temperature limits for preservation of primary calcite clumped isotope paleotemperatures abstract solid state reordering of c o bonds in the calcite lattice can alter the clumped isotope composition of paleotemperature archives such as fossil brachiopod shells without inducing significant changes in shell microstructure and trace element concentrations metrics commonly used to gauge preservation quality to correctly interpret the paleoenvironmental significance of clumped isotope derived paleotemperatures it is necessary to understand the temperature time domain in which solid state c o bond reordering is important we address this question using a combination of laboratory and natural geological experiments on paleozoic brachiopod shells the laboratory experiments involve heating fossil brachiopod calcite at different temperatures and times to directly observe rates of 13 c 18 o bond reordering the resulting arrhenius parameters are indistinguishable from values previously determined for an optical calcite with similar trace element compositions we develop an alternative kinetic model for reordering that accounts for non first order reaction progress observed during the initial several hundred minutes of laboratory heating experiments and show that the simplified first order approximation model passey and henkes 2012 predicts reaction progress equally well for temperatures and timescales relevant to sedimentary basins we evaluate our laboratory based rate predictions by studying brachiopod calcite from several sedimentary basins with independently constrained burial temperature histories specifically we use the laboratory derived arrhenius parameters to predict the evolution of brachiopod calcite clumped isotope compositions during successive one million year time steps reflecting the burial and exhumation temperature paths of each basin while this exercise is limited by the relatively large uncertainties in the temperature histories of these basins we find general correspondence within error between predicted and observed clumped isotope values we present simplified temperature time diagrams for calcite showing domains where primary clumped isotope compositions will be preserved partially reordered and fully reordered in conclusion calcite samples dwelling at 100 c or lower for 10 6 10 8 year timescales should not be affected by solid state c o bond reordering

carbonate clumped isotope variability in shallow water corals temperature dependence and growth related vital effects geochemical variations in shallow water corals provide a valuable archive of paleoclimatic information however biological effects can complicate the interpretation of these proxies forcing their application to rely on empirical calibrations carbonate clumped isotope thermometry 47 is a novel paleotemperature proxy based on the temperature dependent clumping of 13 c 18 o bonds similar 47 temperature relationships in inorganically precipitated calcite and a suite of biogenic carbonates provide evidence that carbonate clumped isotope variability may record absolute temperature without a biological influence however large departures from expected values in the winter growth of a hermatypic coral provided early evidence for possible 47 vital effects here we present the first systematic survey of 47 in shallow water corals sub annual red sea 47 in two porites corals shows a temperature dependence similar to inorganic precipitation experiments but with a systematic offset toward higher 47 values that consistently underestimate temperature by 8 c additional analyses of porites siderastrea astrangia and caryophyllia corals argue against a number of potential mechanisms as the leading cause for this apparent 47 vital effect including salinity organic matter contamination alteration during sampling the presence or absence of symbionts and interlaboratory differences in analytical protocols however intra and inter coral comparisons suggest that the deviation from expected 47 increases with calcification rate theoretical calculations suggest this apparent link with calcification rate is inconsistent with ph dependent changes in dissolved inorganic carbon speciation and with kinetic effects associated with co 2 diffusion into the calcifying space however the link with calcification rate may be related to fractionation during the hydration hydroxylation of co 2 within the calcifying space although the vital effects we describe will complicate the interpretation of 47 as a paleothermometer in shallow water corals it may still be a valuable paleoclimate proxy particularly when applied as part of a multi proxy approach

laboratory modeling of the mechanisms of piping erosion initiation a laboratory modeling program has been conducted to assess the mechanics of initiating the piping erosion process in sandy soils the models were performed on several soils differing in gradation grain size grain shape and specific gravity observations and monitoring of pore pressures within the samples during the modeling identified four stages in the development of piping initiation initial movement progressive heave boil formation and total heave by linking the observed behavior with the measured pore pressure regime in the sample a model for the mechanics of piping development has been developed finite element seepage analyses were performed to model the progression of piping development in the laboratory models and corroborate the developed model of mechanics the findings of the study identified a new model for the initiation of piping development that can be applied to the assessment of piping in the field

comparing oxygen isotope records of silurian calcite and phosphate δ18o compositions of brachiopods and conodonts oxygen isotope compositions of silurian calcitic brachiopod shells from gotland are compared with those of phosphatic inarticulate brachiopod shells and conodonts from identical stratigraphic horizons the 18ophosphate values of inarticulate brachiopod shells vary widely 13 0 to 17 5 v smow and are significantly lower than those of coeval conodont samples 17 5 to 19 5 v smow conodont samples from individual beds have homogenous 18ophosphate values with variations close to the analytical precision 0 2 together with a significant correlation of conodont 18ophosphate and articulate brachiopod shell 18ocarbonate values r 0 85 this observation suggests that primary marine oxygen isotope compositions are better preserved in conodont apatite than in inarticulate brachiopod shell apatite however with decreasing 18ocarbonate values the 18ophosphate values of conodonts are higher than expected for theoretical isotopic equilibrium with brachiopod calcite different habitats of conodonts and brachiopods cannot account for the observed offset in 18o because both organisms were thriving on a broad shallow marine carbonate platform whereas 18ophosphate values of silurian conodonts are close to 18ophosphate values of modern and mesozoic tropical biogenic apatites most silurian calcitic brachiopod shells from gotland are depleted in 18o when compared to modern or mesozoic brachiopods we therefore suggest that silurian conodonts from gotland record paleotemperature and 18o of silurian sea water more faithfully than coeval calcitic brachiopod shells

diagenesis of phosphatic hardgrounds in the monterey formation a perspective from bulk and clumped isotope geochemistry understanding the authigenesis of carbon ate fluorapatite through isotopic geochem istry can yield important information on fundamental geologic processes occurring on continental margins around the world this is particularly true for phosphatic hardgrounds which are often found in regions of upwell ing but of which questions remain about the initial formation and subsequent diagen esis here we apply standard isotopes 13 c 18 o alongside the novel clumped isotope 47 used in this study for the first time to reconstruct the temperature of formation of carbonate ions within the lattice of sedimen tary carbonate fluorapatite we investigated phosphatic hardgrounds of miocene age 12 7 10 8 ma sampled at el capitan state beach in the monterey formation the range of isotopic signatures observed is between 1 5 and 8 0 for 13 c relative to the vienna peedee belemnite vpdb standard and 9 5 and 6 0 vpdb for 18 o and val ues range between 0 599 and 0 615 for 47 the enriched 13 c and depleted 18 o signa tures are suggestive of recrystallization within the methanogenic zone clumped isotope geo chemistry further constrains this transforma tion as having taken place at a temperature of 61 66 c 5 c in line with previous esti mates for maximum burial of the monterey formation based on the silica phase transi tion the calculated 18 o for the connate fluid shows an expected range for seawater composition for the miocene suggesting only minor contribution of silica derived oxygen to the 18 o of carbonate fluorapatite the combined conventional and clumped isotope data set also points out that methanogenesis took place deeper within the sediment in the middle miocene than at present day within the santa barbara basin this study fur thers our understanding of phosphogenesis and potential links to burial processes in the monterey formation and it shows for the first time that the clumped isotope paleother mometer could be used to under stand funda mental geochemical processes in authigenic sedimentary phosphates

flow velocity measurements in vegetated channels understanding of the hydraulics of flow over vegetation is very important to support the management of fluvial processes in this paper the flow over flexible bottom vegetation is experimentally studied a two dimensional acoustic doppler velocimeter is used to measure the local flow velocities for different vegetation concentrations discharges and flume slopes the influence of vegetation concentration and the depth vegetation height ratio on the measured velocity profiles is analyzed all measured velocity distributions are s shaped and exhibit a three zone profile the relationship between the velocity distribution and the turbulence intensity distribution is also analyzed the characteristics inflection point maximum value asymptotes of the measured velocity distributions and the results of the previous investigators are used to select an analytical expression for the shape of the velocity profile a theoretical velocity profile is deduced using the classical prandtl s mixing length approach with a new expression for the mixing length the deduced four coefficient profile allows description of the flow both inside and above the vegetation the physical and geometrical meaning of the four coefficients are also shown doi 10 1061 asce 0733 9429 2002 128 7 664 ce database keywords velocity profile vegetation channel flow

δ18o po43 and δ18o co32 from belemnite guards from eastern europe implications for palaeoceanographic reconstructions and for the preservation of pristine isotopic values abstract the oxygen isotopic composition of coexisting carbonate and phosphate from belemnite rostra was measured according to well established techniques in 42 samples of early and middle jurassic age and in five samples of oyster shells most of the samples come from various locations in the western carpathians of slovakia and ukraine and from central poland three samples come from the isle of skye the phosphate content of belemnite rostra though variable is systematically very low consistently lower than about 0 3 however this phosphate concentration is close to that found in shells of modern marine organisms including pelecypods gastropods and sepia cuttlebones which in some way could be considered the modern belemnite counterpart the measured oxygen isotopic composition of carbonate is within the normal range of values obtained from these fossils ranging from about 1 3 to about 0 6 pdb 1 with the exception of three samples the 13 c values range from about 0 8 to about 2 8 pdb 1 with the single exception of one sample from the isle of skye the oxygen isotopic composition of phosphate from belemnite rostra ranges from 19 8 to 24 9 v smow 22 of the samples measured showing 18 o values equal to or heavier than 23 0 in contrast the oyster values are considerably lighter in the case of both carbonate and phosphate 18 o enriched values can hardly be related to diagenetic processes that normally cause an oxygen isotope shift towards light values if deposition temperatures are calculated from the heavily enriched values by means of the equation of longinelli and nuti earth planet sci lett 19 1973 373 376 and assuming the 18 o of jurassic ocean water to be equal to 1 taking into account the lack of ice caps during the jurassic the obtained temperatures range from about 8 c to about zero these temperatures are obviously unreliable when mesozoic palaeoceanographic conditions and palaeoclimate are taken into account two different hypotheses are suggested to explain these results other hypotheses being rejected as unreliable 1 phosphate derived from the decaying organic matter of belemnites might have been introduced into belemnite rostra by early diagenetic fluids if the phosphate of belemnite organic matter was isotopically heavy as happens nowadays in the flesh of molluscs the inflow of this phosphate into the rostra could be responsible for the very positive 18 o values shown by many belemnite rostra this hypothesis is suggested by h w 2 previous oxygen isotope measurements on upper cretaceous belemnites yielded 18 o values very close to the most positive values obtained from lower tertiary pelecypods and fish teeth which are known to precipitate their phosphate under isotopic equilibrium conditions with seawater these data suggest the possibility that the phosphate in belemnite rostra is primary phosphate so that the very positive data reported here can be considered the result of good preservation of the pristine isotopic composition of primary phosphate consequently the only way to explain the very positive 18 o values is to consider the oxygen isotopic composition of jurassic ocean water to be more positive than nowadays by at least 3 this hypothesis is suggested by a l and a d m

