the white stone band of the kimmeridge clay formation an integrated high resolution approach to understanding environmental change the kimmeridge clay is a jurassic mudrock succession that shows milankovitch band climatic cyclicity a key issue is to determine how the subtle changes that define this cyclicity result from climatic change using material from the natural environment research council rapid global geological events rgge kimmeridge drilling project boreholes the white stone band was investigated at the lamination scale using backscattered electron imagery and quantitative palynofacies fabric analysis shows the lamination to represent successive deposition of coccolith rich and organic matter rich layers individual laminae contain unsorted palynological debris with a consistent ratio of marine and terrestrial components such mixed organic matter input is interpreted as the result of storm transport linking water column processes to laminae deposition suggests seasonal input with a coccolith bloom followed by a more diverse assemblage including dinoflagellates and photosynthetic chlorobiacean bacteria as the photic zone extended into the euxinic water column organic matter export to the sea bed underwent minimal cycling through oxidation and subsequently became preserved through sulphurization with greatly increased sequestration of carbon this was significantly increased by late season storm driven mixing of euxinic water into the photic zone increased frequency of storm systems would therefore dilute the coccolith input to give an oil shale hence climatically induced changes in storm frequency would progressively vary the organic content of the sediment and generate the climate cycle signal

a low order model of the heinrich event cycle if heinrich events result from free oscillations in the size and basal melting conditions of the laurentide ice sheet a rigorous quantitative analysis of ice sheet physics should describe their dynamics to explore this possibility i exploit two characteristic timescales which arise from ice sheet physics to construct a relaxation oscillator model of the north atlantic s heinrich events the numerical implementation of this model confirms the notion that the periodicity of heinrich events approximately 7 000 years is determined by the gross properties of a steady glacial climate e g an annual average sea level temperature of 10 c and an adiabatic lapse rate

the mutual interaction between continental scale ice sheets and atmospheric stationary waves the great continental ice sheets of the pleistocene represented significant obstacles to the northern hemisphere midlatitude westerlies they must therefore have forced large changes in the atmospheric circulation and consequently also in the patterns of accumulation and melting over the ice sheets themselves a simplified threedimensional coupled ice sheet stationary wave model is developed in order to understand the ice sheet s response to the circulation changes that it induces consistent with ice age climate simulations the ice sheet topography induces an anticyclonic circulation over the ice sheet causing a slight warming over the western slopes and a stronger cooling over the remainder the modeled feedbacks significantly affect the ice sheet configuration with the most important influences being the patterns of summer temperature and the topographically induced precipitation field the time evolution of the ice sheet is also changed by the atmospheric feedbacks and the results suggest the possibility of multiple equilibrium solutions

the thermomechanical response of the greenland ice sheet to various climate scenarios using a three dimensional numerical model for land based ice sheets in the shallow ice approximation simulations are performed to determine the velocity and temperature distributions within the greenland ice sheet through time for various climate scenarios the ice is treated as a rheologically nonlinear heat conducting viscous fluid and the substrate is a heat conducting rigid solid this system is fed from above by prescribing as the climatic inputs the atmospheric temperature and the accumulation ablation rate functions at the free surface and from below by the geothermal heat we present the governing equations in the shallow ice approximation discuss the parameterizations used in the descriptions of the ice surface temperature and accumulation ablation functions briefly state how the complicated initial boundary value problem is numerically solved and how the input data that are available from measurements are implemented results of preliminary calculations disclose how the model performs and delimit its validity we study the role played by basal sliding and make clear that sliding should be accounted for where ever the basal ice is temperate and that the frictional heat generated in this sliding is thermomechanically significant we also study the reaction of the greenland ice sheet to various climate scenarios and make clear that today s thermal regime depends significantly upon the prior climate history moreover the thermomechanical properties of the ice are equally significant as is the thermal interaction of the ice sheet with the rockbed beneath

re evaluation of paleo accumulation parameterization over northern hemisphere ice sheets during the ice age examined with a high resolution agcm and a 3 d ice sheet model

the north american late wisconsin ice sheet and mantle viscosity from glacial rebound analyses abstract observations of sea level and crustal response to glacial loading cycles provide constraints on the mantle rheology function e and as well as on the ice load i with the latter being largely free from a priori glaciological or climate assumptions and appropriate therefore for testing any such hypotheses this paper presents new results for both continental mantle e and i for the late wisconsin ice sheet using geological evidence for relative sea level change rsl and tilting of palaeo lake shorelines complemented with loose constraints from observations of present day radial crustal displacement across north america the focus is on evidence from near or within the former maximum ice margins and the resulting earth response is representative of sub continental mantle conditions the inversion of the sea level information has limited resolution for earth rheology and simple three layer models characterized by depth averaged effective lithospheric thickness h and upper and lower mantle viscosities um and um respectively adequately describe the response function yielding parameters earth model e 6 of h 102 85 120 km um 5 1 1020 3 5 7 5 x1020 lm 1 3 1022 0 8 2 8 x1022 where the numbers in parenthesis are 95 confidence limits the details of the ice sheet with one exception are not strongly dependent on the rheological assumptions within this range the exception is the lower mantle viscosity that remains correlated with the magnitude scaling of the ice sheet a link that is largely broken by introducing constraints from glacial loading effects on the earth s rotation and dynamic flattening the difference between the continental um and the comparable estimate of 1 2 5 x1020 for ocean mantle is statistically significant shoreline gradient information from glacial lakes mcconnell agassiz algonquin and ojibway provide strong constraints on the response within the interior of the ice sheet and the resulting ice sheet model lw 6 is characterized by multiple ice domes from at least 17 18 ka onwards the resolution for earlier periods is largely constrained by global ice volume considerations the two principal domes are over southern nunavut the keewatin dome and over quebec labrador both of 3500 m thickness separated by an ice ridge some 1500 m lower than the domes the latter a requirement imposed by the gradient information over western canada ice thickness gradients east of the cordilleras are partly constrained by the shoreline data for former lake mcconnell as is the lateglacial ice thickness of the keewatin dome and indicate that any ice free corridor between the laurentian and cordilleran components is unlikely to have existed before 13ka reconstructions of the glacial lakes are consistent with the locations and timing of the observational evidence for the four major lake systems with the likely drainage routes identified the evolution of the lw 6 ice volume function expressed as equivalent sea level is characterized by a rapid decrease in ice volume from 15 to 14 5 ka corresponding to the bolling allerod period in the main from rapid ice retreat along the southern margin with further contributions from drainage through the st lawrence river valley and from ice retreat from the major northern straits and gulfs but not hudson strait where the rsl data point to late removal of ice after 10 ka the contribution of the drainage of the lakes to global sea level rise is small

numerical paleoceanographic study of the early jurassic transcontinental laurasian seaway the forces governing marine circulation of a meridional transcontinental seaway is explored with the princeton ocean model the jurassic laurasian seaway which connected the low latitude tethys ocean with the arctic sea is modeled quantitatively the global ocean is found to have a profound influence on seaway dynamics a north south density difference and hence sea level difference of the global ocean was probably the main factor in forcing the seaway flow when the tethys waters were the denser water the net seaway flow was southward and conversely it was northward for denser arctic waters marine bioprovincial boundaries and sediment data indicate that the seaway probably was dominated by boreal faunal groups and reduced salinities several times in the jurassic the model results suggest that this can be explained by southward flowing seaway currents which may have been related to an oceanic thermohaline circulation where no northern high latitude deep convection occurred

adsorption and desorption of phosphate on limestone in experiments simulating seawater intrusion abstract this study investigates the potential release of po 4 3 from carbonate aquifers exposed to seawater intrusion adsorption and desorption of po 4 3 in the presence of deionized water diw and seawater were conducted on a large block of pleistocene age limestone to simulate the effects of seawater intrusion into a coastal carbonate aquifer at the laboratory scale the limestone showed strong adsorption of po 4 3 in diw while adsorption was significantly less in the presence of seawater dissolution of caco3 was found to prevent po 4 3 adsorption at salinities less than 30 psu adsorption of po 4 3 was limited at higher salinities 30 33 psu due to competition with hco 3 ions for adsorption sites at a salinity po 4 3 absorption occurred as caco3 precipitated concentrations of po 4 3 between 2 and 5 mol l were released by desorption when the limestone was exposed to seawater the results of this study suggest that as seawater intrudes into an originally freshwater coastal aquifer adsorbed po 4 3 may be released into the groundwater consequently adsorbed po 4 3 is expected to be released from coastal carbonate aquifers world wide as sea level continues to rise exposing more of the freshwater aquifer to seawater

water rock interactions in a modern coastal mixing zone the chemical evolution of ground water and the diagenetic history of the rocks in a modern saline fresh water mixing zone were investigated to test the hypothesis that this zone is a chemically active environment in which carbonate mineral diagenesis occurs the field site was in the unconfined section of the upper floridan aquifer system in west central florida a regionally extensive hydrostratigraphic unit composed of eocene oligocene limestone and dolomite the mixing zone marked by a steep concentration gradient is 90 m thick at the study site in new port richey pasco county florida interpretation of aqueous geochemical data indicates that the coastal zone is most likely a location where three waters of distinct composition mix a fresh ca hco3 water that derives its composition from calcite dissolution and co2 influx in the up gradient recharge area a na cl water that results from salt water intrusion and a ca so4 rich water that upwells subsequent to contact with underlying gypsiferous beds of the avon park formation are likely all converging in this coastal setting poor core recovery and an enlarged core hole provide evidence of dissolution the ground water however is oversaturated with respect to calcite thus the large scale dissolution features observed are unrelated to modern day mixing the mixing of ca so4 rich ground water in the coastal region led to oversaturation with respect to calcite at the petrographic scale there is little evidence of diagenesis related to the modern mixing zone calcite crystals from the lower section of the cored interval have isotopic signatures that are different than those from the upper section suggesting that the latter has undergone more water rock interactions calcium rich dolomite which occurred relatively late in the paragenetic sequence has thin cathodoluminescent zonations but shows no evidence of subsequent alteration the paragenetic sequence includes marine micritization and cementation meteoric mineralogic stabilization dissolution enhancement of porosity phreatic equant calcite cements and echinoderm overgrowths all typical of the region and not unique to the mixing zone

