strength of single crystal orthopyroxene under lithospheric conditions creep strength of oriented orthopyroxene single crystals was investigated via shear deformation experiments under lithospheric conditions p pressure 1 3 gpa and t temperature 973 1 373 k for the a orientation shear direction 001 on 100 plane the samples have transformed completely to clinoenstatite and much of the deformation occurred after transformation in contrast for the b orientation shear direction 001 on 010 plane samples remained orthoenstatite and deformation occurred through dislocation motion in orthoenstatite the strength of orthopyroxene with these orientations is smaller than for olivine aggregates under all experimental conditions flow of the b orientation samples is described by a power law and the pre exponential constant the apparent activation energy and the stress exponent are determined to be a 10 9 5 s 1 mpa 4 2 q 114 kj mol and n 4 2 however for the a orientation the results cannot be fit by a single flow law and we obtained the following a 108 9 s 1 mpa 3 0 q 459 kj mol and n 3 0 at high temperatures 1 173 k and a 10 27 4 s 1 mpa 14 3 q 296 kj mol and n 14 3 at low temperatures 1 173 k the stress exponent for the low temperature regime is high suggesting that deformation involves some processes where the activation energy decreases with stress such as the peierls mechanism our study shows that orthopyroxene with these orientations is significantly weaker than olivine under the lithospheric conditions suggesting that orthopyroxene may reduce the strength of the lithosphere although the extent to which orthopyroxene weakens the lithosphere depends on its orientation and connectivity

critical shear stress for mechanical twinning of jadeite an experimental study coarse grained natural jadeitite samples from myanmar were experimentally deformed in a griggs type solid medium apparatus at strain rates of 2 10 5 and 5 10 6 s 1 and temperatures of 900 and 1000 c the microfabrics of the deformed samples are investigated by scanning electron microscopy sem using the electron backscatter diffraction ebsd technique the critical shear stress for twinning in the 100 001 system is derived from the orientation distribution of jadeite crystals with and without mechanical twins the results indicate a homogeneous stress field within the sample and a critical shear stress of 150 25 mpa which compares well to that determined by kolle and blacic j geophys res 87 1982 4019 for mechanical twinning of other clinopyroxenes with the critical shear stress known mechanical twinning of jadeite can be used as a paleopiezometer for high stress tectonic environments

high pressure deformation of calcite marble and its transformation to aragonite under non hydrostatic conditions we conducted deformation experiments on carrara marble in the aragonite and calcite stability fields to observe the synkinematic transformation of calcite to aragonite and to identify any relationships between transformation and deformation or sample strength deformation induced microstructures in calcite crystals varied most significantly with temperature ranging from limited slip and twinning at 400 c limited recrystallization at 500 c widespread recrystallization at 600 and 700 c to grain growth at 800 900 c variations in confining pressure from 0 3 to 2 0 gpa have no apparent effect on calcite deformation microstructures aragonite grew in 10 6 10 7 s 1strain rate tests conducted for 18 524 h at confining pressures of 1 7 2 0 gpa and temperatures of 500 600 c as in our previously reported hydrostatic experiments on this same transformation the aragonite nucleated on calcite grain boundaries the extent of transformation varied from a few percent conversion near pistons at 400 c 2 0 gpa and 10 4 s 1 strain rate in a 0 8 h long experiment to 98 transformation in a 21 day test at a strain rate of 10 7 s 7 a temperature of 600 c and a pressure of 2 0 gpa at 500 c porphyroblastic 100 200 m aragonite crystals grew at a rate faster than 8 10 1m s 1 at 600 c the growth of aragonite neoblasts was slower 6 10 1 m s 1 and formed glove and finger cellularprecipitation like textures identical to those observed in hydrostatic experiments the transformation to aragonite is not accompanied by a shear instability or anisotropic aragonite growth consistent with its relatively small volume change and latent heat in comparison with compounds that do display those features

a characterisation of the coastal tufa deposits of south west western australia abstract located in the south west coastal zone of western australia are numerous tufa deposits which are registered as threatened ecological communities tec the tufas occur in near shore shallow bedrock settings and are associated with local groundwater discharge depositional facies mineralogy elemental chemistry and water quality were investigated for five key deposits two conceptual environmental models are identified the first the cascade to barrage pool model is associated with coastal waterfall zones the second a perched spring line and barrage pool model is located predominantly in the supratidal zone tufa morphology texture mineral composition and elemental chemistry vary within and between sites both phytoclast and lithoclast allochthonous and phytoherm forms of tufa are identified depending on location within the facies calcite and to a lesser extent aragonite and mg calcite dominate tufa mineralogy with diagenetic modifications apparent tufa water chemistry is generally na cl hco3 dominated however na cl concentrations increase at sites situated within the supratidal zone currently the most likely potential threat posed to these deposits is increasing nutrient levels in spring waters from agricultural land use within the catchments this could in the future impact on tufa development

intra and inter annual growth rate of modern stalagmites we measure the factors that determine growth rate temperature drip rate calcium ion concentration for 31 waters that feed stalagmites within six cave systems throughout europe water samples were collected at a frequency of at least 1 month to permit the modelling of both inter and intra annual growth rate variations utilising the theory of wolfgang dreybrodt chem geol 29 1980 89 105 chem geol 32 1981 237 245 dreybrodt w 1988 processes in karst systems springer verlag berlin 288 pp inter annual growth rates were measured using the stalagmites that were associated with the analysed water samples growth rate was determined from annual lamina counting specific time markers within the stalagmites and location of bomb 14c when compared to theoretically predicted values a good agreement between theoretical and measured stalagmite growth rates is observed r2 0 69 when compared to site climate and geochemical parameters a good correlation is observed between measured growth rate and mean annual temperature for five sites r2 0 63 and dripwater calcium content r2 0 61 but not drip rate r2 0 09 the good correlation with both calcium and temperature is due to soil co2 production being primarily determined by surface temperature and soil moisture however when we compare our data to that in the grotte de clamouse a site that has little soil cover we observe that the growth rate temperature relationship breaks down due to either the lack of soil co2 production or prior calcite precipitation intra annual data demonstrates that maximum growth rate occurs when calcium concentrations are high and that this occurs under different seasons depending on the hydrology of each site our results demonstrate a stronger dependence of intra annual stalagmite growth rate on dissolved calcium ion concentrations than drip rate for the range of drip rates investigated here 0 01 t 2drip s 1 but for lower drip rates this factor becomes important in controlling growth rate we suggest that for well monitored and understood sites stalagmite growth rate variations can provide useful information for palaeoclimate reconstruction

a flow law for dislocation creep of quartz aggregates determined with the molten salt cell we have used the molten salt cell to conduct an experimental study on the rheology of a natural quartzite containing 0 15 wt water co axial deformation experiments were conducted at constant piston displacement rates approximating constant strain rates at low strain the strengths of our natural quartzite measured in the molten salt cell are approximately half those measured at the same conditions in solid media because unlike solid confining media molten salt does not contribute to the strength of the sample it reduces the friction on the moving piston and it allows clear identification of the hit point we have limited the experimental conditions to those required for dislocation creep and have used only steady state flow stresses measured during climb accommodated dislocation creep to calculate the flow law parameters two flow laws were determined one for samples containing minor amounts of melt 1 2 and one for melt free samples in both cases the power law stress exponent n is 4 0 0 9 which is greater than that previously reported in flow laws for dislocation creep of quartz aggregates determined in solid media the activation energy q is 137 34 kj mol 1 for samples with melt and 223 56 kj mol 1 for those without within the range of previously determined values for quartz aggregates containing 0 1 wt water the pre exponential term a is 1 1 10 4 2 mpa ns 1 for samples without melt and 1 8 10 8 2 mpa ns 1 for those with melt the lower strengths measured in the molten salt cell indicate that previous piezometer relations for quartz experimentally determined in solid media are not correct extrapolation of the flow law for melt free aggregates to natural strain rates predicts higher strengths than most previous quartz flow laws however accurate extrapolation requires determining the dependence of flow stress on fh2o and or ah