laboratory calibration of the calcium carbonate clumped isotope thermometer in the 25 250 c temperature range abstract many fields of earth sciences benefit from the knowledge of mineral formation temperatures for example carbonates are extensively used for reconstruction of the earth s past climatic variations by determining ocean lake and soil paleotemperatures furthermore diagenetic minerals and their formation or alteration temperature may provide information about the burial history of important geological units and can have practical applications for instance for reconstructing the geochemical and thermal histories of hydrocarbon reservoirs carbonate clumped isotope thermometry is a relatively new technique that can provide the formation temperature of carbonate minerals without requiring a priori knowledge of the isotopic composition of the initial solution it is based on the temperature dependent abundance of the rare 13c 18o bonds in carbonate minerals specified as a 47 value the clumped isotope thermometer has been calibrated experimentally from 1 c to 70 c however higher temperatures that are relevant to geological processes have so far not been directly calibrated in the laboratory in order to close this calibration gap and to provide a robust basis for the application of clumped isotopes to high temperature geological processes we precipitated caco3 mainly calcite in the laboratory between 23 and 250 c we used two different precipitation techniques first minerals were precipitated from a caco3 supersaturated solution at atmospheric pressure 23 91 c and second from a solution resulting from the mixing of cacl2 and nahco3 in a pressurized reaction vessel at a pressure of up to 80 bar 25 250 c the calibration lines of both experimental approaches overlap and agree in the slopes with theoretical estimates and with other calibration experiments in which carbonates were reacted with phosphoric acid at temperatures above 70 c our study suggests a universal 47 t calibration t in k 47 in 47 0 98 0 01 3 407 10 9 t 4 2 365 10 7 t 3 2 607 10 3 t 2 5 880 t 0 293 0 004 this new 47 t calibration given in the absolute reference frame that extends the experimentally calibrated temperature range for clumped isotopes to 250 c can be applied to carbonates that grew at intermediate temperatures 20 250 c

oxygen isotope variations in phosphate of biogenic apatites ii phosphorite rocks abstract phosphorites from sedimentary sequences ranging in age from archaean to recent were analysed for 18 o in both the po 4 18 o p and co 3 18 o c in the apatite lattice the oxygen isotope record is considerably better preserved in phosphates than in either carbonates or cherts the use of the longinelli and nuti 8 temperature equation yields temperatures for recent phosphorites that are in good agreement with those measured in the field the 18 o p values of ancient phosphorites decrease with increasing age these changes with time are not likely to be due to post depositional exchange changes in 18 o values of seawater and variations of temperature with time can account for the 18 o p time trend but the latter explanation is preferred in ancient phosphorites 18 o c in structurally bound carbonate in apatite is not a reliable geochemical indicator

crystallinity and diagenesis of sedimentary apatites the crystallinity of sedimentary apatites was determined by fourier transform infrared spectroscopy ft ir using the splitting of a triply degenerate antisymmetric bending vibration of orthophosphate the crystallinity indices of recent marine apatites are low 3 0 3 6 while those of onland ancient apatites are high 4 5 7 8 indicating post depositional recrystallization the infrared spectra reveal that recrystallization is associated with a decrease in carbonate content substituting for po43 and an increase in fluoride order within the apatite structure the relationship between the crystallinity index and po43 18o suggests alteration of the primary isotopic composition by exchange reactions between po43 oxygens and surrounding waters the monterey samples have a large range of crystallinity index that reflects a set of complex and highly variable diagenetic conditions this demonstrates the use of ft ir criteria for differentiating between pristine and altered apatites and as a consequence for relating geochemical markers to formation or diagenetic environments it is suggested that only those samples that have low crystallinity indices c i 3 8 should be considered as pristine apatite spectra of fish remains indicate that differences in rare earth element ree patterns correspond to variations in crystallinity carbonate content and f order in the apatite lattice the fact that crystallinity is not correlated with geologic age suggests that environmental factors such as accumulation rate and pore water chemistry govern the recrystallization process in general sr content decreases and 18op exhibits high variability with increasing crystallinity

is the von karman constant affected by sediment suspension 1 is the von karman constant affected by sediment suspension the presence of suspended sediment in channels and fluvial streams has been known for decades to affect turbulence transfer mechanism in sediment laden flows and therefore the transport and fate of sediments that determine the bathymetry of natural water courses this study explores the density stratification effects on the turbulent velocity profile and its impact on the transport of sediment there is as yet no consensus in the scientific community on the effect of sediment suspension on the von karman parameter two different theories based on the empirical log wake velocity profile are currently under debate one supports a universal value of 0 41 and a strength of the wake that is affected by suspended sediment the other suggests that both and could vary with suspended sediment these different theories result in a conceptual problem regarding the effect of suspended sediment on which has divided the research area in this study a new mixing length theory is proposed to describe theoretically the turbulent velocity profile the analytical approach provides added insight defining as a turbulent parameter which varies with the distance to the bed in sediment laden flows the theory is compared with previous experimental data and simulations using ak eturbulence closure to the reynolds averaged navier stokes equations model the mixing length model indicates that the two contradictory theories incorporate the stratified flow effect into a different component of the log wake law the results of this work show that the log wake fit with a reduced is the physically coherent approximation

the effect of diagenesis on oxygen isotope ratios of biogenic phosphates the effect of diagenesis on the oxygen isotope composition of ancient biogenic phosphates was evaluated by measuring different types of material from middle triassic localities in the southern alps dentin bone and tooth enamel of different taxa hosted by different rock types and metamorphosed to differing degrees were analyzed for their 18 o and 13 c values using a new microanalytical gc irmms technique the 18 o values of the majority of bone and bulk tooth samples were 18 to 19 permil smow with three samples below this range and one close to 20 permil in contrast samples of tooth enamel were 19 4 to 20 7 permil significantly higher than bone and bulk tooth without the enamel data the 18 to 19 permil data could be misinterpreted as primary only when the higher 18 o values of the enamel are considered is it apparent that the bulk data have undergone diagenesis and temperature estimates are 5 c lower than would otherwise be calculated alteration of bulk tooth is also seen in a miocene shark tooth where 18 o values of enamel are 3 permil higher than those of bulk tooth although enamel is routinely analyzed for paleoclimate work of herbivorous mammals bulk bone teeth or shells are almost exclusively used for older marine samples the results of the present study indicate that bulk data should be treated with caution

oxygen isotope exchange in a two layer model of oceanic crust abstract a numerical model is presented for the transport and exchange of oxygen isotopes in an idealized two layer oceanic crust basalt carbonate that is saturated with a non advecting pore fluid open to the overlying ocean the model allows for time varying sedimentation rate porosity chemical diffusivity and temperature dependent 18o fractionation factors reaction is modeled as solution precipitation of calcite in the carbonate sediment and as modified solution precipitation basalt dissolves smectite precipitates in the basalt layer generic models using input parameters that are typical of those measured in dsdp odp cores and constant sedimentation rates illustrate the behavior of the system sufficiently well to allow first order effects to be discerned that have important implications for paleotemperature and ocean floor weathering studies the solution precipitation reactions allow oxygen to be exchanged between the low 18o basalt layer and the high 18o carbonate sediment through the medium of the pore fluids this results in 18o increasing upwards in the basalt and decreasing downwards in the sediment pore fluid 18o values decrease with depth from zero to values of 1 to 3 at the basalt sediment interface and to values of 7 to 15 within the basalt because reaction rates are slow relative to diffusion in the pore fluid high frequency 18o variations in the solid are preserved indefinitely but the amplitude of the variations decreases as e rt where r is the reaction rate fraction reacted per unit time the results suggest that the diagenetic shifts of the 18o values of benthic and high latitude planktonic foraminifera samples younger than oligocene age are typically negligible for samples older than 50 ma diagenetic effects are typically significant and generally cause estimates of bottom and high latitude surface ocean temperatures in the cretaceous and early tertiary to be too high on the other hand the model suggests that diagenesis will shift the 18o values of low latitude planktonic foraminifera to higher values and that paleotemperature estimates of low latitude surface waters particularly in the eocene and oligocene may be too low using a synthetic 18o record for dsdp site 167 we demonstrate how numerical models can be used to correct specific measured records for diagenesis this approach could provide a means of extracting paleotemperature information from heavily altered late cretaceous and older samples and for quantifying the subtle effects of diagenesis on the 18o record at all sites

