early diagenetic transformation of higher plant triterpenoids in deep sea sediments from baffin bay abstract a sediment sequence of early miocene to holocene from ocean drilling program site 645 in central baffin bay was found to contain abundant triterpenoids of higher plant origin including monodesmethyl derivatives and other oxidative degradation products 24 nor triterpenoids of the oleanene ursene and lupane series were found in the nonaromatic hydrocarbon and alcohol fractions of the sediment extracts other diagenetic transformation products included 24 28 dinor olean 17 ene and 24 nor urs 12 en 1 1 one as well as their tentatively identified des a counterparts the identification of these novel degradation products was confirmed by synthesis of a suite of reference compounds the simple reaction sequence applied to obtain 24 nor urs 12 ene from 3 acetoxyurs 12 en 24 oic acid is likely to happen in a similar manner during early diagenesis of organic matter in nature these results have implications for the understanding of the diagenetic reaction sequence leading to the formation of other demethylated triterpenoids of terrigenous origin e g 24 28 dinor lupanes 28 30 dinor 17 hopane is sometimes the dominant hydrocarbon in the most deeply buried samples its co occurrence with higher plant triterpenoids and the low abundance of other regular hopanoids is not considered an indication however that 28 30 dinor 17 hopane is derived from a higher plant precursor molecule it is suggested that two independent sedimentary processes are responsible for the presence of the two types of demethylated triterpenoids observed in baffin bay sediments

sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

early diagenesis of terrigenous triterpenoids and its implications for petroleum geochemistry abstract the distribution of triterpanes in sediments and crude oils is commonly used for oil oil and oil source rock correlation in petroleum geochemistry while isomer ratios of such compounds are applied as maturity parameters the triterpane pattern in terrestrially influenced geological samples is however remarkably less diverse than the triterpenoid skeletons occurring in the extant higher plant biosphere natural observations laboratory experiments and molecular mechanics calculations have revealed that acid catalysed double bond isomerization and skeletal rearrangement reactions of terrigenous triterpenoids during early diagenesis are the key to understanding the triterpane patterns in more matured geological materials examples studied in detail are the double bond isomerization of oleanenes and the subsequent hydrogenation of the products into oleanane and 18 oleanane and the transformation of taraxer 14 ene and lup 20 29 ene into oleanenes although the reactions are likely to be kinetically controlled the main products formed and ultimately preserved are the thermodynamically most stable ones the experimental results and natural observations have significant implications for the use of terrigenous triterpenoid compounds in petroleum geochemistry

burial of organic carbon and pyrite sulfur in sediments over phanerozoic time a new theory in present day marine sediments almost all of which are deposited in normal oxygenated seawater rates of burial of organic carbon c and pyrite sulfur s correlate positively and bear a constant ratio to one another c s 3 on a weight basis by contrast calculations based on the isotopic model of garrels and lerman 1981 indicate that at various times during the phanerozoic the worldwide burial ratio must have been considerably different than the present day value this ratio change is caused by the requirement that increases in the worldwide mass of organic carbon must be accompanied by equivalent decreases in the mass of sedimentary pyrite sulfur in order to maintain a roughly constant level of o2 in the atmosphere such apparently contradictory behavior can be explained if the locus of major organic carbon burial has shifted over time from normal marine environments as at present to non marine freshwater or to euxinic environments in the geologic past a shift to predominantly freshwater burial can help explain predicted high c s ratios in permo carboniferous sediments and a shift to euxinic environments can help explain predicted low c s ratios during the early paleozoic it is demonstrated that the three environments today exhibit distinguishably different average c s ratios

time domain pure state polarization analysis of surface waves traversing california a time domain pure state polarization analysis method is used to characterize surface waves traversing california parallel to the plate boundary the method is applied to data recorded at four broadband stations in california from twenty six large shallow earthquakes which occurred since 1988 yielding polarization parameters such as the ellipticity euler angles instantaneous periods and wave incident azimuths the earthquakes are located along the circum pacific margin and the ray paths cluster into two groups with great circle paths connecting stations mhc and pas or cmb and gsc the first path mhc pas is in the vicinity of the san andreas fault system safs and the second cmb gsc traverses the sierra nevada batholith parallel to and east of the safs both rayleigh and love wave data show refractions due to lateral velocity heterogeneities under the path indicating that accurate phase velocity and attenuation analysis requires array measurements t he rayleigh waves are strongly affected by low velocity anomalies beneath central california with ray paths bending eastward as waves travel toward the south while love waves are less affected providing observables to constrain the depth extent of anomalies strong lateral gradients in the lithospheric structure between the continent and the ocean are the likely cause of the path deflections

