determination of initial sr isotopic compositions of dolostones from the burlington keokuk formation mississippian constraints from cathodoluminescence glauconite paragenesis and analytical methods abstract regionally extensive fine grained dolostones from the mississippian burlington keokuk fm comprise two major generations of dolomite that can be distinguished by their cathodoluminescence chemical compositions and times of formation the petrography and geochemistry of glauconite the predominant clay mineral in the dolostones indicates that it is an authigenic phase some of which formed episodically during various stages of postmarine diagenesis this study evaluates techniques for the determination of the sr isotopic compositions of the dolomite generations through the analysis of nearly pure whole rock samples 95 soluble and mineral separates each composed predominantly of one cathodoluminescent type of dolomite sr isotopic compositions and rb and sr concentrations were measured on samples prepared by three separate methods 1 leaching with 1 25n hcl 2 leaching with 1 25n hcl and concentrated hf and 3 complete dissolution with concentrated hf and hno3 and 6n hcl leaching with hcl removes 24 60 percent of the rb in the samples compared to acid leaching complete sample dissolution yields higher 87sr 86sr ratios and rb concentrations and more reproducible results this indicates that most of the rb and radiogenic 87sr is associated with minor clay fractions in the samples and that hcl leaches rb and sr from clays to a variable extent the relatively high rb sr ratios of the dolostones necessitate an age correction of each sample s 87sr 86sr ratio the determination of such initial 87sr 86sr ratios requires contemporaneous formation of carbonate and clay closure of the rb sr system after diagenesis and constraints on the timing of diagenesis calculated initial 87sr 86sr ratios for the dolostones by method 3 differ considerably from the uncorrected measured 87sr 86sr ratios by any of the dissolution methods these results demonstrate that even minor clay components can make significant contributions to the analyses and that analysis for rb and sr and constraints on the timing and diagenetic history of both the clay and carbon te phases can be critical for the determination of the sr isotopic compositions of even nearly pure dolostones an evaluation of the uncertainties associated with the timing and type of diagenesis indicates that the initial 87sr 86sr ratios of the dolostones are representative of the isotopic composition of the dolomite generations at the time of their formation two major cathodoluminescent types of burlington keokuk dolomites preserve a record of two isotopically distinct diagenetic environments samples composed of the earliest dolomite dolomite i have initial 87sr 86sr ratios ranging from 0 70757 to 0 70808 while samples composed of dolomites ii and ii range from 0 70885 to 0 70942

effects of grand cycle cessation on the diagenesis of upper cambrian carbonate deposits in the southern appalachians u s a abstract the vertical transition from the mainly subtidal alternating shale and carbonate units or grand cycles of the conasauga group middle to upper cambrian to the peritidal dolostone of the knox group upper cambrian to lower ordovician marks a major change in the early paleozoic passive margin sedimentation of the southern appalachians the grand cycles represent an interplay between intrashelf shale basin and carbonate platform deposition the end of grand cycle deposition occurred in response to carbonate platform progradation over the infilled intrashelf basin and is associated with a prominent change in diagenetic patterns observed in the uppermost conasauga group strata the maynardville formation the maynardville records upward shallowing from subtidal shale and limestone into peritidal dolostone this change from a subtidal into a peritidal depositional regime influenced the early diagenesis of the maynardville and in conjunction with the changes in the regional facies distribution at the end of grand cycle deposition extended its influence upon the burial diagenesis of these deposits the subtidal deposits of the maynardville contain a variety of calcite cements dolomite is not abundant in these deposits where it occurs mainly as a fine crystalline ferroan phase associated with argillaceous layers and pressure dissolution features the local source for this dolomite during burial was provided by expulsion of pore fluids from interbedded shale deposits diagenesis of clay minerals and pressure dissolution of carbonates ferruginous coatings on hardgrounds in the subtidal deposits provided an additional local source of iron for the formation of replacement saddle dolomite the subtidal deposits also contain saddle dolomite cement associated with mississippi valley type mvt minerals which indicate the involvement of externally derived fluids during late burial diagenesis of these strata the peritidal deposits on the other hand are extensively dolomitized fine crystalline dolomite most likely represents early diagenetic replacement of tidal flat carbonate sediment coarse crystalline replacement dolomite formed during burial by recrystallization of early dolomite and dolomitization by warm burial brines fenestrae desiccation cracks and evaporite dissolution voids are occluded with dolomite cement which is commonly complexly zoned zoned dolomite precipitated during shallow to intermediate burial and is postdated by saddle dolomite cement saddle dolomite in pore centers dissolutional voids and tectonic fractures formed during late burial from warm fluids associated with the migration of mvt brines the effects of changes in the depositional setting on diagenesis are reflected in similar early diagenesis between the subtidal maynardville and the underlying conasauga group carbonate deposits and between the peritidal deposits of the upper maynardville and the rest of the overlying knox group the depositional environments and early diagenesis also affected the burial diagenesis the changes in regional facies distribution caused by carbonate platform progradation at the end of grand cycle deposition resulted in a decrease in the proportion of siliciclastic components this decrease was accompanied by a decline in the amount of ferroan carbonate in the peritidal deposits the maynardville is conformably overlain by carbonate deposits of the knox group this allowed the maynardville knox succession to behave as a single hydrologic unit for the migration of burial fluids in response to the formation of the ordovician foreland sevier basin to the southeast during the conversion from a passive into a convergent continental margin the nolichucky shale separates the maynardville knox succession from the carbonate deposits of the underlying conasauga group which were in contrast affected by the migration of burial fluids from the cambrian intrashelf shale basin to the west

linear coupling of carbon and strontium isotopes in rotliegend sandstone north sea evidence for cross formational fluid flow isotopic analyses of carbon and strontium in diagenetic dolomite and ankerite present in the eolian lower permian rotliegend sandstone southern north sea show an excellent linear correlation between delta sup 13 c and sup 87 sr sup 86 sr r 0 93 suggesting that the sources of these elements were interlinked the isotopic data indicate that late permian zechstein seas flooded the basin and displaced the interstitial meteoric rotliegent pore fluids producing early dolomite with predominantly marine bicarbonate delta sup 13 c minus 15 per thousand and strontium sup 87 sr sup 86 sr 0 7076 isotopic signatures the isotopic values of this dolomite form a trend to merge with the diagenetically later ankerite which has lower sup 13 c sup 12 c delta sup 13 c minus 4 per thousand and more radiogenic strontium sup 87 sr sup 86 sr 0 7112 the obvious source of low delta sup 13 c carbon was thermal decarboxylation of organic matter in the underlying upper carboniferous mudstones the authors also suggest that the increasing quantities of radiogenic strontium sup 87 sr sup 86 sr 0 720 were released when organic acids dissolved silicates feldspar in the same underlying mudstones the upward movement of fluid or diffusion of ions across formation boundaries therefore progressively became the dominant control on carbonate precipitation in the rotliegend sandstone

diagenetic stabilization of the upper permian dalan formation persian gulf basin abstract the upper permian dalan formation is a supergiant gas reservoir in the persian gulf basin reservoir quality is controlled by the original facies type dolomitization and anhydrite cementation this study focuses on the texture petrographic analysis bulk stable isotope values and trace element composition in order to identify the original mineralogy of carbonate grains and cements and to assess the synsedimentary and diagenetic processes including the timing and setting of dolomitization the limestone data suggest that the initial precipitation of isopachous acicular to fibrous aragonite cements in the marine phreatic environment was followed by dissolution of aragonite grains and cements in the meteoric phreatic zone and neomorphism and low mg calcite cementation blocky and drusy crystals syntaxial overgrowths in the active freshwater phreatic zone the relatively pristine 18o and 13c values low mn and relatively high sr and na contents indicate that this meteoric diagenesis was relatively limited the remaining porous space was cemented by blocky calcite later during burial four types of dolomites are identified within a complex mixture of texturally and isotopically different dolomites dolomicrite dolomicrosparite dolosparite and saddle dolomite dolomicrite formed syndepositionally from the evaporated permian seawater or by reflux of dense evaporated brines during shallow burial the second major episode of dolomitization dolomicrosparite and dolosparite was driven by reflux of warmer and more saline fluids at greater depth which affected both previously non dolomitized and dolomitized sediments the final diagenetic stabilization during deep burial is associated with extensive pressure solution fracturing vein filling of calcite and dolomite cements and crystallization of saddle dolomite

coupled textural and compositional characterization of basaltic scoria insights into the transition from strombolian to fire fountain activity at mount etna italy strombolian and fire fountain activities represent a common expression of explosive basaltic eruptions however the transition between these two eruptive styles and their source mechanisms are still debated we use textural and compositional studies to characterize pyroclastic material from both the strombolian and hawaiian style fire fountain phases of the january june 2000 etna activity we find that basaltic scoria presents distinctive textural and compositional features that reflect different modes of magma vesiculation and crystallization in the two eruptive regimes overall magma that forms strombolian scoria is far more crystallized less vesicular and more evolved indicating strong volatile depletion and longer residence time before being erupted fire fountain scoria indicates a fast rising magma with evidence of moderate syneruptive volatile exsolution the new textural and compositional data set is integrated with previous volcanological and geophysical investigations to provide further insights into the dynamics of fire fountains and to frame the transition from strombolian explosions to fire fountain activity into a model that may apply to future eruptions at mount etna as well as other active basaltic volcanoes

degassing behaviour at basaltic volcanoes new insights from experimental investigations of different conduit geometry and magma viscosity abstract understanding gas magma dynamics in volcanic conduits and linking them with the associated geophysical signals at the surface is of fundamental importance in monitoring active volcanoes in the past a significant number of studies have been devoted to this topic addressing the onset the key factors governing each degassing regime and the related markers at the surface particularly at basaltic volcanoes here we first review such a broad and increasing literature focusing on the main approaches used in the attempt of deciphering conduit dynamics by indirect observations 1 analogue laboratory experiments and 2 seismo acoustic measurements then we combine the two techniques into a novel set of experiments addressing a crucial yet unexplored issue the irregularity i e the departure from an ideal smooth cylindrical shape of the conduit surface we built a set of epoxy conduits with various fractal dimensions dc i e irregularity of the internal surface using silicone oil as a proxy for magma different degassing patterns bubbly slug and churn annular flow were reproduced by changing systematically 1 injected gas flux 5 to 180 10 3 l s 2 analogue magma viscosity 10 to 1000 pas 3 fractal dimension dc of the conduit surface i e dc 2 dc 2 18 and dc 2 99 the experiments were monitored by means of a video camera and a set of sensor aimed to detect the seismic and acoustic signals results show that viscosity strongly influences the transition among degassing patterns and the recurrence rate of slug bursts at the surface moreover we observed an increase of the exponent of the power law equation linking squared seismic amplitude to gas flow rate with conduit roughness the opposite trend was noticed with increasing liquid viscosity these results have important implications for linking seismic tremor to eruption source parameters such as the volume discharge rate at different volcanoes or for investigating its temporal evolution at a single vent

