radiogenic helium concentration and isotope variations in crustal gas pools from sichuan basin china abstract helium is an exhaustible natural resource and the main commercial helium was separated from helium rich natural gas the helium in the sedimentary basin is mainly the radiogenic origin of crustal rocks with high level of uranium and thorium data from 242 natural gas samples were used to investigate the distribution and formation mechanism of helium rich gases in the sichuan basin of china all gas samples show remarkably low 3he 4he ratios with ranging from 0 002 to 0 05 ra which represent typical crustal helium the weiyuan gas pool in the southern sichuan basin possesses high levels of helium 1500 18770 ppm average 2785 7 ppm in precambrian and cambrian strata a positive relationship were observed in the helium and nitrogen contents increased with reservoir layer age for all weiyuan gas samples presinian granite was considered as the main helium source for the weiyuan gas pool gaoshiti moxi and weiyuan gas pools belonged to the same ancient gas pool before the late cretaceous but the helium abundance of gaoshiti moxi gas pool is relatively low 200 891 ppm the change of pressure and fracture system caused by the uplift of weiyuan structure in the himalayan orogenesis led to the helium accumulation and enrichment of weiyuan gas pool the shale of the silurian longmaxi formation has high contents of uranium and thorium and generated a large amount of helium while forming large quantities of hydrocarbon gases generally the helium abundance of shale gases and conventional gases generated from the longmaxi formation ranges from 63 to 1500 ppm and some of the gas pool are sufficient for commercial helium resource exploitation therefore the relative quantities of helium and hydrocarbon gases are act as a key factor influencing the formation of helium rich natural gas reservoirs

role of geomorphic and hydraulic parameters in governing pore water seepage from salt marsh sediments 1 a numerical boundary integral equation model has been used to study the effects of marsh geomorphology and hydraulic parameters on the seepage of pore water into tidal channels and its subsequent recharge by tidal inundation in general the results show that regardless of the geomorphic configuration the locus of maximum seepage flux occurs at or near the intersection of the creek bank and the channel water surface over a tidal cycle typically two thirds of the total seepage discharge occurs through the creek bank with only about a third discharging from the channel bottom in most cases the volume of seepage discharging through the creek bank exceeds by a factor of two or more that emanating from the channel bottom of the creek bank discharge up to half may occur through the seepage face that develops above the tide line at tidal stages below mean tide the ratio of creek bank to bottom seepage only approaches unity when the thickness of the aquifer beneath the bottom is similar to or greater than the width of the channel bottom and the ratio of conductivity to specific yield exceeds 0 5 for given hydraulic parameters total seepage volume varies directly with creek bank slope and aquifer thickness whereas these factors are inversely related to the ratio of the two seepage components channel bottom width on the other hand has no influence on total seepage volume but greatly increases the component ratio as the width approaches zero since most of the seepage discharge is derived from sediments within several meters of the creek bank variations in seepage discharge driven by variations in marsh geomorphology might play a role in the productivity of creekside cord grass several hypotheses are offered and discussed regarding the effects of geomorphology on creekside productivity these results also indicate that placement of seepage meters only on the channel bottom will not give samples or measures representative of the total seepage

a mid ordovician temperate carbonate shelf the black river and trenton limestone groups of southern ontario canada abstract mid ordovician limestones of southern ontario are usually considered to be tropical shelf limestones and interpreted using facies models derived from recent tropical carbonate environments nevertheless depositional rates grain types faunas erosion surfaces mineralogy and geochemistry are more compatible with a temperate or even cold shelf environment in view of the low latitudes 20 s indicated by paleomagnetism this suggests deposition in relatively cold seas deposition below a tropical thermocline or that the paleomagnetic data are wrong similar features in other caradocian limestones of eastern north america show that these inferred cooler conditions were widespread if deposition occurred below a tropical thermocline most shallow water caradocian limestones must be re interpreted as deeper water deposits more likely in view of the evidence for temperate conditions in shallow water is that the whole eastern seaboard of north america was affected by cold currents arising from southern polar ice caps and thus was a temperate shelf environment

physical oceanographic influences on sedimentology of reef sand aprons holocene of aranuka atoll kiribati equatorial pacific abstract depositional facies are the net product of a complex set of processes that impact sediment supply and transport in geomorphic systems although the general facies motifs of many isolated platforms throughout the geologic record are well documented the details of geomorphological and sedimentological patterns and the physical oceanographical processes that can impact sedimentological differentiation are less well constrained on these platforms accumulations of reef associated debris in platform top reef sand aprons can form expansive geomorphic elements hosting prolific hydrocarbon reserves in geologic analogs to better understand the nature and scale of reef sand apron accumulations this project integrates remote sensing field petrographical and granulometrical characterization of surficial holocene sediments with physical oceanographical observations and modeling of aranuka atoll republic of kiribati in the western equatorial pacific results illustrate trends in hydrodynamics geomorphology and sedimentology from the platform margin to the platform interior current meter data and modeling illustrate how the tides 2 5 m spring tide amplitude modulate wave energy open ocean annual average swell height of 2 m distal swell can be larger to produce dominant on platform flow speeds up to 90 cm s on the northern reef sand apron the strongest currents there appear to be impacted by southward propagating waves related to fronts that pass thousands of kilometers north of the atoll not local wind generated waves these hydrodynamical influences are interpreted to have led to the development of the expansive northern reef sand apron 2000 m wide the southeastern apron with currents that reverse with the tides includes a distinct narrower sand apron 1500 m wide concomitantly the hydrodynamical patterns and platformward decrease in energy across the reef sand apron coupled with changes in biota are interpreted to control variability in sedimentary structures bottom types and sediment attributes sediment near the margin on the reef sand apron contains coral and red algal rich coarse sand and gravel passing to foraminifera rich medium to coarse sand toward the lagoon the lagoon includes even finer sediment chiefly fine and very fine sand and patch reefs collectively the results of this study illustrate that selective winnowing differentiation of sediment size type and sorting and nature and size of geomorphic elements ultimately are linked to the hydrodynamical patterns across the platform the sedimentological depositional porosity and permeability and geomorphic facies bodies variability and the processes active on this reef sand apron provide a general conceptual model that may be applicable to predict trends in ancient reservoir analogs

composition and stable isotope geochemistry of natural gases from kansas midcontinent u s a abstract more than 28 1012 ft 3 79 1010 m3 of natural gas and 5 3 109 bbl 8 4 108 m3 of oil have been produced in kansas u s a from paleozoic carbonate and sandstone reservoirs on structural uplifts and shallow embayments along the northern margin of the anadarko basin a heavily explored geologically well characterized state kansas is an excellent place to study hydrocarbon migration and to test geochemical models for the origin of natural gases immature to marginally mature rocks of eastern kansas cherokee and forest city basins produce mixed microbial and thermogenic gases gases in this region have wetness 0 03 51 methane 13c 65 to 43 and methane d 260 to 150 gases from central and western kansas nemaha uplift to hugoton embayment are entirely thermogenic and have wetness 4 51 methane 13c 48 to 39 and methane d 195 to 140 ethane and propane 13c values throughout kansas vary from 38 to 28 and from 35 to 24 respectively mature thermogenic gas generated from source rocks in southwestern kansas and the anadarko basin with 1 0 ro 1 4 is recognized throughout the state lateral migration into shallow reservoirs on the central kansas and northern nemaha uplifts and in the cherokee basin probably occurred along basal pennsylvanian conglomerates and weathered lower paleozoic carbonates at the regional sub pennsylvanian unconformity early thermogenic gas generated by local source rocks with ro 0 7 is recognized in isolated fields in the salina and forest city basins in ordovician reservoirs beneath the sub pennsylvanian unconformity in the cherokee basin and in reservoirs generally above the unconformity in the cherokee and sedgwick basins the eastern central kansas uplift and the hugoton embayment

