mass and heat flux of volcanic gas discharging from the summit crater of iwodake volcano satsuma iwojima japan during 1996 1999 abstract volcanic gas of iwodake has been discharged continuously from high temperature 900 c maximum fumaroles and a degassing vent which formed on the central floor of the summit crater after 1994 although most of the high temperature fumaroles located on the crater wall before 1991 many fumaroles appeared on the crater floor associated with the vent opening suggesting a shift of thermal activity from the peripheral to the central crater a large amount of volcanic gas has been discharged from the fumaroles and vent since heat has been transferred from ascending gas to the surrounding soil a region showing a surface temperature anomaly has developed around the fumaroles and vent to quantify iwodake thermal activity heat and volcanic gas mass fluxes were estimated during 1996 1999 using infrared thermal images and plume velocity and temperature data which were observed by a pitot tube and thermocouple the estimated gas mass flux was compared with the cospec data to investigate the accuracy of our estimation the gas mass flux had been decreased from 230 kg s in october 1996 to 30 kg s in november 1999 although the vent diameter had increased from 20 to 70 m during the same period this mass flux variation had indicated the decline of degassing rate the degassing depth was estimated from the volcanic gas mass flux and temperature the depth showed a tendency of magma head migration to shallower depth during 1996 1999 which was consistent with the drastic change of the surface manifestation

variations in mode of formation and temperature of oceanic deep waters over the past 125 000 years marked changes in the deep water temperature of the different oceanic basins during the past 125 kyr are revealed by a detailed comparison of the oxygen isotopic composition ofbenthicforaminiferafrom sediment cores taken from the norwegian sea and the pacific atlantic and southern oceans the last interglacial deep water temperatures were similar to the modern ones at the 5e 5d transition around 115 kyr bp the deep water temperatures dropped below approximately 0 c in the pacific and southern indian oceans in the atlantic ocean the deep water temperature dropped in 2 successive steps at 115 and 75ky bp the global ocean deep water temperatures were in the 0 to 1 c range for the whole of the last ice age isotope stages 4 2

microbial deposits in the aftermath of the end permian mass extinction a diverging case from the mineral mountains utah usa the lower triassic mineral mountains area utah usa preserves diversified smithian and spathian reefs and bioaccumulations that contain fenestral microbialites and various benthic and pelagic organisms ecological and environmental changes during the early triassic are commonly assumed to be associated with numerous perturbations productivity changes acidifica tion redox changes hypercapnia eustatism and temperature changes post dating the permian triassic mass extinction new data acquired in the mineral mountains sediments provide evidence to decipher the relationships between depositional environments and the growth and distribution of microbial structures these data also help to understand better the controlling factors acting upon sedimentation and community turnovers through the smithian early spathian the studied section records a large scale depositional sequence during the dienerian spathian interval during the transgression depositional environments evolved from a coastal bay with continental deposits to intertidal fenestral microbial limestones shallow subtidal marine sponge microbial reefs to deep subtidal mud dominated limestones storm induced deposits microbialite sponge reefs and shallow subtidal deposits indicate the regression three microbialite associations occur in ascending order i a red beds microbialite association deposited in low energy hypersaline supratidal conditions where microbialites consist of microbial mats and poorly preserved microbially induced sedimentary structure ii a smithian microbialite association formed in moderate to high energy tidal conditions where microbialites include stromatolites and associated carbonate grains oncoids ooids and peloids and iii a spathian microbialite association developed in low energy offshore conditions that is preserved as multiple decimetre thick isolated domes and coalescent domes data indicate that the morphologies of the three microbialite associations are controlled primarily by accommodation hydrodynamics bathymetry and grain supply this study suggests that microbial constructions are controlled by changes between trapping and binding versus precipitation processes in variable hydrodynamic conditions due to the presence of numerous metazoans associated with microbialites throughout the smithian increase in accommodation and spathian decrease in accommodation the commonly assumed anachronistic character of the early triassic microbialites and the traditional view of prolonged deleterious conditions during the early triassic time interval is questioned

variations in permafrost thickness in response to changes in paleoclimate solutions to the stefan problem for the motion of the base of ice bearing permafrost in response to changes in paleoclimate were obtained using perturbation finite difference and finite element methods paleotemperature models were used to investigate the thickness response to compare solution methods to determine the current state of the permafrost and to determine constraints on the models the perturbation and finite difference methods used the approximation of linear temperature profiles while the finite element method did not there was a transient thickness response of about 41 kyr implying that paleotemperature records of greater length are needed for models and that the permafrost loses its memory of past conditions for much longer times faster thawing rates slower freezing rates and greater variations in thickness were found for the perturbation and finite difference solutions compared to the finite element solution these results appear to be caused by the simplifying assumptions in the former solutions a lag about 20 kyr exists between changes in surface temperature and thickness response and a small thermal offset is apparent in the finite element solution small asymmetries exist in the freezing and thawing rates and the thickness response paleotemperature models based on ice cores predict current permafrost thicknesses that are too large models with the long term mean surface temperature of permafrost within a few degrees of the current value of 11 c and with the last glacial period temperatures no more than 6 8 c lower are compatible with current prudhoe bay conditions these include models developed for east siberia from isotopic profiles in deep sea sediments and for barrow alaska modified for prudhoe bay these models predict that the permafrost thickness at prudhoe bay varied by about 10 or less 60 m over the last glacial cycle freezing and thawing rates were less than 6 mm yr 1 at present this permafrost should be near its long term equilibrium thickness and thawing at 1 mm yr 1

biostratigraphy of the last glacial period in europe the european early weichselian early wurmian is characterized by two long and relatively warm interstadials brorup and odderade which can be traced and correlated with certainty across large parts of europe the amersfoort interstadial described earlier from the netherlands has been included in the brorup and represents the older part of it both great interstadials were forested in north west central and southern europe in the north conifer forests prevailed giving way towards the south to deciduous forests the climatic gradient was distinctly steeper mainly due to southward displacement of the gulf stream the two great interstadials are synchronous with the isotopic stages 5a and 5c in the deep sea cores subsequent to eemian brorup and odderade and from within the context of a continuous series two additional and clearly delimited interstadials have been recorded in a new standard profile from oerel nw germany these are now described as the oerel and glinde interstadials they were not forested and belong to the early pleni weichselian the lower one oerel can probably be correlated with the 3rd weichselian wurmian interstadial in southern central europe ognon ii durnten samerberg 3 while the upper one glinde has so far no known counterpart for the younger pleni glacial it is assumed that there was a long phase during which it was not too cold the formation of humic layers during this phase took place at different times partly due to local edaphic factors so that the relevant 14c dates show a wide scatter the hengelo and denekamp interstadials represent only slight ameliorations which facilitated the formation of shrub tundra and can be recorded in certain regions only

triassic latemar cycle tops subaerial exposure of platform carbonates under tropical arid climate the triassic latemar platform in the dolomites italy is the site of several ongoing controversies perhaps the most interesting debate focuses on apparent cyclic deposition within the latemar platform whose nature and duration are still open to debate further disagreement concerns the lack of meteoric diagenesis related isotope shifts at cycle tops that bear circumstantial petrographic evidence for subaerial emergence here an evaluation of the nature of latemar cycle tops is presented combining evidence from previous work and new field petrographic and geochemical data cycle tops are ranked according to increasing exposure duration and spatial extent type i surfaces lacking unequivocal evidence of prolonged supratidal conditions type ii dolomite caps formed in warm evaporitic intertidal lagoonal waters followed by exposure of perhaps intermediate duration type iii clastic rich red calcareous horizons with some showing platform wide extent representing prolonged supratidal conditions and type iv discontinuities in tepee belts genetically related to type ii and iii surfaces but likely representing shorter lived exposure stages petrographic and geochemical criteria indicate that most diagenesis occurred in the shallow marine and burial domain whilst an extensive meteoric overprint of cycle tops is lacking this is underlined by the scarcity of meteoric diagenetic fabrics such as gravitational cements that where present are here interpreted as marine vadose in origin the scarcity of carbon and oxygen isotope signatures commonly assigned to subaerial exposure stages is best explained in the context of mid triassic climate the low latitude tropical but arid setting of the latemar situated in the western extension of the tethys ocean its isolation from nearby continental areas and overall short term emergence episodes are in agreement with a limited degree of meteoric alteration of most cycle tops high amounts of aeolian clastic material beneath some cycle tops along with high fe and mn elemental abundances argue for intermittent subaerial conditions this study proposes an enhancement of the classical allan and matthews 1982 isotope model for subaerial exposure under strongly arid climates as the subaerial exposure nature of latemar cycle tops and therefore eustasy as the cause for cyclicity have been previously challenged due to the lack of meteoric induced isotopic signatures the outcome of this study is of significance for the ongoing latemar stratigraphic controversy