sr s and oso4 isotopes and the depositional environments of the upper miocene evaporites spain abstract upper miocene evaporites in the nijar basin southeastern spain contain thick massive and coarse crystalline selenites of the middle messinian yesares formation on the basis of their sedimentary fabrics and structures such as euhedral terminations of crystals well preserved algal filament inclusions and standing growth orientations these selenites are interpreted to be primary bottom growth deposits most of these selenites have sr concentrations of about 1000 ppm range from 700 to 1800 ppm 87sr 86sr values of yesares selenites vary between 0 70890 and 0 70896 n 18 which are all within the known range of messinian seawater suggesting a marine origin however quantitative modeling of 87sr 86sr vs sr ca of fluids demonstrates that a minor amount of admixed nonmarine fluid e g 20 might have contributed to the yesares marine brines 34s and 18oso4 values of yesares selenites range from 21 to 24 cdt and from 10 to 16 smow respectively these ranges are more variable and most values are heavier than those expected for normal miocene marine gypsum on the basis of quantitative modeling these heavy 34s and 18oso4 values have most likely resulted from reduction and oxidation reactions of sulfur species that occurred in brines rather than from contributions of nonmarine water or from reservoir crystallization effects the use of sr s and o isotopes provides a possible means of distinguishing whether an ancient evaporite was deposited by marine nonmarine or hybrid brines sr isotopes however are insensitive to minor nonmarine contributions on the basis of quantitative modeling and consequently marine sr isotopes for evaporites e g gypsum do not necessarily indicate pure marine depositional environments compared to sr isotopes 34s and 18oso4 of marine gypsum are even more insensitive to minor nonmarine contributions because of much higher so4 concentrations in seawater and seawater evaporated brines than in most freshwaters therefore sr o and s isotopes should be used with caution to interpret depositional environments and to determine parent fluids of ancient evaporites

spectroscopic evidence for a lava fountain driven by previously accumulated magmatic gas the eruption of mount etna in 2000 was notable for an exceptional series of 64 periodic lava fountains propelling lava fragments to heights of up to 900 metres it has been difficult to determine which of two suggested sources of power gas release from the magma itself during its rapid ascent or a build up of pressure from gas accumulated at depth is the driving force for these dramatic jets but one of the etna fountains provided volcanologists with the opportunity to use remote sensing not that remote see picture on the following page to determine the infrared spectra of the gas phase this revealed the chemical composition of the gas that powered this fountain as consistent with an origin in an accumulated gas layer lava fountains are spectacular continuous gas jets propelling lava fragments to heights of several hundred metres which occasionally occur during eruptions of low viscosity magmas1 2 3 4 5 whether they are generated by the effervescent disruption of fast rising bubbly melt2 3 4 5 or by the separate ascent of a bubble foam layer accumulated at depth6 7 still remains a matter of debate8 no field measurement has yet allowed firm discrimination between these two models a key insight into the origin of lava fountains may be gained by measuring the chemical composition of the driving gas phase this composition should differ markedly depending on whether the magma degassing occurs before or during eruption9 10 here we report the analysis of magmatic gas during a powerful 250 600 m high lava fountain measured with fourier transform infrared spectroscopy11 12 13 14 on mount etna sicily the abundances of volcanic gas species determined from absorption spectra of lava radiation reveal a fountain gas having higher co2 s and s cl ratios than other etnean emissions14 15 16 17 18 and which cannot derive from syn eruptive bulk degassing of etna basalt19 20 instead its composition suggests violent emptying of a gas bubble layer previously accumulated at about 1 5 km depth below the erupting crater

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

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

the late devonian frasnian famennian f f biotic crisis insights from δ13ccarb δ13corg and 87sr 86sr isotopic systematics a severe biotic crisis occurred during the late devonian frasnian famennian f f transition f367 myr here we present d 13 ccarb d 13 corg and 87 sr 86 sr isotopic systematics from identical samples of two sections across f f boundary in south china which directly demonstrate large and frequent climatic fluctuations 200 kyr from warming to cooling during the f f transition these climate fluctuations are interpreted to have been induced initially by increased volcanic outgassing and subsequent enhanced chemical weathering linked to the rapid expansion of vascular plants on land which would have increased riverine delivery to oceans and primary bioproductivity and subsequent burial of organic matter thereby resulting in climate cooling such large and frequent climatic fluctuations together with volcanic induced increases in nutrient e g biolimiting fe toxin sulfide and anoxic water supply and subsequent enhanced riverine fluxes and microbial bloom were likely responsible for the stepwise faunal demise of f f biotic crisis d 2005 elsevier b v all rights reserved

sector zoning in calcite cement crystals implications for trace element distributions in carbonates abstract compositional sector zoning in calcite cement crystals from a sedimentary limestone is represented by differences of mg content of over 1300 ppm or 95 and of sr and mn contents of up to 400 ppm or roughly 50 and 80 respectively between crystallographically nonequivalent time synchronous growth sectors 10 1 1 sectors are enriched with both mg and mn relative to 10 1 4 sectors and other sectors show both greater and lesser enrichment this systematic zoning pattern requires effective distribution coefficients for these trace elements to have been different for growth on different faces differential growth rate effects for nonequivalent faces are shown to be unimportant relative to differential growth face element preferences surface crystal structure and differing coordination environments are regarded as the principal factors influencing sector related elemental partitioning differences in calcite and dolomite

local regional and remote seismo acoustic observations of the april 2015 vei 4 eruption of calbuco volcano chile the two major explosive phases of the 22 23 april 2015 eruption of calbuco volcano chile produced powerful seismicity and infrasound the eruption was recorded on seismo acoustic stations out to 1 540 km and on 5 stations is02 is08 is09 is27 and is49 of the international monitoring system ims infrasound network at distances from 1 525 to 5 122 km the remote ims infrasound stations provide an accurate explosion chronology consistent with the regional and local seismo acoustic data and with previous studies of lightning and plume observations we use the ims network to detect and locate the eruption signals using a brute force grid search cross bearings approach after incorporating azimuth deviation corrections from stratospheric cross winds using 3d ray tracing the estimated source location is 172 km from true this case study highlights the significant capability of the ims infrasound network to provide automated detection characterization and timing estimates of global explosive volcanic activity augmenting the ims with regional seismo acoustic networks will dramatically enhance volcanic signal detection reduce latency and improve discrimination capability

isotopic and trace element constraints on the origin and evolution of saline groundwaters from central missouri na ca cl groundwaters with salinities of 1 to 30 discharge from natural springs and artesian wells in mississippian carbonates and ordovician sandstones and carbonates in central missouri carbonate saturation and quartz supersaturation are maintained throughout the salinity range major and trace element and isotopic variations in the waters are used to place constraints on models for rock water interaction and regional hydrology the groundwaters have d values that range from 108 to 45 and 18 o values that range from 14 7 to 6 5 smow these data lie approximately along the meteoric water line ranging from values similar to local recharge in missouri to significantly lower values that are similar to 18 o and d for meteoric recharge in high altitude and high latitude regions of north america the more saline samples have the lowest 18 o and d contents a trend that is opposite to that observed in most other studies of saline waters the h o isotopic correlation and the range in salinity and several major and trace element concentrations in central missouri groundwaters are readily explained by a saline dilute water mixing model 87sr 86sr ratios for the groundwaters range from 0 7155 to 0 7161 these values are significantly higher than previously published values for 1 estimates of 87 sr 86 sr in phanerozoic seawater 0 7068 0 7092 and 2 carbonates of the mississippian burlington keokuk fm 0 7075 0 7105 through which some of the waters migrate as they pass to the surface nd 0 values in the groundwaters range from 10 9 to 8 1 and 147 sm 144 nd ratios range from 0 108 to 0 128 these values are similar to or lower than previously published analyses of carbonates and other authigenic phases from the burlington keokuk fm mean nd 0 7 8 0 8 1 mean 147 sm 144 nd 0 141 the h o sr and nd isotopic data and the results of model calculations preclude 1 models involving the modification of ancient seawater for the origin of the saline waters and 2 extensive interaction between the groundwaters and their host carbonates the waters apparently acquired their 18 o and d values as meteoric recharge and their 87sr 86sr and rare earth element signatures from extraformational crustal sources high 87 sr 86 sr low nd 0 low 147sm 144nd and largely preserved these isotopic signatures during subsequent migration through the carbonates chemical exchange via rock water interaction is required for isotopic exchange to occur therefore the present state of chemical equilibrium between the groundwaters and carbonate aquifer minerals may serve to limit rock water interaction and hence preserve the extraformational isotopic signatures in the waters the integration of geochemical isotopic and hydrologic data on a local and regional scale suggests a history for the central missouri groundwaters involving 1 meteoric recharge in the front range of colorado 2 dissolution of permian halite in the subsurface of kansas 3 interaction with predominantly silicate mineral assemblages in paleozoic strata and possibly precambrian basement with aquisition of crustal sr and ree signatures 4 dilution and migration to shallow aquifer levels in central missouri and 5 mixing with local meteoric recharge through mississippian carbonates with no significant change of the isotopic signatures acquired in stage 3

infrasound reveals transition to oscillatory discharge regime during lava fountaining implication for early warning 1 we present the analysis of 4 million infrasonic signals which include 39 episodes of lava fountains recorded at 5 5 km from the active vents we show that each eruptive episode is characterized by a distinctive trend in the amplitude waveform and frequency content of the acoustic signals reflecting different explosive levels lava fountain starts with an 93 min long violent phase of acoustic transients at 1 25 hz repeating every 2 5 s infrasound suddenly evolves into a persistent low frequency quasi monochromatic pressure oscillation at 0 4 hz we interpret this shift as induced by the transition from the slug discrete strombolian to churn flow sustained lava fountain regime that is reflecting an increase in the gas discharge rate we calculate that infrasonic transition can occur at a gas superficial velocity of 76 m s and it can be used to define infrasonic based thresholds for an efficient early warning system