dislocation creep of polycrystalline dolomite the field of dislocation creep and rheological parameters for coarse grained d 240 m natural dolomite has been determined through experiments performed at temperatures of 700 1000 c effective pressures of 300 900 mpa and strain rates of 10 4 s to 10 7 s at low strain 7 dolomite aggregates deform homogeneously and define a power law between strain rate and differential stress with a stress exponent of 3 0 0 1 but at higher strains through going fine grained 10 m shear zones develop in the dolomite aggregates concomitant with strain weakening recrystallization is limited at low strain and microstructures observed in the low strain samples include undulatory extinction twins grain boundary bulging limited recrystallization along twins and fluid inclusion trails these same microstructures are present outside of the narrow through going shear zones in high strain samples however within the shear zones the grain size is small 10 m with some larger porphyroclasts 20 50 m shear zones nucleate at fine grained zones formed at twin boundaries twin twin intersections and fluid inclusion trails and is likely due to a switch in deformation mechanism due to the large strength contrast between the fine grained zones deforming by diffusion creep and the coarse grained protolith the activation energy q for creep of coarse grained dolomite at low strain is 145 kj mol in contrast to other activation energies for dislocation and diffusion creep of minerals q for dislocation creep of dolomite is considerably less than that for diffusion creep 248 kj mol the results of this study indicate that coarse grained dolomite will initially deform by dislocation creep at natural strain rates and temperatures between 200 and 550 c but due to limited recovery mechanisms fine grained shear zones will nucleate and diffusion creep may control the rheology of these fine grained shear zones in nature at temperatures above 300 c

temporal and environmental significance of microbial lamination insights from recent fluvial stromatolites in the river piedra spain despite extensive research the environmental and temporal significance of microbial lamination is still ambiguous because of the complexity of the parameters that control its development a 13 year monitored record of modern fast accreting calcite stromatolites mean 14 mm year 1 from artificial substrates installed in rapid flow in the river piedra north east spain allows comparison of the sedimentological attributes of successive six month depositional packages with the known climatic hydrophysical and hydrochemical parameters of the depositional system the stromatolites are formed of dense porous and macrocrystalline composite laminae the dense and porous composite laminae which are composed of two to eight laminae consisting largely of calcified cyanobacteria are characterized by i dense composite laminae up to 15 mm thick mostly with successive dense laminae and minor alternating dense and porous laminae and ii porous composite laminae up to 12 mm thick consisting mainly of porous laminae alternating with thinner dense laminae most of the dense composite laminae formed during the warm periods april to september whereas most of the porous composite laminae developed in the cool periods october to march each dense and porous composite lamina represents up to or slightly longer than six months the alternation of these two types of composite laminae parallels seasonal changes in temperature the dense and porous laminae result from shorter for example intraseasonal variations in temperature insolation and hydrological conditions the macrocrystalline laminae with crystals 100 m long occur isolated and grouped into composite laminae up to 1 7 mm thick their occurrence suggests the absence or poor development of microbial mats over periods of weeks to several months thus stromatolite lamination can record different order periodic and non periodic changes in the magnitude of environmental parameters over a single year these results hold important implications for the temporal and environmental interpretation of lamination in microbial structures

quaternary paludal tufas from the ben younes spring system gafsa southwestern tunisia interactions between tectonics and climate abstract tufa deposits that can be fit into a single depositional model are restricted to relatively few publications in the geological literature this paper presents a detailed sedimentological study of quaternary early holocene paludal tufas partly exposed in the ben younes piedmont field data reveal five main paludal lithofacies phytoherm framestones sapropelitic tufa microdetrital tufa microbial laminites and lime muds radiocarbon dating of residual organic matter in tufa shows that the tufa ranges in age from 8790 50 to 3230 60 bp most tufa deposits appear to remain preserved during the different stages of their development lithification and diagenetic modifications of tufa show two major trends an increase in the average carbonate grain size and non selective dissolution of the fabric where deposits are exposed to meteoric diagenesis the studied tufas are water limited and the importance of climate in their formation is as major as implied in other mediterranean equivalents the predominance of paludal conditions in this area is controlled by the flat substrate the spring locations and the water supply the gafsa strike slip fault aside its tectonic role acts as a major regional sill that controlled paleoflow directions discharge locations content volume rate and fluctuations of the water supply

comparative study of the pleistocene cakmak quarry denizli basin turkey and modern mammoth hot springs deposits yellowstone national park usa this study compares and contrasts the travertine depositional facies of two of the largest sites of travertine formation located in very different geological contexts i e the modern mammoth hot spring mhs system in the active volcanic complex of yellowstone national park usa and the pleistocene cakmak quarry a well exposed example of the ballik travertines in the extensional denizli basin turkey new 2d to 3d facies maps of both travertine systems combined with microscopy assist in proposing an integrated spring depositional model based on the existing mhs facies model understanding general controls on meter to kilometer scale travertine deposit architecture and its preservation and provide quantitative estimates of facies spatial coverage and slope using gis the comparison resulted in the distinction of eight facies grouped in five downstream facies zones from vent to distal slope notwithstanding the different geological context of both travertine systems observations show that several of the facies are strikingly comparable draping apron and channel facies top slope pond facies crystalline proximal slope facies and distal slope facies whereas other facies do not have a precise exposed equivalent vent facies pavement apron and channel facies extended pond facies and phyto proximal slope facies combining observations of active springs at mhs with the cakmak vertical travertine quarry exposures demonstrates that lateral and vertical facies transitions are a sensitive record of changes in the spring dynamics flow intensity and paths that become well preserved in the geological record and can be recognized as prograding aggrading retrograding trends or erosive surfaces traceable over tens to hundreds of meters quantification of facies specific coverage at mhs shows that proximal and distal slope facies deposits cover as much as 90 of the total mapped surface area in addition only 7 of the surface is found to be marked by a waterfilm related to an active flowing spring slope statistics reveal that strong slope breaks can often be related to transgressive apron and channel facies belts and that variable but steep slopes up to 40 are dominated by proximal slope facies in agreement with the cakmak exposures integrating travertine facies and architecture of deposits formed in distinct geological contexts can improve the prediction of general spring facies distributions and controls in other modern and ancient subsurface travertine systems

experimental deformation of synthetic wet jadeite aggregates 1 predictions on interplate coupling and shear heating in the deeper levels of subduction zones require an understanding of the rheology of eclogite the strength of eclogite is probably limited by the flow strength of its major constituent omphacite representing a solid solution between the clinopyroxene end members diopside and jadeite here we report the results of deformation experiments on the end member jadeite naalsi2o6 carried out on fine grained synthetic aggregates crystallized in the stability field of jadeite from a synthetic glass precursor a standard procedure was established to yield samples with a uniform microstructure and an average grain size of approximately 10 m the presence of micropores and the detection of small amounts of freezable water by fourier transform infrared spectroscopy ftir in both undeformed and deformed samples indicates the presence of a free aqueous fluid hence wet conditions deformation experiments were carried out in a modified griggs type apparatus at a confining pressure of 2 5 gpa temperatures between 800 c and 1100 c and at strain rates of 4 10 4 s 1 to 2 10 6 s 1 a molten eutectic cscl nacl mixture was used as pressure medium the microfabrics of the deformed samples and the mechanical data indicate deformation in the dislocation creep regime the mechanical data are fit by a power law using a global inversion method yielding an activation energy of q 326 27 kj mol 1 a stress exponent n 3 7 0 4 and a preexponential factor of ln a 3 3 2 0 extrapolation of this flow law for synthetic jadeitite to low geological strain rates and comparison with available flow laws for diopside indicates jadeite to be significantly weaker than diopside in the dislocation creep regime

