aragonite relic preservation in jurassic calcite replaced bivalves shells of the aragonite bivalve neomiodon great estuarine group jurassic scotland replaced by coarse neomorphic calcite contain oriented relics of the original aragonite ultrastructure the presence of these relics in such old altered shells as well as the high sr content of the replacement calcite indicate that the process of calcite replacement of aragonite is not a cumulative slow process involving repeated alteration events but rather a rapid one step process aragonite relics once encased in neomorphic spar will survive as unequivocal evidence of original aragonite mineralogy barring total remobilization of the enclosing stable calcite a generally unlikely event the retention of this residual aragonite and high sr calcite supports recent isotopic studies which suggest that the multiple phases of alteration recrystallization invoked in earlier literature are unlikely events in the diagenesis of most undolomitized limestones retention of aragonite relics appears to be independent of whether alteration occurs in shallow meteoric or as in the case of our neomiodon material deeper burial environments pseudopleochroism of the replaced neomiodon shells appears to be due to organic largely graphitic relics not to the aragonite relics

on the reliability of mesozoic dipole low new absolute paleointensity results from parana flood basalts brazil 1 thellier paleointensity experiments were carried out on early cretaceous parana flood basalts forty two samples from 11 lava flows yielded apparently reliable absolute intensity determinations the mean paleointensity values per flow obtained in this study are ranging from 19 4 4 0 to 46 7 7 0 t and the corresponding virtual dipole moments are ranging from 4 0 0 6 to 10 5 1 1 10 22 am 2 these yield a mean value of 7 2 2 3 x 10 22 am 2 which is about 92 of the present geomagnetic axial dipole our results in conjunction with tarduno et al s 2001 data suggest that the paleostrength during early cretaceous period might be comparable or even much higher than recent field intensity and not anomalousely low as previously suggested thus the mesozoic dipole low mdl may probably be considered as unreliable

oldest isotopically characterized fish otoliths provide insight to jurassic continental climate of europe large shallow epeiric seas and adjacent lagoons such as those described herein likely played a significant role in moderating jurassic coastal and continental climate jurassic bathonian ocean surface temperatures in scotland have been calculated from 18o caco3 values of a suite of the oldest well preserved fish otoliths analyzed to date otolith 18o values range from 4 7 to 1 9 vienna peedee belemnite vpdb while 13c caco3 values vary from 5 4 to 1 5 vpdb representing the oldest stable isotopic record of paleodiet paleoecology and fish migration to date using a global ocean 18o h2o value of 1 0 vienna standard mean ocean water vsmow for an ice free jurassic fish species that migrated from estuarine to open marine water record time averaged temperatures of 23 c estuarine fish assuming a similar temperature record variation in 18o h2o values from 3 7 to 2 0 vsmow that significant mixing of fresh water and seawater occurred in the jurassic in scotland is in general agreement with data presented by others molluscan fauna lithostratigraphy paleogeography and paleocirculation models the 18o values and temperatures derived in this study correspond to the meteorologic and hydrologic parameters of a mid latitude maritime climate with low seasonality a mean temperature of 23 c and abundant precipitation and humidity the 18o h2o values calculated from estuarine fish indicate that rainfall must have a 18o h2o value lower than 3 7 vsmow values of 18o and 13c suggest an environment hydrologically similar to that observed in the everglades of south florida or the estuaries of south texas both notable fish nurseries today however sea surface temperatures were lower than those of modern florida or texas as evidenced by reduced evaporative enrichment of 18o h2o values

geological evaluation of multiple general circulation model simulations of late jurassic palaeoclimate abstract general circulation models gcms are currently used to predict future global change however the robustness of gcms should be evaluated by their ability to simulate past climate regimes their success in retrodiction can then be assessed by reference to the geological record geological evidence provides a database that can be used in the estimation of sea surface temperatures orography and other proxy data useful in palaeoclimatic studies these data can then be used to refine the prescribed boundary conditions for running gcms themselves results from a series of modelling experiments run with late jurassic kimmeridgian boundary conditions and using the uk university global atmospheric modelling programme ugamp gcm and the uk meteorological office gcm are presented simulations from these two quite independently generated models although subtly different confirm a generally warmer jurassic earth with arid zones over the tethys and sw usa parts of gondwana dominated by monsoonal systems and convective rainfall generally higher over the oceans than at present circum polar wetlands are also indicated these results generally conform well to the distributions of known facies in these regions modelled cloudiness is also higher in the jurassic and although unconfirmed geologically such conditions would have contributed to greenhouse conditions at high latitudes and could have influenced both terrestrial biomes and marine ecosystems using one of the gcms ugamp we have also investigated the role of orbital parameters for high latitude climate at times of minimum seasonal forcing comparable with an orbital geometry affecting the earth at 115 ka bp parts of antarctica could have sustained a modest ice sheet over areas exceeding 1 km elevation but such modelled sheets would have been ephemeral features and very dynamic in character

a palaeomagnetic study of jurassic intrusives from southern new south wales further evidence for a pre cenozoic dipole low the results of rock magnetic thermal demagnetization and thellier palaeointensity studies are presented for two high level intrusions from southern new south wales australia the gingenbullen dolerite gb 34 5 s 150 3 e and the gibraltar microsyenite gs 34 5 s 150 4 e were emplaced during the second of three major phases of igneous activity that affected the southern sydney basin and are k ar dated at 172 and 178 ma respectively the magnetic mineralogy of the two intrusions is different the gb is dominated by single domain sd pseudo single domain grains of magnetite whereas the gs has both sd magnetite and haematite components although the haematite component does not record a stable remanence the gb records two opposed components of magnetization above 100 c occupying distinct parts of the blocking temperature spectrum the lower blocking temperature lbt component resides between 150 and 400 c and is of normal polarity having a mean direction of d i 021 79 95 8 k 63 with a corresponding vgp at lat long 54 s 137 e dp 12 dm 13 this component is believed to be a tcrm or tvrm related to the initial opening of the tasman sea at 90 ma the higher blocking temperature hbt chrm component is recognized between 450 and 580 c and is of reverse polarity with a mean direction of d i 174 81 95 11 k 33 and a corresponding vgp at lat long 52 s 153 e dp 17 dm 18 the chrm for the gs resides in the 100 450 c region and although the scatter is high has a similar mean direction d i 167 79 95 24 k 26 to the hbt component of the gb with a pole position at lat long 54 s 158 e dp 30 dm 31 there is no evidence of the gb lbt component in samples from the gs suggesting that this intrusion was magnetically unaffected by the later event which is also seen for other intrusions in the sydney basin the vgps calculated from the chrm directions both plot on the jurassic segment of the australian apwp dunlop et al 1997 providing further palaeomagnetic confirmation for the k ar ages thellier palaeointensity results were of variable quality as expected for rocks of this age the mean vdm values calculated for the chrms of the gb and gs were 1 3 1022 and 4 1 1022 am2 respectively approximately 16 and 51 per cent of the present value on application of a cooling rate correction estimate the gb result falls to a minimum of 0 87 1022 am2 approximately 11 per cent of the present day value representing an overestimate of up to 56 per cent these values arising from a time window previously lacking in thellier estimates provide further confirmation of the existence of a pre cenozoic dipole low the vdm values derived from the overprint in the gb samples yield an average of 4 8 1022 am2 from a range between 44 and 81 per cent of the present day mean vdm and are tentatively attributed to the cretaceous normal superchron cns these results may document evidence for a previously unrecognized low dipole moment during the bulk of the cns a possibility that requires further investigation by performing palaeointensity work on igneous rocks with radiometric ages between 110 and 90 myr that carry unequivocal primary trms

seawater temperatures and carbon isotope variations in central european basins at the middle late jurassic transition late callovian early kimmeridgian abstract oxygen and carbon isotope values and elemental ratios of well preserved belemnite rostra brachiopod shells and bulk carbonates from the upper callovian lower kimmeridgian of the polish jura chain kujawy poland and swabian alb germany are investigated to reconstruct environmental conditions and perturbations in the marine carbon cycle belemnite 18o values show relatively constant temperatures ca 12 c of bottom waters in the polish jura chain basin during a major part of the late callovian middle oxfordian except for a short term cooling to ca 9 c at the callovian oxfordian transition belemnite and brachiopod 18o values show a gradual increase in temperature during the submediterranean late oxfordian the highest temperatures ca 16 c are calculated for the submediterranean oxfordian kimmeridgian transition belemnite and brachiopod mg ca and sr ca ratios are disregarded as a paleotemperature proxy because of their weak correlation with 18o values the belemnite and brachiopod isotope data confirm that the carbon isotope composition of belemnite rostra is affected by a metabolic effect which results in a depletion of belemnite calcite in the 13c isotope belemnite rostra are considered nevertheless as a valuable tracer of temporal variations in the carbon isotope composition of marine carbonates belemnite 13c data show the presence of two positive excursions in the upper callovian and the middle oxfordian in the carbon isotope record of peri tethyan carbonates the excursions are divided by a lower oxfordian interval characterized by decreased 13c values this is most likely a regional feature caused by upwelling lowest belemnite and brachiopod 13c values are observed in the lower part of the submediterranean upper oxfordian and are linked to a well mixed state of the seawater in the basins studied the carbon isotope record of bulk carbonates differs from those of belemnites and brachiopods probably because of strong variations in carbonate production in the polish jura chain basin

discussion on multiple post caledonian exhumation episodes across nw scotland revealed by apatite fission track analysis journal vol 167 675 694 the question of the former extent of jurassic strata over the scottish highlands has been debated since the nineteenth century discussion by arkell 1933 arkell s conclusion that the main part of the highlands was land during that period has been followed by subsequent palaeogeographers wills 1951 ziegler 1990 bradshaw et al 1992 although underhill partington 1993 emphasized the greater effect of doming in the north sea in delivering jurassic sediments to the adjacent basins and postulated a marine connection between the moray firth and hebridean basins along the line of the great glen apatite fission track analysis afta is a powerful method for assessing the former existence of substantial thicknesses of strata over areas where they have subsequently been stripped by uplift and erosion the paper by holford et al 2010 is a welcome application of this technique to nw scotland the authors conclude that thick jurassic rocks may once have covered nw scotland abstract and our results imply that comparable successions with the 2 5 km in the north minch basin were deposited where jurassic rocks are now missing

