126 results for Lowe, David J., Journal article

  • Assessing drivers of plantation forest productivity on eroded and non-eroded soils in hilly land, eastern North Island, New Zealand

    Heaphy, Marie; Lowe, David J.; Palmer, David John; Jones, Hayden S.; Gielen, Gerty J. H. P.; Oliver, Graeme R.; Pearce, Stephen H. (2014-07-02)

    Journal article
    University of Waikato

    Methods: The impact of soil erosion by mass movement on forest productivity was investigated in a paired plot trial in a planted forest in a mainly hilly to steepland catchment (Pakuratahi) near Napier, eastern North Island, New Zealand. Tree growth and form were measured and soil properties analysed to compare productivity and productivity drivers in adjacent non-eroded and eroded plots. Background: The effect of soil erosion on New Zealand production forestry is not well known and there has been no research prior to our study into the relationship between soil nutrient status and planted forests growing in eroded soils in steeplands. Results: Regression analysis showed that the decreased soil total nitrogen, total carbon, total phosphorus, and soil organic matter content in eroded plots had a negative impact on tree volume, resulting in a 10% decrease in measured tree volume. Based on an assessment of log quality, trees in the eroded plots were forecast to produce 16% less volume from high-quality pruned logs (with associated reduction in revenue of around $4000 per hectare), than trees in non-eroded plots. The total recoverable volume (TRV), estimated (for a 25-year rotation) from the measured Pinus radiata D. Don trees growing on the eroded sites, was valued at $68,500, about 9% less than the estimated TRV from trees measured on non-eroded plots ($76,000). Tree form and mean tree height in eroded and non-eroded plots were not significantly different. Conclusions: Soil erosion impacts production in planted forests. Afforestation of erodible land provides a valuable ecosystem service through land and soil stabilisation but this service is currently not reflected in the market prices for timber in New Zealand. Maintaining the productive capacity of erodible soils through practices such as fertilisation or continuous-cover forestry can add further costs to production forestry. To ensure that sustainable forest practices are carried out to protect the productivity of soils, financial incentives may be justified.

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  • INTREPID Tephra-II: - 1307F

    Lowe, David J. (2013)

    Journal article
    University of Waikato

    The INTREPID Tephra project, “Enhancing tephrochronology as a global research tool through improved fingerprinting and correlation techniques and uncertainty modelling”, was an overarching project of the international community of tephrochronologists of the International Focus Group on Tephrochronology and Volcanism (INTAV), which in turn lies under the auspices of INQUA’s Stratigraphy and Chronology Commission (SACCOM). INTREPID’s main aim has been to advance our understanding and efficacy in fingerprinting, correlating, and dating techniques, and to evaluate and quantify uncertainty in tephrochronology, and thus enhance our ability to provide the best possible linking, dating and synchronising tool for a wide range of Quaternary research projects around the world. A second aim has been to re-build the global capability of tephrochronology for future research endeavours through mentoring and encouragement of emerging researchers in the discipline.

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  • "New Zealand Soil Classification” by A.E. Hewitt [Book review]

    Lowe, David J. (1992)

    Journal article
    University of Waikato

    The publication of `New Zealand Soil Classification' by Dr Alan Hewitt this year (Hewitt 1992a) represents a major milestone in New Zealand soil science. That it was one of the final publications of the now defunct DSIR is somehow appropriate because, as classification systems should, it provides (in a mere 133 pages) a synthesis of much of what has been learnt about the soils of New Zealand over the past 60 years or more, The new classification was officially launched at the New Zealand Society of Soil Science Conference in Rotorua on 16 November, 1992.

