natural gas hydrates on the southeast u s margin constraints from full waveform and travel time inversions of wide angle seismic data strong bottom simulating reflectors bsr have been mapped over a region of approximately 50 000 km2 on the southeastern u s margin and have been associated with possible abundance of natural gas hydrates in june 1992 coincident single channel seismic and wide angle ocean bottom seismic data were acquired in the region focusing on the blake ridge and the carolina rise wide angle reflections from the bsrs were clearly observed at offsets up to 6 km joint travel time inversion was conducted with wide angle and vertical incidence data in order to explore possible regional variation and the resultant two dimensional average velocity models imply higher background velocities on the carolina rise full waveform inversion was then performed to determine the seismic origin of the bsrs the best fit model shows a similar low velocity 1 4 km s beneath the bsr at both sites indicating trapped free gas with low saturation 10 the inversion results also indicate that a thin high velocity wedge with a maximum velocity of 2 3 km s is present just above the blake ridge bsr sediment reflectivities were also calculated and higher reflectivities are observed on the carolina rise an increase in reflectivity below the bsr seems to correspond to the gas bearing zone at both sites concentration of hydrates were estimated based on these velocity models whereas average hydrate concentration of 3 of the total sediment volume is suggested for the lower half of the hydrate stability zone at the blake ridge only a very low average concentration of hydrate can be expected at the carolina rise the hydrates seem to be concentrated near the base of the hydrate stability zone and the maximum hydrate concentration is estimated as 20 at the blake ridge and 7 at the carolina rise both of which are too high to be explained by in situ biogenic activity only and require some secondary accumulation mechanism it is suggested that hydrate recycling caused by the stability field migration may have effectively condensed hydrates at both sites additional enhancement by upward fluid expulsion may also be viable for the blake ridge

exploration for gas hydrates in the deepwater northern gulf of mexico part i a seismic approach based on geologic model inversion and rock physics principles this article presents the results of applying a five step process for using high quality seismic data to locate marine gas hydrates the process involved 1 reprocessing of seismic data for higher resolution 2 detailed stratigraphic evaluation and interpretation to locate possible hydrate bearing zones 3 seismic attribute analysis to further delineate these zones 4 seismic inversion to obtain appropriate elastic parameters of these zones in 3d and 5 quantitative estimation of gas hydrate saturation from seismic data using inversion and rock physics principles we used seismic data from keathley canyon 151 and atwater valley 14 in the northern gulf of mexico although careful analysis did indicate the presence of a bottom simulating reflector bsr our study mainly relied on a host of other seismic attributes e g gas chimneys seismically transparent zones other features associated with the petroleum system to characterize the occurrence of gas hydrates in these areas we tested and verified a viable rock model for hydrate bearing sediments using data from the mallik mckenzie delta canada and blake ridge odp leg 164 southeast u s atlantic margin wells and modified it for application in the current area we then used this model to estimate gas hydrate saturation in the host sediments of the northern gulf of mexico focus areas using estimates of p wave and s wave velocities from inversion of reflection seismic data in this paper we present the gas hydrate saturations predicted from the seismic processing methodology prior to 2005 drilling in the focus areas in frontier areas where no well data are available and lithologic heterogeneities are poorly understood implementing a seismic based technique like the one described here to identify potential gas hydrates can provide valuable pre drill information for site selection and for planning future characterization studies of gas hydrate bearing sediments

middle to late devensian glaciation of north east scotland implications for the north eastern quadrant of the last british irish ice sheet we present a review of over 175 years of research into the middle to late devensian weichselian glaciation of north east scotland based crucially on both its lithostratigraphic and geomorphic records the location of the region and surrounding seabed makes this unusually detailed record significant for deciphering the former interactions and dynamics of scottish and scandinavian ice within the north sea basin nsb which continue to be controversial a twelve stage event stratigraphy is proposed based on a parsimonious interpretation of stratigraphic relationships till lithology and regional clast fabrics striae subglacial bedforms ice marginal features and published geochronometry at critical sites the record of regional glaciation supports converging evidence that the north eastern quadrant of the last british and irish ice sheet biis reached its maximum spatial extent in the late middle to early late devensian and later re expanded following widespread internal glacial reorganisations marine transgression and partial retreat from the central nsb retreat was interrupted by several glacial readvances of limited extent field captured data helps identify important events that are not clearly resolved from remote sensing alone particularly regarding growth phases of the last glaciation

the glacial and interstadial sediments at the burn of benholm kincardineshire evidence for onshore pre devensian ice movement in northeast scotland pebbly clays and diamictons containing marine shell fragments and peat lenses exposed beneath subglacially deposited late devensian till at the burn of benholm provide new insights into the glacial history of quaternary sequences in eastern scotland the peat yielded pollen of interstadial affinity including bruckenthalia spiculifolia and non finite radiocarbon dates comparisons with other pre late devensian pollen records in northern scotland suggest that the peat lenses are remnants of an early devensian interstadial deposit of oxygen isotope substage 5c or 5a age reworked faunal assemblages in the shelly sediments include quaternary marine molluscs of low boreal aspect as well as mesozoic and palaeozoic microfossils amino acid ratios from fragments of arctica islandica suggest that the shells are of oxygen isotope stage 9 age or older the fabric and composition of the shelly sediments are consistent with their emplacement as deformation till during the onshore movement of glacially transported rafts of marine sediment folded and sheared contacts between the shelly deposits peat lenses and the overlying late devensian till indicate that the fossiliferous sediments were glacitectonised during the main late devensian glaciation when ice moved from strathmore and overrode the site from the southwest british geological survey nerc 2000

estimation of gas hydrate concentration and free gas saturation at the norwegian svalbard continental margin we estimate the concentration of gas hydrate and free gas at an area located to the north of the knipovich ridge western svalbard margin the method is based on p wave velocities computed by reflection tomography applied to multicomponent ocean bottom seismometer data the tomographic velocity field is fitted to theoretical velocities obtained from a poro elastic model based on a biot type approach the interaction between the rock frame gas hydrate and fluid is modelled from first physical principles we obtain average hydrate concentrations of 7 and maximum free gas saturations of 0 4 and 9 depending on the saturation model

palaeoenvironment of the upper cretaceous coniacian concretion bearing lagerstatten from poland abstract abundantly fossiliferous upper cretaceous sediments including decapod remains in the region of stary waliszow southern poland have been known for many years to date however no study has dealt specifically with detailed palaeoenvironmental and palaeoecological reconstruction the origin of these sediments is still uncertain and has been the source of considerable confusion and controversy mainly due to the strong bioturbation and decalcification of these sediments by using the fossil record comparative taphonomy and geochemical analyses of concretions we provide new insights into the paleoenvironment and the paleoecology of this unique coniacian ecosystem on the basis of ichno and body fossil assemblages composed almost exclusively of benthic organisms such as decapods molluscs and echinoderms which are commonly disarticulated but rarely abraded we suggest that the fossiliferous sediments in stary waliszow were formed in shallow normal saline and well oxygenated waters of the upper sublittoral zone with moderate sedimentation rate and low turbulence of waters the presence of angular terrigenous clasts well preserved delicate land flora and the near absence of planktonic and nektonic fossils strongly imply proximity to the land recorded taxa inhabited a soft bottom environment some organisms were fossilized inside siderite concretions these concretions were formed within the sediment below the zone of active bioturbation during the early stage of diagenesis remarkable preservation of decapod remains is due to phosphatization which replaced the cuticle

