environmental factors controlling the δ13c and δ18o variations of recent fluvial tufas a 12 year record from the monasterio de piedra natural park ne iberian peninsula abstract a 12 year study 2000 2012 of the stable isotopes of recent fluvial tufas has been performed in the monasterio de piedra natural park river piedra ne iberian peninsula an area of mediterranean climate with intense tufa deposition since the pleistocene the biannual monitoring of the tufa calcite 13c and 18o signatures and of the water 18o value has demonstrated a clear seasonal pattern for the tufa calcite oxygen isotope composition with less negative values for cool periods which is consistent with regional temperature oscillations the tufa calcite 13c values only occasionally exhibit a pattern which is inconclusive and opposite to the 18o clear pattern the water 18o signature has a distinct seasonal pattern also opposite to the tufa calcite 18o clear pattern the temperature calculations from the tufa calcite 18o values and average water 18o values agree with the seasonal pattern of measured water temperatures with a mean difference of 2 3 c between the calculated and measured temperatures the anomalous values recorded for both the water and the tufa calcite oxygen isotope composition during a two year period are characterized by smoothing of the seasonal variations of the tufa calcite and by reversal of the water pattern there is also an increase in the differences between the measured and estimated temperatures the detected anomaly is roughly synchronous with a change in the isotopic signature of the regional precipitation 18o values this contribution demonstrates that tufas in this depositional and climatic context are good indicators of seasonal temperature oscillations and that tufas can also record other interannual environmental changes such as variations in the isotopic composition of precipitation these results can be extrapolated to ancient tufa systems developed in similar contexts which would expand the potential of tufas as high resolution records of paleoenvironmental conditions

travertines associated with the alhama jaraba thermal waters ne spain genesis and geochemistry abstract freshwater carbonates are interesting archives in palaeoenvironmental reconstructions however more studies of those systems are needed to fully understand past environments in this work the actively forming travertines of the alhama jaraba thermal system were studied for the first time in order to evaluate the relationship between the geochemical and mineralogical composition and the environmental conditions during their formation with that aim a combination of petrographical mineralogical geochemical and stable isotope analyses were carried out these carbonates provide a natural laboratory for the study of the effect of different variables natural and anthropogenic on carbonate precipitation the results showed that there is a close relationship between the mineralogy of the solid precipitates and the formation temperature and only the samples formed from overheated waters 40 60 c show significant concentrations of aragonite aragonite bearing samples show higher concentrations in sr ba and u while calcitic solids are enriched in mg these differences could be attributed to mineralogy temperature or different precipitation rates the geochemical evaluation of the chemistry of both the solids and their parental waters suggests that differences in the rate of co 2 degassing and in some cases evaporation are the primary environmental controls on isotopic compositions in addition the results show that if strong evaporation and co 2 degassing are involved calcite precipitation occurs under conditions of isotopic disequilibrium with its parental water the results of our study are useful to interpret old depositional environments and palaeotemperatures

rapid precipitation of silica opal a disguises evidence of biogenicity in high temperature geothermal deposits case study from dagunguo hot spring china abstract dagunguo spring located in the tengchong geothermal area in the western part of yunnan province china is a very active spring with water temperatures of 78 to 97 c and ph of 7 7 to 8 8 the vent pool 5 6 m in diameter and up to 1 5 m deep is lined with opal a that was precipitated from the near boiling spring waters a glass suspended in the pool was coated with opal a in two months and two pvc pipes that drained water from the pool in late 2010 became lined with opal a precipitates in less than three months the opal a accumulated at rates of 0 5 to 0 75 mm month in the spring pool and 2 5 to 3 5 mm month in the pvc pipes the opal a precipitates irrespective of where they developed are formed primarily of silicified microbes and opal a spheres along with minor amounts of native sulfur detrital quartz and clay mainly kaolinite the fabrics in these opal a deposits were dictated largely by the growth patterns of the filamentous and rod shaped microbes that dominate this low diversity biota and the amount of opal a that was precipitated around them many of the microbes were preserved as rapid opal a was precipitated on and around them before the cells decayed with continued precipitation however the microbes became quickly engulfed in the opal a precipitates and morphological evidence of their presence was lost in essence the process that controls their preservation ultimately disguised them to the point where cannot be seen critically this loss of morphological identity takes places even before opal a starts its diagenetic transformation towards quartz

calibration of the calcite water oxygen isotope geothermometer at devils hole nevada a natural laboratory abstract the 18 o of ground water 13 54 0 05 and inorganically precipitated holocene vein calcite 14 56 0 03 from devils hole cave 2 in southcentral nevada yield an oxygen isotopic fractionation factor between calcite and water at 33 7 c of 1 02849 0 00013 1000 ln calcite water 28 09 0 13 using the commonly accepted value of calcite water t of 0 00020 k 1 this corresponds to a 1000 ln calcite water value at 25 c of 29 80 which differs substantially from the current accepted value of 28 3 use of previously published oxygen isotopic fractionation factors would yield a calcite precipitation temperature in devils hole that is 8 c lower than the measured ground water temperature alternatively previously published fractionation factors would yield a 18 o of water from which the calcite precipitated that is too negative by 1 5 using a temperature of 33 7 c several lines of evidence indicate that the geochemical environment of devils hole has been remarkably constant for at least 10 ka accordingly a re evaluation of calcite water oxygen isotopic fractionation factor may be in order assuming the devils hole oxygen isotopic value of calcite water represents thermodynamic equilibrium many marine carbonates are precipitated with a 18 o value that is too low apparently due to a kinetic isotopic fractionation that preferentially enriches 16 o in the solid carbonate over 18 o feigning oxygen isotopic equilibrium

comparison of the quaternary travertine sites in the denizli extensional basin based on their depositional and geochemical data abstract in the denizli basin turkey located in the western anatolian extensional province travertine and tufa deposition has been an ongoing process for at least 600 000 years travertine bodies which are 30 to 75 m thick and each covers areas of 1 to 34 km2 are up to 1 km3 in volume today spring waters in this area have temperatures of 19 to 57 c are of the ca mg hco3 so4 type in the pamukkale kelkaya and pinarbasi areas and the ca mg so4 hco3 type at cukurbag thermal waters along the northern margin of the basin are generally hotter than those in the east southeast and south the 18o and d values of the spring waters indicate a meteoric origin the average temperatures of the hydrothermal systems in the denizli basin appear to have decreased from pleistocene to holocene travertine which formed from the hotter water is more widespread than the tufa that formed in the cooler spring waters deposition of the travertine which formed largely on slopes in depressions and along fissure ridges mostly on northern basin margins was controlled by the interplay between various intrinsic and extrinsic parameters the travertines are formed largely of calcite with only minor amounts of aragonite in some of the vertically banded crystalline crust raft and pisoid travertines found in some of the northern sites the aragonitic samples rich in sr are typically found around the spring orifices and along the central axis of the fissure ridges the stable isotope values of the travertine found in the northwest and southeast parts of the basin are different the 13c values of the northern travertine deposits are more positive 3 7 to 11 7 vpbd than those found in the south southeast areas 4 to 5 8 vpdb in contrast the travertine and tufa in the southeastern areas have higher 18o values 15 2 to 7 8 vpdb than those of the northern areas 16 6 to 4 8 vpdb available evidence indicates that spring activity and associated travertine precipitation in the denizli basin were controlled largely by tectonic activity rather than by climatic conditions

