influences on the carbonate hydrochemistry of mound spring environments lake eyre south region south australia abstract mound spring structures composed of tufa precipitated from near ambient temperature spring waters are rare consequently the hydrochemical evolution of the water and the processes that control carbonate deposition in these systems are not well understood this study analysed the water from 3 mound springs in an arid environment in the vicinity of lake eyre south south australia samples were tested for major ion chemistry and stable isotope ratios of water 2 h 1 h and 18 o 16 o most co 2 degasses from water i before emergence as it ascends in the fracture derived spring conduit system below the spring opening and ii after emergence in the turbulent upper tail environment between the spring vent pool and the tail delta however modern carbonate precipitation was generally restricted to tail delta environments spatially disconnected from the areas of strongest co 2 degassing in addition to co 2 degassing and carbonate precipitation evapotranspiration and heterotrophy were inferred to be processes controlling the chemical evolution of water flowing through the tail delta based on considerations of the geometry of the tail delta and evapotranspiration rates it was inferred that infiltration is an important process in determining the tail delta size and hence the morphology of the mound spring environment a reactive transport model was used to assess the importance of these processes for the evolution of carbonate hydrochemistry the model outcomes showed that water loss via evapotranspiration does not significantly affect tufa precipitation despite the springs being located within an arid environment heterotrophy was considered in the model in order to reproduce observed ph and carbonate concentrations highlighting the role of vegetation in controlling the water chemistry the modelling approach adopted here provides a generic framework for the analysis of calcareous spring deposits and places quantitative constraints on data based process conceptualisation

tracing marine cryptotephras in the north atlantic during the last glacial period protocols for identification characterisation and evaluating depositional controls abstract tephrochronology is increasingly being utilised as a key tool for improving chronological models and correlating disparate palaeoclimatic sequences for many sedimentary environments however there is an increased recognition that a range of processes may impart a delay in deposition and or rework tephra these processes can affect the integrity of tephra deposits as time synchronous markers therefore it is crucial to assess their isochronous nature especially when cryptotephras are investigated in a dynamic marine environment a methodology for the identification and characterisation of marine cryptotephras alongside a protocol for assessing their integrity is outlined this methodology was applied to a wide network of north atlantic marine sequences covering the last glacial period a diverse range of cryptotephra deposits were identified and based on similarities in physical characteristics e g glass shard concentration profiles and geochemical homogeneity heterogeneity indicative of common modes of tephra delivery and post depositional reworking a deposit type classification scheme was defined the presence and dominance of different deposit types within each core allowed an assessment of spatial and temporal controls on tephra deposition and preservation overall isochronous horizons can be identified across a large portion of the north atlantic due to preferential atmospheric dispersal patterns however the variable influence of ice rafting processes and an interplay between the high eruptive frequency of iceland and relatively lower sedimentation rates can also create complex tephrostratigraphies in this sector sites within a wide sector to the south and east of iceland have the greatest potential to be repositories for isochronous horizons that can facilitate the synchronisation of palaeoclimatic records

radiocarbon dating of residual organic matter in travertine formed along the yumoto fault in oga peninsula northeast japan implications for long term hot spring activity under the influence of earthquakes abstract radiocarbon dating was performed on trace amounts of organic matter included in travertines formed along the yumoto fault in oga peninsula ne japan the reliability of the dating method was confirmed by the consistency of ages obtained with the stratigraphy of the travertine mound and the ratio of carbon stable isotopes the radiocarbon chronology of the travertines shows that 1 the hot springs at oga have been active for approximately 29 000 years with average depositional rates ranging from 0 24 to 1 75 mm yr and 2 the principal hot spring activity has migrated southward with time variations in the accumulation rates and the progressive migration of the main focus of the hot spring activity imply irregular spring behaviour this behaviour has not been influenced by paleoclimate but may have been controlled by the earthquakes that occur frequently in the region around oga peninsula

origin and palaeo environmental significance of the berrazales carbonate spring deposit north of gran canaria island spain the berrazales carbonate spring deposit is a small outcrop constituted mainly by cascade like geometries four main facies have been identified fibrous dense macrocrystalline formed by rapid degassing under high flow conditions framestones of coated plant moulds formed in moderate energy flow favoured by the presence of biogenic support micrite microsparite are primary precipitates in which crystalline aggregates nucleated on organic filaments and or eps banded micrite coarse crystalline were the result of alternating physically chemically and biologically induced precipitation in areas of varying flow velocities most facies underwent different degrees of micritization processes micrite is distributed as thin lines penetrating the crystals as irregular patches or as micrite layers in the first case organic filaments penetrate crystals suggesting that micritization is mainly biogenically driven in the latter cases micritization is caused mostly by partial dissolution microbe participation in micrite formation increased micrite mgco3 content in comparison with coarse crystalline facies isotopic analyses show positive 13c values 2 63 and 4 29 vpdb and negative 18o 5 65 and 4 48 vpdb values positive 13c values clearly indicate deep sourced fluids the berrazales spring deposit studied here very probably is a small part of a larger carbonate building that was largely eroded by fluvial incision calculations of spring water temperature give a range from 20 c to 35 c characteristic of a cold to warm spring favouring precipitation of calcite and important biogenic activity framestones although the study deposit has textural characteristics of tufas proving that the co2 sourced from deep fluids it should be considered as thermogene travertine being one more example of the difficulty of using those terms for ancient sedimentary deposits carbonate spring deposits very rare in the canary islands are good archives of recent volcanic activity fluvial processes and vegetation regimes prevailing in the islands in recent times

meso cenozoic tectonic evolution of the se brazilian continental margin petrographic kinematic and dynamic analysis of the onshore araruama lagoon fault system abstract the ararauama lagoon fault system composes one of the most prominent set of lineaments of the se brazilian continental margin it is located onshore in a key tectonic domain where the basement inheritance rule is not followed this fault system is characterized by ene wsw silicified tectonic breccias and cataclasites showing evidences of recurrent tectonic reactivations based on field work microtectonic kinematic and dynamic analysis we reconstructed the paleostresses in the region and propose a sequence of three brittle deformational phases accountable for these reactivations 1 ne sw dextral transcurrence 2 nnw sse dextral oblique extension that evolved to nnw sse pure extension 3 ene wsw dextral oblique extension these phases are reasonably correlated with the tectonic events responsible for the onset and evolution of the se onshore rift basins between the neocretaceous and holocene however based on petrographic studies and supported by regional geological correlations we assume that the origin of this fault system is older related to the early cretaceous south atlantic rifting this study provides significant information about one of the main structural trends of the se brazilian continental margin and the tectonic events that controlled its segmentation since the gondwana rifting and compartmentalization of its onshore sedimentary deposits during the cenozoic

faroe marine ash zone iv a new mis 3 ash zone on the faroe islands margin a basaltic tephra layer from mis 3 has been discovered by analysis of cores from the faroe islands margin the tephra layer appears up to 20 cm thick in some records after the first main fall out event the tephra is believed to be mainly deposited and redistributed by bottom currents geochemical analyses suggest that the tephra is relatively undisturbed by allochtonous tephra grains and unmixed the peak occurrences are in the lower part of gis greenland interstadial 12 and we suggest naming this new tephra faroe marine ash zone iv fmaz iv following the nomenclature adopted for previous ash zones found on the faroe islands margin geochemical analyses of the tephra show affinities with the grimsvotn volcanic system in the eastern volcanic zone in south iceland the average age of fmaz iv from four independent age models is 46 800 1000 years bp we suggest that the v5 ash zone found on the reykjanes ridge is a correlative to the fmaz iv

tephrological implications of beam size sample size effects in electron microprobe analysis of glass shards this paper concerns the potential consequences of varying procedures for the determination of tephra geochemistry by electron microprobe application of electron probe microanalysis to tephrostratigraphical methods has increasingly facilitated the resolution and refinement of quaternary chronology associated with records of proxy environmental or proxy climatic change the geographical range over which tephras are recovered has expanded significantly with the identification and analysis of crypto or hidden tephras in areas far removed from tephra sources these tephras are dominated by glass shards which in many distal environments may be either small in size m or may be highly pumiceous with low glass void ratios and thin 10 m shard walls we demonstrate that reducing the size of the electron beam used to analyse shard geochemistry cannot be used reliably to permit analysis of thin glass walls this approach distorts the geochemical data creating analytical differences that may generate inappropriate tephrogeochemical fingerprints additional distortion of the geochemical fingerprint in the form of hybrid analyses may be encountered in glass fragments containing micron sized crystalline phases such as feldspar copyright 2001 john wiley sons ltd

microbial dolomite in fresh water carbonate deposits this article reports evidence for biologically mediated precipitation of dolomite in a fresh water spring in the south east of spain build ups in the spring consisted of calcite minor dolomite barite and gypsum crystals formed by the mineralisation of microbial biofilms and bryophytes a detailed microscopic study coupled with geochemical analysis of the dolomite precipitating biofilms showed that dolomite crystals occurred in association with living coccoid micro organisms providing strong evidence that micro organisms play a fundamental role in the precipitation of this mineral many of the calcite crystals observed were associated with extracellular polymeric substances moreover microbial involvement in the precipitation of calcite was further supported by the presence of living cyanobacteria within the calcite crystals two different types of build up were found in the spring soft spongy moss tufa and laminated crusts two types of crusts were identified as follows simple pink crusts and laminated crusts the latter forming in both sub aquatic and sub aerial environments sub aquatic accumulation of simple detached pink crust fragments occurred sporadically both tufa and the carbonate crusts hosted cyanobacterial dominated biofilms with different bacteria and diatoms and their extracellular polymeric substances the 13c values of calcite showed some biogenic involvement in the origin of this mineral the 18o values were similar in the tufa and carbonate crusts and corresponded to current climatological characteristics the occurrence of different groups of minerals carbonates and sulphates in close spatial association with micro organisms suggests the presence of different macro environmental and micro environmental conditions that facilitate mineral precipitation within biofilms these findings extend the known range of aerobic microbial dolomites to include springs and show that the precipitation of both dolomite and calcite carbonates occurs while organisms are alive