strontium isotope evidence on the history of oilfield brines mediterranean coastal plain israel abstract the isotopic composition of sr in oil field brines from the mediterranean coastal plain was determined in 18 drillholes 13 of which are oil producing wells the brines are characterized by salinities ranging from 35 to 93 g l tds sr from 28 to 350 mg l sr ca molar ratios from 0 011 to 0 053 and 87 sr 86 sr ratios from 0 7075 to 0 7090 e a 0 7081 0 0004 2 the brines are classified into two groups 1 a mavqi im group brines with relatively high 87 sr 86 sr ratios 0 7087 and 0 7090 sampled from elastics dolomites and anhydrites of upper miocene age 2 b heletz group brines with relatively low 87 sr 86 sr ratios 0 7075 to 0 7081 sampled from sandstones and dolomites of lower cretaceous age equations were derived to show the relations between 87 sr 86 sr ratio of the brines and the processes through which they evolved dolomitization and dissolution reprecipitation it is suggested that both groups of brines originated from mediterranean evaporated seawater during the messinian desiccation the strontium isotope composition of the seawater is reflected in that of both groups of brines the mavqi im group containing the original 87 sr 86 sr ratio 0 7088 the heletz group evolved later on through exchange reactions of those primary brines with a carbonate sequence of cretaceous age and consequently new 87 sr 86 sr ratios 0 7078 could have been developed the effect of the dissolution reprecipitation reactions on the carbonate rocks is estimated to be very slight only around 1 by weight

textural and geochemical alternations in late cenozoic bahamian dolomites dolomitized intervals of a core from san salvador island bahamas exhibit variations of two texturally and geochemically distinct end members in the pliocene section of the dolomitized interval the two end members alternate in a pattern that may reflect originally and or diagenetically modified depositional facies formerly mud free intervals locally capped by exposure surfaces are massive crystalline mimetic dolomites cm muddier sediments are replaced by friable microsucrosic dolomites ms cm and ms dolomites also differ in porosity 30 permeability 100 md mol mgco3 44 9 vs 47 7 mol oxygen isotopic composition 1 7 vs 2 7 and strontium content 241 vs 106 ppm these data indicate that depositional and diagenetic fabric are the principal controls governing the distribution of dolomite types differences in texture and geochemistry are suggested as arising through differential rates of crystallization produced as a result of variations in permeability and reactivity of the precursor sediments and rocks

transvaal supergroup carbonates implications for paleoproterozoic δ18o and δ13c records abstract the paleoproterozoic interval is characterized by the first evidence for incontrovertibly free oxygen in the ocean atmosphere system in this study carbonates from the transvaal group the silverton lucknow rooinekke and particularly the duitschland formations were analyzed for isotopes of carbon oxygen and strontium in order to constrain models dealing with the patterns of seawater evolution although the trace element data showed variable alteration of the carbonate samples selected samples with a lesser degree of alteration yielded interpretable results the best measured 87sr 86sr isotope value of 0 7031 at 2 35 ga ago fits well with the published curve for precambrian seawater confirming that paleoproterozoic budget of sr was dominated by input from continental sources during the paleoproterozoic times carbonates with 13c values of about 10 are known to have been present worldwide and they have been studied also during this research the observation that in the duitschland formation such high isotope values and normal marine values were both present within a single formation indeed within its single beds suggested that the large spread of 13c values reflects local or regional rather than global phenomena the oxygen isotope data show a large spread of values from 3 to 16 while their corresponding 13c signals are almost unchanged over this entire range with the lucknow and silverton formations clustering around 10 and the rooinekke formation around 2 the duitschland formation has a bimodal distribution with both 13c populations present the last formation also contains samples with 18o as low as 20 particularly in the vicinity of the bushveld intrusive body these highly 18o depleted samples show homogenization of 13c values towards 5 modelling suggests that the trends could have resulted from post depositional alteration by basinal fluids at near surface to about 50 c temperatures in a rock buffered system the duitschland formation samples particularly at duitschland farm the locality closest to the bushveld complex were then further altered at temperatures up to about 80 c in response to this intrusion

diverse eruptive activity revealed by acoustic and electromagnetic observations of the 14 july 2013 intense vulcanian eruption of tungurahua volcano ecuador

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

an integrated paleomagnetic rock magnetic and geochemical study of the marcellus shale in the valley and ridge province in pennsylvania and west virginia an integrated paleomagnetic rock magnetic and diagenetic study of the devonian marcellus subgroup from threefolds in the valley and ridge province in pennsylvania and west virginia indicates that the unit contains an intermediate temperature chemical remanent magnetization crm with south southeast declinations and shallow negative inclinations residing in pyrrhotite and a crm with more southerly declinations and shallow positive inclinations residing in magnetite rock magnetic results confirm the presence of pyrrhotite and magnetite tilt tests indicate that pyrrhotite and magnetite crms are syntilting to posttilting and paleopoles for both crms are similar and plot on the permian part of the apparent polar wander path for north america the marcellus subgroup has a complex paragenetic sequence which includes bitumen deposition and vein formation the magnetite and pyrrhotite crms formed in the permian probably due to burial diagenetic processes and not orogenic fluids the base of the unit contains the highest total organic content toc values and highest magnetic intensities both of which decrease up section this connection between toc and magnetic intensity suggests that the magnetite formed as a result of the maturation of the organic matter although more work is needed to test this hypothesis the pyrrhotite may have formed as a result of thermochemical sulfate reduction involving organic matter during the production of methane in this gas reservoir the similar permian crm ages may be explained by thrusting which resulted in rapid burial of the marcellus subgroup as it passed through the oil window and into the gas window quickly producing magnetite and pyrrhotite respectively

pyroclastic phases of a rhyolitic dome building eruption puketarata tuff ring taupo volcanic zone new zealand the 14 ka puketarata eruption of maroa caldera in taupo volcanic zone was a dome related event in which the bulk of the 0 25 km3 of eruption products were emplaced as phreatomagmatic fall and surge deposits a rhyolitic dike encountered shallow groundwater during emplacement along a ne trending normal fault leading to shallow seated explosions characterised by low to moderate water magma ratios the eruption products consist of two lava domes a proximal tuff ring three phreatic collapse craters and a widespread fall deposit the pyroclastic deposits contain dominantly dense juvenile clasts and few foreign lithics and relate to very shallow level disruption of the growing dome and its feeder dike with relatively little involvement of country rock the distal fall deposit representing 88 of the eruption products is despite its uniform appearance and apparently subplinian dispersal a composite feature equivalent to numerous discrete proximal phreatomagmatic lapilli fall layers each deposited from a short lived eruption column the puketarata products are subdivided into four units related to successive phases of a shallow lava intrusion and initial dome growth b rapid growth and destruction of dome lobes c slower sustained dome growth and restriction of explosive disruption to the dome margins and d post dome withdrawal of magma and crater collapse phase d was phreatic phases a and c had moderate water magma ratios and phase b a low water magma ratio dome extrusion was most rapid during phase b but so was destruction and hence dome growth was largely accomplished during phase c the puketarata eruption illustrates how vent geometry and the presence of groundwater may control the style of silicic volcanism early activity was dominated by these external influences and sustained dome growth only followed after effective exclusion of external water from newly emplaced magma

sr mg ratios of modern marine calcite empirical indicators of ocean chemistry and precipitation rate holocene biotic and abiotic marine calcite have a similar range of mg contents 0 to 22 and 4 to 21 mol mgco3 respectively yet biotic calcite has sr2 concentrations that are consistently 1250 ppm higher than those of abiotic calcite as in laboratory experiments a positive linear relation is observed between dsr and calcite mg content this produces two distinct linear trends on a plot of sr2 vs mg2 concentrations principal axes of variation for both trends have similar slopes yet distinctly different sr2 concentration intercepts biotic y 0 024x 1298 r2 0 70 abiotic y 0 027x 47 r2 0 77 the similar slopes of these trends reflect the constancy of mgca and srca ratios of modern seawater equations describing the dependence of dsr on calcite mg content are derived from both trends biotic dsr 3 16 x 10t 6 ppm mg 0 169 abiotic dsr 3 52 x 10 6 ppm mg 0 0062 characterization of sr mg trends for holocene materials allows comparison with analogous trends from ancient samples to estimate relative changes in seawater mgca and srca ratios the relatively high sr contents of biotic calcite result from rapid precipitation rates associated with shell accretion in marine organisms calcites precipitated from seawater in laboratory experiments have dsr values that are similar to those of biotic marine calcite suggesting that both precipitate at approximately the same rate our estimates of surface area normalized precipitation rates in planktonic and benthonic foraminifera are comparable to those of seeded ph stat experiments we conclude that the dsr values for biotic and experimental marine calcite are kinetically controlled whereas the lower precipitation rates of abiotic marine calcite yield dsr values that approximate equilibrium conditions experimentally derived equations describing the relation between dsr and calcite precipitation rate indicate that the offset in sr content between biotic and abiotic calcite is the result of abiotic precipitation rates that are two to five orders of magnitude lower than those of biotic precipitates however observations of naturally occurring marine cements suggest that the five order of magnitude offset best represents natural system processes

an example of mixing zone dolomite middle eocene avon park formation floridan aquifer system abstract a late formed dolomite cement in a core of the middle eocene avon park formation peninsular florida provides an example of dolomite cement from a mixing zone and illustrates how dolomite textural alteration and stabilization can occur at earth surface conditions the avon park formation is a pervasively dolomitized peritidal platform carbonate 400 m thick in the floridan aquifer system typical avon park dolomite is inclusion rich fine grained 40 mm noncathodoluminescent highly porous average 20 and formed during the eocene by normal to hypersaline seawater 18o 3 7 pdb 13c 2 0 87sr 86sr 0 70778 sr 167 ppm in a 20 m interval in a core from southwest florida inclusion free cathodoluminescent dolomite overgrows the early formed noncathodoluminescent marine dolomite the cathodoluminescent dolomite cement profoundly alters the texture of avon park dolomite from typical cenozoic like porous poorly crystalline dolomite to hard dense low porosity highly crystalline paleozoic like dolomite the dolomite cement is not a replacement of limestone but an overgrowth of early formed marine dolomite and pore occluding cement from analyses of samples containing both the early marine dolomite and the late dolomite cement quantitative estimates of pure cathodoluminescent dolomite cement are 13c 0 5 and 18o 1 7 87sr 86sr 0 7085 sr 225 ppm the stable isotope compositions are intermediate between avon park marine dolomite and dolomite predicted to be in equilibrium with floridan aquifer freshwater estimated 18o 0 to 0 5 p b indicating the dolomite precipitated from waters intermediate in composition between seawater and freshwater due to the rise in seawater 87sr 86sr since the middle eocene the 87sr 86sr composition of the cathodoluminescent dolomite cement demonstrates that it must have formed after the middle miocene incorporating radiogenic sr from seawater or rocks of middle miocene age or younger a water sample was taken from this same core from an interval in the avon park formation in the dilute part of the modern mixing zone approximately 60 m above the first occurrence of altered dolomite fluids from this interval have 3400 ppm tds and are a mixture of 94 floridan aquifer freshwater and 6 normal seawater these pore fluids are sr rich 24 ppm and so4 rich 755 ppm due to extensive avon park gypsum dissolution and have a 87sr 86sr composition 0 7078 in equilibrium with avon park host rock the salinity of the fluid that precipitated the cathodoluminescent dolomite cement is quantitatively calculated with a fluid fluid mixing model using 1 the sr concentration 24 ppm and 87sr 86sr composition 0 7078 of the von park pore fluid sample from the core 2 the sr concentration 8 ppm and 87sr 86sr compositions of modern 0 7092 and late miocene 0 7089 seawater and 3 the 87sr 86sr composition 0 7085 of the cathodoluminescent dolomite cement these calculations indicate that the dolomite cement precipitated from a mixed marine meteoric fluid with salinity approximately 75 seawater this same fluid would be both calcite supersaturated and contain about 12 ppm sr such a fluid could precipitate dolomite cement with 225 ppm sr using a reasonable kd 0 05 this accounts for the higher sr concentrations in the mixing zone dolomite cement 225 ppm relative to avon park marne dolomite 167 ppm this study demonstrates that 1 dolomite precipitated from a 75 seawater mixing zone fluid that was both calcite saturated and sulfate rich and 2 dramatic textural maturation and stabilization in dolomite can occur in the near surface environment without elevated temperature and burial conditions

