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

anatomy of a world class source rock distribution and depositional model of silurian organic rich shales in jordan and implications for hydrocarbon potential silurian organic rich hot shales were the source of large amounts of hydrocarbons in northern gondwana with supergiant and giant fields in the middle east and north africa a study of these black shales has been conducted in jordan where they represent the source for the risha gas field two organically enriched horizons occur in the silurian in jordan termed the lower hot shale and the upper hot shale deposition of the transgressive lower hot shale occurred during the early llandoverian and was restricted to the earliest silurian paleodepressions three lower hot shale depocenters have been identified in jordan they are located in the western risha eastern wadi sirhan and jafr areas the eastern risha area was part of a larger scale paleohigh covering northeast jordan most of syria and iraq and north central saudi arabia qusaiba area at least in jordan the high coincides with the depocenter of the latest ordovician glaciation sedimentation of the upper hot shale occurred around peak sea level during the late llandoverian and or early wenlockian and was limited to the distal parts of the shelf risha area in front of the prograding silty sandy deltaic front thermal maturity increases from immature in the southern desert outcrops to late or postmature in northern jordan organic richness and pyrolysis data deteriorate significantly with increasing thermal maturity because of hydrocarbon generation prior to maturation maximum organic richness is interpreted to have considerably exceeded 10 with good s2 remaining generative potential yields as reflected in the values of the immature lower hot shale in the shallow borehole bg 14 in the southern desert outcrop area and exploration well hunt jf 1 in the jafr area identification and isopach mapping of the lower hot shale is based on its characteristic uranium enrichment the gamma ray total organic carbon correlation coefficient increases with increasing maturity suggesting that uranium is less vulnerable to maturity effects than the organic matter itself the gamma ray log therefore can be used as a proxy for the prematuration organic richness representing a suitable basis for cross basin comparisons of original organic richness trends a two phase generation of hydrocarbons is interpreted for both the risha and wadi sirhan areas with the first as a pre hercynian phase in the carboniferous and the second as a less intense generation phase during the mesozoic to early tertiary in contrast gas generation of the silurian sourced giant fields in the central part of the arabian peninsula and iran was restricted to the post hercynian in jordan both structural and stratigraphic play concepts are envisaged including fault paleohigh and channel plays key elements that need attention in future exploration of the silurian plays in jordan are ordovician reservoir quality and timing of maturation poor permeabilities have been reported from wells in both the risha and wadi sirhan areas

indication of reducing conditions in early diagenesis the aleksinac oil shale as example abstract an attempt was made to define the early diagenetic reducing conditions in the aleksinac oil shale deposit a freshwater lake sediment of upper oligocene lower miocene this deposit consists of three zones northern central and southern zone 171 samples from 25 cores were investigated originating from various depths i e 9 720 m several potential indicators of reducing conditions were correlated such as the atomic o c ratio of the organic matter the content of pyritic sulfur s pyr and the content of organic carbon c org in most of the layers the concentration of sulfate was found to be limiting factor for development of sulfate reducing conditions corresponding to the content of the organic substance during diagenesis the intensity of reducing conditions in the presence of sufficient amount of sulfate the critical concentration of residual sulfate being 2 0 2 5 mmol 100 g clearly depended on the concentration of organic matter in the sediment but also on the conditions in the water column a greater variety in the intensity of reducing conditions during early diagenesis was observed in the north and central zones while in the south zone during the whole early diagenesis the conditions probably were markedly sulfate reducing in the north and central zones milder and more pronouncedsulfate reducing conditions varied involving occasional shifting of the anoxic zone into the water column the highest frequency of pronounced reducing conditions was observed in the middle 150 340m and upper 40 70m layers indications of further intensification of reducing conditions leading to methanogenesis were not clearly observed

pyrite framboid evidence for oxygen poor deposition during the permian triassic crisis in kashmir abstract the khunamuh formation of the guryul ravine section in kashmir provides one of the most detailed deep water records of the end permian mass extinction in perigondwanan palaeolatitudes examination of pyrite framboid size distributions and sediment microfabric reveals a distinct change in the uppermost permian strata from nonlaminated pyrite free silty mudstones to finely laminated silty shales rich in framboidal pyrite around 1 m above the base of the formation the size frequency distribution of the framboids is identical to populations from severely oxygen restricted modern depositional environments this change to dysoxic benthic conditions coincides with the rapid demise of diverse permian brachiopod and bryozoan assemblages thus the link between extinction and anoxia is clearly seen at guryul ravine and it provides an interesting contrast to other perigondwanan sections developed in shallower water where both the onset of anoxia and the extinction occurred somewhat later in the earliest triassic

extraction of high molecular weight hydrocarbons from source rocks an example from the green river formation uinta basin utah abstract results of extraction experiments performed on immature green river formation source rock samples from the black shale facies uinta basin utah demonstrate the potential of extracting high molecular weight hydrocarbons hmwhc with sequential dichloromethane methanol soxhlet and p xylene sonication techniques the first soxhlet extraction step with dcm meoh removes lower molecular weight alkanes from the source rock while the hmwhc remain in the rock residue sonication of the rock residue with p xylene recovers these hmwhc showing distinct hydrocarbon distributions and preferences in high temperature gas chromatograms extracts obtained by using p xylene soxhlet with original source rocks and sequential soxhlet extraction instead of sonication have relatively lower concentrations of hmwhc sequential extraction of two other source rock types mahogany shale and black shale facies coal did not result in detection of similar hmwhc in the extract this indicates that the presence of these compounds in the black shale facies of the green river formation is a primary source signal and a specific characteristic of this source rock

palaeoceanographic redox environments for the lower cambrian hetang formation in south china evidence from pyrite framboids redox sensitive trace elements and sponge biota occurrence abstract the lower cambrian hetang formation a black shale sequence contains a stone coal a flammable organic rich mudstone unit abundant pyrite framboids occur in this unit with the average mean sizes falling in a narrow range from 4 6 to 5 4 m and the maximum diameters being around 10 m the size distribution pattern of the pyrite framboids indicates a euxinic depositional environment the redox sensitive trace metals of the stone coal samples reveal a large enrichment of mo 10 180 times v 4 40 times u 10 60 times and ni 2 20 times compared to the average upper continental crust value consistent with an anoxic environment for their deposition the redox sensitive element ratios th u v v ni v cr indicate that the depositional environment for the lower part of the stone coal unit was the most anoxic and euxinic in contrast a sponge biota including eleven species of demosponges and hexactinellids and two undetermined forms indicate an oxic or dysoxic environment to reconcile these two facts we propose that although an anoxic euxinic environment predominated during the deposition of the lower cambrian hetang formation black shales occasional currents may also have brought free oxygen to the bottom water column to allow the growth of the sponges on the sea floor

