165e7.303 cal. ka BP at 95.4% probability range; SG06-0967) and AT tephra (30.009 189 SG062012 ka BP at 2 s; SG06-2650). Crown Copyright Ó 2013 Published by Elsevier Ltd. All rights reserved.
1. Introduction distal records of volcanism provide insight into the stratigraphic interfingering and superpositioning of tephra deposits from multiple Volcanic ash (tephra) ejected during large explosive eruptions can volcanic sources, and can elucidate the tempo of explosive volcanism travel thousands of kilometres (e.g., Costa et al., 2012) forming (e.g., Smith et al., 2011a), which is particularly important for hazard isochronous markers in widespread sedimentary records. These assessments. Furthermore, synchronising palaeoenvironmental proxy information within these sedimentary archives using tephra layers can provide invaluable information for assessing potential * Corresponding author. Tel.: þ44 1865 285202. E-mail address: [email protected] (V.C. Smith). spatial leads and lags in palaeoclimate change (e.g., Lane et al., 2011; 1 http://www.suigetsu.org/. Lowe et al., 2012).
0277-3791/$ e see front matter Crown Copyright Ó 2013 Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.quascirev.2013.01.026 122 V.C. Smith et al. / Quaternary Science Reviews 67 (2013) 121e137
The Lake Suigetsu SG06 sediment archive from Honshu Island, all of the eruptions that are preserved within the post-50 cal. ka central Japan (see below), provides one of the most important part of SG06, which can subsequently be applied to other archives palaeoenvironmental records of the Late Pleistocene in the E. Asia/ in which the same tephras are preserved. W. Pacific region (Walker et al., 2009). For much of its depth, the The composition of glass shards from the tephras should provide Suigetsu sediment is annually layered (varved), and contains ter- a unique fingerprint that can be used to correlate the tephra layers to restrial macrofossils, diatoms and pollen, which provide high- particular eruptions, as well as between sedimentary records. Cores resolution proxy palaeoenvironmental information (Nakagawa exist from all around Japan, with many acquired from the Sea of et al., 2012). This archive can potentially answer some funda- Japan and the Pacific on the Integrated Ocean Drilling Project cruises mental questions about Asian palaeoclimate and the drivers of (e.g., Hunt and Najman, 2003 and those reported in Furuta et al., global climatic change when combined with other records and 1986, and Machida and Arai, 2003). Numerous Japanese lakes have datasets. Numerous tephra layers are also preserved within the also been cored, including Lake Biwa (Takashima-oki core; Suigetsu sediments, which are the key to correlating and syn- Satoguchi et al., 1993; Nagahashi et al., 2004), Ichi-no-Megata chronising this record to marine and terrestrial archives in the re- (Okuno et al., 2011), and Lake Mikata (Takemura et al., 1994). gion and beyond. These correlations are essential in establishing Some of these marine and terrestrial records also provide environ- a palaeoclimatic event stratigraphy for the Asia/Pacific region, such mental information from the analysis of proxies and these records as that developed for the North Atlantic (e.g., Blockley et al., 2012). could potentially be precisely synchronised using tephra (including However, a detailed tephrostratigraphy is first required, and the using non-visible cryptotephra in future studies) to further under- layers have to be compositionally characterised so that they can be stand temporal and spatial variations in palaeoclimate. definitively ascribed to particular eruptions or reliably correlated to other distal tephra layers. 1.1. The SG06 record from Lake Suigetsu Japanese researchers, such as Arai (1972), pioneered tephra research, mapping the extent of the Japanese tephra layers in order The SG06 sediment core was extracted in 2006 from Lake Sui- to use them as correlative and relative-age stratigraphic tools. The getsu, Honshu Island, central Japan (35 350000N, 135 530000E; Fig. 1), Japanese volcanic arc is particularly productive, and calderas in the as part of the ‘Suigetsu Varves 2006’ project. The 73.19 m-long core north and south have been the source of many large explosive provides a continuous record of sedimentation spanning the last eruptions. These eruptions dispersed ash over most of Japan, and w150 ka (Nakagawa et al., 2012; Fig. 2). The high-resolution form a well-defined chrono-stratigraphic framework (Machida and palaeoenvironmental archive contains 31 visible tephra layers, Arai, 2003). Tephrochronology requires the characteristics of the and cryptotephra have also been identified, with pilot studies units to be unique (within defined age periods) so that the ash layers showing peaks in shard concentrations approximately every 0.5 m can be reliably correlated to specific volcanoes and eruptions. in the Pleistocene sediments (Staff et al., in press). Tephras are typically characterised using the composition of the Lake Suigetsu was cored numerous times before the 2006 cam- glass shards that are blown to distal regions (e.g., Shane, 2000; paign. Most significantly, four piston cores (SG1, SG2, SG3 and SG4), Lowe, 2011). Tephra researchers in Japan realised the need to extending to w16 m, and a longer 75 m machine-drilled core (SG93) characterise the units, well before electron microprobes were were extracted in 1993 (Takemura et al.,1994; Fukusawa et al.,1995; commonly used to analyse geological material, and used the Kitagawa et al., 1995; Yasuda et al., 2004; Fig. 3). These older cores refractive index of the glass and the phenocryst phases to help were correlated to the 100 m-long Lake Mikata core (Fig. 1C) by identify tephra units (Arai,1972). However, the refractive indices are Takemura et al. (1994) using the visible tephra layers. The Suigetsu often not unique to particular eruptions (cf. Katoh et al., 2004) and in cores contain many tephra layers and some have been correlated to the very distal regions the denser crystals are often not found. Here, the K-Ah, U-Oki, Sakate, DMs, DHg, DSs, AT, Aso-4, K-Tz, Aso-ABCD, we determine the composition of the glass shards in visible tephra and Ata eruptions (Takemura et al., 1994; Nakagawa et al., 2012; layers found within the Lake Suigetsu SG06 sediment core, using Fig. 3; see below for details), based upon the stratigraphic position, a wavelength-dispersive electron microprobe, to correlate tephras appearance of the units, thickness (which partly reflects eruption to source eruptions, and test some of the inferred correlations magnitude and dispersal), and in some cases the refractive indices (Takemura et al., 1994; Nakagawa et al., 2012; see below). of the glass shards. Tephra layers in the upper 2 m of the Lake Sui- The detailed tephrostratigraphy for the SG06 sediment core will getsu sediments (SG2 on Figs. 1C and 3; Fukusawa et al., 1995)are provide information on the dispersal axes and magnitude of thought to be associated with historically known eruptions at eruptions in southern and central Japan, as well as the tempo of 220 AD, 420 AD, 890 AD, and 1770 AD (Fukusawa et al., 1995). volcanism. Furthermore, ages of the eruptions preserved in the lower portion of the core, preceding the radiocarbon timeframe, are 1.2. Sources for the tephra in the SG06 core required to develop a robust chronology for palaeoenvironmental study. The ages of eruptions in the region >50 cal. ka are very Japan lies along a volcanic arc, with more than 130 volcanoes poorly constrained, but recent advances in 40Ar/39Ar techniques spanning the length of the country (Fig. 1A). Many of these have mean that accurate and precise ages can now be obtained for these been active in the Late Pleistocene and Holocene, including some of events. Ages can be obtained for the older tephras by correlating the large caldera volcanoes. Tephra layers from the largest explo- them to the proximal eruption deposits, which contain the denser sive eruptions, eruptions from proximal volcanoes, and eruptions crystal phases that are required for 40Ar/39Ar dating (see Smith that dispersed ash towards Lake Suigetsu are likely to be preserved et al., 2011b). in the Lake Suigetsu sediments. The volcanic explosivity index (VEI; An ultra high-resolution radiocarbon dataset has been acquired Newhall and Self, 1982) provides information on the relative from the SG06 sediment core, which has been combined with varve magnitude and dispersal of the events, and therefore provides counting (Marshall et al., 2012; Schlolaut et al., 2012) to produce some information on the likelihood of finding the deposits in Sui- a wholly terrestrial radiocarbon dataset that will be integrated into getsu. The VEI scale ranges from 0 to 8, with 8 being the largest. the international consensus calibration curve, IntCal, to improve Approximately 1 km3 of tephra, which equates to 0.4 km3 of magma the reliability of calibration of radiocarbon data (Staff et al., 2011; is erupted during VEI 5 events, with an order of magnitude increase Bronk Ramsey et al., 2012). Furthermore, this high-resolution for each VEI increment. The events with the largest magnitude, radiocarbon dataset provides very accurate and precise ages for super-eruptions, have a VEI of 8 and erupt >450 km3 of magma V.C. Smith et al. / Quaternary Science Reviews 67 (2013) 121e137 123
Fig. 1. (A) Volcanoes in and around Japan, modified after Machida (1999). All of the calderas (circles with teeth) are labelled; collapse structures >10 km have slightly larger symbols; and other volcanoes (stratovolcanoes, shield volcanoes, and monogenetic fields) are marked with black dots. (B) Volcanic centres within 300 km of Lake Suigetsu, Honshu Island, Japan. The calderas are labelled in black. (C) Area around Lake Suigetsu, with the locations of the drilling sites in Fig. 3 marked, SG06 (Nakagawa et al., 2012), SG93 (Takemura et al., 1994), and the SG2 piston core (Fukusawa et al., 1995).
