tectonic history of the lunksoos composite terrane in the maine appalachians several ordovician volcanic terranes are preserved between the paleozoic north american margin and the avalon terrane in the northern appalachians of maine they have been interpreted as remnants of an island arc on the basis of their current position in the appalachians or as ocean islands near the margin of avalon on the basis of paleontologic data a study of one of these terranes the lunksoos terrane in northern maine was undertaken through a combination of paleomagnetic and structural analyses in order to understand its tectonic evolution paleomagnetic study of the pre caradoeian pre late ordovician stacyville volcanics revealed three components of magnetization the final magnetization removed d 90 i 36 95 11 8 is interpreted to be primary and yields a paleolatitude of approximately 20 s however a late ordovician remagnetization cannot be excluded the stacyville volcanics now overlie a cambrian and lower ordovician sequence the grand pitch and shin brook formations that is believed to have been deposited at the southern side of iapetus possibly near the margin of avalon during the middle and late ordovieian avalon was at paleolatitude s higher than 40 s while the volcanics were either formed or remagnetized at a paleolatitude of 20 s the pre caradocian stacyville volcanics therefore could not have been deposited directly on the grand pitch shin brook sequence but must have been tectonically emplaced the rockabema diorite which intrudes the entire cambro ordovician sequence constrains the timing of this emplacement to be pre late early silurian these relationships indicate that the lunksoos area is a composite terrane within the maine appalachians the tectonic emplacement scenario is unnecessary if the grand pitch and shin brook formations were not located on the south side of iapetus during the ordovician this alternative however poses conflicts with the interpretation of faunal affinities

influence of water column anoxia and sediment supply on the burial and preservation of organic carbon in marine shales abstract previous work has suggested that the laminated organic rich and bioturbated organic poor shales of the camp run member of the late devonian early mississippian new albany shale formed under anoxic and oxygenated bottomwater conditions respectively and that the interbedding of the two facies was due to the vertical oscillation of a water column anoxic oxic boundary where it impinged on the basin margin we have extended this analysis by examining the chemical and mineralogical differences between the two shale facies in a single borehole core by seeking evidence for deposition of the laminated shales under bottom water oxia or anoxia and by determining whether the laminated shales formed when the carbon supply to the sea floor was higher the results of this study show that the laminated and bioturbated shales are mineralogically and chemically distinct relative to al an index of the aluminosilicate content si ti fe p na ba co cr cu mo ni v zn and zr are all higher whereas mn ca mg and sr are lower in the laminated compared with the bioturbated shales the differences are due to a higher quartz feldspar titanite ilmenite and zircon content in the laminated shales probably indicating a coarser grain size and the greater abundance of manganoan calcite in the bioturbated shales dissolved oxygen was present in bottom waters during the deposition of some of the laminated shale intervals because of the presence of manganoan calcite a phase that can only form in sediments with an oxic surface in addition the organic matter preserved in the two shale types is isotopically different 13corganic values are 1 9z permil lighter on average in the laminated compared with bioturbated intervals possibly indicating a larger fraction of terrestrial organic matter in the latter 15n values are 1 9z permil lighter on average in laminated compared with bioturbated intervals possibly indicating a larger fraction of terrestrial organic matter in the latter 15n values are 1 9z permil lighter on average in laminated compared with bioturbated intervals suggesting that nutrient drawdown was less during the deposition of the organic rich laminated shales the chemical mineralogical and isotopic contrasts between the two shale facies of the camp run member indicate that the conditions of sedimentation were different during their deposition the difference was possibly related to variations in sea level which would have caused the camp run shoreline to move closer to and farther from the core site causing in turn the deposition of coarser and finer grained sediments that contained different mixtures of marine and terrestrial organic matter bottomwater conditions were anoxic during deposition of most laminated intervals bottom water anoxia or dysoxia led to decreased burial and preservation of the essential nutrient phosphorus in the laminated organic rich shales relative to the rocks deposited beneath better oxygenated bottomwaters increased availability of phosphorus in the water column on long timescales leads to increased productivity and a higher settling flux of organic matter causing bottom water oxygen levels to fall this is consistent with the nitrogen isotope evidence suggesting that production was probably higher during the deposition of the organic rich shales thus production variations coupled with enhanced sedimentary regeneration of phosphorus from sediments related to low oxygen bottom water concentrations provide a general mechanism for the formation of the alternating facies of this member of the new albany shale

zone of metal driven anaerobic oxidation of methane is an important sink for phosphorus in the taixinan basin south china sea abstract phosphorus p is an important nutrient and has an important impact on global primary productivity presently the dynamics of the p cycle in low sulfate anoxic settings are largely unknown in this study the adsorption desorption behavior of fe bound p organic p loosely bund p detrital apatite p and refractory p was described in the sulfate and methane transition zone smtz at site 973 4 in the cold seep area of the taixinan basin south china sea results showed that the fe bound p and organic p were influenced by sulfate driven anaerobic oxidation of methane sd aom and metal driven anaerobic oxidation of methane md aom and subsequently the fe bound p and organic p were released as hpo42 into the pore water meanwhile significant increases were detected in authigenic carbonate fluorapatite pcfa and vivianite within the md aom zone which indicate that this zone is an important p sink area the md aom plays an important role in the formation of pcfa and vivianite because md aom provide the necessary hpo42 and fe2 for the formation of these minerals our findings have major implications for understanding the p cycle in low sulfate anoxic settings and are important for understanding the influence of md aom on the phosphate cycle

development of a modified sedex phosphorus speciation method for ancient rocks and modern iron rich sediments abstract we report the development of a modified method for evaluating different reservoirs of sedimentary phosphorus p in ancient marine sedimentary rocks and in modern fe rich sediments utilising the existing sedex scheme for p partitioning in modern sediments we initially demonstrate limitations in the application of the original scheme to sediments and rocks containing crystalline hematite and magnetite we tested additional extractions for these crystalline fe phases using both synthetic minerals and modern and ancient sediments the addition of 6 h oxalate and 6 h citrate dithionate acetate extractions considerably enhanced the total recovery of synthetic magnetite and hematite to 88 7 1 1 and 76 9 3 8 respectively in addition application of the 6 h oxalate extraction to synthetic p containing magnetite recovered 93 9 1 7 of the fe present and 88 2 12 8 of the co precipitated p based upon these results we developed a modified sedex extraction scheme the modified scheme was applied to modern fe rich sediments from golfo dulce costa rica which resulted in 16 higher fe bound p recovery application of the scheme to a variety of ancient marine rocks increased the recovery of fe bound p by up to 22 we also highlight the potential for authigenic carbonate fluorapatite to convert to more crystalline apatite in ancient rocks during deep burial and metamorphism we suggest that in such systems minimum and maximum estimates of the total reactive p pool may be calculated with and without the inclusion of crystalline p it is noted that the application of the revised method may have important implications for understanding the cycling of p in ancient marine environments

regulation of atmospheric oxygen during the proterozoic abstract many studies suggest that oxygen has remained near modern levels throughout the phanerozoic but was much less abundant from the great oxygenation event around 2 4 ga until the late neoproterozoic around 600 ma kump 2008 using a simple model we show that the maintenance of atmospheric po2 at 1 of present atmospheric levels pal is inconsistent with modern biogeochemical cycling of carbon sulfur and iron unless new feedbacks are included low oxygen conditions are stable in our model if the flux of phosphorus to the oceans was greatly reduced during the proterozoic we propose a mechanism to reduce this flux through the scavenging of phosphate ions with an iron trap driven by greater surface mobility of ferrous iron in a low po2 world incorporating this feedback leads to two stable equilibria for atmospheric oxygen the first quantitative hypothesis to explain both proterozoic and phanerozoic o2 concentrations

volcanic record of the subduction of an active spreading ridge taitao peninsula southern chile during the pliocene the taitao peninsula was the locus of the subduction of the chile active spreading ridge beneath the south american margin new field data allow us to distinguish within the taitao ophiolite a genuine ophiolitic body of undetermined age and two volcanic and volcaniclastic units one unit shows evidence for deposition in a shallow water environment and it unconformably overlies the chilean continental basement its established pliocene age demonstrates that it was deposited during the subduction of the chile ridge lavas from both units include enriched mid oceanic ridge basalts morbs together with nb depleted basalts andesites and dacites la nb ratios vary randomly from 1 to 4 in both units and are positively correlated with sio 2 content these chemical characteristics are consistent with upper crustal contamination of morb type basalts by the chilean crust as already suggested from isotopic data we consider these volcanic suites to be the result of eruptions of morb magmas that originated from the downgoing shallowly buried active spreading center and were contaminated during their rise through the chilean continental basement

lower silurian subduction related volcanic rocks in the chaleurs group northern new brunswick canadageological survey of canada contribution no 2008 0166 contribution to natural resources canada s targeted geoscience initiative 3 2005 2010 early silurian volcanic and subvolcanic rocks are preserved in the lower part of the chaleurs group at two locations in northern new brunswick at quinn point mafic to intermediate rocks are hosted by sedimentary rocks of the weir formation and at pointe rochette a bed of felsic tuff occurs near the base of the weir these rocks are interpreted as the first evidence in new brunswick of magmatism associated with late ordovician early silurian subduction of tetagouche exploits back arc oceanic crust at quinn point mafic rocks include a thick basaltic flow or sill and intermediate to mafic cobbles in overlying conglomerate beds the in situ mafic rocks and the conglomerate clasts are chemically alike and display subduction related affinities on tectonic discrimination diagrams at pointe rochette fine grained felsic tuff contains elevated th and u and depleted high field strength elements consistent with a subduction influenced setting although rare earth element ree abundances are low and the re

