reconstructing daily temperatures from growth rates of the intertidal bivalve mollusk chione cortezi northern gulf of california mexico abstract we establish a model for the reconstruction of average daily sea surface temperatures from calcification rates of an intertidal bivalve mollusk the rate of shell production in chione cortezi carpenter 1864 ex sloat ms is mainly controlled by water temperature ontogenetic age and the effect of tidal cycles statistical methods developed by dendrochronologists can successfully extract the water temperature signal from daily growth increment chronologies after removal of noise the growth rates are expressed as scaled daily growth indices average daily water temperatures during the first half of the year are highly correlated with the scaled daily growth index values of recent and subrecent specimens using the multi valued function presented here increment width analysis can reconstruct daily average water temperatures with a mean error of less than 3 this technique provides an independent method for reconstructing temperatures in fossil specimens of species with living representatives and can supplement high resolution temperature reconstructions based on geochemical analysis

strong biological controls on sr ca ratios in aragonitic marine bivalve shells 1 it is well known that skeletal remains of carbonate secreting organisms can provide a wealth of information about past environments sr ca ratios have been successfully used as a temperature proxy in corals and sclerosponges previous work on aragonitic bivalve shells has not been conclusive but suggests a major control of growth rate on sr ca ratios as many studies have used bivalve growth rates to determine temperature we tested if sr ca ratios could predict temperature through its relationship with growth rate shells from the two species of clams from the same family veneroidea studied here saxidomus giganteus and mercenaria mercenaria show vastly different seasonal sr ca profiles a strong relationship between average annual sr ca ratios and annual growth rate was found in s giganteus shells from both washington r2 0 87 and alaska r2 0 64 usa but not in m mercenaria shells from north carolina usa furthermore the sr ca growth rate relationship was also evident upon a more detailed inspection of subannual growth rates in s giganteus r2 0 73 although there were significant positive correlations between sr ca ratios and temperature in s giganteus shells the correlations were weak 0 09 r2 0 27 and thus sr ca ratios cannot be used as a reliable temperature proxy in these species of aragonitic bivalves it is clear from this study that sr ca ratios are not under thermodynamic control in either clam species since thermodynamics predict a negative correlation between sr ca ratios and temperature in aragonite this points toward dominance of biological processes in the regulation of sr2 this is also reflected by the largely differing sr ca partition coefficients dsr in these shells dsr 0 25 when compared to inorganic coral and sclerosponge studies dsr 1 all of which show a negative dependence of sr ca on temperature we suggest that caution be taken when using sr ca in any biogenic aragonite as a temperature proxy when the dsr greatly deviates from one as this indicates the dominance of biological controls on sr ca ratios

precambrian medusoids the cyclomedusa plexus and cyclomedusa like pseudofossils abstract the medusoid fossils that were conventionally referred to cyclomedusa sprigg 1947 are among the commonest elements of the late precambrian ediacara metazoan assemblage in south australia specimens showing varying degrees of similarity have been reported worldwide from precambrian occurrences this study indicates that the fossils traditionally named cyclomedusa are a morphological plexus consisting of heterogeneous medusae the type species c davidi sprigg and c radiata sprigg are considered as a single species because of differences due to preservation c davidi can be compared with a living hydrozoan medusa aequorea in general configuration and an affinity with the family aequoreidae is suggested for the typical cyclomedusa spriggia southcott 1949 which was once regarded as a synonym of cyclomedusa is now re interpreted as a float bearing chondrophore hydrozoan colonial medusa the newly described s wadeae sp nov provides remarkable evidence for the amazingly conservative evolutionary history of the family porpitidae c plana glaessner and wade 1966 may be also chondrophoran in affinity but its configuration remains uncertain a critical review on the previously supposed cyclomedusa and other medusoids from the upper precambrian in southern liaoning china demonstrates that they are cyclomedusa like pseudofossils made by upwards escaping gas bubbles and water currents therefore they can not be used for stratigraphic correlation this example suggests the need for extreme caution in studies of various cyclomedusa like circular structures

coastal upwelling by wind driven forcing in jervis bay new south wales a numerical study for 2011 abstract the princeton ocean model pom was used to investigate an upwelling event in jervis bay new south wales se australia with varying wind directions and strengths the pom was adopted with a downscaling approach for the regional ocean model one way nested to a global ocean model the upwelling event was detected from the observed wind data and satellite sea surface temperature images the validated model reproduced the upwelling event showing the input of bottom cold water driven by wind to the bay its subsequent deflection to the south and its outcropping to the surface along the west and south coasts nevertheless the behavior of the bottom water that intruded into the bay varied with different wind directions and strengths upwelling favorable wind directions for flushing efficiency within the bay were ranked in the following order n 0 northerly nne 30 northeasterly nw 315 northwesterly ne 45 northeasterly ene 60 northeasterly increasing wind strengths also enhance cold water penetration and water exchange it was determined that wind driven downwelling within the bay which occurred with nne ne and ene winds played a key role in blocking the intrusion of the cold water upwelled through the bay entrance a northerly wind stress higher than 0 3 n m 2 was required for the cold water to reach the northern innermost bay

non linear variation with salinity of sr ca and mg ca ratios in water and aragonitic bivalve shells and implications for paleosalinity studies abstract fresh water and sea water usually differ considerably in their sr ca and mg ca ratios this suggests that these ratios in fossil shells could be used to determine paleosalinities calculation of the sr ca and mg ca ratios in mixtures of sea water and average fresh water using a mixing equation shows that the ratios first increase rapidly with salinity to about 100 but subsequently remain nearly constant the source of most of the ca sr and mg in mixtures of fresh and sea water is the sea water thus except at low salinities the trace element to ca ratio of mixtures differs little from that in sea water analysis both of waters across a spectrum of salinities and of aragonitic mollusc shells growing in water of various salinities conforms to the predicted pattern however trace element to ca ratios offer potential for paleosalinity determination in waters of salinity below about 100

uranium in aragonitic marine bivalve shells abstract uranium concentrations in foraminiferal and coral skeletons track oceanic co 3 2 and can be useful as a proxy of ocean acidification but this ph proxy is yet to be investigated in bivalves two saxidomus giganteus shells from the industrialized puget sound wa usa and one from the more pristine kodiak island ak usa were sampled through ontogeny for u ca using laser ablation inductively coupled mass spectrometry all three shells show a similar pattern of seasonal u ca cycles during the first six years of life followed by a sharp decrease to below the detection limit for the remainder of the clams life 10 20 years consistent with a biological or ontogenic forcing vital effect however analyses along a growth line carbonate formed at the same time show a decrease in u ca from the outside of the shell toward the inside consistent with diagenesis clearly u ca is not under environmental control in these aragonite shells but the cause of the variability is not currently clear

late precambrian pennatulids sea pens from the eastern yangtze gorge china paracharnia gen nov abstract pennatulids preserved as membranous carbonised compressions from the shibantan member dengying formation sinian system in the eastern yangtze gorge hubei province represent the first genuine discovery of the late precambrian ediacara type metazoan remains in china the specimens were initially referred to charnia ford 1958 and described as c dengyingensis by ding and chen in 1981 a re examination of the type material and comparing it with other late precambrian frond like forms particularly those from the ediacara assemblage of south australia and from the charnwood assemblage of england indicate that this chinese species represents a distinct genus paracharnia gen nov its characteristic polyp leaves individually free standing on distinct leaf stalks along the lateral sides of the median stem resemble those of many living sea pens represented by pennatula and contribute a significant feature to the precambrian charniidae glaessner 1979 its close association with abundant macroscopic algal remains of vendotaenia sp and its proximity to the overlying basal cambrian small shelly fossil assemblages in the same succession emphasise its palaeontological and biostratigraphic significance

a numerical study of the upwelling circulation off central chile effects of remote oceanic forcing 1 a numerical ocean model is used to study the upwelling circulation off central chile in response to local winds and remote forcing in an idealized study of equatorial forced intraseasonal variability period of 50 days a first mode coastal trapped wave ctw paddle is applied to the northern boundary with coastal sea level amplitude of 12 cm without this ctw forcing the steady seasonal winds upwell undercurrent water from depths of 250 320 m to depths of 180 250 m the subsequent formation of mesoscale and headland eddies drive this water into the gulf of arauco and to depths of 50 120 m with the ctw paddle the circulation is strongly modified the mesoscale and headland eddies reform during the ctw upwelling phase during the ctw upwelling phase the upwelling over winds and eddies is enhanced by up to 40 m on the shelf model simulations are undertaken using realistic winds and a ctw paddle modulated by observed sea level without ctw forcing included in the model the agreement with data is poor in the gulf of arauco area the variability of alongshore currents below 130 m is dominated by ctw activity above 130 m wind driven current variability dominates in agreement with the idealized ctw analysis water is found to be upwelled from depths of 320 m to 100 m or less and 10 c undercurrent water is found at the surface and within the gulf

late archean sm nd isochron age for mafic ultramafic supracrustal amphibolites from the northeastern sino korean craton china isotopic data published by previous workers document the presence of early archean 3 5 ga metabasaltic enclaves in grey gneisses west of bohai bay eastern hebei province p r c metabasaltic and metakomatiitic amphibolites crop out as lower supracrustal members of the archean section northeast of bohai bay in southern jilin eastern liaoning provinces six analyzed specimens of the latter unit contain more magnesium on analysis averaging approximately 13 vs 7 wt percent mgo but although they exhibit a wider range of ree concentrations they average a similar range of ree abundance patterns la lu 24 7x chondrite as the former 24 9 chondrite new sm nd isotopic and ree analyses combined with available petrologic geologic information indicate that metakomatiitic amphibolites from the sino korean craton northeast of bohai bay are late archean in emplacement age a wholerock sm nd isochron age of 2660 75 2 ma was obtained with nd t 4 4 0 5 as in many parts of the sino korean craton the highly positive nd t value suggests a prior extended history 1 0 ga of depletion of subcontinental mantle sources in some incompatible elements and in lree relative to hree a seventh analyzed sample a mafic inclusion in tonalitic gneiss of unknown age has an unusual chemical composition with strong enrichment in lree sr and zr and severe depletion in ni and cr judging from isotopic data which yield a much younger depleted mantle model age of 1 67 ga it could represent a cognate xenolith in a mid proterozoic tonalitic intrusion shown on present maps as archean in age the protolith might have been an evolved alkali basalt