depositional facies and stratal geometry of an upper carboniferous prograding and aggrading high relief carbonate platform cantabrian mountains n spain seismic scale continuous exposures of an upper carboniferous bashkirian moscovian carbonate platform n spain provide detailed information about the lithofacies and stratal geometries quantified with differential global positioning system measurements of microbial boundstone dominated steep prograding and aggrading platform margins progradational and aggradational platform to slope transects are characterized by distinct lithological features and stratal patterns that can be applied to the understanding of geometrically comparable high relief depositional systems the bashkirian is characterized by rapid progradation at rates of 415 970 m my 1 characteristic outerplatform facies are high energy grainstones with coated intraclasts ooids and pisoids moderate energy algal skeletal grainstones to packstones and lower energy algal packstone and boundstone units the moscovian aggradational phase is characterized by aggradation rates of 108 m my 1 coated grain shoals are less common whereas crinoidal bars nucleated in well circulated settings below wave base boundstones form a belt 30 300 m wide at the platform break and interfinger inwards with massive algal skeletal wackestones mud rich banks the progradational phase has divergent outer platform strata with basinward dips of 12 to 2 steep clinoforms with dips of 20 28 are 650 750 m in relief and possibly sigmoidal to concave in the lower part the basinward dipping outer platform strata might be depositional for less than 6 consistent with lithofacies deepening seaward the basinward dip is attributed to the downward shift of upperslope boundstone forced by late highstand and relative sea level fall and to compaction induced differential subsidence during progradation the aggradational phase is characterized by horizontally layered platform strata clinoforms steepen to 30 45 reaching heights of 850 m and are planar to concave the evolution from progradation to aggradation at the bashkirian moscovian boundary is attributed to increased foreland basin subsidence and decreased boundstone accumulation rates progradation was primarily controlled by boundstone growth rather than by highstand shedding from the platform top within the major phases aggradational progradational increments are produced by third to fourth order relative sea level

development patterns and controlling factors of tertiary carbonate buildups insights from high resolution 3d seismic and well data in the malampaya gas field offshore palawan philippines abstract the comprehensive subsurface database of the malampaya buildup late eocene to early miocene offshore nw palawan provides a rare insight into the development of south east asian cenozoic carbonate systems and their controlling factors the newly acquired high resolution three dimensional seismic survey combined with facies and well log analysis allowed a better understanding of the internal architecture of a carbonate platform whose development was largely controlled by tectonic deformation the malampaya carbonate system was initiated in the late eocene as an attached shelf influenced by significant clastic input the late eocene early oligocene shelf was subject to syn depositional extensional tectonics eastward tilting and block faulting that favoured the development of small size buildups on structural highs after a stage of eastward reef progradation an aggrading carbonate shelf frequently affected by subaerial exposure developed from the earliest late oligocene to the early miocene during this period recurrent reactivation of highs along the western and northeastern buildup margins determined the asymmetric morphology and internal architecture of the carbonate system the final demise of the carbonate buildup occurred in the late early miocene it resulted from an increase in subsidence rate and or a sharp increase in nutrient input additional parameters like eustacy oceanographic conditions and the type of carbonate producers played a subordinate role in the buildup development and ultimate demise

radium based pore water fluxes of silica alkalinity manganese doc and uranium a decade of studies in the german wadden sea abstract a decade of studies of metal and nutrient inputs to the back barrier area of spiekeroog island nw german wadden sea have concluded that pore water discharge provides a significant source of the enrichments of many components measured in the tidal channels during low tide in this paper we add studies of radium isotopes to help quantify fluxes into and out of this system activities of radium isotopes in surface water from tidal channels in the back barrier area exhibit pronounced changes in concert with the tide with highest activities occurring near low tide other dissolved components silica total alkalinity ta manganese and dissolved organic carbon doc exhibit similar changes with patterns matching the ra isotopes uranium follows a reverse pattern with highest concentrations at high tide here we use radium isotope measurements in water column and pore water samples to estimate the fluxes of pore waters that enter the tidal channels during low tide using a flushing time of 4 days and the average activities of 224ra 223ra and 228ra measured in the back barrier surface and pore waters we construct a balance of these isotopes which is sustained by a deep pore water flux of 2 4 108 l per tidal cycle this flux transports ra and the other enriched components to the tidal channels and causes the observed low tide enrichments an independent estimate of pore water recharge is based on the depletion of u in the tidal channels the u based recharge is about two times greater than the ra based discharge however other sinks of u could reduce the recharge estimate the pore waters have wide ranges of enrichment in silica alkalinity manganese doc and depletion of u with depth we estimate concentrations of these components in pore water from the depth expected to contribute the majority of the pore water flux 3 5 m to determine fluxes of these components to the tidal channels samples from this depth have minimum concentrations of silica alkalinity manganese and doc we also estimate the exports of these components and import of u due to mixing based on average measured concentrations in the tidal creeks and the 4 day flushing time a comparison of these estimates reveals that the exports negative in the case of u equal or exceed the pore water fluxes by using values slightly higher than the minimum concentrations at 3 5 m to calculate inputs the two estimates could be forced to match we conclude that pore water drainage is the major factor regulating fluxes of ra isotopes silica alkalinity manganese doc and uranium in this system

nature and stability of atoll island shorelines gilbert island chain kiribati equatorial pacific islands rimming pacific atolls typically form narrow low lying lands that are commonly perceived to be particularly vulnerable to global changes such as sea level rise as these low islands form the only habitable land for many island nations understanding the character of shorelines and the rates and controls that operate to bring about changes is an issue of central importance the purpose of this study is to unravel the characteristics of coastal change on atoll islands of the gilbert island chain of the equatorial pacific nation of kiribati especially as they relate to autogenic shoreline processes and el nino southern oscillation variability integration of field observations differential global positioning system data historical aerial photographs and ultra high resolution remote sensing images demonstrates the nature spatial patterns and rates of change from 17 islands on maiana and aranuka atolls the results illustrate that between 2005 and 2009 ca 50 of the shorelines on these islands displayed a discernable shift in position some shorelines were accretionary at net rates up to ca 8 m year 1 and others were erosional up to ca 18 m year 1 long term net rates of change on maiana between 1969 and 2009 were lower than short term net rates measured between 2005 and 2009 both short term and long term observations illustrate some of the greatest change occur near terminations of the largest north south oriented islands associated with longshore movement of coarse sand and gravel direct hits by tropical depressions and marked seasonality factors interpreted as being essential in island growth and shoreline dynamics elsewhere do not directly impact these equatorial atolls and can be eliminated as fundamental controls on shoreline dynamics similarly observations over four years suggested that shoreline variability probably is not influenced directly by marked sea level change although a recent increase in the rates of shoreline change could reflect instability related to the cumulative effect of a long term increase in the rate of sea level rise within this framework of global change local anthropogenic effects autogenic shoreline processes and el nino southern oscillation influenced wind and wave variability control many aspects of these dynamic shorelines these results provide quantitative insights into the character and variability of rates of shoreline change information essential for evaluating and mitigating the vulnerability of island nations such as kiribati

