controls on the 87sr 86sr composition of seawater from the middle eocene to oligocene hole 689b maud rise antarctica a 87sr 86sr isotope curve of the middle eocene to oligocene was produced from analysis of foraminifera in ocean drilling program hole 689b maud rise near the coast of antarctica sediments from the hole are well preserved with no evidence of diagenetic alteration the sequence is nearly complete from 46 3 to 24 8 ma with an average sampling interval of 166 kyr excellent magnetostratigraphy in hole 689b allows calibration to the geomagnetic polarity time scale of cande and kent 1992 marine strontium isotopic ratios were nearly stable from 46 3 to 35 5 ma averaging near 0 70773 after which they began to increase a slow increase began after 40 4 ma rising at a rate of only about 8 10 6 m y from base values of 0 707707 from 35 5 ma to 24 8 ma the average slope increased to 40 10 6 m y the slope remained constant at least until 24 8 ma when the record becomes discontinuous owing to unconformities we evaluate several possible controls on the marine strontium isotope curve that could have led to the observed growth in 87sr 86sr ratios near the eocene oligocene boundary three mechanisms are considered including the onset of antarctic glaciation increased mountain building in the himalayan tibetan region and decreased hydrothermal activity none of the mechanisms alone seems to adequately explain the increased 87sr 86sr ratios during the oligocene glaciation as a weathering agent was too episodic and probably began too late to explain the upturn in marine 87sr 86sr ratios there is evidence that uplift in the himalayan tibetan region began in the miocene much too late to control oligocene strontium isotope ratios lastly hydrothermal flux changes since the eocene were apparently not great enough alone to account for the rise in marine 87sr 86sr ratios we suggest that a combination of causes such as decreased hydrothermal activity perhaps followed by increased glaciation and mountain building might best explain the growth of the marine 87sr 86sr curve during the oligocene

climatic impact of the millennium eruption of changbaishan volcano in china new insights from high precision radiocarbon wiggle match dating climatic impact here we report a new high precision 14 c wiggle match age of a d 9463 obtained from a 264year old tree trunk with bark killed during the eruption using the oxcal s bayesian modeling approach with 27 sequentially sampled annual rings of decadal intervals the new chronology conforms well to the calendar date of a d 946 for the eruption inferred from historical documentary evidence we find no stratospherically loaded sulfate spike that might be associated with the a d 946 eruption in the global volcanism record from the gisp2 ice core suggesting the stratospheric sulfate aerosols produced during the eruption were not transported to the arctic region due probably to its relatively low stratospheric sulfur emission and the seasonal effects of the atmospheric circulation at the time of the eruption that likely occurred in the winter of a d 946 947 since the stratospheric volcanic sulfates are the main cause of large scale climate perturbations this finding indicates that the millennium eruption of changbaishan volcano might have limited regional climatic effects rather than global or hemispheric impact as implied by its magnitude citation xu j b pan t liu i hajdas b zhao h yu r liu and p zhao 2013 climatic impact of the millennium eruption of changbaishan volcano in china new insights from high precision radiocarbon wiggle match dating geophys res lett 40 doi 10 1029 2012gl054246

origin of limestone conglomerates in the choson supergroup cambro ordovician mid east korea abstract the choson supergroup cambro ordovician of mid east korea consists mainly of shallow marine carbonates and contains a variety of limestone conglomerates these conglomerates are largely comprised of oligomictic rounded lime mudstone clasts of various size and shape equant oval discoidal tabular and irregular and dolomitic shale matrices most clasts are characterized by jigsaw fit mosaic disorganized or edgewise fabric and autoclastic lithology each conglomerate layer is commonly interbedded with limestone dolomitic shale couplets and occasionally underlain by fractured limestone layer capped by calcareous shale limestone conglomerates in the choson supergroup consist of 1 disorganized polymictic conglomerate cd 2 horizontally stratified conglomerate cs 3 mosaic conglomerate cm and 4 disorganized edgewise oligomictic conglomerate cd e these conglomerates are either depositional cd and cs or diagenetic cm and cd e in origin diagenetic conglomerates formed under the conditions of 1 alternating deposition and preservation of carbonate rich and carbonate poor layers and 2 early differential cementation of carbonate rich layers in situ fragmentation may result from brittle fracturing and ductile deformation due to compaction and dewatering enhanced by dissolution processes fluidization is promoted by the overlying impermeable calcareous shale beds and has probably reinforced in situ fragmentation of the underlying limestone beds in situ fragmentation and rounding process is important whereby earlier semiconsolidated portions of limestone are incorporated into the still fluid portion which can be termed autoconglomeration process a synthesis of 145 beds of limestone conglomerates in the choson supergroup suggests that less than about 7 of the conglomerate layers 10 145 are depositional whereas the rest more than 93 135 145 are identified as diagenetic conglomerates the common occurrence of diagenetic conglomerates warrants further study on limestone conglomerates elsewhere in the world

shallow burial dolomitization and dedolomitization of cenozoic cool water limestones southern australia geochemistry and origin abstract the gambier limestone a bryozoan rich cool water carbonate of late eocene to early miocene age in the otway basin of southeastern australia is about one third variably dolomitized limestone and dolostone individual dolomite crystals range from 10 to 500 m and are of three types 1 silt size crystals 4 64 m diameters having a brightly luminescent core 10 20 m of nearly stoichiometric dolomite with 1 mol mnco3 and sio2 but no fe surrounded by a thin dull or alternating dark and bright cl cortex that is nonstoichiometric with 44 46 mol mgco3 but sharp to diffuse zoning in mn and fe 2 sand size crystals which also have a brightly luminescent and stoichiometric core and dark and bright non stoichiometric thin inner cortex but are mostly a thick outer cortex at ca 50 m diameter that is nonluminescent and nonstoichiometric with some fe but no mn and 3 identical sand size crystals with a variably leached core and inner cortex that is either a void or a void filled with late calcite cement these three crystal populations represent two distinct dolomites and their alteration product the smallest of the silt size crystals which are rarely preserved are also the cores of the larger crystals upon which grew an inner and outer cortex of somewhat different composition the 18o values of dolomite rhombs 1 6 to 2 9 correlate positively with 13c values 0 7 to 3 0 with the lowest values from silt size or small sand size crystals and the highest values from large sand size crystals with leached unfilled cores low and variable 18o and 13c values in conjunction with high and variable mn and fe contents in both the core and inner cortex of all crystals are consistent with formation from a mixture of brackish water and seawater higher values for the outer cortex in sand size crystals are typical of those expected for precipitation from normal or near normal seawater low sr mn and fe contents in the largest crystals in conjunction with fluid inclusions of seawater salinity in the outer cortex are also consistent with the bulk of the large crystals having precipitated from seawater using the sr isotope evolution curve for cenozoic seawater sr isotope ratios of the dolomites can be divided into four distinct groups which correspond to times of major transgressions this cenozoic example in which dolomite petrography and crystal chemistry can be explained in terms of simple transgression regression offers a simple sedimentological explanation for many similar dolomites where processes of formation cannot be so easily constrained

evidence of the eldgja iceland eruption in the gisp2 greenland ice core relationship to eruption processes and climatic conditions in the tenth century glaciochemical studies and the evaluation of tephra in the gisp2 ice core provide information on the characteristics and potential environmental and climatic effects of the mid to late ad 930s voluminous fissure eruption of eldgja iceland the similarity in the chemical composition of basaltic glass shards found in a section of core dated at ad 938 4 compared to proximal glass from the eldgja eruption verifies the presence of eldgja debris a dacitic glass present in the same layer probably originated from eldgja as well in which case eldgja was the primary contributor of sulphur rich aerosols to the atmosphere in the late ad 930s we cannot completely exclude the possibility that another explosive eruption in the ad 930s produced this dacitic glass estimated maximum stratospheric loading is 100 x 1012 g h 2so4 over a 3 6 year period following the eruption but loading could be as low as half of that value a search of historical and proxy records for the late ad 930s to early 940s fail to show a co

refining the eruptive history of ulleungdo and changbaishan volcanoes east asia over the last 86 kyrs using distal sedimentary records abstract the eruptive histories of ulleungdo south korea and changbaishan north korea china border volcanoes are not well constrained since their proximal stratigraphies are poorly exposed or largely inaccessible however determining the past behaviour of these volcanoes is critical since future eruptions are likely to disperse ash over some of the world s largest metropolitan regions alkaline tephra deposits erupted from both centres are routinely identified in marine cores extracted from the sea of japan as well as high resolution lacustrine records east of the volcanoes here we review the distal ash occurrences derived from ulleungdo and changbaishan and provide new data from the lake suigetsu central honshu japan sediment core in order to provide a more complete and constrained eruption framework the intensely dated lake suigetsu archive provides one of the most comprehensive distal eruption records for both centres despite being located ca 500 km e of ulleungdo and ca 1000 km sse of changbaishan the suigetsu record is utilised to precisely date and geochemically fingerprint using major minor and trace element glass compositions ash fall events that reached central honshu here we identify a new non visible cryptotephra layer in the suigetsu sediments which reveals a previously unreported explosive event from changbaishan at 42 750 42 323 intcal13 yrs bp 95 4 confidence interval this event is chronologically and geochemically distinct from the b j baegdusan japan basin tephra reported in the sea of japan ca 50 ka furthermore we also confirm that the widespread u ym tephra erupted from ulleungdo reached central japan and is herein dated to 40 332 39 816 intcal13 yrs bp 95 4 confidence interval this terrestrial 14c derived age of the u ym can be used to constrain the chronology of marine records containing the same marker layer this reviewed and integrated tephrostratigraphic framework highlights the pivotal role that distal sedimentary records can play in evaluating the eruptive histories and hazard potential of ulleungdo and changbaishan

