tephra beds in deep sea cores off northern new zealand implications for the history of taupo volcanic zone mayor island and white island volcanoes twenty piston cores were collected from water depths of 650 3300 m from offshore bay of plenty north island new zealand they contain tephra from 11 okataina volcanic centre and 4 taupo volcanic centre rhyolite eruptions during the last 50 kyr that produce a tephrostratigraphic framework across the tectonically and volcanically complex region of southern havre trough alderman trough and the bay of plenty continental shelf this allows correlation between offshore and onshore sequences up to 200 km from source volcanoes covering much of marine isotope stages 3 and 2 the framework temporally constrains poorly dated and newly recognised volcanic events macroscopic tephra layers from the peralkaline mayor island volcano are documented for the first time at pre 50 post 50 40 5 37 4 22 2 and 14 2 ka in addition to the well known 7 ka tuhua event these macroscopic layers represent some of the most explosive events from this volcano and provide new marker horizons they are dispersed up to 90 km north east to east of the edifice minor tephra dispersal is also recorded at 17 8 25 5 35 and pre 50 ka the tephra contain high sio2 73 75 5 wt glass and subordinate basaltic components and each tephra represents a distinct magma batch that can be fingerprinted the mayor island tephra form two temporal trends toward less evolved magma compositions punctuated by a large caldera forming event at 36 ka the historically active andesitic white island volcano does not have widely dispersed tephra and the oldest primary deposit found is 21 ka five pre 50 ka rhyolite eruptions from an unknown taupo volcanic zone source provide evidence for explosive activity in a time interval poorly documented on land the cores demonstrate the patchy and uneven preservation of large magnitude tephra falls caused by local faulting bioturbation and ponding in bathymetrically complex regions reworked tephra layers are common and often lack indicative lithological features such units could easily be misinterpreted as primary events without micro beam geochemical analyses of glass shards

correlation between rate of sea level change and frequency of explosive volcanism in the mediterranean volcanic activity has frequently been linked to quaternary environmental change either by driving climate modification1 2 or in response to environmental changes3 although a link has been established between large explosive eruptions and small 0 5 c brief 1 2 years falls in global temperatures4 both the evidence and mechanisms responsible for longer episodes of eruption induced planetary cooling remain questionable1 2 5 6 in contrast recent research based on ice core data suggests that rapid climate changes during the past 110 000 years increased explosive volcanic activity7 here we present a statistical analysis relating the frequency of explosive activity of mediterranean volcanoes based on dated8 9 10 11 tephra layers in deep sea sediment cores to the rate of late quaternary sea level change the nonlinear correlation between the two is tentatively explained in terms of dynamic responses of the volcanoes to stress related influences on various spatial scales the correlation supports a mechanism or mechanisms by which the climate driven growth and decay of large ice sheets can influence the eruptive chronologies of distant volcanic edifices via changes in global sea level

chronology and dynamics of a large silicic magmatic system central taupo volcanic zone new zealand the central taupo volcanic zone in new zealand is a region of intense quaternary silicic volcanism accompanying rapid extension of continental crust at least 34 caldera forming ignimbrite eruptions have produced a complex sequence of relatively short lived nested and or overlapping volcanic centers over 1 6 m y silicic volcanism at taupo is similar to the yellowstone system in size longevity thermal flux and magma output rate however taupo contrasts with yellowstone in the exceptionally high frequency but small size of caldera forming eruptions this contrast reflects the thin rifted nature of the crust which precludes the development of long term magmatic cycles at taupo 11 refs 4 figs 1 tab

the application of icp ms methods to tephrochronological problems pearce nicholas westgate j a perkins w t preece s j 2004 the application of icp ms methods to tephrochronological problems applied gechemistry 19 3 pp 289 322 rae2008

an exceptionally widespread ignimbrite with implications for pyroclastic flow emplacement pumice rich pyroclastic flows leave deposits called ignimbrites1 which are common in the eruption records of arc and intracontinental volcanoes2 3 pyroclastic flows represent the most dangerous manifestation of volcanism4 because of their volumes rapid emplacement at high temperatures and capacity to extend 100 km from the source however maximum distances travelled and extents of areas destroyed by pyroclastic flows remain poorly known historic examples have been relatively small the largest reaching to only 35 km from the vent5 but prehistoric ignimbrites over 150 km across are known3 6 10 the largest ignimbrites are invariably partly buried or eroded and only minimum estimates of their size and hence of their destructive capacity can be made here we describe the l myr old kidnappers ignimbrite erupted from the taupo volcanic zone in new zealand which we have correlated for 385 km and which thus represents the most wide spread ignimbrite yet known we suggest that this wide distribution primarily reflects a coupling of high initial flow velocities with large mass fluxes and that favourable flow paths and emplacement of flows over a wet substrate may have aided their mobility

intensified deep pacific inflow and ventilation in pleistocene glacial times the production of cold deep waters in the southern ocean is an important factor in the earth s heat budget1 the supply of deep water to the pacific ocean is presently dominated by a single source the deep western boundary current east of new zealand here we use sediment records deposited under the influence of this deep western boundary current to reconstruct deep water properties and speed changes during the pleistocene epoch in physical and isotope proxies we find evidence for intensified deep pacific ocean inflow and ventilation during the glacial periods of the past 1 2 million years the changes in throughflow may be directly related to an increased production of antarctic bottom water during glacial times possible causes for such an increased bottom water production include increasing wind strengths in the southern ocean or an increase in annual sea ice formation leaving dense water after brine rejection and thereby enhancing deep convection we infer also that the global thermohaline circulation was perturbed significantly during the mid pleistocene climate transition between 0 86 and 0 45 million years ago

glacial to interglacial mineral magnetic and palaeoceanographic changes at chatham rise sw pacific ocean core chat 1k from 3556 m depth east of new zealand shows marked changes in magnetic susceptibility correlating very well with 18o of foraminifera over the last 150 ka susceptibility is high during interglacial stages 1 and 5 and substages 5a to 5e are well marked the susceptibility is shown to be enhanced during interglacials and is neither an artefact of glacial carbonate dilution nor due to an interglacial increase of terrigenous material mineral magnetic property measurements arm sirm s ratio also show the same well defined glacial interglacial variability interpreted as an interglacial increase of single domain magnetite grains less than 0 1 m in size examination by tem of magnetic extracts reveals abundant cubic to octahedral grains of 0 02 0 2 m size often arranged in long chains characteristic of bacterial magnetite this material is much more abundant in interglacial than glacial samples it is suggested that during interglacials with lower productivity and organic carbon input to the bed the oxic zone in the sediments which can be colonised by magnetotactic bacteria is thicker and therefore is colonised for longer by magnetite producers this yields a climate controlled stratigraphy which leads that of infaunal benthic foraminifera by no more than a few centimetres