a platform to basin transition for lower aptian carbonates shuaiba formation of the northeastern jebel akhdar sultanate of oman abstract the platform to basin transition of the lower aptian shuaiba carbonate platform throughout a large part of the arabian peninsula has hitherto mainly been documented from subsurface data and has widely been regarded as having been progradational in northeastern jebel akhdar however the shuaiba platform did not prograde and was scarp bounded early lithification accounts for the rigid nature of the scarp a biological framework being nearly absent early exposure surfaces neptunian dykes sills internal breccias and other sediment features as well as the geographic coincidence of the platform scarp with older and younger scarps suggest a tectonic control of margin morphology and dynamics a contemporaneous peak of allodapic sediments and reactivation of older basement structures in adjacent basins also tends to indicate the importance of structural influence on platform margin organization

a dynamic model for the permian panhandle and hugoton fields western anadarko basin panhandle hugoton the largest north american gas field has long been controversial because of extreme subnormal pressures variable gas composition and tilted fluid contacts commonly attributed to hydrodynamic flow despite the absence of an effective updip aquifer these anomalies are addressed in terms of a basin scale petroleum system history largely independent of the geographically underlying pre permian system hydrocarbons were already being generated in the deep anadarko basin during the early permian with efficient southward migration from all potential source rocks via bounding faults and pennsylvanian permian alluvial fans giant amarillo uplift drape structures trapped hydrocarbons immediately following permian evaporite deposition the pre laramide panhandle field at maximum burial depth and pressure contained most of the oil and gas now found in mid continent permian reservoirs the early tertiary laramide orogeny redistributed panhandle field fluid columns possibly spilling gas into the hugoton embayment subsequent erosion of permian reservoir facies in eastern kansas allowed water discharge to outcrops at elevations below the regional hydraulic head as regional pressure dropped in response the panhandle field gas cap expanded rapidly forcing a late tertiary quaternary mass movement of gas northward to fill hugoton and associated fields panhandle hugoton pressures upon discovery were subnormal relative to drilling depth but normal relative to reservoir outcrop elevations in eastern kansas indicating that pressures are controlled by aquifer communication with the surface instead of burial depth variations in fluid contacts pressure and gas composition suggest that reservoir fluids are still moving driven by decompression and the rapid volumetric expansion of a supergiant gas accumulation

controls on morphology and sedimentology of carbonate tidal deltas abacos bahamas abstract although the physical processes controlling siliciclastic shoal bodies are reasonably well understood the sedimentary processes that shape carbonate tidal shoal systems are poorly constrained the tidal deltas of the northwestern abaco islands bahamas provide a unique opportunity to explore the relationships between physical and sedimentary processes in a variety of sizes and shapes of tidal deltas the length of tidal deltas range in size from 350 m to 2 km from the inlet to the termination of the delta lobe and shoal crests consist primarily of well sorted ooid sands mean grain size between 400 and 500 m mcmanus sorting factor 0 70 coated grains are rare off the shoals and sorting decreases with distance from the shoal crests velocities in the rocky inlets can exceed 2 m s in the daily tidal cycles and the systematic distribution of grain types reflects tidal velocity variations areas with the highest velocities 0 80 m s correspond to hard rocky bottoms with some skeletal grains these regions of elevated velocities are focused within the inlets where jets of high velocity currents form during each tidal cycle these current jets extend outward from the inlet throat and velocities decrease outwards as the flow disperses velocities between 40 and 80 cm s occur in the regions with abundant ooids and peloids are most abundant in the lowest velocity regions the results of this study illustrate a clear relationship between quotidian physical processes and their geomorphic and sedimentologic products in a carbonate system in this context carbonates appear to share many geomorphic similarities with siliciclastic analogs the results represent an important step beyond qualitative facies interpretations and towards quantitative specified environmental and sedimentologic characterizations for carbonate systems

the significance of fixed ammonium in palaeozoic sediments for the generation of nitrogen rich natural gases in the north german basin in contrast to predominantly hydrocarbon rich natural gases in the western part of the central european basin ceb accumulations of natural gases from the eastern part of the north german basin ngb are nitrogen rich with up to 90 n2 this study is focused on the behaviour of fixed ammonium in clay minerals of organic rich palaeozoic sediments in the eastern part of the ngb as a major source of nitrogen rich natural gases carboniferous shales have been investigated for a better understanding of nitrogen fixing during diagenesis storage during burial and release during devolatilization processes or fluid rock interactions the total nitrogen contents in the studied carboniferous shales of the ngb reach up to 2700 ppm with an inorganic fixed portion in the form of nh4 n of more than 60 the results of this study indicate an increasing proportion of the mineralogically fixed ammonium with increasing thermal maturity and storage up to catagenetic conditions the isotopic composition of fixed nh4 is relatively homogeneous in the majority of the shales and ranges from 1 to 3 5 in contrast samples from the basin centre show a significant decrease in ammonium contents down to 460 ppm coupled with a shift in 15n up to 5 6 suggesting a release of nitrogen on a large scale calculation of nitrogen loss and isotopic fractionation indicate that more than 30 of nitrogen was released as ammonium probably as a consequence of fluid rock interaction with highly saline brines

tidal variations in groundwater storage and associated discharge from an intertidal coastal aquifer 1 we applied a hydrogeological numerical simulation to investigate spatial and temporal variations in groundwater flow and discharge at a well studied tidal flat margin in the german wadden sea the simulation was forced by high resolution sea level boundary conditions accuracy of the simulation was checked by comparing simulated with measured pressure heads obtained from direct burial pressure sensor measurements overall discharge calculated from the simulation for a time period of almost 12 month averages 0 97 m3 per meter of margin length per tide but may vary significantly most pronounced with the spring neap tide cycle the simulation predicts that the maximum hydraulic gradient at ebb tide controls the magnitude of discharge whereas duration of ebb tide is less important additionally simulated and measured pressure gradients can be used to investigate the influence of varying lithology on the groundwater flow regime the presence of a low permeable holocene silt layer ubiquitous in the study area creates a layered unconfined semiconfined aquifer system both parts of the aquifer are hydraulically connected to the deeply incising tidal creek but show a different response to the tidal forcing groundwater flow in the upper unconfined margin sediments can be described as a circulation of seawater where inflow and outflow are coupled to changes in saturation sediments below the confining layer release groundwater from storage during falling and ebb tide and recharge during rising and high tide we can show that tidally driven water exchange between semiconfined aquifers and coastal waters may have a major impact on total groundwater discharge

