Academic literature on the topic 'Tephra geochemistry'
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Journal articles on the topic "Tephra geochemistry"
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Matsu'ura, Tabito, Isoji Miyagi, and Akira Furusawa. "Late Quaternary cryptotephra detection and correlation in loess in northeastern Japan using cummingtonite geochemistry." Quaternary Research 75, no. 3 (May 2011): 624–35. http://dx.doi.org/10.1016/j.yqres.2010.12.004.
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AbstractWe detected late Pleistocene cummingtonite-bearing cryptotephras in loess deposits in NE Japan and correlated them with known tephras elsewhere by using major-element compositions of the cummingtonite. This is the first time cryptotephras have been identified by analysis of a crystal phase rather than glass shards. In central NE Japan, four cummingtonite-bearing tephras, the Ichihasama pumice, the Dokusawa tephra, the Naruko–Nisaka tephra, and the Adachi–Medeshima tephra, are present in late Pleistocene loess deposits. Because the cummingtonite chemistry of each tephra is different and characteristic, it is potentially a powerful tool for detecting and identifying cryptotephras. An unidentified cummingtonite-bearing cryptotephra previously reported to be present in the late Pleistocene loess deposits at Kesennuma (Pacific coast) did not correlate with any of the known cummingtonite-bearing tephras in central NE Japan, but instead with the Numazawa–Kanayama tephra (erupted from the Numazawa caldera, southern NE Japan), although Kesennuma is well beyond the previously reported area of the distribution of the Numazawa–Kanayama tephra. Three new cummingtonite-bearing cryptotephras in the mid and late Pleistocene loess deposits (estimated to be less than 82 ka, 100–200 ka, and ca. 250 ka) on the Isawa upland were also detected.
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Rabek, Karen, Michael T. Ledbetter, and Douglas F. Williams. "Tephrochronology of the Western Gulf of Mexico for the Last 185,000 Years." Quaternary Research 23, no. 3 (May 1985): 403–16. http://dx.doi.org/10.1016/0033-5894(85)90044-4.
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Tephra in 31 piston cores from the western Gulf of Mexico and 7 piston cores from the equatorial Pacific were analyzed by electron microprobe. Six ash layers in the western Gulf of Mexico were easily distinguished by TiO2, FeO, and CaO contents and correlated by geochemistry in order to determine the distribution pattern for each ash layer. Correlation by geochemistry is an easier, more accurate method than biostratigraphic correlation; some of the tephras were miscorrelated by biostratigraphy. The six tephras were dated by geochemical identification in a piston core with oxygen-isotope stratigraphy and the ages are Y5 (30,000 yr B.P.), Y6 (65,000 yr B.P.), Y8 (84,000 yr B.P.), X2 (110,000 yr B.P.), W1 (136,000 yr B.P.), and W2 (185,000 yr B.P.). Data from this study corroborated correlations of the Y8 tephra in the western Gulf of Mexico with the D layer in the eastern equatorial Pacific Ocean. None of the other five layers in the Gulf of Mexico, however, were found in the Pacific Ocean. The limited distribution of the Y5, Y6, X2, and W2 ash layers close to Mexico indicates possible sources in Mexico. Tephra from the late Pleistocene La Primavera pumice in Mexico, however, does not correlate with the marine tephra.
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Hopkins, Jenni L., Janine E. Bidmead, David J. Lowe, Richard J. Wysoczanski, Bradley J. Pillans, Luisa Ashworth, Andrew B. H. Rees, and Fiona Tuckett. "TephraNZ: a major- and trace-element reference dataset for glass-shard analyses from prominent Quaternary rhyolitic tephras in New Zealand and implications for correlation." Geochronology 3, no. 2 (September 23, 2021): 465–504. http://dx.doi.org/10.5194/gchron-3-465-2021.
