organic carbon δ13c variations in sedimentary rocks as chemostratigraphic and paleoenvironmental tools abstract carbon isotopic variations in marine carbonate rocks and organic matter can provide important information on stratigraphic correlations and paleoenvironments in particular carbon isotopic variations in marine organic materials may yield information about the concentration of oceanic dissolved co 2 and or the physiology of the microalgal community this paper reviews evidence from laboratory experiments and oceanographic studies aimed at understanding controls on carbon isotopic fractionation by marine phytoplankton we also review factors affecting carbon isotopic compositions of bulk sedimentary organic matter and individual biomarker compounds guidelines for analysis of isotopic compositions of organic materials and interpretations of these results for use as chemostratigraphic and paleoenvironmental tools are presented we recommend caution in interpreting carbon isotopic variations of sedimentary organic matter because no environmental factor explains adequately variations in the carbon isotopic composition of modern phytoplankton studies of ancient materials should include compound specific isotopic analyses of known phytoplankton biomarkers or organism specific isotopic analyses with bulk isotopic results to assess the proportions of allochthonous organic materials the degree of reworking and the extent of thermal degradation to confirm any trends present in values of bulk sedimentary organic matter

elastic full waveform inversion of multi component obc seismic data elastic full waveform inversion of seismic reflection data represents a data driven form of analysis leading to quantification of sub surface parameters in depth in previous studies attention has been given to p wave data recorded in the marine environment using either acoustic or elastic inversion schemes in this paper we exploit both p waves and mode converted s waves in the marine environment in the inversion for both p and s wave velocities by using wide angle multi component ocean bottom cable seismic data an elastic waveform inversion scheme operating in the time domain was used allowing accurate modelling of the full wavefield including the elastic amplitude variation with offset response of reflected arrivals and mode converted events a series of one and two dimensional synthetic examples are presented demonstrating the ability to invert for and thereby to quantify both p and s wave velocities for different velocity models in particular for more realistic low velocity models including a typically soft seabed an effective strategy for inversion is proposed to exploit both p and mode converted ps waves whilst p wave events are exploited for inversion for p wave velocity examples show the contribution of both p and ps waves to the successful recovery of s wave velocity

palynology dacryoconarids and the lower eifelian middle devonian basal chotec event case studies from the prague and appalachian basins

carbon and oxygen isotope stratigraphy of the lower mississippian kinderhookian lower osagean western united states implications for seawater chemistry and glaciation a positive carbon isotope 1 3 c excursion has been recognized in upper kinderhookian and early osagean carbonates in three sections in southeast idaho and nevada the oldest 1 3 c peak 7 is dated to the isostichaconodont zone and a younger peak occurs in the typicus zone the shifts are recorded in a range of carbonate lithofacies representing various water depths along the shelf lithofacies sampled for 1 3 c and 1 8 o at the samaria mountain section in southeast idaho record the shallowest water conditions indicated by cross bedded skeletal and peloidal grainstones the deepest water conditions are present in the pahranagat range section in eastern nevada which consists mainly of bioturbated lime mudstone and skeletal wackestone the 1 3 c values from these widely separated sedimentary basins show a consistent trend that correlates with early mississippian curves generated from brachiopod calcite in western europe and the midcontinent of north america as well as dolomites in utah and wyoming 1 8 o values become more positive up section generally paralleling the positive trend in 1 3 c during the late kinderhookian no subaerial exposure surfaces are recognized in the sections examined in southeast idaho and nevada and at least the 1 3 c trends are interpreted as primary seawater fluctuations sea level changes occurred near the beginning of the late kinderhookian 1 3 c shift early to middle parts of the isosticha zone and within the peak of the 1 3 c excursion kinderhookian osagean boundary although tectonic changes associated with the antler orogeny have likely modified the eustatic signature

widespread prolonged late middle to late ordovician upwelling in north america a proxy record of glaciation late middle to late ordovician subtidal ramp carbonates of new mexico texas and oklahoma contain abundant spiculitic chert to 70 chert by volume and phosphate 1 5 wt indicating that these rocks formed in an extensive upwelling zone upwelling began in the late middle ordovician ca 454 ma and persisted until the end of the ordovician late ordovician cherty carbonates also occur along the u s cordilleran margin in board of organic rich graptolitic shale and chert the widespread occurrence of late ordovician cherty and phosphatic carbonates on southern and western laurentia in addition to phosphate rich cool water carbonates over much of the north american midcontinent suggests vigorous thermohaline circulation related to prolonged 10 14 ma gondwana glaciation

environmental significance of foraminiferal morphogroups in jurassic north sea deltas abstract the distribution of morphological groups of foraminifera has been analysed in toarcian and bajocian deposits of the northern north sea and the yorkshire coast the deposits are referred to prodeltaic lower delta front and interdistributary bay environments and contain mainly or entirely agglutinating assemblages of low to intermediate diversity a total of 33 agglutinating species are recognized in the studied material and these are arranged into eleven morphotypes composing seven subgroups and four morphogroups the categories are distinguished on the basis of main morphological features of the taxa combined with their life positions and micro habitats as inferred from modern analogues the prodelta deposits were formed in a normal saline and slightly stagnant depositional setting with foraminiferal faunas composed mainly of surficial and infaunal morphogroups the lower delta front and interdistributary bay sediments were deposited in shallow hyposaline waters strongly dominated by an epifaunal morphogroup with a partly phytal association a model of agglutinated morphotype distribution reveals increasing morphotype diversity and by inference ecological niche span from interdistributary bay through lower delta front to prodeltaic environments

sedimentology and orientation of tentaculite shells in turbidite lime mudstone to packstone lower devonian barrandian bohemia abstract a turbidite origin of upper pragian lime mudstone is proposed on the basis of imbrication and graded bedding in the lower parts of beds and the abundance of calcisiltite components deposition of lime mud and calcisiltite dominated the middle parts of the turbidite beds this muddy part of turbulent gravity surges settled on the submarine slope as a dense suspension downslope sliding continued after deposition from sediment gravity flows as dewatering occurred and the sediment underwent plastic deformation the spatial orientation of embedded tentaculite shells is unusual but corroborates the sediment gravity flow origin of the beds the apices of narrow conical shells show preferred positions of ca 50 upward or ca 50 downward with upward directions more common 63 5 the shells avoid both bedding parallel and bedding perpendicular orientations double cone envelopes arranged according to a subhorizontal mirror plane are the basic orientation pattern this double cone pattern of movement of narrow cone particles was successfully simulated by simple experiments in turbulent water the steep inclination of shells reflects rapid solidification of dense turbulent mud solidification was probably intensified by later sliding and thrusting shears during the early plastic stage of sediment deformation azimuth directions show only slight peaks parallel and perpendicular to the direction of downslope propagation of the gravity flow the complex distribution of tentaculitid shells was analyzed by factor analysis which yielded four types of orientation patt rns that indicate a prevailing orientation of gravity flows towards the ssw and sse

early palaeozoic cooling events peri gondwana and beyond the short lived end ordovician hirnantian glaciation allied to marine mass extinction is variously considered as a short lived event or as the peak of long drawn out climatic cooling through at least late ordovician early silurian times evidence from early palaeozoic facies faunas and stable isotope excursions used to interpret climatic cooling events ranges farther from late mid cambrian to late silurian times glacigenic sediments structures and geomorphology provide direct evidence of glacial episodes cool water carbonate deposition which is particularly widespread during the late ordovician boda event in high latitude peri gondwana gondwana and beyond into mid low palaeolatitudes is interpreted as indicating global cooling not warming as has been proposed such carbonates also characterize mid latitude continents widely at horizons earlier in the ordovician and more locally in the mid silurian in high latitude gondwana cool water carbonate mounds have distinctive facies controlled mound faunas across palaeocontinents other facies evidence for palaeoclimates includes black shale deposition including deglacial organic rich hot shales which indicate transgression in epeiric seas and sea level curves interpreted from facies and faunal successions correlation is shown between facies evidence and positive c isotope excursions from which cyclicities are apparent the possible interface of orbitally controlled rhythms is considered against evolving palaeobiogeography and changes in global sea level and in pco2 facies and faunal evidence from peri gondwanan terranes armorica central europe alborz is assessed with that from gondwana mostly north africa south america and correlatives in avalonia baltica and laurentia to establish a wider picture of early palaeozoic cooling events

shallow structure characterization by 2d elastic full waveform inversion assessing the effectiveness of elastic full waveform inversion fwi algorithms when applied to shallow 2d structures in the presence of a complex topography is critically important by using fwi we overcome inherent limitations of conventional seismic methods used for near surface prospecting acoustic tomography and multichannel spectral analysis of surface waves the elastic forward problem formulated in the frequency domain is based on a mixed finite element p0p1 discontinuous galerkin method to ensure accurate modeling of complex topography effects at a reasonable computing cost the inversion problem uses an fwi algorithm to minimize the misfit between observed and calculated data based on results from a numerical experiment performed on a realistic landslide model inspired from the morphostructure of the super sauze earthflow we analyzed the effect of using a hierarchical preconditioning strategy based on a simultaneous multifrequency inversion of damped data to mitigate the strong nonlinearities coming from the surface waves this strategy is a key point in alleviating the strong near surface effects and avoiding convergence toward a local minimum using a limited memory quasi newton method improved the convergence level these findings are analogous to recent applications on large scale domains although limited sourcereceiver offset ranges low frequency content of the source and domination of surface waves on the signal led to some difficulties regarding the impact of data decimation on the inversion results we have learned that an inversion restricted to the vertical data component can be successful without significant loss in terms of parameter imagery resolution in our investigations of the effect of increased source spacing we found that a sampling of 4 m less than three times the theoretical maximum of one half wavelength led to severe aliasing

stable carbon isotope record of shallow marine evaporative epicratonic basin carbonates ordovician williston basin north america secular variations in stable carbon isotope values of marine carbonates are used widely to correlate successions that lack high resolution index fossils various environmental processes however commonly may affect and alter the primary marine carbon isotope signal in shallow epicratonic basins this study focuses on the marine carbon isotope record from the carbonate evaporite succession of the upper katian upper ordovician red river formation of the shallow epicratonic williston basin usa it documents the carbon isotope signal between the two major ordovician positive shifts in 13c the early katian guttenberg and the hirnantian excursions eight 13c stages are identified based on positive excursions shifts from positive to negative values and relatively uniform 13ccarb values a correlation between carbon isotope trends and the relative sea level changes based on gross facies stacking patterns shows no clear relation based on the available biostratigraphy and 13c trends the studied williston basin curves are tied to the isotope curves from the north american midcontinent quebec anticosti island and estonia which confirm the late katian age aphelognathus divergens conodont zone of the upper red river formation the differences in the 13c overall trend and absolute values coupled with the petrographic and cathodoluminescence evidence suggest that the carbon isotope record has been affected by the syndepositional environmental processes in the shallow and periodically isolated williston basin and stabilized by later burial diagenesis under reducing conditions and the presence of isotopically more negative fluids

