structure and composition of organic reefs and carbonate mud mounds concepts and categories defined here as essentially in place calcareous deposits created by sessile organisms organic reefs are diverse and complex structures with a long geological history their classification has been the subject of fierce debate often characterized by reliance on subjective features such as wave resistance and qualitative attempts to discriminate between first and second class reefs in contrast emphasis is here placed on the objective characteristic of the type of sedimentary support which largely determines the sedimentary composition of the deposit constructional and depositional processes result in three principal sedimentary components matrix m essentially in place skeletons s and cavity cement c whose proportions can be represented on msc triangular plots separately or together these components also provide the structural support for the reef on these compositional and structural bases three main categories of organic reef are recognized 1 matrix supported reefs agglutinated microbial reefs cluster reefs segment reefs 2 skeleton supported reefs frame reefs 3 cement supported reefs cement reefs agglutinated microbial reefs possess laminated clotted or aphanitic fabrics created by microbial trapping of particulate sediment in place skeletons and large primary cavities are rare early cementation may provide added support topographic relief is limited by the need for currents to provide sediment to accreting surfaces cluster reefs skeletal reefs in which essentially in place skeletons are adjacent but not in contact resulting in matrix support characterized by relatively high matrix skeleton ratios and low volumes of extra skeletal early cement sediment trapping is an important corollary of skeletal growth and cluster reef organisms are tolerant of loose sediment absence of framework limits the topographic relief that cluster reefs can attain relative to spatial extent and may permit bedding to develop within the reef close cluster reefs have skeletons up to 1 unit distance apart spaced cluster reefs have skeletons more than 1 and up to 2 unit distances apart with increasing separation of skeletons they grade to level bottom communities segment reefs matrix supported reefs in which skeletons are adjacent and may be in contact but are mostly disarticulated and mainly parauthochtonous matrix abundance is high and early cement relatively low moderate relief can develop in response to intense on reef sediment production frame reefs skeletal reefs in which essentially in place skeletons including calcified microbes are in contact characterized by relatively high skeleton matrix ratio skeletal support enables them to raise themselves above the substrate independently of cementation and particulate sedimentation simultaneously by creating partly open shelter cavities skeletal support may facilitate early cementation both relief and early lithification promote marginal talus formation skeletal shape and orientation distinguish conical stick like dendritic domical and laminar frames each of these may be open or filled open frame reefs

early diagenesis in differing depositional environments the response of transition metals in pore water the cycling of fe mn ni co cu cr v and mo during early diagenesis was investigated in sediments from five different depositional environments in the california borderland dissolved o2 no3 no2 and so4 were also measured at each site to establish the position of redox boundaries pertinent to this study sites were chosen to allow the comparison of several parameters of potential importance to the cycling of these metals bottom water o2 concentration sediment redox conditions cycling of metal oxide carrier phases and the relative contribution of biogenic and terrigenous material to the detrital metal flux at 10 m oxygen and above the sequence of terminal electron acceptor utilization was typical of pelagic sediments differing only in scale under these conditions the recycling of mn oxides resulted in an enriched layer near the interface at bottom water 02 concentrations 5 m mn oxides are not recycled under these conditions fe oxides and so42 are important oxidants the depth of the zone of manganese oxidation with respect to the interface affects the efficiency of metal scavenging by manganese oxides trapping and recycling of ni and co with mn oxides results in remobilization from reducing sediments and enrichment in oxic sediments scavenging of these metals is favored by a deep oxic zone in the sediments in contrast cr v and mo appear to be transported to the sediments as reduced species and are released from the sediments by oxidation the source of the reduced species is assumed to be biogenic material the accumulation of these metals is favored by reducing conditions in the sediments cu is enriched in the sediments by transport with detrital biogenic material followed by adsorption onto sediment solids cu is released at the interface and rapidly removed onto the solids at all sites except the one pelagic site at the base of the slope the magnitude of cu released in the slowly accumulating pelagic sediment exceeds the cu binding capacity of the solids resulting in pore water cu concentrations in excess of 100 nm in general metal cycling associated with the early diagenesis of sediments was observed to decouple transport processes from burial processes for the transition metals measured in this study

lack of evidence for enhanced preservation of sedimentary organic matter in the oxygen minimum of the gulf of california a test of the hypothesis that hydrogen rich organic matter accumulates preferentially in sediments under oxygen minima has been carried out by examining the composition of laminated and homogeneous diatomaceous sediments of the guaymas basin in the gulf of california the laminated sediments occur where an intense oxygen minimum intersects the slope around the margins of the basin above and below the depth of the oxygen minimum the sediments are homogenized by a burrowing infauna the two sediment types have very similar bulk chemical and mineral compositions and the organic matter is overwhelmingly marine the total organic carbon contents and rock eval parameters hydrogen and oxygen indices of the two sediment types are not significantly different whereas a road organic carbon maximum in the homogeneous sediments is centered at roughly 1200 m depth on the slope of the basin this maximum lies deeper than the core of the oxygen minimum thus both the concentration and the nature of the organic matter in the sediments of this highly productive marginal marine basin are not related to the concentration of dissolved oxygen in the bottom waters

combination of discontinuity characteristics and gis for regional assessment of natural rock slopes in a mountainous area ne turkey abstract geographical information systems gis have a very large spectrum of users as in many engineering applications gis are frequently used in geotechnical projects especially in producing various thematic and zoning maps such as various susceptibility and hazard maps instability maps for large areas with similar characteristic can be produced in a practical way by evaluating the results obtained by the data collected from field and laboratory studies in order to introduce a methodology for producing rock slope instability maps for a large area discontinuity controlled slope failures in the kose granitoid complex ne turkey were selected to determine the types of failure such as planar wedge and toppling and possible instable slope orientations kinematic analyses were carried out in the limited areas the relationships between orientations of natural slopes and discontinuities obtained from kinematic analyses were evaluated with gis software finally discontinuity controlled instability maps were produced for the study area resulting maps show that the most common type of failure is wedge type additionally the distributions of unstable areas along road networks were determined various land use types such as agriculture grassland settlement and forest were also classified in order to predict the possible effects of slope instabilities the methodology introduced in this study indicates highly promising results for the assessment of rock slope instability in large areas

