the magmatic plumbing system of the askja central volcano iceland as imaged by seismic tomography the magmatic plumbing system beneath askja a volcano in the central icelandic highlands is imaged using local earthquake tomography we use a catalog of more than 1300 earthquakes widely distributed in location and depth to invert for the p wave velocity vp and the vp vs ratio extensive synthetic tests show that the minimum size of any velocity anomaly recovered by the model is 4 km in the upper crust depth 8 km below sea level bsl increasing to 10 km in the lower crust at a depth of 20 km bsl the plumbing system of askja is revealed as a series of high vp vs ratio bodies situated at discrete depths throughout the crust to depths of over 20 km we interpret these to be regions of the crust which currently store melt with melt fractions of 10 the lower crustal bodies are all seismically active suggesting that melt is being actively transported in these regions the main melt storage regions lie beneath askja volcano concentrated at depths of 5 km bsl with a smaller region at 9 km bsl their total volume is 100 km3 using the recorded waveforms we show that there is also likely to be a small highly attenuating magmatic body at a shallower depth of about 2 km bsl

a tale of shales the relative roles of production decomposition and dilution in the accumulation of organic rich strata middle upper devonian appalachian basin abstract a new consensus on the processes responsible for organic carbon burial in ancient epeiric seas has emerged more firmly grounded in the uniformitarian framework of modern oceanography and biogeochemistry this consensus recognizes the interdependent roles of sedimentation primary production and microbial metabolism in favor of earlier end member models e g production vs preservation in this study one of the classic stratigraphic sequences upon which the preservation end member was based is re interpreted in light of this new consensus the study employs an extensive new sedimentological biogeochemical database from cores drilled in western new york the database spans over 500 m and 15 my of devonian deposition in the appalachian basin and provides a framework for comparative study of organic matter burial the major conclusions are 1 few organic rich units were deposited under pervasive anoxic sulfidic water columns 2 establishment and breakdown of seasonal thermoclines on annual or longer timescales were the predominant mode of stratification and 3 under such conditions remineralization of bio limiting nutrients may have played a key role in organic matter burial by creating a eutrophication pump this pump may have augmented an already rising nutrient inventory such that productivity levels exceeded the threshold required for development of suboxic to anoxic conditions in sediments and episodically in bottom waters a final conclusion asserts that the master variable for organic matter accumulation was relative sea level change which exerted influence on clastic dilution preservation and production processes sea level rise events led to sediment starvation and organic carbon concentration in distal basin sediments as well as to decreased effectiveness of seasonal mixing and thus longer build up intervals for remineralized nutrients episodic mixing of nutrient enriched bottom waters led to enhanced production ultimately increased clastic sediment delivery and water column mixing during relative sea level fall diluted surface sediment organic content such that respiratory demand could be met by increased oxygen supply thus terminating deposition of strata enriched in organic carbon

evidence for gloeocapsomorpha prisca in late devonian source rocks from southern alberta canada abstract organic rich intervals within the late devonian camrose member of southern alberta canada show optical and chemical characteristics very similar to those of ordovician samples whose organic matter is dominated by gloeocapsomorpha prisca derived alginite this includes saturate fraction gas chromatograms dominated by n alkanes with a pronounced odd carbon number up to c19 and much lower abundances of c19 n alkanes acyclic isoprenoids and biomarkers microscopy reveals these samples contain g prisca like alginite with a morphology that previously has been suggested for the growth of this organism under higher salinity conditions which is in agreement with the depositional environment of the camrose member one unusual feature of the g prisca rich samples is the very high concentration of c21 and c23n alkylnaphthalenes and n alkylbenzenes in the aromatic fractions of their extracts the origin of these compounds is not known but their occurrence could be related to the high concentrations of c21 and c23n alkyl phenols that have been noted in pyrolysates of estonian kukersites by previous workers other camrose member extracts show very different distributions that are more typical for carbonates deposited under anoxic higher salinity conditions many oils that occur in nisku formation reservoirs in the enchant hays field in southern alberta show saturate fraction gas chromatograms and other evidence that indicate an important contribution to these oils from the g prisca rich intervals these are thought to have a contribution from camrose member source rocks hence caution should be used in only attributing g prisca geochemical characteristics to cambro ordovician oils as on rare occasions they can also occur in younger source rocks and their derived oils

geochemical characterisation of middle devonian oils in nw alberta canada possible source and maturity effect on pyrrolic nitrogen compounds abstract molecular geochemical compositions of a suite of middle devonian sourced and reservoired oils from the rainbow zama shekilie sub basins in n w alberta canada reveal the presence of at least two oil families in the study area the distribution of each oil family is geographically restricted to a single sub basin consistent with the oils being sourced locally within a series of closed generation migration trapping systems the diversity in the biomarker distributions of the oils indicates the wide range of depositional environments and source materials existing in each sub basin rather than mixing of end member oils across different sub basins clear maturity differences are observed between the oils from the rainbow and zama subbasins pre cretaceous thermal anomalies along the reactivated regional precambrian basement faults are proposed as one of the major causes for the relatively high maturity levels for the middle devonian source rocks in the study area we infer that depositional environment and thermal maturity have had a strong impact on the geochemical characteristics of the saturated and aromatic hydrocarbons in the rainbow shekilie zama oils but may not influence the pyrrolic nitrogen compounds to a significant extent however recognition of possible source and maturity effects on pyrrolic nitrogen compounds in other studies suggests that these factors should be considered before the pyrrolic nitrogen compounds are used to characterize petroleum migration

water column euxinia and wildfire evidence during deposition of the upper famennian hangenberg event horizon from the holy cross mountains central poland a palynological study of the uppermost famennian section from kowala quarry holy cross mountains central poland allowed recognition of two miospore zones lv retispora lepidophyta apiculiretusispora verrucosa and ln retispora lepidophyta verrucosisporites nitidus based on palynology and sedimentology the black shale within the upper part of the section is identified as equivalent to the hangenberg black shale which is known globally this black shale contains compounds characteristic of photic zone euxinia including isorenieratane and its derivatives such compounds are absent in the organic poor marls and shales occurring below the ln zone and are present only as traces in the layers just above the black shale indicating fluctuations in the oxygen minimum zone during uppermost famennian sedimentation palynofacies show high amounts of amorphous organic matter and prasinophyte concentrations in the black shale and a subsequent significant decrease of amorphous organic matter concomitant with a rapid increase of terrestrial input mainly miospores with common tetrads in the layers above the black shale this supports the relatively rapid change in the taxonomic composition of phytoplankton caused by fluctuations of the chemocline the whole succession corresponds to one sea level rise and fall the presence of high concentrations of peri condensed polycyclic aromatic hydrocarbons and large amounts of small charcoal particles at the hangenberg event horizon indicate the occurrence of wildfires such observations suggest that atmospheric o2 levels had exceeded the critical threshold of 13 above which wildfires may occur by latest famennian time

chemostratigraphy of the posidonia black shale sw germany ii assessment of extent and persistence of photic zone anoxia using aryl isoprenoid distributions aquatic depositional environments where anoxic conditions extend from bottom waters into the photic zone occurred frequently during the geologic past periods of photic zone anoxia pza can be recognized by the presence of specific lipids produced exclusively by the green sulphur bacteria chlorobiaceae that are preserved in the sedimentary record chlorobiaceae perform anoxygenic photosynthesis that requires light penetration into h2s saturated waters sediment samples integrate paleoenvironmental conditions over time intervals ranging from at best a few decades to more commonly several millennia photic zone anoxia recognized in paleoenvironmental analyses is thus defined as episodic with no further interpretation on the duration and persistence of the anoxic events we provide here a high resolution multiproxy chemostratigraphy study for the toarcian posidonia black shale from the dotternhausen section in sw germany in order to assess duration and seasonal fluctuation of photic zone anoxia based on the relative abundance of derivatives of chlorobiaceae lipids we assess the variability in the degree and persistence of photic zone anoxia using an aryl isoprenoid ratio air obtained by calculating the proportion of the short chain c13 17 versus the intermediate chain c18 22 aryl isoprenoids higher relative abundance of the short chain analogues is interpreted as indicating more intensive aerobic degradation of aryl isoprenoids air varies between values of 0 5 indicative of persistent pza phases and 3 0 for short termed episodic pza events absolute concentration of aryl isoprenoids is negatively correlated with the air which is in agreement with a progressive diagenetic breakdown of aryl isoprenoids the air decreases are validated using independent palecological and geochemical redox indicators for the posidonia shale in sw germany d 2004 elsevier b v all rights reserved

the slaufrudalur pluton southeast iceland an example of shallow magma emplacement by coupled cauldron subsidence and magmatic stoping the tertiary slaufrudalur pluton is the largest granitic intrusion exposed in iceland five glacial valleys cut through the uppermost 900 m of the pluton exposing spectacular sections through its roof walls and interior the wall contacts are subvertical and sharp only in the northeast and southwest is the wall contact characterized by brittle faulting the pluton roof is smooth at map scale so that the overall cross sectional shape of the pluton and its internal layering indicate emplacement by incremental floor sinking through cauldron subsidence a pronounced elongation of the pluton parallel to the trend of regional fissure swarms and its angular shape in map view indicate strong tectonic control on horizontal ring fault propagation whereas faulted wall contacts represent step over structures between the earlier formed ring faults on outcrop scale the roof contact exhibits numerous steps faults and apophyses associated with conjugate fracture sets that are parallel and perpendicular to the strike of the length of the pluton these structures were presumably formed by sequential inflation and deflation of the pluton during episodic magma intrusion and therefore are closely coupled to cauldron subsidence as a result of roof fracturing and magma injection along the fractures roof material is found partly or completely detached within the granite the slaufrudalur pluton therefore provides new insight into the coupling of the emplacement mechanisms of cauldron subsidence and magmatic stoping in the upper crust

