anaerobic oxidation of methane in hypersaline messinian environments revealed by 13c depleted molecular fossils abstract the messinian sequence of evaporitic deposits in italy includes authigenic carbonates that have been suggested to derive from the microbial degradation of organic compounds but the biogeochemical mechanisms that led to their formation remained unknown to unravel these mechanisms 13 c depleted carbonate rocks including native sulphur bearing limestone calcare solfifero from two locations in sicily and bedded limestone from the northern apennines have been studied their 13 c values as low as 49 reflect incorporation of carbon derived from the oxidation of methane which was previously suggested to have been linked to bacterial sulphate reduction molecular fossils extracted from the limestones reveal that methane was indeed oxidized in an anaerobic process by archaea and sulphate reducing bacteria the observed biomarker patterns resemble those of methane seep carbonates which form as a consequence of the anaerobic oxidation of methane aom aom specific 13 c depleted archaeal biomarkers such as pmi 13 c 101 to 75 as well as compounds derived from sulphate reducing bacteria iso and anteiso fatty acids 13 c as low as 85 were identified in the messinian carbonates although the biomarker results clearly point to aom the compound inventory also revealed distinct differences to patterns found at marine methane seeps for example sn 3 hydroxyarchaeol is in some samples the only hydroxyarchaeol present something usually not found at seeps archaeol is less depleted in 13 c than pmi at most sites 13 c 55 to 30 pointing to the co occurrence of methanogenic or halophilic archaea with archaea involved in aom 1 the presence of calcite pseudomorphs after lenticular gypsum 2 18 o enrichment in carbonates and 3 the biomarkers o phytanyl o sesterterpanyl glycerolether extended archaeol tetrahymanol and possibly phytanylglycerol monoethers as well as non isoprenoidal macrocyclic glycerol diethers confirm that carbonate formation took place under evaporitic conditions aom has previously been shown to be inhibited in some brine pools on the modern seafloor our observations however demonstrate that aom functions in hypersaline environments as well

formation of an a ā lava delta insights from time lapse multibeam bathymetry and direct observations during the stromboli 2007 eruption five consecutive multibeam bathymetries collected before during and after the 2007 stromboli eruption combined with visual inspections allowed us to document the morphological evolution of an a lava fed delta and to reconstruct the main processes acting during its submarine emplacement the 2007 stromboli delta extended down to 600 m water depth and covered an area of 420 103 m2 with a maximum thickness of 65 m and a total estimated volume of 7 106 m3 i e three times larger than its subaerial counterpart the lava delta grew mainly through the emplacement of discrete lobes about 50 150 m in size lobes were fed from point sources along the paleoshoreline and their subaqueous pathways seem to be mainly controlled by the submarine morphology with flows mostly filling in depressions left by previous lobes the main controlling factors on the lobe morphology and thickness are the effusion rates and the pre eruption morphology i e the geometry and gradients of the basal surface data also shows that sudden slope failure of portions of the submarine delta may occur simultaneously with accretion implying that a significant part of the delta material can be transported to greater depths by submarine gravity flows the present study is relevant for future monitoring and hazard assessment during the growth of active lava fed deltas as well as for a better interpretation of ancient volcaniclastic successions inland

underwater observations of active lava flows from kilauea volcano hawaii underwater observation of active submarine lava flows from kilauea volcano hawaii in march june 1989 revealed both pillow lava and highly channelized lava streams flowing down a steep and unconsolidated lava delta the channelized streams were 0 7 1 5 m across and moved at rates of 1 3 m s the estimated flux of a stream was 0 7 m 3 s jets of hydrothermal water and gas bubbles were associated with the volcanic activity the rapidly moving channelized lava streams represent a previously undescribed aspect of submarine volcanism

products of subglacial volcanic eruptions under different ice thicknesses two examples from antarctica late cenozoic subglacially erupted volcanic sequences are scattered throughout the antarctic peninsula two of the best preserved examples at mount pinafore alexander island c 5 5 6 ma and brown bluff graham land c 1 ma are complete enough to be regarded as sequence holotypes for this uncommonly preserved eruptive depositional setting despite a common glacial association the sedimentary lithofacies in the two outcrops suggest flowing and ponded water conditions respectively indicating significant differences in the depositional palaeoenvironments the original ice thicknesses exerted a major control on the lithofacies which resulted from each eruptive phase at mount pinafore the lithofacies were confined within a steep sided valley during successive eruptions beneath thin 100 150 m wet based ice the much thicker succession at brown bluff is a tindar tuya edifice which formed within a small basin probably 15 km across confined by ice 400 m thick

ferromanganese nodules and micro hardgrounds associated with the cadiz contourite channel ne atlantic palaeoenvironmental records of fluid venting and bottom currents abstract ferromanganese nodule fields and hardgrounds have recently been discovered in the cadiz contourite channel in the gulf of cadiz 850 1000 m this channel is part of a large contourite depositional system generated by the mediterranean outflow water ferromanganese deposits linked to contourites are interesting tools for palaeoenviromental studies and show an increasing economic interest as potential mineral resources for base and strategic metals we present a complete characterisation of these deposits based on submarine photographs and geophysical petrographic mineralogical and geochemical data the genesis and growth of ferromanganese deposits strongly enriched in fe vs mn av 39 vs 6 in this contourite depositional system result from the combination of hydrogenetic and diagenetic processes the interaction of the mediterranean outflow water with the continental margin has led to the formation of late pleistocene holocene ferromanganese mineral deposits in parallel to the evolution of the contourite depositional system triggered by climatic and tectonic events the diagenetic growth was fuelled by the anaerobic oxidation of thermogenic hydrocarbons 13 c pdb 20 to 37 and organic matter within the channel floor sediments promoting the formation of fe mn carbonate nodules high 87 sr 86 sr isotopic values up to 0 70993 0 00025 observed in the inner parts of nodules are related to the influence of radiogenic fluids fuelled by deep seated fluid venting across the fault systems in the diapirs below the cadiz contourite channel erosive action of the mediterranean outflow water undercurrent could have exhumed the fe mn carbonate nodules especially in the glacial periods when the lower core of the undercurrent was more active in the study area the growth rate determined by 230 th excess 232 th was 113 11 mm ma supporting the hypothesis that the growth of the nodules records palaeoenvironmental changes during the last 70 ka ca rich layers in the nodules could point to the interaction between the mediterranean outflow water and the north atlantic deep water during the heinrich events siderite rhodochrosite nodules exposed to the oxidising sea bottom waters were replaced by fe mn oxyhydroxides slow hydrogenetic growth of goethite from the seawaters is observed in the outermost parts of the exhumed nodules and hardgrounds which show imprints of the mediterranean outflow water with low 87 sr 86 sr isotopic values down to 0 70693 0 00081 we propose a new genetic and evolutionary model for ferromanganese oxide nodules derived from ferromanganese carbonate nodules formed on continental margins above the carbonate compensation depth and dominated by hydrocarbon seepage structures and strong erosive action of bottom currents we also compare and discuss the generation of ferromanganese deposits in the cadiz contourite channel with that in other locations and suggest that our model can be applied to ferromanganiferous deposits in other contouritic systems affected by fluid venting

highly isotopically depleted isoprenoids molecular markers for ancient methane venting abstract we propose that organic compounds found in a miocene limestone from marmorito northern italy are source markers for organic matter present in ancient methane vent systems cold seeps the limestone contains high concentrations of the tail to tail linked acyclic c20 isoprenoid 2 6 11 15 tetramethylhexadecane crocetane a c25 homolog 2 6 10 15 19 pentamethylicosane pme and a distinctive glycerol ether lipid containing 3 7 11 15 tetramethylhexadecyl phytanyl moieties the chemical structures of these biomarkers indicate a common origin from archaea their extremely 13c depleted isotope compositions 13c 108 to 115 6 pdb suggest that the respective archaea have directly or indirectly introduced isotopically depleted methane derived carbon into their biomass we postulate that a second major cluster of biomarkers showing heavier isotope values 13c 88 is derived from sulfate reducing bacteria srb the observed biomarkers sustain the idea that methanogenic bacteria in a syntrophic community with srb are responsible for the anaerobic oxidation of methane in marine sediments marmorito may thus represent a conceivable ancient scenario for methane consumption performed by a defined two membered bacterial consortium 1 archaea that perform reversed methanogenesis by oxidizing methane and producing co2 and h2 and 2 srb that consume the resulting h2 furthermore the respective organic molecules are unlike other compounds tightly bound to the crystalline carbonate phase the marmorito carbonates can thus be regarded as cold seep microbialites rather than mere authigenic carbonates

progradational gravel beach sequences in a moderate to high energy microtidal marine environment the anatomy of progradational gravel beaches was analysed in two different tectonic settings the strongly subsiding messinian foreland basin of the eastern southern alps and the rising pleistocene marine terraces of the outer margin of the apenninic chain progradation took place near the mouths of fan delta or braid delta distributaries debouching in microtidal landlocked basins palaeo adriatic and palaeo ionian seas a wind wave climate comparable to that of the present day was characterized by periodic intense storm activity most of the beachface progradation is thought to have taken place during the post storm recovery and fair weather stages whereas the impact of storms is mostly recorded by the cutting of erosional surfaces on the beachface and by emplacement of poorly sorted and coarse grained gravels on the shoreface by storm intensified seaward trending flows and behind the highest berms by washover processes analysis of the sequences led to the identification of a number of typical divisions which are differently developed in the two settings compared here the characteristics of the apenninic sequences suggest a strongly variable wind wave climate with periodic changes from a relatively dissipative barred morphology during storms accompanied by strong longshore currents and rip development to a more reflective state typical of recovery and fair weather stages the southern alpine sequences on the other hand are characterized by poor evidence of barred morphology and of longshore currents and widespread effects of shear and gravity sorting in the lower beachface gravels these features indicate a comparatively more reflective average state due to location of beaches along the deeply embayed head of the palaeo adriatic and the very narrow directional width of the incoming wave spectrum which was almost shore normal most of the time in addition to well developed shape zonation of gravels the common presence of wave generated gravel megaripples in the southern alpine sequences indicates the greater influence of long period waves due to the greater available fetch distances in both settings the cyclicity is thought to be genetically related to minor changes of sea level

zeolite compositions as proxies for eruptive paleoenvironment we report chemical compositions of authigenic alteration minerals in subglacially erupted hyaloclastite breccias from james ross island antarctica which provide a geochemical proxy for paleoenvironment analyses of zeolites phillipsite and chabazite from several lava fed deltas on the island were compared with published compositions of zeolites from known freshwater and marine environments using values of na k ca 3 0 for phillipsites and 1 0 for chabazites the data successfully distinguish between marine and freshwater alteration however our study also suggests that volcanic breccias may not be sealed to fluids even when the pore spaces are completely filled the james ross island data show that at higher elevations in lava fed deltas the zeolites preserve their original freshwater influenced i e glacial compositions whereas at lower elevations na k ca ratios are generally higher and indicate a later marine influence we suggest that water may penetrate several kilometers into the volcanic pile by movement along fractures and or grain boundaries

late jurassic early cretaceous hydrocarbon seep boulders from novaya zemlya and their faunas the paper describes late jurassic early cretaceous seep carbonate boulders from the russian arctic island of novaya zemlya collected in 1875 by a e nordenskiold during his expedition to siberia the carbonates are significantly depleted in heavy carbon isotopes 13c values as low as ca 40 and show textures typical for carbonates formed under the influence of hydrocarbons such as fibrous carbonate cements and corrosion cavities the rocks contain index fossils of late oxfordian early kimmeridgian late tithonian jurassic and latest berriasian early valanginian cretaceous age the fossil fauna is species rich and dominated by molluscs with subordinate brachiopods echinoderms foraminifera serpulids and ostracods most of the species including two chemosymbiotic bivalve species likely belong to the background fauna only a species of a hokkaidoconchid gastropod and a possible abyssochrysoid gastropod can be interpreted as restricted to the seep environment other seep faunas with similar taxonomic structure are suggestive of rather shallow water settings but in case of novaya zemlya seep faunas such structure might result also from high northern latitude

evolution of the northwestern iblean mountains sicily uplift plicocene pleistocene sea level changes paleoenvironment and volcanism the late miocene to pleistocene evolution of the northwestern iblean plateau sicily is marked by a complex interplay of subaerial and submarine volcanism subsidence and uplift eustatic sea level changes and shallow water carbonate and clay sedimentation volcanic activity occurred in distinct phases differing drastically in volume chemical composition eruptive and depositional sites and eruptive mechanisms six of the newly defined formations in the northwestern iblean plateau are either entirely volcanic or contain significant amounts of volcanics the eastern part of a shallow marine basin was filled completely by late pliocene tholeiitic lava flows militello formation that had advanced subaerially from the south southeast lava deltas advanced southwestward on top of earlier pillow breccia debris flow deposits intertongued with soft trubi marls and chalks true submarine eruptions monte caliella formation simultaneously produced densely packed pillow piles up to 250 m thick inferred water depths based on volcanologic and paleoecologic criteria of interbedded and overlying calcarenites agree well