geochemical and isotopic constraints on the diagenetic history of a massive stratal late cambrian royer dolomite lower arbuckle group slick hills sw oklahoma usa abstract the diagenetic history of the late cambrian massive royer dolomite from the lower arbuckle group slick hills sw oklahoma usa has been evaluated through comprehensive geochemical analyses the dolomite probably formed during early diagenesis from contemporaneous late cambrian seawater evidenced by similar 87 sr 86 sr ratios from 0 70891 to 0 70913 of most 70 dolomite samples to coeval late cambrian seawater from 0 7089 to 0 7092 very light 18o values 10 2 to 12 9 pdb however indicate that the dolomite was significantly modified during burial correlation of various geochemical parameters sr fe 18o and 87 sr 86 sr demonstrates that dolomite samples with increased modification are characterized by lower sr and higher fe concentrations lighter 18o values and less radiogenic 87 sr 86 sr ratios this correlation coupled with the light 18o values of the dolomite demonstrates that meteoric water recharged into overlying carbonates was responsible for burial modification of the dolomite geochemical comparison of the dolomite with associated limestone and quantitative modelling of 18o sr and 87 sr 86 sr variation during water rock interaction suggest that the dolomite underwent long lasting modification the timing of meteoric modification was coincident with the development of regional overlying unconformities corresponding to emergence of the carbonate platform similar diagenetic modification has probably been responsible for 18o depletion and trace element modification of ancient dolomites in many other areas although many of these dolomites have been interpreted to have formed either in mixing zone environments or in subsurface environments

climate controlled early dolomite late triassic cyclic platform carbonates hungary abstract the 2 km thick late triassic hungarian carbonate platform has a completely dolomitized lower part and a limestone dominated upper part the platform succession is made up of meter scale possibly precessional 20 ky carbonate cycles in the lower platform main dolomite cycles are completely dolomitized and capped by caliche laminites and pisolites in the upper platform dachstein limestone dolomite is confined to laminite caps of cycles that are bounded by clayey paleosols most of the dolomitization in the platform interior occurred early in tidal flat settings during each high frequency cycle subtidal dolomites are slightly coarser grained are low in fe2 and mn2 and have the heaviest 18o signature this indicates they formed from evaporative oxidizing brines sourced from supratidal flats intertidal supratidal dolomites are fine grained commonly fe2 and or mn2 rich and slightly enriched in 18o compared to the marine calcite cement they formed from marine water that was weakly to moderately reducing dachstein paleosols have light 18o and 13c signatures reflecting meteoric soil waters repeated emergence stabilized the dolomites to low sr2 and na dolomite similar to cenozoic platform dolomites in contrast to these early cyclic dolomites coarse grained platform margin dolomites with very low mn2 and fe2 and light 18o signatures formed as thermally driven warm oxidizing marine water associated with jurassic rifting of the neo tethys pennini ocean circulated through the margin early dolomitization of cycles may have been controlled by high frequency sea level changes but the overall vertical distribution of early dolomite on the platform does not reflect long term eustasy rather the intense dolomitization of the lower platform reflects a semiarid hot subtropical seasonal setting and megamonsoonal climate global cooling and increased humidity toward the latest triassic and early jurassic inhibited pervasive early dolomitization leaving the upper platform largely as limestone

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

north atlantic sea surface temperatures for the last 1 1 million years summary a 1 2 ma time series of north east atlantic sea surface temperature sst has been assembled from the spliced record of piston core k 708 7 0 68 0 ma and hydraulic piston cores taken in nearby dsdp hole 552a 1 2 0 68 ma a no analogue fauna precludes making credible sst estimates in the interval 1 2 1 1 ma but the record above 1 1 ma is suitable for sst estimates and related time series analysis the amplitude of sst variation is considerably higher in the brunhes than in the upper matuyama this is due both to colder glacial sst minima after 0 85 ma and to increasingly warm interglacial sst maxima from 0 7 to 0 4 ma the dominant periodicity in the sst signal is centred near 95 000 years it increases in amplitude by a factor of four from the bottom of the record to the top with the largest increase occurring between 0 7 and 0 4 ma this suggests a relatively gradual evolution of 100 000 year power over half a million years of the late quaternary rather than a single abrupt change at 0 9 ma significant but progressively smaller spectral peaks occur at periods of 54 000 41 000 31 000 23 000 and 19 000 years both the 54 000 year and 31 000 year signals may be a response to insolation forcing by minor obliquity terms long term 18 o records show small responses by the ice sheets at or near these two periods indicating the probable initial response of the climate system to these insolation rhythms in phase relationships between 18 o and sst at these periods suggest that the ice sheets then impose these rhythms on the ocean with no lag the mechanism by which such small insolation and ice volume signals become enhanced in the sst record is not clear

correlations between so2 flux seismicity and outgassing activity at the open vent of villarrica volcano chile 1 the characteristics of the open vent activity of villarrica volcano chile were studied in detail by integrating visual observations of the lava lake analysis of the seismic tremor and measurements of so2 flux the outgassing activity comprises a persistent gas plume emission from the bottom of the crater as well as frequent explosive events three main styles of bubble bursting were identified at the surface of the active lava lake seething magma small short lived lava fountains and strombolian explosions seething magma consists of continual burst of relatively small bubbles a few meters in diameter with varying strength over the entire surface of the lava lake small lava fountains seen as a vigorous extension of seething magma commonly have durations of 20 120 s and reach 10 40 m high above the lava lake correlations between seismicity and visual observations indicate that the seismic tremor is mostly caused by the explosive outgassing activity furthermore for different periods between 2000 and 2006 during which the activity remained comparable the real time seismic amplitude measurement system rsam and so2 emission rates show a very good correlation higher so2 emissions appeared to be related to higher levels of the lava lake stronger bubble bursting activity and changes in the morphology and texture of the crater floor background low levels of activity correspond to a lava lake located 80 m below the crater rim small and or blocky morphology of the roof seismic amplitude rsam lower than 25 units few volcano tectonic earthquakes and daily averages of so2 emissions lower than 600 mg d

pt effects of pleistocene glacial periods on permafrost gas hydrate stability zones and reservoir of the mittelplate oil field northern germany abstract during the past two million years low surface temperatures as well as episodically advancing ice sheets from scandinavia acted on the subsurface pt regime of northern germany their likely effects on the petroleum system of schleswig holstein were investigated for the entire quaternary mean annual ground temperature magt was reconstructed at a resolution of 1000 years by calibrating oxygen isotope records from odp site 659 to the climate of northern germany of the past 120 kyr the resulting magt trend served as input to an ice sheet model and a permafrost model along a 2d section crossing the petroleum bearing south western part of schleswig holstein here advances and retreats of the scandinavian ice sheet during saalian and elsterian glaciation stages were reconstructed maximum ice thicknesses of up to 1700 m and up to 20 periods of regional permafrost in northern germany were reconstructed for the past 1 25 million years based on a basal heat flow of 50 mw m 2 permafrost thicknesses exceeded 100 m during most of these periods temporarily extending down to depths of more than 300 m favourable surface temperatures and long durations of cold periods provided favourable conditions for onshore gas hydrate stability zones at mittelplate implementing these glacial dynamics into 2d basin modelling petromod ies aachen germany of the mittelplate oil field reveals five phases of gas hydrate stability at depths down to 750 m the latest of these events occurred during the weichselian about 20 kyr ago the effect of the ice sheets on pore pressure in the subsurface strongly depends on the hydraulic boundary conditions at the ice base e g frozen vs temperate ice sheet base excess pore pressure in the reservoir of more than 10 mpa during ice overriding is possible and probable the calculated temperature effect of the pleistocene cooling on the mittelplate reservoir is in the range of 3 7 c even today temperature in the reservoir is still lowered by about 4 c in comparison to pre pleistocene times despite the fact that a significant influence of glacial effects on petroleum generation can be ruled out at mittelplate we state that pt effects in reservoirs related to glacial processes in formerly glaciated areas have been underestimated in the past

coupling of vampers within iloveclim experiments during the lgm and last deglaciation the vampers vrije universiteit amsterdam permafrost snow model has been coupled within iloveclim an earth system model this advancement allows the thermal coupling between permafrost and climate to be examined from a millennial timescale using equilibrium experiments during the last glacial maximum 21 ka and transient experiments for the subsequent deglaciation period 21 11 ka it appears that the role of permafrost during both stable and transitional glacial interglacial climate periods is seasonal resulting in cooler summers and warmer winters by approximately 2 c maximum this conclusion reinforces the importance of including the active layer within climate models in addition the coupling of vampers also yields a simulation of transient permafrost conditions not only for estimating areal changes in extent but also total permafrost gain loss