carbon and oxygen isotope fractionations between aragonite and calcite of shells from modern molluscs carbon and oxygen isotope fractionations between calcite and aragonite were investigated by analyzing marine gastropods and bivalves that lived under temperate to tropical climates species that secrete both aragonite and calcite layers were studied to ensure similitude of changes in the isotopic composition of water in diet and in metabolic activity during shell growth aragonite and calcite layers from the adult parts of the shell were identified and mapped by using raman spectroscopy powder samples were obtained by micro drilling under a stereo microscope thirty six pairs of aragonite calcite samples were obtained from ten gastropod and five bivalve species biogenic aragonite is c 13 enriched by 0 95 0 81 and o 18 enriched by 0 37 0 65 relative to co existing biogenic calcite direction and magnitude of the carbon isotope fractionation are compatible with those already determined by using low temperature experimental approaches the observed oxygen isotope difference between biogenic aragonite and calcite is assigned to the difference similar to 0 4 parts per thousand in the acid fractionation factor values that must be taken into account during digestion of carbonate polymorphs at 90 degrees c it is concluded that biogenic calcium carbonate polymorphs precipitate close to but not in isotopic equilibrium with seawater therefore empirical oxygen isotope fractionation equations that were established on the basis of modern mollusc shells and ambient waters should be preferred for the calculation of aquatic paleotemperatures

sedimentology and geochemistry of a human induced tufa deposit implications for palaeoclimatic research geochemical variations across laminated tufas and travertines may reflect the growth style of the carbonate build up and not just climate related changes this work presents the study of a carbonate deposit formed on a ravine wall in gran canaria island spain from a broken pipe system used for irrigation of banana plantations the deposit is a few tens of metres long and has a stepped morphology formed by successive cascade barriers and pools the main facies are framestones of coated stems laminated bindstones phytoclastic wackestones and silty mudstones all of which display micritic or coarse crystalline textures lamination from a framestone with coarse crystalline texture was studied from a petrological sedimentological and geochemical perspective and water palaeotemperatures were calculated lamination displaying five orders of magnitude from daily to annual or higher was controlled by the discontinuous supply of water lamination consists of crystalline laminae discontinuity couplets at all observed scales estimated mean precipitation rates are 0 7 mm year 1 but discontinuity of sedimentation at all lamination orders may have involved greater precipitation rates whereas elemental geochemistry suggests variable conditions not far from chemical equilibrium stable isotopes suggest that calcite precipitated under disequilibrium conditions however the small dimensions of the deposit and the relatively high flow velocities allowed lack of 13c and 18o isotope fractionation in co2 nor in calcite leading to independent temperature calculations both with mean values of 25 c isotopic trends found throughout lamination cannot be explained by strong changes in water temperature nor in 13cdic or 18ow the correction made to eliminate these isotopic trends yielded narrower temperature ranges this paper discusses the accuracy of temperature estimations despite the difficulties coming from disequilibrium and how isotopic trends through time could be explained by the growth of the deposit and not by climate related changes

equilibrium oxygen hydrogen and carbon isotope fractionation factors applicable to geologic systems as demonstrated by the chapters in this short course stable isotope techniques are an important tool in almost every branch of the earth sciences central to many of these applications is a quantitative understanding of equilibrium isotope partitioning between substances indeed it was harold urey s 1947 thermodynamically based estimate of the temperature dependence of 18o 16o fractionation between calcium carbonate and water and a recognition of how this information might be used to determine the temperatures of ancient oceans that launched the science of stable isotope geochemistry the approach pioneered by urey has since been used to estimate temperatures for a wide range of geological processes e g emiliani 1955 anderson et al 1971 clayton 1986 valley this volume in addition to their geothermometric applications equilibrium fractionation data are also important in the study of fluid rock interactions including those associated with diagenetic hydrothermal and metamorphic processes baumgartner and valley this volume shanks this volume finally a knowledge of equilibrium fractionation is a necessary first step in evaluating isotopic disequilibrium a widespread phenomenon that is increasingly being used to study temporal relationships in geological systems cole and chakraborty this volume in the fifty four years since the publication of urey s paper equilibrium fractionation data have been reported for many minerals and fluids of geological interest these data were derived from 1 theoretical calculations following the methods developed by urey 1947 and bigeleisen and mayer 1947 2 direct laboratory experiments 3 semi empirical bond strength models and 4 measurement of fractionations in natural samples each of these methods has its advantages and disadvantages however the availability of a variety of methods for calibrating fractionation factors has led to a plethora of calibrations not all of which are in agreement in this chapter we evaluate the major methods for determining fractionation factors

stable isotope geochemical study of pamukkale travertines new evidences of low temperature non equilibrium calcite water fractionation abstract in this paper we present the first detailed geochemical study of the world famous actively forming pamukkale and karahayit travertines denizli basin sw turkey and associated thermal waters sampling was performed along downstream sections through different depositional environments vent artificial channel and lake terrace pools and cascades of proximal slope marshy environment of distal slope 13 c travertine values show significant increase from 6 1 to 11 7 pdb with increasing distance from the spring orifice whereas the 18 o travertine values show only slight increase downstream from 10 7 to 9 1 pdb mainly the co 2 outgassing caused the positive downstream shift 6 in the 13 c travertine values the high 13 c values of pamukkale travertines located closest to the spring orifice not affected by secondary processes suggest the contribution of co 2 liberated by thermometamorphic decarbonation besides magmatic sources based on the gradual downstream increase of the concentration of the conservative na k cl evaporation was estimated to be 2 5 which coincides with the moderate effect of evaporation on the water isotope composition stable isotopic compositions of the pamukkale thermal water springs show of meteoric origin and indicate a local meteoric water line of denizli basin to be between the global meteoric water line craig 1961 and western anatolian meteoric water line imsek 2003 detailed evaluation of several major and trace element contents measured in the water and in the precipitated travertine along the pamukkale mm section revealed which elements are precipitated in the carbonate or concentrated in the detrital minerals former studies on the hungarian egerszalok travertine kele et al 2008a b 2009 had shown that the isotopic equilibrium is rarely maintained under natural conditions during calcite precipitation in the temperature range between 41 and 67 c in this paper besides the detailed geochemical analyses along downstream sections we present new evidences of non equilibrium calcite water fractionation in lower temperature range 13 3 to 51 3 c our measurements and calculations on natural hot water travertine precipitations at pamukkale and egerszalok revealed that the 18 o travertine is equal with the 18 o hco3 at the orifice of the thermal springs which means that practically there is no oxygen isotope fractionation between these two phases high rate of co 2 degassing with rapid precipitation of carbonate could be responsible for this as it was theoretically supposed by o neil et al 1969 thus for the determination of the deposition temperature of a fossil travertine deposit we propose to use the water bicarbonate oxygen isotope equilibrium fractionation instead of the water travertine fractionation which can result 8 9 c difference in the calculated values our study is the first detailed empirical proof of o neil s hypothesis on a natural carbonate depositing system the presented observations can be used to identify more precisely the deposition temperature of fossil travertines during paleoclimate studies

review of calcium carbonate polymorph precipitation in spring systems abstract many spring deposits throughout the world are characterized by spectacular deposits of calcium carbonate that are formed of various combinations of aragonite and calcite and in very rare cases vaterite the factors that control the precipitation of the aragonite and calcite have been the subject of considerable debate that has been based on natural precipitates and information gained from numerous laboratory experiments synthesis of this information indicates that there is probably no single universal factor that controls calcite and aragonite precipitation in all springs instead the reason for aragonite as opposed to calcite precipitation should be ascertained by considering the following ordered series of possibilities for each system first aragonite commonly with calcite as a co precipitate will form from spring water that has a high co 2 content and rapid co 2 degassing irrespective of the mg ca ratio and scale of precipitation second aragonite can be precipitated from waters that have low levels of co 2 degassing provided that the mg ca ratio is high enough to inhibit calcite precipitation third the presence of biofilms may lead to the simultaneous precipitation of aragonite and calcite irrespective of co 2 degassing or mg ca ratio either within the different microdomains that develop in the biofilm or because of diurnal changes in various geochemical parameters associated with the biofilm although the precipitation of calcite and aragonite has commonly been linked directly to water temperature there is no clear evidence for this proposition it is possible however that temperature may be influencing another parameter that plays a more direct role in the precipitation of these caco 3 polymorphs despite the advances that have been made the factors that ultimately control calcite and aragonite are still open to debate because this long standing problem has still not been fully resolved

