mechanical properties of shale gas reservoir rocks part 1 static and dynamic elastic properties and anisotropy abstractunderstanding the controls on the elastic properties of reservoir rocks is crucial for exploration and successful production from hydrocarbon reservoirs we studied the static and dynamic elastic properties of shale gas reservoir rocks from barnett haynesville eagle ford and fort st john shales through laboratory experiments the elastic properties of these rocks vary significantly between reservoirs and within a reservoir due to the wide variety of material composition and microstructures exhibited by these organic rich shales the static young s modulus and dynamic p and s wave moduli elastic parameters generally decrease monotonically with the clay plus kerogen content the variation of the elastic moduli can be explained in terms of the voigt and reuss limits predicted by end member components however the elastic properties of the shales are strongly anisotropic and the degree of anisotropy was found to correlate with the amount of clay and organic content as well as the shale fab

evolution of southern caribbean plate boundary vicinity of trinidad and tobago two processes oblique collision of an island arc and strike slip motion parallel to the south american coast have been suggested as dominant in the tectonic evolution of the southeastern corner of the caribbean field work in the el pilar fault zone of trinidad and interpretation of offshore seismic data lead us to conclude that the dominant process was strike slip motion on five or more major fault systems within a 250 km wide east west trending plate boundary zone extending north to south from grenada to the mouth of the orinoco river during the last 30 m y movements in this fault zone 1 diverted the orinoco river eastward 2 juxtaposed blocks with diverse stratigraphic characteristics and 3 generated secondary extensional compressional and strike slip str ctures including anticlines of northeast to north northeast trend of which the tobago arch the central range of trinidad and the deformed mud diapirs off the southeastern coast of trinidad are the most prominent

gravel topped offshore bar sequences in the lower carboniferous of southern ireland within the kinsale formation lower carboniferous of southern ireland are pebbly sandstones and conglomerates contained in what is known locally as the garryvoe conglomerate facies in this facies there are three main groups of lithologies a heterolithic mudrocks and sandstones characterized by a wide variety of wave produced structures b sandstones dominated by swaley cross stratification scs parallel lamination and rare hummocky cross stratification hcs and c pebbly sandstones and conglomerates occurring as discrete beds or as gravel clasts dispersed through scs sets successions of the facies comprise units of heterolithic mudrock and rippled sandstone alternating repeatedly with coarsening upward units of scs pebbly sandstone capped by top surface granule and pebble lags the garryvoe conglomerate facies accumulated in a system of offshore bars on a muddy shallow marine shelf that was dominated by waves and currents generated by storms sands and gravels were bypassed from a contemporaneous northerly coastal zone to the shelf where they were moulded by the storm generated flow into low broad sand ridges offshore bars the elongate bars were spaced kilometres apart oriented obliquely to the coast and separated by muddy interbar troughs their surfaces were largely covered by hummocky and swaley forms long term gradual seaward migration of the offshore bars concentrated gravels on landward flanks from the dispersed pebbly sands that were on the crests and seaward flanks exceptionally intense storms could form laterally extensive winnowed gravel lags above thinned bar sequences such storms could also flush gravel bearing turbidity currents into muddy interbar trough areas

geochemical characterization of lithofacies and organic facies in cretaceous organic rich rocks from trinidad east venezuela basin abstract organic rich cretaceous sediments from southern trinidad show differences in hydrocarbon source potential which can be geochemically related to lithofacies and organic facies sediments which exhibit good to excellent potential for oil were deposited during the campanian through cenomanian in clastic starved environments as evidenced by the inverse relationship between hydrogen index and the parameters al2o3 toc and th u principal components analysis pca of combined toc rock eval major oxide and trace element data shows three lithofacies carbonate siliceous and clastic within samples exhibiting hydrocarbon source potential the highest petroleum potential is associated with the siliceous and carbonate lithofacies which consist of hemi pelagic sediments deposited under low oxygen conditions the clastic lithofacies have lower petroleum potential and represent nearshore sediments which have been transported to the continental slope via submarine canyons extractable saturated and aromatic hydrocarbon compositions vary with lithology pca of conventional biomarker and 2 and 3 ring aromatic hydrocarbon distributions shows that the carbonate lithofacies are characterized by an enrichment in steranes and dibenzothiophenes two organic facies can be recognized within the carbonate lithofacies that differ in their relative bundance of tricyclic terpanes gammacerane and bisnorhopane the siliceous lithofacies are characterized by an abundance of bisnorhopane 20r steranes and a slight enrichment in napthalenes relative to phenanthrenes the clastic lithofacies exhibit high hopane contents relative to steranes an enrichment in moretanes and 18 h oleanane and an enrichment in phenanthrenes relative to napthalenes

how porosity and permeability vary spatially with grain size sorting cement volume and mineral dissolution in fluvial triassic sandstones the value of geostatistics and local regression although it is well known that sandstone porosity and permeability are controlled by a range of parameters such as grain size and sorting amount type and location of diagenetic cements extent and type of compaction and the generation of intergranular and intragranular secondary porosity it is less constrained how these controlling parameters link up in rock volumes within and between beds and how they spatially interact to determine porosity and permeability to address these unknowns this study examined triassic fluvial sandstone outcrops from the uk using field logging probe permeametry of 200 points and sampling at 100 points on a gridded rock surface these field observations were supplemented by laser particle size analysis thin section point count analysis of primary and diagenetic mineralogy quantitative xrd mineral analysis and sem edax analysis of all 100 samples these data were analyzed using global regression variography kriging conditional simulation and geographically weighted regression to examine the spatial relationships between porosity and permeability and their potential controls the results of bivariate analysis global regression of the entire outcrop dataset indicate only a weak correlation between both permeability porosity and their diagenetic and depositional controls and provide very limited information on the role of primary textural structures such as grain size and sorting subdividing the dataset further by bedding unit revealed details of more local controls on porosity and permeability an alternative geostatistical approach combined with a local modeling technique geographically weighted regression gwr subsequently was used to examine the spatial variability of porosity and permeability and their controls the use of gwr does not require prior knowledge of divisions between bedding units but the results from gwr broadly concur with results of regression analysis by bedding unit and provide much greater clarity of how porosity and permeability and their controls vary laterally and vertically the close relationship between depositional lithofacies in each bed diagenesis permeability and porosity demonstrates that each influences the other and in turn how understanding of reservoir properties is enhanced by integration of paleoenvironmental reconstruction stratigraphy mineralogy and geostatistics

design criteria for laboratory measurements of low permeability rocks the advantages and limitations of two versions of the pulse technique for laboratory measurements of low permeabilities 10 16 to 10 24 m are discussed the transient pulse technique developed by brace et al 1968 is the preferred method because of the ease of data reduction the modified transient pulse technique developed by trimmer et al 1980 can be used when the assumptions inherent in the transient pulse technique are invalid the systematic error associated with the transient pulse technique is a function of the ratio of the effective sample pore volume to the reservoir volumes if this ratio is less than 0 25 then the error associated with the transient technique is less than 10 the modified transient pulse technique does not suffer from this systematic error criteria are also presented for optimizing the experimental configuration for measurement durations as well as ease of data reduction

the significance of large scale sedimentary structures in the silurian succession of western ireland large scale sedimentary structures are described from the lough muck formation wenlock of north galway ireland they consist of bed packages separated by truncation surfaces of varying orientations they had previously been interpreted as rotational slumps generated on a shelf slope interface it is shown that the structures formed in a tidally influenced environment far removed from a slope they bear strong similarities to structures described from other tidal channel environments and it is proposed that they represent deposition on aggradational margins of such channels the supposed slope shelf transition is therefore not present at this level in the silurian succession and much of the lough muck formation may be of a dominantly shallow marine origin

progradational gravel beach sequences in a moderate to high energy microtidal marine environment the anatomy of progradational gravel beaches was analysed in two different tectonic settings the strongly subsiding messinian foreland basin of the eastern southern alps and the rising pleistocene marine terraces of the outer margin of the apenninic chain progradation took place near the mouths of fan delta or braid delta distributaries debouching in microtidal landlocked basins palaeo adriatic and palaeo ionian seas a wind wave climate comparable to that of the present day was characterized by periodic intense storm activity most of the beachface progradation is thought to have taken place during the post storm recovery and fair weather stages whereas the impact of storms is mostly recorded by the cutting of erosional surfaces on the beachface and by emplacement of poorly sorted and coarse grained gravels on the shoreface by storm intensified seaward trending flows and behind the highest berms by washover processes analysis of the sequences led to the identification of a number of typical divisions which are differently developed in the two settings compared here the characteristics of the apenninic sequences suggest a strongly variable wind wave climate with periodic changes from a relatively dissipative barred morphology during storms accompanied by strong longshore currents and rip development to a more reflective state typical of recovery and fair weather stages the southern alpine sequences on the other hand are characterized by poor evidence of barred morphology and of longshore currents and widespread effects of shear and gravity sorting in the lower beachface gravels these features indicate a comparatively more reflective average state due to location of beaches along the deeply embayed head of the palaeo adriatic and the very narrow directional width of the incoming wave spectrum which was almost shore normal most of the time in addition to well developed shape zonation of gravels the common presence of wave generated gravel megaripples in the southern alpine sequences indicates the greater influence of long period waves due to the greater available fetch distances in both settings the cyclicity is thought to be genetically related to minor changes of sea level

aquifer scale controls on the distribution of nitrate and ammonium in ground water near la pine oregon usa summary geochemical and isotopic tools were applied at aquifer transect and subtransect scales to provide a framework for understanding sources transport and fate of dissolved inorganic n in a sandy aquifer near la pine oregon no3 is a common contaminant in shallow ground water in this area whereas high concentrations of nh4 n up to 39 mg l are present in deep ground water n concentrations n cl ratios tracer based apparent ground water ages n isotope data and hydraulic gradients indicate that septic tank effluent is the primary source of no3 n isotope data n cl and n c relations 3h data and hydraulic considerations point to a natural sedimentary organic matter source for the high concentrations of nh4 and are inconsistent with an origin as septic tank n low recharge rates and flow velocities have largely restricted anthropogenic no3 to isolated plumes within several meters of the water table a variety of geochemical and isotopic data indicate that denitrification also affects no3 gradients in the aquifer ground water in the la pine aquifer evolves from oxic to increasingly reduced conditions suboxic conditions are achieved after about 15 30 y of transport below the water table no3 is denitrified near the oxic suboxic boundary denitrification in the la pine aquifer is characterized well at the aquifer scale with a redox boundary approach that inherently captures spatial variability in the distribution of electron donors

