ground ice and slope sediments archiving late quaternary paleoenvironment and paleoclimate signals at the margins of el gygytgyn impact crater ne siberia an accumulation terrace close to the el gygytgyn impact crater in northeastern siberia contains stratigraphic and periglacial evidence of the paleoenvironmental and paleoclimatic history and permafrost dynamics during late quaternary time a succession of paleo active layer deposits that mirror environmental changes records periods favorable for the establishment and growth of ice wedge polygonal networks and sediment variations these two elements of the periglacial landscape serve as complementary paleoenvironmental archives that can be traced back to 14 000 cal yr bp the slope sediments and the ground ice contained therein have prominent relative maxima and minima in properties grain size total organic content oxygen isotopes they document a regional early holocene thermal maximum at about 9000 cal yr bp followed by a transition to slightly cooler conditions and a subsequent transition to slightly warmer conditions after about 4000 cal yr bp results from sedimentary analysis resemble morphological and geochemical oxygen and hydrogen isotopes results from ice wedge studies in which successive generations of ice wedge polygonal networks record warmer winters in late holocene time moreover peaks of light soluble cation contents and quartz grain surface textures reveal distinct traces of cryogenic weathering we propose a conclusive sedimentation model illustrating terrace formation in a permafrost terrain

numerical reconstructions of lgm climate across the eurasian arctic abstract although limits of the eurasian ice sheet at the last glacial maximum lgm are known relatively well from geological evidence the palaeoclimate coexistent with this ice sheet has yet to be identified confidently a simple ice sheet model has been used to determine lgm climate conditions by finding the ice sheet mass balance configuration that permits model results to match with geological data relating to the extent of lgm ice cover these conditions are compared with atmospheric general circulation model agcm calculations of the climate at the lgm which reveal the meteorological conditions associated with the ice sheet mass balance the western margin of scandinavia is characterised by a maritime climate influenced by the nearby warm seasonally sea ice free ocean conditions however further east the warming effect of the north atlantic diminishes and an extreme polar desert climate dominates across the kara sea similar to east antarctica today the lgm climate that we establish is in contrast to many previous reconstructions involving snow laden warm westerly winds originating from the north atlantic affecting the entire eurasian arctic severely cold conditions across the eurasian arctic are compatible with a stable circulation cell over the kara sea that isolates the region climatically and or cold dry westerly winds from the fennoscandian ice sheet that flow across the rest of the eurasian arctic

the limitations of cement stratigraphy as revealed in some lower carboniferous oolites from south wales abstract the use of staining and cathodoluminescence to correlate carbonate cements is often coupled with the conception of diagenetic environments that are uniform through a large volume of rock at any instant in time thus it is often assumed that individual growth zones within carbonate cements are present throughout a unit and have a chronological significance detailed study of meteoric phreatic cements in the oolite group lower carboniferous south wales indicates that individual growth zones can only be traced with any certainty between adjacent pores and are often only identifiable in a few square millimetres of thin section additionally cement sequences with apparently identical cathodoluminescence appearance are often demonstrably of different ages the complex variation in cements through the oolite group partly reflects the extremely localised controls on groundwater chemistry in the shallow subsurface it is also due to the superimposition of a number of phases of subaerial exposure at successively higher levels during deposition of the group the chemistry of a calcite cement reflects the geochemical environment at the time of precipitation at that location in the diagenetic system it is likely that that environment has been frequently repeated both in space and time

late pleistocene and holocene paleoenvironments of the north pacific coast abstract unlike the north atlantic the north pacific ocean probably remained free of sea ice during the last glacial maximum lgm 22 000 to 17 000 bp following a eustatic low in sea level of ca 120 m at 19 000 bp a marine transgression had flooded the bering and chukchi shelves by 10 000 bp post glacial sea level history varied widely in other parts of the north pacific coastline according to the magnitude and timing of local tectonism and glacio isostatic rebound glaciers covered much of the continental shelf between the alaska peninsula and british columbia during the lgm maximum glacier extent during the lgm was out of phase between southern alaska and southern british columbia with northern glaciers reaching their outer limits earlier between 23 000 and 16 000 bp compared to 15 000 14 000 bp in the south glacier retreat was also time transgressive with glaciers retreating from the continental shelf of southern alaska before 16 000 bp but not until 14 000 13 000 bp in southwestern british columbia major climatic transitions occurred in the north pacific at 24 000 22 000 15 000 13 000 and 11 000 9000 bp rapid climate changes occurred within these intervals including a possible younger dryas episode an interval of climate warmer and drier than today occurred in the early holocene cooler and wetter conditions accompanied widespread neoglaciation beginning in some mountain ranges as early as the middle holocene but reaching full development after 3000 bp

paleodrainage on the chukchi shelf reveals sea level history and meltwater discharge abstract chirp subbottom data collected across the chukchi shelf offshore nw alaska imaged numerous paleochannels and valleys that appear to have been downcut and incised during sea level falls associated with glacial intervals in contrast the two most recent incisions appear to have been formed during the period of sea level rise following the last glacial maximum lgm the architecture and infill associated with these two incisions suggests that they were formed by an increase in discharge these events appear to be unrelated to sea level fluctuations but rather triggered by climatic variations during the most recent deglaciation i e meltwater discharge radiocarbon dates from sediment cores within the southern incised valley suggest that the two episodes of meltwater discharge may correlate with meltwater pulse 1 a 14 000 cal yr bp and evidence of iceberg scouring on outer chukchi shelf 12 000 to 13 000 cal yr bp respectively regional transgression across the interfluves on the middle chukchi shelf appears to postdate the second meltwater discharge and may correlate with meltwater pulse 1 b 11 500 cal yr bp this evidence suggests that in glacially dominated landscapes episodes of large discharge to the shelf might be out of phase with the sea level cycle in addition the presence of glacial meltwater drainage on the shelf implies a greater volume of continental glaciation during the lgm than previously recognized

climate impacts of an ice sheet in east siberia during the last glacial maximum abstract recent evaluations of geomorphological evidence in east siberia strongly suggest that no ice sheet existed on the east siberian arctic shelf during the last glacial maximum lgm contrary to the hypothesis of some authors because most general circulation model gcm simulations of the lgm have included such an ice sheet the impact of an east siberian ice sheet is crucial for understanding previous model simulations of the lgm the experiments in this study use the global environmental and ecological simulation of interactive systems genesis 2 0 gcm and the equilibrium vegetation ecology eve vegetation model to simulate the lgm climate with previously published simulation and without new simulation an east siberian ice sheet most lgm simulations have shown increased southerly advection into beringia resulting from the dynamics of the continental ice sheets which acts to alleviate the hemispheric glacial cooling in beringia the east siberian ice sheet provides a secondary source of warm air advection into beringia in the simulation with an east siberian ice sheet a glacial anticyclone develops over the ice sheet during winter resulting in subsidence of air flowing off the ice sheet increased southerly advection along the western margin of the ice sheet and warming to the south of the ice sheet during summer the ice sheet blocks northerly flow from the arctic also resulting in warming south of the ice sheet the primary vegetation difference is in the ratio of tundra to polar desert the more mild climate with the ice sheet present produces more tundra and less polar desert

hydrogen and oxygen isotope evidence for origin of mvt forming brines southern appalachians abstract hydrogen and oxygen isotope compositions of fluid inclusion hosted brines from mississippi valley type mvt deposits in the southern appalachians were analyzed to test whether the dominant water in the brines was seawater as suggested by previously reported na cl br relations measurements were made for deposits in the two main paleoaquifers in the area the lower cambrian shady and lower ordovician knox and included the large east tennessee ore field and the austinville district 18 o and d values for sphalerite hosted brines in the two main paleoaquifers cluster in separate fields those in the lower cambrian paleoaquifer form an elongate array that extends from 18 o 2 and d 41 to 18 o 5 and d 87 0 those in the lower ordovician paleoaquifer form a cluster at about 18 o 7 and d 35 stable isotope compositions of fluid inclusion hosted brines in fluorite from the lower ordovician paleoaquifer form an array that extends from the lower ordovician hosted sphalerite cluster toward the composition of modern formation waters in the lower ordovician paleoaquifer which plot along the meteoric water line stable isotope compositions of fluids in barite form an array that extends toward very low sd values typical of organic matter or gas these data permit but do not require the interpretation that the mineralizing brines contain seawater with hydrogen and oxygen isotope compositions that were modified by reaction with country rocks particularly with organic matter and or hydrocarbon gas when the appalachian data are plotted together with those from other mvt districts in the mid continent the combined data form a broad array that extends downward from hydrogen and oxygen isotope compositions typical of seawater toward low d values such as would form by fluid interaction with organic matter or gas consideration of published isotopic compositions of brines from other mvt deposits suggests that interaction with organic matter and or gas may be an important process in the evolution of ore forming brines

the origin and evolution of canadian shield brines evaporation or freezing of seawater new lithium isotope and geochemical evidence from the slave craton abstract new chemical and isotopic data for deep seated calcium chloride brine from the miramar con gold mine yellowknife n w t strongly suggest that the brine salinity is of marine origin diagnostic marine properties include uniformly elevated br cl ratios typical of seawater concentrated beyond halite saturation and li br ratios 0 0254 0 0325 and 6 li compositions 32 1 to 36 3 similar to seawater 32 3 the mean 6 li for all mine water samples of 35 1 may reflect minor uptake of li by secondary minerals this interpretation is supported by analyses of altered metabasalt from fault zones which is enriched in li but depleted in 6 li 14 7 to 15 6 relative to the unaltered metabasalt 5 4 the mechanism responsible for concentrating the hypersaline brine end member is not unequivocal as evidence exists to support both evaporative and cryogenic processes on the one hand the devonian sedimentary record in the great slave lake region in conjunction with yellowknife brine isotopic compositions 2 h and 34 s so 4 that are similar to various devonian fluids support an evaporative origin on the other hand the na cl br cl relationship in the brine strongly suggests a cryogenic mechanism regardless of the concentrative mechanism the chemical data indicate that the yellowknife parent brine was concentrated 28 to 30 fold relative to seawater the extreme depletion of mg and enrichment of ca in the brines accompanied by sr ca ratios similar to that of seawater are accounted for by dolomitization of an aragonite rich marine sediment by the brine before infiltration into the crystalline basement rocks subsequent alteration of silicate minerals in the shield added additional ca and sr to the brine as indicated by their radiogenic 87 sr 86 sr ratios up to 0 7147 based on mineral balance calculations the major mineral products of the cryogenic and evaporitic concentration and evolution paths are significantly different the cryogenic evolution results in some 15 mirabilite 60 hydrohalite and 18 dolomite whereas the major minerals formed from the evaporitic evolutionary sequence are 36 halite 8 gypsum 17 dolomite and 30 albite the great similarity between the calcium chloride brine from yellowknife and other such canadian shield brines indicates that they may share a common marine origin

rapid growth and strain rates inferred from synkinematic garnets penokean orogeny minnesota recent reinterpretations of the early proterozoic penokean orogeny in minnesota invoke a plate tectonic model with characteristics similar to phanerozoic collisional belts deformation during collision produced large flattening strains 89 and the development of a tectonic foliation and progressive metamorphism up to amphibolite facies as indicated by the presence of synkinematic s1 garnets biotite garnet thermometry and plagioclase garnet biotite muscovite barometry give southward increasing temperatures and pressures and indicate burial to depths of 21 25 km similar to medial and internal zones of collisional orogens worldwide gibbs method modeling on zoned synkinematic garnets indicates virtually no change in pressure p or temperature t during garnet growth growth and rotation of garnets at a point in p t space in an actively evolving deformational and thermal regime are surprising and suggest rapid garnet growth rates and high rates of strain during orogeny this is consistent with previous studies that indicate more rapid rates of tectonometamorphic processes in the precambrian relative to younger orogenic belts

life and extinction of megafauna in the ice age arctic understanding the population dynamics of megafauna that inhabited the mammoth steppe provides insights into the causes of extinctions during both the terminal pleistocene and today our study area is alaska s north slope a place where humans were rare when these extinctions occurred after developing a statistical approach to remove the age artifacts caused by radiocarbon calibration from a large series of dated megafaunal bones we compare the temporal patterns of bone abundance with climate records megafaunal abundance tracked ice age climate peaking during transitions from cold to warm periods these results suggest that a defining characteristic of the mammoth steppe was its temporal instability and imply that regional extinctions followed by population reestablishment from distant refugia were characteristic features of ice age biogeography at high latitudes it follows that long distance dispersal was crucial for the long term persistence of megafaunal species living in the arctic such dispersal was only possible when their rapidly shifting range lands were geographically interconnected the end of the last ice age was fatally unique because the geographic ranges of arctic megafauna became permanently fragmented after stable interglacial climate engendered the spread of peatlands at the same time that rising sea level severed former dispersal routes

