The Y-3 tephra: A Last Glacial stratigraphic marker for the central Mediterranean basin

The paper reviews the existing data on the Y-3 tephra layer, first recognised in the Ionian Sea (Mediterranean basin). The collection and collation of old and new data on distal tephra occurrences in terrestrial, marine and lacustrine successions indicate that the Y-3 layer is dispersed over a wide area of the central Mediterranean basin. The peculiar homogeneous chemical composition of this layer makes its recognition rather straightforward and permits it being distinguished from other stratigraphically adjacent tephras. The best age estimate for the Y-3 layer of ca 30–31 cal ka BP, its peculiar stratigraphic position close to the Marine Isotope Stage 3/2 transition or Heinrich Event 3 onset, as well as its wide dispersion makes this layer an important marker to link and date late Pleistocene terrestrial and marine archives of the central Mediterranean basin.     

Laser-ablation ICP-MS zircon U-Pb ages for key Pliocene-Pleistocene tephra beds in unglaciated Yukon and Alaska

Tephrochronology is one of the most effective ways to correlate and date Quaternary deposits across large distances. However, it can be challenging to obtain direct ages on tephra beds when they are beyond the limit of radiocarbon dating, do not contain mineral phases suitable for ⁴⁰K-⁴⁰Ar (or ⁴⁰Ar/³⁹Ar) dating, or suitable glass shards for fission-track dating are not available. Zircon U-Pb dating by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is an emerging technique for dating young (<1 Ma) tephra. Here, we demonstrate that LA-ICP-MS zircon U-Pb dating can produce reliable ages for key tephra beds found in Yukon and Alaska. We assessed five different techniques for calculating tephra maximum depositional ages from zircon U-Pb ages for eight tephra beds. Our preferred zircon U-Pb ages (reported with 2σ uncertainties), based on a Bayesian model for calculating maximum depositional ages, are broadly consistent with previously established chronology constructed from stratigraphy, paleomagnetism, and/or glass fission track and ⁴⁰Ar/³⁹Ar ages: Biederman tephra (178 ± 17 ka), HP tephra (680 ± 47 ka), Gold Run tephra (688 ± 44 ka), Flat Creek tephra (708 ± 43 ka), PA tephra (1.92 ± 0.06 Ma), Quartz Creek tephra (2.62 ± 0.08 Ma), Lost Chicken tephra (3.14 ± 0.07 Ma), and GI tephra (542 ± 64 ka). We also present newly revised glass fission-track and ⁴⁰Ar/³⁹Ar ages recalculated from previous determinations using updated ages for the Moldavite tektite and Fish Canyon Tuff standards, and updated K decay constants. For Pleistocene age zircon crystals, corrections for ²³⁰Th disequilibrium and common-Pb are significant and must be treated with caution. Similarly, apparent tephra ages are sensitive to the choice of method used to calculate a maximum depositional age from the assemblage of individual crystallization ages. This study demonstrates that LA-ICP-MS zircon U-Pb dating can be successfully applied to numerous Pliocene-Pleistocene Alaskan-Yukon tephra, providing confidence in applying this method to other stratigraphically important tephra in the region.     

One Million Years tephra record at IODP Sites U1436 and U1437: Insights into explosive volcanism from the Japan and Izu arcs

The 1 Myr tephra records of IODP (International Ocean Discovery Program) Holes U1436A and U1437B in the Izu‐Bonin fore‐ and reararc were investigated in order to assess provenance and eruptive volumes, respectively. In total, 304 tephra samples were examined and 260 primary tephra layers were identified. Tephra provenance was determined by means of major and trace element compositions of glass shards and distinguished between Japan and Izu‐Bonin arc origin of the tephra layers. A total of 33 marine tephra compositions were correlated to the Japan arc and 227 to the Izu arc. Twenty marine tephra layers were correlated between the two drilling sites. Additionally, we defined eleven correlations of marine tephra deposits to major widespread Japanese eruptions; from the 1.05 Ma Shishimuta‐Pink Tephra to the 30 ka Aira‐Tn Tephra, both from Kyushu Island. These eruptions provide independent time markers within the sediment record and six correlations were used to date tephra layers from Japan in Hole U1436A to establish an alternative age model for this hole. Furthermore, the minimum distal tephra volumes of all detected events were calculated, which enabled the comparison of the tephra volumes that derived from the Japan and the Izu‐Bonin arcs. For some of the major Japanese eruptions these are the first volume estimations that also include distal deposits. All of the Japanese tephras derived from events with eruption magnitude M_v ≥ 5.6 and three of the investigated eruptions reach magnitudes M_v ≥ 7. Volcanic events of the Izu‐Bonin arc have mostly eruption magnitudes M_v ≤ 5.     