phytoliths as quantitative indicators for the reconstruction of past environmental conditions in china ii palaeoenvironmental reconstruction in the loess plateau abstract quantitative reconstruction of the climatic history of the chinese loess plateau is important for understanding present and past environment and climate changes in the northern hemisphere here we reconstructed mean annual temperature mat and mean annual precipitation map trends during the last 136 ka based on the analysis of phytoliths from the weinan loess section 34 24 n 109 30 e near the southern part of the loess plateau in northern china the reconstructions have been carried out using a chinese phytolith climate calibration model based on weighted averaging partial least squares regression a series of cold and dry events as indicated by the reconstructed mat and map are documented in the loess during the last glacial periods which can be temporally correlated with the north atlantic heinrich events our mat and map estimations show that the coldest and or driest period occurred at the upper part of l2 unit late mis 6 where mat dropped to ca 4 4 c and map to ca 100 mm two other prominent cold dry periods occurred at lower ll 5 ca 77 62 ka and l1 1 ca 23 10 5 ka where the mat and map decreased to about 6 1 6 5 c and 150 370 mm respectively ca 6 6 6 2 c and 400 200 mm lower than today however the highest mat average 14 6 c max 18 1 c and map average 757 mm max 1000 mm occurred at sl interval mis 5 during the interstadial of l1 4 l1 2 mis 3 and during the holocene warm wet period the mat was about 1 2 c and map 100 150 mm higher than today in the weinan region the well dated mat and map reconstructions from the chinese loess plateau presented in this paper are the first quantitatively reconstructed proxy record of climatic changes at the glacial interglacial timescale that is based on phytolith data this study also reveals a causal link between climatic instability in the atlantic ocean and climate variability in the chinese loess plateau

a tephra lattice for greenland and a reconstruction of volcanic events spanning 25 45 ka b2k tephra layers preserved within the greenland ice cores are crucial for the independent synchronisation of these high resolution records to other palaeoclimatic archives here we present a new and detailed tephrochronological framework for the time period 25 000 45 000 a b2k that brings together results from 4 deep greenland ice cores in total 99 tephra deposits the majority of which are preserved as cryptotephra are described from the ngrip neem grip and dye 3 records the major element signatures of single glass shards within these deposits indicate that 93 are basaltic in composition all originating from iceland specifically 43 originate from grimsvotn 20 are thought to be sourced from the katla volcanic system and 17 show affinity to the kverkfjoll system robust geochemical characterisations independent ages derived from the gicc05 ice core chronology and the stratigraphic positions of these deposits relative to the dansgaard oeschger climate events represent a key framework that provides new information on the frequency and nature of volcanic events in the north atlantic region between gs 3 and gi 12 of particular importance are 19 tephra deposits that lie on the rapid climatic transitions that punctuate the last glacial period this framework of well constrained time synchronous tie lines represents an important step towards the independent synchronisation of marine terrestrial and ice core records from the north atlantic region in order to assess the phasing of rapid climatic changes during the last glacial period

ash layers from iceland in the greenland grip ice core correlated with oceanic and land sediments four previously known ash layers ash zones i and ii saksunarvatn and the settlement layer all originating in iceland have been identified in the central greenland ice core grip this correlation of the ash between the different environments is achieved by comparison of the chemical composition of glass shards from the ash this establishes and confirms detailed correlations between the different types of depositional records and the absolute dating of the younger part of the ice core by counting annual layers dates the eruptions accurately a precise connection with dates obtained by14c beyond the range of dendrochronology is established which provides an excellent confirmation of230th 234u dates from corals four additional icelandic ash layers have also been identified in the core but not yet correlated with known ash deposits

north atlantic ocean circulation and abrupt climate change during the last glaciation the most recent ice age was characterized by rapid and hemispherically asynchronous climate oscillations whose origin remains unresolved variations in oceanic meridional heat transport may contribute to these repeated climate changes which were most pronounced during marine isotope stage 3 the glacial interval 25 thousand to 60 thousand years ago we examined climate and ocean circulation proxies throughout this interval at high resolution in a deep north atlantic sediment core combining the kinematic tracer protactinium thorium pa th with the deep water mass tracer epibenthic 13c these indicators suggest reduced atlantic overturning circulation during every cool northern stadial with the greatest reductions during episodic hudson strait iceberg discharges while sharp northern warming followed reinvigorated overturning these results provide direct evidence for the ocean s persistent central role in abrupt glacial climate change

widespread tephra dispersal and ignimbrite emplacement from a subglacial volcano torfajokull iceland the tephra dispersal mechanisms of rhyolitic glaciovolcanic eruptions are little known but can be investigated through the correlation of eruptive products across multiple depositional settings using geochemistry and geochronology we correlate a regionally important pleistocene tephra horizon the rhyolitic component of north atlantic ash zone ii ii rhy 1 and the thorsmork ignimbrite with rhyolitic tuyas at torfajokull volcano iceland the eruption breached an ice mass 400 m thick leading to the widespread dispersal of ii rhy 1 across the north atlantic and the greenland ice sheet locally pyroclastic density currents traveled across the ice surface depositing the variably welded thorsmork ignimbrite beyond the ice margin and 30 km from source the widely dispersed products of this eruption represent a valuable isochronous tie line between terrestrial marine and ice core paleoenvironmental records using the tephra horizon estimates of ice thickness and extent derived from the eruption deposits can be directly linked to the regional climate archive which records the eruption at the onset of greenland stadial 15 2

four climate cycles of recurring deep and surface water destabilizations on the iberian margin centennial climate variability over the last ice age exhibits clear bipolar behavior high resolution analyses of marine sediment cores from the iberian margin trace a number of associated changes simultaneously proxies of sea surface temperature and water mass distribution as well as relative biomarker content demonstrate that this typical north south coupling was pervasive for the cold phases of climate during the past 420 000 years cold episodes after relatively warm and largely ice free periods occurred when the predominance of deep water formation changed from northern to southern sources these results reinforce the connection between rapid climate changes at mediterranean latitudes and century to millennial variability in northern and southern polar regions

non synchronous deposition of north atlantic ash zone ii in greenland ice cores and north atlantic and norwegian sea sediments an example of complex glacial stage tephra transport tephra provides regional chronostratigraphical marker horizons that can link different climate archives with highly needed accuracy and precision the results presented in this work exemplify however that the intermittent storage of tephra in ice sheets and during its subsequent iceberg transport especially during glacial stages constitutes a potential source of serious error for the application of tephrochronology to nordic seas and north atlantic sediment archives the peak shard concentration of the rhyolitic component of the north atlantic ash zone ii naaz ii tephra complex often used to correlate marine and ice core records in marine isotope stage mis 3 is shown to lag the eruption event by ca 100 400 years in some north atlantic and norwegian sea cores while still allowing for a correlation of archives on millennial timescales this time delay in deposition is a major obstacle when addressing the lead lag relationship on short timescales years to centuries a precise and accurate determination of lead lag relationships between archives recording different parts of the climate system is crucial in order to test hypotheses about the processes leading to abrupt climate change and to evaluate results from climate models copyright 2011 john wiley sons ltd

establishing tephrostratigraphic frameworks to aid the study of abrupt climatic and glacial transitions a case study of the last glacial interglacial transition in the british isles c 16 8 ka bp abstract distally dispersed tephra layers have become an important tool in the investigation of palaeoenvironmental and archaeological records across the globe they offer possibilities for the synchronisation and improved chronological control in those records to which they can be traced and hence contribute to an improved understanding of the pattern and timing of environmental and archaeological change during periods of rapid climatic adjustment however their use as robust isochronous markers for synchronising records is frequently compromised by uncertainties relating to stratigraphical context precise chronology and chemical composition here we collate and review the tephrostratigraphical information dating to the last glacial interglacial transition lgit c 16 8 ka bp in the british isles based on published and unpublished records obtained from 54 sites based on details of their stratigraphic position chronology and chemical composition we propose that 26 individual eruption events may be represented in this collective record which spans the lgit the great majority of these eruptives can be traced in origin to iceland but we also report on the recent discoveries of ultra distal tephra from the north american cascades range including for the first time the mount st helens j tephra at a site in southern ireland these particular ultra distal discoveries have resulted from a reinterpretation of older data demonstrating the potential importance of unknown analyses in older tephra datasets the outcome of this review is a comprehensive but provisional tephrostratigraphic framework for the lgit in the british isles which helps to focus future research on parts of the scheme that are in need of further development or testing the results therefore make an important contribution to the wider european tephrostratigraphic framework while adding new discoveries of transcontinental isochronous tephra markers

a new high resolution holocene tephra stratigraphy in eastern iceland improving the icelandic and north atlantic tephrochronology a new and improved holocene tephra stratigraphy and tephrochronological framework for eastern and northern iceland is presented investigations of a sediment sequence from lake logurinn have revealed a comprehensive tephra record spanning the last 10 200 years a total of 157 tephra layers have been identified whereof 149 tephra layers have been correlated to its source volcanic system using geochemistry stratigraphy and age fifteen layers have chemical composition of two affinities that possibly represent two very closely spaced eruptions thus these 157 tephra layers are believed to represent 172 explosive eruptions nineteen tephra marker layers have been identified in the lake logurinn record g1922 a1875 v1477 v1410 h1636 k1625 o1362 g1354 k1262 v874 hrafnkatla sn 1 grakolla hy h3 h4 ho ll1755 and reitsvik 8 tephra markers new potential tephra markers are the silicic askja l 9400 cal bp the low titanium basalt layers ll 1774 10 150 cal bp and ll 1755 9990 cal bp assigned to veidivotn bardarbunga and the tephra layers ll 1527 8 7850 cal bp ll 911 2 2370 cal bp ll 908 4 2350 cal bp ll 781 9 1930 cal bp ll 644 4 1480 cal bp not yet correlated to a source volcanic system a silicic tephra marker layer reitsvik 8 correlated to the fosen tephra in norway has been identified in lake logurinn the lake logurinn tephra record has been connected and integrated with the icelandic terrestrial tephrochronology and stratigraphy through 102 tephra layers the marine tephra stratigraphy through 39 layers and overseas through 9 tephra layers this record is the first high resolution tephra stratigraphical and chronological framework for the holocene in eastern iceland as well as the most detailed and continuous record and has considerable potential to serve as a key section or a stratotype for the holocene in eastern iceland and the north atlantic

hotspot volcanism close to a passive continental margin the canary islands the canarian archipelago is a group of volcanic islands on a slow moving oceanic plate close to a continental margin the origins of the archipelago are controversial a hotspot or mantle plume a zone of lithospheric deformation a region of compressional block faulting or a rupture propagating westwards from the active atlas mountains fold belt have been proposed by different authors however comparison of the canarian archipelago with the prototypical hotspot related island group the hawaiian archipelago reveals that the differences between the two are not as great as had previously been supposed on the basis of older data quaternary igneous activity in the canaries is concentrated at the western end of the archipelago close to the present day location of the inferred hotspot this is the same relationship as seen in the hawaiian and cape verde islands the latter archipelago associated with a well defined but slow moving mantle plume shows anomalies in a plot of island age against distance which are comparable to those seen in the canary islands these anomalies cannot therefore be used to argue against a hotspot origin for the canaries individual islands in both archipelagoes are characterized by initial rapid growth the shield building stages of activity followed by a period of quiescence and deep erosion erosion gap which in turn is followed by a post erosional stage of activity the absence of post shield stage subsidence in the canaries is in marked contrast with the major subsidence experienced by the hawaiian islands but is comparable with the lack of subsidence evident in other island groups at slow moving hotspots such as the cape verdes comparison of the structure and structural evolution of the canary islands with other oceanic islands such as hawaii and reunion reveals many similarities these include the development of triple mercedes star rift zones and the occurrence of giant lateral collapses on the flanks of these rift zones the apparent absence of these features in the post erosional islands may in part be a result of their greater age and deeper erosion which has removed much of the evidence for their early volcanic architecture we conclude that the many similarities between the canary islands and island groups whose hotspot origins are undisputed show that the canaries have been produced in the same way

