distribution of recent benthic foraminifera on the sunda shelf south china sea in this study we investigate the species composition and spatial distribution patterns of rose bengal stained and unstained benthic foraminifera from the central part of the sunda shelf in the south western south china sea in relation to environmental factors the uppermost centimetre of the surface sediments 150 mu m from 45 sites from inner 60 m to outer shelf 226 m water depths revealed 584 species including 443 stained species the univariate analyses of individual species abundances and community parameters and next canonical correspondence analysis were used to relate the faunal data to a set of measured environmental parameters four biofacies recognised on the sunda shelf are most strongly correlated to water depth primary production and sediment type of the habitat the inner shelf biofacies cca cluster a defined by ammomassilina alveoliniformis and asterorotalia pulchella occurs in fine grained sediments classified as modem terrigenous mud in the region with the highest primary production values the high energy inner shelf biofacies cca cluster b defined by heterolepa dutemplei and textularia lythostrota occurs in modem terrigenous sand and silt dominated sediments northeast from the natuna island the high energy outer shelf biofacies cca cluster c defined by cibicidoides pachyderma and textularia bocki is sandwiched between assemblages of biofacies d it occurs in the region characterised by neritic relict sand in the shallow waters on the sunda shelf the relationship of benthic foraminiferal faunal composition to grain size of sediments indirectly signals the prevailing bottom hydrodynamic conditions the dominance of the epibenthic foraminifera attached to bigger particles e g cibicides lobatulus planulina arimiensis and much higher abundances of empty tests suggest greater current velocities northeast of natuna island the outer shelf biofacies cca cluster d is defined by facetocochlea pulchra and bulimina marginata it occurs in an area covered with modem terrigenous silt and mud and is characterised by lower annual primary production but seasonally influenced by weak upwelling c 2006 elsevier b v all rights reserved

quantitative characterization of connectivity and conductivity of sandstone carriers during secondary petroleum migration applied to the third member of eocene shahejie formation dongying depression eastern china abstract studies on migration pathways remain qualitative albeit extensive quantification of migration forcing in this study hydrocarbon carriers are defined as carrier units and their corresponding carrier beds for the third member of eocene shahejie formation in the dongying depression bohai bay basin eastern china on the basis of their lithofacies and physical properties spatial relationships and data availability secondary migration conduits are then quantified a carrier unit is defined as a stratigraphic unit that contains microscopically porous and permeable carrier beds and is covered by regional seals the carrier beds are macroscopically and physically connected to each other within a carrier unit and are hydrodynamically connected during secondary migration a method of quantifying sandstone carrier units using common physical properties is developed first a carrier unit containing potential carrier beds is identified on the basis of lithofacies and their lateral changes second physical connectivity of sandstone carrier beds is assessed on the basis of percolation theory third the hydrodynamic connectivity of a sandstone carrier unit is analyzed using effective parameters that may reflect the hydraulic circulation in the carrier unit last the conductivity of a sandstone carrier bed is quantitatively characterized using appropriate physical property parameters the results for sandstone carrier units in the third member of the shahejie formation are used in numerical models addressing pleistocene secondary migration the model results explain the discovered accumulation and hydrocarbon shows well and the model predictions on exploration targets have been confirmed by drilling

simulation and characterization of pathway heterogeneity of secondary hydrocarbon migration carriers are important links between sources and traps for hydrocarbon migration and accumulation in a petroleum system oil and gas commonly migrate along narrow and irregular pathways in porous media even in macroscopically homogeneous media a migration simulator based on the invasion percolation theory which couples the buoyancy of a hydrocarbon column as the driving force with capillary pressure as the resisting force satisfactorily explains migration processes in heterogeneous media in macroscopically homogeneous carriers migration pathways are generally perpendicular to equipotential lines but locally the pathways can be irregular because of the influence of microscopic heterogeneity the degree of irregularity of these pathways depends on the difference between competing driving and resisting forces when numerous pathways form in a migration accumulation system the flux of migrating hydrocarbons may vary among these pathways in macroscopically heterogeneous carriers the irregularity of migration pathways is exacerbated when the driving force is relatively weak hydrocarbons tend to migrate in carriers where the hydraulic conductivity is relatively large these pathways differ from those predicted only on the basis of flow potential simulation of the migration process in the middle jurassic carrier beds of the paris basin demonstrates the characteristics of the migration simulator in the analysis of migration pathway heterogeneity results are comparable to or superior to those achieved with previous simulation approaches

temperature and salinity effects on alkenone ratios measured in surface sediments from the indian ocean abstract we compare alkenone unsaturation ratios measured on recent sediments from the indian ocean 20 n 45 s with modern sea oceanographic parameters for each of the core sites we estimated average seasonal cycles of sea surface temperature sst and salinity which we then weighted with the seasonal productivity cycle derived from chlorophyll satellite imagery the unsaturation index u37k ranges from 0 2 to 1 and correlates with water temperature but not with salinity theu37k versus sst relationship for indian ocean sediments u37k 0 033 sst 0 05 is similar to what has been observed for core tops from the pacific and atlantic oceans and the black sea a global compilation for core tops givesu37k 0 031 t 0 084 r 0 98 which is close to a previously reported calibration based on particulate organic matter from the water column for temperatures between 24 and 29 c however the slope seems to decrease to about 0 02u37k unit c for indian ocean core tops the ratios of total c37alkenones total c38alkenones and the slope of theu37k sst relationship are similar to those previously observed for cultures ofemiliania huxleyibut different from those previously published forgephyrocapsa oceanica eithere huxleyiis a major producer of alkenones in the indian ocean or strains ofg oceanicaliving in the northern indian ocean behave differently from the one cultured in contrast with coccolithophorid assemblages the ratios of c37alkenones to total c38alkenones lack clear geographic pattern in the indian ocean

an experimental study of secondary oil migration experiments using long glass columns packed with glass beads or sand have been done to investigate secondary oil migration under hydrostatic conditions different combinations of bead sizes oil densities oil water interfacial tensions and column orientations have been tested in some experiments the oil was replaced by air the observations included the oil migration pathway the minimum oil column height needed for migration and the rate of advance of the migration front migration was found to take place along restricted pathways and an imbibition front often formed at the bottom of the oil zone the minimum oil zone height needed for migration can be predicted accurately if the values of the drainage and imbibition capillary pressures are known for the saturations at which the oil just becomes disconnected in most experiments the migration front advanced at a constant rate which depended on the fluid properties bead size initial oil height and pore structure migration rate is dependent on buoyant and capillary forces but the dependence on capillary forces becomes weaker as the oil length increases column orientation also has been found to affect migration efficiency

dinoflagellate cyst biostratigraphy of the upper albian to lower maastrichtian in the southwestern barents sea abstract the present study of five wells from upper albian to lower maastrichtian succession in the southwestern barents sea yields the first dinoflagellate cyst based palynological event biostratigraphy for the area the research focuses on the upper cretaceous kveite and kviting formations due to the lack of formal palynological documentation and enables the formation of a biozonation of greater resolution than currently achievable by micropalaeontology four new interval zones and one abundance subzone are described from base upward palaeohystrichophora infusorioides and palaeohystrichophora palaeoinfusa interval zone intra early cenomanian intra late cenomanian dinopterygium alatum interval zone intra early coniacian late santonian palaeoglenodinium cretaceum interval zone early campanian and the chatangiella bondarenkoi interval zone late campanian encompassing the heterosphaeridium bellii abundance subzone intra late campanian the zones are well correlated to existing palynological zonations from the norwegian greenland sea where the previously described subtilisphaera kalaalliti interval zone intra late albian intra early cenomanian heterosphaeridium difficile interval zone middle turonian to intra early coniacian and cerodinium diebelii interval zone early maastrichtian are recognised these data also reveal the presence of three significant unconformities of late cenomanian early turonian middle campanian and late maastrichtian paleocene age

deep water agglutinated foraminiferal changes and stable isotope profiles across the cretaceous paleogene boundary in the rotwandgraben section eastern alps austria abstract the studied interval extends from 2 5 m below to 1 m above the cretaceous paleogene k p boundary and encompasses the uppermost abathomphalus mayaroensis po subzones poa guembelitria cretacea and pob globoconusa conusa p or parvularugoglobigerina eugubina and lowermost p1 subzone p1a or subbotina pseudobulloides planktonic foraminiferal zones the agglutinated benthic foraminiferal assemblages of the uppermost abathomphalus mayaroensis zone are moderately diversified and composed of mixed epifaunal and infaunal morphogroups in the lower part of the guembelitria cretacea subzone benthic foraminifers are extremely rare and represented only by a few epifaunal species in the upper part of this subzone they are still not abundant but assemblages are again moderately diversified in the globoconusa conusa subzone deep water agglutinated foraminifers are abundant highly diversified and represented by mixed epifaunal and infaunal morphogroups bulk rock stable isotope analysis shows a significant drop of both 13 c and 18 o values at the k p boundary it appears that a drastic decrease in abundance and diversity of deep water agglutinated foraminifers as well as a change of the community structure from mixed epifaunal and infaunal to one dominated by epifaunal morphogroups are related to a reduction in marine primary productivity the instantaneous environmental stress and the collapse of primary productivity are compatible with a large bolide impact

biostratigraphy and paleoceanography of the cretaceous seaway between norway and greenland abstract the narrow seaway between greenland and norway in cretaceous time was over 1500 km long and 300 km wide and partly of bathyal water depth during aptian through campanian it received a large volume of fine grained siliciclastic sediments with intercalated gravity flow sandstone wedges as a conduit for heat transport between the low latitudes and polar region atlantic watermasses particularly affected the eastern norwegian margin of this seaway despite its high latitude setting calcareous and few siliceous planktonic microfossils thus play an important role in regional stratigraphy and facies analysis and a majority of fossil events correlate to nw european basins the eastern margin sedimentary succession may be subdivided in several broad lithologic units 1 thin multicolored marly sediments of hauterivian barremian age with a shallow marine falsogaudryina nodosariid ostracod assemblage 2 dark mudstones and minor sands aptian early cenomanian in age with an upper bathyal agglutinated assemblage and monotypic hedbergella floods 3 thick mudstone facies with thin slope apron turbidite sands and an impoverished benthic planktonic assemblage of late cenomanian coniacian age deposited in an upper bathyal oxic dysaerobic environment where turonian sedimentation rates are low a planktonic foraminiferal assemblage with whiteinella hedbergella dicarinella and marginotruncana occurs 4 grayish laminated mudstones santonian campanian in age with local sands in the north a low diversity middle to upper bathyal benthic planktonic foraminiferal assemblage and an inoceramus prisms and radiolarian diatom flood a campanian agglutinated foraminiferal bloom also is known from the atlantic oceanic realm 5 more marly sediments of maastrichtian age with a low diversity planktonic benthic foraminiferal assemblage using the distribution of 1755 foraminiferal and dinoflagellate microfossil events in over 30 exploration wells a rasc ranking and scaling probabilistic zonation served as a template to build a cretaceous zonal model with 19 assemblage and interval zones including over 100 events variance analysis ranks 72 events according to reliability in correlation three new index taxa include uvigerinammina una and ammoanita globorotaliaeformis albian and fenestrella bellii campanian widespread planktonic flood events occur in late albian through early cenomanian early mid turonian late santonian earliest campanian and mid maastrichtian the result of northwards shifts of warmer water masses and disruptions in water stratification in the dysaerobic basins an earliest cretaceous hiatus separates jurassic from cretaceous strata ongoing block faulting coupled to thermal subsidence and global sealevel rise increased water depth in aptian albian time from neritic to bathyal and created sand accommodation space in dysaerobic restricted settings in cenomanian coniacian time sedimentation rates in the central basin increased 10 fold whereas paleo waterdepth did not deepen this relatively brief less than 10 m y tectonic episode resulting in deposition of deep water sands is tentatively linked to stress re orientation in the rockall area a widespread upper maastrichtian danian hiatus the result of shoulder uplift reflects break up prior to the onset of paleogene seafloor spreading in the norwegian sea

