11 results for Alloway, Brent V.

  • Colin George Vucetich (1918–2007)—pioneering New Zealand tephrochronologist

    Lowe, David J.; Tonkin, Philip J.; Neall, Vincent E.; Palmer, Alan S.; Alloway, Brent V.; Froggatt, Paul C. (2008)

    Journal article
    University of Waikato

    Many Quaternarists, tephrochronologists, and soil scientists mourned the passing in New Zealand of Colin Vucetich—gentle mentor, pedologist, and pioneering tephrochronologist—on 25 April (Anzac Day), 2007. Colin was in his 89th year. As well as forming a 25-year partnership with W.A. “Alan” Pullar, with whom he published three classic papers on tephrostratigraphy based on field work undertaken by the pair largely in their own time, Colin inspired and mentored numerous postgraduates in his later career as an academic at Victoria University of Wellington. There he taught pedology, soil stratigraphy, and tephrochronology until his retirement as Reader (Associate Professor) in 1982. In retirement he was an honorary lecturer and supervisor at Massey University (Palmerston North) until 1991 (Fig. 1, Fig. 2 and Fig. 3).

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  • Fingerprints and age models for widespread New Zealand tephra marker beds erupted since 30,000 years ago: a framework for NZ-INTIMATE

    Lowe, David J.; Shane, Phil A.R.; Alloway, Brent V.; Newnham, Rewi M. (2008-01)

    Journal article
    University of Waikato

    The role of tephras in the NZ-INTIMATE project is a critical one because most high-resolution palaeoclimatic records are linked and dated by one or more tephra layers. In this review, first we document eruptive, distributional, and compositional fingerprinting data, both mineralogical and geochemical, for 22 key marker tephras erupted since 30,000 years ago to facilitate their identification and correlation. We include new glass compositional data. The selected marker tephras comprise 10 from Taupo and nine from Okataina volcanoes (rhyolitic), one from Tuhua volcano (peralkaline rhyolitic), and one each from Tongariro and Egmont volcanoes (andesitic). Second, we use four approaches to develop 2σ-age models for the tephras (youngest to oldest): (1) calendar ages for Kaharoa and Taupo/Y were obtained by wiggle-matching log-derived tree-ring sequences dated by 14C; (2) Whakaipo/V was dated using an age–depth model from peat; (3) 14 tephras in the montane Kaipo peat sequence (Waimihia/S, Unit K, Whakatane, Tuhua, Mamaku, Rotoma, Opepe/E, Poronui/C, Karapiti/B, Okupata, Konini, Waiohau, Rotorua, Rerewhakaaitu) were dated by simultaneously wiggle-matching stratigraphic position and 51 independent 14C-age points against IntCal04 using Bayesian probability methods via both OxCal and Bpeat; and (4) the five oldest tephras, erupted before ca 18,000 cal. yr BP, were dated by calibrating limited numbers of 14C ages using IntCal04 (Okareka) or comparison curves of the expanded Cariaco Basin sequence (Te Rere, Kawakawa/Oruanui, Poihipi, Okaia). Kawakawa/Oruanui tephra, the most widely distributed marker tephra, was erupted probably ca 27,097±957 cal. yr BP. Potential dating approaches for the older tephras include their identification in Antarctic ice cores (if present) or annually laminated sediments for which robust calendar-age models have been constructed, high-precision AMS 14C dating on appropriate material from environmentally stable sites, systematic luminescence dating, or new radiometric techniques (e.g. U–Th/He) if suitable minerals are available and errors markedly reduced. Further application of Bayesian age-modelling to stratigraphic sequences of 14C ages, possibly augmented with luminescence ages, may help refine age models for pre-Holocene tephras with the largest errors. Finally, we discuss the critical role these marker tephras play in the ongoing construction of an event stratigraphy for the New Zealand region, which is a key objective of Australasian and Southern Hemisphere INTIMATE projects.