volatile emission during the eruption of baitoushan volcano china north korea ca 969 ad magma volume dre 24 5 km3 the main phase ca 95 vol is represented by comenditic tephra deposited dominantly as widespread fallout blankets and proximal ignimbrites the eruption column is estimated to have reached ca 25 km and thus entered the stratosphere a late phase 5 vol is represented by trachyte emplaced chiefly as moderately welded ignimbrites the comendites contain 3 and the trachytes 10 20 vol phenocrysts mainly anorthoclase hedenbergite and fayalite primary glassy melt inclusions with no signs of leakage were found only in phenocrysts in the comenditic tephra whereas those in phenocrysts in the trachytes are devitrified the comendite magma is interpreted to have been generated by fractional crystallization from a trachyte magma represented by melt inclusions in the phenocrysts in the comendite tephra the mass of volatiles emitted to the atmosphere during the eruption was estimated using the petrologic method the average h2o concentration of the comenditic matrix glass is 1 5 wt probably largely secondary and of the corresponding melt inclusions 5 2 wt melt inclusions in feldspar and quartz present the highest halogen concentrations with a calculated average for chlorine of 4762 ppm and for fluorine of 4294 ppm the comenditic matrix glasses are represented by a fluorine rich 3992 ppm f and fluorine poor group 2431 ppm f averaging 3853 ppm for chlorine only 20 of all sulfur analyses of the comenditic matrix glasses and melt inclusions are above the detection limit of 250 ppm s the difference between pre and post eruptive concentration of h2o is at least 3 7 0 6 wt h2o taking into consideration re hydration of the matrix glass and possible leakage of melt inclusions the difference between pre and post eruptive concentrations of the halogens amounts to 909 90 ppm cl and 1863 280 ppm and 302 40 ppm f the difference for s was estimated based on the average of the maximum s concentrations in the melt inclusions 455 ppm s and the detection limit resulting in 205 40 ppm s the calculated mass of volatiles injected into the atmosphere based on the erupted magma volume and volatile data is 1796 453 megatons for h2o 45 10 megatons for chlorine 42 11 megatons for fluorine and 2 0 6 megatons for sulfur the 969 20 ad eruption of baitoushan volcano one of the largest eruptions of the past 2000 years is thought to have had a substantial but possibly short lived effect on climate

lahar deposits generated after the millennium eruption of the changbaishan tianchi volcano in the erdaobaihe river system china abstract after the plinian millennium eruption including the me i and me ii eruptive stages of changbaishan tianchi volcano in 969 20 ce two large volume lahars were deposited mainly on the northern flank of the erdaobaihe river which flows through the only outlet from tianchi lake 1 a lahar deposit containing gray and black pumice lahar g b p and 2 a lahar deposit containing lithic particles lahar l based on the sedimentary characteristics of lahar outcrops and grain size and compositional analyses performed using standard dry sieving techniques examination of thin sections and geochemical analyses the origins transport and deposit processes and fluid phase variations of the two lahar deposits are studied these two lahar deposits are fan like in the flat medial area 23 60 km from the crater and fill channels in the distal mountainous area 60 km from the crater lahar l in the medial area represents a complete composite lahar flow deposit with a frontal debris head very coarse gravel texture extremely poor sorting massive and matrix supported structure and a hyperconcentrated fluid phase body and tail coarse sandy texture very poor sorting faint horizontal stratification with thin lenses of gravel clast supported structure lahar l in the distal area represents the material that passed the debris flow head and the fluid phase changes from debris flow to hyperconcentrated poor sorting clear thin horizontal stratification downcurrent the fluid phase of lahar g b p changes from debris flow in the medial area medium gravel to fine sand very poor sorting thick horizontal stratification with floating pumice on each unit surface to hyperconcentrated flow poor sorting thin horizontal stratification clear normal graded bedding and to stream flow moderate sorting cross bedding in the distal area lahar g b p was likely formed by the mixing of water from tianchi lake and pyroclastic flows of me ii lahar l was likely triggered by a sudden release dam break from tianchi lake an assessment of the risk posed to the stability of tianchi lake is as important as an assessment of the eruption risk

timing and climate forcing of volcanic eruptions for the past 2 500 years volcanic eruptions contribute to climate variability but quantifying these contributions has been limited by inconsistencies in the timing of atmospheric volcanic aerosol loading determined from ice cores and subsequent cooling from climate proxies such as tree rings here we resolve these inconsistencies and show that large eruptions in the tropics and high latitudes were primary drivers of interannual to decadal temperature variability in the northern hemisphere during the past 2 500 years our results are based on new records of atmospheric aerosol loading developed from high resolution multi parameter measurements from an array of greenland and antarctic ice cores as well as distinctive age markers to constrain chronologies overall cooling was proportional to the magnitude of volcanic forcing and persisted for up to ten years after some of the largest eruptive episodes our revised timescale more firmly implicates volcanic eruptions as catalysts in the major sixth century pandemics famines and socioeconomic disruptions in eurasia and mesoamerica while allowing multi millennium quantification of climate response to volcanic forcing

the caldera forming eruption of volcan ceboruco mexico of magma erupted 95 of which was deposited as fall layers during most of the deposition of p1 eruptive intensity mass flux was almost constant at 4 8 107 kg s 1 producing a plinian column 25 30 km in height size grading at the top of p1 indicates however that mass flux waned dramatically and possibly that there was a brief pause in the eruption during the post p1 phase of the eruption a much smaller volume of magma erupted although mass flux varied by more than an order of magnitude we suggest that caldera collapse began at the end of the p1 phase of the eruption because along with the large differences in mass flux behavior between p1 and post p1 layers there were also dramatic changes in lithic content p1 contains 8 lithics post p1 layers contain 30 60 and magma composition p1 is 98 rhyodacite post p1 layers are 60 90 rhyodacite however the total volume of magma erupted during the jala pumice event is close to that estimated for the caldera these observations appear to conflict with models which envision that after an eruption is initiated by overpressure in the magma chamber caldera collapse begins when the reservoir becomes underpressurized as a result of the removal of magma the conflict arises because firstly the p1 layer makes up too large a proportion 75 of the total volume erupted to correspond to an overpressurized phase and secondly the caldera volume exceeds the post p1 volume of magma by at least a factor of three the mismatches between model and observations could be reconciled if collapse began near the beginning of the eruption but no record of such early collapse is evident in the tephra sequence the apparent inability to place the jala pumice eruptive sequence into existing models of caldera collapse which were constructed to explain the formation of calderas much greater in volume than that at ceboruco may indicate that differences in caldera mechanics exist that depend on size or that a more general model for caldera formation is needed

the early archaean nondweni greenstone belt southern kaapvaal craton south africa part i stratigraphy sedimentology mineralization and depositional environment abstract the nondweni greenstone belt is an exceptionally well preserved 3 4 ga succession of predominantly volcanic rocks near the southern margin of the kaapvaal craton nondweni group rocks show both similarities and differences to the barberton sequence of similar age 300 km to the north in contrast with the latter none of the nondweni lavas exceed 23 mgo and spinifex textures are exclusively of pyroxene type the characteristics of the lavas and magma genesis are discussed in part ii of this series of papers three formations are recognized in the nondweni group the lowermost mogongolozi formation comprises basaltic andesites komatiitic andesites and basalts with intercalated coarser grained pyroxenites and gabbros the toggekry formation is a felsic unit of quartz sericite schists with small cu zn massive sulphide ore bodies of volcanogenic origin the uppermost witkop formation comprises mainly basalts komatiites and komatiitic basalts intercalated with chert layers and capped by a clastic sedimentary succession the total exposed thickness of the nondweni group is 16 500 m is the result of duplication of stratigraphy and tectonic thickening during early d1 thrusting in the bedding plane of much thinner lithological units tuffaceous sediments comprise a relatively minor component of the stratigraphy but are indicative of depositional environment banded chert layers are largely derived from accumulations of accretionary lapilli tuffs although a diverse origin is indicated for some varieties at the base of the witkop formation a number of undeformed banded coarse grained graphitic quartzite bodies entirely devoid of sedimentary structures are considered to have originated as hydrothermal deposits resulting from fumarolic activity selective brecciation of layers resulted from explosive release of fluids and gases the textures of these bodies are in marked contrast to the highly rounded pseudo conglomerates from the clastic sedimentary succession at the top of the witkop formation this 500 m thick succession passes upwards through reworked tuffs and alluvial fan deposits into a zone of evaporites and stromatolites swallow tail twin crystals of barite and an evaluation of crystal interfacial angles are indicative f replacement of primary evaporative gypsum most primary features of the nondweni greenstone belt suggest a shallow water or subaerial depositional environment and together with characteristics of the magma composition indicate a tectonic setting in a subduction related continental margin setting

microfossils and possible microfossils from the early archean onverwacht group barberton mountain land south africa there is widespread textural evidence for microbial activity in the cherts of the early archean onverwacht group layers with fine carbonaceous laminations resembling fossil microbial mats are abundant in the cherty metasediments of the predominantly basaltic hooggenoeg and kromberg formations in rare cases filamentous microfossils are associated with the laminae the morphologies of the fossils as well as the texture of the encompassing laminae suggest an affinity to modern mat dwelling cyanobacteria or bacteria a variety of spheroidal and ellipsoidal structures present in cherts of the hooggenoeg and kromberg formations resemble modern coccoidal bacteria and bacterial structures including spores the development of spores may have enabled early microorganisms to survive the relatively harsh surficial conditions including the effects of very large meteorite impacts on the young earth

multi proxy dating the millennium eruption of changbaishan to late 946 ce ranking among the largest volcanic eruptions of the common era ce the millennium eruption of changbaishan produced a widely dispersed tephra layer known as the b tm ash which represents an important tie point for palaeoenvironmental studies in east asia hitherto there has been no consensus on its age with estimates spanning at least the tenth century ce here we identify the cosmogenic radiocarbon signal of 775 ce in a subfossil larch engulfed and killed by pyroclastic currents emplaced during the initial rhyolitic phase of the explosive eruption combined with glaciochemical evidence from greenland this enables us to date the eruption to late 946 ce this secure date rules out the possibility that the millennium eruption contributed to the collapse of the bohai kingdom manchuria korea in 926 ce as has previously been hypothesised further despite the magnitude of the eruption we do not see a consequent cooling signal in tree ring based reconstructions of northern hemisphere summer temperatures a tightly constrained date for the millennium eruption improves the prospect for further investigations of historical sources that may shed light on the eruption s impacts and enhances the value of the b tm ash as a chronostratigraphic marker