oxygen isotope mapping in the panorama vms district pilbara craton western australia applications to estimating temperatures of alteration and to exploration whole rock oxygen isotope data are presented for the panorama district in the archean pilbara craton of western australia where near perfect exposure reveals a cross section through a complete volcanogenic massive sulfide vms hydrothermal alteration system the 18o values decrease with depth in the volcanic pile across semi conformable alteration zones to values below 6 immediately above a large 180 km2 subvolcanic intrusion altered rocks in the upper parts of the subvolcanic intrusion have lower 18o values 6 8 than least altered granite 8 apart from sericite quartz altered zones which are slightly higher 8 10 corridors of low 18o values crosscut this regional zonation and are coincident with transgressive feldspar destructive alteration zones which underlie vms mineralization the whole rock oxygen isotope distribution patterns are interpreted to represent alteration temperature where high 18o values correspond to low temperature alteration and low 18o values correspond to high temperature alteration alteration temperatures which were calculated using modal alteration mineral abundances and an assumed fluid 18o are consistent with this interpretation increasing temperatures with depth in the volcanic pile and high temperatures in transgressive corridors leading up to vms deposits are consistent with a convective hydrothermal model in which heat from the subvolcanic intrusion drove seawater through the volcanic pile granite hosted sericite quartz alteration zones are 18o enriched and are tentatively interpreted to have formed from a mixed magmatic evolved seawater fluid

tectonic implications of finite strain variations in baraboo interval quartzites ca 1700 ma mazatzal orogen wisconsin and minnesota usa abstract variably deformed baraboo interval quartzites 1750 1630 ma are now correlated by detrital zircon ages holm d schneider d coath c d 1998 age and deformation of early proterozoic quartzites in the southern lake superior region implications for extent of foreland deformation during final assembly of laurentia geology 26 907 910 and were analyzed using finite strain techniques which document a se nw tectonic shortening orientation from the baraboo syncline south to the flambeau syncline north fabric interpretations using bedding and the principal strain axis orientations indicate there was a mix of layer parallel and layer normal synfolding shortening in the plane of tectonic transport se nw in the thrust belt finite strain magnitudes increase from the foreland barron sioux quartzites south toward the baraboo syncline electron backscatter device ebsd fabric diagrams pole figures of quartz optic axes also demonstrate an increasingly penetrative strain to the south anisotropy of low field ac magnetic susceptibility ams as a strain proxy preserve kmin measurements in the baraboo syncline quartzites that are sub horizontal e w and intersect bedding ams measurements in underlying rhyolite on opposite limbs of the baraboo syncline are clean appear to be primary magmatic as kmax intersects bedding but require a complex folding interpretation that is inconsistent with field kinematic indicators the flat lying foreland barron and sioux quartzites preserve a mix of results quartzites with no strain finite strain and ebsd measurements or small strains that preserve vertical shortening ams measurements in the foreland preserve kmin axes that are sub horizontal and parallel to the regional shortening orientation in the adjacent thrust belt the mazatzal orogen produced a thrust belt that is orders of magnitude wider 500 km and of higher metamorphic grade than most thrust belts where both the thrust belt and foreland are quartzites

intratest oxygen isotope variability in the planktonic foraminifer n pachyderma real vs apparent vital effects by ion microprobe abstract intratest oxygen isotope variations in the planktonic foraminifer neogloboquadrina pachyderma sinistral left coiling from north atlantic core top and multi net samples were assessed by ion microprobe analysis from 2 to 6 m spots with precision and accuracy better than 0 7 in 18 o 2 sd within a single foraminiferal test from a core top sample comprising both ontogenetic calcite and outer crust 18 o values vary from 0 5 to 3 7 pdb exceeding the range of equilibrium 18 o in the specimens habitat by a factor of three the isotopic difference between the ontogenetic calcite and the crust averages 1 8 neither of the two types of foraminiferal calcite precipitates in equilibrium with ambient seawater the ontogenetic calcite exhibits a negative vital effect 18 o m e 18 o measured 18 o equilibrium ranging from 0 5 to 1 the largest negative fractionation is associated to the inner walls of juvenile chambers in contrast a positive vital effect of about 0 8 was observed in the crust with respect to the highest equilibrium 18 o values at water depths below 200 m hence two vital effects that are opposite in sign are effective within a single foraminiferal test indicating that whole test values of this species are highly sensitive to the degree of encrustation and amplify or attenuate environmental signals the negative vital effect of the ontogenetic calcite was verified by ion microprobe analysis of four nonencrusted net sampled specimens reflecting three different depth intervals intra ontogenetic oxygen isotope ratios in these juvenile tests range from 0 6 to 3 0 and exhibit a negative vital effect even larger than that observed in core top samples based on these data the large range of apparent vital effects reported for this foraminiferal species can be assessed by a mass balance calculation assuming that the degree of encrustation is variable

optically continuous silcrete quartz cements of the st peter sandstone high precision oxygen isotope analysis by ion microprobe a detailed oxygen isotope study of detrital quartz and authigenic quartz overgrowths from shallowly buried 1 km quartz arenites of the st peter sandstone in sw wisconsin constrains temperature and fluid sources during diagenesis quartz overgrowths are syntaxial optically continuous and show complex luminescent zonation by cathodoluminescence detrital quartz grains were separated from 53 rocks and analyzed for oxygen isotope ratio by laser fluorination resulting

quantitative assessment of volcanic ash hazards for health and infrastructure at mt etna italy by numerical simulation abstract we performed a quantitative hazard assessment to determine the potential impacts of volcanic tephra fall on human health and infrastructure in the vicinity of mt etna italy using the numerical model vol calpuff we explored the dynamics of long lasting weak plume eruptions and their effects on the surrounding region input data are based on credible estimates of the main parameters characterising the expected events as derived from the historically observed and reconstructed explosive record of mt etna monte carlo techniques are used to capture the effects on estimates of finer ash concentration and total ground deposition due to volcanological uncertainties and meteorological variability numerical simulations compute the likelihoods of experiencing critical 10 m volcanic particle vp 10 concentrations in ambient air and tephra ground deposition at various populated locations around the volcano including the city of catania and at key infrastructure such as airports and main roads results show how the towns and infrastructure on the east side of the volcano are significantly more exposed to ash related hazards than those on the west side in accordance with wind statistics simulation outcomes also illustrate how at the sites analysed the amount of deposited particulate matter is proportional to the intensity i e mass flow rate of the event whereas predicted values of vp 10 concentrations are significantly larger for smaller events due to the reduced dispersal of low altitude plumes the use of a simple re mobilization model highlights the fact that particle re suspension needs to be considered in the estimation of vp 10 values our findings can be used to inform civil protection agencies responsible for mitigating tephra fall impacts to human health road transport and aviation safety

oxygen isotope zonation and alteration in the northern noranda district quebec evidence for hydrothermal fluid flow volcanic rocks of the new vauze norbec area central noranda volcanic complex consist of andesites and rhyolites that have been chemically and isotopically altered by synvolcanic semiconformable alteration processes including spilitization chloritization silicification and epidote quartz alteration andesites have whole rock delta 18 o values of 1 9 to 9 7 per mil those with megascopic mineralogical evidence of hydrothermal alteration have ones of 5 1 to 9 7 per mil rhyolites also show a broad range in delta 18 o values 4 4 to 13 7 per mil all of the volcanic rocks are either enriched or depleted in 18 o with respect to fresh rhyolite 8ppm or fresh andesite 6ppm a marked upward stratigraphic increase in delta 18 o values and the strata bound occurrence and regional zoning of alteration minerals provide evidence of district scale hydrothermal alteration these alteration patterns formed under the conditions of an increasing thermal gradient and a downward decrease in water rock ratio controlled by the cooling of the flavrian lake synvolcanic intrusion

chlorine 36 and 14c chronology support a limited last glacial maximum across central chukotka northeastern siberia and no beringian ice sheet abstract the pekulney mountains and adjacent tanyurer river valley are key regions for examining the nature of glaciation across much of northeast russia twelve new cosmogenic isotope ages and 14 new radiocarbon ages in concert with morphometric analyses and terrace stratigraphy constrain the timing of glaciation in this region of central chukotka the sartan glaciation last glacial maximum was limited in extent in the pekulney mountains and dates to 20 000 yr ago cosmogenic isotope ages 30 000 yr as well as non finite radiocarbon ages imply an estimated age no younger than the zyryan glaciation early wisconsinan for large sets of moraines found in the central tanyurer valley slope angles on these loess mantled ridges are less than a few degrees and crest widths are an order of magnitude greater than those found on the younger sartan moraines the most extensive moraines in the lower tanyurer valley are most subdued implying an even older probable middle pleistocene age this research provides direct field evidence against grosswald s beringian ice sheet hypothesis

paleoglaciology s grand unsolved problem the paleoglaciological concept that during the pleistocene glacial hemi cycles a super large structurally complex ice sheet developed in the arctic and behaved as a single dynamic system as the antarctic ice sheet does today has not yet been subjected to concerted studies designed to test the predictions of this concept yet it may hold the keys to solutions of major problems of paleoglaciology to understanding climate and sea level changes the russian arctic is the least known region exposed to paleoglaciation by a hypothetical arctic ice sheet but now it is more open to testing the concept implementation of these tests is a chaillenging task as the region is extensive and the available data are controversial well planned and coordinated field projects are needed today as well as broad discussion of the known evidence existing interpretations and new field results here we present the known evidence for paleoglaciation of the russian arctic continental shelf and reconstruct possible marine ice sheets that could have produced that evidence

nd o and sr isotopic constraints on the origin of precambrian rocks southern black hills south dakota abstract the nd o and sr isotopic characteristics of precambrian metasedimentary metavolcanic and granitic rocks from the black hills of south dakota are examined two late archean granites 2 5 2 6 ga have t dm ages of 3 05 and 3 30 ga suggesting that at least one of the granites was derived through the melting of significantly older crust early proterozoic metasedimentary rocks have t dm ages that range from 2 32 to 2 45 ga these model ages in conjunction with probable stratigraphic ages ranging from 1 9 to 2 2 ga indicate that mantle derived material was added to the continental crust of this region during the early proterozoic previous studies of the harney peak granite complex have reported u pb and rb sr ages of about 1 71 ga and most granite samples examined in this study have sr isotopic compositions consistent with that age two granite samples taken from the same sill however give two point rb sr and sm nd ages of 2 08 0 08 and 2 20 0 20ga 2200 nd 15 5 respectively in addition whole rock and apatite samples of the spatially associated tin mountain pegmatite give a sm nd isochron age of 2000 100 ma 2200 nd 5 8 1 8 the sm nd o and rb sr isotopic systematics of these granitic rocks have been complicated to some degree by both crystallization and post crystallization processes and the age of the pegmatite and parts of the harney peak granite complex remain uncertain processes that probably complicated the isotopic systematics of these rocks include derivation from heterogeneous source material assimilation mixing of ree between granite and country rock during crystallization via a fluid phase and post crystallization mobility of sr the nd isotopic compositions of the pegmatite and the harney peak granite indicate that they were not derived primarily from the exposed metasedimentary rocks

tectonic implications of metamorphism and gravity field in the penokean orogen of northern michigan published geologic data together with new metamorphic pressure and temperature data and gravity data provide strong evidence for northward directed thrusting of lower proterozoic rocks in northern michigan and wisconsin metamorphic studies indicate pressures of 7 kbar at watersmeet node and 4 kbar at the peavy node the republic metamorphic node located 30 km to the north of peavy attained pressures of 2 3 kbar all three metamorphic highs reached temperatures in the range of 600 650 c and are correlated with areas of negative gravity anomalies relative to surrounding regions in the peavy high the center of the gravity anomaly lies on the sillimanite isograd and we suggest that the source of this negative anomaly may be remobilized underlying archean gneiss the highest grade rocks of the republic node lie well within a residual gravity anomaly which is interpreted to have a very shallow source and the watersmeet high lies above gneiss domes which show negative gravity anomalies a north south geologic cross section constructed from a two dimensional gravity model which extends northward from the dunbar dome in the magmatic arc terrane of wisconsin across a terrane boundary interpreted as a suture and marked by the niagara fault and across the peavy metamorphic node suggests that the dunbar dome was transported northward onto the continental foreland during the penokean orogenic event these north verging fold thrust sheets or nappes produced prominent tectonic thickening at the peavy and watersmeet as indicated by the relatively high metamorphic pressures there the thrust sheets evidently thinned to the north as suggested by the relatively low pressures at republic we suggest that the archean continental edge defined by the steep gradient in the regional northeast trending gravity high lies beneath the magmatic rocks of wisconsin and thus extends south of the niagara fault suture