bacterial and algal hydrocarbons in sediments from a saline antarctic lake ace lake capillary gas chromatography mass spectrometry c gc ms and iatroscan thin layer chromatography flame ionisation detection tlc fid were used to study hydrocarbon distributions in a sediment core from ace lake a saline meromictic lake in the vestfold hills of antarctica hydrocarbons were abundant in most core sections up to 125 g g dry wt particularly in near surface samples and the distributions were very complex major constituents were identified as phytane 2 6 10 15 19 pentamethyleicosane tetrahydrosqualene a mixture of phytenes cholesta 3 5 diene and fern 7 ene smaller amounts of sterenes and hopenes were also present the predominance of the first 3 acyclic isoprenoids in sediments buried less than 30 cm is consistent with high populations of methanogenic bacteria known to be present phytenes were abundant in all core sections and there was no relationship between their abundance and that of phytane which suggests that they were not derived from methanogenic bacteria phytadienes were minor constituents at all depths studied an unusual feature of some distributions was the high concentrations of fern 7 ene which was the major hydrocarbon in the 20 25 cm core section this alkene was only abundant in sediments which contained high concentrations of methanogen markers suggesting that it may also be indicative of anoxic depositional environments a possible source might be from purple non sulphur bacteria high concentrations of straight chain c29 and c34 alkenes were also found in these sediments but their origin has not been determined major changes in the hydrocarbon distributions with depth indicate that the depositional environment in the lake has altered dramatically since the lake was formed less than 8000 years ago the present condition of permanent anoxic bottom waters probably developed only in the last 1000 years

a new method for measuring shale porosity with low field nuclear magnetic resonance considering non fluid signals abstract porosity is a key parameter for the evaluation of potential shale oil and gas resources low field nuclear magnetic resonance nmr is a rapid technique for measuring shale porosity without causing damage to the testing samples previous nmr methods for porosity characterization are mainly based on the nmr t2 distribution of saturated oil shale but for shales with high total organic carbon toc and clay mineral contents not all signals of nmr detection originate from the pore fluid nine continental shales in damintun sag were selected and subjected to pyrolysis x ray diffraction xrd mercury injection capillary pressure micp weighing before and after fluid saturation and nmr tests to improve the accuracy of nmr porosity measurements according to the nmr t2 distribution and t1 t2 map of shale with different oil contents original extracted and saturated oil states we revealed that the non fluid signals kerogen and structural water accounted for 15 77 43 10 with a mean of 28 87 of saturated oil shale a stronger nmr signal intensity was observed for the extracted shale with higher toc and clay mineral contents a t2 distribution of oil present in the pores of oil saturated shale was constructed based on the difference between the oil saturated shale and extracted shale and was combined with the calibration equation of oil the relationship between oil volume and its nmr signal intensity to directly evaluate the porosity the porosity that was calculated based on the t2 distribution versus the weighing method had an absolute error of 0 7 and the relative error was

adsorbed and free hydrocarbons in unconventional shale reservoir a new insight from nmr t1 t2 maps abstract characterizing free and adsorbed hydrocarbon is crucial for the resources assessment and mobility evaluation of shale oil plays the complex feature of hydrogen bearing components in shale reservoirs requires new analytical methods to study the occurrences of different states of hydrocarbons in this study forty core samples from five shale oil research wells in the jiyang depression of china were analyzed using various analytical tools including nuclear magnetic resonance nmr t1 t2 mapping leco total organic carbon toc analysis routine and special programmed rock eval pyrolysis solvent extraction and fractionation as well as mercury injection capillary pressure micp experiments additional experiments were conducted on a powdered shale for nmr t1 t2 maps under four states as received after being dried at 110 c after special programmed pyrolysis to 350 c and after solvent extraction the results showed that residual water signals in the nmr t1 t2 map disappeared after being dried at 110 c free oil signals decreased dramatically when the sample was thermally treated to 350 c while adsorbed oil signals decreased sharply after solvent extraction a good accordance was observed between the organic hydrogen t2 spectra and three modes of rock eval pyrograms representing free hydrocarbons adsorbed hydrocarbons and hydrocarbons from kerogen bitumen decomposition a positive correlation was also found between the intensity of nmr t1 t2 map signals and the free and adsorbed hydrocarbon contents from geochemical analysis t2 cut off values of adsorbed hydrocarbons and free hydrocarbons were determined to be 0 2 ms and 1 ms respectively core samples with a high oil saturation index porosity and relative content of hydrocarbons display a low t1 t2 ratio indicative of a high shale oil mobility as a complementary method to the rock eval analysis nmr t1 t2 mapping is a non destructive technique for the characterization of adsorbed and free hydrocarbons at the core scale with limited sample preparation the results of this study are helpful for nmr characterization of shale reservoirs

algal and bacterial hydrocarbons in particulate matter and interfacial sediment of the cariaco trench particulate matter samples 53 m size fractions and sediment from the sediment water interface were collected in the cariaco trench an anoxic marine basin on the continental shelf of venezuela and analyzed for hydrocarbons concentrations of hydrocarbons were highest 10 20 ng 1 in oxic surface waters 0 150 m and at the top of the anoxic zone 350 600 m and were low 3 4 ng l in the low oxygen zone above the oxic anoxic interface 150 250 m and anoxic bottom waters 600 1150 m branched c25 trienes and tetraenes dominated the hydrocarbon distributions in 53 m particles particle size and depth distributions of the hydrocarbons demonstrate the importance of algal hydrocarbons in surface waters coupled with increased abundances of bacterial hydrocarbons especially in the 53 m particles in the anoxic zone these observations illustrate the importance of oxic anoxic interfaces even in the oceanic water column as zones of intense microbial alteration of organic matter and as sources of some of the organic compounds found in sediments

hydrocarbon evaporative loss from shale core samples as revealed by rock eval and thermal desorption gas chromatography analysis its geochemical and geological implications abstract the s1 peak generated by rock eval analysis of source rock and reservoir interval core and cuttings samples has been routinely employed for in place hydrocarbon resources assessment by petroleum geochemists geologists and even engineers significant evaporative loss of gaseous and light hydrocarbons up to c10 can occur during core and cuttings collection and storage and subsequent sample preparation in the laboratory before instrumental analysis consequently a correction to the s1 values is needed in order to obtain a more accurate estimate of the resources to investigate the effect of evaporative loss on both the amount and the composition of the hydrocarbons retained in shale a time series of rock eval and thermal desorption gas chromatography td gc analyses have been carried out on an organic rich devonian duvernay formation shale core sample from the western canada sedimentary basin wcsb and an organic lean ordovician lotbiniere formation shale core sample from quebec canada the results suggest that the content of total organic carbon toc may play an important role in retaining and preserving light hydrocarbons in sedimentary rocks a total loss of gaseous and light liquid hydrocarbons up to c9 is shown to take place within 21 h of sample preparation for the low toc 11 devonian duvernay shale core sample after 360 h of exposure to the open air the powdered duvernay shale sample shows only 15 decline in its rock eval s1 peak and still contains high relative concentrations of c7 c9 hydrocarbons in addition the evaporative loss of some isomers of c5 c7 hydrocarbons from the organic rich shale is not fully in agreement with their gc retention elution behavior but appears to be partially controlled by their adsorption desorption on the organic matter and mineral matrix this suggests that the c5 c8 gasoline range hydrocarbon parameters should be used with caution for oil oil correlation for unconventional shale and tight petroleum systems while the findings in this study validate the current industrial practice that targets organic rich and mature shale intervals for unconventional shale gas and oil exploration because of their large hydrocarbon storage capacity the results also have an important implication that high toc content may adversely affect the production efficiency of shale and tight hydrocarbon reservoirs due to the strong adsorption of hydrocarbons by the high maturity organic matter

organic geochemical characteristics and depositional setting of paleogene oil shale mudstone and sandstone from onshore penyu basin chenor pahang malaysia abstract the eastern chenor pahang area of the penyu basin contains an untapped potential in part due to poor knowledge of its organic facies characteristics the sedimentary succession of eastern chenor pahang area is dominated by fine to coarse grained sandstone occurring in association with oil shale and mudstone in a predominantly fining upward sequence detailed geochemical and petrographic characterization was carried out on oil shale and mudstone samples to evaluate the origin and type of organic matter om as well as the paleoenvironmental conditions and organic richness of the paleogene sedimentary succession the facies are only enriched in total organic carbon toc potential hydrocarbon yield s2 and extractible organic matter eom the types of organic matter are important index reflecting the potential of the source rock s based on elemental ratios the analyzed samples are shown to contain types i and ii kerogens this finding is supported by the high hydrogen index hi of 300 mg hc g toc and the presence of abundant liptinitic materials biomarker signatures n alkanes n c25 high c29 c30 17 h hopane ratios 0 8 3 3 and high c29 steranes 49 78 low total sulfur and v v ni ratio suggest a predominantly terrestrial source input with some contribution from aquatic microorganisms as indicated by the common occurrence of amorphous organic matter combining this results with n alkane patterns kerogen types and organic petrography predominance of c29 sterane probably indicates a contribution of aquatic organisms such as green and brown algae consistent with botrycoccus braunii race a and pediastrum contribution and some influence of higher plants om integration of biomarker studies with bulk geochemical and petrographic analysis suggests that the analyzed samples were deposited under suboxic conditions in a fresh water lacustrine environment this finding is corroborated by the ratios of pristane phytane v ni and sr br high bioproductivity and a stratified fresh water column with suboxic bottom water condition enhanced om preservation in the analyzed mudstone and shale facies the high om content in these samples maybe related to the fine grained matrix of the mud rocks and the paleoclimate in the area

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

evolution of lacustrine systems along the miocene mur murz fault system eastern alps austria and implications on source rocks in pull apart basins tectonically controlled lakes developed during miocene lateral extrusion of the eastern alps mineralogy and the inorganic and organic geochemistry of rocks from three boreholes were investigated to reconstruct the evolution of lake ingering and lake groisenbach and to study the distribution of source rocks in pull apart basins gas prone coal and oil prone sapropelic shale accumulated during the initial shallow stages of lake ingering thereafter the lake deepened rapidly 125 m thick prodelta shale containing a type ii kerogen was deposited in the brackish several hundred meter deep hydrologically closed lake afterwards decreasing subsidence allowed the filling of the lake by prograding deltas during the advance of the deltaic systems the lake became shallower hydrologically open and the brackish influence terminated source rock quality decreased significantly during the filling stage of the lake a consequence of dilution of autochthonous organic matter and of enhanced input of land plants despite its considerable dimensions formation and filling of lake ingering lasted only two million years lake groisenbach was considerably smaller and more susceptible to high frequency changes in lake chemistry although the water body was temporarily oligosaline brackish conditions did not occur high sulphur contents were due to anoxic events and the inflow of ca rich waters abundant dissolved silica favoured diatoms blooms

characterizing the shale gas resource potential of devonian mississippian strata in the western canada sedimentary basin application of an integrated formation evaluation devonian mississippian strata in the northwestern region of the western canada sedimentary basin wcsb were investigated for shale gas potential in the subsurface thermally mature strata of the besa river horn river muskwa and fort simpson formations attain thicknesses of more than 1 km 0 6 mi encompassing an area of approximately 125 000 km2 48 300 mi2 and represent an enormous potential gas resource total gas capacity estimates range between 60 and 600 bcf section of particular exploration interest are shales and mudrocks of the horn river formation including the laterally equivalent lower besa river mudrocks muskwa formation and upper besa river formation which yield total organic carbon toc contents of up to 5 7 wt fort simpson shales seldom have toc contents above 1 wt horn river and muskwa formations have excellent shale gas potential in a region between longitudes 122w and 123w and latitudes 59n and 60n national topographic system nts 94o08 to 94o15 in this area which covers an areal extent of 6250 km2 2404 mi2 average toc contents are higher 3 wt as determined by wire line log calibrations and have a stratal thickness of more than 200 m 656 ft gas capacities are estimated to be between 100 and 240 bcf section and possibly greater than 400 tcf gas in place a substantial percentage of the gas capacity is free gas caused by high reservoir temperatures and pressures muskwa shales have adsorbed gas capacities ranging between 0 3 and 0 5 cm3 g 9 6 16 scf t at reservoir temperatures of 60 80c 140 176f whereas besa river mudrocks and shales have low adsorbed gas capacities of less than 0 01 cm3 g 0 32 scf t liard basin region because reservoir temperatures exceed 130c 266f potential free gas capacities range from 1 2 to 9 5 cm3 g 38 4 to 304 scf t when total pore volumes 0 4 6 9 are saturated with gas the mineralogy has a major influence on total gas capacity carbonate rich samples indicative of adjacent carbonate platform and embayment successions commonly have lower organic carbon content and porosity and corresponding lower gas capacity 1 toc and 1 porosity seaward of the carbonate slave point edge muskwa and lower besa river mudrocks can be both silica and toc rich up to 92 quartz and 5 wt toc and most favorable for shale gas reservoir exploration because of possible fracture enhancement of the brittle organic and siliceous rich facies however an inverse relation between silica and porosity in some regions implies that zones with the best propensity for fracture completion may not provide optimal gas capacity and a balance between favorable reservoir characteristics needs to be sought

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

compositional variations in sedimentary lacustrine organic matter and their implications for high alpine holocene environmental changes lake st moritz switzerland abstract organic matter accumulation and preservation in lakes with different geomorphological and climatic regimes is directly influenced not only by local but also by regional and more global climatic conditions thus compositional variations in lacustrine organic matter can be used as good indicators of paleoenvironmental conditions of deposition relatively high average toc 1 0 6 5 wt and good lamination characterize most of the holocene sequence of lake st moritz an alphine lake located in se switzerland however variations in the type and quality of the organic matter at discrete intervals have been distinguished using bulk parameters and biomarker distributions the most prominent change occurs at the late glacial holocene boundary where 13 c om hydrogen index and lipid concentrations indicate a substantial increase in primary productivity organic matter production and preservation appear to dominate from the early holocene until approximately 3 8 ka bp although variations in sterol contents and fatty acid distributions indicate superimposed fluctuations such as between 8 3 and 8 1 ka bp and 5 1 to 4 8 ka bp these variations in the lake trophic state can be correlated with other proglacial lakes in the region as well as with similar lacustrine records on both sides of the alps the result of this comparison indicates a synchronous character of major to medium amplitude climatic shifts on a european scale

biogeochemistry of the miocene lacustrine deposit at clarkia northern idaho u s a abstract the lipid preservation observed in the sediments from clarkia reflects an extremely immature thermal history many biomarkers have still retained functionality even after 17 20 million years the soluble components are predominantly higher plant and algal derived lipids and the original sources for these compounds are still preserved in the sediment thus biogeochemical data are in agreement with the associated palaeontological evidence chemical changes noted in the lipids preserved in these sediments are similar to those observed in modern fresh water mesotropic or eutrophic lacustrine sediments therefore it can be inferred that the processes that operate in modern lacustrine sediments are similar to those that took place within the sediments at clarkia 17 20 million years ago

porosity of devonian and mississippian new albany shale across a maturation gradient insights from organic petrology gas adsorption and mercury intrusion the evolution of porosity in shales with increasing maturity was examined in a suite of five new albany shale samples spanning a maturity range from immature vitrinite reflectance ro 0 35 to postmature ro 1 41 devonian to lower mississippian new albany shale samples from the illinois basin used in this study contain marine type ii kerogen having total organic carbon contents from 1 2 to 13 0 wt organic petrology co2 and n2 low pressure adsorption and mercury intrusion capillary pressure techniques were used to quantify pore volumes pore sizes and pore size distributions increasing maturity of the new albany shale is paralleled by many changes in the characteristics of porosity the total porosity of 9 1 vol in immature new albany shale decreases to 1 5 vol in the late mature sample whereas total pore volumes decrease from 0 0365 to 0 0059 cm3 g in the same sequence reversing the trend at even higher maturity the postmature new albany shale exhibits higher porosity and larger total pore volumes compared to the late mature sample with increasing maturity changes in total porosity and total pore volumes are accompanied by changes in pore size distributions and relative proportions of micropores mesopores and macropores porosity related variances are directly related to differences in the amount and character of the organic matter and mineralogical composition but maturity exerts the dominant control upon these characteristics we conclude that organic matter transformation due to hydrocarbon generation and migration is a pivotal cause of the observed porosity differences

the record of hydroclimatic changes in the sediments of a kettle hole in a young glacial landscape north central poland abstract multidisciplinary research on the bottom sediments of a kettle hole at the retno site the brodnica lake district north central poland provided some information about changes in hydroclimatic conditions in the late glacial and the holocene detailed analysis sedimentological palynological macroremains geochemical and radiocarbon dating helped to identify 6 stages in the development of the depression in the village of gaj near retno lake with 11 phases of hydroclimatic conditions sediments of the retno profile with a total thickness of 6 72 m reflected individual natural stages in the development of the depression from a lake to a peat bog most of the environmental changes were gradual a sequence of late glacial and early holocene lacustrine sediments mainly gyttja occurred in the floor of the profile the upper 4 10 m consisted of paludal deposits peat of transitional and raised bogs divided at a depth of 1 56 1 54 m b g l by a thin layer of clay dated late subboreal early subatlantic the presence of this layer indicates a sudden change in the environmental conditions associated with a water level rise at that time denudation processes started within the drainage basin probably induced by human activity the important effects related to contemporary anthropopressure included desiccation of the peat bog muck formation in the uppermost 10 cm layer and elevated trophic conditions resulting in a change of the vegetation cover

biomarkers and geochemical indicators of holocene environmental changes in coastal lake sarbsko poland organic rich samples from the holocene sedimentary sequence of lake sarbsko were investigated to reconstruct variations in the aquatic system in response to environmental change the aims were to i identify organic matter om sources ii examine changes in soluble om composition in relation to fluctuations in limnological conditions and iii validate the sensitivity of organic geochemical indicators in tracing environmental changes diatom frustules are abundant in all samples alginite macerals and terrigenous organic matter further contribute to the sedimentary om organic petrography total organic carbon toc n ratio values and high content of biogenic silica sio2 biogenic argue for a predominant algal source of om in contrast the n alkane distributions high relative abundance of c29 steroid hydrocarbons and high content of detrital quartz in the sediments provide evidence for the input of terrigenous material as a major om source within the basin the terpenoid biomarker composition indicates a contribution from conifers and angiosperms from the diterpenoids in the samples a contribution from species of the coniferales family pinaceae is concluded toc s and mg ca values as well as steroid hopanoid concentration ratios reflect enhanced water salinity in this coastal lake due to ingression of brackish water from the baltic sea during the atlantic and sub atlantic periods as indicated by the positive relationship between d 13 c of toc and mg ca d 13 c values are influenced by changing contribution of marine vs freshwater phytoplankton additional isotopic heterogeneity in d 13 c may result from differences in terrigenous om supply vs autochthonous om production in the lake the isotopic composition of calcites supports the establishment of freshwater conditions in the lake during the sub boreal period pristane phytane and fe mn ratios are interpreted to reflect differences in the redox conditions oxygenation of bottom waters was temporarily variable with highest levels of oxygen availability during the sub boreal freshwater lake high contents of hopanoid hydrocarbons argue for enhanced microbial activity in the water column and sediment the occurrence of 2b methyl hopanes is related to the presence of cyanobacteria or methylotrophic bacteria

characterization of gas shale pore systems by porosimetry pycnometry surface area and field emission scanning electron microscopy transmission electron microscopy image analyses examples from the barnett woodford haynesville marcellus and doig units the nanometer scaled pore systems of gas shale reservoirs were investigated from the barnett marcellus woodford and haynesville gas shales in the united states and the doig formation of northeastern british columbia canada the purpose of this article is to provide awareness of the nature and variability in pore structures within gas shales and not to provide a representative evaluation on the previously mentioned north american reservoirs to understand the pore system of these rocks the total porosity pore size distribution surface area organic geochemistry mineralogy and image analyses by electron microscopy were performed total porosity from helium pycnometry ranges between 2 5 and 6 6 total organic carbon content ranges between 0 7 and 6 8 wt and vitrinite reflectance measured between 1 45 and 2 37 the gas shales in the united states are clay and quartz rich with the doig formation samples being quartz and carbonate rich and clay poor higher porosity samples have higher values because of a greater abundance of mesopores compared with lower porosity samples with decreasing total porosity micropore volumes relatively increase whereas the sum of mesopores and macropore volumes decrease focused ion beam milling field emission scanning electron microscopy and transmission electron microscopy provide high resolution 5 nm images of pore distribution and geometries image analysis provides a visual appreciation of pore systems in gas shale reservoirs but is not a statistically valid method to evaluate gas shale reservoirs macropores and mesopores are observed as either intergranular porosity or are confined to kerogen rich aggregates and show no preferred orientation or align parallel with the laminae of the shale networks of mesopores are observed to connect with the larger macropores within the kerogen rich aggregates

controls of hydrocarbon generation on the development of expulsion fractures in organic rich shale based on the paleogene shahejie formation in the jiyang depression bohai bay basin east china abstract the development of expulsion fractures in organic rich shale is closely related to hydrocarbon generation and expulsion from kerogen organic rich shales from the upper part of the fourth member and the lower part of the third member of the paleogene shahejie formation in the jiyang depression bohai bay basin east china are used as an example based on thin sections sem and thermal simulation experiments the characteristics of hydrocarbon generation and the conditions supporting the development of expulsion fractures were explored the key factors influencing these fractures include the presence of kerogens their distribution along laminae and around particle boundaries their exposure to heat and the build up in pressure due to confinement by low permeability the development of excess pore fluid pressures and intrinsic low rock fracture strength are the main influencing factors pressurization by rapid generation of hydrocarbon provides impetus for fracture initiation and cause bitumen to migrate quickly the shale laminae results in distinctly lower fracture strength laminae parallel than laminae normal and this directs the formation of new fractures in the direction of weakness when pore fluid pressure increases maximum and minimum principal effective stresses decrease by different proportions with a larger reduction in the maximum principal effective stress this increases the deviatoric stress and reduces the mean stress thus driving the rock towards failure moreover the tabular shape of the kerogen aids the generation of hydrocarbon and the initiation of expulsion fractures from the tip and edge the resulting fractures extend along the laminae when the tensile strength is lower in the vertical direction than in the horizontal direction particle contact boundaries are weak and allow fractures to expand around particles and to curve as the stress strength regime changes when pore fluid pressure fields at different fracture tips overlap fractures will propagate and interconnect forming a network this paper could provide us more detailed understanding of the forming processes of expulsion fractures and better comprehension about hydrocarbon expulsion primary migration in source rocks

the biomarker record of lake albano central italy implications for holocene aquatic system response to environmental change abstract a study of lipid biomarkers in predominantly laminated organic carbon rich sediments in lake albano central italy has been used to reconstruct changes in the aquatic system variations and changes in the lake catchment area during the holocene biomarkers of aquatic organic matter such as dinosterol isoarborinol tetrahymanol diplopterol and diploptene reflect two major changes in the mixing behaviour and the biological assemblages of lake albano at around 6 5 and 3 8 ky bp respectively biomarkers for higher land plants such as friedelin long chain n alkanes amyrenone and amyrenone display different distribution patterns indicating changes in the lake s catchment at 6 5 and 5 0 ky bp resulting from soil erosion and changes in the local vegetation analogously the recognised changes in the water column structure and biological components are coherent with previous reconstructions based on independent parameters the new data highlight the importance of multiproxy studies to better characterize palaeoenvironmental changes that are in turn the first step towards elucidating their trigger mechanisms i e climate vs human induced

the effects of natural environmental changes on sedimentation in lake kuttanen a small closed lake in finnish lapland a sediment core from lake kuttanen a small closed lake in finnish lapland was investigated to determine the effects of holocene water table changes aeolian activity and forest fires on sediment physical properties and sediment geochemistry sediment properties were examined by water content loss on ignition loi and dry matter sedimentation rate analyses sediment geochemistry was studied by determining the acid soluble accumulation rates of al ca cu fe k mg mn na p and zn the fe mn ratio was calculated to study changes in the redox potential and charcoal concentrations were measured to determine the occurrence of local and regional fires the sediment accumulation rate was determined using 14c and b activity measurements principal components analysis pca was used to examine variations within the data and intercorrelations among the variables after the isolation of the basin all the element accumulation values were high because of the erosional supply from the catchment before stable so

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