trace element geochemistry of archaean and proterozoic rocks from eastern karelia u s s r abstract several komatiite and komatiitic basalt occurrences have been found in the greenstone successions of the eastern part of the baltic shield soviet karelia with both archaean and proterozoic ages being represented some flows exhibit internal layering with well developed spinifex textures similar to those described from the classic komatiite provinces of canada and australia marked differences have been found in the trace element geochemistry of these rocks some archaean volcanics exhibit flat ree distributions with approximately chondritic ratios of ca ti al zr v and y whereas others show depletion in lree and zr proterozoic komatiitic basalts differ from the archaean ones by their relative lree ba and sr enrichment these geochemical features are ascribed to an established heterogeneity in the archaean mantle source and its further development by the proterozoic major and trace element variations suggest relative immobility during metamorphism of all the analyzed elements except volatiles and alkalis these trends being adequately explained by olivine with minor chromite fractionation

faunal and stable isotopic analyses of benthic foraminifera from the southeast seep on kimki ridge offshore southern california usa abstract we investigated the benthic foraminiferal faunal and stable carbon and oxygen isotopic composition of a 15 cm push core na075 092b obtained on a telepresence enabled cruise to the southeast seep on kimki ridge offshore southern california the seep core was taken at a depth of 973 m in the vicinity of a beggiatoa bacterial mat and vesicomyid clams calyptogena and compared to previously published data of living assemblages from 714 m four reference cores obtained at 1030 m and another one at 739 m all of the reference sites are also from the inner continental borderland but with no evidence of methane seepage no endemic species were found at the seep site and most of the taxa recovered there have been reported previously from other seep or low oxygen environments q and r mode cluster analyses clearly illustrated differences in the faunal assemblages of the seep and non seep sites the living assemblage at southeast seep was characterized by abundant takayanagia delicata cassidulina translucens and spiroplectammina biformis whereas the non seep san pedro basin reference assemblage was comprised primarily of chilostomella oolina and globobulimina pacifica density and species richness were lower at the seep site compared to the non seep site reflecting the harsher living conditions there the dead assemblage at the seep site was dominated by gyroidina turgida compared to cassidulina translucens at the 1030 m non seep site and cassidulina translucens pseudoparrella pacifica and takayanagia delicata at the 739 m non seep site density was three times lower at southeast seep than at the non seep sites of comparable water depth but species richness was 30 higher stable carbon isotopic values were considerably depleted in the seep samples compared to the non seep samples with a progression from lightest to heaviest average 13c values evident at the seep site reflecting microhabitat preference and vital effect the deep infaunal species of globobulimina the shallow infaunal species uvigerina peregrina the epifaunal species cibicidoides wuellerstorfi and the shallow infaunal but aragonite shelled species hoeglundina elegans the 13c values downcore among each benthic species indicates ongoing fluid seepage through at least the last 3800 cal yr b p at southeast seep besides the continual local seepage evidence from 13c values of planktic foraminifera in the seep core suggest two pulses of methane at 3000 and 3700 cal yr b p were released that were large enough to influence much of the water column paired benthic and planktic foraminiferal stable oxygen isotope records provide evidence that there were no paleoenvironmental changes such as increased bottom water temperature or changes in oxygen isotopic composition of bottom and pore waters during this 3800 year record to induce the methane releases instead southeast seep appears to be the result of local faulting providing pathways for fluid to flow to the seafloor at a fault stepover or transpressional bend in the regional strike slip system

foraminiferal response to an active methane seep environment a case study from the adriatic sea abstractit has been analysed the taxonomic structure and isotopic composition of the cytoplasm and tests of living rose bengal stained protoplasm full and dead empty tests benthic foraminifera 63 m in surface sediments from sites with and without methaneseepage at water depths of about 25 m water in the northern adriatic sea and compared these data to isotope analyses of carbonaterocks at the same locations foraminiferal density is higher in seep samples than in control ones despite the low oxygen and highsulphide contents in sediments the 13 c values in foraminiferal cytoplasm at the seep sites are lower than those in cytoplasm ofthe same species in control samples suggesting that beggiatoa may be a food source for the foraminifera and explaining thehigher foraminiferal density at the seep site in contrast the 13 c values of tests of living and dead benthic foraminifera at seep siteswere not significantly different from those in tests of the same species collected at the control sites therefore the carbon isotopevalues of foraminiferal tests in this area do not reflect the ones of the methane seepage although the authigenic carbonate incalcareous sandstones of the methane seepage area is significantly negative and indicates the contribution of methane seepage thesimilar carbon isotope values measured in the foraminiferal tests from shallow settings of the north eastern adriatic sea seemtherefore to be independent of methane seepages 2006 elsevier b v all rights reserved

how are benthic foraminiferal faunas influenced by cold seeps evidence from the miocene of italy abstract the miocene termina formation of the northern apennines italy hosts small marl bodies containing a fossil megafauna that is not seen elsewhere in the formation this fauna consists of concentrations of large lucinid clams having living representatives that occur in cold seep settings where they house chemosymbiotic bacteria together with the megafauna a 13 c depletion of their carbonate contents suggests a cold seep derived origin for these bodies they belong to the cluster of mostly carbonate oligo miocene bodies outcropping in the apennine range from piedmont to southern italy where they are included in deep marine units at different geological settings the relatively soft lithology of the bodies from the termina formation permitted the extraction of the microfossil component so that a taxonomically detailed investigation of benthic foraminifera was performed moreover a comparison with assemblages from nearby non seep deposits has allowed an evaluation of their use for recognizing fossil seeps a total of more than 200 species and subspecies of benthic foraminifera has been identified in seep bodies and surrounding non seep deposits and allowed paleodepth estimates within the middle bathyal zone 600 1000 m similarly to present day isobathyal settings the foraminiferal diversity is high with a major contribution by the accessory taxa that account for up to nearly 50 of the total assemblage based upon the microhabitat categories the epifaunal assemblages are largely outnumbered by the infaunal ones our results show that significant differences do not exist between the foraminiferal assemblages recovered from seep influenced bodies and the ones from the enclosing deposits these results agree with the findings from present day seep environments for which however a still limited and insufficient data set is at the moment available a further complication that should be considered is the effect of time averaging on fossil assemblages which would be responsible for some homogenization between foraminiferal stocks of normal marine non seep settings and adjacent assemblages controlled by short term events such as the ones produced by cold seepage

archaean oil migration in the witwatersrand basin of south africa abstract the late archaean witwatersrand supergroup of south africa hosts the largest known gold uranium pyrite ore deposits oil preserved in fluid inclusions in quartz grains in siliciclastic sedimentary rocks of that supergroup implies that hydrocarbon generation and migration occurred during the archaean and may have been involved in mineralization processes through reference to phanerozoic analogues oil bearing fluid inclusions entrapped in healed microfractures in detrital quartz grains and in early syntaxial quartz overgrowths imply that the onset of oil migration coincided with early to intermediate stages of burial while intra granular porosity was still preserved multiple generations of oil migration are indicated by i oil inclusions within early diagenetic cements at different levels in the stratigraphic succession ii more than one type of oil in entrapment sites iii oil entrapment in multiple stages of the quartz paragenetic sequence oil generation and migration are considered to have occurred throughout and for some considerable time after development of the witwatersrand basin consistent with progressive burial and kerogen maturation in more than one tectonic regime oil bearing fluid inclusions within detrital sandstone fragments suggest that oil migration also occurred in a sedimentary succession on the kaapvaal craton prior to 2 9 ga oil in the witwatersrand supergroup was most likely derived from multiple source areas with the principal source probably being shales within the lower witwatersrand supergroup the hydrocarbon migration history of the basin has important implications for understanding the textural relationship between gold bituminized oil and uraninite in the giant gold uranium pyrite ore deposits

dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the paleocene isotopic records across the latest paleocene thermal maximum lptm indicate that bottom water temperature increased by more than 4 c during a brief time interval 104 years of the latest paleocene 55 6 ma there also was a coeval 2 to 3 excursion in the 13c of the ocean atmosphere inorganic carbon reservoir given the large mass of this reservoir a rapid 13c shift of this magnitude is difficult to explain within the context of conventional hypotheses for changing the mean carbon isotope composition of the ocean and atmosphere however a direct consequence of warming bottom water temperature from 11 to 15 c over 104 years would be a significant change in sediment thermal gradients and dissociation of oceanic ch4 hydrate at locations with intermediate water depths in terms of the present day oceanic ch4 hydrate reservoir thermal dissociation of oceanic ch4 hydrate during the lptm could have released greater than 1 1 to 2 1 1018 g of carbon with a 13c of approximately 60 the release and subsequent oxidation of this amount of carbon is sufficient to explain a 2 to 3 excursion in 13c across the lptm fate of ch4 in oceanic hydrates must be considered in developing models of the climatic and paleoceanographic regimes that operated during the lptm

novel high pressure culture experiments on deep sea benthic foraminifera evidence for methane seepage related δ13c of cibicides wuellerstorfi in field studies of active hydrocarbon seeps the carbon isotopic composition of rose bengal stained benthic foraminiferal tests 13ctest and bottom water dic 13cdic deviates from their normal marine ratios this circumstance led to ongoing discussions on whether aerobic foraminifers like cibicides wuellerstorfi are capable of living at seepage sites and more importantly if their tests reflect the low 13c values of emanating methane to evaluate the discrepancy between 13cdic and 13ctest we conducted methane seepage emulating culture experiments on undepressurized sediments from the hakon mosby mud volcano a modern methane seepage structure that hosts living c wuellerstorfi with distinct negative 13c values the collected sediments were cultured at a site alike pressure and mean bottom water methane concentration using newly developed high pressure aquaria over an experimental period of 5 months our novel technology enabled a successful reproduction of all calcareous deep sea benthic foraminiferal species living at that site notably the first c wuellerstorfi cultured in the laboratory to show the influence of methane on 13ctest we ran parallel experiments with 99 12c and 99 13c methane in the experimental bottom water during the experimental running time methanotrophs in the water column obviously converted the experimentally added methane source to 13c enriched and depleted dic respectively since whole sediment cores were cultured it was impossible to keep 13cdic constant over the 5 month duration which is reflected in a variability of 13ctest in foraminiferal shells irrespective of that the methane source is reflected in 13ctest of foraminiferal shells and for the natural seep conditions simulating 12c experiment the mean 13cdic and 13ctest in c wuellerstorfi were equal although for future culturing experiments improvements of the experimental conditions are advisable our first results are evidence that persistent methane emanation impacts the carbon isotopic composition of deep sea benthic foraminifera

