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1.
We present in this work a tephrostratigraphic record from a sediment piston core (JO 2004) from Lake Ohrid. Five tephra layers were recognised, all from explosive eruptions of southern Italy volcanoes. A multidisciplinary study was carried out, including stratigraphy, AMS 14C chronology and geochemistry. The five tephra layers were correlated with terrestrial proximal counterparts and with both marine and lacustrine tephra layers already known in the central Mediterranean area. The oldest is from Pantelleria Island (P11, 131 ka BP). Other three tephra layers are from Campanian volcanoes: X6, Campanian Ignimbrite-Y5 and SMP1-Y3 (107, 39 and 31 ka BP respectively). The youngest tephra layer corresponds to the FL eruption from Etna Volcano (3.4 ka BP). In three cases these recognitions confirm previous findings in the Balkans, while two of them were for the first time recognised in the area, with a significant enlargement of the previous assessed dispersal areas.  相似文献   

2.
Tephra-fall deposits from Cook Inlet volcanoes were detected in sediment cores from Tustumena and Paradox Lakes, Kenai Peninsula, Alaska, using magnetic susceptibility and petrography. The ages of tephra layers were estimated using 21 14C ages on macrofossils. Tephras layers are typically fine, gray ash, 1-5 mm thick, and composed of varying proportions of glass shards, pumice, and glass-coated phenocrysts. Of the two lakes, Paradox Lake contained a higher frequency of tephra (0.8 tephra/100 yr; 109 over the 13,200-yr record). The unusually large number of tephra in this lake relative to others previously studied in the area is attributed to the lake's physiography, sedimentology, and limnology. The frequency of ash fall was not constant through the Holocene. In Paradox Lake, tephra layers are absent between ca. 800-2200, 3800-4800, and 9000-10,300 cal yr BP, despite continuously layered lacustrine sediment. In contrast, between 5000 and 9000 cal yr BP, an average of 1.7 tephra layers are present per 100 yr. The peak period of tephra fall (7000-9000 cal yr BP; 2.6 tephra/100 yr) in Paradox Lake is consistent with the increase in volcanism between 7000 and 9000 yr ago recorded in the Greenland ice cores.  相似文献   

3.
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.  相似文献   

4.
A suite of deep‐sea cores were collected along transects up to 100 km across the fore‐arc and back‐arc regions of the predominantly submarine Kermadec arc near Raoul and Macauley islands, southwest Pacific. The cores reveal a macroscopic tephra record extending back >50 ka. This is a significant addition to the dated record of volcanism, previously restricted to fragmented late Holocene records exposed on the two islands. The 27 macroscopic tephra layers display a wide compositional diversity in glass (～50–78 wt% SiO2). Many tephra layers comprise silicic shards with a subordinate mafic shard population. This could arise from magma mingling and may reflect mafic triggering of the silicic eruptions. Broadly, the glass compositions can be distinguished on diverging high‐K and low‐K trends, most likely arising from different source volcanoes. This distinction is also reflected in the tephra records exposed on Raoul (low‐K) and Macauley (high‐K) islands, the likely source areas. Heterogeneous tephra comprising shards of both high‐ and low‐K affinity, silicic and mafic compositions, and more homogeneous tephra with subordinate outlier shard compositions, are best explained by post‐depositional mixing of separate eruption deposits or contemporaneous eruptions. Evidently, the slow sedimentation rates of the calcareous oozes (～101–102 mm ka?1) were insufficient to adequately separate and preserve closely spaced eruption deposits. This exemplifies the difficulty in assessing eruption frequencies and magmatic trends, and erecting a tephrostratigraphy, using geochemical fingerprinting in such environments. Despite these difficulties, the ca. 5.7 ka Sandy Bay Tephra erupted from Macauley Island can be correlated over a distance of >100 km, extending east and west of the island, showing that the mostly submerged volcanoes are capable of wide tephra dispersal. Hence there is potential for developing chronostratigraphies for the southwest Pacific beyond the region covered by the extensive rhyolite marker beds from the Taupo Volcanic Zone. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