regional groundwater focusing of nitrogen and noble gases into the hugoton panhandle giant gas field usa the hugoton panhandle giant gas field located across sw kansas and the texas and oklahoma panhandles in the usa is the case type example of high nitrogen concentrations in a natural gas being linked with high helium concentrations we collected 31 samples from producing wells in a north south traverse of the 350 km long field the samples reflect the previously observed north south change in 4he n2 with values changing from 0 020 to 0 049 respectively 3he 4he 21ne 22ne and 40ar 36ar vary between 0 14 0 25 ra 0 0373 0 0508 and 818 1156 respectively and are caused by quantifiable contributions from mantle crustal and atmosphere derived sources the atmosphere derived 20ne 36ar ratios are indistinguishable from groundwater values the crustal 4he 21ne and 4he 40ar ratios show a 60 excess of 4he compared to predicted production ratios in the crust and are typical of noble gases released from the shallow crust the mantle 3he n2 and groundwater recharge 36ar n2 ratios enable us to rule out significant magmatic or atmosphere contributions to the gas field n2 which is dominantly crustal in origin correlated 20ne n2 and 4he n2 shows mixing between two distinct crustal n2 components one n2 component n2 is associated with the crustal 4he and groundwater derived 20ne and the other with no resolvable noble gas contribution measured 15nn2 values vary from 2 7 to 9 4 the n2 and non he associated n2 endmembers are inferred to have 15nn2 3 and 13 and contribute from between 25 60 and 75 40 of the nitrogen respectively the non he associated nitrogen is probably derived from relatively mature organic matter in the sedimentary column the 15nn2 value is not compatible with a crystalline or high grade metamorphic source and similar to the 4he is inferred to be from a shallow or low metamorphic grade source rock 4he mass balance requires a regional crustal source its association with significant magmatic 3he pointing to a tectonically active source to the west of the hugoton system the volume of groundwater required to source the 20ne in the gas field demonstrates the viability of the groundwater system in providing the collection transport and focusing mechanism for the 4he and n2 the n2 20ne ratio shows that the n2 transport must be in the aqueous phase and that the degassing mechanism is probably contact between the regional groundwater system and the preexisting reservoir hydrocarbon gas phase

the quantification of diffusive hydrocarbon losses through cap rocks of natural gas reservoirs a reevaluation discussion 1 a calculation scheme is presented to estimate the quantities of diffusive gas loss through the water saturated cap rock of natural gas reservoirs over geologic time reexamination of earlier calculations in a 1982 paper by leythaeuser et al revealed that the estimate of the rate of diffusive hydrocarbon losses through the cap rock of the harlingen netherlands natural gas reservoir was based on oversimplified assumptions concerning the boundary conditions at the reservoir cap rock interface according to this recalculation the time required to reduce the present day methane content of the harlingen gas field by one half is approximately 70 m y not the previously published value of 4 5 m y consequently diffusion losses through the cap rock appear to affect the long erm stability of natural gas reservoirs to a lesser extent than suggested by the earlier results

comparison of four numerical models for simulating seepage from salt marsh sediments a boundary integral equation method biem model and three differently formulated finite element method fem models were implemented to explore the spatial and temporal patterns in marsh pore water seepage that each generated the biem model is based on the laplace equation coupled to a dynamic free surface condition that assumes that as the water table changes the aquifer instantaneously loses or gains an amount of water equal to the change in head times the specific yield the fem models all implement a simplified richards equation that allows gradual desaturation or resaturation and thus flow in both the saturated and unsaturated zones of the aquifer two of the fem models are based on the governing equation for the usgs model sutra and thus take into account fluid and aquifer compressibility one of these was modified to take into account the effect of tidal loading on the total stress which is assumed to be constant in the derivation of the original version of sutra the third fem model assumes that neither the fluid or aquifer matrix is compressible so that changes in storage are due solely to changes in saturation the unmodified sutra model generated instantaneous boundary fluxes that were up to two orders of magnitude greater and spatially more uniform than those of the other models the fem model without compressibility generated spatial and temporal patterns of the boundary fluxes very similar to those produced by the biem model the sutra model with the tidal stress modification gave fluxes similar in magnitude to the biem and no compressibility models but with distinctly different distributions in space and time these results indicate that accurate simulation of seepage from marsh soils is highly sensitive to aquifer compressibility and to proper formulation of the effect of tidal loading on the total stress in the aquifer they also suggest that accurate simulation may require total stress correction not only for tidal loading but for changes in the water table as well finally to aid the development of methods for the measurement of compressibility we present a schematic pore scale model to illustrate the factors that may govern the compressibility of marsh soils

storm driven groundwater flow in a salt marsh 1 storms can cause significant groundwater flow in coastal settings but prior studies of the effects of storms on groundwater flow and transport have largely focused on very large storms and used salinity as a tracer we have little information about the effects of smaller storms on coastal flow and how storm induced variability affects key tidal wetlands like salt marshes which may remain saline throughout a storm here we show that even the distant passage of a moderate storm can strongly increase groundwater flow and transport in salt marsh ecosystems and adjacent barrier islands groundwater monitoring and radium isotope tracer analyses revealed significant influx of saline creek water into the confined aquifer below the marsh platform driven by storm surge this pulse of fluids reached depths exceeding 5 m and surge enhanced tides propagated through the aquifer to affect flow in the upland 100 m from the creek bank groundwater discharge from the marsh varied significantly prior to the storm doubling during inundating tides compared to a period of noninundating neap tides storm surge then caused groundwater discharge to decline 50 compared to similar inundating tides ra and nutrient poor creek water that entered the confined aquifer below the marsh was quickly enriched in nutrients and carbon even on 12 h tidal cycles so that nutrient discharge was likely proportional to groundwater discharge storm related flow could also drive significant contaminant discharge from developed coastlines the enhanced transport and variability observed here likely affected hundreds of kilometers of the coastline impacted by the storm

permo carboniferous hydrocarbon accumulations mid continent u s a approximately 19 4 billion bbl of oil and 119 tcf of nonassociated gas have been discovered in the mid continent as of january 1 1978 although these volumes of hydrocarbons were trapped in thousands of fields throughout the mid continent the bulk of these resources were emplaced in a relatively few fields about 14 2 billion bbl of oil have been found in 111 significant and giant oil fields and 103 tcf of nonassociated gas have been discovered in 57 significant and giant gas fields permo carboniferous reservoirs are important in 101 of the large oil fields and 55 of the large gas fields these fields contained 9 5 billion bbl of oil and 99 tcf of gas respectively our calculations of the total oil and gas accumulations in permo carboniferous reservoirs are extrapola ed from these data about 2 1 billion bbl of oil and 5 1 tcf of nonassociated gas accumulated in lower carboniferous mississippian reservoirs most of this oil and gas was stratigraphically trapped in upper mississippian sandstones and carbonates which are truncated at the pre pennsylvanian unconformity surface approximately 8 8 billion bbl of oil and about 31 9 tcf of nonassociated gas have been found in upper carboniferous pennsylvanian reservoirs in the mid continent most of these oil and gas accumulations were stratigraphically trapped in lenticular sandstone bodies the environments in which the majority of these sandstones were deposited range from fluvial deltaic to shallow marine about 2 billion bbl of oil and 77 7 tcf of nonassociated gas accumulated in permian reservoirs most of these hydrocarbons accumulated in rocks of lower permian age in the hugoton panhandle panoma fields the oil and gas in these fields were trapped by regional changes in lithofacies with associated hydrodynamic gradients significant stratigraphic accumulations of oil and gas will continue to be discovered in the mid continent even though much of this region is now in a late mature stage of exploration and development

isotopic variations of the fixed nitrogen in metamorphic rocks the content and isotopic composition of fixed nitrogen nh 4 n in metasedimentary rocks phyllites mica schists and gneisses from prograde metamorphic zones in the erzgebirge saxon ore mountains g d r were measured and show that the nitrogen content decreases and 15n increases with increasing metamorphic grade the geochemical and isotopic behaviour of nitrogen during contact metamorphism was investigated in a mica schist profile through the contact aureole of a granitic pluton the nitrogen concentrations of the wall rocks decrease towards the contact whereas the 15n values become higher various model experiments were carried out in the laboratory to explain the changes observed in the rock samples the nitrogen isotope fractionation factor was determined for the isotopic exchange in the system ammonium sulphate ammonia at 250 c 1 0143 0 0012 and 350 c 1 0128 0 0006 in accordance with the model experiments the conclusion seems warranted that the change in nitrogen content and its isotopic composition in rocks during metamorphic processes depend mainly on the metamorphic temperature