mid pleistocene silicic tephra beds in the auckland region new zealand their correlation and origins based on the trace element analyses of single glass shards abstract the trace element composition of individual glass shards from twelve distinct mid pleistocene silicic tephra beds from the auckland region new zealand has been determined by laser ablation la icp ms analysis this is the first application of such data to tephra correlation studies in new zealand these analyses support earlier major element based correlations between three surface sections oruarangi and okariha at port waikato and st kentigern s at east auckland and a long core patiki road west auckland the correlations provide a higher resolution record of taupo volcanic zone tvz activity than is preserved in more proximal deposits where burial and erosion obscure much of the volcanic record a combination of major and trace element analysis enables the correlation of three units exposed in the auckland region with their proximal equivalents ignimbrites from the tvz namely deposits associated with 1 the ongatiti ignimbrite 1 21 0 04 ma 2 an un named post ahuroa pre unit e ignimbrite sample ut1274 from the rocky hill section king country and 3 the unit e ignimbrite 1 ma combined major and trace element data show a marked evolution in magma chemistry with the large ongatiti and unit e ignimbrite eruptions occurring after a change in composition caused by replenishment reactivation of the magma chamber changes in magma chemistry between these deposits resulted from a combination of assimilation of metasedimentary country rocks and periods of fractional crystallisation of a plagioclase dominated assemblage trace element data and the wider dispersal of the silicic tephras in the auckland region suggests that they are all sourced from the mangakino volcanic centre mvc in the tvz this study illustrates for the first time in a new zealand context the potential for correlating tephra deposits using single glass shard trace element chemistry

a long late quaternary record from lake poukawa hawke s bay new zealand abstract the lake poukawa basin is a large co seismic depression located at 20 m above mean sea level in hawke s bay in eastern north island new zealand we present a detailed environmental history of the basin for the last c 60 ka based on analyses of the top 105 m of a 200 m core record dating control is provided by radiocarbon optically stimulated luminescence osl and u th disequilibrium ages the chronology is supported by nine tephras of inferred age including marker tephras kawakawa 22 590 230 yr bp at 18 25 m core datum tahuna c 35 43 ka at 33 1 m core datum and rotoehu 45 50 ka at 39 1 m core datum disagreements between some of the older tephra ages and the numerical ages from the osl and u th dating mean that more than one age model can be applied three major lithostratigraphic units are identified a basal calcareous silt with lignitic peats between 105 28 and 98 58 m of marine oxygen isotope stage mis 3 age an extended sequence of detrital shelly sands and silts between 98 58 and 8 m of mis 3 and 2 age and a holocene peat unit mis 1 from 8 to 0 m alternatively but less likely the basal unit may represent stage mis 5a and the detrital shelly sands would then contain an amalgam of mis 4 3 and 2 deposits we propose a notably moist phase represented by the peat which our numerical dating model places near the start of isotope stage 3 this suggests the existence of mild conditions during an interstadial in central new zealand at c 55 50 ka when a podocarp beech broadleaf forest of near interglacial affinity surrounded the basin the interstadial is marked by both lake and peat formation in the basin after 50 ka a thermal decline set in though the climate remained moist initially under these conditions the poukawa basin was rapidly infilled by alluvial fan deposits from the surrounding hills the floor of the basin was occupied by grasses and sedges responding to both the highly disturbed environment and swampy conditions in the basin after the deposition of the rotoehu ash effective precipitation declined markedly and woody shrubs expanded across the previously swampy basin floor the data suggest an apparent thermal decline of c 6 7 c for much of mis 2 and the latter half of mis 3 the holocene was marked by the establishment of fen and lake environments on the basin floor prior to human disturbance podocarp broadleaf forest surrounded the basin

fallout of volcanic ash to the deep south china sea induced by the 1991 eruption of mount pinatubo philippines an ongoing sediment trap experiment in the central south china sea provided the opportunity to investigate directly the mode and rates of a medial fallout of volcanic ash following the june 15 1991 eruption of mount pinatubo philippines within less than three days after the release of the major eruption plume ash accumulation 9 kg m 2 was simultaneously recorded by traps positioned in 1190 and 3730 m water depth at a distance of 586 km to the west of the volcano a numerical simulation of the fallout reveals that the vertical trajectories of the pyroclasts in both the atmosphere and ocean were controlled by particle aggregation the aggregation process caused a premature subaerial fallout of fine grained ash after crossing the air sea interface vertical settling of the ash clusters was enhanced by absorption of water leading to settling rates of more than 1670 m d aggregates were observed at all depths and their rapid settling is reflected in identical pyroclast spectra in intermediate and deep water this implies that particle sorting must have been complete in the upper water column and that the fallout was not perturbed by oceanic currents the tephra blankets an area of 37 10 4 km 2 in a fan shaped westward distribution which reflects the prevailing direction of the upper level winds our data show that atmospheric tephra dispersal patterns are recorded almost instantaneously on the deep sea floor and corroborate the key role of deep sea ash layers as highly reliable chronostratigraphic markers and as a geological tool to infer ancient wind fields

orbitally influenced vegetation record of the mid pleistocene climate transition offshore eastern new zealand odp leg 181 site 1123 a census of plio pleistocene 5 0 ma terrestrial palynomorph assemblages from odp site 1123 located 1100 km offshore eastern new zealand and in a water depth of 3290 m reveals marked variations in warm cyathea tall tree podocarpus prumnopitys dacrydium cupressinum and cold halocarpus phyllocladus nothofagus fusca type coprosma climate indicator species at milankovitch scale periodicities time series analysis indicates that the vegetation record is covariant with marine climate proxies carbonate content and is strongly coherent at the 40 ka and 100 ka orbital frequency a pronounced increase in amplitude and a coeval decrease in frequency of climate cycles from 40 to 100 ka occurs between 0 92 and 0 62 ma and provides a rare vegetation record of a fundamental reorganisation of earth s climate system the mid pleistocene climate transition despite the long distance from land and great water depth terrestrial palynomorphs are relatively abundant in this high resolution marine sediment record where they reflect a southern north island source the predominance of robust spores and buoyant pollen cyathea podocarpus prumnopitys indicates considerable current sorting and degradation of more delicate morphotypes during transport across the eastern north island shelf little evidence is found for sorting and transport processes being significantly modulated by climate