developing a holocene tephrostratigraphy for northern japan using the sedimentary record from lake kushu rebun island abstract palaeoclimate records in east asia offer significant potential to further our understanding of monsoon dynamics and can serve as a link between north atlantic and tropical climate systems the sedimentary core from lake kushu rebun island provides the first high resolution palaeoclimate record from northern japan in order for this regionally significant archive to be synchronised to other records and to generate a more detailed holocene tephra lattice for east asia we present the first cryptotephra stratigraphy for northern japan using the kushu rk12 core the detailed rk12 tephrostratigraphy integrates local and far travelled tephras originating from japan russia china north korea and most likely indonesia five key cryptotephra layers have been identified precisely dated and correlated to the specific eruptions or the source region b tm tephra changbaishan volcano sh 12 tephra shiveluch volcano ko g tephra komagatake volcano ma f j tephra mashu volcano and rk12 0819 tephra with possible indonesian origin these tephra horizons are very widely dispersed providing opportunities to synchronise distant palaeoclimate records from the polar region through high northern latitudes to the tropics which facilitate interregional comparison of palaeoclimate and environmental data in addition a number of the geochemically analysed horizons contain other minor numbers of compositionally distinct glass which can also be grouped and correlated to their source volcanoes these minor analyses are of interest since they provide new insight into regional tephra dispersal e g ash dispersal potential of aira and towada and could suggest that there are other potential eruptions that have yet to be identified in the geological record e g potential changbaishan eruptions the integrated lake kushu cryptotephra record extends the ash dispersal of several key tephra horizons in the region the presence of the shiveluch sh 12 tephra in lake kushu ca 1900 km away documents the first example of a russian tephra reaching the japanese archipelago furthermore glass compositions suggest that the core could preserve an eruption event derived from indonesia highlighting the future possibility to significantly extend and interlink the tephra lattice across the entirety of asia this is an essential step for the understanding of how climate changes propagate over large geographical areas indeed several of these tephra markers coincide with significant ecological changes reflected in the pollen proxy record at lake kushu using this high resolution palaeoenvironmental record we however find no significant ecological impact following the large late holocene millennium eruption from changbaishan china north korea

the intav intercomparison of electron beam microanalysis of glass by tephrochronology laboratories results and recommendations abstract the international focus group on tephrochronology and volcanism intav of the international union for quaternary research inqua has conducted an intercomparison of tephrochronology laboratories with electron beam microanalytical data on volcanic glasses submitted from 27 instruments at 24 institutions in 9 countries this assessment includes most active tephrochronology laboratories and represents the largest intercomparison exercise yet conducted by the tephrochronology community the intercomparison was motivated by the desire to assess the quality of data currently being produced and to stimulate improvements in analytical protocols and data reporting that will increase the efficacy of tephra fingerprinting and correlation participating laboratories were each supplied with a mount containing three samples for analysis 1 rhyolitic lipari obsidian id3506 2 phonolitic sheep track tephra from mt edziza british columbia canada and 3 basaltic laki 1783 a d tephra a fourth sample rhyolitic old crow tephra was also distributed most laboratories submitted extensive details of their analytical procedures in addition to their analytical results most used some combination of defocused or rastered beam and modest beam current to reduce alkali element migration approximately two thirds reported that they routinely analyze one or more secondary standards to evaluate data quality and instrument performance despite substantial variety in procedures and calibration standards most mean concentrations compare favorably between laboratories and with other data typically four or fewer data contributions had means for a given element on a given sample that differed by more than 2 standard deviations from the overall means obtaining accurate na 2 o concentrations for the phonolitic tephra proved to be a challenge for many laboratories only one half of the data sets had means within 1 standard deviation of the 8 2 wt na 2 o value obtained by other methods one mean is higher and 14 are lower three of the data set means fall below 7 wt na 2 o most submissions had relative precision better than 1 5 for the major elements for low abundance elements the precision varied substantially with relative standard deviations as small as 10 and as large as 110 because of the strong response to this project the tephrochronology community now has a large comparative data set derived from common reference materials that will facilitate improvements in accuracy and precision and which can enable improved use of published data produced by the participating laboratories finally recommendations are provided for improving accuracy precision and reporting of electron beam microanalytical data from glasses

optimising the use of marine tephrochronology in the north atlantic a detailed investigation of the faroe marine ash zones ii iii and iv abstract tephrochronology is central to the intimate 1 goals for testing the degree of climatic synchroneity during abrupt climatic events that punctuated the last glacial period since their identification in north atlantic marine sequences the faroe marine ash zone ii fmaz ii fmaz iii and fmaz iv have received considerable attention due to their potential for high precision synchronisation with the greenland ice cores in order to optimise the use of these horizons as isochronous markers a detailed re investigation of their geochemical composition sedimentology and the processes that deposited each ash zone is presented shard concentration profiles geochemical homogeneity and micro sedimentological structures are investigated for each ash zone preserved within core jm11 19pc retrieved from the southeastern norwegian sea on the central north faroe slope this approach allows a thorough assessment of primary ash fall preservation and secondary depositional features and demonstrates its value for assessing depositional integrity in the marine environment results indicate that the fmaz ii and iv are well resolved primary deposits that can be used as isochrons for high precision correlation studies we outline key recommendations for future marine tephra studies and provide a protocol for optimising the application of tephrochronology to meet the intimate synchronisation goals

the reset project constructing a european tephra lattice for refined synchronisation of environmental and archaeological events during the last c 100 ka this paper introduces the aims and scope of the reset project response of humans to abrupt environmental transitions a programme of research funded by the natural environment research council uk between 2008 and 2013 it also provides the context and rationale for papers included in a special volume of quaternary science reviews that report some of the project s findings reset examined the chronological and correlation methods employed to establish causal links between the timing of abrupt environmental transitions aets on the one hand and of human dispersal and development on the other with a focus on the middle and upper palaeolithic periods the period of interest is the last glacial cycle and the early holocene c 100 8 ka during which time a number of pronounced aets occurred a long running topic of debate is the degree to which human history in europe and the mediterranean region during the palaeolithic was shaped by these aets but this has proved difficult to assess because of poor dating control in an attempt to move the science forward reset examined the potential that tephra isochrons and in particular non visible ash layers cryptotephras might offer for synchronising palaeo records with a greater degree of finesse new tephrostratigraphical data generated by the project augment previously established tephra frameworks for the region and underpin a more evolved tephra lattice that links palaeo records between greenland the european mainland sub marine sequences in the mediterranean and north africa the paper also outlines the significance of other contributions to this special volume collectively these illustrate how the lattice was constructed how it links with cognate tephra research in europe and elsewhere and how the evidence of tephra isochrons is beginning to challenge long held views about the impacts of environmental change on humans during the palaeolithic

composition and origin of ash zones from marine isotope stages 3 and 2 in the north atlantic abstract the composition and distribution of four north atlantic ash zones from the faroe islands margin is presented including the widespread north atlantic ash zone ii naaz ii 52 53 ka bp and three mainly basaltic ash zones here referred to as the faroe marine ash zones fmaz i ca 15 4 14 c ka bp ii ca 23 14 c ka bp also referred to as the fugloyarbanki tephra and iii ca 33 14 c ka bp one core from the south east labrador sea was also analysed naaz ii was found in all investigated cores indicating very large eruption events in the early marine isotope stage mis 3 detailed investigations of naaz ii in high resolution cores show that two separate layers can be distinguished a lower mixed alkalic basalt and rhyolitic layer and an upper predominantly tholeiitic basalt tephra the main component of the basaltic fmaz ii was found in all cores from the faroe island margin and the labrador sea indicating that this tephra is the most widespread tephra from mis 2 in the north atlantic discovered so far we discuss the possibility to use these tephra layers for exact correlations between marine records and land sections such as the greenland ice cores and terrestrial records on the european mainland

40ar 39ar dating of the thorsmork ignimbrite and icelandic sub glacial rhyolites abstract robust correlation of paleoclimatic archives e g marine sediments ice speleothems necessitates an increase of the number of independent and accurately dated stratigraphic markers using numerical methods icelandic rhyolitic volcanism has a strong chronological interest because these products are found as tephra in the north atlantic marine archives as well as in greenland ice cores in this study we have dated using the 40ar 39ar method subglacial rhyolites of the tindfjallajokull kerlingarfjoll and torfajokull volcanoes which are the main sources of rhyolitic tephra identified in marine and glaciological records the thorsmork ignimbrite tindfjallajokull which correlates with the rhyolitic component ii rhy 1 of the north atlantic ash zone ii naaz ii layer is dated at 55 6 2 4 ka an age that agrees with the ones given by the ice core chronologies gicc05 55 4 1 2 ka the eruptions of rau fossafjoll and fannborg are respectively dated at 77 0 3 0 ka and 149 3 3 4 ka these new ages along with the published ones confirm as already concluded by flude et al 2010 that there is no clear evidence at least at the latitude of iceland that climate warming is the main mechanism that triggered rhyolitic eruptions combining major and trace element compositions with our new age determinations it appears that the rau fossafjoll and the snaefell rhyolitic eruptions have not yet been discovered in marine sediment cores nevertheless given the accuracy and precision of our dating these rhyolitic eruptions have the potential to become chronostratigraphic markers once tephra shards corresponding to these eruptions are discovered in ice and or marine sediment records the fannborg eruption might be recorded in the marine core link 16 during mis 6 prior to the transition to mis5e

