diagenesis and hydrocarbon accumulation brent sandstone jurassic bergen high area north sea diagenesis of brent group sandstones in the bergen high area was studied and related to the history of hydrocarbon maturation and pore fluid environment calcite and kaolinite are low temperature diagenetic precipitates that formed as meteoric pore water entered the brent at the end of brent deposition and later during late cimmerian erosion a major period of feldspar dissolution associated with quartz and illite cementation occurred at huldra field precipitation of diagenetic illite in brent sandstones was closely linked with hydrocarbon maturation in the adjacent viking graben and accumulation of generated fluids in traps at structural highs at huldra field illite k ar ages suggest onset of illite diagenesis in the latest cretaceous initial reservoiring of hydroca bons during the latest paleocene to early eocene 58 ma and filling of the reservoir by early oligocene 38 ma pore water character during illite diagenesis interpreted from oxygen isotope and quartz overgrowth fluid inclusion data was warmer than predicted by burial history analysis and one and a half to two times seawater salinity the incursion of saline isotopically evolved fluids at huldra suggests replacement of paleometeoric water by basin compaction fluid illite k ar ages from veslefrikk field indicate a minimum age of hydrocarbon accumulation at about 30 ma modern pore water chemistry in the brent at veslefrikk is unlike the suggested water chemistry at huldra and indicates that migrating compaction water did not completely displace older fresh connate water this sugge ts that hydrocarbons migrated into veslefrikk as a discrete phase without great volumes of associated compaction water

diagenesis of the hild brent sandstones northern north sea isotopic evidence for the prevailing influence of deep basinal water abstract the deeply buried 3 8 4 3 km brent reservoir sandstones of the hild field northern north sea have undergone intense diagenetic alteration fluid inclusion o c h sr isotope and k ar age data combined with petrography and burial history constrain the conditions and timing of the main diagenetic transformations as well as the nature and origin of diagenetic fluids non ferroan calcite cement formed at shallow depth the reconstructed diagenesis of the hild brent reservoirs displays notable differences with diagenetic models developed in many fields of the northern north sea in particular diagenesis in hild is characterized by the prevailing influence of deep basinal water a feature related to the immediate proximity of the viking graben this study further illustrates that diagenetic processes related to compaction derived fluids commonly reported in sediments located within rift basins should also be expected to occur in neighboring sub basins along rift margins

mass transfer and problems of secondary porosity creation in deeply buried hydrocarbon reservoirs abstract secondary porosity created by the post depositional leaching of detrital grains and cements can be of great economic importance the term secondary porosity is only descriptive and does not give any information on whether the porosity of the rock has been enhanced in reality there are two end member volumetric outcomes to the leaching process firstly the mineral can be completely dissolved and its components transported out of the system in such an instance the porosity of the rock will be enhanced secondly it is possible that a mineral will decompose and by product minerals will be precipitated which will occupy approximately the same volume as the original mineral the latter case is more likely where the pore waters are close to equilibrium with the majority of the minerals of the rock this will occur at elevated temperatures and or where the pore waters have been in contact with the rock for a long time these conditions are commonly met during intermediate to deep burial many metastable minerals such as high temperature feldspars probably decompose in this way a consequence of the decomposition of such metastable minerals is that primary porosity will be swapped for secondary and that older and more deeply buried rocks will contain a higher proportion of secondary porosity the mass transport equation may be used to examine the physico chemical environment where enhanced porosities most likely occur during leaching by using a simple non equilibrium mass transport model based on the silica system it is possible to demonstrate the relative importance of flow rate reaction rates specific surfaces and temperature in controlling the areal extent of leaching wide leaching zones are related to high flow rates which in turn promote a high throughput of undersaturated fluid and dispersion leaching over a wide area is also favoured by low reaction rates which will occur at low temperatures although it is true to say that less of a given silicate mineral can be dissolved by an undersaturated pore water at low temperature than at high temperature it is probable that pore fluids from deeply buried sediments are more likely to be close to equilibrium with a given mineral than for instance meteoric water thus the most likely environment for the production of widespread enhanced porosity is in the shallow subsurface the lower flow rates and higher temperatures that are encountered during deep burial diagenesis will result in far narrower more intense leaching zones as a result providing sufficient reactive mineral is present any undersaturated pore water will approach equilibrium in a short distance in order to transport undersaturated pore waters appreciable distances in the deep subsurface it is necessary to minimize their interaction with the host rock this could occur if the pore fluid were to move through a fracture system where it would interact with a far smaller surface area of reactive mineral than if it moved through the pore network

