geochemistry of central tethyan upper permian and lower triassic strata abadeh region iran nearly 2 km of upper permian to lower triassic limestones are exposed in the hambast mountain abadeh region iran lime mud matrix and most bioclasts of permian age are recrystallized into large calcite crystals and contain 600 4000 ppm sr suggesting a probable aragonite precursor low bulk rock 18 o values 7 to 10 pdb and recrystallized textures are also indicative of diagenetic alteration within the murghabian and abadehian two gradual upward increases in carbonate and organic matter 13 c compositions each roughly 3 pdb in magnitude are documented both are attributed to increased organic productivity and sequestration of organic matter in sediments within the julfian and across the permian triassic p t boundary two sharp upward decreases in carbonate and organic matter 13 c values each 4 pdb in magnitude are observed both are best explained by mixing of a deep water mass having low 13 c values and a shallow water mass having high 13 c compositions early triassic 13 c values initially low 1 pdb increase to 3 pdb within 100 m above the p t boundary variations in 13 c compositions of carbonate and organic matter and changes in 13 c 13 ccar 13 corg indicate that early triassic 13 c values were controlled by productivity cycles

climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

eemian cooling in the norwegian sea and north atlantic ocean preceding continental ice sheet growth changing conditions in the north atlantic region may drive global climate changes1 2 according to previous reconstructions of the last interglacial the eemian north atlantic sea surface tempera tures ssts were similar to present day values3 in the norwegian sea even warmer conditions appeared as a single pulse of short duration4 5 whereas the greenland ice record suggests that the warm interglacial air temperatures were interrupted by several cold periods6 here we use faunal and stable isotope analyses of foraminifera in two sediment cores from the north atlantic ocean and norwegian sea to reconstruct high resolution records of sst and sea surface salinity sss during the eemian interglacial our results which differ significantly from the greenland record6 show a sharp decrease in sst and sss of the norwegian sea associated with a more moderate cooling and freshening of the north atlantic at the middle of isotope substage 5e several millennia before the beginning of continental ice sheet growth changes in the norweg ian sea surface conditions appear to have represented an important climate change affecting global atmospheric and thermohaline circulations

barremian danian chemostratigraphic sequences of the cauvery basin india implications on scales of stratigraphic correlation abstract chemostratigraphic concepts postulate that distinct chemozones could be recognized from rock records to help correlate geographically separated strata many studies have upheld this view but were limited to classic boundaries such as cenomanian turonian or cretaceous tertiary only a few elements and isotopic compositions were made use in such studies an attempt to recognize chemozones of barremian danian strata of the cauvery basin south india through whole rock chemistry had revealed many complex signals and depositional events as expressed by bulk geochemical profiles the signals indicate major shift in sedimentation pattern from dynamic depocenter to stable depositional conditions during santonian varying sensitivities of different elements towards prevalent depositional conditions are also inferred trends of geochemical composition indicated domination of single depositional control all through the depositional history basinal configuration that limited terrestrial sediment source and episodic influx of detrital materials presence of distinct change in whole rock geochemistry across geochronological and lithostratigraphic boundaries is deciphered through a statistical tool anova these results demonstrate that visual delineation of chemozones in a long ranging rock record would be tenuous and has to be exercised with caution

the end permian mass extinction a rapid volcanic co2 and ch4 climatic catastrophe abstract the end of the permian was a time of crisis that culminated in the earth s greatest mass extinction there is much speculation as to the cause for this catastrophe here we provide a full suite of high resolution and coeval geochemical results trace and rare earth elements carbon oxygen strontium and clumped isotopes reflecting ambient seawater chemistry and water quality parameters leading up to the end permian crisis preserved brachiopod low mg calcite based seawater chemistry supplemented by data from various localities documents a sequence of interrelated primary events such as coeval flows of siberian trap continental flood basalts and emission of carbon dioxide leading to warm and extreme greenhouse conditions with sea surface temperatures sst of 36 c for the late permian although anoxia has been advanced as a cause for the mass extinction most biotic and geochemical evidence suggest that it was briefly relevant during the early phase of the event and only in areas of upwelling but not a general cause instead we suggest that renewed and increased end permian siberian trap volcanic activity about 2000 years prior to the extinction event released massive amounts of carbon dioxide and coupled with thermogenic methane emissions triggered extreme global warming and increased continental weathering eventually these rapidly discharged greenhouse gas emissions less than 1000 years before the event ushered in a global hothouse period leading to extreme tropical ssts of 39 c and higher based on these sea surface temperatures atmospheric co 2 concentrations were about 1400 ppmv and 3000 ppmv for the late and end permian respectively leading up to the mass extinction there was a brief interruption of the global warming trend when sst dropped concurrent with a slight but significant recovery in biodiversity in the western tethys it is possible that emission of volcanic sulfate aerosols resulted in brief cooling just after the onset of intensified warming during the end of the permian after aerosol deposition global warming resumed and the biotic decline proceeded and was accompanied by suboxia in places of the surface ocean which culminated in the greatest mass extinction in earth history

eemian early weichselian n s temperature gradients north atlantic nw europe abstract based on benthic marine organisms and or vegetation development at coastal sites in the eastern atlantic region temperature profiles of the last interglacial stage 5e and the early weichselian interstadial odderade stage 5a have been constructed from 40 to 80 degrees north the shape of the eemian summer temperature profile is very similar to the present but at all sites the eemian temperatures are a few degrees c warmer than present the odderade temperature conditions are very similar to the present both in the north on svalbard and in the south the nederlands france however in norway denmark and nw germany the odderade climate is much cooler than today sea surface temperature sst estimates inferred from planktonic foraminifera from the norwegian sea and the north atlantic show the same temperature trends as those inferred from the coastal sections these observations confirm the close relationship between western european climate and north atlantic surface conditions based on comparison between these temperature trends and insolation data we suggest that the development to an interstadial or interglacial type of climate in w europe is controlled by orbital forcing furthermore these results stress that quaternary stratigraphers working at high and low latitudes should be especially careful when using climatic inferences as a basis for correlation to interglacials or interstadials

magnetic properties of hydrothermally synthesized greigite fe3s4 i rock magnetic parameters at room temperature summary greigite of variable purity has been synthesized hydrothermally at 140 c by injecting a mohr s salt solution into a sodium sulphide solution containing dissolved zerovalent sulphur ageing for 30 960 min and rapidly quenching oxygen was rigorously excluded during the synthesis scanning electron microscope sem observations yield a grainsize range up to 400nm the variable purity was deduced from a varying specific saturation magnetization 3 29 am2 kg i the mjm or ors os ratio varies between 0 3 and 0 4 which is indicative of fine grained greigite concurring with sem observations hysteresis measurements at low temperatures indicate the presence of grains that are superparamagnetic at room temperature coercivity parameters b 13 43 mt bo cr 37 73 mt are the highest obtained to date for synthetic greigite and compare well with those measured for natural greigite ranges for other rock magnetic parameters are discussed greigite hysteresis parameters overlap those of magnetite to a large degree a diagnostic interparametric ratio for greigite is its high o xin ratio the range of the present greigite is 40 75 kam

magnetomineralogy and revised excursions for the last interglacial glacial cycle in the grande pile lacustrine sequence france abstract a paleomagnetic record for the grande pile lacustrine sequence deposited during the last interglacial glacial cycle has been constructed based on continuous sampling n 792 of a 15 m long oriented core gpxx the nrm intensity magnetic susceptibility and saturation isothermal remanent magnetization show pronounced variations related to the climatic zonations in the sequence the stratigraphic consistency of the paleomagnetic directions vary considerably due to variations in signal noise ratios paleosecular variation patterns occur throughout most of the core as well as several zones of inferred geomagnetic excursions the application of magnetic fabric ams shows that some apparent lanterne weichselian excursions reside in deformed sediments while anomalous paleomagnetic directions in the 70 000 to 120 000 yr b p time interval appear in sediments with low signal noise ratios and a high degree of compaction the signature is hence not likely to reflect genuine records of geomagnetic field variations in these levels discrepancies between the magnetostratigraphy of gpxx and a previously investigated core implies that the earlier claimed regional correlations based on the paleomagnetic signature of low intensity levels should be critically reassessed the grande pile sequence is not regarded as a magnetostratigraphic standard for the last interglacial glacial cycle

