environmental and physiological influences on isotopic and elemental compositions of brachiopod shell calcite implications for the isotopic evolution of paleozoic oceans abstract brachiopods from the demissa bed middle devonian hamilton group biologically regulated the incorporation of mg sr and na into their shell calcite significant taxonomic differences in the elemental contents of three species athyris spiriferoides mediospirifer audacula and mucrospirifer mucronatus may be related to differences in calcification processes in contrast no significant difference or vital effects were observed between the isotopic values of mediospirifer audacula and athyris spiriferoides from erie 18o 0 03 p 0 949 13c 0 76 p 0 083 and genessee counties 18o 0 39 p 0 471 13c 0 06 p 0 854 this suggests that these brachiopods did not exert a biological control over their isotopic compositions and that their shell calcites reflect ambient physicochemical conditions isotopic compositions in unaltered shell calcites of brachiopods from genessee county which was close to the basin depocentre are heavy for carbon 13c x 5 01 pdb and oxygen 18o x 2 85 pdb compared to the species sampled at the basin s edge erie county 13c x 2 79 pdb 18o x 3 83 pdb there is a significant separation in isotopic values between the deeper and shallower water brachiopods of the basin 18o 0 98 p 0 0005 13c 2 22 p 0 0005 the 18o variation suggests a temperature salinity change with water depth whereas the change in 13c composition probably records an enrichment depletion of organic matter with water depth this observation has significant implications for paleozoic ocean isotopic evolution studies because many global changes in marine 18o and 13c are based on isotopic shifts of similar magnitude

continuous high velocity aseismic zone beneath the izu bonin arc since 1904 eleven unusually deep earthquakes have been reported near the southern end of the izu bonin arc about 24 n 142 e these isolated events are separated from ordinary deep earthquakes in the wadati benioff w b zone of the izu bonin i b arc by a distance of about 300 km parallel to the trench axis they also are located 200 km closer to the trench than the natural extension of the shallower earthquakes above them using 3 d ray tracing a detailed analysis is performed of the difference in travel time residuals between the anomalous events and the deep events within the w b zone to the north this analysis yields higher reliability and resolution than can be obtained from ordinary tomographic imaging we find that these unusual events occurred in a high velocity zone which is connected to the northern w b zone of the i b arc the aseismic high velocity zone has a p velocity at least 3 faster than the surrounding mantle both our result and previous evidence for a horizontally lying slab west of the w b zone at 27 n e g okino et al 1989 are consistent with the existence of a prominent contortion of the subducted slab in the i b region

effect of soil characteristics on relative values of piezocone t bar and ball penetration resistances it has been reported in the literature that net cone penetration resistance is normally higher than the penetration resistance measured using full flow cylindrical t bar or spherical ball penetrometers and also that the ball penetration resistance is generally very close to the t bar penetration resistance in this paper a worldwide high quality database three onshore sites and seven offshore sites was used to identify soil characteristics that contribute to differences in the relative magnitudes of penetration resistance measured with cone t bar and ball penetrometers for soils covered in this database the ratio of t bar to net cone penetration resistance qt bar qnet lay between 0 75 and 1 decreasing with depth from near unity at shallow depths for the four sites where ball penetrometer data were available the ratio of ball to t bar penetration resistance qball qt bar was found to fluctuate around unity with an average just greater than 1 but no distinguishable trend with depth the m

oxygen isotope analysis of the eyes of pelagic trilobites testing the application of sea temperature proxies for the ordovician the oxygen isotope composition of well preserved trilobite eye calcite retaining its original optical properties represents a possible source of information on paleozoic sea temperatures species of the epipelagic telephinid genera carolinites and opipeuterella from strata of early to middle ordovician age in spitsbergen and australia were analyzed and compared with benthic asaphid species scanning electron microscope sem cathodoluminescence cl electron microprobe and electron backscatter diffraction ebsd techniques were used to assess eye preservation prior to isotope analysis some apparently well preserved eyes are identified from the valhallfonna spitsbergen and emanuel australia formations the eyes show a wide variation in 18o values 6 2 to 9 8 for the valhallfonna formation 3 2 to 10 4 for the emanuel formation and 3 6 to 7 4 for the horn valley siltstone australia intra eye secondary ion mass spectrometry sims isotope results reveal an even larger range in 18o in some specimens 18o of 2 4 to 10 4 suggesting that the trilobite eyes have undergone cryptic recrystallization a sub set of trilobite cuticle from the three formations were analyzed for their carbonate clumped isotope compositions 47 and yielded crystallization temperatures above 50 c consistent with diagenetic alteration the sims and 47 results suggest that classic preservation assessment protocols for the stable isotope study of deep time carbonate samples may be insufficient especially for these techniques there is a need for extensive microstructural characterization of lower paleozoic biogenic carbonates by techniques including ebsd sims and 47 before their stable isotope signatures can be used with certainty in paleoclimate studies

isotopic records of brachiopod shells from the russian platform evidence for the onset of mid carboniferous glaciation we performed isotopic analyses of carboniferous brachiopod shells from the russian platform to examine global and regional environmental change along the western and eastern margins of laurussia during the formation of pangea and specifically to examine the isotopic evidence for the onset of mid carboniferous glaciation shell preservation was evaluated from shell microstructure cathodoluminescence trace element content and isotopic comparison with matrix material most interior nonluminescent nl prismatic shell appears to be chemically well preserved as indicated by low to undetectable si al fe and mn contents with minor exception nl shell 13c and 18o values are higher than those of corresponding cements and matrix the 13c record for the russian platform clearly shows a 3 increase from 2 4 0 7 to 5 5 0 6 in the serpukhovian or early bashkirian this shift was first reported by popp et al popp b n anderson t f sandberg p a 1986 brachiopods as indicators of original isotopic compositions in some paleozoic limestones geol soc am bull 97 1262 1269 but had not been documented for a single region widespread occurrence of high 13c values in the late carboniferous support the interpretation of popp et al with regard to this shift as a record of increased burial of organic carbon north american sections show a mid carboniferous 13c shift of only 1 5 we hypothesize that the reduced 13c shift reflects enhanced upwelling on the epicontinental seas of north america after the closing of the seaway between laurussia and gondwana the 18o record for the russian platform shows a 1 8 increase in the mid carboniferous correlative with increased occurrence of glacial sediments and a drop in sea level as a first approximation ice volume calculations suggest that 0 7 of the mid carboniferous 18o shift is due to changes in seawater 18o and 1 1 is due to 5 c cooling concurrent positive 13c and 18o shifts provide evidence for a relationship between mid carboniferous glaciation and burial of organic carbon presumably through changes in atmospheric co2 levels