5.
This paper presents an event stratigraphy based on data documenting the history of vegetation cover, lake‐level changes and fire frequency, as well as volcanic eruptions, over the Last Glacial–early Holocene transition from a terrestrial sediment sequence recovered at Lake Accesa in Tuscany (north‐central Italy). On the basis of an age–depth model inferred from 13 radiocarbon dates and six tephra horizons, the Oldest Dryas–Bølling warming event was dated to ca. 14 560 cal. yr BP and the Younger Dryas event to ca. 12 700–11 650 cal. yr BP. Four sub‐millennial scale cooling phases were recognised from pollen data at ca. 14 300–14 200, 13 900–13 700, 13 400–13 100 and 11 350–11 150 cal. yr BP. The last three may be Mediterranean equivalents to the Older Dryas (GI‐1d), Intra‐Allerød (GI‐1b) and Preboreal Oscillation (PBO) cooling events defined from the GRIP ice‐core and indicate strong climatic linkages between the North Atlantic and Mediterranean areas during the last Termination. The first may correspond to Intra‐Bølling cold oscillations registered by various palaeoclimatic records in the North Atlantic region. The lake‐level record shows that the sub‐millennial scale climatic oscillations which punctuated the last deglaciation were associated in central Italy with different successive patterns of hydrological changes from the Bølling warming to the 8.2 ka cold reversal. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

6.
Here we present a tephrostratigraphic record (core Co1202) recovered from the northeastern part of Lake Ohrid (Republics of Macedonia and Albania) reaching back to Marine Isotope Stage (MIS) 6. Overall ten horizons (OT0702‐1 to OT0702‐10) containing volcanic tephra have been recognised throughout the 14.94 m long sediment succession. Four tephra layers were visible at macroscopic inspection (OT0702‐4, OT0702‐6, OT0702‐8 and OT0702‐9), while the remaining six are cryptotephras (OT0702‐1, OT0702‐2, OT0702‐3, OT0702‐5, OT0702‐7 and OT0702‐10) identified from peaks in K, Zr and Sr intensities, magnetic susceptibility measurements, and washing and sieving of the sediments. Glass shards of tephra layers and cryptotephras were analysed with respect to their major element composition, and correlated to explosive eruptions of Italian volcanoes. The stratigraphy and the major element composition of tephra layers and cryptotephras allowed the correlation of OT0702‐1 to AD 472 or AD 512 eruptions of Somma‐Vesuvius, OT0702‐2 to the FL eruption of Mount Etna, OT0702‐3 to the Mercato from Somma‐Vesuvius, OT0702‐4 to SMP1‐e/Y‐3 eruption from the Campi Flegrei caldera, OT0702‐5 to the Codola eruption (Somma‐Vesuvius or Campi Flegrei), OT0702‐6 to the Campanian Ignimbrite/Y‐5 from the Campi Flegrei caldera, OT0702‐7 to the Green Tuff/Y‐6 eruption from Pantelleria Island, OT0702‐8 to the X‐5 eruption probably originating from the Campi Flegrei caldera, OT0702‐9 to the X‐6 eruption of generic Campanian origin, and OT0702‐10 to the P‐11 eruption from Pantelleria Island. The fairly well‐known ages of these tephra layers and parent eruptions provide new data on the dispersal and deposition of these tephras and, furthermore, allow the establishment of a chronological framework for core Co1202 for a first interpretation of major sedimentological changes. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