trace element composition of single glass shards in distal minoan tephra from sw turkey volcanic glass from the seventeenth century bc c 3600 bp minoan eruption of santorini thera has been recovered from a 4 cm thick tephra deposit at golhisar golu a small lake in sw turkey analysis of single grains of this glass by laser ablation inductively coupled plasma mass spectrometry la icp ms provides for the first time an accurate determination of the trace element composition of the juvenile glass component of this eruption free from contaminants such as phenocrysts or detrital material individual glass shards 150 m show a large degree of variation in their trace element composition indicative of substantial small scale compositional heterogeneity in the magma this is a result of the proximity of crystallizing phases and provides insights into the chemical evolution of the minoan magma the range of elemental compositions displayed by individual glass shards combined with the consistency of many trace element ratios are characteristics of the minoan glass these features provide a trace element signature for the minoan tephra which will be of value in stratigraphic correlation across the eastern mediterranean

a terrestrial palynological record for the last two glacial cycles from southwestern new zealand abstract a pollen profile from okarito pakihi bog in south westland new zealand extending from near present back to marine isotope stage mis 6 provides a continuous record of vegetation and climate change for the past two glacial cycles independent chronological control was obtained by ams radiocarbon dating of organic sediments in the upper part of the sequence and osl dating of inorganic silts in the lower part with a unique tie point provided by the ca 26 5 cal ka kawakawa tephra as was probably a common occurrence in this region the basin developed as a moraine dammed proglacial lake and remained lacustrine until the early holocene when a peat bog developed survival of the depositional site through subsequent multiple ice advances unusual in a glaciated landscape was probably assisted by lateral displacement of the basin relative to its source area across the alpine fault there is good correspondence between inferred periods of substantial treeline depression in the pollen profile and the record for ice advance in this region more cooling events are evident in the pollen record however presumably due to the fragmentary nature of glacial geomorphology the pollen record also shows broad consistency with the mis record and hence with the milankovitch orbital forcing model but with some departures including an early onset to the last glacial maximum lgm several sub milankovitch scale events are also evident including a mid lgm warming and lateglacial reversals during both the last and the penultimate deglaciation

laser ablation inductively coupled plasma mass spectrometry and tephras a new approach to understanding arc magma genesis the development of laser ablation inductively coupled plasma mass spectrometry has revolutionized the analysis of tephras by providing 1 an efficient and precise method for determining abundances of a wide variety of trace elements at low concentrations in individual glass shards and 2 assessment of geochemical heterogeneities within individual ash horizons this development is important for petrogenetic studies of intraoceanic arc systems where tephras provide the most complete temporal record of magmatism results from the izu bonin and mariana arc systems indicate that despite close geographical proximity and similar tectonic evolution they contrast strongly in terms of geochemical evolution since 35 ma whereas the mariana tephras have exceptional compositional diversity ranging from low k oligocene to high k miocene and subsequently medium k compositions pliocene quaternary the izu bonin arc has been dominated by low k compositions throughout the mariana increases in k are paralleled by increases in abundances of incompatible trace elements and by increased values of diagnostic ratios e g nb yb and th yb regarded as monitors of potential mantle source fertility the relative uniformity of nb yb and nb zr ratios in izu bonin tephras indicates that cyclic processes of backarc basin development and mantle depletion do not necessarily induce large scale temporal geochemical variations in the associated arc temporal variability within the mariana arc and its divergence from the izu bonin arc ca 13 ma can be traced to a major injection of subducted sediment in the mariana system at this time

onshore offshore correlation of pleistocene rhyolitic eruptions from new zealand implications for tvz eruptive history and paleoenvironmental construction abstract taupo volcanic zone tvz in the north island new zealand is arguably the most active quaternary rhyolitic system in the world numerous and widespread rhyolitic tephra layers sourced from the tvz form valuable chronostratigraphic markers in onshore and offshore sedimentary sequences in deep sea cores from ocean drilling program odp leg 181 sites 1125 1124 1123 and 1122 located east of new zealand ca 100 tephra beds are recognised post dating the plio pleistocene boundary at 1 81 ma these tephras have been dated by a combination of magnetostratigraphy orbitally tuned stable isotope data and isothermal plateau fission track ages the widespread occurrence of ash offshore to the east of new zealand is favoured by the small size of new zealand the explosivity of the mainly plinian and ignimbritic eruptions and the prevailing westerly wind field although some tephras can be directly attributed to known tvz eruptions there are many more tephras represented within odp cores that have yet to be recognised in near source on land sequences this is due to proximal source area erosion and or deep burial as well as the adverse effect of vapour phase alteration and devitrification within near source welded ignimbrites despite these difficulties a number of key deep sea tephras can be reliably correlated to equivalent aged tephra exposed in uplifted marine back arc successions of wanganui basin where an excellent chronology has been developed based on magnetostratigraphy orbitally calibrated sedimentary cycles and isothermal plateau fission track ages on tephra significant pleistocene tephra markers include the kawakawa omataroa rangitawa onepuhi kaukatea kidnappers b potaka unit d ahuroa ongatiti rewa sub rewa pakihikura ototoka and table flat tephras six other tephra layers are correlated between odp core sites but have yet to be recognised within onshore records the identification of pleistocene tvz sourced tephras within the odp record and their correlation to wanganui basin and other onshore sites is a significant advance as it provides 1 an even more detailed history of the tvz than can be currently achieved from the near source record 2 a high resolution tephrochronologic framework for future onshore offshore paleoenvironmental reconstructions and 3 well dated tephra beds correlated from the offshore odp sites with astronomically tuned timescales provide an opportunity to critically evaluate the chronostratigraphic framework for onshore plio pleistocene sedimentary sequences e g wanganui basin cf naish et al 1998 quaternary science reviews 17 695 710