methane related carbonate cements in pockmarks of the north sea abstract some pockmarks on the norwegian continental shelf contain patches of cemented sediment that can provide hardgrounds attractive to a variety of benthonic organisms detailed examination of a sandstone sample from a pockmark in norwegian block 25 7 in the north sea has revealed the presence of mg calcite and aragonite cements some of the latter forming botryoids all cement types are characterized by extremely light carbon isotopic compositions with a mean 13c value of 56 1 pdb which shows that the cements contain carbonate produced by oxidation of biogenic methane oxidation occurred in both the oxic and anoxic diagenetic zones trace amounts of interstitial methane mean 13c 40 8 and higher hydrocarbon gases up to c5 with a c1 cn ratio of 0 855 0 874 in the pockmark sediments indicate that some thermogenic methane may be mixed with the biogenic gas

the composition and diagenesis of interstitial solutions ii fluxes and diagenesis at the water sediment interface in the high latitude north and south atlantic studies of the major element composition of in situ sampled pore waters are reported for the north atlantic and southern ocean between africa and antarctica the pattern of diagenetic modification of pore water composition is similar throughout the entire atlantic enrichment of na ca2 and alkalinity and depletion of mg2 and k are nearly universal only siliceous oozes consistently provide very limited evidence of cation diagenesis the changes observed and the calculated fluxes across the seawater sediment interface are much the same as those reported previously for other areas of the atlantic and caribbean fluxes of the major cations across the interface continue to be indicated as a major factor in the geochemical cycling of these elements particularly na mg2 and k diagenetic modelling indicates that aerobic oxidation of organic matter and consequent dissolution of caco3 is a dominant reaction throughout the north atlantic the data indicate that o2 oxidation to at least 30 cm is prevalent at nearly all stations dissolution of caco3 in response to the introduction of metabolic co2 can lead to significant post depositional modification of the sediments the modelling also indicates a 1 1 stoichiometric relationship between na release and mg2 uptake by sedimentary components although dissolved silica concentrations in biogenic siliceous sediments are among the highest yet reported 700 m calculations demonstrate that solubility control cannot be through equilibria with the mineral sepiolite further the influence of cation silicate surface phases generally upon solubility is contraindicated by si oh 4 mg2 h relationships evaluation of the influence of fluid advection on pore water profiles indicates that at the stations studied in the north atlantic it is small a more general consideration of the potential contribution of fluid advection to shaping interstitial water profiles demonstrates that advection can be a dominant factor in such circumstances serious misinterpretation of the nature of diagenetic reactions may result from a lack of knowledge and consideration of fluid advection

fish otoliths in superficial sediments of the mediterranean sea abstract otoliths represent a significant biogenic carbonate component in marine sediments that may provide valuable information for paleoenvironmental and biogeographic reconstructions in spite of their importance relatively little is still known about the taxonomic composition abundance and early taphonomic characteristics of recent otolith death assemblages which would add to their value to interpret situations in the geological record here we present data on the distribution of fish otoliths from bottom sediments collected in the central mediterranean sea ranging in depth from 51 to 3300 m the preservation of otoliths ranges from fresh semi translucent white specimens to dull coloured dark ones although whitish specimens are predominant across all the samples this diversity in lustre and colour and at times texture reflects the degree of early taphonomic processes undergone by these aragonitic bodies post mortem under submarine conditions never being exposed to diagenetic processes on land in general a correlation with depth is observed with best preservation observed in otoliths sampled at depths

