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1.
The youngest volcanic eruptions in East‐Central Europe—new findings from the Ciomadul lava dome complex,East Carpathians,Romania 
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下载免费PDF全文 Violent explosive eruptions occurred between c. 51 and 29 thousand years ago—during the Last Glacial Maximum in East‐Central Europe—at the picturesque volcano of Ciomadul, located at the southernmost tip of the Inner Carpathian Volcanic Range in Romania. Field volcanology, glass geochemistry of tephra, radiocarbon and optically stimulated luminescene dating, along with coring the lacustrine infill of the two explosive craters of Ciomadul (St Ana and Mohos), constrain the last volcanic activity to three subsequent eruptive stages. The explosivity was due to the silicic composition of the magma producing Plinian‐style eruptions, and the interaction of magma with the underlying, water‐rich rocks resulting in violent phreatomagmatic outbursts. Tephra (volcanic ash) from these eruptions are interbedded with contemporaneous loess deposits, which form thick sequences in the vicinity of the volcano. Moreover, tephra layers are also preserved in the older Mohos crater infill, providing an important archive for palaeoclimate studies. Identifying the final phreatomagmatic eruption of Ciomadul at c. 29.6 ka, which shaped the present‐day landform of the 1600‐m‐wide St Ana explosion crater, we were able to correlate related tephra deposits as far as 350 km from the source within a thick loess‐palaeosol sequence at the Dniester Delta in Roxolany, Ukraine. A refined tephrostratigraphy, based on a number of newly found exposures in the Ciomadul surrounding region as well as correlation with the distal terrestrial and marine (e.g. Black Sea) volcano‐sedimentary record, is expected from ongoing studies. 相似文献
2.
The Aegean island of Thera (Santorini) was covered by tephra from its cataclysmic Late Bronze Age (ca. 3600 yr B.P.) eruption. Vertical exposures of the eruptive sequence show secondary, nonvolcanic, circular (in cross section) features composed of stratified sediment. Many are inaccessible from the floors of modern quarries and appear to be caves filled with younger sediment, but show no connection to the land surface. A filled cave was found in the wall of a modern gully outside the modern quarries, and a filled cave was found in a terrace scarp, well above the modern gully. Natural (and probably rapid) incision by gullies into the thick tephra deposit left many locations with lateral access to tephra. Inhabitants from post‐Minoan to recent times excavated tephra for materials and buildings, and caves were subsequently filled by sporadic (possibly seasonal) flood events that deposited sediment. These gullies may have provided access for modern tephra removal that isolated the filled caves high on the modern quarry walls. © 2003 Wiley Periodicals, Inc. 相似文献
3.
The Ebisutoge–Fukuda tephra (Plio‐Pleistocene boundary, central Japan) has a well‐recorded eruptive style, history, magnitude and resedimentation styles, despite the absence of a correlative volcanic edifice. This tephra was ejected by an extremely large‐magnitude and complex volcanic eruption producing more than 400 km3 total volume of volcanic materials (volcanic explosivity index=7), which extended more than 300 km away from the probable eruption centre. Remobilization of these ejecta occurred progressively after the completion of a series of eruptions, resulting in thick resedimented volcaniclastic deposits in spatially separated fluvial basins, more than 100 km from the source. Facies analysis of resedimented volcaniclastic deposits was carried out in distal fluvial basins. The distal tephra (≈100–300 km from the source) comprises two different lithofacies, primary pyroclastic‐fall deposits and reworked volcaniclastic deposits. The resedimented volcaniclastic succession shows five distinct sedimentary facies, interpreted as debris‐flow deposits (facies A), hyperconcentrated flow deposits (facies B), channel‐fill deposits (facies C), floodplain deposits with abundant flood‐flow deposits (facies D) and floodplain deposits with rare flood deposits (facies E). Resedimented volcaniclastic materials at distal locations originated from unconsolidated deposits of a climactic, large ignimbrite‐forming eruption. Factors controlling inter‐ and intrabasinal facies changes are (1) temporal change of introduced volcaniclastic materials into the basin; (2) proximal–distal relationship; and (3) distribution pattern of pyroclastic‐flow deposits relative to drainage basins. Thus, studies of the Ebisutoge–Fukuda tephra have led to a depositional model of volcaniclastic resedimentation in distal areas after extremely large‐magnitude eruptions, an aspect of volcaniclastic deposits that has often been ignored or poorly understood. 相似文献
4.
《Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy》2000,25(9-11):719-724
Volcanological studies in the Bronze Age settlement of Akrotiri (Santorini, Greece) and in the Roman towns of Pompeii and Herculaneum (Vesuvius, Italy) provided information about the precursory phenomena preceding the Minoan and AD 79 plinian eruptions. Both the eruptions were characterised by seismic precursors with very different magnitudes and effects. The Minoan eruption was preceded by strong earthquake(s) that destroyed the Akrotiri settlement and forced an early evacuation of the island before the onset of the eruption. Instead, only some low magnitude shakings occurred before the AD 79 eruption of Vesuvius, which caught Roman towns and their inhabitants in the middle of their every-day life. Clear evidences of real volcanic precursors (both magmatic and phreatic) are not recorded in the deposits of the two eruptions. The onset of volcanic activity in both cases was represented by phreatomagmatic pulses of low energy shortly followed by the main eruption. 相似文献
5.
J. McPhie 《Australian Journal of Earth Sciences》2013,60(4):417-433
The Hianana Volcanics consist of bedded tuff and dacitic lava that form a locally mappable unit within the extensive, Late Permian silicic volcanic sequence of northeastern New South Wales. Principal components of the bedded tuff are crystal and volcanic lithic fragments ranging from coarse ash to lapilli, accompanied by variable amounts of fine ash matrix. Well denned plane parallel thin bedding is characteristic. Sandwave bed forms, including low‐angle cross‐beds and wavy beds, are confined to an area of 2–3 km2 coinciding with the thickest sections (70 m) of bedded tuff. A high‐aspect ratio flow of porphyritic dacitic lava overlies the bedded tuff in the same area. The setting, lithofacies, extent and geometry of the bedded tuffs of the Hianana Volcanics are comparable with modern tuff rings which are composed of the deposits from base surges generated by explosive phreatomagmatic eruptions at primary volcanic vents. Many of these have also discharged lava late in their activity. Proximal parts of the Hianana tuff ring were buried by the porphyritic lava after the phreatomagmatic eruptions had ceased. In more distal sections, the bedded tuff is less than 10 m thick and dominantly comprises fine grained, plane parallel, very thin beds and laminae; these features suggest an origin by fallout from ash clouds that accompanied the phreatomagmatic eruptions. The distal ash was covered and preserved from erosion by a layer of welded ignimbrite, the source of which is unknown. 相似文献
6.
