asphalt volcanoes as a potential source of methane to late pleistocene coastal waters natural petroleum seepage emits large volumes of oil and methane to the oceans every year accompanied by the formation of asphalt volcanoes on the sea floor the discovery of seven asphalt volcanoes off the coast of southern california may help to explain high methane emissions recorded during the late pleistocene

biotic and geochemical response to anoxic events the aptian pelagic succession of the gargano promontory southern italy microfossil distribution patterns and high resolution 13 c and 18 o curves calibrated against planktonic foraminiferal and calcareous nannofossil data are provided for the aptian pelagic coppitella section of the gargano promontory southern italy the succession consists of cyclically arranged couplets of bioturbated grey marlstones and off white marly limestones referable to the marne a fucoidi in the lower portion of the section two thin black shales were recognized the high resolution 13 c curve presented here correlates with those of other alpine tethyan sections albeit with lower absolute values the onset of deposition of organic rich sediments falls at the top of the interval of unchanging carbon isotope values whereas the upper black shale is documented from the interval of the main aptian positive 13 c excursion according to our biostratigraphic data the deposition of organic matter in the gargano promontory persisted through early late aptian boundary time using a chemostratigraphic definition only the lower black shale is referred to the selli level as far as the biotic response is concerned the onset of the nannoconid crisis is recorded considerably below the lower black shale whereas the globigerinelloides eclipse is recorded below and within the upper black shale the distribution of meso eutrophic indices zygodiscus spp radiolaria vs moderate fertility indices rhagodiscus asper and lithraphidites carniolensis testifies to a modest increase of surface water fertility only throughout the stratigraphically higher black shale the occurrence of a benthic foraminiferal fauna albeit impoverished in both the basal and upper black horizons clearly documents dysaerobic rather than completely anoxic conditions on the sea floor relative sea level rise at the time of the selli event in the gargano promontory is documented by drowning and foundering of the apulia platform margin situated adjacent to the basin in which the marne a fucoidi accumulated

seasonal cycles of particle and solute transport processes in nearshore sediments 222rn226ra and 234th238u disequilibrium at a site in buzzards bay ma radiochemical measurements leading to the estimation of particle mixing rates and irrigation rates in the sediments of a site in buzzards bay massachusetts have been made over two nearly full seasonal cycles both particle mixing and sediment irrigation show significant seasonal variability at this site the variability is consistent with biologically driven transport mechanisms 234th238u disequilibrium measurements were used to estimate particle mixing rates based on three cores taken from december through march and four taken from june through october a cold season average mixing rate of 5 6 cm2 yr and a warm season average rate of 17 cm2 yr were found excess 234th inventories in the upper 5 cm of the sediments also varied seasonally with a cold season average value of 1 8 dpm cm2 significantly less than both the warm season value of 3 4 dpm cm2 and the predicted average value for buzzards bay 3 dpm cm2 222rn226ra disequilibrium in sediment pore waters was used to estimate sediment irrigation based on a total of seven cores three seasonal groupings of results were made 1 december through march when 222rn deficits could be explained by vertical molecular diffusion alone 2 early summer june when irrigation was important to at least 20 cm the maximum depth of the sampled region and 3 early fall when irrigation was important to about 10 cm a nonlocal exchange vertical molecular diffusion model emersonet al 1984 was used to obtain quantitative estimates of irrigation rates when the exchange parameter was allowed to vary exponentially with depth below the sediment water interface model rn deficit profiles fit measured profiles quite well

steryl ethers in a valanginian claystone molecular evidence for cooler waters in the central pacific during the early cretaceous abstract coring on shatsky rise by ocean drilling project leg 198 recovered sediments rich in organic matter 2 0 corg from three time intervals the early aptian corresponding to oceanic anoxic event oae 1a the valanginian and the berriasian episodes of enhanced sequestration of organic matter during the valanginian are well documented in the tethyan realm notably those associated with a positive 13c isotopic excursion and with changes in plankton assemblages including a demise in nannoconids the 13c excursion has been previously reported in the pacific but the occurrence of valanginian sediments rich in organic matter 1 corg is unprecedented a distinctive feature of the biomarker composition of these valanginian sediments at shatsky rise is the presence of a suite of steryl ethers which extends the temporal record of these compounds from the neogene to the early cretaceous the biological source of steryl ethers remains enigmatic although the sedimentary occurrences of these compounds in quaternary and neogene environments characterized by cool water high seasonal productivity and or nutrient enrichment by upwelling in combination with their liquid crystal properties raise the possibility that they may represent storage lipids akin to wax esters and triacylglycerols prior occurrences of steryl ethers suggest that their presence in the valanginian may reflect an oceanic environment characterized by upwelling consistent with the likely position of shatsky rise within the equatorial divergence zone of the pacific during the early cretaceous alternatively or in addition the appearance of these compounds may represent a biological response to cooler temperatures and thereby augment evidence for global cooling during the early valanginian consistent with independent paleontological evidence for contemporaneous upwelling induced increases in productivity in the western atlantic

organic geochemistry of lower cretaceous sediments from northwestern pacific guyots odp leg 143 organic geochemical data of lower cretaceous shallow water sediments from two sites 865 and 866 drilled during odp leg 143 are presented the organic matter is mainly terrestrial at the bottom of the sedimentary column at site 865 whereas algal and or bacterial organic matter is dominant at site 866 this is the first evidence of shallow water deposition of organic matter during the early cretaceous in the northwestern pacific the lower aptian organic carbon rich layers from the shallow water sediments of site 866 are geochemically similar to coeval mid water sediments of site 463

stratigraphy and structure of the lower cretaceous of lampazos sonora northwest mexico and its relationship to the gulf coast succession the stratigraphy and structure of the lower cretaceous aptian albian rocks exposed in the area of lampazos sonora are redefined and correlated to well known stratigraphic successions of chihuahua and northeast mexico coahuila and nuevo leon originally seven stratigraphic units were proposed for the cretaceous rocks exposed in the lampazos area but in this article only five units el aliso agua salada lampazos espinazo del diablo and los picachos formations have been used and we propose herein to discontinue usage of the other two nogal and la mesa formations this aptian albian succession of east central sonora yields facies and fossil content remarkably similar to coeval sequences in the gulf of mexico realm chihuahua coahuila and nuevo leon these sections contain abundant microfossils benthic and planktonic foraminifera colomiellids nannoconids and radiolarians that permit detailed biostratigraphic determinations a complete aptian lower albian section base of k 6 through top of k 15 of the biochronologic scheme of longoria 1984 was identified abrupt lithic changes through the aptian albian section of lampazos revealed three major paleoceanographic events having an overall regional marine transgression including an early aptian k 6 to k 7 event a late aptian k 10 to k 11 event and an early albian k 13 to k 14 maximum flooding phase we used physical and biochronologic data to tie the aforementioned events to geochemically constrained aptian albian oceanic anoxic events oaes in santa rosa canyon of nuevo leon the close correlation between the oceanic events in east sonora northwest mexico and central nuevo leon northeast mexico invokes the closer paleogeographic development of the two regions and undoubtedly links the area of lampazos to a rapid encroachment of the paleo gulf of mexico through north central mexico the mexican sea into northwestern mexico chihuahua trough and sonoran basin the early aptian biozones k 6 to k 7 transgression has its maximum extension during the early albian biozones k 13 to k 14 culminating with the drowning of the carbonate platforms the lower cretaceous rocks exposed in the lampazos area are complexly folded and faulted the more conspicuous structures are isoclinal and box shaped folds and thrust faults mostly oriented north south and northwest southeast having vergences to both the northeast and southwest a very conspicuous feature is the opposite vergence of thrust faults either converging or diverging two dextral strike slip faults northeast southwest and east west separate the area into three large blocks that have different patterns of folds and thrust faults also it is evident that the area was affected by at least two episodes of normal faulting furthermore the structural style of deformation present in the lampazos succession is remarkably similar to the style of deformation of coeval rocks in northeastern mexico especially to the structure of the chihuahua tectonic belt the lampazos succession is paleogeographically and tectonically related to the chihuahua tectonic belt and it is considered to be the westernmost extension of the ancestral gulf of mexico the fact that the lampazos succession can be lithocorrelated to known sequences in northeastern chihuahua lucero ahumada and loma plata formations and northeast mexico cupido san angel la pena and tamaulipas formations which are know to be source rocks in exploration wells in nuevo leon and coahuila makes the lampazos area of sonora potentially attractive as an exploration target