estuaries of the past and present a biofacies perspective abstract estuaries are complex sedimentary and ecological systems where controlling factors are variable largely depending on wave vs tidal dominance and fluvial processes paleoenvironmental reconstruction of their ancient counterparts in the form of coastal valley deposits in the subsurface or outcrop requires a multidisciplinary approach microfossils can play an integral part in identifying estuarine subenvironments foraminifera can be abundant in modern estuaries and resemble characteristics of brackish ichnofaunal communities in featuring low species diversity but high abundances of opportunistic species different feeding strategies and common infaunal species whereas sediment distribution is highly controlled by energy regimes foraminifera seem to respond to salinities and tidal exposure whereas individual taxa can widely range bathymetrically the combination of certain taxa becomes diagnostic for estuarine environments fossil marginal marine assemblages are dominated by agglutinated species due to taphonomic loss of the calcareous component that is often dominant in modern estuaries when comparisons between fossil and modern assemblages are undertaken it is advisable to compare with recent subsurface or remnant assemblages for a more accurate basis of paleoenvironmental interpretation more integrated research with detailed taphonomic observations is needed on ancient coastal valley deposits to find the paleoecological requirements of extinct taxa and their link to sedimentary facies and ichnofacies

southwestern barents sea margin late mesozoic sedimentary basins and crustal extension abstract the deep sedimentary basins of the southwestern barents sea were formed in response to several late mesozoic early cenozoic tectonic events within the north atlantic rift zone which culminated with continental breakup and formation of a mainly sheared margin in early tertiary times due to deteriorating data quality the development of the margin bordering sorvestsnaget basin is not well known to improve on this we use both seismic interpretation and gravity modelling to estimate the depth to the middle jurassic mj sequence boundary which marks the onset of mesozoic rifting the horizon represents a first order contrast in seismic velocity and density and the gravity field correlates well with its depth of burial only one seismic line enables tracing of the mj from surrounding areas into the sorvestsnaget basin down to a depth of at least 17 km in the northeastern part of the basin the deep basin is reflected in a general thinning of the crust from 30 36 km within the barents sea to 20 24 km in the margin area the gravity modelling show that the middle jurassic lower cretaceous sequences are of comparable thicknesses in the tromso and sorvestsnaget basins however adjacent to the rifted margin segment the deep northern part of the sorvestsnaget basin is affected by additional large late cretaceous normal faulting and subsidence these faults also caused additional structuring of the intrabasinal veslemoy high post middle jurassic crustal thinning in the southwestern barents sea shows maximum cumulative values exceeding 4 within the tromso and the northern sorvestsnaget basins the corresponding crustal extension is estimated to 70 85 km in a west to northwest direction there is no uniform increase in crustal thinning toward the continent ocean boundary which we attribute to the transform origin of the margin however there is a gradual migration of tectonic activity toward the incipient margin as the time of continental breakup was approached

response of middle jurassic benthic foraminiferal morphogroups to dysoxic anoxic conditions in the pieniny klippen basin polish carpathians abstract the distribution of foraminiferal morphological groups has been analyzed in upper aalenian lower bajocian black siltstones and mudstones of the pieniny klippen belt polish carpathians the deposits are assigned to middle neritic outer and upper bathyal zones represented by three succession and contain agglutinated and calcaeous foraminifera assemblages separate classifications of agglutinated and calcareous morphogroups are established and used for a palaeocological study the groups are distinguished on the basis of morphological features modes of life and feeding habits as inferred from modern analogues infaunal preferences of some foraminifera have been supported by comparison with other infaunal indicators such as trace fossil tiering and abundance of infaunal ostracods a new quantitative method to estimate dissolution of calcareous tests has been tested on the most common genus lenticulina it reveals a special survival strategy of this genus in suboxic muddy and flocculent substrate the distribution of morphogroups in comparison with other palaeoecological taphonomical and sedimentological indicators allows interpretations of organic input rate of sedimentation level of oxygenation position of the redox boundary and p h the studied deposits represent regional anoxic dysoxic event which occured within a semienclosed silled basin

bacterial and algal hydrocarbons in sediments from a saline antarctic lake ace lake capillary gas chromatography mass spectrometry c gc ms and iatroscan thin layer chromatography flame ionisation detection tlc fid were used to study hydrocarbon distributions in a sediment core from ace lake a saline meromictic lake in the vestfold hills of antarctica hydrocarbons were abundant in most core sections up to 125 g g dry wt particularly in near surface samples and the distributions were very complex major constituents were identified as phytane 2 6 10 15 19 pentamethyleicosane tetrahydrosqualene a mixture of phytenes cholesta 3 5 diene and fern 7 ene smaller amounts of sterenes and hopenes were also present the predominance of the first 3 acyclic isoprenoids in sediments buried less than 30 cm is consistent with high populations of methanogenic bacteria known to be present phytenes were abundant in all core sections and there was no relationship between their abundance and that of phytane which suggests that they were not derived from methanogenic bacteria phytadienes were minor constituents at all depths studied an unusual feature of some distributions was the high concentrations of fern 7 ene which was the major hydrocarbon in the 20 25 cm core section this alkene was only abundant in sediments which contained high concentrations of methanogen markers suggesting that it may also be indicative of anoxic depositional environments a possible source might be from purple non sulphur bacteria high concentrations of straight chain c29 and c34 alkenes were also found in these sediments but their origin has not been determined major changes in the hydrocarbon distributions with depth indicate that the depositional environment in the lake has altered dramatically since the lake was formed less than 8000 years ago the present condition of permanent anoxic bottom waters probably developed only in the last 1000 years

modelling of secondary migration and entrapment of a multicomponent hydrocarbon mixture using equation of state and ray tracing modelling techniques modelling of secondary migration and entrapment of a multicomponent hydrocarbon mixture using equation of state and ray tracing modelling techniques

petroleum migration pathways and charge concentration a three dimensional model petroleum migration pathways through a basin are determined by the three dimensional distribution of discontinuous sealing surfaces which are usually parallel to bedding the petroleum migrates below the sealing surface taking the structurally most advantageous route the three dimensional distribution of migration pathways within the petroleum system can be modeled on a personal computer using a program based on the parameters discussed in this paper application of the model to the paris and williston basins demonstrates that a good correlation between predicted pathways and discovered accumulations can be made using simple models pathways form a dense network overlying generating areas in the central parts of basins toward the basin margins these routes commonly become increasingly focused into discrete pathways by the sealing surface morphologies eventually these pathways may reach the surface as seepages it is important to integrate surface outcrops of migration routes surface seepages into migration modeling deflection of the pathways from the structurally most advantageous route below the sealing surface may be caused by lateral sealing barriers due to facies variation in the carrier rock below the seal fault juxtaposition or cross formational seals such as salt intrusions deflection of pathways also occurs where there are hydrodynamic conditions in response to topography driven groundwater flow zones of vertical migration are associated with facies changes along the horizon of the sealing surface into a nonsealing facies or juxtaposition to nonsealing strata by faults vertical migration from either normally or abnormally pressured strata is most likely to occur into normally or lesser pressured strata at intrabasinal highs where hydrocarbons can be stored and transferred at times of temporary seal rupture reverse modeling of individual pathways from fields and seepages to potential sources is a powerful exploration tool it assists in predicting the boundaries of the leaking accumulations or areas of petroleum expulsion

minimum saturations and buoyancy in secondary migration percolation theory it is often argued requires a minimum nonwetting phase saturation of approximately 15 for hydrocarbon migration but field measurements usually fail to find residual oil on the pathway taken during hydrocarbon migration from a source to a reservoir we use numerical simulations and experiments to show that percolation theory when applied to the process of oil invading a pore space leads to the conclusion that field scale saturations in secondary migration can be on the order of 1 or less our capillary invasion experiments on berea sandstone and numerical simulations of fluid invasion on networks show that the minimum saturation for flow of the nonwetting phase decreases as the reciprocal square root of the linear size this result applies to cyli drical samples that have height equal to diameter our numerical simulations include the effects of sample aspect ratio buoyancy and pore size distribution all the numerical results reduce to a single relation between threshold saturations and sample size normalized by a function of the pore size distribution we find that a pore size distribution that has many more small pores than large pores as is typical in rocks and soils substantially reduces the influence of buoyancy on threshold saturations the common practice of using uniform flat pore size distributions to simulate rocks overestimates the effects of buoyancy experiments show that for larger samples the permeability at threshold for flow is higher than conventionally expected in a typical geological situation this h gh permeability is large enough to carry oil to a reservoir over geologic time at saturations of less than 1 of the pore volume our laboratory permeability and saturation experiments confirm the expectations of percolation theory including the fractal dimension of the first invasion path size dependent saturation is the prediction of invasion percolation theory the percolation model is applicable to the secondary migration problem as well as to migration of gas in reservoirs migration of gas or fluids from radioactive waste repositories and migration of nonaqueous phase liquid pollutants in groundwater

long chain alkenones preserved in miocene lake sediments abstract over the last few decades the occurrence of long chain alkenones lcas in quaternary lacustrine settings has been reported the distributions being remarkably different from those of open ocean settings we report here the occurrence of lcas with modern lake type composition from middle miocene sedimentary strata in the dahonggou section qaidam basin northern tibetan plateau this is the first report of lcas with preserved lake compositions in pre quaternary lacustrine sediments the discovery implies that the producers of modern lacustrine lcas could originate from similar lake species living at least as far back as the miocene epoch it also sheds new light on the potential of alkenones as palaeotemperature indicators in lacustrine systems back to at least 10 5 ma

ecostratigraphic trends of jurassic agglutinated foraminiferal assemblages as a response to sea level changes in shelf deposits of svalbard norway foraminiferal analysis proves to be a useful tool for the interpretation of major factors controlling the eco sedimentary environment changes in benthic foraminiferal features including morphogroups are mainly affected by variations in nutrient availability and oxygenation rate the integration of foraminiferal data with total organic carbon toc values together with differentiation of oxygen restricted biofacies orb based on sedimentological features and macroinvertebrate composition will improve the interpretations derived upper jurassic shelf deposits from svalbard norway are revealed to be particularly sensitive to the record of fluctuations in nutrients and oxygenation showing two extreme cases in toc content high toc concentrations are characterized by low values of the shannon weaver index h and diversity index in foraminifera pointing to a low diversity and dominance of r mode epifaunal foraminifera trochammina moreover differentiated orb can be characterized by parallel lamination in shales and an absence of macrobenthic invertebrates including trace fossils unfavourable benthic conditions are interpreted mainly related with a high consumption of oxygen by microbes in the sediment associated to the degradation of the organic matter low toc values are related to higher values of diversity h and diversity index and foraminiferal assemblages dominated by infaunal forms the differentiated orbs are characterized by coarse fabrics scarcity or absence of parallel lamination presence of trace fossils and abundance of macroinvertebrate shelly epifauna this is related to a better pore water circulation and higher oxygenation degree congruent with the comparatively more favourable conditions in the infaunal habitats ecostratigraphic trends along the studied section allow the differentiation of stratigraphic intervals reflecting variations in parameters related to the sea level dynamics transgressive phases reveal upward trends in palaeoenvironmental parameters characterized by decreasing grain size and increasing in both toc values and epifaunal foraminifera differentiated orb reveals diminution in abundance and diversity of trace fossils and benthic shelly macroinvertebrates upwards maximum flooding intervals show the maintenance or accentuation of the previously registered features the thinnest fabrics and the highest values in toc and in opportunistic epifaunal foraminifera with orb dominated by parallel lamination a regressive phase is characterized by coarsening upwards sediments decreasing toc values and increasing infaunal foraminifera orb reveals a diminution in parallel lamination together with an increase in trace fossil abundance and diversity as well as in benthic shelly macroinvertebrates

modern deep sea benthic foraminifera a brief review of their morphology based biodiversity and trophic diversity most fossil deep sea foraminifera are multichambered and have relatively robust calcareous or agglutinated shells modern assemblages on the other hand include many fragile monothalamous single chambered forms and komokiaceans a superfamily of protist currently placed within the foraminifera with soft test walls these groups are poorly known and most of the hundreds of morphospecies recognized in deep sea samples are undescribed the relative abundance of robust and fragile taxa varies with water depth and food supply calcareous and other hard shelled species tend to predominate in relatively eutrophic areas particularly on continental margins but decrease as a proportion of the entire live fauna i e including soft shelled species with increasing water depth even above the ccd carbonate compensation depth most of the species on which the foraminiferal proxies used in palaeoceanography are based live in these bathyal regions at abyssal depths and particularly below the ccd faunas are largely agglutinated and dominated by monothalamous forms these assemblages have a much lower fossilization potential than those found on continental margins in addition to carbonate dissolution these patterns probably reflect adaptations to increasingly oligotrophic conditions on the ocean floor with increasing depth and distance from land bathyal species include herbivores and opportunistic deposit feeders omnivores that consume labile organic material in addition to deep infaunal deposit feeders and must contribute significantly to carbon cycling many abyssal monothalamous foraminifera in constrast accumulate stercomata waste pellets composed of fine sediment particles and probably ingest sediment associated bacteria and more refractory organic matter some monothalamous species without stercomata may be bacteriovores although they probably process organic carbon at a slower rate than calcareous species the shear abundance of monothalamous taxa at abyssal depths suggests that they are important in carbon cycling on a global scale the loss of a substantial proportion of foraminiferal biomass and biodiversity from the fossil record should be considered when using foraminifera to reconstruct palaeoproductivity for example by using the benthic foraminiferal accummulation rate bfar different dietary preferences among calcareous species have implications for the stable carbon isotope signal preserved in their shell

