intercontinental correlation by sea level events in the early silurian of north america and china yangtze platform potential for eustatic sea level changes on continental platforms during early silurian llandovery time was highly propitious due to the double effects of lingering glaciation in gondwana and the rapid rate of sea floor spreading which assisted the general dispersion of many era tonic realms through middle paleozoic oceans following the initial mass melting of the late ordovician early silurian glaciers in north africa and arabia four smaller cycles of sea level fluctuation were recorded by recurrent shelly communities in a predominantly carbonate setting on the north american platform peaks in sea level rise occurred in late rhuddanian or early idwian a 4 b 1 positions early fronian c 1 position early telychian c 4 position and late telychian c 6 position times although absolute time control is poor the periodicity of these events may have been every 2 5 m y in the more submerged regions of the north american platform such as iowa and anticosti island diverse faunal associations distinguished by the presence of stricklandiid brachiopods were especially productive at peak times of transgression co occurrence of the calcareous green alga cyclocrinites with certain of these faunas indicates that maximum water depth was still within the photic zone at the other extreme low stands in sea level are identified by diminished faunal diversity as well as a combination of typical sedimentary structures and evaporite indicators located on a well defined precambrian craton the yangtze platform is now a large region in central and southwestern china during successive stages of the early silurian a thick sequence of graptolitic shales shelly carbonates and red beds were deposited on the platform of the four sea level peaks defined in north america three are recognized in the yangtze region there is very good evidence for a latest llandovery or earliest wenlock transgression based on the extensive distribution of the salopinella coronocephalus sichuanoceras fauna another clear and well dated sea level peak involves the occurrence of faunas with characteristic stricklandiid and pentamerid brachiopods at a level equivalent to the lower telychian c 4 position the initial silurian transgression appears to have reached its peak on the yangtze platform primarily during early idwian time b 1 position but this is based less surely on changing patterns in graptolite diversity at present there is no compelling evidence for a widespread early fronian c 1 position transgression in china successful matching of the other sea level events however substantially refines intercontinental correlation for lower silurian strata in the yangtze region of china and the central regions of north america

high resolution 87sr 86sr chemostratigraphy of the silurian implications for event correlation and strontium flux analyses of 87sr 86sr in silurian conodonts recovered from localities in north america and europe representing 13 of the 14 defined silurian conodont zones provide a high resolution record of seawater chemistry for the silurian period these data which are characterized by little or no scatter depict several high frequency cycles superimposed on a gradual longer term rise in 87sr 86sr for the silurian high frequency cycles have a duration of about one conodont zone and many correlate with sequence boundaries recognized around the world these data provide a much higher resolution image of secular changes in 87sr 86sr during the silurian and may require a rethinking of models of strontium isotope flux in marine basins

mapping sand and clay filled depressions on a coastal chalk clifftop using gravity and seismic tomography refraction for landslide hazard assessment in normandy france in this study we present a complete and successful case study where gravity and seismic refraction surveys detect and map previously poorly known sand and clay filled depressions within the top chalk layers in a costal context near dieppe normandy france this study was commissioned by local authorities after a coastal chalk cliff collapse exposed a sand and clay filled depression which turned into a 100 000 m3 landslide this resulted in a massive clifftop retreat exceeding 40 m which threatened infrastructure and amenities for risk and safety assessment coastal managers commissioned brgm to i determine the depth and extent of the sand and clay filled depression and ii map the presence of similar cliff top depressions in a 2 km long and 400 m wide band inland of the coast both geophysical methods allow the detection and mapping of the sand and clay filled depressions which are characterised by a co localized deepening of the first seismic horizon and a positive gravity anomaly seven auger holes confirm the geophysical interpretation with depth to the top of the chalk 60 m in some instances a map of the depth to the top of chalk is inverted using the gravity residuals the successful mapping of the previously poorly documented sand and clay filled depressions on the dieppe clifftop using both gravity and seismic refraction tomography was used in part to generate a coastal landslide hazard zonation map which is a useful tool for coastal managers who need to make hazard mitigating decisions

high resolution strontium isotope stratigraphy across the cambrian ordovician transition we have analyzed 214 fossil apatite samples from nine stratigraphic sections worldwide that cover the lower cambrian to lower ordovician for their strontium isotope ratios of these samples 180 from six sections that cover the cambrian ordovician transition 5 ma reveal how the extent of isotopic alteration can differ greatly according to lithology and sample type from three limestone sections 126 euconodont samples yield the most consistent 87sr 86sr ratios and are used in this article to constrain seawater 87sr 86sr across the cambrian ordovician boundary by contrast protoconodonts paraconodonts and inarticulate brachiopods are far less likely to retain a primary 87sr 86sr signature and appear to be of only limited value for chemostratigraphy seawater 87sr 86sr fell from maximum values for the phanerozoic of more than 0 7092 during the early late cambrian to 0 7090 by the earliest ordovician high resolution sampling has permitted the recognition of sinusoidal variations with a wavelength on the order of 1 ma that are superimposed on the overall fall in 87sr 86sr these variations may be caused by high order cycles in seawater 87sr 86sr or diagenetic alteration