high resolution stratigraphy with strontium isotopes the isotopic ratio of strontium 87 to strontium 86 shows no detectable variation in present day ocean water but changes slowly over millions of years the strontium contained in carbonate shells of marine organisms records the ratio of strontium 87 to strontium 86 of the oceans at the time that the shells form sedimentary rocks composed of accumulated fossil carbonate shells can be dated and correlated with the use of high precision measurements of the ratio of strontium 87 to strontium 86 with a resolution that is similar to that of other techniques used in age correlation this method may prove valuable for many geological paleontological paleooceanographic and geochemical problems

tracing ground water evolution in a limestone aquifer using sr isotopes effects of multiple sources of dissolved ions and mineral solution reactions uplifted pleistocene coral reef terraces on barbados west indies constitute an aquifer that is built on low permeability tertiary pelagic rocks that overlie the barbados accretionary prism the downdip segments of the aquifer are composed of younger reef limestones that contain more aragonite and have higher 87sr 86sr and sr ca ratios than the updip parts of the aquifer ground waters and host limestones display similar stratigraphic trends in 87sr 86sr and sr ca the ground waters have lower 87sr 86sr values however indicating that they acquire a significant fraction of their dissolved sr through interaction with components of tertiary rocks which compose the underlying aquitard and parts of overlying soils geochemical modeling results indicate that ground water evolution is controlled by 1 variations in the age and composition of the aquifer and aquitard rocks and 2 the relative roles of calcite dissolution calcite recrystallization and the transformation of aragonite to calcite sr isotopes can provide unique information for tracing ground water evolution which requires consideration of the multiple components and processes that make up even relatively simple limestone aquifer systems

87sr 86sr ratios in permo carboniferous sea water from the analyses of well preserved brachiopod shells abstract sr isotopic analyses of well preserved portions of permo carboniferous brachiopods distributed globally confirm the general shape of the sr isotope age curve established by previous workers for this time interval there is little variation between the sr isotopic composition of unaltered portions of brachiopods and that of portions of the same shell interpreted to be diagenetically altered based on cathodoluminescence elemental and stable isotopic data however the sr isotopic composition in diagenetically altered micritic matrix adjacent to the shell is more radiogenic the sr isotopic composition in the unaltered portions of calcitic megafossils has potential as a stratigraphie tool

carbon isotope δ13ccarb heterogeneity in deep water cambro ordovician carbonates western newfoundland abstract carbonates of western newfoundland span the cambro ordovician interval and preserve a record of slope basinal deposition in the cow head group near cow head this unit consists of conglomerates and ribbon and laminated limestone interbedded with shale that is well exposed in sea cliffs at cow head peninsula these conglomerates although prevalent throughout the section vary in thickness and abundance stratigraphically and record both local disruption and large scale episodic sedimentation events microfacies drilled for carbon isotope 13 c carb analysis of conglomerates reveal isotopic heterogeneity within individual samples in some cases more than 1 while this might be an expected outcome of drilling multiple areas of a heterogeneous conglomerate hand sample permil level variability was observed both between individual clasts in a sample between different parts of the same matrix and between a clast and its surrounding matrix no associated variation in 18 o carb or trace element distributions exists to suggest that this 13 c carb variability is the result of later stage meteoric diagenesis the 13 c carb variability suggests multiple sources of dissolved inorganic carbon dic associated with carbonate precipitation for phases within these individual samples these data indicate that processes such as local organic matter remineralization and early authigenic carbonate precipitation during lithification at the sediment water interface swi are either contributing to or controlling 13 c carb values in cambrian carbonates perhaps more so than at other intervals in earth history

sector zoning in natural and synthetic calcites abstract sector zoning refers to a compositional difference between coeval growth sectors in a crystal and results from differences in fluid crystal element partitioning between nonequivalent faces of the crystal sector zoning involving the trace elements mg mn fe and sr is common in natural calcite cements and sector zoning of mn has been induced in synthetic calcite crystals differences in surface structure between nonequivalent faces are seen as the principal causes for face dependent partitioning

application of the trace element and isotope geochemistry of strontium to studies of carbonate diagenesis carbonate rocks and natural waters exhibit a wide range in the concentration and isotopic composition of strontium this wide range and the quantifiable covariation of these parameters can provide diagnostic tools for understanding processes of fluid rock interaction careful consideration of the uncertainties associated with trace element partitioning sample heterogeneity and fluid rock interaction mechanisms is required to advance the application of the trace element and isotope geochemistry of strontium to studies of diagenesis goundwater evolution ancient seawater chemistry and isotope stratigraphy a principal uncertainty involved in the application of sr concentration variations to carbonate systems is the large range of experimental and empirical results for trace element partitioning of sr between mineral and solution this variation may be a function of precipitation rate mineral stoichiometry crystal growth mechanism fluid composition and temperature calcite and dolomite in ancient limestones commonly have significantly lower sr concentrations 20 70 p p m than would be expected from published trace element distribution coefficient values and sr ca ratios of most modern sedimentary pore waters this discrepancy probably reflects the uncertainties associated with determining distribution coefficient values as techniques improve for the analytical measurement and theoretical modelling of sr concentration and isotopic variations the petrological analysis of carbonate samples becomes increasingly important the presence of even small percentages of non carbonate phases with high rb concentrations and high 87 sr86 sr values such as clay minerals can have significant effects on the measured 87 sr 86 sr values of carbonate rocks due to the decay of 87rb to 87 sr for example a permian marine limestone with 50 p p m sr and 1 p p m rb will have a present day 87 sr 86 sr value that is 2 10 4 higher than its original value this difference is an order of magnitude greater than the analytical uncertainty and illustrates the importance of assessing the need for and accuracy of such corrections a quantitative evaluation of the effects of water rock interaction on sr concentrations and isotope compositions in carbonates strengthens the application of these geochemical tracers geochemical modelling that combines the use of trace elements and isotopes can be used to distinguish between different mechanisms of water rock interaction including diffusive and advective transport of diagenetic constituents in meteoric pore fluids during the recrystallization of carbonate minerals quantitative modelling may also be used to construct diagnostic fluid rock interaction trends that are independent of distribution coefficient values and to distinguish between mixing of mineral end members and fluid rock interaction

geochemical characteristics of upper jurassic lower cretaceous platform carbonates in hazine magara gumushane northeast turkey implications for dolomitization and recrystallization1 the upper jurassic lower cretaceous berdiga formation of the eastern pontides turkey represents a carbonate platform succession composed of pervasively dolomitized intra shelf to deep shelf fac

himalayan tectonics weathering processes and the strontium isotope record in marine limestones the time evolution of the isotopic composition of seawater strontium the ratio of strontium 87 to strontium 86 over the last 500 million years has the form of an asymmetric trough the values are highest in the cambrian and recent 0 7091 and lowest in the jurassic 0 7067 superimposed on this trend are a number of smaller oscillations consideration of the geochemical cycle of strontium and the dynamics of weathering shows that only himalayan style continental collisions can influence the isotope ratio on the scale observed the contemporary himalayan orogeny is by far the largest since the late precambrian pan african event that produced the high in the cambrian

controls on the spatial and temporal variability of vadose dripwater geochemistry edwards aquifer central texas abstract a 4 yr study of spatial and temporal variability in the geochemistry of vadose groundwaters from caves within the edwards aquifer region of central texas offers new insights into controls on vadose groundwater evolution the relationship between vadose and phreatic groundwaters and the fundamental influence of soil composition on groundwater geochemistry variations in sr isotopes and trace elements mg ca and sr ca ratios of dripwaters and soils from different caves as well as phreatic groundwaters provide the potential to distinguish between local variability and regional processes controlling fluid geochemistry and a framework for understanding the links between climatic and hydrologic processes the sr isotope compositions of vadose cave dripwaters mean 87sr 86sr 0 7087 and phreatic groundwaters mean 87sr 86sr 0 7079 generally fall between values for host carbonates mean 87sr 86sr 0 7076 and exchangeable sr in overlying soils mean 87sr 86sr 0 7088 dripwaters have lower mg ca and sr ca ratios and higher 87sr 86sr values than phreatic groundwaters dripwater 87sr 86sr values also inversely correlate with both mg ca and sr ca ratios mass balance modeling combined with these geochemical relationships suggest that variations in fluid compositions are predominantly controlled by groundwater residence times and water rock interaction with overlying soils and host aquifer carbonate rocks consistent differences in dripwater geochemistry i e 87sr 86sr mg ca and sr ca between individual caves are similar to compositional differences in soils above the caves while these differences appear to exert significant control on local fluid evolution geochemical and isotopic variations suggest that the controlling processes are regionally extensive temporal variations in 87sr 86sr values and mg ca ratios of dripwaters from some sites over the 4 yr interval correspond with changes in both aquifer and climatic parameters these results have important implications for the interpretation of trace element and isotopic variations in speleothems as paleoclimate records as well as the understanding of controls on water chemistry for both present day and ancient carbonate aquifers

infrasound from the 2012 2013 plosky tolbachik kamchatka fissure eruption abstract we use both regional and local infrasound data to investigate the dynamics of the 2012 2013 eruption of tolbachik volcano kamchatka russia during select periods of time analysis of regional data recorded at the ims array is44 in southern kamchatka 384 km from the vent focuses on the eruption onset in november 2012 while analysis of local data focuses on activity in february and august 2013 signals recorded from tolbachik suggest a change in eruptive intensity possibly occurred from november 27 30 2012 local infrasound data recorded at distances of 100 950 m from the vent are characterized primarily by repeated transient explosion signals indicative of gas slug bursts three methods are employed to pick slug burst events in february and august the nature of slug bursts makes a monopole acoustic source model particularly fitting permitting volume outflux and slug radius calculations for individual events volume outfluxes and slug radii distributions provide three possible explanations for the eruption style of tolbachik volcano from mid february to late august cumulative outflux for slug bursts i e mass of emissions from individual bursts derived by infrasound for both february and august range from

