gas condensate migration and oil fractionation in deltaic systems abstract the term evaporative fractionation is proposed to describe several phenomena involved in the secondary alteration of reservoired oil firstly it is suggested that oil is frequently partially vaporized in the reservoir secondly that gas bearing substantial portions of the oil in solution is conducted along faults to form independent gas condensate accumulations thirdly that residual oils formed in this fashion bear internal evidence of fractionation in addition to the conspicuous loss of light ends there is an increase in the content of light aromatic and naphthenic hydrocarbons relative to paraffins in the residual oil evaporative fractionation effects are recognized for the first time in the distillation and physical property data of us bureau of mines routine method oil analyses fractionation effects are postulated to be the cause of sigmoid as opposed to normal curvilinear aromatic profiles the effects of evaporative fractionation are widespread in oils throughout the united states they are evident in approximately 75 of oils in the gulf coast region and in a large proportion of the gas condensate accumulations the process is a major and apparently unrecognized means of petroleum alteration and of generation of gas condensates experimental evidence shows that partial vaporization results in enhanced levels of light aromatic hydrocarbons in residual oils oil samples were partially vaporized in excess methane at elevated pressure and temperature followed by removal of the vapour the gas chromatographic features of many gulf coast oils were reproduced various levels of light end depletion and enhancement of aromaticity were brought about

impact of the late glacial eruption of the laacher see volcano central rhineland germany abstract within a period of a few weeks toward the end of the allerod interstadial the major plinian eruption of the laacher see volcano produced some 20 km3 of eruptiva covering and preserving the late glacial landscape in the german central rhineland over an area of more than 1000 km2 correlation of terrestrial archives with the greenland ice core records and improved calibration of the radiocarbon timescale permit a precise accurate age determination of the laacher see event some 200 yr before the onset of the younger dryas cold episode carbonized trees and botanical macrofossils preserved by laacher see tephra permit detailed regional paleoenvironmental reconstruction and show that open woodland were typical for the cool and humid hemiboreal climatic conditions during the late allerod this woodland provided the habitat for a large variety of animal species documented at both paleontological and final paleolithic archeological sites preserved below laacher see deposits of special interest are numerous animal tracks intercalated in middle laacher see deposits at the south of the neuwied basin this knowledge may help to evaluate possible supraregional impacts of this volcanic event on northern hemispheric environment and climate during the late allerod

cross shore wave transformation and mean flow circulation abstract an analysis of wave and current evolution in shoaling and breaking waves in the cross shore plane adopts the integral method used successfully for turbulent shear flows the field equations are integral conservation equations for mass momentum and energy which describe the cross shore flow as an initial value problem reynolds stress closure assumes added complexity as a result of the fluctuating wave motion for the wave fluctuations closure relationships consistent with the integral methodology are based on profiles of mean quantities established from steady fourier wave theory within the surf zone turbulence closure is dominated by breaking wave energy dissipation computations reproduce the trends of wave shoaling set up and undertow and the global trends compare favorably with field and laboratory data the various contributions to the complete balances of mass momentum and energy are examined in detail leading to an especially descriptive picture of the evolutionary processes in the complete nearshore zone from deep water through the shoaling breaker and surf zones to the beach

geochemical relationships of petroleum in mesozoic reservoirs to carbonate source rocks of jurassic smackover formation southwestern alabama algal carbonate mudstones of the jurassic smackover formation are the main source rocks for oil and condensate in mesozoic reservoir rocks in southwestern alabama this interpretation is based on geochemical analyses of oils condensates and organic matter in selected samples of shale norphlet formation haynesville formation trinity group tuscaloosa group and carbonate smackover formation rocks potential and probable oil source rocks are present in the tuscaloosa group and smackover formation respectively extractable organic matter from smackover carbonates has molecular and isotopic similarities to jurassic oil although the jurassic oils and condensates in southwestern alabama have genetic similarities they show significant compositional variations due to differences in thermal maturity and organic facies lithofacies organic facies reflect different depositional conditions for source rocks in the various basins the mississippi interior salt basin was characterized by more continuous marine to hypersaline conditions whereas the manila and conecuh embayments periodically had lower salinity and greater input of clastic debris and terrestrial organic matter petroleum and organic matter in jurassic rocks of southwestern alabama show a range of thermal transformations the gas content of hydrocarbons in reservoirs increases with increasing depth and temperature in some reservoirs where the temperature is above 266 f 130 c gas condensate is enriched in isotopically heavy sulfur apparently derived from thermochemical reduction of jurassic evaporite sulfate this process also results in increased h2s and co2 in the gas and depletion of saturated hydrocarbons in the condensate liquids thermochemical sulfate reduction probably depends on the mineralogic composition of the reservoir rock as well as temperature because some deep 18 000 ft or 5 5 km and hot 320 f or 160 c smackover and norphlet reservoirs contain low sulfur petroleum

an attempt to recognise oil populations and potential source rock types in paleozoic sub and mesozoic cenozoic supra salt strata in the southern margin of the pre caspian basin kazakhstan republic abstract fifty six rock and 28 crude oil samples from the sub salt and supra salt section of the southern pre caspian basin were analyzed by organic geochemical means eighty five percent of the rock samples from the cretaceous to carboniferous section contain predominantly gas prone mixed type ii iii organic matter rock eval t max values of selected samples range from 437 c for triassic and 449 c for kungurian samples the oil sample set represents two geographically distinct oil populations with one containing two sub populations termed population 1a and population 1b fourteen low sulfur bearing moderately mature oils grouped into population 1a are found to the east and west of the town of atrau excluding oil samples ke and o they represent lightly to moderately biodegraded supra salt and non biodegraded sub salt oils oil to source correlation indicates an origin from artinskian marine siliciclastic source rocks containing mixed type ii iii organic matter deposited under dysoxic conditions high sulfur bearing non degraded population 1b consisted of 13 oils from supra salt reservoirs occurring in an area northeast of aktau these oils most likely originated from an organic matter type similar to that which sourced the population 1a oils however the higher sulfur content supported by several lithology sensitive biomarkers present in the population 1b oils suggest a carbonate rich source rock it is proposed that population 1b oils may have originated from age equivalent marine carbonate to clay rich artinskian clastic sources population 2 oil from the northwestern atrau area is found in a supra salt reservoir it is thought to originate from a triassic supra salt non marine clastic source rock containing mixed type ii iii organic matter deposited under dysoxic and less saline conditions

the microbial input in carbonate anhydrite facies of a sabkha palaeoenvironment from guatemala a molecular approach abstract nine representative rock samplesincluding four anhydrites an oil stained dolomite and a laminated mudstone source rock from a sabkha type palaeoenvironment la felicidad 1 well guatemala have been compared in order to tentatively characterize each facies by a geochemical signature each sample has been studied by using basic parameters toc rock eval pyrolysis yields and analyses of alkanes and aromatics by computerized gc ms the following families of compounds have been reviewed n alkanes branched and cyclic alkanes n alkylbenzenes benzohopanes monoaromatic steroids d ring aromatic 8 14 secohopanoids alkylnaphthalenes alkylphenanthrenes alkyldibenzothiophenes and triaromatic steroids despite close geochemical relationships of all the sample a more in depth investigation taking into account molecular patterns and semi quantitative data reveals significant differences among the samples anhydrites may be differentiated from carbonates which illustrates the efficiency of organic geochemistry in environmental palaeoreconstruction even in organiccarbon lean sediments toc 0 04 0 08 in anhydrites in these anoxic marginally mature sediments the strong predominance of triterpanes over steranes tt to st 20 associated with other molecular features leads to the conclusion that the main contribution to the organic matter of all facies is by bacteria several prominent components including novel families iso c23 and iso c27 alkanes tetracyclic terpanes d ring aromatic 8 14 secohopanoids 1 phenylpentadecane undecylnaphathalene and their mono and dimethylated counterparts have been interpreted as derived from halophilic bacteria these conclusions may be extended to all crude oils from the same area which may be considered as true bacterially derived petroleums the la felicidad 1 well data are discussed with reference to other palaeosabkha type sequences from the sw aquitaine basin france in which the bacterial input is less important however in these sabkha sequences 1 phenylpentadecane undecylnaphthalene and related structures have also been identified