application of a polythermal three dimensional ice sheet model to the greenland ice sheet response to steady state and transient climate scenarios abstract steady state and transient climate change computations are performed with the author s three dimensional polythermal ice sheet model simulation code for polythermal ice sheets for the greenland ice sheet the distinctive feature of this model is the detailed consideration of the basal temperate ice layer in which the water content and its impact on the ice viscosity are computed its transition surface to the cold ice region is accounted for by continuum mechanical jump conditions on this interface the simulations presented include steady states subject to a range of physical parameters and two different climates present and glacial conditions as well as three types of transient scenarios namely i sinusoidal milankovic period forcing ii paleoclimatic forcing from the greenland ice core project core reconstruction and iii future greenhouse warming forcing

mixing zone diagenesis in the subsurface of florida and the bahamas abstract three cores from great bahama bank and southern florida contain examples of mixing zone diagenesis where typical shallow water aragonite rich sediments were altered to low mg calcite the 40 50 m thick mixing zones are identified on the basis of downcore covariant trends from depleted meteoric 18o 3 2 0 7 13c 1 6 1 8 to enriched marine isotopic values 18o 1 0 0 3 13c 1 9 0 7 the age of the mixing zones varies from late pliocene to pleistocene so these cores provide three independent examples of mixing zone diagenesis mixing zone diagenesis produced a limestone composed of low mg calcite with petrographic fabrics including moldic porosity blocky to dogtooth calcite cementation and recrystallization of lime mud to micrite and microspar the mixing zone diagenetic model predicts alteration in only part of the mixing zone because the alteration recorded in these cores shows continuous alteration through the entire mixing zone we consider the mixing of waters itself to be largely irrelevant rather diagenesis was probably driven by the difference in solubility between aragonite and calcite with some additional dissolution of aragonite driven by the microbial oxidation of buried organic matter the mixing zone has been proposed as a likely location for dolomitization with the exception of some clearly sea floor dolomite in one core unda the mixing zones in these cores lack dolomite despite the sediment clearly having been altered in the mixing zone the lack of dolomite in these mixing zones combined with the extensive literature questioning the chemical reasoning for mixing zone dolomite supports rejection of the mixing zone dolomite model

reactive transport modeling of calcite dissolution in the fresh salt water mixing zone abstract dissolution of calcite in the saltwater mixing zone of coastal carbonate aquifers has been the subject of numerous studies they conclude that dissolution is driven by mixing of freshwater and saltwater which may lead to undersaturation even if both end members are saturated however as transport in the mixing zone is rather complex a fully coupled reactive transport model is needed to properly understand the interplay between transport and chemistry we perform 1 and 2d simulations to gain insight into the processes controlling dissolution rate exploring its sensitivity to the chemistry of end members and the dispersivity of the medium we conclude that the results of sanford and konikow sanford w e konikow l f 1989 simulation of calcite dissolution and porosity changes in saltwater mixing zones in coastal aquifers water resources research 25 655 667 which used a two step method solely transporting the amount of calcite dissolved are essentially correct but their solution is essentially kinetic with a rate dependent on the time increment used the 1d simulations allow us to show that maximum dissolution rates do occur neither at the location nor for the end members of maximum undersaturation for non reactive mixing in the 1d case enhanced transport at the freshwater end causes dissolution to concentrate there however in the 2d case representative of coastal aquifers maximum dissolution occurs at the saline side near the discharge zone because of a very active convection cell that develops there which enhances mixing and thus reaction rates this mechanism may explain observations at blue holes and should display a positive feedback with dissolution causing an increase in permeability that would lead to increased seawater flux and mixing thus enhancing further dissolution

annual layering in the upper jurassic kimmeridge clay formation uk quantified using an ultra high resolution sem edx investigation abstract this paper reports the results of an ultra high resolution investigation of the geochemistry of the late jurassic kimmeridge clay formation kcf using scanning electron microscope energy dispersive x ray analysis sem edx sub millimetre banding is revealed in which each band approximately 112 m thick comprises a couplet of coccolith rich and coccolith poor sediment major element analysis reveals that regularly spaced peaks in the relative amount of calcium are associated with coccolith rich bands it is argued that each couplet represents an annual layer the calcium peaks corresponding to an annual bloom of coccolithophorids there is also a broad correlation between the calcium aluminium ratio and the ratios of sodium aluminium phosphorus aluminium and potassium aluminium to calcium aluminium ratios we tentatively suggest that there may be a link here sodium phosphorous and potassium today being key nutrients for coccolith productivity aluminium is taken as representing the background terrigenous clay fraction if each banded couplet is indeed annual and if the thickness of such bands were to be representative of the kcf as a whole then the post compactional thickness is broadly in agreement with sedimentation rates of 100 m per year calculated by oschmann 1990 this study confirms the view that the kcf in southern england accumulated in a predominantly anoxic environment that favoured the preservation of organic material within the bottom sediment bundles of bands clustering in groups of about 8 10 are tentatively related to short term changes in insolation possibly sun spot cycles

heterogeneous distributions of co 2 may be more important for dissolution and karstification in coastal eogenetic limestone than mixing dissolution mixing dissolution a process whereby mixtures of two waters with different chemical compositions drive undersaturation with respect to carbonate minerals is commonly considered to form cavernous macroporosity e g flank margin caves and banana holes in eogenetic karst aquifers on small islands macroporosity commonly originates when focused dissolution forms globular chambers lacking entrances to the surface suggesting that dissolution processes are decoupled from surface hydrology mixing dissolution has been thought to be the primary dissolution process because meteoric water would equilibrate rapidly with calcium carbonate as it infiltrates through matrix porosity and because pco2 was assumed to be homogeneously distributed within the phreatic zone here we report data from two abandoned well fields in an eogenetic karst aquifer on san salvador island bahamas that demonstrate pco2 in the phreatic zone is distributed heterogeneously the pco2 varied from less than log 2 0 to more than log 1 0 atm over distances of less than 30 m generating dissolution in the subsurface where water flows from regions of low to high pco2 and cementation where water flows from regions of high to low pco2 using simple geochemical models we show dissolution caused by heterogeneously distributed pco2 can dissolve 2 5 to 10 times more calcite than the maximum amount possible by mixing of freshwater and seawater dissolution resulting from spatial variability in pco2 forms isolated globular chambers lacking initial entrances to the surface a morphology that is characteristic of flank margin caves and banana holes both of which have entrances that form by erosion or collapse after cave formation our results indicate that heterogeneous pco2 rather than mixing dissolution may be the dominant mechanism for observed spatial distribution of dissolution cementation and macroporosity generation in eogenetic karst aquifers and for landscape development in these settings copyright 2015 john wiley sons ltd

cyclicity in the egret member kimmeridgian oil source rock jeanne d arc basin offshore eastern canada the origin of the observed variability in lithology total organic carbon and petrophysical properties of the egret member source rock interval in the jeanne d arc basin offshore eastern canada is examined detailed analyses of petrophysical logs indicate that the egret member is cyclic three different orders of cycles recognizable on well logs occur in the egret member the large and medium scale cycles are correlatable among wells the estimated cyclicities of the large and medium scale cycles fall into the milankovitch like cycle bands suggesting that the depositional cycles are the product of orbitally forced sea level and climatic changes and implying that egret member deposition lasted at least 1 65 million years using chronological information drawn from sedimentary cycles both spatial and vertical temporal variations in sedimentation rate are examined for the member a correlation exists between low sedimentation rates and high total organic carbon values in this basin it is most probable that the organic rich layers were deposited during times of high sea level stands and warmer periods

comprehensive evolution of a petroleum system in absolute time the example of brynhild norwegian north sea abstract petroleum systems are inherently complex comprising multiple components and processes which variably interact in space and time to form petroleum accumulations improved understanding of these complex systems requires a holistic approach of integrating diverse geological geophysical and organic and inorganic geochemical data here we present an applied and comprehensive re os geochronological and geochemical study on the brynhild petroleum system from the norwegian north sea essential components of this system include shale source rocks of the mandal and farsund formations reservoir sandstones of the ula formation and their bitumen extracts and produced brynhild crude oil rock eval trace metal and re os data reveal the excellent oil generation potential of the shaley source rocks high contents of organic matter containing large amounts of type i kerogens and constrain their depositional conditions anoxic bottom waters in a high productivity regime driven by enhanced supply of land derived nutrients seven re os shale ages between 146 and 134 ma are consistent with existing volgian ryazanian age estimates and constrain the initial 187os 188os of the shales to 0 52 in the lowermost farsund formation and 0 75 in the uppermost mandal formation solvent extracted reservoir rocks of the ula formation contain insoluble organic matter with type iii type iv kerogens likely supplied by erosion of older a precise 179 ma re os age with unrealistically low initial 187os 188os coal bearing sediments or organic rich shales the brynhild crude oil has relatively low 187os 188os and a generation age of 44 ma based on an asphaltene only re os isochron maltenes from the brynhild crude oil are isotopically affected by interaction with organic rich source rocks that represent the seal for the brynhild oil field compared with the crude oil bitumen from ula formation sandstones have contrasting re os properties high 187os 188os ratios and young generation ages between 8 and 0 ma based on asphaltene bitumen maltene re os triplets asphaltene only re os regressions and re os model ages for components with extremely high 187re 188os the 44 ma and 8 0 ma re os ages agree well with regional burial models that indicate oil generation from 44 ma to present day a genetic link between crude oil and bitumen is indicated by their similar alkane patterns v and ni contents and v ni and pristane phytane ratios modeling of 187os 188os for individual organic components through time shows that shales of the mandal formation developed 187os 188os ratios that match those of the crude oil and bitumen at 44 ma and 8 ma respectively and therefore confirm the source for both hydrocarbon phases we suggest that bitumen formed during in reservoir mixing of a 44 ma old early mature asphaltene poor oil brynhild crude oil with an 8 ma old asphaltene rich oil