carbon to phosphorus ratios in sediments implications for nutrient cycling defining the transformations of phosphorus p in sediments is critical to assessing the geochemical behavior of sedimentary p and the behavior of reactive p preactive poxide associated pauthigenic porganic relative to organic carbon corganic this study includes the determination of p components and corganic concentrations on samples from sites in the california current region ocean drilling program odp leg 167 sites 1010 1011 1012 1014 1016 and 1021 in the benguela current region odp leg 175 sites 1082 1084 and 1085 and on blake nose in the western atlantic odp leg 17 1b sites 1050 and 1052 sample depths range up to 650 m and ages range up to 65 ma our data demonstrate the transformation of labile forms of p porganic and poxide associated to pauthigenic throughout the sediment column in all redox states and at all sedimentation rates investigated until a substantial portion of reactive p is in the authigenic form 80 c p organic ratios are always greater than or equal to the redfield ratio in all of the sediments we studied sediments with corganic concentrations 2 wt have corganic preactive ratios less than the redfield ratio and corganic preactive ratios increase linearly with corganic consistent with degradation of corganic with age in general corganic preactive ratios for sediments with corganic concentrations 2 wt from a variety of redox states and sedimentation rates center around the redfield ratio although some ratios are as high as 3 times the redfield ratio however corganic preactive ratios up to 400 do not approach the high ratios observed for c p organic ratios up to 4500 because of the efficient transfer of labile forms of p to pauthigenic corganic preactive ratios better describe the geochemical behavior of sedimentary p

phosphate removal by oceanic hydrothermal processes an update of the phosphorus budget in the oceans abstract we present a compilation of dissolved phosphate and solid phase p data from the oceanic crust to evaluate the effects of hydrothermal processes on the oceanic budget of p concentrations of phosphate in fluids that emanate from ridge axis hydrothermal systems are less than that in bottom seawater the extent of removal in these fluids is at least 30 and in some hydrothermal systems dissolved phosphate is removed completely from the circulating fluid evidence for the removal of phosphate in each of six ridge flank hydrothermal systems is based on systematic variations in porewater profiles of phosphate and speeds of porewater flow the extent of removal is 80 in these ridge flank systems these removal processes are recorded in the basaltic crust as an increase in p concentration that coincides with an increase in extent of alteration and content of ferric iron phosphate also is removed in hydrothermal plumes by coprecipitation with fe oxyhydroxide particles which eventually deposit on the seafloor each of these hydrothermal processes results in a flux of p into the oceanic crust bottom seawater flow through ridge axis hydrothermal systems removes at most 0 4 of the preindustrial dissolved riverine flux of p while ridge flanks remove at least 5 but less than 50 of the dissolved riverine flux consistent with p data from deep sea drilling project dsdp sites 417 and 418 removal of phosphate by coprecipitation with fe rich particles in hydrothermal plumes along ridge axes accounts for 18 33 of the dissolved riverine flux thus hydrothermal systems remove about 50 of the preindustrial dissolved riverine flux of phosphate we have included these new estimates in a revised budget for oceanic p

stable isotope geochemical study of pamukkale travertines new evidences of low temperature non equilibrium calcite water fractionation abstract in this paper we present the first detailed geochemical study of the world famous actively forming pamukkale and karahayit travertines denizli basin sw turkey and associated thermal waters sampling was performed along downstream sections through different depositional environments vent artificial channel and lake terrace pools and cascades of proximal slope marshy environment of distal slope 13 c travertine values show significant increase from 6 1 to 11 7 pdb with increasing distance from the spring orifice whereas the 18 o travertine values show only slight increase downstream from 10 7 to 9 1 pdb mainly the co 2 outgassing caused the positive downstream shift 6 in the 13 c travertine values the high 13 c values of pamukkale travertines located closest to the spring orifice not affected by secondary processes suggest the contribution of co 2 liberated by thermometamorphic decarbonation besides magmatic sources based on the gradual downstream increase of the concentration of the conservative na k cl evaporation was estimated to be 2 5 which coincides with the moderate effect of evaporation on the water isotope composition stable isotopic compositions of the pamukkale thermal water springs show of meteoric origin and indicate a local meteoric water line of denizli basin to be between the global meteoric water line craig 1961 and western anatolian meteoric water line imsek 2003 detailed evaluation of several major and trace element contents measured in the water and in the precipitated travertine along the pamukkale mm section revealed which elements are precipitated in the carbonate or concentrated in the detrital minerals former studies on the hungarian egerszalok travertine kele et al 2008a b 2009 had shown that the isotopic equilibrium is rarely maintained under natural conditions during calcite precipitation in the temperature range between 41 and 67 c in this paper besides the detailed geochemical analyses along downstream sections we present new evidences of non equilibrium calcite water fractionation in lower temperature range 13 3 to 51 3 c our measurements and calculations on natural hot water travertine precipitations at pamukkale and egerszalok revealed that the 18 o travertine is equal with the 18 o hco3 at the orifice of the thermal springs which means that practically there is no oxygen isotope fractionation between these two phases high rate of co 2 degassing with rapid precipitation of carbonate could be responsible for this as it was theoretically supposed by o neil et al 1969 thus for the determination of the deposition temperature of a fossil travertine deposit we propose to use the water bicarbonate oxygen isotope equilibrium fractionation instead of the water travertine fractionation which can result 8 9 c difference in the calculated values our study is the first detailed empirical proof of o neil s hypothesis on a natural carbonate depositing system the presented observations can be used to identify more precisely the deposition temperature of fossil travertines during paleoclimate studies

rare earth element and sr nd isotope geochemistry of phosphatic rocks in neoproterozoic ediacaran doushantuo formation in zhangcunping section from western hubei province south china abstract phosphatic rocks are widely distributed in neoproterozoic ediacaran doushantuo formation in yangtze platform south china in this study we examined samples from the zhangcunping section in western hubei province with major element rare earth element ree and sr nd isotopic analyses on the phosphorites and the host dolostone rocks we employed an acid leaching method to separate the carbonate acetic acid leachable and phosphate hydrochloric acid leachable fractions in all the samples the geochemical differences between the different fractions can be recognized based on the p2o5 ree contents and sr nd isotopic characteristics the carbonate fractions in the rocks display low total ree concentrations with seawater like ree patterns super chondritic y ho ratios moderate negative ce anomalies and positive eu anomalies indicating these carbonates have retained the signatures of paleo seawater on the contrary the phosphate fractions display high total ree concentrations with hat shaped ree patterns generally lower y ho ratios weak negative ce anomalies and positive eu anomalies which may have recorded the features of diagenetic fluids negative ce anomalies and positive eu anomalies displayed in the carbonate fractions of the studied samples may also indicate the anoxic environments of ocean basins in south china during the deposition of the neoproterozoic ediacaran doushantuo formation a geochemical comparison between lower phosphorite layer and upper phosphorite layer indicates a greater degree of diagenesis occurred in the lower phosphorite layer than the upper phosphorite layer the negative end t values of the samples suggest continental crustal sources for the rees and the lower values in the phosphorite samples 6 9 to 6 0 than the dolostone samples 5 5 to 3 8 may suggest different processes for them and it is likely that the rees in the phosphorites have been modified by diagenetic fluids with ree contributions of pore fluids derived from the clastic silicates in the strata which generally have lower end t values whereas the dolostone took the rees from the ambient seawater mainly

a comparison of early paleogene export productivity and organic carbon burial flux for maud rise weddell sea and kerguelen plateau south indian ocean 1 marine biological productivity has been invoked as a possible climate driver during the early paleogene through its potential influence on atmospheric carbon dioxide concentrations however the relationship of export productivity the flux of organic carbon c from the surface ocean to the deep ocean to organic c burial flux the flux of organic c from the deep ocean that is buried in marine sediments is not well understood we examine the various components involved with atmosphere to ocean c transfer by reconstructing early paleogene carbonate and silica production using carbonate and silica mass accumulation rates mars export productivity using biogenic barium bio ba mars organic c burial flux using reactive phosphorus p mars redox conditions using uranium and manganese contents and the fraction of organic c buried relative to export productivity using reactive p to bio ba ratios our investigations concentrate on paleocene eocene sections of sites 689 690 from maud rise and site 738 from kerguelen plateau in both regions export productivity organic c burial flux and the fraction of organic c buried relative to export productivity decreased from the paleocene early eocene to the middle eocene a shift is indicated from an early paleogene two gyre circulation in which nutrients were not efficiently recycled to the surface via upwelling in these regions to a circulation more like the present day with efficient recycling of nutrients to the surface ocean export productivity was enhanced for kerguelen plateau relative to maud rise throughout the early paleogene possibly due to internal waves generated by the plateau regardless of gyre circulation

evolution from an oblique subduction back arc mobile belt to a highly oblique collisional margin the cenozoic tectonic development of thailand and eastern myanmar

brunswick subduction complex in the canadian appalachians record of the late ordovician to late silurian collision between laurentia and the gander margin of avalon the brunswick subduction complex in the new brunswick part of the canadian appalachians records the late ordovician to late silurian collision between laurentia and the gander margin of avalon the brunswick complex is anomalously well preserved compared with equivalent rocks and structures elsewhere owing to its unique position in the deepest part of the quebec reentrant of the laurentian margin this part of the margin experienced less underthrusting and exhumation and overprinting by orogen parallel faulting than the adjacent promontories where collision started earlier the early southeast to east vergent thrust related structures represent a progressive d1 deformation that formed in response to northwestward subduction of the previously extended gander margin and subsequent tectonic unroofing of the subduction complex the original shallow northwestward dipping envelope to s1 was deformed in the late silurian by d2 upright folds and associated shear zones into a steep belt during terminal collision the d2 structures probably formed in response to sinistral transpression together d1 and d2 indicate that convergence was oblique and sinistral most rocks incorporated in the subduction complex formed in the tetagouche back arc basin that evolved from rifting of an arenig magmatic arc built on the gander margin into a wide marginal basin subduction was initiated in the late ordovician 455 ma in the back arc basin following collision of the middle ordovician popelogan arc with laurentia in the caradoc shortly after its opening in the late arenig 473 ma the closure history of the iapetus ocean involved more than one subduction zone and arc continent collision and rivals the southwestern pacific ocean in its complexities