determination of aragonite trace element distribution coefficients from speleothem calcite aragonite transitions the processes that govern the incorporation of trace elements into speleothems can often be linked to environmental changes although element incorporation into speleothem calcite is now reasonably well understood current knowledge regarding trace element variability in speleothem aragonite is very limited of particular interest is whether trace element distribution coefficients are above or below one in order to assess the extent to which prior aragonite precipitation has affected speleothem aragonite trace element records this study uses nine calcite to aragonite transitions in seven speleothems from diverse environmental settings to derive the first quantitative estimates of the distribution coefficients for several elements in speleothem aragonite dmg ar 9 7e 5 9 01e 5 dba ar 0 91 0 88 dsr ar 1 38 0 53 and du ar 6 26 4 54 1 sd for one speleothem from western germany the distribution coefficients are generally higher which is potentially related to the very low growth rates 11 m year of this sample in particular dsr ar appears to show a negative correlation with growth rate when growth rate is below 20 m year in summary our results demonstrate that speleothem aragonite dmg ar is below one du ar is considerably above one and dsr ar is above one or close to unity for dba ar reaching a similar conclusion is difficult due to the relatively high uncertainty enhanced prior aragonite precipitation will thus result in lower u and higher mg concentrations in speleothem aragonite although in many cases mg in speleothem aragonite is most likely dominated by other processes this result suggests that u concentrations in aragonitic stalagmites could serve as a very effective proxy for palaeo rainfall

depositional facies and aqueous solid geochemistry of travertine depositing hot springs angel terrace mammoth hot springs yellowstone national park u s a petrographic and geochemical analyses of travertine de positing hot springs at angel terrace mammoth hot springs yellow stone national park have been used to define five depositional facies along the spring drainage system spring waters are expelled in the vent facies at 71 to 73 8c and precipitate mounded travertine composed of aragonite needle botryoids the apron and channel facies 43 728c is floored by hollow tubes composed of aragonite needle botryoids that encrust sulfide oxidizing aquificales bacteria the travertine of the pond facies 30 62 8c varies in composition from aragonite needle shrubs formed at higher temperatures to ridged networks of calcite and aragonite at lower temperatures calcite ice sheets calcified bubbles and aggregates of aragonite needles fuzzy dumbbells pre cipitate at the air water interface and settle to pond floors the prox imal slope facies 28 54 8c which forms the margins of terracette pools is composed of arcuate aragonite needle shrubs that create small microterracettes on the steep slope face finally the distal slope facies 28 30 8c is composed of calcite spherules and calcite feather crys tals despite the presence of abundant microbial mat communities and their observed role in providing substrates for mineralization the com positions of spring water and travertine predominantly reflect abiotic physical and chemical processes vigorous co 2 degassing causes a 12 unit increase in spring water ph as well as rayleigh type covariations between the concentration of dissolved inorganic carbon and corre sponding d 13 c travertine d 13 c and d 18 o are nearly equivalent to aragonite and calcite equilibrium values calculated from spring water in the higher temperature 50 738c depositional facies conversely

silurian and devonian biogeography of china integration of newly available chinese data for the biogeography of the silurian and devonian makes possible a number of globally sigificant advances the early silurian the llandoverian can now be shown to have been moderately provincial rather than cosmopolitan as considered earlier the uralian cordilleran region defined previously for the late silurian can now be shown with chinese information to have been in existence with a co occurring north atlantic region since the beginnings of the silurian and to have been somewhat more provincial than the late silurian the view of late silurian provincialism with two major regions is further substantiated with the help of chinese data for the early devonian it is now possible to define a south china region that includes the bulk of the yangtze platform region of south china plus adjacent tonkin in north vietnam the boundary of the south china region is present in central yunnan and extends in an approximately north south direction the south china region is still prominent during the lower eifelian half of the middle devonian relatively cosmopolitan devonian conditions affect china by the latter givetian half of the middle devonian as is also the case in most other parts of the world except for eastern north america and the southern hemisphere malvinokaffric realm the chinese upper devonian is cosmopolitan in a manner similar to that of the rest of the world it is notable during the lower devonian that the nonmarine vertebrate fauna is unusually provincial and very distinct from faunas known in europe and north america as well as from those present in northern asia it is suggested that previous distinctions between lower devonian uralian and mongolo okhotsk regions are more likely provincial or even subprovincial the presence of the atrypacean genus tuvaella in the silurian of east central asia is shown to represent the restricted occurrence of a single genus rather than being indicative of a major biogeographic unit however it may indicate the presence of a subprovincial unit or of an endemic center

the δ18o and δ13c records in an aragonite stalagmite from furong cave chongqing china a 2000 year record of monsoonal climate abstract a 7 cm long aragonite stalagmite fr0510 1 from furong cave chongqing was dated by 210pb and 230th methods revealing a 2000 year record of climate history under the influence of the east asian monsoon the fr0510 1 record resembles dongge cave da record on 10 100 year scales but quite different from the wanxiang cave wx42b record indicating that while stalagmite 18o record represents local regional moisture change spatial variability of the monsoonal rainfall over eastern china must take into account during the past 2000 years climate in chongqing was relatively wet in the intervals of 50 bc ad 250 ad 1150 1450 and ad 1600 1950 and relatively dry during the periods of ad 250 1150 and ad 1450 1600 dry conditions were prevailing over the medieval warm period whereas wet climates were dominant during the most time of the little ice age in chongqing area

equilibrium vs kinetic fractionation of oxygen isotopes in two low temperature travertine depositing systems with differing hydrodynamic conditions at baishuitai yunnan sw china abstract in order to understand the behavior of oxygen isotopic fractionation and obtain more reliable paleoclimatic data from surficial travertine deposits the hydrochemistry carbonate precipitation rates and the temporal and spatial variations in 18 o values of the modern travertine in two low temperature travertine depositing systems canal and pool with differing hydrodynamic conditions at baishuitai yunnan sw china were investigated during the warm rainy season may 24 to november 2 in 2010 it was found that the oxygen isotopic composition of travertine in the two systems showed distinct controlling mechanisms mainly due to different carbonate precipitation rates and water residence times for the canal system with fast flow large deviations between the calculated and measured temperatures indicated that travertine precipitated out of isotopic equilibrium this was due to rapid carbonate precipitation with intense co 2 degassing 18 o travertine values and water temperature increased downstream 1 and 4 c respectively while 18 o water values remained relatively stable it was shown that the 18 o values of travertine in the canal system recorded the 18 o values of dissolved carbonates hco 3 which also increased along the canal controlled by rayleigh distillation effects in contrast in the pools system with slow flow oxygen isotopic equilibrium between dissolved carbonates hco 3 and h 2 o was achieved and the 18 o travertine values did not display spatial variations calculated water temperatures using the equilibrium fractionation factors of coplen 2007 were identical to the measured ones which indicates that travertine in such pools system is suitable for the reconstruction of paleo precipitating temperatures finally by comparing these two systems we have obtained a simple criterion to determine the suitability of travertine to estimate temperatures the 18 o value of baco 3 precipitated from water samples is compared with the theoretical 18 o value of dissolved carbonate calculated using water temperature and 18 o water to check if the oxygen isotopes of the dissolved carbonate are in equilibrium with the water

