an 15 000 year record of el nino driven alluviation in southwestern ecuador debris flows have deposited inorganic laminae in an alpine lake that is 75 kilometers east of the pacific ocean in ecuador these storm induced events were dated by radiocarbon and the age of laminae that are less than 200 years old matches the historic record of el nino events from about 15 000 to about 7000 calendar years before the present the periodicity of clastic deposition is greater than or equal to 15 years thereafter there is a progressive increase in frequency to periodicities of 2 to 8 5 years this is the modern el nino periodicity which was established about 5000 calendar years before the present this may reflect the onset of a steeper zonal sea surface temperature gradient which was driven by enhanced trade winds

origin of tar mats in petroleum reservoirs part ii formation mechanisms for tar mats abstract tar mats and oil legs from several marine source rock derived oil fields including the ula and oseberg fields in the north sea and an unidentified north american example have been analysed geochemically in all cases the tar mats were derived from the same petroleum system as the oil leg oils and were found in the most porous and permeable portions of the reservoir comparing case history data with published data on the subsurface solubility characteristics of asphaltenes in petroleums it is possible to eliminate some potential tar mat formation mechanisms and suggest the most likely causative mechanisms thus the adsorption of asphaltenes on reservoir clays and light to moderate levels of biodegradation are considered unlikely to contribute to tar mat formation in the ula field thermal degradation of the oil in the carrier and reservoir causing asphaltene precipitation may be a major contributing factor to the tar mats there in the oseberg field increased gas solution in the oil leg may have contributed to deasphaltation tentative mass balance calculations the extreme pressure dependence of asphaltene solubility in subsurface crude oils the occurrence of tar mats in zones of elevated permeability plus a simple transport model suggest that during secondary migration an asphaltene rich petroleum phase may be produced in dipping carrier beds and may be carried into the reservoir contributing in some instances to tar mat formation

time dependent spatial amplitude patterns of harmonic tremor at arenal volcano costa rica seismic wave interferences seismograms recorded at the receivers of a small aperture seismic array usually display very similar waveforms and amplitudes as a consequence of their close proximity during the analysis of the volcanic tremor wave field at arenal volcano costa rica we detected significant differences in the amplitudes of harmonic tremor recorded at the stations of a small aperture 210 m seismic array the amplitude distributions are geometrically complex and characterized by strong gradients they occur just for harmonic tremors any other type of seismic event produces nearly uniform amplitudes across the array this suggests some relation with harmonic frequency content moreover the spatial amplitude patterns change with time some of these observations could be explained by an extreme combination of source path and site effects but they also could be produced by interference of different components of the seismic wave field we use numerical calculations to investigate the amplitude pattern generated by two interfering plane waves and are able to reproduce the main features of the observed amplitude patterns we propose mechanisms that might generate seismic wave fields with multiple components and conclude that interference can explain the complexity and variability of the harmonic tremor wave field at arenal volcano online material wave field animation

origin of tar mats in petroleum reservoirs part i introduction and case studies abstract three case studies of petroleum reservoirs containing tar mats oseberg field and ula field both from the north sea and a north american field have been studied using a variety of organic geochemical techniques with special emphasis on the geochemistry of the asphaltenes the results were evaluated in combination with the available geological data and with numerical simulations to evaluate possible mechanisms of tar mat formation part ii wilhelms and larter 1994 in part i the petroleum geochemistry of three sets of tar mats is described the tar mat extracts were characterized by a sharp increase in the asphaltene content 20 60 wt compared with the oil leg extracts 1 5 wt the extract yields kg eom t rock in the tar mats ca 4 46 for the oseberg field 8 18 for the ula field and 8 43 for the north american case study are significantly higher than in the corresponding oil leg extracts which have extract yields of ca 1 14 kg t rock the tar mat extracts are geochemically related to the pooled oil as revealed by geochemical fingerprinting including biomarker analysis the tar mats are situated in high porosity and high horizontal permeability sandstone layers above permeability barriers several zones of low extract yield and immature petroleum geochemical characteristics were observed within the oil legs and between tar mats which might represent minor amounts of petroleum generated locally from indigenous organic matter

a modern analogue of western united states summer palaeoclimate at 6000 years before present a modern summer climate analogue of western united states 6 ka palaeoclimate based on broad scale patterns from proxy data and general circulation model simulations provides details concerning its sum mer synoptic climatology august 1955 serves as a close analogue featuring an amplified subtropical ridge aloft and anticyclonic flow near the surface over the central united states and stronger westerly flow along the canadian northwest united states border the august 1955 summer temperature pattern similar to those from general circulation model simulations exhibits positive anomalies throughout most of the continental interior the august 1955 precipitation pattern corresponds very closely with patterns of effective moisture from proxy data showing widespread aridity and some stronger monsoonal activity in the southwest the analogue suggests that the amplified subtropical ridge is a very important feature of 6 ka palaeoclimate with the circulation pattern differing from that in the early holocene implying interactions between both milankov itch and sub milankovitch forcing factors