testing theoretically predicted stalagmite growth rate with recent annually laminated samples implications for past stalagmite deposition annually laminated stalagmites deposited over the last 30 160 years are analysed to determine their growth rate three natural and artificial cave sites in england france and belgium were chosen for their wide range of variability in growth rate determining variables and multiple samples were taken from each site the annual nature of laminae deposition within the stalagmite calcite was confirmed by comparison to the date of cave void opening 14c analyses or by using dated event horizons measured stalagmite growth rate was determined from annual laminae thickness measurements and compared to that theoretically predicted from the chemical kinetics of the calcite precipitation reaction a good agreement is observed between empirical observations and theoretical predictions although two complicating factors variations in calcite porosity and seasonal cessation of the water supply to the samples both affect the growth rate implications for the extraction of palaeoclimate information from stalagmite growth rate are discussed

cyanobacterial tufa calcification in two freshwater streams ambient environment chemical thresholds and biological processes abstract calcareous freshwater streams near bad urach southwest germany were studied to determine the environmental limits to cyanobacterial calcification daily variations in temperature ph calcium concentration and alkalinity were measured at seasonal intervals from september 1993 to january 1995 in two small woodland streams with lengths of 1 0 and 1 5 km the principal cause of supersaturation in these fast flowing streams is inorganic carbon dioxide outgassing from resurging groundwater locally enhanced by turbulence at waterfalls and cascades photosynthetic uptake of carbon dioxide and temperature effects are negligible nonetheless organic substrates particularly cyanobacteria dominated microbial mats and biofilm significantly localize precipitation by providing suitable nucleation sites precipitation rates on artificial substrates up to 2 2 mm yr on limestone correlate with high saturation index values copper substrates inhibited microbial colonization and received negligible encrustation tufa formation and external calcium carbonate encrustation of cyanobacteria are conspicuous where the annual wateq4f saturation index exceeds 0 8 and are slightly below 0 7 calcium carbonate impregnation of cyanobacterial sheaths has not been observed we infer that in these fast flowing streams cyanobacteria utilize co2 in photosynthesis whereas elsewhere in sluggish freshwater cyanobacteria utilize hco3 leading to sheath impregnation by calcium carbonate even where saturation index is only 0 2 0 3 thus photosynthetic influence on cyanobacterial calcification appears to be negligible in fast flowing co2 rich streams and cyanobacterial calcification takes the form of external encrustation in slow flowing co2 poor streams and lakes cyanobacteria preferentially utilize bicarbonate and sheath impregnation can result modern tropical marine carbonate shelves have saturation indices commonly in the range 0 62 0 82 and cyanobacterial calcification is negligible extrapolation suggests that cyanobacterial calcification could occur in present day seas if saturation index exceeded 0 8 this level corresponding with heavy calcification in the freshwater streams studied may have been widespread in marine environments in the geological past at times when calcified cyanobacteria and environmentally influenced non skeletal calcium carbonate precipitates were abundant

stable isotopes of holocene calcareous tufa in southern poland as paleoclimatic indicators abstract the isotopic composition of oxygen in freshwater calcareous tufa seems to be a sensitive indicator of past climatic changes results of measurements of c 18 o and c 13 c in tufa samples dated with the 14 c method are used to reconstruct holocene climatic changes in southern poland values of c 18 o obtained on tufa samples from four sites raclawka rzerzu nia trzebienice sieradowice representing different hydrodynamic conditions of tufa sedimentation seem to form a selfconsistent series these values with some simplifying assumptions concerning the course of tufa sedimentation were therefore used to estimate mean annual temperatures in the interval ca 9500 2000 yr b p when the resulting curve of thermal changes in southern poland is compared with changes of deposition and erosion of tuffaceous sediments and with results of other methods of reconstruction of paleoclimate in central europe a reasonable agreement among the different specific methods is seen

effect of in stream physicochemical processes on the seasonal variations in δ13c and δ18o values in laminated travertine deposits in a mountain stream channel abstract travertines are potential archives of continental paleoclimate records of stable carbon and oxygen isotopic composition 13 c and 18 o in laminated travertine deposits from endogene spring waters show regular cyclic patterns which may be due to seasonal change in climate determinants such as temperature and rainfall in this study 13 c and 18 o measurements of three travertine specimens that grew naturally over the eight years 2004 2011 at upstream middle and downstream sites in a canal at baishuitai sw china are presented they exhibit clear seasonal variations that generally correlate with biannual laminations specifically 13 c and 18 o values show significant positive correlation with each other for the three travertine specimens with the correlation coefficients increasing downstream along the canal to reveal the factors governing the seasonal and spatial variations in 13 c and 18 o values newly formed travertines precipitated on plexiglas substrates are also examined both 13 c and 18 o of the substrate travertines are low in the summer rainy season and high in the winter dry season showing a great consistency with the patterns in the natural travertines spatially isotope values increase downstream in both seasons with higher increase rates in winter that are related to removal of larger fractions of dissolved inorganic carbon dic from the solution and stronger kinetic isotopic fractionation in winter due to in stream physicochemical processes including caco 3 precipitation and the associated degassing of co 2 seasonal changes in 13 c and 18 o in the travertines are amplified by two times between the upstream and downstream sites this is opposite to trends for epigene meteogene tufas whose seasonal changes in stable isotope compositions are reduced downstream we suggest in stream physicochemical processes are a potential reason for underestimation of annual temperature ranges that are inferred from epigene tufa 18 o data

high resolution records of rainfall events from clay bands in tufa individual rainfall events are recorded as thin clay bands in annually laminated freshwater carbonate tufa runoff from rainfall events entrains clay that then adheres to the tufa surface a specimen collected from southwest japan exhibits 100 clay bands formed during a 15 yr period from 1988 to 2002 the chronology of the clay bands was determined by using the temperature dependent cycle of oxygen isotope ratios in the carbonate and the clay content was quantified by electron probe microanalysis si x ray strength the obtained si x ray strength curve and actual rainfall record follow a nearly identical pattern the clay content of each band correlates with rainfall amount rainfall of 50 mm week produced sufficient amounts of suspended cave clay to produce clay bands in the tufa because the clay bands survive postdepositional alteration this new method can be applied to ancient tufa deposits and has great potential as a high resolution rainfall record for use in climate studies

origin and diagenesis of quaternary travertine shrub fabrics rapolano terme central italy millimetre to centimetre sized arborescent shrub like calcite precipitates are common constituents of hot water travertine shallow pool deposits of quaternary age at rapolano terme tuscany italy in the presently forming travertines the shrubs consist of apparently random associations of i micrite aggregates and ii subhedral to euhedral rhombic spar crystal aggregates in thin section the micrite aggregates appear dark and the spar rhomb aggregates light giving the shrubs a mottled appearance travertines are basically produced by caco3 precipitation due to degassing and evaporation of the spring waters although biological influence may also stimulate precipitation the formation of masses of erect shrubs rather than dense crystal crusts that form on slopes is probably due to limited water flow in the pool environments microbes including bacteria and diatoms are important influences on shrub microfabric and external shape the micrite aggregates are associated with bacteriform bodies seen as tiny rods and spheres the micrite precipitates around these bodies and in adjacent biofilm spar rhomb precipitation appears to be external to the biofilm and may be related to the presence of diatoms which are locally closely associated with the spar rhombs although an essentially inorganic origin particularly for the more euhedral rhombs cannot be ruled out in the older quaternary travertines the original microfabric of the shrubs has been diagenetically altered the original mottled appearance of the shrubs has become uniformly dark and micritic and the evidence for the dual micritic and spar rhomb origin of the shrubs is obscured or destroyed spar micritization of the shrubs is probably due to abiotic and locally biotic dissolution previous studies did not recognize the diagenetic micritization and attributed shrub formation entirely to bacterial activity