the evolution of a dynamic geological system the support of a gis for geochemical measurements at the fumarole field of vulcano italy abstract the island of vulcano aeolian arc southern italy has displayed several periods of volcanic unrest since the end of the last eruption 1890 we report here results obtained from a long term survey concerning variations of both the steam output and the exhaling surface area at the summit crater fumarolic field of la fossa the field measurements analysed in a geographical information system gis show a highly dynamic volcanic system in which deep variations in the geochemistry and the temperature of the released fluids were accompanied by fluctuations in the mass output of steam and the topography of the crater field the use of a gis facilitated digitized reconstructions of maps of the crater field in addition to analysis of the steam flux data the fumarolic field expanded its surface area from 50 m 2 in 1983 to more than 2400 m 2 in 1995 accompanied by an increase in steam output from 152 to about 1400 tonnes per day the possibility that the observed phenomena are related to volcano tectonic activity and to magma uprising is taken into consideration

impact of diagenesis and low grade metamorphosis on isotope δ26mg δ13c δ18o and 87sr 86sr and elemental ca mg mn fe and sr signatures of triassic sabkha dolomites abstract dolomite is a common rock forming mineral in the geological record but its value as archive of ancient seawater 26 mg signatures and their variations in time is at present underexplored unknown factors include the sensitivity of 26 mg ratio to processes in the diagenetic and low grade metamorphic domain this paper documents and discusses the first detailed 26 mg data set from early diagenetic and burial dolomites samples come from the upper triassic hauptdolomit dolomia principale the dolomites italy and include coeval dolomicrites that underwent differential burial diagenesis and low grade metamorphosis in a temperature range between about 100 and more than 350 c magnesium isotope data are complemented by dolomite 13 c 18 o and 87 sr 86 sr isotope ratios as well as ca mg mn fe and sr elemental abundances and data on the dolomite crystal structure as indicated by dolomicrite 87 sr 86 sr ratios and petrographic evidence sabkha calcian d1 dolomites precipitated from evaporated seawater and stabilized at an early marine pore water diagenetic stage to d2 dolomites analysed here with increasing burial temperature dolomite 26 mg ratio scatter in the data set decreases with increasing mg ca ratio and degree of order specifically 26 mg ratio variability is reduced from 0 36 2 at burial temperatures beneath 100 c to about 0 14 2 at temperatures in excess of 350 c respectively with mean 26 mg values ranging constantly near 1 9 this suggests that at least for the rock buffered system investigated here dolomicrite 26 mg proxy data are conservative and preserve near pristine values even at elevated burial temperatures at present the main element of uncertainty is the mg isotope fractionation factor between evaporated seawater and dolomite a possible solution to this problem includes the compilation of data from modern sabkha environments including pore water and calcian dolomite 26 mg isotope signatures

real time measurement of volcanic so 2 emissions validation of a new uv correlation spectrometer flyspec a miniaturized lightweight and low cost uv correlation spectrometer the flyspec has been devel oped as an alternative for the cospec which has long been the mainstay for monitoring volcanic sulfur dioxide fluxes field experiments have been conducted with the flyspec at diverse volcanic systems including masaya nicaragua po as costa rica stromboli etna and vulcano italy villarica chile and kilauea usa we present here those validation measurements that were made simultaneously with cospec at kilauea between march 2002 and february 2003 these experiments with source emission rates that ranged from 95 to 1 560 t d 1 showed statistically identical results from both instruments so2 path concentrations ranged from 0 to 1 000 ppm m with average correlation coefficients greater than r 2 0 946 the small size and low cost create the opportunity for flyspec to be used in novel deployment modes that have the potential to revolutionize the manner in which volcanic and industrial monitoring is performed

from tabular to rhombohedral dolomite crystals in zechstein 2 dolostones from scharzfeld sw harz germany a case study with combined cl and ebsd investigations abstract tabular dolomite crystals found within dolomite rhombs have been investigated by cathodoluminescence cl microscopy and spectroscopy combined with electron backscatter diffraction ebsd for the first time the dolomites formed in the upper permian stassfurt carbonate ca2 at the southern margin of the german polish zechstein basin cathodoluminescence petrography of the dolostone succession revealed that the dolomites developed in four phases electron backscatter diffraction analysis reveals tabular crystal growth during the two first generations while the last two generations are characterized by rhombohedral crystal shapes the tabular dolomite cement crystals and their microcrystalline equivalents in matrix and components have a stoichiometric composition with good to very good lattice ordering manganese and iron contents of the tabular crystals are low and their carbon and oxygen isotope composition confirms an early diagenetic dolomite formation under marine evaporitic conditions from precursor carbonates of upper permian age cl spectroscopy reveals that the tabular dolomite generation 1 has a very high percentage of mn2 on the ca lattice position which results in a visually yellowish green cl emission although relatively increased mn2 contents at the ca lattice position appear to be rather common in evaporitic dolomites the combination of a tabular crystal shape and a preferred input of mn2 at the ca lattice position is a remarkable phenomenon as tabular dolomite crystals so far are exclusively reported from evaporitic diagenetic settings they could be the result of a high mg ca ratio which blocks c axis orientated growth of dolomite crystal the occurrence of well ordered dolomite of which the geochemical zoning can be studied in such detail is rare for the earliest synsedimentary stages of dolomite formation in marine environments because these early stages commonly consist of not or badly ordered ca dolomites a primary geochemical zoning of such dolomite usually gets lost during stabilisation and transformation to better ordering and stoichiometry

ftir remote sensing of fractional magma degassing at mount etna sicily abstract the chemical composition of volcanic gas emissions from each of the four summit craters of mount etna was measured remotely in may 2001 using a fourier transform infrared ftir spectrometer operated on the upper flanks of the volcano the results reveal constant hci hf ratio but distinct so2 hc1 and so2 hf ratios in the emitted gases which in the light of melt inclusion data for etna basalts can be interpreted in terms of escape of gases from partially and variably degassed magma at different depths beneath the summit gases released from the three main summit craters bocca nuova voragine and northeast had an identical composition controlled by bulk degassing of a single magma body that had previously lost c 25 0 of its original sulphur the similar gas composition at all three main craters suggests that these are connected to a central conduit system that branches at relatively shallow depth measurements of the bulk volcanic plume on the same day c 7 km downwind show that degassing from these craters dominated the total gas output of the volcano and that no significant chemical evolution occurred within the plume over a time scale of c 12 min weaker gas emissions from the southeast crater were comparatively depleted in so2 so2 hc1 and so2 hf ratios a factor of two lower implying that this crater is fed either by a separate conduit or by a branch of the central conduit whose geometry favours solubility controlled volatile fractionation still lower so2 hc1 and so2 hf ratios measured for residual degassing of a lava flow erupted from the southeast crater verify the lower solubility and earlier escape of sulphur compared to halogens at etna fractional magma degassing is also implied by strong chemical contrasts between the bulk volcanic plume and fissure gas emissions measured during the july august 2001 flank eruption these results highlight the ability of ftir spectrometry to detect fine spatial and temporal variations in magma degassing processes and thereby constrain models of shallow plumbing systems introduction magmas contain dissolved volatiles h20 co2 s c1 f etc with differing solubility behaviom which gradually reach a saturation pressure and exsolve into a separate gas phase bubbles during magma ascent and crystallization this volatile phase plays a central role in magmatic and volcanic processes e g anderson 1975 and its chemical composition changes from depth to the surface according to the pressure controlled solubility behaviour of each volatile species but also as a function of the dynamics of magma supply and ascent sparks 2003 this volume in fact gas bubbles may rise with either the same velocity as surrounding magma allowing continuous gas melt equilibration and single step bulk gas emission at the surface or with a higher velocity thereby reaching the surface independently of the parental magma batch e g sparks 1978 vergniolle jaupart 1986 in the latter case chemical equilibrium between gas and magma may be inhibited sustained high gas fluxes in excess of lava production on basaltic volcanoes such as etna and stromboli typically require a separated bubble flow and in the long term convective renewal of volatile rich magma from depth francis