characteristics of deep marine dolomite abstract deep marine sediment has not been subjected to the influences of meteoric waters deep burial or tectonic stress that have profoundly altered most rocks available to us in continental exposures hence it preserves the record of formation and early development of its dolomite evaluation of the dsdp x ray and smear slide data files indicates that dolomite is a common component in deep marine sediments it averages 1 and is found in all sampled ocean basins throughout post jurassic time dolomite abundance is not related to the abundance of any other detrital authigenic or alteration mineral except aragonite petrographic examination of 48 samples suggests that deep marine dolomite crystal size and appearance are similar to the size and appearance in modern supratidal deposits do omite does not increase in abundance or in crystal size downhole nor does crystal size increase with increasing age the dolomite is commonly nonstoichiometric avg 56 caco3 and poorly ordered globally it does not change in stoichiometry or order with depth or age dolomite in deep marine sediments does not originate from unusual or regionally important conditions it entered the sediments early most probably as a chemical precipitate from pore waters an uncertain amount estimated to be 10 is detrital

cenozoic dolomites of carbonate islands their attributes and origin abstract dolomites found on and below carbonate islands atolls and oceanic platforms provide useful insights into the origin of dolomite insights that may not be attainable from the study of more ancient cratonic dolomites for this reason they have been the subject of study for decades a critical mass of case studies now exist and some significant conclusions can be drawn from the cumulative data in most cases the association with an island is causal and not genetic nevertheless these dolomite occurrences are referred to herein as island dolomites one type of dolomite on carbonate islands is penecontemporaneous dolomite a phase that forms while the host sediment is in its original depositional setting island examples are holocene in age occur in holocene sediments and originate as a direct precipitate from either normal or evaporated seawater these are microcrystalline poorly ordered ca rich 18o enriched and geochemically unstable phases that are susceptible to recrystallization in the setting in which they formed post depositional dolomite is the other type of dolomite associated with carbonate islands this type of dolomite replaces older precursors and forms as cement distinctive characteristics include a dominance of fabric preserving texture pore lining cement rims that may exhibit micron scale banding with low mg calcite and formation in association with precursor dissolution sr isotopic dating indicates that all examples are neogene or quaternary in age those formed during the middle miocene through pliocene are massive laterally continuous and often multigenerational in contrast younger examples tend to be localized partial replacements of a single generation sr isotope ages also suggest global synchroneity in many dolomitization events which suggests a connection between dolomitization global eustacy and or global climatic factors geochemical attributes of post depositional island dolomites are ca enrichment positive 18o and 13c low sr contents 150 300 ppm and low fe global similarity in petrography and geochemistry of replacive island dolomites argues for a similar origin inferred origins however depend primarily on how 18o and sr data are interpreted values for 18o and dsr must be assumed due to uncertainties in oxygen isotope fractionation and sr partitioning there is no consensus or uniformity in those assumptions thus interpretations can vary and be biased to a desired result covariant trends in 13c and 18o some negative 13c values and high sr all favor a mixing zone origin but examples with these attributes are few lack of covariance in the isotopes mean 18o of 2 0 to 3 5 and low sr future studies should standardize the type of data collected and the analytical techniques employed multiple geochemical attributes should be measured on microsampled components and quantitative modeling should be employed in order to constraint interpretations as much as possible also needed are a better understanding of the kinetic processes that form these dolomites more careful assessment of their recrystallization status and an improved understanding of dsr and 18o at low temperature

ash from changbaishan millennium eruption recorded in greenland ice implications for determining the eruption s timing and impact major volcanic eruptions can impact on global climate by injecting large quantities of aerosols and ash into the atmosphere that alter the radiative balance and chemical equilibrium of the stratosphere the millennium eruption of tianchi paektu china north korea was one of the largest late holocene eruptions uncertainty about the precise timing of the eruption has hindered the recognition of its climate impact in palaeoclimate and historical records here we report the compelling identification of the eruption s volcanic signal in greenland ice cores through the association of geochemically characterized volcanic glass represented in by bimodal populations that compare with proximal material from the source eruption the eruption most probably occurred in the a d 940s 7 years after the eldgja eruption on iceland we examine the eruption s potential for climate forcing using the sulfate records from the ice cores and conclude that it was unlikely to have had a global or extraregional impact

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

integrating the holocene tephrostratigraphy for east asia using a high resolution cryptotephra study from lake suigetsu sg14 core central japan abstract tephra volcanic ash layers have the potential to synchronise disparate palaeoenvironmental archives on regional to hemispheric scales highly productive arc regions like those in east asia offer a considerable number of widespread isochrons but before records can be confidently correlated using these layers a refined and integrated framework of these eruptive events is required here we present the first high resolution holocene cryptotephra study in east asia using the lake suigetsu sedimentary archive in central japan the holocene tephrostratigraphy has been extended from four to twenty ash layers using cryptotephra extraction techniques which integrates the deposits from explosive eruptions from north korea china south korea and along the japanese arc this lake suigetsu tephrostratigraphy is now the most comprehensive record of east asian volcanism and the linchpin site for correlating sequences across this region major element glass geochemical compositions are presented for the tephra layers in the sequence which have been compared to proximal datasets to correlate them to their volcanic source and specific eruptions this study has significantly extended the ash dispersal of many key holocene marker layers and has identified the first distal occurrence of isochrons from ulleungdo and changbaishan volcanoes utilising the high precision lake suigetsu chronology we are able to provide constrained eruption ages for the tephra layers which can be transferred into other site specific age models containing these markers this new framework indicates that several isochrons stratigraphically bracket abrupt climate intervals in japan and could be used to precisely assess the regional and hemispheric synchronicity of these events

kinetics of dolomitization dolomitization of caco3 in the laboratory at 175 c demonstrates that the transformation has two distinct stages an induction stage during which no detectable products form and a nucleation growth stage during which dolomite forms at the expense of the reactant caco3 experiments at 218 c demonstrate that as the mg ca ratio of the solution increases the length of the induction stage decreases addition of co2 to the solution decreases the induction stage and also changes the overall transformation mechanism previously published data show that the induction stage is affected by the temperature of the reaction and the surface area and mineralogy of the reactant the induction stage is often the slowest part of the overall transformation characteristics of natural dolomites that are consistent with the experimental results include the following 1 dolomite selectively replaces fine crystalline caco3 2 most carbonate rocks are 100 dolomite or 100 calcite 3 limestone dolomite contacts are usually sharp and involve a decrease in the number of dolomite rhombs but the size of the rhombs remains constant 4 dolomite in completely dolomitized rocks is more stoichiometric than dolomite in partially dolomitized rocks 5 aragonite is selectively dolomitized in modern sabkha sediments and 6 modern dolomite is most abundant in areas of elevated mg ca ratio or hco3

the impact of high tephra loading on late holocene carbon accumulation and vegetation succession in peatland communities abstract peatlands are major terrestrial stores of carbon c of importance to the global climate system recent studies have made progress in understanding the climatic controls on the c cycle however important interactions between volcanic deposition and peatland c stores remain to be addressed this study uses a 3000 year peatland record from northern japan to examine the interactions between carbon accumulation vegetation community succession and volcanic ash deposition plant macrofossil and testate amoebae records are presented alongside records of total organic carbon nitrogen and phosphorous age depth models are developed using a bayesian approach with seven ams radiocarbon dates and two identified historical tephras from baitoushan ad 969 981 cal bp and hokkaido komagatake ad 1640 310 cal bp volcanoes results show that moderate to high tephra loading can shift peatland plant communities from sphagnum to monocotyledon domination this vegetation change is associated with increased peat humification and reduced carbon accumulation where tephra deposition and reworking has occurred the apparent rate of carbon accumulation can be halved while high tephra loading of the mire surface is sustained sphagnum species vary in their tolerance to tephra deposition after each ash fall sphagnum magellanicum disappeared from the plant macrofossil record whereas sphagnum papillosum showed apparent continuity of development through the 1856 94 cal bp ko c1 tephra high rates of carbon accumulation peaking at 100 g m 2 yr 1 2 3 times faster than the average for northern peatlands were recorded in the sphagnum communities that established after the cessation of tephra deposition and reworking from the ad 969 baitoushan ash fall b tm tephra this peak in c accumulation was coincident with a radical shift in mire nutrient cycling most probably caused by the interaction of s magellanicum with leachates from the underlying tephras the phase of high c accumulation continued for over 300 years offsetting the initial negative impact of the b tm tephra on peatland c accumulation these results suggest that management for ash tolerant sphagnum species could be a highly effective strategy for minimising volcanic disruption to peatland carbon accumulation the study also shows that consideration of volcanic impacts on peatlands is essential for development of more realistic terrestrial carbon balance models in volcanically active regions

a wiggle match age for the millennium eruption of tianchi volcano at changbaishan northeastern china abstract the tianchi volcano located on the border between china and north korea produced a massive plinian eruption of volcanic explosivity index vei 7 around 1000 ad which is referred to as the millennium eruption of tianchi volcano until now this volcanic eruption has not been well dated in this paper we report a series of new calibrated dates using wiggle match dating from carbonized logs collected from fallout deposits on the southern and northern flanks of the tianchi crater fifty ams 14 c ages of tree rings from two logs were obtained for the hengshan site south of the tianchi crater fig 1 these yielded a high precision wiggle match date of 921 941 cal ad 95 4 for the millennium eruption thirty two ams 14 c ages of tree rings of other two logs from the dongfanghong site north of tianchi crater fig 1 produced an age range for the volcanic eruption from 921 to 942 cal ad 95 4 a combined date for the four carbonized logs produced an age of 923 939 cal ad 95 4 for the millennium eruption moreover an exact date of late autumn 938 ad or early spring 939 ad is suggested based on the impact of the tianchi volcano on global climate especially east asian climate and the complete outermost rings of these four trees killed in the eruption