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Abstract. Although analyses of tephra-derived glass shards have been undertaken in New Zealand for nearly four decades (pioneered by Paul Froggatt), our study is the first to systematically develop a formal, comprehensive, open-access reference dataset of glass-shard compositions for New Zealand tephras. These data will provide an important reference tool for future studies to identify and correlate tephra deposits and for associated petrological and magma-related studies within New Zealand and beyond. Here we present the foundation dataset for TephraNZ, an open-access reference dataset for selected tephra deposits in New Zealand. Prominent, rhyolitic, tephra deposits from the Quaternary were identified, with sample collection targeting original type sites or reference locations where the tephra's identification is unequivocally known based on independent dating and/or mineralogical techniques. Glass shards were extracted from the tephra deposits, and major- and trace-element geochemical compositions were determined. We discuss in detail the data reduction process used to obtain the results and propose that future studies follow a similar protocol in order to gain comparable data. The dataset contains analyses of glass shards from 23 proximal and 27 distal tephra samples characterising 45 eruptive episodes ranging from Kaharoa (636 ± 12 cal yr BP) to the Hikuroa Pumice member (2.0 ± 0.6 Ma) from six or more caldera sources, most from the central Taupō Volcanic Zone. We report 1385 major-element analyses obtained by electron microprobe (EMPA), and 590 trace-element analyses obtained by laser ablation (LA)-ICP-MS, on individual glass shards. Using principal component analysis (PCA), Euclidean similarity coefficients, and geochemical investigation, we show that chemical compositions of glass shards from individual eruptions are commonly distinguished by major elements, especially CaO, TiO2, K2O, and FeOtt (Na2O+K2O and SiO2/K2O), but not always. For those tephras with similar glass major-element signatures, some can be distinguished using trace elements (e.g. HFSEs: Zr, Hf, Nb; LILE: Ba, Rb; REE: Eu, Tm, Dy, Y, Tb, Gd, Er, Ho, Yb, Sm) and trace-element ratios (e.g. LILE/HFSE: Ba/Th, Ba/Zr, Rb/Zr; HFSE/HREE: Zr/Y, Zr/Yb, Hf/Y; LREE/HREE: La/Yb, Ce/Yb). Geochemistry alone cannot be used to distinguish between glass shards from the following tephra groups: Taupō (Unit Y in the post-Ōruanui eruption sequence of Taupō volcano) and Waimihia (Unit S); Poronui (Unit C) and Karapiti (Unit B); Rotorua and Rerewhakaaitu; and Kawakawa/Ōruanui, and Okaia. Other characteristics, including stratigraphic relationships and age, can be used to separate and distinguish all of these otherwise-similar tephra deposits except Poronui and Karapiti. Bimodality caused by K2O variability is newly identified in Poihipi and Tahuna tephras. Using glass-shard compositions, tephra sourced from Taupō Volcanic Centre (TVC) and Mangakino Volcanic Centre (MgVC) can be separated using bivariate plots of SiO2/K2O vs. Na2O+K2O. Glass shards from tephras derived from Kapenga Volcanic Centre, Rotorua Volcanic Centre, and Whakamaru Volcanic Centre have similar major- and trace-element chemical compositions to those from the MgVC, but they can overlap with glass analyses from tephras from Taupō and Okataina volcanic centres. Specific trace elements and trace-element ratios have lower variability than the heterogeneous major-element and bimodal signatures, making them easier to fingerprint geochemically.
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Payne, Richard, Jeffrey Blackford, and Johannes van der Plicht. "Using cryptotephras to extend regional tephrochronologies: An example from southeast Alaska and implications for hazard assessment." Quaternary Research 69, no. 1 (January 2008): 42–55. http://dx.doi.org/10.1016/j.yqres.2007.10.007.
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Cryptotephrochronology, the use of hidden, diminutive volcanic ash layers to date sediments, has rarely been applied outside western Europe but has the potential to improve the tephrochronology of other regions of the world. Here we present the first comprehensive cryptotephra study in Alaska. Cores were extracted from five peatland sites, with cryptotephras located by ashing and microscopy and their glass geochemistry examined using electron probe microanalysis. Glass geochemical data from nine tephras were compared between sites and with data from previous Alaskan tephra studies. One tephra present in all the cores is believed to represent a previously unidentified eruption of Mt. Churchill and is named here as the ‘Lena tephra’. A mid-Holocene tephra in one site is very similar to Aniakchak tephra and most likely represents a previously unidentified Aniakchak eruption, ca. 5300–5030 cal yr BP. Other tephras are from the late Holocene White River eruption, a mid-Holocene Mt. Churchill eruption, and possibly eruptions of Redoubt and Augustine volcanoes. These results show the potential of cryptotephras to expand the geographic limits of tephrochronology and demonstrate that Mt. Churchill has been more active in the Holocene than previously appreciated. This finding may necessitate reassessment of volcanic hazards in the region.