taconian orogeny in the new england appalachians collision between laurentia and the shelburne falls arc tectonic models of the ordovician taconian orogeny in western new england usually invoke a collision between the laurentian margin and a magmatic arc identified as the bronson hill arc however in central massachusetts and southern new hampshire rocks in the bronson hill arc are 454 to 442 ma and therefore younger than much of the taconian deformation and metamorphism in western new england and eastern new york which began by 470 ma u pb and single grain evaporation zircon ages combined with geochemical analyses reveal the presence of an older magmatic arc the shelburne falls arc that formed west of the bronson hill arc at 485 to 470 ma the shelburne falls arc formed above an east dipping subduction zone by the early ordovician the taconian orogeny was the result of the collision between laurentia and the shelburne falls arc beginning ca 475 to 470 ma the younger bronson hill arc formed above a west dipping subduction zone that developed along the eastern edge of the newly accreted terrane during the final stages of and subsequent to the taconian orogeny the taconian orogeny ended when plate convergence between laurentia and iapetus was accommodated by the newly developed west dipping subduction zone instead of by crustal shortening in the taconian thrust belt the tectonic history of the new england appalachians is inconsistent with a middle ordovician collision between laurentia and the proto andean margin of gondwana

paleomagnetism of the pennington mountain terrane a near laurentian back arc basin in the maine appalachians paleomagnetic studies of volcanic terranes in the appalachians provide quantitative data on the ordovician paleogeography of the iapetus ocean new paleomagnetic results from submarine volcanics of the middle to late ordovician winterville formation of maine further constrain the evolution of iapetus ten sites yield a tilt corrected direction of d i 327 21 95 9 3 k 27 9 the corresponding paleomagnetic pole calculated for the average site location 46 8 n 291 3 e is located at 26 n 148 e d p 5 d m 10 a 95 7 7 a silurian conglomerate frenchville formation test is inconclusive due to a strong present day field overprint which obscures any primary remanence the presence of a positive tilt test however supports the conclusion that the characteristic magnetization of the winterville formation is a prefolding primary magnetization an ordovician paleolatitude of 111 5 for the pennington mountain terrane of northern maine is indistinguishable from that of the laurentian margin 15 20 during the middle to late ordovician the paleolatitude of the pennington mountain terrane is also similar to but slightly more equatorial than that of the previously studied bluffer pond formation of the nearby munsungun terrane 18 9 we conclude that the ordovician pennington mountain and munsungun volcanic terranes of maine were formed and acquired their characteristic magnetization near the laurentian margin the paleolatitudes of these terranes are also similar to that obtained from the stacyville volcanics of the more outboard lunksoos terrane 20 8 but they contrast strongly with the ordovician miramichi terrane of northern new brunswick that yielded a paleolatitude of 51 21 16 these results from maine support the presence of one or more backarc basins adjacent to the laurentian margin during the middle to late ordovician

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

an intermediate complexity model for simulating marine biogeochemistry in deep time validation against the modern global ocean we present a new high resolution 1 d intermediate complexity box model icbm of ocean biogeochemical processes for paleoceanographic applications the model contains 79 reservoirs in three regions that should be generally applicable throughout much of earth history 1 a stratified gyre region 2 a high latitude convective region and 3 an upwelling region analogous to those found associated with eastern boundary currents transport processes are modeled as exchange fluxes between boxes and by eddy diffusion terms significant improvement in the representation of middepth oxygen budgets was achieved by implementing nonlocal mixing between the high latitude surface and gyre thermocline reservoirs the biogeochemical submodel simulates coupled c n p o and s systematics with explicit representation of microbial populations using a process based approach primary production follows redfield stoichiometry while water column remineralization is depth and redox couple dependent settling particulate organic matter is incorporated into a benthic submodel that accounts for burial and remineralization the c p ratio of burial depends on bottom water oxygen denitrification takes place both by classical and anammox pathways the icbm was tested against modern oceanographic observations from the global ocean data analysis project joint global ocean flux study and other databases comparisons of model output with circulation tracers including salinity cfc 12 and radiocarbon permit a test of the physical exchange scheme vertical profiles of biogeochemically reactive components in each of the three regions are in good agreement with observations under modern conditions the upwelling zone displays a pronounced oxygen minimum zone and water column denitrification while these are not present in the high latitude or gyre regions model generated global fluxes also compare well to independent estimates of primary production burial and phosphorous and nitrogen cycling the icbm appears to adequately simulate the long term kyr evolution of several biogeochemical cycles and improves on previous box models in several important ways in a companion paper the model s performance under euxinic conditions is tested against modern black sea data the simple and adaptable structure of the model should make it applicable to a wide range of paleoceanographic problems the model source code is available in matlabtm 7 m files provided as auxiliary material

geochemistry and u pb zircon age of comenditic metafelsites of the tibbit hill formation quebec appalachians metafelsites in waterloo area quebec represent the only known silicic volcanic rocks in the predominantly basaltic tibbit hill formation low grade metamorphism accompanied by hydration and albitization has converted the felsic volcanic rocks mainly to muscovite quartz albite schists the volcanic parent of these metafelsites was formed partly as lava flows and partly as tuffs the principal compositional type was a comendite a component of intermediate rocks is also present but its extent is undetermined and probably minor u pb zircon studies of the metafelsites have yielded a reliable age of this early cambrian age is probably representative of the age of the tibbit hill formation as a whole the tibbit hill formation accumulated at one of the clearest examples of a rrr rift rift rift triple junction the sutton mountains triple junction of the continental rift system formed as a prelude to the opening of the iapetus ocean its volcanic rocks are products of the youngest major episode of rift rela

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

sedimentary organic carbon to phosphorus ratios as a redox proxy in quaternary records from the mediterranean abstract in this study organic carbon to organic phosphorus c org p org and total phosphorus c org p tot ratios as bottom water redox proxies are explored for two eastern mediterranean sediment records extending back 600 700 kyrs cores kc19c 19 6 m long 2750 m water depth and kc01b 37 0 m long 3643 m water depth contain numerous organic rich layers sapropels throughout the two cores variations found in the c org p ratios correspond to those for other redox proxies such as total s contents and v al ratios accordingly these are interpreted as variations in bottom water oxygenation and inter sapropel redox variability in core kc19c the original c org p signals seem to have been preserved despite intense post depositional sulfidization high resolution p fractionation data of sapropel s5 from a third core ps25pc 3304 m water depth showing high and relatively stable c org p org ratios indicate that sapropel s5 at this deep location was deposited under permanently reducing conditions while p regeneration from organic matter was intense net p burial increased in the sapropel due to enhanced burial of inorganic calcium phosphate likely biogenic ca p sediment p contents and c org p tot ratios in s5 are variable reflecting short term changes in marine conditions productivity redox and sediment chemistry the c org p org and c org p tot ratios thus provide valuable insight into paleoceanographic conditions and pathways of p cycling for mediterranean sediment records extending back at least 600 700 kyrs

a 400 kyr record of combustion oxygen demand in the western equatorial pacific evidence for a precessionally forced climate response we have developed a combustion analysis technique for sediments which measures the amount of o2 consumed by the reduced species we have measured this quantity which we call combustion oxygen demand cod on a carbonate rich sediment core from the ontong java plateau in the western equatorial pacific back to marine oxygen isotope stage 11 the precision of the cod technique is 6 3 mol o2 g 1 which corresponds to 0 0076 wt corg assuming oxidation of organic carbon dominates the signal the cod time series is characterized by values which are about twice as high during glacials as during interglacials the largest shift occurring from 401 mol o2 g 1 in midstage 6 to 144 mol o2 g 1 at 5e and is coherent with the oxygen isotope curve of globigerinoides sacculifer in the same core at the milankovitch frequencies of 100 and 41 kyr pronounced variations in the 19 23 kyr band suggest that the climate of the western equatorial pacific is sensitive to precessional forcing a response not apparent from other records obtained in this region

the extension of grenville basement beneath the northern appalachians results from the quebec maine seismic reflection and refraction surveys from 1983 to 1984 the united states geological survey and the geological survey of canada undertook a series of seismic experiments to determine the crustal structure of the appalachian mountain belt in maine and southeast quebec these experiments included four deep crustal seismic reflection profiles perpendicular to the strike of regional geological trends and several high resolution refraction wide angle reflection profiles both parallel and perpendicular to strike here the data recorded in quebec and the northwest part of maine are interpreted in conjunction with existing reflection profiles from quebec synthetic seismogram calculations in laterally varying media are used to model the refraction wide angle reflection data while reprocessing migration and attribute plotting are used in the interpretation of the reflection data a major zone of reflections extending over a distance exceeding 200 km can be traced from shallow depths beneath the st lawrence lowlands southeast to about 25 km depth beneath the southeast edge of the chain lakes massif this zone of reflections is interpreted as a master decollement separating autochthonous grenville basement from overlying allochthonous rocks of the appalachian orogen including foreshortened miogeoclinal rocks the remnants of one or more magmatic arcs the connecticut valley gaspe synclinorium and the chain lakes massif in the vicinity of the chain lakes massif extension has caused grenville basement to be thinned by as much as 40 reflections from the decollement show strong layering and evidence for basement faulting associated with the guadeloupe and other faults normal incidence and wide angle reflections are observed to be almost continuous beneath the baie verte brompton line and connecticut valley gaspe synclinorium indicating that the baie verte brompton line is confined to the upper crust the connecticut valley gaspe synclinorium is characterized by p wave velocities of about 5 3 km s 1 and is shown to be a shallow structure with a maximum depth of about 3 km rock velocities immediately below the connecticut valley gaspe synclinorium are typical of chain lakes material 6 1 km s 1 a new model for the tectonic development of the region is proposed in which all pre silurian units between the baie verte brompton line and the southeastern edge of the chain lakes massif are allochthonous and confined to the upper crust we infer that the chain lakes massif volcanics of the ascot weedon formation and associated deeper crustal rocks were thrust over grenvillian basement as a composite unit and may now underlie parts of the connecticut valley gaspe synclinorium