the facies properties and depositional environments of nodular limestones and red marly limestones ammonitico rosso in the ankara jurassic sequence central turkey the nodular limestones and red marls of the ankara region deposited during the early to middle jurassic show similar palaeontological and sedimentological characteristics to those of the red nodular limestones form the northern alps adnet limestones and from the southern alps ammonitico rosso the nodular limestones appear to be hardground breccias drowned into the red marly limestones due to the instability of the bottom the association of sponge spicules crinoid fragments small ostracods benthic foraminifers shell debris and common micrite matrix suggests a subtidal environment the subsequent formation of red marly limestones consists of the partial dissolution of the shells this suggests that a low sedimentation rate and or sedimentological breaks took place during the precipitation of the ammonite bearing marls the nodular limestones hardground breccias and the ammonitico rosso type facies of the ankara jurassic succession were formed in a deeper subtidal environment and or deeper shelf extending into the basin the hardground layers drowned into the ammonitico rosso were likely formed on a local carbonate shelf that deepened increasingly through the early to middle jurassic development of a local submarine clastic fan within the carbonate succession of the ankara jurassic basin indicates an irregular bottom topography induced by the syn sedimentary faults

response of middle jurassic benthic foraminiferal morphogroups to dysoxic anoxic conditions in the pieniny klippen basin polish carpathians abstract the distribution of foraminiferal morphological groups has been analyzed in upper aalenian lower bajocian black siltstones and mudstones of the pieniny klippen belt polish carpathians the deposits are assigned to middle neritic outer and upper bathyal zones represented by three succession and contain agglutinated and calcaeous foraminifera assemblages separate classifications of agglutinated and calcareous morphogroups are established and used for a palaeocological study the groups are distinguished on the basis of morphological features modes of life and feeding habits as inferred from modern analogues infaunal preferences of some foraminifera have been supported by comparison with other infaunal indicators such as trace fossil tiering and abundance of infaunal ostracods a new quantitative method to estimate dissolution of calcareous tests has been tested on the most common genus lenticulina it reveals a special survival strategy of this genus in suboxic muddy and flocculent substrate the distribution of morphogroups in comparison with other palaeoecological taphonomical and sedimentological indicators allows interpretations of organic input rate of sedimentation level of oxygenation position of the redox boundary and p h the studied deposits represent regional anoxic dysoxic event which occured within a semienclosed silled basin

effects of surface scattering in full waveform inversion in full waveform inversion of seismic body waves often the free surface is ignored on grounds of computational efficiency asyntheticstudywasperformedtoinvestigatetheeffectsofthissimplification intermsofsizeandfrequency the testmodelanddataconformtoareallong offsetsurveyofthe upper crust across the san andreas fault random fractal variations are superimposed on a background model with strong lateral and vertical velocity variations ranging from 1200to6800m s syntheticdatawerecomputedandinverted forthismodelanddifferenttopographies afullyviscoelastic time domain code was used to synthesize the seismograms and a viscoacoustic frequency domain code was utilized to invert them the inversion was focused on early arrivals which are dominated by p waves but also contain strong p rayleigh wave conversions from the near field of the receiver resulting waveform models show artifacts and a loss of resolution from neglecting the free surface in the inversion but the inversions are stable and they still improve the resolution of kinematic models the extent of deterioration dependsmoreonthesubsurfacethanonthesurfacestructure inversion results were improved at no additional expense by introducing a weak contrast along a staircase function above shotsandreceivers

spatial geochemistry of upper jurassic marine carbonates iberian subplate abstract chemostratigraphy applied to ancient marine carbonates is commonly based on one dimensional stratigraphic sections or core data as demonstrated from modern oceans this approach underestimates the spatial complexity of physico chemical seawater properties here a several hundred kilometer long transect consisting of seven upper jurassic sections from settings ranging from proximal neritic middle shelf to the epioceanic distal fringe across the southern and eastern palaeomargins of the iberian sub plate reveals variability in sedimentologic stratigraphic and geochemical records the comparison of isotopic and elemental data from different carbonate materials matrix micrite carbonate cements in veinlets belemnite rostra and ammonite shells reveals differential diagenetic pathways microfacies cathodoluminescence and geochemical data retrieved from biostratigraphically well constrained sections reveal that epioceanic matrix micrite geochemical data provide valuable proxies for palaeo seawater properties our data are reviewed in the context of published late jurassic records the outcome shows a higher level of complexity including the potential admixture of marine continental and diagenetic geochemical signals in the epicontinental record the stratigraphic trend in carbon isotopes of epioceanic sections agrees upon that of upper jurassic reference sections from the northern tethyan margins while oxygen isotope ratios are relatively 18o enriched palaeo seawater temperatures across the transect investigated were estimated using 18o as tentative proxy for interpreting distance from shore differences in water masses relative depth variations and potential local forcing factors palaeoenvironmental conditions evaluated through the combined record of isotope 18o elemental mn and skeletal content contrast with relative fluctuations in sea level site specific changes in palaeoceanographic parameters such as water depth seawater temperature salinity and upwelling are considered in comparison to examples from ancient and modern oceans

ecostratigraphic trends of jurassic agglutinated foraminiferal assemblages as a response to sea level changes in shelf deposits of svalbard norway foraminiferal analysis proves to be a useful tool for the interpretation of major factors controlling the eco sedimentary environment changes in benthic foraminiferal features including morphogroups are mainly affected by variations in nutrient availability and oxygenation rate the integration of foraminiferal data with total organic carbon toc values together with differentiation of oxygen restricted biofacies orb based on sedimentological features and macroinvertebrate composition will improve the interpretations derived upper jurassic shelf deposits from svalbard norway are revealed to be particularly sensitive to the record of fluctuations in nutrients and oxygenation showing two extreme cases in toc content high toc concentrations are characterized by low values of the shannon weaver index h and diversity index in foraminifera pointing to a low diversity and dominance of r mode epifaunal foraminifera trochammina moreover differentiated orb can be characterized by parallel lamination in shales and an absence of macrobenthic invertebrates including trace fossils unfavourable benthic conditions are interpreted mainly related with a high consumption of oxygen by microbes in the sediment associated to the degradation of the organic matter low toc values are related to higher values of diversity h and diversity index and foraminiferal assemblages dominated by infaunal forms the differentiated orbs are characterized by coarse fabrics scarcity or absence of parallel lamination presence of trace fossils and abundance of macroinvertebrate shelly epifauna this is related to a better pore water circulation and higher oxygenation degree congruent with the comparatively more favourable conditions in the infaunal habitats ecostratigraphic trends along the studied section allow the differentiation of stratigraphic intervals reflecting variations in parameters related to the sea level dynamics transgressive phases reveal upward trends in palaeoenvironmental parameters characterized by decreasing grain size and increasing in both toc values and epifaunal foraminifera differentiated orb reveals diminution in abundance and diversity of trace fossils and benthic shelly macroinvertebrates upwards maximum flooding intervals show the maintenance or accentuation of the previously registered features the thinnest fabrics and the highest values in toc and in opportunistic epifaunal foraminifera with orb dominated by parallel lamination a regressive phase is characterized by coarsening upwards sediments decreasing toc values and increasing infaunal foraminifera orb reveals a diminution in parallel lamination together with an increase in trace fossil abundance and diversity as well as in benthic shelly macroinvertebrates

upper ordovician mohawkian carbon isotope δ13c stratigraphy in eastern and central north america regional expression of a perturbation of the global carbon cycle abstract the guttenberg carbon isotope excursion gice documented from eastern north america demonstrates the effects that regional geochemically distinct water masses upwelling and ocean circulation have on the carbon isotope record from carbonate platforms late turinian chatfieldian carbonates from oklahoma kentucky virginia and west virginia record a positive carbon isotope excursion 3 0 the gice excursion the gice excursion has relations to established biostratigraphy beginning in the north american midcontinent phragmodus undatus conodont zone and continuing through the plectodina tenuis zone sequence and event stratigraphy previously established models for positive carbon isotope shifts on carbonate platforms have been tested during the gice excursion where geochemically distinct water masses are defined for the upper ordovician a major eustatic sea level rise before the gice promoted a greater exchange of open ocean waters onto the carbonate platform of laurentia however restricted or sluggish circulation and exchange between water masses within the epeiric seas and the adjacent iapetus ocean were still apparent local variations documented in the gice excursion are directly related to upwelling of nutrient rich isotopically light waters increased primary productivity and the subsequent organic carbon production and burial

the great latest ordovician extinction on the south china plate chemostratigraphic studies of the ordovician silurian boundary interval on the yangtze platform continuous samples from four ordovician silurian boundary sections of graptolitic shales and mudstones in the yangtze basin yangtze platform on the south china plate spanning the latest ordovician mass extinction of many unrelated groups of organisms were chemically analyzed for the abundances of about 40 common and trace elements and iridium it is observed that the abundances of ir and other siderophile and chalcophile elements e g co cr as mo sb and v show elevated values in the extinction horizon at the base of the graptolite persculptus zone which corresponds to the stratigraphic level for the local systematic boundary in china between the ordovician and silurian iridium abundances show maxima at this extinction level in three of the four sections analyzed with varying strength 230 ppt at yichang 92 ppt at jinxian and 88 ppt at youyang but 50 ppt at xiushan these geochemical patterns appear to be of global significance since similar geochemical anomalies including weak ir anomaly were also recorded at about the same stratigraphic level in many other sections previously studied in quebec yukon arctic and northwest territories canada and scotland although impact by a comet with low platinum group element abundances could have been responsible for the geochemical anomalies we find it is most plausible to attribute the geochemical signal to the effects of a lower sedimentation rate and reducing water conditions at this horizon the beginning of a rapid transgression induced by rapid melting of the ice caps on gondwana carbon isotope excursions in organic material at yichang together with other carbon isotope data from central sweden northwestern canada latvia quebec and wisconsin suggest that after a period of decreasing atmospheric and marine pco2 in the latest ordovician the hirnantian a sudden large pco2 increase in the ocean and atmosphere may have occurred at the extinction horizon at the base of the persculptus zone a greenhouse effect might have existed for a short time what triggered such a sudden pco2 increase is uncertain but a rapid co2 degassing caused by volcanism tectonics and or extraterrestrial impact could have been responsible