evidence for restricted ice extent during the last glacial maximum in the koryak mountains of chukotka far eastern russia field evidence in the koryak mountains lake mainitz region of far eastern russia supports three pleistocene glacial advances the early wisconsinan and pre wisconsinan glaciations are represented by broad lobate moraines extending as much as 30 km north of the koryak mountains field evidence demonstrates that the terminal lateral and medial moraines as well as meltwater channels dead ice topography kettles and outwash plains mark the extent of ice during the last glacial maximum lgm during which glaciers reached no more than 20 km beyond their present limits those emanating from the southern koryak mountains may have reached the bering sea numerical and relative dating techniques support these results and test the theoretical models of the lgm in western beringia erratics on moraines and glaciofluvial terraces common to all valleys at 13 13 8 m above river level yield 36 cl exposure ages ranging from 10 08 to 25 78 ka the koryak mountains lake mainitz record of glaciation is spatially and temporally consistent with the glaciation pattern across central beringia found in other terrestrial and marine records glacier growth in the koryak mountains was sustained by possible increased summer sea surface temperatures and precipitation in the northwest pacific region evidence from the northern koryak mountains lat 64 n long 177 e indicates that the extent of ice in western beringia was limited to mountain and valley glaciers during the lgm this fieldbased research contradicts m g grosswald s theoretical beringian ice sheet hypothesis

sims oxygen isotopes indicate phanerozoic fluids permeated a precambrian gold deposit abstract the reef deposit is an anomalous au cu occurrence in the paleoproterozoic terranes of northern wisconsin better known as host to significant cu zn volcanogenic massive sulfide vms deposits previous work using lead isotopes and fluid inclusions has identified a protracted development of the mineralization from initial formation as the root zone veins of a vms deposit during the penokean orogeny 1 9 1 8 ga with the most recent mineralization remobilization activity associated with late paleozoic mississippi valley type mvt fluid flow haroldson et al 2018a 2018b here we use the oxygen isotope history of the reef deposit to verify and further examine the deposit s protracted development laser fluorination oxygen isotope measurements of primary mineralized quartz veins range in 18o from 6 8 to 10 0 vsmow and a trend is observed of increasing 18o values of parallel vein zones along a 400 m traverse from northwest to southeast likely from a temperature gradient during initial formation temperature estimates for a vms deposit setting 230 to 400 c are consistent with a hydrothermally shifted formation fluid using seawater 18o estimates during the penokean orogeny and evolving to higher 18o by incorporation of magmatic fluids or interaction with local crust in situ oxygen isotope measurement by secondary ion mass spectrometer sims of cross cutting quartz and carbonate range in 18o from 19 4 to 28 4 for quartz 25 3 to 28 1 for dolomite and 9 6 to 29 3 vsmow for calcite high 18o values 19 are measured in a crustiform textured quartz stockwork microveinlet in dolomite observed in late carbonate microveinlets and calcite in settings associated with the late quartz and dolomite and a separate calcite only setting directly linked with gold mineralization remobilization

a three dimensional eulerian model for transport and deposition of volcanic ashes abstract volcanic ash fallout represents a serious threat to people living near active volcanoes because it can produce several undesirable effects such as collapse of roofs by ash loading respiratory sickness air traffic disruption or damage to agriculture the assessment of such volcanic risk is therefore an issue of vital importance for public safety and its mitigation often requires to evaluate the temporal evolution of the phenomenon through reliable computational models we develop an eulerian model named fall3d for the transport and deposition of volcanic ashes the model is based on the advection diffusion sedimentation equation with a turbulent diffusion given by the gradient transport theory a wind field obtained from a meteorological limited area model lam and the source term derived from by buoyant plume theory it can be used to forecast either ash concentration in the atmosphere or ash loading on the ground model inputs are topography meteorological data given by a lam mass eruption rate and a particle settling velocity distribution a test application to the july 2001 etna eruption is presented

the vol calpuff model for atmospheric ash dispersal 2 application to the weak mount etna plume of july 2001 1 here the application of the vol calpuff model by barsotti et al to a weak plume erupted from mount etna in july 2001 is presented and discussed the reconstruction of the explosive event was obtained by using high resolution weather forecasts produced by a mesoscale nonhydrostatic model and volcanic source data coming from observations and analytical studies the plume rise and atmospheric dispersal models were investigated over 5 d of eruption mostly in terms of column height aerial ash concentration and ground deposition modeling results are shown as a function of various source conditions and compared to independent observations derived from satellite images and deposit mapping the application of vol calpuff clearly highlights the crucial role played by meteorological conditions in determining dispersal dynamics some of the most important effects described by the model are 1 the large wind field influence on the plume height determination and tilting 2 the contrasting dispersal patterns of ash particles of different sizes 3 the complex and somehow nonintuitive distribution of ash on the ground resulting in preferential directions of dispersal and quite irregular deposit patterns and 4 the impossibility to reproduce both the column height and the deposit accumulation pattern by adopting a steady state vent mass flow rate over the investigated 4 d period due to observed temporal changes in eruption dynamics modeling results also suggest the need for further integration of simulation outcomes with remote sensing and field reconstructions on ash dispersal processes in future

paleoproterozoic basin development and sedimentation in the lake superior region north america abstract the peneplaned archean craton in the lake superior region was the platform upon which a continental margin assemblage was deposited extension resulted in localized rifts that received thicker accumulations of sediments and volcanic rocks than did adjacent parts of the platform seas transgressed onto the continent several times and an ocean basin opened south of the present day lake superior island arcs that formed during subduction collided with the craton margin as the ocean basin closed oceanic crust is poorly preserved as a dismembered ophiolite sequence the arc volcanics are preserved as the wisconsin magmatic terranes the collision resulted in a fold and thrust belt known as the penokean orogen to the north of the fold and thrust belt a northward migrating foreland basin the animikie basin developed thick turbidite successions were deposited along the basin axis and terrigenous clastics and lake superior type iron formation were deposited on the shelf along the northern margin of the basin the primary paleoclimatic indicators are 1 glaciogenic rocks at the base of the paleoproterozoic succession in michigan indicating ice house conditions 2 remnants of a paleosol on the glaciogenic rocks indicative of deep weathering probably under subtropical conditions and therefore of greenhouse conditions and 3 carbonate minerals after gypsum halite and anhydrite in stromatolitic dolomite indicative of aridity three second order depositional sequences are bounded by major unconformities and can be correlated throughout the lake superior region

wisconsin holocene paleoenvironment of the bering sea evidence from diatoms pollen oxygen isotopes and clay minerals abstract a core from the southeastern bering sea contains a depositional record of the wisconsin glacial interval and the holocene four lithologic units show distinctive changes in diatom species palynomorphs oxygen isotopes in diatom silica and clay minerals unit 4 the oldest probably represents the glacial advance of the early wisconsin and records extensive sea ice cover and a soggy herbaceous tundra on the exposed continental shelf unit 3 represents the stades and interstades of the middle wisconsin including an early period of high seasonal variability and a later period with expansion of winter sea ice in the basin and of tundra onshore unit 2 represents the late wisconsin glacial maximum and subsequent deglaciation with a tundra covered shelf sea ice cover increased to a maximum during which the surface waters were probably covered by sea ice throughout the year subsequent to the sea ice maximum the isotope ratios record a major meltwater event unit 1 represents the holocene with expansion of shrub tundra or scrub forest in the coastal upland and waters of increased temperature and salinity in the bering sea

the russian component of an arctic ice sheet during the last glacial maximum abstract the extent of late weichselian glaciation in arctic russia remains a problem our model of 1995 1998 suggests a continuous and long lived ice sheet centered on the kara sea other reconstructions suggest a smaller and diachronous glaciation the vast majority of dates support the model of restricted glaciation we show that these dates are inconsistent with the geologic record of ice flow across the kara barents divide with second order glacial geology of kola peninsula and with evidence for glacial surges they are also inconsistent with late weichselian climate of the arctic with eurasian continental paleohydrology including meltwater drainage systems cataclysmic megafloods major transgressions of the caspian sea and with the entire paleogeographic context of northern eurasia we believe that due to impeded ventilation of the pleistocene arctic ocean these dates are often too old and that recycling and contamination of the samples would also contribute to the dating errors destructive impacts of late glacial ice sheet surges and megafloods upon the arctic glacial sequences would also aggravate the situation by ignoring the dates until these problems are addressed we find that the field evidence supports continuous glaciation of arctic russia at the lgm and that the resulting ice sheet was part of an arctic ice sheet that included an ice shelf in the arctic ocean and ice sheets in greenland and north america we present 3 d reconstructions of the arctic ice sheet and with an enlarged antarctic ice sheet we show that the ice volume is equivalent to an lgm sea level that was 130 135 m lower than at present the reconstructions depict the arctic ice sheet before and after massive thawing of the bed that allows partial gravitational collapse of the overlying ice with a minimal change in ice volume

tracking meteoric infiltration into a magmatic hydrothermal system a cathodoluminescence oxygen isotope and trace element study of quartz from mt leyshon australia the oxygen isotope and trace element composition of hydrothermal quartz has been integrated with scanning electron microscope cathodoluminescence sem cl images and fluid inclusion properties to track fluid sources and hydrothermal processes in the mt leyshon an deposit australia oxygen isotope and trace element data were collected on parallel traverses across the same quartz sections using secondary isotope mass spectrometry sims and laser ablation inductively coupled plasma mass spectrometry la icp ms respectively with sem cl images obtained before analysis for petrographic context over the 280 to 650 degrees c quartz precipitation range suggested by fluid inclusion microthermometry delta o 18 quartz varies from 0 0 to 14 4 o corresponding to a wide range of equilibrium delta o 18 fluid values from 6 1 to 10 2 o vs v smow the delta o 18 quartz signature varies systematically among distinct sem cl quartz generations both within and between samples and can be correlated with variations in temperature and fluid composition but is independent of intra generational oscillatory zoning in contrast al and li concentrations correlate broadly with cl intensity in oscillatory quartz whereas their concentration is unpredictable in sealed fractures and overgrowths concentrations of b mg na p cl k ti mn fe ge and sn are independent of al li and oscillatory cl features but ti correlates with quartz precipitation temperature although no systematic correlation between delta o 18 quartz and trace element concentrations was found complementary patterns exist in narrow overgrowths of low delta o 18 quartz similar to 0 o and high al g 10 000 ppma these quartz zones likely formed during the incursion of o 18 depleted meteoric water into the magmatically dominated mt leyshon hydrothermal system we interpret the highest al concentrations as the result of high quartz precipitation rates triggered by depressurisation of the hydrothermal cell the decoupling of oxygen isotope and trace element patterns in quartz leads to the suggestion that 1 under most circumstances temperature and fluid chemistry dominate delta o 18 quartz and 2 the trace element record and in particular al and li is influenced by the superimposed effects of quartz precipitation rate c 2007 elsevier b v all rights reserved

last interglacial isotope stage 5 glacial and sea level history of coastal chukotka peninsula and st lawrence island western beringia abstract study of glacial and marine sequences along the outer coast of chukotka peninsula bering strait is the basis for major revisions of the regional stratigraphy the val katlen suite at its type section at the mouth of the enmelen river records the youngest high sea stand of the last interglaciation on chukotka peninsula marine deposits and glacial diamicton stratigraphically below the type section record respectfully the peak of the last interglacial marine oxygen isotope substage 5e and rapid glacierization of the coastal mountains probably during substage 5d or 5b correlative deposits recording a similar sequence of intra stage 5 events but once thought to be of early and middle pleistocene age include the upper and lower pinakul suite at cape pinakul and marine deposits near the nunyamo river on the gulf of anadyr based upon amino acid analyses biostratigraphy and supporting geochronology these deposits enclose warmer than present faunas and floras comparible to last interglacial pelukian marine deposits found along the coast of alaska the last major advance of glacial ice from chukotka peninsula across anadyr strait and onto st lawrence island was likely initiated during the later part of stage 5 based on our reinterpretaion of the stratigraphy at cape pinakul near the nunyamo river and on northwestern st lawrence island chukotkan ice probably reached st lawrence island sometime during oxygen isotope stage 4 ice extend across chukotka during the lgm was very imited