oxygen and carbon isotopic systematics of aragonite speleothems and water in furong cave chongqing china abstract to understand oxygen and carbon stable isotopic characteristics of aragonite stalagmites and evaluate their applicability to paleoclimate the isotopic compositions of active and fossil aragonite speleothems and water samples from an in situ multi year october 2005 july 2010 monitoring program in furong cave located in chongqing of china have been examined the observations during october 2005 june 2007 show that the meteoric water is well mixed in the overlying 300 500 m bedrock aquifer reflected by relatively constant 18o 0 11 0 14 1 of drip waters in the cave which represents the annual status of rainfall water active cave aragonite speleothems are at oxygen isotopic equilibrium with drip water and their 18o values capture the surface water oxygen isotopic signal aragonite to calcite transformation since the last glaciation is not noticeable in furong stalagmites our multi year field experiment approves that aragonite stalagmite 18o records in this cave are suitable for paleoclimate reconstruction with high u 0 5 7 2 ppm and low th 20 1270 ppt the furong aragonite stalagmites provide very precise chronology as good as 20s yrs 2 of the climatic variations since the last deglaciation the synchroneity of chinese stalagmite 18o records at the transition into the bolling allerod t ba and the younger dryas from furong hulu and dongge caves supports the fidelity of the reconstructed east asian monsoon evolution however the furong record shows that the cold older dryas od occurred at 14 0 thousand years ago agreeing with greenland ice core 18o records but 200 yrs younger than that in the hulu record the od age discrepancy between chinese caves can be attributable to different regionally climatic environmental conditions or chronological uncertainty of stalagmite proxy records which is limited by changes in growth rate and subsampling intervals in absolute dating seasonal dissolved inorganic carbon 13c variations of 2 3 in the drip water and 5 7 in the pool and spring waters are likely attributed to variable degrees of co2 degassing in winter and summer the variable 13c values of active deposits from 11 to 0 could be caused by kinetically mediated co2 degassing processes the complicated nature of pre deposition kinetic isotopic fractionation processes for carbon isotopes in speleothems at furong cave require further study before they can be interpreted in a paleoclimatic or paleoenvironmental context

noncrystallographic calcite dendrites from hot spring deposits at lake bogoria kenya abstract complex calcite crystals are an integral component of precipitates that form around the orifices of the loburu and mawe moto hot springs on the shores of lake bogoria kenya two types of large up to 4 cm long noncrystallographic dendrites are important components of these deposits feather dendrites are characterized by multiple levels of branching with individual branches developed through crystal splitting and spherulitic growth scandulitic from latin meaning shingle dendrites are formed of stacked calcite crystals and are generally more compact than feather dendrites these developed through the incremental stacking of rectangular shaped calcite crystals that initially grew as skeletal crystals feather and scandulitic dendrites precipitated from the same waters in the same springs the difference in morphology is therefore related to microenvironments in which they grew feather dendrites grew in any direction in pools of free standing water provided that they were in constant contact with the solute conversely scandulitic dendrites grew on rims of dams where water flowed over the surface in concert with the pulses of spring water thus each calcite crystal in these dendrites represents one episode of crystal growth the orientation of the component crystals in scandulitic dendrites is controlled by the topography of the dam or surface not crystallographic criteria the noncrystallographic dendrites formed from spring waters with initial temperatures of 90 99 c surficial water cooling loss of co2 and presence of other elements that can interfere with crystal growth contributed to the formation of these unusual crystals

tufas and travertines of the mediterranean region a testing ground for freshwater carbonate concepts and developments actively forming travertine and tufa sites are widespread in temperate and warm climates such as the mediterranean region but also develop in other climatic regimes from the arctic to equatorial latitudes the terms travertine and tufa are sometimes applied indiscriminately today however each has a specific definition most studied deposits are active or of quaternary especially holocene age there are fewer tertiary and even less late mesozoic examples on record in part this is because of a recognition problem as these deposits commonly preserve as fragmentary erosional remnants physico chemical precipitation of calcium carbonate is commonly considered to be the main mechanism contributing to tufa and travertine deposition rapid cooling of waters further aids the process in thermal travertine sites however biomediation of calcium carbonate associated with prokaryote microphyte biofilms is now recognized to be equally important in slow flowing and near static sites much of this precipitation occurs in close association with cyanobacterial heterotrophic bacterial and diatoms the mediterranean region figures significantly in the development of travertine and tufa research consequently this article employs key literature on mediterranean examples to illustrate developments and concepts in freshwater carbonate research modern work started in the 1950s and defined many previously unknown outcrops many such sites became the targets for early radiocarbon dating studies since the late 1970s a number of laboratory based and field based classification schemes have been proposed some schemes were based on associated macrovegetation types others were based on petrological characteristics or on geometry and sedimentary facies characteristics of late the sedimentological modelling has benefited greatly from the use of shallow geophysical techniques in order to better define the internal geometries of the deposits two distinct research strands were developed during the 1990s both aimed at a better understanding of environmental change the first considered biocomponents the research was multifaceted and ranged from exploring the role of micro organisms in cement and lime mud precipitation to biostratigraphic analysis of contained pollen and invertebrate remains these provided proxy environmental information which has helped to define past climate variability in the region the second research strand focussed on geochemical signatures as a proxy tool for defining environmental change this definition was made possible by new petrological studies which have greatly aided the recognition of primary depositional fabrics this improved knowledge has reduced the sampling dangers of diagenetic contamination inherent in earlier geochemical studies lithofacies modelling has also brought to light important early post depositional neomorphic changes which obscure primary fabrics and complex diagenetic histories have been revealed stable isotope signatures of carbon and oxygen have also been used to define palaeo water temperature fine tuning of depositional time frames has also been achieved from absolute dating techniques employing radiocarbon and uranium thorium

seasonal temperatures from δ18o in recent spanish tufa stromatolites equilibrium redux this study focuses on recent debate over the value of stable isotope based environmental proxies recorded in riverine tufa stromatolites we recovered a 12 year record 1999 2012 of river bed tufa stromatolites in the river piedra ne spain along with a partly overlapping 15 year record 1994 to 2009 of accumulations in a drainage pipe both deposits formed in water with near identical physico chemical parameters measured water temperature tw data and near constant 18owater composition allowed selection of an equilibrium palaeotemperature equation that best replicated actual temperatures we found as other have that both the epstein et al 1951 and kim o neil 1997 formulas for tw calculation from equilibrium calcite 18o compositions were appropriate for the river piedra where tufa deposition rates are high means between 5 6 and 10 8 mm in six months 18ocalcite in both the river and the pipe deposits record essentially the full actual seasonal tw range only the coldest times tw 10oc when calcite precipitation mass decreased to minimum are likely to be unrepresented an effect most noticeable in the pipe where depositional masses are smaller and below sample resolution while we cannot rule out kinetic effects on 18ocalcite based calculated tw the good fit between measured tw and 18ocalcite calculated tw indicates that temperature is the principal control textural and deposition rate variability between the river and pipe settings are caused by differences in flow velocity and illumination in the river calcification of growing cyanobacterial mat occurred throughout the year producing composite dense and porous laminae whereas in the pipe discontinuous cyanobacterial growth in winter promoted more abiogenic calcification high resolution 18ocalcite data from synchronous pipe and river laminae show that reversals in tw occur within laminae not at lamina boundaries a pattern consistent with progressive increase in calcite precipitation rate as cyanobacterial growth re established in spring