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  • Preface: Enhancing tephrochronology and its application (INTREPID project): Hiroshi Machida commemorative volume

    Lowe, David J.; Davies, Siwan M.; Moriwaki, Hiroshi; Pearce, Nicholas J.G.; Suzuki, Takehiko (2011)

    Journal article
    University of Waikato

    Tephrochronology is the characterization and use of tephras – the explosively-erupted, unconsolidated, pyroclastic products of volcanic eruptions – or cryptotephras (glass-shard and/or crystal concentrations not visible as layers) as a unique stratigraphic linking, synchronizing, and dating tool. The word ‘tephra’ is derived directly from the Greek word tephra meaning ‘ashes’. Although the method is founded in stratigraphy, tephrochronology relies also on characterizing or ‘fingerprinting’ inherent tephra-derived components using laboratory-based analysis to complement field-based evidence. Such analysis includes the petrographic identification of mineral assemblages and the geochemical assay of glass shards, melt inclusions, or crystals (minerals including plagioclase, olivine, pyroxenes, amphiboles, biotite, or Fe–Ti oxides such as titanomagnetite) using the electron microprobe and other instruments including laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) ( [Lowe, 2011] and [1] ). These data are supported by the derivation of numerical ages on tephras/cryptotephras using a range of techniques including radiometric (e.g., radiocarbon, fission track, luminescence), incremental (e.g., layering in ice cores, varves, dendrochronology), age-equivalence (e.g., orbital tuning, magnetopolarity, palynostratigraphy), relative dating (e.g., obsidan hydration), and historical observation. Ages are also obtained using Bayesian-based flexible depositional modelling and wiggle matching (e.g., [Lowe et al., 2007] and Lowe et al., 2008 D.J. Lowe, P.A.R. Shane, B.V. Alloway and R.M. Newnham, Fingerprints and age models for widespread New Zealand tephra marker beds erupted since 30,000 years ago: a framework for NZ-INTIMATE.. Quaternary Science Reviews, 27 (2008), pp. 95–126. [Lowe et al., 2008] ).

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  • 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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  • Volcano-meteorological tsunamis, thec. AD 200 Taupo eruption (New Zealand) and the possibility of a global tsunami

    Lowe, David J.; de Lange, Willem P. (2000)

    Journal article
    University of Waikato

    Meteorological tsunamis are long-period waves that result from meteorologically driven disturbances. They are also generated by phase coupling with atmospheric gravity waves arising through powerful volcanic activity. The AD 1883 Krakatau eruption generated volcano-meteorological tsunamis that were recorded globally. Because of its extreme violence and energy release (≥150±50 megatons explosive yield), and by analogy with the Krakatau event, it is highly possible that the ignimbrite-emplacement phase of the c. ad 200 Taupo eruption of North Island, New Zealand, generated a similar volcano-meteorological tsunami that may have reached coastal areas worldwide. Tsunami deposits of identical age to the Taupo eruption occur in central coastal New Zealand and probably relate to that event; definitive evidence elsewhere has not yet been found. In theory, volcano-meteorological tsunamis are likely to be produced during comparable eruptive events at other explosive volcanoes, and thus represent an additional volcanic hazard at coastal sites far from source. We suggest that evidence for such tsunamis, both for marine and lacustrine environments, may be preserved in geological records, and that further work searching for this evidence using a facies approach is timely.

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  • Mapping and explaining the productivity of Pinus radiata in New Zealand

    Palmer, Jonathan G.; Watt, Michael S.; Kimberley, Mark O.; Hock, Barbara K.; Payn, Tim W.; Lowe, David J. (2010)

    Journal article
    University of Waikato

    Mapping Pinus radiata productivity for New Zealand not only provides useful information for forest owners, industry stakeholders and policy managers, but also enables current and future plantations to be visualised, quantified, and planned. Using an extensive set of permanent sample plots, split into fitting (n = 1,146) and validation (n = 618) datasets, models of P. radiata 300 Index (an index of volume mean annual increment) and Site Index (an index of height growth) were developed using a regression kriging technique. Spatial predictions were accurate and accounted for 61% and 70% of the variance for 300 Index and Site Index, respectively. Productivity predicted from these surfaces for the entire plantation estate averaged 27.4 m³ ha⁻¹ yr⁻¹ for the 300 Index and 30.4 m for Site Index. Surfaces showed wide regional variation in this productivity, which was attributable mainly to variation in air temperature and root-zone water storage from site to site.