experimental investigation of spudcan penetration in multi layer clays with interbedded sand layers highly layered soils are prevalent in several areas of current offshore activity and in particular in emerging provinces and fields however no investigation has been carried out for spudcan penetration in stratified sediments with more than two layers this paper reports centrifuge modelling of spudcan foundations penetrating through 3 6 clay layers with interbedded stronger clay silica sand and carbonate sand layers the aim was to provide insight into the behaviour of spudcan foundations in stratified sediments comprising layers of different drainage conditions and mineralogy the motivation for this paper emanated directly from the future needs identified by the recent revised version of iso 19905 1 it was found that the downward soil deformation was extended into 3 4 underlying layers of sand and clay with thickness ratios t d less than 0 6 the limiting squeezing depth was 0 17 0 18d when approaching stiff clay moderate clay layers and 0 28d when approaching dense sand stiff clay layers these

geochemistry of modern brachiopods applications and implications for oceanography and paleoceanography abstract modern rhynchonellida terebratulida thecideida and a few inarticulated brachiopods were collected live or soon after death at 30 locations from depths of 2 3940 m from the equator to high latitudes covering the atlantic pacific indian caribbean and mediterranean oceans seas well preserved fibers of the secondary layer combined with sr 450 1928 mg kg mn 1 199 mg kg and fe 1 610 mg kg contents confirm with few exceptions the excellent preservation of the modern brachiopod material evaluation of the stable isotope compositions was conducted on 276 specimens and on 374 published samples for a total database of 650 samples from 80 locations it revealed that oxygen isotope incorporation into shell calcite secondary layer of modern articulated brachiopods in most cases occurs in equilibrium with the ambient water and as such reflects surrounding environmental conditions thecideida as a group shallow water and low latitude incorporate oxygen isotopes 3 04 to 0 35 into shell calcite in equilibrium with their ambient water a large majority of genera and species of the terebratulida shallow water and low mid latitude also incorporate oxygen 2 30 to 3 48 into shell calcite in isotopic equilibrium with their surrounding water in contrast equilibrium incorporation of oxygen isotopes into shell calcite by the rhynchonellida is uncertain but a vital effect probably applies to the craniida the question of equilibrium disequilibrium incorporation of carbon isotopes into shell calcite of modern brachiopods remains unresolved at this time isotope compositions range up to 4 5 5 6 and 1 5 for 13 c and up to 5 5 5 9 and 0 3 for 18 o for shallow water low mid and high latitude brachiopods respectively strontium isotopes of modern brachiopods as expected show no significant variation with location latitude water depth temperature salinity and general water conditions once local habitat and ecological influences of fossil brachiopods from similar latitudes are considered their isotopic elemental values should be valuable diagenetic indicators and important oceanographic chemostratigraphic proxies

use of stable oxygen isotope determinations from brachiopod shells in palaeoenvironmental reconstruction abstract stable oxygen isotope analyses were obtained from fossil brachiopod shells from a shallow marine deposit of upper pleistocene age approximately 80 ka in new zealand as part of a palaeoenvironmental investigation bulk analyses of entire shells of calloria inconspicua yielded highly variable results a range of 2 30 rendering these data of limited use as palaeoenvironmental proxies attempts to obtain consistent oxygen isotope values by removing areas of the brachiopod shell thought to be prone to oxygen isotope disequilibrium effects vital effects revealed that the matching anterior portions of ventral and dorsal valves from the same individual which were secreted at the same time also yielded different oxygen isotope ratios the dorsal valve 18o values were higher and less variable than those obtained from the ventral valve of the same individual the investigation was then extended to living representatives of the same species from a similar shallow water habitat from the south island of new zealand the pattern of dorsal valves yielding higher and less variable oxygen isotope values than matching areas of the ventral valves was repeated in seven out of eight individuals investigated although there was considerable variation in the absolute values from specimen to specimen contrary to common practice therefore it seems that in this species it is the much thinner and lighter dorsal valve that provides a more consistent isotopic measurement if converted into absolute temperature estimates the dorsal valve measurements correspond to a temperature midway between the mean and maximum annual temperature experienced by this species in its present day habitat which may make it acceptable as a palaeoenvironmental indicator the high level of variation between individuals including an inferred temperature from one ventral valve above the mean maximum temperature experienced indicates that a range of individuals needs to be investigated in any palaeoenvironmental investigation to avoid misleading interpretations however intra and inter specimen variation in isotopic composition may provide valuable palaeobiological information on growth rates metabolism and possibly also pathological conditions in the past

the horizontally lying slab an unusual earthquake mb 6 2 occurred in the izu bonin island region in july 1982 the event occurring at a depth of 545 km was clearly separated from the main inclined seismic zone by a distance of about 200 km to diagnose the situation we have considered two possibilities 1 the event might be an unusual event in the sense that its location is unrelated to the position of the subducted slab and that there is probably no slab around it or 2 the slab at this depth might be lying horizontally on top of the 650 km discontinuity and the unusual event occurred in this horizontal part both possibilities have been modeled structurally we have computed the p wave travel times for the present event as well as for two other events located unambiguously in the inclined part of the seismic zone by employing a 3 d ray tracing program the computed travel time residuals have been compared with the observations at stations in western japan the observations are found to be consistent with the model of the horizontally lying slab our result thus suggests that the slab might be horizontal at this depth in this part of the izu bonin islands