recent benthic foraminifera from the continental margin of northwest africa community structure and distribution abstract sediment grab samples were collected at 107 locations along the continental margin of northwest africa these samples form a series of depth transects between the straits of gibraltar and dakar senegal the greater than 250 m size fraction was retained for a census of both the live and dead foraminifera after deleting trace occurrences jaccard and correlation coefficient based cluster analyses were performed to decipher the community structure for this margin the geographic distribution of the four major faunal provinces recognized is conventional in that for both the live and dead assemblages three are related to depth upper slope and shelf middle slope and lower slope and continental rise the biotopes and thanatotopes within these provinces are strongly restricted along vertical or latitudinal boundaries when the data are analysed using jaccard coefficients dendrograms constructed from correlation coefficients emphasize depth related faunal communities dominant species such as cibicides lobatulus trifarina fornasinii planulina ariminensis uvigerina finisterrensis and c wuellerstorfi are generally distributed within a definite depth range along this margin and strongly influence the correlation coefficient based dendrograms other distributions are clearly not depth related but correspond to various environmental variables for example cancris auriculus coarse substrate bolivina subaenariensis oxygen minimum cibicidoides kullenbergi and hoeglundina elegans low organic carbon uvigerina peregrina is also a notable exception to depth dependence in that this dominant species and the province it represents are generally confined to the continental slope south of cape blanc its preference for that region may arise from the high organic carbon and fine grain size of the sediment there from low salinity of the bottom water or from other unknown variables the most important vertical faunal boundary occurs between cape barbas and cape blanc between 22 and 21 n latitude in contrast the canary island ridge intersects the continental margin at a saddle depth of about 1500 m but that physiographic barrier has little effect on provincialism of the deep water benthic foraminifera

paleobathymetry in the backstripping procedure correction for oxygenation effects on depth estimates abstract this paper aims to provide a straightforward and easily applicable method for estimating the depositional depth evolution of marine basins vertical movements of the basin floor can be reconstructed from the sedimentary record and more accurately constrained when information from the sedimentary history is combined with palaeodepth estimates derived from fauna to this end we propose to extend an existing method based on the percentage of planktonic foraminifera with respect to the total planktonic and benthic foraminiferal association which is expressed as the percentage planktonics p the ratio between planktonic and benthic foraminifera is related to water depth and the p generally increases with increasing distance to shore however next to water depth the oxygen level of bottom waters has a profound effect on the abundance of benthic foraminifera and as such influences the p depending on basin configuration the oxygen level at the sea floor can vary on milankovitch time scales and is reflected by the fraction of benthic foraminiferal species that indicate an effect of oxygen stress on the biotic system these species can be used as stress markers and their percentage with respect to the total benthic population is here expressed as s to assess whether the effect of sea floor oxygenation impairs depth reconstructions we studied the percentage of planktonic foraminifera p in five well dated sedimentary successions from the lower pliocene of crete corfu and milos in greece additionally we assessed whether different foraminiferal size fractions and counting methods affect the determination of the percentage of planktonic foraminifera the palaeobathymetric evolution calculated for each basin was confirmed for all successions by an independent check on depth related occurrences of benthic foraminifera after correction for bathymetry changes of the basin due to sedimentation compaction and eustatic sea level variations the vertical movement history of the basin floor was inferred we propose a standard methodology for reconstructions of palaeobathymetry of marine sedimentary successions from foraminiferal associations

analysis of neutral monosaccharides in marine sediments from the equatorial eastern atlantic abstract in the samples analysed carbohydrate carbon constitutes from 3 0 to 5 8 wt of the total organic carbon no significant degradation of carbohydrates is observed with increasing depth in the sediment the major part of the carbohydrates appears to be derived from marine organisms variations in relative saccharide contributions with depth indicate changes in the composition of the microbial assemblages periods of increased primary productivity seem to be associated with the presence of cyanobacteria or marine algae characterized by relatively high contributions of xylose 6 o methyl mannose and 3 and or 4 o methyl mannose correlations between the alkenone unsaturation index u k 37 18 o and the relative contribution of glucoheptose indicate that higher sea surface temperatures are associated with a restricted contribution of bacterial saccharides

benthic foraminiferal turnover across the cretaceous paleogene boundary at agost southeastern spain paleoenvironmental inferences abstract we studied upper cretaceous and lower paleogene benthic foraminifera from the agost section southeastern spain to infer paleobathymetrical changes and paleoenvironmental turnover across the cretaceous paleogene k p transition benthic foraminifera indicate uppermost bathyal depths at agost during the abathomphalus mayaroensis biochron from about 400 kyr before the k p boundary through the early plummerita hantkeninoides biochron about 120 150 kyr before that boundary the depth increased to middle bathyal for the remainder of the cretaceous and remained so for the danian part of the studied section parasubbotina pseudobulloides biochron at least 200 kyr after the k p boundary there were no perceivable bathymetrical changes at the k p boundary where 5 of the species became extinct and the species composition of the benthic foraminiferal fauna changed considerably below the boundary infaunal morphogroups constitute up to 65 73 of the faunas directly above the boundary in the black clays of the lower guembelitria cretacea biozone benthic foraminifera are rare several opportunistic taxa e g the agglutinant haplophragmoides sp have short peaks in relative abundance possibly reflecting low oxygen conditions as well as environmental instability with benthos receiving food from short lived local blooms of primary producers above the clays through the end of the studied interval epifaunal morphogroups dominate up to 70 of the assemblages or there is an even mixture or epifaunal and infaunal morphogroups infaunal groups do not recover to pre extinction relative abundances indicating that the food supply to the benthos did not recover fully over the studied interval about 200 kyr after the k p boundary the benthic foraminiferal faunal changes are compatible with the direct and indirect effects of an asteroid impact which severely destabilized primary producers and the oceanic food web that was dependent upon them

petroleum migration and accumulation modeling and applications subsurface hydrocarbon observations at any scale serve as critical clues to understand and reconstruct migration pathways and charge histories through geological time to assess the risk of petroleum exploration targets hydrocarbon migration commonly occurred millions of years ago and the pathways can rarely be observed in wells or in outcrops therefore hydrocarbon migration modeling tools are important to test and quantify the processes and elements which impact hydrocarbon migration this paper presents a new method of analyzing migration in superimposed basins which have experienced multiple stages of basin subsidence and inversion during which multiple episodes of hydrocarbon generation migration and accumulation occurred the new modeling method first identifies the character of the migration and accumulation units by synthesizing geological factors such as heterogeneity of carrier beds and reservoirs second hydrocarbon migration is analyzed as a geologic process for which the invasion percolation ip migration method seems to be most suitable the ip migration method demonstrates a good relationship between migration driving and resisting forces along pathways and thus can be used to reasonably model hydrocarbon migration processes at any scale of units in a basin the new migration method provides insights into quantitative methods that can be applied to petroleum system analysis the new method has been applied to several chinese basins and has proven to be useful for defining exploration targets and resource assessments in mature frontier and especially tectonically complex basins a case study of the upper triassic chang 7 and chang 8 units in the southern ordos basin central china is presented to demonstrate a multistage hydrocarbon accumulation unit modeling results show that the same pairs of reservoir seal sets contained different accumulation units in the geological past with different styles of hydrocarbon migration and different accumulation patterns it can be concluded that the style and character of early hydrocarbon migration have significantly affected the more recent hydrocarbon migration and the present day distribution of hydrocarbons

distribution biomass and diversity of benthic foraminifera in relation to sediment geochemistry in the arabian sea the distribution biomass and diversity of living rose bengal stained deep sea benthic foraminifera 30 mu m were investigated with multicorer samples from seven stations in the arabian sea during the intermonsoonal periods in march and in september october 1995 water depths of the stations ranged between 1916 and 4425 m the distribution of benthic foraminifera was compared with dissolved oxygen organic carbon calcium carbonate ammonium silica chloroplastic pigment equivalents sand content pore water content of the sediment and organic carbon flux to explain the foraminiferal patterns and depositional environments a total of six species communities comprising 178 living species were identified by principal component analysis the seasonal comparison shows that at the western stations foraminiferal abundance and biomass were higher during the spring intermonsoon than during the fall intermonsoon the regional comparison indicates a distinct gradient in abundance biomass and diversity from west to east and for biomass from north to south highest values are recorded in the western part of the arabian sea where the influence of coastal and offshore upwelling are responsible for high carbon fluxes estimated total biomass of living benthic foraminifera integrated for the upper 5 cm of the sediment ranged between 11 mg corg m 2 at the southern station and 420 mg corg m 2 at the western station foraminifera in the size range from 30 to 125 mu m the so called microforaminifera contributed between 20 and 65 to the abundance but only 3 to 28 to the biomass of the fauna highest values were found in the central and southern arabian sea indicating their importance in oligotrophic deep sea areas the overall abundance of benthic foraminifera is positively correlated with oxygen content and pore volume and partly with carbon content and chloroplastic pigment equivalents of the sediment the distributional patterns of the communities seem to be controlled by sand fraction dissolved oxygen calcium carbonate and organic carbon content of the sediment but the critical variables are of different significance for each community

petroleum migration and accumulation in the bozhong sub basin bohai bay basin china significance of preferential petroleum migration pathways ppmp for the formation of large oilfields in lacustrine fault basins abstract this paper discusses migration styles and primary controls of petroleum migration pathways in heterogeneous carrier beds in bozhong sub basin bohai bay basin modeling of secondary petroleum migration pathways has been conducted using a simple three dimensional model which assumes that the positions of petroleum migration pathways are controlled by the morphology of the sealing surfaces the modeling results have accurately predicted the petroleum occurrences and have been supported by petroleum geochemical studies most commercial petroleum accumulations are on the predicted preferential petroleum migration pathways ppmp formed by focusing of numerous small petroleum streams close to the kitchens and most large fields petroleum reserves greater than 1 10 8 ton have more than one preferential petroleum migration pathway to convey petroleum to the traps the focusing of petroleum originated from a large area of the generative kitchens into restricted channels is essential for the formation of large oilfields the strong porosity and permeability heterogeneities of the carrier beds and the relatively high prediction accuracy by a model that does not take into consideration of the effect of heterogeneity suggest that the positions of petroleum migration pathways in heterogeneous carrier beds in the lacustrine fault basins are determined primarily by the morphology of the sealing surfaces at regional scales

modifications of the c37 alkenone and alkenoate composition in the water column and sediment possible implications for sea surface temperature estimates in paleoceanography 1 the literature pertaining to c37 alkenone and c37 and c38 alkenoate production and diagenesis has been reviewed and evaluated for issues that might jeopardize their usefulness in paleotemperature estimation we also examined the use of the c37 alkenones as paleoproductivity indicators the stability of their 13c isotopic compositions and their incorporation into the nonsolvent extractable organic matter fraction biological transformation of organic matter by bacteria and zooplankton does not appear to cause significant changes to the ratio of c37 2 and c37 3 alkenones but there are major alterations in the relative composition of alkenoates studies of water column processes and postdepositional sedimentary changes indicate overall stability in the c37 2 c37 2 c37 3 ratio leading to effective preservation of the paleotemperature signal this is not the case for alkenoates and there also appear to be some doubts about the dependence between sea surface temperature and the sedimentary abundance of the c37 4 alkenone c37 alkenones may provide useful qualitative estimates of marine paleoproductivity although these compounds are apparently only derived from haptophycea changes in their quantitative composition might reflect changes in nutrient availability that on sedimentary timescales should also be generally significant of other algal species one caveat is that in highly productive upwelling systems productivity may be expressed mostly in diatom growth and thus not measurable by the c37 alkenones no changes in 13c c37 alkenone composition are observed upon zooplankton ingestion although this is expected from a theoretical perspective further studies are encouraged in order to fully assess the stability of the isotopic signal during c37 alkenone diagenesis finally alkenones bound in the nonextractable fraction of sedimentary organics have not been adequately studied and further work is required to clarify any possible correspondence with a temperature signal

experimental dissolution of a fossil foraminiferal assemblage paleocene eocene thermal maximum dababiya egypt implications for paleoenvironmental reconstructions abstract dissolution experiments were carried out on a foraminiferal assemblage from the paleocene eocene thermal maximum petm at dababiya egypt in order to 1 reveal the effects of differential dissolution on the composition of the foraminiferal assemblage and 2 develop objective criteria for the evaluation of dissolution in foraminiferal assemblages used in early paleogene paleoenvironmental reconstructions particularly with respect to neritic midway type assemblages from the paleocene eocene transition our results confirm two general observations on modern foraminifera 1 planktic foraminifera are much more vulnerable to dissolution than benthic foraminifera leading to depressed p b ratios and 2 dissolution susceptibility differs between size fractions with the smaller specimens dissolving more rapidly than the bigger ones leading to a larger average size of the remaining assemblage within a size fraction wall structure and thickness are considered to be the main factors controlling differential dissolution susceptibility we propose a ranking scheme for taxa with respect to dissolution resistance among the benthic taxa lenticulina is most resistant followed by the agglutinated gaudryina cf ellisorae and alabamina midwayensis biserial and triserial hyaline taxa and the porcelaneous spiroloculina sp are most susceptible to dissolution whereas rotaliines such as cibicidoides and anomalinoides have an intermediate susceptibility this implies that mild dissolution of a midway type benthic assemblage leads to a relative enrichment in lenticulina gaudryina and rotaliines amongst planktic foraminifera the muricate taxa acarinina and morozovella are most resistant followed by the cancellate subbotina the smooth and generally small globanomalina and zeauvigerina are least resistant to dissolution our data enable to objectively evaluate various degrees of dissolution in benthic and planktic foraminiferal assemblages retrieved from the lower paleogene tethyan outcrops in this way taphonomic artifacts can be readily distinguished from paleoenvironmental signals affecting the primary composition of the assemblages more generally we propose that the combined use of foraminiferal numbers p b ratio and relative abundances of non calcareous agglutinated taxa and lenticulina may provide a powerful proxy for assessing dissolution in hemipelagic assemblages from cenozoic and upper cretaceous continental margins in order to achieve more robust pre quaternary paleoenvironmental reconstructions based on quantitative foraminiferal data application of dissolution proxies like proposed here or in slightly modified form should become a more widely used micropaleontologic procedure particularly continental margin studies dealing with major biotic events e g petm or employing p b ratios for sea level reconstructions should benefit from such an approach

secondary migration of oil experiments supporting efficient movement of separate buoyant oil phase along limited conduits geologic note experimental data suggest that the secondary migration of oil in porous permeable sediments probably occurs in most circumstances along restricted pathways or conduits these conduits are formed after the oil has reached a high enough saturation in the reservoir rock for the buoyancy of the oil to overcome the capillary pressure in the pore throats the oil probably moves vertically until it reaches the top of the reservoir interval the oil then moves updip along the top of the reservoir interval via a narrow restricted pathway until it reaches the trap and begins to accumulate depending on the area of the original oil saturation at the bottom of the reservoir unit and the structural geometry multiple conduits may form along which the oil may flow because these conduits are limited in diameter the amount of oil lost during secondary migration could be limited to the irreducible oil saturation left behind in the conduit provided no small scale traps exist along the path to the main trap rates of oil movement are very rapid in a geologic context suggesting that the timing of primary migration is a good indicator of the timing of secondary migration

an experimental study of secondary oil migration in a three dimensional tilted porous medium a three dimensional physical experiment was conducted to study secondary oil migration under an impermeable inclined cap light colored oil was released continuously at a slow rate of about 0 1 ml min from a point at the base of an initially water saturated porous model with buoyancy as a primary driving force a vertical cylindrical shape of an oil migration pathway was observed first and then a layer shaped lateral migration pathway was observed beneath the top inclined sealing plate once the oil cluster had reached the top cap magnetic resonance imaging was used to observe the migration processesmdashfor example morphology of the migration pathway intermittency of oil bubbles and variation of oil saturation within the migration paths results show that the snap off phenomenon related to fast local imbibition processes occurred more commonly during vertical migration than it did during lateral migration the lateral migration pathway that parallels to the top inclined cap has a typical vertical thickness of 2 to 4 cm 0 8ndash1 6 in i e roughly 40ndash80 pores this thickness is consistent with the prediction derived from scaling laws related to pore size and bond number along the lateral migration direction the sectional area and the horizontal width of the migration pathway fluctuate significantly although the average oil saturation along the pathway remains almost the same after stopping the initial oil injection the sectional area of the migration pathway shrinks significantly therefore we believe that this significant shrinking of the migration pathway is the main reason why only a relatively small volume of oil and gas has been lost during secondary migration

carbohydrates in recent marine sediments ii occurrence and fate of carbohydrates in a recent stromatolitic deposit solar lake sinai abstract in a study on the diagenesis of carbohydrates in a recent stromatolitic deposit solar lake sinai monosaccharides are quantitated after mild acid hydrolysis and gas chromatographic analysis as alditol acetates from the depth profiles of the individual monosaccharides relative to the total organic carbon three categories of carbohydrates can be distinguished the behaviour of the various categories upon burial is discussed in terms of their potential to become a part of the organic matter that survives geological periods the distribution patterns of especially the mono o methyl monosaccharides at various depths are characteristics for the bacterial communities present in the corresponding parts of the sediment column

influence of sediment transport dynamics and ocean floor morphology on benthic foraminifera offshore fraser island australia abstract the extensive longshore sediment transport system along the se margin of australia transports yearly 500 000 m 3 of sand from the gold coast of southern queensland north towards fraser island fraser island which consists of 203 km 3 of quartz sand is presently not increasing in size and north of the island quartz sand is replaced by carbonate sand recent multibeam sonar seafloor imagery and sediment analysis has established that the transported sand is being diverted by strong ebb tidal flow over the continental shelf edge onto the tasman abyssal plain through a series of active gullies that incised the continental slope foraminiferal distribution patterns on the shelf and slope are closely linked to the variable ocean floor morphology and associated physical processes in sample locations outside the continental slope gullies areas unaffected by downslope sediment transport foraminiferal assemblages gradually change in accordance with bathymetric zones and their prevailing ecological parameters species diversity evenness the proportion of infaunal species and the abundance of agglutinated taxa all increase with depth assemblages within gullies of the clastic sand transport route are significantly different estuarine and shelf species are transported over the shelf break and mix with typical slope species along the transport path resulting in continued high species diversities as the sediment and faunal load enters the abyssal plain a faunal portion continues to travel within the capricorn sea valley to over 4000 m depth the erosional nature of gullies results in reduction of agglutinated species subtle topographic features such as ridges or levees within the canyon and deep sea valley act as protection from the main erosional sand transport pathway and support the presence of fragile and erect suspension feeders foraminiferal distribution patterns would have received an entirely different biofacies interpretation without linking them to ocean floor processes as revealed through multibeam sonar imagery

buoyancy and interfacial force effects on two phase displacement patterns an experimental study modeling secondary migration of oil currently is difficult because the physics governing the movement is complex and information on heterogeneity of carrier beds is always incomplete to better understand the basic physical process of secondary migration we discuss displacement patterns based on relative magnitudes among buoyancy interfacial and viscous forces using the results of one dimensional vertical oil water displacement experiments oil was injected at a constant rate from the lower inlet of a glass tube packed with sorted glass beads the injection pressure and oil outflow rate were measured while we observed the displacement pattern runs were done using different grain sizes and injection rates two displacement patterns were recognized during the experiments type a consisted of stable piston like displacement and type b consisted of capillary fingering the difference coincided with the relative magnitudes of the driving forces which can be characterized by the dimensionless modified bond bo and capillary ca numbers type a pattern was produced for high ca bo ratios and type b pattern for low ca bo ratios a flow regime diagram showing the regions of the two displacement patterns was constructed in ca bo space including the effects of gravity our results also showed that excess pressure for the nonwetting phase fluid to intrude into a porous medium was rate dependent

foraminiferal response to seasonality modulated by orbital cycles in the cretaceous mid latitudes the albian record from the lower saxony basin abstract the mid cretaceous serves as an excellent laboratory for testing the dynamics of the climate under greenhouse state of the earth this study is focused on the cyclicity record of foraminiferal assemblages in the lower saxony basin during the middle albian the short eccentricity obliquity and precession cycles are consistently recorded in absolute and relative abundance of most opportunistic benthic and planktic foraminifers the question is why foraminifers reacted to orbital cycles and what they actually record in the equable global climate it is suggested that seasonality changes modulated by orbital cycles are responsible for the milankovitch cyclicity records it is well known that the axial obliquity directly influences seasonal contrasts in mid and high latitudes the precession modulated by the eccentricity of the earth orbit further affects the contrast of seasons therefore seasonal dynamics of precipitation runoff and storm tracks patterns and to a lesser extent temperature contrasts are most likely factors controlling milankovitch scale cyclic fluctuations of foraminiferal assemblages and other proxies sensitive to productivity changes it can be deduced that periods of the highest seasonal contrasts were dominated by opportunistic abundant taxa such as benthic valvulineria gyroidinoides group and planktic hedbergellids which record the strongest obliquity signals the lower saxony and adjacent boreal basins were possibly controlled by humid climate with relatively dry summers and wet winter seasons this study confronted with the presented conceptual model and former climate models supports the conclusion that the temperate zone surrounding tethys was sensitive to seasonal changes modulated by orbital cyclicity the mid latitudinal climate of the greenhouse earth seems to be more dynamic and more seasonal than expected

evidence for control of abyssal agglutinated foraminiferal community structure by substrate disturbance results from the hebble area abstract deep sea agglutinated foraminifera have been quantitatively examined from 28 coretop samples from seven box cores collected in june 1983 at the hebble high energy benthic boundary layer experiment site 40 27 n 62 20 w 4815 4825 m depth and hebble shallow site 40 53 n 63 44 w 4185 m depth on the nova scotian continental rise samples from the relatively tranquil hebble shallow site can be distinguished from the hebble site on the basis of their microfauna a q mode varimax factor analysis of species frequency data delineates three major faunal assemblages 1 1 a faunal assemblage from the hebble site dominated by ammobaculties sp cf a americanus this assemblage exhibits lowest species diversity suggesting a disturbed community and strongly associated with box cores containing fine grained laminated sediments 2 2 an assemblage associated with box cores from the hebble meadow dominated by saccammina tubulata psammosphaera sp cf p fusca a coarsely grained species of psammosphaera and reophax sp 1 3 3 a fauna occurring at the hebble shallow site dominated by hormosinella distans with reophax bacillaris and ammobaculites agglutinans unique to the assemblage this fauna displays a higher ratio of calcareous to agglutinated species significantly higher species diversity lower variability and a greater proportion of hormosinids and species utilizing finer grains than samples from the hebble site which is interpreted as reflecting environmental stability marked heterogeneity exists among agglutinated foraminiferal assemblages within box cores at the hebble meadow within box core faunal variability exceeds between box core variability suggesting that environmental factors influencing the distribution of species are patchy on a scale of approximately 40 cm

seismic indicators of focused fluid flow and cross evaporitic seepage in the eastern mediterranean abstract we present for the first time a synthesis of the evidence of focused fluid flow in the eastern mediterranean providing an updated record that includes recent and past occurrences through the last ca 6 my of evolution of the basin we do this by adding the interpretation of a previously unpublished regional 2d seismic dataset to the existing occurrences of focused fluid flow reported in the literature our interpretation shows a high number 141 of focused fluid flow features which span the stratigraphic interval from late miocene to recent of these features 82 are at the seabed and 59 are buried the previous published record is more difficult to quantify but in comparison shows an overwhelming majority of seabed features with only rare examples of buried features the spectrum of the buried and seabed features covers pockmarks pipes mud volcanoes clastic intrusions and collapse structures clustering of the fluid flow features is observed at different times in specific areas including the nile cone and the levant herodotus cyprus and latakia basins with the buried record we are able to highlight the evolution of the leakage points through time focused fluid flow venting has been occurring since the onset of the messinian salinity crisis and the start of basinwide deposition of evaporites we focus in particular on seismic indicators of leakage through evaporites and of sub evaporitic source for fluids and remobilised sediments we also discuss the role of the evaporites as a seal to ascending fluids and in which circumstances they can be breached fluids and associated remobilised sediments are sourced from different intervals from the sub and supra evaporitic section and possibly within the evaporites only a minor proportion of the fluid flow features are certainly sourced from below the messinian evaporites and most of them are located in the nile levant eratosthenes areas the few examples of pathways that are able to cross thick undeformed and well preserved evaporites are typically correlated to overpressure release and hydrofracturing this confirms that the evaporites do act regionally as a very good seal as expected while fluids are able to cross the evaporites only in their most extreme expression i e in near lithostathic overpressure conditions this is confirmed by our observations made in the eastern mediterranean where in the presence of relatively undisturbed evaporites cross evaporite vertical fluid pathways are only observed at the high end of the flux pressure range and involve sediment remobilisation maps combining these different elements can be used to detect areas potentially more prone to breaching

temporal variability in living deep sea benthic foraminifera a review the deep ocean environment is disturbed by various processes many of which involve episodic inputs of organic matter some inputs e g phytodetritus at mid high latitudes in the north atlantic and northeast pacific are seasonally pulsed others e g falls of whale carcasses are irregular and unpredictable but together they evoke a variety of responses from the benthic biota in the case of deep sea foraminifera only those responses arising from seasonal food pulses have been fairly well documented the population dynamics of deep sea benthic foraminifera total live populations and individual species appear to be controlled largely by two inversely related parameters the flux of organic matter to the seafloor and concentrations of oxygen in the sediment porewater organic matter food inputs are most intense along bathyal continental margins and their oxidation often leads to the depletion of oxygen in surface sediments under these conditions foraminiferal faunas are dominated by low oxygen tolerant infaunal species the abundance of which fluctuate in response to seasonally varying amounts of food and oxygen at some sites e g sagami bay off japan species migrate up and down in the sediments tracking critical oxygen concentrations where oxygen concentrations are consistently low less than about 0 5 ml l 1 as in parts of the california borderland foraminifera may undergo population increases solely in response to food pulses in the abyssal north atlantic and in some continental margin areas of this ocean organic matter inputs are weaker and do not lead to oxygen depletion within surface sediments these systems are food limited and seasonal population fluctuations reflect the availability of food phytodetritus rather than oxygen here the species which respond to phytodetritus are mainly epifaunal or shallow infaunal opportunists which represent a small proportion of highly diverse communities 2 or 3 out of 120 species per core of 25 5 cm2 surface area seasonal phytodetrital pulses to the deep seafloor and hence foraminiferal population dynamics are not entirely predictable being dependent on climatic and upper ocean processes they vary in intensity from year to year and occasionally e g at the porcupine abyssal plain pap in 1997 fail to materialise foraminiferal responses to irregular non seasonal organic matter inputs are poorly known however there is some evidence that whale falls turbidite deposits hydrothermal vents and seeps are exploited by species typical of organically enriched low oxygen environments rather than by a specialised fauna fossil foraminiferal assemblages from bathyal and abyssal environments may provide evidence for an increase or decrease in the seasonality of surface production as well as for longer term changes in palaeoproductivity however the accurate interpretation of this record depends on filling the many gaps which remain in our understanding of relations between benthic foraminiferal ecology and seasonal phenomena in the deep ocean

late cretaceous deep water agglutinated foraminiferal assemblages from the north atlantic and its marginal seas the stratigraphic and biogeographic distribution of more than 170 species of deep water agglutinated benthic foraminifers dwaf from the north atlantic and adjacent marginal seas has been compared with paleoenvironmental data e g paleobathymetry oxygenation of the bottom waters amount of terrigenous input and substrate disturbance six general types of assemblages in which deep water agglutinated taxa occur are defined from the turonian to maastrichtian times 1 high latitude slope assemblages 2 low to mid latitude slope assemblages 3 flysch type assemblages 4 deep water limestone assemblages scaglia type 5 abyssal mixed calcareous agglutinated assemblages 6 abyssal purely agglutinated assemblages latitudinal differences in faunal composition are observed the most important of which is the lack or extreme paucity of calcareous forms in high latitude assemblages east to west differences appear to be of comparatively minor importance most dwaf species occur in all studied regions and are thus considered as cosmopolitan biostratigraphic turnovers in the taxonomic content of assemblages are observed in the lowermost turonian mid campanian and in the upper maastrichtian to lowermost paleocene these datum levels correspond to inter regional and time constant paleooceanographic events which probably also affected the deep water benthic biota this allows us to use deep water agglutinated foraminifers for biostratigraphy in the north atlantic sequences deposited below ccd and to geographically extend the currently used zonal schemes which have been established in the carpathian and alpine areas

long chain unsaturated ketones and esters in living algae and marine sediments abstract series of c37 c39 di and triunsaturated ketones and methyl and ethyl esters of hexatriacontadienoic acid c36 2 have been previously identified in marine sediments and the coccolithophorid emiliania huxleyi these compounds have now been found in four further species of the isochrysidales prymnesiophyta which are not known to bear coccoliths suggesting that they are more widely distributed in living algae than previously thought in addition the ketones have been recognised in sediments of eocene age ca 45 ma which greatly extends their known geological time range and increases their potential as molecular markers for algal input heptatriacontatetraen 2 one c37 4 octatriacontatetraen 3 one c38 4 methyl and ethyl esters of hexatriacontatrienoic acid c36 3 and the ethyl ester of hexatriacontatetraenoic acid c36 4 have also been identified in varying amounts in these algae by gas chromatography and computerised gas chromatography mass spectrometry

foraminiferal and palynological biostratigraphy and biofacies from a santonian campanian submarine fan system in the voring basin offshore norway abstract foraminiferal assemblages from a santonian campanian submarine fan system in the northwestern voring basin offshore norway were investigated with the primary objectives to document the stratigraphic ranges of foraminiferal taxa calibrated with dinoflagellate cysts and to interpret foraminiferal biofacies of different fan sub environments previously proposed based on the analysis of ichnofossils the assemblages are composed of deep water agglutinated foraminifera dwaf without carbonate cemented taxa dwaf taxa of high biostratigraphic value are absent but the complete agglutinated nature of the assemblages and the presence of gerochammina stanislawi and rectogerochammina eugubina are similar to those of the lower campanian fenestrella bellii zone of the norwegian sea more reliable dating was provided by palynology and the age of the interval is estimated to be santonian to campanian the inner to middle fan assemblages contain small numbers of specimens and consequently the species diversity and relative abundance of morphogroups are inconsistent deep infaunal forms may be more common in this sub environment but because the abundance is low this observation should be treated carefully in contrast the abundance and diversity of the assemblages of the overbank fringe and basin plain sub environments are fairly high their morphogroup composition is also similar and comparable to each other when the assemblage size is large the assemblage from the interval with suggested hydrothermal activity is similar to those from outside the channel sub environment the presence of bottom water currents possibly in the form of a western boundary current in the basin is suggested based on the abundant occurrence of tubular forms in the overbank fringe and basin plain sub environments

mechanisms for oil depletion and enrichment on the shijiutuo uplift bohai bay basin china the shijiutuo uplift is a major uplift to the north of the bozhong depression the largest generative kitchen in the bozhong subbasin bohai bay basin although the n35 2 trap on this uplift contains a medium size oil accumulation and the q32 6 trap contains china s third largest offshore oil accumulation the q31 1 trap between the n35 2 and q32 6 traps with very similar evolution history was confirmed to be dry biomarker associations of crude oil and source rock samples were analyzed and three dimensional migration pathway modeling was conducted to investigate the origin of oils and mechanisms for oil enrichment and depletion on the uplift multiple parameter oil source correlation and hierarchical cluster analysis using 10 selected biomarker parameters allowed the identification of four source related oil classes almost all oils from the shijiutuo uplift are derived from the eocene shahejie formation whereas oils found between the shijiutuo uplift and the bozhong depression either are derived from or have important contributions from the oligocene dongying formation variations in oil classes and biomarker parameters suggest sequential migration of oil generated from the shahejie and then dongying formations in the bozhong depression which is reasonably supported by petroleum migration pathway modeling oil charge from two oil prone source rock intervals and more importantly focusing of oil originating from a large area of the bozhong generative kitchen into the same trap accounted for oil enrichment and formation of china s third largest offshore oil field in the q32 6 structure the complexity and primary control of the sealing surface top surface of the carrier bed morphology on the positions of migration pathways caused the q31 1 trap to be shielded from migration of oil originating from the bozhong depression resulting in oil depletion in this trap shadows to petroleum migration may occur because of the three dimensional behavior of petroleum migration and two dimensional migration modeling may be misleading in predicting petroleum occurrences

the morphogroups of small agglutinated foraminifera from the devonian carbonate complex of the prague synform barrandian area czech republic abstract agglutinated foraminifera from the lower and lower part of the middle devonian predominantly limestones of the prague synform barrandian area were classified into five morphogroups morphogroup ed1 was divided to morphotype ed1a which is represented by foraminifera with straight tubular or branched tests irregularly coiled forms are separated to morphotype ed1b ed2 morphogroup includes genera with planoconvex tests which can be divided into morphotype ed2a characterized by planoconvex meandering tests and morphotype ed2b with subglobular tests the ed3 morphogroup contains genera with discoidal flattened planispirally coiled forms the ed4 group consists of globular forms whilst simple globular forms without marked tubular projections are representatives of morphotype ed4a and globular morphotypes ed4b with apertures on marked neck like projections and morphogroup ed5 is represented by very rare multilocular morphotypes the absence of the deep infaunal morphogroups is characteristic the morphogroup distribution has been strongly affected by oxygen concentration the energy of the environment nutrient availability and post mortem processes intervals with diversified and abundant foraminiferal assemblages can be correlated with positive 13 c excursions and also with the deposition of nodular limestones the devonian assemblages from the prague synform were compared with isochronous assemblages from other regions though the taxonomical composition of the early devonian assemblages from these areas are rather different the morphogroup composition is highly comparable and globally indicates similar life and feeding strategies of the early devonian foraminifera

estimation of algal carbonate input to marine aragonitic sediments on the basis of xylose content the input of calcareous green algae to the 63 m fraction of bermuda shallow water carbonate sediments is estimated from combination of mineralogical and xylose data factors for the conversion of algal xylose into algal aragonite were obtained by the analysis of sedimentary remains of halimeda and by chemical oxidation of halimeda and penicillus major producers of the area under investigation application of these conversion factors to core samples generally showed good agreement with field observations thus allowing a distinction to be made between sediments with major algal or coral contributions

quantitative assessment of petroleum loss during secondary migration in the yaojia formation ne songliao basin ne china abstract in the nw songliao basin ne china petroleum is produced from fluvio deltaic sandstones in the upper cretaceous yaojia formation source rocks are dark colored lacustrine shales of the qinshankou formation in this paper two models were developed to characterize the petroleum migration pathways in the lower member member 1 of the yaojia formation in the first model which applies to the northern region of the study area petroleum migrates only in the lowermost carrier bed in member 1 immediately above the area of the source kitchen and later in multiple carrier beds outside this area in the second model which represents migration patterns in the central and southern regions of the study area petroleum migrates in multiple carrier beds both within and outside the area of the source kitchen pressures in the yaojia formation were inferred to be hydrostatic while petroleum expulsion and migration took place therefore seven migration accumulation i e local palaeo drainage systems were defined according to the fluid potential gradients migration loss was found to vary markedly between migration accumulation systems in the study area and was controlled by factors including the shape width and area of the effective source rocks the thickness and distribution of carrier beds inside the source area the migration distance outside the source area and the number of carrier beds involved in petroleum migration using these two models petroleum loss during secondary migration was estimated the loss during secondary migration was approximately 5 21 billion bbl of petroleum which is approximately 6 of the petroleum expelled into the first member of the yaojia formation nearly 80 of the total migration loss occurred in all the carrier beds above the source area

south malvinas falkland basin hydrocarbon migration and petroleum system abstract we report a detailed seismic interpretational study of direct hydrocarbon indicators dhis using 2d multichannel seismic reflection data the study includes analyses of four distinctive types of dhi 1 a bottom simulating reflection bsr 2 enhanced reflections ers 3 pipes and vertical anomaly clusters which indicate focused migration of hydrocarbon fluids and 4 flat spots which indicate a deeper source for the shallower hydrocarbon occurrences the interpretation of these dhis included analysis of spatial distribution amplitude variation with offset avo and instantaneous spectral decomposition these analyses are set in a tectono stratigraphic context in order to evaluate the relationship between intra basinal structures hydrocarbon occurrences and migration pathways the recent discovery of a gas condensate accumulation in the study area darwin well ca 190mmbbl confirms the presence of a mature source rock in the basin and supports a model whereby the observed dhis are connected via an active hydrocarbon plumbing system

origin of channel systems in the upper cretaceous chalk group of the paris basin abstract the upper cretaceous chalk group of the anglo paris basin is known to show wedging beds and channel like features which disrupt the quietly deposited pelagic chalk that covered most of nw europe in the late cretaceous two d reflection seismic data from the brie region se of paris show the presence of at least two distinct intra chalk discordant reflections a top santonian and a mid campanian reflection these reflections are in places associated with up to 120 m deep channel like structures trending preferentially n s and nw se the mid campanian reflection is also sporadically associated with a massive secondary dolomite layer the thicknesses of which may reach 110 m diagenesis does not seem to account for the formation of the discordant reflections as there is neither a one to one relationship between the dolomite and discordant reflections nor are there signs of systematic collapse of the cenozoic succession over the channel like features as a result of intra chalk dissolution both reflections correlate with indurated chalk layers and hardgrounds and represent real unconformities the mid campanian reflection is furthermore associated with a stratigraphic hiatus a submarine origin is suggested due to the uninterrupted deep marine chalk facies below and above both unconformities and the unrealistically large sea level drop of more than 200 m which would be necessary for subaerial exposure of the central paris basin during the campanian the channels are oriented parallel to the margins of the basin and important bathymetric elements which could induce erosion by slope failure are not observed the channels are thus interpreted as having formed by strong mainly slope parallel bottom currents major channeling events are common in the chalk group throughout nw europe and represent palaeoceanographic re organization of bottom currents probably driven by changes in sea level and water temperature

scaled physical model of secondary oil migration a scaled physical model was constructed to simulate gravity and capillary controlled flow of oil into a water saturated sand during secondary hydrocarbon migration the model provided both visualization of the flow patterns and estimates of hydrocarbon transport rates and efficiencies the dimensions and physical properties of the model were designed so the balance of gravity capillary and viscous forces was the same in the model as in the geologic system the physical model was a sand pack between glass plates the pack was 52 cm high 100 cm long 2 5 cm thick and inclined at a 5 dip its porosity was 42 and its permeability was 7 0 10 10 m2 710 d it modeled a geologic carrier bed 27 m thick with 20 porosity and 9 9 10 14 m2 100 md permeability overlying a source rock a dyed oil was injected into the lowest corner at a rate of 1 cm3 day and it exited the highest corner at atmospheric pressure oil movement was followed both visually and by ultrasonic velocity measurements the behavior of fluids in the model led us to the following conclusions for oil transport through water wet homogeneous carrier beds the rate limiting step in charging a trap is not secondary migration but rather the rate of oil release from the source rock high hydrocarbon loss may occur during vertical migration when the carrier bed lies above the source because of extensive dispersion losses during lateral migration are probably minimal because flow is concentrated below the top seal

differential dissolution of upper cretaceous planktonic foraminifera from a temperate region of the south atlantic ocean differential dissolution susceptibility is well known in quaternary planktonic foraminifera but few quantitative dissolution studies have been carried out on pre quaternary species a dissolution ranking scheme is proposed for 19 of the most common uppermost cretaceous planktonic foraminifera from a temperate region of the south atlantic ocean the study is based on quantitative faunal variations in an uppermost maastrichtian segment about 190 kyr long from dsdp site 527 leg 74 from the walvis ridge a calcite dissolution index was formulated from degree of fragmentation of planktonic foraminiferal tests through this segment relative abundance of benthonic foraminifera which are generally known to be more dissolution resistant than planktonic foraminifera covary with degree of fragmentation supporting that degree of fragmentation is a measure of dissolution a prominent change from a state of moderate dissolution to a state of stronger dissolution takes place near the top of magnetic anomaly 30 66 74 ma some species decrease whereas others increase in relative abundance between these dissolution regimes and dissolution susceptibility was ranked from quantified differences between dissolution regimes the most susceptible species are in order from least resistant to most resistant heterohelix globulosa globigerinelloides multispina rugoglobigerina rugosa pseudoguembelina costulata globotruncanita stuartiformis and heterohelix carinata the following eight species are unaffected by dissolution in the sense that they show no significant difference between regimes heterohelix glabrans pseudotextularia browni p elegans racemiguembelina fructicosa planoglobulina brazoensis gublerina cuvillieri globotruncana arca and rosita contusa the most resistant species were ranked in the following order from least resistant to most resistant globigerinelloides subcarinata pseudoguembelina palpebra p polypleura globotruncanella havanensis and abathomphalus mayaroensis

benthic foraminiferal morphogroups of mid to outer shelf environments of the late jurassic prebetic zone southern spain characterization of biofacies and environmental significance abstract benthic foraminiferal assemblages belonging to a mixed carbonate siliciclastic shelf succession of the oxfordian upper jurassic in the prebetic southern spain were analyzed the faunal data obtained on thin sections of strongly lithified sediments allowed the detailed differentiation of a foraminiferal morphogroups system to be applied to the interpretation of paleoenvironmental conditions eleven morphogroups were differentiated according to shell composition general morphology number of chambers and mode of coiling paleoenvironmental analysis combines these features with inferred life style epifaunal shallow infaunal and deep infaunal and feeding strategy suspension feeder deposit feeder herbivores etc of the foraminifera analogies and differences regarding previously established morphogroup systems could be outlined accordingly in the prebetic oxfordian distribution trends of foraminiferal morphogroups allow for a comparison of mid to outer shelf environments occupying the south iberian paleomargin indicating that nutrient supply was the most important factor controlling morphogroup development the mid shelf settings are dominated by epifaunal active herbivores phytodetritivores in shallow to deep substrate position of the redox boundary the outer shelf is dominated by agglutinated and infaunal detritivore bacterial scavenger morphogroups revealing a deep substrate position of the redox boundary particularly favorable trophic conditions in mid shelf environments are related with higher phytodetritus input from more proximal and shallower shelf areas

agglutination of benthic foraminifera in relation to mesoscale bathymetric features in the abyssal ne atlantic porcupine abyssal plain abyssal hills small topographic features rising above the abyssal seafloor 1000 m altitude have distinct environmental characteristics compared to abyssal plains notably the presence of coarser grained sediments as a result they are a major source of habitat heterogeneity in the deep sea the aim of this study was to investigate whether there is a link between abyssal hills and the test characteristics of selected agglutinated benthic foraminiferal species we analysed 1 the overall morphometry and 2 the granulometric and chemical elemental characteristics of the agglutinated tests of ten common foraminiferal species adercotryma glomerata ammobaculites agglutinans cribrostomoides subglobosus lagenammina sp 1 nodulina dentaliniformis portatrochammina murrayi three reophax sp and recurvoides sp 9 at four sites two on top of abyssal hills and two on the adjacent plain in the area of the porcupine abyssal plain sustained observatory northeast atlantic the foraminiferal test data were compared with the particle size distribution and elemental composition of sediments from the study sites in order to explore possible grain size and mineral selectivity we found differences in the visual appearance of the tests i e the degree of irregularity in their shape which was confirmed by morphometric analyses related to seafloor topography the agglutinated foraminifera selected different sized particles on hills and plains reflecting the distinct granulometric characteristics of these settings these characteristics incorporation of coarse particles test morphometry could provide evidence for the recognition of ancient abyssal hill environments as well as other palaeoceanographic settings that were characterised by enhanced current flow furthermore analyses of sediment samples from the hill and plain sites using wavelength dispersive x ray fluorescence wd xrf yielded different elemental profiles from the plains probably a result of winnowing on the hills although all samples were carbonate rich in contrast the majority of the agglutinated tests were rich in silica suggesting a preferential selection for quartz

quantitative evaluation of the transporting capacity of unconformities a case study from the zhongguai area junggar basin nw china abstract unconformities are special geologic bodies with a three layer structure including the rock above the unconformity a weathered clay layer and a leached rock the upper wuerhe upper permian bottom unconformity in northwest junggar basin is the main pathway system linking the zhongguai zg lift with hydrocarbon source kitchens based on the log response characteristics of the unconformity s vertical structure and core calibration a principal component analysis pca was applied to extract and identify the evaluation parameters of the unconformity s vertical structure on the basis of darcy s law the quantitative characterization formula of the unconformity s transport capacity with an actual geological significance was established after taking several factors into consideration the migration probability of the unconformity was used to evaluate the possibility that the unconformity acted as a migration pathway consequently a relationship between the migration probability and the evaluation parameters was developed to analyze the effectiveness of these parameters in characterizing the transporting capacity of the unconformity this study shows that the quotient of the two principal components extracted from the conventional logging curves pc1 pc2 have different reference values in the leached and parent rocks the distribution of thicknesses of the weathered clay layer and the leached rock is well matched with the distribution of paleogeomorphology the parameters representing only a single geological factor are not enough to determine whether the unconformity acted as a migration pathway the flow coefficient cf containing multiple factors can effectively and clearly identify the transporting capacity of the unconformity considering the positive correlation between the parameter cf and the migration probability of the unconformity the oil and gas shows of the area with a parameter cf greater than 10 10 4 cm2 s are abundant which is the superior transporting area of the unconformity and there is a good matching relationship between the distribution of the superior transporting area of the unconformity and that of the hydrocarbon distribution

estimation of environmental paleogradient values based on presence absence data a case study using benthic foraminifera for paleodepth estimation abstract a two step procedure for estimating paleogradient values based on the presence absence of variates e g species chemical elements and traits is presented the first step requires information about the general basic distributions of variates along the gradient using species as variates fundamental ecological niches corresponding to the gradient represent these general distributions the second step involves a transfer equation which is the arithmetic mean of location parameters of variates weighted by their dispersion parameters this procedure strengthens variates with narrow dispersions yielding more information about the location at the gradient than variates with wide dispersion the method proposed here does not require information about frequencies solely the presence of variates is sufficient objective criteria are used to eliminate non overlapping variates along the gradient e g species whose distributions do not overlap in living individuals but are mixed in samples of empty tests this is important in estimating paleogradients because mixing of non overlapping variates is a common effect due to post mortem transport bioturbation or sediment reworking the new method is calibrated for depth estimation using living symbiont bearing benthic foraminifera and empty tests from the nw pacific and living smaller benthic foraminifera from the shelf and continental slope of senegal this approach is then successfully applied for paleodepth estimation of a lower to middle miocene transect in the styrian basin austria where plankton benthos ratios of foraminifera yield poor depth estimations

late cretaceous climate simulations with different co2 levels and subarctic gateway configurations a model data comparison we investigate the impact of different co2 levels and different subarctic gateway configurations on the surface temperatures during the latest cretaceous using the earth system model cosmos the simulated temperatures are compared with the surface temperature reconstructions based on a recent compilation of the latest cretaceous proxies in our numerical experiments the co2 level ranges from 1 to 6 times the preindustrial pi co2 level of 280 ppm on a global scale the most reasonable match between modeling and proxy data is obtained for the experiments with 3 to 5 pi co2 concentrations however the simulated low high latitude temperatures are too high low as compared to the proxy data the moderate co2 levels scenarios might be more realistic if we take into account proxy data and the dead zone effect criterion furthermore we test if the model data discrepancies can be caused by too simplistic proxy data interpretations this is distinctly seen at high latitudes where most proxies are biased toward summer temperatures additional sensitivity experiments with different ocean gateway configurations and constant co2 level indicate only minor surface temperatures changes 1 c on a global scale with higher values up to 8 c on a regional scale these findings imply that modeled and reconstructed temperature gradients are to a large degree only qualitatively comparable providing challenges for the interpretation of proxy data and or model sensitivity with respect to the latter our results suggest that an assessment of greenhouse worlds is best constrained by temperatures in the midlatitudes

migration controls extinction and survival patterns of foraminifers during the permian triassic crisis in south china abstract the permian triassic mass extinction the greatest biotic crisis in earth history triggered the complete replacement of ecosystems with the 5 10 surviving species giving rise to the mesozoic fauna despite a long history of systematic studies on permian triassic foraminifera there have been few investigations into spatial and temporal patterns of survivorship and evolution during this critical interval we interrogate a high resolution data set comprising newly obtained and previously published foraminiferal data including 13 422 specimens in 173 species in 62 genera from seven well studied permian triassic successions that record a transect of platform to basin facies in south china shallow water settings seen at the cili and dajiang sections suffered a single pulse sudden extinction with high extinction rates at the end of the palaeofusulina sinensis zone deeper water and slope environments seen at liangfengya and meishan experienced a two pulse extinction in the clarkina yini and isarcicella staeschei zones basinal settings seen at shangsi gujiao and sidazhai record a single less devastating extinction pulse in and slightly above the c yini zone in the late permian foraminiferal diversity was greatest on the shallow platforms where 76 4 of species recorded in our study lived the two pulses of the permian triassic extinction prompted this foraminiferal diversity hotspot to move to deeper slope settings comprising 75 6 of contemporary species and finally basinal settings comprising 88 8 of species we propose that foraminifera migrated to deeper water to avoid overheating and toxicity in shallow waters that were driven by the emplacement of the siberian traps and coeval volcanic activities around the paleotethys ocean this study provides a methodological framework for investigating survival mechanisms for foraminifers and other taxonomic groups during mass extinction events

origin and diagenesis of carbohydrates in ancient sediments abstract neutral saccharides were determined quantitatively in acid hydrolysates of sediments ranging in age from tertiary to jurassic derived from varying depositional environments and with different diagenetic histories the present data show that intact saccharides can be identified and quantified in ancient sediments and that an increase in temperature has a profound effect on the quantity and quality of the saccharides present in diagenetically altered ssediments

palaeoclimatic signals recognized by chemometric treatment of molecular stratigraphic data abstract the high resolution stratigraphy of various marker compounds has been studied using gc hplc and gc ms in a 13 m gravity core recovered from the kane gap region eastern equatorial atlantic which provides a record of the glacial interglacial episodes over the last million years downhole variations in many presumed source specific components are observed e g in n alkanes from terrigenous land plants and dinosterol from dinoflagellates which may be due to perturbations or cyclicities resulting from climatic change fluctuations in the unsaturation of alkenones attributable to variations in water temperatures show correlations with the glacial interglacial cycles recorded in the 18 o values for planktonic foraminifera thereby providing a potential organic geochemical measure of past climates these molecular abundance data can be linked to the palaeotemperature record following computer treatments using principal component and spectral analyses molecular stratigraphy shows promise as a new chemostratigraphical tool where other means of stratigraphy fail for example through calcium carbonate dissolution

numerical simulation of hydrocarbon migration in tight reservoir based on artificial immune ant colony algorithm a case of the chang 81 reservoir of the triassic yanchang formation in the huaqing area ordos basin china abstract the hydrocarbon migration in tight reservoirs is a complex process the fluid flow patterns of which are notably different from those of conventional reservoirs therefore specific mathematical models are needed to simulate the secondary hydrocarbon migrations this study presents a numerical simulation method based on artificial immune ant colony algorithm aiaca to simulate the secondary hydrocarbon migrations in tight reservoirs it consists of three core parts 1 the release modes of artificial ants based on the intensity of hydrocarbon generation 2 the wandering patterns of artificial ants under the control of the dynamic field and the distribution of pheromones 3 the updating modes of pheromones based on the changes in reservoir wettability the simulation of secondary migration can be realized by the observing the dynamic movements and accumulations of the artificial ants the method has been tested in the chang 8 1 tight sandstone reservoir which is part of the triassic yanchang formation in the huaqing area ordos basin in china and proved to be successful in matching the current data in exploration and development

the cretaceous palaeogene boundary at stevns klint denmark inversion tectonics or sea floor topography the cretaceous palaeogene boundary interval is exposed over 12 km in the coastal cliff stevns klint denmark an important lowermost danian hardground has been interpreted as an originally horizontal marine abrasion surface its present elevation varies from a few metres below to about 35 m above sea level this relief has traditionally been considered as resulting from late or post danian laramide folding new seismic profiles offshore stevns klint show however that the base chalk reflector is not folded is remarkably planar and has a gentle northward dip thus the folding hypothesis cannot be upheld seismic stratigraphic analysis of the chalk group necessitates a fundamental revision of general ideas of chalk deposition a highly irregular sea floor topography was formed at many levels and includes broad valleys ridges channels drifts and mounds a system of major wnw ese oriented valleys and ridges can be traced into the succession exposed in stevns klint and further inland where it corresponds to the relief of the cretaceous palaeogene boundary the marked topographic elements of the chalk sea floor are elongate with a wnw orientation roughly parallel to the axis of the danish basin and to the sorgenfrei tornquist zone forming the ne border of the basin the sea floor relief undoubtedly reflects the influence of strong contour parallel bottom currents the cretaceous palaeogene boundary succession at stevns klint was thus developed on an underlying sea floor topographic relief of about 40 m recognition of the highly irregular current influenced topography of the late cretaceous sea floor stands in marked contrast to the conventional picture of quiet pelagic deposition of the chalk

early diagnesis of carbohydrates in the marine environment ii composition and origin of carbohydrates in skagerrak sediments abstract the distribution and composition of carbohydrates were determined for the upper 15 cm of four cores from the southern slope of the skagerrak high concentrations were found in the upper bioturbated layers rapidly decreasing at sediment depths 3 cm total contents appear to be controlled by bioturbation application of various biomarker criteria suggests that carbohydrates originated from terrestrial macroalgal and planktonic sources input from these sources might be by episodic events rather than by continuous sedimentation as can be hypothesised from the irregular occurrence of marine and terrestrial signals

foraminiferal dissolution at shallow depths of the walvis ridge and rio grande rise during the latest cretaceous inferences for deep water circulation in the south atlantic abstract a high resolution 10 20 kyr record of variations in caco3 content and dissolution was established for latest cretaceous last 0 7 myr deep sea sediments from the south atlantic ocean dsdp site 516 from the rio grande rise and sites 525 and 527 from the walvis ridge the degree of fragmentation of planktonic foraminifera dfp was used as a measure of calcite dissolution high negative correlations between dfp and other independent measures of carbonate dissolution percentage of sand fraction absolute abundance of planktonic foraminifera and planktonic benthic foraminiferal ratio validate its use as a sensitive index of calcite dissolution in upper maastrichtian deep sea sediments very high dfp and a significant negative correlation between dfp and caco3 content suggest that site 516 was located below the foraminiferal lysocline during the entire interval studied such a shallow position of the lysocline paleodepth of site 516 was 1 2 km may be explained by upwelling of corrosive deep waters along the southern margin of the rio grande rise sites 525 and 527 were located above the foraminiferal lysocline however three short periods of enhanced dissolution were recognised at site 525 paleodepth 1 km and one interval of strong dissolution was identified at site 527 paleodepth 2 7 km the lack of correspondence between the dissolution regimes at sites from the walvis ridge suggests limited deep water communication across this physiographic barrier two of the dissolution maxima recognised at site 525 correspond to carbonate maxima at site 527 variations in upwelling intensity along the walvis ridge resulting in fluctuations in primary productivity in this area may be the proximal cause of both carbonate cycles at site 527 and dissolution cycles at site 525 we suggest that development of the bottom ekman layer between a hypothetical westward geostrophic current and the topographical height of the rio grande rise walvis ridge system may be a plausible hydrodynamical explanation for the proposed upwelling along the southern margin of this topographical structure

cenozoic erosion and the preglacial uplift of the svalbard barents sea region abstract the creation of the huge fans observed in the western barents sea margin can only be explained by assuming extremely high glacial erosion rates in the barents sea area glacial processes capable of producing such high erosion rates have been proposed but require the largest part of the preglacial barents sea to be subaerial to investigate the validity of these proposals we have attempted to reconstruct the western preglacial barents sea our approach was to combine erosion maps based on prepublished data into a single mean valued erosion map covering the whole western barents sea and consequently use it together with a simple airy isostatic model to obtain a first rough estimate of the preglacial topography and bathymetry of the western barents sea margin the mean valued erosion map presented herein is in good volumetric agreement with the sediments deposited in the western barents sea margin areas and as a direct consequence of the averaging procedures employed in its construction we can safely assume that it is the most reliable erosion map based on the available information by comparing the preglacial sequences with the glacial sequences in the fans we have concluded that 1 2 to 2 3 of the total cenozoic erosion was glacial in origin and therefore a rough reconstruction of the preglacial relief of the western barents sea could be obtained the results show a subaerial preglacial barents sea thus during interglacials and interstadials the area may have been partly glaciated and intensively eroded up to 1 mm y while during relatively brief periods of peak glaciation with grounded ice extending to the shelf edge sediments have been evacuated and deposited at the margins at high rates the interplay between erosion and uplift represents a typical chicken and egg problem initial uplift is followed by intensive glacial erosion compensated by isostatic uplift which in turn leads to the maintenance of an elevated and glaciated terrain the information we have on the initial tectonic uplift suggests that the most likely mechanism to cause an uplift of the dimensions and magnitude of the one observed in the barents sea is a thermal mechanism

effects of carrier bed heterogeneity on hydrocarbon migration abstract reservoir carrier bed heterogeneity is a common geological phenomenon this study applied a hydrocarbon migration model based on the invasion percolation theory to simulate the formation of hydrocarbon migration pathways in heterogeneous carrier beds the results indicate that the pathways and hydrocarbon accumulations in reservoirs may differ from conventional models when continuous low permeability layers occur as networks within reservoirs such low permeability layers may have formed through depositional or diagenetic processes within reservoir rocks at variable scales oil bearing reservoir in donghe sandstone in hadexun oilfield in northern tarim basin china was analyzed to demonstrate the forming mechanisms of substantial tilting of oil water contact donghe sandstone is a quartz sandstone deposited in an open marine shoreface shelf environment during a major transgression in early carboniferous major diagenetic products are abundant tabular concretions along bedding planes and cross laminae the low permeability concretions serve as fluid flow barriers which compartmentalize the donghe sandstone reservoir as a result the oil water contacts and the saturation of oil in the reservoir appear irregular and tilted in hadexun oilfield and neighboring regions

the depth dependency of planktonic benthic foraminiferal ratios constraints and applications abstract study of the ratio between planktonic and benthic foraminifera in a great number of areas shows that variation of this ratio with depth can be described using organic matter flux equations essentially the share of benthic foraminifera in the total association is inversely proportional to depth as is the amount of organic matter resulting from primary productivity reaching the sea bottom variation in the p b ratio from area to area appears to be strongly dependent on the amount of inbenthic living foraminifera if the ratios are corrected for this the regressions between the proportion of planktonic foraminifera p and depth appear to be near identical in the gulf of mexico the gulf of california the west coast of the usa and the adriatic sea this regression can be described by depth e 3 58718 0 03534 p a study of the behaviour of this function in nine cores from the adriatic upper quaternary reveals that the palaeodepth reconstructions are not influenced by fluctuations in productivity and temperature but that they are significantly influenced by redeposition of fine grained deposits

distribution of recent benthic foraminifera along continental slope of the sunda shelf south china sea the distribution of live rose bengal stained and dead benthic foraminiferal distribution 150 mu m was investigated in sediment surface samples 0 1 cm from the winter upwelling region off borneo on the continental slope of the sunda shelf and from the continental slope of southern vietnam shelf the benthic foraminiferal faunas of both areas are highly diverse h s 2 91 4 25 for living and 4 01 4 38 for dead a canonical correspondence analysis proved that bathyal assemblages are most strongly influenced by the decreasing rates of organic carbon flux with increasing water depth resulting in a pronounced depth related succession of assemblages correlation between estimated c org flux and factor 1 loadings of the cca for modem dead foraminiferal assemblages is very good r 2 0 96 thus a local transfer function y 5 0289x 6 8142 for estimating paleo c org flux rates from the down core samples has been successfully developed for the continental slope of the sunda shelf four benthic foraminiferal biofacies were recognised within the studied depth ranges upper bathyal biofacies siphotextularia foliosa cibicidoides robertsonianus well supplied and well oxygenated middle bathyal biofacies uvigerina auberiana nuttallides rugosus located within the oxygen minimum zone uppermost lower bathyal biofacies lagenammina difflugiformis uvigerina peregrina and lower bathyal biofacies paratrochammina challengeri parrelloides bradyi from the relatively well oxygenated but food limited environment c 2009 elsevier b v all rights reserved

molecular stratigraphy a new tool for climatic assessment variations in sea surface temperatures over the past 500 000 years are inferred from the relative abundance behaviour of two organic compounds c37 alkenones over the upper 8 metres of a sediment core from the eastern equatorial atlantic this molecular record ascribed to contributions from prymnesiophyte algae correlates well with the variations in the 18 signal for the calcareous skeletons of certain planktonic foraminifera thus providing the first demonstration of a new stratigraphical technique which may be especially valuable where methods based on carbonate 18 fail

aspects of hydrocarbon migration in the mesozoic in the paris basin as deduced from an organic geochemical survey abstract this paper describes the main results of a study of hydrocarbon migration in the mesozoic in the paris basin as obtained from the geochemical analysis of cuttings from 41 petroleum boreholes the analytical methods used were pyrolysis gas chromatography mass spectrometry and the determination of stable isotopes hydrocarbon formation and migration were simulated using the temispack mathematical model the following results were found concerning the primary migration pyrolysis of numerous samples of freshly cleaned cuttings allowed the computation of a migration efficiency ratio for each sample by comparing the hc contents actually produced with those remaining in the rock they also allowed the compilation of migration maps for each source rock level as indicated by the migration ratios the hc expulsion starts below the beginning of the oil window 2100 m at a depth of about 2350 m for a transformation ratio of the lias om of 25 these migration ratios increase strongly with depth reaching 88 at 2700 m migration maps served to locate the true source rocks at the base of the lias and to calculate the total quantity of oil expelled 2 billion tons of hc analysis of rock extracts from drained levels shows by comparison with the oil analyses that migration occurred without any variation in hc composition concerning the secondary migration the migration maps used to estimate the amounts of migrated hcs revealed lateral migration phenomena in some rocks toarcian with respect to the other secondary migration paths faults played an important role but failed to favor vertical downward migration by more than 50 m below the lias source rocks as shown by the temispack model the deep trias reservoirs could only be filled laterally when the faults like the bray fault placed the mature hettangian sinemurian source rocks in contact with the trias furthermore the hypotheses of a regional hydrodynamic flow trending ne sw were taken into account in the model to explain the lateral hc migrations to distances often far from their oil kitchen and the rarity of shows northeast of the bray fault

pelagic and benthic sources of sedimentary carbohydrates in a shallow water environment kiel bight baltic abstract the carbohydrate fraction of two cores from kiel bight taken at 25 and 28 m water depth and spanning approximately the last 200 years was analysed for its constituent monomers grain size fractionation of the 25 m core indicated a close association of carbohydrates with the m fraction effects of bioturbation were noticeable down to a sediment depth of 8 cm from the carbohydrate composition the presence of macroalgal sugars is evident calculation of contributions from benthic sources results in a value of 73

utility of goi qgf and qgf e for interpreting reservoir geohistory and oil remigration in the hudson oilfield tarim basin northwest china abstract the physical mechanisms responsible for hydrocarbon migration in carrier beds are well understood however secondary migration is one of poorly understood facets in petroleum system the carboniferous donghe sandstone reservoir in the tarim basin s hudson oilfield is an example of a secondary or unsteady reservoir that is oil in this reservoir is in the process of remigration making it a suitable geologic system for studying hydrocarbon remigration in carrier beds experimental methods including grains containing oil inclusions goi quantitative grain fluorescence qgf and quantitative grain fluorescence on extract qgf e together with the results from drilling logging and testing data were used to characterize the nature of oil remigration in the donghe sandstone the results show that 1 significant differences exist between paleo and current oil reservoirs in the donghe sandstone which implies that oil has remigrated a significant distance following primary accumulation 2 due to tectonic inversion oil remigration is slowly driven by buoyancy force but the oil has not entered into the trap entirely because of the weak driving force oil scarcely enters into the interlayers where the resistance is relatively large 3 the oil remigration pathway located in the upper part of the donghe sandstone is planar in nature and oil moving along this pathway is primarily distributed in those areas of the sandstone having suitable properties residual oil is also present in the paleo oil reservoirs which results in their abnormal qgf e a better understanding of the characteristics of oil remigration in the donghe sandstone in the hudson oilfield can contribute to more effective oil exploration and development in the study area

living deep sea benthic foraminifera from the warm and oxygen depleted environment of the sulu sea the semi enclosed oligotrophic sulu sea is characterised by warm ca 10 c and oxygen depleted 32 m from 56 samples from surface down to 5 cm the stained foraminiferal assemblages of the sulu sea comprised 285 species including 137 agglutinated and 148 calcareous species standing stock values ranged from 595 individuals 10 cm2 on the continental slope to 100 individuals 10 cm2 in the abyssal zone generally in the low productivity and low oxygen environment of the sulu sea stained assemblages are characterized by low standing stock values moderate dominance and low diversity the combination of poor rates of c org flux and low dissolved oxygen content in bottom waters are the main factors controlling the deep sea benthic fauna in the sulu sea the foraminiferal abundances in the upper bathyal zone respond to both food fluxes and oxygen concentrations most of the epifaunal oxyphilic species have their lower limit of occurrence at a water depth of approximately 2000 m dissolved oxygen 1 25 ml l in the sulu sea at constantly dysoxic 1 ml l o2 sites from the lower bathyal and abyssal zone the assemblages comprised low oxygen tolerant species and are more dependant on c org fluxes the correlations between benthic foraminiferal faunas and c org flux and dissolved oxygen values are very good with correlation coefficients of r2 0 956r2 0 956 and 0 88 respectively the living deep sea foraminiferal assemblages consisted mainly of agglutinated tests with dominant species such as lagenammina difflugiformis ammoscalaria tenuimargo various reophax species and small 70 m trochamminaceans like portatrochammina wiesneri stained individuals of the calcareous parrelloides bradyi type 2 occurred in low numbers at oxygen poor sites down to a depth of 5 cm in the sediment column the only stained calcareous infaunal species found deeper than 4000 m was valvulineria mexicana average living depth of 3 cm the general microhabitat preferences of common species were consistent with those from other studies although due to the unique combination of poor food supply and dysoxic conditions most of the infaunal species had shallower average living depths than those reported from other dysoxic locations

effects of oil and gas accumulation on water movement geologic notes the water saturation of an oil reservoir is typically 15 to 40 of the pore space and independent of elevation above a level close above the oil water contact this water is not produced with the oil it is not in hydraulic continuity geometric considerations indicate that it is concentrated in pendular rings separated by immobile films of water adsorbed to solid surfaces of grains and any authigenic minerals present it is water trapped during accumulation of the oil and may therefore have a different composition from the water below the oil water contact formation water cannot flow upward through an oil or gas accumulation nor can bacteria which require a water substrate penetrate above the level of irreducible water saturation bacterial degradation of a significant oil column and water washing of oil most likely occur during secondary migration oil is separated from some solid surfaces by an immobile film of adsorbed water no thicker than 1 mm possibly by only a monomolecular layer and so could be altered in the reservoir by catalysis if authigenic or detrital clay minerals are present

foraminiferal biofacies and depositional environments of the burdigalian mixed carbonate and siliciclastic dam formation al lidam area eastern province of saudi arabia abstract four outcrops along a west to east transect in the al lidam escarpment of saudi arabia were investigated to understand the vertical and lateral distribution of foraminiferal assemblages for paleoenvironmental reconstruction the samples were processed using the standard acetic acid method which extracts foraminifera from lithified carbonate rocks without destroying the fossil content the foraminiferal assemblages from the dam formation are dominated by calcareous porcelaneous miliolina quinqueloculina peneroplis triloculina cornuspira sigmoilinita coscinospira spirolina pyrgo borelis followed by hyaline genera elphidium sp ammonia cibicides discorbinella and a minor percentage of agglutinated forms e g textularina the high percentage of calcareous porcelaneous taxa and the absence of planktonic foraminifera indicate that the dam formation was deposited in a restricted carbonate platform environment very shallow hypersaline shallow marine gently sloping ramp inner ramp to mid ramp which ranges from supratidal to subtidal with local reef patches towards the basin the formation was deposited in an arid subtropical climatic environment with water temperatures ranging from 20 to 35 c based on the observed assemblage composition the present day arabian gulf can be considered as a modern analogue for the dam formation during miocene times

the influence of paleo bathymetry on total organic carbon distribution tested in the cretaceous hammerfest basin barents sea abstract in basin modelling and petroleum system analysis geometries during deposition of sediments paleo water depth and distribution of organic matter are initial parameters used for further interpretation or modelling this paper presents an approach combining backstripping with a probabilistic forward sedimentary model to calibrate paleo water depth pwd the stochastic pwd results serve as an input for organic facies models and the study demonstrates how pwd will influence models for total organic carbon distribution in a sedimentary basin for the early cretaceous hammerfest basin mainly shelfal to upper bathyal bathymetries average pwd values vary between 118 and 318 m result in average total organic carbon toc varying between 0 47 and 5 24 wt across the basin for the different models basin averaged toc values are similar but vertical and lateral distribution pattern change significantly especially towards the shallow end member pwd the results indicate that pwd uncertainties propagate non linearly into source rock distributions

the late cretaceous early paleocene palaeobathymetric trends in the southwestern barents sea palaeoenvironmental implications of benthic foraminiferal assemblage analysis the late cretaceous foraminiferal assemblages from five wells drilled in the southwestern barents sea were analysed using morphogroup analysis in order to understand the palaeoenvironment and palaeobathymetry of the study area morphogroup analysis of assemblages in the upper cretaceous kveite formation suggests stable possibly middle to lower bathyal mesotrophic and relatively well oxygenated environments in the tromso basin during the late cretaceous the depositional setting of upper cretaceous kviting formation in the tectonically more stable hammerfest basin was probably shallower but still represents a deep water environment similar to that of the kveite formation a shallowing regional bathymetry in the southwestern barents sea is indicated by the general decreasing trend in the relative abundance of tubular forms and the species diversity of assemblages which reflects the regional late cretaceous paleocene uplift prior to the break up of the greenland norwegian sea changes in the relative abundance of morphogroups and in the main constituent in the cumulative length of tubular taxa from rhizammina to rhabdammina near the top of kveite formation agree with the possible existence of bottom water currents c 2011 elsevier b v all rights reserved

structural and stratigraphic controls on subsurface fluid flow at the veslemoy high sw barents sea abstract subsurface and seafloor fluid flow anomalies are gaining large interest after the finding of five new hydrocarbon discoveries and observation of large gas flares in the sw barents sea in the present study we have analysed structural and stratigraphic controls on fluid flow towards the seafloor using gravity cores selected based on subsurface gas anomalies observed on seismic data from the veslemoy high sw barents sea the subsurface fluid flow at the veslemoy high is observed to be controlled by 1 the morphology and orientation of regional faults structural highs and sedimentary basins 2 the presence of paleocene silica ooze deposits that changes microstructure with temperature thereby controlling fluid flow and 3 the location of regional and local open faults formed by glacial loading and unloading analysis of extractable organic matter in subsurface holocene sediments corroborates the active migration pathways inferred from seismic data micropalaeontological studies on benthic foraminifera reveal methane seep associated assemblages that confirm the interpretation of subsurface gas anomalies in seismic data we ultimately link these new results to the geological evolution history of the region to give a comprehensive model for the fluid flow system within the study area

end cenomanian benthic foraminiferal extinctions and oceanic dysoxic events in the northwestern pacific ocean abstract the second largest cretaceous extinction event coincided with an oceanic anoxic event at the cenomanian turonian c t boundary this high resolution analysis of upper bathyal benthic foraminifera in central hokkaido japan indicates that the extinction event occurred in the latest cenomanian over a period of 0 2 m y 93 6 93 4 ma analysis of the dissolved oxygen index based on calcareous benthic foraminiferal wall thickness size and morphology shows that low oxygen 0 1 1 5 ml l conditions developed during a period of 0 15 m y before the c t boundary and 1 5 m y after the minimum oxygen condition 0 1 1 ml l prevailed twice during this interval similarly benthic foraminiferal extinctions occurred twice in concert with initiation of the two minimum oxygen levels coincidence of the two extinction horizons with developemt of low oxygen conditions suggests that the main cause of the extinctions was formation of dysoxic intermediate water this report suggests that the global c t boundary extinction event occurred in a stepwise fashion during the latest cenomanian 0 2 0 5 m y due to development of widespread oceanic anoxic dysoxic conditions within intermediate water masses

flow regime associated with vertical secondary migration secondary migration is defined as the movement of hydrocarbons through relatively permeable rocks from source to trap a two phase flow within a porous medium depending on the geometry and capillary pressure distributions of carrier beds secondary migration has both vertical and lateral components the present paper focuses on that part of the migration where the movement is mainly vertical its objective is to propose a description of the dynamics governing the vertical part of secondary migration based on the main physical aspects of two phase flow in a homogeneous porous medium the study is illustrated by laboratory observations performed in a vertical 2 d hele shaw cell filled with a transparent porous medium where the flow of dyed oil invading a wetting fluid is visually observed these observations help us to understand the effect of buoyant capillary and viscous forces on the resulting flow the relative importance of which is characterized by non dimensional numbers extrapolating these observations to natural media it is proposed that vertical secondary migration can be described as a percolation of disconnected and vertically elongated stringers these stringers do not move continuously but as a succession of snap off and re feeding events which result in a jerky upward movement using parameters characterizing the physical properties of the fluid and of the porous medium the geometry and the dynamic behavior of the stringers are estimated the width of stringers occurring during secondary migration in geological media is centimetric and their vertical size ranges from several centimeters to a few meters an upper limit of the mean upward velocity of stringers is proposed as well as an estimate of their spatial density and of the minimum average horizontal distance decametric between two stringers the stringers are sparsely distributed resulting in a low average oil loss and a high efficiency of the vertical migration process

integrated biostratigraphy and carbon isotope stratigraphy for the upper cretaceous kanguk formation of the high arctic sverdrup basin canada