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  • Impact of tephra fall and environmental change: a 1000 year record from Matakana Island, Bay of Plenty, North Island, New Zealand.

    Giles, Teresa M.; Newnham, Rewi M.; Lowe, David J.; Munro, Adam J. (1999-01-01)

    Journal article
    University of Waikato

    Palynological evidence was used to determine the development of vegetation communities on Matakana Island, North Island, New Zealand, over the last 1000 radiocarbon years. The pollen record indicates that changes occurred in the vegetation immediately following fallout deposition of the Kaharoa Tephra approximately 100 km from source at c. 665 years BP. Such changes may be a direct response to the impact of tephra fall, although the possibility of anthropogenic disturbance cannot be discounted. As a result of the eruption some taxa (Leucopogon fasciculatus and Tupeia antarctica) became at least temporarily extinct from the area. Two phases of anthropogenic influence on the environment are recorded in the pollen record: Polynesian, followed by European inhabitation of the island, giving a detailed history of human influence in the area for the millennium.

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  • Globalization of tephrochronology: new views from Australasia

    Lowe, David J. (2008)

    Journal article
    University of Waikato

    Tephra (or volcanic ash) studies, once confined largely to volcanic lands, have become increasingly practised in countries far removed from areas of active or recent volcanism – and Australia is no exception. At the International Union for Quaternary Research (INQUA) conference in Cairns in July/August 2007, Sarah E. Coulter (née Davies), now a postdoctoral ice-core tephrochronologist at Queen’s University Belfast, reportedthe first occurrence of an exotic tephra in Australia in a core from Lynch’s Crater, Atherton Tableland, Queensland (Figure 1). The distal tephra, manifest as a tiny concentration of glass shards, was probably derived from a Papua New Guinean eruption around 75,000–80,000 years ago (S.E. Davies et al., 2007). Its value lies in providing a precise chronostratigraphic marker that potentially allows correlation of other long palaeoenvironmental sequences over wide distances. Davies’ study is but one of a revolutionary development in tephrochronology now focused on detecting diminutive, distal tephras that are invisible in the field and referred to as cryptotephras. From the Greek word kryptein, meaning ‘to hide’ (Hunt, 1999a; Hunt and Hill, 2001; Lowe and Hunt, 2001), cryptotephras typically comprise fine-ashsized (< ~100 μm) glass shards sparsely preserved and ‘hidden’ in peats or in lake, marine or aeolian sediments, or in ice cores (Figure 2). The cryptotephra theme is continued in section III, but beforehand nomenclature associated with the term ‘tephra’, which can be confusing and which sometimes is used incorrectly, is outlined.

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  • Towards rapid assay of cryptotephra in peat cores: review and evaluation of selected methods

    Gehrels, Maria J.; Newnham, Rewi M.; Lowe, David J.; Wynne, Shirley; Hazell, Zoë J.; Caseldine, Chris (2008-02)

    Journal article
    University of Waikato

    Peat bogs are highly effective archives for the preservation and detection of cryptotephra but the conventional methods used to detect these hidden, diminutive layers are destructive and can be time consuming. We briefly review methods that have been used for cryptotephra detection and evaluate the potential of a range of alternative reconnaissance methods, both non-destructive and destructive, to provide for more rapid examination of continuous cryptotephra content in peat cores. The techniques evaluated—magnetic susceptibility (MS), spectrophotometry, and X-ray fluorescence—are used to pick out compositional contrasts between tephra deposits and peat. Measurements of organic content are also evaluated as a potential guide to tephra content based on an inverse relationship. Although we find limitations to each method, particularly where deployed at the distal-most end of tephra dispersal, there is potential for all methods to be used in the detection of cryptotephra where time or material is limited. These methods can also provide additional sedimentological and stratigraphic information for studies of peat cores. However, where a reliable cryptotephra profile is required, we conclude that there is no quick or easy substitute for the conventional extraction-microscopy method.

