alkane terpene and polycyclic aromatic hydrocarbon geochemistry of the mackenzie river and mackenzie shelf riverine contributions to beaufort sea coastal sediment abstract to study the largest source of river sediment to the arctic ocean we have collected suspended particulates from the mackenzie river in all seasons and sediments from the mackenzie shelf between the river mouth and the shelf edge these samples have been analyzed for alkanes triterpenes and polycyclic aromatic hydrocarbons pahs we found that naturally occurring hydrocarbons predominate in the river and on the shelf these hydrocarbons include biogenic alkanes and triterpenes with a higher plant peat origin diagenetic pahs from peat and plant detritus petrogenic alkanes triterpenes and pahs from oil seeps and or bitumens and combustion pahs that are likely relict in peat deposits because these components vary independently the season is found to strongly influence the concentration and composition of hydrocarbons in the mackenzie river while essentially the same pattern of alkanes diagenetic hopanes and alkyl pahs is observed in all river and most shelf sediment samples alkane and triterpene concentration variations are strongly linked to the relative amount of higher plant peat material polycyclic aromatic hydrocarbon molecular mass profiles also appear to be tied primarily to varying proportions of peat with an additional petrogenic component which is most likely associated with lithic material mobilized by the mackenzie river at freshet consistent with the general lack of alkyl pahs in peat the higher pahs found in the river are probably derived from forest and tundra fires a few anthropogenic pyrogenic compounds are manifest only at the shelf edge probably due to a weakening of the river influence we take this observation of pyrogenic pahs and the pronounced source differences between two sediment samples collected at the shelf edge as evidence of a transition from dominance by the mackenzie river to the geochemistry prevalent in arctic regions far removed from major rivers

composition of size fractioned sedimentary organic matter in coastal environments is affected by difference in physical forcing strength the diagenesis of sedimentary organic matter som in three different depositional environments in south texas and dominated by vascular plant input was investigated sediments were collected from mcguill lake a small freshwater lake and two salt marsh sites in nueces delta and copano bay and size fractioned by wet sieving physical forcing or energy indicated by tides tidal current and wind and wind fetch area is weakest in the lake intermediate strength at the nueces delta and strongest at copano bay results from total hydrolyzable amino acid thaa and n alkane analysis and 13c solid state nuclear magnetic resonance spectroscopy nmr showed that the som from all three sites became more degraded towards finer size fractions from 300 m 300 125 m 125 63 m 63 32 m to 32 m relative to the coarse fractions the fine fractions were enriched in the degradation indicator aminobutyric acid and in aliphatic and proteinaceous components as shown from nmr spectra and lower c n ratio values this degradation pattern of som with size is typical for sediments from coastal and lacustrine environments however the contents of organic carbon oc thaas and n alkanes were higher in sandy fractions than in silt and clay fractions from mcguill lake sediment suggesting that the som was relatively undegraded in coarse fractions the size distribution of om in the lake could be explained by the weak physical forcing which may not easily break down coarser plant detritus into smaller pieces the trend contrasted with degradation patterns for sediments from nueces delta and copano bay where som was concentrated in the 32 m fraction which may be due to the strong physical forcing the physical forcing effects could also explain the attachment of clay minerals to sand grains in both the lake and nueces delta because of the relatively weak physical forcing effects while no clay attachment to sand grains was found at the copano bay site because of the strong physical forcing effects physical forcing may be an important mechanism in the processing and transport of om from vascular plants and other organic sources in estuaries and bays before the som is exported to coastal oceans

recent sedimentary hopanoids in the northwestern pacific alongside the japanese islands their concentrations and carbon isotopic compositions two hopanoids 17b h 21b h hop 22 29 ene diploptene and 17b h 21b h bishomohopanoic acid bbc32ha are the most abundant among the pentacyclic triterpenoids found in recent sediments of the pacific ocean alongside the japanese islands the concentration of diploptene normalized to organic carbon content is higher in sediments where c37 polyunsaturated alkene a biomarker of haptophytes is in high concentration suggesting that the diploptene may be associated with the accumulation of marine organic matter in open marine settings d 13 c values of bbc32 ha range from 23 8 to 19 4 relative to pdb being enriched in 13 c relative to diploptene 31 6 to 26 3 by 5 9 the isotopic diaerence indicates the presence of at least partially diaerent sources for the two hopanoids while diploptene is derived from cyanobacteria and chemotrophic bacteria in the water column or sediment bishomohopanoic acid may be produced mainly by heterotrophs in the sediment using marine organic matter in contrast the d 13 c values of the two hopanoids from river and bay sediments are similar 31 to 29 indicating a common source derived from soil components terrestrial plants or bacteria in soils 2000 elsevier science ltd all rights reserved

distribution of terrigenous lipids in marine sediments off northeastern taiwan surface sediments on the continental margin off northeastern taiwan have been analyzed for terrigenous lipids including n alkanes n fatty alcohols and sterols marine input to the sediments is particularly low based on the average n c17 n c29 alkane and n c16 n c28 fatty alcohol ratios 0 15 0 13 and 0 13 0 06 respectively this may be due to the fact that marine lipids are more prone to degradation than terrestrial ones the study area has the highest plant wax n alkane contribution average carbon preference index 3 9 1 2 among the coastal marine areas surrounding taiwan lateral particle transport from the southern east china sea shelf and river runoff from the east taiwan coast are considered to be the major contributors the distributions of plant wax n alkane and n alkanol concentrations normalized to total organic carbon toc in the study area generally show maximum values on the upper slope of the southernmost okinawa trough but not for phytosterols linear regression of toc versus plant wax n alkane concentrations show a weak relationship r 0 64 p 0 001 and an even weaker relationship r 0 42 p 0 05 between toc and plant wax n fatty alcohol concentrations is found this could be attributed to several factors 1 a complex input not a point source of terrigenous organic matter to the study area 2 toc also including marine organic matter 3 temporal variations in river flow due to flooding and 4 different rates of degradation for toc and individual biomarkers however in spite of those factors toc and phytosterol concentrations are positively linearly correlated r 0 85 p 0 001 implying that the dilution of phytosterols in terrigenous organic carbon with marine organic carbon with or without the phytosterols follows a nearly constant ratio which is remarkable in addition the predominant source of diploptene in the sediments does not appear to be of higher plant origin