the global ocean flux of particulate organic carbon areal distribution and magnitude the magnitude and distribution of the particulate organic carbon poc rain rate to the seafloor in the atlantic pacific and indian ocean basins between 61 n and 61 s has been estimated from benthic oxygen flux estimates for water depths 1000 m only the calculation utilizes the extensive data sets of sedimentary organic carbon caco3 and accumulation rate to extrapolate between individual benthic flux measurement sites using an empirically derived correlation between the seafloor oxygen flux and these parameters the poc flux through the 1000 m depth horizon was then estimated from published correlations between sediment trap determined fluxes and water depth total oxygen utilization in the deep ocean is estimated to be 1 2 1014 mol o2 yr 1 a value that agrees well with previous estimates which were based on surface water primary productivity sediment trap and depth relationships and with deep water respiration rates estimated from apparant oxygen utilization aou 14c relationships on the basis of the derived global ocean flux distribution it is concluded that 1 dissolved organic carbon doc inputs are not required to account for estimated deep water respiration rates 2 the majority of the poc input to the deep ocean occurs within 30 of the equator 3 the proportion of primary production that reaches the deep sea does not vary greatly with latitude 4 gyre and continental margin regions contribute roughly equally to the deep poc flux with a relatively minor contribution from the equatorial divergence region 5 of the estimated 7 2 1013 mol c yr 1 of poc that sinks below the 1000 m depth horizon 45 3 3 1013 mol c yr 1 reaches the seafloor where it is oxidized 6 when normalized to basin area average deep flux rates in the atlantic and pacific are similar while highest rates are observed in the indian ocean and 7 the results can be fully reconciled only if the benthic flux of doc is significantly less than the benthic o2 flux

phosphate regeneration from sediments of the peru continental margin by dissolution of fish debris generally oxidative regeneration of phosphate from anoxic sediments is by microbially mediated sulfate reduction processes stoichiometric modelling of such reactions takes into consideration varying proportions of decomposable organically bound p to account for the ratios among nutrients in depth concentration profiles of near surface sediments new results of interstitial water composition from sediments underlying the water masses influenced by coastal upwelling of the eastern boundary current system off peru indicate that dissolution of phosphatic fish debris represents a mechanism for remineralization of phosphate comparable to or larger in magnitude than that by oxidative regeneration of organically bound p dissolved interstitial phosphate from fish debris is revealed by an excess amount of phosphate over that predicted from a simple stoichiometric oxidative regeneration model and by anomalously high dissolved interstitial fluoride concentrations phosphate flux estimates based on diffusion from the sediment suggest that this mechanism may generate up to 10 of the nutrient pool in the waters of the peru undercurrent partitioning of p among the two sources reveals further that fish debris phosphate is about four times more important than organically bound p in nutrient generation from sediments of the peru continental margin not only does this mechanism of regeneration affect the nutrient cycling but may also control widespread phosphorite formation in this area

middle eocene to early oligocene paleoceanography from agulhas ridge southern ocean ocean drilling program leg 177 site 1090 1 the agulhas ridge off the tip of africa between the atlantic and indian oceans is ideally located to capture the evolution of paleogene early neogene circulation patterns associated with global cooling multiproxy records of productivity biogenic barium baex opal caco3 mass accumulation rates mars nutrient and organic carbon burial reactive phosphorus pr mars and redox state of deep waters u enrichment from ocean drilling program odp site 1090 reflect hydrographic shifts in this region between the middle eocene and early oligocene 39 33 ma several peaks in increased export productivity and burial of organic matter occurred within the late eocene 36 5 34 and 33 7 ma which along with surface hydrologic conditions favoring opaline organisms over calcareous organisms could have aided in the draw down of pco2 to a threshold level that facilitated large ice sheet development on antarctica in the earliest oligocene our multiproxy approach illustrates the importance of vertical as well as spatial hydrographic reorganization in amplifying or driving climatic cooling of the middle eocene to early oligocene by facilitating increases in the relative or absolute burial of organic carbon

progressive palaeoenvironmental change during the late barremian early aptian as prelude to oceanic anoxic event 1a evidence from the gorgo a cerbara section umbria marche basin central italy abstract during oceanic anoxic event 1a oae 1a 120 ma li et al 2008 organic carbon rich layers were deposited in marine environments under anoxic conditions on a global scale in this study palaeoenvironmental conditions leading to this event are characterised by studying the upper barremian to the lower aptian succession of the gorgo a cerbara section central italy for this an integrated multi proxy approach 13ccarb 13corg 18o phosphorus total organic carbon toc bulk rock mineralogy as well as redox sensitive trace elements rstes has been applied during the late barremian thin organic rich layers occur episodically and associated corg ptot ratios indicate the presence of intermittent dysoxic to anoxic conditions coarse correlations are observed between toc p and biogenic silica contents indicating links between p availability productivity and toc preservation however the corresponding 13ccarb and 18o records remain quite stable indicating that these brief periods of enhanced toc preservation did not have sufficient impact on the marine carbon reservoir to deviate 13c records around the barremian aptian boundary toc enriched layers become more frequent these layers correlate with negative excursions in the 13ccarb and 13corg records possibly due to a warming period as indicated by the 18o record during the earliest aptian this warming trend is reverted into a cooling trend which is then followed by an important warming step near the onset of oceanic anoxic event 1a oae 1a during this time period organic rich intervals occur which are characterised by the progressive increase in rste the warming step prior the onset of oae 1a is associated with the well known negative spike in 13ccarb and 13corg records an important peak in p accumulation rste enrichments and corg ptot ratios indicating the prevalence of anoxic conditions the selli level itself may document a cooling phase rste enrichments and corg ptot ratios confirm the importance of anoxic conditions during oae 1a at this site the gorgo a cerbara section is interpreted to reflect the progressive impact of palaeoenvironmental change related to the formation of the ontong java plate basalt plateau which started already around the barremian aptian boundary and culminated into oae 1a

age and setting of the bronson hill magmatic arc a re evaluation based on u pb zircon ages in southern new england new u pb zircon ages of selected rocks from the bronson hill anticlinorium in southern new england are as follows microcline gneiss of the dry hill gneiss in the pelham dome believed to be metamorphosed alkali rhyolite is confirmed as late proterozoic yielding an age of 613 3 ma another sample shows strong evidence of zircon inheritance with a minimum mean age of 1402 ma plagioclase rich gneisses with associated amphibolites swanzey pauchaug monson and fourmile gneisses now believed to represent metamorphosed intrusive igneous rocks yield ages from 454 to 442 3 2 ma thus ranging from early late through latest ordovician consistent with other absolute ages of the oliverian plutonic series in the region quartz phyric rhyolite from the upper member of the ammonoosuc volcanics and rhyolite tuff from the partridge formation are dated at 453 2 ma and 449 3 2 ma respectively indicating that eruption of felsic lavas in the overlying volcanic section spanned an interval of approximately 4 m y additional zircon ages are reported from a crosscutting but deformed tonalite dike in the swanzey gneiss 381 3 ma and a coarse grained gabbro from the prescott intrusive complex 407 3 2 ma intrusive into the partridge formation metamorphic overprinting of the region during both the acadian and alleghanian orogenies is indicated by u pb titanite ages of 357 5 ma and 292 5 ma from a tonalite gneiss on prescott peninsula and the dry hill gneiss respectively the above ages and other zircon ages as well as petrography and geochemistry of the fourmile monson swanzey pauchaug and other plagioclase rich gneisses of the bronson hill anticlinorium suggest that they represent the plutonic root of a calc alkaline magmatic arc at least 250 km long that was produced partly or entirely on a continental margin in late ordovician time ca 454 442 ma the physically overlying cover sequence of chemically different tholeiitic arc volcanic and sedimentary rocks of the ammonoosuc volcanics and partridge formation previously thought to rest unconformably on the plagioclase rich plutonic gneisses is now shown to have had a magmatic history overlapping with them the zircon ages in the plutonic gneisses and the cover sequence indicate that both are the same age or slightly younger than the late ordovician caradocian emplacement of the giddings brook slice of the taconian allochthons and too young to have formed above an early and medial ordovician subduction zone

pliocene near trench magmatism in southern chile a possible manifestation of ridge collision eight shallow level intrusions and an ophiolite complex have recently been discovered in a remote region along the pacific coast of southern chile known as the taitao peninsula the magmatic rocks are found only 10 to 15 km from the buried extension of the peru chile trench the ophiolite body includes serpentinized ultramaflc rocks gabbro dikes and an interbedded sequence of volcanic and marine sedimentary rocks more regionally distributed granodiorite plutons and porphyritic stocks and sills intrude pre late jurassic basement as well as tertiary marine sequences of the south american forearc k ar ages of 3 5 to 4 0 ma of the ophiolite and other intrusions suggest that these rocks represent a short lived pulse of pliocene magmatism directly seaward of the taitao peninsula a segment of the chile rise bounded by the tres monies and taitao fracture zones collided with the chilean forearc and was subducted about 2 5 to 4 0 ma because of this good spatial and temporal correlation the magmatic activity of the taitao peninsula is likely to be a direct result of ridge subduction