last glacial maximum ice sheet dynamics in arctic canada inferred from young erratics perched on ancient tors along standing debate regarding the reconstruction of former ice sheets revolves around the use of relative weathering of landscapes i e the assumption that highly weathered landscapes have not been recently glaciated new cosmogenic isotope measurements from upland bedrock surfaces and erratics along the northeastern margin of the laurentide ice sheet lis shed light on this debate 10 be and 26 al concentrations from three perched erratics yielding cosmogenic exposure ages of 17 11 ka are much lower than those measured in two unmodified highly weathered tors upon which they lie which yield cosmogenic exposure ages of 60 ka these findings suggest that non erosive ice covered weathered upland surfaces along the northeastern margin of the lis during the last glacial maximum these data challenge the use of relative weathering to define the margins of pleistocene ice sheets the juxtaposition of non erosive ice over upland plateaus and erosive ice in adjacent fiords requires strong gradients in basal thermal regimes suggestive of an ice stream mode of glaciation r 2003 elsevier science ltd all rights reserved

the periglacial climate and environment in northern eurasia during the last glaciation this paper summarizes the results of studies of the late weichselian periglacial environments carried out in key areas of northern eurasia by several queen teams european science foundation esf programme quaternary environment of the eurasian north the palaeoglaciological boundary conditions are defined by geological data on timing and extent of the last glaciation obtained in the course of the eu funded project eurasian ice sheets these data prove beyond any doubt that with the exception of the northwestern fringe of the taymyr peninsula the rest of the eurasian mainland and severnaya zemlya were not affected by the barents kara sea ice sheet during the last glacial maximum lgm inversed modelling based on these results shows that a progressive cooling which started around 30 ka bp caused ice growth in scandinavia and the northwestern areas of the barents kara sea shelf due to a maritime climate with relatively high precipitation along the western flank of the developing ice sheets in the rest of the eurasian arctic extremely low precipitation rates less than 50 mm yr 1 did not allow ice sheet growth in spite of the very cold temperatures palaeoclimatic and palaeoenvironmental conditions for the time prior to during and after the lgm have been reconstructed for the non glaciated areas around the lgm ice sheet with the use of faunal and vegetation records permafrost eolian sediments alluvial deposits and other evidences the changing environment from interstadial conditions around 30 ka bp to a much colder and drier environment at the culmination of the lgm at 20 15 ka bp and the beginning of warming around 15 ka bp have been elaborated from the field data which fits well with the modelling results

biotic enhancement of weathering atmospheric oxygen and carbon dioxide in the neoproterozoic 1 it has been suggested that biological colonization of the land surface began in the neoproterozoic 1000 544 million years ago ma we hypothesize that this colonization involved selective weathering of p from rocks as well as an amplification of overall weathering rates we show that two recent models despite differences in the feedback mechanisms represented predict that an increase in the weathering flux of p to the ocean would have caused a rise in atmospheric o2 in the neoproterozoic this in turn may have provided a necessary condition for the evolution of animals with hard skeletons seen in the cambrian explosion increased weathering of silicate rocks would also have caused a decline in atmospheric co2 which could have been a causal factor in the neoproterozoic glaciations

the penokean orogeny in the lake superior region abstract the penokean orogeny began at about 1880 ma when an oceanic arc now the pembine wausau terrane collided with the southern margin of the archean superior craton marking the end of a period of south directed subduction the docking of the buoyant craton to the arc resulted in a subduction jump to the south and development of back arc extension both in the initial arc and adjacent craton margin to the north a belt of volcanogenic massive sulfide deposits formed in the extending back arc rift within the arc synchronous extension and subsidence of the superior craton resulted in a broad shallow sea characterized by volcanic grabens menominee group in northern michigan the classic lake superior banded iron formations including those in the marquette gogebic mesabi and gunflint iron ranges formed in that sea the newly established subduction zone caused continued arc volcanism until about 1850 ma when a fragment of archean crust now the basement of the marshfield terrane arrived at the subduction zone the convergence of archean blocks of the superior and marshfield cratons resulted in the major contractional phase of the penokean orogeny rocks of the pembine wausau arc were thrust northward onto the superior craton causing subsidence of a foreland basin in which sedimentation began at about 1850 ma in the south baraga group rocks and 1835 ma in the north rove and virginia formations a thick succession of arc derived turbidites constitutes most of the foreland basin fill along with lesser volcanic rocks in the southern fold and thrust belt tectonic thickening resulted in high grade metamorphism of the sediments by 1830 ma at this same time a suite of post tectonic plutons intruded the deformed sedimentary sequence and accreted arc terranes marking the end of the penokean orogeny the penokean orogen was strongly overprinted by younger tectonic and thermal events some of which were previously ascribed to the penokean principal among these was a period of vertical faulting in the archean basement and overlying paleoproterozoic strata this deformation is now known to have post dated the terminal penokean plutons by at least several tens of millions of years evidence of the penokean orogen is now largely confined to the lake superior region comparisons with more recent orogens formed by similar plate tectonic processes implies that significant parts of a once more extensive penokean orogen have been removed or overprinted by younger tectonic events

optically stimulated luminescence dating supports central arctic ocean cm scale sedimentation rates 1 this paper presents new results from optically stimulated luminescence osl dating on a sediment core raised from the crest of the lomonosov ridge in the central arctic ocean there has been much debate about dating sediment cores from the central arctic ocean and by using an independent absolute dating technique we aim to test whether or not relatively fast cm scale ka sedimentation rates were typical of arctic s pleistocene depositional mode on the basis of mainly paleomagnetic reversal stratigraphy many previous studies suggest mm scale ka sedimentation rates a common feature in these studies is that the first down core paleomagnetic negative inclination is consistently interpreted as the brunhes matuyama boundary at about 780 ka our osl dating results indicate that this assumption is not generally valid and that the first encountered negative inclination represents younger age excursions within the brunhes chron implying reinterpretation of many published core studies where paleoenvironmental reconstructions have been made for the central arctic ocean our dating results furthermore corroborates a correlation of the uppermost 2 3 m of the lomonosov ridge cores to a well dated core located off the barents kara sea margin that in turn is correlated to cores in the fram strait valuable information on the paleoceanographical evolution in the arctic ocean from mis 6 to the holocene is given through this correlation of records from the central arctic ocean to records off the eurasian continental margin

alleghenian age of the upper mississippi valley zinc lead deposit determined by rb sr dating of sphalerite mississippi valley type mvt ore deposits in north america are generally thought to have formed from warm brines which migrated from sedimentary basins to sites of deposition in sedimentary strata of the neighbouring craton long after unification of the sediments1 3 when and how these migrations occurred is not well understood but recent geological evidence suggests that continental scale brine migration can be triggered by tectonic collisions4 6 indirect evidence7 9has suggested an association of north american mvt mineralization with the late palaeozoic alleghenian ouachita orogeny recently however nakai et al 10obtained a rb sr age of 377 29myr for sphalerites from the east tennessee mvt district which they linked to the middle palaeozoic acadian orogeny here we report rb sr dates for sphalerites from the mvt type section the upper mississippi valley umv zinc lead district rb sr data from two distinct sphalerite bands from the west hayden ore body yield two independent but indistinguishable isochrons of permian age 269 6 myr and 270 4 myr consistent with a brine migration episode initiated by the alleghenian ouachita orogeny in conjunction with the previous data indicating a link to the acadian orogeny10 11 our results indicate that north american mvt deposits formed in at least two distinct tectonic episodes

ice sheets and sea level of the last glacial maximum this paper outlines the general issues regarding ice sheets and sea level of the last glacial maximum lgm which formed the basis of an epilog project workshop papers in this special issue of quaternary science reviews provide a comprehensive assessment of these issues from the perspective of geological reconstructions of ice sheet extent records of sea level change ice sheet modelling geophysical models of glacial isostatic adjustment and geochemical proxies of ice volume this new assessment has substantially narrowed the uncertainties in the total changes in ice sheets and sea level and their proxies suggesting a net decrease in eustatic sea level at the lgm ranging from 120 to 135 m r 2001 elsevier science ltd all rights reserved

the 18o 16o ratio of 2 billion year old seawater inferred from ancient oceanic crust an oxygen isotope profile of the 2 billion year old purtuniq ophiolite overlaps with similar profiles of younger ophiolites and the modern oceanic crust this overlap implies i that there was a similar style of seawater ocean crust interaction during the past 2 billion years ii that the oxygen isotope composition of early proterozoic seawater was similar to the modern value iii that early proterozoic sea floor spreading rates were similar to or greater than average modern rates and iv that early proterozoic carbonate rocks and cherts with low 18o 16o ratios do not reflect global scale 18o depletion of early proterozoic oceans

mafalda an early warning modeling tool to forecast volcanic ash dispersal and deposition 1 forecasting the dispersal of ash from explosive volcanoes is a scientific challenge to modern volcanology it also represents a fundamental step in mitigating the potential impact of volcanic ash on urban areas and transport routes near explosive volcanoes to this end we developed a web based early warning modeling tool named mafalda modeling and forecasting ash loading and dispersal in the atmosphere able to quantitatively forecast ash concentrations in the air and on the ground the main features of mafalda are the usage of 1 a dispersal model named vol calpuff that couples the column ascent phase with the ash cloud transport and 2 high resolution weather forecasting data the capability to run and merge multiple scenarios and the web based structure of the procedure that makes it suitable as an early warning tool mafalda produces plots for a detailed analysis of ash cloud dynamics and ground deposition as well as synthetic 2 d maps of areas potentially affected by dangerous concentrations of ash a first application of mafalda to the long lasting weak plumes produced at mt etna italy is presented a similar tool can be useful to civil protection authorities and volcanic observatories in reducing the impact of the eruptive events mafalda can be accessed at http mafalda pi ingv it

oxygen isotope alteration in the noranda mining district abitibi greenstone belt quebec a regional whole rock oxygen isotope survey carried out in the noranda district shows how oxygen isotope alteration can be used to guide exploration for massive sulfide deposits the survey is based on 588 outcrop whole rock oxygen isotope determinations from 478 sites in a approximately 35 by 50 km area between the destor porcupine and cadillac larder lake breaks from east of the horne mine to west of the magusi river mine the mean isotopic composition of all samples is 7 4 or 2 per mil smow nested analysis of variance of 478 isotopic determinations from 371 of these sites shows that 74 percent of the total variance in whole rock delta 18 o r r whole rock is associated with outcrop location 21 percent with outcrop sampling and 5 percent with sample analysis an analysis of 259 determinations indicates that rock type is statistically no more important than outcrop sampling the statistical analysis indicates that isotopic variations greater than or 1 per mil can be used to map the hydrothermal circulation responsible for massive sulfide mineralization specific traverses visually confirm the lack of 18 o dependence on rock type and the utility of a 2 per mil interpretive band the large scale pattern of isotopic alteration in the noranda district is dominated by a nearly continuous 2 to 3 km wide annulus at the margins of the flavrian pluton of delta 18 o r 18 o r 18 o r depletion is surrounded up section by a approximately 10 km wide band of patchy but intense 18 o enrichment 8 5 14ppm the combined pattern of concentric light and heavy alteration has a diameter of approximately 30 km the clericy intrusion shows a similar pattern of isotope alteration on a smaller 10 km diam scale the lake dufault pluton seems to have been isotopically altered by continuing convection driven by the flavrian hydrothermal system modeling suggests that the 18 o depletion is produced by water circulating toward and along the edges of an intrusion and that the surrounding heavy alteration is produced either by seawater recharge or limited hydrothermal discharge the large scale and coherency of the alteration pattern centered on the flavrian pluton is remarkable and indicates that this pluton drove a major long lived approximately 10 m y hydrothermal system in which convection penetrated to an 8 kin depth the intensity and coherency of the 18 o depletion correlates with the tonnage of associated massive sulfide mineralization oxygen isotope depletion may in general mark the margins of plutons that have driven sufficient hydrothermal circulation to produce economic massive sulfide deposits up section it may be possible to screen plutons for up section massive sulfide exploration potential by collecting and isotopically analyzing approximately 50 samples from five traverses across a pluton9s margins additional samples may provide details light fingers that guide exploration to particular deposits