the late pleistocene palaeoclimatic record of north atlantic deep sea sediments revealed by mineral magnetic measurements eight cores of north atlantic deep sea sediment are correlated using simple rapid and non destructive measurements of magnetic susceptibility and isothermal remanence this stratigraphy is demonstrably related to late pleistocene palaeoclimatic variations by comparison with the oxygen isotope and microfossil records of these cores fluctuations in the concentration dependent magnetic properties of the cores largely reflect their lithological composition consisting of climatically modulated cycles of marl glacial horizons and nannofossil chalk interglacial horizons high magnetic concentration characterises glacial horizons which correspond to periods when carbonate productivity was severely restricted and ice rafted detrital inputs were prolific coincident with the migration south of the north atlantic polar front to within 3 of latitude north of the coring site in contrast interglacial horizons are characterised by low magnetic concentration and high carbonate content of the sediment consequent on the retreat of the polar front and the re establishment of coccolith floras in its wake during these periods ratios formed between individual magnetic parameters are independent of magnetic concentration and are thus free of any climatic influences wrought by carbonate oscillations in this study however such ratios exhibit a definite response to palaeoclimatic variations attributable to differences in the composition and grain size of the magnetic mineral assemblage of glacial vis a vis interglacial horizons of the cores these differences in mineral magnetic composition are substantially confirmed by mossbauer effect studies of selected samples representing peak glacial and interglacial horizons of one core such glacial interglacial contrasts in the concentration mineralogy and grain size of the magnetic assemblage most probably result from variations in the source and flux density of detritral inputs induced by changes in climate x ray diffraction studies of the same core indicate that variations in the mineralogy of the detrital fraction of the sediment are consistent with those of the magnetic assemblage together these data point to the conclusion that a subsidiary low latitude possibly aeolian detrital flux supplements high latitude ice rafted input in glacial horizons of the cores the low latitude flux however is also identifiable in interglacial horizons independent evidence suggests that this low latitude aeolian flux may be derived from the sahel region of north africa and transported to the coring site by harmattan winds associated with saharan dust outbreaks

sedimentary records of relative paleointensity of the geomagnetic field theory and practice sediments have proved irresistible targets for attempts at determining the relative variations in the earth s magnetic field because of the possibility of long and continuous sequences that are well dated and have a reasonable global distribution the assumption underlying paleointensity studies using sedimentary sequences is that sediments retain a record reflecting the strength of the magnetic field when they were deposited early theoretical work suggested that because the time required for an assemblage of magnetic particles in water to come into equilibrium with the ambient magnetic field was quite short no dependence on magnetic field was expected nonetheless a number of experiments showed that sedimentary magnetizations varied in accordance with the field albeit not always in a simple linear fashion experiments in which the sediments were stirred in the presence of a field to simulate bioturbation showed a reasonably linear relationship with the applied field and these results spurred the hope that variations in the earth s magnetic field might indeed be recoverable from appropriate sedimentary sequences examination of existing paleointensity data sets allows a few general conclusions to be drawn it appears that sedimentary sequences can and do provide a great deal of information about the variations in relative paleointensity of the earth s magnetic field the dynamic range of sedimentary data sets is comparable to those acquired from thermal remanences moreover when compared directly with such independent measures of magnetic field variations as beryllium isotopic ratios and thermally blocked remanences there is considerable agreement among the various records when viewed over timescales of hundreds to thousands of years relative paleointensity data sets from more than a few thousand kilometers apart bear little resemblance to one another suggesting that they are dominated by nondipole field behavior when viewed over timescales of a few tens of thousands to hundreds of thousands of years however the records show coherence over large distances at least thousands of kilometers and may reflect changes in the dipole field on the basis of a sequence spanning the brunhes and matuyama chrons the magnetic field has oscillated with a period of about 40 ka for the last few hundred thousand years but these oscillations are not clear in the record prior to about 300 ka thus they are probably not an inherent feature in the geomagnetic field and the correspondence of the period of oscillation to that of obliquity is probably coincidence

cement stratigraphy in triassic and jurassic limestones of the weserbergland northwestern germany abstract cement stratigraphy of the korallenoolith oxfordian and trochitenkalk upper muschelkalk formations southern lower saxony hills of germany is based on investigation of 232 carbonate samples by cathodoluminescence cl this enables subdivision of cements into four main generations generation 1 consisting of fine columnar equant and syntaxial cements with blotchy cl and or microdolomite inclusions that is interpreted as originally submarine mg calcitic precipitate generation 2 found in jurassic samples only these cements show intrinsic to non luminescent cl with thin bright orange subzones and they are interpreted as meteoric phreatic calcites generation 3 1 characterized by zoned calcites with variable cl colours these cements precipitated under shallow burial conditions in a phreatic environment during an incipient stage of late diagenesis generation 3 2 with relatively uniform orange cl indicative of precipitation in a stable chemical environment this cement generation is interpreted as late diagenetic deep burial calcites generation 3 3 partially strongly zoned and with a characteristically intense cl contrast it has been identified in only 17 of the 82 trochitenkalk samples deformation twins end within this generation indicating a post tectonic genesis for the subsequent younger cement zones the cements were probably precipitated in a near surface environment characterized by reducing or variable eh conditions generation 4 consisting of calcites that show intrinsic cl with bright orange subzones comparable to generation 2 but lacking deformation twins these cements are interpreted as post tectonic late diagenetic products of a meteoric phreatic environment based on detailed cl petrography fifteen diagenetic events three calcite cements three dolomite generations three fissure generations two stages of dedolomitization aragonite dissolution matrix recrystallization and two stages of hmc lmc transformation can be distinguished and timed relative to cement zonation the progressively decreasing 18o values for cement generations 1 to 3 2 likely reflect increasing temperatures caused by burial the low 18c values of cement generation 4 are probably a reflection of a meteoric diagenetic environment a time burial cementation pathway can be modelled combining cl patterns cement isotopic data and the subsidence history of the study area the main features of this model are 1 1 generation 1 cements are submarine precipitates and their age therefore coincides with sedimentation 2 2 cement generation 3 1 of the trochitenkalk commenced precipitation at a depth of about 120 m reached during late triassic time in case this minimum depth is also the formation depth of generation 3 1 in the korallenoolith formation then precipitation of these cements started during late jurassic time 3 3 cement generation 3 2 of both the trochitenkalk and the korallenoolith formation precipitated at assumed depths 1000 m reached during the doggerian and at the time of jurassic cretaceous transition respectively 4 4 cement generation 4 precipitated after the sediments had undergone telogenesis and must thus be younger than the intra senonian sub hercynian tectonic phase and possibly even younger than the paleocene tectonic pulse laramian phase

last interglacial and holocene climatic development in the norwegian sea region ocean front movements and ice core data planktonic foraminiferal evidence suggests that the ocean front systems between polar and atlantic surface waters in the norwegian sea generally were located closer to greenland during oxygen isotope substage 5e than in the holocene during both these periods oscillations have occurred in the position of the fronts in the western norwegian sea region the substage 5e influence of warm atlantic waters was interrupted by a return to polar conditions these findings support both ice core data and evidence from europe that the last interglacial was a period of rapid climatic shifts

biogeochemistry of nautiloids and paleoenvironmental aspects of buckhorn seawater pennsylvanian southern oklahoma abstract sediments in the buckhorn quarry and adjacent outcrops southern oklahoma are shallow water carbonates which are intercalated with coals and minor conglomerates they belong to the boggy formation of the deese group and are desmoinesian pennsylvanian in age strontium concentrations of shell septa and cameral deposits of pennsylvanian cephalopods are variable and fall either in the low range with 0 17 0 22 or the high range with 0 39 0 60 sr ca atomic ratios these values suggest that extrapallial and or cameral fluids responsible for the formation of all three cephalopod macrostructures were in chemical disequilibrium with ambient seawater thus the biological discrimination for sr was well establihed by pennsylvanian time for nautiloids the mg concentrations appear to be controlled at the species genus levels in contrast the na mn and fe contents of nautiloids are influenced and controlled by the physicochemical conditions of the surrounding seawater information obtained from brachiopod and from the least altered cephalopod samples suggest that buckhorn seawater was physiochemically similar to that of modern ocean water and the postulated temperature and salinity values represent the most reasonable intepretations considering paleontological sedimentological and biogeochemical data salinity of the buckhorn sea which was within 5 s of the pennsylvanian equator ranged from 29 to 34 ppt with a mean of 32 ppt this near normal salinity was complemented by an average water temperature of 36 c 34 38 c for the shallower and of 21 c 14 30 c for the deeper parts of the buckhorn sea of southern oklahoma overall water temperatures fluctuated between 14 and 38 c