isotopic evidence for early to mid cretaceous ocean temperature variability abstract stable isotopic measurements have been made on planktonic and benthic foraminifera of early to mid cretaceous early albian cenomanian age from dsdp site 463 located in the pacific ocean the degree of alteration of the foraminifera has been assessed through the application of scanning electron microscopy the oxygen isotope data support the view that during the cenomanian globigerine foraminifera such as the genus hedbergella inhabited near surface waters whilst the flattened keeled morphotypes lived deeper within the water column the carbon isotope data reveal a more complex pattern as the 13 c values from planktonic species essentially show a large overlap which is interpreted in terms of a weak 13 c gradient existing in the upper part of the ocean in contrast the oxygen isotope data from planktonic foraminifera from the late albian display no discernible depth stratification pattern and the 13 c data also show a large overlap of values indicative of a complete disruption of the upper part of the thermocline a relatively low surface to bottom water temperature gradient within the early middle albian part of the succession may reflect a well mixed ocean inferred cool ocean temperatures and or high salinities for the early albian may reflect increased oceanic poleward heat transport an increase in temperature and or decrease in salinity in the cenomanian suggests a reduction of the poleward heat flux promoting the build up of limited polar ice during this period of tropical warmth

evolution in the test size of deep sea benthic foraminifera during the past 120 m y evidence is presented for stratigraphic variations in test size of the largest deep water 1500 m water depth calcareous trochospiral benthic foraminifera for eight dominant lineages composed of ten genera over the past 120 m y variations in test size show 1 a general trend of increasing test size during the past 120 m y and 2 fluctuations highlighted by six minima and six maxima that are synchronized among genera the long term increase in size corresponds to an increase in the 18o of deep water benthic foraminifera the minimum and maximum sizes correspond to minima and maxima in the 18o respectively in addition three major minima in test size correspond to distinct low dissolved oxygen events these latter synchronisms indicate that oceanic climate and dissolved oxygen or related factors likely controlled evolution in test size of deep water calcareous trochospiral benthic foraminiferal genera

rapid changes in the redox conditions of the western tethys ocean during the early aptian oceanic anoxic event the early aptian 125 to 121 ma records an episode of severe environmental change including a major perturbation of the carbon cycle an oceanic anoxic event oae 1a 122 5 ma a platform drowning episode and a biocalcification crisis we propose to trace changes in the oxygenation state of the ocean during the early aptian anoxic event using the redox sensitive trace element rste distribution phosphorus accumulation rates pars and organic matter characterization in three different basins of the western tethys the following sections have been investigated gorgo a cerbara central italy in the umbria marche basin glaise se france in the vocontian basin and cassis la bedoule se france located in the provencal basin in the gorgo a cerbara section rste distributions show a low background level along the main part of the section contrasted by different maxima in concentrations within the selli level in the glaise section the goguel level displays a weak increase in rste contents coeval with moderate toc values at cassis la bedoule no significant rste enrichments have been observed in sediments equivalent to the selli level these differences in the records of the geochemical proxies of the selli level or its equivalent indicate the deposition under different redox conditions probably related to the paleogeography our data indicate the development of anoxic euxinic conditions in the deeper part of the tethys during oae 1a whereas in the shallower environments conditions were less reducing moreover at gorgo a cerbara the selli level is characterized by rapid changes in the intensity of reducing conditions in the water column ocean eutrophication seems to be a major factor in the development and the persistence of anoxia as suggested by the par evolution higher par values at the onset of oae 1a suggest an increase in nutrient input whereas the return to lower values through the first part of the oae 1a interval may be related to the weakened capacity to retain p in the sedimentary reservoir due to bottom water oxygen depletion this general pattern is contrasted by the data of gorgo a cerbara where the sediments deposited during the oae 1a interval show p enrichments mainly authigenic p this is associated with maxima in toc values and corg ptot ratios suggesting that a part of the remobilized p was trapped in the sediments and as such prevented from returning to the water column

a new approach to discern the hydrocarbon sources oil vs methane of authigenic carbonates forming at marine seeps abstract numerous marine hydrocarbon seeps have been discovered in the past three decades the majority of which are dominated by methane rich fluids however an increasing number of modern oil seeps and a few ancient oil seep deposits have been recognized in recent years oil seepage exerts significant control on the composition of the seep dwelling fauna and may have impacted the marine carbon cycle through geological time to a greater extent than previously recognized yet distinguishing oil seep from methane seep deposits is difficult in cases where 13ccarb values are higher than approximately 30 due to mixing of different carbon sources here we present a comparative study of authigenic carbonates from oil dominated site gc232 and methane dominated site gc852 seep environments of the northern gulf of mexico aiming to determine the geochemical characteristics of the two types of seep carbonates we analyzed 1 major and trace element compositions of carbonates 2 total organic carbon toc total nitrogen tn and carbon isotope 13ctoc of residue after decalcification 3 sulfur isotope signatures of chromium reducible sulfur crs 34scrs and residue after crs extraction 34stos as well as 4 sulfur contents tos of residue after crs extraction carbonates from the studied oil seep are dominated by aragonite and exhibit lower 34scrs values suggesting carbonate precipitation close to the sediment surface in addition oil seep carbonates are characterized by higher toc and tos contents and higher toc tn ratios as well as less negative 13ctoc values compared to methane seep carbonates probably reflecting a contribution of residual crude oil enclosed in oil seep carbonates very low 13ctoc values as low as 68 7 vpdb and low toc tn ratios of methane seep carbonates indicate that the enclosed organic matter is derived mainly from the biomass of methanotrophic biota this study presents new geochemical data that will allow the discrimination of oil seep from methane seep deposits although some of the geochemical patterns are likely to be affected by late diagenesis if applied with caution such patterns can be used to discern the two end member types of seepage oil seeps and methane seeps in the geological record

biogeochemical assessment of sources of organic matter and paleoproductivity during the early aptian oceanic anoxic event at shatsky rise odp leg 198 this study investigates organic rich sedimentary sequences deposited during the early aptian oceanic anoxic event oae1a at sites 1207 and 1213 on shatsky rise odp leg 198 in the west central pacific biomarker analyses provide evidence of the algal and bacterial origin of organic matter om in these sediments where the abundance of steroidal components particularly sterenes and sterones suggests that the om includes major contributions from eukaryotic sources in an environment characterized by high phytoplankton productivity the presence of alkenones at site 1213b is diagnostic of om derived from representatives of haptophyte algae among the calcareous nannoplankton and their 13c values average 31 6 are consistent with those expected during elevated pco2 the occurrence and prominence of 2 methylhopanes and 2 methylhopanones indicates significant contributions to the om from cyanobacteria which are also likely contributors of hopanoids based on their 13c compositions these biomarker data suggest that oceanic conditions perhaps nitrate or iron limited were conducive to cyanobacteria production during oae1a which appears to distinguish this event from other cretaceous oae

repeated pulses of vertical methane flux recorded in glacial sediments from the southeast bering sea 1 there is controversy over the role of marine methane hydrates in atmospheric methane concentrations and climate change during the last glacial period in this study of two sediment cores from the southeast bering sea 700 m and 1467 m water depth we identify multiple episodes during the last glacial period of intense methane flux reaching the seafloor within the uncertainty of the radiocarbon age model the episodes are contemporaneous in the two cores and have similar timing and duration as dansgaard oeschger events the episodes are marked by horizons of sediment containing 13c depleted authigenic carbonate minerals 13c depleted archaeal and bacterial lipids which resemble those found in anme 1 type anaerobic methane oxidizing microbial consortia and changes in the abundance and species distribution of benthic foraminifera the similar timing and isotopic composition of the authigenic carbonates in the two cores is consistent with a region wide increase in the upward flux of methane bearing fluids this study is the first observation outside santa barbara basin of pervasive repeated methane flux in glacial sediments however contrary to the clathrate gun hypothesis kennett et al 2003 these coring sites are too deep for methane hydrate destabilization to be the cause implying that a much larger part of the ocean s sedimentary methane may participate in climate or carbon cycle feedback at millennial timescales we speculate that pulses of methane in these opal rich sediments could be caused by the sudden release of overpressure in pore fluids that builds up gradually with silica diagenesis the release could be triggered by seismic shaking on the aleutian subduction zone caused by hydrostatic pressure increase associated with sea level rise at the start of interstadials

the use of radon 222 as a tracer of sediment irrigation and mixing on the washington continental shelf abstract observations of the natural radioisotope rn 222 were used in conjunction with radiochemical biological and sedimentological techniques to investigate the irrigation and mixing of sediment at three sites about 90 m water depth along the washington continental shelf the rn 222 deficit difference between observed and predicted concentrations within the seabed was greatest near the columbia river during the summer molecular diffusion at most locations and times could account for only a portion of the deficit irrigation and mixing of the seabed explain the remainder biological mixing bioturbation and physical irrigation wave and tidal pumping have relatively little effect on the rn 222 deficit physical mixing erosion and deposition has a significant effect soon after a major erosion event storm however no such event occurred prior to the observations the conclusion is that biological irrigation and molecular diffusion are the primary causes of the rn 222 deficit and that biological irrigation is responsible for the observed spatial and temporal variations in the deficit therefore biological irrigation is greatest near the columbia river during the summer the spatial increase of irrigation near the columbia is probably due to a relatively large population of tube dwelling filter feeding polychaetes the temporal increases of irrigation during the summer is probably due to annual growth cycles of the benthic community and is not due to water temperature changes

considerable methane fluxes to the atmosphere from hydrocarbon seeps in the gulf of mexico the flux of methane a greenhouse gas from submarine hydrocarbon seeps to the atmosphere is not well quantified direct measurements of methane concentrations and isotopic depth profiles in deepwater hydrocarbon plumes indicate that a significant amount of methane from deep ocean sources could reach the surface ocean the fluxes of the greenhouse gas methane from many individual sources to the atmosphere are not well constrained1 marine geological sources may be significant2 but they are poorly quantified and are not included in the intergovernmental panel on climate change budget1 previous results based on traditional indirect sampling techniques and modelling suggested bubble plumes emitted from marine seeps at depths greater than 200 m do not reach the surface mixed layer because of bubble dissolution and methane oxidation3 4 5 here we report methane concentration and isotope depth profiles from direct submersible sampling of deepwater 550 600 m hydrocarbon plumes in the gulf of mexico we show that bubble size upwelling flows and the presence of surfactants inhibit bubble dissolution and that methane oxidation is negligible consequently methane concentrations in surface waters are up to 1 000 times saturation with respect to atmospheric equilibrium we estimate that diffusive atmospheric methane fluxes from individual plumes are one to three orders of magnitude greater than estimates from shallow water seeps6 7 8 greatly expanding the depth range from which methane seep emissions should be considered significant given the widespread occurrence of deepwater seeps we suggest that current estimates of the global oceanic methane flux to the atmosphere1 may be too low

environmental conditions in the south atlantic angola basin during the early cretaceous abstract the south atlantic has experienced periods of intense anoxia and black shale deposition that form an important hydrocarbon source here we have investigated the depositional environment during the initial opening phase of the south atlantic during the early cretaceous the period is crucial as it is characterized by extensive source rock deposition and because it sets the stage for subsequent periods of anoxia within the northern sub basin of the south atlantic within an aptian sequence of organic rich sediments up to 40 total organic carbon toc from deep sea drilling project dsdp site 364 we found a distinct biomarker distribution including the presence of isorenieratane and an array of thiophenic s containing compounds our results indicate that during the time of deposition corresponding to the initial phase of opening of the south atlantic most of the water column in the angola basin was hypersaline 40 and euxinic with euxinia episodically reaching the photic zone the low relative abundance of marine biomarkers in the samples suggests that these extreme conditions were unfavourable for typical marine organisms stratigraphically up section the biomarker distribution changed as the toc content gradually decreased

families of miocene monterey crude oil seep and tarball samples coastal california biomarker and stable carbon isotope ratios were used to infer the age lithology organic matter input and depositional environment of the source rocks for 388 samples of produced crude oil seep oil and tarballs to better assess their origins and distributions in coastal california these samples were used to construct a chemometric multivariate statistical decision tree to classify 288 additional samples the results identify three tribes of 13c rich oil samples inferred to originate from thermally mature equivalents of the clayey siliceous carbonaceous marl and lower calcareous siliceous members of the monterey formation at naples beach near santa barbara an attempt to correlate these families to rock extracts from these members in the nearby cost continental offshore stratigraphic test ocs cal 78 164 well failed at least in part because the rocks are thermally immature geochemical similarities among the oil tribes and their widespread distribution support the prograding margin model or the banktop slope basin model instead of the ridge and basin model for the deposition of the monterey formation tribe 1 contains four oil families having geochemical traits of clay rich marine shale source rock deposited under suboxic conditions with substantial higher plant input tribe 2 contains four oil families with traits intermediate between tribes 1 and 3 except for abundant 28 30 bisnorhopane indicating suboxic to anoxic marine marl source rock with hemipelagic input tribe 3 contains five oil families with traits of distal marine carbonate source rock deposited under anoxic conditions with pelagic but little or no higher plant input tribes 1 and 2 occur mainly south of point conception in paleogeographic settings where deep burial of the monterey source rock favored petroleum generation from all three members or their equivalents in this area oil from the clayey siliceous and carbonaceous marl members tribes 1 and 2 may overwhelm that from the lower calcareous siliceous member tribe 3 because the latter is thinner and less oil prone than the overlying members tribe 3 occurs mainly north of point conception where shallow burial caused preferential generation from the underlying lower calcareous siliceous member or another unit with similar characteristics in a test of the decision tree 10 tarball samples collected from beaches in monterey and san mateo counties in early 2007 were found to originate from natural seeps representing different organofacies of monterey formation source rock instead from one anthropogenic pollution event the seeps apparently became more active because of increased storm activity

mid cretaceous oceanic anoxic events in the pacific ocean revealed by carbon isotope stratigraphy of the calera limestone california usa the paleoceanographic history of the pacific ocean during the mid cretaceous is poorly constrained due to the loss of much of the contemporaneous pacific seafloor to subduction and difficulties in recovering chert rich sediments by ocean drilling pelagic sediments that were originally deposited in the pacific ocean but that have been subsequently accreted during subduction potentially provide an alternative paleoceanographic archive this study presents micropaleontological and carbon isotope data from the calera limestone part of the classic franciscan complex exposed in permanente quarry central california usa in the three stratigraphic sections studied pelagic limestones with low organic carbon contents are the dominant lithology however two stratigraphic intervals are recognized that contain organic carbon and these date to the early aptian and late albian early cenomanian these time intervals correspond to two mid cretaceous oceanic anoxic events oaes early aptian oae1a equivalent to the selli level and late albian oae1d equivalent to the breistroffer event it is well established that both of these events were associated with significant carbon isotope excursions which are also shown to exist in the calera limestone the record of oae1a from the calera limestone complements ocean drilling records by providing further evidence for variability in the sedimentary and stratigraphic record of this event the carbon isotope data from the late albian early cenomanian provide the first detailed chemobiostratigraphic record of this period for the pacific ocean confirming that environmental change occurred at this time in the pacific possibly related to oae1d

palaeoceanography of organic rich rocks of the loma chumico formation of costa rica late cretaceous eastern pacific the late cretaceous late cenomanian campanian loma chumico formation consists of laminated to massive bedded siliceous shales cherts ash fall tuffs volcanic glass beds and volcaniclastic sandstones the loma chumico formation is at least 630 m thick core data in the tempisque basin and can be subdivided in the subsurface into organic rich and organic lean total organic carbon 1 facies rock eval total organic carbon toc data show that toc in the organic rich facies averages 15 5 with values as high as 33 inorganic geochemical petrological and sedimentological analyses indicate that all the lithologies of the loma chumico formation were deposited in middle shelf to outer slope environments adjacent to an active subaerial island arc the organic geochemistry and palaeontology of the loma chumico formation help constrain the factors that controlled biological productivity in the region during the late cretaceous biomarkers identified in organic rich facies by gas chromatography mass spectrometry gc ms show a high abundance of total steranes relative to hopanes in the morote 1 core indicating algal dominated organic input the hopane to sterane ratio of the extract from the manzanillo 1 core indicates a relatively high bacterial component to the organic matter upwelling and extrusive volcanism were the most important factors that controlled nutrient supply including silica flux and biological productivity within the loma chumico formation depositional system episodic radiolarian dinoflagellate or diatom blooms instigated by rapid infusions of volcanogenic silica may have resulted in expansion of the oxygen minimum zone omz enhancing the preservation of organic matter productivity appears to have been uniform even during deposition of the organic lean facies the findings of this study suggest that ocean wide anoxia in the eastern pacific was unlikely during the late cretaceous high toc contents of organic rich radiolarites from central caribbean deep sea drilling project dsdp sites may be related to upwelling produced in the eastern pacific by convergence of the easterly trade winds eastern pacific equatorial upwelling zone or may be part of a more complex pacific atlantic ocean interaction the end of deposition of organic rich rocks began near the end of the latest santonian earliest campanian in the central caribbean and costa rica palaeoceanographic models suggest that improved circulation and ventilation of bottom waters due to early opening of the north atlantic south atlantic seaway may explain this observation this may represent the influx of a previously unrecognized source of colder oxygenated intermediate bottom water proto antarctic intermediate water into the late cretaceous central atlantic and eastern pacific oceans

infaunal burrow ventilation and pore water transport in muddy sediments the ventilation of burrows by tube dwelling benthos is understood to be important in determining rates of exchange of solutes between the sediment and overlying water however few models have attempted to link the burrow ventilation behavior of tube dwelling organisms with their geochemical consequences the classic cylinder model of bioirrigation in muddy sediments aller r c 1980 quantifying solute distributions in the bioturbated zone of marine sediments by defining an average microenvironment geochimica et cosmochimica acta 44 1955 1965 links pore water processes and burrow sizes and distributions in the sediment by assuming that burrows are fully flushed the equivalence between the cylinder model and the more commonly used one dimensional non local exchange model depends upon this assumption however this assumption has seldom been tested in the field we have extended the cylinder model of bioirrigation to include burrow ventilation activities of organisms burrow ventilation is modeled as a simple non local exchange of burrow water with overlying water model simulations indicate that burrow ventilation has a large effect on vertical profiles and fluxes of solute tracers we collected data on burrow geometry in the field by ct scanning freshly collected sediment cores at the same study sites we measured activity profiles of 222 rn a naturally occurring radionuclide tracer of pore water transport with model geometry independently constrained we tested the model by comparing our model predicted profiles with measured profiles our results demonstrate that burrows in the field are not fully flushed our estimated burrow ventilation rates compare favorably with previous laboratory measurements the inclusion of realistic burrow ventilation in this pore water transport model strongly affects modeled solute profiles and fluxes we demonstrate how model parameters can be determined from field samples and present a model that more realistically simulates pore water transport processes in muddy sediments

the use of short lived radionuclides to quantify transitional bed material transport in a regulated river we investigate the use of the short lived fallout radionuclide beryllium 7 7be t1 2 53 4 days as a tracer of medium and coarse sand 0 25 2 mm which transitions between transport in suspension and as bed load and evaluate the effects of impoundment on seasonal and spatial variations in bed sedimentation we measure 7be activities in approximately monthly samples from point bar and streambed sediments in one unregulated and one regulated stream in the regulated stream our sampling spanned an array of flow and management conditions during the annual transition from flood control in the winter and early spring to run of the river operation from late spring to autumn sediment stored behind the dam during the winter quickly became depleted in 7be activity this resulted in a pulse of dead sediment released when the dam gates were opened in the spring which could be tracked as it moved downstream measured average sediment transport velocities 30 80 metres per day m d 1 exceed those typically reported for bulk bed load transport and are remarkably constant across varied flow regimes possibly due to corresponding changes in bed sand fraction results also show that the length scale of the downstream impact of dam management on sediment transport is short c 1 km beyond this distance the sediment trapped by the dam is replaced by new sediment from tributaries and other downstream sources copyright 2006 john wiley sons ltd

formation of the late aptian niveau fallot black shales in the vocontian basin se france evidence from foraminifera palynomorphs and stable isotopes abstract we present paleoceanographic models for the formation of the marlstone facies and the most prominent black shale intervals of the late aptian niveau fallot black shale succession from the vocontian basin se france in the lower part of the succession the composition of benthic foraminiferal assemblages of the niveau fallot 2 and 2 black shales suggests an enhanced burial of organic matter due to more eutrophic conditions and resulting low oxygen conditions at the seafloor in the upper part of the succession including niveau fallot 3 and 4 a third order sea level fall indicated by a decrease in the stable carbon isotope values may have resulted in a reduced water mass exchange between the vocontian basin and the western tethyan ocean this may have led to dysoxic conditions at the seafloor of the vocontian basin and may have favored the formation of organic rich sediments as shown by benthic foraminiferal assemblages decreased evaporation however is proposed as the most important mechanism causing a restriction of deep water formation within the basin which finally led to the formation of the niveau fallot 3 and 4 black shales based on our investigations the formation of the niveau fallot black shales was caused by different factors the most prominent ones include sea level fluctuations increasing productivity and changes in precipitation and evaporation rates furthermore niveau fallot 3 can probably be correlated with the thalmann black shale event in california and a dark horizon at the mazagan plateau dsdp site 545

origins and accumulation of organic matter in expanded albian to santonian black shale sequences on the demerara rise south american margin ocean drilling program leg 207 recovered thick sequences of albian to santonian organic carbon rich claystones at five drill sites on the demerara rise in the western equatorial atlantic ocean dark colored finely laminated cenomanian santonian black shale sequences contain between 2 and 15 organic carbon and encompass oceanic anoxic events 2 and 3 high rock eval hydrogen indices signify that the bulk of the organic matter in these sequences is marine in origin however d 13 corg values lie mostly between 30 and 27 and toc tn ratios range from 15 to 42 which both mimic the source signatures of modern c3 land plants the contradictions in organic matter source indicators provide important implications about the depositional conditions leading to the black shale accumulations the low d 13 corg values which are actually common in mid cretaceous marine organic matter are consequences of the greenhouse climate prevailing at that time and an associated accelerated hydrologic cycle the elevated c n ratios which are also typical of black shales indicate depressed organic matter degradation associated with low oxygen conditions in the water column that favored preservation of carbon rich forms of marine organic matter over nitrogen rich components underlying the laminated cenomanian santonian sequences are homogeneous dark colored lower to middle albian siltstones that contain between 0 2 and 9 organic carbon the organic matter in these rocks is mostly marine in origin but it occasionally

relative sea level change and carbon isotopes data from the upper jurassic oxfordian of central and southern europe studies on cretaceous pelagic limestones have shown a close correspondence between putative sea level curves and the carbon isotope profile suggesting a possible relationship between the two phenomena such a relationship could relate to shelf sea area governing the global burial rate of organic carbon which in turn controls the 13c 12c ratio of dissolved inorganic carbon in the oceanic reservoir in order to see whether or not this relationship might be of more general applicability the major mid oxfordian jurassic transgression is documented to zonal level and appropriate carbon isotope data are presented although the applicability of ammonite zonation to the mid oxfordian is problematic on a regional scale a clear 13c excursion is present in the trunsversariurn zone which is coincident with regional overstep and or evidence of shoreline retreat and or evidence of bathymetric deepening in europe and elsewhere the use of the carbon isotope curve as a proxy for shelf sea area or relative sea level is worthy of further exploration

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

nannofossils and superplumes the early aptian nannoconid crisis a group of calcareous nannoplankton named nannoconids experienced a crisis in the early aptian and recovered only later in the late aptian after a period of virtual absence although no extinctions occurred the widespread nature of the nannoconid crisis suggests a global causal factor this crisis is recorded within the chiastozygus litterarius nannofossil and globigerinelloides blowi planktonic foraminiferal zones postdates magnetic chronozone m0 by approximately 300 kyr and precedes the oceanic anoxic subevent 1a and associated 13c anomaly by some 40 100 kyr selective dissolution and anoxia cannot explain the crisis because nannoconids are dissolution resistant forms and their crisis clearly precedes the deposition of anoxic sediments at least 1 m y prior to the nannoconid crisis the onset of a nannoplankton speciation event may be the response of nannofloras to a major rise in relative sea level the nannoconid crisis seems to be synchronous with the early aptian volcanic eruptions in the pacific ocean hence calcareous nannoplankton were severely affected by the superplume volcanic episode the coccolithophorid bloom nannoconid crisis was possibly induced by the excessive co2 levels in the atmosphere and or caused by changes in nutrient content of oceanic surface waters fertility was enhanced by rapid turnover of nutrients due to the abnormal volcanic activity and accelerated transfer of nutrients from the continents into the oceans under warm and humid conditions of the mid cretaceous greenhouse climate the nannoconid crisis may represent a competition between phytoplankton groups for nutrients or more likely competition between different calcareous nannoplankton the biologic affinity and mode of life of nannoconus are unknown because there is no modern analog of this genus however comparison of lower cretaceous nannofossil assemblages with modern nannoplankton cummunities suggests that nannoconids like extant florisphaera profunda possibly inhabited the lower photic zone concentrations of nutrients in the upper euphotic zone may have triggered blooms of coccolithophorids and nannoconid depletion this model implies that the nannoconid crisis is the result of an abrupt major change in the structure of surface waters caused directly or indirectly by the superplume the adjustments of the biosphere to the new paleoceanographic and climatic conditions required some 40 100 kyr before changing into abnormally high primary productivity and deposition of organic carbon rich sediments with dinoflagellates outcompeting nannoplankton

toward an orbital chronology for the early aptian oceanic anoxic event oae1a 120 ma abstract the early aptian oceanic anoxic event oae1a 120 ma represents a geologically brief time interval in the mid cretaceous greenhouse world that is characterized by increased organic carbon accumulation in marine sediments sudden biotic changes and abrupt carbon isotope excursions indicative of significant perturbations to global carbon cycling the brevity of these drastic environmental changes

an advection diffusion model for222rn transport in near shore sediments inhabited by sedentary polychaetes abstract a porewater solute transport model is proposed to explain the dissolved radon distributions in four profiles from a near shore marine site the macro infauna at the site is dominated by clymenella torquata a sedentary deposit feeding polychaete that actively irrigates its burrow the model includes both an advective component that takes into account the e g c torquata mechanism of burrow irrigation as well as enhanced diffusion like transport brought about by mobile infauna because it explains the existence of subsurface radon minima with a constant source function and is based on the known irrigations habits of c torquata the model provides good fit to observed radon profiles and may be applicable to other solutes that display depth dependent minima sediment advection velocities individual burrow irrigation rates and enhanced diffusion coefficients are estimated based on a minimization of chi squared for model fits to the 222 rn data of each profile the net advection velocity ranged from 0 19 to 0 91 cm d 1 and enhanced diffusion ranged from 13 to 30 times effective molecular diffusion these values are comparable to those determined by previous investigators using other transport models in similar sediments the range of burrow irrigation rates 0 16 0 78 ml h individual is somewhat lower than the average rate for c torquata that had been determined in the laboratory

asphalt volcanism and chemosynthetic life in the campeche knolls gulf of mexico in the campeche knolls in the southern gulf of mexico lava like flows of solidified asphalt cover more than 1 square kilometer of the rim of a dissected salt dome at a depth of 3000 meters below sea level chemosynthetic tubeworms and bivalves colonize the sea floor near the asphalt which chilled and contracted after discharge the site also includes oil seeps gas hydrate deposits locally anoxic sediments and slabs of authigenic carbonate asphalt volcanism creates a habitat for chemosynthetic life that may be widespread at great depth in the gulf of mexico

palaeoecology palaeogeography and depositional environments of upper cretaceous rocks of western venezuela abstract the end of the early cretaceous in northern south america was marked by regional palaeoceanographic change in western venezuela this change was highlighted near the end of the albian by drowning of the maraca formation shallow water carbonate platform regional marine transgression continued during the cenomanian and turonian in western venezuela with drowning of the more southerly guayacan member capacho and escandalosa formations carbonate platform deposition of organic carbon rich intervals of the la luna and navay formations occurred unconformably on maraca formation and guayacan member shallow water carbonates and continued through the early santonian during this interval the maracaibo and barinas apure basins were characterized by low oxygen or anoxic bottom water conditions away from the basin margins deposition of organic carbon lean upper la luna and navay formation strata show that bottom water oxygen content increased from the late santonian through the end of the cretaceous the siliceous and phosphatic late santonian to early maastrichtian tres esquinas member and the glauconitic late campanian to early maastrichtian socuy member both of the la luna formation represent the final phase of la luna deposition in the maracaibo basin tectonic uplift in eastern colombia during the campanian and maastrichtian caused progradation of the colon mito juan and burguita formation deltas and eventual infilling of the maracaibo and barinas apure basins

aptian anoxia in the pacific basin marine strata of aptian age in the pacific basin include two distinct levels that represent episodes during which sediments rich in organic carbon were deposited both episodes lasted less than 1 m y as revealed in strata deposited atop submerged topographic highs one unusually widespread episode of early aptian age 117 5 ma correlates with coeval units in europe and thus is analogous to the cenomanian turonian oceanic anoxic event in its short duration and wide geographic extent the second episode of late aptian age 116 5 ma is restricted to allochthonous pelagic deposits in the franciscan complex of california these results support the concept of widespread and narrowly synchronous anoxic events further they show that organic carbon deposition in the pacific basin took place in intermediate water oxygen minimum zones and thus differed in the mode of deposition and hence paleoceanography from that in other middle cretaceous ocean basins

detection of natural oil slicks in the nw gulf of mexico using modis imagery i we demonstrate the unique capability of the modis instruments in detecting oil slicks in an open ocean environment on 13 may 2006 in the nw gulf of mexico where water depth ranges from 50 to 2500 m one 250 m resolution modis image showed at least 164 surface slicks under sun glint glint reflectance l g ranged between 0 0001 and 0 06 sr 1 after discounting other possible causes we believe these are the result of natural seeps our analysis showed total coverage of 1900 km 2 with individual slicks varying in surface area 1 1 7 14 8 km 2 and length 19 2 12 4 km concurrent sar imagery showed similar area estimates to within 30 this estimate based on a single image is higher than earlier estimates from a database of multi date sar images for the same region inspection of 200 images for the month of may between 2000 and 2008 revealed similar slicks on at least 50 images on 2 june 2005 slicks were detected under sun glint with both negative contrast l g 0 05 sr 1 these slicks could not be detected in glint free modis images collected on the same day because of the near daily revisit and wide sun glint coverage e g 800 km e w between march and october at 25 n systematic and global application of the modis 250 m imagery can help locate natural seeps and improve estimates of seepage rates in the world s ocean

terrestrial record of methane hydrate dissociation in the early cretaceous reconstruction of changing c isotopic composition of early cretaceous atmospheric co2 from fossilized c3 vascular land plant tissue revealed a brief and striking negative excursion d 25 in atmospheric d 13 c followed by a rapid positive compensation d 15 during the aptian ca 117 ma mass balance calculations show that dissociation of a small amount of methane gas hydrate is the most tenable cause of the negative excursion this would also result in an increased co2 o2 mixing ratio as o2 is consumed during ch4 oxidation to co2 spurring the exponential phase of angiosperm biogeographic expansion

reversed polarity characteristic magnetizations in the albian contessa section umbrian apennines italy implications for the existence of a mid cretaceous mixed polarity interval paleomagnetic and paleontologic data from the valle della contessa umbrian apennines italy span a 14 m y gap in previous magnetostratigraphic sections and reveal several intervals of reversed characteristic remanent magnetization chrm in limestones and marls of the albian marne a fucoidi rock magnetic data indicate that the reversed chrm is carried by hematite having high unblocking temperatures 625 690 c hematite with these unblocking temperatures also carries a normal polarity chrm in other intervals a potential bias towards the identification of normal polarity is present since at every horizon measured a normal polarity component carried by magnetite and hematite is isolated at lower unblocking temperatures 300 600 c bulk magnetic properties vary throughout the measured section in the portion containing most of the reversed chrm intervals hematite is the dominant carrier of natural remanent magnetization while magnetite is the dominant carrier stratigraphically above and below these changes correspond approximately with lithology the zone of dominant hematite magnetization is marked by reddish bands pigmentary hematite which can be correlated throughout umbria and are thought to record changes in the oxidation state of the seafloor during deposition two models may account for the observed magnetization directions the reversed magnetizations may record a remagnetization which occurred at least 18 m y after deposition while the beds were still flat lying in reversed polarity chron 33r 83 79 ma or later if the reversed chrm represents a remagnetization the process is potentially of great importance since it can produce magnetization patterns which resemble polarity intervals alternatively the reversed magnetizations may have been acquired during intense seafloor oxidation episodes during the mid albian 107 104 ma and may record unrecognized intervals of reversed geomagnetic field polarity milankovitch like bedding cyclicity can be used to tune the sedimentation rate and obtain estimates of the duration of the potential reversed intervals using these estimates two of the potential reversed polarity intervals are of sufficient duration 100 kyr to be recognizable in both detailed stratigraphic sections and marine magnetic anomaly surveys a primary magnetization model predicts that several intervals of reversed magnetization should be found near the boundary of the biticinella breggiensis and ticinella primula foraminiferal zones and within the prediscosphaera cretacea nannofossil zone on a worldwide basis

paleoceanographic and paleoclimatic similarities between mediterranean sapropels and cretaceous black shales pliocene quaternary sapropels of the mediterranean sea and mid cretaceous black shales share many distinctive properties organic carbon concentrations that often exceed 5 in both types of sequences record episodes of exceptional accumulation of organic matter although both are rich in marine organic matter they have high c n ratios that mimic those of land plant organic matter which suggests less efficient organic matter recycling than in the modern ocean the coupled presence of isorenieratene derivatives and low 15n values that result from microbial primary productivity indicates that photic zone anoxia existed during their formation and implies strong stratification of the surface ocean enrichments of redox sensitive metals and sediment laminations indicate that anoxia existed deeper in the water column and at the seafloor multiple proxies indicate freshening of surface waters of the mediterranean and imply periods of wetter climate during times of sapropel deposition episodes of black shale deposition similarly coincide with times of wetter climate these comparisons suggest that the wetter climate created similar conditions of surface salinity stratification that enhanced microbial primary production and magnified organic matter export during deposition of both the mediterranean sapropels and mid cretaceous black shales

particle mixing rates in deep sea sediments determined from excess 210pb and 32si profiles particle mixing rates have been determined for 5 south atlantic antarctic and 3 equatorial pacific deep sea cores using excess 210 pb and 32 si measurements radionuclide profiles from these siliceous calcareous and clay rich sediments have been evaluated using a steady state vertical advection diffusion model in antarctic siliceous sediments 210 pb mixing coefficients 0 04 0 16 cm 2 y are in reasonable agreement with the 32 si mixing coefficient 0 2 or 0 4 cm 2 y depending on 32 si half life in an equatorial pacific sediment core however the 210 pb mixing coefficient 0 22 cm 2 y is 3 7 times greater than the 32 si mixing coefficient 0 03 or 0 07 cm 2 y the difference in 210 pb and 32 si mixing rates in the pacific sediments results from 1 non steady state mixing and differences in characteristic time and depth scales of the two radionuclides 2 preferential mixing of fine grained clay particles containing most of the 210 pb activity relative to coarser particles large radiolaria containing the 32 si activity or 3 the supply of 222 rn from the bottom of manganese nodules which increases the measured excess 210 pb activity relative to 226 ra at depth and artificially increases the 210 pb mixing coefficient based on 32 si data and pore water silica profiles dissolution of biogenic silica in the sediment column appears to have a minor effect on the 32 si profile in the mixed layer deep sea particle mixing rates reported in this study and the literature do not correlate with sediment type sediment accumulation rate or surface productivity based on differences in mixing rate among three antarctic cores collected within 50 km of each other local variability in the intensity of deep sea mixing appears to be as important as regional differences in sediment properties

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

unusual features of the distribution of radon 222 in the bottom waters of the continental slope of the mid atlantic bight hydrodynamic implications abstract 222rn was measured in the near bottom waters of the continental slope of the mid atlantic bight separate measurements of the 222rn supported by dissolved 226ra allowed the excess 222rn that is derived from the underlying sediments to be distinguished measurements of production of 222rn by the sediments were used to calculate fluxes of 222rn from sediments that would be expected as a result of molecular diffusion on the upper slope and on the lower slope excess 222rn standing crops were respectively greater than and consistent with fluxes of radon from sediments by molecular diffusion as are typical of most ocean environments on the middle slope however observed excess 222rn concentrations and standing crops were significantly lower than what would be expected from the calculated fluxes from the underlying sediments this unusual feature of low radon concentrations on the middle slope is referred to as the low radon zone lrz this lrz was always present over several years and seasons but was variable in intensity excess radon concentration and standing crop and in location on the slope low concentrations of suspended particulate matter and low current velocities observed by others in the same region are consistent with low mixing as a possible cause of the lrz radon profile shapes and recent work by others on near bottom mixing due to interactions between topography and internal waves however suggest that high mixing due to internal waves is a more likely cause of the lrz

further evidence for the development of photic zone euxinic conditions during mesozoic oceanic anoxic events periods in earth history characterized by extensive organic carbon deposition so called oceanic anoxic events oaes are the subject of considerable scrutiny insight into the extent of anoxic conditions in the water column has been provided by the reported occurrence of derivatives of isorenieratene a carotenoid found only in green sulphur bacteria and thus indicative of photic zone euxinia i e a water column containing free h 2 s in north atlantic deep sea sediments deposited during the cenomanian turonian boundary oae2 bonarelli event in this study we have used the distributions of chlorophyll and bacteriochlorophyll degradation products maleimides 1 h pyrrole 2 5 diones and high molecular weight porphyrins to examine further the cenomanian turonian boundary oae2 as well as other oaes of the early toarcian posidonienschiefer event and early aptian selli event in particular methyl isobutyl me i bu maleimide on structural grounds appears to be diagnostic of green sulphur bacteria this compound occurs in five of seven examined marls that record the early toarcian oae marche umbria italy further expanding the geographical range of toarcian sediments where evidence for photic zone euxinic conditions has been found me i bu maleimide occurs in three of six black shales spanning the livello selli marche umbria italy the type locality for the aptian oae1a providing the first evidence for photic zone euxinic conditions during this event with respect to the cenomanian turonian oae maleimide evidence for photic zone euxinic conditions was found in all the north atlantic sites investigated including those characterized by relatively organic lean sediments several tethyan sites and one site off western australia these data indicate that euxinic conditions were common in the water column during mesozoic oceanic anoxic events

compositional and isotopic characteristics of organic matter for the early aptian oceanic anoxic event at shatsky rise odp leg 198 the occurrence of intervals of enhanced sequestration of organic matter om during the mid cretaceous collectively termed oceanic anoxic events oae reflect abrupt changes in global carbon cycling these episodes raise questions about the causes for such perturbations and their linkages to fluctuations in climate marine biota and ocean geochemistry preserved in the sedimentary record detailed assessment of the early aptian event oae1a in the pacific has been precluded by the limited recovery of this stratigraphic interval in contrast to the many records from the tethyan realm the recovery of pelagic sequences of om rich sediments at site 1207 on shatsky rise odp leg 198 corresponding to oae1a has enabled recognition of high resolution temporal variations in the elemental and isotopic compositions of this event in the pacific however the continuous 45 cm om rich interval recovered is likely only the initiation of oae1a rather than a complete section based on natural gamma and uranium logs which suggest that the full thickness of this interval is 1 2 m exceedingly high organic carbon corg 20 and total sulfur ts 5 contents among the highest ever recorded for pelagic cretaceous sequences attest to the enhanced sequestration of om during oae1a 13corg values are lowest 27 7 at the base of the recovered om rich interval followed by a 2 4 positive shift this isotopic profile resembles part of the 13ccarb record at resolution guyot and is comparable with segments c3 and c4 of the cismon 13corg record low 15n values 2 provide evidence for nitrogen fixation perhaps coupled with elevated cyanobacterial populations that suggest that the marine nitrogen cycle in the cretaceous was different from the modern overall the temporal fluctuations in elemental and isotopic data through oae1a at shatsky rise describe differences in production and preservation of om that likely reflect variations in ocean conditions associated with both local and global environmental changes

nannofossil carbonate fluxes during the early cretaceous phytoplankton response to nutrification episodes atmospheric co2 and anoxia 1 greenhouse episodes during the valanginian and aptian correlate with major perturbations in the c cycle and in marine ecosystems carbonate crises and widespread deposition of corg rich black shales quantitative analyses of nannofossil micrite were conducted on continuous pelagic sections from the southern alps northern italy where high resolution integrated stratigraphy allows precise dating of early cretaceous geological events rock forming calcareous nannofloras were quantified in smear slides and thin sections to obtain relative and absolute abundances and paleofluxes that are interpreted as the response of calcareous phytoplankton to global changes in the ocean atmosphere system increased rates of volcanism during the formation of ontong java and manihiki plateaus and the parana etendeka large igneous province lip are proposed to have caused the geological responses associated with early aptian oceanic anoxic event oae 1a and the valanginian event respectively calcareous nannofloras reacted to the new conditions of higher pco2 and fertility by drastically reducing calcification the valanginian event is marked by a 65 reduction in nannofossil paleofluxes that would correspond to a 2 3 times increase in pco2 during formation of the parana endenteka lip a 90 reduction in nannofossil paleofluxes which occurred in a 1 5 myr long interval leading into oae1a is interpreted as the result of a 3 6 times increase in pco2 produced by emplacement of the giant ontong java and manihiki plateaus high pco2 was balanced back by an accelerated biological pump during the valanginian episode but not during oae1a suggesting persisting high levels of pco2 in the late aptian and or the inability of calcareous phytoplankton to absorb excess pco2 above threshold values

strontium isotopic composition of mid cretaceous seawater the 87sr 86sr ratio in fish teeth separated from mid cretaceous marl and black shale from the northeastern apennines and venetian alps italy define three periods of low 87sr 86sr ratio at 121 to 124 million years ago ma 110 to 115 ma and 89 to 91 ma the 87sr 86sr excursions correspond to oceanic anoxic events represented by the livello selli livello 113 livello urbino and livello bonarelli black shale marker beds and probably reflect an increase in the low 87sr 86sr hydrothermal strontium flux associated with the emplacement of the ontong java and kerguelen plateaus 120 to 110 ma and the caribbean plateau 89 to 91 ma the modeled flux is consistent with the volumes and eruption rates of the oceanic plateaus but is far smaller than expected from the proposed cretaceous crustal production rates of 50 to 100 percent greater than modern

significant groundwater input to a coastal plain estuary assessment from excess radon a submarine groundwater discharge zone was identified through the investigation of persistent excess radon in the delaware river and bay estuary this zone the excess radon maximum erm was located approximately 82 km upstream from the mouth of the delaware bay water column radon activity at the erm was elevated relative to the radon activity observed outside of this zone and was as high as 2 73 dpm l 1 a radon budget model developed to assess the contribution of multiple radon sources to the erm indicated that simple molecular diffusion from sediments could not support the observed excess radon activity an additional source of radon is required to sustain the excess radon activity in the erm a groundwater flux of 14 to 29 m 3 s 1 from the two aquifers that subcrop on the delmarva peninsula immediately west of the erm can support the excess radon observed in the water column the stratigraphy and hydrology of these aquifers makes them likely sources of the groundwater discharge that results in the erm the calculated submarine groundwater discharge flux is equivalent to the surface water discharge of the second and third largest tributary rivers of the delaware estuary 2003 elsevier science b v all rights reserved

paleomagnetic calibration of milankovitch cyclicity in lower cretaceous sediments abstract bedded pelagic limestones of early to mid cretaceous age may record cyclic climate variability driven by changes in the earth s orbit milankovitch cycles if properly calibrated the lithologic cycles could provide sedimentary chronometry at far shorter time scales than biostratigraphy and magnetic stratigraphy the lower cretaceous maiolica formation of northern and central italy displays rythmic bedding in sections whose magnetic reversal sequence is clearly correlated to the upper m series marine anomalies the magnetic reversals divide measured sections into 0 5 2 myr increments in which sedimentation rate assuming continous deposition can be measured to 15 25 accuracy paleomagnetically estimated sedimentation rates over a number of polarity zones establish with one exception a narrow range in periods of the carbonate cycles carbonate couplets have an estimated mean period of 23 5 kyr and prominent modulations in bedding thickness bundling have a mean period of 117 kyr kent and gradstein 1985 time scale the close match of sedimentary periodicities to orbital repeat times implies that the carbonate cycles reflect a combination of professional and eccentricity climatic forcing comparison of measured sections from different locations shows that bed to bed correlations are possible regionally cosistent with the milankovitch hypothesis episodes of barremian black shale deposition occur in the troughs of the short eccentricity cycle as roughly one half of the carbonate marl couplet or about 10 kyr duration it is possible to estimate both the timing relative to the top of reversed chron m 0 and duration of a period of unusual organic carbon rich deposition selli horizon in the early part of the cretaceous long normal magnetic polarity interval by tracing the sedimentary cycles up from the barremian strata

new perspective on aptian carbon isotope stratigraphy data from δ13c records of terrestrial organic matter carbon isotope analyses were performed on detrital woody materials in aptian mid cretaceous marine sediments of central hokkaido northern japan a positive 13cwood excursion from 25 4 to 21 8 following a remarkable negative isotope shift is recognized in the early aptian and a small positive anomaly is also found in the latest aptian this 13cwood profile is exactly in phase with the 13ccarbonate curve from a pacific guyot when the age of the guyot carbonates is revised using published sr isotope stratigraphies the highly conformable 13c profiles of pacific and hokkaido sections suggest that 13c compositions of aptian marine and terrestrial carbon reservoirs changed simultaneously by the same amplitude within the ocean atmosphere biosphere system fluctuation patterns of tethyan 13ccarbonate curves are slightly different from those of pacific and hokkaido sections such differences in 13c profiles may be attributed to the local paleoceanographic setting of the aptian mediterranean tethys

tectonic geomorphology and hydrocarbon induced topography of the mid channel anticline santa barbara basin california the geomorphology of the western sector of the mid channel anticline mca santa barbara southern california suggests the actively growing fold is laterally propagating to the west the presence of fold scarps and cross faults that segment the structure suggests that buried faults that are producing the folding are present at shallow depths the summit area of the anticline at the last glacial maximum 22 to 19 ka was probably a small late pleistocene island evidence for presence of the island includes what appears to be terrestrial erosion and is supported by assumption of sea level change and rates of uplift and subsidence pockmarks and domes ranging in diameter from 10 to 100 m and several meters deep are present along the crest and flanks of the mca these features appear to be the result of hydrocarbon emission their formation has significantly modified the surface features producing simple to complex erosional and or constructional topography a large pockmark near the anticline crest dated by two calibrated ams radiocarbon dates of 25 3 and 36 9 ka continues to emit hydrocarbon gases we term the topography produced by hydrocarbon emission as hydrocarbon induced topography hit 2007 elsevier b v all rights reserved

recognition of alkenones in a lower aptian porcellanite from the west central pacific odp leg 198 drilling on shatsky rise recovered a lower aptian porcellanite 120 5 ma deposited during oceanic anoxic event oae 1a that contains c36 c39 alkadienones c37 2 and c39 2 alkadien 2 ones and c36 2 and c38 2 alkadien 3 ones this alkenone distribution differs from that typical of contemporary sediments and haptophyte algae but resembles that of cretaceous sediments from the blake bahama basin the discovery of alkenones in the early aptian extends their sedimentary record by 15 m y to 120 5 m y and demonstrates the potential for long term survival of these diagnostic functional lipids under favorable depositional conditions and subsequent shallow burial it also contributes to the understanding and reconstruction of evolutionary developments in alkenone distributions and biosynthesis over geologic time 2003 elsevier ltd all rights reserved

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

orbital tuning as an inverse problem chronology of the early aptian oceanic anoxic event 1a selli level in the cismon apticore 1 orbital tuning the process of fitting sedimentary cycles to orbital periodicities can estimate with high resolution the timing and duration of key events in the geological record we formulate here orbital tuning as the inverse problem of finding the variation in sedimentation rate that matches sediment cycles with orbital periodicities instead of obtaining a single best estimate we apply a bayesian formulation and define a probability distribution of sedimentation rate variations that result in powerful orbital periodicities by sampling this distribution with a monte carlo method we quantify the uncertainty in the inferred sedimentation rates due to uncertainties in the tuning periods and to components of the sedimentary signal that are unrelated to orbital cycles the method is applied to the chronology of a 30 m interval in the cismon apticore borehole southern alps italy that includes the early aptian oceanic anoxic event 1a selli level estimated to last 1 11 0 11 ma 95 interval the 13c record shows a sudden negative shift of about 1 at the base of the selli level 22 47 ka followed by a recovery to preshift values in 240 ka consistent with a scenario where light carbon is quickly added and then flushed out of the ocean atmosphere system

gaia s breath global methane exhalations abstract methane ch 4 is the most abundant organic compound in the earth s atmosphere where it acts as a greenhouse gas and thus has implications for global climate change the current atmospheric ch 4 budget however does not take into account geologically sourced ch 4 seepage geological sources of ch 4 include natural macro and micro seeps mud volcanoes and other miscellaneous sources such as gas hydrates magmatic volcanoes geothermal regions and mid ocean ridges macro seeps contribute 25 tg teragrams ch 4 yr to the atmosphere whereas micro seepage contributes perhaps 7 tg ch 4 yr mud volcanoes emit 5 tg ch 4 yr and miscellaneous sources emit 8 tg ch 4 yr to the atmosphere thus the total contribution to the atmosphere from geological sources is estimated to be 45 tg ch 4 yr which is significant to the atmospheric organic carbon cycle and should be included in any global inventory of atmospheric ch 4 we argue that the atmospheric ch 4 global inventory of the interplanetary panel on climate change must be adjusted in order to incorporate geologically sourced ch 4 from naturally occurring seepage

sr ca ratios as indicators of varying modes of pelagic carbonate diagenesis in the ooze chalk and limestone realms abstract there has been an interest in the application of sr ca ratios in pelagic carbonates to reconstruct paleoceanographic conditions such as changes in the oceanic ca and sr budgets or calcareous nannoplankton productivity but the effect of burial diagenesis on primary sr ca records has not been sufficiently understood in order to clearly document sr ca records of pelagic carbonates relative to original paleoceanography or secondary diagenetic processes sr ca analyses were performed on bulk sediments from an 822 5 m thick ooze chalk limestone sequence at the mid pacific mountains deep sea drilling project site 463 the sr ca ratios exponentially decrease from 2 3 to 1 1 mmol mol with increasing burial depth in the ooze chalk interval 0 452 0 m below seafloor mbsf the sr ca ratios further decline to as low as 0 4 mmol mol in the limestone interval 452 0 mbsf with relatively high values of 1 1 mmol mol at carbonate poor lithology around 620 mbsf the stratigraphic sr ca trends appear to be consistent with porosity profile and similar sr ca porosity covariation in association with diagnetic changes in lithologies is also common in ontong java plateau sections by adopting a recent diagenetic model from backscattered electron image analysis of ontong java plateau sections it is postulated for site 463 that exponential sr ca decrease in the ooze chalk interval is due to the release of sr into interstitial water via recrystallization i e purification effect and that further decrease in sr ca ratios in the limestone interval is most likely due to acquisition of sr depleted calcite cement at the chalk limestone transition newly proposed as the dilution effect specifically sr ca ratios of deeply buried pelagic limestones are sensitive to the amount of calcite cement that is acquired in proportion to caco3 content i e carbonate rich lithology facilitates precipitation of secondary calcite at the chalk limestone transition therefore paleoceanographic interpretation by means of sr ca ratios in pelagic carbonates will become valid only when these diagenetic effects are appropriately constrained