construction of the silurian and devonian seawater 87sr 86sr curve the estimated path of seawater 87sr 86sr during the silurian and devonian is based on 86 analyses 84 whole rocks presented here and in other published results the seawater 87sr 86sr rose steadily throughout the silurian from a poorly constrained value near 0 70793 sw 114 at the ordovician silurian boundary the 87sr 86sr value at the silurian devonian boundary is near 0 70871 sw 36 based on an earliest devonian limestone suite from new york the 87sr 86sr falls through the early devonian to reach a low near 0 70772 sw 135 in the eifelian and givetian and rises to near 0 70803 sw 104 in famennian time the seawater 87sr 86sr at the devonian mississippian boundary is estimated to be near 0 70805 sw 102 the middle paleozoic sample suite is judged less suitable for defining seawater 87sr 86sr than those from other paleozoic periods the middle paleozoic seawater 87sr 86sr variation indicates domination of continental sr contributions during the silurian and later devonian the high ratio continental sr contribution is controlled by the climate and the area age and composition of exposed crystalline rocks the dominance of the oceanic low ratio sr during the early and part of middle devonian is coincident with a reported increase in continental volcanism the estimated rise and fall of sealevel leading to flooding or exposure of the continents does not appear to control seawater 87sr 86sr during the middle paleozoic

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

paleoenvironmental clues archived in non marine pennsylvanian lower permian limestones of the central appalachian basin usa abstract nonmarine limestones are a key component of the upper middle pennsylvanian through lower permian succession in the appalachian basin previous interpretations of their environments of deposition range from brackish coastal mudflats to hydrologically open freshwater lake complexes with peat forming vegetated marshes to semi closed or closed possibly saline shallow lakes developed on a distal alluvial plain ostracode wackestones packstones some exhibiting laminations and with fish debris articulated ostracode shells and phosphatic clasts define the lower portions of limestone beds or benches passing upward into ostracode peloidal wackestones packstones and intraclastic skeletal peloidal packstones grainstones desiccation features and rooting structures which are developed in the upper portions of the limestones record subaerial exposure pedogenic alteration and desiccation pseudomicrokarst and caliche like vadose and early diagenetic phreatic cements suggest a seasonally dry subhumid to semi arid regional climate many of the sedimentologic and diagenetic features of the limestones are characteristic of palustrine carbonates which coupled with their stratigraphic relation to paleo vertisols siliciclastics and coals indicate that they formed in broad seasonal wetland pond complexes that developed on distal regions of a low gradient distal alluvial plain under seasonally dry subhumid to semi arid climates integration of sr isotopic compositions of shark teeth with previously published stable isotope compositions of the limestones suggests that these purely continental environments were hydrologically semi closed to closed systems repeated stacking of these features at the bed to limestone bench scale defines repeated shallowing upward drying cycles at the 103 to 104 yr scale which were likely climate driven

ultra high resolution multivariate record and multiscale causal analysis of pridoli late silurian implications for global stratigraphy turnover events and climate biota interactions abstract the upper silurian and especially pridoli epoch is a critical interval for the understanding the evolution of earth s biota since it witnessed series of powerful extinction events global reorganizations of paleocommunities and expansion of new clades which assumed dominance in the subsequent devonian period the stratigraphic record of the eastern part of the silurian baltic basin represents an excellent candidate for the fine scale analysis of paleoecological and paleoceanographic dynamics therefore we presenting here stratigraphic record of the milaiciai 103 core south western lithuania of conodonts brachiopods 13ccarb 18ocarb and a series of various geochemical and geophysical proxies most of which were sampled at a very high resolution 11 ka spanning uppermost ludlow pridoli and the lowermost devonian the analysis revealed that the pridoli was characterized by four distinct long term dynamic states here named i normal pridoli i ii silal negative carbon isotopic excursion and extinction event iii normal pridoli ii and iv klonk positive stable carbon isotopic event and excursion the most significant change in most variables is detected approximately in the middle of the pridoli at the beginning of the delotaxis detorta zone at the recovery after silal event of conodonts and at the onset of collapse of brachiopod communities the analysis of dynamic complexity revealed the strong evidence for the presence of 405 ka metronome milankovitch cycles in the record of 13ccarb which constrains the duration of the pridoli epoch to 4 3 0 2 ma the recurrence plot analyses revealed deterministic coordination between 13ccarband conodont paleocommunity dynamics at all scales finally lead lag analysis using conditional joint recurrence revealed that conodont dynamics as a rule were driven by perturbations in the carbon cycle although silal event interval shown opposite pattern thus confirming the unusual nature of this previously unrecognized coordinated climatic and biotic event

