synoptic climatology and intrahemispheric associations of cold air mesocyclones in the australasian sector satellite ir images for seven months in 1992 are interpreted for cold air mesoscale cyclones mesocyclones occurring in the australasian sector 70 e 150 w of the southern ocean time averaged monthly seasonal distributions of mesocyclogenesis mesocyclolysis and tracks of movement along with statistical summaries of mesocyclone attributes e g cloud vortex size speeds of movement are presented and discussed in the context of the larger scale atmospheric circulation maximum frequencies of mesocyclones occurred in the transitional months of april and october 1992 with a secondary peak in july statistically significant differences in mesocyclone track length between months appear related dominantly to changes in speed of the background flow associated with the semiannual oscillation sao of tropospheric pressure height the associations of mesocyclone outbreaks with composite anomaly fields of pressure and height are identified for three subareas of the australasian sector suggested by the analysis of mesocyclone spatial patterns outbreaks occur in the strong southerly geostrophic airflow located between pressure and height anomalies that are negative positive to the eastward westward when outbreaks occurred in the new zealand subarea in 1992 a similarly strong couplet of pressure height anomalies developed in the southern south america antarctic peninsula sector but not when outbreaks occurred south of australia the mesocyclone remote association that is suggested is evaluated by using polar orbiter ir imagery for the southeastern pacific region frequencies of mesocyclones increase decrease west of chile but decrease increase through drake passage when mesocyclone outbreaks occur near new zealand south of australia these long distance associations of mesocyclone outbreaks are consistent with the connectivity of the baroclinic waves and might prove useful in the development of techniques to forecast mesocyclones over the southern ocean

geochemistry of the alginite and amorphous organic matter from type ii s kerogens abstract maceral fractions of the type ii s kerogens from the monterey formation miocene california u s a and duwi formation campanian maastrichtian egypt were separated by density gradient centrifugation the monterey fm kerogen sample was comprised chiefly of light red fluorescing amorphous organic matter aom the flash pyrolyzate of which was characterized by a predominance of alkylbenzenes alkylthiophenes and alkylpyrroles in contrast the pyrolyzates of its alginite concentrate showed a highly aliphatic character typical of this maceral with the series of n alkenes and n alkanes c6 c26 predominating the pyrolyzate of the dominant light brown fluorescing aom of the duwi fm kerogen had a relatively high concentration of alkylbenzenes and alkylthiophenes while its alginite concentrate showed a more aliphatic character upon pyrolysis there was a marked enrichment of thiophenic sulfur in the light colored aom of both samples and also pyrrolic nitrogen in the case of the monterey relative to the alginite the results support a bacterially mediated degradative origin for type ii s amorphous organic matter with algal remains as the primary source of the kerogen

a critical reappraisal of preconsolidation pressure interpretations using the oedometer test over the past 70 years a number of methods have been proposed for the interpretation of the characteristic vertical effective yield stress or preconsolidation pressure of compressible soils as defined using the standard oedometer test the concept of the preconsolidation pressure has been extraordinarily useful in geotechnical engineering for analysing and predicting settlement behaviour and for normalizing other engineering parameters for comparative purposes defining this characteristic stress however is often problematic and relies heavily on graphical techniques that are subject to some uncertainty particularly when using semi log plots for this purpose this paper illustrates fundamental difficulties with the interpretation of oedometer test and presents an alternative technique for defining unambiguous values of the vertical effective yield stress

impact of suboxia on sinking particulate organic carbon enhanced carbon flux and preferential degradation of amino acids via denitrification fluxes of particulate organic carbon poc through the oxygen deficient waters in the eastern tropical north pacific were found to be relatively less attenuated with depth than elsewhere in the eastern north pacific the attenuation coefficient b for the flux was found to be 0 40 versus the composite value of 0 86 determined by martin et al 1987 to examine this further sinking poc was collected using sediment traps and allowed to degrade in oxic and suboxic experiments using a kinetic model it was found that degradation proceeded at similar rates roughly 0 8 day 1 under oxic and suboxic conditions but a greater fraction of bulk poc was resistant to degradation in the suboxic experiments 61 vs 23 amino acids accounted for 37 of poc collected at 75m but following degradation the value dropped to 17 and 16 in the oxic and suboxic experiments respectively poc collected from 500m was 10 amino acids the non aa component of poc collected at 75m was not degraded under suboxic conditions while under oxic conditions it was these results suggest that microbes degrading oc under suboxic conditions via denitrification preferentially utilize nitrogen rich amino acids this preferential degradation of amino acids suggests that 9 more nitrogen may be lost via water column denitrification than is accounted for when a more redfieldian stoichiometry for poc is assumed