periodic mid cretaceous oceanic anoxic events linked by oscillations of the phosphorus and oxygen biogeochemical cycles 1 a series of oceanic anoxic events oaes occurred in the mid cretaceous warm period 120 80 ma that have been linked with high rates of organic carbon burial warm high and low latitude temperatures and sea level changes oaes have been studied individually but a causal mechanism that connects them has been lacking we show that peaks in phosphorus accumulation in marine sediments broadly coincide with oaes 1a 1b 1d 2 and 3 and exhibit a 5 6 myr periodicity which for reactive p is prominent over 100 80 ma oxic anoxic oscillations of this frequency are also found in a model of the coupled n p c and o2 biogeochemical cycles these oscillations are maintained by positive feedbacks between phosphate concentration biological productivity and anoxia in the global ocean and counteracting but slower negative feedbacks involving changes in atmospheric oxygen an increase in phosphorus weathering rate above a critical threshold can shift the system into self sustaining oscillation this could have been caused by tectonic and volcanic forcing increasing atmospheric co2 and global warmth 120 80 ma augmented by the rise of flowering plants around 100 ma with a plausible forcing scenario we are able to reproduce the approximate timing of oaes 1a 1b 1d 2 and 3 in the model

evolution of a permian intraoceanic arc trench system in the solonker suture zone central asian orogenic belt china and mongolia abstract the identification of a fossil arc trench system from the ophiolite decorated solonker suture zone in the southernmost central asian orogenic belt caob enables us to constrain the timing of pre subduction extension ca 299 290 ma subduction initiation ca 294 280 ma ridge trench collision ca 281 273 ma and slab break off ca 255 248 ma in the permian a fraction of proto arc crust ca 45 km long up to 8 km wide is preserved as a volcanic plutonic sequence and is juxtaposed against a wide ca 30 80 km forearc melange this proto arc crust comprises two distinct magma series island arc tholeiite iat and mid ocean ridge basalt morb both of which have strong supra subduction zone ssz geochemical signatures zircons from a gabbro and a plagiogranite yielded weighted mean 206pb 238u ages of 284 0 4 0 and 288 0 6 0 ma the forearc melange consists of numerous ophiolite fragments and continental margin derived olistoliths blocks that predate the ophiolite the olistoliths are best represented by a gabbroic block 291 8 2 3 ma that contains granite xenoliths 312 6 1 8 and 313 6 3 1 ma other dated blocks include a trondhjemite 323 9 2 7 ma a gabbro 296 6 1 7 ma and a tonalite 294 9 2 4 ma small bodies of diabase andesite and diorite in the forearc melange exhibit a wide variety of geochemical signatures we dated zircons from an n morb like diabase 274 4 2 5 ma an e morb like diabase 252 5 2 3 ma a transitional sanukitoid adakite andesite 250 2 2 4 ma a sanukitoid high mg diorite 251 8 1 1 ma and an anorthosite 252 2 1 7 ma the n morb like diabase contains ca 301 394 ma zircon xenocrysts suggesting assimilation of trench sediments when a spreading ridge intersected a trench the other dated rocks simultaneously formed near the permian triassic boundary and captured abundant zircon xenocrysts ca 269 295 ma ca 301 495 ma and ca 923 2501 ma our new formation ages constrain a magmatic episode in response to slab break off beneath a fossil forearc in a young post collisional setting and the youngest xenocryst ages ca 269 273 ma may define the maximum depositional age of trench sediments

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

paleomagnetism of the ordovician bluffer pond formation paleogeographic implications for the munsungun terrane of northern maine the munsungun area of northern maine is an early paleozoic terrane within the central mobile belt cmb of the northern appalachians the bluffer pond formation of the munsungun terrane is composed primarily of pillow basalt and gabbro with minor intercalated sediments and has a maximum thickness of 1230 m this unit is of early late ordovician caradocian age based on paleontological data and folding most likely occurred during the devonian acadian orogeny this region has been metamorphosed to subgreenschist facies samples for paleomagnetic study have been obtained from 15 sites of pillow basalt and seven sites of gabbro within the bluffer pond formation natural remanent magnetization nrm directions are similar to the expected present day field direction and are interpreted to be strongly affected by a viscous overprint detailed stepwise thermal demagnetization fails to adequately resolve a partial overprint direction with intermediate blocking temperature but stable endpoints combined with great circles do isolate a characteristic high temperature component carried by magnetite as indicated by unblocking temperatures and rock magnetic experiments after tilt correction the formation mean calculated from pillow basalt sites only is d 339 i 33 k 12 95 14 n 11 with a corresponding paleopole of 23 n 133 e p 9 m 16 calculated for an average site location of 46 5 n 291 e when both pillow basalt and gabbro sites are used to calculate a tilt corrected formation mean the result is d 339 i 28 k 12 95 12 n 14 and this characteristic component passes a tectonic tilt test the calculated paleopole 26 n 134 e p 7 m 13 from pillows and gabbros falls near but not on the ordovician apparent polar wander path segment for north america and yields a paleolatitude 18 9 s similar to that of the lunksoos terrane which is located farther to the southeast within the cmb of maine the laurentian margin at this time was located at paleolatitudes of 15 20 s the paleogeographic implication of this result is that the munsungun terrane was located near the laurentian margin within the iapetus ocean and this near continent location is consistent with a marginal or back arc basin tectonic environment for the extrusion of the bluffer pond volcanics

subduction of a spreading ridge within the bangong co nujiang tethys ocean evidence from early cretaceous mafic dykes in the duolong porphyry cu au deposit western tibet abstract the intrusion of mafic dykes into a near trench accretionary prism and continental margin magmatism with characteristics that differ from those of adjacent arc magmatism are direct manifestations of the subduction of a spreading ocean ridge and the formation of a slab window in this paper we investigated mafic dykes intruded into the accretionary prism that hosts the duolong porphyry cu au deposit dcad of western tibet la icp ms analysis of u pb in zircon indicates that the dykes formed during the early cretaceous 126 127 ma the dykes are characterized by ehf t values from 2 44 to 11 8 twenty nine mafic dyke samples were divided into three groups based on their locations and geochemical compositions group i has nb 8 31 10 2 ppm nb la 0 71 1 20 and nb u 21 4 37 9 group ii has nb 40 5 52 6 ppm nb la 0 84 1 58 and nb u 18 8 47 8 and group iii has nb 65 7 105 ppm nb la 1 35 2 08 and nb u 36 5 73 8 group i is classified as nb enriched basalts enbs whereas groups ii and iii are classified as high nb basalts hnbs both the enbs and hnbs were derived from an adakite metasomatized mantle wedge that subsequently underwent crystallization of olivine and clinopyroxene the compositional variations of the studied dykes resulted mainly from mantle source heterogeneity the volume of the slab melts gradually increases from group i enbs to group ii hnbs and group iii hnbs leading to gradually increasing incompatible element concentrations considering their geochemical characteristics and field relationships as well as the unique characteristics of continental margin magmatism in the dcad we propose that the dykes emplaced in an extensional accretionary prism were derived from the northward subduction of a spreading ridge in the bangong co nujiang tethys ocean during the early cretaceous the ridge subduction event was also responsible for the generation of coeval adakites intermediate felsic intrusions the maierze bimodal volcanic rocks as well as the metallogenesis of the dcad

beyond methane towards a theory for the paleocene eocene thermal maximum abstract extreme global warmth and an abrupt negative carbon isotope excursion during the paleocene eocene thermal maximum petm have been attributed to a massive release of methane hydrate from sediments on the continental slope 1 however the magnitude of the warming 5 to 6 c 2 3 and rise in the depth of the ccd 2 km 4 indicate that the size of the carbon addition was larger than can be accounted for by the methane hydrate hypothesis additional carbon sources associated with methane hydrate release e g pore water venting and turbidite oxidation are also insufficient we find that the oxidation of at least 5000 gt c of organic carbon is the most likely explanation for the observed geochemical and climatic changes during the petm for which there are several potential mechanisms production of thermogenic ch4 and co2 during contact metamorphism associated with the intrusion of a large igneous province into organic rich sediments 5 is capable of supplying large amounts of carbon but is inconsistent with the lack of extensive carbon loss in metamorphosed sediments as well as the abrupt onset and termination of carbon release during the petm a global conflagration of paleocene peatlands 6 highlights a large terrestrial carbon source but massive carbon release by fire seems unlikely as it would require that all peatlands burn at once and then for only 10 to 30 ky in addition this hypothesis requires an order of magnitude increase in the amount of carbon stored in peat the isolation of a large epicontinental seaway by tectonic uplift associated with volcanism or continental collision followed by desiccation and bacterial respiration of the aerated organic matter is another potential mechanism for the rapid release of large amounts of co2 in addition to the oxidation of the underlying marine sediments the desiccation of a major epicontinental seaway would remove a large source of moisture for the continental interior resulting in the desiccation and bacterial oxidation of adjacent terrestrial wetlands

coccolithophore productivity response to greenhouse event of the paleocene eocene thermal maximum abstract during the paleocene eocene thermal maximum petm rapid release of isotopically light c to the ocean atmosphere system elevated the greenhouse effect and warmed temperatures by 5 7 c for 105 yr the response of the planktic ecosystems and productivity to the dramatic climate changes of the petm may represent a significant feedback to the carbon cycle changes but has been difficult to document we examine sr ca ratios in calcareous nannofossils in sediments spanning the petm in three open ocean sites as a new approach to examine productivity and ecological shifts in calcifying plankton the large heterogeneity in sr ca among different nannofossil genera indicates that nannofossil sr ca reflects primary productivity driven geochemical signals and not diagenetic overprinting elevated sr ca ratios in several genera and constant ratios in other genera suggest increased overall productivity in the atlantic sector of the southern ocean during the petm dominant nannofossil genera in tropical atlantic and pacific sites show sr ca variations during the petm which are comparable to background variability prior to the petm despite acidification of the ocean there was not a productivity crisis among calcifying phytoplankton we use the pandora ocean box model to explore possible mechanisms for petm productivity change if independent proxy evidence for more stratified conditions in the southern ocean during the petm is robust then maintenance of stable or increased productivity there likely reflects increased nutrient inventories of the ocean increased nutrient inventories could have resulted from climatically enhanced weathering and would have important implications for burial rates of organic carbon and stabilization of climate and the carbon cycle