biostratigraphy of the last glacial period in europe the european early weichselian early wurmian is characterized by two long and relatively warm interstadials brorup and odderade which can be traced and correlated with certainty across large parts of europe the amersfoort interstadial described earlier from the netherlands has been included in the brorup and represents the older part of it both great interstadials were forested in north west central and southern europe in the north conifer forests prevailed giving way towards the south to deciduous forests the climatic gradient was distinctly steeper mainly due to southward displacement of the gulf stream the two great interstadials are synchronous with the isotopic stages 5a and 5c in the deep sea cores subsequent to eemian brorup and odderade and from within the context of a continuous series two additional and clearly delimited interstadials have been recorded in a new standard profile from oerel nw germany these are now described as the oerel and glinde interstadials they were not forested and belong to the early pleni weichselian the lower one oerel can probably be correlated with the 3rd weichselian wurmian interstadial in southern central europe ognon ii durnten samerberg 3 while the upper one glinde has so far no known counterpart for the younger pleni glacial it is assumed that there was a long phase during which it was not too cold the formation of humic layers during this phase took place at different times partly due to local edaphic factors so that the relevant 14c dates show a wide scatter the hengelo and denekamp interstadials represent only slight ameliorations which facilitated the formation of shrub tundra and can be recorded in certain regions only

methane hydrate induced permeability modification for multiphase flow in unsaturated porous media 1 an experimental study was performed using x ray computed tomography ct scanning to capture three dimensional 3 d methane hydrate distributions and potential discrete flow pathways in a sand pack sample a numerical study was also performed to develop and analyze empirical relations that describe the impacts of hydrate accumulation habits within pore space e g pore filling or grain cementing on multiphase fluid migration in the experimental study water was injected into a hydrate bearing sand sample that was monitored using an x ray ct scanner the ct images were converted into numerical grid elements providing intrinsic sample data including porosity and phase saturations the impacts of hydrate accumulation were examined by adapting empirical relations into the flow simulations as additional relations governing the evolution of absolute permeability of hydrate bearing sediment with hydrate deposition the impacts of pore space hydrate accumulation habits on fluid migration were examined by comparing numerical predictions with experimentally measured water saturation distributions and breakthrough curves a model case with 3 d heterogeneous initial conditions hydrate saturation porosity and water saturation and pore body preferred hydrate accumulations best captured water migration behavior through the hydrate bearing sample observed in the experiment in the best matching model absolute permeability in the hydrate bearing sample does not decrease significantly with increasing hydrate saturation until hydrate saturation reaches about 40 after which it drops rapidly and complete blockage of flow through the sample can occur as hydrate accumulations approach 70 the result highlights the importance of permeability modification due to hydrate accumulation habits when predicting multiphase flow through high saturation reservoir quality hydrate bearing sediments

the tolsta interstadial scotland correlation with d o cycles gi 8 to gi 5 abstract organic sediments buried by till at tolsta head in north lewis in the scottish outer hebridean islands have been re investigated radiocarbon dates of 32 26 kyr bp indicate correlation with the denekamp interstadial of the netherlands and the sandnes alesund interstadial of norway the organic sediments contain an unusually detailed record of the dominantly open grassland vegetation during the interstadial variations in palaeotemperature inferred from the pollen assemblages and sedimentology are provisionally matched with the 18o record of the gisp2 ice core and correlation with the dansgaard oeschger cycles gi 8 gi 5 is proposed the interstadial starts at 38 1k cal yr and 32 8k radiocarbon years the termination of the interstadial and the build up of the late devensian weichselian ice sheets in scotland and north west europe dates from 32k cal yr and 28 7k radiocarbon years whether the tolsta and other contemporaneous episodes are intervals or interstadials is also considered

the structure of methane gas hydrate bearing sediments from the krishna godavari basin as seen from micro ct scanning abstract the indian national gas hydrate program nghp expedition 1 of 2006 cored through several methane gas hydrate deposits on the continental shelf around the coast of india the pressure coring techniques utilized during the expedition hyacinth and pcs enabled recovery of gas hydrate bearing fine grained sediment cores to the surface after initial characterization core sections were rapidly depressurized and submerged in liquid nitrogen preserving the structure and form of the hydrate within the host sediment once on shore high resolution x ray ct scanning was employed to obtain detailed three dimensional images of the internal structure of the gas hydrate using a resolution of 80 m the detailed structure of the hydrate veins present in each core could be observed and allowed for an in depth analysis of orientation width and persistence of each vein hydrate saturation estimates could also be made and saturations of 20 30 were found to be the average across the core section with some portions showing highs of almost 60 saturation the majority of hydrate veins in each core section were found to be orientated between 50 and 80 to the horizontal analysis of the strikes of the veins suggested a slight preferential orientation in individual sample sections although correlation between individual sections was not possible due to the initial orientation of the sections being lost during the sampling stage the preferred vein orientation within sample sections coupled with several geometric features identified in individual veins suggest that hydraulic fracturing by upward advecting pore fluids is the main formation mechanism for the veined hydrate deposits in the k g basin

visual observation of gas hydrate formation and dissociation in synthetic porous media by means of glass micromodels visual observation of gas hydrates at the microscopic scale in synthetic porous media provides unequivocal visual evidence that clathrates can form in systems without the presence of a free gas phase hydrates were formed from a soluble liquid hydrate former tetrahydrofuran c 4 h 8 o from free gas ch 4 and from dissolved gas co 2 clathrates were found to form within the center of pore spaces rather than on grain surfaces cementation of grains only occurred in regions of a small grain size or where a large proportion of pore space was filled with hydrate however even at high clathrate saturations a thin film of free water persisted on grain surfaces the results have important implications for the potential cementing effect of hydrates on sediments and thus for sediment permeability slope stability and seismic interpretation of hydrate bearing sediments

compressional wave velocity measurements through sandy sediments containing methane hydrate an experimental apparatus was built to measure p wave velocity vp of sandy sediment during hydrate formation from brine and free methane gas the influences of hydrate saturation initial brine saturation conversion ratio of water to hydrate and grain size of sand upon vp were investigated the experimental results demonstrate that vp strongly depends on both hydrate saturation and initial brine saturation whereas the influence of the grain size of sand is unremarkable during the formation of hydrate for different experimental runs at identical initial brine saturation vp increases with the increase of hydrate saturation while it decreases dramatically with the increase of initial brine saturation for a given hydrate saturation the correlation between vp and conversion ratio of water into hydrate was studied and it was found that the relation between vp and the conversion ratio of water to hydrate is approximately the same for different experimental runs regardless of how big the differences in initial saturation of brine and the size of sand grain are vp was calculated for four different hydrate distribution models the results suggest that low conversion ratio of water to hydrate hydrate mainly acts as a load component of a dry frame matrix whereas at higher conversion ratio of water to hydrate it partly acts as a cement that coats grains at grain contacts and thereby leads to a dramatic increase in vp compared with the hydrate saturation the conversion ratio of water to hydrate has a large role in distributing hydrate in the pores of sediments

estimating the amount of gas hydrate and free gas from marine seismic data marine seismic data and well log measurements at the blake ridge offshore south carolina show that prominent seismic bottom simulating reflectors bsrs are caused by sediment layers with gas hydrate overlying sediments with free gas we apply a theoretical rock physics model to 2 d blake ridge marine seismic data to determine gas hydrate and free gas saturation high porosity marine sediment is modeled as a granular system where the elastic wave velocities are linked to porosity effective pressure mineralogy elastic properties of the pore filling material and water gas and gas hydrate saturation of the pore space to apply this model to seismic data we first obtain interval velocity using stacking velocity analysis next all input parameters to the rock physics model except porosity and water gas and gas hydrate saturation are estimated from geologic information to estimate porosity and saturation from interval velocity we first assume that the entire sediment does not contain gas hydrate o

the effect of methane hydrate morphology and water saturation on seismic wave attenuation in sand under shallow sub seafloor conditions a better understanding of seismic wave attenuation in hydrate bearing sediments is needed for the improved geophysical quantification of seafloor methane hydrates important for climate change geohazard and economic resource assessment hence we conducted a series of small strain 10 6 seismic frequency 50 550 hz laboratory resonant column experiments on synthetic methane hydrate bearing sands under excess water seafloor conditions the results show a complex dependence of p and s wave attenuation on hydrate saturation and morphology p and s wave attenuation in excess water hydrate bearing sand is much higher than in excess gas hydrate bearing sand and increases with hydrate saturation between 0 and 0 44 the experimental range theoretical modelling suggests that load bearing hydrate is an important cause of heightened attenuation for both p and s waves in gas and water saturated sands while pore filling hydrate also contributes significantly to p wave attenuation in water saturated sands a squirt flow attenuation mechanism related to microporous hydrate and low aspect ratio pores at the interface between sand grains and hydrate is thought to be responsible for the heightened levels of attenuation in hydrate bearing sands at low hydrate saturations 0 44

