environmental control on mediterranean salinity and δ18o a box model is presented to simulate changes in mediterranean long term average salinity and 18o over the past 20 000 years simulations are validated by comparison with observations sensitivity tests illustrate robustness with respect to the main assumptions and uncertainties the results show that relative humidity over the mediterranean remained relatively constant around 70 apparently narrowly constrained to the lower end of the range observed globally over sea surfaces by the basin s land locked character isotopic depletion in run off relative to the present is identified as the main potential cause of depletions in the mediterranean 18o record also slight increases in relative humidity of the order of 5 might have caused very pronounced isotopic depletions such as that in sapropel s5 of the penultimate interglacial maximum the model shows distinctly non proportional responses of 18o and salinity to environmental change which argues against the use of isotope residuals in mediterranean paleosalinity reconstructions

linking the geochemistry of crude oils and petroleum inclusions in the ubarana and lorena oilfields potiguar basin brazilian equatorial margin abstract a study of petroleum inclusions based on ultraviolet fluorescence petrography microspectrophotometry and biomarker analyses was carried out on samples from two wells of the onshore lorena and the offshore ubarana oilfields potiguar basin brazil this study aimed to evaluate the contribution and compositional variability of oils associated with different source rocks through the geochemical correlation of petroleum inclusions and crude oils three groups of inclusions were identified i a group from the lorena reservoir pendencia formation ii a second from the ubarana siliciclastic reservoir acu formation and iii a third from the carbonates adjacent to the ubarana reservoir ponta do mel formation pml fluorescence microspectrophotometry shows that the three groups of inclusions have different api gravity oils variable proportion of saturate aromatic resins and asphaltenes and are not biodegraded moreover pendencia and pml inclusions suggest multiple pulses of hydrocarbon migration while acu inclusions record a homogeneous pulse biomarkers indicate that the pendencia and acu inclusion oils correlate with reservoir oil extracts the pendencia inclusion oils are similar to the lacustrine oils of the umbuzeiro graben pendencia formation whereas the acu inclusion oil displays closer biomarker signature to the areia branca trend of mixed oils alagamar formation source rock however the oil from fluid inclusions of the pml has characteristics of the alagamar formation lacustrine organic facies the absence of mixed oils in the pml suggests an earlier lacustrine oil migration through the carbonate fractures prior to the main infill of mixed oils in the ubarana oilfield

hydrocarbon source rock variability within the austin chalk and eagle ford shale upper cretaceous east texas u s a abstract the austin chalk and eagle ford shale are upper cretaceous deposits that extend across texas from the northeast to southwest these formations contain organic carbon enriched mudstones and chalks that were deposited during transgressions of the cretaceous epeiric sea in north america recent workers in petroleum geochemistry have demonstrated that these organic enriched rocks possessed attributes common to oil source rocks the present study of these austin chalk and eagle ford shale rocks is from the perspective of organic petrology and it augments the earlier geochemical work that documented source variability within units of these formations as with the earlier work the results of this study show that both formations contain intervals that are when mature capable of generating commercial quantities of liquid hydrocarbons however this work further revealed that eagle ford rocks not only exhibit greater or ganic carbon contents but also have greater quantities of oil prone kerogen fluorescent amorphinite and exinite when compared with rocks from the austin chalk these source rock differences relate to levels or degrees of organic preservation dysaerobic to oxic depositional settings seem to be more characteristic of the austin chalk than of the eagle ford shale such oxic environments do not consistently favor the preservation of organic matter usually well preserved kerogen forms under more anoxic conditions such as those that occurred during deposition of some eagle ford units these anoxic conditions suggest that the geographically more extensive eagle ford shale is a more important source for oil than is the austin chalk

changes in planktonic assemblages during sapropel s5 deposition evidence from urania basin area eastern mediterranean 1 a micropaleontological study of planktonic assemblages on the partially laminated sapropel s5 late pleistocene marine isotope stage mis 5e was performed in two piston cores from urania basin area eastern mediterranean west of crete um94pc16 and um94pc31 recovered during a paleoflux project cruise the abundance of florisphaera profunda indicates the development of a deep chlorophyll maximum dcm before the anoxic condition at bottom were established whereas patterns of upper photic zone coccoliths suggest extreme oligotrophy in surface water the short appearance of globorotalia scitula and the presence of globigerinoides ruber in the lower part of sapropel testify to a thermal stratification also recorded by changes in primary producers during g scitula occurrence diatoms mainly represented by pseudosolenia calcar avis appear and bloom because of their capability in using nutrients from dcm scanning electron microscope analyses performed on selected intervals from um94pc16 show that the sapropel is organized in microlaminae mostly composed by siliceous microfossils in particular sapropel s5 could be related to an enhanced nutrient availability in the lower middle part of the photic zone stratified conditions and a higher continental input

living planktonic foraminifera in the eastern south atlantic during spring indicators of water masses upwelling and the congo zaire river plume abstract planktonic foraminifera were collected from pumped surface water samples and net tows over the upper 150 m of the water column in the eastern south atlantic ocean during october and november 1989 of the 24 recorded species 12 occur abundantly and form 6 foraminiferal assemblages the assemblages correlate with the physico chemical properties of the 6 vapor surface water masses the correlation of species with low salinity is due to properties co variant with salinity at several locations high concentrations of planktonic foraminifera were observed caused by frontal mixing or reproduction the g sacculifer g ruber white assemblage marks the south equatorial under current minor contribution of g menardii and n dutertrei to this assemblage reflects the subsurface equatorial under current the n dutertrei g siphonifera assemblage reflects the south equatorial counter current and equatorial under current the n pachyderma g bulloides assemblage reflects the coastal upwelling over the shelf and the filaments of mixed oceanic and upwelled water in the coastal of the benguela current bc the angola benguela front at the interface of the warm currents and the bc is reflected by the g inflata g bulloides assemblage an unusual coincidence of g sacculifer g bulloides in one assemblage results from the interaction of the subtropical gyre and the oceanic branch of the bc the g rubber pink n dutertrei assemblage is attributed to the warm low saline plume in front of the congo zaire river

the diagenetic fate of taraxer 14 ene and oleanene isomers abstract the extractable organic matter in holocene to early miocene deep sea sediments from site 645 odp leg 105 in baffin bay contains almost exclusively biological markers of terrigenous origin pentacyclic triterpenoids of the ursene and amyrin oleanene type often occur as the most abundant compounds in the aliphatic hydrocarbon ketone and alcohol fractions of the sediment extract a specific diagenetic reaction involves the conversion of taraxer 14 ene into olean 12 ene in the upper 700 metres of the sedimentary sequence the taraxerene to oleanene conversion is complete before the onset of isomerisation of diasterenes at c 20 in the sediment as well as in laboratory simulation experiments olean 12 ene further isomerises to olean 13 18 ene and olean 18 ene the latter of which may be the direct precursor of 18 h and 18 h oleanane found in sediments containing more mature organic matter and in crude oils the subsurface interconversion of these triterpenoid skeletons indicate that oleanane does not necessarily start life as an oleanoid

reconstructing past planktic foraminiferal habitats using stable isotope data a case history for mediterranean sapropel s5 abstract a high resolution stable o and c isotope study is undertaken on all planktic foraminiferal species that are reasonably continuous through an eemian sapropel s5 from the western side of the eastern mediterranean the data are considered within a context of high resolution isotope records for two further s5 sapropels from the central and easternmost sectors of the basin alkenone based sea surface temperature records for all three sapropels and planktic foraminiferal abundance records for the same sample sets through all three sapropels results are compared with similar data for holocene sapropel s1 the adopted approach allows distinction between species that are most suitable to assess overall changes in the climatic hydrographic state of the basin including depth related differentiations and the main seasonal developments and species that are most affected by variable biological controls or local regional and transient physico chemical forcings it is found that a priori assumptions about certain species palaeohabitats based on modern habitat observations may become biased when non analogue conditions develop in the case of mediterranean sapropel s5 these consisted of enhanced freshwater dilution elevated productivity shoaling of the pycnocline between intermediate and surface waters and stagnation of the subsurface circulation under these conditions some species are found to shift into habitat settings that differ considerably from those occupied today the present multiple species approach can identify such anomalous responses and thus offers a sound background for further shell chemistry investigations and quantitative interpretation of the isotopic profiles we capitalise on the latter potential and offer the first quantitative estimates of monsoon flooding into the mediterranean during the deposition of eemian sapropel s5

error analysis of paleosalinity calculations a detailed error analysis is performed for the calculation of open ocean salinity changes from carbonate oxygen 18 proxy data measurement errors are generally negligible however errors due to the goodness of fit of various regressions used in the calculation are significant depending on the method used and on the proxies available error bars 1 for the salinity range from 0 6 to 1 8 in particular expected errors for the midlatitude and tropical salinity differences at the last glacial maximum are around 1 1 to 2 5 the largest errors occur because of the differences between temporal and spatial seawater oxygen 18 salinity relationships and through the use of nonconcurrent temperature measurements methods of improving paleosalinity estimates should focus on eliminating these large sources of uncertainty

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

surface water temperature salinity and density changes in the northeast atlantic during the last 45 000 years heinrich events deep water formation and climatic rebounds we developed a new method to calculate sea surface salinities sss and densities ssd from planktonic foraminiferal 18o and sea surface temperatures sst as determined from planktonic foraminiferal species abundances sst sss and ssd records were calculated for the last 45 000 years for biogeochemical oceanic flux study bofs cores 5k and 8k recovered from the northeast atlantic the strongest feature is the dramatic drop in all three parameters during the heinrich ice rafting events we modelled the possibility of deepwater formation in die northeast atlantic from the ssd records by assuming that the surface waters at our sites cooled as they flowed further north comparison with modelled north atlantic deepwater densities indicates that there could have been periods of deepwater formation between 45 000 and 30 000 14c years b p interrupted by iceberg meltwater input of heinrich event 3 and 4 at 27 000 and 38 000 14c years b p and during the holocene no amount of cooling in the northeast atlantic between 30 000 and 13 000 years could cause deep water to form because of the low salinities resulting from the high meltwater inputs from icebergs our records indicate that after each heinrich event there were periods of climatic rebound with milder conditions persisting for up to 2000 years as indicated by the presence of warmer and more saline water masses after these warm periods conditions returned to average glacial levels these short term cold and warm episodes in the northeast atlantic are superimposed on the general trend towards colder conditions of the last glacial maximum lgm heinrich event 1 appears to be unique as it occurs as insolation rose and was coeval with the initial melting of the fennoscandian ice sheet we propose that meltwater input of heinrich event 1 significantly reduced north atlantic deep water formation reducing the heat exchange between the low and high latitudes thus delaying deglaciation by about 1500 radiocarbon years 2000 calendar years