volcanic history mineralization and alteration of the crandon massive sulfide deposit wisconsin the early proterozoic crandon massive sulfide deposit occurs in a 280 km long east trending greenstone belt along the southern margin of the southern province of the canadian shield the deposit is conformably contained within a sequence of subaqueous andesitic to dacitic pyroclastics flows and associated chemical sedimentary rocks which strike n 85 degrees w and dip 70 degrees to 90 degrees n regional metamorphism in the area achieved lower greenschist facies regional dip of the rocks is near vertical but smaller scale or penetrative deformation features are rare the footwall of the deposit consists of a thick sequence of andesitic tuff overlain by a series of volcanic breccias some of the breccias resulted from local fumarolic activity whereas other breccias represent a complex history of phreatic and phreatomagmatic volcanism and silicification some distance from the deposit examination of the breccia types distribution and thicknesses suggests at least two source areas for the breccias the breccias served as permeable conduits for the ore fluids directing them laterally toward a syndepositional graben where the fluids were vented into a topographic depression on the ocean floor during a hiatus in local volcanic activity up to 100 m of massive sulfide consisting of laminae of pyrite and sphalerite with minor chalcopyrite galena quartz chlorite sericite and dolomite and minor interbedded tuff chert argillite sandy tuff and dolomite were deposited following chemical sedimentation hydrothermal venting continued producing crosscutting vein mineralization vein development is intimately linked to the distribution of breccia in the footwall ascending fluids continued to migrate laterally through the permeable breccia and deposited vein mineralization which plugged the original vent areas with fine grained precipitates of silica and sulfide secondary porosity was created by refracturing of tuff and breccia vein mineralization localized in the footwall of the massive sulfides exhibits a systematic compositional variation with time and space from west to east beneath the west end of the deposit the earliest veins consist of quartz and grade eastward into quartz chalcopyrite pyrite quartz pyrite sphalerite chalcopyrite pyrite sphalerite and finally pyrite veins the distribution and degree of veining suggests two source areas which correspond to the two source areas for the lithic breccias recoverable reserves in the deposit are estimated at 61 million metric tons averaging 1 1 percent cu 5 6 percent zn 0 5 percent pb 37 g metric ton ag and 1 0 g metric ton au alteration of the footwall rocks at crandon consists primarily of silicification sericitization pyritization and minor chloritization interaction of ore fluid with wall rock has resulted in enrichment in sio 2 fe k f s cu zn as sb ba au hg pb bi se and cd and depletion in al mg ca na v and sr the morphology of the alteration zone at crandon is tabular due to control by primary and secondary porosity

the genetic relationship between upper mississippi valley district lead zinc mineralization and minor base metal mineralization in iowa wisconsin and illinois minor base metal occurrences are present in paleozoic dolomites and to a lesser extent in slates and sandstones in a broad zone surrounding the main upper mississippi valley zinc lead district in iowa wisconsin and illinois these occurrences are of interest because they may be remnants of fluid pathways of upper mississippi valley zinc lead mineralization outlying base metal occurrences contain mainly pyrite marcasite sphalerite galena and calcite they occur in a variety of forms including vertical veins gash veins disseminated breccias vug linings and paleokarst replacement bodies two paragenetic types of mineralization are evident occurrences in which sulfides are generally early and calcite is late and occurrences in which carbonate either calcite or dolomite but predominantly calcite is early and sulfides are generally late similarities exist among mineralogy geologic setting and some geochemical aspects of the main upper mississippi valley district and outlying occurrences however paragenetic fluid inclusion and stable isotope data indicate major differences in the genetic history of the outlying occurrences fluid inclusion homogenization temperatures for outlying sphalerite and calcite range from 37 8 degrees to 115 8 degrees c these temperatures are generally lower than those reported previously for these minerals from the main upper mississippi valley deposits 46 degrees 220 degrees c although measured salinities for inclusions in sphalerite in outlying occurrences 15 6 23 8 equiv wt nacl are similar to those for sphalerite from the main upper mississippi valley district 19 6 23 equiv wt nacl salinities for inclusions in calcite in outlying occurrences 5 1 18 1 equiv wt nacl are considerably higher than those determined for calcite 4 8 5 1 equiv wt from the main upper mississippi valley district the delta 34 s values for outlying sulfates range from 21 to 31 per mil cdt and are similar to those of the main upper mississippi valley district 22 36ppm overall values of delta 34 s for sulfides from outlying occurrences range from 22 to 36 per mil and contrast to that obtained from pitch and flat deposits 6 30ppm and gash veins approximately 1ppm from the main upper mississippi valley district although sulfides from this district formed from reduced connate water sulfate the wide range in sulfur isotope data was caused by the ore forming fluid reacting to varying degrees with isotopically light diagenetic pyrite values of delta 13 c and delta 18 o for outlying calcites 9 to 5ppm pdb and 21 29ppm smow respectively tend to be heavier than calcites from pitch and flat deposits in the main upper mississippi valley district delta 13 o 13 to 2ppm delta 18 o 17 23ppm the delta 18 o values for fluid inclusions in outlying mineralization 8 to 6ppm are similar to those obtained from the main upper mississippi valley district mineralization 5 to 6ppm however delta d values 95 to 20ppm are lighter than values 47 to 2ppm for the main district these isotopic values support a connate seawater source for the mineralizing fluids from both areas sulfur carbon and oxygen isotope data suggest that some outlying mineralization was more strongly influenced by local diagenetic processes than by processes that formed the main upper mississippi valley deposits

glacial age hydrography of the far northwest pacific ocean stable isotope data on benthic foraminifera from more than 30 cores on the northern emperor seamounts and in the okhotsk sea are synthesized in paleohydrographic profiles spanning the depth range 1000 4000 m holocene core top benthic foraminiferal 18o and 13c data are calibrated to modern hydrographic properties through measurements of 13c of co2 and 18o of seawater cibicidoides stable isotope ratios are close to the 13c and equilibrium 18o of seawater whereas uvigerina 18o and 13c are variably offset from cibicidoides glacial maximum 13c of cibicidoides displays a different vertical profile than that of the holocene when results are adjusted by 0 32 to account for the secular change in 13c during the last glacial maximum the data coincide with the modern seawater and foraminiferal curves deeper than 2 km however at shallower depths 13c gradually increases by as much as 1 above the modern value furthermore above 2 km the benthic 18o decreases by 0 5 these results are consistent with a benthic front at 2 km in the north pacific see herguera et al 1992 but they differ from interpretations based on trace metal data which indicate a source of nutrient depleted deep water during glaciation the isotopic data suggest that during glaciation there was a better ventilated watermass at intermediate depths in the far northwestern pacific it was relatively fresher than deep waters there and deep waters were as nutrient rich as today

palaeoclimate a fresh look at arctic ice sheets during the last glacial maximum ice sheets in eurasia terminated at the edge of the laptev sea seismic data now suggest that a separate ice sheet was repeatedly centred further east in the east siberian sea during previous glacial periods

the control of cathodoluminescence in dolomite by iron and manganese variations in the cathodoluminescent properties of carbonates are usually attributed to differing proportions of manganese mn2 as the most important activator and iron fe2 as the main inhibitor of luminescence interactions between manganese and iron concentrations and the luminescent properties of dolomite are demonstrated by petrographic and chemical analyses of 86 samples of dolomite representing a range of depositional environments and ages cambrian to cretaceous and a wide geographical distribution north america and europe iron and manganese are positively correlated in the dolomites with the former showing a greater range of variation very small amounts of manganese are sufficient to activate the luminescence and as little as 100 ppm mn2 is present in highly luminescing samples the intensity of luminescence is not proportional to the manganese concentration iron begins to quench luminescence as its concentration reaches 10 000 ppm above that level luminescence is rapidly lost and total extinction occurs among samples containing more than 15 000 ppm fe2 regardless of the manganese concentration

tectono stratigraphic evolution of the early proterozoic wisconsin magmatic terranes of the penokean orogen the early proterozoic penokean orogen developed along the southern margin of the archean superior craton the orogen consists of a northern deformed continental margin prism overlying an archean basement and a southern assemblage of oceanic arcs the wisconsin magmatic terranes the south dipping niagara fault suture zone separates the south facing continental margin from the accreted arc terranes the suture zone contains a dismembered ophiolite the wisconsin magmatic terranes consist of two terranes that are distinguished on the basis of lithology and structure the northern pembine wausau terrane contains a major succession of tholeiitic and calc alkaline volcanic rocks deposited in the interval 1860 1889 ma and a more restricted succession of calc alkaline volcanic rocks deposited about 1835 1845 ma granitoid rocks ranging in age from about 1870 to 1760 ma intrude the volcanic rocks the older succession was generated as island arcs and or closed back arc basins above the south dipping subducti

oxygen isotope ratios of archean plutonic zircons from granite greenstone belts of the superior province indicator of magmatic source zircons commonly preserve primary magmatic oxygen isotope ratios even through high grade metamorphic events unlike quartz which more readily loses its primary 18o value by subsolidus exchange intrusive bodies from the superior province canada have an average 18o zircon of 5 8 0 6 n 59 rocks those from granite greenstone belts have an average 18o zrc 5 8 0 6 n 55 in contrast to those from metasedimentary belts that average 18o zrc 6 7 0 2 n 4 the 18o zircon values from granite greenstone belts indicate a maximum allowable input of 14 supracrustal high 18o material into archean magmas of the superior province relative to mantle 18o values igneous bodies of the superior province have been separated into two groups based on geochemistry unenriched plutons and sanukitoids magmatic oxygen isotope ratios inferred from these zircons indicate up to a subtle but significant division of 1 between the two geochemical sets of rocks this distinction is apparent only in the 18o zrc and not in more commonly analyzed less refractory minerals such as quartz and feldspar oxygen isotope data correlate with geochemical modeling of sanukitoids the average 18o zrc for sanukitoids is 6 4 0 2 in comparison to 5 5 0 4 for unenriched plutons there is almost no overlap in values the elevation of sanukitoid 18o zrc indicates input from a high 18o source such as fluids from the subducting oceanic crust melts of subducted sediments or continental crust all of the plutons analyzed in this study have been dated by u pb zircon techniques and the combination of u pb ages and 18o zrc indicates little variability of 18o versus age during archean plutonism in the superior province therefore recycling of sediments and other high 18o sources was not a dominant process during crustal growth from 3003 to 2670 ma in the superior province

model for the evolution of oxygen isotope ratios in the pore fluids of mudrocks during burial abstract the determination of oxygen isotopic ratios in authigenic silicates and pore fluids provides vital information on the nature of water rock interactions in the subsurface and the origin of porosity occluding phases in reservoir rocks the 18 o values of pore fluids generally increase during burial through water rock interaction the transformation of detrital smectite to illite is thought to have a major influence on the isotopic evolution of pore fluids but previous attempts to model this effect have failed to accurately reproduce the observed water rock isotopic trends with depth a revised model has been developed which incorporates an empirical rate equation for the illitization reaction the input variables include the initial mineral and pore water isotopic compositions time porosity depth functions and geothermal histories and the assumption is made that the isotopic equilibration of the solid phases with pore waters only takes place during reaction the model is tested against the most complete data set available from the texas gulf coast usa and produces a good fit with the available pore fluid and mineral data the sensitivity of the model is tested for variations in the following parameters the illite water fractionation factor the fractionation of oxygen isotopes between the smectitic and illitic components of the detrital illite smectite the oxygen isotope fractionation between pore waters and the interlayer water within the smectite and the porosity depth function the results of the model are shown to be strongly dependent on the porosity depth function the best fit between the model and real data is provided by the dickinson equation for undercompacted shale modified to have a constant porosity below 2600 m to simulate the effects of overpressuring the model is also sensitive to the degree of oxygen isotopic fractionation between the illite and smectite within the sediment at the time of burial but not to the extent of fractionation between interlayer water within smectite and the adjacent pore waters the uncertainty within the illite water fractionation factor has only a minor effect on the results of the model although only incorporating a single mechanism for water rock interaction the model provides a tool for testing the interpretations of subsurface pore fluid evolution trends during sediment diagenesis