pre and post bomb radiocarbon in fish otoliths measurements of radiocarbon in seawater dissolved inorganic carbon dic or suitable proxies such as hermatypic corals are a valuable source of information on carbon flux and ocean circulation however knowledge of the global distribution of both pre and post bomb radiocarbon is limited due to the sources of these data suitable hermatypic corals are restricted to shallow tropical and subtropical waters and oceanographic collections of seawater are prohibitively expensive what is needed is a proxy for ocean radiocarbon that can be collected at most latitudes and depths and which can be reliably aged here i report accelerator mass spectrometry analyses of radiocarbon from selected regions of fish otoliths and show that such measurements are suitable for determining both pre and post bomb radiocarbon in all oceans and at most depths radiocarbon data obtained from otoliths can extend our knowledge of carbon flux in the oceans and atmosphere and help to develop further understanding of the fate of atmospheric co2 and ocean circulation the data presented here represent the first pre and post bomb time series of radiocarbon levels from temperate waters furthermore i demonstrate that the dramatic increase in radiocarbon in the atmosphere and oceans attributable to the atmospheric testing of thermonuclear bombs during the 1950 s and 1960 s provides a chemical mark on fish otoliths that is suitable for the validation of age in fishes

snowbands over the english channel and irish sea during cold air outbreaks persistent northerly to easterly cold air outbreaks affected the uk during the winters of 2009 10 and 2010 11 with the resulting convection frequently organizing into snowbands over the english channel and irish sea sounding data and composite radar reflectivity images from the met office nimrod precipitation radar network reveal that these bands formed along the major axis of each body of water or sea when the boundary layer flow was roughly parallel to each of those axes along channel for both seas a band was present the majority of times that the 850 hpa flow was along channel of these times of along channel flow the 850 hpa wind speed and surface to 850 hpa temperature difference were significantly greater when bands were present than when they were not for the english channel only the land sea temperature difference was also significantly greater when bands were present than when they were not in a real data weather research and forecasting model wrf control simulation of a typical band over the english channel a trough develops over the water and offshore air streams from either side converge along it in the absence of surface fluxes the trough convergence and organized precipitation fail to develop altogether orography and roughness length variations are less important in band development affecting only the location and morphology

marine molluscs and late quaternary environmental studies with particular reference to the late glacial period in northwest europe a review abstract although it is now commonly thought that temperature is a minor factor in limiting the distribution of marine invertebrates particularly on a local scale there is evidence to suggest that some boreal molluscs particularly those which occur in similar environments on both sides of the north atlantic are valuable as oceanic temperature indicators this applies particularly to planktotrophic species whose northern limits of distribution are apparently controlled by summer surface temperature the oceanography of the eastern north atlantic is briefly considered in relation to zoogeographic subdivisions based on temperature and it is concluded that the latter are fairly crude and apply only to shelf seas most glaciomarine molluscan faunas are not specific to that environment an exception being that dominated by the bivalve portlandia arctica the role of marine molluscs in palaeoenvironmental research at the local level for the 13 11 ka bp period is illustrated by a site at inchinnan scotland it is concluded that a shell bed at this locality consists partly of a little modified life assemblage and partly of shells which have been gently reworked under conditions of generally rapid deposition during the same time interval the changing composition of molluscan faunas on the nw european seaboard suggests that a weak drift of north atlantic water replaced polar water at or a little later than 13 ka bp off scotland and a few hundred years later off northern norway evidence for relatively warm intervals early and late in the 13 11 ka bp period has been found particulary on the scottish coast and to a lesser extent more generally the later warm interval may be related to the southward movement of the polar front at the beginning of the younger dryas the value of the bivalve shell itself in the determination of temperature seasonality and calendar years is briefly discussed

