maceral composition and origin of organic matter input in neoproterozoic lower cambrian organic rich shales of salt range formation upper indus basin pakistan abstract the appropriate thermal maturity oil window or lower of the neoproterozoic rocks is a prerequisite for preserving robust and primary biological assemblages the neoproterozoic lower cambrian organic rich shales present in the upper part of salt range formation pakistan with abundant organic matter om total organic carbon toc up to 46 at relatively low thermal maturity protobitumen reflectance bro 0 2 0 4 represents by far the lowest thermal maturity neoproterozoic lower cambrian rocks analyzed to date the detailed petrographic description of neoproterozoic lower cambrian organic matter in the current study was lacking from previous source rock studies of coeval strata from oman eastern siberia australia and elsewhere eight organic rich shales of the salt range formation from three different outcrops have been analyzed for maceral composition and source rock characterization using organic petrography scanning electron microscopy and standard source rock assessment techniques the organic petrography reveals the organic rich shales are predominantly composed of alginites lamalginite and telalginite bituminite protobitumen and mineral bituminous groundmass overall the maceral assemblages suggest the deposition of these shales took place under a salinity stratified water column in a shallow restricted basin where both oxygenic and anoxygenic modes of primary production were operative the top oxygenated part of the water column was populated with the phototropic mat forming cyanobacterium whereas the lower low dissolved oxygen zone was dominated by algal mats and sulphate reduction bacteria the rare and scattered thucholites present within the salt range formation shales were derived from the radiation induced polymerization of adjacent om by the radioactive grains the heat from the radioactive grains however found to have a negligible effect on the overall thermal maturity of these shales

recent current observations in the eastern yellow sea observations of current velocity pressure and temperature in the eastern yellow sea from january 10 through april 12 1986 together with geostrophic winds calculated from surface atmospheric pressure distributions are analyzed for a study of the synoptic band response of the yellow sea to the wintertime winds north wind pulses in the winter monsoon are found to give rise to northward flow bursts in the yellow sea trough which appear to peak just as the wind relaxes and to be driven by a synoptic band north to south rise in bottom pressure synchronous with the north wind pulses the existence of a similar rise in coastal sea level indicates that the observed southward pressure rise is but an offshore extension of a setup along the west coast of south korea forced by the north wind pulses the advection by northward flow bursts of warm water from the south apparently causes the measured temperature to be substantially higher in the trough than in coastal waters at the same latitude and the observed rate of cooling in the trough to be less than half of that in coastal waters to the east a winter to spring transition is also found in the bottom pressure records obtained in the trough in which the mean north to south gradient in winter reverses suddenly in early march a similar reversal also appears in sea level records along the west coast of south korea the reversal appears to be triggered by the weakening of the north winds at the arrival of spring

submarine groundwater discharge sgd into the yellow sea revealed by 228ra and 226ra isotopes implications for global silicate fluxes abstract we estimated the magnitude of submarine groundwater discharge sgd into the yellow sea which is one of the largest continental shelves in the world using 226 ra and 228 ra isotopes on the basis of 228 ra and 226 ra mass balance models we estimated the advective flux of 226 ra through sgd to be 270 10 12 dpm yr 1 in the yellow sea using this 226 ra flux and the measured 226 ra activity in coastal groundwater the submarine discharge of groundwater mostly brackish groundwater was calculated to be at least 40 of the river water input 2 3 10 11 m 3 yr 1 then on the basis of the sgd and the concentration of si in coastal groundwater we estimated the flux of si through sgd to be 20 100 of that associated with river discharge 23 10 9 mol yr 1 this large sgd is likely to be due to the high tidal range up to 10 m and the wide distribution of sandy sediments in the yellow sea favorable for the recirculation of seawater through bottom sediments and rocks this result from such a large area implies that the si flux through sgd may be significant on a global scale

evolution of primary producers and productivity across the ediacaran cambrian transition abstract nearly all extant animal phyla first appeared during the ediacaran cambrian transition a revolution in primary producer ecology and marine productivity has been proposed as a bottom up ecological driver for this rapid diversification of metazoans however the control s driving the evolution of primary producers and primary productivity around the ediacaran cambrian transition and their potential relationship to the cambrian explosion are not fully understood in this study we measured the nitrogen content and the nitrogen isotopic composition of kerogen in the piyuancun and hetang formations using samples collected from the chunye 1 well on the lower yangtze block in western zhejiang our isotope results suggest that nitrate was the dominant n source fueling primary productivity during deposition of the entire piyuancun formation and lower hetang formation with only a minor contribution from n 2 fixation quantitative reconstructions of paleoproductivity based on organic carbon and pyrite content and sedimentation rate indicate that productivity either stayed the same or increased during the transition from the piyuancun formation to the overlying hetang formation thus fixed n availability was not the ultimate factor limiting primary productivity during the ediacaran cambrian transition combining our data with published nitrogen isotope records from the early middle ediacaran to cambrian stage 4 suggests that no 3 was the dominant n species fueling phytoplanktonic productivity during the broad cambrian explosion interval from its earliest roots in the ediacaran through the main episode in cambrian stage 3 eukaryotes lack the ability to fix nitrogen and preferentially assimilate nitrate the no 3 dominated euphotic zone from the early middle ediacaran to cambrian stage 3 may have promoted the radiation of relatively large eukaryote phytoplankton which may have been an important driver of early animal diversification

denitrification in the eastern arabian sea evaluation of the role of continental margins using ra isotopes abstract the 228 ra 226 ra activity ratios henceforth denoted as 228 226 have been measured both at the surface and at 300 m depth as a function of distance from the western continental margins of india to the open arabian sea between 15 n and 21 n a two dimensional eddy diffusion model is used to fit the measured 228 226 profiles to deduce horizontal eddy diffusivities in both zonal towards open ocean and meridional towards the equator directions these range between 1 3 106 and 3 1 106 cm2 s 1 assuming that the organic rich and deeply anoxic continental margin sediments at 300 m depth can be a source of organic c to the core of the denitrification layer and that the deficit flux in the carbon budget can be covered by this supply the required gradient dc dz in doc content of waters from coast to open arabian sea is computed using the kx value the required gradient is computed to be 4 mol dm 3 100 km 1 which is within the error associated with doc measurements