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Begét, James E., Richard D. Reger, DeAnne Pinney, Tom Gillispie, and Kathy Campbell. "Correlation of the Holocene Jarvis Creek, Tangle Lakes, Cantwell, and Hayes Tephras in South-Central and Central Alaska." Quaternary Research 35, no. 2 (March 1991): 174–89. http://dx.doi.org/10.1016/0033-5894(91)90065-d.
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AbstractThe geochemistry, petrography, and distribution of the Jarvis Creek Ash (Péwé, 1965, 1975a) indicate that this tephra from the lower Delta River area of central Alaska is correlative with vol volcanic ash from sites in south-central Alaska near Tangle Lakes (upper Delta River area) and the Cantwell ash from Hayes volcano found in the upper Nenana River area (Riehle et al., 1990). Volcanic glass compositions of distal Jarvis Creek and Tangle Lakes tephra samples are compositionally restricted, while several discrete glass populations are present in some samples are compositionally collected nearer Hayes volcano. These correlations extend the known distribution of Hayes volcano tephras across the Alaska Range and into central Alaska, a distance of more than 650 km. New geochronologic data for the Jarvis Creek Ash suggest it was deposited ca. 3660 ± 125 yr B.P., consistent with previous age estimates of tephra eruptions at the Hayes volcano. The name “Jarvis Creek Ash” has well-established priority with respect to “Cantwell ash” or other local names for this tephra layer from the Hayes volcano.
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Herrmann, Achim D., John T. Haynes, Richard M. Robinet, and Norlene R. Emerson. "Machine Learning Applied to K-Bentonite Geochemistry for Identification and Correlation: The Ordovician Hagan K-Bentonite Complex Case Study." Geosciences 11, no. 9 (September 9, 2021): 380. http://dx.doi.org/10.3390/geosciences11090380.
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Altered tephras (K-bentonites) are of great importance for calibration of the geologic time scale, for local, regional, and global correlations, and paleoenvironmental reconstructions. Thus, definitive identification of individual tephras is critical. Single crystal geochemistry has been used to differentiate tephra layers, and apatite is one of the phenocrysts commonly occurring in tephras that has been widely used. Here, we use existing and newly acquired analytical datasets (electron probe micro-analyzer [EPMA] data and laser ablation ICP-MS [LA-ICP-MS] data, respectively) of apatite in several Ordovician K-bentonites that were collected from localities about 1200 km apart (Minnesota/Iowa/Wisconsin and Alabama, United States) to test the use of machine-learning (ML) techniques to identify with confidence individual tephra layers. Our results show that the decision tree based on EPMA data uses the elemental concentration patterns of Mg, Mn, and Cl, consistent with previous studies that emphasizes the utility of these elements for distinguishing Ordovician K-bentonites. Differences in the experimental setups of the analyses, however, can lead to offsets in absolute elemental concentrations that can have a significant impact on the correct identification and correlation of individual K-bentonite beds. The ML model using LA-ICP-MS data was able to identify several K-bentonites in the southern Appalachians and establish links to K-bentonites samples from the Upper Mississippi Valley. Furthermore, the ML model identified individual layers of multiphase eruptions, thus illustrating very well the great potential of applying ML techniques to tephrochronology.
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Schiller, M., W. W. Dickinson, N. A. Iverson, and J. A. Baker. "A re-evaluation of the Hart Ash, an important stratigraphic marker: Wright Valley, Antarctica." Antarctic Science 31, no. 3 (April 26, 2019): 139–49. http://dx.doi.org/10.1017/s0954102019000129.