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  • Towards a climate event stratigraphy for New Zealand over the past 30,000 years (NZ-INTIMATE project)

    Alloway, Brent V.; Lowe, David J.; Barrell, David J.A.; Newnham, Rewi M.; Almond, Peter C.; Augustinus, Paul Christian; Bertler, Nancy A.N.; Carter, Lionel; Litchfield, Nicola J.; McGlone, Matt S.; Shulmeister, Jamie; Vandergoes, Marcus J.; Williams, Paul W.; NZ-INTIMATE members (2007-01)

    Journal article
    University of Waikato

    It is widely recognised that the acquisition of high-resolution palaeoclimate records from southern mid-latitude sites is essential for establishing a coherent picture of inter-hemispheric climate change and for better understanding of the role of Antarctic climate dynamics in the global climate system. New Zealand is considered to be a sensitive monitor of climate change because it is one of a few sizeable landmasses in the Southern Hemisphere westerly circulation zone, a critical transition zone between subtropical and Antarctic influences. New Zealand has mountainous axial ranges that amplify the climate signals and, consequently, the environmental gradients are highly sensitive to subtle changes in atmospheric and oceanic conditions. Since 1995, INTIMATE has, through a series of international workshops, sought ways to improve procedures for establishing the precise ages of climate events, and to correlate them with high precision, for the last 30 000 calendar years. The NZ-INTIMATE project commenced in late 2003, and has involved virtually the entire New Zealand palaeoclimate community. Its aim is to develop an event stratigraphy for the New Zealand region over the past 30 000 years, and to reconcile these events against the established climatostratigraphy of the last glacial cycle which has largely been developed from Northern Hemisphere records (e.g. Last Glacial Maximum (LGM), Termination I, Younger Dryas). An initial outcome of NZ-INTIMATE has been the identification of a series of well-dated, high-resolution onshore and offshore proxy records from a variety of latitudes and elevations on a common calendar timescale from 30 000 cal. yr BP to the present day. High-resolution records for the last glacial coldest period (LGCP) (including the LGM sensu stricto) and last glacial-interglacial transition (LGIT) from Auckland maars, Kaipo and Otamangakau wetlands on eastern and central North Island, marine core MD97-2121 east of southern North Island, speleothems on northwest South Island, Okarito wetland on southwestern South Island, are presented. Discontinuous (fragmentary) records comprising compilations of glacial sequences, fluvial sequences, loess accumulation, and aeolian quartz accumulation in an andesitic terrain are described. Comparisons with ice-core records from Antarctica (EPICA Dome C) and Greenland (GISP2) are discussed. A major advantage immediately evident from these records apart from the speleothem record, is that they are linked precisely by one or more tephra layers. Based on these New Zealand terrestrial and marine records, a reasonably coherent, regionally applicable, sequence of climatically linked stratigraphic events over the past 30 000 cal. yr is emerging. Three major climate events are recognised: (1) LGCP beginning at ca. 28 000 cal. yr BP, ending at Termination I, ca. 18 000 cal. yr BP, and including a warmer and more variable phase between ca. 27 000 and 21 000 cal. yr BP, (2) LGIT between ca. 18 000 and 11 600 cal. yr BP, including a Lateglacial warm period from ca. 14 800 to 13 500 cal. yr BP and a Lateglacial climate reversal between ca. 13 500 and 11 600 cal. yr BP, and (3) Holocene interglacial conditions, with two phases of greatest warmth between ca. 11 600 and 10 800 cal. yr BP and from ca. 6 800 to 6 500 cal. yr BP. Some key boundaries coincide with volcanic tephras.

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  • Tephrochronology of last termination sequences in Europe: a protocol for improved analytical precision and robust correlation procedures (a joint SCOTAV–INTIMATE proposal)

    Turney, Chris S.M.; Lowe, J. John; Davies, Siwan M.; Hall, Valerie; Lowe, David J.; Wastegard, Stefan; Hoek, Wim Z.; Alloway, Brent V. (2004)

    Journal article
    University of Waikato

    The precise sequence of events during the Last Termination (18 000–9000 ka 14C yr BP), and the extent to which major environmental changes were synchronous, are difficult to establish using the radiocarbon method alone because of serious distortions of the radiocarbon time-scale, as well as the influences of site-specific errors that can affect the materials dated. Attention has therefore turned to other methods that can provide independent tests of the chronology and correlation of events during the Last Termination. With emphasis on European sequences, we summarise here the potential of tephrostratigraphy and tephrochronology to fulfil this role. Recent advances in the detection and analysis of ‘hidden’ tephra layers (cryptotephra) indicate that some tephras of Last Termination age are much more widespread in Europe than appreciated hitherto, and a number of new tephra deposits have also been identified. There is much potential for developing an integrated tephrochronological framework for Europe, which can help to underpin the overall chronology of events during the Last Termination. For that potential to be realised, however, there needs to be a more systematic and robust analysis of tephra layers than has been the practice in the past. We propose a protocol for improving analytical and reporting procedures, as well as the establishment of a centralised data base of the results, which will provide an important geochronological tool to support a diverse range of stratigraphical studies, including opportunities to reassess volcanic hazards. Although aimed primarily at Europe, the protocol proposed here is of equal relevance to other regions and periods of interest.