organic geochemical study of sequences overlying coal seams example from the mansfield formation lower pennsylvanian indiana abstract roof successions above two coal seams from the mansfield formation lower pennsylvanian in the indiana portion of the illinois basin have been studied with regard to sedimentary structures organic petrology and organic geochemistry the succession above the blue creek member of the mansfield formation is typical of the lithologies covering low sulphur coals 2 the transgressive regressive packages above both seams reflect the periodic inundation of coastal mires by tidal flats and creeks as inferred from bioturbation and sedimentary structures such as tidal rhythmites and clay draped ripple bedforms geochemistry and petrology of organic facies above the blue creek coal suggest that tidal flats formed inland in fresh water environments these overlying fresh water sediments prevented saline waters from invading the peat contributing to low sulphur content in the coal above the unnamed coal trace fossils and geochemical and petrological characteristics of organic facies suggest more unrestricted seaward depositional environment the absence of saline or typically marine biomarkers above this coal is interpreted as evidence of very short periods of marine transgression as there was not enough time for establishment of the precursor organisms for marine biomarkers however sufficient time passed to raise so42 concentration in pore waters resulting in the formation of authigenic pyrite and sulphur incorparation into organic matter

nile water as a cause of eastern mediterranean sapropel formation evidence for and against during the late pleistocene sapropels layers of organic carbon rich sediment formed throughout the entire eastern mediterranean basin in close association with glacial interglacial transitions the current theory for the mechanism of sapropel formation involves a density stratification of the water column due to the invasion of a large quantity of low saline water which resulted in oxygen depletion of the bottom waters most workers believe that this low salinity water was glacial meltwater that entered the mediterranean via the black sea and a series of interconnected glacial lakes but the suggestion also has been made that the freshwater originated from the nile river in this study the oxygen isotope values of planktonic foraminifera globigerinoides ruber have been examined in six gravity cores and one piston core from the southern levantine basin and compared with the oxygen isotope records ofg ruber from other areas of the eastern mediterranean this study deals mainly with the latest sapropel which was deposited approximately 7000 to 9000 years ago results indicate that nile discharge probably does reduce salinities somewhat in the immediate area surrounding the mouth of the nile but this water is rapidly mixed with the highly saline waters of the easternmost mediterranean using a mixing equation and surface water salinity limitations an approximate oxygen isotope balance of surface waters was calculated for the time of latest sapropel deposition this calculation shows that neither nile river discharge nor black sea input nor both together are large enough to account for the large scale oxygen isotope depletion associated with latest sapropel deposition in the eastern mediterranean this suggests that part of the isotopic change at termination i is probably due to increased surface water salinities during the last glacial maximum in addition evidence from the timing of sapropel 1 deposition and the dissolved oxygen balance indicates that deposition of the latest sapropel is associated with increased surface water production of biogenic material as much as three times higher than that of present day

the oleananes origin maturation and limits of occurence in southern nigeria sedimentary basins oleananes occur within well defined age and paleogeographic boundaries in the sedimentary province of southern nigeria thus signifying that the biomarkers may be analogous to index fossils in anambra syncline lower benue trough the biomarkers are found in rocks which are as old as late upper cretaceous in tertiary niger delta the concentration composition and distribution of the oleananes in rocks and oils are determined mainly by palaeodepositional environment and thermal history and are independent of age and geographical location of specific samples oleanane content varies with increasing burial depth with peak concentration coinciding within rm range 0 4 0 6 implying early generation of hydrocarbons from the basin s typically resin rich kerogens it is evident that the oleanane content parameter is superior to the hopane and sterane isomerisation indices for monitoring thermal maturation in the delta and for differentiating paralic from paralic marine source facies as well as early from late generated oils

rainy periods and bottom water stagnation initiating brine accumulation and metal concentrations 1 the late quaternary a working hypothesis is proposed to account for the present accumulation of brines in isolated pockets of the ocean floor and for the formation of the underlying organic and metal rich sediments these are the tyro and bannock basins in the east mediterranean the red sea deeps and the orca basin in the northern gulf of mexico initiation of brine derived deposition in the red sea deeps and orca basin occurred between 12 000 and 8000 years b p this time bracket also encompasses the formation of the latest east mediterranean sapropel and the wettest global climate since the last glacial maximum this wet period first appeared in the tropics around 12 000 years b p then in the subtropical and middle latitudes during the same period the 23 000 year precession cycle brought the summer insolation of the northern hemisphere to its peak at 11 000 years b p with retreating northern hemisphere ice sheets the red sea deeps and the orca basin became anoxic during this humid period and metal rich sapropel deposition then began in contrast the tyro and bannock basins began accumulating a brine long before and persisted beyond this climatic stage the hypothesis involves two propositions 1 as in the eastern mediterranean sea marine anoxia was mainly the consequence of the large influx of continental runoff and local precipitation longer residence time of bottom waters so called stagnation in silled rimmed basins would have resulted from lower salinity at the sea surface in areas of deep water formation in the eastern mediterranean the red sea and the gulf of mexico and 2 miocene or older evaporites underlie these basins or outcrop on their flanks leaching from these evaporites was an ongoing process before the quasi stagnation phase but the initial leachate much less saline than the present brines was continuously flushed by bottom circulation the climate induced quiescence of bottom waters in these basins enabled the leachate to accumulate the feedback of stagnation by increased density progressively raised the salinity of entrapped bottom waters to the present brine concentration the high density has resisted brine removal by bottom circulation until present time long after cessation of the initiating wet period the brines therefore are stagnant fossil waters

accounting for shape reliability in modeling contour derived topographic properties for use in soil terrain correlation abstract elevation contours are known to be poor quality data for digital terrain modeling but they are often the only available topographic information at national scale especially in developing countries we investigated several methods to derive elevation and slope data from contours for two contiguous watersheds in burundi two key issues in digital terrain modeling were addressed 1 finding the best elevation interpolator and 2 assessing the related uncertainty and its propagation to slope models the key validation criterion was the reproduction of the terrain shape as inferred from the pattern of contours which is more important than absolute accuracy in soil terrain correlation a method using a triangulated irregular network tin and four grid based methods were compared and combined the most satisfactory results were achieved by combining the tin based method with a grid based method treating contours as inequality constraints proved useful in simulating the elevation uncertainty the zevenbergen and thorne and the evans young slope algorithms were compared based on their sensitivity to the elevation uncertainty outputs from simulation were filtered to produce realistic alternative elevation models in that case the slope variance values were similar for the two algorithms suggesting similar performances checking for shape reliability was found critical for the validation of topographic models

seasonal stable isotopic variations in living planktonic foraminifera from bermuda plankton tows abstract seasonal variations in surface water temperature and the 18o 16o ratios of calcite tests of living planktonic foraminifera collected in the upper 10 mare are coincident in the sargasso sea off bermuda the 18o of seasonally restricted globorotalia truncatulinoides and globigerinoides ruber pink and white may be used to determine the seasonal temperature contrast of the oceans in the past a preliminary model based on yearly absolute abundance and isotopic composition of these two species is able to approximate the composite 18o of fossil specimens of these species carbon and oxygen isotopic compositions of most species are size dependent with the largest differences occuring in 13c as a function of size the calcite tests of all living species were depleted in 13c relative to the 13c of total dissolved co2 at 0 and 50 m with no seasonal pattern in 13c being discernible in any species in almost all cases fossil specimens from box core sediments are significantly enriched in 13c and slightly enriched in 18o relative to their counterparts in the living fauna because the sediment populations are generally composed of larger sized specimens compares to the plankton of larger size specimens compared to the plankton

pluvial conditions in the eastern sahara following the penultimate deglaciation implications for changes in atmospheric circulation patterns with global warming during the transition from the penultimate glacial to the last interglacial period isotope stages 6 5e or terminal ii large freshwater lakes abruptly infilled sandy depressions in arid regions of the eastern sahara geochemical and mineralogical studies of samples from lacustrine sequences in the western desert of southern egypt indicate 1 the sediments are chalk composed of authigenic chemical precipitates predominantly low mg calcite with carbonate contents averaging about 80 the low dilution of the chemical precipitate by detrital input implies that physical erosion and transport of detrital grains were minimized by extensive vegetation cover in the catchment area the fauna and flora associated with the lake deposits and middle paleolithic occupation sites on the paleo shorelines attest to a more amenable environment 2 vastly different rainfall or atmospheric circulation patterns than at present must have existed based on consistently negative 18opdb values for the chalk as low as 9 5 which would require precipitation from lake waters significantly more depleted in 18o than the modern local spring water 18osmow 1 8 3 the lakes were stable perennial water bodies with relatively long residence times sufficient to produce isotopic covariant signals in the chalks apparently the lakes disappeared as abruptly as they appeared without going through a terminal phase of evaporative enrichment extremely arid conditions again prevailed during the transition from the last glacial to the present interglacial terminal i a similar change from arid to pluvial conditions occurred thus it is proposed that during transitions from glacial to interglacial climates rapid global warming can lead to temporary alteration to atmospheric circulation with an intersification of the southwest monsoons bringing large quantities of isotopically light moisture to the eastern sahara

modeling a 200 yr interruption of the holocene sapropel s1 an oceanic general circulation model previously used to simulate the conditions associated with the holocene sapropel s1 is used to simulate the effects of a climate deterioration represented as a cooling event on the sapropelic circulation mode the enhanced cooling 2 3 c induces deep convection in the adriatic and the gulf of lions and intermediate water formation in the aegean where in all cases there had previously been only stagnant unventilated waters the depths of ventilation to 1250 m are in agreement with core data from this period the short decadal timescales involved in modifying the sapropelic circulation suggest that such a climatic deterioration may be associated with the interruption of s1 between 7100 and 6900 14c yr b p which divided the sapropel into two subunits

oxygen isotope composition of living neogloboquadrina pachyderma sin in the arctic ocean data from the nansen basin of the arctic ocean are used to investigate the habitat and conditions under which the polar planktic foraminifer neogloboquadrina pachyderma sin calcifies the vertical distribution of 18o values of net sampled speciments together with their abundances and proportion of calcification are compared with 18o values from both water samples and foraminiferal tests from core top sediments within the nansen basin the average depth of habitat of n pachyderma sin changes from about 150 m in the southern part to about 80 m in the northern the average depth of calcification however in both regimes varies between 100 and 200 m water depth 18o data from net sampled n pachyderma sin are directly reflected in the core top sediment data but compared to equilibrium calcite 18o values derived from measurements of the ambient water a consistent offset of about 1 over all depth intervals is observed while in the southern part of the nansen basin advection through fram strait of planktic foraminifers from further south may play a role the data from the northern part of the nansen basin give clear evidence that the observed offset in 18o values is caused by a vital effect of n pachyderma sin

oil source rock correlation in the tempoku basin of northern hokkaido japan abstract geochemical correlation studies of seven oils and source rocks from the onshore tempoku basin of northern hokkaido were carried out low sulfur high wax and high pristane phytane ratios of the oils suggest that they were generated mainly from nonmarine source rocks source rock evaluation and hydrous pyrolysis data show that coals and coaly shales in the paleogene haboro formation and cretaceous hakobuchi group have oil generating potential these nonmarine source rocks are correlated as the major source of the tempoku oils using sterane and triterpane distributions and carbon isotope compositions correlation studies also suggest a minor contribution from marine source rocks of the neogene onishibetsu or paleogene magaribuchi formations to the oils of the yuchi and wakkanai fields located in the western part of the basin

planktic foraminifers and hydrography of the eastern and northern caribbean sea the distribution of living planktic foraminifers and their relation to the hydrography of the caribbean sea was investigated in plankton net tows and surface sediment samples taken along the antilles island arc during april may 1996 the planktic foraminiferal community was strongly influenced by spatial variations in salinity that were largely due to the influx of orinoco river water into the southeastern caribbean sea and inflowing sargasso sea water in the north along the antilles island arc globigerinoides ruber was the dominant species in the surface waters throughout in the southeastern caribbean sea where orinoco river outflow influences the planktic community standing stocks of planktic foraminifers 100 m between 4 and 50 specimens m 3 were medium to low the southeastern faunas between tobago and guadeloupe were characterized by increased proportions of neogloboquadrina dutertrei highest standing stocks of 159 specimens m 3 in the upper 20 m of the water column were recorded in the northeastern caribbean sea and the assemblages were characterized by high proportions of globigerinita glutinata associated with cyclonic eddies in the anegada passage where sargasso sea water flows into the caribbean sea low standing stocks of 18 specimens m 3 indicate oligotrophic conditions together with the oligotrophic surface waters the subtropical underwater enters the caribbean sea through the anegada passage in water depths between 100 and 300 m these waters are characterized by higher concentrations of globorotalia truncatulinoides relative to the adjacent water masses comparison of the living planktic foraminiferal fauna with empty test assemblages from the water column and from surface sediments shows that differences in the faunal composition mostly correspond to the distribution of water masses and to the differential dissolution of species in the vicinity of islands globigerinoides ruber reaches higher relative frequencies than in the open ocean pointing towards a higher tolerance of this species towards neritic conditions than in other species

biological productivity during sapropel s5 formation in the eastern mediterranean sea evidence from stable isotopes of nitrogen and carbon we determined 15n 14n ratios in modern surface and sapropel s5 sediments of the mediterranean sea to clarify differences in the nutrient regime associated with sapropel formation in the modern situation high 15n of unused nitrate 15 20 remaining in the surface waters during the winter phytoplankton bloom evidences p limitation of biological production in winter 15n of surface sediments decrease towards the east of the basin 5 to 2 5 this is a consequence of either eastward increasing nitrogen fixation during the summer months or of particulate matter being supplied predominantly by the p limited winter bloom very low 1 1 15n values in sapropel s 5 from four locations require a very light source of nutrient n assimilated at a minimum of ten times the modern export flux because the isochronous records show no spatial gradient in 15n we exclude both ekman type upwelling and direct riverine discharge as likely sources of nutrients our data are consistent with an anti estuarine thermohaline circulation in the upper 500m during s5 time allowing for the trapping of nutrients in the eastern basin the most likely scenario for s5 is that phosphorus release from a relatively shallow redox boundary resulted in an imbalanced supply of n p 16 1 to the photic zone the result was a slow assimilation of carbon during summer stratification and extensive n2 fixation providing the majority of the export flux from a n limited system

reconstructing sea surface temperature and salinity using δ 18 o and alkenone records the oxygen isotope 18o composition of foraminiferal tests from deep sea sediments is widely used as a palaeoclimate proxy but it includes contributions from sea surface temperature global ice volume and local salinity which are difficult to separate recently a new technique for deriving palaeotemperatures has been developed which is based on the abundance ratios of unsaturated alkenones in phytoplankton algae1 2 here we use a combination of oxygen isotope and alkenone records in a deep sea core from the juncture of the arabian sea and the bay of bengal to extract the salinity signal from the former record variations in salinity are related to the balance between evaporation and precipitation3 and are thus a sensitive indicator of climate change our 170 kyr salinity record enables us to reconstruct changes in the indian monsoon over this period considerably extending earlier studies which reached back to 18 kyr ago 4 8 like these previous studies we find that large variations in the monsoon occurred during the transition from the last glacial period to the present interglacial but our results also provide a view of the monsoon throughout the last glacial and demonstrate the potential of this approach for reconstructing palaeosalinity

glacial holocene salinity changes in the mediterranean sea hydrographic and depositional effects oxygen isotope changes as recorded by pleistocene foraminifera from open ocean sediments are primarily a function of changes in the isotopic composition of the global seawater reservoir caused by ice volume changes with a secondary temperature component1 oxygen isotope records from marginal basins such as the gulf of mexico2 the mediterranean sea3 5 and the red sea6 also exhibit the global signal but are far more complicated owing to the strong overprint of local climate conditions in particular glacial interglacial changes in continental aridity and river runoff produce significant salinity changes in these semi enclosed basins using available oxygen isotope records we estimate that glacial 18 000 yr bp salinities in the eastern and western mediterranean sea were 2 7 and 1 2 higher respectively than at present these elevated glacial salinities played an important part in preconditioning the eastern mediterranean for the eventual accumulation of organic carbon rich sediments sapropels at the end of deglaciation

the petroleum geochemistry of canadian beaufort tertiary non marine oils abstract molecular isotopic and elemental data for a set of 28 paleogene and 3 cretaceous oils from the mackenzie delta and offshore canadian beaufort sea have been evaluated the depositional environment and organic matter characteristics of the source units for these oils have been predicted the paleogene oils of the canadian beaufort are molecularly distinctive and clearly contain a major land plant component oleanane and the 17 h and 17 h 24 28 bisnorlupanes are present as well as the following compound types 24 norlupanes and possibly higher homologues de a lupane noroleanenes norursene dehydroabietane 28 30 bisnorhopanes several molecular and isotopic characteristics are useful in assessing and ordering the extent of biodegradation and thermal maturation of these oils the cretaceous oils are separately sourced from the paleogene oils the latter oils comprise two distinct land plant derived genetic families distinguished by the presence absence of 24 28 bisnorlupanes 24 norursene 24 norlupane and 24 noroleanenes the kugmallit richards family contains each of these compound types and is considered to originate from the eocene richards formation in contrast lupanoids and noroleanenes are absent in oils of the reindeer moose channel family the occurrence of 28 30 bisnorhopane and or oleanane in these oils suggests a paleocene origin although these source rock predictions are supported by the available data they must be considered speculative until detailed molecular isotopic and elemental compositional data are available regionally for potential source rocks of the eocene and paleocene source units in the canadian beaufort

forward modeling of carbonate proxy data from planktonic foraminifera using oxygen isotope tracers in a global ocean model the distribution and variation of oxygen isotopes in seawater are calculated using the goddard institute for space studies global ocean model simple ecological models are used to estimate the planktonic foraminiferal abundance as a function of depth column temperature season light intensity and density stratification these models are combined to forward model isotopic signals recorded in calcareous ocean sediment the sensitivity of the results to the changes in foraminiferal ecology secondary calcification and dissolution are also examined simulated present day isotopic values for ecology relevant for multiple species compare well with core top data hindcasts of sea surface temperature and salinity are made from time series of the modeled carbonate isotope values as the model climate changes paleoclimatic inferences from these carbonate isotope records are strongly affected by erroneous assumptions concerning the covariations of temperature salinity and 18ow habitat imposed biases are less important although errors due to temperature dependent abundances can be significant

the oxygen and carbon isotope distribution in the mediterranean water masses abstract the oxygen and carbon stable isotope compositions of the present day mediterranean waters have been measured in order to evaluate their variability which is related to the specific climatic and hydrological conditions within the basin the experimental equation between the 18 o value and the salinity of water based on 300 measurements on surface intermediate and deep waters sampled during the vicomed 2 and 3 cruises in the western central and eastern mediterranean has a slope of 0 27 a value which is significantly lower than the slope of 0 45 as defined in the northeast atlantic ocean this difference in the 18 o salinity relationship which occurs immediately in the alboran basin is basically a characteristic of the climatic regime of the mediterranean i e of an excess evaporation over fresh water input the largest variations of these two parameters 18 o of water and 13 c of co 2 are observed in the surface waters mostly in the western mediterranean this evolution mirrors the progressive eastward restriction which separates the less evaporated and more productive western basins from the more evaporated and less productive eastern basins the intermediate waters constitute a homogeneous layer however their 18 o values decrease eastward by 0 35 at maximum due to progressive dilution by mixing with overlying and underlying water masses their 13 c values decrease also eastward by 0 35 at maximum due to an increasing input of nutrients issued from the regeneration of sinking organic particles the deep waters have similar 18 o values but slightly higher 13 c values often by less than 0 1 than the overlying intermediate waters indicating generally well ventilated conditions due to active winter convection

application of organic geochemistry to sequence stratigraphic analysis four corners platform area new mexico u s a abstract the sequence stratigraphic model of sedimentation postulates the existence of a time condensed section deposited at very low sedimentation rates occurring in the uppermost transgressive systems tract and the lowermost highstand systems tract this condensed interval has of often been equated with zones of increased hydrocarbon source potential and invoked as a petroleum source rock often in the absence of supporting geochemical data in this study isotopic molecular lithostratographic and paleontological data are presented for 51 outcrop samples from a cenomanian turonian section at red wash new mexico u s a interpretations are made within a sequence stratigraphic framework ramp model sedimentation rates are estimated in order to define the location of the codensed intervalm for comparison with the zone of best source potential approximately 80 m of section were sampled the interval of maximum flooding and westernmost progression of the cretaceous seaway shoreline as defined by paleontological data is stratigraphically immediately below the occurrence of discontinuities in total organic carbon content hydrogen index and fluoramorphinite concentration in the kerogen the overall transgressive event is accompanied by increases in relative concentrations of 24 n propylcholestane total steranes and rearranged steranes these changes are consistent with a simultaneous decrease in the ratio of terrigenous organic matter to marine algal input as westward flooding proceeded the simultaneous occurrence of discontinuities in kerogen related parameters and continuous trends in bitumen related parameters probably implies mobilization of soluble organic matter across the flooding event boundary sedimentation rate estimates for six intervals in the red wash section show that the best oil source rock potential occurs immediately above the condensed interval and maximum flooding surface within the highstand systems tract previous studies of cretaceous sections in other portions of the western interior basin have located the best source rock potential below the condensed zone we conclude that the equivalence between source rock occurence and condensed sections as applied through the sequence stratigraphic model requires modification before the model may be used to predict the location of oil source rocks in a ramp setting in this respect it is critical that the data in sequence stratigraphic studies be used to define the model and not allow the model to dictate the interpretation of the data