petrology and major element geochemistry of peru margin phosphorites and associated diagenetic minerals authigenesis in modern organic rich sediments abstract new petrographic and major element geochemical data from modern peru margin upper slope outer shelf phosphorites are presented which provide insight into their origin and paragenetic relationship with other authigenic minerals glauconite pyrite and dolomite occurring in organic rich sediments glauconites are precipitated relatively early following the partial reduction of ferric iron and following this process phosphate pyrite and then dolomite precipitation take place at progressively deeper levels in the sediment in association with microbial reduction of sulfate as in many ancient economic phosphorite deposits the phosphatic facies here consist of nodules crusts coatings and strata composed of phosphatic pelletal grains ooids structureless grains intraclasts clumps and biogenic grains in association with organic rich biosiliceous sediments all are considered to have formed within a few centimeters or within a few tens of centimeters below the sediment water interface important factors that influence which morphology will tend to develop include the amount of available pore space the presence of suitable nucleation sites the amount and size of siliciclastic detritus incorporated as inclusions and the relative solution chemistries of the precipitating solutions bacterial mediation may play an important but as yet unspecified role in the precipitation process textural data and factor analysis of chemical data suggest that structureless pellets are relatively inclusion free na f mg co3 substituted pore water precipitates whereas ooids are inclusion rich pore water precipitates poor in lattice substituted components variations in nodular cement birefringence and crystallinity are suggested to have been produced by similar lattice substitutions that directly reflect pore water carbonate ion concentrations and thus relative degrees of organic matter degradation phosphate and dolomite are intimately mixed yet mineralogically distinct phases in phosphatized dolomicrites depth stratified threshold carbonate ion concentrations may control the lower limit at which phosphatic minerals may precipitate below depths of a few centimeters excessive carbonate ion concentrations and diminished reactive iron and sulfate concentrations favor the development of dolomite while precluding further development of phosphatic minerals and pyrite periodic sediment reorganization bioturbation current winnowing and erosion mass wasting etc plays an important role in both concentrating pelletal grains and maintaining nodules and crusts at critical depth levels in the sediment as well as mixing ordered mineral parageneses into complicated sequences

oxygen isotopes of phosphate and the origin of island apatite deposits abstract in an attempt to test the hypothesis that insular phosphorites on high islands e g nauru formed by chemical reactions between seabird guano and carbonate the oxygen isotope compositions of phosphate 18op in modern guano and in the apatite component of phosphorites of various ages and locations have been investigated guano from several species of seabird appears to have 18op values that are in equilibrium with the ambient seawater temperature at each site however recent apatites closely associated with modern guano can have 18op values that are as much as 2 higher than their inferred guano phosphate source this shift in 18op values could be the result of isotopic re equilibration with percolating meteoric waters which have been enriched by evaporative processes in the upper part of the soil profile bacterial degradation of the guano in the soil zone is a possible mechanism for resetting the 18op values in this environment ancient apatites on high islands such as nauru ocean island and makatea have 18op values that are significantly lower than the 18op values of recently formed apatites the results indicate that ancient apatite deposits could not have formed by processes similar to those forming recent apatites without unreasonably high palaeotemperatures and or equilibration with water with much lower 18o values such as meteoric water in a karstic terrain at the time of maximum infiltration if the 18op values in apatite are subject to modification during subaerial weathering and diagenesis perhaps aided by the metabolic activity of micro organisms the application of 18op signatures of insular phosphorites to palaeoenvironmental reconstructions is limited to post depositional history and provides few clues to original setting

constraints on the formation and diagenesis of phosphorites using carbonate clumped isotopes the isotopic composition of apatites from sedimentary phosphorite deposits has been used previously to reconstruct ancient conditions on the surface of the earth however questions remain as to whether these minerals retain their original isotopic composition or are modified during burial and lithification to better understand how apatites in phosphorites form and are diagenetically modified we present new isotopic measurements of 18 o values and clumped isotope based 47 temperatures of carbonate groups in apatites from phosphorites from the past 265 million years we compare these measurements to previously measured 18 o values of phosphate groups from the same apatites these results indicate that the isotopic composition of many of the apatites do not record environmental conditions during formation but instead diagenetic conditions to understand these results we construct a model that describes the consequences of diagenetic modification of phosphorites as functions of the environmental conditions i e temperature and 18 o values of the fluids during initial precipitation and subsequent diagenesis this model captures the basic features of the dataset and indicates that clumped isotope based temperatures provide additional quantitative constraints on both the formational environment of the apatites and subsequent diagenetic modification importantly the combination of the model with the data indicates that the 18 o values and clumped isotope temperatures recorded by phosphorites do not record either formation or diagenetic temperatures but rather represent an integrated history that includes both the formation and diagenetic modification of the apatites

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

formation of dolomite at 40 80 c in the latemar carbonate buildup dolomites italy from clumped isotope thermometry the temperature of formation of replacement dolomite and 18 o h 2 o of dolomitizing fluid in the latemar carbonate buildup dolomites italy were estimated independently from carbonate clumped isotope thermometry dolomite formed at 42 72 9 11 c 2 standard deviations sd from fluid with 18 o h 2 o that averages 0 3 3 3 vienna standard mean ocean water 2 sd the estimated temperature and 18 o h 2 o are similar to those of modern diffuse flow fluids at mid ocean ridges the kind of fluid that has been proposed previously as the dolomitizing fluid in the latemar buildup based on the trace element compositions of dolomite calcite in limestone preserves original 18 o but records clumped isotope temperatures 44 76 9 11 c 2 sd that are higher than those at which the limestone formed temperature recorded by calcite but not 18 o was likely reset during dolomitization clumped isotope thermometry has great potential for application to studies of burial and diagenesis by retrieving independent estimates of temperature and 18 o h 2 o with uncertainties as low as 5 c 2 standard errors se and 0 75 2 se respectively from a single stable isotope analysis of a carbonate mineral

the retention of primary oxygen isotope compositions of fossil elephant skeletal phosphate fossil elephant remains from sediments of plio pleistocene age in the vicinity of lake turkana kenya provide insights into the ability of the phosphate oxygen system to preserve original 18o values 18op in the depositional environment individual fossil specimens exhibit systematic variations in the 18op values of their various tooth and bone components differences in 18op values between these skeletal components can be as high as 3 6 despite the fact that equivalent phases for individual modern elephants have 18op values which vary by less than 0 6 xrd traces of the different skeletal phases of modern and fossil samples also infer differential preservation of primary apatite crystallinities among the various fossil phases fossil samples of dentine cementum and bone have x ray spectra with sharper and more intense peaks compared to their modern counterparts but little change in crystallinity is observed for fossil enamel samples a model based on the premise that the enamel phase preserves primary isotope signatures and that the accompanying skeletal phases are partially re equilibrated with the fluids associated with the microbial decomposition of the elephant s carcass is consistent with the features of the 18op dataset this isotopic evidence in conjunction with the physical and chemical attributes of enamel has led us to postulate that enamel could be preserving primary isotope signatures while other skeletal components are affected to varying degrees by alteration processes in the burial environment

diagenetic stability of the isotopic composition of phosphate oxygen palaeoenvironmental implications meteoric diagenesis of the lower pliocene varswater formation phosphate deposit cape province south africa has altered the chemistry of the francolite component the isotopic composition of the phosphate oxygen has been changed as have other chemical and isotopic parameters that are known to be susceptible to meteoric diagenesis from authors

high temperature environments of human evolution in east africa based on bond ordering in paleosol carbonates many important hominid bearing fossil localities in east africa are in regions that are extremely hot and dry although humans are well adapted to such conditions it has been inferred that east african environments were cooler or more wooded during the pliocene and pleistocene when this region was a central stage of human evolution here we show that the turkana basin kenya today one of the hottest places on earth has been continually hot during the past 4 million years the distribution of 13c 18o bonds in paleosol carbonates indicates that soil temperatures during periods of carbonate formation were typically above 30 c and often in excess of 35 c similar soil temperatures are observed today in the turkana basin and reflect high air temperatures combined with solar heating of the soil surface these results are specific to periods of soil carbonate formation and we suggest that such periods composed a large fraction of integrated time in the turkana basin if correct this interpretation has implications for human thermophysiology and implies a long standing human association with marginal environments

flow in alluvial river curves uniform flow in curved wide erodible bed channels is formulated on the basis of the conservation of flux of moment of momentum to obtain relations for the vertical distributions of radial plane velocity and radial shear stress the expression for the radial stress exerted on the bed is utilized in a force equilibrium analysis of the moving bed layer to obtain relations for the average transverse slope of the bed and for the radial bed profile the reduction of primary bed shear stress due to the net radial transport of streamwise momentum toward the outer concave bank is then calculated by introducing the derived expressions for the velocity components into the momentum equation for the primary flow direction it is found that the stress reductions in deep narrow channels can exceed 50 bed profiles and velocity distributions measured in natural and laboratory streams are found to be in good conformity with those calculated from this moment based theory

tracing sources and cycling of phosphorus in peru margin sediments using oxygen isotopes in authigenic and detrital phosphates abstract many bio geochemical processes that bring about changes in sediment chemistry normally begin at the sediment water interface continue at depth within the sediment column and may persist throughout the lifetime of sediments because of the differential reactivity of sedimentary phosphate phases in response to diagenesis dissolution precipitation and biological cycling the oxygen isotope ratios of phosphate 18op can carry a distinct signature of these processes as well as inform on the origin of specific p phases here we present results of sequential sediment extraction sedex analyses combined with 18op measurements aimed at characterizing authigenic and detrital phosphate phases in continental margin sediments from three sites sites 1227 1228 and 1229 along the peru margin collected during odp leg 201 our results show that the amount of p in different reservoirs varies significantly in the upper 50 m of the sediment column but with a consistent pattern for example detrital p is highest in siliciclastic rich layers the 18op values of authigenic phosphate vary between 20 2 and 24 8 and can be classified into at least two major groups authigenic phosphate precipitated at near the sediment water interface in equilibrium with paleo water oxygen isotope ratios 18ow and temperature and phosphate derived from hydrolysis of organic matter porg with subsequent incomplete to complete re equlibration and precipitated deeper in the sediments column the 18op values of detrital phosphate which vary from 7 7 15 4 suggest two possible terrigenous sources and their mixtures in different proportions phosphate from igneous metamorphic rocks and phosphate precipitated in source regions in equilibrium with 18ow of meteoric water more importantly original isotopic compositions of at least one phase of authigenic phosphates and all detrital phosphates are not altered by diagenesis and other biogeochemical changes within the sediment column these findings help to understand the origin and provenance of p phases and paleoenvironmental conditions at near the sediment water interface and to infer post depositional activities within the sediment column