volcanic steam output directly measured in fumaroles the observed variations at vulcano island italy between 1983 and 1987 the mass of steam emitted by the fumaroles of the crater of vulcano aeolian islands italy was evaluated by using a direct measuring method measurements were effected with this method between 1983 and 1987 in nine field campaigns the results of which are given in this paper the steam flux measurements were performed by an instrument expressly designed for steam condensation the estimates of the thermal energy transported daily by the steam gave values of up to 10e12 j the sharp variations in the total mass outputs recorded in 1984 and 1985 are here interpreted as being a consequence of the probable accumulation of fluid pressure at depth during the evolution of volcanic activity the different results obtained from the various areas of the fumarolic field during the evolutionary phases have led to the hypothesis that different subsystems exist that feed the fumaroles and that their activity is triggered by volcano tectonics this method can be applied in the evaluation of both fumarolic steam and thermal energy outputs and therefore it is particularly useful in geothermal exploration in the evaluation of the environmental impact of volcanic degassing and in the forecasting of volcanic eruptions the evaluation of the steam output is also useful for quantifying the release of other gaseous species and giving univocal interpretations regarding their variations in concentrations furthermore this direct method provides a new way of calibrating the flux estimates effected by other telemetric techniques lidar cospec etc

visible and invisible volcanic plumes 1 volcanic plumes discharging from craters or fumaroles are usually observed at active volcanoes these plumes are divided into two categories from their appearance one is a transparent invisible plume composed of volcanic gases and the other is a white visible plume containing water droplets in addition to the vapors the difference in plume visibility is caused by changes in the conditions that control water condensation in the plume we present a simple model describing the condition for the water condensation in the plume as a function of the exit temperature volcanic gas composition atmospheric temperature and humidity and tested the model with a field observation the result indicates that we can estimate the exit temperature from the visibility of the plume under known atmospheric conditions

microbially catalyzed dolomite formation from near surface to burial abstract over the past century a number of models have been developed to explain the vast stratigraphic distribution of authigenic dolomite these models include hydrogeological geochemical and geomicrobiological interpretations that shed light on kinetic constraints on low temperature dolomite formation and in particular how certain microbes can overcome such limitations in this review we focus on the direct and indirect mechanisms by which microbes facilitate the nucleation and shallow burial diagenetic stabilization of dolomite in marine sediments we also consider the likely effects of local and global scale biogeochemical perturbations over the distribution and activities of subsurface microbes and thus potentially over the stratigraphic distribution of dolomite considering the many advances that have been made in the fields of geomicrobiology and biogeochemistry during the past 20 years investigating the important role microbes play in sedimentary systems will undoubtedly contribute to a more complete interpretation of dolomite formation in the rock record

shallowing upward carbonate cycles in the belingwe greenstone belt zimbabwe a record of archean sea level oscillations abstract shallowing upward carbonate cycles in the 2650 ma cheshire formation belingwe greenstone belt zimbabwe closely resemble their proterozoic and phanerozoic counterparts the cycles form part of a karstified carbonate ramp sequence that is overlain by and grades basinward into siliciclastic turbidites a single section of 74 cycles 1 5 m average thickness was studied in detail two basic cycle types are recognized both with an asymmetric facies stacking pattern one cycle type contains open marine subtidal shale at the base shale is intercalated with storm generated sandstone and grainstone beds that become more common and thicken upward indicating progressive shallowing wave rippled ooid intraclast grainstone beds and bedsets overlie shale or form the base of the second cycle type grainstone formed at or above fair weather wave base as shoreface sand sheets in an agitated shallow subtidal setting microbial laminites constitute the top of both cycle types and are interpreted as peritidal deposits in the upper part of the studied section microbial boundstones with aragonite pseudomorphs are intercalated with or overlie laminites and formed in a supratidal environment the vertical facies distribution within a cycle is indicative of rapid submergence followed by gradual shallowing of relative sea level high frequency eustatic sea level changes are favored over an autocyclic mechanism and tectonically induced allocyclicity as the controlling mechanism for the cyclicity hierarchies of stratigraphic cyclicity occur on different scales and may be a result of the combined effects of several orders of sea level oscillations cycle recurrence ratios correspond well to the milankovitch frequencies calculated for the late archean suggesting that orbital climatic forcing may have been in operation in archean times

reservoir geology of devonian carbonates and chert implications for tertiary recovery dollarhide field andrews county texas 1 devonian strata of the thirtyone formation at dollarhide field andrews county texas originally contained 144 million bbl of oil in place with 18 6 million bbl produced by primary recovery 39 3 million bbl projected to be produced by secondary recovery waterflood and 27 4 million bbl projected to be produced by tertiary recovery co 2 flood devonian strata contain five main lithologies from bottom to top 1 carbonate chert mudstone deposited in a basinal environment 2 burrowed chert dolomite 10 35 ft or 3 11 m thick which accumulated as siliceous spiculitic wackestone and carbonate mud in a low energy slope environment 3 laminated tripolitic chert 0 65 ft or 0 20 m thick deposited as a sponge spicule sand in submarine channels and fans on the slop 4 bioclastic limestone 47 92 ft or 14 28 m thick which accumulated as crinoidal grainstones in moderate to high energy outer shelf environments and 5 upper dolomite 50 90 ft or 15 27 m thick with dolomitized peloidal grainstones deposited in high energy shallow subtidal to intertidal environments and thin chert beds deposited in supratidal environments deposition of the 180 ft thick 55 m reservoir section occurred during a basinward progradation of shelf and slope facies porosity within devonian strata is controlled mainly by depositional facies porosity occurs in two stratigraphic zones separated by the tight bioclastic limestone the lower porosity zone laminated tripolitic chert and part of the burrowed chert dolomite 0 100 ft or 0 30 m thick is relatively homogeneous not stratified with high porosity commonly 25 35 moderate permeability 5 20 md and short fractures causing elevated permeabilities near the bottom the lower reservoir is thick in fan shaped and elongate areas where sponge spicules were deposited on submarine fans and in submarine channels the upper porosity zone 0 90 ft or 0 27 m thick is within the upper dolomite and is heterogeneous with stratified porosity that bifurcates coalesces and pinches out in several di ferent intervals the relative homogeneity and moderate permeability of the lower reservoir should help achieve a uniform sweep during co 2 flooding higher permeabilities near the base of the lower reservoir should minimize co 2 override thereby improving sweep efficiency the thinner more heterogeneous less continuous more stratified more permeable pay in the upper reservoir will result in more rapid and less uniform co 2 sweep

steam output from fumaroles of an active volcano tectonic and magmatic hydrothermal controls on the degassing system at vulcano aeolian arc the results from measurements of extensive parameters steam output and exhaling surface area taken at the crater fumarolic field of vulcano island aeolian arc southern italy are reported along with a detailed description of the measuring method the steam emission rate increased by 1 order of magnitude during the observation time 1983 1995 while its concentration in the released gases was only slightly changed during the same period the total exhaling surface expanded from 50 m2 to more than 2400 m2 and evolved following preferential trends that coincide with the main tectonic structures of the island the observed peaks in steam output show a positive correlation with episodes of volcanic activity unrest the temporal increase of steam output and the observed development in the exhaling surface areas are consistent with a volcano tectonic triggering of the exhaling activity particularly the peaks in the steam output are interpreted as a consequence of degassing from an active magma slowly moving toward the surface

dolomite formation in caribbean islands driven by plate tectonics abstract postdepositional dolomite occurs in the shallow subsurface of several caribbean islands in tertiary and pleistocene carbonates e g on barbados grand cayman jamaica and st croix recent investigations have interpreted these dolomites as relatively early diagenetic formations from chemically modified seawater mainly on the basis of petrography stratigraphic association and stable isotope values interpretations of the hydrologic regimes during dolomitization vary and usually include freshwater seawater mixing thermal or density driven convection of seawater or a combination thereof this paper offers two alternative interpretations based on the relatively low sr isotope ratios of the dolomites 0 7085 to 0 7092 and their proximity to active plate margins dolomitization may have been driven by plate tectonics i e either by thermal convection of pore fluids at active spreading centers or by tectonic expulsion of fluids from accretionary prisms the dolomitizing solution was seawater that was enriched in 86sr by magmatic hydrothermal solutions or by interaction with siliciclastics in an accretionary prism respectively