the baroclinic response of straits and bays to coastal trapped wave scattering abstract a result for the conservation of bottom pressure along coastal isobaths is used to show how coastal trapped wave ctw energy may be scattered into baroclinic and barotropic motions within straits and bays central to this scattering problem is the decoupling of ctws and internal kelvin waves ikws for broad flat shelves where the former are shown to be either barotropic at the coast or trapped out on the shelf slope and break in this case the horizontal gradients of incident ctw bottom pressure that map into vertical gradients at the strait or bay mouth may be represented as a set of ikws a pair of decoupled long wave equations are derived to describe the approximate baroclinic and barotropic response of the strait or bay to forcing by these ikws as well as the scattered ctws on the adjacent shelf the results are applied to bass strait where about 1 of the energy of a mode 1 incident ctw is shown to force a 10 day period ikw with temperature and velocity oscillations of about 1 c and 20 c

oxygen and carbon isotope ratios of lampsilis cardium unionidae from two streams in agricultural watersheds of iowa usa abstract climate archives preserved as seasonal variation in oxygen and carbon isotope ratios 18o and 13c in unionid shells potentially provide records of pre instrumental environmental conditions in mid to high latitude continental regions this study measured 18o and 13c values of biogenic carbonate and 18owater to investigate the timing of growth line formation and to examine the utility of lampsilis cardium as an environmental archive we tested the hypotheses that 1 l cardium precipitates its shell in isotopic equilibrium with the environment during biomineralization and 2 growth lines form seasonally during winter months these questions were addressed by monitoring water chemistry by tagging l cardium to record growth and by combining sclerochronology and stable isotope geochemistry temperature and 18owater were measured fortnightly from september 2002 to july 2004 with a break in sampling from december 2003 to february 2004 in two iowa rivers boone river and buffalo creek these data were used to calculate expected 18o values to compare to measured shell values one hundred fifty four individuals were marked at the postero dorsal margin in september 2002 and june 2003 to monitor growth seven recaptured shells collected in july 2004 were analyzed for shell 18o and 13c across three growth lines including growth lines prior to the initial marking period from the growing edge toward the umbo comparison of shell 18o with expected values revealed precipitation of 18o in equilibrium with the ambient environment from early spring to early fall winter values were not recorded due to winter growth cessation change in temperature or reaching a threshold temperature appeared to control the onset and cessation of growth moreover the locations of seasonal growth lines corresponded to winter growth cessation allowing the assignment of calendar years to growth lines seasonal growth lines were distinguished from non seasonal disturbance lines by their seasonal location inferred from the 18o time series recorded in shell growth thus we can faithfully reconstruct ontogeny through time and environmental and climate conditions from mid to high latitudes using l cardium variation in 13cshell followed a more or less sinusoidal trend similar to the seasonal profiles of 18oshell suggesting that seasonal processes influenced the variation in carbon isotopes reduced amplitudes and more negative 13cshell values with increasing age suggest that kinetic and or metabolic isotope effects become important through ontogeny as observed in other bivalves the profiles of 13cshell potentially record local differences in landscape vegetation however specific factors influencing 13cshell are unknown and further study of water quality are required to fully assess the variation of 13cshell as an environmental proxy

unionid shells hyriopsis cumingii record manganese cycling at the sediment water interface in a shallow eutrophic lake in china lake taihu abstract aquatic eutrophication is becoming a serious environmental problem throughout the world the utility of bivalves as bio filters to improve water quality and reduce algal blooms has been widely acknowledged but the potential usefulness of bivalve shells as retrospective monitors of eutrophication induced environmental change has received little attention here we present the first multi year high resolution mn ca shell records of the freshwater mussel hyriopsis cumingii lea 1852 from a shallow eutrophic lake lake taihu china mn ca shell time series of the two studied shells exhibit a high degree of synchrony after being placed in a precise temporal context by means of growth pattern analysis there is a large inter annual variability of mn ca shell records during 2011 2015 with the highest value occurring in 2013 mn ca shell also displays a pronounced intra annual variability with maxima consistently occurring during late spring early summer the high reproducibility of mn ca shell time series among contemporaneous specimens highlights the existence of strong environmental rather than biological control on the incorporation of mn into the shells in particular the striking feature of late spring early summertime mn ca shell maxima is synchronous with the occurrence of reducing conditions beneath the sediment water interface swi the latter results in substantial increases of biologically available mn 2 in the sediment pore water and organic particles the element being rapidly taken up from these sources by the mussels with subsequent incorporation of mn into their shells therefore mn ca shell can potentially serve as a high resolution proxy of the mobility of mn at the swi as demonstrated by the present study documenting and understanding geochemical properties of bivalve shells can help to retrospectively monitor eutrophication induced environmental change in aquatic ecosystems

seasonal temperature salinity changes and thermocline development in the mid atlantic bight as recorded by the isotopic composition of bivalves stable isotope records across annual growth increments in specimens of the surf clam spisula solidissima from the mid atlantic bight shelf from 10 m and 45 m depths reflect the changes in temperature and nutrient concentrations on the shelf over the year the 18 o and 13 c records from clams at the two depths record well mixed conditions in the water column during the winter months and the development of a thermocline during the summer spring high productivity and a transient salinity excursion in surface waters are also recorded reconstructing the paleoceanography of late cenozoic temperate continental shelves may be possible using stable isotope records from fossil spisula solidissima and other bivalves

oxygenation variations in the atmosphere and shallow seawaters of the yangtze platform during the ediacaran period clues from cr isotope and ce anomaly in carbonates abstract the late neoproterozoic era witnessed a significant oxygenation in earth s surface in line with the naissance and diversity of early animals however detailed variations of the oxygenation during this period remain controversial chromium isotope in ancient carbonates has shown its ability to trace the oxygenation history of the atmosphere hydrosphere system in this study we analyzed cr isotope and ce anomaly data of carbonates from the ediacaran doushantuo and dengying formations in the yangtze gorges area south china in order to reconstruct oxygenation variations in the atmosphere and shallow seawaters of the yangtze platform during the ediacaran period after evaluating and excluding detrital and diagenetic effects well preserved 53crauth signatures were obtained post marinoan carbonates record slightly positive 53crauth values 0 18 0 43 and slightly negative ce anomaly suggesting generally oxidizing conditions in the atmosphere with po2 over 1 pal and in shallow seawaters of the yangtze platform during the post marinoan phase which may have been related to the diversity of early ediacaran organisms shuram wonoka correlative carbonates are characterized by the fluctuations of 53crauth values 0 25 to 0 97 and a significant negative 13c excursion which may have resulted from partial oxidation of the large deep water doc reservoir under enhanced oxidative weathering conditions this process released 13c depleted carbon into dic pool and isotopically unfractionated cr iii into water columns the latter of which immediately precipitated by adsorption onto the detrital materials meanwhile an increase in local anoxia and even euxinia in the intrashelf basin of the yangtze platform driven by enhanced microbial sulfate reduction and the resultant h2s possibly limited regional biological evolution during this phase late ediacaran carbonates record elevated 53crauth values 0 40 0 96 together with the decreasing trend in ce ce values indicating a more oxygenated environment in the atmosphere and shallow seawaters of the yangtze platform during the late ediacaran phase which may have been beneficial to the diversification of late ediacaran animals

high resolution nitrogen stable isotope sclerochronology of bivalve shell carbonate bound organics nitrogen stable isotope ratios 15n of organic material have successfully been used to track food web dynamics nitrogen baselines pollution and nitrogen cycling extending the 15n record back in time has not been straightforward due to a lack of suitable substrates in which 15n records are faithfully preserved thus sparking interest in utilizing skeletal carbonate bound organic matter cbom in mollusks corals and foraminifera here we test if calcite pecten maximus shells from the bay of brest and the french continental shelf can be used as an archive of 15n values over a large environmental gradient and at a high temporal resolution approximately weekly bulk cbom 15n values from the growing tip of shells collected over a large nitrogen isotope gradient were strongly correlated with adductor muscle tissue 15n values r2 0 99 n 6 p 0 0001 we were able to achieve weekly resolution on average over the growing season from sclerochronological profiles of three shells which showed large seasonal variations up to 3 4 however there were also large inter specimen differences up to 2 5 between shells growing at the same time and location generally high resolution shell 15n data follow soft tissue 15n values but soft tissues integrate more time hence soft tissue data are more time averaged and smoothed museum archived shells from the 1950s 1965 and 1970s do not show a large difference in 15n values through time despite expected increasing n loading to the bay over this time which could be due to anthropogenic n sources with contrasting values compiling shell cbom 15n data from several studies suggests that the offset between soft tissue and shell 15n values tissue shell differs between calcite and aragonite shells we hypothesize that this difference is caused by differences in amino acids used in constructing the different minerals which should be specific to the caco3 polymorph being constructed future work should use compound specific isotope analyses csia to test this hypothesis and to determine whether certain amino acids could specifically track n sources or possibly identify amino acids that are more resistant to diagenesis in fossil shells in conclusion bivalve shell cbom 15n values can be used in a similar manner to soft tissue 15n values and can track various biogeochemical events at a very high resolution

climate records from a bivalved methuselah arctica islandica mollusca iceland we measured annual shell growth rates of a 374 year old radiometrically confirmed bivalve mollusk specimen of arctica islandica linnaeus this bivalve represents the oldest ever reported individual animal in addition we analyzed 1051 individual powder samples from ontogenetic years two to 40 80 of the entire shell height for isotope analyses oxygen and carbon isotopes exhibit clear intra annual cycles the highest measured carbon isotope values on average 2 73x occurred during summer i e during maximum primary productivity the d 18 oaragonite derived temperature time series cover the period of ad 1496 1533 temperatures calculated from oxygen isotopes ranged from 4 5 to 9 3 8c and exhibit a mean value of 6 2 8c the latter coincides well with the 1854 2003 mean value of 6 81 8c for sea surface temperature between february and september growing season of a islandica neither oxygen nor carbon isotopes exhibit age related unidirectional trends however d 13 caragonite and d 18 oaragonite values fluctuated at decadal periods of four six and eight to nine years nao type periods as well as 12 14 years which may represent teleconnections to cycles in the tropical atlantic annual shell growth is positively correlated to intra annual d 18 oaragonite minima i e warm summer temperatures r 2 0 34 and to intra annual d 13 caragonite minima higher food supply r 2 0 42 using a linear multiregression model 65 of the variation in annual shell growth can be explained by summer temperature and food supply the formation of extremely narrow annual increments coincides with major volcanic eruptions e g tambora 1815 a period of extremely variable growth occurred during the culmination of the little ice age in iceland between ca ad 1550 and 1620 shell growth during ad 1765 1780 however was characterized by very little year to year variability probably as the result of extremely mild climate near the end of the little ice age this study demonstrates that shells of a islandica provide