dispersion model for varying vertical shear in vegetated channels a dispersion model for a wide range of depthwise vertical shear is derived by using perturbation analysis and power m law velocity profile for m 1 the velocity profile provides linear shear whereas m 1 provides nonlinear shear and for m 20 the velocity profile resembles the flow through emergent vegetation the power law represented parametrically simulates well the complex shear profiles involved in emergent and submerged vegetated flows the proposed model shows reasonable agreement with past data on vegetated flows for a wide range of nonlinear shear velocities

did cooling oceans trigger ordovician biodiversification evidence from conodont thermometry the ordovician period long considered a supergreenhouse state saw one of the greatest radiations of life in earth9s history previous temperature estimates of up to 70 c have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time we present a very different global climate record determined by ion microprobe oxygen isotope analyses of early ordovician silurian conodonts this record shows a steady cooling trend through the early ordovician reaching modern equatorial temperatures that were sustained throughout the middle and late ordovician this favorable climate regime implies not only that the oxygen isotopic composition of ordovician seawater was similar to that of today but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period

carbonate clumped isotope bond reordering and geospeedometry carbonate clumped isotope thermometry is based on the preference of 13c and 18o to form bonds with each other at elevated temperatures such bond ordering is susceptible to resetting by diffusion of c and o through the solid mineral lattice this type of bond reordering has the potential to obscure primary paleoclimate information but could also provide a basis for reconstructing shallow crustal temperatures and cooling rates we determined arrhenius parameters for solid state reordering of c o bonds in two different calcites through a series of laboratory heating experiments we find that the calcites have different susceptibilities to solid state reordering reaction progress follows a first order rate law in both calcites but only after an initial period of non first order reaction that we suggest relates to annealing of nonequilibrium defects when the calcites are first heated to experimental temperature we show that the apparent equilibrium temperature equations or closure temperature equations for carbonate clumped isotope reordering are analogous dodson s equations for first order loss of daughter isotopes for each calcite the sensitivity of apparent equilibrium temperature to cooling rate is sufficiently high for inference of cooling rates within a factor of 5 or better for cooling rates ranging from tens of degrees per day to a few degrees per million years however because the calcites have different susceptibilities to reordering each calcite defines its own cooling rate apparent equilibrium temperature relationship the cooling rates of carrara marble inferred from carbonate clumped isotope geospeedometry are 10 6 10 3 degrees per annum and are in broad agreement with rates inferred from thermochronometric methods cooling rates for 13c depleted calcites from the late neoproterozoic doushantou cap carbonates in south china are on the order of 102 104 degrees per annum consistent with rapid cooling following formation of these calcites by a short lived hydrothermal event bristow et al 2011 nature v 474 p 68 71 most of the uncertainty in these estimates relates to uncertainty in arrhenius parameters for different calcites thus while the carbonate clumped isotope geospeedometer shows promise for recording cooling rates in settings and lithologies where other geospeedometers may not be applicable the uncertainty in cooling rate will be large without independent knowledge of the reordering kinetics of each study material thus the full potential of the method will only be realized if reordering kinetics can be accurately determined for each study material or predicted on the basis of mineral composition texture or other observable parameters

a revised calibration of the clumped isotope thermometer abstract a growing number of materials and environmental settings are studied using the carbonate clumped isotope 47 thermometer the method has been applied in both biogenic and non biogenic carbonate systems in marine and terrestrial settings over a wide range of geological timescales the current 47 temperature calibration gives good temperature estimates for most biogenic materials however systematic biases are commonly observed at low temperatures in this study we report additional calibration data that covers a wider temperature range at more evenly distributed temperatures and are measured at higher analytical precision than the original calibration combining these data with the original calibration yields a 47 t relationship that is similar to the original calibration though slightly less steep 47 0 0526 0 0025 10 6 t 2 0 0520 0 0284 this revised calibration is in better agreement with biogenic carbonates including those grown at low temperatures the difference between the original and revised calibrations is significant for carbonates forming below 16 c or above 49 c 47 values of 0 68 and 0 56 additionally we include a comprehensive analysis of the sources of error associated with 47 measurements and estimated temperatures and recommend measurement strategies for obtaining the desired precision as an illustration we apply the revised calibration and uncertainty analysis to 3 previously published studies at low temperatures the revised calibration results in significant differences from the original calibration and hence affects the interpretation of the environmental signal recorded in light of our 47 errors analysis in cases where the temperature signals are small we find that replicate analyses are critical to identify a temperature signal

dinosaur bones fossils or pseudomorphs the pitfalls of physiology reconstruction from apatitic fossils abstract a prerequisite to any attempt to reconstruct thermophysiology of ancient animals through analysis of stable isotopes of oxygen is the assumption that apatitic fossils are isotopically unaltered parts of their original skeletons we suggest that sufficient evidence is available to seriously question this assumption because living bones contain about 1 3 by weight of organic matrix mass balance considerations show that at least half of an apatitic fossil must be new material added post mortem furthermore living apatitic skeletons contain almost no rare earth elements and uranium whereas apatitic fossils bear high concentrations of these elements additionally we found that while in living fish correlation between 18o of oxygen in the phosphate and that in the carbonate of apatite is poor these two values are linearly correlated in fossil fish this suggests diagenetic recrystallization has taken place perfect preservation of micro textures such as haversian canals does not prove the pristine condition of a fossil some of the most beautifully preserved fossils are highly silicified most apatitic fossils probably are pseudomorphs replacing original skeletal elements whereas distribution of stable isotopes of oxygen in fossils might provide information about their burial environment it could be misleading in attempts to interpret the organisms physiology this cautionary note is supported by the similarity of 18op in bones of coexisting fossil fish dinosaurs and various other reptiles at different latitudes the overlap of predicted 18op values in fish and mammals living in contact with the same environmental water also weakens the hope that ectotherms can be distinguished from endotherms by the isotopic composition of oxygen in their bones and teeth

velocity and sediment concentration profiles in river flows an equation for the exponent in the power law velocity distribution is formulated by relating the rate of energy dissipation due to turbulent shear of the sediment bed layer to the increased rate of fluid shear energy dissipation produced by the moving sediment the suspended sediment concentration distribution corresponding to the power law velocity profile is calculated and simplified the relation derived for the power law exponent is found to be in good agreement with data from a large group of flume and river flows the powerlaw velocity profile and the corresponding concentration distribution are shown to be in excellent conformity with the distributions measured by vanoni and brooks

the limited growth of vegetated shear layers 1 in contrast to free shear layers which grow continuously downstream shear layers generated by submerged vegetation grow only to a finite thickness because these shear layers are characterized by coherent vortex structures and rapid vertical mixing their thickness controls exchange between the vegetation and the overlying water experiments conducted in a laboratory flume show that the growth of these obstructed shear layers is arrested once the production of shear layer scale turbulent kinetic energy ske is balanced by dissipation of ske within the canopy this equilibrium condition along with a mixing length closure scheme was used in a one dimensional numerical model to predict the mean velocity profiles of the experimental shear layers the agreement between model and experiment is very good but field application of the model is limited by a lack of description of the drag coefficient in a submerged canopy

oxygen and carbon isotopes in jordanian phosphorites and associated fossils abstract stable isotopes have proven to be efficient tools for paleoenvironmental analysis and interpretation of paleotemperature oxygen and carbon isotopes were analyzed in carbonate flourapatite francolite oyster shells tests of foraminifera and ostracods from the phosphorite unit throughout jordan isotopic analysis showed 18 o to be enriched in authigenic francolite in upper cretaceous in nw jordan indicating lower temperatures a deeper depositional environment and lower salinity than central jordan in central jordan the local basin of hafira shows enrichment of 18 o indicating a deeper depositional environment than shallower highs in mutarammil and wadi el hasa the 13 c shows that the depositional environment was oxic to suboxic and may have reached the suboxic to anoxic interface in the deeper environment in nw jordan 18 o values in tests of foraminifera and ostracods are similar to 18 o values of authigenic phosphate which is enriched in nw jordan indicating lower temperature lower salinity and a deeper environment than central jordan in central jordan 13 c shows more depletion in the sultani section due to land derived organic carbon food web supply carried by terrestrial water draining to the sea the 18 o in oyster shells show an upward enrichment in the wadi el hasa section which indicate an increase of intense upwelling enrichment of nutrients development of productivity and growth of oyster buildups meanwhile hafira shows enrichment of 18 o and lower temperature in agreement with foraminifera and ostracods the two samples of oysters from se jordan although affected by diagenesis show heavier oxygen to the north indicating a deeper water environment and lower salinity in the same basin

modeling the effects of diagenesis on carbonate clumped isotope values in deep and shallow water settings the measurement of multiply isotopically substituted clumped isotope carbonate groups provides a way to reconstruct past mineral formation temperatures however dissolution reprecipitation i e recrystallization reactions which commonly occur during sedimentary burial can alter a sample s clumped isotope composition such that it partially or wholly reflects deeper burial temperatures here we derive a quantitative model of diagenesis to explore how diagenesis alters carbonate clumped isotope values we apply the model to a new dataset from deep sea sediments taken from ocean drilling project site 807 in the equatorial pacific this dataset is used to ground truth the model we demonstrate that the use of the model with accompanying carbonate clumped isotope and carbonate 18 o values provides new constraints on both the diagenetic history of deep sea settings as well as past equatorial sea surface temperatures specifically the combination of the diagenetic model and data support previous work that indicates equatorial sea surface temperatures were warmer in the paleogene as compared to today we then explore whether the model is applicable to shallow water settings commonly preserved in the rock record using a previously published dataset from the bahamas we demonstrate that the model captures the main trends of the data as a function of burial depth and thus appears applicable to a range of depositional settings