molecular isotopic characterisation of hydrocarbon biomarkers in palaeocene eocene evaporitic lacustrine source rocks from the jianghan basin china immature organic matter in lacustrine source rocks from the jianghan basin eastern china was studied for distributions and stable carbon isotopic compositions 13 c of hydrocarbon biomarkers all of the bitumens contain isorenieratane 13 c ca 17 indicating the presence of chlorobiaceae and thus periods of euxinic conditions extended into the photic zone aliphatic hydrocarbon fractions are dominated by pristane and phytane and contain relatively low amounts of 4a and 4 methylsteranes c 30 13 c ca 16 believed to originate from 4 methylsterols in dinoflagellates 13 c values of gammacerane ca 24 and c 30 17 21 h hopane ca 23 are consistent with an origin from bacterivorous ciliates that fed on chlorobiaceae the bitumens contain low relative amounts of organo sulphur compounds one rock contains c 37 and c 38 n alkanes 13 c ca 36 derived from alkadienes and alkenones of prymnesiophytes the distributions of hydrocarbon biomarkers suggest that they were initially sulphurised during early diagenesis and later released during early thermal maturation

upper permian main dolomite microbial carbonates as potential source rocks for hydrocarbons w poland abstract various microbialite lithofacies were common in the shallow water environments which flourished under highly saline and arid climate conditions in the polish part of the zechstein upper permian main dolomite ca2 carbonates data came from detailed analysis of 78 cores from wells located at the southern and northern margins of the main dolomite basin in west poland microbialite lithofacies are represented by columnar planar and domal stromatolites clotted thrombolites and biolaminites developed in high to low energy environments within the upper slope lower parts of oolitic barrier shoal restricted lagoon and tidal flat and tidal channel zones in barrier environments ooids were predominant whereas in lagoonal settings microbial oncoids and peloids were common in basinal settings laminated dolomudstones formed which are regarded as hemipelagic and are partly pelagic microbial in origin microbial communities coexisted with algae and developed mainly within shallow marine environments microbialites are built of cyanobacterial filaments and organo mineral coccoidal forms possibly of bacterial origin organic geochemistry data confirm that organic matter was transformed by cyanobacteria and bacteria which may have played a main role in hydrocarbon generation this is confirmed by c29 to c35 hopanes pr ph ratio below 1 0 and the presence of gammacerane as typical for ca2 profiles the role and occurrence of algae as confirmed by c29 steranes in hydrocarbon generation was possibly minor thus it is concluded that the main dolomite microbialites could be the likely source rocks for hydrocarbons with calculated original toc values from 0 8 to ca 2 0 wt these units also form the reservoir rocks with porosities reaching 20

geochemical evidence for euxinia during the late devonian extinction events in the michigan basin u s a abstract several mass extinction events occurred in the late devonian but the trigger for these events remains elusive in this study geochemical evidence in the late devonian antrim shale michigan basin u s a records episodic euxinia contemporaneous with these extinction events diagnostic changes in iron proxy data and elevated trace metal enrichments correspond to the kellwasser crisis in this study carbon sulfur iron and trace metal geochemistry preserved in the antrim formation validates the establishment and expansion of euxinic conditions associated with the kellwasser crisis and the frasnian famennian boundary the strength of the sequential extraction iron mineral data presented here in concert with trace metal and sulfur isotope proxies provides definitive signatures of euxinia when other data may be more ambiguous in regard to paleoredox conditions during the time of the frasnian famennian boundary extensive sulfide oxidation at the chemocline the result of fe limiting conditions within the basin provides an alternative explanation for the oceanic decline in 34 s so 4 during and following the frasnian famennian event our geochemical evidence indicating the presence of anoxia in the michigan basin is consistent with data from other globally distributed locations euxinia should be considered a key driver for these global extinction events and possibly others such as the hangenberg event in the late devonian

ground deformation at soufriere hills volcano montserrat during 1998 2000 measured by radar interferometry and gps abstract we examine the motion of the ground surface on the soufriere hills volcano montserrat between 1998 and 2000 using radar interferometry insar to minimise the effects of variable atmospheric water vapour on the insar measurements we use independently derived measurements of the radar path delay from six continuous gps receivers the surfaces providing a measurable interferometric signal are those on pyroclastic flow deposits mainly emplaced in 1997 three types of surface motion can be discriminated firstly the surfaces of thick valley filling deposits subsided at rates of 150 120 mm year in the year after emplacement to 50 30 mm year two years later this must be due to contraction and settling effects during cooling the second type is the near field motion localised within about one kilometre of the dome both subsidence and uplift events are seen and though the former could be due to surface gravitational effects the latter may reflect shallow

crocetane a potential marker of photic zone euxinia in thermally mature sediments and crude oils of devonian age abstract crocetane an irregular c 20 isoprenoid in sediments generally associated with gas hydrate settings is a molecular indicator for the anaerobic oxidation of methane green sulfur bacteria gsb are the main source for specific aromatic carotenoids e g isorenieratane in sedimentary environments and are molecular indicators of photic zone euxinia pze the present study comprises a detailed molecular and isotopic study of crocetane and gsb derived carotenoids in devonian sediments of the western canada sedimentary basin wcsb covering a range of thermal maturities in addition a series of oils generated from devonian source rocks of the basin have been analysed for crocetane crocetane was found in ten sediments from the wcsb and in seven devonian wcsb crude oils its abundance was found to increase with thermal maturity whereas the components derived from c 40 derived carotenoids decrease steadily we were not able to identify 2 6 10 15 19 pentamethylicosane pmi neither in the duvernay formation sediments nor in the wcsb crude oils consistent with previous findings the preferred proposed natural product precursor for crocetane is thus gsb derived carotenoids this is corroborated by their similar structural features and the 13 c value of combined crocetane and phytane in these samples however contributions from other carotenoids cannot be fully excluded crocetane can provide evidence for pze conditions in highly mature samples and crude oils of devonian age

eutrophication by decoupling of the marine biogeochemical cycles of c n and p a mechanism for the late devonian mass extinction the late devonian mass extinction was unusually protracted and ecologically selective with preferential diversity losses among reefbuilding organisms and tropical shallow water faunas in general we have investigated the link between the extinction s unique characteristics and changes in biogeochemical cycling through analyses of the 13 c and c n p atomic ratios of organic matter buried across the kellwasser horizons in western new york state each horizon is characterized by 1 a long term 4 5 excursion in 13 c 3 of which occurs within the horizon and 2 a dramatic increase in the burial ratios of c n p from values of 100 15 1 to an average of 5000 170 1 on the basis of these results we propose that 1 increased efficiency of biolimiting nutrient recycling resulting from cyclic water column stratification and mixing promoted eutrophication during kellwasser deposition in new york and 2 the isotope excursions represent the composite effect of long term global organic c burial and local changes in photosynthetic c isotope fractionation related to nutrient availability this eutrophication model forges a mechanistic link between proposed late devonian climatic cooling and the selective demise of taxa likely to have been narrowly adapted to oligotrophic conditions

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

mudstones and embedded concretions show differences in lithology related but not source related biomarker distributions abstract the mudstones of the western australian gogo formation harbour numerous carbonate concretions which often contain preserved fossils of lagerstatte like quality these are especially notable in places where the mudstone has eroded giving way to nodule fields which afford valuable paleobiological records it is however a challenge to determine their paleoenvironmental context here we analysed concretions from a core drilled in the canning basin gogo formation at two different depths concretions were compared to the surrounding mudstone found at the same depth electron microscopy and x ray spectroscopy showed that the concretions were carbonate rich and contained detrital fragments biomarker data showed that mudstone and concretions had very similar distributions and presented marine biosignatures including indicators of anoxic depositional conditions a stratified water column and photic zone euxinia the concretions contained higher amounts of c 27 steranes indicating that more labile organic matter such as animal remains could have triggered concretion formation statistical analyses of the results showed that concretions and shales differed p p 31 homohopanes and hopane sterane ratios p

seismicity and subsidence following the 2011 nabro eruption eritrea insights into the plumbing system of an off rift volcano nabro volcano situated to the east of the afar rift zone erupted on 12 june 2011 eruptions at such off rift volcanoes are infrequent and consequently the plumbing systems are poorly understood we present posteruption synthetic aperture radar sar images from the terrasar x satellite and posteruption continuous seismic activity from a local seismic array interferometric analysis of sar data reveals a circular 12 km wide signal subsiding at 200 mm yr we inverted for the best fit mogi source finding a 4 1 107 m3 yr volume decrease at 7 1 km depth between 31 august and 7 october 2011 we located 658 and relocated 456 earthquakes with local magnitudes between 0 4 and 4 5 seismicity beneath the se edge of nabro at 11 km depth is likely associated with high strain rates from deep magma flow into the modeled reservoir this suggests that magma is supplied through a narrow conduit and then stored at 7 km depth we interpret seismicity at 4 6 km depth as brittle fracturing above the inferred magma reservoir focal mechanisms delineate a thrust fault striking ne sw and dipping 45 to the se across the caldera floor we propose that the crustal response is to slip on this fault which crosscuts the caldera rather than to deform on ring faults the ne sw fault plane is not associated with measurable surface deformation indicating that it does not contribute much to the caldera deformation we show that subsidence of the caldera is controlled by magma chamber processes rather than fault slip