a multidisciplinary approach to understanding carbonate deposition under tectonically controlled hydrothermal circulation a case study from a recent travertine mound in the euganean hydrothermal system northern italy a multidisciplinary study was carried out on an upper pleistocene travertine mound montirone hill abano terme south of padova veneto italy with the aim of developing a comprehensive understanding of the processes interacting in structurally controlled thermal springs and the consequent deposition of thermal limestones the sedimentology geochemistry structural characteristics and hydrogeology of the mound which is associated with the euganean geothermal field and the related complex structural framework of the schio vicenza fault system were investigated a palaeo environmental model of the deposit has been reconstructed clarifying the connection between the travertine deposition and the regional structural setting calcium rich thermal waters rose from spring orifices estimated temperature from 54 c to 61 c based on geochemical calculations and produced a mound made of coalescent shield like bodies the dominant lime mudstone facies resulted from the accumulation of lime mud at the bottom of shallow crater like basins located on top of stacked cones soft sediment deformations affecting the lime mud sediment were most probably produced by the recurrent uprising of gas bubbles the overlying crystalline crusts were deposited on the flanks of the mound by waters overflowing from the vents with laminar flux a deep hydrothermal circuit with a long period of water rock interaction is supported by geochemical analyses furthermore a local extensional regime enhancing the migration of thermal fluids to the surface is inferred based on the results of the structural analysis carried out on the fault fracture mesh that affects the mound these results corroborate the well established relation among travertine deposits hydrothermal systems and fault systems and substantiate the structurally controlled conceptual model of the euganean hydrothermal system suggesting that both the thermal and the fault systems were active at least since 34 ka

stratigraphy and distribution of tephra layers in marine sediment cores from the faeroe islands north atlantic the stratigraphical position of eight discrete tephra layers is investigated in four marine sediment cores from north and south of the faeroe islands the tephras are correlated to the marine oxygen isotope stratigraphy and the interstadial stadial cycles dansgaard oeschger cycles of the greenland ice cores a very prominent volcanic event occurred during interstadial 23 in marine oxygen isotope stage mis 5c correlating with a cold event within this otherwise warm interval two tephra horizons in mis 5a correlate with the beginning and end of interstadial 21 respectively the most widely distributed ash is the well known ash zone 2 from the lower part of mis 3 in the two cores from north of the faeroe islands it consists of two discrete layers a lower one composed of rhyolitic and basaltic tephra and an upper layer composed exclusively of basaltic glass the two tephra falls coincide with the two warm intervals of dansgaard oeschger cycle no 15 a hitherto unknown basaltic tephra was recorded just above heinrich event h4 in the lower part of the warm interstadial 8 and dated to ca 33 14c ka bp another frequently recorded layer termed the fugloyarbanki tephra is likewise basaltic it is dated to 23 1 14c ka bp it was deposited after the peak warm phase of interstadial 3 at the mis 3 2 transition finally a tephra dated ca 15 4 14c ka bp was found in two cores from north of the ridge it was deposited at the beginning of the deglaciation between the last glacial maximum and heinrich event h1

the age and chronostratigraphical significance of north atlantic ash zone ii rhyolitic tephra with the geochemical characteristics of north atlantic ash zone naaz ii are described from the giant piston core md95 2006 from the northeast atlantic ocean shard size distribution indicates that the tephra represent a wind sorted primary air fall deposit but with a mode close to 200 m they are too coarse to be air fall deposits at the core site which lies ca 1000 km from the possible tephra source randomly sampled shards reveal a single geochemical population belonging to the icelandic transitional alkali magma series suggesting that they are unlikely to represent ice rafted debris derived from icelandic icebergs the tephra probably represent air fall deposits transported to the core site by sea ice within the northeast atlantic gyre the naaz ii peak coincides with the rapid climate transition cooling at the end of interstadial 15 which can be assigned an age of 53 260 2660 yr bp from direct correlation with the greenland ice core gisp2 record a comparison of the md95 2006 neogloboquadrina pachyderma sinistral relative abundance and gisp2 18o records relative to the naaz ii isochron suggests that this climatic event was synchronous across the north atlantic by direct correlation of interstadial maxima between the two records the gisp2 time scale is transferred to md95 2006 comparison of corrected and calibrated radiocarbon ages derived from monospecific foraminifers with the gisp2 ages at the same stratigraphical horizon suggest major age differences these probably result from large variations in atmospheric 14c concentration and highlight the significant uncertainties associated with radiocarbon calibration during marine isotope stage 3 copyright 2004 john wiley sons ltd

geochronology and stratigraphy of the roque nublo cycle gran canaria canary islands the roque nublo cycle of pliocene age is the second main cycle of subaerial volcanic activity in gran canaria during this cycle a stratovolcano at least 2500 m high developed in the central part of the island its volcanic products covered an area of about 540 km 2 the detailed stratigraphy of the roque nublo cycle together with a magnetostratigraphic study and six new k ar dates which complement 22 previously published ones have led to the reconstruction of the volcanic history of this cycle in which six main stages have been distinguished the revised chronology of the roque nublo cycle implies an overlap in age with the earliest rocks of the third cycle of subaerial activity in gran canaria no volcanic hiatus occurred between the second and third cycles as was previously thought to be the case

independent tephrochronological evidence for rapid and synchronous oceanic and atmospheric temperature rises over the greenland stadial interstadial transitions between ca 32 and 40 ka b2k abstract understanding the dynamics that drove past abrupt climate changes such as the dansgaard oeschger do events depends on combined proxy evidence from disparate archives to identify leads lags and synchronicity between different climate system components independent and robust chronologies are required cryptotephrochronology is a key geochronological tool as cryptotephra horizons can act as isochrons linking disparate and or distant records here we investigated marine sediment core md99 2284 from the norwegian sea to look for previously identified greenland ice core cryptotephra horizons and define time parallel markers between the archives we explored potential secondary transport and depositional mechanisms that could hamper the isochronous integrity of such horizons we identified six cryptotephra layers of which four correlate to previously known greenland ice core horizons none of those were identified in other marine cores and thus this study contributes greatly to the north atlantic tephra framework tripling the original amount of existing isochrons between ca 25 and 60 ka b2k the latter allow a synchronization between md99 2284 and the greenland ice cores between ca 32 40 ka b2k which is in the north atlantic the shortest time interval during the last glacial period to be constrained by four independent tephra isochrons these findings provide essential tephra based evidence for synchronous and rapid oceanic and atmospheric temperature rises during the greenland stadial interstadial transitions furthermore it enables us to estimate the average peak duration of interstadial temperature overshoots at approximately 136 years as such this well targeted high resolution investigation successfully demonstrates the use of cryptotephra for geochronological purposes in the marine realm

aragonite laminae in hot water travertine crusts rapolano terme italy small 5 30 m aggregates of aragonite needles occur in calcite crystal crusts of present day hot water slope travertines at rapolano terme in tuscany italy the aggregates are mainly concentrated in irregular wispy and dark laminae which cross cut calcite crystal feathers to create a pervasive millimetre scale banded appearance in the deposit they also occur less commonly scattered irregularly through the calcite layers the aragonite needle aggregates are in the form of crosses fascicles sheaf shaped bundles or dumbbell shaped rosettes and spherulites locally irregular masses of needles also occur the fascicles rosettes and spherulites have hollow centres which resemble microbial components fungal spores bacterial colonies and pollen suggesting that the aragonite crystals are biotically nucleated the lamination is interpreted to reflect diurnal control stimulation of microbial activity during daylight concentrates cells in laminae and promotes aragonite calcification calcite feather crystals although traversed by the aragonite aggregate laminae have a clear appearance under the light microscope they form more or less continuously through the diurnal cycle by abiotic precipitation the constant association of aragonite with organic nuclei irrespective of whether the latter are in laminae or scattered through the calcite layers supports a biotic control on aragonite formation lamination in pleistocene travertines is superficially similar to that in the present day deposits but is diagenetically altered in the pleistocene deposits the calcite feathers appear dark under the light microscope and the aragonite aggregates where they are not altered to dark calcite are dissolved together with parts of the adjacent spar calcite and therefore appear light coloured

a north atlantic tephrostratigraphical framework for 130 60 ka b2k new tephra discoveries marine based correlations and future challenges abstract building chronological frameworks for proxy sequences spanning 130 60 ka b2k is plagued by difficulties and uncertainties recent developments in the north atlantic region however affirm the potential offered by tephrochronology and specifically the search for cryptotephra here we review the potential offered by tephrostratigraphy for sequences spanning 130 60 ka b2k we combine newly identified cryptotephra deposits from the ngrip ice core and a marine core from the iceland basin with previously published data from the ice and marine realms to construct the first tephrostratigraphical framework for this time interval forty three tephra or cryptotephra deposits are incorporated into this framework twenty three tephra deposits are found in the greenland ice cores including nine new ngrip tephras and twenty separate deposits are preserved in various north atlantic marine sequences major minor and trace element results are presented for the new ngrip horizons together with age estimates based on their position within the ice core record basaltic tephras of icelandic origin dominate the framework with only eight tephras of rhyolitic composition found new results from marine core md99 2253 also illustrate some of the complexities and challenges of assessing the depositional integrity of marine cryptotephra deposits tephra based correlations in the marine environment provide independent tie points for this time interval and highlight the potential of widening the application of tephrochronology further investigations however are required that combine robust geochemical fingerprinting and a rigorous assessment of tephra depositional processes in order to trace coeval events between the two depositional realms

tephra horizons identified in the western north atlantic and nordic seas during the last glacial period extending the marine tephra framework abstract geochemically distinct volcanic ash tephra deposits are increasingly acknowledged as a key geochronological tool to synchronize independent paleoclimate archives recent advances in the detection of invisible crypto tephra have led to the ongoing establishment development and integration of regional tephra lattices these frameworks offer an overview of the spatial extent of geochemically characterized tephra from dated eruptions a valuable tool for precise correlation of paleorecords within these areas here we harness cryptotephra analysis to investigate the occurrence of two well known tephra markers from the last glacial period i e fmaz ii 1 26 7 ka b2k and naaz ii ii rhy 1 55 3 ka b2k in marine sediment cores from the nordic irminger and labrador seas in addition we assess the imprint of bioturbation on two of these tephra deposits using computed tomography ct imagery we have successfully identified fmaz ii 1 in the nordic and irminger seas the tephra deposit is a visible deposit in the nordic seas whereas it appears as a single high concentration peak within the fine grained shard size fraction i e 25 80 m in the irminger sea both horizons are primary airfall deposits and this study is the first to identify a fmaz ii 1 deposit of isochronous nature in the irminger sea region in addition we have identified a new tephra horizon in the irminger sea which is stratigraphically associated with fmaz ii 1 and geochemically similar to the known 2 jpc 192 1 population we discuss its potential to serve as a new reference tie point for correlations in the region lastly we have successfully identified naaz ii ii rhy 1 of isochronous nature in both the irminger and labrador sea the layers are interpreted to be deposited by either direct airfall or by sea ice drifting past the sites compared to the existing frameworks which previously mainly focused on sites east of iceland our findings expand the knowledge and utility of the fmaz ii 1 and naaz ii ii rhy 1 horizons

volcanic ash layers illuminate the resilience of neanderthals and early modern humans to natural hazards marked changes in human dispersal and development during the middle to upper paleolithic transition have been attributed to massive volcanic eruption and or severe climatic deterioration we test this concept using records of volcanic ash layers of the campanian ignimbrite eruption dated to ca 40 000 y ago 40 ka b p the distribution of the campanian ignimbrite has been enhanced by the discovery of cryptotephra deposits volcanic ash layers that are not visible to the naked eye in archaeological cave sequences they enable us to synchronize archaeological and paleoclimatic records through the period of transition from neanderthal to the earliest anatomically modern human populations in europe our results confirm that the combined effects of a major volcanic eruption and severe climatic cooling failed to have lasting impacts on neanderthals or early modern humans in europe we infer that modern humans proved a greater competitive threat to indigenous populations than natural disasters

centennial to millennial scale ice ocean interactions in the subpolar northeast atlantic 18 41 kyr ago in order to monitor the evolution of the british irish ice sheet biis and its influence in surface ocean structure during marine isotopic stages mis 2 and 3 we have analyzed the sediments recovered in core md04 2829cq rosemary bank north rockall trough northeast atlantic dated between 41 and 18 ka b p ice rafted debris flux and composition 40ar 39ar ages of individual hornblende grains multispecies planktonic stable isotope records planktonic foraminifera assemblage data and faunal based sea surface temperatures ssts demonstrate a close interaction between biis dynamics and surface ocean structure and water properties in this region the core location lies beneath the north atlantic current nac and is ideal for monitoring the shifts in the position of its associated oceanic fronts as recorded by faunal changes these data reveal a succession of biis sourced iceberg calving events related to low sst usually synchronous with dramatic changes in the composition of the planktonic foraminifera assemblage and with variations in the stable isotope records of the taxa neogloboquadrina pachyderma sinistral coiling and globigerina bulloides the pacing of the calving events from typically dansgaard oeschger millennial timescales during late mis 3 to multicentennial cyclicity from 28 ka b p represents the build up of the biis and its growing instability toward heinrich event he 2 and the last glacial maximum our data confirm the strong coupling between biis instabilities and the temperature and salinity of surface waters in the adjacent northeast atlantic and demonstrate the biis s ability to modify the nac on its flow toward the nordic seas in contrast subsurface water masses were less affected except during the greenland stadials that contain hes when most intense water column reorganizations occurred simultaneously with the deposition of cream colored carbonate sourced from the laurentide ice sheet

volcanism and the greenland ice cores the tephra record abstract in recent years increased awareness of the considerable potential offered by tephrochronology in palaeoclimatic studies has fuelled a renewed interest in the tephra record preserved within the greenland ice cores this renewal has occurred in tandem with the development of continuous flow analysis techniques which provide high resolution volcanic aerosol records these chemical records are of considerable value for identifying tephra horizons composed of glass shards and also provide the basis for a new high precision ice core timescale thus allowing ages to be assigned to volcanic events tephra horizons of glass shards in the ice cores play a critical role for 1 testing and building chronological frameworks for the ice cores and other sequences 2 synchronising disparate palaeoclimatic sequences and testing phase relationships 3 atmospheric pathway reconstruction and 4 verifying the source of volcanic aerosol peaks here we review the results of over 25 years of research into tephra horizons in the grip gisp2 and ngrip cores we provide high precision ages for horizons based on recently developed timescales and draw together geochemical characterisations of the products of 45 volcanic events deposited on the greenland ice sheet and identified in the cores there is a clear disparity between the number of volcanic aerosol peaks and the number of tephra horizons of glass shards identified thus far however this synthesis highlights the critical role of the greenland ice cores firstly in the reconstruction of the history of icelandic volcanic eruptions and secondly the considerable value of some tephra horizons in facilitating the correlation of these key climatic archives to north atlantic marine sequences other noteworthy issues include the potential of these cores to preserve tephra horizons from more distal volcanic sources such as north america to resolve the debate surrounding the thera eruption and the observation that some tephra horizons are preserved within the ice without coeval volcanic aerosol signals

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

norwegian sea tephrostratigraphy of marine isotope stages 4 and 5 prospects and problems for tephrochronology in the north atlantic region abstract this paper presents an account of the tephrostratigraphy of south eastern norwegian sea core md99 2289 for the interval spanning marine isotope stage mis 5 and part of mis 4 from 70 000 to 130 000 years ago tephra deposits from in the order of 100 mainly basaltic volcanic eruptions in iceland and on jan mayen are described in terms of their stratigraphic context and geochemical composition representing the most comprehensive record of iceland and jan mayen volcanism over this time span the most important transport mechanism of tephra to the core site is considered to have been iceberg rafting which is thought to be responsible for a centennial to millennial scale time lag between the volcanic eruption events and the subsequent deposition of tephra in deep sea sediments while this clearly limits the use of some of the tephras as isochronous markers twelve discrete tephra deposits show stratigraphical and geochemical characteristics that suggest them to have been deposited near contemporaneously with their source volcanic events and hence suitable candidates as regional isochrones four of these accords with the geochemical signatures of tephra deposits previously described from the nordic seas region potential problems for the application of tephrochronology highlighted by this work are discussed and recommendations for strategies to overcome them are proposed

tracing volcanic events in the ngrip ice core and synchronising north atlantic marine records during the last glacial period five basaltic tephra horizons have been identified in the ngrip ice core during the last glacial period geochemical analyses indicate that these tephras are of icelandic origin with one horizon identified as the faroe marine ash zone iii fmaz iii an important marker horizon in several marine records within the faroe islands margin the fmaz iii is a few millimetres thick and is constrained to 38 122 723 yr b2k before year ad 2000 according to the greenland ice core chronology gicc05 this event falls directly at the thermal peak of greenland interstadial 8 gi 8 and a marine ice correlation based on the position of this tephra suggests a close coupling of the marine and atmospheric systems at this time the remaining tephras originate from the eastern volcanic zone with the katla volcanic system pinpointed as the dominant source these are thought to represent previously unknown volcanic events which add considerably to our knowledge of icelandic volcanism during this period independent ages are assigned to these events and together with major element characterisation form the backbone of the tephrochronology framework presented here despite the identification of these tephras this study also demonstrates that the sulphate record may not always act as a suitable proxy for the identification of tephra horizons in ice core records

traces of volcanic ash from the mediterranean iceland and north america in a holocene record from south wales uk a tephra record is presented for a sediment core from llyn llech owain south wales spanning the early to mid holocene seven cryptotephra deposits are discovered with three thought to correlate with known eruptions and the remaining four considered to represent previously undocumented events one deposit is suggested to correlate with the 6 9 cal ka bp lairg a tephra from iceland whereas more distant sources are proposed as the origin for two of the tephra deposits a peak of colourless shards in early holocene sediments is thought to tentatively correlate with the 9 6 cal ka bp fondi di baia tephra campi flegrei and a second cryptotephra is tentatively correlated with the 3 6 cal ka bp aniakchak cfe ii tephra alaska the fondi di baia tephra has never been recorded beyond proximal sites and its discovery in south wales significantly extends the geographical distribution of ash from this eruption the remaining four cryptotephra deposits are yet to be correlated with known eruptions demonstrating that our current understanding of widespread tephra deposits is incomplete this new tephra record highlights the potential for sites at more southerly and westerly locations in northwest europe to act as repositories for ash from several volcanic regions

composition and origin of volcanic ash zones in late quaternary sediments from the reykjanes ridge evidence for ash fallout and ice rafting abstract seven quaternary volcanic ash zones including the well known ash zones az i and az ii have been investigated in five well dated sediment cores from the reykjanes ridge between 59 and 60 n the zones were defined on their geochemical composition morphological variation of the particles and stratigraphic position the ash zones az i and az ii show a mixture of colorless bubble wall shards and brown blocky glasses whereas ash zones vz 1 to 5 are composed of dark to light brown volcanic glasses ranging in shape and texture from blocky nonvesicular shards to highly vesicular pumiceous types the dark brown glass shards of ash zones vz 1 to 5 represent subalkalic and low k subalkalic basaltic series geochemical correlation of the ash zones with possible source areas indicates that they all derived from iceland the colorless shards in az i and az ii are of rhyolitic composition the eastern volcanic zone on iceland is the most important source with abundant volcaniclastics being produced by subaerial subglacial eruptions and secondary erosion of volcanic rocks explosive volcanism on iceland is manifested by marine ash layers az i and az ii most of the volcaniclastic zones vz 1 to 5 coincide chronologically with peak abundances of coarse ice rafted material ird indicating that most of this volcanic glass was incorporated into the icelandic ice sheet and released to the ocean by iceberg calving and subsequent melting however two layers in vz 1 and vz 5 have no correlatives in the ird record suggesting that they were probably transported by local sediment gravity flows from this we must infer that most of the ice rafting episodes bearing volcanic particles as observed in sediments from reykjanes ridge monitor glacier fluctuations on iceland

north atlantic deep sea sedimentation of late quaternary tephra from the iceland hotspot piston cores recovered from the north atlantic were used to study the sedimentation of holocene and pleistocene volcanic ash in the irminger and iceland basins ash zones 1 11 100 yr b p 2 55 000 yr b p and 3 305 000 yr b p were identified from their major element glass composition the silicic and alkalic ash zones 1 and 2 originate from the southeastern volcanic zone of iceland where they correlate with the solheimar ignimbrite from katla volcano and the thorsmork ignimbrite from tindfjallajokull volcano respectively the low alkali composition of silicic ash zone 3 indicates a source from one of the silicic centers in the active rift system ash zones 2 and 3 occur in the irminger basin as dispersed glass shards over a depth interval of several tens of centimeters their compositional and granulometric characteristics reflect an initial fallout on pack ice north of iceland followed by ice rafting sedimentation in the denmark strait prior to bioturbation 18o stratigraphy of foraminifera in the cores indicates that the ash zones were deposited during a cold interval at the time when seas north of iceland were ice covered sedimentary features indicate that turbidity currents were also involved in the dispersal of ash zones 1 and 2 south of iceland the initiation of these gravity currents from the shelf can be attributed to either glacier bursts jokulhlaups carrying tephra or the entrance of pyroclastic flows into the ocean

british ice sheet dynamics inferred from north atlantic ice rafted debris records spanning the last 175 000 years sediment core md04 2822 from the rockall trough northeast atlantic provides lithological evidence for the expansion of the british ice sheet bis onto the hebridean margin during both the penultimate marine isotope stage mis 6 wolstonian saalian and last glaciation devensian weichselian a composite chronology is constructed using i the benthic foraminiferal oxygen isotope record matched to an orbitally tuned stacked record of global ice volume specmap ii the synchronisation of the planktonic foraminiferal neogloboquadrina pachyderma sinistral and itrax xrf ca records to the greenland ice core ngrip back to ca 123 ka and iii the synchronisation of the same n pachyderma sinistral and itrax xrf ca records to the atmospheric methane record of the antarctic ice core epica dome c beyond 123 ka the first offshore evidence for the expansion of the last bis within mis 4 is presented suggesting extensive glaciation of northwestern britain during the devensian weichselian as early as 70 ka the proximity of this long sediment core to the glaciated margin of northwestern scotland makes it ideal to capture the ice rafted debris ird signal of the bis for the last 175 ka via a continuous flux record of ird british geological survey nerc 2009 all rights reserved