disequilibrium trace element partitioning in jurassic sparry calcite cements implications for crystal growth mechanisms during diagenesis sparry calcite cements from middle jurassic limestones in central england contain complex non concentric zoning patterns produced by a combination of sector zonation and a sector specific lamellar or polygonal zonation electron microprobe analyses of individual zones within crystals document 1 a sympathetic covariation of fe mg and sr between two non equivalent sectors and 2 episodic further increase of sr contents coupled with exclusion of fe mg and mn within the more enriched sectors comparison of results from three different localities demonstrates the regional consistency of this pattern although the magnitude of the differential trace element partitioning varies from combined petrographic and geochemical data the trace element variation in the crystals can be shown to bear no simple relationship with either 1 the chemical evolution of the 9bulk9 precipitating porefluid or 2 the relative overall growth rates of the different crystal faces previous sector zoning models based on crystal surface configurations and internal structure are unable to account directly for the geochemical patterns observed in this study differences between growth mechanisms on the crystal faces of the studied spars are likely to have exerted a significant influence on trace element partitioning in particular they offer a plausible explanation for the geometric and compositional characteristics of the sector specific episodic zoning on the most enriched crystal faces in general crystal morphology and composition will be intimately linked by the growth mechanisms operating on different faces and by their response to changes in the diagenetic environment the validity of diagenetic interpretations from bulk geochemical analysis of sparry calcite cements thus rests upon a detailed analysis of any zonation that they contain

abu dhabi sabkha persian gulf revisited application of strontium isotopes to test an early dolomitization model a study of brines and diagenetically altered minerals from coastal sabkha of abu dhabi persian gulf was undertaken to test the flood recharge evaporative pumping model for early dolomitization using strontium isotopes as a tracer the sup 87 sr sup 86 sr ratio of the sabkha brines defines a pattern of both horizontal and vertical mixing of coastal seawater and continental ground water consistent with a previously proposed model the sup 87 sr sup 86 sr ratio of the diagenetic dolomites indicates early dolomitization by marine recharge waters the sup 87 sr sup 86 sr ratio of gypsum from the dolomitization area 1 4 to 4 4 km from high tide mark and seaward reflects precipitation from marine brines but more landward 6 to 9 km gypsum and anhydrite record a continental signal in the minerals suggests a paragenetic evaporative sequence dolomite yields gypsum yields anhydrite the dolomitizing fluid is evaporated seawater that recharges the sabkha aquifer during supratidal flooding and is afterward pumped upward through the saturated zone by evaporative processes

minor and trace element distributions in the bonneterre dolomite cambrian southeast missouri evidence for possible multiple basin fluid sources and pathways during lead zinc mineralization the sources and flow paths of basinal fluids that precipitated the dolomite hosted mississippi valley type orebodies of southeast missouri have historically been a subject of debate this study presents geochemical data for epigenetic dolomites of the bonneterre dolomite directly above the lamotte sandstone aquifer and from the viburnum trend orebodies samples of epigenetic replacement dolomite were collected at the bonneterre dolomite lamotte sandstone contact from 35 drill cores covering an area of more than 25 000 km 2 west of the st francois mountains there are distinct aerial trends in fe mn and sr contents of the dolomite from values of 3 47 wt 0 38 wt and 27 ppm in the south to 0 82 wt 0 12 wt and 54 ppm in the north respectively in and near the viburnum trend lead zinc subdistrict the distributions of fe mn and sr are reversed from values of 0 50 wt 0 10 wt and 105 ppm in the south to 3 15 wt 0 55 wt and 40 ppm in the north respectively fe and mn contents of gangue dolomite cement in the viburnum trend orebodies show a similar south to north enrichment ranging from 1 41 mole feco 3 and 0 11 mole mnco 3 in the south to 2 34 mole and 0 23 mole in the north respectively on the basis of fractionation of minor and trace elements between fluids and dolomites the data are interpreted to indicate a regional south to north flow of water from the arkoma basin through the lamotte sandstone a second fluid flow system with a northern source possibly the illinois basin precipitated the late phases of gangue dolomite cement in the viburnum trend and may have been active during the earlier precipitation of the dolomite at the lamotte bonneterre contact the inferred fluid flow paths suggest a more complex multiple basin fluid involvement than previously suggested for the mississippi valley type pb zn mineralization of southeast missouri

using unsupervised machine learning to identify changes in eruptive behavior at mount etna italy abstract volcanoes frequently generate infrasound signals that need to be processed before they can be used to monitor and track changes in eruptive activity unsupervised machine learning is complementary to existing processing methods and can be used for data exploration to identify features of interest in the data here i examine three days of infrasound data from mount etna italy that encompasses the 24 december 2018 fissure eruption the continuous infrasound data is divided into overlapping windows and for each window i extract seven features in the time and frequency domains that characterize the signal i apply the k means clustering algorithm to group the data into seven clusters and generate a discrete time series of cluster labels the cluster labels clearly identify a change in eruptive activity from strombolian explosions at the summit to lava fountaining at the fissure feature distributions and representative waveforms for each cluster are analyzed and source mechanisms are hypothesized this work illustrates how advances in unsupervised machine learning can be leveraged to explore volcano infrasound data sets and demonstrates the potential of these techniques for monitoring eruptive activity

a silicate weathering mechanism linking increases in marine 87sr 86sr with global glaciation the 87sr 86sr ratio of sea water is generally regarded as a proxy for the rate of chemical weathering of the continents interpretation of the 87sr 86sr record in marine limestones requires an understanding of how changes in this quantity are linked to climate and tectonic events a connection between the strontium isotope record and the extent of global glaciation has been proposed1 8 but without a well established mechanism glaciation may influence marine 87sr 86sr by changing global riverine sr fluxes that is rock weathering rates and or 87sr 86sr ratios that is relative mineral weathering rates here we investigate how the 87sr 86sr release from silicate weathering is affected by glaciation using the sr isotope systematics of granitoid soils on alpine glacial moraines in the wind river range wyoming we observe a negative correlation between the 87sr 86sr ratio of exchangeable sr in soils and the soil age indicating that the 87sr 86sr ratio of sr released in the early stages of weathering is significantly higher than in later stages we estimate that this mechanism can increase global riverine 87sr 86sr by an average of 0 0002 during periods of glacial interglacial cycling when superimposed on long term trends controlled by tectonic processes2 7 9 10 this shift can account for the correlation between the rate of change of marine 87sr 86sr and the intensity of glaciation over at least the past 10 myr

building biogenic beachrock visualizing microbially mediated carbonate cement precipitation using xfm and a strontium tracer the fate of reef islands is a topic of ongoing debate in the face of climate change induced sea level rise and increased cyclone intensity increased erosion and changes to the supply of reef derived sediment may put sand reef cays at risk of dramatic morphological changes these changes may have negative implications for the existence of reef cay environments which host vital sea turtle and bird rookery habitats beachrock consolidated carbonate beach sediment in the intertidal zone forms naturally on many tropical beaches and reduces the erosion rates of these beaches when compared to unconsolidated sand in spite of the critical role beachrock plays in stabilizing some reef cay shores the method of beachrock formation is still incompletely understood in this investigation beachrock was synthesized using beach sand and beachrock samples from heron island great barrier reef australia in aquarium experiments in which natural beachrock formation conditions were simulated beachrock was produced in two aquaria wherein the water chemistry was influenced by microorganisms derived from the natural beachrock inoculum whereas no cementation occurred in an aquarium that lacked a microbial inoculum and was controlled only by physicochemical evapoconcentration the new cements in the synthesized beachrock were analyzed using synchrotron based x ray fluorescence microscopy and were identified using a sr tracer added to the experimental seawater the resulting precipitates cement sand grains together and contain abundant microfossils of the microorganisms on whose exopolymer they nucleated demonstrating the fundamental role microbes play in beachrock formation these results are of interest because beachrock could be utilized as a natural coastline stabilization strategy on sand reef cays and in turn protect the unique habitats reef islands support

fluid inclusion rb sr isochrons for dating mineral deposits the precise dating of mineral deposits has important implications for understanding the lifetime of ore forming systems and their temporal relationship to various geological events not all deposits provide material suitable for conventional radiometric dating or data which are amenable to unequivocal interpretation nor is it easy to verify that such samples have remained isotopically closed since their formation fluid inclusions provide an alternative closed system approach by analysing the isotopic composition of rband sr in inclusions within quartz from the carrock fell tungsten vein deposits cumbria we demonstrate here the feasibility of obtaining rb sr fluid inclusion isochrons the age for the mineralization 392 5 myr is in good agreement with the mean k ar age 387 6 myr for the vein micas and confirms the significance of fluid inclusions as precise rb sr geochronometers

detecting imminent eruptive activity at mt etna italy in 2007 2008 through pattern classification of volcanic tremor data abstract volcano monitoring aims at the recognition of changes in instrumentally observable parameters before hazardous activity in order to alert governmental authorities among these parameters seismic data in general and volcanic tremor in particular play a key role recent major explosive eruptions such as okmok aleutians and chaiten chile in 2008 and numerous smaller events at mt etna italy have shown that the period of premonitory seismic activity can be short only a few hours which entails the necessity of effective automatic data processing near on line here we present a synoptic pattern classification analysis based on self organizing maps and fuzzy cluster analysis which is applied to volcanic tremor data recorded during a series of paroxysmal eruptive episodes and a flank eruption at etna in 2007 2008 in total eight episodes were analyzed in six of these significant changes in the dynamic regime of the volcano were detected up to 9 h prior to the onset of eruptive activity and long before changes in volcanic tremor amplitude and spectral content became evident in classical analysis in two cases the state transition was

relationship between tremor and volcanic activity during the southeast crater eruption on mount etna in early 2000 1 the southeast crater of mount etna italy was characterized by a violent eruptive activity between 26 january and 24 june 2000 this activity produced 64 lava fountain episodes with repose periods from 3 hours to 10 days we estimated a volume of about 15 20 106 m3 lava and at least 2 3 106 m3 of tephra we compared the paroxysmal volcanic activity to its associated seismic signature the high number of events highlighted a strict correlation between tremor and volcanic activity seismic and volcanic characteristics such as the frequency of occurrence the duration of lava fountains and the associated tremor energy suggested the subdivision of the studied period into two stages separated by the 20 february event combining volcanic with seismic data we observed some useful relationships among lava fountain height sustained column height and reduced displacement in addition we found that the entire episode was well correlated with the duration of the amplitude increase computing the tremor energy linked to each event the total energy associated with lava fountains episodes results in 76 of the energy released during the whole period finally the different ratios among the overall spectral amplitude of the seismic signals of the stations located at different altitudes suggested to us the elaboration of a simple qualitative model to explain the dynamic behavior of the tremor source during the whole episode