relation between sedimentation rate and burial of organic phosphorus and organic carbon in marine sediments organic carbon and organic phosphorus concentrations in marine sediment cores with known sedimentation rates were determined and collected from the literature with the exception of organic rich sediments from upwelling areas organic phosphorus concentrations in marine sediments do not correlate linearly with organic carbon concentrations the c p ratios of organic matter buried in marine sediments vary systematically with sedimentation rate over the range studied 0 0001 to 2 5 cm y low c p ratios 200 atomic occur in sediments with sedimentation rates both less than 0 002 cm y and greater than 1 cm y higher c p ratios up to 600 are found at intermediate sedimentation rates a simple steady state model is developed for the early diagenesis of organic carbon and organic phosphorus in marine sediments the processes included are sediment burial pore water diffusion and bacterial decomposition of organic matter by oxic respiration and sulfate reduction preferential regeneration of phosphorus relative to carbon is assumed to take place during oxic respiration the modeling shows that both organic matter preservation and the degree of elemental fractionation between phosphorus and carbon depend strongly on the overall sedimentation rate very high sedimentation rates coastal deltaic environment result in a good preservation of deposited organic matter with an initial c p ratio close to the redfield value at very slow sedimentation rates pelagic environment the oxidation of the sedimentary organic matter is nearly complete and produces a low c p residual organic material this residual organic matter may represent either refractory detrital organic compounds enriched in phosphorus or in situ synthesized low c p bacterial remains the high c p ratios at intermediate sedimentation rates slope and shelf environment reflect the preferential regeneration of phosphorus during the incomplete decomposition of the metabolizable organic matter

geochemistry of the boil mountain ophiolitic complex northwest maine and tectonic implications a coherent ophiolitic complex of pyroxenite serpentinite metagabbro mafic volcanics felsic volcanics and sediments crops out in nw maine adjacent to the chain lakes massif the complex here informally referred to as the boil mountain ophiolitic complex is about 500 m y old the volcanic sequence is not typical of ophiolites in that it contains a large proportion of felsic volcanics the mafic volcanics are divided into two geochemical groups a stratigraphically lower group is depleted in ti zr y cr and ree contents similar to basalts from supra subduction zone ophiolites an upper mafic group has trace element contents similar to normal mid ocean ridge basalts the felsic volcanics are mostly rhyolitic and similar to low k rhyolites found in the forearc of the marianas trench and in an island arc sequence in the klamath mountains california the flat ree patterns of the felsic volcanic rocks are similar to those found in siliceous rocks in the oman ophiolite the presence of thick sequences of felsic volcanics the abundance of pyroxenite the low ti zr and ree contents of some mafic rocks the flat ree patterns of the felsic volcanics and the composition of clinopyroxene all suggest the complex was formed in the vicinity of a subduction zone the complex may be correlated with ophiolitic fragments in the eastern part of the dunnage zone in newfoundland rather than the main ophiolite belt of the western appalachians

the ordovician volcanics of the elmtree belledune inlier and their relationship to volcanics of the northern miramichi highlands new brunswick an investigation of the geology and chemistry of the basic igneous rocks in the elmtree and belledune inliers in northern new brunswick shows that the bulk of the middle ordovician rocks of the ophiolitic fournier group are best interpreted as the products of volcanism and sedimentation in an extensive ensimatic back arc basin southeast of a volcanic arc the oceanic back arc basin igneous rocks form the basement to renewed arc related basaltic volcanism in late middle to late ordovician time the fournier group is separated from the structurally underlying shale dominated elmtree formation of the tetagouche group by an extensive tectonic melange which incorporates lenses of serpentinite mafic volcanic rocks and sedimentary rocks of both the tetagouche and fournier groups the mafic volcanic rocks in the elmtree formation correlate best with those intercalated with the lithologically similar sediments of the llandeilian caradocian boucher brook formation in the northern miramichi highlands the melang

phosphorus speciation and its bioavailability in sediments of the jiaozhou bay abstract phosphorus p is an important macronutrient that can limit primary productivity in coastal marine ecosystems in this study four sediment cores were collected in the jiaozhou bay to study the phosphorus forms and their bioavailability including exchangeable or loosely sorbed p ex p iron bound p fe p authigenic p ca p detrital p de p and organic p op which were separated and quantified using a sequential extraction method sedex the results showed that the concentration of total p tp in core sediments ranged from 6 23 to 10 46 mol g and inorganic p ip was the dominated p form fe p and de p were the main chemical forms of ip in core sediments the profile variation of op presented the most significant among the phosphorus forms whereas the concentrations of ex p fe p and ca p varied slightly with depth indicating that the transformation of ex p fe p ca p and op could occur during sedimentary p burial moreover the distribution of p species was influenced by many factors including terrigenous input biological processes organic matter degradation and increasing human activities high total organic carbon toc op ratio occurred in the jiaozhou bay ranging from 73 to 472 average 180 81 in core sediments which was caused by the increasing terrestrial organic matter the ratio of toc p reactive ranged from 24 to 101 average 46 15 in core sediments lower than the redfield ratio implying a surplus of sedimentary reactive p compared with toc potential bioavailable p bap accounted for about 28 2 60 8 average 47 1 7 4 of tp in core sediments and presented an increasing trend since 1980s which might be responsible for the shift of phytoplankton community composition during these decades

stratigraphic context geochemical and isotopic properties of magmatism in the siluro devonian inliers of northern maine implications for the acadian orogeny this paper reports detailed stratigraphic analysis whole rock geochemistry and nd isotopic ratios of basalts from the northern maine inliers these data place constraints on first order controversies about the tectonic conditions leading up to and during the early stages of the acadian orogeny in northern maine late silurian and early devonian stratigraphic sequences indicate a progressive change from shallow water and subaerial exposure ripogenus and the forks formations east branch group to a rapidly subsiding basin prior to the onset of acadian deformation subsidence was accompanied by mafic to intermediate volcanism of the west branch spider lake and fish pond volcanics and that continued with intrusion of the syn deformational greenville plutonic belt including the flagstaff lake igneous complex whose properties we report in this paper trace element geochemistry indicates that magmatism is transdiscriminant showing aspects of within plate volcanic arc and back arc affinities and nd isotopic ratios are moderately positive 2 3 to 3 8 indicating either an uncontaminated and moderately enriched mantle source or a depleted mantle source contaminated by continental crust four possible tectonic models of the acadian orogeny and the siluro devonian sedimentary volcanic sequences of northern maine are evaluated in the context of a subsiding basin associated with this magmatism developed on the amalgamated laurentian plate these include 1 slab detachment during southeast directed subduction of the laurentian continental margin 2 laramide style thrust basins above a shallow northwest dipping subduction zone 3 back arc extension followed by thin skinned shortening above a northwest dipping subduction zone and 4 moluccan style dual dipping subduction zones

phosphorus recycling and burial in baltic sea sediments with contrasting redox conditions in this study redox dependent phosphorus p recycling and burial at 6 sites in the baltic sea is investigated using a combination of porewater and sediment analyses and sediment age dating pb 21

redox sensitivity of p cycling during marine black shale formation dynamics of sulfidic and anoxic non sulfidic bottom waters abstract a high resolution geochemical record of a 120 cm black shale interval deposited during the coniacian santonian oceanic anoxic event 3 odp leg 207 site 1261 demerara rise has been constructed to provide detailed insight into rapid changes in deep ocean and sediment paleo redox conditions high contents of organic matter sulfur and redox sensitive trace metals cd mo v zn as well as continuous lamination point to deposition under consistently oxygen free and largely sulfidic bottom water conditions however rapid and cyclic changes in deep ocean redox are documented by short term 15 20 ka intervals with decreased total organic carbon toc s and redox sensitive trace metal contents and in particular pronounced phosphorus peaks up to 2 5 wt p associated with elevated fe oxide contents sequential iron and phosphate extractions confirm that p is dominantly bound to iron oxides and incorporated into authigenic apatite preservation of this fe p coupling in an otherwise sulfidic depositional environment as indicated by fe speciation and high amounts of sulfurized organic matter may be unexpected and provides evidence for temporarily non sulfidic bottom waters however there is no evidence for deposition under oxic conditions instead sulfidic conditions were punctuated by periods of anoxic non sulfidic bottom waters during these periods phosphate was effectively scavenged during precipitation of iron oxyhydr oxides in the upper water column and was subsequently deposited and largely preserved at the sea floor after 15 25 ka sulfidic bottom water conditions were re established leading to the initial precipitation of cds zns and pyrite subsequently increasing concentrations of h2s in the water column led to extensive formation of sulfurized organic matter which effectively scavenged particle reactive mo complexes thiomolybdates at site 1261 sulfidic bottom waters lasted for 90 100 ka followed by another period of anoxic non sulfidic conditions lasting for 15 20 ka the observed cyclicity at the lower end of the redox scale may have been triggered by repeated incursions of more oxygenated surface to mid waters from the south atlantic resulting in a lowering of the oxic anoxic chemocline in the water column alternatively sea water sulfate might have been stripped by long lasting high rates of sulfate reduction removing the ultimate source for hs production

authigenic apatite formation and burial in sediments from non upwelling continental margin environments abstract evidence for precipitation of authigenic carbonate fluorapatite cfa in long island sound and mississippi delta sediments suggests that formation of cfa is not restricted to environments of active coastal upwelling we present porewater data suggestive of cfa formation in both these areas application of a sequential leaching procedure designed specifically to separate authigenic carbonate fluorapatite from other phosphorus containing phases including detrital apatite of igneous or metamorphic origin provides strong supporting evidence for authigenic apatite formation in these sediments the size of the authigenic apatite reservoir increases with depth indicating continued formation of cfa during early diagenesis this depth increase is mirrored by a decrease in solid phase organic p at both sites suggesting that cfa is forming at the expense of organic p mass balance considerations application of diagenetic models to interstitial water nutrient data and the saturation state of the interstitial water are consistent with this interpretation diagenetic redistribution of phosphorus among the different solid phase reservoirs is observed at both sites and results in near perfect retention of p by these sediments over the depth intervals sampled formation of cfa in continental margins which do not conform to the classically defined regions of phosphorite formation renders cfa a quantitatively more important sink than has previously been recognized including this reservoir as a newly identified sink for reactive p in the ocean the residence time of p in the modern ocean must be revised downward the implication for ancient oceans of cfa formation in continental margin sediments other than phosphorites is that phosphorite formation may be less a representation of episodicity in removal of reactive p from the oceans than of localized concentration of cfa in phosphatic sediments by secondary physical processes