mixing zone origin of 13c depleted calcite cement oseberg formation sandstones middle jurassic veslefrikk field norway abstract carbonate cement is one of the more volumetrically important diagenetic components of sandstones the sandstones of the fan delta facies of the oseberg formation brent group in veslefrikk field contain abundant carbonate cemented zones commonly comprised of 30 40 carbonate by volume the cement is predominantly poikilotopic ferroan calcite with minor amounts of ankerite and siderite petrographie evidence for high porosities at the time of calcite precipitation indicate that cementation occurred under shallow burial conditions probably less than 500 m crosscutting textural relations demonstrate that calcite cementation was predated and postdated by tectonic stresses that produced both grain fractures and through going fractures respectively in the non calcite cemented parts of the formation major compaction pressure solution feldspar dissolution and cementation by quartz and clays postdated calcite cementation the oxygen isotopic composition of the calcite averages 8 5 0 pdb and shows large variations within individual calcite cemented zones up to 10 0 in 18 o the depleted and variable oxygen isotopic composition in conjunction with evidence for shallow precipitation indicate calcite growth occurred in a mixing zone environment variably influenced by meteoric water isotopic variation within many individual cemented zones is symmetric about the center of the zones indicating that growth of the cemented zones was from the center outwards in a concretionary fashion the high fe and mn content of the calcite avg 1 3 mol fe avg 0 4 mol mn and its association with disseminated pyrite indicate that porewater was reducing during precipitation carbon isotopic data avg 13 c 15 7 0 pdb range 3 to 3 1 0 show that major amounts of organic carbon at least partly derived by sulfate reduction of biogenic methane were incorporated in the calcite other documented occurrences of early 13 c depleted carbonate cemented sandstones are similar to the carbonate cement in veslefrikk field in their association with methane oxidation and their low temperature formation however the cement at veslefrikk differs in its mineralogical and morphological occurrence and in the fact that it formed from a porewater strongly influenced by mixing with meteoric water key geologic factors that determined the traits of calcite cement in veslefrikk field are the combination of nearshore marine deposition of permeable sands close proximity of organic rich marine muds and variations in relative sea level which provided opportunities for invasion by meteoric water these geologic factors had a similar impact on other brent group deltaic sandstones and are believed to explain some of the differences between the geochemistry of carbonate cements in deltaic and shelf sandstones of the north sea and elsewhere

distribution of otoliths in surficial sediments of the u s atlantic continental shelf and slope and potential for reconstructing holocene fish stocks we examined more than 1100 surface sediment samples from the atlantic continental margin of the united states to determine the feasibility of using fossil fish otoliths as diagnostic tools in reconstructing paleoenvironments and latitudinal distribution of fish stocks during the holocene although 63 of the 1107 samples collected were from shelf areas 140 m the total number of shelf derived otoliths represents only 0 3 of the entire sampled assemblage the majority of otoliths occurred on the continental slope 400 2000 m with a maximum concentration in sediments at 500 to 600 m water depth otoliths of the most commonly occurring species ceratoscopelus maderensis exhibit a marked distributional boundary just south of cape hatteras north carolina 33 n which mimics the distribution of their living counterparts north of this boundary c maderensis constitutes greater than 70 of the preserved otolith assemblage whereas more southerly regions contain no otoliths of this species although c maderensis typically migrates diurnally over a depth of 300 600 m otoliths taken from live captured c maderensis exhibit 14c values comparable to that of the dissolved inorganic carbon dic of surface seawater in the study area accelerator mass spectrometry radiocarbon analyses of cooccurring otoliths and planktonic foraminifera from a sediment core collected south of martha s vineyard 40 15 n 70 51 w 265 m demonstrate temporal concordance throughout the holocene otoliths appear to be viable underutilized paleoceanographic tools specimens are found in sufficient abundance to permit temporal reconstructions of the distribution of c maderensis and potentially several other icthyospecies along the u s atlantic continental margin

coast of departure and coast of arrival two important concepts for the formation and structure of convective snowbands over seas and lakes abstract a case with intense convective snowbands over the baltic sea is examined using the high resolution limited area model the intention is to gain a better insight into the importance of the shape of the coasts the orography and the surface roughness on the formation and evolution of the snowbands among the factors studied are the shape of the coast from which the air departs and that to which it arrives these factors are so important that two new concepts coast of departure and coast of arrival are introduced