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  • Volcanic hazards in Auckland, New Zealand: a preliminary assessment of the threat posed by central North Island silicic volcanism based on the Quaternary tephrostratigraphical record

    Alloway, Brent V.; Newnham, Rewi M.; Lowe, David J. (1999-01-01)

    Journal article
    University of Waikato

    The City of Auckland (population c. 1 million), built on a basaltic volcanic field active as recently as c. AD 1400, faces an additional volcanic threat: that from several large and productive rhyolitic and andesitic eruptive centres of the central North Island, 140-280 km to the south and southeast. Non-basaltic tephra fallout layers originating from these distal eruptive centres are numerous and widespread in the Auckland region and have primary thicknesses ranging from c. 1 mm to = 0.6 m; ignimbrites up to 9 m thick are also documented but are uncommon. The assessment of volcanic hazards in Auckland is made problematical by the different types of volcanic threat posed by these two spatially distinct source areas, and by the lack of recognition hitherto given to the threat from the distal sources. This paper reviews the Quaternary records of distal volcanism affecting Auckland and outlines current investigations into the assessment of environmental impacts of past eruptions. Our preliminary results indicate that the potential threat to Auckland from the distal volcanic sources has been underestimated and that further research into the impacts of Quaternary volcanism on Auckland's environment and infrastructure is essential. The importance of this threat was underscored in mid-1996 when a small magnitude eruption of Mt Ruapehu necessitated closure of Auckland International Airport for three nights.

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  • John A. Westgate - Global tephrochronologist, stratigrapher, mentor

    Froese, Duane G.; Alloway, Brent V.; Lowe, David J. (2008)

    Journal article
    University of Waikato

    The growth of tephra studies and tephrochronology as a field of research in the last four decades owes an enormous debt to the contributions of John Westgate. John has been one of the clear leaders of this field over this time. Through a career spanning some 40 years, he has been instrumental in the development of research techniques that have led to the global expansion of tephra studies. In particular, he has stressed a multi-proxy approach to tephrochronology, requiring the careful application of glass composition, petrology, and the understanding of field settings and stratigraphy in the development of robust tephrostratigraphic frameworks (Fig. 1 and Fig. 2). In turn, these techniques and records have helped to solve some of the most complex and longstanding problems in the geosciences, geoarchaeology, and other disciplines. John has had a major impact in all countries where he has worked, where he has been a committed researcher, leading and encouraging in his usual fashion and always publishing high-quality and groundbreaking papers that will be used for generations to come. Here we provide a brief summary of John's exceptional career, documenting his very substantial influence on tephra studies worldwide.

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  • Stratigraphy and chronology of the Stent tephra, a c. 4000 year old distal silicic tephra from Taupo Volcanic Centre, New Zealand.

    Alloway, Brent V.; Lowe, David J.; Chan, R.P.K.; Eden, Dennis N.; Froggatt, Paul C. (1994-03-01)

    Journal article
    University of Waikato

    Tephrostratigraphic and chronologic studies in two areas of the North Island have identified a previously unrecorded, thin, distal silicic tephra derived from the Taupo Volcanic Centre. In Taranaki, three radiocarbon ages of the uncorrelated tephra are consistent with the independent radiocarbon chronology obtained from enveloping Egmontsourced tephras. In western Bay of Plenty, where the uncorrelated tephra is also directly dated, it is overlain by Whakaipo Tephra (c. 2.7 ka) and underlain by Hinemaiaia Tephra (c. 4.5 ka). From these sites in Taranaki and western Bay of Plenty, seven radiocarbon dates obtained on the uncorrelated silicic tephra yield an error-weighted mean age of 3970 ±31 conventional radiocarbon years B.P. The ages on the uncorrelated tephra (informally referred to as Stent tephra) from both areas are statistically identical but significantly different from those on both Waimihia and Hinemaiaia Tephras. occurrence of Stent tephra in Taranaki, c. 160 km upwind from the postulated source area, and in western Bay of Plenty, suggests that it represents the product of a moderately large plinian eruption. Until recently, its validity as a discrete eruptive event had been problematical, because a near-source equivalent deposit between Waimihia and Hinemaiaia Tephras was not recognised in the Taupo area. However, a revised stratigraphy proposed by C. J. N. Wilson in 1993 for eastern sectors of the Taupo area shows that multiple tephra layers were erupted from Taupo volcano between c. 3.9 and 5.2 ka. Of these newly recognised layers, unit-g--the product of a moderately large eruption (>0.15 km3) at c. 4.0 ka--is tentatively correlated with Stent tephra. Other eruptive units recognised by Wilson are either too old or too small in volume to be considered as likely correlatives.