geochemical characterization of solid bitumen in the chesterian mississippian sandstone reservoir of the hitch field southwest kansas solid bitumen was identified within the mississippian chester sandstone reservoir in the hitch field southwest kansas the adjacent etzold field has similar reservoir properties but lacks solid bitumen although the hitch and etzold fields were thought to be in pressure communication and have common source rocks hitch and etzold crude oils and core extracts were characterized geochemically to gain a better understanding of the reservoir filling history and geological and geochemical controls on solid bitumen formation in the hitch reservoir based on a variety of geochemical characteristics we propose that the hitch and etzold oils are mixtures derived from ordovician and late devonian early mississippian woodford shale source rocks the solid bitumen in the hitch reservoir probably results from mixing of oils having different geochemical compositions which filled the reservoir over an extended period no evidence of severe biodegradation or thermal alteration is observed a reservoir filling scenario is proposed in an effort to explain why the hitch oils are geochemically more heterogeneous than etzold oils furthermore gas de asphalting and regional pressure drops as a result of post laramide orogeny may have contributed to a phase change in the reservoir fluid and deposition of solid materials by disturbance of thermodynamic equilibrium the major significance of this study is related to improving our knowledge on the occurrence of the presence of solid bitumen in reservoirs that can introduce barriers into the reservoir complicating waterflood operations and leading to erroneous oil in place calculations and subsequently lower than expected oil recovery

climatic regionalization and the spatio temporal occurrence of extreme single year drought events 1500 1998 in the interior pacific northwest usa tree ring records from western juniper juniperus occidentalis var occidentalis hook growing throughout the interior pacific northwest identify extreme climatic pointer years cpys i e severe single year droughts from 1500 1998 widespread and extreme cpys were concentrated in the 16th and early part of the 17th centuries and did not occur again until the early 20th century the 217 yr absence of extreme cpys may have occurred during an extended period of low variance in the pacific decadal oscillation we mapped climatic boundaries for the interior pacific northwest based on the location of sites with similar precipitation variability indices three regions the northwest based on chronologies from nine sites the southwest four sites and the east five sites were identified our results suggest that western juniper radial growth indices have substantial interannual variability within the north western range of the species central oregon particularly when compared with western juniper growing in its eastern range eastern oregon southeastern idaho and northern nevada and southwestern range southern oregon and northeast california we suspect that the substantial differences in the variability of western juniper radial growth indices are linked to the influence of enso events on winter spring precipitation amounts

a study of the holzener asphaltkalk northern germany observations regarding the distribution composition and origin of organic matter in an exhumed petroleum reservoir abstract the holzener asphalkalk deposit is located on the southwestern flank of the hils syncline northern germany it consists of a series of kimmeridgian portlandian bitumen impregnated limestones cumulative thickness of nearly 200 m overlain unconformably by neocomian claystones and underlain by older jurassic and triassic sediments the most bitumen rich limestone layers have been extensively mined with the result that there is three dimensional access to what is probably an exhumed series of stacked petroleum reservoirs geochemical petrological and petrophysical techniques were used to gain some insight into the distribution and the source of the organic matter in two of the 13 layers of the deposit most disseminated organic matter was found to be soluble in organic solvents and rich in non hydrocarbons its distribution appears to be controlled by ooid versus carbonate matrix abundances the occurrence of fractures and degree of impregnation small meso to micro pores have high bitumen saturations whereas large pores meso to macro have much lower saturations mature petroleum is thought to have once filled all pores but alteration has probably removed as much as 85 of it mainly from the large pores regional geochemical considerations pyrolysis and stable carbon isotope data indicate that the original petroleum was most probably derived from the underlying posidonia shale toarcian source rock asphaltene pyrolysis data indicate that an algal lacustrine co source might have also contributed to the deposit

high resolution climatic evolution of coastal northern california during the past 16 000 years holocene and latest pleistocene oceanographic conditions and the coastal climate of northern california have varied greatly based upon high resolution studies ca every 100 years of diatoms alkenones pollen caco 3 and total organic carbon at ocean drilling program odp site 1019 41 682 n 124 930 w 980 m water depth marine climate proxies alkenone sea surface temperatures ssts and caco 3 behaved remarkably like the greenland ice sheet project gisp 2 oxygen isotope record during the balling allerod younger dryas yd and early part of the holocene during the yd alkenone ssts decreased by 3 c below mean bolling allerod and holocene ssts the early holocene ca 11 6 to 8 2 ka was a time of generally warm conditions and moderate caco 3 content generally 4 the middle part of the holocene ca 8 2 to 3 2 ka was marked by alkenone ssts that were consistently 1 2 c cooler than either the earlier or later parts of the holocene by greatly reduced numbers of the gyre diatom pseudoeunotia doliolus 10 and by a permanent drop in caco 3 to 3 starting at ca 5 2 ka coastal redwood and alder began a steady rise arguing for increasing effective moisture and the development of the north coast temperate rain forest at ca 3 2 ka a permanent ca 1 c increase in alkenone sst and a threefold increase in p doliolus signaled a warming of fall and winter ssts intensified higher amplitude and more frequent cycles of pine pollen alternating with increased alder and redwood pollen are evidence that rapid changes in effective moisture and seasonal temperature enhanced el nino southern oscillation enso cycles have characterized the site 1019 record since about 3 5 ka