non tropical carbonate deposits on the modern new zealand shelf abstract extensive ca 50 000 km 2 shallow marine platforms 70 caco 3 despite proximity to a tectonically active plate margin in these regions the terrigenous sediment supply is presently low and growth of epibenthos is fostered by firm substrates rock gravels shells seaweeds and the generally energetic nature and high nutrient levels of open shelf waters rapid transition into adjacent terrigenous dominated facies is characteristic irrespective of water depth the carbonates are coarse grained and fragmental carbonate mud is rare calcite dominates over aragonite high mg calcite widespread off northern new zealand is rare in the south skeletal material is dominated by bryozoans and bivalve molluscs with significant local contributions from foraminifers barnacles calcareous red algae and echinoderms the name bryomol is suggested for this distinctive temperate region skeletal carbonate facies which can be usefully subdivided based on dominant zoarial growth forms of the bryozoan component known to be habitat related bioerosion is an important mechanism of skeletal fragmentation and degradation many grains especially aragontic bivalves are infested by endolithic borers and have low preservation potential ages of skeletal material in the surficial deposits range from more than 20 000 years b p to modern which is consistent with both low rates of carbonate production and sediment accumulation and the wide range in preservation state of grains some data suggest that the skeletal carbonates are dispersed and mixed mainly during infrequent movement of sand ribbons sand waves and sand sheets driven by storm assisted tidal flows tracts of modern palimpsest and relict carbonates can occur in juxtaposition the facies characteristics of the new zealand shelf carbonate deposits contrast significantly with those of the classical bahaman type carbonate model however they are similar to those reported from many other mid to high latitude carbonate shelves and afford good analogues for most onland occurrences of new zealand cenozoic limestones

origin of helium and nitrogen in the panhandle hugoton field of texas oklahoma and kansas united states helium and nitrogen variations in panhandle hugoton field phf gases are products of interaction between hydrocarbon gas from the anadarko basin and at least two water masses with dissolved nitrogen and helium the two most distinct water masses are from the palo duro basin highest he n2 and the hugoton embayment lowest he n2 geochemical data indicate several hundred million years of helium generation in porous rock helium migrated to the gas by diffusion through water saturated rock and by west to east water flow sediment and basement helium generation and helium migration were modeled to validate timing and source of phf helium models indicate a predominantly sedimentary helium source with some basement helium charge on the amarillo uplift helium in the central and eastern phf diffused from underlying rocks whereas gases on the west and southwest sides were enriched in nitrogen and helium delivered by hydrodynamic water flow nitrogen in high nitrogen gases was probably sourced as ammonium released from clays by cation exchange with brines derived from overlying salt units the amount of mudrock nitrogen and helium source relative to other potential helium sources arkose radioactive dolomite correlates to decreasing gas he n2 the high helium concentrations in phf gases result from multiple favorable circumstances old pore water accumulated dissolved helium during hundreds of millions of years of helium generation in sediment high water gas and low pressure favored higher helium concentrations in gas hydrodynamic flow delivered helium rich pore water from basins west of the phf

15n 14n variations in cretaceous atlantic sedimentary sequences implication for past changes in marine nitrogen biogeochemistry at two locations in the atlantic ocean dsdp sites 367 and 530 early to middle cretaceous organic carbon rich beds black shales were found to have significantly lower 15n values lower15n 14n ratios than adjacent organic carbon poor beds white limestones or green claystones while these lithologies are of marine origin the black strata in particular have 15n values that are significantly lower than those previously found in the marine sediment record and most contemporary marine nitrogen pools in contrast black organic carbon rich beds at a third site dsdp site 603 contain predominantly terrestrial organic matter and have c and n isotopic compositions similar to organic matter of modern terrestrial origin the recurring15n depletion in the marine derived cretaceous sequences prove that the nitrogen they contain is the end result of an episodic and atypical biogeochemistry existing isotopic and other data indicate that the low15n relative abundance is the consequence of pelagic rather than post depositional processes reduced ocean circulation increased denitrification and hence reduced euphotic zone nitrate availability may have led to cretaceous phytoplankton assemblages that were periodically dominated by n2 fixing blue green algae a possible source of this sediment15n depletion lack of parallel isotopic shifts in cretaceous terrestrially derived nitrogen site 603 argues that the above change in nitrogen cycling during this period did not extend beyond the marine environment

a currents of removal approach for interpreting carbonate sedimentary processes abstract this study develops a currents of removal methodology to examine and quantify the nature of physical transport processes affecting the formation of bioclastic deposits in the cocos keeling islands an indian ocean atoll this approach is based on the hydraulic settling and threshold of entrainment characteristics of bioclastic deposits and measured current energy potential mobility pm analysis of 157 samples quantifies the proportion of deposits able to be transported in each geomorphic zone results show that under mean energy conditions wave induced currents entrain and transport sediment within the atoll and show that transport of sediment is not solely reliant on storm energy conditions gradients of pm values are used to reconstruct sediment transport pathways from the reef flat 85 100 pm through shallow passages 75 100 pm to sand aprons 50 75 pm and shallow 0 20 pm and deep lagoon 0 pm comparison of settling velocity distributions of bed material and sediment retained in sediment trap experiments show that actual mobility levels correspond with pm estimates potential mobility analysis also identifies the immobile portions of deposits which increase lagoonward constituent analysis of immobile fractions and analysis of settling frequency distributions are used to differentiate the importance of physical and biological processes in the formation of deposits throughout cocos and identify the role of each geomorphic zone in the transport system the pattern of sediment is controlled by physical processes between the reef flat the primary sediment production zone with sediment transported through the shallow passage conduits to the sand aprons the formation of shallow and deep lagoon deposits is controlled by autochthonous sediment production and storm deposition potential mobility analysis is a powerful tool enabling physical transport processes within bioclastic sedimentary environments to be quantified the ability to examine an individual deposit s hydraulic behaviour and development also enables depositional processes to be examined at a much finer resolution than previously attempted using conventional textural approaches

evolution of permian evaporite basin in texas panhandle permian leonardian to ochoan evaporites in the texas panhandle were deposited in a range of marine shelf to supratidal environments along an arid coastline carbonates in these strata generally were deposited in inner shelf systems and include subtidal to supratidal facies landward of shelf environments evaporites were deposited in brine pans and salt flats brine pan facies are laminated anhydrite and banded salt that formed in shallow hypersaline waters such as restricted lagoons or supratidal salines salt flat facies are mainly chaotic mixtures of mudstone and halite possibly formed by salt deposition on and within mud flats that bordered brine pans or in brine soaked mud flat depressions periodically mud flats built across the evaporite systems and were suppl ed with red terrestrial clastics mainly mud and silt these facies occur together in at least three different types of lithogenetic units strata in the clear fork group leonardian are considered deposits of a coastal evaporite basin that was progressively filled by terrestrial clastics these rocks exhibit regressive cycles of brine pan salt flat and mud flat facies in contrast san andres strata guadalupian were deposited in a broad marine embayment with persistent brine pan conditions and contain cycles of inner shelf and brine pan facies post san andres strata late guadalupian and ochoan were deposited in the inner reaches of a broad interior salt basin and are composed mainly of mud flat salt flat and halite rich brine pan facies