modelling of the oxygen isotope evolution of seawater implications for the climate interpretation of the δ18o of marine sediments it is often argued that the 18o value of oceanic water was maintained close to 0 for hundreds of millions of years as a consequence of oxygen isotope exchange between oceanic crust and seawater however for several decades the interpretation of the biosedimentary oxygen isotope record has conflicted with the igneous record because with increasing age a general trend of decreasing 18o values about 6 is observed in most carbonates cherts and phosphates especially for the paleozoic and early mesozoic we developed a dynamical model of seawater crust interaction that computes the 18o value in these two reservoirs as function of time this model takes into account the continuous production of crust at oceanic ridges its expansion rate the permeability profile with space and time the mineralogical mode of the crust and the kinetics of oxygen isotope exchange between rock forming minerals and seawater the model indicates that the 18o value of seawater may vary by 2 with a time response ranging from 5 to 50 ma for expansion rates of 1 to 10 cm a 1 the variation of 2 is fixed by both integrated water rock ratio and closure time of the seawater crust system by sediments variations in the oxygen isotope ratio of seawater through time have important implications for the interpretation of the systematically low 18o values of pre jurassic marine sediments according to our model marine paleotemperatures could be up to 10 c lower than those expected when applying the classical hypothesis of an ice free ocean with a 18o value of 1

oxygen isotope variations in phosphate of biogenic apatites i fish bone apatite rechecking the rules of the game abstract the major advantage of the oxygen in phosphate isotope paleothermometry is that it is a system which records temperatures with great sensitivity while bone and teeth building organisms are alive and the record is nearly perfectly preserved after death fish from seven water bodies of different temperatures 3 23 c and different 18 o values 16 to 3 of the water were analysed the 18 o values of the analysed po 4 vary from 6 to 25 the system passed the following tests a the temperatures deduced from isotopic analyses of the sequence of fish from lake baikal are in good agreement with the temperatures measured in the thermally stratified lake b the isotopic composition of fish bone phosphate is not influenced by the isotopic composition of the phosphate which is fed to the fish but only by temperature and water composition isotopic analysis of fossil fish in combination with analysis of mammal bones should be a useful tool in deciphering continental paleoclimates

3d scour below pipelines under waves and combined waves and currents this paper presents the results of an experimental investigation on three dimensional local scour below a rigid pipeline subjected to wave only and combined wave and current conditions the tests were conducted in a conventional wave flume the major emphasis of the investigation was on the scour propagation speed free span expansion rate along the pipeline after local scour was initiated at a controlled location the effects of flow ratio steady current velocity vs combined waves current velocity flow incidence angle and pipeline initial embedment depth on free span expansion rate were investigated it was observed that the scour along the pipeline propagated at a constant rate under wave only conditions the scour propagation rate decreased with increasing embedment depth however increased with the increasing keuglegan carpenter kc number under combined wave and current conditions the effect of velocity ratio on scour propagation velocity along the pipeline was quantified empirical relationships between the scour propagation rate vh and key parameters such as the kc number and embedment depth e d were established based on the testing results

transverse bed slope in alluvial channel bends the study has reviewed existing analytical models for the prediction of the steady state transverse bed profile in channel bends formulated an alternative model and compared their predictive capability by laboratory and field data the alternative model which is based on a theory for the critical conditions for sediment entrainment gives good agreement between measured and predicted bed slopes the study shows that the key parameter in all available models is grain size the prediction of the complete bed topography of a given bend for a given flow data requires knowledge of the spatial variation of the grain size

flow resistance law in channels with flexible submerged vegetation in this paper experimental data collected in a straight flume having a bed covered by grasslike vegetation have been used to analyze flow resistance for flexible submerged elements at first the measurements are used to test the applicability of kouwen s method then a calibration of two coefficients appearing in the semilogarithmic flow resistance equation is carried out finally applying the p theorem and the incomplete self similarity condition a flow resistance equation linking the friction factor with the shear reynolds number the depth vegetation height ratio and the inflection degree is deduced

temperatures and oxygen isotopic composition of phanerozoic oceans abstract the temperature of ancient oceans is an important constraint for understanding the climate history of our planet the classical oxygen isotope paleothermometry on fossil shells while very proficient when applied to the younger cenozoic portion of the geologic record is believed to yield only unreliable results for the phanerozoic deep time either because the empirically well documented secular trend to more negative 18 o values with increasing age was generated by post depositional recrystallization processes or if primary implies ecologically unpalatable hot early oceans here we present a compilation of 18 o measurements for 58 532 low mg calcite marine shells that cover almost the entire phanerozoic eon argue that the secular decline of about 6 is primary propose that it reflects the changing oxygen isotopic composition of sea water and define a new baseline trend for 18 o of paleo sea water the latter providing a new template for calculation of ambient habitat temperatures of fossil specimens the resulting pattern for fossil taxa foraminifera brachiopods belemnites and bivalves mimics their modern counterparts in temperature ranges and modes this conceptual framework enables application of actualistic concepts to ambient habitat temperatures of fossils and provides us with a long overdue tool for interpretation of deep time geologic history

sedimentary phosphate formation in warm shallow waters new insights into the palaeoceanography of the permian phosphoria sea from analysis of phosphate oxygen isotopes abstract oxygen isotopic analyses of the structural phosphate 18 o p in sedimentary phosphorites of the upper permian phosphoria formation reveal that phosphogenesis occurred across a broad range of palaeoenvironments the 18 o p values from well preserved hand picked phosphate grain separates range from 20 2 to 13 7 0 5 smow with the lowest values in the most landward shallow water deposits and the highest values in the most basinward deeper water deposits the relationship between the maximum burial depth and 18 o p is opposite to that predicted if burial diagenesis was responsible for the isotopic signature of these phosphate grains this suggests that the regional trend in oxygen isotopic data is not due to burial diagenesis the range in oxygen isotopic values does correspond to the potential range of palaeotemperatures in the shallow and broad epicontinental phosphoria sea the range is 14 42 c 3 5 c assuming a seawater 18 o of 2 5 smow palaeotemperatures along an offshore to onshore transect indicate that upwelling involved temperate 14 26 c mean of 21 c but not cold waters and that warming across the palaeoshelf resulted in mean shallow water temperatures of 34 37 c the latter values approximate those predicted by climate and ocean circulation models these warm palaeotemperatures provide further evidence that phosphogenesis in the epicontinental phosphoria sea occurred under palaeoceanographic conditions that were different from modern phosphorite depositional systems this suggests that a purely actualistic approach to the interpretation of the phosphoria phosphorites is not valid

clumped isotope geochemistry the study of naturally occurring multiply substituted isotopologues clumped isotope geochemistry is concerned with the state of ordering of rare isotopes in natural materials that is it examines the extent to which rare isotopes d 13 c 15 n 18 o etc bond with or near each other rather than with the sea of light isotopes in which they swim abundances of isotopic clumps in natural materials are influenced by a wide variety of factors in most cases their concentrations approach within ca 1 relative the amount expected for a random distribution of isotopes deviations from this stochastic distribution result from enhanced thermodynamic stability of heavy isotope clumps slower kinetics of reactions requiring the breakage of bonds between heavy isotopes the mass dependence of diffusive and thermo gravitational fractionations mixing between components that differ from one another in bulk isotopic composition biochemical and photochemical fractionations that may reflect combinations of these simpler physical mechanisms and in some cases other processes we do not yet understand although clumped isotope geochemistry is a young field several seemingly promising applications have already emerged most importantly it appears that proportions of 13 c 18 o bonds in carbonate minerals are sensitive to their growth temperatures independent of bulk isotopic composition thus clumped isotope analysis of ancient carbonates can be used as a quantitative paleothermometer that requires no assumptions about the 18 o of waters from which carbonates grew this approach has been used to reconstruct marine temperatures across the phanerozoic reaching back to the silurian terrestrial ground temperatures across the cenozoic thermal histories of aqueously altered meteorites among other applications clumped isotope geochemistry is also placing new constraints on the atmospheric budget and stratospheric photochemistry of co 2 and should be capable of placing analogous new constraints on the budgets of other atmospheric gases finally this field could be extended to encompass sulfates volatile hydrocarbons organic moieties and other materials

the evolution of latitudinal temperature gradients from the latest cretaceous through the present abstract latitudinal temperature gradients are a defining characteristic of the climate system using thermometric indicators including 18o plant and animal fossils glycerol dialkyl glycerol tetraether gdgt proxies and clumped isotope estimates we document marine and terrestrial temperature gradients for the latest cretaceous late paleocene early eocene early oligocene pliocene and recent the changes in gradients reflect the transition greenhouse to icehouse conditions the evolution of latitudinal temperature gradients in marine and terrestrial realms are similar but has some distinctive differences marine temperatures are generally warmer than those on land except for the late paleocene early eocene the marine records show distinct inflection points at 30 and 50 latitude indicating the existence of frontal systems in the ocean except for the late paleocene early eocene the marine records show an increasingly steeper trend from latest cretaceous through recent being most pronounced after the early oligocene greenhouse icehouse transition this trend reflects the increasing intensity of high latitude and polar cooling as the icehouse state developed during the late paleocene early eocene the oceans were characterized by slightly warmer tropics and much warmer higher latitudes than at present the continents have generally had tropical temperatures like those of today varying by