logging while drilling and wireline velocities site nghp 01 10 krishna godavari basin india abstract at site nghp 01 10 krishna godavari basin india the downhole wireline logging tool measured higher porosity and sonic velocities in gas hydrate bearing sediments compared to the logging while drilling lwd acquired data in two closely spaced wells 10 m using a rock physics model that assumes random fractures in unconsolidated sediments using hashin shtrikman bounds we show that difference in physical properties could be due to intra site difference in the distribution and pattern of hydrate filled fractures rather than differences in the volume of gas hydrate our fracture inclusive model suggests that between the two holes the porosity and hydrate saturation of the background sediments is similar while porosity and hydrate saturation of the fracture systems change considerably resulting in the change of the sonic log responses relative changes in hydrate saturation between sediments and fractures at 90 m below the sea floor mbsf depth at a prominent seismic horizon suggests that fracture filling hydrate could have partly originated as pore filling material in the sediments and grew as fracture filling material as a result of fluid flow the volume fracture profile of hydrate fracture porosity fracture saturation between the two holes further suggests that the higher concentration of fractures in the wireline hole may not be a natural in situ condition but rather a manifestation of the drilling compounded with time lapse in data recording between the lwd and wireline log data frequently reported worldwide intra site variability in hydrate saturation from lwd and wireline logs in close proximity could be more related to interpretative methods than actual geologic variability

natural gas hydrate investigations by synchrotron radiation x ray cryo tomographic microscopy srxctm 1 we report the 3d microstructure analyses of natural gas hydrates sampled from gulf of mexico the samples were characterized by synchrotron radiation x ray cryo tomographic microscopy srxctm using the tomcat beam line at the swiss light source sls the srxctm demonstrates its applicability to unlock some microscopic features of the marine hydrates in particular of crystallite size and grain boundary network the gas hydrate domains are surrounded by a network of pores of typically a few micrometers which are largely due to decomposition out of the srxctm data the porosity total volume of the voids the void surface area and number of the total gas filled voids have been calculated the results reveal the capability of srxctm to access the 3d microstructure which is of fundamental importance to model the petrophysical properties of natural gas hydrates

hydrate morphology physical properties of sands with patchy hydrate saturation 1 the physical properties of gas hydrate bearing sediments depend on the volume fraction and spatial distribution of the hydrate phase the host sediment grain size and the state of effective stress determine the hydrate morphology in sediments this information can be used to significantly constrain estimates of the physical properties of hydrate bearing sediments including the coarse grained sands subjected to high effective stress that are of interest as potential energy resources reported data and physical analyses suggest hydrate bearing sands contain a heterogeneous patchy hydrate distribution whereby zones with 100 pore space hydrate saturation are embedded in hydrate free sand accounting for patchy rather than homogeneous hydrate distribution yields more tightly constrained estimates of physical properties in hydrate bearing sands and captures observed physical property dependencies on hydrate saturation for example numerical modeling results of sands with patchy saturation agree with experimental observation showing a transition in stiffness starting near the series bound at low hydrate saturations but moving toward the parallel bound at high hydrate saturations the hydrate patch size itself impacts the physical properties of hydrate bearing sediments for example at constant hydrate saturation we find that conductivity electrical hydraulic and thermal increases as the number of hydrate saturated patches increases this increase reflects the larger number of conductive flow paths that exist in specimens with many small hydrate saturated patches in comparison to specimens in which a few large hydrate saturated patches can block flow over a significant cross section of the specimen

compressional and shear wave velocities in uncemented sediment containing gas hydrate 1 the competing hypotheses for gas hydrate formation at the particle scale in sediments describe processes of pore filling frame building or cementation new measurements of compressional vp and shear wave vs velocities in fine grained sands subjected to low confinement and monitored during formation of tetrahydrofuran hydrate indicate that hydrate nucleates in the pore space presumably at grain boundaries and grows with limited impact on the sediment shear stiffness vp and vs until crystals begin to interact with the granular skeleton at 40 hydrate concentration vs increases significantly more than vp at higher hydrate concentrations reflecting larger changes in the specimen s shear stiffness than its bulk stiffness the results indicate that seismic velocities and or their ratio vp vs have limited capability for locating hydrate or constraining hydrate concentrations

experimental tumbling of echinoderms taphonomic patterns and implications abstract despite a wide array of published actualistic studies on echinoderm taphonomy the detailed pattern of decay and disarticulation of their skeletons is still not well understood here we provide results of tumbling experiments using a rotating barrel filled with artificial seawater and medium sized quartz sand to mimic physical forces experienced by echinoderms during transportation in high energy conditions in particular we determined semi quantitatively transportation induced rates and patterns of damage and disintegration of freshly killed ophiuroid asteroid and crinoid skeletons that were not allowed to decay initially our experiments showed that echinoderm specimens disintegrated in a characteristic sequence toward an increase of the degree of disarticulation abrasion and roundness or thinness of echinoderm ossicles the sequence of disintegration in crinoids began with the partial disintegration of distal arms after 2 h a time equivalent to 1 km of transport the initial split of ophiuroid and asteroid arms and crinoid cirri occurred after 24 h 12 km and complete destruction of the asteroid mouth and ophiuroid disk area occurred after 72 h 36 km the duration of transport necessary to promote initial fragmentation in asteroid and ophiuroid arms and crinoid cirri into isolated ossicles was 120 h 60 km the complete disarticulation of crinoid ophiuroid and asteroid arms and crinoid cirri occurred after 312 h 156 km and 408 h 204 km respectively although it has been argued that the quality of preservation can be a poor index of post mortem transport echinoderms allowed limited initial decay in the presence of rapid and relatively constant physical disturbance an approximation of the distance of transport can be made our data demonstrate that articulated ossicles can remain for several days sufficient time for long even a few hundred km transportation this finding illustrates that articulated echinoderm remains do not necessarily imply low energy and highlights the importance of a reliable discrimination of autochthonous and allochthonous components of fossil echinoderm assemblages application of in particular isolated fossil echinoderm ossicles in e g paleoenvironmental and paleoecological reconstructions may lead to serious misinterpretations and should be supplemented by observations of abrasion traces

evidence for two pre flandrian palaeosols in buchan north east scotland evidence is presented for the existence of two distinct pre flandrian palaeosols at a single site kirkhill quarry in buchan north east scotland this is the first such site reported from scotland and it is possible that the two palaeosols represent interglacial episodes which are equivalent in age to last interglacial compare with ipswichian and the penultimate interglacial compare with hoxnian a combination so far unknown in the british isles the stratigraphy also demonstrates that the part of the buchan plateau under study may have been glaciated on at least three separate occasions

storm related taphofacies and paleoenvironments of malvinokaffric assemblages from the lower middle devonian in southwestern gondwana abstract taphofacies of malvinokaffric macroinvertebrate bearing rocks from the uppermost pragian to lower givetian in southwestern gondwana are evaluated during the lower middle devonian the parana basin southern brazil was positioned at high latitudes in southwestern gondwana 60 to 80 s integrated litho and taphofacies interpretations in siliciclastic environments presented here provide paleoecological and paleoenvironmental insights the six taphofacies recognized here showed changing depositional conditions in paleoenvironments ranging from shoreface to offshore shelf settings they vary in recurrence and abundance but all facies exhibit evidence of storm events winter storms are to be expected at latitudes 60 to 80 s under cool climate zone storm related taphofacies recurrence during the latest pragian to early givetian points to two agents of sedimentation direct wave erosion by winter storms and sedimentary processes related to combined flow during deposition e g turbidity currents and oscillatory flow winter storms are considered more capable of affecting sediment transport than hurricanes due to longer duration and larger coverage area in higher latitudes therefore winter storms of high latitudes should generate more persistent currents in space and time finally the taphofacies lithofacies and high latitude paleogeographic context of the parana basin suggest the action of storm influence in the genesis of all lower middle devonian malvinokaffric assemblages here recognized