diagenesis and evolution of microporosity of middle upper devonian kee scarp reefs norman wells northwest territories canada petrographic and chemical evidence the middle upper devonian kee scarp reef complexes of norman wells northwest territories canada are oil producing stromatoporoid dominated carbonates episodic increases in the rate of sea level rise produced multiple cycles of reef growth that exhibit backstepping characteristics these carbonates composed of invariably altered limestones have original interskeletal intraskeletal and intergranular porosity mostly occluded by nonferroan dull luminescent cements secondary porosity represented by micropores of various types developed during diagenesis by aggrading neomorphism and dissolution the micropores represent the main reservoir porosity in the kee scarp limestone micropores in the kee scarp limestone can be classified into four categories based on thei shapes 1 stepwise rhombic about 1 m to 2 m in diameter developed mainly in stromatoporoids 2 intercrystalline rhombic about 1 m in diameter developed mainly in algal aggregates 3 microvugs 4 m to 10 m in diameter developed mainly in algal aggregates and 4 microchannels about 12 m in length and 0 5 m in width developed in algal aggregates and stromatoporoids the stepwise rhombic and microvugs are developed mainly at the kee scarp reef margin and constitute the best type of reservoir porosity petrographic chemical and isotopic studies of kee scarp reef components reveal a complex diagenetic history involving marine fluids modified by increasing water rock interaction and burial early diagenetic processes include marine cementation and micritization followed by neomorphic replacement of high mg calcite and aragonite reef components resulting in the creation of the first generation of microporosity via dissolution on a micron scale later diagenesis represented by microfracturing and cementation with two generations of equant calcite and stylolitization was responsible for the second generation of microporosity very minor silicification dolomitization and vertical fracturing occurred at variable depths portions of well preserved marine cements stromatoporoids an rare crinoids of postulated high mg calcite precursor mineralogy have escaped diagenetic alteration and preserve the original marine dgr18o and dgr13c signatures 4 7 0 3 pmil pdb for oxygen 1 0 0 4 pmil pdb for carbon minor and trace element data show less preservation of the postulated original marine composition neomorphic stabilization of skeletal components caused further depletion in dgr18o but very little change in dgr13c an argument for modification of the original marine fluids with increasing burial variations in magnitude of water rock interaction with depth facies changes and porosity modifications probably exerted some control on fractionation and distribution of stable isotopes and trace elements in ree components

submarine hydrothermal weathering global eustasy and carbonate polymorphism in phanerozoic marine oolites abstract the age and fabric of 347 phanerozoic marine oolites have been compiled in order to evaluate secular variations in the original mineralogy of these physicochemically precipitated sedimentary carbonates variation in the abundance of oolite correlates with positions of global sea level ooids were common during transgressions and regressions but were rare during lowstands and highstands the rarity of oolite during continental emergence early cambrian permo triassic late tertiary quaternary probably relates to a diminished areal extent of shallow carbonate environments causes for a similar paucity during continental submergence silurian devonian late cretaceous are more problematic higher atmospheric co2 and lower hydrospheric co3 concentration during highstands may have inhibited a biotic carbonate precipitation ooids coeval with highstands display a preponderance of fabrics evincing a primary calcite mineralogy ooids formed during lowstands are more diverse but record dominance of aragonite variations in cortical mineralogy relate more closely to flooded continental areas than to sea level elevations supporting the suggestion of mackenzie and pigott 1981 that variations in hydrospheric carbonate concentrations were more important in determining phanerozoic ooid mineralogy than were magnesium calcium concentrations these data on oolite abundance and mineralogy demonstrate that abiotic phanerozoic marine carbonates have been responsive to secular changes in atmospheric hydrospheric chemistry and global eustasy and suggest that these changes are directly related to past rates of submarine weathering and sea floor hydrothermal activity

the rock magnetic signal of climate change in the maar lake sequence of lac st front france summary rock magnetic properties of the maar lake sediments of lac st front massif central france reflect environmental changes during the last climatic cycle high magnetic concentrations are measured in the sediments deposited under glacial climatic conditions while lower concentrations correspond with more temperate climatic periods low and high temperature measurements indicate that the remanence is carried by titanium poor magnetite however some maghemite and haematite is present in sediments deposited under temperate conditions normalized intensities and coercivities of the anhysteretic remanent magnetization arm are clearly higher for the sediments deposited during the temperate climatic periods of the eemian st germain i ii and mid glacial than for glacial sediments but other magnetic parameters hardly differ between these groups due to slight differences in magnetic composition and possible effects of grain interactions it is not straightforward to relate this different arm behaviour to magnetic grain size variations for the holocene sediments rock magnetic parameters indicate a larger grain size this trend is also suggested by granulometric experiments with an optical laser granulometer dissolution of smaller grains is the most likely explanation for this larger grain size changes in magnetic composition and grain size are extremely limited for the glacial sediments but magnetic concentration varies considerably magnetic concentration maxima in the glacial sediments of lac st front correlate with those of the nearby lac du bouchet thouveny et al 1994 correlating the susceptibility records of these sequences with the 18o record of the grip ice cores thouveny et al 1994 suggests that magnetic concentration maxima may correspond with short cold climatic episodes associated with heinrich events

geochemistry of some ordovician and devonian trilobite cuticles from north america abstract this study reports on the isotopic trace and minor elemental analysis of some ordovician and devonian trilobite cuticles from ontario canada and new york state u s a the devonian trilobite phacops rana and the ordovician trilobite isotelus gigas obtained from shale and limestone constitute most of the studied specimens specimens from shales are generally better preserved than their counterparts from limestones trilobites from shales exhibit the highest sr na mg mn and fe contents but diagenetic evaluation has to be carried out on individual populations to select the best preserved specimen s in well preserved specimens there is no significant change in geochemical content due to maturity location of sampling within the cuticle species or age of the specimen therefore fragments of a cuticle are representative of an entire specimen and the elemental contents of the cuticular calcite reflect homogeneous body fluid composition during deposition in comparison with originally low mg calcite shells of brachiopods and high mg calcite skeletons of crinoids the studied trilobites possessed cuticles of an intermediate mg calcite composition it is postulated that the mg content varied from 2 to 7 mole mgco 3 this intermediate mg calcite composition for trilobites complements the results of studies on the calcite fraction of many modern marine arthropods isotopic compositions of well preserved trilobites are similar to those obtained from contemporaneous brachiopods oxygen and carbon isotope values of altered specimens suggest that marine meteoric mixed water was the predominant diagenetic fluid

gravity current flow over obstacles when a gravity current meets an obstacle a proportion of the flow may continue over the obstacle while the rest is reflected back as a hydraulic jump there are many examples of this type of flow both in the natural and man made environment e g sea breezes meeting hills dense gas and liquid releases meeting containment walls two dimensional currents and obstacles where the reflected jump is in the opposite direction to the incoming current are examined by laboratory experiment and theoretical analysis the investigation concentrates on the case of no net flow so that there is a return flow in the finite depth upper layer the theoretical analysis is based on shallow water theory both a rigid lid and a free surface condition for the top of the upper layer are considered the flow may be divided into several regions the inflow conditions the region around the hydraulic jump the flow at the obstacle and the flow downstream of the obstacle both theoretical and empirical inflow conditions are examined the jump conditions are based on assuming that the energy dissipation is confined to the lower layer and the flow over the obstacle is described by hydraulic control theory

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

climate variations in europe over the past 140 kyr deduced from rock magnetism rapid shifts in climate during the last glacial are now well documented particularly from the oxygen isotope records of the two greenland ice cores grip1 2 and gisp23 in the grip record1 2 these climate events are also seen during the preceding eemian interglacial which may be an analogue for the future climate warmed by the greenhouse effect but these shifts are not found in the eemian section of the gisp2 core3 casting doubt on whether the rapid shifts in the grip oxygen isotope record really do represent a climate signal here we present magnetic susceptibility pollen and organic carbon records from maar lake deposits in the massif central france these data provide an independent record of past climate and we find that they correlate well with the ice core records during the last glacial during the eemian two rapid cooling events seen in our record also correlate with those seen in the grip ice core supporting the idea that rapid climate change did occur in the eemian interglacial and demonstrating that it extended to continental europe

hydrothermal diagenesis of paleozoic seamount carbonate components we present geochemical results of paleozoic carbonate components brachiopods biogenic low mg calcite blmc crinoids biogenic high mg calcite bhmc and whole rock admixture of aragonite and calcite wrac from open ocean permo carboniferous seamounts of japan situated in the tropical mid panthalassic ocean the diagenetic history of these and other carbonate allochems was determined by visual optical inspection of their external morphology and luminescence by evaluation of their microstructures and by assessment of their trace element and stable isotope distributions the degree and trends of the diagenetic alteration tests were then reconciled with their concomitant sr isotope values and compared to those of the established seawater sr isotope curve the altered carbonate material from three of the four time slices support the novel concept of diagenesis in the presence of marine hydrothermal fluids leading to less radiogenic sr isotope values in addition sr isotope values of unaltered blmc from three of the four time slices do not concur with the values for the concurrent time of the established seawater 87sr 86sr curve an adjustment of their stratigraphic position is untenable and unsatisfactory in light of their biostratigraphic assignment which suggests that sr isotope diagenesis is much more complex and complicated than is espoused in the literature consequently the concept of less radiogenic sr isotope values in diagenetic marine carbonates has profound implications for the veracity of the established seawater 87sr 86sr profile and curve and it needs to be re evaluated in light of the findings

an analysis of eemian climate in western and central europe on the basis of 31 pollen diagrams and additional data for botanical macrofossils an analysis is made of the last interglacial eemian climatic history in western and central europe the main tool for this analysis is the climatic indicator species method only selected woody species are used for the quantification of data partial climatic range diagrams are presented for abies alba acer monspessulanum acer tataricum buxus sempervirens tilia tomentosa the problem of time correlation and pollen zonation of the eemian is discussed the climatic analysis itself is based on an improved version of the indicator species method in this version not every site is analysed for its climatic values instead maps and tables on the migrational history of hedera ilex buxus abies and species of acer tilia and abies are the basis for climatic maps showing respectively january and july isotherms for the periods of the corylus zone e4a and the carpinus zone e5 it is concluded that mean january temperatures were as much as 3 c higher at amsterdam the netherlands than at present and mean temperatures in july were 2 c higher however the thermal maximum in winter was later zone e5 than the summer thermal maximum zone e4a winter temperatures changed parallel to rise and fall of global sea level precipitation changes are more difficult to estimate in the first part of the eemian precipitation must have been relatively low but from zone e4b onward it increased to higher values reaching 800 mm and probably substantially more in zones e5 and e6 hence the eemian climate was in its beginning relatively more contintental and later from e4b onward more oceanic however as compared with the holocene the eemian climate was generally speaking more oceanic

high resolution climate records from the north atlantic during the last interglacial the two deep ice cores recovered by the grip1 and gisp22 projects at summit greenland agree in detail over the past 100 000 years3 and demonstrate dramatic climate variability in the north atlantic region during the last glacial before the current period of holocene stability this glacial climate instability has subsequently been documented in the marine sedimentary record of surface ocean conditions in the north atlantic4 before 100 kyr ago the two ice core records are discrepant however casting doubt on whether the oxygen isotope fluctuations during the last interglacial eemian seen in the grip core1 5 represent a true climate signal here we present high resolution records of foraminiferal assemblages and ice rafted detritus from two north atlantic cores for the interval 65 kyr to 135 kyr ago extending the surface ocean record back to the eemian the correlation between our records and the greenland ice core records is good throughout the period in which the two ice cores agree suggesting a regionally coherent climate response during the eemian our marine records show a more stable climate than that implied by the grip ice core suggesting that localized phenomena may be responsible for the variability in the latter record during the eemian

marine evidence for climatic instability during the last interglacial in shelf records from northwest europe data from the greenland ice sheet and continental records from europe have indicated climatic fluctuations during the last interglacial eemian oxygen isotope substage 5e similar fluctuations have not however been documented previously from marine environments here we show the existence of two cold events during substage 5e in two marine benthic foraminiferal shelf records from northwest europe and suggest that these cooling events are a result of fluctuations in the strength of the north atlantic surface water circulation

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

carbon oxygen and strontium isotopes in paleozoic carbonate components an evaluation of original seawater chemistry proxies abstract brachiopods trilobites cements and whole rock matrix material were evaluated for their reliability as proxies of original seawater carbon oxygen and strontium isotope chemistry in this process coeval material was evaluated from individual horizons of formations spanning the permian to cambrian unaltered shells of low mg calcite articulated brachiopods retain original seawater oxygen carbon and strontium isotope compositions as old as late ordovician assessments of older specimens are hampered by a lack of suitable material coeval brachiopod whole rock sets a definitive assessment of cement marine chemistry is difficult due to the paucity of material but despite this caveat cements hold some promise for retaining original carbon and possibly strontium isotope seawater values in contrast the potential of whole rock material as a proxy of original seawater chemistry is quite complex in some but not all instances the carbon isotopic composition of whole rock after detailed scrutiny and evaluation appears to represent an original seawater chemistry signal in a few instances their oxygen isotope compositions reflect original seawater values unlike the stable isotope compositions the strontium isotopes of all studied whole rock material permian to upper cambrian appear not to reflect original seawater chemistry values thus the potential for retaining original seawater isotope chemistry and serving as specific proxies in order of decreasing reliability are 1 unaltered low mg calcite brachiopods c o and sr isotopes 2 pristine marine cements c and sr isotopes and 3 whole rock material c isotopes carbon oxygen and strontium isotope compositions of ordovician trilobites mirror those of coeval unaltered brachiopods cambrian trilobites hold significant promise as an important proxy of original seawater isotope chemistry but further studies are needed to ascertain their full potential the survey of isotopes in some ordovician and cambrian intermediate low mg calcite trilobites demonstrates their potential as an important proxy of original seawater chemistry

pollen analysis of a long upper pleistocene continental sequence in a velay maar massif central france abstract a new 20 m sequence is presented which is based on 279 spectra derived from a coring at le bouchet lake massif central france the vegetational history of this region is described back to the end of the last interglacial ribains interglacial the two preglacial early glacial forested interstadials st geneys 1 and st geneys 2 are evidence for the first time in the massif central in spite of the altitude of the site 1200 m they suggest a quite temperate vegetation with the same mesophilous character as during the holocene the pleniglacial appears to be threefold with two cold episodes lower and upper pleniglacial divided by a long complex period of moderate climatic improvement the vegetation history of this mountain region is compared with that evidenced for the same period on the basis of the sequence of les echets at a lower altitude 267 m botanical and climatic inferences are discussed

brachiopod taxa and shell portions reliably recording past ocean environments toward establishing a robust paleoceanographic proxy 1 fossils of rhynchonelliform brachiopods marine invertebrates constitute 70 of the samples used for delineating a well known phanerozoic trend in oxygen isotope composition 18o of low mg calcite shells the trend represents secular variations in temperature and or 18o of ancient seawater however the use of brachiopods as a paleoceanographic proxy is based on the presupposition that the shell calcite is precipitated in isotopic equilibrium with ambient seawater here we show that high resolution time series of the shell 18o values along the maximum growth axes of two long lived cool water brachiopods are identical to greater than or less than those of calcite precipitated in isotopic equilibrium with ambient seawater depending on the difference in shell growth rates coupled with 18o data from subtropical and warm temperate brachiopod species examined in our previous studies we provide a sound framework illustrating which taxa and shell portions reliably recorded past ocean environments