the paleozoic minimum of 87sr 86sr ratio in the capitanian permian mid oceanic carbonates a critical turning point in the late paleozoic abstract the secular change in 87sr 86sr ratio of the paleozoic recorded the lowest value below 0 7070 in late middle permian i e the permian minimum suggesting that a major reform in oceanography occurred before the paleozoic mesozoic transition we have detected the correlative lowest 87sr 86sr value 0 706914 0 000012 from the middle upper permian paleo atoll limestone in japan formed primarily on an ancient seamount in mid panthalassa the stratigraphic horizon of the minimum was constrained to the capitanian interval 265 8 260 4 ma middle permian by fusulines as the mid oceanic data represent the global average the present study confirmed the chemostratigraphical utility of the capitanian minimum of 87sr 86sr ratio in global correlation after the long term nearly 280 million years decrease throughout the paleozoic since the cambrian a remarkable turnover of seawater 87sr 86sr values appeared in the capitanian immediately before the guadalupian lopingian middle late permian boundary a major global change likely appeared in the capitanian to change the sr isotope balance in seawater from a mantle flux dominated to a continental flux dominated regime the initial rifting of pangea probably started in the capitanian and the rifting induced new connection of many intra supercontinental drainage systems to the superocean may have caused the overturn in global sr isotopic trend

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

a positive trend in seawater 87sr 86sr values over the early middle frasnian boundary late devonian recorded in well preserved conodont elements from the holy cross mountains poland abstract over the early middle frasnian boundary interval late devonian the oceans experienced major changes in global carbon cycling and nutrient dynamics with a prominent positive carbon isotope shift at the base of the palmatolepis punctata zone middle frasnian the aim of this study was to construct seawater 87 sr 86 sr ratio curves for the pa transitans pa hassi zonal interval using well preserved conodont apatite from two sections in the holy cross mountains south central poland the final curves suggest that seawater 87 sr 86 sr values were steady at 0 70794 0 70799 during the transitans zone but began to rise in the early punctata zone towards a value of 0 70814 in the late punctata zone an increase of 0 0002 the increase in seawater 87 sr 86 sr values over the early middle frasnian boundary appears to be the second of two prominent short term rises in 87 sr 86 sr values which led to an overall shift in values from a givetian plateau of between 0 70780 and 0 70785 to a late frasnian plateau of between 0 7080 and 0 7082 correlation with a regional positive 13 c anomaly and evidence for eutrophication in the marine environment suggests that the causes of these phenomena may be linked and that the positive 87 sr 86 sr shift was caused by an increase in the continental flux of sr to the oceans i e the weathering flux a possible explanation for an increase in the weathering flux is the denudation of a new acadian eovariscan orogen which would have been mostly weathered in the humid warm tropical equatorial region

strontium and carbon isotope stratigraphy of the llandovery early silurian implications for tectonics and weathering abstract a high resolution 87sr 86sr curve and paired 13c carbonate organic data set is generated for the llandovery series from the ikla drill core in estonia a 13c carbonate curve is also presented from the pancake range in nevada observed 87sr 86sr values in the ikla drill core are at a minimum in the early llandovery rhuddanian stage 0 7079 to 0 7080 and then trend to more radiogenic ratios in the basal part of the telychian stage an 87sr 86sr high near 0 7084 is observed in the telychian at the top of the studied section the range of values is in general agreement with the data from previous sample sets of brachiopods and conodonts recovered from localities in north america and europe that record a rising trend in the 87sr 86sr ratio throughout the llandovery from approximately 0 7080 to 0 7084 the major increase in the 87sr 86sr ratio during the late llandovery may be due to weathering of radiogenic source rocks that were uplifted during early silurian continent continent collisions the sr rise potentially coincides with the occurrence of an unusually thick sequence of k bentonite beds representing large magnitude ash falls in the early telychian a previously documented negative 13c excursion in marine carbonates in the lower telychian interval of the ikla core is quasi synchronous with the increase in 87sr 86sr our new organic matter 13c data from the ikla core confirm that this negative 13c carbonate excursion is not a result of diagenesis furthermore a negative 13c excursion in carbonates from the early telychian portion of the pancake range section in nevada seems to confirm the global scope of this carbon cycle perturbation

