occurrence stratigraphy and geochemistry of late quaternary tephra layers in the aegean sea and the marmara sea abstract several discrete tephra layers occur in 2 5 10 3 m long cores from the aegean sea whereas a single tephra is identified in 3 5 9 7 m long cores from the marmara sea major and trace element data on these tephras delineate eight distinct groups the geochemical data and multivariate statistics allow the correlation of the tephra layers with six previously described marine tephras from the eastern mediterranean sea potential terrestrial sources are suggested for the others the chronostratigraphy of the tephra layers was established using several radiocarbon dates and the oxygen isotope stratigraphy from two long piston cores four widespread tephra layers occur within the upper quaternary sediments of the aegean sea the two youngest widespread tephra layers were derived from the santorini volcano of south central aegean sea z2 the minoan eruption ca 3 6 ka and y2 the cape riva eruption ca 21 7 ka the y2 tephra is also identified in three piston cores from the marmara sea the two older widespread tephra layers originated from the eruptions which emplaced the campanian ignimbrite of the italian volcanic provinces i e the y5 tephra ca 39 3 ka and from the nisyros volcano of the southeastern aegean sea the consistent occurrence of the nisyros tephra below the y5 tephra confirms similar findings in a lake core on the island of lesbos linear extrapolations using the oxygen isotope stratigraphy suggest an age of 42 44 ka for the nisyros eruption three additional tephra layers with a limited regional distribution are identified in the aegean sea cores two of these tephras originated from the yali volcano of the southeastern aegean sea and from the aeolian islands i e x1 tephra a series of six mugearite tephra beds in the south skiros basin is interpreted as a set of redeposited turbidites

single crystal 40ar 39ar dating of a late quaternary paroxysm on kos greece concordance of terrestrial and marine ages the late quaternary plinian eruption forming the kos plateau tuff on the island of kos greece was one of the largest in the mediterranean a precise date for this eruption would significantly improve the chronology of the deep sea tephra layer w 3 because reliable correlation of w 3 with the kos plateau tuff has been previously established we have dated sanidine from the eruption at 161 3 1 1 ka using the laser fusion single crystal 40ar 39ar technique this age represents a significant refinement over both conventional and highly precise cassignol method k ar ages and the 40ar 39ar age is shown to be in remarkably good agreement with the age of w 3 inferred from recent astronomically calibrated oxygen isotope chronologies

absolute calibration of the greenland time scale implications for antarctic time scales and for δ14c abstract we propose a new age scale for the two ice cores grip and gisp2 that were drilled at greenland summit based on accelerator mass spectrometry 14c dating of foraminifera in core md95 2042 paleoceanography 15 2000 565 calibrated by means of recently obtained paired 14c and 230th measurements on pristine corals marine radiocarbon calibration curve spanning 10 500 to 50 000 years bp thousand years before present based on paired 230th 234u 238u and 14c dates on pristine corals geological society of america bulletin 2003 submitted for publication the record of core md95 2042 can be correlated very precisely to the greenland ice cores between 30 and 40 ka bp our scale is 1 4 ka older than the grip ss09sea time scale journal of quaternary science 16 2001 299 at the older end of marine isotope stage 3 we use published 230th dates from speleothems to calibrate the record using this scale we show a 14c record that is broadly consistent with the modelled record earth planet sci lett 200 2002 177 and with the data of hughen et al science 303 2004 202 but not consistent with the high values obtained by beck et al science 292 2001 2453 or by voelker et al radiocarbon 40 1998 517 we show how a set of age scales for the antarctic ice cores can be derived that are both fully consistent with the greenland scale and glaciologically reasonable

dansgaard oeschger and heinrich event imprints in alboran sea paleotemperatures past sea surface temperature sst evolution in the alboran sea western mediterranean during the last 50 000 years has been inferred from the study of c37 alkenones in international marine global change studies md952043 core this record has a time resolution of 200 years allowing the study of millennial scale and even shorter climatic changes the observed sst curve displays characteristic sequences of extremely rapid warming and cooling events along the glacial period comparison of this alboran record with 18o from greenland ice greenland ice sheet project 2 core shows a strong parallelism between these sst oscillations and the dansgaard oeschger events five prominent cooling episodes standing out in the sst profile are accompanied by an anomalous high abundance of neogloboquadrina pachyderma sinistral which is confined to the duration of these cold intervals these features and the isotopic record reflect drastic changes in the surface hydrography of the alboran sea in association with heinrich events hl 5

mediterranean sea surface radiocarbon reservoir age changes since the last glacial maximum sea surface reservoir ages must be known to establish a common chronological framework for marine continental and cryospheric paleoproxies and are crucial for understanding ocean continent climatic relationships and the paleoventilation of the ocean radiocarbon dates of planktonic foraminifera and tephra contemporaneously deposited over mediterranean marine and terrestrial regions reveal that the reservoir ages were similar to the modern one 400 years during most of the past 18 000 carbon 14 years however reservoir ages increased by a factor of 2 at the beginning of the last deglaciation this is attributed to changes of the north atlantic thermohaline circulation during the massive ice discharge event heinrich 1

a refined astronomically calibrated 40ar 39ar age for fish canyon sanidine abstract intercalibration between the astronomical and radio isotopic dating methods provides a means to improving accuracy and reducing uncertainty of an integrated multi chronometer geologic timescale here we report a high precision 40 ar 39 ar age for the fish canyon sanidine fcs neutron fluence monitor by multi collector noble gas mass spectrometry through cross calibration with a1 tephra sanidines a1ts of the direct astronomically tuned faneromeni section crete the astronomically intercalibrated 40 ar 39 ar age of fcs of 28 172 0 028 ma 2 external errors is within the uncertainty of but more precise 0 10 than the previous 40 ar 39 ar age determined by intercalibration with astronomically tuned tephras from the melilla basin morocco using this proposed age for fcs combined with measurements using the a1ts as the neutron fluence monitor a weighted mean bishop tuff 40 ar 39 ar sanidine age of 0 7674 0 0022 ma 2 external errors is indistinguishable from the id tims u pb zircon age 0 7671 0 0019 ma the consistency between the astronomically calibrated 40 ar 39 ar sanidine age and u pb zircon age for this quaternary unit suggests that agreement between these two radio isotopic dating techniques is now achievable at better than 0 3 2 in the youngest part of geologic time

the late mis 5 mediterranean tephra markers a reappraisal from peninsular italy terrestrial records abstract we present new tephrostratigraphic records from the late mis 5 ca 110 80 ka terrestrial sediments from southern and central italy on the one hand the central italy record consists of an outcropping lacustrine sequence from the sulmona intermountain basin that contains four trachytic phonolitic tephra layers pop3 pop2a pop2b pop1 all of which show a k alkaline affinity that is typical for the roman co magmatic province the pop3 and pop1 layers were dated by 40 ar 39 ar method at 106 2 1 3 ka 2 and 92 4 4 6 ka 2 respectively the sequence in southern italy on the other hand is represented by post tyrrhenian coastal deposits of the cilento area campania which contain two trachytic layers cil2 cil1 that show the same k alkaline affinity based on their chemical compositions and radiometric ages pop3 and pop1 are firmly correlated with the marine tephra layers x 5 105 2 ka and c 22 ca 90 ka which in turn match tephras tm 25 and tm 23 11 respectively in the lacustrine sequence of lago grande di monticchio southern italy of note the pop1 layer also matches the adriatic sea tephra prad 2517 that was previously correlated with the older x 5 layer the tephra couplet pop2a and pop2b ca 103 and 103 5 ka extrapolated ages are compatible with the tm 24b and tm 24 3 tephras in monticchio which match both the stratigraphic positions and the chemical compositions in the cilento area as well as the already described x 6 layer ca 108 ka cil2 we recognise a new stratigraphic superimposed layer cil1 that matches the pop3 tm 25 c 27 x 5 mediterranean marker s in summary the data presented here provide new chemical and 40 ar 39 ar chronological constraints towards a robust late mis 5 tephrostratigraphy of the central mediterranean although at the same time they also reveal how the tephrostratigraphy itself might be flawed when dealing with tephra markers that are not adequately constrained and characterised

out of tune the dangers of aligning proxy archives abstract tuning is a widespread technique to combine date and interpret multiple fossil proxy archives through aligning supposedly synchronous events between the archives the approach will be reviewed by discussing a number of literature examples ranging from peat and tephra layers to orbital tuning and 18o series from marine and ice deposits potential problems will be highlighted such as the dangers of circular reasoning and unrecognised chronological uncertainties and some solutions suggested fossil proxy research could become enhanced if tuning were approached in a more quantitative reliable and objective way and especially if individual proxy archives were non tuned and kept on independent time scales