further studies of the nature composition and ages of contemporary phosphorite from the namibian shelf major and minor element and radiochemical data are examined for a set of phosphorite concretions and other phosphatic material from the namibian shelf the concretions were separated on a morphological basis from grab samples taken in a transect of shallowing depth over the diatomaceous ooze belt compositional data indicate that the samples are fairly pure carbonate fluorapatite and trend towards a maximum 32 p2o5 content a range of compositional variability similar to other samples from the namibian shelf is observed radiochemical systematics confirm that pelletal phosphorite and glauconitized pelletal phosphorite from depths 170 m are at radioactive equilibrium and are therefore old and reworked the concretions collected from depths shallower than 78 m are entirely recent with maximum ages in the range 500 3800 years they may be much younger despite distinct textural and small compositional differences similar ages are found for separates from the same grab samples of fish scales and an unidentified high magnesian phosphate mineral are also shown to have incorporated uranium recently

oxygen isotope exchange kinetics of mineral pairs in closed and open systems applications to problems of hydrothermal alteration of igneous rocks and precambrian iron formations the systematics of stable isotope exchange between minerals and fluids are examined in the context of modal mineralogical variations and mass balance considerations both in closed and in open systems on mineral pair 18 o plots samples from terranes that have exchanged with large amounts of fluid typically map out steep positively sloped non equilibrium arrays analytical models are derived to explain these effects these models allow for different exchange rates between the various minerals and the external fluids as well as different fluid fluxes the steep arrays are adequately modelled by calculated isochron lines that involve the whole family of possible exchange trajectories these isochrons have initially steep near vertical positive slopes that rotate toward a 45 equilibrium slope as the exchange process proceeds to completion the actual data point array is thus analogous to the hand of an isotopic clock that measures the duration of the hydrothermal episode the dimensionless ratio of the volumetric fluid flux to the kinetic rate parameter u k determines the shape of each individual exchange trajectory in a fluid buffered system u k 1 the solutions to the equations 1 are independent of the mole fractions of the solid phases 2 correspond to taylor s open system water rock equation and 3 yield straight line isochrons that have slopes that approach 1 f where f is the fraction reacted of the more sluggishly exchanging mineral the isochrons for this simple exchange model are closely congruent with the isochrons calculated for all of the more complex models thereby simplifying the application of theory to actual hydrothermal systems in nature in all of the models an order of magnitude of time in units of kt separates steep non equilibrium arrays e g slope 10 from arrays approaching an equilibrium slope of unity on a diagram because we know the approximate lifetimes of many hydrothermal systems from geologic and heat balance constraints we can utilize the 18 o 16 o data on natural mineral assemblages to calculate the kinetic rate constants k s and the effective diffusion constants d s for mineral h 2o exchange these calculated values k qtz 10 14 k feld 10 13 10 12 agree with experimental determinations of such constants in nature once the driving force or energy source for the external infiltrating fluid phase is removed the disequilibrium mineral pair arrays will either 1 remain frozen in their existing state if the temperatures are low enough or 2 re equilibrate along specific closed system exchange vectors determined solely by the temperature path and the mineral modal proportions thus modal mineralogical information is a particularly important parameter in both the open and closed system scenarios and should in general always be reported in stable isotopic studies of mineral assemblages these concepts are applied to an analysis of 18 o 16 o systematics of gabbros plagioclase clinopyroxene and plagioclase amphibole pairs granitic plutons quartz feldspar pairs and precambrian siliceous iron formations quartz magnetite pairs in all these examples striking regularities are observed on and plots but we point out that plots have many advantages over their equivalent diagrams as the latter are more susceptible to misinterpretation using the equations developed in this study these regularities can be interpreted to give semiquantitative information on the exchange histories of these rocks subsequent to their formation in particular we present a new interpretation indicating that precambrian cherty iron formations have in general undergone a complex fluid exchange history in which the iron oxide magnetite precursor has exchanged much faster with low temperature 400 c fluids than has the relatively inert quartz

13c18o clumping in speleothems observations from natural caves and precipitation experiments the oxygen isotope composition of speleothems is an important proxy of continental paleoenvironments because of its sensitivity to variations in cave temperature and drip water 18 o interpreting speleothem 18 o records in terms of absolute paleotemperatures and 18 o values of paleo precipitation requires quantitative separation of the effects of these two parameters and correcting for possible kinetic isotope fractionation associated with precipitation of calcite out of thermodynamic equilibrium carbonate clumped isotope thermometry based on measurements of 47 a geochemical variable reflecting the statistical overabundance of 13 c 18 o bonds in co 2 evolved from phosphoric acid digestion of carbonate minerals potentially provides a method for absolute speleothem paleotemperature reconstructions independent of drip water composition application of this new technique to karst records is currently limited by the scarcity of published clumped isotope studies of modern speleothems the only modern stalagmite reported so far in the literature yielded a lower 47 value than expected for equilibrium precipitation possibly due to kinetic isotope fractionation here we report 47 values measured in natural speleothems from various cave settings in carbonate produced by cave precipitation experiments and in synthetic stalagmite analogs precipitated in controlled laboratory conditions designed to mimic natural cave processes all samples yield lower 47 and heavier 18 o values than predicted by experimental calibrations of thermodynamic equilibrium in inorganic calcite the amplitudes of these isotopic disequilibria vary between samples but there is clear correlation between the amount of 47 disequilibrium and that of 18 o even pool carbonates believed to offer excellent conditions for equilibrium precipitation of calcite display out of equilibrium 18 o and 47 values probably inherited from prior degassing within the cave system in addition to these modern observations clumped isotope analyses of a flowstone from villars cave france offer evidence that the amount of disequilibrium affecting 47 in a single speleothem can experience large variations at time scales of 10 kyr application of clumped isotope thermometry to speleothem records calls for an improved physical understanding of dic fractionation processes in karst waters and for the resolution of important issues regarding equilibrium calibration of 47 in inorganic carbonates

constraints on water transport and alteration in the oceanic crust from the isotopic composition of pore water the oxygen isotopic compositions of pore fluids from sediments of older oceanic crust commonly decrease with depth increases in calcium ion concentrations always accompany the 18o 16o decreases these changes are attributed principally to the alteration of basalts or alteration of volcanic ash in the sediments oxygen isotope material balance calculations suggest that 5 20 of the upper kilometer of basalt is altered at the time of subduction of the oceanic crust this corresponds to a flux of 18o into the oceanic crust of 2 3 1015 moles per million years evaluation of the oxygen and hydrogen isotope data from the pore fluids also suggests that the principal process of mass transfer in the sediments of older oceanic crust is diffusion convection of water in the basalts of the oceanic crust appears to continue until subduction

pleistocene phosphorites off the west coast of south africa we report here relatively modern phosphogenesis on the continental margin off south africa where palaeontologically old limestone middle eocene middle miocene has been phosphatized in late pleistocene times 62 76 kyr in an area of only moderate and seasonal present day upwelling1 2 previously modern phosphogenesis had been reported as occurring only off namibia3 15 peru chile16 21 and very recently east australia22 23 this report and those describing the late quaternary east australia phosphorite22 23 suggest that contrary to established opinion strongly enhanced upwelling may not be necessary for phosphorite formation and that oceanic phos phogenic models need not be based exclusively on localized oceanographie regimes such as exist off peru and namibia

geochemistry of brachiopods oxygen and carbon isotopic records of paleozoic oceans abstract combined trace element and isotope studies of 319 brachiopods covering the ordovician to permian time span show that 13c and 18o in well preserved specimens varied during the paleozoic the overall 13c secular trend is in accord with the previously published observations but its details are obscured by vital isotopic fractionation effects at generic level nonetheless the results suggest that the negative correlation between marine 13ccarbonate and 34ssulphate deteriorates at time scales of 106 years due to the long residence time and thus slow response of so42 in the ocean for oxygen isotopes all devonian and older specimens have 18o of 4 while the well preserved permian samples have near present day 18o of about 1 pdb this isotopic dichotomy is probably not due to post depositional phenomena salinity or biogenic fractionation effects this leaves open the perennial arguments for a change in 18 o 16 o of sea water versus warmer ancient oceans the present data are difficult to explain solely by the temperature alternative the coincidence of the proposed shift in 18o with the large late paleozoic changes in marine 87 sr 86 sr 13 c 12 c 34 s 32 s and sea level stands argues for a tectonic cause and for a change in 18 o 16 o of sea water although such explanation is difficult to reconcile with global balance considerations and with isotopic patterns observed in alteration products of ancient basalts and ophiolites whatever the precise cause or combination of causes the implications for tectonism and or paleoclimatology are of first order significance

δ18o and ree contents of phosphatic brachiopods a comparison between modern and lower paleozoic populations 18o values of both carbonate 18 7 25 1 and phosphate 15 1 16 7 components of the francolite from the fossil brachiopod shells are interpreted as the result of a partial resetting of pristine isotopic compositions the similarity of hat shape ree patterns of some lower ordovician linguloids with those of extant littoral specimens suggests the preservation of a 500 myr old record of ree marine chemistry in agreement with the known paleogeography the phosphatic brachiopods have been deposited in a coastal environment under shallow and oxygenated marine waters however the contents and distribution of ree in some strongly altered brachiopod shells reveal an alteration of the original negative ce anomalies and both nd and sm enrichments that transformed the initial hat shape patterns of linguloids into strongly convex or bell shape patterns

paleoclimate reconstruction using carbonate clumped isotope thermometry carbonate clumped isotope thermometry is a relatively new paleotemperature proxy based on measurements of the degree of ordering of 13 c and 18 o into bonds with each other making the 13 c 18 o 16 o 2 2 ion group in lattices of carbonate minerals this technique has several unusual properties that complement existing methods of paleoclimate reconstruction most importantly it is based on a homogeneous isotope exchange equilibrium and thus constrains temperature independent of the isotopic composition of waters from which carbonates grew this method also appears to be generally insensitive to vital effects that compromise many other paleothermometers based on the chemical properties of biominerals or organic matter at least for those organisms that have been subjected to systematic study to date corals and foraminifera however discrepancies among some calibrations particularly at low temperatures may point toward the existence of vital effects in mollusks and other organisms this review discusses the principles and calibrations of the technique its uses in combination with conventional stable isotope measurements to constrain the 18 o of past waters preservation of paleotemperatures in ancient materials as well as current problems in our understanding of calibrations and interlaboratory data comparisons

reconstructing past sea surface temperatures correcting for diagenesis of bulk marine carbonate abstract a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate is used to obtain information on how sea surface temperatures have varied in the past by correcting measured 18o values of bulk carbonate for diagenetic overprinting comparison of bulk carbonate and planktonic foraminiferal 18o records from odp site 677a indicates that the oxygen isotopic composition of bulk carbonate does reflect changes in sea surface temperature and 18o at odp site 690 we calculate that diagenetic effects are small and that both bulk carbonate and planktonic foraminiferal 18o records accurately reflect paleogene warming of high latitude surface oceans biased from diagenesis by no more than 1 c the same is likely to be true for other high latitude sites where sedimentation rates are low at dsdp sites 516 and 525 the effects of diagenesis are more significant measured 18o values of eocene bulk carbonates are more than 2 lower at deeply buried site 516 than at site 525 consistent with the model prediction that the effects of diagenesis should be proportional to sedimentation rate model corrections reconcile the differences in the data between the two sites the resulting paleotemperature reconstruction indicates a 4 c cooling of mid latitude surface oceans since the eocene at low latitudes the contrast in temperature between the ocean surface and bottom makes the carbonate 180 values particularly sensitive to diagenetic effects most of the observed variations in measured 18o values are accounted for by diagenetic effects rather than by sea surface temperature variations we show that the data are consistent with constant equatorial sea surface temperatures through most of the cenozoic with the possible exception of the early eocene when slightly higher temperatures are indicated we suggest that the lower equatorial sea surface temperatures for the eocene and oligocene reported in other oxygen isotope studies are artifacts of diagenetic recrystallization and that it is impossible to reconstruct accurately equatorial sea surface temperatures without explicitly accounting for diagenetic overprinting

sedimentology geochemistry and origin of phosphatic chalks the upper cretaceous deposits of nw europe santonian lower campanian and lower maastrichtian phosphatic chalks in northern france southern england and belgium are europe s largest sedimentary phosphatc deposits the stratigraphy sediment ology petrography mineralogy and geochemistry of the lithofacies are reviewed and new data presented depositional and diagenetic models for phosphatic chalk deposits are developed using published experimental work and from observations of modern high and low productivity phosphogenic systems it is concluded that phosphatic chalks were deposited in well oxygenated current swept environments phosphatization required a delicate balance to be maintained between moderate organic carbon and carbonate sedimentation rates reduced bulk sediment accumulation rate and an enhanced rate of bioturbation precipitation of carbonate fluorapatite francolite accompanied the bacterially mediated decomposition of organic matter occurring within centimetres of the sediment seawater interface and taking place preferentially within microbial bodies and coatings in addition to the organically derived component pore water phosphate levels were enhanced by phosphate absorbed on ferric oxyhydroxides which was liberated during iron reduction mineralization was probably a dominantly post oxic process but occurred in a thick sediment mixed layer in which marine organic matter was undergoing intense mixed aerobic and anaerobic microbial degradation phosphogenesis occurred predominantly on the ne margins of the anglo paris basin where shallower sea floors and suitable palaeoceanographic conditions prevailed phosphogenic episodes were limited by sea level fluctuations which controlled the effectiveness of the erosional currents that formed and maintained the phosphatic basins and may have stimulated local productivity

comment on oxygen and carbon isotopic composition of ordovician brachiopods implications for coeval seawater by h qing and j veizer

revised phosphate water fractionation equation reassessing paleotemperatures derived from biogenic apatite oxygen isotopes of biogenic apatite have been widely used to reassess anomalous temperatures inferred from oxygen isotope ratios of ancient biogenic calcite more prone to diagenetic alteration however recent studies have highlighted that oxygen isotope ratios of biogenic apatite differ dependent on used analytical techniques this questions the applicability of the phosphate water fractionation equations established over 25 years ago using earlier analytical techniques to more recently acquired data in this work we present a new phosphate water oxygen isotope fractionation equation based on oxygen isotopes determined on fish raised in aquariums at controlled temperature and with monitored water oxygen isotope composition the new equation reveals a similar slope but an offset of about 2 to the earlier published equations this work has major implications for paleoclimatic reconstructions using oxygen isotopes of biogenic apatite since calculated temperatures have been underestimated by about 4 to 8 c depending on applied techniques and standardization of the analyses

the implication of the oxygen isotope records in coexisting cherts and phosphates 18 o values have been determined for 53 coexisting chert phosphate pairs from the phanerozoic and precambrian in addition 18 o values were also determined for 18 biogenic phosphates from the phanerozoic the oxygen isotope data for the chert phosphate pairs permit the calculation of the temperatures of formation of the chert phosphate pairs as well as the 18 o of the waters in which they equilibrated in turn the calculated 18 o of the waters permit the calculation of temperatures from the isotopic data of the biogenic phosphates the temperatures for the tertiary and mesozoic samples are compatible with the literature values determined from oxygen isotope data for well preserved calcareous marine skeletal remains the temperatures calculated from the chert phosphate pairs of the paleozoic are usually higher and vary in cycles of about a 150 million year period the early precambrian temperatures are as high as 80 c and decrease with time the use of chert phosphate pairs for temperature determinations are sufficiently promising to warrant further investigations of this type on well preserved chert phosphate or carbonate phosphate pairs

longitudinal dispersion coefficient in single channel streams using a new channel shape equation for straight channels and a more versatile channel shape or local flow depth equation for natural streams a method is developed for prediction of the longitudinal dispersion coefficient in single channel natural streams including straight and meandering ones the method involves derivation of a new triple integral expression for the longitudinal dispersion coefficient and development of an analytical method for prediction of this coefficient in natural streams the proposed method is verified using 70 sets of field data collected from 30 streams in the united states ranging from straight manmade canals to sinuous natural rivers the new method predicts the longitudinal dispersion coefficient where more than 90 calculated values range from 0 5 to 2 times the observed values the advantage of the new method is that it is capable of accurately predicting the longitudinal dispersion coefficient in single channel natural streams without using detailed dye concentration test data a comparison between the new method and the existing methods shows that the new method significantly improves the prediction of the longitudinal dispersion coefficient

oxygen isotope variations in phosphate of biogenic apatites iii conodonts abstract the method for measurement of the isotopic composition of oxygen in phosphates has been improved and adapted for analysis of small quantities of apatite down to 10 mg this extension enables one to analyze hand picked conodont samples with an analytical reproducibility better than 0 5 1 46 samples of conodonts ranging from the ordovician to the pennsylvanian of north america were analysed some insoluble phosphatic residues ichthyoliths and inarticulate brachiopods of the same time range were also measured the range of the 18o values of the analysed conodonts is between 15 and 19 it shows a general trend of decreasing d18o with increasing age from an average value of about 19 in the pennsylvanian to 17 in the ordovician this trend parallels that previously detected in marine phosphorites for the time range between the devonian and pennsylvanian our data are in agreement with independent paleoclimatic information specifically we detect maximum18o enrichment at the end of the pennsylvanian and minimum enrichment at the end of the devonian the difference between these two extremes is equivalent to about 10 c from about 40 to 30 c assuming constant isotopic composition of ocean water the success of oxygen isotopic analysis of conodonts raises the possibility of their use in paleozoic paleo oceanography in a similar way to foraminifera in the mesozoic cenozoic

antarctic ice growth before and after the eocene oligocene transition new estimates from clumped isotope paleothermometry across the eocene oligocene transition the oxygen isotopic composition 18o of benthic and planktonic foraminifera increased by over 1 this shift is thought to represent a combination of global cooling and the growth of a large ice sheet on the antarctic continent to determine the contribution of each of these factors to the total change in 18o we measured the clumped isotopic composition of planktonic foraminifera tests from ocean drilling program site 689 in the southern ocean near surface temperatures were 12 c in the intervals 0 1 5 myr before and 1 2 myr after the major oi 1 transition in agreement with estimates made using other proxies at nearby sites temperatures cooled by 0 4 1 1 c between these intervals indicating that the long term change in 18o seen in planktonic foraminifera at this site is predominantly due to changes in ice volume a larger instantaneous cooling may have occurred during oi 1 but is not captured in this study due to sampling resolution the corresponding change in the isotopic composition of seawater 18osw is 0 75 0 23 which is within the range of previous estimates and represents global ice growth equivalent to roughly 110 120 of the volume of the modern antarctic ice sheet or 80 90 m of eustatic sea level change

determination of oxygen isotope fractionation between water and phosphate from living lingulids potential application to palaeoenvironmental studies abstract lingulids are inarticulate brachiopods with phosphatic shells which live exclusively in marine waters their distribution is generally restricted to the continental shelf within the 40 belt from temperate to equatorial areas they show a range of morphological physiological and behavioral features that have remained remarkably constant since the cambrian the oxygen isotope fractionation between water and phosphate from living lingulids was determined as a tool to investigate the temperature and or salinity of past coastal seawater oxygen isotope measurements were performed according to the silver phosphate method on a collection of lingulids coming from well known and varied marine environments a global 18o variation of 3 5 was found for these lingulids which proves their good sensitivity to environmental factors namely the oxygen isotope composition and the temperature of seawater oceanographic data provided average temperature and salinity values in the living sites of the studied specimens least squares treatment of the data gave the following fractionation equation t c 112 2 15 3 4 20 0 71 18o po4 18o h2o which is similar to the equations determined by longinelli and nuti 1973a and kolodny et al 1983 for other phosphate bearing invertebrates and fishes all these results suggest that a unique equation describes the phosphate water fractionation of many marine organisms except for mammals