(>1000 km3 of tephra; Self, 2006). Visible tephra layers from dominate (Machida and Arai, 2003); thus, tephras erupted from eruptions along the arc with a VEI > 7 are likely to be preserved in volcanoes southwest of Suigetsu are more likely to be present in SG06 unless the eruptions were from volcanoes >1000 km away or SG06. Information about the largest eruptions in Japan and those the dispersal axis was directed away from Lake Suigetsu, or both. from volcanoes close to Lake Suigetsu in the last w150 ka (Fig. 1B) Tephras from smaller eruptions, with VEI of w5, could also be and that probably dispersed ash over Lake Suigetsu are summarised preserved in SG06, again depending on the proximity of the vol- in Table 1. canic source and the wind direction at the time of the eruption. Tephras from the largest eruptions have typically occurred in the Mapped tephra dispersal suggests that southwesterly winds large caldera volcanoes in southern Kyushu, >550 km from 124 V.C. Smith et al. / Quaternary Science Reviews 67 (2013) 121e137
SG06 visible tephras SG2 visible tephras SG93 stratigraphy 25 cm
SG06-0558 117 cm 158 cm 187 cm SG06-0967 K-Ah
SG06-1288 U-Oki SG06-1293
SG-I
SG06-1965 Sakate
SG06-2504 Daisen-Hoki (upper) SG06-2534 Daisen-Hoki (lower) SG06-2601 & SG06-2602 AT SG06-2650
SG-II
SG06-3485 SG06-3668 Radiocarbon limit (~50 ka cal. BP) SG06-3912 SG06-3974 SG06-4124 SG06-4141 SG06-4281 DSP SG06-4318 SG-III
SG06-4963 Aso-4 SG06-4979 SG06-5181 K-Tz SG06-5287 Ata SG06-5353 SG06-5385
SG-IV
SG06-6344 SG06-6412 SG06-6454 & SG06-6457 SG06-6510 Finely laminated clay SG06-6634 Laminated clay Clay Peaty clay Peat Visible tephra SG-V
Fig. 3. Tephrostratigraphy of Lake Suigetsu. Some of the tephras in SG06 have previ- ously been correlated to those in SG93 (Nakagawa et al., 2012). The layers within the SG93 core were identified by Takemura et al. (1994). The position of the tephra layers in the 2 m-long SG2 piston core are from Fukusawa et al. (1995). The visible tephra layers within SG06 are described, characterised, and correlated to eruptives elsewhere using the major element analyses of constituent glass shards in this study.
Kikai, Aira, Ata, and Aso, which were generated during massive eruptions in the Late Pleistocene (Table 1). The largest eruptions (VEI 7-8), with widespread tephra deposits, from Kyushu are the 6.86e7.44 cal. ka BP Kikai-Akahoya (K-Ah), one of the largest known Holocene eruptions on Earth (VEI ¼ 7.2); 29.428e 30.148 cal. ka BP Aira tephra formation (AT); 86.8e87.3 ka Aso-4 (Aoki, 2008); w95 ka Kikai-Tozurahara (K-Tz); w100 ka Ata; w123 ka Aso-3; and w140 ka Aso-2 eruptions (Machida and Arai, 2003). These eruptions generated large volumes of tephra (up to Fig. 2. The composite SG06 sediment core with depths of visible tephras marked with 600 km3) and dispersed it mostly to the NE over central Honshu grey lines. Red lines indicate the key marker layers (often tephras or turbidites) used to construct the composite SG06 depth scale (see Nakagawa et al., 2012 for more infor- (Machida and Arai, 2003). The largest known events from Hokkaido mation). Composite depth is from the August 2009 model. (For interpretation of the in the last 150 ka are the Shikotsu-1, Kutcharo-Shoro, Toya-2, and references to colour in this figure legend, the reader is referred to the web version of Kutcharo-Hb eruptions (Machida and Arai, 2003; Table 1). Since the this article.) source volcanoes are more than 600 km from Suigetsu, and tephra dispersal is rarely towards the SW, it is unlikely that many of these Suigetsu, and northern Honshu and Hokkaido >600 km away from Hokkaido eruptions are recorded as visible layers in Suigetsu. the lake. Tephras from these events are widely dispersed and found Many of the numerous volcanoes within 300 km of Lake Sui- in sedimentary sequences in and around Japan (Machida, 1999, getsu (Fig. 1B) have been active in the last 150 ka (Hayakawa, 1996; 2002; Machida and Arai, 2003). Kyushu has many large calderas, Suzuki, 1996; Machida and Arai, 2003; Crosweller et al., 2012; V.C. Smith et al. / Quaternary Science Reviews 67 (2013) 121e137 125
Table 1 The main explosive eruptions in the Japan region since w150 ka that could be preserved as visible tephra layers in SG06.
Volcano Eruption Tephra VEI Tephra Dispersal Age (cal. ka BP) Known thickness Distance from References volume near Suigetsu (cm) Suigetsu (km) (km3) Large eruptions Kyushu Kikai Akahoya K-Ah 7.2 150 NE 6.86e7.44 20 640 SW 1 (6.28 0.13 14C) Tozurahara K-Tz 7.5 150 NE w95 2e51 Aira Aira tephra AT 8 450 NE 29.428e30.148 10e20 670 SW 1 formation (24.83 0.09 14C) Ata (Ibusuki Volcanic Ata Ata 7.5 300 NE w100 <1 695 SW 1 Field) Aso Aso-4 8 600 NNE 87 9KeAr2; >15 530 SW 1e3 86.8e87.33 Aso-A, B, C, D 6 E w90 e 1 Aso-3 7 150 E w123 w1 1,4 Aso-2 6.7 50 w140 e 1,4 Hokkaido Shikotsu Shikotsu-1 Spfa-1; Spfl 7.2 180 SE w42 e 890 NE 1 Toya Toya-2 Toya 7.4 150 Central w115 e 880 NE 1 Kutcharo Shoro Kc-Sr 7 170 SE 39.7e45.2 e 1150 NE 1 (37.5 1.5 14C) Hb Kc-Hb; Kp-4 7.2 150 W w117 e 1 South Korea Ulleungdo U4 U-Oki >10 SE 10.177e10.255 2 480 WNW 1,5,6,7 Changbaishan, China/ Korea border Tianchi/Baitoushan Millennium eruption B-Tm 50 E 0.921e0.941 e 950 NW 1,8 of Tianchi Volcano Smaller eruptions from sources closer to Suigetsu Honshu Towada Hachinohe Pumice To-H; To-HP; 6.9 50 E 10.19e18.55 e 680 NNE 1,9 Unit L (11.5 1.5 14C) Ofudo To-BP1(Of); 6.7 46 E 34.5e43.2 e 1,9 Unit N (w33 2 14C) Daisen Ueno-hoki Uh w5 21.97e21.34 215 SW 10,11 Kusatanihara D-KsP; KsP w5 12,13 Higashi DHg; HgP w5 14 Odori Od 5 10,11,12,14 Misen DMs; MsP 5 28.41e29.32 10,11,13 (24.01 0.15 14C) Shitano-hoki DSs; Sh w5 28.64e29.52 11 (24.37 0.12 14C) Nisehoki Nh 6.2 17 40.35e41.38 11 (35.65 0.2 14C) Kurayoshi Pumice DKP 6.9 50 NE w46 10,11,12,14 Sekigane DSP 5.1 E w65 >0 10,11,12,14 Namadake DNP 6 80 E w80 >0 10,11,12,14 Hiruzebara Pumice DHP 6 w110 10,11,12,14 Matsue DMP 5.7 12 W w125 10,11,12,14 Sambe/Sanbe Fuppu 6 100 w16 300 W 15 Ukinuno SUk; Sakate 5 SE 19.48e20.29 e 1,11 (16.74 0.16 14C) Ikeda SI 5 10 SE w37 e 2 Oda/Unan Sod, Sun 5 13 w53 1 Kisuki SK; Sanbe 6.7 20 NE w112 >01 Ontake Mitake On-Mt 6 E w60 e 150 NE 1 Ontake-4 5.7 w72 9 Senbon Matsu 5 1 w76 9 Ontake-3 5 1 w82 9 Nagawa On-Ng 5.3 NE w83 e 1 Ina On-In 6 10 E w93 e 1 Katamachi On-kt 5.8 NNE w94 e 1 Daiichi Pumice O-Pm1 6.6 50 E w95 e 1 Haruna Hassaki (Murota ignimbrite) 5 3 w41 e 285 ENE 1 Hr-HP 5 3 w50 e 1 Hakone Tokyo Pumice Hk-TP 6.1 >20 w49 e 290 E 1 Akagi Kanuma Pumice Ag-KP 5.7 26 E w32 e 315 NE 1 Yunokuchi/Yunoguchi Ag-UP 5.7 5 Central w53 e 1 Tateyama/Takeyama Tateyama-E Tt-E 5.4 1 w60e75 e 190 ESE 1 Tateyama-D Tt-D 6 10 w130 e 1
All radiocarbon dates from literature were calibrated using OxCal v4.1.7 (see Bronk Ramsey, 2009) using the IntCal09 calibration curve (Reimer et al., 2009). References: 1. Machida and Arai (2003) and references therein; 2. Matsumoto (1996);3.Aoki (2008);4.Ono et al. (1977);5.Okuno et al. (2010);6.Smith et al. (2011b);7.Staff et al. (2011);8. Yin et al. (2012);9.Hayakawa (1985); 10. Katoh et al. (2004); 11. Katoh et al. (2007); 12. Tsukui (1984); 13. Domitsu et al. (2002); 14. Tsukui (1985); and 15. Hayakawa (1996). 126 V.C. Smith et al. / Quaternary Science Reviews 67 (2013) 121e137