conodont apatite δ88 86sr and δ44 40ca compositions and implications for the evolution of palaeozoic to early mesozoic seawater abstract we present high precision tims double spike stable isotope measurements of both 44 40 ca and 88 86 sr together with radiogenic 87 sr 86 sr ratios determined from conodont apatite these data represent five intervals ranging from the early ordovician to late triassic the conodont 44 40 ca values relative to nist 915a range from 0 47 to 0 15 with an apparent shift to more positive values between the early silurian and late devonian early carboniferous similar to the brachiopod based marine 44 40 ca record farkas et al 2007a we calculated a 44 40 ca seawater bio apatite fractionation factor of about 1 9 which allowed us to reconstruct a palaeo seawater 44 40 ca record from bio apatites despite a slightly positive offset of about 0 2 to 0 5 the 44 40 ca record obtained from bio apatites is consistent with the previously reported 44 40 ca seawater record inferred from carbonates we find that unlike the carbonate 44 40 ca records the 88 86 sr measurements from conodont apatite show unexpectedly large variations up to 1 with ratios ranging from 0 6 to 0 3 these reconnaissance data reveal a reasonable correlation between 88 86 sr and radiogenic 87 sr 86 sr r 2 0 60 n 13 p 0 002 suggesting that the controls from differential weathering regimes and or continental crustal compositions buffered ancient seawater compositions

radiogenic isotopes systematics and applications to earth surface processes and chemical stratigraphy radiogenic isotopes have wide application to chemical stratigraphy geochronology provenance studies and studies of temporal changes in earth surface processes this paper briefly reviews the principles of radiogenic isotope geochemistry and the distribution of a number of elements of interest in the environment and then uses this information to explore the range of applications to chemical stratigraphy and other fundamental subjects of sedimentary geology many of these applications center on the reconstruction of secular variations in paleoseawater isotope signals these seawater isotope curves can be used for stratigraphic correlation and to assess changes through earth history in processes such as tectonic uplift climate change biogeochemical cycling ocean circulation crustal growth and surface water evolution understanding the modern biogeochemical cycle of the element isotope system of interest is essential for gaining the maximum information regarding the operation of ancient cycles the main sources of uncertainty for reconstructing seawater isotope curves involve diagenetic alteration sample impurities and errors in age assignments rigorous sample selection criteria and pretreatment methods are keys to reconstructing the most accurate seawater isotope curves applications are discussed for the rb sr sm nd la ce lu hf re os u th pb k ar and cosmogenic isotope systems d 2003 elsevier b v all rights reserved

a conodont based silurian chronostratigraphy ranges of 79 conodont species are used to effect a graphic correlation of upper llandoverian pridolian silurian rocks in 30 stratigraphic sections in europe and north america a silurian composite standard section css developed by this method provides the total stratigraphic ranges for all species for which there is information in the system these ranges are stated in terms of the sequence of silurian rocks at cellon austria which is the standard reference section srs the llandoverian wenlockian and ludlovian pridolian boundaries are recognized based on the position of the golden spike in the boundary stratotypes the leasows hughley brook and pozary sections which form parts of the css range data for graptolite species in ten of the stratigraphic sections are used to approximate positions of all other boundaries between silurian series and stages that have been designated in boundary stratotypes that are not parts of the composite standard section the pridolian is shown to have had a longer duration than either the ludlovian or wenlockian and the llandoverian possibly approximated the pridolian in duration the css is divisible into 48 standard time units stu9s of conceptually equal length hence the chrono stratigraphy based on it resolves at a level two to four times higher than any previously proposed for the silurian the css is also divided into a succession of conodont chronozones that are based on zones proposed by walliser 1964 aldridge 1972 and barrick and klapper 1976 conodont chronozones can be recognized with confidence only in sections that are parts of the css framework

evaluation of the salinic i tectonic cancaniri glacial and ireviken biotic events biochemostratigraphy of the lower siluriansuccession in the niagara gorge area canada and u s a abstract well preserved brachiopods from the niagara gorge area anticosti island britain gotland and estonia were utilised to delineate a complex isotopic evolution for llandovery wenlock seawater the sr isotope record reflects the salinic i tectophase of the late llandovery in the continuous increase in 87sr 86sr values from 0 708070 to 0 708346 the salinic ii tectophase is marked by relative constancy of sr isotope values until the late wenlock when it rises from 0 708345 to 0 708430 the second tectonic phase was therefore likely only of a regional nature the carbon isotopes during the llandovery fall within a band of about 1 to 3 a range comparable to modern low latitude brachiopods a large positive 13c excursion of about 3 identifies the ireviken event excursion characterizes the early wenlock the biotic crisis and the isotope excursion itself may be ultimately related to the onset and duration of the cancaniri glaciation although a direct causative scenario is as yet unknown the oxygen isotopic trends of well preserved brachiopods clearly reflect a warm climate interval during the latest llandovery associated with the silurian sea level highstand subsequently in the early wenlock the sea level fell with the onset of the cancaniri glaciation in the southern hemisphere this is reflected in a significant positive 18o excursion particularly in brachiopods from the niagara gorge area brachiopods from lower latitudes were awash in warm tropical currents and therefore exhibit somewhat more negative 18o values indicating a lesser cooling gradient