tidal impacts on riparian salinities near estuaries groundwater dependent riparian biota is known to be sensitive to changes in soil and groundwater salinity in estuarine systems the groundwater flow and salinity behaviour in a phreatic aquifer adjoining a partially penetrating tidal estuary is investigated through two dimensional numerical experiments for a lateral cross section which explore the influence of factors such as aquifer and soil materials tidal amplitudes and regional groundwater hydraulic gradients the density contrast between estuarine water and the fresh groundwater drives saltwater penetration of the aquifer even in the case of a marked groundwater hydraulic gradient towards the estuary we show that tidal fluctuations in estuaries can significantly affect the groundwater salinity distribution in adjacent density stratified phreatic aquifers this has consequences for the expected distribution of salinity sensitive biota in the hyporheic zone as well as vegetation and fauna dependent on water in the riparian soil and aquifer the shape of the dense saltwater wedge propagating into the adjacent groundwater system is also modified by the estuarine tidal signal although this effect appears to have only minor influence on the maximum distance penetrated into the aquifer i e location of the toe of the wedge tide induced changes to riparian groundwater salinity are advection driven as evidenced by the modified time averaged groundwater flow dynamics

the durability of bioclastic sediments and implications for coral reef deposit formation the generation and composition of carbonate sediment within tropical carbonate settings is controlled by the skeletal production of caco3 in conjunction with physical biological and chemical processes which act to break down and disperse skeletal remains using the results of detailed tumbling barrel experiments this paper discusses the role the physical durability of common constituents of reef sediment plays in the composition of coral reef deposits the durability of the skeletal remains of six reef sediment constituents was determined experimentally using tumbling barrels results indicate that constituent durability varies considerably amongst common reef sediment constituents calcareous algae halimeda was the least durable constituent tested followed by larger benthic foraminifera baculogypsina sphaerulata and marginopora vertebralis and the pelecypod fragum fragum two species of branching coral acropora sarmentosa and acropora nasuta were found to be the most resistant to physical destruction these findings provide increased power to interpret reef and island deposits and the potential role skeletal durability plays in the retention of constituent skeletons within coral reef associated sedimentary systems

the transient nature of the empty bucket model of reef sedimentation abstract the geometry of modern reefs has been likened to an empty bucket with the narrow reef rim comprising the container pail that encloses the water filled bucket while the analogy is valid the assumption that this constitutes a final geometry is not examples from the indian pacific and atlantic oceans individually and collectively demonstrate current filling of the lagoons by reef perimeter sand aprons since sea level only approximated its present position 3 to 6 ky ago it follows that the observed extent of modern highstand lagoon filling is minimal if the filling process was to continue unabated the result would be a flat topped bank but during the pleistocene low stands of sea level aborted the filling process extrapolating these relationships to the geologic record suggests that the empty bucket model of unfilled reef lagoon space is greatest during icehouse high frequency glacial fluctuations of sea level alternatively filled buckets in which cycle thickness approximates accommodation space are probably largely restricted to greenhouse time intervals the co occurrence of quaternary high amplitude frequency sea level changes with rapidly growing scleractinian corals probably enhanced the occurrence of empty bucket morphologies

tidally driven multiscale pore water flow in a creek marsh system intertidal wetlands are complex hydrological systems characterized by strong dynamic interactions between coastal surface water and groundwater driven particularly by tides we simulated such interactions with a focus on three dimensional variably saturated pore water flow in a creek marsh system that bordered a tidally dominated main channel simulated intra tidal groundwater dynamics exhibited significant flow asymmetry with non zero mean flow velocities over the tidal period the tidally averaged flow led to pore water circulation with three dimensionality linked strongly to the marsh topography over a range of spatial scales near the creek bank around the creek meander and over long marsh sections inclined towards the main channel particle tracking revealed that time scales associated with these circulations differed by orders of magnitude under the simulated conditions the creek served as the main outlet of the pore water circulation paths especially those linked with infiltration into the upper marsh surface areas away from the main channel local net efflux influenced by the creek channel curvature varied along the creek but produced a total discharge largely proportional to the creek length water infiltrating the soil in the lower marsh surface areas away from the creek tended to discharge directly to the main channel however the total discharge to the main channel was much less than that into the creek this study highlights the hydrological complexity of intertidal marshes and the need for further research on interactions among marsh morphology hydrology and ecology which underpin the functionalities of these wetland systems

controls on platform scale patterns of surface sediments shallow holocene platforms bahamas isolated carbonate platforms occur throughout geological history and commonly exhibit considerable spatial variability to evaluate the controls on the nature of sediment accumulation across the expansive shallow platform tops this study systematically compares and contrasts patterns in surface sediments from several shallow 10 m holocene bahamian examples remote sensing data field observations petrographic characterization and quantitative grain size analyses reveal the spatial patterns of sediment accumulation on crooked acklins platform and the berry islands bank integration of these data with synoptic observations of waves tides and currents along with regional geochemical data provides a means to explore the factors that influence platform scale sedimentary patterns these data illustrate that the platform interiors of both crooked acklins platform and berry islands bank are blanketed with medium to coarse sand size sediment peloids are most common in the interior of crooked acklins platform whereas the berry islands bank includes more abundant composite grains in both areas very little mud is present with surface sediments averaging 2 mud comparison of these results with published data from little bahama bank great bahama bank and caicos platform suggest that contrary to previous interpretations the presence of open margins and or brisk winds are not necessary for the occurrence of a platform top with little mud although the muddy sediment fraction of the interior can be suspended by elevated wave energy wind generated current speeds in protected platform interiors are relatively low instead in parts of the platform interiors transport and winnowing of fines is enhanced greatly by tidal currents which carry suspended sediments off the shallow platforms even if shielded by islands beyond physical influences however regional geochemical compilations suggest that the bahamian tides supply highly supersaturated waters rich in dissolved oxygen to these platform interiors this exchange is interpreted to facilitate favourable conditions for calcium carbonate precipitation in the form of ooids marine cements and hardened peloids across vast expanses of the platform interiors such fundamental controls on holocene platform scale sediment dynamics are likely to have influenced carbonate systems through the geological record

effects of unstable flow on solute transport in the marsh soil and exchange with coastal water recent studies of marsh hydraulics have focused on tide induced pore water circulation as the main drive for solute transport in the marsh soil and exchange with coastal water our study revealed another important mechanism provided by unstable fingering flow which largely modified solute transport paths in the marsh interior downward penetration of salt fingers forced ambient pore water and solute plumes to move upward and exit the marsh soil through marsh platform at relatively high concentrations up to two orders of magnitude higher than exit solute concentrations at the tidal creek bed the mixing of solute with ambient pore water in the marsh interior was intensified greatly by fingering flow a critical distance to the creek was determined based on a field scale model simulation to distinguish tidal circulation dominated and fingering flow dominated solute transport zones the new transport mechanism has implications for understanding the fate of solutes in particularly salt marshes of low creek densities

