Tephra Horizons Research Articles

КАЛЬДЕРА КРАШЕНИННИКОВА (ВОСТОЧНАЯ КАМЧАТКА): ВОЗРАСТ И МАГНИТУДА ИЗВЕРЖЕНИЯ

New data on the composition of the pyroclastic deposits of the Krasheninnikov caldera allowed us to correlate it to the previously studied tephra horizon Geys30, which until recently was erroneously attributed to an eruption within the Geysernaya caldera. Pyroclastic flow deposits from the eruption that led to the formation of the Krasheninnikov caldera were found on the southern shore of Kronotsky Lake, and its distal tephra was found in the sediments of the Central Kamchatka Depression (CKD) at a distance of up to 200 km from the source (from Milkovo to Kliuchi villages). The age of this tephra was previously estimated at ~30 ka, which now allows us to accept this estimate for the Krasheninnikov caldera. The identification of the tephra of the caldera-forming eruption in distal sections allows a minimum estimate of the erupted pyroclastic volume of ~13 km3 and the eruption magnitude of 6.1.

Identification of tephra horizons in a glacier on the Ushkovsky volcano (Kamchatka)

Identification of tephra and its allocation (association) with known eruptive events allows obtainng chronostratigraphic markers, on the basis of which an age scale for dating glacial strata can be developed. To determine the sources of ash in the ice core obtained in 2022 during drilling of glacier in the crater of the Ushkovsky volcano in Kamchatka, the chemical composition of volcanic glass in individual ash particles was analyzed. The accuracy of determination of the volcanic glass composition was verified by analyzing of international standard samples of volcanic and synthetic glass. Based on a comparison of the data we obtained with published data on the composition of tephra glasses from the present-day eruptions in Kamchatka, we determined affiliation of each tephra horizon to specific volcano-source. We have found that the main source of tephra in the ice core of the Ushkovsky Glacier is the Kliuchevskoi volcano, which is the closest and the most productive one among the Kamchatka volcanoes. Ash particles from Bezymyannyi volcano were identified in two horizons. A mixed population of particles was found in one of the horizons, including the ash particles from volcanoes Kizimen, Kliuchevskoi and Bezymyannyi. Analysis of published data on the chronology and distribution of ash plumes from known eruptive events made it possible to confidently correlate the tephra horizon at a depth of 762–777 cm with the initial phase of the eruption of the Kizimen volcano in late 2010–early 2011. Ash from the uppermost tephra buried in the glacier at depths of 89–94 cm belongs to the Bezymyannyi volcano eruption, which the most likely occurred in October 2020. Single particles with rhyolitic composition of glass in the sample from the depth of 348–354 cm may belong to the eruption of the Shiveluch volcano in December 2018. The results of our work can be used on further studying of the ice core from the Ushkovsky volcano, in particular for comparison and correlation with the chronostratigraphic data obtained by glacio-chemical and isotope methods.

ПОЛЕВЫЕ РАБОТЫ НА СЕВЕРНЫХ СКЛОНАХ КРОНОЦКОГО ВУЛКАНА В ИЮЛЕ-АВГУСТЕ 2023 г.

In July-August 2023, field work was carried out on the northern slopes of Kronotsky volcano in the territory of the Kronotsky State Reserve, which is rarely visited by researchers. The aim of our work was to sample lavas that build the volcanic edifice in this sector, and also to search for traces of the volcano’s explosive activity in the Holocene. This report lists and illustrates interesting findings and the main results of the work. In particular, lava flows, dikes and pyroclastic horizons were sampled at altitudes ranging from 780 to 2200 m; several cinder and lava cones were discovered; samples of cognate inclusions and xenoliths were found. In addition, Holocene soil-pyroclastic sections, presumably containing tephra horizons from Kronotsky volcano, were documented in detail and sampled.

The Whakamaru magmatic system (Taupō Volcanic Zone, New Zealand), part 1: Evidence from tephra deposits for the eruption of multiple magma types through time