origin of a rhyolite that intruded a geothermal well while drilling at the krafla volcano iceland magma fl owed into an exploratory geothermal well at 2 1 km depth being drilled in the krafl a central volcano in iceland creating a unique opportunity to study rhyolite magma in situ in a basaltic environment the quenched magma is a partly vesicular sparsely phyric glass containing 1 8 of dissolved volatiles based on calculated h 2 o co 2 saturation pressures it degassed at a pressure intermediate between hydrostatic and lithostatic and geothermometry indicates that the crystals in the melt formed at 900 c the glass shows no signs of hydrothermal alteration but its hydrogen and oxygen isotopic ratios are much lower than those of typical mantle derived magmas indicating that this rhyolite originated by anhydrous mantle derived magma assimilating partially melted hydrothermally altered basalts

magma sponge hypothesis and stratovolcanoes case for a compressible reservoir and quasi steady deep influx at soufriere hills volcano montserrat 1 we use well documented time histories of episodic gps surface deformation and efflux of compressible magma to resolve apparent magma budget anomalies at soufriere hills volcano shv on montserrat wi we focus on data from 2003 to 2007 for an inflation succeeded by an episode of eruption plus deflation we examine mogi type and vertical prolate ellipsoidal chamber geometries to accommodate both mineralogical constraints indicating a relatively shallow pre eruption storage and geodetic constraints inferring a deeper mean pressure source an exsolved phase involving several gas species greatly increases andesite magma compressibility to depths 10 km i e for water content 4 wt crystallinity 40 and this property supports the concept that much of the magma transferred into or out of the crustal reservoir could be accommodated by compression or decompression of stored reservoir magma i e the magma sponge our results suggest quasi steady deep mainly mafic magma influx of the order of 2 m3s 1 and we conclude that magma released in eruptive episodes is approximately balanced by cumulative deep influx during the eruptive episode and the preceding inflation our magma sponge model predicts that between 2003 and 2007 there was no evident depletion of magma reservoir volume at shv which comprises tens of km3 with radial dimensions of order 1 2 km in turn implying a long lived eruption

an integrated biomarker isotopic and palaeoenvironmental study through the late permian event at lusitaniadalen spitsbergen abstract the largest extinction of the phanerozoic occurred near the permian triassic p tr boundary some 252 ma ago several scenarios and drivers have been proposed for this event here we report for the first time an integrated study comprising sedimentological data biomarker distributions abundances and selected stable carbon and hydrogen isotopes along with bulk isotopes 34spyrite 13ccarb 13corg for a late permian section from lusitaniadalen spitsbergen norway sedimentological and geochemical data support a marine transgression and collapse of the marine ecosystem in the late permian strong evidence for waxing and waning of photic zone euxinia throughout the late permian is provided by chlorobiaceae derived biomarkers including 13c data and 34spyrite implying multiple phases of h2s outgassing and potentially several pulses of extinction a rapid decrease in abundance of various land plant biomarkers prior to the marine collapse event indicates a dramatic decline of land plants during the late permian and or increasing distance from palaeoshoreline as a consequence of sea level rise changes in d of selected biomarkers also suggest a change in source of organic matter om or sea level rise we also found biomarker and isotopic evidence for a phytoplanktonic bloom triggered by eutrophication as a consequence of the marine collapse compound specific isotope analyses csia of algal and land plant derived biomarkers as well as 13c of carbonate and bulk om provide strong evidence for synchronous changes in 13c of marine and atmospheric co2 attributed to a 13c depleted source the source could be associated with isotopically depleted methane released from the melting of gas clathrates and or from respired om due to collapse of the marine ecosystem

lipid biomarker stratigraphic records through the late devonian frasnian famennian boundary comparison of high and low latitude epicontinental marine settings abstract the pervasiveness of black shale preservation in association with late devonian biological crises suggests marine anoxia played a major role in driving ecological perturbations however devonian black shale deposition is still mechanistically poorly understood we have compiled detailed biomarker lipid chemostratigraphic records for 83 different rock samples using molecular constituents of bitumens of upper kellwasser equivalent black shales from two foreland basins from the low paleolatitude appalachian basin new york state and from the high paleolatitude madre de dios basin bolivia in order to better understand local environmental conditions and organic source inputs during this depositional event despite strong indications from stable nitrogen isotopic signatures for fixed nitrogen nutrient limitation the biomarker assemblages with consistently low moderate hopane sterane ratios 28 c 29 sterane ratios at higher paleolatitude in the more nutrient replete madre de dios basin suggest prasinophyte microalgae flourished in this setting in accordance with palynological evidence for high contributions of tasmanites cysts in these strata all samples contain only very low absolute amounts of aryl isoprenoids with 2 3 6 trimethyl substitution and other aromatic carotenoids up to several orders of magnitude lower than concentrations reported from other phanerozoic euxinic basins these data are consistent with local marine paleo redox models for both basins lacking a persistently shallow sulfidic aquatic zone and demonstrate that temporally persistent or spatially pervasive photic zone euxinia is not necessarily associated with all black shale sequences in the late devonian

the deep magmatic system of the campi flegrei caldera italy 1 melt inclusions in phenocrysts of the minopoli2 shoshonite and fondo riccio latite eruptive products campi flegrei caldera 10 2 to 9 5 ka bp constrain the nature of deep phlegraean magmatic fluids their role in volcanism and give new insights into the magmatic plumbing system the analyzed melt inclusions show that co2 is an abundant gaseous species confirming the results of geochemical studies on the magmatic gas fraction involved in present day fumarolic emissions volatile concentrations within the melt inclusions require gas melt equilibria between 8 and 9 km depth and closed system degassing in presence of ascending co2 rich fluids of deep provenance magmas later re equilibrate at depths up to 3 2 km i e above the top of the carbonate basement these observations correlate well with independent geophysical and geochemical evidence and are useful constraints for volcanic hazards assessment at campi flegrei

biomarkers reveal the role of photic zone euxinia in exceptional fossil preservation an organic geochemical perspective photic zone euxinia pze has proven important for elucidating biogeochemical changes that occur during oceanic anoxic events including mass extinction and conditions associated with unique fossil preservation organic geochemical analyses of a 380 ma invertebrate fossil which included well preserved soft tissues from the gogo formation canning basin western australia showed biomarkers and stable isotopic values characteristic of pze and a consortium of sulfate reducing bacteria which lead to exceptional fossil and biomarker preservation the carbonate concretion contained phytoplankton green sulfur bacteria chlorobi and sulfate reducing bacteria biomarkers with an increasing concentration toward the nucleus where the fossil is preserved the spatial distribution of cholestane unequivocally associated with the fossilized tissue and its high relative abundance to the total steranes suggest that the fossil is a crustacean the presence of an active sulfur cycle in this devonian system including sulfate reduction and the resulting pze played a pivotal role in the preservation of soft tissue from the fossil and its associated low maturity biomarker ratios

geochemical characteristics of early carboniferous petroleum systems in western australia abstract a geochemical study was conducted to establish oil oil correlations and evaluate potential source rocks within the latest devonian earliest carboniferous succession of the onshore canning basin western australia aromatic hydrocarbons together with the routinely used saturated biomarker ratios and stable carbon isotopes demonstrate that the recently discovered ungani oilfield located on the southern margin of the fitzroy trough are similar but not identical to the early carboniferous larapintine 4 l4 oil family present to the north of the fitzroy trough on the lennard shelf the l4 oil family has been correlated to a lower carboniferous tournaisian source rock core sample from the laurel formation at blackstone 1 although its bulk geochemical properties signify that it could generate substantially more gas than liquid hydrocarbons the ungani oils can be distinguished from the l4 oils by their higher concentrations of paleorenieratane and isorenieratane coupled with more depleted 13c values for n alkanes pristane and phytane compared with other components hopane isomerisation ratios show distinct grouping of the two oil families that reflect both source and maturity variations the oil from wattle 1 st1 on the lennard shelf has an unusual composition exhibiting some molecular and isotopic features similar to both the l4 and ungani oils source rocks for the ungani and wattle 1 st1 oils are unknown since their geochemical signature does not match that of the tournaisian laurel formation or the middle upper givetian frasnian devonian gogo formation which sourced the devonian reservoired larapintine 3 oils at blina and janpam north 1 it is postulated that such potential oil prone source rocks could occur within the famennian tournaisian succession

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

palaeozoic and mesozoic tectonic evolution and palaeogeography of east asian crustal fragments the korean peninsula in context east and southeast asia comprises a complex assembly of allochthonous continental lithospheric crustal fragments terranes together with volcanic arcs and other terranes of oceanic and accretionary complex origins located at the zone of convergence between the eurasian indoaustralian and pacific plates the former wide separation of asian terranes is indicated by contrasting faunas and floras developed on adjacent terranes due to their prior geographic separation different palaeoclimates and biogeographic isolation the boundaries between asian terranes are marked by major geological discontinuities suture zones that represent former ocean basins that once separated them in some cases the ocean basins have been completely destroyed and terrane boundaries are marked by major fault zones in other cases remnants of the ocean basins and of subduction accretion complexes remain and provide valuable information on the tectonic history of the terranes the oceans that once separated them and timings of amalgamation and accretion the various allochthonous crustal fragments of east asia have been brought into close juxtaposition by geological convergent plate tectonic processes the gondwana derived east asia crustal fragments successively rifted and separated from the margin of eastern gondwana as three elongate continental slivers in the devonian early permian and late triassic late jurassic as these three continental slivers separated from gondwana three successive ocean basins the palaeo tethys meso tethys and cenotethys opened between these and gondwana asian terranes progressively sutured to one another during the palaeozoic to cenozoic south china and indochina probably amalgamated in the early carboniferous but alternative scenarios with collision in the permo triassic have been suggested the tarim terrane accreted to eurasia in the early permian the sibumasu and qiangtang terranes collided and sutured with simao indochina east malaya in the early middle triassic and the west sumatra terrane was transported westwards to a position outboard of sibumasu during this collisional process the permo triassic also saw the progressive collision between south and north china with possible extension of this collision being recognised in the korean peninsula culminating in the late triassic north china did not finally weld to asia until the late jurassic the lhasa and west burma terranes accreted to eurasia in the late jurassic early cretaceous and proto east and southeast asia had formed palaeogeographic reconstructions illustrating the evolution and assembly of asian crustal fragments during the phanerozoic are presented d 2005 international association for gondwana research published by elsevier b v all rights reserved