millennial scale phase relationships between ice core and mediterranean marine records insights from high precision 40ar 39ar dating of the green tuff of pantelleria sicily strait abstract with the advent of annually resolved polar ice records extending back to 70 ka marine and continental paleoclimate studies have now matured into a discipline where high quality age control is essential for putting on an equal pace layer counted timescale models and late quaternary sedimentary records high resolution u th dating of speleothem records and 40ar 39ar dating of globally recorded geomagnetic excursions have recently improved the time calibration of quaternary archives reflecting the cross disciplinary effort made to synchronize the geologic record at the millennial scale yet tie points with such an absolute age control remain scarce for paleoclimatic time series extending beyond the radiocarbon timescale most notably in the marine record far travelled tephra layers recorded both onland and offshore provide an alternative in such instance to synchronize continental and marine archives via high resolution 40ar 39ar dating of the parent volcanic eruption high resolution 40ar 39ar data are reported herein for one such volcanic marker the green tuff of pantelleria and its y 6 tephra equivalent recorded throughout the central and eastern mediterranean published radiochronometric and 18o orbitally tied ages for this marker horizon scatter widely from about 41 ka up to 56 ka our new 40ar 39ar age at 45 7 1 0 ka 2 reveals that previous estimates are biased by more than their reported errors would suggest including recent orbital tuning of marine records hosting the tephra bed that are reevaluated in the context of this study this improved estimate enables potential phase lags and leads to be studied between deep sea and terrestrial archives with unrivaled near millennial 40ar 39ar precision in the marine record

40ar 39ar dating of latest pleistocene 41 ka marine tephra in the mediterranean sea implications for global climate records abstract fifty one 40 ar 39 ar laser heating analyses of sanidine crystals in the c 13 tephra layer recovered out of a piston core raised from 3000 m depth in the tyrrhenian sea yielded apparent ages between 25 and 112 ka twenty four of these measurements define an age probability maximum and generate an isochron of 41 1 2 1 ka 2 with a 40 ar 36 ar intercept of 288 21 that is indistinguishable from the modern atmosphere however the entire population is skewed toward older apparent ages with smaller peaks at 48 ka 55 ka 67 ka and 110 ka the composition of glass shards in the c 13 tephra overlaps that of the sio 2 rich phase of the 150 km 3 campanian ignimbrite which erupted from the campi flegrei caldera 130 km northwest of the core site although the 41 1 2 1 ka isochron is 15 older than k ar and 14 c ages for the campanian ignimbrite it is indistinguishable from recent 40 ar 39 ar age determinations the campanian ignimbrite eruptions were also chemically similar to and correlated with the y 5 ash layer the most voluminous and widely dispersed late pleistocene tephra in the mediterranean region the age of the y 5 layer was constrained originally at 38 0 2 5 ka on the basis of astronomical dating of o isotope stages the 40 ar 39 ar ages astronomical dating plus chemical similarities permit correlation of the c 13 tephra layer with both the campanian ignimbrite and the y 5 tephra layer the older ages preserved in the c 13 tephra layer may reflect xenocrysts incorporated during the explosive eruption accompanying collapse of the campi flegrei caldera 41 ka the c 13 tephra layer is correlated with a 10 be peak in an adjacent marine core o isotope stage 3 12 and immediately preceded a cooling episode corresponding to heinrich event 4 thus the age of these features is constrained by radioisotope dating the 41 ka peak in 10 be deposition is a global phenomenon whose age matches that of the laschamp geomagnetic excursion thus our results provide a new tie point among several polar ice core and marine proxy records of paleoclimate during the past 50 kyr precise age information independent of radiocarbon dating can be recovered from latest pleistocene marine tephra using the 40 ar 39 ar laser heating method despite the presence of multiple components that may have been incorporated during or after its deposition

cooling rates of plinian fall and pyroclastic flow deposits in the bishop tuff inferences from water speciation in quartz hosted glass inclusions cooling rates inferred from water speciation in rhyolitic glass inclusions in quartz phenocrysts from the bishop tuff california vary over more than 5 orders of magnitude from about 10 to 10 4 c s 1 many of the cooling rates are within the previously published experimentally calibrated range of this technique but the slowest rates 10 4 c s 1 are extrapolated such extrapolation suggests cooling rates as low as 10 8 c s 1 0 3 c year 1 for the interiors of thick pyroclastic flow deposits the temperatures at which oh and molecular h2o species would be in equilibrium range from 400 c for glass inclusions from plinian fall deposits to 250 c for the most slowly cooled glassy inclusions from pyroclastic flow deposits notwithstanding appreciable uncertainties cooling rates correlate with depositional process fall vs flow deposition and distance above the cold ground or below overlying hot pyroclastic flow deposits plinian inclusions within 2 5 m of the cold pre bishop ground cooled at 1 10 c s 1 consistent with thermal modeling of small pumice clasts falling through cold air very slow inferred cooling rates for pyroclastic flow deposits 10 6 to 10 8 c s 1 also agree with thermal conduction models faster cooling rates 10 1 to 10 4 c s 1 for inclusions in the lowermost 0 5 m of pyroclastic flow deposits reflect the effect of quenching against the cold ground at blind spring hill east of long valley caldera intermediate cooling rates 10 3 to 10 6 c s 1 are observed in plinian deposits overlain by and partially interbedded with pyroclastic flow deposits indicating that reheating of rapidly cooled plinian inclusions can reset water speciation melt inclusions in pyroclastic flow deposits are quenched to glass only if the deposit is relatively thin or has a relatively low emplacement temperature in relatively thick or hot deposits inclusions may be quenched to glass at the base of the deposit where it is more rapidly cooled by contact with the pre eruption ground

an 18 m thick volcaniclastic interval in pantelleria trough sicily channel deposited from a large gravitative flow during the green tuff eruption abstract a 30 m long piston core from the floor of pantelleria trough penetrated an 18 m thick volcaniclastic interval under and overlain by hemipelagic sediments the distribution and thickness of the interval is mapped in 3 5 khz profiles across the trough core sediments have been analysed for grain size carbonate content detrital petrology and physical properties such as bulk density and magnetic susceptibility chemical analyses of tephra and included minerals have been made by electron microprobe the volcaniclastic interval is correlated with the youngest large explosive eruption on pantelleria the 50 ka green tuff ignimbrite eruption on the basis of the sedimentation rate of overlying sediment calcareous nannofossil and foraminiferal biostratigraphy a calibrated radiocarbon age of 43 47 2 ka possibly infinite in the underlying marls and many similarities in tephra and mineral chemistry and abundance the lower 8 m of the volcaniclastic interval consists of poorly sorted massive units of lapilli tuff interpreted as resulting from the direct flow of a pyroclastic flow into the sea with the energetic hyperconcentrated flows crossing the length of pantelleria trough and eventually freezing on the low gradients the overlying 10 m thick turbidite probably developed from the dilute turbulent pyroclastic flow of the co ignimbrite cloud and the resulting turbulent subaqueous flow eroded bioclastic material from the shelf and deposited a well graded bed from sand through silt to mud the poorer sorting of the volcaniclastic interval compared with the green tuff ignimbrite on land supports the concept that ignimbrite deposits are sorted by aggrading bed processes

rapid environmental changes in southern europe during the last glacial period oxygen isotope records from greenland ice cores1 2 indicate numerous rapid climate fluctuations during the last glacial period north atlantic marine sediment cores show comparable variability in sea surface temperature and the deposition of ice rafted debris3 4 5 in contrast very few continental records of this time period provide the temporal resolution and environmental sensitivity necessary to reveal the extent and effects of these environmental fluctuations on the continents here we present high resolution geochemical physical and pollen data from lake sediments in italy and from a mediterranean sediment core linked by a common tephrochronology our lacustrine sequence extends to the past 102 000 years many of its features correlate well with the greenland ice core records demonstrating that the closely coupled ocean atmosphere system of the northern hemisphere during the last glacial4 extended its influence at least as far as the central mediterranean region numerous vegetation changes were rapid frequently occurring in less than 200 years showing that the terrestrial biosphere participated fully in last glacial climate variability earlier than 65 000 years ago our record shows more climate fluctuations than are apparent in the greenland ice cores together the multi proxy data from the continental and marine records reveal differences in the seasonal character of climate during successive interstadials and provide a step towards determining the underlying mechanisms of the centennial millennial scale variability