Smithsonian Institution, 2012). It is likely that ash from the mod- The accuracy of the electron microprobe analyses (EMPA) was erate, explosive eruptions (VEI w5) from these volcanoes is also assessed using MPI-DING reference glasses, and during all runs the preserved in the SG06 sequence, especially tephra from the vol- secondary standards (see Supplementary Material for the analyses) canoes generally upwind of Lake Suigetsu, Daisen and Sanbe (Fig. 1; were within 1 standard deviation of the preferred values (Jochum Table 1). The Daisen and Sanbe (also transliterated as Sambe) vol- et al., 2006). Analytical errors of these EMPA are <0.8% RSD for Si, canoes have experienced many VEI 5-6 eruptions in the last 130 ka 1% for Al, and w3% for most other major elements, excluding those (Tsukui,1985; Tamura et al., 2003; Katoh et al., 2004, 2007). Limited in low abundance: Ti (w16%), Mn (w50%), Cl (w20%) and P (w15% information has been published on these eruptions and the glass for concentrations >0.1 wt.% and >50% for w0.05e0.1 wt.%). composition is not well characterised, which may partly be due to Detection limits for the minor elements, P and Cl, are 0.02 wt.% poor preservation of the glass in the Daisen deposits (Kotaki et al., and 0.03 wt.%, respectively. Because of variable secondary hydra- 2011). Towada in northern Honshu is the source of some of the tion, all the glass analyses have been normalised to 100% for largest eruptions on the island in the last 150 ka, but the tephras comparative purposes. Normalised data are presented in all tables from these were dispersed mainly to the east over the Pacific Ocean and figures. The raw compositional data for glass shards from all 30 (Machida and Arai, 2003). Other volcanoes that have had eruptions visible tephra layers in SG06, and for glass in proximal tephra VEI 5 are: Ontake stratovolcano (Matsumoto and Kobayashi, 1995; samples, are included in the Supplementary Material. Kimura and Yoshida, 1999), the dominantly andesitic Akagi vol- cano; Haruna caldera; Tateyama (also transliterated as Takeyama) 4. Major element composition of the glass shards stratovolcano; Hakone caldera; and the Asama dacitic shield vol- cano, the most active volcano in Honshu (Table 1; Suzuki, 1996; 4.1. Visible tephras within SG06 Machida and Arai, 2003; Crosweller et al., 2012; Smithsonian Institution, 2012). The composition of glass shards of the visible tephra layers range from basaltic through to rhyolitic and phonolitic (Fig. 5; 2. Stratigraphy and occurrence of visible tephras in SG06 Tables 2 and 3). The thickest tephra layers, SG06-2650 and SG06- 4963, provide ideal makers for dividing the units into chro- Visible tephra layers in the SG06 core range from 0.1 cm to nostratigraphic groupings (post-SG06-2650, between SG06-2650 35.1 cm in thickness, although only 3 layers are more than 3 cm and SG06-4963, and pre- SG06-4963) for comparative purposes. T thick and most are less than 1 cm (Table 2). The 30 visible tephras The most abundant oxides, SiO2,K2O, CaO and FeO , can be deter- are variable in grain-size and colour (Fig. 4; see descriptions in mined with good precision using an electron microprobe, and Table 2). The thickest tephra layers in the SG06 core are SG06-2650 therefore used for discrimination and description. (35.1 cm; Fig. 4b), SG06-4963 (3.5 cm; Fig. 4f), and SG06-5181 Many of the tephra layers are compositionally distinct with (4 cm). The 35.1 cm-thick SG06-2650 tephra is comprised of respect to the major element composition of constituent glass brown, medium ash that is slightly normally graded, the upper shards (Fig. 5). These major element compositions are typically 7.9 cm finer ash appears to be reworked. Sometimes the colour quite homogenous, with narrow compositional ranges (<2 wt.% varies within an individual tephra, for example, the 1.3 cm-thick SiO2 and <1.3 wt.% CaO). However, a few tephra layers are com- SG06-4141 tephra grades from dark fine ash at the base (0.35 cm positionally heterogeneous, with glass compositions that are thick) through to a darker brown ash with bands of white ash. The bimodal (SG06-4318 and SG06-5385; Table 3) or span a wide range visible tephras in the SG06 core tend to occur as continuous layers (e.g., >2.5 wt.% SiO2; SG06-0558, SG06-2601, SG06-4281, SG06- but the layer at 2504 cm is only partially preserved, and pods of ash 6454, and SG06-6634; Table 3). (0.3 cm thick) are found over a 1.4 cm zone at 5385 cm. The glass composition of the uppermost visible tephra in the SG06 core, SG06-0588, is rhyolitic and spans a wide range with 3. Methodology 74.4e78.0 wt.% SiO2 and 2.25e3.99 wt.% K2O. Glass shards in the underlying SG06-0967 tephra are also rhyolitic but have more ho- Samples of the 30 visible tephra layers in the SG06 sediment core mogenous, and higher FeOT compositions (2.25e2.89 wt.%) that are were collected from core sub-sections. The tephra samples were dissimilar to those of other rhyolite tephras in the upper part of the labelled by the depth in the core (in cm, composite core model August core (Figs .4a and 6a, b; Tables 2 and 3). The unit below, SG06-1288, 2009; Nakagawa et al., 2012). The same tephra is often preserved in is phonolitic in composition and distinct from other visible tephras multiple sections (Fig. 2) from the parallel cores (see Table 2). Samples in the core, the glass shards have very high K2O contents (6.57e of proximal tephras from large magnitude eruptive events were also 7.48 wt.%; Fig. 6a, b; Table 3). The tephra layers between SG06- analysed for comparison and to aid correlation. These proximal sam- 1288 and the thick SG06-2650, SG06-1293, SG06-1965, SG06- ples of K-Ah, AT, Aso-4, Aso-D, and Ata were collected from outcrops 2504, SG06-2534, SG06-2601 and SG06-2602 (Table 3), are com- close to the source volcanoes (at localities recorded in Appendix A). positionally similar. The glass shards in these tephras are rhyolitic in All tephra samples were wet sieved, dried in an oven at 60 C, composition and contain w74e78 wt.% SiO2, 2.2e4.7 wt.% K2O, and mounted in epoxy resin blocks, and polished. More than 500 glass 0.4e2.4 wt.% FeOT (Fig. 6a, b). Compositions of some oxides are shards from 30 distinct visible tephra layers from the SG06 archive distinctive and can be used to help distinguish the different eruption were analysed for major element geochemistry. These analyses of deposits (Table 2). Glass in the thick SG06-2650 tephra is compo- individual glass shards were performed using a JEOL-8600 wave- sitionally homogeneous, with 77.02e78.41 wt.% SiO2, 3.24e length-dispersive electron microprobe at the Research Laboratory 3.55 wt.% K2O, 1.03e1.20 wt.% CaO (n ¼ 35; Fig. 6a, b; Table 3). for Archaeology and the History of Art (RLAHA), University of Ox- Constituent glasses of SG06-3485 are basaltic andesite in com- T ford. An accelerating voltage of 15 kV, beam current of 6 nA, and position, with low SiO2 (53.1e55.4 wt.%) and high FeO contents 10 mm-diameter beam were used. Peak counting times were 30 s for (8.15e11.88 wt.%; n ¼ 13; Fig. 6c and e; Table 3). All the tephra layers Si, Al, Fe, Ca, K and Ti; 40 s for Cl and Mn; 60 s for P; and 10 s for Na. directly below are rhyolitic in composition, SG06-3668, SG06-3912, The total background counts were collected for the same period of SG06-3974 (Fig. 4d), SG06-4124, SG06-4141, and SG06-4281. These time, with half the time on either side of the peak. The electron tephra layers have slightly different glass compositions, which help microprobe was calibrated using a suite of mineral standards, and to distinguish them (Fig. 6cef; Table 3). Both SG06-3912 and SG06- the PAP absorption correction method was used for quantification. 4124 have higher K2O (4.46e4.90 wt.%; n ¼ 11; Table 3) than the Table 2 Visible tephra layers within SG06.