Archean felsic volcanic rocks form a 2000 m thick succession stratigraphically below the Helen Iron Formation in the vicinity of the Helen Mine, Wawa, Ontario. Based on relict textures and structures, lateral and vertical facies changes, and fragment type, size and distribution, the felsic volcanic rocks have been subdivided into (a) lava flows and domes (b) hyalotuffs, (c) bedded pyroclastic flows, (d) massive pyroclastic flows, and (e) block and ash flows.Lava flows and domes are flow-banded, massive, and/or brecciated and occur throughout the stratigraphic succession. Dome/flow complexes are believed to mark the end of explosive eruptive cycles. Deposits interpreted as hyalotuffs are finely bedded and composed dominantly of ash-size material and accretionary lapilli. These deposits are interlayered with bedded pyroclastic flow deposits and probably formed from phreatomagmatic eruptions in a shallow subaqueous environment. Such eruptions led to the formation of tuff cones or rings. If these structures emerged they may have restricted the access of seawater to the eruptive vent(s), thus causing a change in eruptive style from short, explosive pulses to the establishment of an eruption column. Collapse of this column would lead to the accumulation of pyroclastic material within and on the flanks of the cone/ring structure, and to flows which move down the structure and into the sea. Bedded pyroclastic deposits in the Wawa area are thought to have formed in this manner, and are now composed of a thicker, more massive basal unit which is overlain by one or more finely bedded ash units. Based on bed thickness, fragment and crystal size, type and abundance, these deposits are further subdivided into central, proximal and distal facies.Central facies units consist of poorly graded, thick (30–80 m) basal beds composed of 23–60% lithic and 1–8% juvenile fragments. These are overlain by 1–4 thinner ash beds (2–25 cm). Proximal facies basal beds range from 2–35 m in thickness and are composed of 15–35% lithic and 4–16% juvenile fragments. Typically, lithic components are normally graded, whereas juvenile fragments are inversely graded. These basal beds are overlain by ash beds (2–14 in number) which range from 12 cm to 6 m in thickness. Distal basal beds, where present, are thin (1–2 m), and composed of 2–8% lithic and 6–21% juvenile fragments. Overlying ash beds range up to 40 in number.The climax of pyroclastic activity is represented by a thick (1000 m) sequence of massive, poorly sorted, pyroclastic flow deposits which are composed of 5–15% lithic fragments and abundant pumice. These deposits are similar to subaerial ash flows and appear to mark the rapid eruption of large volumes of material. They are overlain by felsic lavas and/or domes. Periodic collapse of the growing domes produced abundant coarse volcanic breccia. The overall volcanic environment is suggestive of caldera formation and late stage dome extrusion. 相似文献
7.
《International Geology Review》2012,54(17):2164-2183
ABSTRACTTephra fallout beds in marine sediments provide chronologically precise and highly resolved records of volcanism at time scales relevant to Quaternary climate cycles. While the record of discrete (visible) thin tephra beds is readily accessible, the significance of the dispersed (invisible) tephra record remains unclear. Here we evaluate the role of dispersed tephra for orbital-scale volcanic time variations in the Quaternary (<1.2 Ma) carbonate mud of IODP Hole U1437B (Northwest Pacific). The carbonate mud contains cyclic series of discrete fallout tephra beds from the oceanic Izu Bonin (~85% of tephra beds) and the continental Japan (~15%) volcanic arcs, respectively. Our results show the inorganic aluminosilicate (lithogenic) fraction is a mixture of dispersed Izu Bonin and Japan ash, and Asian dust. The time distribution of the Izu Bonin ash with its distinct composition appears to confirm and enhance the cyclic time variation of the discrete ash beds at Hole U1437B. Dispersed Japan ash resembles Asian dust in trace elements and is only distinguishable in Sr-Nd isotope space. Collectively, our results confirm the existence of periodic, orbital-scale fluctuations of arc volcanic frequency. Orbital-scale time variations of marine ash may be best established by series of discrete marine ash beds, yet the concomitant dispersed ash flux must also be recorded in order to understand the total flux of arc volcanic ash into the ocean basins and thus the role of the volcanism-climate link. 相似文献
8.
A tephra layer offers an isochronous surface in sediments, thus serving as a key bed and/or an age marker. Recent high-resolution sediment research (e.g. varved sediments) has revealed optically invisible tephra fingerprints and provided high-precision tephra ages. However, a tephra-based correlation cannot succeed without detailed knowledge of the tephra characteristics in a proximal area to correlate with tephra in high-resolution sediments in remote areas. Here we documented the detailed characteristics of Towada-Chuseri (To-Cu) tephra, which is associated with the Middle Holocene volcanic explosivity index 5 eruption of Towada volcano, northeast Japan. We used To-Cu tephra samples to achieve the proximal–distal correlation of three members: Chuseri pumice (Cu), Kanegasawa pumice (Kn) and Utarube ash (Ut). These distal occurrences correlate with proximal To-Cu tephra based on volcanic glass morphology and refractive index, as well as on major element composition of volcanic glass shards. Refractive indices allow the preliminary correlation of each member, and major element composition helps in distinguishing Ut from the other members. Glass morphology provides additional support. These correlations reveal that To-Cu, especially Cu, covered central to northeast Japan while confirming that To-Cu is the representative tephra in the Middle Holocene of the Tohoku region. 相似文献
9.