phosphorus distribution c n p ratios and δ13coc in arctic temperate and tropical coastal sediments tools for characterizing bulk sedimentary organic matter abstract onshore offshore trends in phosphorus p organic carbon oc and total nitrogen tn concentration p distribution elemental organic c n p ratios and stable carbon isotopic composition of oc 13 c oc of surficial sediments are presented from three river dominated coastal regimes the mackenzie river beaufort shelf in the canadian arctic the mississippi delta and louisiana shelf in the temperate gulf of mexico and the tropical amazon shelf these parameters measured in surficial sediments from the three sites are used to assess changes in the importance of terrestrial and marine organic matter sources to sediments as a function of distance from the locus of riverine discharge trends in elemental ratio data from the arctic transect and a portion of the gulf of mexico transects can be explained in terms of a two end member mixture of terrestrial and marine phytodetritus in the arctic transect covariation of organic c p ratios with 13 c oc is consistent with a two end member mixture of terrestrial and marine organic matter a similar relationship between c p ratios and 13 c oc is not evident in gulf of mexico or amazon shelf sediments at these sites the two end member model fails to explain the data adequately the most striking feature of the onshore offshore trends in elemental oc op and oc tn ratios is the occurrence of low ratios in sediments from deep water stations in the gulf of mexico and all stations on the amazon shelf resulting from p and n enrichments exceeding the redfield ratio for marine plankton three explanations are discussed to account for these low ratios 1 the dominance of refractory op and on compounds in the residuum of degraded organic matter 2 differential sorption of op and n compounds regardless of lability on the surfaces of the fine grained sediments characteristic of these sites and 3 a dominance of bacterial biomass or components derived from bacterial biomass elemental ratios and 13 c oc signatures indicate that differential sorption may be most important in the deep water gulf of mexico sites in contrast elemental ratios and 13 c oc on the amazon shelf are most consistent with a sedimentary organic matter pool dominated by bacterial biomass or derivative substances

glacial interglacial variations in marine phosphorus cycling implications for ocean productivity 1 using a box model of organic carbon c and phosphorus p cycling in the global ocean we assess the effects of changes in the continental supply of reactive p oceanic mixing and sea level on the marine p cycle on glacial interglacial timescales our model results suggest that mixing is a dominant forcing during early glaciation causing retention of p in the deep ocean thereby lowering primary production and associated organic c and p burial sea level fall is the dominant forcing during late glaciation when reduced coastal trapping of reactive p enhances its transfer to the open ocean restoring primary production and p burial during postglacial periods changes in circulation and weathering dominate open ocean processes and oceanic primary production peaks as primary production is reduced upon glaciation changes in the marine p cycle are unlikely to drive enhanced primary production and co2 drawdown during glaciation

evidence for a ridge subduction event in the ordovician rocks of north central maine modern and past ridge subduction events are characterized by the intrusion of midocean ridge basalt morb magmas into an overlying accretionary prism the fi eld relationships and trace element geochemistry of ordovician mafi c igneous rocks of the weeksboro lunksoos and munsungun anticlinoria of north central maine indicate that they resulted from such an event the bean brook gabbro intrudes the hurricane mountain melange and other related sedimentary strata of continental derivation the gabbro and associated dry way volcanics have morb trace element chemistries while the bluffer pond and stacyville volcanics are more enriched e morb all of which indicate derivation from a mid ocean ridge on petrogenetic diagrams mafi c samples plot in morb fi elds or when th is used as a discriminator in arc fi elds along trends that originate from morb fi elds and extend toward the composition of upper continental crust these trends are consistent with the presence of silicic and metasedimentary xenoliths in the dry way volcanics and bean brook gabbro and indicate the magmas were not subduction products but were contaminated by th rich upper continental crust the nearby chain lakes massif likely represents the basement to the chain lakes microcontinent and the geographic relationship and ages of the massif hurricane mountain melange and dry way bean brook magmatic rocks indicate northwestdirected subduction modern coordinates on the southeastern margin of the chain lakes microcontinent within the early to middle ordovician taconic ocean subduction at this boundary probably terminated because of the ridge subduction analogous to neogene california

structural and magmatic responses to spreading ridge subduction an example from southwest japan subduction of a spreading ridge is expected to leave a geological signature upon the overriding accretionary prism distinct from that of conventional convergent plate boundaries the late oligocene early miocene rocks of the shimanto accretionary prism at cape muroto shikoku island record a tectonomagmatic fabric that is anomalous with respect to typical accretionary prisms these accreted strata have been imprinted with an unusual late stage event that involved 1 regional cusp like flexing of structural trends in the prism 2 near trench magmatism and 3 pervasive faulting this event overlaps in time with the opening of the shikoku back arc basin circa 26 14 ma the shikoku basin spreading ridge trends perpendicular to the strike of the accretionary prism and is now located immediately offshore of cape muroto the regional flexing of structural trends in the prism affects rocks as old as cretaceous although the flexure is most tightly developed in the late oligocene early miocene portion of the prism where it is steeply plunging kinematic analysis of the flexure and the pervasive fault system indicates that the flexure most likely resulted from indentation of the prism by a rigid feature at cape muroto the core of the flexure forms a locus for mafic dikes that are petrochemically equivalent to some mid ocean ridge basalts morb from the shikoku back arc basin preliminary paleomagnetic data suggest that the dikes were intruded during the later stages of flexure development these data combined with plate reconstructions for the area at 15 ma indicate that indentation of the prism most likely resulted from early miocene orthogonal subduction of the topographically elevated shikoku basin spreading ridge in the muroto area morb magmatic rocks in the core of the flexure appear to have emanated from the active spreading ridge during subduction

a sediment nutrient oxygen feedback responsible for productivity variations in late miocene sapropel sequences of the western mediterranean abstract cyclic sediments observed throughout the mediterranean during the late miocene have been related to precessional forcing of ocean stratification individual couplets typically 2 m thick sequences of sapropels and diatom rich marls can be reliably traced from western spain to crete and were formed in restricted marginal basins micropaleontological evidence indicates paradoxically that the organic carbon rich sapropels were formed under low productivity conditions marked by surface water stratification and deep anoxia whereas the diatom rich marls were formed under high productivity conditions marked by upwelling here we present geochemical evidence mainly from detailed phosphorus determinations and paleo redox proxies indicating that a sediment nutrient oxygen feedback herein dubbed the sno effect is in part responsible for driving the observed productivity variations during stratification anoxic conditions in these basins cause the release of the limiting nutrient phosphorus from reducible oxide phases in the sediments basin stagnation causes the buildup of phosphorus below the photic zone subsequent overturn driven by precessionally driven winds injects phosphorus rich bottom waters into the photic zone the biotic response to this overturn is high productivity in marls directly overlying the sapropels culminating in diatom mat formation exhaustion of the stored excess phosphorus results in lower productivity marls which grade back into sapropels due to lower wind stresses and the return of stagnant basin conditions these findings indicate that the sno effect may in part be responsible for precessional scale productivity variations observed in parts of the mediterranean and perhaps present in other restricted ocean basins like the miocene monterey formation and the modern santa barbara basin

sequential extraction and analysis of phosphorus in marine sediments streamlining of the sedex procedure we streamlined the five step sedex sedimentary extraction procedure for characterizing sedimentary phosphorus to a four step procedure we combined extraction of adsorbed and oxide associated pools into a single step retaining steps for authigenic detrital and organic p in addition we used automated spectrophotometric flow injection analysis fia to determine p concentrations rather than traditional spectrophotometric techniques we decreased our total extraction and analytical time from 12 d for 24 replicate samples to 5 d without sacrificing our geo chemical objectives detection limits or analytical reproducibility

geochemical environment of the coniacian santonian western tropical atlantic at demerara rise abstract organic carbon rich shales deposited during the coniacian santonian oceanic anoxic event 3 were drilled during odp leg 207 at demerara rise we present integrated high resolution geochemical records of core intervals from odp sites 1259 and 1261 both from nannofossil biozone cc14 our results reveal systematic variations in marine and detrital sediment contribution depositional processes and bottom water redox conditions during black shale formation at two locations on demerara rise in different paleo water depths a combination of redox proxies fe s p al c p redox sensitive sulfide forming trace metals mn cd mo ni v zn and other analytical approaches bulk sediment composition p speciation electron microscopy x ray diffraction evidence anoxic to sulfidic bottom water and sediment conditions throughout the deposition of black shale these extreme redox conditions persisted and were periodically punctuated by short termed periods with less reducing bottom waters irrespective of paleo water depth sediment supply at both sites was generally dominated by marine material carbonate organic matter opal although relationships of detrital proxies as well as glauconitic horizons support some influence of turbidites winnowing bottom currents and or variable detritus sources along with less reducing bottom water at the proposed shallower location odp site 1259 at site 1261 located at greater paleo depth redox fluctuations were more regular and steady hemipelagic sedimentation sustained the development of mostly undisturbed lamination in the sedimentary record strong similarities of the studied deposits exist with the stratigraphic older cenomanian turonian oae2 black shale sections at demerara rise suggesting that the primary mechanisms controlling continental supply and ocean redox state were time invariant and kept the western equatorial atlantic margin widely anoxic over millions of years