Sample Bore hole layers Composite Thickness Description Glass compositions (wt.%) Correlation 14C date a (SG06-) depth of the (cm) based on glass AB CD SiO 2 K2O CaO (cal. yrs BP) base (cm) chemistry 588 A-03-14 B-03-03a e D-03-05 587.9 0.2 Fine grey ash 74.40e77.97 2.25e3.99 1.45e2.37 3966e4064 967 A-06-01 B-05-04 C-07-g e 964.5 2.8 Fine-medium white ash 72.60e74.60 2.77e3.03 1.82e2.34 Kikai-Akahoya 7165e7303 (K-Ah) 1288 A-07-16 B-07-01 ee1286.1 1.9 Normal-graded, medium, 60.49e62.00 6.57e7.48 1.42e2.03 Ulleungdo-U4 10,177e10,255 white to fine grey ash (U-Oki) 1293 A-07-17 1292.8 0.3 Fine grey ash 77.35e78.20 3.17e3.37 1.08e1.18 10,241e10,326 1965 A-11-00 B-10-02 ee1963.8 0.7 Fine-medium white ash 76.11e77.43 2.41e3.67 1.35e1.83 19,487 112 2504 A-13-07 B-12e150.8 cm ee2503.4 0.1 Discontinuous layer of fine 75.67e77.61 3.25e3.63 1.09e1.43 28,425 194 white-grey ash
2534 A-13-08 B-13-02 ee2533.8 0.6 Fine brown-white ash 75.52e76.77 3.04e3.87 1.07e1.56 28,848 196 121 (2013) 67 Reviews Science Quaternary / al. et Smith V.C. 2601 B-13-06a 2600.4 0.2 Medium brown-white ash 72.67e77.91 2.75e4.68 0.62e2.36 29,765 190 e76.58 2.96e4.16 0.89e1.59 29,775 191 2602 e B-13-06b ee2601.1 0.4 Medium brown-white ash 74.14 2650 A-14-01 B-13-Bottom ee2615.2 35.1 Medium brown ash, slightly 77.02e78.41 3.24e3.55 1.03e1.20 Aira Tephra 30,009 189 normally graded Formation (AT) 3485 e B-18-03 ee3484.9 0.5 Fine, dark black ash 53.11e55.43 0.33e0.67 8.50e10.06 43,713 156 3668 A-19-04 B-19-03 ee3667.8 0.3 White ash, slightly coarser in 76.85e78.39 3.11e3.49 1.00e1.40 46,364 202 the middle a ee e e e e 3912 e B-20- 3911.7 0.1 Medium brown white ash 69.64 73.63 4.46 4.90 1.06 2.33 49,974 337 3974 e B-20-07 ee3973.8 0.0 Fine-medium, very white ash 75.72e78.29 2.84e4.42 0.73e1.57 50,929 378 4124 e B-21-03 C-17-06 e 4123.8 0.2 Fine-medium white ash 76.33e77.77 3.95e4.59 0.49e0.64 4141 e B-21-04 ee4139.9 1.3 Fine dark ash at the base that 76.87e78.35 3.77e4.20 0.92e1.36 grades into dark brown ash with white ash bands 4281 e B-22-01 C-18-04 e 4280.6 0.3 Medium dark ash 73.27e76.69 2.67e2.97 1.30e2.04 4318 A-23-01 B-22-03 ee4316.9 1.5 Alternating layers of coarse 45.10e52.18 0.33e0.77 9.39e11.73 dark grey, and white fine ash 68.87e71.67 2.15e2.51 2.27e3.24 4963 A-28-01 B-28-01 C-19-03 e 4959.1 3.5 Medium brown ash 70.06e72.38 4.17e4.82 0.97e1.57 w87 ka Aso-4 C-19-04 4978.3 0.2 Medium brown ash 70.46e72.26 4.04e4.71 0.91e1.56 w87 ka Aso-4 4979 A-28e31.3 cm B-28e35.5 cm 5181 A-29e01 B-29-04 ee5178.1 2.4 Fine-medium brown ash 77.76e78.50 3.14e3.40 1.00e1.15 w95 ka Kikai-
Tozurahara e (K-Tz) 137 5287 ee C-21-01 e 5282.9 4.0 Massive, fine-medium 69.16e69.88 4.43e4.76 1.69e1.92 Aso-ABCD brown ash 5353 A-30-02 B-30-02 ee5351.1 1.5 Fine-medium brown ash 73.69e74.61 2.80e2.98 1.72e1.98 w100 ka Ata 5385 A-30-03 B-30e93.2 cm ee5383.9 1.4 Diffuse pods (<0.3 cm thick) 66.54e68.48 0.69e0.81 3.94e5.05 of fine, light grey ash 73.27e73.72 5.25e5.41 0.69e0.78 6344 A-37-01 B-37-02 ee6342.9 0.8 Fine grey ash 70.12e73.77 0.96e1.13 2.69e3.73 2.25 2.33e3.39 6412 A-37-07 B-38-03 ee6412.0 0.4 Fine white ash that is slightly 69.93e73.27 1.87e darker and coarser in the middle 6454 A-38-24.1 cm B-38e77.6 cm ee6454.0 0.1 Fine grey ash 74.61e77.27 2.62e4.32 1.43e1.99 6457a A-38- B-38-07 ee6456.9 0.1 Fine white ash 76.55e77.14 3.02e5.44 0.69e1.38 6510 A-38-b B-39-39.4 cm ee6510.3 0.1 Fine grey ash 65.55e66.92 1.42e1.70 4.61e5.07 6634 A-40-02 B-40-04 a ee6633.9 0.1 Fine white ash 74.01e77.55 2.04e2.67 1.44e2.48
The sections marked in bold are the ones that were sampled. Composite depth is based on August 2009 correlation version. Normalised mean glass compositions are provided (see Table 3, and the Supplementary Material for all the raw data). a14C age estimates are provided at the 95.4% hpd range for the uppermost units (down to SG06-1293) and the others are provided at 2 s level, see Staff et al. (2011) and Bronk Ramsey et al. (2012) for data and methods. 127 128 V.C. Smith et al. / Quaternary Science Reviews 67 (2013) 121e137
Fig. 4. Selected photographs of tephra layers in SG06, with sample name and core section labelled. Scale bars on the right are 1 cm. glass shards of other tephras, and SG06-3912 has distinctly lower most oxides, which probably reflects this alteration. The glass SiO2 (69.6e73.6 wt.%). SG06-4281 is rhyolitic in composition, composition in the next tephra below, SG06-6457, is also rhyolitic, despite its dark appearance. The SG06-4281 glass shards are whilst the tephra below it (SG06-6510) is dacitic (65.6e66.92 wt.% compositionally heterogeneous and extend to less evolved major SiO2, n ¼ 11; Fig. 6g, h; Table 3). The lowermost tephra, SG06-6634, element glass compositions than those of the other tephras above, is a compositionally heterogeneous, with rhyolitic glass shards that ranging from 73.3 to 76.7 wt.% SiO2 and 2.67 to 2.97 wt.% K2O have 74.0e77.5 wt.% SiO2 and 1.44e2.48 wt.% CaO (n ¼ 9; Fig. 6g, h; (n ¼ 13). Despite the variation in colour in SG06-4141 (Table 2), the Table 3). glass shards in the tephra are compositionally homogeneous P2O5 and Cl were also analysed for the SG06 samples, and the (Fig. 6cef; Table 3). Glass shards in SG06-4318 (Fig. 4e), the low- abundances in most of the tephras is typically low (Table 3). In the ermost tephra in this phase of activity, are bimodal in composition, rhyolites, P2O5 content ranges from below detection limit up to with a basaltic (45.1e52.2 wt.% SiO2, 9.39e11.73 wt.% CaO; n ¼ 9) w0.1 wt.%, while Cl ranges from w0.1 to 0.4 wt.%. Some of these and a dacitic-rhyolitic component (68.9e71.7 wt.% SiO2; 2.27e rhyolitic glass shards have higher Cl contents with averages of 3.24 wt.% CaO; n ¼ 9; Fig. 6cef; Table 3), which correspond to the w0.24e0.29 wt.%, namely, SG06-2504, SG06-2534, SG06-2601, darker and lighter layers, respectively. SG06-2602, SG06-3974, SG06-4281, SG06-4318, and SG06-6510 Tephra layers within the deeper section of the SG06 core (4963e (Table 3). Glass shards in the dacitic tephras, as expected, have 6634 cm) tend to have glass compositions that are quite distinct slightly higher P2O5. (Fig. 6g, h; Table 3). Glass shards in SG06-4963 comprise low- SiO2 rhyolite (70.1e72.4 wt.% SiO2; n ¼ 41; Fig. 6g, h; Table 3). The 4.2. Proximal tephras SG06-4979 tephra is compositionally identical (Table 2) to the low- SiO2 rhyolite tephra above, SG06-4963. The SG06-5181 rhyolitic ash Samples of K-Ah, AT, Aso-4, Aso-A, Aso-D, and Ata, were ana- (77.8e78.5 wt.% SiO2) is compositionally homogeneous with a nar- lysed (Table 4). Glass shards in the K-Ah deposits are composi- row compositional range (Fig. 6g, h; Table 3). Glass in the SG06- tionally heterogeneous, with 70.38e77.80 wt.% SiO2, 2.32e T 5287 tephra has a high-K2O content (4.43e4.76 wt.%) despite be- 3.45 wt.% K2O, and 1.14e3.54 wt.% FeO (n ¼ 18; Fig. 7a; Table 4). ing a high-SiO2 dacite (69.2e69.9 wt.%). SG06-5353 glass shards are Glass from each of the proximal phases of the AT eruption, namely rhyolitic and can be distinguished from other units in these deeper the Osumi pumice (basal fallout), Tarumizu Ignimbrite, Tsumaya sections of the SG06 core using SiO2 (73.7e74.6 wt.%) and K2O Ignimbrite, and the Ito Ignimbrite (the massive upper unit), were (2.80e2.98 wt.%) compositions. Glass shards from the pods of analysed. There is no compositional variation between units, with tephra at 5385 cm (SG06-5385; Fig. 6g, h; Table 3) have dacitic all phases having the same homogeneous glass composition, with (66.5e68.5 wt.% SiO2; 0.69e0.81 wt.% K2O; n ¼ 9) and rhyolitic 77.39e78.44 wt.% SiO2 and 3.23e3.74 wt.% K2O(n ¼ 54; Table 4). populations (73.27e73.72 wt.% SiO2; 5.25e5.41 wt.% K2O; n ¼ 2). New proximal data was obtained for Aso-4, and the two thickest The SG06-6344 (Fig. 4g) glass is rhyolitic with low K2O contents units from the Aso-ABCD sequence, unit A (Aso-A) and the older (0.96e1.13 wt.%; Table 3). Glass shards in SG06-6412 span a similar unit D (Aso-D). These trachytic-rhyolite eruptions are distinct from SiO2 range (69.9e73.3 wt.%; n ¼ 30) to SG06-6344, but the shards those of other Japanese tephras as they have high-K2O contents. have higher K2O (1.87e2.25 wt.%) and lower CaO (2.33e3.39 wt.%) The rhyolitic Aso-4 unit has 70.78e72.75 wt.% SiO2 and 4.19e contents (Fig. 6g, h; Table 3). All of the tephras nearer the base of 4.49 wt.% K2O(Table 4). The Aso-A and Aso-D units have lower T the SG06 core are 0.1 cm thick, fine ash layers, which are either grey SiO2 and higher CaO and FeO contents than Aso-4 (Fig. 7e). The or white in colour. Analyses of glass in the grey SG06-6454 layer Aso-D tephra is slightly less evolved than the Aso-A and occupies suggest apparent alteration, with only a few analyses (n ¼ 3) giving a wider compositional range (Table 4). The glass in the Ata ignim- major element totals >91 wt.%. These three analyses indicate that brite is compositionally homogeneous, with 73.17e74.76 wt.% SiO2 the tephra was rhyolitic, but that there is significant variation in and 2.82e3.00 wt.% K2O(n ¼ 12; Fig. 7g; Table 3). V.C. Smith et al. / Quaternary Science Reviews 67 (2013) 121e137 129
Fig. 5. Compositions of the SG06 tephras, which are named here using the depth (composite scale, August 2009 model) of the tephra in the core (specifically, the depth of the base of the tephra layer in centimetres). (a, b) Compositions range from basaltic through to rhyolitic and phonolitic, and subalkaline glasses (all samples except the phonolitic SG06-1288 T glass) range from low-K (tholeiite series) through to high-K (calc-alkaline series) compositions (c, d) FeO and CaO compositions of many of the tephras in SG06. (e, f) SiO2 and K2O glass compositions of tephra layers versus stratigraphic position. Some of the tephras are compositionally homogeneous, while others have multiple populations or span a wide range of compositions.