a far field record of the end ordovician glaciation the ellis bay formation anticosti island eastern canada abstract the end ordovician was a critical period in earth history it was a time of global climatic change with large scale continental glaciations a wealth of recent work has documented the stratigraphical records from the near field areas i e from various gondwanan continental relics where glaciation was more severely felt there is an urgent need to re examine the stratigraphic record from the far field areas at greater levels of resolution than it has been hitherto possible in order to understand the timing duration and character at the glaciation centred around the ordovician silurian o s boundary one of the best exposed and most complete stratigraphic records from paleotropical areas near the boundary is on anticosti island in eastern canada the east west trending 200 km long ellis bay hirnantian outcrop belt with superb coastal exposures at both ends of anticosti island is slightly oblique to the paleoshoreline with near shore siliciclastic dominated facies restricted to the eastern part of the island and more offshore carbonate dominated facies present along the central and western parts these mixed carbonate siliciclastic facies accumulated along a storm dominated beach to offshore profile they are organized into a stacked set of shallowing upward offshore to shoreline facies successions typically coarsening upward separated by deepening upward facies successions typically fining upward formed during intervening transgressions high frequency glacio eustatic fluctuations were the dominant control on the development of tr sequences observed in the ellis bay succession of anticosti island although tectonic subsidence had a substantial secondary effect on thickness five tr sequences are recognized allowing for precise correlation along the ellis bay outcrop belt in the eastern sections relatively thin tr sequences are locally bounded by unconformities a typical sequence begins with thin transgressive limestone overlain by a maximum flooding calcareous shale grading up into regressive storm influenced proximal to transitional zone fine sandstone grainstone and shale which are sharply overlain by shoreface to foreshore sandstone grainstone in the central and western sections the thicker tr sequences have more symmetrical transgressive regressive components reflecting greater subsidence compensated by a higher carbonate sediment supply two discrete glacial periods are recognized during the deposition of the hirnantian ellis bay succession with the younger one recording large sea level changes 50 m in magnitude caused by the development of very large ice sheets over western gondwana abundant ice conditions on the globe during the end ordovician and the resulting high amplitude eustasy appear to have left distinctive stratigraphical imprints on mixed paleotropical siliciclastic carbonate ramps

searching for travertines calcretes and speleothems in deep time processes appearances predictions and the impact of plants common models for modern calcite precipitation in and around caves soils springs and streams involve co 2 supplied by thick high p co 2 biogenic soils which were probably thin or non existent before vascular plants indeed plant influenced chemical weathering might have caused accelerated terrestrial carbonate production from the devonian onwards however terrestrial carbonates have also been documented from the archaean proterozoic cambrian ordovician and silurian mechanisms which could have caused non marine carbonates to precipitate without organic rich soils are described and some geological events likely to have influenced non marine carbonate precipitation up to the origin of vascular plants are highlighted as organisms have evolved so have the petrographic characteristics of non marine carbonates some examples of this are also given here

integrated graptolite conodont biostratigraphy and organic carbon chemostratigraphy of the llandovery of kallholn quarry dalarna sweden abstract a revised graptolite and conodont biostratigraphy together with new organic carbon isotope data for the middle aeronian to lower telychian llandovery lower silurian of kallholn quarry central sweden are presented the base of the section is marked by an unconformity between the ordovician boda limestone and aeronian shales with limestone nodules belonging to the pribylograptus leptotheca biozone these are overlain by strata assigned to the lower lituigraptus convolutus biozone the stimulograptus sedgwickii biozone previously recorded from the section is absent and marked by an unconformity which is overlain by radiolarian rich graptolitic shales belonging to the stimulograptus halli biozone the overlying telychian strata are assigned to the spirograptus guerichi spirograptus turriculatus and streptograptus crispus biozones conodonts indicate that the boundary between the distomodus staurognathoides biozone and pterospathodus eopennatus superzone lies within the sp turriculatus biozone as it does also in the ohesaare core estonia the 13corg record shows mostly minor fluctuations but with a distinct twin peaked positive excursion in the upper sp turriculatus biozone close to the boundary with the overlying streptograptus crispus biozone the excursion in the kallholn section may correlate with the earliest positive shift in 13c values at the onset of the excursion associated with the valgu event or it may represent a new excursion provisionally named the kallholn excursion preceding this many more bentonites 36 occur in the section than previously recorded geochemical studies are needed to confirm whether the osmundsberg bentonite which may or may not be equivalent to the o bed in estonia and latvia is present

subaerial speleothems and deep karst in central sweden linked to hirnantian glaciations the limestones of the upper katian boda mud mounds ordovician of the siljan district in central sweden are deeply fractured the fissures were partly synsedimentary and are often lined with stromatolite like crusts these crusts thus far are the only known subaerial ordovician speleothems they reach depths of up to 30 m below the former mound top macroscopically the crusts form decimetre sized cone shaped domal aggregates stalactites and stalagmites microfabric and morphology identify them as microbially mediated speleothems in a dark environment combined sr and c isotope values indicate a formation of the speleothems from meteoric waters without influence of a significant soil horizon for the first time the age of the speleothems can be precisely constrained by 13 c whole rock and brachiopod shell isotope data to the mid hirnantian repeated and or prolonged subaerial exposure of the boda mud mounds during the hirnantian is evident from karst surfaces and early cements in the mound capping carbonates the speleothems and the karst surfaces record an estimated sea level fall in the range of 80 130 m within the time window of the hirnantian isotopic carbon excursion this massive regression coincides with maximum ice sheet extent inferred from sections in west gondwana supplementary material 87 sr 86 sr isotope ratio of selected brachiopod shells and results of energy dispersive x ray spectroscopy are available from http www geolsoc org uk sup18809

ordovician meteoric carbon and oxygen isotopic values implications for the latitudinal variations of ancient stable isotopic values abstract columnar and clear blocky calcite cement from a middle ordovician carbonate succession in east tennessee is interpreted as meteoric in origin columnar and clear blocky calcite from this succession does not show extremely large 13c depletions reported from meteoric phases of younger rocks meteoric fluid 18o values calculated from clear blocky calcite are 2 to 3 more negative than approximately coeval sea water a relationship typical of modern low latitude coastal meteoric water comparison with meteoric 18o values from ordovician units elsewhere suggests that the geographic distribution of these values may be broadly similar to that observed today therefore we tentatively suggest that geographic distribution of meteoric 18o values during both icehouse and greenhouse eras are similar

the marine phosphorus cycle phosphorus introduced to the ocean must ultimately be removed if a steady state is to be maintained over geologic time aeolian input is insignificant and there is evidently no hydrothermal contribution rivers dominate p input to the ocean the fluvial p flux is poorly quantified due to the interactions of two factors 1 man s influence on river nutrient fluxes and 2 inherent complexities in understanding the biological and inorganic associations of p in estuarine and coastal waters our best estimate of the natural or pre man p input flux is about 10 x 10 sup 9 moles p cm sup 2 ocean surface year of the identified flux of phosphorus to the sediments about 90 percent is in the form of biogenic debris or its regeneration products the burial of phosphatic fish debris is negligible p removal by direct reaction of phosphate in seawater with sea floor basalts during mid ocean ridge hydrothermal circulation is insignificant p removal by processes such as sorption on clay surfaces or formation of authigenic fe and al phosphate phases is presently unquantified and remains a serious uncertainty in the phosphorus cycle the identified sources and sinks approximately balance yielding a residence time for p in the oceans of about 10 sup 5 yrs

fluid inclusion and stable isotope constraints c o h on the dagbasi fe cu zn skarn mineralization trabzon ne turkey abstract the dagbasi fe cu zn skarn mineralization developed along the contact between the block and lens shaped limestones of the lower cretaceous berdiga formation and the upper cretaceous dagbasi granitoid the exoskarn type mineralization is characterized by prograde stage garnet and pyroxene while the retrograde stage is characterized by epidote tremolite actinolite and chlorite quartz and calcites were observed in both stages of the skarn development the ore minerals mainly consist of magnetite and hematite with a lesser amount of pyrrhotite pyrite chalcopyrite sphalerite and minor galena the homogenization temperatures th and salinity values of the prograde stage halite bearing fluid inclusions are in the range of 412 514 c and 48 8 61 8 wt nacl equ respectively the second stage liquid and vapor rich fluid inclusion assemblage reveals that boiling at temperatures of 353 458 c took place after the formation of halite bearing fluid inclusions final stage liquid rich fluid inclusions were characterized by low th 160 and 327 c and salinity values 0 5 and 6 2 wt nacl equ the decreasing salinity trend of the fluid inclusions versus th indicated that meteoric water was involved in the hydrothermal solutions eutectic temperatures te of the prograde stage fluid inclusions were found to be cacl2 dominated while retrograde stage inclusions contained different salt combinations rather than a specific salt type the minimum trapping pressures of the early stage brine fluid inclusions were calculated to be between 710 and 884 bar while later stage inclusions had much lower trapping pressures between 195 and 445 bar the 18o isotopes of prograde stage quartz garnet and pyroxenes are close to the composition of the hydrothermal solutions of magmatic sources moreover retrograde stage quartz epidote tremolite actinolite and calcite minerals and their equilibrated solutions were found to be highly depleted by 18o isotopes therefore the fluid inclusion and stable isotope constraints suggest that the hydrothermal solutions of magmatic origin were responsible for the prograde skarn stage while a mixture of magmatic and meteoric solutions were responsible for the ore formation in a shallow skarn environment

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

reconstructing plate boundaries in the jurassic neo tethys from the east and west vardar ophiolites greece and serbia jurassic subduction initiation in the neo tethys ocean eventually led to the collision of the adria africa and eurasia continents and the formation of an 6 000 km long alpine orogen spanning from iberia to iran reconstructing the location and geometry of the plate boundaries of the now disappeared neo tethys during the initial moments of its closure is instrumental to perform more realistic plate reconstructions of this region of ancient ocean basins in general and on the process of subduction initiation neo tethyan relics are preserved in an ophiolite belt distributed above the dinaric hellenic fold thrust belt here we provide the first quantitative constraints on the geometry of the spreading ridges and trenches active in the jurassic neo tethys using a paleomagnetically based net tectonic rotation analysis of sheeted dykes and dykes from the west and east vardar ophiolites of serbia maljen and ibar and greece othris pindos vourinos and guevgueli based on our results and existing geological evidence we show that initial middle jurassic 175 ma closure of the western neo tethys was accommodated at a n s trending west dipping subduction zone initiated near and parallel to the spreading ridge the west vardar ophiolites formed in the forearc parallel to this new trench simultaneously the east vardar ophiolites formed above a second n s to nw se trending subduction zone located close to the european passive margin we tentatively propose that this second subduction zone had been active since at least the middle triassic simultaneously accommodating the closure of the paleo tethys and the back arc opening of neo tethys

sedimentary corg p ratios paleocean ventilation and phanerozoic atmospheric po2 the corg p ratios of organic rich facies tocn1 exhibit considerable variation through the phanerozoic from b10 1 in the permian phosphoria formation to n1000 1 in some devonian black shales relative to the composition of phytoplankton c p 106 1 which provide the bulk of organic c and p to organic rich marine sediments the range of phanerozoic sedimentary corg p ratios largely reflects the influence of benthic redox conditions on diagenetic pathways of c and p remobilization enhanced preservationoforganiccatlowerredoxpotentials combinedwithenhancedsedimentaryretentionofremineralizedorganicpathigher redox potentials results in a strong relationship between benthic redox conditions and sedimentary corg p ratios the strong secular coherence of the phanerozoic corg p record i e limited variation within narrow time slices suggests that these ratios are controlled primarily by factors influencing benthic redox conditions on a global scale such as atmospheric po2 inversion and scaling of the phanerozoic corg p record yields a new atmospheric po2 model that has strong similarities to existing models based on elemental and isotopic mass balances yet differs in some potentially significant respects in particular the new model suggests that atmospheric po2 wasmarkedlylowerduringtheearlytomiddlepaleozoicthanpreviouslyinferred duringmostofthedevonian atmospherico2levels mayhavebeensufficientlylow b13 astopreventthesustainedcombustionofplantmaterial thisfeatureofthemodelmayaccount for ananomalous gapinthefossilcharcoalrecordduringthedevonian theredox dependentburialofpintheoceanresults inpositive and negative feedback mechanisms that tend to stabilize atmospheric oxygen concentrations on geologic timescales temporal variations in the burial of p relative to c suggest that the strength of these feedback mechanisms varied over the phanerozoic 2007 elsevier b v all rights reserved

determination of both chemical and stable isotope composition in milligramme size carbonate samples abstract isotopic analysis of carbonates involves dissolution of the sample in 100 phosphoric acid analysis of the acid after reaction using inductive coupled plasma source spectrometry gives the chemical composition of the same sample molar fractions of cations in carbonate minerals can be determined to about 0 1 for ca 0 04 for mg 0 06 for fe 60 ppm for mn and 90 ppm for sr even the minor carbonate component in shales can be analyzed if a correction for leaching of clay minerals is made by reference to the al content of the solution however loss in accuracy ensues because of the uncertainty in the correction

the diagenesis of phosphorus in a nearshore marine sediment abstract chemical analyses have been made for total inorganic phosphorus total organic phosphorus and organic carbon in plankton and in anoxic sediments from long island sound u s a when combined with laboratory experiments the measurements of other studies on the same sediments and mathematical modelling the results indicate that 1 1 a large proportion of dissolved phosphate in the upper 10 cm of sediment zone of bioturbation is provided by the release of adsorbed phosphate during the reduction of ferric oxyhydroxides 2 2 below the zone of bioturbation phosphate is liberated to solution solely via organic matter decomposition and the release is stoichiometrically coupled to bacterial sulfate reduction and ammonia formation 3 3 a steady state diagenetic model can be used to predict the profile of organic phosphorus from that of dissolved phosphate at depths below the zone of bioturbation 4 4 the flux of dissolved phosphate out of the sediment must arise largely from phosphate liberation occurring very close 5 5 there is a large preferential loss of phosphorus relative to carbon from organic matter at the time of or prior to burial whereas after burial phosphorus is not lost preferentially at this location