ice age as a trigger of active quaternary volcanism and tectonism abstract the stress accumulation within the crust caused by the surface mass redistribution associated with the glaciation deglaciation cycle during the quaternary was numerically evaluated in order to examine the relationship between active quaternary volcanism and tectonism in island arc areas and ice age the vertical gradient of horizontal stress difference in the lithosphere for a meltwater of 130 m in equivalent sea level reaches a maximum value of 0 8 mpa km which is corresponding to the equivalent buoyancy of about 100 kg m3 for magma filled cracks for an earth model with a lithospheric layer of 20 30 km thickness and with a viscosity greater than 1023 pa s the changes in stress difference during the stages of deglaciation of 10 000 years amount to 13 mpa for both the top and bottom of the thin lithosphere thus the additional stress difference within the crust may be effective for island arc areas with thin lithospheric thickness we therefore speculate that the stress accumulation associated with ice age may be an important trigger and or accelerator on the active quaternary volcanism and tectonism for the areas along the circum pacific

developments in the analysis of volcanic glass shards by laser ablation icp ms quantitative and single internal standard multielement methods abstract laser ablation inductively coupled plasma mass spectrometry la icp ms has been applied to the analysis of fine grained 125 250 m volcanic glass shards separated from tephra deposits our earlier calibration strategies used ce as an internal standard which required the use of another trace element analytical technique to determine ce followed by off line data correction by comparison with well characterised glass separates we have progressed from these earlier studies to use a minor isotope of a major element routinely determined by epma in tephrochronological studies as an internal standard for la icp ms analysis internal standards used during this study include 29si 30si or 44ca for fully quantitative determinations or 57fe for a single internal standard multi element calibration so called semiquantitative analysis no subsequent off line data correction is required the differences between each technique are minimal and choice of technique depends largely upon instrument sensitivity as little as 80 g of material is consumed during a single determination which takes approximately two minutes and detection limits are below 1 part per million accuracy is generally 15 when compared with other analytical techniques and precision may vary between 5 and 20 the worse precisions reflecting within sample variability rare earth and other trace element data can be used to correlate or distinguish individual tephra deposits with confidence and specific examples are illustrated with quaternary tephra deposits from alaska and india and cretaceous tephra deposits from banks island in arctic canada

on the response of himalayan glaciers to climate change modelling the response of himalayan glaciers to rapid climate change is an important problem the poorly understood effects of debris cover and the variable response of the glaciers have made it difficult to understand their dynamics we propose a simple model for debris covered glaciers and validate it against data from dokriani glacier india numerical investigations of the model show that the response of debris covered glaciers to a warming climate has two timescales there is a period when the glacier loses ice by thinning but the front is almost stationary and it develops a long slow flowing tongue this stationary period which can be 100 years for glaciers with a large extent of debris cover is negligible for bare glaciers the quasi stagnant tongue does not develop in response to cooling an analysis of remote sensing data in the light of these results indicates that the variable response of the glaciers in the himalaya is consistent with a climate that is warming on average but has considerable spatial variability in the warming rates we estimate the average warming rate to be about the same as the global average

demise of one volcanic zone and birth of another a 12 m y marine record of major rhyolitic eruptions from new zealand ocean drilling program sites 1123 and 1124 provide an unprecedented 12 m y record of major rhyolitic eruptions from the coromandel and taupo volcanic zones of new zealand macroscopic tephras n 197 were dated using magnetostratigraphy supplemented by geochemical correlation with subaerial tephra isothermal plateau fission track ages and orbitally tuned stable isotope data eruptions began in the coromandel volcanic zone ca 12 ma 1 6 1 m y earlier than previously known thereafter volcanism was fairly continuous with a tempo and intensity that increased through the late miocene pliocene and into the quaternary when the taupo volcanic zone formed the transition from the coromandel to the taupo zone previously placed as ca 4 2 ma was seamless without obvious breaks or changes in ash composition this well dated history of long lived and productive volcanism allows for more confident correlation with other circum pacific tephra records thus helping confirm the occurrence of widespread coeval eruptions throughout the region

a new 14 c age for the oruanui wairakei eruption new zealand the oruanui eruption was the largest known outburst of taupo volcano new zealand and is among the larger quaternary eruptions documented the eruption deposits are variously known as the oruanui wairakei kawakawa tephra or aokautere ash formations and represent a bulk volume probably exceeding 500 km 3 four new 14 c age determinations on carbonized vegetation in the non welded oruanui ignimbrite are combined to give a conventional age of 22590 230 yr b p compared with the previously accepted figure of 20000 yr b p this new age resolves the anomaly of apparently older 14 c ages being obtained from a demonstrably younger new zealand deposit and strengthens correlation of this eruption with an antarctic ice core acid anomaly the trace of this eruption has great potential as a time plane marker in the antarctic just prior to the last glacial maximum the close similarity in ages between the oruanui and a comparable sized eruption ito aira tn in japan suggests that this period of activity may represent the best chance of resolving any linkages between large scale explosive silicic volcanism and climate changes

correlation and characterisation of individual glass shards from tephra deposits using trace element laser ablation icp ms analyses current status and future potential pearce nicholas denton j s perkins w t westgate j a 2007 correlation and characterisation of individual glass shards from tephra deposits using trace element laser ablation icp ms analyses current status and future potential journal of quaternary science 22 7 pp 721 736 rae2008

review of methods of estimating rhyolitic tephra volumes applications to the taupo volcanic zone new zealand there have been at least 35 rhyolitic plinian eruptions in the last 50 kyr from 2 volcanic centres in taupo volcanic zone tvz new zealand to determine the total volume of erupted material calculation techniques are reviewed and further developed all involve extrapolation from isopach maps three methods assume an exponential decay of thickness with distance from source and a further two are based on the area enclosed by each isopach comparison of methods shows those based on area to be more accurate except the log log plot of area and thickness which requires excessive extrapolation a log volume vs thickness plot is considered superior because minimal extrapolation is needed for most tephras volumes calculated by the different methods are in reasonable agreement volumes previously calculated by the crystal concentration method are 2 3 times greater than those from the six methods used here total pumice fragmentation is probably not required for the liberation of crystals and this would decrease calculated volumes during the last 50 kyr magma has been erupted at a constant mean rate in the taupo volcanic zone a simple step function shows a strong relationship between deviations from the mean rate and either the next erupted volume or the time to the next eruption extrapolation of these step functions suggests future eruptions in less than 400 years for okataina and about 8000 years for taupo the volume of rhyolitic material erupted from tvz within the last 50 kyr is estimated at 360 km3 of tephra 350 km3 of ignimbrite and 55 km3 of extrusive equivalent to about 350 km3 of magma at an average rate of eruption of 7 km3 year at least 4200 km3 of rhyolitic magma has been erupted since the inception of tvz about 0 6 m y ago if back are spreading of tvz at 7 mm yr is compensated for by dyke intrusion into the upper 10 km of crust 8400 km3 of magma is required the total volume of magma generated by partial melting is estimated at 12 600 km3 removal of this melt would cause subsidence of 2 1 km the present depth to subvolcanic basement in tvz

vertical density currents a review of their potential role in the deposition and interpretation of deep sea ash layers marine tephra layers form important chronostratigraphic markers and may also provide information on eruption dynamics and chronology recent experiments and field data from the 1991 pinatubo eruption challenge tacit assumptions that following atmospheric fallout on the ocean surface marine sedimentation of ash grade material occurs by stokes law settling of individual grains laboratory experiments have demonstrated that vertical density currents can be initiated at representative mass flux rates further experiments described herein involving sustained particle fluxes entering stratified environments demonstrate that ash particles can decouple from the transporting fluid whose vertical motions are limited by the stable density gradient in the ocean vertical density currents generated by ash loading and gravitational destabilization of the water column can overcome the strong stable density gradients in the ocean and transport ash particles vertically 1 3 orders of magnitude faster than possible by stokesian settling greatly reducing their residence time sea bed sedimentation is inferred to involve settling of individual coarse or dense grains through the entire water column plus suspension fallout from the polydisperse turbid layer delivered by convective plumes yielding normal distribution grading the turbid layer may continue laterally as a nepheloid current under the influence of bottom slopes and or geostrophic forces either mechanism possibly modifying the grain size distribution of the suspension and hence the resulting ash layer by transporting selected fractions into different depositional locations consequently and regardless of any subsequent reworking deep sea ash isopachs may not directly reflect an eruptive signal and the ash layers may not directly record the order rate or location of arrival of ash particles at the ocean surface

microanalysis of tephra by la icp ms strategies advantages and limitations assessed using the thorsmork ignimbrite southern iceland abstract micron scale analysis of vesicular volcanic glass can be problematic because thin vesicle walls and junctions limit the area available for analysis subsurface vesicles limit the vertical thickness available microcrysts at or below the surface may contaminate glass analyses and some glasses show compositional banding in addition distal tephra are very small 10 100 m and material may be sparse we have analysed the mpi ding reference glasses and natural tephra samples pumice scoria and fiamme from the thorsmork ignimbrite southern iceland using laser ablation inductively coupled plasma mass spectrometry la icp ms three different reduction strategies are used averaging uncertainty weighting and log linear regression we then assess the data quality achieved using the various strategies using our technique we show that the main limiting factor on data quality is precision particularly for natural tephra analyses at 20 000 cps relative standard deviations rsds in the thorsmork tephra are 5 10 approximately twice those achieved in the mpi ding glasses 3 5 at the same conditions rhyolitic pumice and fiamme from the thorsmork ignimbrite are compositionally homogenous the proximal deposit also contains subordinate basalt scoria therefore the deposit is bimodal the thorsmork rhyolite correlates with the north atlantic ash zone 2 naaz2 tephra described in a marine sediment core lacasse and garbe schonberg 2001 jvgr 170 113 147

towards a protocol for the trace element analysis of glass from rhyolitic shards in tephra deposits by laser ablation icp ms laser ablation inductively coupled plasma mass spectrometry la icp ms is used widely to analyse single volcanic glass shards from quaternary tephra deposits for stratigraphic correlation as yet no generally accepted protocol for these analyses exists and published methods report significant differences in crater size and calibration strategies using ca as the internal standard cai s and not sii s for the analysis of rhyolitic glass can cause significant problems because of ablation of i ca rich phenocrysts notably ubiquitous plagioclase but also calcic amphibole apatite and allanite or ii mounting epoxy resin which can contribute to the ca internal standard signal using cai s can cause underreporting of many elements which concentrate in ca rich phenocrysts making their ablation difficult to recognize but when using sii s no such underreporting occurs additionally larger ablation craters 50 m diameter potentially incorporate even small volumes of phenocryst material whereas smaller craters 20 m diameter more frequently miss phenocrysts thus for the la icp ms analysis of rhyolitic glass shards smaller ablation craters should be employed and calibrated using sii s allowing recognition and removal of analyses incorporating ca rich phenocrysts and avoiding issues related to the ablation of the mounting resin

a multiple approach radiometric age estimate for the rotoiti and earthquake flat eruptions new zealand with implications for the mis 4 3 boundary abstract pyroclastic fall deposits of the paired rotoiti and earthquake flat eruptions from the taupo volcanic zone new zealand combine to form a widespread isochronous horizon over much of northern new zealand and the southwest pacific this horizon is important for correlating climatic and environmental changes during the last glacial period but has been the subject of numerous disparate age estimates between 35 1 2 8 and 71 6 ka all errors are 1 s d obtained by a variety of techniques a potassium argon k ar age of 64 4 ka was previously determined on bracketing lavas at mayor island volcano offshore from the taupo volcanic zone we present a new more precise 40ar 39ar age determination on a lava flow on mayor island that shortly post dates the rotoiti earthquake flat fall deposits of 58 5 1 1 ka this value coupled with existing ages from underlying lavas yield a new estimate for the age of the combined eruptions of 61 0 1 4 ka which is consistent with u th disequilibrium model age data for zircons from the rotoiti deposits direct 40ar 39ar age determinations of plagioclase and biotite from the rotoiti and earthquake flat eruption products yield variable values between 49 6 2 8 and 125 3 10 0 ka with the scatter attributed to low radiogenic ar yields and or alteration and or inheritance of xenocrystic material with inherited ar rotoiti earthquake flat fall deposits occur in new zealand in association with palynological indicators of mild climate attributed to marine isotope stage mis 3 and thus used to suggest an age that is post 59 ka the natures of the criteria used to define the mis 4 3 boundary in the northern and southern hemispheres however imply that the new 61 ka age for the rotoiti earthquake flat eruption deposits will provide the inverse namely a more accurate isochronous marker for correlating diverse changes across the mis 4 3 boundary in the southwest pacific

reconstructing the quaternary evolution of the world s most active silicic volcanic system insights from an 1 65 ma deep ocean tephra record sourced from taupo volcanic zone new zealand abstract the taupo volcanic zone tvz central north island new zealand is the most frequently active quaternary rhyolitic system in the world silicic tephras recovered from ocean drilling programme site 1123 41 47 16 s 171 29 94 w 3290 m water depth in the southwest pacific ocean provide a well dated record of explosive tvz volcanism since 1 65 ma we present major minor and trace element data for 70 quaternary tephra layers from site 1123 determined by electron probe microanalysis 1314 analyses and laser ablation inductively coupled plasma mass spectrometry 654 analyses trace element data allow for the discrimination of different tephras with similar major element chemistries and the establishment of isochronous tie lines between three sediment cores 1123a 1123b and 1123c recovered from site 1123 these tephra tie lines are used to evaluate the stratigraphy and orbitally tuned stable isotope age model of the site 1123 composite record trace element fingerprinting of tephras identifies 4 5 m and 7 9 m thick sections of repeated sediments in 1123a 49 0 53 5 mbsf metres below seafloor and 1123c 48 1 56 0 mbsf respectively these previously unrecognised repeated sections have resulted in significant errors in the site 1123 composite stratigraphy and age model for the interval 1 15 1 38 ma and can explain the poor correspondence between 18o profiles for site 1123 and site 849 equatorial pacific during this interval the revised composite stratigraphy for site 1123 shows that the 70 tephra layers when correlated between cores correspond to 37 38 individual eruptive events tephras 7 of which can be correlated to onshore tvz deposits the frequency of large volume tvz derived silicic eruptions as recorded by the deposition of tephras at site 1123 has not been uniform through time rather it has been typified by short periods 25 50 ka of intense activity bracketed by longer periods 100 130 ka of quiescence the most active period at least 1 event per 7 ka occurred between 1 53 and 1 66 ma corresponding to the first 130 ka of tvz rhyolitic magmatism since 1 2 ma 80 of tephras preserved at site 1123 and the more proximal site 1124 were erupted and deposited during glacial periods this feature may reflect either enhanced atmospheric transport of volcanic ash to these sites up to 1000 km from source during glacial conditions or more speculatively that these events are triggered by changes in crustal stress accumulation associated with large amplitude sea level changes only 8 of the 37 38 site 1123 tephra units 20 can be found in all three cores and 22 tephra units 60 are only present in one of the three cores whether a tephra is preserved in all three cores does not have any direct relationship to eruptive volume instead it is postulated that tephra preservation at site 1123 is patchy and influenced by the vigorous nature of their deposition to the deep ocean floor as vertical density currents at this site at least 5 cores would need to have been drilled within a proximity of 10 s to 100 s of metres of each other to yield a 99 chance of recovering all the silicic tephras deposited on the ocean surface above it in the past 1 65 ma

late quaternary oceanic fronts along chatham rise indicated by phytoplankton assemblages and refined calcareous nannofossil stratigraphy for the mid latitude sw pacific abstract a quantitative analysis was carried out of planktonic diatoms biogenic opal and calcareous nannofossils biogenic calcite in late quaternary sediments mis 1 6 from four cores along a n s transect east of new zealand from 39 50 s to 50 04 s across the e w trending submarine ridge the chatham rise this was done to trace movements of oceanic fronts and to improve calcareous nannofossil stratigraphy for the last 130 000 yr in the sw pacific sites odp 1123 and q 858 are below present day subtropical surface waters north of chatham rise site dsdp 594 is below present day mixed temperate subantarctic surface water south of the rise and site odp 1120 is below subantarctic surface water the more diverse and opportunistic planktonic diatoms provided marker species for subtropical surface waters alveus marina fragilariopsis doliolus rhizosolenia bergonii and azpeitia nodulifer and others for subantarctic surface waters nitzschia kerguelensis thalassiosira lentiginosa application of these tracers permits the following conclusions 1 subtropical conditions persisted north of chatham rise throughout the past 130 000 yr in spite of the cooling of surface waters during colder periods 2 during warm times mis 5 and mis 3 and in mis 1 the sporadic occurrence of subtropical species south of chatham rise indicates occasional admixture of subtropical surface waters that far south 3 subantarctic waters extended to the southern slopes of the chatham rise during mis 5b late mis 5a to early mis 4 during the warmer time intervals in early mis 3 and during latest mis 3 to early mis 2 4 subantarctic frontal conditions existed over southern chatham rise during early mis 4 and late mis 3 to early mis 2 and 5 it is probable that during cooler times mis 6 mis 5b and in mis 2 intensified particle transport from the bounty trough to the northern flank of chatham rise occurred by intensified boundary currents the larger abundance fluctuations in both microfossil groups at the sites south of chatham rise than north of chatham rise reflect northward shifts of the circumpolar subantarctic water csw and a contemporaneous disappearance of australasian subantarctic water asw implying an elevated temperature gradient between the surface water masses north and south of the chatham rise at the times of such northward shifts of csw calcareous nannofossils are less diverse than diatoms and are less specialised some calcareous nannofossil species show abundance shifts at the same time at different latitudes two of these abundance shifts can be used for correlation between subtropical and subantarctic sediments in the sw pacific 1 reversal in the relative abundance of calcidiscus leptoporus and coccolithus pelagicus associated with the mis 2 1 boundary and 2 drop in abundance of gephyrocapsa muellerae or medium sized gephyrocapsa at the mis 4 3 boundary an additional abundance shift seems to be restricted to subtropical to mixed temperate subtropical subantarctic surface waters 3 increase in abundance of g muellerae or medium sized gephyrocapsa at the beginning of mis 2 below the okareka tephra

paleovegetation of marine isotope stages 4 and 3 in northern new zealand and the age of the widespread rotoehu tephra abstract paleolake sediment constrained by tephrochronology from onepoto basin volcanic crater in auckland northern new zealand 36 48 s provides one of the few uninterrupted records of paleovegetation for marine oxygen isotope stages mis 4 and 3 76 000 26 000 yr b p in the region this period was characterized by cool temperate conifer hardwood forest that lacked some of the warmer taxa typical of the holocene the period 64 400 60 500 yr b p was marked by opening of forest canopy and expansion of small trees and shrubs and correlates to the thermal minima of mis 4 however the landscape was never as open as the forest shrubland mosaic of the mis 2 the beginning of mis 3 60 500 50 500 yr b p was marked by the dramatic expansion and then decline of conifer hardwood forest dominated by dacrydium cupressinum a species that prefers wetter conditions this forest was succeeded by the typically montane nothofagus at 50 500 yr b p corresponding to a thermal decline thus mis 3 began with an abrupt change to moist cool conditions that lasted about 5000 yr followed by gradual cooling and dryer conditions this supports some interpretations from other parts of the southwest pacific region that mis 3 was a period of increased precipitation the widespread and stratigraphically important rotoehu tephra erupted from okataina volcanic centre has been variously dated at 45 000 65 000 yr b p at onepoto sedimentation rate and paleovegetation reconstruction imply an age of c 44 300 yr b p the tephra provides a correlation horizon in the marine and terrestrial realms during a period mis 3 difficult to date by radiometric methods

regional sediment recycling in the abyssal southwest pacific ocean an active plate boundary with a high sediment output three major submarine channels and the world9s largest deep western boundary current dwbc make up an extensive recycling system along the 4500 km continental margin east of new zealand seismic reflection sedimentary and oceanographic data demonstrate that detritus from the rising mountains of the new zealand plate boundary is transferred to the southwest pacific abyssal floor by turbidity currents flowing along solander 450 km long bounty 950 km and hikurangi 1400 km channels these conduits discharge directly into the dwbc which transports material north to form a series of sediment drifts the northernmost drift containing sediment from hikurangi channel and eroded drifts to the south is now subducting into kermadec trench geochemical data suggest that sediment is recycled through the mantle to re emerge in the arc volcanic rocks thus one cycle is completed and a new one begins

optical dating of paleosols bracketing the widespread rotoehu tephra north island new zealand abstract optical dating of the fine grained mineral fraction of paleosols developed on or within loess bracketing the widespread rotoehu tephra at two sites in central north island new zealand was undertaken using infrared excitation of potassium feldspars optical ages suggest that rotoehu tephra was deposited at ca 45 ka and support several previous age determinations our optical ages are also consistent with individual k ar ages from bracketing lava flows though inconsistent with the currently preferred age for the tephra 64 4 ka which is the weighted mean of them our data also suggests that the age of two other important time stratigraphic markers tihoi and tahuna tephras estimated to have been deposited at 46 and 43 ka respectively may have instead been formed between 25 and 35 ka in the light of this the chronology of other north island tephra beds older than 30 ka may have to be revised

fluctuations of the campanian explosive volcanic activity south italy during the past 190 000 years as determined by marine tephrochronology abstract a statistical analysis of the time variations of the frequency of explosive events is derived from the detailed record of marine tephra in deep sea sediment cores of the central mediterranean sea the sequence of campanian events south italy shows several volcanic pulses during the past 190 000 years which were compared to the continental data these episodes which match the different phases of the geochemical evolution of magmas in this area occurred with a 23 kyr periodicity this may be related to the life time of the magma chambers involved in this area with such time cycles precessional forcing of the volcanic activity and or glacio eustatic pressure variations may be envisaged as causal phenomena

correlating tephras and cryptotephras using glass compositional analyses and numerical and statistical methods review and evaluation abstract we define tephras and cryptotephras and their components mainly ash sized particles of glass crystals in distal deposits and summarize the basis of tephrochronology as a chronostratigraphic correlational and dating tool for palaeoenvironmental geological and archaeological research we then document and appraise recent advances in analytical methods used to determine the major minor and trace elements of individual glass shards from tephra or cryptotephra deposits to aid their correlation and application protocols developed recently for the electron probe microanalysis of major elements in individual glass shards help to improve data quality and standardize reporting procedures a narrow electron beam diameter 3 5 m can now be used to analyze smaller glass shards than previously attainable reliable analyses of microshards defined here as glass shards in part 2 of the review we describe critically assess and recommend ways in which tephras or cryptotephras can be correlated in conjunction with other information using numerical or statistical analyses of compositional data statistical methods provide a less subjective means of dealing with analytical data pertaining to tephra components usually glass or crystals phenocrysts than heuristic alternatives they enable a better understanding of relationships among the data from multiple viewpoints to be developed and help quantify the degree of uncertainty in establishing correlations in common with other scientific hypothesis testing it is easier to infer using such analysis that two or more tephras are different rather than the same adding stratigraphic chronological spatial or palaeoenvironmental data i e multiple criteria is usually necessary and allows for more robust correlations to be made a two stage approach is useful the first focussed on differences in the mean composition of samples or their range which can be visualised graphically via scatterplot matrices or bivariate plots coupled with the use of statistical tools such as distance measures similarity coefficients hierarchical cluster analysis informed by distance measures or similarity or cophenetic coefficients and principal components analysis pca some statistical methods cluster analysis discriminant analysis are referred to as machine learning in the computing literature the second stage examines sample variance and the degree of compositional similarity so that sample equivalence or otherwise can be established on a statistical basis this stage may involve discriminant function analysis dfa support vector machines svms canonical variates analysis cva and anova or manova or its two sample special case the hotelling two sample t2 test randomization tests can be used where distributional assumptions such as multivariate normality underlying parametric tests are doubtful compositional data may be transformed and scaled before being subjected to multivariate statistical procedures including calculation of distance matrices hierarchical cluster analysis and pca such transformations may make the assumption of multivariate normality more appropriate a sequential procedure using mahalanobis distance and the hotelling two sample t2 test is illustrated using glass major element data from trachytic to phonolitic kenyan tephras all these methods require a broad range of high quality compositional data which can be used to compare unknowns with reference training sets that are sufficiently complete to account for all possible correlatives including tephras with heterogeneous glasses that contain multiple compositional groups currently incomplete databases are tending to limit correlation efficacy the development of an open online global database to facilitate progress towards integrated high quality tephrostratigraphic frameworks for different regions is encouraged

neogene palaeoceanography of chatham rise southwest pacific based on sediment geochemistry approximately one thousand sediment samples from odp site 1123 on the chatham rise east of new zealand have been examined for inorganic elemental concentrations odp 1123 provides a record of sediment drift deposition under the deep western boundary current the main inflow of deep water to the pacific ocean since the early oligocene though a major hiatus spans the late early oligocene to the early miocene normalisation of the elemental concentrations by aluminium was used to allow for the effects of variable carbonate dilution the elemental ratios were used as proxies for sediment composition and as palaeoceanographic indices the samples were collected at a resolution designed to sample adequately any variation in elemental ratios at the scale of the milankovitch orbital cycles the sampled intervals span the early oligocene early miocene mid miocene and late pleistocene to recent anomalous si al k al ti al values in the upper pleistocene section often associated with horizons of low carbonate are attributed to tephras derived from north island not all of the tephras detected geochemically had been detected visually in the cores a total of 37 tephra events between 1 17 ma bp and the present are recognised based on this and the shipboard investigations the tephra events cluster at intervals of approximately 326 000 years 326 ka perhaps due to variations in eruption frequency on north island and or to variations in the regional palaeowind intensity and direction in the late pleistocene to recent p al inferred nutrient availability percent calcium carbonate caco3 and ba al inferred productivity varied regularly at a period of 40 000 years with these factors lagging minimum global ice volumes interglacials during the mid miocene caco3 ba al p al and si al all gradually increased with caco3 and p al showing regular 138 000 yr cyclicity and ba al showing 44 ka cyclicity inferred productivity ba al may have been rising in association with increasing nutrient availability p al at the same time as increased vigour of the deep western boundary current that was connected to a period of rapid ice sheet growth in antarctica in the early miocene p al and si al were much higher than subsequently and both caco3 and p al exhibited 131 000 yr cycles by far the highest nutrient levels and inferred productivity at this site apparently occurred during the early oligocene as revealed by long term changes in p al and si al a progressive rise in k al but stable ti al from the early oligocene to the recent probably indicates increased proportions of illite in the clay mineral fraction of the drift sediments caused by increased flux of debris from the southern alps

early to middle pleistocene tephrochronology of north island new zealand implications for volcanism tectonism and paleoenvironments thick volcaniclastic sequences of early to middle pleistocene age in southern north island new zealand contain rhyolitic tephra beds that record the early history of the taupo volcanic zone tvz at least 54 different tephra beds are recorded and their chronology is defined by glass fission track ages and paleomagnetism the tephra beds span the interval ca 2 0 0 6 ma and provide an event frequency of 1 19 k y significantly higher than the frequency of sheet forming ignimbrites preserved in the tvz at this time 1 100 k y the distal tephra beds thus provide a record of volcanism not revealed in the proximal volcanic region and suggest a major period of explosive activity at ca 1 79 1 60 ma several important marker horizons are identified pakihikura tephra 1 63 ma mangatewaiiti tephra 1 24 ma potaka tephra 1 00 ma kidnappers b tephra 1 00 ma and kaukatea tephra 0 88 ma these tephra beds allow direct correlation between 1 marine and nonmarine facies and 2 the fore arc and back arc regions of new zealand the tephra beds provide a framework for a paleoenvironmental reconstruction of the southern north island volcaniclastic transport routes from the tvz to basins in the south and southeast and through the site of present mountain ranges supplied material to a terrestrial lowland fore arc area in the interval 1 64 0 7 ma uplift and deformation since 0 7 ma have disrupted paleodrainage routes diverting them to the north and southwest

revision of the marine chronology in the wanganui basin new zealand based on the isothermal plateau fission track dating of tephra horizons abstract the occurrence of tephra horizons in basins adjacent to volcanic arcs provide an excellent opportunity for establishing a reliable chronostratigraphic framework for detailed sedimentological studies in this study three widespread and stratigraphically important rhyolitic tephra horizons interbedded in plio pleistocene strata of the wanganui basin new zealand are dated by application of the isothermal plateau fission track itpft technique to hydrated glass shards all glass samples were corrected for annealing and consequently yield reliable ages rangitawa tephra yielded statistically indistinguishable ages from three localities that are in excellent agreement with recently determined zircon fission track age estimates of ca 0 35 ma itpft ages of 1 05 0 05 and 1 63 0 15 ma for potaka pumice and pakihikura pumice respectively are considerably older than previous ft estimates but consistent with new magnetostratigraphic data that places the potaka within the jaramillo subchron and pakihikura within the matuyama chron between the cobb mountain and olduvai subchrons combining our fission track ages with the magnetostratigraphy the true age of sediments within the wanganui basin is found to be significantly underestimated sedimentation rates of between ca 680 630 m ma from 1 63 ma to 0 35 ma are calculated in the eastern part of the basin and are much lower than those calculated using the previous ft chronology this new itpft age data demonstrates that the existing plio pleistocene marine chronology in new zealand will require age revision and has important implications when considering the evolution of several other sedimentary basins in southern north island that contain the same itpft dated tephra horizons

eruptions of pavlof volcano and their possible modulation by ocean load and tectonic stresses all nine magmatic eruptions at pavlof volcano in six of the years from 1973 to 1984 have occurred between september 9 and november 20 volumes of erupted material range from 0 1 to 15 9 106 m3 dense rock equivalent at an average rate of 3 106 m3 yr 1 the volumes are estimated from eyewitness reports for two eruptions the others are estimated from a relationship that we derive between eruption volume and harmonic tremor duration and amplitude the volume of lava erupted is approximately time predictable a significant correlation exists between the eruptions and yearly nontidal variations in sea level and may result from ocean loading calculated volume changes beneath the volcano due to ocean loading are from 0 02 to 2 times eruption volumes and we postulate that the volcano acts as a long period several month volume strain meter with lava being preferentially erupted when strain beneath the volcano is compressive the volcano did not erupt during the period 1978 1980 when tilt seismic data and sea level data indicate that deep aseismic slip may have occurred models of this event predict a volume increase beneath the volcano that might have compensated strain from magma injection these observations indicate that pavlof volcano may be responsive to small slow changes in ambient stresses or strains and that these changes may modify or trigger eruptions

fingerprints and age models for widespread new zealand tephra marker beds erupted since 30 000 years ago a framework for nz intimate abstract 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 2 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