sand waves on an epicontinental shelf northern bering sea abstract sand waves and current ripples occupy the crests and flanks of a series of large linear sand ridges 20 km 5 km 10 m high lying in an open marine setting in the northern bering sea the sand wave area which lies west of seward peninsula and southeast of bering strait is exposed to the strong continuous flow of coastal water northward toward bering strait a hierarchy of three sizes of superimposed bedforms all facing northward was observed in successive cruises in 1976 and 1977 large sand waves height 2 m spacing 200 m have smaller sand waves height 1 m spacing 20 m lying at a small oblique angle on their stoss slopes the smaller sand waves in turn have linguoid ripples on their stoss slopes repeated studies of the sand wave fields were made both years with high resolution seismic reflection profiles side scan sonographs underwater photographs current meter stations vibracores and suspended sediment samplers comparison of seismic and side scan data collected along profile lines run both years showed changes in sand wave shape that indicate significant bedload transport within the year gouge marks made in sediment by keels of floating ice also showed significantly different patterns each year further documenting modification to the bottom by sediment transport during calm sea conditions in 1977 underwater video and camera observations showed formation and active migration of linguoid and straight crested current ripples current speeds 1 m above the bottom were between 20 and 30 cm s maximum current velocities and sand wave migration apparently occur when strong southwesterly winds enhance the steady northerly flow of coastal water many cross stratified sand bodies in the geologic record are interpreted as having formed in a tidal or storm dominated setting this study provides an example of formation and migration of large bedforms by the interaction of storms with strong uniform coastal currents in an open marine setting

shallow marine to fluvial transition in the siwalik succession of the kameng river section arunachal himalaya and its implication for foreland basin evolution abstract an understanding of the depositional environment and paleogeography of the siwalik foreland basin are crucial in interpreting the basin configuration sediment transport pathways and its evolutionary history this study examines the sedimentology of the siwalik succession of the kameng river valley arunachal himalaya northeastern india the facies characteristics of the fine grained well sorted sediments of the dafla formation and its complex polymodal paleocurrent pattern in this section reveals deposition in a variety of open marine to deltaic environment the overlying subansiri formation characterized by coarse grained thick multistoried sandstone and showing more consistent sw ward paleocurrent indicate deposition from a large axial braided river system the proposed redefinition of the boundary between the lower siwalik dafla and the middle siwalik subansiri formations implies their transition at around 7 5 ma instead of 10 5 ma suggested earlier the revised age of the transition is consistent with the age of arrival of the transhimalayan sediments at 7 ma and also denotes the time of marine to fluvial transition in this area presence of marine sediments in the kameng section with similar records further west indicates the existence of an extensive seaway in the eastern himalaya during the lower siwalik time the extant paleodrainage reconstructions have been recast on the basis of new data on the sedimentology and paleocurrent from this section it is inferred that the changing sea level uplifting shillong plateau and drainage evolution in the eastern himalayan foreland during the middle miocene time controlled the marine to fluvial transition in the basin

evidence of superimposition of storm waves on tidal currents in rocks from the tithonian neocomian umia member kutch india abstract the general opinion is that hummocky cross stratification is generated from superposition of storm waves on a unidirectional current however constraints on the type of the current field have not been clearly established sedimentary structures preserved in rocks of the tithonian neocomian umia member kutch india indicate hummocky cross stratification developed from storm wave interference with ebb tide currents facies indicate repeated progradation of the shoreline and the increasingly important role of sand transport by currents in offshore direction stratigraphic analyses identify two major stages of shoreline progradation each is composed of distinctive shelf to shoreface transitions in the tidally influenced shoreface parts of these transitions the azimuths of units with nearly unidirectional hummocky cross stratification are consistent with the direction of ebb tidal cross stratification suggesting offshore sand transport by superposition of waves on an ebb tidal current

effects of rock mineralogy and pore structure on stress dependent permeability of shale samples we conducted pulse decay permeability experiments on utica and permian shale samples to investigate the effect of rock mineralogy and pore structure on the transport mechanisms using a non adsorbin

kinetics of pressure solution at halite silica interfaces and intergranular clay films pressure solution is widely regarded as a potentially important deformation mechanism along crustal faults and during aliagenesis yet the mechanisms and kinetics of this process remain highly controversial to better understand the fundamental factors controwing the rates of pressure solution at the grain to grain scale we conducted experiments in which convex halite lenses were pressed against fiats of fused silica in brine fluid pressures were maintained at 0 1 mpa temperatures and mean contact normal stresses ranged from 8 3 o to 90 2oc and 0 5 to 13 5 mpa respectively the geometry and growth rate of the contact spot between the two lenses and the rate at which the lenses approached one another convergence were monitored using reflected light interferometry and transmitted light photomicrography convergence occurred when halite and silica lenses were pressed together in brine halite silica experiments no undercutting was observed and dry control experiments indicated negligible dislocation creep convergence rates in experiments at 50 2oc ranged from 0 01 to 0 05 m d depending on mean normal stress and contact spot radius the data are consistent with intergranular pressure solution ips rate limited by diffusion through an intergranular film with a very high diffusion coefficient 10 5 10 7 cm2 s the data further suggest that the diffusion coefficient and or thickness of this film increases with decreasing normal stresses at least for normal stresses less than about 4 mpa as no island channel boundary structures were observed we propose that this film consists of a continuous layer of strongly adsorbed i e structured water that is maintained between the halite and silica lenses during deformation convergence rates in similar experiments conducted at a constant load of 0 11 n but at 8 3 o 50 2 o and 90 2oc were approximately constant at a given normal stress and contact spot size the cause of this temperature insensitivity is unknown but might result from changes in interphase boundary structure or thickness with increasing temperature that are sufficient to offset the expected thermal activation an experiment was also conducted in which a halite lens was pressed against a fused silica fiat coated with an 0 8 m thick film of na montmorillonite in brine this clay film produced an approximately fivefold increase in convergence rates over those observed in a halite silica experiment conducted without clay at the same load and temperature the strong sensitivity of ips rates both to contact spot radius and to the presence of second phases along grain boundaries suggests that fine grained clay rich fault gouges and multiphase granular aggregates should be particularly susceptible to pressure solution creep in the middle to upper crust

athens subepisode wisconsin episode non glacial and older glacial sediments in the subsurface of southwestern michigan usa abstract we describe the first complete sediment core to bedrock in southwestern michigan of a radiocarbon defined sequence of michigan subepisode marine oxygen isotope stage mis 2 glacial sediments athens subepisode mis 3 non glacial sediments and two older tills using sedimentological lithological and radiocarbon analyses organics from athens subepisode lacustrine and palustrine sediments yield radiocarbon ages of 41 920 42 950 and 43 630 45 340 and 43 500 14 c yr bp we propose the name port sheldon formation for these organic bearing sediments we interpret the underlying diamictons as two basal tills separated by glaciolacustrine fines the youngest till hemlock crossing till lying below the port sheldon formation is a dark gray gravel poor clay loam to loam with a mean kaolinite illite ratio of 0 98 0 04 the oldest till glenn shores till is a dark grayish brown gravel rich clay loam to sandy loam with mean kaolinite illite ratio of 1 22 0 08 about 130 water well records demonstrate that organic sediments and underlying diamictons are common in the subsurface of ottawa county these tills are likely illinois episode mis 6 or older but an ontario subepisode mis 4 age cannot be ruled out deep bedrock basins in lower michigan provide an untapped archive of pre michigan subepisode history

allogenic controls on the evolution of storm to tidal shelf sequences in the early proterozoic uncompahgre group southwest colorado usa dominantly coarse grained shallow marine metasedimentary rocks of the early proterozoic uncompahgre group ug record periods of shoaling and drowning on different temporal scales that are attributed to episodic long term oscillations in relative sea level with superimposed shorter duration excursions in relative sea level long term events are probably tectonic whereas short term events are eustatic the 2 5 km thick uncompahgre group consists of 250 600 m thick dominantly coarse grained quartzite units q1 q4 and 200 300 m thick mudstone pelite units p1 p5 five depositional systems comprise the uncompahgre group the outer shelf system oss is composed of bouma type beds and intercalated mudstones that are transitional vertically to parallel laminated to wave rippled sandstones and hummocky cross stratified sandstones of the inner shelf system iss trough cross stratified sandstones comprise the shoreface system shs the tidal inner shelf shoreface system tis shs consists of a complex interlayering of cross bedded sandstones thin bedded conglomerates mudstones and rippled sandstones trough cross bedded pebbly sandstones and thin to thick bedded conglomerates represent the alluvial system alls depositional systems in the ug are associated in transgressive and highstand systems tracts that make up four sequences 1 to 4 sequence boundaries do not correspond with lithostratigraphic boundaries but are defined by subtle unconformities the basal q1 p1 unit lower sequence 1 consists of alls to tis shs to iss comprising a transgressive systems tract a maximum marine incursion is reflected by deposition of oss facies in stratigraphic units p1 p2 shoaling in the transition from p2 to the uppermedial portion of q2 oss iss shs to a thick tis shs alls records the highstand systems tract of upper sequence 1 a subtle disconformity paraconformity delineates a type 2 sequence boundary at the top of the highstand systems tract the drowning to shoaling pattern is replicated in sequence 2 upper q2 to p3 to upper medial q3 sequence 3 upper q3 to p4 to upper medial q4 and an incomplete sequence 4 upper q4 through p5 thinner shoaling intervals of oss iss shs in p3 and in lower q2 q3 and q4 represent parasequences sequences of 107 years duration are attributed to periods of increasing and decreasing subsidence rates due to tectonism marginal to the sedimentary basin parasequences record shorter duration temporal controls of c 104 to 105 years related to eustatic oscillations as a consequence of shoaling and aggradation progradation in the highstand systems tract tis shs and alls overlie and are temporally separated from oss to iss to shs this transition records filling of the basin to sea level leading to a shelf geometry that was conducive to tidal amplification a composite relative sea level curve integrating long term pulsatory subsidence and short term eustasy best explains the stratigraphic evolution of the uncompahgre group

cardium formation u cretaceous at seebe alberta storm transported sandstones and conglomerates in shallow marine depositional environments below fair weather wave base as a result of detailed mapping at seebe alberta we have defined five coarsening upward sequences in the turanian cardium formation the sequences begin with bioturbated mudstones and coarsen int