aliphatic hydrocarbons and triterpenes of the congo deep sea fan abstract hydrocarbons were analyzed in sediments from the congo river deep sea fan from the congo river and in sinking particles collected by sediment traps 40 m above the sediment studied sites encompassed three lobes of decreasing age of formation along the canyon sites a f and c and a another lobe system disconnected from the active channel since 4 ka site e terrestrial long chain odd n alkanes were dominant in all sediments of the lobe system unsaturated terpenoids sourced by higher plants such as gammacerene lupene ursene and oleanene were also detected at site c characterized by high accumulation rates 10 20 cm yr 1 the organic matter spends less time in the oxic layer than at other sites and high phytadiene concentrations 10 17 g g oc 1 evidenced recent terrestrial and phytoplanktonic remains reworked in anaerobic conditions in these sediments organic carbon normalized concentrations of terrestrial alkanes and terpenoids were several fold higher than in the lobe sediments with lower accumulation rates sites a and f arguing for a more rapid degradation of terrestrial hydrocarbons than bulk organic carbon in the first steps of pre diagenesis ample variations in the contributions of biomarkers from higher plants ferns bacteria and angiosperms indicate an heterogeneous contribution of the soil and vegetation detritus delivered to the congo lobe sediments lower concentrations in terrestrial hydrocarbons at site e 45 km away from the active canyon indicated that river particles are still admixed to the dominant marine organic matter diploptene and hop 7 21 ene have a dual origin from terrestrial and marine microorganisms scatter in their relationship to gammacerene argues for a contribution of marine microorganisms in addition to soils sourced microorganisms the close distribution patterns of diploptene hop 21 ene hop 7 21 ene and neohop 13 18 ene is in line with the hypothesis of sequential clay catalyzed isomerisation of bacterial hopenes terrestrial biomarker accumulation fluxes at site c are one order of magnitude higher than vertical pelagic flux demonstrating the magnitude of the inputs delivered through turbiditic transport in the submarine canyon crude oil contamination was evidenced at the disconnected site e ucm c 21 to c 26 tricyclic diterpanes cpi and in smaller amounts in some sediments from sites a and c it may be related to marine crude oil extraction and transport a short chain mode of alkanes with an even predominance is evidenced in sediments of the lobe complex and likely sources crude oil microorganisms and ferns are discussed

geochemical evidence for a large methane release during the last deglaciation from marmara sea sediments abstract recent methane inventories have revealed the potential impact of gas hydrates on the global carbon cycle and hence in climate change milkov 2004 however only a few studies have traced methane release in the geologic record here we show geochemical evidence for a large scale methane release at mid latitudes during the last deglaciation the sea of marmara an enclosed sea between the mediterranean and black seas is located in a tectonically active basin with gas hydrate expulsion and the formation of shallow gas hydrates since depths in the basin are shallower than 1100 m future global temperatures are expected to have a great influence in destabilizing methane clathrates among the suite of biomarkers we have focused on diplopterol and diploptene profiles in core md012430 retrieved from the central basin in the marmara sea our results indicate that during the last 15 000 years hopanoids showed important concentration variations with a pronounced peak during the deglaciation the lack of a relationship between diplopterol diploptene and phytoplanktonic biomarker concentrations as well as a depleted isotopic composition have linked the hopanoid maxima to methanotrophic activity suggesting that an intense methane release occurred at the onset of deglaciation in the marmara sea the vulnerability of the hydrate stability zone to changes in temperature and pressure under this range of shallow water depths as well as the relative timing of the hopanoid maxima and sea surface temperature rise points to thermal destabilization of hydrates as a trigger for methane release in the water column

a novel proxy for terrestrial organic matter in sediments based on branched and isoprenoid tetraether lipids we propose a novel tracer for terrestrial organic carbon in sediments based on the analysis of tetraether lipids using high performance liquid chromatography mass spectrometry hplc ms analysis of terrestrial soil and peats shows that branched tetraether lipids are predominant in terrestrial environments in contrast to crenarchaeol the characteristic membrane lipid of non thermophilic crenarchaeota which is especially abundant in the marine and lacustrine environment based on these findings an index was developed the so called branched and isoprenoid tetraether bit index based on the relative abundance of terrestrially derived tetraether lipids versus crenarchaeol this bit index was applied to surface sediments from the angola basin where it was shown to trace the outflow of the congo river furthermore analyses of particulate organic matter from the north sea showed relatively higher bit indices in water column particulate organic matter near large river inputs a survey of globally distributed marine and lacustrine surface sediments shows that the bit index in these environments correlates with the relative fluvial input of terrestrial organic material making this index generally applicable the new proxy allows the rapid assessment of the fluvial input of terrestrial organic material in immature sediments up to 100 ma old

chemical and isotopic signature of bulk organic matter and hydrocarbon biomarkers within mid slope accretionary sediments of the northern cascadia margin gas hydrate system abstract the chemical and isotopic compositions of sedimentary organic matter som from two mid slope sites of the northern cascadia margin were investigated during integrated ocean drilling program iodp expedition 311 to elucidate the organic matter origins and identify potential microbial contributions to som gas hydrate is present at both locations iodp sites u1327 and u1328 with distinct patterns of near seafloor structural accumulations at the cold seep site u1328 and deeper stratigraphic accumulations at the slope basin site u1327 source characterization and evidence that some components of the organic matter have been diagenetically altered are determined from the concentrations and isotopic compositions of hydrocarbon biomarkers total organic carbon toc total nitrogen tn and total sulfur ts the carbon isotopic compositions of toc 13ctoc 26 to 22 and long chain n alkanes c27 c29 and c31 13c 34 to 29 suggest the organic matter at both sites is a mixture of 1 terrestrial plants that employ the c3 photosynthetic pathway and 2 marine algae in contrast the 15ntn values of the bulk sediment 4 to 8 are consistent with a predominantly marine source but these values most likely have been modified during microbial organic matter degradation the 13c values of archaeal biomarker pentamethylicosane pmi 46 4 and bacterial sourced hopenes diploptene and hop 21 ene 40 9 to 34 7 indicate a partial contribution from methane carbon or a chemoautotrophic pathway our multi isotope and biomarker based conclusions are consistent with previous studies based only on the elemental composition of bulk sediments that suggested a mixed marine terrestrial organic matter origin for these mid slope sites of the northern cascadia margin

spatial heterogeneity in lipid biomarker distributions in the catchment and sediments of a crater lake in central india the basin scale spatial variability in lipid biomarker proxies in lacustrine sediments which are established tools for studying continental environmental change has rarely been examined it is often implicitly assumed that a lake sediment core provides an average integral of catchment sources here we evaluated the distribution of lipid biomarkers in a modern ecosystem and compared it with the sedimentary record we analyzed lipid biomarkers in terrestrial and aquatic organisms and in lake surface sediments from 17 locations within the saline alkaline lonar crater lake in central india terrestrial vegetation and lake surface sediments were characterized by relatively high average chain length acl index values 29 6 32 8 of leaf wax n alkanes consistent with suggestions that plants in drier and warmer climates produce longer chain alkyl lipids than plants in cooler and humid areas a heterogeneous spatial distribution of acl values in lake surface sediments was found at locations away from the shore the values were highest 31 or more possibly indicating different sources and or transport of terrestrial biomarkers in floating benthic microbial mats and surface sediment n heptadecane carotenoids diploptene phytol and tetrahymanol occurred in large amounts interestingly these biomarkers of a unique bacterial community were found in substantially higher concentrations in nearshore sediment samples we suggest that human influence and subsequent nutrient supply resulted in increased primary productivity leading to an unusually high concentration of tetrahymanol in the nearshore sediments in summary the data showed that substantial heterogeneity existed within the lake but leaf wax n alkanes in a core from the center of the lake represented an integral of catchment conditions however lake level fluctuation may potentially affect aquatic lipid biomarker distributions in lacustrine sediments in addition to source changes

episodic methane release events from last glacial marginal sediments in the western north pacific 1 according to recent observations of anomalous bottom simulating reflections bsr the northwest pacific marginal sediments around japan main islands bear large abundances of methane hydrate satoh 2002 during the last glacial direct and indirect evidence accumulated from geochemical data suggests that methane episodically released from hydrate trapped in the seafloor sediments dickens et al 1995 hinrichs et al 2003 kennett et al 2000 here we show that marginal sediments from the western north pacific contain a hopanoid 17 h 21 h hop 22 29 ene diploptene derived from the activity of methanotrophic bacteria in water column and or surface sediment during a warming period interstadial 3 in the last glacial the carbon isotopic compositions of diploptene range between 41 0 and 27 9 relative to pdb in the horizon indicative of a contribution of methanotrophic bacteria foraminiferal isotope signals were also found with highly depleted 13c compositions of planktonic foraminifera 1 9 pdb and benthic foraminifera 0 8 pdb suggesting indirect records of enhanced incorporation of 13c depleted co2 formed by methanotrophic process that use 12c enriched methane as their main source of carbon from combined isotopic data of molecular diploptene and foraminifera the most prominent signal of methane release was detected in the sediments deposited around 25 4 cal kyr bp 100 year time span corresponding to the interstadial 3 this is the first evidence of methane hydrate instability in the open western north pacific during the last glacial considering the glacial interglacial hydrographic conditions in this region the instability of methane hydrate may be modulated by intermediate water warming and or the lowering of sea level our results suggest that the western north pacific marginal regions may be a profound effect on rapid global warming climate changes during the last glacial

petrology and geochemistry of siliciclastic rocks of mixed feldspathic and ophiolitic provenance in the northern apennines italy provenance in clastic sedimentary rocks in the northern apennines is determined by integrated petrographic and geochemical criteria thus mafic poor arkoses in the gottero formation senonian paleocene deposited prior to the alpine orogeny were derived from granitic provenance in the sardinian corsican massif in the gottero formation chemical criteria distinguish between very low input of detrital mafic material and co c and ni added entirely by adsorption on clay minerals post alpine orogeny feldspathic sandstones in the macigno formation mid oligocene lower miocene and cervarola formation lower miocene reflect a more diverse provenance of granitic metamorphic ophiolitic and sedimentary rocks in the apennines and alps the macigno and cervarola rocks are distinguished by serpentine gabbro and diabase fragments and higher chlorite contents than in the gottero rocks chemically the macigno and cervarola rocks contain distinctive signatures expressed in higher mgo co cr and ni contents of the mafic ultramafic detritus a wider range and more scattered cr and ni variation and higher niggli ti for a given niggli al alk content the mgo co cr and ni abundances indicate up to 10 ultramafic ophiolitic detritus in the macigno and cervarola sandstones and up to 17 ophiolitic detritus in associated shales estimated by comparison of mixtures of feldspathic sands with ligurian peridotites up to 10 basaltic ophiolitic detritus in these sediments is suggested by cao and fe2o3 total abundances petrographic data indicate that a major part of the detritus in the macigno and cervarola formations is from alpine granitic basement of calc alkaline granite to tonalite plutons and gneisses but apart from higher ba in macigno and cervarola sandstones than in the gottero sandstones this is difficult to identify chemically the trace elements cr ni ba rb ce la y co cu ga pb and zn generally have positive correlations with niggli al alk a chemical surrogate measure of sheet mineral clays micas and chlorites content whereas sr which is associated with carbonate and feldspar shows negative correlation with al alk an olistostrome unit contains the most weathered detritus but otherwise shows similar chemical variation to the other formations methods to 1 identify separately mafic and ultramafic inputs 2 recognize in shales co cr and ni derived from ophiolitic sources and non ophiolitic sources 3 estimate the minimum mafic ultramafic proportion in a sediment may have general application elsewhere in sedimentary and metasedimentary rocks

stratigraphy and depositional setting of slurry and contained reflected beds in the marnoso arenacea formation langhian serravallian northern apennines italy this work presents the stratigraphy and facies analysis of an interval of about 2500 m in the langhian and serravallian stratigraphic succession of the foredeep turbidites of the marnoso arenacea formation a high resolution stratigraphic analysis was performed by measuring seven stratigraphic logs between the sillaro and marecchia lines 60 km apart for a total thickness of about 6700 m the data suggest that the stratigraphy and depositional setting of the studied interval was influenced by syndepositional structural deformations the studied stratigraphic succession has been subdivided into five informal stratigraphic units on the basis of how structurally controlled topographic highs and depocentres a consequence of thrust propagation change over time these physiographic changes of the foredeep basin have also been reconstructed through the progressive appearance and disappearance of thrust related mass transport complexes and of five bed types interpreted as being related to structurally controlled basin morphology apart from bouma like type 4 beds type 1 tripartite beds characterized by an internal slurry unit tend to increase especially in structurally controlled stratigraphic units where intrabasinal topographic highs and depocentres with slope changes favour both mud erosion and decelerations type 2 beds with an internal slump type chaotic unit characterize the basal boundary of structurally controlled stratigraphic units and are interpreted as indicating tectonic uplift type 3 beds are contained reflected beds that indicate different degrees of basin confinement while type 5 are thin and fine grained beds deposited by dilute reflected turbulent flows able to rise up the topographic highs the vertical and lateral distribution of these beds has been used to understand the synsedimentary structural control of the studied stratigraphic succession represented in the marnoso arenacea formation by subtle topographic highs and depocentres created by thrust propagation folds and emplacements of large mass transport complexes

linked debrites in sand rich turbidite systems origin and significance abstract the outer parts of a number of small late jurassic sandy deep water fans in the northern north sea are dominated by the stacked deposits of co genetic sandy and muddy gravity flows sharp based structureless and dewatered sandstone beds are directly overlain by mudclast breccias that are often rich in terrestrial plant fragments and capped by thin laminated sandstones pseudonodular siltstones and mudstones the contacts between the clast rich breccias and the underlying sandstones are typically highly irregular with evidence for liquefaction and upward sand injection the breccias contain fragments up to metre scale of exotic lithologies surrounded by a matrix that is extremely heterogeneous and strewn with multiphase and variably sheared sand injections and scattered coarse and very coarse sand grains often coarser than in the immediately underlying sand bed markov chain analysis establishes that the breccias consistently overlie sandstones and the character of the breccias and their external contacts rule out a post depositional origin via in situ liquefaction intrastratal flowage or bed amalgamation and disruption the breccias are interpreted as debrites that rode on a water rich sand bed just deposited by a co genetic concentrated gravity current as such they are referred to as linked debrites to distinguish them from debrites emplaced in the absence of a precursor sand bed the distinction is important because these linked debris flows can achieve significant mobility through entrainment of both water and sediment from beneath and they ride on a low friction carpet of liquefied sand this explains the paradox presented by fan fringes in which there are common debrites when conventional thinking might predict that deposits of low concentration gravity currents should be more important here in fact evidence for transport by low concentration turbidity currents is rare in these systems several possible mechanisms might explain the formation of linked flows but the ultimate source of both sandy and clast rich flow components must be in shallower water on the basin margin the debrites are not triggered from distal slopes flow partitioning may have occurred by upslope erosion and retardation of the mudclast charged portion of an erosional sandy density current partial flow transformation of a precursor debris flow and or hydraulic segregation and reconcentration of the flaky clasts and carbonaceous matter during transport linked debrites are not restricted to small sand rich fans and similar mechanisms may be responsible for the long runout of debris flows in other systems the recognition of a distinct class of linked debrites is of wider importance for facies prediction reservoir heterogeneity and even carbon fluxes and sequestration on continental margins

aquatic biomarkers record pleistocene environmental changes at paleolake olduvai tanzania abstract several hypotheses invoke climatic variability as a driving force for hominin evolution thus high resolution records of climate and environmental variability from anthropologically significant locations can help test these hypotheses sedimentary sequences recovered by the olduvai gorge coring project ogcp help evaluate climatic and environmental changes at olduvai gorge tanzania through the analyses of various biogeochemical proxies the stratigraphic sequence of ogcp core 2a can be correlated with horizons associated with hominins and is chronologically constrained by distinctive dated horizons such as the bed i basalt and tuff ib the lacustrine interval from 76 6 to 86 9 m depth is ideally suited for high resolution analyses of biogeochemical proxies as it is rich in organic carbon 1 toc the hydrogen isotopic composition of nc31 in this interval of ogcp core 2a records the effects of precession driven wet dry cycles on the terrestrial environment that led to alternations between woodland and grassland ecosystems comparable to those documented by previous investigations of outcrop analogues at olduvai here we examine stratigraphic variations in the abundance of biomarkers c28 steradienes c17 and c23 n alkanes c27 and c28 a norsteranes fern 8 ene and chromans derived from aquatic organisms algae cyanobacteria sponges macrophytes etc to determine the response of paleolake olduvai to climate variability in general these aquatic biomarkers reflect the productivity of the lake environment and exhibit the same precession driven wet dry cycles recorded by terrestrial biogeochemical signatures however they also provide evidence of abrupt

selective organic matter preservation in burn down turbidites on the madeira abyssal plain 1 oxidized intervals of five organic rich madeira abyssal plain map turbidites deposited during the miocene pliocene and pleistocene all displayed comparable major loss of total organic carbon toc 84 3 1 accompanied by a negative isotopic 13c shift ranging from 0 3 to 2 9 major but significantly lower loss of total nitrogen ntot 61 7 1 also occurred leading to a decrease in toc relative to ntot c ntot and a 1 3 to 2 7 ntot isotopic 15n shift compound specific isotopic measurements on plant wax n alkanes indicate the terrestrial organic component in the unoxidized deposits is 13c enriched owing to significant c4 contribution selective preservation of terrestrial relative to marine organic carbon could account for the 13c behavior of toc upon oxidation but only if a 13c depleted component of the bulk terrestrial signal is selectively preserved in the process although the c ntot decrease and positive 15n shift seems inconsistent with selective terrestrial organic preservation results from analysis of a modern eolian dust sample collected in the vicinity indicate these observations are compatible regardless of the specific explanation for these isotopic observations however our findings provide evidence that paleoreconstruction of properties such as pco2 using the 13c of toc is a goal fraught with uncertainty whether or not the marine sedimentary record considered is contaminated with significant terrestrial input nonetheless despite major and selective loss of both marine and terrestrial components as a consequence of postdepositional oxidation intensive organic geochemical proxies such as the alkenone unsaturation index u37k appear resistant to change and thereby retain their paleoceanographic promise

a comparison of sedimentary aliphatic hydrocarbon distribution between the southern okinawa trough and a nearby river with high sediment discharge twelve surface sediments from the southern okinawa trough ot and nine surface sediments from a nearby river the lanyang river lr with high sediment discharge were analyzed for comparison of their aliphatic hydrocarbon distributions performing cluster analysis on all hydrocarbon data of lr and ot sediments showed that the two areas had a similarity level of only 0 15 meaning that they were quite dissimilar the average ratio of terrigenous to aquatic n alkanes was 0 99 for lr sediments and 9 64 for ot sediments indicating that the concentrations of n alkanes in lr and ot sediments were quite different furthermore the mean pristane phytane ratios for lr and ot sediments were 1 01 and 2 57 respectively the difference between them was significant student s t test at the 99 significance level the carbon preference index cpi of c25ec33 n alkanes averaged 3 26 range 2 16e4 59 for lr sediments and 2 92 range 2 35e5 24 for ot sediments no significant difference was found between the two cpi averages student s t test at the 99 confidence level however higher plant n alkanes generally maximized at c29 for lr sediments but maximized at c31 for all ot sediments strongly indicating significant differences in the origins of the hydrocarbons in these two areas all present results appear to suggest that lr sediments are not a major hydrocarbon source for ot sediments in addition there was no positive linear correlation between diploptene hop 22 29 ene and terrestrial higher plant n alkanes for lr and ot sediments

drained and undrained strength interpretation for low plasticity silts the engineering behavior of low plasticity silts is more difficult to characterize than is the behavior of clay or sand due to their tendency to dilate during shear establishing a consistent and practically useful failure criterion for low plasticity silts can be very difficult consideration of how the undrained shear strength of silt is related to changes in pore pressure provides a more useful and practical framework for understanding the undrained strengths of these materials and for characterizing undrained strengths for practical purposes using a value of skempton s a as a failure criterion has been found to result in very reasonable values of undrained strength and to reduce scatter in the results as compared to using other criteria using a failure criterion based on an appropriate value of a results in consistent values of su p and tolerably small values of strain at failure for low plasticity dilative silts that pose the greatest problems with respect to definition of failure using

distribution and origin of hybrid beds in sand rich submarine fans of the tanqua depocentre karoo basin south africa abstract this study documents the stratigraphic and palaeogeographic distribution of hybrid event beds that comprise both debris flow cohesive and turbidity current non cohesive deposits this is the first study of such beds in a submarine fan system to combine outcrop and research borehole control and uses a dataset from the skoorsteenberg formation of the tanqua depocentre in the karoo basin south africa three types of 0 1 1 0 m thick hybrid beds are observed which have a basal weakly graded fine grained sandstone turbidite division overlain by a division of variable composition that can comprise 1 poorly sorted carbonaceous rich material supported by a mud rich and micaceous sand matrix 2 poorly sorted mudstone clasts in a mud rich sand silt matrix or 3 gravel grade rounded mudstone clasts in a well sorted mud poor sandstone matrix these upper divisions are interpreted respectively as 1 the deposit of a debris flow most likely derived from shelf edge collapse 2 the deposit of a debris flow most likely developed through flow transformation from turbidity current that eroded a muddy substrate and 3 from a turbidity current with mudstone clasts transported towards the rear of the flow all three hybrid bed types are found concentrated at the fringes of lobes that were deposited during fan initiation and growth the basinward stepping of successive lobes means that the hybrid beds are concentrated at the base of stratigraphic successions in medial and distal fan settings hybrid beds are absent in proximal fan positions and rare and thin in landward stepping lobes deposited during fan retreat this distribution is interpreted to reflect the enhanced amounts of erosion and availability of mud along the transport route during early lowstands of sea level therefore hybrid beds can be used to indicate a fan fringe setting infer lobe stacking patterns and have a sequence stratigraphic significance

stable carbon isotope ratios of intact gdgts indicate heterogeneous sources to marine sediments thaumarchaeota the major sources of marine glycerol dibiphytanyl glycerol tetraether lipids gdgts are believed to fix the majority of their carbon directly from dissolved inorganic carbon dic the 13c values of gdgts 13cgdgt may be powerful tools for reconstructing variations in the ocean carbon cycle including paleoproductivity and water mass circulation if they can be related to values of 13cdic to date isotope measurements primarily are made on the c40 biphytane skeletons of gdgts rather than on complete tetraether structures this approach erases information revealed by the isotopic heterogeneity of gdgts within a sample and may impart an isotopic fractionation associated with the ether cleavage to circumvent these issues we present 13c values for gdgts from twelve recent sediments representing ten continental margin locations samples are purified by orthogonal dimensions of hplc followed by measurement of 13c values by spooling wire microcombustion swim isotope ratio mass spectrometry irms with 1 precision and accuracy of 0 25 using this approach we confirm that gdgts generally around 19 are isotopically heavy compared to other marine lipids however measured 13cgdgt values are inconsistent with predicted values based on the 13c content of dic in the overlying water column and the previously published biosynthetic isotope fractionation for a pure culture of an autotrophic marine thaumarchaeon in some sediments the isotopic composition of individual gdgts differs indicating multiple source inputs the data appear to confirm that crenarchaeol primarily is a biomarker for thaumarchaeota but its 13c values still cannot be explained solely by autotrophic carbon fixation overall the complexity of the results suggests that both organic carbon assimilation ca 25 of total carbon and multiple source s of exogenous gdgts contributing generally 30 of input to sediments are necessary to explain the observed 13cgdgt values the results suggest caution when interpreting the total inputs of gdgts to sedimentary records biogenic or open slope sediments rather than clastic basinal or shallow shelf sediments are preferred locations for generating minimally biased gdgt proxy records

cyclic strength of a natural liquefiable sand stabilized with colloidal silica grout this paper summarizes the experimental results of a series of cyclic simple shear tests on liquefiable silty sand with and without sample improvement with colloidal silica grout the objective of t

earthquakes as a triggering mechanism for debris flows and turbidites on the calabrian ridge abstract debris flows and turbidites have been described in piston cores bottom photographs and side looking sonar records from basin floors amid the rugged irregular topography of the calabrian ridge a sediment transport process is inferred which began with a rotational slump on the steep basin wall subsequently transformed into a debris flow and turbid cloud such events occurred approximately every 1500 years because the debris flow turbidite deposits are correlative between basins some relatively widespread mechanism such as an earthquake is required to initiate the slope failure the estimated intensity of ground shaking as a result of historical earthquakes on the nearby calabrian and hellenic arcs has been used to develop a relationship between frequency of occurrence and intensity of ground shaking extrapolation of this relation to infrequent large magnitude events shows that the 1500 yr event is small enough to be geologically plausible but large enough to cause slope failure on basin walls it is possible that the historical record fortuitously contains one of these large magnitude long repeat time events which may have caused the most recent of the observed debris flows in 1903

diploptene an indicator of terrigenous organic carbon in washington coastal sediments the pentacyclic triterpene 17 beta h 21 beta h hop 22 29 ene diploptene occurs in sediments throughout the columbia river drainage basin and off the southern coast of washington state in concentrations comparable to long chain plantwax n alkanes the same relationship is evident for diploptene and long chain n alkanes in soils from the willamette valley microorganisms indigenous to soils and soil erosion are indicated as the biological source and physical process respectively for diploptene in coastal sediments similarity between the stable carbon isotopic composition delta 13cpdb of diploptene isolated from soil in the willamette valley 31 2 0 3 and from sediments deposited throughout the washington coastal environment 31 2 0 5 supports this argument values of delta for diploptene in river sediments are variable and 8 17 lighter indicating that an additional biological source such as methane oxidizing bacteria makes a significant contribution to the diploptene record in river sediments selective biodegradation resulting from a difference in the physicochemical association within eroded particles can explain the absence of the more 13c depleted form of diploptene in washington coastal sediments but this mechanism remains unproven

diploptene in varved sediments of saanich inlet indicator of increasing bacterial activity under anaerobic conditions during the holocene saanich inlet has been a highly productive fjord since the last glaciation during odp leg 169s nearly 70 m of holocene sediments were recovered from hole 1034 at the center of the inlet the younger sediments are laminated anaerobic and rich in organic material 1 2 5 wt corg whereas the older sediments below 70 mbsf are non laminated aerobic with glacio marine characteristics and have a significantly lower organic matter content this difference is also reflected in the changes of interstitial fluids and in biomarker compositions and their carbon isotope signals the bacterially derived hopanoid 17 h 21 h hop 22 29 ene diploptene occurs in saanich inlet sediments throughout the holocene but is not present in pleistocene glacio marine sediments its concentration increases after 6000 years bp up to present time to about 70 g g corg whereas terrigenous biomarkers such as the n alkane c31 are low throughout the holocene 51 g g corg and even slightly decrease to 36 g g corg at the most recent time the increasing concentrations of diploptene in sediments younger than 6000 years bp separate a recent period of higher primary productivity stronger anoxic bottom waters and higher bacterial activity from an older period with lesser activity heretofore undifferentiated carbon isotopic compositions of diploptene in the holocene are between 31 5 and 39 6 pdb after 6000 years bp these differences in the carbon isotopic record of diploptene probably reflect changes in microbial community structure of bacteria living at the oxic anoxic interface of the overlying water column the heavier isotope values are consistent with the activity of nitrifying bacteria and the lighter isotope values with that of aerobic methanotrophic bacteria therefore intermediate 13c values probably represent mixtures between the populations in contrast carbon isotopic compositions of n c31 are roughly constant at 31 4 1 1 pdb throughout the holocene indicating a uniform input from cuticular waxes of higher plants prior to 6000 years bp diploptene enriched in 13c of up to 26 3 pdb is indicative of cyanobacteria living in the photic zone and suggests a period of lower primary productivity more oxygenated bottom waters and hence lower bacterial activity during the earliest holocene

a 35 000 year record of terrigenous and marine lipids in amazon fan sediments elemental and lipid analyses were carried out on sediments recovered from ocean drilling program odp site 942 to provide a 35 kyr record of organic matter input to amazon fan sediments total organic carbon toc and higher plant biomarker mass accumulation rates were an order of magnitude greater during the last glacial period compared to the current interglacial due to sea level controlled variations in amazon river sediment supply large maxima were also seen at similar to 12 ka which are most likely due to discharge events higher plant n alkane average chain lengths did not change throughout the record suggesting consistency in the source vegetation type the abundance of taraxerol relative to other plant biomarkers increased at similar to 12 ka indicating increased mangrove input due to either higher mangrove productivity or increased erosion of mangrove deposits the mass accumulation rates mars of some bacterial and eustigmatophyte biomarkers varied closely with those of higher plant biomarkers and so seem to have a non marine source long chain alkenones were present in some of the sediments generally in very low concentration indicating dilution of the marine signal with terrestrial organic matter c 2005 elsevier ltd all rights reserved

reworking of amino acid in marine sediments stable carbon isotopic composition of amino acids in sediments along the washington coast the stable carbon isotopic composition of nine individual amino acids were investigated in phytoplankton and zooplankton estuarine plankton terrigenous material marine fecal material and clay mineral isolates collected along the washington coast the clay fraction was isolated from suspended sediments of the columbia river the mineral source and three shelf and slope stations mineral deposition sites in the sediments terrigenous amino acids were replaced by those of marine origin and microbial reworking of the amino acids further influenced their d 13 c compositions based on changes in isotopic composition individual amino acids could be roughly divided into three groups 1 leucine and proline had isotopic shifts similar to bulk organic matter on average 80 of these river delivered amino acids were replaced by marine derived material 2 alanine isoleucine glutamic acid aspartic acid and phenylalanine had intermediate isotopic shifts these isotopic compositions are consistent with both the expected isotopic fractionation associated with microbial resynthesis of amino acids using marine substrates and or preservation of 50 of the terrigenous component in the marine environment 3 glycine and valine exhibited isotopic values outside the range of our sampled end members their unusual isotopic compositions are attributed to reworking of their isotopic signal during diagenesis microbial resynthesis of amino acids during growth on mixed substrates may account for nearly all the observed variation in amino acid isotopic composition similarity between the amino acid isotopic composition of the fecal material and that of the clay isolates suggests that alterations of the isotopic composition of the amino acids might occur while the amino acids are in distinct organicrich debris prior to long term association with the sediment

the transfer of organic signatures from bedrock to sediment abstract a case study in the canadian arctic demonstrates how an organic geochemical signature in the regional bedrock can be transferred by erosion and redeposition to younger geological formations and surface sediments the hydrocarbon composition recorded in laurentian lower palaeozoic carbonate bedrock was incorporated into overlying miocene and quaternary formations and modern mass waste alluvium snow ice and proglacial deposits and further distant in ice rafted detritus the retention of the original geological organic signature is reflected in consistent thermal maturities hopane ratios and environmental indicators sterane distributions in the modern sediments the geological signature is variably mixed with a modern microbial organic signature reflected in high values of carbon preference index and diploptene these data show that hydrocarbon occurrences in bedrock may be detected by the analysis of surface detritus especially in carbonate terrains however they also indicate that environmental signatures may be misleading if they are inherited from older geological units

sources of sedimentary organic matter in the mississippi river and adjacent gulf of mexico as revealed by lipid biomarker and δ13ctoc analyses abstract changes in the organic matter om composition c n 13 c toc and lipid biomarker compounds of surface sediments 0 1 cm were examined along the dispersal pathway from mississippi river and marsh estuarine end members to the adjacent shelf and canyon regions of the gulf of mexico organic carbon content decreased fourfold from the marsh to the offshore sites with corresponding changes in organic matter sources biomarkers representing allochthonous higher plant and autochthonous algal plankton bacteria sources demonstrated regional differences in the sources of sediment organic matter som a two end member mixing model using 13 c toc indicated that c 3 vascular plant sources comprised 80 and 50 of the toc at the river and marsh sites respectively however sources of som differed in these regions with contributions of soil organic matter terrigenous plant sources dominant in the river 13 c toc 25 while marsh plants likely contributed to the enriched signatures found in the marsh sediments 13 c toc 18 allochthonous om contributions calculated from fatty acid and sterol biomarkers in the river and marsh regions 39 48 and 50 72 respectively differed from those determined using 13 c toc this was likely due to overlapping 13 c toc values for vascular plants and freshwater microalgae and the higher lipid content of the autochthonous sources although biomarkers representing terrigenous sources decreased with distance offshore they comprised approximately 17 34 of the fatty acid and sterols at even the most distal slope and canyon sites suggesting that these deeper regions could be an important sink for terrigenous carbon in contrast the shelf sites were enriched in algal material 60 78 autochthonous oc with biomarkers for diatoms dominating suggesting that terrigenous carbon is either diluted in or bypasses this region results from this study suggest that processes including hydrodynamic sorting diagenesis and variations in river flow should be considered in future studies investigating the fate of terrigenous om in coastal and shelf regions

spatial variations in the composition of turbidites due to hydrodynamic fractionation 1 this study uses measurements from physical experiments to document turbidity currents which are density currents composed of suspended sediment and water to be effective at hydrodynamically fractionating minerals on the basis of grain density and grain shape alone resulting in large scale spatial variations in the composition of their deposits while grain composition varies spatially the population sampled at any one location is hydrodynamically equivalent spatial variations in composition of the deposits are modeled using exponential decay functions which are based on initial concentration of grain types and their respective differences in settling velocity we further discuss implications of this process for addressing practical geophysical problems in which mineralogical distributions are important such as provenance and geochronology studies subsurface imaging and predicting bulk properties of subsurface reservoirs

prediction of hydrocarbon recovery from turbidite sandstones with linked debrite facies numerical flow simulation studies abstract a series of two dimensional numerical flow simulations were carried out to investigate the production characteristics of a sheet sandstone bed with a linked debrite interval a deterministic geological model was used based on a two dimensional representation of a bed from the marnoso arenacea formation the model was 60 km long and 1 m thick and contained three zones arranged in a vertical facies arrangement typical of many linked debrite beds i a lower coarse to medium grained clean turbidite sandstone interval ii a middle muddy sandstone debrite interval iii an upper fine grained clean laminated sandstone interval simulation involved only a 3 km long sector of the model with one injector well and one production well placed 1 km apart in the middle of the sector model the simulated sector was moved progressively down the length of the bed in 1 km steps sampling different parts of the bed with different facies proportions the petrophysical properties of the debrite interval were varied to produce different porosity permeability cases all other modelling parameters including the upper and lower interval petrophysics were kept constant results indicate that in most cases key production parameters such as cumulative oil production with time and water cut are proportional to the volume of movable oil between the wells this relationship does not hold however for cases with relatively low values of debrite porosity 0 15 and permeability kh 100 md where the debrite interval accounts for more than 20 of the interwell volume in these models production efficiency declines systematically with reducing reservoir quality and increasing debrite percentage resulting in relatively low oil production and early water breakthrough

ground settlement in simi valley following the northridge earthquake significant differential settlements were observed on a flat undeveloped generally silty but highly stratified alluvial site in eastern simi valley calif due to groundshaking from the 1994 northridge earthquake the observed settlements were due to both liquefaction of soil beneath the ground water table and dry shaking of loose soils above it a nearby strong motion recording station provided highly reliable ground motion data for analysis extensive cone penetration tests cpt along with occasional seismic cones scpt flat plate dilatometer tests dmt and soil sampling were performed previously developed methods were adopted for converting the cpt data to equivalent standard penetration test blow count spt n values for establishing liquefaction potential and predicting settlement site specific calibration of cpt data was performed to establish a correlation between cpt readings and the percentage of fines contours of predicted ground settlement agreed very well with the location and the observed differential settlements along a ground fissure that developed shortly after the earthquake

terrestrial organic carbon contributions to sediments on the washington margin elemental and stable carbon isotopic compositions and biomarker concentrations were determined in sediments from the columbia river basin and the washington margin in order to evaluate geochemical approaches for quantifying terrestrial organic matter in marine sediments the biomarkers include an homologous series of long chain n alkanes derived from the surface waxes of higher plants phenolic and hydroxyalkanoic compounds produced by cuo oxidation of two major vascular plant biopolymers lignin and cutin all marine sediments including samples collected from the most remote sites in cascadia basin showed organic geochemical evidence for the presence of terrestrial organic carbon using endmember values for the various biomarkers determined empirically by two independent means we estimate that the terrestrial contribution to the washington margin is 60 for shelf sediments 30 for slope sediments and decreases further to 15 in basin sediments results from the same geochemical measurements made with depth in gravity core 6705 7 from cascadia seachannel suggest that our approach to assess terrestrial organic carbon contributions to contemporary deposits on the washington margin can be applied to the study of sediments depositing in this region since the last glacial period

beds comprising debrite sandwiched within co genetic turbidite origin and widespread occurrence in distal depositional environments co genetic debrite turbidite beds occur in a variety of modern and ancient turbidite systems their basic character is distinctive an ungraded muddy sandstone interval is encased within mud poor graded sandstone siltstone and mudstone the muddy sandstone interval preserves evidence of en masse deposition and is thus termed a debrite the mud poor sandstone siltstone and mudstone show features indicating progressive layer by layer deposition and are thus called a turbidite palaeocurrent indicators ubiquitous stratigraphic association and the position of hemipelagic intervals demonstrate that debrite and enclosing turbidite originate in the same event detailed field observations are presented for co genetic debrite turbidite beds in three widespread sequences of variable age the miocene marnoso arenacea formation in the italian apennines the silurian aberystwyth grits in wales and quaternary deposits of the agadir basin offshore morocco deposition of these sequences occurred in similar unchannellized basin plain settings co genetic debrite turbidite beds were deposited from longitudinally segregated flow events comprising both debris flow and forerunning turbidity current it is most likely that the debris flow was generated by relatively shallow few tens of centimetres erosion of mud rich sea floor sediment changes in the settling behaviour of sand grains from a muddy fluid as flows decelerated may also have contributed to debrite deposition the association with distal settings results from the ubiquitous presence of muddy deposits in such locations which may be eroded and disaggregated to form a cohesive debris flow debrite intervals may be extensive 26 x 10 km in the marnoso arenacea formation and are not restricted to basin margins such long debris flow run out on low gradient sea floor 0 1 may simply be due to low yield strength 50 pa of the debris water mixture this study emphasizes that multiple flow types and transformations between flow types can occur within the distal parts of submarine flow events

short length scale variability of hybrid event beds and its applied significance abstract hybrid event beds hebs are a type of deep water sediment gravity flow deposit that generally comprise a basal clean sandstone overlain by a variety of muddier and less permeable sandy facies they are thought to be emplaced by combinations of turbidity currents transitional flows and debris flows all as part of the same transport event to date a number of studies have highlighted the common presence of hebs mainly in the outer and marginal parts of deep water systems where they replace beds composed dominantly of clean sand up dip and or axially over scales of km to 10 s km in addition to these broad patterns important yet poorly understood short length facies changes over metres to 100 s m occur modifying the overall texture and reservoir characteristics at or beneath typical spacing of production wells the nature and origin of the short length scale transitions is here addressed in four well exposed heb prone outcrops the cretaceous paleocene gottero sandstone and the miocene cilento flysch both in italy the carboniferous mam tor sandstone in northern england and the carboniferous basal ross sandstone formation western ireland a series of detailed correlation panels show marked lateral variations in internal bed make up for most of the hybrid event beds studied this variability typically involves lateral changes in the proportions of the cleaner basal sandstone and the overlying muddy sandstone division that occur without substantial change in the overall event bed thickness the variability is inferred to reflect the complex fingering between the up dip sandstone dominated part of the event bed and the down dip linked debrite due to internal erosion ploughing of the debrite into the basal clean sand where the upper part of the bed is dominated by large mudstone rafts these may have foundered into liquefied sand and been injected and partly fragmented by the sand intrusions the variable thickness and continuity of the basal clean sandstones have important implications for reservoir characterisation significant variability in bed character at interwell scale can be anticipated rugose contacts between the intra bed facies divisions may impact on drainage and sweep efficiency during hydrocarbon production

stable carbon isotopic correlation of individual biolipids in aquatic organisms and a lake bottom sediment abstract isotope ratio monitoring gc ms irm gcms analyses of individual hydrocarbons isolated from the surface sediment of a small eutrophic lake priest pot u k and a phytoplankton tow sample from the upper water column have been undertaken in order to assign sources of sedimentary lipids the 13c values for the sedimentary n alkanes showed no clear distinction between lower molecular weight components c17 c19 of presumed algal origin and higher members c23 c33 of presumed higher plant origin thus indicating a limitation to the use of compound specific isotope analysis in the freshwater system studied in contrast the 13c values of sedimentary hopenes were markedly depleted by over 20 compared with those in the phytoplankton sample from the upper water column hop 22 29 ene in the surficial sediment had a 13c value of 55 2 which contrasts witht he value of the phytoplankton component 32 7 attributed to cyanobacteria these values indicate that a highly 13c depleted source provides a major contribution to the sedimentary component it is proposed that the sedimentary hopenes originate in part from methanotrophic bacteria demonstrating the presence of a bacterial methane cycle in this environment

hybrid event bed character and distribution linked to turbidite system sub environments the north apennine gottero sandstone north west italy this study documents the character and occurrence of hybrid event beds deposited across a range of deep water sub environments in the cretaceous palaeocene gottero system north west italy detailed fieldwork 5200 m of sedimentary logs has shown that hybrid event beds are most abundant in the distal confined basin plain domain 31 of total thickness in more proximal sectors hebs occur within outer fan and mid fan lobes up to 15 of total thickness whereas they are not observed in the inner fan channelised area six hybrid event bed types heb 1 to heb 6 were differentiated mainly on basis of the texture of their muddier and chaotic central division h3 the confined basin plain sector is dominated by thick max 9 57 m average 2 15 m and tabular hybrid event beds heb 1 to heb 4 their h3 division can include very large substrate slabs evidence of extensive auto injection and clast break up and abundant mudstone clasts set in a sandy matrix dispersed clay ca 20 these beds are thought to have been generated by highly energetic flows capable of delaminating the sea floor locally and carrying large rip up clasts for relatively short distances before arresting the unconfined lobes of the mid fan sector are dominated by thinner average 0 38 m hybrid event beds heb 5 and heb 6 their h3 divisions are characterised by floating mudstone clasts and clay enriched matrices dispersed clay 25 with hydraulically fractionated components mica organic matter and clay flocs these hybrid event beds are thought to have been deposited by less energetic flows that underwent early turbulence damping following incorporation of mud at proximal locations and by segregation during transport although there is a tendency to look to external factors to account for hybrid event bed development systems like the gottero imply that intrabasinal factors can also be important specifically the type of substrate available muddy or sandy and where and how erosion is achieved across the system producing specific hybrid event bed expressions and facies tracts this article is protected by copyright all rights reserved

liquefaction and soil failure during 1994 northridge earthquake the 1994 northridge california earthquake caused widespread permanent ground deformation on the gently sloping alluvial fan surface of the san fernando valley the ground cracks and distributed deformation damaged both pipelines and surface structures to evaluate the mechanism of soil failure detailed subsurface investigations were conducted at four sites three sites are underlain by saturated sandy silts with low standard penetration test and cone penetration test values these soils are similar to those that liquefied during the 1971 san fernando earthquake and are shown by widely used empirical relationships to be susceptible to liquefaction the remaining site is underlain by saturated clay whose undrained shear strength is approximately half the value of the earthquake induced shear stress at this location this study demonstrates that the heterogeneous nature of alluvial fan sediments in combination with variations in the groundwater table can be responsible for complex patterns of permanent ground deformation it may also help to explain some of the spatial variability of strong ground motion observed during the 1994 earthquake

identification of unusual 17β h moret 22 29 ene in lake sediments an unusual 17 h moret 22 29 ene in lake sediments was identified for the first time based on the coincidence of its hydrogenation product with 17 h 21 h moretane in terms of mass spectrum and gas chromatographic retention time our survey revealed that 17 h moret 22 29 ene is present in sediments of 4 acid lakes 2 brackish lakes and 4 fresh lakes the abundance of 17 h moret 22 29 ene relative to diploptene is high in acid lakes whereas it is very low or almost absent in the latter two types of lakes this suggests that the formation of 17 h moret 22 29 ene is closely associated with the acidic conditions of these lake environments the dehydration of 17 h 21 h moretan 29 ol is proposed as a possible pathway of formation of 17 h moret 22 29 ene in lake sediments although the proposed precursor has yet to be identified