geochemical characterization of solid bitumen migrabitumen in the jurassic sandstone reservoir of the tut field shushan basin northern western desert of egypt abstract asphaltene rich solid bitumen was identified within the pore spaces of the middle jurassic khatatba sandstone reservoir in the tut field shoushan basin egypt despite good reservoir properties have been detected the solid bitumen forms barriers in the reservoir which prevents economic petroleum production petrographical and organic geochemical techniques were applied in order to characterize the source rock of the bitumen and its formation mechanisms organic geochemical results confirm the presence of actively migrating non biodegraded hydrocarbons within the khatatba sandstones biomarker data suggest that the solid bitumen originated from a marine shale source rock that was deposited in mildly anoxic to suboxic conditions biomarker oil source rock correlation with the organic rich sediments of the khatatba formation indicates that the shale and coaly shale within the khatatba formation are an effective source rock in the area the natural deasphalting is the predominant mechanism for the formation of the asphaltene rich solid bitumen in the khatatba sandstones adsorption of asphaltenes onto authigenic kaolinite played a major role in the fixation of bitumen furthermore gas deasphalting caused by gas injection may have contributed to a phase change in the reservoir fluid and deposition of solid bitumen the injected gas is generated from khatatba type iii kerogen or older source rocks in the shoushan basin during the mature stage of hydrocarbon generation

pollen analysis of a late glacial and holocene sediment core from mono lake mono county california pollen analysis of a 752 cm core from mono lake mono county california indicates generally high lake levels 11 600 7000 14c yr b p moderate lake levels until ca 4000 14c yr b p and fluctuating levels to the present drying events with lake levels near or below the historic minimum are dated ca 8800 4000 2400 and 1100 14c yr b p chronologic control is provided by six radiocarbon dates and six volcanic ashes the rate of upland vegetation change is greatest 11 000 4000 and 1130 14c yr b p juniperus and sequoaidendron pollen declines 11 000 yr b p marking the transition from late glacial juniper woodland to holocene steppe high values 5 20 of sequoaidendron pollen are unique to this study and may indicate the presence of these trees east of the sierra crest the pollen based reconstructions of climate are generally cooler and wetter than today with relatively dry but cool climate during the early holocene the contrast between higher lake levels and more arid vegetation during the early holocene can be explained by insolation driven seasonality greater summer insolation produced summer drought but lower winter insolation led to greater snowpack greater spring runoff and higher lake levels increased artemisia and other compositae pollen percentages mark the establishment of modern vegetation ca 2000 14c yr b p during the late holocene the pollen based reconstructions of climate generally match the mono lake fluctuations proposed by stine 1990 but fewer fluctuations are recorded

degradation and maturity controls on oil field petroleum column heterogeneity in the gullfaks field norwegian north sea abstract a geochemical mapping of the gullfaks reservoir petroleum column based on 226 reservoir core extracts and 23 drill stem test dst and repeat formation test rft oil samples indicates the presence of statistically testable lateral compositional heterogeneities in the petroleum column these different petroleum populations can be related to lateral filling of the field from two source basins and a more pervasive subsequent episode in reservoir biodegradation petroleum maturity gradients within the field were detected using conventional biomarker gc ms methods on saturated hydrocarbon fractions the degree of biodegradation was monitored by quantitative gc of n alkanes in whole oil samples using a squalane internal standard the observed compositional differences in the gullfaks petroleum column are consistent with diffusion being the primary mixing process thermal convection being eliminated on both compositional and modeling grounds compositional differences between core extracts and dst samples from the same intervals suggest that fractionation of petroleum might occur during testing and that interpretation of reservoir petroleum columns from mixed sample sets should be treated cautiously

recognition and quantification of the effects of primary migration in a jurassic clastic source rock from the norwegian continental shelf a detailed quantitative geochemical study was made of a mature jurassic clastic source rock sequence in order to attempt to recognize and quantify petroleum migration effects two different quantitative approaches were followed to monitor primary migration effects on both the bitumen 1 e g whole rock extract and the bitumen 2 e g isolated kerogen extract fractions these methods were a comparisons of toc normalized extract yields and quantified molecular compositions of petroleums from both tightly carbonate cemented zones and those from less cemented zones and b comparison of petroleums from shale laminae vs those from interbedded siltstone laminae on this basis it was possible to assess apparent primary migration efficiency relative expulsion efficiencies in certain shale samples and relative import efficiencies in siltstone bands ranged from 11 total extract to 85 saturated hydrocarbons and individual n alkanes no carbon number dependent fractionation effects were observed for n alkanes of bitumen 1 in the c15 to c35 range i e expulsion efficiencies were independent of carbon number suggesting bulk oil flow with chromatographic modification as the predominant transport mechanism

fractionation of azaarenes during oil migration abstract a comparative study of alkylbenzoquinolines in crude oils and rock extracts bitumens from japan and sumatra shows that the ratios of nitrogen masked isomers nmis to nitrogen exposed isomers neis and the ratio of higher homologs to lower homologs is higher in crude oils than in corresponding bitumens also a regular increase in the ratios of nmis to neis with increasing migration distance is observed for a series of crude oils from the sarukawa oil field northeastern japan these results are attributed to the preferential migration of nmis caused by their weak adsorption on clay minerals and or their low solubility in interstitial water and the selective removal of lower honologs caused by their irreversible adsorption onto clays during oil migration which are regarded as geochromatographic phenomena it is suggested that those ratios can be used to estimate the degree of fractionation of oils during primary and secondary migration