the western desert versus nile delta a comparative molecular biomarker study abstract the western desert and the nile delta are prolific petroleum producing basins the correlation and matching between their petroleum systems have been briefly studied overall geochemical and biological marker analyses of twelve crude oil and condensate samples taken from seven oil gasfields located in the nile delta and the western desert basins of egypt were effective in identifying and geographically defining two major oil families related by age and source rock depositional environment these samples were classified respectively as late cretaceous tertiary and jurassic early cretaceous the source rocks giving rise to the late cretaceous tertiary oils are associated with abundant terrestrial organic matter the source rocks giving rise to jurassic early cretaceous oil are presumably generated from a mixed terrestrial marine source meanwhile the western desert oil samples show prominent c 30 steranes elevated c 27 monoaromatic steroids and a distinct homohopane distribution suggesting this oil type is derived from a more marine influenced source rock than terrigenous sourced oil in the nile delta the most crucial geochemical fingerprinting biomarkers that have been used to differentiate between nile delta and the western desert oil are oleananes highly branched isoprenoids hbi sterane isomerization 24 norcholestanes aromatic steroid hydrocarbons and c 30 24 n propylcholestanes

biomarker distributions in australian oils predominantly derived from terrigenous source material oils found in many australian sedimentary basins contain a relatively high input of terrigenous organic source material a study of a large number of these oils has permitted a number of biomarker distributions to be determined that appear to be characteristic for oils derived from terrigenous source material these features include the presence of sesquiterpanes absence of tricyclic terpanes relatively high concentrations of a c24 tetracyclic terpane predominance of c29 steranes presence of two unidentified c27 and c30 terpanes and virtual absence of 18 h oleanane the latter observation is significant since it appears that 18 h oleanane appears only in oils of tertiary age derived from terrigenous source material an attempt has also been made to compare the results for the australian oils with published results for oils derived from terrigenous source material in other parts of the world the number of reports in the literature for these oils is fairly limited but it appears that some of the observations for the australian oils can be extended to them this study is an initial attempt to devise a classification scheme that can be used to determine the origin of an oil unambiguously from biomarker parameters in order for this approach to be successful a relatively large number of biomarker parameters need to be assigned as characteristic of a particular type of source material

mass flux and undertow in a surf zone abstract the mass of water carried shoreward by the breaking waves in a surf zone will in a two dimensional situation be compensated by a seaward return flow the undertow it is shown that the undertow is driven by the local difference between radiation stress and the set up pressure gradient which only balance each other in average over the depth turbulent shear stresses are required to maintain a steady situation comparison with measurements confirms the theoretical results

source dependent biomarker properties of five crude oils from the gulf of suez egypt abstract five crude oils from some producing wells in the southern part of the gulf of suez were characterized using a variety of organic geochemical parameters the results reveal significant differences within the oils from the gulf of suez basin that suggest two oil types and one mixed type type 1 oils from ras fanar and east zeit fields show a high relative abundance of gammacerane indicating a marine saline source depositional environment another related feature of these oils is the predominance of c 35 over c 34 17 h homohopanes type 2 oils from gama and amal 9 wells show oleanane indices over 20 indicating that they originated from an angiosperm rich tertiary source rock type 3 oil from amal 10 well has geochemical characteristics intermediate between those of types 1 and 2 this may reflect mixing of oils from the sources of both types 1 and 2 the geochemical characteristics of the oils vary sufficiently to suggest multiple sources the type 1 oils possess geochemical characteristics consistent with upper cretaceous brown limestone or lower eocene thebes formation carbonate source rocks type 2 oils are very similar in geochemical character to the lower miocene rudeis formation source rocks

forest disturbance in the central north island new zealand following the 1850 bp taupo eruption the 1850 bp taupo eruption covered c 30 000 km2 of the central north island with airfall deposits and c 20 000 km2 with ignimbrite this paper reviews pollen and charcoal analyses of lake and peat sediment cores from sites at various distances and directions from the taupo vent to establish the effects of this eruption on the surrounding forests forests within range of the ignimbrite were destroyed and forests located up to 170 km east of the vent suffered variable degrees of damage from ashfall stands of pteridium esculentum and other seral taxa flourished immediately after the eruption fires occurred during the eruption and continued for several decades after the degree and nature of vegetation disturbance above the taupo tephra varied according to the thickness of ashfall local topographical features and probably the vigour of the forest revegetation was complete within 200 years of the eruption even at sites overwhelmed by the taupo ignimbrite post eruption forests were similar to those exi

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

evolution and environmental impacts of the eruption of laacher see volcano germany 12 900 a bp abstract laacher see volcano lsv 40 km south of bonn explosively erupted ca 6 3 km 3 of chemically strongly zoned phonolite magma probably during spring 12 900 years ago the resulting eruption column having reached at least 20 km in height the bulk of the laacher see tephra lst was deposited east of the volcano within the neuwied basin lst ashes form the most important stratigraphic marker in lateglacial deposits over much of central europe a minimum of 2 mt total s was calculated to have been released during the eruption by comparing pre and posteruptive volatile concentrations in glass inclusions and pumice matrix glasses because a separate s bearing vapor phase was probably present in the magma prior to eruption as indicated by the high melt h 2 o contents close to saturation level the actual amount of s released during the eruption could have significantly exceeded 2 mt the sulfuric acid aerosol layer resulting from the massive stratospheric s input probably resided in the stratosphere for years and most likely had a significant impact on climate and thus the environment increased precipitation in central europe and or impairment of the vegetation cover for several years is suggested by several proxies especially increased sediment supply into lakes proximal to the eruptive center major environmental impacts include an initial blast that felled trees up to 4 km away from vent fast deposition of huge tephra volumes led to the complete disruption of rhine river within the lower neuwied basin and the damming up of a lake ca 140 km 2 in areal extent sudden collapse of the temporary tephra dam caused a catastrophic flood wave downstream whose deposits are recognized as far north as bonn reworking of unconsolidated tephra deposits over several 100 km 2 was widespread and extensive generating abundant lahars and flood plain deposits a braided river system established in neuwied basin probably persisted up to several years recent reports for a second eruption of lsv are not confirmed

cross shore mean flow in the surf zone abstract the seaward mean returnflow or undertow in the surf zone which compensates for the shoreward mass flux above the wave trough level is found to be driven by the force imbalance between the wave momentum flux on the one hand and the set up on the other hand in qualitative agreement with the model of dyhr nielsen and sorensen 1970 a model which quantifies this imbalance is shown to yield theoretical results in good accordance with experiments when the proper boundary conditions are accounted for

lower tertiary and upper cretaceous source rocks in louisiana and mississippi implications to gulf of mexico crude oil the lower tertiary sparta formation wilcox group and the midway group in southern louisiana include organic rich source facies that generate crude oil at relatively high thermal maturities the wilcox group is an important source of wilcox crude oil and regional kerogen variations explain two crude oil subfamilies wilcox crude oils in downdip areas of southern louisiana migrated short distances but long range lateral migration about 150 km best explains wilcox crude oils far updip from mature source rocks crude oils in oligocene and younger reservoirs in southern louisiana migrated vertically from deep lower tertiary source rocks some crude oils in upper cretaceous tuscaloosa reservoirs were emplaced by long range lateral migration from tuscaloosa source rocks g ven little evidence of upper tertiary source rocks and the overmaturity problems of mesozoic source rocks most crude oils in upper tertiary and pleistocene reservoirs of the gulf continental shelf are best explained by vertical migration from deep lower tertiary source rocks even so it is simplistic to assume an exclusive lower tertiary origin many tertiary and pleistocene crude oils of this study probably include an overprint of high maturity hydrocarbons from mesozoic sources