petrophysical characteristics of shales with different lithofacies in jiaoshiba area sichuan basin china implications for shale gas accumulation mechanism abstract the petrophysical characteristics of unconventional reservoirs have significant impacts on hydrocarbon storage and transport in this study 26 shale samples with various lithofacies from lower silurian longmaxi shales in the jiaoshiba area of sichuan basin are investigated the pore network morphology porosity and pore structure parameters is comprehensively characterized using scanning electron microscopy helium pycnometry and low pressure gas adsorption techniques permeability coefficients are derived from pulse decay measurements on parallel to bedding samples geological controls on the pore shape porosity pore size pore size distribution and permeability of the shales are analyzed and quantitative relationships with which to estimate the permeabilities and pore throat apertures controlling gas flow are developed three general lithofacies are summarized in view of their mineralogy siliceous argillaceous siliceous mixed and argillaceous shales pore structure parameters porosity specific surface area and pore volume show positive correlations with total organic carbon toc content organic matter hosted pores contribute to approximate 67 of the porosity of siliceous shales while inorganic matter contributes to 55 of the porosity of argillaceous shales klinkenberg corrected permeabilities range between 0 01 and 46 4 d and are controlled by the alignment of clay flakes negative relationships exist between toc content porosity and permeability values siliceous shales generally have the lowest permeabilities whereas the argillaceous shales with developed oriented clay flakes have relatively high permeabilities the seepage pore apertures estimated using the winland correlation range from 9 to 476 nm these values are much higher than those obtained from nitrogen adsorption analysis adsorption pore apertures a power correlation exists between seepage pore apertures and total clay minerals content of shales studied a fracture model sheet is used to predict absolute permeability based on seepage pore apertures the predictions are reasonable and justify the application of the sheet model and seepage pore apertures the siliceous shales are featured by a high toc content large porosity and specific surface area and low permeability which are favorable to gas preservation

swaley cross stratification in medium to coarse sandstone produced by oscillatory and combined flows examples from the proterozoic kansapathar formation chhattisgarh basin m p india abstract the proterozoic kansapathar formation is the topmost unit of the siliciclastic chandarpur group of rocks which records a fluvial to marine transition and comprises a fining upwards transgressive succession overlain by a coarsening upwards prograding succession the kansapathar formation around panduka m p is composed of medium to coarse grained well sorted quartzarenite and is replete with swaley cross strata scs trough cross strata and other structures of intermediate morphology in laterally continuous exposures scs are more common in the northeastern part of the study area whereas trough cross strata are more dominant in the southwestern part we have recognised the scs on the basis of the stratal geometry originally described by leckie and walker 1982 scs occur as nested sets of elliptical swales which are commonly symmetrically filled the trough cross strata are variable in scales and dominantly sw directed the major axes of swales show a strong nnw sse preferred orientation orthogonal to the orientation of trough cross strata and at a low angle to the shoreline orientation determined from the megaripple orientation in the immediately underlying unit scs described herein in contrast to many examples reported from elsewhere formed in medium to coarse sand and the maximum inclinations of their lower bounding surfaces and of the infilling laminae are greater than those of fine grained hummocky cross strata hcs and scs this is explicable since medium to coarse grained sediments did not experience significant suspension transport and thus the development of low angle lamination was suppressed the symmetrically filled swales do not show any evidence of lateral migration and might have been formed by bidirectional oscillatory flow the trough cross strata could have been formed by translatory current dominated combined flow the spectrum of structures may owe their origin to symmetrical oscillatory flow transforming into asymmetric flow during onshore propagation of waves this is expected to be common in shoreface environment the spatial variation in relative frequency of occurrence of various types of cross strata is also consistent with the palaeogeographic reconstruction of the study area the trough cross strata seem to be more common towards the constantly shifting sands of nearshore thus the relative frequency of trough cross strata and scs has been used as a clue to determine relative proximity to shoreline

experimental investigation of matrix permeability of gas shales predicting long term production from gas shale reservoirs has been a major challenge for the petroleum industry to better understand how production profiles are likely to evolve with time we have conducted laboratory experiments examining the effects of confining stress and pore pressure on permeability experiments were conducted on intact core samples from the barnett eagle ford marcellus and montney shale reservoirs the methodology used to measure permeability allows us to separate the reduction of permeability with depletion because of the resultant increase in effective confining stress and the increase in permeability associated with knudsen diffusion and molecular slippage also known as klinkenberg effects at very low pore pressure by separating these effects we are able to estimate the relative contribution of both darcy and diffusive fluxes to total flow in depleted reservoirs our data show that the effective permeability of the rock is significantly enhanced at very low pore pressures because of the slippage effects we use the magnitude of the klinkenberg effect to estimate the effective aperture of the flow paths within the samples and compare these estimates to scanning electron microscopy image observations our results suggest effective flow paths to be on the order from tens of nanometers in most samples to 100 200 nm in a relatively high permeability eagle ford sample finally to gain insight on the scale dependence of permeability measurements the same core plugs were crushed and permeability was again measured at the particle scale using the so called gas research institute method the results show much lower permeability than the intact core samples with very little correlation to the measurements on the larger scale cores

spacing and distribution of bed perpendicular joints throughout layered shallow marine carbonates granada basin southern spain abstract this contribution focuses on the controls exerted by sedimentological petrographic and mechanical rock properties on the distribution of bed perpendicular joints throughout layered carbonates the study was conducted on tortonian shallow marine skeletal grainstones and rudstones cropping out in the granada basin southern spain the results of combined field and laboratory analyses are consistent with the rock grain size of the studied carbonates exerting a key control on distribution of the bed perpendicular joints a positive correlation between joint spacing and mechanical unit thickness is computed for the grainstones whereas joints are almost absent in rudstones the rock grain size affected the diagenetic processes such as cementation and dissolution and therefore the resulting porosity and uniaxial compressive strength ucs values quantitative data show that higher ucs values are commonly associated with greater calcite amounts lower values of porosity and finer grain sizes and hence denser bed perpendicular joint sets in conclusion this study documents that it is possible to infer the density of bed perpendicular joints in layered carbonates based on the sedimentological petrographic and mechanical parameters considering the impact that this type of joints has on subsurface fluid flow the acquired knowledge can help the management of geofluids as well as the overall prediction of carbonate reservoir quality

impact of rock fabric on water imbibition and salt diffusion in gas shales abstract understanding water uptake of gas shales is critical for designing fracturing and treatment fluids previous imbibition experiments on unconfined gas shales have led to several key observations the water uptake of dry shales is higher than their oil uptake furthermore water imbibition results in sample expansion and microfracture induction this study provides additional experimental data to understand the effects of rock fabric complex pore network clay swelling and osmotic potential on imbibition behavior we systematically measure and compare the imbibition rates of deionized water and oil into wet dry and confined unconfined rock samples from different shale members of the horn river basin we also measure the ion diffusion rate from shale into water during imbibition experiments the results show that initial water saturation decreases the water uptake of shale samples however it has no effect on oil imbibition rates the liquid imbibition and ion diffusion rates along the lamination are higher than those against the lamination the results also suggest that confining the shale samples decreases the water imbibition rate parallel to the lamination however it has a negligible effect on water uptake perpendicular to the lamination furthermore confining does not significantly affect the ion diffusion rates the comparative study suggests that for both confined and unconfined samples water uptake is higher than oil uptake however previous experiments on crushed shale samples show that the oil uptake of crushed packs is higher than their water uptake xu and dehghanpour 2014 the data suggest that the connected pore network of the intact samples is water wet while the majority of rock including poorly connected pores is oil wet this argument is backed by bse images and complete spreading of oil on fresh break surfaces of the rock

late ordovician sand wave complexes on anticosti island quebec a marine tidal embayment laterally discontinuous mixed carbonate siliciclastic sandstones in the upper vaureal and lower ellis bay formations of anticosti island were deposited on an equatorial carbonate ramp with a slope of less than 1 the 10 18 m thick sandstones are interpreted as subaqueous sand wave complexes analogous to detached parts of modern shoreface connected sand ridges these record storm enhanced tidal modification of a northerly derived shoal retreat massif that may have formed in response to recovery from global sea level lowstands in the late ordovician ashgill late rawtheyan hirnantian the sand wave complexes formed within a tidal embayment that was confined by the precambrian shield to the north and northwest by rising tectonic highlands of the humber zone in newfoundland to the east and by active tectonic highlands in the quebec appalachians gaspesie to the south paleocurrent distributions parallel to the western margins of the strait of belle isle suggest that the north end of the embayment w

use of nitrogen isotopes and other geochemical tools to evaluate the source of ammonium in a confined glacial drift aquifer ottawa county michigan usa abstract this study utilized several isotopic tracers and geochemical parameters to characterize the source and hydrogeochemical setting of elevated ammonium nh 4 concentrations 2 mg l in a confined glacial drift aquifer in ottawa county michigan results from this investigation indicate that nh 4 is attributed to degrading in situ organic matter and not from surficial anthropogenic sources tritium 18 o and 2 h values suggest that primary recharge in the confined aquifer occurred during the middle to late holocene and before the mid 1900 s geochemical constituents including redox parameters and a suite of common ions demonstrate a compositional difference between the confined and unconfined aquifers in the study area and therefore further support the isolation of the confined aquifer from a significant amount of recent recharge post 1950 s insignificant 15 n nh 4 fractionation 0 81 to 1 38 implies that nh 4 in the confined aquifer originated from degrading in situ organic matter a complete rotosonic glacial sediment core collected to characterize the physical setting of the nh 4 rich aquifer confirmed the presence of in situ organic matter in the confined aquifer a limited set of 15 n no 3 and 18 o no 3 values suggest that the application of manure to row crops may be contributing nitrate up to 10 mg l to nearby shallow residential wells as implemented in this study the use of multiple geochemical and isotopic parameters including 15 n nh 4 can be applied to evaluate the potential source of nh 4 in an aquifer