luminescence dating and its application to key pre late devensian sites in scotland abstract relatively few sites have been identified in scotland that contain records that predate the peak of the late devensian glaciation ca 18 ka bp where such records have been identified they have assumed a key role in developing our understanding of climate change in scotland radiocarbon dating has been the primary chronological tool applied to these sites but the reliability of age determinations in excess of 30 ka is questionable in this paper we describe the results of a programme which applies luminescence dating methods to eight key pre late devensian sites in scotland methods were developed and tested to enable the identification of samples for which luminescence dating was only able to provide an upper limit on the age because of the limited light exposure that the sample experienced at deposition these new approaches were applied to four sites where independent age control was available this meant that the choice of sediments from test sites was restricted to those sediments which were formed in the last 40 000 years and hence were amenable to radiocarbon dating the luminescence age estimates for the control sites and the pre late devensian sites are discussed within the context of any existing chronological control on a site by site basis

direct geometrical simulation of pore space evolution through hydrate dissociation in methane hydrate reservoirs abstract the identification of methane hydrate behavior in porous media is one of the most challenging yet rewarding pore level visualization and simulation tasks the hydrate morphology influences the physical characteristics of the host sediments as during the hydrate formation and dissociation processes the pore space and flow pathways constantly evolve here a direct three phase pore morphological simulation approach is proposed verified and utilized to simulate hydrate deformities and predict fluid occupancies and absolute and effective permeabilities of hydrate bearing geological formations the proposed technique simulates capillary dominant displacements by applying a set of geomaterial rules directly to the pixels of pore level porous media images the case studies are sandy microstructures generated based on the particle size distributions of the mallik gas hydrate deposit the fluid occupancy profiles absolute permeability and hydraulic tortuosity curves are comparable with the experimental datasets the sensitivity analysis shows that although the gas relative permeability is less sensitive to the hydrate specifications the porosity grain size distribution and hydrate content and occupancy remarkably influence the rock absolute permeability

skeletal microstructure of uintacrinoid crinoids and inferences about their mode of life uintacrinoids uintacrinoidea are among the most bizarre of all the crinoids these stratigraphically important late cretaceous crinoids are characterized by an atypical large stalkless globular cup without cirriferous centrodorsal and extremely long arms owing to this unusual morphology the mode of life of these crinoids has confused palaeontologists for more than a century while uintacrinoids have been commonly regarded as pelagic forms either swimming actively or floating passively by means of a putative buoyancy mechanism some recent authors have favoured a benthic mode of life however evidence supporting a benthic lifestyle hypothesis is still limited here we describe the stereom microstructure of marsupites and uintacrinus in marsupites thecal plates are typically comprised of coarse to medium clearly structural galleried stereom which alternates with zones of fine and deeply penetrating galleried stereom oriented perpendicular to the plate margins the latter stereom type corresponds to the external ribbed ornament of the theca and is indicative of collagenous sutural fibers for binding adjacent plates in uintacrinus thecal plates are almost entirely composed of fine galleried stereom diagnostic for collagenous sutural fibers in both taxa a perforate stereom layer that is known to increase plate strengthening and resistance to abrasion in some recent echinoderms is developed most externally and also produces a characteristic interior growth banding pattern no skeletal adaptations for maintaining buoyancy such as skeletal lightening and hollow architecture that are known to occur in nektonic and pseudoplanktonic crinoids are observed instead the stereom organization in uintacrinoids closely resembles those observed in recent benthic crinoids our findings thus strongly support a benthic mode of life of uintacrinoids their widespread distribution within a short time interval can be best explained by having a very long term planktonic larval stage as previously hypothesized by some authors

quaternary stratigraphy of the fladen area central north sea a multidisciplinary study based on detailed stratigraphic investigations on a 200 6m long core bgs borehole no 81 26 from the fladen ground area british sector core material from the sleipner field norwegian sector and shallow seismic profiles between the core sites the following conclusions are drawn 1 the north sea was glaciated sometime during th elaterpart of matuyama reversed period a complete glacial interglacial glacial cycle is recorded in these sediments 2 in a period of marine sedimentation in the middle pleistocene a transgression regression cycle under boreal arctic regime is recorded 3 the fladen area has subsided between 0 9 and 0 6 m ka through the later parts of the quaternary 4 a major glacial event dated at between 130 and 200 ka is recorded as a thick till unit in 81 26 this till which was deposited by ice moving from the southwest scotland probably represents a period when the scandinavian and british ice sheets coalesced in the north sea 5 based on the seismic data and the stratigraphy of the sleipner core an ice free open embayment dry land is favoured for the central north sea during the late weichselian 6 from the amino acid data it is shown that there has been an episodic style of sedimentation through the quaternary 7 of the investigated sediments which span the last 1 mill year ca 98 have been deposited under arctic to boreal arctic conditions

lagrangian observations of the deep western boundary current in the north atlantic ocean part i large scale pathways and spreading rates twenty six rafos floats were deployed in the deep western boundary current dwbc of the north atlantic ocean between the grand banks and cape hatteras in 1994 95 and tracked acoustically for up to two years half of the floats were launched in the upper chlorofluorocarbon cfc maximum associated with upper labrador sea water 800 m and the other half near the deep cfc maximum that identifies the overflow water from the nordic seas 3000 m the float observations reveal the large scale pathways of these recently ventilated water masses in the subtropics the shallow float tracks show directly that upper labrador sea water is diverted away from the western boundary and into the interior at the location where the dwbc encounters the gulf stream near 368n the crossover region consistent with previous hydrographic studies east of the crossover region only one upper labrador sea water float out of seven 15 permanently crossed to the south side of the stream in two years caught in a cold core ring formation event the other shallow floats recirculated north of the gulf stream apparently confined by the mean potential vorticity gradient aligned with the stream the deep floats closely followed the topography to the crossover region then revealed a bifurcation in fluid parcel pathways one branch continues equatorward along the western boundary and the other turns first eastward along the gulf stream path then southward the deep float pathways including the bifurcation in the crossover region can be explained in terms of the deep potential vorticity distribution comparison of the float results with results from recent modeling studies suggests that the deep flow is strongly influenced by both the depth of the main pycnocline and bottom depth the effective spreading rates of upper labrador sea water and overflow water estimated directly from the float data southward at 0 6 6 0 2 cm s21 and 1 4 6 0 4 cm s21 respectively agree well with tracer derived spreading rates mean velocities in the dwbc equatorward at 2 4 cm s21 upper labrador sea water and 4 5 cm s21 overflow water are consistent with other in situ measurements one deep float drifted almost 4000 km along the western boundary in two years revealing a fast track for the spreading of overflow water in the dwbc these observations emphasize the importance of the crossover region in the spreading and mixing of recently ventilated water masses addressed in part ii of this study

exploration for gas hydrates in the deepwater northern gulf of mexico part ii model validation by drilling this study examines the accuracy of the predictions of gas hydrate saturations made based on five step analysis of 3d seismic data prior to 2005 drilling logging conventional coring and pressure core sampling through the gas hydrate stability zone at two focus sites in the northern gulf of mexico these predictions are detailed in part i 2008 here we conduct a detailed analysis of the gas hydrate saturation using both resistivity and p wave velocity log data and analyze the pre drilling predictions which were made almost exclusively on the basis of seismic data with no local logging control well log measurements core data analysis and pressure core degas experiments all indicated general agreement with the pre cruise analysis regarding the location and approximate concentration of gas hydrates in the sediments we find that seismic predictions are generally consistent with log based estimates after upscaling to seismic frequencies we recalibrated the pre drill model based on the new field data so that a refined version of the model could be used for future work