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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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  • Comparison of spatial prediction techniques for developing Pinus radiata productivity surfaces across New Zealand

    Palmer, David John; Hock, Barbara K.; Kimberley, Mark O.; Watt, Michael S.; Lowe, David J.; Payn, Tim W. (2009)

    Journal article
    University of Waikato

    Spatial interpolation is frequently used to predict values across a landscape enabling the spatial variation and patterns of a property to be quantified. Inverse distance weighting (IDW), ordinary kriging (OK), regression kriging (RK), and partial least squares (PLS) regression are interpolation techniques typically used where the region of interest's spatial extent is relatively small and observations are numerous and regularly spaced. In the current era of data ‘mining’ and utilisation of sparse data, the above criteria are not always fully met, increasing model uncertainties. Furthermore, regression modelling and kriging techniques require good judgement, experience, and expertise by the practitioner compared with IDW with its more rudimentary approach. In this study we compared spatial predictions derived from IDW, PLS, RK, and OK for Pinus radiata volume mean annual increment (referred to as 300 Index) and mean top height at age twenty (referred to as Site Index) across New Zealand using cross-validation techniques. Validation statistics (RMSE, ME, and R2) show that RK, OK, and IDW provided predictions that were less biased and of greater accuracy than PLS predictions. Standard deviation of rank (SDR) and mean rank (MR) validation statistics showed similar results with OK the most consistent (SDR) predictor, whereas RK had the lowest mean rank (MR), closely followed by IDW. However, the mean performance rankings for validation observations classified according to their distance to the nearest model data point indicate that although PLS provided the poorest predictions at relatively close separation distances (<2 km), in the medium range ( 4–8 km) performance was of similar ranking to that of the other techniques, and at greater separation distances PLS outperformed the other techniques. Maps illustrating the spatial variation of P. radiata forest productivity are provided.

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  • Stratigraphy and chronology of a 15ka sequence of multi-sourced silicic tephras in a montane peat bog, eastern North Island, New Zealand.

    Lowe, David J.; Newnham, Rewi M.; Ward, Chris M. (1999-12-01)

    Journal article
    University of Waikato

    We document the stratigraphy, composition, and chronology of a succession of 16 distal, silicic tephra layers interbedded with lateglacial and Holocene peats and muds up to c. 15 000 radiocarbon years (c. 18 000 calendar years) old at a montane site (Kaipo Bog) in eastern North Island, New Zealand. Aged from 665 +/- 15 to 14 700 +/- 95 14C yr BP, the tephras are derived from six volcanic centres in North Island, three of which are rhyolitic (Okataina, Taupo, Maroa), one peralkaline (Tuhua), and two andesitic (Tongariro, Egmont). Correlations are based on multiple criteria: field properties and stratigraphic interrelationships, ferromagnesian silicate mineral assemblages, glass-shard major element composition (from electron microprobe analysis), and radiocarbon dating. We extend the known distribution of tephras in eastern North Island and provide compositional data that add to their potential usefulness as isochronous markers. The chronostratigraphic framework established for the Kaipo sequence, based on both site-specific and independently derived tephra-based radiocarbon ages, provides the basis for fine-resolution paleoenvironmental studies at a climatically sensitive terrestrial site from the mid latitudes of the Southern Hemisphere. Tephras identified as especially useful paleoenvironmental markers include Rerewhakaaitu and Waiohau (lateglacial), Konini (lateglacial-early Holocene), Tuhua (middle Holocene), and Taupo and Kaharoa (late Holocene).