submarine springs and coastal karst aquifers a review this article reports on current knowledge of coastal karst aquifers in which conduit flow is dominant and its aim is to characterise the functioning of these systems which are closely linked to the sea first earlier and recent studies of these aquifers are discussed on the basis of their findings it can be shown that two essential mechanisms are involved in the functioning of these systems i e aquifer discharge through submarine springs and saline intrusion through conduits open to the sea then the conditions that give rise to these aquifers are described and particular emphasis is placed on the influence of deep karstification when the sea level falls the base level variations are attributed to the glaciations or in the specific case of the mediterranean to the salinity crisis in the messinian period it is this inherited structure sometimes containing very deep conduits below sea level that today conditions the aquifer flow the flow in the conduits open to the sea depends on the hydraulic head gradient between the aquifer and the sea and is therefore a function of the water density and head losses in the aquifer this survey of coastal karst aquifers has revealed some common characteristics that show the development and or functional capacity of their karstic drainage networks a classification of such systems into three categories is proposed with the aim of assisting in the decision making concerning potential exploitation of water resources in coastal regions

precipitation over greenland retrieved by a dynamic method and its relation to cyclonic activity abstract in order to calculate the vertical motion over some high mountain regions such as greenland an equation without the quasigeostrophic approximation in coordinates has been developed a dynamic method for retrieving precipitation over greenland is based on this equation the retrieved annual mean precipitation distribution for 1987 and 1988 is in very good agreement with the observed annual accumulation pattern over the greenland ice sheet the major weather system producing precipitation over greenland is the frontal cyclone based on the precipitation characteristics greenland can be divided into five subregions precipitation over the north coastal and central interior regions primarily occurs in summer for the three other subregions if the composite monthly mean sea level pressure charts for high and low monthly precipitation amounts are constructed a clear relationship between precipitation and cyclonic activity emerges if a mean cyclone exists in the labrador sea heavy precipita

orographic precipitation and the relief of mountain ranges 1 the influence of climate on the relief of mountain ranges has long been supposed but has received little quantitative investigation the simplified system of a longitudinal river profile in a bedrock channel coupled to a physically based model of orographic precipitation is used to explore how orographically influenced patterns of precipitation affect the relief of fluvially sculpted mountain ranges it is shown that the impact on the orography depends on the nature of the precipitation regime significant changes in relief also occur for imposed temperature changes of realistic magnitude although the ability of the relief to respond to any given change depends sensitively on its response time and the timescale of the forcing

unraveling petroleum mixtures from the south viking graben north sea a study based on δ13c of individual hydrocarbons and molecular data abstract mixtures of compositionally different petroleum occur in the norwegian north sea one of the world s major oil producing regions the objective of the present contribution was to appraise the source maturity in reservoir mixing and alteration processes in a set of condensate and oil samples covering the main producing areas in the south viking graben svg furthermore this study focused on unraveling complex mixtures of petroleum and quantifying mixing ratios of hydrocarbons generated from jurassic source rocks the present research was based on a multiparameter approach that comprised the molecular composition of light hydrocarbons and heterocyclic and polycyclic aromatic compounds as well as the 13c of individual hydrocarbons in oils condensates and upper and middle jurassic source rock extracts from the svg according to the relative contribution of oils from type iii kerogen rich source rocks seven populations a g of mixed petroleum were identified by combining source related ratios of heterocyclic and non heterocyclic aromatic hydrocarbons and 13c values of n alkanes pristane pr and phytane ph the heterocyclic and polycyclic aromatic hydrocarbons provided a useful means to discriminate mixed hydrocarbons from source rocks of distinct organic matter type depositional environment and lithology in the svg the 13c enrichments of c10 c14 n alkanes and pr and ph were good indicators of the scale of the terrigenous source contribution and allowed quantitative determination of the proportions of jurassic source contributions enriched in type ii and type iii kerogens in complex petroleum mixtures from the southern part of the svg

enhancement of accumulation and anoxic degradation of organic matter controlled by cyclic productivity a model abstract the aim of the study is to determine the relative influences of the genetic sources the export efficiency and the anaerobic degradation of organic carbon as factors controlling short term cyclic organic rich sedimentation in areas of high marine productivity a cyclic organic sequence of the kimmeridge clay formation of yorkshire u k was studied as an example of ancient sedimentation this formation outcropping in the cleveland basin near marton is known as a lateral equivalent of the major oil source rock unit of the north sea on the basis of petrographic and geochemical results a new model is proposed to explain the short term cyclic sedimentation of organic carbon under continuously anoxic bottom conditions the model assumes that the cyclicity is primarily controlled by variations of mineral free phytoplanktonic productivity such variations are thought to induce changes in carbon recycling in the photic zone so that the export efficiency of the metabolizable organic matter is modified a high sulphate reduction intensity relative to the organic matter flux is observed for the highest productivity periods which also reflects an enhancement of export efficiency as the redox conditions did not change significantly such variations in sulphate reduction intensity must be attributed not only to quantitative variations in the export productivity but also to its qualitative variations with more metabolizable organic matter reaching the anoxic domain during high productivity periods biosedimentary processes depending on productivity such as aggregation are thought to play an important role in reducing the transit time of metabolizable organic matter to the sediment finally the model implies that the amplitude of export productivity variations probably were larger than that of toc variations recorded in sediment which are mainly due to biologically refractory organic matter from plankton

atmospheric circulation around the greenland crest the greenland ice sheet program 2 gisp2 required meteorological support for the layout of the field camp ice core site landing strip snow sampling sites and air sampling sites an automatic weather station installed in may 1987 provided the initial data for the support of several components of the program using the 2 year wind speed and direction distributions the automatic weather station aws network was expanded to six sites with four sites located approximately 100 km from the highest point in greenland in the cardinal directions and sites located at gisp2 and at the air sampling site the wind direction and speed wind roses for august and september 1994 show that there is considerable variation in the wind field around the greenland crest the constancy ratio of the vector wind speed to the scalar wind speed of the monthly wind vectors was lowest at the southern site and increased as one moved clockwise around the crest to the eastern site vorticity and divergence were determined from triangles formed by three aws sites the mean horizontal divergence for august and september 1994 was 1 4 x 10 5 s 1 and the vorticity was 3 7 x 10 5 s 1 apparently the flow around the greenland crest is most influenced by topography when the 500 hpa contours indicate a pressure ridge over central greenland the surface winds showed anticyclonic flow positive horizontal divergence and negative vertical vorticity in the mean this configuration indicates the presence of an inversion wind especially at the sites located on the slopes to the west and east of the crest

substantial contribution to sea level rise during the last interglacial from the greenland ice sheet during the last interglacial period the eemian global sea level was at least three metres and probably more than five metres higher than at present1 2 complete melting of either the west antarctic ice sheet or the greenland ice sheet would today raise sea levels by 6 7 metres but the high sea levels during the last interglacial period have been proposed to result mainly from disintegration of the west antarctic ice sheet3 with model studies attributing only 1 2 m of sea level rise to meltwater from greenland4 5 this result was considered consistent with ice core evidence4 although earlier work had suggested a much reduced greenland ice sheet during the last interglacial period6 here we reconsider the eemian evolution of the greenland ice sheet by combining numerical modelling with insights obtained from recent central greenland ice core analyses our results suggest that the greenland ice sheet was considerably smaller and steeper during the eemian and plausibly contributed 4 5 5 m to the sea level highstand during that period we conclude that the high sea level during the last interglacial period most probably included a large contribution from greenland meltwater and therefore should not be interpreted as evidence for a significant reduction of the west antarctic ice sheet

permeability loss with depth in the cenozoic carbonate platform of west central florida relationships between matrix permeability and depth in shallow buried 500 m cenozoic limestones of florida were investigated using more than 12 000 minipermeameter measurements on 1210 m of slim hole core these data are considered representative of the matrix permeability reduction that accompanies early burial of shallow water subtidal to peritidal nonreefal carbonates of sta ble cratonic margins platforms shelves and ramps measured matrix permeabilities range from less than 4 0 to 6450 md for both limestones and dolostones although the median permeability of limestones 88 md exceeds that for dolostones 15 md sucrosic dolostones which have high intercrystalline po rosities have median matrix permeabilities of 1000 md non sucrosic dolostones which are much less porous have median matrix permeabilities of only 13 md neither population of dolostones exhibits a permeability with depth trend low permeability limestones consist of mudstones wackestones tidal laminites pedogenetically altered limestone lime mud rich breccia and well cemented grain supported rocks these low permeability limestones all exhibit median matrix permeabilities less than 35 md and none exhibit permeability with depth trends in contrast high mud packstones low mud packstones very low mud packstones and grainstones exhibit larger median matrix permeabilities 69 129 181 and 418 md respectively and a systematic reduction with depth in their mean and maximum permeabilities least squares exponential regressions indicate that burial depth explains 22 31 of the permeability variance in these grain supported rocks the balance of the variability within each textural class is attributed to variation in facies grain types grain sizes sorting etc and the amount of early preburial cementation in the absence of permeability enhancement by deep subsurface diagenesis or fracturing extrapolation of the permeability with depth trends suggests that the limestones that have the best reservoir potential in the deeper subsurface are grain supported limestones that have higher than begin page 1254 average matrix permeabilities in the near surface realm petrographic analyses and consideration of diagenetic histories suggest that matrix permeability of the dolostones and low permeability limestones was determined by early near surface dolomitization and cementation respectively and has yet to be affected by burial processes petrographic observations also suggest that the depth signal in grain supported limestones results from mechanical compaction and the onset of grain to grain pressure solution extrapolation of the matrix permeability data indicates that permeability loss with burial occurs faster than the documented burial related porosity loss for the same group of rocks this indicates that limestone permeability is more sensitive to burial compaction than limestone porosity thus preservation of reservoir quality rock during burial is more dependent on permeability preservation than on porosity preservation

a paleoceanographic approach to the kimmeridge clay formation the upper jurassic lower cretaceous kimmeridge clay formation kcf is northern europe s premier source rock and can be understood using a new but relatively simple oceanographic model this explains or accommodates most current observations about the kcf and its depositional environment and draws upon paleogeographic paleoclimatic geochemical sedimentological and paleontological evidence