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

distribution and structure of hydrocarbons in four organic rich ordovician rocks abstract organic matter in four north american rocks of ordovician age has been analysed using geochemical and optical techniques including reflected light and fluorescence microscopy rock eval pyrolysis elemental analysis of isolated kerogens gas chromatography gc and gas chromatography mass spectrometry gc ms of hydrocarbons in the solvent extracted bitumens the samples analysed were guttenberg oil rock and black shales from the vinini womble and big fork formations in the united states the origin of some of the biomarkers found in the bitumen and the vitrinite particles observed in reflected light are discussed briefly with reference to possible algal and bacterial precursors the results indicate that the four samples are potentially excellent oil source rocks although the guttenberg oil rock is too immature to have generated a substantial quantity of hydrocarbons

oceanic anoxia at the precambrian cambrian boundary the precambrian cambrian pc c boundary separates fossils representing two discrete evolutionary phases the neoproterozoic soft bodied ediacarian biotas and cambrian small shelly faunas the biological discontinuity is suspected to have been a result of mass extinction however recent discoveries of the ediacarian biotas in cambrian sediments have led to an understanding that the faunal change was gradual through the pc c transition th u ratios which are high in oxidizing conditions and low in reducing conditions show a considerable positive correlation with 13c values at all studied sites of the pc c boundary this correlation indicates that reported 13c variation across the pc c boundary from numerous localities corresponds to redox variation in the depositional environment the negative 13c anomaly that occurs worldwide at the pc c boundary therefore corresponds to the widespread development of an oxygen deficient shallow marine environment this finding suggests that widespread oceanic oxygen deficiency which has been interpreted to reflect phanerozoic mass extinction events also occurred immediately before the cambrian explosion

nutrient fluxes via radium isotopes from the coast to offshore and from the seafloor to upper waters after the 2009 spring bloom in the yellow sea abstract the horizontal and vertical transport of nutrient rich water both from the coast and from the seafloor to the overlying water column should play an important role in supplying nutrients required for the periods of vegetative or reproductive growth of phytoplankton in the present work radium isotopes 223ra 224ra and 226ra in the southern yellow sea were measured after a spring bloom in june 2009 the exponential like decrease of 223ra away from the coast to offshore waters yielded horizontal eddy diffusivities kh of 2 93 1 47 107 cm2 s 1 by neglecting the advection this estimate was smaller than that with advection indicator by as much as 21 when using an analytic model for 223ra and 226ra the corresponding horizontal nutrient fluxes were 1525 mol m 2 d 1 din 15 9 mol m 2 d 1 dip and 826 mol m 2 d 1 dsi which would supply around 16 of n and 3 of p requirements based on the primary productivity the decrease of 224ra and 223ra activities from sediments to the upper water column suggests the vertical eddy diffusion coefficient kz of 6 23 5 58 cm2 s 1 below the thermocline which was within the yellow sea cold water mass yscwm the calculated vertical fluxes of nutrient were 4945 mol m 2 d 1 din 236 mol m 2 d 1 dip and 5315 mol m 2 d 1 dsi accounting for up to 52 of n and 40 of p requirements for the phytoplankton growth these results demonstrate the role of yscwm as a relative nutrient rich pool for the supply of nutrient to the southern yellow sea via the vertical diffusion process relative to the horizontal process during the summer season such processes will be strengthened during the weak density stratification in spring when algal blooms occur

biochemical evolutionary significance of ordovician oils and their sources abstract geochemical data from several ordovician oils and kerogens from distinct basins in canada united states estonia and australia show some unique compositional characteristics the oils analyzed by gas chromatography and gas chromatography mass spectrometry are characterized by an odd dominance in the c9 c19 molecular weight range of normal paraffins and an odd dominated homologous series of cyclohexyl substituted normal paraffins the oils contain an unusually small amount of c20 components and pristane and phytane are conspicuous by their virtual absence the compositions of the oils and kerogens correlate closely and display characteristics that have not been observed in younger sediments the predominant organism found in the source kerogens for these unique oils is gloeocapsamorpha prisca a primitive prokaryotic organism data from the analysis of gloeocapsamorpha rich kerogens and the association of this organism with ordovician source rocks indicate a genetic relationship exists between the organism and the unusual oil chemistry the chemistry of the oils and kerogens suggests that gloeocapsamorpha was either non photosynthetic or that it fixed light using a chlorophyll that did not contain a phytyl side chain e g a bacteriochlorophyll the widespread occurrence of oils and kerogens possessing such a uniform composition appears unique to the ordovician certainly to the early paleozoic this suggests that paleocological conditions of ordovician anoxic environments were very similar and g prisca was particularly well adapted to these conditions

cambrian burgess shale type deposits share a common mode of fossilization although cambrian burgess shale type bst biotas are fundamental to understanding the radiation of metazoans the nature of their extraordinary preservation remains controversial there remains disagreement about the importance of the role of early mineral replication of soft tissues versus the conservation of primary organic remains most prior work focused on soft bodied fossils from the two most important bst biotas those of the burgess shale canada and maotianshan shale chengjiang china fossils from these two deposits do not provide ideal candidates for specimen level taphonomic study because they have been altered the burgess shale by greenschist facies metamorphism and the maotianshan shale by intensive subsurface weathering elemental mapping of soft bodied fossils from 11 other bst deposits worldwide demonstrates that bst preservation represents a single major taphonomic pathway that may share a common cause wherever it occurs the conservation of organic tissues and not early authigenic mineralization is the primary mechanism responsible for the preservation of bst assemblages early authigenic mineral replacement preserves certain anatomical features of some specimens but the preservation of non biomineralized bst fossils requires suppression of the processes that normally lead to the degradation of organic remains in marine environments