J. N. Pattan M. Shyam Prasad E. V. S. S. K. Babu 《Journal of Earth System Science》2010,119(4):531-539
We have identified an ash layer in association with Australasian microtektites of ∼0.77 Ma old in two sediment cores which
are ∼450 km apart in the central Indian Ocean Basin (CIOB). Morphology and chemical composition of glass shards and associated
microtektites have been used to trace their provenance. In ODP site 758 from Ninetyeast Ridge, ash layer-D (13 cm thick, 0.73–0.75
Ma) and layer-E (5 cm thick, 0.77–0.78 Ma) were previously correlated to the oldest Toba Tuff (OTT) eruptions of the Toba
caldera, Sumatra. In this investigation, we found tephra ∼3100 km to the southwest of Toba caldera that is chemically identical
to layer D of ODP site 758 and ash in the South China Sea correlated to the OTT. Layer E is not present in the CIOB or other
ocean basins. The occurrence of tephra correlating to layer D suggests a widespread distribution of OTT tephra (∼3.6 × 107 km2), an ash volume of at least ∼1800 km3, a total OTT volume of 2300 km3, and classification of the OTT eruption as a super-eruption. 相似文献
10.
Volcanic hazards assessments at andesite stratovolcanoes rely on the assessment of frequency and magnitude of past events. The identification and correlation of proximal and distal andesitic tephra, which record the explosive eruptive history, are integral to such assessments. These tephra are potentially valuable stratigraphic marker beds useful to the temporal correlation and age dating of Quaternary volcanic, volcaniclastic and epiclastic sedimentary deposits with which they are interbedded. At Mt Ruapehu (New Zealand) and Mt Rainier (USA), much of the detail of the recent volcanic record remains unresolved because of the difficulty in identifying proximal tephra. This study investigates the value of geochemical methods in discriminating andesitic tephra. Our dataset comprises petrological and geochemical analyses of tephra that span the late Quaternary eruptive record of each volcano. Our data illustrate that andesitic tephra are remarkably heterogeneous in composition. Tephra compositions fluctuate widely over short time intervals, and there are no simple or systematic temporal trends in geochemistry within either eruptive record. This complexity in tephra geochemistry limits the application of geochemical approaches to tephrostratigraphic studies, beyond a general characterisation useful to provenance assignation. Petrological and geochemical data suggest that the products of andesite systems are inherently variable and therefore intractable to discrimination by simple geochemical methods alone. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
11.
《第四纪科学杂志》2017,32(4):493-500
12.
Studies of recent eruptions have improved our understanding of volcanic ash transport and deposition, but have also raised important questions about the behaviour of far-travelled (distal) volcanic ash. In particular, it is difficult to reconcile estimates of distal ash mass and transport distance determined from eyewitness accounts, mapped deposits, satellite-based observations and cryptotephra records. Here we address this problem using data from well-characterized eruptions that, collectively, include all four data types. Data from recent eruptions allow us to relate eyewitness accounts to mapped deposits on the ground and satellite-based observations of ash in the air; observations from an historical eruption link eyewitness accounts to cryptotephra deposits. Together these examples show that (i) 10–20% of the erupted mass is typically deposited outside the mapped limits; (ii) estimates of the ash mass transported in volcanic clouds cannot account for all of this unmapped ash; and (iii) ash fall observed at distances beyond mapped deposits can have measurable impacts, and can form cryptotephra deposits with high (>~1000 cm−3) shard counts. We conclude that cryptotephra data can be incorporated into volcanological studies of ash transport and deposition and provide important insight into both the behaviour and impacts of far-travelled volcanic ash particles. 相似文献
13.
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
14.