7.
A total of 24 tephra-bearing volcanic layers have been recognized between 550 and 987 m depth in the Siple Dome A (SDM-A) ice core, in addition to a number already recognized tephra in the upper 550 m (Dunbar et al., 2003, Kurbatov et al., 2006). The uniform composition and distinctive morphological of the particles composing these tephra layers suggest deposition as a result of explosive volcanic eruptions and that the layers therefore represent time-stratigraphic markers in the ice core. Despite the very fine grain size of these tephra (mostly less than 20 microns), robust geochemical compositions were determined by electron microprobe analysis. The source volcanoes for these tephra layers are largely found within the Antarctic plate. Statistical geochemical correlations tie nine of the tephra layers to known eruptions from Mt. Berlin, a West Antarctic volcano that has been very active for the past 100,000 years. Previous correlations were made to an eruption of Mt. Takahe, another West Antarctic volcano, and one to Mt. Hudson, located in South America (Kurbatov et al., 2006). The lowest tephra layer in the ice core, located at 986.21 m depth, is correlated to a source eruption with an age of 118.1 ± 1.3 ka, suggesting a chronological pinning point for the lower ice. An episode of anomalously high volcanic activity in the ice in the SDM-A core between 18 and 35 ka (Gow and Meese, 2007) appears to be related to eruptive activity of Mt. Berlin volcano. At least some of the tephra layers found in the SDM-A core appear to be the result of very explosive eruptions that spread ash across large parts of West Antarctica, off the West Antarctic coast, as well as also being recognized in East Antarctica (Basile et al., 2001, Narcisi et al., 2005, Narcisi et al., 2006). Some of these layers would be expected to should be found in other deep Antarctic ice cores, particularly ones drilled in West Antarctica, providing correlative markers between different cores. The analysis of the tephra layers in the Siple Dome core, along with other Antarctic cores, provides a timing framework for the relatively proximal Antarctic and South American volcanic eruptive events, allowing these to be distinguished from the tropical eruptions that may play a greater role in climate forcing.  相似文献   

8.
Several reworked tephra layers in gravity-flow deposits are present in lacustrine core sediments collected from Hotel and Rudy Lakes on King George Island, South Shetland Islands, maritime sub-Antarctica. This study tests the values of tephra for establishing regional tephrochronologies for lakes in ice-covered landscapes in the vicinity of volcanoes. The tephra record is more abundant in a long Hotel Lake core (515 cm long). This study uses volcanic glass samples from five tephra layers of Hotel Lake and from one tephra layer of Rudy Lake. Morphologically, tephras are mixtures of basaltic and pumice shards, both having various degrees of vesicularity. Major element analyses of glass shards reveal that the majority of the glass fragments belong to basic glass (<60 wt% SiO2), compositionally ranging from basalt to low-silica andesite and subalkaline series medium-K tholeiites, probably sourced from Deception Island located 130 km southwest of King George Island. Less than 20% of tephra belongs to silicic glass and occurs in three tephra horizons E of Hotel Lake. However, source volcano(es) for about 10% of basic tephra and silicic tephra are not readily identified from nearby volcanic centers. Except for the studied tephra in Rudy Lake, all tephra samples in Hotel Lake are not ashfall deposits but reworked and redeposited pyroclasts derived from retreating ice sheet, resulting in the occurrence of geochemically equivalent tephra samples in different tephra horizons. The dating of the studied tephra horizons represents the timing of deglaciation rather than that of volcanic eruptions. The result of this study implies that combined with sedimentological information more chemical criterion is necessary to study tephrochronology and regional correlation and to understand paleoenvironmental changes using tephra.  相似文献   