cambrian palaeoscolecids cycloneuralia from gondwana and reappraisal of species assigned to palaeoscolex abstract the discovery of new palaeoscolecid material cycloneuralia from the emu bay shale konservat lagerstatte of kangaroo island south australia cambrian series 2 stage 4 and from the murero biota of ne spain cambrian series 3 stage 5 drumian has prompted a reappraisal of palaeoscolex whittard 1953 the genus to which species from these and other cambrian localities have most recently been assigned available data from scanning electron microscopy show the presence of hadimopanella type sclerites covering the surface of these taxa permitting taxonomic schemes based on microfossils and whole body compression fossils to be reconciled the sclerite pattern size and shape indicate that several of the cambrian species assigned to palaeoscolex need to be reassigned to wronascolex ivantsov and zhuravlev 2005 a genus originally described from siberia the studied material includes wronascolex antiquus glaessner 1979 and wronascolex iacoborum sp nov from kangaroo island australia and two new specimens of wronascolex from the iberian ranges spain sem examination of the types of palaeoscolex ratcliffei robison 1969 a cambrian species from utah to which murero material has been compared suggests that this species should possibly be assigned to wronascolex these taxa are also considered in a cambrian palaeobiogeographic context together with the presence of isolated hadimopanella sclerites showing a distribution of wronascolex largely confined to palaeotropical environments

exceptional fossil record distribution of soft tissue preservation through the phanerozoic preservation of soft bodied fossil biotas konservat lagerstaten that preserve traces of volatile nonmineralized tissues readily degraded by bacteria are not evenly spaced through geologic time when compared to outcrop area exceptional faunas appear to be over represented in the cambrian and jurassic these concentrations in time correspond to particular environments indicating that controls on the distribution of exceptional faunas may have operated on a global scale the reduction in the number of exceptional faunas after the cambrian may reflect the evolution and diversification of deep bio turbators specific conditions favoring stagnation and episodic burial were required to ensure preservation in younger rocks

interstratification and other reaction microstructures in the chlorite berthierine series transmission electron microscopy tem results show there is a series of periodically and nonperiodically interstratified structures composed of berthierine and chlorite layers in low temperature chlorite that is one of the alteration products of granulite facies archean ironstone from the eastern border of the beartooth mountains montana an antiphase domain structure suggests that the interstratified structures are intermediate transformation products formed by reaction from berthierine serpentine structure to chlorite periodically interstratified structures consisting of chlorite c and serpentine like s or berthierine layers include cs ccs cccs ccccs and ccccccs the layer sequences in interstratified chlorite berthierine are indicative of the reaction mechanisms that produce the interstratified structures e g crystallization from solution or solid state transformation the reaction from berthierine to chlorite is crystallographically much like a cell preserved phase transformation even though it is highly reconstructive berthierine can be considered a polymorph of the fe rich chlorite mineral chamosite with berthierine as the los temperature phase interstratification and integrowths in the chlorite berthierine series may be common phenomena in low temperature layer silicates resembling chlorite although such relations are difficult to recognize from chemical analyses or powder x ray diffraction patterns they can be observed readily with tem method

terminal proterozoic mid shelf benthic microbial mats in the centralian superbasin and their environmental significance abstract a combined sedimentological and biogeochemical study has been conducted on several terminal proterozoic mid shelf microbial mat facies from the centralian super basin isotopic and organic geochemical analysis of the bitumen and kerogen indicated that two sources of organic matter from planktonic and benthic microbial mat populations contributed to the sediment the planktonic source provided a suite of n alkanes with c20 whereas the benthic source contributed an overlay of n alkanes c20 with a strong even preference together with mid chain methyl alkanes kerogen and biomarkers derived from the microbial mat were found to be depleted in 13c relative to planktonic material pyrite in the micorbial mats was also found to be depleted in 34s compared to surrounding facies the combination of these observations suggested that the mats may have been at least partly composed of sulfide oxidising bacteria these organisms have specific environmental tolerances that set limits on palaeo environment their requirement for oxygen indicates that the water column above the mid shelf could not have been anoxic accordingly from the results and age determinations reported here it would appear that mid shelf environments of the centralian superbasin of australia were seeing significant levels of oxygen through the ediacarian

mineralogy and stratigraphy of phyllosilicate bearing and dark mantling units in the greater mawrth vallis west arabia terra area constraints on geological origin 1 analyses of mro crism images of the greater mawrth vallis region of mars affirm the presence of two primary phyllosilicate assemblages throughout a region 1000 1000 km these two units consist of an fe mg phyllosilicate assemblage overlain by an al phyllosilicate and hydrated silica assemblage the lower unit contains fe mg smectites sometimes combined with one or more of these other fe mg phyllosilicates serpentine chlorite biotite and or vermiculite it is more than 100 m thick and finely layered at meter scales the upper unit includes al smectite kaolin group minerals and hydrated silica it is tens of meters thick and finely layered as well a common phyllosilicate stratigraphy and morphology is observed throughout the greater region wherever erosional windows are present this suggests that the geologic processes forming these units must have occurred on at least a regional scale sinuous ridges interpreted to be inverted channels and narrow channels cut into the upper clay bearing unit suggesting that aqueous processes were prevalent after and possibly during the deposition of the layered units we propose that layered units may have been deposited at mawrth vallis and then subsequently altered to form the hydrated units the fe mg phyllosilicate assemblage is consistent with hydrothermal alteration or pedogenesis of mafic to ultramafic rocks the al phyllosilicate hydrated silica unit may have formed through alteration of felsic material or via leaching of basaltic material through pedogenic alteration or a mildly acidic environment these phyllosilicate bearing units are overlain by a darker relatively unaltered and indurated material that has probably experienced a complex geological history

