changes in atmospheric co2 and its carbon isotopic ratio during the penultimate deglaciation abstract the largest natural increases in atmospheric co 2 concentration as recorded in ice cores occur when the earth climate abruptly shifts from a glacial to an interglacial state open questions remain regarding the processes at play the sequences of events and their similarities along different glacial interglacial transitions here we provide new combined data of atmospheric co 2 and its carbon isotopic ratio 13 co 2 for the penultimate glacial interglacial transition termination ii from the antarctic epica dome c ice core together with the strongest antarctic warming this transition bears the largest co 2 increase 104 ppmv of the last nine terminations ending with an overshoot of 21 ppmv occurring within 300 y and leading to higher levels than those of the late pre industrial holocene the full co 2 rise is accompanied by an overall decrease of the 13 co 2 minimum values on which three positive excursions are superimposed peak to peak 13 co 2 changes in our record can reach 1 the ice core atmospheric 13 co 2 appears more depleted by 0 2 during termination ii compared to termination i paralleling a similar carbon isotopic depletion recorded in marine data during both terminations most of co 2 and 13 co 2 variations are attributed to southern ocean stratification breakdown and decreased efficiency of the biological pump compared to termination i termination ii ice core data point to different timings of decrease in iron supply and sea ice extent suggesting that they could account for distinct patterns of the carbon cycle

the changes in isotope composition and accumulation of snow at vostok station east antarctica over the past 200 years high resolution records of isotope composition dd and accumulation of snow have been obtained from 10 12 m deep snow pits dug in the vicinity of vostok station during the 1979 80 and 1999 2000 antarctic field seasons we employ meteorological balloon sounding and snow stake data to interpret the isotope record in terms of past temperature changes our reconstruction suggests that snow accumulation rate and the near surface air temperature at vostok have varied during the past 200 years between 15 and 30 kg m 2 a 1 and between 56 and 558c respectively with a slight general tendency to increase from the past to the present both parameters reveal a 50 year periodicity that correlates with the pacific decadal oscillation index implying a climatic teleconnection between central antarctica and the tropical pacific

geochemical characterisation of middle devonian oils in nw alberta canada possible source and maturity effect on pyrrolic nitrogen compounds abstract molecular geochemical compositions of a suite of middle devonian sourced and reservoired oils from the rainbow zama shekilie sub basins in n w alberta canada reveal the presence of at least two oil families in the study area the distribution of each oil family is geographically restricted to a single sub basin consistent with the oils being sourced locally within a series of closed generation migration trapping systems the diversity in the biomarker distributions of the oils indicates the wide range of depositional environments and source materials existing in each sub basin rather than mixing of end member oils across different sub basins clear maturity differences are observed between the oils from the rainbow and zama subbasins pre cretaceous thermal anomalies along the reactivated regional precambrian basement faults are proposed as one of the major causes for the relatively high maturity levels for the middle devonian source rocks in the study area we infer that depositional environment and thermal maturity have had a strong impact on the geochemical characteristics of the saturated and aromatic hydrocarbons in the rainbow shekilie zama oils but may not influence the pyrrolic nitrogen compounds to a significant extent however recognition of possible source and maturity effects on pyrrolic nitrogen compounds in other studies suggests that these factors should be considered before the pyrrolic nitrogen compounds are used to characterize petroleum migration

molecular memory effects recording the accumulation history of petroleum reservoirs a case study of the heidrun field offshore norway abstract the immobile portion of the oil occupying the pore space of reservoir sandstones which is mostly represented by visible impregnations is shown by the present study to contain geochemical signals that record their filling history the clue to unravelling these signals is sequential extraction of such impregnations of residual oil by a high pressure solvent flow through cell in which the solvent percolates through the intact and primary pore system of the rock sample gas chromatography mass spectroscopy gc ms analysis of residual oils extracted from samples of certain reservoir sandstones within the heidrun field offshore norway reveal significant contrasts in the chemical maturity of the first and the last fractions recovered as high as 0 69 versus 0 50 for the mpi 1 ratio corresponding to 0 79 versus 0 67 rc the hypothesis is proposed that by using this extraction technique oil impregnations from different portions of the pore system i e from large versus small pores are obtained separately this interpretation is especially supported by the regular occurrence of reservoir sandstones in which the residual oil exhibits maturity contrasts between those fractions extracted from large and small pores of the same rock within the heidrun field the distribution of reservoir sandstones with such maturity contrasts is strictly controlled by their position in the oil column and the location of their fault compartment these contrasts are interpreted to reflect the maturity levels of end members of the petroleum charges which have filled this trap during an extended period of geological time reservoir sandstone samples containing such end member charges are limited to the uppermost portion of the oil column lower in the oil column the pore system of all reservoirs contains oil impregnations of a uniform maturity level regardless of their pore size origin this distribution is believed to indicate an early stage of the accumulation history of the heidrun field characterised by the formation of a palaeo oil water contact well above the present one moreover the four fault compartments studied each controlled by bordering faults with different sealing capacities were not filled during the same stages of the accumulation history in summary the present study has shown that oil impregnations depending on their location within the pore system of individual reservoir sandstones can retain molecular memory effects which in turn allow the accumulation history of petroleum fields to be reconstructed

xanthones novel aromatic oxygen containing compounds in crude oils abstract xanthone and its alkylated homologues were determined to be present in 64 of 69 investigated oils from offshore norway central graben viking graben haltenbanken this is the first description of xanthones in crude oils these compounds were identified by comparison with authentic standards by coinjection based on mass spectra and relative retention times on two different gc columns the elution order of the four methylxanthones was established as 1 4 2 3 by using a bpx 5 column about 2 3 of the oils contain concentrations of xanthone lower than 5 g g oil but some oils are clearly enriched in the parent compound the highest amount of xanthone in the sample set was 38 g g oil the relative abundance of xanthone the sum of the methylxanthones and the sum of the c 2 xanthones is mainly controlled by maturity partitioning processes may effect changes in the distribution of methylxanthones as observed for a biodegradation sequence from the gullfaks field molecular dynamics calculations support the observation of a better preservation of the shielded isomers 1 and to a lesser extent 4 methylxanthone in the oil phase compared to the non shielded isomers 2 and 3 methylxanthone the ratio of these two different isomer groups may be useful as an indicator of secondary migration distances as demonstrated for an oil sequence from the tampen spur and haltenbanken oils however biodegradation could also cause an increase of the shielded isomers relative to the non shielded isomers due to sterical hindrance by the methyl groups restricting access to the oxygen functionalities the origin of xanthones in crude oils and source rocks is not known but they could be generated as diagenetic products formed by oxidation of xanthenes in the reservoir or originate by geosynthesis from aromatic precursors

reconstructing the last interglacial at summit greenland insights from gisp2 the eemian last interglacial 130 115 ka was likely the warmest of all interglacials of the last 800 ka with summer arctic temperatures 3 5 c above present here we present improved eemian climate records from central greenland reconstructed from the base of the greenland ice sheet project 2 gisp2 ice core our record comes from clean stratigraphically disturbed and isotopically warm ice from 2 750 to 3 040 m depth the age of this ice is constrained by measuring ch4 and 18o of o2 and comparing with the historical record of these properties from the north greenland ice core project ngrip and north greenland eemian ice drilling neem ice cores the 18oice 15n of n2 and total air content for samples dating discontinuously from 128 to 115 ka indicate a warming of 6 c between 127 121 ka and a similar elevation history between gisp2 and neem the reconstructed climate and elevation histories are compared with an ensemble of coupled climate ice sheet model simulations of the greenland ice sheet those most consistent with the reconstructed temperatures indicate that the greenland ice sheet contributed 5 1 m 4 1 6 2 m 95 credible interval to global eustatic sea level toward the end of the eemian greenland likely did not contribute to anomalously high sea levels at 127 ka or to a rapid jump in sea level at 120 ka however several unexplained discrepancies remain between the inferred and simulated histories of temperature and accumulation rate at gisp2 and neem as well as between the climatic reconstructions themselves

air content paleo record in the vostok ice core antarctica a mixed record of climatic and glaciological parameters under present day climatic conditions the air content of ice shows a high sensitivity to the atmospheric pressure and hence to the elevation at the surface of the ice sheet this observation has been used to infer past ice sheet thickness variations of antarctica and greenland a high resolution air content profile more than 1000 measurements covering approximately the last 200 000 years was obtained along the 2546 m long vostok ice core three analytical techniques were used leading to consistent results which show large amplitude and rapid air content variations the vostok results support thicker thinner ice in the central part of east antarctica during warm cold periods

densification of layered firn in the ice sheet at dome fuji antarctica in order to better understand the densification of polar firn firn cores from the three sites within 10 km of dome fuji antarctica were investigated using surrogates of density dielectric permittivities e v and e h at microwave frequencies with electrical fields in the vertical and horizontal planes respectively dielectric anisotropy e e v e h was then examined as a surrogate of the anisotropic geometry of firn we find that layered densification is explained as a result of complex effects of two phenomena that commonly occur at the three sites basically layers with initially smaller density and smaller geometrical anisotropy deform preferentially throughout the densification process due to textural effects second layers having a higher concentration of cl ions deform preferentially during a limited period from the near surface depths until smoothing out of layered cl ions by diffusion we hypothesize that cl ions dissociated from sea salts soften firn due to modulation of dislocation movement moreover firn differs markedly across the three sites in terms of strength of geometrical anisotropy mean rate of densification and density fluctuation we hypothesize that these differences are caused by textural effects resulting from differences in depositional conditions within various spatial scales