2001 flank eruption of the alkali and volatile rich primitive basalt responsible for mount etna s evolution in the last three decades abstract since the early 1970s enhanced eruptive activity of mount etna has been accompanied by selective geochemical changes in erupted lavas among which a gradual increase of alkalis whose origin is still debated here we provide further insight into the origin of this recent evolution based on a detailed study of the chemistry and dissolved volatile content of melt inclusions trapped in olivine crystals of unusual plagioclase poor primitive basalt that was extruded during a highly explosive flank eruption in july august 2001 two types of lava were erupted simultaneously along a n s fracture system trachybasalts from the upper vents 2950 2700 m were simply drained out by fracturing of the central volcanic conduit they are identical to summit crater lavas and contain mg poor olivines fo 70 72 with evolved and volatile poor melt inclusions that represent late stage crystallisation during shallow open conduit degassing in contrast plagioclase poor basalt 80 of total extruded through the lower vents 2550 2100 m derived from lateral dyke intrusion of a more primitive and volatile rich magma across the sedimentary basement this primitive melt is best preserved in rare fo 82 4 80 5 skeletal olivines present in lapilli deposits from the most powerful activities at the 2550 m vent its high dissolved contents of h 2 o 3 4 wt co 2 0 11 to 0 41 wt s 0 32 wt cl 0 16 wt and f 0 094 wt point to its closed system ascent from 400 to 250 mpa 12 to 6 5 km depth b s l however the predominance of euhedral olivine phenocrysts with common reverse zoning cores fo 76 78 and rims fo 78 80 and decrepited inclusions shows that most of the erupted basalt derived from a slightly more evolved crystallizing body of the same magma that was invaded by the uprising primitive melt prior to erupting the few preserved inclusions in these olivines indicate pre eruptive storage of that magma body at about 5 km depth b s l in coherence with seismic data we propose that the 2001 flank eruption resulted from gradual overpressuring of etna s shallow plumbing system due to the influx of volatile rich primitive basalt that may have begun several months in advance we find that this basalt is much richer in alkalis 2 0 wt k 2 o and has higher s cl 2 0 but lower cl k and cl f ratios than all pre 1970s etnean lavas 1 4 wt k 2 o s cl 1 5 as further exemplified by melt inclusions in entrained olivine xenocrysts combining these new observations with previously published data we argue that the 2001 basalt represents a new alkali rich basic end member feeding mt etna only few amount of which had previously been extruded during a 1974 peripheral eruption and more recently during brief paroxysmal summit events over the last three decades this new magma has progressively mixed with and replaced the former k poorer trachybasalts filling the plumbing system leading to extrusion of gradually more primitive and alkali richer lavas its geochemical singularities cannot result from shallow crustal contaminations instead they suggest the involvement of an alkali richer but cl poorer arc type component during recent magma genesis beneath etna

early proterozoic volcanogenic massive sulfide deposits in wisconsin an overview the early proterozoic greenstone belt of northern wisconsin possesses some of the best volcanogenie volcanic hosted massive sulfide potential in north america a 100 millionton resource of base and precious metal bearing mineralization distributed in 13 or more deposits and occurrences and clustered in three districts has been identified in the belt host rocks for the volcanogenie massive sulfide mineralization are part of the 144 mi long east west trending ladysmith rhinelander metavolcanic complex which consists of various greenschists amphibolites cherty iron formations and sericite to quartz sericite schists these 1880 to 1860 ma metamorphic rocks are concealed beneath pleistocene glacial cover development of the flambeau deposit initiation of mine permitting for the lynne deposit and reactivation of the crandon project indicate that the belt will receive a higher level of activity than in the past geologic and geophysical data compiled since the late 1960s define three depositional environments each containing volcanogenie massive sulfide mineralization in the 1880 to 1860 ma ladysmith rhinelander metavolcanic complex 1 a main volcanic arc sequence the structural core of the complex 2 a laterally equivalent and or younger back are basin volcanic volcaniclastic succession that includes a series of marie volcanic piles and 3 major felsic volcanic centers in the back arc basin and along the flanks of the main volcanic arc volcanogenie massive sulfide mineralization in all three depositional environments includes 1 syngenetic and epigenetic strata bound to stratiform massive sulfide mineralization within along the flanks of or near the top of the felsic volcanic centers 2 syngenetic strata bound to stratiform massive sulfide mineralization associated with cherty magnetic iron formation within the main volcanic arc sequence and 3 epigenetic stringer sulfide mineralization and syngenetic stratiform massive sulfide mineralization associated with marie volcanic piles developed within the back arc basin identified volcanogenie massive sulfide deposits and occurrences are classified by metal content into three groups cu zn cu and zn pb cu each group exhibits various styles of mineralization which include sheets mounds stacked lenses and replacements potentially economic deposits are associated with felsic volcanic centers and sulfide bearing meta argillite formations that are favorable stratigraphic units deposited before after or during the ore forming event s stratigraphic correlations supported by lead isotope data suggest that most volcanogenie massive sulfide deposits in the greenschist succession formed in a narrow time interval

fold axes oblique to the regional plunge and proterozoic terrane accretion in the southern lake superior region abstract the niagara fault is believed to represent the suture between a magmatic arc terrane and a passive margin assemblage which were tectonically juxtaposed about 1 85 ga ago during the penokean orogeny accretion related deformation is concentrated within an 12 km wide belt that straddles the suture a distinctive structural feature of this belt is the rotation of early fold axes toward parallelism with the direction of bulk extension resulting in a great circle stereonet distribution of fold axes within a vertical axial plane rocks of both arc and passive margin assemblages crop out in this more highly strained belt but there has been no material transfer between them across the fault structural style and metamorphic assemblages demonstrate deep level beneath the brittle ductile transition erosion of the terrane accretion boundary in the southern lake superior region there is some evidence for pure shear during the accretion event but we are unable to evaluate the amount or sense of simple shear

evolution of quartz cementation and burial history of the eau claire formation based on in situ oxygen isotope analysis of quartz overgrowths abstract individual quartz overgrowths in siltstone of the late cambrian eau claire formation fm are systematically zoned in oxygen isotope ratio 18 o in situ analysis of 18 o was performed with 3 and 15 m beam spots by secondary ion mass spectrometer sims on detrital quartz grains and quartz overgrowths these results from thin lenses within impermeable mudstones reflect samples that were sealed from basin wide fluid flow and compliment previous studies of more permeable sandstones individual grains of detrital quartz dq are homogeneous in 18 o the average 18 o values in fine grained detrital quartz in mudstones and siltstones and in coarser grained quartz in the eau claire fm mt simon and st peter sandstones ss are essentially identical at 18 o 10 vsmow suggesting that detrital quartz is dominantly igneous in origin the 18 o values of overgrowth quartz oq of buried samples from the illinois basin are higher and quartz overgrowths are systematically zoned outward from the detrital cores these gradients are similar to those from the underlying mt simon ss and are best explained by increasing temperatures during burial pressure solution is evident in thin section and may have supplied significant silica for overgrowths in contrast to the deeply buried samples from the illinois basin quartz overgrowths in samples from the wisconsin arch are homogeneous and higher in 18 o those overgrowths are interpreted as quartz cements formed in a near surface environment based on these 18 o oq results and the modeled thermal history during burial of the basin the earliest formed quartz overgrowths were produced at low temperature from low 18 o water around 450 ma the 18 o values in traverses of single overgrowths decrease by up to 9 1 showing continued cementation with increased burial pressure solution and heating until 250 ma in traverses of the outermost zone of some overgrowths oxygen isotope values become constant or increase slightly possibly due to clay mineral dehydration reactions or later fluid infiltration we present a new cementation and basin evolution model in which the 18 o of cement correlates to the age of formation and the late overgrowths formed between 270 and 250 ma during and or after the migration of brines that formed the pb zn deposits of the upper mississippi valley district 270 ma cementation around 270 ma would have reduced permeability possibly ending the flow of ore forming brines

paleoecology of late glacial peats from the bering land bridge chukchi sea shelf region northwestern alaska insect fossils and pollen from late pleistocene nonmarine peat layers were recovered from cores from the shelf region of the chukchi sea at depths of about 50 m below sea level the peats date to 11 300 11 000 yr b p and provide a limiting age for the regional pleistocene holocene marine transgression the insect fossils are indicative of arctic coastal habitats like those of the mackenzie delta region mean july temperatures 10 6 14 c suggesting that 11 000 yr ago the exposed chukchi sea shelf had a climate substantially warmer than modern coastal regions of the alaskan north slope the pollen spectra are consistent with the age assignment to the birch interval 14 000 9000 yr b p the data suggest a meadow like graminoid tundra with birch shrubs and some willow shrubs growing in sheltered areas

age and origin of authigenic k feldspar in uppermost precambrian rocks in the north american midcontinent authigenic k feldspar occurs widely in the north american midcontinent in an alteration profile developed on uppermost precambrian rocks in the study areas of west central wisconsin and southeast missouri the alterationprofiles are kaolinitic and interpreted as former saprolite formed by weathering prior to deposition of upper cambrian sandstone k feldspar in granitic alteration profiles of west central wisconsin occurs either as coarse grained red crystals and veins replacing kaolinite or as overgrowths and fine grained crystals in pore space of partly altered granite in a granitic profile of southeast missouri k feldspar replaces primary feldspar and probably kaolinite in a diabasic profile k feldspar is disseminated and forms veins in saprolite and it replaces the outer 3 5 cm of core stones dating was conducted with the 4 0 ar 3 9 ar method using incremental heating observed spectral types are plateaus 6 near plateaus 3 undulatory 14 and stair step 5 undulatory patterns are attributed chiefly to recoil and integrated ages of these are usually within the error of plateau ages where present indicating a balanced enrichment depletion of 3 9 ar due to recoil stair step spectra are attributed to severe recoil plateau 4 0 ar 3 9 ar ages of 446 427 ma late ordovician and silurian were obtained from coarse grained k feldspar replacing kaolinite in wisconsin suggesting a duration of the alteration episode of 19 m y however potentially accurate nonplateau age measurements integrated and near plateau ages suggest that alteration continued for a considerable time thereafter possibly to ca 399 395 ma early devonian integrated 4 0 ar 3 9 ar ages of ca 362 ma late devonian and or early mississippian were obtained from fine grained k feldspar plateau ages of ca 450 late ordovician were obtained from k feldspar of the diabase profile in missouri duration of k feldspar alteration in this region was at least 16 m y and may have been as long as 52 m y the late devonian early mississippian k feldspar formed at temperatures of 100 c from saline fluid averaging 10 nacl equivalent and having a 1 8 o value of 3 5 this brine may have originated from the michigan basin east central iowa basin and or the illinois basin coincident with the acadian orogeny the middle ordovician to early devonian dates of k feldspar do not generally correspond in time with orogenic activity at the continental margin and the mechanism s for forming the k feldspar are uncertain fluid sources proposed for some or all of the k feldspar include the michigan basin taconic mountains reelfoot rift illinois basin and midcontinent epeiric seas middle ordovician k feldspar of missouri very likely formed at elevated temperatures but evidence of fluid temperature is lacking for other pre late devonian k feldspar

the rapid heating defocused beam technique a co2 laser based method for highly precise and accurate determination of δ18o values of quartz abstract we describe a laser fluorination technique specifically for quartz that allows both high accuracy and high precision determination of oxygen isotope ratios regardless of grain size the rapid heating defocused beam technique rhd utilizes a defocused 32 w co 2 laser at full power which delivers 17 w 20 w mm 2 to the sample to quickly react quartz in contrast other recent laser fluorination studies use a tightly focused laser beam and slow heating i e sharp and kirschner 1995 fouillac and girard 1996 kirschner and sharp 1997 and find laser analysis of fine grained quartz to be inaccurate three quartz standards nbs 28 qz bra and qz cwru were analyzed using the rhd technique at the university of wisconsin to test for grain size effects rhd analyses show no correlation between grain size and 18 o values and are in excellent agreement with 18 o values obtained using conventional fluorination techniques additional analyses of the same quartz standards performed at university of wisconsin using slow heating and a focused beam yield 18 o values that are both less precise and significantly up to 0 8 lower than the accepted values attempts to use the rhd technique with a 20 w co 2 laser which delivers 8 w 10 w mm 2 to the sample at brgm were unsuccessful probably due to insufficient power density of the defocused beam we conclude that the rhd technique yields excellent accuracy and precision but that power densities of 15 20 w mm 2 may be necessary across a large part of the sample surface we recommend the use of lasers with at least 30 w of power