tephra layers in late quaternary sediments of the central adriatic sea abstract magnetic susceptibility curves of ten cores collected in the western adriatic shelf and in the mid adriatic deep allowed us to recognize thirty tephra layers whose age based on physical and biostratigraphic data encompass a time interval ranging from less than 70 ka to the present chemical features of the tephra defined by sem eds analyses performed on glass shards indicate alkaline affinity mainly with k na 1 and trachytic compositions with two minor benmoreitic and phonolitic groups these characteristics are consistent with campanian and subordinate etnean provenances because of chemical and age constraints the glass shards can be referred to six tephra layers already described in the literature such as c20 c14 citara ischia c10 campanian ignimbrite c2 nyt neapolitan yellow tuff ams pf agnano monte spina phlegrean fields from campanian area and y1 from etna volcano indicating an age ranging from about 70 to 4 ka ams pf and c2 nyt dated 4 4 and 12 3 ka respectively are the most widespread tephra beds in the study cores the occurrence of ams pf never recorded in marine sequences up to now represents a very good marker for holocene adriatic sediments c2 nyt already recorded in the central tyrrhenian sea in lacustrine sediments from southern italy and in the campanian area is a good stratigraphic marker for inter sea and sea land correlations y1 tephra dated 14 2 ka also occurs in on land sediments of central italy and in marine sediments from the tyrrhenian and ionian seas it now represents one of the most widespread stratigraphic markers in the central mediterranean region

oldest human footprints dated by ar ar fossilized human trackways are extremely rare in the geologic record these bear indirect but invaluable testimony of human hominid locomotion in open air settings and can provide critical information on biomechanical changes relating to bipedalism evolution throughout the primitive human lineage among these the devil s footsteps represent one of the best preserved human footprints suite recovered so far in a pleistocene volcanic ash of the roccamonfina volcano southern italy until recently the age of these footprints remained speculative and indirectly correlated with a loosely dated caldera forming eruption that produced the brown leucitic tuff despite extensive hydrothermal alteration of the pyroclastic deposit and variable contamination with excess 40ar detailed and selective 40ar 39ar laser probe analysis of single leucite crystals recovered from the ash deposit shows that the pyroclastic layer and the footprints are 345 6 kyr old 1 confirming for the first time that these are the oldest human trackways ever dated and that they were presumably left by the modern human predecessor homo heidelbergensis close to climatic termination iv

the origin of trachyte and pantellerite from pantelleria italy insights from major element trace element and thermodynamic modelling abstract trachyte and peralkaline rhyolite pantellerite and comendite frequently comprise the felsic end member in bimodal suites in continental rift and oceanic island settings in these settings the relationship between the mafic mildly alkaline or transitional basalt and felsic lavas is ambiguous major and trace element models and isotopic data are often consistent with an origin for felsic lavas from either fractional crystallization of transitional basalt or partial melting of alkali gabbro followed by fractional crystallization in this paper we present representative mineral analyses and whole rock analyses from forty samples of a basalt trachyte pantellerite suite collected at pantelleria italy in the strait of sicily rift zone and compare the results of major and trace element modelling with the results of thermodynamic melts modelling from these results we conclude that metaluminous trachyte formed as a result of 70 to 75 low pressure 0 1 gpa fractional crystallization of an assemblage of plagioclase clinopyroxene olivine magnetite and apatite from a hydrous 1 0 1 5 wt h2o transitional basalt magma at relative oxygen fugacities approximately one log unit below the fayalite magnetite quartz buffer fmq 1 the daly gap a lack of intermediate 49 62 wt sio2 volcanic rocks at pantelleria is concluded to be primarily the result of rapid differentiation through that interval relatively rapid crystallization at low pressure may have effected the partial degassing of water saturated 4 wt h2o metaluminous trachyte magma some metaluminous trachyte lavas have positive eu anomalies high k rb ratios high concentrations of ba and low concentrations of incompatible trace elements these are interpreted to be the result of up to 40 accumulation of alkali feldspar comenditic trachyte pantelleritic trachyte and pantellerite formed after an additional 20 to 80 fractional crystallization of an assemblage dominated by alkali feldspar from metaluminous trachyte magma the most evolved pantellerite lavas and tuffs are the result of a total of 95 fractional crystallization of transitional basalt with phenocrysts that equilibrated at low temperatures 4 wt water contents

evaluation of the astronomically calibrated time scale for the late pliocene and earliest pleistocene an astronomically calibrated time scale was recently established hilgen 1991a b for the pliocene and earliest pleistocene based on the correlation of dominantly precession controlled sedimentary cycles sapropels and caco3 cycles in mediterranean deep sea sections to astronomical solution ber90 berger and loutre 1991 this time scale which differed substantially from the conventional time scales then widely used is essentially confirmed by a new generation of radiometric dates using the ar 40 ar 39 laser fusion technique to evaluate this time scale we here extract both precession and obliquity related components from late pliocene earliest pleistocene climatic proxy records in the mediterranean and determine coherencies and phase time lags between these components and the respective orbital variations this work is found to support the new time scale because significant coherencies are found between the astronomically related components in our proxy records and the orbital variations not only at the main period of precession but also at the main period of obliquity and because of the eccentricity modulation of precession in the low frequency eccentricity bands of the spectrum but the calculated time lag between obliquity and 41 kyr components in the climatic proxy records shows a significant increase of 5 6 1 kyr with respect to the late pleistocene if the phase relation with precession is kept constant this increase can be explained by a change in the climate response time to obliquity or to precession by a small uncertainty in the astronomical solution or by a combination of these factors

calcareous nannofossils planktonic foraminifera and oxygen isotopes in the late quaternary sapropels of the ionian sea core m 25 4 12 a long piston core 12 20 m recovered in the ionian sea during cruise m25 4 of the r v meteor summer 1993 at a water depth of 2467 m shows an almost complete sequence of sapropels s 1 s 3 to s 10 over the last 330 ka this paper presents the results of an integrated study based on quantitative biostratigraphic analyses performed on both calcareous nannofossils and planktonic foraminifera coupled with the 18o record a decrease in syracosphaera sp 1 and an increase in the abundance of the genus rhabdosphaera and of helicosphaera carteri florisphaera profunda and of the reworked specimens has been found in the calcareous nannofossil assemblage within the sapropels the planktonic foraminiferal assemblage of the sapropels is characterized by a peak in the frequency of globigerinoides ruber var alba and rosea and neogloboquadrina dutertrei the 18o record of globigerinoides ruber and globigerina bulloides allows recognition of isotope stages 1 to 9 and shows a negative fluctuation that corresponds to the sapropel layers these features support the idea of increased productivity coupled to the presence of reduced salinity surface waters that caused the deposition of the sapropels however the need for a good understanding of the ecological requirements of modern assemblages is stressed this is necessary to correctly interpret fossil assemblages this in turn will allow a better understanding of the palaeoceanographic conditions leading to sapropel deposition

palaeoecology of three interstadial events during oxygen isotope stages 3 and 4 a lacustrine record from lago grande di monticchio southern italy abstract three interstadial events recorded in a pollen diagram from lago grande di monticchio southern italy 40 56 40 n 15 36 e can be correlated with dansgaard oeschger events 12 14 and 20 of the grip summit greenland ice core based on a chronology of varve counts the events are dated respectively to the intervals 37 600 40 000 43 600 50 000 and 72 000 74 600 calendar yr bp the interstadials are of unequal duration the longest occupying 6400 years they appear to begin and end abruptly each is characterised by a sequence of pollen changes in the mesic forest component similarities in these sequences of mesic forest trees imply similar patterns of climatic change within each interstadial the sequences resemble that of the late glacial interstadial at monticchio although tree pollen abundance values reach as much as 60 during the interstadials there is always a substantial proportion of herb pollen tree growth may have been constrained by low co2 levels during the glacial phase of the last glacial interglacial cycle this record illustrates the potential of long continental records to present opportunities for detailed ecological and chronological analyses of sub interglacial warming events during oxygen isotope stages 3 and 4