a critical assessment of mollusk 18 o 16 o mg ca and 44 ca 40 ca ratios as proxies for cretaceous seawater temperature seasonality seasonal temperature fluctuations of tethyan coastal water are recorded in a pristine 80 my old rudist shell from turkey in order to critically assess factors other than seawater temperature that might have influenced the shell geochemical record three different paleo temperature proxies 18o mg ca and 44ca were applied in a qualitative manner all three proxies reflect the same cyclical trends and thus yield robust evidence for seasonal fluctuations in late cretaceous surficial seawater temperature this suggests the successful application of the new 44ca temperature proxy to fossil mollusk calcite the direct comparison of the three data sets however demonstrates that all proxies are fraught with problems similar to other studies 18o 16o ratios point to warmer summer temperature maxima than those in comparable costal settings today nevertheless the 18o 16o proxy is subject to environmental factors that might lead to an overestimation of peak temperatures moreover mg ca molar ratios are less sensitive to environmental factors but were strongly affected by the ion regulating capability of the rudist bivalve that responded to the low mg ca ratio of cretaceous seawater similarly uncertainties of the 44ca composition of cretaceous seawater and the complex bio calcification of mollusks presently limit the interpretation of 44ca values in terms of absolute seawater temperature the multiproxy approach applied here however documents that these limitations do not obscure the dominant patterns of seasonal sea surface temperature variations recorded in the biogeochemical rudist archive

testing the effect of carbonate saturation on the sr ca of biogenic aragonite a case study from the river ehen cumbria uk it has been suggested that the incorporation of strontium into biogenic aragonite may be influenced by the degree of carbonate saturation in aquatic environments we measured the sr ca ratios of river water and the aragonitic shells of freshwater bivalves margaritifera margaritifera from two sites with different carbonate saturation states in the river ehen cumbria uk shell sr ca and river water sr ca are 0 1 mmol mol and 0 42 mmol mol lower respectively at the high carbonate saturation site however the distribution coefficients of strontium into aragonite kd are the same 0 28 at both sites these analyses show that sr uptake into aragonite bivalve shells is not affected by the degree of carbonate saturation of the water perhaps reflecting a strong biological control on trace element incorporation

environmental controls on the stable isotopic composition of mercenaria mercenaria potential application to paleoenvironmental studies 1 we have investigated the environmental controls of seasonally resolved records of oxygen and carbon isotopes of modern mercenaria mercenaria bivalves collected live from five coastal sites along the east coast of north america seasonal profiles of 18o and 13c obtained by subsampling the incremental growth layers of aragonite were compared with in situ historical records of temperature and salinity we show that m mercenaria 18o profiles track accurately the seasonal variations of water temperature and that variations in growth rates do not affect the shell 18o values growth rates are strongly reduced or interrupted below water temperatures ranging from 8 to 10 c implying that only bivalves sampled in tropical areas track the full amplitude of seasonal variations although further measurements of water 18o and a better understanding of seasonal variations of the water 18o salinity relationships are necessary mercenaria mercenaria bivalves appear to precipitate their shell close to isotopic equilibrium whereas the amplitude of the seasonal profiles of 18o reflects variations in water temperature the annual average 18o decreases with latitude reflecting the trend of rainfall and riverwater 18o with latitude over the northern american continent

an intensity ratio calibration method for the accurate determination of mg ca and sr ca of marine carbonates by icp aes an inductively coupled plasma atomic emission spectroscopy icp aes method for the accurate and precise simultaneous measurement of the mg ca and sr ca content of carbonates was established while a precision of 0 3 1 standard deviation sd is easily obtainable for both mg ca and sr ca analysis a ca matrix effect complicates achieving similar levels of accuracy with conventional calibration procedures an alternative ratio calibration procedure is proposed which overcomes the ca matrix effects and ensures the accuracy of the mg ca and sr ca analysis of marine carbonates to 0 3 almost an order of magnitude better than conventional calibration methods the longer term precision is 0 1 if the batch run average values are corrected for longer term drift the method is suitable for analysis of foraminiferal calcite and coral aragonite and can easily be adjusted for the analysis of other carbonates or microsamples

anisotropic rayleigh wave phase velocity maps of eastern china we explore the variations of rayleigh wave phase velocity beneath eastern china in a broad period range 20 200 s rayleigh wave dispersion curves are measured by the two station technique for a total of 734 interstation paths using vertical component broadband waveforms at 39 seismic stations in eastern china from 466 global earthquakes in addition 599 waveform inversion interstation measurements were added to this data set the interstation dispersion curves are then inverted for high resolution isotropic and azimuthally anisotropic phase velocity maps at periods between 20 and 200 s at shorter periods sampling the crustal depth range phase velocities are higher in the southeastern part of the region reflecting the thinner crust there the jiangnan belt separates cathaysia from the yangtze craton the latter with thicker crust and a deep high velocity cratonic root the eastern part of yangtze craton however east of 115 116 e does not display a deep root and has a thin lithosphere azimuthal anisotropy at long periods 120 s shows fast propagation directions broadly similar to that of the absolute plate motion beneath cathaysia and eastern yangtze craton anisotropy in the asthenosphere is strong and suggests coast perpendicular flow asthenospheric flow from beneath china s thick continental lithosphere toward the thinner lithosphere of the margin and the resulting decompression melting may be the fundamental causes of the intraplate basaltic volcanism along the eastern coast of china

tropical atlantic seasonal dynamics in the early middle eocene from stable oxygen and carbon isotope profiles of mollusk shells there are disagreements whether the tropical sea surface temperature during the warm early to early middle eocene was equal to the present temperature or significantly lower in order to determine the sea surface temperature of the eastern tropical atlantic in the early middle eocene we have established 18o and 13c profiles along the transect of growth of excellently preserved shells of turritella gastropods and a macoma bivalve from tropical west africa this method makes possible a distinction between the winter and the summer temperature the 18o and 13c data indicate sea surface temperatures of 29 31 c which declined to 23 25 c during seasonal upwelling these conditions are similar to those of today and suggest that significant seasonal dynamics prevailed in the early middle eocene tropics the new data further contradict that the tropics cooled during the generally warm early to early middle eocene as inferred in studies on foraminifera 18o

biological and water chemistry controls on sr ca ba ca mg ca and δ18o profiles in freshwater pearl mussel hyriopsis sp abstract we investigated oxygen isotope and sr ca ba ca and mg ca ratios in shells of a commercially cultured freshwater pearl mussel hyriopsis sp unionidae and ambient water the first order fluctuations of oxygen isotope ratios of the outer shell layer along the maximum growth axis recorded the mussels annual growth from 2002 to 2007 clear annual sr ca cycles suggest that sr was incorporated into the shells at a high rate during warm seasons all three examined shells showed a clear decrease in annual average sr ca with age inter and intra annual trends suggest that sr incorporation was higher during periods of faster growth the ba concentration and the ba ca ratio of ambient water showed neither an annual periodicity nor a seasonal trend in contrast to the findings of an inorganic aragonite precipitation experiment ba ca was positively correlated with ambient temperature in addition ba ca and sr ca ratios were positively correlated with each other these results suggest that not thermodynamic equilibrium partitioning but the shell growth rate controls ba incorporation into hyriopsis shells the mg ca profiles of the three shells suggest that complex factors control the incorporation of mg into shell aragonite water temperature and annual growth rates did not significantly influence mg incorporation and substantial interspecimen differences suggested that physicochemical factors do not exert any systematic control on mg ca ratios in hyriopsis instead the mg content of shell aragonite might reflect biological contamination with organic material or adsorption phenomena during crystal precipitation rather than regulated substitution into the aragonite crystal lattice our results suggest that trace element profiles in aragonitic bivalve shells could be interpreted as the result of strong biological controls over riding environmental influences on trace element incorporation

current molded storm damaged sinuous columnar stromatolites mesoproterozoic of northern china abstract a thin 50 cm horizon of sinuous stromatolites occurs within a succession of elongate upright columns in the 1 4 ga tieling formation near jixian china the upright columns form aligned closely spaced ridges separated by narrow runnels with signs of current scour the sinuous and upright stromatolites and their intervening matrix were originally mainly composed of carbonate mud in end on view the sinuous columns incline back and forth each column consists of well defined laminae that successively rotate relative to column curvature maintaining their orientation approximately at right angles to the column axis in inclined parts of the columns laminae are typically asymmetric and the steeper side faces the direction of column inclination we interpret this column sinuosity to be a response to changes in current direction with accreting laminae facing into currents that supplied sediment we find no evidence for heliotropism mat growth towards the sun in these examples adjacent columns typically show similar shapes bending back and forth together but their angles of curvature and inclination can change laterally from column to column from near vertical to 45 over distances of 30 cm columns can show breakage and separation of adjacent laminae some of this is enhanced by compaction and stress but the occurrence of sinuous columns on their sides or upturned in spaces between undisturbed columns indicates that column curvature developed during growth and that toppling of columns was syndepositional we infer that sinuosity developed in response to changes in current direction that column inclination reflects current strength and that breakage and toppling was produced by strong currents curved and sinuous columns could reflect shoaling this would also have exposed them to storm damage and to the effects of currents that scoured sufficient matrix to locally break and topple columns markedly sinuous mesoproterozoic columns also occur in siberia and north america suggesting that similar conditions and processes of stromatolite formation may have been widespread at this time formation and preservation of the sinuous stromatolites described here required a combination of conditions that included abundant fine grained carbonate sediment microbial mats capable of trapping it reduced early lithification and absence of bioturbation