first record of the hirnantian upper ordovician δ13c excursion in the north american midcontinent and its regional implications the most prominent of the two major global delta c 13 excursions in the ordovician the hirnantian delta c 13 excursion hice which is previously recorded from the uppermost ordovician in a few sections in nevada quebec arctic canada baltoscandia scotland and china is documented for the first time from the north american midcontinent samples through the girardeau limestone and leemon formation in missouri and illinois show elevated delta c 13 values of 4 parts per thousand to 5 parts per thousand although not determined precisely the beginning of the hice is likely to be in the upper part of the orchard creek shale and it ends in the upper leemon formation being extraordinarily useful chronostratigraphically the presence of the hice makes it possible to provide a firm dating of the study interval whose age has long been controversial comparison between the study sections and coeval hice sequences in north america and europe show striking similarities especially in sea level history indicating that major local lowstands reflect eustatic sea level changes a comparison with hirnantian diamictite successions in north and south africa and argentina suggests that these lowstands correspond to two major gondwanan glacial episodes less

bathymetric and isotopic evidence for a short lived late ordovician glaciation in a greenhouse period the end ordovician glaciation is distinct among phanerozoic glaciations in that co 2 levels were generally high yet major continental ice sheets accumulated on the gondwana supercontinent new oxygen isotopic data indicate substantial changes in sea water temperatures and ice volume coinciding with glacio eustatic changes in sea level reflecting the growth and decay of the gondwana ice cap major glaciation was apparently confined to the hirnantian and was 0 5 1 m y long rather than the 35 m y of earlier estimates carbon isotope values indicate significant changes in carbon cycling as the oceans changed from a state with warm saline bottom waters to a state with cold deep water circulation and then back again we believe that the changes in the carbon cycle effected a reduction in p co 2 levels in the oceans and atmosphere and thus promoted glaciation but were unable to sustain icehouse conditions in a greenhouse world

relations between submarine fissures internal breccias and mass flows during triassic and earlier rifting periods deep fissures in shallow water limestones filled with deep water sediments are described from many places especially in the triassic and jurassic of the tethys and in the middle to upper devonian of the variscian mountains mass flows occur in the same formations and areas on the island of hydra greece it was possible to show that both phenomena are linked by internal breccias of well fitted limestone fragments they are indicative of slope or near slope positions and are very probably caused by flexure like deformations of shallow burial limestones seismic shocks producing overpressure may be instrumental in the disintegration of the semi lithified limestones thus providing the material for mass flows these events are associated with a tectonical subsidence as shown by deep water matrix in the brecciated shallow water limestones they occur in areas and periods of submarine rifting especially in late devonian and triassic time at least four triassic brecciation events can be traced from greece to the alps and correspond presumably to major transgressions in the cratonic basin of middle europe

oxygen and carbon isotopic composition of ordovician brachiopods implications for coeval seawater one hundred and two articulate brachiopods and twenty one marine cements from ordovician strata were analyzed for oxygen and carbon isotopes these together with 200 previously published analyses of ordovician brachiopods mostly of upper ordovician age define a general trend of increasing 18o values with decreasing age from a minimum of 10 5 in the earliest ordovician to a maximum of 1 5 at the ordovician silurian boundary the 13c values show a general positive correlation with 18o and increase from 2 5 in the earliest ordovician to as high as 7 at the ordovician silurian boundary the magnitudes of ordovician excursions for both 18o and 13c are similar to those reported previously for the entire phanerozoic different genera of brachiopods from the same stratigraphie level did not yield any large differences in their isotopic compositions suggesting that vital effects did not influence decisively the isotope values of the studied skeletal parts petrographic examination and trace element analyses indicate that brachiopod shells from llandeilo to ashgill strata are well preserved and thus may have retained their primary isotopic signatures the same criteria for the tremadoc arenig and some llanvirn brachiopods suggest partial diagenetic alteration of 18o values in these samples but this does not preclude their utility as a recorder of a primary 13c signal the observed 18o trend for the well preserved portion of the record may reflect progressive cooling during ordovician perhaps complemented by a changing 18o values of seawater the latter could have been a consequence of a net increase in the rate of high temperature water rock interaction relative to its low temperature counterpart as indicated also by the large coeval decrease of marine 87sr86sr superimposed on the above long term 18o trend is a positive excursion of about 2 at the end of the ordovician probably reflecting a large expansion of polar ice caps the magnitude of this excursion indicates a degree of glaciation comparable to that at the height of the quaternary glacial episodes the secular 13c trend may reflect a progressive increase in marine organic productivity and or enhanced organic deposition in the ordovician oceans particularly noticeable at the time of the terminal ordovician glaciation

evolutionary dynamics of pragian dacryoconarida lower devonian tentaculitoidea evidence from palaeontological data and 13c of marine carbonates from czech republic abstract a detailed palaeontological study was performed on 38 successive assemblages of dacryoconarids tentaculitoidea sampled along the cerna rokle section praha basin czech republic this section represents the whole pragian stage lower devonian and roughly corresponds to a 6 ma time span dacryoconarid assemblages change in abundance and diversity oxygen and carbon isotope compositions of the dacryoconarid bearing carbonates were measured to evaluate the possible influence and control of the environmental conditions on the evolutionary dynamics of the dacryoconarid faunas large and rapid 13c excursions occur in the marine carbonate sequence of the cerna rokle section some of which apparently correspond with faunal variations however no clear and simple relationship appears between carbon isotope ratio fluctuations and dacryoconarid evolutionary dynamics occurrence and extinction of the dacryoconarid species appear to be mainly related to biotic factors environmental variations cannot be regarded as having preponderantly influenced the dacryoconarid evolution which more probably resulted from intrinsic biotic factors

new isotopic data solving an old biostratigraphic problem the age of the upper ordovician brachiopod holorhynchus giganteus recent work has shown that there is a pronounced positive late ordovician excursion in both 13 c and 18 o which appears to be global and identifies a clear chemostratigraphic interval that is confined to part of the hirnantian stage pre hirnantian rawtheyan brachiopod carbonate values of 13 c are typically in the range 1 to 1 pdb and lower hirnantian values are typically in the range of 4 to 7 o pdb this contrast in isotopic values has been used to assess the age of the distinctive late ordovician brachiopod holorhynchus giganteus the age of the holorhynchus association is important in terms of its relationship to the major late ordovician extinction that was initiated at the start of the hirnantian the species which traditionally was regarded as uppermost ordovician hirnantian in age has been shown on stratigraphic evidence to be pre hirnantian at many locations if this is so it predates the first phase of extinction and is not associated with the hirnantia fauna which characterizes the interval between the two main episodes of late ordovician extinction however at its type locality in the asker district of norway the stratigraphic evidence has pointed to it being hirnantian in age to resolve this ambiguity analyses have been made on holorhynchus at three locations 1 in the east baltic region where holorhynchus occurs below demonstrable hirnantian rocks 2 in the boda limestone of central sweden where holorhynchus occurs high on a carbonate mud mound where its age is unclear and 3 in the type area of the species in norway at all three locations the 13 c values are low indicating a pre hirnantian pre extinction age for holorhynchus the re assessment of the age of the asker sequence in norway implies the presence of a cryptic unconformity there and suggests uplift rather than subsidence during the latest ordovician this study emphasizes the value of chemostratigraphy in high resolution stratigraphy

the late ordovician mass extinction abstract near the end of the late ordovician in the first of five mass extinctions in the phanerozoic about 85 of marine species died the cause was a brief glacial interval that produced two pulses of extinction the first pulse was at the beginning of the glaciation when sea level decline drained epicontinental seaways produced a harsh climate in low and mid latitudes and initiated active deep oceanic currents that aerated the deep oceans and brought nutrients and possibly toxic material up from oceanic depths following that initial pulse of extinction surviving faunas adapted to the new ecologic setting the glaciation ended suddenly and as sea level rose the climate moderated and oceanic circulation stagnated another pulse of extinction occurred the second extinction marked the end of a long interval of ecologic stasis an ecologic evolutionary unit recovery from the event took several million years but the resulting fauna had ecologic patterns similar to the fauna that had become e

deep sea benthic foraminiferal recolonisation following a volcaniclastic event in the lower campanian of the scaglia rossa formation umbria marche basin central italy we studied the distribution of deep water agglutinated foraminiferal dwaf assemblages across a 15 cm thick volcaniclastic layer in the lower campanian scaglia rossa limestones of the umbria marche basin above the volcaniclastic layer which is devoid of foraminifera a remarkable pattern of recovery among dwaf has been observed the complete recovery of dwaf in terms of trophic groups and complexity of assemblages is observed in the first 5 cm above the volcaniclastic layer representing 4 8 kyr based upon the mean sedimentation rate of the campanian scaglia rossa formation in its initial stage the recovery pattern is remarkably similar to that observed following the 15 june 1991 mount pinatubo ashfall in the abyssal south china sea where various species of reophax a small organically cemented species of textularia and the calcareous species quinqueloculina seminula and bolivina difformis are the earliest recolonisers on top of the tephra layer such similarities between modern and fossil analogues strengthens the reliability of environmental reconstructions based on dwaf fl 2002 elsevier science b v all rights reserved

mass extinctions and sea level changes abstract review of sea level changes during the big five mass extinctions and several lesser extinction events reveals that the majority coincide with large eustatic inflexions the degree of certainty with which these eustatic oscillations are known varies considerably thus the late ordovician and end cretaceous extinctions are associated with unequivocal major regressions demonstrated from numerous widespread regions in contrast the multiple high frequency sea level changes reported for the frasnian famennian crisis based on the supposed depth preferences of conodont taxa have little support from sequence stratigraphic analyses which reveals the interval to be one of highstand the end permian mass extinction has long been related to a severe first order lowstand of sea level newell n d 1967 revolutions in the history of life geol soc am spec pap 89 63 91 based primarily on the widespread absence of latest permian ammonoid markers but field evidence reveals that the interval coincides with a major transgression newell s hypothesis that marine extinctions are related to shelf habitat loss during severe regression remains tenable for the end guadalupian and end triassic extinction events but not for other crises rapid high amplitude regressive transgressive couplets are the most frequently observed eustatic changes at times of mass extinction with the majority of extinctions occurring during the transgressive pulse when anoxic bottom waters often became extensive the ultimate cause of the sea level changes is generally unclear a glacioeustatic driving mechanism can only be convincingly demonstrated for the end ordovician and end devonian events at other times it is speculated that they may relate to the widespread regional doming and subsequent collapse caused by the impingement of superplumes and ultimate eruption on the base of the lithosphere