dissolution methods for strontium isotope stratigraphy guidelines for the use of bulk carbonate and phosphorite rocks diverse carbonate dissolution methods have been applied to bulk carbonate rocks in order to target least altered components for strontium isotope stratigraphy sis this is especially important for precambrian and cambrian studies for which no suitable skeletal material is available one proven method for bulk limestones involves the removal of up to a third of the powdered sample using an acid pre leach before partial dissolution of the rest of the sample using a weak acid or acid buffer solution we applied a similar technique to dissolve a range of lithologies limestone dolostone and phosphorite and compared the strontium isotopic composition of various leaches to contemporaneous seawater our results vindicate this approach and allow us to conclude that some dolomitic and phosphatic rock components may retain a near primary seawater 87sr 86sr composition once contaminant strontium from secondary calcite and other phases has been removed commonly applied trace element e g mn sr mg ca and isotopic c o screening cut offs were also examined in the light of these results and proved unreliable particularly in the case of dolostones and partially dolomitized limestones we recommend that rigid sample selection and sequential leaching procedures be applied to all sis studies of bulk materials and propose a general protocol for strontium isotope studies on marine authigenic rocks which may also be applicable to rare earth element and other geochemical studies of marine authigenic minerals in the future

the strontium isotopic composition of ordovician and silurian brachiopods and conodonts relationships to geological events and implications for coeval seawater utilized for strontium isotope measurements the results document a gradual decrease in 87 sr 86 sr from 0 7091 to 0 7087 from tremadoc to llandeilo a sharp decline to 0 7078 during the late llandeilo early caradoc little change during caradoc and the ashgil and a steady rise to 0 7087 through the silurian these long term 10 7 yr variations with magnitudes in the range of 10 23 are interpreted to be controlled primarily by continental collisional tectonics and its associated erosion and weathering the gradual decrease in 87 sr 86 sr ratio during the early ordovician may record the reduction in uplift and weathering rates due to waning of the pan african orogenies the rapid decline near the llandeilo caradoc boundary suggests a strong hydrothermal flux likely due to increased sea floor spreading and a possible superplume event the latter may have caused the prominent transgressive phase the largest in the phanerozoic which would have muted continental flux input although the caradoc was the main interval for the taconic orogeny its impact on the sr continental flux may have been delayed until the early llandovery this effect complemented by reworking of glacial deposits near the ordovician silurian boundary and enhanced by phases of the silurian salinic orogeny may have combined to give the progressive increase in the strontium isotope ratio through the silurian the scale and directionality of these changes makes the strontium isotope curve valuable for dating and correlation purposes copyright 1998 elsevier science ltd

the strontium isotopic composition of brigantian late dinantian seawater abstract strontium isotopic determinations of different fossiliferous biominerals from brigantian late dinantian carbonates in northern england reveal that many are affected by diagenetic overprinting of their original 87 sr 86 sr ratios only pristine non luminescent articulate brachiopod shell material can be used to gain reliable estimates of carboniferous and by deduction palaeozoic ocean chemistries conodonts are found to be the only type of phosphatic biomineral capable of preserving original palaeoseawater chemistries however this only applies to specimens subjected to minimal burial temperatures other phosphatic biominerals are conclusively shown to be readily susceptible to diagenetic overprinting of original sr isotopic ratios a brigantian strontium curve compiled from pristine brachiopod calcite shows a relatively complex evolution with time but it can be resolved into two separate components operating on different time scales a cyclic sinusoidally shaped component with a frequency of 1 ma appears to fluctuate about a longer term more gradual linear increase in the brigantian seawater isotopic composition

sr and nd isotopes at the prmian triassic boundary a record of climate change abstract we present a detailed curve of seawater 87sr 86sr for the middle permian to triassic based on analyses of conodonts from overlapping sections in the u s a pakistan correlated using conodont biostratigraphy the isotope ratio decreased in the middle permian at an average rate of 0 000062 ma 1 reached a minimum in the capitanian 257 258 ma and increased in the late permian at an average rate of 0 000097 ma 1 the late permian rate of increase was roughly two and a half times greater than the average increase over the past 40 ma and approximately equal to the highest cenozoic rates which occurred over much shorter time intervals modeling results suggest that decreasing middle permian 87sr 86sr ratios were driven by changes in the riverine sr flux to the oceans while increasing ratios in the late permian triassic are attributed to both increased riverine 87sr 86sr and flux the reduced middle permian riverine flux coincides with extreme continental aridity associated with the formation of pangea and recorded by massive evaporite deposits in addition mountains in the equatorial region of pangea may have created a rain shadow thereby minimizing precipitation in regions that currently contribute the bulk of chemical weathering products to the ocean increasing riverine 87sr 86sr in the late permian is suggested by the observation that 143nd 144nd values decrease at the same time however the source of radiogenic sr is not known frequently cited mechanisms for increasing 87sr 86sr in runoff such as glaciations and continent to continent collisions coincide instead with decreasing seawater 87sr 86sr in the middle permian one possible source may have been deep erosion into older orogens associated with a dramatic increase in chemical weathering in the late permian the cause of enhanced weathering appears to have been increased levels of atmospheric co2 with associated global warming and increased humidity proposed sources of co2 include dissociation of gas hydrates and oxidation of organic matter during extreme sea level regression as well as volcanic emissions from siberian traps eruptions continental floral and faunal distributions are consistent with this interpretation as are oceanic 13c patterns and variations in shallow water sediment lithologies

detailed record of the neogene sr isotopic evolution of seawater from dsdp site 590b a detailed study of strontium isotope variations in neogene marine carbonate sediments from deep sea drilling project site 590b using techniques that allow the 87sr 86sr ratio to be determined to better than 0 00001 gives a high resolution record of the sr isotopic evolution of seawater the data show that the rate of change of the marine 87sr 86sr ratio has varied significantly even on time scales as short as 1 m y periods of particularly rapid growth appear to follow major marine regressions and probably reflect an increase in the delivery of radiogenic sr from the continents coupled with a decreased submarine carbonate dissolution rate greater carbonate compensation depth periods of relatively slowly changing 87sr 86sr follow major marine transgressions on the basis of correlations with the marine oxygen isotope record and the times of major continental glacier growth it is inferred that the effects of sea level variations are modified by climatic factors that affect the intensity of continental weathering and runoff the effects of sea floor generation rate variations are not discernible for the neogene the maximum attainable stratigraphic resolution using sr isotopes is between 0 1 and 2 m y for this time period

calibration of a conodont apatite based ordovician 87sr 86sr curve to biostratigraphy and geochronology implications for stratigraphic resolution the ordovician 87 sr 86 sr isotope seawater curve is well established and shows a decreasing trend until the mid katian however uncertainties in calibration of this curve to biostratigraphy and geochronology have made it diffi cult to determine how the rates of 87 sr 86 sr decrease may have varied which has implications for both the stratigraphic resolution possible using sr isotope stratigraphy and efforts to model the effects of ordovician geologic events we measured 87 sr 86 sr in conodont apatite in north american ordovician sections that are well studied for conodont biostratigraphy primarily in nevada oklahoma the appalachian region and ohio valley our results indicate that conodont apatite may provide an accurate medium for sr isotope stratigraphy and strengthen previous reports that point toward a signifi cant increase in the rate of fall in seawater 87 sr 86 sr during the middle ordovician darriwilian stage our 87 sr 86 sr results suggest that sr isotope stratigraphy will be most useful as a high resolution tool for global correlation in the mid darriwilian to mid sandbian when the maximum rate of fall in sr

strontium isotope stratigraphy of the middle devonian brachiopods and conodonts a set of 145 strontium isotope ratios based on skeletal components of emsian to frasnian age reveals a detailed structure of the seawater 87sr 86sr curve that can ultimately serve as a tool for high resolution isotope stratigraphy in the devonian brachiopod and conodont samples were collected in the eifel region of germany the area around the global stratotype for the middle devonian with an apparent average temporal resolution in the 105 y range preservation of the brachiopod shell material has been assessed by optical microscopy sem and cathodoluminescence and only the better preserved internal secondary layer of the shell has been utilized for strontium isotope measurements the 87sr 86sr curve shows a short decline from 0 7081 to 0 7078 through the late emsian followed by short term fluctuations with an amplitude of up to 10 4 around a mean of 0 7078 during the eifelian and givetian and a rise from late givetian into the late devonian the above high frequency oscillations and spikes are likely a reflection of condensed sedimentary records due to erosional and nondepositional events but a direct confirmation for such a scenario can be claimed only for the latest eifelian otomari event insufficient stratigraphic resolution precludes testing for the other events and isotopic spikes conodont skeletal elements even if well preserved at cai 2 5 yielded results that are mostly enriched in radiogenic 87sr if compared to coeval brachiopods although this enrichment is usually within the 10 5 range conodonts despite their superior stratigraphic resolution should be utilized only as a material of second choice in cases where brachiopods are rare or absent

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

sr c and o isotope geochemistry of ordovician brachiopods a major isotopic event around the middle late ordovician transition here we present sr c and o isotope curves for ordovician marine calcite based on analyses of 206 calcitic brachiopods from 10 localities worldwide these are the first ordovician wide isotope curves that can be placed within the newly emerging global biostratigraphic framework a total of 182 brachiopods were selected for c and o isotope analysis and 122 were selected for sr isotope analysis seawater 87sr 86sr decreased from 0 7090 to 0 7078 during the ordovician with a major quite rapid fall around the middle late ordovician transition most probably caused by a combination of low continental erosion rates and increased submarine hydrothermal exchange rates mean 18o values increase from 10 to 3 through the ordovician with an additional short lived increase of 2 to 3 during the latest ordovician due to glaciation although diagenetic alteration may have lowered 18o in some samples particularly those from the lower ordovician maximum 18o values which are less likely to be altered increase by more than 3 through the ordovician in both our data and literature data we consider that this long term rise in calcite 18o records the effect of decreasing tropical seawater temperatures across the middle late ordovician transition superimposed on seawater 18o that was steadily increasing from 3 standard mean ocean water smow by contrast 13c variation seems to have been relatively modest during most of the ordovician with the exception of the globally documented but short lived latest ordovician 13c excursion up to 7 nevertheless an underlying trend in mean 13c can be discerned changing from moderately negative values in the early ordovician to moderately positive values by the latest ordovician these new isotopic data confirm a major reorganization of ocean chemistry and the surface environment around 465 to 455 ma the juxtaposition of the greatest recorded swings in phanerozoic seawater 87sr 86sr and 18o at the same time as one of the largest marine transgressions in phanerozoic earth history suggests a causal link between tectonic and climatic change and emphasizes an endogenic control on the o isotope budget during the early paleozoic better isotopic and biostratigraphic constraints are still required if we are to understand the true significance of these changes we recommend that future work on ordovician isotope stratigraphy focus on this outstanding middle late ordovician event

strontium isotope 87sr 86sr stratigraphy of ordovician bulk carbonate implications for preservation of primary seawater values the present study on bulk carbonate 87 sr 86 sr stratigraphy represents a companion work to earlier research that presented a conodont apatite based ordovician seawater 87 sr 86 sr curve for the tremadocian katian stages 485 445 ma here we directly compare the curve based on conodont apatite including some new data not published in earlier work with a new curve based on 87 sr 86 sr results from bulk carbonate from the tremadocian sandbian stages we sampled eight lower to upper ordovician carbonate successions in north america to assess the reliability of bulk carbonate to preserve seawater 87 sr 86 sr and its utility for 87 sr 86 sr chemostratigraphy a high resolution 87 sr 86 sr curve based on 137 measurements of bulk conodont apatite is used as a proxy for seawater 87 sr 86 sr 87 sr 86 sr seawater in total 230 bulk carbonate samples that are paired to conodont samples were measured for 87 sr 86 sr in order to determine the conditions under which 87 sr 86 sr seawater is preserved in bulk carbonate results indicate that well preserved bulk carbonate can faithfully record the 87 sr 86 sr seawater trend but that its 87 sr 86 sr values are commonly more variable than those of conodont apatite on average bulk carbonate samples of the same age vary by 10 20 10 5 compared to 5 10 10 5 for conodont apatite the amount of isotopic alteration of bulk carbonate from seawater 87 sr 86 sr 87 sr 86 sr was determined by taking the difference between 87 sr 86 sr values of bulk carbonate and the approximated seawater trend based on the least radiogenic conodont 87 sr 86 sr values cross plots comparing 87 sr 86 sr values to bulk carbonate sr concentration sr and conodont color alteration indices cai an estimate of the thermal history of a rock body indicate that bulk carbonate is most likely to preserve 87 sr 86 sr seawater minimally altered when either 1 bulk carbonate sr is greater than 300 ppm or 2 carbonate rocks experienced minimal thermal alteration with burial temperatures less than 150 c carbonates with intermediate sr e g between 130 and 300 ppm can also yield 87 sr 86 sr seawater values but results are less predictable and local diagenetic conditions may play a greater role modeling results support the argument that seawater 87 sr 86 sr can be preserved in bulk carbonates with low sr if pore water rock ratios are low 87 sr 86 sr is similar to the seawater 87 sr 86 sr value preserved in limestone bulk carbonate samples that meet these criteria can be useful for high resolution measurements of 87 sr 86 sr seawater with a sample variation on par with fossil materials 5 particularly for successions where well preserved fossil material i e conodonts or brachiopods is not available such as precambrian strata sequences recording mass extinction events or otherwise fossil barren facies these criteria and model predictions based on bulk carbonate sr must be considered in the context of whether a limestone accumulated under calcite seas e g ordovician with relatively high seawater sr ca or aragonite seas in which case the diagenetic transformation of aragonite to calcite may result in incorporation of non seawater sr

ocean nutrient pathways associated with the passage of a storm storms that affect ocean surface layer dynamics and primary production are a frequent occurrence in the open north atlantic ocean in this study we use an interdisciplinary dataset collected in the region to quantify nutrient supply by two pathways associated with a storm event entrainment of nutrients during a period of high wind forcing and subsequent shear spiking at the pycnocline due to interactions of storm generated inertial currents with wind the post storm increase in surface layer nitrate by 20 mmol m 2 was predominantly driven by the first pathway nutrient intrusion during the storm alignment of post storm inertial currents and surface wind stress caused shear instabilities at the ocean pycnocline forming the second pathway for nutrient transport into the euphotic zone during the alignment period pulses of high turbulent nitrate flux through the pycnocline up to 1 mmol m 2 day 1 approximately 25 times higher than the background flux were detected however the impact of the post storm supply was an order of magnitude lower than during the storm due to the short duration of the pulses cumulatively the storm passage was equivalent to 2 5 5 of the nitrate supplied by winter convection and had a significant effect compared to previously reported sub mesoscale dynamics in the region as storms occur frequently they can form an important component in local nutrient budgets