mesoscale coastal processes during gale iop 2 abstract during intensive observation period 2 of the genesis of atlantic lows experiment a number of mesoscale phenomena were observed with special and conventional observing systems over the land and coastal waters this study involved analysis of these data for the period 24 26 january 1986 in order to define the structure and dynamics of three features the coastal front a shallow cyclone that propagated along the coastal front modifying it as it moved northward and a low level jet that formed in the strong coastal pressure gradient field the coastal front formed in an existing pressure trough over the gulf stream as a result of both ageostrophic deformation and differential diabatic heating there existed considerable variability in the frontal strength and position on both the mesoalpha and mesobeta scales the level of strongest frontogenesis was near the surface with frontolysis calculated above 950 mb the marine atmospheric boundary layer mabl over the gulf stream was conducive to cyclon

calcite cemented concretions in cretaceous sandstone wyoming and utah u s a abstract spheroidal cannon ball calcite cemented concretions some of gigantic size were studied from three cretaceous shelf sandstone units ferron frontier and second frontier the concretions have diameters between 2 cm and 6 m those larger than 40 cm in diameter in the ferron and frontier have septarian structure rare concretions in the second frontier with cone in cone also have septaria the pattern of carbon and oxygen isotopic data and intergranular volume igv data across concretions indicate that concretion growth was complex not all concretions grew progressively from their centers toward their edges in many concretions displacive fascicular optic high mg calcite foc precipitated simultaneously throughout the concretions pervasive growth pattern although the earliest cementation was concentrated in and near their centers remaining pores were subsequently filled by poikilotopic calcite of lower mg content displacive foc cement in the bodies of concretions and in cone in cone structure and the large igv values indicate that these carbonate phases formed at burial depths no greater than tens of meters igv values indicate that spar cement continued to depths of at least 50 m and possibly deeper the association of organic matter and microbial structures or microbial byproducts with displacive foc and cone in cone calcite raises the possibility that biogenic processes were responsible for the apparently rapid growth of the displacive calcite the oxygen isotope composition of pore waters was fairly uniform in the range of 18o of 4 to 6 smow during 80 of concretion growth but became even more depleted in 18o during the last stage of growth and during septarian fracture filling ranging into values as depleted as 14 smow 13c in calcite is negative 4 to 18 v pdb but variable reflecting a range of microbial processes under both oxidizing and reducing conditions earlier calcites fall mostly in the range of 10 to 16 v pdb relatively later calcite in veins and on concretion margins is more enriched in 13c fe and mn concentrations in calcites have a rough positive correlation with higher 13c values the concentration of mg derived from seawater and altered volcanic rock fragments covaries positively with the degree of meteoric influence lower mg contents correlate positively with relatively depleted 18o values 87sr 86sr values are typical of sr derived from coeval seawater or marine skeletal debris growth of concretions 4 to 6 m in diameter apparently in 5 my requires some spatial localization of growth sites by a self organization process and probably a large supply of carbonate shells in the original sediment elongation of larger concretions in the plane of bedding suggests that advective rather than diffusive supply of cement components dominated late in concretion growth history concretions formed close to the tops of parasequence boundaries

methane derived high mg calcite submarine cement in holocene nodules from the fraser delta british columbia canada carbonate nodules and slabs in late holocene shelly terrigenous deposits of the modern fraser river delta 49 n are formed close to the seafloor by precipitation from saline pore waters of mainly fibrous to bladed crystals of high mg 10 20 mol mgco3 calcite cement as coalescing isopachous crusts on grains previous reports that the cement is low mg calcite are not supported by this study highly negative 13c values of 7 to 59 for the cements indicate that the bulk of their carbonate carbon was derived from the microbiological degradation of organic matter in the deltaic deposits during shallow burial in particular the production of biogenic methane ch4 by anaerobic bacterial fermentation its upward migration chemical or biological oxidation to co2 and neutralization in the near surface sediment and diffusion to microenvironments relatively enriched in organic components are a possible set of conditions influencing the process and sites of carbonate cementation methane derived mg calcite appears also to be the major submarine cement in several other modern occurrences of lithified shallow water terrigenous sands and muds at non tropical latitudes

sandstone porosity loss a big picture view of the importance of compaction proper assessment of the relative importance of porosity loss by compaction and cementation is important to the prediction of porosity in sandstones studies of mass transport during diagenesis and the modeling of basin fluid flow quantitative estimation of the amounts of porosity loss by compaction and cementation can be made from standard point count data on cement and pore space abundance this method is discussed and its sources of error are evaluated error in the method arises mainly from uncertainty in initial sandstone porosities and the amount of local grain dissolution during burial data on the porosity of modern sands indicate that assumed initial porosities of 40 to 45 will produce small average errors in the calculation of compactional porosity loss for clean sandstones grain dissolution whether resulting in local porosity enhancement by export in solution of former grain mass or local precipitation of authigenic cement will cause an underestimation of the significance of compaction a large database of point count data from diverse sandstones is used to provide a broad perspective on the importance of compaction and cementation to sandstone porosity loss it is shown that the global importance of compactional porosity loss has generally been under appreciated in fact compaction mechanical and chemical is probably the dominant mechanism of porosity loss in most sandstones the extent of compactional porosity loss is related to sand grain composition and basin thermal structure

a renewed look at calcite cement in marine deltaic sandstones the brent reservoir heather field northern north sea uk wireline and seismic acoustic impedance imaging show that the marine part of the clastic brent group reservoir in the heather field northern north sea contains much calcite cement in the flank parts of the structure the non marine ness formation and crest parts of the structure contain negligible calcite cement this localised calcite cement has led to relatively poor reservoir performance since first oil in 1978 although a new suite of wells has boosted production with plans to keep the field active until 2030 understanding the origin and distribution of calcite cement would help the development of more realistic reservoir models and boost production rates through optimum well location we have thus used a suite of techniques including standard point counting sem eds mineralogy bse microscopy fluid inclusion thermometry and stable isotope analysis to develop new and improved models of calcite distribution calcite seems to have attributes of both early and late diagenetic cement 30 to 40 intergranular volume in calcite cemented beds seems to support pre compactional growth but high temperature fluid inclusions and the presence of primary oil inclusions suggests late growth much calcite may have developed early but it seems to have recrystallized and possibly undergone redistribution at close to maximum burial or had a late growth event calcite cement probably originated as marine derived micrite bioclasts or early marine cement but adopted the isotopic characteristics of high temperature growth as it recrystallized quartz grains have corroded outlines in calcite cemented areas with one sample with 79 calcite cement displaying signs of nearly total replacement of quartz grains by calcite the flank localisation of calcite remains to be explained although it could be due to primary depositional factors early diagenetic loss of calcite from crestal regions or late diagenetic loss of calcite from crestal regions controversially the growth of calcite seems to be associated with quartz dissolution although the geochemical and petrophysical cause of this remains obscure diagenetic loss of quartz from sandstones cannot easily be explained by conventional modelling approaches and yet seems to be an important phenomenon in heather sandstones

the impact of diagenesis on the heterogeneity of sandstone reservoirs a review of the role of depositional facies and sequence stratigraphy diagenesis exerts a strong control on the quality and heterogeneity of most clastic reservoirs variations in the distribution of diagenetic alterations usually accentuate the variations in depositional porosity and permeability linking the types and distribution of diagenetic processes to the depositional facies and sequence stratigraphic framework of clastic successions provides a powerful tool to predict the distribution of diagenetic alterations controlling quality and heterogeneity the heterogeneity patterns of sandstone reservoirs which determine the volumes flow rates and recovery of hydrocarbons are controlled by geometry and internal structures of sand bodies grain size sorting degree of bioturbation provenance and by the types volumes and distribution of diagenetic alterations variations in the pathways of diagenetic evolution are linked to 1 depositional facies hence pore water chemistry depositional porosity and permeability types and amounts of intrabasinal grains and extent of bioturbation 2 detrital sand composition 3 rate of deposition controlling residence time of sediments at specific near surface geochemical conditions and 4 burial thermal history of the basin the amounts and types of intrabasinal grains are also controlled by changes in the relative sea level and therefore can be predicted in the context of sequence stratigraphy particularly in paralic and shallow marine environments changes in the relative sea level exert significant control on the types and extent of near surface shallow burial diagenetic alterations which in turn influence the pathways of burial diagenetic and reservoir quality evolution of clastic reservoirs carbonate cementation is more extensive in transgressive systems tract tst sandstones particularly below parasequence boundaries transgressive surface and maximum flooding surface because of the abundance of carbonate bioclasts and organic matter bioturbation and prolonged residence time of the sediments at and immediately below the sea floor caused by low sedimentation rates which also enhance the formation of glaucony eogenetic grain coating berthierine odinite and smectite formed mostly in tst and early highstand systems tract deltaic and estuarine sandstones are transformed into ferrous chlorite during mesodiagenesis helping preserve reservoir quality through the inhibition of quartz cementation the infiltration of grain coating smectitic clays is more extensive in braided than in meandering fluvial sandstones forming flow barriers in braided amalgamated reservoirs and may either help preserve porosity during burial because of quartz overgrowth inhibition or reduce it by enhancing intergranular pressure dissolution diagenetic modifications along sequence boundaries are characterized by considerable dissolution and kaolinization of feldspars micas and mud intraclasts under wet and warm climates whereas a semiarid climate may lead to the formation of calcrete dolocrete cemented layers turbidite sandstones are typically cemented by carbonate along the contacts with interbedded mudrocks or carbonate mudstones and marls as well as along layers of concentration of carbonate bioclasts and intraclasts commonly hybrid carbonate turbidite arenites are pervasively cemented proximal massive turbidites normally show only scattered spherical or ovoid carbonate concretions improved geologic models based on the connections among diagenesis depositional facies and sequence stratigraphic surfaces and intervals may not only contribute to optimized production through the design of appropriate simulation models for improved or enhanced oil recovery strategies as well as for co2 geologic sequestration but also support more effective hydrocarbon exploration through reservoir quality prediction