the late ordovician early silurian glacial period abstract late ordovician to early silurian tillites and evidence of extensive glacial erosion were first discovered in the western sahara in the late 1950 s although the concept of a glacial period at this time had been around since the late 19th century further evidence of glaciation is now available from west africa south africa the arabian peninsula eastern north america west and central southe america and europe several glacial episodes can be distinguished the earliest evidence local mountain glaciation appears to be of caradoc age the major episode may have begun in caradoc time and lasted much of ashgill time when a major ice sheet covered at least north central and west africa which was then centered near the south pole however independent palaeontological and sea level evidence from areas far removed from the centre of glaciation suggests a time span for this episode of less than 2 ma this conflict has yet to be resolved the latest evidence of glaciation is wenlock in age but is confined to south america which by then was replacing africa over the south polar region however this latest episode may simply have been a rather intensive mountain glaciation rather than being of ice sheet dimensions the lack of land in the north polar region probably explains the absence of tillites from the then northern hemisphere land masses the total area affected by glaciation in early palaeozoic time in north africa alone is at least 6 106 km2 combined with other glaciated areas glaciation may have been on the scale of that of present day antarctica

retrieving lateral variations from surface wave dispersion curves surface wave analysis is usually applied as a 1d tool to estimate v s profiles here we evaluate the potential of surface wave analysis for the case of lateral variations lateral variations can be characterized by exploiting the data redundancy of the ground roll contained in multifold seismic data first an automatic processing procedure is applied that allows stacking dispersion curves obtained from different records and which retrieves experimental uncertainties this is carried out by sliding a window along a seismic line to obtain an ensemble of dispersion curves associated to a series of spatial coordinates then a laterally constrained inversion algorithm is adopted to handle 2d effects although a 1d model has been assumed for the forward problem solution we have conducted different tests on three synthetic data sets to evaluate the effects of the processing parameters and of the constraints on the inversion results the same procedure applied to the synthetic data was then tested on a field case both the synthetic and field data show that the proposed approach allows smooth lateral variations to be properly retrieved and that the introduction of lateral constraints improves the final result compared to individual inversions

phanerozoic large igneous provinces lips heatt haline euxinic acidic thermal transgression episodes and mass extinctions abstract the phanerozoic consists of three mutually exclusive climate states icehouse greenhouse and hothouse the greenhouse is the default state representing 70 of the phanerozoic it is characterized by a weak thermal mode pole driven deep water formation with little or no continental sea ice and weakly oxic cool water sinking near the poles nitrogen limitation characterizes greenhouse oceans in which ammonium may be the dominant bioavailable form of nitrogen the steady state greenhouse default must be forced to produce either of the other two states continent continent collision produces the intense chemical weathering that draws down atmospheric co2 and results in the icehouse state that comprises 20 25 of the phanerozoic icehouses have ice caps in contact with the ocean that produce icebergs and foster sea ice formation sea ice formation fills the ocean with highly oxic phosphorus limited icewater except for a thin layer of warm surface water in the tropics of the 23 most conspicuous mass extinctions of the phanerozoic including the late ediacaran 4 are associated with ice volume related regressions and 3 are problematic we suggest that the other 16 mass extinctions occurred when greenhouse climate was forced to hothouse climate large igneous provinces lips can trigger the heatt haline euxinic acidic thermal transgression mechanism which can force greenhouse climate to a hothouse climate state the rapid voluminous co2 emissions of lips cause a series of events that result in very slow but pronounced haline mode circulation mid latitude driven deep water formation that produces warm saline bottom water at very dry hot subtropical and middle latitudes this water upwells at the poles causing warm and moist equable climate hothouse development promotes deep sea anoxia that is generated in concert with co2 buildup and warming the spread of anoxia favors reduced nitrogen over nitrate and limited iron dust curtails nitrogen fixation this leads to dominance of primary productivity by primitive green algae and or cyanobacteria progression to euxinia that reaches the photic zone severely curtails primary productivity via poisoning even as availability of usable nitrogen plummets the result is eukaryotic mass extinction we suggest that the 16 phanerozoic mass extinctions referred to above resulted at least in part from the heatt process evidence for this relationship at 11 of the most severe extinctions is convincing data sets for the other 5 are strongly suggestive of heatt related mass extinction but do not yet have enough documentation to reliably characterize them as heatt episodes

autoradiography by x ray excited optical luminescence xeol application to scheelite and fluorite mineralisation this paper investigates the practical application of xeol as an autoradiography technique of use in characterising the mineralogy of geological samples a simple apparatus is described in which thin sections are excited with a low power x ray tube operated at 19 kv 0 9 ma luminescence is detected on photographic film 400 asa using a camera focused through a leaded glass window onto the rear of the thin section xeol autoradiographs recorded for exposure times varying from 3 to 120 min are presented for zinc sulphide powder a test sample scheelite in a wolframite bearing quartz vein and fluorite plus calcite in a fluorite calcite quartz vein the latter two samples being collected from mineralised localities in the eastern highlands of scotland u k these xeol autoradiographs show not only the distribution of the specified phases but also delineate textural information of value in interpreting mineralisation processes

origin sequence stratigraphy and depositional environment of an upper ordovician hirnantian deglacial black shale jordan the upper ordovician succession of jordan was located 60 s less than 100 km from the hirnantian ice sheet margin new graptolite dates indicate glaciation ended in jordan in the late hirnantian persculptus biozone the succession records two glacial advances within the ammar formation and the subsequent deglaciations organic rich black shales batra formation form part of the final deglacial transgressive succession that in filled an existing low stand glacial continental shelf topography the base of the black shale is coincident with the maximum flooding surface during transgression interfluves and sub basin margins were breached and black shale deposition expanded rapidly across the region the top of the black shales coincides with peak highstand the expanding puddle model sensu wignall for black shale deposition adapted for the peri glacial setting provides the best explanation for this sequence of events we propose a hypothesis in which anoxic conditions were initiated beneath the halocline in a salinity stratified water column a fresher surface layer resulted from ice meltwater generated during early deglaciation during the initial stages of marine incursion nutrients in the monimolimnion were isolated from the euphotic zone by the halocline increasing total organic carbon toc and 13corg up section indicates the organic carbon content of the shales was controlled mainly by increasing bioproductivity in the mixolimnion the strakhov model mixolimnion nutrient levels were sustained by a continual and increasing supply of meltwater derived nutrients modulated by obliquity changes in high latitude insolation anoxia was sustained over tens to hundreds of thousands of years the formation of black shales on the north gondwana shelf was little different to those observed in modern black shale environments suggesting that it was the nature of the ordovician seas that pre disposed them to anoxia

global analyses of brachiopod faunas through the ordovician and silurian transition reducing the role of the lazarus effect global analyses of 88 families and 284 genera of brachiopods from middle ashgill late ordovician to early middle rhuddanian early silurian indicate that 18 6 and 12 5 of families and 51 0 and 41 3 of genera were eliminated in the first and second phases of the end ordovician mass extinction respectively with the total loss of 28 4 of families and 69 0 of genera in the crisis new investigation demonstrates that brachiopods at both generic and familial levels suffered greater during the first phase than during the second phase four groups victims relicts survivors and new arrivals are distinguished by their stratigraphical ranges generic survivors occurring in the kosov province during the hirnantian can be split into three types with respect to their changing abundance increasing declining and lazarus taxa among the 88 genera that survived numerous declining genera occurred in the hirnantian 16 lazarus families and 18 lazarus genera are provisionally known and may be regarded

origin of red pelagic carbonates as an interplay of global climate and local basin factors insight from the lower devonian of the prague basin czech republic abstract red pelagic sediments are relatively common in the phanerozoic they are often interpreted as products of sea bottom oxidation during greenhouse climate showing a conspicuous alternation with black shales and thus carrying important palaeoceanographic information the lower devonian pragian carbonate strata of the prague basin czech republic praha formation contain a marked band of red pelagic carbonate up to 15 m thick which can be correlated for several tens of km we investigated seven sections 17 to 255 m thick of the prague basin using the methods of facies analysis outcrop gamma ray logging diffuse reflectance spectroscopy optical microscopy element geochemistry magneto mineralogy and electron microprobe analysis the aim was to find the mineral carriers of the red colour investigate the stratigraphic context of the red carbonates and evaluate the local and global prerequisites for their formation the red pigmentation represents enrichment by hematite with respect to goethite approximately 31 of the total reflectance falling in the red colour band represents a threshold for red coloration the red pigmentation is carried by submicronic hematite dispersed in argillaceous pelagic calcilutite and or inside skeletal allochems gamma ray log correlation indicates that the red carbonate band developed in stratigraphic levels with low sedimentation rates typically from 1 to 7 1 mm kyr which are comparable to the mesozoic rosso ammonitico facies the red beds and the whole praha formation pragian to early emsian are characterized by low toc values

two dimensional shallow soil profiling using time domain waveform inversion near surface characterization has now gained significance among exploration geophysicists and many methods are being proposed to retrieve the 2d structures of shallow soils because most of these methods are based on the modal inversion of the surface waves they can only be applied to laterally homogeneous or smoothly heterogeneous soil models we have developed a time domain waveform inversion method for 2d near surface exploration that offers an alternative approach to existing surfacewave techniques for layered soils with a flat surface our method directly fits the input rayleigh waveforms to retrieve the 2d soil structure without need of any modal identification allowing the inversion of soil models that can be challenging with modal inversion based approaches in our method the forward problem formulated in the time domain is based on a 2 5d staggered grid finite difference scheme to simulate the p sv wavefield soil modeling was achieved by dividing soil layers into specific number of blocks with discontinuous interfaces the inversion strategy depends on attributing suitable values for the interface depth and s wavevelocity for each block to reconstruct a numerical soil model that fit the input waveforms because we cannot know the source signature during data acquisition source deconvolution by a reference station is applied to observed and calculated waveforms to make a waveform inversion free of the source signature numerical experiments revealed that our method was able to sufficiently reconstruct soil structures with strong lateral velocity gradient or soils with a blind layer in noisy environments using a single source and reasonable number of receivers we also applied this method to real waveform data and we succeeded in obtaining good correlation between the inverted 2d soil model and the existing borehole data