a numerical study of coastal trapped waves in jervis bay australia abstractcoastal trapped waves ctws in jervis bay were investigated using a jervis bay ocean model jbom based on the princeton ocean model under the typical temperature stratification in jervi

fine grained agglutinated elongate columnar stromatolites tieling formation ca 1420 ma north china the mesoproterozoic tieling formation near jixian northern china contains thick beds of vertically branched laterally elongate columnar stromatolites carbonate mud is the primary component of both the stromatolites and their intervening matrix its abundance is attributed to water column whiting precipitation stimulated by cyanobacterial photosynthesis neomorphic microspar gives the stromatolites a streaky microfabric and small mud flakes are common in the matrix the columns consist of low relief mainly non enveloping laminae that show erosive truncation and well defined repetitive lamination in plan view the columns form disjunct elongate ridges 10 cm wide separated by narrow matrix filled runnels the stromatolite surfaces were initially cohesive rather than rigid and prone to scour and are interpreted as current aligned microbial mats that trapped carbonate mud the pervasive ridge runnel system suggests scale dependent biophysical feedback between i carbonate mud supply ii current duration strength and direction and iii growth and trapping by prolific mat growth together these factors determined the size morphology and arrangement of the stromatolite columns and their laminae as well as their branching patterns alignment and ridge runnel spacing ridge runnel surfaces resemble ripple mark patterns but whether currents were parallel and or normal to stromatolite alignment remains unclear the formation and preservation of tieling columns required plentiful supply of carbonate mud mat building microbes well adapted to cope with this abundant sediment and absence of both significant early lithification and bioturbation these factors were time limited and tieling stromatolites closely resemble coeval examples in the belt purcell supergroup of laurentia the dynamic interactions between mat growth currents and sediment supply that determined the shape of tieling columns contributed to the morphotypical diversity that characterizes mid late proterozoic branched stromatolites this article is protected by copyright all rights reserved

and ratios in skeletal calcite of mytilus trossulus covariation with metabolic rate salinity and carbon isotopic composition of seawater minor element and isotopic compositions of marine bivalve calcite are frequently used as proxy records of seawater temperature and salinity although molluscan calcite is secreted at or near oxygen isotope equilibrium the influence of metabolic activity i e vital effects on skeletal srca ratios and 13c values is not well known we present measurements of skeletal chemistry from a consecutive samples milled in chronological order from the organism s final year of growth and b adjacent samples within three separate growth bands of the marine mussel mytilus trossulus to investigate chemical disequilibrium effects among different parts of the shell seawater temperature and salinity were monitored for one year at squirrel cove british columbia at the end of the year a young rapidly growing mussel mussel a and an old slowly growing mussel mussel b were harvested from this site growth bands within the shells were sampled to provide a chronological record of shell carbonate chemistry results from consecutive samples show 1 a significantly higher average srca ratio in mussel a than that in mussel b and 2 13c values that correlate well with salinity in mussel a but not in mussel b results from time equivalent adjacent samples show 1 higher srca and 13c values near the ventral margin than at time equivalent regions on lateral margins of the shell and 2 little or no variation in 18o values these observations suggest that skeletal chemistry srca and 13c is primarily controlled by rate of mantle metabolic activity and secondarily modified by variation in seawater salinity because metabolic activity in the mantle at the site of carbonate precipitation varies with shell curvature the composition of calcite secreted along lateral margins is influenced to a greater extent by metabolic activity than calcite secreted coevally at the central margin of the shell hence the chemistry of calcite secreted at the ventral margin is precipitated in near equilibrium with seawater and allows accurate estimation of seawater srca ratios and carbon isotopic composition in contrast shell precipitation along lateral margins is dominantly controlled by metabolic activity and calcite chemistry is not in equilibrium with ambient seawater in this context we present a biomineralization model where variations in skeletal srca and 13c values are explained in the context of mantle metabolic activity and seawater salinity

barium and molybdenum records in bivalve shells geochemical proxies for phytoplankton dynamics in coastal environments barium calcium and molybdenum calcium ratios were investigated in shells of the tropical scallop comptopallium radula three juvenile specimens were harvested alive in the southwest lagoon of new caledonia after a 1 year hydrological survey calcite samples representing a few hours of biomineralization were laser ablated along the maximal growth axis and analyzed for ba and mo content using an inductively coupled plasma mass spectrometer absolute dates of shell precipitation assigned on the basis of periodic formation of shell growth patterns led to the accurate reconstruction of ontogenetic variations of elemental ratios with subweekly resolution inter individual variability of ba ca and mo ca time series was low indicating an environmental control on the incorporation of these elements within shells both profiles were characterized by a background level punctuated by sharp peaks the ingestion of diatoms enriched in ba adsorbed on iron oxyhydroxides associated with the frustules is the most likely cause of the formation of ba ca peaks some contribution of diatom associated barite is also possible in every instance ba ca would possibly be a proxy for the timing and magnitude of diatom blooms among all the theories that could be advanced to explain the occurrence of mo ca peaks the most plausible appears to be the ingestion of phytoplankton cells grown upon no3 and therefore containing high levels of mo required for the activity of nitrate reductase if this is so then mo ca could be a new proxy for nitrate uptake by phytoplankton in coastal ecosystems helping to reconstruct the balance between new and regenerated production in paleoenvironments

a group of rifting events in the terminal paleoproterozoic in the north china craton abstract rifting events of the terminal paleoproterozoic are well preserved in the north china craton they include an aulacogen and cratonic marginal rift basins mafic dyke swarms two anorthosite suites and rapakivi granites all of these events took place after metamorphism deformation and magmatism of the late paleoproterozoic between 2 0 ga and 1 85 ga or 1 80 ga the rifting events belong to an anorogenic event group reflecting breakup of a late paleoproterozoic united north china craton an intracratonic rift basin in the center of the north china craton is named the yanshan taihangshan aulacogen a stratigraphic thickness of 9193 m was deposited within the basin including three groups and twelve formations with time range ca 1 8 ga to 0 85 ga the oldest changcheng group of the sequence was deposited in a graben and is mainly composed of alluvial basal conglomerates terrestrial clastic rocks and shallow marine sandstone and carbonates with super high potassium basalt trachyte the marginal basins occur around the northern western and southern margins of the north china craton respectively located in langshan baiyun obo helanshan mountain and the adjacent regions between henan shanxi and shaanxi provinces the stratigraphic sequences of the basins are generally made up of clastic rocks in the lower parts and carbonates in the upper part with a thick volcanic sequence with u pb age of 1840 14 ma exposed in the southern marginal regions based on stratigraphic sequences isotopic data and volcanic features the initial rifts took place at about 1 85 ga to 1 80 ga mafic dyke swarms are largely developed in central parts of the north china craton where they intrude archean granulite and high amphibolite rocks a new single zircon u pb isotopic age of 1769 2 5 ma has been reported from a mafic dyke in east henshan mountain northwestern shanxi province an anorthosite suite agms is exposed along two deep fault belts in northern hebei province isochron ages of 1683 193 ma by rb sr and 1735 239 ma by sm nd were measured from an anorthosite body the rapakivi granites crop out along the miyun qiangzilu xinglong fault in an e w direction and are characterized by megacrysts of alkali feldspars mantled by plagioclase thus showing many of the petrographic features of classic rapakivi granites worldwide a typical rapakivi body preserved in shachang of miyun county beijing has a u pb age of 1716 31 ma super high potassium volcanics located in the upper changcheng group have been dated at 1683 67 ma and 1625 6 ma the time range for all magmatic events is between 1 72 ga and 1 62 ga

calibration of the mg ca of globorotalia truncatulinoides r for the reconstruction of marine temperature gradients 1 recent work has provided useful mg ca to water temperature calibrations for shallow dwelling planktonic foraminifer species globorotalia truncatulinoides right coiling r is a deep dwelling species that can serve as a source of information about the temporal variability in the water characteristics of the thermocline we present a temperature calibration for the mg ca in the shell of g truncatulinoides r and examine some of the practical issues associated with evaluating the usefulness of the technique the mg ca in the primary and the secondary calcite of individual g truncatulinoides r correlates exponentially with water column temperatures showing a change of 10 in the mg ca per 1 c r2 0 92 a limited comparison with plankton tow samples demonstrates that the average mg ca temperature was offset 1 c from the average temperature calculated using the 18o calibration of o neil et al 1969 and the mg ca temperatures have a range similar to the 18o temperatures comparisons of the mg in the core top samples to water depth of deposition indicates that dissolution does not alter the measured value of mg in the primary calcite

sea surface water temperatures over the period 1884 1983 reconstructed from oxygen isotope ratios of a bivalve mollusk shell arctica islandica southern north sea although climate system modeling cannot be imagined without long sea surface temperature sst records observational data is spatiotemporally incomplete and inhomogeneous prior to about 1950 moreover almost no high resolution sst proxies exist from temperate and boreal marine settings here we present a temporally equidistant high resolution sst proxy record of the southern north sea during the period 1884 1983 calculated from oxygen isotope ratios 18oaragonite of arctica islandica l a bivalve mollusk shell arctica islandica produces daily growth increments which enable precise intraannual dating the growing season of specimens from about 25 m water depth upper well mixed layer of the ocean started in february and ended in september observational coads etc and 18oaragonite derived sst data during february through september compare well to each other especially after 1950 apart from similar overall sst trends we found north atlantic oscillation type cycles of 7 9 years in our proxy sst record and in various different instrumentally determined sst chronologies no vital effects exist so that 18oaragonite ratios determined across the shell i e throughout lifetime of the studied specimen reflect ambient water temperatures that occurred during shell growth results of our study demonstrate that a islandica provides long independent and high resolution sst proxy chronologies from higher latitudes such records can complement and further validate observational sst data and help improving climate system models