fumarole monitoring with a handheld infrared camera volcan de colima mexico 2006 2007 abstract this paper describes a methodology for the monitoring of fumarole temperatures at medium ranges 6 km using a handheld infrared camera wavelength range 8 13 5 m as a relationship between fumarole temperatures gas flux and volcanic activity has been demonstrated by a number of studies fumarole temperature data has a potential use as a monitoring tool volcan de colima is an andesitic stratovolcano with a 300 m diameter summit crater formed by the destruction of the 2004 lava dome by a series of explosions in 2005 between january 2006 and august 2007 sequences of thermal images were recorded from a viewpoint 6 km to the north during regular 24 48 hour monitoring excursions the temperatures of fumaroles on the crater rim and the ground surface on the volcano s flanks were measured a methodology was developed to remove data affected by clouds or volcanic water vapour based on rates of temperature change and scatter within the data for the remaining data it is demonstrated mathematically that at this range typical variations in atmospheric transmissivity will affect the apparent temperatures by 2 c while a 25 change in fumarole heat flux would change it by 5 10 c the mean night time apparent temperature of the fumaroles was calculated for each excursion and showed an irregular decline over the 19 month period subtracting the radiant heat flux of flank rocks from those of the fumaroles removes seasonal variations and gives the clearest view of trends in the fumarole heat flux a sharp drop in fumarole temperature during february 2007 coincided with the emergence of a lava dome in the crater the declining fumarole temperature is interpreted to reflect decreasing gas flux from the crater in line with a change in eruptive regime from frequent small ash rich explosions to slow effusion of lava

the reconstruction of former ice sheets and their mass balance characteristics using a non linearly viscous flow model on a utilise un modele d ecoulement visqueux non lineaire pour etudier l influence des caracteristiques du bilan de masse des conditions aux limites sur le fond rocheux et de la topographie sous glaciaire sur l etendue et la forme des calottes glaciaires le but est de rendre possible l utilisation des traces geologiques de l extension glaciaire passee pour reconstituer les paleoclimats

late pliocene to holocene platform evolution in northern belize and comparison with coeval deposits in southern belize and the bahamas the full text is not available on soar access this article via the commercial databases licensed by university libraries http libcat wichita edu vwebv holdingsinfo searchid 817 reccount 30 recpointer 1 bibid 1334578

dolomitization of holocene mg calcite supratidal deposits ambergris cay belize dolomitized crusts and associated sediments 845 2925 yr old on ambergris cay belize central america compose a significant portion of the holocene sediment section on many supratidal flats the dolomitic sections are as thick as 0 7 m and contain an average of 70 calcic dolomite dolomite occurs as a replacement of high mg calcite micrite matrix and allochems and as passively precipitated cements isotopic analyses suggest that dolomitization appears to be promoted primarily by reactions of the magnesian calcite supratidal sediments with essentially near normal marine waters the effects of seasonal influxes of meteoric and hybrid fluids however are also clearly evident in the crusts as indicated by isotopes dolomite crystal etching the selective leaching of aragonite and the local loss of mg 2 from the host micrite and included skeletal fragments the amounts rapid rates of dolomitization and initial mg calcite mineralogy of the sediments make the ambergris cay supratidal flats exceptional in the holocene and this area may be a model for the genesis of some ancient peritidal dolomites

sedimentological record of subglacial conditions and ice sheet dynamics of the vistula ice stream north central poland during the last glaciation abstract deposits of the vistula ice stream draining the scandinavian ice sheet during the last glaciation were investigated at four field sites in north central poland using micro and macroscale features the study reveals several till units with specific structural textural and lithological characteristics the individual till units are either macroscopically massive or bedded and the contacts between the units are either sharp or transitional the nature of the contacts with the underlying sediments ductile deformation structures largely undeformed clayey clasts tectonic lamination thin horizontal stringers of sorted sediments ploughing marks boulder pavements and striated upper surfaces of pebbles in the till indicate both bed deformation and enhanced basal sliding under high subglacial water pressure conditions it is suggested that the till is a hybrid deposit generated by some combination of lodgement deformation and ploughing punctuated by periods of basal decoupling the depth of deformation at any point in time was thinner up to several decimetres than the maximum till thickness c 2 5 m the ice sliding velocity estimations indicate velocities of less than 100 to over 2000 m yr 1 which suggests an unstable and highly dynamic ice lobe consistent with spatial variability of till characteristics sand wedges in the deposits beneath the till and the nature of the till bed interface indicate permafrost under the advancing ice sheet we suggest that under the increasing ice thickness a layer of thawed water saturated sediment formed on top of the still frozen ground due to inefficient drainage and contributed to ice streaming by promoting pervasive deformation and basal sliding

dolomitization time boundaries and unconformities examples from the dolostone of the taurus mesozoic sequence south central turkey abstract a mesozoic carbonate unit in the taurus platform consists of thick dolostone sequences with both massive thick beds and thinner beds intercalated with limestone dolomite preferentially replaced micrite in the original carbonate in an initial phase of dolomitization dolomicrite formed which later as through dissolution and recrystallization resulted in clear dolomite crystals and dolosparites an additional type of dolomite is dolosparite filling voids these dolomite crystals represent either replacement of precursor calcite cement or growth into void space dissolution of late coarsely crystalline dolosparite precipitation of saddle crystals local dedolomitization and some late calcite cement in the voids all indicate short term atmospheric exposure of the sequence during or after the main dolomitization event dolomitization does not appear to be restricted to a specific environment there is no evidence that the dolomite formation occurred in an evaporite supratidal or high intertidal setting our present state of knowledge does not allow an unequivocal explanation of the dolomitization event of massive platform dolomites however the association of dolomitization with sea level fluctuations such as repetitive and minor transgressive and regressive periods might be a clue to the mechanism for the formation of thick dolomite beds in the taurus mesozoic platform as noted by the increasing of the dolostone limestone ratio near the time boundaries triassic jurassic and jurassic cretaceous stable isotope data support mostly marine derived solutions as the dolomitizing fluid marine solutions can be the only source of the large quantities of mg 2 ions needed for dolomitization of massive platform dolomite as was suggested by land 1985 and given and wilkinson 1987

modeling sub sea permafrost in the east siberian arctic shelf the laptev sea region 1 models of sub sea permafrost evolution vary significantly in employed physical assumptions regarding the paleo geographic scenario geological structure thermal properties initial temperature distribution and geothermal heat flux this work aims to review the underlying assumptions of these models as well as to incorporate recent findings and hence develop an up to date model of the sub sea permafrost dynamics at the laptev sea shelf in particular the sub sea permafrost model developed here incorporates thermokarst and land ocean interaction theory and shows that the sediment salinity and a temperature based parametrization of the unfrozen water content are critical factors influencing sub sea permafrost dynamics from the numerical calculations we suggest development of open taliks may occur beneath submerged thaw lakes within a large area of the shelf

h2o emission rate by the volcanic plume during the 2000 2002 miyakejima volcanic activity 1 extremely intense degassing at miyakejima volcano japan was observed after the 2000 eruption the h2o emission rate was estimated using a record of infrared thermal images at 400 kton day in november 2000 by april 2002 h2o emission rate had decreased exponentially to 100 kton day the h2o emission rate varied in parallel with the so2 emission rate except for the early stage in september 2000 the ratio of h2o to so2 emission rate after november 2000 remained constant at about 10 which is consistent with the h2o so2 ratio in the magma the large rate of h2o and so2 emission requires efficient degassing at shallow depth the agreement between the gas composition of the plume and that of dissolved volatiles in melt inclusions indicates h2o discharged from the vent was mostly magmatic in origin after november 2000

dolomite occurrence evolution and economically important associations abstract dolomite is not a simple mineral it can form as a primary precipitate a diagenetic replacement or as a hydrothermal metamorphic phase all that it requires is permeability a mechanism that facilitates fluid flow and a sufficient supply of magnesium dolomite can form in lakes on or beneath the shallow seafloor in zones of brine reflux and in early to late burial settings it may form from seawater from continental waters from the mixing of basinal brines the mixing of hypersaline brine with seawater or the mixing of seawater with meteoric water or via the cooling of basinal brines bacterial metabolism may aid the process of precipitation in settings where sulfate reducing species flourish and microbial action may control primary precipitation in some hypersaline anoxic lake settings dolomite is a metastable mineral early formed crystals can be replaced by later more stable phases with such replacements repeated a number of times during burial and metamorphism each new phase is formed by the partial or complete dissolution of an earlier dolomite this continual re equilibration during burial detracts from the ability of trace elements to indicate depositional conditions and resets the oxygen isotope signature of the dolomite at progressively higher temperatures because subsurface dolomite evolves via dissolution and reprecipitation a bed of dolomite can retain or create porosity and permeability to much greater burial depths and into higher temperature realms than a limestone counterpart dolomitization also creates new crystals with new rhomb growth following the dissolution of less stable precursors repetition of this process without complete pore cementation can generate intercrystalline porosity a number of times in the rock s burial history intercrystalline porosity is a highly interconnected style of porosity that gives dolomite reservoirs their good fluid storage capacity and efficient drainage the fact that many dolomite reservoirs formed via brine reflux means that they sit beneath an evaporite seal in both platform and basinwide evaporite settings the same association of evaporites sulfate source and entrained hydrocarbons means that burial conditions are also suitable for thermochemical sulfate reduction and the precipitation of base metals this tends to occur at higher temperatures 60 c 80 c and so the resulting dolomites tend to be ferroan and consist of saddle shaped crystals