The Whakamaru group eruptions (349 ± 4 ka; Downs et al., 2014) are the largest known eruptions in the history of the young Taupō Volcanic Zone, Aotearoa New Zealand. The complex field relationships of the ignimbrites have thus far obscured the timing and history of their eruption(s). We present new evidence from fall deposits correlated with the Whakamaru eruptions to complement the ignimbrite record. Two coastal sections are characterized in detail. We group the tephra horizons into three packages: the older, smaller Tablelands and Paerata tephras; the overlying Kohioawa tephras (correlated with Whakamaru group eruptions); and the younger Murupara and Bonisch tephras. Major- and trace-element compositions suggest these tephras represent six distinct high-silica magma types, with the Kohioawa tephras representing three distinct magma compositions that are atypical of the TVZ. The distribution of Kohioawa magma types (types A, B, and C) changes through time, with the oldest deposits containing exclusively type A magma, the middle deposits containing types A and B, and the youngest deposits containing all three Kohioawa types. A combination of horizon-scale mineralogy and rhyolite-MELTS modeling suggests that only Kohioawa types B and C are saturated in sanidine – the presence of sanidine is atypical in Taupō Volcanic Zone magmas but has been previously documented in the Whakamaru group ignimbrites. Rhyolite-MELTS geobarometry reveals shallow storage pressures (∼50–150 MPa) for Kohioawa magmas. At least three different melt-dominated magma bodies sourced the Kohioawa tephras – these magma bodies were laterally juxtaposed and co-erupted for most of the Whakamaru eruptions. Magmas that preceded and post-dated the Whakamaru eruptions have more typical TVZ compositions, emphasizing the unique features of the Whakamaru system.

Youngest Toba Tuff deposits in the Gundlakamma River basin, Andhra Pradesh, India and their role in evaluating Late Pleistocene behavioral change in South Asia

AbstractThe eruption of Toba ca. 75 ka was the largest volcanic eruptive event during the Quaternary, and evidence for this eruption is widespread in terrestrial sediment sequences in South Asia as primary and reworked distal ash deposits. Youngest Toba Tuff horizons (YTT) have been widely employed as isochrons to understand and link regional sediment sequences and the evidence for environmental and cultural change in the archaeological records preserved within them. We identify the YTT deposits at Retlapalle, Andhra Pradesh, India, and present the optical ages of the K-feldspar grains recovered from sediments immediately underlying and overlying the tephra horizon. We combine these results with particle size and magnetic susceptibility analyses to establish the depositional conditions of YTT, which indicate that accumulation and reworking ceased by ca. 64 ka. We explore the role of YTT deposits as an isochron for examining the effect of the 75 ka Toba super-eruption, highlighting the need for an independent chronological assessment of YTT before using it as a Late Pleistocene chronological marker in reconstructing South Asian paleo-landscapes and hominin adaptations. Further, our findings support the regional continuity of human occupations within South Asia, spanning the eruption of Toba and the enduring utility of Middle Paleolithic tools.

Late Quaternary tephrostratigraphy and pollen stratigraphy of Uwa Formation, Shikoku Island, SW Japan: Reconsidering the MIS 11 super-interglacial horizon

We investigated a late Quaternary terrestrial sedimentary sequence (Uwa Formation) in core IC2, from a site adjacent to that of the reported core IC on NW Shikoku Island, SW Japan, and developed its tephra and pollen stratigraphy to refine the age model of the formation. First, we identified 19 horizons with high glass shard concentrations in the IC2 core sediments as possible tephras or cryptotephras, and correlated them with reported tephras on the basis of the major- and trace-element compositions of their glass shards. All correlated widespread tephras and cryptotephras were products of volcanoes in the Kyushu volcanic zone (Aso, Kakuto, Aira, Ata, and Kikai calderas). Second, we confirmed the presence in core IC2 of two pollen zones dominated by Quercus subgen. Cyclobalanopsis , which is an indicator of very warm interglacial vegetation. In the Japanese Islands, these two vegetation zones have usually been considered to characterize marine isotopic stages (MISs) 1 and 11. A previous study of the Uwa Formation correlated the upper pollen zone to MIS 1, but the lower zone was not correlated to MIS 11; rather, it was inferred to be older than MIS 12 because it was stratigraphically below the “Oda” tephra (equivalent to a distal Kasamori 5 [Ks5] tephra [MIS 12]). In this study, however, noting that the Naruohama-IV tephra (Nh-IV; MIS 10d) and Ks5 cannot be distinguished by their shard chemistries, we inferred that the suggested “Oda” tephra actually correlates to Nh-IV, rather than to the Ks5 tephra. By re-assigning the “Oda” tephra to Nh-IV, we could correlate the underlying Quercus subgen. Cyclobalanopsis -abundant zone to MIS 11 and, consequently, a pair of pollen zones indicating cool and warm conditions below the MIS 11 pollen zone to MISs 12 and 13, respectively. The resulting age model whereby tephra and pollen constraints are integrated showed a roughly constant sedimentation rate from MIS 13, without any long-term gaps; further, our MIS 13 horizon in core IC2 corresponds to the reported 1 Ma tephra horizon in core IC. Therefore, these findings represent a dramatic change in the Uwa Formation age model and validate the Uwa Formation as one of the most useful terrestrial archives of Quaternary tephrostratigraphy and paleoclimatic fluctuation in SW Japan. • 1.Tephra and pollen stratigraphies of Uwa Basin deposits on Shikoku were investigated (83/85 characters) . • 2.Tephrostratigraphy was revised by single-shard major- and trace-element compositions (84/85 characters) . • 3.The tephra-based age model is consistent with the pollen stratigraphy (69/85 characters) . • 4.The MIS 11 period was found to be characterized by a very warm pollen assemblage (80/85 characters) . • 5.In the revised age model, the sedimentation rate is approx. Constant from MIS 1 to 13 (85/85 characters) .

Volcanism and the Greenland ice cores: A new tephrochronological framework for the last glacial-interglacial transition (LGIT) based on cryptotephra deposits in three ice cores

Chemical profiles from Greenland ice cores show that the frequency of volcanism was higher during the last glacial-interglacial transition (LGIT) and early Holocene, (17–9 ka b2k) than in any other period during the last 110 kyr. This increased frequency has partly been linked to climate-driven melting of the Icelandic ice sheet during the last deglaciation, with regional isostatic changes thought to alter mantle viscosity and lead to more eruptions. Our study is the first to construct a comprehensive tephrochronological framework from Greenland ice cores over the LGIT to aid in the reconstruction of volcanic activity over this period. The framework is based on extensive high-resolution sampling of three Greenland ice cores between 17.4 and 11.6 ka b2k and comprises a total of 64 cryptotephra deposits from the NGRIP, GRIP and NEEM ice cores. We show that many of these tephras are preserved within the core without an associated chemical signature in the ice, which implies that reconstructions of volcanism based solely on glacio-chemical indicators might underestimate the number of events. Single glass shards from each deposit were geochemically characterised to trace the volcanic source and many of these deposits could be correlated between cores. We show that the 64 deposits represent tephra deposits from 42 separate volcanic events, and of these, 39 are from Iceland, two from the north Pacific region (Japan and USA) and one has an unknown source. Six deposits can be correlated to terrestrial and/or marine tephra deposits in the Northern Hemisphere and the remaining 36 are unreported in other archives. We did not locate tephra from the compositionally distinctive Laacher See eruption (∼13 ka b2k) in our records. Combining our new discoveries with the previously published tephra framework, raises the number of individual tephra horizons found in Greenland ice over this interval to 50. This significantly improves the regional tephrochronological framework, our knowledge of the eruptive history of Iceland during the LGIT and provides new tephra constraints over key LGIT climate events. Consequentially, this framework can guide sampling strategies of future tephra studies in the terrestrial and marine realms aiming to link these records to the Greenland ice cores to assess regional climate synchroneity.

Geochronology and glass geochemistry of major Pleistocene eruptions in the Main Ethiopian Rift: Towards a regional tephrostratigraphy

The Main Ethiopian Rift (MER) is renowned as a focus of investigations into human origins. It is also the site of many large volcanic calderas, whose eruptions have spanned the timeframe of speciation, cultural innovation, and dispersal of our species. Yet, despite their significance for dating human fossils and cultural materials, the timing and geochemical signatures of some of the largest eruptions have remained poorly constrained at best. Here, through a programme of field surveys, geochemical analysis and 40Ar/39Ar dating, we report the ages of MER ignimbrites and link them to widespread tephra layers found in sequences of archaeological and paleoenvironmental significance. We date major eruptions of Fentale (76 ± 18 ka), Shala (ca. 145–155 ka), Kone (184 ± 42 ka and ca. 200 ± 12 ka) and Gedemsa (251 ± 47 ka) volcanoes, and correlate a suite of regionally important tephra horizons. Geochemical analysis highlights the predominantly peralkaline rhyolitic melt compositions (7.5–12 wt% Na2O + K2O, 70–76 wt% SiO2) across the central MER and remarkable similarity in incompatible trace element ratios, limiting the correlation of deposits via glass composition alone. However, by integrating stratigraphic and geochronological evidence from proximal deposits, lake sediment cores and distal outcrops at archaeological sites, we have traced ash layers associated with the ca. 177 ka Corbetti, ca. 145–155 ka Shala and ca. 108 ka Bora-Baricha-Tullu-Moye eruptions across southern Ethiopia. In addition to strengthening the tephrochronological framework that supports paleoenvironmental and archaeological work in the region, our findings have wider implications for evaluating the hypothesis of a middle Pleistocene ‘ignimbrite flare-up’ in the MER, and for evaluating the impacts of these great eruptions on landscapes, hydrology, and human ecology.

Quaternary marine tephrochronology of Rock Garden accretionary ridge, Hikurangi Subduction Margin, New Zealand

The Taupō Volcanic Zone (TVZ) of the North Island, New Zealand (NZ), is one of the most active Quaternary rhyolitic systems globally, producing voluminous eruptions and associated tephra that punctuate the NZ stratigraphic record. Due to dominantly westerly winds tephras are well preserved in the marine sedimentary record off NZ's east coast and provide important isochrons for chronostratigraphic correlation of marine sediment cores. Two MeBo200 (Bremen seafloor drill rig) sediment cores (GeoB20824–4 and GeoB20846–1) were collected from Rock Garden (RG) offshore of Hawke Bay in water depths of 610–670 metres below sea level (mbsl) with 24 tephra beds (both primary and secondary) that provide a well-dated proximal marine record of TVZ volcanism. The tephra layers are dated by a combination of accelerator mass spectrometry (AMS) 14C of the underlying biogenic carbonates, secondary ion mass spectrometry (SIMS), and correlation of onshore deposits using geochemical fingerprinting. Here we present SIMS U-Pb dating of 189 zircons extracted from five tephra layers from core GeoB20824–4 and six from core GeoB20846–1. AMS radiocarbon ages were carried out on sediments at three depths in core GeoB20824–4 and two depths in core GeoB20846–1, all within the upper 4 metre below seafloor (mbsf). We present major element data for 11 tephra deposits from core GeoB20824–4 and 13 from core GeoB20846–1 analysed by electron microprobe (748 analyses). We identify 10 significant Quaternary tephra horizons including: Kawakawa/Oruanui, Onepuhi (or Rangitawa), Kaukatea, Kidnappers-B, Potaka/Kidnappers, Rewa, and Sub-Rewa. Three tephra layers are geochemically correlated to unnamed but previously recognized tephra from Ocean Drilling Program (ODP) cores further east of RG. In addition to these previously identified tephra, several tephra layers are present in both MeBo200 cores that have not been recognized in existing published on- or offshore records. We attribute the finding of these new tephra deposits to the proximal location of the cores to the source location (unlike existing ODP records), the expanded stratigraphic record at these proximal locations afforded by the new coring technique applied here, and the potentially poor preservation of equivalent deposits in the terrestrial record. The identification of Quaternary TVZ tephras within MeBo200 cores, and their correlation to on- and offshore records is a significant advance as it provides: (1) a tool for correlation of marine sediment cores at the tectonostratigraphically important RG site, (2) a more detailed history of the TVZ from a proximal marine tephra record, (3) a well-dated tephra bed record from marine sediment cores with radiocarbon ages for younger ( ≤45 kyr), and U-Pb zircon ages for older (up to 1.3 Myr) tephra beds, and (4) a first approximation to the regional tephra distribution of key tephra beds

High‐resolution chronology of 24 000‐year long cores from two lakes in the Polar Urals, Russia, correlated with palaeomagnetic inclination records with a distinct event about 20 000 years ago

ABSTRACTBased on radiocarbon dating, a tephra horizon, varve counts and palaeomagnetism, detailed age models covering the last ~24 k cal abp, have been developed for the stratigraphy in the lakes Bolshoye Shchuchye and Maloye Shchuchye in the Polar Ural Mountains, Russia. The inclination curves from these lakes show nearly identical palaeomagnetic secular variations in the studied cores from both lakes, allowing for a precise correlation between the cores. A large and very distinct inclination deviation, named the Bolshoye Shchuchye Event, was identified in all cores retrieved from both lakes. It lasted over a period of 1245 years, from 20 470 to 19 225 cal abp.The well‐dated palaeomagnetic inclination graph offers a new possibility to correlate archives in this part of the Arctic for the last ~24 k cal abp, probably also over longer distances. The sedimentation rate shows the same trend in all cores from both lakes, including high input during the Last Glacial Maximum and gradually lowering after ~18 k cal abpto lower and stable Holocene values.

A tale of two signals: Global and local influences on the Late Pleistocene loess sequences in Bulgarian Lower Danube

In Central and Eastern Europe, research has been focused on loess associated with a plateau-setting, which preserves distinct and well-developed loess and palaeosol units linked to orbital scale changes. This has led to the view that during the last glacial period the Middle and Lower Danube predominantly experienced dry continental climates and supported steppic environments. However outside of the typical plateau setting, some authors have reported a presence of embryonic palaeosols within loess units suggesting sufficient moisture for short-term pedogenesis, and therefore either large scale moisture delivery systems and/or influence of local climatic and/geomorphic factors. Here the palaeoenvironmental and palaeoclimatic history is reconstructed based on two loess-palaeosol profiles in Slivata, North Bulgaria. The site is located in proximity to both the Carpathian and Balkan Mountains and rest on the Danube river terrace. To understand the timing of sediment deposition and dust fluxes chronological approaches combining quartz optically stimulated luminescence (OSL), feldspar post infrared-infrared stimulated luminescence (pIR-IRSL), and tephra correlation were applied. The results are coupled with high-resolution particle size and magnetic susceptibility analysis to provide an overview of past environmental conditions at the site. Finally, zircon U–Pb ages are used to understand potential changes to sediment delivery patterns, in the context of the site development.The investigated profile at Slivata 2 preserves a loess-palaeosol record spanning 52–30 ka, with a very complex sedimentary sequence that switches between periods of enhanced dust flux and sediment accumulation, and palaeosol development. The Slivata 2 sequence is also punctuated by multiple thin “palaeosol” like units that are interpreted as colluvial “soil” deposits on the basis of sedimentology, provenance, and geochronology, indicating a highly variable and dynamic landscape responding to the surrounding environment. The chronology shows very rapid sediment accumulation at Slivata 1 during LGM, with mass accumulation rates similar to sites in the Carpathian Basin, suggesting strong winds and high sediment supply rates. Yet LGM loess is punctuated by a thin palaeosol, which developed between 20–19 ka. This coincides with a temporary glacial retreat in the Carpathian Mountains and higher moisture availability in Eastern Carpathians, and therefore points to localised influences on loess-palaeosol development. Moreover data from Slivata 1 shows soil development and by extension landscape and climate stabilisation shortly prior to 14 ka. The pre-Holocene onset of pedogenesis at Slivata supports ecological and glacial evidence of weak Younger Dryas from the South Carpathian Mountains.Lastly this paper provides a geochemical analysis of the thin tephra horizon preserved in the Slivata 2 profile, which was correlated to the Cape Riva/Y-2 tephra. Consequently Slivata is the most northerly terrestrial site found to contain this tephra horizon, which has implications for the understanding of the size of the Santorini's Cape-Riva/Y-2 explosion. The identification of the Cape Riva (Y-2) tephra horizon and new remodelled age of 21.92 ± 0.56 cal ka BP provides a new tephrostratigraphic marker for eastern European LGM loess.

Holocene mountain landscape development and monsoon variation in the southernmost Russian Far East

A c. 9720‐year history of a mountain lake–mire complex on the Shufan Plateau (southern Primorye, Russian Far East) is based on a multi‐proxy study of peat deposits. The chronology is based on eight radiocarbon dates in addition to two dated tephra horizons. The sediment contains eight cryptotephra layers attributable to Baitoushan, a volcano on the Korea/China border. Pollen, diatom and botanical macrofossil analyses indicate climate fluctuations during the Holocene and a compositional response of biodiverse mountain forests to changes in temperature and humidity. Widespread, diverse broadleaf‐dominated forest marked a warm Early Holocene (~9500–9280 cal. a BP). Korean pine (Pinus koraiensis) rose to dominance in the Middle Holocene (after c. 7630 cal. a BP). Evergreen conifers, fir (Abies) in particular, became widespread after 2.9 ka BP and show a positive response to the Little Ice Age cooling. Over the c. 10 000‐year record, moisture appears largely controlled by gradually declining intensity of the summer monsoon, trending from moist conditions in the Early Holocene to cooler and drier conditions in the Late Holocene with shorter‐term hydrological changes superimposed. Peat composition indicates significant changes in mire vegetation, and diatom assemblages indicate four stages of inundation and three dry stages in the basin, probably controlled by precipitation changes. The initial importance of atmospheric precipitation shifted over time to a greater input from groundwater. During a long episode in the Late Holocene the basin may have dried out. Forest fires occurred during much of the Middle and Late Holocene, and their prominence, as marked by macro‐charcoal, is related to changes in humidity. Human activities mark the past few centuries. Medieval fires were probably anthropogenic, and there is evidence of agricultural impact on the landscape during the Jin Empire settlement period 900–700 years ago and of more recent forest exploitation, particularly a reduction in conifer taxa.

A tephra-based approach to calibrating relative geomagnetic paleointensity stacks to absolute values

Relative paleointensity (RPI) stacks provide a relative, global paleointensity variation, which reflects variations in the geocentric axial dipole moment. Previous calibrations of an RPI stack rely on adjusting a mean RPI to a mean of virtual axial dipole moments (VADMs), which are selected from absolute paleointensity (API) databases. To achieve more quantitative calibration of an RPI stack into absolute values, we propose a novel approach that compares (1) tephra-derived APIs and (2) the same tephras' horizons, in the oxygen isotope stratigraphy, tied RPIs (hereafter termed the “TA-TOR” approach). For the TA-TOR approach, APIs were newly determined for welded tuffs of 15 pyroclastic flow deposits in Japan. Eight of the 15 new APIs and 2 previously reported APIs have tephra horizons in the oxygen isotope stratigraphy. Based on the 10 data of the TA-TOR approach, combined with 4 data of the transitional field, VADMs calculated from the APIs (VADMAPI) were compared with isochronous RPIs from two RPI stacks, PISO-1500 and Sint-2000. The 14 data points in RPI vs. VADMAPI diagrams show a linear relationship with correlation coefficients of 0.83–0.89. Using the observed linear relationships, the two RPI stacks were reliably calibrated to VADM values (VADMRPI) for the period since 1.1 Ma. Compared with the VADMs calibrated by the previous studies, the present calibration provides a 12–13% smaller median/mean and a larger dispersion as represented by a 15–53% larger standard deviation for the two RPI stacks. The similarities between the cumulative distributions of VADMRPI from the two stacks and those of VADMs selected from the API database indicate the reliability of the present calibration. These results show that the present calibration, which relies on the TA-TOR approach, accurately converts a RPI stack into VADMRPI values and will contribute to studies on time variations in the geocentric axial dipole moment, sedimentary RPI, and cosmogenic radionuclides. Variations in VADMRPI for the past 1.1 Myr, obtained from PISO-1500 and Sint-2000 via the present calibration, can be used as standard geocentric axial dipole variations for this period.

Sedimentary record of Pleistocene aeolian - alluvial deposits on Vrgada Island (eastern Adriatic coast, Croatia)

Vrgada Island is situated in the central part of the eastern Adriatic coast. Upper Cretaceous limestones crop out on the surface and Pleistocene sediments cover them in some parts of the island. In this study we focus on a coastal cliff elongated in the N – S direction, situated in the northern part of the island. Aeolian-alluvial deposits, which are 12.5 m thick have been analysed. Three different facies in this succession are described. Lowermost facies A has a strong aeolian influence marked by increased silt and clay percentage and was deposited during colder climate conditions. Structureless sand in facies B was deposited from dense, cold water formed by melting snow and ice from the nearby Dinaric mountains. Bioturbated sandy facies C was probably formed during warmer climate. Unusually high percentage of augite in the lowermost part of facies A can be explained by volcanic dust input, most likely from the Roman or Campanian volcanoes in Italy. Combination of surface textures on quartz grains detected from SEM photographs indicate a short transport of sediment, no matter which mechanism) was dominant. Age correlation of possible tephra horizon from Vrgada island with confirmed tephra from Susak Island and dated ice/snow melting period from nearby mountains points to Upper Pleistocene age of sediments, most likely MIS 3 and MIS 2. The sediments from the Vrgada Island represent a transitional zone between the north Adriatic islands, where aeolian sediments dominate and the South - Eastern Adriatic archipelago, where mixed alluvial and aeolian sediments were observed.

Cryptotephras in the Lateglacial ICDP Dead Sea sediment record and their implications for chronology

Due to a lack of visible tephras in the Dead Sea record, this unique palaeoenvironmental archive is largely unconnected to the well‐established Mediterranean tephrostratigraphy. Here we present first results of the ongoing search for cryptotephras in the International Continental Drilling Program (ICDP) sediment core from the deep Dead Sea basin. This study focusses on the Lateglacial (~15–11.4 cal. ka BP), when Lake Lisan – the precursor of the Dead Sea – shrank from its glacial highstand to the Holocene low levels. We developed a glass shard separation protocol and counting procedure that is adapted to the extreme salinity and sediment recycling of the Dead Sea. Cryptotephra is abundant in the Dead Sea record (up to ~100 shards cm-3), but often glasses are physically and/or chemically altered. Six glass samples from five tephra horizons reveal a heterogeneous geochemical composition, with mainly rhyolitic and some trachytic glasses potentially sourced from Italian, Aegean and Anatolian volcanoes. Most shards likely originate from the eastern Anatolian volcanic province and can be correlated using major element analyses with tephra deposits from swarm eruptions of the Süphan Volcano ~13 ka BP and with ashes from Nemrut Volcano, presumably the Lake Van V‐16 volcanic layer at ~13.8 ka BP. In addition to glasses that match the TM‐10‐1 from Lago Grande di Monticchio (15 820±790 cal. a BP) tentatively correlated with the St. Angelo Tuff of Ischia, we further identified a cryptotephra with glass analyses which are chemically identical with those of the PhT1 tephra in the Philippon peat record (13.9–10.5 ka BP), and also a compositional match for the glass analyses of the Santorini Cape Riva Tephra (Y‐2 marine tephra, 22 024±642 cal. a BP). These first results demonstrate the great potential of cryptotephrochronology in the Dead Sea record for improving its chronology and connecting the Levantine region to the Mediterranean tephra framework.

Late Quaternary tephrostratigraphy and cryptotephrostratigraphy of core MD012422: Improving marine tephrostratigraphy of the NW Pacific

We investigated the deep-sea sedimentary sequence of core MD012422 corresponding to the last 350 ka (since marine isotopic stage, MIS 10) from off Shikoku Island, NW Pacific Ocean, and refined its tephrostratigraphy. We detected many tephras and cryptotephras and correlated them with terrestrial tephras on the basis of the major- and trace-element compositions of their glass shards. Then we cross-checked our results against the reported marine tephrostratigraphy in the NW Pacific area and assessed the relative timing of tephra eruptions and bioevents. Many widespread tephras and cryptotephras originated from the Kyushu volcanic zone (Kuju, Aso, Kakuto, Aira, Ata, and Kikai volcanoes/calderas), along with the Takayama-Ng1 tephra (Tky-Ng1) from Suiendani volcano in central Honshu, were detected in the core. These tephras were used to validate and refine the reported NW Pacific marine tephrostratigraphy and to develop useful time-synchronous markers for this ocean area. Among the tephras, Ata-Torihama (Ata-Th) occurs at the MIS 7/8 transition (ca. 240 ka) and its horizon overlaps with a calcareous nannofossil biohorizon, the first appearance datum (FAD) of Emiliania huxleyi. Ata-Th and this biohorizon are stratigraphically above the Tky-Ng1 (MIS 8/9 transition, 290–300 ka) and Kakuto (Kkt, MIS 9/10 transition, 330–340 ka) tephras, and these tephras have the same stratigraphic relationship with this biohorizon in deep-sea sediments from the East China Sea, off Shikoku Island, and off central Honshu. However, in deep-sea cores from off northern Honshu, an inconsistency between the tephrostratigraphy and the FAD of E. huxleyi has been reported. This inconsistency can be explained by poor preservation of calcareous fossils in the deep waters off northern Honshu, which are more corrosive to calcium carbonate than the shallower waters off Shikoku Island. These findings emphasize the importance of cross-checking biohorizons against tephra horizons and of linking tephras between terrestrial and marine sequences to assess the synchronicity of globally correlated age indicators.

Rapid Tephra Identification in Geological Archives With Computed Tomography: Experimental Results and Natural Applications

Volcanic ash (tephra) horizons represent powerful chronological and stratigraphic markers: rapid and widespread deposition allows for correlation of geological records in time and space. Recent analytical advances enable identification of invisible ash (cryptotephra) up to thousands of kilometers from its volcanic source. This momentum has greatly expanded the reach and potential of tephrochronology: some deposits can now be traced across continents and oceans. However, the laborious laboratory procedures required to identify tephra horizons in geological archives hold back the pace of progress. By allowing the rapid visualization of ash at micrometer (µm) scales, computed tomography (CT) holds great promise to overcome these restrictions. In this study, we further demonstrate the potential of this tool for the tephra community with experimental results and applications on conventionally analyzed archives. A custom-made scanner helps us strike a balance between the convenience of whole-core medical scanners and the µm-resolution of micro-CT systems. Using basic image processing tools that can be readily mastered by tephrochronologists, we identified invisible horizons down to ∼500 shards in synthetic cores. In addition, procedures for the removal of image artifacts can be used to visualize other paleoenvironmental indicators such as bioturbation burrows, ice rafted debris or mineral dust. When applied on segments of manually counted natural archives, our approach captures cryptic glass shard maxima down to ∼300 shards/cm3. We also highlight the value of CT to help optimize sampling strategies by identifying micrometer-scale ash horizons that were not detected in shard count profiles. In conclusion, this work helps broaden the applicability of CT as a promising frontier in tephrochronology that can advance the field by optimizing the efficiency and accuracy of isochron detection.

Revised tephrochronology for key tephras in the 130-ka Ōrākei Basin maar core, Auckland Volcanic Field, New Zealand: implications for the timing of climatic changes

ABSTRACT Tephrochronology is of paramount importance in New Zealand where paleoclimate studies use ages of volcanic ash layers as chronological makers. Maar lakes in the Auckland Volcanic Field (AVF) are characterised by continuous sediment accumulation over extended periods of time (>10,000 years) providing outstanding archives for paleoclimate studies also containing distally-sourced known-age rhyolitic, andesitic and locally-sourced basaltic tephra. Using a multi-method age model for the sediment sequence from Ōrākei Basin (ca. 130,000 years) combining radiocarbon dating, tephrochronology, luminescence dating, and tuning of relative magnetic paleointensity, we present new ages, and test and refine the reliability of existing tephra ages for 14 basaltic, 18 andesitic and eight rhyolitic tephra horizons. Our results show overall strong agreement with previously published ages (except the new age derived for the Okareka tephra, here reported as 23,525 cal yr BP) but reduce the error ranges. Larger differences in tephra ages compared to previously published ages occur predominantly beyond the radiocarbon dating limit. The revised ages have potential implications for studies involving tephrochronology (sensu stricto), for volcanic eruption recurrence rates in the AVF and for the timing of climatic changes observed in northern New Zealand, such as a possibly cooler marine isotope stage (MIS) 5b than MIS4.

A first chronology for the East Greenland Ice-core Project (EGRIP) over the Holocene and last glacial termination

Abstract. This paper provides the first chronology for the deep ice core from the East Greenland Ice-core Project (EGRIP) over the Holocene and the late last glacial period. We rely mainly on volcanic events and common peak patterns recorded by dielectric profiling (DEP) and electrical conductivity measurement (ECM) for the synchronization between the EGRIP, North Greenland Eemian Ice Drilling (NEEM) and North Greenland Ice Core Project (NGRIP) ice cores in Greenland. We transfer the annual-layer-counted Greenland Ice Core Chronology 2005 (GICC05) from the NGRIP core to the EGRIP ice core by means of 381 match points, typically spaced less than 50 years apart. The NEEM ice core has previously been dated in a similar way and is only included to support the match-point identification. We name our EGRIP timescale GICC05-EGRIP-1. Over the uppermost 1383.84 m, we establish a depth–age relationship dating back to 14 967 years b2k (years before the year 2000 CE). Tephra horizons provide an independent validation of our match points. In addition, we compare the ratio of the annual layer thickness between ice cores in between the match points to assess our results in view of the different ice-flow patterns and accumulation regimes of the different periods and geographical regions. For the next years, this initial timescale will be the basis for climatic reconstructions from EGRIP high-resolution proxy data sets, e.g. stable water isotopes, chemical impurity or dust records.

Tephra horizons identified in the western North Atlantic and Nordic Seas during the Last Glacial Period: Extending the marine tephra framework

Geochemically distinct volcanic ash (tephra) deposits are increasingly acknowledged as a key geochronological tool to synchronize independent paleoclimate archives. Recent advances in the detection of invisible (crypto) tephra have led to the ongoing establishment, development and integration of regional tephra lattices. These frameworks offer an overview of the spatial extent of geochemically characterized tephra from dated eruptions – a valuable tool for precise correlation of paleorecords within these areas. Here, we harness cryptotephra analysis to investigate the occurrence of two well-known tephra markers from the Last Glacial Period (i.e. FMAZ II-1 (26.7 ka b2k) and NAAZ II (II-RHY-1) (55.3 ka b2k)), in marine sediment cores from the Nordic, Irminger and Labrador Seas. In addition, we assess the imprint of bioturbation on two of these tephra deposits using Computed Tomography (CT) imagery. We have successfully identified FMAZ II-1 in the Nordic and Irminger Seas. The tephra deposit is a visible deposit in the Nordic Seas, whereas it appears as a single high concentration peak within the fine-grained shard size fraction (i.e. 25-80 μm) in the Irminger Sea. Both horizons are primary airfall deposits, and this study is the first to identify a FMAZ II-1 deposit of isochronous nature in the Irminger Sea region. In addition, we have identified a new tephra horizon in the Irminger Sea, which is stratigraphically associated with FMAZ II-1, and geochemically similar to the known 2-JPC-192-1 population. We discuss its potential to serve as a new reference tie-point for correlations in the region. Lastly, we have successfully identified NAAZ II (II-RHY-1) of isochronous nature in both the Irminger and Labrador Sea. The layers are interpreted to be deposited by either direct airfall or by sea-ice drifting past the sites. Compared to the existing frameworks, which previously mainly focused on sites east of Iceland, our findings expand the knowledge and utility of the FMAZ II-1 and NAAZ II (II-RHY-1) horizons.