extent and persistence of photic zone euxinia in middle late devonian seas insights from the canning basin and implications for petroleum source rock formation abstract late devonian mass extinctions attributed to extensive anoxia and or euxinia of the oceans are associated with widespread deposition of organic rich shales also in the epeiric waters of the canning basin western australia photic zone euxinia pze prevailed during the givetian frasnian with geochemical evidence for pze on the northern lennard shelf and southern barbwire terrace margins of the fitzroy trough on the lennard shelf shales record episodic pulses of pze associated with high algal activity due to enhanced nutrient supply whereas a restricted marine setting on the barbwire terrace is thought to be the main driver for the development of persistent pze and associated bacterial predominance structural evidence indicates that the fitzroy trough was a confined basin during the late devonian with the possibility of limited ocean circulation widespread pze is expected to have developed in the poorly mixed water column if the basin received sufficient nutrient supply for enhanced primary production notwithstanding the presence of anoxia during deposition of potential source rocks only two small devonian sourced oil fields and numerous oil shows have been found in the canning basin biomarker assemblages show that the oils produced from the lennard shelf fields i e blina 1 blina 4 and janpam north 1 have substantially different molecular compositions to the minor oil recovered from mirbelia 1 on the barbwire terrace a correlation was established between the lennard shelf oils and rock extracts from the gogo formation at blina 1 and mcwhae ridge 1 based on their hopane sterane and carotenoids abundances a definitive source correlation was not obtained for the mirbelia 1 oil but it did show some genetic affinity to the givetian frasnian extracts from the barbwire terrace suggesting that local source rocks are developed in the region

steady state characteristics of the greenland ice sheet under different climates the greenland ice sheet is modelled to simulate its extent and volume in warmer climates and also to find out whether the ice sheet would re form on theice free bedrock under present climatic conditions the ice sheet model is a three dimensional thermo mechanical model with a fine resolution grid thebedrock surface beneath the ice sheet was mapped using radio echo sounding measurements by the electromagnetic institute copenhagen the modelexperiments show that increased temperature will result in ice margin retreat but the ice sheet is relatively stable it takes a rather high temperature rise of atleast 6ic for the ice sheet to disappear completely which indicates that the ice sheet probably survived the last interglacial also it appears that the greenlandice sheet is not a mere relict ice mass from a previously colder climate but that the ice sheet will still re form on the bare bedrock under the present or evenslightly warmer climatic conditions

implications of magma transfer between multiple reservoirs on eruption cycling volcanic eruptions are episodic despite being supplied by melt at a nearly constant rate we used histories of magma efflux and surface deformation to geodetically image magma transfer within the deep crustal plumbing of the soufriere hills volcano on montserrat west indies for three cycles of effusion followed by discrete pauses supply of the system from the deep crust and mantle was continuous during periods of reinitiated high surface efflux magma rose quickly and synchronously from a deflating mid crustal reservoir at about 12 kilometers augmented from depth during repose the lower reservoir refilled from the deep supply with only minor discharge transiting the upper chamber to surface these observations are consistent with a model involving the continuous supply of magma from the deep crust and mantle into a voluminous and compliant mid crustal reservoir episodically valved below a shallow reservoir at about 6 kilometers

the rheology of two phase magmas a review and analysis abstract we consider the current state of our understanding of the rheology of two phase magmas that is suspensions of either bubbles or crystals in a viscous silicate melt the discussion is restricted to strain rates at which the suspending melt can be considered newtonian we start by considering the range of textures found in magmas and the bubble deformation and particle motions caused by shearing we then review proposed models for suspensions focussing on those functions of the form r f or f that have been most widely used to describe magmatic systems r is the relative apparent viscosity of the suspension is the volume fraction of the suspended phase is the driving stress and is the strain rate both theoretical and empirical methods are presented and then compared against the available analogue i e non magmatic and magmatic data the paper contains new data and significant re analysis of previously published data we present a new semi empirical constitutive model for bubble bearing magmas that is valid for steady and unsteady flow and large strains and strain rates this equation utilises a new parameter the capillarity cx that encapsulates the combined effect of shearing and unsteadiness on bubble suspensions we also present a new scheme for dealing with polydispersivity of bubble suspensions new data on the rheology of particle suspensions undergoing forced oscillations are presented these data show that the cox merz rule only holds for dilute particle suspensions 0 25 a re analysis of all available experimental data that relate rheology to particle aspect ratio provides distinct curves of maximum packing as a function of aspect ratio for smooth and rough particles with magmatic data lying on the curve appropriate for rough particles we analyse several rheological datasets of crystal bearing basaltic magmas and find that they are in good agreement with the constitutive equations derived from analogue data by contrast the same equations do not agree well with data for high viscosity haplogranitic melts this may be an effect of fracturing or viscous dissipation within these samples the paper concludes with a practical rheological recipes section giving a step by step method for calculating a constitutive equation for a two phase magmatic suspension and assessing its likely accuracy

a two magma chamber model as a source of deformation at grimsvotn volcano iceland grimsvotn volcano is the most active volcano in iceland and its last three eruptions were in 1998 2004 and 2011 here we analyze the displacement around grimsvotn during these last three eruptive cycles using 10 gps stations the observed displacements in this region generally contain a linear component of tectonic and glacio isostatic origin in agreement with the previously estimated values of plate motions and vertical rebound larger amplitude deformation observed close to grimsvotn at the gfum continuous gps station clearly reflects a major volcanic contribution superimposed on a tectonic component we estimate and subtract the tectonic trend at this station using regional observed displacement the direction and pattern of the residual volcanic displacement for coeruptive and intereruptive periods are consistent for all three of these eruptive cycles the posteruptive inflation is characterized by an exponential trend followed by a linear trend in this study we explain this temporal behavior using a new analytic model that has two connected magma chambers surrounded by an elastic medium and fed by a constant basal magma inflow during the early posteruptive phase pressure readjustment occurs between the two reservoirs with replenishment of the shallow chamber from the deep chamber afterward due to the constant inflow of magma into the deep reservoir the pressurization of the system produces linear uplift a large deep reservoir favors magma storage rather than surface emission based on displacement measured at gfum station we estimate an upper limit for the radius of the deep reservoir of 10 km

identification of aryl isoprenoids in source rocks and crude oils biological markers for the green sulphur bacteria abstract a series of c13 to c31 aryl isoprenoids 1 alkyl 2 3 6 trimethylbenzenes have been identified in reef hosted oils and their source rocks from the middle and upper silurian of the michigan basin and middle devonian of the alberta basin canada their structure has been confirmed by unambiguous synthesis of the c14 member of the series their structure and isotopic composition indicate that they are derived from isorenieratene from the chlorobiaceae family of sulphur bacteria these results are consistent with geological and geochemical studies that show that the source rocks were deposited under metahaline to hypersaline sulphate and sulphide rich water columns the distribution of other biomarkers in these oils and source rocks indicates that a diverse biota contributed organic matter to the source environment in conjunction with the aryl isoprenoids they show that there is a remarkable similarity in composition between the two sets of oils and source rocks despite their great temporal and geographic separation this reflects the similarity of their environments and emphasizes the importance of sedimentary facies in controlling the composition of organic matter in source rocks and their derived oils

reconstruction of the glacial ice covers of greenland and the canadian arctic islands by three dimensional perfectly plastic ice sheet modelling a three dimensional perfectly plastic ice sheet model developed for determining the surface elevations and the flow pattern of an ice sheet with given bottom topography and ice margin positions is applied to the reconstruction of the glacial ice covers of greenland and the canadian arctic islands in the northern regions two different reconstructions have been performed with ice margins along the present 600 and 200 m sea depth contours respectively in central greenland the ice margin is considered to be at the outermost ice margin deposits on the coastal shelf to the west and at the present 200 m sea depth contour to the east the main conclusions to be drawn from the reconstructions are 1 the flow pattern of the glacial ice cover of greenland shows a great resemblance to the present one the central ice divide being displaced less than 50 km from its present position and being no more than 200 m higher than today 2 the main ice divide of the ice sheet covering the canadian arctic islands the innuitian ice sheet was located over the highlands of eastern ellesmere island with local domes positioned over the present ice caps indicating that even the deep ice of wisconsin age in these ice caps is of local origin this is also the case for the devon island ice cap 3 even in the not very likely case of a rather extensive glacial ice cover in north west greenland the ice flow pattern upstream of the camp century deep drill site would not have changed radically compared to the present flow pattern thus it is concluded that even advanced ice margins in late wisconsin time could at most have resulted in an elevation of the deposition site of the late wisconsin ice at camp century 600 m higher than at present the consequences of this conclusion are discussed

the mechanics of sill inception propagation and growth experimental evidence for rapid reduction in magmatic overpressure abstract a model of magma propagation in the crust is presented using a series of analogue experiments where dyed water is injected at a constant flux into layers of solidified gelatine the gelatine layers are transparent and when intruded deform in an almost ideal elastic manner under the experimental conditions low gelatine concentration 2 5 or 3 wt and low temperature 5 10 c the upper gelatine layer was 1 0 to 1 5 times stiffer than the lower layer with either a weak or strong interface strength between the gelatine layers the gelatine is seeded with 20 50 m diameter pmma rhb neutrally buoyant particles that are fluoresced by a pulsed vertical laser sheet centred on the injection point digital image correlation dic is used to calculate incremental strain and finite strain in the deforming host material as it is intruded this is mapped in 2d for the developing experimental volcanic plumbing system that comprises a feeder dyke and sill since the gelatine deforms elastically strain measurements correlate with stress our results indicate that for constant magma flux the moment of sill inception is characterised by a significant magmatic pressure decrease of up to 60 this is evidenced by the rapid contraction of the feeder dyke at the moment the sill forms sill propagation is then controlled by the fracture properties of the weak interface with fluid from the feeder dyke extracted to help grow the sill pressure drops during sill inception and growth are likely to be important in volcanic systems where destabilisation of the magmatic plumbing system could trigger an eruption

detecting the source of heinrich layers an organic geochemical study 1 there are controversies regarding the origin of heinrich layer 3 h3 the massive ice rafting and meltwater event in the north atlantic during the last glacial cycle spanning a time window between 29 and 30 kyr b p some argue in favor of a laurentide ice sheet source similar to other heinrich layers while a contending view argues for the european ice sheet source existing geochemical proxies such as 40ar 39ar 206pb 204pb or nd etc could not be used to distinguish among various sources of ice rafted debris in h3 because of their low abundances suggesting a background glacial sediment signal in order to circumvent this problem a biomarker based approach is used to characterize the provenance of h layers 2 3 and 4 and other non heinrich layers the presence of hopanes and steranes and their aromatic counterparts in the h layers is incompatible with recent sediments and is attributed to the transportation of organic matter because of the glacial erosion of source rocks the most diagnostic and useful signatures of this ancient organic matter in the h layers are the dominance of c34 hopanoids over c33 and the occurrence of isorenieratane along with palaerenieratane biomarkers signatures in h layers 2 and 3 of the labrador sea suggest no difference in their source hydrocarbon distributions suggest that these sediments were derived from the middle to late ordovician and silurian source rocks of the hudson bay of eastern canada biomarker data of the h layer 4 from the northwest atlantic reveal that the sediments of this layer have a similar source to the h layers in the labrador sea

organic geochemistry and palynofacies of the early middle frasnian transition late devonian of the holy cross mountains southern poland abstract geochemical and palynological investigation of the lower to middle frasnian reef to basin succession at the well known kowala quarry holy cross mountains demonstrates the variable character of organic matter om deposited in different oxidative reductive conditions during sedimentation of the basinal deposits anoxic conditions in the water column prevailed in the organic rich sediments deposited during the palmatolepis punctata zone set d anoxia occurred in the photic zone as inferred from the presence of isorenieratane aryl isoprenoids and gammacerane in the same kind of deposits but occurring during the palmatolepis hassi zone set f anoxia apparently occurred mainly in the deeper parts of the basin and only sporadically reached the photic zone this interpretation is based on the lack of isorenieratane traces of aryl isoprenoids and the presence of gammacerane in the investigated samples the basinal clay enriched sediments of sets d and f are divided by an organic poor set e typical for the carbonate platform fore reef environment characterized by oxic conditions a palynostratigraphical study of the frasnian section from the kowala quarry allowed recognition of two miospore zones geminospora semilucensa perotrilites donensis sd and archaeoperisaccus ovalis verrucosisporites grumosus og relatively small quantitative and qualitative changes of the organic particles miospores tracheids prasinophytes and acritarchs are interpreted primarily in terms of sea level fluctuations and enhanced productivity in particular the appearance of abundant abnormally large mature leiospheres in set d can be the result of progressive eutrophication related to environmental changes recorded in the recently detected major positive carbon isotope anomaly as during the frasnian famennian mass extinction interval this eutrophication could have been stimulated by a rapid increase in primary production and subsequently expanding anoxic conditions but it is evident only in the early phase of the middle frasnian 13 c excursion the processes of the secondary hydrothermal fluid migration taking place after the lithification of the sediments caused partial om oxidation the products of these processes are such phenyl derivatives of aromatic hydrocarbons as phenylphenanthrenes terphenyls phenyldibenzothiophenes and phenyldibenzofurans moreover an oxygen compound rarely described from sedimentary om dibenzo p dioxin and its methyl and dimethyl derivatives seems to be the additional product of hydrothermal om oxidation

shallow axial magma chamber at the slow spreading erta ale ridge thermal models predict that spreading velocity at mid ocean rifts should influence the geometry of the underlying magma chamber insar data from the slow spreading ethiopian rift identify a shallow elongated magma chamber a feature usually associated with fast spreading rifts beneath the erta ale segment implying that spreading velocity may not be so important after all

seismic attenuation imaging of campi flegrei evidence of gas reservoirs hydrothermal basins and feeding systems 1 passive high resolution attenuation tomography is used here to image the geological structure in the first upper 4 km of the shallow crust beneath the campi flegrei caldera southern italy the inverse q was estimated for each source receiver path using the coda normalization method s waves and the slope decay method p waves and s waves inversion was performed using a multi resolution method which ensures a minimum cell size resolution of 500 m the study of the resolution matrix as well as the synthetic tests guarantee an optimal reproduction of the input anomalies in the center of the caldera between 0 and 3 5 km in depth high attenuation vertical structures are connected at the surface with the main volcanological features e g the solfatara and mofete fumarole fields and depict vertical q contrast imaging important geological structures such as the la starza fault these high attenuation volumes extend between the surface and a depth of about 3 km where a hard rock layer is imaged by the sharp contrast of the quality factors the retrieved image of the campi flegrei has been jointly interpreted taking into account evidence from seismological geological volcanological and geochemical investigations this analysis has allowed an unprecedented view of the feeding systems in this area and in particular it recognizes the vertically extending high attenuation structures that correspond to gas or fluid reservoirs beneath pozzuoli solfatara solfatara mofete mt nuovo and agnano this high attenuation system is possibly connected with the magma sill revealed at about 7 km in depth by passive travel time tomography

elastic deformation models of krafla volcano iceland for the decade 1975 through 1985 the dynamics of the shallow magma reservoir at krafla volcano in ne iceland have been analyzed with three types of elastic models based on over 70 surveys of tilt and displacement made from 1975 to 1985 a period of continuous volcano tectonic activity modeling results are integrated with geophysical and geological information to estimate the position geometry and volume change of magma reservoir domains subjected to periodic inflation and deflation dominating influences on magma reservoir dynamics are examined in the context of activity in krafla s associated rift system and the deformation of its caldera from 1975 1985 rather than the fluid filled cavity concept of mogi 1958 and most recent workers our models are idealized as strained regions with spherical double spherical or general ellipsoidal symmetry the models are mathematically generalized from that of mogi 1958 and are derived by inversion of displacements model results from different displacement components are remarkably consistent although models based on vertical displacements typically have errors of fit much closer to expected measurement errors than those based on tilt or horizontal displacements about one half of the double sphere and ellipsoid models have significantly better fits than single sphere models double sphere model results are consistent with a 2 to 3 km center to center separation of magma storage zones from at least 2 km to 4 km depth by portions of the fissure system as implied by s wave attenuation patterns for 1976 1977 however all models suggest pressurization zones of more limited extent than possible domains of storage inferred from s wave attenuation ellipsoid models typically implied unrealistically shallow depths of magma storage caldera inflation rates decreased after january 1978 when the caldera periodically reinflated to its level prior to the initial december 1975 deflation event from 1975 1980 the volume and duration of inflation between deflation events was strongly correlated with the volume of the previous deflation after 1980 there was a significant increase in the duration of inflation periods and a decrease in rates of caldera inflation and fissure system widening consistent with these results the magma reservoir is conceptualized as a hot rock mass containing numerous magma chambers and pressure sensitive conduits connecting the chambers and deep magma sources magma is injected into the fissure system at critical pressures determined by the confining stress and rock mass strength the duration and volume of inflation required to reach a critical pressure threshold is largely dependent on the volume of magma released in the previous deflation reduction of the extension rate across the krafla fissure system after 1980 suggests that extensional forces were also reduced a resultant rise of confining pressure on the magma reservoir and a reduced capacity of the fissure system to accommodate dike injection in combination would have increased critical stress levels for reservoir deflation and reduced the pressure gradient driving magma supply from deep sources

subsidence of askja caldera 2000 2009 modelling of deformation processes at an extensional plate boundary constrained by time series insar analysis abstract many calderas in the world show long term unrest in the form of elevated rates of deformation and seismicity related to pressure changes and magma movements within their magmatic plumbing systems we present new observations of the style of deformation at the askja caldera iceland since 2000 using interferometric analysis of synthetic aperture radar images insar acquired by the canadian radarsat 2 satellite when combined with previously acquired detailed geodetic observations by various techniques we obtain an overview of askja s behaviour through more than four decades the combined dataset reveals that during this non eruptive period askja continuously subsides at a rate of 2 5 3 cm yr in 2000 2009 somewhat lower than the 5 cm yr rate inferred for the 1983 1998 period this behaviour of askja is evaluated and compared to those of other restless calderas the wrapped interferograms show three main features 1 concentric fringes depicting subsidence in the centre of the main askja caldera 2 oval fringes elongated along the rift portraying subsidence and 3 subsidence in an area north of the vatnajokull glacier the average line of sight los velocity from ground to satellite was used as input for inverse modelling of a deflating pressure source beneath the caldera embedded in a homogeneous elastic half space two different source geometries were tested a point pressure source and a horizontal penny shaped crack the concentric fringes centred in the askja caldera are best fit by a point source located at 65 05 n 16 78 w at a depth of 3 2 3 8 km with a volume decrease of 0 0012 0 0017 km3 yr from 2000 to 2009 consistent with previous studies provisional 2d fem models including structural complexities in the crustal layers indicate that the tectonic setting of askja plays an important role in the continuous long term high subsidence rates observed there in order to fully understand the cause and effects of the complicated tectonic setting we encourage the use of a more realistic rheological model of the area which could lead to reinterpretation of previous model results

molecular and petrographic indicators of redox conditions and bacterial communities after the f f mass extinction kowala holy cross mountains poland abstract pyrite framboid diameter analysis and organic geochemistry of the triangularis crepida boundary section at kowala holy cross mountains poland imply suboxic to oxic and sporadically euxinic bottom waters during the lower famennian in addition morphological web like structures typical for microbial mats as well as the recognition of 2 methylhopanes and monomethyl alkane cyanobacteria biomarkers is evidenced of microbial activity after the global frasnian famennian f f extinction event the presence of cyanobacterial mats also suggests suboxic to oxic environments and at the same time photic bottom water conditions however isorenieratane and its derivatives were detected in almost all samples the presence of this well known biomarker of green sulfur bacteria implies that euxinic conditions were present in the upper part of the water column at least intermittently or that temporal euxinia occurred in the water column presence of euxinic conditions is confirmed by the occurrence of small sized pyrite framboids which were particularly dominant in the lower part of the section the shift towards low 13 c values in both micritic limestones and in sedimentary organic matter seen at the beginning of the period of diminished photic zone might reflect an influx of newly respired co 2 to surface waters caused by enhanced respiration at depth after the f f transition in the checiny zbrza basin

effective petroleum source rocks of the world stratigraphic distribution and controlling depositional factors six stratigraphic intervals representing one third of phanerozoic time contain petroleum source rocks that have provided more than 90 of the world s discovered original reserves of oil and gas in barrels of oil equivalent the six intervals are 1 silurian generated 9 of the world s reserves 2 upper devonian tournaisian 8 of reserves 3 pennsylvanian lower permian 8 of reserves 4 upper jurassic 25 of reserves 5 middle cretaceous 29 of reserves and 6 oligocene miocene 12 5 of reserves this uneven distribution of source rocks in time displays no obvious cyclicity and the factors that controlled the formation of source rocks vary from interval to interval maps that show facies structural forms and petroleum source rocks were prepared for this study analysis of the maps indicates that several primary factors controlled the areal distribution of source rocks their geochemical type and their effectiveness i e the amounts of discovered original conventionally recoverable reserves of oil and gas generated by these rocks these factors are geologic age paleolatitude of the depositional areas structural forms in which the deposition of source rocks occurred and the evolution of biota the maturation time of these source rocks demonstrates that the majority of discovered oil and gas is very young almost 70 of the world s original reserves of oil and gas has been generated since the coniacian and nearly 50 of the world s petrole m has been generated and trapped since the oligocene the term petroleum as used in this study includes oil gas condensate and gas but does not include bitumen and other solid and semisolid oil derivatives

molecular proxies as indicators of freshwater incursion driven salinity stratification salinity related stratification in marine environments is one of the main drivers for the development of persistent anoxia and euxinia it therefore plays a vital role in the sedimentary preservation of organic matter and has also been associated with oceanic anoxic events during several mass extinctions in earth s history here we present a novel molecular proxy using relative abundances of methyltrimethyltridecylchromans mttcs as indicators of riverine freshwater incursions into middle to late devonian paleoreefs exposed to conditions of prevailing anoxia photic zone euxinia and water column stratification this paper aims at re instigating a discussion about the origin of these compounds to potentially broaden their utilization as paleoproxies adding freshwater stratification to the general salinity reconstructions the co variation of mttc abundance profiles and 13c values with other biomarker parameters in the sediments studied here indicate a link of mttcs to terrigenous input pointing towards a previously suggested early diagenetic formation of these compounds from phytol with higher plant derived alkylphenols

space geodetic evidence for multiple magma reservoirs and subvolcanic lateral intrusions at fernandina volcano galapagos islands 1 using interferometric synthetic aperture radar insar measurements of the surface deformation at fernandina volcano galapagos ecuador acquired between january 2003 and september 2010 we study the structure and the dynamics of the shallow magmatic system of the volcano through the analysis of spatial and temporal variations of the measured line of sight displacement we identify multiple sources of deformation beneath the summit and the southern flank at least two sources are considered to represent permanent zones of magma storage given their persistent or recurrent activity elastic deformation models indicate the presence of a flat topped magma reservoir at 1 1 km below sea level and an oblate spheroid cavity at 4 9 km b s l the two reservoirs are hydraulically connected this inferred structure of the shallow storage system is in agreement with previous geodetic studies and previous petrological analysis of both subaerial and submarine lavas the almost eight year long observation interval provides for the first time geodetic evidence for two subvolcanic lateral intrusions from the central storage system in december 2006 and august 2007 subvolcanic lateral intrusions could provide the explanation for enigmatic volcanic events at fernandina such as the rapid uplift at punta espinoza in 1927 and the 1968 caldera collapse without significant eruption

molecular characterization of organic matter in sediments from the keg river formation elk point group western canada sedimentary basin abstract distributions of free and sulfur bound biomarkers in organic rich sediments from the lower and upper keg river formation elk point group western canada reveal deposition of these sediments under reducing conditions in agreement with the geological data the predominance of aryl isoprenoids of chlorobiaceae origin indicates that photic zone anoxia occurred during time of deposition a series of novel aryl isoprenoids with a carboxylic acid function was identified by gc ms and the structure of the predominant 3 methyl 5 2 3 6 trimethylphenyl pentanoate was proven by synthesis of an authentic standard the occurrence of these acids gives evidence that oxidative breakdown at least partially accounts for the diagenetic fate of aromatic carotenoids li etnh 2 desulfurization of two kerogen concentrates yielded only low amounts of sulfur bound hydrocarbons and suggests that either sulfur sequestration was not a predominant process or more probably that a major part of the hydrocarbons initially sulfurized were released upon maturation giving further evidence that poly sulfide bonds are cleaved at relatively low levels of thermal stress

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

molecular indicators of palaeoenvironmental conditions in an immature permian shale kupferschiefer lower rhine basin north west germany from free and s bound lipids a study of the distributions of free and s bound biomarkers and their 13c values in the extract of a bulk sample of the permian kupferschiefer from the lower rhine basin has been carried out to provide a more detailed characterization of the biological inputs the distributions and isotopic compositions of selected components released from nickel boride desulphurization have been compared with those of components in the free fraction the free biomarkers occur in greater abundance than their s bound counterparts the distribution and carbon isotopic composition of both free and bound components in the extract indicate a major cyanobacterial and algal input likewise the free and bound aromatic hydrocarbons contain components which reveal an origin from the carotenoids of chlorobiaceae green sulphur bacteria providing molecular evidence for the occurrence of photic zone anoxia in the water column most of the components in the complex mixture of mono di tri and tetra aromatics in the free aromatic hydrocarbon fraction result from cyclization and aromatization reactions

placers of cosmic dust in the blue ice lakes of greenland a concentration process occurring in the melt zone of the greenland ice cap has produced the richest known deposit of cosmic dust on the surface of the earth extraterrestrial particles collected from this region are well preserved and are collectable in large quantities the collected particles are generally identical to cosmic spheres found on the ocean floor but a pure glass type was discovered that has not been seen in deep sea samples iron rich spheres are conspicuously rare in the collected material

intrusion triggering of the 2010 eyjafjallajokull explosive eruption the ash cloud that brought chaos to european air traffic in april this year was the result of emissions from an icelandic volcano that had been intermittently active for about 18 years a combination of detailed space based geodetic measurements and seismic monitoring of the eyjafjallajkull volcano in the run up to the ash producing explosive summit eruption reveals an unusual deformation pattern that may be attributed to its off rift setting with relatively cool subsurface structure and limited magma at shallow depth as to the predictability of such a dramatic reawakening the immediate precursors to the initial eruption of the volcano in 2010 were subtle and difficult to detect but the clear signs of volcanic unrest during the weeks months and years preceding it may provide better clues to the catastrophic explosion

the greenland ice sheet margin a mine of ice for paleo environmental studies abstract stable isotope analysis of surface ice samples from three locations on the margin of the greenland ice sheet have provided 18 o records dating back into the wisconsinan the samples were collected in profiles transverse to the ice margin on a location about 40 km northeast of jakobshavn west greenland and at two locations in warming land north greenland the holocene wisconsinan transition as detected by a large aburpt shift was found between 470 and more than 850 m from the ice edge the magnitude of the shift was about 8 and 12 in the west and north greenland records respectively the west greenland record which is the more detailed documents that some variations in the wisconsinan are apparently preserved in the ice margin isotopic records by linking locations in the accumulation and ablation zones with the same observed value the surface ice of the ablation zone can be dated back to at least the wisconsinan holocene transition if the velocity of the ice motion is measured or estimated by ice flow modelling this means that dated records of ice constituents gas composition chemistry content of microparticles micro meteorites etc can be established by mining the easily accessible surface ice of the ablation zone

a new model for the kellwasser anoxia events late devonian shallow water anoxia in an open oceanic setting in the central asian orogenic belt the frasnian famennian mass extinction event devastated tropical marine ecosystems and ranks in the top six in taxonomic and ecological severity the close stratigraphic association between the extinction and the kellwasser anoxia events support a link between oceanographic anoxia and extinction the upper and lower kellwasser horizons have been identified in epicontinental and basinal settings in laurussia gondwana siberia and south china the hongguleleng formation late devonian in northwestern xinjiang china contains both the frasnian famennian boundary and the rebound from the frasnian famennian extinction event in a highly fossiliferous shallow marine setting associated with a devonian oceanic island arc complex part of the central asian orogenic belt or caob here we show that the hongguleleng formation also records the upper kellwasser anoxia event through analysis of multiple geochemical proxies in contrast to previous studies asserting that the kellwasser events were restricted to epicontinental seaways and basins our results indicate that it occurred not only along the shallow continental margins of the closing rheic ocean but also in shallow water in the open oceanic part of paleotethys previous explanations for the kellwasser events from epicontinental margins and basins call for the migration of deep anoxic bottom water into shallow water environments as a kill mechanism for shallow marine ecosystems or attribute it to sea level rise and subsequent stagnation there is no evidence that the devonian oceans completely overturned during the kellwasser events similarly many transgressive events in the devonian are not associated with black shales we therefore suggest an alternative mechanism for the kellwasser events based on new evidence from the caob where anoxia is driven by episodic eutrophication of surface waters

upper permian zechstein microbialites supratidal through deep subtidal deposition source rock and reservoir potential zechstein 2 z2 carbonate microbialites flourished under arid paleoclimatic conditions in the late permian microbial carbonates from the roker formation outcrop in northeast england with its subsurface equivalent being the main dolomite from northwest central poland the z2 carbonate deposits developed in supratidal through deep subtidal zones and consist of various stromatolites and thrombolites planar stromatolites and thrombolites characterize intertidal and supratidal facies and biohermal stromatolites with oolitic grainstone and crinkled stromatolites typify shallow subtidal facies the z2 subtidal and or intertidal microbialites with oolites form complexes more than 10 m 33 ft thick and are important reservoir facies for hydrocarbons subtidal slope and intertidal lagoonal microbial mudstone and wackestone have poor reservoir properties but contain total organic carbon as much as 2 wt and are considered as potential source rocks the thermal maturity assessed from c27 17 trisnorhopane tm and c27 18 trisnorhopane ts as the ts ts tm ratio c30 moretane hopane ratio sterane ratio expressed as 20s 20s 20r and ratio shows to indicates a mature character of organic matter with respect to oil generation

sedimentary characteristics and evolution of domanik facies from the devonian carboniferous regression in the southern volga ural basin abstract the domanik facies are organic matter rich siliceous clay carbonate sediments of upper devonian to lower carboniferous age in the volga ural and timan pechora petroleum provinces different studies have been inferred for these sediments across the eastern european russian platform such as sedimentary environments tectonic and hydrogeological regimes paleotemperature changes and so on however less attention are paid to the petroleum formation in this area especially that the link between low amplitude uplift and petroleum concentrated into fractured zones in the center of the sags is not clear in this study we particularly explained this relationship from analyzing the sedimentary evolution of the domanik facies in the southern volga ural basin southeastern russian platform the results show that the sediments in this area were formed during a period of regression in uncompensated sags and depressions from the middle frasnian semiluksk chron late devonian until the early tournaisian early carboniferous the semiluksk formation in this area is dominated by typical domanik carbonate sediments which are dark siliceous clayey and bituminous with complex faunal assemblages from the upper frasnian lower tournaisian carbonates are developed and become less abundant as the axial parts of the kama kinel sags narrow we propose that during the formation of the domanik facies when the basin reached anomalous isostatic gravity the reefs that grew widely on the slope subsided due to the differential compaction of the basin at the same time the center of the basin underwent uplift this process formed tectonic fractures and petroleum could migrate and concentrate in the low amplitude intrabasinal uplifts therefore these uplifts could be characterized by maximal basin thicknesses sediments with high petroleum concentrations and abnormally high pressure and thus could be reasonable zones for the exploration and development of low porosity and low permeability domanik reservoirs

water column structure during deposition of middle devonian lower mississippian black and green gray shales of the illinois and michigan basins a biomarker approach abstract the extractable organic matter of organic rich black shales and associated organic poor bioturbated green gray shales of the illinois and michigan basins of north america is analyzed to constrain the water column structure during their deposition all black shale samples contain derivatives of the biomarker isorenieratene a diaromatic carotenoid pigment produced exclusively by the brown strain of the green sulfur bacteria chlorobiaceae chlorobiaceae are phototrophic organisms requiring euxinic anoxic and sulfidic conditions to survive and the presence of isorenieratene derivatives indicates that the middle devonian early mississippian epeiric seas of north america experienced bottom water euxinic conditions during black shale deposition analysis of green gray shales also reveals the presence of isorenieratene derivatives and in some cases isorenieratane the highly bioturbated fabric of these sediments indicates the presence of oxygen in bottom waters during their deposition thus we suggest that short term shoaling of the oxycline across the basin slope may have occurred during their deposition though they were deposited predominantly under an oxygenated water column i e above the chemocline most green gray shales contain three pseudohomologous series of branched alkanes with quaternary substituted carbon atoms baqcs which are absent in black shale samples recent studies suggest that baqcs are produced by benthic chemoautotrophs dwelling at the redox boundary separating anoxic sediments from moderately oxygenated waters comparison of the biomarker content i e regular isoprenoid baqcs between black and green gray shales indicates different sources of organic matter and suggests that phytoplanktonic productivity in the upper water column was enhanced during black shale deposition the results of this study indicate that the alternation of green gray and black shales in these basins results from the vertical fluctuations of the chemocline these fluctuations seem to be driven by changes in phytoplanktonic productivity our data when associated to previous studies of other black shales from canada and europe confirm that photic zone euxinia was a widespread feature of low latitude epeiric seas during the middle devonian lower mississippian

conditions for the growth of a long lived shallow crustal magma chamber below mount pelee volcano martinique lesser antilles arc 1 the compositional homogeneity of silicic andesites emitted during the 13 500 year long last eruptive cycle of mount pelee suggests that the physical state of the magma chamber was largely unmodified during this period experimental phase equilibria on mount pelee recent products indicate that pre eruptive magma temperatures and pressures were in the range of 875 900 c and 2 0 5 kbar respectively the estimated average eruption rate was 7 5 10 4 km3 a with an average volume of about 0 3 km3 per eruption an analytical model for a spherical magma chamber indicates that a magma flux of 4 5 10 4 km3 a can maintain a magma chamber of 0 3 km3 above 875 c below mount pelee however observations of plutons suggest that magma chambers may grow by addition of sheet like intrusions with numerical simulation we show that a minimum sheet accretion rate of a few centimeters per year is required to grow a persistently active magma chamber independently of the intruded volumetric flux this minimum injection rate is higher if the heat transfer is enhanced by convection processes the limited ability of an arc crust to extend and accommodate dikes suggests that magma injections are sills or if they are dikes that most of the volume injected in the magma chamber is eventually erupted in a conductively cooling igneous body formed by sills injected at a rate of a few centimeters per year most of the injected magma completely solidifies and only a small part of the body about 10 20 is above 875 c and able to feed eruptions

biomarker similarities between the saline lacustrine eocene green river and the paleoproterozoic barney creek formations abstract the paleoproterozoic barney creek formation which is currently interpreted as a restricted deep marine paleoenvironment plays a disproportionate role in our understanding of proterozoic ocean chemistry and the rise of complex life the barney creek formation hosts several unusual biomarker features specifically its methylhopane and carotenoid signatures herein we demonstrate that the saline lacustrine eocene green river formation shares a similar distribution of methylhopanes and carotenoids which is characteristic of saline lacustrine organic matter more generally these distinct methylhopane and carotenoid patterns are not observed together in marine organic matter of any geologic age these results imply a saline lacustrine depositional environment for the barney creek formation which agrees with earlier but now abandoned depositional models of this formation as a result models of proterozoic ocean chemistry and emergence of complex life that rely on a marine barney creek formation should be reexamined alternatively if paleoproterozoic marine biomarker signatures resemble those of younger saline lacustrine systems then this must be recognized to accurately interpret geologic biomarker and paleoenvironmental records

the role of volatiles in magma chamber dynamics many andesitic volcanoes exhibit effusive eruption activity1 with magma volumes as large as 107 109 m3 erupted at rates of 1 10 m3 s 1 over periods of years or decades during such eruptions many complex cycles in eruption rates have been observed with periods ranging from hours to years2 3 4 5 6 7 longer term trends have also been observed and are thought to be associated with the continuing recharge of magma from deep in the crust and with waning of overpressure in the magma reservoir here we present a model which incorporates effects due to compressibility of gas in magma we show that the eruption duration and volume of erupted magma may increase by up to two orders of magnitude if the stored internal energy associated with dissolved volatiles can be released into the magma chamber this mechanism would be favoured in shallow chambers or volatile rich magmas and the cooling of magma by country rock may enhance this release of energy leading to substantial increases in eruption rate and duration

sill intrusion as a source mechanism of unrest at volcanic calderas the interpretation of dynamic processes that occur in volcanic calderas is not simple the ground deformations and the local seismicity which in other volcanic contexts are usually regarded as precursors to eruption in caldera environment in many cases are not followed by any eruption we formulate a general hypothesis that can explain these behaviors our hypothesis is that the intrusion of a sill can be responsible for the dynamics observed during unrest at calderas in order to investigate the reliability of this hypothesis we developed a dynamic model of sill intrusion in a shallow volcanic environment in our model the sill fed by a deeper magma reservoir intrudes below a horizontal elastic plate representing the overlying rocks and expands with axisymmetric geometry the model is based on the numerical solution of the equation for the elastic plate coupled with a navier stokes equation for simulating the dynamics of the sill intrusion we performed a number of simulations with the objective of showing the main features of the model in the experiments when the feeding process stops the vertical movement reverses its trend and the area of maximum uplift undergoes subsidence under certain conditions the subsidence can occur even during the intrusion of the sill the stress field produced by the intrusion is mainly concentrated in a circular zone that follows the sill intrusion front the features predicted by the model are consistent with many observations carried out on different calderas as reported in the scientific literature

recycling and re hydration of degassed magma inducing transient dissolution crystallization events at stromboli italy abstract intrusive degassing and recycling of degassed and dense magma at depth have been proposed for a long time at stromboli the brief explosive event that occurred at the summit craters on 9 january 2005 threw out bombs and lapilli that could be good candidates to illustrate recycling of shallow degassed magma at depth we present an extensive data set on both the textures and the mineral bulk rock and glassy matrix chemistry of the 9 jan products the latter have the common shoshonitic basaltic bulk composition of lavas and scoriae issued from typical strombolian activity in contrast they differ by the heterogeneous chemistry of their matrix glasses and their crystal textures that testify to crystal dissolution event s just prior magma crystallization upon ascent and eruption comparison between mineral paragenesis of the natural products and experimental phase equilibria suggest water induced magma re equilibration we propose that mineral dissolution is related to water enrichment of the recycled degassed magma via differential gas bubble transfer and to some extents its physical mixing with volatile rich magma blobs however all these features illustrate transient processes even though evidence of mineral dissolution is ubiquitous at stromboli its effect on the bulk magma chemistry is minor because of the subtle interplay between mineral dissolution and crystallization in magmas having comparable bulk chemistry

tectonic framework and phanerozoic evolution of sundaland abstract sundaland comprises a heterogeneous collage of continental blocks derived from the india australian margin of eastern gondwana and assembled by the closure of multiple tethyan and back arc ocean basins now represented by suture zones the continental core of sundaland comprises a western sibumasu block and an eastern indochina east malaya block with an island arc terrane the sukhothai island arc system comprising the linchang sukhothai and chanthaburi blocks sandwiched between this island arc formed on the margin of indochina east malaya and then separated by back arc spreading in the permian the jinghong nan uttaradit and sra kaeo sutures represent this closed back arc basin the palaeo tethys is represented to the west by the changning menglian chiang mai inthanon and bentong raub suture zones the west sumatra block and possibly the west burma block rifted and separated from gondwana along with indochina and east malaya in the devonian and were accreted to the sundaland core in the triassic west burma is now considered to be probably cathaysian in nature and similar to west sumatra from which it was separated by opening of the andaman sea basin south west borneo and or east java west sulawesi are now tentatively identified as the missing argoland which must have separated from nw australia in the jurassic and these were accreted to se sundaland in the cretaceous revised palaeogeographic reconstructions illustrating the tectonic and palaeogeographic evolution of sundaland and adjacent regions are presented

aryl isoprenoids and diaromatic carotenoids in paleozoic source rocks and oils from the western canada and williston basins abstract aryl isoprenoids in the range c13 c31 have been identified in source rock bitumens and oils from several paleozoic age petroleum systems in the western canada and williston basins the principal compounds possess the 2 alkyl 1 3 4 trimethyl substitution pattern characteristic of diaromatic carotenoids found in the chlorobiaceae family of photosynthetic sulfur bacteria two c40 perhydrodiaromatic carotenoids which are structurally related to the presumed precursors of the aryl isoprenoids have also been identified in oils and source rock bitumens of the duvernay late devonian petroleum system pyrolysis gas chromatograms of kerogens isolated from several paleozoic source rocks show an unusual abundance of 1 2 3 4 tetramethylbenzene it is proposed that this compound arises from cleavage of diaromatic carotenoid moieties which have been incorporated into the kerogen structure with increasing maturation concentrations of the aryl isoprenoids in duvernay source rock bitumens increase to a point whereas the c40 perhydrodiaromatic carotenoids decrease steadily previous studies have suggested that aryl isoprenoids may be indicators of enhanced salinity environments this is not supported by the present work which shows high concentrations in source rocks associated with presumed normal marine salinities there is however a general association with intervals of condensed clastic or mixed clastic carbonate sedimentation within carbonate depositional systems from the association found and from parallels to modern habitats of photosynthetic bacteria it can be inferred that these biomarkers indicate prolific bacterial growth in a stratified water column at and below the oxic anoxic boundary layer in sub tropical to tropical marine environments

photic zone euxinia during the permian triassic superanoxic event carbon and sulfur isotopic data together with biomarker and iron speciation analyses of the hovea 3 core that was drilled in the perth basin western australia indicate that euxinic conditions prevailed in the paleowater column during the permian triassic superanoxic event biomarkers diagnostic for anoxygenic photosynthesis by chlorobiaceae are particularly abundant at the boundary and into the early triassic similar conditions prevailed in the contemporaneous seas off south china our evidence for widespread photiczone euxinic conditions suggests that sulfide toxicity was a driver of the extinction and a factor in the protracted recovery

changes of palaeoenvironmental conditions recorded in late devonian reef systems from the canning basin western australia a biomarker and stable isotope approach abstract although the late devonian extinctions were amongst the largest mass extinction events in the phanerozoic the causes nature and timing of these events remain poorly restrained in addition to the most pronounced biodiversity loss at the frasnian famennian f f boundary and the end famennian there were also less extensively studied extinction pulses in the middle to late givetian and the frasnian here we used a combination of palynological elemental molecular and stable isotope analyses to investigate a sedimentary record of reef systems from this time period in the canning basin western australia the acquired data generally showed distinct variations between sediments from i the time around the givetian frasnian g f boundary and ii later in the frasnian and indicated a distinct interval of biotic stress particularly for reef builders in the older sediments alterations of pristane phytane ratios gammacerane indices chlorobi biomarkers dkerogen and chroman ratios describe the change from a restricted marine palaeoenvironment with an anoxic euxinic hypolimnion towards a presumably open marine setting with a vertically mixed oxic to suboxic water column simultaneous excursions in 13c profiles of carbonates organic matter om and hydrocarbons in the older sediments reflect the stratification induced enhancement of om recycling by sulfate reducing bacteria alterations in sterane distributions and elevated abundances of methyltrimethyltridecylchromans mttcs and perylene indicate an increased terrigenous nutrient input via riverine influx which would have promoted stratification phytoplankton blooms and the development of lower water column anoxia the detected palaeoenvironmental conditions around the g f boundary may reflect a local or global extinction event our data furthermore suggest a contribution of the higher plant expansion and photic zone euxinia to the late devonian extinctions consistent with previous hypotheses furthermore this work might contribute to the understanding of variations in devonian reef margin and platform top architecture relevant for petroleum exploration and development in the global devonian hydrocarbon resources

decadal to monthly timescales of magma transfer and reservoir growth at a caldera volcano caldera forming volcanic eruptions are low frequency highimpact events capable of discharging tens to thousands of cubic kilometres of magma explosively on timescales of hours to days with devastating effects on local and global scales1 because no such eruption has been monitored during its long build up phase the precursor phenomena are not well understood geophysical signals obtained during recent episodes of unrest at calderas such as yellowstone usa and campi flegrei italy are difficult to interpret and the conditions necessary for large eruptions are poorly constrained2 3 here we present a study of pre eruptive magmatic processes and their timescales using chemically zoned crystals from the minoan caldera formingeruption of santorini volcano greece4 which occurred in the late 1600s bc the results provide insights into how rapidly large silicic systems may pass from a quiescent state to one on the edge of eruption5 6 despite the large volume of erupted magma4 40 60 cubic kilometres and the 18 000 year gestation period between the minoan eruption and the previous major eruption most crystals in the minoan magma record processes that occurred less than about 100 years before the eruption recharge of the magma reservoir by large volumes of silicic magma and some mafic magma occurred during the century before eruption and mixing between different silicicmagmabatches was still taking place during the final months final assembly of large silicic magma reservoirs may occur on timescales that are geologically very short by comparison with the preceding repose period with major growth phases immediately before eruption these observations have implications for the monitoring of long dormant but potentially active caldera systems

carbonaceous particles reveal that late holocene dust causes the dark region in the western ablation zone of the greenland ice sheet a dark region in the western ablation zone of the greenland ice sheet is caused by outcropping ice layers that contain more dust than the surrounding brighter ice these higher amounts of dust were deposited in the accumulation zone of the ice sheet and travelled with the ice to the ablation zone to deduce the period and the causes of this higher dust deposition carbonaceous particles in ice samples from the dark region and from brighter reference ice were analysed and used for dating samples including ice from directly below the surface contain high amounts of modern organic carbon probably from microorganisms on the ice surface deeper samples reveal low amounts of carbonaceous particles which are originally deposited in the accumulation zone the amount of outcropping carbonaceous particles in the dark region seems significantly higher than in the reference ice one of the samples that contained material initially deposited in the accumulation zone was dated and revealed late holocene ages coinciding with a period of enhanced eolian activity in the nearby tundra therefore variable eolian activity during the holocene effected dust fluxes towards the ice and hence leads to albedo variations in the present ablation zone of the ice sheet

a damage model for volcanic edifices implications for edifice strength magma pressure and eruptive processes monitoring of large basaltic volcanoes such as piton de la fournaise la reunion island france has revealed preeruptive accelerations in surface displacements and seismicity rate over a period of between 1 h and several weeks before magma reaches the surface such eruptions are attributed to ruptures of pressurized magma reservoirs elastic models used to describe surface deformation would assume that accelerations in surface deformation are due to increases in reservoir pressure this assumption requires changes in magma or pressure conditions at the base of the magma feeding system that are unrealistic over the observed timescale another possible cause for these accelerations is magma pressure in the reservoir weakening the volcanic edifice in the present study we modeled such weakening by progressive damage to an initially elastic edifice we used an incremental damage model with seismicity as a damage variable with daily increments elastic moduli decrease linearly with each damage increment applied to an initially elastic edifice with constant pressure at the base of the system this damage model reproduces surface displacement accelerations quite well when damage is sufficient process dynamics is controlled by the damage parameter taken as the ratio between the incremental rupture surface and the surface to be ruptured in this case edifice strength and magma reservoir pressure decrease with decreasing elastic moduli whereas surface displacement accelerates we discuss the consequences of pressure decreases in magma reservoirs