chironomid based lateglacial climatic reconstruction for southeast scotland this paper presents the first chironomid based climatic reconstruction for the uk lateglacial obtained from a lake basin in southeast scotland whitrig bog comparison of chironomid lithological geochemical and pollen data reveals a marked vegetation lag behind the warming following deglaciation warm water chironomid taxa e g chironomus had replaced cold water chironomid taxa e g paracladius prior to the arrival of shrubs and trees and when local soils were still poorly developed in addition to clear evidence for the younger dryas stadial chironomid data also reveal two short term cold episodes that punctuate the lateglacial interstadial both of which are also reflected in pollen and lithological data as reversals from open birch scrub woodland to open herbaceous tundra coinciding with inwash of minerogenic matter into the basin 1997 john wiley sons ltd

some numerical considerations in the geochemical analysis of distal microtephra abstract the use of late quaternary tephra horizons as isochronous markers for high resolution correlation between records is of growing importance in a number of scientific fields particular advancements have been made through the identification of microtephra deposits very distal deposits of volcanic ash invisible to the naked eye the successful correlation of ash layers and volcanic eruptions depends on the acquisition of the major element chemistries of a tephra layer derived from microprobe analyses of individual glass shards this is particularly important for microtephras where aeolian fractionation has removed much of the mineral phase of the ash deposit which often aids tephra discrimination there are however difficulties in distinguishing precisely between different eruptions of the same volcano using major element composition and this may not always be resolved by the use of trace elements given the potential of tephrochronology as a correlative tool in many disciplines it is important to resolve this difficulty one way forward is to perform more robust statistical analyses on the geochemical data as in general analyses are confined to a series of bi plots of major elements here the authors explore some of the problems associated with dealing with microprobe data generated for individual tephras and pay particular attention to the unit sum problem using a subset of data generated as part of a eurodelta project on tephra distribution in the adriatic the authors demonstrate that this problem is detectable in major element data from tephras and have consequently applied the logratio method before further analyses of the data it is demonstrated that the use of logratios combined with discriminant functions analysis provides a more robust assessment of likely chemical correlations between tephras and are superior to the use of bi plots alone and obviate the need for any data normalization a particular point of contention between tephrochronologists

holocene tephrostratigraphy of varved sediment records from lakes tiefer see ne germany and czechowskie n poland a detailed holocene tephrostratigraphic framework has been developed for two predominately varved lake sediment sequences from ne germany lake tiefer see and central n poland lake czechowskie a total of thirteen tephras and cryptotephras of icelandic provenance were detected and chemically fingerprinted in order to define correlatives and to integrate known tephra ages into the sediment chronologies out of these three cryptotephras askja ad1875 askja s and h asseldalen were identified in both records thus allowing a detailed synchronization of developing high resolution palaeoenvironmental proxy data the early holocene saksunarvatn ash layer and the middle holocene lairg b and hekla 4 cryptotephras in lake tiefer see are further important anchor points for the comparison with other high resolution palaeoclimate records in central and northern europe tentative correlations of cryptotephras have been made with a historical basaltic grimsv otn eruption ad890 e ad856 and three late holocene rhyolitic eruptions including the 2 1 ka glen garry and two unknown high silicic cryptotephras of probably icelandic provenance 1 9 cal ka bp

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

identification and significance of a visible basalt rich vedde ash layer in a late glacial sequence on the isle of skye inner hebrides scotland this paper reports the discovery of a visible tephra horizon of late glacial age from the site of loch ashik in the isle of skye the inner hebrides scotland although the tephra shards have a bimodal geochemical composition identical to that of the vedde ash a well known marker horizon within late glacial sequences the horizon at ashik is dominated by basaltic shards and devitrified tephra shards giving the layer its characteristic black colour only rhyolitic shards have previously been reported from vedde ash horizons in the british isles this new evidence raises some important questions about the factors that govern the distribution and accumulation of basaltic tephra and about the methods used to detect ash shards in basins distal to centres of volcanic activity copyright 2001 john wiley sons ltd

the last 40 ka tephrostratigraphic record of lake ohrid albania and macedonia a very distal archive for ash dispersal from italian volcanoes abstract a 1075 cm long core lz1120 was recovered in the south eastern part of the lake ohrid republics of macedonia and albania and sampled for identification of tephra layers magnetic susceptibility investigations show rather high magnetic values throughout the core with peaks unrelated to the occurrence of tephra layers but instead to the relative abundance of detrital magnetic minerals in the sediment naked eye inspection of the core allowed us to identify of two tephra layers at 896 897 cm and 1070 1075 cm laboratory inspection of the grain size fraction 125 m allowed for the identification of a third cryptotephra at 310 315 cm major element analyses on glass shards of the tephra layers at 896 897 cm and 1070 1075 cm show a trachytic composition and indicate a correlation with the regionally dispersed y 3 and y 5 tephra layers dated at ca 30 and 39 cal ka bp the cryptotephra at 310 315 cm has a mugearitic benmoreitic composition and was correlated with the fl eruption of mt etna dated at 3370 70 cal yr bp these ages are in agreement with five 14 c ams measurements carried out on plant remains and macrofossils from the lake sediments at different depths along the core the recognition of distal tephra from italian volcanoes allows us to link the lake ohrid succession to other archives located in the mediterranean area and in eastern europe the benmoreitic mugearitic tephra layer at 310 315 cm is the first recognition in the balkan area of a distal ash deposit from a mid intensity explosive eruption of mt etna as far as 600 km from the source

the chronology of palaeoenvironmental changes during the last glacial holocene transition towards an event stratigraphy for the british isles the overall aim of the tigger iib project is to increase our understanding of the manner and rates by which ecosystems responded to climate changes during the last glacial holocene transition success in this venture requires better constrained palaeoenvironmental reconstructions than have been achieved thus far and the tigger project focused in particular on three main aims 1 off setting the limitations of conventional radiocarbon dating in order to provide a more secure chronology of events 2 increasing the resolution and precision of palaeoclimatic reconstructions 3 widening the scope of site specific palaeoecological investigations in this paper we focus on the first of these strategies and describe the progress made in developing a more coherent timescale for the climate history of the lateglacial period this has been achieved by using a number of independent methods including calibration of ams radiocarbon dates obtained from terrestrial plant macrofossils mcr estimates of summer temperatures based on coleopteran records analysis of stable carbon isotope ratios in terrestrial plant macrofossils and tephrochronology following bjorck et al 9s 1998 recommendations we integrate the new results to construct a provisional event stratigraphy for the last glacial holocene transition in the british isles which is based on a sequence of features that are believed to be time parallel this approach is considered to provide a more coherent framework for direct comparison of the palaeoenvironmental evidence from britain with that from elsewhere

tephrabase tephrochronology and the development of a centralised european database tephrabase was launched on the world wide web in 1995 as a tool for tephrochro nological research in order to facilitate the identification correlation and dating of tephra deposits this database may be interrogated through multiple routes including by source volcano date location and tephra chemistry datasets include stratigraphy geochemistry chronology and spatial information currently all the european data refer to late quaternary icelandic sourced tephras post 12 k yr bp the sites 62 where the tephra deposits are found include iceland the united kingdom ireland the faroe islands sweden and russia in addition there are also data on tephra layers in central mexico use of tephrabase highlights the importance of selected geochemical data but this has to be used with care as major element characteristics alone do not always produce unique definitions for single tephra deposits for the most accurate results multiple criteria must be used tephrabase can be found at http www tephrabase org copyright 2007 john wiley sons ltd

source of ash zone 1 in the north atlantic geochemical evidence shows that the silicic component of the widespread ash zone 1 in the north atlantic is derived from a major ignimbrite forming eruption which occurred at the katla caldera in southern iceland during the transition from glacial to interglacial conditions in younger dryas time both trace and major element evidence of the rhyolitic products excludes the oraefajokull volcano as a source the high ti basaltic component in the marine ash zone can also be attributed to contemporaneous eruption in the katla volcanic complex dispersal of tephra from this event is primarily attributed to the generation of co ignimbrite ash columns in the atmosphere with ash fallout on both sea ice and on the ocean floor north and east of iceland owing to the changing ocean circulation characteristics of the glacial regime including suppression of the irminger current and a stronger north atlantic current tephra was rafted on sea ice south into the central north atlantic and deposited as dispersed ash zone 1 sediments south of iceland also show evidence of the formation of ash turbidites generated either by the entrance of pyroclastic flows into the sea or during discharge of jokulhlaups or glacier bursts from this subglacial eruption