a 2000 yr record of sacramento san joaquin river inflow to san francisco bay estuary california oxygen and carbon isotopic measurements of fossil bivalves macoma naarfa contained in estuarine sediment are used to reconstruct a late llolocene record of sitlinity and stream flow in san francisco bay discharge into the bay is a particularly good indicator of paleoclin ate in california because the bay s influent streams drain 40 of the state the isotopic record suggests that hetween al oul 1670 ant1 1900 calcnd r yc trs yr cal 1i i inflow to the bay was sul stantially greirler tlian the cstinli tecl precliversion inllow ol 1100 m3 s an unconforn ity representing a 900 yr hiatus is present in the core between 1670 ancl 750 yr cirl ii 13 possil ly r lusc cl by i n tjor 11ydrologic rl event over the p ist 750 yr strcitn ilow to s iii i ril cisco ikty ii is vitrirtl wit11 i pcriotl ol 200 yr i1lter11itte wet iltttl tlry i tlrougl t intc r rls typiritlly 11 rvc i lstecl 40 to 100 yr

heterogeneous distribution of pyrobitumen attributable to oil cracking and its effect on carbonate reservoirs feixianguan formation in the jiannan gas field china few previous studies have focused on solid bitumen distribution and its effect on gas reservoir quality during oil cracking solid bitumen is commonly found in both gas and nongas reservoirs of the triassic feixianguan formation in the jiannan gas field the natural gases are mainly secondary cracking gases of oil generated from source rock of the permian wujiaping formation and the reservoir experienced temperatures above 150 c 302 f for about 35 m y a relatively narrow range of values and a wide range of values and widespread solid bitumen indicate that oil cracking took place in the gas field low concentrations of commonly 8 0 can be high quality gas reservoirs after oil cracking and should be favorable targets for future gas exploration in the northeastern sichuan basin and adjacent areas

paleoclimate simulations for north america over the past 21 000 years features of the simulated climate and comparisons with paleoenvironmental data maps of upper level and surface winds and of surface temperature and precipitation illustrate the results of a sequence of global paleoclimatic simulations spanning the past 21 000 years for north america we review a the large scale features of circulation temperature and precipitation that appear in the simulations from the ncar community climate model version 1 ccm 1 b the implications of the simulated climate for the past continental scale distributions of three plant taxa picea spp pseudotsuga menziesii and artemisia tridentata which are broadly representative of the vegetation across the continent and c the potential explanations in terms of atmospheric circulation or surface energy and water balance processes for mismatches between the simulations and observations most of the broad scale features of previous paleoclimatic simulations with the ncar ccm 0 for north america are present in the current simulations many of the elements of a conceptual model based on previous climate simulations that describes the controls of paleoclimatic variations across north america during the past 21 000 years are found in simulations reviewed here these include 1 displacement of the jet stream by the laurentide ice sheet to the south of its present position in both winter and summer 2 generation of a glacial anticyclone over the ice sheet at the lgm and the consequent induction of large scale sinking motions induced over eastern north america 3 changes in the strength of surface atmospheric circulation features through time including weakening of the aleutian low in winter and strengthening of the eastern pacific and bermuda high pressure systems in summer as the ice sheet decreased in size 4 development of a heat low at the surface and a strengthened ridge in the upper atmosphere over the continent at the time of the maximum summer insolation anomaly 5 increases in summer temperature earlier in regions remote from the ice sheet these increases appear earlier in the present ccm 1 simulations than in the previous ccm 0 ones however and 6 continuation of negative winter temperature anomalies into the middle holocene in general simulated surface conditions that are discordant with paleoenvironmental observations can be attributed to the simulation of particular atmospheric circulation patterns e g those that suppress precipitation or advect warm air into a region with these mismatches amplified in beringia and the southeastern united states by surface energy and water balance processes

characterisation of non producible oil in eocene reservoir sandstones bad hall nord field alpine foreland basin austria abstract an asphaltene rich non producible petroleum tar fills the pore spaces of an eocene sandstone reservoir in the alpine foreland basin near bad hall austria despite good reservoir properties the solid bitumen prevents economic petroleum exploitation petrographical and geochemical techniques were applied in order to characterise the source rock of the bitumen and the formation mechanisms of the tar biomarker data argue for a marine shaly to marly source and indicate that the schoneck formation the main source rock in the area also sourced the bad hall nord structure the methylphenanthrene index implies a source rock maturity equivalent to 0 7 rr indicating a lateral migration distance in the order of 15 20 km natural deasphalting is the predominant mechanism for the formation of the tar adsorption of asphaltenes onto authigenic kaolinite played a major role during deasphalting and in the fixation of asphaltenes gas injection and migration related asphaltene precipitation are further feasible mechanisms

analysis of petroleum fractions by tlc fid applications to petroleum reservoir description abstract thin layer chromatography and flame ionization detection iatroscan tlc fid offers a rapid and accurate method for quantifying saturated and aromatic hydrocarbons and resin asphaltene fractions in solvent extracts of petroleum source rocks reservoir rocks and crude oils while the instrument is superficially simple special precautions need to be taken in calibration and parameter setting due to complexities arising from the operational characteristics of the detector system nevertheless the technique offers superior speed and precision to conventional mplc analysis of petroleum fractions this paper describes the choice of operational parameters provides comparison with the traditional group type analysis technique mplc and presents some geochemical applications

increased northeast pacific climatic variability during the warm middle holocene 1 we use a pair of decadally resolved planktonic foraminiferal 18o records from santa barbara basin sbb to show that the warmest interval of the current interglacial the middle holocene was characterized by increased decadal to centennial scale climatic variability modern relationships between the pacific decadal oscillation pdo the el nino southern oscillation enso and upper water conditions in sbb also suggest a preference of the northeast ne pacific climate during the warm mid holocene toward the warm phase of the pdo and more intense enso warm events el ninos in the context of future climate this study suggests increasing decadal to centennial scale climatic variability in a globally warmed world