laminated carbonate deposits in roman aqueducts origin processes and implications carbonate deposits in roman aqueducts of patara and aspendos southern turkey were studied to analyse the nature of their regular layering optical microscopy and electron backscattered diffraction results show an alternation of dense coarsely crystalline translucent laminae composed of bundles and fans of elongate calcite crystals with their c axes parallel to the long axis and porous fine grained laminae with crystals at near random orientation the 18o and 13c data show a strong cyclicity and anti correlation whereby high and low 18o values correspond to dense columnar and porous fine grained laminae respectively geochemical analyses show similar cyclic changes in carbonate composition electron microprobe and laser ablation inductively coupled mass spectrometry analyses show that porous fine grained laminae are enriched in elements associated with detrital material fe mg k al and si whereas the dense columnar laminae are nearly pure calcite the gradient in major and trace element distribution regular changes in crystal type and in oxygen and carbon isotope composition from porous fine grained to dense columnar laminae reflect changes in water chemistry discharge temperature and biological activity because of the strong bimodal cyclicity of the mediterranean climate in southern turkey the observed laminae can be attributed to calcite deposition during the dry porous fine grained and wet season dense columnar respectively this observation implies that with proper geochemical and microstructural control lamination in carbonate deposits in roman aqueducts can be used for relative dating of aqueduct construction and maintenance and to obtain data on external factors that influenced the aqueducts such as palaeoclimate and natural hazards carbonate deposits in roman aqueducts show properties of both flowstone speleothems and riverine fresh water tufa as many aqueducts of nearly identical channel geometry are present in different climate zones and with different source water characteristics they can be used as natural experiment setups to test and improve existing models of how laminated fresh water carbonates record climate on time scales ranging from seasonal to millennial

origin of annual laminations in tufa deposits southwest japan abstract laminated tufas and a tufa depositing stream in sw japan shirokawa ehime prefecture were studied monthly over a 3 yr period a series of samples from the tufa clearly reveals the pattern of annual laminations the annual layering pattern was primarily controlled by changes in the rate of calcite precipitation as calculated from water chemistry the concentration of dissolved caco 3 which correlates with the precipitation rate was high in summer autumn and low in winter spring owing to changes in the partial pressure of co 2 in underground air regular seasonal changes in underground pco 2 probably resulted from two temperature dependent processes the diffusion of soil co 2 and the ventilation of underground air these changes in addition to water temperature changes altered the precipitation rate which has a clear seasonal pattern especially in the lower stream the seasonal precipitation rate was high in summer autumn and low in winter spring which is consistent with the seasonal lamination pattern seen in the tufas the textures of collected samples show that the laminations consist of densely calcified summer autumn june october laminae and lightly calcified winter spring november may laminae we infer that the increased precipitation rate stimulated thick calcite encrustation on cyanobacterial filaments to produce the dense textures this interpretation is supported by the lowered organic inorganic carbon production ratio in summer autumn seasonal variations in cyanobacterial assemblages are present but do not reflect the seasonal lamination pattern because the relevant processes are temperature dependent the seasonal lamination pattern at shirokawa is thought to generally apply to other laminated tufas deposited in temperate climates however a reversed pattern can result from local and climatic circumstances dense laminae were deposited in winter near the source of the spring at shirokawa because calcite precipitation was high owing to low underground pco 2 in winter reversed patterns reported from northwestern europe were probably influenced by seasonal rainfall which is reflected in hydrological conditions

the role of gypsum and or dolomite dissolution in tufa precipitation lessons from the hydrochemistry of a carbonate sulphate karst system the precipitation of freshwater carbonates tufa along karstic rivers is enhanced by degassing of carbon dioxide co2 downstream of karstic springs however in most karstic springs co2 degassing is not enough to force the precipitation of tufa sediments little is known about the role of dissolution of gypsum or dolomite in the hydrochemistry of these systems and how this affects the formation of tufa deposits here we present a monitoring study conducted over a year in trabaque river spain the river has typical karst hydrological dynamics with water sinking upstream and re emerging downstream of the canyon mixing of calcium magnesium bicarbonate and calcium sulphate waters downstream of the sink enhances the dissolution of carbonates and potentially plays a positive role in the formation of tufa sediments however due to the common ion effect dissolution of dolomite and or gypsum causes precipitation of underground calcite cements as part of the incongruent dissolution of dolomite dedolomitization process which limits the precipitation of tufa sediments current precipitation of tufa is scant compared to previous holocene tufa deposits which likely precipitated from solutions with higher saturation indexes of calcite sicc values than nowadays limited incongruent dissolution of dolomite dedolomitization favours higher sicc values this circumstance occurs when waters with relatively high supersaturation of dolomite and low so42 composition sink in the upper sector of the canyon in such a scenario the process of mixing waters enhances the exclusive dissolution of limestones preventing the precipitation of calcite within the aquifer and favouring the increase of sicc values downstream of the springs such conditions were recorded during periods of high water level of the aquifers and during floods this research shows that the common ion effect caused by the dissolution of gypsum and or dolomite rocks can limit or favour the precipitation of tufa sediments depending on the occurrence or not of incongruent dissolution of dolomite dedolomitization copyright 2016 john wiley sons ltd

low temperature plasticity of olivine during high stress deformation of peridotite at lithospheric conditions an experimental study abstract deformation experiments on natural peridotite from the almklovdalen complex norway were carried out in a griggs type apparatus at temperatures of 20 300 and 600 c confining pressures of 1 0 to 2 5 gpa and strain rates of 3 10 6 to 8 10 5 s 1 the experiments yield maximum differential stresses in the range of 1 0 to 2 9 gpa falling mostly between byerlee s law and goetze s criterion and thus indicating semi brittle behaviour whereas strength of samples deformed at 20 c increases significantly with increasing confining pressure a systematic pressure dependence of strength is not obvious at 300 and 600 c the intracrystalline deformation features of the main constituent olivine were analysed by light and electron microscopic techniques sem ebsd tem deformation microstructures systematically vary with temperature but are insensitive to confining pressure samples deformed at 20 c reflect predominantly brittle failure by intragranular microcracks and shear zones microstructures from samples deformed at higher temperatures show evidence of low temperature plasticity of olivine in the form of pronounced undulatory extinction associated with high dislocation densities pile up of dislocations leads to the formation of either fracture arrays at 300 c or deformation lamellae parallel 100 and cellular structures at 600 c indicating intragranular work hardening a gradual increase in glide controlled crystal plastic deformation of olivine at increasing temperature is interpreted to be responsible for the variation in mechanical behaviour and microstructural characteristics the mechanical data and microstructural observations consistently suggest a temperature for the transition from the strength controlling dominance of brittle to crystal plastic deformation mechanisms close to 600 c the tested peridotite samples show a lower strength than quartzite samples at comparable experimental conditions possibly related to crystallographic differences of olivine and quartz the agreement between microfabrics of experimentally and naturally deformed peridotites demonstrates the importance of low temperature plasticity of olivine during high stress deformation at lithospheric conditions related in particular to seismic activity in the mantle

deformation of mafic schists from subducted oceanic crust at high pressure and temperature conditions abstract we conducted triaxial deformation experiments using a griggs type solid pressure medium apparatus on two mafic schists that experienced different peak metamorphic conditions from the sambagawa metamorphic belt a greenschist and an epidote amphibole schist at a confining pressure of 1 gpa 400 c and strain rate of 10 5 1 s differential stresses for all mafic schists were higher than 1 gpa the greenschist samples were weaker than epidote amphibolite samples under all experimental conditions microstructures of recovered samples of greenschist indicate that deformation of mafic schist is accommodated by semi brittle deformation samples of the epidote amphibole schist deformed at 500 c show shear localization along a single fault oriented parallel to the foliation while mechanical data shows no rapid stress drop on the surface of the fault we observe the formation of slickensides with little gouge all sample types exhibit a high stress exponent n 15 and strain rate strengthening i e positive a b values frictional behavior that inhibits earthquake nucleation differential stress increased with increasing confining pressure while the friction coefficient decreased with increasing confining pressure and temperature greenschist and epidote amphibolite facies metamorphism typically occurs at hot subduction zones such as cascadia and southwest japan the lack of seismicity within the subducting oceanic crust at hot subduction zones could be explained by semi brittle deformation or frictional sliding with a positive a b during deformation of these types of metamorphic rocks weak and aseismic fault zones in subducting slabs might promote slab mantle decoupling at the corner of the mantle wedge and detachment and underplating of oceanic crust from the subducting slab to forearc crust

stable isotopic compositions of recent freshwater cyanobacterial carbonates from the british isles local and regional environmental controls recent 50 years old freshwater cyanobacterial carbonates from diverse environments streams lakes waterfalls throughout britain and ireland were analysed for their stable carbon and oxygen isotope compositions the mean 18o value of 5 9 pdb for river and stream data represents calcite precipitation in equilibrium with the mean oxygen isotopic composition of precipitation in central britain 7 5 smow assuming a mean water temperature of 9 c the mean 18o of lake data 4 5 pdb is statistically different reflecting the effects of residence time and or variations in the oxygen isotopic composition of rainfall carbon isotopes have wide variations in both fluviatile and lake data sets 3 to 12 pdb these variations are principally controlled in the fluviatile samples by contribution of isotopically light soil zone carbon relative to isotopically heavier carbon from limestone aquifer rock dissolution lake samples have the heaviest carbon isotope values reflecting a trend toward isotopic equilibrium between atmospheric co2 and aqueous hco 3 we infer that isotopic compositions of ancient cyanobacterial carbonates should also record environmental information although the effects of stabilization and diagenesis on primary 18o values will need careful consideration primary carbon isotope compositions should be well preserved although in marine samples values will be buffered by the isotopic composition of aqueous marine bicarbonate

classification and environmental models of cool freshwater tufas abstract tufa deposits are common in the quaternary record facies developments are dependent upon localised carbonate precipitation generally these take the form of phytoherm build ups together with associated detrital deposits derived from disagragation of the former phytoherm cements differ from speleothems and floe calcite accumulations in being biologically mediated or modified this paper recognises the following five types perched spring line cascade fluviatile paludal and lacustrine facies each type is composed of distinctive constructional and detrital sediment associations these unique sediment combinations are the product of an interplay between angle of slope water discharge rate standing water bodies phytal and microbial colonization and ambient temperature the proposed models will be of value in the interpretation of ancient and partially exposed tufas

geochemistry of carbon dioxide in six travertine depositing waters of italy abstract the chemical compositions of six travertine depositing hot spring waters in italy are described with emphasis on the carbon dioxide system all springs contained high concentrations of co 2 20 mm l 1 with equilibrium partial pressures well above those which could have been formed in contact with a soil atmosphere after surfacing the co 2 is rapidly lost to the atmosphere with evasion rates close to the springs ranging from 0 45 4 41 mm m 2 s 1 partial pressures of c02 showed an exponential decline with distance which is consistent with the static film model where temperature and turbulence are constant downstream co 2 transfer coefficients which ranged from 66 to 360 cm h 1 were consistent with moderately turbulent flow however there was no correlation between turbulence measured as the mean shear stress and co 2 evasion rate the channels investigated had all been modified by man and most possessed even widths and gradients all waters became increasingly supersaturated with aragonite and calcite downstream and both of these minerals were present in fresh travertine deposits the supersaturation was driven almost exclusively by gas evasion comparison of daytime and nighttime evasion rates demonstrated that photosynthetic activity was an insignificant source of co 2 flux in the reaches investigated carbon dioxide evasion is therefore primarily responsible for the supersaturation and probably also the deposition of travertine at these sites the caco 3 content of the travertines ranged from 91 3 to 96 0 wt with 1 7 4 1 caso 4 traces of organic matter and acid insoluble minerals

wet dry seasonal and spatial variations in the δ13c and δ18o values of the modern endogenic travertine at baishuitai yunnan sw china and their paleoclimatic and paleoenvironmental implications abstract seasonal and spatial variations in the 13 c and 18 o values of the modern endogenic thermogene travertine deposited in a calcite depositing canal at baishuitai yunnan sw china were examined to understand their potential for paleoclimatic and paleoenvironmental implications the sampling sites were set in the upstream middle reach and downstream of the canal and the modern endogenic travertine samples were collected semimonthly to measure their 13 c and 18 o values it was found that both 13 c and 18 o values of the endogenic travertine were low in the warm rainy season and high in the cold dry season and correlated with each other the low 18 o values in warm rainy season were mainly related to the higher water temperature and the lower 18 o values of rainwater and the low 13 c values are caused by the dilution effect of overland flow with low 13 c values in the warm rainy season and the reduced co 2 degassing of canal water caused by the dilution effect of the overland flow the linear negative correlation between the travertine 18 o or 13 c values and rainfall amount may be used for paleo rainfall reconstruction if one knows the 18 o or 13 c values of the fossil endogenic travertine at baishuitai though the reconstruction was not straightforward it was also found that there was a progressive downstream increase of the 18 o and 13 c values of the travertine along the canal the former being mainly due to the preferential evaporation of h 2 16 o to the atmosphere and the latter to the preferential release of 12 co 2 to the atmosphere during co 2 degassing however the downstream increase of the travertine 18 o and 13 c values was less intensive in rainy season because of the reduced evaporation and co 2 degassing during the rainy season to conclude the downstream travertine sites could be more favorable for the paleo rainfall reconstruction while the upstream travertine sites are more favorable for the paleo temperature reconstruction so this study demonstrates that endogenic travertine like epigenic meteogene tufa could also be a good candidate for high resolution paleoclimatic and paleoenvironmental reconstruction

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

textural transition in an aragonite travertine formed under various flow conditions at pancuran pitu central java indonesia abstract a large travertine mound at pancuran pitu central java indonesia displays various types of lamination reflecting different hydrological conditions to understand the geomicrobiological processes of the laminated travertines we investigated the mound s hydrology water chemistry texture microbial composition and volume percentage of carbonate mineral vpc we identified four types of travertines dense travertine 80 vpc flow rate 200 cm s lithified microbial travertine 60 vpc flow rate 70 cm s fragile microbial travertine 30 vpc flow rate 10 cm s and poorly lithified microbial mat

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

accurate differential stress measurement using the molten salt cell and solid salt assemblies in the griggs apparatus with applications to strength piezometers and rheology abstract calibrations have been developed for the molten salt cell and solid salt assemblies used in tri axial griggs type piston cylinder deformation apparatus griggs apparatus that enable accurate differential stress determinations in both assemblies at high pressures and high resolution differential stress measurements in the molten salt cell elastic response of the apparatus was characterized by loading alumina and wc rods and flow strengths were measured for high purity nickel and molybdenum and a ti zr mo alloy in replicate experiments in a griggs apparatus and a heard tri axial gas apparatus gas apparatus at identical pressures temperatures and strain rates the elastic response of the griggs apparatus is nonlinear at low total loads 1 760 mpa on a 5 mm diameter sample but becomes linear at loads greater than 15 kn plastic deformation experiments on water insensitive metals indicate that differential stresses measured in the molten salt cell msc and solid salt ssa assemblies in the griggs apparatus are greater than those measured in the gas apparatus at all conditions but vary systematically and reproducibly a simple linear calibration gas apparatus 0 73 griggsmsc 10 mpa where differential stress 1 3 can be applied to the differential stresses obtained using the msc in the griggs apparatus to obtain sample flow strength a similar linear calibration gas apparatus 0 73 griggsssa 48 mpa 30 mpa can be applied to the differential stresses obtained using the griggs apparatus with a solid salt assembly to obtain accurate sample flow strength these calibrations have been tested by applying them to mechanical data for carbonates deformed in the griggs apparatus and gas apparatus the calibrations are also applied to data from previous studies performed in the griggs apparatus on clinopyroxenites and quartzites and compared to results from similar experiments using the gas apparatus when the experimental starting materials and conditions are the same the recalculated flow strengths measured in the griggs apparatus experiments agree with those measured in the gas apparatus however discrepancies in differential stress are still observed in cases where starting materials differ or water available to silicate samples varies presumably through hydrogen diffusion through sample jackets and hydrogen fugacities of the surrounding confining media

palaeoenvironmental records in holocene spanish tufas a stable isotope approach in search of reliable climatic archives tufa deposits are potential terrestrial archives of palaeoenvironmental and palaeoclimatic information this study assesses the potential of stable isotopic archives from two closely juxtaposed holocene tufa sites in se spain the ruidera site contains deep water lacustrine micrites and tufas whereas the nearby alcaraz site represents a shallow barrage tufa understanding site characteristics is critical to interpreting the stable isotopic variations these holocene lacustrine micrites have isotopic compositions consistent with modern european lake shore microbial carbonates where the isotopic chemistry is strongly influenced by hydrological and residence time effects all the lacustrine micrite d13c values were influenced by microenvironmental microbial effects to some degree because of these effects stable isotope data from lacustrine microbial micrites and tufas will not normally yield precise information on the isotopic composition of palaeoprecipitation temperature or vegetation composition of an area in contrast holocene tufas that formed in shallow fast flowing riverine settings may contain valuable palaeoclimatic archives the tufa deposits must be largely autochthonous as at alcaraz where in situ reed stem encrustations are present records of relative change in air temperature and changes in the source of airmasses are potentially resolvable in the d18o data these interpretations can be verified by other independent climatic data where chronology is constrained variations in riverine tufa d13c values probably record changes in local vegetation and or soil respiration covariation between d18o and d13c values may be intrinsically linked to climatic factors such as aridity tentative palaeoclimatic interpretations for the middle holocene at alcaraz based on the isotope data suggest warming or increasing influence of mediterranean sourced precipitation between approximately 5000 3000 radiocarbon years bp accompanied by increased aridity these interpretations are consistent with the sparse independent palaeoclimatic data and climate modelling results for the holocene of se spain this study supports the growing evidence that well chosen tufa sites could yield valuable palaeoclimatic information

oxygen isotope fractionation in travertine depositing pools at baishuitai yunnan sw china effects of deposition rates abstract travertine 18o values can be used to reconstruct paleo temperatures if the oxygen isotope fractionation factors between travertine and water are accurately understood for this purpose the 18o values of pool travertine and its parent water and the deposition rates of the calcite were investigated at baishuitai yunnan sw china over the course of the full hydrological year april 23 2006 april 25 2007 the results show that the travertine water isotope fractionation factors are close to the commonly accepted equilibrium line of kim and o neil 1997 this differs from the results obtained by yan et al 2012 who found that the oxygen isotope fractionation factors in the travertine depositing pools were close to the line suggested as equilibrium relationship by coplen 2007 the average calcite deposition rate 2 30 mg cm 2 d 1 in the present study is six times larger than that 0 38 mg cm 2 d 1 in yan et al 2012 if slower calcite precipitation leads to equilibrium oxygen isotopic fractionation then the results of this study support the results of coplen 2007 that indicate that the equilibrium fractionation factor may be greater than the commonly accepted one derived by kim and o neil 1997 the relationship between oxygen isotope fractionation factor and calcite deposition rate in our study also agrees with the results of dietzel et al 2009 who found that the kinetic isotope effect favors preferential incorporation of 16o in solid calcite as the calcite deposition rate increases there was a threshold for calcite precipitation rate control on oxygen isotopic equilibrium in our case of travertine depositing pools when the calcite deposition rate was lower than 0 38 mg cm 2 d 1 oxygen isotopic equilibrium between calcite and water was attained therefore calcite deposition rate is a potentially important consideration when using 18o in natural carbonates as a proxy for terrestrial and ocean temperature

factors controlling present day tufa dynamics in the monasterio de piedra natural park iberian range spain depositional environmental settings sedimentation rates and hydrochemistry the tufa record and hydrochemical characteristics of the river piedra in the monasterio de piedra natural park ne spain were studied for 6 years the mean discharge of this river was 1 22 m3 s the water was supersaturated with calcium carbonate the hco3 ca2 and tdic concentrations decreased along the 0 5 km long studied stretch whereas the calcite si showed no systematic downstream or seasonal variation over the same stretch several sedimentary subenvironments exist in which four broad types of tufa facies form 1 dense laminated tufa stromatolites 2 dense to porous massive tufa 3 porous coarsely laminated tufa with bryophytes and algae and 4 dense hard laminated deposits in caves the half yearly period thickness and weight of sediment accumulated on 14 tablets installed in several subenvironments showed that the deposition rate was greater in fast flowing river areas and in stepped waterfalls and lower in slow flowing or standing river areas and in spray and splash areas mechanical co2 outgassing is the main factor controlling calcite precipitation on the river bed and in waterfalls but this process does not explain the seasonal changes in depositional rates the deposition rates showed a half yearly period pattern recorded in all fluvial subenvironments persistent over time 5 26 mm 0 86 g cm2 in warm periods 2 26 mm 0 13 g cm2 in cool periods mass balance calculations showed higher calcite mass values in warm 21 58 mg l than in cool 13 68 mg l periods this biannual variation is mainly attributed to the seasonal differences in temperature that caused changes in inorganic calcite precipitation rate and in biomass and the correlative photosynthetic activity tufa sedimentation was therefore controlled by both physicochemical and biological processes the results of this study may help test depositional rates and their environmental controls and thus assess the climatic and hydrological significance of ancient tufas in semi arid conditions in particular in the quaternary

deformation of antigorite serpentinite at high temperature and pressure abstract deformation experiments were conducted in a griggs type apparatus to constrain the rheology of antigorite serpentinite at high temperatures and pressures samples deformed at temperatures of 400 625 c and pressures of 0 85 1 5 gpa experienced semi brittle deformation resulting in localization on faults at 5 to 25 strain samples deformed at 300 c exhibited transitional behavior the stresses measured for our samples are in good agreement with recent experiments conducted in the deformation dia apparatus however our results indicate that steady state ductile flow is not achieved in contrast with interpretations based on the deformation dia experiments extrapolation of our data to geologic conditions suggests that serpentinites may be weak enough during localized frictional sliding to account for slab wedge decoupling inferred from geologic observations experiments conducted above the thermal stability of antigorite at 700 c and 1 5 gpa show evidence for distributed deformation this observation does not support the hypothesis that intermediate depth earthquakes result directly from dehydration embrittlement in addition samples exhibit velocity strengthening from 300 to 700 c a frictional behavior that inhibits earthquake nucleation

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

crystallographic preferred orientations may develop in nanocrystalline materials on fault planes due to surface energy interactions a layer of substantially noncrystalline material composed of partially annealed nanopowder with local melt was experimentally generated by comminution during 1 5 mm total slip at 2 5 10 6 m s 1 pconf 0 5 gpa and 450 c or 600 c on saw cut surfaces in novaculite the partially annealed nanopowder comprises angular grains mostly 5 200 nm diameter in a variably dense packing arrangement a sharp transition from wall rock to partially annealed nanopowder illustrates that the nanopowder effectively localizes shear consistent with generation of nanoparticles during initial fragmentation not by progressive grain size reduction dislocation densities in nanopowder grains or immediate wall rock are not significantly high but there are planar plastic defects spaced at 5 200 nm parallel to the host quartz grain s basal plane we propose these plastic defects developed into through going fractures to generate nanocrystals the partially annealed nanopowder has a crystallographic preferred orientation cpo that we hypothesize developed due to surface energy interactions to maximize coincident site lattices csl during annealing this mechanism may also have generated cpos recently described in micro nanocrystalline calcite fault gouges

a servohydraulically controlled deformation apparatus for rock deformation under conditions of ultra high pressure metamorphism a deformation apparatus has been developed to study the mechanical behaviour of high pressure and ultra high pressure metamorphic rocks it is based on the conventional griggs design and the molten salt cell concept introduced by h e green ii both the axial loading and the confining pressure are servohydraulically controlled alternatively a self made multilayer pressure vessel or a commercial stripwound construction are used the pressure cell is improved with respect to systems described previously by the use of different salt mixtures with low eutectic temperatures by a mechanically stable arrangement of the thermocouples and by an optimization of the frictional characteristics of the axial loading system the apparatus has been successfully used in deformation experiments on cylindrical aragonite and coesite samples 3 to 4 mm in diameter and 6 to 10 mm in length at confining pressures up to 3 7 gpa and temperatures up to 1170 c

simulating coseismic deformation of quartz in the middle crust and fabric evolution during postseismic stress relaxation an experimental study abstract non steady state deformation and annealing experiments on vein quartz are designed to simulate earthquake driven episodic deformation in the middle crust three types of experiments were carried out using a modified griggs type solid medium deformation apparatus all three start with high stress deformation at a temperature of 400 c and a constant strain rate of 10 4 s 1 type a some are followed by annealing in the stability field of quartz for 14 15 h at zero nominal differential stress and temperatures of 800 1000 c type a b or by annealing for 15 h at 900 c and at a residual stress type a c the quartz samples reveal a very high strength 2 gpa at a few percent of permanent strain the microstructures after short term high stress deformation type a record localized brittle and plastic deformation statisc annealing type a b results in recrystallisation restricted to the highly damaged zones the new grains aligned in strings and without crystallographic preferred orientation indicate nucleation and growth annealing at non hydrostatic conditions type a c results in shear zones that also develop from deformation bands or cracks that formed during the preceding high stress deformation in this case however the recrystallised zone is several grain diameters wide the grains are elongate and a marked crystallographic preferred orientation indicates flow by dislocation creep with dynamic recrystallisation quartz microstructures identical to those produced in type a b experiments are observed in cores recovered from long valley exploratory well in the quaternary long valley caldera california with considerable seismic activity the experiments demonstrate the behaviour of quartz at coseismic loading type a and subsequent static annealing type a b or creep at decaying stress type a c in the middle crust the experimentally produced microfabrics allow to identify similar processes and conditions in exhumed rocks

diagenesis of laminated travertine crusts arbuckle mountains oklahoma abstract waterfall travertine deposits in the arbuckle mountains of oklahoma contain laminated coarsely crystalline neomorphic crusts which retain virtually no evidence of their organic origin the precursors of these neomorphic crusts are laminated organic crusts composed of two basic alternating layers 1 layers of filamentous cyanophyte bushes in which each bush is encased by one or more elongate spar crystals and 2 layers in which equidimensional crystals surround individual cyanophyte filaments as diagenesis commences the elongate calcite spar crystals enclosing algal bushes grow into the overlying more finely crystalline calcite layers by aggradational neomorphism forming coarse columnar crystals oriented perpendicularly to the laminae as the crystals increase in size they incorporate the inclusion rich laminae of the surrounding material thereby maintaining the laminated appearance the end product of this diagenetic process is a dense laminated crust composed almost entirely of columnar calcite crystals which commonly reach lengths of more than 1 cm such crusts display almost no evidence of their former constituents however after immersion in hydrochloric acid and application of an organic stain remains of algal bushes are visible within thin sections many other nonmarine carbonate deposits include similar looking crusts that appear to be solely inorganic in origin in light of the present findings caution certainly is warranted before automatically assuming an inorganic origin for such crusts

mass occurrence of oncoids at the cambrian series 2 series 3 transition implications for microbial resurgence following an early cambrian extinction abstract the traditional lower middle cambrian transition cambrian series 2 series 3 transition is marked by the first major biotic extinction of the phanerozoic eon this biotic crisis has been arguably linked to changes in ocean chemistry and or marine environments but their casual relationships remain controversial to better understand the microbial responses to paleoceanographic changes across this critical transition we have studied the environmental conditions for mass occurrence of oncoids in the western north china platform oncoids at the lower middle cambrian transition form 1 to 3 m thick massive beds show spherical subspherical morphology and contain 8 14 light dark cortical laminar couplets the light laminae are thicker and contain densely intertwined filamentous cyanobacteria that have calcified sheaths and a prostrate growth pattern the dark laminae are thinner and rich in organic matter relics pyrite framboids and heterotrophic bacteria in most oncoids cortical laminae show the same growth orientation for more than five light dark laminar couplets suggesting much less frequent grain overturning than generally thought both light and dark laminae contain well preserved organomineralization fabrics textures including extracellular polymeric substances epss nanoglobules polyhedrons and micropeloids suggesting oncoid formation in shallow marine environments with high alkalinity and active sulfate reduction the presence of pyrite framboids and heterotrophic bacterial relics implies anoxic dysoxic bottom water conditions stratigraphic correlation indicates that time equivalent oncolites and other microbialites are widespread not only in north china but also in other early cambrian successions globally the mass occurrence of oncoids coincides with the kalkarindji large igneous province of australia a prominent negative 13 c excursion roece or redlichiid olenellid extinction carbon isotope excursion a significant increase in 87 sr 86 sr and a large positive shift in 34 s the coincidence of these events suggests that the early cambrian biotic crisis may have been caused by an ocean anoxic event resulting from enhanced volcanic release of co 2 global warming and increased continental weathering preservation of massive oncolites is likely related to decreased metazoan grazing following an early cambrian biotic crisis during which archaeocyathids and many early cambrian trilobite taxa went to extinction the oncoid mass occurrence provides evidence for the resurgence of microbial life in anoxic dysoxic marine shelf environments concomitant with the early cambrian extinction event

the recrystallized grain size piezometer for quartz d 1 0 3 56 0 27 s 1 26 0 13 with no change in slope at the regime 2 3 transition and no effect of temperature or a b stability field another experimental piezometer relation for regime 1 of hirth and tullis 1992 differs in slope suggesting that different recrystallization mechanisms require different piezometer calibrations index terms 3902 mineral physics creep and deformation 5120 physical properties of rocks plasticity diffusion and creep 8030 structural geology microstructures 8159 tectonophysics rheology crust and lithosphere 8164 tectonophysics stresses crust and lithosphere citation stipp m and j tullis the recrystallized grain size piezometer for quartz geophys res lett 30 21 2088 doi 10 1029 2003gl018444 2003

calcite precipitation rates in the field measurement and prediction for a travertine depositing stream abstract rates of calcite precipitation from a travertine depositing stream were determined from changes in stream composition between consecutive sampling points and were compared with rates predicted from a laboratory derived rate law plummer et al 1978 the agreement in rates was generally within an order of magnitude and routinely within a factor of 3 least agreement between measured and predicted rates was obtained for sections of flowpath where relatively little change in bulk chemical composition occurred which were the sections with the greatest mass transfer calculation error and for the stream segment including a waterfall which was the section with the greatest error in estimated surface area reaction rate obtained from the mass of calcite precipitated onto seed crystals placed in the stream significantly underestimated the mass transfer rate for the travertine depositing stream of warm river cave and falling spring creek virginia the coupling of equilibrium speciation models with mass balance calculations and simple field measurements allowed successful field based quantification of reaction rates

annually laminated sequences in the internal structure of some belgian stalagmites importance for paleoclimatology abstract fifteen stalagmites from four caves and one sealed tunnel in southern belgium are composed of alternations of annually deposited white porous and dark compact laminae this is demonstrated by comparing the number of laminae with the local history of the site for modern stalagmites and with radioisotopic ages for late glacial and holocene stalagmites annual cyclicity in the internal structure of these speleothems is explained by the highly seasonal variations of the water excess which influences underground water flow comparison between climatic data and modern stalagmites of a closed tunnel shows that growth laminae can record climatic variations 1 there is a good correlation r 0 84 between lamina thickness in a stalagmite and water excess 2 during years with a high water excess dark compact laminae are more developed which makes the speleothem darker vertical successions of several laminae represent microsequences that may have recorded climatic variations with a time resolution of 1 2 year in a late glacial stalagmite successive laminae microsequences form very regular cycles of 11 years separated by a thick darkcompact lamina it is supposed that as for modern stalagmites the thick dark compact lamina corresponds to a period of high water excess hence this 11 year cycle may reflect a climatic cycle

improving flow laws and piezometers for quartz and feldspar aggregates we have modified the molten salt cell msc in order to measure the flow stress of quartz and feldspar ag gregates deforming by dislocation creep the flow stress of cararra marble measured in the msc is within 5 mpa of that measured in a gas apparatus quartz and feldspar aggregates deformed at 900o 1100oc and confining pressures of 1000 1500 mpa in copper and calcite solid confining pressure media are about twice as strong as those deformed in the msc whereas quartz aggregates deformed in talc and solid nac1 have about the same strength as that measured in the msc these results suggest that the stress exponent in the flow law is larger and the dynamically recrystalized grain size is more sensitive to stress than previously reported acking rings stainless steel

kick and cook experiments on peridotite simulating coseismic deformation and post seismic creep terra nova 24 62 69 2012 abstract experiments comprising deformation at 600 c and annealing at 700 1000 c were performed on natural peridotite to examine the microfabric evolution at conditions corresponding to those prevailing just below the seismogenic zone in suboceanic upper mantle the found olivine microstructures indicate that deformation occurs by low temperature plasticity at low and high annealing temperatures zones of high strain are replaced by subgrains and recrystallized grains respectively the microstructures after annealing at 1000 c resemble core and mantle structures from shear zone peridotites often interpreted as imprint of steady state dislocation creep our study shows that such structures can form by a sequence of low temperature plasticity at high stress and subsequent recrystallization at low stress as corresponding to coseismic deformation and post seismic creep in this case palaeopiezometers are not applicable and a local cpo in aggregates of new grains does not necessarily indicate the activated glide system

an experimental study into the rheology of synthetic polycrystalline coesite aggregates coesite has been found as a relic in ultrahigh pressure metamorphic uhpm crust worldwide and is expected to play a major role in the mechanical behavior of continental crust at uhpm conditions we performed triaxial compression tests on synthetic polycrystalline coesitite in a solid medium apparatus at confining pressures of 3 1 to 3 7 gpa temperatures of 700 to 1160 c and strain rates betweeen 6 10 7 and 1 10 3 s 1 the problem of the limited stress resolution of the solid medium apparatus was addressed by applying two extreme friction corrections that yield lower and upper bounds to the differential stress the correlation between the mechanical data and the microstructural record of the deformed samples as a function of temperature and imposed strain rate is consistent with deformation by dislocation creep we deduced parameters of a power law as n 3 1 and q 275 50 kj mol 1 extrapolation of the experimental data to natural conditions cannot be constrained by comparison with natural microstructures due to the lack of preserved coesite other than as single crystal inclusions nevertheless the extrapolation indicates a low strength of order 10 mpa for natural strain rates at typical uhpm conditions absent deformation of the uhpm brossasco granite dora maira massif western alps thus implies low stresses deformation must have been localized in very weak shear zones during burial and exhumation

the upper jurassic lower cretaceous carbonate terrigenous succession and the development of a carbonate mound in western shikoku japan abstract the stratigraphy and sedimentology of the upper jurassic lower cretaceous torinosu group were studied in western shikoku western kochi prefecture the torinosu group is interpreted as a transgressive succession deposited in a foreland basin the group can be divided into a lower coarse siliciclastic unit the tsukadani formation and an upper carbonate and fine siliciclastic unit the yatsuji formation the tsukadani formation is characterized by conglomerates with chert gravel and probably represents submarine fan deposits the gravels were derived from an exposed accretionary wedge containing pelagic siliceous rocks the yatsuji formation includes a limestone unit up to 150 m in thickness and a few kilometres in lateral extension which comformably rests on siliciclastic rocks and marlstone the limestone unit is interpreted as a carbonate mound and laterally shows considerable variation in thickness the conglomerate with limestone gravels which infills the channel and flanks of the mounds supports a topographic relief associated with the carbonate build ups the facies of the limestone unit changes vertically from marlstone to stromatoporoid facies change in fossil components associated with a decrease of terrigenous components indicates that the initial community was replaced by the reef forming community which is interpreted as a response to the decrease of terrigenous influx periodical input of terrigenous sediment originating from movement of thrust mass interrupted the carbonate deposition

a griggs deformation apparatus set up at lille the classical solid medium apparatus griggs apparatus is generally viewed as a machine of poor accuracy with a large amount of uncertainty however a new generation of equipment with new assemblies and experimental procedures has greatly enhanced the capability of the apparatus experiments performed on the apparatus set up in our laboratory on t oriented yule marble samples show that the yield strength of material can be measured with reasonable precision within 10 mpa and a yield strength as low as 50 mpa can be detected the apparatus is particularly adapted to work on small specimens e g single crystals a few millimetres in size

geochemical and isotopic composition of organic matter in the kupferschiefer of the polish zechstein basin relation to maturity and base metal mineralization vs the present depth of the kupferschiefer soluble organic matter som yields and relative proportions of saturated and aromatic hydrocarbons of the som provide evidence for an oxidative alteration of organic matter in highly mineralized kupferschiefer samples near the rote faule zones this is confirmed by differences in the composition of the saturated and aromatic hydrocarbon fractions of the soluble organic matter saturated hydrocarbons from rote faule samples are dominated by short chain n alkanes and higher abundances of pristane and phytane relative to heptadecane n c17 and octadecane n c18 respectively compared with samples more distant to the rote faule zone compositional changes of the aromatic hydrocarbon fractions with decreasing distance to that zone are characterized by the occurrence of polycyclic aromatic hydrocarbons and elevated ratios of phenanthrene to methylphenanthrenes that are attributed to demethylation reactions and resulted in a decrease of the methylphenanthrene index mpi 1 kupferschiefer samples from the barren zone of the polish basin do not show these alteration patterns the observed variations in organic matter composition with burial depth are consistent with changes due to increasing thermal maturation maturity assessment is achieved from mpi 1 and the methyldibenzothiophene ratio mdr from the relationship between the maturity of organic matter in terms of vitrinite reflectance values and depth of the kupferschiefer strata a continuous increase in reflectance of vitrinite is obtained within the polish basin the alteration pattern of organic matter related to base metal mineralization of the kupferschiefer corresponds to changes in the isotopic composition of organic carbon and calcite kerogen within or close to rote faule zone is enriched in 13c caused by the preferential release of isotopically light organic compounds through progressive degradation of organic matter the opposite tendency towards lower 13c and 18o values of calcite provides evidence for isotopic exchange between carbonate and the oxidizing ore bearing solutions and for organic matter remineralization in contrast organic matter and calcite from the kupferschiefer do not show regular trends in 13c with increasing thermal maturation

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