carbon and oxygen isotope composition of globigerinoides ruber in two deep sea cores from the levantine basin eastern mediterranean abstract carbon and oxygen isotope analyses have been carried out on 114 samples of globigerinoides ruber from two deepsea cores ban 82 15 pc and ban 82 18 gc raised on the outer slopes of the mediterranean ridge these cores 1050 and 462 cm long respectively contain the sedimentary history of the eastern mediterranean in the last 300 000 years and include sapropelitic layers s 1 to s 10 the climatic fluctuations recorded by the isotopic signal are in general well correlatable with those obtained in previous studies on the mediterranean quaternary most sapropelitic intervals correspond to warm climatic conditions with a maximum recorded in core 15 pc at approximately 125 000 yrs b p isotope stage 5e only s 6 and partially s 8 reflect glacial conditions thus indicating the existence of an alternative model for the deposition of organic rich layers the magnitude of fluctuations in oxygen isotope composition about 7 is unusually wide for the eastern mediterranean and the record is generally shifted toward negative values for approximately 1 this is probably due to the nile discharge that strongly affects these levantine basin cores oxygen and carbon curves are in phase showing the large influence of organic productivity on the carbon isotope composition

source and significance of selected polycyclic aromatic hydrocarbons in sediments hovea 3 well perth basin western australia spanning the permian triassic boundary abstract stable carbon isotopic data for polycyclic aromatic hydrocarbons pahs chrysene and triphenylene benzo e pyrene 9 methylphenanthrene in sediments of comparable thermal maturity from a petroleum drill core hovea 3 well perth basin western australia spanning the largest mass extinction event in the past 500 million years permian triassic boundary are consistent with an algal kerogen source in the basal triassic as opposed to a combustion and or higher plant source in the underlying permian sediments the 13c values of extractable pahs are less negative in the permian inertinitic interval 24 7 to 29 2 than the triassic sapropelic interval 30 to 33 3 a strong correlation is evident between 13c of individual pahs 13c of kerogen and rock eval pyrolysis hydrogen index providing unequivocal evidence that pah 13c is mainly controlled by organic matter type abundant algal derived pahs in basal triassic sediments may be a global feature the lack of coal globally in the basal triassic sediments is also consistent with this observation the early triassic coal gap appears to coincide with the global extinction of peat forming plants at the end of the permian coal did not reappear until the middle triassic and permian levels of plant diversity and thick peat deposits did not recover until the late triassic the pah isotopic data support the contention that a global anoxic event at the end of the permian period contributed to the gradual worldwide asphyxiation and ultimate extinction of many marine and terrigenous organisms

circulation changes and nutrient concentrations in the late quaternary aegean sea a nonsteady state concept for sapropel formation sapropel forming conditions we identify the start of seasonal stratification and highlight a lag in d 18 o response of the planktonic foraminifer n pachyderma to termination t1b as identified in the d 18 o record of g ruber by use of a simple model we determine that this offset cannot be a function of bioturbation effects the lag is of the order of 1 kyr and suggests that isolation of intermediate deep water preceded the start of sapropel formation by up to 1 5 kyr using this discovery we propose an explanation for the major unresolved problem in sapropel studies namely the source of nutrient supply required for export productivity to reach levels needed for sustained sapropel deposition we suggest that nutrients had been accumulating in astagnant basin for 1 1 5 kyr and that these accumulated resources wereutilized duringthe deposition of s1 in addition we provide a first quantitative estimate of the diffusive 1 e mixing timescale for the eastern mediterranean in its stratified sapropel mode which is of the order of 450 years index terms 1050 geochemistry marine geochemistry 4835 4850 3030 marine geology and geophysics micropaleontology 3339 meteorology and atmospheric dynamics ocean atmosphere interactions 0312 4504 4267 oceanography general paleoceanography 4870 oceanography biological and chemical stable isotopes keywords sapropel mediterranean holocene foraminifera climate variability

vertical distribution and isotopic fractionation of living planktonic foraminifera from the panama basin a model1 2 which explains the vertical and seasonal distribution of planktonic foraminifera was developed using data from the western north atlantic and is comprised of three tenets 1 the conditions in the photic zone upper 80 100 m exclusively dictate planktonic foraminifera species composition and abundance throughout the water column 2 species are vertically stratified within the photic zone according to their temperature preference depth distribution according to temperature preference has been proposed by several authors3 based on isotope analyses of sediments due to seasonal temperature variations seasonal variations in the 18o composition of seawater and species specific isotope fractionation rigorous proof of this hypothesis cannot be provided from sediment analyses alone 3 the chlorophyll maximum is a major food source zone which is preferentially exploited by foraminifera our data from the panama basin which are presented here are confirmation of this model the panama basin in the eastern equatorial pacific which has a shallow and steep thermocline was sampled for living planktonic foraminifera a multiple opening closing net and environmental sensing system mocness 4 was used to collect 13 sets of eight vertically stratified oblique samples we report here the quantitative distribution and stable isotopic composition of planktonic foraminifera from four mocness tows taken over 5 days during august 1979 rv knorr cruise 73 at 5 20 n 8 50 w each tow consisted of eight samples which integrated 12 5 m intervals from 0 to 100 m for moc 126 25 m intervals from 0 to 200 m for moc 127 100 150 m intervals from 0 to 1 000 m on moc 128 and 250 m intervals from 0 to 2 000 m on moc 131

characterisation of oil and potential source rocks in the northeastern song hong basin vietnam indications of a lacustrine coal sourced petroleum system oil discovered in the b10 stb 1x well in the northeastern song hong basin vietnam has typical lacustrine coaly geochemical features indicating the existence of a principally lacustrine sourced petroleum system with minor contributions from a coal source the presence of lacustrine source rocks in the basin is indicated by distinct high amplitude seismic reflectors in undrilled half grabens and outcrops of oligocene immature mudstones and humic coals at dong ho and on bach long vi island the mudstones from dong ho generally have a toc content of 8 17 wt and hi values 500 mg hc g toc the organic matter is principally composed of fluorescing amorphous organic matter and liptodetrinite alginite with botryococcus morphology is present the organic matter corresponds to type i kerogen the bach long vi island mudstones contain 2 7 wt toc and have hi values from 200 700 mg hc g toc the organic matter is largely similar to that in the dong ho mudstones but in addition may contain some marine organic material the b10 stb 1x oil shows features common to both the dong ho and bach long vi island mudstones but was probably principally generated from a source similar to the dong ho mudstones with contributions from higher land plant organic matter a prominent activation energy peak dominates the activation energy distributions of the mudstones and upon artificial maturation hydrous pyrolysis the mudstones show extensive hydrocarbon generation over a narrow temperature range hydrocarbon expulsion has been estimated to occur at a vitrinite reflectance of 0 75 ro the source of the b10 stb 1x oil may be located in the thuy nguyen graben and maturity modelling shows that the lacustrine mudstones will be thermally mature in this graben

formation and evolution of nonmarine petroleum in songliao basin china in large lake basins source rocks containing sapropelic kerogen have a high transformation ratio and a high potential for petroleum and they offer the material basis for the formation of a large nonmarine oil field on the basis of geologic and geochemical data and the results of thermal simulation of kerogen it is confirmed that the maturation sequence of kerogen is type i type ii and type iii

paired δ18o signals of neogloboquadrina pachyderma s and turborotalita quinqueloba show thermal stratification structure in nordic seas abstract the vertical density gradients in the nordic seas are crucial for the preconditioning of the surface water to thermohaline sinking in winter these gradients can be reconstructed from paired oxygen isotope data in tests of different species of planktonic foraminifera the isotopic signatures of which represent different calcification depths in the water column comparison of 18 o values from foraminiferal tests in plankton hauls sediment traps and nearby core top samples with the calculated 18 o calcite profile of the water column revealed species specific 18 o vital effects and the role of bioturbational admixture of subfossil specimens into the surface sediment on the basis of core top samples obtained along a west east transect across various hydrographic regions of the nordic seas 18 o values of turborotalita quinqueloba document apparent calcification depths within the pycnocline at 25 75 m water depth the isotopic signatures of neogloboquadrina pachyderma s reflect water masses near and well below the pycnocline between 70 and 250 m off norway where the atlantic inflow leads to thermal stratification here temperatures in the calcification depth of n pachyderma s differ from sea surface temperature by approximately 2 5 c in contrast n pachyderma s calcifies very close to the sea surface 20 50 m in the arctic domain of the western nordic seas however further west n pachyderma s prefers somewhat deeper more saline water at 70 130 m well below the halocline that confines the low saline east greenland current this implies that the 18 o values of n pachyderma s do not fully reflect the freshwater proportion in surface water and that any reconstruction of past meltwater plumes based on 18 o is too conservative because it overestimates sea surface salinity minimum 18 o differences n pachyderma s and t quinqueloba may serve as proxy for sea regions with dominant haline and absent thermal stratification whereas thermal stratification leads to 18 o differences of 0 4 to 1 5

oleanane or lupane reappraisal of the presence of oleanane in cretaceous tertiary oils and sediments nonpolar gc columns are normally used for gc ms analysis of saturate fractions from crude oils under these conditions lupane coelutes with oleananes and some minor c30 compounds of non terrigenous origin having lupane like mass spectra because any peak eluting fractionally earlier than 17 21 h hopane in the m z 191 mass chromatogram is routinely assigned to oleanane the presence of lupane may sometimes have been overlooked lupane and oleananes are easily separated using reverse phase hplc triterpane concentrates from 10 crude oils known to contain oleananes were hplc separated lupane was unambiguously identified in six of the oils by full scan gc ms analysis of fractions having the hplc retention time of authentic lupane gc separation of lupane and oleananes is possible using polar gc columns having a polyethylene glycol stationary phase organic geochemistry 23 1995 21 allowing estimation of the lupane lupane oleanane ratio high ratios were measured in the marraat oil west greenland 0 8 and the amauligak oil from the beaufort mackenzie delta 0 26 the results suggest that lupane may be more frequently occurring than previously thought and that this compound is preferably associated with high latitude samples high concentrations of 28 nor and 24 28 bisnortriterpanes oleananes lupanes and taraxastanes were detected in the marraat oil

geochemical application of sterane and triterpane biomarkers to a description of oils from the taranaki basin in new zealand abstract the distributions of sterane and terpane biomarkers in a suite of 25 oils from onshore and offshore regions of the taranaki basin of new zealand have been determined by gc ms features of these distributions include the presence of relatively high concentrations of a number of c 24 tetracyclic terpanes the virtual absence of tricyclic terpanes a predominance of c 29 normal iso and dia steranes and the presence of a number of non hopanoid triterpanes in one member of the suite urenui 18 h oleanane is the most abundant component m z 191 ion chromatogram of the terpane class of biomarkers based upon the distributions of 18 h oleanane the mckee and moturoa families of oils can be delineated these terpane distributions are qualitatively similar to those encountered in crude oils from a number of far eastern basins and from the handil field of the mahakam delta indonesia the taranaki oils are of approximately the same thermal maturity maturity parameters calculated from the distributions of c 29 steranes and of 17s h 21 h and 17 h 21s h hopanes confirm recent findings of incomplete nuclear isomerisation in oils derived from tertiary sediments an attempt has been made to correlate the mckee 1 and maui 4 crude oils with potential source rocks from depths of 3708 m and 3825 m respectively the rocks studied have attained insufficient maturity to have been the sources of these oils

extended hopanoids in peat environments abstract detailed results are presented for the distributions of triterpenoid alkanes acids and alcohols of the hopane family in ten samples of peat from three environments and of contributing organisms in the case of lyne of skene scotland extended hopanoids of the and configuration appear at the very earliest stage of diagenesis such environments appear to be characterised by particular distributions of c 32 hopanoid acids and alcohols and a high preponderance of the c 31 hopane

tertiary oils from upper assam basin india a geochemical study using terrigenous biomarkers abstract the upper assam basin in northeast india is a tertiary sub basin of the assam arakan basin hydrocarbons are present in the langpar formation upper palaeocene lakadong member of the sylhet formation lower eocene and the barail oligocene tipam lower miocene and girujan middle miocene formations in the basin a detailed study to understand the nature and origin of the oils from different stratigraphic horizons using terrigenous and other biomarkers has been carried out further the variation in maturities of oils occurring in different stratigraphic horizons has also been studied the study shows that rearranged oleananes oleananes and bicadinanes are present in these oils implying land plant input to their source rocks the oils have been classified into different groups using ratios of rearranged oleananes oleananes bicadinanes and steranes indicating presence of multiple source rocks in the basin with subtle variation in characteristics maturity studies show that oils from younger horizons barail tipam and girujan are more mature than oils from older horizons langpar and lakadong there is an apparent mismatch in maturity of oils as measured by different biomarker maturity parameters this is due to the mixing of two different charges of oils having different maturities and generated from two different source rock kitchens in the same reservoir principal component analysis pca of biomarker data has also been able to classify the oils into various groups a new parameter has been developed using ratios of rearranged oleananes for determining maturity of these oils

comparative organic petrology of interlayered sandstones siltstones mudstones and coals in the upper carboniferous ruhr basin northwest germany and their thermal history and methane generation in the coal mining ruhr area upper carboniferous rocks ca 4000 m consist of interlayered sandstones siltstones mudstones and coals they were deposited in a tropical paralic environment where alternating fluvial sedimentation occasional marine ingressions and swamp growth resulted in an irregular cyclic succession the total sedimentary package contains on an average 6 vol of organic matter about 70 vol of the organic matter occurs in coal seams the rest as dispersed organic matter in clastic rocks the organic matter is autochthonous in the coals and allochthonous in associated sandstones and siltstones it consists of about 70 vitrinite 20 inertinite and 10 liptinite the overall maceral group composition is the same for coals and dispersed organic matter this surprising similarity is caused by a nearly exclusive input of land plant derived organic matter to swamps and fluvial systems and a similar degree of preservation highest average liptinite contents of total macerals were found in unrooted mudstones highest average inertinite contents in coarse grained siltstones and highest average vitrinite percentages in sandstones

saturated and olefinic terrigenous triterpenoid hydrocarbons in a biodegraded tertiary oil of northeast alaska abstract dinorlupanes norlupanes olean 12 ene 18 olean 12 ene and urs 12 ene occur in a heavily biodegraded tertiary oil tested from the ocs y 0849 1 well drilled on the hammerhead prospect in the beaufort sea offshore northeast alaska these indicators and other source related characteristics of the hammerhead oil ring a degraded oleanoids ursanoids and lupanoids v and ni less than 2 0 ppm v v ni less than 0 5 indicate a land plant angiospermous character in the source facies the olefins in the hammerhead and canadian oils are considered to be contributed directly from the source rather than extracted from adjacent immature non source sediments during migration as indicated by a the accompanying presence in the oil of saturated angiosperm markers and b the absence of measurable amounts of other olefins characteristic of immature organic matter e g diasterenes and hopenes

biomarker and n alkane isotope profiles for tertiary oils relationship to source rock depositional setting abstract biomarker and n alkane isotope profiles have been measured for 29 late cretaceous tertiary oils from se asia china papua new guinea new zealand and the u s a the results are interpreted with respect to six kinds of source rock depositional setting fluvio deltaic fd freshwater transitional tr lacustrine lac saline lacustrine sal marine deltaic md and marine carbonate mc a comparison of biomarker and n alkane isotope results suggests that parameters such as the oleanane hopane ratio may overestimate the higher plant contribution to marine oils the abundance of bicadinanes is much more variable than that of oleanane probably because of a specific association with the highly resinous dipterocarp hardwoods of se asia however traces do occur in an oil from outside the paleogeographic range of the dipterocarp family confirming that there is also a more general angiosperm source the bicadinane isomeric distribution is shown to depend on maturity leading to new maturity parameters which are resistant to even very heavy biodegradation retention indices based on the regular hopane series are provided for the main bicadinane and methyl bicadinane isomers and for a group of oleanane related triterpanes of unknown structure the presence of the latter compounds may indicate locally deposited as opposed to transported higher plant matter in the source source rock depositional setting is the primary control on the shape of the n alkane isotope profile with negatively sloping curves being characteristic of fd and tr oils and flat or positively sloping curves typical of marine oils the difference is probably related to the bacterial reworking of higher plant matter in the fd environment a slight isotopic anomaly at n c 17 correlates with the abundance of algal derived steranes and may indicate a minor marine contribution to the source of an fd oil

multispecies approach to reconstructing eastern equatorial pacific thermocline hydrography during the past 360 kyr 1 stable isotope data from eastern equatorial pacific eep core tr163 19 2 15 n 90 57 w 2348 m are presented for the surface dwelling foraminifers globigerinoides ruber and g sacculifer and thermocline dwelling globorotalia menardii and neogloboquadrina dutertrei using species specific normalization factors derived from experimental and plankton tow data we reconstruct a 360 kyr record of water column hydrography across the past three glacial cycles we demonstrate that g ruber maintains a mixed layer habitat throughout the entire record while g sacculifer records a mixture of thermocline and mixed layer conditions and g menardii and n dutertrei record thermocline properties we conclude that g sacculifer is not appropriate for paleoceanographic applications in regions with steep vertical hydrographic gradients results suggest that this region of the eep had a thicker mixed layer and deeper 13cdic boundary between the surface and equatorial undercurrent during the last two glacial periods a shift in n dutertrei and g sacculifer geochemistry prior to 185 kyr suggests water column structure and chemocline gradients changed possibly due to a shift in the position of the undercurrent relative to this site the timing and magnitude of glacial interglacial 13c variations between species indicates that near surface carbon chemistry is controlled by changes in productivity atmospheric circulation and advected intermediate water sources north of the antarctic polar front these results demonstrate that when properly calibrated for species differences multispecies geochemical data sets can be invaluable for reconstructing water column structure and properties in the past

interannual variability of planktic foraminiferal populations and test flux in the eastern north atlantic ocean jgofs planktic foraminiferal assemblages vary in response to seasonal fluctuations of hydrographic properties between water masses and after periodical changes and episodic events e g reproduction storms distinct annual variability of the planktic foraminiferal flux is also known from sediment trap data in this paper we discuss the short term impacts on interannual flux rates based on data from opening closing net hauls obtained between the ocean surface and 500 m water depth data were recorded during april may june and august at around 47 n 20 w biotrans in 1988 1989 1990 1992 1993 and during may 1989 and 1992 at 57 n 20 22 w species assemblages closely resemble each other when comparing the mixed layer fauna with the fauna of the upper 100 m and the upper 500 m of the water column in addition species assemblages 100 m are almost indistinguishable from assemblages that are 125 m in test size the standing stock of planktic foraminifers at biotrans can vary by more than one order of magnitude over different years however species assemblages may be similar when comparing corresponding seasons early summer assemblages june are distinctly different from late summer assemblages august significant variations in the species composition during spring april may are independent of the mixed layer depth spring assemblages are characterized by high numbers of globigerinita glutinata in particular day to day variations of the number of specimens and in species composition may have the same order of magnitude as interannual variations this appears to be independent of the reproduction cycle species assemblages at 47 n and 57 n are similar during spring although surface water temperatures and salinities differ by up to 10 c and 0 7 psu we suggest that the main factors controlling the planktic foraminiferal fauna are the trophic properties in the upper ocean productive layer planktic foraminiferal carbonate flux as calculated from assemblages reveals large seasonal variations a quasi annual periodicity in flux levels and substantial differences in timing and magnitude of peak fluxes at the biotrans station the average annual planktic foraminiferal caco 3 fluxes at 100 and 500 m depth are estimated to be 22 4 and 10 0 g m 2 yr 1 respectively

calcareous nannofossils and the origin of eastern mediterranean sapropels a quantitative analysis of calcareous nannofossil assemblages was carried out with an optical microscope on four deep sea cores raised from the eastern mediterranean and selected to form a nw se transect a total of 748 samples were studied including a very detailed analysis of sapropels s5 and s6 in two out of the four cores this paper is restricted to the discussion of the results obtained on florisphaera profunda which provided important insights on the mechanisms of sapropel formation an intricated and unravelled puzzle for the scientists of the last decades on the basis of abundance variations of f profunda the only species of calcareous nannoplankton which inhabits the lower part of the photic zone i suggest that sapropel formation was triggered by increased primary production either confined to a deep chlorophyll maximum dcm a concept previously introduced by rohling and gieskes 1989 or extended to a thicker layer of the photic zone when increased primary production was confined to the dcm sapropel s3 s4 s5 s7 and s1 this latter only in the eastern part of the basin the abundance of f profunda was enhanced greatly with respect to all other species living in the higher part of the photic zone on the contrary when the increased primary production was extended to a thicker layer of the photic zone glacial sapropels s6 and s8 the production of most nannoplankton species was favored decreasing the relative proportion of f profunda

paleoenvironmental changes from stable isotopes in planktonic foraminifera from eastern mediterranean sapropels abstract parallel stable oxygen isotope analyses of six planktonic foraminiferal species from an eastern mediterranean deep sea core present clear evidence for abnormal hydrographic regimes during deposition of sapropels s6 and s7 samples from s7 are characterized by a strong depletion of 18 o in epipelagic species while meso and bathypelagic forms are much less depleted this indicates a shallow pycnocline during deposition of s6 all species show a tendency towards lower values pointing to a far more extended pycnocline density stratification of the watercolumn is suggested by the isotopic differences between the species neogloboquadrina dutertrei globigerina bulloides and globorotalia scitula the latter represents the deepest element and shows the highest 18 o values carbon isotopes show two species groups each containing an epi meso and bathypelagic species under normal marine conditions group i globigerinoides ruber neogloboquadrina dutertrei and globorotalia truncatulinoides has relatively high 13 c values while species of group ii globigerina bulloides globorotalia scitula and globigerina quinqueloba show relatively low 13 c values indicating a stronger vital effect during sapropel deposition 12 c isotopes are enriched which we interpreted as the result of increased biological activity due to low oxygen stress conditions g scitula shows different eco phenotypes during times of sapropel deposition and the same may be true for the other members of group ii failure to adapt to adverse environmental conditions may be the cause for the absence of the two group i members globigerinoides ruber and globorotalia truncatulinoides in sapropel s6

regional source rock potential of lacustrine oligocene kishenehn formation northwestern montana intermontane basins of the northern united states overthrust belt have received only minor attention from petroleum geologists and geochemists in the modern literature despite the common occurrence of oil shales and thick sediment columns in such basins the present study investigates the petroleum source rock potential of the freshwater lacustrine sediments including mudstones oil shales and lignites of the kishenehn basin of northwestern montana and southeast british columbia outcrop samples of the tertiary kishenehn formation include excellent albeit immature petroleum source rocks average total organic carbon contents and hydrogen indices exceed 6 and 500 mg g respectively and numerous samples contain type i kerogen all samples studied are thermally immat re to marginally mature having vitrinite reflectance values of 0 28 to 0 51 ro organic geochemical and petrographic analyses of the kishenehn sediments allow estimates of detailed depositional setting and specific biological input to the sediment column the southernmost sediments in the basin contain the least land plant organic matter input and possess the richest petroleum source potential although vitrinite reflectance values are not particularly sensitive to maturity differences in this sample set molecular geochemical data were found to be useful in evaluating fine maturity distinctions and are used here to establish the order of kishenehn outcrops on the basis of maturity this use of molecular markers as maturation and depositional setting indicators for freshwater lacustrine environments has widespread application in thrust belts the results of this tudy will be useful in exploration of over two dozen intermontane basins throughout the northern extent of the united states overthrust belt

a dynamic concept for eastern mediterranean circulation and oxygenation during sapropel formation we propose that intermittent bottom water ventilation occurred throughout periods of sapropel deposition and that the recently reported sapropel interruptions represent centennial scale episodes of enhanced frequency intensity of that process in essence the modern high frequency variability in deep water formation affected by climatic variability over the northern basins on seasonal to longer time scales prevailed also at times of sapropel deposition although the overall ventilation state was much reduced this concept is supported by detailed multiple species isotope records for three aegean cores the presence of abundant globorotalia truncatulinoides within especially sapropels s7 and s8 in the western levantine basin observations of three rapid benthic repopulations within sapropel s6 in the deep western levantine basin a report of continuous benthic presence through sapropel s1 at intermediate deep locations offshore libya and further supporting information from the literature in the aegean records concomitant abundance of low oxygen tolerant benthic foraminifera and presence of the more oxyphilic benthic foraminifer uvigerina mediterranea with surface similar 13c values indicate repeated deep water re oxygenation events throughout the deposition of s1 the observations of a continuous benthic presence through s1 offshore from libya imply that no persistent anoxia developed at mid depth levels in that region which is far removed from direct deep ventilation influences the abundance of deep mesopelagic g truncatulinoides through several sapropels from the western levantine basin also suggests the presence of bio available oxygen at many hundreds of meters of depth moreover the rapid intermittent benthic repopulations within sapropels from the deep eastern mediterranean imply that bottom water anoxia was spatially restricted and or of a highly intermittent nature the short time scales of these repopulation events are incompatible with titration of an extensively anoxic water column and subsequent re establishment of water column anoxia we suggest that where anoxic azoic conditions were present they most likely were restricted to a veneer at the sediment water interface the extent of such an anoxic blanket depends on the balance between advective oxygen supply into the deep sea and biological and chemical oxygen demand the demand functions imply a decoupling of oxygenation from water mass advection allowing export production and corg posting rates to the sea floor to delimit the extent of the anoxic blanket in both space and time low productivity regions would develop no anoxic blanket allowing for the observed persistence of deep dwelling planktonic and bottom dwelling benthic faunas

modeling the paleocirculation of the mediterranean the last glacial maximum and the holocene with emphasis on the formation of sapropel s 1 an ocean general circulation model is used to simulate the thermohaline circulation in the mediterranean sea during the last glacial maximum and the holocene when the sapropel s1 was deposited the model is forced by prescribed surface temperatures and salinities where present day values lead to very realistic surface buoyancy fluxes different paleoreconstructions for the surface salinity and temperature distributions during these periods are tested in both periods under all reconstructions antiestuarine flow is maintained at gibraltar and sicily the holocene circulation has fresh intermediate water produced in the adriatic and an upward salt flux from the old waters below help maintain its outflow at sicily the depth of ventilation around the basin is broadly consistent with the shallowest sapropel layers observed shoaling of the eastern pycnocline occurs in all experiments in both periods possibly indicating enhanced productivity although the reasons for this are different in each case

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

seasonal salinity changes during mediterranean sapropel deposition 9000 years b p evidence from isotopic analyses of individual planktonic foraminifera using stable isotopic analyses of individual tests of planktonic foraminifera with different seasonal and depth habitats we have investigated temporal variations in surface water salinities in the eastern mediterranean during the past 13 000 years low oxygen isotopic values document the presence of anomalously low salinity conditions in the eastern mediterranean at about 13 000 years b p 4000 years before the deposition of the youngest sapropel by 11 000 years b p during the deposition of presapropel sediments low salinity surface waters were more pervasive but were restricted to summer months and only affected the surface of the water column at the onset of sapropel deposition about 9000 years b p surface salinities in the eastern mediterranean had decreased by almost 4 and had extended to depths of at least 75 m the low salinity surface lens was not however a permanent feature of the eastern mediterranean during sapropel deposition low salinity surface conditions occurred in the fall and winter seasons but normal sea surface salinities returned during spring months on a seasonal and or interannual basis thus a low salinity surface lens could have existed continuously for months or decades at a time but would have been interrupted intermittently by a return to normal conditions any triggering mechanism proposed for mediterranean sapropels must account for the seasonal fluctuations and ephemeral nature of low salinity conditions in the eastern mediterranean despite normal salinities returning occasionally during spring months a low salinity surface lens may have greatly inhibited the production of levantine intermediate water prevented the formation of adriatic deep water and consequently reduced ventilation of the eastern mediterranean

opening the carbon isotope vital effect black box 2 quantitative model for interpreting foraminiferal carbon isotope data interpretation of carbon isotope records from late quaternary planktonic foraminifers are confounded due to the presence of a significant physiological component in the carbon isotopic signal a quantitative carbon isotope qc model is presented which relates the carbon isotopic composition of a foraminiferal shell to the physiological processes of respiration and symbiont photosynthesis and to the 13c value of seawater co2 the qc model is calibrated with physiological and stable isotopic data from laboratory experiments with living planktonic foraminifers model simulations of chamber and shell 13c values with the symbiont bearing foraminifers orbulina universa and globigerinoides sacculifer suggest 1 variations in symbiont density and photosynthetic rate light level or habitat depth are the primary physiological parameters controlling intraspecific carbon isotopic variability in these species 2 respiration has little effect on the 13c of o universa and 3 each chamber in a multichambered foraminiferal test will have a distinct 13c value depending on its position in the test whorl size 13c value relationships reported for g sacculifer from fossil assemblages can be explained as a function of increasing symbiont density during ontogenetic development

late pleistocene variability of the carbon isotopic composition of organic matter in the eastern mediterranean monitor of changes in carbon sources and atmospheric co2 concentrations the organic carbon isotopic record of the sapropels s1 and s3 s10 and intercalated marl oozes has been determined in a 12 m piston core from the eastern mediterranean the 13corganic values are systematically lighter mean 21 0 0 82 in all sapropels and heavier mean 18 8 1 07 in the marl oozes these differences are not due to variable marine and terrestrial organic matter mixtures because all values are heavier than modern plankton in the mediterranean there is no relationship between the corganic n ratios and the isotopic values and published information on the abundance and distribution of organic biomarkers shows that terrestrial material constitutes a minor fraction of the total organic matter temperature effects on isotope fractionation are also discounted because the change in 13corganic values between glacial and interglacial horizons is in the opposite sense diagenesis which can produce relatively small changes in the carbon isotopic composition of sedimentary organic matter under certain circumstances is unlikely to have caused the observed differences because this mechanism would cause an enrichment in 12c implying that all values were even heavier originally and there is no secular trend in the 13corganic record the observed differences in 13corganic between the two lithologies are probably produced by changes in the isotopic composition and the concentration of dissolved co2 first freshwater flooding during the formation of the sapropels caused the isotopic composition of the dissolved inorganic carbon in the surface waters of the mediterranean to become lighter because of the 13c deficiency in fresh waters hence photosynthesis would have produced isotopically lighter organic material second changes in atmospheric pco2 between glacial and interglacial periods as shown by the vostok ice core caused marked changes in the concentration of free dissolved co2 in the mixed layer lower values during glacial maxima caused a smaller fractionation of the carbon isotopes by phytoplankton whereas levels were less limiting during the interglacials concentrations of dissolved co2 could also have been much higher during the deposition of the sapropels because of the supply of regenerated co2 to the mixed layer by upwelling and this could have further lightened the 13corganic values in the sapropels themselves carbon isotope records may provide an alternative method for estimating atmospheric pco2 levels over longer time periods than can be obtained from ice cores

impact of the azores front on the distribution of planktic foraminifers shelled gastropods and coccolithophorids abstract the azores front current system south of the azores islands has been studied in order to reveal the direct impact of an open oceanic thermohaline front on the distribution of the calcareous plankton planktic foraminifers pteropods heteropods and coccolithophorids were sampled from the upper 2500 m of the water column during august 1997 and january 1999 in addition the hydrography was recorded across the frontal jet on combined ctd and xbt transects in august 1997 a strong seasonal thermocline capped the azores front af at about 60 90 m water depth below the thermocline a distinct hydrographic front was indicated by temperature and salinity gradients the central af was an area of low planktic foraminiferal gastropod and coccolithophorid production and was a faunal barrier for shallow and deep dwelling species highest numbers of planktic foraminifers gastropods and coccolithophores were recorded from above the thermocline north of the af the most frequent planktic foraminiferal and pteropod species were globigerinoides ruber white and limacina inflata respectively below 100 m planktic foraminifers were most frequent north of the af and gastropod shells were rare in particular the deep dwelling planktic foraminifer globorotalia scitula was frequent only at sampling sites north of the af in january 1999 the surface water temperature of the azores front current system was lower and the thermocline was deeper than in august 1997 the planktic foraminiferal standing stock was three times higher than in august 1997 and no water depth related faunal changes occurred the fauna was dominated by globorotalia truncatulinoides and turborotalita humilis was frequent during both january and august the fauna from south of the azores was different from that to the southeast recording the occurrence of two different water masses in this study we present a micropaleontological definition of the af in order to provide a paleoceanographic tool that may be used to decipher the late quaternary current system of the north atlantic ocean

steroidal hydrocarbons of the kishenehn formation northwest montana abstract the oligocene kishenehn formation of northwest montana and southeast british columbia consists of fluvial and lacustrine sediments marlstones lignites and oil shales deposited in an elongate intermontane half graben the petroleum source rock potential and steroidal hydrocarbon distribution of selected shales of the kishenehn formation were examined several steroidal hydrocarbon series were documented including 4 desmethylsteranes 4 methylsteranes sterenes diasterenes spirosterenes c ring monoaromatic steroids and b ring monoaromatic anthrasteroids non steroid hydrocarbons present include hopenes hopanes moretanes perylene botrycoccane a series of alkylcyclohexanes and a fused ring aromatic tentatively identified as a tetrahydrochrysene source rock analysis indicates that the kishenehn formation possesses excellent petroleum source potential conventional thermal maturity parameters vitrinite reflectance and rock eval tmax values as well as maturity parameters derived from molecular parameers n alkane steroid and hopanoid distributions suggest that much of the kishenehn formation is currently undergoing organic diagenesis typical molecular indicators of thermal immaturity include the occurrence of high relative amounts of a 5 h desmethylsteranes b 14 h b ring monoaromatic anthrasteroids and c 4 ch3 methylsteranes a near shore freshwater lacustrine depositional environment is indicated with some input of terrigenous organic matter high cpi c23 c31 n alkanes and relatively high ethylcholestane content while the presence of 4 methylsteroids and botryococcane indicate significant contributions from dinoflagellates andbotryococcus braunii the occurrence in the kishenehn formation of a diverse selection of 4 methyl and 4 desmethyl aliphatic and aromatic steroids provides a unique opportunity to monitor co variance of molecular maturity indicators in sediments depositedunder relatively constant depositional conditions

temperature and salinity records of the tyrrhenian sea during the last 18 000 years abstract we have used the modern analogue technique to derive sea surface temperature sst records of the last 18 000 years from two well dated deep sea cores recovered in the tyrrhenian sea results show two major cooling events synchronous with the european and north atlantic oldest and younger dryas events a later cooling of lower amplitude is observed between about 8000 and 4500 yr bp tyrrhenian ssts were similar to those of the upper holocene only during the bolling allerod event and at the beginning of the holocene we compared the sst and the planktonic foraminiferal oxygen isotope records to estimate the surface salinity variations our reconstruction shows that salinity decreased in the tyrrhenian sea during the three cold events whereas high ssts correlate with high salinities during most of the last 18 000 years tyrrhenian sea salinity variations were similar to those of the north atlantic ocean near the entrance of the mediterranean sea the salinity gradient between the two basins was thus constant indicating that the western mediterranean circulation pattern and the freshwater budget were not significantly different from the modern one the case was however different during the middle holocene when the strong salinity decrease associated with the sapropel deposit in the eastern mediterranean basin had no equivalent in the north atlantic ocean this peculiar event can only be explained by a local climatic change and an increase of precipitation

compound specific stable carbon isotope analysis as a tool for correlating coal sourced oils and interbedded shale sourced oils in coal measures an example from turpan basin north western china molecular geochemical methods have shown that it is often diacult to diaerentiate between coal and interbedded shale sourced oils even though coals and interbedded shales may exhibit considerable organic influx variation e g land plant vs algal organic matter due to the changes of depositional setting however compound specific stable carbon isotopic compositions are sensitive to the source input variations typically specific molecules are more depleted in 13 c with increasing content of aqueous biota this hypothesis is examined and exemplified by comparing the stable carbon isotopic ratios of n alkanes from source rock extracts and related oils of the turpan basin northwestern china stable carbon isotopic values of n alkanes extracted from coals and interbedded shales show that d 13 c values of n alkanes with less than 20 carbon atoms vary only slightly however there are dramatic changes in the isotopic compositions of higher molecular weight n alkanes furthermore n alkanes from coal extracts are enriched in 13 c relative to that of interbedded shales with excursions up to 2 3 this comparison enables the diaerentiation of coal and interbedded shale sourced oils and provides information useful in assessing the hydrocarbon system of a basin 2000 elsevier science ltd all rights reserved

deep dwelling planktonic foraminifera of the northeastern pacific ocean reveal environmental control of oxygen and carbon isotopic disequilibria abstract we assess the utility of four species of living planktonic foraminifera as tracers of thermocline and intermediate water masses in the northern pacific ocean based on their water column distribution and shell isotopic composition assuming oxygen isotopic equilibria with the water column we infer apparent calcification depths this allows an estimate of apparent carbon isotopic disequilibria we then relax the assumption of oxygen isotopic equilibrium to examine habitat effects on kinetic disequilibrium processes in the california current left coiling neogloboquadrina pachyderma and globigerina calida calcify in the upper thermocline globorotalia scitula resides within the shallow salinity minumum potential density 25 1 26 7 while globoquadrina hexagona is associated with the deeper north pacific intermediate water 26 7 26 9 apparent carbon isotopic disequilibria corrected for oxygen isotopic disequilibria range from 1 0 1 9 in these asymbiotic species the carbon isotopic disequilibrium can be modeled as a single exponential function of temperature or a logarithmic function of potential food supply we infer that carbon isotopic disequilibrium increases with metabolic rate related to temperature and or food supply kinetic processes of oxygen and carbon isotopic disequilibria yields reasonable depth habitats if the slope of the oxygen carbon isotopic shift is about 0 35 consistent with culture data our finding of a link between environment metabolism and isotopic disequilibrium observed in oceanic settings suggests the potential to better reconstruct the structure and biological processes of the upper water column from geologic data

palaeoceanography of the last deglaciation in the alboran sea western mediterranean stable isotopes and planktonic foraminiferal records abstract oxygen isotope changes of the foraminiferal species globigerina bulloides and uvigerina peregrina eleven radiocarbon dates on the sediment fraction above 50 m and 13 biostratigraphical events allow us to correlate and to date the sediment record of the last climatic cycle in four cores from the alboran sea nine ecozones are recognized which differ from those previously established for atlantic sediments cored immediately west of gibraltar these ecozones can be grouped into two broad phases from the last glacial maximum up to near 9 500 yr b p cold north atlantic microfaunas are the major component of the assemblages during this interval dominant species replace each other according to the varying temperature and density stratification of the water masses from 9 500 yr b p up to the present time subtropical forms from the central atlantic dominate the northern atlantic forms an abrupt increase in the percentages of g inflata occurred near 7 000 b p this event was diachronous within the mediterranean during the last glacial g inflata was endemic inside the mediterranean and its abrupt increase near the end of the deglaciation did not result from replenishment from the atlantic between 4 000 and 5 000 yr b p percentages of g bulloides also increased abruptly warming conditions associated with the onset of a seasonal thermal stratification and a contrasting winter vertical convection are strongly suggested

molecular genetic markers and maturity indices in intermontane lacustrine facies kishenehn formation montana abstract molecular markers have considerable promise as thermal maturation indicators in source rocks having a well defined depositional environment this occurs in the kishenehn formation northwest montana and southeast british columbia an oligocene unit comprised of fluvial and lacustrine shales up to 3 km of these non marine sediments were deposited in a 900 sq km elongated half graben atop the precambrian rocks of the lewis thrust sheet specific outcrops of the coal creek member of the kishenehn formation are known to contain excellent potential source rocks including extensive oil shales the source rock potential and molecular marker geochemistry of most of the major kishenehn outcrops have now been investigated and regional results are presented in this paper source rock analysis of a regional suite of kishenehn samples indicates excellent petroleum potential immature type i kerogen throughout the basin several classes of distinctive diagenetic molecular markers occur within the coal creek member of the kishenehn formation including diasterenes spirosterenes methylspirosterenes b ring monoaromatic anthrasteroids hopanes and moretanes molecular markers indicative of non marine deposition include dehydroabietane conifer input and an onocerane recently identified in leaf fossils of miocene lacustrine beds in adjacent idaho triterpane ratios are significantly more sensitive than vitrinite reflectance methods in assessing thermal maturation in the kishenehn and are successfully used in this study to order outcrop locations according to thermal maturity level the systematic variation of specific markers with increasing thermal maturation suggests that molecular correlation is feasible and could provide a method of assessing stratigraphic continuity in the basin

oleananes in oils and sediments evidence of marine influence during early diagenesis abstract the oleananes as markers for the angiosperms provide valuable source and age information when present in an oil nevertheless they are not quantitatively related to the land plant input and indeed their presence reflects only a small leak in diagenetic processes leading primarily to aromatic oleanoids because they are minor products the abundance of oleananes in terrigenous oils and sediments may be highly sensitive to changes in early diagenetic conditions here we present evidence that contact of plant matter with seawater during early diagenesis enhances the expression of oleananes in a mature sediment or oil oleananes are absent or present at very low concentrations in samples from the base of an eocene coal seam affected by postdepositional seawater intrusion however their abundance increases toward the top of the seam in correlation with organic sulphur dibenzothiophene phenanthrene and the homohopane index similarly in deltaic sediments from the south sumatra basin oleanane hopane is strongly correlated with indicators of marine influence such as c 27 c 29 steranes and the homohopane index in each case increasing oleanane abundance is accompanied by a reduction in the extent of aromatisation and for the south sumatra basin the proportion of a ring contracted oleananes an angiosperm derived miocene coal from the philippines deposited under freshwater conditions shows abundant aromatic oleanoids but no oleananes these results show that oleananes need to be used with caution as age and source markers in fluvio deltaic and lacustrine petroleum systems on the other hand their sensitivity to early diagenetic conditions may make them useful in locating effective source rocks in such systems

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

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

do planktic foraminifera accurately record shifts in the carbon isotopic composition of seawater σco2 abstract both the carbon isotopic composition of seawater and physiological vital effects such as respiration and symbiont photosynthesis influence the 13 c value of foraminiferal calcite the symbiont bearing planktic foraminifera orbulina universa was grown in a series of laboratory experiments to determine whether vital effects differentially obscure the 13 c signal such that changes in the 13 c of seawater co 2 cannot be quantitatively evaluated foraminifera were cultured under three different irradiance levels to elicit a full range of symbiont photosynthetic effects and in seawater with 13 c values ranging between 1 77 ambient and 5 76 power regression analysis of isotope data from individual shells plotted against culture irradiance yields three curves which are nearly parallel but are offset by the difference between the carbon isotopic composition of the culture waters when irradiance groups are combined and o universa 13 c values are plotted against seawater 13 c three parallel linear regressions are obtained with slopes ranging between 0 93 and 0 96 because the slopes are near unity it is concluded that the 13 c of o universa accurately tracks changes in the carbon isotopic composition of seawater regardless of the magnitude of its physiological vital effect o universa oxygen isotope data show that individuals maintained in the low and medium irradiance groups secrete their shells in isotopic equilibrium according to established paleotemperature equations in contrast individuals grown under high irradiance levels maximum symbiont photosynthetic rates are on average 0 35 depleted in 18 o relative to equilibrium symbiont enhanced calcification rates in the high light group may be responsible for the observed 18 o difference

monitoring tectonically controlled marine to lacustrine transitions using organic facies ridge basin california u s a abstract ridge basin is an elongate intermontane basin filled with upper miocene pliocene clastics located 80 km north northwest of downtown los angeles over 13 km of marine lacustrine and fluvio deltaic sandstones and shales are present because of southeastward depocenter migration throughout basin development no more than 4 5 km of vertical section are present in any one location this has resulted in an ideal situation to study organic facies variability namely a thick thermally immature stratigraphic succession with only minor variations in maturity level in this paper we use molecular isotopic and petrographic data to help identify systematic variability in organic facies in the castaic ridge route and peace valley fms all late miocene and relate these variations to the paleolimnology tectonic history and oil source rock potential of the basin as strike slip movement continued along the san gabriel fault during the late miocene the sedimentation regime changed from a marine dominance to one controlled by lacustrine and fluvio deltaic processes this transition results in changes in the organic facies within the basin as reflected in a a systematic decrease in organic carbon isotope ratios b an increase in relative yields of phenolic and n aliphatic structures in the kerogen pyrolysate c an increasing occurrence of perhydro carotene indicating episodic development of a halocline in the water column and d decreasing pristane phytane and c 29 c 28 sterane ratios unusual patterns of kerogen maceral distribution and a ring sterane methylation are also observed these geochemical data support the existence of a marine embayment in the early late miocene yielding to a lacustrine and fluvio deltaic setting which experienced considerable variation in bathymetry salinity and oxicity low levels of thermal maturity preclude the occurrence of hydrocarbon source rocks although source rock potential is present in sporadic localities optical and molecular maturity indicators show no systematic variation with stratigraphic succession this lack of variation is consistent with the known tectonic development in the basin and the shingled sedimentation pattern resulting from a migrating depocenter internal variability in the sterane and hopane epimer ratios may eventually be useful in estimating the uneven extent of overburden in the peace valley and ridge route fms leading to applications elsewhere in intermontane lacustrine basins with tectonically migrating depocenters

tertiary deltaic and lacustrine organic facies comparison of biomarker and kerogen distributions abstract biological marker and kerogen compositional data in tertiary deltaic and lacustrine settings were compared and contrasted the two settings are represented by a coals and organic carbon rich shales in a ick deltaic sequence from the far east constituting three distinct organic facies and b humic coals and spropelic oil shales in a restricted intermontane freshwater lacustrine sequence from western montana u s a constituting two distinct organic facies wedistinguish the organic facies in each depositional setting by systematic differences in gross compound class distributions kerogen and infrared spectral characteristics molecular character of pyrolyzates sterane carbon number distribution and sterane hopane ratios the kerogens of the three deltaic organic facies are characterized by varying quantities of vitrinite resinite sporinite cutinite and fluorescent amorphinite triterpane distributions reveal numerous terrigenous compounds including oleanane oleanenes and unidentified c 30 presumably resin derived components the two organic facies of the freshwater lacustrine setting are distinguishedased upon either a vitrinite or an alganite fluorescent amorphinite predominance in the kerogen numerous characteristics facies related markers are also present including dehydroabietane land plant resins and 4 methylsteranes perhaps from freshwater dinoflagellate input the available molecular and petrographic data are evaluated and characteristics are proposed for distinguishing five organic facies of these two depositional settings the successful simultaneous use of molecular geochemistry and organic petrography in this study provides a format for refining the organic facies concept

paleosalinity and δ18o a critical assessment in paleoceanography a traditional application of oxygen isotope ratios in fossil carbonate from deep sea cores concerns the reconstruction of paleotemperatures recently isotopic data have been increasingly employed in the reconstruction of paleosalinities as well this application involves a number of basic assumptions a critical review of which is presented here as the calculation of paleosalinity from 18o residuals assumes constant and linear surface water salinity s 18o relationships we investigate this basic assumption for areas with important and variable freshwater budget and or sea ice influences we show that it is particularly unwarranted to assume such temporally invariant linearity in temperate and subpolar seas because of the effects of freezing and melting more critically we argue that the determinant of many regions s 18o is advection not the local water balance so that the basic 18o of seawater in many regions of the world ocean would likely have changed in a manner somewhat different from that expected from the ice volume record although the differences may not be significant for the gross reconstruction of such features as past sea level we believe they do potentially bias paleosalinity reconstructions mostly toward high salinities to fully exploit the potential of oxygen isotope records as quantitative paleosalinity indicators both the spatial and temporal variabilities need to be constrained hence we recommend that 1 for any time slice of specific interest to paleoceanographic and paleoclimatological studies a coupled ocean atmosphere isotope model or at least an ocean isotope model driven by a paleoclimate isotope model should be used to define the distribution of the base mixing end member 18o of sea water 2 much further regional scale research is needed on flux rates and isotopic compositions of the various terms in the freshwater budget as well as on the variability in the various advective terms the latter variability may be assessed from reconstructions of past seaice distributions and of volume fluxes isotopic compositions of outflow from marginal seas and through sea straits passages

changes in hydrocarbon maturity indices with coal rank and type buller coalfield new zealand abstract the buller coalfield south island new zealand is an inverted late paleogene basin that contains middle eocene bituminous coals which exhibit considerable variation in both coal rank across basin and coal type in seam twenty two fractionated bitumen extracts of brunner coal measures coal samples from 12 drillholes were analyzed by gc and gc ms to characterize the effect of coal rank and type on conventional hydrocarbon maturity indices at the beginning and end of the oil window 0 56 1 26 ro max the carbon preference index pristane phytane and isoprenoid n alkane ratios evolve throughout the high volatile bituminous b rank stage while other biomarker ratios 18 h 22 29 30 trisnorneohopane 17 h 22 29 30 trisnorhopane ts tm 18 h 21 h 30 norneohopane c 29 ts 17 h 21 h 30 norhopane and c 30 diahopane hopane do not show appreciable change in value until medium volatile bituminous rank various aromatic based ratios appear to be more effective in delineating rank throughout the entire oil window in particular the methylphenanthrene index and vitrinite reflectance are positively correlated over the entire bituminous rank range however subtle changes in depositional conditions variable coal type complicate these rank estimates within a given coal seam variation in cpi isoprenoid n alkane and hopane sterane ratios appear to be related to the hydrogen content of the coal while the homohopane index and the oleanane hopane ratio covary with sulfur content as with depressed vitrinite reflectance values mpi is similarly lowered in the perhydrous samples the mechanisms that control these hydrocarbon parameters during deposition and diagenesis are complex and convoluted however changes in bacterial activity and community with marine incursion appear to play an important role due to these anomalies none of the hydrocarbon maturity indices calculated can be singularly used to constrain coal rank

biological marker distribution and significance in oils and rocks of the monterey formation california abstract the biological marker distributions of several oils core extracts and solid bitumens of the monterey formation of california have been studied sterane terpane and monoaromatic steroid hydrocarbons were analyzed in samples from the san joaquin los angeles ventura and santa maria basins the sterane patterns of both oils and extracts are characterized by 1 a low relative concentrations of diasteranes 2 b low 20s 20r 5 14 17 ethylcholestane ratios 3 c relatively high concentrations of cholestane vs methyl and ethylcholestane isomers san joaquin basin samples contain significant amounts of the 5 isomer which is generally absent in samples from other basins the carbon number distribution of 5 14 17 20r steranes is similar for all oils regardless of api gravity depth or basin location and is suggestive of open marine depositional conditions for the source material involved 17 h l8 h 21 h 28 30 bisnorhopane is present in almost all samples certain san joaquin basin oils and extracts contain 1 a a series of 25 nor hopanes including 25 28 30 trisnorhopane 2 b a distinctive monoaromatic steroid hydrocarbon distribution 3 c an aliphatic hydrocarbon fraction devoid of n paraffins biological marker characteristics suggest that the monterey oils examined originated early in the maturational sequence from elastics poor source material api gravities of the monterey formation oils examined vary monotonically with 1 a bisnorhopane hopane ratios 2 b aromatized regular sterane ratios and 3 c the concentration of monoaromatized steranes relative to terpanes and regular steranes these oil gravity correlations exist regardless of sample depth or basin location

constraints upon the use of 24 ethylcholestane diastereomer ratios as indicators of the maturity of petroleum abstract we have measured the ratio 20 s 20 s 20 r the relative abundances of the 24 ethylcholestane diastereomers in nine pairs of closely adjacent samples of coals and shales which represent a range of geological ages and different sedimentary basins within some sample pairs the values were similar in others they were very different the differences between the values for coal and shale members of pairs are attributed to effects of sediment matrix type upon the processes which cause the changes in the ratio the kinetic parameters e and s for the changes in the 20 s 20 s 20 r ratio have been estimated using previously published measurements for the hod 1 well shale and jupiter 1 well coal and these values were found to be very different the process in the coal sequence has a much lower activation energy and is therefore less responsive to differences in heating rate regimes than is the case for the shale sequence values of the 20 s 20 s 20 r ratio in two other sequences are shown to be consistent with this explanation and the implications of these observations for the practice of using sterane isomer ratios for assessment of maturity of sediments and crude oils are discussed

review and new aspects concerning the formation of eastern mediterranean sapropels abstract in this paper it is proposed that the formation of eastern mediterranean sapropels occurred in an anti estuarine type of circulation which was to some degree weakened relative to the present in response to reduction of the eastern mediterranean excess of evaporation over freshwater input this reduction of excess evaporation would have been imposed by intensifications of 1 the indian ocean summer sw monsoon influencing the eastern mediterranean via increased nile discharge and 2 the system of mediterranean depressions an element of the westerly atlantic system causing increased precipitation and decreased evaporation both the indian ocean summer monsoon and the westerly atlantic system would be intensified in response to the occurrence of distinct minima in the cycle of precession it is demonstrated that reduced excess evaporation whether or not coinciding with global phases of deglaciation would lead to reduction of surface water salinities in the eastern mediterranean causing isolation of previously formed high salinity cooler deep water thus mixing was severely reduced possibly even restricted to eddy diffusion with only occasional convective events that because of the existing density gradient hardly ever would reach the deepest parts of the basin the consequently diminished oxygen advection down from a few hundred meters in the water column favoured preservation of the sinking organic matter this would however suffice only to enable the formation of sapropels with low organic carbon contents the high organic carbon contents observed in various sapropels are argued to reflect superimposed increases of export production the described scenario accounts for previously reported 1 increases of organic carbon content with increasing depth of deposition within individual sapropels and 2 asymmetrical sequences of sapropel deposition characterized by gradual build up and rather abrupt ending it is furthermore in agreement with 3 isotopic and faunal reconstructions of the history of exchange transports through both the strait of sicily and the strait of gibraltar and 4 faunal and floral reflections of the presence or absence of a distinct deep chlorophyll maximum with its associated increases in export production indicating the presence or absence of a shallow pycnocline within the euphotic layer moreover the described scenario 5 is in no way conflicting with the reports of sapropels in the western mediterranean and 6 seems to be endorsed by occasionally intercalated intervals suggestive of somewhat improved oxygenation amidst anoxic benthic desert levels a situation that has been observed in a few quaternary and pliocene sapropels