mg ca sr ca and stable isotope δ18o and δ13c ratio profiles from the fan mussel pinna nobilis seasonal records and temperature relationships 1 we present new annually resolved 18o 13c mg ca and sr ca ratio records for two shells of the fast growing mediterranean fan mussel pinna nobilis collected from proximal spanish coast sea grass meadows the relationship between the potential geochemical proxies and ontogenetic and environmental controlling factors is investigated specifically the use of shell mg ca and sr ca ratios as potential calcification temperature proxies the latter calculated from measured shell 18o values has been assessed the 18o cycles along the growth axis indicate that our p nobilis specimens are 10 5 and 4 5 years old shell sr ca ratios do not exhibit any consistent interannual cyclicity and are not correlated to temperature a subtle ontogenetic effect on shell mg ca ratios was observed during the first 4 5 years of recorded growth but was highly evident during the organism s later growth years in p nobilis shells different mechanisms influence ontogenetic variation in shell mg ca and 18o records shell mg ca ratios from the first 4 5 years of growth correlate significantly to temperature in a best fit relationship described by the equation mg ca 17 16 1 95 exp 0 022 0 004 t p nobilis shell mg ca records therefore are a valid temperature proxy only during an early growth phase for the same range of temperatures shell mg ca ratios in p nobilis are approximately 1 3 lower than those reported for inorganic calcite but 3 to 4 times higher than in another bivalve species mytilus trossulus and 4 to 16 times higher than in foraminifera we suggest these offsets are due to a higher degree of similarity between seawater and calcification fluid composition in p nobilis than in other bivalves and foraminifera the observed shell mg ca ratio change per c of 2 2 also is lower than that observed for inorganic and other biogenic calcites our findings strongly support taxon and species specific mg ca temperature relationships for bivalves and other calcifying organisms an appreciation of the physiology and calcification mechanisms of any biogenic carbonate archive therefore is paramount prior to the application of stable isotope and element ca ratio proxies for paleotemperature reconstructions

palaeomagnetic data late precambrian magnetostratigraphy and tectonic evolution of eastern china abstract in this paper middle and upper proterozoic 1900 1600 ma apw paths are presented for north and south china based on palaeomagnetic results obtained from the jixian yangzi gorges shennongjia and fuzhou areas in eastern china two or three loops are present the second of these has an age of about 1000 800 ma and is probably roughly equivalent to the sveconorwegian and grenville loops apw paths loops reversed polarity zones and pole positions combined with geological data permit definition of several markers that are useful in regional correlation these form the basis for a proposed stratigraphic subdivision of the middle and upper proterozoic in china a tentative palaeogeographic map has been drawn for the north china and yangzi blocks for the period from 1700 ma to 600 ma

controls over the strontium isotope composition of river water abstract strontium concentrations and isotope ratios have been measured in river and ground waters from the ganges orinoco and amazon river basins when compared with major element concentrations the data set has allowed a detailed examination of the controls over the strontium isotope systematics of riverine input to the oceans in the following environments 1 1 typical drainage basins containing limestones evaporites shales and alumino silicate metamorphic and igneous rocks 2 2 shield terrains containing no chemical or biogenic sediments and 3 3 the floodplains that constitute the largest areas of many large rivers the strontium concentration and isotope composition of river waters are largely defined by mixing of strontium derived from limestones and evaporites with strontium derived from silicate rocks the strontium isotope composition of the limestone endmember generally lies within the phanerozoic seawater range which buffers the 87 sr 86 sr ratios of major rivers a major exception is provided by the rivers draining the himalayas where widescale regional metamorphism appears to have led to an enrichment in limestones of radiogenic strontium derived from coexisting silicate rocks the strontium isotope systematics of rivers draining shield areas are controlled by the intense transportlimited nature of the weathering reactions and thereby limits variations in the strontium flux from these terrains floodplains are only a minor source of dissolved strontium to river waters and precipitation of soil salts in some floodplains can reduce the riverine flux of dissolved strontium to the oceans the most effective mechanisms for altering the isotope ratio and flux of riverine strontium to the oceans are increased glaciation and large scale regional metamorphism of the type produced during continental collision both mechanisms provide a means for increasing the 87 sr 86 sr ratio of the global riverine flux

assessing the reproducibility and reliability of estuarine bivalve shells saxidomus giganteus for sea surface temperature reconstruction implications for paleoclimate studies studies using oxygen isotopes y 18 o of mollusk shells to determine paleotemperature need to assume water y 18 o values which could severely influence calculated temperatures we analyzed aragonitic shells of the butter clam saxidomus giganteus deshayes 1839 to determine the reproducibility of the isotopic signal between individuals and to assess how precisely temperature could be calculated given known salinity and temperature furthermore carbon isotopes are also investigated as an environmental proxy the abundance of well preserved s giganteus shells in archeological and geological deposits in northwestern north america makes them a particularly suitable species for paleoclimate studies seasonally resolved stable oxygen isotope profiles in three s giganteus shells collected from the same site in puget sound washington usa were well correlated 0 77br 2 b0 87 although there were differences up to 0 58x in high resolution y 18 o profiles of the three shells the difference between the average y 18 o of each shell was less than half of this 0 19x and half of what has been reported for between colony coral variability y 13 c profiles on the other hand were more complex with shell y 13 c being about 2 5x lower than expected equilibrium values however this roughly conforms to the idea that about 10 of the shell carbon originates from metabolic co2 both y 18 o and y 13 c indicate that s giganteus do not grow during periods of reduced salinity despite the excellent reproducibility of y 18 o between shells and the fact that salinity effects were duly considered calculated temperature still differed from instrumental temperature applying different salinity y 18 o water relationships to average shell y 18 o and considering salinity from the shell collection site and a nearby offshore station resulted in calculated average water temperatures ranging from 1 7 to 6 4 8c warmer than measured although we could not determine if s giganteus precipitate their shells in isotopic equilibrium we believe that the difficulty in predicting temperature arose from not being able to accurately determine

neoproterozoic sulfur isotope variation in australia and global implications abstract seven sulfur isotope stages are apparent in australian neoproterozoic sections 1 from 840 ma to the sturtian glaciation 700 ma 34ssulfate varied little 19 to 17 5 and 34ssulfide ranged from 20 to 23 2 the sturtian glaciation was followed by 3 a rise in 34ssulfide to an average of 30 seen also in china namibia and canada and in 34ssulfate at least to 26 and possibly to 45 the sharp rise in 34s of all sulfur fractions sulfate sulfide and organic leads us to speculate that sulfide depleted in 34s was deposited on the abyssal plain and that residual sulfate enriched in 34s remained beneath a stagnant ice covered ocean during the sturtian glaciation and was brought to the shallow continental margin during the post glacial transgression 4 34ssulfide and 34ssulfate fall from 640 to 607 ma 34ssulfate down to 17 probably from oxygen excess through massive organic carbon burial which causes weathering of sulfide depleted in 34s continental sulfide and previously deposited sulfide on the abyssal plain 5 the oxic environment of the marinoan 605 595 ma glaciation minimises sulfate reduction unlike the sturtian so that 34ssulfate is unvarying 6 the post glacial environment has sulfide depleted in 34s average 34ssulfide

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

seasonal stable isotope variations of the modern amazonian freshwater bivalve anodontites trapesialis in a floodplain lake of the amazon river near the city of iquitos northeastern peru a one year monitoring experiment was conducted during which water samples and living bivalves anodontites trapesialis were collected with the aim to investigate seasonal 18o variation in and fractionation between bivalve aragonite and host water both host water and molluscan growth increments show more than 8 seasonal variation in 18o in the floodplain lake under study the 18o variation of the water is controlled by contrasting dry and wet season evaporation precipitation regimes molluscan 18o appears to be in equilibrium with the host water although an approximately 4 0 offset occurs 13c records of water and bivalves are in good agreement suggesting that both 18o and 13c of the shells of freshwater bivalve a trapesialis are good recorders of palaeo environmental conditions the 13c of dissolved inorganic carbon dic is governed by plant growth and or by changes in aquatic chemistry affecting the dic pool

the giant pacific oyster crassostrea gigas as a modern analog for fossil ostreoids isotopic ca o c and elemental mg ca sr ca mn ca proxies 1 modern analogs are an essential part of palaeoclimate studies because they provide the basis for the understanding of geochemical signatures of fossils ostreoids are common in many sedimentary sequences and because of their fast growth high temporal resolution sampling of past seasonal variability is possible here two shell structures of modern giant pacific oysters crassostrea gigas the chalky substance and foliate layers have been sampled for trace element distributions mg sr mn and stable isotope variability c o ca oxygen isotopes exhibit a clear seasonal signature mean carbon isotope values of different oysters agree within 0 1 but ontogenic variability is complicated by shell growth patterns and potential small vital effects the calcium isotope ratios are found to be constant throughout ontogeny within analytical precision at a value of 44 40ca 0 68 0 16 2 sd srm 915a which is consistent with other bivalve species calcium isotope ratios in oyster shell material might thus be a possible proxy for palaeo seawater calcium isotope ratios element ca ratios are significantly higher in the chalky substance than in the foliate layers and especially high sr ca and mn ca ratios are observed for the first growth season of the oysters mg ca ratios in the chalky substance show a negative correlation with 18o values compatible with a temperature dependence whereas this correlation is absent in the foliate layers seasonal changes of sr ca are controlled by metabolic processes whereas for mn ca an additional environmental control is evident

controls on magnesium manganese strontium and barium concentrations recorded in freshwater mussel shells from ohio abstract freshwater bivalve shells may record inter annual fluctuations in water chemistry which in turn may archive variations in solute load due to pollution or discharge events here using weekly surface water chemistry collected at two locations and shells of lampsilis cardium grown in the surface water we investigate if the mg ca mn ca sr ca and ba ca ratios measured at high resolution in the shells on an intra annual time scale consistently reflect the chemistry of the surface water two relationships appear highly correlated sr cacarb and sr cawater and mn cacarb and temperature ba cacarb correlated strongly with ba cawater in one shell but temperature in another shell yielding inconclusive results mn cacarb and mg cacarb were not strongly correlated with elemental ratios in the water but mn cacarb did show variable weak to moderate correlation with ph we found consistent partition coefficient dme values between individual shell samples grown in the same water with mean dmg 0 0006 dmn 17 dba 0 13 and dsr 0 176 sr cacarb and sr cawater exhibited the strongest most consistent correlation with partitioning coefficients that were consistent with published values suggesting sr cacarb can be used as a proxy for sr cawater in freshwater mussels