evolution of a classic sand ridge field maryland sector north american inner shelf the ridge and swale topography of the middle atlantic bight is best developed on the delaware maryland inner shelf here sand ridges can be seen in all stages of formation several aspects of the ridge field are pertinent to the problem of ridge genesis the first is ridge morphology there is a systematic morphologic change from shoreface ridges through nearshore ridges to offshore ridges which reflects the changing hydraulic regime as successively more seaward ridges are examined maximum side slope decreases the ratio of maximum seaward slope to maximum landward slope decreases and the cross sectional area increases these changes in ridge morphology with depth and distance from shore appear to be equivalent to the morphologic changes experienced by a single ridge during the course of the holocene transgression a second aspect is the change in bottom sediment characteristics that accompanies these large scale morphologic changes megaripples sand waves and mud lenses appear in the troughs between nearshore and offshore ridges these changes indicate that the storm flows which maintain ridges are less frequently experienced in the deeper sector and that the role of high frequency wave surge becomes less important relative to the role of the mean flow component in shaping the sea floor a third aspect is the systematic relationship of grain size to topography grain size is 90 out of phase with topography so that the coarsest sand lies between the axis of the landward trough and the ridge crest while the finest sand lies between the ridge crest and the axis of the seaward trough this relationship is characteristic of large scale bedforms finally flow was measured and transport calculated on the same ridge during a one month period november 1976 threshold was exceeded only during storm events mean transport was southerly and a little seaward with respect to both the ridge crest and the shoreline these flow measurements are in conformity with the pattern of smaller bedforms a 43 year time series of bathymetric change for this ridge reveals a systematic pattern of landward flank erosion seaward flank deposition and seaward crest migration sand ridges are considered the consequence of constructive feedback between an initial topography and the resulting distribution of bottom shear stress the relationship between grain size and topography supports this model but does not account directly for the oblique angle of the ridge with respect to the coastline this feature may be due to a more rapid alongshore migration rate of the inshore edge of the ridge than the offshore edge and the relationship between this migration rate and the rate of shoreface retreat

early permian giant cross beds near nqutu south africa interpreted as part of a shoreface ridge abstract sandstones and siltstones of a giant cross bed sedimentary association at the base of the coal bearing vryheid formation cannot be satisfactorily explained in terms of the currently accepted fluviodeltaic model for these strata in view of the sedimentary structures and associational characteristics of the facies a shoreface ridge interpretation is adopted instead the sandridge probably detached from the shoreface was situated on the slope towards the basin plain and associated with some elements of a minor submarine fan complex rapid shoreface by pass in the course of a marine transgression seems to have provided favourable conditions for sandridge formation the major bedform appears to have been in water of about 45 m depth possibly some kilometres from the contemporary shoreline there is evidence that it was mainly constructed by the action of strong easterly flowing currents probably of relaxant or geostrophic origin these were aided by ebb dominant tidal currents possible actualistic models include north sea and bering sea sandridges currents of the strength needed to build such large bedforms could only have existed in an open ended seaway and it is suggested that the ecca sea must have communicated at least intermittently with open ocean to the northeast and possibly the southeast as well as towards the west

clay mineral diagenesis and quartz cementation in mudstones the effects of smectite to illite reaction on rock properties abstract the late cretaceous to early tertiary sequence of the voring and more basins from the norwegian sea has been examined with respect to mineralogy based on 319 cutting samples from five wells a clear relationship between mineralogy and well log data is demonstrated a significant change with respect to velocity porosity and density occurs within the depth interval corresponding to 80 90 c at shallow depths temperatures

hydrogeology and redox geochemistry of ch4 in a late wisconsinan till and loess sequence in central iowa the hydrogeology and redox geochemistry of ch4 in two hydrogeological settings within a late wisconsinan till and loess sequence in central iowa were investigated using ch4 eh dissolved o2 no3 n nh4 n dissolved fe so4 h2s dissolved organic carbon doc particulate organic carbon poc 13c ch4 2h ch4 13c of dissolved inorganic carbon dic and 14c ch4 depleted 13c ch4 and 2h ch4 values enriched 13c dic values and the lack of higher hydrocarbons suggest that the ch4 is microbial and is formed by co2 reduction carbon 14 dates of ch4 indicate that 14 000 to 17 000 year old poc and doc in the 1oess and till compose the substrate for methanogenesis production of ch4 probably began after deglaciation at about 12 000 years b p and has continued to the present groundwater recharge particularly in the upland topographic position at the site has decreased ch4 concentrations in the upper part of the till

carbon isotope fractionation during natural gas generation from kerogen abstract in petroleum exploration it is important to be able to determine the origin of any gas which is found this paper describes a new method of estimating the source type and maturity of a gas based on a rayleigh fractionation model kerogen is divided conceptually into a labile dominantly oil generating fraction and a refractory gas prone component 13 c of methane from either kerogen type and ethane propane and butane for gases from labile kerogen can be defined as a function of 13 c of the gas precursor groups in kerogen a kinetic isotope fractionation factor k and the extent of gas generation the isotopic ratio of the methane precursors relative to bulk kerogen determined from laboratory pyrolysis are 17 5 for labile kerogen and 1 4 for refractory kerogen values for ethane propane and butane from labile kerogen based on field correlations are 4 9 2 2 and 1 6 respectively the corresponding fractionation factors are 0 9892 0 9919 0 9947 and 0 9975 for methane ethane propane and butane respectively from labile kerogen and 0 9984 for methane from refractory kerogen using these parameters summary diagrams are constructed which allow differentiation of these sources from each other and from biogenic gases and cracked oil and recognition of gases of mixed origin if an independent estimate of 13 c for the source kerogen is possible then 13 c of the gas components can be used to estimate maturity in terms of the gas generation index the fraction of gas potential which has been realized

late wisconsinan drift stratigraphy of the lake michigan lobe in southwestern michigan three lake michigan lobe till sheets are exposed in a 20 to 25 m high section glenn shores section along the lake michigan shoreline in southwestern michigan the glenn shores till lowest is directly overlain by stratified silt sand and gravel containing organic material dated at 37 150 to 48 000 yr b p the ganges till middle and saugatuck till uppermost are overlain by lacustrine sediments the three till units can be differentiated by the 7a 10a x ray diffraction peak height ratio of their clay size fraction clay mineral analyses of more than 200 samples collected from moraines till plains and multi till exposures 2 to 60 km inland suggest that saugatuck till at the lakeshore is equivalent to till in the lake border valparaiso and sturgis kalamazoo morainic systems whereas ganges till can be traced in the subsurface from the lakeshore to where it crops out within the tekonsha moraine the presence of lacustrine sediments between ganges and saugatuck tills implies that a significant retreat 60 km of the lake michigan lobe occurred between the formation of the tekonsha moraine and that of the sturgis kalamazoo morainic system on the basis of morainal correlations we propose that saugatuck till correlates with wadsworth till in illinois whereas ganges till probably correlates with the upper part of the yorkville till in illinois

chronostratigraphy and tectonostratigraphy of the columbus basin eastern offshore trinidad the columbus basin forming the easternmost part of the eastern venezuela basin is situated along the obliquely converging margins of the caribbean and south american plates the two primary structural elements that characterize the basin are 1 transpressional northeast southwest trending anticlines and 2 northwest southeast oriented down to the northeast extension normal faults the basin was filled throughout the pliocene and pleistocene by more than 40 000 ft 12 200 m of clastic sediment supplied primarily by the paleo orinoco delta system the delta prograded eastward over a storm influenced and current influenced shelf during the pliocene pleistocene depositing marine and terrestrial clastic megasequences as a series of prograding wedges atop a lower pliocene to pre pliocene mobile shale facies biostratigraphic and well log data from 41 wells were integrated with thousands of kilometers of interpreted two dimensional and three dimensional seismic data to construct a chronostratigraphic framework for the basin as a result several observations were made regarding the basin s geology that have a bearing on exploration risk and success 1 megasequences wedge bidirectionally 2 consideration of hydrocarbon system risk across any area requires looking at these sequences as complete paleofeatures 3 reservoir location is influenced by structural elements in the basin 4 the lower limit of a good quality reservoir in any megasequence deepens the closer it comes to the normal fault bounding the wedge in a proximal location 5 reservoir quality of deep marine strata is strongly influenced by both the type of shelf system developed bypass or aggradational and the location of both subaerial and submarine highs and 6 submarine surfaces of erosion partition the megasequences and influence hydrostatic pressure migration and trapping of hydrocarbons and the distribution of hydrocarbon type begin page 1906

storm graded layers on inner continental shelves examples from southern brazil and the atlantic coast of the central united states abstract size graded layers have been reported from the united states and brazilian atlantic continental shelves amid a bedform association that includes ripples megaripples sand waves and sand ridges graded layers are most apparent in the lag gravels and shell hashes that overlie an older substrate in the troughs between sand ridges but also occur as thinner isolated beds within the sand ridges at least four different models seem to be applicable to graded bed formation the stratigraphic graded model grading occurs within and immediately above the basal lag gravel of the holocene transgressive sand sheet it is a consequence of the generation of the sand sheet by erosional shoreface retreat such graded sequences are formed by landward facies displacement over thousands of years but the process is storm mediated and sequences may contain thinner storm graded layers the storm graded model calls for entrainment of sediment by storm flow and subsequent graded deposition under waning energy in the bedform migration model the migration of megaripples and sand waves may produce thin graded beds at any level within the holocene sand sheet and sand ridge migration can cause graded sequences in the basal part of the holocene sand sheet the bottom liquefaction model relies on storm wave pumping of the seafloor sands with their resultant liquefaction and settling of coarser clasts beds in which sorting is confined to coarse shell material may be of this origin these models are believed to be complementary rather than mutually exclusive

low altitude organic deposits in michigan evidence for pre woodfordian great lakes and paleosurfaces reports of 136 glacially buried organic deposits below 200 m in altitude and other related data provide a basis for identifying relicts of several low level pleistocene paleosurfaces in southern michigan the carbonaceous material is concentrated in five areas and probably represents low places on pre woodfordian landscapes with local base levels far lower than the present topography these findings have implications regarding adjacent ancestral great lakes that existed sometime prior to final glaciation of the peninsula