organic matter characteristics of cenomanian turonian source rocks implications for petroleum and gas exploration onshore senegal one hundred and fifteen samples of cenomanian turonian sediments from the senegal margin basin believed to be the main source rocks in the area have been characterised to determine their organic facies and their oil generating potential the samples have been subjected to detailed organic petrographic studies palynofacies maceral analysis vitrinite reflectance measurements combined with rock eval and leco determinations total organic carbon values comprised between 0 3 and 3 5 indicate poor to moderate primary bioproductivity and or unfavourable organic matter om preservation rather high c n ratio values supported by the presence of well preserved ligno cellulosic debris and of collotelinite suggest a notable contribution of terrestrial om this is supported by hydrogen and oxygen index values that testify to type iii om s c ratio values lower than 0 36 together with the presence of abundant reworked organic particles indicate that the studied sediments were deposited in a transitional and mixing zone between a coastal area with well oxygenated waters and a fully marine environment with more or less pronounced anoxia the rather low marine productivity and poor om preservation are here strongly reinforced by a very marked dilution of the om by mineral inputs in addition to these combined factors indicating that the om is mainly of the gas prone type a moderate maturity is shown by tmax and vitrinite reflectance values ranging from 435 to 445 c and 0 4 to 0 9 respectively the reservoir facies consisting of sandstones interbedded with shales are characteristic of prograding fluvio deltaic formations developed during maastrichtian regression faults and rollover structures most probably constitute the main migration pathways and traps for hydrocarbons respectively overall the characteristics of the studied formations highlight the importance of local factors in om accumulation even during the so called global cenomanian turonian anoxic event

ubiquitous occurrence of high molecular weight hydrocarbons in crude oils abstract for many years the presence of waxes in crude oils has been associated with organic matter derived from terrigenous sources high temperature gas chromatography htgc has been used to establish the ubiquitous presence of high molecular weight hmw hydrocarbons extending as high as c 120 in crude oils hmw hydrocarbons c 40 have been observed in crude oils derived from terrigenous lacustrine and marine source materials modified extraction techniques have also led to the detection of hmw hydrocarbons in source rock extracts the fractions of hmw hydrocarbons are complex mixtures of long chain aliphatic and alkyl aromatic hydrocarbons and can represent up to 8 of a whole oil the carbon preference index cpi of hmw alkylcyclopentanes in the c 42 c 46 range provides useful information on the characteristics of the original depositional environment age maturity and degree of biodegradation do not appear to affect the cpi of alkylcyclopentanes used for evaluating depositional environments differences in the distributions of the hmw hydrocarbons between the source rock extracts and the crude oils in the reservoirs may reflect changes occurring due to migration

meso scale aeolian sediment input to coastal dunes the nature of aeolian transport events abstract observations of aeolian transport in coastal areas have focused on short term experiments because of limitations imposed by instrumentation this paper uses a case study at greenwich dunes prince edward island national park canada to analyze how sediment transport takes place at the beach over periods of weeks to months a monitoring station provided hourly time series of vegetation cover shoreline position fetch distances surficial moisture content presence of ice and snow wind speed and direction and transport processes over nine months analysis shows that high wind speeds may not generate any net transport into the dunes because of the limitations imposed by snow ice cover moisture and short fetch distances despite extreme winds during intense storms such events often lead to wave scarping rather than aeolian sediment input to the foredunes when sediment was transported on the beach the magnitude was regulated by a combination of factors including angle of wind approach fetch distance moisture content and duration of the wind event in particular angle of wind approach and therefore fetch distance may demote a high magnitude wind event with strong transport potential to one with no transport at all which poses challenges for predicting the effects of individual storms over the course of several months a significant proportion of sediment delivery to the foredunes was associated with wind events of low to medium magnitude it is suggested here that large magnitude wind events have low probabilities of resulting in transport towards the foredune because factors such as wave inundation play an increasing role in preventing sediment movement across the beach this has implications for modelling and management and highlights differences between the magnitude and frequency of aeolian transport events in the coastal environment compared to those in deserts and to fluvial sediment transport

meso scale modelling of aeolian sediment input to coastal dunes the collection of a time series coupling hourly wind data speed and direction with sand transport over months has provided new insights into the dynamics of transport events that input sediment to the foredune at greenwich dunes prince edward island national park canada this paper summarises the key aspects of aeolian sedimentmovement for a period of 9 months and presents amodelling approach for resolving aeolian transport to coastal dunes at the meso scale the main hypothesis of the modelling approach is that a small number of key factors control both the occurrence and the magnitude of transport events thresholds associated with these factors may be used to filter the time series and isolate potential transport periods over the year the impacts of nearshore processes are included in the approach as part of the dynamics of coastal dunes as are supply limiting factors and trade offs between fetch distances angle of wind approach and beach dimensions a simple analytical procedure based on previously published equations is carried out to assess the general viability of the conceptual approach results show that the incorporation of moisture and fetch effects in the calculation of transport for isolated potential transport periods result in improved predictions of sediment input to the dune net changes measured with three different techniques suggest that survey data with coarse temporal resolution underestimates the amount of sand input to the dune because sediment is often removed from the embryo dune and foredune by other processes such as wave scarping predictions obtained by the proposed modelling approach are of the same order of magnitude as measured deposition andmuch less than predicted bymodels based solely onwind speed and direction areas for improvement and alternative modelling approaches such as probabilistic approaches similar to weather forecasting are covered in the discussion

palynology organic geochemistry and carbon isotope analysis of a latest ordovician through silurian clastic succession from borehole tt1 ghadamis basin southern tunisia north africa palaeoenvironmental interpretation abstract palynological and palynofacies analyses combined with organic carbon isotope measurements have been performed on terminal ordovician through silurian clastic sediments from the north african margin of gondwana southern tunisia a first carbon isotopic signal 13corg from gondwanan silurian sedimentary sequences is presented showing interesting correlation with existing coeval isotopic curves from other areas changes in lithology palynofacies characteristics palynomorph diversity carbon isotope developments and organic geochemistry parameters appear to be all causally linked and to reflect changes in palaeoceanographic conditions in particular the detailed chronostratigraphic correlation and the observed similarities in patterns of carbon isotopic developments and palyno and litho facies changes through the study section has permitted to identify the supposedly global earliest wenlock ireviken event and late ludlow lau event isotopic excursions for the first time in high latitude gondwana this confirms that these excursions were linked to global changes in the oceanic system the present results suggest that from rhuddanian to early wenlock times an extended period of black shale deposition occurred over the north african gondwanan margin progressively transgressing from basin palaeodepressions to basin palaeohighs palynofacies and organic geochemistry support a coastal upwelling promoted productivity increase during this interval associated to a decrease in diversity of the marine microplanktonic communities the earliest wenlock strong positive isotopic shift appears associated with this protracted period of massive black shale deposition and thus of organic carbon burial on continental platforms located in high latitude settings this could well explain the apparent paradox between excessive carbonate deposition simultaneous to a carbon isotopic shift towards lighter values observed in low palaeolatitude localities laurentia and baltica the strong distinct isotope excursion occurring in late ludlow times is possibly linked to the well know lau event evidence for extensive organic carbon burial is lacking to explain this strong excursion some significant changes in the marine palynomorph communities are recorded in connection to the increase in stable isotope values 13corg additionally a strong correlation between abundance of terrestrially derived palynomorphs miospores and 13corg development is recorded which seems to support increased clastic input from a terrestrial source

bakken madison petroleum systems in the canadian williston basin part 2 molecular markers diagnostic of bakken and lodgepole source rocks abstract the uppermost devonian mississippian bakken formation black shale and the mississippian lodgepole formation carbonate represent two of the most important source rocks in the canadian williston basin quantitative analyses of both saturated and aromatic hydrocarbon fractions reveal significant differences in the relative distributions and absolute concentrations for a wide range of molecular markers between the extracts of the two source units among others the bakken shales are characterized by their high relative abundance of trimethyl aryl and diaryl isoprenoids likely derived from green sulfur bacteria chlorobiaceae in contrast the lodgepole carbonates at similar maturity levels display a c35 homohopane prominence and abundant benzohopanes ring d monoaromatic 8 14 secohopanes and a tetracyclic monoaromatic hydrocarbon the distinctive nature of molecular marker fingerprints diagnostic of the two source rocks is clearly related to their different organic inputs and depositional environments additionally the large difference in the absolute concentrations of these compounds observed in both source units may potentially lead to biased geochemical interpretations if strictly conventional saturate based biomarker approaches were used for oil oil and oil source correlation

sedimentary organic matter sources and depositional environment in the yegua formation brazos county texas abstract the complex depositional environment of the eocene yegua formation brazos county texas can be better understood by integrating organic matter om geochemistry with stratigraphy yegua sediments represent parasequences separated by exposure surfaces organic petrography and geochemistry biomarkers c n ratios and carbon isotopes indicate the presence of both terrestrial and marine om in transgressive sediments in contrast regressive sediments contain only terrestrial om these differences relate to contrasting om sources and depositional styles on the shelf om in the sediments is immature and the potential for generating hydrocarbons is poor the study suggests that organic geochemical data can help in distinguishing transgressive and regressive environments in sedimentary formations

new insights into the origin of perylene in geological samples abstract the origin of the polycyclic aromatic hydrocarbon pah perylene in sediments and petroleum has been a matter of continued debate reported to occur in phanerozoic organic matter om fossil crinoids and tropical termite mounds its mechanism of formation remains unclear while a combustion source can be excluded structural similarities to perylene quinone like components present in e g fungi plants crinoids and insects potentially suggest a product precursor relationship here we report perylene concentrations 13c 12c and d h ratios from a holocene sediment profile from the qingpu trench yangtze delta region china perylene concentrations differ from those of pyrogenic pahs and rise to prominence in a stratigraphic interval that was dominated by woody vegetation as determined by palynology including fungal spores in this zone perylene concentrations exhibit an inverse relationship to the lignin marker guaiacol d h ratios between 284 and 317 similar to the methoxy groups in lignin as well as co variation with spores from wood degrading fungi 13c 12c of perylene differs from that of land plant wax alkanes and falls in the fractionation range expected for saprophytic fungi that utilise lignin which is isotopically lighter than cellulose and whole wood during progressive lignin degradation the relative carbon isotopic ratio of the perylene decreases we therefore hypothesise a relationship of perylene to the activity of wood degrading fungi to support our hypothesis we analysed a wide range of phanerozoic sediments and oils and found perylene to generally be present in subordinate amounts before the evolutionary rise of vascular plants and to be generally absent from marine sourced oils few exceptions being attributed perhaps to a contribution of marine and or terrestrial derived fungi anoxia especially under marine conditions and or contamination of core material by fungi a series of low molecular weight aromatic quinones bearing the perylene backbone were detected in devonian and cretaceous sediments potentially representing precursor components to perylene

depositional environment of the lower silurian akkas hot shales in the western desert of iraq results from an organic geochemical study abstract the lower silurian hot shales in the lower part of akkas formation in akkas field western iraq were studied to determine their depositional environments for this purpose organic and inorganic proxies were used these include total organic carbon content toc sulfur pyrite and carbonate content measurements as well as the saturated and aromatic biomarkers organic carbon content toc pyrite and carbonate contents were high and pristane phytane ratio pr ph was low in these hot shales indicating deposition under anoxic marine conditions the presence of gammacerane suggests water column stratification the presence of aryl isoprenoids originating from aromatic carotenoids of green photosynthetic sulfur bacteria indicates deposition under euxinic conditions extending from the photic zone to the sediment water interface the conditions became more oxygenated upward which led to the deposition of organic poor gray green shales in the upper part of akkas formation with low pyrite and carbonate contents and high pr ph ratios

aeolian sand transport at the lanphere dunes northern california aeolian sand transport was studied at the lanphere dunes a coastal dune complex in northern california by comparing slipface advance rates with transport predicted based on local wind data the slipfaces of a 2 5 m high transverse ridge and 10 m high parabolic dune were monitored over a period of three months to estimate sand discharge the study was performed during the dry season which has the maximum sand driving potential over the three month study period average sand discharge was 12 5 m3 per m width per year at the transverse ridge and 8 8 m3 per m width per year at the parabolic dune a method was developed for modelling slipfaces that are sinuous and where sediment transport rates are not constant across the width of the slipface field measurements were used to generate three dimensional representations of dune slipfaces periodic measurements over the course of three months were used to compute the volume of displaced sediment theoretical sand transport was computed from local wind data using the bagnold model and compared with the observed transport rates predicted rates were substantially lower than observed rates wind velocities rarely exceeded the threshold velocity discrepancies between the observed and predicted values appear to be caused by a combination of wind data recording procedures and differences between wind velocities at the anemometer location and the site where sand transport was measured wind data collected by weather bureaux have been utilized in numerous studies for modelling sediment transport such data typically have sample intervals of one hour or greater and are often averaged prior to reporting the effect of averaging was investigated by comparing sand transport estimates based on daily average wind velocities with those based on the original hourly observations the daily average data were depleted of high velocity winds and sand transport estimates were accordingly much lower than those based on the hourly data copyright 2000 john wiley sons ltd

a euxinic southern north atlantic ocean during the cenomanian turonian oceanic anoxic event abstract during mid cretaceous times large amounts of organic carbon corg became sequestered in black shales possibly due to oceanic anoxic events characterized by the development of an extended oxygen minimum zone omz here we provide the first direct evidence for an open ocean omz in the cenomanian turonian c t southern north atlantic and in fact show that the base of the photic zone was euxinic as revealed by molecular fossils from photosynthetic green sulfur bacteria in c t black shales this together with evidence for bottom water anoxia and accumulation of redox sensitive trace metals and hydrogen rich organic matter indicates a continuously euxinic water column concurrent with the high corg accumulation rates which are 15 150 times greater in the southern than in the northern north atlantic and the low biological productivity this suggests that preservation controlled the accumulation of corg in c t black shales

origin sequence stratigraphy and depositional environment of an upper ordovician hirnantian deglacial black shale jordan the upper ordovician succession of jordan was located 60 s less than 100 km from the hirnantian ice sheet margin new graptolite dates indicate glaciation ended in jordan in the late hirnantian persculptus biozone the succession records two glacial advances within the ammar formation and the subsequent deglaciations organic rich black shales batra formation form part of the final deglacial transgressive succession that in filled an existing low stand glacial continental shelf topography the base of the black shale is coincident with the maximum flooding surface during transgression interfluves and sub basin margins were breached and black shale deposition expanded rapidly across the region the top of the black shales coincides with peak highstand the expanding puddle model sensu wignall for black shale deposition adapted for the peri glacial setting provides the best explanation for this sequence of events we propose a hypothesis in which anoxic conditions were initiated beneath the halocline in a salinity stratified water column a fresher surface layer resulted from ice meltwater generated during early deglaciation during the initial stages of marine incursion nutrients in the monimolimnion were isolated from the euphotic zone by the halocline increasing total organic carbon toc and 13corg up section indicates the organic carbon content of the shales was controlled mainly by increasing bioproductivity in the mixolimnion the strakhov model mixolimnion nutrient levels were sustained by a continual and increasing supply of meltwater derived nutrients modulated by obliquity changes in high latitude insolation anoxia was sustained over tens to hundreds of thousands of years the formation of black shales on the north gondwana shelf was little different to those observed in modern black shale environments suggesting that it was the nature of the ordovician seas that pre disposed them to anoxia

perylene an indicator of alteration processes or precursor materials abstract perylene is a polycyclic aromatic hydrocarbon pah that is found pervasively in both marine and freshwater sediments yet its origin remains obscure we have explored relationships between perylene and possible precursor materials in two 210 pb dated sediment cores from lake ontario in which contributions of aquatic and land plant organic matter and concentrations of anthropogenic pahs have been measured no significant correlations were identified between perylene occurrence and indicators of terrigenous or aquatic sources of organic matter distinct differences between perylene and anthropogenic pah sedimentary profiles rule out an industrial source for perylene at these locations the general pattern of low to absent perylene concentrations in upper oxic sediments and increasing concentrations with depth indicates that in situ diagenesis under anoxic conditions produces perylene and that its formation is kinetically controlled the results of our study suggest that perylene is formed from non specific precursor materials by biotic or abiotic transformation processes if this scenario accurately describes its formation then perylene is an indicator of depositional conditions rather than the source of organic matter

biomarker and stable carbon isotope systematics of fossil wood from the second lusatian lignite seam of the lubstow deposit poland abstract decay of fossil wood gelification collected from the middle miocene 2nd lusatian lignite seam at the lubstow open cast mine poland is characterised by its maceral variety fluorescence intensity and cellulose content cellulose decomposition leads to lower molar h c ratio values of the organic matter as indicated by higher total organic carbon toc content of samples characterised by low cellulose content biochemical formation of hydrocarbons in the wood due to enhanced microbial activity is evidenced by higher hydrocarbon content in the extracts higher relative proportions of n alkanes and hopanoids are observed in the hydrocarbon fractions of wood remains characterised by low cellulose yield the results provide evidence for the formation of these compounds during biogeochemical transformation of organic matter hopanoid contents are considered to reflect the activity of aerobic bacteria and or fungi because of enhanced perylene content in the hydrocarbon fractions from gelified wood samples fungi are considered as the major precursor carriers of this polycyclic aromatic hydrocarbon the results provide evidence that biomarker composition of fossil wood can be used to trace biochemical transformation processes chemotaxonomical classification of fossil wood fragments as gymnosperms most probably species of the coniferales families taxodiaceae cupressaceae are based on the molecular composition of terpenoid hydrocarbons and a mean 13 c value of 24 5 depletion of gelified samples in 13 c as compared to ungelified wood is caused by the effect of progressive decomposition of cellulose the data indicate that cellulose 13 c data mean 13 c 20 8 are also affected by wood decomposition and so only samples with comparable cellulose content should be used for the reconstruction of environmental changes inter species as well as intra plant variation in carbon isotope differences and of decay resistance between cellulose and lignin have to be taken into account

geochemical characterization of free versus asphaltene sorbed hydrocarbons in crude oils implications for migration related compositional fractionations based on the existing petroleum migration models that focus on the role of organic sorption a laboratory study has been performed to simulate the migration effects on the various fractions of oil in this study one free oil fraction defined as bitumen 1 existing outside of or loosely attached to asphaltene and three to four absorbed oil fractions defined as bitumens 2 3 4 and 5 more strongly attached to asphaltene macromolecules that were obtained from three oil samples collected from the bohai bay basin east china were analyzed in detail based on the laboratory partition of oil components between the solvent phase oil and the asphaltene phase petroleum migrationrelated effect on saturate fraction was re evaluated our observation indicates that the compositional variation from bitumen 1 to bitumen 4 or 5 includes the following 1 the resin content increases while the saturate content and saturates aromatics ratio decrease 2 the relative abundance of short chain n alkanes decreases while that of the long chain n alkanes increases 3 pr nc17 ph nc18 and pr ph ratios stay virtually unchanged while the relative abundances of terpanes to n alkanes and steranes to n alkanes decrease 4 the ratios of c21 c21 c29 steranes and c23 c23 c30 terpanes in the free oil fraction are similar to or even lower than those in the whole absorbed fraction suggesting relatively stronger affinities of these smaller terpane and sterane molecules to asphaltenes in contrast to the relatively larger ones and 5 the isomerization parameters of c27 and c29 steranes are slightly higher in the free fraction than in the whole absorbed oil fraction large variations were observed in the distributions of steranes among the four bitumen fractions of the x52 oil and were considered to be related to the heterogeneity of the source rocks in addition to the partition of these compounds between the asphaltene phase and the solvent phase q 2002 elsevier science ltd all rights reserved

identification of aryl isoprenoids in source rocks and crude oils biological markers for the green sulphur bacteria abstract a series of c13 to c31 aryl isoprenoids 1 alkyl 2 3 6 trimethylbenzenes have been identified in reef hosted oils and their source rocks from the middle and upper silurian of the michigan basin and middle devonian of the alberta basin canada their structure has been confirmed by unambiguous synthesis of the c14 member of the series their structure and isotopic composition indicate that they are derived from isorenieratene from the chlorobiaceae family of sulphur bacteria these results are consistent with geological and geochemical studies that show that the source rocks were deposited under metahaline to hypersaline sulphate and sulphide rich water columns the distribution of other biomarkers in these oils and source rocks indicates that a diverse biota contributed organic matter to the source environment in conjunction with the aryl isoprenoids they show that there is a remarkable similarity in composition between the two sets of oils and source rocks despite their great temporal and geographic separation this reflects the similarity of their environments and emphasizes the importance of sedimentary facies in controlling the composition of organic matter in source rocks and their derived oils

lower silurian hot shales in north africa and arabia regional distribution and depositional model abstract lowermost silurian organic rich hot shales are the origin of 80 90 of palaeozoic sourced hydrocarbons in north africa and also played a major role in petroleum generation on the arabian peninsula in most cases the shales were deposited directly above upper ordovician peri glacial sandstones during the initial early silurian transgression that was a result of the melting of the late ordovician icecap deposition of the main organic rich shale unit in the north african arabian region was restricted to the earliest silurian rhuddanian stage acuminatus atavus and probably early cyphus graptolite biozones during this short period 1 2 m y a favourable combination of factors existed which led to the development of exceptionally strong oxygen deficiency in the area in most countries of the study area the post rhuddanian silurian shales are organically lean and have not contributed to petroleum generation the distribution and thickness of the basal silurian hot shales have been mapped in detail for the whole north african region using logs from some 300 exploration wells in libya tunisia algeria and morocco in addition all relevant accessible published and unpublished surface and subsurface data of the lower silurian shales in north africa and arabia have been reviewed including sedimentological biostratigraphic and organic geochemical data the lowermost silurian hot shales of northern gondwana are laterally discontinuous and their distribution and thickness were controlled by the early silurian palaeorelief which was shaped mainly by glacial processes of the late ordovician ice age and by pan african and infracambrian compressional and extensional tectonism the thickest and areally most extensive basal silurian organic rich shales in north africa occur in algeria tunisia and western libya while on the arabian peninsula they are most prolific in saudi arabia oman jordan and iraq the hot shales were not deposited in egypt which was a large palaeohigh at that time the depositional model presented may help in better understanding the source potential of the basal silurian shales in less explored regions of north africa and arabia including morocco northern niger and the kufra basin in southeast libya

a general framework for modeling sediment supply to coastal dunes including wind angle beach geometry and fetch effects a series of spatially explicit equations are derived that form the foundation of a modeling framework that provides insight into how the interaction of the fetch effect and angle of wind approach leads to tradeoffs that govern the magnitude of aeolian sediment transport across beaches of different geometry the spatial distribution of sediment transport rate per unit width at any point on the beach is shown to vary predictably as a function of wind angle critical fetch and beach geometry and this has evident implications for the total volume and distribution of sediment transport into the dunes behind the beach as well as the proportion of sediment lost from the beach dune system at the downwind margin as the wind field shifts from onshore shore perpendicular to oblique shore parallel approach angle total sediment transport rate across a dune line segment will reflect a tradeoff between transport reduction because of the cosine effect and transport enhancement because of potentially longer fetch distances traversed by the wind prior to encountering the dune line this tradeoff is most evident on long narrow beaches when beach width is less than the critical fetch for such beaches and with onshore winds the total sediment transport rate across the dune line will be less than that predicted for a wide beach because of the constraint imposed by the fetch effect however as the angle of wind approach becomes oblique the available fetch becomes progressively longer transport limitations imposed by the fetch effect are negated and transport enhancement across the dune line is to be expected with very large angles of wind approach the cosine effect dominates the interaction and transport reductions across the dune line occur until the wind is shore parallel and sediment supply to the dunes ceases altogether this sequence of adjustments and tradeoffs were only partially understood prior to this study and yet they form the foundation of coastal dune modeling the framework proposed in this paper serves to place future studies of process form interaction in beach dune systems on a robust theoretical foundation it also facilitates the testing of various alternative hypotheses regarding the uneven spatial and temporal distribution of dune height and growth rate in coastal environments

aeolian sand transport an optimized model consideration of the available equations for prediction of aeolian sand transport led to the development of a model which relies on optimization techniques for the production of improved performance the model has been applied to the characterization of dunesand movement in coastal environments in eastern australia

the ratios of dibenzothiophene to phenanthrene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks abstract the ratio of dibenzothiophene to phenanthrene and the ratio of pristane to phytane when coupled together provide a novel and convenient way to infer crude oil source rock depositional environments and lithologies such knowledge can significantly assist in identifying the source formation s in a basin thereby providing valuable guidance for further exploration the ability to infer this information from analysis of a crude oil is especially valuable as frequently the earliest samples in a new area may be shows and or drill stem test samples from exploratory wells which are characteristically drilled on structural highs stratigraphically remote from the source formation s a cross plot of dibenzothiophene phenanthrene versus the pristane phytane ratios measured on seventy five crude oils from forty one known source rocks ranging in age from ordovician to miocene consistently classified the oils into the following environment lithology groups marine carbonate marine carbonate mixed and lacustrine sulfate rich lacustrine sulfate poor marine and lacustrine shale and fluvial deltaic carbonaceous shale and coal the dibenzothiophene phenanthrene ratio alone is an excellent indicator of source rock lithology with carbonates having ratios 1 and shales having ratios the dibenzothiophene to phenanthrene and the pristane to phytane ratios can also be used to classify source rock paleodepositional environments the classification scheme is based on the premise that these ratios reflect the different eh ph regimes resulting from the significant microbiological and chemical processes occurring during deposition and early diagenesis of sediments the dibenzothiophene phenanthrene ratio assesses the availability of reduced sulfur for incorporation into organic matter and the pristane phytane ratio assesses the redox conditions within the depositional environment interpretation of these ratios has been aided by quantitative biomarker analysis and by carbon isotope data for pristane and phytane obtained by gas chromatography isotope ratio mass spectrometry

the quantitation and origin of c40 n alkanes in crude oils and source rocks a gas chromatographic method using n alkane standards n c 20 n c 30 n c 40 n c 50 and n c 60 and a deuteriated alkane internal standard n c 24 d 50 is presented for the quantitative analysis of high molecular weight alkanes c 40 hmwas the samples were injected in pulsed splitless mode using this method hmwas ranging up to c 100 can be determined and a gc response factor for n c 60 of up to 83 that of n c 30 was obtained the hmwa distributions in three typical high wax oils and a source rock extract from the nanyang depression china were determined the results show that the concentrations of hmwas in the three crude oils range from 22 8 to 38 0 mg g oil accounting for about 16 of the total concentration of c 22 n alkanes the concentration of hmwas in the source rock extract from the dong 10 well is twice as large compared to the concentration in the crude oil in dong 12 well which may be associated with fractionation during migration from the source rock to the reservoir the formation of c 40 c 60 it alkanes may be associated with cutan cutin sources within kerogen org geochem 31 2000 589 and also with biochemical and geochemical processes under strongly reducing conditions the n c 21 to n c 35 n alkanes in typical high wax oils from the nanyang depression have a weak odd over even carbon number predominance whereas the n c 40 to n c 60 n alkanes show a strong odd over even carbon number predominance this phenomenon is tentatively considered to be related to the occurrence of different hydrocarbon generation and preservation characteristics of n alkanes with different carbon numbers

the effect of wind gusts moisture content and fetch length on sand transport on a beach this paper reports on an analysis of instantaneous sediment transport in relation to wind gusts moisture content and fetch length from a field study carried out at skallingen denmark wind speeds were measured with cup anemometers and instantaneous sediment transport with vertical traps coupled to electronic balances moisture content was measured gravimetrically using samples taken along a beach profile at intervals of 1 to 2 h sediment transport and wind speeds were sampled at 1 hz and a 5 s running mean was used to smooth the data from the trap because of limitations of the balance resolution three measures of the threshold of sediment motion the intermittency threshold minimum threshold and maximum threshold were explored using data from five runs carried out on october 26 2000 the intermittency threshold and maximum threshold were largely insensitive to wind speed but varied spatially along the fetch distance the minimum threshold increased significantly with increasing mean wind speed as a result of reduced time for drying of the surface layer examination of time series for instantaneous wind speed and sediment transport for a number of runs on october 26 and november 6 2000 showed close agreement between fluctuations in wind speed and fluctuations in sediment transport cross spectral analysis of instantaneous wind speed and sediment transport for one run on each day where there was continuous transport showed high coherence between the two variables over a range of frequencies from 0 2 hz to 0 01 hz plots of all non zero instantaneous sediment transport values versus wind speed show considerable scatter in general transport rates are highest for traps located further from the upwind non erodible boundary i e along the fetch best fit power relationships show r2 values generally ranging from 0 4 to 0 6 and exponents ranging from 4 5 to 6 94 i e much higher than the traditional value of 3 found in most transport equations traps located close to the upwind boundary had lower r2 values and exponents 2 5

annual to decadal morphodynamics of the foredune system at greenwich dunes prince edward island canada the purpose of this study was to quantify relationships between season sediment availability sediment transport pathways and beach foredune morphology at greenwich dunes pei this was done for periods ranging from a few days to multiple decades using erosion pins bedframe measurements annual surveys and digital photogrammetry using historical aerial photographs the relative significance of seasonal annual processes versus response of the foredune system to broader geomorphic controls e g relative sea level rise storms etc was also assessed the data show that there are clear seasonal differences in the patterns of sand supply from the beach to the foredune at greenwich and that there are differences in sediment supply to the foredune between the east and west reaches of the study area resulting in ongoing differences in foredune morphology they also demonstrate that models that incorporate wind climate alone or even models that include other factors like beach moisture would not be able to predict the amount of sediment movement from the beach to the foredune in this environment unless there were some way to parameterize system morphology especially the presence or absence of a dune ramp finally the data suggest that the foredune can migrate landward while maintaining its form via transfers of sediment from the stoss slope over the crest and onto the lee slope although the rate of foredune development or recovery after disturbance changes over time due to morphological feedback the overall decadal evolution of the foredune system at greenwich is consistent with and supports the davidson arnott 2005 conceptual model of dune transgression under rising sea level copyright 2012 john wiley sons ltd

black shale grey shale fossils and glaciers anatomy of the upper ordovician silurian succession in the tazzeka massif of eastern morocco abstract a 400 m thick clastic succession of late ordovician through silurian age crops out in the tazzeka massif eastern morocco biostratigraphic data chitinozoa acritarchs constrain these rocks to the late katian through hirnantian coeval with glaciation in gondwana with a 8 myr hiatus at the ordovician silurian boundary sedimentological analysis reveals six facies associations including interbedded black and grey shale couplets poorly oxygenated shelf sediments a bioturbated shale with wave rippled sandstone inner shelf deposits several occurrences of diamictite of probable glaciogenic origin interbedded sandstone and mudstone storm and fair weather wave agitated shoreface rippled sandstone storm return flow deposits and amalgamated sandstone deposits delta front debris flows direct evidence for glaciation in the hirnantian deposits is poor third order sequence stratigraphic analysis reveals two transgressive systems tracts late katian and intra hirnantian two highstand systems tracts both intra hirnantian lowstand wedges probably corresponding to two principal glacial lowstands two maximum flooding surfaces late katian and intra hirnantian and a major ravinement surface hirnantian silurian contact remote from the centre of glaciation the tazzeka succession is suggested to be an excellent reference section with which to understand glacially moderated sea level changes in the late ordovician silurian late llandovery or younger shale geochemistry indicates organic enrichment toc 4 5 this organic enrichment greatly increases the known extent of the upper of two silurian organic shales across north africa potential hydrocarbon source rocks across the region

occurrence and distribution of high molecular weight hydrocarbons in selected non marine source rocks from the liaohe qaidam and tarim basins china abstract extracts of 18 potential source rocks from the qaidam liaohe and tarim basins china have been characterized by high temperature gas chromatography htgc and found to contain high molecular weight hydrocarbons hmwhcs above c40 these rocks were originally formed in freshwater lacustrine saline lacustrine and terrigenous bog environments with mudstone calcareous mudstone coaly shale and coal lithologies their ages range from triassic to miocene and maturities from immature to mature covering a vitrinite reflectance range ro for the liaohe and tarim samples of 0 54 0 84 the combined distributions of the n alkane and alkylcyclopentane homologues in the extracts can be used to characterize the nature of the original depositional environment in certain samples the carbon number predominance of the n alkanes changes from an odd even predominance to even odd predominance above c40 possibly suggesting different precursors for the n alkanes above and below c40 concentrations of the hmwhcs were also observed to increase with maturity of the source rocks this is the first comprehensive report on the occurrence of hmwhcs in source rocks and their discovery introduces the possibility of using these compounds for oil source rock correlation purposes in future studies along with the more conventional biomarkers

aeolus ii an interactive program for the simulation of aeolian sedimentation abstract a computer program has been developed to simulate two or three dimensional topographic change associated with aeolian sediment transport because predictions generated by available models of aeolian transport can vary by about an order of magnitude for a given set of environmental conditions selection of an appropriate model is problematic this program includes a number of models and provides for interactive selection of a desired model combination s to allow for comparison between model predictions topography represented by a set of coordinates in two or three dimensions is defined by bins of sediment differential rates of transport between adjacent bins resulting from variations in grain size slope and surface moisture content are used to determine mass flux and to adjust the topography in an iterative fashion sub routines allow the simulation of temporally varying levels of surface moisture resulting from evaporation and periodic restoration of upwind boundary conditions the wind field can be represented by a constant shear velocity by a spatial cross shore distribution of shear velocities or by a time series of values representing multiple wind events output is in the form of a graphic display or tabulated results written to disk example results are presented which qualitatively suggest that simulated topographic changes are reasonable areas where further refinement is needed to improve correspondence with reality are identified and discussed

aliphatic and aromatic biomarkers from gondwanan sediments of late ordovician to early devonian age an early terrestrialization approach abstract twenty one core samples of late ordovician to early devonian age from sections in southern tunisia north african platform gondwana and containing marine and terrestrial organic matter with microbial input were investigated to link the aliphatic and aromatic hydrocarbon distributions with the terrestrial and marine palynomorph content e g acritarchs prasinophytes chitinozoans cryptospores and trilete spores in addition to several biomarkers of algal bacterial origin long chain n alkanes that might be derived from land plants as well as the terrestrial diterpane norabietane were found several land plant derived biomarkers such as retene cadalene simonellite tetrahydroretene and c19 isohexylalkyl naphthalene were observed in the aromatic fractions while these terrestrial biomarkers could be clearly recognized in the middle silurian lower devonian samples their presence in the upper ordovician lower silurian sediments is more doubtful because of much lower relative abundances the land plant biomarkers show a fairly good correlation with the occurrence and abundance of cryptospores and trilete spores derived from bryophytes and tracheophytes which covered the emerged areas around the ghadamis basin during the silurian and devonian the early tracheophytes e g cooksonia lycophytes and zosterophylls are therefore suggested as a new terrestrial source for most of the saturated and aromatic biomarkers found in sediments of middle silurian to early devonian age

high frequency sediment transport responses on a vegetated foredune wind flow and sand transport intensity were measured on the seaward slope of a vegetated foredune during a 16 h storm using an array of sonic anemometers and wenglor laser particle counters the foredune had a compound seaward slope with a wave cut scarp about 0 5 m high separating the upper vegetated portion from the lower dune ramp which was bare of vegetation wind direction veered from obliquely offshore at the start of the event to obliquely onshore during the storm peak and finally to directly onshore during the final 2 h as wind speed dropped to below threshold sand transport was initially inhibited by a brief period of rain at the start of the event but as the surface dried and wind speed increased sand transport was initiated over the entire seaward slope transport intensity was quite variable both temporally and spatially on the upper slope as a result of fluctuating wind speed and direction but overall magnitudes were similar over the whole length ten minute average transport intensity correlates strongly with mean wind speed measured at the dune crest and there is also strong correlation between instantaneous wind speed and transport intensity measured at the same locations when the data are smoothed with a 10 s running mean transport on the beach for onshore winds is decoupled from that on the seaward slope above the small scarp when the wind angle is highly oblique but for wind angles 45 from shore perpendicular some sand is transported onto the lower slope copyright 2012 john wiley sons ltd

field evaluation of some sand transport models fluorescent tracer procedures originally developed for research on fluvial sediment movement were used to monitor the movement of three commercially purchased sands in a natural dune environment results were compared with estimates of transport rates from three theoretical models estimates from models by bagnold 1941 and hsu 1971 were larger by as much as one order of magnitude than the rates observed in the tracer study the model of a a kadib 1965 provided closer correspondence to observed transport rates for medium sand mean diam 0 653 mm but underestimated rates for coarse sand mean diam 0 992 mm

air flow over foredunes and implications for sand transport more than 4000 hourly wind profiles measured on three topographically different foredunes are analysed and discussed wind flow over the foredunes is studied by means of the relative wind speed the ratio between wind speed at a certain location and the reference wind speed at the same height relative wind speeds appear to be independent of general wind speed but dependent on wind direction for perpendicular onshore winds the flow over the foredune is accelerated due to topographic changes and decelerated due to changes in surface roughness accelerations dominate over decelerations on the seaward slope the pattern of acceleration and deceleration in relation to wind direction is more or less comparable for different foredunes but the magnitudes differ an increase in foredune height from 6 to 10m leads to an increase in speed up near the top of the seaward slope from 110 to 150 per cent during onshore wind but further increase of foredune height from 10 to 23 m appears to have little effect due to increased roughness and deflection of flow topography also influences the direction of the flow between beach and top the flow deflects in the direction of the normal during onshore winds during offshore winds the flow is deflected to the parallel near the dunefoot deflection is always in the direction of the parallel and increases with steeper topography the maximum deflection near the dunefoot was 90 over a 23 m high dune observed during offshore winds patterns of erosion and sedimentation resulting from winds from different directions can be explained by the observed accelerations and decelerations owing to speed up on the seaward front of the foredune sand transport capacity of the wind increases which results in erosion if vegetation is absent during strong onshore wind sand is lifted near the dunefoot and moves over the foredune in suspension during weaker winds vertical wind velocities do not exceed fall velocities of the sand grains and most of the sand is deposited near the dunefoot

black shale deposition in an upper ordovician silurian permanently stratified peri glacial basin southern jordan abstract the lower palaeozoic upper ordovician silurian succession of north africa contains one of the world s most prolific black shale source rocks yet the origin of these rocks remains contentious the black shale of the batra formation in jordan was deposited at high palaeolatitude during rapid hirnantian to early silurian deglaciation here we report geological and organic geochemical results that provide evidence for an increase in photic zone primary productivity during ice melting the decay of this organic matter through oxidative respiration resulted in euxinia which enhanced the potential for organic matter preservation the occurrence of isorenieratane in all samples indicates euxinia extended from the photic zone to the sediment water interface the stratified basins and fjords of east antarctica provide a likely modern analogue

geochemical evaluation of the besikli oil field kahta adiyaman turkey abstract mesozoic source rocks and crude oils from the besikli oil field adiyaman turkey havebeen characterized by a variety of organic geochemical techniques the potential source rocksinvestigated include the karababa a b and c members and the karabogaz formations thekarababa a member and the karabogaz formation of clayey limestone and limestone areimportant source rocks in the basin the crude oils examined in this study were obtained fromreservoir formations of the same age throughout the oil field the source rock screening analysisindicates that the karababa a member and the karabogaz formation have substantialoil generation potential the karababa b and c members have no source potential because theydo not contain sufficient amount of total organic matter content 0 12 0 24 toc wt selectedsource rock and oil samples were characterized in detail and distributions and concentrations both relative and absolute concentrations of biomarkers at different oils were examined thebiomarker characteristics were combined with other geochemical and geological data to interpretthe sources depositional environments and the age of the oils oil source rock correlations weremade between source rocks and crude oils based on qualitative and quantitative biomarkerdistributions petrographic descriptions and vitrinite reflectance measurements were used toevaluate petrographic properties of source rocks and maturity levels of the formations thesource rocks for the oil from the karababa a member and karabogaz formation are not matureenough and therefore oil should have migrated from the outside of the study area

the lower silurian qalibah formation of saudi arabia an important hydrocarbon source rock 1 the lower silurian qalibah formation represents a distinct lithostratigraphic time transgressive sequence it is disconformably bounded below by the upper ordovician to possibly lower silurian sarah formation and above by the continental to marginal marine lower devonian and possibly upper silurian tawil sandstone formation this paper redefines the qalibah formation within these boundaries in its reference section near the town of al qalibah in northwest saudi arabia the qalibah is 499 m thick whereas in a subsurface composite section it reaches 955 m the qalibah formation is a coarsening upward progradational sequence consisting of a lower qusaiba shale member and an upper sharawra sandstone member the basal hot shale of the qusaiba is a black euxinic bottomset shale up to 70 m thick which was deposited during the early silurian sea level rise following the deglaciation of gondwana this paleozoic shale is organic rich and the most likely source rock of the low sulfur high gravity oil condensate and gas discovered in recent years in the paleozoic rocks of central and eastern saudi arabia lithologically similar silurian sequences were deposited over most of the broad stable shelf of gondwana from the middle east to the african sahara

source facies of the paleozoic petroleum systems in the tabei uplift tarim basin nw china implications from aryl isoprenoids in crude oils abstract aryl isoprenoids have been detected for the first time in crude oils from paleozoic petroleum systems in the tabei uplift tarim basin northwestern china the principal compounds possess the 1 alkyl 2 3 6 trimethyl substitution pattern characteristic of diaromatic carotenoids found in the chlorobiaceae family of photosynthetic sulfur bacteria with a predominance of c13 c23 homologues in these samples flash pyrolysates of the asphaltene fractions isolated from crude oils show an unusual abundance of 1 2 3 4 tetramethylbenzene an indicator for a significant contribution of diaromatic carotenoids to the source kerogen of these oils the wide distribution of these compounds in crude oils reveals that penetration of the photic zone by sulfidic waters during deposition enabled prolific growth of photosynthetic green sulphur bacteria chlorobiaceae this suggests that the source rocks for the paleozoic petroleum systems in the tabei uplift were likely deposited under euxinic conditions with sulfate and sulfide rich water bodies which doesn t support previously published conclusions of a middle upper ordovician source that marks the slope facies at the margins of structural uplifts

shape effects in aeolian grain transport wind tunnel experiments are reported the results of which show that grain transport rate is responsive to characteristic grain shape it is relatively less sensitive to changes of sorting unless these involve the fraction smaller than 50 m a cubic relationship between transport rate and velocity gradient appears to be valid only for well worked natural grains having high sphericity

transport by wind of granular materials of different grain shapes and densities aeolian transport rates were measured for three sands a quartz sand relative density 2 68 sphericity 0 73 a shelly sand relative density 2 64 sphericity 0 59 carbonate content 67 and granular aluminium oxide relative density 3 95 sphericity 0 67 low sphericity depresses the transport rate particularly at high wind speeds high density also does so but the effect is more marked at low transporting wind speeds the sand of low sphericity undergoes longer saltations than the other materials but is dislodged less frequently than they are and is transported less freely in a given wind of the more spherical materials the denser was the least effective at extracting energy from the wind for grain transport in the range of our experiments both of the more spherical materials showed evidence of a fairly sudden transition of transport behaviour at modest wind speed it is inferred that this marks the transfer of the function of grain dislodgement from direct wind action to inter granular collision the transition did not occur in experiments on the material of lower sphericity for a given transport rate wind speed near the bed is highest for the grains of low sphericity by a considerable margin and lowest for the more compact quartz grains propensity for transport by wind is greatest for the quartz sand less so for the heavy material and least for the material of low sphericity

effects of source thermal maturity and biodegradation on the distribution and isomerization of homohopanes in petroleum abstract the distributions of c31 c35 17 21 h homohopanes in marine petroleums can be used to describe redox conditions in the source rock depositional environment for example high c35 homohopane indices c35 c31 c35 are typical of petroleums generated from source rocks deposited under anoxic marine conditions where the c35 backbone of the precursor bacteriohopanetetrol is preferentially preserved homohopane distributions have been used to distinguish petroleums from different organic facies of the same source rock homohopane distributions are altered by secondary processes for example the c35 homohopane index decreases with increasing api gravity and thermal maturity of related oils from the monterey formation offshore california similar decreases in the homohopane index are observed for expelled oils from monterey source rock during hydrous pyrolysis biodegradation can result in selective loss of high or low molecular weight homologs apparently depending on the bacterial population in the reservoir bacterial demethylation of homohopanes appears necessary to explain 25 norhopanes in at least one biodegraded oil hydrous pyrolysis studies of the phosphatic and siliceous members in the monterey formation show that identical heating conditions result in different homohopane c 22 epimer ratios furthermore a reversal in the trend of the epimer ratio at high experimental temperatures is observed for the phosphatic but not for the siliceous lithology this could be caused by the combined effects of isomerization and differential thermal destruction of epimers at high temperatures possibly mediated by rock mineralogy

a field experiment on the role of small scale wind gustiness in aeolian sand transport estimates of aeolian sand transport generally use an average wind speed to assess the wind energy to determine if variation in small scale wind gustiness on the order of several seconds duration has a significant effect on sand movement detailed field measurements were made of wind speed and transport rate average wind speed and several gust parameters were derived from the wind data the results indicate that small scale gust information does not improve prediction of transport rates

wind blown sand on beaches an evaluation of models five models for predicting rates of aeolian sand transport were evaluated using empirical data obtained from field experiments conducted in april 1994 at a beach on inch spit co kerry republic of ireland measurements were made of vertical wind profiles to derive shear velocity estimates beach slope and rates of sand transport sediment samples were taken to assess characteristics of grain size and surface moisture content estimates of threshold shear velocity were derived using grain size data after parsing the field data on the basis of the quality of shear velocity estimation and the occurrence of blowing sand 51 data sets describing rates of sand transport and environmental conditions were retained mean grain diameter was 0 17 mm surface slopes ranged from 0 02 on the foreshore to about 0 11 near the dune toe mean shear velocities ranged from 0 23 m s 1 just above the observed transport threshold to 0 65 m s 1 rates of transport ranged from 0 02 kg m 1 h 1 to more than 80 kg m 1 h 1 these data were used as input to the models of bagnold bagnold r a 1936 the movement of desert sand proc r soc london a157 594 620 kawamura kawamura r 1951 study of sand movement by wind translated 1965 as university of california hydraulics engineering laboratory report hel 2 8 berkeley zingg zingg a w 1953 wind tunnel studies of the movement of sedimentary material proc 5th hydraulics conf bull 34 iowa city inst of hydraulics pp 111 135 kadib kadib a a 1965 a function for sand movement by wind university of california hydraulics engineering laboratory report hel 2 8 berkeley and lettau and lettau lettau k and lettau h 1977 experimental and micrometeorological field studies of dune migration in k lettau and h lettau eds exploring the world s driest climate university of wisconsin madison ies report 101 pp 110 147 correction factors to adjust predictions of the rate of transport to account for the effects of slope and moisture content were calculated using the models of bagnold bagnold r a 1973 the nature of saltation and bed load transport in water proc r soc london ser a 332 473 504 and belly belly p y 1964 sand movement by wind u s army corps eng cerc tech mem 1 washington d c 38 pp respectively none of the models was able to produce a strong correspondence between measured and predicted rates of transport best results were obtained using the bagnold and zingg models and the kadib model was the least viable of this group the influence of sediment moisture content appeared to be the critical factor in degrading model viability overall none of the models is adequate for general applications to coastal aeolian environments where moisture content complications tend to override the predictive competence of the simple transport formulations c 1998 elsevier science b v