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AbstractReliably dated surficial deposits for reconstructing palaeoclimate are rare in the McMurdo Dry Valleys of Antarctica. While many tephra have been found and dated, none is well characterized. In the Wright Valley, the Hart Ash is poorly dated and described. This paper reports profiles through tephra, the chemical signature of the glass shards and new high-precision multi-crystal laser fusion of 40Ar/39Ar ages. Major and trace element analyses of glass shards indicate the tephra are phonolitic and most probably sourced from Mount Discovery in the Erebus volcanic province. Two chemically distinct and stratigraphically separate tephra layers within the Hart Ash were found in three closely spaced soil profiles. The complex stratigraphy between these profiles could not be delineated without the geochemistry of the tephra. Importantly, our data suggest that only one tephra may be an in situ fall-out deposit, which gave a robust age of 2.97 ± 0.02 Ma. This new age for the Hart Ash tephra, which is 10 cm thick and is preserved at the current surface, provides a maximum age for surface deposits in the lower Wright Valley. This study highlights that well-characterized tephra enhance stratigraphic correlations in the Dry Valleys and improve the accuracy of palaeoenvironmental interpretations.
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Maier, Katherine L., Emma Gatti, Elmira Wan, Daniel J. Ponti, Mark Pagenkopp, Scott W. Starratt, Holly A. Olson, and John C. Tinsley. "Quaternary Tephrochronology and Deposition in the Subsurface Sacramento–San Joaquin Delta, California, U.S.A." Quaternary Research 83, no. 2 (March 2015): 378–93. http://dx.doi.org/10.1016/j.yqres.2014.12.007.
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We document characteristics of tephra, including facies and geochemistry, from 27 subsurface sites in the Sacramento–San Joaquin Delta, California, to obtain stratigraphic constraints in a complex setting. Analyzed tephra deposits correlate with: 1) an unnamed tephra from the Carlotta Formation near Ferndale, California, herein informally named the ash of Wildcat Grade (<~1.450 to >~ 0.780 Ma), 2) the Rockland ash bed (~ 0.575 Ma), 3) the Loleta ash bed (~ 0.390 Ma), and 4) middle Pleistocene volcanic ash deposits at Tulelake, California, and Pringle Falls, Bend, and Summer Lake, Oregon, herein informally named the dacitic ash of Hood (<~0.211 to >~ 0.180 Ma). All four tephra are derived from Cascades volcanic sources. The Rockland ash bed erupted from the southern Cascades and occurs in up to > 7-m-thick deposits in cores from ~ 40 m subsurface in the Sacramento–San Joaquin Delta. Tephra facies and tephra age constraints suggest rapid tephra deposition within fluvial channel and overbank settings, likely related to flood events shortly following volcanic eruption. Such rapidly deposited tephra are important chronostratigraphic markers that suggest varying sediment accumulation rates in Quaternary deposits below the modern Sacramento–San Joaquin Delta. This study provides the first steps in a subsurface Quaternary stratigraphic framework necessary for future hazard assessment.
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Bennett, K. D. "Tephra geochemistry: a comment on Hunt and Hill." Holocene 4, no. 4 (December 1994): 435–38. http://dx.doi.org/10.1177/095968369400400412.
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Begét, James E., and Mary J. Keskinen. "Trace-element geochemistry of individual glass shards of the Old Crow tephra and the age of the Delta glaciation, central Alaska." Quaternary Research 60, no. 1 (July 2003): 63–69. http://dx.doi.org/10.1016/s0033-5894(03)00095-4.
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AbstractTwo widespread tephra deposits constrain the age of the Delta Glaciation in central Alaska. The Old Crow tephra (ca. 140,000 ± 10,000 yr), identified by electron microprobe and ion microprobe analyses of individual glass shards, overlies an outwash terrace coeval with the Delta glaciation. The Sheep Creek tephra (ca. 190,000 yr) is reworked in alluvium of Delta age. The upper and lower limiting tephra dates indicate that the Delta glaciation occurred during marine oxygen isotope stage 6. We hypothesize that glaciers in the Delta River Valley reached their maximum Pleistocene extent during this cold interval because of significant mid-Pleistocene tectonic uplift of the east-central Alaska Range.
Dissertations / Theses on the topic "Tephra geochemistry"
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Atkins, M. "A geochemical and geochronological study of U and Th radioisotopes in paleosols, loess and tephra : A Middle-Rhine case study." Thesis, University of Reading, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370805.
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Pickett, Rachel Cara. "A tephra-dated record of palaeoenvironmental change since ~ 5,500 years ago from Lake Rotorua, North Island, New Zealand." The University of Waikato, 2008. http://hdl.handle.net/10289/2521.
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A palaeolimnological study was carried out on a high-resolution, 7.62 m-long core (RU188-07) from northern Lake Rotorua, North Island. The core consists predominantly of olive diatomaceous ooze, laminated in places, and contains five tephras including Tarawera (1886 A.D.), Kaharoa (c. 1314 A.D.), Taupo (c. 233 A.D.) and Whakatane (c. 5500 cal. years B.P.). The core terminated in Whakatane Tephra giving the sediment a maximum age of 5530 60 cal. years B.P. An age model for the sediment was developed using tephrochronology. Radiocarbon dates obtained on the sediment returned ages too old because of contamination by old CO2 or CH4, or both. Investigations carried out on the core included spectrophotometric, sedimentological and geochemical analyses, and diatom identifications, which provided a number of proxies from which inferences were made about lake history, catchment development, and palaeoclimate since c. 5500 cal. years B.P. The laminations, evident only in the upper, post-Kaharoa Tephra part of the record, comprise alternations of thin, dark, detrital deposits and pale, relatively fine-grained diatom assemblages. Sediment geochemistry indicates that the Rotorua catchment has undergone several changes since c. 5500 cal. years B.P., alternating between periods of variable and stable environmental conditions. Following the Whakatane and Waimihia eruptions and up to approximately 3000 cal. years B.P., the catchment surrounding Lake Rotorua was rather unstable. Fluctuations in many of the proxies during this period are likely to be associated with a variable climate with periods of storminess, coinciding with the establishment of ENSO conditions in New Zealand. A notable feature of the record is two phases of stability, the first following the Taupo eruption (from c. 1700 cal. years B.P. to c. 630 cal. years B.P.) and the second from c. 580 cal. years B.P. to c. 300 cal. years B.P. The latest, most significant event in the catchment history of Lake Rotorua was the settlement by Polynesians. M.S. McGlone implied from pollen profiles (from Holden's Bay) that initial settlement took place around the time of the Kaharoa eruption (c. 630 cal years B.P.; c. 1314 A.D.), but the sediment chemistry and erosion profiles obtained here, from the northern part of Lake Rotorua, indicate that although there may have been some early clearing in the northern catchment for tracks or buildings, large-scale clearing in the area probably did not occur until considerably later, c. 300 cal. years B.P. Also contained within the sediments are three layers of reworked tephric material that probably originate from the transfer of coarse grained tephra from shallow to deeper water during large storms at c. 1300 cal. years B.P, c. 520 cal. years B.P, and c. 220 cal. years B.P. Each event coincides with storm events inferred from records from Lake Tutira in eastern North Island. Because of Lake Rotorua's inland position, these inferred storm events probably represent only the largest cyclonic events (e.g. ex-tropical cyclones).
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Hannon, Jeffrey S. "Reconstructing the Generation, Evolution, and Migration of Arc Magmatism using the Whole-rock Geochemistry of Bentonites: A Case Study from the Cretaceous Idaho-Farallon Arc System." University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1613745220524224.
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David, Brian T. ""Chemical fingerprinting" of volcanic tephra found in Kansas using trace elements." Thesis, Manhattan, Kan. : Kansas State University, 2009. http://hdl.handle.net/2097/1413.
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Walkup, Laura Casey. "TEPHROSTRATIGRAPHIC AND GEOCHEMICAL INVESTIGATION OF COMPOSITIONALLY HETEROGENEOUS SILICIC TEPHRA IN THE MIDDLE AWASH REGION, AFAR, ETHIOPIA." Miami University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=miami1375966531.