estimation of intact and remoulded undrained shear strengths from penetration tests in soft clays difficulties in obtaining high quality soil samples from deepwater sites have necessitated increasing reliance on piezocone t bar and ball penetration tests to determine soil properties for design purposes this paper reports the results of an international collaborative project in which a worldwide high quality database of lightly overconsolidated clays was assembled and used to evaluate resistance factors for the estimation of intact and remoulded undrained shear strength from the penetration resistance of each device the derived factors were then compared with existing theoretical solutions to evaluate the influence of particular soil characteristics the overall statistics showed similar levels of variability of the resistance factors with low coefficients of variation for all three types of penetrometer however correlations of the resistance factors with specific soil characteristics indicated that the resistance factors for the piezocone were more influenced by soil stiffness or rigidity inde

pile and penetrometer end bearing resistance in two layered soil profiles the paper examines the influence of soil strength and stiffness on the end resistance mobilised by a cone or displacement pile in a two layered soil profile i e strong soil overlying or underlying weak soil the investigation involved a series of numerical analyses that idealise pile cone penetration assuming the spherical cavity expansion analogue it is shown how the end resistance mobilised by a penetrometer in a dense sand i e strong soil varies with the number of penetrometer diameters d from a weak soil assumed here to be either a loose sand or soft clay and depends on the ratio of the steady state penetration resistances of the strong and weak layers the penetrometer resistance in the weak soil is not affected by an adjacent strong layer at penetrations greater than 2d a design procedure based on a numerical parametric study is proposed and this is subsequently shown to compare well with centrifuge test data and with previous numerical research

how well can we resolve the deep seismic slab with seismic tomography the three dimensional p and s velocity tomographic images around the wadati benioff zone under the island arcs of the northwest pacific are analyzed estimations of resolution and error show that the fast seismic anomalies associated with the subduction zones are generally real and resolvable the anomalies are slab like in most parts of the upper mantle and become folded and broadened with depth near the bottom of the upper mantle fingering of the slabs including segmenting and shallow angle spreading is indicated the fingering under japan and the izu bonin trench has a tendency to flatten to sub horizontal while possible downward spreading is seen under parts of the kuril trench

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

timing of early and middle permian deglaciation of the southern hemisphere brachiopod based 87sr 86sr calibration abstract earth s transition from an icehouse to hothouse during the late paleozoic was characterized by a series of high paleolatitude glacial interglacial events however the exact timing of these events remains unresolved here we report on fifty five calcitic shells of brachiopods and bivalves screened to obtain reliable 87sr 86sr ratios for cisuralian 298 9 272 95 ma and guadalupian 272 95 259 1 ma seawater specifically we used well preserved shells to build a 87sr 86sr seawater curve for the sydney basin and then with the marine look up table of the permian calculated numerical ages of the stratigraphic succession this allowed us to match seawater changes to the coeval p1 p3 glacial interglacial cycles recorded in the sedimentary successions of the sydney basin evaluation of the 87sr 86sr results revealed that onsets of the p2 and p3 glaciations in the sydney basin should be assigned to the early artinskian and late wordian respectively the range of 87sr 86sr values recorded by brachiopods from the wandrawandian siltstone coupled with recent geochronological dating of the broughton formation suggest that glacial phase p3 lasted about 2 myr and was confined to the late wordian early capitanian dating obtained using the sr isotope proxy from brachiopods agrees with the geochronologic ages and they suggest that the glacial phases p1 to p3 became progressively shorter in duration and less intense conversely the corresponding interglacials became progressively longer and thus documenting the gradual transition of the permian icehouse to an ice free greenhouse world our study confirms that strontium isotopes measured in screened brachiopod shell archives are sufficiently robust to date paleozoic marine sedimentary successions and are most valuable in sedimentary successions that otherwise lack geo chronological dating

brachiopod fabric classes and biogeochemistry implications for the reconstruction and interpretation of seawater carbon isotope curves and records abstract shell calcite of modern and ancient brachiopods is an important proxy in reconstructing oceanographic conditions of seawater our investigation reveals significant magnesium and carbon isotope relationships between two classes of ancient brachiopods brachiopods of the extinct class strophomenata constructed two or three layer shells with a primary layer of randomized granular calcite a secondary layer of cross bladed laminar calcite and at times a tertiary layer of large prismatic calcite contemporaneous but extant rhynchonellata also have two or three layer shells but their secondary layer consists of calcite fibers instead of cross bladed laminar calcite furthermore inter crystalline space is limited in between the fibers of the secondary layer of the rhynchonellata but higher in the laminar secondary layer of strophomenata 18 o values of the two classes of brachiopods from the same stratigraphic interval of the lopingian nesen formation of north iran show a considerable overlap with no significant difference p 0 263 in contrast carbon isotope values are significantly different p 0 001 between contemporaneous strophomenata mean 2 18 and rhynchonellata mean 4 13 an evaluation of literature data of permian asselian and carboniferous visean and serpukhovian strophomenata mean 2 32 n 59 and rhynchonellata mean 4 94 n 105 confirms a similar differentiation in their carbon isotope values its higher magnesium contents suggest that the strophomenata probably secreted shell calcite at a faster rate than their coeval rhynchonellata this process may account for the 13 c differentiation observed between specimens of these two brachiopod classes however the different amount and composition of the organic matter of the strophomenata may also play a role in shaping their more negative carbon isotope signature thus the class of brachiopod and their associated different fabric must be adjusted for in their 13 c results and taken into consideration during the reconstruction of paleozoic global 13 c carbonate based seawater curves invariably in some earlier studies undetected impacts imposed by the class fabric on 13 c may account for some of the variation or trends documented in deep time seawater 13 c curves reconstructed with brachiopod populations from north america europe and russia

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

effects of cone tip roughness in situ stress anisotropy and strength inhomogeneity on cpt data interpretation in layered marine clays numerical study abstract this paper explores the effects of cone tip roughness factor soil in situ stress ratio and strength non homogeneity on cone tip resistance in three layer clay deposits aiming at presenting a general cpt data interpretation framework to extract soil layered profiles and strengths large deformation finite element ldfe analysis has been carried out simulating continuous penetration of the standard cone penetrometer from the seabed surface with the consideration of cone tip roughness factor in situ stress ratio and soil strength non homogeneity within a practical range in the ldfe analyses a thin relatively stiff or soft clay layer was interbedded in a uniform or nc clay deposit with various strength ratios between two successive layers and thickness ratios of the thin layer to the cone diameter explored the results have shown that the noted factors have significant influence on net cone penetration resistance in stratified deposits these influences in the layered deposits were found to be similar in magnitude to those on the cone limiting resistance in a single clay layer leading to the resultant influence on a thin layer correction factor for cone penetration resistance minimal this was confirmed by the evidence of the evolving soil flow mechanisms around the cone tip therefore the design charts and formulas developed for a smooth cone in uniform three layer soils are applicable for delineating layer boundaries and interpreting the undrained shear strength of each identified layer for a partially rough cone in three layer non homogeneous clay deposits however the cone tip roughness factor was shown to have an influence in the layer boundary identification especially for the cone penetration from a stiff layer to a soft layer

neotethys seawater chemistry and temperature at the dawn of the end permian mass extinction abstract the end of the permian was a time of great death and massive upheaval in the biosphere atmosphere and hydrosphere over the last decades many causes have been suggested to be responsible for that catastrophe such as global warming anoxia and acidification the gyanyima limestone block was an open ocean seamount in the southern neotethys at subtropical latitude and it affords us insight into open ocean oceanographic changes during the end of the permian after careful screening using multiple tests we reconstructed carbonate seawater curves from the geochemical data stored in pristine brachiopod shell archives from the shallow water limestone of the changhsingian gyanyima formation of tibet the reconstructed strontium isotope curve and data for the late changhsingian are relatively invariant about 0 707013 but in the upper part of the succession the values become more radiogenic climaxing at about 0 707244 the 87 sr 86 sr curve and trend are similar to those observed for the upper permian succession in northern italy but dissimilar less radiogenic to whole rock results from austria iran china and spitsbergen the ce ce anomaly results ranging from 0 310 to 0 577 for the brachiopods and from 0 237 to 0 655 for the coeval whole rock before the event and of 0 276 for whole rock during the extinction event suggest normal redox conditions these ce values are typical of normal open ocean oxic water quality conditions observed in modern and other ancient counterparts the biota and ce information clearly discounts global anoxia as a primary cause for the end permian biotic crisis carbon isotopes from brachiopod shells and whole rock are relatively invariant for most of the latest permian interval which is in stark contrast to the distinct negative carbon isotope excursion observed near and about the event estimates of seawater temperature at shallow depth fluctuated from 22 2 to 29 0 c up to unit 8 2 and then gradually rise from 29 7 c in unit 8 13 to values exceeding 35 c at a stratigraphic level about 120 ky before the permian triassic boundary and just before the onset of the extinction interval this dramatic increase in seawater temperature has been observed in global successions from tropical to mid latitude and from restricted to open ocean localities e g northern italy iran the brachiopod archive and its geochemical proxies from tibet support the paradigm that global warming must have been an important factor of the biotic crisis for the terrestrial and marine faunas and floras of the late paleozoic world

a high resolution middle to late permian paleotemperature curve reconstructed using oxygen isotopes of well preserved brachiopod shells abstract climatic warming has been widely cited as a driver for many mass extinction events in earth history including the middle late permian guadalupian lopingian boundary glb mass extinction and end permian mass extinction epme investigated in this study however the role of warming in driving the epme event is under debate because current paleotemperature studies indicate the rapid increase in sea surface temperature postdate the onset of the epme event and a reliable paleotemperature record across the glb event is lacking here we present a high resolution and successive 18 o record using low mg calcite shells of brachiopods blmcs from a single stratigraphic section in central china to reconstruct paleotemperature changes from the middle to the latest permian after a rigorous screening for diagenesis our data show a 1 0 decrease in 18 ocalcite and thus climatic warming during the middle capitanian followed by a gradual 2 0 increase climatic cooling during the late wuchiapingian from the latest wuchiapingian to the early changhsingian 18 o decreased gradually and reached the lowest values of 4 0 and thus rapid climatic warming immediately before the permian triassic boundary the two warming events are coeval with the onset of the emeishan large igneous province and the siberian traps large igneous province respectively suggesting the two volcanic events are the plausible drivers of these climatic warming events a close comparison of paleontological and geochemical records indicates that the warming events occurred predate the glb and epme events this is in contrast with conodont 18 oapatite data which document the rapid climatic warming lagged the onset of the extinction event the comparison between 18 o of blmcs and 18 o of conodonts from the same section shows that the long term trends are similar but at higher temporal resolution discrepancies are present entailing further investigation in the near future our study confirms that 18 o of the brachiopod shells underwent important changes during the end of paleozoic highlighting that sea surface temperature is a key factor to understand the biosphere history since it changes simultaneously with the biological crises and that blmcs are invaluable archive for tracking physical and chemical conditions of past oceans

how deep can we see the high velocity anomalies beneath the japan islands high velocity anomalies are found in the lower mantle beneath the japan islands and their vicinity through an analysis of detailed three dimensional p wave velocity structure based on a tomographic inversion of isc data beneath the sea of japan the high velocity anomalies in the lower mantle are slab like and appear to extend below the deep focus earthquakes of the high velocity pacific slab descending from the japan trench this slab like high velocity body extending into the lower mantle steepens below a depth of 500 600 km resolution analyses confirms the existence of a slab like high velocity region in the lower mantle though the depth extent is not well resolved on the other hand the pacific slab descending from the izu bonin trench seems to be fingering that is high velocity anomalies are penetrating into the lower mantle beneath latitude 26 n and not penetrating but horizontally bending in the deeper portion of the upper mantle around 29 n

understanding biomineralization in the fossil record abstract biomineralization the formation of minerals by organisms is a key aspect in the understanding of the fossil record knowing how biominerals form and their properties is important in the correct use of fossils in geochemistry the understanding of evolution and in the interpretation of how geological events have influenced the fossil record throughout the phanerozoic the focus of this contribution rather than a conventional review on the status of this research field is on the importance of highlighting the traditional link between paleontology and biomineralization

deep penetrating spudcan foundations on layered clays centrifuge tests installation of independent legged jack up rigs in sea bed sediments where a strong layer overlays weaker soil can lead to catastrophic punch through with potential leg buckling or toppling of the unit although approximate methods of analysis exist for estimating the penetration resistance these do not account for the distortion of the upper layer as it punches through into the lower layer and there has been only limited visual depiction of the failure mechanism that occurs for the case of strong clay overlying weaker soil this paper reports results of centrifuge model tests undertaken to provide insight into spudcan foundation behaviour during undrained vertical penetration through a stronger clay layer into weaker material varying the strength ratio between lower and upper soil layers the thickness of the upper layer relative to the spudcan diameter and the strength gradient of the lower layer the model tests included half spudcan tests against a transparent window allowing the soil flow to be

brachiopods as indicators of original isotopic compositions in some paleozoic limestones the original stable isotopic composition of paleozoic marine carbonate rocks is important to establish a baseline for evaluating diagenetic alteration and providing a reliable data base for modeling exogenic geochemical cycles of the elements we have compared the 18 o and 13 c values in the nonluminescent portions of brachiopods with similar published data of whole brachiopods other whole fossils and estimates of original isotopic composition of marine cements the oxygen and carbon isotopic records for each of these paleozoic components show generally good internal consistency significant discrepancies however were noted between results on the different components isotopic and trace element data presented in this study suggest that permo carboniferous whole brachiopods are little altered chemically nonetheless a more reliable but not fool proof approach for obtaining pristine isotopic values is microsampling of least altered regions based on cathodoluminescence in conjunction with staining techniques and elemental analyses the carbon and oxygen isotopic compositions of all components decrease in 18 o and 13 c in geologically older material neither temporal trend is monotonic however oxygen isotopic results suggest an important positive shift in 18 o of about 2 during the early carboniferous whereas the carbon isotope trend shows a major positive shift 2 3 during the mid carboniferous

paleobathymetry of a silurian shelf based on brachiopod assemblages an oxygen isotope test primary 18 o signals of 97 brachiopod shells from the lower silurian llandovery carbonate succession of anticosti island were used to test the hypothesis of water depth and water temperature gradient for the silurian onshore offshore benthic assemblages ba1 ba5 the analyzed shells were from the pentamerus palaformis pentamerus oblongus stricklandia planirostrata ehlersella davidsonii and triplesia anticostiensis communities which have been interpreted to occupy different water depths screening of the shells using petrographic and chemical criteria confirmed good preservation of original material shells of p palaformis p oblongus e davidsonii and t anticostiensis have very similar mean 18 o values 5 vienna peedee belemnite vpdb while shells of s planirostrata have a somewhat lighter value 5 6 the 18 o values in corroboration with taphonomic and paleoecologic data suggest the following 1 that the water mass of the anticosti carbonate shelf was warm and well mixed vertically during the early silurian 2 that the pentamerid brachiopod paleocommunities that lived at 20 90 m of water depth show little 18 o differentiation in their shell composition and 3 that the pentamerus stricklandia and triplesia communities need to be investigated at the species level as both taphonomic and oxygen isotopic data indicate that the stricklandia planirostrata community most likely lived in a notably warmer shallower water than the pentamerus palaformis community and that triplesia anticostiensis ba5 lived at water temperature comparable to that of the pentamerus habitat ba3 this may suggest either that at the generic level the pentamerus stricklandia and triplesia clorinda equivalent communities may have had substantial overlap in their spatial distribution in the ba3 ba4 paleobathymetric settings or that the isotope signals are too faint to record water depth differences on a tropical shelf

effect of trapped cavity mechanism on interpretation of t bar penetrometer data in uniform clay abstractthis paper describes large deformation finite element ldfe analysis of the penetration of the t bar penetrometer in uniform clay identifying soil flow mechanisms around the t bar the ex

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

stable isotopes in late pennsylvanian brachiopods from the united states implications for carboniferous paleoceanography stable isotopic analyses have been performed on nearly 500 nonluminescent brachiopod shells from kansas new mexico and texas to evaluate temporal and geographic variability in the carbon and oxygen isotopic record for late pennsylvanian time brachiopod specimens were collected from missourian and virgilian shales and examined in thin section for preservation of microstructure and absence of cathodoluminescence as a primary test for shell preservation regional variations are observed in the 18o and 13c values of nonluminescent brachiopod shells of the same genera average 18o values for the three genera analyzed crurithyris composita and neospirifer are highest in kansas 1 9 intermediate in texas 2 3 and lowest in new mexico 3 6 vital effect on the 18o of these genera appears minimal 18o data and other evidence suggest warmer temperatures for the shallow new mexico localities and slightly higher salinity for the kansas sea relative to the texas sea the 13c values of composita average about 1 higher than those of co occurring crurithyris and neospirifer suggesting microhabitat differences or vital effects preservation of this species effect argues for preservation of original 13c values average 13c values are highest in texas intermediate in kansas and lowest in new mexico although these values range from 2 6 to 4 9 for individual genera the regional variation in 13c averages less than 1 data for nonluminescent brachiopods and marine cements reveal a mid carboniferous 13c increase of 2 in paleotethyan sea water this increase is not seen in samples from the north american epicontinental seas which opened to the panthalassa ocean this regional difference in 13c appears to be due to changes in ocean circulation associated with the closing of the equatorial seaway and formation of pangea

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

how cold were the early permian glacial tropics testing sea surface temperature using the oxygen isotope composition of rigorously screened brachiopod shells abstract brachiopod carbonate from early permian brachiopod shells from low palaeolatitude north iran and higher palaeolatitude pakistan karakorum were screened for diagenesis and analysed for oxygen isotope ratios to derive seawater palaeotemperatures screening techniques employed included sem ultrastructural analysis cathodoluminescence cl image analysis of cl images trace element sr mn fe determinations and carbon and oxygen stable isotope determinations the karakorum shells were found to be diagenetically altered but those from north iran were judged to be pristine using data from pristine material two distinct time slices were analysed the early and middle asselian two contrasting 18 o values for seawater 0 and 1 0 v smow were used to account for different extensions of the gondwanan ice caps the 18 o data from north iran indicate a range of seawater temperatures from 24 3 to 30 3 c for 18 o seawater 0 v smow or from 30 3 to 35 4 c for 18 o seawater 1 0 v smow for the early asselian results for 18 o from the middle asselian indicate seawater temperatures of 24 4 to 28 0 c for 18 o seawater 0 or 29 2 to 32 8 c for 18 o seawater 1 0 the maximum calculated temperatures in the middle asselian are about 2 c lower than those for the early asselian the average temperature for both time slices is similar to modern tropical sea surface temperatures indicating that low latitude early permian ocean waters in iran did not undergo significant cooling during the final glacial iii episode of gondwanan glaciation this confirms other evidence based on biotic provinces which suggests that during the permo carboniferous glaciation the low latitude warm belt became narrower and confined to the western tethys and cathaysian provinces and was not subject to a reduction in temperature but rather a reduction in size

paleoceanographic conditions at approximately 20 and 70 ka recorded in kikaithyris hanzawai brachiopoda shells abstract the 13c and 18o values of fossil brachiopod shells have been widely used as paleoenvironmental proxies in this study we investigated intrashell and intraspecific variations in the isotopic and minor element concentrations of well preserved shells of the brachiopod kikaithyris hanzawai yabe from the last glacial period 20 ka last glacial maximum lgm and 70 ka marine isotope stage 4 mis4 collected in the central ryukyus and used these data to estimate the paleoceanographic conditions seawater temperature concentration of dissolved inorganic carbon dic and 13c value of dic 13cdic the 13c and 18o profiles along the maximum growth axis obtained from the inner shell surface show three distinct intervals corresponding to changes in shell morphology these results suggest that the bulk isotopic compositions of brachiopods with complex shell morphologies are unsuitable for paleoenvironmental reconstructions nevertheless there exists a specific shell portion with relatively small intrashell and intraspecific variations the past seawater temperatures derived from the 18o values of this portion are consistent with the alkenone and planktic foraminiferal mg ca based past seawater temperatures reported in previous studies the past 13cdic values estimated from the 13c values of the specific shell portion are within the range of the past 13cdic values calculated from known atmospheric and oceanographic parameters the past dic concentrations reconstructed from the brachiopod based 13cdic values are lower than the present concentrations in the east china sea which can be explained by low partial pressure of co2 during the last glacial period these results indicate that the 13c and 18o values obtained from k hanzawai shells are potential paleoenvironmental indicators the intrashell and intraspecific variations in the k hanzawai shells are different for each minor element some anomalously high mn and fe concentrations in the shells are probably caused by metabolic factor s not by meteoric diagenesis this suggests that the minor element concentrations are useful but not perfect for distinguishing diagenetically altered and unaltered portions of the shells of k hanzawai in the studied succession

micro and nanostructures reflect the degree of diagenetic alteration in modern and fossil brachiopod shell calcite a multi analytical screening approach cl fe sem afm ebsd abstract fossil carbonate skeletons of marine organisms are archives for understanding the development and evolution of palaeo environments however the correct assessment of past environment dynamics is only possible when pristine skeletons and their biogenic characteristics are unequivocally distinguishable from diagenetically altered skeletal elements and non biogenic features in this study we extend our work on diagenesis of biogenic aragonite casella et al 2017 to the investigation of biogenic low mg calcite using brachiopod shells we examined and compared microstructural characteristics induced by laboratory based alteration to structural features derived from diagenetic alteration in natural environments we used four screening methods cathodoluminescence cl cryogenic and conventional field emission scanning electron microscopy fe sem atomic force microscopy afm and electron backscatter diffraction ebsd we base our assessments of diagenetic alteration and overprint on measurements of a images of optical overprint signals b changes in calcite crystal orientation patterns and c crystal co orientation statistics according to the screening process altered and overprinted samples define two groups in group 1 the entire shell is diagenetically overprinted whereas in group 2 the shell contains pristine as well as overprinted parts in the case of group 2 shells alteration occurred either along the periphery of the shell including the primary layer or at the interior facing surface of the fibrous columnar layer in addition we observed an important mode of the overprinting process namely the migration of diagenetic fluids through the endopunctae corroborated by mineral formation and overprinting in their immediate vicinity while leaving shell parts between endopunctae in pristine condition luminescence cl and microstructural imaging fe sem screening give first order observations of the degree of overprint as they cover macro to micron scale alteration features for a comprehensive assessment of diagenetic overprint these screening methods should be complemented by screening techniques such as ebsd and afm they visualise diagenetic changes at submicron and nanoscale levels depicting the replacement of pristine nanocomposite mesocrystal biocarbonate nmb by inorganic rhombohedral calcite irc the integration of screening methods allows for the unequivocal identification of highly detailed alteration features as well as an assessment of the degree of diagenetic alteration