40ar 39ar laser dating of single grains ages of quaternary tephra from the east eifel volcanic field frg four late pleistocene tephra deposits from the east eifel volcanic field have been dated by 40ar 39ar single grain laser fusion of k feldspar and phlogopite crystals this is a high speed and high precision technique which because it is grain specific can directly detect the presence of older contaminating material our results indicate that the huttenberg tephra from wehr volcano erupted 213 4 ka bp and that the rieden volcanic complex erupted at least over the period 410 to 470 ka bp essential rieden phonolite lapilli contain abundant sanidine with apparent ages older than the eruption age

systematics of xenocrystic contamination preservation of discrete feldspar populations at mccullough pass caldera revealed by 40ar 39ar dating single crystal 40ar 39ar dating of k feldspars from silicic volcanic rocks containing xenocrysts often yields a spectrum of ages slightly older than those of juvenile sanidine phenocrysts in contrast feldspars from thin low volume units of the tertiary 14 ma mccullough pass tuff define discrete age populations at 14 ma 15 ma and 1 3 ga reflecting the time of eruption xenocrysts from an older ignimbrite exposed in the caldera wall and proterozoic basement k feldspars respectively conductive cooling and diffusion modelling suggests preservation of such discrete populations is likely only when xenocrystic material is incorporated into the magma very near or at the surface or is engulfed in thin rapidly cooled pyroclastic flows during emplacement incorporation of xenocrysts into the subvolcanic magma chamber into thick rhyolite domes or lava flows or into large welded ignimbrite sheets will result in partial or total resetting of the k ar isotopic system similarly petrographic evidence such as exsolution lamellae may be homogenized under these conditions but not in thin ignimbrites extremely low diffusion rates for disordering of the al si tetrahedral siting of basement feldspars suggests that they will retain their ordered structural state given rhyolitic magma temperatures thus even when petrographic and k ar isotopic evidence for xenocrystic contamination is obscured it may be preserved in the form of al si ordering

40ar39ar geochronology of rhyolites erupted following collapse of the yellowstone caldera yellowstone plateau volcanic field implications for crustal contamination abstract single crystal laser probe 40 ar 39 ar dating of 133 grains of sanidine and plagioclase has enabled us to resolve the eruption ages of the upper basin member rhyolites the lava flows and related tuffs that erupted within the yellowstone caldera shortly after its collapse 630 ky ago on eruption of the lava creek tuff two lavas and a tuff that erupted from the eastern ring fracture zone yield an eruptive age of 481 8 ka whereas two flows from the western ring fracture zone yield eruptive ages of 516 7 and 198 8 ka most of the units contain old xenocrysts explaining why previous attempts at dating these earliest post caldera units by the conventional k ar method yielded poorly resolved and in some cases anomalous ages the tuff shows the most severe contamination grains from a single pumice lapilli in the tuff show as large an age range as those from bulk vitrophyre indicating that the xenocrysts were incorporated in the magma prior to its near surface explosive fragmentation diffusion calculations indicate that the xenocrysts could not have remained in the magma for more than a few years without degassing and giving ages indistinguishable from the phenocrysts thus the contamination represented by the xenocrysts probably occurred during fracturing and conduit propagation rather than during caldera collapse which took place more than 100 ky earlier the apparent ages of xenocrysts and their compositions as determined by electron microprobe suggest that the eocene absaroka volcanics are the main contaminant with a single xenocryst probably coming from precambrian basement rocks most of the xenocrysts are difficult to distinguish optically or chemically from feldspar phenocrysts illustrating the necessity of single crystal to date many young volcanic rocks accurately

tyrrhenian sea tephrochronology of the oxygen isotope record for the past 60 000 years abstract a chronology of the marine oxygen isotope record of the past 60 ka is proposed by correlating eight marine ash layers with terrestrial volcanic deposits dated by the 14c and or k ar methods detailed oxygen isotope analyses were made on the planktonic foraminifera of three cores collected in the central tyrrhenian sea the origin of the ash layers was determined by major and trace elements analyses then the major pyroclastic terrestrial deposits were sampled and analysed in order to provide land sea correlations two ash layers occurred during the warm event that followed the first step of the deglaciation and which was dated at 12 6 0 5 ka b p another ash layer is present near the last glacial maximum that we have dated at 17 5 0 3 ka b p during isotopic stage 3 five ash layers were recognized and dated which allowed us to assign ages to the isotopically light oxygen peaks warmer interstadials at 31 1 5 ka and 33 4 1 6 ka denekamp at 37 5 2 ka hengelo and successively at 49 2 ka 52 4 2 2 ka 57 2 2 ka and 60 5 2 2 ka moershoofd complex

geochemical characterization of quaternary tephras from the campanian province italy the campanian province has a rich history of human interaction with volcanic eruptions in a region currently inhabited by 3 million people it is crucial to have precise and accurate geochemical characterization of volcanic units within the region so as to identify the spatial distribution of past events furthermore tephrochronology is becoming an important tool in the region for correlating past environmental records unfortunately many of the key units have been geochemically analysed using relatively imprecise methods making correlation problematic although robust correlations have been established in the campanian province using a range of methods including stratigraphy and geochronology more distal correlation requires precise geochemical characterisation of individual glass shards here we report major oxide data geochemically characterising 17 key tephra units within the campanian province using wavelength dispersive spectrometry wds the new data confirm the trachytic nature of most of the eruptions to effect more precise correlations between units especially in distal locations proximal units must be individually analysed for major oxides using wds on the vitreous phase and statistically analysed for robust correlations in cases where similar geochemistry exists analysis of trace and rare earth elements may be necessary

formation of the green tuff pantelleria the strongly peralkaline green tuff pantelleria is an example of a thin densely welded air fall tuff which mantles an area of at least 85 km2 offshore the tuff is correlated with the y 6 ash layer in the central mediterranean sea and the total volume of the eruption is estimated at 7 km3 d r e new petrological data suggests that the tuff was erupted from a zoned magma chamber containing a cooler more fractionated upper zone relative to be bulk of the magma analysis of the distribution of accessory lithic fragments in terms of existing models of eruption dynamics indicates emplacement by a plinian type eruption it is shown that due to the low viscosity of pantelleritic ejecta dense welding can occur at moderate tephra accumulation rates and a rate of the order of 1 cm minute is suggested for the green tuff this yields an estimate for the eruption duration of rather less than one day it is predicted that welded tuff should be formed during large plinian eruptions of pantelleritic magma and therefore that welded airfall tuffs should be common in areas of peralkaline volcanism

the greenland ice core chronology 2005 15 42 ka part 2 comparison to other records a new greenland ice core chronology gicc05 based on multi parameter counting of annual layers has been obtained for the last 42 ka here we compare the glacial part of the new time scale which is based entirely on records from the northgrip ice core to existing time scales and reference horizons covering the same period these include the grip and northgrip modelled time scales the meese sowers gisp2 counted time scale the shackleton fairbanks grip time scale sfcp04 based on 14c calibration of a marine core the hulu cave record three volcanic reference horizons and the laschamp geomagnetic excursion event occurring around greenland interstadial 10 gicc05 is generally in good long term agreement with the existing greenland ice core chronologies and with the hulu cave record but on shorter time scales there are significant discrepancies around the last glacial maximum there is a more than 1 ka age difference between gicc05 and sfcp04 and a more than 0 5 ka discrepancy in the same direction between gicc05 and the age of a recently identified tephra layer in the northgrip ice core both sfcp04 and the tephra age are based on 14c dated marine cores and fixed marine reservoir ages for the laschamp event gicc05 agrees with a recent independent dating within the uncertainties

tephrostratigraphy study for the last 18 000 14 c years in a deep sea sediment sequence for the south adriatic abstract a detailed tephrostratigraphy supported by accelerator mass spectrometry ams 14c dating and isotopic and geochemical analyses has been carried out for a deep sea core collected from the southern adriatic sea which spans the last 18 14c kyr fourteen ash layers have been recognized in the marine core and the origin was determined by comparing their age and geochemistry with tephra detected in terrestrial deposits the geochemical signatures of marine ash layers indicate a prevailing campanian and subordinate etnean and eolian provenances collectively they are attributed to sources in the phlegraean fields lam lagno amendolare ln1 ln2 gm1 c 2 nyt neapolitan yellow tuff c 1 agnano pomici principali ams pf agnano monte spina ast astroni somma vesuvius l9 pomici di base l8 greenish mount etna et1 y1 biancavilla ignimbrite lipari e 1 gabellotto fiumebianco and palinuro seamount pal 1 some of these eruptions have been detected for the first time in marine cores astroni lam l9 l8 and three were detected and dated by marine tephra ln1 ln2 and pal 1 providing new more precise stratigraphic markers for the last 18 kyr in the south adriatic marine record