5. Discussion Similar compositions are typically erupted from the same volcano over long periods of time (e.g., volcanoes within the Taupo Volcanic 5.1. Glass compositions of the SG06 tephras Zone, New Zealand, Smith et al., 2005; and Campi Flegrei caldera, Italy; Smith et al., 2011a). Therefore, it is possible that many of these Major element glass chemistry is distinct for most of the visible successive units represent different eruptions from the same volcano. tephras within the core (Fig. 6). It appears that some of the tephra Further chemical analysis of the proximal and distal deposits, layers are compositionally similar, especially those that erupted in including acquiring trace element compositions of the glass shards, particular time periods: the successive thin tephra units above the may help to correlate them (e.g., Tomlinson et al., 2012). thick SG06-2650, which include SG06-2504, SG06-2534, SG06-2601, There is significant compositional heterogeneity within glass and SG06-2602; and SG06-3668, SG06-3974, and SG06-4124 (Fig. 6). shards of some individual tephra units, namely SG06-0558, SG06- 130 V.C. Smith et al. / Quaternary Science Reviews 67 (2013) 121e137
Table 3 Average glass compositions (normalised) of the visible tephra layers in SG06.
(wt%) SG06-0558 SG06-0967 SG06-1288 SG06-1293 SG06-1965 SG06-2504 SG06-2534 SG06-2601
A-03-14 B-05-04 A-07-16 A-07-17 B-10-02 A-13-07 A-13-08 B-13-6a
Avg. 1 s Avg. 1 s Avg. 1 s Avg. 1 s Avg. 1 s Avg. 1 s Avg. 1 s Avg. 1 s
SiO2 75.64 1.14 74.09 0.49 60.85 0.42 77.81 0.29 76.96 0.33 76.16 0.96 76.28 0.31 75.50 1.59 TiO2 0.19 0.05 0.54 0.03 0.50 0.07 0.15 0.04 0.11 0.03 0.23 0.05 0.16 0.03 0.18 0.05 Al2O3 13.49 0.54 13.17 0.17 19.55 0.17 12.38 0.13 13.44 0.36 13.20 0.61 13.30 0.17 13.57 1.14 FeOT 1.17 0.35 2.51 0.16 3.16 0.19 1.32 0.12 0.80 0.11 1.42 0.16 1.17 0.15 1.14 0.24 MnO 0.06 0.02 0.09 0.04 0.14 0.05 0.04 0.03 0.04 0.03 0.04 0.04 0.04 0.03 0.03 0.02 MgO 0.28 0.09 0.48 0.05 0.30 0.06 0.13 0.02 0.20 0.04 0.23 0.09 0.28 0.05 0.19 0.14 CaO 1.91 0.24 1.99 0.11 1.61 0.17 1.13 0.04 1.52 0.12 1.30 0.15 1.37 0.10 1.39 0.47
Na2O 3.88 0.34 4.02 0.17 6.51 0.79 3.75 0.16 3.74 0.21 3.76 0.13 4.02 0.21 4.23 0.47 K2O 3.09 0.62 2.89 0.07 7.07 0.28 3.25 0.07 2.99 0.34 3.41 0.18 3.29 0.17 3.47 0.54 P2O5 0.08 0.02 0.07 0.02 0.10 0.03 (wt%) SG06-2602 SG06-2650 SG06-3486 SG06-3668 SG06-3912 SG06-3974 SG06-4124 SG06-4141 B-13-6b B-14-01 B-18-03 B-19-03 B-20a B-20-07 B-21-03 B-21-04 Avg. 1 s Avg. 1 s Avg. 1 s Avg. 1 s Avg. 1 s Avg. 1 s Avg. 1 s Avg. 1 s SiO2 75.63 0.47 77.64 0.31 53.83 0.63 77.65 0.53 71.68 1.04 76.74 0.66 76.79 0.36 77.58 0.34 TiO2 0.18 0.04 0.14 0.03 1.32 0.19 0.11 0.04 0.50 0.06 0.14 0.04 0.04 0.02 0.20 0.04 Al2O3 13.57 0.20 12.41 0.15 17.01 1.49 12.63 0.50 14.99 0.45 13.09 0.45 13.56 0.23 12.43 0.15 FeOT 1.54 0.46 1.27 0.09 10.13 1.16 1.06 0.33 1.83 0.18 0.90 0.22 0.49 0.07 0.97 0.13 MnO 0.06 0.02 0.06 0.04 0.17 0.07 0.05 0.04 0.07 0.07 0.05 0.04 0.09 0.05 0.06 0.05 MgO 0.34 0.17 0.13 0.02 4.73 0.76 0.14 0.03 0.40 0.09 0.19 0.17 0.09 0.02 0.21 0.03 CaO 1.42 0.15 1.12 0.04 9.37 0.50 1.18 0.13 1.38 0.34 1.17 0.22 0.57 0.04 1.20 0.11 Na2O 4.04 0.28 3.68 0.27 2.69 0.24 3.80 0.23 4.28 0.89 4.12 0.32 3.97 0.11 3.21 0.12 K2O 3.42 0.48 3.39 0.08 0.48 0.09 3.28 0.14 4.67 0.12 3.41 0.42 4.28 0.17 3.93 0.12 P2O5 (wt%) SG06-4281 SG06-4318 SG06-4963 SG06-4979 SG06-5181 SG06-5287 SG06-5353 B-22a-01 B-22-03 B-28-01 C-19-04 B-29-04 C-21-01 A-30-02 Avg. 1 s Avg. 1 s Avg. 1 s Avg. 1 s Avg. 1 s Avg. 1 s Avg. 1 s Avg. 1 s SiO2 74.80 1.10 70.23 0.92 46.59 2.56 71.58 0.58 71.44 0.63 78.06 0.18 69.57 0.20 74.12 0.25 TiO2 0.21 0.04 0.34 0.05 1.85 0.25 0.44 0.04 0.43 0.05 0.25 0.03 0.63 0.03 0.50 0.03 Al2O3 14.10 0.45 15.68 0.37 11.32 0.53 15.10 0.29 15.11 0.27 11.91 0.07 15.40 0.12 13.20 0.09 FeOT 1.52 0.25 2.53 0.37 11.64 1.05 1.63 0.17 1.60 0.16 1.08 0.07 2.37 0.13 2.18 0.10 MnO 0.04 0.05 0.05 0.03 0.18 0.04 0.11 0.05 0.12 0.05 0.04 0.03 0.11 0.04 0.10 0.03 MgO 0.41 0.08 0.85 0.18 14.53 1.43 0.40 0.07 0.41 0.07 0.20 0.02 0.62 0.03 0.45 0.03 CaO 1.73 0.22 2.75 0.29 11.12 0.82 1.20 0.18 1.23 0.19 1.08 0.04 1.81 0.06 1.89 0.06 Na2O 4.19 0.24 4.82 0.23 2.22 0.15 4.79 0.18 5.07 0.16 3.93 0.13 4.73 0.16 4.48 0.20 K2O 2.83 0.13 2.34 0.12 0.44 0.16 4.54 0.17 4.37 0.18 3.28 0.07 4.55 0.09 2.88 0.05 P2O5 0.08 0.01 0.13 0.02 (wt%) SG06-5385 SG06-6344 SG06-6413 SG06-6454 SG06-6457 SG06-6510 SG06-6634 A-30-03 A-37-01 B-38-03 A-38-24.1 cm B-38-07 A-38-b B-40-4a Avg. 1 s Avg. 1 s Avg. 1 s Avg. 1 s Avg. 1 s Avg. 1 s Avg. 1 s.d. Avg. 1 s SiO2 66.83 1.28 73.49 0.32 71.80 1.01 72.18 0.87 75.63 1.43 76.80 0.17 66.29 0.40 76.51 1.32 TiO2 0.78 0.03 0.30 0.02 0.75 0.08 0.43 0.05 0.20 0.03 0.13 0.06 0.63 0.05 0.40 0.11 Al2O3 15.14 0.24 14.25 0.07 13.67 0.66 13.96 0.27 13.67 0.86 12.94 0.27 16.29 0.28 12.44 0.46 FeOT 5.15 0.42 1.21 0.06 3.67 0.38 3.45 0.30 1.17 0.30 0.98 0.11 4.31 0.17 1.79 0.36 MnO 0.20 0.04 0.08 0.05 0.14 0.03 0.10 0.04 0.05 0.06 0.06 0.06 0.14 0.05 0.03 0.03 MgO 1.50 0.20 0.20 0.03 0.75 0.17 0.49 0.10 0.38 0.20 0.19 0.10 1.31 0.10 0.37 0.12 CaO 4.56 0.44 0.73 0.07 3.21 0.37 2.65 0.24 1.70 0.28 1.11 0.26 4.85 0.16 1.75 0.36 Na2O 4.78 0.62 4.28 0.20 4.65 0.13 4.47 0.22 3.85 0.41 3.66 0.38 4.15 0.21 3.99 0.19 K2O 0.76 0.03 5.33 0.11 1.04 0.05 2.14 0.08 3.34 0.88 3.88 1.07 1.56 0.08 2.47 0.22 P2O5 0.17 0.02 0.03 0.03 0.16 0.02 0.08 0.02 All raw analyses are in the Supplementary Material. 2601, SG06-3912, SG06-4281, SG06-4318, SG06-5353, SG06-6454, are tapping magmas with a range of compositions. Large silicic and SG06-6634 (Tables 2 and 3; Fig. 5). In addition, glass in the events commonly erupt multiple magma bodies (e.g., Smith et al., proximal K-Ah and Aso-4 tephras span a wide compositional range 2004) and/or are triggered by more mafic magma (e.g., Shane (Table 4; Fig. 7). This variation could indicate that the eruptions et al., 2008). It seems that Aso-4 and K-Ah tapped V.C. Smith et al. / Quaternary Science Reviews 67 (2013) 121e137 131 Fig. 6. (a, b) Glass compositions of the tephras in the upper part of the core, down to and including the thick SG06-2650 unit. (cef) The compositions of glass from the tephras between SG06-2650 and SG06-4963. The basaltic tephra layer SG06-3485 and the basaltic sub-component of SG06-4318, are not included in (d) and (f). (g, h) The tephras in the deepest parts of the core, from SG06-4963 downwards, are more compositionally distinct than those in the upper parts of the core. These more distinct compositions likely reflect different source volcanoes. compositionally heterogeneous magma systems. However, it 2012). Here, we directly compare the glass compositions of the should also be noted that, it is possible that some of the compo- SG06 units with those of the proximal eruption units to inde- sitional variability within SG06 could also be associated with pendently verify these previous correlations (Fig. 7). The SG06 data deposition from contemporaneous (or near-contemporaneous) were compared with our new proximal data (Table 4) and with eruptions of different volcanoes. published compositional data of the eruptions, reported by Machida and Arai (2003 and references therein), and with average 5.2. Correlation of SG06 to particular eruptions and volcanic centres compositions reported by Aoki and Machida (2006). Glass com- positions of the tephra layers within the Takashima-oki core Some of the SG06 tephra layers were correlated previously (TO86) from Lake Biwa (w25 km south of Lake Suigetsu) have using the SG93 core (Fig. 3; Takemura et al., 1994; Nakagawa et al., been determined (Nagahashi et al., 2004), and therefore we can 132 V.C. Smith et al. / Quaternary Science Reviews 67 (2013) 121e137 Table 4 Average glass compositions (normalised) of the proximal tephra units sampled. Eruption K-Ah AT (all) AT-Osumi AT-Tsumaya AT-Ito Aso 4 Aso-A Aso-D Ata Sample ITJ3 ITJ8 ITJ5 ITJ7 ITJ8 ITJ12 ITJ11 ITJ10 ITJ9 (wt%) Avg. 1 s.d. Avg. 1 s.d. Avg. 1 s.d. Avg. 1 s.d. Avg. 1 s.d. Avg. 1 s.d. Avg. 