hydrocarbon biomarkers of neoproterozoic to lower cambrian oils from eastern siberia the neoproterozoic era is of widespread geobiological interest because it marks the critical transition from a world of microbes to one where animals become an established feature of the landscape much research into this time period has focused on the ventilation of the oceans as this is widely considered a primary factor driving the diversification of complex multicellular life in this study proterozoic to cambrian aged oils from eastern siberia were analyzed for their hydrocarbon biomarker contents and compound specific carbon isotopes in order to further our understanding of the prevailing environment and its microbial and metazoan communities geochemically these oils are broadly comparable to those of the ediacaran cambrian sedimentary rocks and oils of the south oman salt basin organic matter in the source sedimentary rocks included significant contributions from green algae demosponges and bacteria including cyanobacteria and methanotrophic proteobacteria although the ages of the siberian oils and putative parent source rock intervals are poorly constrained the geochemical similarities between the ediacaran oman huqf and nepa botuoba katanga family of siberian oil samples are impressive leading to the inference that their source rocks are coeval on the other hand oils from the baykit high are distinctive likely older and possibly of cryogenian age

deep sea carbonates reading the carbon isotope signal the carbon isotope signal in deep sea sediments reflects a mix of 1 global changes in the rates of exchange of the ocean s carbon reservoir with biosphere soil and sediments 2 global and regional changes in surface water productivity 3 internal shifts in water mass structure and circulation basin basin fractionation oxygen minimum development and 4 organism specific fractionation effects due to changes in micro habitat and or ontogenic fractionation vital effects additional complications arise from differential preservation it is impossible to entirely isolate these various factors as a rule of thumb long period signals that are parallel for planktonic and benthic data reflect external global fractionation patterns whilst short period signals are more likely tied to internal patterns water mass fractionation the various approaches to interpretation are illustrated with three case studies the glacial holocene transition the messinian carbon shift and the miocene monterey excursion

active and passive microwave signatures of antarctic firn by means of field measurements and satellite data the angular dependence and polarization behaviour of back scattering and emission of polar firn at 5 2 ghz and 10 3 ghz were measured during an oversnow traverse in dronning maud land antarctica the signatures emphasize the importance of snow stratification in the interpretation of microwave remote sensing measurements highest backscattering coefficients and little angular variations were observed for refrozen firn near the coast in permanently dry snow areas with high accumulation rates and homogeneous snow morphology showed low backscattering coefficients and high emissivities pronounced layering and related density variations in low accumulation zones resulted in increased polarization differences of brightness temperatures and increased like polarized backscattering coefficients this behaviour is confirmed by the analysis of c band scatterometer measurements of the active microwave instrument aboard the european space agency s ers 1

resolution enhancement of spaceborne scatterometer data a method for generating enhanced resolution radar images of the earth s surface using spaceborne scatterometry is presented the technique is based on an image reconstruction technique that takes advantage of the spatial overlap in scatterometer measurements made at different times to provide enhanced imaging resolution the reconstruction algorithm is described and the technique is demonstrated using both simulated and actual seasat a scatterometer sass measurements the technique can also be used with ers 1 scatterometer data the sass derived images which have approximately 4 km resolution illustrate the resolution enhancement capability of the technique which permits utilization of both historic and contemporary scatterometer data for medium scale monitoring of vegetation and polar ice the tradeoff between imaging noise and resolution inherent in the technique is discussed

organic geochemistry in a sequence stratigraphic framework the siliciclastic shelf environment of cretaceous series se france for a better understanding of siliciclastic shelf environments correlation between sequence stratigraphy and organic geochemistry is used our study is focused on the cretaceous deposits of marcoule gard france particularly on a close packed siltites layer 200 400 m thick which is well characterized as a marine flooding facies of a single trangressive regressive cycle during the uppermost albian and the lower cenomanian the stratigraphic data indicate a change in the depositional environment from offshore to shoreface organic geochemistry is used in order to characterize origin and variability of the organic matter in relation to the stratigraphic data the study is carried out on core samples from 2 drill holes mar 203 and mar 501 analyses of the aliphatic and aromatic hydrocarbons were performed using gc ms and focused on biomarker distributions the biomarkers indicate a contribution of mixed terrestrial and marine organic matter the changes in molecular signatures are related to variations in the source of organic matter marine versus terrestrial preservation conditions largely influenced by clay and early diagenesis environmental oxidation reduction and acidic conditions as well as bioturbation various environmental zones characterized by different molecular signatures can be distinguished resin derived biomarkers can be assigned to higher plant material input and may reflect the evolution and diversity of gymnospermae versus angiospermae during the transgressive regressive cycle the relative sea level variations are clearly correlated with the nature and the preservation of the organic matter for example the pr ph and pr n c 17 ratios as well as the regular steranes distributions underline the maximum flooding surface evidenced by other studies we observe a good correlation between the organic data and sequence stratigraphy changes in geochemical signatures reflect the 3rd order depositional cycles

branched aliphatic alkanes with quaternary substituted carbon atoms in modern and ancient geologic samples a pseudohomologous series of branched aliphatic alkanes with a quaternary substituted carbon atom baqcs specifically 2 2 dimethylalkanes and 3 3 and 5 5 diethylalkanes were identified in warm 65 c deep sea hydrothermal waters and late cretaceous black shales 5 5 diethylalkanes were also observed in modern and holocene marine shelf sediments and in shales spanning the last 800 million years of the geological record the carbon number distribution of baqcs indicates a biological origin these compounds were observed but not identified in previous studies of 2 0 billion to 2 2 billion year old metasediments and were commonly misidentified in other sediment samples indicating that baqcs are widespread in the geological record the source organisms of baqcs are unknown but their paleobiogeographic distribution suggests that they have an affinity for sulfides and might be nonphotosynthetic sulfide oxidizers

a decade of quikscat scatterometer sea ice extent data polar sea ice is an important input to global climate models and is considered to be a sensitive indicator of climate change while originally designed only for wind estimation radar backscatter measurements collected by wind scatterometers have proven useful for estimating the extent of sea ice during the quick scatterometer quikscat mission seawinds data were used to operationally map the sea ice extent the resulting sea ice maps were used to mask near surface winds to support seawinds primary mission of measuring near surface winds over the ocean this paper describes the operational seawinds sea ice extent mapping algorithm provides validation comparisons and presents results from the ten year data product starting with enhanced resolution horizontal polarization and vertical polarization backscatter images the algorithm employs an iterative maximum likelihood classifier with fixed thresholds to segment sea ice and open ocean pixels residual classification errors are reduced through binary image processing techniques and sea ice growth retreat constraint methods the algorithm results are compared with sea ice concentrations derived from special sensor microwave imager data and with radarsat synthetic aperture radar imagery the results suggest differences in the sensitivities of active and passive products given their channel sets and specific algorithms derived sea ice extents over the full decade long quikscat mission data set are analyzed to show important trends in sea ice extent for the antarctic and arctic regions

shallow stratification prevailed for 1700 to 1300 ma ocean evidence from organic carbon isotopes in the north china craton abstract the late paleoproterozoic to early mesoproterozoic from 1700 ma to 1300 ma was highlighted by the assembly of the nuna supercontinent expansion of euxinic marine environments and apparent stasis in the diversity of eukaryotes the isotopic composition of carbonate carbon 13ccarb was surprisingly constant during this interval but little is known about the secular variation in the organic carbon isotopic composition 13corg here we report 13corg data from the latest paleoproterozoic 1650 ma to early mesoproterozoic 1300 ma succession in north china the 13corg values range from 25 to 34 and are dependent on sedimentary facies in subtidal and deeper environments 13corg values are low and constant ca 32 but relatively enriched and more variable in shallower intertidal and supratidal environments we attribute the facies dependent variation in 13corg to the presence of a shallow chemocline a probable result of a shallow chemocline is that it supported significant contributions of organic matter produced by chemoautotrophic and or anaerobic photoautotrophic microbes in relatively deep environments from the latest paleoproterozoic to early mesoproterozoic continental shelf of north china

biomarker evidence for photosynthesis during neoproterozoic glaciation laterally extensive black shales were deposited on the sao francisco craton in southeastern brazil during low latitude neoproterozoic glaciation 740 to 700 million years ago these rocks contain up to 3 0 weight organic carbon which we interpret as representing the preserved record of abundant marine primary productivity from glacial times extractable biomarkers reflect a complex and productive microbial ecosystem including both phototrophic bacteria and eukaryotes living in a stratified ocean with thin or absent sea ice oxic surface waters and euxinic conditions within the photic zone such an environment provides important constraints for parts of the snowball earth hypothesis

a reconstruction of archean biological diversity based on molecular fossils from the 2 78 to 2 45 billion year old mount bruce supergroup hamersley basin western australia abstract bitumens extracted from 2 7 to 2 5 billion year old ga shales of the fortescue and hamersley groups in the pilbara craton western australia contain traces of molecular fossils based on a combination of molecular characteristics typical of many precambrian bitumens their consistently and unusually high thermal maturities and their widespread distribution throughout the hamersley basin the bitumens can be characterized as probably of archean age accepting this interpretation the biomarkers open a new window on archean biodiversity the presence of hopanes in the archean rocks confirms the antiquity of the domain bacteria and high relative concentrations of 2 methylhopanes indicate that cyanobacteria were important primary producers oxygenic photosynthesis therefore evolved 2 7 ga ago and well before independent evidence suggests significant levels of oxygen accumulated in the atmosphere moreover the abundance of cyanobacterial biomarkers in shales interbedded with oxide facies banded iron formations bif indicates that although some archean bif might have been formed by abiotic photochemical processes or anoxygenic phototrophic bacteria those in the hamersley group formed as a direct consequence of biological oxygen production biomarkers of the 3 methylhopane series suggest that microaerophilic heterotrophic bacteria probably methanotrophs or methylotrophs were active in late archean environments the presence of steranes in a wide range of structures with relative abundances like those from late paleoproterozoic to phanerozoic sediments is convincing evidence for the existence of eukaryotes in the late archean 900 ma before visible fossil evidence indicates that the lineage arose sterol biosynthesis in extant eukaryotes requires molecular oxygen the presence of steranes together with biomarkers of oxygenic photosynthetic cyanobacteria suggests that the concentration of dissolved oxygen in some regions of the upper water column was equivalent to at least 1 of the present atmospheric level pal and may have been sufficient to support aerobic respiration

exceptionally preserved microbially induced sedimentary structures from the ediacaran post glacial successions in the kimberley region northwestern australia abstract a set of exceptionally preserved microbially induced sedimentary structures miss is described from the post glacial yurabi formation of late ediacaran age in the kimberley region northwestern australia these miss comprise oriented grains bamboo leaf like cracks polygonal cracks worm like cracks sinuous cracks gas domes pyrite concentrated laminae and micrite laminae most of the yurabi miss are morphologically comparable with their ancient and modern counterparts micrometre or nannometre scale bacteria or biofilm like inorganic objects are detected from most miss and are interpreted as bacterial bodies or remains that have been replaced with inorganic minerals upon fossilization oriented grains indirectly support microbial control on their accumulation both pyrite conformable laminae and micrite laminae suggest degradation and decay of original microbial mats upon diagenesis sinuous cracks were likely generated in a soft sediment deformation process whereas other sand cracks bamboo leaf like cracks worm like cracks polygonal cracks could have formed from sediment surface layer microbial organics shrinkage upon desiccation gas domes may have formed as the result of anoxic redox reactions and being filled with gases and sediments transported from below two proxies bedding plane coverage percentage and accumulative thickness of single miss bearing beds are developed to semi quantitatively evaluate miss abundance on bedding plane and vertical outcrop respectively the yurabi miss have substratum preference to fine sandstone facies and intertidal settings the yurabi formation yields the most abundant and diverse post glacial miss assemblages during the late ediacaran worldwide both kimberley and global fossil records indicate that miss may have proliferated in shallow marine ecosystems soon after the retreat of ediacaran gaskiers glaciation during late neoproterozoic

a chemostratigraphic overview of the late cryogenian interglacial sequence in the adelaide fold thrust belt south australia within the neoproterozoic sequence of the adelaide fold thrust belt south australia two of the most severe ice ages in earth history sturtian and marinoan are recorded in the glacigenic rocks which mark the base and top of the 4 5 km thick umberatana group the focus of the present chemostratigraphic study rock units from three drillholes and ten measured outcrop sections located in the southern and central flinders ranges and on the stuart shelf were sampled for isotopic analysis of their co existing calcite 13ccal dolomite 13cdol and kerogen 13corg strontium and sulphur isotopic analyses were also run on selected samples the sample sites are in tectonic domains where regional metamorphism has been insufficient to significantly alter the isotopic composition of the kerogen the resulting data when integrated with the lithostratigraphy of the umberatana group yield one of the most complete records of secular variation in the c isotope signature of the late cryogenian ocean between 750 and 680 ma its composite 13ccarb curve begins with a sharp positive excursion 3 to 1 5 in the dolomitic tindelpina shale which caps sturtian glacial diamictites wilyerpa formation then follows a steady climb through the shoaling upward tapley hill formation reaching 4 in the brighton limestone and culminating in a plateau of 13c enrichment within the platformal carbonates of the etina formation 8 to 10 the upper part of the temporal trend shows a decline to 6 to 7 in the stromatolite reef facies of the enorama shale and a dramatic drop to 8 to 9 5 followed by a recovery to 3 in the youngest carbonate unit trezona formation beneath the marinoan glacigenic elatina formation the latter is capped by a thin dolostone the nuccaleena formation which records a consistent up section decrease in 13c 1 to 3 superimposed on this overall pattern of c isotopic variation are second and third order fluctuations attributable to eustatic sea level change pyritic sulphur in the lower tapley hill formation 34s 9 to 40 is distinctly heavier than that in the underlying wilyerpa formation 4 to 20 minimum 87sr 86sr values obtained from the brighton limestone 0 7071 and etina formation 0 7076 are consistent with their late cryogenian age this sturtian to marinoan interglacial succession is more complete than equivalent sequences elsewhere and thus provides a useful reference for global chemostratigraphic correlation notable features of its c isotope curve are the strong post wilyerpa positive excursion also seen in key sections from svalbard and western mongolia the etina plateau of 13c enrichment which is remarkably similar to maxima in the terminal proterozoic c isotope records of western mongolia north western canada and brazil and the spectacular depletion of 13c in the lower trezona relative to similar carbonate facies in the underlying etina formation and enorama shale a preglacial offset in 13ccarb values of such proportions 14 is almost unprecedented except perhaps for that recently documented in the upper ombaatjie formation beneath tillites of the ghaub formation otavi group namibia it represents a key piece of evidence in the case presented by the proponents of a neoproterozoic snowball earth

scatterometer backscatter imaging using backus gilbert inversion wind scatterometer measurements are collected over an irregular grid and processing is required to generate backscatter images on an earth centered grid the most common algorithms used for this are drop in the bucket dib and variations of the scatterometer image reconstruction sir algorithm these algorithms are also used for radiometer brightness temperature imaging the backus gilbert bg algorithm has been used for radiometer imaging but has not been applied to scatterometer backscatter imaging in this paper the application of bg to scatterometer backscatter imaging is explored and its performance is compared to dib and sir like sir optimally tuned bg is capable of producing higher resolution images than dib though its noise performance is slightly inferior to sir s while bg and sir produce similar results for radiometer data the higher relative noise level of scatterometer data increases the differences between the sir and bg algorithm performance and limits the performance of bg relative to sir in scatterometer imaging comparison of the sir and bg algorithms in scatterometer imaging offers important insights into the inversion reconstruction problem

subtidal stromatolites in monterey formation and other organic rich rocks as suggested source contributors to petroleum formation the miocene monterey formation contains thin organic rich laminations that mimic benthic mats forming today in coastal upwelling regimes of the eastern pacific modern mats are comprised dominantly of filamentous sulfur oxidizing bacteria of the family beggiatoaceae the characteristic spongy texture imparted to the sediments by these bacterial mats is most readily recognized using scanning electron microscopy sem the spongy network becomes progressively compressed with increasing compaction and diagenesis but is still distinguishable rock eval pyrolysis of modern mats reveals high s1 peaks and unusually high oxygen indices both parameters decrease gradually with diagenesis as evidenced by mat laminated monterey formation samples of different thermal grades in addition anomalously light nitrogen isotopic signatures of modern mats may be retained the dgrn15 values of mat laminated monterey formation samples although diagenetically enriched in 15n are still lighter than would be expected for algally dominated organic matter in marine low oxygen environments on the basis of organic richness and high hydrogen indices of mat laminated samples and coincidence of mat laminated rocks and oil in some fields in the san joaquin valley of california the organic matter assemblage contained within filamentous bacterial mats is suggested to be a significant contributor to petroleum formation additional evidence for this conclusion is provided by similar investigations of subtidal cyanobacterial mats in carbonate rocks such as the green river formation oil shales

post depositional migration of elements during diagenesis in brown clay and turbidite sequences in the north east atlantic abstract two cores from a ne atlantic pelagic clay area of low accumulation rate each contain a single turbidite with different age thickness and composition diagenesis following introduction of exotic turbidite material into the pelagic clay sequence has resulted in distinctive colour changes the diagenetic process is thought to be driven by bacterially mediated organic oxidation and compositional differences in the turbidites and clays allow examination of the effects on metal concentrations of this process in one core a long turbidite section emplaced 330 000 years ago is overlain by clay organic oxidation has apparently proceeded from the turbidite top downwards and has maintained a u concentration peak below the oxidation front marked by a colour change the u source is believed to be u initially associated with the organic matter in the oxidised section of the turbidite vanadium and cu behave similarly but upward migration of the redox sensitive metals mn and ni is also seen in the second core an 8 cm turbidite section was emplaced about 170 000 years ago in a clay column in this case organic consumption now appears complete but evidence for diagenetic effects is found in a 16 cm compositional alteration halo of the underlying pelagic clay fe ii has been enriched and the hydrogenous component of mn co ni and cu removed from the pelagic clay to form the halo

tracking large tabular icebergs using the seawinds ku band microwave scatterometer abstract knowledge of iceberg locations is important for safety reasons as well as for understanding many geophysical and biological processes originally designed to measure wind speed and direction over the ocean seawinds is a microwave scatterometer that operates at 13 4 ghz ku band on the quikscat satellite radar measurements from seawinds are collected and processed on a daily basis using resolution enhancement techniques to produce daily radar images because icebergs scatter microwave energy more than sea ice and sea water icebergs are detected as high backscatter targets surrounded by lower backscatter regions in daily seawinds images as a result iceberg positions are determined in real time and a time series of iceberg positions is maintained in an antarctic iceberg database by brigham young university s microwave earth remote sensing mers laboratory since seawinds operates independent of both solar illumination and cloud cover and has a large daily spatial coverage this paper demonstrates that seawinds is an excellent platform to detect and track large tabular icebergs these icebergs are generally larger than 5 km and are typically characterized as a rough ice plateau above the surrounding sea water or sea ice the number of icebergs tracked in the mers antarctic iceberg database is found to be generally greater than the number of icebergs tracked by the national ice center the movement patterns of all icebergs detected by seawinds are also analyzed and 90 of icebergs are found to travel a counter clockwise path around antarctica and accumulate in the weddell and scotia seas iceberg detection and tracking is demonstrated via multiple case studies that highlight icebergs c 19a and a 22a using the mers database and through real time operational support of the 2005 2008 and 2009 nsf antarctic cruises iceberg positions are validated by using collocated high resolution satellite imagery and by navigating the nsf ships to physically intercept several large tabular icebergs in the weddell and scotia seas

bitumen ii from the paleoproterozoic here s your chance pb zn ag deposit implications for the analysis of depositional environment and thermal maturity of hydrothermally altered sediments abstract the formation of sedimentary exhalative sedex pb zn deposits is linked to ocean euxinia but recent evidence suggests that ferruginous conditions may have dominated the deep ocean during the middle proterozoic a maximum period for sedex distribution biomarkers of sulfate reducing and sulfide oxidising bacteria are valuable indicators of euxinic conditions in such settings organic matter om from sedex deposits is often affected by alteration and or migration but om entrapped within the kerogen mineral matrix bitumen ii may be less affected than the freely extractable om bitumen i we analysed bitumen ii from the paleoproterozoic here s your chance hyc pb zn ag deposit to find evidence of euxinic conditions in the depositional environment n alkane distributions in bitumen ii are markedly distinct from previously reported bitumen i bitumen ii contains long chain n alkanes up to c 36 or c 38 and a strong even over odd distribution in a number of samples which are 4 to 7 depleted in 13 c compared to n alkanes in bitumen i and verified as indigenous by comparison with 13 c of isolated kerogen these features are interpreted as evidence of sulfate reducing and sulfide oxidising bacteria confirming that hyc was deposited under euxinic conditions bitumen ii has the potential to reveal information from om that is degraded and or overprinted in bitumen i commonly used methylphenanthrene maturity ratios give conflicting information as to the relative maturity of bitumens i and ii bitumen i contains a far higher proportion of methylated phenanthrenes than bitumen ii as bitumen ii is sequestered within the kerogen mineral matrix it may have restricted access to the methyl pool of organic compounds that can donate methyl groups to aromatic hydrocarbons parameters that include both phenanthrene and methylphenanthrenes do not appear suitable to compare the maturity of bitumens i and ii hence there is no clear evidence that bitumen ii is of lower thermal maturity than bitumen i

neoproterozoic stratigraphy of the centralian superbasin australia abstract the basement of central australia includes the arunta block and the 1200 1100 ma musgrave block succeeded by 1075 1000 ma bimodal volcanic rifts and dolerite dykes a regional hiatus at 1000 800 ma interpreted as reflecting a central post volcanic underplated upland was followed at 800 ma by a second swarm of dykes in the musgrave block gawler craton and stuart shelf associated with the crustal sagging that initiated the centralian superbasin the centralian superbasin is defined here to encompass the neoproterozoic fill of the amadeus georgina ngalia officer and savory basins the intra cratonic superbasin was disrupted internally 540 600 ma ago petermann ranges orogeny by a central uplift and associated thrusts and by mid carboniferous 320 ma tectonism alice springs orogeny to form the structural basins listed above the stratigraphy and sedimentology of the relatively well known areas can be used as a basis for predicting those of the poorly known regions new results from acritarch biostratigraphy and isotope chemostratigraphy in conjunction with conventional lithostratigraphy and sequence analysis allow better stratigraphic resolution than previously possible field observations in the recently discovered savory basin in western australia provide a basis for correlations with the adjacent basins

the possible role of benthic microbial mats during the formation of carbonaceous shales in shallow mid proterozoic basins a considerable portion of the upper member of the mid proterozoic newland formation meagher county montana consists of carbonaceous silty shales striped shale facies this type of shale facies is common in proterozoic basins and is host to several major base metal deposits the striped shales were deposited in a subtidal setting basinward of carbonates characterized by cryptalgal laminites mudcracks and flat pebble conglomerates the carbonaceous silty shales are considered remnants of benthic microbial mats irregular internal laminae patterns of particle trapping mechanical deformation during penecontemporaneous soft sediment deformation and filamentous microbiota provide evidence for this interpretation the dolomitic clayey shale contains graded silt clay couplets and these are interpreted as storm layers modern subtidal microbial mats can only survive under special conditions but in the proterozoic it is suggested that benthic microbial mats colonized the shallow seafloor during periods of low sediment input leading to the formation of carbonaceous shales

the cottons breccia ediacaran and its tectonostratigraphic context within the grassy group king island australia a rift related gravity slump deposit abstract the cottons breccia is part of the upper neoproterozoic ediacaran 586 572 ma grassy group exposed on king island tasmania this formation has been widely interpreted as an unambiguous tillite in support of tectono climatic models that invoke catastrophic latest neoproterozoic global glaciation however dissenting opinions interpret the cottons breccia as a tectonic breccia in this paper we review the tectonostratigraphy of the cottons breccia and the enclosing grassy group we find no unambiguous evidence for a direct glacial origin as postulated by some early workers an interpretation of the cottons breccia as a deposit within half graben in the shoulder regions of an actively developing latest neoproterozoic volcanic rifted margin is consistent with all the available sedimentological structural geochronological and tectonic evidence

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

features of meteorological events preserved in a high resolution law dome east antarctica snow pit snow pitandshallow firn corerecordsofoxygenisotoperatios d 18 o and traceionspeciesweregeneratedatahigh accumulationsiteonlaw dome eastantarctica concordancebetweenaccumulationeventsidentifiedin recordsupto 7 7kmapartconfirms that the observed glaciochemical variations are the result of regional rather than local sur face effects this allows calibration of the snow pit records with measured meteorological parameters netaccumulationperiodsthatcomprisethesnow pitrecordareidentifiedusing hourly snow accumulation measurements from a co located automatic weather station aws particular focus isgiventothreenetaccumulationperiods preservedduringaustral summer 1999 2000 that correspond to the top 0 5m of the snow pit local meteorological conditions recorded during the summer accumulation periods by the aws are combined with regional and synoptic scale meteorology derived from casey station 110km away and advancedvery high resolution radiometer satellite imagery to identify potential source regions forchemical signals preserved in summer snowat law dome

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

facies and origin of shales from the mid proterozoic newland formation belt basin montana usa shales constitute more than 60 of the world s sediments yet while facies models for sandstones and carbonates are at a high level of sophistication the study of shales has clearly lagged behind in the mid proterozoic newland formation six major shale facies types deposited in nearshore to basinal environments are distinguished on the basis of bedding characteristics textural features and the proportions of silt clay and carbonate textural features of these shale types are related to sedimentary environments as deduced from associated lithologies the shales are undisturbed by bioturbation and their textural and sedimentary characteristics reflect subaqueous growth of microbial mats erosion and deposition by storms deposition of flocculated vs dispersed clays continuous slow background sedimentation winnowing by waves or currents and subaerial exposure

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

cottons breccia of king island tasmania glacial or non glacial cryogenian or ediacaran abstract the cottons breccia of king island tasmania is a 100 m thick carbonate clast diamictite traditionally interpreted as the product of a cryogenian or ediacaran glaciation it was recently reinterpreted as a mass flow deposit unrelated to glaciation within an active rift basin we reaffirm the glacial periglacial interpretation on the basis of sedimentary facies internal facies relations clast lithology and isotopic composition clast fabric analysis and consistent stratigraphic position beneath a typical post glacial cap dolostone the cumberland creek dolostone closely resembles basal ediacaran cap dolostones world wide in terms of colour texture sedimentary structures and isotopic characteristics because it was deposited above storm wave base differences in 13 c between closely adjacent sections suggest diachronous deposition during post glacial marine transgression of a basin with steep local topography this is compatible with an active rift basin in which glacigenic diamictites of the end cryogenian marinoan pan glacial episode were lodged

use of c band scatterometer for sea ice edge identification this paper describes use of advanced scatterometer ascat c band scatterometer data for determination of the sea ice edge the variation in backscatter with measurement geometry is different for the sea ice surface compared to the open water surface utilizing the ascat antenna configuration with three different look angles for the same surface spot a new ascat sea ice parameter has been defined one year of ascat measurements has been collocated with background sea ice information to derive probability distributions for the ascat sea ice parameter given the known ice condition the result can be used in an inverse methodology a bayesian approach to calculate the probability of sea ice from the ascat measurements the method has been tested for a full year and validated against high resolution satellite images and ice charts from an operational ice service it reveals a realistic ice edge result however with weather induced noise problems in terms of false sea ice for automatic ice edge detection ancillary information is needed to remove this noise the paper shows how the method also can be used for ice edge detection with passive microwave data from ssm i and how it can be extended to utilize ascat together with ssm i in a multisensor approach

molecular and isotopic characterization of biomarkers in the frick swiss jura sediments a palaeoenvironmental reconstruction on the northern tethys margin abstract molecular and stable carbon isotope compositions of source specific hydrocarbons have been used to reconstruct palaeoenvironmental conditions during deposition of the middle hettangian to upper sinemurian sediments on the northern epicontinental tethys margin frick swiss jura increasing algal cyanobacterial and phytoplanktonic i e dinoflagellate contributions associated with the 13 c enrichment of cyanobacteria derivatives i e hopanes and monomethylalkanes suggest enhanced primary productivity upsection this is related to the 13 c enrichment of dissolved co 2 in the upper layers and the progressive increase of depth and oxygenation of the water column in the middle hettangian shallow water environments lagoon the occurrence of green sulfur bacteria chlorobiaceae derivatives indicates that the lower part of the water column was strictly anoxic and rich in h 2 s since these bacteria require very low light intensity to grow these euxinic conditions may be extended up to the photic zone allowing for anaerobic photosynthesis light penetration depth is most likely reduced by high productivity and or turbidity in the photic zone in these sediments 13 c depleted hopanoids 39 5 are most likely associated with phototrophic purple sulfur bacteria utilizing isotopically light organic carbon at the base of the aerobic zone these purple sulfur bacteria may have consumed the h 2 s used by chlorobiaceae in the deeper layers and thus sustained the algae and cyanobacteria productivity in the upper layers the 13 c depleted carbonate 13 3 may be partially related to the anaerobic oxidation of the organic matter during bacterial sulfate reduction

carbon isotopic composition of individual biomarkers in gilsonites utah abstract carbon isotopic compositions of saturated hydrocarbon aromatic hydrocarbon nso resin and asphaltene fractions of vein forming gilsonites cowboy bonanza independence wagonhound and harrison veins in the ne uinta basin utah are all similar and isotopically resemble mahogany zone shale extracts of the green river formation 13 c 29 to 31 individual molecular fossils in the gilsonites show a wider variability in compositions indicative of their paleoecological origins within the eocene uinta greater green river paleolake system carbon isotopic compositions of c28 and c29 steranes 13 c 25 to 32 pristance and phytane 33 to 34 and perhydro carotene carotane 13 c 33 2 suggest that organisms producing these compounds grew near the lake surface the c33 carotenoid lexane is isotopically identical to the c40 carotenoid carotane supporting a common c40 carotenoid precursor two groups of hopanes can be differentiated in the gilsonites based on carbon isotopic compositions c29 c31 and c32 hopanes and moretanes 40 9 to 44 3 consistent with a source from midwater bacteria and c30 hopanes and moretanes 51 0 and 60 5 for which the strong 13c depletion suggests at least partial derivation from methylotrophs the isotopic signatures of these molecular fossils suggest the source beds of the gilsonites were deposited in a stratified paleolake system with a depositional environment similar to that which formed the mahogany zone shales of the piceance creek basin algal biomarkers in the gilsonites are isotopically uniform throughout the area of the gilsonite vein occurrence 1500 km3 and resemble those in the mahogany zone shale in the piceance creek basin over 50 km to the east this remarkable lateral uniformity suggests that very similar photic zone water conditions existed across the entire uinta piceance creek paleolake system at the time of deposition of the gilsonite source bed mahogany zone shale sterane isotopic compositions are effective for the genetic correlation of the solid bitumens immature oils in contrast the carbon isotopic compositions of the bacterial biomarkers in the gilsonites vary significantly suggesting that conditions in deeper waters of the paleolake system were more variable carbon isotopic signatures of individual hopane biomarkers in the green river formation appear to be valuable for identifying different source facies characteristics within the same paleolake depositional system

occurrence and origin of mono di and trimethylalkanes in modern and holocene cyanobacterial mats from abu dhabi united arab emirates n alkanes highly branched isoprenoids monomethylalkanes mmas dimethylalkanes dmas and trimethylalkanes tmas are the most abundant components in the hydrocarbon fractions of extracts of four modern and two holocene cyanobacterial mats t1500 and 5110 170 y bp collected in abu dhabi united arab emirates the homologous families of mmas dmas and tmas were identified by comparison of mass spectral and relative retention time data with published data dmas were also identified by synthesis of authentic standards 3 9 dimethyltricosane 5 9 dimethyltricosane and 11 15 dimethylheptacosane mmas dmas and tmas of the cyanobacterial mats can be separated into two groups on the basis of their distribution patterns and structures mmas and dmas in the c16 c22 range are characterized by methyl substituents mainly located at c 6 or 6 and c 7 or 7 and are derived from cyanobacteria they are relatively abundant components in the modern cyanobacterial mats but with increasing age of the mats they become much less abundant on the contrary mmas dmas and tmas in the c24 c45 range are exclusively found in the holocene cyanobacterial mats their longest chains mainly contain an odd number of carbon atoms and they always carry the methyl substituents at odd numbered carbon atoms the similarity in composition of this very specific group of branched alkanes with that encountered in insect epicuticular waxes suggests that these sedimentary hydrocarbons originate from insects which probably grazed on the cyanobacterial mats

natural flux of greenhouse methane from the timor sea to the atmosphere 1 methane gas bubbles from the cornea seep were sampled at the sea surface in the timor sea continental shelf area in june 2005 total bubble gas flux was 0 076 to 0 76 l m 2 h 1 during the 6 h d 1 periods of low neap tides in june 2005 this bubble gas contained an average of 26 mmol ch4 l 1 and about 0 16 and 0 006 mmol l 1 of ethane and propane we estimate the daily flux from the sea surface to the atmosphere to be 0 012 to 0 12 mol ch4 m 2 d 1 or 0 13 to 1 3 t ch4 d 1 from an area of about 0 7 km2 this methane flux came from a 500 1400 m carbonate pavement dome on the seafloor at 84 m water depth the seep hard ground was swath mapped and 3 5 khz subbottom profile data indicate that the seep dome was strongly reflective with poor penetration into the subsurface consistent with the presence of a carbonate hard ground carbon and deuterium isotope ratios 13c 41 to 42 d 157 to 158 of the seep bubble gas indicate that this methane had a thermogenic origin and was in the same isotopic range as gas within the late cretaceous cornea oil and gas field we could not detect inputs of fluids containing nutrients or short lived radium isotopes at this site commonly associated with other cold seeps tens to a hundred of kilometers seaward from the cornea seep site water column dissolved methane concentrations in this sector of the timor sea shelf and slope were 100 500 times supersaturated with respect to the atmosphere and thus the water column is expected to be degassing additional methane to the atmosphere perhaps there are thousands of other methane seeps of similar magnitude to the cornea seep on this shelf and slope to account for all the excess dissolved methane 86 000 t measured in the water column these measured and calculated fluxes provide evidence for the hypothesis that shallow sea seeps may be a significant source of atmospheric methane in contrast to deep sea vents where most of the methane is dissolved and oxidized in seawater and does not reach the atmosphere

structural and tectonic evolution of western cuba fold and thrust belt 1 we present balanced and restored cross sections across the western cuba fold and thrust belt to illustrate its structure and tectonic evolution based on the interpretation of multichannel seismic profiles field data and balancing techniques the nnw sse trending soroa cross section intersects from south to north 1 the los palacios basin 2 the sierra del rosario antiformal stack 3 the bahia honda thrust unit 4 the frontal 3 km thick imbricated thrust sheets and 5 the foredeep basin at depth a duplex that links the sierra del rosario unit and the frontal imbricates is defined using the thickness of the cover thrust sheets of the imbricated north american margin the minimum calculated shortening is of 130 km in a sse or south direction to fit large scale plate tectonic reconstructions however a more allochthonous alternative using thinner cover sequences is also discussed which restores the bahia honda unit 220 km to the south of its present position syntectonic deposits in combination with a forward kinematic model provide a good constraint for the tectonic evolution of the orogen the internally deformed bahia honda unit overthrusted the north america margin cover successions during danian and selandian times 65 5 60 ma before the stacking of these cover rocks during selandian and thanetian times 60 56 ma the growth of a large antiformal stack beneath the sierra del rosario occurred at early middle eocene 56 45 ma generating about 4 km of structural relief between the paleoisland of cuba and the synorogenic seafloor before the final infill of the foredeep

cenozoic tectonic history of the north america caribbean plate boundary zone in western cuba structural studies of well dated jurassic to lower miocene rocks in western cuba constrain the sequence of structural events affecting this oblique collisional zone between the late cretaceous island arc and the jurassic cretaceous north america passive margin in the southeastern gulf of mexico and straits of florida results of detailed mapping and collection of fault slip data at 34 sites define a regionally consistent five phase tectonic model for the period from the late paleocene to the post early miocene during the late paleocene to the early eocene the cuban island arc collided with the north american passive margin bahamas platform northwest ward overthrusting during the collision defines tectonic phase i a nne ssw compression concurrent with early eocene left lateral strike slip faulting along the pinar fault zone defines phase ii this result is consistent with structural mapping showing sinistral shear within the 065 striking pinar fault zone an ene wsw to e w compression defining phase iii overprinted phase ii faults in the lower eocene and older rocks post early miocene normal faulting characterizes phase iv inversion of fault slip data indicates two contemporaneous directions of tension of 120 and 170 strike slip faults that overprint phase iv normal faults yield a 120 compression phase v the direction of compression associated with the arc continent collision rotates clockwise from nw se in the late paleocene early eocene phase i to nne ssw phase ii and to ene wsw by the middle eocene phase iii the rotation in the compression direction occurred because the arc turned toward an oceanic area in the present day area of central and eastern cuba progressive collision led to complete subduction of the remnant oceanic crust by middle to late eocene time

comparison of microwave backscatter anisotropy parameterizations of the antarctic ice sheet using ascat the c band eumetsat advanced scatterometer ascat was launched in 2007 and provides backscatter measurements with excellent azimuth and incidence angle diversity in polar regions c band backscatter measurements can be used to retrieve near surface snow firn properties such as grain size and accumulation rate however the antarctic ice sheet ais exhibits strong microwave backscatter anisotropy as a function of both incidence and azimuth angles and this anisotropy must be well understood before such physical parameter retrieval can be accurately performed this paper presents a detailed comparison of several different parameterizations of both the azimuth and the incidence anisotropy parameterizations used here result in residuals similar to the radiometric performance of ascat indicating accurate characterization of the anisotropy the analysis of these parameterizations provides an insight into the physical mechanisms taking place near the surface of the ais 30 day composite maps of several parameters are presented and discussed in the context of near surface glaciology this anisotropy characterization will form the basis of a technique for extraction of physical parameters of the ais

enhanced resolution reconstruction of ascat backscatter measurements a wind scatterometer measures the normalized radar cross section of the earth s surface in order to estimate the ocean near surface wind each measurement is the weighted integral of over an area so samples of are filtered by a measurement spatial response function srf enhanced resolution data may be produced from measurements and their associated srf using image reconstruction algorithms these enhancedresolution data products are useful for land and ice studies in addition to high resolution ocean wind retrieval the spatial resolution and noise may be improved by combining data for multiple passes trading off temporal resolution for spatial resolution in this paper we consider the production of enhanced resolution image reconstruction from the advanced scatterometer ascat on the metop satellites for land and ice regions two previously introduced image reconstruction algorithms the weighted average ave and scatterometer image reconstruction sir are applied to ascat data as well as a conventional gridding method we select optimum values of the reconstruction parameters for ascat the imaging algorithms are compared and evaluated as quantified by the spatial resolution pixel mean and variance and pixel correlation of the produced images the effective spatial resolution of the ave and sir reconstructed images is on the order of 15 to 20 km an improvement over the nominal spatial resolution of 25 and 50 km for the spatially averaged swath oriented ascat l1b products

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

salinity variations in the northern coorong lagoon south australia significant changes in the ecosystem following human alteration to the natural water regime abstract european settlement and drought have significantly impacted the hydrology of the coorong a shallow coastal lagoon complex in south australia which is part of a terminal wetland at the mouth of the river murray an increased salinity associated with lower water levels and progressive isolation from ocean flushes contributed to a severe decline in ecological diversity over the past decades here we have conducted a molecular and stable isotopic study of a sedimentary core from the northern coorong lagoon spanning more than 5000 years to investigate the recent palaeoenvironmental history of the ecosystem major alterations were evident in many biogeochemical parameters in sediments deposited after the 1950s coinciding with the beginning of intensified water regulations the most prominent shift occurred in 13 c profiles of c 21 c 33 n alkanes from average values of 23 5 to an average of 28 2 further changes included decreases in carbon preference index cpi and average chain length acl of the n alkane series as well as significant increases in algal e g c 20 hbi long chain alkenes and c 29 alkadiene and bacterial e g 13 c depleted short chain n alkanes and hopanoids 13 c 35 9 to 30 1 derived hydrocarbons long chain n alkanes with a strong odd even predominance as observed here are typically attributed to terrigenous plants in the coorong however terrigenous input to sedimentary om is only minor therefore changes in the before mentioned parameters were attributed to a source transition from a major contribution of macrophytes towards predominantly microalgae and bacteria d values of c 21 c 33 n alkanes showed a general trend towards more enriched values in younger sediments indicating an overall rising salinity however the most pronounced positive shift in these profiles again occurred after the 1950s altogether this study demonstrates that the recent human induced changes of the coorong hydrology compounded by a severe drought led to an increase in salinity and alterations of primary production which have been much more significant than natural variations occurring throughout the holocene over several thousands of years

reconnaissance paleomagnetic results from western cuba abstract a paleomagnetic study of mesozoic rocks from the sierra de los organos and sierra del rosario fold belts of western cuba revealed postfolding magnetisation in diabases of the late jurassic el sabalo formation and carbonates of the middle cretaceous pons and the late cretaceous carmita and moreno formations steep components with inclinations of about 70 were isolated from all three formations at the same time postfolding shallow components were also found in a few samples of the pons limestones we rule out a possibility to account for these results by either horizontal movements or non dipole field anomaly neither very appealing is a hypothesis of a post remagnetization tilt of the entire region all the components appear to be confined to a plane perpendicular to the main structural trends we hypothesize that the remanences might have been distorted or re aligned during deformation this assumption however is far from being proven in contrast well defined characteristic components were isolated from basalts of the aptian albian encrucijada d i 247 23 k 14 a95 9 0 and the late cretaceous orozco d i 228 22 k 110 a95 4 7 formations from the bahia honda zone in the north of western cuba the remanence in the encrucijada formation is shown to predate deformation mean inclinations in both formations match those in cretaceous volcanics from central cuba and all the results show lower latitudes than expected from the reference data for the north american plate thus implying that volcanic domains of cuba were displaced northward by about 1000 km prior to the middle eocene cretaceous declinations in western and central cuba differ by about the same amount as the major structural trends of these two areas suggesting oroclinal bending of cuba at the same time both areas are rotated counterclockwise with respect to north america thus implying movements on a broader scale

neoproterozoic sulfur isotope variation in australia and global implications abstract seven sulfur isotope stages are apparent in australian neoproterozoic sections 1 from 840 ma to the sturtian glaciation 700 ma 34ssulfate varied little 19 to 17 5 and 34ssulfide ranged from 20 to 23 2 the sturtian glaciation was followed by 3 a rise in 34ssulfide to an average of 30 seen also in china namibia and canada and in 34ssulfate at least to 26 and possibly to 45 the sharp rise in 34s of all sulfur fractions sulfate sulfide and organic leads us to speculate that sulfide depleted in 34s was deposited on the abyssal plain and that residual sulfate enriched in 34s remained beneath a stagnant ice covered ocean during the sturtian glaciation and was brought to the shallow continental margin during the post glacial transgression 4 34ssulfide and 34ssulfate fall from 640 to 607 ma 34ssulfate down to 17 probably from oxygen excess through massive organic carbon burial which causes weathering of sulfide depleted in 34s continental sulfide and previously deposited sulfide on the abyssal plain 5 the oxic environment of the marinoan 605 595 ma glaciation minimises sulfate reduction unlike the sturtian so that 34ssulfate is unvarying 6 the post glacial environment has sulfide depleted in 34s average 34ssulfide

composition and syngeneity of molecular fossils from the 2 78 to 2 45 billion year old mount bruce supergroup pilbara craton western australia shales of very low metamorphic grade from the 2 78 to 2 45 billion year old ga mount bruce supergroup pilbara craton western australia were analyzed for solvent extractable hydrocarbons samples were collected from ten drill cores and two mines in a sampling area centered in the hamersley basin near wittenoom and ranging 200 km to the southeast 100 km to the southwest and 70 km to the northwest almost all analyzed kerogenous sedimentary rocks yielded solvent extractable organic matter concentrations of total saturated hydrocarbons were commonly in the range of 1 to 20 ppm g g rock but reached maximum values of 1000 ppm the abundance of aromatic hydrocarbons was 1 to 30 ppm analysis of the extracts by gas chromatography mass spectrometry gc ms and gc ms metastable reaction monitoring mrm revealed the presence of n alkanes mid and end branched monomethylalkanes cyclohexylalkanes acyclic isopre noids diamondoids tri to pentacyclic terpanes steranes aromatic steroids and polyaromatic hydrocarbons neither plant biomarkers nor hydrocarbon distributions indicative of phanerozoic contamination were de tected the host kerogens of the hydrocarbons were depleted in 13 c by 2 to 21 relative to n alkanes a pattern typical of although more extreme than other precambrian samples acyclic isoprenoids showed carbon isotopic depletion relative to n alkanes and concentrations of 2 methylhopanes were relatively high features rarely observed in the phanerozoic but characteristic of many other precambrian bitumens molecular parameters including sterane and hopane ratios at their apparent thermal maxima condensate like alkane profiles high mono and triaromatic steroid maturity parameters high methyladamantane and methyldiaman tane indices and high methylphenanthrene maturity ratios indicate thermal maturities in the wet gas gener ation zone additionally extracts from shales associated with iron ore deposits at tom price and newman have unusual polyaromatic hydrocarbon patterns indicative of pyrolytic dealkylation the saturated hydrocarbons and biomarkers in bitumens from the fortescue and hamersley groups are characterized as probably syngenetic with their archean host rock based on their typical precambrian molecular and isotopic composition extreme maturities that appear consistent with the thermal history of the host sediments the absence of biomarkers diagnostic of phanerozoic age the absence of younger petroleum source rocks in the basin and the wide geographic distribution of the samples aromatic hydrocarbons detected in shales associated with iron ore deposits at mt tom price and mt whaleback are characterized as clearly archean based on their hypermature composition and covalent bonding to kerogen copyright 2003 elsevier ltd

isotope stratigraphy of the ediacarian neoproterozoic iii of the adelaide rift complex australia and the overprint of water column stratification abstract this study establishes a high resolution 13c chemostratigraphic framework for the type ediacarian terminal proterozoic section in the adelaide rift complex a framework that contributes to the emerging global chronostratigraphic synthesis of a period that saw momentous changes in the earth s surface environment only 15 m of the 3 5 km thick type section consists of shallow water carbonates of the kind that have formed the basis of most previous studies of neoproterozoic chemostratigraphy however the organic 13corg record reveals a surprising richness of information and shows excellent utility in correlation between sections in the adelaide rift complex lateral variations in 13corg profiles correspond to expected diachronous patterns of basin fill with the addition of 87sr 86sr data correlation can also be made to the officer and amadeus basins consistent with known lithostratigraphic and sequence stratigraphic constraints sublittoral micritic carbonates of the upper nuccaleena formation cap dolostone and lower and middle wonoka formation show strong basinwide 13c depletion 13ccarb 3 to 10 despite compelling evidence for preservation of depositional 13ccarb such as good textural preservation evidence for sea floor lithification and in the wonoka formation pristine 87sr 86sr and low mn sr associated with the depleted carbonates are rare subaqueous evaporite relatively heavy 13corg and anomalously 13c depleted organic carbon of benthic microbial mat origin and a common cause salinity stratification of the water column is postulated the indicated palaeogeographic setting an evaporative mediterranean like basin tenuously connected to the world ocean is entirely consistent with previous suggestions of one or more messinian type desiccation events to explain very deep 1 km incised valleys or canyons in the adelaide rift complex and officer basin at horizons within the wonoka formation and correlates positive excursions in 13corg during basin stratification may in part be due to 12c depletion of surface waters by photosynthetic carbon fixation despite the proposed semi isolation of australian ediacarian basins from the world ocean major 13c excursions which can to some extent be differentiated by the monotonic rise in ediacarian marine 87sr 86sr appear to be correlatable to the upper windermere supergroup northwest canada

mid chain branched mono and dimethyl alkanes in hot spring cyanobacterial mats a direct biogenic source for branched alkanes in ancient sediments hot spring cyanobacterial mats from yellowstone national park u s a and the orakei korako thermal area new zealand have been found to contain suites of monomethyl alkanes compounds frequently reported in cultured and natural populations of cyanobacteria the complete range of possible structural isomers for mid chain branching for c17 c18 and c16 c18 alkanes occurs in the two mats respectively several c19 dimethyl and c20 multibranched alkanes were also observed as major hydrocarbons of the orakei korako mat the recognition of series of mid chain branched alkanes in modern cyanobacterial mats suggests that their occurrence in ancient sediments may reflect direct biogenic contributions rather than formation by diagenetic processes

melt detection in antarctic ice shelves using scatterometers and microwave radiometers ku band dual polarization radar backscatter measurements from the seawinds on quikscat scatterometer are used to determine periods of surface freeze and melt in the antarctic ice shelves the normalized horizontal polarization radar backscatter sigmao and backscatter polarization ratio are used in maximum likelihood estimation of the ice state this method is used to infer the daily ice surface conditions for 25 study locations located on the ronne ross larsen amery shackleton and other ice shelves the temporal and spatial variations of the radar response are observed for various neighborhood sizes surrounding each given location during the study period criteria for determining the dates of melt onset and freeze up for each austral summer are presented validation of the ice state and melt onset date estimates is performed by analyzing the corresponding brightness temperature tb measurements from special sensor microwave imager ssm i radiometers quikscat sigmao measurements from 1999 to 2003 are analyzed and found to be effective in determining periods of melt in antarctic ice sheets at high temporal and spatial resolutions these estimates can be used in studies of the climatic effects of the seasonal and interannual melting of the antarctic ice sheets

atmospheric form drag coefficients over arctic sea ice using remotely sensed ice topography data spring 2009 2015 sea ice topography significantly impacts turbulent energy momentum exchange e g atmospheric wind drag over arctic sea ice unfortunately observational estimates of this contribution to atmospheric drag variability are spatially and temporally limited here we present new estimates of the neutral atmospheric form drag coefficient over arctic sea ice in early spring using high resolution airborne topographic mapper elevation data from nasa s operation icebridge mission we utilize a new three dimensional ice topography data set and combine this with an existing parameterization scheme linking surface feature height and spacing to form drag to be consistent with previous studies investigating form drag we compare these results with those produced using a new linear profiling topography data set the form drag coefficient from surface feature variability shows lower values 0 5 1 10 3 in the more deformed ice regimes of the central arctic north of greenland and the canadian archipelago which increase with coastline proximity the results show moderate interannual variability including a strong increase in the form drag coefficient from 2013 to 2014 2015 north of the canadian archipelago the form drag coefficient estimates are extrapolated across the arctic with advanced scatterometer satellite radar backscatter data further highlighting the regional interannual drag coefficient variability finally we combine the results with existing parameterizations of form drag from floe edges a function of ice concentration and skin drag to produce to our knowledge the first pan arctic estimates of the total neutral atmospheric drag coefficient in early spring from 2009 to 2015

an 860 km surface mass balance profile on the east antarctic plateau derived by gpr abstract snow accumulation and its variability on the east antarctic plateau are poorly understoodduetosparseandregionallycon nedmeasurements wepresenta5 3ghz c band ground penetratingradar gpr pro lewith atotal length of860kmrecovered duringthe jointnorwegian us internationalpolar year traverse 2007 08 mean surface mass balance smb over the last 200years was derived fromthe gpr data by identifying the volcanic deposition of the tambora eruption in 1815 it varies between9 1 and 37 7kgm 2 a 1 over the pro le with a mean of 23 7kgm 2 a 1 and a standard deviation of4 7kgm 2 a 1 the 200year smb estimated is signi cantly lower than most of the smb estimates overshorter time periods in this region this can be partly explained by a smb minimum in the vicinity ofthe ice divide however it is more likely that a recent increase in smb observed by several studies islargely responsible for the observed discrepancy introduction many recent studies have concentrated on the surface massbalance smb vaughan and others 1999 arthern andothers 2006 monaghan and others 2006 van de berg andothers 2006 and mass changes davis and others 2005 zwally and others 2005 of the antarctic ice sheet in orderto assess antarctica s contribution to changes in global sealevel new techniques such as radar altimetry have madeit possible to study continent wide elevation changes withhigh accuracy these changes are often related to changesin precipitation on the east antarctic plateau eap davisand others 2005 zwally and others 2005 however thesetechniques only cover short time periods it is important toobtain ground truth over longer time periods to understandhow observed changes relate to the past to date there have been very few in situ measurements ofsmb available from the interior of the eap the present smbestimates are mainly based on remote sensing e g arthernand others 2006 or numerical modelling e g monaghanand others 2006 van de berg and others 2006 calibratedby very sparse in situ measurements for the interior ofthe continent there are also indications that there are anon negligible number of zero accumulation sites so calledglazedareas intheinterioroftheeapthatareoftennottakeninto account by mass balance estimates and can changetheirvalue signi cantly frezzotti andothers 2002 scambosandothers 2008 it isclear that moreaccumulation dataarerequired to study the spatial and temporal variability of smband to improve the spatial resolution and accuracy of large scale accumulation studies the smb is the aggregate of many processes such asprecipitation from clouds and clear skies the formationof hoar frost at the surface and within the snowpack sublimation melting and runoff wind scouring and driftdeposition eisen and others 2008 snow accumulation canbe derived using various methods e g eisen and others 2008 snow pit rn and ice core studies provide valuableinformation about mean smb for a certain point location takahashi and others 1994 isaksson and others 1996 ansch utz and others in press these point measurementscan be spatially extended by ground penetrating radar gpr smb is proportional to the re ector depth withinthe rn pack as variations in vertical strain rates can beneglected in the top tens of metres of the ice sheet nye 1963 gpr has previously been successfully used to followisochronous rn layers providing detailed information aboutthe smb variability across antarctica fujita and others 1999 richardson naslund 2004 rotschky and others 2004 spikes and others 2004 arcone and others 2005a although large regions of the eap still remain uncovered we show smb derived by gpr data collected duringthe rst leg of the norwegian us scienti c traverse ofeastantarctica http traverse npolar no duringthe2007 08austral summer nus07 this joint project is part of thelarger trans antarctic scienti c traverses expeditions icedivideofeast antarctica taste idea andthe internationalpartnerships in ice coringsciences ipics goldman 2008

biogeochemistry of the 1640 ma mcarthur river hyc lead zinc ore and host sediments northern territory australia abstract the formation of the mcarthur river lead zinc deposit involves thermogenic or biologic oxidation of sedimentary organic matter the products of which generated a massive stratiform sulfide ore body and secondary carbonate and silica precipitates formed within the sediment pile down the flow pathway and above the reaction zone the fine grained texture of the mineralization indicates that primary ore texture is preserved and coupled with the regional thermal maturity indicate that this deposit is an ideal location to study organic matter signals related to ore formation and the sedimentary environment biomarker data point to a marine environment of deposition and are consistent with data previously collected from the host barney creek formation in the adjacent glyde subbasin an unusual biomarker distribution found in some samples from within two orebody is considered to be related to the presence of sulfide oxidizing bacteria these organisms flourished after turbidite deposition when oxygen in the upper part of the water column was mixed down to the sediment water interface the biomarker data are supported by micropalaeontologic observations from the same samples and are consistent with intermittent oxygenation of the water column to the sediment water interface this observation suggests an extension of the known occurrence of sulfide oxidizing bacteria back in time by 800 million years to 1640 ma

molecular and stable carbon isotopic composition of monomethylalkanes from one oil sand sample source implications abstract unusually abundant long chain monomethylalkanes mmas c 25 c 36 and their short chain homologues c 14 c 22 have been tentatively identified in a late triassic oil sand sample from the lunnan oilfield tarim basin nw china molecular distributions and stable carbon isotopic compositions of these compounds have been determined to investigate their bio and or geosynthetic sources the results show that the most abundant isomers of short chain mmas were 4 methyl m z 70 5 methyl m z 84 6 methyl m z 98 and 7 methyl m z 112 alkanes whereas in long chain mmas there is a clear predominance of the 9 methyl and 10 methyl isomers combined with the compound specific stable carbon isotopic analysis it is concluded that short chain mmas and long chain mmas must have different sources the similar isotopic compositions of mmas and n alkanes in this sample suggest that they may share the same sources the short chain mmas as previously suggested are probably related to a cyanobacterial origin while the long chain mmas may be mainly associated with microorganisms or heterotrophic bacteria rather than cyanobacteria

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

possible origin of n alkanes with a remarkable even to odd predominance in recent marine sediments abstract n alkane distributions with a remarkable even to odd predominance c16 c24 were found in marine surface sediments the previously proposed diagenetic reduction of the corresponding n fatty acids could not be considered as a source for these n alkane based on a comparison of compositional features of n alkane n fatty acid and n alcohol distributions carbon isotope analyses and other geochemical parameters the data indicate that the even predominant n alkanes were derived directly from marine bacteria

toward a robust retrieval of snow accumulation over the antarctic ice sheet using satellite radar 1 the sensitivity of radar measurements to snow accumulation rate is determined by the firn volume characteristics of the ice sheets here we present a new approach for calculating the volume backscattering of dry firn which is combined with recently developed empirical parameterizations of firn grain size and density as functions of depth surface temperature and accumulation rate to this end dense medium radiative transfer theory is applied to calculate the volume scattering and absorption coefficients the coefficients for the density transition between snow and dense firn are evaluated using polynomial interpolation for testing the method we used measured accumulation rates envisat asar c band wide swath mode images and quikscat ku band backscattering data from dronning maud land antarctica the comparison between measured and simulated backscattering coefficients shows that no tuning parameter is necessary to obtain the correct absolute level of scattering intensity the robustness of accumulation rate retrievals depends on the consideration of technical and environmental factors due to the presence of sastrugi on the ice sheet surface the measured intensities are sensitive to the radar look direction wind compaction of snow and depth hoar formation change the depth dependent snow density and grain size profiles theoretical simulations revealed that the backscattering coefficient at c band is more sensitive to changes of accumulation rates than at ku band penetration depths can vary significantly dependent on radar frequency and firn characteristics this has to be taken into account when comparing accumulation rates from different locations

microbial mats implicated in the generation of intrastratal shrinkage synaeresis cracks intrastratal shrinkage often termed synaeresis cracks are commonly employed as diagnostic environmental indicators for ancient salinity stressed transitional fluvial marine or marginal marine depositional environments despite their abundance and use in facies interpretations the mechanism of synaeresis crack formation remains controversial and widely accepted explanations for their formation have hitherto been lacking sedimentological ichnological petrographic and geochemical study of shallow marine mudstone beds from the ordovician beach formation of bell island newfoundland has revealed that crack development cf synaeresis cracks on the upper surface of mudstone beds is correlated with specific organic geochemical and sedimentological parameters contorted sinuous sand filled cracks are common at contacts between unbioturbated mudstone and overlying sandstone beds cracks are absent in highly bioturbated mudstone and are considered to pre date firmground assemblages of trace fossils that include planolites and trichophycus the tops of cracked mudstone beds contain up to 2 1 wt total organic carbon relative to underlying mudstone beds that contain around 0 5 wt total organic carbon high resolution carbon isotope analyses reveal low 13corg values 27 6 on bed tops compared with sandy intervals lacking cracks 24 4 to 24 9 cracked mudstone facies show evidence for microbial matgrounds including microbially induced sedimentary structures on bedding planes and carbonaceous laminae and tubular carbonaceous microfossils in thin section non cracked mudstone lacks evidence for development of microbial mats microbial mat development is proposed as an important prerequisite for intrastratal shrinkage crack formation both microbial mats and intrastratal shrinkage cracks have broad palaeoenvironmental distributions in the precambrian and early phanerozoic in later phanerozoic strata matgrounds are restricted to depositional environments that are inhospitable to burrowing and surface grazing macrofauna unless evidence of synaeresis i e contraction of clay mineral lattices in response to salinity change can be independently demonstrated the general term intrastratal shrinkage crack is proposed to describe sinuous and tapering cracks in mudstone beds

relating microwave backscatter azimuth modulation to surface properties of the greenland ice sheet azimuth dependence of a normalized radar cross section over the greenland ice sheet is modeled with a simple surface scattering model the model assumes that azimuth anisotropy in surface roughness at scales of 3 300 m is the primary mechanism driving the modulation to evaluate the contribution of azimuth anisotropy in surface roughness to the radar backscatter the model is compared to models based on isotropic surface roughness the models are inverted to estimate snow surface properties using measurements from the c band european remote sensing satellite advanced microwave instrument in scatterometer mode results indicate that the largest mesoscale rms surface slopes are found in the lower portions of the dry snow zone estimates of the preferential direction in surface roughness are highly correlated with katabatic wind fields over greenland which is consistent with wind formed sastrugi as the dominant mechanism causing azimuth modulation of the maximum improvement of the azimuth modulation surface model compared to its isotropic counterparts occurs in the lower regions of the dry snow zone where the azimuth variability of is the largest in regions with azimuth modulation over 1 db the mean root mean square error estimate of the azimuth dependent surface scattering model is 0 46 db compared with 0 70 db for similar models using isotropic roughness

a hierarchical tectonic model of the gulf of mexico and caribbean region abstract a quantitative computer graphic methodology hierarchical tectonic analysis has been used to model the tectonic evolution of the gulf of mexico and caribbean region this method employs a highly structured hierarchical description of the relative motions of pairs of tectonic elements in order to quantify the timing and style of plate interactions the main features described in this model are 1 1 a revised fit of pangea 2 2 the opening of the gulf of mexico in the middle late jurassic 3 3 the formation of a proto caribbean ocean due to the separation of north and south america during the early cretaceous 4 4 the formation of the greater antilles arc along the western margin of the proto caribbean ocean 5 5 the insertion of the farallon plate between north and south america during the middle cretaceous resulting in the northeastward advance of the greater antilles arc and the subduction of proto caribbean oceanic crust 6 6 the complete subduction of the proto caribbean ocean and the collision of the greater antilles arc with the bahamas platform in the late cretaceous 7 7 the truncation of the caribbean section of the farallon plate from its pacific counterpart and the formation of the panama arc latest cretaceous and 8 8 the westward movement of north and south america with respect to the caribbean plate resulting in the opening of the yucatan basin paleocene and subsequently in the evolution of the cayman trough and e w zone of strike slip

organic geochemistry and mineralogy i characterisation of organic matter associated with metal deposits abstract as geochemical appraisals of mineral regions of commercial prospectivity evolve the organic matter associated with metal rich ores has attracted greater attention petroleum basin and modern seafloor hydrothermal vent studies have suggested that organic matter can have a significant influence on the behaviour of mineralising fluids there have been many isolated reports of certain organic compositional or morphological e g pyrobitumen features showing an apparent relationships with hydrothermal fluids or minerals raising expectations that organic based parameters might be useful to mineral exploration however the understanding of organic inorganic relationships in earth systems is far from complete for example the detailed mechanics of the interaction of organics with hydrothermal fluids over geological time remain largely undefined organic geochemistry studies have traditionally involved the measurement and interpretation of the hydrocarbon composition of sedimentary rocks here we review the types of aliphatic hydrocarbons aromatic hydrocarbons and metalloporphyrins often detected from organic geochemical investigations in mineral rich regions such molecular data can be particularly diagnostic of biochemical sources and the palaeo environments at the time mineral associated organic matter was deposited sub surface trends of hydrocarbon alteration may also reflect major biogeochemical processes such as thermal maturity and biodegradation organic geochemistry data can also occasionally provide information about the nature e g origin composition temperatures and migration pathways of hydrothermal fluids and can make a contribution to holistic ore genesis models the well preserved organic matter associated with the economic here s your chance pb zn ag mine paleoproterozoic barney creek formation mcarthur basin australia and the transition metal rich early permian kupferschiefer formation germany poland have attracted significant attention a more detailed summary of the organic character of these deposits is provided to highlight the contribution organic geochemistry can make to understanding mineralisation processes most organic geochemical studies of highly mineralised regions however have not adequately addressed the significance of organic matter to mineralisation a slightly different analytical focus than traditionally used for exploration appraisal of petroleum hydrocarbons may be required to properly evaluate the significance of organic species to the mobilisation transport and deposition of ore metals the characterisation and subsequent thermodynamic modeling of organic substances and complexes within metalliferous hydrothermal systems will contribute to a better understanding of the nature and role of organic inorganic fluids or other affiliated organics in ore systems

chlorobiaceae in palaeozoic seas revealed by biological markers isotopes and geology biomarker hydrocarbons in oils and sediments have considerable potential for assessing the nature of biological processes in the past but only a few can be uniquely related to particular organisms reef hosted oils in the silurian of the michigan basin canada and the devonian of western canada have high abundances of 1 alkyl 2 3 6 trimethylbenzenes their precise structures suggest that they are diagenetic products of aromatic carotenoids of the green sulphur bacteria individual components are enriched in 13c by 7 8 relative to the saturated hydrocarbons of the same oil an isotopic anomaly of this magnitude and direction correlates with a component of photosynthetic carbon assimilation by the reductive tricarboxylic acid cycle these results together with data on palaeoenvironments provide compelling evidence for the existence in ancient restricted seas of microbial communities containing chlorobiaceae organisms with distinctive biochemistry which leave morphologically identifiable remains

suspected microbial mat related crack like sedimentary structures in the palaeoproterozoic magaliesberg formation sandstones south africa abstract the occurrence of patchy preservation of ripples and of palimpsest ripples on many sandstone bed surfaces of the c 2 1 ga magaliesberg formation pretoria group transvaal supergroup south africa suggests that microbial mats grew within the upper parts of sandy deposits of the braid deltaic tidally controlled epeiric marine coastline palaeoenvironment inferred for this stratigraphic unit recently limited occurrences of petee ridges cracked sand layers elephant skin textures wrinkle structures and manchuriophycus like cracks have been found substantiating the envisaged role for microbial mats binding sandy sediment and providing cohesion during active sedimentation by fluvial and tidal processes ripple marks associated with most of these biogenic sedimentary structures enable evaluation of genetic processes for the ripples currents waves wind as well as estimation of wave heights and water depths cf tanner w f 1967 ripple mark indices and their uses sedimentology 9 89 104 tanner w f 1971 numerical estimates of ancient waves water depths and fetch sedimentology 16 71 88 the petee ridges are interpreted as reflecting spring low tidal desiccation which cracked the mats followed by disruption of sand beneath the mat due to loading from incoming tides or subsequent deposits slightly sinuous sand cracks on ripple crests are related to a similar combination of low tidal desiccation and formation of wind ripples with subsequent high tides providing the deeper water conditions and larger wave heights calculated from the tanner w f 1971 numerical estimates of ancient waves water depths and fetch sedimentology 16 71 88 formula synaeresis cracking is inferred for both elephant skin cracks and manchuriophycus structures these inferred suspect microbial sedimentary structures when studied in relation to data derived from associated ripples thus enable better estimation of depositional conditions within the magaliesberg palaeoenvironment and indicate minimum epeiric tidal ranges of c 112 cm in general these structures are found associated with evidence for shallower water and higher energy conditions which probably protected the microbial mats from degradation by heterotrophic bacteria through fast burial a possible association of such mat related structures with epeiric marine or passive margin coastline conditions may be pertinent for much of the precambrian clastic record

the chemical structure of a pronounced series of iso alkanes in south oman crudes gas chromatograms of the saturated hydrocarbon fractions of the south oman crudes are characterised by a striking series of peaks called x peaks throughout this paper eluting between the n alkanes mainly in the c20 c26 range a gs ms study combined with optimised gc resolution shows that each peak is a superposition of subpeaks which correspond to a complex series of monomethylalkanes the x20 peak in the chromatogram for instance is found to be composed of virtually co eluting peaks corresponding to 5 6 7 8 9 and 10 methylnonadecane the larger x22 x23 and x24 peaks are superpositions of a similar set of monomethylalkanes and in addition a series of presumably dimethylalkanes of which the structures are only partly solved the large abundance of these iso alkanes is very specific for south oman crudes and may be caused by their pre cambrian origin or a specific source material

contrasting sterane signatures in neoproterozoic marine rocks of australia before and after the acraman asteroid impact abstract organic matter preserved in marine mudstones from three late neoproterozoic depocentres the officer and amadeus basins and the adelaide fold belt was examined using standard microscopic and geochemical methods including gas chromatography mass spectrometry gc ms total organic carbon toc contents of these sediments are typically low

interrelationship of the terranes in western and central cuba comment k piotrowska s paper piotrowska 1993 addresses some of the fundamental problems of cuban and western caribbean geology these include the definition original position and later displacement of suspect terranes in the area problems that have been controversial for many years the model presented by k piotrowska her fig 4 is extremely simple in her model tectonic terranes such as los organos and escambray originally formed part of the yucatan borderland from which they were detached and transported northward during the cretaceous the farallon plate pushed the escambray terrane until it reached its present position finally the escambray terrane was overthrust and pressed into the zaza zone ophiolites and cretaceous volcanic arc suites later during the middle eocene the los organos terrane detached from the yucatan and overthrust the farallon plate zaza zone in this case in order to support this scenario piotrowska 1993 relies on opinions rather than observa

fractionation between inorganic and organic carbon during the lomagundi 2 22 2 1 ga carbon isotope excursion article i nfo the lomagundi 2 22 2 1 ga positive carbon isotope excursion in shallow marine sedimentary carbonates has been associated with the rise in atmospheric oxygen but subsequent studies have demonstrated that the carbon isotope excursion was preceded by the rise in atmospheric oxygen the amount of oxygen released to the exosphere during the lomagundi excursion is constrained by the average global fractionation between inorganic and organic carbon which is poorly characterized because dissolved inorganic and organic carbon reservoirs were arguably larger in the paleoproterozoic ocean at a time of lower solar luminosity and lower ocean redox state decoupling between these two variables might be expected we determined carbon isotope values of carbonate and organic matter in carbonates and shales of the silverton formation south africa and in the correlative sengoma argillite formation near the border in botswana these units were deposited between 2 22 and 2 06 ga along the margin of the kaapvaal craton in an open marine deltaic setting and experienced lower greenschist facies metamorphism the prodelta to offshore marine shales are overlain by a subtidal carbonate sequence carbonates exhibit elevated 13 c values ranging from 8 3 to 11 2 vs vpdb consistent with deposition during the lomagundi positive excursion the total organic carbon toc contents range from 0 01 to 0 6 and 13 c values range from 24 8 to 13 9 thus the isotopic fractionation between organic and carbonate carbon was on average 30 3 2 8 n 32 in the shallow marine environment the underlying sengoma shales have highly variable toc contents 0 14 to 21 94 and 13 c values 33 7 to 20 8 with an average of 27 0 3 0 n 50 considering that the shales were also deposited during the lomagundi excursion and taking 13 c values of the overlying carbonates as representative of the 13 c value of dissolved inorganic carbon during shale deposition a carbon isotope fractionation as large as 37 appears to characterize the production of bulk organic matter in the deeper part of the pretoria basin at that time this enhanced fractionation relative to that observed in shallow water environments likely reflects heterotrophic secondary and chemotrophic productivity at and below a pronounced redoxcline consistent with the euxinic conditions inferred from independent evidence for the deeper part of the pretoria basin greater variability in organic carbon vs carbonate carbon isotopic values on the shallow marine carbonate platform suggests that the carbon cycling was dominated by a large dissolved inorganic carbon reservoir during the lomagundi excursion our study suggests that in contrast to the late neoproterozoic and phanerozoic when carbon isotope fractionation between carbonate and organic carbon in the open ocean was mostly controlled by primary producers in the paleoproterozoic redox stratified ocean heterotrophic and chemotrophic productivity overprinted a signal of primary productivity below the redoxcline this strong imprint of heterotrophic and chemotrophic productivity on organic carbon isotope records complicates the reconstruction of spatial patterns and secular trends in the 13 c values of dissolved inorganic carbon in the paleoproterozoic seawater

sterane and triterpane biomarkers in the precambrian nonesuch formation north american midcontinent rift abstract molecular fossils and organic matter from microbial communities living around 1 1 ga ago are well preserved in the nonesuch formation of the us midcontinent rift system although some compound classes of biological markers have been recognized repeatedly in previous studies of nonesuch rocks and associated petroleums steranes and triterpanes have not been detected failure to detect these compounds was due primarily to instrumental limitations and the relatively high thermal maturity of samples collected within zones of copper mineralization our analyses of nonesuch samples from the white pine mine and nonmineralized localities in michigan and wisconsin reveal suites of c 26 c 30 steranes and c 27 c 35 pentacyclic triterpanes similar to those found in phanerozoic oils and sedimentary rocks of marine origin stereoisomeric distributions in the nonesuch samples are consistent with moderate thermal maturity except in the mineralized zone near white pine

structure and distribution of branched aliphatic alkanes with quaternary carbon atoms in cenomanian and turonian black shales of pasquia hills saskatchewan canada abstract twelve pseudohomologous series of branched alkanes with one or two quaternary carbon atoms baqcs c14 c33 range are present in the extractable organic matter of cenomanian and turonian black shales of pasquia hills saskatchewan canada five of these pseudohomologous series are also observed in a holocene sample from the russian arctic three of the pseudohomologous series were identified by kenig et al pnas 100 2003 12554 12558 as 3 3 and 5 5 diethylalkanes deas and 2 2 dimethylalkanes dmas the nine other pseudohomologous series of baqcs are tentatively identified on the basis of their characteristic mass spectral fragmentation and retention indices as 3 3 dimethylalkanes dmas 3 ethyl 3 methyl and 5 ethyl 5 methylalkanes 9 9 7 7 and 6 6 diethylalkanes deas 3 3 3 3 and 5 5 5 5 tetraethylalkanes and 5 butyl 5 ethylalkanes pseudohomologous series of branched alkanes with tertiary carbon atoms such as monomethyl and monoethylalkanes are also present in the same carbon number range all these pseudohomologous families share the particularity of including isomers with exclusively odd or exclusively even carbon numbers clearly indicating a biosynthetic origin baqcs such as 5 5 deas 3 3 deas and 3 ethyl 3 methylalkanes seem to be widespread in sediments and sedimentary rocks ranging from modern to 2 1 billion years a xenobiotic source for baqcs can be excluded at this point baqcs seem to have a very low biodegradability in part explaining their widespread occurrence in ancient sediments

biomarkers of black shales formed by microbial mats late mesoproterozoic 1 1 ga taoudeni basin mauritania a b s t r a c t hydrocarbon biomarkers in late mesoproterozoic black shales from the taoudeni basin mauritania northwestern africa were analysed for palaeoenvironmental reconstruction within the atar group touirist formation shales showed the highest content of organic carbon 20 at very low maturity rc less than 0 6 microfacies and biomarker data indicate a shallow marine high productivity low oxygen setting with benthic mats as key players for the accumulation of organic matter both high c s ratios and the occurrence of rearranged hopanes indicate that euxinic conditions were not prevalent likely reflecting the shallow depositional environment steranes were not observed indicating only a minor importance of modern eukaryotic algae although low in abundance a palynological survey however reveals the presence of simple ornamented acritarchs input of highly aromatic biopolymers typical of mesoproterozoic acritarchs or microbial exopolymeric substances may be the origin of an unusually high aromaticity observed for the biomarker extracts high amounts of hopanes suggest that the benthic mats were dominated by cyano bacteria furthermore the presence of 2 3 6 trimethyl aryl isoprenoids points at contributions of organic matter from anoxygenic phototrophic bacteria however low concentrations of these compounds argue against major photic zone anoxia in the overlying water column and rather suggest a role of anoxygenic phototrophs as part of the benthic microbial mat community the high abundances of hopanes in these samples suggest that nitrogen limited conditions may have been common in the taoudeni basin at 1 1 ga these results are consistent with ideas of widespread nitrogen deficiency that emerged in mesoproterozoic oceans due to high denitrification rates in anoxic deep waters cyano and other phototrophic bacteria as well as a limited number of acritarch species were able to cope with such conditions much better than modern algae with their higher nitrogen and trace metal demands 2011 elsevier b v all rights reserved

observations of the antarctic ice sheet with the seasat scatterometer relation to katabatic wind intensity and direction the seasat a satellite scatterometer radar initially designed to measure ocean wind intensity and direction also provided observations on the antarctic ice sheet the signal of the back scatter coefficient decreases strongly from 10 to 20 db when the incidence angle of the observations increases from 0 to 65 an additional 5 db signal is found which is correlated with the direction and intensity of katabatic winds independent of the incidence angle and polarization of the signal by using simplified models of the volume scattering within the snowpack which is mostly sensitive to snow grain size and surface scattering from the air snow interface which depends on roughness it is evident that the signal of the scatterometer could result from the effects of snow dunes at low incidence angle and of micro roughness and volume back scatter at incidence angles greater than 25 the instrument therefore provides a means of measuring the direction and intensity of katabatic winds

significance of styles of epicontinental shale sedimentation in the belt basin mid proterozoic of montana u s a abstract within the strongly shale dominated sediment fill of the mid proterozoic belt basin a large variety of shale types can be distinguished sedimentological investigations of several formations have yielded valuable data about lateral associations of shale types as well as about the principal mechanisms of shale deposition depositional environments of shales in the belt basin range from red bed mudstones of ancient flood plains to deep water mudstones in a turbidite setting graded silt mud couplets are ubiquitous in most shales of the belt basin however they differ in detail and can be related to a variety of depositional processes such as low density turbidity currents sheet floods storms and wave reworking in several formations there is evidence that microbial mats colonized the sediment surface and probably protected the sediment surface from erosion shales from comparable phanerozoic settings generally lack the silt mud couplets that are so commonly observed in shales from the belt basin and other proterozoic epicontinental basins this difference probably reflects the proliferation of bioturbating organisms in the phanerozoic the absence of benthic microbial mats in phanerozoic shales is probably due to the evolution of metazoan grazers towards the end of the proterozoic

the biogeochemical evolution of the coorong during the mid to late holocene an elemental isotopic and biomarker perspective since the mid 1990s the coorong a 130 km long coastal wetland of international importance in southeastern south australia has undergone serious decline due largely to prolonged drought and reduced inflows of surface and ground water from its hinterland tenuously connected to the ocean at its northern extremity it is effectively separated into two lagoons by a narrow channel at its mid point the southern part is now permanently hypersaline here we report the results of an attempt to track the biogeochemical status of the estuary over the last 5000 years employing a consortium of elemental isotopic and biomarker parameters the sediment samples analysed came from two cores each 6 7 m in length retrieved from sites located halfway along the present day northern and southern lagoons the sediments at the southern locality are richer in total organic carbon and total nitrogen than those in the northern core reflecting higher net deposition of organic matter om and nutrients in the southern lagoon comparison of the d 13 corg and d 15 n profiles of the two cores reveals that the lower reaches of the coorong have always been a restricted o2 depleted water body that is both more saline and prone to more intensive denitrification of no 3 aq than the northern lagoon prominent among the aliphatic hydrocarbons preserved in the sediments of the southern lagoon are the c20 highly branched isoprenoid hbi 2 6 10 trimethyl 7 3 methylbutyl dodecane a putative marker of epiphytic diatoms and c15 c35 n alkanes with a marked odd even predominance in the c21 range these and other biomarkers are consistent with om derived from a mixed population of algae cyanobacteria and other eubacteria 13 c nmr spectra confirm that this om is largely algal derived but with a significant contribution from the seagrass ruppia megacarpa and possibly other aquatic macrophytes particularly in pre european sediments the c isotopic signature of the hbi alkane is consistently heavier than those of the c23 c 25 c 27 and c29 n alkanes presumably from planktonic chlorophytes aquatic metaphytes which in turn are heavier than the coexisting even carbon numbered homologues of likely bacterial origin with decreasing age these biomarker alkanes display an overall increased depletion in 13 c and enrichment in d trends that have accelerated over recent decades as the south lagoon has become progressively more hypersaline and ecologically impoverished however coeval negative excursions in the dd profiles of the epiphyte marker and n alkanes along with coincident diatom inferred reductions in palaeosalinity together highlight a series of hitherto unrecognised freshening events attributable to enhanced inflow of surface runoff and shallow groundwater

interrelationship of the terranes in western and central cuba abstract present day cuba is a complex of terranes in the western and central parts of the island the sierra de los organos and the escambray terranes which are genetically related and the volcanosedimentary cretaceous sequences of the greater antilles arc are distinguished the escambray and sierra de los organos massifs are terranes that were detached from their source areas near the yucatan a rift separating the yucatan from the florida bahama plate was involved separation of the escambray sequence from that of the sierra de los organos took place in the early cretaceous along a ne sw trending transform fault the escambray sequence was transported together with the greater antilles island arc in front of the farallon plate about 80 ma ago the volcanosedimentary cretaceous sequence of the greater antilles island arc was thrust over the ophiolitic association in this way the zaza zone was formed at that time some overthrusting and metamorphism took place in the escambray massif which was then overthrust and pressed into the zaza zone at about 45 50 ma ago detachment and nappe overthrusting took place in the sierra de los organos and overthrust units reached the margin of the margin of the florida bahama plate various structures are involved in the zaza zone including 1 the volcanosedimentary cretaceous sequences of the greater antilles arc which is a tectonized and overthrust terrane and 2 the ophiolitic association the greater antilles arc terrane is thrust over this association both of these tectonic units were folded together the sierra de los organos and the escambray terranes were thrust onto the zaza zone and then deformed together with it during later phases

abundance and geochemical significance of c2n dialkylalkanes and highly branched c3n alkanes in diverse meso and neoproterozoic sediments several series of branched alkanes with quaternary carbon centers have been detected by gc ms in the saturated hydrocarbon fractions of neoproterozoic sedimentary rocks associated with fossilised microbial mats officer basin south australia and of shallow water carbonates spitsbergen east greenland and baffin island canada a series of 5 5 diethylalkanes was predominant in most of these sediments and was typically accompanied by related series in lower abundance which based on mass spectral characteristics are tentatively assigned as 6 6 diethylalkanes 5 butyl 5 ethylalkanes and 6 butyl 6 ethylalkanes each series displays strong odd or even carbon number preferences several of the sediments contained additional series of structurally undefined c3n alkanes notable for very negative retention time factors which become more negative with increasing molecular weight indicating that branching increases with each c3 addition the strongly sequential carbon preference of the respective c2n and c3n branched alkane series and a predominantly light 13c signature of the 5 5 diethylalkanes cf co occurring n alkanes are consistent with an origin from organisms with a distinct physiology and or carbon source the relatively wide occurrence and high abundance of these branched alkanes in proterozoic sediments containing benthic microbial mats suggests a relationship with specific paleoenvironmental conditions for example strong water column redox gradients that may have been more prevalent than in the phanerozoic

proliferation of miss forming microbial mats after the late neoproterozoic glaciations evidence from the kimberley region nw australia abstract a total of 20 morphological types of microbially induced sedimentary structures miss are recognized from the late neoproterozoic tillite bearing successions of the kimberley northwestern australia which include alpha petees triradiate cracks multidirectional linear ridges millimeter ripples erosional remnants and pockets and so on of these triradiate cracks multidirectional linear ridges and millimeter ripples are reported for the first time from the neoproterozoic worldwide most kimberley miss are morphologically comparable with their ancient and present day counterparts whose biogenicity have been well demonstrated in the kimberley during the interglacial period miss have colonization preference to relatively coarse sandy substrates ranford formation and their abundance decreased towards the younger strata throssell shale in contrast miss abundance increased from the older strata yurabi formation towards the younger strata flat rock formation during the postglacial period however overall both miss abundance and bedding plane coverage percentage increased from the marinoan younger marinoan gaskiers interglacial successions to younger marinoan gaskiers postglacial successions indicating a proliferation of microbial mats after the younger marinoan gaskiers glaciation the increase of microbial mats could have ameliorated marine biogeochemical conditions and ecosystems and thus laid the foundation for the rise of ediacaran biota in australian basins