petrologic and geochemical constraints on the origin of subsurface dolomite enewetak atoll an example of dolomitization by normal seawater dolomite is present 1 250 1 400 m below sea level in eocene strata of enewetak atoll petrographically the deep enewetak dolomite postdates brittle compaction of rigid grains in the host eocene strata the 87 sr 86 sr ratio of these dolomites 0 70865 0 70901 indicates that they formed at one or more times between the middle miocene and the present since the top of the lower miocene is more than 900 m above the deep dolomitic interval the dolomite must have formed at a minimum burial depth of 900 m stable oxygen isotope determinations suggest dolomite precipitation from cold marine water lower miocene and eocene carbonate strata on the atoll are apparently in open communication with cold modern ocean water suggesting that those same strata were in open communication with ocean water during dolomitization at a depth of about 1 000 m modern pacific ocean water becomes undersaturated with respect to calcite but is still supersaturated with respect to dolomite therefore it is proposed that the deep enewetak dolomite precipitated from cold deep ocean water undersaturated with respect to calcite at a burial depth of more than 900 m

limestone pseudoconglomerates in the late cambrian gushan and chaomidian formations shandong province china soft sediment deformation induced by storm wave loading this paper focuses on the formative processes of limestone pseudoconglomerates in the gushan and chaomidian formations late cambrian of the north china platform shandong province china the gushan and chaomidian formations consist mainly of limestone and shale marlstone interlayers wackestone to packstone grainstone and microbialite as well as numerous limestone conglomerates seventy three beds of limestone pseudoconglomerate in the gushan and chaomidian formations were analysed based on clast and matrix compositions internal fabric sedimentary structures and bed geometry these pseudoconglomerates are characterized by oligomictic to polymictic limestone clasts of various shapes i e flat to undulatory disc blade and sheet marlstone and or grainstone matrix and various internal fabrics i e intact thrusted edgewise and disorganized as well as transitional boundaries limestone pseudoconglomerates formed as a result of soft sediment deformation of carbonate and argillaceous interlayers at a shallow burial depth differential early cementation of carbonate and argillaceous sediments provided the requisite conditions for the formation of pseudoconglomerates initial deformation i e burial fragmentation liquefaction and injection and subsequent mobilization and disruption of fragmented clasts are two important processes for the formation of pseudoconglomerates burial fragmentation resulted from mechanical rupture of cohesive carbonate mud whereas subsequent mobilization of fragmented clasts was due to the injection of fluid materials liquefied carbonate sand and water saturated argillaceous mud under increased stress storm wave loading was the most probable deformation mechanism as an external triggering force subsequent re orientation and rounding of clasts were probably prolonged under normal compactional stress eventually disrupted clasts along with matrix materials were transformed into pseudoconglomerates by progressive lithification soft sediment deformation is prevalent in alternate layers of limestone and mud marl stone and or grainstone regardless of their depositional environments

extensive ash falls in and around the sea of japan from large late quaternary eruptions abstract five widespread ashes of late quaternary age have been recognized on land and also in deep sea sediments in and around the sea of japan all are favorable for determining the magnitude and type of the great eruptions and for establishing a quaternary chronology around japan accurate determination of refractive indices of volcanic glass shards and phenocrysts together with chemical data have enabled successful characterization of the tephra layers and correlation between land and sea of the five tephras two are alkalic and are the products of major eruptions of two korean volcanoes the baegdusan tomakomai ash b tm and the ulreung oki ash u oki the b tm ash is recognized at the top of most cores in the northern part of the sea of japan and also on hokkaido and the northern part of honshu where a reliable archeological age is given around the 11th century the u oki ash occurs between the kikai akahoya and aira tn ashes in cores from adjacent to the ulreung do to central honshu where three radiocarbon ages of around 9300 yr b p were obtained the other three tephras are subalkalic and are correlated with large scale eruptions producing voluminous pyroclastic flows and calderas in kyushu the kikai akahoya k ah aira tn at and aso 4 ashes the former two have been well described already but their fallout areas are partly revised in this manuscript the at ash is the most prominent marker recognized not only on land of japan but also in cores from the whole area of the sea of japan and part of the pacific ocean the airfall aso 4 ash simultaneous with the aso 4 pyroclastic flow eruption is also described it mantles very extensive areas and serves as an important time marker about 70 000 years ago

volcanic forcing of climate over the past 1500 years an improved ice core based index for climate models 1 understanding natural causes of climate change is vital to evaluate the relative impacts of human pollution and land surface modification on climate we have investigated one of the most important natural causes of climate change volcanic eruptions by using 54 ice core records from both the arctic and antarctica our recently collected suite of ice core data more than double the number of cores ever used before reduces errors inherent in reconstructions based on a single or small number of cores which enables us to obtain much higher accuracy in both detection of events and quantification of the radiative effects we extracted volcanic deposition signals from each ice core record by applying a high pass loess filter to the time series and examining peaks that exceed twice the 31 year running median absolute deviation we then studied the spatial pattern of volcanic sulfate deposition on greenland and antarctica and combined this knowledge with a new understanding of stratospheric transport of volcanic aerosols to produce a forcing data set as a function of month latitude and altitude for the past 1500 years we estimated the uncertainties associated with the choice of volcanic signal extraction criteria ice core sulfate deposition to stratospheric loading calibration factor and the season for the eruptions without a recorded month we forced an energy balance climate model with this new volcanic forcing data set together with solar and anthropogenic forcing to simulate the large scale temperature response the results agree well with instrumental observations for the past 150 years and with proxy records for the entire period through better characterization of the natural causes of climate change this new data set will lead to improved prediction of anthropogenic impacts on climate the new data set of stratospheric sulfate injections from volcanic eruptions for the past 1500 years as a function of latitude altitude and month is available for download in a format suitable for forcing general circulation models of the climate system

modern marine dolomite cement in a north jamaican fringing reef minor quantities of ordered dolomite delta sup 18 o 2 0 per thousand pdb composition ca sub 1 22 mg sub 0 78 co sub 3 sub 2 have formed from near normal seawater in a subtidal hardground as part of a modern fringing coral reef crystals 5 mu m in diameter precipitated within the past 1 8 ka in the form of syntaxial fringes on mg calcite marine cements and skeletal allochems the crystals have a fine modulated microstructure and c reflections both apparently formed during crystal growth

geochemistry of historical age silicic tephras in iceland the major element chemistry of nine silicic tephras of historical age from iceland is assessed as a key step in the development of the recent tephrochronology of the north atlantic region the tephras include the largest such layers produced by each of the five central volcanoes hekla o raefajokull eyjafjallajokull torfajokull and askja since the ninth century ad h 1104 o1362 e 1821 landnam tephra c 870 a 1875 and four other tephras h 1158 h 1510 h 1947 o1727 the determination of grain discrete major element chemistry of the glass fraction is a fundamental stage in the identification and correlation of tephra and allows links to be made between icelandic source areas with precise dating evidence and distal deposits elsewhere in the north atlantic region although major element data can be used to discriminate between tephra layers produced by the different central volcanoes on its own it cannot be used to identify all the holocene layers produc

late pleistocene to present day eruptive history of the changbaishan tianchi volcano china dprk new field geochronological and chemical constraints abstract volcanic unrest during 2002 2006 renewed attention on changbaishan tianchi volcano as the source of the powerful explosive eruption vei 6 to 7 millennium eruption of 946 ce common era however progress in understanding the potential risk is complicated by discordant accounts of the most recent explosive eruptive history several eruptions since the late pleistocene such as the tianwenfeng twf qixiangzhan qxz millennium me baguamiao bgm liuhaojie lhj 1403 ce event 1403 and even a 1903 ce event have been proposed but the stratigraphic order ages distributions and even the very existence of some of these are still not fully ratified based on recent detailed stratigraphic logs of over 100 surface exposures and three deep trenches coupled with new geochronologic and petrochemical data including trace elements on glass and pyroxene we can now clarify these relationships herein we propose that the 946 ce millennium eruption be formally re named the generalized millennium eruption gme to avoid entrenched confusion and to formally acknowledge the composite comendite trachyte nature of the eruption thus three eruptions the twf qxz and the gme are confirmed the twf eruption is the first powerful explosive eruption at changbaishan tianchi and we find evidence that this eruption may have initiated the tianchi caldera it produced an extensive fallout pumice deposit that on the basis of new optically stimulated luminescence osl and radiocarbon 14c ages of overlying sedimentary strata indicates an eruption age 42 ka this new age constraint coupled with geochemical fingerprints confirms a correlation to the 50 6 kyr b j ash in japan sea the next eruption was the predominately effusive qxz that produced a clastogenic lava flow down the north slope of the edifice an age of 4 8 ka is proposed based on new radiocarbon 14c ages of charcoal at the base and from overlying sediment although the age of the gme is well established as late 946 ce there are some intriguing details in historical records of ash falls in japan that indicate two separate events on nov 3 946 ce and feb 7 947 ce we speculate that these correspond to the comendite and trachyte stages of the gme respectively subsequent to the gme no evidence of any post gme eruptions have been found these findings clarify and refine the history of the explosive stage of the changbaishan tianchi volcano that began 51 kyr this improved understanding should serve as a basis for further studies at changbaishan tianchi and inform a better constrained assessment of volcano hazard

european summer temperature response to annually dated volcanic eruptions over the past nine centuries the drop in temperature following large volcanic eruptions has been identified as an important component of natural climate variability however due to the limited number of large eruptions that occurred during the period of instrumen tal observations the precise amplitude of post volcanic cooling is not well constrained here we present new evidence on summer temperature cooling over europe in years following volcanic eruptions we compile and analyze an updated net work of tree ring maximum latewood density chronologies spanning the past nine centuries and compare cooling sig natures in this network with exceptionally long instru mental station records and state of the art general circu lation models results indicate post volcanic june august cooling is strongest in northern europe 2 years after an eruption 0 52 0 05 c whereas in central europe the temperature response is smaller and occurs 1 year after an eruption 0 18 0 07 c we validate these estimates by comparisonwith the shorter instrumental network and evaluate the statistical significance of post volcanic summer tempera ture cooling in the context of natural climate variability over the past nine centuries finding no significant post volcanic temperature cooling lasting longer than 2 years our results question the ability of large eruptions to initiate long term temperature changes through feedback mechanisms in the climate system we discuss the implications of these findings with respect to the response seen in general circulation models and emphasize the importance of considering well documented annually dated eruptions when assessing the