origin of oil in the sureste basin mexico geochemical and biological marker analyses of oils and rock samples from the sureste basin of mexico were effective in identifying and geographically limiting four major oil families related by age and source rock depositional environment oxfordian tithonian early cretaceous and tertiary the source rocks giving rise to the jurassic and cretaceous oils are associated with marine carbonate environments in contrast the source rocks giving rise to the tertiary oils are associated with a marine deltaic siliciclastic depositional setting biomarker and isotope differences observed in the oils derived from marine carbonate environments can be interpreted in terms of salinity clay content and oxygen depletion variations these differences provide diagnostic criteria for recognizing and differentiating five distinct organic rich depositional regimes as the sources for these oil types an anoxic hypersaline marine carbonate environment associated with a narrow and shallow semirestricted sea oxfordian age family 1 oil an anoxic marine carbonate environment associated with a silled basin geometry tithonian age family 2 oils subtype 2a an anoxic marine carbonate environment associated with a shallow gentle broad marine carbonate ramp in a distal position tithonian age family 2 oils subtype 2b a clay rich suboxic anoxic marine carbonate environment associated with a carbonate platform in a proximal position tithonian age family 2 oils subtype 2c and an anoxic marine evaporitic environment early cretaceous age family 3 oils the tertiary oils family 4 are derived from bacterially reworked terrigenous and marine organic source materials deposited in a marine deltaic environment the tithonian related oils in the mexican southern side of the gulf of mexico accumulated both offshore and onshore and throughout the stratigraphic column from kimmeridgian to pleistocene reservoirs suggesting vertical pathways as the principal secondary migration mechanism the lateral variations of these oils can be interpreted to reflect the tithonian paleogeography in the area and could be useful in predicting differences in the oil compositions

correlations of gulf coast petroleums on the basis of branched acyclic alkanes abstract mass 211 chromatograms of c 15 n alkane free saturated hydrocarbon fractions of oils represent numerous homologous series of methyl branched acyclic alkanes including isoprenoids mass 211 patterns facilitated the subdivision fingerprinting of 88 of 282 gulf coast petroleums into merely seven classes evaluation of reservoir ages suggests that the patterns undergo progressive change with time an end member pattern occurs in jurassic reservoirs a second closely related occurs principally in oils found in lower cretaceous reservoirs minor changes result in an upper cretaceous pattern which is duplicated in numerous oils occuring in all succeeding tertiary and quaternary stages over most of coastal and offshore louisiana laterally extensive source formations and pervasive vertical migration are indicated although branched alkane concentrations can be brought toward thermodynamic equilibrium by mineral catalysis the consistency of the observations indicates that this is minor suggesting a biomarker status for the compounds involved both facies variability and metabolic evolution might be significant in the generation of the observed patterns

geochemical and carbon isotopic studies of crude oil destruction bitumen precipitation and sulfate reduction in the deep smackover formation abstract crude oil generated by the lower smackover source facies migrated to upper smackover reservoirs where slow thermal cracking of crude oil resulted in the formation of gas condensate and late solid bitumen ultimately only pyrobitumen methane and nonhydrocarbon gases including hydrogen sulfide persist in the deepest smackover reservoirs the carbon isotopic compositions of crude oils became heavier during crude oil destruction the carbon isotopic compositions of asphaltenes nso compounds and saturated hydrocarbons in late solid bitumen and the lower smackover source facies became isotopically lighter during crude oil destruction it is suggested that some isotopically light components from crude oils were incorporated in late solid bitumen by reactions involving thermochemical sulfate reduction thermochemical sulfate reduction and crude oil destruction occurred over a long span of geologic time at temperatures in the 120 150 c range

the impact of the laacher see tephra on terrestrial and aquatic ecosystems in the black forest southern germany late glacial lake sediments containing the laacher see tephra lst 11 000 yr bp have been analysed for pollen and diatoms at two sites hirschenmoor rotmeer in the montane belt of the black forest southern germany in order to detect the possible impact of this major volcanic eruption on terrestrial and aquatic biota the pollen assemblages at both sites show a minor increase in grasses and sedges following the tephra deposition whereas the pollen of aquatic macrophytes do not show any consistent pattern partial redundancy analysis and monte carlo permutation tests suggest however that the lst had no statistically significant effect either on the terrestrial or aquatic pollen assemblages at either site when the effects of time and climatic change are allowed for statistically the diatom assemblages at both sites changed after the deposition of the lst and diatom inferred ph estimates suggest a short but non significant excursion towards lower values multivariate analyses of the diatom data indicate a statistically significant impact of the deposition of the lst and associated changes in sediment lithology on the diatom assemblages when the effects of climatic change and time are allowed for statistically however owing to the interaction between tephra and lithology it is not possible to conclude if the diatom changes were caused by the deposition of the lst or by lithological changes

correlation of source rocks and migrated hydrocarbons by gc ms in the middle triassic of svalbard abstract samples of lower and middle triassic sediments from nine different locations on svalbard have been analysed by gc ms to study migration processes short range migration was investigated by analyses of interbedded shales and siltstones from three of the locations in addition shale samples from six locations were analysed to study long range migration the maturity of the samples varied from immature through moderately mature to oil window maturity the qualitative distribution of biological markers was seen to be fairly similar in all the analysed locations irrespective of lithology this implies that no source characteristic parameters from gc ms analyses could be applied to exclude any of the analysed source rocks based on maturity considerations it was concluded that short range migration from shales to siltstones had probably been the most important process

gas hydrate and crude oil from the mississippi fan foldbelt downdip gulf of mexico salt basin significance to petroleum system abstract structure ii gas hydrate methane ethane hydrate and crude oil occur on the sea floor at 1920 1930 m water depth in atwater valley at block 425 near the juncture of the lower slope of the gulf of mexico salt basin and the abyssal plain the site is in the eastern mississippi fan foldbelt mff a distinct structural province at the downdip limit of the gulf of mexico salt basin the presence of thermogenic hydrocarbons confirms an active petroleum system in the deep eastern mff the hydrate bound c 2 c 5 hydrocarbon gases of the mff are isotopically distinct when compared to other gases from the upper and middle slope being strongly depleted in 13 c the biomarkers m z 191 and 217 of oil inclusions from at 425 gas hydrate are also distinct when compared to oils of the upper gulf slope and the smackover trend biomarkers of at 425 oil are consistent with a marine source rock deposited in an area of strong siliciclastic influx with possible higher plant organic matter the presence of a shale or mudstone source rock at the downdip limit of the gulf raises new questions as to paleogeography during source rock deposition emergent highlands immediately to the south and east of the downdip limit of the gulf of mexico salt basin during the mesozoic may explain the occurrence of the shale or mudstone source rock that gave rise to the gas and oil at at 425

gas geochemistry of the macuspana basin mexico thermogenic accumulations in sediments impregnated by bacterial gas a gas survey was performed in the macuspana basin south of mexico two distinct gas families were identified family 1 is represented by homogeneous and purely thermogenic gas associated with condensates expelled at the end of the oil window and family 2 is composed of a mixture of bacterial dry gas and thermogenic gas derived from source rocks at high maturity chemical and isotopic parameters as well as noble gas data provided information about the sources the proportions of mixing and directions of hydrocarbon migration of these two families considering the risk associated with further oil and gas exploration in the basin deeper zones present higher exploratory interest for family 1 gas fields and associated oil accumulations in contrast the bacterial gas fields should be considered a less promising target for future oil and gas exploration

