integrated biogeochemical and hydrologic processes driving arsenic release from shallow sediments to groundwaters of the mekong delta abstract arsenic is contaminating the groundwater of holocene aquifers throughout south and southeast asia to examine the biogeochemical and hydrological processes influencing dissolved concentrations and transport of as within soils sediments in the mekong river delta a 50 km2 field site was established near phnom penh cambodia where aqueous as concentrations are dangerously high and where groundwater retrieval for irrigation is minimal dissolved as concentrations vary spatially ranging up to 1300 g l in aquifer groundwater and up to 600 g l in surficial clay pore water groundwaters with high as concentrations are reducing with negligible dissolved o2 and high concentrations of fe ii nh 4 and dissolved organic c within near surface environments these conditions are most pronounced in sediments underlying permanent wetlands often found within oxbow channels near the mekong river there labile c co deposited with as bearing fe hydr oxides under reducing conditions drives the reductive mobilization inclusive of fe and as reduction of as here conditions are described under which as is mobilized from these sediments and near surface as release is linked to aquifer contamination over long time periods 100s to 1000s of years site biogeochemistry is coupled with extensive hydrologic measurements and accordingly a comprehensive interpretation of spatial as release and transport within a calibrated hydraulic flow field is provided of an as contaminated aquifer that is representative of those found throughout south and southeast asia

differing controls over the cenozoic pb and nd isotope evolution of deepwater in the central north pacific ocean dissolved pb and nd isotope ratios of seawater as recorded by chemical marine precipitates such as hydrogenetic ferromanganese crusts have been used as paleoenvironmental proxy tracers for the north pacific however all ferromanganese crusts studied so far have either been subject to phosphatization or hydrothermal influence in their old part or only the young parts have been analyzed thus the pb and nd isotope compositions of north pacific deep waters prior to 20 ma are not well constrained we present new results for three ferromanganese crusts one of which cj01 shows no phosphatization and is located far away from the epr its age is inferred to be 75 ma and thus provides for the first time an opportunity to trace the nd and pb isotope evolution of central north pacific seawater back to the latest cretaceous the three crusts no matter whether phosphatized or not display very similar pb and nd isotope trends with age suggesting no modification of the pb and nd isotope distribution by post depositional phosphatization our data suggest that dissolved pb in deep waters of the central north pacific over the cenozoic and latest cretaceous has mainly been derived from eolian dust and only to a minor extent from weathering of island arcs for pb these trends broadly resemble the pb isotope evolution of the eolian silicate dust fraction of core ll44 gpc3 in the central north pacific we suggest that the isotope evolution of dissolved pb in central north pacific seawater has been mainly controlled by pb released from eolian dust from north america prior to 50 ma and after 40 ma from asia in contrast the nd isotope time series of the crusts are by no means similar to the nd isotope evolution of the silicate dust fraction in core gpc3 suggesting a decoupling from the pb and negligible contributions from dust to the dissolved nd in the central north pacific deep water the rise of nd isotope ratios of pacific seawater during the cenozoic has most likely been caused by the increasing volcanic activity and erosion of the volcanic arcs around the pacific

cenozoic evolution of asian climate and sources of pacific seawater pb and nd derived from eolian dust of sediment core ll44 gpc3 1 the large diameter piston core ll44 gpc3 from the central north pacific ocean records continuous sedimentation of eolian dust since the late cretaceous two intervals resolved by nd and pb isotopic data relate to dust coming from america prior to 40 ma and dust coming from asia since 40 ma the intertropical convergence zone itcz separates these depositional regimes today and may have been at a paleolatitude of 23 n prior to 40 ma such a northerly location of the itcz is consistent with sluggish atmospheric circulation and warm climate for the northern hemisphere of the early to middle eocene since 40 ma correlations between nd 7 55 end t 10 81 and pb 18 625 206 4pb 18 879 15 624 207 4pb 15 666 38 611 208 4pb 38 960 0 8294 207 6pb 0 8389 2 0539 208 6pb 2 0743 isotopes reflect the progressive drying of central asia triggered by the westward retreat of the paleo tethys comparisons between the changes with time in the isotopically well defined dust flux and nd and pb isotopic compositions of pacific deep water allow one to draw two major conclusions 1 dust bound nd became a resolvable contribution to pacific seawater only after the one order of magnitude increase in dust flux starting at 3 5 ma therefore eolian nd was unimportant for pacific seawater nd prior to 3 5 ma 2 the lack of a response of pacific deep water pb to this huge flux increase suggests that dust bound pb has never been important instead mobile pb associated with island arc volcanic exhalatives probably consists of a significant contribution to pacific deep water pb and possibly to seawater elsewhere far away from landmasses