volcanic ash from the 1362 a d oraefajokull eruption iceland in the greenland ice sheet a continuous record of electrical conductivity measurements ecm was made on site during the drilling of a 200 m ice core at summit greenland and was used to identify horizons in the ice that might be linked to volcanic eruptions in one detailed section that we studied a large peak in the number of particles two orders of magnitude above the background was measured the particle peak was not associated with an ecm peak however the particles were identified as volcanic ash on the basis of both particle morphology and chemical composition the ash composition suggests an explosive rhyolitic eruption and is believed to have originatedfrom oraefajokull in iceland in 1362 a d

patterns of burial and tectonically controlled dolomitization in an upper devonian fringing reef complex leduc formation peace river arch area alberta canada abstract cumulative patterns of dolomitization in a subsurface upper devonian carbonate platform in the peace river arch area alberta are related to progressive burial 1 km fracturing focused basin derived fluids along subvertical structural conduits and into adjacent permeable strata in the early mississippian 3 wt fe dolomite in the platform heralding increased fe mobilization during burial diagenesis a negative shift in 18o values 6 5 to 15 is associated with successive fracture related dolomites and is interpreted to reflect an increase in fluid temperatures fracture related flow was probably rapid petrographic and isotopic signatures of fracture related dolomitization can be traced 300 m upsection from the leduc formation

holocene tephras highlight complexity of volcanic signals in greenland ice cores 1 acidity peaks in greenland ice cores have been used as critical reference horizons for synchronizing ice core records aiding the construction of a single greenland ice core chronology gicc05 for the holocene guided by gicc05 we examined sub sections of three greenland cores in the search for tephra from specific eruptions that might facilitate the linkage of ice core records the dating of prehistoric tephras and the understanding of the eruptions here we report the identification of 14 horizons with tephra particles including 11 that have not previously been reported from the north atlantic region and that have the potential to be valuable isochrons the positions of tephras whose major element data are consistent with ash from the katmai ad 1912 and oraefajokull ad 1362 eruptions confirm the annually resolved ice core chronology for the last 700 years we provide a more refined date for the so called ad860b tephra a widespread isochron found across nw europe and present new evidence relating to the 17th century bc thera aniakchak debate that shows n american eruptions likely contributed to the acid signals at this time our results emphasize the variable spatial and temporal distributions of volcanic products in greenland ice that call for a more cautious approach in the attribution of acid signals to specific eruptive events

funnel shaped breccia filled clastic dykes in the late cambrian chaomidian formation shandong province china abstract some examples of a funnel shaped structure filled with both angular and rounded clasts occur in a peloidal grainstone bed of the chaomidian formation late cambrian in the jiulongshan area shandong province china the clasts consist of peloidal grainstone which is the same as that of the walls of the funnels the structures are interpreted as dykes formed by upward escape of pore water and or fluidized sediment through a narrow conduit which was gradually widened by the force of the intruding fluid sediment the erosional capacity of the pressurized fluid sediment mixture consequently diminished upwards which explains the gradual decrease in intensity of fragmentation from the adjoining walls in this direction

record of volcanism since 7000 b c from the gisp2 greenland ice core and implications for the volcano climate system sulfate concentrations from continuous biyearly sampling of the gisp2 greenland ice core provide a record of potential climate forcing volcanism since 7000 b c although 85 percent of the events recorded over the last 2000 years were matched to documented volcanic eruptions only about 30 percent of the events from 1 to 7000 b c were matched to such events several historic eruptions may have been greater sulfur producers than previously thought there are three times as many events from 5000 to 7000 b c as over the last two millennia with sulfate deposition equal to or up to five times that of the largest known historical eruptions this increased volcanism in the early holocene may have contributed to climatic cooling

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

the magnitude and impact of the 431 ce tierra blanca joven eruption of ilopango el salvador the tierra blanca joven tbj eruption from ilopango volcano deposited thick ash over much of el salvador when it was inhabited by the maya and rendered all areas within at least 80 km of the volcano uninhabitable for years to decades after the eruption nonetheless the more widespread environmental and climatic impacts of this large eruption are not well known because the eruption magnitude and date are not well constrained in this multifaceted study we have resolved the date of the eruption to 431 2 ce by identifying the ash layer in a well dated high resolution greenland ice core record that is 7 000 km from ilopango and calculated that between 37 and 82 km3 of magma was dispersed from an eruption coignimbrite column that rose to 45 km by modeling the deposit thickness using state of the art tephra dispersal methods sulfate records from an array of ice cores suggest stratospheric injection of 14 2 tg s associated with the tbj eruption exceeding those of the historic eruption of pinatubo in 1991 based on these estimates it is likely that the tbj eruption produced a cooling of around 0 5 c for a few years after the eruption the modeled dispersal and higher sulfate concentrations recorded in antarctic ice cores imply that the cooling would have been more pronounced in the southern hemisphere the new date confirms the eruption occurred within the early classic phase when maya expanded across central america

the significance of maar volcanoes for palaeoclimatic studies in china abstract the sediments of maar lakes often provide paleoenvironmental records which are highly suitable for palaeoclimatic studies the main advantages of the records from maar lakes compared with other lacustrine records are as follows first the presence of varves annually laminated layers and tephra layers as well as other materials like terrestrial plant macrofossils charcoals organic carbon organic shells suitable for isotopic dating like ams 14c 210pb 137cs 238u 230th 40ar 39ar provides the possibility of developing several independent chronologies enabling the development of robust high resolution chronologies second maars and maar lakes can provide continuous sedimentary records spanning tens of thousands of years tianyang maar in china is hosted the longest known record spanning at least 400 kyr bp that are ideal for the investigation of climate change on different timescales including orbital millennial centennial and annual decadal third recent studies of biomarkers based on long chain alkenones lcas and glycerol dialkyl glycerol tetraethers gdgts have demonstrated the potential of maar lakes for quantitative paleotemperature reconstruction in this study we review some of the more significant achievements of palaeoclimatic research based on maar lake sediment sequences from china with the focus on chronology multiple timescales and quantitative paleoclimatic reconstruction

late pleistocene mixing zone dolomitization southeastern barbados west indies field geochemical and petrographic data for late pleistocene dolomites from southeastern barbados suggest that the dolomite precipitated in the zone of mixing between a coastal meteoric phreatic lens and normal marine waters the dolomite is localized in packstones and wackestones from the algalamphistegina fore reef calcarenite facies stable isotopic evidence suggests that meteoric water dominated the diagenetic fluids responsible for dolomitization carbon isotopes in pure dolomite phases average about 15 0 pdb this light carbon is attributed to the influence of soil gas co2 and precludes substantial mixing with seawater a narrow range of oxygen isotopic compositions coupled with a wide range of carbon compositions attest to the meteoric diagenetic overprint dolomitization likely occurred with as little as a five per cent admixture of seawater strontium compositions of the dolomites indicate probable replacement dolomitization of original unstable mineralogy the dolomite is characterized by low sodium values low concentrations of divalent manganese and iron suggest oxidizing conditions at the time of dolomitization a sequence of petrographic features suggests a progression of diagenetic fluids from more marine to more meteoric early marine diagenesis was followed by replacement dolomitization of skeletal grains and matrix limpid euhedral dolomite cements precipitated in primary intra and interparticle porosity subsequent to replacement dolomitization as waters became progressively less saline dolomite cements alternated with thin bands of syntaxial calcite cement the final diagenetic phase precipitated was a blocky calcite spar cement representing diagenesis in a fresh water lens this sequence of diagenetic features arose as the result of a single fall in eustatic sea level following deposition a stratigraphic eustatic diagenetic model constrains both the timing and rate of dolomitization in southeastern barbados dolomitization initiated as sea level began to fall immediately following the oxygen isotope stage 7 3 high stand some 216 000 yr bp due to the rapidity of late pleistocene glacio eustasy dolomitization locally complete is constrained to have occurred within about 5000 yr

evolution of fluids and metamorphic ore remobilization in the felbertal scheelite deposit eastern alps abstract the felbertal scheelite deposit displays a variety of host rocks and ore types macroscopic and microscopic evidence indicates the formation of the ore mineralization in a geothermal system including explosion and subaqueous surface phenomena at an active continental margin in upper proterozoic upper riphaean lower vendian time the alpine metamorphism and tectonism caused a pervasive metamorphic hydrothermal ore redeposition and a spatial redistribution from smaller volumes to larger volumes of low grade ores especially in the western field microthermometrical studies on quartz scheelite beryl calcite and fluorite in the metamorphosed felbertal scheelite deposit show two types of fluid inclusions aqueous fluid inclusions with variable amounts of co 2 up to 20 wt as well as aqueous fluid inclusions without a measurable co 2 content both types are of alpine origin and were trapped during the alpine retrograde metamorphism therefore the microthermometrical data do not record the conditions of the original pre alpine tungsten formation however it was possible to construct a path for the fluid evolution and the cogenetic ore redeposition during the alpine retrograde metamorphism from the microthermometrical and petrographical data

ice cores as an index of global volcanism from 1850 to the present to evaluate an important cause of past climate change climate researchers need reliable estimates of volcanic aerosol loading in the atmosphere previous indices the dust veil index volcanic explosivity index and those by mitchell 1970 sato et al 1993 and khmelevtsov et al unpublished manuscript 1993 all have drawbacks ice core acidity and sulfate records because they contain physical evidence of atmospheric loading are a promising source of information on past volcanic aerosols but these records contain large nonvolcanic signals as well we have compared northern hemisphere nh and southern hemisphere sh annual average versions of five indices with eight nh and six sh ice core records for the period 1850 to the present in an attempt to identify the volcanic signal common to all records the indices are all highly correlated with each other for the nh although the individual ice core records are in general not well correlated with each other or with any of the indices a composite derived from averaging the cores the ice core volcano index ivi shows promise as a new index of volcanic aerosol loading this new index correlates well with the existing non ice core volcanic indices and with high frequency temperature records for the sh the individual ice cores and indices are better correlated the shivi is again highly correlated with all indices and individual ice cores but not with high frequency temperature records for both hemispheres the southern oscillation index shows no significant correlation with the volcanic indices ice cores or the ivi thus providing no evidence for the impact of volcanic eruptions on el nino southern oscillation events