proterozoic stratigraphy and tectonic framework of china the time span of the proterozoic is taken as from 2600 to 600 ma with subdivision boundaries at 1850 and 1050 ma respectively as 2600 ma seems more appropriate for the initial proterozoic in china siberia and parts of gondwanaland and 600 ma is an inferred age of the precambrian cambrian boundary based on recent study of the yangtze gorge section the proterozoic of china includes the lower proterozoic wutaian and hutuo an the middle proterozoic changchengian and jixianian and the upper proterozoic qingbaikou an and sinian based mainly on tectono sedimentary types and associations seven stratigraphic super regions are recognized in the proterozoic of china and stratigraphic successions of various representative regions are shown in two tables one for the sinian and another for the pre sinian proterozoic palaeogeographic outline of the main super regions and chronometric limit of the principal stratigraphic units are briefly discussed three types of stable sinian successions are distinguished the yangtze type the quruktagh type and the jiaoliao type which are correlated mainly on the basis of tillite horizons and of sabelliditids and the ediacara type of fossils semi stable and mobile types of sinian deposits in southeast china are also briefly mentioned the proterozoic tectonic units of china and the nature of their boundaries are shown on a sketch map showing basement structures crustal sectors of continental nature are designated as continental tectonic domains while broad and complicated crustal sectors of mainly transitional and partly oceanic nature may be called continental margin tectonic domains the boundaries between these domains are usually the principal crustal consumption zones on this basis three continental domains the north china the south china and the southern gondwana and two continental margin domains the northern siberian mongolian and the east china are distinguished platforms continental nuclei massifs and uplifts are used to denote subdivisions within the tectonic domains the development of aulacogens is an outstanding feature in the continental domains especially in the middle proterozoic aulacogens may be classified into an intra platform type and a platform margin type early proterozoic aulacogens are usually brachy axial and intermittent and show conspicuous deformation at closure much like a geosyncline thirteen aulacogens of different types are shown on the sketch map the boundary nature of continental domains is analysed in terms of island arcs and marginal seas and also of emplacement of granite rocks in border parts the north china domain was basically consolidated at around 1850 ma and has a passive northern margin stretching from nei mongol to central tianshan but the southern margin was active and was twice subducted by the qinling marine realm at 1700 and 1000 ma approximately the yangtze platform was not completely consolidated until 1050 ma bp but has a core older than 1850 ma a broad continental margin terrain had developed in the jiangnan region and farther to the southeast in the middle and late proterozoic at least two island arc belts with interarc basins an inner fanjingshan and an outer sibao may be discerned in the middle proterozoic and a late proterozoic island arc zone over 1000 km in length was developed along the southern margin of the jiangnan uplift represented by the banxi group and equivalent strata this kind of broad complicated continental margin tract which has a long development history may be called the open type or the west pacific type

reconstructing intra annual growth of freshwater mussels using oxygen isotopes abstract intra annual growth rates from the bivalve mollusk lampsilis cardium unionidae were reconstructed using measured oxygen isotope 18o profiles together with high resolution environmental records mussels from a single cohort 2007 were grown in two different settings at the columbus zoo aquarium freshwater mussel conservation research center mrc located in central ohio usa outside specimens were collected from sediment laden cages deployed in the o shaughnessy reservoir a single inside specimen was collected from the raceways in the mrc measured 18ocarb profiles from these specimens were calibrated with a predicted oxygen isotope envelope i e the daily range of potential 18ocarb values calculated from hourly water temperatures and weekly 18owater samples collected in 2010 this exercise suggests the outside specimens commenced 2010 shell deposition in late april and ceased in latest october six month growing season in contrast the inside growing season lasted only three months early july and early september calculated daily growth rates from both sites were faster early in the year but highly episodic throughout maximum daily growth rates for the outside and inside specimens were 300 and 436 m day respectively analysis of annual growth rates from the entire cohort suggests the inside specimens grew slower following transplantation in subsequent years however their growth rates were nearly identical to the outside population our results suggest that despite the fact that both populations have similar annual growth rates they have different intra annual growth patterns thus caution should be exercised when extrapolating intra annual growth patterns from cultured specimens to natural populations

the shell of the queen scallop aequipecten opercularis l as a promising tool for palaeoenvironmental reconstruction evidence and reasons for equilibrium stable isotope incorporation abstract the queen scallop aequipecten opercularis has been an important part of the marine fauna of the northeast atlantic region since the miocene and is a suitable candidate for palaeoenvironmental studies using stable isotopes modern shells were investigated to determine if carbonate is precipitated in isotopic equilibrium in this species and to confirm that growth continues through the year specimens of a opercularis were cultured under monitored semi natural conditions over an autumn winter period and the analyses of these specimens were supplemented with isotope data from preserved indigenous north sea specimens the results indicated that the cultured specimens grew in relatively low temperatures that oxygen isotopes of shell exterior carbonate were precipitated in isotopic equilibrium and that a large proportion of the ambient temperature range was recorded in shell carbonate the indigenous north sea specimens exhibited a good correspondence to predicted oxygen isotope values for summer the isotopic record related to winter was however somewhat truncated due to growth decelerations in the specimens carbon isotopes of shell exterior carbonate were calculated as being derived primarily from external sources and showed comparatively little influence from metabolically derived carbon this suggests that carbon isotopes were at least close to equilibrium with ambient waters the limited incorporation of metabolic products suggests that a opercularis would be a good monitor of changing carbon isotope ratios in seawater dissolved inorganic carbon the occurrence of equilibrium shell precipitation is explained using a pteriomorph shell calcification model which proposes that transport of ions through the periostracum caused the composition of the extrapallial fluid to be effectively the same as seawater carbonate secretion is therefore not influenced significantly by biological vital effects

isotope paleontology growth and composition of extant calcareous species abstract isotope paleontology uses the isotopic composition of fossil remains of organisms to make inferences about the physical surroundings of growth of the organisms especially temperature and to obtain clues about life history and modes of growth in calcareous fossils oxygen isotopes are mainly used in the former and carbon isotopes in the latter however since physical surroundings and organism response are intimately associated both types of information are contained in each of the isotopic signals to explore the potential of isotope paleontology and to provide a basis for reconstruction a broad range of extant organisms has been studied taking the pioneering work of epstein and associates as a starting point results are summarized for a representative sampling of these studies with emphasis on work at the laboratories of the authors from the mid seventies to the present the organisms considered are nannoplankton benthic algae planktonic and benthic deep sea foraminifera larger foraminifera sponges corals bryozoans polychaetes arthropods bivalves gastropods cephalopods and vertebrates fish otoliths the survey broadly suggests that regarding oxygen isotopes materials tend to be precipitated close to equilibrium with the surrounding seawater as postulated by urey and that for carbon isotopes disequilibrium is the rule life spans growth rates differential seasonal growth and age of reproductive activity can be extracted under favorable circumstances from individual shells and skeletal parts in detail the interpretation of isotope records of individual shells is quite complicated and simple models will fail to give satisfactory results in many or most cases

stratigraphic and sedimentary records of the rift to drift evolution of the northern north china craton at the paleo to mesoproterozoic transition article i nfo this paper presents a stratigraphic and sedimentary study of late paleoproterozoic to early mesoproterozoic successions of the northern margin of the north china craton including the changcheng and nankou groups a reconstruction of the tectono sedimentary history of these two groups demonstrates that the northern north china craton experienced a two stage evolution as recorded by the changcheng group early synrift subsidence and sedimentation were controlled by normal faults and accompanied by volcanism in contrast a late postrift stage was characterized by broad subsidence and widespread occurrence of shallow marine clastic and carbonate rocks a transgressive unconformity is identified and together with its time equivalent conformable contact clearly separates the synrift and postrift sequences the diachronous unconformity can be related to continental rifting and the separation of the north china craton from the adjacent india craton at roughly 1600 ma and is thus interpreted as a breakup unconformity this age of ca 1600 ma is constrained by newly reported precise shrimp u pb zircon ages of transgressive deposits in the overlying mesoproterozoic dahongyu and gaoyuzhuang formations just coincident with the paleoproterozoic to mesoproterozoic transition the 1600 ma time estimate for the tectonic departure of the north china craton from the india craton is comparable with the timing for the breakup of columbia a pre rodinia supercontinent containing almost all of the earth s continental blocks

cerium anomaly variations in ediacaran earliest cambrian carbonates from the yangtze gorges area south china implications for oxygenation of coeval shallow seawater abstract the late neoproterozoic ocean witnessed the naissance of animals which is believed to have been stimulated by an increase in oxygen levels in the ocean however apart from the emergence of animal fossils little supporting evidence has been found for the rise of oxygen in shallow seawater here we present ce anomaly data a redox proxy with a higher reduction potential than many other redox proxies for carbonates from well preserved marine successions the doushantuo formation dengying formation and lower yanjiahe formation of the ediacaran period and the upper yanjiahe formation of early cambrian on the neoproterozoic yangtze platform in the yangtze gorges area in order to constrain the redox evolution of the shallow marine environment calculated ce anomalies were screened using the following criteria al 36 in acetic acid leached carbonate to target samples that preserve primary seawater ree features and ce anomalies the samples satisfying this screening show seawater like ree distribution patterns in leached carbonates and may have recorded ce anomalies of the seawater from which the carbonates precipitated these data show that the doushantuo formation has ce ce values between 0 92 and 0 71 the dengying formation between 0 90 and 0 40 and the yanjiahe formation between 0 52 and 0 72 the ce ce values of the doushantuo formation suggest that shallow waters during the doushantuo stage 635 551 ma were anoxic to suboxic from the bottom to the top of the dengying formation ce ce values decrease systematically which cannot be explained by a change in depositional depth of the carbonate but suggests that the shallow waters became more oxygenated during the dengying stages from 551 ma to ediacaran cambrian boundary these results may provide direct evidence for an increase in oxygen levels in the shallow marine environment during the ediacaran period

climate impact of late quaternary equatorial pacific sea surface temperature variations magnesium calcium data from planktonic foraminifera in equatorial pacific sediment cores demonstrate that tropical pacific sea surface temperatures ssts were 2 8 0 7 c colder than the present at the last glacial maximum glacial interglacial temperature differences as great as 5 c are observed over the last 450 thousand years changes in sst coincide with changes in antarctic air temperature and precede changes in continental ice volume by about 3 thousand years suggesting that tropical cooling played a major role in driving ice age climate comparison of sst estimates from eastern and western sites indicates that the equatorial pacific zonal sst gradient was similar or somewhat larger during glacial episodes extraction of a salinity proxy from the magnesium calcium and oxygen isotope data indicates that transport of water vapor into the western pacific was enhanced during glacial episodes

preliminary evaluation of potential stable isotope and trace element productivity proxies in the oyster crassostrea gigas abstract as most bivalve mollusks are filter feeders or deposit feeders predatory septibranchs poromyacea being the notable exception they are closely linked with the activity of primary producers perhaps this is nowhere more evident than in shallow water habitats influenced by seasonal phytoplankton blooms in these systems photoautotrophs are capable of changing the physical and chemical properties of the water column in turn clams ingest large quantities of phytoplankton and precipitate their shells in these chemically altered waters thus clam shells likely archive valuable information about phytoplankton dynamics in shallow water habitats to better understand this relationship we investigated geochemical records from two potential productivity proxy systems archived in shells of the oyster crassostrea gigas that live in the san francisco bay estuary california usa here we present multi year records of shell carbon isotope 13ccarb and barium calcium ba cacarb variation these archives are compared with records of environmental variation using oxygen isotopes 18ocarb as a temporal marker we also present high resolution 13ccarb 18ocarb and ba ca profiles associated with the 2003 spring phytoplankton bloom our results suggest that the prominent positive 13ccarb excursion present in shell material deposited in the spring of 2003 most likely reflects photosynthetic enrichment of the dissolved inorganic carbon pool calibration of stable isotopes with calculated chlorophyll a concentrations measured during the bloom suggests that our 13ccarb sample variation reflects phytoplankton abundance with 3 to 4 day resolution these findings highlight the potential utility of stable isotope records as tools for reconstructing patterns of primary productivity elevated ba ca values are recorded each year in the spring thus like stable isotope profiles ba ca profiles from these specimens demarcate individual years of shell growth and establish ontogenetic age low and high resolution ba ca profiles do not however correlate with the 2003 spring phytoplankton bloom casting doubt on the relationship between ba ca ratios and phytoplankton blooms although the ba ca peak timing loosely correlates with freshwater discharge events peak amplitude does not leaving the environmental cause trigger of these peaks unknown nevertheless the san francisco bay estuary seems like an ideal environment in which to further investigate the relationship between skeletal geochemical variation and patterns of primary productivity

a mesoproterozoic paleomagnetic pole from the yangzhuang formation north china and its tectonics implications abstract a new paleomagnetic study has been carried out on mesoproterozoic sediments in the jixian area north china detailed stepwise thermal demagnetization allows us to isolate three components from 141 oriented drill core samples 14 sites a low temperature component component a identified from most of samples falls close to the present local earth field direction a middle temperature component component b is found only in 21 samples from four sites the component b directions after bedding correction yield a paleopole position at 336 0 e 10 2 n with a 95 17 1 which is close to the lower cambrian pole of the north china block characteristic remanent directions with dual polarities obtained from high temperature component c pass fold test the directions yield a pole position at 190 4 e 2 4 n with a 95 11 9 this result indicates that the north china block was located in low latitude at ca 1 35 ga recently several studies suggested that laurentia baltica and siberia were also situated at low latitudes from well dated paleopoles between ca 1 5 and 1 25 ga this would imply that the north china block laurentia and baltica might drift together or close in the mesoproterozoic

glacial events of the past and their geological significance abstract traces of glaciations are unevenly distributed in the stratigraphic column and exhibit rhythmicity of several ranks this rhythmicity makes it possible to establish the corresponding hierarchy of climatic events in descending order glacio and thermo eras glacial and interglacial periods and epochs as well as smaller events which appear to be compared to the most important climatic fluctuation during the pleistocene the direct factors causing initiation and termination of glaciations were climatic fluctuations the palaeolatitudinal position of the continents controlled a degree of asymmetry and perhaps a certain diachronism of glaciations in different hemispheres during the glacial periods in high and middle latitudes of the earth the glacial and cold temperate climates either were predominant or alternated the thermo eras and at least some interglacial periods were characterized by warm temperate and warm climates at high and middle latitudes glaciations have been numerous and important geological events they affected all outer spheres of the earth from asthenosphere to atmosphere they apparently stimulated the biological evolution too the study of ancient glaciations is important from both the scientific and economical points of view

macroscopic worm like body fossils from the upper precambrian 900 700 ma huainan district anhui china and their stratigraphic and evolutionary significance abstract abundant and varied macroscopic worm like body fossils from the late precambrian liulaobei formation huainan group and the jiuliqiao formation feishui group in the huainan district northern anhui province china are further investigated through this progress report after the initial discovery by zheng wenwu and a recent study by wang guixiang sinosabellidites zheng in the liulaobei formation is a worm like organism of questionable metazoan origin it has merely a superficial resemblance with the tubes of late vendian early cambrian true sabelliditida but has much in common with the accompanying macroscopic algal remains of tawuia hofmann both pararenicola wang and protoarenicola wang are representatives of primitive worm like animals in the jiuliqiao formation their macroscopic size elongate cylindrical body anterior aperture and apparatus prominent and elastic annulations are characteristic for their metazoan origin although they lack sufficient evidence for their definite relationship with any known kind of living worms the liulaobei formation and the jiuliqiao formation are dated at about 850 ma and 740 ma respectively regional geology and stratigraphic correlation and the occurrence of the distinctive chuaria tawuia assemblage suggest a time range between less than 900 ma and over 700 ma for the whole shallow water marine sedimentary sequence of the huainan and feishui groups this latter group is disconformably covered by the drop stone facies diamictites and tillites of the late precambrian luoquan glaciation apart from the enigmatic sinosabellidites both pararenicola and protoarenicola are claimed to be the oldest multicellular animals so far discovered in the world and the first reliable evidence for the pre ediacarian evolutionary history of manifest metazoan life

an evaluation of mg ca sr ca and ba ca ratios as environmental proxies in aragonite bivalve shells the influence of salinity and water chemistry on mg ca sr ca and ba ca ratios in the aragonitic shells of the manila clam was investigated clams were reared at constant temperature 20 c under different controlled conditions of salinity commonly encountered in their natural habitat clams were held in three tanks with a constant salinity of 35 for the first 35days and then two tanks were changed to lower salinities 20 and 28 for the next 29days individual shell mg ca sr ca and ba ca ratios were studied through time despite stable conditions temperature salinity and mg cawater for clams reared at salinity 35 during the experiment mg ca shell ratios increased through the time moreover the salinity decrease at t35 slowed the increase of mg ca shell ratios at salinity 28 and resulted in an mg cashell decrease at salinity 20 despite similar mg cawater ratios in the different salinity treatments microprobe analyses illustrate that mg varies along contemporaneous growth lines the variable shell mg ca ratios suggest that incorporation of magnesium into shell carbonate is strongly regulated by the organism and not by environmental conditions interestingly microprobe analyses illustrated that mg was not associated with shell sulfur as other studies have suggested sr ca shell ratios of clams reared at salinity 35 and under constant conditions were also not as constant as expected if sr ca ratios were an environmental proxy there was an inverse correlation between shell sr ca and salinity despite a slight positive correlation between salinity and sr ca ratios of the water indicating that sr ca ratios do not reflect environmental conditions a strong inverse correlation between salinity and ba ca shell ratios and a positive correlation between ba ca shell and ba ca water was observed therefore ba ca shell ratios seem to be a promising proxy of high resolution 1day salinity variations in estuarine waters via the relationship between ba ca water and salinity this study clearly illustrates that both mg ca and sr ca ratios in aragonite shells are not under environmental control and that ba ca ratios are with the later tracking high resolution water ba ca ratios and hence estuarine salinity variations

application of a radially viewed inductively coupled plasma optical emission spectrophotometer to simultaneous measurement of mg ca sr ca and mn ca ratios in marine biogenic carbonates 1 we developed and applied an analytical system for the simultaneous determination of magnesium calcium strontium calcium and manganese calcium ratios in biogenic carbonates using a perkin elmer 4300 optima dv inductively coupled plasma optical emission spectrophotometer in radial mode intensity ratio responses to calibration standard elemental ratios were linear over suitable working ranges we evaluated instrumental response using solution replicates and we analyzed planktonic foraminifera in multiple runs ca concentrations were kept in a relatively narrow range typically 0 6 2 4 mm ca although we found no resolvable ca matrix effect over a much wider range each analysis required a minimum sample volume of 300 l and took 3 5 min instrument time an analytical run of 30 samples plus standards blanks and control materials typically took 5 6 hours reproducibility interrun precision 1s rsd for solutions was 1 2 1 5 and 1 2 for mg ca sr ca and mn ca ratios far smaller than reproducibility for foraminiferal replicates over multiple analytical runs there was no independent reference material for assessing accuracy detection limits were equivalent for an 0 5 mm ca solution to 0 058 mmol mol for mg ca 0 015 mmol mol for sr ca and 0 005 0 020 mmol mol for mn ca precautions included limiting length of time the peristaltic tubing for the autosampler was used avoiding mg contamination from plastic ware and screening out results from samples with very low ca concentrations 0 25 mm ca