carbon and oxygen isotope record across pridoli to givetian stage boundaries in the barrandian basin czech republic abstract carbon and oxygen isotope composition and the chemistry of limestones clayey limestones and shales were studied across stage boundaries from pridoli to givetian in the barrandian basin no substantial isotopic shifts were found at the pragian emsian and emsian eifelian boundaries a gradual shift in 13c values from 2 6 to 3 6 was observed in pridoli and lochkovian limestones this shift is inferred to have been related to a combination of higher productivity increased deposition of organic matter and shallowing of the basin the global kacak otomari event just below the eifelian givetian boundary is marked by an abrupt change in carbon isotopic values from about 1 to 3 in pelagic carbonates no 13c shift was found in shallow water carbonates at the eifelian givetian boundary high 18o values up to 1 3 in pragian emsian and early eifelian limestones indicate that the barrandian basin was relatively isolated from the world ocean during those intervals lower 18o values up to 7 5 in late eifelian limestones may indicate the end of isolation

an organic carbon isotope record of late ordovician to early silurian marine sedimentary rocks yangtze sea south china implications for co2 changes during the hirnantian glaciation studies of 13c of marine sedimentary organic carbon in six clastic sections with sediments deposited from the latest ordovician to earliest silurian in the yangtze sea on the south china plate show a positive 13corg excursion of up to 4 in the latest ordovician hirnantian stage corresponding in time to a major continental glaciation on gondwana various factors that might be responsible for the 13corg increase are considered including input and contribution from exogenic carbon sources secondary processes such as heterotrophy and thermal maturation and changes in yangtze sea surface water temperature productivity primary producers dissolved co2 concentrations and the isotopic composition of dissolved inorganic carbon current data are consistent with the interpretation that the observed 13corg increase may have resulted from a decrease in the surface water dissolved co2 in the yangtze sea during the hirnantian glaciation probably reflecting a significant decrease in glacial ocean atmosphere pco2 levels at that time

carbon isotope record of late cambrian to early ordovician carbonates of the argentine precordillera a more than 2000 m thick cambrian ordovician carbonate platform succession developed on the exotic argentine precordillera terrane during rifting from laurentia and drifting towards gondwana on base of these carbonates a carbon isotope curve could be developed for the cambrian ordovician we measured 13ccarb and 13corg values on bulk rocks selected components and diagenetic cements whereas the carbon isotope signals of intertidal and supratidal rocks are altered by diagenesis most subtidal carbonates exhibit primary marine values we can report reliable curves for the middle late cambrian transition and for the latest cambrian to earliest middle ordovician the 13c curve matches well with the published data from global cambrian ordovician boundary sections excursions and shifts in the carbon isotope curve correspond to events in sequence stratigraphy this indicates the interdependence on sea level which rules the productivity and or preservation of organic carbon and therefore the partition between corg and ccarb burial

geochemical indicators of depositional environment and source rock potential for the upper ordovician maquoketa group illinois basin two depositional cycles are recognized within the upper ordovician maquoketa group of the illinois basin in a core from the new jersey zinc 1 parrish well of fulton county illinois organic carbon corg total sulfur 13c content of the organic carbon dgr13corg hydrogen and oxygen indices hi and oi from rock eval pyrolysis and yields of extractable organic matter eom vary through the cycles dark brown to black laminated shales are present in the lower portion of each cycle and have high values of corg 1 0 3 0 hi 500 1000 mg hydrocarbon hc g total organic carbon toc and eom 500 2500 ppm and more negative dgr13corg values dgr13corg 30 to 30 5 mil gray to greenish gray bioturbated shales are present in the upper portion of each cycle and have low values of corg 1 0 hi 500 mg hc g toc and eom 500 ppm and more positive dgr13corg values 28 5 to 29 5 pmil compared to the laminated shales although thermally immature to marginally mature in this core the laminated shales represent potential source rocks for petroleum because they contain good to excellent quantities of oil prone organic matter and are more deeply buried in other areas of the basin kerogen elemental data and rock eval data suggest that the source of organic matter in the maquoketa was uniform with the notable exception of graptolite rich layers distributions of saturated hydrocarbons for maquoketa samples resemble those derived from amorphous organic matter the organic walled microfossil gloeocapsomorpha prisca was not identified in kerogens of the maquoketa shale and its absence is most likely due to an unfavorable depositional environment and or climate variations in bulk geochemical data and carbon isotopic compositions within the maquoketa group indicate substantial reworking and degradation of organic matter associated with bioturbation and oxygenated depositional conditions organic rich shale was deposited in an environment where circulation of the water column was sluggish and dissolved oxygen concentrations were low resulting in the preservation of organic matter organic poor shale was deposited in an environment where circulation of the water column was strong dissolved oxygen concentrations were high and burrowing organisms thoroughly reworked the sediment resulting in the degradation of organic matter a maximum difference in carbon isotopic ratios of 2 pmil between organic rich and organic poor units of the maquoketa roup suggests that heterotrophic reworking of organic matter was important in the depositional environment the carbon isotopic composition and h c ratio of kerogen for graptolite rich shale suggests that organic productivity may have played an intermittent role in the accumulation of organic matter in the maquoketa shale

carbon isotope stratigraphy in the latest ordovician of estonia on the basis of bulk carbonate carbon isotope data from six drill cores and the type section of the porkuni stage of estonia 13c curves were compiled which altogether cover nearly the whole succession of the latest ordovician hirnantian well known as a time of short lived glaciation and mass extinction in pre porkuni and silurian rocks 13c values were low from 0 2 to 1 7 for the porkuni stage three intervals of the curve were established 1 lower a positive shift up to 6 7 2 middle part with variable values from 3 3 to 5 4 and 3 upper phase with slightly decreased values from 3 2 to 3 6 the correlation with the dob s linn scotland kerogen 13c curve shows that the first two intervals coincide with the normalograptus extraordinarius graptolite biozone the third one with the n persculptus biozone

the morphogroups of small agglutinated foraminifera from the devonian carbonate complex of the prague synform barrandian area czech republic abstract agglutinated foraminifera from the lower and lower part of the middle devonian predominantly limestones of the prague synform barrandian area were classified into five morphogroups morphogroup ed1 was divided to morphotype ed1a which is represented by foraminifera with straight tubular or branched tests irregularly coiled forms are separated to morphotype ed1b ed2 morphogroup includes genera with planoconvex tests which can be divided into morphotype ed2a characterized by planoconvex meandering tests and morphotype ed2b with subglobular tests the ed3 morphogroup contains genera with discoidal flattened planispirally coiled forms the ed4 group consists of globular forms whilst simple globular forms without marked tubular projections are representatives of morphotype ed4a and globular morphotypes ed4b with apertures on marked neck like projections and morphogroup ed5 is represented by very rare multilocular morphotypes the absence of the deep infaunal morphogroups is characteristic the morphogroup distribution has been strongly affected by oxygen concentration the energy of the environment nutrient availability and post mortem processes intervals with diversified and abundant foraminiferal assemblages can be correlated with positive 13 c excursions and also with the deposition of nodular limestones the devonian assemblages from the prague synform were compared with isochronous assemblages from other regions though the taxonomical composition of the early devonian assemblages from these areas are rather different the morphogroup composition is highly comparable and globally indicates similar life and feeding strategies of the early devonian foraminifera

oxygen and carbon isotopes and event stratigraphy near the ordovician silurian boundary anticosti island quebec the growth and destruction of continental ice sheets in north africa and adjacent parts of gondwana during the hirnantian stage had profound influence on the sedimentary style of mixed carbonate siliciclastic sequences on anticosti island quebec canada these strata deposited in a tropical mid shelf setting show direct evidence of local sea level changes of up to 40 m after correction for tectonic and load induced subsidence this indicates maximum global glacio eustatic changes of 32 to 36 m this implies maximum ice volume of about 12 to 14 106 km3 and related changes in the oxygen isotopic composition of global sea water amounting to as little as 0 5 to 0 6 given that the oxygen isotope ratios in syn glacial samples from the anticosti sequence range from 8 9 to 2 8 18o it is not possible to clearly distinguish the effects of ice cap development from temperature and diagenetic controlled variation the strong negative shift in 13c values at the top of the ellis bay formation may indicate a pronounced increase in atmospheric co2 coincident with destruction of the late ordovician ice caps

interplay of cementation mechanical compaction and chemical compaction in nodular limestones of the rosso ammonitico veronese middle upper jurassic northeastern italy abstract the rosso ammonitico veronese middle upper jurassic is a thin 25 30 m lithostratigraphic unit consisting of red mostly nodular pelagic limestones deposited on a current swept structural high in the southern alps sedimentation rates were very low and omission surfaces and mineralized hardgrounds were widespread facies are varied and commonly show evidence of early lithification near the sediment water interface petrographic observations of both mud and grain supported facies rich in thin shelled bivalves enabled reconstruction of the diagenetic evolution some layers or nodules within layers underwent a phase of early lithification acquiring a rigid framework that prevented deformation and rearrangement of grains during later burial in the uncemented beds and in the matrix of nodular beds the effects of subsequent mechanical and chemical compaction are clearly recognizable the response to chemical compaction varied with texture grain supported sediments developed fitted fabrics whereas in mud supported sediments dissolution seams were generated after these diagenetic processes when all the layers had acquired the same degree of coherence laterally extensive stylolites developed cutting across older depositional and or diagenetic fabrics total compaction was evaluated quantitatively by different methods diverse compaction values related to the changing interplay of early cementation and burial diagenetic processes were obtained but an average of about 60 volume reduction for the whole formation is estimated

benthic foraminiferal assemblages in explorers cove antarctica a shallow water site with deep sea characteristics abstract during november and december 1993 we sampled foraminiferal populations living at a 25 28m deep site in explorers cove mcmurdo sound antarctica by means of an airlift suction apparatus and sediment coring mean standing stocks stained specimens per 10cm2 were 8 55 2 60 all specimens 1mm 0 10cm layer 62 1 27 5 all specimens 500 m 0 10cm layer 483 all specimens 63 m 0 1cm layer and 632 all specimens 28 m 0 1cm layer the fauna comprises diverse taxa including both hard shelled and soft shelled forms the coarser fractions 1mm are dominated by large agglutinated foraminifera mainly spheres and domes psammosphaerids saccamminids notodendrodiids but also contain some large calcareous taxa cibicides pyrgo the finer fractions 500 63 28 m yield numerous soft bodied monothalamous foraminifera in addition to the more commonly studied calcareous and multilocular agglutinated forms many species adopt epifaunal or shallow infaunal 0 1cm layer microhabitats but a few smaller ones are more deeply infaunal 1cm a variety of trophic strategies can be inferred from the limited available evidence some abundant large species crithionina spp gromia oviformis may be shallow infaunal or epifaunal deposit feeders but the most striking feature of the fauna is the conspicuous occurrence of large epifaunal species which appear to be suspension feeders e g astrammina astrorhiza notodendrodes cibicides some of these foraminifera can probably switch trophic mode for example from suspension feeding to osmotrophy in response to a fluctuating food supply the explorers cove fauna includes a mix of wide ranging and endemic species the main features of the fauna are consistent with environmental similarities uniformly low temperatures physical tranquillity episodic food inputs between explorers cove and deeper water settings in the northern hemisphaere comparable faunas i e those in which large agglutinated taxa are a conspicuous element are found in deep sublittoral and fjordic areas 100 1000m as well as at some bathyal and abyssal localities down to several thousands of metres which receive a substantial organic matter input from processes such as upwelling foraminifera probably play a major ecological role in these systems particularly in trophic interactions and organic carbon cycling their success may depend on two main attributes first they possess extremely efficient food gathering organelles reticulopodia and second they become quiescent when starved but can rapidly increase their metabolic rate when presented with food our scuba accessible study site in explorers cove provides a unique opportunity to clarify the role that these important protists play in shallow antarctic waters as well as in more remote deep water environments