Five widespread tephra layers are found in late Quaternary sediments (0–130,000 yr B.P.) of the Eastern Mediterranean Sea. These layers have been correlated among abyssal cores and to their respective terrestrial sources by electron-probe microanalysis of glass and pumice shards. Major element variations are sufficient to discriminate unambiguously between the five major layers. Oxygen isotope stratigraphy in one of the cores studied was used to data four of the five layers. Two of the widespread layers are derived from explosive eruptions of the Santorini volcanic complex: the Minoan Ash (3370 yr B.P.) and the Acrotiri Ignimbrite (18,000 yr B.P.). An additional layer, found in one core only, is most likely correlated to the Middle Pumice Series of Santorini (approximately 100,000 yr B.P.). Two layers are correlated to deposits on the islands of Yali and Kos and date to 31,000 and 120,000 yr B.P., respectively. One layer originated from the Neapolitan area of Italy 38,000 yr B.P. 相似文献
15.
四海龙湾玛珥湖沉积物中碱流质火山灰的来源及其意义 总被引：5，自引：1，他引：5
四海龙湾玛珥湖位于东北新生代龙岗火山区内,在玛珥湖沉积物距湖底69-70cm处分离出新鲜的火山灰。根据火山灰产出的层位、原生沉积特征、形貌和碱流质化学成分特征,属于长白山天池火山公元1199-1200年大喷发的产物。这一结果不仅表明天池火山历史时期大喷发的规模比原来估计的还要大,并且为建立千年以来四海龙湾沉积物及古气候演化的时间标尺提供了依据。 相似文献
16.
The 18.7 ka phreatomagmatic flank eruption on Etna (Italy): relationship between eruptive activity and sedimentary basement setting 总被引：1，自引：0，他引：1
This paper documents a phreatomagmatic flank eruption that occurred 18 700 ± 100 a BP , on the lower north-eastern slope of Etna during the Ellittico volcano activity, which produced fall and surge deposits. This type of eruption is connected to a sedimentary basement ridge at Etna. The interaction between the rising magma and the shallow groundwater hosted in the volcanic pile overlying the impermeable sediments resulted in phreatomagmatic instead of strombolian activity. Three eruptive phases are distinguished based on field and analytical data: (i) an explosive phreatomagmatic opening, (ii) a main phase producing coarse lithic-rich fallout and a strombolian deposit, and (iii) the final pulsating surge-forming phase. The discovery of this phreatomagmatic flank eruption, which occurred at lower altitude, raises important issues for previous hazard assessments at Etna. 相似文献
17.
长白山天池地区全新世以来火山活动及其特征 总被引：10，自引：0，他引：10
长白山火山全新世规模最大的喷发活动发生在公元1199-1200年,即800年前的大爆发,被确定为普林尼或布里尼(Plinian)式喷发。这次大爆发形成体积巨大的、分布广泛的以空中降落堆积物为主的火山喷发碎屑堆积物,在长白山火山周围,远至日本都留下了地质记录。文章辨认并划分了这次大爆发火山碎屑物的成因类型:火山喷发空中降落堆积物(airfalltephra)、火山碎屑流(pyroclasticflow)状堆积物和火山泥流(lahar)堆积物,并且点、面结合,近、远和国内、国外兼顾,分析了这些火山碎屑物的主要特征、分布和相互关系,进而确定这些火山碎屑物分别属于两次普林尼式爆发。第1次(早期)普林尼式爆发称赤峰期,火山喷发模式为:普林尼式喷发柱(赤峰空落浮岩层)-火山碎屑流(长白山火山碎屑流层),随即主要由火山碎屑流诱发火山泥流(二道白河火山泥流层);第2次(晚期)普林尼式爆发称园池期,喷发模式为:普林尼式喷发柱(园池空落浮岩火山灰层)-火山碎屑流(冰场火山碎屑流层)。在层序上将气象站期碱流岩置于800年前大爆发火山碎屑物之下是正确的,其时代为晚更新世-全新世早期。 相似文献
18.