role of bacterial mats in oxygen deficient marine basins and coastal upwelling regimes preliminary report bacterial mats play an important role in the sedimentation history of many marine biogenic regimes observations of the living mats suggest that in shallow waters they are dominated by photosynthetic cyanobacteria while in deeper waters the mats are dominated by nonphotosynthetic sulfur oxidizing bacteria fossilized remains of analogous mat structures from the miocene monterey formation are commonly associated with oil producing and phosphate rich zones preliminary observations suggest that bacterial mats may be a source of the organic matter that in time is thermally altered to hydrocarbons

neoproterozoic early cambrian biota and ancient niche a synthesis from molecular markers and palynomorphs from bikaner nagaur basin western india abstract the time frame of present study is neoproterozoic early cambrian an enigmatic and consequential time in the history of earth the present study elucidates the terminal proterozoic biota and palaeoenvironment by characterizing the soluble and insoluble fractions of organic matter extracted from sediment core samples recovered from marwar supergroup bikaner nagaur basin western india the normal alkanes range from c15 to c33 wherein c19 to c21n alkanes predominate and carbon preference index ranges from 1 12 to 1 19 pristane phytane ratio varies between 0 9 and 1 2 the kerogen matter occurs as homogenous laminae and discrete organic remains which are mostly derived from microbial mat triterpenoids include cheilanthanes and hopanes which are confirming evidences of microbial input algal presence has also been confirmed from palynological data green algae evolved to be a major biota during the neoproterozoic early cambrian time and this is validated by the appreciable abundance of c29 steranes in the bitumen fraction the amorphous pieces of kerogen residues lack any visibly distinct internal features however a very few simple ornamented acritarchs like micrhystridium sp lophosphaeridium sp and leiosphaeridia sp are observed in the organic residues micro ftir spectroscopy of the amorphous organic particles reveals the presence of long chain aliphatic components and unusually high c c aromatic ring stretching band the organic remains were deposited in restricted marine water and elevated saline condition as indicated by several salinity biomarkers the present study clearly demonstrates a microbial mat dominated niche with significant eukaryotic green algae that had been capable of surviving in the high salinity of the terminal proterozoic oceans

bound carboxylic acids in the alberta oil sands abstract the alberta oil sands contain 1 2 organic solvent insoluble organic matter chemisorbed to the inorganic matrix analysis of the monocarboxylic fraction 1 14 of the chemisorbed material has revealed the presence of c12 c32 normal iso anteiso alkenoic acids mono and diunsaturated acids cyclopropylalkanoic and cyclic terpenoid carboxylic acids some of the main components of the acyclic acids were similar to those which have been identified in various petroleums and alberta oil sand bitumens in small concentrations by mackenzie et al advances in organic geochemistry 1981 pp 637 649 wiley heyden 1983 and attributed to bacterial degradation of the oils via the aerobic pathway of biosynthesis the presence of these acids in the chemisorbed fraction and virtual absence in the bitumen lends additional support to earlier proposals that the alberta oil sand bitumens have undergone severe microbial degradation

224ra in continental shelf waters abstract measurements of 224 ra off the coasts of south carolina and georgia reveal that significant activities occur up to 70 km offshore although some of this activity may be transported from estuarine salt marsh and nearshore source regions high near bottom activities in stratified waters suggest that additional 224 ra is being supplied by the decay of 228 th in mid shelf sediments this 228 th is probably derived from the decay of 228 ra in the water column 224 ra is potentially a powerfull tracer of water mixing on the shelf however a good understanding of its input functions is required before this potential may be realized

hydrocarbon biomarkers from ordovician sediments and the fossil alga gloeocapsomorpha prisca zalessky 1917 numerous ordovician oils worldwide are known to show unusual and distinctive distributions of hydrocarbons which it has been suggested are derived from a unique benthonic mat forming non photosynthetic prokaryotic organism gloeocapsomorpha prisca zalessky 1917 which is the major contributor of organic matter organic matter rich sediments from the canning and amadeus basins of australia known to contain g prisca fossils and to have the characteristic predominance of odd carbon number c13 c19 n alkanes were investigated to determine other hydrocarbon distributions sediments from both basins contained abundant n alkylcyclohexanes with odd carbon number predominance c13 c19 and methyl n alkylcyclohexanes c14 c20 which in immature sediments showed an even carbon number predominance the isomer distribution of these latter compounds was determined by direct comparison with synthetic standards the sediments from both basins also contained very similar distributions of steranes and pentacyclic triterpanes and the derived kerogens had a characteristically light carbon isotope signature pyrolysis of a g prisca rich kerogen yielded a hydrocarbon mixture with a similar composition to the sediment extract except that there was a marked increase in the relative abundance of pristane phytane alkylcyclohexanes steranes and hopanes relative to n alkanes we argue on the basis of the geological geochemical and palynological data that g prisca was probably planktonic photosynthetic and very possibly eukaryotic and that the striking character of ordovician oils and sediments derive from bacterial and other diagenetic imprints superimposed on the primary signature of this organism

biomarker and isotopic signatures of an early cambrian lagerstatte in the stansbury basin south australia abstract the lower cambrian series 2 emu bay shale biota found at big gully on the north coast of kangaroo island south australia is by far the richest burgess shale type bst fauna in the southern hemisphere while the trace element geochemistry of the host shale shows it accumulated beneath an oxic water column this appears difficult to reconcile with the exceptional preservation of organs such as gut glands muscles and eyes in some of its fauna micro scale sealed vessel mssv pyrolysis of kerogen isolated from a solvent extracted sample of fossiliferous emu bay shale provided independent confirmation of its redox status and also implicated cyanobacteria in the preservation of its fauna thermal extraction and pyrolysis each yielded alkanes displaying a low ratio of pristane to phytane pr ph 1 and n alkanes with a marked odd even predominance in the 20 range the latter molecular signature is diagnostic of gloeocapsomorpha prisca and is the first indication that mats of this or a similar coccoid cyanobacterium were involved in the taphonomy of a bst deposit hopanes including 2 methylhopanes are far more abundant than steranes and the shale s bulk organic matter has 13 c values in the range 32 to 28 providing further evidence of the cyanobacterial affinity of its microbial biomass thus mat forming cyanophytes rather than sulfur oxidising bacteria may have played a key role in maintaining a sharp redox boundary at the sediment water interface during deposition of the emu bay shale lagerstatte thereby enabling the survival of soft body parts within its fossil fauna for long enough to permit inorganic replication of their fine detail during late diagenesis

biological markers in bitumens and pyrolyzates of upper cretaceous bituminous chalks from the ghareb formation israel abstract the sterane and triterpane distributions of three bituminous chalks from the upper cretaceous ghareb formation israel were investigated both in the original extractable bitumens and in extracts obtained after pyrolysis of whole rock and isolated kerogen samples at 450 c pyrolysis was performed in a closed system under hydrous whole rock and anhydrous conditions isolated kerogens the carbon number distributions of steranes and triterpanes differ significantly between original bitumen and pyrolyzates unlike the bitumens in which diasteranes were not detected the anhydrous pyrolyzates contain small amounts of diasteranes the presence of water during pyrolysis leads to an increase of sterane isomerization the abundant formation of diasteranes and an increase of the 18 h trisnorneohopane 17 h trisnorhopane ratio sterane isomerization maturation parameters show a closer match between original bitumen and pyrolyzates after pyrolysis in a closed system when compared with an open system

hydrocarbon shows and petroleum source rocks in sediments as old as 1 7 109 years we report the discovery of indigenous live oil in 1 4 gyr old rocks in the mcarthur basin of northern australia previously reported occurrences of indigenous precambrian oil are 1 gyr old1 5 potential petroleum source rocks in the mcarthur basin range in age from 1 4 to 1 7 gyr and were deposited in marine and lacustrine environments in parts of the basin they have been buried sufficiently deeply to have generated hydrocarbons they span the period corresponding to the appearance of eukaryotic organisms and because of their low degree of thermal alteration they provide a valuable resource for the study of primitive biota through their hydrocarbon biomarkers the hydrocarbon composition of the oil is consistent with a derivation from organic matter of prokaryotic origin these results show that exploration of previously ignored mid proterozoic sediments may lead to the discovery of new reserves of oil

nature of mixed layer clays and mechanisms of their formation and alteration abstract mixed layer clay minerals are intermediate products of reactions involving pure end member clays they come from natural environments ranging from surface to low grade metamorphic and hydrothermal conditions most often mixed layering is essentially two component but more complicated interstratifications have also been documented variable tendency to form regular 1 1 interstratifications has been observed and explanations of this phenomenon have been proposed mixed layer clays are either di or trioctahedral di trioctahedral interstratifications are rare most mixed layer clays contain smectite or vermiculte as a swelling component exceptions are all trioctahedral serpentine chlorite in low temperature environments and mica chlorite and talc chlorite at high temperatures solid state transformation and dissolution crystallization are the two mechanisms responsible for the formation of different mixed layer clays in general the weathering reactions that produce mixed layering are revers

diagenesis of free and bound lipids in terrestrial detritus deposited in a lacustrine sediment recent sediments from an oligotrophic lake loch clair having uniform organic input for 2000 yr show changes in lipid abundance and composition with increasing depth attributed to diagenesis stability of free lipids decreases in the order n alkanes alkan 2 ones sterols n alkanoic acids n alkanols n alkenoic acids diagenetic loss of shorter chain homologues is complete within 400 yr stabilisation of bound relative to free lipids increases the proportion of the former with sediment age and reduces loss of shorter chain bound homologues in an eutrophic lake cross mere shorter chain free and bound sedimentary lipids show increased abundance compared with loch clair the relative importance of higher input of shorter chain lipids derived from aquatic detritus and slower initial diagenesis due to the anoxic hypolimnion as causative factors for this difference between lake types cannot yet be assessed

mineralogy of fine grained rims in the alh 81002 cm chondrite abstract the mineralogy of fine grained rims in alh 81002 a relatively primitive cm carbonaceous chondrite has been determined by using transmission electron microscopy the most abundant phase is mg rich serpentine which occurs in small 20 nm crystals with cylindrical or fibrous morphologies cronstedtite an fe rich phyllosilicate occurs as relatively large 100 to 2500 nm platy crystals some cronstedtite is coherently intergrown with tochilinite in many cases cronstedtite has been partially altered to serpentine the compositions and textures of these two phases provide a mineralogical and morphologic alteration sequence that parallels the known compositional trend for cm chondrite matrix accessory minerals embedded within the phyllosilicates include chlorite pentlandite gypsum olivine kamacite taenite and chromite regions containing only anhydrous minerals also occur the hydrated and anhydrous regions are in direct contact with each other suggesting that the rims accreted material from multiple reservoirs

using the radium quartet for evaluating groundwater input and water exchange in salt marshes the fluxes of 226ra half life 1600 years and 228ra half life 5 7 years from the north inlet salt marsh to the sea are much larger than can be supported by decay of their th parents in the surface marsh sediments these fluxes are sustained almost entirely by groundwater flow through the marsh an average groundwater flow of approximately 10 cm3 cm 2 day 1 is indicated if the groundwater activities we have measured are representative the fluxes of 223ra half life 11 4 day and 224ra half life 3 6 day are factors of 22 and ten more than those expected from the flux of 226ra groundwater also sustains most of the flux of the short lived isotopes the measured ra activity ratio pattern in the marsh creeks matches the groundwater signature but is distinct from the pattern of the parent thorium isotopes in the sediment we present a model to explain the anomalous distribution pattern of these isotopes despite their large throughput the inventories of desorbable 226ra and 228ra in the top 15 cm sediment layer are very low nevertheless the activities of 226ra and 228ra in the porewaters are large indicating a low distribution coefficient 10 for radium and a short retention time 10 days in the surface sediment layer we surmise that groundwater flow may be a significant source of radium isotopes in the waters of shallow estuaries and coastal margins this source must be recognized while considering mass balance of any tracer be it radium nutrients other metals or 18o

biomarker signatures from neoproterozoic early cambrian oil western india abstract the neoproterozoic early cambrian time is the cradle of multicellular eukaryotic life and thereafter metazoan life started populating the planet biomarkers which record the chronicles of biotic events on earth have been investigated using gas chromatography mass spectrometry from a suite of nine oil samples extracted from oil stained sediments and a crude oil of neoproterozoic early cambrian age from bikaner nagaur basin western india the biomarker distribution is characterized by high concentration of both tricyclic terpanes and pentacyclic hopanes the predominance of c 29 regular sterane over c 27 and c 28 steranes indicates green algal contribution and may imply the prominence and diversification of the same algal group the low pristane phytane ratio and occurrence of substantial quantity of gammacerane monomethyl 2 methyl 2 2 4 8 trimethyltridecyl chroman and 1 1 7 8 tetramethyl 1 2 3 4 tetrahydrophenanthrene are indicative of stratified water column as well as anoxic and enhanced salinity condition of the environment of deposition this paper reports for the first time the presence of methyltrimethyltridecyl chromans mttcs from neoproterozoic early cambrian time putative c 19 norsteranes probably indicative of sponge input are recorded in the studied samples and also reported from other infracambrian oils and sediments normal alkanes n c 17 and n c 18 and isoprenoids pristane and phytane are highly depleted in 13 c the overall biomarker distribution and carbon isotope data of oils from bikaner nagaur basin show similarities with those of other infracambrian oils like huqf oils from oman and baykit high oils from eastern siberia

lower cambrian shelf and shelf margin buildups flinders ranges south australia1 carbonate buildups in the flinders ranges of mid early cambrian age grew during a period of high archaeocyath diversity and are of two types 1 low energy archaeocyath sponge spicule mud mounds and 2 high energy archaeocyath calcimicrobe calcified microbial microfossil bioherms mud mounds are composed of red carbonate mudstone and sparse to abundant archaeocyath floatstone have a fenestral fabric display distinct stromatactis contain abundant sponge spicules and form structures up to 150m wide and 80 m thick bioherms are either red or dark grey limestone and occur as isolated small structures 2 20 m in size surrounded by cross bedded calcarenites and calcirudites or as complexes of mounds and carbonate sands several hundreds of metres across red bioherms comprise masses of white epiphyton with scattered archaeocyaths and intervening areas of archaeocyath rich lime mudstone grey bioherms are complex intergrowths of archaeocyaths encrusting dark grey renalcis and thick rinds of fibrous calcite cement the bioherms were prone to synsedimentary fracturing and exhibit large irregular cavities up to 1 5 m across lined with fibrous calcite the buildups are isolated or in contiguous vertical succession mud mounds occur alone in low energy frequently nodular limestone facies individual bioherms and bioherm complexes occur in high energy on shelf and shelf margin facies the two types also form large scale shallowing upward sequences composed of basal deep water mud mounds grading upward into archaeocyath calcimicrobe bioherm complexes and bioherms in cross bedded carbonate sands the uppermost sequence is capped by ooid grainstone and or fenestral to stromatolitic mudstone the calcimicrobe and metazoan associations form the two major biotic elements which were to dominate reefs throughout much of subsequent phanerozoic time

an isotopic biogeochemical study of neoproterozoic and early cambrian sediments from the centralian superbasin australia abstract organic matter from neoproterozoic and early cambrian sediments of the amadeus and officer basins of the centralian superbasin australia has been studied for biomarker distributions and the carbon isotopic compositions of kerogen and individual hydrocarbons these sediments represent both shallow and deep water marine facies in the older sections and marine and saline lacustrine carbonate deposits in the cambrian hydrocarbon biomarker patterns were found to be quite consistent with the known sedimentary environments and provide valuable insights into the biogeochemical changes which accompanied the transition from a microbially dominated ocean to the early stages of metazoan radiation in particular carbon isotopic data for n alkyl and isoprenoid lipids presented here and in earlier studies showed a reversal in carbon isotopic ordering between the proterozoic and phanerozoic by comparison with the 13c of kerogen n alkyl lipids from deep water proterozoic sediments were enriched in 13c and appear to be derived mainly from heterotrophs whilst open marine phanerozoic counterparts are 13c depleted and evidently derived mainly from autotrophs data from the samples studied here are consistent with a model invoking a change in the redox structure of the ocean possibly aided by the innovation of faecal pellets

protection of organic matter by mineral matrix in a cenomanian black shale abstract three types of pathways degradation recondensation natural sulphurization and selective preservation are commonly considered for the formation of kerogen dispersed in sedimentary rocks a fourth pathway has been recently put forward however from studies on recent marine sediments the so called sorptive protection mechanism this pathway is based on the adsorption of otherwise labile organic compounds onto minerals thus preventing their diagenetic degradation and promoting their subsequent condensation into kerogen the main results of the present study are derived from a combination of microscopic and pyrolytic methods applied on a cenomanian kerogen they provide i evidence on an ancient material for a crucial role of the mineral matrix both in organic matter om preservation during kerogen formation and in kerogen stability once formed ii indications that the dominant protective process likely involves physical protection by minerals resulting from alternation of organic and clay nanolayers of approximately 100 nm in thickness rather than om adsorption as molecular monolayers and iii observations of the relatively poor stability of an isolated kerogen contrary to the inertness commonly assumed for fossil macromolecular organic matter

molecular indicators of redox and marine photoautotroph composition in the late middle ordovician of iowa u s a abstract saturated and aromatic hydrocarbons were used to evaluate depositional redox conditions and marine photoautotroph contributions to middle caradocian strata of the central united states ia at the base of the spechts ferry member of the decorah formation 13c enriched aryl isoprenoids derivatives of green sulfur bacteria become abundant indicating the development of photic zone anoxia this is coincident with the disappearance of the organic walled microfossil gloeocapsomorpha prisca and a marked decrease in the relative abundances of cyanobacterial biomarkers the development of dysoxic to anoxic conditions and or associated changes in basin circulation potentially affected the distributions and abundances of these organisms in the overlying guttenberg member g prisca derived organic matter becomes dominant but relative cyanobacteria abundances remain low in addition the percentage total organic carbon is greater than 20 even though selected biomarker ratios pristane phytane ratios greater than 3 and homohopane indices less than 0 5 and the presence of bioturbation indicate that bottom waters were oxygenated it is suggested that deposition of g prisca affected both organic matter preservation and depositional redox conditions observed variations in redox indicators and marine photoautotroph contributions are associated with changes in siliciclastic deposition reported macrofauna turnover and with evidence for oceanic cooling and a change in circulation patterns documented in the eastern united states

geochemical evidence for oxygenated bottom waters during deposition of fossiliferous strata of the burgess shale formation abstract deciphering the oxygenation potential of bottom waters during deposition of the fossiliferous strata of the burgess shale is key to understanding the paleoecology of the organisms preserved as fossils and the processes involved in their preservation methods of paleo redox determination that are based upon trace fossils organic carbon content or size analysis of pyrite framboids are problematic when applied to the burgess shale fortunately patterns in redox sensitive trace elements hold great potential for determining paleo redox conditions for these greenschist facies rocks because they are independent of both age and metamorphic grade four burgess shale type bst fossil bearing sections were studied three lie within the burgess shale formation whereas one lies within the slightly younger duchesnay unit of the middle chancellor formation the geochemical proxies of seawater redox conditions that were used are mo u th v cr v v ni ni co and v sc each of these redox sensitive indices suggests that oxygenated conditions prevailed in the overlying seawater during deposition of beds within which bst preservation developed non fossiliferous beds at the base of the mt stephen trilobite beds yield three geochemical indices v v ni v sc ni co that indicate deposition under dysoxic to anoxic conditions thus the only beds to have been deposited under anoxic conditions are barren of fossils of soft bodied taxa further contradicting the notion that bottom water anoxia is a factor in bst preservation the laminated nature of the burgess shale and evidence for subsurface anoxia coupled with evidence for oxygenated bottom waters presence of bacterial mats and surficial trace fossils suggest that the burgess shale was deposited in the exaerobic zone oxic anoxic boundary at the water sediment interface implications of this reinterpretation of the depositional environment of the burgess shale include 1 taphonomic models for bst preservation must account for the presence of oxygen in bottom waters 2 paleoecological interpretations of the burgess shale need to account for a probable autochthonous benthic component in what is a complex assemblage of fossils that includes elements derived from the platform and 3 the possibility of burgess shale communities based upon chemosynthesis and or bacteria grazing must be considered

kerogen origin evolution and structure kerogen commonly defined as the insoluble macromolecular organic matter om dispersed in sedimentary rocks is by far the most abundant form of om on earth this fossil material is of prime importance as the source of oil and natural gas moreover kerogen can provide essential information on major topics such as past environments climates and biota this review reports the main advances in kerogen studies since the comprehensive synthesis edited by durand durand b ed kerogen insoluble organic matter from sedimentary rocks editions technip paris 1980 it is organized into eight sections the first two are concerned with the successive definitions of kerogen and the definition used here the different techniques used for kerogen isolation without loss or degradation and basic kerogen analysis the third and fourth focus on sedimentary om sources and preservation processes in relation to depositional environment including sedimentation conditions favourable for kerogen accumulation and extrapolation to past geological time great strides have been made in the latter topics over the last 25 years owing to a combination of classical studies in organic geochemistry and studies in other domains such as biogeochemistry oceanography hydrology and soil science along with the development of powerful analytical tools the next two sections deal with the different kerogen classifications by type and kerogen evolution and maturation upon burial in sediments structural modelling of coal and kerogen based on physical and or chemical structural analysis is described in the following section although only statistical the models thus derived provide a synthetic view of the main structural resemblances and differences among various samples in relation to source maturity or physicochemical properties finally the last section explores some of the advances in kerogen understanding expected for the near future the review includes a list containing about 500 references

sensitivity of biomarker properties to depositional environment and or source input in the lower toarcian of sw germany abstract a sequence of lower toarcian sediments which are highly contrasting in their depositional environment over a 5 m depth interval has been investigated in detail for the variability of geochemical properties which are used for source characterization and oil to source correlation lower liassic marls are representative of a well aerated shallow water environment in contrast to the immediately overlying bituminous shales which are deposited under extremely reducing conditions various properties have been found to vary considerably within these two units amongst the most important are carbon isotopic composition of the kerogen the pristane phytane ratios nickel as opposed to vanadyl porphyrins and the c27 dia regular steranes although maturation within the profile does not change some of the maturation dependent biomarker properties such as the monoaromatic steroid side chain cracking and the tm ts ratio exhibit large changes which can be assigned to diagenetic processes another maturation dependent property the 20s 20r epimerization of c29 steranes exhibits smaller changes which could also be due to early diagenetic processes the study suggests that reducing and oxidizing conditions i e eh and ph in the sediment exert an influence on several biomarker precursor product pathways in maturation studies initial variations due to depositional conditions have therefore to be taken into account

paleoenvironmental implications of novel c30 steranes in precambrian to cenozoic age petroleum and bitumen petroleums and bitumens from early proterozoic 1800 ma to miocene 15 ma age marine strata contain 24 isopropylcholestanes a novel group of c30 steroids the abundance of these compounds relative to 24 n propylcholestanes varies with source rock age late proterozoic vendian and early cambrian oils and or bitumens from siberia the urals oman australia and india have a high ratio of 24 isopropylcholestanes to 24 n propylcholestanes 1 while younger and older samples have a lower ratio 0 4 temporal changes in this parameter may reflect the relative abundance of certain porifera sponges and certain marine algae through time geochemical indicators such as this which can constrain the source rock age of a migrated oil are useful in source rock identification during petroleum exploration

radium isotopes as tracers of iron sources fueling a southern ocean phytoplankton bloom elevated levels of productivity in the wake of southern ocean island systems are common despite the fact that they are encircled by high nutrient low chlorophyll hnlc waters in the crozet plateau region it has been hypothesized that iron from island runoff or sediments of the plateau could be fueling the austral summer phytoplankton bloom here we use radium isotopes to quantify the rates of surface ocean iron supply fueling the bloom in the crozet plateau region a 1d eddy diffusion mixing model applied to a 228 ra profile t1 2 5 75 years at a station north of the islands suggests fast vertical mixing in the upper 300 m kz 11 100 cm 2 s 1 with slower mixing between 300 and 1000 m kz 1 5 cm 2 s 1 this estimate is discussed in the context of kz derived from the ctd ladcp data in combination with the dissolved fe profile at this location we estimated a vertical flux of between 5 6 and 31 nmol fe m 2 d 1 the cross plateau gradients in the short lived radium isotopes 224 ra t1 2 3 66 d and 223 ra t1 2 11 4 d yielded horizontal eddy diffusivities kh o f 39 and 6 6 m 2 s 1 respectively if we assume that the islands surface runoff alone were supplying dissolved fe to the bloom region then the flux estimates range from 2 3 to 14 nmol fe m 2 d 1 if the plateau sediments are considered a source of fe and conveyed to the bloom region through deep winter mixing combined with horizontal transport then this flux may be as high as 64 390 nmol fe m 2 d 1 combined these fe sources are sufficient to initiate and maintain the

a comparison of thermal maturity parameters between freely extracted hydrocarbons bitumen i and a second extract bitumen ii from within the kerogen matrix of permian and triassic sedimentary rocks abstract in this study we compared various maturity dependent aromatic steroid and triterpenoid hydrocarbon ratios in bitumens that are freely extractable from sedimentary rocks bitumen i with those in second extracts that comprised hydrocarbons closely associated with the kerogen mineral matrix bitumen ii bitumen ii was released through kerogen isolation and demineralisation using hcl and hf h3bo3 the samples studied although of similar age come from different localities they represent a range of facies and two kerogen types ii and iii and all were deposited under marine conditions the results show that the more stable isomers of methylnaphthalene mn and methylphenanthrene mp are relatively more abundant in bitumen ii the difference between the methylnaphthalene ratio mnr of bitumens i and ii when plotted against the ratio of clay to total organic carbon clay toc gives an excellent correlation r2 0 88 the highest clay toc ratio corresponds with the biggest difference in mnr for the respective bitumens consistent with the more stable isomers being preferentially retained within the clay kerogen matrix since the mp isomers are higher in bitumen ii than in bitumen i it was anticipated that their methylphenanthrene index mpi 1 values a commonly used measure of thermal maturity would also be different for most samples the measured mpi 1 in bitumen i is generally higher than that in bitumen ii except for three samples thus showing a bias towards a lower thermal maturity for the second extract the opposite is true of the mp ratio and mnr this may be attributed to the fact that phenanthrene p which is part of the denominator in mpi 1 is more stable than its methylated counterparts steroid and triterpenoid maturity parameters also showed differences between the two extracts with c27 diasterane sterane and ts ts tm being higher in bitumen i only the former parameter is positively correlated with the clay toc ratio suggesting that clay content probably influences the diagenetic transformation of steroid precursors to diasteranes the observed differences between the maturity parameters of bitumen i and bitumen ii may be especially important in sedimentary rocks that contain high percentages of clay minerals

improved methods for isolating and validating indigenous biomarkers in precambrian rocks hydrocarbon biomarkers in highly mature precambrian rocks have the potential to provide important information about the diversity ecology and evolution of early life but studying them presents special analytical challenges extractable hydrocarbons are present in archean and most paleoproterozoic sedimentary rocks in such trace concentration that even slight contamination from petroleum derived materials in situ or during drilling storage sampling handling and laboratory analysis would compromise the results and thereby any consequent inferences here we report protocols that we have developed for the analysis of cores from several recently completed deep time scientific drilling initiatives by paying special attention to cutting cleaning crushing and extraction it is possible to significantly reduce laboratory blanks to acceptable levels when these methods are utilized meaningful variations in the patterns of biomarkers over stratigraphic and lithologic boundaries provide compelling evidence for syngeneity

carbon isotopic evolution of the terminal neoproterozoic and early cambrian evidence from the yangtze platform south china profound geotectonic climatic and biological changes occurred during the terminal neoproterozoic and its transition into the early cambrian these changes are reflected in temporal variations of the carbon isotopic composition of seawater recorded in a sedimentary succession on china s yangtze platform however in addition to secular changes in carbon isotopes the studied succession reflects additional variations in accordance with the deposition in different sedimentary facies ranging from shallow water platformal to deeper water basinal settings likely a consequence of incorporation of variable amounts of 13 c depleted

the emu bay shale konservat lagerstatte a view of cambrian life from east gondwana recent fossil discoveries from the lower cambrian emu bay shale ebs on kangaroo island south australia have provided critical insights into the tempo of the cambrian explosion of animals such as the origin and seemingly rapid evolution of arthropod compound eyes as well as extending the geographical ranges of several groups to the east gondwanan margin supporting close faunal affinities with south china the ebs also holds great potential for broadening knowledge on taphonomic pathways involved in the exceptional preservation of fossils in cambrian konservat lagerstatten ebs fossils display a range of taphonomic modes for a variety of soft tissues especially phosphatization and pyritization in some cases recording a level of anatomical detail that is absent from most cambrian konservat lagerstatten