9.
We present a new tephrostratigraphic record from the Holocene lake sediments of the Sulmona basin, central Italy. The Holocene succession is represented by whitish calcareous mud that is divided into two units, SUL2 (ca 32 m thick) and SUL1 (ca 8 m thick), for a total thickness of ca 40 m. These units correspond to the youngest two out of six sedimentary cycles recognised in the Sulmona basin that are related to the lake sedimentation since the Middle Pleistocene. Height concordant U series age determinations and additional chronological data constrain the whole Holocene succession to between ca 8000 and 1000 yrs BP. This includes a sedimentary hiatus that separates the SUL2 and SUL1 units, which is roughly dated between <2800 and ca 2000 yrs BP. A total of 31 and 6 tephra layers were identified within the SUL2 and SUL1 units, respectively. However, only 28 tephra layers yielded fresh micro-pumices or glass shards suitable for chemical analyses using a microprobe wavelength dispersive spectrometer. Chronological and compositional constraints suggest that 27 ash layers probably derive from the Mt. Somma-Vesuvius Holocene volcanic activity, and one to the Ischia Island eruption of the Cannavale tephra (2920 ± 450 cal yrs BP). The 27 ash layers compatible with Mt. Somma-Vesuvius activity are clustered in three different time intervals: from ca 2000 to >1000; from 3600 to 3100; and from 7600 to 4700 yrs BP. The first, youngest cluster, comprises six layers and correlates with the intense explosive activity of Mt. Somma-Vesuvius that occurred after the prominent AD 79 Pompeii eruption, but only the near-Plinian event of AD 472 has been tentatively recognised. The intermediate cluster (3600–3100 yrs BP) starts with tephra that chemically and chronologically matches the products from the “Pomici di Avellino” eruption (ca 3800 ± 200 yrs BP). This is followed by eight further layers, where the glasses exhibit chemical features that are similar in composition to the products from the so-called “Protohistoric” or AP eruptions; however, only the distal equivalents of three AP events (AP3, AP4 and AP6) are tentatively designated. Finally, the early cluster (7600–4700 yrs BP) comprises 12 layers that contain evidence of a surprising, previously unrecognised, activity of the Mt. Somma-Vesuvius volcano during its supposed period of quiescence, between the major Plinian “Pomici di Mercato” (ca 9000 yrs BP) and “Pomici di Avellino” eruptions. Alternatively, since at present there is no evidence of a similar significant activity in the proximal area of this well-known volcano, a hitherto unknown origin of these tephras cannot be role out. The results of the present study provide new data that enrich our previous knowledge of the Holocene tephrostratigraphy and tephrochronology in central Italy, and a new model for the recent explosive activity of the Peninsular Italy volcanoes and the dispersal of the related pyroclastic deposits.  相似文献   

10.
A tephra record is presented for a sediment core from Llyn Llech Owain, south Wales, spanning the early- to mid-Holocene. Seven cryptotephra deposits are discovered with three thought to correlate with known eruptions and the remaining four considered to represent previously undocumented events. One deposit is suggested to correlate with the ~6.9 cal ka bp Lairg A tephra from Iceland, whereas more distant sources are proposed as the origin for two of the tephra deposits. A peak of colourless shards in early-Holocene sediments is thought to tentatively correlate with the ~9.6 cal ka bp Fondi di Baia tephra (Campi Flegrei) and a second cryptotephra is tentatively correlated with the ~3.6 cal ka bp Aniakchak (CFE) II tephra (Alaska). The Fondi di Baia tephra has never been recorded beyond proximal sites and its discovery in south Wales significantly extends the geographical distribution of ash from this eruption. The remaining four cryptotephra deposits are yet to be correlated with known eruptions, demonstrating that our current understanding of widespread tephra deposits is incomplete. This new tephra record highlights the potential for sites at more southerly and westerly locations in northwest Europe to act as repositories for ash from several volcanic regions.  相似文献   

11.
The emerging tephrostratigraphy of NW Europe spanning the last termination (ca. 15–9 ka) provides the potential for synchronizing marine, ice‐core and terrestrial records, but is currently compromised by stratigraphic complications, geochemical ambiguity and imprecise age estimates for some layers. Here we present new tephrostratigraphic, radiocarbon and chironomid‐based palaeotemperature data from Abernethy Forest, Scotland, that refine the ages and stratigraphic positions of the Borrobol and Penifiler tephras. The Borrobol Tephra (14.14–13.95 cal ka BP) was deposited in a relatively warm period equated with Greenland Interstadial sub‐stage GI‐1e. The younger Penifiler Tephra (14.09–13.65 cal ka BP) is closely associated with a cold oscillation equated with GI‐1d. We also present evidence for a previously undescribed tephra layer that has a major‐element chemical signature identical to the Vedde Ash. It is associated with the warming trend at the end of the Younger Dryas, and dates between 11.79 and 11.20 cal ka BP. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