volcanism co2 and palaeoclimate a late jurassic early cretaceous carbon and oxygen isotope record a composite tethyan late jurassic early cretaceous carbon and oxygen isotope curve is presented c isotope data provide information on the evolution and perturbation of the global carbon cycle o isotope data are used as a palaeotemperature proxy in combination with palaeontological information the resulting trends in climate and in palaeoceanography are compared with biocalcification trends and oceanographic conditions favouring or inhibiting biocalcification positive c isotope anomalies in the valanginian and aptian correlate with episodes of increased volcanic activity regarded as a source of excess atmospheric carbon dioxide a major warming pulse accompanies the aptian but not the valanginian c isotope event the observed change in early aptian temperatures could have triggered the destabilization of sedimentary gas hydrates and the sudden release of methane to the biosphere as recorded as a distinct negative carbon isotope pulse preceding the positive excursion both c isotope anomalies are accompanied by biocalcification crises that may have been triggered by p co 2 induced changes in climate and in surface water chemistry elevated nutrient levels in river influenced coastal waters and in upwelling regions further weakened marine calcification these conditions contrast with normal trophic conditions prevailing in the latest jurassic and favouring biocalcification the c and o isotope curves record a stable mode of carbon cycling and stable temperatures we conclude that biocalcification is mostly triggered and inhibited by co 2 conditions in the atmosphere ocean system

long term sea level fluctuations driven by ocean basin dynamics earth9s long term sea level history is characterized by widespread continental flooding in the cretaceous period 145 to 65 million years ago followed by gradual regression of inland seas however published estimates of the late cretaceous sea level high differ by half an order of magnitude from 40 to 250 meters above the present level the low estimate is based on the stratigraphy of the new jersey margin by assimilating marine geophysical data into reconstructions of ancient ocean basins we model a late cretaceous sea level that is 170 85 to 270 meters higher than it is today we use a mantle convection model to suggest that new jersey subsided by 105 to 180 meters in the past 70 million years because of north america9s westward passage over the subducted farallon plate this mechanism reconciles new jersey margin based sea level estimates with ocean basin reconstructions

correlations of hauterivian and barremian early cretaceous stage boundaries to polarity chrons recent ammonite finds in italian maiolica limestones allow direct correlation of hauterivian and barremian ammonite zones stage boundaries to polarity chrons at laghetto and alpetto lombardy italy lower aptian ammonites occur just above polarity zone m0 and below the selli level and upper barremian ammonites occur in polarity zone m1n these correlations are consistent with the barremian aptian boundary being close to older boundary of polarity chron cm0 the uppermost hauterivian ammonite faraoni guide level has been correlated to cm4 at bosso umbria marche confirming the recent correlation of the hauterivian barremian boundary to cm4 at monte acuto umbria marche ammonites spanning the valanginian hauterivian boundary interval and the last appearance of the nannofossil t verenae occur close to the cm11 cm11n boundary the valanginian hauterivian boundary has previously been placed between the first appearance of l bollii and the last appearance of t verenae or between cm10 and cm11 the published polaveno lombardy magnetostratigraphy for the cm3 cm11 interval has now extended to cm16 this 260 m section recording the cm3 cm16 interval is the most complete single section record of cretaceous m sequence polarity chrons no diagnostic ammonites have been found in this section however the correlations of nannofossil and calpionellid events to polarity chrons are consistent with previous studies