dwarfism of irregular echinoids echinocorys from poland during the campanian maastrichtian boundary event abstract the echinoid genus echinocorys is one of the dominant irregular echinoid in the cretaceous of poland our analysis of the body size trends of these echinoids shows that they underwent dwarfism in the early maastrichtian the reduction in body size in these echinoids was likely an ecological response to the major climate perturbations connected with the campanian maastrichtian boundary event cmbe that was characterized by a long lasting negative carbon isotope excursion and cooling this is consistent with the fact that food limitations and cold temperatures are among the major factors decreasing growth rates in modern echinoids so far in the case of echinoids the so called lilliput effect has been only recognized in the early danian early paleogene heart urchins atelostomata thus our study shows that the reduction in the body size in echinoids was a more common biotic response to environmental stress than previously thought

allt odhar and dalcharn two pre late devensian late weichselian sites in northern scotland the lithostratigraphy and biostratigraphy of two sites allt odhar and dalcharn in north central scotland are described where pollen spectra of temperate affinity have been obtained from organic deposits that underlie till the pollen record from allt odhar in association with evidence from plant macrofossils and coleoptera shows the expansion of birch woodland and its eventual replacement by open grassland under a climatic regime slightly cooler than that prevailing in the northern highlands of scotland at the present day the organic sediments accumulated during an early devensian interstadial episode which has been dated by the uranium series disequilibrium method to ca 106 ka bp evidence for one and possibly two devensian glaciations may be preserved at the site the pollen record from dalcharn by contrast reflects the middle and later stages of an interglacial cycle with the transition from pine forest to grassland the overlying till sequence contains evidence of at least two separate glacial episodes the age of the warm stage cannot be established precisely on present evidence but there are indications that it may predate the last ipswichian interglacial these are the first sites from the mainland of scotland to provide evidence of wooded conditions during interstadial and interglacial episodes of the middle late pleistocene

multiproxy devensian late glacial and holocene environmental records at an atlantic coastal site in shetland marine erosion at clettnadal west burra island off the west coast of shetland caused the drainage of a small water body at clettnadal exposing deposits of late devensian and holocene age pollen diatom and invertebrate analyses have provided variable records of environmental change during stratigraphical event gi 1 event gs 1 is revealed by the non pollen evidence especially by coleoptera by sediment stratigraphy and by radiocarbon dating in contrast the pollen evidence indicates that an arctic tundra flora in which dwarf shrubs were prominent persisted throughout the late glacial the holocene brought colonisation by tree birch but by ca 9000 14 c yr bp the taxon had almost disappeared this contrasts strongly with other holocene pollen records for shetland where both betula and corylus avellana type survived longer at some sites for example until ca 2900 yr bp the extreme westerly and exposed coastal situation of clettnadal appears to be responsible both for a muted late glacial response in the pollen record of terrestrial vegetation and for the early replacement of woodland by a maritime grassland the results provoke questions concerning biological stability at times of marked climatic change copyright 2003 john wiley sons ltd journal of quaternary science

microstructural evolution of gas hydrates in sedimentary matrices observed with synchrotron x ray computed tomographic microscopy the formation process of gas hydrates in sedimentary matrices is of crucial importance for the physical and transport properties of the resulting aggregates this process has never been observed in situ at submicron resolution here we report on synchrotron based microtomographic studies by which the nucleation and growth processes of gas hydrate were observed at 276 k in various sedimentary matrices such as natural quartz with and without admixtures of montmorillonite type clay or glass beads with different surface properties at varying water saturation both juvenile water and metastably gas enriched water obtained from gas hydrate decomposition was used xenon gas was employed to enhance the density contrast between gas hydrate and the fluid phases involved the nucleation sites can be easily identified and the various growth patterns are clearly established in sediments under saturated with juvenile water nucleation starts at the water gas interface resulting in an initially several micrometer thick gas hydrate film further growth proceeds to form isometric single crystals of 10 20 m size the growth of gas hydrate from gas enriched water follows a different pattern via the nucleation in the bulk of liquid producing polyhedral single crystals a striking feature in both cases is the systematic appearance of a fluid phase film of up to several micron thickness between gas hydrates and the surface of the quartz grains these microstructural findings are relevant for future efforts of quantitative rock physics modeling of gas hydrates in sedimentary matrices and explain the anomalous attenuation of seismic sonic waves

benthic observations on the madeira abyssal plain currents and dispersion abstract an experiment to measure near bottom currents on the madeira abyssal plain is described the moorings placed near 33 n 22 w were separated by 5 40 km with instruments at 10 100 and 600 m above the bottom depth 5300 m rotor stalling occurred to of the time but does not hinder the analysis which separated currents into tidal 3 cm s 1 inertial 1 3 cm s 1 and low frequency 2 5 cm s 1 components the m2 tide is found to be principally barotropic with magnitude ellipticity orientation and phase adequately predicted by the tidal model of schwiderski 1979 oscillations of near inertial frequency are found to be bottom intensified have a wavelength of 100 km directed nearly due south and 3 km vertically their phase velocity is directed downward suggesting the bottom as the source the vertical group velocity is estimated at 150 m day 1 upward and corresponds to the 4 6 day lag observed between 10 and 600 m for the envelope of inertial amplitude low frequency statistics are presente

was autotomy a pervasive adaptation of the crinoid stalk during the paleozoic the crinoids were the most diverse and numerically most common echinoderms in the paleozoic as well as being one of the most important groups of sessile invertebrates autotomy self mutilation in the stem that is the casting off of the more distal part is only known to occur in one extant group of crinoids the post paleozoic isocrinine sea lilies these crinoids have a long distal stalk with regularly spaced articulations i e cryptosymplexies adapted for autotomy they are connected together by short mutable collagenous tissues that undergo irreversible destabilization during autotomy the distal opening of the axial canal is then sealed by new growth of calcite paleozoic crinoids lacked cryptosymplectial articulations but have other adaptations that may have singly or collectively facilitated autotomy these include the linking of adjacent short lengths of stalk i e noditaxes by short ligaments the evolutionary trend to narrow the axial canal occlusion of the axial canal in some species and the ability to seal the axial canal other morphological features of relevance to autotomy include the common division of the stem into morphologically distinct regions and attachment by a distal recumbent radicular runner the ability to autotomize the distal stem in many paleozoic crinoid clades was at the very least latent if overt it would have facilitated escape from environmental disturbance it may in part explain the great abundance of disarticulated crinoid stem fragments in many ordovician to permian sedimentary deposits

a laboratory investigation into the seismic velocities of methane gas hydrate bearing sand remote seismic methods which measure the compressional wave p wave velocity vp and shear wave s wave velocity vs can be used to assess the distribution and concentration of marine gas hydrates in situ however interpreting seismic data requires an understanding of the seismic properties of hydrate bearing sediments which has proved problematic because of difficulties in recovering intact hydrate bearing sediment samples and in performing valid laboratory tests therefore a dedicated gas hydrate resonant column ghrc was developed to allow pressure and temperature conditions suitable for hydrate formation to be applied to a specimen with subsequent measurement of both vp and vs made at frequencies and strains relevant to marine seismic investigations thirteen sand specimens containing differing amounts of evenly dispersed hydrate were tested the results show a bipartite relationship between velocities and hydrate pore saturation with a marked transition between 3 and 5 hydrate pore saturation for both vp and vs this suggests that methane hydrate initially cements sand grain contacts then infills the pore space these results show in detail for the first time using a resonant column how hydrate cementation affects elastic wave properties in quartz sand this information is valuable for validating theoretical models relating seismic wave propagation in marine sediments to hydrate pore saturation

synchrotron x ray computed microtomography study on gas hydrate decomposition in a sedimentary matrix in situ synchrotron x ray computed microtomography with sub micrometer voxel size was used to study the decomposition of gas hydrates in a sedimentary matrix xenon hydrate was used instead of methane hydrate to enhance the absorption contrast the microstructural features of the decomposition process were elucidated indicating that the decomposition starts at the hydrate gas interface it does not proceed at the contacts with quartz grains melt water accumulates at retreating hydrate surface the decomposition is not homogeneous and the decomposition rates depend on the distance of the hydrate surface to the gas phase indicating a diffusion limitation of the gas transport through the water phase gas is found to be metastably enriched in the water phase with a concentration decreasing away from the hydrate water interface the initial decomposition process facilitates redistribution of fluid phases in the pore space and local re formation of gas hydrates the observations allow also rationalizing earlier conjectures from experiments with low spatial resolutions and suggest that the hydrate sediment assemblies remain intact until the hydrate spacers between sediment grains finally collapse possible effects on mechanical stability and permeability are discussed the resulting time resolved characteristics of gas hydrate decomposition and the influence of melt water on the reaction rate are of importance for a suggested gas recovery from marine sediments by depressurization this article is protected by copyright all rights reserved

measured acoustic wave velocities of r11 ccl3f hydrate samples with and without sand as a function of hydrate concentration we report acoustic laboratory measurements on initially unconsolidated sand packs with hydrate formation taking place in the pore space both p and s wave velocities were measured hydrate was formed from water and the refrigerant r11 ccl3f at 2 c and atmospheric pressure measurements were performed on two types of initially unconsolidated sand packs with average grain size 100 m and 280 m respectively p wave velocities varied from about 1700 m s at low hydrate content to 3810 m s at a calculated hydrate fraction in the pore space equal to 0 52 s wave velocities were only detectable at hydrate fractions larger than 0 35 where s wave velocities up to 2230 m s were measured our measurements indicate that acoustic measurements are not sensitive to small amounts of hydrate in a system of initially unconsolidated sand the data show a very distinct change in behavior when the hydrate fraction exceeds 0 35 the concentration at which hydrate cementation of the sand grains is believed to occur measurements for samples without sand samples containing water r11 and hydrate are also reported for hydrate without sand p wave velocities ranged from about 1400 m s at very low hydrate content to about 2500 m s at a measured hydrate fraction equal to 0 68 for these samples reliable s wave data were not detected

methane hydrate formation in partially water saturated ottawa sand bulk properties of gas hydrate bearing sediment strongly depend on whether hydrate forms primarily in the pore fluid becomes a load bearing member of the sediment matrix or cements sediment grains our compressional wave speed measurements through partially water saturated methane hydrate bearing ottawa sands suggest hydrate surrounds and cements sediment grains the three ottawa sand packs tested in the gas hydrate and sediment test laboratory instrument ghastli contain 38 1 porosity initially with distilled water saturating 58 31 and 16 of that pore space respectively from the volume of methane gas produced during hydrate dissociation we calculated the hydrate concentration in the pore space to be 70 37 and 20 respectively based on these hydrate concentrations and our measured compressional wave speeds we used a rock physics model to differentiate between potential pore space hydrate distributions model results suggest methane hydrate cements unconsolidated sediment when forming in systems containing an abundant gas phase

the quaternary deposits and landforms of scotland and the neighbouring shelves a review abstract a thick sequence of quaternary sediments up to 1000 m has been deposited in the north sea basin and perhaps five major glacial episodes the first occurring prior to ca 1 8 2 1 ma bp and the last during the late devensian can be recognised between the glacial events periods of low salinity arctic marine or glacio marine sedimentation have been dominant although episodes of ameliorated climate when north atlantic drift waters had access to the north sea have been identified a number of horizons in separate boreholes have been correlated with the last interglacial oxygen isotope stage 5e and a sequence of water mass movements around the scottish coasts can be reconstructed for the last ca 125 ka on land sequences of quaternary deposits relating to several glacial and non glacial terrestrial and marine events occur in different areas but due to poor dating correlation between these sequences cannot yet be achieved in particular north east scotland has a complex glacial history with evidence for ice sheet glaciation on at least four occasions evidence from the outer hebrides north east scotland and the north sea basin indicates that the late devensian scottish ice sheet had a rather restricted extent only reaching a short distance offshore along much of the east and west coasts at this time ice free areas existed in north east scotland on the isle of lewis and probably in caithness and orkney whilst part of the outer shelf around st kilda was dry land a marine embayment extended down the east coast of scotland between the scottish and scandinavian ice sheets and independent ice caps existed on the outer hebrides and probably on shetland deglaciation of the greater part of the country took place prior to ca 13 ka bp whilst the climate was still very cold the ice retreat appears to have been orderly with stagnant ice masses being trapped only in topographically suitable locations a number of retreat stages or minor readvances occurred during the general deglaciation the firth of clyde was one of the last areas outside the highlands to be deglaciated and this occurred in a rapid possibly catastrophic fashion shortly prior to ca 13 ka bp despite the mild climate at the start of the lateglacial interstadial it is not known if there was complete deglaciation prior to the loch lomond readvance the readvance glaciers however may have started to advance during the latter part of the interstadial when declining terrestrial temperatures coincided with a period of mild marine conditions the loch lomond readvance maximum can only be dated to some time after ca 10 9 ka bp and it is likely that final ice free conditions were not achieved until the earliest holocene

a critical evaluation of pollen stratigraphic investigations of pre late devensian sites in scotland abstract this paper reviews pollen stratigraphic evidence from proposed interglacial and pre late devensian interstadial sites in scotland the paper has two major parts in the first the stratigraphic details of each of the sites are summarised and discussed the sites are classified as interglacial or interstadial according to the interpretations adopted by recent authors though as discussed in later sections such distinction is problematic and somewhat arbitrary in the second part general problems of interpretation are discussed in the light of the stratigraphic details problems of dating and correlation are severe since most of the sediments lie close to or beyond the limit of conventional radiocarbon dating thus the normal approach has been to use pollen stratigraphic comparisons with type sites in southern or eastern england this practice is considered questionable problems of assessing the provenance of pollens and spores are perhaps even more important and at some sites are so severe as to render pollen assemblages of limited value the problems discussed are a secondary reworking of pollen b long distance wind transport of nonregional pollen c pollen deterioration and d low pollen concentrations many of the problems discussed are of general significance being applicable to late quaternary pollen diagrams from other regions in the concluding section of the paper certain procedures are proposed that may permit a clearer assessment of potential problems of taphonomy in pollen stratigraphy

seismic reflections of gas hydrate from perturbational forward modeling we perturb the elastic properties and attenuation in the arctic mallik methane hydrate reservoir to produce a set of plausible seismic signatures away from the existing well these perturbations are driven by the changes we impose on porosity clay content hydrate saturation and geometry the key is a data guided theoretical rock physics model that we adopt to link velocity and attenuation to porosity mineralogy and amount of hydrate we find that the seismic amplitude is very sensitive to the hydrate saturation in the host sand and its porosity as well as the porosity of the overburden shale however changes to the amount of clay in the sand only weakly alter the amplitude attenuation which may be substantial must be taken into account during hydrate reservoir characterization because it lowers the amplitude to an extent that may affect the hydrate volume prediction the spatial structure of the reservoir affects the seismic reflection a thinly layered reservoir produces a noticeably different amplitude than a massive reservoir with the same hydrate volume

lagrangian observations of the deep western boundary current in the north atlantic ocean abstract in this study the authors analyze the trajectories of 18 rafos floats launched in the deep western boundary current dwbc between the grand banks and cape hatteras to investigate the kinematics and dynamics in the region where the dwbc crosses under the gulf stream near 36 n the crossover region floats deployed in the chlorofluorocarbon cfc maximum associated with upper labrador sea water depth 800 m illustrate the entrainment process of this water mass into the gulf stream the behavior of the floats and fluid parcels in the crossover region is strongly dependent on the meandering of the gulf stream when the stream is close to its mean position fluid parcels entrained from the upper dwbc travel along the northern edge of the stream when a meander trough is present downstream of the entrainment location dwbc fluid parcels cross the gulf stream and sometimes are expelled on the south side this represents a previously unrecognized mechanism for transporting upper labrador sea w

relative water and gas permeability for gas production from hydrate bearing sediments relative water and gas permeability equations are important for estimating gas and water production from hydrate bearing sediments however experimental or numerical study to determine fitting parameters of those equations is not available in the literature in this study a pore network model is developed to simulate gas expansion and calculate relative water and gas permeability based on the simulation results fitting parameters for modified stone equation are suggested for a distributed hydrate system where initial hydrate saturations range from sh 0 1 to 0 6 the suggested fitting parameter for relative water permeability is nw 2 4 regardless of initial hydrate saturation while the suggested fitting parameter for relative gas permeability is increased from ng 1 8 for sh 0 1 to ng 3 5 for sh 0 6 results are relevant to other systems that experience gas exsolution such as pockmark formation due to sea level change co2 gas formation during geological co2 sequestration and gas bubble accumulation near the downstream of dams

taphonomy of cystoids echinodermata diploporita from the napoleon quarry of southeastern indiana usa the lower silurian massie formation as an atypical lagerstatte abstract diploporites like most pelmatozoan echinoderms are characterized by complex multi element skeletons prone to complete disarticulation if left exposed for extended periods of time consequently preservation of abundant articulated diploporite thecae is rare and generally restricted to environments where rapid burial events could catastrophically entomb individuals one such environment is represented by the lower portion of the wenlock age massie formation at the new point stone quarry near napoleon southeastern indiana which we recognize as a konservat lagerstatte yet taphonomic evidence does not support live burial diploporites holocystites spp are dominantly preserved as intact thecae without any portions of brachioles and with damage plate shifting and plate loss plate jumbling on one side post mortem encrustation is common but epibionts are typically present on the well preserved sides of thecae geopetal sediment fill of thecae shows that the well preserved side commonly faced upward following burial this taphonomic state is paradoxical as burial of live diploporites would have resulted in preservation of complete individuals with no encrusters and only compaction induced damage rapid burial of diploporites following a short interval of exposure would have resulted in preservation similar to observed patterns but with encrusters and geopetal infills indicating that the poorly preserved side faced up and burial after extended exposure would have resulted in thorough disarticulation of thecae rather a variable and in some cases complex taphonomic history is suggested for diploporites from the napoleon quarry with at least some individuals having experienced one or more brief episodes of exhumation prior to final burial early diagenetic cementation of initial theca filling sediment is the most likely mechanism for keeping thecae intact during subsequent exposure

deepwater geohazard prediction using prestack inversion of large offset p wave data and rock model successful deepwater drilling is defined as reaching the total well depth in the desired hole size safely i e not exceeding the fracture pressure while controlling hydrocarbon or water influx and ensuring that casings are placed across desired intervals the oil and gas industry has succeeded in this mission thousands of time around the world but drilling challenges abound especially in deepwater

palaeoecological aspects of the diversification of echinoderms in the lower ordovician of central anti atlas morocco abstract echinoderms are one of the major components of benthic faunas in the lower ordovician sequence near zagora central anti atlas morocco the fezouata shale tremadocian late floian has yielded numerous exquisitely preserved echinoderm assemblages ranging through several stratigraphic levels and palaeoenvironmental conditions these associations offer a unique opportunity to document both evolutionary and palaeoecological aspects of echinoderm diversification in high latitude siliciclastic dominated western gondwana sediments where rapid in situ burials facilitated excellent faunal census conditions lower shoreface deposits of the fezouata shale provide the most complete record of successive echinoderm faunas in late tremadocian times these relatively shallow shelf deposits show the progressive replacement of low diversity opportunistic cambrian like dwarfed communities dominated by cornute stylophorans in unhospitable dysoxic environmental conditions by higher diversity benthic assemblages more typical of the great ordovician biodiversification event and dominated by blastozoans on well oxygenated sea floors the turnover of the ordovician radiation was apparently slightly delayed in more proximal settings eocrinoid meadows persisted in shallower environmental conditions up to the middle floian in the late floian they were replaced by diploporite dominated communities typical of later ordovician high latitude peri gondwanan faunas from a palaeobiogeographic point of view low diversity assemblages display relatively strong affinities with cosmopolitan late cambrian echinoderm faunas whereas high diversity communities are dominated by peri gondwanan taxa

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

paleoenvironmental proxies in echinoid spines eucidaris galapagensis doderlein 1887 along a natural water temperature gradient abstract the use of paleoenvironmental proxies such as oxygen isotopes in echinoderm skeletons has been a matter of controversial debate many previous studies showed a variety of environmental as well as biological processes causing deviations from equilibrium incorporation of geochemical proxies during the formation of echinoderm skeletons however given the global distribution of echinoids their fast spine growth and their occurrence throughout the entire phanerozoic species specific calibrations of geochemical proxies in echinoid spines can disclose a valuable bio archive for reconstructing ancient environmental conditions throughout earth s history if samples are adequately preserved in the sedimentary record here we present data on oxygen isotopes 18 o carbon isotopes 13 c and mg ca ratios measured in eucidaris galapagensis doderlein 1887 spines which were sampled along the natural water temperature gradient of the galapagos archipelago we found a negative correlation of 18 o calcite with ambient water temperature following the equation 1000 ln 23 03 10 3 t 1 k 47 90 we also found 13 c calcite be positively correlated with water temperature following the equation 13 c calcite vpdb 47 585 0 164 t k mg ca ratios also showed a significant correlation with water temperature however with a low correlation coefficient the large scatter of 18 o calcite values within the upwelling region indicates higher growth rates during seasons of colder water temperatures considering this and the observed steeper slope in the temperature 18 o calcite relationship our data suggest that the common assumption of respiration affecting oxygen isotope fractionation does not apply for the tropical species e galapagensis overall our data show that e galapagensis spines represent valuable paleoenvironmental archives which might have the potential to provide sub annually resolved water temperature records if spine architecture and growth pattern are well constrained

problems encountered with the 14c dating of peat abstract pairs of neighbouring short columns of peat from two sites in northern england were divided into contiguous 1 cm thick slices that were sub sampled for pollen and plant macro fossil analysis for each slice the remaining peat was then split into humic acid humin and fulvic acid fractions and radiocarbon dated this research demonstrates that significant variations can occur in the radiocarbon content of discrete chemically defined fractions of peat a total of 127 radiocarbon dates was obtained the results from the four columns of peat are highly variable and mutually inconsistent the fulvic acid fraction although normally younger than the corresponding humic acid and humin fractions has very little effect on a combined date in these samples however it is removed from all samples prior to dating in order to remove any carbonates which could contaminate samples the variations in the ages obtained for the humic acid and corresponding humin fractions range from the humin fraction being 630 years older than the humic acid srr 4029 to the humic acid being 1210 years older than the humin fraction srr 4007 even when a two sigma confidence is allowed no correlation was apparent between pollen concentration 13 c enrichment degree of humification and the conventional radiocarbon ages

sedimentology palaeoecology and geochronology of marine isotope stage 5 deposits on the shetland islands scotland hall a m gordon j e whittington g duller geoff a t heijns h 2002 sedimentology palaeoecology and geochronology of marine isotope stage 5 deposits on the shetland islands scotland journal of quarternary science 17 1 51 67

rock physics of a gas hydrate reservoir gas hydrates are solids composed of a hydrogen bonded water lattice with entrapped guest molecules of gas there are convincing arguments that vast amounts of methane gas hydrate are present in sediments under the world s oceans as well as in onshore sediments in the arctic this hydrate is possibly the largest carbon and methane pool on earth as such methane hydrate may be the principal factor in global climate balancing one may also treat this methane pool as a potential energy source these considerations ignite the scientific and business community s interest in quantifying the amount of methane hydrate in the subsurface gas hydrate reservoir characterization is in principle no different from the traditional hydrocarbon reservoir characterization similar and well developed remote sensing techniques can be used seismic reflection profiling being the dominant among them seismic response of the subsurface is determined by the spatial distribution of the elastic properties by mapping the elastic contrast the geophysicist can illuminate tectonic features and geobodies hydrocarbon reservoirs included to accurately translate elastic property images into images of lithology porosity and the pore filling phase quantitative knowledge is needed that relates the rock s elastic properties to its bulk properties and conditions specifically to quantitatively characterize a natural gas hydrate reservoir we must be able to relate the elastic properties of the sediment to the volume of gas hydrate present and if at all possible the permeability one way of achieving this goal is through rock physics effective medium modeling several attempts to construct a relation between hydrate concentration and the compressional velocity in sediments have followed the path of modifying the popular wyllie s time average equation which states that total traveltime through rock is the volume weighted sum of traveltimes through the solid phase and the fluid phase considered independently of each other i e v p 1 1 v

physical properties of hydrate bearing sediments 1 methane gas hydrates crystalline inclusion compounds formed from methane and water are found in marine continental margin and permafrost sediments worldwide this article reviews the current understanding of phenomena involved in gas hydrate formation and the physical properties of hydrate bearing sediments formation phenomena include pore scale habit solubility spatial variability and host sediment aggregate properties physical properties include thermal properties permeability electrical conductivity and permittivity small strain elastic p and s wave velocities shear strength and volume changes resulting from hydrate dissociation the magnitudes and interdependencies of these properties are critically important for predicting and quantifying macroscale responses of hydrate bearing sediments to changes in mechanical thermal or chemical boundary conditions these predictions are vital for mitigating borehole local and regional slope stability hazards optimizing recovery techniques for extracting methane from hydrate bearing sediments or sequestering carbon dioxide in gas hydrate and evaluating the role of gas hydrate in the global carbon cycle

microstructural evidence for stalk autotomy in holocrinus the oldest stem group isocrinid abstract holocrinid crinoids holocrinus are among the oldest if not the oldest post paleozoic crinoids which are widely considered the stem group isocrinids for the post paleozoic monophyletic subclass articulata owing to their phylogenetic and stratigraphic position the morphology and paleobiology of these crinoids have received considerable attention although the holocrinid stalk is similar to that of fossil and living isocrinids it lacks flat and rigid synostosial articulations which are sites specialized for autotomy holocrinids were thus long considered sessile without the ability to re attach however taphonomic data such as specific pattern of preferred disarticulation at the distal facet of nodals indicated that holocrinus was likely capable of stalk autotomy and relocation this trait that is considered an anti predatory adaptation against benthic predation has recently served as example of fundamental change in benthic marine communities such as the mesozoic marine revolution mmr here i describe stereom microstructure of the stalk of early middle triassic holocrinus the holocrinid stalk is mainly constructed of straight stereom passageways passing through the columnals that are diagnostic of long through going ligaments at the distal symplexial nodal facet however fine and dense stereom in which pores are irregular in outline and show no alignment is observed the latter stereom type strongly resembles synostosial stereom in living isocrinids that is associated with short ligaments specifically designed for autotomy these findings thus strongly support stalk shedding abilities in holocrinids these results emphasize that microstructural observations coupled with taphonomic data may provide more insights into functional inferences than macromorphological data alone

theoretical modeling insights into elastic wave attenuation mechanisms in marine sediments with pore filling methane hydrate the majority of presently exploitable marine methane hydrate reservoirs are likely to host hydrate in disseminated form in coarse grain sediments for hydrate concentrations below 25 40 disseminated or pore filling hydrate does not increase elastic frame moduli thus making impotent traditional seismic velocity based methods here we present a theoretical model to calculate frequency dependent p and s wave velocity and attenuation of an effective porous medium composed of solid mineral grains methane hydrate methane gas and water the model considers elastic wave energy losses caused by local viscous flow both i between fluid inclusions in hydrate and pores and ii between different aspect ratio pores created when hydrate grows the inertial motion of the frame with respect to the pore fluid biot s type fluid flow and gas bubble damping the sole presence of pore filling hydrate in the sediment reduces the available porosity and intrinsic permeability of the sediment affecting biot s type attenuation at high frequencies our model shows that attenuation maxima due to fluid inclusions in hydrate are possible over the entire frequency range of interest to exploration seismology 1 106 hz depending on the aspect ratio of the inclusions whereas maxima due to different aspect ratio pores occur only at sonic to ultrasound frequencies 104 106 hz this frequency response imposes further constraints on possible hydrate saturations able to reproduce broadband elastic measurements of velocity and attenuation our results provide a physical basis for detecting the presence and amount of pore filling hydrate in seafloor sediments using conventional seismic surveys

devensian organic interstadial deposits and ice sheet extent in buchan scotland pre late devensian organic deposits in the buchan area of northeast scotland were investigated for their geomorphological and palaeoecological pollen plant macrofossils coleoptera properties close ecological agreement exists between fossil indicators and allows the inference that the environment in the vicinity of the deposits was a dwarf shrub tundra of the type met today in high latitude areas of scandinavia and arctic russia the latest in a series of radiocarbon dates from the site produced determinations beyond the limits of the method although the geomorphological and fossil evidence appears to point to an interstadial date within oxygen isotope stages 5a or 5c the site has special significance for arguments concerning the much debated concept of moraineless buchan indeed evidence is presented which supports the concept of extensive ice sheet glaciation during the late devensian for this crucial geographical area if buchan is to be seen as a further casualty amongst other disputed ice free enclaves then a return to earlier models of extensive ice sheet glaciation in the late devensian of scotland would seem to be necessary 1998 john wiley sons ltd

imaging methane hydrates growth dynamics in porous media using synchrotron x ray computed microtomography commercial scale methane ch4 extraction from natural hydrate deposits remains a challenge due to among other factors a poor understanding of hydrate host sediment interactions under low temperature and high pressure conditions that are conducive to their existence we report the use of synchrotron x ray computed microtomography cmt to image for the first time time resolved pore scale methane ch4 hydrate growth from an aqueous solution containing 5 wt barium chloride bacl2 and pressurized ch4 hosted in glass beads all contained in an aluminum cell with an effective volume of 3 5 ml multiple two dimensional 2 d cross sectional images show ch4 hydrates with 7 5 m resolution distributed in patches throughout the system without dependence on distance from the cell walls the time resolved three dimensional 3 d images constructed from the 2 d slices exhibited pore filling hydrate formation from dissolved ch4 gas similar to natural ch4 hydrates si in the marine environment furthermore the 3 d images show that the aqueous phase was the wetting phase of the glass beads i e the host and the formed hydrate were separated by an aqueous layer these results provide some fundamental understanding of the nucleation phenomenon of gas hydrate formation at the pore scale pore filling ch4 hydrate growth is likely to result in a reduced bulk modulus and thus could affect seafloor stability during the reverse phenomenon i e dissociation of natural hydrate deposits

water permeability in hydrate bearing sediments a pore scale study permeability is a critical parameter governing methane flux and fluid flow in hydrate bearing sediments however limited valid data are available due to experimental challenges here we investigate the relationship between apparent water permeability k and hydrate saturation sh accounting for hydrate pore scale growth habit and meso scale heterogeneity results from capillary tube models rely on cross sectional tube shapes and hydrate pore habits thus are appropriate only for sediments with uniform hydrate distribution and known hydrate pore character given our pore network modeling results showing that accumulating hydrate in sediments decreases sediment porosity and increases hydraulic tortuosity we propose a modified kozeny carman model to characterize water permeability in hydrate bearing sediments this model agrees well with experimental results and can be easily implemented in reservoir simulators with no empirical variables other than sh results are also relevant to flow through other natural sediments that undergo diagenesis salt precipitation or bio clogging

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr