climate warming in the latest permian and the permian triassic mass extinction high resolution oxygen isotope records document the timing and magnitude of global warming across the permian triassic p tr boundary oxygen isotope ratios measured on phosphate bound oxygen in conodont apatite from the meishan and shangsi sections south china decrease by 2 in the latest permian translating into low latitude surface water warming of 8 c the oxygen isotope shift coincides with the negative shift in carbon isotope ratios of carbonates suggesting that the addition of isotopically light carbon to the ocean atmosphere system by siberian traps volcanism and related processes resulted in higher greenhouse gas levels and global warming the major temperature rise started immediately before the main extinction phase with maximum and harmful temperatures documented in the latest permian meishan bed 27 the coincidence of climate warming and the main pulse of extinction suggest that global warming was one of the causes of the collapse of the marine and terrestrial ecosystems in addition very warm climate conditions in the early triassic may have played a major role in the delayed recovery in the aftermath of the permian triassic crisis

holocene depositional history of a large glaciated estuary penobscot bay maine abstract data from seismic reflection profiles sidescan sonar images and sediment samples reveal the holocene depositional history of the large 1100 km 2 glaciated penobscot bay estuary of coastal maine previous work has shown that the late wisconsinan ice sheet retreated from the three main passages of the bay between 12 700 and 13 500 years ago and was accompanied by a marine transgression during which ice and sea were in contact isostatic recovery of the crust caused the bay to emerge during the immediate postglacial period and relative sea level fell to at least 40 m sometime between 9000 and 11 500 years ago during lowered sea level the ancestral penobscot river flowed across the subaerially exposed head of the bay and debouched into middle passage organic matter rich mud from the river was deposited rapidly in remnant glacially scoured depressions in the lower reaches of middle and west passages behind a shallow 20 m water depth bedrock sill across the bay mouth east passage was isolated from the rest of the bay system and received only small amounts of locally derived fine grained sediments during the holocene transgression that accompanied the eustatic rise of sea level the locus of sedimentation shifted to the head of the bay here heterogeneous fluvial deposits filled the ancestral valley of the penobscot river as base level rose and the migrating surf zone created a gently dipping erosional unconformity marked by a thin during and since the late holocene transgression of sea level waves and currents have eroded reworked and redistributed holocene sediments 1 atop the shallow margins 2 within constricted channels 3 around topographic highs and 4 over the shallow bedrock sill at the bay mouth the variable distribution characteristics and thickness 0 to more than 30 m of holocene deposits in penobscot bay primarily reflect 1 the irregular glacially eroded bedrock topography beneath the bay 2 the paleogeography of the bay during the sea level lowstand 3 the postglacial location of the ancestral penobscot river and 4 the wave and current regime during and since the holocene sea level transgression

trace and rare earth element compositions of silurian conodonts from the vesiku bone bed histological and palaeoenvironmental implications abstract in situ minor trace and rare earth element ree compositions have been measured in conodonts from the lower silurian vesiku bone bed estonia with the aim to visualize and to quantify conodont apatite elemental geochemistry to evaluate compositional differences between conodont histologies and to evaluate the use of conodont chemistry as a palaeobiological or palaeoenvironmental proxy tissue selective analyses of minor trace and rare earth element compositions of albid hyaline and basal tissues demonstrated significant chemical offsets among these histologies the albid tissue had the lowest ree and trace element concentrations suggesting crystallinity determined better resilience to diagenetic alteration as documented in previous studies conversely the basal tissue had highest concentrations of rees and many trace elements except for sr that showed an opposite trend the higher concentrations in albid and hyaline tissues supports the in vivo sr incorporation by conodont crown nonetheless the obtained sn normalized ree patterns were uniform through all the analyzed conodont taxa and different tissues implying common diagenetic history absence of a ce anomaly and defined negative eu anomaly indicate reducing conditions during early burial these results validate current interpretations of the palaeoenvironmental conditions during the deposition of vesiku bone bed and bolsters the use of rees in palaeozoic marine vertebrates as an important palaeoenvironmental proxy

assessing the fidelity of marine vertebrate microfossil δ18o signatures and their potential for palaeo ecological and climatic reconstructions abstract conodont biogenic apatite has become a preferred analytical target for oxygen isotope studies investigating ocean temperature and palaeoclimate changes in the palaeozoic despite the growing application in geochemically based palaeoenvironmental reconstructions the paucity or absence of conodont fossils in certain facies necessitates greater flexibility in selection of robust oxygen bearing compounds for analysis vertebrate microfossils teeth dermal denticles spines offer a potential substitute for conodonts from the middle palaeozoic vertebrate bioapatite is particularly advantageous given a fossil record extending to the present with representatives across freshwater to fully marine environments thus widening the scope of oxygen isotope studies on bioapatite however significant tissue heterogeneity within vertebrates and differential susceptibility of these tissues to diagenetic alteration have been raised as potential problems affecting the reliability of the oxygen isotope ratios as palaeoclimatic proxies well preserved vertebrate microfossils and co occurring conodont fossils from the upper devonian and lower carboniferous of the lennard shelf canning basin western australia were analysed using bulk gas isotope ratio mass spectrometry girms and in situ secondary ion mass spectrometry sims methodologies with the latter technique allowing investigation of specific tissues within vertebrate elements the 18oconodont results may be interpreted in terms of palaeolatitudinally and environmentally sensible palaeo salinity and temperature and provide a baseline standard for comparison against vertebrate microfossil 18o values despite an absence of obvious diagenetic modification girms of vertebrate denticles yielded 18o values depleted in 18o by 2 4 relative to co occurring conodonts sims analysis of dentine tissues exhibited significant heterogeneity while hypermineralised tissues in both scales and teeth produced 18o values comparable with those of associated conodonts the susceptibility of permeable phosphatic fossil tissues to microbial activity fluid interaction and introduction of mineral precipitates post formation is demonstrated in the dentine of vertebrate microfossils which showed significant heterogeneity and consistent depletion in 18o relative to conodonts the hypermineralised tissues present in both teeth and scales appear resistant to many diagenetic processes and indicate potential for palaeoclimatic reconstructions and palaeoecological investigations

thermal maturity of carbonaceous material in conodonts and the color alteration index independently identifying maximum temperature with raman spectroscopy abstract the color alteration index cai of conodont specimens is commonly used for identifying the maximum temperature to which units of sedimentary rock particularly carbonates have been heated observable color variations in these fossils are thought to be a result of the thermally induced structural evolution of organic carbonaceous matter cm such temperature history information is extremely valuable for applications in hydrocarbon exploration as well as for constraining other temperature related geological processes in sedimentary systems however the identification of cai depends on the qualitative visual assessment of color which along with a host of other potential complications may yield inaccurate determinations of maximum temperature raman spectroscopy allows thermally induced structural changes in cm to be quantified and it has been used to estimate the thermal maturity in metasedimentary rocks for almost two decades here we use raman spectroscopy of carbonaceous material rscm in conodont specimens and their mississippian to upper triassic host rocks from british columbia canada to estimate maximum temperatures based on the transformation structural reorganization of disordered carbon to graphite this study demonstrates that the maximum temperatures experienced by conodont specimens as calculated from rscm using the iterative fitting of raman spectra ifors technique correlate well with cai but lie outside the suggested ranges in some instances this may be due to complex thermal histories of these conodont specimens or the influence of diagenetic alteration not thermal histories on conodont color we recommend the application of raman spectroscopic analyses of cm in conodonts and their host rocks to obtain more confident accurate and precise estimations of maximum temperature that are independent of cai

diagenetic alteration of the structure and δ18o signature of palaeozoic fish and conodont apatite potential use for corrected isotope signatures in palaeoenvironmental interpretation abstract the oxygen isotopic compositions of carboniferous conodonts and fish microfossils ichthyoliths from identical samples were analysed in tandem in order to test whether these phosphatic media can be reliably used for palaeoclimatic reconstruction the structure of conodonts and of most ichthyoliths analysed are somewhat analogous to the enamel and dentine bone tissue respectively of modern mammals therefore the diagenetic susceptibilities of the taxa analysed may provide important clues to other palaeoclimatic studies utilising a variety of biogenic apatite thermal maturation indices and scanning electron microscopy were used to characterise the preservation of biogenic apatite despite a high conodont colour alteration index cai of 5 5 conodont elements appear to have been only mildly affected by diagenetic alteration in contrast ichthyoliths were commonly recrystallised and exhibited diagenetic apatitic overgrowths containing amorphous pyrolytic carbon interpreted as indicating that at least some overgrowth material derived from the original biogenic apatite diagenetic alteration has resulted in ichthyolith 18 o values being systematically lower by on average 2 9 1 0 3 relative to conodont apatite conodont samples yielded regionally correlatable isotope values which can be interpreted in terms of more palaeoenvironmentally sensible palaeotemperatures relative to ichthyolith values densely crystalline enamel like conodont elements are interpreted as the more robust phosphatic medium to preserve original isotopic compositions the strong correlation r 0 8 of the 18 o values of the more structurally pristine conodont and commonly recrystallised ichthyolith apatite indicates that i despite diagenetic lowering of absolute isotope values original palaeoenvironmental records may be preserved and ii diagenetic overprinting may result in a stable offset and therefore be correctable locally

comparing oxygen isotope records of silurian calcite and phosphate δ18o compositions of brachiopods and conodonts oxygen isotope compositions of silurian calcitic brachiopod shells from gotland are compared with those of phosphatic inarticulate brachiopod shells and conodonts from identical stratigraphic horizons the 18ophosphate values of inarticulate brachiopod shells vary widely 13 0 to 17 5 v smow and are significantly lower than those of coeval conodont samples 17 5 to 19 5 v smow conodont samples from individual beds have homogenous 18ophosphate values with variations close to the analytical precision 0 2 together with a significant correlation of conodont 18ophosphate and articulate brachiopod shell 18ocarbonate values r 0 85 this observation suggests that primary marine oxygen isotope compositions are better preserved in conodont apatite than in inarticulate brachiopod shell apatite however with decreasing 18ocarbonate values the 18ophosphate values of conodonts are higher than expected for theoretical isotopic equilibrium with brachiopod calcite different habitats of conodonts and brachiopods cannot account for the observed offset in 18o because both organisms were thriving on a broad shallow marine carbonate platform whereas 18ophosphate values of silurian conodonts are close to 18ophosphate values of modern and mesozoic tropical biogenic apatites most silurian calcitic brachiopod shells from gotland are depleted in 18o when compared to modern or mesozoic brachiopods we therefore suggest that silurian conodonts from gotland record paleotemperature and 18o of silurian sea water more faithfully than coeval calcitic brachiopod shells

nd isotope composition of conodonts an accurate proxy of sea level fluctuations abstract analyses of the nd isotope composition of conodonts from the anti atlas morocco the montagne noire france and the rhenohercynian domain germany provide insight into the temporal and lateral variations in seawater geochemistry in the western part of the variscan sea during the late devonian most of the isotopic excursions accurately record changes in sea level the end values decreased during regression phases when erosion accelerated supply of unradiogenic nd from old continental sources a rise in sea level generated a positive shift in end values due to input of more radiogenic oceanic water into the seawater reservoir of the shelf areas the method has great potential for sea level research paleoceanography and correlation because sea level changes can be precisely recognized even in successions with uniform monotonous lithologies however it has a significant limitation being valid only in epeiric seas and shelf areas we have used the nd isotope record to reconstruct the eustatic sea level changes in late frasnian early famennian time the onset of the organic rich kellwasser units coincides with negative trends in end values this accords with oxygen deficiency at the sea bottom being initiated by short term regressive events which in turn would be consistent with cooling periods of glacial origin as previous authors have suggested

methane generated pockmarks on young thickly sedimented oceanic crust in the arctic vestnesa ridge fram strait acoustic backscatter imagery in the fram strait between greenland and spitzbergen reveals a 1 3 km wide 50 km long belt of 50 pointlike backscatter objects decorating the 1300 m deep crest of vestnesa ridge a 1 2 km thick sediment drift possibly underlain by a transform parallel oceanic basement ridge crustal ages 3 14 ma a 3 5 khz seismic reflection profile indicates that at least some objects are pockmarks 100 200 m in diameter and 10 20 m deep the pockmarks possibly also mud diapirs may have been formed by evolution of methane generated by the decomposition of marine organic matter in the vestnesa ridge sediment drift the ridge may be underlain by an anticlinal carapace of methane hydrate calculated to be 200 300 m thick comparable to the hydrate thickness measured just to the south the rising methane would collect in the ridge crest trap intermittently escaping to the sea floor this hypothesis is supported by multichannel evidence for bright spots and bottom simulating reflectors in the area the pockmark belt may also be located above a transcurrent fault sediment slumps on the flanks of vestnesa ridge and northeast of molloy ridge may have been triggered by plate boundary earthquakes and facilitated by methane hydrates

sedimentary framework of the southern maine inner continental shelf influence of glaciation and sea level change abstract although the tidally influenced shoreline of maine is longer than that of virtually any other state almost no research on its geology has been published in order to go some way towards remedying this 1500 km of high resolution seismic reflection data and 800 km of sidescan sonar imagery have been collected on the basis of these data and observations made during ten submersible dives more than 800 bottom samples were collected and evaluated for texture and composition the understanding of the sedimentary framework of the southern maine shelf and the processes that maintain it are summarized and future research directions to evaluate the strategic mineral potential are indicated in the past 14 000 years the maine shelf has experienced a deglaciation and two marine transgressions separated by a regression the deglaciation was accompanied by the first transgression and deposited till interbedded with up to 40 m of glaciomarine sediment the presumpscot formation across the shelf the first transgression culminated about 12 500 yrs b p and its landward limit is marked by large glaciomarine deltas 50 100 km landward of the present day coast sea level fell until about 9500 yrs b p when shorelines were cut at about the 65 m depth and some large lowstand deltas were deposited sea level has risen since then and in the general absence of modern river sediment input marine processes have reworked the older sediment five shelf environments have been defined in terms of their surficial sediment and stratigraphy nearshore ramps are sandy regions extending to about 30 m deep offshore of sandy beaches these may be reworked lowstand deltas and possess the thickest bodies of sand in the region nearshore basins are mud filled troughs seaward of coastal areas lacking significant river input slumping glaciomarine deposits provide most of the holocene mud that floors these basins rocky zones are extensive areas of exposed rock most common in the 30 50 m depth range these are areas of high carbonate productivity and provide shell fragments to adjacent areas the outer basins are muddy regions that begin at the 65 m shoreline and extend beyond the 100 m isobath to the deep gulf of maine finally shelf valleys are former stream courses that connect nearshore ramps and basins to the outer basins these bedrock framed valleys are filled with sand and mud and are apparently still active conduits for the offshore movement of sediment the mineralogy of the shelf sediment is complex and it is not yet clear whether glacial homogenization has obliterated distinctions between river drainage basins and the adjacent shelf studies are continuing into northern maine and analysis of the heavy mineralogy of the shelf sediment utilizing a 2 m humphrey spiral to process large grab samples and cores has begun

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

growth of disk shaped bubbles in sediments disc shaped methane bubbles often observed in marine sediments result from growth in a medium that elastically resists expansion of the bubbles and yields by fracture we have modeled this process to obtain estimates of growth times by using a reaction diffusion model coupled to a linear elastic fracture mechanics lefm for comparison we also modeled the growth of a constant eccentricity bubble in a nonresistant medium discoidal bubbles that grow in sediments that obey lefm grow much faster than spherical bubbles two to fourfold faster for the times and conditions tested here and become more eccentric with time aspect ratios falling from 0 3 to 0 03 ove r8do fgrowth in addition their growth is not continuous but punctuated by fracture events furthermore under some conditions lefm predicts that bubble growth can become arrested which is not possible for a bubble in a nonresistant medium even for nonspherical bubbles cessation of growth occurs when the dissolved gas concentration gradient near the bubble surface disappears as a result of the increase in bubble gas pressure needed to overcome sediment elasticity copyright 2003 elsevier science ltd 1 introduction the production of volatile substances usually methane dur ing diagenesis can lead to saturation of the pore waters and the subsequent formation of gas bubbles the presence of such bubbles can engender significant geochemical and geotechnical consequences as previously discussed in martens and klump 1980 and hovland and judd 1992 including greatly en hanced methane fluxes to the atmosphere through ebullition given the important effects of bubbles the dearth in our knowl edge of their rates of formation and of the processes that control those rates is surprising in particular little solid or systematic estimates of these rates exist and what we do have is largely in the form of crude deductions of seasonal growth that are based on limited observations in martens and klump 1980 recently we undertook a research program to redress this paucity of information by a combined program of bubble growth experiments and theoretical modelling our first effort in this field produced a theoretical model of the growth for a spherically shaped bubble in a sediment that does not offer resistance to the expansion of the bubble boudreau et al 2001a b this model balances the methanogenic production of the volatile solute with its diffusion to the growing bubble to obtain an equation for the radius of the bubble r t with time

the effect of diagenesis on oxygen isotope ratios of biogenic phosphates the effect of diagenesis on the oxygen isotope composition of ancient biogenic phosphates was evaluated by measuring different types of material from middle triassic localities in the southern alps dentin bone and tooth enamel of different taxa hosted by different rock types and metamorphosed to differing degrees were analyzed for their 18 o and 13 c values using a new microanalytical gc irmms technique the 18 o values of the majority of bone and bulk tooth samples were 18 to 19 permil smow with three samples below this range and one close to 20 permil in contrast samples of tooth enamel were 19 4 to 20 7 permil significantly higher than bone and bulk tooth without the enamel data the 18 to 19 permil data could be misinterpreted as primary only when the higher 18 o values of the enamel are considered is it apparent that the bulk data have undergone diagenesis and temperature estimates are 5 c lower than would otherwise be calculated alteration of bulk tooth is also seen in a miocene shark tooth where 18 o values of enamel are 3 permil higher than those of bulk tooth although enamel is routinely analyzed for paleoclimate work of herbivorous mammals bulk bone teeth or shells are almost exclusively used for older marine samples the results of the present study indicate that bulk data should be treated with caution

organic maturation levels thermal history and hydrocarbon source rock potential of the namurian rocks of the clare basin ireland abstract vitrinite reflectance data from two inland cored boreholes confirm high maturation levels throughout the onshore part of the irish clare basin and suggest erosion of 2 to 4 km of late carboniferous cover and elevated palaeogeothermal gradients in the carboniferous section the observed maturation gradients are fully consistent with the published hypothesis of a late carboniferous permian superplume beneath pangaea but local vertical reversals in gradients also suggest a complex thermal regime probably involving advective heating the uppermost visean lower namurian clare shale is laterally extensive and up to 300 m thick although this unit is post mature toc values of up to 15 suggest that it could have considerable hydrocarbon source rock potential in any less mature offshore parts of the basin

δ18o values of mudrocks more evidence for an 18o buffered ocean abstract the whole rock 18 o of mudrocks as well as the 18 o of the clay sized silicate fraction does not change in any systematic manner over paleozoic and late proterozoic time therefore the 18 o of the ocean has not changed except a per mil or so as the result of glaciation deglaciation over the last billion years of earth history

δ18o composition of conodont apatite indicates climatic cooling during the middle pridoli phosphatic microfossils such as conodonts and fish microremains dermal scales from the upper silurian pridoli of lithuania have been studied for their oxygen isotope composition the conodont c

isotopic composition of recent shark teeth as a proxy for environmental conditions abstract the o c and sr isotope compositions of teeth from ten species belonging to five families and three orders of sharks were measured to determine the influence of habitat diet and possible species specific fractionation effects on the isotopic composition of biogenic phosphate from fish the sharks were recently caught in subtropical waters off the kwazulu natal kzn coast of south africa as well as from cold waters in prince william sound pws alaska and victor bay vb nunavut canada 18 o values of tooth phosphate 18 o p range from 20 9 to 23 5 for the kzn sharks for most species the range in measured 18 o p values is about 0 6 but it may be as high as 1 1 for different teeth from a single shark dentine and enameloid within individual teeth have no apparent differences in 18 o p values the 18 o p values of the kzn shark teeth reflect the typical habitat of the studied species primarily the thermal structure of the water column off kzn at depths between 20 and 280 m the 18 o p values of teeth from different greenland sharks from vb and pacific sleeper sharks from pws are very homogeneous averaging 25 8 and 24 7 respectively these values appear to be in equilibrium with deep 500 m ocean waters in each case at temperatures of about 0 3 c or less there is little discernable evidence for species specific fractionation effects for the oxygen isotope composition of phosphate in the studied marine fish the oxygen isotope composition of carbonate in apatite averages about 9 1 higher than corresponding 18 o p values in agreement with equilibrium fractionation between carbonate and phosphate but with a large variance 1 1 5 18 o c values also vary by up to 1 between enameloid and dentine within single teeth but in a non systematic way differences in 13 c values between carbonate in enameloid and dentine is also large up to 8 but the 13 c values vary systematically enameloid is always enriched in 13 c compared to dentine and the 13 c content increases with developmental stage of the teeth 13 c values measured for enameloid 1 6 to 4 8 appear to approach equilibrium with dissolved inorganic carbon in seawater in contrast 13 c values for dentine range from 6 4 to 2 3 for kzn sharks and 9 0 to 10 8 for the cold water sleeper sharks and are compatible with a predominantly dietary carbon source the 87 sr 86 sr ratios of teeth from kzn sharks as well as those from pws and vb are uniform averaging 0 709167 sr content varies from 1270 to 2100 ppm a range that is similar to that in well preserved fossilized teeth seawater sr is thus clearly incorporated in vivo concentrations of sm and nd are in the ppb range and contrast the ppm range in fossilized teeth indicating a postmortem incorporation of rare earth elements in apatite of the teeth

did cooling oceans trigger ordovician biodiversification evidence from conodont thermometry the ordovician period long considered a supergreenhouse state saw one of the greatest radiations of life in earth9s history previous temperature estimates of up to 70 c have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time we present a very different global climate record determined by ion microprobe oxygen isotope analyses of early ordovician silurian conodonts this record shows a steady cooling trend through the early ordovician reaching modern equatorial temperatures that were sustained throughout the middle and late ordovician this favorable climate regime implies not only that the oxygen isotopic composition of ordovician seawater was similar to that of today but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period

chemical diagenesis of a multicomponent carbonate system 2 stable isotopes abstract this study examines the oxygen and carbon isotopic distribution in the brachiopods crinoids rugose corals and matrix cement from the mississippian burlington limestone iowa and missouri and the silurian read bay formation arctic canada the isotopic data can be reconciled with textural and trace element observations only if the 18o content of ancient oceans differed from that of the present oceans this postulated secular variation in the 18o content of seawater requires a separate evaluation of the mississippian and silurian carbonate components examination of the 18o content of the least altered low mg calcite fossil components of the two formations suggests that the 18o of mississippian seawater was on average about 1 5 lighter and that of silurian seawater was about 5 5 lighter than the 18o of present day ocean water the average diagenetic shift in 18o for the read bay formation which stabilized in a partly closed diagenetic phreatic meteoric system is about 1 for the original low mg calcite and about 2 for the original high mg calcite and aragonite components conversely for the burlington limestone which stabilized in an open diagenetic phreatic meteoric system the average diagenetic shift in 18o is about 3 for the original low mg calcite and about 4 f r the original high mg calcite components the 13c values of the originally low mg calcite or high mg calcite with less than 7 mole mgco3 brachiopods and rugose corals the originally high mg calcite crinoids and the originally aragonite lime mud of the burlington limestone and read bay formation are bimodally distributed this bimodal 13c distribution is independent of geologic age inferred original mineralogy of the component degree of diagenetic alteration and the type of diagenetic meteoric system with components from both the read bay formation and burlington limestone contributing to both 13c groups the mode of the light 13c group is 0 25 and for the heavy 13c group it is 3 25 pdb both 13c groups also show a decrease in 13c of about 1 with increasing diagenetic alteration stabilization

constraints on pennsylvanian glacioeustatic sea level changes using oxygen isotopes of conodont apatite conodonts from u s midcontinent cyclothems were studied for oxygen isotopes in order to constrain pennsylvanian glacioeustatic sea level fluctuations pennsylvanian deposits of the midcontinent united states are composed of cyclic alternations of thin transgressive limestones offshore gray to black phosphatic shales and thick regressive limestones a sequence that is underlain and overlain by nearshore to terrestrial shales with paleosols and coal beds glacioeustatic sea level fluctuations are considered the primary cause for the formation of these cyclothems oxygen isotope analyses of conodont apatite from the black 20 1 0 5 vienna standard mean ocean water vsmow and gray shale units 20 5 0 5 vsmow show lowest average 18 o values whereas conodont elements from the regressive 21 0 0 3 vsmow and transgressive limestone units 21 1 0 6 vsmow are enriched in 18 o the maximum change in 18 o of conodonts from the black shale and carbonate units from individual cyclothems is 1 7 the 1 7 c difference in 18 o compares relatively well to pleistocene interglacial glacial changes in 18 o of equatorial surface dwelling foraminifers and suggests that pennsylvanian glacioeustatic sea level changes may have been of comparable amplitude however since the pennsylvanian glacial maxima are represented by terrestrial sediments and are not documented in the conodont oxygen isotope record pennsylvanian glacioeustatic sea level changes were probably larger than the 120 m fluctuations recorded for the pleistocene glaciations

conodont alteration and tectonothermal evolution of a diagenetic unit in the iberian variscan belt ponga cuera unit nw spain tectonothermal analysis of a mainly carbonate unit located in the external part of the variscan orogen in nw spain is dealt with using the conodont colour alteration index cai and the study of textures of these microfossils the kubler index of the illite ki is used as a complementary method the area is characterized by a great uniformity in the cai values which in most cases are

late quaternary relative sea level change in the western gulf of maine evidence for a migrating glacial forebulge new radiocarbon dated cores obtained by vibracorers in the western gulf of maine confirm that a short lived relative sea level lowstand of 55 m occurred at 11 10 5 ka these cores and younger salt marsh data also reveal that rates of transgression varied throughout the holocene probably due to local variations in glacial isostasy the isostatic component is resolved by subtracting published approximations of eustatic sea level from our well determined observations of local relative sea level a large peak in the isostatic curve coincides with the lowstand and is interpreted as a forebulge 20 25 m in amplitude forebulge migration is estimated at 7 11 km 100 yr based on the timing of lowstands across the region

fish tooth δ18o revising late cretaceous meridional upper ocean water temperature gradients the oxygen isotope composition of fossil fi sh teeth a paleo upper ocean temperature proxy exceptionally resistant to diagenetic alteration provides new insight on the evolution of the low to middlelatitude thermal gradient between the middle cretaceous climatic optimum and the cooler latest cretaceous period the new middle cretaceous low to middle latitude thermal gradient agrees with that previously inferred from planktonic foraminifera 18o recovered from deep sea drilling project and ocean drilling program drilling sites although the isotopic temperatures derived from 18o of fish teeth are uniformly higher by 3 4 c in contrast our new latest cretaceous thermal gradient is markedly steeper than those previously published for this period fish tooth 18o data demonstrate that low to middle latitude thermal gradients of the middle cretaceous climatic optimum and of the cooler latest cretaceous are similar to the modern one despite a cooling of 7 c between the two periods our new results imply that no drastic changes in meridional heat transport are required to explain the late cretaceous climate based on climate models such a cooling without any change in the low to middle latitude thermal gradient supports an atmospheric co2 decrease as the primary driver of the climatic evolution recorded during the late cretaceous

shallow water pockmark formation in temperate estuaries a consideration of origins in the western gulf of maine with special focus on belfast bay abstract a systematic mapping program incorporating more than 5000 km of side scan sonar and seismic reflection tracklines in the western gulf of maine has identified more than 70 biogenic natural gas deposits occupying 311 km2 in nearshore muddy embayments many of these embayments also contain pockmark fields with some exhibiting geologically active characteristics including the observance of plumes of escaping fluids and sediment pockmarks hemispherically shaped depressions of various size and depths formed through fluid escape of gas and or pore water are sometimes found within or outside gas fields although many gas fields lack pockmarks altogether although the origin of the natural gas remains unclear if coastal environments at times of lower sea level were similar to the present numerous lake wetland valley fill and estuarine sources of organic rich material may have formed on the inner shelf if these deposits survived transgression and remain buried they are potential gas sources intensive mapping of the belfast bay pockmark field in 1998 produced the first nearly continuous side scan sonar mosaic of a gulf of maine pockmark field with a corresponding 3 dimensional geological model generated from seismic data statistical analysis of pockmark geometry gas deposit loci and subsurface evidence for gas enhanced reflectors suggest that gas migration from deeper lateral sources along permeable subsurface strata may be the mechanism for pockmark formation in areas lacking gas curtain seismic reflections the coarse grained transgressive ravinement unconformity between pleistocene glacial marine mud and holocene mud may act as a conduit for distributing methane to the field s margins

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

stratigraphic evolution of the inner continental shelf in response to late quaternary relative sea level change northwestern gulf of maine accumulations of deltaic and littoral sediments on the inner continental shelf of maine gulf of maine preserve a record of postglacial sea level changes and shoreline migrations the depositional response of coastal environments to a cycle of regression lowstand and transgression was examined with seismic reflection profiles vibracores and radiocarbon dates collected from sediments at the mouths of the kennebec and penobscot rivers sequence stratigraphic analysis of these data reveals two distinctly different successions of late quaternary deposits that represent end members in an evolutionary model for this glaciated coast seaward of the kennebec river coarse grained shorelines with foreset beds occur at depths of 20 60 m and outline the lobate margin of the kennebec river paleodelta a complex rock framed accumulation of glaciomarine and deltaic sediments capped by estuarine and marine deposits sand derived from this system today supports large barrier spits and extensive salt marshes in contrast the mouth of the penobscot river is characterized by thick deposits of glaciomarine mud overlain by marine mud of holocene age including gas charged zones that have locally evolved into fields of pockmarks the distinct lack of sand and gravel seaward of the penobscot river and its abundance seaward of the kennebec river probably reflect differences in sediment sources and the physiography of the two watersheds the contrasting stratigraphic framework of these systems demonstrates the importance of understanding local and regional differences in sediment supply sea level change bedrock structure and exposure to waves and tides in order to model river mouth deposition on glaciated coasts evolution of shelf deposits was largely controlled by relative sea level which locally fell from a highstand 60 to 70 m at 14 ka contemporary with deglaciation to a lowstand 55 m at 10 8 ka the sea level lowering was accompanied by fluvial incision of older deposits producing a regressive basal unconformity major rivers deposited abundant sediment over this surface sea level then rose at varying rates extensively reworking formerly emergent parts of the shelf and producing a shoreface ravinement surface in areas exposed to waves a tidal ravinement surface has developed in sheltered embayments where erosion is due mainly to tidal currents incised valleys in both settings preserve transgressive estuarine deposits that contain lagoonal bivalves and salt marsh foraminifera at depths of 15 30 m these deposits accumulated ca 9 2 7 3 ka locally a period of relatively slow sea level rise

oxygen isotope variations in phosphate of biogenic apatites i fish bone apatite rechecking the rules of the game abstract the major advantage of the oxygen in phosphate isotope paleothermometry is that it is a system which records temperatures with great sensitivity while bone and teeth building organisms are alive and the record is nearly perfectly preserved after death fish from seven water bodies of different temperatures 3 23 c and different 18 o values 16 to 3 of the water were analysed the 18 o values of the analysed po 4 vary from 6 to 25 the system passed the following tests a the temperatures deduced from isotopic analyses of the sequence of fish from lake baikal are in good agreement with the temperatures measured in the thermally stratified lake b the isotopic composition of fish bone phosphate is not influenced by the isotopic composition of the phosphate which is fed to the fish but only by temperature and water composition isotopic analysis of fossil fish in combination with analysis of mammal bones should be a useful tool in deciphering continental paleoclimates

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

raman spectral elemental crystallinity and oxygen isotope variations in conodont apatite during diagenesis abstract conodont apatite has long been used in paleoenvironmental studies often with minimal evaluation of the influence of diagenesis on measured elemental and isotopic signals in this study we evaluate diagenetic influences on conodonts using an integrated set of analytical techniques a total of 92 points in 19 coniform conodonts from ordovician marine units of south china were analyzed by micro laser raman spectroscopy m lrs laser ablation inductively coupled plasma mass spectrometry la icp ms high resolution x ray microdiffraction hxrd and secondary ion mass spectrometry sims each conodont element was analyzed along its full length including the albid crown hyaline crown and basal body in either a whole specimen i e reflecting the composition of its outer layer or a split specimen i e reflecting the composition of its interior in the conodonts of this study the outer surfaces consist of hydroxyfluorapatite and the interiors of strontian hydroxyfluorapatite ionic substitutions resulted in characteristic raman spectral shifts in the position ss1 and width ss2 of the 1 po43 stretching band although multiple elements were enriched sr2 mg2 and depleted fe3 mn2 ca2 during diagenesis geochemical modeling constraints and known raman spectral patterns suggest that sr uptake was the dominant influence on diagenetic redshifts of ss1 all study specimens show lower ss2 values than modern bioapatite and synthetic apatite suggesting that band width decreases with time in ancient bioapatite possibly through an annealing process that produces larger more uniform crystal domains most specimens consist mainly of amorphous or poorly crystalline apatite which is inferred to represent the original microstructure of conodonts in a subset of specimens some tissues especially albid crown exhibit an increased degree of crystallinity developed through aggrading neomorphism however no systematic relationship was observed between crystallinity and raman spectral or elemental parameters oxygen isotopes show substantial variation within the conodont study specimens albid crown is on average 0 28 0 32 more depleted in 18o equivalent to 1 2 1 4 c higher temperatures than hyaline crown and basal body and the interiors of conodont elements are 1 08 0 37 more depleted in 18o equivalent to 3 0 6 4 c higher temperatures relative to their outer layers although albid crown is widely regarded as better preserved than other conodont tissue types its 18o depleted composition and greater development of secondary crystallinity suggest that in fact it may be the most strongly altered tissue type we conclude that raman spectral la elemental and hxrd microstructural data can provide useful information about the extent of diagenetic alteration of conodont elements and that such information should be taken into consideration in using conodont elemental and oxygen isotope data in paleoenvironmental studies

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

raman spectroscopy of fossil bioapatite a proxy for diagenetic alteration of the oxygen isotope composition abstract fossil bioapatite may yield biogeochemical signals of paleoenvironments captured by living organisms bioapatite may be diagenetically altered however with ions added or removed post mortem such change is typically assessed using destructive and demanding techniques here raman spectroscopy is used as a rapid and non destructive way to identify significant diagenetic alteration of fossil bioapatite we found spectral parameters of phosphate symmetric stretching 1 po43 to be very sensitive to variations in apatite chemistry particularly with respect to common diagenetic components co32 f sr2 the raman spectral parameters were subsequently applied to a set of modern biogenic and geologic magmatic apatite samples as potential endmembers for diagenetic alteration raman spectra were also collected from enamel and dentin respectively resistant vs alteration prone of fossil teeth phosphate oxygen isotopic values from the same enamel dentin samples were used as an index of alteration and provided definition of raman spectral parameters as relates to diagenetic alteration diagenetically altered samples were characterised by spectra with 1 po43 widths at half maximum height less than 13 0 cm 1 and 1 po43 band positions greater than 964 7 cm 1 raman spectroscopy is shown to have potential as a tool for pre screening fossil apatite samples before further analyses

microtopography and surficial sediment patterns in the central gulf of maine a 3 5 khz survey and interpretation abstract the seafloor of the gulf of maine is dominated by ice contact glaciomarine and postglacial sedimentary deposits based on 2085 km of 3 5 khz seismic profiling hummocky topography interpreted as morainal in origin is present over about half of the seafloor in water depths of 100 300 m small exposures 2 of overlying multilayered glaciomarine reflectors extend with the hummocky surface under much of an acoustically transparent layer covering about one third of the survey area this postglacial marine silty clay unit is up to 25 m thick other less common facies include an acoustically opaque smooth bed 10 and bedrock 6 the continuous seismic records reveal the sedimentary sequence and the complex patchy distribution of deposits accumulated during and after the retreat of the late wisconsinan laurentide ice sheet from the gulf of maine over the bedrock and morainal hummocks the meltwaters of glacial retreat locally deposited the glaciomarine multilayered acoustic reflectors the still younger acoustically transparent marine silts and clays display a smooth nearly level surface except for apparent scour around bedrock promontories and v shaped depressions suggestive of pockmark formation in four locations similarly postglacial to contemporary reworking of the seafloor produced the sand waves of georges shoals and smooth sandy seabed areas that are acoustically opaque

material spatial variability and slope stability for weak rock masses the presence of weak materials bedding or discontinuities at critical locations could lead to local or large scale failures of natural or excavated slopes or tunnels material spatial variation of eagle ford shale in texas was established based on laboratory and field testing results a random field model was used to characterize the material spatial variation and the correlation distance for the eagle ford shale strength variability was evaluated impacts of material property variability and spatial variability on slope stability were analyzed using monte carlo simulation with distinct element modeling using random field elements implicitly embedded in the numerical analyses this study provides insight into the significance of material spatial variation on stability possible failure mechanisms and critical locations of weak materials in a shale mass

revised phosphate water fractionation equation reassessing paleotemperatures derived from biogenic apatite oxygen isotopes of biogenic apatite have been widely used to reassess anomalous temperatures inferred from oxygen isotope ratios of ancient biogenic calcite more prone to diagenetic alteration however recent studies have highlighted that oxygen isotope ratios of biogenic apatite differ dependent on used analytical techniques this questions the applicability of the phosphate water fractionation equations established over 25 years ago using earlier analytical techniques to more recently acquired data in this work we present a new phosphate water oxygen isotope fractionation equation based on oxygen isotopes determined on fish raised in aquariums at controlled temperature and with monitored water oxygen isotope composition the new equation reveals a similar slope but an offset of about 2 to the earlier published equations this work has major implications for paleoclimatic reconstructions using oxygen isotopes of biogenic apatite since calculated temperatures have been underestimated by about 4 to 8 c depending on applied techniques and standardization of the analyses

sand budgets at geological historical and contemporary time scales for a developed beach system saco bay maine usa abstract saco bay hosts one of the largest sand beach and salt marsh systems in northern new england usa unsuccessful remedies for chronic beach erosion have generated controversy and differing theories regarding 1 the source s of sand to the bay 2 the sand transport paths and 3 the role of jetties in beach erosion we constructed a sand budget for the bay by evaluating the past and present sand transport pathways fluxes and reservoir volumes side scan sonar and bottom samples were employed to map the offshore areas seismic reflection profiles and vibracores were used to measure the volume of offshore sand on land ground penetrating radar and cores constrained the sand volume and stratigraphy time series maps and aerial photographs provided data on historical sand movement and current meters and recent harbor dredge data allowed contemporary sand movement to be estimated in the saco river estuary at the present time 56 million m3 of sand reside in the shoreface and 22 million m3 of sand are beneath the barrier beach and dunes the saco river has been the major source of sand to the bay providing an estimated 10 000 16 000 m3 of sand per year the net direction of sand movement is to the north where river derived sand has historically fed growth of barrier spits construction of the north jetty at the saco river mouth profoundly altered the prehistoric patterns of sand movement and storage in the bay causing the northward migration of almost 6 million m3 of sand between 1867 and 1955 contemporary dredging of tidal inlets involves sand volumes approximately equal to the influx of sand delivered by the saco river

fabric retentive non luminescent brachiopods as indicators of original delta 13 c and delta 18 o composition a test abstract fabric retentive non luminescent helderbergian brachiopods from open marine deposits analogous to brachiopods used in other studies to determine paleo oceanic stable isotopic composition exhibit depleted 13c values immediately below the erosional contact and more enriched values of 13c at greater stratigraphic distances below this surface in addition 13c values of these brachiopods display a marked shift across the erosional surface and values above it are essentially the same as those 30 m or more beneath the surface complementing these trends whole rock analyses metastable high agnesian calcite constituents echinoderms as well as early equant calcite cement also exhibit an increased depletion trend in 13c values as the helderberg oriskany contact is approached from below fabric retentive luminescent as well as obviously recrystallized brachiopods display stable isotopic values similar to those of fabric retentive non luminescent brachiopods thus best preserved fabric retentive non luminescent brachiopods exhibit values similar to obviously recrystallized brachiopods diagenetically altered metastable constituents echinoderms stable early meteoric cements and whole rock samples helderberg strata of new york state were affected by early meteoric diagenesis during a siegenian exposure event prior to deposition of the overlying marine oriskany sandstone meteoric diagenesis during this exposure gave rise to a characteristic carbon isotopic depletion trend approaching the helderberg oriskany contact all of the skeletal constituents underwent isotopic exchange during early diagenetic exposure to meteoric waters consequently the practice of using fabric retentive non luminescent brachiopods as indicators of their original chemistry and by extension paleo oceanic chemistry is questioned

oxygen isotope variations in phosphate of biogenic apatites iii conodonts abstract the method for measurement of the isotopic composition of oxygen in phosphates has been improved and adapted for analysis of small quantities of apatite down to 10 mg this extension enables one to analyze hand picked conodont samples with an analytical reproducibility better than 0 5 1 46 samples of conodonts ranging from the ordovician to the pennsylvanian of north america were analysed some insoluble phosphatic residues ichthyoliths and inarticulate brachiopods of the same time range were also measured the range of the 18o values of the analysed conodonts is between 15 and 19 it shows a general trend of decreasing d18o with increasing age from an average value of about 19 in the pennsylvanian to 17 in the ordovician this trend parallels that previously detected in marine phosphorites for the time range between the devonian and pennsylvanian our data are in agreement with independent paleoclimatic information specifically we detect maximum18o enrichment at the end of the pennsylvanian and minimum enrichment at the end of the devonian the difference between these two extremes is equivalent to about 10 c from about 40 to 30 c assuming constant isotopic composition of ocean water the success of oxygen isotopic analysis of conodonts raises the possibility of their use in paleozoic paleo oceanography in a similar way to foraminifera in the mesozoic cenozoic

conodont sr ca and δ18o record seawater changes at the frasnian famennian boundary abstract the oxygen isotopic composition 18 o p and strontium calcium sr ca p ratios have been measured in late devonian conodonts palmatolepis sp from contemporaneous sections at coumiac france and m rirt morocco the sequences encompass two anoxic horizons the lower kellwasser lkw and upper kellwasser ukw events with the top of the ukw coinciding with the mass extinction at the frasnian famennian boundary the genus palmatolepis survived the faunal crisis but exhibited plastic responses to the environmental changes which are recorded in the evolution of shape during the anoxic events the present study demonstrates that shape 18 o p and sr ca p values of conodonts are correlated in both localities excluding diagenesis as the driving process for the measured 18 o p and sr ca p values the conodonts 18 o p and sr ca p values are correlated in both localities and distributed into either a pre crisis and crisis group using the relationships between the 18 o p and sr ca p values we estimate that the variation of the seawater sr ca ratio during the frasnian famennian mass extinction was of about 20 its initial value this drastic decrease of the seawater sr ca ratio is discussed in the light of the reef demise that occurred during the faunal crisis

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

the spatial and temporal diversification of early palaeozoic vertebrates recent discoveries have dramatically altered traditional views of the stratigraphic distribution and phylogeny of early palaeozoic vertebrates and permit a reappraisal of biogeographic patterns and processes over the first 120 million years of vertebrate evolution stratigraphic calibration of the phylogenetic trees indicates that most of the pre silurian record can be inferred only through ghost ranges assessment of the available data suggests that this is due to a shift in ecological niches after the latest ordovician extinction event and a broadening of geographical range following the amalgamation of euramerica during the early silurian two major patterns are apparent in the bio geographic data firstly the majority of jawless fishes with dermoskeletal plated armour were highly endemic during cambrian ordovician time with arandaspids restricted to gondwana galeaspids to china and anatolepids astraspids and possibly heterostracans confined to laurentia these laurentian groups began to disperse to other continental blocks as the old red sandstone continent amalgamated through a series of tectonic collisions the second maj or pattern in contrast encompasses a number of microsquamous and naked jawed and jawless primitive vertebrates such as conodonts thelodonts placo derms chondrichthyans and acanthodians which dispersed rapidly and crossed oceanic barriers to attain cosmopolitan distributions although many have laurentian origins a clear difference in dispersal potential exists between these two types of fishes overall the development of biogeographic patterns in early palaeozoic vertebrates involved a complex interaction of dispersal vicariance and tectonic convergence

ophiolites as faithful records of the oxygen isotope ratio of ancient seawater the solund stavfjord ophiolite complex as a late ordovician example

oxygen isotope evolution of biogenic calcite and apatite during the middle and late devonian oxygen isotope ratios of well preserved brachiopod calcite and conodont apatite were used to reconstruct the palaeotemperature history of the middle and late devonian by assuming an oxygen isotopic composition of 1 v smow for devonian seawater the oxygen isotope values of eifelian and early givetian brachiopods and conodonts give average palaeotemperatures ranging from 22 to 25 c late givetian and frasnian palaeotemperatures calculated from 18o values of conodont apatite are close to 25 c in the early frasnian and increase to 32 c in the latest frasnian and early famennian oxygen isotope ratios of late givetian and frasnian brachiopods are significantly lower than equilibrium values calculated from conodont apatite 18o values and give unrealistically warm temperatures ranging from 30 to 40 c diagenetic recrystallization of shell calcite different habitats of conodonts and brachiopods as well as non equilibrium fractionation processes during the precipitation of brachiopod calcite cannot explain the 18o depletion of brachiopod calcite moreover the 18o depletion of brachiopod calcite with respect to equilibrium 18o values calculated from conodont apatite is too large to be explained by a change in seawater ph that might have influenced the oxygen isotopic composition of brachiopod calcite the realistic palaeotemperatures derived from 18o apatite may suggest that biogenic apatite records the oxygen isotopic composition and palaeotemperature of palaeozoic oceans more faithfully than brachiopod calcite and do not support the hypothesis that the 18o 16o ratio of devonian seawater was significantly different from that of the modern ocean

a pockmark field in the patras gulf greece and its activation during the 14 7 93 seismic event abstract during a recent oceanographical geophysical survey carried out in the southeastern part of the gulf of patras in western greece for the construction of an outfall an active pockmark field was found the pockmark field was formed in soft layered holocene silts the pockmarks are associated with acoustic anomalies attributed to gas charged sediments the pockmarks vary in size and shape from 25 to 250 m in diameter and from 0 5 to 15 m in depth and are among the largest and deepest observed in the world on july 14th 1993 during the survey a major earthquake of magnitude 5 4 on the richter scale occurred in the area during the 24 hour period prior to the earthquake the bottom water temperature anomalously increased on three occasions whilst for a few days after the earthquake it was noted that the majority of the pockmarks were venting gas bublles it is considered that the three abrupt sea water temperature increases were probably the result of upward migrating high temperature gas bubbles in the water column it is further suggested that the earthquake was the triggering mechanism and that the gas expulsion was caused by the reduction in the pore volume in the sediments resulting from changes in the stress regime prior to the earthquake therefore it can be suggested that in seismic areas adjacent to pockmark fields earthquake prediction may be achieved by monitoring the water temperature and or the rate of gas venting in the pockmark field our analysis indicates that the pockmark field in the patras gulf has formed slowly during the holocene by continuous gas venting which is periodically being interrupted by short duration events of enhanced gas seepage triggered by earthquakes