the origins of petroleum in the northern gulf of mexico abstract the distribution and chemistry of oils in the northern gulf of mexico and the adjacent onshore can be explained by multiple sources fades variations maturation and post generation alteration genetic families include jurassic smackover flexure trend upper cretaceous and paleogene oils smackover oils have high sulfur contents pristane phytane ratios c 35 c 34 hopane ratios 1 0 and c 30 c 29 hopane ratios usuall 1 0 flexure trend oils are similar and contain abundant extended hopanes high sulfur contents and v ni v 0 5 these oils are inferred to be sourced in upper jurassic lower cretaceous strata upper cretaceous oils contain a distinctive suite of tricyclic and nonhopanoid triterpanes oleanane is low or absent paleogene oils can be recognized by the presence of 18 h oleanane and a lack of extended hopanes these oils occur from south texas to southern and offshore louisiana two subfamilies can be recognized based on the relative abundance of triterpanes and steranes these oils have a presumed paleogene source mixing of oil types is quite prevalent at the geographic boundaries of oil types the initial control on the distribution of oil and gas in the northern gulf of mexico is provided by the areal extent of source rocks secondary control is due to cenozoic deposition which provides the thermal stress to generate as well as destroy oil salt tectonics provide conduits for migrating fluids to escape the zone of thermal destruction mesozoic source strata again become important in the deep gulf of mexico where cenozoic sediments thin

impact of hot fluid advection on hydrocarbon gas production and seepage in mud volcano sediments of thick cenozoic deltas hydrocarbon seeps are ubiquitous at gas prone cenozoic deltas such as the nile deep sea fan ndsf2 where seepage into the bottom water has been observed at several mud volcanoes mvs3 including north alex mv namv4 here we investigated the sources of hydrocarbon gases and sedimentary organic matter together with biomarkers of microbial activity at four locations of namv to constrain how venting at the seafloor relates to the generation of hydrocarbon gases in deeper sediments at the centre high upward flux of hot 70 c hydrocarbon rich fluids is indicated by an absence of biomarkers of anaerobic oxidation of methane aom and nearly constant methane ch4 concentration depth profile the presence of lipids of incompatible thermal maturities points to mixing between early mature petroleum and immature organic matter indicating that shallow mud has been mobilized by the influx of deep sourced hydrocarbon rich fluids methane is enriched in the heavier isotopes with values of 13c 46 6 vpdb and d 228 vsmow and is associated with high amounts of heavier homologues c2 suggesting a co genetic origin with the petroleum on the contrary at the periphery a lower but sustained ch4 flux is indicated by deeper sulphate methane transition zones and the presence of 13c depleted biomarkers of aom consistent with predominantly immature organic matter values of 13c ch4 60 vpdb and decreased concentrations of 13c enriched c2 are typical of mixed microbial ch4 and biodegraded thermogenic gas from plio pleistocene reservoirs of the region the maturity of gas condensate migrated from pre miocene sources into miocene reservoirs of the western ndsf is higher than that of the gas vented at the centre of namv supporting the hypothesis that it is rather released from the degradation of oil in neogene reservoirs combined with the finding of hot pore water and petroleum at the centre our results suggest that clay mineral dehydration of neogene sediments which takes place posterior to reservoir filling may contribute to intense gas generation at high sedimentation rate deltas

non climatic factors and the environmental impact of volcanic volatiles implications of the laki fissure eruption of ad 1783 studies of the potential of icelandic volcanic eruptions to modify the environment of the british isles have primarily concentrated on the degree of induced climate change but models and temperatu

oligocene to holocene hydrocarbon migration and salt dome carbonates northern gulf of mexico abstract the geochemistry and geology of damon mound salt dome in brazoria county texas provides an insight to the timing of hydrocarbon migration and carbonate caprock development in the houston salt dome province reservoir rocks flanking the salt dome received a charge of crude oil from deeply buried eocene source rocks during early oligocene early miocene time the light 13c of the carbonate caprock at damon mound 24 8 to 31 7 pdb is consistent with an origin from bacterial oxidation of crude oil with similar 13c 27 1 to 28 8 pdb a minimum weight estimate of carbonate caprock at damon mound is 32 7 106 metric tons suggesting bacterial oxidation of about 34 2 106 barrels of crude oil to form the carbonate late oligocene early miocene erosional exposure of the carbonate caprock provided a hard substratum to initiate the development of a coral reef in an otherwise unfavourable mud dominated environment although the bulk of the reef carbonate displays normal marine 13c some late carbonate cements show light 13c values 22 1 to 29 6 from bacterial hydrocarbon oxidation buried carbonate caprocks and coral reef facies serve as carbonate reservoir rocks over gulf of mexico salt domes lending support to the hypothesis that intense hydrocarbon oxidation can in itself give rise to some carbonate reservoir rocks ongoing hydrocarbon migration from deeply buried cretaceous source rocks and the development of embryonic carbonate caprocks over shallow salt domes on the present gulf of mexico continental slope offer analogies and contrasts to the processes that gave rise to carbonates at damon mound in the geological past

pathways of migration of oil and gas in the south mississippi salt basin abstract the south mississippi salt basin is one of three interior basins characterized by structures formed by movement of the late jurassic louann salt an analysis of pathways of migration within the basin has revealed that it is possible to explain why hydrocarbons have accumulated in some structures yet are absent from others that would appear to be favorable of the more than 840 fields within the basin 74 including the largest known accumulations have hydrocarbons stacked in reservoirs in more than one formation these stacked reservoirs result from vertical migration brought about by faulting more than 750 fields have hydrocarbons confined to one formation in traps associated with four distinct trends of production that decrease in age systematical iy from the margin of the basin into the interior the hydrocarbons in these trends have accumulated by intrastratal migration without the agency of faulting from a nearby source in the same unit as the reservoir on the northwest side of the basin migration between units brought into contact along unconformities has resulted in ten fields vertical migration brought about by faulting around shallow salt diapirs has allowed hydrocarbons to escape so that only 5 of 56 such structures have ever produced oil or gas these conclusions derived from geological deductions are supported by preliminary geochemical data but more extensive and detailed geochemical analyses of oils from the various sources are under way

organic geochemistry of the oils from the southern geological province of cuba abstract the aliphatic hydrocarbon composition acyclic isoprenoids hopanoids and steroids of oils from the most productive fields in the southern geological province of cuba have been studied this province is defined by its position with respect to the cretaceous overthrust belt generated during the formation of oceanic crust along the axis of the proto caribbean basin the relative abundances of 18 h 22 29 30 trisnorneohopane gammacerane and diasteranes suggest that pina oils are related to the carbonate oils from the placetas unit in the northern province low ts ts tm and c27 29 rr rr sd ratios the cristales and jatibonico oils exhibit some differentiating features such as higher ts ts tm and absence of gammacerane the oils from this province do not exhibit significant differences in either hopane c32 22s s r and c30 or sterane c29 20s s r maturity ratios however the relative content of 5 h 14 h 17 h cholestanes c29 ratio indicates that pina oils are more mature than cristales and jatibonico oils several of these oils cristales jatibonico and pina 26 are heavily biodegraded lacking n alkanes norpristane pristane and phytane the two former oils do not contain acyclic isoprenoid hydrocarbons other biodegradation products the 25 norhopanes are found in all the oils their occurrence is probably due to mixing of severely biodegraded oil residues with undegraded crude oils during accumulation in the reservoir