87sr 86sr ratios in permo carboniferous sea water from the analyses of well preserved brachiopod shells abstract sr isotopic analyses of well preserved portions of permo carboniferous brachiopods distributed globally confirm the general shape of the sr isotope age curve established by previous workers for this time interval there is little variation between the sr isotopic composition of unaltered portions of brachiopods and that of portions of the same shell interpreted to be diagenetically altered based on cathodoluminescence elemental and stable isotopic data however the sr isotopic composition in diagenetically altered micritic matrix adjacent to the shell is more radiogenic the sr isotopic composition in the unaltered portions of calcitic megafossils has potential as a stratigraphie tool

micromorphology and differential preservation of upper permian brachiopod low mg calcite abstract calcareous shells of rhynchonelliform brachiopods from the nesen formation late permian of iran were studied by scanning electron microscope cathodoluminescence and trace element chemistry to define their microstructure and state of preservation in the strophomenata shell succession the secondary layer consists of cross bladed laminar calcite and in a few species there is a tertiary layer of prisms in the rhynchonellata shell succession the secondary layer consists of elongated fibers and the tertiary layer of prisms all specimens were classified into six micromorphological types based on the fabric of the layer and the morphology of their microstructural units laminae fibres and prisms shell micromorphology and enclosing whole rock were further analyzed by cathodoluminescence and trace chemistry to assess preservation of brachiopod low mg calcite and specifically of their layers and microstructural units relative color frequencies were determined for each morphological type and degree of luminescence based on the lithology of the host rocks to evaluate the main factors that affect shell preservation results suggest that diagenetic alteration may depend on shell fabric and taxonomy as well as lithology of the host rock but it appears that the first and the second features are the most important factors in determining the degree of brachiopod low mg calcite preservation in general the fibrous secondary layer is likely more often and better preserved than its laminar counterpart irrespective of host rock lithology furthermore tertiary layers tend to be better preserved than secondary ones in rhynchonellata low mg calcite shells whereas no preferential preservation of either layer over the other was observed in the shells of strophomenata this information is important when selecting fossil brachiopod low mg calcite shells as geochemical proxies for paleoclimatic paleoecologic paleoenvironmental and other studies

how long and how stable was the last interglacial abstract surface ocean indicators in the north atlantic during marine isotope stage mis 5 correlate closely with the vegetational succession in northeastern france the melisey i silty layer which marks the end of the last interglacial biozone in la grande pile pollen record appears coeval with the polar front advance c24 registered in the core v29 191 by a sharply increased presence of ice rafted detritus and the cold water foraminifer neogloboquadrina pachyderma sinistral since this event is younger than the peak of mis 5d the last interglacial as recognized in northern france correlates not only with the mis 5e but also with a substantial part of mis 5d the last interglacial in la grande pile was twice as long as the holocene and the climate in its first half was apparently not less stable than during the current interglacial if the future natural climates were to develop as analogs of the past then the onset of the next glacial environments on land would be still many millennia ahead

gravity current propagation up a valley the authors gratefully acknowledge the national science foundation grant oce 0824636 and the office of naval research grant n00014 09 1 0844 for their support of the 2013 whoi geophysical fluid dynamics summer school where much of the research presented in this paper was performed

eustasy and sea water sr composition application to high resolution sr isotope stratigraphy of miocene shallow water carbonates oceanic 87 sr 86 sr isotope ratios are strongly influenced by rates of silicate weathering and therefore linked not only to glaciation but also to sea level change the present study combines analysis of sequence stratigraphy and basin architecture with sr isotope stratigraphy in miocene shallow water sediments in southern portugal and crete greece the common method is to use smoothed global sea water sr isotope reference curves but here a different approach is chosen instead measured sr isotope curves are correlated with unsmoothed reference curves by identification of similar fluctuations in the order of several 100 kyr transgressive intervals are characterized by increasing sr isotope ratios interpreted as corresponding to intensified silicate weathering as a consequence of deglaciation while lowstand deposits have low sr isotope ratios comparison of sr isotope curves and sedimentary sequences in the studied basins with independent global d 18 o data and data on global sea level might suggest a general relationship supporting a connection to global climate change because of these relationships the method presented herein has a high potential for use in high resolution age dating and is also applicable in shallow water sediments

some new aspects for the modelling of isothermal remanent magnetization acquisition curves by cumulative log gaussian functions rock samples containing ferri magnetic minerals acquire an isothermal remanent magnetization irm after exposure to a direct magnetic field measuring irm b allows to produce irm acquisition curves which were modelled by cumulative log gaussian clg functions robertson and france 1994 to discriminate the different magnetic phases an approach of how to find the best model has been added to this method from the investigation of a magnetite sample it is inferred that with the method the remanence acquisition coercive force for each magnetic component in a sample can be deduced the method allows to detect minute concentrations of magnetically hard material in a predominant magnetically soft sample and vice versa it furthermore allows to extrapolate the irm behaviour of samples that do not reach saturation irm in the experiment the study of a natural hematite renders it possible that even well defined hematite may be contaminated by ferri magnetic impurities biasing the remanence acquisition coercive force of the sample towards lower values

a rock magnetic record from lake baikal siberia evidence for late quaternary climate change rock magnetic measurements of sediment cores from the academician ridge region of lake baikal siberia show variations related to late quaternary climate change based upon the well dated last glacial interglacial transition variations in magnetic concentration and mineralogy are related to glacial interglacial cycles using a conceptual model interglacial intervals are characterized by low magnetic concentrations and a composition that is dominated by low coercivity minerals glacial intervals are characterized by high magnetic concentrations and increased amounts of high coercivity minerals the variation in magnetic concentration is consistent with dilution by diatom opal during the more productive interglacial periods we also infer an increased contribution of eolian sediment during the colder windier and more arid glacial conditions when extensive loess deposits were formed throughout europe and asia eolian transport is inferred to deliver increased amounts of high coercivity minerals as staining on eolian grains during the glacial intervals variations in magnetic concentration and mineralogy of lake baikal sediment correlate to the specmap marine oxygen isotope record the high degree of correlation between baikal magnetic concentration mineralogy and the specmap oxygen isotope record indicates that lake baikal sediment preserves a history of climate change in central asia for the last 250 ka this correlation provides a method of estimating the age of sediment beyond the range of the radiocarbon method future work must include providing better age control and additional climate proxy data thereby strengthening the correlation of continental and marine climate records

biochemostratigraphy of the upper frasnian in the namur dinant basin belgium implications for a global frasnian famennian pre event the upper frasnian sequence of the namur dinant basin in southern belgium consists of mixed siliclastic carbonate succession of a ramp setting where the sequence spans the rhenana linguiformis conodont zones earlier studies investigated the chemostratigraphic variations during the frasnian famennian event but little has been yet known about the nature of the counterpart variations that immediately preceded that time interval despite the scarcity of well preserved brachiopods sixty one calcitic shells were collected mainly from beds of the neuville and les valisettes formations lower and upper rhenana zones to investigate biochemostratigraphic profiles of oxygen carbon isotope and rare earth element ree variations of the time interval immediately before the frasnian famennian boundary the 18o and 13c values of the well preserved shells range from 9 5 to 5 6 vpdb 7 7 1 1 n 33 and from 1 8 to 3 8 vpdb 1 1 1 7 n 33 respectively which are within the documented global values the c and o isotope profiles exhibit parallel shifts particularly at the top of the neuville formation top of the lower rhenana zone which are associated with a sea level rise and shrinkage in the brachiopod community also the th u 0 9 0 6 n 16 and ce ce 2 2 0 5 n 16 ratios suggest deposition under reducing conditions consistent with sea transgression

isotopic and chemical intra shell variations in low mg calcite of rudist bivalves mollusca hippuritacea disequilibrium fractionations and late cretaceous seasonality isotopic 13c 18o and elemental mg sr mn fe compositions were analysed in sclerochronological profiles of several shells of late cretaceous rudist bivalves from greece turkey somalia and the arabian peninsula the preservation of original compositions of low mg calcite of outer shell layers is indicated by constant and high sr generally low fe and mn and the preservation of fibrous prismatic ultrastructures cyclic variations in 18o and mg are interpreted to reflect seasonal temperature salinity cycles and thus annual growth increments in shells of torreites amplitudes of correlated 13c and 18o cycles cannot be related to reasonable palaeotemperatures or salinity this isotopic pattern reflects vital fractionations of an extent which is unknown from modern bivalves in contrast almost identical ranges and amplitudes of 18o cycles are observed in 13 shells of five species from santonian campanian localities in central greece and northern turkey suggesting that seasonal variations in environmental conditions were recorded without significant vital fractionations the effect of seasonal salinity changes on 18o of the shells is evaluated and mean palaeotemperatures are constrained within the range of 30 32 5 c the annual range of temperature was estimated to be 7 c assuming a constant salinity this agrees with other isotopic proxies of late cretaceous palaeotemperatures and with global circulation models which predict higher low latitude sea surface temperatures than the present ones