isotopic characterization of rapid climatic events during ois3 and ois4 in villars cave stalagmites sw france and correlation with atlantic and mediterranean pollen records abstract we present a new mid latitude speleothem record of millennial scale climatic variability during ois3 from the villars cave that combined with former published contemporaneous samples from the same cave gives a coherent image of the climate variability in sw france between 55 ka and 30 ka the 0 82 m long stalagmite vil stm27 was dated with 26 tims u th analyses and its growth curve displays variations that are linked with the stable isotopes both controlled by the climatic conditions it consists in a higher resolved replicate of the previously published vil stm9 and vil stm14 stalagmites where dansgaard oeschger do events have been observed the good consistency between these three stalagmites and the comparison with other palaoeclimatic reconstructions especially high resolution pollen records odp 976 from the alboran sea monticchio lake record from southern italy and the nearby md04 2845 atlantic ocean record permits to draw a specific climatic pattern in sw france during the ois3 and to see regional differences between these sites main features of this period are 1 warm events corresponding to greenland interstadials gis that are characterized by low speleothem 13 c high temperate pollen percentages warm temperatures and high humidity among these events gis 12 is the most pronounced one at villars characterized by an abrupt onset at 46 6 ka and a duration of about 2 5 ka the other well individualized warm event coincides with gis 8 which is however much less pronounced and occurred during a cooler period as shown by a lower growth rate and a higher 13 c 2 cold events corresponding to greenland stadials gs that are clearly characterized by high speleothem 13 c low temperate pollen abundance low temperature and enhanced dryness particularly well expressed during gs coinciding with heinrich events h5 and h4 the main feature of the villars record is a general cooling trend between the do 12 event 45 5 ka and the synchronous stop of the three stalagmites at 30 ka 1 with a first well marked climatic threshold at 41 ka after which the growth rate and the diameter of all stalagmites slows down significantly this climatic evolution differs from that shown at southern mediterranean sites where this trend is not observed the 30 ka age marks the second climatic threshold after which low temperatures and low rainfalls prevent speleothem growth in the villars area until the lateglacial warming that occurred at 16 5 0 5 ka this 15 ka long hiatus as the older villars growth hiatus that occurred between 67 4 and 61 ka are linked to low sea levels reduced ocean circulation and a southward shift of the polar front that likely provoked local permafrost formation these cold periods coincide with both low summer 65 n insolation low atmospheric co 2 concentration and large ice sheets development especially the fennoscandian

constructing a stacked benthic δ18o record composite stacks were constructed by superimposing 6 to 13 benthic foraminiferal 1 8 o records covering the period 0 850 ka an initial timescale for each core was established using radioisotopic age control points and assuming constant sedimentation rates between these points the average of these records is our 13 core untuned stack next we matched the 41 kyr component of each record individually to variations in earth s obliquity four of the 13 records produced timescales that were inconsistent with one or more of the known radioisotopic ages the nine remaining cores were averaged to create a minimally tuned stack six of the minimally tuned cores were assembled into a tropical stack for each stack we estimated the uncertainty envelope from the standard deviation of the constituents spectral analysis of the three stacks indicates that benthic 1 8 o is dominated by a 100 kyr oscillation that has a narrow spectral peak the contribution of precession to the total variance is small when compared to prior results from planktic stacks

the eruptive history of pantelleria sicily channel in the last 50 ka six silicic eruptive cycles have been recognized in the last 50 ka at pantelleria the products of each cycle exhibit a compositional variation from pantellerite to less peralkaline rhyolite or to trachyte the relationships between the range of chemical variation the erupted volume and the time of eruptions allow us to estimate an average differentiation rate of 5 crystal fractionation per 1000 years and a constant long term rate of magma discharge of 0 1 km3 per 1000 years pressure increase in the magma chamber caused by the addition of new magma accumulation of highly differentiated volatile rich magma in the roof zone and a concomitant build up of a vapour phase is postulated as a possible triggering mechanism for eruptions

high resolution 40ar 39ar chronostratigraphy of the post caldera 20 ka volcanic activity at pantelleria sicily strait abstract the island of pantelleria sicily strait the type locality for pantellerite has been the locus of major caldera forming eruptions that culminated ca 50 ka ago in the formation of the cinque denti caldera produced by the green tuff eruption the post caldera silicic activity since that time has been mostly confined inside the caldera and consists of smaller energy eruptions represented by more than twenty coalescing pantelleritic centers structurally controlled by resurgence and trapdoor faulting of the caldera floor a high resolution 40 ar 39 ar study was conducted on key units spanning the recent post 20 ka intracaldera activity to better characterize the present day status and forecast the short term behavior of the system based on the temporal evolution of the latest eruptions the new 40 ar 39 ar data capture a long term 15 ka decline in eruption frequency with a shift in eruptive pace from 3 5 ka 1 to 0 8 ka 1 associated with a prominent paleosol horizon marking the only recognizable volcanic stasis around 12 14 ka this shift in extraction frequency occurs without major changes in eruptive style and is paralleled by a subtle trend of decreasing melt differentiation index we speculate that this decline probably occurred i without short term variations in melt production differentiation rate in a steady state compositionally zoned silicic reservoir progressively tapped deeper through the sequence and ii that it was possibly modulated by outboard eustatic forcing due to the 140 m sea level rise over the past 21 ka the intracaldera system is experiencing a protracted stasis since 7 ka coupled with recent geodetic evidence of deflation and subsidence of the caldera floor the system appears today to be on a wane with no temporal evidence for a short term silicic eruption

a radiometric calibration of the specmap timescale the astronomical theory of climate change asserts that earth s climate is affected by changes in its orbit which vary the seasonal and latitudinal distribution of solar radiation this theory is the basis of the orbitally tuned specmap timescale a key constraint for this important chronology was the mid point of the penultimate deglaciation initially dated to 127 000 years ago recent work suggests this event may be considerably older casting doubt on the astronomical theory the specmap timescale and the accuracy of orbitally tuned chronologies difficulties with u th coral dating of sea level events have impeded progress on this problem because most corals are not closed systems here we use a new approach to u th dating that corrects for open system behavior and produces a sea level curve of sufficient resolution to confidently correlate with specmap over the last 240 000 years permitting a reassessment of both this critical chronology and a central tenet of climate change theory high precision ages for 24 oxygen isotope events provide a 240 000 year chronology for marine 18o records that is independent of orbital tuning assumptions although there appear to be significant differences between the radiometric and orbitally tuned timescales near the lastglacial maximum and at the marine isotope stage 7 6 boundary a comparison of radiometric and specmap ages for identical isotope events suggest that the specmap timescale is quite accurate and that its errors were in general overestimated despite suborbital complexity orbital cyclicity is clearly evident in our record high amplitude sea level oscillations at periods greater than 20 000 years are very close in phase to summer insolation in the northern hemisphere although sea level changes cannot be uniquely tied to a specific season or latitude of insolation forcing the simplest explanation is that long period high amplitude sea level change is linked to northern hemisphere insolation forcing these results validate the principles of orbital tuning and suggest such timescales are generally robust

centennial to millennial scale climate oscillations in the central eastern mediterranean sea between 20 000 and 70 000 years ago evidence from a high resolution geochemical and micropaleontological record abstract here we present a high resolution faunal floral and geochemical stable isotopes and trace elements record from the sediments of ocean drilling program site 963 central mediterranean basin which shows centennial millennial scale resemblance to the high northern latitude rapid temperature fluctuations documented in the greenland ice cores between 20 and 70 kyr bp oxygen and carbon isotopes planktic foraminifera and calcareous nannofossil distributions suggest that dansgaard oeschger d o and heinrich events he are distinctly expressed in the mediterranean climate record moreover recurrent though subdued oscillations not previously identified in the lateglacial mediterranean sediments document a significant centennial scale climate variability in the basin that is greater than previously thought alternations between climate regimes dominated by polar outbreaks during d o stadials and warm d o interstadials with associated intensification of continental runoff are well expressed in the odp site 963 these place the mediterranean basin as an often overlooked recorder of the interplay between large and regional scale climate controls at intermediate latitudes and of the possible interactions between different components of the climate system significant changes in ba ca values measured in globigerinoides ruber shells from a number of d o stadials and interstadials suggest enhanced freshwater input from the north eastern mediterranean borderland during the d o interstadials however the short duration of 3d stratification events never led to complete oxygen consumption along the water column but clear effects of sluggish 3d circulation in the basin are testified to by negative excursions in 13c measured in selected species of planktic and benthic foraminifera hes are constantly associated with lightening in the 18o record of planktic foraminifera possibly because of the impact of iceberg melting in the iberian margin on mediterranean thermohaline circulation interestingly in two cases in particular he2 and he5 fresher water inputs also affected deeper horizons of intermediate waters suggesting a basin wide impact