ordovician reef and mound evolution the baltoscandian picture the widespread growth of reefs formed by a framework of biogenic constructors and frame lacking carbonate mounds began on baltica during ordovician time previously ordovician reef and mound development on baltica was considered to be sporadic and local a review of all known bioherm localities across the baltic basin reveals a more consistent pattern ordovician bioherms grew in a wide e w aligned belt across the baltic basin and occur in several places in norway substantial reef development began simultaneously across the region during the late sandbian early katian interval and climaxed during the late katian pirgu age the current spatiotemporal distribution of bioherms is a result of interdependent factors that involve original drivers of reef development such as relative sea level climate during the time of deposition and effects of post depositional erosion oceanographic conditions were likely more favourable during times of cooler global climates low sea level and glacial episodes at the same time the likelihood that bioherms are preserved from long term erosion is higher when deposited during low sea level in deeper parts of the basin a main factor controlling the timing of the reef and mound evolution was baltica s shift toward palaeotropical latitudes during late ordovician time the time equivalence between initial reef growth and the guttenberg isotope carbon excursion gice suggests that global climatic conditions were important

accretionary mechanisms and temporal sequence of formation of the boda limestone mud mounds upper ordovician siljan district sweden abstract late ordovician mud mounds in the boda limestone siljan area central sweden consist mainly of massive spiculitic stromatactis limestone similar to other well known paleozoic mud mounds the mound cores are predominantly formed by spiculite and ostracod rich mudstone and or wackestone and networks of spar filled syndepositional cavities the mounds of the boda limestone are specific in two ways 1 large parts of the lower mound cores are formed by a palaeoporella framestone and or bafflestone with signs of early recrystallization and cementation and 2 the stromatactis facies is accompanied by masses of limestone with non stromatactis cryptocrystalline patches cryptocrystalline patches are filled with massive fibrous low mg calcite have cloudy transitional margins contain randomly spaced skeletal grains and dolomitic micro inclusions and are interpreted as recrystallized patches of the original host lime mud models of formation of paleozoic mud mounds generally hypothesize accretionary processes that are based on sponge biomass degradation and associated diagenetic processes in the boda limestone palaeoporella skeleton disintegration early recrystallization and additionally cementation were essential for the mound formation the boda mounds exemplify that formation of paleozoic mud mounds reflects a spectrum of different essentially diagenetic accretionary mechanisms this diversity should be taken into account in future discussions about paleozoic mud mound formation the new name osmundsberget formation is given for a hirnantian succession of brachiopod rich limestone above the boda limestone the osmundsberget formation occurs only in direct geographical vicinity to the mud mounds

petrology and 40ar 39ar dating of paragneisses from the devrekani massif central pontides northern turkey implications for the jurassic high t metamorphism in an extensional tectonic environment abstract the devrekani massif in the northern part of the central pontides northern turkey provides important clues to the regional tectonics and geodynamic processes associated with jurassic high grade metamorphic conditions this study reports new paragenetic assemblages mineral compositions whole rock geochemistry and 40ar 39ar geochronological data from the paragneisses in the massif and discusses the p t conditions and geodynamic implications of the jurassic metamorphism during continental extension in the central pontides upper amphibolite to lower granulite facies paragneisses form one of the main lithological units in the massif within these there are five different mineral parageneses with diagnostic mineral assemblages of quartz k feldspar an0 1ab4 26or73 96 plagioclase an18 35 biotite xphl 0 28 0 57 mg mg fe2 0 33 0 61 sillimanite cordierite mg mg fe2 0 48 0 71 and garnet alm43 80grs0 18prp5 23and0 4sps10 33 with minor hercynite based on na in crd thermometry and gasp barometry results the peak metamorphic conditions are 775 25 c and 6 1 kbar in the massif the field relations petrography and bulk chemical data suggest that the paragneisses derived from shale wackestone and pelitic sedimentary protoliths are typical rock lithologies of an active continental margin they display enrichments in lile over hfse coupled with negative nb and ti anomalies which are geochemical signatures of subduction related sources it is likely that the peak metamorphism took place during the middle upper jurassic period ca 174 156 ma suggesting that the metamorphic rocks cooled to 300 350 c at ca 156 ma the mineral assemblages reveal that the prograde history passed from sillimanite zone conditions up to the cordierite garnet k feldspar zone the petrological and geochronological data indicate that the protoliths are related to multiple sources such as volcano sedimentary successions we conclude that the devrekani massif represents the products of pre jurassic sedimentation and permo carboniferous continental arc magmatism overprinted by jurassic metamorphism

nd isotope records of late ordovician sea level change implications for glaciation frequency and global stratigraphic correlation abstract detailed records of ice sheet advances and retreats are reconstructed for the hirnantian and katian ages of the late ordovician using nd isotopes e nd as a sea level proxy in three study sections from the western margin of laurentia two shallow water platform sections located south and north of the paleo equator and one deep water section located in a continental slope rise setting when sea level was high and paleo shorelines had migrated eastward the e nd value of seawater in the vicinity of each of the study sections shifted toward the e nd value of the eastern panthalassa ocean 4 0 by contrast when sea level was low and paleo shorelines had migrated westward the e nd value of seawater shifted toward the e nd value of the continental weathering flux from laurentia 8 5 0 2 2 mean these stratigraphic patterns of changing e nd values are interpreted to reflect the eustatic sea level fluctuations that previous studies have documented in response to gondwanan ice sheet advances and retreats thus linking the e nd sea level proxy to late ordovician global scale climate changes the e nd profiles for the two platform sections yielded similar proxy sea level curves with five cycles of oscillation recorded during the latest katian and hirnantian three additional cycles of late katian sea level change are recognized in the e nd profile of the deep water continental slope rise section the combination of e nd 13 c and graptolite biostratigraphic data facilitates a precise interregional correlation of the hirnantian age and the paleoclimate changes that took place during this interval the new correlations support previous findings that the hirnantian ice age comprised two major glacial periods separated by a minor interglacial during the early part of the metabolograptus persculptus biozone the younger glacial confined to mid m persculptus biozone time led to more extensive sea surface cooling than did the earlier one and resulted in extensive eustatic sea level drawdown and c cycle changes it records the strata most often recognized as hice the hirnantian carbon isotope excursion in sedimentary successions worldwide such as anticosti island scotland estonia siberia and south china the results of this study support and strengthen the view that glaciation predated the hirnantian age in the late ordovician and that the records of small positive 13 c excursions in katian successions from baltica and eastern north america are themselves proxy indicators of glaciation frequency and eustatic sea level changes