predominance of archaea derived hydrocarbons in an early triassic microbialite abstract we investigated the distribution of lipids in lower triassic sedimentary rocks 252 247 myr from south china including a shallow water microbialite in the uppermost section of the outcrop archaeal derived hydrocarbons were the major constituents of the microbialite from the latest early triassic among these we detected i abundant c 40 acyclic and monocyclic biphytanes possibly derived from glycerol dialkyl glycerol tetraether lipids and their degradation products c 30 39 pseudohomologues and ii a c 25 head to tail linked regular isoprenoid hydrocarbon possibly derived from dialkyl glycerol diether lipids dgds and its degradation products c 21 24 pseudohomologues and abundant pristane and phytane through combination of compound specific stable carbon isotope analysis of isoprenoid hydrocarbons which had average 13 c values of 35 to 30 and their molecular distribution it was not possible to unambiguously define the archaeal source for the biphytanes in the microbialite the 13 c values for pristane and phytane were similar to those for head to tail linked c 21 25 isoprenoids potential source organisms for these compounds were halophilic archaea except for methane seep microbialites no other ancient or recent phototrophic microbialites have been reported to contain predominantly archaeal isoprenoid hydrocarbons our findings suggest the presence of a new type of microbialite

changing redox conditions at cold seeps as revealed by authigenic carbonates from alaminos canyon northern gulf of mexico anaerobic oxidation of methane in anoxic sediments at cold seeps often leads to formation of authigenic carbonates close to the seafloor along continental margins recent work however indicated that the redox conditions in sediments may vary to some degree during seepage activity in order to shed new light on the extent of this variability authigenic carbonates from alaminos canyon lease block 645 of the northern gulf of mexico have been characterized by means of inorganic and organic geochemistry the carbonates were collected from seep deposits representing various seafloor morphologies including extensive pavements mounds fractured carbonate slabs surrounded by dense bivalve shells and vestimentiferan tubeworm colonies the deposits almost entirely consist of aragonite the 18o values of aragonite vary from 2 6 to 5 8 v pdb suggesting precipitation in slight disequilibrium with the surrounding pore fluids the 13c values of aragonite between 33 9 and 20 4 v pdb agree with variable amounts of carbonate derived from oxidation of thermogenic methane and crude oil methane was primarily oxidized in an anaerobic process as revealed by the presence of 13c depleted molecular fossils of methane oxidizing archaea 13c values as negative as 118 and sulfate reducing bacteria 13c values as negative as 97 the syntrophic partners in the anaerobic oxidation of methane the observed inventories of molecular fossils in the authigenic carbonates mirror those of known consortia of anaerobic methane oxidizing archaea anme and sulfate reducing bacteria namely the anme 2 desulfosarcina desulfococcus dss and anme 3 desulfobulbus dbb consortia in contrast the same carbonates exhibit shale normalized rare earth elements patterns that all display real negative ce anomalies ce ce 0 78 suggesting that at least temporarily oxic conditions prevailed the episodic occurrence of oxic conditions is confirmed by the presence of molecular fossils of aerobic methanotrophic bacteria including 4 methylcholesta 8 14 24 dien 3 ol and two bacteriohopanepolyols aminotetrol and aminotriol the 13c values of the biomarkers of aerobic methanotrophs are as negative as 58 and are consequently less 13c depleted than the molecular fossils of the prokaryotes performing anaerobic oxidation of methane a pattern in accord with culture experiments overall our results suggest that redox conditions at cold seeps are variable this variability probably reflects changes in seepage flux the combination of an inorganic and an organic geochemical approach used here is promising to better assess the variability and diversity of past fluid and gas expulsion at seeps

emplacement of lobate sheet flows with hyaloclastites onto soft sediment the erquy neoproterozoic lava pile armorican massif france abstract the neoproterozoic volcano sedimentary succession of the heussaye headland erquy belongs to the cadomian block located in the north east of the armorican massif france the volcanism dated at approximately 608 7 ma zircon u pb data occurred in a back arc basin this site exhibits a noteworthy verticalized pile of moderately metamorphosed greenschist facies basaltic andesite flows of arc back arc tholeiite affinity alternating with metasedimentary layers sandstones and siltstones a large range of volcanic facies characteristic of an underwater soft substrate environment can be continuously studied for over than 200 m parallel to the flow edges they include pillow lavas lava lobes fluidal peperites and sediment matrix hyaloclastites the presence of parallel lava lobes in a sector where one lava flow is capped by a variably thick hyaloclastite carapace together with the occurrence of asymmetric turbiditic folds in interbedded metasedimentary layers suggests the existence of an easterly facing gentle paleoslope the sudden thinning of this hyaloclastite carapace in two spots located approximately 60 m from each other is attributed to the synvolcanic activity of two conjugate normal paleofaults this hypothesis is supported by the observation of a hyaloclastite accumulation in one of the two spots close to a strike slip fault which may have been extensional at the time of the volcanism water entered the lava flow along the faults resulting in an interstitial network of hyaloclastites by quench fragmentation in the upper part of the hanging wall block all these observations are consistent with a model of lava emplacement along a subaqueous slope resulting from synmagmatic extensional faulting in a marginal basin context

time integrated variation of sources of fluids and seepage dynamics archived in authigenic carbonates from gulf of mexico gas hydrate seafloor observatory article i nfo authigenic carbonate rocks recovered from the gulf of mexico gas hydrate seafloor observatory in mississippi canyon block 118 mc118 at approximately 900 m water depth were studied using mineralogical bulk geochemical and lipid biomarker analyses carbonate rocks occurred as fractured blocks and nodular masses incorporated in carbonate breccias the carbonates were comprised mainly of high mg calcite and aragonite the stable carbon isotope composition

a new straight chain hydrocarbon biomarker associated with anaerobic methane cycling abstract 13c depleted e and z n tricos 10 enes are prominent biomarkers in an anaerobic microbial mat at black sea methane seeps these n alkenes co occur with archaeal irregular c25 isoprenoid hydrocarbons namely 2 6 10 15 19 pentamethylicosane pmi and enes pmi low 13c values 73 and 77 for n tricosenes and pmi imply the anabolism of methane carbon by their source biota the n tricosenes apparently originate from microorganisms closely associated with if not identical to isoprenoid producing methane metabolizing archaea methane seep deposits of tertiary to jurassic ages showed the absence of n tricosenes but 13c depleted n tricosane 13c as low as 87 a plausible diagenetic product was observed in enhanced concentrations in 7 out of 9 samples studied it is proposed that a preference of n tricosane over the enveloping n alkanes may provide a specific hydrocarbon fingerprint for the anaerobic cycling of methane in ancient settings

patterns of carbonate authigenesis at the kouilou pockmarks on the congo deep sea fan abstract different types of seep carbonates were recovered from the kouilou pockmarks on the congo deep sea fan in approximately 3100 m water depth the carbonate aggregates are represented by pyritiferous nodules crusts and slabs tubes and filled molds the latter are interpreted to represent casts of former burrows of bivalves and holothurians the nodules consisting of high mg calcite apparently formed deeper within the sediments than the predominantly aragonitic crusts and slabs nodule formation was caused by anaerobic oxidation of methane dominantly involving archaea of the phylogenetic anme 1 group whereas aragonitic crusts resulted from the activity of archaea of the anme 2 cluster evidence for this correlation is based on the distribution of specific biomarkers in the two types of carbonate aggregates showing higher hydroxyarchaeol to archaeol ratios in the crusts as opposed to nodules formation of crusts closer to the seafloor than nodules is indicated by higher carbonate contents of crusts probably reflecting higher porosities of the host sediment during carbonate formation this finding is supported by lower 18 o values of crusts agreeing with precipitation from pore waters similar in composition to seawater the aragonitic mineralogy of the crusts is also in accord with precipitation from sulfate rich pore waters similar to seawater moreover the interpretation regarding the relative depth of formation of crusts and nodules agrees with the commonly observed pattern that anme 1 archaea tend to occur deeper in the sediment than members of the anme 2 group methane represents the predominant carbon source of all carbonates 13 c values as low as 58 9 v pdb and the encrusted archaeal biomarkers 13 c values as low as 140 v pdb oxygen isotope values of some nodular carbonates ranging from 3 9 to 5 1 v pdb are too high for precipitation in equilibrium with seawater probably reflecting the destabilization of gas hydrates which are particularly abundant at the kouilou pockmarks

cryptic biostalactites in a submerged karst cave of the belize barrier reef revisited pendant bioconstructions cemented by microbial micrite abstract microbial carbonates are important components of postglacial tropical coral reef frameworks curious calcium carbonate protrusions in a submarine karst cave in the belize barrier reef platform were initially interpreted as being largely the product of physicochemical precipitation around a meshwork of serpulid tubes new petrographical mineralogical geochronological and inorganic and organic geochemical data suggest that sulfate reducing bacteria played a substantial role in carbonate formation just as in cryptic settings of other modern tropical coralgal reefs the bacterial involvement in carbonate authigenesis is indicated by the content and isotopic composition of carbonate associated sulfate the presence of non isoprenoidal sn 1 mono o alkyl glycerol monoethers mages and terminally branched fatty acids and the observation that the majority of molecular fossils assigned to sulfate reducing bacteria are tightly associated with the carbonate mineral lattice the carbonate protrusions that were formerly named pseudostalactites are termed biostalactites here to underline the significance of biological activity during carbonate formation the belize biostalactites are composed of four carbonate phases including serpulid tubes lithified sediment and microbial carbonate as well as unconsolidated sediment usually found in macroborings of bivalve molluscs lithified sediment and microbial carbonate are fine grained with clotted mottled and peloidal textures while serpulid tubes are aragonitic lithified sediment and microbial carbonates are mixtures of high magnesium calcite and aragonite magnesium calcite content increases with increasing consolidation lithified sediment and microbial carbonate are interpreted as fine biodetrital sediment that was subsequently cemented by authigenic micrite scalenohedral high magnesium calcite and acicular aragonite cements played a subordinate role in cementation carbon and oxygen stable isotope ratios of lithified sediment and microbial carbonate exhibit similar ranges as modern reefal microbialites our study exemplifies that heterotrophic bacteria can be a crucial agent that contributes to the formation of carbonate build ups by cementing skeletal frameworks in cryptic environments

lava seawater interactions at shallow water submarine lava flows hydrothermal plumes associated with nearshore lava flows from kilauea volcano hawaii were studied on five occasions during 1989 1990 to address the current lack of data on direct lava seawater interactions the following enrichments were found in the sea surface hydrothermal plumes above the active underwater lava flows h2 15 000x ambient seawater concentrations mn 250x and si 20x water temperatures reached 46 c lower concentrations and temperatures were observed in the plumes with increasing distance from shore with h2 si and mn concentrations linearly related to seawater temperature unlike deep sea spreading center hydrothermal plumes no ch4 enrichment was observed the elevated h2 is likely to be from water rock reactions rather than from the release of magmatic gas the plume mass heat ratios presented here suggest that submarine flood basalts although aerially large should be relatively small immediate contributors to oceanic geochemical cycles compared to hydrothermal circulation through the crust

authigenic carbonates at cold seeps in the marmara sea turkey a lipid biomarker and stable carbon and oxygen isotope investigation abstract cold seeps along the north anatolian fault in the marmara sea turkey have been recently explored during international expeditions through submersible surveys seafloor mapping and extensive sampling of sediments biota carbonates and pore waters in this study we investigated the main mineralogy carbon and oxygen isotopic compositions and lipid biomarkers in authigenic carbonates retrieved from active seepage areas in the marmara sea abundant microbial lipid biomarkers with light 13 c values as low as 113 as well as light 13 c caco 3 values of bulk carbonate 34 to 21 provided evidence that anaerobic oxidation of methane aom mediated by methanotrophic archaea anme and their bacterial partners is the major process leading to sequestration of methane derived carbon diagnostic lipid distributions indicated that anme 2 archaea and associated sulphate reducing bacteria srb as the prevalent aom mediating microbes diverse non isoprenoid dialkyl glycerol ethers dages including tentatively identified novel compounds were identified with similar 13 c values as lipid biomarkers of srb 105 to 68 though dages are often assigned to srb other unknown bacteria closely involved in aom are likely as source organisms as well despite dominant aom related lipid biomarker patterns the stable carbon isotopic composition of bulk carbonates in two samples from south cinarcik basin and central high in combination with higher hydrocarbon signatures and environmental parameters suggested that oxidation of non methane hydrocarbons including oil may be a contributor to the dissolved inorganic carbon pool and may also be involved in carbonate authigenesis at hydrocarbon seepage settings as previously proposed in the gulf of mexico

presence of sulfate does not inhibit low temperature dolomite precipitation abstract the hypothesis that sulfate inhibits dolomite formation evolved from geochemical studies of porewaters from deep sea sedimentary sequences and has been tested with hydrothermal experiments we examined the sulfate inhibition factor using aerobic culture experiments with virgibacillus marismortui and halomonas meridiana two moderately halophilic aerobic bacteria which metabolize independent of sulfate concentration the culture experiments were conducted at 25 and 35 c using variable so42 concentrations 0 14 28 and 56 mm and demonstrate that halophilic aerobic bacteria mediate direct precipitation of dolomite with or without so42 in the culture media which simulate dolomite occurrences commonly found under the earth s surface conditions hence we report that the presence of sulfate does not inhibit dolomite precipitation further we hypothesize that if sedimentary dolomite is a direct precipitate as in our low temperature culture experiments the kinetic factors involved are likely to be quite different from those governing a dolomite replacement reaction such as in hydrothermal experiments consequently the occurrence and presumably growth of dolomite in so42 rich aerobic cultures may shed new light on the long standing dolomite problem