variability in magnesium carbon and oxygen isotope compositions of brachiopod shells implications for paleoceanographic studies abstract this study presents the carbon oxygen and magnesium isotope compositions of two modern brachiopods terebratalia transversa and frieleia halli and one fossil specimen 2 3 ma terebratula scillae the aim of this study is to investigate the variability of these isotopic compositions and to evaluate the potential of brachiopods as a proxy of past seawater 26mg values the two investigated brachiopod shells present the same range of 26mg variation up to 2 this variation cannot be ascribed to changes in environmental parameters temperature or ph as has been previously observed the primary layer of calcite shows the largest degree of oxygen and carbon isotope disequilibrium relative to seawater in contrast the 26mg value of the primary layer is comparable to that of the secondary calcite layer value in both t scillae and t transversa negative trends are observable between magnesium isotopic compositions and oxygen and carbon isotopic compositions these trends can be explained by kinetic effects linked to changes in growth rate during the brachiopod life the innermost calcite layer of t transversa is in isotopic equilibrium for both oxygen and magnesium and could therefore be the best target for reconstructing past 26mg values of seawater

an attempt at correlation between the velay pollen sequence and the middle pleistocene stratigraphy from central europe abstract long continuous lacustrine sequences constitute on the continent a precious tool for coupling the long term continental environmental changes with deep sea and ice core records using the count from the top method moreover they can contribute to long distance correlation on the continent itself and thus help to classify discontinuous sedimentary records palynostratigraphical correlation is proposed here between the velay long sequence and the late middle pleistocene series from central europe with special attention to temperate episodes the similarities between the praclaux and the holsteinian interglacial suggest that they are both contemporaneous with marine isotopic stage mis 11 even if absolute dates are still divergent the evidence of two major warm periods with an interglacial type of vegetation between the holsteinian and the eemian is confirmed by the velay record

cautionary note on magnetic grain size estimation using the ratio of arm to magnetic susceptibility the ratio of anhysteretic remanent magnetization arm to magnetic susceptibility is widely used for rapid estimation of magnetic grain size variations on interpreting arm variations no significant influence of interactions among magnetic grains on arm acquisition is usually assumed implicitly although some previous experiments using artificial sediments and biogenic magnetites opposed this assumption our rock magnetic study of deep sea surface sediments from the pacific ocean showed that arm depends strongly on the concentration of magnetic minerals and on the r value of cisowski 1981 an index of the strength of magnetic interactions this result demonstrates that arm can be influenced significantly by magnetic interactions in natural sediments we corrected for the influence of the magnetic interactions using the observed concentration dependence of arm regional variations of arm values before the correction were geologically unnatural in terms of magnetic grain size variations previous interpretations of arm variations on magnetic grain size without consideration of magnetic interactions may not be valid

rock magnetic properties of eemian maar lake sediments from massif central france a climatic signature the hypothesis of a climate variability within the last interglacial eemian suggested by oxygen isotope data of a greenland ice core grip was later supported by magnetic susceptibility organic matter and pollen signatures in the eemian lake sediments of the lac du bouchet france in the present paper we analyse in detail the rock magnetic properties of these sediments in order to determine the origin of the magnetic susceptibility variations furthermore in order to verify the empirical relation between magnetic susceptibility and climate we studied two eemian sequences from neighbouring lakes lac st front and ribains maar lake rock magnetic investigations mainly consisted of analyses of anhysteretic and isothermal remanent magnetizations along with hysteresis measurements carried out on pilot samples lac du bouchet susceptibility variations are at least partly affected by postdepositional magnetite dissolution lac st front sediments show a complex behaviour resulting in partly contradicting interpretations of rock magnetic parameters possible explanations may be the presence of a very fine grained magnetite or the presence of maghemite ribains maar lake sediments show a homogeneous magnetic mineralogy without major variations in most of the rock magnetic parameters susceptibility records of the three lakes were compared under the simplified assumption that magnetic susceptibility mainly reflects variations of the detrital titano magnetite input only a poor correlation between the three eemian susceptibility sequences is observed suggesting that local effects including dissolution and dilution effects may have altered the original detrital climatic signal the purely detrital origin of the lac du bouchet eemian susceptibility variations must thus be questioned but it nevertheless appears to be the only lake whose susceptibility variations can tentatively be correlated with the grip eemian oxygen isotope record

towards a better understanding of magnesium isotope ratios from marine skeletal carbonates abstract this study presents magnesium stable isotope compositions of various biogenic carbonates of several marine calcifying organisms and an algae species seawater samples collected from the western dutch wadden sea and reference materials the aim of this study is to explore the influence of mineralogy taxonomy and environmental factors e g seawater isotopic composition temperature salinity on magnesium isotopic 26mg ratios of skeletal carbonates using high precision multi collector inductively coupled plasma mass spectrometry we observed that the magnesium isotopic composition of seawater from the semi enclosed dutch wadden sea is identical to that of open marine seawater we further found that a considerable component of the observed variability in 26mg values of marine skeletal carbonates can be attributed to differences in mineralogy furthermore magnesium isotope fractionation is species dependent with all skeletal carbonates being isotopically lighter than seawater while 26mg values of skeletal aragonite and high magnesium calcite of coralline red algae indicate the absence or negligibility of metabolic influences the 26mg values of echinoids brachiopods and bivalves likely result from a taxon specific level of control on mg isotope incorporation during biocalcification moreover no resolvable salinity and temperature effect were observed for coralline red algae and echinoids in contrast mg isotope data of bivalves yield ambiguous results which require further validation the data presented here point to a limited use of mg isotopes as temperature proxy but highlight the method s potential as tracer of seawater chemistry through earth s history

oxygen and carbon isotope and sr ca signatures of high latitude permian to jurassic calcite fossils from new zealand and new caledonia abstract calcite fossils from new zealand and new caledonia provide insight into the permian to jurassic climatic history of southern high latitudes southern hl and triassic southern intermediate latitudes southern il these results permit comparison with widely studied coeval sections in low latitudes ll and il oxygen isotope ratios of well preserved shell materials indicate a partially pronounced sea surface temperature sst gradient in the permian whereas for the triassic no indication of cold climates in the southern hl is found the late jurassic of new zealand is characterized by a slight warming in the oxfordian kimmeridgian and a subsequent cooling trend in the tithonian systematic variations in the 13c values of southern hl samples are in concert with those from ll sections and confirm the global nature of the carbon isotope signature and changes in the long term carbon cycle reported earlier systematic changes of sr ca ratios in late triassic brachiopods falling from 1 19 mmol mol in the oretian early norian to 0 67 mmol mol in the warepan late norian and subsequently increasing to 1 10 mmol mol in the otapirian rhaetian are observed also sr ca ratios of late jurassic belemnite genera belemnopsis and hibolithes show synchronous changes in composition that may be attributed to secular variations in the seawater sr ca ratio for the two belemnite genera an increase from 1 17 mmol mol in the middle heterian oxfordian to 1 78 mmol mol in the mangaoran late middle tithonian and a subsequent decrease to 1 51 mmol mol in the waikatoan late tithonian is documented

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

lock exchange flows in sloping channels two dimensional variable density navier stokes simulations have been conducted in order to investigate the effects of a slope on the classical lock exchange flow simulations of full lock releases show that the flow goes through an initial quasi steady phase that is characterized by a constant front velocity this quasi steady front velocity has a maximum for slope angles around 40 and it persists up to a dimensionless time of the order of 10 the flow subsequently undergoes a transition to a second phase with a larger unsteady front velocity these computational findings were confirmed by experimental observations of lock exchange flows in a tube of circular cross section the reason for the observed transition from a quasi steady front velocity to a larger unsteady value is found in the continuous acceleration of the stratified fluid layers connecting the two fronts by the streamwise component of the gravity vector this acceleration leads to a situation where the fluid layers behind the current front move faster than the front itself initially the resulting addition of fluid to the current front from behind affects only the size of the front while its velocity remains unchanged eventually the current front is unable to absorb more fluid from behind and its velocity has to increase thereby triggering the transition to the second unsteady phase the transition time is determined as a function of the slope and the density ratio of the two fluids

chemical stabilization of low mg calcite an example of brachiopods abstract trace element study of brachiopod shells from the upper ordovician ellis bay formation anticosti island quebec canada shows that they underwent only a slight 20 diagenetic equilibration with meteoric waters despite 450 million years of postdepositional history this in contrast to large trace element repartitioning observed in their enclosing rocks attests to the relative stability of low mg calcite even within the realm of meteoric waters paleozoic brachiopods apparently exerted a biological control on the distribution of na and mg in their low mg calcitic shells preferentially incorporating the former and discriminating against the latter trace constituent

18o16o and 13c12c in lower paleozoic articulate brachiopods implications for the isotopic composition of seawater three hundred and eleven articulate brachiopods with extensive geographic coverage spanning the cambrian to silurian stratigraphic interval were analyzed for oxygen and carbon isotopic composition cambrian samples have 18o 7 ordovician samples 2 4 and silurian samples 1 9 confirming the previously established trend towards lighter isotopic compositions with increasing age throughout the lower paleozoic forty nine best preserved ordovician and silurian samples were identified based on scanning electron microscopy and trace element analysis they were found to bracket the isotopic compositions of over 85 of specimens from these stratigraphic intervals supporting widespread preservation of the isotopic signal some latest ordovician and lower ludlovian samples associated with shale sequences are apparently enriched in 18o these are interpreted as an environmental phenomenon perhaps related to water temperature and glaciation a number of silurian samples of varying genera and stratigraphic levels are highly enriched in 13c up to 6 some are shale related but some are associated with carbonate bearing basins these are also thought to represent near original compositions but a single environmental cause is unknown the present data show that luminescence is not a decisive criterion for evaluating the degree of brachiopod preservation whole shell values were isotopically similar to their nonluminescent portions for both oxygen and carbon

rock magnetism of late neogene and pleistocene deep sea sediments relationship to sediment source diagenetic processes and sediment lithology we use bivariate scatter plots to illustrate variations in selected rock magnetic properties low field susceptibility anhysteretic and isothermal remanence of late neogene and pleistocene deep sea sediments from 16 sites in the arctic ocean north atlantic equatorial atlantic and north pacific ocean and the arabian sea our intention is to examine the ability of the rock magnetic properties to differentiate the sediments according to factors such as lithology geographical area and the dominant mode of terrigenous sedimentation which at these sites is via ice rafting via bottom currents or via eolian processes overall correlations between sediment magnetic properties and gross lithology is poor and factors such as the source and transport path of terrigenous sediment and detrital magnetic minerals together with the action of reductive diagenetic processes are the major controls on the magnetic properties on the bivariate scatter plots sites with major ice rafted contributions tend to have high sedimentary ferrimagnetic mineral concentrations relatively coarse ferrimagnetic grain sizes and scattered sample point distributions in contrast sites where we infer significant bottom current supply of terrigenous material have tightly grouped sample point distributions carbonate sediments in which the terrigenous component is supplied by eolian processes tend to have a broad range of magnetic mineral concentration caused by glacial interglacial fluctuations in carbonate accumulation and eolian activity sediments containing significant volcanogenic material have high concentrations of relatively coarse grained ferrimagnetic material reductive diagenesis is a significant determinant of sediment magnetic properties in high productivity areas and has the effect of preferentially removing the fine grained ferrimagnetic fraction causing a coarsening of the ferrimagnetic grain size distribution and a rise in the antiferromagnetic ferrimagnetic ratio

diagenetic evaluation of a pennsylvanian carbonate succession bird spring formation arrow canyon nevada u s a 1 brachiopod and whole rock comparison abstract diagenetic evaluation of the pennsylvanian bird spring formation arrow canyon nevada u s a involved the detailed petrographic and geochemical examination of its brachiopod and whole rock components 13 c 18 o and 87 sr 86 sr of whole rock wr statistically p 0 0001 do not agree with isotope values of coeval brachiopod low mg calcite lmc more importantly a detailed investigation of the best preserved fine grained whole rock material demonstrates that it does not universally preserve its carbon isotope values in contrast with hypothetical predictions furthermore lumped trace chemistry or stable isotope tests do not unequivocally identify brachiopod or whole rock fine to coarse grained samples that carry an original seawater signal instead diagenetic evaluation involving as many screening tests as possible on a horizon by horizon level to compensate for spatial and temporal variations is necessary to identify the sample s that carries an original seawater signature many brachiopods from the bird spring formation are blue to non luminescent and carry microstructures and trace element contents similar to those of their modern tropical counterparts concurrence of chemical results between well preserved brachiopods and whole rock if originally low mg calcite is achieved in 22 of coeval samples for 13 c blmc wr with natural limits of 0 25 in 20 of samples for 18 o blmc wr with natural limits of 0 25 and in 9 of samples for 87 sr blmc wr with global limits of 0 000025 after an adjustment for mineralogical fractionation if whole rock is considered originally aragonite the concurrence of 13 c blmc wr drops to 0 and for 18 o blmc wr it drops to 6 furthermore comparison of stable isotopes of our well preserved brachiopods with those of preserved whole rock from the literature suggests that they are significantly different p 0 0001 with results of the latter dataset being more negative by about 0 77 2 57 with mineralogical adjustment for 13 c pdb and 1 31 2 11 for 18 o pdb thus our integrated screening and comparative tests indicate that 1 an overwhelming number of the whole rock samples from the bird spring formation carry a diagenetic instead of a primary signal for both carbon and oxygen isotopes and 2 many of the biogenic low mg calcite brachiopods in this succession carry an original chemical signal suitable for the reconstruction of high resolution seawater isotope curves representative of the pennsylvanian north american epeiric sea and potentially of the global oceans

the role of the deep ocean in north atlantic climate change between 70 and 130 kyr ago the suggestion1 that changes in north atlantic deep water nadw production are linked through surface heat flux to the atmospheric temperature over greenland is supported by earlier indications2 3 that nadw production decreased during glacial times and by the subsequent finding4 6 that it declined during the younger dryas cool period at the end of the last glaciation changes in north atlantic surface temperatures have been found7 to mirror high frequency temperature changes recorded in greenland ice cores over the past 80 kyr but the connection to abyssal circulation has yet to be established except for one or two isolated oscillations8 9 here we present carbon and oxygen isotope analyses of benthic foraminifera in a high resolution north atlantic deep sea sediment core for the period 70 130 kyr ago these data allow us to reconstruct the history of nadw production which shows a close correlation with greenland climate variability for much of this time interval suggesting that the climate influence of nadw variability was widespread we see no evidence however for changes in nadw production during substage 5e the eemian interglacial period in contrast with recent ice core data10 which suggest severe climate instability in greenland during this time period our results may support suggestions based on data from a second ice core that this apparent instability is an artefact caused by ice flow11 alternatively the eemian climate instability may have had a different origin from the subsequent climate events

petrology and diagenetic evolution of neoproterozoic ooids libby formation western montana u s a abstract radial concentric and twinned sparry ooids from the upper belt supergroup originally formed as mixed mg calcite and aragonite and aragonite textural evidence suggests that mg calcite ooids may have formed along with the ooids having an original aragonite mineralogy strontium concentrations of 2400 to 2900 ppm support an aragonitic precursor to the twinned sparry ooids and sr values of 2500 ppm strongly suggest that the radial concentric ooids had an aragonitic component in addition to the mg calcite suggested by the preserved fabric trace element mn mg fe and sr values of ooids and early carbonate cements suggest that diagenetic trends for these proterozoic carbonates are similar to those established for their phanerozoic and archean counterparts mg fe and mn increase and sr decreases with successively later carbonate phases

toward the discrimination of fine grained ferrimagnets by magnetic measurements in lake and near shore marine sediments the magnetic properties of low field susceptibility frequency dependent susceptibility fd and susceptibility of anhysteretic remanent magnetisation arm are used to define sets of natural soil and sediment samples within which by the criteria of king et al 1982 and maher 1988 the modal ferrimagnetic grain diameter is less than 0 07 0 1 m within this sample set two distinct groups with low and high values respectively for the quotients arm and arm fd are defined the first group includes sediment samples from sites where published studies propose a detrital origin for the fine grained ferrimagnetic content where catchment samples are available for comparison they fall within the same envelope as do clays from palaeosol samples within chinese loess this envelope of low quotient values also overlaps with the values for the fine grained synthetic magnetite samples within maher s 1988 new mt series the high quotient envelope of values includes sediments from the adriatic sea and clays from saltmarsh and shallow water marine sediments in nw britain in these cases no catchment source is postulated for the fine grained magnetite the size range of magnetite in this set appears to be almost exclusively stable single domain ssd and a bacterial origin seems likely sample sets from estuarine environments between river inflow sites and the open sea show intermediate values which in the case of the potomac are ordered by distance down river although at this stage magnetic measurements alone cannot discriminate between bacterial and fine grained detrital ferrimagnets in sediments they hold out some promise of doing so provided the distinctions proposed here can be substantiated by transmission electron microscopy

the effect of confining boundaries on viscous gravity currents newtonian viscous gravity currents propagating along horizontal and inclined channels with semicircular and v shaped boundaries are examined similarity solutions are obtained from the governing mathematical equations and compared with closely matching data from laboratory experiments in which the propagation of glycerine along different channels was recorded geological applications of the results are discussed briefly

the eem stable isotope record along the grip ice core and its interpretation a 3029 m long deep ice core extending nearly to bedrock has been drilled at the very top of the greenland ice sheet summit by the greenland ice core project grip an international european joint effort organized by the european science foundation the ice core reaches back to 250 000 yr b p according to dating based partly on stratigraphic methods and partly on ice flow modeling a continuous and detailed stable isotope 18o profile along the entire core depicts dramatic temperature changes in greenland through the last two glacial cycles including abrupt climatic shifts during the eem sangamon interglaciation which is elsewhere recorded as a warm and stable period the stratigraphic continuity of the eemian layers has therefore been scrutinized new ice core studies comprising cloudy band observations deconvolution and frequency analyses lead to the conclusion that the climate instability suggested during the eem interglaciation in greenland is likely to be real though no conclusive evidence is available whereas latitudinal displacements of the north atlantic ocean current are considered the immediate cause of the glacial climate instability longitudinal displacements may be the immediate cause of the eemian instability if so the eemian climate changes will be much subdued outside the arctic region and will probably only be recognizable in sedimentary sequences of high sensitivity and temporal resolution

eemian climatic and hydrographical instability on a marine shelf in northern denmark abstract benthic foraminifera and stable isotope data from the last interglaciation eemian substage 5e from a borehole at skagen denmark provide evidence for major environmental and hydrographic changes during this period during the first millennium of the eemian water masses covering northern denmark became gradually warmer temperate conditions prevailed during most of the interglaciation but these were interrupted by two periods with decreased water temperatures the first cooling event s 1 was not very distinct at skagen but the second event s 2 seen in both the foraminiferal and oxygen isotope record represents a large shift to subarctic conditions carbon isotopes indicate a change in ocean circulation during both events no comparable climate variations are seen within the holocene record at the site the final cooling of the water masses associated with the substage 5e 5d boundary occurred within a few hundred years these last interglacial climatic changes were probably caused by variations in strength and or position of the north atlantic drift possibly as a result of varying vigor of the atlantic conveyor in addition minor variations in the fossil assemblages also indicate fluctuations in the inflow of atlantic water to the skagerrak kattegat area during the warm intervals of substage 5e

wasp waisted hysteresis loops mineral magnetic characteristics and discrimination of components in mixed magnetic systems rock magnetic studies of complex systems that contain mixtures of magnetic minerals or mixed grain size distributions have demonstrated the need for a better method of distinguishing between different magnetic components in geological materials hysteresis loops that are constricted in the middle section but are wider above and below the middle section are commonly observed in mixed magnetic assemblages such wasp waisted hysteresis loops have been widely documented particularly with respect to rare earth permanent magnets basaltic lava flows remagnetized paleozoic carbonate rocks and an increasingly wide range of other rocks our modelling combined with a review of previous work indicates that there are several conditions that give rise to as well as magnetic properties that are characteristic of wasp waisted hysteresis loops first at least two magnetic components with strongly contrasting coercivities must coexist this condition can arise from either mixtures of grain sizes of a single magnetic mineral or a combination of magnetic minerals with contrasting cocrcivities or a combination of these two situations second materials that give rise to wasp waisted hysteresis loops will have relatively high ratios of the coercivity of remanence to coercive force b cr b c because b0 is controlled by the soft low coercivity component whereas bcris controlled by the hard high coercivity component third values of b cr b c 10 usually only occur for strongly wasp waisted loops when the low coercivity component comprises an overwhelmingly large fraction of the total volume of magnetic grains fourth a given mixture of superparamagnetic and single domain sd grains is more likely to give rise to wasp waisted hysteresis loops than an equivalent mixture of sd and multidomain grains fifth our results provide empirical confirmation that the total magnetization of a material is the sum of the weighted contributions of each component in the absence of significant magnetic interaction between particles thus to contribute significantly to wasp waisted behavior a mineral magnetic component must give rise to a significant portion of the total magnetization of the rock as a result minerals with weak magnetic moments such as hematite need to occur in large concentrations to cause wasp waistedness in materials that also contain ferrimagnetic minerals we outline a method for determining the magnetic components that can give rise to wasp waisted hysteresis loops this method is based on high and low temperature magnetic measurements that are used to identify the dominant remanence bearing mineral s and on mineral magnetic techniques that are used to discriminate between different magnetic domain states the method is illustrated with several examples from archaeological geological and synthetic materials

large carbonate associated sulfate isotopic variability between brachiopods micrite and other sedimentary components in late ordovician strata carbonate associated sulfate cas is trace sulfate incorporated into carbonate minerals during their precipitation its sulfur isotopic composition is often assumed to track that of seawater sulfate and inform global carbon and oxygen budgets through earth s history however many cas sulfur isotope records based on bulk rock samples are noisy to determine the source of bulk rock cas variability we extracted cas from different internal sedimentary components micro drilled from well preserved late ordovician and early silurian age limestones from anticosti island quebec canada mixtures of these components whose sulfur isotopic compositions vary by nearly 25 can explain the bulk rock cas range large isotopic variability of sedimentary micrite cas 34 s depleted from seawater by up to 15 is consistent with pore fluid sulfide oxidation during early diagenesis specimens recrystallized during burial diagenesis have cas 34 s enriched by up to 9 from hirnantian seawater consistent with microbial sulfate reduction in a confined aquifer in contrast to the other variable components brachiopods with well preserved secondary layer fibrous calcite a phase independently known to be the best preserved sedimentary component in these strata have a more homogeneous isotopic composition these specimens indicate that seawater sulfate remained close to about 25 v cdt through hirnantian end ordovician events including glaciation mass extinction carbon isotope excursion and pyrite sulfur isotope excursion the textural relationships between our samples and their cas isotope ratios highlight the role of diagenetic biogeochemical processes in setting the isotopic composition of cas

the stratigraphic and geochemical imprints of late ordovician glaciation on far field neritic carbonates anticosti island eastern canada abstract the storm dominated open marine neritic carbonate facies continuously exposed in coastal cliffs and wide rocky tidal flat exposures at the western end of anticosti island form a 315 m thick expanded section spanning the ordovician silurian boundary these carbonate facies display deepening shallowing trends of different orders resulting in a hierarchical stacking of sedimentary cycles the carbonate facies within these multi order cycles represent sediments that were deposited from shoreline to deeper outer carbonate ramp 80 m in water depth and exhibit sea level changes of several tens of metres in magnitude field petrographic and geochemical evidence support a well preserved primary 18o signal in close equilibrium with the original paleoenvironmental conditions the 18o intracycle variations up to 1 0 in magnitude reveal repeated decreasing and increasing values during the transgressive and regressive portions of decametre tr cycles respectively although temperature salinity and ice volume influenced the recorded primary 18o signal orbital scale glacioeustasy ultimately controlled facies and cycle development and 18o signal during the katian immediately before the latest ordovician hirnantian glaciation the 3 5 myr long 18o signal recorded by our entire succession supports a protracted period of cooling leading into the main phase of latest ordovician hirnantian glaciation spectral analysis of the 18o record also reveals decametre variations which are associated with decametre scale transgressive regressive tr cycles possibly reflecting eccentricity orbital signals our study shows the importance of a thick expanded stratigraphic succession sampled at the highest resolution possible to decipher potential linkages between facies changes multi order stratigraphic cycles 18o signal and the earth s orbital parameters

oxygen and carbon stable isotope records of the lochkovian pragian boundary interval from the prague basin lower devonian czech republic abstract climate changes close to the lochkovian pragian event are still widely discussed carbonate 18o and 13c and conodont apatite 18o from medial to distal carbonate ramp sediments were analysed to provide further stable isotope data from the stratotype area in the prague basin the uppermost silurian to lower emsian 18o trends are put into an updated conodont biostratigraphy framework carbonate 18o and 13c are discussed in the context of facies dependent diagenesis the 13c pattern measured from different sections enables the correlation of intervals with development of different facies inside the prague basin positive 13c shifts are often coupled with trends of decreasing computed gamma ray cgr values interpreted as regressions whereas negative 13c shifts commonly coincide with opposite trends in cgr the lochkovian pragian boundary interval coincided with an increase in carbonate 13c and an increase in the 18o of conodont apatite and carbonate which we interpret as consequence of climate cooling generally the lochkovian was warmer than the pragian and earliest emsian