petroleum origin and accumulation in basin evolution a quantitative model basin data geologic geophysical geochemical hydrodynamic and thermodynamic can be combined for quantified hydrocarbon prediction a three dimensional deterministic dynamic basin model can be constructed to calculate all the measurable values with the help of mass and energy transport equations and equations describing the physical and or physicochemical changes in organic matter as a function of temperature input data consist of heat flux initial physical and thermal properties of sediments paleobathymetric estimates sedimentation rate and amount and type of organic matter subsequently the model computes pressure temperature physical and thermal properties of sediments maturity of organic matter and the hydrocarbon potential of any source rock as a func ion of space and time thus the complex dynamic processes of petroleum formation and occurrence in a given sedimentary basin can be quantified for example hydrocarbon potential maps for any given source rock and any geologic time slice of the basin evolution can be provided as computer printouts the computer model can be applied to any stage of an exploration campaign and updated as more information becomes available

thorium 230 profiling in deep sea sediments high resolution records of flux and dissolution of carbonate in the equatorial atlantic during the last 24 000 years variations in carbonate flux and dissolution which occurred in the equatorial atlantic during the last 24 000 years have been estimated by a new approach that allows the point by point determination of paleofluxes to the seafloor an unprecedented time resolution can thus be obtained which allows sequencing of the relatively rapid events occurring during deglaciation the method is based on observations that the flux of unsupported 230th into deep sea sediments is nearly independent of the total mass flux and is close to the production rate thus excess 230th activity in sediments can be used as a reference against which fluxes of other sedimentary components can be estimated the study was conducted at two sites ceara rise western equatorial atlantic and sierra leone rise eastern equatorial atlantic in cores raised from three different depths at each site from measurements of 230th and caco3 changes in carbonate flux with time and depth were obtained a rapid increase in carbonate production starting at the onset of deglaciation was found in both areas this event may have important implications for the postglacial increase in atmospheric co2 by increasing the global carbonate carbon to organic carbon rain ratio and decreasing the alkalinity of surface waters and possibly the north atlantic deep water increased carbonate dissolution occurred in the two regions during deglaciation followed by a minimum during mid holocene and renewed intensification of dissolution in late holocene during the last 16 000 years carbonate dissolution was consistently more pronounced in the western than in the eastern basin reflecting the influence of antarctic bottom water in the west this trend was reversed during stage 2 possibly due to the accumulation of metabolic co2 below the level of the romanche fracture zone in the eastern basin

particulate removal of230th and231pa in the biologically productive northern north pacific settling particles were collected by sediment traps at four stations in the high latitudes of the north pacific and analyzed for234th 232th 230th 228th and231pa in the northern north pacific including the bering sea the average activity ratio of unsupported230th to231pa in settling particles was 5 5 whereas that in the gulf of alaska in the eastern north pacific was about 14 the northern north pacific may be an efficient sink for231pa relative to230th because the average ratio in the world ocean is equal to the production ratio of 10 8 in seawater the activity ratios of230th 231pa of the settling particles agree well with those of the surface sediments at the respective stations this indicates that both nuclides in the surface sediments originated from settling particles and their dissolution or uptake during early diagenesis are not effective the ratio of the particulate nuclide flux f to the overlying water column production rate p did not correlate well with the total mass flux for230th however that for231pa increased almost linearly with increase in total mass flux and reached unity when the total mass flux was about 110 mg m2 d this suggests that231pa transported from oligotrophic regions is being actively removed in the biologically productive northern north pacific

210po and210pb distributions in the central and eastern indian ocean abstract disequilibrium between 210 po and 210 pb and between 210 pb and 226 ra has been mapped in the eastern and central indian ocean based on stations from legs 3 and 4 of the geosecs indian ocean expedition 210 po 210 pb activity ratios are less than 1 0 in the surface mixed layer and indicate a residence time for po of 0 6 years 210 po and 210 pb are generally in radioactive equilibrium elsewhere in the water column except at depths of 100 500 m where po may be returned to solution after removal from the surface water and in samples taken near the bottom at a few stations 210 pb excesses relative to 226 ra are observed in the surface water but these excesses are not as pronounced as in the north pacific and north atlantic the difference is attributable to a lower flux of 210 pb from the atmosphere to the indian ocean below the main thermocline 210 pb activities increase with depth to a broad maximum before decreasing to lower values near the bottom departures from this pattern are especially evident at stations taken in the bay of bengal where 210 pb 226 ra activity ratios as low as 0 16 are observed and near the mid indian ridge the data suggest that removal of 210 pb at oceanic boundaries coupled with eddy diffusion along isopycnals can explain gradients in 210 pb near the boundary application of a simple model including isopycnal diffusion chemical removal production and radioactive decay produces fits the observed 210 pb 226 ra gradients for eddy diffusion coeffients of 10 7 cm 2 s high productivity in surface waters of the bay of bengal makes this region a sink for reactive nuclides in the northern indian ocean