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

pelagic carbonate chemostratigraphy sr mg 18o 13c abstract a synthesis of the elementary sr and mg and isotopic 18 o and 13 c geochemistry of mesozoic to recent bulk pelagic carbonates suggests that the influence of late burial diagenesis is considerably less than was previously thought and that bulk carbonate geochemistry could be important for both paleoceanography and stratigraphy numerous chemical fluctuations in sr ca mg ca and 13 c 12 c ratios have occurred in the ocean during the last 140 ma the main factors responsible are 1 variations in submarine hydrothermal activity and 2 sea level fluctuations the validity of the chemostratigraphic methodology can be demonstrated by the synchroneity and the worldwide occurrence of various geochemical shifts

lithium in foraminiferal shells implications for high temperature hydrothermal circulation fluxes and oceanic crustal generation rates the lithium content of planktonic foraminiferal calcite has been determined to evaluate temporal variability of seawater li concentrations over the past 116 m y mean foraminiferal calcite lithium calcium in each time interval is no more than 16 greater nor 25 less than the mean li ca of all samples li ca minima are observed for samples from 50 60 m y and 80 90 m y with li ca about 25 lower than in adjacent time intervals at no time during the past 40 m y does mean li ca appear to be higher than that at present subject to the limitations imposed by sample coverage and diagenesis a similar conclusion holds for the past 116 m y coupled with an oceanic mass balance model for li these data suggest that 1 oceanic li concentrations and therefore high temperature hydrothermal circulation fluxes during the past 40 m y and perhaps the past 100 m y have not been more than perhaps 30 40 greater than at present for intervals any longer than a million years at most and 2 these fluxes werenot a factor of two higher 100 m y ago by inference variations in oceanic crustal generation rates over these time periods are similarly limited decreases in hydrothermal circulation fluxes and crustal generation rates or fluctuations up to 20 in these rates of a few million years duration arenot necessarily ruled out by the li ca data the lack of variability in li ca over time is not unequivocal evidence that hydrothermal fluxes have not varied because the rates of removal processes may be linked to changes in input fluxes

the applicability of trace elements in freshwater shells for paleogeochemical studies experimental studies on modern aragonitic shells of the gastropods melanopsis praemorsum and m tuberculata yielded bulk distribution coefficients of 0 31 for sr and of 0 48 for ba between the shells and their ambient waters these partition coefficients are about three times lower than their inorganic equivalents h2o leaching experiments of modern shells indicate that sr and ba dissolve congruently with no effect on the original sr and ba contents of the shells conversely the na ca mg ca and k ca ratios in the shells and in the extrapallial fluids are constant independent of variations in the habitat water chemistry this vital effect dominates the shell composition regarding the latter three ion ratios moreover dissolution experiments suggest that there is leaching of a significant fraction of na mg and k which is presumably not bound to the mineral s lattice this preferential dissolution starts before any mineralogical alteration occurs the laboratory data are supported by a sharp decrease of the na ca ratio observed in aragonitic fossils during early diagenesis in contrast with its constancy in live specimens these results clearly demonstrate that sr and ba can be used for environmental studies whereas na mg and k cannot

high resolution 40ar 39ar dating of the oldest oceanic basement basalts in the western pacific basin 1 we report new 40ar 39ar ages for the oldest pacific oceanic floor at ocean drilling program site 801c in the pigafetta basin and site 1149d close to the izu bonin subduction zone in the nadezhda basin these ages were determined by applying high resolution incremental heating experiments including 15 30 heating steps to better resolve the primary argon signal from interfering alteration signatures in these low potassium ocean crust basalts combined with previous results from pringle 1992 for site 801b and 801c we arrive at a multistage history for the formation of the pigafetta ocean crust the oldest part of the pacific plate was formed at the spreading ridges at 167 4 1 4 3 4 ma n 2 2 internal absolute error offering an important calibration point on the geological reversal timescale grts since it represents the old end of the mesozoic magnetic anomalies this mid ocean ridge basalt sequence however is overlain by more tholeiites and alkali basalts that were formed 7 3 1 5 myr later around 160 1 0 6 ma n 7 2 internal error the older age group is confirmed independently by radiolarian ages ranging from late bajocian to middle bathonian 167 173 ma bartolini and larson 2001 and by profound differences in the structural characteristics of this basement section pockalny and larson 2003 thin layers comprising hydrothermal deposits separate these sequences which in addition to the difference in isotopic age show distinct major and trace element compositions this indicates that key volcanic and hydrothermal activity took place 400 600 km away from the spreading ridges on the basis of a jurassic 66 km myr half spreading rate in the pacific it remains unclear if these processes were active continuously after the initial formation of the pacific oceanic crust but all our observations seem to point to an episodic history site 1149d gives another important calibration point on the grts of 127 0 1 5 3 6 ma n 1 2 internal absolute error for anomaly m12 that is slightly younger when compared to current timescale compilations 134 2 2 1 ma gradstein et al 1995 this might suggest that the dated basalt from site 1149d does not represent the age of the ocean crust formed at its ridge axis it may also be part of the early cretaceous intraplate events that have produced dolerite sills in the pacific crust at sites 800 and 802 around 114 126 ma

numerical paleoceanographic study of the early jurassic transcontinental laurasian seaway the forces governing marine circulation of a meridional transcontinental seaway is explored with the princeton ocean model the jurassic laurasian seaway which connected the low latitude tethys ocean with the arctic sea is modeled quantitatively the global ocean is found to have a profound influence on seaway dynamics a north south density difference and hence sea level difference of the global ocean was probably the main factor in forcing the seaway flow when the tethys waters were the denser water the net seaway flow was southward and conversely it was northward for denser arctic waters marine bioprovincial boundaries and sediment data indicate that the seaway probably was dominated by boreal faunal groups and reduced salinities several times in the jurassic the model results suggest that this can be explained by southward flowing seaway currents which may have been related to an oceanic thermohaline circulation where no northern high latitude deep convection occurred

apatite for destruction isotopic and geochemical analyses of bioapatites and sediments from the upper devonian escuminac formation miguasha quebec abstract the paleoenvironmental context and diagenetic history of the middle frasnian escuminac formation were investigated through geochemical rare earth elements and isotopic rb sr nd sm analyses of fossil fish material and sediments samples of sediments and bioapatite were collected from the base to the top of the escuminac formation strontium isotope ratios 87 sr 86 sr for bioapatites vary from 0 70804 to 0 70845 and overlap with frasnian seawater sr isotope compositions though most of the biogenic apatites analyzed show a variable drift from marine values toward a more radiogenic continental signature this trend is possibly the result of post mortem sr exchange between fossils and a fluid isotopically distinct from the waters in which they developed all bioapatites are heavily enriched in rare earth elements ree and display a shale normalized pattern that shows heavy ree hree depletion and a slight middle ree mree enrichment the e nd t values of the sediments range from 4 8 to 6 4 and are consistent with a sedimentary provenance derived from an appalachian source for the escuminac formation in contrast more radiogenic e nd t values ranging from 2 6 to 4 6 were obtained for the bioapatites the discrepancy between sediments and fossil material e nd t implies the presence of a second diagenetic nd reservoir for the escuminac bioapatites we propose that this reservoir reflects in part seawater the similarity between the nd isotope compositions of the escuminac fossils and late devonian conodonts from poland argues for a close connection between waters of the devonian rheic ocean and the escuminac formation collector basin

the dagpazari carbonate platform mut basin southern turkey facies and environmental reconstruction of a coral reef system during the middle miocene climatic optimum abstract plate tectonics and climate change have deeply influenced the evolution of coral reef systems of the mediterranean during the miocene most of this information is based on studies of coral reefs from the western and central sectors of the mediterranean this study reports facies analyses sr isotope stratigraphy and environmental reconstructions of the dagpazari coral reef system located within the mut basin in southern turkey stratigraphic correlations and sr isotope ratios on several oyster shells date the dagpazari reef to the early langhian ten different facies have been recognized and their arrangement has led to the identification of two main depositional units interpretation of the biotic associations indicates that the dagpazari depositional system developed constantly within the euphotic zone the reef framework was mainly built by massive faviid and poritid zooxanthellate corals whereas loose grain sediments were essentially produced by halimeda coralline red algae or influenced by the presence of seagrass colonizations this study highlights for the first time the great importance of halimeda as sediment producer in the eastern mediterranean coral reef systems this role is related to the common occurrence of halimeda plates within almost all the reef facies but especially to the presence of large in situ bioherms dominated by the algal segments dagpazari langhian halimeda bioherms also represent the oldest of these structures so far recorded in the fossil record the development of the dagpazari platform was mainly controlled by eustatic fluctuations of the sea level and by the morphology of the antecedent substrate in particular the occurrence of a pre existent topographic high promoted the constant presence of shallow water environments throughout the depositional history of the reef system with the production of euphotic carbonates both landward and basinward and the consequent formation of a small elliptical platform 87sr 86sr ages place the dagpazari reef system exactly within the middle miocene climatic optimum phase the most recent warm phase of the earth this suggests that zooxanthellate corals were able to exert their reef building capacity in shallow water settings even during periods of global warming thus being not exclusively an adaptation to cooling climates as proposed in the recent debates

improvements in procedure and paleointensity selection criteria picrit 03 for thellier and thellier determinations application to hawaiian basaltic long cores abstract in this paper we first describe the paleointensity furnaces and the procedures specifically designed to minimize oxidation of the samples during thellier and thellier paleointensity experiments routinely used at gif we also propose some improvements to the set of criteria commonly used to select the results of the thellier experiments in order to further increase the reliability of paleointensity determination finally to be included in databases the new set of paleointensity criteria picrit 03 paleointensity criteria in 2003 is discussed and the results obtained from two long hawaiian basaltic cores the scientific observation hole 4 soh 4 and the hawaiian scientific drilling project 1 hsdp1 are used to illustrate its effectiveness some of the results are re evaluated and a new composite record of absolute paleointensity and inclination spanning 420 kyr is presented the inclination values obtained from the two cores combined support the hypothesis of persistent shallow inclinations at hawaii in intensity the upper 100 kyr are covered by the data from soh 4 with 309 reliable determinations out of 766 examined obtained from 143 units which belong to the kilauea volcano at the top of this core the 341 reliable data covering the 100 420 kyr interval are from 149 units of core hsdp1 belonging to the mauna kea volcano the interval 320 to 420 kyr is particularly detailed because of high extrusion rate of the volcano the use of more stringent criteria decreases the number of determinations considered as reliable in previous publications but it improves their accuracy and robustness

widespread basement erosion during the late paleocene early eocene in the laramide rocky mountains inferred from 87sr 86sr ratios of freshwater bivalve fossils reconstruction of the timing and pattern of exhumation of basement involved uplifts during the laramide is essential to the understanding of the mechanisms of crustal shortening and thickening in the region we use reconstructions of the 87 sr 86 sr ratios of late cretaceous early cenozoic river water from fossil shells in six basins of the rocky mountains contextualized by modern river water sr chemistry studies to trace the erosion of precambrian basement cores in the laramide ranges the 87 sr 86 sr ratios and sr concentration of modern river water in the rocky mountains are controlled by river bedrock lithology weathering of precambrian silicate rocks in the cores of laramide ranges produces high 87 sr 86 sr ratios in highland rivers weathering of paleozoic and mesozoic carbonates along the basin margins reduces the 87 sr 86 sr ratios and increases sr concentration of rivers as they flow basinward lowland rivers that have headwaters in precambrian basement mostly have 87 sr 86 sr ratios 0 711 whereas rivers confined to or with very long reaches in basins have 87 sr 86 sr ratios between 0 709 and 0 711 river water 18 o values do not change in response to changes in catchment elevation our results from fossil shells show that carbonate weathering dominated the river water sr chemistry in the alberta foreland williston and crazy mountains basins and that proterozoic low grade metamorphic carbonates in the belt purcell supergroup were not exposed in the canadian rocky mountains during late cretaceous early paleocene time silicate weathering influenced the sr chemistry of surface waters in the powder river basin during the late paleocene and the washakie basin during the early eocene suggesting precambrian silicate basement rock was extensively exhumed and eroded the observation that precambrian basement was eroded earlier around the powder river basin than around the washakie basin is consistent with a previous study that suggests laramide ranges in northeast wyoming reached high elevation earlier than the ranges adjacent to the sevier thrust belt widespread basement erosion in late paleocene early eocene time was controlled by tectonic exhumation and may have been intensified by the wet and warm global climate

climate controlled fabric destructive reflux dolomitization and stabilization via marine and synorogenic mixed fluids an example from a large mesozoic calcite sea platform croatia the jurassic cretaceous dolomites adriatic platform croatia resulted from climate influenced post depositional reflux dolomitization as opposed to synsedimentary peritidal and deeper burial dolomitization and subsequent stabilization within a mesozoic calcite sea isolated platform the dolomites are stratiform 10 to 200 m thick fabric destructive 20 to over 500 m crystals nonluminescent and zoned with respect to ca bulk dolomites have low mn 10 to 30 ppm moderate sr 60 to over 200 ppm positive 13c and 18o values only moderate ordering 0 25 to 0 6 and single phase fluid inclusions temperatures 3 vpdb and sr 100 ppm composes most jurassic and 40 of cretaceous dolomites making up turbid dolomite cores and initial clear dolomite rims a first generation of low ca dolomite lcd 1 50 to 53 mol ca 18o 1 to 3 vpdb 100 180 ppm sr forms cement and variably replaces stabilizes earlier hcd cores hcd and lcd 1 formed in refluxing marine dominated pore waters under semi arid climate 55 mol phases a second generation of much younger low ca dolomite lcd 2 fracture associated more negative 18o from 1 4 to 1 vpdb sr 100 ppm enriched in radiogenic 87sr overgrows and variably replaces earlier cretaceous dolomites it formed during eocene oligocene deformation and uplift to 1 km burial depths 50 c from synorogenic mixed marine meteoric pore fluids circulating via faults fractures and local permeable zones porosity loss by dolomite cementation coupled with localized rapid cenozoic uplift variably arrested stabilization to lcd

calcite raft geochemistry as a hydrological proxy for holocene aquifer conditions in hoyo negro and ich balam sac actun cave system quintana roo mexico abstract two cores from calcite rafts deposits located in cenote ich balam and hoyo negro were dated and analyzed for 87sr 86sr 18o 13c sr ca and cl ca the geochemical records show changing aquifer salinity spanning the last 8 5 cal kyrs bp and interrelationships with holocene climate trends wet and dry periods during the wet mid holocene the salinity of the meteoric water mass wm at 7 8 8 3 cal kyrs bp was relatively high at 1 5 2 7 ppt and then became less saline 1 0 1 5 ppt during the last 7000 yrs as climate became progressively drier high salinity of the meteoric wm during the wet mid holocene is attributed to increased turbulent mixing between the meteoric and underlying marine wm increased precipitation in terms of amount frequency and intensity e g hurricanes causes higher flow of meteoric water towards the coast and mixing at the halocline a phenomenon recorded with recent instrumental monitoring of the aquifer conversely during dry periods reduced precipitation and flow in the meteoric wm would result in lower salinity karst properties and holocene sea level rise also seem to have an effect on the aquifer when the regionally extensive network of shallow cave passages 10 12 m water depth are flooded at 8000 cal yrs bp there is a rapid shift in salinity this study demonstrates that calcite raft deposits can be used as paleo environmental recorders documenting the effects of sea level and climate change on aquifer condition

intensity of the earth s magnetic field evidence for a mesozoic dipole low the variation of the strength of the earth s magnetic field throughout geological time is known only poorly large uncertainties spoil indirect paleointensity determinations based on magnetic anomaly amplitude or remanence of sedimentary rocks even when paleointensity data are obtained from direct thermomagnetic studies of magmatic units fundamental problems related to the actual nature of the primary remanence and to the effects of different cooling rates may result in erroneous determinations these uncertainties combined with well known experimental difficulties can explain the large scatter in paleointensity data reported in most previous review papers because experimental difficulties are more rigourously dealt with using the thellier method which also offers some opportunities to minimize some fundamental uncertainties we carried out a compilation of all triassic and younger paleointensity determinations made using this method this selected data set indicates the occurrence of large long term changes of the geomagnetic dipole strength with time the average dipole strength seems to have been approximately constant since late cretaceous time but a dipole strength only one third of the cenozoic value prevailed during most of mesozoic time following a period of larger strength ending possibly during early jurassic times the mesozoic dipole low may be correlated with a cessation of relative motion between the geomagnetic axis and the mantle the terrestrial dynamo seems therefore to exhibit different long term stable states which are probably controlled by the thermal structure in the lowermost mantle

sr isotope stratigraphy of the upper jurassic of central portugal lusitanian basin based on oyster shells strontium isotope stratigraphy was performed on oyster shells from the late jurassic of the lusitanian basin central portugal this represents the first approach to obtain numerical ages for these strata the new chronostratigraphic data provide a more precise age determination of several units after a basin wide hiatus sedimentation in the late jurassic is proven in the cabo mondego and cabacos formations to resume as early as the middle oxfordian the alcobaca formation can be placed in the latest late oxfordian to late kimmeridgian while data from the upper part of the abadia formation indicate an early to late kimmeridgian age the farta pao formation ranges from the latest kimmeridgian to the latest tithonian the largely synchronous sobral arranho i and arranho ii members are overlain by the late early to late tithonian freixial member the brief local carbonate incursion of the arranho i member marks the kimmeridgian tithonian boundary oysters are shown once more to be suitable for strontium isotope studies their calcitic shells are often unaffected by diagenesis in particular for marginal marine jurassic and cretaceous strata where belemnites are usually absent oysters may serve as a valuable tool for isotope stratigraphy

87sr 86sr and sr ca investigation of jurassic mollusks from scotland implications for paleosalinities and the sr ca ratio of seawater measurements of 87 sr 86 sr sr ca 18 o and 13 c were performed on molluskan fos sils from the great estuarine group scot land to deduce paleosalinity patterns and hydrodynamic environments in this classic jurassic marginal marine succession fos sils are found as winnowed accumulations in shell beds that bear low diversity assem blages consistent with deposition in a la goonal paleoenvironment previous studies have concluded that estuarine mixing of seawater and freshwater took place based on correlated trends in 18 o and 13 c most notably in the mussel praemytilus strathair densis from the kildonnan member this interpretation is shown to be incorrect based on 87 sr o 13 c and the sr ca ratio this is consistent with a lagoonal hydrology controlled more by seasonal changes in evaporation precipitation and flooding than by direct inputs of seawater or river ine water transported over large distances lagoons containing the oyster praeexogyra in the duntulm formation have similar in ferred o and c isotope characteristics but based on their 87 sr 86 sr ratios they have a higher proportion of seawater than the praemytilus lagoons of the kildonnan member the data thus far suggest that many of the lagoonal environments in the great es tuarine group were nearly hydrologically closed at least over the interval represent ing the molluskan invasion of these habi tats rendering o and c isotopes unreliable proxies of paleosalinity because strontium isotopes are not directly affected by evap oration of the lagoons knowledge of marine and freshwater 87 sr 86 sr ratios along with estimates of sr concentration are used to calculate the proportion of seawater in the brackish water mixture unio is nearly al ways the most radiogenic taxon compared to other genera in closely adjacent sedimen tary strata confirming its freshwater affin ity the purported marine brackish bivalve tancredia yields a low paleosalinity of 4 only slightly more saline than unio and praemytilus at 1 3 the oyster praeexo gyra hebridica yields paleosalinities between 2 and 26 attesting to the wide salinity tolerance of this species thus far only neomiodon from the dun tulm and staffin bay formations show co variant relationships between 87 sr 86 sr and ca sr ratio that can be reconciled with a dynamic response to seawater freshwater mixing the slopes of these trends converge at 0 7068 which is close to the early cal lovian seawater composition of 0 7069 us ing values of dsr from modern aragonite se creting mollusks the sr ca ratio of middle jurassic seawater is constrained from the best correlated mixing line to be 5 4 0 6 millimoles mole in contrast sr ca ratios in the great estuarine group lagoons and continental watershed range from 5 4 to 19 0 these are much higher than the av erage value of 2 3 for modern rivers but typical of sr ca ratios in rivers draining arid climate regions the semirestricted hy drodynamic regime inferred from the high seawater like 18 o values and high but uni form sr ca ratios in many of the great es tuarine group mollusks is consistent with a seasonally dry mediterranean style climate for the middle jurassic of britain

strontium isotopic variations in jurassic and cretaceous seawater a high resolution seawater strontium isotope curve has been generated through the analysis of well dated and well preserved belemnites and oysters from the middle and upper jurassic and the lower cretaceous of great britain analysis of fe and mn concentrations in these fossils has yielded criteria for eliminating samples that are diagenetically altered the strontium isotope curve remains relatively flat through the aalenian and early bajocian rapidly descends through the late bajocian and bathonian and reaches a minimum in the callovian and oxfordian it then begins a rapid increase in the kimmeridgian and portlandian that continues through much of the early cretaceous the curve levels off in the barremian suddenly dips downwards in the aptian and recovers gradually through the albian the strontium isotopic variations are sufficiently large and the data are presented with sufficient stratigraphic detail to allow precise correlation to the classic ammonite zones and lithologic sections of great britain using the techniques of strontium isotope stratigraphy model results indicate that much of the variation in seawater 87sr86sr between 120 and 40 ma can be explained by changing the intensity of mid ocean ridge hydrothermal fluxes proportionally to estimated mid ocean ridge crustal generation rates it is also possible that the variations during the rest of the mesozoic and the permian are primarily reflections of changing hydrothermal inputs the model results have several important implications first they provide an example in which the variations in the strontium isotope curve are not necessarily driven by changes in fluvial inputs second they suggest that from at least the aptian through the eocene variations in continental weathering were minimal this heightens the importance of the rapid rise in seawater 87sr86sr beginning 40 ma as a significant transition to an extended period of increasing fluvial 87sr fluxes continuing to the present finally the results suggest that several documented short term excursions towards lower 87sr86sr in the latest triassic pliensbachian toarcian callovian oxfordian aptian albian and cenomanian turonian are interpretable as pulses of seafloor hydrothermal activity if so the strontium isotope record offers a means of constraining the timing duration and magnitude of known or proposed hydrothermal events in the geological record

vertical gps ground motion rates in the euro mediterranean region new evidence of velocity gradients at different spatial scales along the nubia eurasia plate boundary we use 2 5 to 14 years long position time series from 800 continuous global positioning system gps stations to study vertical deformation rates in the euro mediterranean region we estimate and remove common mode errors in position time series using a principal component analysis obtaining a significant gain in the signal to noise ratio of the displacements data following the results of a maximum likelihood estimation analysis which gives a mean spectral index 0 7 we adopt a power law white noise stochastic model in estimating the final vertical rates and find 95 of the velocities within 2 mm yr with uncertainties from filtered time series 40 smaller than from the unfiltered ones we highlight the presence of statistically significant velocity gradients where the stations density is higher we find undulations of the vertical velocity field at different spatial scales both in tectonically active regions like eastern alps apennines and eastern mediterranean and in regions characterized by a low or negligible tectonic activity like central iberia and western alps a correlation between smooth vertical velocities and topographic features is apparent in many sectors of the study area glacial isostatic adjustment and weathering processes do not completely explain the measured rates and a combination of active tectonics and deep seated geodynamic processes must be invoked excluding areas where localized processes are likely or where subduction processes may be active mantle dynamics is the most likely process but regional mantle modeling is required for a better understanding

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

ca isotope study of ordovician dolomite limestone and anhydrite in the williston basin implications for subsurface dolomitization and local ca cycling abstract a difference of 0 61 is reported between dolomite 1 66 and its precursor limestone 1 05 in the yeoman formation red river equivalent of the williston basin southeastern saskatchewan the significance of the large difference found and the preference for light isotope enrichment in the dolomite is evaluated with assistance from 87 sr 86 sr ratios and dolomitization models previously proposed for the studied rocks in particular i explore the possibility that 44 ca values in dolomite reflect the 44 ca values of the dolomitizing fluids without any correction for mineral fluid fractionation this hypothesis is based on recent studies showing negligible isotopic fractionation between carbonates and ca 2 bearing waters at very low precipitation rates fantle and depaolo 2007 jacobson and holmden 2008 if correct calcium isotopes hold promise as a tool for discriminating among numerous hydrological models of dolomite formation as a case in point the 44 ca value of the yeoman dolomite 1 66 is too low to reflect ca derived from the following sources 1 the original limestone 1 05 2 overlying beds of anhydrite 1 28 or 3 evaporated seawater 0 25 paleozoic carbonates ranging as low as 1 7 appear to be the lightest source of ca in the basin succession suggesting that the mg containing dolomitizing fluid was a connate water with a previous history of water rock interactions with paleozoic carbonates possibly involving earlier episodes of dolomitization and light ca release into migrating basinal fluids the relatively high seawater 44 ca values inferred from measurements of yeoman limestone and lake alma anhydrite suggest that seawater in the williston basin 450 ma was 0 22 0 46 higher in 44 ca than the contemporaneous ocean based on globally distributed brachiopods farkas et al 2007 this finding suggests that 44 ca values preserved in the deposits of epeiric seas may bias the 44 ca reconstruction of the ocean secular record if local ca cycling effects are not taken into account equations describing the isotope balance of ca in an epeiric sea indicate that seawater 44 ca values may be higher lower or equal to the 44 ca value of the ocean depending on the sizes of local scale ca deposition and weathering fluxes in relation to seawater ca exchange fluxes

the sedimentary facies of a late bathonian regressive episode the kilmaluag and skudiburgh formations of the great estuarine group inner hebrides scotland the kilmaluag and skudiburgh formations of the bathonian great estuarine group represent a unique palaeoenvironment within the british jurassic the kilmaluag formation is divided into two distinctive facies the clastic facies of n skye comprises calcareous mudstones and shales with subordinate sandstones and argillaceous limestones the depositional setting was one of shallow ephemeral lagoons closed from the sea sublittoral lagoon mudflat and channel environments are identified and fossil faunas indicate low salinity the argillaceous limestone facies of southern skye eigg and muck formed in a similar depositional setting although sandstones are not present alternations of carbonate rocks some dolomitic and calcareous shales probably reflect palaeoclimatic fluctuations between humid and arid periods the overlying skudiburgh formation is interpreted as being alluvial floodplain channel and overbank deposits are identified by the presence of mottled mudstones sands and lensoidal silts syndepositional carbonate nodules are interpreted as calcrete which occasionally coalesced to form extensive hardpan calcrete horizons the vertical facies sequence reflects a late bathonian regression the coastal plain terrestrial environments of the skudiburgh formation were transgressed during the callovian stage an event which ended paralic deposition in the hebridean jurassic

iaga paleointensity database distribution and quality of the data set abstract the aim of this paper is to provide details about the design of the paleointensity database and focus on the distribution of the available data set version 2003 of the paleointensity database comprises 3128 data from 215 references only absolute paleointensity determinations from igneous rocks and baked contacts are considered regardless which method of paleointensity determination was used the entries in the database correspond to cooling units all polarities as well as all units are considered normal reverse or transitional the earth s magnetic field is the only surface trace of the working of the geodynamo and is therefore a very important tool for our understanding of the earth s deep interior especially its variation with geologic time however to study the long term variation of the paleomagnetic field non dipole effects have to be removed in recent years the production rate of paleointensity data has strongly increased and the most reliable methods were more frequently used however the present data set still has an important temporal bias with 35 of the rocks having ages less than 1 ma as well as a strong geographic bias towards the northern hemisphere especially north america and europe for most time intervals secular variation cannot be averaged out neither temporally nor spatially therefore interpretation of the averaged field is very limited and is avoided here for the future a harmonization or a combination of all iaga databases would be desirable furthermore the input of raw data at the specimen level would be useful in order to allow reinterpretation of data with more developed and sophisticated methods based on our increasing understanding of rock magnetism finally new reliable data are very much needed

limited latitudinal mantle plume motion for the louisville hotspot hotspots that form above upwelling plumes of hot material from the deep mantle typically leave narrow trails of volcanic seamounts as a tectonic plate moves over their location these seamount trails are excellent recorders of earth s deep processes and allow us to untangle ancient mantle plume motions during ascent it is likely that mantle plumes are pushed away from their vertical upwelling trajectories by mantle convection forces it has been proposed that a large scale lateral displacement termed the mantle wind existed in the pacific between about 80 and 50 million years ago and shifted the hawaiian mantle plume southwards by about 15 of latitude here we use 40ar 39ar age dating and palaeomagnetic inclination data from four seamounts associated with the louisville hotspot in the south pacific ocean to show that this hotspot has been relatively stable in terms of its location specifically the louisville hotspot the southern hemisphere counterpart of hawai i has remained within 3 5 of its present day latitude of about 51 s between 70 and 50 million years ago although we cannot exclude a more significant southward motion before that time we suggest that the louisville and hawaiian hotspots are moving independently and not as part of a large scale mantle wind in the pacific

short term environmental change in a jurassic lagoon deduced from geochemical trends in aragonite bivalve shells the bathonian age inverbrora member of the brora coal formation northern scotland was deposited in a predominantly fresh water coastal lagoon setting however two prominent shell beds within the mostly argillaceous succession have been interpreted as resulting from temporary inundation of marine water and establishment of brackish conditions the ensuing lagoon hydrology and paleoenvironment were investigated by measuring stable isotopic 18o and 13c and trace element mg sr mn ba variations within five exceptionally well preserved aragonite shells of the bivalve isognomon murchisoni transects were sampled across the visible growth banding with a resolution of 0 25 0 15 mm for stable isotopes and 0 05 mm for trace elements oxygen and carbon isotope data define a broadly covariant trend 18o between 0 4 and 4 8 peedee belemnite pdb 13c between 2 2 and 0 7 pdb that supports a variably brackish water setting with slight seasonal evaporation absolute trace element values vary from shell to shell but show consistent patterns of covariation profiles of mg ca across shell layers display multiple sharp episodic minima that are coincident with peaks in sr ca and ba ca this is interpreted as documenting inundation of the restricted brackish water lagoon by relatively cooler seawater leading to a temporary increase in metabolic activity of the bivalves less frequent minima in mg ca sr ca 18o and 13c record fresh water influx and dramatic salinity reduction in the lagoon bivalve metabolic efficiency was decreased and in some cases breaks in shell growth occurred this study shows that in hydrodynamically complex settings trace element variation in bivalve shells can provide a detailed record of short term environmental change

diagenesis and origin of calcite cement in the flemish pass basin sandstone reservoir upper jurassic implications for porosity development abstract the flemish pass basin is a deep water basin located offshore on the continental passive margin of the grand banks eastern newfoundland which is currently a hydrocarbon exploration target the current study investigates the petrographic characteristics and origin of carbonate cements in the ti 3 member a primary clastic reservoir interval of the bodhran formation upper jurassic in the flemish pass basin the ti 3 sandstones with average q 86 0 f 3 1 r 10 9 contain various diagenetic minerals including calcite pyrite quartz overgrowth dolomite and siderite based on the volume of calcite cement the investigated sandstones can be classified into 1 calcite cemented intervals 20 calcite and 2 poorly calcite cemented intervals porous petrographic analysis shows that the dominant cement is intergranular poikilotopic 300 500 m calcite which stared to form extensively at early diagenesis the precipitation of calcite occured after feldspar leaching and was followed by corrosion of quartz grains intergranular calcite cement hosts all liquid inclusions mainly in the crystal core but rare primary two phase liquid and vapor fluid inclusions in the rims with mean homogenization temperature t h of 70 2 4 9 c and salinity estimates of 8 8 1 2 eq wt nacl the mean 18 o and 13 c isotopic compositions of the intergranular calcite are 8 3 1 2 vpdb and 3 0 1 3 vpdb respectively whereas fracture filling calcite has more depleted 18 o but similar 13 c values the shale normalized rare earth element ree sn patterns of calcite are generally parallel and exhibit slightly negative ce anomalies and positive eu anomalies fluid inclusion gas ratios co 2 ch 4 and n 2 ar of calcite cement further confirms that diagenetic fluids originated from modified seawater combined evidence from petrographic microthermometric and geochemical analyses suggest that 1 the intergranular calcite cement precipitated from diagenetic fluids of mixed marine and meteoric riverine waters in suboxic conditions 2 the cement was sourced from the oxidation of organic matters and the dissolution of biogenic marine carbonates within sandstone beds or adjacent silty mudstones and 3 the late phases of the intergranular and fracture filling calcite cements were deposited from hot circulated basinal fluids calcite cementation acts as a main controlling factor on the reservoir quality in the flemish pass reservoir sandstones over 75 of initial porosity was lost due to the early calcite cementation the development of secondary porosity mostly enlarged moldic pores and throats by later calcite dissolution due to maturation of organic matters e g hydrocarbon and coals was the key process in improving the reservoir quality

a 4300 year strontium isotope record of estuarine paleosalinity in san francisco bay california abstract strontium isotopic compositions of carbonate mollusk shells from estuarine sediments cored beneath san francisco bay are used to derive a record of mean annual salinity and average freshwater inflow to the estuary for intervals during the past 4300 yrs the large difference in the 87sr 86sr ratio between seawater 0 7092 and the average freshwater entering the estuary 0 7065 produces a correlation between 87sr 86sr and salinity in bay waters that can be detected with high precision measurements paleosalinity is inferred from the 87sr 86sr ratio measured in fossil carbonate shells of bivalves preserved in the sediment because salinity in san francisco bay is primarily controlled by the freshwater inflow from the sacramento and san joaquin rivers the paleosalinity record can be converted to a paleodischarge record using a transfer function derived from historical data salinity data are referenced to modern values estimated for the estuary after correcting for the lower discharge caused by diversion since 1850 a d data are presented from richardson bay located near the estuary mouth modern mear arrival salinity mas of ca 24 and from san pablo bay located about 30 km upstream modern mas of ca 18 20 for richardson bay the data cover the periods 0 600 yrs b p and 2200 4300 yrs b p based on radiocarbon dating for san pablo bay the periods 0 130 yrs b p and 2500 2800 yrs b p are represented the richardson bay data indicate extended periods of low salinity relative to modern indicating higher freshwater inflow at ca 80 220 310 440 500 3100 3400 and 4300 yrs ago the data indicate high salinity relative to modern hence lower freshwater inflow at about 40 140 210 270 2100 and 3450 3700 yrs b p for san pablo bay where salinity resolution is better salinity was lower than modern during the period at ca 50 and 2550 2650 yrs b p and higher than modern at ca 90 110 155 and 2510 2530 yrs b p the data suggest that mean annual discharge to san francisco bay typically varies between values that are below the modern value 600 m3 s and values 2 to 3 times as high the average paleosalinity is typically substantially lower than the modern values the 4300 yr average freshwater inflow is estimated to be 1200 200 m3 s the record indicates that quasi cyclic variations in mean annual discharge occur naturally with a period of about 200 yrs or less

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

cooling rate effects on paleointensity estimates in submarine basaltic glass and implications for dating young flows 1 cooling rate effects on the intensity of thermoremanent magnetization trm have been well documented in ceramics in that case laboratory cooling is generally more rapid than the initial cooling leading to an overestimate of the paleofield by 5 10 in thellier type paleointensity experiments the reverse scenario however has never been tested we examine the effects of cooling rate on paleointensity estimates from rapidly quenched submarine basaltic glass sbg samples from 13 sites at 17 30 18 30 s on the east pacific rise absolute cooling rates determined by relaxation geospeedometry at five of these sites range from 10 to 330 c min 1 at the glass transition 650 c over the dominant range of remanence blocking temperatures 200 400 c the natural cooling rates are approximately equal to or slightly slower than the laboratory cooling rates during the thellier experiment these results suggest that while the cooling rate effect might introduce some within site scatter it should not result in a systematic bias in paleointensity from sbg paleointensity estimates from the 15 sites range from 29 to 59 t with an average standard error of 1 t comparison with models of geomagnetic field intensity variations at the site indicate the youngest group of samples is very recent indistinguishable from present day and the oldest is at least 500 and probably several thousand years old these age estimates are consistent with available radiometric ages and geologic observations

possible links between long term geomagnetic variations and whole mantle convection processes the earth s internal magnetic field varies on timescales of months to billions of years the field is generated by convection in the liquid outer core which in turn is influenced by the heat flowing from the core into the base of the overlying mantle much of the magnetic field s variation is thought to be stochastic but over very long timescales this variability may be related to changes in heat flow associated with mantle convection processes over the past 500 myr correlations between palaeomagnetic behaviour and surface processes were particularly striking during the middle to late mesozoic era beginning about 180 myr ago simulations of the geodynamo suggest that transitions from periods of rapid polarity reversals to periods of prolonged stability such as occurred between the middle jurassic and middle cretaceous periods may have been triggered by a decrease in core mantle boundary heat flow either globally or in equatorial regions this decrease in heat flow could have been linked to reduced mantle plume head production at the core mantle boundary an episode of true polar wander or a combination of the two

geomagnetic field intensity in early jurassic investigation of the newark supergroup eastern north america abstract a collection of 220 samples from early jurassic newark supergroup volcanic units watchung talcott holyoke hampden and deerfield basalts and intrusive units manitook and palisades sills was studied with the aim of testing the previously suggested occurrence of a low average dipole moment of the earth s magnetic field some 200 ma ago after viscosity tests alternating field demagnetization of all samples and thermal variation studies of saturation magnetization of 74 selected samples we find that only 8 of the entire collection was a priori suitable for paleointensity experiments using the original thellier and thellier method we have obtained 17 reliable paleointensity values of average quality from the palisades sill and the holyoke basalt although these two units recorded substantially different field directions they provide similar estimates of the virtual dipole moment 9 4 1 2 and 11 3 2 2 10 22 a m 2 respectively these values are within the range of secular variation of the recent geomagnetic field

depletion of 13c in seawater σc02 on modern carbonate platforms significance for the carbon isotopic record of carbonates seawater co2 from modern carbonate platforms bahama banks and florida is depleted in 13c by as much as 4 relative to open ocean water depletion in 13c is caused by isotopically light co2 input from respiration of marine and terrestrial organic matter during water mass residence on the bank as such depletion in 13c is related to changes in water chemistry driven by evaporation freshwater discharge and caco3 withdrawal deviation of modern platform seawater 13c values away from those of surface seawater suggests that 13c values of ancient cratonic carbonate must be cautiously interpreted initial depositional environment as well as alteration during diagenesis must be considered in extracting valid secular trends for oceanic 13c variation

oxygen and strontium isotopes as provenance indicators of fish at archaeological sites the case study of sagalassos sw turkey abstract in this paper we investigate the potential use of oxygen and strontium isotope ratios 18 o p and 87 sr 86 sr measured in archaeological fish enamel as provenance indicators 18 o p and 87 sr 86 sr were measured in a suite of archaeological carp remains recovered from the anatolian townsite of sagalassos dated to the early byzantine period ad 450 650 and compared to that of modern fish river and lake waters from the anatolian region we used sequential leaches in weak acetic acid to remove diagenetic sr from fossil tooth enamel monitoring the effectiveness of this approach by measuring the sr ca ratios of the leachates via an isotope dilution thermal ionization mass spectrometry method id tims 18 o p values mostly excluded a riverine origin 87 sr 86 sr ratios of one fish overlapped with the 87 sr 86 sr signatures of two lakes in the anatolian region and at least one lake golcuk could be removed as a candidate owing to a very distinctive 87 sr 86 sr signature not found in any of the fish remains most of the tooth samples analyzed could not be assigned a precise geographical origin since the 87 sr 86 sr ratios measured in enamel did not match that of any of the local lakes selected as potential origin this result suggests that carp may have originated from lakes that have not yet been sampled although this conclusion is not supported by other archaeological evidence alternatively the lack of correspondence between lakes and fish sr isotope ratios highlights several possible sources of uncertainties including spatial heterogeneity in 87 sr 86 sr ratio within a lake the contribution of dietary strontium to the 87 sr 86 sr ratio of fish tooth enamel and post mortem alteration of the tooth sr isotope signal during fossilization in spite of the high precision of the strontium isotope analyses and the wide range of variation in the surface waters of the anatolian lakes and rivers this method may remain limited to distinguishing between lakes situated in regions of bedrock of very distinct age and geology until these sources of uncertainty are more fully investigated

magnetic hysteresis monitoring of cretaceous submarine basaltic glass during thellier paleointensity experiments evidence for alteration and attendant low field bias on the basis of studies of holocene samples submarine basaltic glass sbg is thought to be an ideal paleointensity recorder because it contains unaltered single domain magnetic inclusions that yield thellier paleointensity data of exceptional quality to be useful as a recorder of the long term geomagnetic field older sbg must retain these optimal properties here we examine this issue through rock magnetic and transmission electron microscope tem analyses of cretaceous sbg recovered at ocean drilling program site 1203 northwestern pacific ocean these sbg samples have very low natural remanent magnetization intensities nrm 2 g and tem analyses indicate a correspondingly low concentration of crystalline inclusions thellier experiments on samples with the strongest nrm intensity 5 10 11 am 2 show a rapid acquisition of thermoremanent magnetization trm with respect to nrm demagnetization taken at face value this behavior implies magnetization in a very weak 17 t ambient field but monitoring of magnetic hysteresis properties during the thellier experiments on subsamples of the sbg samples used for paleointensity determinations indicates systematic variations in values over the same temperature range where the rapid trm acquisition is observed a similar change in properties during heating is observed on monitor sbg specimens using low temperature data with progressive heatings the verwey transition becomes more distinct we suggest that these experimental data record the partial melting and neocrystallization of magnetic grains in sbg during the thermal treatments required by the thellier method resulting in paleointensity values biased to low values we further propose that this process is pronounced in cretaceous and jurassic sbg relative to holocene sbg because devitrification on geologic time scales i e tens of millions of years lowers the transition temperature at which the neocrystallization can commence magnetic hysteresis monitoring may provide a straightforward means of detecting the formation of new magnetic inclusions in sbg during thellier experiments

strontium isotopes in early jurassic seawater abstract the analysis of well preserved well dated belemnites and oysters from the jurassic of great britain has resulted in a well constrained detailed seawater strontium isotope curve for the early jurassic the preservation of fossil low mg calcite was monitored using mn fe 13 c and 18 o iron was the most useful indicator with about 75 of the samples containing more than 150 ppm fe showing 87 sr 86 sr ratios elevated relative to adjacent points on the curve high mn concentrations less often correlated with elevated 87 sr 86 sr ratios however low mn concentrations 87 sr 86 sr 13 c and 18 o proved to be insensitive to diagenesis as it affects 87 sr 86 sr the principal features of the strontium isotope curve include a rise to about 0 70772 in the latest triassic and earliest jurassic hettangian from the hettangian the curve begins a roughly linear descent through the sinemurian and pliensbachian following a small levelling off and increase in the late pliensbachian the curve falls rapidly to its early jurassic minimum of 0 70706 it then gently increases through the toarcian until the falciferum zone where it shows an apparently abrupt increase to 0 70719 before continuing its slow increase to 0 70728 in the aalenian bajocian middle jurassic this reversal of the downwards trend established in the sinemurian and pliensbachian had not been previously identified the sinemurian and pliensbachian section of the curve potentially allows correlation and dating to within 1 or 2 ammonite subzones 0 5 to 1 ma

the fidelity of oxygen and strontium isotope values from shallow shelf settings implications for temperature and age reconstructions abstract the oxygen and strontium isotopic ratios of marine carbonates are widely employed to derive paleotemperature and age respectively while open ocean samples are the standard source for these measures shelf settings can also provide detailed records however the implementation of shelf data for these purposes has been hindered by the perception that local environmental conditions such as freshwater influx confound regional and global signals here we directly evaluate this concern by assessing the spatial variability in the isotopic composition of biogenic carbonate precipitated along the depositional strike of an inner shelf environment data are derived from mollusc shells collected from a stratigraphically restricted transgressive unit in the early eocene 55 ma of the us gulf coastal plain gcp lithofacies and fossil assemblages suggest that an estuary was present in the westernmost study region whereas more typically marine facies predominated elsewhere isotopic composition varies predictably with paleoenvironmental setting shells from the estuary have 18o values and 87sr 86sr ratios that reflect high freshwater input specimens in the eastern gcp however from within and between outcrops separated by up to 400 km all yield similar results serial microsampling reveals congruence not only in mean 18o values but also in winter and summer extremes estimated paleotemperatures mean annual temperature of 26 c agree well with proxy and model evidence for the early eocene and the gcp and 87sr 86sr ratios are consistent with the established early eocene seawater ratio the fidelity of isotopic values relative to environment indicates that shallow shelf records have much to contribute to studies of ancient climate and ocean chemistry

reconstruction of late bajocian bathonian marine palaeoenvironments using carbon and oxygen isotope ratios of calcareous fossils from the polish jura chain central poland abstract oxygen and carbon isotope analyses were carried out on upper bajocian bathonian calcitic belemnite rostra and oyster shells as well as aragonitic ammonite nautiloid and trigoniid shells from the ore bearing czestochowa clay formation in south central poland all samples were studied by means of cathodoluminscence microscopy trace element x ray and scanning electron microscope sem analysis in order to select best preserved material sem studies allowed classifying some aragonitic ammonite and nautiloid shells 99 aragonite as diagenetically altered average 18o values of oysters belemnites and trigoniids translate into relatively low palaeotemperatures of 10 1 9 2 and 7 4 c respectively the comparable 18o values of bivalves and belemnites indicate that belemnites had a nectobenthic lifestyle and did not record surface water temperatures the ammonite fauna is interpreted to have been nektonic however palaeotemperatures derived from ammonite 18o around 18 6 c may be overestimated due to a lower than normal marine salinity of surface waters the reduced salinity is inferred as well from sedimentological observations and faunal composition the obtained 18o values indicate cool climatic conditions during the late bajocian bathonian in south central poland which may have been linked with the occurrence of a cold climatic episode despite the fact that all studied shells were not precipitated in carbon isotope equilibrium with ambient waters the 13c shell values enabled us to roughly estimate isotope composition of dissolved inorganic carbon dic in the late bajocian bathonian sea of south central poland water 13cdic values calculated from ammonite 13c are lower in comparison to 13cdic values calculated from oyster and belemnite carbon isotope ratios which in conjunction with ammonite 18o values indicates lower salinity of surface or shallow near coastal waters

paleointensity of the earth s magnetic field in the jurassic new results from a thellier study of the lesotho basalt southern africa thellier paleointensity experiments carried out on the jurassic 180 m y old karoo basalt lesotho southern africa provided paleointensity estimates for 40 samples from 10 distinct lava flows with reversed magnetization mean paleointensity was found to be equal to 24 2 11 3 t standard deviation with a minimum of 12 t and a maximum of 41 3 t this corresponds to a mean virtual dipole moment vdm of 4 6 2 0 1022 am2 the between flow dispersion is ascribed to paleosecular variation which thus would approach up to 40 of the mean paleointensity as is observed from the published paleointensity data set covering last 20 m y this result yields further evidence for the period of low geomagnetic field in jurassic to early cretaceous time mesozoic dipole low a symmetrical intensity versus time pattern is suggested for this time interval with a minimum vdm of 3 1022 am2 in late jurassic and substantially higher 4 5 1022 am2 vdms in early to middle jurassic and early cretaceous respectively

strontium isotope variations in middle jurassic late bajocian callovian seawater implications for earth s tectonic activity and marine environments abstract strontium isotope ratios of well preserved belemnite rostra and ammonite shells are presented from stratigraphically well dated upper bajocian callovian sediments of the polish jura chain in central poland nekto benthic belemnites show a narrow trend of changes of 87 sr 86 sr ratio that are interpreted to record secular variations in the strontium isotope composition of seawater a new fit of the seawater strontium isotope curve for the late bajocian callovian is presented based on current and literature data the data show a gradual decrease of seawater 87 sr 86 sr ratio throughout the late bajocian earliest middle callovian lowest 87 sr 86 sr ratios 0 706850 and the flat minimum of the curve were reached in the latest middle and the late callovian the middle jurassic decrease in seawater 87 sr 86 sr ratio is interpreted to have been a result of the increased volcanic activity of the seafloor studied nektonic ammonites are considered to have lived in surface or shallow near coastal waters of the polish jura chain basin and been affected by the freshwater influx a slight enrichment of ammonite shells in 87 sr isotope is linked to a change in strontium isotope composition of the surface or near coastal waters due to the riverine strontium input

variable ti content and grain size of titanomagnetite as a function of cooling rate in very young morb transmission electron microscopy observations and rock magnetic measurements on a pillow from the new flow extruded in 1993 at the juan de fuca ridge demonstrate that ti content in large up to 40 m titanomagnetite grains varies as a function of the cooling rate large grains in the interior of the pillow have a narrow composition range of approximately x 0 6 where x represents the ulvospinel content in the solid solution series with magnetite in contrast the titanomagnetite grains near the pillow rim are progressively smaller and have a broad composition range average x 0 45 within 0 5 cm of the rim a significant portion of the grains is single domain sd to superparamagnetic sp and appears to have little or no ti this lower ti content provides a ready explanation for the higher curie temperature near the glassy margin of the pillow moreover determination of the oxidation state of the titanomagnetite does not show low temperature oxidation anywhere within the pillow indicating no rapid alteration to titanomaghemite as previously suggested for this very young mid ocean ridge basalt morb in order to explain the curie temperatures submicrometer titanomagnetite in interstitial glass in the interior of the pillow also shows variable x values these grains make contributions to susceptibility that show up as high up to 580 c curie temperatures in thermomagnetic analyses and they appear to be sd to sp the variation of x values for the titanomagnetite in the morb is consistent with thermodynamic and kinetic considerations because crystallization of titanomagnetite in the morb is controlled by processes depending on cooling rate and crystal melt fractionation

tropical seasonality in the late campanian late cretaceous comparison between multiproxy records from three bivalve taxa from oman abstract geochemical proxy records from calcite shells of bivalves constitute an important archive for the reconstruction of palaeoenvironmental conditions on sub annual timescales however the incorporation of these trace element and stable isotope proxies into the shell is influenced by a multitude of physiological and environmental factors that need to be disentangled to enable reliable reconstruction of palaeoclimate and palaeoenvironment in this study records of multiple proxies in three bivalve taxa from the same late campanian locality in oman are used to study the expression of various geochemical proxies in relation to each other and to the palaeoenvironment micro x ray fluorescence mapping allows the localization discussion and evasion of diagenetically altered parts of the fossil shells x ray fluorescence line scanning calibrated with laser ablation inductively coupled plasma mass spectrometry is used to measure trace element profiles through well preserved calcitic parts of the shells records of stable carbon and oxygen isotope ratios of shell calcite are combined with these high resolution trace element concentration profiles to study sub annual variations in shell chemistry and reconstruct changes in the palaeoenvironment of the bivalves on a seasonal scale spectral analysis routines are used to detect cyclicity in stable isotope 18o and 13c and trace element mg ca sr ca s ca and zn ca records differences in seasonal expression between these chemical proxies and between individual shells are discussed in terms of the relative influence of palaeoenvironment and potential species specific physiological effects stable oxygen isotope ratios between shells suggest a local palaeotemperature seasonality of 8 c around an annual mean of 28 c with the shell of the rudistid torreites sanchezi milovanovici yielding slightly higher average temperatures the discussion of the application of various mg ca palaeotemperature calibrations on mg ca records in these bivalve species emphasizes the complexity of using trace element proxies in extinct bivalve species it shows that long term changes in mg ca ratios in ocean water need to be taken into account and that mg ca ratios in bivalves might be influenced by vital effects sr ca and s ca ratios in these fossil taxa are likely controlled by growth and metabolic rates of the shell although an influence of local salinity on strontium to calcium ratios cannot be excluded sub annual variations in zinc concentrations in shell calcite may reflect seasonal variations in palaeoproductivity and redox conditions in the water column

paleointensity record in zero age submarine basalt glasses testing a new dating technique for recent morbs abstract thellier thellier paleointensity experiments were conducted on a collection of glasses from three very recent submarine axial flows two were erupted along the juan de fuca ridge at around 46 n and one along the east pacific rise south at around 18 s the within sample dispersion of paleointensity results from the animal farm flow epr south is very low and leads to a well defined mean value of 35 6 1 t 95 error on the mean based on 11 glass chips from four independent samples today s geomagnetic field intensity in the area is 31 2 t comparing animal farm results with published field model reference curves developed for the past 400 yr suggests an eruptive date estimated between 1880 a d and 1950 a d taking into account different sources of errors this is consistent with qualitative evidence for the age of this flow and constitutes the first precise demonstration of using paleointensity as a dating tool for very recent mid ocean ridge basalts morbs however in the juan de fuca area results show a more erratic pattern with samples varying by up to 30 higher and lower from the expected value of about 55 t the dispersion is attributed to the large local crustal magnetic anomalies in this area that can lead to inconsistent intensity values over the same unit local magnetic anomalies should thus always be checked when doing paleointensity on morb samples which should also be distributed as widely as possible in a flow unit when no significant magnetic anomalies are detected the paleointensity dating tool is anticipated to be especially efficient to investigate the volcanic cyclicity along the epr axis during the last several hundred years

the sources and transport of sr and nd isotopes in the baltic sea we have determined the concentration and isotopic composition of sr and nd in waters from the baltic sea the baltic sea is an intracontinental stratified brackish water estuarine like system and the rivers emptying into it drain a suite of terranes ranging from proterozoic archean in the north to phanerozoic in the south the sampled brackish waters range in salinity from seawater sw at 35 289 to a minimum of 2 460 at the surface in the innermost part of the gulf of bothnia the sr concentrations show generally conservative behavior indicating a simple two component mixing however small deviations 3 70 from a perfect mixing line reveal that the imprints from rivers with different sr concentrations are preserved in the blending strontium concentrations from a depth profile across the redoxcline in the baltic proper indicate that vertical particle transport alters the sr concentration in the water our estimated concentration of sr in the average freshwater input to the baltic is 0 03 ppm which is only about 0 4 of the sw concentration the sr isotopic data range from e sr sw 0 in seawater to e sr bw sw 7 8 in the least saline baltic water bw sample in the gulf of bothnia the isotopic composition of sr versus 1 sr in the baltic sea follows an almost perfect mixing line which shows that seawater sr is mixed with much more radiogenic components calculated end member values of e sr sw for each sample show that the riverine input into the gulf of bothnia has e sr sw 120 200 and 10 50 e units in the baltic proper these values are in general agreement with direct measurements of river waters in each region however the calculated values in the gulf of bothnia are lower than the measured river water input in this region which indicates the presence of less radiogenic sr presumably originating from the river waters draining the southern part of the basin which are partially transported northward and mixed with sr from the gulf of bothnia rivers the nd concentration in the baltic sea is not conservative varying between 5 and 45 ppt with the highest concentrations in the bottom waters due to vertical particulate transport a plot of e nd o in baltic water yields a good correlation with the calculated freshwater end member e sr sw the data show that it is possible to unravel the different freshwater sources into the baltic and to identify the zones of particulate removal of both non conservative species such as the ree and of quasi conservative species such as sr the use of isotopic tracers in this estuarine environment may provide a much better insight into mixing and element transport it should also be possible to trace lateral movements of freshwater inputs

low intensity of the geomagnetic field in early jurassic time from a large collection of jurassic continental tholeiites cropping out in europe and africa we selected 90 samples for paleointensity determinations the samples were carefully selected to avoid any secondary magnetizations especially viscous magnetization use of the thellier method reveals that magnetic property changes due to heating begin often at quite low temperatures but fortunately without modifying noticeably their natural remanent magnetization thermoremanent magnetization ratio twenty eight well clustered paleointensity estimates were obtained from two european dikes that were emplaced during early jurassic time the kerforne dike at brenterc h in brittany northwestern france and the messejana dike on the iberian peninsula spain and portugal virtual dipole moments calculated from both magmatic units are similar and only about one third of present day values these new data lend support to the recently postulated low dipole moment of the mesozoic geomagnetic field

evidence from apatite fission track analysis for the post devonian burial and exhumation history of the northern highlands scotland abstract devonian and older rock samples from outcrops in the northern scottish highlands have undergone protracted cooling since they reached palaeotemperatures of 110 c or more in the late palaeozoic to early mesozoic the results not only suggest that the northern highlands region has experienced kilometre scale exhumation since the late palaeozoic but also that devonian and possibly permo carboniferous sedimentation was probably more extensive than current outcrop patterns would imply a permian outcrop sample from the minches basin reached a maximum palaeotemperature of 70 90 c prior to the onset of cooling in the early tertiary while data from devonian and older samples suggest an acceleration in the rate of cooling in the early tertiary the magnitude of early tertiary palaeotemperatures on the mainland adjacent to the inner moray firth imf indicate similar amounts of tertiary exhumation to those derived from compaction analyses for the imf however to the west the magnitude of tertiary cooling cannot be solely ascribed to exhumation and a contribution of heating due to hydrothermal effects and or elevated heat flow associated with the tertiary igneous complex may also need to be invoked

magnetic alteration of zero age oceanic basalt the youngest sampled submarine lava flow which erupted june 1993 on the juan de fuca ridge provides the basis for a tight constraint on the initial or zero age magnetization state of morb detailed profiles of magnetic hysteresis parameters curie temperatures and unblocking temperatures of nrm with respect to the chilled margin of a pillow fragment show evidence of significant oxidation which preferentially affected the finest grain size fraction and principal remanence carrier of the titanomagnetite magnetic mineralogy the oxidation must have occurred during or immediately after initial cooling implying that morb is already appreciably magnetically altered before aging nevertheless successful results of thellier paleointensity experiments on the basalt sample lend support to the idea that crustal magnetization represented by morb preserves a record of geomagnetic intensity variations that may be reflected in small scale magnetic anomalies

testing determinations of absolute paleointensity from the 1955 and 1960 hawaiian flows abstract a new exhaustive study of the flows erupted in 1955 and 1960 from the kilauea volcano big island of hawaii has been conducted in order to constrain the dispersion inherent to the data of absolute paleointensity reported so far and ultimately to determine what are the most critical parameters to obtain suitable determinations the mean directions derived from both flows agree with the expected field within less than 2 paleointensity experiments have been performed using a double heating thellier procedure completed by systematic ptrm checks almost all samples display a linear nrm trm straight line but only 20 of the samples have provided suitable results less than 10 away from the expected field in the other cases the deviation from the expected paleointensity is related to the quality of the ptrm checks which thus provides a threshold value for acceptance of ptrm checks all successful determinations less than 10 away from the expected value have a maximum drat selkin and tauxe 2000 that never exceeds 5 while the mean value of all deviations is lower than 3 5 another interesting feature is the existence of a link between the unblocking temperature spectra and the accuracy of the paleofield which points out the origin of difficulties in the presence of a wide distribution of grain sizes and or the existence of several magnetic phases the results also indicate that magnetite with a narrow range of high unblocking temperatures and little variability in grain size is a favorable situation to obtain suitable determinations with a high success rate these observations may well explain the dispersion inherent to the previous studies of the hawaiian flows

strength of the geomagnetic field in the cretaceous normal superchron new data from submarine basaltic glass of the troodos ophiolite 1 we present here new paleointensity data from 39 sampling sites collected from the quenched margins of pillow lavas and dikes exposed within the troodos ophiolite similar to 92 ma formed during the cretaceous normal superchron cns a period of approximately 40 million years when the geomagnetic field reversed extremely infrequently if at all monte carlo simulations suggest that a minimum of 25 estimates are necessary for a reasonably robust estimate for the average field strength our data suggest a dipole strength equivalent to the present field or nearly twice the post cns average the mean and standard deviation of the dipole moment 81 43 zam 2 z 10 21 from the 57 data points compiled here agree remarkably well with those predicted from the long paleointensity record derived from dsdp site 522 the new data set for the cns suggests a picture of a strong and stable field during the period of time when it stopped reversing moreover the similarity of the cns data with the present geomagnetic field suggests that it is presently in a state of unusual polarity stability

carbon oxygen and strontium isotopes as a tool to decipher marine and non marine environments implications from a case study of cyclic upper cretaceous sediments the interplay of late cretaceous basin subsidence and oscillations in sea level pro duced a mixed freshwater marine succession within the upper cretaceous gosau group of the northern calcareous alps cored sections from wells of the glinzendorf and gieshubl syncline as well as sediments from the outcrop area of grunbach neue welt and slovakian equivalents have been investigated for their stable isotopic composition bulk carbonate d 13 c and d 18 o values of 116 fine grained samples shales siltstones marls and 87 sr 86 sr values of 10 samples from the borehole markgrafneusiedl t1 were analysed in order to distinguish between non marine and marine deposits and to compare and correlate isotope characteristics of the different gosau synclines and basins non marine samples have significantly lower meand 13 c values compared to the mean of marine samples the discrimination between a marine and non marine group usingd 18 o is also highly sig nificant statistically even though the difference between the average non marine and marine values is small strontium isotope values of marine intervals are near the range of values of normal upper cretaceous sea water but show a trend towards higher ratios in marginal marine and non marine deposits although diagenesis and the detrital carbonate admixture partly influence the isotopic composition the original environmental signal can still be reliably identified

are oxygen and carbon isotopes of mollusc shells reliable palaeosalinity indicators in marginal marine environments a case study from the middle jurassic of england stable isotope analyses of non luminescent texturally pristine oyster calcites praexogyra hebridica are presented from bathonian inner ramp limestones in central eastern england a relatively large range of values 18 o 2 0 to 2 3 pdb 13 c 0 9 to 3 7 pdb define a crude positive covariance which can be regionally correlated with an offshore tonearshore increase in faunal restriction this palaeoenvironmental stress gradient has previously been interpreted as a consequence of fluctuating nearshore palaeo salinities due to episodic or seasonal runoff from surrounding hinterlands covariant 18 o 13 c trends from euryhaline bivalves are commonly ascribed to regional salinity gradients the most isotopically depleted examples representing the greatest influence of fresh water however bathonian palaeogeography indictates that the most isotopically depleted oysters inhabited relatively offshore settings assuming an average growth temperature of 25 c these shells were secreted in near normal sea water 18 o 0 4 smow in contrast isotopically heavy oyster calcites were produced in highly evaporated nearshore lagoonal waters 18 o up to 4 8 smow modelling the oxygen isotope and chemical evolution of residual waters during evaporation suggests that up to 65 of the nearshore water mass was lost probably in a complex of hydrodynamically choked lagoons evaporites were not precipitated in the sediment and geochemical modelling suggests that the lagoon waters may have been brackish rather than marine in origin the regional 13 c trend is contrary to that predicted on the basis of palaeosalinity and may have resulted from variations in organic carbon production decay and fixation in early diagenesis

paleointensity results from the jurassic new constraints from submarine basaltic glasses of odp site 801c 1 tholeiite of the oldest oceanic crust was drilled during odp legs 129 and 185 at hole 801c in the western pacific fresh appearing submarine basaltic glass sbg was recovered from the tholeiites 167 ma which has been shown to be nearly ideal for determining absolute paleointensity paleointensities of the younger off axis alkalic basalts 160 ma overlying the tholeiites had been studied earlier here we report results from the older tholeiitic on axis sequence we subjected a total of 73 specimens from 17 cooling units to absolute paleointensity experiments of these 30 specimens and six cooling unit averages met our strictest reliability criteria yielding an average of 11 9 3 9 t the bulk of evidence suggests a paleolatitude of the site of 14 s with an uncertainty of 10 this translates the intensity to a value for the virtual axial dipole moment of 28 zam2 slightly lower than values determined from the plagioclase crystals in the three cooling units of the younger alkalic basalts overlying the tholeiites tarduno cottrell 2005 our value is low when compared to the long term median value of the field of 42 zam2 our results and those of the published literature therefore support the contention of a low magnetic field strength in the jurassic average of 28 14 zam2 n 138 individual estimates as initially suggested by prevot et al 1990 our interpretation of the body of available data argue for low field strengths for the entire jurassic extending into the early cretaceous

reconstruction of jurassic bathonian palaeosalinity using stable isotopes and faunal associations abstract the bathonian is an interval from which salinity controlled benthic faunas are particularly well known this study examines late bathonian faunas from dorset uk from the wattonensis beds fuller9s earth of known marine origin the overlying elongata beds and the boueti bed marking the base of the forest marble 18 o values of belemnites belemnopsis from the wattonensis beds range from 1 4 to 0 7 and carbon isotope values range from 2 3 to 0 5 vpdb isotope values of well preserved rhynchonella from the wattonensis beds range from 2 4 to 1 3 for oxygen and 1 1 to 0 6 vpdb for carbon the 18 o data suggest high palaeotemperatures possibly up to 28 c a similar spread of data is derived from brachiopods goniorhynchia boueti from the boueti bed given the marine origin of the wattonensis beds and overlap of data the reduced faunal diversity of the boueti bed is considered unlikely to be the result of reduced salinity brachiopods therefore should not be regarded more sceptically as evidence for fully marine conditions as has been suggested the oysters praeexogyra hebridica elongata and brachiopods rhynchonella from the elongata beds have isotope values that also imply fully marine conditions and are interpreted as being indicative of slightly cooler conditions

strontium isotopic paleontological method as a high resolution paleosalinity tool for lagoonal environments a combined strontium isotopic 87 sr 86 sr and paleontological method is newly applied to a modern lagoon in egypt s nile river delta to test its applicability as a paleosalinity proxy analyses of 22 surficial samples collected throughout the lagoon include 81 sr isotopic analyses of mollusks foraminifera ostracods barnacles bryozoans serpulid worm tubes pore water and gypsum crystals two salinity groups are distinguished in each sample a lower salinity group 1 ppt mixed with a higher salinity group 3 10 ppt that respectively are interpreted as the modern biocoenosis and an older relict fauna the relict fauna denotes higher salinity conditions in the lagoon prior to closure of the aswan high dam 1964 and the modern fauna records freshening of the lagoon recent decreased salinity is a response to regulated nile river flow and increased discharge into manzala of fresh water via canals and drains quantification of this short term salinity change holds promise for study of modern lagoons in other world settings and may provide paleoclimatic information for older lagoon sequences in the nile river delta and the geologic record

tectonic forcing of early to middle jurassic seawater sr ca the jurassic period ca 201 145 ma is marked by fundamental reorganizations of paleogeography paleoceanography ecosystems and the progressive shift from aragonite to calcite as the favored marine biogenic carbonate polymorph sr ca ratios of well preserved jurassic oysters and belemnites from sections in the uk and poland demonstrate that the sr ca ratio of seawater varied systematically throughout the early and middle jurassic in parallel with already documented seawater 87 sr 86 sr the sr flux from increased mid ocean ridge activity in the early jurassic outbalanced the input of riverine sr leading to gradually lower seawater 87 sr 86 sr associated with the parallel and strong decrease in seawater sr ca ratios this downward trend was reversed by enhanced continental input in the toarcian and aalenian but resumed in the bajocian and continued to the callovian parallel changes of seawater 87 sr 86 sr and sr ca suggest a common cause for these long term variations and are best explained by changes in the balance of continental weathering and hydrothermal fluxes these findings underline the strong control of global tectonic processes on the evolution of biomineralization and downplay the role of biomineral evolution in influencing strontium chemistry of seawater in the mid mesozoic

the norwest bend formation implications for the evolution of neogene drainage in southeastern australia abstract strontium isotope data indicate that sediments of the norwest bend formation were deposited within a large estuarine system during the latest miocene to early pliocene probably 5 ma the norwest bend formation is divisible into two members a lower sand dominated member and an upper oyster coquina member these two units are separated by an irregular erosion surface that has no correlative within the adjacent loxton parilla sands tectonism in the western murray basin adjacent to the adelaide foldbelt has exerted a considerable control over the formation of these estuarine sediments the lower norwest bend formation occupies a paleodrainage system that was restricted to a region west of the hamley fault and was presumably incised following uplift of this western block flooding of this paleodrainage system produced the lower norwest bend estuarine system later tectonism on the hamley fault resulted in the formation of the erosion surface within the norwest bend formation we suggest that the norwest bend estuarine system owes its existence to marginal tectonism associated with the young uplift of the mt lofty flinders ranges the paleodrainage system incised prior to deposition of the norwest bend formation differs markedly in geometry from the present murray river gorge system this suggests that the modern murray river system developed after deposition of the late miocene pliocene norwest bend formation

holocene paleointensities thellier experiments on submarine basaltic glass from the east pacific rise a complete description of the geomagnetic field requires both paleodirectional and paleointensity data although the paleointensity data base has grown steadily over the last three decades it remains limited in time and space the majority of data are of holocene age and come from europe furthermore it has been difficult to assess the reliability of the paleointensity determinations here we present paleointensity determinations on precisely dated holocene 0 to 3500 years old submarine basaltic glass from the east pacific rise 15 s to 22 s although hysteresis measurements and low temperature isothermal remanent magnetization irm acquisition experiments document a significant contribution of superparamagnetic grains high blocking temperatures above 400 c and curie temperatures between 490 c and 550 c indicate a single domain low ti magnetite as the carrier of the remanent magnetization this notion is further supported by the fact that saturation of remanence is achieved in moderate fields of about 200 300 mt submarine basaltic glass proves to be nearly ideal for paleointensity determinations in that it produces a high success rate for thellier experiments twenty six out of 30 samples resulted in acceptable paleointenisty determinations multiple experiments on splits from the same sample show good reproducibility the paleointensities for zero age glasses correspond precisely with the present field intensity at the site of recovery the results of the remaining samples range from 16 7 to 53 9 t with corresponding virtual axial dipole moments vadm of 3 61 1022 to 11 9 1022 a m2 the intensities vary rapidly with time excluding a westward drifting nondipole component as the source for these fluctuations basaltic glass is frequently recovered in both dredged and drilled material from the ocean floor the availability of submarine basaltic glass throughout the world oceans therefore holds great potential for a better distribution of paleointensity data through time and space