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Matthews, Naomi Elizabeth. "Magma chamber assembly and dynamics of a supervolcano : Whakamaru, Taupo Volcanic Zone, New Zealand." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:71fedeaf-7153-4a7d-9113-9f32071ec721.
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This thesis employs crystal-specific techniques, combined with field observations, petrology, geochemistry and numerical modelling to reconstruct the magmatic system associated with the ~ 340 ka Whakamaru supereruption, New Zealand. Comparisons are drawn with the ~ 74 ka Youngest Toba Tuff (YTT) supereruption. Whakamaru Group Ignimbrites contain five pumice types, characterised by different mineralogies and crystal contents. Pumice petrography and geochemistry indicate that basaltic magma mixing occurred, possibly triggering eruption. Geothermobarometers suggest an eruption temperature of ~ 770°C and magma storage at ~ 5 km depth. High-resolution thermal records from Ti-in-quartz analysis indicate a thermal pulse of ~ 100°C prior to eruption. Diffusion timescales show multiple recharge events with the most significant event occurring ~ 35 y prior to eruption. Zircon U-Pb data show that most crystallisation occurred at ~ 400 ka, with antecrysts and xenocrysts incorporated. Zircon trace-element data suggest multiple recharge events and complex mixing over ~ 100 ky, consistent with an incrementally growing reservoir. Oxygen-isotope data illustrate that zircon, quartz and feldspar crystallised together in equilibrium, with isotopically homogenous magma sources feeding the reservoir over time. Whakamaru and YTT tephra thickness and grain-size data were used in ash dispersal modelling. Results indicate the YTT eruption had a ~ 35 km column height and erupted volumes of 1500 – 1900 km³, with deposition from a co-ignimbrite phase; whereas Whakamaru had a Plinian column ~ 45 km high with SE dispersal and a minimum volume of ~ 400 km³. The widespread dispersal of large volumes of fine ash from both eruptions would have had global environmental consequences. The data are integrated to reconstruct a new Whakamaru magma reservoir model. The complex crystal records indicate the system was characterised by long periods of incremental assembly, mixing, recycling of material, and reactivation during multiple recharge episodes which perturbed the system and primed the magma for eruption.
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Bramham, Law Cassian. "The role of aquatic systems and the re-occupation and settlement of the North European Plain during the Lateglacial." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:4e9960f9-29d9-4cf3-af14-097cd50a51e4.
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The Lateglacial between ∼14,600 - 11,500 cal yr BP is characterised by the rapid fluctuation of climatic conditions following the termination of the Last Glacial Maximum. During this period, the North European Plain (NEP) was re-occupied and settled by hunter-gather groups utilising a succession of lithic technocomplexes. Contrasting models of population expansion exist to explain the re-occupation of the NEP by ∼14,600 cal yr BP. Both rapid climatic amelioration and increased food resource availability on the NEP are suggested as possible stimuli. Studies of food resource availability as a stimulus for re-occupation and settlement of the NEP have long been dominated by the prevailing view that large mammal hunting was the dominant subsistence strategy. A number of archaeological finds across the NEP however, suggest that the exploitation of aquatic resources such as fish may have played a role in a more varied subsistence strategy during the period ∼14,600 - 11,500 cal yr BP. This thesis sets out to examine the development of palaeolake systems and examine their potential as a resource base for Lateglacial hunter-gatherers. This is achieved through the analysis of sedimentary organic matter and cladoceran records from five Lateglacial sites in northern Germany and southern Denmark, providing important information on basin development and the presence or absence of fish. The results suggest that significant variability existed in the development and resource availability of the basins over a local scale. Observed variability in the organic matter and cladoceran records within chronozone boundaries suggests that the Lateglacial – Holocene development of aquatic systems across the NEP cannot be solely explained by external climate change, and that local environmental and ecological factors are likely to have played a major part in their development. This thesis demonstrates that the local variance in aquatic conditions and fish populations would have offered, at best, limited and ephemeral resource availability and were therefore unlikely to have formed a major resource base for hunter-gatherer groups across the NEP. It is more likely that lakes were exploited opportunistically and as such formed only a minor component of a subsistence strategy more focussed on large mammal hunting.
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Caron, Benoît. "EMISSION DE CENDRES PENDANT L'ACTIVITE EXPLOSIVE DES VOLCANS ITALIENS EN ZONE DISTALE : ESTIMATION, CARACTERISATION PHYSICO-CHIMIQUE ET CONTRUCTION D'UNE BASE DE DONNEE POUR MIEUX EVALUER LES ALEAS VOLCANIQUES DANS LE SUD DE L'ITALIE." Phd thesis, Université Paris Sud - Paris XI, 2010. http://tel.archives-ouvertes.fr/tel-00545633.
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En plus de la destruction des sites à proximités des volcans, l'accumulation de cendres volcaniques dans les zones distales peut causer de graves dommages. De plus l'évaluation de ces dangers n'est pas pleinement prise en compte dans les plans de mitigation actuels. L'étude de la dispersion des retombées pyroclastiques produites par les éruptions explosives des volcans Italiens lors du Quaternaire est le sujet de cette thèse. L'étude tephrostratigraphique de trois carottes lacustres des lacs de Shkodra et Ohrid (Albanie) et d'une carotte marine du Nord de la mer Ionienne a été réalisée. Dix-sept niveaux de tephra ont été corrélés aux éruptions explosives de A.D. 472, Avellino (3.9 cal. ka BP) du Vésuve, Monte Pilato (A.D.1200), Gabellotto-Fiumebianco (8.6 cal ka BP) et Monte Guardia (22 ka BP) de l'île de Lipari, FL (3.4 cal. ka BP) de l'Etna, Astroni (4.2 cal. ka BP), Agnano Monte Spina (4.5 cal. ka BP), Agnano Pomici Principali (12.3 cal. ka BP), SMP1-Y3 (31 ka) et l'Ignimbrite Campanienne-Y5 (39 ka) des Champs Phlégréens, X6 (107 ka) de la région Campanienne, et de P11 (131 ka) de l'île de Pantelleria. Cinq autres niveaux de tephra possèdent la composition que les dépôts de l'éruption vésuvienne de Mercato. Cela suggère une activité explosive entre les éruptions pliniennes de Mercato (8.9 cal ka BP) et Avellino (3.9 cal ka BP). Toutes ces données ont été intégrées, avec les données préexistantes de la littérature, dans la banque de données d'un SIG. Cette banque de données couplée à un SIG permet de grandement améliorer les dispersions des cendres et représente un outil qui améliore la mitigation des risques volcaniques dans la région centrale de la Méditerranée.
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"Tephrostratigraphy of Pliocene Drill Cores from Kenya and Ethiopia, and Pleistocene Exposures in the Ledi-Geraru Research Project Area, Ethiopia: Geological Context for the Evolution of Australopithecus and Homo." Doctoral diss., 2019. http://hdl.handle.net/2286/R.I.53904.
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abstract: East African extensional basins have played a crucial role in revealing the evolution and characteristics of the early stages of continental rifting and for providing the geological context of hominin evolution and innovation. The numerous volcanic eruptions, rapid sedimentation and burial, and subsequent exposure through faulting and erosion, provide excellent conditions for the preservation of tectonic history, paleoenvironment data, and vertebrate fossils. The reconstruction of depositional environments and provision of geochronologic frameworks for hominin sites have been largely provided by geologic investigations in conjunction with paleontological studies, like the Ledi-Geraru Research Project (LGRP). High-resolution paleoclimate records that can be directly linked to hominin fossil outcrops have been developed by the Hominin Sites and Paleolakes Drilling Project (HSPDP) which collected sedimentary-paleolake cores at or near key hominin fossil sites.
Two chapters of this dissertation are a result of research associated with the HSPDP. For HSPDP, I establish a tephrostratigraphic framework for the drill cores from the Northern Awash (Afar, Ethiopia) and Baringo-Tugen Hills-Barsemoi (Kenya) HSPDP sites. I characterize and fingerprint tephra through glass shard and feldspar phenocryst geochemistry. From tephra geochemical analyses, I establish chronostratigraphic ties between the HSPDP cores’ high-resolution paleoclimate records to outcrop stratigraphy which are associated with hominin fossils sites.