middle and upper ordovician carbon isotope chemostratigraphy in baltoscandia a correlation standard and clues to environmental history abstract the baltoscandian epeiric sea was characterised by relatively slow but continuous carbonate deposition from the middle ordovician up to the silurian relatively good preservation of ordovician and silurian carbonate rocks in baltoscandia makes this region unique for chemostratigraphical and palaeoenvironmental studies previous palaeozoic carbon isotope studies have revealed isotopic events in different lithologies over the baltoscandian palaeobasin and some of them on different palaeocontinents we propose a composite carbon isotope curve for the baltoscandian region a new subdivision of the middle and upper ordovician succession into seventeen chemostratigraphic zones and an improved nomenclature of isotopic excursions based on analyses of 13 c carb data from 25 drillcore and outcrop sections of estonia latvia and sweden the composite carbon isotope curve is compared with biostratigraphical data on conodont and chitinozoan distribution the katian hirnantian interval with highly fluctuating isotopic values shows climatic cyclicity of about two million years in baltoscandia no abrupt changes occur in the dapingian sandbian part of the baltoscandian isotope curve but the mid darriwilian excursion nearly coincides with the onset of cooler temperatures similar to modern like equatorial sea surface temperatures and related global biodiversification increase suggesting a climatic background for this event

late jurassic magmatism and stratigraphy in the eastern sakarya zone turkey evidence for the slab breakoff of paleotethyan oceanic lithosphere abstractmiddle late jurassic cimmerian events in turkey have been actively discussed in the past three decades but proposed tectonic models associated with magmatism metamorphism and stratigraphic features remain controversial to address this issue upper jurassic mafic lavas are investigated at three locations alucra gumushane and olur in the eastern sakarya zone northeastern turkey these lavas are submarine and form planar flows parallel with the bedding plane in the upper jurassic carbonate sequence near the base or just below in the clastic sedimentary rocks the basaltic lavas show calc alkaline features and possess nb ta values and nb u nb la and ce pb ratios that are greater than those of island arc basalts multielement patterns are almost hump shaped similar to ocean island basalts which experience pb depletion and weak negative nb ta zr hf and ti anomalies the low initial 87sr 86sr ratios 0 70372 0 70554 positive initial end values 2 7 to 4 4 and initial pb isotope rat

strontium isotope diagenesis of biogenic aragonite and low mg calcite abstract using petrographie and geochemical criteria it is possible to identify marine sr isotopic compositions and diagenetic overprints in carbonate samples the 87 sr 86 sr ratio of originally low mg calcite brachiopods and aragonite molluscs from the boggy magoffin and brush creek formation members increases with progressive post depositional alteration in the presence of diagenetic meteoric waters in contrast brachiopods from the codroy formation exhibit an increase in non radiogenic sr with diagenetic alteration based on the seawater 87 sr 86 sr curve this alteration probably occurred in the presence of marine water during the mid permian triassic or late cretaceous early tertiary the degree of change in radiogenic sr probably reflects the physicochemical nature of the diagenetic microsystem diffusion controlled altered material shows the smallest degree of change in sr isotopic ratios as well as microstructural and other geochemical modifications in contrast fluid controlled altered material shows the greatest shift in isotopic ratios with concomitant microstructural and geochemical changes data of diagenetically well defined biogenic carbonates show that mississippian seawater 87 sr 86 sr was constant with a mean of about 0 70773 and a range of 0 7076 0 7078 the revised high resolution curve shows significantly higher variations for pennsylvanian seawater 87 sr 86 sr 0 7076 0 7093 a low perturbation marks the midvirgilian 0 7076 0 7078 and high perturbations are observed for the early missourian 0 70846 and latest morrowan 0 70913 the mean value determined for the latest morrowan is similar to 87 sr 86 sr ratios measured for modern carbonates and seawater it is further suggested that seawater 87 sr 86 sr varies by as much as 0 000154 at any given time

partial diagenetic overprint of late jurassic belemnites from new zealand implications for the preservation potential of δ7li values in calcite fossils the preservation potential and trends of alteration of many isotopic systems e g li mg ca that are measured in fossil carbonates are little explored yet extensive paleoenvironmental interpretations have been made on the basis of these records here we present a geochemical dataset for a late jurassic 153 ma belemnite belemnopsis sp from new zealand that has been partially overprinted by alteration we report the physical pathways and settings of alteration the resulting elemental and isotopic trends including 7li values and li ca ratios and assess whether remnants of the primary shell composition have been preserved or can be extrapolated from the measured values the 18o and 13c values as well as sr ca and mn ca ratios were analysed along two profiles in addition 6 samples were analysed for 87sr 86sr sr ca and mn ca ratios five samples from the same specimen and 2 from the surrounding sediment were analysed for 7li values li ca sr ca and mn ca ratios and are compared to results for 6 other late jurassic belemnite rostra belemnopsis sp andhibolithes sp from the same region the 87sr 86sr ratios are lower less radiogenic in the most altered part of the rostrum whereas 7li values become more positive with progressive alteration the direction and magnitude of the trends in the geochemical record indicate that one main phase of alteration that occurred in the late cretaceous caused most of the diagenetic signature in the calcite despite relatively deep burial down to 4 km and thus elevated temperatures this diagenetic signature has subsequently been preserved even for the highly mobile element lithium suggesting that primary lithium isotope values can be maintained over geological timescales at least in thick macrofossil shells our best 7li estimate for pristine late jurassic 155 148 ma belemnites is 27 1 which points to a late jurassic seawater 7li of 29 32 compatible with the modern value of 31

palaeokarst evidence for widespread regression and subaerial exposure in the middle katian upper ordovician of baltoscandia significance for global climate we report on widespread and contemporary palaeokarst in the middle katian upper ordovician of sweden estonia and latvia the first major palaeokarst horizon to be reported from the ordovician of baltoscandia the solution features occurwithin a fewmetres of thick zone of limestone immediately belowthe widespread fjacka shale and are related to an unconformity with preserved palaeorelief in the slandrom limestone in sweden and the time equivalent saunja formation in estonia and latvia facies evidence for a karst origin comes fromseveral outcrops and core sections and includes 1 frequent karren likemorphologies interpreted as swiss cheese karst sensu baceta et al 2001 2 local occurrences of solution collapse breccia 3 presence of bladed pseudospar crystals in solution cavities and 4 carbon isotope values indicating meteoric influence to the succession these findings are herein put in context with previously reported large scale erosional channels that may cut down several tens of metres below the fjacka shale in the subsurface baltic sea area and with regional anomalous thickness variations in the slandrom limestone and saunja formation all together forming strong support for regional exposure of the baltoscandian continent in the middle katian high resolution stable isotopic data show that the regression and lowstand of sea level overlap with thewaynesville carbon isotope excursion it resulted in basin wide cessation of carbonate production near the amorphognathus superbus and a ordovicicus conodont zonal boundary the contemporary development of palaeokarst in different confacies belts of the basin suggests that this was an extraordinary sea level lowstand herein interpreted as reflecting a middle katian glaciation less

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

first balanced cross section across the taurides fold thrust belt geological constraints on the subduction history of the antalya slab in southern anatolia eastern mediterranean subduction accommodated africa eurasia convergence since mesozoic time and produced multiple subducted slab fragments in the mantle below anatolia these included the north dipping cyprus and ene dipping antalya slabs which are currently separated by an upper mantle slab gap segmentation of these slabs and associated mantle flow may have contributed to 400 km of post to middle eocene plate convergence was accommodated between the taurides and its beydaglari platform foreland and instead must have been accommodated south of beydaglari the associated southward plate boundary jump separated the antalya slab from the african plate and the cyprus slab the isolated antalya slab was left in an intraplate setting and is probably still attached to beydaglari today we suggest the continental composition of the antalya slab may have prevented its detachment finally the gap between the antalya and cyprus slabs existed since at least eocene time their decoupling likely did not contribute to late neogene central anatolian plateau uplift

the end ordovician mass extinction a single pulse event abstract the end ordovician mass extinction eome is widely interpreted as consisting of two pulses associated with the onset and demise of the gondwana glaciation respectively with the second pulse eradicating the distinctive glacially related hirnantian benthic biota hbb a global review of occurrence data of latest ordovician benthic marine organisms reveals that virtually all warm water benthic assemblages previously assigned to the hbb comprise two distinct and clearly postglacial faunas both younger middle and late hirnantian respectively than the cool water hirnantia fauna latest katian to early hirnantian the newly recognised three transitional benthic faunas i e tbfs 1 3 can be closely tied to graptolite conodont and chitinozoan biozonations the hirnantian isotope carbon excursion hice and the glaciation thereby providing an integrated much higher resolution timescale for understanding the tempo and nature of the eome at this finer resolution we postulate a more profound impact of the first pulse of the eome than hitherto envisaged as evidenced by opportunistic expansion of the hirnantia fauna globally and the complete absence of metazoan reefs in its immediate aftermath we also argue based on high quality data from well documented benthic groups in south china i e brachiopods tabulate and rugose corals trilobites and sponges that the magnitude of the second pulse of the eome caused by the deglaciation has been overestimated because the two postglacial faunas i e tbfs 2 3 were part of a subsequent recovery phase of marine ecosystems rather than contributing to biodiversity decline thus it is more plausible to reinterpret the eome as a single pulse rapid event that was followed by a prolonged initial recovery intermittently impeded by climatic shocks through the hirnantian prior to the onset of a progressive reestablishment of marine ecosystems during the early silurian rhuddanian and aeronian associated with an overall amelioration of climatic conditions

latest cretaceous a 2 type granites in the sakarya zone ne turkey partial melting of mafic lower crust in response to roll back of neo tethyan oceanic lithosphere abstract an integrated study of comprehensive geochronological geochemical and sr nd hf isotopic data was undertaken for the a type topcam pluton that intruded within the sakarya zone ne turkey with the aims of elucidating its origin and tectonic significance and gaining new insights into the generation of aluminous a type granites new la icp ms zircon u pb crystallization ages of 72 and 73 ma indicate emplacement in the late cretaceous time just after extensive metaluminous i type magmatism in the area the pluton consists mainly of alkali feldspar quartz plagioclase amphibole and biotite with accessory minerals such as magnetite apatite and zircon the outcrop is composed of granite syenite monzonite and quartz monzonite and possesses a wide range of sio2 content 57 70 wt with elevated ga al ratios and low mg mostly

a long lived late cretaceous early eocene extensional province in anatolia structural evidence from the ivriz detachment southern central turkey abstract central anatolia exposes previously buried and metamorphosed continent derived rocks the kirsehir and afyon zones now covering an area of 300 400 km so far the exhumation history of these rocks has been poorly constrained we show for the first time that the major 120 km long top ne ivriz detachment controlled the exhumation of the hp lt metamorphic afyon zone in southern central anatolia we date its activity at between the latest cretaceous and early eocene times combined with previously documented isolated extensional detachments found in the kirsehir block our results suggest that a major province governed by extensional exhumation was active throughout central anatolia between 80 and 48 ma although similar in dimension to the aegean extensional province to the east the central anatolian extensional province is considerably older and was controlled by a different extension direction from this we infer that the african slab s that subducted below anatolia must have rolled back relative to the aegean slab since at least the latest cretaceous suggesting that these regions were underlain by a segmented slab whether or not these early segments already corresponded to the modern aegean antalya and cyprus slab segments remains open for debate but slab segmentation must have occurred much earlier than previously thought

stable isotope δ13ccarb and org δ15norg and trace element anomalies during the late devonian punctata event in the western canada sedimentary basin late devonian marine deposits in the western canada sedimentary basin were analyzed for 1 accumulations of bioproductivity and paleoredox trace element proxies and for 2 variations of 13c carb and org and 15norg in order to understand and interpret the regional history of the global yet short term punctata event geochemical perturbation statistical correlations suggest that changes in detrital input and associated micronutrient delivery were the main driver of a eutrophication event noted early and possibly also late in the punctata zone around the isolated miette platform manifested by increased toc positive 13c excursions and concurrent enrichments of all elemental proxies evaluation of data within a regional sequence stratigraphic perspective revealed a eustatic sea level influence with proxy accumulations associated mostly with early transgression iic1 deposition and preservation of organic matter rich facies occurred during conditions of enhanced primary production and facilitated bottom water suboxia anoxia following eutrophication lower 15norg and 13corg values predominated and persisted throughout much of the punctata zone before rebounding toward its close suggesting a time interval of environmental stagnation and lower overall productivity during which n2 fixing autotrophs may have had an ecological advantage under nitrate limited conditions the punctata event approximately coincided with the advent of archaeopterid forest expansion beginning around mid frasnian time which fundamentally altered the nature of continental weathering through extensive soil formation and increased nutrient delivery to the oceans this evolutionary event may have amplified the detrital influx already elevated by sea level lowstand and early transgression and increased denudation of rising mountain ranges in near equatorial regions

age constraints on intra formational unconformities in upper jurassic lower cretaceous carbonates in northeast turkey geodynamic and hydrocarbon implications abstract upper jurassic lowermost cretaceous carbonate build ups are imaged on seismic data in the black sea they form important untested hydrocarbon reservoirs that are the focus of active exploration outcrop analogues to these build ups around the black sea contain a series of subaerial exposure surfaces the hiatuses associated with a number of these subaerial exposure surfaces have been dated in a well exposed callovian or upper oxfordian to barremian shallow water inner platform carbonate succession the berdiga formation in the eastern pontides using strontium isotope stratigraphy and foraminiferal biostratigraphy they span the latest kimmeridgian to tithonian or berriasian and the hauterivian to barremian less well constrained but broadly contemporaneous stratigraphic gaps in multiple successions around the black sea provide additional insights and point to a regional driving mechanism the timing of hiatus formation does not correspond to periods of eustatic lowstand it does coincide however with late tithonian to berriasian and hauterivian to early aptian episodes of rifting in the greater caucasus basin located farther to the north thus it is possible that subaerial exposure was caused by rift flank uplift during periods of regional extension uplift due to slab break off is discounted as a control because it post dates rather than pre dates locally developed kimmeridgian magmatism rift flank uplift is likely to have also affected carbonate build ups on the intervening rift shoulders of the eastern black sea the shatskiy ridge and the mid black sea high at outcrop subaerial exposure is often associated with karstification and secondary porosity development similar processes may have occurred in the offshore helping to enhance the reservoir quality of these exploration targets

tectonic units of the alpine collision zone between eastern alps and western turkey abstract we present a map that correlates tectonic units between alps and western turkey accompanied by a text providing access to literature data explaining the concepts used for defining the mapped tectonic units and first order paleogeographic inferences along strike similarities and differences of the alpine eastern mediterranean orogenic system are discussed the map allows 1 for superimposing additional information such as e g post tectonic sedimentary basins manifestations of magmatic activity onto a coherent tectonic framework and 2 for outlining the major features of the alpine eastern mediterranean orogen dinarides hellenides anatolides and taurides are orogens of opposite subduction polarity and direction of major transport with respect to alps and carpathians and polarity switches across the mid hungarian fault zone the dinarides hellenides taurides and apennines consist of nappes detached from the greater adriatic continental margin during cretaceous and cenozoic orogeny internal units form composite nappes that passively carry ophiolites obducted in the latest jurassic earliest cretaceous or during the late cretaceous on top of the greater adriatic margin successions the ophiolites on top of composite nappes do not represent oceanic sutures zones but root in the suture zones of neotethys that formed after obduction suturing between greater adria and the northern and eastern neotethys margin occupied by the tisza and dacia mega units and the pontides occurred in the latest cretaceous along the sava izmir ankara erzincan suture zones the rhodopian orogen is interpreted as a deep crustal nappe stack formed in tandem with the carpatho balkanides fold thrust belt now exposed in a giant core complex exhumed in late eocene to miocene times from below the carpatho balkan orogen and the circum rhodope unit its tectonic position is similar to that of the sakarya unit of the pontides we infer that the rhodope nappe stack formed due to north directed thrusting both rhodopes and pontides are suspected to preserve the westernmost relics of the suture zone of paleotethys

freshwater calcite precipitates from in vitro mesocosm flume experiments a case for biomediation of tufas freshwater carbonates tufas develop today from the arctic to the tropics many being localized about springs and upper water courses some quaternary tufas especially in the mediterranean region extend over tens of square kilometres and exceed 30 m in thickness radiometric dating of holocene deposits shows that many have accumulated at an average rate of 1 mm year 1 however local precipitation may be much faster and some holocene deposits may even have outpaced their tropical marine carbonate counterparts recently the study of active sites has attempted to quantify the precipitation mechanisms which lead to tufa deposition however field observation and sampling procedures suffer from the inherent disadvantages of uncontrolled fluctuations in environmental conditions during the study programme these disadvantages compromise any interpretations particularly where controls on spar versus micrite precipitation are concerned many of these problems have been overcome in the current study by the construction and operation of laboratory mesocosm flumes which simulate the natural conditions e g ph flow rate ambient temperature and daylight in which freshwater carbonate tufa is deposited three mesocosms were supplied with natural river water from tufa precipitating streams and two mesocosms were supplied with uv treated sterile river water from the same source one of the untreated flume mesocosms was linked with a calcium reactor which replaced calcium ions removed during the precipitation process in order to maintain tufa growth over extended experimental runs low magnesium calcite precipitates both rhombic sparite grown from long crystallite dendrites and short crystallite dendrite triad precursors and micrite peloids grown from spherulitic precursors were precipitated in intimate association with biofilm extracellular polymeric substances within the four mesocosms supplied with natural river water virtually no tufa like precipitate was obtained from the flumes supplied with uv treated river water a second extended run flume experiment was also carried out for comparison purposes using a calcium hydroxide solution in deionized water collectively these experiments provide convincing evidence confirming that the presence of a microbial biofilm strongly influences the precipitation of carbonates in riverine freshwater settings in particular experimental results show that micropeloidal micrite and short crystallite calcite dendrites are only produced in the presence of microbial extracellular polymeric substances

kinematics of late cretaceous subduction initiation in the neo tethys ocean reconstructed from ophiolites of turkey cyprus and syria formation of new subduction zones represents one of the cornerstones of plate tectonics yet both the kinematics and geodynamics governing this process remain enigmatic a major subduction initiation event occurred in the late cretaceous within the neo tethys ocean between gondwana and eurasia suprasubduction zone ophiolites i e emerged fragments of ancient oceanic lithosphere formed at suprasubduction spreading centers were generated during this subduction event and are today distributed in the eastern mediterranean region along three e w trending ophiolitic belts several models have been proposed to explain the formation of these ophiolites and the evolution of the associated intra neo tethyan subduction zone here we present new paleospreading directions from six upper cretaceous ophiolites of turkey cyprus and syria calculated by using new and published paleomagnetic data from sheeted dyke complexes our results show that nne ssw subduction zones were formed within the neo tethys during the late cretaceous which we propose were part of a major step shaped subduction system composed of nne ssw and wnw ese segments we infer that this subduction system developed within old triassic lithosphere along fracture zones and perpendicular weakness zones since the neo tethyan spreading ridge formed during gondwana fragmentation would have already been subducted at the pontides subduction zone by the late cretaceous our new results provide an alternative kinematic model of cretaceous neo tethyan subduction initiation and call for future research on the mechanisms of subduction inception within old and cold lithosphere and the formation of metamorphic soles below suprasubduction zone ophiolites in the absence of nearby spreading ridges

diachronous demise of the neotethys ocean as a driver for non cylindrical orogenesis in anatolia continent continent collision drives crustal deformation topographic rise and geodynamic change africa eurasia convergence accommodated in the eastern mediterranean involved subduction of the neotethyan oceanic lithosphere in anatolia subduction was followed by collision of continental crust of greater adria with eurasia to form the izmir ankara erzincan suture zone discerning the effects of this collision from pre collisional ophiolite obduction related orogeny of greater adria is notoriously difficult estimates on the timing of collision in central anatolia are based on a forearc to foreland basin transition along the eurasian margin and suggest a 60 ma age of initial collision here we assess whether this age is also representative for collision in eastern anatolia and across the cenozoic sivas basin that straddles the greater adria europe suture to this end we retro deform regional block rotations in the pontides the kirsehir block and the taurides building a first order regional block circuit around the sivas basin we show that up to 700 km of convergence must have been accommodated across the sivas basin after central anatolian kirsehir pontide collision at 60 ma an order of magnitude more than estimated crustal shortening and that wholesale lithospheric subduction must have occurred throughout much of the cenozoic paleocene collision would require that this subduction consumed continental lithosphere which is unlikely we consequently infer that oceanic subduction continued much longer in eastern anatolia perhaps well into the miocene we postulate that prolonged oceanic subduction and slab pull drew the eastern taurides north relative to the central taurides leading to shortening and oroclinal bending in central anatolia the diachronous demise of the neotethys ocean in anatolia as a function of its paleogeography is thus a likely driver for the strong non cylindricity of the cenozoic anatolian collisional orogen

benthic phosphorus regeneration net primary production and ocean anoxia a model of the coupled marine biogeochemical cycles of carbon and phosphorus we examine the relationships between ocean ventilation primary production water column anoxia and benthic regeneration of phosphorus using a mass balance model of the coupled marine biogeochemical cycles of carbon c and phosphorus p the elemental cycles are coupled via the redfield c p ratio of marine phytoplankton and the c p ratio of organic matter preserved in marine sediments the model assumes that on geologic timescales net primary production in the oceans is limited by the upwelling of dissolved phosphorus to the photic zone the model incorporates the dependence on bottom water oxygenation of the regeneration of nutrient phosphorus from particulate matter deposited at the water sediment interface evidence from marine and lacustrine settings modern and ancient demonstrates that sedimentary burial of phosphorus associated with organic matter and ferric oxyhydroxides decreases when bottom water anoxia dysoxia expands steady state simulations show that a reduction in the rate of thermohaline circulation or a decrease of the oxygen content of downwelling water masses intensifies water column anoxia dysoxia and at the same time increases surface water productivity the first effect reflects the declining supply of oxygen to the deeper parts of the ocean the second effect is caused by the enhanced benthic regeneration of phosphorus from organic matter and ferric oxyhydroxides sedimentary burial of organic carbon and authigenic calcium phosphate mineral francolite on the other hand is promoted by reduced ocean ventilation according to the model global scale anoxia dysoxia leads to a more efficient recycling of reactive phosphorus within the ocean system consequently higher rates of primary production and organic carbon burial can be achieved even when the continental supply of reactive phosphorus to the oceans remains unchanged

whole rock geochemistry zircon u pb and hf isotope systematics of the cangaldag pluton evidences for middle jurassic continental arc magmatism in the central pontides turkey abstract the central pontides turkey includes several igneous complexes which are predominantly permo carboniferous and middle jurassic in age the cangaldag pluton is one of the largest igneous bodies located in the northern central pontides whose age and tectono magmatic evaluation is important to constrain the geological evolution of the northern neotethys the pluton tectonically overlies the cangaldag metamorphic complex which represents an arc back arc complex of middle jurassic age the cangaldag pluton consists mainly of non metamorphic gabbroic diorite dacite porphyry and lesser amount of granitic rocks geochemically the various rock types are akin to volcanic arc magmas displaying th nb and light rare earth element heavy rare earth element enrichments in situ u pb age results of zircons from dacite porphyry and granite samples yield ages of 161 5 ma and 170 2 ma respectively corresponding in situ average 176hf 177hf initial ratios are 0 28287 0 00004 and 0 28213 0 00002 for the dacite porphyry and granite samples respectively these results are consistent with derivation from a subduction modified mantle source based on hf isotope compositions tdm model ages vary between 624 and 1512 ma and suggest that the arc magmatism associated with the cangaldag pluton may have involved partial melting of neoproterozoic mesoproterozoic crustal rocks a common feature in gondwana derived terranes the geochemical hf isotope and geochronological data reported here confirm the presence of a continental arc system during the middle jurassic in the central pontides and suggests that the cangaldag pluton formed during northward subduction of the intra pontide branch of the northern neotethys

influence of water column anoxia on the elemental fractionation of carbon and phosphorus during sediment diagenesis abstract organic carbon oxidation and benthic total phosphorus flux measurements from sites covering a range of bottom water oxygen concentrations have been compiled the data show that p regeneration relative to carbon oxidation is much more extensive in sediments overlain by oxygen depleted waters these results are consistent with studies showing that low oxygen bottom water concentrations correlate with reduced total phosphorus burial efficiencies and enhanced organic carbon burial efficiencies based on these observations a positive feedback is proposed between water column anoxia enhanced benthic phosphorus regeneration and marine productivity this feedback may help explain the widespread accumulation of organic rich marine sediments from anoxic waters observed in the geologic record

a new interpretation of the sedimentary cover in the western siljan ring area central sweden based on seismic data abstract two new reflection seismic profiles over the paleozoic successions of the western part of the siljan ring impact structure show a contrasting seismic signature the more southerly c 10 km long mora profile reveals a highly disturbed structure with only a few kilometers of relatively horizontally layered structures observed however interpretations of refracted arrivals in the data that can be correlated to reflections indicate the silurian clastic rocks to be about 200 m thick in the central part of the profile weak reflections from about 600 m depth suggest a 400 m thick ordovician limestone sequence to be present cores from the area show a mainly shale lithology for the silurian and only a thin sequence of ordovician strata suggesting a rapid thickening of the ordovician towards the north on the more northern c 12 km orsa profile clear reflections from the paleozoic successions are seen along the entire profile except on the southernmost few kilometers based on interpretations of refracted arrivals the silurian succession appears to be considerably thinner here and possibly absent at some locations the ordovician is also interpreted to be thinner in this area with a maximum thickness of about 200 300 m along most of the profile a deeper reflection from about 2 km within the crystalline basement may represent a dolerite sill the lack of clear basement reflections on the mora profile can be attributed to near surface conditions and the acquisition geometry the seismic data and recent coring in the area suggest the presence of a deeper paleo basin towards the southwest with significantly more shales being deposited and the paleozoic successions being severely disturbed the shallow coring and seismic data will help form the basis for locating future boreholes for deeper drilling to study impact processes and the paleozoic evolution of central sweden

end ordovician extinctions a coincidence of causes the end ordovician hirnantian extinction was the first of the five big phanerozoic extinction events and the first that involved metazoan based communities it comprised two discrete pulses both linked in different ways to an intense but short lived glaciation at the south pole the first occurring at or just below the normalograptus extraordinarius graptolite biozone mainly affected nektonic and planktonic species together with those living on the shallow shelf and in deeper water whereas the second within the n persculptus graptolite biozone was less focused eradicating faunas across a range of water depths in all about 85 of marine species were removed proposed kill mechanisms for the first phase have included glacially induced cooling falling sea level and chemical recycling in the oceans but a general consensus is lacking the second phase is more clearly linked to near global anoxia associated with a marked transgression during the late hirnantian most recently however new drivers for the extinctions have been proposed including widespread euxinia together with habitat destruction caused by plate tectonic movements suggesting that the end ordovician mass extinctions were a product of the coincidence of a number of contributing factors moreover when the deteriorating climate intensified causing widespread glaciation a tipping point was reached resulting in catastrophe

biogeochemistry phosphorus burial the formation and burial of calcium phosphate minerals removes large quantities of phosphorus from the ocean radiotracer experiments reveal that bacteria in marine sediments mediate the production of these mineral phases at remarkably fast rates