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

mass balance and surface movement of the greenland ice sheet at summit central greenland during the grip deep drilling in central greenland the ice sheet topography and surface movement at summit has been mapped with gps measurements of the surface velocity are presented for a strain net consisting of 13 poles at distances of 25 60 km from the grip site some results are the grip site is located approximately 2 km nw of the topographic summit the surface velocity at the gisp 2 site is 1 7 m yr in the w direction the present mass balance at summit is calculated to be 0 03 0 04 m yr i e close to steady state this result is the best now available for summit a small thinning rate might be a transient response of the greenland ice sheet due to the temperature increase at the wisconsin holocene transition

formation of phreatic caves in an eogenetic karst aquifer by co2 enrichment at lower water tables and subsequent flooding by sea level rise formation of extensive phreatic caves in eogenetic karst aquifers is widely believed to require mixing of fresh and saltwater extensive phreatic caves also occur however in eogenetic karst aquifers where fresh and saltwater do not mix for example in the upper floridan aquifer these caves are thought to have formed in their modern settings by dissolution from sinking streams or by convergence of groundwater flow paths on springs alternatively these caves have been hypothesized to have formed at lower water tables during sea level low stands these hypotheses have not previously been tested against one another analyzing morphological data and water chemistry from caves in the suwannee river basin in north central florida and water chemistry from wells in the central florida carbonate platform indicates that phreatic caves within the suwannee river basin most likely formed at lower water tables during lower sea levels consideration of the hydrological and geochemical constraints posed by the upper floridan aquifer leads to the conclusion that cave formation was most likely driven by dissolution of vadose co2 gas into the groundwater sea level rise and a wetter climate during the mid holocene lifted the water table above the elevation of the caves and placed the caves tens of meters below the modern water table when rising water tables reached the land surface surface streams formed incision of surface streams breached the pre existing caves to form modern springs which provide access to the phreatic caves phreatic caves in the suwannee river basin are thus relict and have no causal relationship with modern surficial drainage systems neither mixing dissolution nor sinking streams are necessary to form laterally extensive phreatic caves in eogenetic karst aquifers dissolution at water tables potentially driven by vadose co2 gas offers an underappreciated mechanism to form cavernous porosity in eogenetic carbonate rocks copyright 2012 john wiley sons ltd

hydrogeochemical properties of a salinity affected coastal aquifer in western japan coastal groundwater aquifers are often exposed to heavy pumping and consequently to risks of saltwater intrusion in many cases however the observed increase in groundwater salinity can only be partly explained by actual saltwater intrusion from the sea other salinity increasing processes may also significantly contribute to the total salt content of the groundwater this paper describes a geochemical investigation that was carried out to investigate recent salinity increases in groundwater for the motooka coastal area in fukuoka japan a strong increase in electrical conductivity at 15 20 m depth was observed corresponding to the freshwater and saltwater interface oxidation reduction potentials observed in deeper groundwater were low indicating long residence time for the groundwater these results together with hydrogen oxygen isotope ratio analysis indicated that the deeper groundwater is affected by seawater consequently observed tritium concentration in the shallow groundwater system was higher than that of the deeper groundwater system and a c 14 isotope dating of shell samples collected at 2 m depth indicated an age of about 2000 years the overall results suggest that the aquifer was originally below the current sea floor and that deeper saline groundwater is not mixed with the shallower fresh groundwater the deeper groundwater is therefore mainly affected by old seawater in other words modern saltwater intrusion has not yet occurred even if some wells contain saline water the study shows that even though coastal aquifers are heavily pumped the reason for the rise in groundwater salinity may not necessarily be due to seawater intrusion further geochemical and hydrological investigations will be necessary to identify the underlying mechanisms copyright c 2006 john wiley sons ltd less

regional hydrogeochemistry of a modern coastal mixing zone in west central florida groundwater samples were collected along flow paths in the unconfined upper floridan aquifer that cross the inland freshwater recharge area and the coastal discharge area a groundwater flow and solute transport model was used to evaluate groundwater flow and mixing of fresh and saline groundwater along a cross section of the unconfined upper floridan aquifer results show that between 8 and 15 of the fresh and 30 31 of the saline groundwater penetrates to the depth in the flow system where contact with and dissolution of gypsum is likely the deeply circulating fresh and saline groundwater returns to the near surface environment discharging caso4 rich water to the coastal area where it mixes with fresh cahco3 groundwater resulting in a prediction of calcite precipitation in the modern mixing zone

late jurassic early cretaceous climate change record in clay minerals of the norwegian greenland seaway abstract the humid climate of northwestern europe during the late jurassic early cretaceous was punctuated by a widespread arid phase there are few well constrained and complete sections that document this climate shift from semi humid to arid and back to more humid conditions detrital clay minerals formed in soils and derived through weathering may be used as palaeoclimatic proxies and here clay mineral assemblages from several well constrained sections from the norwegian continental shelf are presented as a n s transect of the norwegian greenland seaway palaeoclimate signals in most of the clay mineral sections are complicated by diagenetic overprinting yet towards the boreal realm of the norwegian greenland seaway there is a discernible palaeoclimatic signal in the clay mineralogy of well 16 3 4 at 30 n kaolinite is known to have reappeared in the clay mineralogical record in the upper part of calpionellid zone b early mid berriasian however we find an absence of kaolinite at 40 n in well 16 3 4 from the north sea until the late berriasian suggesting that initiation of the first humid phase in the early cretaceous norwegian greenland seaway was diachronous

radiaxial fibrous calcites as low magnesian calcite cement precipitated in a marine meteoric mixing zone radiaxial fibrous calcite rfc has previously been interpreted as a marine or replacive cement study of the dongjeom formation early ordovician korea shows that rfc can form in marine meteoric mixing zones as a low magnesian calcite lmc cement rfc in the shallow marine dongjeom formation occurs in arenaceous limestones at the top of a transgressive facies overlying a regressive facies it shows well developed growth zonation and lighter oxygen isotope values and more radiogenic strontium isotope ratios than those of early ordovician marine calcite such petrographic and chemical evidence indicates that the rfc was precipitated as a primary lmc cement in a marine and meteoric mixing zone owing to the unique environment of formation the dongjeom rfc is characterized by growth zonal fabric comprising alternating subzones which may indicate precipitation from varying fluids in addition this study documents the importance of substrate for development of rfc early nucleation for rfc occurred mainly on microcrystalline skeletal grains and internal sediments whereas on homogeneously altered substrates thin coated banding structure developed ultimately forming coarse crystalline spar this suggests that microcrystalline substrates are preferred sites for nucleation of rfc

sensitivity of a greenland ice sheet model to ice flow and ablation parameters consequences for the evolution through the last climatic cycle sensitivity experiments are conducted to test the influence of poorly known model parameters on the simulation of the greenland ice sheet by means of a three dimensional numerical model including the mechanical and thermal processes within the ice two types of experiments are performed steady state climatic conditions and simulations over the last climatic cycle with a climatic forcing derived from the grip record the experiments show that the maximum altitude of the ice sheet depends on the ice flow parameters deformation and sliding law coefficients geothermal flux and that it is low when the ice flow is fast on the other hand the maximum altitude is not sensitive to the ablation strength and consequently during the climatic cycle it is driven by changes in accumulation rate the ice sheet extension shows the opposite sensitivity it is barely affected by ice flow velocity and the ice covered area is smaller for large ablation coefficients for colder climates when there is no ablation the ice sheet extension depends on the sea level an interesting result is that the variations with time of the altitude at the ice divide summit do not depend on the parameters we tested the present modelled ice sheets resulting from the climatic cycle experiments are compared with the present measured ice sheet in order to find the set of parameters that gives the best fit between modelled and measured geometry it seems that compared to the parameter set most commonly used higher ablation rate coefficents must be used