late pleistocene holocene oceanographic variability in the okhotsk sea geochemical lithological and paleontological evidence sedimentary geochemical and paleontological data extracted from a sediment core taken from the central okhotsk sea record climatic and sedimentary changes over the past 100 ky benthic foraminiferal oxygen isotope record and accelerator mass spectrometry ams 14c data provide the basis for the core age chronology planktonic and benthic foraminiferal 18o and 13c measurements magnetic susceptibility ice rafted debris and coarse fraction content carbonate and organic carbon content and diatom and pollen spectra show major changes in regional climate sea surface conditions ice extent and sedimentary regime which are correlated with the global glacial interglacial changes of marine isotope stages mis 1 through 5 3 regional cooling and intensification of winter sea ice formation during the last glaciation increased the northern shelf surface water density and sea of okhotsk intermediate water soiw formation in addition to major milankovitch scale changes lithological geochemical and paleontological indices also show suborbital oscillations in okhotsk sea hydrology sedimentation and regional climate these shorter term oscillations are characterized by coupled maxima in ice rafted debris and sediment coarse fraction lithodynamic indices ldi values and most are associated with cold events involving enhanced winter ice formation and intensification of soiw and north pacific intermediate water npiw formation the terminations of ldi maxima were induced by climate warming and reductions in ice formation and were accompanied by sharp decreases in planktonic foraminiferal 18o during the glacial terminations of mis 2 and 4 however the onset of suborbital scale ldi maxima occurs close to sharp negative 18o shifts in planktonic foraminifera 18opf associated with climate warming in these special cases the ldi maxima occurred under warm climate and rising sea levels and did not lead to increases in soiw or npiw ventilation

pleistocene glaciations in chukotka russia moraine mapping using satellite synthetic aperture radar sar imagery abstract using satellite synthetic aperture radar sar imagery we are able to identify many glacial features on the russian landscape that were previously unobservable by scientists outside russian institutes observations from sar imagery provide information on glacial extent moraine morphology and non sedimentary glacial features such as valley morphology and flow direction moraine sequences in several areas of chukotka record multiple pleistocene glacial events moraine position along with several morphologic characteristics such as relative degradation and surface slope can be determined from sar imagery and used to estimate relative age of glacial features by conducting comparative studies on moraines of known age in alaska we are able to estimate the ages of moraines in russia and develop a framework for the correlation of glacial history across bering strait our study of these images suggests that the last major glaciation late wisconsin was much less extensive than older pleistocene events whose marks remain on the landscape beyond the younger moraines

geomorphological correlation of late pleistocene glacial complexes of western and eastern beringia abstract many fundamental problems exist in comparing the chronology and correlation of late pleistocene glaciations between western and eastern beringia however geomorphological analysis complemented by palynological studies and radiocarbon age estimates of glacial complexes found in the ulakhan chistai bolshoi annachag and pekulney ranges northeastern russia and the kigluaik mountains and brooks range alaska allow for broad comparisons the data clearly confirm that in all regions the latest late pleistocene glaciation 24 0 10 5 ka was restricted in extent and characterized by well defined valley glaciers and coalescing valley glacier complexes emanating from local mountain centers differences in glacier size were due to local orographic and climatological characteristics

emergent marine record and paleoclimate of the last interglaciation along the northwest alaskan coast the last interglacial high sea level stand the pelukian transgression of isotope substage 5e is recorded along the western and northern coasts of alaska by discontinuous but clearly traceable marine terraces and coastal landforms up to about 10 m altitude the stratigraphy indicates that sea level reached this altitude only once during the last interglacial cycle from the type area at nome to st lawrence island in the bering sea to the eastern limit of the beaufort sea pelukian deposits contain extralimital faunas indicating that coastal waters were warmer than present amino acid ratios in molluscs from these deposits decrease to the north toward barrow consistent with the modern regional temperature gradient fossil assemblages at nome and st lawrence island suggest that the winter sea ice limit was north of bering strait at least 800 km north of its present position and the bering sea was perennially ice free microfauna in pelukian sediments recovered from boreholes indicate that atlantic water may have been present on the shallow beaufort shelf suggesting that the arctic ocean was not stratified and the arctic sea ice cover was not perennial for some period in coastal regions of western alaska spruce woodlands extended westward beyond their modern range and in northern alaska on the arctic coastal plain spruce groves may have entered the upper colville river basin the flaxman member of the gubik formation on the alaskan arctic coastal plain was deposited during marine isotope substage 5a and records the breakup of an intra stage 5 ice sheet over northwestern keewatin

full glacial upland tundra vegetation preserved under tephra in the beringia national park seward peninsula alaska the nature of the full glacial vegetation of beringia has been the subject of a great deal of investigation and debate here we present a reconstruction of an intact example of the full glacial upland vegetation of part of the northern seward peninsula at one point in time the area was blanketed by more than 1 m of tephra ca 18 000 14c bp ca 21 500 cal bp and the former land surface was preserved in the permafrost the discovery of the land surface provides a unique opportunity to study a fossil ecosystem preserved in situ macrofossils were used to reconstruct the vegetation growing at several sites on the buried land surface the macrofossil assemblages indicate a vegetation characterized by graminoids and forbs with the occasional occurrence of salix arctica the vegetation was dominated by kobresia myosuroides other sedges carex and grasses with a ne scale mosaic related to snow accumulation and moisture availability overall the vegetation was a closed dry herb rich tundra grassland with a continuous moss layer growing on calcareous soil that was continuously supplied with loess nutrient renewal by loess deposition was probably responsible for the relatively fertile vegetation and the occurrence of a continuous mat of acrocarpous mosses good physiognomic analogues can be suggested but no exact modern vegetational analogues have been found probably because the full glacial environment and climate with loess deposition do not occur today 2000 elsevier science ltd all rights reserved

pleistocene raised marine deposits on wrangel island northeast siberia and implications for the presence of an east siberian ice sheet two previously undocumented pleistocene marine transgressions on wrangel island northeastern siberia question the presence of an east siberian or beringian ice sheet during the last glacial maximum lgm the tundrovayan transgression 459 000 780 000 yr b p is represented by raised marine deposits and landforms 15 41 m asl located up to 18 km inland the presence of high sea level 64 000 73 000 yr ago the krasny flagian transgression is preserved in deposits and landforms 4 7 m asl in the krasny flag valley these deposits and landforms were mapped dated and described using amino acid geochronology radiocarbon optically stimulated luminescence electron spin resonance oxygen isotopes micropaleontology paleomagnetism and grain sizes the marine deposits are eustatic and not isostatic in origin all marine deposits on wrangel island predate the lgm indicating that neither wrangel island nor the east siberian or chukchi seas experienced extensive glaciation over the last 64 000 yr

late paleoproterozoic climate tectonics and metamorphism in the southern lake superior region and proto north america evidence from baraboo interval quartzites abstract red supermature quartzites of the baraboo interval of the lake superior region contain detrital zircon that ranges in age from 1782 to 1712 ma deposition clearly occurred after the geon 18 penokean orogeny these late paleoproterozoic sedimentary rocks consist largely of quartz kaolinite or pyrophyllite and hematite detrital feldspar and muscovite are rare or absent their chemical index of alteration ranges from 96 8 to 98 6 among the most chemically mature clastic sediments in the geological record the quartzites are underlain by mature feldspar free paleosols accounting for the absence of feldspar in the overlying sediments and indicating the presence of first cycle quartzose detritus such physical and chemical characteristics imply that late paleoproterozoic deposition in the lake superior region occurred in a stable tectonic setting with subdued topographic relief in a warm humid climate folding and low grade metamorphism of the quartzites is thought to reflect 1630 ma foreland

response to grosswald and hughes 2004 brigham grette et al 2003 chlorine 36 and 14c chronology support a limited last glacial maximum across central chukotka northeastern siberia and no beringian ice sheet and gualtieri et al 2003 pleistocene raised marine deposits on wrangel island northeastern siberia implications for arctic ice sheet history

north american ice sheet reconstructions at the last glacial maximum abstract the areal extent of the last glacial maximum lgm ice sheets is well known in north america but there is no direct geological proxy for ice sheet thickness or volume uncertainties associated with glaciological and geophysical reconstructions give widely varying estimates of north american ice sheet nais volume at lgm in an effort to quantify the uncertainty associated with glaciological reconstructions we conducted a suite of 190 numerical simulations of the last glacial cycle in north america prescribing different climatic mass balance glaciologic and isostatic treatments for the least constrained model variables lgm ice sheet reconstructions were evaluated using the well established geologic record of ice sheet area and southern extent at lgm dyke and prest 1987 these constraints give a subset of 33 simulations that produce reasonable lgm ice cover in north america ice sheet dispositions and the associated parameter settings in this subset of tests provide insight into the plausible range of nais thickness form and mass balance regime at lgm ice volume in this subset of tests spans a range of 28 5 38 9 10 15 m 3 at lgm with a predominant cluster at 32 36 10 15 m 3 taking floating ice and displaced continental water into account this corresponds to 69 94 m eustatic sea level msl more than 75 of the accepted tests fall in the range 78 88 msl we argue that this is a plausible estimate of the volume of water locked up in the nais at lgm

involvement of variably sourced fluids during the formation and later overprinting of paleoproterozoic au cu mineralization insights gained from a fluid inclusion assemblage approach abstract au cu mineralized quartz veins of the reef deposit wisconsin usa originally formed prior to or early in the paleoproterozoic penokean orogeny in central north america as either the root zone of a gold rich vms deposit or in an orogenic gold setting nearly 400 m y later magmatic hydrothermal fluids associated with a continental scale anorogenic magmatic event remobilized mineralization within the veins and still later during the paleozoic remobilization and perhaps upgrading of au and other metals occurred in response to circulation of fluids associated with mississippi valley type deposits found in overlying supracrustal rocks fluid constraints on the formation of the reef deposit and later overprinting over a 1 5 b y timeframe are examined using the fluid inclusion assemblage fia approach distinctive assemblages are examined on individual merit each offering individual stories to aid in our understanding of the protracted development of the reef deposit presumably primary fluid inclusions in au and cu bearing quartz sulfide veins that formed during the paleoproterozoic event show h2o co2 ch4 nacl compositions based on microthermometry and laser raman spectroscopy possibly primary h2o nacl and secondary h2o co2 ch4 nacl fia formed prior to regional deformation and are recognized as discrete relict and neonate clusters the intersection of isochores from the highest density neonate inclusions of either fluid composition indicates re equilibration at lower amphibolite conditions during regional deformation quartz hosted secondary fluid inclusion assemblages characterized by h2o ch4 and co2 ch4 compositions formed at high temperatures and have not been re equilibrated and are interpreted to post date regional metamorphism these fia occur along healed fractures with chalcopyrite mineralization these inclusions are likely associated with fluid circulation driven by emplacement of the adjacent wolf river batholith ca 1 45 ga that altered pyrite to pyrrhotite and remobilized or emplaced chalcopyrite at temperatures as high as 700 c this reduced fluid was in equilibrium with locally observed graphitic sediments secondary lower temperature

two early proterozoic successions in central wisconsin and their tectonic significance geological mapping of 7 500 km 2 of previously virtually unmapped precambrian rocks in central wisconsin suggests the presence of two early proterozoic sedimentary volcanic plutonic successions evidence for the two successions includes structural stratigraphic metamorphic and lithologic relations that are consistent throughout the area the older succession unconformably overlies archean rocks it is characterized by amphibolite facies metamorphism folding about west to northwest plunging isoclinal f 1 fold axes with more open coaxial f 2 folding basal quartzite and pelitic sediments of the older succession are overlain by volcanic rocks and intruded by syntectonic tonalite granodiorite and trondhjemite plutons the younger succession consists primarily of a greenschist facies calc alkaline basalt rhyolite sequence that unconformably overlies the older amphibolite facies rocks structures in the greenschist sequence trend northeasterly with fold axes that plunge easterly the plutonic rocks are dominantly syntectonic to late tectonic granites and quartz monzonites with only minor tonalite in most areas the two successions have been juxtaposed along major faults the older amphibolitic sequence may correlate with the chocolay group farther north in the lake superior region and the younger green schist rocks with the menominee and or baraga groups if this correlation is correct the deformation metamorphism and intrusion of the green schist succession would have occurred during the penokean orogeny metamorphism to amphibole rank isoclinal folding and tonalite intrusion of the older succession would be a major pre penokean erogenic event within the early proterozoic that may correlate with the post chocolay pre menominee break in northern michigan wisconsin and minnesota we suggest that this earlier event has been unrecognized and that it may be a significant part of the early proterozoic history of the lake superior region