classification of offshore gulf of mexico oils and gas condensates five groups of petroleums can be recognized in the offshore gulf of mexico on the basis of carbon isotope and sulfur isotope ratios sulfur content and relative abundances of nickel and vanadium of 355 oils analyzed 341 96 1 are evidently closely related and cannot be subdivided on the basis of carbon or sulfur isotopes we suggest that these oils represent a single broad superfamily however two subgroups within this set are distinguishable on the basis of sulfur content and relative abundances of nickel and vanadium group 1a sigma 13 c 26 5 0 4 parts per mil sigma 34 s 5 6 2 4 parts per mil s 0 25 0 15 v ni v 0 27 0 10 and group 1b sigma 13 c 26 5 0 3 parts per mil sigma 34 s 5 9 1 2 parts per mil s 0 73 0 43 v ni v 0 67 0 07 group 1a oils are broadly distributed across the louisiana and adjacent texas continental shelf whereas group 1b oils are found along the louisiana shelf edge and continental slope group 1b oils have substantial genetic affinities to those from the campeche shelf offshore mexico of mesozoic origin the remaining 14 analyzed petroleums include supermature condensates from offshore texas and oils from offshore southern florida believed to be cogenetic with those from the jurassic smackover formation a three dimensional appraisal of geohistory suggests that petroleum generation began in the eocene in the region of the rio grande delta progressed coastwise to the mississippi delta area by the miocene and then occurred in regions of progres ively deeper water during the pliocene pleistocene

oil quality in deep water settings concerns perceptions observations and reality as exploration migrates into deeper water crude oil quality becomes increasingly important variations in oil quality which are reflected in such properties as api gravity viscosity sulfur content and acid number impact both value and producibility in fact issues of oil quality in deep water may in some cases be more critical than issues of hydrocarbon volume problems associated with deep water are commonly thought to be amplified largely as a result of the expansion of the biodegradation window the expanded window is a result of lower temperatures at the mud line a review of data from the gulf of mexico and the gulf of guinea reveals that other factors may have a greater influence on oil quality for example in the gulf of mexico strong evidence exists that the nature of the source rock is a major factor in establishing sulfur content and api gravity oils derived from an upper jurassic oxfordian calcareous source rock generate oils with higher sulfur contents than those derived from cretaceous argillaceous source rocks in the gulf of guinea although many of the newly discovered pools are shallowly buried and evidence for biodegradation exists crude oil quality is mitigated by multiple charging events in both regions evidence also exists for phase segregation which introduces light oils and condensates into the shallow part of the sedimentary sequence both phase segregation and multiple charging events appear to be largely a result of an individual trap s structural evolution the available data therefore suggest that some of the risks associated with oil quality may be reduced through a more detailed assessment of a prospect s filling history and structural evolution and an understanding of the nature of the source facies however there clearly are such situations as offshore brazil where the risks associated with oil quality appear more difficult to mitigate

organic geochemical characterisation of depositional palaeoenvironments of source rocks and oils in brazilian marginal basins abstract an investigation of bulk isotopic and molecular features of a wide selection of source rocks and oils from brazilian marginal basins ranging from lower cretaceous to tertiary in age provides a number of organic geochemical criteria that characterise and distinguish their depositional palaeo environments the methods employed include evaluation of organic carbon contents rock eval pyrolysis vitrinite reflectance measurements determination of carbon isotope ratios elemental and visual kerogen analysis assessment of oils and solvent extracts by liquid and gas chromatography and quantitative biological marker investigations using gc ms for aliphatic hydrocarbons and uv vis spectrophotometry for metalloporphyrins selected data were evaluated using principal component analysis the results enable the recognition and differentiation of seven depositional regimes lacustrine freshwater lacustrine saline water marine evaporitic marine carbonate marine deltaic marine highly anoxic with a predominance of calcareous mudstone lithology and marine anoxic with predominance of siliciclastic lithology diagnostic features in the biological markers from these depositional environments include the carbon number distributions of n alkanes pristane phytane ratios absolute concentrations of carotane higher acyclic isoprenoids c 30 hopane and steranes and the abundance of the latter relative to 4 methylsteranes the occurrence and abundance of particular biological markers such as gammacerane tricyclic and tetracyclic terpanes 18 h oleanane 28 30 bisnorhopane and 25 28 30 trisnorhopane and the relative abundances of nickel and vanadyl porphyrins

varve chronology and palynology of the lateglacial in northwest germany from lacustrine sediments of hamelsee in lower saxony abstract the hamelsee is a dolina from a collapse over permian salt that occurred at the end of the pleniglacial it is more than 21 m deep and contains 18 m of lacustrine sediments the lateglacial sediments in the central part of the lake consist of 2 7 m from 15 to 17 7 m of sapropelic and silty muds which are mostly laminated and partly bioturbated minor slumps occur mainly during colder phases the subdivision of the lateglacial is based on pollen zones multidisciplinary studies of the microfacies from thin sections geochemistry pollen analysis and rotifer analysis allow environmental and palaeoclimatological interpretations to be made the biozones of the lateglacial and their boundaries are marked by rapid climatic changes though covering comparatively short periods of time they are not monotonous but characterized by minor internal climatic fluctuations the sediments of the meiendorf and oldest dryas are not laminated the allerod sediment is seasonally varved without interruption and encompasses 625 yr the eruption of the laacher see volcano 12 900 cal bp had an impact on the climate during the following 10 yr the transition from the allerod to the younger dryas took some 50 yr and it occurred 200 yr after the eruption of the laacher see volcano the abrupt change at the end of the lateglacial 11 560 cal bp occurred within less than 10 yr however many proxies reacted with a time lapse of 15 to 30 yr

buoyancy driven propagation of isolated fluid filled fractures implications for fluid transport in gulf of mexico geopressured sediments a large portion of the sediments within the northern gulf of mexico contain pore fluid pressures in excess of hydrostatic development of geopressure is generally attributed to compaction disequilibrium caused by rapid deposition of low permeability sediments in the miocene and plio pleistocene numerous studies have examined the formation of overpressures and or expulsion of geopressured fluids into overlying hydropressured strata however very little attention has been given to fluid flow within the geopressured zone itself movement of oils from cretaceous or older source rocks into plio pleistocene reservoirs in the gulf basin requires as much as 10 km of vertical migration in a few million years precipitation of cements in some geopressured sediments also implies large scale fluid flow new evidence from a deep well in the eugene island area offshore louisiana indicates that geopressured sediments are mechanically very weak with a poisson s ratio greater than 0 4 and a shear modulus or rigidity less than 1 gpa in addition large scale fluid flow either through interconnected pores or fractures is not occurring in this location at least at present an alternative hypothesis is that upward fluid transport in geopressured sediments is caused by buoyancy driven propagation of isolated fluid filled fractures using linear fracture mechanics i show that vertical fractures with lengths of a few meters can propagate at velocities of 1000 m yr mass flux rates 100 kg m2 yr are significant assuming a mechanism for formation of fluid filled fractures exists such as hydrofracturing when fluid pressures exceeded the minimum confining stress fracture propagation velocity and mass flux rate are strongly dependent on the shear modulus of geopressured sediments

quasi 3d modelling of nearshore currents abstract existing concepts of wave induced nearshore current models in the cross shore vertical plane 2dv and depth integrated 2dh are combined to a quasi 3d mathematical model this combination is tested for reproducing correct results in 2dv and 2dh situations the importance of the various contributions to the wave induced secondary circulation in the vertical plane is investigated for realistic parameter ranges which leads to the conclusion that both the non breaking and the breaking fraction of a random wave field in the surf zone generate important secondary currents additional computations show the relevance of a 3d approach of nearshore currents even in seemingly simple situations like a plane sloping beach with obliquely incident waves