stratigraphic variation in marine carbonate carbon isotope ratios stratigraphic variation in the carbon isotopic 13c value of marine carbonate and organic matter preserved within it has become a popular tool for supporting paleoclimatic hypotheses and refining stratigraphic correlation virtually every important biostratigraphic and sequence stratigraphic event of the last 800 million years has had a 13c dataset collected to aid in interpreting the causal environmental factors that contributed to the event the stratigraphic resolution obtainable using 13c has yielded critical temporal constraints on the interplay between carbon cycle variation and environmental events such as mass extinction and eustasy although the non uniqueness of the carbon isotopic response to different environmental stimuli has frustrated the identification of a unified mechanism linking marine 13c variation with distinct environmental forcing functions the interpretation of 13c variation can nonetheless provide important insights into processes that influence major global climatic and surficial systems early studies of marine carbonate minerals suggested that the 13c value of ancient oceans was essentially 0 versus the peedee belemnite standard pdb clayton and degens 1959 schidlowski et al 1975 see also keith and weber 1964 it was later recognized however that departures from the pdb standard represented secular variation in the 13c values of the marine environment rather than analytical noise that the record was potentially rich with stratigraphic and paleoenvironmental information scholle and arthur 1980 veizer et al 1980 wadleigh and veizer 1982 arthur et al 1985 holser et al 1986 zachos and arthur 1986 and that variation was intimately linked to the global carbon oxygen and sulfur cycles kump and garrels 1986 holser et al 1988 it is now well established that carbonate 13c values vary within 3 from the pdb standard for

large perturbations of the carbon and sulfur cycle associated with the late ordovician mass extinction in south china high resolution 13 c data of organic carbon from a continuous section of the late ordovician early silurian reveal two positive 13 c excursions that are associated with the mass extinction in south china the fi rst stratigraphic 34 s measurements on pyrite tied to well established biostratigraphy indicate a large perturbation of the sulfur cycle consistent with major sea level changes related to the glaciation the elevated 34 s values of pyrites and a large short lived negative 34 s excursion of 20 associated with the decay of the glaciation suggest deep water anoxia during the hirnantian stage in contrast to the conventional view that the global oceans were oxygenated we suggest that deep water anoxia may have contributed to the late ordovician mass extinction in south china and possibly elsewhere

niobian wolframite from glen gairn in the eastern highlands of scotland a microprobe investigation electron microprobe data are presented from zoned niobian wolframite crystals in a quartz wolframite cassiterite vein and wall rock from a zinnwaldite bearing granite pluton that forms part of the late caledonian glen gairn granitic complex in the eastern highlands of scotland compositions range from nb and ta rich wolframite fe mn w nb ta o 4 forming strongly zoned difficult to polish regions of crystals to almost pure hubnerite mnwo 4 forming relatively unzoned easily polished regions nb and ta substitution is very restricted in mn rich 80 mol hubnerite wolframites but increases regularly in more fe rich compositions through a coupled substitution mechanism between mn 2 w 6 and fe 3 nb ta 5 most of the wolframite crystals contain two forms of zonation a physical zonation observed optically and by electron imaging and a compositional zonation revealed by x ray traverses compositional zoning is progressive involving gradual changes in mineral chemistry from core to rim on which is superimposed a form of oscillatory zoning involving repeated resetting of compositions physical zones are layers of uniform width separated by distinct boundaries they are arranged parallel to crystal faces and reflect intermittent crystal growth these zones vary in width from less than 5 m in the niobium rich wolframite to over 200 m in regions of niobium poor hubneritic wolframite hydrothermal alteration particularly of the intensely zoned niobium rich regions has resulted in assemblages of altered nb and ta rich wolframite tungstite secondary hubneritic wolframite and scheelite nb rich inclusions 5 10 m across are found sporadically in the larger wolframite crystals progressive variation in wolframite chemistry is readily explained in terms of gradually changing physiochemical conditions such as ph f o 2 temperature pressure and fluid composition during crystallization the oscillatory zonation reflects cyclicity of those conditions plausible models which could explain such effects include 1 a intermittent mixing of chemically distinct magmatic and meteoric fluids 2 b repeated hydraulic fracturing and injection of fluids leading to fluctuating pressure and temperature of the hydrothermal fluid volatile species f cl co 2 may have been effective as complexing agents thus affecting the supply of nb from the fluid deposition of nb and ta rich compositions were probably favoured by high f o 2 low ph conditions

cherty carbonate facies of the montoya group southern new mexico and western texas and its regional correlatives a record of late ordovician paleoceanography on southern laurentia abstract the upper ordovician montoya group in southern new mexico and westernmost texas records predominantly subtidal deposition on a gently dipping carbonate ramp that was subsequently nearly entirely dolomitized the medial unit of the montoya group the aleman formation is unique because it contains abundant chert 10 70 by volume the chert occurs as 1 thin continuous beds of sponge spicules within mudstone or calcisiltite 2 discontinuous lenses or nodules within skeletal wackestones and packstones or 3 as a replacement of skeletal grains and burrows coeval skeletal grainstones and muddy peritidal facies contain little chert phosphate up to 5 wt occurs within the underlying upham formation and the aleman formation as replacement of fossils and peloids the abundance of chert and phosphate in these subtidal facies indicates they formed within a region of strong upwelling regional correlation with upper ordovician cherty units along the periphery of southern laurentia and other low latitude continents suggests that upwelling was widespread and long lived during the late ordovician the upwelling is interpreted to record vigorous oceanic circulation produced by the onset of glaciation on gondwana during this period late ordovician relative sea level curves around the periphery of laurentia indicate correlative third order 1 3 my duration fluctuations that may provide a means for high resolution global correlations however the mechanism s that produced these long term fluctuations are unclear

benthic foraminiferal morphogroups of mid to outer shelf environments of the late jurassic prebetic zone southern spain characterization of biofacies and environmental significance abstract benthic foraminiferal assemblages belonging to a mixed carbonate siliciclastic shelf succession of the oxfordian upper jurassic in the prebetic southern spain were analyzed the faunal data obtained on thin sections of strongly lithified sediments allowed the detailed differentiation of a foraminiferal morphogroups system to be applied to the interpretation of paleoenvironmental conditions eleven morphogroups were differentiated according to shell composition general morphology number of chambers and mode of coiling paleoenvironmental analysis combines these features with inferred life style epifaunal shallow infaunal and deep infaunal and feeding strategy suspension feeder deposit feeder herbivores etc of the foraminifera analogies and differences regarding previously established morphogroup systems could be outlined accordingly in the prebetic oxfordian distribution trends of foraminiferal morphogroups allow for a comparison of mid to outer shelf environments occupying the south iberian paleomargin indicating that nutrient supply was the most important factor controlling morphogroup development the mid shelf settings are dominated by epifaunal active herbivores phytodetritivores in shallow to deep substrate position of the redox boundary the outer shelf is dominated by agglutinated and infaunal detritivore bacterial scavenger morphogroups revealing a deep substrate position of the redox boundary particularly favorable trophic conditions in mid shelf environments are related with higher phytodetritus input from more proximal and shallower shelf areas

changes in marine isotopic composition and the late ordovician glaciation well preserved brachiopod shells and marine cements from limestone coquinas which cap carbonate mudmounds in the siljan area of central sweden have the heaviest stable oxygen and carbon isotope values yet reported for lower palaeozoic marine sediments the coquinas formed during the eustatic regression at the onset of the late ordovician glaciation the isotopic compositions reflect simultaneous shifts in both carbon and oxygen more than 5 13 c and up to 2o 18 o away from more normal lower palaeozoic values in similar carbonates from within the mounds oxygen isotope data are consistent with a change in the isotopic composition of the sea water probably accompanied by a decrease in temperature the changes in carbon values suggest enhanced deposition of organic carbon a process which would have decreased p co 2 in the ocean and the atmosphere and thus contributed to rapid global cooling

a new look at modern agglutinated benthic foraminiferal morphogroups their value in palaeoecological interpretation morphogroups offer a way of overcoming taxonomic differences and thereby making comparisons between assemblages of different geological ages relating morphogroups to environments has proved useful in palaeoecological interpretations the model proposed by jones and charnock in 1985 has subsequently been adapted and still serves as the main reference for such palaeoecological interpretations new data from 400 samples from marsh to deep sea off nw europe are used here to refine the model by providing the range of abundance of each morphogroup in each environment it is shown that this range of variation is great so that there is considerable overlap between environments nevertheless the mean values show patterns of distribution tubular forms morphogroup a are characteristic of slope environments especially those under the influence of geostrophic currents morphogroup b is not common in marginal marine environments but is an indicator of shallow fjord to deep sea the elongate forms of morphogroup c are widely distributed but c1 is especially common in marginal marine and shelf to upper slope settings the quinqueloculine coiled c2 subgroup is characteristic of marsh and marginal marine environments in the temperate zone but around antarctica this form is common down to 2000 m the plano convex low trochospiral trochamminids of morphogroup d are typical of marshes therefore these trends have application to palaeoecology of similar well oxygenated temperate environments

the sulphur isotopic composition of trace sulphates in carboniferous brachiopods implications for coeval seawater correlation with other geochemical cycles and isotope stratigraphy the carboniferous 34s record based on the analysis of structurally substituted sulphate sss in brachiopod shells is characterized by a significant decline from values around 21 1 in the tournaisian to 12 1 in the gzelian superimposed on this broad evolution is a higher order structure with a relative minimum in the late visean followed by a maximum in the bashkirian on the 107 year time scale 34s is positively correlated with 13ccarb in contrast to the long term negative linkage between sulphur and carbon observed for the entire phanerozoic this indicates that mechanisms other than the redox balance control the carbon and sulphur cycles on this time scale the 87sr 86sr and 34s records display parallel trends during the tournaisian to moscovian this positive correlation suggests that tectonics may be of importance for the evolution of 34s on time scales of 107 years a possible scenario to explain the co evolution of the isotope systems and their linkage to tectonism and palaeoclimate invokes an increased nutrient supply to the oceans during periods of enhanced uplift and continental weathering this nutrient flux may have resulted in increased burial of organic matter and enhanced bacterial sulphate reduction

climatic and oceanographic isotopic signals from the carbonate rock record and their preservation stable isotopic data from marine limestones and their constituent fossils and marine cements can provide quantitative evidence for changes in global climate and ocean circulation oxygen isotopic data can indicate changes in temperature and ocean composition whereas stratigraphic variation in carbon isotope ratios may reflect changes in the carbon cycle that can be linked to changes in oceanic productivity and atmospheric greenhouse gases terrestrial carbonates meteoric cements calcretes and speleothems similarly offer significant potential for understanding the evolution of terrestrial climates by providing evidence for the composition of rainwater and the nature of vegetative cover primary environmental isotopic signals may be obscured by the effects of post depositional diagenetic alteration cementation and replacement reactions can take place in a wide range of diagenetic environments the diagenetic history of an individual limestone is determined by a combination of its mineralogical diagenetic potential and depositional setting together with subsequent changes in relative sea level and burial history carbon isotopic values are less prone to alteration during diagenesis than oxygen values but shifts can be significant where organogenic carbon is incorporated linear covariation of carbon and oxygen values is not a reliable indicator of diagenetic alteration water rock interaction and fluid mixing may produce non linear distributions attempts to determine long term changes in climatic and oceanographie conditions through isotope stratigraphy of shallow water limestones must include an assessment of the diagenetic history of the materials analysed petrographic examination using conventional microscopy backed up where appropriate by cathodoluminescence and scanning electron microscopy together with elemental and strontium isotopic analysis can help to identify the effects of diagenetic alteration where material with a range of different degrees of alteration is preserved in the same sediment it may be possible to compare patterns of isotopic and elemental variation and to attempt to unravel the effects of diagenesis in order to determine primary environmental isotopic signals recent research has shown that these techniques can be successfully employed in both phanerozoic and precambrian sediments

latest cenomanian earliest turonian low oxygen tolerant benthonic foraminifera a case study from the sergipe basin n e brazil and the western anglo paris basin southern england abstract distinctive sedimentological geochemical isotopic and micropalaeontological response characterise the nature of sediments deposited under hypoxic anoxic bottom conditions during the latest cenomanian to earliest turonian of most of the world s basins the composition of the biota is a direct response to overall environmental conditions the recognition of distribution patterns of low oxygen tolerant microfauna is therefore of primary importance in evaluating and reconstructing the regional palaeoceanographic settings where such events took place a case study is presented from two coeval stratigraphic sequences the sergipe basin northeastern brazil and the western anglo paris basin southern england the associated benthonic foraminiferal assemblages from oxygen depleted environments consist mostly of opportunistic r selected species basic patterns in community trophic structures appear to have primarily dictated the composition of the biota the assemblages from outer shelf to upper slope oxygen depleted environments are commonly characterised by 1 low diversity 2 limited intraspecific variation 3 predominance c 40 60 of the total foraminiferal assemblage of epifaunal deposit feeding plano concavo convex trochospiral calcareous hyaline morphotypes gavelinellids conorboidids rosalinids and bagginids 4 variable numbers c 10 30 of infaunal bacterial detrital scavengers tapered and elongate morphotypes turrilinids bolivinids buliminellids fursenkoinids polymorphinids and caucasinids 5 epifaunal shallow infaunal deposit feeding lenticular morphotypes coiled vaginulinids c 5 19 6 variable numbers c 10 30 of agglutinated specimens lituolids discamminids eggerellids textulariids trochamminids ammodiscids tritaxiids and valvulinids and 7 dominance about 60 80 of minute c 100 200 m in maximum diameter width or length calcareous hyaline taxa during widespread dysaerobic quasi anaerobic episodes highly oxygen depleted bottom conditions are marked by the absence of benthonic microfauna minor taxonomic differences between the two studied areas are mostly due to palaeobiogeographic provincialism

early cambrian foraminifera from west africa agglutinated foraminifera have been recovered from siltstones in the walidiala valley taoudeni basin west africa associated faunas suggest an early cambrian age for these strata these now earliest known unequivocal foraminifera help constrain hypotheses concerning the origin of skeletalization at the beginning of the phanerozoic

cephalopod limestone deposition on a shallow pelagic ridge the tafilalt platform upper devonian eastern anti atlas morocco as a result of early variscan tectonic movements and of differential subsidence a platform and basin topography was created along the northern margin of the sahara craton during the late devonian in the moroccan anti atlas mountains the tafilalt platform is an approximately n s running ridge which developed since the late middle devonian it separated a slowly subsiding shallow basin in the east tafilalt basin from a rapidly subsiding furrow in the west mader basin platform deposits are characterized by highly reduced thicknesses shallow subtidal to supratidal deposits in the late frasnian and by unconformities at the lower upper frasnian and the frasnian famennian boundaries after a local transgression over emergent areas in the north water depth probably never reached more than several tens to about 100 m in the lower famennian cephalopod limestones of this age deposited on the platform represent a very diverse facies pattern comprising quartz rich brachiopod coquinas crinoidal limestones thick bedded cephalopod limestones and nodular limestones sedimentation rates ranged from 1 to 5 mm 1000 yr in the late famennian more uniform marl and nodular limestone facies suggest slightly deeper environments platform margins are characterized by higher rates of subsidence debris flow deposits and slump structures in the relatively shallow tafilalt basin marls with intercalated nodular limestones were deposited in the mader basin sandy and calcareous turbidites suggest deeper water conditions in the late devonian during the strunian tournaisian the whole area was overwhelmed by a thick deltaic sequence the general facies distribution is in agreement with depositional models of other upper devonian and lower carboniferous cephalopod limestones in the european variscan orogenic belts in all these cases condensed cephalopod limestones occupy a distinct palaeogeographic position in predictable facies sequences that reflect pre orogenic phases in the variscan geodynamic cycle moreover close parallels exist with condensed sequences in the triassic and jurassic that occur in a very similar position within the alpine orogenic cycle

late ordovician carbon isotope trend in estonia its significance in stratigraphy and environmental analysis abstract carbon isotope changes during most of late ordovician time from the mid caradoc kinnekulle k bentonite until the beginning of the silurian were investigated as the corresponding sequence of rocks is stratigraphically nearly complete in estonia an attempt was made to use it to elaborate the general pattern of carbon isotope changes in the late ordovician complications were caused by several local or regional hiatuses in the middle and late caradoc and hirnantian a total of 385 whole rock samples were studied from eight drill cores in northern and central estonia the following positive carbon isotope events were observed 1 the mid caradoc excursion peak 13c value 2 2 in the uppermost part of the keila stage also known in sweden 2 the first late caradoc excursion 1 9 in the lower part of the rakvere stage 3 the second late caradoc excursion 2 4 in the upper part of the nabala stage 4 the early ashgill excursion 2 5 in the lowermost part of the pirgu stage 5 the widely known large hirnantian excursion in estonia the peak value reaches 6 7 in the porkuni stage the study interval comprises a long 10 ma period characterized by low magnitude carbon isotope changes and a following brief 2 ma interval with large changes no obvious lithological preference for hosting the positive shifts was recorded in principle the 13c values exceeding the background values may occur in all types of rocks present in a sedimentary basin several 13c positive excursions values 1 5 to 3 in the mohawkian of north america are evidence that the minor caradoc and early ashgill 13c positive shifts in baltoscandia may have counterparts in laurentia if correctly correlated these shifts may have global significance the hirnantian excursion is usually linked to a major glacial event even if some carbon cycling mechanisms are not completely understood the environmental causes suggested for the earlier minor shifts range from global climatic and glacial events to very local changes in basin regime and sea level our study supports the primary role of climatic or climatically triggered oceanic processes

oxygen isotope and mg ca composition of late visean mississippian brachiopod shells from sw iberia palaeoclimatic and palaeogeographic implications in northern gondwana abstract latest visean brachiopod shells gigantoproductus sp from the pedroches basin of sw spain were sampled in order to obtain chemical and isotopic evidence that may help first to assess if primary geochemical and isotopical signals are preserved in these shells and second to reconstruct temporal variations in palaeoceanographic and palaeoclimatic conditions in northern gondwana during this time span microtexture cathodoluminescence cl and ultrastructure under sem of the brachiopods were examined to avoid sampling of shell portions altered after deposition shell portions classified as non luminescent nl and non luminescent to slightly luminescent nl sl present geochemical signatures within the ranges considered normal for recent brachiopods that have not undergone significant diagenetic modification these include low to undetectable fe and mn contents high sr values and 18o values similar to those of carbonates in equilibrium with seawater on the other hand valve areas that are luminescent l or moderately luminescent with luminescent portions ml l present higher fe and mn contents lower sr concentrations and lower 18o values than those corresponding to nl and nl sl shells this suggests a greater diagenetic alteration of these portions and that they acted as microzones of reaction with the diagenetic fluids temporal trends through the studied interval show a spread in 13c values much lower than that observed for contemporaneous samples up to 1 6 thus obscuring the 13c global signal at the time scale resolution of this study in contrast the 18o record of brachiopod calcite 18oc shows an overall increase of 1 relative to v pdb from the oldest to the youngest samples this is accompanied by a 30 decrease in mg ca ratios of the brachiopod calcites confirming that at least part of this shift in 18oc was related to cooling combination of mg ca and 18oc proxies established in this paper although not full proof for brachiopods yet allowed for the calculation of a temperature drop of 3 3 c and a change in seawater 18ow that becomes 0 4 more positive during this interval the data are consistent with regional seawater cooling that accompanied an increase in continental ice volume over a relatively short time period of

within shell variations in carbon and oxygen isotope compositions of two modern brachiopods from a subtropical shelf environment off amami o shima southwestern japan 1 this study examines the fidelity of carbon 13c and oxygen 18o isotope compositions of two modern brachiopod species kikaithyris hanzawai and basiliola lucida to use as proxies of 13c values of total dissolved inorganic carbon and temperature and or 18o values of seawater respectively well preserved shells of k hanzawai and living individuals of b lucida were collected from a subtropical shelf environment off amami o shima southwestern japan some portions of the shells are in isotopic equilibrium with the ambient seawater while other portions are not the degree of disequilibrium differs between the two species and between different portions of each shell statistically significant positive correlations are recognized between the 13c and 18o values of these samples which can be ascribed to a kinetic fractionation effect far from the posterior shell edge and along the axis of shell growth the 18o values of the secondary shell layer of k hanzawai mostly fall within the expected range of equilibrium calcite the 13c values from the inner surface of the secondary shell layer in both species are relatively constant and are equivalent to or very close to equilibrium calcite therefore these portions of the shells are most suitable for collecting reliable environmental proxy data although the 13c and 18o values of modern brachiopod shells are predominantly controlled by a kinetic fractionation effect the appropriate selection of species and shell portions that reflect the isotopic composition of ambient seawater can facilitate the reconstruction of secular variations in oceanic 13c or 18o values

carbon isotope stratigraphy of lochkovian to eifelian limestones from the devonian of central and southern europe lower to middle devonian carbonates of the prague syncline the carnic alps the montagne noire and the cantabrian mountains were investigated for 13ccarb and 13corg these values were measured on bulk rocks selected components and cements many carbonates exhibit primary marine values but some are altered by diagenesis a 13c curve can be presented for the latest pridolian to emsian time interval several sharp or broad positive excursions are obvious in the woschmidti postwoschmidti sulcatus kitabicus late serotinus and kockelianus conodont zones the excursion at the silurian devonian boundary is known worldwide and therefore considered global in nature some of the others are described for the first time from central and southern europe and their global nature has to be verified by further investigations in other regions most excursions relate to and or started during major regressions whereas sea level highstands correspond to minimal 13c values similar relationships between sea level changes and 13c have been observed from other early palaeozoic intervals the transgressive chotec and kacak events are marked by positive isotope excursions this type of combination is usually observed in late palaeozoic to cenozoic black shale events

palaeozoic uplands and unconformity in the north china block constraints from zircon la icp ms dating and geochemical analysis of bauxite the problem of location of the north china block ncb during the palaeozoic and its history of uplift and erosion have not been established satisfactorily a regional unconformity was developed in the ncb between the upper ordovician and the middle upper carboniferous zircon grains in the samples collected for isotopic age dating from the unconformable surface in central north china show two main clusters of ages around c 444 and c 313 ma and a scatter of ages between c 2500 and c 550 ma silurian and devonian ages were not observed similarities between the zircon rare earth element and trace elements show that the c 444 and c 313 ma zircon grains were derived from rocks in the active margins of the ncb geological and isotopic evidence suggests that between c 444 and 312 ma north china was uplifted and that there was a long gap in sedimentation this major change in the environment of north china from marine to continental upland occurred at the same time as the separation of north china from northern gondwana the closure of the northern palaeotethys along the altai inner mongolia zone and the collision between gondwana and laurasia

the late cretaceous early paleocene palaeobathymetric trends in the southwestern barents sea palaeoenvironmental implications of benthic foraminiferal assemblage analysis the late cretaceous foraminiferal assemblages from five wells drilled in the southwestern barents sea were analysed using morphogroup analysis in order to understand the palaeoenvironment and palaeobathymetry of the study area morphogroup analysis of assemblages in the upper cretaceous kveite formation suggests stable possibly middle to lower bathyal mesotrophic and relatively well oxygenated environments in the tromso basin during the late cretaceous the depositional setting of upper cretaceous kviting formation in the tectonically more stable hammerfest basin was probably shallower but still represents a deep water environment similar to that of the kveite formation a shallowing regional bathymetry in the southwestern barents sea is indicated by the general decreasing trend in the relative abundance of tubular forms and the species diversity of assemblages which reflects the regional late cretaceous paleocene uplift prior to the break up of the greenland norwegian sea changes in the relative abundance of morphogroups and in the main constituent in the cumulative length of tubular taxa from rhizammina to rhabdammina near the top of kveite formation agree with the possible existence of bottom water currents c 2011 elsevier b v all rights reserved

tectonostratigraphic evolution of the upper cretaceous cenozoic central anatolian basins an integrated study of diachronous ocean basin closure and continental collision

the ireviken event in the lower silurian of gotland sweden relation to similar palaeozoic and proterozoic events abstract for a long time the silurian was thought to represent a time of stable environmental conditions in the greenhouse period that followed the late ordovician glaciation during the past decade knowledge about the silurian has increased markedly and today it is known that the conditions in the silurian were much more variable than previously assumed detailed isotopic investigations have revealed several distinct positive excursions in both carbon and oxygen isotope values in low latitudes these periods of high c and o isotope values are in many cases characterised by the growth of reefs and the formation of extended carbonate platforms the sediments deposited during these excursions contain impoverished fossil assemblages especially with respect to conodonts graptolites and trilobites a conspicuous isotope excursion coincident with facies changes and a marked mass extinction is observed near the llandovery wenlock boundary this event is called the ireviken event after its type locality on the island of gotland sweden jeppsson l 1987 in palaeobiology of conodonts ellis horwood ltd chichester pp 129 145 here isotope data from nine sections at the nw coast of gotland are presented that cover the time interval of the ireviken event the 13c mean values rise from 1 4 to 4 5 and the 18o values increase from 5 6 to 5 0 the relative timing of stable isotope development extinctions and facies development is discussed it is shown that first extinctions precede the isotope excursion this indicates that extinction events and stable isotope development are only indirectly connected but might reflect the same causes other events characterised by similar relationships between positive isotope excursions mass extinctions and facies development are found in younger parts of the silurian late wenlock and ludlow in the late ordovician the late cambrian and with some reservations in the proterozoic the similarities between these events indicate analogous controlling mechanisms for the silurian climatic changes between humid and arid conditions in low latitudes were postulated in an earlier study of the authors a palaeoceanographic climatic model was postulated which is consistent with most of the sedimentological palaeontological and geochemical data here we demonstrate that this model may be applicable also for the older events

global carbon isotopic events associated with mass extinction and glaciation in the late ordovician mass extinctions and glacioeustatic sea level changes in the lower part of the hirnantian final stage of the ashgill are accompanied by shifts in marine stable isotope compositions previously published stable isotope changes have been used to identify the onset and demise of the gondwana glaciation and to suggest relationships between biotic changes and carbon cycling within the oceans however the existing isotopic data set had limitations because it was derived from ordovician low latitude settings and from carbonates or organic carbon in separate areas we report new data from ordovician high latitude carbonates and demonstrate parallel shifts in organic and carbonate 13c from baltica brachiopod shells from a high palaeolatitude periglacial setting in argentina have elevated 13c values similar to those described previously from low latitude sites the new data demonstrate that the positive hirnantian 13c excursion previously only recognised from low palaeolatitude areas was widespread and probably global in extent the poor preservation state of the brachiopods unfortunately prevented the determination of a reliable oxygen isotopic value from the same material preliminary carbon isotopic data from thermally immature organic matter from estonia provide the first indication of a synchronous shift in organic and inorganic 13c in sediments from the same basin this work provides new data of critical importance for constraining models of end ordovician palaeoceanography and climate change

stratigraphic significance and resolution of spectral reflectance logs in lower devonian carbonates of the barrandian area czech republic a correlation with magnetic susceptibility and gamma ray logs abstract spectral reflectance sr is a relatively novel technique which is used as a proxy for organic carbon and siliciclastic input in carbonate sediments in particular in core research this study summarizes results from high resolution outcrop sr logging of a lower devonian distal ramp carbonate section of the barrandian area czech republic the sr data were correlated with parallel petrophysical and geochemical data with an aim to improving their cyclostratigraphic and event stratigraphic interpretation potential and the gaps sr data can fill transgressive regressive trends indicated by facies stacking patterns caco 3 data and spectral gamma ray grs logs are well correlated in the regional context and point to third order eustatic sea level fluctuations peak regressions of the tr cycles are sensitively marked by cie l a b parameters and percent reflectance in colour bands the sr and magnetic susceptibility ms data are markedly cyclic on a more detailed scale their inferred periods vary between 49 2 and 205 kyr indicating that they may have been forced by orbital cycles in the milankovitch band the sr and ms cycles are either in phase or out of phase the latter cycles point to a strong diagenetic forcing of the colour cyclicity hematite concentration cycles inferred from sr signal in the pragian red hemipelagic carbonates are interpreted as reflecting changing bottom oxygenation and subsurface redox gradients during early diagenesis the cie l parameter was found to be related to the presence of diagenetic hematite which indicates that cyclostratigraphic analysis of simple greyscale data can be affected by considerable error due to chromacity although the cie l parameter is partly correlated with caco 3 concentrations the ms data are not which suggests that the ms signal can be significantly influenced by diagenetic minerals and its cyclostratigraphic interpretation can be potentially misleading the sr data backed up by grs ms and caco 3 data indicate that the red colour in the pragian hemipelagic limestones originated from early diagenetic hematite precipitation under the conditions of an oxygenated ocean floor this suggests that deep sea bottom oxygentation may have been in operation during the early devonian which is traditionally perceived as a typical greenhouse period the sr data can be obscured in several m thick zones of elevated cie l and other colour changes leaching zones related to postdepositional alteration along subvertical faults however this fault related telogenic alteration has little influence on the ms signal the combined use of sr and ms has a synergic effect and can significantly improve the interpretation of their respective cyclic signals particularly in relation to the diagenetic overprint and possible carriers of the ms

shell of the great scallop pecten maximus as a high frequency archive of paleoenvironmental changes 1 we investigate the environmental and biological controls on oxygen isotope ratios in the shells of modern pecten maximus bivalves collected alive in the bay of brest france seasonal 18o profiles obtained by drilling the daily calcite ridges deposited at the surface of the left valve were compared with in situ measurements of temperature and salinity we show that p maximus 18o values accurately track seasonal variations in bottom water temperature shell growth rate has no significant effect on shell 18o values our study demonstrates that daily variations in water temperature can be reconstructed within about 0 5 c temperatures estimated with the paleotemperature equation established in this study were compared with temperatures derived from previously published equations the comparison indicates that the most commonly used paleotemperature equation for biogenic calcite epstein et al 1953 provides inaccurate temperature estimates but the kim and o neil 1997 equation established from abiogenic calcite precipitation provides results very similar to ours and should therefore be used for scallop individuals coming from populations where proper empirical calibration cannot be done pecten maximus bivalves precipitate calcite in isotopic equilibrium with seawater produce large daily growth striae are stenohaline and are well preserved in archeological and geological deposits making them an excellent high frequency archive of paleoenvironmental change