an investigation of the in reservoir conversion of oil to gas compositional and kinetic findings from closed system programmed temperature pyrolysis abstract the thermal alteration of reservoired petroleum upon burial was simulated by closed system non isothermal pyrolysis samples of a medium gravity oil from the norwegian north sea central graben were pyrolysed in microscale sealed glass or quartz vessels at heating rates of 0 1 0 7 and 5 0 k min 1 up to temperatures varying from 300 to 650 c the composition of the oil and gas in each vessel was determined by a single step on line gas chromatographic analysis with increasing rate of heating the onset of all oil degradation reactions was shifted to higher temperatures the same successive compositional changes occurred in each case increase in the total yield of gc detectable compounds significant gas c1 c4 generation accompanied by a decrease in yield of heavy components aromatisation and attainment of maximum gas yield and finally a cracking of the c2 gas components the stable final mixture consisted of methane aromatic hydrocarbons pyrobitumen and possibly hydrogen kinetic modelling of the oil to gas conversion resulted in a narrow gas potential vs activation energy distribution between 66 and 70 kcal mol assigning 35 of the total gas potential 460 mg per g of oil to an energy of 66 kcal mol and 29 to 67 kcal mol pre exponential factor 1 1 1016 s 1 by extrapolation to natural maturation conditions the onset of gas generation is predicted to occur between 160 and 190 c for geological heating rates between 0 53 and 5 3 k ma 1 predictions from the model are in accordance with the observed preservation of liquid hydrocarbons in a deep hot 165 c petroleum reservoir from the saga 2 4 14 well norwegian continental shelf

late pleistocene continental climate and oceanic variability recorded in northwest pacific sediments core v21 146 provides a continuous record of northwest pacific pelagic sedimentation spanning the past 530 000 years downcore variations of 18o from benthic foraminiferal calcite were correlated to the specmap record to provide an age model for late pleistocene paleoclimatic and paleoceanographic variation fluxes of caco3 and eolian material have been determined by combining information about linear sedimentation rates bulk densities and component percentages the mass accumulation rate mar of caco3 varies from 58 to 1435 mg cm kyr 1 and exhibits the pacific ocean pattern of higher accumulation associated with glacial periods for the younger portion of the record however the pattern of caco3 accumulation appears to shift during the mid brunhes so that prior to 350 000 years ago it exhibits an opposite pattern of greater accumulation during interglacial periods the flux of eolian dust is a proxy measure of the source area aridity and correlates well to the loess soil stratigraphy in china dust fluxes range from 43 to 718 mg cm kyr 1 and are greater by a factor of about 4 during glacial times cross spectral analysis of the eolian flux and oxygen isotope records shows an inphase and coherent relationship at each of the major orbital periodicities of 100 41 and 19 kyr eolian grain sizes generally used as a proxy record of wind intensity range from 8 4 2 9 m to 6 2 13 6 m a change in grain size variability occurs near about 300 ka such that the older portion is characterized by lower frequency and higher amplitude fluctuations than the younger portion power spectra for the eolian grain size record show dominant peaks at 100 and 50 kyr and a broad 25 35 kyr peak but coherency to the oxygen isotope curve at only the 100 and 33 kyr periodicities the phase relationship for eccentricity between the eolian grain size and 18o records suggests that at the 100 kyr frequency the smallest grain sizes are associated with glacial conditions

boundary scavenging in the pacific ocean a comparison of 10be and 231pa concentrations of u th 231pa and 10be were measured in holocene sediments from two cores collected off the west coast of south america two cores from the east pacific rise two from the equatorial pacific and one from the south pacific central gyre our results together with data from 5 cores reported in the literature show that boundary scavenging plays a major role in the removal of 10be from the pacific ocean deposition rates of 10be at three margin sites are more than an order of magnitude greater than at sites of red clay accumulation in the deep central pacific deposition of 231pa is 4 to 5 fold greater at the margin sites the residence time of 10be with respect to chemical scavenging defined as its inventory in the water column divided by its rate of removal to the sediments varies regionally from 1000 years at the red clay sites in the deep central pacific to 100 years at the margin sites different factors control boundary scavenging of pa and be for example scavenging of 231pa is enhanced by metal oxide coatings of particles whereas this seems to have little influence on the scavenging of 10be 1990

the record of late pleistocene biogenic sedimentation in the eastern tropical pacific ocean we have generated 300 kyr records of biogenic opal calcite and organic carbon corg for three cores in the eastern and central equatorial pacific ocean and have compared the records to determine whether common periods of biogenic sedimentation have occurred throughout the region we find that corg has been deposited in common pulses throughout the area while opal has a much more local pattern of variation calcite varies regionally but the record is shaped by superimposed dissolution and productivity processes the most intense corg peak occurs at 18 ka and can have greater than 2 times the holocene corg content other major corg peaks occur 150 ka and perhaps at 280 ka we have compared the corg record in one of the cores v19 28 to a model deepwater oxygen record developed from 13c data in the nearby v19 30 to test whether the corg record has been mostly shaped by degradation or by the rain of organic matter from the euphotic zone we found no coherence between the two records implying that the corg record is primarily a measure of productivity by comparing the opal calcite and corg records in v19 28 a core which is at or above the lysocline we found that both increased calcite and opal deposition matches high corg accumulation we also found however that the calcite and opal records were uncorrelated so that episodes of high opal deposition do not necessarily accumulate calcite rapidly we hypothesize that at least two different plankton communities have been dominant in the waters above this site one rich in opal secreting plankton and one more dominated by calcite producers the opal rich plankton community was dominant during the intervals 10 15 ka and 35 60 ka supplement data table 2 is available with entire articleon microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document p88001 2 50 payment must accompany order

glacial to interglacial changes in carbonate and clay sedimentation in the atlantic ocean estimated from 230th measurements abstract the cause of the climatically controlled fluctuations in the carbonate content of deep sea sediments remains the subject of uncertainty and debate three variables are involved supply of biogenic carbonate loss by dissolution and dilution by non carbonate phases it is suggested that 230 th which is produced in the ocean at a constant rate provides a reliable reference for measuring variations in rate of sedimentation on a regional scale results of a preliminary analysis based on published data indicate that for depths at and above the lysocline the carbonate fluctuations observed in cores from the north atlantic ocean are due primarily to variations in the terrigenous clay input which was 2 5 times higher during glacials than during interglacials carbonate deposition appears to have been somewhat reduced during glacials but probably not by more than a factor of 2 from published 230 th 232 th profiles it appears that the south atlantic ocean also received increased inputs of terrigenous clay during glacial periods