new evidence for high discharge to the chukchi shelf since the last glacial maximum using chirp subbottom profiling across the chukchi shelf offshore nw alaska we observed a large incised valley that measures tens of kilometers in width the valley appears to have been repeatedly excavated during sea level lowering however the two most recent incisions appear to have been downcut during the last sea level rise suggesting an increase in the volume of discharge modern drainage from the northwestern alaskan margin is dominated by small low discharge rivers that do not appear to be large enough to have carved the offshore drainage the renewed downcutting and incision during the deglaciation and consequent base level rise implies there must have been an additional source of discharge paleoprecipitation during deglaciation is predicted to be at least 10 less than modern precipitation and thus cannot account for the higher discharge to the shelf glacial meltwater is the most likely source for the increased discharge

effects of paleoweathering and supergene activity on volcanogenic massive sulfide vms mineralization in the penokean volcanic belt northern wisconsin michigan and east central minnesota usa implications for future exploration abstract three cycles of paleoweathering and supergene activity have been identified within the penokean volcanic belt pvb of northern wisconsin michigan and east central minnesota usa these cycles are responsible for significant subaerial weathering erosion oxidation and most importantly local supergene au ag and cu enrichment that has a major economic impact upon volcanogenic massive sulfide vms style mineralization within the pvb the paleoweathering profile regolith saprolite that developed on the exposed pvb surface now marks an angular unconformity with stratigraphically overlying late paleoproterozoic baraboo interval quartzites and late cambrian sandstones differential uplift of the pvb surface is a direct result of the 1850 ma compressional tectonic event that occurred during the penokean orogeny the uplifted pvb paleosurface experienced its first weathering cycle in the mid to late paleoproterozoic vms mineralization near the paleosurface was exhumed and affected during this protracted cycle which ceased upon deposition of baraboo interval quartzites 1788 1714 ma further uplift and subsequent unroofing of the quartzites during the mazatzal orogeny 1650 1630 ma initiated a second paleoweathering cycle that culminated within the neoproterozoic cambrian transition during this cycle of accelerated and uninterrupted paleoweathering new and surviving supergene au ag cu enriched profiles geochemically matured over exhumed mineralized sections in terrains with favorable fault block movements supergene systems that developed during both cycles were highly acidic environments low protolith reactivity and high hypogene pyrite concentrations promoted acidity of supergene fluids thus facilitating enhanced cu au and ag mobility in those systems that lacked sufficient carbonate zn and pb were lost to surrounding aqueous regimes the second paleoweathering cycle ended with the deposition of overlying late cambrian sandstone 497 485 4 ma erosional retreat of the overlying paleozoic sequence exposed many of these supergene deposits to a third possibly brief paleoweathering cycle before the onset of quaternary continental glaciation vms profiles not protected by sandstone outliers or within down dropped fault blocks were glacially eroded of the 14 or more known vms deposits and occurrences in the belt four have preserved or partially preserved paleoweathering profiles the most significant are at the flambeau and back forty deposits where au ag enriched indigenous gossans with extensive or local underlying supergene enriched cu sulfide zones have developed over hypogene massive sulfide horizons these profiles demonstrate efficient cumulative or multicyclic au ag and cu enrichment to ore grades although commonly small 2 million tonnes such supergene enriched deposits are generally shallow allowing for development by low cost open pit methods and production of exceptionally high grade direct shipping copper and or gold ores as such the buried pvb unconformity is considered a prime exploration target that is highly prospective for new discoveries of commercially viable supergene enriched vms resources

u pb geochronology of the wolf river batholith north central wisconsin evidence for successive magmatism between 1484ma and 1468ma abstract single grain zircon u pb age determinations were completed on individual phases of the mesoproterozoic anorogenic wolf river batholith wrb of wisconsin and the nearby wausau syenite complex in order to a define the age more precisely and accurately b determine whether there is a resolvable age difference within units of the wrb and c determine whether the wausau syenite complex is coeval with any or all parts of the wrb u pb results for many individual zircon grains from the wrb plot near concordia and yield ages ranging from 1468 4 ma to 1484 2 ma plutons of the northeastern lobe of the wrb peshtigo monzonite hager porphyry belongia granite and high falls granite have a weighted average crystallization age of 1470 3 1 2 ma which is younger than the main complex plutons wolf river granite wiborgite porphyry red river granite and waupaca granite which yields a weighted average crystallization age of 1475 6 1 7 ma excluding one sample of wolf river granite from hogarty which yields an age of 1484 2 ma two samples from the main complex also contain zircons with younger apparent ages of 1470 1471 ma these younger grains may reflect late stage alteration of some zircons coeval with emplacement of the northeastern lobe the wausau syenite and the nine mile granite of the nearby wausau syenite complex 1522 ma and 1506 ma respectively are significantly older than the wrb and definitely not coeval or comagmatic the syenite complex may be a precursor to the larger wrb magmatism sm nd t dm ages for most wrb samples indicate crust formation ages from 1 8 ga to 1 9 ga compatible with formation of the magmas from late paleoproterozoic penokean crust one unit which locally intrudes archean gneiss has a small component of that older rock involved in its evolution the two wausau complex units have younger tdm ages and appear to have incorporated slightly greater amounts of juvenile constituents

dynamic recrystallization of quartz correlation between natural and experimental conditions quartz veins in the eastern tonale mylonite zone italian alps were deformed in strike slip shear due to the synkinematic emplacement of the adamello pluton a temperature gradient between 280 c and 700 c was effected across this fault zone the resulting dynamic recrystallization microstructures are characteristic of bulging recrystallization subgrain rotation recrystallization and grain boundary migration recrystallization the transitions in recrystallization mechanisms are marked by discrete changes of grain size dependence on temperature differential stresses are calculated from the recrystallized grain size data using paleopiezometric relationships deformation temperatures are obtained from metamorphic reactions in the deformed host rock flow stresses and deformation temperatures are used to determine the strain rate of the tonale mylonites through integration with several published flow laws yielding an average rate of approximately 10 14s 1 to 10 12s 1 the deformation conditions of the natural fault rocks are compared and correlated with three experimental dislocation creep regimes of quartz of hirth tullis linking the microstructures of the naturally and experimentally deformed quartz rocks a recrystallization mechanism map is presented this map permits the derivation of temperature and strain rate for mylonitic fault rocks once the recrystallization mechanism is known

the respiratory health hazards of volcanic ash a review for volcanic risk mitigation studies of the respiratory health effects of different types of volcanic ash have been undertaken only in the last 40 years and mostly since the eruption of mt st helens in 1980 this review of all published clinical epidemiological and toxicological studies and other work known to the authors up to and including 2005 highlights the sparseness of studies on acute health effects after eruptions and the complexity of evaluating the long term health risk silicosis non specific pneumoconiosis and chronic obstructive pulmonary disease in populations from prolonged exposure to ash due to persistent eruptive activity the acute and chronic health effects of volcanic ash depend upon particle size particularly the proportion of respirable sized material mineralogical composition including the crystalline silica content and the physico chemical properties of the surfaces of the ash particles all of which vary between volcanoes and even eruptions of the same volcano but adequate information on these key characteristics is not reported for most eruptions the incidence of acute respiratory symptoms e g asthma bronchitis varies greatly after ashfalls from very few if any reported cases to population outbreaks of asthma the studies are inadequate for excluding increases in acute respiratory mortality after eruptions individuals with pre existing lung disease including asthma can be at increased risk of their symptoms being exacerbated after falls of fine ash a comprehensive risk assessment including toxicological studies to determine the long term risk of silicosis from chronic exposure to volcanic ash has been undertaken only in the eruptions of mt st helens 1980 usa and soufriere hills montserrat 1995 onwards in the soufriere hills eruption a long term silicosis hazard has been identified and sufficient exposure and toxicological information obtained to make a probabilistic risk assessment for the development of silicosis in outdoor workers and the general population a more systematic approach to multi disciplinary studies in future eruptions is recommended including establishing an archive of ash samples and a website containing health advice for the public together with scientific and medical study guidelines for volcanologists and health care workers

the flin flon paleosol revisited a ca 1 85 ga paleosol developed on seafloor altered mafic rocks is preserved beneath continental sandstones and conglomerates of the missi group near flin flon manitoba previous work has focused

late weichselian ice sheets in arctic and pacific siberia abstract interpretation of space images coupled with field data on glacial geomorphology and glacial geology of northern eurasia have provided compelling evidence for a continuous late weichselian ice sheet covering the entire arctic margin of the continent in addition to the scandinavian ice sheet three ice sheets of the same order the karan east siberian and beringian are identified within the major eurasian ice sheet also there is evidence and other considerations suggesting a former ice sheet in the sea of okhotsk ice spreading centers of the ice sheets were situated on the continental shelves off the siberian coasts thus we can term the ice sheets siberian so far the conventional stratigraphic approach to the problem of siberian glaciation has proven fruitless and yielded nothing but uncertainty while geomorphological studies have discovered a wealth of glacial landforms in arctic siberia it was these landforms and their spacing that made the existence of former siberian ice sheets evident the east siberian ice sheet rested on the shelves of the eastern laptev and east siberian seas and its flow was directed radially including up the yana and indigirka rivers the beringian ice sheet was grounded on the chukchi bering and beaufort sea shelves overriding the chukchi and seward peninsulas from the north and flowing through the bering strait it was continued by a thick floating ice shelf buttressed by the submarine aleutian commander ridge the okhotsk ice sheet was grounded on the okhotsk shelf specific gemorphic signatures of marine ice sheets the glacially cut corners have been identified on all promontories jutting out into the bering and okhotsk seas the beringian and okhotsk ice sheets are consistent with the results of deep sea drilling in the adjacent north pacific during leg 145 of d v joides resolution

an automatic procedure to forecast tephra fallout tephra fallout constitutes a serious threat to communities around active volcanoes reliable short term forecasts represent a valuable aid for scientists and civil authorities to mitigate the effects of fallout on the surrounding areas during an episode of crisis we present a platform independent automatic procedure with the aim to daily forecast transport and deposition of volcanic particles the procedure builds on a series of programs and interfaces that automate the data flow and the execution and subsequent postprocess of fallout models firstly the procedure downloads regional meteorological forecasts for the area and time interval of interest filters and converts data from its native format and runs the calmet diagnostic model to obtain the wind field and other micro meteorological variables on a finer local scale 3 d grid defined by the user secondly it assesses the distribution of mass along the eruptive column commonly by means of the radial averaged buoyant plume equations depending on the prognostic wind field and on the conditions at the vent granulometry mass eruption rate etc all these data serve as input for the fallout models the initial version of the procedure includes only two eulerian models hazmap and fall3d the latter available as serial and parallel implementations however the procedure is designed to incorporate easily other models in a near future with minor modifications on the model source code the last step is to postprocess the outcomes of models to obtain maps written in standard file formats these maps contain plots of relevant quantities such as predicted ground load expected deposit thickness and for the case of or 3 d models concentration on air or flight safety concentration thresholds

investigation of the complex dynamics and structure of the 2010 eyjafjallajokull volcanic ash cloud using multispectral images and numerical simulations 1 we investigated the structure and evolution of the 2010 eyjafjallajokull volcanic cloud and its dispersal over iceland and europe integrating satellite multispectral images and numerical simulations data acquired by medium resolution imaging spectrometer meris and advanced spaceborne thermal emission and reflection radiometer aster have been analyzed to quantify the cloud extent and composition the vol calpuff dispersal code was applied to reconstruct the transient and 3 d evolution of the cloud source parameters estimated on the base of available a posteriori volcanological data sets have been used quantitative comparisons between satellite retrievals and modeling results were performed for two selected instants of time during the first and third eruptive phases on a regional scale sensitivity of the model to initial volcanological conditions has been analyzed at continental scale several complex non intuitive features of cloud dynamics have been highlighted and strengths and limitations of the adopted methods identified the main findings are the level of quantitative agreement between satellite observations and numerical results depends on ash cloud composition particle sizes and concentration with better agreement for smaller particles and higher concentrations the agreement between observations and modeling outcomes also depends on the temporal stability of volcanological conditions and the complexity of the meteorological wind field the irregular dispersion of ash as reconstructed from satellite data and numerical modeling can be well explained by the different response of particle sizes to strong vertical wind shear and by resuspension processes acting at ground level eruptive source conditions are the main source of uncertainty in modeling especially during an ongoing crisis and at long range scales