cretaceous cold seep communities and methane derived carbonates in the canadian arctic lower cretaceous cold seep fossil assemblages have been found in the canadian arctic archipelago serpulid worm tubes and bivalves are most abundant in these communities in contrast fossils are scarce in the surrounding strata the fossils are contained in an isotopically light delta 13 c 25 to 50 per mil carbonate rock groundmass that is interpreted to have formed from bacterial oxidation of methane the rocks were deposited at intermediate depth 400 meters in a cold marine environment nearby normal faults may have provided a conduit for seeping methane and hydrogen sulfide needed to fuel chemosynthetic bacteria and in turn the higher life forms

calcite cementation in shallow marine eocene sandstones and constraints of early diagenesis the lower eocene shallow marine roda sandstone member forms part of the paleogene fill of the tremp graus basin in the southern spanish pyrenees it is composed of mixed siliciclastic carbonate sandstones that were severely modified in composition and texture shortly after deposition during pauses in sedimentation moreover part of the sand was lithified by an early marine fringe cement this early diagenetic cement stabilized the sandstone framework and prevented mechanical compaction where early cement was absent mechanical compaction severely reduced the primary porosity during a first burial phase ductile grains were squeezed between rigid grains obstructing pore connections this caused the development of distinct porosity patterns in the sandstone bodies after the first burial phase two major phases of uplift and erosion resulted in the truncation of the roda sandstone member in the northern part of the area studied after the erosional phases the sandstones were buried again recharge of the sandstone bodies with fresh water caused replacement of aragonite and high magnesian calcite by low magnesian calcite simultaneously a second generation of sparry calcite cement was precipitated replacement and cementation were completed first in the most porous and permeable levels represented by those parts of the sandstone that contained the early cement the intervals compacted during the first burial were cemented later or cementation was completed later

the influence of coastal shape on winter mesoscale air sea interaction abstract in the case of cold air outbreaks the combination of the coastal shape and the sea surface temperature sst pattern is shown to have a profound effect in establishing a low level mesoscale atmospheric circulation as a result of differential heating due to both variations in overwater path length and the sst a convergence or divergence line then forms along a line exactly downwind of the major bend in the coastline this is consistent with the structure of the cloud patterns seen in a high resolution landsat picture of the cloud streets the major features are also simulated well with a boundary layer model the dominant convergence line is marked by notably larger clouds to its cast the convective roll clouds grow downstream in accord with the deepening of the boundary layer to its west i e coastal side near the convergence line where the induced pressure field forces a strong westerly component in the boundary layer the wind shear across the inversion gives rise to kelvin helmholtz w