A new study of the stratigraphy and composition of the Rocourt Tephra is performed at five sites in Belgium and brackets the age of the tephra between 90.3 and 74 ka. The volcanic glass grains have a typical shape of phreatomagmatic eruption products. A large set of tephra minerals were analyzed, namely clinopyroxene, orthopyroxene, amphibole, and Cr-spinel. The compositions of these minerals have been compared with the lava xenocrysts, megacrysts, and phenocrysts of the proximate Eifel volcanic province for which the origin has been determined (mantle xenoliths, high-pressure cumulates, and middle- to low-pressure magmatic phases). This allowed us to determine the likely origin of the tephra minerals. The Rocourt Tephra source could be a West Eifel volcano that was fed by a deep-seated magma batch rich in high- to middle-pressure minerals. 相似文献
19.
Plio-Pleistocene microtephra in DSDP site 231, Gulf of Aden 总被引：1，自引：0，他引：1
Sarah J. Feakins Francis H. Brown Peter B. deMenocal 《Journal of African Earth Sciences》2007,48(5):341-352
We reconstruct a Plio-Pleistocene microscopic tephrostratigraphy for DSDP Site 231 in the Gulf of Aden. Systematic microtephrostratigraphy increases the potential for identifying tephra horizons for regional stratigraphic correlation and age control, as well as providing information about eruptive histories. Microtephra reveal three main pulses of volcanism c. 4.0–3.2 Ma, 2.4 Ma and 1.7–1.3 Ma, corresponding to peaks in volcanic activity recorded in the East African Rift System. Previous studies of DSDP Site 231 have reported six visible tephra horizons (up to 25 cm thick) with geochemical compositions matching East African tuffs. We find 68 additional microtephra horizons through microscopic examination of 1050 samples (each integrating c. 3 ka) in over 200 m of marine sediments. We report the major and minor element geochemical compositions of individual glass shards in six of these microtephra horizons and establish a robust correlation at 168.73 m to the Lokochot Tuff (3.58 Ma), which together with previously identified tephra, provides a tightly constrained chronostratigraphy for the mid Pliocene. 相似文献
20.
Recent work on the weathering of high standing islands (HSI’s) of New Zealand (Goldsmith et al., 2008), Dominica (Goldsmith et al., 2010) Martinique and Guadeloupe (Rad et al., 2006) and portions of the Philippines (Schopka et al., 2011) shows weathering rates based on stream water chemistry for areas draining andesitic terrains are comparable to weathering rates determined for basaltic terrains, indicating that andesite weathering might be much more important in drawing down atmospheric CO2 than previously recognized. While an easily erodible parent material has been largely attributed to sustaining rates at these locations, little is known to known regarding its associated reaction kinetics. We conducted a series of batch dissolution experiments on andesitic material collected from ∼10,000 year old tephra deposits from Dominica to determine the dissolution rate of major and trace mineral phases to better understand geochemical processes controlling weathering flux from these areas. Dissolution experiments were conducted over a range of pH (4 and 7) on bulk samples and mineral separates.The dissolution rates based on Si release from the Dominica tephra bulk samples were similar, and ranged from 0.04 to 0.13 μmole Si/g-day in water, and ∼0.14 to 0.27 μmole Si/g-day in dilute acid (initial pH ∼4). Although the bulk of the ash is predominately composed of vesicular felsic (Na–Al–Si) volcanic glass, reaction rates and stoichiometry indicate ash dissolution is dominated by the reactivity of trace Mg or Ca-bearing silicate phases (olivine, pyroxene or amphiboles) and Ca–phosphate phases (apatite), especially under slightly acidic conditions. Analysis of reacted phases by SEM shows little evidence of alteration of glassy material, whereas surfaces of Ca–Mg inosilicates, olivine and apatite show etched features indicative of dissolution. Results of the dissolution experiments suggest that, although these phases are relatively minor components of the ash, they contribute disproportionately to the overall weathering flux, and their reactivity may be particularly important in areas where physical weathering and erosion are constantly exposing new fresh surfaces available for chemical reaction. 相似文献