age and origin of the boil mountain ophiolite and chain lakes massif maine implications for the penobscottian orogeny the boil mountain ophiolite complex of west central maine is widely interpreted to mark the lower ordovician penobscottian suture between the dunnage chain lakes and gander terranes the ophiolite consists of two distinct volcanic groups including a lower island arc tholeiite sequence and an upper mid ocean ridge basalt sequence a new middle ordovician 477 1 ma u pb age on a tonalite sill that intrudes the lower volcanic gabbroic sequence is younger than other ca 500 ma age constraints for the ophiolite and represents a maximum age for the ophiolite prior to final emplacement over gneissic rocks of the chain lakes massif a comparison of ages and paleogeography of the boil mountain ophiolite with ophiolitic sequences in quebec and newfoundland indicates that the taconian and penobscottian orogenies and ophiolite obduction occurred simultaneously although on different margins of the iapetus ocean the taconian ophiolite sequences were obducted onto the appalachian margin of laurentia during its col

phosphorus accumulation in marine sediments and the oceanic phosphorus cycle ideas about key factors in the oceanic mass balance of dissolved reactive phosphate have changed substantially i present an integrated overview of these here with an emphasis on evaluating the burial sinks for p and defining areas needing further research the major source of reactive p to the ocean is river input reactive p is delivered to the oceanic sediment water interface primarily in particulate organic matter p scavenged by hydrothermal iron rich oxyhydroxide particles with uptake in proportion to deep water phosphate concentrations represents a substantially smaller flux to the sediment water interface diagenetic transformations are important influences on the form of reactive p burial in marine sediments p burial occurs with organic carbon burial and as p associated with iron rich oxyhydroxide particles and coatings formation of authigenic p rich phases presumably apatite at the expense of organic p and oxide associated p is significant in open ocean marine sediments the authigenic p sink may represent a substantially larger portion of the sedimentary burial than indicated by previous estimates focused on p burial in organic rich continental margin sediments

nutrient leakage from the north pacific to the bering sea iodp site u1341 following the onset of northern hemispheric glaciation 1 intergrated ocean drilling program expedition 323 recovered a sediment record covering the last 4 3 ma from the bering sea integrated ocean drilling program site u1341 bowers ridge 2177 m water depth to resolve pliocene pleistocene paleoenvironmental changes in this marginal basin 190 sediment samples were analyzed for their bulk element composition aluminium contents in bowers ridge sediments are variable but overall higher toward younger sediments probably related to the intensification of the northern hemispheric glaciation and increasing sea ice transport in the bering sea the gradual increase of terrigenous input is mirrored by decreasing sio2 and excess si sixs contents but the overall si enrichment of the deposits reflects continuous opal deposition since the pliocene at bowers ridge unlike in the north pacific the sixs record at site u1341 does not support a dramatic decrease in opal export following the onset of the northern hemispheric glaciation around 2 7 ma but sio2xs have higher accumulation rates up to 8 g cm2 ka between 2 6 and 1 8 ma bp during this period the major oceanic opal deposition centers shifted globally from open marine high latitude regions to upwelling areas we here discuss how the onset of north pacific stratification at 2 7 ma bp may have caused leakage of nutrient rich deep intermediate north pacific water into the bering sea via the deep kamtchatka strait leading to increased opal deposition and likely reactive organic matter export at bowers ridge as a result magnetic and geochemical records were overprinted by intensified diagenesis significantly affecting their applications as paleoceanographic proxies

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

diagenetic calcite varieties from travertines of central italy abstract quaternary travertines in latium and tuscany italy were deposited by warm springs containing abundant co2 and h2s the major rock formers were bacteria that precipitated calcite to form shrubs pisolites mats foamrock and clastic silt size sediment the calcite cement in these rocks shows extraordinary morphology the elementary building block is a subspherical clump of bacteria 10 to 40 m in diameter which becomes surrounded by a single crystal of calcite shaped like a pecan shell sem shows that these crystals are riddled with cavities voids representing bacteria and contain internal moats later the bacteria rich crystals became coated with clear chemically precipitated inorganic calcite cement but even these crystals are strange s they have curving edges and consist of a series of scales parallel to the rhomb faces like superimposed gothic arches other cement crystals bear a forest of sharp spikes parallel to the c axis like a fakir s bed the final sparry calcite that fills large pore spaces occurs as large bladed crystals with apparent basal parting planes primarily inorganic sediment includes ray crystals and pisolites ray crystals can be up to 1 m 39 in long and in some places show daily bacteria rich growth bands indicating deposition rates of as much as 1 m 39 in per year these formed as travertine dams on sloping surfaces and at ancient spring orifices crystals can be shaped like cedar tree needles or club shaped stromatolites show undulose extinction and in the sem consist of helically twisted calcite ribbons inorganic pisolites formed in hot spring mouths and are made of smoothly concentric rings of tightly bundled radial rods like fasces end of article last page 461

influence of water column anoxia on the burial and preservation of carbon and phosphorus in marine shales abstract organic p and organic c concentrations were measured in several well characterized phanerozoic marine shale sequences with the primary focus being the camp run member of the devonian mississippian new albany shale sequences were selected with close spatial association of bioturbated and laminated sediments which reflect deposition from oxic and anoxic waters respectively average organic c p mole ratios calculated from the data are 150 for bioturbated shales and 3900 for the laminated shales of the new albany differences in the extent and mechanisms of early diagenesis related to the oxygenation of waters at the sediment water interface can account for the c p ratios of buried organic matter low c p ratios of bioturbated sediments are attributed to 1 1 the increased ability of bacteria to store p in well oxygenated environments which leads to the production of low c p ratio bacterial biomass and 2 2 the extensive oxidation of sedimentary organic matter resulting in the formation of residual organic phases with low c p ratios high organic c p ratios of laminated sediments are explained by a combination of 1 1 the limited ability of bacteria to store p under anoxic conditions 2 2 extensive p regeneration from sedimentary organic matter 3 3 enhanced c preservation relative to the bioturbated shales it is also shown that relative to organic c laminated shales are not as effective a p sink as are bioturbated shales this provides a mechanism in anoxic environments for burying large quantities of organic matter without simultaneously sequestering the p needed to sustain further productivity

geology and paleobiology of islands in the ordovician iapetus ocean review and implications a history of islands in the iapetus ocean and their destruction is recorded by widespread occurrences of lower to upper ordovician volcanic and epiclastic rocks and some limestone through the axial parts of the appalachian caledonide orogen in north america and northwestern europe assemblages of arenigian and llanvirnian benthic shelly fossils chiefly brachiopods from these rocks constitute the celtic biogeographic province that is distinguished by its endemic genera and by some that are older than in other biogeographic provinces some that are younger than elsewhere and others that have not hitherto been found together evidence from these fossils and from the geology of the rocks pertaining to them suggests that north american terranes that included islands of arenigian llanvirnian age lay at middle to high latitudes both in mid ocean and within the armorican continental margin whereas coeval rocks in west central ireland and norway that have toquima table head shelly fossils were originally part of the laurentian continental margin eradication of the celtic assemblage and the reduction of ordovician faunal provinciality in the appalachian caledonide region coincide with llanvirnian obduction subduction of hundreds of kilometres of iapetus ocean crust late llanvirnian and younger ordovician rocks in the remnant basin including some of peri insular origin have brachiopods of scoto appalachian affinities no discrete islands of ashgillian age have been recognized although fossiliferous volcaniclastic and polymictic conglomerates indicate intermontane basins in some places shelly fossils in these rocks and those in the siltstones and limestones from the gaspe peninsula are like those of ashgillian age elsewhere

speciation bioavailability and preservation of phosphorus in surface sediments of the changjiang estuary and adjacent east china sea inner shelf abstract the speciation potential bioavailability and preservation of phosphorus p in surface sediments of the changjiang yangtze river estuary and adjacent east china sea ecs inner shelf were investigated through the analyses of p fractions and sediment bulk properties a sequential extraction method sedex was used to separate and quantify the following six sedimentary p reservoirs exchangeable p ex p authigenic p au p detrital p de p organic p or p refractory p re p and fe bound p fe p total p tp in surface sediments ranged from 15 0 to 21 4 mol g 1 and was highest near the changjiang river mouth the average contribution of each form of p to tp was 55 6 de p 17 8 re p 16 1 or p 5 5 au p 2 5 ex p and 2 5 fe p respectively de p showed relatively higher concentrations in the river mouth and the ecs shelf region off the changjiang estuary high concentrations of or p were found mainly in mud areas showing a similar distribution pattern with silt sediment surface area ssa and total organic carbon toc re p was mainly distributed near the estuarine area and the zhe min coast bioavailable p bap accounted for 9 5 32 0 of tp with a mean of 21 2 and showed a similar distribution pattern to that of or p de p ssa and toc ssa loadings both decreased with increasing of ssa while or p ssa loadings varied little with ssa indicating that or p may have reached an adsorption desorption equilibrium on mineral surfaces toc to total organic p top sum of re p and or p ratios less than the redfield ratio 84 in average may have indicated efficient remineralization of organic matter in mobile muds of the changjiang estuary and adjacent ecs inner shelf furthermore the relatively high toc or p ratios 72 422 with a mean of 188 likely suggest a higher degree of preferential regeneration of labile or p over toc in sediments

evidence for enhanced phosphorus regeneration from marine sediments overlain by oxygen depleted waters phosphorus regeneration and burial fluxes determined from in situ benthic flux chamber and solid phase measurements at sites on the californian continental margin peruvian continental slope north carolina continental slope and from the santa monica basin california are reported comparison of these sites indicates that o2 depleted bottomwaters enhance p regeneration from sediments diminishing overall phosphorus burial efficiency based on these observations a positive feedback linking ocean anoxia enhanced benthic phosphorus regeneration and marine productivity is proposed on shorter timescales these results also suggest that o2 depletion in coastal regions caused by eutrophication may enhance p regeneration from sediments thereby providing additional p necessary for increased biological productivity