relationships between hydrocarbon evolution and the geochemistry of solid bitumen in the guanwushan formation nw sichuan basin abstract recently the devonian guanwushan formation in the northwestern sichuan basin gained industrial attention when solid bitumen was discovered in reservoirs and outcrops this discovery initiated the exploration and development of the devonian natural gas devonian in the northwestern sichuan basin is a new stratum for the exploration and development of paleozoic marine natural gas in sichuan basin however the unclear recognition on the genesis the sources and the hydrocarbon evolution history of solid bitumen and natural gas seriously restricted further exploration and development based on the solid bitumen reflectance carbon isotopes saturated hydrocarbon chromatography and solvent extract bitumen biomarkers combined with the component and carbon isotopes of natural gas comprehensive analyses have been performed on the origin of the solid bitumen and the accumulation and evolution of the natural gases the results showed that the outcrop solid bitumen is derived from biodegraded oil from the lower cambrian source rocks and is characterised by low bitumen reflectance low saturated aromatic hydrocarbon ratios seriously damaged normal alkanes and severe migration of the gas chromatographic baseline the reservoir bitumen formed through thermal cracking of oil from lower cambrian and lower permian source rocks and is characterised by high bitumen reflectance high saturated aromatic hydrocarbons and complete normal alkanes the differences of tectonic evolution take control of the two different genesis bitumen the longmen mountain strata in the northwestern sichuan basin were uplifted sharply after the jurassic and the early generated crude oil was biodegraded during uplifting and formed the outcrop bitumen however strata in well shuangtan 3 st3 continued to subside and the paleo reservoir thermal cracked during deep burial into dry gas and heavy components gathered to form reservoir bitumen revealing the devonian hydrocarbon evolution in sichuan basin is of highly significance and is meaningful to guide further researches on the gas source correlation of natural from paleo strata it is of great significance to reveal the devonian hydrocarbon evolution in sichuan basin and to guide further researches on the gas source correlation of natural gas from paleo strata

mid holocene climates of the americas a dynamical response to changed seasonality simulations of the climatic response to mid holocene 6 ka bp orbital forcing with two coupled ocean atmosphere models foam and csm show enhancement of monsoonal precipitation in parts of the american southwest central america and northernmost south america during northern hemisphere summer the enhanced onshore flow that brings precipitation into central america is caused by a northward displacement of the inter tropical convergence zone driven by cooling of the equatorial and warming of the northern subtropical and mid latitude ocean ocean feedbacks also enhance precipitation over the american southwest although the increase in monsoon precipitation there is largely driven by increases in land surface temperature the northward shift in the equatorial precipitation band that causes enhanced precipitation in central america and the american southwest has a negative feedback effect on monsoonal precipitation in northern south america the simulations demonstrate that mid holocene aridity in the mid continent of north america is dynamically linked to the orbitally induced enhancement of the summer monsoon in the american southwest with a spatial structure wet in the southwest and dry in the mid continent similar to that found in strong monsoon years today changes in winter precipitation along the west coast of north america in central america and along the gulf coast caused by southward displacement of the westerly storm tracks indicate that changes in the northern hemisphere winter monsoon also play a role in regional climate changes during the mid holocene although the simulations with foam and csm differ in detail the general mechanisms and patterns are common to both the model results thus provide a coherent dynamical explanation for regional patterns of increased or decreased aridity shown by vegetation lake status and aeolian data from the americas

a 4300 year strontium isotope record of estuarine paleosalinity in san francisco bay california abstract strontium isotopic compositions of carbonate mollusk shells from estuarine sediments cored beneath san francisco bay are used to derive a record of mean annual salinity and average freshwater inflow to the estuary for intervals during the past 4300 yrs the large difference in the 87sr 86sr ratio between seawater 0 7092 and the average freshwater entering the estuary 0 7065 produces a correlation between 87sr 86sr and salinity in bay waters that can be detected with high precision measurements paleosalinity is inferred from the 87sr 86sr ratio measured in fossil carbonate shells of bivalves preserved in the sediment because salinity in san francisco bay is primarily controlled by the freshwater inflow from the sacramento and san joaquin rivers the paleosalinity record can be converted to a paleodischarge record using a transfer function derived from historical data salinity data are referenced to modern values estimated for the estuary after correcting for the lower discharge caused by diversion since 1850 a d data are presented from richardson bay located near the estuary mouth modern mear arrival salinity mas of ca 24 and from san pablo bay located about 30 km upstream modern mas of ca 18 20 for richardson bay the data cover the periods 0 600 yrs b p and 2200 4300 yrs b p based on radiocarbon dating for san pablo bay the periods 0 130 yrs b p and 2500 2800 yrs b p are represented the richardson bay data indicate extended periods of low salinity relative to modern indicating higher freshwater inflow at ca 80 220 310 440 500 3100 3400 and 4300 yrs ago the data indicate high salinity relative to modern hence lower freshwater inflow at about 40 140 210 270 2100 and 3450 3700 yrs b p for san pablo bay where salinity resolution is better salinity was lower than modern during the period at ca 50 and 2550 2650 yrs b p and higher than modern at ca 90 110 155 and 2510 2530 yrs b p the data suggest that mean annual discharge to san francisco bay typically varies between values that are below the modern value 600 m3 s and values 2 to 3 times as high the average paleosalinity is typically substantially lower than the modern values the 4300 yr average freshwater inflow is estimated to be 1200 200 m3 s the record indicates that quasi cyclic variations in mean annual discharge occur naturally with a period of about 200 yrs or less

geochemical effects of primary migration of petroleum in kimmeridge source rocks from brae field area north sea i gross composition of c15 soluble organic matter and molecular composition of c15 saturated hydrocarbons in mature oil prone source rocks of the upper jurassic kimmeridge clay in the brae field area north sea the yield and the gross composition of solvent extractabte pctroleum likc compounds as well as the molecular proportions of c15 saturated hydrocarbons are primarily controlled by the effects of hydrocarbon expulsion during primary migration within sample series extending from shale centres towards adjacent reservoir sandstones regular and pronounced yield decreases have been documented as well as marked compositional changes for c15 soluble organic matter and its compound class fractions saturated hydrocarbons aromatic hydrocarbons nso compounds and for normal and isoprenoid alkanes relative migration losses indicating relative expulsion efficiencies were determined for the c15 alkanes throughout the outer five meters of thick shales relative expulsion efficiencies increase regularly and drastically for all compounds considered e g exceeding 90 for the c15 n alkanes in the outermost shale samples samples from thin 5 50 cm shale layers interbedded between reservoir sandstones reveal similarly high expulsion efficiencies for n alkanes the degree of depletion remains uniform throughout the molecular range c15 to c30i e no compositional fractionation occurred during primary migration which is interpreted to reflect expulsion of oil as a single phase fluid a simple conceptual model is proposed to explain the mechanisms and relationships of generation and expulsion processes in time and space a geochemically relevant conclusion is that the c15 soluble organic matter recovered by solvent extraction of mature source rocks represents only a portion of the total non volatile petroleum like material originally generated

heterogeneity of oil composition within a reservoir as a reflection of accumulation history abstract the unaltered petroleums of a small oil field in the f r germany reveal pronounced spatial heterogeneities in bulk and molecular composition over most of the field area the oil in high porosity high permeability sand intervals bears a higher proportion of saturated hydrocarbons and has a higher maturity chemical signature as compared to oils occupying lower porosity lower permeability zones for all sands with less than about 13 porosity a regular relationship was observed between oil composition and porosity permeability with a decrease of the latter petrophysical properties increasingly lower chemical maturities and increasingly different bulk chemical compositions lower proportions of saturated hydrocarbons and higher proportions of nso compounds were recorded maximum contrasts measured for chemical maturities are e g 0 63 versus 0 82 vitrinite reflectance equivalents rc values calculated on the basis of the methylphenanthrene index according to radke and welte 1983 0 31 versus 0 84 for the ratio of triaromatic to mono plus triaromatic steroid hydrocarbons and 0 38 versus 0 47 for the 20s 20s 20r ratio of c29 5 h 14 h 17 h steranes these spatial heterogeneities in the composition of the oils are interpreted to reflect 1 i successive stages of trap filling due to episodes of increasing burial and maturation of the relevant source rocks in combination with 2 ii low rates of in reservoir mixing of these individual oil charges by convection or diffusion recognition of compositional heterogeneities within the oil column of individual fields may not only provide a basis for the reconstruction of reservoir filling history but may also have important implications for improving petroleum production

simulated changes in extreme temperature and precipitation events at 6 ka abstract we have employed a high resolution regional climate model rcm to test the sensitivity of extreme climate events to 6 ka orbital forcing using western north america as a case study calculated differences 6 ka control in annual extreme precipitation event frequency were mostly positive throughout the rcm domain as were differences in extreme event contribution to total annual precipitation these annual mean differences were driven by changes in the seasonal distribution of extreme precipitation events at 6 ka which was in turn linked to changes in the daily variability of upper level zonal wind speeds over the northeast pacific positive differences in the frequency of extreme maximum daily temperature values occurred inland in the rcm domain with peak differences of 28 days year over the great basin likewise days in which the maximum daily temperature exceeded 32 c were 24 more frequent in the 6 ka integration than in the control integration and heat waves lasted up to 12 days longer mean first and last freeze dates were generally earlier in the 6 ka integration along the pacific coast and over the southern great basin and later over the northern great basin and interior of the pacific northwest we propose that by exerting controls on paleoclimate archives unique from changes in the mean climate state such changes in the frequency and duration of extreme climate events could have played a substantial role in shaping the mid holocene paleoclimate record of the region and that extreme climate events may have been similarly important in other regions and during other time periods

fire and vegetation history from the coastal rain forest of the western oregon coast range high resolution charcoal and pollen analyses were used to reconstruct a 4600 yr long history of fire and vegetation near taylor lake in the wettest forests of coastal oregon today fires in these forests are rare because the season of ignition does not coincide with months of dry fuels from ca 4600 to 2700 cal yr b p fire episodes occurred at intervals of 140 30 yr while forest vegetation was dominated by disturbance adapted taxa such as alnus rubra from ca 2700 cal yr b p to the present fire episodes have become less common occurring at intervals of 240 30 yr and firesensitive forest taxa such as tsuga heterophylla and picea sitchensis have become more prominent fire occurrence during the midholocene was similar to that of the more xeric forests in the eastern coast range and suggests that summer drought was widespread after ca 2700 cal yr b p a decrease in fire episode frequency suggests that cooler conditions and possibly increased summer fog allowed the establishment of present day picea sitchensis forests within the watershed these results provide evidence that fire has been an important disturbance agent in the coast range of oregon and variations in fire frequency and climate have led to the establishment of present day forests c 2002 university of washington

how well can we simulate past climates evaluating the models using global palaeoenvironmental datasets abstract global syntheses of palaeoenvironmental data are required to test climate models under conditions different from the present data sets for this purpose contain data from spatially extensive networks of sites the data are either directly comparable to model output or readily interpretable in terms of modelled climate variables data sets must contain sufficient documentation to distinguish between raw primary and interpreted secondary tertiary data to evaluate the assumptions involved in interpretation of the data to exercise quality control and to select data appropriate for specific goals four data bases for the late quaternary documenting changes in lake levels since 30 14 c kyr bp the global lake status data base vegetation distribution at 18 14 c kyr and 6 14 c kyr bp biome 6000 aeolian accumulation rates during the last glacial interglacial cycle dirtmap and tropical terrestrial climates at the last glacial maximum the lgm tropical terrestrial data synthesis are summarised each has been used to evaluate simulations of last glacial maximum lgm 21 calendar kyr bp and or mid holocene 6 cal kyr bp environments comparisons have demonstrated that changes in radiative forcing and orography due to orbital and ice sheet variations explain the first order broad scale in space and time features of global climate change since the lgm however atmospheric models forced by 6 cal kyr bp orbital changes with unchanged surface conditions fail to capture quantitative aspects of the observed climate including the greatly increased magnitude and northward shift of the african monsoon during the early to mid holocene similarly comparisons with palaeoenvironmental datasets show that atmospheric models have underestimated the magnitude of cooling and drying of much of the land surface at the lgm the inclusion of feedbacks due to changes in ocean and land surface conditions at both times and atmospheric dust loading at the lgm appears to be required in order to produce a better simulation of these past climates the development of earth system models incorporating the dynamic interactions among ocean atmosphere and vegetation is therefore mandated by quaternary science results as well as climatological principles for greatest scientific benefit this development must be paralleled by continued advances in palaeodata analysis and synthesis which in turn will help to define questions that call for new focused data collection efforts

orbital suppression of wind driven upwelling in the california current at 6 ka 1 marine records clearly show activity in the california current cc system to have been altered during the mid holocene however the specific nature of cc activity during this period remains ambiguous as proxies that suggest cooler than present sea surface temperatures co occur in mid holocene marine sediments with multiple proxies that suggest decreased coastal upwelling to test the sensitivity of wind driven upwelling in the cc to mid holocene orbital forcing we have employed a high resolution regional climate model rcm the seasonality of modern cc wind driven coastal upwelling simulated by the rcm is in strong agreement with observational data further we show that changes in the seasonality of solar insolation induced by mid holocene milankovitch forcing decrease early and peak season coastal upwelling in the cc along with increasing late season coastal upwelling these results are in agreement with several marine and terrestrial proxies suggesting that relative to present cc activity during the mid holocene was characterized by a longer and less vigorous upwelling season with decreased seasonal contrast

the factors controlling the abundance and migration of heavy vs light oils as constrained by data from the gulf of suez part ii the significance of reservoir mass transport processes abstract reservoir flow processes have a major impact on the oil quality and distribution of heavy vs light oils both within reservoirs and on the petroleum system scale in the gulf of suez gos gravitational segregation of black oil columns is a common phenomenon an understanding of the mass transport processes in these reservoirs is important for evaluating their impact on the composition of migrating petroleum 2d simulation results show that pressure diffusion is a too slow process to be the main cause for the vertical compositional gradients a reservoir filling model which is a refined version of the geological model of gussow linked to the composition of the gos expelled petroleum fluids and their pvt behaviour and constrained by the gos oil field data is presented this model gives viable explanations for a formation of gravitationally segregated oil columns b tar mat occurrences and their affinity to low maturity heavy oils and c wide spread occurrences of heavy oils and their relationship with light oils in this model continuous density overturning by compositionally controlled bulk flow is the prime cause for the formation of gravitationally segregated columns occurring when a the charge to the reservoir displays a maturity related decrease in density with time and b the reservoir volume relative to the charge volume is large enough for the reservoir to retain a wide maturity range lateral compositional variability in many reservoirs is today interpreted to image the initial filling of the reservoirs it is demonstrated that such lateral gradients can form effectively from re orientation of vertical gradients via ordinary diffusion these gradients have symmetry elements relative to the petroleum mass distribution in the reservoir fill and spill from gravitationally segregated columns enhance the efficiency of the migration of heavy oils

extracting holocene paleohydrology and paleoclimatology information from modern extreme flood events an example from southern california abstract the extraction of paleohydrological and paleoclimatological information from a modern hydrological system shown to represent unique and extreme hydroclimatological conditions is illustrated by an example from the mojave river drainage basin in southern california the mojave river allows only the most extreme floods to reach its terminal basin in the silver lake playa and to form ephemeral lakes all the other floods are lost by transmission into the alluvial aquifer along its 200 km channel this filtering out of regular floods by the river provides an essential tool in establishing a physical link between atmospheric and hydrologic conditions we demonstrate such a link between anomalous present day atmospheric circulation patterns over the north pacific ocean extreme storms in southern california that produced the heaviest precipitation on record the largest floods of record in the mojave river watershed and ephemeral lakes in its terminal playa this physical link determines the possible cause of the formations of perennial short duration shallow lakes in silver lake playa during the late holocene and characterizes the hydroclimatic conditions that prevailed during these lacustrine episodes hydrological simulations of this river and its filtering character demonstrate that these lakes could have formed only if the most extreme modern storms and floods were more frequent in at least an order of magnitude during specific time episodes we conclude that such extreme hydroclimatic conditions occurred more frequent in past episodes during which the holocene lakes formed in turn this conclusion indicates that the cause of these storms and floods i e the anomalous atmospheric circulation pattern must have been more frequent this research outlines a way to extract information on holocene climates in hydrologic settings that demonstrate a unique cause and effect relationship

intercomparison of simulated global vegetation distributions in response to 6 kyr bp orbital forcing abstract the response of ten atmospheric general circulation models to orbital forcing at 6 kyr bp has been investigated using the biome model which predicts equilibrium vegetation distribution as a diagnostic several common features emerge a reduced tropical rain forest as a consequence of increased aridity in the equatorial zone b expansion of moisture demanding vegetation in the old world subtropics as a consequence of the expansion of the afro asian monsoon c an increase in warm grass shrub in the northern hemisphere continental interiors in response to warming and enhanced aridity and d a northward shift in the tundra forest boundary in response to a warmer growing season at high northern latitudes these broadscale features are consistent from model to model but there are differences in their expression at a regional scale vegetation changes associated with monsoon enhancement and high latitude summer warming are consistent with palaeoenvironmental observations but the simulated sh

response of extreme floods in the southwestern united states to climatic variations in the late holocene a regional synthesis of paleoflood chronologies on rivers in arizona and southern utah reveals that the largest floods over the last 5000 years cluster into distinct time periods that are related to regional and global climatic fluctuations the flood chronologies were constructed using fine grained slackwater deposits that accumulate in protected areas along the margins of bedrock canyons and selectively preserve evidence of the largest events high magnitude floods were frequent on rivers throughout the region from 5000 to 360014c yrs bp dendrocalibrated age 3800 2200 bc and increased again after 2200 bp 400 bc with particularly prominent peaks in magnitude and frequency around 1100 900 bp ad 900 1100 and after 500 yrs bp ad 1400 in contrast the periods 3600 2200 bp 2200 400 bc and 800 600 yrs bp 1200 1400 ad are marked by sharp decreases in the occurrence of large floods on these rivers in the modern record storms that generate large floods 10 year in the region fall into three categories 1 winter north pacific frontal storms 2 late summer and fall storms that draw in moisture from recurved pacific tropical cyclones and 3 summer storms mainly convective thunderstorms winter storms and tropical cyclones are associated with the most severe floods on the rivers in this study and are the most probable causes of the paleofloods over the last 5000 years floods from both winter storms and tropical cyclones occur when deep mid latitude troughs steer storm systems into the region composite anomaly maps of daily 700 mbar heights indicate that these floods are associated with a low pressure anomaly off the california coast and a high pressure anomaly over the aleutians or gulf of alaska a strong connection exists between the negative phase of the southern oscillation index often associated with el nin o conditions and the large floods associated with winter storms and tropical cyclones the paleoflood records confirm the existence of centennial scale variations in the conditions conducive to the occurrence of extreme floods and flood generating storms in this region the episodes with an increased frequency of high magnitude floods coincide with periods of cool wet climate in the western u s whereas warm intervals such as the medieval warm period are times of dramatic decreases in the number of large floods a positive relationship between the paleofloods and long term variations in the frequency of el nin o events is evident over the last 1000 years this relationship continues over at least the last 3000 years with warm coastal sea surface temperatures indicative of el nin o like conditions

migration of hydrocarbons in the tampen spur area norwegian north sea a reservoir geochemical evaluation abstract this paper describes the application of reservoir geochemical protocols to a study of oil field and regional petroleum compositional variations in the major fields in the tampen spur area the tampen spur high is located in the middle of several oil mature to gas mature source rock kitchens and most of the structures might receive petroleum from several different directions based on the definition of several different petroleum populations within the tampen spur area we define five major petroleum charging systems correlating the petroleum population variations with geological information allows us to derive likely migration fill scenarios for many of the oil fields and requires us to invoke a new upper jurassic carrier system in parts of the area connecting brent group reservoirs across major faults based on this hypothesis two exploration wells were drilled on structures to test this carrier and petroleum was found in one of the structures an understanding of the migration pathways and petroleum drainage efficiency of the basins is of great economic interest because most of the smaller substructures are marginally economic thus it is important to provide an effective risk analysis and ranking of the satellite prospects prior to drilling this study has demonstrated that filling and migration in a geological province are controlled by a series of complex processes and that the filling history of the structures within the tampen spur is more complicated than suggested earlier

geochemical characterization of a tar mat in the oseberg field norwegian sector north sea abstract concentrations of heavy oil usually at or near the oil water contact in reservoirs are called tar mats this phenomenon can arise from reservoir oil alteration processes such as deasphalting biodegradation or maturation effects of tar mats include reduction in water drive efficiency and lower oil quality in the bottom section of a reservoir the study of tar mats can be greatly improved by the systematic application of petroleum geochemical techniques and a new classification scheme is proposed based on these methods application of these general concepts to a tar mat occurrence in the oseberg field showed that although some biodegradation probably occurred in the early stages of field formation there was little evidence to indicate that this process was a significant factor in the formation of the main tar mat deasphalting was considered to be the major if not the only process leading to tar mat formation in this field