cometary impacts into ocean their recognition and the threshold constraint for biological extinctions the montagnais impact crater is presently the only site in the ocean where the effect of a meteorite fall on marine organisms has been studied the impact crater is 45 km in diameter and was formed at 50 8 ma by a fall of probably an old cometary nucleus 3 4 km in diameter into shallow 600 m ocean comparison of the impact structure and related deposits with those on land shows several major differences of which the most significant is the absence of an elevated crater rim instead the crater perimeter is bevelled and eroded as a consequence of impact induced bottom currents and turbulent return water flow into the excavating cavity by this process most of the fall out breccia is reworked back into the crater cavity where it accumulates in much larger thickness than in impact craters on land at a microscopic scale the shock metamorphism features are about the same as those for land impacts geochemically impacts of comet nucleii may not leave a recognizable signature at the impact horizon except for a minor increase in iridium thus stratigraphic horizons associated with extinctions and or major changes in biota have to be closely examined for other impact indicators like the presence of tectites glass spherules and quartz grains with shock features occurrence of megatsunami wave deposits extensive erosion on continental margins margin failures and faunal mixing above erosional unconformities are other potential impact indicators there is no single indicator that can provide sufficient proof of an impact event such interpretations have to be based on multiparameter studies of global extent since many of the impact indicators are only of regional extent the lack of extinction of any marine plankton genera or of bottom dwellers at the montagnais impact site allows us to place a lower limit for biological extinctions caused by cometary impacts on those with nucleus 4 km in diameter the calculated frequency for a cometary impact which could result in a 10 extinction of marine genera is about 6 10 7 yr 1 and for the k t boundary type of extinctions about 2 10 8 yr 1 even allowing for a large degree of uncertainty in these estimates it is unlikely that the biological extinction events for the last 250 ma identified by sepkoski 1990 could have been all caused by meteorite impacts

sulfurized carbohydrates an important sedimentary sink for organic carbon abstract in contrast to the general belief that carbohydrate carbon ccho is preferentially degraded and is not extensively preserved in the sedimentary record it is shown here that ccho forms a large fraction of the organic matter om of the total organic carbon toc rich upper jurassic kimmeridge clay formation as a result of early diagenetic sulfurization a previously unrecognized pathway of om preservation this is evident from both changes in the molecular composition of the insoluble om and from 13ctoc shifts of 6 with varying ccho contents furthermore experiments simulating the natural sulfurization of the ccho rich alga phaeocystis spp demonstrated that sulfurization can indeed lead to a substantial preservation of ccho with a molecular fingerprint identical to that of the kimmeridge clay and many other recent and ancient marine om rich sediments these results imply that preservation of ccho can exert a fundamental control on 13ctoc in om rich sediments complicating the interpretation of 13ctoc records with regard to estimating terrestrial versus aquatic om fractions reconstruction of past atmospheric co2 levels and global carbon budget models

sources and deposition of organic matter in cretaceous passive margin deep sea sediments a synthesis of organic geochemical studies from deep sea drilling project site 603 outer hatteras rise abstract the results of organic geochemical studies of rock samples from cretaceous strata at site 603 on the outer hatteras rise are reviewed and integrated with their lithostratigraphic information although most of the strata contain little organic carbon black shales enriched in organic matter were found in two settings these rocks exist as claystones in the aptian to turonian hatteras formation and as marlstones in the neocomian blake bahama formation terrigenous organic matter predominates in these deposits except in cenomanian and valanginian rocks where marine material becomes dominant organic carbon concentrations in cenomanian black claystones are higher than any previously reported from the western north atlantic but lower than the concentrations found in the eastern north atlantic black shales at site 603 appear to result from downslope transport and rapid reburial of coastal and ocean margin sediments by turbidity flows deep basin anoxia is not a major factor except during the cenomanian turonian when the entire atlantic ocean may have briefly become anoxic organic matter in the sediments from all locations is thermally immature

the influence of lateral spreading on settlements beneath a fill the discrepancy between calculated consolidation settlements and measured settlements under a 3 8 m high section of an earth embankment is investigated in this paper a conventional one dimensional analysis underestimated the observed settlement by 40 a two dimensional finite element analysis was carried out to assess the effects of lateral spreading on vertical movements and the results were in close agreement with the measured values key words case history consolidation finite element analysis settlement

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

volcanism around k t boundary time its role in an impact scenario for k t extinction events abstract a widespread debate on the cretaceous tertiary k t boundary 65 1 ma extinctions has largely revolved around an impact or a volcanic cause evidence for both events is strengthened by recent work impact triggered deccan volcanism or independent impact and mantle plume events have been suggested this review examines evidence for both events and suggests that they overlapped in time but with globally uneven effects the combined effects produced generally inhospitable k t environments leading to mass extinctions although some life forms flourished afterwards volcanic contributions to the k t boundary environment probably include increased platinum group element pge and acid rain fall out particularly from large scale mantle upwellings e g deccan cameroon and coral sea events a previously proposed post k t greenland starting plume apparently already existed in the cretaceous k t features such as the iridium ir anomaly most likely include longer term volcanic as well as sudden meteoritic impact contributions volcanic contributions were greatest from southern hemisphere sources whereas meteorite impacts featured in the northern hemisphere

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

quantifying rates of methanogenesis and methanotrophy in lake kinneret sediments israel using pore water profiles full seasonal sets of chemical and isotope profiles from the pore water of lake kinneret sea of galilee israel were produced to study methanogenesis and methanotrophy processes and the couplings between methane ch4 sulfur and iron sulfate is depleted within the upper 10 cm of the sediment mainly by traditional bacterial sulfate reduction by organic matter maximum sulfate reduction rates calculated from sulfate concentration profiles are found at the water sediment interface 0 1 cm 2 1 4 3 10212 6 0 2 3 10212 mol cm23 s21 ch4 concentrations and modeling of dissolved inorganic carbon dic and its stable carbon isotope d13cdic suggest that maximum methanogenesis rates of 2 5 3 10213 6 1 5 3 10213 mol cm23 s21 occur at 5 12 cm depth in the sediments and that it ends at 20 cm of the produced ch4 50 75 is converted to gas bubbles of ch4 before it reaches the bottom water model results suggest the occurrence of anaerobic oxidation of ch4 aom in the deep sediments of the lake below the zone of methanogenesis methane ch4 is an important greenhouse gas with emissions from anthropogenic and natural sources roughly estimated to be around 350 and 120 tg c yr 21 tg 2 1 3 1012 g respectively wuebbles and hayhoe 2002 among the natural sources continental emissions contribute more than 70 wuebbles and hayhoe 2002 however the parameters controlling these emissions are not well understood therefore it is essential to resolve the rate of the processes behind ch4 emissions from continental systems this study aims at this objective investigating lacustrine environment using a geochemical approach ch4 in its natural sources is produced mainly through microbial processes methanogenesis chemical profiles in pore water of organic rich sediments indicate that various microbes use a series of electron acceptors during the remineralization of organic matter in the order of decreasing chemical potential and methanogenesis accounts for the last stage of the microbial respiration in stratified lakes developing an anoxic hypolimnion methanogenesis and sulfate reduction are key terminal

quantification of co occurring reaction rates in deep subseafloor sediments net rates of biogeochemical reactions in subseafloor sediments can be quantified from concentration profiles of dissolved reactants or products and physical properties of the sediment to study net rates of microbial activities in deep sediments we developed a robust approach that is well suited to use over a broad range of sediment depths our approach is based on a finite difference solution to a continuity equation that considers molecular diffusion sediment burial fluid advection and reaction under the assumption of steady state numerical procedures are adopted to identify the maximum number of depth intervals with statistically different reaction rates the approach explicitly considers downcore variation in physical properties and sample spacing uncertainties in the rate estimates are quantified using a monte carlo technique we tested our approach using synthetic concentration profiles generated from analytical solutions to the continuity equation we then applied the approach to concentration profiles of dissolved sulfate sulfide methane and manganese in the 420 m thick sediment column of eastern equatorial pacific ocean drilling program site 1226 our results indicate that i sulfate reduction and iron reduction occur at most sediment depths ii net methane production occurs in discrete depth intervals and iii manganese reduction occurs near the seafloor and deep in the sediments these results provide quantitative evidence that multiple respiration pathways co exist in the same depth intervals of these deep subseafloor sediments

the biogenic methane potential of european gas shale analogues results from incubation experiments and thermodynamic modelling abstract core samples from the lower jurassic posidonia shale lower toarcian wealden black shales both from the lower saxony basin northern germany and from the cambrian ordovician alum shale southern sweden have been investigated for their biogenic gas potential in incubation experiments the sample set represents all stages of thermal maturity from immature to overmature methane and to a higher degree carbon dioxide are generated from all samples by added microorganisms in general overmature samples rr 1 5 show lowest gas generation rates the highest generation rates for produced methane up to 89 mol g 1 day 1 and carbon dioxide 139 mol g 1 day 1 were detected in immature alum shale samples when different hydrocarbon degrading inocula where added whereas the lowest methane production rates were detected in wealden sediments the lightest 13c values for produced methane and carbon dioxide have been detected in posidonia shale samples of oil window maturity such samples are some of the most sensitive for gas generation and exhibit the strongest decreases of hydrogen indices after incubation hydrogeochemical modelling of methane generation fate and behaviour showed that methane formed during the early diagenesis got lost from posidonia shale the mainly investigated shale in this study as the mature posidonia shale is according to the incubation experiments still sensitive for gas generation a production scenario of generically generated methane due to oil degradation is simulated the basic conditions resemble the conditions in the antrim shale in the michigan basin gas production due to dewatering and pressure decrease results in an increase of the gas volumes coupled to a progressive enrichment of carbon dioxide in the produced gas moreover calcite scaling may be the consequence during progressive production similar to the antrim shale in the michigan basin such calcite precipitation has been demonstrated to predominantly occur in natural samples at oil window maturity

diagenesis of organic matter in a 400 m organic rich sediment core from offshore namibia using solid state 13c nmr and ftir abstract although rates and mechanisms of early diagenesis have been well studied the effects of microbial metabolism on the molecular composition of the sedimentary organic matter som over long periods of time need more investigation in this study we characterize the early diagenesis of marine som from organic rich sediments of the ocean drilling program site 1082 located off namibia in the vicinity of the benguela coastal upwelling system we used both fourier transform infrared spectroscopy ftir and nuclear magnetic resonance spectroscopy 13 c nmr to assess the quantitative partitioning of the organic carbon into major compound classes aliphatic aromatic ester carboxylic amide and carbons from carbohydrates then we calculate the som composition in the main biomolecules proteins carbohydrates lipids and lignin on the basis of previous 13 c nmr based estimates of the molecular composition of the organic mixtures results show that the som is still labile at 7 m below the seafloor mbsf and composed of about 25 proteins and 15 carbohydrates with increasing depth the protein content exponentially decreases to 13 at 367 mbsf whereas the carbohydrate content decreases linearly to 11 the lignin and lipid content consistently represent around 10 and 40 of the som respectively and show an increase with depth due mostly to selective enrichment as the more labile components are lost by degradation thus these components of the som are considered refractory at the depth scale considered the calculated remineralization rates are extremely slow ranging from 5 6 mol c m 3 ky 1 at the top of the core to 0 2 mol c m 3 ky 1 according to the organic carbon flux to the seafloor knowing the labile carbon losses we propose a method to calculate the initial toc before the diagenesis took place

15n 14n variations in cretaceous atlantic sedimentary sequences implication for past changes in marine nitrogen biogeochemistry at two locations in the atlantic ocean dsdp sites 367 and 530 early to middle cretaceous organic carbon rich beds black shales were found to have significantly lower 15n values lower15n 14n ratios than adjacent organic carbon poor beds white limestones or green claystones while these lithologies are of marine origin the black strata in particular have 15n values that are significantly lower than those previously found in the marine sediment record and most contemporary marine nitrogen pools in contrast black organic carbon rich beds at a third site dsdp site 603 contain predominantly terrestrial organic matter and have c and n isotopic compositions similar to organic matter of modern terrestrial origin the recurring15n depletion in the marine derived cretaceous sequences prove that the nitrogen they contain is the end result of an episodic and atypical biogeochemistry existing isotopic and other data indicate that the low15n relative abundance is the consequence of pelagic rather than post depositional processes reduced ocean circulation increased denitrification and hence reduced euphotic zone nitrate availability may have led to cretaceous phytoplankton assemblages that were periodically dominated by n2 fixing blue green algae a possible source of this sediment15n depletion lack of parallel isotopic shifts in cretaceous terrestrially derived nitrogen site 603 argues that the above change in nitrogen cycling during this period did not extend beyond the marine environment

multiple factors in the origin of the cretaceous tertiary boundary the role of environmental stress and deccan trap volcanism a review of the scenarios for the cretaceous tertiary k t boundary event is presented and a coherent hypothesis for the origin of the event is formulated many scientists now accept that the event was caused by a meteorite impact at chicxulub in the yucatan peninsula mexico our investigations show that the oceans were already stressed by the end of the late cretaceous as a result of the long term drop in atmospheric co2 the long term drop in sea level and the frequent development of oceanic anoxia extinction of some marine species was already occurring several million years prior to the k t boundary the biota were therefore susceptible to change the eruption of the deccan traps which began at 66 2 ma coincides with the k t boundary events it erupted huge quantities of h2so4 hcl co2 dust and soot into the atmosphere and led to a significant drop in sea level and marked changes in ocean temperature the result was a major reduction in oceanic productivity and the creation of an almost dead ocean the volcanism lasted almost 0 7 m y extinction of biological species was graded and appeared to correlate with the main eruptive events elements such as ir were incorporated into the volcanic ash possibly on soot particles this horizon accumulated under anoxic conditions in local depressions and became the marker horizon for the k t boundary an oxidation front penetrated this horizon leading to the redistribution of elements the eruption of the deccan traps is the largest volcanic event since the permian triassic event at 245 ma it followed a period of 36 m y in which the earth s magnetic field failed to reverse instabilities in the mantle are thought to be responsible for this eruption and therefore for the k t event we therefore believe that the k t event can be explained in terms of the effects of the deccan volcanism on an already stressed biosphere the meteorite impact at chicxulub took place after the onset of deccan volcanism it probably played a regional rather than a global role in the k t extinctions

fractionation of ruthenium from iridium at the cretaceous tertiary boundary new data on ru ir abundance ratios are presented for nonmarine hell creek montana frenchman river saskatchewan and marine cretaceous tertiary boundary sites brazos river texas beloc haiti dsdp 577 and dsdp 596 the ru ir ratio varies from 0 5 to 1 within 4000 km of chicxulub and increases to 2 3 at paleodistances 65 ma of up to 12 000 km from the impact site for ci chondrites ru ir 1 5 a ballistic model of ejecta cloud cooling and expansion which employs the available vapor pressure versus temperature data for ru and ir predicts qualitatively similar global variation in the ru ir ratio but by only a factor of 1 5 we infer that several other factors such as remobilization of pge during diagenesis preferential oxidation of ru condensation kinetics and atmospheric chemical and circulation processes may account for the observed larger ru ir variation

cretaceous black shales as active bioreactors a biogeochemical model for the deep biosphere encountered during odp leg 207 demerara rise abstract a transport reaction model was designed to identify the combination and importance of biogeochemical processes operating in four sites drilled during odp leg 207 demerara rise equatorial atlantic almost 100 ma after their deposition deeply buried cretaceous black shales still act as active bioreactors in great sediment depths and control the biogeochemical reaction network of the whole sediment column according to a model calibrated at the four drill sites through inverse modeling techniques methanogenesis could be identified as a key process that dominates not only organic matter degradation but also sulfate availability through the anaerobic oxidation of methane above the black shales a complete depletion of sulfate within the black shale sequences promotes the remobilization of biogenic barium that reprecipitates as authigenic barite at the top of the sulfate depletion zone temporal dynamics of degradation processes caused continuous shifts of the barite precipitation zone during burial thus inhibiting the formation of an authigenic barite front or causing the dissolution of earlier formed fronts major deviations of pore water sulfate profiles from a linear gradient coincide with depths of decelerated or accelerated transport caused by local porosity minima or maxima model determined reaction rates are by far lower than those found in shallower sediments due to the low metabolic activities that are characteristic for the deep biosphere but even after almost 100 ma changing organic matter quality still influences the degradation within the black shale sequences as it is indicated by model results

kerogen asphaltene sulfur relationships in sulfur rich monterey oils abstract monterey oils in the santa maria basin onshore and offshore are generally low maturity oils because of low thermal exposure relatively shallow burial for short times they are generated as heavy high sulfur oils because of the composition of the unusual type ii source kerogens which are exceptionally rich in organic sulfur 8 14 these high sulfur kerogens which we designate type ii s appear to generate oil at significantly lower thermal exposures than ordinary type ii kerogens with less than 6 s in contrast to common type ii kerogens which generate oil largely by cleavage at oxygen bridge groups and carbon carbon bonds eliminating co2 h2o and hydrocarbon fragments type ii s kerogens have an additional complement of weak bonds associated with bound sulfur the preferential cleavage at weak sulfur linkages tends to produce larger fragments leading to high initial amounts of asphaltenes resins and sulfur rich aromatics together with smaller amounts of saturated hydrocarbons elemental analyses of monterey kerogens and asphaltenes clearly support the concept that the asphaltenes are essentially fragments of kerogen cleaved sufficiently to be soluble or peptized in this heavy oil system solubilization of asphaltenes is attributed to their interactions with the abundant resins and aromatics this sysstem is sufficiently stable under source and reservoir conditions to allow expulsion and migration for reasonable distance without significant fractionation or changes in gross properties initial asphaltenes have essentially the same atomic h c ratios as the source kerogen but have significantlyy lower o c ratios and slightly lower s c ratios the n c ratios are nearly the same for kerogens and their derived asphaltenes with increasing maturity the h c ratios in asphaltenes decrease much like maturation changes in kerogen the s c ratio also decreases significantly however the o c ratios initially low in asphaltenes and n c ratios increase slightly due to material balance caused by other losses these element composition and atomic ratio relationships allow some important inferences concerning source kerogen composition from analysis of asphaltenes alone this can be useful when potential source rock samples are not available for analysis and or when a choice between alternate source rock possibilities must be made

kerogen origin evolution and structure kerogen commonly defined as the insoluble macromolecular organic matter om dispersed in sedimentary rocks is by far the most abundant form of om on earth this fossil material is of prime importance as the source of oil and natural gas moreover kerogen can provide essential information on major topics such as past environments climates and biota this review reports the main advances in kerogen studies since the comprehensive synthesis edited by durand durand b ed kerogen insoluble organic matter from sedimentary rocks editions technip paris 1980 it is organized into eight sections the first two are concerned with the successive definitions of kerogen and the definition used here the different techniques used for kerogen isolation without loss or degradation and basic kerogen analysis the third and fourth focus on sedimentary om sources and preservation processes in relation to depositional environment including sedimentation conditions favourable for kerogen accumulation and extrapolation to past geological time great strides have been made in the latter topics over the last 25 years owing to a combination of classical studies in organic geochemistry and studies in other domains such as biogeochemistry oceanography hydrology and soil science along with the development of powerful analytical tools the next two sections deal with the different kerogen classifications by type and kerogen evolution and maturation upon burial in sediments structural modelling of coal and kerogen based on physical and or chemical structural analysis is described in the following section although only statistical the models thus derived provide a synthetic view of the main structural resemblances and differences among various samples in relation to source maturity or physicochemical properties finally the last section explores some of the advances in kerogen understanding expected for the near future the review includes a list containing about 500 references

nitrogen cycling during the cretaceous cenomanian turonian oceanic anoxic event ii low 15n values ranging from 1 2 to 3 9 and atomic carbon nitrogen c n ratios of 25 50 are characteristic of black shales deposited during the cenomanian turonian boundary interval and oceanic anoxic event ii oae ii an observed antithetic relationship between c n ratios and 15n could suggest a predominance of terrestrially derived organic matter or a diagenetic control on 15n variability shifting bulk 15n values lower however hydrogen indices hi generally 450 and a positive correlation of hi with c n mitigates against a significant terrestrial organic matter fraction high c n values are likely the result preferential degradation of labile n rich compounds during early diagenesis and loss of n as ammonium from sediments through time a hypothetical model that considers the degradation of a 15n enriched labile protein fraction yields only small 1 2 negative shifts in 15n however 15n depletion during diagenesis is contrary to normal isotope kinetics which should result in 15n enrichment of bulk organic matter therefore we conclude that the bulk 15n values in this study reflect primary changes in the nitrogen cycle the 15n data support the hypothesis of expanded nitrogen fixation driven by upwelling of nutrient nitrogen poor phosphorus replete waters during oae ii and from the mid cenomanian to santonian at demerara rise the low 15n values which are significantly lower than bulk 15n values in modern regions where nitrogen fixation is known to be important probably result from a more significant fraction of dissolved inorganic nitrogen being produced by nitrogen fixation during the peak of oae ii a marked shift to lower 15n values is observed this shift possibly reflects greater utilization of 15n depleted ammonium during a chemocline upward excursion cue dominance of low 15n values from other periods of more widespread marine anoxia is likely the result of similar processes

chemical composition of north american microtektites and tektite fragments from barbados and dsdp site 612 on the continental slope off new jersey abstract we have determined the major element and trace element content of tektite fragments and microtektites found in deep sea sediments from barbados and dsdp site 612 on the continental slope off new jersey the major element and trace element contents were determined using energy dispersive x ray analysis and instrumental neutron activation analysis respectively the compositions are consistent with the conclusion that the samples from both occurrences belong to the north american tektite strewn field the chemistry of the samples from both occurrences is however not identical with the bediasite or georgianite chemistry there are differences especially in the lower sodium and higher k and cr and possibly higher volatile element contents of the tektite fragments from dsdp site 612 the differences in chemistry between bediasites georgianites and the tektites from the sites analyzed here show that there are geographical variations in composition in the north american strewn field like in the czechoslovakian or australasian strewn field the relatively high volatile element contents e g sb and au of the site 612 tektite fragments together with the occurrence of mineral inclusions and a layered structure of some specimens indicates that these specimens are or close to muong nong type tektites if the dsdp site 612 tektites are muong nong type then the source crater has to be close to that site and is therefore probably on the continental shelf as had previously been suggested tektites on land usually occur in deposits which are much younger than the tektites the so called age paradox the association of tektites and microtektites together in one layer with a stratigraphic age that is consistent with the radiometric age would seem to resolve this paradox

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

determination of organic degradation rates in 100 my old sediments application to cretaceous black shale intervals from demerara rise odp leg 207 abstract thick organic rich albian to santonian black shale sequences were recovered from ocean drilling program sites 1261 and 1257 on the demerara rise offshore surinam at depths of 564 and 174 m below seafloor bsf respectively total organic carbon toc concentration varies between 3 9 and 17 3 wt rock eval pyrolysis parameters and elemental analysis indicate that the kerogen samples are of type ii thermally immature and with well preserved organic matter the hydrogen index hi values fluctuate between 608 and 765 mg hydrocarbon hc g toc and correlate well with c n and the sorg c atomic ratios indicating varying early diagenesis conditions between samples higher c n and sorg c values for kerogen from site 1261 suggest more reducing depositional conditions than at site 1257 long term organic diagenesis is marked by a linear decrease in the oxygen index oi at site 1261 from 34 to 22 mg co2 g toc ester and carboxyl functional groups are the main target of the degradation as inferred from the decrease in c o and o c c fourier transform infrared spectroscopy ftir bands as well as in the ch oh and the o ch3 chx n bands in 13c nuclear magnetic resonance nmr spectra degradation rate at site 1261 determined combining quantitative nmr spectra and bulk elemental characterization is between 1 7 and 12 1 mol m3 yr per 1 toc at the lower end of reported rates in a similar context kerogen samples from site 1257 do not show any decrease in oxygen content with depth indicating significantly lower degradation rate we propose that the long term exposure to moderate temperature 30 c at site 1261 activated the organic matter thereby sustaining microbial diagenesis

20 my of nitrogen fixation during deposition of mid cretaceous black shales on the demerara rise equatorial atlantic ocean abstract thick sequences of dark colored organic carbon rich finely laminated santonian cenomanian claystones and homogeneous albian siltstones were recovered from ocean drilling program sites 1257 1258 and 1260 on the demerara rise in the western equatorial atlantic ocean total organic carbon toc concentrations vary from 2 to over 20 wt in the sequences of black shales that were deposited over a period of 20 million years similarly long periods of elevated marine productivity implied by the high toc concentrations are uncommon in the geological record and must have required unusual paleoceanographic conditions the importance of nitrogen fixing bacteria to sustaining the amplified export production of organic matter is indicated by 15n values that remain between 4 and 0 a range that is notably less positive than the average of 5 for modern ocean sediments although containing mostly marine organic matter the black shales have toc tn molar ratios between 20 and 40 that mimic those of land plant organic matter the anomalously large toc tn ratios suggest selective organic matter degradation probably associated with low oxygen conditions in the water column that favored preservation of nitrogen poor forms of organic matter relative to nitrogen rich components deposition of black shales on the demerara rise was likely a consequence of the mid cretaceous warm and wet greenhouse climate that strengthened thermohaline stratification of this part of the atlantic ocean which in turn encouraged bacterial nitrogen fixation enhanced primary production magnified organic matter export and ultimately established anoxic conditions at the seafloor that improved preservation of organic matter for much of the 20 my period represented by these thick sequences

coexisting altered glass and fe ni oxides at the cretaceous tertiary boundary stevns klint denmark direct evidence of meteorite impact abstract the cretaceous tertiary k t boundary at stevns klint denmark is noteworthy for its large ir anomaly that is taken as evidence of extraterrestrial components but the origin of the smectite in this marl has been variously interpreted to have a detrital meteorite impact or volcanic origin we have carried out scanning electron microscopy and transmission electron microscopy tem analytical electron microscopy observations of the impact and contiguous layers within the k t marl at stevns klint tem images show abundant smectite much of which occurs with layers curving around and grading into cores of nanometer scale glass shards the smectite composition is unusual in having both significant octahedral al and mg the glass and smectite major element compositions are similar and unique relative to glasses of terrestrial and extraterrestrial origin with the exception for one kind of glass at the k t boundary in haiti abundant 10 20 nm diameter iron oxides having as much as 10 ni and minor zn are intergrown with smectite we interpret these domains to be altered meteorite fragments which formed when impact glass was transformed to smectite the direct association of unique glass and meteorite fragments is unambiguous evidence for meteorite impact these data may imply fall out of globally distributed impact derived particles over an extended time period the relations imply that tem observations may be a powerful tool in detecting other impact events in the geological record

work as a criterion for determining in situ and yield stresses in clays discussion this is a discussion of a paper by the same title which appeared in vol 24 canadian geotechnical journal pp 549 564 the authors of the original paper are d e becker j h a crooks k been and m g jefferies

a study of sulphur enrichment in the humic fraction of marine sediments during early diagenesis abstract the evolution of the sulphur content of humic acids extracted from a near shore sediment core was investigated special attention was taken to avoid s contamination of the humic materials during extraction the s c ratios increased continuously with depth to values which strongly suggest s addition to the humic matrix during early diagenesis by reactions between organic matter and h2s or its oxidation products their light isotopic composition supports this view however subsequent isotopic exchange has obscured the mechanism initially involved since a large fraction of the enrichment occurred above the sulphidic zone redox boundaries such as the interface of anoxic microniches within more oxidized zones or the sulphidic suboxic boundary of the sediment column must have been important sites for s addition bioturbation by increasing the contact between sedimentary zones of a different redox regime will likely enhance such processes

organic geochemical study of mineralization in the keweenawan nonesuch formation at white pine michigan the role of organic matter in the formation of metal ores has been investigated in the nonesuch formation at white pine michigan organic matter in mineralized strata was characterized by isotopic molecular and spectrophotometric procedures and compared to organic matter in non mineralized rocks samples from the white pine copper mine contain little organic carbon in comparison to samples from non mineralized sections of the nonesuch formation residual organic matter in mine samples is depleted in solvent extractable matter is relatively aromatic in character and appears to be thermally overmature yet no difference in carbon isotopic contents exists between kerogcn isolated from mineralized and non mineralized rocks comparisons suggest that oxidation of organic matter was involved in the reduction of oxidized metalliferous brines to precipitate copper sulfides and native copper and silver in this setting

living microbial ecosystems within the active zone of catagenesis implications for feeding the deep biosphere earth s largest reactive carbon pool marine sedimentary organic matter becomes increasingly recalcitrant during burial making it almost inaccessible as a substrate for microorganisms and thereby limiting metabolic activity in the deep biosphere because elevated temperature acting over geological time leads to the massive thermal breakdown of the organic matter into volatiles including petroleum the question arises whether microorganisms can directly utilize these maturation products as a substrate while migrated thermogenic fluids are known to sustain microbial consortia in shallow sediments an in situ coupling of abiotic generation and microbial utilization has not been demonstrated here we show using a combination of basin modelling kinetic modelling geomicrobiology and biogeochemistry that microorganisms inhabit the active generation zone in the nankai trough offshore japan three sites from odp leg 190 have been evaluated namely 1173 1174 and 1177 drilled in nearly undeformed quaternary and tertiary sedimentary sequences seaward of the nankai trough itself paleotemperatures were reconstructed based on subsidence profiles compaction modelling present day heat flow downhole temperature measurements and organic maturity parameters today s heat flow distribution can be considered mainly conductive and is extremely high in places reaching 180 mw m2 the kinetic parameters describing total hydrocarbon generation determined by laboratory pyrolysis experiments were utilized by the model in order to predict the timing of generation in time and space the model predicts that the onset of present day generation lies between 300 and 500mbelow sea floor 5100 5300mbelow mean sea level depending on well location in the case of site 1174 5 10 conversion has taken place by a present day temperature of ca 85 c predictions were largely validated by on site hydrocarbon gas measurements viable organisms in the same depth range have been proven using 14c radiolabelled substrates for methanogenesis bacterial cell counts and intact phospholipids altogether these results point to an overlap of abiotic thermal degradation reactions going on in the same part of the sedimentary column as where a deep biosphere exists the organic matter preserved in nankai trough sediments is of the type that generates putative feedstocks for microbial activity namely oxygenated compounds and hydrocarbons furthermore the rates of thermal degradation calculated from the kinetic model closely resemble ratesof respiration and electron donor consumption independently measured in other deep biosphere environments we deduce that abiotically driven degradation reactions have provided substrates for microbial activity in deep sediments at this convergent continental margin

sulfate reduction and methanogenesis in a thioploca dominated sediment off the coast of chile continental shelf sediments of the central chile upwelling area are dominated by the presence of dense mats of the filamentous sulfur depositing bacterium thioploca spp we examined rates and pathways of s and methane cycling in these sediments along a transect from the bay of concepcion to the continental slope sulfate reduction rates 170 4670 nmol cm 3 d 1 were equal to or exceeded rates reported for other subtidal marine sediments elemental s and pyrite were the dominant end products of sulfate reduction in thioploca mats on the continental shelf whereas in the highly reducing beggiatoa dominated sediments of the nearby bay of concepcion acid volatile s was the principal end product dissolved organic c values were lowest at the stations with the highest sulfate reduction rates and increased offshore sediment porewater methane concentrations in all surface sediments were low 12 nmol cm 3 and methane production rates at the station most dominated by thioploca were extremely low 0 5 nmol cm 3 d 1 low methane production rates and concentrations were matched by low methane oxidation rates 0 1 nmol cm 3 d 1 radio tracer studies showed that methane production was almost exclusively from methylamines substrates which are noncompetitive with sulfate reduction rather than from acetate or co2 h2 bacterial mpn most probable number counts also indicated the presence of a methylotrophic population of methanogens surprisingly high numbers of autotrophic acetogenic bacteria were found suggesting that the bacterial population involved in anaerobic doc degradation is more complex than expected in spite of the high sulfate reduction rates sulfide concentrations in the shelf and slope were low or undetectable 0 5 m and sulfate concentrations were never depleted below bottom water levels down to depths of 25 30 cm calculations suggest that thioploca were oxidizing a maximum of 35 of sulfide production not enough to prevent sulfate depletion either other sulfide oxidizers were also present or transient hydrodynamic conditions coupled with bioturbation resulted in oxidation of the sediments

relationships between mineral surfaces and organic carbon concentrations in soils and sediments abstract relationships between mineral specific surface area and organic carbon oc concentration are examined for sediments and soil a horizons from throughout the world i found published elsewhere that continental shelf sediments from many different regions exhibit downcore loss of oc to a refractory background level which shows a consistent relationship with mineral surface area slope 0 86 mg m 2 oc this trend is equivalent to a monolayer of organic matter over all surfaces and is termed the monolayer equivalent me level sediments and soils from other environments are compared to this empirically derived relationship several continental slope areas show extension of this relationship to considerable depth marked excesses of oc above this trend which persist downcore were found in sediments with high carbonate mineral content or slope sediments with low dissolved oxygen concentrations in the overlying water column about half of the soils examined also adhered to this relationship while soils with high carbonate content low ph or poor drainage showed oc concentrations higher than the me level oc concentrations below the me level are found in deltaic regions and areas with low organic matter delivery such as the deep sea or arid soils the nature of mineral surfaces was examined using n2 adsorption desorption isotherms and most surface area was found to be present as pores with