Three chapters of this dissertation are a result of field work with the LGRP. I report new geological investigations (stratigraphic, tectonic, and volcanic) of two previously unmapped regions from the eastern Ledi-Geraru (ELG), Asboli and Markaytoli. Building upon this research I present interpretations from tephra analyses, detailed stratigraphic analyses, and geologic mapping, of the Pleistocene (~2.6 to < 2.45 Ma) basin history for the LGRP. My work with the LGRP helps to reconstruct a more complete Early Pleistocene depositional and geologic history of the lower Awash Valley.
Overall, this dissertation contributes to the reconstruction of hominin paleoenvironments and the geochronological framework of the Pliocene and Pleistocene faunal/hominin records. It further contributes to rift basin history in East Africa by elaborating the later structural and stratigraphic history of the lower Awash region.Dissertation/Thesis
Doctoral Dissertation Geological Sciences 2019
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Innocenti, Sabrina. "Lavas and tephras of Merapi volcano,Java, Indonesia insights from textural analyses and geochemistry /." 2006. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-1695/index.html.
Full textBook chapters on the topic "Tephra geochemistry"
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Bitschene, Peter Rene, and Hans-Ulrich Schmincke. "Fallout Tephra Layers: Composition and Significance." In Sediments and Environmental Geochemistry, 48–82. Berlin, Heidelberg: Springer Berlin Heidelberg, 1990. http://dx.doi.org/10.1007/978-3-642-75097-7_4.
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Zimmerman, S. R. H., S. R. Hemming, and S. W. Starratt. "Holocene sedimentary architecture and paleoclimate variability at Mono Lake, California." In From Saline to Freshwater: The Diversity of Western Lakes in Space and Time. Geological Society of America, 2019. http://dx.doi.org/10.1130/2020.2536(19).
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ABSTRACT Mono Lake occupies an internally drained basin on the eastern flank of the Sierra Nevada, and it is sensitive to climatic changes affecting precipitation in the mountains (largely delivered in the form of snowpack). Efforts to recover cores from the lake have been impeded by coarse tephra erupted from the Mono Craters, and by disruption of the lake floor due to the uplift of Paoha Island ~300 yr ago. In this study, we describe the stratigraphy of cores from three recent campaigns, in 2007, 2009, and 2010, and the extents and depths of the tephras and disturbed sediments. In the most successful of these cores, BINGO-MONO10-4A-1N (BINGO/10-4A, 2.8 m water depth), we used core stratigraphy, geochemistry, radiocarbon dates, and tephrostratigraphy to show that the core records nearly all of the Holocene in varying proportions of detrital, volcanic, and authigenic sediment. Both the South Mono tephra of ca. 1350 cal yr B.P. (calibrated years before A.D. 1950) and the 600-yr-old North Mono–Inyo tephra are present in the BINGO/10-4A core, as are several older, as-yet-unidentified tephras. Laminated muds are inferred to indicate a relatively deep lake (³10 m over the core site) during the Early Holocene, similar to many records across the region during that period. The Middle and Late Holocene units are more coarsely bedded, and coarser grain size and greater and more variable amounts of authigenic carbonate detritus in this interval are taken to suggest lower lake levels, possibly due to lower effective wetness. A very low lake level, likely related to extreme drought, is inferred to have occurred sometime between 3500 and 2100 cal yr B.P. This interval likely corresponds to the previously documented Marina Low Stand and the regional Late Holocene Dry Period. The BINGO/10-4A core does not preserve a complete record of the period encompassing the Medieval Climate Anomaly, the Little Ice Age, and the historical period, probably due to erosion because of its nearshore position.
Conference papers on the topic "Tephra geochemistry"
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Garcia, Michael O., Adonara Mucek, Donald A. Swanson, Kendra Lynn, and Aaron J. Pietruszka. "GEOCHEMISTRY OF KEANAKĀKO‘I TEPHRA FROM KĪLAUEA VOLCANO, HAWAI‘I." In GSA Annual Meeting in Denver, Colorado, USA - 2016. Geological Society of America, 2016. http://dx.doi.org/10.1130/abs/2016am-280876.
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