tephrochronology and the extended intimate integration of ice core marine and terrestrial records event stratigraphy 8 128 ka b2k the comparison of palaeoclimate records on their own independent timescales is central to the work of the intimate integrating ice core marine and terrestrial records network for the north atlantic region an event stratigraphy has been established from the high precision greenland ice core records and the integrated gicc05 chronology this stratotype provides a palaeoclimate signal to which the timing and nature of palaeoenvironmental change recorded in marine and terrestrial archives can be compared to facilitate this wider comparison without assuming synchroneity of climatic change proxy response intimate has also focussed on the development of tools to achieve this in particular the use of time parallel marker horizons e g tephra layers volcanic ash coupled with the recent temporal extension of the greenland stratotype as part of this special issue we present an updated intimate event stratigraphy highlighting key tephra horizons used for correlation across europe and the north atlantic we discuss the advantages of such an approach and the key challenges for the further integration of terrestrial palaeoenvironmental records with those from ice cores and the marine realm

textural transition in an aragonite travertine formed under various flow conditions at pancuran pitu central java indonesia abstract a large travertine mound at pancuran pitu central java indonesia displays various types of lamination reflecting different hydrological conditions to understand the geomicrobiological processes of the laminated travertines we investigated the mound s hydrology water chemistry texture microbial composition and volume percentage of carbonate mineral vpc we identified four types of travertines dense travertine 80 vpc flow rate 200 cm s lithified microbial travertine 60 vpc flow rate 70 cm s fragile microbial travertine 30 vpc flow rate 10 cm s and poorly lithified microbial mat

revisiting the faroe marine ash zone iii in two greenland ice cores implications for marine ice correlations nineteen new icelandic tephra layers are identified in ngrip and neem ice spanning greenland interstadial 9 gi 9 and the early phase of gi 8 38 000 40 500 b2k fourteen tephras are identified in the ngrip record and five direct correlatives are identified in neem thus indicating the occurrence of 14 separate volcanic events with two exceptions the tephras are tholeiitic basalt in composition and despite having very similar geochemical signatures can in most cases be discriminated from one another using their tio2 values all of these tephra layers fall within the compositional range of the faroe marine ash zone iii fmaz iii deposit previously identified in ocean cores from the faroes region and previously correlated to ngrip 2066 95m by davies et al 2010 thus the fmaz iii in the marine realm is most likely a complex ash zone that represents a series of closely timed grimsvotn eruptions that as yet can only be stratigraphically separated in the high resolution ice core records the geochemical signatures and stratigraphic positions of the new ice core layers means that the fmaz iii tephra deposit as currently defined in the marine realm cannot be correlated to ngrip 2066 95m or any other ice core tephra horizons preserved during this interval copyright 2013 john wiley sons ltd

oxygen isotope fractionation in travertine depositing pools at baishuitai yunnan sw china effects of deposition rates abstract travertine 18o values can be used to reconstruct paleo temperatures if the oxygen isotope fractionation factors between travertine and water are accurately understood for this purpose the 18o values of pool travertine and its parent water and the deposition rates of the calcite were investigated at baishuitai yunnan sw china over the course of the full hydrological year april 23 2006 april 25 2007 the results show that the travertine water isotope fractionation factors are close to the commonly accepted equilibrium line of kim and o neil 1997 this differs from the results obtained by yan et al 2012 who found that the oxygen isotope fractionation factors in the travertine depositing pools were close to the line suggested as equilibrium relationship by coplen 2007 the average calcite deposition rate 2 30 mg cm 2 d 1 in the present study is six times larger than that 0 38 mg cm 2 d 1 in yan et al 2012 if slower calcite precipitation leads to equilibrium oxygen isotopic fractionation then the results of this study support the results of coplen 2007 that indicate that the equilibrium fractionation factor may be greater than the commonly accepted one derived by kim and o neil 1997 the relationship between oxygen isotope fractionation factor and calcite deposition rate in our study also agrees with the results of dietzel et al 2009 who found that the kinetic isotope effect favors preferential incorporation of 16o in solid calcite as the calcite deposition rate increases there was a threshold for calcite precipitation rate control on oxygen isotopic equilibrium in our case of travertine depositing pools when the calcite deposition rate was lower than 0 38 mg cm 2 d 1 oxygen isotopic equilibrium between calcite and water was attained therefore calcite deposition rate is a potentially important consideration when using 18o in natural carbonates as a proxy for terrestrial and ocean temperature

holocene tephrostratigraphic framework and monsoon evolution of east asia key tephra beds for synchronising palaeoclimate records abstract in east asia our understanding of holocene climate change forcing mechanisms and propagation require the precise chronological control of palaeoclimate records to allow robust integration of data sets the existing chronologies predominantly based on 14c method however are not sufficient to constrain key questions about abrupt climate shifts that occur within a century in the transitions between states widely dispersed tephra layers allow precise dating and synchronisation of sedimentary archives providing a chronological framework for integrating records especially where the visible tephra record is complemented by the addition of cryptotephra non visible ash despite significant tephra studies in this region however a comprehensive holocene tephra framework is not available to address this issue we carry out a thorough review on holocene tephra investigations undertaken in japan using widespread tephra beds we present an integrated tephra framework and suggest the way forward for establishing this as a wider approach for east asia the framework is based on twenty two ash layers that are mainly from japan and to a lesser extent china n korea s korea and russia each tephra is assessed in terms of chronology geochemistry and distribution the framework is compared with high resolution palaeoclimate records from east asia using this we demonstrate regional variations in monsoon evolution and more importantly the potential of tephra isochrons in constraining such variations given the scarce identification of tephra layers in those well resolved palaeoclimate records we advocate a more systematic employment of the cryptotephra method which would potentially lead to a significant advance in east asian tephrochronology and the correlation of palaeoclimate archives in the region

variability of north atlantic heat transfer during mis 2 1 short term changes in sea surface conditions controlling the thermohaline circulation in the northern north atlantic are expected to be especially efficient in perturbing global climate stability here we assess past variability of sea surface temperature sst in the northeast atlantic and norwegian sea during marine isotope stage mis 2 and in particular during the last glacial maximum lgm five high resolution sst records were established on a meridional transect 53 n 72 n to trace centennial scale oscillations in sst and sea ice cover we used three independent computational techniques simmax modern analogue technique artificial neural networks ann and revised analog method ram to reconstruct sst from planktonic foraminifer census counts simmax and ann reproduced short term sst oscillations of similar magnitude and absolute levels while ram owing to a restrictive analog selection appears less suitable for reconstructing cold end sst the simmax and ann sst reconstructions support the existence of a weak paleo norwegian current during dansgaard oeschger do interstadials number 4 3 2 and 1 during the lgm two warm incursions of 7 c water to occurred in the northern north atlantic but ended north of the iceland faroe ridge a rough numerical estimate shows that the near surface poleward heat transfer from 53 across the iceland faroe ridge up to to 72 n dropped to less than 60 of the modern value during do interstadials and to almost zero during do stadials summer sea ice was generally confined to the area north of 70 n and only rarely expanded southward along the margins of continental ice sheets internal lgm variability of north atlantic 40 n sst in the glamap 2000 compilation sarnthein et al 2003b pflaumann et al 2003 indicates maximum instability in the glacial subpolar gyre and at the iberian margin while in the nordic seas sst was continuously low

identification of cryptotephra horizons in a north east atlantic marine record spanning marine isotope stages 4 and 5a 60 000 82 000 a b2k abstract tephrochronology is one of the few techniques that offer considerable but as yet largely unrealised potential for the correlation of north atlantic palaeoclimatic archives spanning the mis 4 and 5a substage period a phase of pronounced global cooling during the initiation of the last glacial period in this investigation two previously unidentified rhyolitic tephra horizons believed to be sourced from iceland were isolated within the giant piston core md04 2822 retrieved from the rockall trough north east atlantic one horizon was deposited at the beginning of greenland stadial 19 70 150 a b2k and the other around the cooling transition at the end of greenland interstadial 20 75 320 a b2k density separation epma and la icp ms techniques were utilised for the identification of these cryptotephra within the fine fraction sediment

cryptotephrochronology of the eemian and the last interglacial glacial transition in the north east atlantic the eemian interglacial and the onset of the subsequent glacial period serve as the most recent analogue for the natural operation of the climate system during the current interglacial pronounced climatic oscillations occurred during this period but their nature and pattern are poorly understood due to dating limitations and unknown phase relationships between different regions and archives tephrochronology offers considerable potential for precise correlation of disparate palaeoclimatic archives preserving evidence of these rapid climatic transitions through the tracing of common isochronous tephra horizons we outline the identification of three previously unknown cryptotephra horizons within a marine core from the rockall trough north east atlantic this sequence preserves a high resolution record of this interval and shard size geochemical heterogeneity and the co variance of shard concentrations with ice rafted debris data are utilized to demonstrate that primary airfall was the most likely transport and depositional pathway the main geochemical populations of these horizons have similar transitional alkali major and trace element compositions suggesting that they were derived from a common icelandic source potentially the oraefajokull volcanic system these tephra horizons represent additions to the north atlantic event stratigraphy for this period and tentative correlations to icelandic terrestrial deposits are proposed for two horizons

tracing marine cryptotephras in the north atlantic during the last glacial period improving the north atlantic marine tephrostratigraphic framework tephrochronology is increasingly being recognised as a key tool for the correlation of disparate palaeoclimatic archives underpinning chronological models and facilitating climatically independent comparisons of climate proxies tephra frameworks integrating both distal and proximal tephra occurrences are essential to these investigations providing key details on their spatial distributions geochemical signatures eruptive sources as well as any available chronological and or stratigraphic information frameworks also help to avoid mis correlation of horizons and provide important information on volcanic history here we present a comprehensive chronostratigraphic framework of 14 tephra horizons from north atlantic marine sequences spanning 60 25 cal ka bp horizons previously discovered as visible or coarse grained deposits have been combined with 11 newly recognised volcanic deposits identified through the application of cryptotephra identification and characterisation methods to a wide network of marine sequences their isochronous integrity has been assessed using their physical characteristics all horizons originated from iceland with the vast majority having a basaltic composition sourced from the grimsvotn kverkfjoll hekla vatnafjoll and katla volcanic systems new occurrences improved stratigraphic placements and a refinement of the geochemical signature of the naaz ii are reported and the range of the fmaz iv has been extended in addition several significant geochemical populations that further investigations could show to be isochronous are reported this tephra framework provides the foundation for the correlation and synchronisation of these marine records to the greenland ice cores and european terrestrial records to investigate the phasing rate timing and mechanisms controlling rapid climate changes that characterised the last glacial period