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  • Development of models to predict Pinus radiata productivity throughout New Zealand

    Watt, Michael S.; Palmer, David John; Kimberley, Mark O.; Hock, Barbara K.; Payn, Tim W.; Lowe, David J. (2010)

    Journal article
    University of Waikato

    Development of spatial surfaces describing variation in productivity across broad landscapes at a fine resolution would be of considerable use to forest managers as decision support tools to optimize productivity. In New Zealand, the two most widely used indices to quantify productivity of Pinus radiata D. Don are Site Index and 300 Index. Using an extensive national data set comprising a comprehensive set of national extent maps, multiple regression models and spatial surfaces of these indices for P. radiata were constructed. The final models accounted for 64% and 53%, respectively, of the variance in Site Index and 300 Index. For Site Index, variables included in the final model in order of importance were mean annual air temperature, fractional mean annual available root-zone water storage, mean annual windspeed, length and slope factor, categories describing Land Environments of New Zealand (LENZ), and major soil parent material. The variables included in the final model of 300 Index in order of importance included the degree of ground frost during autumn, fractional mean annual available root-zone water storage, categories describing LENZ, vegetation classification, foliar nitrogen, taxonomic soil order, and major soil parent material. These results highlight the utility of thematic spatial layers as driving variables in the development of productivity models.

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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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  • A new attraction-detachment model for explaining flow sliding in clay-rich tephras

    Kluger, Max O.; Moon, Vicki G.; Kreiter, Stefan; Lowe, David J.; Churchman, G.Jock; Hepp, Daniel A.; Seibel, David; Jorat, M. Ehsan; Mörz, Tobias (2017-02-01)

    Journal article
    University of Waikato

    Altered pyroclastic (tephra) deposits are highly susceptible to landsliding, leading to fatali-ties and property damage every year. Halloysite, a low-activity clay mineral, is commonly associated with landslide-prone layers within altered tephra successions, especially in depos-its with high sensitivity, which describes the post-failure strength loss. However, the precise role of halloysite in the development of sensitivity, and thus in sudden and unpredictable landsliding, is unknown. Here we show that an abundance of mushroom cap–shaped (MCS) spheroidal halloysite governs the development of sensitivity, and hence proneness to landslid-ing, in altered rhyolitic tephras, North Island, New Zealand. We found that a highly sensitive layer, which was involved in a flow slide, has a remarkably high content of aggregated MCS spheroids with substantial openings on one side. We suggest that short-range electrostatic and van der Waals interactions enabled the MCS spheroids to form interconnected aggre-gates by attraction between the edges of numerous paired silanol and aluminol sheets that are exposed in the openings and the convex silanol faces on the exterior surfaces of adjacent MCS spheroids. If these weak attractions are overcome during slope failure, multiple, weakly attracted MCS spheroids can be separated from one another, and the prevailing repulsion between exterior MCS surfaces results in a low remolded shear strength, a high sensitivity, and a high propensity for flow sliding. The evidence indicates that the attraction-detachment model explains the high sensitivity and contributes to an improved understanding of the mechanisms of flow sliding in sensitive, altered tephras rich in spheroidal halloysite.

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  • Advancing tephrochronology as a global dating tool: applications in volcanology, archaeology, and palaeoclimatic research

    Lane, C.S.; Lowe, David J.; Blockley, S.P.E.; Suzuki, T.; Smith, V.C. (2017)

    Journal article
    University of Waikato

    Layers of far-travelled volcanic ash (tephra) from explosive volcanic eruptions provide stratigraphic and numerical dating horizons in sedimentary and volcanic sequences. Such tephra layers may be dispersed over tens to thousands of kilometres from source, reaching far beyond individual volcanic regions. Tephrochronology is consequently a truly global dating tool, with applications increasingly widespread across a range of Quaternary and geoscience disciplines. This special issue of the International Focus Group on Tephrochronology and Volcanism (INTAV) showcases some of the many recent advances in tephrochronology, from methodological developments to diverse applications across volcanological, archaeological, and palaeoclimatological research.