12.
This article reports the first discovery of middle Holocene cryptotephra from a peat sequence in Estonia, eastern Baltic. Two sequences, Mustjärve and Parika (located 110 km apart), were chosen for a pilot study aimed at finding traces of tephra fallout during the middle Holocene. Peat accumulation at both sites started in the early Holocene (c. 9500–9000 14C yr BP; c . 11 000–10000 cal. yr BP) and continued throughout the whole Holocene. The radiocarbon-dated intervals between c. 2000 and 5000 14C yr BP (c. 2000–5500 cal. yr BP) were chosen from both sites for the study. Colourless tephra shards were identified at 312–316 cm below the peat surface in the Mustjärve peat sequence, while no tephra was found in peat of the same age at Parika. Electron microprobe analyses suggest a correlation with the initial phase of the Hekla-4 eruption (c. 4260 cal. yr BP), although the age-depth model indicated an age around 4900 cal. yr BP. Small concentrations of colourless to light brown tephra shards at 266–270 cm in the Mustjärve sequence indicate that the Kebister tephra (c. 3750 cal. yr BP) might also be present, but geochemical analyses were not possible. The low concentration and small size of the tephra particles indicate that Estonian bogs are probably on the verge of where tephrochronology is possible in northwestern Europe. Further studies of full Holocene sequences are required in order to discover traces of other ash plumes reaching as far east as the eastern Baltic area.  相似文献   

13.
A study of six tephra layers discovered in different deposits between 1600 and 2700 m a.s.l. in the Apennine chain in central Italy allowed precise stratigraphic constraints on environmental and climatic changes between ca. 4.5 and 3.8 cal ka BP. Chemical analyses allowed the correlation of these tephra layers with the eruptions of Agnano Mt Spina (AMST) from Phlegrean Field and Avellino (AVT) from Somma–Vesuvius. Major environmental changes in the high mountains of the Central Apennines occurred just after the deposition of the AMST and predate the deposition of the AVT. At this time, renewed growth of the Calderone Glacier occurred, marking the onset of the Apennine “Neoglacial”. The presence of the AMST and AVT enabled us to make a precise, physical correlation with other archives in central Italy. Synchronization of records between sites showed that the period intervening the deposition of the AMST and AVT layers coincided with environmental changes that were not always exactly in phase. This highlights the fact that stratigraphic correlations using only radiocarbon chronologies (the most common method used for dating archives during the Holocene) could produce erroneous correlation of events, giving rise to oversimplified paleoclimatic reconstructions.  相似文献   

14.
The major and trace element concentrations of volcanic glass shards from visible tephra layers in the SG93 and SG06 cores from Lake Suigetsu, central Japan, were determined by femtosecond laser ablation–inductively coupled plasma–mass spectrometry. The glass-shard analyses, together with the petrographic properties of the tephra samples, allow the Suigetsu tephra layers to be broadly classified into tephras derived from calderas on Kyushu Island, and from Daisen and Sambe volcanoes in the Chugoku district of southwest Japan. The layers correlated with tephras from Kuju caldera and Daisen volcano, and with the younger Sambe tephras, have adakitic elemental features. A Suigetsu tephra sample correlated with the Sambe−Kisuki tephra based on petrographic properties has an elemental pattern similar to that of the Toya tephra from Hokkaido Island, northeast Japan. This match implies that tephras from northeast Japan, as well as Kyushu–Chugoku tephras, are possible correlatives of the Suigetsu tephra layers. Both petrographic properties and major–trace element data of volcanic glass shards are essential for robust tephra correlations, and hierarchical cluster analysis proved additionally useful in statistically evaluating relationships among the tephras.  相似文献   