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  • Tephrochronology

    Lowe, David J.; Alloway, Brent V. (2015-06-18)

    Book item
    University of Waikato

    Tephrochronology is the use of primary, characterized tephras or cryptotephras as chronostratigraphic marker beds to connect and synchronize geological, paleoenvironmental, or archaeological sequences or events, or soils/paleosols, and, uniquely, to transfer relative or numerical ages or dates to them using stratigraphic and age information together with mineralogical and geochemical compositional data, especially from individual glass-shard analyses, obtained for the tephra/cryptotephra deposits. To function as an age-equivalent correlation and chronostratigraphic dating tool, tephrochronology may be undertaken in three steps: (i) mapping and describing tephras and determining their stratigraphic relationships, (ii) characterizing tephras or cryptotephras in the laboratory, and (iii) dating them using a wide range of geochronological methods. Tephrochronology is also an important tool in volcanology, informing studies on volcanic petrology, volcano eruption histories and hazards, and volcano-climate forcing. Although limitations and challenges remain, multidisciplinary applications of tephrochronology continue to grow markedly.

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  • Far-flown markers

    Lowe, David J.; Alloway, Brent V.; Shane, Phil A.R. (2015)

    Book item
    University of Waikato

    Tephras are fragmentary materials that are blasted explosively into the air during volcanic eruptions. Distributed throughout Zealandia, tephras provide useful markers for connecting and dating land surfaces, sediment layers, and archaeological sites.

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  • Far-flung markers

    Lowe, David J.; Alloway, Brent V.; Shane, Phil A.R. (2008)

    Book item
    University of Waikato

    Tephras are fragmentary materials that are blasted explosively into the air during volcanic eruptions. Distributed throughout Zealandia, tephras provide useful markers for connecting and dating land surfaces, sediment layers, and archaeological sites.

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  • Vegetation and climate of Auckland, New Zealand, since ca. 32 000 cal. yr ago: support for an extended LGM

    Newnham, Rewi M.; Lowe, David J.; Giles, Teresa M.; Alloway, Brent V. (2007-06)

    Journal article
    University of Waikato

    Auckland occupies a climatically sensitive position close to a major biogeographic boundary in the southern mid-latitudes. A new pollen record from Kohuora maar crater, Auckland, displays vegetation and climatic changes for the past ca. 32 000 years. Of particular interest are the inferred climatic patterns for the first part of the interval, encompassing the Last Glacial Maximum (LGM). The Kohuora record corresponds closely with pollen records from other Auckland sites indicating that the patterns observed are at least regional in extent. It is also broadly consistent with a variety of palaeoenvironmental evidence from across New Zealand, including the glacial record from Westland, other palynological records from North Island, other palaeoecological records from the South Island, and aeolian quartz sequences from western North Island. These records show that glacial conditions prevailed across most, if not all, of New Zealand during the interval ca. 29-19 k cal. yr BP, longer and earlier than the LGM sensu stricto. We suggest that the term extended LGM (eLGM) may be more appropriate for the New Zealand region. Within this predominantly cold interval, the Auckland pollen records indicate a climatic amelioration for the interval ca. 26-24 k cal. yr BP, also consistent with other palaeocological data from Canterbury, that fall within a period of climate amelioration recognised between the first two eLGM glacial advances in Westland. We refer to this warming interval as the eLGM Interstadial. The ca. 27 k cal. yr BP Kawakawa/Oruanui tephra is instrumental in most of these inter-site comparisons and occurs after the first peak of eLGM cooling in a short-lived comparatively mild phase. A subsequent return to apparently colder climate in the Auckland records may indicate a volcanic cooling effect or, more likely, widespread landscape disturbance following this major eruption event. Strong correspondence between biotic responses, glacial fluctuations and aeolian quartz deposition linked to major shifts in strength and latitudinal extent of the southern westerlies suggest that both the eLGM and eLGM Interstadial may be more widely registered, at least across the Southern Ocean. Support for this assertion comes from parallel investigations in western and southernmost South America and isotopic and palaeoecological records from Southern Ocean marine cores. Recent reconstructions of the globally averaged ice-equivalent sea-level history are in line with this evidence from the Southern Hemisphere, suggesting that the eLGM may have a global registration. In light of these observations, we suggest a re-examination of the defined timing of the LGM along with renewed effort to establish climatic patterns during this period and understand their causes. Copyright © 2007 John Wiley & Sons, Ltd.

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