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

a continuous simulation of global ice volume over the past 1 million years with 3 d ice sheet models sea level records show large glacial interglacial changes over the past million years which on these time scales are related to changes of ice volume on land during the pleistocene sea level changes induced by ice volume are largely caused by the waxing and waning of the large ice sheets in the northern hemisphere however the individual contributions of ice in the northern and southern hemisphere are poorly constrained in this study for the first time a fully coupled system of four 3 d ice sheet models is used simulating glaciations on eurasia north america greenland and antarctica the ice sheet models use a combination of the shallow ice and shelf approximations to determine sheet shelf and sliding velocities the framework consists of an inverse forward modelling approach to derive a self consistent record of temperature and ice volume from deep sea benthic 18o data over the past 1 million years a proxy for ice volume and temperature it is shown that for both eustatic sea level and sea water 18o changes the eurasian and north american ice sheets are responsible for the largest part of the variability the combined contribution of the antarctic and greenland ice sheets is about 10 for sea level and about 20 for sea water 18o during glacial maxima however changes in interglacials are mainly caused by melt of the greenland and antarctic ice sheets with an average time lag of 4 kyr between melt and temperature furthermore we have tested the separate response to changes in temperature and sea level for each ice sheet indicating that ice volume can be significantly influenced by changes in eustatic sea level alone hence showing the importance of a simultaneous simulation of all four ice sheets this paper describes the first complete simulation of global ice volume variations over the late pleistocene with the possibility to model changes above and below present day ice volume constrained by observations of benthic 18o proxy data

integrated stratigraphy of the kimmeridge clay formation upper jurassic based on exposures and boreholes in south dorset uk for the purposes of a high resolution multi disciplinary study of the upper jurassic kimmeridge clay formation two boreholes were drilled at swanworth quarry and one at metherhills south dorset uk together the cores represent the first complete section through the entire formation close to the type section we present graphic logs that record the stratigraphy of the cores and outline the complementary geophysical and analytical data sets gamma ray magnetic sus ceptibility total organic carbon carbonate 13 c org of particular note are the new borehole data from the lowermost part of the formation which does not crop out in the type area detailed logs are available for download from the kimmeridge drilling project web site at http kimmeridge earth ox ac uk of further interest is a mid eudoxus zone positive shift in the 13c org record a feature that is also registered in tethyan carbonate successions suggesting that it is a regional event and may therefore be useful for correlation the lithostratigraphy of the cores has been precisely correlated with the nearby cliff section which has also been examined and re described magnetic susceptibility and spectral gamma ray measurements were made at a regular spacing through the succession and facili tate core to exposure correlation the strata of the exposure and core have been subdivided into four main mudrock lithological types a medium dark dark grey marl b medium dark dark grey greenish black shale c dark grey olive black laminated shale d greyish black brownish black mudstone the sections also contain subordinate amounts of siltstone limestone and dolostone comparison of the type section with the cores reveals slight lithological variation and notable thick ness differences between the coeval strata the proximity of the boreholes and different parts of the type section to the purbeck isle of wight disturbance is proposed as a likely control on the thickness changes

sequence stratigraphical interpretation of organic facies variations in marine siliciclastic systems general principles and application to the onshore kimmeridge clay formation uk

a marine biogeochemical perspective on black shale deposition abstract deposition of marine black shales has commonly been interpreted as having involved a high level of marine phytoplankton production that promoted high settling rates of organic matter through the water column and high burial fluxes on the seafloor or anoxic sulfidic water column conditions that led to high levels of preservation of deposited organic matter or a combination of the two processes here we review the hydrography and the budgets of trace metals and phytoplankton nutrients in two modern marine basins that have permanently anoxic bottom waters this information is then used to hindcast the hydrography and biogeochemical conditions of deposition of a black shale of late jurassic age the kimmeridge clay formation yorkshire england from its trace metal and organic carbon content comparison of the modern and jurassic sediment compositions reveals that the rate of photic zone primary productivity in the kimmeridge sea based on the accumulation rate of the marine fraction of ni was as high as 840 g organic carbon m 2 yr 1 this high level was possibly tied to the maximum rise of sea level during the late jurassic that flooded this and other continents sufficiently to allow major open ocean boundary currents to penetrate into epeiric seas sites of intense upwelling of nutrient enriched seawater would have been transferred from the continental margins their present location onto the continents this global flooding event was likely responsible for deposition of organic matter enriched sediments in other marine basins of this age several of which today host major petroleum source rocks bottom water redox conditions in the kimmeridge sea deduced from the v mo ratio in the marine fraction of the kimmeridge clay formation varied from oxic to anoxic but were predominantly suboxic or denitrifying a high settling flux of organic matter a result of the high primary productivity supported a high rate of bacterial respiration that led to the depletion of o2 in the bottom water a high rate of burial of labile organic matter albeit a low percentage of primary productivity in turn promoted anoxic conditions in the sediment pore waters that enhanced retention of trace metals deposited from the water column

artificial neural network modelling as an aid to source rock characterization abstract a data based approach is used to establish detailed and accurate geochemical characterization in oil source rock intervals using well logs and noisy information from cuttings the method starts by extracting examples from the intervals of interest using generalized relationships between total organic content toc and well log responses the examples were used to train an artificial neural network ann that extracted more detailed and accurate relationships between toc and well log responses specific to the study area a combination of the quickprop algorithm and dynamic node creation scheme was utilized to facilitate efficient training the trained ann is useful for mapping source rock intervals in the area of interest this method performs satisfactorily when applied to the egret source rock of the jeanne d arc basin offshore eastern canada

a search in north greenland for a new ice core drill site a new deep ice core drilling site has been identified in north greenland at 75 12 n 42 30 w 316 km north northwest nnw of the grip drill site on the summit of the ice sheet the ice thickness here is 3085 m the surface elevation is 2919 m the north grip ngrip site is identified so that ice of eemian age 115 130 ka bp calendar years before present is located as far above bedrock as possible and so the thickness of the eemian layer is as great as possible an ice flow model similar to the one used to date the grip ice core is used to simulate the flow along the nnw trending ice ridge surface and bedrock elevations surface accumulation rate distribution and ratio echo sounding along the ridge have been used as model input the surface accumulation rate drops from 0 23 m ice equivalent year 1 at grip to 0 19 m ice equivalent year 1 50 km from grip over the following 300 km the accumulation is relatively constant before is starts decreasing again further north ice thickness up to 3250 m bring the temperature of the basal ice up to the pressure melting point 100 250 km from grip the ngrip site is located 316 km from grip in a region where the bedrock is smooth and the accumulation rate is 0 19 m ice equivalent year 1 the modeled basal ice here has always been a few degrees below the pressure melting point internal radio echo sounding horizons can be traced between the grip and ngrip sites allowing us to date the ice down to 2300 m depth 52 ka bp an ice flow model predicts that the eemian age ice will be located in the depth range 2710 2800 m which is 285 m above the bedrock this is 120 m further above the bedrock and the thickness of the eemian layer of ice is 20 m thicker than at the grip ice core site

terminating the 100 kyr ice age cycle we report a simulation of the most recent 100 000 year glaciationdeglaciation cycle of the late pleistocene ice age a simulation that delivers an ice sheet chronology that is in close accord with that inferred from the geological record our analyses are performed with a reduced model of the climate system that incorporates significant improvements to the representation of both climate forcing and mass balance response in a previously described theory based upon a coupled one level energy balance model ebm and vertically integrated ice sheet model ism the theory fully incorporates the influences of orbital insolation forcing glacial isostatic adjustment and variations in the atmospheric concentrations of greenhouse gases it correctly predicts the main geographical regions of the northern hemisphere that were glaciated at last glacial maximum 21 000 years ago as well as the abrupt termination of the glacial epoch that occurred subsequently the latter feature of the ice age cycle is obtained without the need to incorporate unconstrained and therefore controversial physical processes into the model a limitation of all previous attempts to understand this global scale climate cycle our analyses suggest that the radiative impact on surface glaciation due to the changing atmospheric concentration of co2 is critical to the ability of the model to deliver a synthetic history of glaciation and deglaciation that is in accord with inferences based upon surface geological and geomorphological evidence with the incorporation of this influence model predicted ice thickness distributions at last glacial maximum lgm are very similar to those of the recently described ice 4g reconstruction that was based upon the inversion of postglacial relative sea level histories

a geochemical investigation of samples from the volgian bazhenov formation western siberia russia abstract in this paper we present analyses of five core samples from the volgian bazhenov formation three different organic facies a b and c are proposed based on microscopical bulk and biomarker analyses facies a and b have much in common including low hopane sterane ratios c 35 c 34 hopane ratios slightly above 1 0 small amounts of tricyclic terpanes and a range of alkylthiophenes in their pyrolysates however facies a and b show some differences for example facies a shows a slight even odd c 22 c 27 n alkane predominance in some of the samples while facies b lacks 28 30 bisnorhopane and shows significantly different n alkane isoprenoid ratios these findings contrast with those of facies c which shows very low organic sulfur an odd even predominance in the higher n alkanes a high c 29 c 27 sterane ratio a very high hopane sterane ratio and is very low in tricyclic terpanes the timing of hydrocarbon generation from facies a together with the type and amount of organic matter appears to be similar to that of the upper jurassic of the norwegian continental shelf it appears that facies a and b have similar types of organic matter with a somewhat higher input of terrestrial debris in the latter and contrastingly in facies c an even greater proportion of terrestrial organic matter

carbonate diagenesis in a high transmissivity coastal aquifer biscayne aquifer southeastern florida usa abstract cores collected through the biscayne aquifer plio pleistocene in hollywood southeastern florida as part of the hollywood coastal salinity barrier project provided an opportunity to examine the diagenesis of limestones and sandstones at the meteoric to marine water transition of one of the most transmissive aquifers in the world the saline water front and thus coastal mixing zone has migrated landward approximately 1 km in the hollywood area as the result of wellfield withdrawals no changes in mineralogy such as dolomitization cement types and abundances paragenetic sequence or porosity are evident that can be correlated with the current or likely pre development wellfield withdrawals location of the mixing zone an approximately 2 downhole increase in calcite 18 o values is present in a core hmw 6d that penetrates the pre development mixing zone which may be related to either a down hole increase in salinity or to the interaction of meteoric waters with marine carbonate sediments during calcite cementation the biscayne aquifer in hollywood is currently a relatively quiescent diagenetic environment the limited current diagenesis appears to consist of the dissolution of trace skeletal aragonite remaining in the aquifer as suggested by a meteoric water sr ca ratio similar to that of molluscan aragonite it is proposed that a punctuated equilibria model may be applicable to diagenesis in the biscayne and other aquifers in which limestones and sandstones entered a long period of diagenetic stasis after a period of relatively rapid textural and mineralogical stabilization

new precipitation and accumulation maps for greenland annual total precipitation and the annual accumulation on the greenland ice sheet are evaluated and presented in two maps the maps are based on accumulation measurements of 25 1 pits and cores obtained from the upper accumulation zone and precipitation measurements made at 35 meteorological stations in the coastal region to construct the accumulation map the annual precipitation was split into solid and liquid precipitation components annual total precipitation exceeding 2500 mm w e occurs on the southeastern tip of greenland while the minimum precipitation is estimated to occur on the northeastern slope of the ice sheet the mean annual precipitation for all of greenland is 340 mm w e the largest annual accumulation of about 1500 mm w e is found on the glaciers in the southeastern corner of greenland while the smallest accumulation is found on the northeastern slope of the ice sheet west of danmarkshavn the mean accumulation on the greenland ice sheet is estimated at 310 mm w e the regional difference in accumulation is examined with respect to the 850 hpa m bar level circulation the present surface topography is found to play an important role in determining regional accumulation on the ice sheet

microphysical and geometrical controls on the pattern of orographic precipitation patterns of orographic precipitation can vary significantly both in time and space and such variations must ultimately be related to mountain geometry cloud microphysics and synoptic conditions here an extension of the classic upslope model is presented which incorporates an explicit representation in the vertical dimension represents the finite growth time of hydrometeors their downwind advection by the prevailing wind and also allows for evaporation for a simple mountain geometry the authors derive an analytical solution for the precipitation rate which can be understood in terms of four nondimensional parameters the finite growth time and slanting hydrometeor trajectories give rise to some interesting possibilities a precipitation rate that maximizes at intermediate values of the horizontal wind speed localized precipitation efficiencies in excess of 100 and a reverse rain shadow with more precipitation falling on the leeward flank than on the windward flank

a sequence stratigraphy of the kimmeridgian and bolonian stages late jurassic wessex weald basin southern england a sequence stratigraphic framework for the late jurassic kimmeridgian and bolonian stages of the wessex weald basin southern england is proposed based on the integration of sedimentological geophysical and geochemical data the nerc funded rapid global geological events rgge boreholes of swanworth quarry 1 and 2 and metherhills 1 are used as reference sections eleven complete depositional sequences and their component systems tracts are recognized within the kimmeridge clay formation bounded by 12 sequence boundaries km1 12 seventy four boreholes have been used in this study during the kimmeridgian a major transgression associated with tectonic movements led to a marked change in basin geometry major deepening of the sea during the late kimmeridgian eudoxus zone led to a change from unconformities of basinwide extent to those confined to the basin margins the progressive deepening of the basin towards a highstand in the mid bolonian wheatleyensis to pectinatus zones was associated with a broad scale change in sedimentary faunal and geochemical characters the layer cake basin architecture and thickening of the kimmeridge clay formation towards the basin centre suggests a dominantly aggradational system the partially enclosed nature of the kimmeridgian and bolonian seas generated basin dynamics more analogous to those of modern day meromictic lakes consequently sequence stratigraphic approaches derived from continental shelf margins are inappropriate in epicontinental basins of this type

depositional conditions and organic matter preservation pathways in an epicontinental environment the upper jurassic kashpir oil shales volga basin russia abstract the middle volgian kashpir oil shales formation located on the russian platform is a lateral equivalent of the north sea and west siberian petroleum source rocks in the volga basin this formation is 6 m thick and shows alternations of marls and black shales the organic carbon content is often higher than 1 although bioturbation and benthos are abundant even in the black shales in the marls highly degraded organic matter om dominates while aliphatic sulphur rich om is dominant in the black shales the combination of sedimentological and geochemical studies allowed to determine that the redox conditions of the sediment regularly fluctuated from oxic to anoxic under relatively productive waters while climatic conditions were increasingly arid it is proposed that om deposition occurred in relation to the increasing aridity through the combination of recurrent disruption of salinity stratification and aeolian supply of iron which both promoted phytoplankton productivity

critical form and feedbacks in mountain belt dynamics role of rheology as a tectonic governor 1 the rheology that governs deformation within a convergent orogen also controls its topographic form or in other words the covaration of its height or thickness and its width under conditions pertaining to small orogens and for rheologies ranging from linear viscous to coulomb plastic we show that this topographic form is insensitive to the distributions of fluxes into and out of the wedge and is thus a fundamental property of the system it can therefore be thought of as a critical topographic form directly analogous to the well studied case of a coulomb plastic rheology which predicts a constant critical taper angle independent of its size the tendency of the system to evolve toward a critical topographic form can be regarded as a tectonic governor that strongly damps the response of the orogen to changes in climate or tectonic forcing scaling relationships can be derived for the variation of orogen width height and exhumation rate as a function of accretionary flux and precipitation rate this study explores how sensitive these scaling relationships are to the assumed rheology it is found that the scaling relationships vary by less than a factor of 2 across the range of typical geological rheologies from coulomb friction to power law viscous to linear viscous these scaling relationships provide a first order representation of the behavior of convergent wedges and are relatively insensitive to the underlying assumptions

surface roughness on the greenland ice sheet from airborne laser altimetry high resolution airborne laser altimetry is used to determine the small scale surface relief in central greenland and estimate the contribution from spatial noise to stratigraphic records the standard deviation of the surface roughness is 1 6 cm water equivalent corresponding to a standard deviation of annual layer thickness of 2 3 cm we this estimate agrees with an independent assessment of the spatial variability 2 5 cm we based on nine shallow ice cores the agreement suggests that the statistical nature of the surface in central greenland remains unchanged throughout the year by conducting airborne altimetry around proposed drilling sites the expected noise level in the core can be evaluated and sites selected where this level is lowest

geochemical evolution and timescale of seawater intrusion into the coastal aquifer of israel this study is an attempt to quantify the geochemical processes and the timescale of seawater intrusion into a coastal aquifer from changes in the major ionic composition of the water and the natural distribution of the cosmogenic isotopes 14c and 3h for that purpose we sampled saline and brackish groundwaters from the israeli coastal aquifer a multilayer sampler mls was used to obtain very high resolution 10 cm profiles across the fresh saline water interface fsi the chemical and stable isotope data revealed three distinct water types end members that are located in different zones on the route to the coastal aquifer 1 slightly modified mediterranean seawater sws 2 slightly diluted with up to 20 fresh groundwater saline groundwater sds and 3 fresh groundwater fgw the sws samples generally show an excess of total alkalinity and total dissolved inorganic carbon dic and a depletion of 13cdic and 14cdic with respect to normal seawater indicating that anaerobic oxidation of organic matter is the first diagenetic reaction that affects seawater during its penetration into the bottom sediments sds waters appear when sws is slightly diluted gain ca2 and sr2 and is depleted in k suggesting that the main processes that transform sws into sds are slight dilution with fresh groundwater and cation exchange at the fresh saline water interface sds generally shows conservative mixing with fgw inspection of chemical data from coastal aquifers around the world indicates that intensive ion exchange in slightly diluted saline groundwater is a globally important phenomenon of seawater intrusion most of our saline groundwater samples contain substantial amounts of 3h suggesting that penetration of mediterranean seawater and its inland travel to a distance of 50 100 m onshore occurred 15 30 yr ago this is supported by the 14cdic mass balance that explains the relatively low 14cdic activities in the sds as influenced by diagenesis and not by simple radioactive decay

northern hemisphere storm tracks in present day and last glacial maximum climate simulations a comparison of the european pmip models abstract extratropical weather systems are an essential feature of the midlatitude climate and global circulation at the last glacial maximum lgm the formation of regions of high transient activity referred to as storm tracks is strongly affected by the presence of large ice sheets over northern america and scandinavia and by differences in sea surface temperature sst distributions in the framework of the palaeoclimate modelling intercomparison project simulations of the lgm climate have been run with a wide range of atmospheric general circulation models agcms using the same set of boundary conditions allowing a valuable comparison between simulations of a climate very different from the present one in this study the authors focus on the storm track representation in the models and its relationship with the surface temperatures the mean flow and the precipitation storm tracks are described using transient eddy diagnostics such as mean sea level pressure variance and three dimensional

seawater redox variations during the deposition of the kimmeridge clay formation united kingdom upper jurassic evidence from molybdenum isotopes and trace metal ratios 1 the kimmeridge clay formation kcf and its equivalents worldwide represent one of the most prolonged periods of organic carbon accumulation of the mesozoic in this study we use the molybdenum mo stable isotope system in conjunction with a range of trace metal paleoredox proxies to assess how seawater redox varied both locally and globally during the deposition of the kcf facies with lower organic carbon contents toc 1 7 wt were deposited under mildly reducing suboxic conditions while organic rich facies toc 7 wt accumulated under more strongly reducing anoxic or euxinic local conditions trace metal abundances are closely linked to toc content suggesting that the intensity of reducing conditions varied repeatedly during the deposition of the kcf and may have been related to orbitally controlled climate changes long term variations in 98 95mo are associated with the formation of organic rich intervals and are related to third order fluctuations in relative sea level differences in the mean 98 95mo composition of the organic rich intervals suggest that the global distribution of reducing conditions was more extensive during the deposition of the pectinatites wheatleyensis and lower pectinatites hudlestoni zones than during the deposition of the upper pectinatites hudlestoni and pectinatites pectinatus zones the global extent of reducing conditions during the kimmerigidan was greater than today but was less widespread than during the toarcian early jurassic oceanic anoxic event this study also demonstrates that the mo isotope system in jurassic seawater responded to changes in redox conditions in a manner consistent with its behavior in present day sedimentary environments

the source rock horizons of the ionian basin nw greece abstract the organic geochemical study of six geological sections and two wells in the ionian zone nw greece allows us to distinguish five horizons of possible source rocks the vigla shales cenomanian turonian the upper posidonia beds callovian tithonian the lower posidonia beds toarcian aalenian the marls at the base of the ammonitico rosso early toarcian and shale fragments incorporated within the triassic breccias these horizons have good hydrocarbon potential and an organic matter type i to ii in the deeper parts of the botsara sub basin the oil window is located in the interval between 3700 5800 m depth consequently the triassic shales have already entered the gas window the lower and upper posidonia beds and the marls at the base of the ammonitico rosso are mature in terms of oil generation the vigla shales maturity corresponds to the early maturation stage the timing of the principal oil source horizons maturation is the late jurassic for the triassic shale beds and the serravalian for the lower posidonia beds the preservation of the organic matter in the lower and upper posidonia beds through toarcian to tithonian and in the marls at the base of the ammonitico rosso during early toarcian are directly related to the geometry of the syn rift period of the ionian basin the organic matter preservation in the vigla shales is related to the sub basins that were preserved by the continuation of halokinetic movements during the post rift period the geometry of the restricted sub basins that were formed during the syn rift and post rift period of the ionian basin evolution favored water stagnation and the development of local euxinic conditions in the bottom waters these conditions were accentuated during the anoxic events that are known to have affected the tethys ocean during the early toarcian and late cenomanian the organic rich shale fragments within the triassic breccias were initially deposited as stratigraphic layers in sub basins of the evaporitic basin the establishment of evaporitic sedimentation in the entire basin favored the preservation of the organic matter the processes that resulted in the formation of the evaporite dissolution collapse breccias caused also the fragmentation of the organic rich layers which are present actually as organic rich shale fragments within the triassic breccias

are the kimmeridge clay deposits affected by burn down events palynological and geochemical studies on a 1 metre long section from the upper kimmeridge clay formation dorset uk abstract two independent analytical approaches palynology and inorganic geochemistry were applied to identify potential oxygen burn down events in the late jurassic kimmeridge clay formation kcf the kcf interval of the rotunda ammonite zone spanning 121 82 122 72 m depth was sampled from the swanworth quarry 1 borehole dorset uk at 2 5 5 0 cm resolution samples were analysed for total organic carbon toc concentrations of elements that are known to be productivity and or nutrient related e g cu p detrital e g al ti zr and redox sensitive sulphide forming e g v mo fe mn s and palynofacies components including analysis of organic walled dinoflagellate cysts dinocysts on a species level the toc contents generally exceed 2 wt with a maximum of 8 8 wt at 122 37 cm depth and elevated values in the central part of the investigated interval this interval of relatively higher toc values correlates well with the maximum recovery of marine palynomorphs and low al values suggesting that the toc is primarily of marine organic matter om changes in v al mo al fe al mn al and s patterns at 122 37 m depth mark a shift from anoxic conditions in the lower part of the studied interval to more oxic conditions in its upper part such a shift could explain the relatively high toc and marine palynomorph concentrations in the lower part of the studied interval as a result of better preservation and the subsequent decrease as an effect of a post depositional burn down i e om oxidation as the amount of marine palynomorphs and toc content diminishes from the middle part of the section upwards species specific changes in dinocyst assemblages can be observed in particular concentrations of circulodinium spp cyclonephelium spp sirmiodinium grossi senoniasphaera jurassica and systematophora spp decrease rapidly in comparison to other species such as glossodinium dimorphum and cribroperidinium sp 1 which may suggest selective degradation of dinocysts due to oxidation we suggest that post depositional oxygenation of bottom and pore waters within the sediment was most probably the cause for decreasing toc values and reduced recovery of marine palynomorphs towards the top of the studied interval in comparison to high toc and marine palynomorph values in the central part of the studied interval due to anoxic conditions

evaluation of recent precipitation studies for greenland ice sheet the retrieval of an accurate spatial and temporal record of contemporary greenland precipitation is a uniquely challenging task because of the extreme variability in both atmospheric processes and the resulting precipitation distribution over relatively small spatial scales a comparison of precipitation data sets composed of monthly mean values from recent studies shows a convergence on the general features of the long term spatial patterns but substantial disagreement on the temporal variability both regionally and for all of greenland there is general agreement on a long term greenland average of about 35 cm yr 1 and on long term values for regional scales although differences for outlying data sets exceed 50 of the observed glaciological estimate for particular regions a fundamental problem is the inadequate topographic representation of greenland in the numerical analyses nearly all of the data sets are overly dry for high elevation areas as seen from comparisons with glaciological observations from summit the east central region of greenland is found to be particularly susceptible to the temporal discontinuities in data sets which employ operational analyses in contrast there is strong agreement among all methods on the temporal variability for the west central region over a 15 year period from the comparison it is concluded that none of the data sets is able to capture all of the regional scale features in general however the deficiencies of each data set are readily identifiable from comparison and evaluation in the context of circulation features agreement among the methods on particular regions and timescales gives increased confidence in drawing conclusions related to aspects of greenland s precipitation climatology in particular an enhanced precipitation retrieval method is found to be less susceptible to data artifacts than other methods using operational analyses in the north anomalously high precipitation is associated with cyclonic development near the fram strait for west central greenland the close agreement among methods is related to the dominant contribution of the mean circulation

preservation of carbohydrates through sulfurization in a jurassic euxinic shelf sea examination of the blackstone band toc cycle in the kimmeridge clay formation uk a complete total organic carbon toc cycle in the upper jurassic kimmeridge clay formation kcf comprising the extremely toc rich 34 blackstone band was studied to investigate the controlling factors on toc accumulation compared with the under and overlying strata toc in the blackstone band was enriched by a factor of six and concomitantly the 13ctoc shows a 4 enrichment al normalized toc values indicated that the enhanced toc values were probably caused by increased toc accumulation and not by a decreased dilution with inorganic matter the amounts of short chain alkylated thiophenes and the sulfur rich unresolved complex mixture ucm in the kerogen pyrolysates as well as the toc al ratios correlated linearly with 13ctoc for sediments with toc al ratios 1 7 the alkylated thiophenes and sulfur rich ucm both originate from sulfurized carbohydrate carbon ccarb suggesting that the primary cause of the toc maximum is the enhanced contribution of ccarb to toc since carbohydrates can be substantially 13c enriched over lipids in biomass the enhanced contribution of ccarb explains the enriched 13ctoc values compound specific isotope data showed that primary productivity during deposition of the kcf toc cycle varied little while a two member isotopic mixing model showed that the preservation of ccarb relative to that of the lipid carbon may have increased by a factor of 10 in the blackstone band the enhanced preservation of ccarb was most likely caused by more frequent or longer lasting events of photic zone euxinia as revealed by the concentration of isorenieratene derivatives enhanced contributions of ccarb have also been observed in other kcf cycles suggesting that enhanced preservation of ccarb rather than an increase in primary production exerted direct control on the toc cycles of the kcf

simulation of vatnajokull ice cap dynamics 1 we apply a coupled model of ice sheet dynamics and subglacial hydrology to investigate the dynamics and future evolution of the vatnajokull ice cap iceland in this paper we describe a new theoretical approach to introducing longitudinal stress coupling in the ice dynamics solution and we analyze our ability to simulate the main features of vatnajokull with and without longitudinal stress effects equilibrium ice cap configurations exist for vatnajokull but under a narrow range of climatic boundary conditions equilibrium reconstructions have an average ice thickness greater than what is observed at vatnajokull consistent with our inability to capture surge dynamics in vatnajokull s outlet glaciers hydrological regulation of basal flow longitudinal stress coupling and a simple parameterization of the subglacial heat flux from vatnajokull s geothermal cauldrons all help to reduce average ice thickness in the equilibrium reconstructions but cases that reproduce the present day ice volume have an ice cap area that is 5 10 less than the actual ice cap present day reconstructions that adopt a realistic climate spin up for the period 1600 1990 provide improved fits to the modern day ice cap geometry this indicates that climatic disequilibrium also plays a significant role in dictating vatnajokull s morphology simulations for the period 1600 2300 illustrate that air temperature is the dominant control on vatnajokull s volume and area longitudinal stress coupling and hydrological coupling both increase vatnajokull s sensitivity to future warming

enhanced trapping of molybdenum by sulfurized marine organic matter of marine origin in mesozoic limestones and shales there have been many studies devoted to trace metals and their value in assessing the paleoredox conditions of ancient marine deposition among them molybdenum mo is frequently cited as an effective proxy for sediments and sedimentary rocks recently helz et al helz g r miller c v charnock j m mosselmans j l w pattrick r a d garner c d vaughan d j 1996 mechanisms of molybdenum removal from the sea and its concentration in black shales exafs evidences geochim cosmochim acta 60 3631 3642 and adelson et al adelson j m helz g r miller c v 2001 reconstructing the rise of recent coastal anoxia molybdenum in chesapeake bay sediments geochim cosmochim acta 65 237 252 suggested that mo does not behave conservatively in the water column when h2s reaches a threshold concentration above this concentration a switch operates and mo is scavenged by forming bonds with metal rich notably iron particles sulfur rich organic molecules and pyrite in this paper mo trapping by sulfur rich organic matter om in ancient marine deposits is emphasized the following mesozoic geological formations were selected for study because of their relatively high concentration of sulfurized om the akkuyu formation turkey the calcaires d orbagnoux france and kimmeridge clay uk and its timeequivalent in boulonnais france the kashpir oil shales russia and the la luna formation venezuela the sulfur rich om is identified by either measured organic s abundance or kerogen microscope observation our results show that mo is systematically more enriched relative to the other redox sensitive sulfide forming elements studied u v ni cu zn cr and mo enrichment is positively correlated with the amount of sulfurized om but not with pyrite abundance these results illuminate the role played by sulfurized om in geologic scale mo capture and retention but they also underline the role played by reactive iron significant om sulfurization is only possible when reactive iron is limited nevertheless pyrite formation though limited could act as an initial mo trap prior to mo uptake by om that is sulfurized after the pyritization step in future paleoenvironmental reconstructions attention must be paid to this enhanced mo enrichment in the presence of sulfurized organic matter in such cases the use of mo could lead to overestimation of the reducing conditions of the depositional environment

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

geochemical study of organic matter rich cycles from the kimmeridge clay formation of yorkshire uk productivity versus anoxia abstract in this contribution we study two meter scale cycles from the kimmeridge clay formation cored near marton yorkshire which shows cyclic organic matter om distribution our aim is to try to understand the factors responsile for om accumulation the first cycle called lower cycle shows a total organic carbon toc content between 1 and 10 whereas the second called upper cycle shows a toc content varying between 5 and 35 the geochemical composition major elements and trace elements the organic geochemistry toc hi palynofacies and mineralogy of the sediments have been determined in both cycles the cyclicity is expressed through variations in the nature and in the relative abundance of the various types of organic matter constituents furthermore dilution effects by inorganic components of the sediment cannot account for the toc cyclicity for lower cycle the mo v and u content is low and little variable as is the intensity of the oxidation which om suffered from this indicates that variations in phytoplanktonic productivity may be held responsible for the cyclicity in steady and mildly reducing redox conditions in the upper cycle cyclicity also appears to depend on productivity but variations in the concentration of mo v and u and in the oxidation state of the om suggest the environment was temporarily more reducing it is proposed that larger amounts of h 2 s were released into marine bottom waters as a result of initial om decomposition forced the oxic anoxic boundary to rise in the water column and thus favoured om storage the main driving force for variations in the om concentration was the productivity of organic matter walled phytoplankton redox conditions of the depositional environment could have had a positive action but only by acting as a positive feedback effect

influence of partial confinement and holocene river formation on groundwater flow and dissolution in the florida carbonate platform much of what is known about groundwater circulation and geochemical evolution in carbonate platforms is based on platforms that are fully confined or unconfined much less is known about groundwater flow paths and geochemical evolution in partially confined platforms particularly those supporting surface water in north central florida sea level rise and a transition to a wetter climate during the holocene formed rivers in unconfined portions of the florida carbonate platform focusing on data from the santa fe river basin we show river formation has led to important differences in the hydrological and geochemical evolution of the santa fe river basin relative to fully confined or unconfined platforms runoff from the siliciclastic confining layer drove river incision and created topographic relief reorienting the termination of local and regional groundwater flow paths from the coast to the rivers in unconfined portions of the platform the most chemically evolved groundwater occurs at the end of the longest and deepest flow paths which discharge near the center of the platform because of incision of the santa fe river at the edge of the confining unit this pattern of discharge of mineralized water differs from fully confined or unconfined platforms where discharge of the most mineralized water occurs at the coast mineralized water flowing into the santa fe river is diluted by less evolved water derived from shorter shallower flow paths that discharge to the river downstream formation of rivers shortens flow path lengths thereby decreasing groundwater residence times and allowing freshwater to discharge more quickly to the oceans in the newly formed rivers than in platforms that lack rivers similar dynamic changes to groundwater systems should be expected to occur in the future as climate change and sea level rise develop surface water on other carbonate platforms and low lying coastal aquifer systems copyright 2012 john wiley sons ltd

the relative roles of compaction and early cementation in the destruction of permeability in carbonate grainstones a case study from the paleogene of west central florida u s a abstract how compaction can yield a progressive decrease in the permeability and pore structure of carbonate grainstones is not well documented in this study the destruction of permeability by compaction relative to early cementation is examined in forty five shallow buried 30 440 m grainstones with a range in permeability of 12 to 5180 md compaction and cementation indices calculated from thin section point count data indicate a group of grainstones dominated by cementation and another by compaction log linear cross plots of permeability versus these indices suggest that permeability loss in these two groups occurs by different processes the nature of those processes is elucidated by capillary pressure data and the distribution of cement and compaction fabrics as a function of permeability as cement abundance increases in the cement dominated samples a continuous distribution of cement develops along grain surfaces which is followed by the development of partial and then complete pore filling mosaics permeability is progressively reduced with this succession of cement fabrics and an increasingly greater percentage of pore space is positioned behind progressively smaller throats permeability loss results from porosity reduction progressive constriction of pore throats and increased tortuosity of flow paths once permeability is reduced to tens of millidarcies effective pore radii are all less than 1 m and many are less than 0 1 m but there is no evidence for complete blocking of all pore throats in this suite of samples in absolute terms the pore lining cements reduce permeability by thousands of millidarcies whereas the pore filling cements reduce permeability only by hundreds of millidarcies mechanical compaction is the dominant cause of permeability reduction between 5000 and about 500 md in the compaction dominated samples linear grain contacts and embayed grains become more abundant and close to overly close packing textures become more homogeneously distributed as permeability decreases however there is no concurrent change in the amount of pore space accessed by large or small throats indicating that mechanical compaction does not uniformly constrict or seal pore throats instead the data suggest that mechanical compaction reduces permeability by reducing porosity lengthening pore throats and increasing tortuosity at about 500 md the compaction dominated trend steepens on the log linear plot of permeability versus porosity a change that corresponds to the development of grain to grain pressure solution unlike mechanical compaction grain to grain pressure solution constricts and eliminates pore throats and isolates pore space resulting in a loss of large throats and an increase in the amount of pore volume accessed by small throats in contrast to cement dominated samples the most effective pore radii are still greater than 1 m at tens of millidarcies of permeability such low amounts of permeability can be reached even when pressure solution is not pervasively distributed throughout a sample

kerogen facies and maturity of the kimmeridge clay formation in southern and eastern england abstract the upper jurassic kimmeridge clay formation of southern and eastern england was deposited under anoxic or dysaerobic conditions in a stratified shelf sea anoxic conditions developed in the intra shelf weald and central channel basins of southern england and the cleveland basin of eastern england with generally dysaerobic conditions in the flanking shelf areas only in the basin margins such as in northern scotland were oxic bottom water conditions prevalent the maturity and distribution of the kerogen facies which can be explained in terms of the palaeogeography and burial history of the upper jurassic of southern and eastern england are discussed along with the effects of their variation on commonly used geochemical parameters relationships to clay mineralogy are also examined kerogens are largely type ii amorphous sapropels of marine origin with variable amounts of terrestrially derived type iii material type iii kerogens predominate in the basin margin areas whereas type ii kerogens are restricted to the basin centres over the intermediate shelf areas mixed type ii type iii kerogens are prevalent both the sedimentation rate and differential organic matter preservation can be demonstrated to be the major controls on the kerogen facies of the kimmeridge clay formation variations in the kerogen facies appear to be responsible for the often spurious and scattered maturity measurements from the kimmeridge clay formation using vitrinite reflectance spore coloration and rock eval pyrolysis parameters the results often conflicting with geological models for the post jurassic burial history this appears to be due to the highly variable content of terrestrial and recycled type iii kerogens from older sediments in the mudstones causing the conventional maturity indices to often not reflect the true maturity of the autochthonous marine type ii kerogens

depositional environments organic carbon accumulation and solar forcing cyclicity in smackover formation lime mudstones northern gulf coast upper jurassic smackover lime mudstones a major hydrocarbon source rock in the u s gulf coast show three distinct lithofacies the basal laminated lithofacies consists of organic and siliciclastic rich lamina sets that alternate with organic poor clean carbonate lamina sets both lamina sets are composed of lamina couplets interpreted to be varves this lithofacies lacks current induced structures allochems and rip up clasts benthic and planktonic fossils are absent one organic rich lamina set and one organic poor lamina set comprise one cycle 0 5 3 cm thick the middle thin bedded lithofacies is composed of organic and siliciclastic rich carbonate beds that alternate with organic poor clean carbonate beds both bed types are internally laminated one organic rich bed and one organic poor bed comprise one cycle 2 60 cm thick the upper burrowed lithofacies is extensively bioturbated massive shows no evidence of cyclicity and contains little organic carbon sedimentologic characteristics suggest that the basal laminated lithofacies was deposited under anoxic conditions below storm wave base in a basinal environment the middle thin bedded lithofacies is copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received march 5 1996 revised manuscript received august 2 1996 final acceptance december 10 1996 2basin research institute louisiana state university baton rouge louisiana 70803 3lss international 1440 lake front circle suite 180 the woodlands texas 77380 formerly with department of geology and geophysics louisiana state university baton rouge louisiana 70803 4department of geology and geophysics louisiana state university baton rouge louisiana 70803 the study was supported by grants from the center for energy studies and the basin research institute of louisiana state university we thank h d klemme and g t moore for providing unpublished data p meyers and l m pratt reviewed an earlier version of the manuscript and offered valuable comments j wrenn kindly provided characteristics of organic matter we thank j kropog w s leblanc k lyle p o neill and b simpson for technical assistance we appreciate the helpful comments of r l folk b kirkland and c h moore critical comments by k t biddle n b harris b a prather and p d wagner significantly improved the quality of concepts presented

ice core analysis at site a greenland preliminary results ice core drilling at site a greenland 70 45 n 35 57 5 w 3145m a s l by the polar ice coring office recovered two cores of about 100 m each which are now in storage awaiting further analysis field studies show that visible strata in the cores record both individual storms and individual years a typical year comprises 15 storm deposits pore close off occurs between 75 and 80 m depth the grain growth rate in isothermal firn and ice is about 7 8 x 1o 3 mm 2 a l the 10m temperature is about 29 5 c and the accumulation rate over the last 200 years is about 290 mm a i ice melt events occur about once every 40 years and major events can be correlated between cores separated by 20 m

modeling precipitation over ice sheets an assessment using greenland the interaction between ice sheets and the rest of the climate system at long time scales is not well understood and studies of the ice ages typically employ simplified parameterizations of the climate forcing on an ice sheet it is important therefore to understand how an ice sheet responds to climate forcing and whether the reduced approaches used in modeling studies are capable of providing robust and realistic answers this work focuses on the accumulation distribution and in particular considers what features of the accumulation pattern are necessary to model the steady state response of an ice sheet we examine the response of a model of the greenland ice sheet to a variety of accumulation distributions both observational datasets and simplified parameterizations the predicted shape of the ice sheet is found to be quite insensitive to changes in the accumulation the model only differs significantly from the observed ice sheet for a spatially uniform accumulation rate and the most important factor for the successful simulation of the ice sheet s shape is that the accumulation decreases with height according to the ability of the atmosphere to hold moisture however the internal ice dynamics strongly reflects the influence of the atmospheric circulation on the accumulation distribution