cretaceous oceanic anoxic event 2 triggered by a massive magmatic episode oceanic anoxic events oaes were episodes of widespread marine anoxia during which large amounts of organic carbon were buried on the ocean floor under oxygen deficient bottom waters oae2 occurring at the cenomanian turonian boundary about 93 5 myr ago is the most widespread and best defined oae of the mid cretaceous although the enhanced burial of organic matter can be explained either through increased primary productivity or enhanced preservation scenarios the actual trigger mechanism corresponding closely to the onset of these episodes of increased carbon sequestration has not been clearly identified it has been postulated that large scale magmatic activity initially triggered oae2 refs 4 5 but a direct proxy of magmatism preserved in the sedimentary record coinciding closely with the onset of oae2 has not yet been found here we report seawater osmium isotope ratios in organic rich sediments from two distant sites we find that at both study sites the marine osmium isotope record changes abruptly just at or before the onset of oae2 using a simple two component mixing equation we calculate that over 97 per cent of the total osmium content in contemporaneous seawater at both sites is magmatic in origin a approximately 30 50 fold increase relative to pre oae conditions furthermore the magmatic osmium isotope signal appears slightly before the oae2 as indicated by carbon isotope ratios suggesting a time lag of up to approximately 23 kyr between magmatism and the onset of significant organic carbon burial which may reflect the reaction time of the global ocean system our marine osmium isotope data are indicative of a widespread magmatic pulse at the onset of oae2 which may have triggered the subsequent deposition of large amounts of organic matter

sr_nd_pb isotope systematics in amazon and congo river systems constraints about erosion processes abstract 87 sr 86 sr 143 nd 144 nd 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb isotopic ratios and rb sr sm nd u pb and th concentrations have been measured in the suspended loads of the congo and amazon rivers and their tributaries in the dissolved load 87 sr 86 sr rb sr nd sm u pb and th concentrations are also reported these results show that nd sm th and pb are almost insoluble and that their mass balance is controlled by particulates whereas rb sr and u are fractionated between soluble and particulate phases the 87 sr 86 sr ratios can only be interpreted after computing the amount of carbonate recycling and the partitioning for silicates between soluble and insoluble this paper presents a method based on the lead isotopic system that can be used to test the steady state of erosion which is tacitly assumed in many river and erosion studies the results presented show that the steady state is validated in each river of the congo basin and in the lowland rivers of the amazon basin but in not verified in the rivers from the andes rio solimoes and rio madeira 87 sr 86 sr 206 pb 204 pb and 208 pb 204 pb ratios are positively correlated and negatively correlated with 143 nd 144 nd ratios a number of arguments indicate that these correlations are mixing lines the end members being orogenic and shield components respectively for the amazon basin analysis of the river loads shows that the orogenic zone is favoured some 5 times more than the shield on an equal area basis this leads to a reinterpretation of sm nd data for shales and casts some doubts upon the proposition of secular variations in the sm nd ratio of the continental crust

lead isotopic record of barremian aptian marine sediments implications for large igneous provinces and the aptian climatic crisis we present initial isotopic ratios of lead for early cretaceous barremian aptian sections from shatsky rise pacific and gorgo a cerbara italy our pb isotopic data track an interval representing oceanic anoxic event oae 1a which is characterized by quasi global deposition of organic carbon rich black shale pb isotopic compositions of sediments from shatsky rise decrease at the end of barremian time from radiogenic continental values to unradiogenic values and subsequently remained less radiogenic until the end of early aptian time we explain the isotopic shift by a significant increase in supply rate of unradiogenic pb most likely due to massive volcanism in contrast the pb isotopic compositions from the italian section which was situated at the western end of tethys are mostly identical to those of upper continental crust showing no significant change in supply rate of unradiogenic pb the discrepancy between two sites is attributed to quiescent deep submarine eruptions of pacific large igneous provinces lips such as the ontong java plateau ojp which severely limited dispersion of pb carrying particles out of the pacific ocean published os isotopic data from the italian section indicate two episodes of massive eruptions of ojp or contemporaneous manihiki and hikurangi plateaus starting from earliest aptian time slightly later than that indicated by the sedimentary pb isotopic record from shatsky rise differences in isotopic variations between pb and os likely reflect differences in their chemical behaviors in the oceans i e pb isotopic compositions would have varied in response to local or regional changes in sediment provenances whereas large scale changes in os inputs are required to explain variations in seawater os isotopic compositions our pb isotopic data together with the published os isotopic record provide new evidence for the eruptive history of ojp together with contemporaneous pacific plateaus and its environmental consequences starting from end barremian time and extending through early aptian time

fluctuations in biosiliceous production and the generation of early cretaceous oceanic anoxic events in the pacific ocean shatsky rise ocean drilling program leg 198 integration of geophysical logs with sedimentological biostratigraphic and physical properties data from poorly recovered chert rich sequences at ocean drilling program leg 198 sites 1207 and 1213 allows us to propose an aptian albian early cretaceous depositional history for shatsky rise north pacific ocean the logs indicate that the lower aptian and lower albian deposits are relatively lithified and unporous compared to contiguous sediments these characteristics are best explained by increased siliceous cementation that resulted from an elevated flux of radiolarians to the seafloor the intervals of increased biosiliceous production may record a biotic response to enhanced nutrient delivery coeval with but longer in duration than oceanic anoxic events oaes 1a early aptian and 1b early albian on shatsky rise oae 1a is represented by organic carbon rich sediments but oae 1b is not thus black shale deposition in the pacific ocean was only possible when a carbon burial threshold was crossed we speculate that this threshold was related to the balance between productivity and carbon oxidation and that ultimately the supply of biolimiting nutrients through hydrothermal alteration of basalt may have been the key to the development of black shale in the pacific basin

geographic control on pb isotope distribution and sources in indian ocean fe mn deposits abstract high precision pb isotope data have been obtained on indian ocean fe mn deposits with a large geographic coverage these data reveal a strong geographic control on the distribution of pb isotopes as well as sources of pb within this basin the provinciality of pb isotopes at the scale of the whole indian ocean as well as that of individual basins broadly matches the pattern of deepwater flow the existence of several sources of pb is best illustrated by the presence of three well defined pb isotopic arrays each of which is confined to clear cut geographic domains these arrays imply a dominance of binary mixing of pb sources within each of these domains the domains consist of the north indian n indian north of 20 s southwest indian sw indian 20 s to 50 s west of 45 e south indian s indian 20 s to 50 s east of 45 e and antarctic indian a indian south of 50 s and clearly exhibit a strong control by latitude the s indian domain and mozambique channel samples form a cluster suggesting that there are more than just two sources contributing in these regions we show that the n indian is dominated by sources of pb derived from the high himalayas and the trans himalayan complex and most likely inherited from interaction at the water interface with bengal and indus fan sediments the sw indian and a indian domains share a common unradiogenic component represented by circumpolar waters derived from the pacific ocean and flowing through the drake passage into the atlantic and indian oceans however the radiogenic sources of pb in these two domains are clearly distinct in the sw indian the radiogenic pb signal reflects the tongue of north atlantic deep water flowing around the tip of south africa while in the a indian the source of radiogenic pb is less certain but quite probably originates in the weddell sea region these data illustrate the complexity of the spatial pb isotopic distribution and pb sources within a single ocean basin at the present day which should be borne in mind when interpreting long term radiogenic isotope paleorecords from fe mn crusts

palaeoceanographic significance of the tethyan livello selli early aptian from the hybla formation northwestern sicily biostratigraphy and high resolution chemostratigraphic records high resolution micropalaeontological and chemostratigraphic records for the hauterivian aptian succession outcropping at calabianca nw sicily provide new insight into the palaeoclimatic and palaeoceanographic evolution of the tethys ocean calcareous nannofossil and planktonic foraminiferal biostratigraphy together with 13c chemostratigraphy allowed the identification of a hiatus in the barremian and a major one including most of the upper aptian the entire lower albian and part of the middle albian the livello selli equivalent was identified on the basis of lithology and well constrained by calcareous plankton biostratigraphy as well as by the 13c curve the multi proxy record from the calabianca section is consistent with previous documentation of tethyan sections and others worldwide early aptian global events such as black shale deposition nannoconid crisis c isotopic negative spike and positive excursion associated with the oae1a increase in abundance of leupoldinids and clavate hedbergellids are superimposed on local regional events being strictly related to climate changes and increased run off based on micropalaeontological results and geochemical proxies ba p v ni the livello selli equivalent is interpreted as a high productivity event associated with variable but overall anoxic dysoxic conditions in the lower water column the onset of new physical chemical and biological conditions in the oceans and of the mid cretaceous greenhouse climate are interpreted as consequences of the superplume episode

tropical warming and intermittent cooling during the cenomanian turonian oceanic anoxic event 2 sea surface temperature records from the equatorial atlantic oceanic anoxic event 2 oae 2 occurring during the cenomanian turonian c t transition is evident from a globally recognized positive stable carbon isotopic excursion and is thought to represent one of the most extreme carbon cycle perturbations of the last 100 myr however the impact of this major perturbation on and interaction with global climate remains unclear here we report new high resolution records of sea surface temperature sst based on tex86 and 18o of excellently preserved planktic foraminifera and stable organic carbon isotopes across the c t transition from black shales located offshore suriname french guiana demerara rise ocean drilling program leg 207 site 1260 and offshore senegal cape verde basin deep sea drilling project leg 41 site 367 at site 1260 where both sst proxy records can be determined a good match between conservative sst estimates from tex86 and 18o is observed we find that late cenomanian ssts in the equatorial atlantic ocean 33 c were substantially warmer than today 27 29 c and that the onset of oae 2 coincided with a rapid shift to an even warmer 35 36 c regime within the early stages of the oae a marked 4 c cooling to temperatures lower than pre oae conditions is observed however well before the termination of oae 2 the warm regime was reestablished and persisted into the turonian our findings corroborate the view that the c t transition represents the onset of the interval of peak cretaceous warmth more importantly they are consistent with the hypotheses that mid cretaceous warmth can be attributed to high levels of atmospheric carbon dioxide co2 and that major oaes were capable of triggering global cooling through the negative feedback effect of organic carbon burial led co2 sequestration evidently however the factors that gave rise to the observed shift to a warmer climate regime at the onset of oae 2 were sufficiently powerful that they were only briefly counterbalanced by the high rates of carbon burial attained during even the most extreme interval of organic carbon burial in the last 100 myr

isotopic evidence for the origin of the manihiki and ontong java oceanic plateaus abstract pb nd and sr isotopic results for lavas of the cretaceous ontong java and manihiki oceanic plateaus fall well within the modern day oceanic island or hotspot field the data provide no evidence of old continental basements but indicate a major involvement of kerguelen type or em i like mantle in the sources of both plateaus which appear to have probably been formed at least in part by hotspots however the presently active hotspots that pacific plate reconstructions suggest might have been possible plateau sources lack kerguelen type isotopic compositions either these hotspots did not participate in the formation of the two plateaus or if they did kerguelen type material must have been volumetrically much more important early in their existence two hypotheses for the origins of these plateaus which involve hotspot sources are consistent with the sparse available geochemical geochronological and geophysical data the first holds that the plateaus formed cataclysmically in association with surfacing plume heads the second posits a relatively steady but robust hotspot at or near a ridge crest and requires a much longer period of formation a near ridge origin appears to be indicated by evidence that most of the pacific plateaus were built largely on relatively young ocean crust however we suggest that a near ridge origin is also compatible with the plume head concept in that plume heads appear very likely to become associated with spreading axes through their influence on rift propagation which should be substantially greater than for ordinary hotspots in either case the lack of hotspot tracks seamount chains attached to the two plateaus would be a consequence of ridge migration or rift propagation in a near ridge setting

new constraints upon isotope variation during the early cretaceous barremian cenomanian from the pacific ocean carbon and oxygen isotope data from a succession of cretaceous barremian cenomanian age recovered from the pacific ocean dsdp site 463 are presented the carbon isotope curve reveals a large isotope excursion within the early aptian where 1 3 c values reach 4 8 in the l cabri g ferreolensis foraminifera zone a decrease in 1 3 c values is observed at the base g algerianus zone before a return to more positive values at the top of the g algerianus t bejaouaensis zone the pronounced early aptian positive event is preceded by a large negative isotope excursion confined to the g blowi zone synchronous with this excursion are increased total organic carbon values and increases in mn and fe concentrations integrated biostratigraphic and magnetostratigraphic data together with the carbon isotope profile suggest that the organic rich units of site 463 are correlatable with oceanic anoxic event la the input of isotopically light volcanic co 2 in concert with the intensification and upwelling of intermediate water enriched in 1 2 c could account for the observed trends a potential trigger may have been the destabilization of the water column and the prodigious co 2 emissions associated with hydrothermal activity and the emplacement of the ontong java plateau coupled with faunal evidence the subsequent positive carbon isotope excursion is interpreted to be resulting from high but decreasing productivity and possibly increasing ocean stratification resulting in strong carbon isotopic gradients and 1 3 c enriched surface waters the decrease in 1 3 c within the g algerianus zone is coincident with more positive 1 8 o values if these are interpreted in terms of temperature this interval may be characterized by a period of cooling and possibly a waning of c o r g cycling a return to lower 1 3 c values during the middle albian is considered to be related to the increased influence of upwelling as opposed to a waning of c o r g cycling upwelling introduced isotopically light carbon to the surface arresting the stratified oceanic conditions

carbon isotope composition of lower cretaceous fossil wood ocean atmosphere chemistry and relation to sea level change the carbon isotope composition of fossil wood fragments collected through a biostratigraphically well constructed aptian lower cretaceous shallow marine siliciclastic succession on the isle of wight southern britain shows distinct variations with time the results indicate that the stratigraphic signature of delta sup 13 c sub wood through the aptian was influenced primarily by fluctuations in the isotopic composition of co sub 2 in the global ocean atmosphere system as registered in marine carbonates elsewhere and was not governed by local paleoenvironmental and or paleoecological factors negative and positive excursions in delta sup 13 c sub wood through the lower aptian occur in phase with inferred transgressions and regressions respectively a pattern that contrasts with that observed in many previous studies for different time intervals the relationship between delta sup 13 c variations and relative sea level change is tentatively interpreted as a response to various climatic and eustatic factors relating to rapid sea floor spreading thermal uplift of ocean floor emplacement of plateaus volcanic co sub 2 emissions weathering and sedimentary rate

eolian inputs of lead to the north pacific we evaluate the importance of natural eolian pb to the dissolved oceanic pb budget by measuring the isotopic composition of pb in 35 holocene and late quaternary sediment samples from the north pacific and in 10 samples of chinese loess when the pacific is divided into sediments provinces based on published end and sedimentological data pb from the central north pacific tends to be the most radiogenic and homogeneous due to the dominance of eolian chinese loess lead from the marginal north pacific and the sparsely sampled regions south of 5 n are less radiogenic and more variable owing to hemipelagic inputs from various volcanic arcs and older continental crust located around the pacific rim 208pb 204pb ratios provide the most distinctive provenance information due to the relatively high ratios in chinese loess the chinese loess samples come from 3 localities and span up to 2 myr of time acetic acid leachate bulk loess and loess silicate fractions were analyzed separately leachate pb is considerably less radiogenic than silicate pb the isotopic composition of the silicate component closely matches the sediment data from the central north pacific confirming the dominance of eolian loess in this region we divided up a suite of published hydrogenous pb isotope data from the pacific ocean according to their locations within the three independently defined sediment provinces these data define three distinct fields differentiated primarily by their 206pb 204pb ratios which increase going from the central to southern to marginal provinces this relationship with sediment province strongly suggests that natural eolian and probably hemipelagic inputs significantly impact the seawater pb budget direct support for the dominance of eolian chinese loess in the central north pacific dissolved pb budget comes from the close match between loess leachate pb and the central province hydrogenous pb data eolian inputs are likely to dominate local seawater pb budgets only where eolian pb fluxes are high relative to hemipelagic pb fluxes and where the flux of pb carried by deep water advection is low

lamina scale analysis of sedimentary components in cretaceous black shales by chemical compositional mapping implications for paleoenvironmental changes during the oceanic anoxic events abstract relative abundances and distribution patterns of mineral components in finely laminated livello bonarelli lb black shale from the cenomanian turonian boundary cretaceous were investigated by 10 m resolution compositional mapping using an electron probe microanalyzer sedimentary components such as biogenic silica si bio calcium phosphate calcium carbonate and pyrite were reconstructed by image processing of the compositional maps total organic carbon c org content was also determined at a sampling interval of 1 5 mm the depth profiles of these sedimentary components covering 60 of the total 104 cm lb sequence indicate the highly variable nature of their deposition especially the c org contents vary widely ranging from org are clearly discernible in the lb and correspond to dark colored intervals repeated occurrences of c org rich and si bio rich intervals are one of the most prominent features in the lb these features could be explained partly by dilution of c org by si bio but largely by the presence of two distinct paleoenvironmental settings one involves predominant deposition of organic matter and the other is dominated by si bio deposition the thickness of individual intervals varies widely mostly ranging from 1 5 to 35 mm representing oceanic changes on the order of 10 3 10 4 years furthermore we found 100 m scale laminations of fine grained pyrite aluminosilicate and calcium carbonate which when superimposed on the alternation of c org rich and si bio rich intervals suggests 10 2 year scale fluctuations in oceanic environments

early diagenetic dolomite cements examples from the permian lower magnesian limestone of england and the pleistocene carbonates of the bahamas abstract early diagenetic dolomite cements are found in the permian lower magnesian limestone of eastern england and the pleistocene carbonates of great abaco island bahamas in the lower magnesian limestone the dolospar occurs as isopachous rinds that have grown both centripetally and centrifugally on the dolomitized micrite envelopes of hollow centered allochems because compactional fractures penetrate both the allochem walls and the cement rinds dolomite cementation is inferred to have predated any significant sediment accumulation in the great abaco carbonates limpid dolomite forms isopachous rinds around inter and intragranular porosity and is postdated by meteoric calcite cement both examples of early diagenetic dolomite cement textures developed as a consequence of changes in pore fluid chemistry from marine to mixed meteoric marine to meteoric waters therefore the presence of this cement type may point toward aliagenetic environments resulting from marine regressions

trace element abundances in the rock canyon anticline pueblo colorado marine sedimentary section and their relationship to caribbean plateau construction and oxygen anoxic event 2 1 rapid eruption of submarine lava flows during formation of the caribbean plateau correlates closely with ocean anoxic event 2 oae2 which bracketed the cenomanian turonian boundary 93 5 ma these events also correspond with a positive excursion in carbon isotopic composition of seawater hydrothermal activity associated with large scale submarine volcanism may have been responsible for this abrupt change in ocean chemistry we determined the distribution of major minor and trace element abundances in the rock canyon marine sedimentary section pueblo colorado after normalizing element concentrations to zr to remove the variable contribution of terrigenous material to these sediments we detected an interval of concentrated metal abundance anomalies that coincides with the abrupt beginning of the positive 13c isotope excursion the metal abundance anomalies indicate that intermittent hydrothermal activity in the form of both water rock exchange and magmatic degassing introduced large concentrations of trace metals into the cretaceous ocean at the same time that extinctions of benthic species turnover in plankton communities and increases in isotopically light organic carbon burial occurred the stratigraphic position of this interval of trace metal anomalies matches events associated with oae2 and indicates that intermittent hydrothermal activity on a massive scale triggered abrupt changes in carbon burial and deep ocean oxygen contents

intrabasement reflections of the ontong java plateau implications for plateau construction 1 the early cretaceous ontong java plateau ojp in the western equatorial pacific earth s most voluminous large igneous province lip is characterized by intrabasement seismic reflections to investigate the nature of such reflections we have analyzed new and all older multichannel seismic mcs reflection data from the ojp using an instantaneous phase velocity analysis technique and synthetic seismograms intrabasement reflections are most prevalent on the main ojp especially on its crest on mcs data the reflections 1 are semicontinuous and subparallel to the top of igneous basement 2 in places have the opposite phase of seafloor reflections and 3 have an average frequency of 20 hz we calculate synthetic seismograms using impedance contrasts between massive lava and pillow lava flows obtained from downhole logs at ojp scientific drill sites and show that these lithologies can produce intrabasement reflections similar to those observed in the mcs data alternatively to evaluate the possibility of sediment sedimentary rock interbeds causing the intrabasement reflections we use published early cretaceous sedimentation rates determined from ojp drill sites and published estimates for the duration of massive ojp volcanism to calculate a range of possible sedimentary interbed thicknesses the range proves to be below the detection limit of the mcs data therefore we conclude that the intrabasement reflections arise from alternating relatively thin lava flows produced at low effusion rates and relatively thick massive flows generated at high effusion rates both originating from vents and fissures on the ojp probably on its crest

timing and magnitude of early aptian extreme warming unraveling primary δ18o variation in indurated pelagic carbonates at deep sea drilling project site 463 central pacific ocean abstract in order to elucidate early aptian marine paleotemperature evolution across the period of enhanced organic carbon corg burial oceanic anoxic event oae 1a stable isotope analyses were performed on pelagic limestones at deep sea drilling project site 463 central pacific ocean the 18o data exhibit a distinct anomaly by 2 spanning the oae 1a interval i e a 6 m thick phytoplanktonic corg rich unit constrained by magneto bio and 13c stratigraphy elucidation of paleotemperature significance of the 18o shift is made by taking account of recent sr ca evidence at the same section which revealed that geochemical signals in carbonate poor lithologies are relatively unaltered against burial diagenesis by discriminating 18o values from carbonate poor samples caco3 contents 5 30 wt it appears that an abrupt rise in sea surface temperatures ssts by 8 c 1 7 shift in 18o occurred immediately before oae 1a whereas a cooling mode likely prevailed during the peak corg burial in terms of its stratigraphic relationship as to the corg rich interval and to a pronounced negative 13c excursion as well as its timescale the observed sst rise resembles those associated with the paleocene eocene thermal maximum and more strikingly jurassic toarcian oae this observation is consistent with the hypothesis that these paleoenvironmental events were driven by a common causal mechanism which was likely initiated by the greenhouse effect via massive release of ch4 or co2 from the isotopically light carbon reservoir and terminated by a negative productivity feedback

magnetic stratigraphy of kimmeridgian aptian sections from umbria marche italy new details on the m polarity sequence 1 the magnetic stratigraphy of the maiolica and calcari ad aptici pelagic limestones is documented from four umbro marchean land sections italy the overall biostratigraphic age of the sampled strata encompasses the whole kimmeridgian lower aptian the data were gathered from two new sections arcevia contessa and by resampling more densely than in the past two additional classical sections bosso gorgo a cerbara a detailed record of the polarity chrons m21n m14 and m9 m0 was derived and no difference was observed with respect to the sequence of m polarity chrons inferred from oceanic magnetic anomalies barely measurable remanent magnetization from chron m14 to m10n at contessa concurred with previous evidence from bosso indicating that the maiolica from umbria marche is characterized by a recording gap during chrons m14n to m11 possibly due to diagenetic magnetite dissolution related to the late valanginian carbon isotope event at arcevia and bosso the boundary between maiolica and calcari ad aptici occurs at the top of chron m19n and in the upper part of chron m20n respectively showing that the onset of maiolica sedimentation may be diachronous by 1 5 2 myr along the umbria marche domain arcevia is the most expanded mid upper tithonian land section documented so far here the subchrons m20n 1 and m19n 1 are found to represent 3 2 and 10 1 in time of chrons m20n and m19n respectively evidence is also provided for a reversal excursion occurring within the m20n 1 subchron at bosso an excursion and a reversal excursion were found within chrons m16n and m16 respectively