a 2400 yr mesoamerican rainfall reconstruction links climate and cultural change droughts are a recurring feature of mexican climate but few high resolution data are available to test for climate change forcing of mesoamerican civilizations we present a quantitative 2400 yr rainfall reconstruction for the basin of mexico from a precisely dated and highly resolved speleothem that documents highly variable rainfall over the past 2400 yr dry conditions peaked during a 150 yr long late classic ca 600 900 ce common era mega drought that culminated at 770 ce which followed centuries of climatic drying that spanned the fall of the city of teotihuacan ca 550 ce the wettest conditions in the 1450s ce were associated with fl ooding in the basin of mexico our data suggest that rainfall variability was likely forced by the el nino southern oscillation and impacts on spring fed irrigation agriculture may have been a stressor on mesoamerican civilizations

continuous 60 year stable isotopic and earth alkali element records in a modern laminated tufa jaruga river krka croatia implications for climate reconstruction abstract a continuous 60 year record 1938 1998 of stable isotope compositions of carbon and oxygen as well as trace metal mg sr ba concentrations in a laminated calcite crust precipitated in a short artificial tunnel on a non equilibrium groundwater fed karstic river is presented chemical and isotopic records have been compared to hydrometeorological data available for the last 48 years an attempt is made to relate isotopic and geochemical variations in the crust to environmental parameters such as temperature precipitation and changes in vegetation cover as well as to postdepositional recrystallisation of the older crust material isotopic composition of the crust is largely influenced by non equilibrium precipitation which favours the incorporation of isotopically depleted c and o into the carbonate furthermore because of the complicated hydrological situation there is no observable correlation between the stable oxygen isotope composition of water and temperature the result is that the 18 o isotopic thermometers overestimate the measured precipitation temperatures temperatures calculated from mg ca ratios of water and the carbonate match the 18 o palaeotemperatures within 2 4 c in the older part of the crust precipitated before the onset of industrial pollution of the river it was demonstrated that the application of mg palaeothermometry in natural systems where the mg ca ratio of water is influenced not only by temperature but also by other environmental parameters such as precipitation surface runoff groundwater retention time and anthropogenic influences is subject to a large uncertainty up to 10 c

thickness and stable isotopic characteristics of modern seasonal climate controlled sub annual travertine laminas in a travertine depositing stream at baishuitai sw china implications for paleoclimate reconstruction a continuous high resolution monthly record of stable isotopes 13c and 18o in a well laminated freshwater travertine deposited at baishuitai sw china from may 1998 to november 2001 was presented the travertine exhibits clear annual bands with coupled brown white color laminations throughout field investigation it was found that the thin 1 5 2 2 mm brown porous lamina was formed in the monsoonal rainy season from april to september whereas the thick 5 8 mm dense white lamina was formed in the dry season from october to march the comparisons of lamina thickness and stable isotope signals in the travertine with the meteorological records allow us to constrain the relevant geochemical processes in the travertine formation under different climate conditions and to relate climate variables to their physicochemical proxies in the travertine record sympathetic variations in lamina thickness 13c and 18o along the sampled profile reflect changes in hydrogeochemistry showing that thin lamina and low 13c and 18o values occur in warm and rainy seasons the decreased amount of calcite precipitation and low 13c values during the warm and rainy seasons is caused by dilution of overland flow after rainfall the low 18o values are believed to be related to the rainfall amount effect in subtropical monsoonal regions this process is thought to be markedly subdued whenever the amount of rainfall is lower than a given threshold accordingly distinct minima in lamina thickness 13c and 18o are interpreted to reflect events with above average rainfall possibly heavy floods and vice versa this study demonstrates the potential of freshwater travertine to provide valuable information on seasonal or even monthly rainfall variations

stable isotopic and elemental characteristics of recent tufa from a karstic krka river south east slovenia useful environmental proxies tufa samples from 16 consecutive barrages along a 13 km section of a groundwater fed krka river slovenia were analysed for their petrographical mineralogical elemental and stable carbon 13c and oxygen 18o isotope composition to establish their relation to current climatic and hydrological conditions waters constantly oversaturated with calcite and the steep morphology of the krka riverbed stimulate rapid co2 degassing and subsequent tufa precipitation the carbon isotope fractionation 13c between dic and tufa in the krka river evolves toward isotopic equilibrium being controlled by continuous co2 degassing and tufa precipitation rate downstream the 13c increased from 1 9 to 2 5 vienna peedee belemnite however since tufa precipitation rates remain similar downstream the major controlling factor of carbon isotope exchange is most probably related to the continuous 12co2 degassing downstream leaving the carbon pool enriched in 13c in the case of oxygen the isotope fractionation was found to be from 1 0 to 2 3 smaller than reported in the literature the observed discrepancies are due to different precipitation rates of calcite deposits as krka tufas on cascades grow relatively faster compared to slowly precipitated calcite deposits in cave or stream pools due to non equilibrium oxygen isotope exchange between krka tufa and water the 18o proxy showed from 1 2 to 8 2 c higher calculated water temperatures compared to measured water temperatures demonstrating that 18o proxy based temperature equations are not reliable for water temperature calculations of fast growing tufa on cascades because mg is bound to the terrigenous dolomite fraction in the krka tufa samples the mg ca was also found to be an unreliable temperature proxy yielding over up to 20 c higher calculated water temperatures this article is protected by copyright all rights reserved

stable isotope characterisation of recent aragonite travertine deposits associated with the fitero thermal waters spain the travertines of the fitero thermal springs with more than 98 of aragonite in most of the samples are studied in this paper the main objective is to improve the general understanding of aragonite precipitation since the deposits of almost pure aragonite are very scarce this study presents a complete mineralogical and isotopic characterisation including the evaluation of the 18o and 13c fractionation during precipitation as valuable information for paleoclimate and paleoenvironmental studies samples of a laminated travertine deposit constituted by almost pure aragonite were taken from a pipe discharging water at 40 c waters suffered an important co2 outgassing as suggested by the geochemical calculations and the 13c values of travertines and waters this outgassing triggers the oversaturation and precipitation of carbonate phases temperature seems to be the main factor controlling the precipitation of aragonite or calcite as checked by studying another travertine sample with higher calcite content various 18o isotope fractionation equations for aragonite and calcite were used the results indicate that precipitation took place close to equilibrium according to some of these equations the fact that the equilibrium is maintained in a natural system with an important co2 loss is surprising however it can be explained by an hco3 water oxygen isotopic equilibrium and a direct transfer of the hco3 isotope signal to the carbonate without fractionation due to the fast co2 loss and precipitation finally considering other natural aragonite samples a fractionation equation is defined for natural aragonite in the temperature range between 23 and 80 c

uranium series dating of travertine from suttő implications for reconstruction of environmental change in hungary abstract terrestrial carbonate formations such as travertines speleothems and lake sediments are important archives of terrestrial climate forcing at the sutt section in hungary a complex succession of travertine is covered by a loess palaeosol sequence both are high resolution terrestrial archives of climate and environment change uranium series 230th u dating was carried out to set up a more reliable chronological frame for the travertine as the growth of travertine is very complex pore cements may cause serious problems for precise dating the state of alteration of primary spar and micrite was characterised by microscopic cathodoluminescence and microprobe analyses the travertine from sutt showed homogeneous phases of primary calcite minor micropores and rare pore cements the carbon isotopic composition indicates that the source of carbon was a mixture of atmospheric and soil derived co2 calculated water temperatures based on oxygen isotope data range from 22 c to 31 c an attempt to provide an independent relative dating approach by palaeomagnetic techniques failed 230th u ages were determined applying an isochron approach using the leachate leachate method as the travertine deposits have a dense structure the bulk sampling method was successfully applied in determining uranium series ages with much higher precision than former studies with alpha spectrometry travertines from sutt yielded mid pleistocene ages ranging from the antepenultimate glacial to the penultimate interglacial 310 240 ka these results are in agreement with those from optically stimulated luminescence osl dating and amino acid racemisation aar dating of the overlying sediment indicating at least an mis 7 age for the travertine

oxygen isotope fractionation in marine aragonite of coralline sponges oxygen isotope values of the extant caribbean coralline sponge ceratoporella nicholsoni are compared with published temperatures and 18o of water calculated from salinities the measured values from aragonitic sponge skeletons have a mean offset of 1 0 0 1 from calculated calcite equilibrium values aragonite calcite 1 0010 this is in good agreement with published values from synthetic aragonite they further agree with published near equilibrium oxygen isotope values of temperate and cold water molluscs and foraminifera extrapolated to the temperature range of the coralline sponges these results and the mode of skeleton formation of ceratoporella nicholsoni suggest that these sponges precipitate aragonite close to isotopic equilibrium the temperature dependence of oxygen isotopic fractionation between the aragonite of ceratoporella nicholsoni and water is only roughly constrained by the available data due to the narrow temperature range of the caribbean reef sites however as the data suggest oxygen isotopic equilibrium we can calculate a well constrained temperature equation combining temperate and cold water equilibrium values from molluscs and foraminifera with our sponge data full size image 1 k and full size image 1 k

chemical and stable isotope composition of recent hot water travertines and associated thermal waters from egerszalok hungary depositional facies and non equilibrium fractionation abstract combined petrographical mineralogical geochemical and stable isotope analyses were conducted on an actively forming egerszalok travertine mound to determine the factors that govern carbonate precipitation and thus influence the use of travertines in paleoclimate reconstruction stable isotope analyses of oxygen carbon and hydrogen demonstrate both biological and abiological factors to control travertine deposition processes of morphology related outgassing had major effects upon isotopic composition continuous co 2 degassing and temperature change of the thermal water between the spring orifice and distal parts of the system caused stable carbon and oxygen isotope compositions of the precipitating travertines to increase from 2 7 to 4 3 relative to v pdb and from 10 5 to 14 7 relative to v smow respectively the travertines at the spring orifice t 67 c are composed of almost pure calcite with a 13 c value of 2 7 relative to v pdb enabling classification as intermediate between thermometeogene and thermogene in lower temperature water away from the spring orifice various amounts of aragonite 5 35 with higher sr concentrations precipitate from solution this phenomenon is exceptional in hot spring carbonate deposits and could be explained by fast carbonate precipitation due to the morphology related outgassing oxygen and hydrogen isotope measurements of the thermal water confirmed evaporation to be causing limited kinetic isotope fractionation however 18 o values of the travertine do show isotope shifts away from the equilibrium fractionation curve which is most probably related to the rapid calcite precipitation and transportation along the flow path our data closely follow the temperature 18 o calcite water relationship observed for other travertine localities this is slightly displaced from the experimental curve and determines an empirical travertine curve our study shows that this shift may result in an approximately 8 c difference in paleotemperature calculations depending upon which fractionation curve is used

the impact of diffusive transport of methane on pore water and sediment geochemistry constrained by authigenic enrichments of carbon sulfur and trace elements a case study from the shenhu area of the south china sea abstract sulfate driven anaerobic oxidation of methane sd aom controls methane release from marine sediments to the ocean a variety of authigenic precipitates within sediments has been widely used to identify past occurrences of sd aom however the lack of a systematic evaluation of the formation conditions of these precipitates sometimes impedes the recognition of sd aom in past environments characterized by diffusive transport of methane carbon sulfur and trace element geochemistry of pore water and sediments was investigated at a site affected by upward methane diffusion in the shenhu area of the south china sea here the sulfate methane transition zone smtz is located 7 6 m below the seafloor based on sulfate and methane concentrations the slope of 34s vs 18o values of sulfate is consistent with diffusive transport of methane concentration and isotope profiles of pore water species point to diffusive rather than advective transport of solutes enhanced sulfate reduction inferred from 34s values of sulfate agrees with the local occurrence of relatively abundant 34s enriched iron sulfide minerals the time required to produce the observed authigenic iron sulfides around the smtz is estimated to be 1 1 ka based on the amount of iron sulfide minerals and the present diffusive flux of sulfate no enrichment of authigenic carbonate barium ba and molybdenum mo was detected in the studied sediments this observation is consistent with the calculation that the current fluxes of pore water calcium magnesium ba and mo are too low to allow for authigenic enrichments the low fluxes are largely controlled by diffusion which facilitates the formation of 34s enriched iron sulfide minerals the observed enrichment patterns unlike those of sediments affected by advective seepage are expected to be prevalent in modern and ancient continental margin sediments and may contribute to the identification of past methane rich zones and overlying sd aom zones as sinks for methane in the geological record

mineralogical crystallographic and isotopic constraints on the precipitation of aragonite and calcite at shiqiang and other hot springs in yunnan province china two active spring vent pools at shiqiang yunnan province china are characterized by a complex array of precipitates that coat the wall around the pool and the narrow ledges that surround the vent pool these precipitates include arrays of aragonite crystals calcite cone dendrites red spar calcite unattached dodecahedral and rhombohedral calcite crystals and late stage calcite that commonly coats and disguises the earlier formed precipitates some of the microbial mats that grow on the ledges around the pools have been partly mineralized by microspheres that are formed of si and minor amounts of fe the calcite and aragonite that are interspersed with each other at all scales are both primary precipitates some laminae for example change laterally from aragonite to calcite over distances of only a few millimetres the precipitates at shiqiang are similar to precipitates found in and around the vent pools of other springs found in yunnan province including those at gongxiaoshe zhuyuan eryuan and jifei in all cases the dwater and 18owater indicate that the spring water is of meteoric origin these are thermogene springs with the carrier co2 being derived largely from the mantle and reaction of the waters with bedrock variations in the 13ctravertine values indicate that the waters in these springs were mixed to varying degrees with cold groundwater and its soil derived co2 calcite and aragonite precipitation took place once the spring waters had become supersaturated with respect to caco3 probably as a result of rapid co2 degassing these precipitates which were not in isotopic equilibrium with the spring water are characterized by their unusual crystal morphologies the precipitation of calcite and aragonite seemingly together can probably be attributed to microscale variations in the saturation levels that are in turn attributable to microscale variations in the rate of co2 degassing

wet dry seasonal variations of hydrochemistry and carbonate precipitation rates in a travertine depositing canal at baishuitai yunnan sw china implications for the formation of biannual laminae in travertine and for climatic reconstruction travertine or tufa is a chemical sedimentary deposit that is precipitated from springfed stream water supersaturated with calcite due to co2 degassing liu et al 1995 pentecost 1995 ford and pedley 1996 these deposits have biannual laminations which could provide valuable paleoclimatic and paleoenvironmental information with high resolution liu et al 2006 kano et al 2007 brasier et al 2009 lojen et al 2009