high resolution mapping of two large scale transpressional fault zones in the california continental borderland santa cruz catalina ridge and ferrelo faults new mapping of two active transpressional fault zones in the california continental borderland the santa cruz catalina ridge fault and the ferrelo fault was carried out to characterize their geometries using over 4500 line km of new multibeam bathymetry data collected in 2010 combined with existing data faults identified from seafloor morphology were verified in the subsurface using existing seismic reflection data including single channel and multichannel seismic profiles compiled over the past three decades the two fault systems are parallel and are capable of large lateral offsets and reverse slip during earthquakes the geometry of the fault systems shows evidence of multiple segments that could experience throughgoing rupture over distances exceeding 100 km published earthquake hypocenters from regional seismicity studies further define the lateral and depth extent of the historic fault ruptures historical and recent focal mechanisms obtained from first motion and moment tensor studies confirm regional strain partitioning dominated by right slip on major throughgoing faults with reverse oblique mechanisms on adjacent structures transpression on west and northwest trending structures persists as far as 270 km south of the transverse ranges extension persists in the southern borderland a logjam model describes the tectonic evolution of crustal blocks bounded by strike slip and reverse faults which are restrained from northwest displacement by the transverse ranges and the southern san andreas fault big bend because of their potential for dip slip rupture the faults may also be capable of generating local tsunamis that would impact southern california coastlines including populated regions in the channel islands

methanogenic calcite 13c depleted bivalve shells and gas hydrate from a mud volcano offshore southern california methane and hydrogen sulfide vent from a cold seep above a shallowly buried methane hydrate in a mud volcano located 24 km offshore southern california in 800 m of water bivalves authigenic calcite and methane hydrate were recovered in a 2 1 m piston core aragonite shells of two bivalve species are unusually depleted in 13c to 19 13c the most 13c depleted shells of marine macrofauna yet discovered carbon isotopes for both living and dead specimens indicate that they used in part carbon derived from anaerobically oxidized methane to construct their shells the 13c values are highly variable but most are within the range 12 to 19 this variability may be diagnostic for identifying cold seep hydrate systems in the geologic record authigenic calcite is abundant in the cores down to 1 5 m subbottom the top of the methane hydrate the calcite is depleted in 13c 13c 46 to 58 indicating that carbon produced by anaerobically oxidized methane is the main source of the calcite methane sources include a geologic hydrocarbon reservoir from miocene source rocks and biogenic and thermogenic degradation of organic matter in basin sediments oxygen isotopes indicate that most calcite formed out of isotopic equilibrium with ambient bottom water under the influence of gas hydrate dissociation and strong methane flux high metal content in the mud volcano sediment indicates leaching of basement rocks by fluid circulating along an underlying fault which also allows for a high flux of fossil methane

the early proterozoic pechenga varzuga belt a case of precambrian back arc spreading abstract the pechenga varzuga belt pvb in the kola peninsula russia comprises the western pechenga and the eastern imandra varzuga portions these are two major asymmetric synform structures infilled with proterozoic volcanogenic and sedimentary rocks dated between 2 45 and 1 9 ga two main stages of tectonic magmatic activity took place 1 a 2 45 2 3 ga basal siliceous high mg volcanic series typical for the sumian sariolian episodes and 2 the jutuli ludia and kalevian episodes which began 2 2 ga ago the lower level of the second sequence is made up of subaerial alkali basalts the upper 2 1 1 95 ga old portions of the sequence consist of tholeiitic pillow lavas hyaloclastites and ferropicrite basalt flows associated with deep water sediments such as phyllites silicites and turbidites the tholeiites exhibit ree distribution patterns similar to those of morb while the ferropicrite basalts resemble intraplate olivine basalts of continental and oceanic environments calc alkaline subaerial volcanism took place along the south western flank of the pechenga zone a final igneous stage is characterized by the emplacement of potassium granitic intrusions the main lapland thrust mlt occurs along the southern border of the paleoproterozoic lapland umba granulite belt and is a narrow zone of compression thrusting and folding accompanied by high pressure granulite metamorphism it is approximately coeval with the upper part of the pechenga varzuga belt and is interpreted as representing a complementary structure i e the zone of subduction of the karelian belomorian craton beneath the kola block thus the upper part of the pechenga varzuga belt is considered to have originated as a back arc basin in the rear of a zone of north directed subduction and continent collision it was eventually closed with the appearance of igneous suites typical of such events the pechenga varzuga belt main lapland thrust system thus provides an instance of an ancient 2 0 1 9 ga ago collision of lithospheric plates accompanied by back arc spreading and then closure of the back arc basin the geodynamic development is similar that which occurred more recently within the alpine himalayan belt

limits to the sensitivity of living benthic foraminifera to pore water carbon isotope anomalies in methane vent environments episodic 13c depletions in the carbon isotopic composition of benthic foraminiferal tests preserved in the stratigraphic record have been interpreted as an active incorporation of methane derived carbon understanding the extent to which these isotope excursions reflect basin wide fluxes of methane carbon to bottom waters versus a local supply of methane carbon within the sediments in which benthic foraminifera live or a postmortem diagenetic imprint is critical to the interpretation of 13c paleoceanographic proxies here we evaluate the impact of chemical gradients measured in pore waters adjacent to active methane vents on carbon assimilation by living benthic foraminifera and show that those living near methane vents do not assimilate the distinctly 13c depleted methane derived dissolved inorganic carbon into their tests from the pore water in which they were found our observations can be explained by the recently articulated physiological limits imposed on deep sea fauna by low oxygen and high pco2 environments understanding the importance of the different processes involved in the observed disequilibrium between the carbon isotopic composition of the benthic forams and the pore waters where they were found has important implications on the reliability of carbon isotopic composition of benthic foraminifera for paleoceanographic reconstructions in particular the observation on the inhospitability of these environments for benthic foraminifera at least for reproduction and growth raises the issue on the overprint either in the late adult stages of foraminifera that grew in a different neighboring environment or during early diagenesis in these geochemically active environments

seasonal variability in the δ18o and δ13c of planktonic foraminifera from an upwelling environment sediment trap results from the san pedro basin southern california bight stable isotopic analyses 18o and 13crpar on four species of planktonic foraminifera collected from high resolution time series sediment trap sampling indicate that rapid and significant seasonal variability occurred in response to rapid changes in both the hydrographic environment and the isotopic composition of ambient seawater specimens were collected at a depth of 500 m for 28 consecutive 1 week periods in the san pedro basin within the southern california bight a region seasonally influenced by upwelling hydrographic monitoring of the study area revealed a 6 week period late april to mid june during which pulses of upwelling occurred causing significant increases in the oxygen isotopic composition of surrounding waters while decreasing the carbon isotopic composition analyses of globigerina bulloides orbulina universa neogloboquadrina dutertrei and neogloboquadrina pachyderma right coiling indicate that during the upwelling period these species live respectively at the surface in the surface mixed layer within the thermocline and below the thermocline globigerina bulloides ascends from well below the thermocline to the surface at the onset of upwelling and increases production to its maximum simultaneously as its morphology changes to less calcified open forms both n dutertrei and n pachyderma follow isothermal ranges migrating to shallower waters during upwelling and subsequently descending after upwelling ceases neogloboquadrina dutertrei appears to inhabit the region associated with both the thermocline base and chlorophyll maximum when it is most abundant following upwelling orbulina universa increases its depth habitat as solar irradiance increases but this species decreases in abundance during upwelling the 18o signal of o universa appears to be a useful indicator of seasonal temperature variations above the thermocline whereas the 18o of g bulloides documents near surface temperatures during upwelling the 13c signal of both n dutertrei and n pachyderma appears to record the 13c of equilibrium calcite for the regions of the thermocline and just below the thermocline respectively due to the relative preservation potentials of the four species analyzed only n dutertrei and n pachyderma are likely to be preserved in the sedimentary record in regions of oxygenated bottom waters thus an actual record of hydrographic conditions during upwelling as would be found in tests of g bulloides is not preserved instead conditions before n pachyderma and just after n dutertrei are more likely recorded

attachment of foraminifera to vestimentiferan tubeworms at cold seeps refuge from seafloor hypoxia and sulfide toxicity abstract a survey of foraminiferal microhabitats at several gulf of mexico bathyal abyssal hydrocarbon seeps reveals that many epibenthic species live not on the sediment but attached to vestimentiferan tubeworms centimeters to decimeters above the seafloor thus avoiding the oxygen depletion and h 2 s toxicity at the sediment water interface this observation explains how certain species with a relatively high oxygen requirement e g cibicides spp may become components of foraminiferal death assemblages in seep sediments thus when the sedimentary record of foraminifera is used to interpret the history of past methane venting the species from elevated microhabitats cannot be ignored but they need to be considered separately from the sediment dwellers

the relationship between pore water carbon isotopic composition and bottom water oxygen concentration abstract we present pore water 13c profiles from the western north atlantic and the eastern pacific oceans and interpret them using a stoichiometric model of the relationship between carbon isotopic composition and oxygen concentration pore water 13c at the depth in the sediments where oxygen approaches zero is largely determined by the oxygen concentration of the overlying bottom water although sulfate reduction adds a significant amount of isotopically light carbon at some locations the 13c difference between bottom water and pore water at o2 0 13c increases from 1 in sediments of three low bottom water oxygen basins in the southern california borderlands to 4 in sediments underlying well oxygenated water in the western north atlantic we suggest that the relationship between bottom water oxygen and 13c could form the basis for a new way to use the benthic foraminifera 13c record to estimate bottom water oxygen concentration paleo oxygen values derived from a pair of benthic foraminifera species which record the bottom water pore water o2 0 13c difference will be independent of the preformed 13c of the deep water mass

foraminifera as indicators of methane rich environments a study of modern methane seeps in santa barbara channel california methane hydrates have been implicated as a possible forcing mechanism for rapid climate change during the late quaternary via the release of methane from marine reservoirs carbon isotopic excursions of foraminifera observed in high resolution sediment records from santa barbara basin odp site 893 have been interpreted as evidence of episodes of methane release during the late quaternary however the potential relationship between methane in the modern environment and its effect on the stable isotopic composition of benthic and planktonic foraminifera is not well understood short cores taken inside a 500 m diameter pockmark with active methane seeps in santa barbara channel ca usa yield information on the effect of high concentrations of environmental methane on foraminiferal assemblages and their stable isotopic composition these seeps reside at 120 m water depth in the eastern portion of the channel associated with faults and fractures in the miocene monterey formation planktonic foraminiferal assemblages and radiocarbon ages show that surface sediments are of late glacial age 25 300 calendar years this finding suggests an absence of holocene and deglacial sedimentation in the seep area likely due the formation of the pockmarks and subsequent winnowing or lack of sedimentation benthic foraminiferal assemblages are marked by high abundance of bolivina tumida a species previously observed during interstadial episodes and the early holocene in santa barbara basin interpreted to include episodes of high methane flux from the basin while oxygen isotopic values of both benthic and planktonic foraminifera appear normal for cool glacial conditions negative carbon isotopic values are seen in benthic foraminifera primarily in the near surface intervals in one interval 1 2 cm below surface both benthic and planktonic species record highly negative carbon isotopic values implying that isotopically light methane influenced the entire water column this spike is of similar or larger magnitude than several earlier observed spikes in the late quaternary record from odp site 893 single specimen isotopic analyses give an indication of the total range of carbon isotopic values recorded 0 01 to 25 23 for benthics 0 07 to 22 22 for planktonics in the spike interval since modern methane seeps are commonly associated with authigenic carbonate precipitation scanning electron microscopy was used to assess the possibility that post depositional alteration may have affected the isotopic composition of the test these experiments indicate that authigenic carbonate is absent and therefore unable to account for the highly negative carbon isotopic signatures these data improve our understanding of methane associated environments by showing that foraminiferal isotopic composition and assemblages may be used to discern the flux of methane from the oceanic reservoir in the geologic record

pechenga ferropicrites and other early proterozoic picrites in the eastern part of the baltic shield ti poor komatiites and ti rich picrites exist among the widely occurring primitive mgo rich volcanics in the early proterozoic successions of the kola peninsula both have been encountered in the imandra varzuga belt but only picrites are found in the pechenga complex the picritic rocks are divided into two types the first type restricted to the kolasjoki and pilgujarvi suites and the tominga series is called ferropicrite due to its exceptionally high total iron content which usually exceeds 14 feotot the second type found in the south pechenga series and in the umba and panarechka suites has more typical iron content and geochemically resembles suisaarian picrites from southern karelia ferropicrites occur as pillow lavas lava breccias tuffs massive lavas and up to 50 m thick differentiated spinifex textured flows in addition to high feotot contents these rocks are characterized by low al2o3 contents and by high concentrations of tio2 zr and other incompatible elements they are strongly lree enriched and have immobile trace element characteristics similar to within plate transitional or alkali basalts it is shown that with regard to both the major and trace element compositions the parental magma of the ni bearing intrusions of the pilgujarvi suite is similar to ferropicrite suggesting that the emplacement of the intrusions took place contemporaneously with ferropicritic volcanism the high incompatible element contents of the ferropicritic rocks rule out a genetic relationship with associated tholeiitic basalts proposed geotectonic settings for the pechenga area including an intracratonic rift zone a passive continental margin an oceanic island arc a mature continental volcanic arc and a collisional suture zone are discussed the presence of ti rich picritic rocks does not support a subduction related environment

the influence of microhabitats on the carbon isotopic composition of deep sea benthic foraminifera we report 13c and 18o values for rose bengal stained benthic foraminifera from a set of box cores from continental margin environments in the atlantic and pacific oceans these isotopic results are compared with foraminiferal distribution data and pore water 13c profiles to evaluate the importance of environmental microhabitat effects on the carbon isotopic composition of benthic foraminifera the 13c values of infaunal taxa are consistently lower than those of epifaunal taxa suggesting that microhabitat effects on test composition do exist the 13c differences between foraminiferal carbonate and bottom water dissolved inorganic carbon are not correlated with the 18o differences between benthic foraminifera tests and equilibrium calcite but they do correlate with variations in the chemistry of sediment pore waters however interspecific 18o differences as well as 13c differences between species with similar vertical distributions in the sediments indicate that taxon specific vital effects also influence test composition

is methane venting at the seafloor recorded by δ13c of benthic foraminifera shells the research was supported by wcnurp grant pf806880 and by nsf grants oce 9731157 oce 9815186 and oce 9906944 curation of sediment cores at the osu norcor repository is supported by nsf

heat flow in the witwatersrand basin and environs and its significance for the south african shield geotherm and lithosphere thickness the late archaean early proterozoic witwatersrand basin is situated in the center of the kaapvaal craton south africa two new heat flow determinations and 71 new heat flow estimates permit excellent definition of the heat flow pattern nonvertical heat conduction explains much of the observed local heat flow variability regionally the heat flow in the basin is uniform and the overall mean 51 6 mw m 2 is higher than the mean heat flow for archaean cratons published data indicate that heat generated in the basin s strata 7 5 mw m 2 is largely responsible for the excess heat flow the subsediment heat flux is 43 5 mw m 2 seven new heat flow and heat production determinations in archaean granite domes northwest of the basin average 33 2 mw m 2 and 2 3 0 8 w m 3 respectively contrasted with the heat flux across the floor of the basin the lower heat flow in the domes probably reflects a smaller radiogenic contribution from the crystalline crust below the domes published heat production data from upturned granitic basement exposed in the vredefort dome in the center of the basin indicate that the radioactive contribution from the crust below the basin is 26 5 m w m 2 subtracting this value and the contribution from the strata 7 5 mw m 2 from the basin s surface heat flow 51 mw m 2 indicates that the heat flux through the moho is approximately 17 mw m 2 calculated lithospheric temperatures agree closely with pressure temperature regimes inferred from studies of mantle inclusions in kimberlites in the kaapvaal craton both data sets indicate that the cratonic lithosphere is considerably cooler and thicker than that below an equilibrium ocean implications of the cold thick cratonic lithosphere for understanding the distribution of southern african diamondiferous kimberlites and the density and buoyancy of the lithosphere are discussed

environmental and biological effects on the stable isotope composition of recent deep sea benthic foraminifera from the western mediterranean sea abstract the influence of microhabitat organic matter flux and metabolism on the stable oxygen and carbon isotope composition of live rose bengal stained and dead empty tests deep sea benthic foraminifera from the gulf of lions western mediterranean sea have been studied the total range of observed foraminiferal isotope values exceeds 1 0 for 18o and 2 2 for 13c demonstrating a wide range of coexisting disequilibria relative to 18o of equilibrium calcite 18oeq and 13c of bottom water dissolved inorganic carbon 13cdic the mean 18o values reveal strongest disequilibria for the studied epifaunal to shallow infaunal species cibicidoides pachydermus uvigerina mediterranea uvigerina peregrina while values approach equilibrium in deep infaunal species globobulimina affinis globobulimina pseudospinescens the mean 13c values decrease with increasing average living depths of the different species thus reflecting a dominant microhabitat pore water signal at the axis of the lacaze duthier canyon a minimum 13cdic pore water gradient of approximately 2 1 is assessed for the upper 6 cm of the surface sediment although live individuals of u mediterranea were found in different depth intervals their mean 13c values are consistent with calcification at an average living depth around 1 cm the deep infaunal occurrence of u mediterranea specimens suggests association with macrofaunal burrows creating a microenvironment with geochemical characteristics similar to the topmost centimeter this also explains the excellent agreement between stable isotope signals of live and dead individuals the ontogenetic enrichment in both 18o and 13c values of u mediterranea suggests a slow down of metabolic rates during test growth similar to that previously observed in planktic foraminifera enhanced organic carbon fluxes and higher proportion of resuspended terrestrial organic material at the canyon axis are reflected by 13c values of u mediterranea on average 0 58 lower than those from the open slope these results demonstrate the general applicability of the 13c signal of this species for the reconstruction of past organic matter fluxes in the mediterranean sea further studies on live specimens are needed for a more quantitative paleoceanographic approach

relationships between the distribution and stable isotopic composition of living benthic foraminifera and cold methane seep biogeochemistry in monterey bay california 1 as part of an ongoing effort to explore the use of foraminifera as a means to assess modern and ancient methane release we compared ambient pore water chemistry with the distribution and stable isotopic composition of living rose bengal stained foraminifera in mbari rov ventana tube cores taken from modern seepage areas about 1000 m water depth in monterey bay california benthic foraminiferal isotopic differences between sites clearly indicate that methane influenced pore waters affect foraminiferal distributions and carbonate isotope geochemistry carbon isotope signatures of living benthic foraminifera did not conform to the very negative 30 to 48 methane influenced carbon isotope values of the pore waters they live in instead the influence of methane seep pore waters was reflected in the greater range and carbon isotopic variability of living seep foraminifera compared with published 13c values of foraminifera living in nonseep habitats it is not clear what relative influences biological ecological and physical factors have on the carbon isotopic signatures observed in seep foraminifera substantial carbon isotope differences can exist between individuals of the same seep species for instance 13c values of living globobulimina pacifica varied by as much as 2 9 between seeps within 8 km of each other whereas 13c values of living uvigerina peregrina varied by as much as 1 95 within the same seep provided there is no diagenetic alteration of the test carbonate isotopic results of individual seep foraminifera support the hypothesis that foraminifera can be used to assess past and present methane seepage

benthic foraminifera associated with cold methane seeps on the northern california margin ecology and stable isotopic composition release of methane from large marine reservoirs has been linked to climate change as a causal mechanism and a consequence of temperature changes during the quaternary and the paleocene these inferred linkages are based primarily on variations in benthic foraminiferal stable isotope signatures few modern analog data exist however to assess the influence of methane flux on the geochemistry or faunal characteristics of benthic foraminiferal assemblages here we present analyses of the ecology and stable isotopic compositions of living rose bengal stained and dead fossil foraminifera 150 mm from cold methane seeps on the slope off of the eel river northern california 500 525 m and discuss potential applications for reconstructions of methane release in the past and present calcareous foraminiferal assemblages associated with calyptogena clam bed seeps were comprised of species that are also found in organic rich environments cosmopolitan paleoceanographically important taxa were abundant these included uvigerina bolivina chilostomella globobulimina a ndnonionella we speculate that seep foraminifera are attracted to the availability of food at cold seeps and require no adaptations beyond those needed for life in organic rich reducing environments oxygen isotopic values of the tests of living foraminiferal assemblages from seeps had a high range up to 0 69 as did carbon isotopic values up to 1 02 many living foraminiferal isotope values were within the range exhibited by the same or similar species in non seep environments carbon isotopic values of fossil foraminifera found deeper in the sediments 18 20 cm however were 4 10 u peregrina and 3 60 b subargentea more negative than living d 13 c values these results suggest that d 13 c values of foraminiferal tests reflect methane seepage and species specific differences in isotopic composition and can indicate temporal variations in seep activity a better understanding of foraminiferal ecology and stable isotopic composition will enhance paleo seep recognition and improve interpretations of climatic and paleoceanographic change 2000 elsevier science b v all rights reserved

microhabitat preferences of live benthic foraminifera and stable carbon isotopes off sw svalbard in the presence of widespread methane seepage abstract to constrain the use of and better calibrate benthic foraminiferal carbon isotope based proxies 13c we analyzed live rose bengal stained benthic foraminifera from fjords outer shelves and the upper continental slope of sw svalbard we further investigated whether the presence of widespread methane seepage altered benthic foraminiferal 13c the one to one relationship between the 13c of cibicidoides wuellerstorfi and cibicides lobatulus tests and the 13cdic of bottom water in nordic seas was reconfirmed we also confirmed an almost constant 13c of live specimens of infaunal species melonis zaandamae nonion labradoricum and globobulimina affinis independent of their subbottom sampling depth and pore water 13cdic at any given site this is in contrast to the wide range of intraspecific 13c values of both epifaunal as well as infaunal species observed between sites we did not find significant correlations between foraminiferal 13c minus site specific 13cdic 13cfor dic of the investigated species and the total organic carbon toc contents of surface sediments on the contrary a distinct relationship is observed between high marine organic carbon moc contents and low 13cfor dic values of n labradoricum and to a lesser extent g affinis these findings are important because on the one hand they confirm a systematic influence of the availability of labile moc on deep infaunal species 13c whereas on the other hand they document the independence of epifaunal and infaunal species 13c of toc contents in well ventilated bottom water and organic rich surface sediment generally species mean 13c reflects their average living depths ald5 such that epifaunal and shallow infaunal species depict highest and deep infaunal species lowest 13c values mean 13cfor dic values of neither epifaunal c lobatulus and c wuellerstorfi 0 05 0 06 nor of infaunal m zaandamae 2 40 0 07 n labradoricum 2 69 0 13 and g affinis 3 48 0 15 seem to be significantly influenced by strongly elevated methane concentrations in the water column widespread gas seepage at the sea floor and low pore water 13cdic the latter possibly partly due to methanotrophic oxidation the 13c values of deep infaunal n labradoricum and g affinis minus epifaunal 13c values 13cnlab cib and 13cgaff cib seem to decrease with increasing toc and moc contents however only the 13cnlab cib values correlate significantly with moc contents and thus marine primary productivity dissolved oxygen concentrations estimated on the basis of 13cgaff cib values of 230 mol kg are in accordance with reported well oxygenated bottom water conditions at all stations

horizontal and vertical distributions of planktic foraminifera in the subarctic pacific abstract observations of the horizontal and vertical distributions of modern planktic foraminifera facilitate formation of ecological and geochemical inferences derived from the study of foraminiferal shells in this study we used plankton tows to collect planktic foraminifera at nine sites distributed longitudinally throughout the subarctic pacific a total of nine planktic foraminiferal species were identified the horizontal distributions of the foraminiferal assemblages could be assigned to four regions characteristics of the foraminiferal assemblages and the horizontal distributions of their shell sizes appeared to be influenced by the sea surface structure within each water mass the vertical distributions of globigerina bulloides and globigerina quinqueloba were associated with the depth of the pycnocline those of neogloboquadrina pachyderma and neogloboquadrina incompta were different and appeared to reflect a significant difference of optimum habitat temperatures based on the vertical distribution of shell sizes we found evidence of vertical migrations during shell growth of g bulloides and n incompta this information about the distribution of modern planktic foraminifera will facilitate reconstruction of past oceanographic conditions based on geochemical proxies in the subarctic pacific

the flushing of two deep sea basins southern california borderland a time series of water temperature salinity and nutrient measurements has been made in san pedro and san nicolas basins of the southern california borderland between i977 and 1988 these basins exhibit temporally coincident changes in temperature and nutrient content defining a period of basin flushing 1982 1984 and a period of stagnation 1984 1987 during the flushing period cooler oxygenand no rich water replaces warmer oxygenand no depleted bottom water flushing produces a decrease of 0 2 c in the average temperature of san pedro basin bottom water 790 900 m and an increase in the average oxygen content by 12 pm these values are 0 i and 3 for san nicolas basin 1 400 l 800 m the residence time of water in san pedro basin during the flushing period is 12 6 months and j t2 months in san nicolas basin a box model approach constrained by the time series data for the stagnation period was used to determine values of the effective vertical eddy diffusivities for the 790 m horizon in san pedro basin and 1 400 m horizon in san nicolas basin 1 3 0 4 and 9 9k3 4 cm sk respectively

the ventersdorp contact placer a gold pyrite placer of stream and debris flow origins from the archaean witwatersrand basin of south africa five local varieties of the ventersdorp contact placer at the east driefontein gold mine carletonville are distinguished by clast type assemblage reflecting discrete provenances the placer further comprises six lithofacies which are not restricted to specific provenance varieties the six lithofacies are massive matrix supported conglomerate facies gms massive or crudely bedded clast supported conglomerate facies gm channel based conglomerate facies gt single clast layers facies glag horizontally stratified sandstone facies sh and trough cross stratified sandstone facies st facies gms represents debris flow deposits whereas the other facies are stream deposits lithofacies and provenance varieties are complexly interrelated in local environments which are themselves complexly related to geomorphic elements of a degradation surface the maximum thickness of the placer is 7 m the placer was deposited on a hard i e non alluvial bedrock surface suggesting that it is a pediment mantle it owes its preservation to a capping of conformably overlying basalts economic gold mineralization is present in all the conglomerate facies and all the provenance varieties gold concentrations are high in gravel bar deposits and channel fills but are not restricted to these environments a major feature of gold concentration is its variability between provenance controlled varieties the gold concentration of a specific primary source is interpreted to be a major control on gold concentration in the final deposit the origin of the placer as a pediment mantle and its subsequent preservation by lava flows suggests that there was little potential for selective reworking of heavy minerals nevertheless the ventersdorp contact placer on the carletonville goldfield is one of the richest gold placers in the witwatersrand basin

historical and modern distributions of benthic foraminifers on the continental shelf of monterey bay california historical early 1930s and modern samples provide a detailed account of the spatial distribution of benthic foraminifers on the continental shelf of monterey bay california ten species among a total of 110 present dominated the 110 samples investigated in the historical study a cluster analysis of the foraminiferal abundances in the historical study identified five assemblages inner shelf middle shelf outer shelf southeastern shelf and southwestern shelf specimens with calcareous tests were most prevalent in all the assemblages a cluster analysis of the modern foraminiferal frequencies from 95 samples also defined five assemblages inner shelf middle shelf middle outer shelf arenaceous outer shelf and southern shelf although arenaceous taxa dominate much of the modern fauna the spatial distribution of the modern assemblages is similar to that of the historical record when presumably unrecognized taxa are eliminated from the data both the historical and to a greater degree the modern foraminiferal assemblages exhibit a strong correlation with the sediment grain size distribution

variability in vertical distributions of planktonic foraminifera in the california current relationships to vertical ocean structure 1 geochemical records from planktonic foraminifera are among the few means available to infer past changes in the upper ocean although interpretations can be confounded by variability in foraminifera habitat depths the principal environmental factors affecting foraminiferal vertical distributions were examined through 28 vertically stratified plankton tows taken off southern california in winter spring and summer each species has a dynamic range of preferred habitat depth from the mixed layer to the thermocline characterized by a unique relationship with environmental properties globigerina bulloides neogloboquadrina pachyderma dextral and neogloboquadrina dutertrei can live near the surface but frequently live deeper as stratification increases and a particular isotherm deepens globigerinoides ruber and orbulina universa vary more closely with the depth of the thermocline than the depth of a given isotherm the shifts in habitat depth are of sufficient magnitude to affect 18o records the effects of such shifts are observed for g bulloides and n pachyderma in santa barbara basin sediments geochemical signatures from multiple species of foraminifera each with a different predicted response to environmental change can permit the detection of changes in habitat depth of a given species and thus more accurately indicate past changes in hydrographic structure

detrital origin of hydrothermal witwatersrand gold a review the witwatersrand basin is the largest known gold province in the world the gold deposits have been worked for moren than 100 years but there is still controversy about the ore forming process detailed petrographic studies often reveal that the gold is late in the paragenetic sequence which has led many researchers to propose a hydrothermal origin for the gold however observations such as the occurrence of rounded disc like gold particles next to irregularly shaped or idiomorphic secondary gold particles in the same sample suggest an initial detrital gold source within the witwatersrand strata mineral chemical and isotopic data together with sem cathodoluminescence imaging and fluid inclusion studies provide evidence for small scale variations in the fluid chemistry a requirement for the short range mobilization of the gold the existing data and observations on the witwatersrand rocks support a model of hydrothermally altered metamorphosed placer deposits with at least two subsequent gold mobilization events hydrothermal infiltration in early transvaal time 2 6 2 5 ga and during the 2 020 ga vredefort impact event

palaeomagnetism of precambrian basic intrusion and dykes of northern karelia eastern fennoscandian shield abstract palaeomagnetic results for mafic and ultramafic intrusions and their country rocks in russian karelia are presented the oldest rock type is pyroxene hornblende gabbro regarded as late archaean or palaeoproterozoic in age later at the early stage of formation of a volcanic plutonic association including layered intrusions and metavolcanites gabbro norite dykes were emplaced sm nd isotopic analyses of this association yield mineral and whole rock ages of 2 47 2 35 ga with nd 0 4 to 1 2 for gabbro norite dykes based on field relations the youngest rock types are pyroxene plagioclase porphyry dykes and gabbro dolerite dykes three distinct magnetization components were isolated by alternating field and thermal demagnetization the most common remanence component b with a mean direction of d 30 i 58 k 52 95 10 n 5 geological units is an overprint interpreted to have been acquired at the last stage of the svecofennian orogeny 1 90 1 70 ga component a with a mean direction of d 350 i 49 k 69 95 9 n 5 geological units is also an overprint probably acquired at the onset of the svecofennian orogeny both components are found in all rocks studied component c with a mean direction of d 126 i 73 k 167 95 10 n 3 geological units is isolated as a primary remanence in the pyroxene hornblende gabbro intrusion and gabbro norite dykes the results are compared with other contemporaneous palaeomagnetic poles from finland and russian karelia

uncorking the bottle what triggered the paleocene eocene thermal maximum methane release the paleocene eocene thermal maximum petm was a time of rapid global warming in both marine and continental realms that has been attributed to a massive methane ch 4 release from marine gas hydrate reservoirs previously proposed mechanisms for this methane release rely on a change in deepwater source region s to increase water temperatures rapidly enough to trigger the massive thermal dissociation of gas hydrate reservoirs beneath the seafloor to establish constraints on thermal dissociation we model heat flow through the sediment column and show the effect of the temperature change on the gas hydrate stability zone through time in addition we provide seismic evidence tied to borehole data for methane release along portions of the u s continental slope the release sites are proximal to a buried mesozoic reef front our model results release site locations published isotopic records and ocean circulation models neither confirm nor refute thermal dissociation as the trigger for the petm methane release in the absence of definitive evidence to confirm thermal dissociation we investigate an alternative hypothesis in which continental slope failure resulted in a catastrophic methane release seismic and isotopic evidence indicates that antarctic source deepwater circulation and seafloor erosion caused slope retreat along the western margins of the north atlantic in the late paleocene continued erosion or seismic activity along the oversteepened continental margin may have allowed methane to escape from gas reservoirs trapped between the frozen hydrate bearing sediments and the underlying buried mesozoic reef front precipitating the paleocene eocene boundary methane release an important implication of this scenario is that the methane release caused rather than resulted from the transient temperature increase of the petm neither thermal dissociation nor mechanical disruption of sediments can be identified unequivocally as the triggering mechanism for methane release with existing data further documentation with high resolution benthic foraminiferal isotopic records and with seismic profiles tied to borehole data is needed to clarify whether erosion thermal dissociation or a combination of these two was the triggering mechanism for the petm methane release

massive dissociation of gas hydrate during a jurassic oceanic anoxic event in the jurassic period the early toarcian oceanic anoxic event about 183 million years ago is associated with exceptionally high rates of organic carbon burial high palaeotemperatures and significant mass extinction heavy carbon isotope compositions in rocks and fossils of this age have been linked to the global burial of organic carbon which is isotopically light in contrast examples of light carbon isotope values from marine organic matter of early toarcian age have been explained principally in terms of localized upwelling of bottom water enriched in 12c versus 13c refs 1 2 5 6 here however we report carbon isotope analyses of fossil wood which demonstrate that isotopically light carbon dominated all the upper oceanic biospheric and atmospheric carbon reservoirs and that this occurred despite the enhanced burial of organic carbon we propose that as has been suggested for the late palaeocene thermal maximum some 55 million years ago the observed patterns were produced by voluminous and extremely rapid release of methane from gas hydrate contained in marine continental margin sediments

high resolution records of methane hydrate dissociation odp site 893 santa barbara basin abstract sediment records from odp site 893 santa barbara basin have documented brief negative carbon isotopic excursions in the late quaternary in planktonic and benthic foraminifera these excursions were interpreted as evidence of major releases of methane from the marine hydrate reservoir affecting the entire water column and likely reaching the atmosphere these carbon isotopic excursions are further recorded in the 13c values and concentration of lipid biomarkers of marine methanotrophs in the basin three previously described carbon isotopic excursions are re examined during this study at a resolution of every 3 7 years the original isotopic excursions were sampled at a resolution of once every 50 70 years examination using light microscopy and environmental scanning electron microscopy esem indicates that specimens in this study are in excellent condition with no apparent evidence of postdepositional diagenesis or alteration of the foraminiferal shells alternative hypotheses to account for these conspicuous carbon isotopic excursions include postdepositional carbonate diagenesis of the excursion intervals and changes in surface ocean productivity and carbon export to the sediments in this study we further test the hypothesis that these excursions record the primary signal of methane in the water column by intensive analyses of the previously described carbon isotopic excursions all four carbon isotopic excursions studied are associated with interstadial warming in the basin time periods that are associated with shifts in the benthic foraminiferal assemblages toward low oxygen fauna at high resolution 13c excursions appear very brief 5 10 years duration and within this time planktonic and benthic species record a significant shift in 13c composition planktonics to 3 and benthics to 6 excursion events are synchronous in benthic and planktonic species within the resolution of these records in one interval studied 37 5 ka the bulk organic carbon 13c records a 1 negative shift in concert with the carbon isotopic excursion in benthic and planktonic foraminifera consistent with a carbon isotopic shift of photosynthetically derived marine organic carbon we suggest that alternate explanations invoking changes in productivity and or postdepositional alteration of these intervals cannot account for the entire magnitude of the carbon isotopic excursion nor the diversity of evidence presented here thus methane hydrate destabilization remains a compelling hypothesis to explain the conspicuous 13c excursions observed in odp site 893 and similar late quaternary excursions described elsewhere

seafloor fluid seeps on kimki ridge offshore southern california links to active strike slip faulting abstract the kimki ridge fluid seeps are located in western catalina basin about 60 km southwest of the southern california mainland and at a water depth of approximately 1100 m multichannel seismic reflection profiles collected by the u s geological survey usgs in 2014 show acoustic transparency within the kimki ridge suggesting the possibility of fluid seeps and possible sub seafloor fluid pathways subsequent multibeam bathymetric and backscatter intensity data collected during a cooperative university of washington usgs cruise in early 2016 show subtle seafloor buildups with high acoustic backscatter reflectivity in three places along kimki ridge supporting the existence of fluid seepage a remotely operated vehicle rov dive conducted as part of the nautilus exploration program took place in august 2016 to confirm the presence of these previously unknown seeps and document their characteristics as well as those of any associated biological communities two of the three seeps were explored by rov and showed abundant evidence of fluid seepage including characteristic algal mats chemosynthetic clams and authigenic carbonate formation the seeps are comprised of carbonate buildups 1 3 m thick and 300 500 m across within these areas we interpret broad crater like depressions 30 50 m across and 1 2 m deep to be individual seep vents the seep areas appear to be broad zones of diffuse seepage that support chemosynthetic biologic communities however active venting was not observed geochemical analyses of rock samples collected from the seeps indicate microbially driven anaerobic oxidation of methane at or near the sediment water interface seismic reflection profiles show chimney like fluid pathways along the limbs and in the axis of the fold forming kimki ridge and evidence of methane in shallow sediments can be traced into the adjacent catalina basin a system of closely spaced faults located at the axis of the kimki ridge anticline may serve as pathways to allow fluid flow to the seafloor our data are consistent with other studies that suggest that transpression is an important component in the formation and localization of fluid seeps in a strike slip setting implying that seep formation may be a common occurrence at fault stepovers or transpressional bends in strike slip systems

records of continental slope sediment flow morphodynamic responses to gradient and active faulting from integrated auv and rov data offshore palos verdes southern california borderland abstract variations in seabed gradient are widely acknowledged to influence deep water deposition but are often difficult to measure in sufficient detail from both modern and ancient examples on the continental slope offshore los angeles california autonomous underwater vehicle remotely operated vehicle and shipboard methods were used to collect a dense grid of high resolution multibeam bathymetry chirp sub bottom profiles and targeted sediment core samples that demonstrate the influence of seafloor gradient on sediment accumulation depositional environment grain size of deposits and seafloor morphology in this setting restraining and releasing bends along the active right lateral palos verdes fault create and maintain variations in seafloor gradient holocene down slope flows appear to have been generated by slope failure primarily on the uppermost slope 100 200 m water depth turbidity currents created a low relief

transpressional segment boundaries in strike slip fault systems offshore southern california implications for fluid expulsion and cold seep habitats the importance of tectonics and fluid flow in controlling cold seep habitats has long been appreciated at convergent margins but remains poorly understood in strike slip systems here we present geophysical geochemical and biological data from an active methane seep offshore from del mar california in the inner california borderlands icb the location of this seep appears controlled by localized transpression associated with a step in the san diego trough fault zone and provides an opportunity to examine the interplay between fluid expulsion and restraining step overs along strike slip fault systems these segment boundaries may have important controls on seep locations in the icb and other margins characterized by strike slip faulting e g greece sea of marmara and caribbean the strike slip fault systems offshore southern california appear to have a limited distribution of seep sites compared to a wider distribution at convergent plate boundaries which may influence seep habitat diversity and connectivity

basin internal derivation of hydrocarbons in the witwatersrand basin south africa evidence from bulk and molecular δ13c data abstract gold in the quartz pebble conglomerates of the late archean witwatersrand basin south africa is often intimately associated with carbonaceous matter of organic biogenic origin which occurs in the form of stratiform carbon seams and paragenetically late bitumen nodules both carbon forms are believed to be formed by solidification of migrating hydrocarbons this paper presents bulk and molecular chemical and stable carbon isotope data for the carbonaceous matter all of which are used to provide a clue to the source of the hydrocarbons these data are compared with those from intra basinal shales and overlying dolostone of the transvaal supergroup the 13c values of the extracts from the witwatersrand carbonaceous material show small differences up to 2 4 compared to the associated insoluble organic matter this suggests that the auriferous rocks were stained by mobile hydrocarbons produced by thermal and oxidative alteration of indigenous bitumens a contribution from hydrocarbons derived from intra basinal witwatersrand shales cannot be excluded individual aliphatic hydrocarbons of the various carbonaceous materials were subjected to compound specific isotope analysis using on line gas chromatography combustion stable isotope ratio mass spectrometry gc c irms the limited variability of the molecular parameters and uniform 13c values of individual n alkanes 31 1 1 7 and isoprenoids 30 7 1 1 in the witwatersrand samples exclude the mixing of oils from different sources carbonaceous matter in the dolostones shows distinctly different bulk and molecular isotope characteristics and thus cannot have been the source of the hydrocarbons in the witwatersrand deposits all the various forms of witwatersrand carbon appear indigenous to the witwatersrand basin and the differences between them are explained by variable in general probably short centimeter to meter scale hydrocarbon migration during diagenesis and subsequent hydrothermal infiltration