the origin of common dolomite fabrics clues from the pliocene abstract characteristic features common to dolomites of all ages are found in pliocene dolomites from the netherlands antilles these features include 1 pseudomorphic replacement 2 selective replacement 3 fossil moldic porosity 4 cloudy centered clear rimmed dolomite 5 sucrosic dolomite and 6 dolomite cement the development of a particular feature is controlled by 1 mineralogy of the material being replaced 2 the degree of saturation of the bulk solution with respect to the mineral being replaced and 3 the availability of dolomite nucleation sites low mg calcite lmc cement and fossils were often neither replaced by dolomite nor dissolved but aragonite and high mg calcite hmc were both replaced and dissolved the resistence of lmc to dolomitization was due to solutions saturated with respect to lmc and the lack of nucleation sites cryptocrystalline lmc was more readily replaced by dolomite because it provides more nucleation sites cloudy centered clear rimmed dolomite and sucrosic dolomite formed in sediments with abundant lmc and few nucleation sites fossil moldic porosity developed concurrent with pseudomorphic replacement suggesting that the dolomitizing solution was undersaturated with respect to the mineral being replaced dolomite cement commonly lines pores and fills intraparticle pore space dolomite cement occasionally has inclusions of a precursor lmc cement dolomite cement crystals are larger than replacement crystals because there are fewer nucleation sites for the cement crystals

early archean foredeep sedimentation related to crustal shortening a reinterpretation of the barberton sequence southern africa abstract the upper dominantly terrigenous sedimentary successions of the early archean barberton sequence kaapvaal province record an evolution similar to that of phanerozoic foredeeps and may represent the oldest known foredeep sequence rather than a passive continental margin sequence as previously proposed pre foredeep ocean crust the 3 5 ga old onverwacht group consists of bimodal volcanics with intercalated shallow water sediments gravity modeling and boundary shear zones indicate that deformed onverwacht crust was obducted northward onto sialic continental crust immediately before during or after burial by the synorogenic terrigenous clastic fill foredeep basin deepening due to crustal loading from the south is recorded by basinal iron formation chert and mudstone of the basal fig tree group which accumulated paraconformably on the onverwacht overlying sediments of the fig tree group consist of 2 km of submarine fan greywackes and mudstones shoaling of the basin is indicated by the transition to the overlying braided alluvial and shallow marine sediments of the ca 3 3 ga old moodies group 3 km thick changing ree patterns and relative abundances of ni cr sr th and ur in the sediments of the fig tree and moodies groups indicate a significant ultramafic mafic volcanic component diluted upward in the stratigraphic sequence by an increasing granitic contribution a similar trend is reflected in sandstone petrography in which the ratio of extrusive to intrusive rock fragments decreases upwards in the fig tree group whereas the moodies group sediments are enriched in quartz and potassium feldspar a persistent chert component in both units suggests that the tectonic setting of the basin is analogous to that of phanerozoic recycled orogens the distribution of facies in the fig tree and moodies groups and paleocurrent petrographic and geochemical data indicate progressive unroofing of a southerly source terrane consisting of the onverwacht volcanics and intercalated sediments and the 3 5 3 2 ga old ancient gneiss complex agc in addition older components of the fig tree group were recycled into overlying stratigraphie units the agc consists of mantle derived 3 5 ga old bimodal metavolcanics and metasediments a tonalite gneiss batholith metabasite dikes and meta anorthosites its structures record progressive northwestward uplift beginning around 3 4 ga ago intense homogeneous ductile strains were overprinted by northwest verging major folds rotated by large scale northwestward simple shear followed by imbricate faulting and pseudotachylite formation by 3 3 ga ago the fig tree and moodies groups had also shortened with similar kinematics to those of the agc by partly syndepositional folding and volume loss during the formation of transecting cleavage further folding and slide formation followed during subsolidus diapiric rise of the initially tabular kaap valley tonalite by 3 2 ga and emplacement of trondhjemite plutons from 3 3 to 3 0 ga ago

relationships between lithology and diagenesis in a limeston marl facies transition an electron microprobe study a 3 km long lateral facies transition from oligo miocene skeletal grainstones into packstones and mudstones displays systematic variation in carbonate skeletal fragment alteration and secondary carbonate mineral composition within the skeletal grainstone end member all aragonitic grains have dissolved all mg calcite skeletal fragments have altered to calcite and calcite has been precipitated as both void filling spar and as syntaxial overgrowths on echinoid fragments within the transitional grainstone packstone lithologies some skeletal fragments show preservation of their original mineralogy while calcite ferroan calcite spar and dolomite have precipitated in void spaces within the packstone mudstone end member of the transition aragonitic grains have been preserved and mg calcite skeletal fragments have retained most of their magnesium thin originally porous grainstone layers within the pack stone mudstones contain sideroplesite and ferroan calcite spar in void spaces and iron has been incorporated in skeletal fragments which were originally mg calcite in these grains iron has been incorporated at the expense of magnesium until the grains approach the composition of the surrounding ferroan calcite cement the lateral variation in diagenetic alteration across this facies transition is a function of differing groundwater movement and composition controlled ultimately by the composition porosity and permeability of the host lithologies

a comparison of the volcanic records over the past 4000 years from the greenland ice core project and dye 3 greenland ice cores since 1980 the electrical conductivity method ecm has been used to infer volcanic acid signals in greenland ice cores the method reveals the great majority of major volcanic eruptions including several known from historic records subsequent ion chromatographic analyses of the acid volcanic layers show the chemical composition i e the concentration of the volcanic acids h2so4 hci and hf plus e g the nonvolcanically derived hno3 while ecm data are available from a large number of shallow depth greenland ice cores covering the past 500 1500 years only the greenland ice core project grip greenland ice sheet project 2 gisp2 and dye 3 deep ice cores exist for a detailed comparative study of volcanic signals in greenland ice cores representing several thousand years comparison of the volcanic signals registered in the grip and gisp2 cores will be presented elsewhere the latter cores were augered 30 km apart and essentially represent the same atmospheric conditions such as temperature snow accumulation and chemical composition of the air here we present a comparison between the major volcanic signals over the past 4000 years in the grip core from central greenland and the dye 3 core from se greenland in order to investigate the depositional differences many of the major signals are detected in both cores but some of the differences in the records can be used to infer the latitudinal band of some eruption sites furthermore the influence of the amount of annual precipitation and glaciological postdepositional processes on the volcanic signals is discussed

a mid to late holocene cryptotephra framework from eastern north america abstract holocene cryptotephras of alaskan and pacific northwestern origin have recently been detected ca 7000 km away on the east coast of north america this study extends the emerging north american tephrochronological framework by geochemically characterising seventeen cryptotephra layers from four newly explored peatlands all detected tephras were deposited during the late holocene with no horizons present in the peat between ca 3000 5000 years ago the prevalence of the alaskan white river ash eastern lobe ad 847 1 is confirmed across the eastern seaboard from newfoundland to maine and a regional depositional pattern from mount st helens set w ad 1479 1482 is presented the first occurrences of four additional cryptotephras in eastern north america are described three of which may originate from source regions in mexico kamchatka russia and hokkaido japan the possibility of such tephras reaching eastern north america presents the opportunity to link palaeo archives from the tropics and eastern asia with those from the western atlantic seaboard aiding inter regional comparisons of proxy climatic records

growth fault control of early archaean cherts barite mounds and chert barite veins north pole dome eastern pilbara western australia1pii of original article s0301 9268 97 00062 4 1

tephra layers of large explosive eruptions of baitoushan changbaishan volcano in the japan sea sediments this paper is based on the results of a comprehensive investigations of sediments from seven cores sampled during the international russian chinese cruise 53 of the r v akademik lavrentyev 2010 in the frames of the russian chinese collaboration between the pacific oceanological institute of the far eastern branch of the russian academy of sciences poi feb ras vladivostok russia and the first institute of oceanography fio qingdao china baitoushan chanbaishan volcano had several powerful explosive eruptions during the middle pleistocene holocene which produced widespread tephra layers the paper reports chemical composition of volcanic glasses and minerals from six tephra layers labeled as b og b sado b j b un1 b v and b tm which belong to baitoushan volcano and were identified in sediments of the northwestern part of the sea of japan the tephras were dated using geochronological data for the host sediments the estimated ages for the middle pleistocene tephra is 488 ka the late pleistocene tephras are 71 1 71 9 cal k b sado 50 8 cal ka b j 38 3 cal ka b un1 and 29 0 29 4 cal ka b v the ash layers consist of alkali rich glass of trachydacitic to alkaline rhyolitic composition and specific assemblage of minerals including fe rich augite hedenbergite aegirine augite aegirine arfvedsonite and fayalite the mineral assemblage is typical for alkalic volcanic rocks from continental rift setting aenigmatite a rare mineral from the group of inosilicates was firstly identified in distal tephra of baitoushan volcano supplied into marine sediments the composition of glasses and minerals from all layers are similar it testifies about steady state conditions of the magma accumulation under baitoushan volcano and about the bimodal character of magmatic chambers during the late pleistocene and holocene since 100 ka