petrographical and petrophysical characterization of the late cretaceous naparima hill formation central range trinidad west indies abstract the late cretaceous naparima hill formation in the south trinidad basin southeast caribbean is a prolific source rock with a potential for unconventional hydrocarbon exploration it is exposed across the central range and extends to the city of san fernando this study characterized the naparima hill source rock using petrographic analysis techniques x ray diffraction and thin section analysis and petrophysical techniques these techniques were applied to outcrop samples that were collected from 11 locations firstly petrographic analysis was used to determine the mineral composition and lithofacies secondly plugs were taken perpendicular to bedding and the bulk density was determined in dry conditions thirdly porosity and grain density were determined using a porosimeter at ambient conditions finally permeability measurements were obtained at 10 mpa to 130 mpa effective pressures using the transient pulse decay technique the results show that the source rock is dominated by silica with carbonate as secondary minerals four lithofacies were identified a siliceous calcareous mudstone b calcareous mudstones interbedded with black chert c carbonate rich mudstone with nodular chert and d siliceous mudstone ranges of 5 9 to 30 8 2362 to 2668 kg m3 and 1804 to 2350 kg m3 were determined for porosity grain density and bulk density respectively the permeability ranges from 3 96 10 20 to 5 94 10 18 m2 and shows very little dependence on the effective pressure permeability and porosity are moderately correlated r2 0 6 there is no relationship between permeability and mineralogical composition the observed microfractures diagenetic processes and grain sorting are factors that have affected the permeability porosity relationship to varying degrees however none of these factors can be considered as the main intrinsic factor controlling the permeability of the samples overall it is difficult to predict the permeability of the naparima hill formation with any of the proxies density mineralogy and porosity determined in this study

facies flow and bedform patterns across a storm dominated inner continental shelf proterozoic kaimur formation rajasthan india abstract a comprehensive sedimentation model for an epeiric sea useful for further comparison and prediction is derived crom the proterozoic kaimur formation rajasthan india facies analysis of a steadily regressive shale quartz arenite sequence documents the patterns of flow sediment transport and deposition from beach to offshore across a storm dominated gently sloping

application of aromatic compounds as maturity indicators in source rocks and crude oils concentration ratios of aromatic compounds such as naphthalenes phenanthrenes and dibenzothiophenes are at present attracting increasing attention as maturity indicators in sedimentary rocks and crude oils generally these indicators rely either on an increase with maturity in the degree of alkylation of a given parent compound or a shift in the isomer distribution of alkyl aromatic homologues towards thermally more stable isomers a combination of both concepts in the methylphenanthrene index mpi resulted in an excellent maturity parameter as demonstrated for rock extracts by an improved correlation with mean vitrinite reflectance rm between 0 65 and 1 4 i e in the zone of oil formation in cases that rm measurements were ambiguous this empirical relationship has proved useful in the calculation of theoretical vitrinite reflectance rc values from the mpi on the other hand for potential petroleum source rocks reaching maturity at relatively low temperatures the influence of the organic matter type on the aromatic distributions cannot be neglected consequently organic facies effects should be taken into account in the interpretation of aromatic distributions of such source rocks and related crude oils since the impact of the organic facies is strongly reduced with increasing maturity aromatic maturity parameters are particularly useful in the maturity evaluation of post mature crude oils and condensates in contrast to biological markers substantially higher concentrations of the key alkyl aromatics persist at elevated maturation levels thus aromatic maturity parameters should be considered as versatile tools in organic maturation studies and can complement established maturity indicators based on steranes and terpanes

lithological and zonal porosity permeability distributions in the arab d reservoir uthmaniyah field saudi arabia permeability vs porosity plots for the arab d carbonate reservoir show a relatively poor correlation so permeability estimation still remains an issue for discussion in this study we integrated basic core measurements with stratigraphic and petrographic analyses to determine porosity and permeability distributions and to identify the association of high permeability in darcy range with lithology and defined reservoir zones carbonate rock types in the arab d reservoir have been grouped into three lithofacies granular muddy granular and muddy the granular lithofacies is the most porous and permeable and all permeability measurements in darcy range are associated with it the muddy facies is represented by low porosity and permeability values porosity and permeability distributions of the muddy granular facies spread over the two regions representative of the muddy and the granular facies porosity and permeability distribution patterns of the arab d zones are controlled by both type and the arrangement of different lithologies zones made up of granular facies demonstrate uniformly high porosity and permeability distributions and reveal the highest permeability intervals zones represented by muddy granular and muddy facies indicate more heterogeneous and mostly bimodal porosity and permeability distributions

mechanical and chemical compaction model for sedimentary basin simulators abstract this article presents a sediment compaction model for sedimentary basin simulators the concepts previously used in sedimentary basin models are generalized and described in our model based on the formalism specific to rock and soil mechanics sediment compaction is described on a geological time scale by an elastoplastic model in which the elastic modulus and the strain hardening modulus increase when deformation increases the plastic limit is the maximum vertical effective stress reached by the sediment the rheology of the sediment is defined by a relationship that couples the porosity or volume of the sediment with the vertical effective stress assuming uniaxial deformation the model also incorporates a viscoplastic term in the compaction equation this component macroscopically considers viscous compaction phenomena such as pressure solution the viscosity coefficient is considered to be a function of the temperature some theoretical considerations allow us to conclude that the thermal dependency of the viscosity is given with an arrhenius law in which the activation energy ranges from 20 kj mole to 50 kj mole using viscosity coefficients extrapolated from previous laboratory experiments a sensitivity study shows significant effects of viscous deformation on the compaction of basins older than 1 ma in another study the viscosity coefficient is determined by matching the results of numerical simulations with laboratory and borehole data obtained from literature for chalk a constant viscosity coefficient of 2 5 gpa ma 8 1022 pa s has been determined assuming viscosity as a function of temperature with an activation energy of 40 kj mole chalk viscosity at 15 c is calibrated around 25 gpa ma simulations with different thermal gradients show that porosity is a function of the temperature furthermore simulations covering different lengths of time show that porosity is also a function of time

regional structure and tectonic history of the obliquely colliding columbus foreland basin offshore trinidad and venezuela abstract cenozoic eastward migration of the caribbean plate relative to the south american plate is recorded by an 1100 km long venezuela trinidad foreland basin which is oldest in western venezuela 65 55 ma of intermediate age in eastern venezuela 34 20 ma and youngest beneath the shelf and slope area of eastern offshore trinidad submarine columbus basin 15 0 ma recent in this study of the regional structure fault families and chronology of faulting and tectonic events affecting the hydrocarbon rich columbus foreland basin of eastern offshore trinidad we have integrated approximately 775 km of deep penetration 2d seismic lines acquired by the 2004 broadband ocean land investigations of venezuela and the antilles arc region bolivar survey 325 km of vintage gulfrex seismic data collected by gulf oil company in 1974 and published industry well data that can be tied to some of the seismic reflection lines top cretaceous depth structure maps in the columbus basin made from integration of all available seismic and well data define for the first time the elongate subsurface geometry of the 11 15 km thick and highly asymmetrical middle miocene recent depocenter of the columbus basin the main depocenter located 150 200 km east of trinidad and now the object of deepwater hydrocarbon exploration is completely filled by shelf and deepwater sediments derived mainly from the orinoco delta the submarine darien ridge exhibits moderate 20 140 m seafloor relief forms the steep 12 24 northern structural boundary of the columbus basin and is known from industry wells to be composed of 0 5 4 5 km thick folded and thrust imbricated hydrocarbon bearing section of cretaceous and early tertiary limestones and clastic rocks the eastern and southern boundaries of the basin are formed by the gently 1 7 4 5 northward dipping cretaceous paleogene passive margin of south america that is in turn underlain by precambrian rocks of the guyana shield interpretation of seismic sections tied to wells reveals the following fault chronology 1 middle miocene thrusting along the darien ridge related to highly oblique convergence between the caribbean plate and the passive margin of northern south america continuing thrusting and transpression in an oblique foreland basin setting through the early pleistocene 2 early pliocene recent low angle normal faults along the top of the cretaceous passive margin these faults were triggered by oversteepening related to formation of the downdip structurally and bathymetrically deeper and more seaward columbus basin large transfer faults with dominantly strike slip displacements connect gravity driven normal faults that cluster near the modern shelf slope break and trend in the downslope direction to the south no normal faults are present because the top cretaceous horizon has not been oversteepened as it is adjacent to the foreland basin 3 early pliocene recent strike slip faults parallel the trend of the darien ridge and accommodate present day plate motions

initiation of 2 45 2 1 ga intracratonic basin sedimentation of the hurwitz group keewatin hinterland northwest territories canada continental to shallow marine rocks of the hurwitz group exposed as outliers across the hearne province in northern canada were deposited between 2 45 and 2 11 ga on a 3 3 2 6 ga granite greenstone basement initiation of the hurwitz basin was characterized by low relief and rates of subsidence that never progressed beyond the intensity of regional sagging during stage 1 polymictic conglomerate lower noomut formation was deposited in palaeovalleys cut into archaean basement and subarkose to quartz arenite quartz pebble conglomerate upper noomut formation was deposited on a low relief sand plain abundant first cycle quartz rich sandstones are attributed to intense humid climate weathering in low relief source areas and at sites of temporary storage as well as to repeated fluvial and eolian reworking interbedding of pyritic palaeoplacers and continental redbeds denotes fluctuating levels of atmospheric oxygen disappearance of pyritic palaeoplacers upsection signifies ultimate changeover to an atmosphere with sustained free oxygen stage 2 padlei formation was marked by a climatic shift toward cold glacial conditions as indicated by dropstones greywacke till pellets and possible ikaite pseudomorphs in lacustrine rhythmites stage 3 kinga formation represents a return to wet warm conditions with fluvial eolian deposition of subarkose and quartz arenite on a low relief sand plain maguse member and deposition of supermature quartz arenite in a vast 100 000 km2 minimum shallow water lake or series of lakes whiterock member local chert beds at the top of the kinga formation hawk hill member formed by spring discharge due to regional gravity driven convective groundwater flow an intracratonic setting is implied by 1 a symmetric basin centred fill 2 absence of features indicating a shelf slope break 3 absence of rift rocks 4 a prolonged slow subsidence history 5 likely correlation with other continental to shallow marine deposits scattered across the keewatin hinterland and 6 positioning 1000 2000 km away from closest coeval passive margin sequences we speculate that hurwitz basin formed due to lithospheric stretching related to a large scale mantle upwelling during the protracted breakup of an earliest palaeoproterozoic supercontinent kenorland