1 s.d. Avg. 1 s.d. Avg. 1 s.d. SiO2 73.67 1.47 77.90 0.27 77.72 0.19 77.98 0.27 78.01 0.24 72.61 2.38 69.78 0.18 69.14 0.86 74.29 0.42 TiO2 0.56 0.13 0.13 0.03 0.14 0.02 0.13 0.04 0.13 0.03 0.38 0.16 0.64 0.04 0.63 0.06 0.49 0.03 Al2O3 13.58 0.47 12.51 0.16 12.62 0.10 12.37 0.12 12.57 0.13 14.75 1.12 15.14 0.12 15.45 0.72 13.50 0.18 FeOT 2.60 0.48 1.24 0.13 1.29 0.08 1.27 0.09 1.15 0.18 1.61 0.35 2.30 0.11 2.55 0.23 2.31 0.22 MnO 0.09 0.05 0.06 0.03 0.05 0.03 0.06 0.03 0.06 0.04 0.08 0.03 0.10 0.05 0.10 0.05 0.11 0.04 MgO 0.51 0.15 0.13 0.02 0.12 0.01 0.13 0.02 0.12 0.02 0.39 0.18 0.63 0.03 0.65 0.07 0.44 0.05 CaO 2.16 0.45 1.12 0.05 1.12 0.04 1.13 0.07 1.10 0.05 1.17 0.55 1.82 0.07 2.11 0.50 1.87 0.09 Na2O 4.01 0.14 3.40 0.15 3.43 0.13 3.39 0.18 3.36 0.13 4.16 0.83 4.68 0.17 4.69 0.10 4.01 0.14 K2O 2.72 0.23 3.45 0.10 3.49 0.08 3.40 0.09 3.49 0.11 4.63 0.67 4.70 0.11 4.44 0.31 2.91 0.05 P2O5 0.09 0.04 0.02 0.02 0.03 0.02 0.02 0.02 0.02 0.02 0.08 0.05 0.11 0.02 0.12 0.02 0.07 0.02 Cl 0.12 0.02 0.12 0.02 0.13 0.03 0.11 0.01 0.10 0.02 n 18 54 18 21 15 12 24 20 12 All raw analyses are in the Supplementary Material. directly compare these glass compositional data of the distal that we sampled. In addition, BT10 from TO86 (Nagahashi et al., tephras with our new data to establish if the same eruptions are 2004) has the same glass chemistry. The AT compositions from preserved in the higher resolution SG06 record. The TO86 tephras Machida and Arai (2003) again have slightly higher SiO2 contents were correlated to particular eruptions using the refractive index (Fig. 7d). of the glass and/or minerals (Satoguchi et al., 1993; Nagahashi Published compositions of post-AT eruption deposits are plotted et al., 2004). Many marine records around Japan have also been with those of the post-SG06-2560 tephra layers, including data correlated using the visible tephra units (Machida and Arai, 2003 from the w1 ka cal. B-Tm and the w15 ka cal. To-H (see Table 1 for and references therein). These correlations were typically based detailed eruption information). None of the published proximal on thickness and colour, and in some cases the refractive index of compositions match those of these post-AT tephras preserved in the glass and minerals. SG06. However, some of the glass compositions of the TO86 units Different analytical conditions have been used to collect the are similar to those of the visible tephras in Suigetsu, with BT6 published glass compositional data to which we compare. Alkaline being similar to SG06-1965, BT7 similar to SG06-2534, and the elements are mobile under an electron beam, causing permanent broad compositional range displayed by both BT8 and BT9 being damage to the glass shards; thus, the analytical setup needs to be similar to SG06-2601. The TO86 layers have been correlated to optimised to ensure compositional data are not compromised. eruptions based on the refractive index of the glass and minerals; Different analytical setups do produce very different results (see BT6 has been correlated to the w20 cal. ka Sanbe Ukinuno (SUk; Kuehn et al., 2011). Here, we only compared the composition of the Sakate) eruption and BT7 has been correlated to either the Shitano- T most abundant major elements, SiO2,K2O, CaO, FeO , as these are Hoki or Odori eruptions from Daisen (Satoguchi et al., 1993). typically well determined on an electron microprobe, and the latter Glass compositions of the widespread tephra layers between AT three are not as affected by different analytical protocols. Minor (SG06-2560) and Aso-4 (SG06-4963) were also plotted to assess element abundances (e.g., MnO and TiO2) of our samples are often whether the deposits were preserved as visible tephra within significantly different from those reported by Machida and Arai SG06: the w32 cal. ka Ag-Kp, the w35 cal. ka To-Of, the w42 cal. ka (2003) and Nagahashi et al. (2004). Kc-Sr, the w42 cal. ka Spfa-1, the w49 cal. ka Hk-TP, and the w60e SG06-0967 has been previously correlated to K-Ah (Takemura 75 ka Tt-E (data from Machida and Arai, 2003 and references et al., 1994; Nakagawa et al., 2012). The full range of compositions therein; see Table 1 for detailed eruption information). Composi- observed in the sample of proximal K-Ah is not observed in SG06, tions of the w32 cal. ka Ag-Kp, the w42 cal. ka Kc-Sr, and the with only the most evolved compositions found in SG06-0967 w42 cal. ka Spfa-1 are quite similar to those of some of the SG06 (Fig. 7a, b). TO86 layer BT3 (Nagahashi et al., 2004) is also similar layers, but further analyses of the proximal deposits, and trace to SG06-0967 in composition. K-Ah compositions reported by element analyses on both SG06 units and proximal samples, are Machida and Arai (2003) are similar to our K-Ah data, but the SiO2 required to ensure definitive correlations can be made. content is clearly offset, with the published data having concen- SG06-4963 and SG06-5287 were suspected to correlate with trations that are w1 wt.% higher (Fig. 7a, b). Aso-4 and with the Aso-ABCD units, respectively (Nakagawa et al., SG06-1288 was correlated to U-Oki (Takemura et al., 1994; 2012). The thick SG06-4963 and thin SG06-4979 tephra layers Nakagawa et al., 2012), which corresponds to the proximal U4 share the same composition as the w87 ka Aso-4 (Fig. 7e). Both unit of Ulleungdo (Smith et al., 2011b). Glass compositions of SG06-4963 and SG06-4979 are observed in the cores from all three Ulleungdo-U4 and SG06-1288 are distinctly alkali-rich and unlike boreholes, and the thicker deposit is found above the thinner layer, compositions of other eruptives from Japanese volcanoes (Fig. 6). suggesting that they are not primary deposits and an artefact of Ulleugdo-U4 and SG06-1288 are indistinguishable from each other, reworking. Clearly one of the layers is associated with the Aso-4 and share the same composition as the BT4 and BT5 TO86 units eruption, and the other layer either represents another phase of (Fig. 7c). It is not clear whether these two TO86 units represent the Aso-4 eruption or a separate eruption. Two phases (sub-cycles) different Ulleungdo eruptions, or whether there is some reworking are observed in the proximal Aso-4 deposits (Kaneko et al., 2007), within the TO86 core. U-Oki data reported by Machida and Arai although it is not clear how long the time-breaks between the (2003) have higher SiO2 concentrations than our data and those phases were. We suggest that both these SG06 layers are associated from Biwa (Nagahashi et al., 2004), but the K2O, CaO and FeO with the Aso-4 eruption deposits. It is possible that the dispersal contents are all similar. axes of these Aso-4 phases were different, which would account for The thickest SG06 tephra, the 35.1 cm-thick SG06-2650, is only single visible layers being observed in many locations, and two compositionally identical to the proximal AT eruption deposits layers being seen where the axes overlap. V.C. Smith et al. / Quaternary Science Reviews 67 (2013) 121e137 133 Fig. 7. Glass shard major element compositions of some of the SG06 tephras and proximal eruption deposits. Additionally, * denotes data from Machida and Arai (2003); and^ denotes tephra samples from Lake Biwa cores that have been correlated to eruptions using glass refractive indices (Satoguchi et al., 1993) e the two data points are the upper and lower values of the compositional range determined from the average and standard deviation data presented by Nagahashi et al. (2004). (a, b) Compositions of glass of the widespread K-Ah tephra. The glass composition of SG06-0967 matches that of the Biwa BT3 tephra layer and our proximal Kikai-Akahoya tephra (see Appendix A for proximal sample details). Note that glass compositions reported by Machida and Arai (2003) are slightly higher in SiO2. (c) Compositions of glass from proximal unit U4 from Ulleungdo (see Smith et al., 2011b), SG06-1288, BT4 and BT5 tephra layers are indistinguishable. (d) Proximal