Magmatic and phreatomagmatic volcanic activity at Mt. Takahe, West Antarctica, based on tephra layers in the Byrd ice core and field observations at Mt. Takahe

The morphology, grain size characteristics and composition of ash particles in 30 ka to 150 ka tephra layers from the Byrd ice core were examined to characterize the eruptions which produced them and to test the suggestion that they were erupted from Mt. Takahe, a shield volcano in Marie Byrd Land, West Antarctica. Volcanic deposits at Mt. Takahe were examined for evidence of recent activity which could correlate with the tephra layers in the ice core.Coarse- and fine-ash layers have been recognized in the Byrd ice core. The coarse-ash layers have a higher mass concentration than the fine-ash layers and are characterized by fresh glass shards > 50 μm diameter, many containing elongate pipe vesicles. The fine-ash layers have a lower mass concentration and contain a greater variety of particles, typically < 20 μm diameter. Many of these particles are aggregate grains composed of glass and crystal fragments showing S and Cl surface alteration. The grain-size distributions of the coarse and fine-ash layers overlap, in part because of the aggregate nature of grains in the fine-ash layers. The coarse-ash layers are interpreted as having formed by magmatic eruption whereas the fine-ash layers are believed to be hydrovolcanic in origin.Mt. Takahe is the favored source for the tephra because: (a) chemical analyses of samples from the volcano are distinctive, being peralkaline trachyte, and similar in composition to the analyzed tephra; (b) Mt. Takahe is a young volcano (< 0.3 Ma); (c) pyroclastic deposits on Mt. Takahe indicate styles of eruption similar to that inferred for the ice core tephra; and (d) Mt. Takahe is only about 350 km from the calculated site of tephra deposition.A speculative eruptive history for Mt. Takahe is established by combining observations from Mt. Takahe and the Byrd ice core tephra. Initial eruptions at Mt. Takahe were subglacial and then graded into alternating subaerial and subglacial activity. The tephra suggest alternating subaerial magmatic and hydrovolcanic eruptions from 30 to 20 ka B.P., followed by a sustained period of hydrovolcanic eruptions from 20 to 14 ka B.P., which peaked at 18 ka B.P.     

Advancements and best practices for analysis and correlation of tephra and cryptotephra in ice

Geochemical analysis of fine grained (<20 μm) tephra found in ice cores is inherently difficult, due to the typically low number and small size of available particles. Ice core tephra samples require specialized sample preparation techniques to maximize the amount of information that can be gained from these logistically limited samples that may provide important chronology to an ice record, as well as linking glacial, marine and terrestrial sediments. We have developed a flexible workflow for preparation of tephra and cryptotephra samples to allow accurate and robust geochemical fingerprinting, which is fundamental to tephrochronology. The samples can be prepared so that secondary electron imagery can be obtained for morphological characterization of the samples to ensure that the sample is tephra-bearing and then the sample can be further prepared for quantitative electron microprobe analysis using wavelength dispersive techniques (EMP-WDS), scanning electron microscopy with energy dispersive spectrometry (SEM-EDS), laser ablation inductively coupled mass spectrometry (LA-ICP-MS) or secondary ion mass spectrometry (SIMS). Some samples may be too small for typical instrumentation conditions to be used (i.e. 20 μm beam on the EMP) to analyze for geochemistry and we present other techniques that can be employed to obtain accurate, although less precise, geochemistry. Methods include analyzing unpolished tephra shards less than 5 μm in diameter with a 1 μm beam on an SEM; using the “broad beam overlap” EMP method on irregular particles less than 20 μm in diameter, and analyzing microlitic shards as well as aphyric shards using EMP to increase the number of analyzed shards in low abundance tephra layers. The methods presented are flexible enough to be employed in other geological environments (terrestrial, marine and glacial) which will help maximize and integrate multiple environments into the overall tephra framework.     

Distal record of multi-sourced tephra in Onepoto Basin,Auckland, New Zealand: implications for volcanic chronology,frequency and hazards

We have documented 80 tephra beds dating from ca. 9.5 to >50 ka, contained within continuously deposited palaeolake sediments from Onepoto Basin, a volcanic explosion crater in Auckland, New Zealand. The known sources for distal (>190 km from vent) tephra include the rhyolitic Taupo Volcanic Centre (4) and Okataina Volcanic Centre (14), and the andesitic Taranaki volcano (40) and Tongariro Volcanic Centre (3). The record provides evidence for four new events between ca. 50 and 28 ka (Mangaone Subgroup) suggesting Okataina was more active than previously known. The tephra record also greatly extends the known northern dispersal of other Mangaone Subgroup tephra. Ten rhyolitic tephra pre-date the Rotoehu eruption (>ca. 50 ka), and some are chemically dissimilar to post-50 ka rhyolites. Some of these older tephra were produced by large-magnitude events; however, their source remains uncertain. Eight tephra from the local basaltic Auckland Volcanic Field (AVF) are also identified. Interpolation of sedimentation rates allow us to estimate the timing of 12 major explosive eruptions from Taranaki volcano in the 27.5-9.5-ka period. In addition, 28 older events are recognised. The tephra are trachytic to rhyolitic in composition. All have high K₂O contents (>3 wt%), and there are no temporal trends. This contrasts with the proximal lava record that shows a trend of increasing K₂O with time. By combining the Onepoto tephra record with that of the previously documented Pukaki crater, 15 AVF basaltic fall events are constrained at: 34.6, 30.9, 29.6, 29.6, 25.7, 25.2, 24.2, 23.8, 19.4, 19.4, 15.8 and 14.5 ka, and three pre-50 ka events. This provides some of the best age constraints for the AVF, and the only reliable data for hazard recurrence calculations. The minimum event frequency of both distal and local fall events can be estimated, and demonstrates the Auckland City region is frequently impacted by ash fall from many volcanoes.     

Estimation of tephra volumes from sparse and incompletely observed deposit thicknesses

We present a Bayesian statistical approach to estimate volumes for a series of eruptions from an assemblage of sparse proximal and distal tephra (volcanic ash) deposits. Most volume estimates are of widespread tephra deposits from large events using isopach maps constructed from observations at exposed locations. Instead, we incorporate raw thickness measurements, focussing on tephra thickness data from cores extracted from lake sediments and through swamp deposits. This facilitates investigation into the dispersal pattern and volume of tephra from much smaller eruption events. Given the general scarcity of data and the physical phenomena governing tephra thickness attenuation, a hybrid Bayesian-empirical tephra attenuation model is required. Point thickness observations are modeled as a function of the distance and angular direction of each location. The dispersal of tephra from larger well-estimated eruptions are used as leverage for understanding the smaller unknown events, and uncertainty in thickness measurements can be properly accounted for. The model estimates the wind and site-specific effects on the tephra deposits in addition to volumes. Our technique is exemplified on a series of tephra deposits from Mt Taranaki (New Zealand). The resulting estimates provide a comprehensive record suitable for supporting hazard models. Posterior mean volume estimates range from 0.02 to 0.26 km ³. Preliminary examination of the results suggests a size-predictable relationship.     

A 90,000–200,000 yrs marine tephra record of Italian volcanic activity in the Central Mediterranean Sea

A detailed tephrochronological study was undertaken in three deep-sea cores collected in the Tyrrhenian and Ionian Seas. The age and the origin of the marine tephra were inferred from oxygen isotope records of foraminifera and from major element compositions of glass-shards. Seventy-one eruptions were detected in the time interval 90,000–200,000 yrs during which the volcanoes of the Roman and Campanian regions and of the southern Italy were in activity. This is attested by the consistency of the geochemical compositions of both marine and terrestrial deposits. Most of the marine tephra consisted in trachytes and phonolites characterizing a Roman and Campanian origin. Several tephra were proposed as key-horizons for proximal and distal sediments. Among them, one tephra originating from Mount Etna (149,300 yrs) and five tephra from Pantelleria island (130,000 yrs, 163,600 yrs, 192,500 yrs, 197,400 yrs and 198,400 yrs) were northerly dispersed. Several other key horizons originated from the Campanian or Roman provinces were detected as far as 1000 km from the vents.     

The Campanian Ignimbrite and Codola tephra layers: Two temporal/stratigraphic markers for the Early Upper Palaeolithic in southern Italy and eastern Europe

Tephra layers from archaeological sites in southern Italy and eastern Europe stratigraphically associated with cultural levels containing Early Upper Palaeolithic industry were analysed. The results confirm the occurrence of the Campanian Ignimbrite tephra (CI; ca. 40 cal ka BP) at Castelcivita Cave (southern Italy), Temnata Cave (Bulgaria) and in the Kostenki–Borshchevo area of the Russian Plain. This tephra, originated from the largest eruption of the Phlegrean Field caldera, represents the widest volcanic deposit and one of the most important temporal/stratigraphic markers of western Eurasia. At Paglicci Cave and lesser sites in the Apulia region we recognise a chemically and texturally different tephra, which lithologically, chronologically and chemically matches the physical and chemical characteristics of the Plinian eruption of Codola; a poorly known Late Pleistocene explosive event from the Neapolitan volcanoes, likely Somma–Vesuvius. For this latter, we propose a preliminary age estimate of ca. 33 cal ka BP and a correlation to the widespread C-10 marine tephra of the central Mediterranean. The stratigraphic position of both CI and Codola tephra layers at Castelcivita and Paglicci help date the first and the last documented appearance of Early Upper Palaeolithic industries of southern Italy to ca. 41–40 and 33 cal ka BP, respectively, or between two interstadial oscillations of the Monticchio pollen record – to which the CI and Codola tephras are physically correlated – corresponding to the Greenland interstadials 10–9 and 5. In eastern Europe, the stratigraphic and chronometric data seem to indicate an earlier appearance of the Early Upper Palaeolithic industries, which would predate of two millennia at least the overlying CI tephra. The tephrostratigraphic correlation indicates that in both regions the innovations connected with the so-called Early Upper Palaeolithic – encompassing subsistence strategy and stone tool technology – appeared and evolved during one of the most unstable climatic phases of the Last Glacial period. On this basis, the marked environmental unpredictability characterising this time-span is seen as a potential ecological factor involved in the cultural changes observed.     

<Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar dating of the eruptive history of Mount Erebus,Antarctica: summit flows,tephra, and caldera collapse

Eruptive activity has occurred in the summit region of Mount Erebus over the last 95 ky, and has included numerous lava flows and small explosive eruptions, at least one plinian eruption, and at least one and probably two caldera-forming events. Furnace and laser step-heating ⁴⁰Ar/³⁹Ar ages have been determined for 16 summit lava flows and three englacial tephra layers erupted from Mount Erebus. The summit region is composed of at least one or possibly two superimposed calderas that have been filled by post-caldera lava flows ranging in age from 17 ± 8 to 1 ± 5 ka. Dated pre-caldera summit flows display two age populations at 95 ± 9 to 76 ± 4 ka and 27 ± 3 to 21 ± 4 ka of samples with tephriphonolite and phonolite compositions, respectively. A caldera-collapse event occurred between 25 and 11 ka. An older caldera-collapse event is likely to have occurred between 80 and 24 ka. Two englacial tephra layers from the flanks of Mount Erebus have been dated at 71 ± 5 and 15 ± 4 ka. These layers stratigraphically bracket 14 undated tephra layers, and predate 19 undated tephra layers, indicating that small-scale explosive activity has occurred throughout the late Pleistocene and Holocene eruptive history of Mount Erebus. A distal, englacial plinian-fall tephra sample has an age of 39 ± 6 ka and may have been associated with the older of the two caldera-collapse events. A shift in magma composition from tephriphonolite to phonolite occurred at around 36 ka.Editorial responsibility: Julie Donnelly-Nolan     

Explosive silicic volcanism in Iceland and the Jan Mayen area during the last 6 Ma: sources and timing of major eruptions

Fifty-three major explosive eruptions on Iceland and Jan Mayen island were identified in 0–6-Ma-old sediments of the North Atlantic and Arctic oceans by the age and the chemical composition of silicic tephra. The depositional age of the tephra was estimated using the continuous record in sediment of paleomagnetic reversals for the last 6 Ma and paleoclimatic proxies (δ¹⁸O, ice-rafted debris) for the last 1 Ma. Major element and normative compositions of glasses were used to assign the sources of the tephra to the rift and off-rift volcanic zones in Iceland, and to the Jan Mayen volcanic system. The tholeiitic central volcanoes along the Iceland rift zones were steadily active with the longest interruption in activity recorded between 4 and 4.9 Ma. They were the source of at least 26 eruptions of dominant rhyolitic magma composition, including the late Pleistocene explosive eruption of Krafla volcano of the Eastern Rift Zone at about 201 ka. The central volcanoes along the off-rift volcanic zones in Iceland were the source of at least 19 eruptions of dominant alkali rhyolitic composition, with three distinct episodes recorded at 4.6–5.3, 3.5–3.6, and 0–1.8 Ma. The longest and last episode recorded 11 Pleistocene major events including the two explosive eruptions of Tindfjallajökull volcano (Thórsmörk, ca. 54.5 ka) and Katla volcano (Sólheimar, ca. 11.9 ka) of the Southeastern Transgressive Zone. Eight major explosive eruptions from the Jan Mayen volcanic system are recorded in terms of the distinctive grain-size, mineralogy and chemistry of the tephra. The tephra contain K-rich glasses (K₂O/SiO₂>0.06) ranging from trachytic to alkali rhyolitic composition. Their normative trends (Ab–Q–Or) and their depleted concentrations of Ba, Eu and heavy-REE reflect fractional crystallisation of K-feldspar, biotite and hornblende. In contrast, their enrichment in highly incompatible and water-mobile trace elements such as Rb, Th, Nb and Ta most likely reflect crustal contamination. One late Pleistocene tephra from Jan Mayen was recorded in the marine sequence. Its age, estimated between 617 and 620 ka, and its composition support a common source with the Borga pumice formation at Sør Jan in the south of the island.     

Tephrostratigraphy of the last 170 ka in sedimentary successions from the Adriatic Sea

In this study are discussed new SEM-EDS analyses performed on glass shards from five cores collected in the Central Adriatic Sea and two cores recovered from the South Adriatic Sea. A total of 26 tephra layers have been characterized and compared with the geochemical features of terrestrial deposits and other tephra archives in the area (South Adriatic Sea and Lago Grande di Monticchio, Vulture volcano). The compositions are compatible with either a Campanian or a Roman provenance. The cores, located on the Central Adriatic inner and outer shelf, recorded tephra referred to explosive events described in the literature: AP3 (sub-Plinian activity of the Somma-Vesuvius, 2710 ± 60 ¹⁴C years BP); Avellino eruption (Somma–Vesuvius, 3548 ± 129 ¹⁴C years BP); Agnano Monte Spina (Phlegrean Fields, 4100 ± 400 years BP); Mercato eruption (Somma–Vesuvius, 8010 ± 35 ¹⁴C years BP; Agnano Pomici Principali eruption (Phlegrean Fields, 10,320 ± 50 ¹⁴C years BP); Neapolitan Yellow Tuff (Phlegrean Fields, 12,100 ± 170 ¹⁴C years BP). Some of these layers were also observed in the South Adriatic core IN68-9 in addition to younger (AP2, sub-Plinian eruption, Somma–Vesuvius, 3225 ± 140 ¹⁴C years BP), and older layers (Pomici di Base eruption, Somma–Vesuvius, 18,300 ± 150 ¹⁴C years BP). Significant is the tephra record of core RF95-7 that, for the first time in the Adriatic Sea, reports the occurrence of tephra layers older than 60 ka: the well known Mediterranean tephra layers X2 (ca. 70 ka), W1 (ca. 140 ka) and V2 (Roman origin, ca. 170 ka) as well as other tephra layers attributed, on the basis of geochemistry and biostratigraphy, to explosive eruptions occurred at Vico (138 ± 2 and 151 ± 3 ka BP) and Ischia (147–140 ka BP).     

The spatial extent of tephra deposition and environmental impacts from the 1912 Novarupta eruption

The eruption of Novarupta within the Katmai Volcanic Cluster, south-west Alaska, in June 1912 was the most voluminous eruption of the twentieth century but the distal distribution of tephra deposition is inadequately quantified. We present new syntheses of published tephrostratigraphic studies and a large quantity of previously un-investigated historical records. For the first time, we apply a geostatistical technique, indicator kriging, to integrate and interpolate such data. Our results show evidence for tephra deposition across much of Alaska, Yukon, the northern Pacific, western British Columbia and northwestern Washington. The most distal tephra deposition was observed around 2,500?km downwind from the volcano. Associated with tephra deposition are many accounts of acid deposition and consequent impacts on vegetation and human health. Kriging offers several advantages as a means to integrate and present such data. Future eruptions of a scale similar to the 1912 event have the potential to cause widespread disruption. Historical records of tephra deposition extend far beyond the limit of deposition constrained by tephrostratigraphic records. The distal portion of tephra fallout deposits is rarely adequately mapped by tephrostratigraphy alone; contemporaneous reports of fallout can provide important constraints on the extent of impacts following large explosive eruptions.     