carboniferous climate teleconnections archived in coupled bioapatite δ18opo4 and 87sr 86sr records from the epicontinental donets basin ukraine abstract reconstructions of paleo seawater chemistry are largely inferred from biogenic records of epicontinental seas recent studies provide considerable evidence for large scale spatial and temporal variability in the environmental dynamics of these semi restricted seas that leads to the decoupling of epicontinental isotopic records from those of the open ocean we present conodont apatite 18 o po 4 and 87sr 86sr records spanning 24 myr of the late mississippian through pennsylvanian derived from the u pb calibrated cyclothemic succession of the donets basin eastern ukraine on a 2 to 6 myr scale systematic fluctuations in bioapatite 18 o po 4 and 87sr 86sr broadly follow major shifts in the donets onlap offlap history and inferred regional climate but are distinct from contemporaneous more open water 18 o po 4 and global seawater sr isotope trends a 1 to 6 offset in donets 18 o po 4 values from those of more open water conodonts and greater temporal variability in 18 o po 4 and 87sr 86sr records are interpreted to primarily record climatically driven changes in local environmental processes in the donets sea systematic isotopic shifts associated with myr scale sea level fluctuations however indicate an extrabasinal driver we propose a mechanistic link to glacioeustasy through a teleconnection between high latitude ice changes and atmospheric pco2 and regional monsoonal circulation in the donets region inferred large magnitude changes in donets seawater salinity and temperature not archived in the more open water or global contemporaneous records indicate a modification of the global climate signal in the epicontinental sea through amplification or dampening of the climate signal by local and regional environmental processes this finding of global climate change filtered through local processes has implications for the use of conodont 18 o po 4 and 87sr 86sr values as proxies of paleo seawater composition mean temperature and glacioeustasy

ordovician and silurian sea water chemistry sea level and climate a synopsis following the cambrian explosion and the appearance in the fossil record of most animal phyla associated with a range of new body plans the ordovician and silurian periods witnessed three subsequent major biotic events the great ordovician biodiversification event the end ordovician extinction the first animal extinction and second largest of the five mass extinctions of the phanerozoic and the early silurian postextinction recovery there are currently no simple explanations for these three major events combined extrinsic geological and intrinsic biological factors probably drove the biodiversifications and radiations and the appearance and disappearance of marine habitats have to be analysed in the frame of changing palaeogeography palaeoclimate and sea water chemistry the present paper reviews the relationships of the three biotic events to chemical and physical processes occurring in the ocean and atmosphere during the ordovician and silurian including sea level changes geochemical proxies 13c 18o 87sr 86sr of the ocean waters and the evolution of the atmosphere oxygen and carbon dioxide content less

deposition and early alteration of evaporites summary the depositional settings for primary and early diagenetic evaporite deposits generally fall into three categories marginal mixed shallow subaqueous and subaerial shallow and deep subaqueous these three environmental groupings hold for both marine and nonmarine settings although the details of continental evaporites may be far more complex than in most marine fed water bodies the primary evaporite morphologies from many continental playa hypersaline marine and marine marginal depositional settings are reasonably well understood because of the numerous detailed studies of recent holocene and cenozoic deposits that serve as models for sedimentary interpretation the sedimentological features that develop in deeper water settings are inferred based on examination of unaltered cenozoic deposits each environmental setting develops characteristic depositional features and patterns and one facies grades into the next because there may be significant physiochemical changes in water composition during deposition as well as sudden change s in both water depth and basinal circulation description and interpretation of evaporative rocks should not be based on mineralogy alone but on the distinct sedimentary characteristics of each part of a deposit in cases where sediments still reflect their primary mineralogy and morphology most of the environments can now be recognized however geochemical studies are commonly required to determine the source s of the original water the determinative geochemical techniques that presently serve as a support to sedimentologic study include studies of fluid inclusions bromine content of chloride salts and the stable isotopes of strontium sulphur carbon and oxygen only after these and perhaps other chemical analyses are considered can the full depositional history of a region be reasonably unravelled

silurian δ13c stratigraphy a view from north america three positive shifts in 13 c are recognized in well dated carbonate successions in north america and can be confidently correlated with shifts in the baltic region by using conodont and graptolite zonations the 13 c excursions reach distinct peaks of 3 to 4 at the ends of the amorphognathoides and siluricus conodont zones and within the ludensis graptolite zone the three events are associated with the most significant extinction horizons in the silurian and occur near clastic carbonate transitions that mark eustatic or oceanographic changes the magnitudes of the two oldest 13 c peaks compare well with the baltic region however the end siluricus excursion reaches far greater values of as much as 11 in sweden likely reflecting local modification of the global seawater signature