englacial vs lacustrine origin of volcanic table mountains evidence from iceland detailed facies analysis of hyaloclastites and associated lavas from eight table mountains and similar hyaloclastite volcanoes in the icelandic rift zone contradict a rapid and continuous monogenetic entirely subglacial evolution of most volcanoes studied the majority of the exposed hyaloclastite deposits formed in large stable lakes as indicated by widespread up to 300 m thick continuous sections of deep water shallow water and emergent facies salient features include extensively layered or bedded successions comprising mainly debris flow deposits turbidites base surge and fallout deposits consisting of texturally and compositionally variable slightly altered hyaloclastites as well as sheet and pillow lavas in contrast chaotic assemblages of coarser grained more poorly sorted and more strongly palagonitized hyaloclastite tuffs and breccias as well as scoria and lava are interpreted to have formed under sub or englacial conditions in small chimney like ice cavities or ice bound lakes irregularly shaped and erratically arranged hyaloclastite bodies produced at variable water levels appear to have resulted mainly from rapid changes of the eruptive environment due to repeated build up and drainage of ice bound lakes as well as the restricted space between the ice walls we distinguish a deep water facies formed during high water levels of the lake a hydroclastic shallow water and emergent facies leakage of the lake or growth of the volcano above the water surface our model implies the temporary existence of large stable lakes in iceland probably formed by climatically induced ice melting the highly complex edifices of many table mountains and similar volcanoes were constructed during several eruptive periods in changing environments characterized by contrasting volcanic and sedimentary processes

authigenic carbonate formation and its impact on the biomarker inventory at hydrocarbon seeps a case study from the holocene black sea and the plio pleistocene northern apennines italy carbonates are widespread at methane and petroleum seeps and are often precipitated as consequence of an alkalinity increase due to the anaerobic oxidation of methane aom or less often reported of higher hydrocarbons these carbonates are taphonomic windows into earth s history because they excellently protect the in situ formed microbial signatures e g lipid biomarkers from diagenetic destruction a complication for paleoreconstructions however is that seep carbonates also encapsulate variable amounts of allochthonous organic matter sometimes even completely obscuring authigenic microbial signatures seep carbonates from the holocene black sea the pleistocene enza river and the pliocene san lorenzo both northern apennines italy provide hints to better understand i the importance of processes other than aom for the formation of seep carbonates and ii the controls of allochthonous and autochthonous contribution of biomarkers to organic matter in seep carbonates biomarker distributions in different parts of a black sea carbonate clearly demonstrate that high allochthonous organic matter is entrapped if aom carbonates are formed intrasedimentary particularly if methane supply is relatively low and external organic matter input high high allochthonous contributions were also found in the biomarker inventory of ancient seep carbonates from the italian northern apennines enza river and san lorenzo pointing at their precipitation within the sediment specific and complex conditions were indicated from our data for the enza river location carbonate facies and particularly biomarker compositions with abundant signatures of sulfate reducing bacteria suggest that sulfate reduction using alkaline and eventually sulfate and higher hydrocarbon enriched fluids triggered the growth of these seep carbonates our and other data suggest that this process has to be more considered if interpreting seep settings particularly where microbial processes rely on rising fluids from deep petroleum reservoirs

marine cold seeps and their manifestations geological control biogeochemical criteria and environmental conditions characteristics of cold seeps at different geologic settings are the subject of this review primarily based on results of the research consortium sfb 574 criteria are drawn from examples on the erosive convergent margin off costa rica the accretionary margin off chile supplemented by examples from the transform margin of the golf of cadiz and the convergent hikurangi margin off new zealand others are from well studied passive margins of the black sea the golf of mexico the eastern mediterranean sea and the south china sea seeps at all settings transport water and dissolved compounds to the ocean through the seafloor by different forcing mechanism and from different depths of the submerged geosphere 10s of meters to 10s of km the compounds sustain oasis type ecosystems by providing bioactive reductants sulfide methane and hydrogen hereby the interaction between fluid composition flux rates and biota results in a diagnostic hydrocarbon metazoan microbe carbonate association currently well over 100 active sites are known the single most important reaction is microbially mediated anaerobic oxidation of methane with secondary reactions involving s biogeochemistry and carbonate mineral precipitation seep fluids and their seafloor manifestations provide clues as to source depth fluid sediment rock interaction during ascent lifetime and cyclicity of seepage events but less so on the magnitude of return flow at erosive margins cl depleted and b enriched fluids from clay dehydration provide criteria for source depth and temperature the upward material flow generates mud volcanoes at the seafloor above the projected location of dehydration at depth at accretionary margins fluids are derived from more shallow depths by compaction of sediments as they ride on the incoming oceanic plate they are emitted through thrust faults at highly sedimented margins organic rich and evaporite containing strata when present determine the final fluid composition by emitting characteristically gas hydrate derived methane brine associated non methane hydrocarbons or leached elements and their isotopes li 7li b ba from host sediments smectite illite transformation and associated cl depletion from release of interlayer water is a pervasive process at these margins rare earth element pattern in conjunction with redox sensitive metals retained in seep carbonates indicate whether or not they precipitated in contact with oxic bottom water or suboxic fluids clear environmental characterization though currently remains inconclusive more deeply sourced fluids as in transform margins may be characterized by their 87sr 86sr ratios from interaction with oceanic crustal rocks below quantification of flow and reliable estimates of total volatile output from fore arcs remain a challenge to seep research as does understanding the role of geologically derived methane in the global methane cycle

solidification and morphology of submarine lavas a dependence on extrusion rate the results of recent laboratory experiments with wax extruded beneath relatively cold water may be extrapolated to predict the surface morphology of submarine lavas as a function of the extrusion rate and melt viscosity the experiments with solidifying wax indicated that the surface morphology was controlled by a single parameter the ratio of the time taken for the surface to solidify and a time scale for lateral flow for submarine basalts a solution of the cooling problem which is dominated by conduction in the lava but convective heat transfer in the water and estimates of lava viscosities place this parameter within the empirically determined pillowing regime over a wide range of extrusion rates this result is consistent with the observation that pillow basalts are the most common products of submarine eruptions smoother surfaces corresponding to the various types of submarine sheet flows are predicted for sufficiently rapid extrusions of basaltic magma still higher eruption rates in regions of low topographic relief may produce submarine lava lakes minimum emplacement times can be calculated for submarine volcanic constructs of a single lava flow type

ice volcano interaction of the 1996 gjalp subglacial eruption vatnajokull iceland volcanic eruptions under glaciers can cause dangerous floods and lahars1 2 3 and create hyaloclastite fragmented glassy rock mountains4 5 6 7 8 but processes such as the rate of heat transfer between ice and magma edifice formation and the response of the surrounding glacier are poorly understood because of the lack of data here we present observations from the fissure eruption at vatnajokull ice cap iceland in october 1996 in the 13 days of the eruption 3 km3 of ice were melted and the erupted magma fragmented into glass forming a hyaloclastite ridge 6 7 km long and 200 300 m high under 500 750 m of ice meltwater of temperatures of 15 20 c flowed along a narrow channel at the glacier bed into the grimsvotn subglacial lake for five weeks before draining in a sudden flood or jokulhlaup subsidence and crevassing of the ice cap occurred over the eruptive fissure and the meltwater path whereas elsewhere the glacier surface remained intact suggesting that subglacial eruptions do not trigger widespread basal sliding in warm based glaciers

organic matter preservation in the carbonate matrix of a recent microbial mat is there a mat seal effect abstract phototrophic mats microbial mats with a phototrophic top layer are complex systems in terms of microbial diversity biogeochemical cycles and organic matter om turnover it has been proposed that these mats were a predominant life form in proterozoic shallow water settings prior to the emergence of bioturbating organisms in the ediacaran cambrian transition for most of the precambrian microbial mats were not only quantitative important carbon fixing systems but also influenced the transfer and transformation of om before it entered the geosphere the profound alteration of compound inventories during transit through microbial mats implying substantial consequences for om preservation in the proterozoic was recently proposed as a mat seal effect pawlowska et al 2012 geology 41 103 106 to obtain a better understanding of the early diagenetic fate of primary produced om in microbial mats we studied a recent calcifying mat from a hypersaline lake in kiritimati which showed in the deeper mat layers a maximum 14 c carbonate age of 1500 years we particularly focused on om entrapped in the carbonate matrix because of the better potential of such biomineral encapsulated om to reach the geosphere before degradation and remineralization our data indicate that selective preservation is important in phototrophic mats while a diagenetic transformation of lipid fatty acids fas was evident their fatty acyl derived hydrocarbon moieties were not introduced into protokerogen which was instead mainly comprised of cyanobacterial and or algal biomacromolecules our data support the proposed major impact of the mat seal effect on om turnover and preservation i e the suppression of biosignatures derived from the upper mat layers while signals of heterotrophic microbes thriving in deeper mat layers become preferentially preserved e g high hopane sterane ratios this mechanism may have broad consequences for the interpretation of biomarkers from proterozoic shelf environments because biosignatures of phototrophic mat dwellers as well as planktonic signals may have become heavily biased by the production and turnover of om in microbial mat systems

a late miocene methane seep deposit bearing methane trapping silica minerals at joetsu central japan abstract the modern japan sea is characterized by active methane seeps associated with gas hydrates but their ancient counterparts are not fully understood this study describes a newly discovered methane seep carbonate block the nakanomata seep deposit from the upper miocene nodani formation in joetsu city central japan the age of this deposit is constrained to 7 5 6 5 ma based on its fossil diatom assemblage the deposit contains molluscan fossils typical of methane seeps including vesicomyid and bathymodiolin bivalves and provannid gastropods and it retains an almost entirely aragonitic mineralogy despite its miocene age it is composed of clotted microcrystalline aragonite containing nodules and intraclasts and is crosscut by vein like networks of voids and cavities rimmed with acicular aragonite the 13c values of the carbonate phases are as low as 41 1 and the presence of lipid biomarkers pentamethylicosane and crocetane suggests that the deposit originated from the anaerobic oxidation of methane it is suggested that an initially diffuse methane seepage formed the micritic nodules followed by a more rapid and intense methane seepage that led to the development of abundant voids in the sediment finally the sediment was cemented by microcrystalline aragonite and void lining acicular aragonite the seep deposit also contains peculiar globular silica minerals and authigenic quartz during their precipitation these globular silica minerals may have trapped methane gas bubbles and the minerals may be pseudomorphs after silica clathrate sufficient increase in ph and supersaturation of silica which led to the dissolution and subsequent precipitation of these silica minerals could have resulted from the degassing of carbon dioxide promoted by an effective supply of methane and its supersaturation thus forming gas bubbles

evidence for archaeal methanogenesis within veins at the onshore serpentinite hosted chimaera seeps turkey abstract serpentinite hosted ecosystems are potential sites where life may first have evolved on earth serpentinization reactions produce strongly reducing and highly alkaline fluids that are typified by high concentrations of molecular hydrogen h2 and methane ch4 which can be used as an energy source by chemosynthetic life low temperature serpentinization at slow spreading mid ocean ridges provides an ideal environment for rich microbial communities similar environments have also been discovered on land where present day low temperature serpentinization occurs during the circulation of groundwater through exposed ophiolites triggering the production of ch4 and h2 as well as the precipitation of secondary carbonate minerals the rock samples analyzed here are from the chimaera seeps in turkey representing serpentinized peridotites that are cross cut by veins composed of brucite and hydromagnesite hydromagnesite features a mean 13c value of 19 8 caused by kinetic isotope fractionation during air groundwater exchange of co2 followed by co2 hydroxylation to bicarbonate within the groundwater geochemical modeling revealed that mixing of mg and ca rich groundwaters is required for hydromagnesite formation at the expense of brucite within the carbonate hydroxide veins the lipid biomarkers pentamethylicosane pmi and squalane with 13c values of 10 and 14 respectively and unsaturated derivatives thereof were identified archaeol sn2 hydroxyarchaeol and sn3 hydroxyarchaeol are other prominent archaeal biomarkers in the veins also revealing high 13c values from 6 to 13 these isotope patterns combined with the absence of crocetane a biomarker for methanotrophic archaea reveal that the microbial communities of the chimaera seeps performed methanogenesis from a co2 limited pool rather than methanotrophy moreover bacterial dialkyl glycerol diethers dages with unusually high 13c values 9 to 2 and minor monoalkyl glycerol monoethers mages were identified suggesting that bacterial sulfate reduction is also active at the chimaera site this study reveals that archaeal methanogenesis and bacterial sulfate reduction may be prominent at onshore peridotite hosted sites and that biogenic ch4 may contribute to abiotic ch4 emissions from terrestrial seeps

non hawaiian lithostratigraphy of louisville seamounts and the formation of high latitude oceanic islands and guyots guyots are large seamounts with a flat summit that is generally believed to form due to constructional biogenic and or erosional processes during the formation of volcanic islands however despite their large abundance in the oceans there are still very few direct constraints on the nature and formation of guyots in particular those formed at high latitude that lack a thick cap of shallow marine carbonate rocks it is largely accepted based on geophysical constraints and surficial observations sampling that the summit platform of these guyots is shaped by wave abrasion during post volcanic subsidence of volcanic islands here we provide novel constraints on this hypothesis and the summit geology of guyots with a lithostratigraphic analysis of cores from three louisville seamounts south pacific collected during expedition 330 of the integrated ocean drilling program iodp thirteen lithofacies of sedimentary and volcanic deposits are described which include facies not previously recognized on the top of guyots and offer a new insight into the formation of high latitude oceanic islands on a fast moving plate our results reveal that the lithostratigraphy of louisville seamounts preserves a very consistent record of the formation and drowning of volcanic islands with from bottom to top i volcaniclastic sequences with abundant lava fed delta deposits ii submarine to subaerial shield lava flows iii post volcanic shallow to deeper marine sedimentary rocks lacking thick reef deposits iv post erosional rejuvenated volcanic rocks and v pelagic sediments recognition of erosional boundaries between subaerial lava flows and shallow marine sedimentary rocks provides novel support for post volcanic wave planation of guyots however the summit geology of louisville seamounts is dissimilar to that of high latitude hawaiian emperor guyots that have emplaced in a similar tectonic and environmental setting and that include thicker lava stacks with apparently little lava fed delta deposits to explain observed lithostratigraphic discrepancy we propose that louisville seamounts represent a distinct type of intraplate ocean volcano characterized by formation of a smaller island with a central shield volcano surrounded by extended shallow marine shelves formed by lava fed deltas in this interpretation the summit platform of louisville type guyots results from early syn volcanic subaerial to shallow marine constructional volcanic processes and marine erosion enhanced by later post volcanic wave planation this contrasts with larger hawaiian edifices that are capped by thicker shield volcanoes and that develop an extended wave planation surface during post volcanic subsidence in the absence of efficient coral growth the difference between hawaiian and louisville type volcanic islands and guyots can be explained by contrasted dynamic disequilibrium between magmatic growth erosion and subsidence during the island building stage unlike hawaiian type volcanoes louisville seamounts are characterized by alkaline magmatism that extends from the late seamount to island stages this supports more limited magmatic growth during the formation of louisville islands and we hypothesize that this promotes the formation of ephemeral shallow marine platforms and extended lava fed deltas hawaiian type volcanoes and guyots are unusually large in the population of intraplate ocean volcanoes louisville type guyots as defined in this study could therefore represent a very common but yet poorly documented mode of oceanic island formation in the pacific ocean and other similar fast moving plate settings

methane seep brachiopod fauna within turbidites of the sinaia formation eastern carpathian mountains romania abstract this study elucidates the paleoecology and paleobiogeography of the early cretaceous brachiopod peregrinella known in museum collections from a few localities in romania supplemented with new material from a rediscovered locality first mentioned in the 1870s most peregrinella fossils are enclosed in mass waste deposits but at two sites authigenic limestones with assemblages of brachiopods preserved in life position have been recognized paleontological petrographic stable isotopic and organic geochemical investigations of these brachiopod bearing limestones from the upper sinaia formation eastern carpathian mountains romania confirm peregrinella as having lived at methane seeps in a siliciclastic dominated flysch basin the seeps developed on the slope of the external dacides basin the new collections of peregrinella indicate that shells derived from contemporaneous intrabasin methane seeps and were transported downslope by turbidity currents previous paleoecological models that consider peregrinella to be solely derived from transport downslope from shelf environments are questionable especially as peregrinella has never been recovered from typical shelf faunas in the instance documented here from the external dacides basin methane seep faunas with peregrinella are likely to be the origin of such allochthonous faunas the sinaia formation was deposited in a deep water marine basin derived from an intracontinental rift that developed during late jurassic early cretaceous extension the fractured and faulted basin margin provided the backdrop for the development of the methane seepage and the associated fauna foraminifera from background sediments in the sequence with turbidites confirm a late hauterivian to early barremian age for peregrinella within the sinaia formation this is significant because it indicates that peregrinella ranged through into the barremian whereas it has typically been considered to range only as high as the hauterivian

physical controls and resulting morphological forms of quaternary ice contact volcanoes in western canada abstract volcanism in association with large quantities of ice manifests itself in a variety of morphological forms developed under differing physical conditions these physical conditions include the location amount thickness and type of confining ice the location and quantity of trapped water and the surrounding topography ice in the form of thick continental ice sheets thinner alpine glaciers or even perennial accumulations of snow can influence the resulting morphological form of the volcano the chemical composition of the erupting magma effusion rate and total erupted volume will also affect the shape of the resulting edifice quaternary volcanoes influenced by many of these factors are found in western canada the morphological forms range from tuyas to subglacial mounds to stratovolcanoes this paper provides a review of ice contact volcanism and volcanic products formed in these environments using canadian examples for illustration

cooling process recorded in subglacially erupted rhyolite glasses rapid quenching thermal buffering and the formation of meltwater the thermal histories of two subglacial rhyolite glasses from torfajokull complex of south central iceland have been determined from changes in the relaxation of enthalpy in the calorimetric glass transition interval heat capacity measurements of bulk glass samples from rau ufossafjoll sample number js 1 1 and blahnukur sample number js 2 1 by differential scanning calorimetry show marked differences in the temperature of the onset of glass transition tg on reheating the average tg is 750 k for js 1 1 whereas it is 850 k for js 2 1 these differences in the onset of tg are related to quench rate through considerations of the activation energy and timescales for structural relaxation modeled using the kohlrausch williams watt function multiple glass samples from the two torfajokull locations recover different average values and distributions of a fictive temperature t f which we interpret in terms of differences in the thermal histories of the glasses in both glass samples the range of fictive temperatures and by implication apparent cooling rates is lower than those estimated for a glass rapidly quenched by contact with cold glacial melt water and requires that the glass was annealed at temperatures in the glass transition interval associated with relaxation times of the order of 1000 10 000 s the complex cooling histories of the torfajokull samples show that the products of subglacial eruptions may be held at elevated temperatures for several hours and as a result may drive vigorous convection in the ice bound vaults above erupting rhyolite deposits

the paleoproterozoic fossil record implications for the evolution of the biosphere during earth s middle age abstract the paleoproterozoic 2 5 1 6 ga era is a decisive time in earth and life history the paleobiological record microfossils stromatolites biomarkers and isotopes illustrates the biosphere evolution during a time of transitional oceanic and atmosphere chemistries benthic microfossil assemblages are recorded in a variety of oxygenated sulfidic and ferruginous environments representative of the spatial heterogeneities and temporal variations characteristic of this era the microfossil assemblages include iron metabolizing and or iron tolerant prokaryotes sulfur metabolizing prokaryotes cyanobacteria other undetermined prokaryotes and eukaryotes the undetermined microfossils represent a majority of the assemblages and thus raise a challenge to determine the nature and role of microorganisms in these changing environments despite the early evolution of the eukaryotic cellular toolkit early eukaryotic crown group diversification may have been restrained in the paleoproterozoic by ocean chemistry conditions but it increased during the late mesoproterozoic early neoproterozoic despite the continuation of similar conditions through the miscalled boring billion then amplified significantly but perhaps within lower taxonomic levels with the demise of euxinic conditions and increase in ecological complexity the emerging picture is one of a changing and more complex biosphere in which the three domains of life archaea bacteria and eukarya were diversifying in various ecological niches marked by the diversification of identified microfossils stromatolites increasing abundance of preserved biomarkers and appearance of macroscopic problematic fossils or trace fossils

the formation of circular littoral cones from tube fed pāhoehoe mauna loa hawai i pyroclastic cones along the southwest coast of mauna loa volcano hawai i have a common structure a an early formed circular outer rim 200 400 m in diameter composed mostly of scoria and lapilli and b one or more later formed inner rims composed almost exclusively of dense spatter the spatter activity locally fed short lava flows that ponded within the outer rims based on various lines of evidence these cones are littoral in origin relationships between the cones and associated flows the degassed nature of the pyroclasts and although not unequivocal the position of the cones relative to known eruptive vent locations on mauna loa additional support for the littoral interpretation comes from their similarity to smaller littoral cones that have been observed forming during the ongoing kilauea eruption the structure of these mauna loa cones however contrasts with that of standard hawaiian littoral cones in that there is or once was a complete circle of pyroclastic deposits furthermore they are large even though associated with tubefed p hoehoe flows instead of a the following origin is proposed an initial flow of tube fed p hoehoe into the ocean built a lava delta with a base of hyaloclastite collapse of an inland portion of the active tube into the underlying wet hyaloclastites or a water filled void allowed sufficient mixing of water and liquid lava to generate strong explosions these explosions broke through the top of the flow and built up the outer scoria lapilli rims on the solid carapace of the lava delta eventually the supply of water diminished the explosions declined in intensity to spattering and the initial rim was filled with spatter and lava

neogene glacigenic debris flows on james ross island northern antarctic peninsula and their implications for regional climate history detailed sedimentological and microtextural analyses of newly discovered late neogene diamictites and other coarse grained facies mostly sandwiched between hyaloclastite of the james ross island volcanic group and cretaceous sandstone and mudstone indicate deposition mainly by glacigenic debris flows the deposits on james ross island northern antarctic peninsula constrain the depositional setting ice bed dynamics and regional palaeoclimate the sequences on james ross island vary in age but are mainly late miocene and pliocene unlike neogene sedimentary sequences elsewhere in antarctica those on james ross island are unusually well dated by a combination of 40ar 39ar and 87sr 86sr analyses on fresh interbedded lavas and pristine bivalve molluscs respectively the sr isotopic ages of the debris flows cluster around 4 74 4 89 5 44 5 78 and 6 31 ma and probably date relatively warm periods in the northern antarctic peninsula region when the bivalves lived under ice poor or seasonally ice free conditions the bivalves are often remarkably well preserved lack adhering lithified sediment and in at least two locations are large mainly unfragmented and sometimes articulated suggesting that they were alive immediately prior to their incorporation in subaqueous debris flows at the margins of an advancing glacier these fossiliferous glacigenic debris flows signify episodes of ice expansion during relatively warm periods or interglacials of the late miocene and pliocene the james ross island glacigenic sedimentary successions attain thicknesses of up to 150 m and extend over 4 km laterally the high volume of glacigenic sediment delivery implicit in the james ross island successions indicates that a series of dynamic ice fronts crossed the region during the late miocene and pliocene epochs associated evidence in the form of clast abrasion including striations and faceting and bedrock erosion is indicative of basal sliding and subglacial sediment deformation active at the ice bed interface and wet based temperate or polythermal regimes prior to remobilisation the evidence further suggests two local ice caps on james ross island during the warm periods as well as ice overriding by the antarctic peninsula ice sheet from the west and northwest

submarine geology of the hilina slump and morpho structural evolution of kilauea volcano hawaii abstract marine geophysical data including sea beam bathymetry hawaii mr1 sidescan and seismic reflection profiles along with recent robot submersible observations and samples were acquired over the offshore continuation of the mobile kilauea volcano south flank this slope comprises the three active hot spot volcanoes mauna loa kilauea and loihi seamount and is the locus of the hawaiian hot spot the south flank is the site of frequent low intensity seismicity as well as episodic large magnitude earthquakes its sub aerial portion creeps seaward at a rate of approximately 10 cm year the hilina slump is the only large submarine landslide in the hawaiian archipelago thought to be active and this study is one of the first to more highly resolve submarine slide features there the slump is classified into four distinct zones from nearshore to the island s base estimates of size based on these data indicate a slumped area of 2100 km 2 and a volume of 10 000 12 000 km 3 equivalent to about 10 of the entire island edifice the overall picture gained from these data sets is one of mass wasting of the neovolcanic terrain as it builds upward and seaward though reinforcement by young and pre hawaii seamounts adjacent to the pedestal is apparent extensive lava delta deposits are formed by hyaloclastites and detritus from recent lava flows into the sea these deposits dominate the upper submarine slope offshore of kilauea with pillow breccia revealed at mid depths along the lower flanks massive outcrops of volcanically derived sedimentary rocks were found underlying kilauea thus necessitating a rethinking of previous models of volcanic island development the morphologic and structural evolutionary model for kilauea volcano and the hilina slump proposed here attempts to incorporate this revelation a hazard assessment for the hilina slump is presented where it is suggested that displacement of the south flank to date has been restrained by a still developing northeast lateral submarine boundary when it does fully mature the south flank may be more subject to land slips triggered by large long duration earthquakes and thus kilauea may undergo more frequent episodes of failure with increased displacements

tholeiitic alkalic transition at subglacial volcanoes tuya region british columbia canada ash mountain south tuya and tuya butte are three small basaltic volcanoes in the stikine volcanic belt of northern british columbia the volcanoes rise 700 500 and 400 m above their bases and are about 3 2 1 6 and 2 6 km3 in volume respectively they began eruptive activity under several hundred meters of overlying glacial ice or water in an ice impounded lake and undegassed pillow lava was erupted and forms the bases of all three later as the vents grew into shallow water explosive phreatomagmatic activity erupted partly degassed glassy tuffs finally when the volcano emerged through the surface of the ice or water or the water was drained degassed subaerial lava flows were erupted and were converted to assemblages of foreset bedded pillow breccia and pillow lava when subaerial flows crossed a shoreline and flowed into meltwater lakes the undegassed subglacial pillow base of ash mountain is overlain by partly degassed pillows and hyaloclastite tuff cut by dikes at south tuya the pillow base is overlain by hyaloclastite tuffs and lenses of pillow lava at tuya butte the pillow base is overlain by foreset bedded pillow lava pillow breccias and hyaloclastite tuffs which in turn are overlain by subaerial lava flows composing a small shield volcano the undegassed basal subglacial pillow lava of the three volcanoes contain 0 10 0 01 wt sulfur and 0 5 wt h2o the overlying partly degassed assemblages contain 0 06 0 02 sulfur and 0 2 h2o at ash mountain 0 07 0 01 sulfur at south tuya and 0 03 0 01 sulfur at tuya butte the differences in the degree of degassing can be related to the nature of eruption and quenching and the distance of flow of the subaerial lava when the volcanoes switched from subglacial to shallow water or subaerial eruptions as shown by change to more explosive activity and then to subaerial lava flows and by a marked reduction of sulfur in volcanic glass the magma shifted from tholeiitic to alkalic composition this transition occurs at each of the three volcanoes the tholeiitic and alkalic magmas cannot be related by shallow crystal fractionation and apparently originated by differing degrees of deep melting at a mantle source prior to eruption the tholeiitic melts overlay alkalic melts in shallow chambers underlying each of the volcanoes because of their lower density and were therefore the first to erupt under subglacial conditions as the volcano grew through the ice or ice impounded water the volcanic conduit vented to the atmosphere producing a partial depressurization of the conduit and the subsurface chamber this sudden reduction in confining pressure caused enhanced vesiculation of volatile saturated melts particularly of the more volatile rich alkalic melts causing them to rise to the top of the chamber and erupt

three dimensional lithofacies variations in hyaloclastite deposits analysis of the spatial lithofacies variability within lava fed delta formations in southern iceland has revealed complex three dimensional volcanic architectures in hyaloclastite deposits in non glacial settings two depositional environments are studied a lava entering a marine embayment stori nupur and b lava advancing into a body of water of the flanks of a surtseyan cone hjorleifshof i interaction between environmental factors such as shoreline geomorphology water depth wave energy levels the nature of the lava transport system lava supply rate all affect the resulting lava deltas creating complex lithofacies arrangements and stacking patterns recognised here are two types of hyaloclastite deltas one of syn sedimentary origin hjorleifshof i and one derived from primary fragmentation processes stori nupur syn sedimentary systems are dominated by destabilisation of the hyaloclastite pile leading to reworking downslope and share similarities to alluvial delta systems conversely primary fragmented systems are controlled by waxing and waning cycles in volcanic effusivity whereby the hyaloclastite unit recorded is not the product of one lava flow rather than one eruptive event

evolution of an englacial volcanic ridge pillow ridge tindar mount edziza volcanic complex ncvp british columbia canada abstract glaciovolcanic deposits are critical for documenting the presence and thickness of terrestrial ice sheets and for testing hypotheses about inferred terrestrial ice volumes based on the marine record deposits formed by the coincidence of volcanism and ice at the mount edziza volcanic complex mevc in northern british columbia canada preserve an important record for documenting local and possibly regional ice dynamics pillow ridge located at the northwestern end of the mevc formed by ice confined fissure fed eruptions it comprises predominantly pillow lavas and volcanic breccias of alkaline basalt composition with subordinate finer grained volcaniclastic deposits and dykes the ridge is presently 4 km long 1000 m in maximum width and 600 m high fifteen syn and post eruptive lithofacies are recognized in excellent exposures along the glacially dissected western side of the ridge we recognize five lithofacies associations 1 poorly sorted tuff breccia and dykes 2 proximal pillow lava dykes and tuff breccia 3 distal pillow lava poorly sorted conglomerate and well sorted volcanic sandstone 4 interbedded tuff lapilli tuff and tuff breccia units and 5 heterolithic volcanogenic conglomerate and sandstone given the abundance of pillow lavas and the lack of surrounding topographic barriers capable of impounding water we agree with souther souther j g 1992 the late cenozoic mount edziza volcanic complex geol soc can mem vol 420 320 pp that the bulk of the edifice formed while confined by ice but have found evidence for a more complex and variable eruption history than that which he proposed preliminary estimates of water ice depths derived from ftir analyses of h2o give ranges of 300 to 680 m assuming 0 ppm co2 and 857 to 1297 m assuming 25 ppm co2 variations in depth estimates among samples may indicate that water ice depths changed during the evolution of the ridge which is consistent with our interpretations for the origins of different lithofacies associations given that the age of the units are likely to be ca 0 9 ma souther j g 1992 the late cenozoic mount edziza volcanic complex geol soc can mem vol 420 320 pp pillow ridge may be the best documentation of a regional high stand of the cordilleran ice sheet cis in the middle pleistocene and an excellent example of the lithofacies and stratigraphic complexities produced by variations in water levels during a prolonged glaciovolcanic eruption

late cretaceous maastrichtian shallow water hydrocarbon seeps from snow hill and seymour islands james ross basin antarctica fossil hydrocarbon seeps are present in latest cretaceous maastrichtian volcaniclastic shallow shelf sediments exposed on snow hill and seymour islands james ross basin antarctica the seeps occur in the snow hill island formation on snow hill island and are manifest as large sized cement rich carbonate bodies containing abundant thyasirid bivalves and rarer ammonites and solemyid bivalves these bodies have typical seep cement phases with 13c values between 20 4 and 10 7 and contain molecular fossils indicative of terrigenous organic material and the micro organisms involved in the anaerobic oxidation of methane including methanotrophic archaea and sulphate reducing bacteria on seymour island the seeps occur as micrite cemented burrow systems in the lopez de bertodano formation and are associated with thyasirid solemyid and lucinid bivalves and background molluscan taxa the cemented burrows also have typical seep cement phases with 13c values between 58 0 and 24 6 there is evidence from other data that hydrocarbon seepage was a common feature in the james ross basin throughout the maastrichtian and into the eocene the snow hill and seymour island examples comprise the third known area of maastrichtian hydrocarbon seepage but compared to most other ancient and modern seep communities the james ross basin seep fauna is of very low diversity being dominated by infaunal bivalves all of which probably had thiotrophic chemosymbionts but which were unlikely to have been seep obligates absent from the james ross basin seep fauna are typical obligate seep taxa from the cretaceous and the cenozoic reasons for this may have been temporal palaeolatitudinal palaeobathymetric or palaeoecological

13c depleted biphytanic diacids as tracers of past anaerobic oxidation of methane abstract 13 c depleted biphytanic diacids containing 0 2 pentacyclic rings are abundant biomarkers in cenozoic methane seep limestones the strong 13 c depletion 132 to 96 suggests that they derive from euryarchaea metabolizing methane they occur with other biomarkers typically associated with anaerobic oxidation of methane such as crocetane pentamethylicosane pmi archaeol hydroxyarchaeol and glycerol dibiphytanyl glycerol tetraethers gdgts in contrast to gdgt derived biphytane hydrocarbons the biphytanic diacids appear to be almost exclusively derived from methanotrophic euryarchaea

geology of mount murphy volcano an 8 m y history of interaction between a rift volcano and the west antarctic ice sheet volcanic rocks glaciogenic sediments and recycled marine microfossils at mount murphy provide evidence for large scale fluctuations in the mass of the west antarctic ice sheet during neogene time mount murphy is a large shield volcano with an atypical structure its basal unit consists of alternating subaquatic and subaerial rock types through a stratigraphic interval of at least 300 m suggesting that ice level changed several times during shield building much larger changes are suggested by an outcrop of glacial lake sediment near the volcano summit 1 300 m above present ice level it contains an assemblage of recycled marine microfossils derived from marine basins in the interior of west antarctica they suggest multiple intervals of near complete deglaciation in west antarctica between about 24 and 3 5 ma the microfossils were probably deposited by meltwater from the ice sheet during a much higher stand of ice in late pliocene time it has long been suspected that the west antarctic ice sheet is unstable and vulnerable to greenhouse warming because it is grounded more than 1 000 m below sea level our results provide field evidence consistent with that proposal more than the west antarctic ice sheet may be involved however the nature of the evidence and timing of events at mount murphy are similar to the record in east antarctica suggesting continent wide synchroneity of the major glacial and interglacial intervals this conflicts with interpretations of marine data which suggest a shorter history for the west antarctic ice sheet and a more stable history for the entire ice sheet

using 87sr 86sr ratios to date fossil methane seep deposits methodological requirements and an example from the great valley group california abstractmethane seep carbonates preserve information about the history of methane seepage and of the fauna inhabiting these ecosystems for this information to be useful a reliable determination of the carbonates stratigraphic ages is required but this is not always available here we investigate the using strontium isotope stratigraphy to date fossil methane seep carbonates via detailed petrographic and geochemical investigation of the different carbonate phases in biostratigraphically well dated seep carbonates of paleozoic mesozoic and cenozoic age the best results are obtained from banded botryoidal rim cements from carbonate phases showing a weak or no cathodoluminescence signal an oxygen isotope signature close to that of seawater and the lowest mn concentrations we then applied the method to a presumably late jurassic seep carbonate from the great valley group in california strontium isotope ratios of the least diagenetically altered carbonate phases indicate a tithonian late jurassic

lipid biomarker patterns of methane seep microbialites from the mesozoic convergent margin of california abstract in order to reconstruct biogeochemical pathways at mesozoic methane seeps a set of late jurassic tithonian to early cretaceous aptian albian 13 c depleted seep limestones from forearc strata in western california were subjected to detailed molecular isotopic biomarker analyses two of the microbial carbonate deposits are turbidite hosted fault related whereas one is hosted in serpentinite in a diapir related setting the limestones contain 13 c depleted archaeal lipid biomarkers such as crocetane 13 c 80 and pmi 100 indicative of an involvement of anaerobic oxidation of methane aom in carbonate precipitation isotopically depleted crocetane in the tithonian sample represents the oldest reported occurrence of this compound at methane seeps in the set of samples a series of strongly 13 c depleted regular c 21 to c 24 isoprenoids possibly results from diagenetic alteration of archaeal sesterterpanylglycerol diethers as suggested by the presence of the putative intermediate 3 7 11 15 19 pentamethylicosanoic acid 13 c depleted 17 h 21 h and 17 h 21 h hopanes c 30 c 34 with 22 s and 22 r isomer couplets c 31 are present in all samples in distributions indicative of a moderate thermal maturity low 13 c values 78 to 60 suggest that these are derived from anaerobic bacteria involved in aom notably 22 s isomers are consistently enriched in 13 c relative to their 22 r counterparts our samples represent 70 myr of seepage activity and aom along the mesozoic margin of western california filling the gap between the currently oldest methane seep biomarker record from the oxfordian late jurassic and the more widely recognised cenozoic examples

methane seepage effects on biodiversity and biological traits of macrofauna inhabiting authigenic carbonates abstract authigenic carbonate rocks at methane seeps are recognized as hosting diverse and abundant invertebrate assemblages with potential forcing from fluid seepage and hydrography mensurative studies of carbonate macrofauna 0 3 mm at hydrate ridge or revealed little effect of water depth and overlying oxygenation at 600 m and 800 m but a large influence of seepage activity on density taxonomic composition diversity and biological traits feeding lifestyle motility size and calcification rocks exposed to active seepage had 3 4 higher total macrofaunal densities than under inactive conditions assemblages exhibited higher species richness and reduced evenness greater dominance under active seepage than inactive conditions but no difference in h or rarefaction diversity actively seeping sites were characterized by errant motile bacterial grazing small and medium sized heavily calcified species whereas inactive sites exhibited a greater diversity of feeding modes and more burrowers sessile large and lightly calcified species active rocks supported more exogonid syllidae ampharetid and cirratulid polychaetes provannid snails pyropeltid limpets nemerteans and sponges whereas inactive rocks supported higher densities of ophiuroids isopods gammarid amphipods hydroids typosyllis syllidae and tanaids transplant experiments in which rocks were transferred between active and inactive sites at hydrate ridge north 600 m revealed that assemblages respond within 13 months to increase or cessation of seepage taking on the feeding size and calcification characteristics of the background fauna at the new site lifestyles and motility patterns shifted more slowly as the sessile attached species did not track seepage as quickly provannid snails and pyropeltid limpets rapidly colonized rocks transplanted to active sites and disappeared when transplanted to inactive sites given the known variability of fluid fluxes and rapid community response a mosaic of communities changing in space and time is hypothesized to generate the relatively high species diversity at methane seeps

lithogeochemical patterns around pb zn mineralizations in dinantian carbonate rocks of eastern belgium the lithogeochemical distribution patterns of mg sr na zn pb fe mn k corg organic matter and ir insoluble residue in the dinantian limestones and dolomites from the eastern part of belgium have been studied dinant and verviers synclinorium comparison of geochemical data of non mineralized strata revealed higher background values in the strata of the verviers synclinorium where pb zn mineralizations occur in this area a relation may exist with the metallogenetic district herve vesdre theux district proposed by dejonghe 1985b however the higher background values also could relate to the more restricted sedimentation conditions in the verviers synclinorium as opposed to the more open marine conditions in the dinant synclinorium the influence of mineralization on the geochemistry of limestones is limited and unpredictable in dolomites however the effect can be important in these rocks the lithogeochemical distribution of zn pb and mn can be subdivided into three populations i e a regional background a local high background and a halo population the higher trace element concentrations in the halo population is caused by the existence of disseminated sulfide minerals sphalerite galena and pyrite and zn bearing goethite mainly pseudomorphs after pyrite and mn oxides the sulfides relate to the ore emplacement in the local high background only the zn bearing oxides occur their presence and thus the development of the local high background relates to weathering processes

pleistocene reversal of the fraser river british columbia the fraser river in british columbia canada is the longest non dammed river on the west coast of north america and supplies 20 10 6 t yr of sediment to the pacific ocean abundant geomorphological evidence indicates that the fraser river reversed its course to southward flow in the recent geological past investigation of two volcanic dams at dog creek demonstrates northward flow of the fraser until at least 1 06 ma before reversal and erosion of the 270 km long fraser canyon we propose that the submarine nitinat fan off the coast of british columbia records the reversal and sudden input of coarse continental derived sediment ca 0 76 ma this study confirms reversal of the fraser river and places a firm constraint on the maximum age of that reversal reversal likely followed stream capture in response to enhanced glaciofluvial erosion and uplift of the coast mountains

biogeochemical controls on authigenic carbonate formation at the chapopote asphalt volcano bay of campeche abstract the campeche knolls in the bay of campeche southern gulf of mexico were investigated through detailed seafloor mapping rov surveys and sediment and pore water sampling the knolls are elongated submarine hills created by salt tectonics with a positive relief of up to 800 m above the surrounding seafloor several of the knolls are associated with sea surface oil slicks identified from satellite data indicating the presence of hydrocarbon seeps on the seafloor one of the knolls named chapopote was studied in detail during two international research expeditions so174 2 and m67 2 and is characterized by extensive hydrocarbon seepage including large asphalt flows oil and gas seeps and seafloor gas hydrate deposits chemosymbiotic biological communities and authigenic carbonate deposits are associated with the seeps and are the result of both biogeochemical turnover and the interaction between downward diffusing seawater and hydrocarbon rich pore fluids at shallow sediment depth authigenic carbonates are characterized by aragonite exhibit a porous texture and are cemented by a matrix of microsparitic to sparitic aragonite macropores of the carbonates were completely filled with liquid oil carbonate microfabrics include peloidal or clotted fabrics that may indicate the existence of microenvironments resulting from microbial metabolism banded botryoidal aragonite cements line the intra and bioclasts and incompletely fill the pore spaces the stable carbon isotopic composition of authigenic aragonite varies between 28 6 and 17 9 pdb identifying oil oxidation as the primary source of carbon to the dic pool while lipid biomarker data demonstrate the concurrent existence of microbial communities responsible for anaerobic oxidation of methane aom these observations indicate the presence of additional aom independent reactions responsible for carbon sequestration at hydrocarbon seeps and demonstrate the complexity of biogeochemical processes at seep sites in the gulf of mexico basin oxygen isotope data of authigenic aragonite vary from 2 5 to 3 8 pdb indicating carbonate precipitation in slight disequilibrium with the surrounding pore fluids

an archaeal biomarker record of paleoenvironmental change across the onset of the messinian salinity crisis in the absence of evaporites piedmont basin italy abstract a sudden change from normal marine to extreme paleoenvironmental conditions occurred approximately 6 ma ago in the mediterranean basin at the onset of the late miocene messinian salinity crisis one of the most severe ecological crises in earth history strong evaporation and tectonics led to hypersaline conditions resulting in widespread deposition of evaporites and the apparent annihilation of the marine metazoan biosphere in contrast to the prominent occurrence of evaporites elsewhere in the mediterranean evaporites did not form in the deeper part of some marginal basins at the onset of the crisis the strata of the pollenzo section piedmont basin nw italy studied here were deposited in such a paleogeographic setting instead of evaporites a cyclic succession of organic rich shales and carbonates formed during the early phase of the crisis in the study area these sediments record a sharp increase in the contents of archaeal molecular fossils that are mostly represented by isoprenoidal dialkyl glycerol diethers dgds and isoprenoidal glycerol dialkyl glycerol tetraethers gdgts such an expansion of archaeal biomass is best explained by a change of the archaeal communities at the onset of the messinian salinity crisis in particular the appearance of molecular fossils of extremophilic archaea mostly producing dgds archaeol and extended archaeol suggests the emergence of halophilic archaea at the same time lipids of planktonic thaumarchaeota especially crenarchaeol are present across the entire section suggesting the local persistence of normal marine conditions in agreement with the sudden appearance of tetrahymanol in the upper part of the section the persistence of crenarchaeol indicates the establishment of water column stratification after the advent of the messinian salinity crisis to further investigate the piedmont basin paleoenvironmental conditions we test the archaeol caldarchaeol ecometric ace a proxy developed for identifying high paleosalinities in waters and possibly in sediments despite high ace values found for the messinian salinity crisis samples these values are in contrast with the absence of any lithological evidence for high salinities as well with other biomarker independent information indicating low to normal seawater salinities this apparent contradiction is likely explained by the complexity of the sources of archaeal lipids especially of caldarchaeol and archaeol limiting the utility of the ace for the reconstruction of paleosalinities for messinian strata

cretaceous methane seep deposits from new zealand and their fauna abstract six cretaceous methane seep deposits are reported from the raukumara peninsula eastern north island new zealand dinoflagellate dating indicates a late albian to mid cenomanian age for three deposits from port awanui and a mid campanian age for two deposits from waipiro bay and for one from owhena stream the dominant petrographic fabric of the carbonates is detrital micrite and the numerous fenestrae and vugs are filled with various cements including two types of non detrital micrite and botryoidal and banded fibrous calcites these petrographic features in combination with negative 13c values of early diagenetic micrites as low as 29 2 vs v pdb and 13c depleted molecular fossils such as the archaeal biomarkers pentamethylicosane 97 vs v pdb and biphytane 99 and the bacterial biomarker anteiso c15 fatty acid 47 reveal that sulfate dependent anaerobic oxidation of methane aom induced the formation of these deposits the carbonates preserve a typical mollusk dominated late mesozoic deep water seep fauna including the large modiomorphid bivalve caspiconcha the lucinid bivalve ezolucina and limpets hokkaidoconchids and a large abyssochrysoid among the gastropods with close biogeographic relationships to north pacific seep faunas of cretaceous age in contrast to the general marine mollusk fauna of new zealand which shows a high degree of endemism in both the cenozoic and recent new zealand s cretaceous to present day seep faunas consist largely of taxa known from coeval seeps around the world thus while deep water seeps in new zealand were repeatedly or continuously colonized by members of the global seep fauna the general mollusk fauna of the new zealand region developed a considerable degree of endemism during this time

mauna loa lava accumulation rates at the hilo drill site formation of lava deltas during a period of declining overall volcanic growth accumulation rates for lava flows erupted from mauna loa as sampled in the uppermost 280 m of the hilo drill hole vary widely for short time intervals several thousand years but overall are broadly similar to those documented elsewhere on this volcano since 100 ka thickness variations and accumulation rates for mauna loa lavas at the hilo drill site have been strongly affected by local paleotopography including funneling and ponding between mauna kea and kilauea in addition gentle submerged slopes of mauna kea in hilo bay have permitted large shoreline displacements by mauna loa flows ages of eruptive intervals have been determined from published isotopic data and from eustatic sea level curves modified to include the isostatic subsidence of the island of hawaii at 2 2 2 6 mm yr prior to 10 ka rates of mauna loa lava accumulation at the drill site varied from 0 6 to 4 3 mm yr for dateable intervals with an overall rate of 1 8 mm yr major eruptive pulses at about 1 3 and 10 ka each probably representing a single long lived eruption based on lack of weathering between flow units increase the overall accumulation rate to 2 4 mm yr the higher rate since 10 ka reflects construction of thick near shoreline lava deltas as postglacial sea levels rose rapidly large lava deltas form only along coastal segments where initially subaerial slopes have been submerged by the combined effects of eustatic sea level rise isostatic subsidence or spreading of volcano flanks overall accumulation of 239 m of lava at the drill site since 100 120 ka closely balances submergence of the hilo area suggesting that processes of coastal lava deposition have been modulated by rise in sea level the hilo accumulation rate is slightly higher than average rates of 1 2 mm yr determined elsewhere along the mauna loa coast based on rates of shoreline coverage and dated sea cliff and fault scarp exposures low rates of coastal lava accumulation since 100 ka near or below the rate of island wide isostatic subsidence indicate that mauna loa is no longer growing vigorously or even maintaining its size above sea level

characterizing lipid biomarkers in methanotrophic communities of gas hydrate bearing sediments in the sea of okhotsk abstract we studied specific lipid biomarkers of archaea and bacteria that are associated with the anaerobic oxidation of methane aom in a cold seep environment as well as the origin of sedimentary organic matter on the continental slope off ne sakhalin in the sea of okhotsk the organic geochemical parameters demonstrated that most of the sedimentary organic matter containing hydrate layers could be derived from marine phytoplankton and bacteria except for a station lv39 29h which was remarkably affected by terrestrial vascular plant specific methanotrophic archaea biomarkers was vertically detected in hydrate bearing cores lv39 40h coinciding with the negative excursion of the 13corg at core depths of 90 100 cm below the seafloor these results suggest that methane provided from gas hydrates are already available substrates for microbes thriving in this sediment depth in addition the stable isotope mass balance method revealed that approximately 2 77 3 41 of the total organic carbon or 0 036 0 044 dry weight sediment was generated by the activity of the aom consortium in the corresponding depth of core lv39 40h on the other hand the heavier 13c values of archaeol in the gas hydrate stability zone may allow ongoing methanogenesis in deeper sediment depth

quantification of submarine lava flow morphology through analog experiments we developed a technique for determining paleoeffusion rates and emplacement times for submarine lava flows using observations of flow morphology and estimates of eruption volume eruption temperature lava viscosity and preflow topography using laboratory simulations and correlating these results with sea floor observations four submarine lava flow morphologies are considered to be diagnostic of specific effusion rates jumbled folded and lineated sheets and striated pillows we applied this approach to the coaxial flow emplaced in less than 14 days on the juan de fuca ridge in early summer 1993 and we calculated an effusion rate of 100 m3 s giving an emplacement time of 10 days

tentative identification of diagenetic products of cyclic biphytanes in sedimentary rocks from the uppermost permian and lower triassic abstract biphytanes which are derived from glycerol dialkyl glycerol tetraether gdgt lipids are biomarkers for the presence of archaea in geological samples they especially cyclic structures are rarely reported from sediments or oils that are older than the triassic period where their first record may be traced back to the late archean there have been only two studies that have reported diagenetic products of cyclic biphytanes using two dimensional gas chromatography in this study we used full scan and multiple reaction monitoring mrm mass spectrometry ms to tentatively assign a series of diagenetic products of cyclic biphytanes within uppermost permian and lower triassic sedimentary rocks we observed three distinct groups derived from mono bi or tricyclic biphytanes echoing previous studies each group could be further divided into three discrete series according to structure and composition using mrm also revealed that numerous sedimentary rocks contained such diagenetic products but at trace concentration below the limit of detection of full scan ms this indicates that the presence of archaea containing gdgt lipids has been underestimated within paleoenvironments episodic occurrences of biphytanes in the permian triassic transition also provide additional evidence for the distribution of archaea in the geological past

pliocene and pleistocene volcanic interaction with cordilleran ice sheets damming of the yukon river and vertebrate palaeontology fort selkirk volcanic group west central yukon canada abstract neogene volcanism in the fort selkirk area began with eruptions in the wolverine creek basin ca 4 3 ma and persisted to ca 3 0 ma filling the ancestral yukon river valley with at least 40 m of lava flows activity at the ne ch e ddhawa eruptive center overlapped with the last stages of the wolverine creek eruptive centers hyaloclastic tuff was erupted between ca 3 21 and 3 05 ma this eruption caused or was coincident with damming of yukon river the first demonstrable incursion of a cordilleran ice sheet into the fort selkirk area was coincident with a second eruption of the ne ch e ddhawa eruptive center ca 2 1 ma the ne ch e ddhawa subglacial mound was erupted beneath at least 300 m of glacial ice ne ch e ddhawa glaciation the eruption of the fort selkirk center occurred between the last eruption of ne ch e ddhawa and fort selkirk glaciation ca 2 1 1 5 ma till and outwash from fort selkirk glaciation are conformably overlain by nonglacial sediments that contain the fort selkirk tephra fission track dated at ca 1 5 ma these nonglacial sediments also preserve a short magnetic reversal reversed to normal identified as the gilsa polarity excursion temporal control and sedimentology constrain fort selkirk glaciation and the fort selkirk local fauna to marine isotope stage 54 rapid and extensive eruption of the pelly eruptive center filled the yukon river valley with 70 m of lava which buried these glacial and nonglacial sediments and dammed yukon river local striations and erratic pebbles occur on the last of these lava flows they document a subsequent incursion of glacial ice during the last 500 ka of the matuyama chron forks glaciation the last major eruption of mafic lava occurred in the middle pleistocene west of early holocene volcano mountain in basin of black creek lava flowed down the valley presently occupied by black creek and dammed yukon river in the area of the black creek confluence this eruption predated the middle pleistocene reid glaciation minor volcanism has continued in this area since the middle pleistocene at volcano mountain

a new constraint on the antiquity of anaerobic oxidation of methane late pennsylvanian seep limestones from southern namibia late pennsylvanian seep limestones ca 300 ma enclosed in the ganigobis shales in southern namibia formed by microbial activity the process that induced carbonate precipitation was the anaerobic oxidation of methane the presence of 13 c depleted pentamethylicosane pmi 113 and a mixture of crocetane and phytane 112 in concert with similarly 13 c depleted pseudohomologous series of regular isoprenoids reveals that methanotrophic archaea oxidized methane anaerobically at the ancient seep site biphytane and a c 39 pseudohomologue are other archaeal molecular fossils with 13 c values of 99 and 97 respectively the former presence of sulfate reducing bacteria as the syntrophic partners of methanotrophic archaea in the anaerobic oxidation of methane is indicated by isotopically depleted iso and anteiso alkanes these compounds most probably derive from non isoprenoidal monoethers and diethers synthates of sulfate reducing bacteria these findings show that anaerobic oxidation of methane is at least 300 m y old extending the record of this process for 140 m y as the molecular fossils of archaea and bacteria are preserved in a product of their own metabolic activity i e methane derived carbonates with 13 c values as low as 51 the syngenicity of molecular fossils and enclosing deposits is unambiguous this reveals that microbially formed rocks can represent excellent archives for studying past biogeochemical processes

marine organic matter cycling during the ediacaran shuram excursion ediacaran ca 635 541 ma marine carbonates capture a global 13 c carbon isotope excursion to extremely negative values 12 known as the shuram excursion se that cannot be explained by conventional mass balance scenarios furthermore the carbon isotopic variation of bulk organic matter om does not mirror that of carbonate through the excursion suggesting that the om reflects a mixture of different sources to evaluate this hypothesis we investigated thermally immature marine sedimentary rocks that record the se from the sultanate of oman compound specific carbon isotopic analyses of the extractable hydrocarbons reveal low 13 c values of long chain c 20 n alkanes and mid chain monomethyl alkanes as low as 40 such light signatures are rare in marine rocks of any age and provide evidence that the se reflects a primary carbon cycle perturbation the magnitude of the se recorded in these organic phases is smaller than observed in carbonate and implies that the primary perturbation to dissolved inorganic carbon dic was at least 5 7 and more likely 7 12 in magnitude when correcting for end member source mixing due to isotopic differences in stratigraphic patterns of the different organic compounds we propose that bulk organic carbon both bitumen and kerogen reflects source mixing between two distinct pools that previously masked the excursion in bulk 13 c org measurements om sources were derived both from autotrophs fixing 13 c depleted dic and from a less 13 c depleted heterotrophic microbial biomass feeding on a marine om pool sustained by petroleum expelled from older sedimentary om expulsion of these sedimentary fluids also helps explain both the duration and magnitude of the se

pendant bioconstructions cemented by microbial carbonate in submerged marine caves holocene se sicily abstract unusual pendant bioconstructions occur within two submerged caves in the plemmirio marine protected area south of syracuse se sicily these cm to dm sized bioconstructions project downward from the cave roofs the main framework builders are serpulids belonging to the genera protula semivermilia and josephella encrusting bryozoans corals hydrozoans and sponges are subordinately present whereas bivalves and brachiopods are overall rare these faunal associations are characteristic of the studied caves but only in some places they form small bioconstructions that are cemented by microbial carbonates made up by autochthonous peloidal to clotted peloidal and aphanitic micrite the autochthonous micrite stabilizes the pendant bioconstructions herein referred to as biostalactites the microbial carbonate reveals high contents of bacterial lipid biomarkers among the most abundant compounds are mono o alkyl glycerol ethers mages and branched fatty acids 10 me c16 0 iso and anteiso c15 0 and c17 0 interpreted as biomarkers of sulfate reducing bacteria other compounds preserved in the autochthonous carbonates include lipids derived from marine zoo and phytoplankton brassicasterol dinosterol and monounsaturated short chain fatty acids unspecified marine bacteria saturated and monounsaturated short chain fatty acids and land plants long chain fatty acids long chain alcohols stigmasterol sitosterol and campesterol the observed lipid biomarker signatures are remarkably similar to those of post glacial reefal microbialites where microbialite formation in cavities of the coral framework was also mediated by sulfate reducing bacteria in the submerged caves of plemmirio marine protected area serpulid colonies apparently occur preferentially where freshwater is seeping through crevices in the limestone the consequent nutrification is believed to favor serpulid aggregation and the growth of other skeletal i e bryozoans and corals and soft bodied organisms i e sponges and ascidiae the resultant accumulation of biomass and its taphonomy provide niches for sulfate reducing bacteria which induce carbonate precipitation cementing and stabilizing the biostalactites the finding of pendant cemented bioconstructions in the mazzere and granchi caves of the plemmirio marine protected area reveals that sulfate reducing bacteria are involved in microbialite formation in various cryptic environments the formation of such peloidal to clotted peloidal microcrystalline carbonates in cryptic ecosystems is a significant factor for the stabilization of different kinds of bioconstructions spanning from small biostalactites to large reefs

lipid biomarker patterns of authigenic carbonates reveal fluid composition and seepage intensity at haima cold seeps south china sea abstract authigenic carbonates retrieved from sites rov1 and rov2 of the haima hydrocarbon seeps of the south china sea at approximately 1390 m water depth were studied using lipid biomarker analyses abundant molecular fossils of anaerobic methane oxidizing archaea anme and sulfate reducing bacteria srb with strong 13c depletions 13c values as low as 126 in combination with low 13ccarbonate values 42 7 to 36 8 provide evidence that anaerobic oxidation of methane aom was the major process driving the precipitation of the studied seep carbonates the extremely low 13c values of archaeal biomarkers confirm that biogenic methane was the main carbon source but the seepage of accessory crude oil is also suggested by the presence of unresolved complex mixtures in the hydrocarbon fractions a suite of 13c depleted biomarkers indicate the predominance of anme 1 dss consortia at both sites which indicates that the studied carbonates formed during low to medium methane flux somewhat higher contents of archaeal biomarkers and their stronger 13c depletion at site rov2 probably reflect at least temporarily higher seepage intensities than at site rov1 abundant bacterial dialkyl glycerol diethers dages revealing a large offset of their 13c values compared to srb derived terminally branched fatty acids were possibly produced by distinct srb species other than members of the dss cluster the encountered hopanoids are attributed to aerobic methanotrophic bacteria based on their moderate 13c depletion the application of molecular fossils in combination with their compound specific isotope signatures is an efficient tool to reconstruct the composition of seepage fluids and seepage intensities

polyphasic carbonate precipitation in the shallow subsurface insights from microbially formed authigenic carbonate beds in upper miocene sediments of the tertiary piedmont basin nw italy article i nfo authigenic methane derived carbonates hosted in upper miocene slope sediments of the tertiary piedmont basin nw italy are studied by a multidisciplinary approach including petrography stable oxygen and car bon isotopes of carbonates as well as lipid biomarkers in order to explore the relationship between microbial activity and carbonate precipitation in the shallow subsurface the studied rocks show a bed parallel geom etry and are characterized by dolomitic intergranular cement which is typified by positive 13 c values as high as 6 2 vpdb a striking feature of some dolomite beds is an intricate network of septarian like cracks filled with both injected sediments and polyphasic carbonate cements prokaryotic molecular fossils in the dolomite beds comprise archaeol 13 c 40 vpdb and various bacterial dialkyl glycerol diethers dages 13 c 30 vpdb strongly suggesting that dolomite precipitation took place at the interface of the zones of archaeal methanogenesis and bacterial sulphate reduction in contrast extremely negative 13 c values of carbonate cements as low as 56 3 vpdb and various archaeal and bacterial molecular fossils e g pentamethylicosane pmi 106 vpdb are recorded in the crack filling carbonate cements these cements precipitated due to anaerobic oxidation of methane coupled to sulphate reduction we pro pose a scenario for the formation of the diagenetic beds suggesting that carbonate precipitation was the re sult of three microbially driven processes sulphate reduction methanogenesis and finally anaerobic oxidation of methane this unusual sequence was a consequence of a dynamic change of environmental geo chemical conditions and fluid circulation patterns that prevailed in the ancient subseafloor during early dia genesis of the unconsolidated sediments anaerobic oxidation of methane which usually predates methanogenesis during increasing burial postdates methanogenesis in case of the septarian like beds after the beds were affected by crack formation induced by overcritical pore pressure allowing the ingress of sulphate rich water from above and methane rich water from below

distributions and carbon isotopic compositions of lipid biomarkers in authigenic carbonate crusts from the nordic margin norwegian sea abstract we investigated the distributions and 13c values of lipid biomarkers in authigenic carbonate crusts from the nordic margin norwegian sea abundant highly 13c depleted archaeal and bacterial biomarkers revealed that anaerobic oxidation of methane aom is associated with carbonate authigenesis at the hakon mosby mud volcano hmmv and the nyegga pockmark field no conclusive evidence for aom was found in the crust sample from the storegga slide anme 2 methanotrophic archaea and sulfate reducing bacteria from the desulfosarcina desulfococcus cluster were inferred from lipid fingerprints distinct patterns of 13c depleted non isoprenoid dialkyl glycerol diethers dages are possibly associated with unknown microbial partners in the aom

constraints on the history of open basin lakes on mars from the composition and timing of volcanic resurfacing 1 abundant evidence exists for valley network related fluvial activity near the noachian hesperian transition on mars and areally significant quantities of volcanic ridged plains were emplaced during this period as well thus it is worthwhile to explore the hypothesis that lava water interaction occurred on the surface of mars at this time we analyzed the morphology physical properties composition and surface ages of thirty open basin lakes topographic lows with both an inlet valley and an outlet valley that were also resurfaced by volcanic flows hyperspectral imaging data from the compact reconnaissance imaging spectrometer for mars crism and observatoire pour la mineralogie l eau les glaces et l activite omega instruments indicate that of the 30 basins 12 exhibit the spectral properties of basaltic lithologies with diagnostic absorptions of olivine high calcium pyroxene and low calcium pyroxene an olivine high calcium pyroxene mixture is the most commonly identified mineral assemblage consistent with other hesperian aged volcanic units therefore our mineralogical results for over a third of the open basin lake floors analyzed support prior interpretations that the basins were resurfaced by volcanic flows supporting evidence for resurfacing by volcanic flows is also given by the observed morphology and physical properties e g surface roughness thermal inertia of the resurfaced open basin lake floors in these 30 examples however no evidence was found for lava water interaction the ages of emplacement derived through counts of superposed craters of all 30 of the open basin lake volcanic resurfacing units show that resurfacing began in the late noachian near the noachian hesperian boundary was concentrated in the hesperian and continued into the early amazonian the lack of geologic features indicative of lava water interaction suggests that the basins were likely to have been mostly devoid of water at the time of the latest phase of volcanic resurfacing we conclude that there is no geologic evidence that suggests the fluvial activity associated with the studied paleolakes was coeval with the emplacement of the observed volcanic resurfacing units several of which date to the late noachian early hesperian

lava and ice interaction at stratovolcanoes use of characteristic features to determine past glacial extents and future volcanic hazards structures resulting from lava and ice interaction are common at glaciated stratovolcanoes during summit eruptions at stratovolcanoes meltwater is produced and travels freely down steep slopes and thin permeable valley glaciers eroding the ice and enlarging preexisting glacial drainages as a result eruptions in this environment have produced few catastrophic floods lava flowing into the open channels and voids in the glaciers becomes confined and grows thicker filling the available space and producing steep sided bodies with smooth bulbous contact surfaces quenching of lava against ice or by water forms small scale features such as tensional fractures and glass as the amount of meltwater in contact with the lava increases the type and abundance of smaller scale features become similar to those produced during subglacial eruptions into meltwater lakes identification of large and small scale lava ice contact features in the field can be used to reconstruct paleoglacial extent and combined with geochronology of lavas to determine past paleoclimate an understanding of lava ice interaction allows us to better assess the hazards posed by future eruptions at glaciated volcanoes

formation of clastogenic lava flows during fissure eruption and scoria cone collapse the 1986 eruption of izu oshima volcano eastern japan the 1986 eruption of b fissure at izu oshima volcano japan produced among other products one andesite and two basaltic andesite lava flows locally the three flows resemble vent effused holocrystalline blocky or aa lava however remnant clast outlines can be identified at most localities indicating that the flows were spatter fed or clastogenic the basaltic andesite flows are interpreted to have formed by two main processes a reconstitution of fountain generated spatter around vent areas by syn depositional agglutination and coalescence followed by extensional non particulate flow and b syn eruptive collapse of a rapidly built spatter and scoria cone by rotational slip and extensional sliding these processes produced two morphologically distinct lobes in both flows by a earlier non particulate flow of agglutinate and coalesced spatter which formed a thin lobe of rubbly aa lava ca 5 m thick with characteristic open extension cracks revealing a homogeneous holocrystalline interior and b later scoria cone collapse which created a larger lobe of irregular thickness 20 m made of large detached blocks of scoria cone interpreted to have been rafted along on a flow of coalesced spatter the source regions of these lava flows are characterized by horseshoe shaped scarps 30 m high with meso blocks ca 30 m in diameter of bedded scoria at the base one lava flow has a secondary lateral collapse zone with lower ca 7 m scarps backward tilted meso blocks are interpreted to be the product of rotational slip and forward tilted blocks the result of simple toppling squeeze ups of coalesced spatter along the leading edge of the meso blocks indicate that coalescence occurred in the basal part of the scoria cone this low viscosity coalesced spatter acted as a lubricating layer along which basal failure of the scoria cone occurred rotational sliding gave way to extensional translational sliding as the slide mass spread out onto the present caldera floor squeeze ups concentrated at the distal margin indicate that the extensional regime changed to one of compression probably as a result of cooling of the flow front sliding material piled up behind the slowing flow front and coalesced spatter was squeezed up from the interior of the flow through fractures and between rafted blocks the andesite flow although morphologically similar to the other two flows has a slightly different chemical composition which corresponds to the earliest stage of the eruption it is a much smaller lava flow emitted from the base of the scoria cone 2 days after the eruption had ceased this lava is interpreted to have been formed by post depositional coalescence of spatter under the influence of the in situ cooling rate and load pressure of the deposit extrusion occurred through the lower part of the scoria cone and subsequent non particulate flow of coalesced material produced a blocky and aa lava flow the mechanisms of formation of the lava flows described may be more common during explosive eruptions of mafic magma than previously envisaged

sedimentology of an ice contact glaciomarine delta carey valley northern ireland an extensive late pleistocene delta body related to a water plane at 100 m above sea level is exposed in the upper carey valley northern ireland exposures along the modern river show a lowermost facies association of massive diamict and poorly sorted gravel deposited as sediment gravity flows overlain by a gravelly foreset and topset facies association recording the progradation of a large glacier fed delta diamict facies were emplaced as subaqueous debris flows associated gravels are chaotically bedded and were deposited by the downslope slumping of poorly sorted boulder gravel their subtle grading characteristics can be linked with a variety of mass flow processes sediment gravity flow facies originated upvalley from rapidly deposited sediments which accumulated near the exit of a narrow subglacial channel below an ice margin fronting in water subsequent ice retreat allowed the growth of a gilbert type delta regional evidence shows that the delta top records high relative sea levels in response to isostatic downwarping around the periphery of the last british ice sheet the sedimentology and structure of the carey valley infill may be typical of high level glaciomarine deltas preserved in topographic lows around the coastline of north britain

the formation of giant tubular concretions triggered by anaerobic oxidation of methane as revealed by archaeal molecular fossils lower eocene varna bulgaria abstract impressive several meters high tubular concretions in shallow marine calcareous sands and sandstones represent part of the well exposed subsurface plumbing network of an early eocene methane seep system in the balkanides foreland pobiti kamani area varna ne bulgaria an integrated approach including petrography inorganic geochemistry and lipid biomarker analyses was used to reconstruct the evolution of pore fluids and cementation conditions during tube formation and particularly the role of methane related carbonate diagenesis host sediment lithification from marine pore waters was perturbed soon after deposition by oxidation of predominantly microbial methane causing pervasive cementation by a 13 c poor homogeneous calcite cement 13 c values as low as 44 5 v pdb the importance of microbially mediated anaerobic oxidation of methane aom is confirmed by extremely 13 c depleted archaeal biomarkers 13 c values as low as 123 v pdb a suite of macrocyclic dialkyl glycerol diethers mdgd 0 to 2 and sn 3 hydroxyarchaeol comprises a characteristic trait of the eocene tubular concretions and might represent molecular fossils of so far unknown methane oxidizing archaea anme subsurface calcite cementation surrounding the ascending methane plume resulted from the changing pore water chemistry in response to aom and could have on a local scale been encouraged by the concurrent alteration of detrital feldspar fluctuating 13 c up to 8 v pdb and 18 o 0 5 to 9 v pdb signatures within a single tubular sandstone concretion are at least partly the consequence of isotopic resetting during late meteoric water circulation

identifying hazards associated with lava deltas lava deltas formed where lava enters the ocean and builds a shelf of new land extending from the coastline represent a significant local hazard especially on populated ocean island volcanoes such structures are unstable and prone to collapse events that are often accompanied by small explosions that can deposit boulders and cobbles hundreds of meters inland explosions that coincide with collapses of the east lae apuki lava delta at k lauea volcano hawai i during 2005 2007 followed an evolutionary progression mirroring that of the delta itself a collapse that occurred when the lava ocean entry was active was associated with a blast of lithic blocks and dispersal of spatter and fine glassy tephra shortly after delta growth ceased a collapse exposed hot rock to cold ocean water resulting in an explosion composed entirely of lithic blocks and lapilli further collapse of the delta after several months of inactivity by which time it had cooled significantly resulted in no recognizable explosion deposit seaward displacement and subsidence of the coastline immediately inland of the delta was measured by both satellite and ground based sensors and occurred at rates of several centimeters per month even after the lava ocean entry had ceased the anomalous deformation ended only after complete collapse of the delta monitoring of ground deformation may therefore provide an indication of the potential for delta collapse while the hazard associated with collapse can be inferred from the level of activity or the time since the last activity on the delta

molecular indicators of methane metabolisms at cold seeps along the united states atlantic margin abstract anaerobic oxidation of methane aom and the environmental conditions supporting aom on continental margins is an essential component to global methane budgets diagnostic lipid biomarkers and their compound specific isotope analysis preserved in authigenic carbonates at cold seeps can serve as fingerprints to archaeal bacterial consortia involved in aom however despite the discovery of several hundreds of seeps along the united states atlantic margin usam there are relatively few biomarker investigations of cold seep carbonates along this passive margin a lipid biomarker carbon isotope and dna marker gene study was therefore undertaken to determine the microbial origins of authigenic carbonates from two usam seeps norfolk and the baltimore canyon seep fields results from this study capture a distinct archaeal lipid signature from putative methanotrophic archaea including archaeol i sn 2 hydroxyarchaeol 2 6 10 15 19 pentamethylicosane pmi and crocetane the 13c depleted aom related archaeal lipid samples i e archaeol 91 6 sn 2 hydroxyarchaeol 129 2 pmi 92 8 and crocetane 70 9 confirm the dominance of methane assimilation and isotope fractionation during aom these results are consistent with the detection of archaeal anaerobic methanotrophs anmes based on 16s rrna gene sequencing the norfolk authigenic carbonate contained anme 1a 1b 2a 2b and 2c whereas only the anme 2 clade was detected at baltimore and present as the subclusters 2a 2b and 2b the anme 2d clade may also be present particularly at the baltimore seep site given the high abundance of candidatus methanoperedens nitroreducens detected in the mcra gene sequencing the presence of terminally branched fatty acids antesio and iso c15 0 components as well as c16 1 7 with 13c values as low as 107 6 are indicative of sulfate reducing bacteria srb at the norfolk seep site and supports syntrophy of srb with methane oxidizing archaea in contrast nitrate driven aom in syntrophy m nitroreducens at the baltimore seep site is consistent with elevated fatty acid 13c values and lack of deltaproteobacteria at the baltimore seep site taken together the range in lipid composition distribution and carbon isotopic composition observed at the norfolk and baltimore seep sites suggests aom is performed by multiple archaea instead of a single species and may be paired with either or both nitrate and sulfate reduction given the heterogeneous nature of cold seep ecosystems this study fills a critical spatial gap in our knowledge of aom activity at two seep sites along a passive margin

methane index a tetraether archaeal lipid biomarker indicator for detecting the instability of marine gas hydrates abstract gas hydrates represent one of the largest pools of readily exchangeable carbon on earth s surface releases of the greenhouse gas methane from hydrates are proposed to be responsible for climate change at numerous events in geological history many of these inferred events however were based on carbonate carbon isotopes which are susceptible to diagenetic alterations here we propose a molecular fossil proxy i e the methane index mi to detect and document the destabilization and dissociation of marine gas hydrates mi consists of the relative distribution of glycerol dibiphytanyl glycerol tetraethers gdgts the core membrane lipids of archaea the rational behind mi is that in hydrate impacted environments the pool of archaeal tetraether lipids is dominated by gdgt 1 2 and 3 due to the large contribution of signals from the methanotrophic archaeal community our study in the gulf of mexico cold seep sediments demonstrates a correlation between mi and the compound specific carbon isotope of gdgts which is strong evidence supporting the mi methane consumption relationship preliminary applications of mi in a number of hydrate impacted and or methane rich environments show diagnostic mi values corroborating the idea that mi may serve as a robust indicator for hydrate dissociation that is useful for studies of global carbon cycling and paleoclimate change

subglacial intermediate volcanism at kerlingarfjoll iceland magma water interactions beneath thick ice the products of andesite and dacite glaciovolcanism at kerlingarfjoll are unlike others previously described in the literature three sequences of lithofacies are described and interpreted here the andesitic deposits at campsite gully are divided into massive vitriclastic lapilli tuff with intrusions fluidal clast bearing vitriclastic lapilli tuff and stratified pumice rich vitriclastic lapilli tuff at tindur andesitic eruptions produced contorted pillow fragment breccia and the clast supported lithic breccia finally pillow lava with intrusions and crudely bedded vitriclastic lapilli tuff of dacitic composition are described at haraldur abundant vitriclasts the presence of pillow lavas hackly fracturing of lava bodies and lack of oxidation of clasts demonstrate that each of these lithofacies formed in the presence of abundant water this contrasts with all other descriptions of subglacially erupted intermediate magmas which are characterised by jointed and glassy lava flows and domes with a marked scarcity of fragmental material the kerlingarfjoll sequences therefore demonstrate that it is possible for intermediate magmas to generate and interact with significant volumes of water at the base of a glacier preliminary estimates of volatile contents in glassy clasts correspond to quenching pressures equivalent to 500 m water or 550 m ice this is consistent with eruption beneath an ice sheet that was thick enough to overwhelm the underlying topography and where meltwater drainage was controlled by the morphology of the glacier surface it is argued that the drainage of water due to steep topography and or thin and fractured ice as opposed to thermodynamic considerations is the most likely explanation for the absence of evidence for significant magma water interaction in previously described instances of intermediate glaciovolcanism the apparent low viscosity of the kerlingarfjoll magmas may relate to relatively high eruption temperatures and or the inhibition of degassing of the magma due to high ambient pressures and the consequent limitation of groundmass crystallisation

molecular and isotopic analysis of anaerobic methane oxidizing communities in marine sediments convergent lines of molecular carbon isotopic and phylogenetic evidence have previously indicated hinrichs k u hayes j m sylva s p brewer p g delong e f 1999 methane consuming archaebacteria in marine sediments nature 398 802 805 that archaea are involved in the anaerobic oxidation of methane in sediments from the eel river basin offshore northern california now further studies of those same sediments and of sediments from a methane seep in the santa barbara basin have confirmed and extended those results mass spectrometric and chromatographic analyses of an authentic standard of sn 2 hydroxyarchaeol hydroxylated at c 3 in the sn 2 phytanyl moiety have confirmed our previous tentative identification of this compound but shown that the previously examined product was the mono tms rather than di tms derivative further analyses of 13 c depleted lipids appreciably more abundant in samples from the santa barbara basin have shown that the archaeal lipids are accompanied by two sets of products that are only slightly less depleted in 13 c these are additional glycerol ethers and fatty acids the alkyl substituents in the ethers mostly monoethers with some diethers are non isoprenoidal the carbon number distributions and isotopic compositions of the alkyl substituents and of the fatty acids are similar suggesting strongly that they are produced by the same organisms their structures n alkyl and methyl branched n alkyl require a bacterial rather than archaeal source the non isoprenoidal glycerol ethers are novel constituents in marine sediments but have been previously reported in thermophilic sulfate and nitrate reducing organisms which lie near the base of the rrna based phylogenetic tree based on previous observations that the anaerobic oxidation of methane involves a net transfer of electrons from methane to sulfate it appears likely that the non archaeal 13 c depleted lipids are products of one or more previously unknown sulfate reducing bacteria which grow syntrophically with the methane utilizing archaea their products account for 50 of the fatty acids in the sample from the santa barbara basin at all methane seep sites examined the preservation of aquatic products is apparently enhanced because the methane oxidizing consortium utilizes much of the sulfate that would otherwise be available for remineralization of materials from the water column

morphometric study of pillow size spectrum among pillow lavas measurements of h and v dimensions in the horizontal and vertical directions of pillows exposed in vertical cross section were made on 19 pillow lavas from the azores cyprus iceland new zealand tasmania the western usa and wales the median values of h and v plot on a straight line that defines a spectrum of pillow sizes having linear dimensions five times greater at one end than at the other basaltic toward the small size end and andesitic toward the large size end the pillow median size is interpreted to reflect a control exercised by lava viscosity pillows erupted on a steep flow foot slope in lava deltas can however have a significantly smaller size than pillows in tabular pillowed flows inferred to have been erupted on a small depositonal slope indicating that the slope angle also exercised a control pipe vesicles generally abundant in the tabular pillowed flows and absent from the flow foot pillows have potential as a paleoslope indicator pillows toward the small size end of the spectrum are smooth surfaced and grew mainly by stretching of their skin whereas disruption of the skin and spreading were important toward the large size end disruption involved increasing skin thicknesses with increasing pillow size and pillows toward the large size end are more analogous with toothpaste lava than with pahoehoe and are inferred from their thick multiple selvages to have taken hours to grow pseudo pillow structure is also locally developed an example of endogenous pillow lava growth that formed intrusive pillows between normal pillows is described from sicily isolated pillow like bodies in certain andesitic breccias described from iceland were previously interpreted to be pillows but have anomalously small sizes for their compositions it is now proposed that they may lack an essential attribute of pillows namely the development of bulbous forms by the inflation of a chilled skin and are hence not true pillows para pillow lava is a common lava type in the flow foot breccias it forms irregular flow sheets that are locally less than 5 cm thick and failed to be inflated to pillows perhaps because of an inadequate lava supply rate or too high a flow velocity

rare earth elements as tracers for microbial activity and early diagenesis a new perspective from carbonate cements of ancient methane seep deposits abstract ancient methane seep carbonates are geological archives of environmental conditions and record past microbial activity to better understand the information stored in this archive a comparison was made of phase specific major trace and rare earth element ree patterns mineralogies and textures of two early diagenetic carbonate phases in five ancient methane seep deposits including oligocene limestones from the satsop and canyon rivers washington state the cretaceous tepee buttes colorado and the carboniferous ganigobis limestones namibia 1 cryptocrystalline yellow aragonite and 2 banded and botryoidal aggregates of clear fibrous aragonite typify many phanerozoic seep limestones and are common features of authigenic seep carbonates forming close to the sediment water interface today light ree enrichment in yellow aragonite is observed together with high organic matter contents indicated by intense autofluorescence of yellow aragonite and occurs in combination with low mg sr ratios conversely heavy ree enrichment is observed in neomorphic yellow calcite spar typified by high mg sr ratios indicating progressive diagenetic alteration during early diagenesis in marine pore waters affected by a succession of biogeochemical reactions these observations suggest that ree contents and patterns of early diagenetic carbonate phases are a function of the quality of preservation transformation of primary aragonite to calcite resulting from changing pore water compositions during later stage early diagenesis is apparently capable to significantly modify elemental composition the new results reveal that rare earth elements do not necessarily behave conservatively if early diagenesis is controlled to a large extent by evolving pore water compositions in environments strongly affected by biogeochemical processes for such settings a careful assessment of diagenetic alteration is consequently required before calcite resulting from aragonite transformation can be used for reliable paleoenvironment reconstruction