stable isotope profiles ca o c through modern brachiopod shells of t septentrionalis and g vitreus implications for calcium isotope paleo ocean chemistry brachiopod shells are widely used as an archive to reconstruct elemental and isotopic composition of seawater studies focused on oxygen and carbon isotopes over the last decades are increasingly extending to the emerging calcium isotope system to date only little attention has been paid to test the reliability of fossil brachiopods on their modern counterparts in this context the present study investigates two modern brachiopods terebratulina septentrionalis eastern canada 5 30 m depth 7 1 c seasonal temperature variation two layer shell and gryphus vitreus northern mediterranean 200 m depth constant all year round temperature three layer shell both species were sampled along the ontogenetic growth direction and calcium oxygen and carbon isotopes as well as elemental concentration were measured calcium isotopes were analyzed on tims the elemental composition was analyzed by la icp ms and icp aes the results indicate an intra specimen 44 40ca variation ranging from 0 16 to 0 33 pointing to a fairly homogenous distribution of calcium isotopes in brachiopod shells however in the light of the suggested 0 7 increase in calcium isotopes over the phanerozoic such intra specimen variations constrain ocean reconstruction 44 40ca values of t septentrionalis do not seem to be affected by growth rate calcium isotopic values of g vitreus are heavy in the central part of the shell and trend towards lighter values in peripheral areas approaching the maximum isotopic composition of t septentrionalis the maximum inter species 44 40ca difference of 0 62 between t septentrionalis and g vitreus indicates that care should be taken when using different taxa species with different strontium content or brachiopods with specialized shell structure such as g vitreus for ocean water reconstruction in terms of ca isotopic composition t septentrionalis may record ca isotopic fractionation related to seasonal seawater temperature variations in its shell but this is difficult to resolve at the current analytical precision average 18o derived temperatures of the two investigated species are close to on site measured temperatures

structure of the mantle transition zone beneath the north china craton abstract detailed information on deep structural features can improve current understanding of lithospheric thinning and destruction of the north china craton in this study we analyzed receiver functions rfs from teleseismic p waveforms recorded by 246 seismic stations beneath the north china craton ncc to determine the topography of the mantle transition zone mtz the results reveal specific features in the 410 and 660 km discontinuities and outlined mtz thickness beneath the study area the mtz structure shows two anomalously thickened regions beneath the ncc up to 30 40 km thicker than the global average which are mainly concentrated in the eastern and western sections of the eastern ncc encc the thickened regions are discontinuous and separated by a distance of about 400 km double 660 km discontinuities also appear in the southeastern encc combining these results with previous findings we propose a model in which mtz thickening is caused by discrete remnants of the subducted western pacific slab discontinuities resulting from the stagnant slabs may retain evidence of changes in the rate of pacific plate subduction as well as the phase transition of the subducted slabs within the mtz

shell structure patterns and trends of oxygen and carbon stable isotopes in modern brachiopod shells this study investigates 13c and 18o variations in the shells of modern brachiopods representing all extant groups of calcite precipitating brachiopods collected live from 8 locations sem examinations determined the ultrastructural characteristics of each species prior to isotope analyses 13c and 18o analyses of shell carbonate were carried out with samples representing disparate morphological features and ultrastructural shell layers of both ventral and dorsal valves generally 18o values from the fibrous secondary or prismatic tertiary shell layers of the articulated terebratulida and rhynchonellida species were in oxygen isotopic equilibrium with ambient seawater isotopic temperatures extrapolated from these values are close to measured annual mean seawater temperatures 18o values were relatively unaffected by shell specialisation the only exception was antarctic species liothyrella uva which did not have a complete tertiary shell layer typical of this genus and had 18o values of the innermost layer strongly correlated with 13c and mostly not in oxygen isotopic equilibrium with ambient seawater with the exception of the rhynchonellid notosaria nigricans the outer primary layer material was depleted in 13c and 18o and highly variable inclusion of this material even as part of a whole shell sample could lead to misinterpretation of seawater temperature therefore only fossil secondary layer material should be used the anomalous articulated thecideidine brachiopod thecidellina barretti is composed of mainly primary shell material and was not in oxygen isotope equilibrium 18o values from the laminar secondary layer material of the inarticulated craniida are highly variable therefore these species are not recommended for use as palaeoenvironmental proxies this study suggests caution when employing fossil brachiopod shells with similar ultrastructures to modern craniid and thecideidine brachiopods the carbon isotope composition is highly variable in all of the brachiopods studied analysis of samples from specialised regions of the secondary shell layer show a pattern of depletion in 13c relative to non specialised secondary material the carbon isotope variability is independent of 18o and is repeated in most of the articulated species regardless of geographical location this is possibly a vital effect produced by metabolic prioritisation

undrained bearing capacity factors for conical footings on clay introduction the bearing capacity of circular foundations on undrained clay is of fundamental importance in many geotechnical problems in particular there are a number of designs of offshore foundations where the foundation can be treated approximately as a large circular footing for instance some gravity bases the spudcan foundations of jack up units and the more recently developed caisson foundations in most cases the footing is not placed at the ground surface and it is important to take into account the depth of embedment furthermore the base of a spudcan is generally not flat but approximates a shallow cone for foundations on soft clays the effect of the increase of strength of the soil with depth needs to be taken into account and this is particularly important for large foundations the purpose of this note is to present calculations of bearing capacity factors for shallow circular foundations accounting for embedment cone angle rate of increase of strength with depth and surface roughness of the foundation the results have widespread application particularly in the offshore industry the soil is assumed to be rigid plastic with yield determined by the tresca condition with an undrained strength su the method of characteristics is used for the bearing capacity calculation as described by shield 1955 eason shield 1960 houlsby 1982 and houlsby wroth 1982a for application to undrained axisymmetric problems some previous results have been published for this problem using similar numerical techniques e g houlsby wroth 1982b salencon matar 1982 houlsby wroth 1983 tani craig 1995 martin 2001 but the study presented here involves a much more comprehensive coverage of the parameters where comparisons can be made with the previous solutions the factors differ by up to about 0 5 which gives some indication of the level of accuracy attainable with this numerical technique exceptionally the rough footing results given by tani craig 1995 are higher by up to about 5 but this may be due to a problem with their numerical integration procedures see martin randolph 2001