freshwater phytoherm reefs the role of biofilms and their bearing on marine reef cementation abstract bioconstructions in carbonate rich freshwater environments generally lead to the development of thick autochthonous tufa deposits in rivers systems these large plant dominated freshwater reef frameworks phytoherms are capable of damming the water courses to produce chains of lakes the resulting phytoherms profoundly modify both local environment and sedimentation patterns in their vicinity and provide a wide range of niches for biota subaqueous fringe cements coat all exposed surfaces they bind the ephemeral plant frameworks providing a cement framework and give rigidity to the bioconstructions peloids are intimately associated with the development of these cements and frequently infil intra reef and framework cavities evidence is presented to suggest that both micritic fringe cements and peloids are the product of biological mediation associated with a procaryote microphyte biofilm and the presence of organic detritus the bladed low magnesium calcite fringes which develop subsequently on the micrite fringes and peloids are possibly slower formed inorganic precipitates the close morphological similarities between phytoherm fringe cements and peloids and their marine reef counterparts are considered to be more than coincidental it is argued that procaryote microphyte biofilms are also responsible for micritic precipitates in the shallow photic marine realm with bacterial films possibly carrying the process deep into unlit reef cavities and conduits and deep water lithoherms

effects of canary hotspot volcanism on structure of oceanic crust off morocco analysis of over 6400 km of multichannel seismics mcs and 50 sonobuoy reflection and refraction experiments reduced both in the domain of x t and tau p shows that a region within the jurassic quiet zone off morocco underwent dramatic changes as a result of the passage of the lithosphere over the canary hotspot commencing approximately 60 ma a seismic unit ucf interpreted as volcanic in origin is observed within the sediments in a region characterized by a broad bathymetric swell it shows diffractions from its upper surface and an internally chaotic seismic facies and pinches out between sedimentary units of continuous subparallel facies a velocity inversion is noted between the ucf 4 7km s and the underlying sediment 3 1 km s the ucf is time transgressive it lies near the cretaceous s tertiary boundary in the northern portion of the study area and is younger to the south kinematic studies of the movement of the canary hotspot relative to africa show that the hotspot first appeared off nw africa about 60 ma and was located beneath oceanic crust in the region where the ucf is observed depth to basement measurements in areas not effected by the hotspot show a consistent linear trend of increased depth with age in areas effected by the hotspot the thermal rejuvenation is evident as basement depths shoal with increased proximity to the present hotspot the reheating of the crust resets the thermal age of the lithosphere with many of the properties of crust of a younger age subsidence curves of the reheated crust off morocco show good correlation to subsidence curves of other reheated crust on a global basis a zone characterized by high crustal velocities 7 1 7 4 km s and greater crustal thicknesses by 1 2 km is observed in an area that corresponds to the bathymetric swell the region of the ucf and the reelevated basement the high velocities and increased crustal thickness are interpreted to be the result of underplating and assimilation of existing oceanic crust caused by the canary thermal anomaly the presence of high crustal velocities coupled with a thickened crustal section has been noted on various passive margins of the world they have generally been attributed to the thermal processes associated with continental rifting off morocco we believe that similar thermally induced phenomena have occurred but that here the heat anomaly was the midplate volcanism associated with the canary hotspot

trends in δ18o and δ13c values in lacustrine tufa mounds palaeohydrology of searles lake california four tufa facies have been identified in abundant tufa mounds that accumulated in searles lake california usa during the pleistocene covariance of 18 o and 13 c values within the tufa facies has been analysed and correlated with palaeo lake history this study demonstrates that characteristics of 18 o and 13 c values are different in each of the tufa facies and can be related to palaeo lake stages the first facies of tufa formation p has relatively low average 18 o and 13 c values 18 o 27 and 13 c 12 n 14 these low values are attributed to rapid increases in the lake volume this increase was followed by higher average 18 o and 13 c values of both the nodular n facies 18 o 18 and 13 c 41 n 24 and the columnar c facies 18 o 06 and 13 c 40 n 7 these higher values are interpreted to record a decrease in lake volume due to high evaporation and increased biogenic productivity following formation of facies c the lake was essentially dry during formation of the finely laminated lc facies facies lc formed subaerially as spring water flowed up through the central conduit of the mounds and cascaded down their periphery the relatively high 18 oa nd 13 c values for this facies 18 o 14 and 13 c 44 n 12 are due to evaporation and fast co2 degassing although covariant trends are well displayed variations in lake chemistry alter some of these trends due to periods of hyper alkalinity this study confirms the utility of stable isotopic analyses of lacustrine tufa facies to determine palaeo lake history

volcanic aerosol records and tephrochronology of the summit greenland ice cores the recently collected greenland ice sheet project 2 gisp2 and greenland ice core project ice cores from summit greenland provide lengthy and highly resolved records of the deposition of both the aerosol h2so4 and silicate tephra components of past volcanism both types of data are very beneficial in developing the hemispheric to global chronology of explosive volcanism and evaluating the entire volcanism climate system the continuous time series of volcanic so42 for the last 110 000 years show a strong relationship between periods of increased volcanism and periods of climatic change the greatest number of volcanic so42 signals many of very high magnitude occur during and after the final stages of deglaciation 6000 17 000 years ago possibly reflecting the increased crustal stresses that occur with changing volumes of continental ice sheets and with the subsequent changes in the volume of water in ocean basins sea level change the increase in the number of volcanic so42 signals at 27 000 36 000 and 79 000 85 000 years ago may be related to initial ice sheet growth prior to the glacial maximum and prior to the beginning of the last period of glaciation respectively a comparison of the electrical conductivity of the gisp2 core with that of the volcanic so42 record for the holocene indicates that only about half of the larger volcanic signals are coincident in the two records other volcanic acids besides h2so4 and other so42 sources can complicate the comparisons although the threshold level picked to make such comparisons is especially critical tephra has been found in both cores with a composition similar to that originating from the vatnaoldur eruption that produced the settlement layer in iceland mid a d 870s from the icelandic eruption that produced the saksunarvatn ash 10 300 years ago and from the icelandic eruption s that produced the z2 ash zone in north atlantic marine cores 52 700 years ago the presence of these layers provides absolute time lines for correlation between the two cores and for correlation with proxy records from marine sediment cores and terrestrial deposits containing these same tephras the presence of both rhyolitic and basaltic shards in the z2 ash in thegisp2 core and the composition of the basaltic grains lend support to multiple icelandic sources torfajokull area and katla for the z2 layer deposition of the z2 layer occurs at the beginning of a stadial event further reflecting the possibility of a volcanic triggering by the effects of changing climatic conditions

tephrostratigraphy chronology and climatic events of the mediterranean basin during the holocene an overview the identification and characterisation of high frequency climatic changes during the holocene requires natural archives with precise and accurate chronological control which is usually difficult to achieve using only 14c chronologies the presence of time spaced tephra beds in quaternary mediterranean successions represents an additional independent tool for dating and correlating different sedimentary archives these tephra layers are potentially useful for resolving long standing issues in paleoclimatology and can help towards correlating terrestrial and marine paleoclimate archives known major tephras of regional extent derive from central and southern italy the hellenic arc and from anatolia a striking feature of major holocene tephra deposition events in the mediterranean is that they are clustered rather than randomly distributed in time several tephra layers occurred at the time of the s1 sapropel formation between c 8 4 and 9 0 ka bp mercato gabellotto fiumebianco e1 cappadocia and ot

volcanic ash layers from the last glacial termination in the ngrip ice core the tephrochronological record of the 1400 1640 m depth 10 000 16 000 calendar ice core years before present of the ngrip ice core has been established by particle screening of selected samples ash was identified in 20 samples correlation with ice marine and terrestrial records from volcanic source regions in the northern hemisphere positively identifies the saksunarvatn ash and the vedde ash ash zone 1 major element chemistry of the remaining identified ash layers mainly points towards an icelandic origin this tephrochronological record provides new important marker horizons for correlating the timing of the climatic changes associated with the last glacial termination within the north atlantic region as well as outlining more details concerning the frequency and composition of volcanic eruptions occurring at this deglaciation copyright 2005 john wiley sons ltd

consistently dated records from the greenland grip gisp2 and ngrip ice cores for the past 104 ka reveal regional millennial scale δ18o gradients with possible heinrich event imprint abstract we present a synchronization of the ngrip grip and gisp2 ice cores onto a master chronology extending back to 104 ka before present providing a consistent chronological framework for these three greenland records the synchronization aligns distinct peaks in volcanic proxy records and other impurity records chemo stratigraphic matching and assumes that these layers of elevated impurity content represent the same instantaneous event in the past at all three sites more than 900 marker horizons between the three cores have been identified and our matching is independently confirmed by 24 new and previously identified volcanic ash tephra tie points using the reference horizons we transfer the widely used greenland ice core chronology gicc05modelext to the two summit cores grip and gisp2 furthermore we provide gas chronologies for the summit cores that are consistent with the gicc05modelext timescale by utilizing both existing and new gas data ch4 concentration and 15n of n2 we infer that the accumulation contrast between the stadial and interstadial phases of the glacial period was 10 greater at summit compared to at ngrip the 18o temperature proxy records from ngrip grip and gisp2 are generally very similar and display synchronous behaviour at climate transitions the 18o differences between summit and ngrip however changed slowly over the last glacial interglacial cycle and also underwent abrupt millennial to centennial scale variations we suggest that this observed latitudinal 18o gradient in greenland during the glacial period is the result of 1 relatively higher degree of precipitation with a pacific signature at ngrip 2 increased summer bias in precipitation at summit and 3 enhanced rayleigh distillation due to an increased source to site distance and a potentially larger source to site temperature gradient we propose that these processes are governed by changes in the north american ice sheet nais volume and north atlantic sea ice extent and or sea surface temperatures sst on orbital timescales and that changing sea ice extent and ssts are the driving mechanisms on shorter timescales finally we observe that maxima in the summit ngrip 18o difference are roughly coincident with prominent heinrich events this suggests that the climatic reorganization that takes place during stadials with heinrich events possibly driven by a southward expansion of sea ice and low ssts in the north atlantic are recorded in the ice core records

visualizing tephra deposits and sedimentary processes in the marine environment the potential of x ray microtomography localized tephra deposition in marine sequences is the product of many complex primary and secondary depositional processes these can significantly influence the potential applicability of tephra deposits as isochronous marker horizons and current techniques used in isolation may be insufficient to fully unravel these processes here we demonstrate the innovative application of x ray microtomography ct to successfully identify tephra deposits preserved within marine sediments and use these parameters to reconstruct their internal three dimensional structure three dimensional visualizations and animations of tephra dispersal in the sediment permit a more thorough assessment of postdepositional processes revealing a number of complex microsedimentological features that are not revealed by conventional methods these features include bioturbation burrows and horizontally discontinuous tephra packages which have important ramifications for the stratigraphic placement of the isochron in a sedimentary sequence our results demonstrate the potential for utilizing rigorous two and three dimensional microsedimentological analysis of the ichnofabric to enhance and support the use of tephra deposits as isochronous marker horizons and to identify the stratigraphic position that best reflects the primary fallout of ash the application also provides an exceptional insight into the style and rate of sedimentation processes and permits an assessment of the stratigraphic integrity of a tephra deposit we discuss the possibility of applying these ct methods to the identification of cryptotephras within various paleoclimatic sequences and to enhance our understanding of marine sedimentation processes

rapid changes in the mechanism of ocean convection during the last glacial period high amplitude rapid climate fluctuations are common features of glacial times the prominent changes in air temperature recorded in the greenland ice cores1 2 are coherent with shifts in the magnitude of the northward heat flux carried by the north atlantic surface ocean3 4 changes in the ocean s thermohaline circulation are a key component in many explanations of this climate flickering5 here we use stable isotope and other sedimentological data to reveal specific oceanic reorganizations during these rapid climate change events deep water was generated more or less continuously in the nordic seas during the latter part of the last glacial period 60 to 10 thousand years ago but by two different mechanisms the deep water formation occurred by convection in the open ocean during warmer periods interstadials but during colder phases stadials a freshening of the surface ocean reduced or stopped open ocean convection and deep water formation was instead driven by brine release during sea ice freezing these shifting magnitudes and modes nested within the overall continuity of deep water formation were probably important for the structuring and rapidity of the prevailing climate changes

cryptotephras the revolution in correlation and precision dating from its icelandic origins in the study of visible tephra horizons tephrochronology took a remarkable step in the late 1980 s with the discovery of a ca 4300 year old microscopic ash layer in a scottish peat bog since then the search for these cryptotephra deposits in distal areas has gone from strength to strength indeed a recent discovery demonstrates how a few fine grained glass shards from an alaskan eruption have been dispersed more than 7000 km to northern europe instantaneous deposition of geochemically distinct volcanic ash over such large geographical areas gives rise to a powerful correlation tool with considerable potential for addressing a range of scientific questions a prerequisite of this work is the establishment of regional tephrochronological frameworks that include well constrained age estimates and robust geochemical signatures for each deposit with distal sites revealing a complex record of previously unknown volcanic events frameworks are regularly revised and it has become apparent that some closely timed eruptions have similar geochemical signatures the search for unique and robust geochemical fingerprints thus hinges on rigorous analysis by electron microprobe and laser ablation inductively coupled plasma mass spectrometry historical developments and significant breakthroughs are presented to chart the revolution in correlation and precision dating over the last 50 years using tephrochronology and cryptotephrochronology

identification of the fugloyarbanki tephra in the ngrip ice core a key tie point for marine and ice core sequences during the last glacial period a visible tephra horizon in the ngrip ice core has been identified by geochemical analysis as the fugloyarbanki tephra a widespread marker horizon in marine cores from the faroe islands area and the northern north atlantic an age of 26 740 390 yr b2k 1 uncertainty is derived for this tephra according to the new greenland ice core chronology gicc05 based on multi parameter counting of annual layers detection of this tephra for the first time within the ngrip ice core provides a key tie point between marine and ice core records during the transition between mis 3 and 2 identification of this volcanic event within the greenland records demonstrates the future potential of using tephrochronology to precisely correlate palaeoarchives in widely separated localities that span the last glacial period as well as providing a potential method for examining the extent of the radiocarbon marine reservoir effect at this time copyright 2008 john wiley sons ltd

building a tephrostratigraphic framework for the paleolithic of central anatolia turkey the central anatolian volcanic province cavp in turkey preserves widespread deposits of quaternary tephra presently associated with a small but growing number of paleolithic archaeological sites we use multivariate analyses of the abundances of a suite of nine major and minor element oxides determined by electron probe microanalysis from these data we construct a classificatory model for correlating distal tephra to one of five volcanic edifices or eruptive phases within the cavp application of this model to distal deposits of primary tephra fall and reworked tuffaceous sediments from the archaeological sites of korkuyu and kaletepe deresi 3 indicates late to possibly early pleistocene ages for the artifact assemblages there and provides a fundamental tephrostratigraphic framework to examine spatial and temporal variation in hominin behavior comparable to that of other regions such as eastern africa

travitonics using travertines in active fault studies abstract late quaternary travertines deposited from hot springs can reveal much about the neotectonic attributes and histories of structures on the basis of field studies in the aegean region turkey and greece the northern apennines italy and the basin and range province usa we conclude that the following relationships are of predictive value i travertine deposits are preferentially located along fracture traces either immediately above extensional fissures or in the hanging walls of normal faults ii the locations of many travertine fissure ridge deposits coincide with step over zones relay ramps between fault segments networks of intersecting tensional fissures reflecting the complex strains experienced in such settings are probably responsible for enhancing hydrothermal flow iii the morphology of travertine deposits overlying extensional fissures is controlled by the rheology of the underlying materials tufa cones towers pinnacles form on former and present lake floors where fissures underlie unconsolidated sediments whereas fissure ridges develop where fissures cut bedrocks at the surface iv fissure ridges comprise outwardly dipping bedded travertine flanking a central tensional fissure filled by vertically banded travertines fissures can be used to infer local stretching directions v where there are travertines datable by the u series method it is possible to calculate time averaged dilation and lateral propagation rates for individual fissures vi most fissures cutting fissure ridges comprise self similar angular segments with fractal dimensions in the range 1 00 1 12 the properties of bedded travertine combined with stress perturbations at fissure tips probably being responsible for such similar fractal dimensions being inferred from such a wide range of locations fissures gradually increasing in width with depth are products of continuous fracture dilation in contrast to those that form during episodic dilation which display stepped increases of width with depth vii travertine deposited from springs along fault zones accumulate in terraced mounds sited down slope of the spring line viii many post depositional fractures cutting travertine deposits are locally oriented at right angles to deposit margins and ix systematic joints in travertines are restricted to those parts of eroded sheet deposits that have been exhumed

synchronisation of palaeoenvironmental events in the north atlantic region during the last termination a revised protocol recommended by the intimate group abstract the north atlantic intimate group of the inqua palaeoclimate commission has previously recommended an event stratigraphy approach for the synchronisation of records of the last termination using the greenland grip isotopic record as the regional stratotype and intcal98 for the calibration of radiocarbon dates lowe j j hoek w intimate group 2001 inter regional correlation of palaeoclimatic records for the last glacial interglacial transition a protocol for improved precision recommended by the intimate project group quaternary science reviews 20 1175 1187 here we present a revised protocol for time stratigraphic correlation in the north atlantic region over a more extended time period 30 8 ka this employs the new ngrip isotopic record and associated greenland ice core chronology 2005 gicc05 as the regional stratotype intcal04 for the calibration of radiocarbon dates bayesian based statistical procedures for the construction of age models and tephrochronology to validate correlations between regional site records

re evaluation and extension of the marine isotope stage 5 tephrostratigraphy of the faroe islands region the cryptotephra record previous studies of marine sequences from the faroe islands region have identified a series of coarse grained tephra horizons deposited during marine isotope stage mis 5 here we reassess the mis

developing a robust tephrochronological framework for late quaternary marine records in the southern adriatic sea new data from core station sa03 11 tephra layers are assuming an increasingly important role in the dating and correlation of late quaternary marine sequences here we demonstrate their potential by reporting a new study of the sediment sequence of marine core sa03 11 recovered from the southern adriatic sea which spans the last c 39 ka a total of 28 discrete tephra layers are reported from this sequence 10 of which are visible in the core and a further 18 are non visible cryptotephra layers these have been analysed using more than 1400 wds epma measurements of glass chemistry and results have been compared with published chemical measurements obtained from relevant proximal and distal sites which preserve eruptive material dating to within the same time interval the data show that a high proportion of the layers originate from the campi flegrei volcanic field but more distinctive layers are sourced from vesuvius the aeolian islands and vulcano and these provide key marker horizons the results show that the sequence extends in time to the campanian ignimbrite at the base that a number of the layers have robust age estimates that permit a better constrained age depth model to be constructed for the sequence and that the potential exists for importing terrestrially based age estimates into marine contexts thereby circumventing problems of incorporating reservoir uncertainties associated with marine radiocarbon dates the wds epma dataset generated here also provides important new data that constrain key late quaternary tephra layers in the central mediterranean region

the tephrochronology of iceland and the north atlantic region during the middle and late quaternary a review the tephrochronology of iceland and the north atlantic region is reviewed in order to construct a unified framework for the last 400 kyr bp nearly all of the tephra layers described are also characterised geochemically a number of new tephra layers are analysed for the first time for their geochemical signature and a number of pre holocene tephra layers have been given an informal denotation the tephrostratigraphy of ash zone ii is highlighted where possible the rhyolitic tephra layers found outside iceland have been correlated to known icelandic tephra layers or to the volcanic source area the application of tephra fallout in various depositional environments is described and discussed copyright 2000 john wiley sons ltd

integrating the intimate records using tephrochronology rising to the challenge little has challenged our understanding of climate change more so than the abruptness with which large scale shifts in temperature occurred during the late quaternary the causal mechanisms driving

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

volcanic ash reveals time transgressive abrupt climate change during the younger dryas knowledge of regional variations in response to abrupt climatic transitions is essential to understanding the climate system and anticipating future changes global climate models typically assume that major climatic changes occur synchronously over continental to hemispheric distances the last major reorganization of the ocean atmosphere system in the north atlantic realm took place during the younger dryas yd an 1100 yr cold period at the end of the last glaciation within this region several terrestrial records of the yd show at least two phases an initial cold phase followed by a second phase of climatic amelioration related to a resumption of north atlantic overturning we show that the onset of climatic amelioration during the yd cold period was locally abrupt but time transgressive across europe atmospheric proxy signals record the resumption of thermohaline circulation midway through the younger dryas occurring 100 yr before deposition of ash from the icelandic vedde eruption in a german varve lake record and 20 yr after the same isochron in western norway 1350 km farther north synchronization of two high resolution continental records using the vedde ash layer 12 140 40 varve yr b p allows us to trace the shifting of the polar front as a major control of regional climate amelioration during the yd in the north atlantic realm it is critical that future climate models are able to resolve such small spatial and chronological differences in order to properly encapsulate complex regional responses to global climate change

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