modelling of permafrost thickness during the late glacial stage in france preliminary results research on permafrost in france has concentrated on field evidence of fossil permafrost and the mapping of its possible distribution few attempts have been made to estimate permafrost thickness studies devoted to this subject in north america and siberia have shown that permafrost may be very thick several hundred metres may be rapidly laid down in 2000 years in northwest canada and causes complex water flow patterns between the base of the permafrost and the soil surface using the gelsol code developed by the laboratoire central des ponts et chaussees central laboratory of the french department of public works for geotechnical purposes this paper presents the first results of modeling permafrost development at depth these preliminary tests show the influence of parameters such as mean annual ground temperature heat flow thermal conductivity related to lithology and water content of the rocks involved on permafrost depth during the last glacial cycle weichselian the results from sim

meteoric modification of early dolomite and late dolomitization by basinal fluids upper arbuckle group slick hills southwestern oklahoma 1 thick massive dolomite units from the upper arbuckle lower ordovician peritidal carbonate sequence slick hills southwestern oklahoma provide insight into two important problems 1 modification of early dolomite and 2 late dolomitization early dolomite volumetrically dominant is nonluminescent to dully luminescent 87 sr 86 sr ratios of most early dolomite samples are similar to both early ordovician seawater and associated limestones consistent with an early origin from coeval seawater all early dolomite samples are characterized by low delta 18 o values 5 1 to 10 0 o oo pdb indicating postdepositional modification meteoric water buffered by younger carbonates with lower 87 sr 86 sr ratios was probably responsible for modification because lower sr concentrations delta 18 o values and 87 sr 86 sr ratios characterize the more intensively modified early dolomite samples meteoric modification probably occurred during emergence of the carbonate platform in the ordovician late dolomite volumetrically minor is brightly luminescent and occurs mainly in transition zones between early dolomite and associated limestone late dolomite has high 87 sr 86 sr ratios delta 18 o values 5 9 to 2 5 o oo pdb and fe and mn concentrations relative to early dolomite and associated limestone 87 sr 18 o fe and mn enriched fluids derived from the anadarko basin during the late paleozoic are proposed to have formed the late dolomite the fluids migrated through preexisting early dolomite aquifers and dolomitized limestones near the early dolomite limestone contacts which existed at that time although early dolomite remained more porous than limestone during early burial burial alteration by solution compaction and cementation by late dolomite have reduced porosity considerably better reservoir quality is expected to be associated with late dolomite in the arbuckle group

early diagenetic recrystallization of holocene 3000 years old peritidal dolomites ambergris cay belize three peritidal carbonate crusts and associated intercrust sediments total thickness of 30cm aged 3000 years bp on ambergris cay belize contain 32 100 calcian dolomite x 72 5 dolomite ranging in composition from 40 to 46 mol mgco3 x 43 3 dolomite replaced high mg calcite foraminiferal muds penecontemporaneously with sedimentation forming partially dolomitized sediments and lithified crusts dolomitization probably occurred in normal to moderately evaporated seawater and is apparently continuing at the present detailed scanning electron microscope analysis shows a linear increase in mean dolomite crystal size with depth 0 4 m near the top of the section to 1 0 m near the base of the dolomitized section this size increase is not accompanied by any significant decrease in porosity crystal size distributions appear to be log normal and become increasingly broad and flat with depth rietveld x ray pattern fitting structure refinements indicate increasing ca and mg concentrations on their respective sites cation ordering as a function of increasing depth most of the ordering occurs within the first 15 cm of the surface stoichiometry does not increase with depth indicating no relationship between the ca mg ratio and cation ordering strong geochemical trends were observed down section in the dolomite including 1 increasing mn content 44 to 274 ppm and 2 decreasing 13c values 0 9 to 5 5 pdb oxygen isotope values range from 18o 1 3 pdb in the upper part of the section to 2 6 pdb in the lower part of the section and are interpreted to represent two distinct groups of values rather than a continuous trend down section dolomite crystal size increase and shapes of crystal size distributions are consistent with recrystallization via a surface energy driven dissolution reprecipitation process ostwald ripening the observed trends in carbon isotopes and mn content probably result from geochemical re equilibration during recrystallization and reflect reducing conditions and an isotopically light organically derived carbon source oxygen isotope compositions probably reflect relict original dolomite values and are a result of decreasing evaporation due to rising sea level

dolomitization of holocene shallow marine deposits mediated by sulfate reduction and methanogenesis in normal salinity seawater northern belize abstract dolomite constitutes an average of 12 of the holocene organic rich sediments over a 15 km2 area of the cangrejo shoals mudbank in northern belize although it defines a laterally persistent stratiform body that averages 3 m thick it is present throughout the 7 6 m thick sediment section these transgressive sediments are less than 6400 years old and were deposited in shallow marine environments of normal salinity the dolomite is dominantly cement and average crystal size is 7 m there are no significant correlations among amount of dolomite vs sediment texture mineralogy porosity or mole mgco3 in associated particulate high mg calcite depth or location on the shoals the dolomites are poorly ordered and calcic 39 5 44 5 mole mgco3 with low mean mn 210 ppm and relatively high mean sr 1034 ppm concentrations there is no evidence of recrystallization or geochemical alteration of the dolomite 18o values of the dolomites range from 0 5 to 2 8o oopdb and the mean value 2 1o oo suggests that the dolomite precipitated from normal salinity pore water dolomite 13c values range from 5 2o oo to 11 6o oopdb mean seawater 13c 0 5o oo which suggests dolomitization promoted by both bacterial sulfate reduction and methanogenesis in environments with anoxic pore water dolomitization attending these organodiagenetic reactions apparently was reversible over time and episodic rather than continual precipitation is indicated requisite mg and ca were provided by seawater and by some dissolution of host sediments the most rapid period of dolomitization may have been during early transgression when relatively high sedimentation rates sustained high levels of organodiagenesis and pore water alkalinities

dolomitization of triassic microbial mat deposits hungary origin of microcrystalline dolomite abstract dolomite most commonly forms via replacement of precursor carbonate minerals for this reason diagnosing primarily precipitated organogenic dolomite in microbial mat deposits from the rock record is not straightforward even though the deposits exhibit microbial fabric single and multiple dolomite crusts exhibiting microbial fabric occur in a pervasively dolomitized middle triassic platform succession two sections were studied in the transdanubian range in both sections two fabric types occur in the upper part of the metre scale cycles one of that is microbial boundstone fabric type 1 characterised by clusters of dolomite microcrystals which display diagnostic microbial features such as calcimicrobes clotted spherular aggregates and globules the other one is different in the two sections in section 1 it is micritic dolomite fabric type 2 that is characterised by predominantly fine crystals and contains obscured microbial components in section 2 it is bioclastic dolomite fabric type 3 that is rich in reworked dasycladalean alga fragments and consists of dolomite crystals of wide size range from fine to coarse the precipitation of the microcrystalline dolomite phase is interpreted as being facilitated by mats and biofilms favouring tolerating an increasing frequency of subaerial conditions in the upper intertidal setting petrographic analyses revealed that organogenic calcite was also precipitated especially in mat deposits rich in bioclasts synsedimentary dolomitization resulting in fine crystals was coupled with aragonite dissolution and it postdated the organogenic precipitation it took place only in the peritidal caps of the shallowing upward depositional units petrographic analyses provide circumstantial evidence constraining that microcrystalline dolomite did not form via mimetic replacement accordingly the microcrystalline dolomite which shows microbial microfabrics in the studied samples is interpreted as an organogenic primary precipitate both peritidal processes dolomite precipitation and replacement were likely controlled by the environmental factors in a semi arid climate those components of the platform succession that were not dolomitized in the peritidal environment were replaced and cemented by medium and coarsely crystalline dolomite during further burial at elevated temperature as shown by fluid inclusion homogenisation temperature 62 to 83 c and negative stable oxygen isotope values thus the majority of the studied formation consists of fabric destructive dolomite fabric type 4

sulphur dioxide fluxes from mount etna vulcano and stromboli measured with an automated scanning ultraviolet spectrometer gruppo nazionale per vulcanolgia gnv the ec 5th framework project multimo and nerc grant gr9 04655