the green tuff of pantelleria rheoignimbrite or rheomorphic fall detailed stratigraphic analysis of the green tuff of pantelleria shows that this formation can be divided into several members designateda throughh from base to top these members have a coherent pattern when traced from outcrop to outcrop throughout the island shedding light on their origin only memberg completely mantles the entire island the distribution of the other members is controlled by prevailing wind direction or by topography membera is entirely of fall origin membersc ande are of fall and or surge type membersb d andh have the characteristics of thin welded ash flow tuffs membersf andg are ash flow tuffs with textural characteristics of compound cooling units most of the ash flow tuffs exhibit characteristics of ignimbrites vertical fluidization pipes local concentrations of lithic lapilli imbrication of clasts and valley ponding memberg is unusual in that it is highly welded exhibits large scale rheomorphic structures contains huge lithic clasts and has near vertical foliation where it adheres to cliffs and caldera walls

thermochronologic evidence for late eocene andean mountain building at 30 s the andes between 28 30 s represent a transition between the puna altiplano plateau and the frontal principal cordillera fold and thrust belts to the south while significant early cenozoic deformation documented in the andean plateau deciphering the early episodes of deformation during andean mountain building in the transition area is largely unstudied apatite fission track aft and u th sm he ahe thermochronology from a vertical and a horizontal transect reveal the exhumation history of the high andes at 30 s an area at the heart of this major transition interpretation of the age elevation profile combined with inverse thermal modeling indicate that the onset of rapid cooling was underway by 35ma followed by a significant decrease in cooling rate at 30 25ma aft thermal models also reveal a second episode of rapid cooling in the early miocene ca 18ma related to rock exhumation to its present position low exhumation between the rapid cooling events allowed for the development of a partial annealing zone paz we interpret the observed eocene rapid exhumation as the product of a previously unrecognized compressive event in this part of the andes that reflects a southern extension of eocene orogenesis recognized in the puna altiplano renewed early miocene exhumation indicates that the late cenozoic compressional stresses responsible for the main phase of uplift of the south central andes also impacted the core of the range in this transitional sector the major episode of eocene exhumation suggests the creation of significant topographic relief in the high andes earlier than previously thought

recent volcanic history of pantelleria a new interpretation abstract the island of pantelleria is located in the pantelleria rift between sicily and africa this rift is floored by a 20 km thick continental type crust that is characterized by horsts and grabens formed by nw se tensional faults and ne sw shear faults several faults and fractures that intersect the island follow these regional trends prominent volcano tectonic features on the island include two calderas the younger being related to the eruption of the green ignimbrite and the uplifted montagna grande block pantelleria mostly consists of peralkaline silicic rocks with minor trachytes and basalts volcanism on the island is characterized by both explosive and effusive activity reconstruction of the volcanic history of the island since the eruption of the green ignimbrite is based on geological and geochronological data the eruption of the green ignimbrite 50 000 y b p was followed by collapse of the monastero caldera that has been the site of most of the subsequent acid volcanism the montagna grande volcanic complex 35 000 y b p fills the central part while the lower pantelleritic lava flows 16 000 y b p erupted along its rim very probably the young mt gelfiser and khaggiar domes are also located on the caldera rim the montagna grande block rose within the caldera at an estimated average rate between 1 0 and 1 5 cm y for about 20 000 y subsequent pumice cones 9 000 y b p endogenous domes and lava flows also erupted inside this caldera among the main acid volcanic units younger than the green ignimbrite only the mt gelkhamar endogenous dome is not linked to this caldera in the last 50 000 years basaltic activity only occurred in the northern part of the island the basaltic vents are aligned parallel with the main tensional trends of the rift at least two phases have been recognized the older is about 29 000 y b p and the younger is a few thousands of years old a change occurred in the eruptive style after the eruption of the green ignimbrite and collapse of the monastero caldera explosive activity diminished and extrusion of lava became dominant

transferring radiometric dating of the last interglacial sea level high stand to marine and ice core records in order to derive a radiometric age marker for the end of the penultimate glacial interglacial transition we compiled published u series isotope measurements on corals from the period extending from stage 6 to the middle of the last interglacial and computed the corresponding open system ages using thompson et al model thompson w g spiegelman m w goldstein s l speed r c an open system model for u series age determinations of fossil corals earth planet sci lett 210 2003 365 381 we obtain a global mean age of 126 calendar kyr bp ka 1 7kyr 2 for the beginning of the last interglacial sea level high stand after showing that the phase relationships observed between changes in sea level north atlantic benthic and planktonic foraminifera oxygen isotopic records and atmospheric methane over the last deglaciation were likely also valid over the penultimate deglaciation we derive an age of 131 2ka 2kyr 2 for the abrupt increase in atmospheric ch4 and north atlantic surface temperature marking the end of the penultimate glacial interglacial transition this age is consistent with u th dates of the penultimate glacial interglacial transition recorded in speleothems from sites where speleothems isotopic records are synchronous with north atlantic temperature records over the last deglaciation finally we show that the phase obtained between the climatic response and northern hemisphere summer insolation is not constant from termination ii to termination i implying that northern hemisphere summer insolation alone cannot explain the timing of terminations

tracing time in the ocean a brief review of chronological constraints 60 8 kyr on north atlantic marine event based stratigraphies abstract well resolved event based stratigraphies in marine sediments spanning a significant portion of the last glacial period 60 8 kyr provide a unique opportunity for time stratigraphic correlation in the north atlantic region here we review the current methods available to chronologically constrain these event based stratigraphies highlighting in particular the value of tephrochronology as an independent tool to validate correlations between records while the intimate protocols lowe et al 2008 blockley et al 2011 are equally applicable to marine and terrestrial records spatially and temporally variable marine radiocarbon reservoir age effects mres provide a challenge to using marine radiocarbon in the former as an independent chronostratigraphic tool despite the inherent uncertainties associated with tuning we conclude that the mid points of the common abrupt warming transitions associated with the well defined millennial scale climate oscillations the dansgaard oeschger d o cycles observed in the oxygen isotopes of the greenland ice cores and north atlantic sea surface temperature sst records currently provide the most robust correlation tie points from which to derive age control in this invited intimate special issue article we propose a new protocol for establishing marine event based chronostratigraphies in the north atlantic region and focus on areas of chronological potential in palaeoceanographic research

aftershock area expansion and mechanical heterogeneity of fault zone within subduction zones we investigate global variations in the pattern of aftershock area expansion associated with large subduction zone earthquakes the expansion of aftershock areas with time is relatively small in the subduction zones of alaska the aleutians mexico and parts of the kuriles and south america these subduction zones are interpreted to be characterized by moderate to strong interplate coupling in contrast the extent of aftershock expansion is greater for events within the subduction zones of northeast japan and western and south pacific where interplate coupling is inferred to be weak these results are interpreted in terms of an asperity model where a fault zone is represented by a distribution of strong spots asperities and weaker zones the immediate aftershock area is assumed to extend over an area occupied by asperities and the subsequent expansion to occur into the surrounding weaker zones if large asperities abut each other on a fault plane interplate coupling is strong and little expansion of aftershock area occurs smaller and more sparsely distributed asperities cause weak interplate coupling and significant expansion of aftershock area small and densely distributed asperities result in moderate interplate coupling and little aftershock expansion

response to the comment by w h schwarz et al on joint determination of 40k decay constants and 40ar 40k for the fish canyon sanidine standard and improved accuracy for 40ar 39ar geochronology by p r renne et al 2010

radiocarbon calibration beyond 20 000 14c yr b p by means of planktonic foraminifera of the iberian margin we present a new set of 14c ages obtained by accelerator mass spectrometry ams on planktonic foraminifera from a deep sea core collected off the iberian margin md952042 this site at 37 n is distant from the high latitude zones where 14c reservoir age is large and variable many independent proxies alkenones magnetic susceptibility ice rafted debris foraminifera stable isotopes abundances of foraminifera pollen and dinoflagellates show abrupt changes correlative with dansgaard oeschger and heinrich events of the last glacial period the good stratigraphic agreement of all proxies from the fine to the coarse size fractions indicates that the foraminifera 14c ages are representative of the different sediment fractions to obtain reliable 14c ages of foraminifera beyond 20 000 14c yr b p we leached the shells prior to carbonate hydrolysis and subsequent analysis for a calendar age scale we matched the iberian margin u37k profile with that of greenland summit 18o both are proxies for temperature which in models varies synchronously in the two areas the match creates no spurious jumps in sedimentation rate and requires only a limited number of tie points except for ages older than 40 000 14c yr b p greenland s gisp2 and grip records yield similar calendars the 14c and imported calendar ages of the iberian margin record are then compared to data from lacustrine annual varves and from corals and speleothems dated by u th previously used to extend the calibration beyond 20 000 14c yr b p the new record follows a smooth pattern between 23 000 and 50 000 cal yr b p we find good agreement with the previous data sets between 23 000 and 31 000 cal yr b p in the interval between 33 000 and 41 000 cal yr b p for which previous records disagree by up to 5000 cal yr the iberian margin record closely follows the polynomial curve that was previously defined by an interpolation of the coral ages and runs between the lake suigetsu and the bahamian speleothem data sets