migration of crude oil from the smackover source rock to jurassic and cretaceous reservoirs of the northern gulf rim abstract migration of distinctive crude oils from the upper jurassic smackover source rock across the northern gulf rim began at various times during the cretaceous regional source rock differences resulted in two compositional subfamilies of smackover crude oils type i crude oils in upper smackover reservoirs of east texas arkansas louisiana and mississippi reflect an origin from algal derived kerogen deposited in an anoxic environment type ii crude oils in upper smackover reservoirs of alabama and florida reflected an origin from kerogen preserved in a less anoxic environment with a terrestrial component comparison of molecular and carbon isotopic compositions of crude oils suggests that vertical migration of type i smackover crude oils charged many overlying upper jurassic lower cretaceous and upper cretaceous reservoirs some lateral migration to cretaceous reservoirs north of the updip limit of the smackover formation also occurred both type i smackover crude oils and geochemically dissimilar cretaceous sourced oils are found in upper cretaceous tuscaloosa and woodbine reservoirs because of impermeable barriers to migration especially in alabama vertical migration of type ii crude oils was less significant

the framework of hydrocarbon generation and migration gulf of mexico continental slope abstract the occurrence of large volumes of crude oil and thermogenic gas in plio pleistocene reservoirs and holocene seeps of the gulf of mexico slope argues that the process of hydrocarbon generation and migration continues at the present time calculated thermal maturity models based on deep seismic stratigraphy indicate that cretaceous and possibly early tertiary sediments are presently within the thermal maturity range for generation and expulsion of crude oil the cretaceous and early tertiary sediments are suggested as possible source rocks because younger sediments are thermally immature for crude oil generation and older sediments are thermally overmature for crude oil preservation the calculated thermal maturity profile for the slope indicates that some generation of crude oil could occur as shallow as 6 km and that liquid hydrocarbons could be preserved as deep as 9 km thermogenic gas is stable at even greater depths migration with a strong vertical component must be invoked to explain thermogenic hydrocarbons in shallow reservoirs and seeps of the slope the great depth at which liquid hydrocarbons and dry gas can be preserved in reservoirs of the gulf of mexico salt basin indicates that huge volumes of prospective section remain essentially unexplored

sterane and triterpane patterns as diagnostic tools in the mapping of oils condensates and source rocks of the gulf of mexico region abstract four hundred and eighty one gulf of mexico oils and condensates can be subdivided into nine major families based on their sterane m z 217 218 and triterpane m z 191 177 biomarker mass chromatogram patterns these families are 1 carbonate sourced oils reservoired in jurassic cretaceous reservoirs onshore and plio pleistocene reservoirs offshore 2 austin chalk reservoired oils 3 tuscaloosa oils 4 wilcox reservoired oils la 5 south texas palaeogene reservoired oils 6 mississippi delta oils 7 post mature oils of uncertain affinities 8 migration contaminated oils showing attributes of a mixing of immature and post mature sources and 9 oils and condensates lacking biomarkers each oil family is concentrated in specific age defined producing trends ranging in age from jurassic to pleistocene for tertiary reservoirs these producing trends shift geographically with time in a manner analogous to the clockwise migrating cenozoic depocenter model for the northern gulf of mexico at least six ages of marine source rock deposition may be implicated in the genesis of these oils 1 the kimmeridgian oxfordian including smackover and norphlet formations 2 the aptian including pine island bexar and sunniland formations 3 the albian paluxy formation 4 the cenomanian turonian including eagle ford and tuscaloosa formations 5 the coniacian santonian eagle ford and austin chalk and 6 the palaeocene wilcox midway sparta formations the jurassic and cretaceous source rocks correspond to described oceanic anoxic events of probable global significance this paper will concentrate on describing the biomarker patterns of the oils and postulated source rocks but due to reasons of space isotopic elemental and other data will only be briefly discussed

evolution of tricyclic alkanes in the espirito santo basin brazil abstract the distributions of tricyclic isoprenoid alkanes were characterized in the neocomian sequence from the espirito santo basin brazil by high resolution gas chromatography mass spectrometry and co injection with synthetic standards where available a suite of homologous components ranging from c 20 to c 28 were present throughout the sequence as a mixture of stereoisomers whose relative abundance changed with depth the epimerization rates were similar for the various tricyclic compounds irrespective of side chain length achieving equilibrium ratios before the main stage of oil generation this new maturity parameter should be useful as a supplement to sterane hopane measurements

petroleum generation in the southeast texas basin implications for hydrocarbon occurrence at the south liberty salt dome geochemical characteristics of hydrocarbons from the south liberty field liberty county texas were integrated with local stratigraphy pressure temperature seismic data and formation water chemistry to determine the source maturity and migration pathways of hydrocarbons associated with the salt dome in the southeast texas gulf coast fourteen crude oil samples from the soft geopressured cook mountain and yegua both eocene and frio oligocene reservoirs 989 2886 m 3245 9469 ft were analyzed by whole oil high resolution gas chromatography gc and gc mass spectrometry pressure and temperature data from 36 wells were used to model the thermal maturation history in the vicinity of the dome south liberty oils were found to belong to a single genetic family sourced from rocks with a similar level of maturity biomarkers indicate they were formed in a marginal marine environment with notable terrestrial input from a likely lower tertiary source rock probably the downdip lower claiborne and or wilcox group oils were generated within the peak oil window vitrinite reflectance 0 6 0 9 at expulsion temperatures of 125 to 130c thermal modeling indicates the lower claiborne and or upper wilcox beds attained optimum maturity in and around the dome between 8 to 20 ma and 18 to 31 ma respectively oil migration toward the structure probably occurred through faults breaching the deep seated lower claiborne upper wilcox source two severely biodegraded samples were found and these were associated with cooler formation water 50 to 55c with a greater meteoric water component 48 60 comparison with brazoria county oils 100 km 62 mi to the southwest indicates that the south liberty oils belong to the same genetic family with minor differences resulting from a greater input from terrestrial kerogen

kilometer scale upward migration of hydrocarbons in geopressured sediments by buoyancy driven propagation of methane filled fractures several lines of evidence support kilometer scale upward migration of fluids in the gulf of mexico basin discharge of hypersaline brines at the sea floor long term natural hydrocarbon seeps and microseeps gas chimneys lead zinc mineralization in salt dome cap rocks and allochthonous brines in cenozoic sediments we explore the hypothesis that upward fluid transport in geopressured sediments is caused by buoyancy driven propagation of isolated methane filled fractures in other words instead of fluid migrating along a fixed network of interconnected pores or fractures fluid enclosed within an isolated fracture is transported upward by hydrofracturing the mechanically weak geopressured sediments thus the fluid filled fracture propagates upward through the sediments hydrofracture is driven by the pressure difference buoyancy between the enclosed methane and the surrounding sediments our results show that methane filled fractures with half lengths of a few meters should propagate upward through geopressured sediments with velocities of hundreds of meters per year or higher as methane filled fractures increase in volume and decrease in density with decreasing confining pressure they develop the potential to entrain and transport more than 1000 kg m3 of oil or brine methane filled fractures should propagate to the surface unless they are trapped beneath a layer that has high fracture toughness such as salt or are absorbed when they intersect a permeable 10 md sand layer

environmental impact of the laacher see eruption at a large distance from the volcano integrated palaeoecological studies from vorpommern ne germany abstract in order to investigate the environmental impacts of the laacher see eruption 12 900 calendar years b p and the deposition of the laacher see tephra at a large distance from the volcano fine resolution micromorphological diatomological and palynological investigations were carried out on closely spaced areas in the reinberg basin vorpommern ne germany the lower part of the lst originates from atmospheric input whereas the upper part was washed in from the surrounding basin slopes diatom populations expanded as a consequence of the input of silica while simultaneously dissolution of dead diatoms decreased the tephra provided a favourable habitat for many epilithic and epipelic diatom taxa the diatoms show a slight acidification and an increase in specific conductivity of the water whereas no eutrophication is indicated these effects disappeared after lake sediments covered the tephra the pollen diagrams from the reinberg basin as well as many other pollen diagrams from ne germany indicate that the vegetation reacted to rising temperatures after the cooler gerzensee fluctuation to a short lived water level rise connected with higher precipitation after the volcanic eruption and to minor openings in the forest vegetation due to increased fire probably connected with severe thunderstorms

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

source characteristics of marine oils as indicated by carbon isotopic ratios of volatile hydrocarbons carbon isotopic ratios of volatile hydrocarbon fractions of marine oils are diagnostic of organic facies and depositional environments of source rocks for carbonate oils low molecular weight volatile hydrocarbons c9 are isotopically lighter than high molecular weight volatile hydrocarbons c9 c17 in contrast for deltaic oils low molecular weight volatile hydrocarbons are isotopically heavier than high molecular weight volatile hydrocarbons marine shale oils show patterns intermediate between carbonate and deltaic oils this relative variation of carbon isotopic ratios among volatile hydrocarbons of oils is explained by earlier expulsion of marine oils derived from isotopically homogeneous algal bacterial kerogens in rich so rce rocks and secondary cracking of petroleum prior to expulsion for marine oils derived from isotopically heterogeneous terrestrial kerogens in lean source rocks in basins with multiple source rocks carbon isotopic ratios of volatile hydrocarbons are useful for determining oil oil correlation and for inferring oil source rock relationship

geochemistry of oils from the northern timan pechora basin russia abstract a geochemical study of 36 oils from the northern timan pechora basin indicates four oil types two types of sulfur rich oils range 1 4 2 5 sulfur can be identified on the basis of both gross and molecular properties these oils are found primarily in the toravey south toravey and roman trebs fields they are also present in the offshore prirazlom field thereby extending the geographic range of sulfur rich oils into the pechora sea another oil type exhibits a distinctive odd predominance of n alkanes in the range n c 11 through n c 19 and a diminished abundance of n alkanes greater than c 19 these oils which occur primarily in the a titov and labogan fields show striking similarities to ordovician sourced oils from other paleozoic basins throughout the world their biomarker and isotopic compositions for example bear a strong resemblance to oils generated from the ordovician viola limestone of the anadarko basin the fourth oil type occurs in the northwestern portion of the basin in the khylchuyu field some mixing between the various types is evident light oils and condensates of the peschano ozyor shtokman rusanov and vasilkovo fields cannot be readily assigned to any of these four types the upper devonian domanik formation is generally thought to be the major oil source in the timan pechora basin however geochemical characteristics of timan pechora oils analyzed do not closely resemble those of other upper devonian source oils such as those generated from the duvernay formation of western canada these differences might reflect variations in the organic matter preserved in the two basins during the late devonian or may indicate that the upper devonian is not an important hydrocarbon source in the northern timan pechora region the results suggest that the timan pechora oils analyzed are generated from paleozoic carbonate or calcareous shale source rocks at least one of which appears to be of ordovician age

laacher see tephra a widespread isochronous late quaternary tephra layer in central and northern europe a late quaternary tephra layer widespread in central and northern europe resulted from explosive plinian and phreatomagmatic eruptions of the laacher see volcano 11 000 yr b p the tephra is distinguished from other late quaternary andesitic rhyolitic airfall tuff layers in northern europe and from basaltic or trachytic tuff deposits in southern europe by its phonolitic composition and abundance of sanidine plagioclase clinopyroxene amphibole and sphene the proximal tephia sequence at laacher see is divided into three main deposits the predominantly plinian deposits of lower and middle laacher see tephra llst and mlst and phreatomagmatic deposits of the upper laacher see tephra ulst the mlst member is further subdivided into beds a b and c1 c2 and c3 the chemical composition of the magma is highly differentiated phonolite in the llst to mlst b sections but mafic phonolite in the mlst c1 to ulst sections all deposits are considered to be isochronous the frequency maximum of 16 radiocarbon datings indicating an eruption about 11 000 50 yr b p distal ash was deposited in three main fans directed to the northeast lst traced up to 1 100 km distance south lst traced up to 600 km and southwest lst traced up to 100 km tephrostratigraphic correlation of the distal ash deposits is based on a the major element composition of glass shards b lithology and c heavy mineral analyses the northeastern fan consists of deposits from llst mlst b and mlst c1 eruptive phases the southern fan comprises mlst a mlst c2 and ulst deposits and the southwestern fan consists exclusively of ash from the ulst eruptive phase northeastern transport of ash during eruptive phases with high plinian eruption columns but southern and southwestern transport of ash along phases of relatively low eruption columns are interpreted in terms of prevailing southwesterly paleowinds at high altitudes tropopause level but northerly winds dominating in the lower atmosphere the laacher see eruption columns were emplaced into an atmosphere vertically zoned with respect to paleowind directions which also explains the near vent shifting of llst mlst b and mlst c1 iso pach axes from east southeast to northeast within the first 20 km of transport

stable carbon isotope compositions of crude oils application to source depositional environments and petroleum alteration the carbon isotopic composition of the c15 saturate and aromatic hydrocarbon fractions and the gas chromatographs of the c15 saturate fraction of 339 oils were geochemically and statistically evaluated results of this study show that the average isotopic compositions of the c15 aromatic hydrocarbon fractions of oils sourced from terrigenous or marine organic matter are identical the average isotopic composition of the c15 saturate fraction of oils derived from terrigenous organic sources is slightly more negative 0 9 pmil than the average for marine oils but this difference is insufficient to be used as a reliable source indicator reports in the literature stating that marine oils are isotopically more positive than te rigenous oils and that the difference can be utilized to distinguish between the two are therefore not supported by this study the isotopic differences between oils sourced from terrigenous and marine organic matter do not manifest themselves in the range of absolute values of one oil fraction but rather in the isotopic relationship between the saturate and aromatic hydrocarbon fractions the isotopic relationship is the following oils of terrigenous organic source dgr13caro 1 12 dgr13csat 5 45 oils of marine organic source dgr13caro 1 10 dgr13csat 3 75 the difference between the two equations was evaluated statistically and a statistical parameter cv the canonical variable cv 2 53 dgr13csat 2 22 dgr13caro 11 65 was used to distinguish between marine and terrigenous oils cv values larger than 0 47 indicate predominantly a terrigenous organic source for the oil whereas cv values smaller than 0 47 indicate mostly a marine organic source thermal maturity differences in oils and isotopic variations in the source beds can cause as much as 2 pmil variations in the isotopic composition of one family of oils finally stable carbon isotopes can in some situations help correlate biodegraded oils to their nondegraded counterparts

longshore current on a barred beach field measurements and calculation measurements of the longshore current on a barred beach made during the 1990 duck experiment on low frequency and incident band longshore and across shore hydrodynamics delilah field data collection project conducted at duck north carolina revealed an unexpected and persistent broad peak in the current velocity in the trough between the nearshore bar and the shore this paper introduces longshore current and associated wave measurements from delilah together with a numerical model capable of describing the field observations an existing numerical model of the mean current is modified to include a general transport equation for the mean turbulent kinetic energy created by wave breaking and reynolds stress components needed to calculate the longshore current and mean water level are reexpressed to include the turbulent momentum transport in comparison to predictions from the original model the modified model produces much improved agreement with the measured current velocity on the barred profiles in the field measurements and with the velocity profile and mean water level generated on a uniformly sloping laboratory beach by monochromatic waves three forms of a bottom friction coefficient are examined and the open channel flow manning friction coefficient is selected because of best agreement and consistency values of the manning friction coefficient required to calibrate the model agree with values normally assigned to the related bottom roughness in open channel flow

gas venting and subsurface charge in the green canyon area gulf of mexico continental slope evidence of a deep bacterial methane source abstract questions as to the role of modern carbon in methanogenesis and the maximum depth of methane sources in the gulf of mexico continental slope remain unanswered a research submersible was used to sample mixed bacterial and thermal gas 13 c of methane 62 8 d 176 venting to the water column from the gulf slope in green canyon gc 286 the 14 c value of the methane 998 is consistent with fossil carbon another gas vent on gc 185 is 100 methane 13 c 62 9 d 155 and may be from a bacterial source the 14 c 997 of this bacterial methane is also consistent with fossil carbon fossil bacterial methane and thermal hydrocarbons are present in pliocene to pleistocene reservoirs 3509 4184 m of genesis field gc 205 161 160 oil in these reservoirs is biodegraded but gas is not suggesting that gas charge to reservoirs continues presently at 3 4 km depth mixed thermal and bacterial methane may charge the deep reservoirs and fossil methane from depth may ultimately vent on the sea floor at gc 286 and gc 185 results of this study of green canyon suggest that bacterial methane in gas vents and in reservoirs is from deep fossil sources

micromorphology and late glacial holocene genesis of luvisols in mecklenburg vorpommern ne germany abstract in the german soil science literature luvisols formed in weichselian sediments except from the early weichselian are normally regarded as purely holocene soils with the main period of development assumed to have been during the atlantic phase although debated at some length since the 1960s the genesis of the widespread albic luvisols with a simplified ap bw eb ebtb btb g c horizon sequence and developed on the flat and slightly undulating till plains of the north german mecklenburgian stage deglaciation 14 000 bp has yet to be clarified periglacial climate during the late weichselian led to the formation of sand filled wedge shaped structures penetrating bt horizons systematic micromorphologic investigations of soil profiles with sand wedges revealed the occurrence of numerous fragments of rounded limpid clay coatings within periglacial formed lenticular microplates as well as in and at the margins of the sand wedge infillings assuming the younger dryas as the latest possible phase of formation the lenticular microplates and the undisturbed sand wedges postdate clay illuviation undisrupted clay coatings next to fragmented clay coatings prove a subsequent holocene clay illuviation clay illuviation must have occurred at least in warmer phases of the late glacial together with the already accepted pedogenic processes of decalcification organic matter accumulation ahb horizons podzolisation and silicate weathering bwb horizons on sites not influenced by groundwater

geochemical evidence of organic matter source input and depositional environments in the lower and upper eagle ford formation south texas abstract late cretaceous source rocks in the south texas eagle ford formation were characterized based on geochemical features of the iona 1 core which penetrates the lower and upper eagle ford formation this set of immature samples provides a detailed record of the variation of organic matter om sources across different depositional facies our results show that organic matter rich shales are dominated by marine type ii kerogen lower eagle ford lef contains high sulfur kerogen type ii s with s c 0 04 and a minor contribution of terrestrial om is evident in the upper eagle ford uef combined geochemical data from iona 1 core samples based on bulk geochemical rock properties residual oil chromatography and biomarker analyses reveal that the total organic carbon content and extractable bitumen content in the lef are higher than in the uef redox sensitive biomarkers demonstrate that sulfur rich photic zone anoxia euxinia developed in the lef and that persistent oxygenation occurs during deposition of the uef sulfur rich kerogen in the lef in turn generates medium high sulfur containing oils up to 2 6 as a consequence of the elevated sulfur contents in the lef oil bitumen generation initiated earlier and at lower maturity levels than in the uef high levels of anomalous 22s 22s 22r homohopane ratios and 20s 5 14 17 steranes have been observed in the lef interval which is controversial because of the low maturity level indicated by most bulk geochemical thermal maturity parameters including tmax calculated ro 0 45 and ts ts tm as well as c29ts c29ts c29 hopane and c29 sterane ratios these anomalously high thermal maturity parameters are more likely caused by enhanced isomerisations due to high organic sulfur content under reducing depositional environments in the lef rather than by thermal maturation hypothetical diagenetic pathways for the sulfurisation of homohopanoids and steroids are proposed to explain their abnormal isomerisations in the lef

origin of crude oil in the wilcox trend of louisiana and mississippi evidence of long range migration abstract geochemical characterization of crude oils from wilcox reservoirs in central louisiana and southwest mississippi suggests that they represent a single crude oil family that is distinct when compared to crude oils in deeper tuscaloosa and smackover reservoirs this observation is consistent with geologic constraints that suggest an origin of crude oil from within the wilcox group itself although shales of the shallow wilcox group in central louisiana and southwest mississippi contain gas prone kerogen and are thermally immature a more oil prone source facies is present in marine shales of the deep wilcox group in southcentral louisiana thermal maturity measurements based on pyrolysis suggest a broad area of effective wilcox source rock in southcentral louisiana migration distances from source to reservoir rocks of the downdip wilcox trend of southcentral louisiana appear to be relatively short however long range updip migration sometimes greater than 100 km from deeply buried wilcox source facies provides the best explanation for emplacement of crude oil in the shallow wilcox trend of central louisiana and southwest mississippi

organic geochemical indicators of dynamic fluid flow processes in petroleum basins a variety of preliminary geophysical geochemical and geological observations anderson et al geophysics 12 17 april 1991a b anderson oil gas j 85 91 26 april 1993 along with well production data schumacher aapg ann conv abstr april 1993 have led to the hypothesis that fluid injection into eugene island block 330 ei 330 in the u s louisiana gulf coast may be a continuing episodic process with the most recent injections having occurred on short geologic time scales 10 000 yr or less organic geochemical evidence presented here suggests these processes may occur on very short time scales years a process called dynamic fluid injection was proposed to explain these observations and is envisioned as episodic pressure build up followed by rapid escape of gas and oil through geopressure and injection into overlying reservoirs

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

the interaction between the undertow and the boundary layer flow on a beach the theoretical result for undertow in a surf zone found by svendsen 1984a is combined with a boundary layer solution at the bottom and it is shown that in this boundary layer the eddy viscosity is small relative to that produced by the breaking the proper eddy viscosity t between the surface and the bottom boundary layer is determined by comparison with measurements which leads to quite accurate reproduction of the velocity profiles the model also predicts the mean flow in the boundary layer and the mean bottom shear stress and the results are analyzed for sensitivity to inaccuracies in the basic assumptions

biomarkers and carbon isotopes of oils in the jurassic smackover trend of the gulf coast states u s a abstract the geochemistry of 25 oils from 23 fields in alabama and the mississippi and louisiana arkansas jurassic salt basins was evaluated results show that the oils were generated by a carbonate source rock which was deposited under highly anoxic conditions and which contains mainly marine derived organic matter the mississippi and louisiana arkansas oils are geochemically similar indicating similar depositional environments for the source although the alabama oils were also derived from a carbonate source rock they are dissimilar to the mississippi and louisiana arkansas oils terpane biomarkers suggest that in addition to marine derived organic matter the source for the alabama oils had an organic input from a more near shore paralic environment i e with a component of terrestrially derived kerogen within each area the oils are similar therefore the norphlet and upper smackover oils in alabama share a common source and the upper smackover cotton valley and some of the lower tuscaloosa oils where production is from faulted structures in mississippi also share a common source maturities of the oils in the three areas vary from low in the updip mississippi salt basin high in the louisiana arkansas salt basin to very high in portions of alabama based on the maturity of oils in mississippi oil generation and migration commenced during the cretaceous when the source was at modest levels of thermal maturity oils migrated relatively short distances into nearby reservoir rocks some oils reached high maturities in the reservoirs resulting in abundant late forming bitumen and pyrobitumen deposition in pore spaces