temperature control on the incorporation of magnesium strontium fluorine and cadmium into benthic foraminiferal shells from little bahama bank prospects for thermocline paleoceanography surface sediments from little bahama bank lbb intersecting the subtropical thermocline were used to assess the influence of temperature on the incorporation of mg sr f and cd into shells of benthic foraminifera samples were obtained from twelve cores along the southern slope of lbb covering a temperature range of 18 4 5 c between 301 and 1585 m we studied the composition of ten calcitic and one aragonitic species which are often used in paleochemical reconstructions mg ca ratios decrease with increasing water depth in all benthic species both with calcitic and aragonitic mineralogy showing a strong correlation with water temperature similar decrease is seen in sr ca but with no correlation with temperature none of the benthic species studied here exhibits a depth or temperature related change in f ca similar trends are observed when using an ocean wide dataset which includes shallow and deep core tops 300 5000 m we suggest that temperature is the primary control on the mg content of benthic foraminifera based on inorganic precipitation experiments and thermodynamic considerations presented here a 30 40 decrease in the mg distribution coefficient in calcite may be expected as a result of a temperature change from 25 c to 5 c which is about half the observed change in lbb a calibration curve applied to c pachyderma data from core tops along the slope of little bahama bank suggests that water temperature may be inferred from mg ca ratios with an uncertainty of about 0 8 c therefore the mg content of benthic foraminifera may provide a new independent temperature proxy for studying shallow waters paleoceanography the linear decrease in sr ca with increasing depth is not correlated with temperature the trend is constant from the ocean surface down to 5 km suggesting that pressure related effects on the calcification process are a more likely explanation than post depositional dissolution mg ca ratios in aragonitic shells of h elegans covary with temperature in accord with recent observations from corals in contrast the sr and f chemistry of h elegans is very different than that of corals and inorganically precipitated aragonites the disparities between the elemental composition of biogenic and inorganic phases and the large intergeneric and interspecific differences observed both in planktonic and benthic foraminifera implicate temperature related physiological processes in regulating the coprecipitation of elements in foraminiferal shells our work demonstrates that cd ca ratios of shallow calcitic species reflect the vertical distribution of nutrients no significant influence of temperature on the partitioning of cd into the shells was found our data extend the previous deep water calibration boyle 1992 thereby allowing for the reconstruction of the nutrient chemistry of shallow thermocline waters

generation of mesoscale flows over the shelf and slope by shelf wave scattering in the presence of a stable sheared mean current a linearized barotropic model is used to investigate the scattering of barotropic shelf waves by variations of the shelf width in the presence of a sheared but stable mean along shelf current located over the continental slope the mean current is chosen to eliminate all backward propagating waves so no energy is reflected from the scattering region in addition the mean current shear severely limits the number of forward propagating waves which carry energy downstream from the scattering region for a narrowing shelf this tends to increase the strength of the scattering and more importantly generates large amplitude evanescent modes which dominate the velocity fields within and slightly upstream and downstream of the scattering region when viewed in combination with the mean current the wave scattering forms intense mesoscale flows between the mean current and the coast this mechanism may be partially responsible for the highly variable and energetic flows often associated with along shelf currents found over many continental slopes

on the upper precambrian sinian suberathem in china abstract this paper gives a general outline of the upper precambrian sinian suberathem in china including its geographic distribution development stratigraphic sequence and classification the sinian suberathem with a time range of 1950 615 ma constitutes the greater part of the proterozoic it is characterized by the development of stromatolites appearance of eukaryotes and the presence of metazoa in its upper part its sedimentological characteristics are quite similar to those of the overlying paleozoic on the basis of the biological evolution isotopic dating and stages of tectonic development the sinian suberathem can be divided into four systems in ascending order the changcheng ca 1950 1400 ma jixian ca 1400 1000 ma qingbaikou ca 100 800 ma and sinian ca 800 615 ma systems the stratotype for the first three systems is located in jixian county and the type section for the sinian system in the yangzi gorges area the contact between the sinian and cambrian systems is in some places a continuous transition with abundant small shelly fauna above the precambrian cambrian boundary e g in the yangzi gorges yunnan and sichuan with regard to sedimentological characteristics the rocks of the sinian suberathem may be subdivided into three main facies such as 1 carbonate facies of stable region 2 volcanic sedimentary facies of mobile zones and 3 argillo arenaceous carbonate facies of transitional zones progress in the study on the succession of the sinian suberathem has been made in recent years in regard to palaeontology stratigraphy isotopic geochronology magnetostratigraphy and palaeoglaciology they provide important evidence for the stratigraphic correlation of the upper precambrian of china and other continents

influence of temperature on the composition of magnesian calcite overgrowths precipitated from seawater a constant disequilibrium technique was used to determine the composition of magnesian calcite overgrowths precipitated on pure calcite seeds from artificial seawater at 5 25 and 40 c the amount of magnesium incorporated in the overgrowths at a given temperature is independent of the precipitation rate over a wide range of saturation states and is believed to correspond to a composition in true equilibrium with seawater the distribution coefficient of magnesium dmg2 c in the magnesian calcite overgrowths increases almost linearly with temperature being 0 0121 0 0013 at 5 c 0 0172 0 0022 at 25 c and 0 0271 0 0013 at 40 c these values apply only to magnesian calcites precipitated from standard composition seawater since a previous study has shown dmg2 c to be a function of the mg2 ca2 ratio in the parent solution results of this study are compared with values reported previously by other workers and with the compositional distribution of naturally occurring magnesian calcite cements and ooids found in seawater it appears that variations in temperature are not sufficient to account for the compositional variability of naturally occurring inorganic marine magnesian calcite cements

strong kinetic effects on sr ca ratios in the calcitic bivalve pecten maximus although sr ca ratios in abiogenic calcite are strongly controlled by precipitation rates such a kinetic effect has never been demonstrated in calcitic bivalve shells therefore we report sr ca ratios together with daily growth rates in the calcitic shells of four individuals of the bivalve pecten maximus age class i ratios of sr ca were found to be variable among individuals that grew at the same location illustrating that vital effects dominate over environmental controls although daily growth rate was correlated with shell sr ca ratios it explained only half of the sr ca variations however daily shell surface area increment an estimation of the total quantity of carbonate precipitated for a given time explained 74 of the sr ca variability in the shells of p maximus this proves for the first time in a calcitic bivalve that shell sr ca partitioning is mainly controlled by kinetic effects the sr ca ratio should therefore be tested as a potential proxy of calcification rate in modern or fossil calcitic biocarbonates

continental growth and secular evolution constraints from u pb ages and hf isotope of detrital zircons in proterozoic jixian sedimentary section 1 8 0 8 ga north china craton a b s t r a c t in order to understand the precambrian crustal growth and reworking history of the north china craton in situ u pb and lu hf isotope analyses were carried out on the detrital zircons from a well preserved nearly undeformed proterozoic sedimentary section with time interval of 1 8 0 8 ga totally 806 zircons separated from 7 samples collected from each representative stratigraphic unit were measured for upb and lu hf isotopic compositions of which 430 grains yielded concordant u pb ages the concordant zircons show three prominent age groups of 1 6 1 8 ga 1 9 2 2 ga and 2 3 2 6 ga both positive and negative ehf t values were exhibited by zircons from all groups suggesting both juvenile crust addition and crustal reworking for all age groups the hf crustal model ages of zircons reveal that the juvenile materials were continuously added to the crust between 4 0 and 2 0 ga with a prominent peak at 2 7 3 0 ga and a less significant peak at 3 1 3 4 ga the juvenile contributions to the newly formed crust decrease stepwise through time and crustal reworking has dominated over juvenile inputs to the continental crust since 2 6 ga compared with the detrital zircons from modern rivers running within the north china craton the sedimentary rocks contain more older zircons implying the relatively poor preservation of archean crustal rocks in modern river sand and accordingly the weights of archean crystallizations ages and crustal growth inferred from detrital zircons in modern river are significantly underestimated the integrated studies of detrital zircons from both modern river sands and ancient sedimentary rocks are essential to decipher the early crustal growth history more faithfully

a biomineralization model for the incorporation of trace elements into foraminiferal calcium carbonate measurements of srca of benthic foraminifera show a linear decrease with water depth which is superimposed upon significant variability identified by analyses of individual foraminifera new data for cdca support previous work in defining a contrast between waters shallower and deeper than 2500 m measured element partition coefficients in foraminiferal calcium carbonate relative to sea water d have been described by means of a one box model in which elements are extracted by rayleigh distillation from a biomineralization reservoir that serves for calcification with a constant fractionation factor such that d 1 f 1 f where f is the proportion of ca remaining after precipitation a modification to the model recognises differences in element speciation the model is consistent with differences between dsr dba and dcd in benthic but not planktonic foraminifera depth variations in d for sr and ba are consistent with the model as are differences in depth variation of dcd in calcitic and aragonitic benthic foraminifera the shallower depth variations may reflect increasing calcification rates with increasing water depth to an optimum of about 2500 m observations of unusually lower dcd for some deep waters not accompanied by similar dsr or dba may be because of dissolution or a calcification response to a lower carbonate saturation state

a subdivision of the precambrian of china abstract precambrian rocks are widely distributed in china the precambrian is divided into two time units i e the archaean and proterozoic eon each of these is separated into three chronological intervals also with the status of eras with the prefixes early middle or late the time boundary between the archaean and proterozoic eon is placed at 2500 ma according to the present isotopic data the proposed subdivision for the archaean of china is two fold the age of the fuping group is younger than 2800 2900 ma and that of the qianxi group and the corresponding stratigraphic units of eastern liaoning are older than 2800 ma so that 2800 ma is selected as the boundary between the early middle and late archaean based on the representative stratigraphic units the wutai and huto groups and an intervening major unconformity formed by the wutaiian orogeny at 2200 2300 ma the early proterozoic is further divided into two periods with a time demarcation at 2200 ma a major episode of orogeny known as the luliangian movement occurred at the end of the early proterozoic at 1900 ma this disturbance was very extensive and is in a way responsible for the difference in geological conditions between the lower and middle upper proterozoic in china the boundary 1900 ma that relates to the luliangian movement is more important than the boundary corresponding to the age of 1600 ma which is recommended as the time boundary between proterozoic i and ii so we propose to use 1900 ma as the boundary between the early and middle proterozoic in china the time boundary between the middle proterozoic including the changcheng system and the jixian system and the late proterozoic which is composed of the qingbaikou and sinian systems is 1000 ma the age for the boundary between cambrian and precambrian based upon the recent isochron data is inferred to be 610 ma

cenozoic deep sea temperatures and global ice volumes from mg ca in benthic foraminiferal calcite a deep sea temperature record for the past 50 million years has been produced from the magnesium calcium ratio mg ca in benthic foraminiferal calcite the record is strikingly similar in form to the corresponding benthic oxygen isotope 18o record and defines an overall cooling of about 12 c in the deep oceans with four main cooling periods used in conjunction with the benthic 18o record the magnesium temperature record indicates that the first major accumulation of antarctic ice occurred rapidly in the earliest oligocene 34 million years ago and was not accompanied by a decrease in deep sea temperatures