Optical luminescence dating of a loess section containing a critical tephra marker horizon,SW North Island of New Zealand

A new IRSL dataset is presented for the age and setting of a critical Late Glacial Maximum tephra isochron marker. The rhyolitic tephra, known as the Kawakawa Tephra, occurs as a 14 cm thick layer within a 5.9 m thick loess section overlying alluvial gravels in the Rangitikei River valley, SW North Island of New Zealand. Ages range from 21 at the base to 5 ka near the top of the loess and bracket an age of 17.0 ± 2.2 for the tephra. The new IRSL ages are in agreement with published and unpublished luminescence ages from other localities of loess, sand and ash above and below the tephra and of the tephra itself, that indicate an age of ca. 19 ka for the Kawakawa Tephra. This age is considerably younger than the generally accepted ¹⁴C 27.1 ka cal yrs BP age of the Kawakawa Tephra and highlights an unresolved discrepancy between the two dating systems.     

High-precision 40Ar/39Ar dating of pleistocene tuffs and temporal anchoring of the Matuyama-Brunhes boundary

High-precision ⁴⁰Ar/³⁹Ar ages for a series of proximal tuffs from the Toba super-volcano in Indonesia, and the Bishop Tuff and Lava Creek Tuff B in North America have been obtained. Core from Ocean Drilling Project Site 758 in the eastern equatorial Indian Ocean contains discrete tephra layers that we have geochemically correlated to the Young Toba Tuff (73.7 ± 0.3 ka), Middle Toba Tuff (502 ± 0.7 ka) and two eruptions (OTTA and OTTB) related to the Old Toba Tuff (792.4 ± 0.5 and 785.6 ± 0.7 ka, respectively) (⁴⁰Ar/³⁹Ar data reported as full external precision, 1 sigma). Within ODP 758 Termination IX is coincident with OTTB and hence this age tightly constrains the transition from Marine Isotope Stage 19–20 for the Indian Ocean. The core also preserves the location of the Australasian tektites, and the Matuyama-Brunhes boundary with Bayesian age-depth models used to determine the ages of these events, c. 786 and c. 784 ka, respectively. In North America, the Bishop Tuff (766.6 ± 0.4 ka) and Lava Creek Tuff B (627.0 ± 1.5 ka) have quantifiable stratigraphic relationships to the Matuyama-Brunhes boundary. Linear age-depth extrapolation, allowing for uncertainties associated with potential hiatuses in five different terrestrial sections, defines a geomagnetic reversal age of 789 ± 6 ka. Considering our data with respect to the previously published age data for the Matuyama-Brunhes boundary of Sagnotti et al. (2014), we suggest at the level of temporal resolution currently attainable using radioisotopic dating the last reversal of Earths geomagnetic field was isochronous. An overall Matuyama-Brunhes reversal age of 783.4 ± 0.6 ka is calculated, which allowing for inherent uncertainties in the astronomical dating approach, is indistinguishable from the LR04 stack age (780 ± 5 ka) for the geomagnetic boundary. Our high-precision age is 10 ± 2 ka older than the Matuyama-Brunhes boundary age of 773 ± 1 ka, as reported previously by Channell et al. (2010) for Atlantic Ocean records. As ODP 758 features in the LR04 marine stack, the high-precision ⁴⁰Ar/³⁹Ar ages determined here, as well as the Matuyama-Brunhes boundary age, can be used as temporally accurate and precise anchors for the Pleistocene time scale.     

Chronology of Pliocene and Quaternary bioevents and climatic events from fission-track ages on tephra beds, Wairarapa, New Zealand

High-resolution Pliocene and Pleistocene sequences exposed on land in New Zealand are some of the few detailed records of widepread marine bioevents and paleoclimatic changes in the Southern Hemisphere. Marine biostratigraphy calibrated in deep-sea cores by paleomagnetic reversals has been the primary basis for the chronology of these sequences. We have determined ages for several tephra beds which now provide an independent numerical age calibration for a well-studied marine and terrestrial section in Wairarapa. By using the isothermal plateau fission track (ITPFT) method on volcanic glass we have overcome the problems of partial track fading and detrital mineral contamination, which hindered earlier studies, to reveal a new chronology extending back to nearly 5 Ma.

Our ages for the Hikawera Tuff (4.91 ± 0.25 Ma) and Spooner Tuff (3.44 ± 0.13 Ma) are consistent with the appearance and disappearance of many early Pliocene foraminiferial species, validating their age calibration in New Zealand. However, some fossil occurrences, including coccoliths, differ temporally by as much as 0.55 Ma, perhaps due to local tectonic-induced recycling.

Four Pleistocene tephra beds (Potaka tephra (1.00 ± 0.03 Ma), Kaukatea tephra (0.87 ± 0.05 Ma), Rangitawa tephra (ca. 0.35 Ma) and Kawakawa tephra (ca. 0.22 Ma)) are now recognised in the Wairarapa sequence via stratigraphic and new geochemical and age data. These beds allow direct correlation to other marine and terrestrial basins, as well as volcanic regions in New Zealand, and will ultimately aid in a regional paleoenvironmental reconstruction where bioevents are absent. The tephra ages indicate that the marine sediment accumulation rates varied from 90 to 250 m/Ma between different sections of the Pliocene and reached ca. 350 m/Ma in the last 2.4 Ma, when the sequence displays pronounced glacioeustatic cyclic deposition. In the terrestrial realm, the oldest loess in New Zealand is now constrained to between 1.00 and 0.87 Ma.     

Stratigraphy and significance of Brown Tuffs on the Aeolian Islands (southern Italy)

Brown Tuffs (BT) are volcaniclastic ash deposits prominently represented in the stratigraphic profiles of all the Aeolian Islands (and Capo Milazzo on the northern coast of Sicily). Detailed stratigraphy and tephrochronology together with available radiometric ages suggest that they were emplaced over a long time interval spanning from the end of the last interglacial period (ca. 80 ka BP) up to 4–5 ka BP (age of the overlying Punte Nere pyroclastic products on Vulcano). The most complete BT succession is documented on Lipari where 14 distinct and successive units are subdivided by the interbedding of widespread tephra layers, local volcanic products, paleosols and epiclastic deposits and the occurrence of local erosive surfaces. Inter-island occurrence of Ischia-Tephra (a widely known tephra layer in the Aeolian archipelago dated at 56 ka BP) and Monte Guardia pyroclastics from Lipari (dated at 22–20 ka BP) subdivides the BT succession in Upper (UBT), Intermediate (IBT) and Lower BT units (LBT), which can be correlated at regional level: the LBT was emplaced between 80 and 56 ka BP, the IBT between 56 and 22 ka BP and the UBT between 20 and 4–5 ka BP. On the basis of stratigraphy, similarity in lithology and textural features, morphology of glass fragments, composition and consistency of thickness and grain-size variations, UBT units correlate with Piano Grotte dei Rossi tuffs on Vulcano island. They were generated by pulsating hydromagmatic explosive activity giving rise to pyroclastic density currents spreading laterally from a source located inside the La Fossa caldera on Vulcano island. Composition is in agreement with this hypothesis since UBT compositional features match those of Vulcano magmas erupted in that period. The effect of co-ignimbrite ash clouds (or associated fallout processes from sustained eruptive columns) is seen to explain the presence of UBT in areas further away from the suggested source (e.g. Salina and Lipari islands and Capo Milazzo). The origin of UBT exposed on Panarea island is still a matter of debate, due to contrasting compositional data. Due to large uniformity of lithological, textural and componentry characters with respect to the UBT, the lower portions of the BT succession (LBT-IBT) are considered to be the result of recurrent, large scale hydromagmatic eruptions of similar type. Moreover, for the IBT units, the correlation with Monte Molineddo 3 pyroclastics of Vulcano island (on the basis of lithological, compositional and stratigraphic matching) again suggests source(s) related to the Vulcano plumbing system and located within the La Fossa Caldera.     

The last 40 ka tephrostratigraphic record of Lake Ohrid,Albania and Macedonia: a very distal archive for ash dispersal from Italian volcanoes

A 1075 cm long core (Lz1120) was recovered in the south-eastern part of the Lake Ohrid (Republics of Macedonia and Albania) and sampled for identification of tephra layers. Magnetic susceptibility investigations show rather high magnetic values throughout the core, with peaks unrelated to the occurrence of tephra layers but instead to the relative abundance of detrital magnetic minerals in the sediment. Naked-eye inspection of the core allowed us to identify of two tephra layers, at 896–897 cm and 1070–1075 cm. Laboratory inspection of the grain-size fraction > 125 μm allowed for the identification of a third cryptotephra at 310–315 cm. Major element analyses on glass shards of the tephra layers at 896–897 cm and 1070–1075 cm show a trachytic composition, and indicate a correlation with the regionally dispersed Y-3 and Y-5 tephra layers, dated at ca 30 and 39 cal ka BP. The cryptotephra at 310–315 cm has a mugearitic–benmoreitic composition, and was correlated with the FL eruption of Mt. Etna, dated at 3370 ± 70 cal yr BP. These ages are in agreement with five ¹⁴C AMS measurements carried out on plant remains and macrofossils from the lake sediments at different depths along the core.     

The first tephra evidence for a Late Glacial explosive volcanic eruption in the Arxan-Chaihe volcanic field (ACVF), northeast China

A 5 mm thick tephra layer has been identified in the lacustrine sediments of Moon Lake in the Arxan-Chaihe volcanic field (ACVF) in Greater Khingan Mountains (NE China). The visible tephra layer is clearly revealed as a distinct peak in magnetic susceptibility measurements. The tephra layer consists mainly of brown vesicular glass shards and minor amounts of plagioclase, olivine and clinopyroxene. Major and minor element analysis has been carried out on the glass shards and plagioclase minerals. Glass shards show low concentrations of K₂O, similar to the eruptive products derived from post-Miocene volcanoes of the ACVF. The plagioclase phenocrysts in both lava and tephra from ACVF, and in the tephra recorded in Moon Lake are labradorites. During the Late Pleistocene to Holocene, there were also extensive explosive eruptions in the nearby Nuominhe volcanic field (NVF). Volcanic rocks from the ACVF are easily distinguished from those derived from the NVF, having distinctly different K₂O concentrations. This compositional variation is likely the result of different magmatic processes operating in the ACVF and NVF. Radiocarbon dating on organic materials from the lacustrine sediments dates the tephra layer to ca. 14,200 cal yrs BP, which implies that it was generated by a previously unknown Late Pleistocene explosive eruption in the ACVF. These results, for the first time, give a direct tephra record in this area, and suggest that identification of further tephra and/or cryptotephra in local sedimentary basins such as crater lakes of scoria cones and maars will be significant for dating the Late Pleistocene to Holocene volcanic eruptions and will help to establish a detailed record of the volcanic activity in the ACVF. The newly discovered tephra layer also provides a dated tephrochronological marker layer, which will in future studies provide a means to synchronise local sedimentary records of the climatically variable Late Glacial.     

The late Pleistocene pyroclastic deposits of the Campanian Plain: New insights into the explosive activity of Neapolitan volcanoes

The lithological and compositional characteristics of eighteen different pyroclastic deposits of Campanian origin, dated between 125 cal ky BP and 22 cal ky BP, were described. The pyroclastic deposits were correlated among different outcrops mainly located on the Apennine slopes that border the southern Campanian Plain. They were grouped in two main stratigraphic and chronologic intervals of regional significance: a) between Pomici di Base (22.03 cal ky BP; Somma–Vesuvius) and Campanian Ignimbrite (39 cal ky BP; Campi Flegrei) eruptions; and b) older than Campanian Ignimbrite eruption. Three new ¹⁴C AMS datings support the proposed correlations. Six eruptions were attributed to the Pomici di Base-Campanian Ignimbrite stratigraphic interval, while twelve eruptions are older than Campanian Ignimbrite. Of the studied deposits two originated from Ischia island, five are related to Campi Flegrei, and three to Somma–Vesuvius. Two eruptions have an uncertain correlation with Somma–Vesuvius or Campi Flegrei, while six eruptions remain of uncertain source. Minimum volumes of five eruptions were assessed, ranging between 0.5 km³ and 4 km³. Two of the studied deposits were correlated with Y-3 and X-5 tephra layers, which are widely dispersed in the central Mediterranean area. The new stratigraphic and chronologic data provide an upgraded chrono-stratigraphy for the explosive activity of Neapolitan volcanoes in the period between 125 and 22 cal ky BP.