testing clumped isotopes as a reservoir characterization tool a comparison with fluid inclusions in a dolomitized sedimentary carbonate reservoir buried to 2 4 km constraining basin thermal history is a key part of reservoir characterisation in carbonate rocks conventional palaeothermometric approaches cannot always be used fluid inclusions may be reset or not present while 18o palaeothermometry requires an assumption on the parent fluid composition the clumped isotope palaeothermometer however is a promising technique for constraining the thermal history of basins in this study we test if clumped isotopes record temperatures of recrystallisation in deeply buried dolomitic reservoirs through comparison with fluid inclusion data the studied reservoir is the cretaceous pinda formation offshore angola a deeply buried dolomitised sedimentary carbonate hydrocarbon reservoir it provides an ideal test case as samples from industry wells are available over a relatively wide burial depth range of 2000 4000 metres below sea floor mbsf and the constituent dolomites are relatively homogeneous across this depth range fluid inclusion homogenisation temperatures for the pinda formation record a range of temperatures from 110 170 c increasing with depth these closely match present day ambient well temperatures indicating recent resetting of the fluid inclusions clumped isotopes however record temperatures significantly 20 60 c below fluid inclusion and well temperatures for the seven samples analysed the deepest five samples 2800 3700 mbsf record clumped isotope temperatures around 100 120 c interpreted to represent a deep burial recrystallisation event responsible for a massive re dolomitisation of the reservoir the lower clumped isotope temperatures 65 and 82 c of the shallower 2055 and 2740 mbsf samples are interpreted to represent physical mixing of two dolomite generations due to incomplete burial recrystallisation of an early shallow dolomite determination of temperature through clumped isotopes allows calculation of the parent fluid 18o values in the five deepest samples the fluid 18o values of 3 7 6 5 cluster around the modern day porewater composition 5 suggesting burial dolomitisation occurred in the presence of evolved brine mineral 18o values of 4 5 to 7 are lower than pristine cretaceous marine dolomite and are in accordance with burial recrystallisation clumped isotopes are therefore interpreted to record temperatures corresponding to open system burial recrystallisation events this study shows that clumped isotopes are a valuable tool in characterising the thermal history of deeply buried 2000 m carbonate hydrocarbon reservoirs

stable isotopic characterisation of francolite formation stable isotopic data are presented for 112 samples of francolite from 18 separate phosphate deposits values of 13c and 34s in most offshore deposits suggest formation within oxic or suboxic environments either by carbonate replacement or direct precipitation of francolite from water of normal marine compositions the exceptions are concretionary francolite from namibia which has an isotopic composition in keeping with its formation within organic rich sediments and that from offshore morocco which has an isotopic signature of the anoxic suboxic interface onshore deposits from jordan mexico south africa and possibly the permian phosphoria formation in the western u s a are substantially depleted in18o they appear to be too altered for deductions to be made about their environments of formation in other onshore deposits which are unaltered or minimally altered the isotopic composition suggests that some formed within sulphate reducing sediments sedhura morocco whilst francolite from the georgina basin of australia formed at the oxic anoxic boundary where oxidation of biogenic h2s decreases the 34s of pore water in general pelletal samples show non oxic isotopic signatures whilst non pelletal samples show oxic isotopic signatures but samples from namibia peru ica plateau and the californian and moroccan margins are exceptions to this rule morphology may therefore be a misleading indicator of francolite genesis as no definitive relation exists between phosphorite type and isotopic signature

modeling mixed sediment suspended load profiles potential errors in calculated vertical suspended sediment concentration profiles in river flows carrying mixed sediments are investigated these profiles are usually obtained through application of a standard diffusion dispersion model however such models are normally formulated on the basis of a unique grain size for the sediment accordingly in the case of sediment mixtures the grain size distribution is usually divided into several size ranges fractions which are then characterized by their respective geometric means numerical errors induced through this procedure are quantified in a parametric study while depthaveraged concentrations can be over esimated by a factor of 1 2 when the concentration gradient is weak they can be under estimated by a factor of 15 when the gradient is large estimates are found to be particularly sensitive when the chosen reference level is small and the fraction width is large fall velocity coefficients are introduced to correct the discrepancy between the a

scour protection of partially embedded pipelines using sloping curtains abstracta geotextile mattress with sloping curtain gmsc was introduced to protect underwater pipelines from scour in steady currents gmsc is a newly developed countermeasure against river and es

isotope geochemistry of oxygen and carbon in phosphate and carbonate of phosphorite francolite oxygen isotope ratios in phosphate delta sup 18 o sub p were determined in 219 samples of phosphoritic rocks from all major phosphogenic provinces of the world ranging in age from lower proterozoic to recent in 58 samples oxygen was analyzed in the two oxygen lattice sites of francolite both in phosphate and in structural carbonate delta sup 18 o sub c delta sup 13 c was also analyzed in the latter and in coexisting calcite for 10 of them both delta sup 18 o sub p and delta sup 18 o sub c decrease sharply from the recent to the cretaceous and decrease with a gentler slope to the precambrian the nature of the time variation is elucidated by means of a delta sup 18 o sub p vs delta sup 18 o sub c plot which suggests that a the main cause of the time trends is the increase in temperature between recent and the cretaceous b the pre cretaceous trend is overprinted by both low temperature nonequilibrium exchange between sup 18 o depleted water and the rocks and higher temperature exchange between phosphate and carbonate c the observed trend cannot be explained by sup 18 o depleted cretaceous and paleozoic oceans the calcite coexisting with apatite in phosphatic rocks is similar in both delta sup 18 o and delta sup 13 c to the structural carbonatemore of the apatite even though phosphate may exchange its oxygen with environmental water to a greater extent than the authors originally claimed it is probably still a very good isotopic recorder of sedimentary environments less

dating phosphogenesis with strontium isotopes authigenic and replacement francolites in modern phosphorite have values of sup 87 sr sup 86 sr within error of that of modern marine sr 0 70916 plus minus 2 during the phosphatisation of carbonate sr is not inherited from the carbonate but is totally exchanged with sr in ambient water the sup 87 sr sup 86 sr in shallow marine pore waters is indistinguishable from the value for modern marine sr so authigenic francolite which precipitates from pore water accurately records the isotopic ratio of contemporary marine sr by comparing the sup 87 sr sup 86 sr in francolite with published curves for the isotopic evolution of tertiary marine sr we have dated phosphogenetic events affecting the chatham rise 4 90 plus minus 0 35 ma the nambian margin 1 15 plus minus 0 25 ma and 4 70 plus minus 0 35 ma and the sechura desert peru 11 8 plus minus 0 5 ma

glacial interglacial temperature variations in soreq cave speleothems as recorded by clumped isotope thermometry clumped isotope thermometry is based on analyzing mass 47 in co2 extracted from carbonates and uses the tracer mass 47 anomaly 47 47 is defined as the deviation of r47 from that expected for a random distribution of isotopologues and reflects a temperature dependent preference of 13c and 18o to create a bond with each other in co2 or in the carbonate lattice being an internal characteristic of the carbonate mineral it is independent of the isotopic composition of the water in which equilibrium precipitation of the carbonate occurs and can therefore be used to independently determine carbonate growth temperatures this work provides a first examination of the applicability of clumped isotopes thermometry to reconstructing the growth temperatures of speleothems by examining the glacial interglacial variations of the 47 values of speleothem carbonates from soreq cave israel the results indicate that the last glacial maximum temperatures were 6 7 c colder than modern day temperature and a sample at 56 ky bp was 3 c colder than the modern early holocene temperatures were slightly above modern day and late holocene temperatures were slightly below modern day these temperature variations are similar to those previously estimated for eastern mediterranean sea surface water cave water was 18o depleted in the holocene compared to modern day by 0 6 1 and 1 1 more enriched in the last glacial maximum comparison of these cave water 18o values with fluid inclusion d values indicated a late holocene d excess value within the range of modern rainfall implying not vert similar45 relative humidity last glacial maximum and early holocene d excess values were significantly lower suggesting relative humidity of not vert similar60 and not vert similar70 respectively the temperatures reported in this study were empirically corrected for a non equilibrium artifact observed in a modern speleothem the similarity of the temperature variations obtained here to other independent records in the region suggests that the 47 temperature calibration slope observed in inorganic synthetic calcite and marine organisms may also be applied in speleothems but the offset observed in modern temperature suggests that the intercept is different so that a separate calibration is needed for accurate absolute temperature reconstruction using speleothem clumped isotopes similar examination of additional caves would be necessary to determine whether such empirical correction can be generally applied or is it a unique characteristic of soreq cave

analyzing turbulence intensity in gravel bed channels in this paper the results of an experimental investigation of the turbulence intensity in gravel bed channels are described the runs were carried out by measuring with an acoustic doppler velocimeter the turbulence intensity profile along six verticals of a given cross section in a laboratory flume the analysis of the measured intensity distributions has shown the existence of two different regions above and below the tops of the roughness elements in which different intensity profiles occur furthermore the measured profiles have shown a maximum of the turbulence intensity that decreases for increasing values of the roughness height confirming that the turbulence damping efficiency increases when the roughness elements protrude inside the flow the applicability of nezu s relationship derived for a hydraulically smooth bed for the experimental intensity profiles above the roughness elements is positively tested finally a new intensity distribution for a rough bed applicable to the whole water depth is proposed in this profile two coefficients having a known physical meaning the maximum turbulence intensity and the depth at which this maximum is located appear