the la luna formation chemostratigraphy and organic facies in the middle magdalena basin abstract a detailed geochemical study and a sequence stratigraphic interpretation have been conducted on a sedimentary sequence of the upper cretaceous la luna formation in a section outcropping in the eastern flank of the middle magdalena basin mmb colombia the goals were to evaluate geochemical variability related to lithofacies and organic facies changes characterize depositional environment and investigate the possible relationship between geochemical data and sequence stratigraphic cycles the la luna formation is composed of organic rich sediments of monotonous appearance with good to excellent potential for oil generation most of the bulk petrographic and biomarker parameters display a relatively narrow range of variation however the geochemical variations are sufficient to differentiate organic facies types b bc and c in the salada member b and d in the pujamana member and b in the galembo member certain biomarker ratios are consistent within the la luna formation and are characteristic of its depositional environment for example average ratios of diasterane sterane are lower than 1 ts tm averages are less than 0 33 the c 35 c 34 hopane ratio is more than 0 92 and oleanane c 30 hopane ratios range from 0 02 to 0 19 regarding depositional condition indicators the c 35 c 34 hopane ratio shows a good positive correlation with hi this suggests that in carbonate environment changes in this parameter are more strongly related to redox condition than to changes in carbonate content regarding the possible relationship between organic matter characteristics and sea level changes in regressive carbonate shelves during shallow stages hi tends to increase and toc tends to decrease while in regressive siliciclastic shelves both toc and hi decrease continuously some biomarker ratios oleanane c 30 hopane c 20 c 23 tricyclic ts tm increase during base level falls regarding 13 c 12 c isotope composition the aromatic fraction and whole bitumen display an isotopic shift associated to the main deepening event in the section

geochemical study of arsenic release mechanisms in the bengal basin groundwater 1 to investigate arsenic mobility in the bengal basin groundwater we sampled water wells and sediments throughout the region there are strong correlations among high levels of dissolved arsenic and iron ammonia and methane especially in samples from a single site laxmipur no linkage is seen between as and agricultural tracers such as phosphate the association of as and fe occurs because arsenic strongly adsorbs onto feooh particles in river water they flocculate with other fine grained particles at the freshwater saltwater transition zone subsequent bacterially mediated reduction of feooh in the clay releases the adsorbed arsenic weathering of as bearing mica plays a significant role in the as budget the correlated presence of as ch4 and nh4 in water supply wells is the result of diffusion out of organic rich clay into the more permeable zones arsenic is mainly released from recent sediments at 50 m depth deposited in the gbr floodplain as sea level rose throughout the holocene

transgressive facies in the south munster basin ireland this paper describes the sedimentation style associated with the basal carboniferous transgression in southern ireland and the influence which this event had on the palaeogeography of the region the transgression as marked by the base of the carboniferous succession is shown to represent one of several genetically related transgressive pulses which commenced during the late devonian at this time an east west trending graben the south munster basin developed in southern ireland this was initially a non marine depositional site in which sediment was derived from the north and west subsidence and eustatic sea level rise resulted in a marine transgression which proceeded in a rhythmic style resulting in a number of transgressive stillstand pulses the first transgressive pulse t1 advanced in a westerly direction along the basin axis resulting in the development of an epicontinental like sea the shoreline remained essentially static along the northern basin margin initially until a second transgressive pulse t2 resulted in expansion of the marine area the latter proceeded by gradual northward erosive advance of a barred coastal area as far as the northern basin margin where the stability of the bounding platform halted its progress erosion of the barrier shoreface was insufficient to destroy all the backbarrier lagoonal deposits which are preserved as a thin transgressive diachronous unit which grades northwards to a coastal alluvial plain immediately preceding the basal carboniferous transgression t3 a shallow wave dominated storm influenced shelf sea occupied the basinal area two sublittoral sand bar complexes developed on the shelf under the influence of shore parallel current regimes apparently derived from source areas located on either side of the epicontinental sea the basal carboniferous transgression took place in two pulses the first t3a resulted in a rapid reduction in sand supply to the shelf and deposition of clay the barrier shoreline responded by erosively retreating across the lagoon leaving a transgressive lag in its wake its northwards advance was however limited due to the relative stability of the northern platform sand supply to the shelf was completely terminated in the second pulse t3b and the barrier rapidly migrated erosively across the northern platform for a considerable distance such that the coastal plain is overlain by a thin transgressive lag this transgressive phase was immediately followed by shoreline stillstand and progressive shallowing of the shelf an open sandy shelf developed on which offshore sand bars accumulated under a storm and wave dominated regime clay deposition continued in the deeper part of the basinal area but was eventually terminated as the shelf sands prograded centripetally into the basin the main factor that controlled the style of the overall transgression was an interplay between eustatic sea level rise and basin subsidence the rate of relative sea level rise together with the effect of differential subsidence and fluvial input from the north appear to have diminished with time the rate at which successive transgressive pulses advanced northwards shows an overall progressive increase

genetic classification of petroleum systems our genetic classification of petroleum systems is founded on a simple working nomenclature that consists of combining qualifiers from each of the following three categories 1 charge factor supercharged normally charged or undercharged 2 migration drainage style vertically drained or laterally drained and 3 entrapment style high impedance or low impedance the charge factor is estimated on the basis of the richness and volumetrics of mature source rocks the source potential index spi which combines source rock richness and thickness into a single parameter is a convenient shortcut for comparing the petroleum potential of diverse source rocks containing dissimilar kerogen types and for rapidly estimating regional charging capacity in extensively explored basins a positive correlation exists between the magnitude of spi and basin wide petroleum reserves the migration drainage style is determined from the structural and stratigraphic framework of a basin vertical migration drainage which occurs mainly through faults and fracture systems breaching a seal is characteristic of petroleum systems contained within rift basins deltaic sequences salt dome provinces wrench basins and fold and thrust belts in contrast lateral migration drainage is dominant wherever stratigraphically continuous seal reservoir doublets extend over a very large area in a tectonically stable province e g commonly foreland or intracratonic platform basins recognition of the dominant migration style helps to predict the location of zones of petroleum occurrence in relation to the hydrocarbon kitchens the entrapment style which is also dependent on the structural framework and the presence and effectiveness of seals describes the degree of resistance i e impedance working against dispersion of the petroleum charge application of these working concepts should help to significantly reduce geologic risk particularly in new ventures type exploration

the development of orientated symplectites during deformation orientated symplectites have been observed in deformed granulite facies metabasic rocks from the ivrea verbano zone in northern italy the area underwent lower crustal extension accommodated by movement on localized high t shear zones in areas of relatively low strain such as at the margins of shear zones symplectites of orthopyroxene plagioclase and spinel have formed the symplectites are vermiform and orientated parallel to the main foliation and in the regional stretching direction the reaction was synkinematic with the deformation and only developed in potentially dilatant grain boundaries in the rock it was presumably inhibited in grain boundaries subjected to higher normal stress due to the relatively large volume increase involved in the reaction the observations support the interpretation that the deformation was related to regional extension under high t granulite facies conditions the symplectites forming as a result of decreasing pressure

oil source bed recognition and crude oil correlation trinidad west indies abstract potential source rocks capable of generating hydrocarbons in trinidad were identified using routine geochemical parameters tertiary formations have a poor oil source rating due to low organic carbon contents toc produced oils were classified into genetic types on the basis of gas chromatography and gas chromatography mass spectrometry fingerprinting only one genetic oil type sourced from predominantly marine organic matter was recognised biodegradation is evident in several oils analysed chromatographic characteristics and gross geochemical properties of produced oils correlate best with rock extracts from the naparima hill and gautier formations indicating a probable genetic association

oxygen and carbon isotopes and event stratigraphy near the ordovician silurian boundary anticosti island quebec the growth and destruction of continental ice sheets in north africa and adjacent parts of gondwana during the hirnantian stage had profound influence on the sedimentary style of mixed carbonate siliciclastic sequences on anticosti island quebec canada these strata deposited in a tropical mid shelf setting show direct evidence of local sea level changes of up to 40 m after correction for tectonic and load induced subsidence this indicates maximum global glacio eustatic changes of 32 to 36 m this implies maximum ice volume of about 12 to 14 106 km3 and related changes in the oxygen isotopic composition of global sea water amounting to as little as 0 5 to 0 6 given that the oxygen isotope ratios in syn glacial samples from the anticosti sequence range from 8 9 to 2 8 18o it is not possible to clearly distinguish the effects of ice cap development from temperature and diagenetic controlled variation the strong negative shift in 13c values at the top of the ellis bay formation may indicate a pronounced increase in atmospheric co2 coincident with destruction of the late ordovician ice caps

shelf petroleum system of the columbus basin offshore trinidad west indies ii field geochemistry and petroleum migration model abstract petroleum migration patterns in the present day shelf area of the columbus basin reflect a complex interaction of structural evolution stratigraphic architecture and fault seal behavior thermogenic charge access is ultimately controlled by the geographic distribution of sand prone carrier beds and how these vertically stacked stratigraphic units relate spatially to one another along their basinal limits migration in this system consists of two components cross stratal migration through mud dominated deep water slope and basin floor sediments followed by horizon parallel flow along laterally extensive sand prone shelf carrier beds thermogenic charge access to any individual sand occurs only in a linear geographic area where that sand is not shielded from vertical migration by stratigraphically older sands the geochemical characteristics of the trapped petroleum in this system are primarily a reflection of migration distance with the earliest expelled lowest maturity products having progressed farthest along the migration pathway because of the stratigraphic architecture and structural geometry involved a pattern of increasing thermogenic content and maturity with depth at any location is created despite the fact that a significant portion of the migration is horizon parallel in parts of the basin this simple pattern has been overprinted by complex mixing of maturity fractions in single accumulations as a result of late stage differential source rock uplift the observations are inconsistent with previously proposed models for this basin that emphasize petroleum fractionation accompanying vertical migration through the shelf stratigraphic section

bacterial production of methane and its influence on ground water chemistry in east central texas aquifers geochemical and isotopic data for methane and ground water indicate that gaseous hydrocarbons in eocene aquifers in east central texas form by bacterial processes the 13c values of methane from five wells in the clay rich yegua and cook mountain formations range from 71 to 62 methane from ten wells in the cleaner sands of the sparta and queen city formations have 13c values between 57 and 53 the carbon isotopic difference between methanes from the yegua and sparta aquifers is comparable to the isotopic difference in sedimentary organic matter from outcrops of the units suggesting substrate control on the 13c of bacterial methane hydrogen isotopic compositions of methane from the aquifers are similar averaging 181 this high value suggests methane production predominantly by co2 reduction the 13c of dissolved inorganic carbon dic in high bicarbonate waters increases from about 20 to 0 with increasing dic mass balance calculations indicate that the dic added to the ground water has 13c values as high as 10 this 13c enriched carbon is predominantly derived from co2 production by fermentation and anaerobic oxidation reactions combined with co2 consumption by co2 reduction this process is responsible for high bicarbonate contents in these and probably other gulf coast ground waters

storm effects on siliciclastic and carbonate shelf sediments in the medial silurian succession of pennsylvania abstract upper llandoverian through wenlockian strata in the pennsylvania part of the northern appalachian basin formed on a gentle epeiric ramp that extended from marginal tidal flats through coarser grained mid shelf shoals to a muddy basin center over approximately 10 million years the composition of the accumulating sediment evolved from siliciclastic to carbonate while the ramp maintained a relatively similar configuration and position below sea level and while storm generated processes continued as the major producers of sediment characteristics in both siliciclastic and carbonate parts of the succession sedimentary structures and their sequences are generally similar with only a small number of dissimilar features resulting from the differences in composition small scale coarsening and shallowing upward sequences are present in both mid shelf bar and basin transition deposits although specific sequence characteristics are different in siliciclastic and carbonate parts such sequences record cyclic fluctuations of relative sea level while the composition of the sediment evolved over this extended period the gentle ramp gradient was maintained largely by the processes generated by storms such processes were more effective because of the fluctuations of relative sea level

ammonium occurrence in a salinized lowland coastal aquifer ferrara italy to understand the spatial distribution and the possible sources of high ammonium concentration in the unconfined coastal aquifer of the po river delta lowland italy a detailed characterization of inorganic nitrogen species was completed a total of 59 boreholes were drilled to collect core samples and groundwater samples of the aquifer among them four piezometers located along a representative flow line were chosen to monitor the inorganic nitrogen concentrations with depth ammonium is the prevalent nitrogen inorganic species in groundwater and its concentration increases with depth and salinity very high ammonium concentrations are found in coincidence with peaty sediments in the salinized anoxic aquifer and in the low lying aquitard in particular the elevated ammonium concentration derives from mineralization of organic matter present in fine sediments deposited in paleo marsh environments copyright 2012 john wiley sons ltd

origin age and movement of pore water in argillaceous quaternary deposits at four sites in southwestern ontario hydrogeologic information in the form of textural properties field and laboratory determined hydraulic conductivity values vertical hydraulic gradients from piezometer nests and major ion and isotopic contents 18o 2h 3h 13c 14c was obtained from four sites located in southwestern ontario on thick deposits of clayey till and glaciolacustrine clay at each site the piezometers were installed from the water table zone situated 1 4 m below the surface to a maximum depth between 20 and 35 m below the surface values of hydraulic conductivity determined in the laboratory by consolidometer and triaxial methods are in the order of 10 8 10 7 cm s and are similar to values calculated from rates of water level rise in piezometers mean values of average vertical groundwater velocity calculated with the measured values of hydraulic conductivity porosity and hydraulic gradient using the darcy equation for a saturated non fractured porous medium range from 0 13 to 0 26 cm yr tritiated pore waters only occur within 3 6 m of ground surface thereby indicating that groundwaters below this depth recharged prior to at least 1952 18o in the pore waters exhibit a distinctive regular shift with depth from water table values of 9 to 10 smow characteristic of present day precipitation to values between 14 and 17 at depths of 20 40 m which are characteristic of much cooler waters corrected 14c ages of the groundwater are greater than 8000 yr b p thereby suggesting that the groundwaters at depth entered these deposits during or after the formation of these deposits approximately 11 000 to 14 000 yr ago 18o 2h and cl concentration profiles were simulated with a one dimensional model for transport by advection and diffusion in a saturated porous medium reasonable agreement between the model and the field profiles was obtained with values of effective diffusion coefficients of 3 0 10 6 cm2 s for 18o 2h and cl and with groundwater velocities between 0 03 to 0 05 cm yr based on these results it is concluded that the pore water in these deposits is a mixture of late pleistocene and modern waters and that the distribution of 18c 2h and cl in these deposits is influenced predominantly by molecular diffusion apparently more so than by hydraulic flow

sedimentary stylolite networks and connectivity in limestone large scale field observations and implications for structure evolution stylolites are rough surfaces formed by localized rock dissolution and prevalent in carbonates and other sedimentary rocks their impact on porosity and permeability and capacity to accommodate compactive strain are well documented this paper presents a meso scale field study on sedimentary stylolites in carbonates characterizing large scale distributions of stylolites including measurements conducted on longer than kilometer long stylolites our field study suggests that on large scales connections between stylolites become important since connectivity and also lack of connectivity are expected to play a significant role in strain accommodation and hydraulic rock properties we suggest that large scale analysis may require a new characterization scheme for stylolites populations based on their connectivity we therefore divide sedimentary stylolite populations into three end member types which are correlated with the three possibilities for percolation of such systems isolated stylolites with zero percolation connectivity long parallel stylolites with 2 dimensional percolation connectivity and interconnected stylolite networks with 3 dimensional percolation connectivity new statistical parameters and measures are devised and used to quantitatively characterize the different population types schematic mechanistic models are then offered to explain the evolution of the three end member connectivity classes in addition we discuss the effect on fluid flow of the different population types

facies mosaic in the ghuneri member jurassic of the bhuj formation western kutch india abstract in marginal marine environments facies mosaics become complicated through time as and when the regular autocyclic changes are frequently intervened by allocyclic changes the facies mosaic of the marginal marine tithonian ghuneri member 476 m thick exposed in western kutch india is likewise fairly complex with frequent lateral as well as vertical alternations between six facies the basic motif built up of autocyclic facies transitions of the bar lagoon spectrum in response to shift of the shoreline is time and again interfered with by allocyclic changes caused by storm surges these storm surges overtopped the bar and laid their sediments over the indigenous facies as washover the autocyclic facies association is composed of three facies namely 1 bar 2 lagoon margin and 3 lagoon interior the allocyclic facies association comprises 4 proximal storm washover 5 distal storm washover and 6 proximal grain flow of insignificant occurrence facies statistical analysis indicates that the vertical facies transitions between these six facies are fairly unpredictable elimination of the products of instantaneous deposition storm washover facies from the same data base however renders the sequence of congruous autocyclic facies predictable

regressive transgressive sedimentation in the ordovician sequence of the spiti tethys basin himachal pradesh india abstract the spiti basin comprises about 10 000 m of more or less fossiliferous cambrian to cretaceous sedimentary succession in the tethyan tibetan himalaya the ordovician strata in this basin consist of dominant sandstone with minor mudstone siltstone facies and locally developed basal conglomerate and persistent topmost minor carbonates this sequence has been regarded variously as continental and or marine to stretch out the environment of deposition a detailed study on field characteristics palaeocurrents petrography and reported marine fauna and trace fossils was carried out and suggests three major depositional environments viz fluvial transitional and marine the fluvial facies assemblage is characterised by fine to coarse grained multistoried sheets of sublithic arenite with abundant planar cross stratification and low mudstone content and is interpreted as having formed in a braided river environment the generalised palaeoslope is towards ne and nw the transitional facies comprises fine to medium grained sublithic to subarkosic arenites having sheet and lenticular sandstones with small to medium scale trough and planar cross stratification and subordinate herringbone cross stratification sigmoidal reactivation surfaces flaser and tidal bedding etc these features indicate the influence of both non marine fluvial and marine tidal flat environments the marine facies consists of fine to medium grained subarkose sublithic arenite and quartz wacke as well as sandy dolomicrite in the upper part the sandstone facies are generally multistoried having a sheet geometry and are interstratified with mudstone the important sedimentary structures include trough planar and hummocky cross stratifications and parallel lamination the palaeoflow direction is generally towards ne and nw with some minor fluctuations toward the south and west landward side these characteristic features reveal deposition in the nearshore shore zone three different stages of regression and transgression are recognised stage i resulted in the deposition of fluvial facies on the earlier marine domain cambrian representing a regressive phase caused by differential uplift and subsidence probably triggered by magmatic intrusion and or regional tectonics stage ii represents channelising of the fluvial system on tidal flats marking an initiation of transgression finally stage iii denoting the development of shore zone facies caused by basin subsidence and a change in sea level is interpreted as a transgressive phase

seafloor response to flow in a southern hemisphere sand ridge field argentine inner shelf abstract the inner continental shelf adjacent to buenos aires province argentina is characterized by a series of sand ridges averaging 4 7 m in relief and spaced about 2 7 km apart the ridges trend north south forming a 20 to 35 southward opening angle with the northeast southwest trending coast although the adjacent coast is of depositional strand plain origin it is presently undergoing erosional retreat and the formation of the ridges appears to be part of the retreat process seafloor grain size distributions and bedform arrays are responses to the same velocity field that has formed the ridges along transects normal to the ridges grain size variation is 90 out of phase with the topography the coarsest sediment is not at ridge crests or trough axes but instead occurs on the landward slope finest sands are on the seaward slope side scan sonar reveals bedforms aligned obliquely to both ridges and the coast these are inferred to be sand waves the grain size and bedform patterns suggest that the formative flows are northward currents with an offshore flow component near the bottom although flows observed during the study period were dominantly north to south the grain size gradients and bedform orientations are equivalent to those characteristic of the atlantic shelf of north america with a north south inversion the comparison suggests that inner shelf transport directions in response to wind events can be predicted from the regional geometry and climate of the shelf

geology and hydrocarbon accumulations columbus basin offshore trinidad the columbus basin situated on the eastern shelf of trinidad lies at the eastern extremity of a belt of severe deformation along the northern boundary of south america that has been affected by compressional and wrench tectonics in pliocene pleistocene time two major structural trends are present in the columbus basin a series of east northeast trending anticlines and north northwest oriented normal faults the basin was filled during late miocene to holocene time with sediments deposited by an ancestral orinoco river draining a hinterland to the southwest the pliocene pleistocene section which contains the hydrocarbon accumulations in the columbus basin was deposited in three coarsening upward sedimentary sequences followed by a late pleistocene transgressive sequ nce traps for hydrocarbon accumulation were formed by an easterly trending pliocene pleistocene wrench system with associated east northeast oriented anticlines combined with north northwest oriented normal faults oil was sourced in the late miocene lower cruse formation whereas gas was derived both from pliocene pleistocene pro delta shales and as a late high temperature phase of lower cruse hydrocarbon generation the north northwest faults formed migration conduits from the oil source rock to pliocene pleistocene reservoirs the temporal relationship of faulting to oil generation is a major factor affecting the distribution of oil and gas the size of hydrocarbon accumulations is limited to some extent by a lack of an effective hydrocarbon seal particularly in the western half of th basin

geology and hydrocarbon accumulations columbus basin offshore trinidad abstract the columbus basin on the eastern shelf of trinidad lies at the eastern extremity of a belt of severe deformation along the northern boundary of south america that has been affected by compressional and wrench tectonics in the pliocene pleistocene two major structural trends are present in the columbus basin a series of ene trending anticlines and nnw oriented normal faults the basin was filled during the late miocene to holocene with sediments deposited by an ancestral orinoco river draining a hinterland to the southwest the pliocene pleistocene section which contains the hydrocarbon accumulations in the columbus basin was laid down in three coarsening upward sedimentary sequences followed by a late pleistocene transgressive sequence traps for hydrocarbon accumulation were formed by an easterly trending pliocene pleistocene wrench system with associated ene oriented anticlines combined with nnw oriented normal faults oil was sourced in the late miocene lower cruse formation whereas gas was derived both from pliocene pleistocene pro delta shales and as a late high temperature phase of lower cruse hydrocarbon generation the nnw faults formed migration conduits from the oil source rock to pliocene pleistocene reservoirs the temporal relationship of faulting to oil generation is a major factor affecting the distribution of oil and gas the size of hydrocarbon accumulations is limited to some extent by a lack of an effective hydrocarbon seal particularly in the western half of the basin end of article last page 500

arsenic in groundwater testing pollution mechanisms for sedimentary aquifers in bangladesh in the deltaic plain of the ganges meghna brahmaputra rivers arsenic concentrations in groundwater commonly exceed regulatory limits 50 m gl 21 because feooh is microbially reduced and releases its sorbed load of arsenic to groundwater neither pyrite oxidation nor competitive exchange with fertilizer phosphate contribute to arsenic pollution the most intense reduction and so severest pollution is driven by microbial degradation of buried deposits of peat concentrations of ammonium up to 23 mg l 21 come from microbial fermentation of buried peat and organic waste in latrines concentrations of phosphorus of up to 5 mg l 21 come from the release of sorbed phosphorus when feooh is reductively dissolved and from degradation of peat and organic waste from latrines calcium and barium in groundwater come from dissolution of detrital and possibly pedogenic carbonate while magnesium is supplied by both carbonate dissolution and weathering of mica the 87 sr 86 sr values of dissolved strontium define a two component mixing trend between monsoonal rainfall 0 711 6 0 001 and detrital carbonate 0 735

estimating 14c groundwater ages in a methanogenic aquifer this paper addresses the problem of 14c age dating of groundwaters in a confined regional aquifer affected by methanogenesis increasing ch4 concentrations along the groundwater flow system and 13c and 14c isotopic data for dissolved inorganic carbon dissolved organic carbon and ch4 clearly show the effect of methanogenesis on groundwater chemistry inverse reaction path modeling using netpath indicates the predominant geochemical reactions controlling the chemical evolution of groundwater in the aquifer are incongruent dissolution of dolomite ion exchange methanogenesis and oxidation of sedimentary organic matter modeling of groundwater 14c ages using netpath indicates that a significant part of groundwater in the alliston aquifer is less than 13 000 years old however older groundwater in the range of 15 000 23 000 years is also present in the aquifer this paper demonstrates that 14c ages calculated using netpath incorporating the effects of methanogenesis on the carbon pools provide reasonable groundwater ages that were not possible by other isotopic methods

metamorphic incongruent solution diffusion and pressure solution stripes abstract the formation of pressure solution stripes is discussed on the basis of previosly published observations and of local chemical equilibria between solution and solid phases chemically driven mineral reactions can be localized at early sites of nucleation and be enhanced by stresses to create patterns of cleavage stripes these reactions cause transport of material over distances greater than single grains they provide suitable sites and suitable chemistry for later incongruent pressure solution potentially a much faster process than congruent pressure solution discussed in previous literature neither reaction nor straightforward incongruent pressure solution explains the solution of quartz commonly observed at cleavage stripes quartz pressure solution is explicable on certain assumptions about diffusivities and the effects of stresses this involves interaction between quartz and the established incongruent solution of other minerals an overall process termed interdependent pressure solution electrical potential differences will be greatest during early mineral reactions a feature which may provide a means to corroborate the chemical role in initiating pressure solution stripes

relationships between stylolites and cementation in sandstone reservoirs examples from the north sea u k and east greenland abstract the reservoir potential of hydrocarbon sandstone reservoirs may be significantly reduced by compartmentation as a result of the development of stylolites a petrographic and fluid inclusion microthermometric study was performed on sandstones containing abundant stylolites from the buchan galley and scott fields in the outer moray firth offshore scotland and from a palaeo oil bearing sequence in east greenland the main objective of this study was to further constrain the temperatures and burial depths at which stylolitization occurs in sandstone reservoirs the sandstones containing abundant stylolites are also characterized by their highly cemented nature numerous occurrences of quartz overgrowths clearly truncated by sutured stylolites are evident in all of the samples fluid inclusion microthermometry reveals that quartz cementation which is interpreted to be coeval with stylolitization occurred at minimum temperatures of between 86 and 136 c basin modelling of the scott and galley fields indicates that quartz cementation and stylolite development formed at depths greater than 2 5 km which were attained during rapid tertiary burial the occurrence of hydrocarbon fluid inclusions within healed microfractures orientated at high angles to the stylolites suggests that these microfractures provided pathways for hydrocarbon migration in the highly cemented low permeability zones associated with highly stylolitized sandstones

water and argon permeability of phyllosilicate powders under medium to high pressure 1 phyllosilicates are abundant throughout the upper crust they are commonly found in upper crustal faults influence of the mineralogy on the low permeability of phyllosilicate rich rocks is poorly characterized we measured water and argon permeability of eight phyllosilicate powders at room temperature talc pyrophyllite kaolinite illite montmorillonite particle size 2 m and muscovite phlogopite and biotite particle size 20 m tests were performed under hydrostatic conditions with a constant pore pressure of 10 mpa water or argon and varying confining pressure up to 160 mpa results show phyllosilicate powders have very low permeabilities 10 19 m2 to 10 24 m2 depending on mineral pore fluid and effective pressure lowest permeabilities were found for montmorillonite and talc while muscovite was the most permeable permeability decreases with increased compaction of powders and for fully compacted powders after 10 pressure cycles pressure dependency of permeability follows an exponential relationship with a pressure sensitive gradient of 0 004 mpa 1 to 0 015 mpa 1 water permeability is always lower up to 1 8 orders of magnitude than for argon the difference in argon water permeability can be related to the hydrophobicity and hydrogen bonding surface properties of minerals tested talc the most hydrophobic mineral tested showed the smallest difference between argon and water permeability while montmorillonite showed the largest permeability might also be affected by packing controlled by frictional strength of particles as well as by particle size and shape results indicate that type of phyllosilicate mineral pore water chemistry and grain size distribution will strongly affect permeability in phyllosilicate rich regions of the upper crust such as faults

stylolite controlled diagenesis of a mudstone carbonate reservoir a case study from the zechstein_2_carbonate central european basin nw germany this study was developed within the framework of dgmk german society for petroleum and coal science and technology project 718 funded by the companies exxonmobil production deutschland gmbh gdf suez e p deutschland gmbh rwe dea ag and wintershall holding gmbh the authors would like to acknowledge exxonmobil production deutschland gmbh that kindly provided core data elliot humphrey thanks the natural environment research council nerc centre for doctoral training cdt in oil gas for a phd grant egr acknowledges agaur agencia de gestio d ajuts universitaris i de recerca for a beatriu de pinos research project additional funding was provided by the generalitat de catalunya government 2017sgr 824 and the spanish government projects cgl2015 66335 c2 1 r cgl2015 69805 p and pgc2018 093903 b c22 we acknowledge theresa straub and simon gast for their assistance during core data collection we would like to thank miroslaw mirek slowakiewicz and an anonymous reviewer for their critical and constructive comments together with the editorial guidance of edoardo perri

shallow marine and coastal eolian quartz arenites in the neoarchean palaeoproterozoic karutola formation dongargarh volcano sedimentary succession central india abstract the neoarchean palaeoproterozoic karutola formation a 200 m thick supermature quartz arenite occurs interlayered between two thick units of intermediate to basic volcanic rocks of the dongargarh group despite metamorphism and deformation detrital texture and sedimentary structures are well preserved allowing detailed process based facies analysis the facies recognised include 1 inner shelf 2 shoreface 3 delta mouth lower delta plain 4 tidal flat and 5 foreshore backshore a coastal sand sheet dominated by adhesion structures and consisting of alternating eolian and foreshore aqueous deposits records eolian processes operative in the karutola coastal area textural characteristics hint at a significant eolian contribution to the shallow marine sand overall palaeocurrent indicates a nw se shoreline trend with hinterland to the west of the present outcrop belt a surface indicating an abrupt increase in the water depth divides the formation into two units the lower part encloses inner shelf to foreshore backshore deposits and the upper part of the succession records deposition from the shoreface to lower deltaplain environment a tidal flat sandstone mudstone unit is developed only in the north western end of the study area a granite gneiss source terrain cropping out to the west and a hot humid climate appears to have supplied the abundant quartz sand to the karutola shoreline and the sand population attained textural maturity through eolian and aqueous reworking it is postulated that the aqueous eolian interaction inferred for the karutola sand should be common in sandy depositional environments that lacked land vegetation

planar cross bedding associated with rip currents of upper cretaceous formations northeast japan abstract the sedimentary structure produced by rip currents is mainly characterized by seaward dipping planar cross bedding field observations from the upper cretaceous santonian kunitan and taneichi formations in northeast japan show that the occurrence of the cross bedded units extends laterally from the ancient beachlines but is restricted in vertical extent the planar cross set bed of the kunitan formation overlies very coarse grained parallel laminated and trough cross bedded sandstone beds of longshore current origin and underlies a pebbly conglomerated bed that was probably formed by a storm generated bottom current above is a zone of alternated beds of bioturbated and parallel laminated or hummocky cross stratified fine grained sandstones representing either lower shoreface or transitional depositional environments the planar cross bedding of the taneichi formation is intercalated with the underlying trough cross bedding and with the overlying bioturbated or parallel laminated very fine grained sandstone bed which also includes hummocky cross stratification both planar cross set beds of the taneichi and kunitan formations are present in the succession which fines upward suggesting an increasing depth of deposition such field occurrences indicate that bedforms produced within deeply incised rip channels which extend towards the sea can be untouched by ravinement and remain well preserved during transgression