tephra evidence for the most recent eruption of laoheishan volcano wudalianchi volcanic field northeast china abstract wudalianchi volcanic field wdlc is one of the youngest intracontinental monogenetic volcanic fields in china the 1719 1721 ce laoheishan huoshaoshan eruption and the 1776 ce laoheishan eruption are the latest eruptions in wdlc based on the local historical records however most of the recent explosive eruptive products around wdlc are attributed to the 1719 1721 ce laoheishan huoshaoshan eruption while less attentions were paid on the 1776 ce laoheishan eruption there are two types of scoria fall deposits around laoheishan volcano i e the upper light grey high vesicular scoria deposit us and below dark low vesicular scoria deposit bs most of the glass shards from us exhibit 4 na2o while bs show 5 content with trachyandesitic to tephriphonolitic in composition that can be clearly distinguished from those from other nearby volcanic regions such as nuomin 150 km to nangelaqiushan lake nglq arxan chaihe 450 km to nglq longgang 700 km to nglq and jingbohu 550 km to nglq a cryptotephra layer is clearly revealed as a distinct peak in magnetic susceptibility measurements from nglq 8 km northwest to laoheishan volcano glass composition of the cryptotephra layer recorded in nglq is similar to the proximal us around laoheishan volcano on basis of historical records and field observations we ascribed us to the 1776 ce laoheishan eruption and bs to the 1719 1721 ce laoheishan huoshaoshan eruption consequently historical records assigned a precise age 1776 ce for the tephra recorded in nglq and thus can be used to refine the age model of these lacustrine sediments

metamorphosed hydrothermal eruption breccia conglomerate in the felbertal scheelite deposit eastern alps austria abstract a metamorphosed hydrothermal eruption breccia conglomerate has been found in recently opened galleries in the western field of the felbertal scheelite deposit it belongs to the k2 ore body and covers a stratiform quartz mass and surrounding host rocks the quartz mass shows features very similar to siliceous sinters in recent explosion craters e g waiotapu new zealand the breccia displays a variable thickness commonly up to 60 cm it is continuous for at least 100 m along strike and is composed of rock fragments from the surrouding and underlying host rocks including basaltic felsic and quartz rocks these fragments reveal a variable degree of rounding due to subaqueous reworking and an elongation due to tectonism and metamorphism with increasing distance from the quartz mass the quantity of rock fragments in the breccia diminishes rapidly laterally the metamorphosed breccia conglomerate horizon interfingers with biotite amphibolites this breccia indicates 1 at least one hydrothermal eruption 2 the existence of a subaqueous erosional surface 3 the ejection of underlying and surrounding host rocks of the scheelite bearing series 4 the pre existence of the quartz mass and a bimodal rock assemblage including basaltic and felsic volcanites with an earlier tungsten mineralization mainly in quartz fragments and 5 a tungsten mineralization coeval with the formation of the matrix this matrix shows enrichments in w sn mo li be au bi as f p ba th and u

defining the potential source region of volcanic ash in northwest europe during the mid to late holocene abstract far travelled volcanic ash fine grained tephra clouds pose economic and societal risks largely through their potential impact on the aviation industry a long view of ash clouds extending over northwest europe assembled from the study and geochemical characterisation of cryptotephra i e tephra invisible to the naked eye in sedimentary records can help inform the understanding of the frequency of such events and the nature of eruptions that generate them here we review the records of cryptotephra deposition in northwest europe during the mid to late holocene the last eight millennia to gain insights into the sources of volcanic ash reaching this region we consider almost 500 published and unpublished datasets for cryptotephras recorded in sedimentary sequences ranging from ireland to latvia and on the basis of their major element geochemical composition we identify 90 unique ash horizons and their likely provenance the majority 72 of the cryptotephras derive from icelandic eruptions but a large proportion 24 originates from other volcanic regions including alaska the cascades kamchatka mexico the azores and possibly the mediterranean although moderate magnitude eruptions in iceland may potentially disperse ash clouds over europe it appears that only large magnitude events in more distant regions have generally had this capacity and then only when suitable meteorological conditions prevailed nevertheless the cryptotephra records demonstrate that ash clouds from most volcanic regions capable of producing large explosive eruptions in the northern mid to high latitudes particularly those to the west of europe as well as in tropical north america have the potential to extend to northwest europe volcanic ash forecasts for this region need therefore to take into account possible risks posed not only by icelandic eruptions but also by any large magnitude eruptions in north america or the north pacific area

tephrostratigraphy of changbaishan volcano northeast china since the mid holocene abstract a detailed tephrostratigraphy of an active volcano is essential for evaluating its eruptive history forecasting future eruptions and correlation with distal tephra records changbaishan volcano is known for its millennium eruption me ad 940s vei 7 and the me tephra has been detected in greenland ice cores 9000 km from the vent however the pre millennium pre me and post millennium post me eruptions are still poorly characterized in this study we present a detailed late holocene eruptive sequence of changbaishan volcano based on single glass shard compositions from tephra samples collected from around the caldera rim and flanks tephra ages are constrained by optically stimulated luminescence osl and ams 14c dates tephra from the mid holocene pre me eruption can be divided into two pyroclastic fall subunits and it cannot be correlated with any known changbaishan sourced tephra recorded in the japan sea based on major element composition of glass shards such as the b j baegdusan japan basin and b v baegdusan vladivostok oki tephras me pyroclastic fall deposits from the caldera rims and volcanic flanks can be correlated to the juvenile pumice lapilli or blocks within the pyroclastic density current pdc deposits deposited in the valleys around the volcano based on glass shard compositions our results indicate that the glass shard compositions of proximal me tephra are more varied than previously thought and can be correlated with distal me tephra in addition widely dispersed mafic scoria was ejected by the me plinian column and deposited on the western and southern summits and the eastern flank of the volcano data for glass from post me eruptions such as the historically documented ad 1403 ad 1668 and ad 1702 eruptions are reported here for the first time except for the me other holocene eruptions including pre me and post me eruptions had the potential to form widely distributed tephra layers around northeast asia and our dataset provides a proximal reference for tephra and cryptotephra studies in surrounding areas

new evidence for the presence of changbaishan millennium eruption ash in the longgang volcanic field northeast china abstract the changbaishan millennium eruption ad 940s produced a widely distributed tephra layer around northeast asia this tephra layer serves as a marker bed in greenland ice cores and in marine lake archeological and tsunami sediments in japan and the surrounding region however little attention has been paid to the widespread sediments west of changbaishan volcano here we present new stratigraphic geochemical varve chronology and 14c geochronological data from the varved sediments in lake sihailongwan longgang volcanic field northeast china extending the westerly margin of this eruption the distinctive geochemical characteristic of volcanic glass ranging from trachyte to rhyolite similar to those of proximal and distal tephra confirmed the occurrence of changbaishan millennium eruption ash in the lake illustrating the westward dispersal fan of the ash deposits the position of the peak concentration of glass shards of this tephra was dated to 953 37 ad by varve chronology and the radiocarbon samples immediately above this tephra gave a date of 940 1020 ad overlapping the most recent ages for this eruption the occurrence of changbaishan millennium eruption ash in this lake enables a direct and precise synchronization with other high resolution archives in northeast asia such as maar lakes and peat and marine sediments thus providing an isochronous marker for a range of sedimentary contexts

a synchronized dating of three greenland ice cores throughout the holocene as part of the effort to create the new greenland ice core chronology 2005 gicc05 a synchronized stratigraphical timescale for the holocene parts of the dye 3 grip and ngrip ice cores is made by using volcanic reference horizons in electri cal conductivity measurements to match the cores the main annual layer counting is carried out on the most suited records only exploit ing that the three ice cores have been drilled at locations with different climatic con ditions and differences in ice flow however supplemental counting on data from all cores has been performed between each set of reference horizons in order to verify the valid ity of the match after the verification the main dating is transferred to all records us ing the volcanic reference horizons as tie points an assessment of the mean annual layer thickness in each core section confirms that the new synchronized dating is consistent for all three cores the data used for the main annual layer counting of the past 7900 years are the dye 3 grip and ngrip stable isotope records as the high accumulation rate at the dye 3 drill site makes the seasonal cycle in the dye 3 stable isotopes very resistant to firn diffusion an effort has been made to extend the dye 3 holocene record the new syn chronized dating relies heavily on this record of 75 000 stable isotope samples the dat ing of the early holocene consists of an already established part of gicc05 for grip and ngrip which has now been transferred to the dye 3 core gicc05 dates the younger dryas termination as defined from deuterium excess to 11 703 b2k 130 years earlier than the previous grip dating

variations in the strontium isotopic composition of seawater during the neogene the authors report 261 strontium isotopic analyses of well preserved planktonic foraminifers from three deep sea drilling project sites 519 588 and 607 these samples cover the period from 24 ma to present with an average of approximately one sample per 100 ka the combination of high sample density and uniformity of analytical procedures has produced a well defined record of changes in the sup 87 sr sup 86 sr of seawater during the neogene the record can be viewed as a series of essentially linear segments with slopes ranging from as high as 6 times 10 sup minus 5 m y to as low as 0 m y the times associated with major inflections in the curve do not appear to correspond to simple geologic phenomena such as eustatic cycles but are probably controlled by a combination of tectonic and climatic factors that influenced the abundance and isotopic composition of terrestrial strontium input to the oceans the strontium isotopic data are consistent with a progressive increase in the chemical weathering rates of the continents during the neogene probably related to repeated glaciations increased exposure of continents by lowered sea level and increased continental relief resulting from high rates of tectonic uplift

reconciling multiple ice core volcanic histories the potential of tree ring and documentary evidence 670 730 ce chronologically secure volcanic event histories are important for improving our understanding of volcano climate responses and securing ice core chronologies we present an exploratory case study that attempts to reconcile the chemical fingerprints of major volcanism in greenland ice cores for the years 670 730 ce this period experienced considerable volcanic perturbation with multiple volcanic signals registered in all 8 greenland ice core datasets studied including some comparable in magnitude to the great 1815 tambora eruption but reconciling signals with divergent dating between datasets presents a number of challenges to further our understanding of the volcanic history of this period frost rings tree ring growth width and density minima from europe siberia and china are considered together with western european near eastern and chinese documentary evidence these reveal a striking sequence of co occurring inter regional climatic extremes and social crises we further examine a recently proposed 7 year adjustment to the gicc05 chronology used by many greenland ice cores and find that this results in a more coherent volcanic history for these years and an improved agreement with tree ring and written records three major volcanic events can now be identified dated to 681 684 686 and 706 707 with several moderate events further contributing to a sustained climate perturbation reflected in prolonged temperature reductions in high resolution reconstructions