tracking eruptive phenomena by infrasound may 13 2008 eruption at mt etna 1 active volcanoes produce inaudible infrasound due to the coupling between surface magmatic processes and the atmosphere monitoring techniques based on infrasound measurements have been proved capable of producing information during volcanic crises we report observations collected from an infrasound network on mt etna which enabled us to detect and locate a new summit eruption on may 13 2008 when poor weather inhibited direct observations three families of signals were identified that allowed the evolution of the eruption to be accurately tracked in real time each family is representative of a different active vent producing different waveforms due to their varying geometry several competitive models have been developed to explain the source mechanisms of the infrasonic events but according to our studies we demonstrate that two source models coexist at mt etna during the investigated period such a monitoring system represents a breakthrough in the ability to monitor and understand volcanic phenomena

dolomitization of the devonian swan hills formation rosevear field alberta canada the swan hills formation middle upper devonian of the western canada basin is host to several nw se trending gas fields developed in massive replacement dolostone one of these the rosevear field contains two major dolostone trends along opposing margins of a marine channel that penetrates into a platform reef complex dolostones consist predominantly of branching and bulbous strdmatoporoid floatstones and rudstones with well developed moldic and vuggy porosity replacement dolomite is coarsely crystalline 100 600 m inclusion rich composed of euhedral through anhedral crystals and has a blotchy to homogeneous red cathodoluminescence geochemically replacement dolomite is characterized by i nearly stoichiometric composition 50 1 51 1 mol caco3 ii negative 18o values mean 7 5 pdb and iii variable 87sr 86sr ratios ranging from values similar to late devonian early mississippian seawater 0 7082 to radiogenic compositions comparable to saddle dolomite cements 0 7100 dolomitization began after widespread precipitation of early equant calcite spar and after the onset of pressure solution implying that replacement dolomite formed in a burial environment oxygen isotope data suggest that dolomite formed at 35 75 c temperatures reached during burial in late devonian through jurassic time at minimum depths of 450 m the linear nw se orientation of most dolomite fields in the swan hills formation is suggestive of fault control on fluid circulation two models are proposed for fault controlled circulation of dolomitizing fluids at the rosevear field in the first compaction driven updip fluid migration occurred in response to basin tilting commencing in the late palaeozoic deep basinal fluids migrating updip were focused into channel margin sediments along fault conduits the second model calls upon fault controlled convective circulation of i warm devonian mississippian seawater or ii middle devonian residual evaporitic brines the overlap in 87sr 86sr and 18o compositions and similar cathodoluminescence properties between replacement and saddle dolomites provide evidence for neomorphism of some replacement dolomite quantitative modelling of sr and o isotopes and sr abundances suggests partial equilibration of some replacement dolomite with hot radiogenic brines derived during deep burial of the swan hills formation in the late cretaceous palaeocene interaction of replacement dolomite with deep brines led to enrichment in 87sr while leaving 18o similar to pre neomorphism values

array tracking of infrasonic sources at stromboli volcano 1 infrasonic arrays are a powerful tool for volcanic monitoring and hazard assessment explosions were recorded at stromboli using a small aperture array of 4 infrasonic stations allowing precise vent location the acoustic signals were delayed and summed revealing the existence of two main groups of infrasonic waves the ne crater produces short 3 s high amplitude 20 80 pa pressure waves while the sw crater produces small acoustic pressure 10 30 pa with long 5 15 s coda the two groups reflect different in explosive styles and similar spectral content centered on 5 6 hz when stacked together acoustic waveforms for each crater reveal the same pressure pulse which indicates a common source process we infer that the acoustic onset at both craters is generated by the burst of a large gas bubble while the acoustic coda is controlled by a sustained pressure release

a strontium isotopic study of formation waters from the illinois basin u s a abstract the isotopic composition of sr has been measured in 73 formation water samples from paleozoic strata in the illinois basin 87sr 86sr ratios range from 0 7079 to 0 7108 with the exception of four samples the waters are more radiogenic than corresponding paleozoic sea water values the relatively narrow range of slightly elevated 87sr 86sr rations is uniformly distributed in waters throughout the stratigraphic column and in silurian waters across the basin isotopic analyses of core samples from reservoir rocks show an absence of water rock sr isotopic equilibration basin lithology and analyses of detrital rock units indicate that clay minerals in shales and in quartz sandstone matrices represent the only significant source of radiogenic sr for the waters silurian and devonian water show a two component mixing relation which suggests that they comprise a single hydrogeological system that evolved when radiogenic water from new albany shales entered silurian devonian carbonate rocks and mixed with marine interstitial water regional migration of the waters and associated petroleum within the silurian devonian strata proposed in other studies is consistent with the sr isotopic data under favorable circumstances subsurface waters are capable of retaining a sr isotopic recor of their evolution

three dimensional volcano acoustic source localization at karymsky volcano kamchatka russia abstract we test two methods of 3 d acoustic source localization on volcanic explosions and small scale jetting events at karymsky volcano kamchatka russia recent infrasound studies have provided evidence that volcanic jets produce low frequency aerodynamic sound jet noise similar to that from man made jet engines for man made jet noise noise sources localize along the turbulent jet flow downstream of the nozzle discrimination of jet noise sources along the axis of a volcanic jet requires high resolution in the vertical dimension which is very difficult to achieve with typical volcano acoustic network geometries at karymsky volcano an eroded edifice dvor caldera adjacent to the active cone provided a platform for the deployment of five infrasound sensors in july 2012 with intra network relief of 600 m the network was designed to target large scale jetting but unfortunately only small scale jetting and explosions were recorded during the 12 day experiment a novel 3 d inverse localization method srcloc is tested and compared against a more common grid search semblance technique simulations using synthetic signals show that srcloc is capable of determining vertical solutions to within 150 m or better for signal to noise ratios 1 for this network configuration however srcloc locations for explosions and small scale jetting at karymsky volcano show a persistent overestimation of source elevation and underestimation of sound speed the semblance method provides more realistic source locations likely because it uses a fixed realistic sound speed of 340 m s explosion waveforms exhibit amplitude relationships and waveform distortion strikingly similar to those theorized by modeling studies of wave diffraction around the crater rim we suggest that the delay of acoustic signals and apparent elevated source locations are due to raypaths altered by topography and or crater diffraction effects implying that topography in the vent region must be accounted for when attempting 3 d volcano acoustic source localization though the data presented here are insufficient to resolve small scale jet noise sources similar techniques may be successfully applied to large volcanic jets in the future

diagenesis and paleofluid flow in the devonian southesk cairn carbonate complex in alberta canada abstract one of the largest geological features in the deep part of the alberta basin in western canada is the middle to upper devonian southesk cairn carbonate complex sccc the sccc lies at depths of about 5000 m in the vicinity of the disturbed belt of the rocky mountains and is rising to depths of 2000 m in a northeasterly direction over a distance of 150 km the complex contains several natural gas pools which contain up to about 30 h2s the major focus of this study is to construct a detailed diagenetic history and concurrent pore fluid flow over time the southesk cairn complex reveals a complicated diagenetic history that consists of five phases of pore water evolution 1 synsedimentary to shallow burial 2 intermediate burial 3 deep burial 4 maximum burial and 5 present depth each of these phases influenced the character and the quality of the reservoir rocks phase 4 is of special interest because the strontium isotope data of late diagenetic calcite cements suggest the influence of basin external fluids the 87sr 86sr isotope ratios of these calcite cements are high up to 0 7320 directly adjacent to the disturbed belt and they decrease with increasing distance towards the foreland basin 0 7100 the radiogenic strontium signal can be traced for about 100 km into the foreland basin circumstantial evidence suggests that the radiogenic strontium was carried by fluids that were expelled during the laramide orogeny from the rocky mountain main ranges and or the underlying basement

the isotopic record of ocean chemistry and diagenesis preserved in non luminescent brachiopods from mississippian carbonate rocks illinois and missouri fossil brachiopod shells are commonly used as a faithful record of the chemical and isotopic composition of the ancient ocean water in which they grew owing to their stable mineralogy and their presence in marine strata throughout phanerozoic time the utility of these fossils for preserving ocean water compositions is evaluated through analyses of multiple specimens that grew in contemporaneous sea water at individual stratigraphic horizons in the mississippian age burlington keokuk formation of mid continent north america significant variations in sr c and o isotopic compositions are observed in contemporaneous non luminescent shells indicating that apparently pristine brachiopod shell material has been altered by post depositional processes of diagenesis the least altered compositions at each horizon are used to estimate secular variations of 87 sr 86 sr in early mississippian ocean water the estimated rates of change of ocean water 87 sr 86 sr are comparable in magnitude to the rapid sr isotopic changes documented for cenozoic ocean water for which high frequency glacial cycles are inferred as a driving mechanism the rigorous assessment of diagenetic effects on the isotopic signatures of marine phases is requisite for the advancement of high resolution reconstructions of paleo ocean chemistry

strontium and its isotopes in canadian rivers fluxes and global implications systematic sampling of the 39 largest canadian rivers shows that the weighted average 87sr86sr ratio in the dissolved load is 0 7111 similar to previous measurements on such large rivers as the amazon and mississippi consequently we believe that the above estimate is likely representative of the global average this imposes a limit of 6 5 1011g yr 1 on the amount of sr exchanged with basalts in hydrothermal cells on mid oceanic ridges evaluation of geological information suggests that sr from silicate sources is of considerable importance for all but the largest canadian rivers the latter have chemical and isotopic composition consistent with 4 1 carbonate vs silicate derivation of sr but such interpretation is not unique in terms of their water discharge the 39 canadian rivers studied account for 4 2 of the world total and their weighted average concentrations for other dissolved solutes are tds 176 ppm ca 18 ppm cl 6 8 ppm and sr 84 ppb

an unloading foam model to constrain etna s 11 13 january 2011 lava fountaining episode 1 the 11 13 january 2011 eruptive episode at etna volcano occurred after several months of increasing ash emissions from the summit craters and was heralded by increasing so2 output which peaked at 5000 megagrams day several hours before the start of the eruptive activity the eruptive episode began with a phase of strombolian activity from a pit crater on the eastern flank of the se crater explosions became more intense with time and eventually became transitional between strombolian and fountaining before moving into a lava fountaining phase fountaining was accompanied by lava output from the lower rim of the pit crater emplacement of the resulting lava flow field as well as associated lava fountain and strombolian phases was tracked using a remote sensing network comprising both thermal and visible cameras thermal surveys completed once the eruptive episode had ended also allowed us to reconstruct the emplacement of the lava flow field using a high temporal resolution geostationary satellite data we were also able to construct a detailed record of the heat flux during the fountain fed flow phase and its subsequent cooling the dense rock volume of erupted lava obtained from the satellite data was 1 2 106 m3 this was emplaced over a period of about 6 h to give a mean output rate of 55 m3 s 1 by comparison geologic data allowed us to estimate dense rock volumes of 0 85 106 m3 for the pyroclastics erupted during the lava fountain phase and 0 84 1 7 106 m3 for lavas erupted during the effusive phase resulting in a total erupted dense rock volume of 1 7 2 5 106 m3 and a mean output rate of 78 117 m3 s 1 the sequence of events and quantitative results presented here shed light on the shallow feeding system of the volcano

geochemistry and crystal morphology of aragonite cements of mixing zone origin barbados west indies abstract isopachous aragonite ray cement arc lines large rugs 5 cm through a 4 m interval recovered in core samples from a borehole drilled along the southeast coast of barbados the vuggy cement interval is 12 16 m below core top and most of the interval is below the modern water table 13 m the top of the interval corresponds to the top of the 194 ka coral reef terrace which is unconformably overlain by the 122 ka terrace arc was precipitated after a period of meteoric diagenesis during which vuggy porosity was produced arc shows variable ultrastructures including 1 loosely packed randomly oriented rays the 100 arc has uncharacteristically low 13c values relative to predicted and reported values for marine aragonite cement likewise the 18o values are lower than both reported and most predicted o18o values for marine aragonite stable isotope compositions of this cement fall along a mixing line between aragonite equilibrium compositions calculated for meteoric and marine end member fluids strontium concentrations are greater than in most known marine aragonite this suggests precipitation from fluids with an elevated sr ca ratio such fluids are found in modern barbados mixed waters whose elevated sr ca ratios result from updip meteoric dis olution of aragonite magnesium concentrations are slightly higher and more variable than in reported pleistocene marine aragonite sodium concentrations are lower than expected marine values and covary with changes in 13c and 18o values isotope and minor element geochemistry of these cements suggests precipitation from mixed meteoric marine waters fluid mixing models for modern barbados waters suggest precipitation from mixed fluids ranging from 50 to 75 seawater precipitation of aragonite from mixed waters may be facilitated by degassing of co2 charged mixed waters within large vugs and by mg ca ratios sufficiently elevated to inhibit precipitation of calcite

eocene to early miocene growth of enewetak atoll insight from strontium isotope data the margin of enewetak atoll contains 1 260 to 1 405 m of cenozoic carbonates above a volcanic basement previous biostratigraphic studies on two deep wells e1 and f1 yielded conflicting results on the ages of tertiary strata on enewetak and on the presence of oligocene strata strontium isotope ratios support relatively continuous carbonate sedimentation from late eocene to early miocene 23 ma carbonate deposition on the atoll margin started with rapid aggradation during much of the late eocene followed by gradual seaward progradation of depositional facies during the latest eocene oligocene and early miocene the only distinct break in sedimentation from late eocene to early miocene was observed at 850 m in the e1 well here an unconformity formed by subaerial exposure separates backreef upper eocene grainstones from lower oligocene carbonates no contemporaneous subaerial exposure surface and unconformity were observed in the f1 well because correlative rocks were deposited in a slope environment extensive diagenesis occurred in upper eocene oligocene and lower miocene strata at the atoll margin where sea water circulated through in response to thermal convection and tidal pumping the main diagenesc processes are 1 aragonite dissolution 2 radiaxial calcite cementation 3 compaction in slope deposits and 4 dolomitization aragonite dissolution is pervasive below 375 m in the f1 well radiaxial calcite cement is common at 375 825 m in the f1 well compaction related fracturing and pressure solution are common in poorly cemented packstones and grainstones deposited in a slope environment and now buried more than 1 100 m deep dolomite is common in slope carbonates at 1 320 m in the f1 well and in reefal carbonates at 1 245 m in the e1 well stable carbon and oxygen isotope data support formation of radiaxial calcite and dolomite in cool sea water radiaxial calcite cement and dolomite have distinctly higher 87sr 86sr ratios than does adjacent depositional carbonate strontium isotope ratios of radiaxial calcite cements indicate precipitation at burial depths of 100 350 m the absence of meteoric cements and association of radiaxial calcite cement with aragonite dissolution suggest that aragonite dissolution also occurred in moderately deep sea water strontium isotope ratios in dolomites indicate dolomitization by sea water at burial depths greater than 950 m marine diagenesis is dependent on the saturation state of sea water relative to aragonite calcite and dolomite shallow sea water supersaturated with respect to aragonite and high magnesium calcite hmc precipitates aragonite and hmc moderately deep sea water undersaturated with respect to aragonite and hmc super saturated with respect to low magnesium calcite lmc dissolves aragonite converts hmc to lmc and precipitates lmc including radiaxial calcite deep sea water under saturated with respect to calcite supersaturated with respect to dolomite dissolves calcite and precipitates dolomite the intensity of marine diagenesis depends on the amount of sea water circulating through the platform or atoll margin

influence of atmospheric structure and topography on infrasonic wave propagation the effects of topography and atmospheric structures on infrasonic wave propagation from a volcanic source were investigated using observations and numerical modeling this paper presents the first long term observational data set showing spatiotemporal variations in patterns of infrasound propagation at distances of up to 60 km from a persistently active infrasound source sakurajima volcano japan the data show that the amplitudes of infrasonic waves received at distant stations relative to those received at a reference station close to the source can vary up to an order of magnitude over short time intervals and short distances and that they do not follow the theoretical geometric decay expected for homogeneous media moreover waveforms also change significantly in both time and space numerical simulations were performed using a two dimensional finite difference time domain 2 d fdtd method effects of atmospheric structure and topography are included in a vertical section parallel to the wave propagation direction the simulation successfully reproduced the variations of amplitudes and waveforms results are interpreted in terms of wave refraction due to sound and wind speed gradients and wave diffraction at topographic barriers our numerical results indicate that both atmospheric and topographic propagation effects are nonnegligible to evaluate the propagation effects and determine source processes in spatially and temporally varying infrasound data atmospheric data with a time resolution higher than is currently available are required if the data are available the present results suggest that the propagation effects could be evaluated using 2 d fdtd modeling at realistic calculation times

new type of compositional zoning in calcite insights into crystal growth mechanisms compositional zoning of trace elements is observed in time equivalent regions within 10 overline 1 4 growth sectors of natural and synthetic calcite single crystals and has been called intrasectoral zoning to distinguish it from conventional sectoral zoning differential interference contrast microscopy shows that 101 overline 1 4 faces grow by the spiral mechanism cathodoluminescence microscopy and electron probe microanalyses reveal that trace element partitioning differences on 101 overline 1 4 faces correspond exactly to crystallographically controlled orientations of growth steps effective partitioning of mg and mn varies up to a factor of four between time correlative growth steps spreading in different directions effective sr partitioning varies by approximately 20 and is inversely correlated with enrichment trends of mg and mn preferential incorporation of different aqueous species at different growth steps may provide an explanation for morphological and chemical variation in natural calcites

dolomitization of the late cretaceous paleocene platform carbonates golkoy ordu eastern pontides ne turkey abstract late cretaceous paleocene agillar formation in the eastern pontide zone ne turkey is composed of shallow marine platform carbonates that were buried until uplift in late paleocene time the formation which is represented by 100 m thick reefal limestones around golkoy is completely dolomitized on the basis of petrographic and geochemical features four different replacive and cement dolomite phases are present the replacive dolomites which are cut by low amplitude stylolites include 1 fine crystalline planar s dolomite rd1 and 2 coarsely crystalline planar s e dolomite rd2 two types of dolomite cements were developed in minor amounts 1 a coarse dolomite cement cd1 that mostly fills molds vugs and fractures in rd1 dolomites and 2 rim dolomite cement cd2 that commonly develops on the space facing surfaces of rd2 dolomite the replacive dolomites are nearly stoichiometric ca 49 51 mg 48 50 and have 18 o values of 3 5 to 1 6 vpdb 13 c values of 1 1 to 0 8 vpdb and 87 sr 86 sr ratios of 0 707104 to 707458 sr na mn and fe concentrations of replacive dolomites are 102 171 ppm bdl 371 ppm 244 9941 ppm and 2643 8951 ppm respectively petrographic and geochemical data indicate that the replacive dolomites were formed prior to chemical compaction at shallow to intermediate burial depths from late cretaceous paleocene seawater and or seawater slightly modified by water rock interaction process and then recrystallized by meteoric waters at increasing burial depths and temperatures compared with replacement dolomites cd1 dolomites yield lower 18 o values 4 9 to 5 3 vpdb similar 13 c values 1 2 to 0 5 vpdb and higher 87 sr 86 sr ratios 0 707660 0 707609 the cd1 dolomites overlie the low amplitude stylolites and have homogenization temperatures between 94 and 112 c indicating that they were deposited from basinal brines although replacive dolomites and dolomite cements have similar na bdl 413 ppm mn 259 6990 ppm and fe 2184 6690 ppm concentrations the cements have lower sr contents 63 114 ppm like replacive dolomites cd1 dolomite is nearly stoichiometric ca 49 50 mg 47 49 but cd2 dolomite is slightly ca rich ca 51 52 mg 47 48 the cd2 dolomite is overlain by coarsely crystalline mosaic calcite cement indicates that diagenetic fluids eventually evolved to undersaturation with respect to dolomite and oversaturation with respect to calcite

paleowaters in silurian devonian carbonate aquifers geochemical evolution of groundwater in the great lakes region since the late pleistocene abstract changes in the climatic conditions during the late quaternary and holocene greatly impacted the hydrology and geochemical evolution of groundwaters in the great lakes region increased hydraulic gradients from melting of kilometer thick pleistocene ice sheets reorganized regional scale groundwater flow in paleozoic aquifers in underlying intracratonic basins here we present new elemental and isotopic analyses of 134 groundwaters from silurian devonian carbonate and overlying glacial drift aquifers along the margins of the illinois and michigan basins to evaluate the paleohydrology age distribution and geochemical evolution of confined aquifer systems this study significantly extends the spatial coverage of previously published groundwaters in carbonate and drift aquifers across the midcontinent region and extends into deeper portions of the illinois and michigan basins focused on the freshwater saline water mixing zones in addition the hydrogeochemical data from silurian devonian aquifers were integrated with deeper basinal fluids and brines in upper devonian black shales and underlying cambrian ordovician aquifers to reveal a regionally extensive recharge system of pleistocene age waters in glaciated sedimentary basins elemental and isotope geochemistry of confined groundwaters in silurian devonian carbonate and glacial drift aquifers show that they have been extensively altered by incongruent dissolution of carbonate minerals dissolution of halite and anhydrite cation exchange microbial processes and mixing with basinal brines carbon isotope values of dissolved inorganic carbon dic range from 10 to 2 87sr 86sr ratios range from 0 7080 to 0 7090 and 34 s so 4 values range from 10 to 30 a few waters have elevated 13cdic values 15 from microbial methanogenesis in adjacent organic rich upper devonian shales radiocarbon ages and 18o and d values of confined groundwaters indicate they originated as subglacial recharge beneath the laurentide ice sheet 14 50 ka bp 15 to 13 18o these paleowaters are isolated from shallow flow systems in overlying glacial drift aquifers by lake bed clays and or shales the presence of isotopically depleted waters in paleozoic aquifers at relatively shallow depths illustrates the importance of continental glaciation on regional scale groundwater flow modern groundwater flow in the great lakes region is primarily restricted to shallow unconfined glacial drift aquifers recharge waters in silurian devonian and unconfined drift aquifers have 18o values within the range of holocene precipitation 11 to 8 and 7 to 4 5 for northern michigan and northern indiana ohio respectively carbon and sr isotope systematics indicate shallow groundwaters evolved through congruent dissolution of carbonate minerals under open and closed system conditions 13cdic 14 7 to 11 1 and 87sr 86sr 0 7080 0 7103 the distinct elemental and isotope geochemistry of pleistocene versus holocene age waters further confirms that surficial flow systems are out of contact with the deeper basinal scale flow systems these results provide improved understanding of the effects of past climate change on groundwater flow and geochemical processes which are important for determining the sustainability of present day water resources and stability of saline fluids in sedimentary basins

on the transition from strombolian to fountaining activity a thermal energy based driver since 1999 mount etna s italy south east crater system has been characterised by episodic lava fountaining each episode is characterised by initial strombolian activity followed by transition to sustained fountaining to feed high effusion rate lava flow here we use thermal infrared data recorded by a permanent radiometer station to characterise the transition to sustained fountaining fed by the new south east crater that developed on the eastern flank of the south east crater starting from january 2011 we cover eight fountaining episodes that occurred between 2012 and 2013 we first developed a routine to characterise event waveforms apparent in the precursory strombolian phase this allowed extraction of a database for thermal energy and waveform shape for 1934 events we detected between 66 and 650 events per episode with event durations being between 4 and 55 s in total 1508 78 of the events had short waxing phases and dominant waning phases event frequency increased as climax was approached events had energies of between 3 0 106 and 5 8 109 j with rank order analysis indicating the highest possible event energy of 8 1 109 j to visualise the temporal evolution of retrieved parameters during the precursory phase we applied a dimensionality reduction technique results show that weaker events occur during an onset period that forms a low energy sink the transition towards fountaining occurs at 107 j where subsequent events have a temporal trend towards the highest energies and where sustained fountaining occurs when energies exceed 109 j such an energy based framework allows researchers to track the evolution of fountaining episodes and to predict the time at which sustained fountaining will begin

patterns in the recent 2007 2008 activity of mount etna volcano investigated by integrated geophysical and geochemical observations 1 seismic deformation and volcanic gas observations offer independent and complementary information on the activity state and dynamics of quiescent and eruptive volcanoes and thus all contribute to volcanic risk assessment in spite of their wide use there have been only a few efforts to systematically integrate and compare the results of these different monitoring techniques here we combine seismic volcanic tremor and long period seismicity deformation gps and geochemical volcanic gas plume co2 so2 ratios measurements in an attempt to interpret trends in the recent 2007 2008 activity of etna volcano we show that each eruptive episode occurring at the southeast crater sec was preceded by a cyclic phase of increase decrease of plume co2 so2 ratios and by inflation of the volcano s summit captured by the gps network these observations are interpreted as reflecting the persistent supply of co2 rich gas bubbles and eventually more primitive magmas to a shallow depth of 1 2 8 km asl magma storage zone below the volcano s central craters ccs overpressuring of the resident magma stored in the upper ccs conduit triggers further magma ascent and finally eruption at sec a process which we capture as an abrupt increase in tremor amplitude an upward 2800 m asl and eastward migration of the source location of seismic tremor and a rapid contraction of the volcano s summit resumption of volcanic activity at sec was also systematically anticipated by declining plume co2 so2 ratios consistent with magma degassing being diverted from the central conduit area toward sec

late jurassic biogeochemical microenvironments associated with microbialite coated unionids bivalvia asturias n spain abstract the vega formation upper jurassic asturias spain contains two kimmeridgian outcrops the abeu and huerres sections with bivalves coated with carbonate microbialites oncoids the bivalve shells in the abeu section were replaced early by calcite while those of the huerres section were dissolved and the moulds filled by late diagenetic cements for the abeu shells there was a loss of sr and a gain of mg fe and mn during the replacement process but much of the original organic matter was retained part of the s present can be linked to this organic matter and part to the sulphate that replaced the carbonate groups in the calcite the thin microbialites inside the shells of some of the huerres bivalves have allowed us to estimate the influence of the growth rate on the incorporation of trace elements in calcite with an approximately six times lower growth rate the internal microbialite incorporates less mg and s and more fe and mn than the external one while maintaining the sr content the trace element content mg s sr fe and mn of the huerres and abeu microbialites are similar these coatings may therefore have been formed in the same type of freshwater but in different microenvironments given the substantial sulphate content of the microbialites from both sections this freshwater probably came from hot springs however the high fe mn ratio of the abeu microbialites suggests a reducing environment during their formation indeed 18o and 13c data confirm that the abeu and huerres microbialites were formed in different microenvironments the positive covariance for 18o and 13c of the abeu microbialites and replaced shells r2 0 83 and the wide range of variation for 18o 2 80 together suggest that the microbialite crusts grew in isolated ponds where evaporation was dominant in the huerres microbialites the positive covariance for 18o and 13c r2 0 59 and the narrow range of variation for 18o 0 74 indicate that the huerres section was formed in a more open environmental system where degassing predominated over evaporation

conservative behavior of mg isotopes in massive dolostones from diagenesis to hydrothermal reworking abstract mg isotopes in syndepositional dolomite have been suggested to be a potential proxy for understanding seawater chemistry however it is argued that the 26mg values of dolomite could be complicated by the effects of early diagenesis and later hydrothermal activities further investigations into the behaviors of mg isotopes in dolomitization systems are needed to resolve this controversy in the present study we investigated early ordovician dolostones from the tarim basin including diagenetically altered dolomites hydrothermally altered dolomites and well preserved dolostones that precipitated in the slope margin and interior of a carbonate platform different types of dolomites bulk dolostone and limestone were sampled by microdrilling for analyses of c o mg isotope compositions and ree concentrations the dolostone 13c values match those of coeval seawater and the ree distribution patterns in the dolostones are comparable with those in the limestones indicating that the dolostones originated from syndiagenetic dolomitization the 26mg values of the various syndiagenetic dolomites that formed in the slope margin and interior of the carbonate platform are similar averaging approximately 2 06 0 20 no stratigraphic variability in the dolomite mg isotopes can be discerned which implies that the mg isotope compositions of the porewater were homogeneous during massive dolomitization and remained in equilibrium with seawater additionally the 26mg values of the altered dolostone do not show correlations with diagenetic and hydrothermal signals demonstrating that dolomite mg isotopes are insensitive to postdepositional alteration given these facts we propose that mg isotopes in dolostones have conservative behaviors during diagenesis and late stage hydrothermal reworking

real time infrasonic monitoring of the eruption at a remote island volcano using seismoacoustic cross correlation s u m m a r y on 2013 november 20 a submarine eruption started close to nishinoshima island which lies 1000 km south of tokyo real time monitoring of the eruption is crucial for understanding the formation processes of the new volcano island and related disaster prevention in situ monitoring however is difficult in practice because the closest inhabited island chichijima is 130 km away from nishinoshima this study presents an infrasonic monitoring method that uses cross correlating records at a pair of online stations on chichijima one is the horizontal ground velocity recorded at a permanent seismic station operated by the japan meteorological agency jma the seismic records were corrected for atmospheric pressure using an empirical ground response to infrasound the other is the air pressure recorded at the jma meteorological observatory for each station we divided the whole records into 3600 s segments to suppress outliers each segment was normalized by the envelope function we then calculated cross correlation functions between the pair of stations using the fast fourier transform they present clear successive arrivals of infrasound coming from nishinoshima we also conducted an offline tripartite array observation using three low frequency microphones with a station spacing of 50 m installed in 2013 may the array analysis supports the results obtained from the online stations the typical root mean squared amplitude is on the order of 0 01 pa and the typical duration is several days the amplitudes were primarily controlled by the effective sound velocity structure from nishinoshima to chichijima the infrasonic observations together with the meteorological observation at chichijima suggest that infrasonic activity was not present in the first two weeks in 2015 january with the help of a more quantitative estimation of the meteorological effect we could infer eruptive activity in real time now many online seismic stations are available worldwide this study shows that installation of another infrasonic sensor close to the existing seismic station 1 km is useful for monitoring a remote island volcano in real time

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

dynamics of mount nyiragongo lava lake inferred from thermal imaging and infrasound array abstract lava lakes provide a direct observation window into processes which usually remain hidden such as magma convection and outgassing dynamics we here report a coupled analysis of thermal infrared footage and infrasound array recordings at mount nyiragongo d r congo and derive a conceptual model of the lava lake s convective system and outgassing mechanism we suggest that surface flow results from a horizontal pressure gradient at the surface of the lake driving the crust from high pressure regions where hot upwelling magma impinges the surface to low pressure regions where cold downwelling magma pulls away from the surface the ascending current of this convection cell carries gas pockets which once at the surface are dragged across the lake into downwelling sinks such sinks are characterized by persistent chaotic bubble bursting spattering whose intensity and position are tracked from infrasound array analysis fluctuations of these are observed but have not been correlated with oscillations of the lava lake level nor with the variations of surface velocities both recorded from infrared footage we also report the activity of a new eruptive vent which opened early 2016 near an inner circular fracture of the crater s third terrace we show that the vent s activity was intermittent alternating between explosive strombolian activity and effusive activity the latter produced lava flows which spread on the crater s last terrace before cascading into the active lava lake although no significant change in the lake behavior was witnessed while the new eruptive vent was active increased attention should be addressed as this new activity could reflect over pressurization of the shallow magmatic system the variety of phenomena captured by this study complements and expands observations reported at other low viscosity lava lakes chiefly kilauea hawai i and erta ale ethiopia despite nyiragongo s more vigorous convective regime where multiple convective cells can operate simultaneously we suggest that the mechanisms controlling the surface motion and outgassing are similar at all three systems pointing to generic processes governing the dynamics of low viscosity lava lakes