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  • Unique but diverse: some observations on the formation, structure, and morphology of halloysite

    Churchman, G. Jock; Pasbakhsh, Pooria; Lowe, David J.; Theng, B.K.G. (2016-10-11)

    Journal article
    University of Waikato

    New insights from the recent literature are summarised and new data presented concerning the formation, structure and morphology of halloysite. Halloysite formation by weathering always requires the presence of water. Where substantial drying occurs, kaolinite is formed instead. Halloysite formation is favoured by a low pH. The octahedral sheet is positively charged at pH < ~8, whereas the tetrahedral sheet is negatively charged at pH > ~2. The opposing sheet charge would facilitate interlayer uptake of H₂O molecules. When halloysite intercalates certain polar organic molecules, additional (hkl) reflections appear in the X-ray diffractogram, suggesting layer re-arrangement which, however, is dissimilar to that in kaolinite. Associated oxides and oxyhydroxides of Fe and Mn may limit the growth of halloysite particles as does incorporation of Fe into the structure. Particles of different shape and iron content may occur within a given sample of halloysite.

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  • Discovery of halloysite books in altered silicic Quaternary tephras, northern New Zealand

    Cunningham, Michael J.; Lowe, David J.; Wyatt, Justin Burns; Moon, Vicki G.; Churchman, G. Jock (2016-10-11)

    Journal article
    University of Waikato

    Hydrated halloysite was discovered in books, a morphology previously associated exclusively with kaolinite. From ~1.5 μm to ~1500 μm in length, the books showed significantly greater mean Fe contents (Fe2O3 = 5.2 wt%) than tubes (Fe2O3 = 3.2 wt%), and expanded rapidly with formamide. They occurred, along with halloysite tubes, spheroids, and plates, in highly porous yet poorly-permeable, silt-dominated, Si-rich, pumiceous rhyolitic tephra deposits aged ~0.93 Ma (Te Puna tephra) and ~0.27 Ma (Te Ranga tephra) at three sites ~10-20 m stratigraphically below the modern land-surface in the Tauranga area, eastern North Island, New Zealand. The book-bearing tephras were at or near saturation, but have experienced intermittent partial drying, favouring the proposed changes: solubilized volcanic glass + plagioclase -> halloysite spheroids -> halloysite tubes -> halloysite plates -> halloysite books. Unlike parallel studies elsewhere involving both halloysite and kaolinite, kaolinite has not formed in Tauranga presumably because the low permeability ensures the sites largely remain locally wet so that the halloysite books are metastable. An implication of the discovery is that some halloysite books in similar settings may have been misidentified previously as kaolinite.

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  • Dissolution and depletion of ferromagnesian minerals from Holocene tephra layers in an acid bog, New Zealand, and implications for tephra correlation

    Hodder, A.P.W.; de Lange, P.J.; Lowe, David J. (1991)

    Journal article
    University of Waikato

    This study examines the depletion of ferromagnesian silicate minerals from a sequence of thin, distal, mainly rhyolitic tephra layers of Holocene age preserved in an acid peat bog (Kopouatai), North Island, New Zealand. The rate of such depletion has been fast, as indicated by the complete loss of biotite from one tephra layer (Kaharoa Tephra), in which it is normally dominant, in only ca. 770 yr. Chemical dissolution is advocated as the likely cause for the depletion, with amphiboles and other mineral grains commonly showing etch pits, microcaves, and other characteristic surface solution features. Theoretical thermodynamic and kinetic models show a marked increase in the rate of dissolution of all ferromagnesian minerals under conditions of low pH (< 4), but that where silica concentrations in solution are high the relative proportions of minerals remaining are unaffected. However, where concentrations of dissolved silica are low, as in most bog environments, the relative proportions of ferromagnesian minerals are affected as well as absolute amounts being decreased. Amphiboles are depleted relative to pyroxenes, consistent with kinetic studies. The results show that the identification and correlation of tephras on the basis of relative abundances of ferromagnesian minerals alone may be unreliable, and emphasise the need to use multiple criteria in such studies.

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