interpretation of layer boundaries and shear strengths for soft stiff soft clays using cpt data ldfe analyses abstractthis paper describes a new approach for interpreting cone penetrometer data in soft stiff soft clay deposits the identification of layer boundaries and interpretation of shear strength profile were of particular interest the proposed approach was based on an extensive parametric study using large deformation finite element ldfe analyses with a standard cone penetrometer penetrated continuously from the soil surface the ldfe model has been validated against existing theoretical solutions and numerical results with good agreement obtained regardless of strength ratio between two successive layers the interface of soft stiff layers can be identified at 0 8d d is the cone diameter below the kink in penetration resistance curve in the top soft layer the interface of stiff soft layers can be demarked at 1 3d above the kink in the penetration resistance profile in the bottom soft layer the undrained shear strength of a soft clay layer can be interpreted using a single layer approach and the

δ18o and δ13c values of modern brachiopod shells abstract researchers have not rigorously tested the hypothesis that calcite from modern brachiopod shells is precipitated in oxygen isotope equilibrium with ambient seawater isotopic variability at the intraspecimen and intertaxon levels has not been examined without such data for modern brachiopods similar data from ancient brachiopods cannot be accurately interpreted in this study a survey is made of 18 o and 13 c values of terebratulid rhynchonellid thecideidine and craniacean brachiopods from antarctica the bay of fundy curacao japan new zealand norway puget sound palau sicily and south africa this suite of samples provides a wide range of taxonomic levels temperatures salinities and depositional environments for evaluating the degree of isotopic equilibrium attained during precipitation of brachiopod calcite new data indicate that modem brachiopod calcite is not always precipitated in oxygen and carbon isotope equilibrium with ambient seawater calcite from the primary layer and specialized shell structures hinge brachidium foramen interarea muscle scars are depleted in both 18 o and 13 c a characteristic of biological fractionation or vital effects often found in other calcerous marine organisms our findings suggest that these portions of the brachiopod shell should be avoided during sampling of ancient brachiopods secondary layer calcite the material most often analyzed in ancient brachiopods has higher 18 o and 13 c values which approach and sometimes correspond with predicted equilibrium values therefore secondary layer calcite is the most suitable portion of the brachiopod shell for use as an ancient seawater proxy although near equilibrium precipitation in secondary layer calcite is encouraging to those studying the isotopic composition of ancient oceans these data come with caveats large intraspecimen variability in the 18 o values of secondary layer calcite 1 in some samples limits the use of brachiopods as precise indicators of the 18 o value or temperature of ancient seawater the 18 o and 13 c values of secondary layer calcite deviate from predicted equilibrium values toward the lower values of the primary layer and specialized shell structures indicating a measurable vital effect in most cases measured 18 o values are lower than the calculated equilibrium values dictated by seasonal variations in the 18 o value and temperature of seawater ontogenetic variations in the 13 c values of secondary layer calcite have also been measured and must be assessed when interpreting ancient data modern brachiopods occur in a wide range of seawater salinities and temperatures therefore the relation between salinity and the 18 o value of seawater must be known to correctly calculate the temperature of calcite precipitation from secondary layer 18 o values errors of up to 15 c are found if ambient seawater is assumed to have a constant 18 o value e g 0 smow and the 18 o values of secondary layer calcite are used to calculate temperature coupled with vital effects and intraspecimen variability these errors can obscure the resolution of secular variations in the rock record

shell succession assemblage and species dependent effects on the c o isotopic composition of brachiopods examples from the silurian of gotland brachiopods are the most widely used biological constituents for the determination of stable c and o isotopic compositions in paleozoic sediments in the present study critical precautions for obtaining reliable isotope values and maximum possible reliability are discussed samples were taken in the tectonically undisturbed and exceptionally well preserved silurian sequence on gotland sweden the state of preservation of brachiopod shells was examined by cathodoluminescence cl microscopy and by comparison of shell ultrastructures with those of recent brachiopods nine types of ultrastructure are distinguished and attributed either to biological differences or to diagenetic alterations for isotope analyses only largely unaltered areas of the secondary fibrous shell layer should be used shell layers with other types of ultrastructure primary tertiary laminar may have isotopic compositions different from the assumed seawater value even when diagenetically unaltered only brachiopod taxa with a shell succession that includes a sufficiently thick secondary shell layer e g spiriferida rhynchonellida orthida give reliable mutually corresponding isotope values indicating that the shell calcite precipitated at or near equilibrium with ambient seawater brachiopods with other kinds of shell successions strophomenida pentamerida as well as other calcite shelled organisms trilobites ostracodes give non equilibrium isotopic results and therefore should not be used by restricting the samples to one species or to a group of closely related species even minor differences in primary isotopic composition can be excluded in the silurian of gotland the stratigraphically widely distributed spiriferid atrypa reticularis was selected for study considering the type of record four different taphonomic assemblages are defined in autochthonous assemblages of specimens which lived contemporarily original values of carbon as well as oxygen isotopes can be evaluated with a reliability of 0 4 this allows the recognition of minor hydrographically produced differences between neighbouring contemporary facies areas and the determination of small 1 isotopic excursions thus besides being indicators of hydrographic conditions in ancient oceans stable carbon and oxygen isotope compositions can be used as a stratigraphic tool that provides correlations sometimes even within biozones

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