residual oil as a tool in migration and filling history analysis of petroleum reservoirs ghazal field saudi arabia abstract stepwise extraction and molecular analysis of non recoverable oil from intact reservoir core plugs is used to provide constraints on the accumulation history of petroleum in the permo carboniferous unayzah reservoirs at the ghazal field saudi arabia when integrated with existing tools such as oil geochemistry gas geochemistry stable carbon isotopes fluid inclusions and thermal modeling the sequential extraction approach helped decode a previously unrecognized component of the hydrocarbon accumulation history in particular it indicates that the region received early petroleum charges that were less mature than currently produced light oil and gas condensates possibly from the prolific early silurian qusaiba shale source rock and other sources this has significant implications for prospecting for additional oil particularly in the north northwest of the ghazal region where paleo oil accumulations may have been displaced or spilled the lower portion of the unayzah reservoir unayzah c remained water wet during early filling of the upper reservoir unit unayzah a and appears to have been filled only by a late oil charge anomalous molecular and carbon isotopic behavior of residual oil extracts from the uppermost segment of the unayzah reservoir where the free oil first of the sequential extracts is less mature 0 95 rc and isotopically lighter 13c 31 15 than the adsorbed oil last sequential extract 1 05 rc 13c 29 65 suggests a late oil contribution or bitumen contamination from the overlying khuff formation

charging of the penglai 9 1 oil field bohai bay basin china functions of the delta on accumulating petroleum abstract the penglai 9 1 pl9 1 oil field which contains china s third largest offshore oil accumulation in place reserves greater than 2 28 10 8 ton or 1 49 10 9 bbl was found in shallow reservoirs 700 1700 m 2297 5577 ft within the most active fault zone in east china the pl9 1 field contains two oil bearing series the granite intrusions in mesozoic mz and both the sandstone reservoirs in neogene guantao ng and neogene minghuazhen nm formation the origins of the pl9 1 field both in terms of source rock intervals and generative kitchens were determined by analyzing biomarker distributions for 61 source rock samples and 33 oil samples the mesozoic granite intrusions which hold more than 80 of the oil reserves in the field were charged in the west by oil generated from the third member es 3 of the shahejie formation in the bodong depression the neogene reservoirs of the pl9 1 field were charged in the west by oil generated from the third member es 3 of the shahejie formation in the bodong depression and in the south by oil generated from the first member es 1 of the shahejie formation in the miaoxibei depression interactive contact between the large fan delta and the mature source rocks residing in the es 3 formation of the bodong depression resulted in a high expulsion efficiency from the source rocks and rapid oil accumulation in the pl9 1 field which probably explains how can this large oil field accumulate and preserve within the largest and most active fault zone in east china

eight glacial cycles from an antarctic ice core the antarctic vostok ice core provided compelling evidence of the nature of climate and of climate feedbacks over the past 420 000 years marine records suggest that the amplitude of climate variability was smaller before that time but such records are often poorly resolved moreover it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records here we report the recovery of a deep ice core from dome c antarctica that provides a climate record for the past 740 000 years for the four most recent glacial cycles the data agree well with the record from vostok the earlier period between 740 000 and 430 000 years ago was characterized by less pronounced warmth in interglacial periods in antarctica but a higher proportion of each cycle was spent in the warm mode the transition from glacial to interglacial conditions about 430 000 years ago termination v resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases but there are significant differences in the patterns of change the interglacial stage following termination v was exceptionally long 28 000 years compared to for example the 12 000 years recorded so far in the present interglacial period given the similarities between this earlier warm period and today our results may imply that without human intervention a climate similar to the present one would extend well into the future

eemian interglacial reconstructed from a greenland folded ice core efforts to extract a greenland ice core with a complete record of the eemian interglacial 130 000 to 115 000 years ago have until now been unsuccessful the response of the greenland ice sheet to the warmer than present climate of the eemian has thus remained unclear here we present the new north greenland eemian ice drilling neem ice core and show only a modest ice sheet response to the strong warming in the early eemian we reconstructed the eemian record from folded ice using globally homogeneous parameters known from dated greenland and antarctic ice core records on the basis of water stable isotopes neem surface temperatures after the onset of the eemian 126 000 years ago peaked at 8 4 degrees celsius above the mean of the past millennium followed by a gradual cooling that was probably driven by the decreasing summer insolation between 128 000 and 122 000 years ago the thickness of the northwest greenland ice sheet decreased by 400 250 metres reaching surface elevations 122 000 years ago of 130 300 metres lower than the present extensive surface melt occurred at the neem site during the eemian a phenomenon witnessed when melt layers formed again at neem during the exceptional heat of july 2012 with additional warming surface melt might become more common in the future

chemical and isotopic evidence for secondary alteration of natural gases in the hetianhe field bachu uplift of the tarim basin h2s and co2 are found in elevated concentrations in the reservoirs near the carboniferous ordovician unconformity in the hetianhe field of the tarim basin nw china chemical and isotopic analyses have been performed on produced gases formation waters and reservoir rocks to determine the origin of co2 and h2s and to explain the heterogeneous distribution of isotopic and geochemical characteristics of petroleum fluids it is unlikely that h2s and co2 had a mantle component since associated helium has an isotope ratio totally uncharacteristic of this source instead h2s and co2 are probably the result of sulphate reduction of the light hydrocarbon gases lhg increasing h2s concentrations and co2 co2 c1 4 values to the west of the hetianhe field occur commensurately with increasingly heavy hydrocarbon gas 13c values however thermochemical sulphate reduction is unlikely because the temperatures of the reservoirs are too low no h2s or rare pyrite was detected in deeper reservoirs where more tsr should have occurred and inferred 34s values of h2s from late stage pyrite in the carboniferous and ordovician reservoirs are as low as 24 9 such low 34s values discount the decomposition of organic matter as a major source of h2s and co2 bacterial sulphate reduction of the light hydrocarbon gases in the reservoir possibly coupled indirectly with the consumption of organic acids and anions is most likely the result is the preferential oxidation of 12c rich alkanes due to the kinetic isotope effect and decreasing concentration of organic acids and anions modern formation water stable isotope data reveal that it is possible that sulphate reducing bacteria were introduced into the reservoir by an influx of meteoric water from the west by way of an inversion related unconformity this may account for the apparently stronger influence of bacterial sulphate reduction to the west of the hetianhe field and the consequent greatest decrease of the 13c co2 values and the greatest increase in 13c values of the alkane gases

temperature measurements and heat transfer in near surface snow at the south pole to study near surface heat flow on the antarctic ice sheet snow temperatures were measured at south pole station to a depth of 3 m at 15 min intervals during most of 1992 solar heating and water vapor transport were negligible during the 6 month winter as was inter grain net thermal radiation leaving conduction as the dominant heat transport mechanism the rate of temperature change at depth over 15 min intervals was smaller than that at the surface by one order of magnitude at 20 cm depth and two orders of magnitude at 1 m depth a finite difference model with conduction as the only heat transfer mechanism and measured temperatures as the upper and lower boundary conditions was applied to foursets of three thermistors each the thermal conductivity was estimated as that which minimized the difference between modeled and measured 15 min changes in temperatures at the center thermistor the thermal conductivity obtained at shallow depths above 40 cm was lower than that given by existing parameterizations based on density probably because the snow grains were freshly deposited cold and poorly bonded a model using only vertical conduction explains on average 87 ofthe observed 15 min temperature changes at less than 60 cm depth and 92 below 60 cm the difference between modeled andmeasured temperature changes decreased with depth the discrepancies between model and observation correlated more strongly with the air snow temperature difference than with the product of that difference with the square of the wind speed suggesting that the residual errors are due more to non vertical conduction and to sub grid scale variabilis of the conductivity than to windpumping the residual heating rate not explained by the model of vertical conduction exceeds 0 2 w m 3 only in the top 60 cm of the near surface snow

geological conditions and geochemical effects of secondary petroleum migration and accumulation the processes of secondary petroleum migration and reservoir filling remain among the least understood steps with respect to the characterisation and economic assessment of a petroleum system spatial heterogeneities of compositions of unaltered petroleum within individual fields have repeatedly been recognised and interpreted to result from compositional changes of multiple petroleum charges during the accumulation history in combination with limited degree of in reservoir mixing of petroleum fluids england w a mackenzie a s mann d u quigley t m 1987 the movement and entrapment of petroleum fluids in the subsurface j geol soc london 144 327 347 leythaeuser d ruckheim j 1989 heterogeneity of oil composition within a reservoir as a reflection of accumulation history geochim cosmochim acta 53 8 2119 2123 most previous attempts to improve this situation have aimed at an understanding of the conditions and effects of the flow of petroleum fluids by studying case histories on regional or field scales in the study reported here we have in addition attempted to reconstruct the mode of filling of sandstone reservoir rocks on pore scales

the local insolation signature of air content in antarctic ice a new step toward an absolute dating of ice records an accurate chronology of ice cores is still needed for interpreting the paleoclimatic record and to understand the relation between insolation and climate a new domain of research in this area has been stimulated by the work of m bender linking the record of n2 o2 ratio in the air trapped in the ice with the local insolation here we investigate the potential of the air content of polar ice v as another and complementary ice proxy of local insolation we propose that the long term changes in air content recorded in ice from the high antarctic plateau is dominantly imprinted by the local summer insolation the v measurements covering the last 440 000 yr and obtained along the epica dc edc ice core are presented 86 of the variance observed in the v record can be explained neither by air pressure nor by temperature changes and then should reflect properties influencing the porosity at close off other than temperature a wavelet analysis indicates a dominant obliquity period around 41 ka over the last 440 ka we propose a mechanism which can account for the observed anti correlation between local insolation and v and explain how the local insolation via the integrated summer insolation can affect the near surface snow structure and consequently the porosity at close off the v and the integrated summer insolation changes show high coherency over all the record and a variable phase relationship with a maximum phase difference of about 4000 yr around 200 ka ago the phase difference may reflect the difference between the edc2 chronology based on an inverse dating method and an accurately dated insolation curve our work by proposing a new and complementary ice proxy for local insolation should eventually contribute to the establishment of an absolute dating of the ice paleo record

simulations of the last glacial maximum ice sheet surface climate implications for the interpretation of ice core air content this paper reports on analyses of the surface pressure surface wind and seasonality of temperature and precipitation in the central parts of greenland and antarctica as simulated by different general circulation models gcms for the present and for the last glacial maximum lgm climates these parameters in addition to the mean surface temperature influence the air content of the ice either directly or through their influence on the pore volume to correctly interpret the air content of the ice in terms of past ice sheet elevation changes the variations of these parameters must therefore be known most of the simulations discussed here have been carried out within the framework of the paleoclimate modeling intercomparison project moreover a stretched grid gcm has been used with a high resolution over the ice sheets we show that not taking into account changes of surface pressure at constant altitude between the lgm and today leads to an overestimation of past ice sheet elevation up to 150 m while wind speed changes are too weak to have a significant influence on ice core air content the results concerning changes of the amplitude or phase of the seasonal variations of precipitation and temperature are somewhat ambiguous most but not all of the models suggest an intensification of the seasonal cycle of surface temperatures over central greenland and to a lesser extent over central east antarctica neglecting these changes might lead to an underestimation of past elevation by up to 140 m for the greenland ice sheet but this number is subject to large uncertainties

does mean annual insolation have the potential to change the climate long term climatic changes such as glacial interglacial cycles are usually explained in term of changes in solar energy received at the top of the atmosphere in particular daily insolation in the high northern hemisphere latitudes during summer is widely used in interpreting palaeoclimate records this insolation forcing is strongly marked by changes in precession however some climate variations are much more imprinted by changes in obliquity this was the case for sea surface temperature in the north atlantic during the eemian period as well as for the vostok ice core deuterium excess history over the last 250 ka therefore we investigate the insolation forcing in order to identify characteristics that could explain the observed climate response this is mainly the case for annual mean insolation variations simple hypotheses for how this forcing could act on climate are also suggested these being mainly related to changes in the moisture transport induced by the annual insolation gradient between low and high latitudes along these lines a simple conceptual model of annual mean temperature variations illustrates the role of annual mean insolation on climate c 2004 elsevier b v all rights reserved

metamorphism of stratified firn at dome fuji antarctica a mechanism for local insolation modulation of gas transport conditions during bubble close off 1 the evolution of the structure of a 112 59 m long firn core recovered at dome fuji east antarctica was investigated in order to improve understanding of firn densification and bubble formation processes which are important for interpreting local insolation proxies used for astronomical dating of deep ice cores using selected samples we measured physical properties including 1 the relative dielectric permittivities in both the vertical and horizontal planes 2 the bulk density at a resolution of millimeters 3 the three dimensional geometric structure of pore space and 4 crystal orientation fabrics we found that the firn at dome fuji contains horizontal strata with thicknesses of several centimeters near the surface of the ice sheet these strata are characterized by contrasting bulk density earlier field studies suggest that summer insolation causes densification of surface firn down to 30 m density maxima exhibited a clear positive correlation with the strength of structural anisotropy and c axis clustering around the vertical in contrast the correlation is negative in deeper firn confirming previous findings that initially less dense firn became denser than initially dense firn in addition numerous examples of textures indicating that deformation preferentially occurred in weaker layers were found moreover the initially dense firn layers were more permeable for air near the bottom of firn we propose a model linking firn properties with conditions for the gas transport processes near the bottom of firn the model explains how stronger insolation can lead to bulk ice with a lower o2 n2 ratio and smaller total gas content

orbital tuning chronology for the vostok climate record supported by trapped gas composition abstract we present data on the o2 n2 ratios of trapped gas samples for the entire length of the vostok climate record as in other cores o2 n2 ratios in these samples are less than the atmospheric ratio by a small and variable amount because o2 is selectively excluded during the gas trapping process and because o2 is also preferentially lost in poorly preserved core samples samples younger than 150 ka have large and variable o2 depletions samples older than 200 ka have o2 n2 ratios that replicate well and vary smoothly with depth we plot o2 n2 ratios of well replicated samples older than 160 ka using a chronology derived by matching the 18o of paleoatmospheric o2 18oatm to northern hemisphere june insolation on this timescale o2 n2 varies coherently with local 78 s summertime insolation based on time series analysis of the o2 n2 record and the dynamics of snow metamorphism at the surface we conclude that summertime insolation influences physical properties of ice grains that control the degree of o2 exclusion during bubble closeoff o2 n2 in vostok is thus arguably a property that records local summertime insolation and can be used to test independent chronologies for the core we show that the 18oatm chronology supported by the coincidence of o2 n2 ratios with insolation is also compatible with recent radiometric dating of corals from high sea stands we further successfully test the 18oatm tuning chronology by showing that it predicts a chronology for the gisp2 core which is essentially indistinguishable from the standard gisp2 chronology and therefore in excellent agreement with the radiometric chronology of hulu cave china an accurate chronology for the vostok ice core is now in place

carbazole distributions in rocks from non marine depositional environments abstract pyrrolic nitrogen compounds have been studied from extracts of the rocks collected from the tertiary saline lacustrine strata in the qaidam basin and the middle lower jurassic coal bearing strata in the turpan basin nw china biomarker signatures revealed the presence of three sample groups related to saline lacustrine conditions in the qaidam basin and freshwater lake and swamp depositional settings in the turpan basin significant differences in carbazole distributions were observed among the sample groups from different depositional environments generally a strong predominance of 1 4 1 5 dimethylcarbazoles over 1 3 1 6 dimethylcarbazoles was found for the qaidam rocks from the saline lacustrine settings with a ratio of 1 3 1 6 1 4 1 5 dimethylcarbazole ranging from 0 35 to 0 66 while enhanced amounts of 1 3 1 6 dimethylcarbazoles relative to 1 4 1 5 dimethylcarbazoles were detected for the turpan samples from the swamp environments with the 1 3 1 6 1 4 1 5 dimethylcarbazole ratio 0 8 samples from the freshwater lake environments in the turpan basin showed intermediate values for the 1 3 1 6 1 4 1 5 dimethylcarbazole ratio in addition a predominance of 2 4 dimethylcarbazole over 2 6 dimethylcarbazole was observed for the qaidam samples whereas most turpan samples showed elevated amounts of 2 6 dimethylcarbazole relative to 2 4 dimethylcarbazole moreover 3 methylcarbazole occurred as the least abundant c 1 carbazole isomer for most qaidam rocks while the turpan samples from swamp settings often showed an enhanced abundance of 3 methylcarbazole the 1 3 1 6 1 4 1 5 dimethylcarbazole ratio was observed to have a positive correlation with 3 4 methylcarbazole 2 6 2 4 dimethylcarbazole and pr ph respectively these observations may indicate that c 1 and c 2 carbazoles with a methyl group at c 3 c 6 prevailed for swamp settings whereas isomers with a methyl at c 4 c 5 were dominant for the freshwater or saline lacustrine environments although variations in benzocarbazoles were detected in the bitumens an obvious correlation was not observed for the different depositional environments

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

acidic biomarkers from albacora oils campos basin brazil abstract acidic biomarkers of 8 different oil samples from albacora oil field campos basin brazil were analyzed in order to obtain additional information about biodegradation and thermal evolution for this purpose we selected oils lacustrine saline origin showing different biodegradation levels and at different distances from the fault that acted as migration pathway in the area previous analyses using hydrocarbon biomarkers suggested a mix of oil charges characterizing two distinct oil cycles interrupted by meteoric water circulation in these reservoirs analyses of the naphthenic acid biomarkers revealed a parallelism between the hydrocarbon and the acidic biomarkers notwithstanding there is evidence that the carboxylic acid biomarkers more resistent to biodegradation can provide information on past reservoir history when most important neutral biomarkers have been biodegraded the limitations to the use of these biomarkers are their de novo synthesis in the biodegradation process and the complexity of the sample manipulation prior to the analysis

the influence of facies and depositional environment on the occurrence and distribution of carbazoles and benzocarbazoles in crude oils a case study from the gulf of suez egypt abstract two major hinge zones separate the gulf of suez gos of egypt into three tectonic sub provinces namely the northern central and southern sectors based on bulk and molecular parameters the crude oils from the gos can be subdivided into three groups according to their geographical origin from the three sectors the geochemical characteristics of the oils are consistent with inferred depositional environments of anoxic marine carbonate facies in the central sector compared to a more oxic environment that has received an increased proportion of clastic input in the southern sector while the northern is intermediate in character most of the oils cover a relatively narrow maturity range 0 86 0 98 r c in the peak oil window the biomarker parameter ts ts tm is controlled by variations of facies and depositional environment but not by maturity concentrations of pyrrolic nitrogen compounds in the gos crude oils are in general relatively low but show a large range of variability in crude oils of the northern sector a strong predominance of c 4 and c 5 carbazoles over the lower homologues is observed towards the south the relative abundance of carbazole and the methylcarbazoles increases successively variations within the methylcarbazoles and c 2 carbazoles are rather small and therefore are not useful for a straightforward classification of oil families however atypical patterns in some of the oils particularly from the northern sector give evidence for contributions from yet unidentified local sources which might not be of general importance in the gos petroleum province benzo b carbazole is near or even below detection limit in the gos crude oils the benzocarbazole a a c ratio shows a consistently positive correlation with api gravity pr ph and ts ts tm and a negative correlation with the sulphur content based on these observations it is inferred that facies and depositional environment of the relevant source rocks are the major factors influencing the benzocarbazole distributions in the central sector of the gos in which oils are predominantly sourced from carbonates deposited under strongly reducing conditions a a c values are mainly below 0 5 in the southern sector where source rocks were deposited under less reducing conditions and received significant clastic input as well as in the northern sector the a a c values are mainly above 0 5

a new device for the measurement of air content in polar ice a new device for measuring air content in polar ice has been designed built and tested with 22 samples of antarctic ice the new technique is based on the barometric method which implies 1 air extraction under vacuum by melting refreezing of the ice sample placed in a calibrated cell and 2 accurate air pressure and temperature measurements the new apparatus simplifies the experimental procedures decreases the duration of measurement and can eventually be used in the field it provides results with an accuracy equivalent to or better than other methods previously used

observing and modeling the influence of layering on bubble trapping in polar firn interpretation of ice core trace gas records depends on an accurate understanding of the processes that smooth the atmospheric signal in the firn much work has been done to understand the processes affecting air transport in the open pores of the firn but a paucity of data from air trapped in bubbles in the firn ice transition region has limited the ability to constrain the effect of bubble closure processes here we present high resolution measurements of firn density methane concentrations nitrogen isotopes and total air content that show layering in the firn ice transition region at the west antarctic ice sheet wais divide ice core site using the notion that bubble trapping is a stochastic process we derive a new parameterization for closed porosity that incorporates the effects of layering in a steady state firn modeling approach we include the process of bubble trapping into an open porosity firn air transport model and obtain a good fit to the firn core data we find that layering broadens the depth range over which bubbles are trapped widens the modeled gas age distribution of air in closed bubbles reduces the mean gas age of air in closed bubbles and introduces stratigraphic irregularities in the gas age scale that have a peak to peak variability of 10 years at wais divide for a more complete understanding of gas occlusion and its impact on ice core records we suggest that this experiment be repeated at sites climatically different from wais divide for example on the east antarctic plateau

an ice core perspective on the age of the matuyama brunhes boundary abstract two intervals of enhanced 10be flux thought to be associated with periods of low dipole intensity and identified as the matuyama brunhes transition and a precursor event have been observed in the bottom section of the epica dome c ice core the peaks span 764 776 ka and 788 798 ka on the new edc3 chronology with a stated absolute age uncertainty of 6 ka 2 this chronology uses orbital tuning of atmospheric oxygen 18 18oatm to correct for anomalies in ice flow in the bottom 500 m of the core an additional 28 18oatm data points have been measured to improve resolution and verify the accuracy of the tuning and the stated timescale uncertainty both the dating of the increased 10be and that relative to climatic records are compared to paleointensity records found in orbitally tuned marine sediments the mid point of the 10be peak associated with the m b is approximately 10 ka younger than the age determined radioisotopically from lavas with transitional orientations taking into account recent revisions to the 40ar 39ar dating standard and improved precision climatic constraints on the edc3 agescale make an error of this magnitude in the ice chronology implausible this age difference however is consistent with recent modeling suggesting that directional changes are spatially asynchronous and may precede the dipole intensity minimum in some locations although formally less precise than the published age from astrochronologically dated marine sediments ice core ages are potentially more accurate because they are not subject to lock in depth uncertainties

using ice cores and gaussian process emulation to recover changes in the greenland ice sheet during the last interglacial the shape and extent of the greenland ice sheet gis during the last interglacial lig is a matter of controversy with different studies proposing a wide range of reconstructions here for the first time we combine stable water isotopic information from ice cores with isotope enabled climate model outputs to investigate the problem exploring the space of possible ice sheet geometries by simulation is prohibitively expensive we address this problem by using a gaussian process emulator as a statistical surrogate of the full climate model the emulator is calibrated using the results of a small number of carefully chosen simulations and then permits fast probabilistic predictions of the simulator outputs at untried inputs the inputs are gis morphologies parameterised through a dimension reduction technique adapted to the spherical geometry of the setting based on the emulator predictions the characteristics of morphologies compatible with the available ice core measurements are explored leading to a reduction in uncertainty on the lig gis morphology moreover a scenario based approach allows to assess the gains in uncertainty reduction which would result from the availability of better dated lig measurements in greenland ice cores

applications of petroleum geochemistry to exploration and reservoir management abstract petroleum geochemistry improves exploration efficiency by accounting for many of the variables that control the volumes of crude oil and natural gas available for entrapment including source rock distribution richness and quality thermal maturity and the timing of generation migration accumulation relative to trap formation it is most powerful when used with other disciplines such as seismic sequence stratigraphy and reservoir characterization four key technology milestones form the basis for most modern applications of geochemistry to exploration these are the concepts and applications of 1 petroleum systems and exploration risk 2 biomarkers stable isotopes and multivariate statistics for genetic oil oil and oil source rock correlation 3 calibrated three dimensional thermal and fluid flow modeling and 4 controls on petroleum composition by secondary processes petroleum geochemistry offers rapid low cost evaluation tools to aid in understanding development and production problems some technology milestones in reservoir geochemistry include 1 assessment of vertical and lateral fluid continuity 2 determination of proportions of commingled production from multiple zones and leaky casing 3 prediction of oil quality in reservoir zones and 4 prediction of gas oil and oil water contact locations as described in the conclusions future research will continue a trend toward predictive geochemistry examples of predictive tools that draw major research support include piston core surveys to assess deepwater petroleum systems prior to drilling and three dimensional basin modeling to predict the regional timing of generation migration and accumulation of petroleum among other research objectives models are needed to better predict the distribution and quality of petroleum in reservoirs

densification of layered firn of the ice sheet at neem greenland densification of firn at the north greenland eemian ice drilling neem camp is investigated using density surrogates dielectric permittivities v and h at microwave frequencies with electrical fields in the vertical and horizontal planes respectively dielectric anisotropy v h is then examined as a surrogate for the anisotropic geometry of firn its size fluctuations and mutual correlations are investigated in samples taken at depths from the surface to 90m the initial of 0 06appears within the uppermost 0 2 m after that decreases rapidly until 21 26 m depth below this decreases slowly layers with more ions of fluorine chlorine and some cations deposited between the autumn and the subsequent summer deform preferentially during all these stages this layered deformation is explained partly by the textural effects initially formed by the seasonal variation of metamorphism and partly by ions such as fluorine chlorine and ammonium which are known to modulate dislocation movement in the ice crystal lattice insolation sensitive microstructure appears to be preserved all the way to the pore close off within layers of the summer to autumn metamorphism like previous authors we hypothesize that calcium is not the active agent in the reported deformation calcium correlations

uk 37 temperature estimates from eemian marine sediments in the southern coast of hainan island tropical china abstract this study concerns high resolution sea surface temperature sst changes for the eemian interglacial period reconstructed from the southern coast of hainan island china the lower marine unit in the sediment core is composed of monotonous mud 31 m thick dated to be from the eemian interglacial period or lower part of marine isotope stage 5 mis 5 determined by optically stimulated luminescence osl the high sedimentation rate and the richness of organic matter and marine fossils provide good opportunity for the study of palaeo environments in the northern margin of the south china sea scs sediment grain size foraminifer sediment color index and long chain alkenone were used to reveal the near shore sedimentary environments and temperature at millennial scale specifically a high resolution uk 37 sst record was reconstructed for the eemian interglacial period the new evidence in northwestern margin of scs shows that the maximum value of sst during the eemian interglacial is approximately 29 c and the lowest is 26 5 c the trend of decreasing sst from 29 c throughout the marine sequence is consistent with the variations in sediment grain size reflecting the cooling trend of sst and sea level lowering tendency during the last interglacial period this new eemian sst result agrees with other records in the region of scs showing a coherent descending trend but spatial heterogeneity exists in timing and amplitude the insolation changes might be the main force for initiating the sst evolution during the penultimate interglacial period

giant irregular pockmark craters in the palaeogene of the outer moray firth basin uk north sea a cluster of irregular pockmark craters of palaeogene age in block 15 18 in the outer moray firth uk north sea have been mapped on 3d seismic data with well control the craters range from 0 5 to 4 km in diameter between 50 and 200 m in depth and have been buried by tertiary subsidence and sedimentation to present day depths of between 1000 and 1400 m sub sea they are circular to elliptical in plan view and are located in a delta front and upper pro deltaic slope position on the dornoch delta the structures are confined to the top of the lower eocene balder formation and regional mapping across the moray firth basin shows they are restricted to an area of ca 15 15 km2 well data show that the craters are sand filled and have excavated an argillaceous and tuffaceous unit the crater filling sands are sealed by overlying mudstone units planar wing like features emanate from the margins of the craters well control indicates that these seismically identified wings consist of sandstone suggesting that the craters have been modified by an episode of sand remobilisation and injection the proposed mechanism for the formation of these structures is large scale fluid eruption probably shallow gas at the early eocene seafloor these craters are significantly larger in size than those typically observed on contemporary sea floors we argue that the gas is more likely to have been sourced from deeper jurassic or carboniferous sediments within the witch ground graben than from shallow biogenic origins these structures rank in scale alongside the largest known pockmarks and demonstrate that natural fluid and hydrocarbon seeps have a long ancestry in this basin

solar heating rates and temperature profiles in antarctic snow and ice observations of temperature maxima at about 10 cm depth in cold antarctic snow during summer have previously been explained by proposing that solar heating is distributed with depth whereas thermal infrared cooling is localized at the surface the solid state greenhouse an increase in temperature from the surface to 10 cm depth t 4 k found by rusin 1961 on the antarctic plateau was successfully reproduced by schlatter 1972 in a combined radiative transfer and heat transfer model

petroleum migration and mixing in the pearl river mouth basin south china sea abstract two oil groups have been investigated in the pearl river mouth basin using their geochemical characteristics in combination with source data the two oil groups may be extrapolated into two end member oils petroleum populations a and b the oil population a with abundant 4 methylsteranes derived from the deeper wenchang source rocks migrated and accumulated earlier the oil population b with absent 4 methylsteranes was expelled from the enping source rocks and is associated with a relatively later phase of migration and accumulation the two distinctive oil populations migrated updip through the marine blanket like sandstone carriers within the zhuhai formation to accumulate in a series of traps along the main migration pathways at different times most of the accumulations are mixtures of the two end member oils the variations of 4 methylsterane concentrations in the accumulations can be related to the contributions from the two sources the oils which migrated furthest contain greater contributions from the wenchang source rocks whereas those with shorter migration paths have greater contributions from the enping sources the later migrated oils closer to the depression areas are highly mature and the former oils in the liuhua oil fields are of relatively low maturity which may indicate the main migration direction along the hui liu structure ridge hlsr oils with abnormally high maturity in the middle of the hlsr may suggest oil filling points from which branch conduits connected the source kitchens to the main migration pathway oils with abnormally low maturities may reveal minor contributions from some small sags in the dongsha massif in a latest phase

modeling the densification of polar firn including heat diffusion application to close off characteristics and gas isotopic fractionation for antarctica and greenland sites 1 modeling the densification of polar firn is essential to estimate variations of close off characteristics density close off depth delta age in relation with past climate parameters temperature and accumulation rates furthermore the air composition in the firn is modified by gravitational and thermal fractionation and stable isotope measurements of permanent gases like nitrogen or argon can provide information on the amplitude of these fractionations in this work we propose a new model coupling firn densification and heat diffusion in addition to the determination of the firn thickness and gas ice age differences the model allows a reconstruction of the time evolution of the temperature for different sites in antarctica vostok and greenland gisp2 and therefore the evolution of gravitational and thermal isotopic fractionations in firn under present day conditions the modeled profiles are in good agreement with the available temperature measurements in firn for sites with low accumulation rates such as vostok the results show the existence of temperature gradients in the firn column even when no rapid climatic changes occur the comparison of the modeled 15n results to measurements allows to better constrain the 18o temperature relationship used to infer the surface temperature history and for gisp2 the model validates the long term borehole based temperature

polar ice structure and the integrity of ice core paleoclimate records abstract polar ice is a unique archive of the climatic conditions in the past however ice sheets flow and this flow may affect the integrity of paleoclimate records a useful method to analyze the effect of ice flow upon climate records is the combination of microstructure mapping with ice core line scanning microstructure and stratigraphy have been mapped along the entire epica dml ice core with this combined method on the macroscale the stratigraphy seems perfectly preserved down to ca 1700 m depth mis4 below which minor undulations start to develop layers inclined up to 15 and millimeter scale z folds are observed below 2050 m depth notwithstanding the epica dml climate record appears not seriously disturbed down to ca 2400 m depth which marks the climatic transition from the last interglacial mis5e to the mis6 glacial period below this depth the synchronization with the epica dome c record is lost and stratigraphic disturbances appear up to the meter scale on the microscopic scale we observe dynamic recrystallization already in deep firn leading to substantial microstructural changes prior to bubble close off the concentration of visible micro inclusions in the holocene part of the core seems to increase with depth which could possibly indicate post depositional formation of salts in glacial period ice the concentration of visible micro inclusions in certain layers is so high that these strata appear as light scattering bands often called cloudy bands another interesting stratigraphic feature is what we call bubble free bands viz millimeter thick strata deprived of bubbles and rich in clathrate hydrates which are found within the bubble hydrate transition zone 800 1200 m depth and are probably caused by anomalously fast clathration while there is hardly any interaction between visible micro inclusions and grain boundaries down to 2500 m depth in the deeper ice warmer than 10 c many grain boundaries seem to harvest micro inclusions here we discuss these observations and their relevance for the interpretation of climate records

on the potential of coupling air content and o2 n2 from trapped airfor establishing an ice core chronology tuned on local insolation the potential to access an ice core chronology tuned on local insolation has been demonstrated for the first time in the work of m bender 2002 linking the variations of o2 n2 ratios in the air trapped in the vostok ice with local 78 s summertime insolation more recently it has been shown that the long term changes in air content v recorded in ice from the high antarctic plateau are also dominantly imprinted by the local summer insolation raynaud et al 2007 this paper presents a new v record from vostok which is compared with the published vostok o2 n2 record for the same period of time 160 390 ka bp by using the same spectral analysis methods the spectral differences between the two properties and the possible mechanisms linking them with insolation through the surface snow structure and the close off processes are discussed the main result of our study is that the two experimentally independent local insolation proxies lead to absolute orbital timescales which agree together within less than 1 ka on average this result strongly adds credibility to the total content and the o2 to n2 ratio of the air trapped in ice as reliable and complementary tools for accurate dating of existing and future deep ice cores

maturity effect on carbazole distributions in source rocks from the saline lacustrine settings the western qaidam basin nw china abstract carbazole distributions and biomarker compositions have been investigated in a series of source rocks from the tertiary strata in the western qaidam basin nw china typical biomarker signatures high gammacerane high c 35 hopane and low pr ph indicate a saline lacustrine environment maturity parameter c 29 sterane s s r ranges from 0 06 to 0 58 indicating immature ca 0 35 stages significant variations were observed for carbazole distributions with maturation as for c 1 carbazoles the relative amounts of 1 mc methylcarbazole show a decrease trend in the immature stage and an increase trend in the mature stage while the other three isomers 2 3 and 4 mcs show a generally opposite change indicating a two stage variation as for c 2 carbazole isomers complex variations were observed for their relative amounts an overall increase for 1 7 dmc dimethylcarbazole a slight two stage change for 1 8 and 1 3 dmcs and a marked two stage variation for 2 4 2 5 and 2 6 dmcs comparison of the distributions of carbazole and benzocarbazoles revealed a preferential generation for benzocarbazoles at high maturity levels benzocarbazole ratio a a c varies only in a narrow range 0 52 0 61 in the entire maturity range suggesting limited maturity dependence the results here support the idea that carbazole distributions have strong maturity effect in a wide maturity range and the two stage variations for some pyrrolic nitrogen isomers may indicate their different geochemical controls between the immature and mature stages

modeled antarctic precipitation part ii enso modulation over west antarctica the impacts of the el nino southern oscillation enso on the antarctic region are of special importance in evaluating the variability and change of the climate system in high southern latitudes in this study the enso signal in modeled precipitation over west antarctica since 1979 is evaluated using forecast precipitation from several meteorological analyses and reanalyses additionally a dynamical retrieval method drm for precip itation is applied over the last two decades the southern oscillation index soi has an overall anticorrelation with precipitation over the west antarctic sector bounded by 758 908s 1208w 1808 while it is positively correlated with precipitation over the south atlantic sector bounded by 658 758s 308 608w decadal variations are found as the relationship between the soi and west antarctic precipitation is stronger in the 1990s than that in the 1980s the polar front jet stream west antarctic precipitation and the soi show a well ordered correspondence during the 1990s as the jet zonal speed is negatively correlated to the soi and positively correlated to west antarctic precipitation these relationships are weaker during the 1980s consistent with the change in sign of the correlation between the soi and west antarctic precipitation the decadal variations are apparently related to changes in the quasi stationary eddies that determine the local onshore and offshore flow over west antarctica

bubbly ice densification in ice sheets ii applications a mathematical model for simulating the densification of bubbly glacier ice is used to interpret the following experimental data from the vostok central antarctica ice core two ice porosity profiles obtained by independent methods and a bubble pressure profile obtained by direct measurements of air pressure within individual bubbles the rheological properties of pure polycrystalline ice are deduced from the solution of the inverse problem the model and the inferred ice flow law are then validated using porosity profiles from seven other ice cores drilled in antarctica and greenland in the temperature range from 55 to 20 c the following expression is adopted for the constitutive law 2e 1 2 exp q 1 t s 1 t r s where e and are the effective strain rate and stress respectively is the creep exponent taken as 3 5 r s is the gas constant and t t s is the temperature standard temperature the numerical values obtained for the linear and non linear viscosities are 1 2 9 1 3 mpayear and 2 0 051 0 019 mpa year and the apparent activation energy q is confirmed to be 60 kj mole 1 the corresponding flow law is in good agreement with results of both mechanical tests and independent estimations based on the analysis of different natural phenomena associated with glacier ice deformation when the model is constrained by the porosity and bubble pressure profiles from vostok the mean air content in holocene ice is inferred to be about 0 088 cm 3 g 1 the corresponding mean air pressure in bubbles at the end of pore closure is about 0 083 mpa whereas the atmospheric pressure at this depth level would be 0 063 mpa the influence of the climatic change on the ice porosity profile is discussed it resulted in an increased air content in ice at vostok during the last glacial maximum 0 096 cm 3 g 1

distribution of air bubbles in the edml and edc antarctica ice cores using a new method of automatic image analysis air bubbles in ice cores play an essential role in climate research not only because they contain samples of the palaeoatmosphere but also because their shape size and distribution provide information about the past firn structure and the embedding of climate records into deep ice cores in this context we present profiles of average bubble size and bubble number for the entire edml antarctica core and the top 600 m of the edc antarctica core and distributions of bubble sizes from selected depths the data are generated with an image processing framework which automatically extracts position orientation size and shape of an elliptical approximation of each bubble from thick section micrographs without user interaction the presented software framework allows for registration of overlapping photomicrographs to yield accurate locations of bubble like features a comparison is made between the bubble parameterizations in the edml and edc cores and data published on the vostok antarctica ice core the porosity at the firn ice transition is inferred to lie between 8 62 and 10 48 for the edc core and between 10 56 and 12 61 for the edml core

on the use of δ18oatm for ice core dating abstract deep ice core chronologies have been improved over the past years through the addition of new age constraints however dating methods are still associated with large uncertainties for ice cores from the east antarctic plateau where layer counting is not possible indeed an uncertainty up to 6 ka is associated with aicc2012 chronology of epica dome c edc ice core which mostly arises from uncertainty on the delay between changes recorded in 18oatm and in june 21st insolation variations at 65 n used for ice core orbital dating consequently we need to enhance the knowledge of this delay to improve ice core chronologies we present new high resolution edc 18oatm record 153 374 ka and o2 n2 measurements 163 332 ka performed on well stored ice to provide continuous records of 18oatm and o2 n2 between 100 and 800 ka the comparison of 18oatm with the 18ocalcite from east asian speleothems shows that both signals present similar orbital and millennial variabilities which may represent shifts in the intertropical convergence zone position themselves associated with heinrich events we thus propose to use the 18ocalcite as target for 18oatm orbital dating such a tuning method improves the ice core chronology of the last glacial inception compared to aicc2012 by reconciling ngrip and mid latitude climatic records it is especially marked during dansgaard oeschger 25 where the proposed chronology is 2 2 ka older than aicc2012 this 18oatm 18ocalcite alignment method applied between 100 and 640 ka improves the edc ice core chronology especially over mis 11 and leads to lower ice age uncertainties compared to aicc2012

on the impact of impurities on the densification of polar firn abstract understanding polar firn densification is crucial for reconstructing the age of greenhouse gas concentrations extracted from ice cores and for the interpretation of air in ice as a dating tool or as a climate proxy firn densification is generally modeled as a steady burial and sintering process of defined layers where the structure of the layering is maintained along the whole firn and ice column however available high resolution density data as well as firn air samples question this picture and point to a lack of understanding of firn densification based on analysis of high resolution density and calcium concentration records from antarctic and greenland ice cores we show for the first time that also impurities may have a significant impact on the densification analysis of firn cores shows a correlation between density and the calcium ion ca concentration and this correlation increases with depth the existence of this relationship is independent of the local climatic conditions at the core sites analyzed the strong positive correlation between the density and the logarithm of ca concentration indicates that impurities induce softening and lead to faster densification over a wide range of concentrations in one core the impurity effect manifests itself so strongly that the density develops a seasonal cycle closely following the seasonal cycle of ca our results clearly show that the structure of the firn layering changes with depth and suggest that the increased variability in density observed in deep firn recently described as a universal feature of polar firn may arise from the influence of ca and or other impurities the impurity effect is likely to have direct implications on our understanding of glacial firn densification and on glacial gas age estimates

the controls on the composition of biodegraded oils in the deep subsurface part 1 biodegradation rates in petroleum reservoirs abstract biodegradation rates in oilfields have been assessed conservatively using whole oil column minimum rate estimates diffusion controlled oil column compositional gradient modelling and mixed oil kinetic models biodegradation rate constants first order are around 10 6 10 7 yr 1 for hydrocarbons in the degradation zones these corresponding well with zero order field wide minimum rate estimates of about 10 8 kg hydrocarbons kg oil year for the whole oil column with biodegradation induction times of around 1 2 ma to perturb an entire oil column for light oil reservoirs and 10 20 ma for heavy oil reservoir degradation the results indicate that where we see continuous gradients in the oil columns degradation must have been occurring episodically for many millions of years to remove the n alkanes from an oil i e about 10 of an oil around ca 15 ma is needed for a heavy oil ca 5 ma for a light n sea oil the timescales of oilfield degradation and filling are thus very similar and consequently the degree of biodegradation will be substantially controlled by oilfield charge history assessment of mixed degraded non degraded oil occurrence provides an independent confirmation that these rates are realistic and that timescales of degradation and field charging are similar the maximum effective rate constant of degradation ultimately controlled by the limiting effect of diffusion of alkanes to the oil water contact owc ca 10 4 yr 1 for a 130 m thick oil column first order rate constant is well above the estimated rate constants indicating oil biodegradation rate is not limited by electron donor supply i e hydrocarbons but by supply of nutrients or oxidants this suggests that diffusive transport of nutrients and electron acceptors in the aquifer to the site of biodegradation may be adequate to maintain the low rate biosphere

global budget of water isotopes inferred from polar ice sheets 1 water isotope ratios in ice cores and marine sediments are a key indicator of past temperature and global ice volume quantitative interpretation of these ratios requires understanding of the storage capacity and exchanges among the ocean atmosphere and cryosphere we combine numerical models of ice dynamics and tracer transport to predict bulk ice properties by simulating the fine layering of ice sheets locally validated at ice core sites the 18o 16o content of ice sheets is found to vary between the present and 20 kyr ago from 34 to 37 for greenland from 41 to 42 5 for west antarctica and always remained near 56 5 for east antarctica their combined effect on sea water 18o 16o is a 0 08 0 12 increase 20 kyr ago a 1 11 decrease if ice sheets were to vanish we confirm that ice volume changes in antarctica and greenland linearly affect ocean composition though at different rates

dating the vostok ice core by an inverse method using the chronological information available in the vostok records we apply an inverse method to assess the quality of the vostok glaciological timescale the inversion procedure provides not only an optimized glaciological timescale and its confidence interval but also a reliable estimate of the duration of successive events our results highlight a disagreement between orbitally tuned and glaciological timescales below 2700 m i e 250 kyr b p thousands of years before present this disagreement could be caused by some discontinuity in the spatial variation of accumulation upstream of vostok moreover the stratigraphic datings of central greenland ice cores grip and gisp2 appear older than our optimized timescale for the late glacial this underlines an unconsistency between the physical assumptions used to construct the vostok glaciological timescale and the stratigraphic datings the inverse method allows the first assessment of the evolution of the phase between vostok climatic records and insolation this phase significantly varies with time which gives a measure of the nonlinear character of the climatic system and suggests that the climatic response to orbital forcing is of different nature for glacial and interglacial periods we confirm that the last interglacial as recorded in the vostok deuterium record was long 16 2 2 kyr thousands of years however midtransition of termination ii occurred at 133 4 2 5 kyr bp which does not support the recent claim for an earlier deglaciation finally our study suggests that temperature changes are correctly estimated when using the spatial present day deuterium temperature relationship to interpret the vostok deuterium record

deep ice cores the need for going back in time abstract after the success of epica the european project for ice coring in antarctica which at dome c east antarctica has provided access to climate and environmental records covering the last 800 ka thousands of years the ice core community is now engaged in the challenge to obtain older records obtaining a 1 5 million year ma record of climate and greenhouse gases is one of the priorities of the international partnerships in ice core sciences ipics largely motivated by the yet unexplained shift in climate cyclicity around the mid pleistocene transition mpt around 1 2 ma ago from epica results and recently published articles we further examine how such a 1 5 ma old ice core will help and is indeed indispensable to depict and understand this transition

fractionation of benzocarbazoles between source rocks and petroleums the concentrations of the a and c isomers of benzocarbazoles in a number of crude oils and source rock bitumens were obtained by in house methods and from reported published data the changes in benzocarbazole concentrations and the benzocarbazole a a c ratio relating to source maturity facies and migration are described with increasing source maturity in north sea oils and source rocks up to 0 85 vitrinite reflectance equivalent benzocarbazole concentrations increase due to generation followed by a decrease above 0 85 vitrinite reflectance equivalent due to expulsion dilution by newly generated hydrocarbons comparison of benzocarbazole concentrations between reservoired petroleum and related source petroleum revealed a concentration bias in favour of source petroleum where concentrations of benzocarbazoles reached up to 10 times that found in equivalent reservoired petroleum the differences in benzocarbazole concentrations between related oils and source rocks indicate that the major fractionation is introduced during primary migration and expulsion because when secondary migration is limited as in the miller field we see extensive benzocarbazole fractionation between reservoired petroleum and associated source petroleum the relationships between source rock toc content and petroleum benzocarbazole concentrations and a a c ratios indicate that source organic matter exerts a strong influence on benzocarbazole distributions the introduction of a reservoir source fractionation parameter rsfp defined as the ratio between the concentrations of benzo a benzo c carbazole in reservoired petroleum versus the concentration of benzo a benzo c carbazole in source petroleum enables description of the relationship between reservoired petroleum and source petroleum from different petroleum systems petroleum deriving from clastic source rocks demonstrated high levels of benzocarbazole fractionation between reservoired petroleum and source petroleum during primary and secondary migration compared to petroleum deriving from carbonate systems the rsfp parameter may also be used to examine fractionation effects during migration between different compound types the more polar benzocarbazoles are fractionated more strongly than dibenzothiophene and phenanthrene between reservoired petroleum and source petroleum whereas sometimes source maturity signals do dominate the benzocarbazole signals in migrated oils in other circumstances often associated with clastic source rocks no clear maturity signal is transferred to migrated oils

climatic and glaciological information inferred from air content measurements of a law dome east antarctica ice core the total air content v of ice has been measured along the dome summit south dss core from law dome east antarctica the main features of this record are the very well preserved sub annual fluctuations of v down to at least 900 m depth and the significant increase of the v values during the last deglaciation the sub annual variations reflect changes in close off porosity and we interpret the v seasonal peaks as tracers of depth hoar layers for the longer time scale the large v fluctuations observed are interpreted in terms of elevation and or close off porosity changes under different assumptions we analyze the possible influence of a different global pressure field and or a change in seasonal temperature and precipitation cycles during the last glacial period our estimates of surface elevation changes derived from the v data are then compared with independent reconstructions of past elevations

firn processes and δ15n potential for a gas phase climate proxy abstract in order to quantify the sequence of events between changes in atmospheric composition and climate changes recorded in ice cores we must accurately account for the age difference between ice and gas at a given depth this gas age ice age difference depends on the age of the ice at the bottom of the firn layer where the bubbles are closed off firn densification models are used to calculate how this age difference varied in the past but have an uncertainty on the order of 1000 years for central antarctic sites here we explore the possibility that 15 n of n 2 is a gas phase proxy of climate which can be used to synchronize gas and ice records we present the 15 n record from the epica dome c edc ice core covering the last three glacial terminations and five glacial interglacial cycles between 300 and 800 ka previous studies have shown that gravitational settling enriches 15 n as a function of the diffusive column height in the firn if densification models prediction of deeper firn close off under glacial conditions is correct then we would expect heavier 15 n during glacial periods and a negative correlation with temperature instead edc 15 n is positively correlated with the ice deuterium content a proxy for temperature as previously reported at vostok dome fuji and epica dronning maud land we propose a mechanism that links accumulation rate firn permeability and convective mixing in the top meters of the firn to explain this correlation between 15 n and ice deuterium content the tightest correlation is observed over glacial terminations supporting the idea that 15 n is a property in the gas phase that records changes in surface conditions linked to deglacial warming

an oceanic cold reversal during the last deglaciation a detailed deuterium excess profile measured along the dome c epica european project for ice coring in antarctica core reveals the timing and strength of the sea surface temperature changes at the source regions for dome c precipitation we infer that an oceanic cold reversal took place in the southern indian ocean 800 years after the antarctic cold reversal the temperature gradient between the oceanic moisture source and antarctica is similar to the dome c sodium profile during the deglaciation illustrating the strong link between this gradient and the strength of the atmospheric circulation

physical and climatic parameters which influence the air content in polar ice abstract under present day climatic conditions the air content of polar ice v generally shows a high sensitivity to the atmospheric pressure and hence to the surface elevation of the ice sheet wherethe ice is formed the results presented here are from sixteen different sites fourteen in antartica one in greenland and one in the yukon territories canada and they allow a better understanding of the parameters which influence the air content in ice it is demonstrated the v can be expressed very simply as a function of the atmospheric pressure p i the temperature t i and the porous volume of ice v i at which the air in the firn becomes isolated in terms of pressure from the atmosphere during the process of pore close off our results confirm a v i increase with temperature and show no clear v i dependence on snow accumulation rate the possible non linearity of the v i t i relation we obtain could be due to a wind influence on v i and or to a second order effect of the accumulation rate our v i results are compared to measurements of the volume of closed pores versus depth in the firn to close we discuss the parameterization that we can obtain to interpret the air content variations observed in deep ice cores over periods covering glacial interglacial transitions in terms of paleoclimatic conditions prevailing at the surface of the ice sheet

a dynamic biodegradation model suggested by petroleum compositional gradients within reservoir columns from the liaohe basin ne china abstract a suite of petroleum reservoir extracts from the liaohe basin ne china was analyzed to investigate the effects and controls of biodegradation on petroleum composition systematic changes seen as marked gradients in petroleum bulk composition component concentrations and molecular indicators have been observed in two biodegraded oil columns in the es3 column 1700 1850 m biodegradation has removed substantial amounts of normal and isoprenoid alkanes more severe biodegradation occurs in the shallower es1 column 1500 1650 m with both steranes and hopanes being partially removed temperature has an overall control on biodegradation in the two columns a lower reservoir temperature leading to a higher degree of biodegradation however observed variation in the degree of biodegradation in the es3 column at different sites is controlled by water leg size with a higher level of degradation being associated with a thicker water leg the supply of nutrients from the water leg is thought to have a significant impact upon the degree of biodegradation in addition to water leg size nutrient supply the compositional gradients also are controlled by the relative rate of mixing of fresh oil charge gradients can only be conserved in biodegraded petroleum columns if the rate of diffusive mixing is similar to or lower than the rate at which the hydrocarbons are removed a biodegradation model is proposed that couples geochemical and geological factors to provide a coherent approach for assessing the impact of degradation on petroleum our geochemical study indicates that biodegradation occurs mainly within a narrow region at or near the base of the oil column the stable compositional gradients are produced after an initial induction period involving diffusive transport of alkanes to the oil water contact owc and diffusion of biodegradation products such as 25 norhopanes and other metabolites away from the reaction site the mixing of continuously charged oil with residential biodegraded oil by diffusion may be considered as one of the most important factors controlling the biodegradation process the conceptual model illustrates all of these processes and opens the possibility of model driven prediction of oil properties and sweetspot location in reservoirs

hydrogen isotopic compositions of individual alkanes as a new approach to petroleum correlation case studies from the western canada sedimentary basin isotopic compositions of carbon bound hydrogen in individual n alkanes and acyclic isoprenoid alkanes from a number of crude oil samples were measured using gas chromatography thermal conversion isotope ratio mass spectrometry the precision of this technique is better than 3 for most alkanes compared to the large range of d variation among the samples up to 160 the oils were selected from major genetic oil families in the western canada sedimentary basin with source rocks ranging in age from ordovician and possibly cambrian to cretaceous the hydrogen isotopic composition of alkanes in crude oils is controlled by three factors isotopic compositions of biosynthetic precursors source water d values and postdepositional processes the inherited difference in the lipid s biosynthetic origins and or pathways is reflected by a small hydrogen isotopic variability within n alkanes but much larger differences in the d values between n alkanes and pristane phytane the shift toward lighter hydrogen isotopic compositions from paleozoic to upper cretaceous oils in the wcsb reflects a special depositional setting and or a minor contribution of terrestrial organic matter the strong influence of source water d values is demonstrated by the distinctively lower d values of lacustrine oils than marine oils and also by the high values for oils with source rocks deposited in evaporative environments thermal maturation may alter the d values of the alkanes in the oil to some extent but secondary oil migration does not appear to have had any significant impact the fact that oils derived from source rocks that could be of cambrian age still retain a strong signature of the hydrogen isotopic compositions of source organic matter and source water indicates that d values are very useful for oil source correlation and for paleoenvironmental reconstructions

modelling of the densification of polar firn characterization of the snow firn transition the transformation of dry snow to firn is described by the transition between densification by deformationless restacking and densification by power law creep the observed decrease with temperature of the density at the snow firn transition seems to result from the competition between grain boundary sliding and power law creep these two densification processess occur concurrenlly in snow although there are probably micro regions in which sliding alone occurs validation ofa geometrical densifi cation model developed for ceramics has been obtained from densification data from several antarctic and greenland sites and from the characterization of the structure of polar firn

air content along the greenland ice core project core a record of surface climatic parameters and elevation in central greenland we present here measurements of the air content of the ice v performed along the greenland ice core project grip ice core the main features of the long term trends are 1 a decrease of 13 between the last glacial maximum lgm and the earliest part of the holocene and 2 an increase of 8 during the holocene the results are discussed in terms of changes in atmospheric pressure surface elevation and porosity at close off the v record contains a significant signal of past changes of surface elevation in qualitative agreement with ice sheet modeling simulations it suggests a thickening of central greenland during the transition from the lgm to the early holocene and a significant thinning through the holocene period it also stresses the large influence on past v variations of changes in ice porosity which are not explained by the present day spatial relationship with temperature and may reflect changes in other surface climatic parameters like precipitation seasonality or wind stress the potential role of temporal variations of atmospheric pressure patterns is also evaluated air content results in the grip ice older than 110 ka indicate values approximately in the same range as those observed during the last 40 000 years with generally higher air content corresponding to isotopically warmer ice

quantitative fluorescence techniques for detecting residual oils and reconstructing hydrocarbon charge history abstract two new fluorescence techniques quantitative grain fluorescence qgf and quantitative grain fluorescence on extract qgf e can detect palaeo oil zones and current residual oil zones in petroleum wells respectively qgf and qgf e measure the fluorescence emission spectra of trace fluorescence from reservoir grains and their extracts qgf is measured on dry disaggregated reservoir grains after a cleaning procedure involving solvent hydrogen peroxide and acid whereas qgf e is measured on the solvent extract from the qgf cleaned grains palaeo oil zones have distinct qgf spectra with spectral peaks between 375 and 475 nm and elevated fluorescence intensities compared with spectra for rocks that have always been water saturated current and residual oil zones have distinct qgf e spectra with spectral peaks at around 370 nm and elevated qgf e intensities compared with that for current water zones both qgf and qgf e responses increase upwards from the palaeo oil water and residual oil water contacts respectively an oil producing well from timor sea nw australia was investigated in detail using the qgf and qgf e techniques to illustrate how they can be used to reconstruct hydrocarbon migration history

geochemical characteristics and implications of hydrocarbons in reservoir rocks of junggar basin china abstract a practical sequential extraction approach has been applied to two core samples collected from oil zones of triassic sandstones in junggar basin northwest china five bitumen fractions were obtained from each sample using this approach these fractions are free oil components in inter granular pores bitumen 1 adsorbed oil components on grain surfaces and liberated by hcl treatment bitumen 2 oil bearing fluid inclusions hosted by grains bitumen 3 and adsorbed oil components on clay mineral surfaces and liberated by hcl and hcl hf treatments bitumens 4 and 5 striking differences have been observed both in bulk compositions and in aliphatic biomarker distributions e g terpanes and steranes among the five bitumen fractions this phenomenon is ascribed to the indigenous compositional variations and differential maturation behaviors between adsorbed oil components in a network of polar compounds resins and asphaltenes and free oil components in even a same oil charge in addition to fractional adsorption effects and compositional changes of the oil charges in reservoir rocks during filling process the molecular compositions and homogenization temperatures of oil bearing fluid inclusions in these two samples indicate that trapping of these types of inclusions apparently ceased in sample a while continued in sample b after the initial oil charge suggesting that the relative content of polar components in the initial oil charge compared to the later oil charges plays a dominant role controlling the trapping of oil bearing fluid inclusions in an oil saturated zone sequential extraction studies are important and useful for reservoir geochemistry especially in the cases where only limited samples of oil and reservoir rocks are available and or where compositional heterogeneity of free oils has disappeared in a reservoir karlsen d a nedkvitne t larter s r bjorlykke k 1993 hydrocarbon composition of authigenic inclusions application to elucidation of petroleum reservoir filling history geochim cosmochim acta 57 3641 3659

hemispheric roles of climate forcings during glacial interglacial transitions as deduced from the vostok record and lln 2d model experiments the vostok ice contains fingerprints of atmospheric greenhouse trace gases antarctic temperature northern hemisphere temperature and global ice volume sea level changes during the last glacial interglacial cycles and thus allows us to investigate the sequences of these climatic events in particular during the transitions from full glacial to interglacial conditions the use of the updated co2 record presented here and a reexamination of the sea level proxy confirm that the succession of changes has been similar through each of the four marked transitions found at vostok antarctic air temperature and co2 increase in parallel and almost synchronously while the rapid warmings over greenland take place during the last half of their change and coincide with the marked decay in continental ice volume the vostok results thus emphasize a fundamental difference between south and north in terms of climate dynamics our results confirm the role of co2 as an important amplifier of the glacial interglacial warming in the south it appears also that the marked warming observed at high northern latitudes lagging behind the co2 increase by several thousand years is roughly synchronous with the decay of the northern ice sheets suggesting a major role of climatic feedback due to this decay such a climatic scenario is supported by sensitivity experiments performed with the lln 2 d model forced by the northern hemisphere insolation and co2 model results indicate that the decay of the northern ice sheets and the northern hemisphere temperature depend primarily on the northern summer insolation these results nevertheless could be affected if mechanisms specific to the southern hemisphere appear to play a major role in driving the northern hemisphere climate the model also helps to constrain the time response of ice volume to insolation and co2 changes

fluid geochemistry of the acqui terme visone geothermal area piemonte italy the main geothermal reservoir of acqui terme visone hosts na cl waters which are in chemical equilibrium at 120 130 c with typical hydrothermal minerals including quartz albite k feldspar illite chlorite or smectite anhydrite calcite and an unspecified ca al silicate in the acqui terme visone area these geothermal waters ascend along zones of high vertical permeability and discharge at the surface almost undiluted or mixed with cold shallow waters to the sw of acqui terme other ascending geothermal waters either undiluted or mixed with low salinity waters enter relatively shallow secondary reservoirs where they reequilibrate at 65 70 c both chemical and isotopic data indicate that bacterial so4 reduction affects all these waters especially those discharged by the secondary reservoirs therefore geothermal waters must get in contact with oil acquiring the relatively oxidized organic substances needed by so4 reducing bacteria this oil water interaction process deserves further investigations for potential economic implications

sequence of events from the onset to the demise of the last interglacial evaluating strengths and limitations of chronologies used in climatic archives the last interglacial lig represents an invaluable case study to investigate the response of components of the earth system to global warming however the scarcity of absolute age constraints in most archives leads to extensive use of various stratigraphic alignments to different reference chronologies this feature sets limitations to the accuracy of the stratigraphic assignment of the climatic sequence of events across the globe during the lig here we review the strengths and limitations of the methods that are commonly used to date or develop chronologies in various climatic archives for the time span 140 100 ka encompassing the penultimate deglaciation the lig and the glacial inception climatic hypotheses underlying record alignment strategies and the interpretation of tracers are explicitly described quantitative estimates of the associated absolute and relative age uncertainties are provided recommendations are subsequently formulated on how best to define absolute and relative chronologies future climato stratigraphic alignments should provide 1 a clear statement of climate hypotheses involved 2 a detailed understanding of environmental parameters controlling selected tracers and 3 a careful evaluation of the synchronicity of aligned paleoclimatic records we underscore the need to 1 systematically report quantitative estimates of relative and absolute age uncertainties 2 assess the coherence of chronologies when comparing different records and 3 integrate these uncertainties in paleoclimatic interpretations and comparisons with climate simulations finally we provide a sequence of major climatic events with associated age uncertainties for the period 140 105 ka which should serve as a new benchmark to disentangle mechanisms of the earth system s response to orbital forcing and evaluate transient climate simulations

early pleistocene glacial cycles and the integrated summer insolation forcing long term variations in northern hemisphere summer insolation are generally thought to control glaciation but the intensity of summer insolation is primarily controlled by 20 000 year cycles in the precession of the equinoxes whereas early pleistocene glacial cycles occur at 40 000 year intervals matching the period of changes in earth s obliquity the resolution of this 40 000 year problem is that glaciers are sensitive to insolation integrated over the duration of the summer the integrated summer insolation is primarily controlled by obliquity and not precession because by kepler s second law the duration of the summer is inversely proportional to earth s distance from the sun

molecular correlation of free oil adsorbed oil and inclusion oil of reservoir rocks in the tazhong uplift of the tarim basin china the free adsorbed and inclusion oils were recovered by sequential extraction from eleven oil and tar containing reservoir rocks in the tazhong uplift of tarim basin the results of gas chromatography gc and gc mass spectrometry analyses of these oil components and seven crude oils collected from this region reveal multiple oil charges derived from different source rocks for these oil reservoirs the initially charged oils show strong predominance of even over odd n alkanes in the range n c12 to n c20 and have ordinary maturities while the later charged oils do not exhibit any predominance of n alkanes and have high maturities the adsorbed and inclusion oils of the reservoir rocks generally have high relative concentrations of gammacerane and c28 steranes similar to the cambrian lower ordovician source rocks in contrast the free oils of these reservoir rocks generally have low relative concentrations of gammacerane and c28 steranes similar to the middle upper ordovician source rocks there are two interpretations of this result 1 the initially charged oils are derived from the cambrian lower ordovician source rocks while the later charged oils are derived from the middle upper ordovician source rocks and 2 both the initially and later charged oils are mainly derived from the cambrian lower ordovician source rocks but the later charged oils are contaminated by the oil components from the silurian tar sandstones and the middle upper ordovician source rocks

ice core analysis at site a greenland preliminary results ice core drilling at site a greenland 70 45 n 35 57 5 w 3145m a s l by the polar ice coring office recovered two cores of about 100 m each which are now in storage awaiting further analysis field studies show that visible strata in the cores record both individual storms and individual years a typical year comprises 15 storm deposits pore close off occurs between 75 and 80 m depth the grain growth rate in isothermal firn and ice is about 7 8 x 1o 3 mm 2 a l the 10m temperature is about 29 5 c and the accumulation rate over the last 200 years is about 290 mm a i ice melt events occur about once every 40 years and major events can be correlated between cores separated by 20 m

aromatic biomarkers as indicators of source depositional environment maturity and secondary migration in the oils of cambay basin india abstract aromatic biomarkers have been analysed for source depositional environment maturity and secondary migration in crude oils from different formations of paleocene to eocene age in the ahmedabad mehsana block of north cambay basin and the broach block of south cambay basin north cambay basin oils are characterized by a high abundance of 1 2 5 and 1 2 7 trimethylnaphthalenes tmn and low to medium ratio of dibenzothiophene phenanthrene and low ratio of pristane phytane indicates that these oils have been derived from a source containing predominantly higher plants and that the organic matter was deposited in restricted marine or lacustrine environments in anoxic to suboxic conditions the relative abundance of 1 2 7 tmn suggests that it was derived from the structural degradation of oleanane type triterpenoids present in angiosperms south cambay basin oils are less abundant in 1 2 5 and 1 2 7 tmns and low ratio of dibenzothiophene phenanthrene and high ratio of pristane phytane indicating that the oils were derived from higher plant source organic matter deposited under marine or fluvial deltaic environment in oxic conditions maturity sensitive ratios based on phenanthrene naphthalene dibenzothiophene and their alkyl substituted isomers have been used to calculate the equivalent vitrinite reflectance these parameters indicate a wide range of thermal maturity of the oils ranging from 0 60 to 0 93 vrc methylphenanthrene index and methyldibenzothiophene ratios indicate that the maturity of north and south cambay basin oils are different the north cambay basin oils are less mature than south cambay basin oils pyrrolic nitrogen distribution indicates that the alkylated carbazoles and benzocarbazoles are more abundant in south cambay basin oils as compared to north cambay basin oils these data indicate that north cambay basin oils are less migrated compared to south cambay basin oils this systematic investigation of the aromatic biomarkers in oils of cambay basin has resulted in a new generation migration and entrapment model that has led to the development of new exploration leads

simple relations for the close off depth and age in dry snow densification a physical model for the snow firn densification process salamatin and others 2006 and martinerie and others 1992 1994 correlation for the firn density at the pore closure are employed to perform a scale analysis and computational experiments in order to deduce simplified relations for the close off depth and ice age in quasi stationary ice formation conditions the critical snow density at which ice grain rearrangement stops is used to take into account variability of snow structures subjected to densification the results obtained are validated on a representative set of ice core data from 22 sites which covers wide ranges of present day temperatures and ice accumulation rates a simple analytical approximation for the density depth profile is proposed