stable oxygen and carbon isotopes of live benthic foraminifera from the bay of biscay microhabitat impact and seasonal variability we determined the stable oxygen and carbon isotopic composition of live rose bengal stained benthic foraminifera n150 am size fraction of seven taxa sampled along a downslope transect between 140 to 2000 m water depth in the bay of biscay at the five stations hoeglundina elegans cibicidoides pachydermus uvigerina peregrina uvigerina mediterranea preferentially occupy shallow infaunal niches whereas melonis barleeanus and uvigerina elongatastriata occupy an intermediate infaunal microhabitat and globobulimina spp live in a deep infaunal niche close to the zero oxygen boundary when compared with d 18 o values of calcite formed in equilibrium with bottom waters u peregrina forms its test in close equilibrium with bottom water d 18 o all other foraminiferal taxa calcify with a constant offset to calculated equilibrium calcite there is no systematic relationship between the foraminiferal microhabitat depth and the dd 18 o between foraminiferal and equilibrium calcite we calculated correcting factors for the various taxa which are needed for constructing multispecies based oxygen isotope records in paleoceanographic studies of the study area the d 13 c values of foraminiferal taxa investigated in this study do neither record bottom water d 13 cdic in a 1 1 relationship nor with a constant offset but appear to be mainly controlled by microhabitat effects the increase of d 13 c values of shallow infaunal taxa with increasing water depth reflects the decrease of the exported flux of organic carbon along the bathymetric transect and early diagenetic processes in the surface sediment this is particularly the case for the shallow infaunal u peregrina the d 13 c values of deep infaunal globobulimina spp are much less dependent on the exported organic matter flux we suggest that the dd 13 c between u peregrina and globobulimina spp can shed light on the various pathways of past degradation of organic detritus in the benthic environments at a station in 550 m water depth where periodic eutrophication of sediment surface niches was demonstrated previously we performed a two year seasonal survey of the isotopic composition of foraminiferal faunas no marked seasonal changes of the stable carbon isotopic composition of shallow intermediate and deep infaunal foraminiferal taxa were observed thus the d 13 c values of foraminiferal individuals belonging to the n150 am fraction may result from rather long term calcification processes lasting for several weeks or months which limit the impact of ephemeral 12 c enrichment of shallow infaunal niches on the isotope chemistry of adult individuals during eutrophic periods only highly opportunistic taxa reproducing or calcifying during

paleoceanographic evolution of the gulf of tehuantepec mexican pacific during the last 6 millennia oceanographic dynamics in the gulf of tehuantepec gt are the direct consequence of climate variability mainly influenced by the strong wind regime locally called tehuanos and the interactions

low δ13c in tests of live epibenthic and endobenthic foraminifera at a site of active methane seepage 1 to investigate the use of benthic foraminifera as a means to document ancient methane release we determined the stable isotopic composition of tests of live rose bengal stained and dead specimens of epibenthic fontbotia wuellerstorfi preferentially used in paleoceanographic reconstructions and of endobenthic high latitude cassidulina neoteretis and cassidulina reniforme from a cold methane venting seep off northern norway we collected foraminiferal tests from three push cores and nine multiple cores obtained with a remotely operated vehicle and a video guided multiple corer respectively all sampled sites except one control site are situated at the hakon mosby mud volcano hmmv on the barents sea continental slope in 1250 m water depth at the hmmv in areas densely populated by pogonophoran tube worms 13c values of cytoplasm containing epibenthic f wuellerstorfi are by up to 4 4 lower than at control site thus representing the lowest values hitherto reported for this species live c neoteretis and c reniforme reach 13c values of 7 5 and 5 5 vienna pee dee belemnite vpdb respectively whereas 13c values of their empty tests are higher by 4 and 3 however 13c values of empty tests are never lower than those of stained specimens although they are still lower than empty tests from the control site this indicates that authigenic calcite precipitates at or below the sediment surface are not significantly influencing the stable isotopic composition of foraminiferal shells the comparatively high 13c results rather from upward convection of pore water and fluid mud during active methane venting phases at these sites these processes mingle tests just recently calcified with older ones secreted at intermittent times of less or no methane discharge since cytoplasm containing specimens of suspension feeder f wuellerstorfi are almost exclusively found attached to pogonophores which protrude up to 3 cm above the sediment and 13c values of bottom water dissolved inorganic carbon dic are not significantly depleted we conclude that low test 13c values of f wuellerstorfi are the result of incorporation of heavily 13c depleted methanotrophic biomass that these specimens feed on rather than because of low bottom water 13cdic alternatively the pogonophores which are rooted at depth in the upper sediment column may serve as a conduit for depleted 13cdic that ultimately influences the calcification process of f wuellerstorfi attached to the pogonophoran tube well above the sediment water interface the lowest 13c of live specimens of the endobenthic c neoteretis and c reniforme are within the range of pore water 13cdic values which exceed those that could be due to organic matter decomposition and thus in fact document active methane release in the sediment

diagenetic mg calcite overgrowths on foraminiferal tests in the vicinity of methane seeps methane is a potent greenhouse gas and some episodes of past global warming appear to coincide with its massive release from seafloor sediments as suggested by carbon isotope records of foraminifera here we present structural geochemical and stable carbon isotope data from single foraminiferal calcite tests and authigenic mg calcite overgrowths in a sediment core recovered from an area of active methane seepage in western svalbard at ca 340 m water depth the foraminifera are from intervals in the core where conventional bulk foraminiferal 13c 13c values are as low as 11 3 mg ca analyses of the foraminiferal tests reveal that even tests for which there is no morphological evidence for secondary authigenic carbonate can contain mg rich interlayers with mg ca up to 220 mmol mol transmission electron microscopy tem of the contact point between the biogenic calcite and authigenic mg calcite layers shows that the two phases are structurally indistinguishable and they have the same crystallographic orientation secondary ion mass spectrometry sims analyses reveal that the mg rich layers are strongly depleted in 13c 13c 13c as low as 34 1 these very low 13c 13c values indicate that the authigenic mg calcite precipitated from pore waters containing methane derived dissolved inorganic carbon at the depth of the sulfate methane transition zone smtz as the depth of the smtz can be located several meters below the sediment seawater interface interpretation of low foraminiferal 13c 13c values in ancient sediments in terms of the history of methane seepage at the seafloor must be undertaken with care

pycnocline variations in the eastern tropical and north pacific 1958 2008 abstractclimatic variability of the pycnocline in the eastern tropical and north pacific has oceanographic and ecological implications gridded monthly profiles of temperature and salinity from the simple ocean data assimilation soda reanalysis 1958 2008 were used to derive estimates of four variables related to the density structure of the upper ocean water column surface temperature pycnocline depth mixed layer depth and stratification potential energy anomaly the pycnocline is primarily a thermal gradient in this region except in subarctic waters at the northern extreme of the study area where salinity becomes more important than temperature in determining stratification spatial patterns of mean and standard deviation of the four pycnocline variables are presented partitioning of variance between seasonal and interannual scales shows the predominance of interannual variability in the tropics and seasonal variability at higher latitudes low frequency variations trends in the pycnocline

stable carbon isotope records of carbonates tracing fossil seep activity off indonesia stable isotope records of carbonates from up to 20 m long sediment cores from the forearc basin of the sunda arc display significant 13c depletion deviating from expected normal marine levels by 5 to 40 peedee belemnite pdb this depletion is interpreted to be caused by methane seepage and associated authigenic carbonate precipitation in sediments near the seafloor about 2 m sized globular carbonate particles found in isotopically depleted samples support this interpretation their shape suggests microbial mediation of the precipitation process investigation of benthic foraminiferal assemblages in cores which record seep influence indicate times of high abundance with an up to twentyfold increase of the population and a dominance of opportunistic infaunal taxa we relate these events to the seepage of methane thus providing an understanding of the duration and age of this postdepositional process postulated seep activity is most intense between 3 7 kyr b p and 27 33 kyr b p as cores with 13c isotope depletion were taken atop active fault zones in the forearc we suggest a tectonic control of the seepage records of seep activity thus may have the potential to archive imprints of tectonic activity

deep circulation of the north atlantic over the last 200 000 years geochemical evidence variations in the cadmium calcium ratio of north atlantic deep water are recorded in the fossil shells of benthic foraminifera the oceanic distribution of cadmium is similar to that of the nutrients hence the cadmium calcium ratio in shells records temporal variations in nutrient distributions data from a north atlantic sediment core show that over the past 200 000 years there has been a continuous supply of nutrient depleted waters into the deep north atlantic the intensity of this source relative to nutrient enriched southern waters diminished by about a factor of 2 during severe glaciations this evidence combined with carbon isotope data indicates that the continental carbon inventory may have been less variable than previously suggested

correlation of marine and coastal terrestrial records of central california response to paleoceanographic and paleoclimatic change during the past 19 000 years new benthic foraminiferal census data combined with previously published planktic foraminiferal and pollen data from the continental margin off central california provide a unique opportunity to document concurrent paleoceanographic and paleoclimatic changes in the region during the late quaternary all three datasets were evaluated in gravity core s3 15g collected at a depth of 3491 on the western levy of the monterey fan 36 23 53 n 123 20 52 w accelerator mass spectrometry radiocarbon dates and the ratio of the planktic foraminiferal species neogloboquardrina pachyderma ehrenberg to neogloboquadrina incompta cifelli provide a good age depth model for the last 19 000 years covering the last glacial bolling allerod younger dryas and holocene intervals separate q mode cluster analyses of the hemipelagic as well as mixed combined hemipelagic and turbiditic mud samples grouped the benthic foraminiferal fauna into two clusters reflecting faunal adaptation to changing climatic conditions during the pleistocene and holocene r mode cluster analysis also differentiated glacial uvigerina senticosa and globobulimina auriculata and interglacial melonis pompilioides and gyroidina planulata faunas a general trend of slightly increasing oxygen in the deep sea is suggested from the pleistocene to holocene based on the reduction in abundance of g auriculata and increased frequency of m pompilioides q mode cluster analysis of the planktic foraminifera illustrates a change in the surface water from a glacial subpolar fauna in the pleistocene to a transitional fauna in the holocene whereas the pollen record separated into three clusters two of pleistocene age glacial and transitional and one in the holocene interglacial reflecting the terrestrial floral adaptation in the california coast ranges of central california to the warmer climate in the holocene decoupling is evident between the benthic and planktic foraminiferal and terrestrial floral responses to changing oceanographic and climatic conditions the floral response leads the surface dwelling fauna by several millennia and is followed by the deep dwelling benthic foraminiferal fauna a millennium later

links between palaeoproterozoic palaeogeography and rise and decline of stromatolites fennoscandian shield through a review of literature and new data we have documented two major events in the palaeoproterozoic history of stromatolites as indicated by palaeontological and palaeoenvironmental studies with a time resolution of between 40 and 200 ma we confirm semikhatov and raaben s and awramik s albeit approximately maximum in diversity and abundance of stromatolites between 2330 and 2060 ma ago jatulian diversification we suggest that this taxonomic diversity was driven by a major phase of cratonisation formation of the karelian carbonate platform and numerous rift related shallow water carbonate basins supersaturated with ca 2 mg 2 and co2 the jatulian stromatolite explosion is synchronised with a positive 13ccarb shift of jatulian age carbonates we also document stromatolite decline which occurred on the fennoscandian shield somewhere between 2060 and 1900 ma ago this decline both in abundance and in taxonomic diversity is interpreted as having been caused by the first phase of oceanisation the oceanisation led to the considerable reduction in ecological niches that could be utilised by cyanobacteria the post jatulian decline of stromatolites coincides with an abrupt downward 13corg shift from 19 to 38 and is roughly coeval with the appearance of the first eukaryotic algae documented elsewhere the systematics of the fennoscandian diversity of palaeoproterozoic stromatolites is identical to that reported from india and china and reveals a dissimilarity with abundance and diversity patterns in australia and northern america

late holocene foraminifera of blake ridge diapir assemblage variation and stable isotope record in gas hydrate bearing sediments abstract the presence of gas hydrates on the blake ridge diapir northeastern atlantic ocean offers an opportunity to study the impact of methane seepage on the ecology and geochemistry of benthic foraminifera in the late holocene three push cores covering a time span of 1000 yrs were retrieved from three distinct microhabitats at the top of the diapir at a water depth of 2150 m i sediments away from seepage control core ii sediments overlain by clusters of methanotrophic and thiotrophic bivalves and iii chemoautotrophic microbial mats the foraminiferal assemblages at the two seep sites are marked by a reduction in benthic foraminiferal species diversity coupled with a near absence of agglutinated species however an opportunistic population rise in ch4 or h2s tolerant calcareous species e g globocassidulina subglobosa and cassidulina laevigata that utilize the abundant trophic resources at the seeps has led to an increase in the overall assemblage density there the 18o and 13c values of three species of benthic foraminifera gyroidinoides laevigatus globocassidulina subglobosa and uvigerina peregrina and the planktonic species globorotalia menardii were acquired from all three cores the benthic species from methane seeps yield 13c values of 0 1 to 4 2 vpdb that are distinctly more 13c depleted relative to the 13c of 0 4 to 1 0 vpdb at the control off seep site the species from a mussel bed site exhibit more negative 13c values than those from microbial mats possibly reflecting different food sources and higher rate of anaerobic oxidation of methane the positive 13c values in the paired planktonic species suggest that authigenic carbonate precipitation did not overprint the observed 13c depletions hence the probable cause of negative 13c of benthic foraminifera is primary calcification from dissolved inorganic carbon dic containing mixed carbon fractions from a highly 13c depleted microbially oxidized methane and b a seawater source

isotope data on the age and genesis of layered basic ultrabasic intrusions in the kola peninsula and northern karelia northeastern baltic shield abstract new u pb zircon ages and sm nd data are presented for layered basic ultrabasic intrusions of the kola peninsula and northern karelia in the northeastern part of the baltic shield all ages are in the range between 2 5 and 2 4 ga but there appear to exist three phases of intrusion thus the monchegorsk intrusion and the fedorovy pansky massif have ages between 2493 and 2470 ma the kivakka and lukkulaisvaara massifs of the olanga group of intrusions between 2445 and 2435 ma while the imandra lopolith is 2396 7 ma old a narrow range of negative nd t values between 2 3 and 1 2 suggests formation by partial melting of a semi homogeneous enriched mantle source

iron and lree enriched mantle source for early proterozoic intraplate magmatism as exemplified by the pechenga ferropicrites kola peninsula russia ferropicritic magmatism has produced a variety of volcanic and subvolcanic formations in the upper part of the early proterozoic pechenga group including sills tuffs pillowed and massive lavas and thick differentiated lava flows that possess spinifex textured upper parts and lower cumulate parts enriched in olivine various olivine and pyroxene spinifex types can be distinguished the occurrence of the spinifex texture in the pechenga ferropicrites demonstrates that this texture is not restricted to rocks of komatiitic affinity the existence of kaersutitic amphibole in spinifex textured ferropicrites is discussed as a paleodepth indicator of the volcanism the parental ferropicritic magma contained about 15 wt mgo other geochemical characteristics include high feotot and tio2 and low al2o3 contents and high abundances of lree and hfse many incompatible element ratios correspond to those found in modern ocean island basalts a notable exception are ratios involving phssphorous due to the relatively low p2o5 content of ferropicrites the al2o3 vs mgo kd feo diagram is used to show that ferropicritic magma is not simultaneously saturated in olivine and garnet at high pressures and hence it was segregated from a garnet free mantle residue this implies that the lree enriched nature of the magma was inherited from the mantle source region the positive initial nd value 1 4 0 4 suggests a long time integrated depletion and therefore the inferred enrichment event in the mantle source must have taken place relatively shortly prior to melt segregation geochemical and isotopic data are compatible with a mantle plume related origin of the pechenga ferropicrites but the application of this model is limited by the present uncertainty on the duration of the volcanism

history of hydrocarbon charge on the atlantic margin evidence from fluid inclusion studies west of shetland fluid inclusions in jurassic reservoir sandstones help us to understand the history of hydrocarbon charge in the west of shetland region the sandstones contain both hydrocarbon and aqueous fluid inclusions hydrocarbons are present in trails of secondary inclusions through detrital grains and as primary inclusions in quartz overgrowths this is direct evidence for at least two episodes of hydrocarbon charge before the present oil entered the rock consistent with indirect evidence from burial history modeling and organic geochemistry fluorescence colors indicate that the two oils are of distinct composition the first oil was degraded reflecting an episode of uplift and exposure to near surface fluids before reburial and migration of a second live oil oils comparable to these two paleocharges were mixed to produce the oils that are encountered in the current reservoir pores showing that they were preserved despite repeated tectonic events at the atlantic margin

the δ13c in benthic foraminiferal tests of fontbotia wuellerstorfi schwager relative to the δ13c of dissolved inorganic carbon in southern ocean deep water implications for glacial ocean circulation models on a transect between 20 and 70 s in the eastern atlantic ocean and weddell sea water samples from 19 hydrographic stations and bottom water from 55 surface sediment samples taken with a multiple corer were investigated for the stable carbon isotopic composition of the total dissolved inorganic carbon 13c co2 these measurements were compared to 13c values determined on live specimens of the benthic foraminifer fontbotia wuellerstorfi and closely related genera from the same stations in addition at 16 stations the stable carbon isotope composition of sedimentary organic carbon was measured general deepwater and bottom water mass circulation patterns as inferred from the 13c co2 are in close agreement with those known from other nonconservative tracers very low 13c values of upper circumpolar deep water 0 3 pee dee belemnite pdb in the polar front region and the eastern limb of the weddell gyre coincide with nutrient maxima however a significant decoupling of the dissolved phosphate signal from the 13c co2 signal is indicated in the abyssal weddell sea we attribute this to temperature dependent fractionation processes during gas exchange of surface waters with the atmosphere at sites of bottom water formation multiple corer water from the sediment water interface is slightly 13c depleted relative to deepwater and bottom water 13 co2 the surface sediment organic carbon 13c is 3 to 4 lower south of the polar front than north of it and the 13corg in freshly accumulated phytodetritus is 3 to 4 lower than surface sediment organic carbon 13c comparison of live f wuellerstorfi 13c and related genera with bottom water 13c co2 exhibits at most stations between the subtropical front 41 s and the southern boundary of the antarctic circumpolar current 55 s a significant lowering of foraminiferal 13c values compilation of a mean last glacial interglacial 13c amplitude 13c from six published southern ocean cores results in a shift of 0 99 0 13 pdb this shift is greater than that in all other regions however all of these cores are from positions close to recent oceanic fronts thus for these peripheral areas of the southern ocean we suggest about half of the glacial interglacial shift can be explained by varying frontal zone positions and widths accompanied by a change in mode and height of export production

general geology and evolutionary history of the early proterozoic polmak pasvik pechenga imandra varzuga ust ponoy greenstone belt in the northeastern baltic shield abstract the early proterozoic polmak pasvik pechenga imandra varzuga ust ponoy greenstone belt is situated in the northeastern part of the baltic shield and is discontinuously developed over a length of ca 1000 km it comprises five main zones which are separated by longitudinal and a number of transverse syndepositional faults each zone contains a number of lithostratigraphic units at the rank of groups that are subdivided into several sedimentary and volcanic formations with a total thickness over 16 000 m the sequence comprises a series of sedimentary volcanic rhythms usually separated by stratigraphic breaks marked by palaeo weathering the groups are separated by major disconformities which may mark record rift inversion or orogenic episodes at least seven distinctive lithostratigraphic markers occur in the belt including two komatiitic volcanic series separated by immature conglomerates two red coloured proto evaporitic formations separated by the alkaline volcanics and two different black shale formations perhaps the main characteristic of the belt is the apparently long history of sedimentary volcanic development at the same site spanning a time period of 2500 to 1800 ma a three stage rift development model is considered 1 an intracontinental rift stage 2500 2100 ma separated by the major inversion 2400 2330 ma and comparable with present day afar triangle and east african rifts 2 a transitional from intracontinental to to intercontinental rift stage 2100 1970 ma with possible short lived spreading about 1990 1970 ma 3 a collision related intercontinental rift stage 1970 1800 ma followed by the svecofenian orogeny 1800 1700 ma the observed distribution of platinum group elements pge mineralization is related to layered gabbro norite complexes fedorova and panskie tundry gora general skaya intrusions dated at 2470 ma which are apparently co magmatic and coeval with the first komatiitic volcanic series seidorechka formation found in the eastern part of the belt only the major chromite occurences are connected with a layered gabbro norite intrusion imandra lopoloth which is co magmatic and coeval between 2440 2330 ma with the second komatiitic volcanic series rusinga polisarka akhmalahti and malbekk formations the ni cu deposits of the belt are connected with a differentiated gabbro werhlite complex which is co magmatic and coeval ca 1970 ma with the specific fe and ti rich ferropicrites with komatiitic affinities

oil preserved in fluid inclusions in archaean sandstones oil is generally thought to be geologically young as it is thermodynamically unstable when subjected to elevated temperatures over long periods in open systems1 2 indeed almost all petroleum production comes from rocks younger than 400 million years ref 3 although the oldest known oil occurs in rocks 1 650 myr old4 suitable source rocks were abundant in older geological successions5 and circumstantial evidence suggests that some of these generated hydrocarbons early in their history6 here we report the discovery of oil preserved in fluid inclusions in sandstones dating back 3 000 myr most inclusions lie within healed microfractures confined to individual detrital quartz grains indicating that their oil was emplaced before archaean or palaeoproterozoic metamorphism sealed all voids and thus came from older in some cases archaean sources the fluid inclusions apparently acted as inert pressure vessels that protected the oil from subsequent degradation by circulating fluids and mineral catalysts because of its great age this oil can potentially yield valuable information about the size and diversity of the early biosphere particularly if it contains molecular fossils biomarkers of the primordial organisms from which it was derived

imported quartz cement in aeolian sandstone grew from water of uniform composition but has complex zonation the origins and volumes of waters which mass transport silica in sedimentary basins remain obscure many previous analytical studies have illustrated cases where quartz cements in sandstones originate from complex and variable fluids by contrast we show by using a combination of separation and analytical techniques that in lower permian sandstones of the southern north sea the cementing fluid was isotopically uniform during growth of quartz cement with a 1b o of 19 6 1 0 v smow in this relatively uniform fluid quartz cements grew and developed complex cathodoluminescence cl zonations petrographic data show that 8 10 quartz cement locally 30 was imported into this 380 km 2 180 m thick aeolian sandstone and cement distribution controlled by depositional permeabilities we infer a large scale high volume flux of evolved meteoric fluid during 2 km deep burial and show that complex cl zonation may arise from relatively subtle changes in water composition

old carbon in living organisms and young cac03 cements from abyssal brine seeps abyssal brine springs at the base of the florida escarpment in the gulf of mexico 3 280 m 26 o2 n 84 55 w are surrounded by communities of abundant heterotrophic organisms1 4 and carbonate cemented crusts5 these organisms are apparently supported by local chemosynthetic primary production because the 13c content of their tissues is lower than that found in typical photosynthetically fixed organic carbon6 and the enzymes associated with chemosynthetic metabolism are present in their tissues7 8 here we report that fossil methane is the dominant source of carbon found in living tissues and recent authigenic carbonate minerals associated with abyssal brine seeps at the base of the florida escarpment most organic carbon and authigenic carbonates adjacent to the seeps contain progressively less modern carbon as their 13c contents approach that of methane carried in the brine incorporation of fossil methane 1 3 modern carbon into living tissues and carbonate cements results in recently formed materials which are depleted in 14c therefore 14c cannot be used to indicate the age of authigenic materials produced at the pore water seepage environments that speckle the continental margins of the world

massive methane release triggered by seafloor erosion offshore southwestern japan vast amounts of methane hydrate exist beneath continental margins but whether this methane releases from sediment on a large scale and affects the oceans and atmosphere remains unclear analysis of newly acquired three dimensional seismic images and drilling data from a large gas hydrate province reveal a recently eroded v shaped depression the depression sharply cuts through a relic bottom simulating reflection bsr and hydrate laden sediments the shape of the relic bsr indicates that the seafloor depression was once a large anticline that has recently been eroded and released an estimated 1 51 10 11 m 3 of methane we hypothesize that erosion of the seafloor via bottom water currents unroofed buoyant hydrate laden sediments and subhydrate overpressured free gas zones beneath the anticline once triggered gas driven erosion created a positive feedback mechanism releasing gas and eroding hydrate bearing sediment we suggest that erosive currents in deep water methane hydrate provinces act as hair triggers destabilizing kilometer scale swaths of the seafloor where large concentrations of underlying overpressured methane exist our analysis suggests that kilometer scale degassing events are widespread and that deep water hydrate reservoirs can rapidly release methane in massive quantities

evidence of a critical richardson number in moored measurements during the upwelling season off northern california evidence is found for a cutoff gradient richardson number of ri 0 25 in the moored measurements of temperature and current obtained during the second coastal ocean dynamics experiment code 2 conducted off northern california during the upwelling season of march august 1982 the cutoff at ri 0 25 was noticed even when the instruments were separated by depth intervals as large as 40 m or when the time series having a sampling interval of 7 5 min were averaged over an hour during several strong wind events which tended to increase the mean shear ri 0 25 occurred in the main thermocline beneath the surface mixed layer over the shelf on the other hand several instances were found when a low ri was not directly related to any wind event suggesting that superposition of various waves can locally generate unstable conditions the deeper water over the shelf and slope was generally stable with ri 0 25 these results suggest that in coastal areas with strong currents the intensification of mean vertical shear seems to be very important in bringing about kelvin helmholtz type instabilities as compared with the open ocean without strong currents where superposition of internal waves is believed to be primarily responsible for causing the instabilities because the density structure almost everywhere in the ocean is in the form of steps and because the overall richardson number across vertical scales as large as 20 m are frequently near critical it follows that appreciably thick regions in the ocean frequently remain on the brink of kelvin helmholtz instability even though the actual mixing may take place within thin interfaces between relatively homogeneous layers a small increase of the overall shear then greatly increases the frequency of billow events and vertical mixing and a small decrease of the overall shear greatly decreases such activity it is suggested that in numerical circulation models the richardson number be constantly checked and vertical mixing be used to maintain the richardson number above a minimum value of 0 25

relationship of clathrate instability to sediment deformation in the upper neogene of california widespread soft sediment deformation ssd in upper bathyal continental margin sediments has been explained by compaction related dewatering and related physical processes that can destabilize margin sediments we present the hypothesis that ssd in such facies resulted in part from instability of gas hydrates clathrates leading to overpressurization in sediments and resulting fluid flow and brecciation clathrate related deformation must be widespread in upper bathyal continental margin methanogenic sequences at depths where clathrates are destabilized by changes in bottom water temperatures and sea level a close association exists between an array of ssd features with clathrate hosting sediments in ocean drill cores similar features are conspicuous in the partly laminated upper neogene upper bathyal sediments of the sisquoc formation in southern california suggesting that clathrates may have been responsible for abundant and well developed ssd in these units the lithology methane producing organic content and depositional environment of the sisquoc formation are similar to those features in modern clathrate hosting settings these characteristics in conjunction with the upper bathyal paleobathymetry of the unit the geothermal gradient of the region and 13 c values of benthic foraminifera and dolomite concretions suggest the occurrence of clathrates in the shallow subsurface of these sediments we suggest that the analyzed parts of the sisquoc formation represent an exhumed zone of ssd resulting from clathrate instability in the shallow subsurface of the continental margin sedimentary rocks exhibiting an association of ssd features that resulted from clathrate formation and dissociation are named clathrites

the effects of anaerobic methane oxidation on benthic foraminiferal assemblages and stable isotopes on the hikurangi margin of eastern new zealand abstract a study of benthic foraminiferal assemblages from cold hydrocarbon seeps of the hikurangi margin new zealand was undertaken during rv sonne cruise so191 3 to establish what effects if any methane influenced pore waters had on the foraminiferal assemblages and the carbon isotopes of their tests the results of this study indicate that hikurangi margin foraminiferal assemblages are consistent with modern and fossil seeps worldwide foraminiferal distribution species richness density and diversity were little different between seep and non seep sites though there were noteworthy exceptions the non seep reference core samples were greatly enriched in agglutinate species which constituted 45 of the total assemblage of that core by contrast seep sites contained a maximum of 11 agglutinate foraminifera seep and non seep sites were not separated by density or diversity except for the single site beneath a bacterial mat that exhibited the lowest density and diversity of all sites assemblages at all sites were dominated by uvigerina peregrina a species known to inhabit fossil and modern seeps elsewhere but that also is well documented from normal marine environments carbon isotope data significantly differentiates seep and non seep sites through the greater 13 c depletion and heterogeneity of 13 c values in seep foraminifera 13 c values for u peregrina were as low as 15 2 pdb in addition specimens of pyrgo depressa and hoeglundina elegans exhibited minimum 13 c values of 29 8 and 35 7 pdb respectively showing the influence of carbon that was derived from sulphate dependent anaerobic oxidation of methane authigenic carbonates and vesicomyid bivalve shells from seep station 198 also recorded depleted 13 c values with the lightest values 55 4 pdb clearly within the range of biogenic methane sources

combined carbonate carbon isotopic and cellular ultrastructural studies of individual benthic foraminifera 2 toward an understanding of apparent disequilibrium in hydrocarbon seeps 1 numerous previous studies show disequilibrium between stable carbon isotope ratios of foraminiferal calcite and pore water dissolved inorganic carbon in hydrocarbon seeps calling into question the utility of this widely used paleoceanographic tracer as a proxy we use a recently developed method to compare stable carbon isotope ratios of foraminiferal carbonate with cell ultrastructural observations from individual benthic foraminifera from seep under chemosynthetic bivalves and nonseep habitats in monterey bay california to better understand control s of benthic foraminiferal carbon isotope ratios two attributes previously proposed to cause the isotopic offsets are diet and symbionts ultrastructural analysis shows that positive staining with rose bengal indicates presence of foraminiferal cytoplasm bacterial biomass or a combination of both and thus is not an unequivocal indicator of viability we also show for the first time that some living seep foraminifera have endobionts results from our unique yet limited data set are consistent with suggestions that in our sites several foraminiferal species collected from seep clam beds may not survive there diet and symbiont presence do not appear to be major contributors to disequilibrium little calcification of seep tolerant foraminiferal species occurs while seep conditions prevail and microscale variability in habitats could influence 13c of benthic foraminiferal carbonate results further suggest that our knowledge of benthic foraminiferal ecology and biomineralization especially in extreme habitats such as seeps must be bolstered before we fully understand the fidelity of paleoenvironmental records derived from benthic foraminiferal test 13c data