glass compositional data of all the AT units are the same, and are similar to those of SG06-2650 and BT10 which we thus designate as correlatives. (e, f) Compositions of glass in tephras from Aso eruptions. SG06-4963 and SG06-4979 are compositionally indis- tinguishable from proximal Aso-4 tephra, and we consider them to be correlatives. SG06-5287 is very similar to numerous proximal Aso units, Aso-3, Aso-A and Aso-D. (g) Glass in SG06-5181 is compositionally similar to that in BT25 and BT26 that have been correlated to K-Tz based on glass refractive indices. The SiO2 contents of these tephras in SG06 is lower than those reported for K-Tz by Machida and Arai (2003), but all other elements are similar. (h) The glass chemistry of SG06-5353 is indistinguishable from that of our proximal Ata sample, and within the compositional range of data given by Machida and Arai (2003). The deeper SG06-5287 tephra is compositionally similar to the tephras have compositions that are similar to the Aso units and are pre-Aso-4 units from Aso caldera, for which compositional data are likely to correlate to eruptions from Aso. The Aso-ABCD events are available. SG06-5287 is similar to our new data for Aso-A and Aso-D considerably younger than the w123 ka Aso-3 tephra, and since the and published data for Aso-3, although Aso-3 appears to be slightly w100 ka Ata tephra occurs at 5353 cm in SG06 (see below), SG06- enriched in SiO2 and K2O(Fig. 7e). TO86 BT23, BT24 and BT28 5287 must correlate to the Aso-ABCD events. The presence of Aso- 134 V.C. Smith et al. / Quaternary Science Reviews 67 (2013) 121e137 ABCD is not consistent with mapped dispersal, indicating that the a continuous bed (see details in Satoguchi et al.,1993). This suggests dispersal of these events needs to be further investigated. Since that the sediments in the TO86 core may be disturbed in some parts. SG06-5287 is 4 cm thick, it is possible that these eruptions were There are discrepancies between our compositional data and significantly larger in magnitude than previously thought, and the those given by Machida and Arai (2003) and in some other publi- dispersal direction was towards the north. cations. As we have already noted, data reported by Machida and The 1.5 cm-thick SG06-5353 tephra is compositionally similar to Arai (2003) tend to have higher SiO2 contents (w1 wt.%) than our the proximal Ata deposits that were analysed in this study (Fig. 7g), data for the same units (see SG06-1288, U-Oki, and U4 data above; and plot within the broader compositional range reported by Fig. 7c). In other cases, the glass compositions are very different; for Machida and Arai (2003). SG06-5353 is clearly distal Ata tephra, example, Domitsu et al. (2002) have correlated one of the tephra which is consistent with mapped Ata dispersal (Machida and Arai, layers in a Sea of Japan core (KY96-17 P-2) to U-Oki, but the glass 2003). compositions do not match our data (U4 and SG06-1288) or the U- In addition to our glass chemistry data for Aso-4, Aso-A, Aso-D, Oki compositions reported by Machida and Arai (2003). These and Ata, there are glass compositional data available for the follow- variations in the glass major element compositions from suppos- ing pre-Aso-4 (SG06-4963) eruptions: the w95 ka K-Tz, the w100 ka edly the same eruption units are clearly associated with different Om-Pm1, the w112e115 ka Toya, the w117 ka Kc-Hb, the w123 ka analytical setups because the abundances of particular oxides are Aso-3, the w141 ka Aso-2, and the w110e180 ka Numasawa- systematically offset. Full datasets and secondary standard data Tagashira (Nm-Tg) as reported by Machida and Arai (2003) and ref- have not been published for these widespread tephra units, which erences therein (see Table 1) and Aoki and Machida (2006). SG06- is problematic when trying to assess the accuracy of these data. We 5181 was previously correlated to K-Tz (Takemura et al., 1994; hope that all future publications will include all such data as Nakagawa et al., 2012). Unfortunately, we do not have proximal data Supplementary Information to allow the construction of a robust for K-Tz, but there are glass major element data for K-Tz in Machida tephrostratigraphic framework and geochemical database for and Arai (2003), and for TO86 BT25 and BT26, which have been tephras in and around Japan. previously correlated to K-Tz (Nagahashi et al., 2004). The compo- sitions of the Biwa deposits overlaps with our SG06-5181 data, sug- 5.3. Refining eruption ages gesting that these tephras are correlatives (Fig. 7g). The proximal K- Tz data in Machida and Arai (2003) have higher SiO2 contents A detailed age model has been constructed for the upper portion (w1 wt.%), but concentrations of the other elements are similar to of the SG06 core using radiocarbon data and varve counts (Staff those in SG06-5181. Considering SiO2 compositions in Machida and et al., 2011; Bronk Ramsey et al., 2012). This high-resolution age Arai (2003) are higher than ours and therefore probably a result of model is used to constrain the ages of the post-50 ka eruptions in different analytical protocols, it is highly likely that SG06-5181 is the radiocarbon timeframe, as has been done for U-Oki (10.177e associated with the K-Tz eruption. Glass compositions of SG06-6634 10.255 cal. ka BP at the 95.4% probability range; SG06-1288 are similar to those of the w117 ka Kc-Hb tephra, and probably tephra in SG06; Smith et al., 2011b; Staff et al., 2011), and pro- a correlative although the compositions do not exactly match. vides improved age estimates for the eruptives preserved in SG06 Some of the successive tephra units within the TO86 core are (Fig. 8; Table 2). almost identical in composition to each other, for example BT4 and The recently published age models of Staff et al. (2011; post- BT5 (U-Oki); BT11 and BT12; BT16 and BT17; BT25 and BT26 (K-Tz); 12 ka) and Bronk Ramsey et al. (2012;11.2e52.8 ka BP) constrain the and BT29 and BT30 (Nagahashi et al., 2004). These layers with the ages of the post-50 ka tephras to a few hundred years, a significant same composition are typically 10e50 cm apart, but from the de- improvement on existing age ranges (Fig. 8; Table 2). An age of scriptions it appears that at least one of the layers in each case is not 3.966e4.064 cal. ka BP (95.4% probability range; w2 s) was obtained (a) SG06-0588 tephra - 3966-4064 (95.4%) (b) SG06-0967 tephra - 7165-7303 (95.4%) K-Ah tephra 0.02 0.01 0.01 0.005 0 0 Probability density Probability density 4200 4100 4000 3900 7400 7300 7200 7100 Modelled date (cal. BP) Modelled date (cal. BP) (c) SG06-1293 tephra - 10242-10329 (95.4%) 0.02 0.01 0 Probability density 10400 10300 10200 10100 Modelled date (cal. BP) Fig. 8. Posterior probability density functions generated for the visible tephra layers using the composite depth and age models of Staff et al. (2011) and Bronk Ramsey et al. (2012). The brackets at the base of the distribution represent the 68.2%, 95.4% and 99.7% probability ranges. V.C. Smith et al. / Quaternary Science Reviews 67 (2013) 121e137 135 for SG06-0588 (Fig. 8a), 10.242e10.329 cal. ka BP (95.4% probability would be particularly useful for developing further the chrono- range) for SG06-1293 (Fig. 8c), 19.487 112 SG062012 ka BP (2 s, logical framework for the older parts of the SG06 record. normal distribution) for SG06-1965, 28.425 194 SG062012 ka BP (SG062012 ages are modelled; see Bronk Ramsey et al., 2012 for de- 6. Conclusions tails; 2 s) for SG06-2504, 28.848 196 SG062012 ka BP (2 s) for SG06- 2534, 29.765 190 SG062012 ka BP (2 s) for SG06-2601, 29.775 191 The SG06 sediment core from Lake Suigetsu preserves a detailed SG062012 ka BP (2 s) for SG06-2602, 43.713 156 SG062012 ka BP (2 record of explosive volcanism from Japan with 30 visible tephra s) for SG06-3485, 46.364 202 SG062012 ka BP (2 s) for SG06-3668, layers, ranging from <1 mm through to 35 cm in thickness, pre- 49,974 337 SG062012 ka BP (2 s) for