influence of the geologic and geomorphologic characteristics and of crab burrows on the interrelation between surface water and groundwater in an estuarine coastal wetland the interrelation between surface water and groundwater in intertidal flats is often studied through mathematical models in many cases these models need to be supported by an integral analysis of the geologic geomorphologic hydrologic and biological characteristics of the environment that are to be obtained from field surveys the marshy environment of the river ajo in the samborombon bay wetland argentina is a typical example of an estuarine coastal zone geologic and geomorphologic surveys were carried out as well as measurements of surface water and groundwater level changes as a response of the aquifer to tidal forcing the banks of the river ajo are either scarped with storm flats or mildly sloped with intertidal flats and numerous crab burrows sediments are mainly silty clayey with low permeability and lie over silty sandy layers at the erosion scarps the tidal wave enters the aquifer as a sub horizontal flow through the pore space of the sediments the tidal range in the aquifer depends on the lithological characteristics of the sediments and on the side changes of their hydraulic conductivity the rise of the water table at high water and its subsequent fall are nearly sinusoidal with a period similar to that of the tide at the river at the intertidal flats instead the tidal wave enters the aquifer mainly as a sub vertical flow through the crab burrows as the crab burrows are not interconnected they are not distinct pathways for preferential flow therefore the groundwater flux into the river is very slow during low water and the recovery of the water table takes a long time the tidal influence upon the water table on both kinds of banks affects only a narrow strip of the aquifer not only are the characteristics of the marshy environment of the river ajo representative of most of the samborombon bay wetland they can also be extended to other similar coastal wetlands to help preserve these invaluable environments

noble gas composition of deep brines from the palo duro basin texas deep groundwaters in sedimentary basins can be sufficiently old 10 m y to have accumulated both radiogenic 4he and 40ar differences in the ratio of u th k for aquifer lithologies lead to variations for 4he40ar in the groundwater these variations can be used to resolve chronologically significant noble gas components application of a binary model to brine samples from the palo duro basin texas yields u th 4he residence times of 100 to 300 m y concentrations of two non radiogenic noble gases 20ne and 36ar provide information on the salinities of the water that recharged these aquifers

role of stratigraphy in governing pore water seepage from salt marsh sediments 1 numerical modeling experiments have been used to study the effects of marsh stratigraphy on the seepage of pore water into tidal channels if the mud sand contact lies at the elevation of the channel bottom and the hydraulic conductivity of the basal sand is at least an order of magnitude greater than the overlying mud the locus of maximum seepage shifts from the tide line as in a purely mud marsh to the toe of the creek bank the ratio of creek bank seepage to bottom seepage also shifts from greater than to less than one furthermore as the ratio of the hydraulic conductivities of sand to mud increases the ratio of the total seepage from the sand mud marsh to that from a pure mud marsh increases in a nonlinear fashion reaching an asymptotic limit of about 20 at a conductivity ratio of about 1000 if the mud sand boundary is progressively lowered so that mud also lies beneath the channel the seepage dynamics gradually revert toward those of a purely mud marsh the ecological implications of these results for regularly flooded low marshes are discussed

nitrogen isotope compositions of metasedimentary rocks in the catalina schist california implications for metamorphic devolatilization history abstract in the catalina schist subduction zone metamorphic complex california metasedimentary rocks show a decrease in n concentration and an increase in 15nair with increasing metamorphic grade lowest grade lawsonite albite rocks contain 632 185 ppm n with 15 n 1 9 0 6 whereas highgrade amphibolite equivalents contain 138 76 ppm n with 15 n 4 3 0 8 loss of n accompanied devolatilization reactions that evolved h2o rich c o h s n fluids through consumption of chlorite and phengitic white mica and production of mineral assemblages containing muscovite biotite garnet and kyanite whole rock n concentrations of up to 200 ppm in veins and pegmatites produced during high p t metamorphism reflect the redistribution of n during devolatilization and partial melting of the metasedimentary rocks bulk fluid rock n isotope fractionations 15n 15nfluid 15nrock of 1 5 1 were calculated with the rayleigh distillation equation taking into account variability in rock composition by comparison of samples with similar k2o concentrations these fractionations are similar to but slightly lower than published calculated fractionations for n2 nh4 exchange at the temperature range of 350 600 c over which most of the devolatilization occurred in the catalina schist approximately 3 4 to 2 25 the n systematics appear to be explained by n2 nh4 exchange and a devolatilization process intermediate in behavior to batch volatilization and rayleigh distillation the observed shifts in n concentration and 15n cannot be explained by nh3 nh4 exchange at these temperatures using the equilibrium models the distillation devolatilization process implicated in this study may govern the behavior of other trace elements partitioned into hydrous fluids during devolatilization e g b cs u similarity of the calculated fluid 15n 1 5 to 5 5 with compositions of natural gases inferred to be derived from metasedimentary sources indicates the possibility of using n as a tracer of large scale volatile transport

generation of nitrogen and methane from sedimentary organic matter implications on the dynamics of natural gas accumulations nitrogen n2 contents of natural gases in rotliegend and buntsandstein reservoirs of the north german basin regionally approach 100 a review is given of the various hypotheses primordial origin volcanic or magmatic origin radiogenic origin atmospheric origin organic origin inorganic nitrogen in sedimentary rocks presented to account for nitrogen anomalies in this area and other parts of the world the objective of the present study was to investigate sedimentary organic matter in particular coals as a potential source of molecular nitrogen in the subsurface comparison of reservoir sizes and gas generation potentials indicates that carboniferous coal measures which are considered as the source of the natural gas in the north german basin can readily account for the nitrogen quantities found in present day reservoirs laboratory pyrolysis experiments were carried out to investigate the kinetics of generation of methane and molecular nitrogen from coals of different type and rank under experimental conditions nitrogen is formed at higher temperatures than methane supporting the concept of a fractional generation of methane and nitrogen in natural systems based on the kinetic parameters derived from laboratory experiments methane and nitrogen generation rates from coals were calculated for geologic heating rates gas containing more than 50 nitrogen is generated under these conditions at temperatures in excess of 300 c nitrogen rich gases are thus formed only in the final stage of gas generation after methane generation has practically ceased it is concluded that the amounts of gas encountered in nitrogen rich gas accumulations represent only a small fraction possibly 1 of the total gas generation potential of this area while the bulk of the generated gas has escaped to the atmosphere the present day composition of the reservoir gases reflects the composition of only the most recently generated gas on a geologic time scale

nitrogen isotope record of fluid rock interactions in the skiddaw aureole and granite english lake district the skiddaw granite and its contact metamorphic aureole in the english lake district provide an excellent opportunity to test the capability of the n isotope system to trace devolatilization and large scale transfer of crustal fluids in the aureole skiddaw group metasedimentary rocks with relatively uniform lithology and major element compositions show a dramatic decrease in n content toward the granite contact from or 800 ppm at distances 2 5 km from the contact to 1 5 km these rocks have extremely uniform delta 15 n air near 3 7 per mil whereas closer to the contact or 1 km delta 15 n is shifted to higher values up to 8 7 per mil the coupled decreases in n content and increases in delta 15 n are compatible with the removal of n having low delta 15 n in fluids during continuous prograde devolatilization reactions involving the break down of white mica and the stabilization of biotite cordierite and andalusite bearing assemblages in the same metasedimentary rocks the lack of obvious trends in major element concentrations including sio 2 tio 2 sio 2 al 2 o 3 and the ratios of other major oxides to tio 2 and al 2 o 3 with distance from the granitic contact is consistent with minimal change in major element composition during the contact metamorphism ratios of whole rock n b rb and ba concentrations to whole rock k 2 o content are believed to reflect the differing fluid mica partitioning and involving varying relative proportions of white mica and biotite of these trace elements during devolatilization reactions greisenized skiddaw granite from a borehole is enriched in n range of 17 225 ppm for whole rocks and white mica separates relative to the unaltered granite whole rock 30 ppm and has delta 15 n of 1 0 to 4 8 per mil the n concentrations and delta 15 n of the wall rocks and greisenized granites combined with c isotopic data carbonate and carbonaceous matter for the same rocks are consistent with the mobilization of fluids having low delta 15 n and delta 13 c pdb values from the devolatilized aureole into the cooling intrusive body such transport is consistent with the predictions of recent theoretical models of late stage hydrothermal evolution in cooling intrusive systems