near surface permafrost degradation how severe during the 21st century a previously presented model on nearly complete near surface permafrost degradation in the arctic during the 21st century is critically reviewed an alternative model with a more complete mathematical formulation of the physical processes acting in permafrost terrain is presented which suggests that permafrost will mostly prevail in this century in areas north of 70 n furthermore permafrost will survive at depth in most areas between 60 to 70 n based on paleoclimatic data and in consequence of this study it is suggested that scenarios calling for massive release of methane in the near future from degrading permafrost are questionable

sedimentary architecture and genesis of holocene shallow water mud mounds northern belize cangrejo and bulkhead shoals are areally extensive holocene biodetrital mud mounds in northern belize they encompass areas of 20 km2 and 35 km2 in distal and proximal positions respectively on a wide and shallow water microtidal carbonate shelf where storms are the major process affecting sediment dynamics sediments at each mound are primarily biodetrital and comprise part of a eustatically forced dominantly subtidal cycle with a recognizable deepening upward transgressive systems tract condensed section and shallowing upward highstand systems tract antecedent topographic relief on pleistocene limestone bedrock also provided marine accommodation space for deposition of sediments that are a maximum of 7 6 m thick at cangrejo and 4 5 m thick at bulkhead despite differences in energy levels and location facies and internal sedimentological architectures of the mud mounds are similar on top of pleistocene limestone or buried soil developed on it are mangrove peat and overlying to laterally correlative shelly gravels deposition of these basal transgressive premound facies tracked the rapid rate of sea level rise from about 6400 6500 years bp to 4500 years bp and the thin basal sedimentation unit of the overlying mound core appears to be a condensed section following this the thick and complex facies mosaic comprising mound cores represents highstand systems tract sediments deposited in the last 4500 years during slow and decelerating sea level rise within these sections there is an early phase of progradationally offlapping catch up deposition and a later and current phase of aggradational keep up deposition the mound cores comprise stacked storm deposited autogenic sedimentation units the upper bounding surfaces of which are mostly eroded former sediment water interfaces below which depositional textures have largely been overprinted by biogenic processes associated with thalassia colonized surfaces vertical stacking of these units imparts a quasi cyclic architecture to the section that superficially mimics metre scale parasequences in ancient rocks the locations of the mud mounds and the tidal channels transecting them have apparently been stable over the last 50 years characteristics that might distinguish these mud mounds and those mudbanks deposited in more restricted settings such as florida bay are their broad areal extent high proportion of sand size sediment fractions and relatively abundant biotic particles derived from adjoining open shelf areas

a palaeoclimatic record from the ledo paniselian aquifer in belgium indications for groundwater recharge and flow in a periglacial environment abstract understanding the mechanisms of groundwater recharge and flow in periglacial environments remains enigmatic methane releases from melting permafrost in a warming world are a hot topic in contemporary climate research noble gas analyses have been proposed to study methane driven degassing in lakes as well as in permafrost terrains the ledo paniselian aquifer is shown to provide an analogue for such processes from the last period of global warming after the lgm it is postulated that recharge from methane bubbling thermokarst lakes to groundwater took place and can be recognized by a specific signature in the groundwater the ledo paniselian aquifer offers unique opportunities to study periglacial groundwater recharge during the lgm as it was located in the permanent permafrost area to the south of the ice sheet at that time it contains holocene and pleistocene groundwaters which are separated by a recharge gap referring to permafrost during the lgm this is confirmed by noble gas temperature ngt data in the samples immediately upstream of this gap several potential indicators for the specific methanogenic recharge conditions from thawing permafrost are being put forward based on noble gases chemical and isotopic data immediately upstream of the age gap groundwaters show strikingly deviating hco3 so42 13c 18o and 2h compared to the regional trend while their 14c model ages are too young and ngts seem too high these samples are affected by degassing which is not an artefact of sampling and which according to their radiogenic helium concentrations occurred early on during recharge or shortly thereafter the origin of these samples could be explained by the conditions prevailing as the permafrost thawed and groundwater recharge could resume it is inferred that the degassed samples were infiltrated during or shortly after the lgm when recharge from methane bubbling thermokarst lakes to groundwater took place associated to the melting permafrost

consolidation of sediments by glaciers relations between sediment geotechnics soft bed glacier dynamics and subglacial ground water flow a theory of subglacial consolidation is developed which shows how the meltwater flux beneath a glacier leaves a consolidation signature from which many important glacier dynamic properties can be inferred conditions under which water is discharged through channels or in a thin film at the ice bed interface or by ground water flow are discussed and it is concluded that glaciers flowing over aquifers of high transmissibility can induce deep circulation patterns quite different from non glacial circulation

multiphase partial and selective dolomitization of carnian reef limestone transdanubian range hungary partially dolomitized carbonate successions provide a good opportunity to understand the commonly multistage process of dolomitization petrographic methods fluid inclusion microthermometry and stable isotope measurements were applied to reconstruct the diagenetic evolution and dolomitization of a partially dolomitized carnian reef limestone from the transdanubian range hungary the diagenetic history began with reef diagenesis and formation of dolomite micro aggregates in microbial fabric elements this was followed by the development of euhedral porphyrotopic dolomite crystals through overgrowths around the previously formed dolomite micro aggregates during the earliest burial stage increasing burial resulted in the extension of the dolomite patches via formation of finely crystalline replacement dolomite from the late norian when the carnian reef carbonates reached the depth of 1 0 to 1 8 km the diagenetic evolution continued in an intermediate to deep burial setting contemporaneously an extensional regime was established leading to fracturing the progressive burial resulted in the recrystallization of the pre existing dolomite with increasing temperature while saddle dolomite cement was precipitated in fractures in connection with the alpine orogeny intense denudation took place during the late cretaceous accompanied by fracturing similar tectonically controlled denudation and fracturing occurred in several stages during the cenozoic as a result of these processes the studied carnian carbonates were raised to a near surface position or became subaerially exposed leading to dedolomitization of the last dolomite phase and precipitation of calcite cement in cavities and fractures this study revealed that by investigating partially and selectively dolomitized rock types it is possible to document and understand those stages of the multiple dolomitization process which can barely be detected in the completely dolomitized rock bodies recognition of the dolomitization phases could provide the basis for the analysis of their relations with the depositional diagenetic and tectonic processes and stages of basin evolution

numerical simulation of permafrost growth and decay a series of numerical models on permafrost growth and decay are presented with special emphasis on the climatic conditions in western europe during the last glacial stage numerical modelling of growth and decay of the active layer suggests penetration depths in the range between 0 6 to 1 4 m permafrost is estimated to have grown depending on the sediment type to a thickness of 90 m to 140 m in northern germany and the netherlands within 10 000 y during the peak period of the last glacial stage permafrost continued to exist at depth for about 2000 y after the climatic improvement following the younger dryas permafrost growth under rivers and lakes is shown to be unlikely under the climatic conditions of the last glacial stage in northern germany a time period of 10 000 to 42 000 years and a massive climatic excursion of the order of 11 c is required to remove the thick permafrost layers in siberia and alaska of today 1998 john wiley sons ltd

secular variations in seawater chemistry controlling dolomitisation in shallow reflux systems insights from reactive transport modelling dolomitization often plays a critical role in the pore network development of platform carbonates with implications for reservoir quality distribution understanding both the hydrological system driving dolomitization and the chemistry of the fluids involved is fundamental to constrain predictions of the geometry and the petrophysical properties of dolomite bodies here the role of secular variations in seawater mg ca as a control on dolomitization and early porosity modification was evaluated using one dimensional reactive transport models and fluids based on modern aragonite sea mississippian and aptian calcite sea seawaters the sensitivity of dolomitization to a range of extrinsic controls brine salinity temperature fluid flow rate and pco2 and to intrinsic reactivity of the sediments effective reactive surface area was also explored simulations suggest faster calcite replacement by dolomite for seawaters with higher mg ca indicating that dolomitization potential is determined more by mg ca rather than saturation index increasing evaporative concentration enhances reaction rate independent of the effect of enhanced density driven fluid flux in addition to brine composition effective surface area of precursor sediments and temperature exert a critical control on replacement rate while secular variations of ph and carbonate alkalinity associated with changes in pco2 are only secondary controls above flow rates of 0 01 m yr 1 replacive dolomitization is reaction limited rather than flux limited favouring alteration of fine grained carbonates and suggesting that preferential alteration of grainstone units is rare unless head gradients are low post replacement dolomite cementation is flux dependent and thus favoured in areas of high head gradient and high permeability sediments and contrary to replacement supersaturation is a more important driver than mg ca while uncertainties remain regarding low temperature dolomitization kinetics the capability of numerical simulations to decouple individual controls provides new insights which can be used in conjunction with traditional comparative sedimentology to generate more rigorous conceptual models for individual reservoir settings