a revision of the structure and stratigraphy of pre green tuff ignimbrites at pantelleria strait of sicily abstract at pantelleria peralkaline silicic magmas were erupted across a range of eruptive typologies and magnitudes pyroclastic flows plinian to strombolian pumice fallout and lava flows in this paper we focus on the intermediate cycle of eruptive activity which is bracketed by ignimbrite units slightly older than the two caldera collapses which marked the volcanological activity of the island this age interval 180 85 ka was punctuated by six ignimbrite forming eruptions silicic and variably peralkaline for a cumulative erupted magma volume of approximately 6 km 3 dense rock equivalent based on new 40 ar 39 ar na k feldspar ages and petrographic data we propose an updated volcanostratigraphic scheme for these welded and rheomorphic ignimbrites that can be summarised as follows i the age of the old la vecchia caldera collapse is now tightly constrained between 140 and 146 ka and the caldera forming eruption can be traced to a lithic rich welded tuff breccia that outcrops in two opposite sectors of the island south west and north east ii four ignimbrite units previously considered unrelated are now merged in two distinct eruptive paroxysmal events at 107 and 85 ka in particular the 85 ka eruptive event is comparable in magnitude to the younger caldera forming green tuff plinian eruption iii the recurrence patterns of the 107 and 85 ka eruptions compared to the green tuff allow us to qualitatively assess that the climax in production of low temperature silicic and peralkaline melt was focused in the age interval 85 45 ka

synchronisation of palaeoenvironmental records over the last 60 000 years and an extended intimate event stratigraphy to 48 000 b2k the intimate protocol for the correlation of marine ice core and terrestrial records is here updated reflecting recent developments in palaeoclimate research originally focussed on last glacial to interglacial transition lgit 22 000 11 500 years b p the intimate group has now extended its study period back to 60 000 years as a first step the intimate event stratigraphy has now been extended to include 8000 48 000 b2k based on a combined ngrip and grip isotope profile against a gicc05 chronology and key tephra horizons from iceland and continental european volcanic sources in this lead article of this intimate special issue we introduce some of the recent achievements of the intimate community and discuss the challenges associated with extending the intimate approach back in time focussing in particular on the chronological problems inherent in comparing different proxy records the intimate approach has thus far been limited predominantly to the north atlantic and australasian regions and we also discuss the potential to extend the intimate protocol beyond these regions

high resolution stratigraphic correlation of benthic oxygen isotopic records spanning the last 300 000 years abstract in order to compare the response of different oceanographic regions to global climate change very detailed stratigraphic techniques are required the global signal of ice volume changes recorded in the oxygen isotopic composition of foraminifera can provide the tool for developing the necessary high resolution stratigraphy in order to evaluate the resolution of a stratigraphy based on detailed isotopic records two techniques are used to correlate a set of benthic oxygen isotope records from seven piston cores taken in the north and south atlantic the indian and the equatorial and north pacific oceans the first technique was modified from the graphic correlation procedure of shaw 1964 this procedure requires the identification of isotopic events that are correlated from core to core detailed correlations for intervals of the cores between events are provided by a series of straight line segments connecting all common events the second technique developed by martinson et al 1982 uses inverse procedures to define a continuous non linear mapping function that correlates the isotopic records the mapping function maximizes the correlation coefficient between data sets being compared the techniques are independent in that they rely on different criteria for correlating the data series stratigraphic correlations obtained by these procedures are in excellent agreement the mean difference between the correlations is on the order of the sampling intervals of each core and when corrected for sedimentation rates suggests that benthic isotope records from the suite of seven cores can be correlated to a resolution of 2000 to 4000 yrs

time scale controversy accurate orbital calibration of the early paleogene 1 timing is crucial to understanding the causes and consequences of events in earth history the calibration of geological time relies heavily on the accuracy of radioisotopic and astronomical dating uncertainties in the computations of earth s orbital parameters and in radioisotopic dating have hampered the construction of a reliable astronomically calibrated time scale beyond 40 ma attempts to construct a robust astronomically tuned time scale for the early paleogene by integrating radioisotopic and astronomical dating are only partially consistent here using the new la2010 and la2011 orbital solutions we present the first accurate astronomically calibrated time scale for the early paleogene 47 65 ma uniquely based on astronomical tuning and thus independent of the radioisotopic determination of the fish canyon standard comparison with geological data confirms the stability of the new la2011 solution back to 54 ma subsequent anchoring of floating chronologies to the la2011 solution using the very long eccentricity nodes provides an absolute age of 55 530 0 05 ma for the onset of the paleocene eocene thermal maximum petm 54 850 0 05 ma for the early eocene ash 17 and 65 250 0 06 ma for the k pg boundary the new astrochronology presented here indicates that the intercalibration and synchronization of u pb and 40ar 39ar radioisotopic geochronology is much more challenging than previously thought

a depth derived pleistocene age model uncertainty estimates sedimentation variability and nonlinear climate change 1 a new chronology of glaciation spanning the last 780 000 years is estimated from 21 marine sediment cores using depth as a proxy for time to avoid biasing this depth derived age estimate the depth scale is first corrected for the effects of sediment compaction to provide age uncertainty estimates the spatial and temporal variability of marine sediment accumulation rates are estimated and modeled as an autocorrelated stochastic process depth derived ages are estimated to be accurate to within 9000 years and within this uncertainty are consistent with the orbitally tuned age estimates nonetheless the remaining differences between the depth and orbitally tuned chronologies produce important differences in the spectral domain from the 18o record using the depth derived ages we infer that there are weak nonlinearities involving the 100 kyr and obliquity frequency bands which generate interaction bands at sum and difference frequencies if an orbitally tuned age model is instead applied these interactions are suppressed with the system appearing more nearly linear

abrupt climate change an alternative view hypotheses and inferences concerning the nature of abrupt climate change exemplified by the dansgaard oeschger d o events are reviewed there is little concrete evidence that these events are more than a regional greenland phenomenon the partial coherence of ice core y 18 o and ch4 is a possible exception claims however of d o presence in most remote locations cannot be distinguished from the hypothesis that many regions are just exhibiting temporal variability in climate proxies with approximately similar frequency content further suggestions that d o events in greenland are generated by shifts in the north atlantic ocean circulation seem highly implausible given the weak contribution of the high latitude ocean to the meridional flux of heat a more likely scenario is that changes in the ocean circulation are a consequence of wind shifts the disappearance of d o events in the holocene coincides with the disappearance also of the laurentide and fennoscandian ice sheets it is thus suggested that d o events are a consequence of interactions of the windfield with the continental ice sheets and that better understanding of the wind field in the glacial periods is the highest priority wind fields are capable of great volatility and very rapid global scale teleconnections and they are efficient generators of oceanic circulation changes and more speculatively of multiple states relative to great ice sheets connection of d o events to the possibility of modern abrupt climate change rests on a very weak chain of assumptions

enhanced aridity and atmospheric high pressure stability over the western mediterranean during the north atlantic cold events of the past 50 k y multiproxy paleoenvironmental records pollen and planktonic isotope from ocean drilling program site 976 alboran sea document rapid ocean and climate variations during the last glacial that follow the dansgaard oeschger climate oscillations seen in the greenland ice core records thus suggesting a close link of the mediterranean climate swings with north atlantic climates continental conditions rapidly oscillated through cold arid and warm wet conditions in the course of stadial interstadial climate jumps at the time of heinrich events i e maximum meltwater flux to the north atlantic western mediterranean marine microflora and microfauna show rapid cooling correlated with increasing continental dryness enhanced aridity conceivably points to prolonged wintertime stability of atmospheric high pressure systems over the southwestern mediterranean in conjunction with cooling of the north atlantic