glacial to holocene changes in carbonate and clay sedimentation in the equatorial pacific ocean estimated from thorium 230 profiles uranium series nuclide concentrations have been measured on sediments from five box cores from an equatorial pacific transect 230thexcess activities show discontinuities at the holocene glacial boundary as dated by 14c the glacial sedimentation rates determined by 230th and 14c are 2 5 3 0 cm kyr the holocene rates from 230th are much lower than those dated by 14c 1 9 2 3 cm kyr because of carbonate dissolution 230th sedimentation fluxes exceed water column supply by factors of 1 2 1 8 in the holocene and 1 8 3 0 in the glacial sections a number of models have been applied to calculate carbonate dissolution rates the results show that carbonate dissolution rates in the holocene in g cm kyr equal 1 5 10 3 exp 1 4d where d is water depth in kilometers a point by point estimation of sediment fluxes through time show that clay accumulation rates in the area have been near constant at 0 1 0 2 g cm kyr over the past 20 kyr whereas carbonate accumulation rates have decreased dramatically from 0 6 1 0 g cm kyr in the glacial sections of the cores to 0 2 0 6 g cm kyr in the holocene the errors caused by the uncertainties in the age of the termination of the last glacial period have been investigated and results show that a range of 11 14 kyr leads to an error upper limit of about 30 in the estimation of caco3 dissolution rates the response time of caco3 and 230thex concentrations in the mixed layer of sediments due to an impulse of change in caco3 dissolution rate has also been discussed showing that the observed changes in carbonate dissolution may be explained in terms of a single or a continuous change depending upon the thickness of the mixed layer

wisconsin holocene paleoenvironment of the bering sea evidence from diatoms pollen oxygen isotopes and clay minerals abstract a core from the southeastern bering sea contains a depositional record of the wisconsin glacial interval and the holocene four lithologic units show distinctive changes in diatom species palynomorphs oxygen isotopes in diatom silica and clay minerals unit 4 the oldest probably represents the glacial advance of the early wisconsin and records extensive sea ice cover and a soggy herbaceous tundra on the exposed continental shelf unit 3 represents the stades and interstades of the middle wisconsin including an early period of high seasonal variability and a later period with expansion of winter sea ice in the basin and of tundra onshore unit 2 represents the late wisconsin glacial maximum and subsequent deglaciation with a tundra covered shelf sea ice cover increased to a maximum during which the surface waters were probably covered by sea ice throughout the year subsequent to the sea ice maximum the isotope ratios record a major meltwater event unit 1 represents the holocene with expansion of shrub tundra or scrub forest in the coastal upland and waters of increased temperature and salinity in the bering sea

planktonic foraminifera in the western north pacific during the past 150 000 years comparison of modern and fossil assemblages abstract planktonic foraminiferal abundance variations in 186 deep sea piston core tops from the western north pacific were used to create a calibration set to characterize the present day kuroshio gyre system q mode factor analysis helped identify six faunal assemblages 93 variance related to modern water masses two tropical assemblages differing in relative dissolution three assemblages representing subtropical subpolar and transitional conditions and a gyre margin assemblage lying between the kuroshio current and the mainland of asia multivariate regression produced transfer functions relating observed summer august and winter february sea surface temperatures sst to the assemblages with standard errors of estimate of 1 5 c and 2 5 c respectively data from 24 piston cores was used to interpret variations of the kuroshio gyre system during the past 150 000 yr stratigraphic control is based on oxygen isotopic measurements the extinction of pink pigmented globigerinoides ruber at 120 000 b p coiling direction changes in neogloboquadrina pachyderma north of 30 n and dissolution variations between resistant and fragile taxa major dynamic changes in the circulation of the kuroshio gyre occurred during the last two glacial maxima at 15 20 000 b p isotopic stage 2 and at 140 150 000 b p isotopic stage 6 these intervals are characterized by 1 lowered sea levels which reduced flow into the sea of japan and sea of okh okhotsk 2 advance of the polar front from its modern position at about 42 n to 35 38 n 3 southward penetration of the oyashio current along the pacific coast of japan to tokyo 4 2 3 c lowered sst in tropical areas little or no change in subtropical areas and a 4 6 c decrease in transitional areas and 5 an overall decrease in carbonate dissolution relative to interglacial stages the maximum interglacial at 120 000 b p isotopic substage 5e shows a retreat of the polar front north of its modern position and an overall relative increase in interglacial carbonate dissolution that does not become severe until substage 5d

removal of230th and231pa from the open ocean concentrations of230th and231pa were measured in particulate matter collected by sediment traps deployed in the sargasso sea site s2 the north equatorial atlantic site e and the north equatorial pacific site p as well as in particles collected by in situ filtration at site e concentrations of dissolved th and pa were determined by extraction onto manganese dioxide adsorbers at site p and at a second site in the sargasso sea site d dissolved230th 231pa activity ratios were 3 6 at sites p and d in contrast for all sediment trap samples from greater than 2000 m unsupported230th 231pa ratios were 22 35 average 29 7 ratios were lower in particulate matter sampled at shallower depths particles filtered at 3600 m and 5000 m at site e had ratios of 50 and 40 results show that suspended particulate matter in the open ocean preferentially scavenges th relative to pa most of the230th produced by decay of234u in the open ocean is removed by adsorption to settling particulate matter in contrast less than 50 of the231pa produced by decay of235u is removed from the water column by this mechanism mixing processes transport the remainder to other sinks

basin modelling a new comprehensive method in petroleum geology abstract integrated basin modelling is used to understand and reconstruct the geological and thermal evolution of a sedimentary basin to quantify this information and hence to derive among other results the history of generation migration and accumulation of petroleum this new methodical approach is rapidly gaining world wide recognition throughout the geo scientific community because it offers two distinct advantages when addressing geological problems firstly it enables a logical quantitative treatment of very complex interrelated geological processes and secondly it permits these processes to be examined on the basis of an absolute geological time scale the prerequisites for basin modelling are 1 the translation of logical and consistent geological concepts into numerical form and then into suitable computer programs and 2 the application of these programs using high speed computers with large memories using such an approach is an important part of modern petroleum exploration because 1 1 provision is made for total coverage of the basin by allowing extrapolation to non drilled often deeper parts of the basin accessible only by using seismic data 2 2 a three dimensional view of the basin can be constructed and followed through geological time 3 3 an internal logic is utilised which is consistent with physical and chemical laws 4 4 geological geophysical and geochemical data are integrated and modelled iteratively and therefore control each other this paper shows the rapidly widening scope of basin modelling and points out some of the present day limitations and necessary research directions for the future it describes concepts for modelling of tectonic processes and for simulating expulsion of liquid petroleum

accumulation rates of th 230 pa 231 and some transition metals on the bermuda rise abstract measurements of 238u 234u 230th 232th 231pa mn fe co ni cu and zn were made on 23 samples from core gpc 5 a 29 m giant piston core from a water depth of 4583 m on the northeastern bermuda rise 33 41 2 n 57 36 9 w this area is characterized by rapid deposition of sediment transported by abyssal currents unsupported 230th and 231pa are present throughout the core but because of large variations in the sedimentation rate show marked departures from exponential decay with depth the trend with depth of the 231 pa ex 230 th ex ratio is consistent with the average accumulation rate of 36 cm 1000 y reported earlier on the basis of radiocarbon dating and caco3 stratigraphy when expressed on a carbonate free basis concentrations of mn co ni cu zn 230thex and 231paex all show cyclic variations positively correlated with those of caco3 the correlations can be explained by a model in which all of these constituents including caco3 are supplied to the sediments from the water column at a constant rate concentration variations are controlled mainly by varying inputs of terrigenous detritus with low inputs occurring during interglacials and high inputs during glacials relationships between the metal and 230thex concentrations permit estimates of the rates at which the metals are removed to the sediment by scavenging from the water column the results in g cm2 1000 y are 4300 1100 for mn 46 16 for ni and 76 26 for cu these rates are somewhat larger than ocean wide averages estimated by other methods and the absolute rate of 230th accumulation in gpc 5 averages about nine times higher than production in the overlying water column this part of the bermuda rise and similar bottom current deposits may act as important accumulators of elements scavenged from seawater

boundary scavenging and deep sea sediment dating constraints from excess 230th and 231pa apparent sedimentation rates derived from excess 230th and 231pa in deep sea sediments accumulated during the last 25 000 years in the pacific ocean are mostly lower than the average rates determined by other independent such as 14c and 18o dating methods which may be a consequence of generally higher accumulation rates of aluminosilicate and carbonate during the last glacial that diluted the excess 230th and 231pa activities in glacial sediments the pattern of enhanced scavenging of nuclides in ocean margin areas i e boundary scavenging also changed from the glacial to the holocene fluxes of 230th and 231pa throughout the ocean varied over time responding to changes in the nature and intensity of boundary scavenging which in turn were influenced by changes in particle flux and particle composition the lower intensity of boundary scavenging of 231pa during the last glacial may also have contributed to the lower apparent sediment accumulation rates based on excess 231pa for cores in ocean margin areas

gas generation from source rocks aspects of a quantitative treatment abstract quantitative aspects of gas generation in source rocks are discussed first in terms of stoichiometric considerations based on the elemental compositions of different kerogen types i ii iii and coal the maximum amounts of available carbon and hydrogen for the formation of hydrocarbons during maturation were calculated considering a closed source rock system type i kerogen has the highest and coal the lowest specific gas yield the second part discusses the problem whether experimentally derived gross kinetic parameters activation energies and frequency factors can be applied to hydrocarbon generation reactions in the geological environment the third part comprises a detailed case history of gas formation in the upper carboniferous of northern germany for three selected wells in the study area the temperature histories were defined using a computer aided integrated basin modelling approach significantly different temperature histories in those three wells were then used to compute the gas generation from 320 myr ago to present the drastic influence of changes in the kinetic input parameters 50 or 54 kcal mol 1 for the activation energy of oil cracking on timing and duration of gas formation has been demonstrated the results confirmed that accurate knowledge of both the temperature history and the kinetic parameters is of equal importance

210pb scavenging in the north atlantic and north pacific oceans the radionuclide210pb shows significant geographic variations in the extent of its removal from the open ocean water column this texture of scavenging is defined by mapping 1 the integrated deficiency of210pb in the water column relative to its supply from the atmosphere and from in situ decay of dissolved226ra and 2 inventories of excess210pb in deep sea sediments the ratio of210pb deficiency to its supply termed the scavenging effectiveness is 20 in the north equatorial pacific and 50 in the north atlantic this variation is related to the combined effects of uptake of210pb onto sinking particles and lateral transport of210pb to areas of more intense removal sediment inventories of excess210pb normalized to the210pb deficiency in the overlying water column permit evaluation of the relative importance of these effects in the north equatorial pacific virtually all of the210pb removed from the water column is present in the underlying sediments but in the mid latitude north atlantic the sediments comprise only about 50 of the210pb removed the deficiencies of210pb in the mid latitude north atlantic sediments south of 50 n are qualitatively offset by surpluses in high latitude sediments north of 50 n higher primary productivity and new production in the surface waters of the high latitude north atlantic and north equatorial pacific relative to the oligotrophic central north atlantic may account for the greater fluxes of210pb to bottom sediments in those areas

geochemistry of eolian dust in pacific pelagic sediments implications for paleoclimatic interpretations geochemical data rees th sc were determined for the operationally defined eolian dust oded fraction 63 m of late quaternary sediment samples n 57 from the north and equatorial pacific ocean paleoclimate studies commonly have assumed that this sediment fraction represents eolian materials from continental source regions this study shows on the basis of geochemical data published mineralogical data and mixing models that the oded fraction actually is a mixture of materials from two endmember sources the continental crust eolian transported weathering products and the oceanic crust primarily volcanogenic material mixing model results show that the average ash content is significant in the oded fraction equatorial pacific 43 north pacific 24 we have used this information to reconsider and refine the results of previous paleoclimate studies in the northwest pacific the flux of the eolian fraction is greater during glacial stages and shows a latitudinal maximum between 35 n and 42 n eolian fluxes are greatest during interglacial periods in the equatorial pacific these results are consistent with previous interpretations in contrast to previous assumptions eolian mass accumulation rates may not be a valid indicator of paleo aridity because they are correlated with grain size furthermore the relative abundance of the two endmembers is correlated with the average grain size of the dust fraction the continental crust component is associated with larger grains this compositional effect should be considered in future studies which commonly utilize grain size as a proxy indicator of paleo wind intensity

extrapolation of the kinetics of oil and gas formation from laboratory experiments to sedimentary basins it is generally accepted that the formation of oil and gas from sedimentary organic matter or kerogen is adequately described by kinetic models based on first order kinetics with rate constants obeying an arrhenius equation these models which are extensively used in oil exploration to assess the petroleum potential of sedimentary basins are based on geological observations1 2 3 4 5 6 but are formally quite similar to models designed to simulate oil shale pyrolysis7 8 9 or coal processing10 11 12 the idea of blending these two approaches is not new see for example ref 2 but until now the most sophisticated attempts reproduced only the gross features of kerogen cracking on a geological timescale5 or were uncontrolled by geochemical measurements13 14 here we show that the kinetic parameters determined from the laboratory pyrolysis of an immature kerogen sample apply to the conditions of sedimentary basins altough the time and temperature scale are completely different

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

thermal evolution of sedimentary basins and significance for hydrocarbon generation abstract the temperature history of source rocks is especially important when considering kinetic aspects of hydrocarbon generation the thermal evolution of sedimentary basins is controlled by deep seated crustal mechanisms and by the sedimentary fill lithospheric phenomena e g rifting accretion are responsible for the principal variations in heat input changes in the thickness of the lithosphere cause variations in heat flow and hence in the temporal evolution of energy input at the base of sedimentary basin heat transfer within the basin occurs by conduction and convection a deterministic mathematical model based on an energy and mass balance approach is used to analyze the influence of various parameters on the thermal history of a basin consequently the role of heat flow sedimentation rates different lithologies surface and or sediment water interface temperatures erosional and nondepositional periods and pressures can be investigated comprehensively examples from modeling studies in different basins clearly demonstrate that the temperature history of a certain source rock is determined by the combined effects of these parameters no single parameter can be identified as the most important certain parameters dominate only during a specific period of basin evolution depending on the changing boundary conditions two source rocks at different depths and age levelsmore can be affected differently by the same boundary conditions modeling studies that emphasize single parameters such as only heat flow generally lead to erroneous results and misleading conclusions therefore in modeling studies the geologic evolution of an entire basin must be considered computer aided basin studies can numerically simulate all relevant geologic processes and more precisely reconstruct the temperature history throughout the basin less

geometry of isograds thermodynamic constraints on inversion abstract inverted isograds have been reported from metamorphic terrains ranging in age from precambrian to tertiary most of the workers believe that metamorphic inversion was caused by an inverted temperature gradient associated with large scale thrusting however isograds are not isotherms and the former may develop at large angles to the latter it is shown here that the orientation of isograds depends not only on the orientation of isotherms but also on the value of t p of an isograd reaction and that of the temperature gradients accordingly four different sets of conditions for inversion are recognised two for inverted temperature gradients one for a horizontal temperature gradient and one for a normal temperature gradient these conditions have been worked out for four different isograds staurolite in staurolite out muscovite breakdown and partial melting of granitic compositions it is shown that isograds may be in normal or inverted attitudes depending on the orientation and magnitude of the temperature gradient and also on the slope t p of an isograd reaction published accounts of metamorphic inversion do not provide all of these data but explain them in terms of only an inverted temperature gradient which may not be correct and may need re investigation

removal of 230th and 231pa at ocean margins abstract uranium thorium and protactinium isotopes were measured in particulate matter collected by sediment traps deployed in the panama basin and by in situ filtration of large volumes of seawater in the panama and guatemala basins concentrations of dissolved th and pa isotopes were determined by extraction onto mno 2 adsorbers placed in line behind the filters in the in situ pumping systems concentrations of dissolved 230 th and 231 pa in the panama and guatemala basins are lower than in the open ocean whereas dissolved 230 th 231 pa ratios are equal to or slightly greater than ratios in the open ocean particulate 230 th 231 pa ratios in the sediment trap samples ranged from 4 to 8 in contrast to ratios of 30 or more at the open ocean sites previously studied particles collected by filtration in the panama basin and nearest to the continental margin in the guatemala basin contained 230 th 231 pa ratios similar to the ratios in the sediment trap samples the ratios increased with distance away from the continent suspended particles near the margin show no preference for adsorption of th or pa and therefore must be chemically different from particles in the open ocean which show a strong preference for adsorption of th ocean margins as typified by the panama and guatemala basins are preferential sinks for 231 pa relative to 230 th furthermore the margins are sinks for 230 th and to a greater extent 231 pa transported by horizontal mixing from the open ocean

the scavenging of u 230th and 231pa during pulsed hydrothermal activity at 20 s east pacific rise abstract uranium th and pa isotopes were measured in eight box cores from two transects to the west of the east pacific rise at 10 s and 20 s sediment geochemistry al ca fe mn and water column paniculates mn suggest that highly metalliferous plumes rich in fe and mn are emanating from the rise crest at 19 s measurements of 230thxs and 231paxs indicate decreasing sediment accumulation rates from the rise flank 0 4 cm ky 1 to the tiki basin 0 23 cm ky 1 over this geographical area al is found to have a constant flux of 3 6 10 4 g cm 2 ky 1 application of an al constant flux model to ridge crest metalliferous sediment reveals two 1 000 year pulses of hydrothermal activity during the holoccne since 11 000 y bp these hydrothermal pulses are characterised by hydrothermal fe mn ratios 3 5 1 enhanced 230th and 231pa scavenging and low 230thxs 231paxs ratios 3 4 the similarity of the 230thxs and 231paxs ratio to the dissolved seawaterrauo suggests that in fracuonation of the isotopes occurs during scavenging supplementary supply of dissolved 230th and 231pa in a westwards moving water mass is suggested

equatorial pacific calcite preservation cycles production or dissolution in the equatorial pacific ocean the depth and shape of the calcite lysocline appears to have changed significantly in response to climate forcing farrell and prell 1989 taking the farrell and prell record at face value the lysocline apparently became steeper during each of the last eight glacial stages also the accumulation rate of calcite during the last glacial maximum was 2 4 times higher than it was during the previous interglacial arrhenius 1952 1988 broecker 1971 farrell 1991 a numerical model for calcite dissolution in sediment is used to interpret these observations the model was validated by comparison with observations from the present day ocean these results are presented elsewhere if the lysocline fluctuations in the equatorial pacific are primarily a dissolution record then changes in the glacial pacific co3 of 20 40 m can be inferred here i offer the alternative explanation that cycles in equatorial production are responsible for the observations higher rates of calcite and organic carbon rain to the sediment in the equatorial region would have depressed the calcite lysocline and increased the calcite accumulation rate as observed a twofold increase in glacial production appears to be adequate to explain the observations but a precise determination is prevented by uncertainties in some of the model parameters

transuranic nuclides in two coastal marine sediments off peru the fluxes of plutonium isotopes as well as their depth profiles are similar for northern and southern hemispheric varved sediments taken off western american coasts the inventories are in excess of the values predicted for atmospheric fallout in these anoxic sediments there is a general increase in concentration from depths to the near surface these observations are explainable on the bases that anoxic deposits have a substantially higher retentivity of sedimented materials compared to that of their bioturbated oxic counterparts and that there are inputs of resuspended materials previously deposited in the marine environment the 241am distributions are explained by ingrowth from 241pu assuming a substantial input of the parent from the u s thermonuclear tests during the 1950 s and the immobilization of both pu and am in the deposits

increased production of cosmogenic 10be during the last glacial maximum beryllium 10 half life 1 5 myr is produced by spallation of nitrogen and oxygen atoms by cosmic rays in the upper atmosphere its production rate is proportional to the flux of cosmic rays which is modulated by solar activity and the strength of the earth s magnetic field1 2 weakening of the magnetic field allows more cosmic rays to impinge on the earth s atmosphere thereby increasing 10be production here we report that the ocean wide average accumulation rate of 10be in pacific sediments which reflects the global average production rate of 10be ref 3 was at least 25 greater during the height of the most recent ice age 24 000 16 000 yr ago than during the holocene the past 10 000 yr the higher production rate of 10be records the lower intensity of the geomagnetic field during that period and is consistent with the hypothesis developed to explain the younger 14c ages of fossil corals compared with ages obtained by u th dating4 these results also point to a more general need to consider variations in production rate in geochronological studies using other cosmogenic nuclides

the distribution and behaviour of 230th and 231pa at an ocean margin baja california mexico uranium th and pa isotopes were measured in sediments collected by box core along a transect normal to the baja california continental margin six cores were analyzed ranging in depositional environment from manganese nodule bearing pelagic red clay to hemipelagic sediments displaying mn reduction in the upper 5 cm in the hemipelagic cores solid phase mn peaks due to diagenetic remobilization occur within the upper layers which are well mixed with respect to unsupported sup 230 th and sup 231 pa the fact that sup 230 th and sup 231 pa are not concentrated at the mn peaks suggests that little mobility of these nuclides occurs within the sediment column unsupported sup 230 th sup 231 pa activity ratios in the biomixed layer of the sediments range from 10 9 to 6 6 generally decreasing towards the inshore stations the flux of sup 230 th and sup 231 pa across the sediment water interface is almost in balance with the theoretical water column supply in the most distal core but rapidly increases inshore this evidence from the sediment column confirms that enhanced sup 230 th and sup 231 pa removal occurs at ocean margins and that sup 231 pa is removed from the water column to the sediments in preference to sup 230 th

thermal constraints on crustal rare gas release and migration evidence from alpine fluid inclusions the palfris marl of the helvetic alpine nappes contains four distinct vein fill generations ch4 rich gas is found in abundant fluid inclusions within these carbonate veins while free ch4 gas has also been produced from exploratory boreholes through this formation the stable isotope and helium neon and argon isotopic composition of these fluids has been determined a constant radiogenic 40ar concentration of 1 25 0 13 1 ppm in these differently sited fluids requires an intimate association between the 40arrad source and the hydrocarbon phase this can only be reasonably explained if the 40arrad was input into the hydrocarbon phase during hydrocarbon generation migration or storage prior to entrapment in the fluid inclusions stable isotope results constrain the maturity of hydrocarbon production while fluid inclusion formation pressures and temperatures record values of up to 2 5 kbars and 250 c these values place limits on the range of thermal conditions in which the hydrocarbon 40arrad relationship was established all fluids within inclusions also contain radiogenic 4he40ar values at predicted crustal production ratios these observations provide the first evidence that both 4herad and 40arrad can be quantitatively released on a regional scale bounded by the thermal conditions required to produce the hydrocarbon phase and the conditions under which the fluid inclusions were formed t 190 250 c these results require that negligible quantities of excess 40arrad decoupled from 4herad have been released into this system given the wide array of mechanisms which can potentially cause decoupling of these two species this result provides an important constraint on the role of these processes within the sedimentary fluid regime in contrast the free borehole gas contains excess radiogenic 4he and 21ne relative to 40arrad in proportions which can be accounted for by local production and subsequent diffusion from the surrounding marl the latter pattern is consistent with rare gas migration in lower temperature environments a conceptual model which considers both diffusional and metamorphic release of helium and argon and the ability of the surrounding fluid regime to transport the rare gases from their respective mineral production sites is consistent with both these results and data from regional rare gas studies

the distribution of 230th and 231pa in the deep sea surface sediments of the pacific ocean in order to determine the areal extent and distribution of 231pa sinks in the pacific ocean we have analyzed 34 deep sea surface sediment samples from widely distributed locations for their pa th and u isotopes while the 230thxs content varies by more than a factor often the 231paxs content is confined in a relatively narrow range with a mean value of 2 8 1 4 dpm g there is a positive correlation between 230thxs and 231paxs and using the regression line it is possible to calculate the 230thxs231paxs activity ratios in samples for which only 230th data are available we then constructed a map of 230thxs231paxs distribution using 230paxs231paxs 11 the production ratio in the water column as a criterion for identifying preferential 231pa sinks we have identified an area covering 30 40 of the pacific ocean this area includes most of the pacific margins the northwest pacific the antarctic ocean and perhaps the mid ocean ridge regions and is nearly coincident with that of high sediment accumulation rates this suggests that the paniculate flux is important for the removal of 231pa from the ocean two models for the removal of 231pa produced in the open ocean are 1 1 lateral transport into the vertical flux in regions of high particulate flux damaster 1979 andersonet al 1983a b or 2 2 uptake at the sediment water boundary the second model is more likely to be correct to distinguish unequivocally between the two proposed models we would need sediment trap data for the western north pacific

kinetic studies of asphaltene pyrolyses and their geochemical applications abstract pyrolysis kinetics are determined for a series of asphaltene samples associated with different types of kerogens the activation energy distributions obtained for asphaltenes related to type i kerogens cover a wide range with significant hydrocarbon generation with activation energies above 350 kj mol the ranges of activation energy distributions are relatively narrow for asphaltenes associated with type ii and iii kerogens with little hydrocarbons generated with activation energies above 350 kj mol if the type of associated kerogen can be reasonably constrained the pyrolysis kinetics of the asphaltenes is potentially a very useful tool for assessing the maturity levels of reservoired oils the results of pyrolysis kinetics indicate that there is still significant potential for asphaltenes to regenerate hydrocarbons

a mechanism for the formation of methane hydrate and seafloor bottom simulating reflectors by vertical fluid expulsion bottom simulating reflectors bsr are observed commonly at a depth of several hundred meters below the seafloor in continental margin sedimentary sections that have undergone recent tectonic consolidation or rapid accumulation they are believed to correspond to the deepest level at which methane hydrate clathrate is stable we present a model in which bsr hydrate layers are formed through the removal of methane from upward moving pore fluids as they pass into the hydrate stability field in this model most of the methane is generated below the level of hydrate stability but not at depths sufficient for significant thermogenic production the methane is primarily biogenic in origin the model requires either a mechanism to remove dissolved methane from the pore fluids or disseminated free gas carried upward with the pore fluid the model accounts for the evidence that the hydrate is concentrated in a layer at the base of the stability field for the source of the large amount of methane contained in the hydrate and for bsrs being common only in special environments strong upward fluid expulsion into the hydrate stability field does not occur in normal sediment depositional regimes so bsrs are uncommon upward fluid expulsion does occur as a result of tectonic thickening and loading in subduction zone accretionary wedges and in areas where rapid deposition results in initial undercconsolidation in these areas hydrate bsrs are common the most poorly quantified aspect of the model is the efficiency with which methane is removed and hydrate is formed as pore fluids pass into the hydrate stability field the critical boundary in the phase diagram between the fluid plus hydrate and fluid only fields is not well constrained however the amount of methane required to form the hydrate and limited data on methane concentrations in pore fluids from deep sea boreholes suggest very efficient removal of methane from rising fluid that may contain less than the amount required for free gas production in most fluid expulsion regimes the quantity of fluid moved upward to the seafloor is great enough to continually remove the excess chloride and the residue of isotope fractionation resulting from hydrate formation thus as observed in borehole data there are no large chloride or isotope anomalies remaining in the local pore fluids the differences in the concentration of methane and probably of co2 in the pore fluid above and below the base of the stability field may have a significant influence on early sediment diagenetic reactions

generation of nitrogen and methane from sedimentary organic matter implications on the dynamics of natural gas accumulations nitrogen n2 contents of natural gases in rotliegend and buntsandstein reservoirs of the north german basin regionally approach 100 a review is given of the various hypotheses primordial origin volcanic or magmatic origin radiogenic origin atmospheric origin organic origin inorganic nitrogen in sedimentary rocks presented to account for nitrogen anomalies in this area and other parts of the world the objective of the present study was to investigate sedimentary organic matter in particular coals as a potential source of molecular nitrogen in the subsurface comparison of reservoir sizes and gas generation potentials indicates that carboniferous coal measures which are considered as the source of the natural gas in the north german basin can readily account for the nitrogen quantities found in present day reservoirs laboratory pyrolysis experiments were carried out to investigate the kinetics of generation of methane and molecular nitrogen from coals of different type and rank under experimental conditions nitrogen is formed at higher temperatures than methane supporting the concept of a fractional generation of methane and nitrogen in natural systems based on the kinetic parameters derived from laboratory experiments methane and nitrogen generation rates from coals were calculated for geologic heating rates gas containing more than 50 nitrogen is generated under these conditions at temperatures in excess of 300 c nitrogen rich gases are thus formed only in the final stage of gas generation after methane generation has practically ceased it is concluded that the amounts of gas encountered in nitrogen rich gas accumulations represent only a small fraction possibly 1 of the total gas generation potential of this area while the bulk of the generated gas has escaped to the atmosphere the present day composition of the reservoir gases reflects the composition of only the most recently generated gas on a geologic time scale

asian aridity and the zonal westerlies late pleistocene and holocene record of eolian deposition in the northwest pacific ocean rea d k and leinen m 1988 asian aridity and the zonal westerlies late pleistocene and holocene record of eolian deposition in the northwest pacific ocean palaeogeogr palaeoclimatol palaeoecol 66 1 8 a 30 000 year record of eolian deposition in the northwestern pacific ocean provides a history of the aridity of the asian source region and information on the changing latitude and intensity of the zonal westerlies the position of the maximum in eolian flux to the deep sea remained unchanged at 38 to 40 n during this entire time period but the dust flux record of aridity is greatest 6000 years ago at the holocene climatic optimum eolian grainsize data indicate that the northern margin of the westerly jet stream retreated northward during the holocene to a poleward extreme at about 6000 years ago and then moved back toward the equator the change in wind intensity across this margin was continually reduced throughout the holocene these sorts of data enhance our understanding of the behavior of the atmosphere during times of climate change and can be used to test computer generated models of past climatic conditions

paleoproductivity and carbon burial across the california current the multitracers transect 42 n the multitracers experiment studied a transect of water column sediment trap and sediment data taken across the california current to develop quantitative methods for hindcasting paleoproductivity the experiment used three sediment trap moorings located 120 km 270 km and 630 km from shore at the oregon california border in north america we report here about the sedimentation and burial of particulate organic carbon corg and caco3 in order to observe how the integrated caco3 and corg burial across the transect has changed since the last glacial maximum we have correlated core from the three sites using time scales constrained by both radiocarbon and oxygen isotopes by comparing surface sediments to a two and a half year sediment trap record we have also defined the modern preservation rates for many of the labile sedimentary materials our analysis of the corg data indicates that significant amounts 20 40 of the total corg being buried today in surface sediments is terrestrial at the last glacial maximum the terrestrial corg fraction within 300 km of the coast was about twice as large such large fluxes of terrestrial corg obscure the marine corg record which can be interpreted as productivity when we corrected for the terrestrial organic matter we found that the mass accumulation rate of marine corg roughly doubled from the glacial maximum to the present because preservation rates of organic carbon are high in the high sedimentation rate cores corrections for degradation are straightforward and we can be confident that organic carbon rain rate new productivity also doubled as confirmation the highest burial fluxes of other biogenic components opal and ba also occur in the holocene productivity off oregon has thus increased dramatically since the last glacial maximum caco3 fluxes also changed radically through the deglaciation however they are linked not to caco3 production but rather to changes in deepwater carbonate chemistry between 18 ka and now

a 150 000 year climatic record from antarctic ice during much of the quaternary the earth s climate has undergone drastic changes most notably successive glacial and interglacial episodes the past 150 kyr includes such a climatic cycle the last interglacial the last glacial and the present holocene interglacial a new climatic time series for this period has been obtained using 18 o data from an antarctic ice core

late pleistocene paleoclimatology of the central equatorial pacific flux patterns of biogenic sediments high resolution records of the concentration and mass accumulation rate mar or flux of biogenic sediments from core rc11 210 in the central equatorial pacific are compared for the entire late pleistocene the fluxes of calcium carbonate and organic carbon correlate well the opal flux pattern shows no direct correlation with the other two rather opal flux maxima correlate with slopes of i e both precede and follow the organic carbon and carbonate mar peaks organic carbon and calcite therefore may both be better indicators of past productivity than opal which is an indicator of transition at this location we interpret the sequence low biogenic fluxes high opal fluxes high carbonate carbon and opal fluxes as representing the transition from low to high sea surface biological productivity the phase relationships for eccentricity of the biogenic sedimentation records were compared to those of other climatic indications including the oxygen isotope record of ice volume the ice core co2 record the pacific 13c record the deep nutrient cd ca record and the eolian grain size record of wind intensity we find that starting from maximum ice volume phase angle of 0 the phase relationships of the 100 000 year periodicity show in the first quadrant maximum wind intensity 30 and maximum calcite and carbon flux 45 occurring first followed by maximum opal flux 75 and then maximum deep nutrients 95 minimum pacific 13c occurs at a phase angle of 155 the maximum co2 in the vostok record and minimum ice volume is at 180 thus in the eccentricity climate cycle glacial conditions lead to stronger wind driven circulation which enhances productivity which in turn results in enhanced oceanic and atmospheric carbon dioxide and minimum ice volume