thermal simulation of subsea saline permafrost thermal analyses of the response of offshore permafrost to emergence and submergence have traditionally employed simple closed form solutions where phase change is confined to a discrete freezing temperature these have led to rather rapid rates of return to thermal equilibrium which have proved difficult to explain in the light of recent deep temperature measurements in offshore permafrost profiles this paper reviews the need for an appropriate unfrozen water content relationship for a saline frozen soil and describes some simulations of long term thermal response in offshore permafrost using the author s geothermal simulator simulations of submergence assumed an initial permafrost thickness of 600 m and a mean soil surface temperature of 9 0 c the salinity was assumed constant at 30 the initial temperature profile was linear varying between 9 0 c and a freezing point of 1 8 c at the bottom of ice bonded permafrost the temperature of the ground surface was assumed to have changed to 0 8

petrogenesis of 1 9 ga limestones and dolostones and their record of paleoproterozoic environments abstract fibrous calcite cements from limestones of the paleoproterozoic pethei group in northwest canada have relatively constant 13 c values near 1 that indicate the c exogenic cycle of ca 1 9 ga ago had similar balances between oxidized and reduced reservoirs of carbon as has existed throughout most of the phanerozoic 87 sr 86 sr ratios of these cements are near 0 7051 and support a progressively increasing influx of radiogenic sr from continental weathering into the paleoproterozoic oceans 18 o values of the cements vary from 14 to 8 5 although the original values of the cements were probably higher because the cements have been subseqently altered as evidenced by their variable trace element contents proposed higher temperatures or substantially lower 18 o values of ancient seawater based on such values may be in error fabric retentive dolomites generally regarded as syndepositional also have variable 18 o values the highest of which are ca 30 greater than the highest values of the fibrous calcite cements the dolomites have more radiogenic sr isotopic compositions indicating that they formed from fluids that interacted with rocks such as those of the clastic sediments which underlie the limestones these fluids may have partially altered the 18 o values and chemical compositions of the fibrous calcite cements late stage calcitic and dolomitic cements that formed from late diagenetic fluids have similar 18 o values and radiogenic sr isotopic ratios as the fabric retentive dolomites if these potentially syndepositional dolomites have had their primary isotopic compositions reset through interaction with diagenetic fluids this would have significant implications to other studies using early dolomite to constrain ancient environmental conditions

groundwater flow under a paleo ice stream of the scandinavian ice sheet and its implications for the formation of stargard drumlin field nw poland

textural and geophysical characterization of explosive basaltic activity at villarrica volcano 1 villarrica volcano chile is one of the most active volcanoes in south america its activity is currently characterized by continuous degassing from a summit lava lake vent punctuated by explosive events during november 2004 a multidisciplinary experiment was deployed for a 10 d period to define the style of emission and infer shallow conduit dynamics at this basaltic center this involved collection of thermal seismic and infrasonic data to describe the background activity confined inside the crater and use of samples to texturally and chemically characterize the ejecta from more energetic explosions able to attain the crater rim the background activity was characterized by gas bursting with a frequency of 9 events per minute this involved emission of gas puffs fed by bubble bursting with larger bursts emplacing sheets of magma onto the lower crater walls the ejecta population from the more energetic events was characterized by the coexistence of both scoriae and golden pumice these two types of clasts have different textures but identical glass compositions suggesting that they underwent different conduit histories the golden pumice is interpreted as the expanding inner part of a short lived jet fed by a rapidly ascending magma batch the scoria forms the outer portion of the jet and comprises degassed material entrained during passage of the fresh batch through material residing in the upper most portion of the conduit we thus have a largely degassed upper column that feeds persistent bubble bursting through which fresh batches occasionally rise to feed events of relatively higher energy

s cl and f degassing as an indicator of volcanic dynamics the 2001 eruption of mount etna 1 the recent eruption of mount etna july 2001 offered the opportunity to analyze magma derived volatiles emitted during pre and syn eruptive phases and to verify whether their composition is affected by changes in volcanic dynamics this paper presents the results of analyses of f cl and s in the volcanic plume collected by filter packs and interprets variations in the composition based on contrasting solubility in magmas a rayleigh type degassing mechanism was used to fit the acquired data and to estimate henry s solubility constant ratios in etnean basalt this model provided insights into the dynamics of the volcano abundances of sulfur and halogens in eruptive plumes may help predict the temporal evolution of an ongoing effusive eruption

dolomite cation order in the geological record abstract dolomite is a carbonate mineral frequently found in sedimentary rocks from proterozoic to holocene in the iberian peninsula dolomites appear in a wide number of geological formations and they can be considered as representative of dolomites crystallised in most post sedimentary environments on earth in this paper we present a first systematic study of the cation order of dolomites formed from neoproterozoic to late holocene we found that the lowest values of cation order quantified by measuring i01 5 i11 0 intensity ratios on diffractograms mainly correspond to dolomites formed in about the last 30 myr in contrast older dolomites usually reach maximum i01 5 i11 0 intensity ratios furthermore higher values of cation order seem to be related to higher values of the full width half maximum of 10 4 diffraction peaks fwhm10 4 assuming that a decrease in fwhm10 4 i e an increase in the crystallite size in sedimentary environments indicates mineral ripening our results show that mg ca ordering in dolomites might take place mainly by a dissolution re crystallisation ageing process operating over large geological periods

permafrost heat flow and the geothermal regime at prudhoe bay alaska temperature measurements through permafrost in the oil field at prudhoe bay alaska combined with laboratory measurements of the thermal conductivity of drill cuttings permit an evaluation of in situ thermal properties and an understanding of the general factors that control the geothermal regime a sharp contrast in temperature gradient at approx 600 m represents a contrast in thermal conductivity caused by the downward change from interstitial ice to interstitial water at the base of permafrost under near steady state conditions interpretation of the gradient contrast in terms of a simple mode for the conductivity of an aggregate yields the mean ice content approx 39 and thermal conductivities for the frozen and thawed section 8 1 and 4 7 mcal cm s sup 0 c respectively these results yield a heat flow of approx 1 3 hfu which is similar to other values on the alaskan arctic coast the anomalously deep permafrost is a result of the anomalously high conductivity of the siliceous ice rich sediments curvature in the upper 160 m of the temperature profiles represents a warming of approx 1 8 sup 0 c of the mean surface temperature and a net accumulation of 5 6 kcal cm sup 2 by the solid earth surface during the last 100 years or so rising sea levelmore and thawing of ice rich sea cliffs probably caused the shoreline to advance tens of kilometers in the last 20 000 years inundating a portion of the continental shelf that is presently the target of intensive oil exploration a simple conduction model suggests that this recently inundated region is underlain by near melting ice rich permafrost to depths of 300 500 m its presence is important to seismic interpretations in oil exploration and to engineering considerations in oil production with confirmation of the permafrost configuration by offshore drilling heat conduction models can yield reliable new information on the chronology of arctic shorelines less

quantification of the mass flux of h2o gas steam at three active volcanoes using thermal infrared imagery we apply a measurement technique that utilizes thermal video of vapor dominated volcanic plumes to estimate the h2o gas flux at three degassing volcanoes results are compared with h2o flux measurements obtained using other methods to verify the thermal camera derived values our estimation of the h2o emission rate is based on the mass and energy conservation equations h2o flux is quantified by extracting the temperature and width of the gas plume from the thermal images calculating the transit velocity of the gas plume from the thermal video and combining these results with atmospheric parameters measured on site these data are then input into the equations for conservation of mass and energy selected volcanoes for this study were villarrica in chile stromboli in italy and santa ana in el salvador h2o fluxes estimated from the thermal imagery were 38 250 kg s 1 at villarrica 4 5 14 kg s 1 for stromboli s central crater and 168 219 kg s 1 at santa ana these compare with h2o flux values estimated by other methods of 73 220 3 70 and 266 kg s 1 at the three volcanoes respectively the good agreement between thermal image derived results and those estimated by other methods seem to validate this method

rock buffered recrystallization of marion plateau dolomites at low temperature evidenced by clumped isotope thermometry and x ray diffraction analysis abstract much debate exists on the extent to which early dolomites recrystallize and preserve the signature of their primary diagenetic setting here we combine clumped isotopes thermometry with x ray diffraction and thin section petrography to study dolomite recrystallization under shallow burial