integrated 3 d reservoir modeling based on 3 d seismic the tertiary malampaya and camago buildups offshore palawan philippines three dimensional 3 d seismic interpretation and drilling results indicate complex sedimentary geometries of the malampaya and camago build ups offshore palawan philippines with localized progradation due to unidirectional offbank transport alternating with vertical aggradation successive reduction of size during buildup growth and backstepping of the protected landward margin in response to transgression ultimately appear to have triggered the demise of carbonate production and platform drowning the shallow water platform top sediments repeatedly show signs of subaerial exposure before reflooding a modeling functionality was developed to allow development of multiple scenario 3 d reservoir models in an exploration or appraisal stage the model enables merging of seismic scale observations based on 3 d volume and horizon analyses with subseismic scale information from well data however inherent noise within the seismic data introduced by the complex buildup morphology has resulted in inconsistent attribute distribution and fault dimming these difficulties are compounded by erratic velocity distribution within the limestone nonhyperbolic move out and a narrow relatively low frequency spectrum all of which prevent the use of the 3 d seismic volume as hard data but rather allow its use as a soft constraint for guiding the geological interpretation and ultimately the modeling process seismic data quality in such complex morphologic settings and scarcity of well data hamper greatly the use of geostatistically driven modeling approaches therefore a new functionality was developed within shell s proprietary integrated 3 d modeling suite geocap which allows deterministic model reservoirs using seismic horizon and volume interpretation sequence and cyclo stratigraphic architecture and the concept of reservoir rock type seismic velocity in clean carbonate formations is predominantly a function of porosity distribution to assess time to depth conversion uncertainty the reservoir rock type based models were first produced in the time domain only after differential 3 d depth conversion of these models could the scenarios be reconstructed in the depth domain the depth models subsequently were used to derive permeability and saturation 3 d distortions and thus hydrocarbon volumes for each deterministic scenario the models were then used for simulation purposes

hydraulic characteristics of bioclastic deposits new possibilities for environmental interpretation using settling velocity fractions this paper examines the hydraulic behaviour of heterogeneous bioclastic sediments using settling velocity fractions bioclastic deposits are divided into fractions by splitting hydraulically sorted samples compositional analysis of fractions shows that grains exhibit marked variation in composition shape size and density which control the hydraulic behaviour of bioclastic deposits despite the heterogeneous grain properties of fractions analogous to sieve fractions sedimentation analysis shows that they possess a narrow range of settling velocity values flume experiments also show that the settling velocity fractions possess a narrow range of threshold velocity values a threshold relationship is identified in which the velocity required to entrain mixed settling fractions increases from 20 5 to 65 0cm s 1 for settling fractions with mean settling values of 5 5 chi 2 2 cm s 1 to 1 4 chi 36 0 cm s 1 respectively heterogeneous settling fractions due to intergrain effects were found to possess larger threshold velocities than individual components showing that the composition of bioclastic deposits controls hydraulic behaviour thus caution must be exercised in using the threshold relationship for homogeneous sediments or deposits of markedly different composition as settling velocity fractions reflect narrow hydraulic settling and threshold properties of sediments the mean settling velocity of fractions is considered a good indicator with which to interpret transport and depositional processes comparison of settling and sieve size distributions shows that size distributions do not reflect the hydraulic behaviour of bioclastic deposits and should not be used to interpret environmental processes the study indicates that examination of settling velocity fractions for which hydraulic settling and threshold properties are known coupled with compositional analysis of these fractions will allow much greater environmental interpretation of deposit forming and energy processes in reef environments

nitrogen cycling in the sediments of santa barbara basin and eastern subtropical north pacific nitrogen isotopes diagenesis and possible chemosymbiosis between two lithotrophs thioploca and anammox riding on a glider abstract this article presents data on the isotopic composition of pore water ammonium and n org in the anoxic sediments of the santa barbara basin and the eastern subtropical north pacific esnp region ammonium 15 n behaves differently in the two regions reflecting variability in bacterial processes of sedimentary nitrogen cycling in santa barbara basin stoichiometry of tco 2 and nh 4 production defined by pore water chemistry indicates that the only reaction influencing pore water ammonium concentration in these sediments appears to be organic matter decomposition pore water ammonium was found to be 1 3 heavier than decomposing organic matter in contrast the upper 15 30 cm of esnp pore waters have ammonium with 15 n that is more than 10 heavier than decomposing organic matter at greater depth the 15 n of deeper pore waters approaches that of decomposing organic matter mass balance calculations indicate that the observed isotopic enrichment is not due to the preferential loss of isotopically enriched organic matter pore water profiles show that the zone with heavy isotopes is characterized by a tco 2 nh 4 inputs ratio of 4 or less we attribute this to the presence of thioploca bacteria who transport no 3 to depth and reduce it to nh 4 while oxidizing sulfide based on pore water stoichiometry and reaction diffusion modeling of pore water isotopic composition we propose that the 15 n enriched ammonium is produced as the result of chemosymbiosis between thioploca and anammox like bacteria in these sediments our work provides the new insights into benthic microbial ecology and the role of coupled individual metabolic pathways in sedimentary nitrogen cycling in santa barbara basin factors which contribute to the isotopic fractionation of 1 3 between pore water ammonium and solid n org were also considered in this sediments 23 of the rain of organic nitrogen is lost to diagenesis therefore the isotopic effect of degradation on the residual n org is estimated to be small 0 7 the most likely cause of fractionation is preferential degradation of an isotopically heavier more labile marine fraction relative to an isotopically lighter more refractory terrestrial component of the organic matter but other possibilities cannot be ruled out when corrected for the observed fractionation it appears that the 15 n of these sediments may represent non steady state conditions

molecular nitrogen in natural gas accumulations generation from sedimentary organic matter at high temperatures the occurrence of natural gas accumulations with high percentages up to 100 of molecular nitrogen in various hydrocarbon provinces represents a largely unresolved problem and a serious exploration risk in this context a geochemical and basin modeling study was performed to evaluate the potential of sedimentary organic matter to generate molecular nitrogen the masses of nitrogen present in coals if converted into molecular nitrogen are sufficient to fill commercial gas reservoirs a calculation for gas accumulations in northern germany where percentages of molecular nitrogen range from less than 5 to greater than 90 reveals that the molecular nitrogen generated in underlying coal bearing strata is sufficient to account for the nitrogen gas even in the largest fi lds in addition much of the total nitrogen in clay rich rock types such as shales and mudstones is fixed in sedimentary organic matter and may add to the nitrogen generation capacity of the coals a kinetic interpretation of the nitrogen and methane generation characteristics of humic coals during laboratory pyrolysis indicates that nitrogen is generated from organic matter in sedimentary basins at higher temperatures than methane minimum temperatures for preferential nitrogen generation are in excess of 300 c for extremely low heating rates or isothermal conditions lasting over 300 m y thus nitrogen rich gases are mainly formed in the final stage of gas generation when sedimentary rocks grade into metamorphic rocks applications of the kinetic parameters for the generation of nitrogen and methane from coaly organic matter in carboniferous sedimentary rocks are presented for part of the northwest german basin in this area immense volumes of the methane rich gas gener ted during the late paleozoic and mesozoic were lost to the atmosphere the present gas composition mainly reflects the latest cenozoic gas generation this cenozoic gas is nitrogen rich where the carboniferous source rock sequences are highly mature and deeply buried