identification of the changbaishan millennium b tm eruption deposit in the lake suigetsu sg06 sedimentary archive japan synchronisation of hemispheric wide palaeoclimate archives the b tm tephra dispersed during the highly explosive changbaishan millennium eruption ca 940 950 ce and a key marker layer within the greenland ice cores has now been identified in the lake suigetsu sg06 sedimentary sequence central japan the major element geochemistry of the volcanic glasses within this tephra layer are compared to a new glass dataset from the distal type locality tomakomai port hokkaido and other published millennium eruption b tm deposits to verify this correlation the discovery of the b tm tephra in the lake suigetsu record provides to date the most southerly identification of this ash and crucially the first direct tie point between this high resolution mid latitude palaeoclimate archive and the greenland ice cores these findings present significant encouragement for on going research into the tephrostratigraphy of east asia focusing on the identification of widely dispersed tephra layers which can facilitate the synchronisation of disparate palaeoclimate archives and thus enable the assessment of spatio temporal variations in past climatic change

ultra distal kamchatkan ash on arctic svalbard towards hemispheric cryptotephra correlation abstract rapidly deposited and geochemically distinct volcanic ash tephra markers represent a powerful chronological tool that enables precise dating and correlation of geological archives recent analytical advances now allow fingerprinting of non visible ash cryptotephra over thousands of kilometers this has opened up tantalizing possibilities for the intercontinental synchronization of records we present geochemical evidence to demonstrate that ash from a svalbard lake sediment core correlates to the kamchatkan ks 2 eruption by expanding the known dispersal range of cryptotephra by thousands of kilometers and linking the pacific and atlantic arctic this study raises cryptotephra analysis to a new level also the presented findings mark a step towards a hemispheric tephrochronological framework finally this study highlights the importance of looking beyond proximal volcanic sources to find a correlation

patagonian ash on sub antarctic south georgia expanding the tephrostratigraphy of southern south america into the atlantic sector of the southern ocean

pseudoconglomerate and a re examination of some paleoenvironmental controversies pseudoconglomerate an unusual fragmental rock that contains pebblelike clasts is described from the barberton greenstone belt south africa it occurs in concordant and discordant bodies that are closely associated with silicification carbonation and in situ brecciation and veining pseudoconglomerate is interpreted as a product of submarine exhalative activity in a hemipelagic environment it is thought to develop in subsurface breccia bodies that form by hydraulic disaggregation of the host rock breccia clasts are jostled during continued fluid flow and become rounded as the result of attrition between adjacent fragments the previous interpretation of this rock as a normal marine sediment at barberton and possibly in other archean and paleozoic sequences may have resulted in paleoenvironmental misinterpretation

tephra dispersal during the campanian ignimbrite italy eruption implications for ultra distal ash transport during the large caldera forming eruption the campanian ignimbrite eruption dispersed ash over much of the central eastern mediterranean sea and eastern europe the eruption started with a plinian phase that was followed by a series of pyroclastic density currents pdcs associated with the collapse of the plinian column and the caldera the glass compositions of the deposits span a wide geochemical range but the plinian fallout and pdcs associated with column collapse the lower pumice flow only erupted the most evolved compositions the later pdcs the breccia museo and upper pumice flow erupted during and after caldera collapse tap a less evolved component and intermediate compositions that represent mixing between the end members the range of glass compositions in the campanian ignimbrite deposits from sites across the central and eastern mediterranean sea allow us to trace the dispersal of the different phases of this caldera forming eruption we map the fallout from the plinian column and the plumes of fine material associated with the pdcs co pdcs across the entire dispersal area this cannot be done using the usual grain size methods as deposits in these distal regions do not retain characteristics that allow attribution to either the plinian or co pdc phases the glass compositions of the tephra at ultra distal sites 1500 km from the vent match those of the uppermost pdc units suggesting that most of the ultra distal dispersal was associated with the late co pdc plume that was generated during caldera collapse

a new bipolar ice core record of volcanism from wais divide and neem and implications for climate forcing of the last 2000 years volcanism is a natural climate forcing causing short term variations in temperatures histories of volcanic eruptions are needed to quantify their role in climate variability and assess human impacts we present two new seasonally resolved annually dated non sea salt sulfur records from polar ice cores wais divide wdc06a from west antarctica spanning 408 b c e to 2003 c e and neem neem 2011 s1 from greenland spanning 78 to 1997 c e both analyzed using high resolution continuous flow analysis coupled to two mass spectrometers the high dating accuracy allowed placing the large bi hemispheric deposition event ascribed to the eruption of kuwae in vanuatu previously thought to be 1452 1453 c e and used as a tie point in ice core dating into the year 1458 1459 c e this new age is consistent with an independent ice core timescale from law dome and explains an apparent delayed response in tree rings to this volcanic event a second volcanic event is detected in 1453 c e in both ice cores we show for the first time ice core signals in greenland and antarctica from the strong eruption of taupo in new zealand in 232 c e in total 133 volcanic events were extracted from wdc06a and 138 from neem 2011 s1 with 50 ice core signals predominantly from tropical source volcanoes identified simultaneously in both records we assess the effect of large bipolar events on temperature sensitive tree ring proxies these two new volcanic records synchronized with available ice core records to account for spatial variability in sulfate deposition provide a basis for improving existing time series of volcanic forcing

formation of dolomite in the coorong region south australia abstract cores of unlithified holocene sediment from shallow ephemeral lakes in the coorong region s a contain dolomite at various stratigraphic intervals two distinct dolomite types are recognized using stable carbon and oxygen isotope data unit cell calculations transmission electron microscopy tem and bulk composition data detailed x ray diffraction xrd analyses show that the dolomite is ordered but that ordering is variable average unit cell parameters indicate that the crystal lattice of one type of dolomite type a is expanded in the co direction c o 16 08 a and contracted in the ao direction a o 4 799 a relative to ideal dolomite c 0 16 02 a and a o 4 812 a respectively type a dolomite occurs in the centers of the larger basins the mole fraction of mgco3 is as much as 53 1 the unusual crystal chemistry and tem data indicating a heterogeneous microstructure suggest that this dolomite is generated by rapid precipitation from brines which have highly elevated mg ca ratios dolomite ordering reflections are present in electron diffraction patterns but are weak stable oxygen and carbon isotope values are tightly grouped ave 18 o 7 6 s d 0 6 13 c 3 5 s d 0 7 the other type of dolomite type b is ca rich has lower stable isotope values ave 18 o 6 4 13 c 1 2 than type a dolomite has a more homogeneous microstructure is expanded in both the ao and co axes and is generally better ordered than type a dolomite these data suggest type b dolomite is precipitated more slowly from less evaporitic brines than type a dolomite

tephrostratigraphical investigation of lake sediments and a peat bog in northeastern china since 20 000 years this is a detailed tephrostratigraphical investigation of late quaternary deposits in the longgang and changbaishan volcanic fields of northeastern china a total of 45 reference samples which were collected from either side of the chinese korean border showed very similar geochemical characteristics to the millennium eruption of tianchi volcano through comparing the published data of the glass shards detected in gushantun with these reference samples further description is that the glass shards in the sediment of gushantun came from the tianchi volcano eruption in ad 1702 1668 and 1597 a basaltic tephra layer found in the sediment of hanlongwan associated with an eruption of the jinlongdingzi volcano which happened in 1500 2100 cal yr bp by comparing with the published data from sihailongwan and xiaolongwan tianchi and jinlongdingzi volcano are both active and erupted several times during the historical period reference samples and the tephra layers detected in hanlongwan sihailongwan gushantun

constraints and interpretation of 87sr 86sr ratios in cenozoic dolomites replacement dolomitization by seawater has been modeled in order to quantify the sr isotope signature in cenozoic dolomites as a function of precursor mineralogy and 87sr 86sr ratio reaction stoichiometry and 87sr 86sr ratio of the dolomitizing fluids high sr carbonates such as aragonite may introduce a significant precursor memory into an otherwise seawater dominated sr isotope signature if small quantities of seawater per unit volume of precursor carbonate are involved dolomitization of low sr carbonates i e low mg calcite are shown to create an isotopic signature indistinguishable from that of the seawater involved in the reaction therefore by comparison with the sr isotope evolution curve of seawater the 87sr 86sr ratios of the dolomites can be used to record the oldest possible age of dolomitization and the youngest age of deposition the implications for this approach have been applied to data obtained from a dolomitized core from little bahama bank bahamas two periods of dolomitization are recognized one in the early late miocene involving middle miocene or older rocks and a second one around 2 4 ma ago affecting early pliocene carbonates

new distribution coefficient for the incorporation of strontium into dolomite and its implications for the formation of ancient dolomites late tertiary dolomites form the bahamas exhibit a strong inverse correlation between sr and mol mgco sub 3 it is proposed that this relation is a result of a distribution coefficient dependent on the concentration of ca in dolomite because these dolomites precipitated from water with a sr sup 2 ca sup 2 ratio similar to that of seawater a distribution coefficient d sub sr sup dolomite of 0 0118 is calculated for sr in stoichiometric dolomite this coefficient increases by about 0 0039 for every additional mol caco sub 3 in nonstoichiometric dolomite these data have three important implication first the new d sub sr sup dolomite is substantially lower than previously suggested second a relation has been established among the sr sup 2 ca sup 2 ratio of dolomite forming waters the major element composition of dolomites and the sr content of dolomites allowing the determination of the sr sup 2 ca sup 2 ratio of fluids involved in the formation of ancient dolomites third some published data sets on dolomites show a similar relation between sr content and major element composition suggesting that these dolomites may also have formed from seawater other data sets deviate from the correlation defined by little bahama bank dolomites indicating either dolomitization in fluids other than seawater or changes ofmore the sr sup 2 ca sup 2 ratio of seawater through time less