15.
We document the mineralogical and geochemical composition of tephra layers identified in the late Quaternary sediments of Puyehue Lake (Southern Volcanic Zone of the Andes, Chile, 40°S) to identify the source volcanoes and to present the first tephrostratigraphic model for the region. For the last millennium, we propose a multi-criteria correlation model based on five tephra layers identified at seven coring sites. The two upper tephras are thin fine-grained green layers composed of more than 80% rhyodacitic glass shards, and associated to the AD 1960 and AD 1921-22 eruptions of the Puyehue-Cordon de Caulle volcanic complex. The third tephra is a sandy layer dominated by orthopyroxene, and related to the AD 1907 eruption of Rininahue maar. An olivine-rich tephra was deposited at the end of the 16th century, and a tephra characterized by a two-pyroxene association marks the second half of the first millennium AD. In addition, we detail the tephra succession of an 11.22-m-long sediment core covering the last 18,000 yr. The results demonstrate that the central province of the Southern Volcanic Zone has been active throughout the last deglaciation and the Holocene, with no increase in volcanic activity during glacial unloading.  相似文献   

16.
以渤海湾西岸现代岸线附近的NP3、CH110和BT113三个钻孔全新世岩心为研究对象,采用沉积岩石学、AMS 14C(accelerator mass spectrometry 14C,加速器质谱14C)测年、微体生物聚类分析等方法精细判别沉积相,重建渤海湾西岸全新世沉积演化历史,并利用微体生物组合分带对水深变化的指示,定量讨论全新世相对海面变化。结果表明:渤海湾西岸全新世受海陆交互作用影响,经历了沼泽-潮滩-浅海-前三角洲-三角洲前缘-三角洲平原环境的演化过程。全新世初始阶段,研究区中部和北部发育沼泽环境,南部未见沉积,与上更新统河流相沉积呈不整合接触。全新世早期,研究区潮滩环境发育。潮滩层厚度约1 m,历时数百至1千余年。至7000 cal BP前后水深增大,研究区进入浅海环境。约6000 cal BP,沿岸南北两端先后进入三角洲过渡环境,中部三角洲环境约开始于1500 cal BP。渤海湾西岸地区全新世的环境演化同时记录了该地区的相对海面变化:约10000 cal BP前后,渤海湾相对海平面已接近21.3~20.4 m。约8000 cal BP,相对海平面介于18.6~17.0 m。约6000 cal BP时相对海平面低于6.8 m,5000~1000 cal BP,相对海平面高于-2.5 m,1000~800 cal BP,相对海平面介于-1.3~-0.4 m。8000~5000 cal BP时,相对海面上升约15.0 m,上升速率达5 m/1 ka。  相似文献   

17.
A hitherto unknown distal volcanic ash layer has been detected in a sediment core recovered from the southeastern Levantine Sea (Eastern Mediterranean Sea). Radiometric, stratigraphic and sedimentological data show that the tephra, here termed as S1 tephra, was deposited between 8970 and 8690 cal yr BP. The high-silica rhyolitic composition excludes an origin from any known eruptions of the Italian, Aegean or Arabian volcanic provinces but suggests a prevailing Central Anatolian provenance. We compare the S1 tephra with proximal to medial-distal tephra deposits from well-known Mediterranean ash layers and ash fall deposits from the Central Anatolian volcanic field using electron probe microanalyses on volcanic glass shards and morphological analyses on ash particles. We postulate a correlation with the Early Holocene ‘Dikkart?n’ dome eruption of Erciyes Da? volcano (Cappadocia, Turkey). So far, no tephra of the Central Anatolian volcanic province has been detected in marine sediment archives in the Eastern Mediterranean region. The occurrence of the S1 tephra in the south-eastern part of the Levantine Sea indicates a wide dispersal of pyroclastic material from Erciyes Da? more than 600 km to the south and is therefore an important tephrostratigraphical marker in sediments of the easternmost Mediterranean Sea and the adjacent hinterland.  相似文献   