marine tephrochronology of the mt edgecumbe volcanic field southeast alaska usa abstract the mt edgecumbe volcanic field mevf located on kruzof island near sitka sound in southeast alaska experienced a large multiple stage eruption during the last glacial maximum lgm holocene transition that generated a regionally extensive series of compositionally similar rhyolite tephra horizons and a single well dated dacite med tephra marine sediment cores collected from adjacent basins to the mevf contain both tephra fall and pyroclastic flow deposits that consist primarily of rhyolitic tephra and a minor dacitic tephra unit the recovered dacite tephra correlates with the med tephra whereas many of the rhyolitic tephras correlate with published mevf rhyolites correlations were based on age constraints and major oxide compositions of glass shards in addition to lgm holocene macroscopic tephra units four marine cryptotephras were also identified three of these units appear to be derived from mid holocene mevf activity while the youngest cryptotephra corresponds well with the white river ash eruption at 1147 cal yr bp furthermore the sedimentology of the sitka sound marine core ew0408 40jc and high resolution swath bathymetry both suggest that extensive pyroclastic flow deposits associated with the activity that generated the med tephra underlie sitka sound and that any future mevf activity may pose significant risk to local population centers

seven tephra isochrones in scotland this paper reports the presence and geochemical characteristics of seven separate tephras in scotland that fell in ad 1510 and about 450 bp 2100 bp 3600 bp 3830 bp 5600 bp and around 6000 bp the results come from 14 peat bogs spread throughout the highlands and islands where 26 tephra deposits have been characterized using over 400 grain discrete electron probe micro analysis firstly tephras are identified and defined by major element characteristics at a reference site secondly tephras are linked between sites on the basis of geochemistry and dated informal names based on british sites are suggested for tephras not yet linked to precise sources in iceland despite some apparent variation in colour all analysed grains in these seven deposits are silicic or intermediate in composition sio2 57 this phenomenon does not appear to be an artifact of preservation for two reasons first small 40 m basic glass shards in peat bogs in northern iceland are found to have undergone minimal alte

chironomid inferred late glacial air temperatures at whitrig bog southeast scotland this paper presents the first chironomid inferred mean july air temperature reconstruction for the late glacial in britain the reconstruction suggests that the thermal maximum occurred early in the interstadial with temperatures reaching about 12 degreesc there was then a gradual downward trend to about 11 degreesc punctuated by four distinct cold oscillations of varying intensity at the beginning of the younger dryas mean july temperatures fell to about 7 5 degreesc but gradually increased to about 9 degreesc before a rapid rise at the onset of the holocene the chironomid inferred temperature curve agrees closely both in general trends and in detail with the grip ice core oxygen isotope curve the reconstructed temperatures are 2 4 degreesc lower than coleopteran inferred temperatures but are closer to those inferred from plant macrofossils and glacial equilibrium line altitudes during the younger dryas copyright c 2000 john wiley sons ltd

late glacial and holocene palaeoceanography of the north icelandic shelf high resolution gravity cores and box cores from the north icelandic shelf have been studied for palaeoceanographic history based on lithological and biostratigraphical foramin iferal data results from two outer shelf cores covering the last 13 6 k 14 c yr bp are presented in this paper the sediments accumulated in north south trending basins on each side of the kolbeinsey ridge at water depths of ca 400 m sedimentation rates up to 1 5 m kyr 1 are observed during the late glacial and holocene the vedde and saksunarvatn tephras are present in the cores as well as the hekla 1104 a new tephra kol gs 2 has been identified and dated to 13 4 k 14 c yr bp and another tephra geochemically identical to the borrobol tephra has been found at the same level at present the oceanographic polar front is located on the north icelandic shelf which experiences sharp oceanographic surface boundaries between the cold east icelandic current and the warmer irminger current past changes in sedimentological and biological processes in the study area are assumed to be related to fluctuations of the polar front the area was deglaciated before ca 14 kyr bp but there is evidence of ice rafting up to the end of the gs 1 greenland stadial 1 younger dryas period increasing again towards the end of the holocene foraminiferal studies show a relatively strong gs 2 pre 13 kyr bp palaeo irminger current followed by severe cooling and then by unstable conditions during the remainder of the gi 1 greenland interstadial 1 bolling allerod and gs 1 younger dryas another cooling event occurred during the preboreal before the holocene current system was established at about 9 kyr bp after a climatic optimum between 9 and 6 kyr bp the climate began to deteriorate and fluctuate copyright 2000 john wiley sons ltd

early to middle holocene silicic tephra horizons from the katla volcanic system iceland new results from the faroe islands comparatively few icelandic tephra horizons dated to the early part of the holocene have so far been detected outside iceland here i present several tephra horizons that have been recorded in a holocene peat sequence on the faroe islands geochemical analyses show that at least two dacitic and one rhyolitic tephra layers were erupted from the katla volcanic system on southern iceland between ca 8000 and 5900 cal yr bp the upper two layers can be correlated with the silk tephras described from southern iceland whereas the third dated to ca 8000 cal yr bp has a geochemistry virtually identical to the rhyolitic component of the vedde ash the results suggest that the late weichselian and early holocene eruption history of the katla volcano was probably more complex than inferred from iceland a new early holocene rhyolitic tephra dated to ca 10 500 cal yr bp probably originates in the snaefellsnes volcanic centre in western iceland these new findings may play an important role in developing a holocene tephra framework for northwest europe copyright 2002 john wiley sons ltd

magnetic characterisation and correlation of a younger dryas tephra in north atlantic marine sediments a technique for identifying non visible basaltic tephra rich horizons of younger dryas yd greenland stadial gs 1 age in northeast atlantic sediments using rapid non destructive magnetic measurements is presented three high resolution marine sediment cores have been studied in an e w transect across the hebridean margin st kilda basin md95 2007 barra fan md95 2006 and rockall trough md04 2822 magnetic susceptibilities and remanent magnetisations were measured at contiguous 1 cm resolution on bulk sediments in all three cores an interval with higher proportions of hard magnetic minerals coincides with a clearly defined peak in basaltic tephra shard 250 m counts which can be constrained to the early part of the yd gs1 based on faunal climate proxies electron microprobe analyses of the magnetically distinct basaltic tephra interval in all three cores displays the same major element geochemistry as published for the vedde basaltic i tab 1 i e sourced from the icelandic volcano katla the identification of transitional alkalic basaltic tephras within marine sediments could potentially be facilitated by magnetic analysis as a useful chronostratigraphic screening tool copyright 2009 john wiley sons ltd

interferometric correlation and intertidal sediment properties around the dornoch firth north east scotland abstract interferometric correlation a function of various image pair parameters including spatial and temporal distribution allows the similarity in surface scattering conditions from different viewing angles and at different times to be determined permitting a surface classification to investigate the link between interferometric correlation and sediment properties namely the texture of intertidal sediments repeat pass satellite imagery of the area around the dornoch firth on the northeast coast of scotland have been employed using a ers 1 2 tandem pair of sar slc images of the mouth of the firth combined with field data a high resolution intertidal sediment sampling program we examine how relatively small changes in grain size volume distributions along a predominantly sandy coastline affect coherence levels results indicate that medium textured sediments i e mean grain size 0 25 mm to 0 50 mm or 2 to 1 with a smooth featureless surface free from sandbars and the casts of sandworms which trap water demonstrate areas of high coherence i e over 0 7

mid holocene glacier peak and mount st helens we tephra layers detected in lake sediments from southern british columbia using high resolution techniques abstract a glacier peak tephra has been found in the mid holocene sediment records of two subalpine lakes frozen lake in the southern coast mountains and mount barr cirque lake in the north cascade mountains of british columbia canada the age depth relationship for each lake suggests an age of 5000 5080 14 c yr b p 5500 5900 cal yr b p for the eruption which closely approximates the estimated age 5100 5500 14 c yr b p of the dusty creek tephra assemblage found near glacier peak the tephra layer which has not been reported previously from distal sites and was not readily visible in the sediments was located using contiguous sampling magnetic susceptibility measurements wet sieving and light microscopy the composition of the glass in pumice fragments was determined by electron microprobe analysis and used to confirm the probable source of this mid holocene tephra layer using the same methods the a d 1481 1482 mount st helens we tephra layer was identified in sediments from dog lake in southeastern british columbia suggesting the plume drifted further north than previously thought this high resolution method for identifying tephra layers in lake sediments which has worldwide application in tephrachronologic paleoenvironmental studies has furthered our knowledge of the timing and airfall distribution of holocene tephras from two important cascade volcanoes

the use of microtephra horizons to correlate late glacial lake sediment successions in scotland evidence is presented to show that two measurable concentrations of microtephra particles can be detected in deposits of late devensian late glacial age in three sites in scotland one layer is attributed to the vedde ash a marker horizon within the younger dryas chronozone the second is a new tephra reported for the first time which we name the borrobol tephra this occurs consistently near the base of the late glacial interstadial organic sediments at each site and is thought to date to around 12 5 14c ka bp geochemical determinations using an electron microprobe confirm the identification of the vedde ash suggest the borrobol tephra to have an icelandic origin and demonstrate the consistency of the geochemical signals at all three sites 1997 john wiley sons ltd

vedde ash layer discovered in a small lake basin on the scottish mainland a thin layer of micro tephra particles has been discovered in a lake sediment sequence from sutherland scotland the tephra is attributed to the vedde ash on the basis of ash geochemistry the vedde ash which has been dated to c 10 300 radiocarbon years bp and which was thus deposited during the younger dryas chronozone has previously been reported from lake sequences in norway from sediment cores from the ne north atlantic and from greenland ice cores but this is the first reported record from the british mainland it is likely that this ash layer also occurs in other lake sediment sequences in northern britain thus providing the potential for more precise correlations of younger dryas sequences than has hitherto been the case the way in which correlation by tephrochronology may revolutionize approaches to reconstructing the sequence of events in thene atlantic region during the last glacial interglacial transition is briefly considered

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

a younger dryas ash bed in western norway and its possible correlations with tephra in cores from the norwegian sea and the north atlantic abstract a bed of volcanic ash up to 23 cm thick is found in lacustrine and marine sediments in western norway it is formally mamed the vedde ash bed and its age is approximately 10 600 yr b p i e mid younger dryas the bed consits of pure glass having a bimodal basaltic and rhyolitic somposition the geochemistry of the glass shards suggests an icelandic source by means of stratigraphic position and geochemistry the ash is correlated with ash zones found in cores from the continental shelf the norwegian sea and the north atlatic

a late younger dryas early holocene tephrostratigraphy for fosen central norway a number of rapid climate oscillations occur during the lateglacial early holocene 15 8 ka bp period and a well developed tephrostratigraphy in association with these oscillations increases the po

late holocene faunal and landscape change in the bahamas we report an intertidal bone rich peat deposit on the windward atlantic ocean coast of abaco the bahamas the age of the gilpin point peat c 950 900 cal yr bp is based on five overlapping radiocarbon dates one each from single pieces of wood of buttonwood conocarpus erectus and sabal palm sabal palmetto and single bones of the cuban crocodile crocodylus rhombifer albury s tortoise chelonoidis alburyorum and green turtle chelonia mydas the short time interval represented by the charcoal rich peat suggests rapid sedimentation following initial anthropogenic fires on abaco the site s diverse snail assemblage is dominated by terrestrial and freshwater species the peat is exposed today only during exceptionally low tides suggesting a lower sea level at the time of deposition as well as a degrading shoreline during the past millennium fossils from gilpin point represent a late holocene vertebrate community at the time of first human presence only 10 of the 17 identified species of amphibians

three new distal tephras in sediments spanning the last glacial interglacial transition in scotland three new microtephras are reported from a number of lake sites from the inner hebrides and scottish mainland one occurs stratigrapically in the middle of greenland interstadial 1 gi 1 and has been named the penifiler tephra it is rhyolitic and possesses a geochemical signature that is very similar to that of the borrobol tephra which also occurs in three of the sequences reported here but which lies close to the lower boundary of gi 1 the second occurs stratigraphically in the early holocene below the saksunarvatn ash and is named the ashik tephra this tephra is geochemically bimodal with a rhyolitic component comparable to the an druim tephra that occurs later in the holocene and a basaltic component which is similar to the saksunarvatn ash a third tephra occurs stratigraphically above the saksunarvatn ash and is provisionally named the breakish tephra the consistent inter site correlation demonstrated for these new tephras at several sites enhances the regional tephrostratigraphic framework and increases the potential for correlating palaeoenvironmental events during gi 1 and the early holocene however the occurrence of multiple tephras with similar geochemistry in close stratigraphic and temporal proximity has implications for the rigour with which tephrostratigraphic investigations must be performed copyright 2006 john wiley sons ltd

laacher see tephra a widespread isochronous late quaternary tephra layer in central and northern europe a late quaternary tephra layer widespread in central and northern europe resulted from explosive plinian and phreatomagmatic eruptions of the laacher see volcano 11 000 yr b p the tephra is distinguished from other late quaternary andesitic rhyolitic airfall tuff layers in northern europe and from basaltic or trachytic tuff deposits in southern europe by its phonolitic composition and abundance of sanidine plagioclase clinopyroxene amphibole and sphene the proximal tephia sequence at laacher see is divided into three main deposits the predominantly plinian deposits of lower and middle laacher see tephra llst and mlst and phreatomagmatic deposits of the upper laacher see tephra ulst the mlst member is further subdivided into beds a b and c1 c2 and c3 the chemical composition of the magma is highly differentiated phonolite in the llst to mlst b sections but mafic phonolite in the mlst c1 to ulst sections all deposits are considered to be isochronous the frequency maximum of 16 radiocarbon datings indicating an eruption about 11 000 50 yr b p distal ash was deposited in three main fans directed to the northeast lst traced up to 1 100 km distance south lst traced up to 600 km and southwest lst traced up to 100 km tephrostratigraphic correlation of the distal ash deposits is based on a the major element composition of glass shards b lithology and c heavy mineral analyses the northeastern fan consists of deposits from llst mlst b and mlst c1 eruptive phases the southern fan comprises mlst a mlst c2 and ulst deposits and the southwestern fan consists exclusively of ash from the ulst eruptive phase northeastern transport of ash during eruptive phases with high plinian eruption columns but southern and southwestern transport of ash along phases of relatively low eruption columns are interpreted in terms of prevailing southwesterly paleowinds at high altitudes tropopause level but northerly winds dominating in the lower atmosphere the laacher see eruption columns were emplaced into an atmosphere vertically zoned with respect to paleowind directions which also explains the near vent shifting of llst mlst b and mlst c1 iso pach axes from east southeast to northeast within the first 20 km of transport

identification of the icelandic landnam tephra ad 871 2 in scottish fjordic sediment certain marginal marine environments such as the scottish fjord systems contain high resolution records of palaeoclimatic change in which decadal to centennial climatic events can be resolved this paper explores the possibilities of using tephrochronology to stratigraphically constrain the timing of such events in the loch sunart record md04 2831 on the nw coast of scotland uk one tephra horizon containing both silicic and basaltic shards is identified within late holocene sediment with geochemical analyses of the basaltic shards suggesting an origin in the veidivotn bar arbunga volcanic system radiocarbon age estimates and stratigraphic information suggests that the ad 871 landnam tephra is the most likely candidate the shards identified within this horizon appear hydrated and indicate the operation of post depositional weathering processes possibly influenced by the saline conditions of the fjord environment

a new and less destructive laboratory procedure for the physical separation of distal glass tephra shards from sediments abstract tephrochronology a key tool in the correlation of quaternary sequences relies on the extraction of tephra shards from sediments for visual identification and high precision geochemical comparison a prerequisite for the reliable correlation of tephra layers is that the geochemical composition of glass shards remains unaltered by natural processes e g chemical exchange in the sedimentary environment and or by laboratory analytical procedures however natural glasses particularly when in the form of small shards with a high surface to volume ratio are prone to chemical alteration in both acidic and basic environments current techniques for the extraction of distal tephra from sediments involve the cleaning of samples in precisely such environments and at elevated temperatures the acid phase of the cleaning process risks alteration of the geochemical signature of the shards while the basic phase leads to considerable sample loss through dissolution of the silica network here we illustrate the degree of alteration and loss to which distal tephras may be prone and introduce a less destructive procedure for their extraction this method is based on stepped heavy liquid flotation and which results in samples of sufficient quality for analysis while preserving their geochemical integrity in trials this method out performed chemical extraction procedures in terms of the number of shards recovered and has resulted in the detection of new tephra layers with low shard concentrations the implications of this study are highly significant because i the current database of distal tephra records and their corresponding geochemical signatures may require refinement and ii the record of distal tephras may be incomplete due to sample loss induced by corrosive laboratory procedures it is therefore vital that less corrosive laboratory procedures are developed to make the detection and classification of distal glass tephra more secure

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

new radiocarbon dates for the vedde ash and the saksunarvatn ash from western norway abstract the vedde ash bed mid younger dryas and the saksunarvatn ash early holocene are important regional stratigraphic event markers in the north atlantic the norwegian sea and the adjacent land area it is thus essential to date them as precisely as possible the occurrence of the saksunarvatn ash is reported for the first time from western norway and both tephras are dated precisely by ams analyses of terrestrial plant material and lake sediment at krakenes the vedde ash has been previously dated at sites in western norway to about 10 600 yr b p it is obvious in the younger dryas sediments at krakenes and its identity is confirmed geochemically the mean of four ams dates of samples ofsalix herbacealeaves adjacent to the tephra is 10 310 50 yr b p the saksunarvatn ash is not visible in the early holocene lake sediment at krakenes after removal of organic material and diatoms the identity of the tephra particles was confirmed geochemically and their stratigraphic concentration was estimated from curve matching of a series of seven ams dates of terrestrial plant macrofossils and whole sediment the radiocarbon age of the ash is 8930 9060 yr b p corresponding to an age of 9930 10 010 cal yr b p 7980 8060 cal yr b c

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