environment of the early paleozoic vertebrates abstract a comprehensive review of the known pre devonian vertebrate localities suggests that the non marine environment was not invaded until about wenlock early mid silurian time known well dated late cambrian ordovician and early silurian vertebrate localities are all in the marine environment considerations of paleogeography for the pre wenlock indicate that most of the vertebrate localities are too distant from shorelines to provide any basis for transport from the non marine environment to a marine depositional site as a favored explanation the articulated nature of the vertebrates from some of these pre wenlock occurrences also supports this interpretation reconsideration of both the physiological and embryological evidence relative to living vertebrates and some related chordates is also consistent with the view that the vertebrates originated in the marine environment

are aragonite stalagmites reliable paleoclimate proxies tests for oxygen isotope time series replication and equilibrium the use of aragonite stalagmites as paleoclimate proxies has become increasingly common because of their often exceptional uranium series dating precision and fast growth rates which allow near annual climate resolution however aragonite is known to be susceptible to open system behavior and may recrystallize to calcite under typical cave conditions as a result the fidelity of the oxygen isotopic variations preserved in aragonite stalagmites is not yet as firmly established as for calcite stalagmites and few studies have investigated oxygen isotope replication and equilibrium with cave drip waters i present new data and review findings from the literature that show that aragonite stalagmites may pass both the equilibrium and replication tests in some cases but that other aragonites are clearly precipitated out of equilibrium with cave drip waters as a case study 18 o data for three exceptionally well dated stalagmites from juxtlahuaca cave mexico are presented two of the stalagmites are aragonite and the third was measured on a diagenetically calcitized aragonite stalagmite these results show that the modern aragonite precipitates in apparent oxygen isotopic equilibrium with drip waters and the two aragonite speleothems replicate strongly over the past 530 yr thus confirming a common paleoclimate signal observations of 18 o systematics in previously published aragonite stalagmite 18 o records from china and belize show that at least two samples clearly precipitated modern aragonite out of isotopic equilibrium with cave drip waters because the equilibrium test only applies to modern precipitation for which temperature and drip water 18 o values are known both equilibrium and replication tests are required for confident interpretation of aragonite stalagmite 18 o time series and studies that fail or do not attempt such tests should be considered cautiously

discerning the interactions between environmental parameters reflected in d13c and d18o of recent fluvial tufas lessons from a mediterranean climate region abstract 13 c and 18 o of recent continuous tufa records obtained during a monitoring period spanning 3 to 13 years are compared with the corresponding known environmental conditions three rivers in ne iberia located along a 200 km n s transect are used for this comparison the isotopic variations through space and time are discussed in terms of the environmental and geological parameters that operate on different scales focusing on discerning the interactions between these parameters and providing examples of possible misinterpretation of climatic conditions which is important to past climate studies based on isotopic data the calculation of the actual isotopic fractionation coefficients and the comparison with the literature derived coefficients demonstrates that the studied tufa formation was close to isotopic equilibrium to reflect the water temperature the difference between mean measured water temperature tw and mean calculated tw based on 18 o calcite and measured 18 o water is less than 2 7 c tendencies of these calculated tw are similar to the regional air temperature tair tendencies through time in particular in the case of the 13 year record although certain deviations exist over shorter time spans the best agreement between measured and calculated tw and between 18 o calcite based tw tendencies and tair tendencies corresponds to the tufa stromatolite facies differences between the 18 o calcite records of the three rivers cannot be attributed to temperature changes but to the varying influences of groundwater inputs and isotopic rainfall composition in each river without considering these parameters 18 o calcite based tw calculations yield inaccurate results when comparing the study sites 13 c calcite values do not exhibit distinct patterns over time and 13 c calcite variations are likely caused by local processes that do not reflect general environmental changes these findings underscore the significance of accounting for both groundwater behaviour and rainfall stable isotope composition when interpreting climate parameters in carbonate systems particularly when differences between the isotopic signatures of deposits exist in the same region

temperature dependence of oxygen and clumped isotope fractionation in carbonates a study of travertines and tufas in the 6 95 c temperature range conventional carbonate water oxygen isotope thermometry and the more recently developed clumped isotope thermometer have been widely used for the reconstruction of paleotemperatures from a variety of carbonate materials in spite of a large number of studies however there are still large uncertainties in both 18o and 47 based temperature calibrations for this reason there is a need to better understand the controls on isotope fractionation especially on natural carbonates in this study we analyzed oxygen carbon and clumped isotopes of a unique set of modern calcitic and aragonitic travertines tufa and cave deposits from natural springs and wells together these samples cover a temperature range from 6 to 95 c travertine samples were collected close to the vents of the springs and from pools and tufa samples were collected from karstic creeks and a cave the majority of our vent and pool travertines and tufa samples show a carbonate water oxygen isotope fractionation comparable to the one of tremaine et al 2011 with some samples showing higher fractionations no significant difference between the calcite water and aragonite water oxygen isotope fractionation could be observed the 47 data from the travertines show a strong relationship with temperature and define the regression 47 0 044 0 005 106 t2 0 205 0 047 the ph of the parent solution mineralogy and precipitation rate do not appear to significantly affect the 47 signature of carbonates compared to the temperature effect and the analytical error the tufa samples and three biogenic calcites show an excellent fit with the travertine calibration indicating that this regression can be used for other carbonates as well this work extends the calibration range of the clumped isotope thermometer to travertine and tufa deposits in the temperature range from 6 c to 95 c

carbonatation processes at the el berrocal natural analogue granitic system spain inferences from mineralogical and stable isotope studies the el berrocal granite u bearing quartz vein system has been studied as a natural analogue of a high level radioactive waste repository the main objective is to understand the geochemical behaviour of natural radionuclides occurring under natural conditions in this framework the carbonatation processes have been studied from a mineralogical and isotopic and point of view since carbonate anions are powerful complexing agents for u vi under both low temperature hydrothermal and environmental conditions the carbonatation processes in the system are identified by the presence of secondary ankerite with minor calcite scattered in the hydrothermally altered granite and mn calcite in fracture filling materials the isotopic signatures of these carbonates lead us to conclude that ankerite and calcite from the former were formed at the end of the same hydrothermal process that altered the granite at a temperature range of between 72 and 61 c for ankerite and between 52 and 35 c for calcite the effect of edaphic co2 on both carbonates greater on calcite than on ankerite is demonstrated calcites from fracture fillings are at least binary mixtures in different proportions of hydrothermal calcite formed between 25 and 100 c and supergenic calcite formed at 25 c according to their signatures the effect of edaphic co2 in both calcites is also evident it is assumed that i hydrothermal calcite from fracture fillings and ankerite from the hydrothermally altered granite are the result of the same hydrothermal process their chemical differences being due to the intensity of the water rock interaction which was stronger in the altered granite than in the fractures and ii all of these carbonatation processes are responsible for ancient and recent migration retention of uranium observed in the hydrothermally altered granite and fracture fillings

climatic change recorded by stable isotopes and trace elements in a british holocene tufa combined stable isotope d18o and d13c and trace element mg sr geochemistry from bulk tufa calcite and ostracod shell calcite from an early holocene british tufa reveal clear records of holocene palaeoclimatic change variation in d18o is caused principally by change in the isotopic composition of holocene rainfall recharge itself caused mainly by change in air temperature the d13c variability through much of the deposit reflects increasing influence of soil zone co2 owing to progressive woodland soil development bulk tufa mg ca and sr ca are controlled by their concentrations in the spring water importantly mg ca ratios are not related to d18o values and thus show no temperature dependence first order sympathetic relationships between d13c values and mg ca and sr ca are controlled by aquifer processes residence times co2 degassing and calcite dissolution reprecipitation and probably record intensity of palaeorainfall recharge effects stable isotope records from ostracod shells show evidence of vital effects relative to bulk tufa data the ostracod isotopic records are markedly spiky because the ostracods record snapshots of relatively short duration years whereas the bulk tufa samples record averages of longer time periods probably decades the d18o record appears to show early holocene warming a thermal maximum at ca 8900 cal yr bp and the global 8200 yr bp cold event combined d13c mg ca and sr ca data suggest that early holocene warming was accompanied by decreasing rainfall intensity the mg ca data suggest that the 8200 yr bp cold event was also dry warmer and wetter conditions were re established after the 8200 yr bp cold event until the top of the preserved tufa sequence at ca 7100 cal yr bp

