the geochemistry of rhenium and osmium in recent sediments from the black sea abstract the os isotopic composition of recent sediments from the black sea are reported with the concentrations of re os and major and minor elements osmium concentrations range from 0 23 to 0 69 ppb and re concentrations range from 21 to 85 ppb concentrations of both elements are large relative to average crustal material and are positively correlated with organic carbon 187 os 186 os ratios range from 5 7 to 7 1 all of these values are less radiogenic than the estimated 187 os 186 os ratio of seawater and average continental crust material variations in the os isotopic composition of these sediments are attributed to mixing of a hydrogenous component 187 os 186 os ratio between 7 and 9 and a less radiogenic detrital component 187 os 186 os ratio between 1 and 4 a mixing model is used to determine the fraction of os in the sediment associated with each component and the burial fluxes of re and os in the black sea are calculated in addition the data are used to estimate the magnitude of systematic error which such initial os isotopic heterogeneity may introduce into re os age determinations of ancient organic rich sediments

evidence in pre 2 2 ga paleosols for the early evolution of atmospheric oxygen and terrestrial biota the loss of fe from some pre 2 2 ga paleosols has been considered by previous investigators as the best evidence for a reduced atmosphere prior to 2 2 ga i have examined the behavior of fe in both pre and post 2 2 ga paleosols from depth profiles of fe 3 ti fe 2 ti and fe ti ratios and fe 3 ti vs fe 2 ti plots this new approach reveals a previously unrecognized history of paleosols essentially all paleosols regardless of age retain some characteristics of soils formed under an oxic atmosphere such as increased fe 3 ti ratios from their parental rocks the minimum oxygen pressure p o 2 for the 3 0 2 2 ga atmosphere is calculated to be about 1 5 of the present atmospheric level which is the same as that for the post 1 9 ga atmosphere the loss of fe common in paleosol sections of all ages was not due to a reducing atmosphere but to reductive dissolution of ferric hydroxides formed under an oxic atmosphere this reductive dissolution of ferric hydroxides occurred either 1 after soil formation by hydrothermal fluids or 2 during and or after soil formation by organic acids generated from the decay of terrestrial organic matter terrestrial biomass on the early continents may have been more extensive than previously recognized

seismic reflection and refraction investigations of lake kinneret central jordan valley israel abstract seismic reflection and refraction studies in lake kinneret which is located in the northern part of the dead sea rift have been carried out in the seismic reflection work several instruments including sparker boomer and air guns were used the acoustic penetration was limited giving information on the uppermost sediments only in the seismic refraction study the energy source was seismic explosives charges placed below the water table in shotholes located onshore at either end of two lines the seismic signals were picked up by hydrophones and transmitted to the shore based recording stations by special radio transmitters the seismic refraction profiles show different sedimentary structures at various parts of the lake the layer underlying the top sedimentary sequence is of higher seismic velocity in the northern section than in the southern section this suggests a difference in the stratigraphic section between the two parts unconformities and faults which account for the structures observed here probably exist under the lake the shallow reflection data indicate active tectonic processes in this area folds and faults have been observed in the uppermost sediments the most deformed areas are along the margins but some deformation also occurs at the center of the lake in its deepest portion the area is also seismically active

recognition of an infracambrian source rock based on biomarkers in the baghewala 1 oil india heavy sulfur rich oil produced from the infracambrian 540 640 ma jodhpur formation in the baghewala 1 well represents a new exploration play in the bikaner nagaur basin in india and the punjab basin in pakistan the baghewala 1 oil is nonbiodegraded and thermal maturation dependent biomarker ratios indicate generation from the source rock within the early oil window age diagnostic and source dependent biomarkers indicate that the oil originated from algal and bacterial organic matter with no higher plant input in an infracambrian carbonate rich source rock deposited under anoxic marine conditions these characteristics support a local origin of the baghewala 1 oil from organic rich laminated dolomites in the infracambrian bilara formation significant amounts of petroleum could originate from equivalents of the proposed bilara source rock in the punjab basin pakistan where the precambrian to lower paleozoic section is thicker and more deeply buried than in india deeper burial of the source rock in the punjab basin than in the bikaner nagaur basin could generate more mature equivalents of the baghewala 1 oil the baghewala 1 oil is geochemically similar to another heavy oil from the infracambrian salt range series in the nearby karampur 1 well in pakistan and to oils derived from carbonate evaporite facies of the infracambrian huqf group about 2000 km 1243 mi to the southwest in the eastern flank province of southern oman these findings are consistent with published evidence that subsiding rift basins in northwest india pakistan and southern oman were in close proximity during the infracambrian along the middle eastern edge of gondwanaland

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

global versus local processes during the pliensbachian toarcian transition at the peniche gssp portugal a multi proxy record abstract the toarcian oceanic anoxic event t oae 183 ma was an episode of extreme warmth environmental changes and carbon cycle perturbation we present a high resolution study of the peniche section lusitanian basin portugal recently defined as the toarcian global stratotype section and point to provide a review of the pliensbachian toarcian pl to environmental and climatic changes a large 7 negative carbon isotope excursion cie is recorded within the t oae interval in bulk organic matter distinct small scale 13c negative shifts modulating the t oae carbon isotope signal are correlated across different european basins which have implications on the estimation of the t oae duration the increase in kaolinite content and chemical index of alteration from the pl to boundary up to the t oae interval is interpreted as reflecting a shift towards warmer and wetter climate conditions the common occurrence of coarse grained turbidites within the t oae interval is possibly linked with changes of the hydrological cycle and storm intensity low total organic carbon contents together with the absence of redox sensitive trace element enrichments indicate oxygen deficient conditions unfavourable for organic matter preservation mercury data show a clear increase at the base of the t oae cie followed by a return to background values providing further evidence that karoo ferrar volcanism might have triggered the series of environmental disturbances during the early toarcian however the highest mercury values are recorded in samples containing abundant pyritized wood fragments highlighting the influence of local chemical processes on mercury enrichments which should be considered before any interpretation of the hg records

late pleistocene paleomagnetic secular variation from the sea of galilee israel 1 stable magnetization of laminated lacustrine lisan formation show typical paleomagnetic secular variation and a possible geomagnetic field excursion 14c ages from the top and assumed 0 9 mm yr deposition rate constrain the recorded section between 29 28 ka and 22 23 ka samples were recovered from two trenches at the southwestern shore of the sea of galilee a graben within the dead sea transform system the angle between the two site mean directions is 21 but retilting the beds to horizontal reduces it to 7 indicating pre folding probably depositional magnetization aberrations of field directions at one locality where vgps deviate 40 from the geographic north and low nrm intensities between 29 28 ka and 25 24 ka are contemporaneous with the mono lake excursion if the correlation is correct the new data support the hypothesis that the excursion was global justifying its utilization as a chronological datum

evidence of terrestrial organic matter deposition across the early toarcian recorded in the northern lusitanian basin portugal abstract the pliensbachian toarcian lower jurassic in the lusitanian basin portugal is particularly well exposed through marl limestone alternations very rich in nektonic and benthonic macrofauna in the general context of toarcian oceanic anoxic event t oae the lower toarcian polymorphum and levisoni ammonite zones marks important sedimentological changes in the marine paleoenvironment to better understand the paleoenvironmental changes that occurred during the latest pliensbachian early toarcian a high resolution study of organic matter was undertaken in the alcabideque section in the northern sector of the basin based on the analysis of 14 samples from a section 20 m thick this study involved organic geochemistry total organic carbon toc sulfur and biomarkers and palynofacies the results confirm that sediments are particularly poor in organic matter with the highest toc values reaching 0 41 wt around the top of polymorphum zone the palynofacies analysis provides evidence that the organic matter largely consists of particles belonging to phytoclasts and palynomorphs groups the phytoclasts present were generally degraded and oxidized with significant representation in the emaciatum and polymorphum zones the palynomorphs were mainly composed by sporomorphs with a sporadic increase in marine palynomorphs mainly dinocysts at the top of the emaciatum and polymorphum zones continental organic matter was predominant at the base of levisoni zone t oae through the deposition of brownish marls chocolate marls which was confirmed by the occurrence of tetrads and polyads pollen grain agglomerates and by biomarkers with the major presence of long chain n alkanes n alkane c17 c20 tricyclic terpane c24 tetracyclic terpane and c29 regular sterane the gammacerane index shows a peak at the top of polymorphum zone clearly associated with the increase of marine palynomorphs and the maximum marine influence in the series

variations in the sterane carbon number distributions of marine source rock derived crude oils through geological time abstract the analysis of the sterane data of a large set of crude oils 414 derivedfrom marine carbonate 27 and siliciclastic source rocks 14 where influences of terrestrial or lacustrine derived organic matter can reasonably be excluded shows that there are increases in the relative content of c28 steranes and decreases in the relative content of c29 steranes through geological time there are no consistent variations in the relative content of c27 steranes through time with one major exception a proterozoic oil from oman palaeozolic and older crude oils are thus generally characterised by strong predominances of c29 steranes and low relative concentrations of c28 steranes significantly higher proportions of c28 steranes and lower proportions of c29 steranes occur in oils derived from jurassic and upper cretaceous source rocks these changes through time do not appear to reflect the chemical evolution of the sterols of one particular variety of marine organism the increase in c28 steranes may be related to the increased diversification of phytoplantonic assemblages in the jurassic and cretaceous possible sources of the c28 sterols necessary for the observed changes in crude oil steranes includes diatoms coccolithophores and dinoflagellates although the technique does not give an accurate means of determining the age of the source rock of a crude oil it is possible to distinguish younger crudes derived from the upper cretaceous and tertiary from palaeozoic and older crudes

relationship between petroleum composition and depositional environment of petroleum source rocks crude oils of nonmarine source can be distinguished from those of marine shale source and from oils originating in marine carbonate sequences by using a battery of geochemical parameters as demonstrated with a sample suite of nearly 40 oils a novel parameter based on the presence of c30 steranes in the oil was found to be a definitive indication of a contribution to the source from marine derived organic matter a second novel parameter based on monoaromatized steroid distributions was effective in helping to distinguish nonmarine from marine crudes and can be used to gauge relative amounts of higher plant input to oils within a given basin sterane distributions were similarly useful for detecting higher plant input but were less effective than monoaromatize steroid distributions for making marine versus nonmarine distinctions concentrations of high molecular weight paraffin can also be effective nonmarine indicators but are influenced by maturation and biodegradation processes certain algal derived nonmarine oils may show little high molecular weight paraffin response oils from carbonate sources with a few exceptions can be distinguished by having low pristane phytane ratios low carbon preference indexes and high sulfur contents gammacerane indexes and carbon isotope ratios of the whole crude are not effective in distinguishing these types of environmental differences on a global basis

lipid geochemistry of sediments from upton broad a small productive lake major lipid classes isolated from 3 sections of the sediment profile of upton broad a shallow lake formed about 500 yr ago were correlated with input and with changes attributable to early diagenesis surficial sediment contains lipids characteristics of the known recent algal and microbial input preservation of chlorophyll pigments and absence of appropriate markers suggest that diagenesis is minimal older deposits from the eutrophic phase of the lake s history contain higher levels of bacterial lipids and diagenetic products the earliest sediment contains lipids characteristic of terrigenous input subjected to more extensive diagenesis than the younger sediment recognition of early diagenesis in anoxic sediment suggests that distributions of the shorter chain homologous free n alkanes alkanols and alkanoic acids result from microbial synthesis using material initially deposited at the sediment surface rather than partial preservation of the lipids of primary source organisms

lower jurassic epicontinental carbonates and mudstones from england and wales chemostratigraphic signals and the early toarcian anoxic event sections through lower jurassic epicontinental carbonates from southern britain junction bed and equivalent show a positive carbon isotope excursion 13ccarbonate detectable in bulk rock in the falciferum zone of the lower toarcian isotopic data from organic matter in more clay rich sections from wales and north east england together with determinations on belemnite calcite indicate that highest 13c values are localized in the upper exaratum subzone of the falciferum zone levels of particular enrichment in organic carbon were developed in the early to mid exaratum subzone and hence pre date this 13c maximum these phenomena reflect the impact of the early toarcian oceanic anoxic event in the british area similar isotopic trends have been recorded in other toarcian sections from tethyan europe and are interpreted as reflecting the chemistry of sea water on the assumption of isotopic correlation between the english and tethyan sections the 13c maximum would be everywhere dated as latest exaratum subzone in terms of the north european ammonite scheme absolute oxygen isotope values in carbonates probably reflect both early diagenetic cementation and later temperature related burial diagenesis although a palaeotemperature maximum is tentatively identified as characterizing the early falciferum zone subsequent climatic deterioration may have been triggered by drawdown of co2 related to regional excess carbon burial during the oceanic anoxic event using the positive 13c excursion as a correlative level in sections from different faunal provinces britain italy and spain implies that lower toarcian zonal stratigraphy is diachronous between northern and southern europe there is evidence for partitioning of water masses between the north european shelf and the tethyan continental margin during the early jurassic

acoustic reflectivity and shallow sedimentary structure in the sea of galilee jordan valley abstract mapping the floor of the sea of galilee lake kinneret with a shallow seismic system of 3 5 khz resulted in interesting data that were not obtained previously with standard single channel seismic systems over most of the lake acoustic penetration is not possible probably because of the high gas content in the top sedimentary sequence however in a few areas excellent penetration of about 20 m was achieved one area is a terrace in the southern part of the lake south of a small bathymetric escarpment at depths of 13 21 m along israel latitudinal grid 238 it is unclear whether the existence of gas in the sediment or other parameters are responsible for the marked difference in acoustic penetration on both sides of the scarp another area with acoustic penetration is in the vicinity of hot and salty submarine springs although there is no difference in the composition of the upper sedimentary layers between these areas and neighbouring areas there is a marked difference in the acoustic penetration the contact between areas with acoustic penetration to areas without acoustic penetration is very sharp the craters of the submarine springs are usually located on the borders of the areas with acoustic penetration or even at some distance away from them it is possible that the activity of the hot and salty submarine springs controls the acoustic penetration however determination of the exact mechanism for the existence of the zones of acoustic penetration must await further studies of the sediments especially for measurements of various parameters that control the seismic response of the rock another discovery made with the shallow seismic profiles is the existence of some bathymetric irregularities on the floor of the sea of galilee in view of the high sedimentation rate in the lake which tends to smooth the floor a bathymetric irregularity such as a linear bathymetric step could be a surface expression of an active fault

natural mass dependent variations in the isotopic composition of molybdenum we present the first observations of natural mass dependent fractionation of the isotopic composition of molybdenum mo using multi collector inductively coupled plasma mass spectrometry variations in the isotopic composition of mo are reported as 97 95mo 97mo 95mo sample 97mo 95mo standard 1 1000 external analytical precision of 97 95mo is 1 between sediments deposited under anoxic conditions 97 95mo 1 02 to 1 52 relative to our in house standard and ferromanganese nodules 97 95mo 0 63 to 0 42 97 95mo of pacific ocean seawater 97 95mo 1 48 lies within the range of values for anoxic sediments closest to modern black sea anoxic sediments molybdenites from continental ore deposits have intermediate 97 95mo ranging from 0 26 to 0 09 variations in the abundances of 92mo 95mo 96mo 97mo and 98mo are consistent with mass dependent fractionation a sporadic unidentified interference occurs at mass 94 and 100mo is not measured we hypothesize that the 97 95mo offset between anoxic sediments and ferromanganese nodules results from mo isotope fractionation during inefficient scavenging of mo from seawater by mn oxides under oxic conditions the similarity in 97 95mo of anoxic sediments and seawater is consistent with the very efficient removal of mo from seawater under anoxic conditions in the presence of h2s the data can be interpreted in terms of a steady state mass balance between the mo flux into the oceans from the continents and the mo flux out of the oceans into oxic and anoxic sediments such an interpretation is quantitatively consistent with existing estimates of the removal fluxes of mo to anoxic and oxic sediments these findings suggest that 97 95mo in seawater may co vary with changes in the relative proportions of anoxic and oxic sedimentation in the oceans and that this variation may be recorded in 97 95mo of anoxic sediments hence the mo isotope system may be useful in paleoredox investigations

rise of atmospheric oxygen and the upside down archean mantle 1 the establishment of an oxygen rich atmosphere dramatically altered the evolution of life on earth most of the recent discussion of the topic has been focused on the timing of the event rather than on its mechanism here we draw upon recent developments in the understanding of earth s interior to propose that the rise of oxygen followed a geologically abrupt period of mantle overturn and or intense plume activity near the archean proterozoic transition 2470 2450 million years ago the magmatic event has already been linked to the widespread deposition of oxide facies banded iron formation and the rise of oxygen has been implicated as the trigger for iron deposition and earth s first major glaciation we argue that these events are all related to a change in redox state of volcanic gases brought about by deep seated late archean and earliest paleoproterozoic magmatism

geochemical and biological marker assessment of depositional environments using brazilian offshore oils abstract a combined geochemical and molecular characterization of a wide selection of oils from the major brazilian offshore basins has been undertaken the elemental sulphur nickel and vanadium and bulk oapi and 13c properties of each sample been considered together with its molecular composition determined using liquid and gas chromatography and quantitative biological marker investigations using gas chromatography mass spectrometry for alkanes the results reveal significant differences in the chemical features of the various oils which enable them to be divided into five groups the distinction of the groups appears to reflect differences in the depositional environment of the source rocks of the oils each group is correlated tentatively with source rocks laid down in a specific depositional regime namely lacustrine freshwater lacustrine saline water marine evaporitic marine carbonate or marine deltaic the diagnostic features that allow this classification are the relative abundance and carbon number distributions of n alkanes pristane phytane ratios sulphur nickel and vanadium contents carbon isotope data the absolute concentrations of hopanes and steranes and their abundance relative to 4 methylsteranes and also the occurrence and abundance of several specific biological markers including 18 h oleanane gammacerane carotane tricyclic terpanes higher acyclic isoprenoids 28 30 bisnorhopane and 25 28 30 trisnorhopane this investigation shows the value of a combined geochemical and molecular approach in the assessment of the palaeoenvironment of deposition of the source rocks which gave rise to the oils

post depositional mobility of platinum iridium and rhenium in marine sediments the discovery of high concentrations of iridium in cretaceous tertiary boundary sediments engendered the hypothesis1 that a meteorite collided with the earth 65 million years ago coincident with the mass extinction that occurred at that time iridium spikes of various magnitudes have subsequently been reported at more than 10 other extinction horizons2 11 it has been suggested on the other hand that geochemical processes might create or modify many of these spikes5 11 4 but a critical evaluation of these suggestions has been hindered by incomplete understanding of low temperature iridium geochemistry other platinum group elements ru rh pd re os pt au are often found to be associated with ir spikes and inter element ratios have been used to assess the cosmic or terrestrial nature of the enrichments5 7 9 28 29 but the geochemical influences on these relative abundances are also poorly constrained here we describe analyses of recent abyssal marine sediments which allow us to characterize the behaviour of pt re and ir during early diagenesis these elements are redistributed by changes in sedimentary redox conditions such changes can probably account for many of the small platinum group element spikes found in the geological record and may render ambiguous attempts to interpret inter element ratios

the rise of atmospheric oxygen when did atmospheric oxygen rise to near present concentrations and what led to this rise as kasting explains in his perspective recent results have provided stronger than ever evidence that the switch from an anoxic to an oxic atmosphere occurred around 2300 millions years ago but researchers remain divided over the mechanism catling et al resurrect a previously proposed mechanism involving hydrogen escape to space with a couple of new twists whether their mechanism is viable depends on the oxidation state of the continental and oceanic crust at this crucial time of earth9s evolution

the development of continental crust through geological time the south african case nd isotopic compositions and147sm144nd ratios were measured in fifty eight south african shales and greywackes with depositional ages ranging from 0 2 to 3 3 b y elements such as the rare earths which are poorly soluble in water and not fractionated during exogeneous processes preserve the signature of the original crustal source the147sm144nd ratios appear to be approximately constant throughout the time interval sampled we calculated nd model ages of crustal differentiation knowing that the shales represent a true blend of different continental areas we consider these model ages representative of the mean ages of their primitive continental sources then using the inverse technique developed by alle gre and rousseau in 1984 we computed a growth curve for the continental crust in south africa two periods of important crustal genesis archaean and around 1 5 b y can be compared with the observed geology and with other continental crust growth curves obtained in previous studies in southern africa and in australia the observation of large variations in the mgo content and ni cr u and th concentrations between archaean south african shales and post archaean samples compared to the constancy of the147sm144nd ratios leads us to propose that the archaean crust was composed of both granite 70 5 and a mafic component 29 5 which could have been komatiite the small dispersion of 147sm 144nd ratios suggests that erosion and sedimentation processes yielded homogeneous archaean shales the present day continental crust is much more heterogeneous because it has undergone several episodes of recycling thus recent shales are characterized by more variable 147sm 144nd ratios

the use of acoustic imaging to reveal fossil fluvial systems a case study from the southwestern sea of galilee abstract the analysis of reflected high resolution seismic data shows a distinct separation of regions with good and poor seismic penetration additional analysis of core data revealed good correlation between grain size and seismic penetration as a case study a shallow geophysical survey using a chirp profiler was conducted in the southwestern part of the sea of galilee by correlating the seismic and core data we found that areas with good seismic penetration represent coarse clastics while poor seismic penetration is related to fine clays new detailed bathymetric mapping and bottom morphology images combined with the penetration characteristics of the chirp signal reveal a large alluvial fan consisting mainly of coarse material sand to pebbles a fine grained band of mostly clay size material associated with an asymmetric bathymetric channel continues the trend of the old entrance of the yavniel creek into the sea of galilee we interpret the fine clay stripe to be a low energy streambed of the yavniel creek the clear relations between the reflected chirp signal and the grain size of the water bottom sediments suggests that this type of survey can be used to characterize depositional environments

secular environmental precursors to early toarcian jurassic extreme climate changes the early toarcian oceanic anoxic event t oae about 183 myr ago was a global event of environmental and carbon cycle perturbations which deeply affected both marine biota and carbonate production nevertheless the long term environmental conditions prevailing prior to the main phase of marine extinction and carbonate production crisis remain poorly understood here we present a similar to 8 myr long record of early pliensbachian middle toarcian environmental changes from the lusitanian basin portugal in order to address the long term paleoclimatic evolution that ultimately led to carbonate production and biotic crises during the t oae paleotemperature estimates derived from the oxygen isotope compositions of well reserved brachiopod shells from two different sections reveal a pronounced similar to 5 degrees c cooling in the late pliensbachian margaritatus spinatum ammonite zones boundary this cooling event is followed by a marked similar to 7 10 degrees c seawater warming in the early toarcian that after a second cooling event in the mid polymorphum zone culminates during the t oae calcium carbonate caco3 contents the amount of nannofossil calcite and the mean size of the major pelagic carbonate producer schizosphaerella all largely covary with paleotemperatures indicating a coupling between climatic conditions and both pelagic and neritic caco3 production furthermore the cooling and warming episodes coincided with major marine regressions and transgressions respectively suggesting that the growth and decay of ice caps may have exerted a strong control on sea level fluctuations throughout the studied time interval this revised chronology of environmental changes shows important similarities with neogene and paleozoic episodes of deglacial black shale formation and thus prompts the reevaluation of ice sheet dynamics as a possible agent of mesozoic events of extinction and organic rich sedimentation c 2010 elsevier b v all rights reserved

kerogen assemblages and δ13ckerogen of the uppermost pliensbachian lower toarcian succession of the asturian basin northern spain abstract the toarcian oceanic anoxic event toae is characterised by a perturbation of the global carbon cycle and the widespread deposition of organic matter om rich strata sediments in the northern areas of the west tethys shelf in several northern european epicontinental basins contrariwise in the southern areas of the west tethys shelf such as western and southern iberian and northern gondwana margins om rich strata sediments are spatially and temporally restricted to better understand the relationship between om production depositional conditions and palaeoceanographic controls on the occurrence of om rich facies in the northern iberian margin we collected and analysed 18 samples from the rodiles section asturian basin for geochemical total organic carbon toc total sulfur ts 13ckerogen and 13cwood and palynofacies analysis the studied upper pliensbachian lower toarcian succession has toc values reaching up to 2 9 wt the relative dominance of non opaque phytoclasts and the 13ckerogen values average of 24 in the lowermost toarcian tenuicostatum zone agrees with previous interpretations indicating that this area was located in a dominantly winter wet climate zone a change in the kerogen assemblages is observed at the tenuicostatum serpentinum zones boundary onset of toae related to an increase in amorphous om aom a slight increase in non opaque phytoclasts and terrestrial palynomorphs and a negative 13ckerogen excursion reaching 31 5 is recorded in the same interval these observations suggest a increase in continental weathering and fluvial runoff associated with more humid conditions likely resulting in increased superficial productivity and deposition and preservation of om under at least suboxic conditions above the toae interval the 13ckerogen record values around 24 and the drastic drop in toc and aom content indicate that bottom water oxygenation improved after the toae our results demonstrate a link between early toarcian climate dynamics and the deposition of om rich strata sediments

duration of the early toarcian carbon isotope excursion deduced from spectral analysis consequence for its possible causes abstract the marked 3 8 negative carbon isotope excursion associated with the early toarcian oceanic anoxic event oae 183 myr ago in the early jurassic period is thought to represent one of the most important perturbations of the c cycle in the last 200 myr however the origin of this excursion remains strongly debated primarily due to uncertainties in the estimation of its duration which ranges from 200 kyr to 1 myr here we present a new orbital calibration of the early toarcian carbon isotope excursion based on spectral analyses of two independent datasets generated from the sedimentary record of two hemipelagic sections from portugal peniche and sw germany dotternhausen in order to better constrain the timescale and hence the origin of this excursion these analyses reveal that orbital cycles exert a strong influence on both the calcium carbonate content in portugal and on the greyscale of black shales in germany which allow us to propose a duration of 1 9 myr for the early toarcian and of 900 kyr for the entire carbon isotope excursion the shift towards lower carbon isotope values lasted 150 kyr and carbon isotope values remained low for 450 kyr the subsequent increase of carbon isotope values lasted 300 kyr this calibration suggests that the sustained input of isotopically light carbon at the origin of the excursion occurred over 600 kyr and thus dismisses causal mechanisms implying relatively small source reservoirs such as the massive dissociation of methane hydrates in the light of our new cyclostratigraphic timescale the massive input of isotopically light carbon associated with the emplacement of the karoo ferrar basaltic province appears as the most likely cause of the toarcian global carbon isotope excursion we also show that the c isotope perturbation coincided with a transition from precession eccentricity dominated cycles to obliquity eccentricity dominated cycles suggesting that the oae was marked by a fundamental change in the response of the climate system which allowed the obliquity signal normally better recorded at high latitudes to be a dominant forcing factor of short term sedimentary cycles at tropical latitudes

saturated hydrocarbon biomarkers in oils of late precambrian age from eastern siberia abstract large quantities of petroleum derived from source rocks of late precambrian early cambrian age have been discovered in the lena tunguska region of eastern siberia over the last twenty five years we have examined three oils with presumed late precambrian vendian source rocks from this region for c 15 saturated hydrocarbon biomarkers using gas chromatography gc and gas chromatography mass spectrometry gc ms our results show these oils to have many characteristics in common with other oils of similar age from eastern siberia and oman amongst the compounds detected in the three oils analyzed were 1 n alkanes which show a marine derived distribution 2 centrally branched monomethyl alkanes 3 acyclic isoprenoids pr ph 1 4 tricyclic and tetracyclic terpanes 5 hopanes 6 c 29 unrearranged steranes and 7 c 30 nuclear steranes all of these compounds with the exception of the 4 methylsteranes which on current biochemical knowledge are unexpected in oils of this age can be assigned a prokaryotic source this and other evidence such as the lack of diasteranes suggest microorganism were the major contributors to organic matter deposited as part of a carbonate source rock

toarcian oceanic anoxic event induced unusual behaviour and palaeobiological changes in thalassinoides tracemakers abstract the early toarcian early jurassic global marine mass extinction is associated with one of the most important environmental perturbations of the mesozoic the toarcian oceanic anoxic event t oae usually interpreted as a global oceanic anoxic event in the lusitanian basin lb one of the reference areas for the study of the t oae despite an elevated extinction rate among marine invertebrates the anoxia hypothesis has been discarded based on geochemical and isotopic data in the fonte coberta section the t oae is characterised by the extinction of the previously well represented brachiopod taxa a decreased abundance of ammonoids and the establishment of a well developed endobenthic community mainly composed by thalassinoides tracemaker which indicates favourable environmental parameters at least for this community thus the palaeoenvironmental changes associated with the t oae event bear a minor incidence on the macrobenthic tracemaker community at the level of extinctions and changes in diversity or abundance yet they exert a major effect on the behaviour and palaeobiology of tracemakers the thalassinoides specimens show an exclusively horizontal development and unusual architectural features during the extinction interval tied to behavioural adaptations to nutrient availability and or substrate firmness smaller burrow diameters are registered at the base of the t oae and then an increase is observed during the t oae this could be associated with a palaeobiological response lilliput effect to palaeoecological changes at the beginning of the t oae followed by a progressive change to pre event environmental parameters this study therefore sheds light on how environmental alterations can determine specific behavioural and palaeobiology changes of the producer as reflected by variations in significant features of thalassinoides architecture

changes in foraminiferal assemblages and environmental conditions during the t oae early jurassic in the northern lusitanian basin portugal abstract the foraminiferal assemblages and other microfossils from the rabacal area maria pares section in the lusitanian basin portugal provide new insights regarding the toarcian oceanic anoxic event t oae complementary analysis of the 13c total organic carbon toc and geochemical redox and palaeoproductivity proxies reflect environmental changes that affected the microfossil assemblages detailed analyses of foraminiferal assemblages their diversity abundance morphogroups and lifestyle and geochemistry led us to discern phases of the biotic crisis and subsequent stages of recovery environmental instability which began in the lattermost part of the polymorphum zone is marked by a lesser abundance of foraminifera and ostracods increased opportunist foraminifera fluctuations in toc values and the enrichment factor of phosphorous pef as well as the onset of a negative carbon isotopic excursion cie the peak phase of the biotic crisis corresponds with the lowest values for foraminiferal diversity and abundance including a barren sample for benthic microfossils the abundance and diversity of echinoderms brachiopods dinoflagellate cysts and calcareous nannofossils dropped sharply during the peak phase this biotic crisis also entails extinction of the order metacopina and a local disappearance of echinoderms and brachiopods anoxic conditions at sea bottom did not develop given the almost continuous record of foraminifera and trace fossils yet oxygen depleted conditions occurred the lower part of the levisoni zone contains thin nodular limestones corresponding to a tempestitic turbiditic facies in this context the re oxygenation of bottom waters was favoured as indicated by the presence of thalassinoides and the low values of toc and redox sensitive elements mo ni and u the survival phase in the wake of the biotic crisis is characterized by greater diversity and abundance of foraminifera and echinoderms holothuroids and ophiuroids the lowest 13c values are recorded during this phase with a dominance of opportunist eoguttulina and facultative opportunist paralingulina tenera foraminifera finally recovery after the biotic crisis is evidenced by high values for specialists and potentially deep infaunal foraminifera indicating oxic conditions in the sediment

update of the carbon and oxygen isotopic records of the early late pliensbachian early jurassic 187ma insights from the organic rich hemipelagic series of the lusitanian basin portugal abstract a high resolution carbon and oxygen isotopic bulk carbonate record from organic rich hemipelagic series of early late pliensbachian age 187 ma is presented for the lusitanian basin portugal and compared to the record of other sedimentary basins this dataset provides an excellent basis for discussing newly raised questions concerning the hypothesis of major carbon cycle perturbations prior to the toarcian oceanic anoxic event in addition to the recognition in the studied series of two positive carbon isotope excursions previously defined elsewhere corresponding to the ibex and margaritatus uppermost stokesi gibbosus subzones zones a third positive excursion is identified here for the first time at the davoei zone in the lusitanian basin these excursions are associated with organic rich facies intervals the younger excursion may be related to worldwide enhanced preservation of organic matter in the margaritatus zone we suggest that until these organic rich facies are well age constrained at a wider scale and high resolution carbon data are provided from other locations and that worldwide anoxia is proven this interval should be referred to as an organic matter preservation interval late pliensbachian ompi this period is probably linked with the complex chain of events that eventually led to the toarcian oceanic anoxic event

structural control of groundwater flow regimes and groundwater chemistry along the lower reaches of the zerka river west jordan using remote sensing gis and field methods a hydrogeological study was completed within a sub catchment of the zerka river drainage basin in western jordan the system is characterized by anticlinal bending with an axis trending ssw nne and plunging a few degrees in the ssw direction the anticlinal structure diverts groundwater flow towards the ssw while the strike slipe faults cause the groundwater to diverge where the fault is perpendicular to the groundwater flow lines and to converge where the fault is parallel to the groundwater flow lines a direct relationship was found between the location of springs and the type of groundwater flow with regard to the amount of discharge wherein large spring discharges are located in zones of converging groundwater flow lines in areas where faults are not abundant the groundwater retention time in the aquifers is long and a zonation of the electrical conductivity was detected due to mineral dissolution by controlling groundwater flow the anticlinal setting produces three genetic groups of groundwater flow systems 1 alkaline earth alkaline water which is predominately a bicarbonate type composition 2 alkaline earth alkaline water which is predominately bicarbonate sulfate and 3 alkaline earth alkaline water with a high alkaline component

evidence for major environmental perturbation prior to and during the toarcian early jurassic oceanic anoxic event from the lusitanian basin portugal the timing and causal relationships between the pronounced negative c isotope excursion and paleoenvironmental perturbations associated with the toarcian oceanic anoxic event early jurassic remain unclear particularly because biotic crises and carbonate production decrease appear to have been initiated earlier than the main c isotope anomaly here we present a new quantification of late pliensbachian early toarcian calcareous nannofossils abundance and size from the peniche reference section portugal together with o and c isotope records of well preserved brachiopod shells from the same section the brachiopod shell 13c curve parallels that of bulk carbonate and records two pronounced negative isotopic excursions close to the pliensbachian toarcian boundary 2 and during the toarcian oceanic anoxic event 3 5 our results indicate that both c isotope negative excursions were characteristic of benthic and shallow water environments suggesting that these two carbon cycle perturbations affected all epioceanic reservoirs coeval shifts toward lower values of brachiopod oxygen isotope compositions and closely correlated northward migrations of mediterranean ammonite fauna suggest that both events coincided with major rises in seawater temperatures probably as a result of increased co2 levels and enhanced greenhouse conditions co2 induced changes in seawater chemistry likely affected the calcification potential of both neritic and pelagic systems as evidenced by synchronous drops of platform derived carbonate accumulation and drastic reductions in size 3 m of the main pelagic carbonate producer schizosphaerella we suggest that the early toarcian paleoenvironmental crisis occurred in two distinct episodes that were most likely related to two successive phases of intense volcanic degassing in the karoo ferrar province

carbon isotope record of the early jurassic toarcian oceanic anoxic event from fossil wood and marine carbonate lusitanian basin portugal thetoarcianoceanicanoxicevent oae intheearlyjurassic 183maago wascharacterizedbywidespreadnear synchronous deposition of organic rich shales in marine settings as well as perturbations to several isotopic systems characteristically two positive carbon isotope excursions in a range of materials are separated by an abrupt negative shift carbon isotope profiles from toarcian fossil wood collected in england and denmark have previously been shown to exhibit this large drop 7 i n 13 c values interpreted as due to an injection of isotopically light co2 into the ocean atmosphere system however the global nature of this excursion has been challengedonthebasisofcarbon isotopedatafromnektonicmarinemolluscs belemnites whichexhibitheavierthanexpectedcarbonisotope values here we present new data principally from fossil wood and bulk carbonate collected at centimetre scale from a hemipelagic section at peniche coastal portugal this section is low in organic carbon average toc 0 5 and the samples should not have suffered significant diagenetic contamination by organic carbon of marine origin the carbon isotope profile based on wood shows two positive excursions separated by a large and abrupt negative excursion which parallels exactly the profile based on bulk carbonate samples from the same section albeit with approximately twice the amplitude 8 in wood versus 3 5 in carbonate these data indicate thatthe negative carbon isotope excursion affected the atmosphereand by implication the global ocean as well the difference in amplitude between terrestrial organic and marine carbonate curves can be explained by greater water availability in the terrestrial environment during the negative excursion for which there is independent evidence from marine osmiumisotope records and plausibly changes in atmospheric co2 content for which independent evidence is also available the peniche succession is also notable for the occurrence of re deposited sediments their lowest occurrence coincides with the base of the negative excursionandtheirhighestoccurrencecoincideswithitstop thus slopeinstabilityandsedimentsupplycouldhavebeenstronglylinked to the global environmental perturbation an association that may misleadingly simulate the effects of sea level fall

developing a structural and conceptual model of a tectonically limited karst aquifer a hydrogeological study of the hastenrather graben near aachen germany interdisciplinary and comprehensive field work combining hydraulic and geophysical experiments yielded an improved understanding of the fractured and partly karstified kohlenkalk aquifer in the hastenrather graben near aachen germany the aquifer is used for drinking water production and located in a geologically and tectonically complex area shaped by various tectonic events a workflow which combines implicit 3d structural modeling with hydrogeological conceptual model building enabled determining hydrogeological boundary conditions at specific boundary cross sections calculating the aquifer volume and analyzing the hydraulic influence of faults on the aquifer system electrical resistivity tomography seismic refraction tomography well logging and a coring campaign combined with available maps and additional literature research served as basis for the setup of the 3d structural model this 3d model comprises all important structural elements including the fault system deep folded structures and thrusts in the graben center integration of geological structure and hydraulic studies yielded a conceptual model of the hydrogeology describing the kohlenkalk aquifer and neighboring layers hydraulic conductivity of the aquifer system varies between 6 0 10 7 and 6 4 10 4 m s 1 with a decreasing trend from the ne graben shoulder to the graben center analysis of piezometric heads and resulting groundwater contour maps indicated four hydrogeological units which are partly limited by faults data on groundwater recharge as well as anthropogenic influences on the groundwater resources are part of the conceptual model

flat pebble conglomerates a local marker for early jurassic seismicity related to syn rift tectonics in the sesimbra area lusitanian basin portugal flat pebble conglomerates have been identified in the lower toarcian levisoni zone carbonates of the sesimbra region 30 km south of lisboa portugal and related to submarine mass movements their origin is explained through a three stage model based on the comparative analysis of potential generating mechanisms taking into account timing and type of geodynamic evolution in the lusitanian basin a differential lithification of thin carbonate and non bioturbated horizons embedded within a more argillaceous matrix b disruption by seismic shocks related to active extensional faulting and block tilting and c gravity sliding mixing material resulting from broken lithified horizons this sequential process originated flat pebble conglomerates during early jurassic phases of syn rift evolution in the southern lusitanian basin q 2001 elsevier science b v all rights reserved

a carbonate submarine fan sequence from the jurassic of portugal abstract a prograding carbonate submarine fan sequence is described from the toarcian aalenian of western portugal the sequence is predominantly composed of shallow water carbonate grains but can be interpreted using the current siliclastic submarine fan models basin plain to outer fan braided channel midfan and large channel fill sequences can be recognized the source of the carbonate grains was a platform developed on an uplifted hercynian horst to the west of present mainland portugal the fan sequence overlies restricted basin deposits with organic rich mudstones and shales this association of restricted basin facies and a thick over 300 m carbonate grainstone could be an attractive hydrocarbon play however such limestone sequences are easily misinterpreted as in situ shelf carb nates

development of a 3d groundwater model based on scarce data the wadi kafrein catchment jordan in this work a 3d groundwater flow model integrating all important geological features of the hydrogeological system is developed to investigate hydrological processes in the wadi kafrein area of jordan a large amount of available geological and hydrological data is integrated to construct a 3d groundwater flow model for the wadi kafrein area using the newly developed mapping approach the translation of the highly detailed geological formations to an unstructured finite element grids can be accomplished with high precision the existing data set for model calibration is scarce which is a typical situation for many hydrogeological case studies at first the steady state calibration of the groundwater model is carried out based on the observation wells then the time and space dependent recharge from precipitation are applied at the top surface of the finite element model the transient simulation is conducted during the period of 1996 2008 considering the abstraction rates of the production wells and discharge of the springs the calculated water levels are close to the observed values the difference is partly caused by return flows from irrigation and the groundwater inflow from the adjacent aquifers which are not taken into consideration so far since the wadi kafrein area is an important agricultural area in the semiarid region of the lower jordan valley the model developed in this study can be regarded as a useful tool for analyzing the hydrological processes and improving groundwater management practices elsewhere affected by similar geological and hydrogeological conditions

a paleoweathering profile from griqualand west south africa evidence for a dramatic rise in atmospheric oxygen between 2 2 and 1 9 bybp a core drilled near wolhaarkop in griqualand west south africa intersected highly oxidized kuruman iron formation below red beds of the gamagara formation the lateral equivalents of the kuruman iron formation in this drill hole consist largely of siderite ankerite magnetite greenalite and quartz the oxidation of the kuruman iron formation in wol 2 occurred almost certainly during weathering prior to the deposition of the gamagara formation the date of this weathering episode is bracketed between about 2 2 and 1 9 bybp by the age of the ongeluk lavas in the transvaal sequence below the unconformity and by the age of the hartley lavas in the olifantshoek group above the unconformity the ratio of iron to sio2 in the several facies of the weathered kuruman iron formation in wol 2 is nearly the same as that in their unweathered equivalents since sio2 loss during weathering was almost certainly minor the similarity of the fe sio2 ratio in the weathered and unweathered bif indicates that nearly all the feo in the kuruman iron formation was oxidized and retained as feo3 during weathering such a high degree of iron retention is best explained by an o2 content of the atmosphere or 0 03 atm at the time of weathering such an o2 pressure is very much greater than that suggested by the composition of paleosols developed on basalt or 2 2 bybp but is consistent with the highly oxidized nature of the 1 85 by flin flon paleosol the new data suggest that po2 rose dramatically from about 1 percent pal present atmospheric level to or 15 percent pal between 2 2 and 1 9 bybp

the biogeochemistry of ellesmere lake u k i source correlation of leaf wax inputs to the sedimentary lipid record abstract analyses of the free lipid distributions from ellesmere lake sediments taken from two depths and comparison with leaf wax lipid distributions from six deciduous tree species around the lake were made in order to assess lipid sources close correlations of aliphatic lipid distributions in the carbon number range c 20 c 50 were seen c 28 and c 29 sterols were observed in both sediment and leaf waxes but c 27 sterols were only present in the sediments and were thus assigned a nonleaf wax source unsaturated steroidal ketones were observed both in the sediment and in certain leaf waxes and were assigned specific sources alkan 2 ones were not present in the leaf waxes but were present in the sediment samples with an almost identical distribution to the sediment n alkanes indicating a microbially mediated source c 20 c 30 n aldehydes which have not previously been widely reported in free lipid distributions of freshwater lacustrine sediments were prominent in the surface sediment and in the leaf waxes examined

the tectonic framework of a complex pull apart basin seismic reflection observations in the sea of galilee dead sea transform abstract a multi channel seismic reflection survey consisting of 20 lines with a total length of 180 km was conducted in the sea of galilee the data provide new insights into the pliocene quaternary evolution of the kinarot beit shean pull apart basin kbsb along the dead sea transform two distinct zones are defined beneath the lake 1 a graben that underlies most of the lake bounded by steep north south longitudinal strike slip faults and 2 shallow pre rift units underlying the northwestern wider part of the lake we suggest that before approximately 4 ma the kbsb grew due to northward movement of the korazim plateau and by crustal stretching along the rift axis since the pliocene 4 ma lateral slip has been transferred from the southern segment of the basin s western marginal fault to normal faults in the galilee and to the eastern margin of the korazim plateau by the newly formed almagor fault which makes a restraining bend along the transform n s lithospheric stretching below the kbsb has diminished and the korazim plateau has changed from being a detached block to a compressional saddle a phase of rapid subsidence and formation of a half graben structure in the northern part of the basin approximately 1 ma ago was coeval with major deformation in areas adjacent to the kbsb indicating major reorganization of the plate boundary in the region currently most transform motions are probably taken up along a single fault on the eastern side of the kbsb implying that the main trough under the sea of galilee is in a late stage of growth as a pull apart

determination of molybdenum isotope fractionation by double spike multicollector inductively coupled plasma mass spectrometry 1 molybdenum isotopic compositions are precisely determined by mc icp ms measurements using a mo double spike the double spike is added prior to chemical purification so that laboratory and instrumental mass fractionations are separated from natural mass dependent fractionation fractionation is determined on four mo mass ratios providing an internal consistency check the external standard reproducibility is at 0 06 per mil on the 98mo 95mo ratio 2 standard deviation using a normal microconcentric nebuliser with a cyclonic spray chamber the minimum quantity of mo is 1 g for high precision results a hydrothermal molybdenite shows fractionation of 0 3 per mil on the 98mo 95mo ratio relative to our standard johnson matthey 1000 g ml 0 3 icp standard solution lot 602332b fine grained sediments show fractionation of 0 1 and 0 3 per mil on the 98mo 95mo ratio the observed mo isotope fractionation is small but resolvable with the presented high resolution technique

gravity field over the sea of galilee evidence for a composite basin along a transform fault the sea of galilee lake kinneret is located at the northern portion of the kinneret bet shean basin in the northern dead sea transform three hundred kilometers of continuous marine gravity data were collected in the lake and integrated with land gravity data to a distance of more than 20 km around the lake analyses of the gravity data resulted in a free air anomaly map a variable density bouguer anomaly map and a horizontal first derivative map of the bouguer anomaly these maps together with gravity models of profiles across the lake and the area south of it were used to infer the geometry of the basins in this region and the main faults of the transform system the sea of galilee can be divided into two units the southern half is a pull apart that extends to the kinarot valley south of the lake whereas the northern half was formed by rotational opening and transverse normal faults the deepest part of the basinal area is located well south of the deepest bathymetric depression this implies that the northeastern part of the lake where the bathymetry is the deepest is a young feature that is actively subsiding now the pull apart basin is almost symmetrical in the southern part of the lake and in the kinarot valley south of the lake this suggests that the basin here is bounded by strike slip faults on both sides the eastern boundary fault extends to the northern part of the lake while the western fault does not cross the northern part the main factor controlling the structural complexity of this area is the interaction of the dead sea transform with a subperpendicular fault system and rotated blocks

sources of groundwater salinity along the flow path disi dead sea jordan the groundwater along the eastern escarpment of the dead sea shows a variety of chemical compositions with ec values ranging between 500 and a few thousand s cm in this article the different groundwaters were correlated to the aquifers from where they originate and the water rock interactions were elaborated at it was found that the start of intercalations of permo triassic and jurassic rocks in the area and the basaltic dykes and sills are the sources which cause a drastic increase in the salinity of the water these rocks contents of residual evaporites contact metamorphism products sills dykes and secondary altered mineral assemblage of plagioclase pyroxenes and fe mn minerals cause also drastic changes in ionic ratios saturation indices and groundwater types fresh groundwater flows entering the area become gradually after a few kilometres highly salinized and of earthalkali type with prevailing chloride and sulfate instead of being bicarbonate waters

warming driven mass extinction in the early toarcian early jurassic of northern and central spain correlation with other time equivalent european sections abstract causes of the major mass extinction recorded during the early toarcian early jurassic are controversial many authors have concluded that the mass extinction is caused by the widespread oceanic anoxia derived from a postulated early toarcian oceanic anoxic event etoae supposedly synchronous in all basins and global in extent another group of papers links the mass extinction with a major climate change that occurred synchronously with the mass extinction the results of the study of five sections of the uppermost pliensbachian and lower middle toarcian deposits located in northern and central spain are presented detailed ammonite based biostratigraphy coupled with stable isotope analysis of belemnite calcite and bulk carbonates as well as total organic carbon toc analyses have been performed in all sections records of the vertical distribution of mainly benthic fossils have been compiled in four of the studied sections results obtained in the spanish outcrops have been compared and correlated with other european sections the excellent mutual relation between the patterns of the early toarcian progressive warming and the concomitant progressive losses of species evidences a cause and effect relationship between the increase of temperature and the mass extinction from an uppermost pliensbachian cooling interval warming started at the lower toarcian tenuicostatum zone increase of average seawater palaeotemperature is associated with a progressive and substantial drawdown in the number of species of nektonic planktonic and benthic organisms representing the extinction interval a prominent increase in seawater temperature occurred around the lower toarcian tenuicostatum serpentinum zonal boundary average temperatures at the serpentinum zone increased about 7 c marking the extinction boundary the high temperatures continued during the middle toarcian bifrons chronozone representing the repopulation interval the anoxia linked to the postulated etoae cannot be the responsible for the mass extinction because it has been synchronously recorded in the oxygenated environments of many european and northern african platforms deposition of laminated organic rich black shale facies above 5 wt toc indicating anoxic environments was mostly confined geographically to the western europe euxinic basin and mainly deposited after the extinction event during the interval of faunal recovery

pge re os and mo isotope systematics in archean and early proterozoic sedimentary systems as proxies for redox conditions of the early earth abstract re os data and pge concentrations as well as mo concentrations and isotope data are reported for suites of fine clastic sediments and black shales from the barberton greenstone belt south africa fig tree and moodies groups 3 25 3 15 ga the belingwe greenstone belt zimbabwe manjeri formation ca 2 7 ga and shales from the witwatersrand ventersdorp and transvaal supergroups south africa ranging from 2 95 to 2 2 ga moderately oxidizing conditions are required to mobilize re and mo in the environment mo fractionation only occurs in solution and these parameters thus have potential use as paleoredox proxies for the early earth pge re abundance patterns of barberton greenstone belt sediments are uniform and very similar in shape to those of komatiites this indicates 1 that the pge came from a source of predominantly ultramafic composition and 2 that pge were transported and deposited essentially in particulate form sediments from the younger belingwe greenstone belt show more fractionated pge re patterns and have re os ratios 10 to 100 higher than those of barberton sediments their pge abundance patterns and re os ratios are intermediate between those of the mid archean shales and neoproterozoic to recent black shales they reflect scavenging of re from solution in the sedimentary environment 98 95 mo values of black shales of all ages correlate with their concentrations the barberton greenstone belt samples have 1 3 ppm mo similar to a granitoid basaltic source this mo has 98 95 mo between 1 9 and 2 4 relative to present day mean ocean water molybdenum momo and is thus not isotopically fractionated relative to such a source similar to the pge this indicates transport in solid form sediments from the belingwe greenstone belt show in part enhanced mo concentrations up to 6 ppm and mo isotope fractionation 98 95 mo up to 1 4 relative to momo the combined pge re and mo data show mainly reducing conditions in the mid archean and suggest that by 2 7 ga the atmosphere and oceans had become more oxidizing substantially younger samples from the transvaal supergroup to ca 2 2 ga surprisingly have mainly low mo concentrations around 1 ppm and show no significant mo isotope fractionation relative to the continental source among possible explanations for this are a return to reducing atmospheric conditions after 2 7 ga reservoir effects or mo removal by sulfide precipitation following sulfate reduction in early proterozoic oceans

near east paleomagnetic secular variation recorded in sediments from the sea of galilee lake kinneret abstract paleomagnetic records of declination and inclination from sediments recovered from the bed of lake kinneret 32 4 n 35 7 e have been dated by radiocarbon techniques the sediments span the last 5000 yr the changes in inclination down the sediment cores are more pronounced than the declination fluctuations and are repeatable between the three coring sites which are several kilometers apart magnetic susceptibility logs display 13 maxima in the 5 m long sequences with a pronounced susceptibility minimum about 1000 yr b p many of the susceptibility maxima and minima can be easily correlated between coring sites and are shown to be dominantly related to changes in sediment carbonate content the natural remanent magnetization intensity follows a similar pattern to that of susceptibility and the natural remanence of the kinneret sediments is presumed to reside in detrital magnetite grains carried into the lake by the river jordan from the basalt rich bedrock of the rift floor and the golan heights the 14c chronology is strongly supported by a pollen study in which pronounced changes in the proportion of olive pollen were interpreted as being due to extensive cultivation of olives around galilee in the hellenistic and byzantine periods the kinneret paleosecular variation records if accurately dated point to a complex spatial pattern of holocene secular variation with significant variations over distances as small as 1000 2000 km

hydrochemical variation in the springs water between jerusalem ramallah mountains and jericho fault palestine the spatial and temporal changes of the composition of the groundwater from the springs along the wadi qilt stream running from the jerusalem ramallah mountains towards the jericho plain is studied during the hydrological year 2006 2007 the residence time and the intensity of recharge play an important role in controlling the chemical composition of spring water which mainly depends on distance from the main recharge area a very important factor is the oxidation of organics derived from sewage and garbage resulting in variable dissolved co2 and associated hco3 concentration high co2 yields lower ph values and thus under saturation with respect to calcite and dolomite low co2 concentrations result in over saturation only at the beginning and at the end of the rainy season calcite saturation is achieved the degradation of dissolved organic matter is a major source for increasing water hardness besides dissolution of carbonates dissolved species such as nitrate chloride and sulfate are leached from soil and aquifer rocks together with only small amounts of mg mg not only originates from carbonates but also from mg cl waters are leached from aquifer rocks leaching of mg cl brines is particularly high at the beginning of the winter season and lowest at its end two zones of recharge are distinguishable zone 1 represented by ein fara and ein qilt is fed directly through the infiltration of meteoric water and surface runoff from the mountains along the eastern mountain slopes with little groundwater residence time and high flow rate the second zone is near the western border of jericho at the foothills which is mainly fed by the under groundwater flow from the eastern slopes with low surface infiltration rate this zone shows higher groundwater residence time and slower flow rate than zone 1 groundwater residence time and the flow rate within the aquifer systems are controlled by the geological structure of the aquifer the amount of active recharge to the aquifer and the recharge mechanism the results of this study may be useful in increasing the efficiency of freshwater exploitation in the region some precautions however should be taken in future plans of artificial recharge of the aquifers or surface water harvesting in the wadi because of evaporation and associated groundwater deterioration the runoff water should be artificially infiltrated in zones of wadis with high storage capacity of aquifers natural infiltration along the wadis lead to evaporation losses and less quality of groundwater

numerical analysis of the groundwater regime in the western dead sea escarpment israel west bank water is scarce in the semi arid to arid regions around the dead sea where water supply mostly relies on restricted groundwater resources due to increasing population in this region the regional aquifer system is exposed to additional stress this results in the continuous decrease in water level of the adjacent dead sea the interaction of an increasing demand for water due to population growth and the decrease of groundwater resources will intensify in the near future thus the water supply situation could worsen significantly unless sustainable water resource management is conducted in this study we develop a regional groundwater flow model of the eastern and southern judea group aquifer to investigate the groundwater regime in the western dead sea drainage basin of israel and the west bank an extensive geological database was developed and consequently a high resolution structural model was derived this structural model was the basis for various groundwater flow scenarios the objective was to capture the spatial heterogeneity of the aquifer system and to apply these results to the southern part of the study area which has not been studied in detail until now as a result we analyzed quantitatively the flow regime the groundwater mass balance and the hydraulic characteristics hydraulic conductivity and hydraulic head of the cretaceous aquifer system and calibrated them with pest the calibrated groundwater flow model can be used for integrated groundwater water management purposes in the dead sea area especially within the framework of the sumar project

aspects of the structural evolution of the lusitanian basin in portugal and the shelf and slope area offshore portugal abstract the study provides a regional seismic interpretation and mapping of the mesozoic and cenozoic succession of the lusitanian basin and the shelf and slope area off portugal the seismic study is compared with previous studies of the lusitanian basin from the late triassic to the cretaceous the study area experienced four rift phases and intermittent periods of tectonic quiescence the triassic rifting was concentrated in the central part of the lusitanian basin and in the southernmost part of the study area both as symmetrical grabens and half grabens the evolution of half grabens was particularly prominent in the south the triassic fault controlled subsidence ceased during the latest late triassic and was succeeded by regional subsidence during the early early jurassic hettangian when deposition of evaporites took place a second rift phase was initiated in the early jurassic most likely during the sinemurian pliensbachian this resulted in minor salt movements along the most prominent faults the second phase was concentrated to the area south of the nazare fault zone and resulted here in the accumulation of a thick sinemurian callovian succession following a major hiatus probably as a result of the opening of the central atlantic resumed deposition occurred during the late jurassic evidence for late jurassic fault controlled subsidence is widespread over the whole basin the pattern of late jurassic subsidence appears to change across the nazare fault zone north of the nazare fault fault controlled subsidence occurred mainly along nnw sse trending faults and to the south of this fault zone a nne ssw fault pattern seems to dominate the oxfordian rift phase is testified in onlapping of the oxfordian succession on salt pillows which formed in association with fault activity the fourth and final rift phase was in the latest late jurassic or earliest early cretaceous the jurassic extensional tectonism resulted in triggering of salt movement and the development of salt structures along fault zones however only salt pillow development can be demonstrated the extensional tectonics ceased during the early cretaceous during most of the cretaceous regional subsidence occurred resulting in the deposition of a uniform lower and upper cretaceous succession marked inversion of former normal faults particularly along ne sw trending faults and development of salt diapirs occurred during the middle miocene probably followed by tectonic pulses during the late miocene to present the inversion was most prominent in the central and southern parts of the study area in between these two areas affected by structural inversion fault controlled subsidence resulted in the formation of the cenozoic lower tagus basin northwest of the nazare fault zone the effect of the compressional tectonic regime quickly dies out and extensional tectonic environment seems to have prevailed the miocene compressional stress was mainly oriented nw se shifting to more n s in the southern part

palynofacies and organic geochemistry of the sinemurian carbonate deposits in the western lusitanian basin portugal coimbra and agua de madeiros formations abstract the lower jurassic in the lusitanian basin portugal is mainly represented by hemipelagic carbonated deposits rich in organic matter om in this study supported by a high resolution stratigraphic and sedimentological framework the analysis of the om content of the coimbra and agua de madeiros formations in the reference outcrop sections of s pedro de moel and peniche is presented this is a multidisciplinary approach to the study of 31 samples in these series supported by organic petrography palynofacies spore coloration index sci and random vitrinite reflectance rr and organic geochemistry total organic carbon toc and biomarkers the palynofacies analysis provides evidence that the om is mainly composed of particles belonging to the amorphous organic matter aom group the phytoclasts correspond mostly to the non opaque translucent subgroup generally degraded and oxidized with significant representation in some stratigraphic levels of the coimbra formation and the polvoeira member at peniche the palynomorphs are mainly composed of classopollis pollen grains zygospores acritarchs and prasinophyte phycomata the toc data confirm that most samples are om rich with some stratigraphic horizons of the coimbra formation reaching 8 8 wt the predominance of marine om was confirmed by the pr nc17 and ph nc18 ratios the pr fi and homohopane ratios c35 c34 indicate that some stratigraphic horizons were deposited under dysoxic anoxic conditions despite the organic rich nature of these two units the random vitrinite reflectance rr 0 45 the spore coloration index 3 0 4 0 and the presence of hopanes suggest that these rocks in terms of om maturity are thermally immature

evidence for extensive basalt flows on the sea floor spatially limited strong acoustic reflectors interbedded with turbidite sediments appear in abundance in the region flanking the dellwood knolls northeast pacific where turbidite sediments nearly cover a newly formed spreading center near the continental margin off central british columbia in the median valley similar reflective layers are seen within the sediments as well as on the sediment surface and the conclusion has been made that all of the strong reflections are from extensive basalt flows which have had their source at the dellwood knolls and have been subsequently buried by rapid sedimentation the smooth gently sloping turbidite sediment surface appears to provide an ideal base over which flows can travel easily some of the flows are seen as far as 60 km from their source evidence for the existence of extensive flows is also found on the juan de fuca ridge where at one location the regional topographic relief of the axial valley floor along a 30 km section of the ridge axis is only 30 m such extreme low relief must be due in part to extensive basalt flows a simple model for the cooling of an underwater flow yields the general dependence of the flow extent on such parameters as the flow thickness and initial temperature as an example a flow 1 m thick can probably travel several kilometres if erupted at 1 250 c even the most extensive flows observed need be only about 3 m thick if erupted at this temperature

late pliensbachian early toarcian palaeoenvironmental dynamics and the pliensbachian toarcian event in the middle atlas basin morocco abstract geochemical and palynofacies analysis of 38 samples from the middle atlas basin ait moussa and issouka sections morocco allowed to investigate sea level changes climate and tectonics and impact on depositional environments in the westernmost tethyan gondwana margin during the late pliensbachian early toarcian and the pliensbachian toarcian event pl toa event the studied sections from the middle atlas basin have low total organic carbon contents overall kerogen assemblages are dominated by the phytoclast group thus showing a strong terrestrial affinity and some degree of proximity to the source deposition occurred dominantly in oxic and proximal environments upper pliensbachian kerogen assemblages from ait moussa are dominated by terrestrial particles and agree with the overall regressive character of the sedimentary succession uppermost pliensbachian lowermost toarcian kerogen assemblages from ait moussa show an increase in marine particles considering the overall sedimentological context of the middle atlas basin these kerogen assemblages are interpreted to reflect local variation in accommodation space driven by different sedimentation rates or tectonic compartmentalization or ecological conditions such as nutrient availability temperature turbidity etc in the early toarcian above a major regional discontinuity and at the beginning of the pl toa event increases in botryococcus sp aom and terrestrial palynomorphs suggest episodes of coastal erosion associated with transgression likely driven by a combination of eustatic tectonic changes and warmer and more humid climates leading to an increase in continental weathering and fluvial runoff on the other hand increases in sporomorphs and pollen grains occurring in tetrads and agglomerates indicate regressive episodes associated with increased sedimentation rates driven by enhanced continental weathering and fluvial runoff this study shows the strong relationship between sea level and the combined response of litho hydro and biosphere during the early toarcian with implications to understand organic productivity and organic matter accumulation and preservation in the tethys ocean during the pl toa event

rhenium in the black sea comparison with molybdenum and uranium rhenium concentrations were measured in the black sea to determine the behavior of this redox sensitive element in an anoxic basin under reducing conditions re is removed from solution leading to its depletion from black sea deep waters compared with uranium water column re and mo profiles show evidence of removal from mid depths suggesting that these elements are scavenged either in the water column or slope sediments to a greater degree than u black sea surface waters are enriched in re reflecting re in rivers draining into the northern black sea that are enhanced up to 80 fold over other large world rivers this enrichment is most likely anthropogenic and may be due to coal burning in the region a simple two box model is used to demonstrate that re concentrations in the black sea are not in steady state with respect to current riverine inputs and authigenic fluxes riverine inputs of u and mo are not as significant perhaps reflecting the fractionation of re from the other elements during a high temperature combustion process re2o7 is volatile above 270 c

molybdenum isotope fractionation during adsorption by manganese oxides the isotopic composition of mo 97 95mo in seawater is 2 heavier than mo in marine ferromanganese crusts and nodules barling et al earth planet sci lett 193 2001 447 457 siebert et al earth planet sci lett 211 2003 159 171 to explore this phenomenon we have conducted an experimental investigation into the mass dependent fractionation of mo isotopes during adsorption onto mn oxyhydroxide two series of experiments were carried out a time series in which adsorption proceeded for 2 96 h and a ph series in which ph varied from 6 5 to 8 5 the extent of mo adsorption by mn oxyhydroxides decreases with increasing ph a trend typical of anion adsorption and takes 48 h to reach steady state lighter mo isotopes are preferentially adsorbed experimentally determined fractionation factors soln mnox exhibit no systematic variation with either time or experimental ph the mean soln mnox for all experiments is 1 0018 0 0005 2 s d comparison of the mo isotopic data for experimental solutions and mo adsorbed to mn oxyhydroxide with predictions for closed system equilibrium and rayleigh fractionation models indicates that isotope fractionation occurs as a result of closed system equilibrium exchange between dissolved and adsorbed mo the isotopic offset between dissolved and adsorbed mo is comparable to that observed between mo in seawater and mo in ferromanganese nodules and crusts it is therefore likely that adsorption of mo to mn oxyhydroxides is a significant factor in the fractionation of mo isotopes in the oceans

rhenium and osmium isotopes in black shales and ni mo pge rich sulfide layers yukon territory canada and hunan and guizhou provinces china rhenium and osmium abundances and osmium isotopic compositions were determined by negative thermal ionization mass spectrometry for samples of devonian black shale and an associated ni enriched sulfide layer from the yukon territory canada the same composition information was also obtained for samples of early cambrian ni mo rich sulfide layers hosted in black shale in guizhou and hunan provinces china this study was undertaken to constrain the origin of the pge enrichment in the sulfide layers samples of the ni sulfide layer from the yukon territory are highly enriched in re os and other pge with distinctly higher re 192os but similar pt re compared to the black shale host re os isotopic data of the black shale and the sulfide layer are approximately isochronous and the data plot close to reference isochrons which bracket the depositional age of the enclosing shales samples of the chinese sulfide layers are also highly enriched in re os and the other pge re 192os are lower than in the yukon sulfide layer re os isotopic data for the sulfide layers lie near a reference isochron with an age of 560 ma similar to the depositional age of the black shale host the osmium isotopic data suggest that re and pge enrichment of the brecciated sulfide layers in both the yukon territory and in southern china may have occurred near the time of sediment deposition or during early diagenesis during the middle to late devonian and early cambrian respectively

positive δ13c excursion in carbonate and organic fractions from the paleoproterozoic aravalli supergroup northwestern india abstract carbon and oxygen isotopic investigations have been carried out on the archean and paleoproterozoic carbonate rocks of the udaipur region in the aravalli mountain belt northwestern india the study has led to the interesting finding of 13 c enrichment in the carbonate rocks of the jhamarkotra formation 13 c carb up to 11 1 v pdb belonging to the 2200 1900 ma paleoproterozoic aravalli supergroup further it is observed that the organic carbon from phosphorite bearing stromatolitic dolomites of the same formation are also enriched in 13 c 13 c org up to 11 1 however it must be emphasized that the 13 c enriched carbonates and the organic fractions are from different stratigraphic levels although in the same formation the former being at a lower stratigraphic level a critical analysis of the field geological petrological as well as the isotopic data indicates that the observed 13 c excursion in the carbonate carbon is not due to local causes such as methanogenesis or evaporitic conditions the shallow water environment of deposition of these carbonates as well as the immediately overlying formations rules out the stratified ocean model for the observed excursion the model involving high sedimentation rates and organic carbon burial has been preferred to explain the 13 c excursion in the carbonates of the jhamarkotra formation the 13 c enrichment in organic fraction occurred in localized regions of the aravalli sedimentary basin where high productivity was supported by phosphorous supply indicating that the diffusion limited pathways of organic carbon fixation were operative in the paleoproterozoic itself the 13 c enriched carbonate rocks of the jhamarkotra formation serve as the indian example for the paleoproterozoic global 13 c excursion

sedimentary organic matter and early toarcian environmental changes in the lusitanian basin portugal abstract the objective of this study is to investigate the relationship between early toarcian climatic events and the composition of kerogen assemblages in the lusitanian basin portugal in particular we aim to understand how the pliensbachian toarcian event pl toa event and toarcian oceanic anoxic event toae affected the continental areas of the western iberian margin and how possible variations in continental sources of organic matter om were expressed in marginal marine and hemipelagic depositional environments during the early toarcian we present here a characterisation total organic carbon toc total sulphur ts 13c in kerogen concentrate 13ckerogen and palynofacies of kerogen assemblages from several uppermost pliensbachian emaciatum ammonite zone lower toarcian sections in the lusitanian basin western iberian margin including the peniche section which contains the toarcian gssp in all sections toc concentration is low average 0 4 wt with the highest values reaching up to 2 1 wt in a discrete level located approximately 10 5 m above the base of the levisoni zone at peniche the toae negative carbon isotope excursion is observed in kerogen concentrate at the base of the levisoni zone throughout the basin palynofacies analysis demonstrates that the kerogen assemblages are mostly of terrestrial affinity with the dominance of the phytoclast group and terrestrial palynomorphs and with punctual increases in amorphous organic matter freshwater e g botryococcus sp and marine microplankton dinoflagellate cysts acritarchs and prasinophyte algae in specific stratigraphic intervals a change in palynofacies assemblages associated with the toae is observed around the base of levisoni zone although with slight differences between sections the toae interval records an increase in non opaque translucent phytoclasts nop and cuticle fragments and is also associated with an increased contribution of terrestrial palynomorphs increase in sporomorphs and classopollis in tetrads and agglomerates and decrease in marine palynomorphs the increases in nop and terrestrial palynomorphs support the postulated enhancement of the hydrological cycle and increased export of terrestrial om into marine environments during the early toarcian especially during the toae in the western iberian margin understanding the impact of the early toarcian climatic events on land based ecosystems may provide important insights into current climate change

paleosols and their relevance to precambrian atmospheric composition a discussion the identification of precambrian paleosols and their use as indicators of the composition of the atmosphere during weathering are still subjects in their formative stages the new data in the paper by palmer phillips and mccarthy 1989 are a welcome addition to the paleosol literature we do however disagree with some of the authors interpretations of their data and with the conclusions which they reach regarding the significance of

hydrogeochemical modeling of the shallow groundwater in the northern jordan valley the reasons for the rapid degradation and salination of the shallow aquifer in the northern jordan valley were investigated shallow groundwater surface water and thermal water were sampled from the study area for this purpose the geochemical mass balance technique was used to quantify the contribution of different sources geochemical processes and rock types to the final water composition applying the netpath software package the isotopic compositions of the water were also investigated the results suggest three potential recharge sources the yarmouk river the jordan river and the mukheibah thermal water evaporation significantly contributes to the current chemistry of the shallow water as is indicated by the geochemical models and the isotopic results tritium analyses indicate that the water is clearly new less than 50 years the relatively high values of nitrate in some wells may be of anthropogenic origin

early archean fossil bacteria and biofilms in hydrothermally influenced sediments from the barberton greenstone belt south africa abstract sem imaging of hf etched 3 3 3 5 ga cherts from the onverwacht group south africa reveals small spherical 1 m diameter and rod shaped structures 2 3 8 m in length which are interpreted as probable fossil coccoid and bacillar bacteria prokaryotes respectively preserved by mineral replacement other possibly biogenic structures include smaller rod shaped bacteriomorphs 900 m textures in the sediments in which these biogenic structures occur suggest that they were probably deposited in a shallow water environment which was subjected to intermittent subaerial exposure pervasive hydrothermal activity is evidenced by oxygen isotope studies as well as the penecontemporaneous silicification of all rock types by low temperature 220 c hydrothermal solutions

mobility of authigenic rhenium silver and selenium during postdepositional oxidation in marine sediments sedimentary records of redox sensitive trace elements hold significant potential as indicators of paleoceanographic environmental conditions records of re can reveal the intensity of past reducing conditions in sediments at the time of deposition whereas records of ag may record the magnitude of past diatom fluxes to the seafloor confidence in paleoenvironmental reconstruction from records of either metal however requires it to have experienced negligible redistribution since deposition this study examines diagenetic rearrangements of re and ag that occur in response to exposure to bottom water o2 in environments of low sedimentation rate including madeira abyssal plain turbidites and eastern mediterranean basin sapropels authigenic re was remobilized quantitatively by oxidation but poorly retained by the underlying sediments all records are consistent with previous work demonstrating that only a limited reimmobilization of re occurs preferentially in corg rich reducing sediments silver was also mobilized quantitatively by oxidation but it was subsequently immobilized more efficiently in all cases as sharp peaks immediately into anoxic conditions below active oxidation fronts and these peaks remain immobile in anoxic conditions during long term burial comparison of ag s and se records from various cores suggests that ag is likely to have been immobilized as a selenide a mechanism previously proposed for hg in similar situations mercone et al 1999 coexisting narrow peaks of ag and hg with se offer a means of assessing whether oxidative burndown has ever occurred at the top of corg and sulfide rich sedimentary units although these results suggest that caution must be used when inferring paleoenvironmental information from records of ag and re in cores with low sediment accumulation rates 5 cm ka 1 they should not affect the promise that authigenic ag and re records hold for paleoenvironmental reconstruction in sediments with higher accumulation rates and where anoxic conditions have been maintained continuously

application of the 187re 187os system to black shale geochronometry the decay of 187re to 187os provides a tool for determining depositional ages of black shales re and os concentrations and os isotopic compositions of whole rock samples of the bakken shale a mississippian devonian boundary black shale yield a whole rock isochron with an age of 354 49 ma this age is in agreement with the accepted age of the bakken shale 360 ma the initial 187os186os ratio of the isochron is 6 2 3 3 this value is indistinguishable from the 187os186os ratios observed in modern black sea sediments the concentration of common os in bakken shale samples is strongly correlated with total nitrogen indicating that a large fraction of the os in these samples is associated with a hydrogenous component which overwhelms any os supplied to the sediment in association with detrital material or cosmic dust the dominance of the hydrogenous component imparts a relatively homogeneous initial 187os186os ratio to the sediment at the time of deposition the degree of scatter about the isochron exceeds the degree of scatter expected from either analytical error or from the estimated degree of initial isotopic heterogeneity the pattern of scatter is consistent with postdepositional mobilization of re and or os on a small spatial scale we suggest that this mobilization may be a consequence of petroleum formation and migration in the bakken shale

organic geochemistry of mid continent middle and late ordovician oils ordovician oils in mohawkian and cincinnatian reservoirs of the united states mid continent retain the biochemical imprint of middle and upper ordovician oceanic life before the evolution of land plants and most vertebrates thus these oils have some geochemical features that distinguish them from younger oils these features include 1 a predominance of n c15 n c17 and n c19 alkanes in the saturated hydrocarbon fraction 2 relatively low amounts of longer chain n alkanes 3 low amounts of chlorophyll derived isoprenoids such as pristane and phytane and 4 abundant c29 sterane relative to c27 with rearranged forms diasteranes predominant over normal steranes ordovician oils also generally contain little sulfur and have a somewhat variable light stable carbon isotopic composition with dgr13csat and dgr13caro values of 28 to 31 pmil pdb but these features are typical of many marine oils the unusual chemistry of these ordovician oils supports the interpretation of reed illich and horsfield 1986 that prokaryotic organisms provided the organic matter for most ordovician oils although their claim for gloeocapsamorpha a problematic unicellular prokaryote possibly a blue green alga or an unusually large bacterium cannot be proven from oil chemistry alone knowing that indigenous mid continent ordovician oils were derived from prokaryotic organisms may aid in future exploration for these reservoirs

the occurence of unusual c27 and c29 sterane predominances in two types of oman crude oil abstract two types of oman crude oils reveal unusual sterane distributions type a which is the more common 74 examples is characterised by a predominance of c 29 iso and normal steranes and generally none or only very low relative concentrations of rearranged steranes the triterpanes are characterised by the predominance of the c 29 17 h 21 h norhopane over the c 30 17 h 21 h hopane and non predominant c 20 c 30 tricyclic terpanes the c 29 steranes of this type of crude were not derived from the c 29 sterols of land plant origin frequently proposed as the source of c 29 steranes since there is good geological evidence that these crudes were generated from a pre cambrian source rock a geological period when land plants did not exist the type b crude oil 11 known examples is characterised by a strong predominance of c 27 iso normal and rearranged steranes relatively lower concentrations of 17 h 21 h hopanes and relatively high concentrations of c 20 c 30 tricyclic terpanes the remarkably different biomarker characteristics of these crude oils imply that the organisms active in the depositional environment of the respective source rocks were significantly different

the geochemical cycle of rhenium a reconnaissance rhenium re is one of a suite of elements including uranium and molybdenum that display conservative behavior in seawater and are enriched in anoxic sediments the decay of187re to187os provides a geochronometer in ancient sedimentary rocks and gives rise to os isotopic variations in nature in order to better characterize its sources to seawater re was measured in three major rivers amazon orinoco ganges brahmaputra and some of their tributaries re concentrations span four orders of magnitude from 0 02 to 400 pmol kg with the highest concentrations found in rivers draining black shales in the venezuelan andes mainstream re levels in the three rivers are between 1 and 10 pmol kg with a flux weighted average of 2 3 pmol kg the residence time for re in the oceans is estimated to be 750 000 yr with respect to river inputs re profiles from the atlantic and pacific oceans confirm that re behaves conservatively in seawater with no significant uptake onto particles and or recycling within the water column this is also true in the anoxic water column of the black sea re removal into anoxic sediments occurs at or below the sediment water interface as demonstrated in sediment pore waters from chesapeake bay in oxic sediments re is not cycled with manganese oxides and it is not enriched in very slowly accumulating pelagic sediments with a large hydrogenous iron and manganese component or in manganese nodules burial of re in anoxic sediments which accumulate on 0 3 of the ocean floor removes approximately 50 of the riverine re flux to the oceans hence oceanic re concentrations may be very sensitive to changes in the area of anoxic sedimentation

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

detrital pyrite in witwatersrand gold reefs x ray diffraction evidence and implications for atmospheric evolution pyrite is easily oxidized and therefore unambiguous evidence of detrital pyrite grains in metasediments is a significant constraint on when an oxygenated atmosphere developed compact rounded pyrite in the witwatersrand gold reefs of south africa has a detrital habit and is texturally equivalent to and spatially associated with detrital zircon and chromite x ray precession photography reveals that petrographically featureless as poor grains are untwinned single crystals of high diffraction quality this new evidence from crystallography is consistent with mechanically abraded pyrite from primary lode gold deposits and excludes an origin by replacement of a pre existing detrital phase further evidence of a detrital origin for the compact rounded pyrite is afforded by isolated grains of arsenian pyrite displaying truncated as rich growth bands the geographically extensive witwatersrand fluvial conglomerates evidently had a matrix of quartz and pyrite sand and pyritic mud in their unconsolidated state and thus the late archean atmosphere of earth was likely essentially anoxic

transverse faults at the northern end of the southern basin of the dead sea graben abstract classical models for pull apart basins along strike slip faults predict normal motion along the transverse faults which cross the basin a detailed geophysical investigation was carried out across the northern end of the southern sub basin of the dead sea depression the study included analysis of newly obtained 3 5 khz seismic profiles and reinterpretation of existing single channel sparker seismic profiles and multichannel seismic profiles the unique combination of very shallow and deep seismic profiles reveals the recent activity of a transverse fault in the study area and helps trace its direction the northern end of the southern sub basin was probably characterized by normal movement during the miocene early pleistocene thereafter during the late pleistocene present the mode of its activity changed to strike slip movement