18.
Thirty-two tephra layers were identified in the time-interval 313–366 ka (Marine Isotope Stages 9–10) of the Quaternary lacustrine succession of the Fucino Basin, central Italy. Twenty-seven of these tephra layers yielded suitable geochemical material to explore their volcanic origins. Investigations also included the acquisition of geochemical data of some relevant, chronologically compatible proximal units from Italian volcanoes. The record contains tephra from some well-known eruptions and eruptive sequences of Roman and Roccamonfina volcanoes, such as the Magliano Romano Plinian Fall, the Orvieto–Bagnoregio Ignimbrite, the Lower White Trachytic Tuff and the Brown Leucitic Tuff. In addition, the record documents eruptions currently undescribed in proximal (i.e. near-vent) sections, suggesting a more complex history of the major eruptions of the Colli Albani, Sabatini, Vulsini and Roccamonfina volcanoes between 313 and 366 ka. Six of the investigated tephra layers were directly dated by single-crystal-fusion 40Ar/39Ar dating, providing the basis for a Bayesian age–depth model and a reassessment of the chronologies for both already known and dated eruptive units and for so far undated eruptions. The results provide a significant contribution for improving knowledge on the peri-Tyrrhenian explosive activity as well as for extending the Mediterranean tephrostratigraphical framework, which was previously based on limited proximal and distal archives for that time interval.  相似文献   

19.
The generation of reliable age models for palaeoenvironmental and archaeological records in the Eurasian Arctic is often problematic when using conventional dating techniques. Tephrochronology can potentially improve the chronologies of such records and synchronise disparate sedimentary archives. However, to date, systematic tephra studies are lacking for this region. This paper presents the first cryptotephra data from the White Sea region (northwestern Russia) based on a peat core spanning the past ~1800 years. We identify seven geochemical glass populations that derive from six Icelandic volcanoes and correlate four of them to north European tephra isochrons; these include Askja ad 1875, the basaltic component of the ad 877 Landnám tephra, and tephras BTD-15 (c. ad 1750–1650) and SL-2/SB-2 (ad 803–767) from unknown eruptions of Katla and Snæfellsjökull, respectively. The remaining three populations originate from Grímsvötn, Hekla and Katla; however, their attribution to individual eruptions remains ambiguous. These findings highlight the potential to extend the Late Holocene tephrochronological framework of northern Europe to the west Eurasian Arctic. The detection of at least three basaltic tephras in the core suggests that basaltic shards can be transported over larger distances than previously known and that peatlands are well suited to preserve such components.  相似文献   

20.
Volcanic ash preserved in marine sediment sequences is key for independent synchronization of palaeoclimate records within and across different climate archives. Here we present a continuous tephrostratigraphic record from the Labrador Sea, spanning the last 65–5 ka, an area and time period that has not been investigated in detail within the established North Atlantic tephra framework. We investigated marine sediment core GS16-204-22CC for increased tephra occurrences and geochemically analysed the major element composition of tephra shards to identify their source volcano(es). In total we observed eight tephra zones, of which five concentration peaks show isochronous features that can be used as independent tie-points in future studies. The main transport mechanism of tephra shards to the site was near-instantaneous deposition by drifting of sea ice along the East Greenland Current. Our results show that the Icelandic Veidivötn volcanic system was the dominant source of tephra material, especially between late Marine Isotope Stage (MIS) 4 and early MIS 3. The Veidivötn system generated volcanic eruptions in cycles of ca. 3–5 ka. We speculate that the quantity of tephra delivered to the Labrador Sea was a result of variable Icelandic ice volume and/or changes in the transportation pathway towards the Labrador Sea.  相似文献   

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