paleomagnetic results from the silurian of the yangtze paraplatform gpdyke n d huang k xu g zhang w y and kent d v 1987 paleomagnetic results from the silurian of the yangtze paraplatform in d v kent and m km editors laurasian paleoma etism and tectonics teetonophysics 139 123 132 samples have been collected from sites from three localities located in sichuan and in yunnan provinces the samples were taken from limestones and red siltstones covering most of the silurian of the south china block the results from the limestone sites were disappointing and all the sites that yielded successful results were from red siltstones characteristic high temperature components were successfully isolated from fifteen of these sites the sites from xiushan county sichuan 28 48o n 108 99 0 e successfully pass the fold test at the 99 level indicating that the magnetization was acquired before folding in the mesozoic the direction obtained from this locality is directed toward the east with shallow positive inclinations d 85 6 o i 12 1 cuss 5 33 the results obtained from a single red bed locality from qijiang county sichuan 28 58 n 106 85 e yield a similar direction the results from the upper silurian of yunnan 25 5 n 103 73o e were obtained from only two sites and the isolated directions were towards the west with shallow inclinations this direction is opposed to the characteristic directions obtained from sichuan and are interpreted as a reversed silurian direction the paleomagnetic pole position determined from all sites given equal weight n 15 falls at 4 9 n lat 194 7 e long with ass 5 61 o

a multi proxy limnologic record of rapid early holocene hydrologic change on the northern great plains southwestern saskatchewan canada clearwater lake saskatchewan is a relatively shallow topographically closed perennial lake cen trally located in the palliser triangle region of western canada despite its present day small size clearwater lake is one of only a few lacustrine basins in this vast 400 000 km2 region of the northern great plains whose stratigraphic record extends to the early holocene multiple proxy indicators are used to interpret the early holocene limnologic and hydrologic conditions in the basin changes in solute chemistry and concentration are reflected by siliceous microfossils and the endogenic and authigenic mineralogy of the sediment the diatoms also provide evidence of fluctuations in water depth and water column stratification plant macrofossil assemblages sediment texture and bedding features and detrital mineralogy help to reconstruct drainage basin conditions and water level changes stable o nd c isotopic composition of inorganically precipitated endo genic carbonate minerals provide insight into

review of aragonite and calcite crystal morphogenesis in thermal spring systems abstract aragonite and calcite crystals are the fundamental building blocks of calcareous thermal spring deposits the diverse array of crystal morphologies found in these deposits which includes monocrystals mesocrystals skeletal crystals dendrites and spherulites are commonly precipitated under far from equilibrium conditions such crystals form through both abiotic and biotic processes many crystals develop through non classical crystal growth models that involve the arrangement of nanocrystals in a precisely controlled crystallographic register calcite crystal morphogenesis has commonly been linked to a driving force which is a conceptual measure of the distance of the growth conditions from equilibrium conditions essentially this scheme indicates that increasing levels of supersaturation and various other parameters that produce a progressive change from monocrystals and mesocrystals to skeletal crystals to crystallographic and non crystallographic dendrites to dumbbells to spherulites despite the vast amount of information available from laboratory experiments and natural spring systems the precise factors that control the driving force are open to debate the fact that calcite crystal morphogenesis is still poorly understood is largely a reflection of the complexity of the factors that influence aragonite and calcite precipitation available information indicates that variations in calcite crystal morphogenesis can be attributed to physical and chemical parameters of the parent water the presence of impurities the addition of organic or inorganic additives to the water the rate of crystal growth and or the presence of microbes and their associated biofilms the problems in trying to relate crystal morphogenesis to specific environmental parameters arise because it is generally impossible to disentangle the controlling factor s from the vast array of potential parameters that may act alone or in unison with each other

c and o stable isotope variability in recent freshwater carbonates river krka croatia three types of recent carbonate precipitates from the river krka croatia were analysed 1 bulk tufa from four main cascades in a 34 km long section of the river flow through the krka national park 2 a laminar stromatolite like incrustation formed in the tunnel of a hydroelectric power plant close to the lowest cascade and 3 recent precipitates collected on artificial substrates during winter spring and summer periods stable isotope compositions of carbon d 13 c and oxygen d 18 o in the carbonate and organic carbon d 13 corg were determined and compared with d 18 o of water and d 13 c of dissolved inorganic carbon dic the source of dic which provides c for tufa precipitation was determined from the slope of the line dic dic0 1 vs d 13 c dic dic dic0 sayles curry 1988 the d 13 c value of added dic was 13ae6 corresponding to the dissolution of co2 with d 13 c between 19ae5 and 23ae0 vienna pee dee belemnite vpdb the observed difference between the measured and calculated equilibrium temperature of precipitation of bulk tufa barriers indicates that the higher the water temperature the larger the error in the estimated temperature of precipitation this implies that the climatic signals may be valid only in tufas precipitated at lower and relatively stable temperatures the laminar crust comprising a continuous record of the last 40 years of precipitation shows a consistent trend of increasing d 13 c and decreasing d 18 o the lack of covariation between d 13 c and d 18 o indicates that precipitation of calcite was not kinetically controlled for either of the elements d 13 c and d 18 o of precipitates collected on different artificial substrates show that surface characteristics both of substrates and colonizing biota play an important role in c and o isotope fractionation during carbonate precipitation

contrasts in variations of the carbon and oxygen isotopic composition of travertines formed in pools and a ramp stream at huanglong ravine china implications for paleoclimatic interpretations abstract water samples and modern endogenic thermogene travertine calcite deposited on plexiglass substrates in travertine pools and a ramp stream were collected along the huanglong ravine sichuan sw china at regular 10 day intervals from early may to early november in 2010 including both wet and dry conditions temporal and spatial variations in the 13 c and 18 o values of the modern travertine were examined to understand their potential for paleoclimatic and paleoenvironmental interpretations it was found that 13 c and 18 o of travertine formed in the ramp stream were low in the warm rainy season and high in the cold dry season their positive correlation was mainly due to dilution and rainfall seasonal effects on 13 c and 18 o values respectively i e low 13 c values were caused by dilution by overland flow with depleted 13 c values and reduced co 2 degassing in the warm rainy season while low 18 o values of travertine were because of low 18 o values of water induced by seasonal variation in oxygen isotopic ratios of rainwater meanwhile kinetic effect on oxygen isotopic fractionation during ramp travertine deposition existed and reduced this positive correlation in contrast the 13 c and 18 o values of the pool travertines displayed a converse behavior which was caused mainly by the temperature effect low 18 o values and high 13 c values in the warm rainy season were correlated chiefly with the higher water temperatures therefore the 13 c and 18 o values of the travertine may be used for paleo rainfall or paleotemperature reconstruction respectively this study demonstrates that endogenic travertine like epigenic meteogene tufa may be a suitable candidate for high resolution paleoclimatic and paleoenvironmental reconstructions however since travertines deposited under differing hydrodynamic conditions e g pools with still water contrasted to fast flow streams have different climatic responses it is necessary to check the depositional facies of fossil travertine samples before they can be used for palaeoclimate temperature and or rainfall reconstruction