SG06-3912, and 50.929 378 served in the core. The detailed major element composition of glass SG062012 ka BP (2 s) for SG06-3974. As has been noted above, these shards from these tephras indicates that many are from large tephras have not been correlated to particular eruption sources, but explosive eruptions (VEI > 7) from the southern Kyushu Island. The can be correlated to tephras preserved in other records using the glass compositions of the tephra deposits analysed are typically glass major element compositions. The new SG06 age models also quite distinct, but our ability to correlate all of the layers was hin- provide age ranges of 7.165e7.303 cal. ka BP (95.4% probability dered by the lack of published glass chemistry for many of the Jap- range; SG06-0967; Fig. 8b) and 30.009 189 SG062012 ka BP (2 s; anese eruption deposits, especially those from the volcanoes in SG06-2650) for the widespread K-Ah and AT tephras, respectively. central Honshu. However, we were able to correlate the following These are an improvement on previous estimates of 6.86e tephras in SG06 to the eruptives for which we have proximal glass 7.44 cal. ka BP for the K-Ah, and 29.428e30.148 cal. ka BP for the major element data, SG06-0967 is 7.165e7.303 cal. ka BP K-Ah, AT tephra (Machida and Arai, 2003; Table 1). SG06-1288 is 10.177e10.255 cal. ka BP U-Oki, SG06-2650 is 29.428e 30.148 cal. ka BP AT (all at 94.5% range, w2 s), SG06-4963 is w89 ka 5.4. Future dating of the pre-50 ka tephra units Aso-4, SG06-5181 is w95 ka K-Tz, SG06-5287 is Aso-ABCD, and SG06-5353 is w100 ka Ata. The high-resolution chronology for the Tephras can be particularly useful for refining the chronology of upper SG06 core (up to w50 cal. ka; Staff et al., 2011; Bronk Ramsey the core because the ages of the eruptions can be determined using et al., 2012) has also been employed to provide improved ages for the 40Ar/39Ar methods. 40Ar/39Ar ages of the eruptions are crucial to tephras within this timeframe (i.e. down to SG06-3974; Table 2). accurately constrain the portions of the core that extend beyond Some of the tephras can also be dated using 40Ar/39Ar methods as the radiocarbon limit of w60 ka. Many of the large magnitude described by Smith et al. (2011b). eruptions have been previously dated using K-Ar methods, e.g., Ata Some published compositional data for some of the proximal and Aso-4 (Matsumoto, 1996). The precision and accuracy of the tephras are not accurate, and these analyses cannot be relied upon ages of these eruptions can be improved using improved 40Ar/39Ar to enable their correlation with some of the SG06 tephras; the methods. However, normally only biotite and sanidine crystals can major element chemistry of proximal units need to be better be dated using 40Ar/39Ar techniques, with ages from the latter being characterised. The acquisition of trace element compositions of more reliable (Deino and Potts, 1990). Unfortunately, none of the glass would be useful where major element data are ambiguous in Japanese volcanoes erupt sanidine, but deposits from Ulleungdo, affecting correlations. South Korea, w300 km off the Honshu coast, are alkali-rich and Pilot studies have shown that discrete cryptotephra are pre- sanidine-bearing. served within the Suigetsu record; thus, the core could provide one SG06-1288 correlates to the U-Oki tephra, U4, one of seven of the most detailed records of volcanism in Japan. Lake Suigetsu is pyroclastic units preserved on Ulleungdo (Machida et al., 1984; in an ideal position as it is far from the most productive and Okuno et al., 2010; Smith et al., 2011b). Smith et al. (2011b) acquired explosive volcanoes (VEI > 6) that are located in Hokkaido and an 40Ar/39Ar age for the SG06-1288 tephra by correlating the distal Kyushu, and the lake itself is tectonic (i.e. not a volcanic edifice), so tephra to the proximal U4 unit using glass compositions, extracting the sediments are not swamped with glass shards from numerous crystals from the coarser proximal Ulleungdo deposits, and dating tephras that might be expected to arise in a proximal volcanic the large sanidine crystals (each a few millimetres in length). An setting. The developments of a cryptostratigraphic record alongside age of 10.0 0.3 ka (1s, MSWD 0.71, probability 0.89) was acquired, that presented here for the visible tephras has the potential to which agrees well with the radiocarbon age for SG06-1288 enable the construction of a tephra stratotype for Japan based on (10.202e10.231 cal. ka BP at the 68.2% probability range; Smith the SG06 core from Lake Suigetsu. Detailed tephrostratigraphic et al., 2011b; Staff et al., 2011). The agreement between the work will help constrain activity, timing and magnitude of erup- 40Ar/39Ar and radiocarbon data indicates that the dates from both tions from Honshu volcanoes, as well as refining knowledge of the methods are accurate, as well as being fairly precise at this younger eruptive history of other volcanoes around Japan, including the end of the 40Ar/39Ar timescale. large caldera volcanoes in southern Kyushu and northern Hokkaido There is potential for other tephras from Ulleungdo to be pre- islands. The tephra layers are also the key to synchronising palae- served in the SG06 core as cryptotephra; older Ulleungdo units, with oclimate records across the region and beyond, as many of the alkali-rich glass compositions, have been found in cores from the tephra layers are found over thousands of kilometres. Sea of Japan (e.g., Chun et al., 2007; Park et al., 2007), suggesting that some of the other pyroclastic units are quite widely dispersed. Acknowledgements Therefore, more 40Ar/39Ar dates could be acquired for the SG06 core. In addition, there have been improvements in the dating of biotite VCS, CBR and RS acknowledge funding from the Oxford Uni- within eruption deposits using 40Ar/39Ar methods (e.g., Mark et al., versity Press John Fell Fund (Oxford University). The authors would in press). Biotite has been documented in some of the tephras from like to thank to Sian Crosweller and the VOGRIPA team for pro- Japanese volcanoes (Machida and Arai, 2003), and many of the units viding information on the eruptions; Nick Pearce for providing in the Lake Biwa TO86 core contain biotite (Satoguchi et al., 1993). proximal samples of Aso-A and Aso-D; and Katsuya Gotanda, The volcanic deposits of Daisen and Sanbe tend to have biotite as Tsuyoshi Haraguchi, Yusuke Yokoyama, Ryuji Tada, Hitoshi Yone- a main phenocryst phase (Machida,1999; Tamura et al., 2003). These nobu for helping acquire the SG06 core (funded by NERC e NE/ volcanoes lie upwind of Lake Suigetsu and are likely to be the source D000289/1 and Kakenhi, Japan e 211001002); and David Lowe and of many tephras within SG06, and therefore ages of these units two other reviewers for detailed and constructive reviews. 136 V.C. Smith et al. / Quaternary Science Reviews 67 (2013) 121e137 Appendix A. Proximal tephra samples from Japan Sample no. Eruption Phase Site Grid ref ITJ3 Kikai-Akahoya (K-Ah) Takatoge pass 31 31011.200 N 130 46034.100 E ITJ4 Aira Tephra Formation (AT) Tenhindan archaeological site, 30 km SE of Sakurajima ITJ5 Aira Tephra Formation (AT) Osumi pumice (basal fall) Fumoto, at the coast 31 25035.200 N 130 45017.100 E ITJ6 Aira Tephra Formation (AT) Tarumizu Ignimbrite Fumoto, at the coast 31 25035.200 N 130 45017.100 E ITJ7 Aira Tephra Formation (AT) Tsumaya Ignimbrite Fumoto, at the coast 31 25035.200 N 130 45017.100 E ITJ8 Aira Tephra Formation (AT) Ito Ignimbrite (upper unit) Fumoto, at the coast 31 25035.200 N 130 45017.100 E ITJ9 Ata Ignimbrite (Ata) Fumoto, at the coast 31 25035.200 N 130 45017.100 E ITJ10 Aso-D Noga, Taketa City, 15 km E of Aso 32 56025.100 N 131 18031.900 E ITJ11 Aso-A Noga, Taketa City, 15 km E of Aso 32 56025.100 N 131 18031.900 E ITJ12 Aso-4 Oyatsu Mashiki e 10 km SW Aso Appendix B. Supplementary material ODP Leg 186. 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