k ar dating incomplete extraction of radiogenic argon from alkali feldspar abstract complete recovery of radiogenic argon from high temperature alkali feldspars is more difficult than is commonly believed at a temperature sufficiently high for quantitative release of ar from biotites and hornblendes as much as 15 of the radiogenic ar can remain trapped in the melt of an alkali feldspar sample feldspar melts at a higher temperature than biotite or hornblende and lacks structural volatiles which act to flush ar from a viscous melt thus even for extractions at 1670 c for 40 min a small but measurable amount usually less than 2 of total remains behind although this quantity of residual gas may be marginally within analytical error its presence can be detected readily by remelting an extracted sample together with recent basalt for routine analyses a recommended procedure is to melt feldspar and basalt together at 1670 c or higher it is clear that inadequate experimental conditions rather than diffusive loss of radiogenic ar can be responsible for some erroneously young feldspar ages

major and trace element characterization of tephra layers offshore pantelleria island insights into the last 200 ka of volcanic activity and contribution to the mediterranean tephrochronology a detailed tephrochronological study was carried out on the deep sea core collected from site 963a in the sicily channel during odp leg 160 the chronology of the succession is provided by an age depth model based on isotope stratigraphy and quantitative eco biostratigraphy major trace and rare earth element content was obtained on single glass grains through electron probe micro analysis and laser ablation inductively coupled plasma mass spectrometry techniques from six well preserved tephra layers characterized by a discrete thickness found along the succession these deposits were correlated with the volcanic activity of pantelleria and dated at 42 5 127 5 128 1 129 1 188 7 and 197 7 ka this detailed chemical characterization of the studied deposits aims to provide a valuable reference database for scientists working on both proximal and distal products erupted at pantelleria island during the late pleistocene this study moreover offers the opportunity to better identify pantelleria related marker tephras within the tephrochronological framework of the central and eastern mediterranean area copyright 2012 john wiley sons ltd

a 90 000 200 000 yrs marine tephra record of italian volcanic activity in the central mediterranean sea abstract a detailed tephrochronological study was undertaken in three deep sea cores collected in the tyrrhenian and ionian seas the age and the origin of the marine tephra were inferred from oxygen isotope records of foraminifera and from major element compositions of glass shards seventy one eruptions were detected in the time interval 90 000 200 000 yrs during which the volcanoes of the roman and campanian regions and of the southern italy were in activity this is attested by the consistency of the geochemical compositions of both marine and terrestrial deposits most of the marine tephra consisted in trachytes and phonolites characterizing a roman and campanian origin several tephra were proposed as key horizons for proximal and distal sediments among them one tephra originating from mount etna 149 300 yrs and five tephra from pantelleria island 130 000 yrs 163 600 yrs 192 500 yrs 197 400 yrs and 198 400 yrs were northerly dispersed several other key horizons originated from the campanian or roman provinces were detected as far as 1000 km from the vents

revised tuning of ocean drilling program site 964 and kc01b mediterranean and implications for the δ18o tephra calcareous nannofossil and geomagnetic reversal chronologies of the past 1 1 myr 1 high resolution color reflectance records of kc01 and kc01b calabrian ridge ionian sea are presented and compared with a modified spliced high resolution color reflectance record of ocean drilling program odp site 964 this comparison revealed that kc01b is characterized by intensive deformation between 27 and 28 5 m piston depth and that some sapropels are tectonically reduced in thickness moreover the piston coring has caused considerable stretching in the top of kc01 and kc01b using a new splice of odp site 964 as guide previous astronomical tuned timescales of kc01b and odp site 964 were evaluated this evaluation resulted in a new sapropel based astronomical timescale for the last 1 1 myr the new timescale implies a much more uniform change in sedimentation rate for the ionian sea cores two prominent excursions to lighter values in the 18o record of the planktonic foraminiferal species globigerinoides ruber occur during marine isotopic stages 12 and 16 applying the new timescale these shifts correspond with maxima in obliquity and are punctuated by minima in the precession cycle they are absent in global ice volume records and are interpreted as reflecting a summer low salinity surface water lens that floats on top of extremely saline intermediate and deep waters at times of the very low sea levels during these glacial periods all biostratigraphic and magnetostratigraphic events found in kc01b and odp site 964 were re dated according to the new timescale and the ages of 33 tephra layers were reviewed the new ages for the calabrian ridge 2 and 3 magnetic events in the brunhes are concordant with minima in the global sint800 composite record derived from worldwide deep sea records of relative paleointensity and have been attributed to the big lost and la palma excursions respectively

40ar 39ar k ar and 230th 238u dating of the laschamp excursion a radioisotopic tie point for ice core and climate chronologies abstract a brief period of enhanced 10 be flux that straddles the interstadial warm period known as dansgaard oeschger event 10 in greenland and its counterpart in antarctica the antarctic isotope maximum 10 is but one consequence of the weakening of earth s magnetic field associated with the laschamp excursion this 10 be peak measured in the grip ice core is dated at 41 250 y b2k before year 2000 ad in the most recent gicc05 age model obtained from the northgrip core via multi parameter counting of annual layers uncertainty in the age of the 10 be peak is however no better than 1630 y at the 95 confidence level reflecting accumulated error in identifying annual layers the age of the laschamp excursion guillou h singer b s laj c kissel c scaillet s jicha b 2004 on the age of the laschamp geomagnetic excursion earth planet sci lett 227 331 343 is revised on the basis of new 40 ar 39 ar unspiked k ar and 238 u 230 th data from three lava flows in the massif central france together with the 40 ar 39 ar age of a transitionally magnetized lava flow at auckland new zealand combined these data yield an age of 40 700 950 y b2k where the uncertainty includes both analytical and systematic 40 k and 230 th decay constant errors taking the radioisotopic age as a calibration tie point suggests that the layer counting chronologies for the northgrip and gisp2 ice cores are more accurate and precise than previously thought at depths corresponding to the laschamp excursion

evidence of magma mixing in the daly gap of alkaline suites a case study from the enclaves of pantelleria italy the island of pantelleria consists of trachytes pantellerites and minor mildly alkaline basalts rocks of intermediate composition falling in the so called daly gap such as mugearites benmoreites and mafic trachytes occur only in the form of enclaves in trachytes and pantellerites inside the main caldera of the island caldera cinque denti which collapsed during the green tuff ignimbrite eruption at 50 ka the enclaves include volcanic subvolcanic and intrusive rock types the enclaves in host trachyte contain traces of glass devitrified glass occurs within enclaves in host pantellerites minerals in the enclaves show regular compositional variations with whole rock silica content glass present in the medium grained samples is interpreted to be the result of incipient melting the major and trace element compositions of the enclaves show regular and linear variations between an evolved mafic magma hawaiite and a felsic end member similar to the green tuff trachyte fractional crystallization modelling of compatible and incompatible trace elements v ni zr la sm lu nb y th does not reproduce the observed trends rocks of intermediate composition within the daly gap can be explained only by magma mixing between an already differentiated mafic magma hawaiite and an anorthoclase rich trachytic melt in the lower and higher parts respectively of a stratified magmatic chamber medium grained enclaves are interpreted as the result of fragmentation of solidified mixing layers in the roof of the magma chamber during the eruption of the green tuff when the collapse of the caldera took place diffusion calculations suggest a residence time of 5 days for the enclaves in their host magmas

geology of the peralkaline volcano at pantelleria strait of sicily situated in a submerged continental rift pantelleria is a volcanic island with a subaerial eruptive history longer than 300 ka its eruptive behavior edifice morphologies and complex multiunit geologic history are representative of strongly peralkaline centers it is dominated by the 6 km wide cinque denti caldera which formed ca 45 ka ago during eruption of the green tuff a strongly rheomorphic unit zoned from pantellerite to trachyte and consisting of falls surges and pyroclastic flows soon after collapse trachyte lava flows from an intracaldera central vent built a broad cone that compensated isostatically for the volume of the caldera and nearly filled it progressive chemical evolution of the chamber between 45 and 18 ka ago is recorded in the increasing peralkalinity of the youngest lava of the intracaldera trachyte cone and the few lavas erupted northwest of the caldera beginning about 18 ka ago inflation of the chamber opened old ring fractures and new radial fractures along which recently differentiated pantellerite constructed more than 25 pumice cones and shields continued uplift raised the northwest half of the intracaldera trachyte cone 275 m creating the island s present summit montagna grande by trapdoor uplift pantellerite erupted along the trapdoor faults and their hingeline forming numerous pumice cones and agglutinate sheets as well as five lava domes degassing and drawdown of the upper pantelleritic part of a compositionally and thermally stratified magma chamber during this 18 3 ka episode led to entrainment of subjacent crystal rich pantelleritic trachyte magma as crenulate inclusions progressive mixing between host and inclusions resulted in a secular decrease in the degree of evolution of the 0 82 km3 of magma erupted during the episode

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr