porosity trends in the skagerrak formation central graben united kingdom continental shelf the role of compaction and pore pressure history this paper describes reservoir properties in the triassic skagerrak formation in the central north sea this prolific sandstone reservoir often possesses anomalously high porosity for its depth of burial simple statistical analysis of wire line log derived porosity data is used to derive empirical trends as a function of both depth and vertical effective stress that show variations between neighboring hydrocarbon fields and between different parts of the basin porosity data from the josephine j ridge quadrant 30 of the united kingdom continental shelf ukcs show a marked degradation with depth but the porosities are significantly higher than in similarly deeply buried areas such as the puffin high to the west quadrant 29 or the forties montrose high to the north quadrant 22 to understand the porosity patterns better the data have been analyzed by plotting against vertical effective stress this allows a better comparison to be made between fields and wells within the high pressure high temperature hpht realm high pressure here refers to fluid pressures above 10 000 psi whereas high temperatures are above 300 f 149 c results show that porosity and fractional effective reservoir the proportion of net sandstone with a porosity greater than a predetermined cutoff decrease systematically with increasing vertical effective stress data from the different j ridge fields fall on a common compaction trend even though they are derived from structures with marked variations in present day depth of burial and static formation overpressure trends from the other areas of the central graben the puffin and forties montrose highs indicate more indurate reservoir states the observed porosity trends are independent of fluid type within the reservoir and the absolute magnitude of overpressure the main observed hydrocarbon effect is the result of buoyancy forces the analysis supports the contention that after accounting for facies related grain size variations compaction controls average reservoir properties differences in compaction state between areas are postulated to relate primarily to structurally controlled timing of overpressure development relative to burial and how these affect the resultant vertical effective stress history both the puffin and forties montrose highs are directly attached to the basin margins across stepped faults these marginal terraces were open to lateral fluid flow for longer probably because across fault seals were only established late in the burial history when higher temperatures promoted cementation and the destruction of permeability within fault cores as a result they developed overpressures in the last 5 10 m y or so and are largely normally compacted the j ridge horst block is hydrologically more isolated within the basin center by across fault juxtaposition seals here overpressure development appears to have started earlier possibly between 50 and 60 ma retarding compaction and allowing preservation of higher porosities compaction continues to present day driven by the large static vertical effective stress gradients in these deeply buried reservoirs the observed empirical trends offer a means of predicting average reservoir properties in deep untested exploration targets

influence of grain fabric and lamination on the anisotropy of hydraulic conductivity in unconsolidated dune sands in local scale groundwater flow problems like for instance in contaminated groundwater studies it becomes increasingly important for proper prediction of contaminant migration to incorporate small scale geological and associated parameter heterogeneity in groundwater flow models of the micro scale geological heterogeneities the effect of grain fabric and lamination in unconsolidated sediments on the vertical anisotropy of effective hydraulic conductivity has received relatively little attention this is mainly due to the low conductivity contrast between laminae in combination with the friable nature of unconsolidated sediment which makes it sensitive to disturbances during experimental procedures as an alternative digital image analysis of sediment thin sections was applied to separate and quantify both causes of anisotropy the effective value of vertical anisotropy ratio of unconsolidated eolian dune sand as determined experimentally on distributed orientated core plugs ranges between 1 10 and 1 50 this wide range is partly caused by artificial noise introduced by distributed sampling in a heterogeneous medium and assuming thereby that the sampled material is homogeneous by applying digital image analysis of thin sections high resolution logs of hydraulic conductivity were generated simple upscaling of these values to effective conductivity parallel and perpendicular to sedimentary laminae provided quantitative estimates of the vertical anisotropy caused by lamination anisotropy values range between 1 0 and 1 075 the anisotropy ratio due to grain fabric ranges in value between 1 05 and 1 45 assuming that both anisotropy due to grain fabric and lamination are orientated identically if this is not the case the effective anisotropy is the weighted mean of anisotropies of the constituent layer types this study shows that for eolian sands the anisotropy owing to grain fabric dominates the effective value of anisotropy if conductivity contrast between laminae increases the contribution of anisotropy caused by grain fabric to the effective value of anisotropy decreases

heterogeneous characteristics of streambed saturated hydraulic conductivity of the touchet river south eastern washington usa traditionally a streambed is treated as a layer of uniform thickness and low saturated hydraulic conductivity k in surface and ground water studies recent findings have shown a high level of spatial heterogeneity within a streambed and such heterogeneity directly affects surface and ground water exchange and can have ecological implications for biogeochemical transformations nutrient cycling organic matter decomposition and reproduction of gravel spawning fish in this study a detailed field investigation of k was conducted in two selected sites in touchet river a typical salmon spawning stream in arid south eastern washington usa in stream slug tests were conducted to determine k following the bouwer and rice method for the upper and lower sites each 50 m long and 9 m wide and roughly 20 m apart a sampling grid of 5 m longitudinally and 3 m transversely was used the slug tests were performed for each horizontal coordinate at 0 3 0 45 0 6 0 75 0 9 1 05 and 1 2 1 35 m depth intervals unless a shallower impenetrable obstruction was encountered additionally water levels were measured to obtain vertical hydraulic gradient vhg between each two adjacent depth intervals results indicated that k ranged over three orders of magnitude at both the upper and lower sites and differed between the two sites at the upper site k did not differ significantly among different depth intervals based on nonparametric statistical tests for mean median and empirical cumulative distribution but the spatial pattern of k varied among different depth intervals at the lower site k for the 0 3 0 45 m depth interval differed statistically from those at other depth intervals and no similar spatial pattern was found among different depth intervals zones of upward and downward water flow based on vhg also varied among different depth intervals reflecting the complexities of the water flow regime detailed characterization of the streambed as attempted in this study should be helpful in providing information on spatial variations of streambed hydraulic properties as well as surface and ground water interaction copyright 2009 john wiley sons ltd

a pressure solution creep law for quartz from indentation experiments 1 indenter experiments have been performed on quartz crystals in order to establish a pressure solution creep law relevant at upper to middle crustal conditions this deformation mechanism contributes to earth s crust geodynamics controlling processes as different as fault permeability strength and stress evolution during interseismic periods or mechanochemical differentiation during diagenesis and metamorphism indenter experiments have been performed at 350 c and 20 120 mpa during months with differential stress varying from 25 to 350 mpa several experimental parameters were varied nature of quartz synthetic or natural nature of fluid manner in which the solid solution solid interface was filled and orientation of the indented surfaces versus quartz crystallographic c axis significant strain rates could only be obtained when using high solubility solutions naoh 1 mol l 1 displacement rates of the indenter were found activated by differential stress with exponential dependence as theoretically predicted the mean thickness of the trapped fluid phase below the indenter was estimated in the range 2 10 nm moreover the development of this trapped fluid phase was relatively fast and allowed fluid penetration into previously dry contact regions by marginal dissolution the indenter displacement rate was driven by differential stress and its kinetics was controlled by diffusion along the trapped fluid and the development of a morphological roughness along the interface conversely marginal strain energy driven dissolution was observed around the indenter and its kinetics was controlled by free surface reaction these experimental results are applied to model the interactions between pressure solution and brittle processes in fault zones providing characteristic time scales for postseismic transitory creep and sealing processes in quartz rich rocks

diagenesis in north sea hpht clastic reservoirs consequences for porosity and overpressure prediction upper jurassic clastic reservoirs of the fulmar formation in the central north sea possess anomalously high porosities for their present day depth of burial reservoirs with the highest overpressures have the highest porosities possess less macroquartz cement and have significant secondary porosity quartz cementation in hpht high pressure high temperature reservoirs has been inhibited by a combination of factors high overpressure limited fluid movement presence of early grain coating cements high pore fluid salinity and possibly petroleum migration secondary porosity has contributed to reservoir quality with an average of 4vol extra porosity created quantitative prediction of porosity would require an improved depositional model for the fulmar accurate thermal and pressure modelling and detailed knowledge of field filling and leakage histories theoretical calculations indicate that diagenetic reactions occurring in the fulmar formation smectite illitisation and quartz cementation did not generate significant overpressure because seal permeabilities were too high and the rate of volume increase associated with the reactions too small therefore diagenetic reactions can effectively be ignored when modelling overpressure generation in the central north sea although cementation will affect rock permeability and rates of fluid dissipation

exceptional reservoir quality in hpht reservoir settings examples from the skagerrak formation of the heron cluster north sea uk abstract as the exploration of hydrocarbons moves into more complex and deeper basinal settings the need to understand the effect of high temperatures and high pressures on reservoir quality and rock properties becomes even more important the fluvial channel sandstone reservoirs of the skagerrak formation in the central north sea exhibit anomalously high porosities and permeabilities considering their depth of burial 3500 m below sea floor despite the complex depositional setting diagenetic history high overpressure and temperatures encountered in the skagerrak formation hydrocarbons are currently being produced the skagerrak formation reservoirs used in this study have encountered overpressures of 40 mpa and temperatures up to 185 c at present day maximum burial to identify the role played by the high pressure and high temperature encountered in the reservoir sandstones a multidisciplinary approach involving petrographic fluid inclusion and burial history modelling studies has been adopted our interpretation of the results is that the generation of shallow overpressure in these fields limited mechanical compaction and also played an important role in minimizing pressure solution in the chemical compaction regime as evidenced by reduced quartz cementation fluid inclusions found in the quartz overgrowths indicate late stage development with temperatures of formation in the range 130 to 170 c coincident with late stage deeper burial hydrocarbon emplacement occurred after quartz cementation and has had little to no effect on porosity preservation the formation of well developed authigenic chlorite 70 surface coating and to a lesser extent illite clay coats with burial had a positive effect on porosity preservation even though permeability was marginally reduced in the illite rich sandstones a schematic porosity and quartz cement evolution model has been developed which allows for pre drill prediction of reservoir quality in the heron cluster and provide valuable insights for other complex high pressure high temperature reservoirs

structures and mechanisms associated with development of a fold in the cantabrian zone thrust belt nw spain a detailed history of progressive fold development based on mesostructural analysis is provided for a metre scale fold in the cantabrian fold and thrust belt of northwestern spain the well exposed asymmetric syncline displays a wide variety of structures including extensional faults thrusts veins tectonic stylolites bedding plane faults drag folds and a main limb thrust that transects the entire fold important constraints on fold development are provided by the spatial distribution and style of deformation angular relations and cross cutting relations among the structures fold mechanisms varied as a function of structural position while the northwest limb was subjected to pure shear shortening in the form of contractional faults the southeast limb was bent under tangential longitudinal strain resulting in a combination of outer arc extensional faulting in

three dimensional model of modern channel bend deposits 1 we present a three dimensional model of heterogeneous modern channel bend deposits developed through purely structure imitating interpolation kriging of hydraulic properties this model augmented with ground penetrating radar data and directional variograms agrees with detailed observations in similar modern environments and leads to a process based interpretation of the presented hydraulic conductivity structure integration of all available information permitted delineation and characterization of the modern streambed as a distinct hydrostratigraphic unit without coring or outcrop studies our results imply that the modern streambed is commonly oversimplified in available analytical and numerical models of groundwater surface water interactions where it is assumed to be homogeneous and isotropic and characterized by a constant width and thickness this three dimensional approach that integrates concepts and principles developed in sedimentology hydrogeology geophysics and geostatistics has potential implications on model development of stream aquifer systems

hydrogeologic facies models to delineate large scale spatial trends in glacial and glaciofluvial sediments recent interest in contaminant transport in ground water has led hydrogeologists to the conclusion that predicting the movement of solutes requires information on the distribution of spatial trends and heterogeneities in porous media description of spatial trends has long been of interest to sedimentologists who have produced a large body of geologic information on the subject in this paper facies models are used to construct conceptual models of hydrogeologic facies for glacialmeltwater stream sediment and till these hydrogeologic facies models which delineate large scale trends in heterogeneity are appropriate for use in designing hydrogeologic field tests and for estimating input to regional ground water flow and transport models this paper treats each facies as a homogeneous anisotropic hydrogeologic unit the models presented herein conceptualize the hydrogeologic relationships among facies and illustrate one method of converting the apparent chaos in nature into an orderly system that can be tested scientifically and modeled mathematically the principles used to create conceptual models of hydrogeologic facies for the types of sediment considered in this paper can be extended to other sedimentary environments it should be recognized however that such models do not address the small scale heterogeneity present within individual facies additional basic research is required to measure hydraulic conductivity variation within representative hydrogeologic facies and to develop statistical descriptions to represent the variations such detailed descriptions of hydraulic conductivity may be necessary to describe ground water flow at a local scale for analysis of contaminant transport

twin lake tracer tests setting methodology and hydraulic conductivity distribution following evaluation of three potential sites a fluvial sand aquifer with high 0 7 1 6 m d 1 linear average groundwater flow velocities was instrumented with a fully penetrating injection well and 82 monitoring installations over a 40 m flow path length two natural gradient tracer migration experiments have employed pulse injections of a nonreactive radioisotope 131i in a study of hydraulic conductivity structure and dispersive characteristics of the flow system the use of a gamma emitting radionuclide in these experiments allowed measurement of tracer distribution by scanning fully penetrating boreholes with a scintillation detector this technique provided many advantages in data collection over conventional tracers including unprecedented resolution of the vertical distribution of tracer measurements without pumping and the attendant concerns for flow system perturbation and minimal manpower for sample analysis tracer breakthroughs at monitors along the axis of flow revealed the presence of heterogeneities in aquifer hydraulic conductivity at two scales over the 40 m path length six regions with hydraulic conductivities substantially different from adjacent strata were identified thicknesses of these regions varied from 0 2 to more than 3 m their lateral extents in the direction of groundwater flow ranged from 15 m to more than 40 m smaller strata with an average thickness of 0 34 m and lengths of less than 10 m were detected within all six of the hydraulic conductivity regions but there was no evidence of increases in local dispersivity with increased transport distance as a result of these variations the six hydraulic conductivity regions do however have measurable effects on whole aquifer dispersion stratification characteristics of the tested aquifer believed to have been deposited in a sandy braided river are consistent with those observed in similar modern environments estimation of the magnitude and spatial structure of hydraulic conductivity variations in aquifers of concern would be greatly aided by studies of the stratification characteristics in well exposed modern or lithified sedimentary analogues

87sr 86sr ratios in hydrothermal waters and deposits from the east pacific rise at 21 n abstract 87 sr 86 sr ratios of three hydrothermal waters collected on the east pacific rise at 21 n define a mixing line between seawater and a hydrothermal end member at 0 7030 which is derived by seawater basalt interaction at ca 350 c and water rock ratio of about 1 5 sr concentrations are not affected in the process while mg uptake from seawater is almost complete up to2 3 of this hydrothermal component is involved in anhydrite precipitation while the sr isotopic ratio in sulfides chalcopyrite sphalerite cannot be distinguished from that of sulfate it is estimated that ca 1 10 10 moles of strontium are yearly cycled in the hydrothermal systems of mid oceanic ridges thereby affecting the 87 sr 86 sr budget of seawater mass balance between river runoff limestone precipitation and ridge basalt alteration suggests that the 87 sr 86 sr ratios of the river runoff are in the range 0 7097 0 7113 and are largely dominated by limestone alteration

chemical and sr isotopic variations during diagenesis of miocene siliceous sediments of the monterey formation california the monterey formation of california preserves miocene siliceous sediments at progressive generally with depth diagenetic stages diatomite opal a ct chert opai ct quartz chert for initially clay poor sediments and diatomaceous shale ct porcelanite porous opal ct quartz porcelanite for sediments that were initially clay rich the chemistry of most diatomite is controlled by three primary phases biogenic silica carbonate and detrital clay and several subsidiary phases organic material apatite pyrite and detrital minerals including quartz and plagioclase the elemental abundances of the clay poor diagenetic sequence decrease sharply with advancing diagenetic state for those elements controlled by clay al ti k rb cs fe some group b metals carbonate ca mg sr ba apatite p ca sr ba v and organics v ni while silica shows a congruent increase these first order variations reflect the initial compositions of the siliceous sediments modified by the addition of silica the removal of carbonate and apatite and the migration of petroleum during silica diagenesis anomalous abundances of mn ni cr mo and some other group b metals are associated with trapped refractory organic material and suggest that petroleum catagenesis and migration occurred during silica diagenesis migration may have been facilitated by the release of bound water during silica dehydration reactions second order variations in k rb k cs rb sr 87 sr 86 sr with advancing diagenetic state suggest ion exchange and ion expulsion by reaction of detrital phases with pore fluids diagenetic processes partially equilibrated but did not homogenize depositional 87 rb 86 sr 87 sr 86 sr mixing lines generated by detrital clays and authigenic carbonate and silica in siliceous sediments from the santa maria region however similar mixing lines in diatomites from the santa lucia area are reset to nearly horizontal slopes in associated ct porcelanites the degree of equilibration may be a function of the rate of formation of relatively impermeable quartz chert which isolated the siliceous system from further interaction with pore fluids the rapid formation of quartz chert in the santa maria region is believed to have prevented isotopic homogenization processes from reaching completion initial chemistry of the siliceous systems controlled the rates and pathways of silica diagenesis silica diagenesis in turn altered the chemistry of the siliceous sediment

stress field fluctuations along the dead sea rift since the middle miocene the dead sea transform dst is the suture between the african and the arabian plates both of which subduct northward under the eurasian plate the collision of these plates with eurasia and their relative motion are the source for their internal deformation especially in the vicinity of the dead sea transform geological observations indicate that two distinct paleostrain regimes operated adjacent to the dead sea rift and in the sinai israel subplate 1 wnw shortening less than 10 and nne extension beginning in the turonian is associated with the development of the syrian arc fold belt and attributed to the syrian arc stress field sas and 2 middle miocene to recent nnw shortening and ene extension associated with the 105 km sinistral displacement along the dead sea transform and the opening of the red sea is attributed to the dead sea stress field dss it was originally suggested that the sas terminated during the middle miocene with initiation of the dss however trend and age analysis of many structures shows that formation of sas compatible structures continued after the middle miocene up to the recent in some middle miocene and younger rocks structures such as faults dikes volcanic lineaments and tectonic stylolites compatible with both stress fields were reported in a few locations structures compatible with both stress fields crosscut each other it is suggested that the movements which resulted in the development of the syrian arc and other sas compatible structures are continuing to the recent and that dss movements are superimposed upon them the overlapping of sas and dss structures adjacent to the dst results from spatial and temporal fluctuations in the overall stress state we propose that such variations could be caused by the superposition of large earthquake stress drops associated with movements along the dst on a steady background plate scale stress regime associated with the sas thus dss compatible structures should form in preseismic activity periods when dst related elastic strain is high on the other hand the sas compatible structures should form during interseismic activity times subsequent to large local stress release along the dst

manganiferous cherts of the franciscan assemblage i general geology ancient and modern analogues and implications for hydrothermal convection at oceanic spreading centers there are several hundred ophiolitic manganiferous chert deposits primarily of late jurassic to early cretaceous age known within the franciscan assemblage of california the sequences typically consist of one to three massive manganiferous chert lenses containing 30 to 50 percent mn and averaging 1 m in thickness by 15 m subcircular diameter these are separated by an average 2 to 10 m of thin bedded radiolarian cherts and overlie basalts or greenstones both their geology and chemistry indicate that the ore lenses are hydrothermal and may have formed on the flanks of a mid ocean ridge or within a back arc basin it is proposed that the sequences developed as a result of sea floor spreading over a series of deep hydrothermal seawater convection cells paralleling a spreading center and spaced roughly 5 to 10 km apart chemical profiles of mn fe si al cu ni zn co ba ti the rare earth elements and 87 sr 86 sr have been determined through two complete sections these profiles indicate hydrothermal input of mn si cu ni zn and ba and detrital or hydrogenous input of al and co they illustrate the use of ti as a measure of relative detrital sedimentation rates fe is strongly fractionated from mn within the ores fe mn 0 1 and fe mn ratios decrease upward throughout each section suggesting preferential deposition of fe within the sediment and of mn at the seawater interface rare earth element distributions reflect the interaction of sea water and underlying basalts sr isotopic ratios of the ores and basalts demonstrate both strong and moderate seawater influences respectively fluid inclusion analyses on veins of undetermined age show seawater salinity temperatures of roughly 200 degrees c and tentative entrapment pressures corresponding to 1 700 m water depth early and intermediate veins were injected into unconsolidated siliceous sediment producing a characteristic bleached and pseudobrecciated texture an analogy is drawn with the present day field of hydrothermal mounds near the galapagos rift and with ophiolitic complexes of the northern apennines and other localities

geochemistry of manganese bearing cherts associated with alpine ophiolites and the hawasina formations in oman abstract based on correlation coefficients and analogies with studies on recent mn enrichments the major and trace elements of mn occurrences associated with ophiolites that have been variously affected by regional alpine metamorphism were attributed to different origins mn zn v ce nd and la are hydrothermal al ti k zr rb ga sc and some fe and pb are detrital and si p u y nb and the remainder of the fe are biogenic preliminary studies of mn occurrences in the wahrah formation of oman reveal a very similar geochemistry as the extensive exposure of this formation does not display any evidence of hydrothermal systems only a hydrothermal supply of mn to seawater from a distant source is envisaged for these and other deposits

the role of fluid pressure and diagenetic cements for porosity preservation in triassic fluvial reservoirs of the central graben north sea anomalously high porosities and permeabilities are commonly found in the fluvial channel sandstone facies of the triassic skagerrak formation in the central north sea at burial depths greater than 3200 m 10 499 ft from which hydrocarbons are currently being produced the aim of our study was to improve understanding of sandstone diagenesis in the skagerrak formation to help predict whether the facies with high porosity may be found at even greater depths the skagerrak sandstones comprise fine to medium grained arkosic to lithic arkosic arenites we have used scanning electron microscopy petrographic analysis pressure history modeling and core analysis to assess the timing of growth and origin of mineral cements with generation and the impact of high fluid pressure on reservoir quality our interpretation is that the anomalously high porosities in the skagerrak sandstones were maintained by a history of overpressure generation and maintenance from the late triassic onward in combination with early microquartz cementation and subsequent precipitation of robust chlorite grain coats increasing salinity of pore fluids during burial diagenesis led to pore filling halite cements in sustained phreatic conditions the halite pore filling cements removed most of the remaining porosity and limited the precipitation of other diagenetic phases fluid flow associated with the migration of hydrocarbons during the neogene is inferred to have dissolved the halite locally dissolution of halite cements in the channel sands has given rise to megapores and porosities of as much as 35 at current production depths

spatial variability of hydraulic conductivity of an unconfined sandy aquifer determined by a mini slug test abstract the spatial variability of the hydraulic conductivity in a sandy aquifer has been determined by a mini slug test method the hydraulic conductivity k of the aquifer has a geometric mean of 5 05 10 4 m s 1 and an overall variance of 1n k equal to 0 37 which corresponds quite well to the results obtained by two large scale tracer experiments performed in the aquifer a geological model of the aquifer based on 31 sediment cores proposed three hydrogeological layers in the aquifer concurrent with the vertical variations observed with respect to hydraulic conductivity the horizontal correlation length of the hydraulic conductivity has been determined for each of the three hydrogeological layers and is found to be small 1 2 5 m the asymptotic longitudinal dispersivity of the aquifer has been estimated from the variance in hydraulic conductivity and the horizontal correlation length to be in the range of 0 3 0 5 m compared with a value of 0 42 m obtained in one of the tracer tests performed

multi level slug tests in highly permeable formations 2 hydraulic conductivity identification method verification and field applications abstract using the developed theory and modified springer gelhar sg model an identification method is proposed for estimating hydraulic conductivity from multi level slug tests the computerized algorithm calculates hydraulic conductivity from both monotonic and oscillatory well responses obtained using a double packer system field verification of the method was performed at a specially designed fully penetrating well of 0 1 m diameter with a 10 m screen in a sand and gravel alluvial aquifer msea site shelton nebraska during well installation disturbed core samples were collected every 0 6 m using a split spoon sampler vertical profiles of hydraulic conductivity were produced on the basis of grain size analysis of the disturbed core samples these results closely correlate with the vertical profile of horizontal hydraulic conductivity obtained by interpreting multi level slug test responses using the modified sg model the identification method was applied to interpret the response from 474 slug tests in 156 locations at the msea site more than 60 of responses were oscillatory the method produced a good match to experimental data for both oscillatory and monotonic responses using an automated curve matching procedure the proposed method allowed us to drastically increase the efficiency of each well used for aquifer characterization and to process massive arrays of field data recommendations generalizing this experience to massive application of the proposed method are developed

architecture of the sierra ladrones formation central new mexico depositional controls on the permeability correlation structure statistical models of hydrogeological heterogeneity are often used in aquifer and reservoir characterization the number of data required to estimate objectively the spatial correlation structure of permeability however is often prohibitive the objective of this study was to develop a better understanding of how information about depositional processes can be used to characterize hydrogeological heterogeneity an outcrop of the fluvial interfluvial sierra ladrones formation of new mexico was studied for this purpose on the basis of previous studies of paleogeography and our own field observations deposits of the sierra ladrones formation are interpreted as marginal ancestral rio grande flood plain and tributary deposits architectural elements were mapped over a 0 16 km sup 2 peninsular outcrop of pliocene pleistocene deposits of the central albuquerque basin geostatistical analysis of the architectural element map data indicates non orthogonal anisotropy in the horizontal direction the orientations of the strongest n30 degree w and weakest n90 degree e correlation correspond to the orientation of the tributary system and the ancestral rio grande flood plain respectively in the vertical direction the correlation structure exhibits exponential behavior corresponding to the average element thicknesses the results demonstrate that information about depositional environment can be used to help to quantify statistically subsurface heterogeneity 28 refs 9 figs 1 tab

mineralogy and geochemistry of two metamorphosed sedimentary manganese deposits sierra nevada california usa abstract laminated to massive rhodochrosite hausmannite and mn silicates from the smith prospect and manga chrome mine sierra nevada california were deposited as ocean floor sediments associated with chert and shale the principal lithologies at smith are chert argillite rhodochrosite hausmannite and chlorite rich layers and relatively uncommon layers of jacobsite the manga chrome mine also contains layers rich in manganoan calcite and caryopilite tephroite rhodonite spessartine and accessory alleghanyite and sonolite formed during metamorphism volcaniclastic components are present at manga chrome as metavolcanic clasts and as mn poor red garnet and hematite rich layers there is no evidence such as relict lithologies that mn was introduced into mn poor lithologies such as chert limestone or mudstone replacement of mn poor phases by mn rich phases is observed only in the groundmass of volcanic clasts that appear to have fallen into soft mn rich mud manganiferous samples from the smith prospect and manga chrome mine have high mn fe and low concentrations of ni cu zn co u th and the rare earth elements that are similar to concentrations reported from other ancient mn deposits found in chert greenstone complexes and from manganiferous sediments and crusts that are forming near modern sea floor vents the sierra nevada deposits formed as precipitates of mn rich sediments on the sea floor probably from mixtures of circulating hydrothermal fluids and seawater the composition of a metabasalt from the smith prospect is consistent with those of island arc tholeiites metavolcanic clasts from the manga chrome mine are compositionally distinct from the smith metabasalt and have alkaline to calc alkaline affinities a back arc basin is considered to be the most likely paleoenvironment for the formation of the mn rich lenses at the manga chrome mine and by association the smith prospect layers of rhodochrosite hausmannite and chert preserve the composition and some textures of the sedimentary protoliths at both sierra nevada deposits jacobsite rich layers probably represent a fe rich protolith caryopilite and manganoan calcite represent additional protoliths at the manga chrome mine the metamorphic assemblage prehnite chlorite epidote calcite in a metabasalt from the smith prospect constrains regional metamorphic conditions to a maximum temperature of 325 c and a pressure of 2 kbar slightly higher temperatures are indicated by the presence of actinolite in another metabasalt compositions of mn rich minerals in smith samples are consistent with these metamorphic conditions

measurement of anisotropic hydraulic conductivity in unconsolidated sands a case study from a shoreface deposit oyster virginia in this study an integrated field and laboratory method which can be used to evaluate the magnitude and distribution of anisotropic hydraulic conductivity at the scale of bedding structures in unconsolidated sediment is demonstrated undisturbed sediment cores 10 16 cm in diameter and 18 25 cm long are obtained using a split barrel core sampler two undisturbed 5 72 cm diameter 7 90 cm long subcores oriented parallel and perpendicular to the primary bedding structures are then obtained from each field core the hydraulic conductivities of the subcores are then measured with a constant head permeameter the sampling and experimental procedures are designed to minimize potential sources of error sixty four 10 16 cm cores were sampled in a coastal sand outcrop located 300 m from a subsurface injection experiment near oyster virginia four distinct lithologies were sampled in horizontal transects with a spacing of 0 5 m between core locations in addition iron oxide bands which were prevalent throughout the exposure were sampled from both ends of the outcrop the average hydraulic conductivity values are consistent with the observable geologic features grain size sorting and iron oxide banding hydraulic conductivity is greater in the parallel oriented subcore for 90 of the core pairs and mean hydraulic conductivity ratios of parallel to perpendicular oriented subcores k k for the different lithologies ranged from 1 33 to 1 57 the major control on the anisotropy in this sediment is interpreted to be preferential grain orientations resulting from depositional processes with additional influences from the prominence of the bedding structures and secondary features such as hydrous iron oxide banding

breccia hosted manganese rich minerals of alpi apuane italy a marine redox generated deposit mn rich beds occur within the brecce di seravezza formation bsfm intercalated between norian metadolostone megalodontic marble and hettangian marble in the alpi apuane italy the bsfm is a rockfall talus deposit that accumulates at the base of the footwall scarp of normal faults bordering extensional marine coastal basins the type sequence of metabreccia ends with a bed of chloritoid schist interpreted as the metamorphic equivalent of lateritic soils the four main types of mn mineral assemblages are 1 braunite piemontite and rare hausmannite 2 piemontite braunite hollandite and minor rhodochrosite and kutnahorite 3 braunite hollandite and rare piemontite the other minerals are quartz calcite muscovite phlogopite baryte and minor hematite rutile and apatite during the alpine orogeny pressures of 4 6 kb and temperatures of 350 380 c were attained mn assemblages with hematite and phlogopite indicate o2 10 8 for t 350 c and o2 10 6 when braunite appears on the mn rich rocks ti fe nb sn ta hf th ga rb pr k na nd were identified as detrital in origin and are positively correlated with al u is positively correlated with co pb bi mo the rare earth element patterns normalized to seawater show a negative slope towards the heavy rare earth elements with positive ce anomalies in some samples positive ce and eu anomalies in other samples and negative ce and positive eu anomalies in a third group the eu concentrations are nearly constant and the eu anomalies reflect differences in the concentration of other rare earth elements for ce a positive correlation with al2o3 sio2 indicate that a detrital signature prevails on that produced by duration of seawater exposure but a significant good correlation of la tm lu with mg could indicate at least for these elements a seawater signature only in some samples ba eu sr show anomalously high concentrations likely of hydrothermal origin however generally in all the chemical variation diagrams the bsfm samples fall outside the field of hydrothermal and hydrogenous deposits as defined in the literature for other mn deposits in addition metabasites and metavolcaniclastic beds are absent from the bsfm sequence and bsfm coastal basins were for the most part separated from the open ocean and related streams that must be excluded as possible mn sources owing to the arid climate of late triassic the runoff was negligible and the groundwater oxidizing and alkaline were unable to mobilize mn the bsfm basins are then the most suitable depositional environment for mn the water column was stagnant and stratified only where bottom of the basin was deeper than the oxic anoxic boundary reducing marine bottom waters percolated within the fractured basement and leached mn from disseminated minerals of metamorphic rocks and then rising along fault and fractures supplied mn to the bottom waters afterwards when tectonic uplift and sealevel drop brought the bottom into the oxic field mn precipitated and formed the mn rich matrix of the bsfm deposits

linking the influence of diagenetic properties and clay texture on reservoir quality in sandstones from nw borneo abstract reservoir studies in the sandakan sub basin nw borneo are challenging and inexplicable due to complex diagenetic effects such as compaction cementation dissolution and depositional means including grain size sorting and packing with reference to clay texture these diagenetic effects together impart significant amounts of uncertainty on reservoir quality assessment in this regard we documented the mineralogical diagenetic and reservoir properties of sandstones from the sandakan formation nw borneo through thin sections sem xrd xrf he porosimeter and poroperm in order to analyze the influential parameters we used matrix grain rearrangement and clay coating around detrital grains for the reservoir quality our results show that the sub litharenites to quartz arenite that dominate in the sandstones are drawn from recycled orogenic sand furthermore reservoir properties of the sandstones were ascertained to be controlled by diagenesis micro quartz with clay coatings and pressure dissolution of feldspar with the alteration of lithic fragments the result shows that the physical compaction rearrangements and ductility of grains were the reasons that reduced porosity and permeability the main reason for porosity reduction in the present study is pressure dissolution that resulted in the form of chemical compaction induced by micas with grain contacts nonetheless through sem and petrography clay coatings around the grains and dissolution of feldspar were found to optimally contribute to the preservation of reservoir properties dissolution of feldspar and kaolinization resulted in the formation of secondary porosity that allows meteoric water to percolate through the open and detachment spaces of quartz or other grains this percolation is also responsible in enhancing the pore throat radii in the reservoir media of the analyzed sandstones these traits are obliging to diagenetic effects on porosity and permeability which are linked with the physical compaction and clays coating to reduce and preserve the reservoir properties respectively of same type of reservoirs globally

lead concentrations in the northeast pacific evidence for global anthropogenic perturbations lead concentrations were determined by isotope dilution mass spectrometry in 34 surface and deep water samples collected in the northeast pacific between hawaii and california and off the california coast using a deep water sampler protected against fouling by contamination from the ship and hydrowire measured concentrations lie more than one order of magnitude below previously published open ocean values and they show that in most cases 90 or more of the total lead is in a dissolved form lead concentrations are about 10 fold higher in surface and thermocline waters than in deep waters values drop as low as 1 ng kg 5 pmol kg below 3500 m depth lead profiles thus appear different compared to those of most trace metals which show enrichment in deep waters compared to surface concentrations lead concentrations in surface waters increase from 5 to 15 ng kg 25 to 75 pmol kg along a transect starting from a location 200 km off the california coast and continuing towards the center of the north pacific gyre this increase is congruent with that observed for 210 pb concentrations in the same waters sampled at the same time lead is supplied to the open north pacific largely from the atmosphere at a rate of about 60 ng cm 2 yr which exceeds the prehistoric oceanic output flux of authigenic lead recorded in pelagic sediments about tenfold this excess originates from emissions from smelters and combustion of leaded gasoline overwhelming natural lead inputs that entered the ocean during prehistoric time probably largely through rivers vertical lead concentration profiles below the surface mixed layer are probably not in steady state there concentrations must be increasing in response to the increase of anthropogenic inputs because the estimated lead residence times are more than 20 years in the thermocline and about 80 years in deep waters based on an estimated 10 fold input and concentration increase since the mid eighteenth century in the surface mixed layer in the central northeast pacific it is calculated that the 10 ng kg average concentration between 100 and 900 m is 2 to 5 times larger and the 1 8 ng kg average concentration between 900 and 5000 m depth is about 2 times larger than it was in the mid eighteenth century profiles of lead concentrations in the north atlantic are expected to be shifted generally to larger values by a factor of 2 to 3 compared to those in the north pacific because of the effects of greater industrial lead contamination while lead concentration profiles in the south pacific are expected to be shifted generally to lower values compared to the north pacific by about this same factor because of the effects of lesser industrial lead contamination

overpressure preventing quartz cementation a reply chemical compaction and the relative importance of the pressure dissolution and illite mica induced dissolution imid models have remained a contentious issue as is the role played by stress in chemical compaction this paper offers further support and evidence as discussed in stricker et al 2016b focusing on the reservoir quality of the triassic skagerrak formation sandstones in the high pressure high temperature hpht central graben north sea the reply discusses alterative reservoir quality interpretations and comments as raised by maast 2016 a series of theoretical and experimental studies as well as field based evidence is presented providing strong support to the important role of stress e g vertical effective stress during chemical compaction the evidence leads to the conclusion that the process of chemical compaction is stress and temperature driven and significantly enhanced by clay minerals playing a catalytic role by increasing the width of diffusion pathway or by modifying the kinetics of the dissolution process

geologic and hydrologic controls on the movement of water through a thick heterogeneous unsaturated zone underlying an intermittent stream in the western mojave desert southern california 1 a two dimensional axially symmetric unsaturated flow model was developed to test hypotheses about geologic and hydrologic controls on the movement of water through the thick heterogeneous unsaturated zone underlying oro grande wash in the mojave desert california heterogeneity within the unsaturated zone was simulated with multiple realizations of subsurface geology estimated on the basis of transition probability markov chain statistics model results show lateral spreading of water away from the wash was best approximated by realizations that include thin horizontally extensive clay layers that impede the downward movement of water there was a wide range in model responses for these realizations and the movement of water through unsaturated zones containing thin horizontally extensive clay layers may be more difficult to predict than water movement through unsaturated zones where clay layers are less extensive for realizations having less extensive clay layers the range of model responses decreased with time and model results became increasingly similar as water encountered larger volumes of material

fluid overpressure as a control on sandstone reservoir quality in a mechanical compaction dominated setting magnolia field gulf of mexico the reservoir quality porosity and permeability of deeply buried hydrocarbon reservoir sandstones in sedimentary basins is significantly affected by burial diagenesis many deep reservoirs develop anomalous fluid overpressures during burial previous studies on the effect of fluid overpressure on reservoir quality in these deep reservoirs have been inconclusive because of the difficulty in constraining the individual contributions of various porosity preserving factors that are simultaneously active in these reservoirs owing to its rapid burial and low burial temperatures the neogene gravity flow sandstone reservoirs from the magnolia field gulf of mexico offers a unique opportunity to investigate in isolation the effect of fluid overpressure on reservoir quality examination of petrography pore pressure and routine core analysis datasets showed a positive correlation between high fluid overpressure and enhanced reservoir quality this study confirms that fluid overpressure preserves reservoir quality in deeply buried sandstone reservoirs in compaction dominated high sedimentation basin settings

hydrothermal mn deposits of the franciscan assemblage ii isotope and trace element geochemistry and implications for hydrothermal convection at spreading centers abstract major element trace element and sr nd pb and o isotopic data for a franciscan mn deposit suggest an origin by seafloor hydrothermal circulation based on q mode factor analysis the cherts and mn lenses of the blue jay mine formed from a combination of 4 components representing 1 biogenic 1 hydrothermal and 2 detrital sources rb sr u th pb and o isotopic systematics in the mn lenses were affected by input from the hydrothermal circulation of material leached from the underlying basalts nd isotopic compositions in both cherts and mn lenses are identical and within the range measured for pacific ocean water suggesting the ree were not mobilized by hydrothermal activity correlation of 18 o with sio 2 and mno 2 in the mn lenses implies the lenses formed by simple mixing of hydrothermally derived mn oxides with seawater and biogenic silica 18 o of the cherts is both uniform and depleted relative to dsdp jurassic cherts but similar to microquartz bearing cherts of the monterey formation this suggests that diagenetic activity exerted more control on oxygen isotope compositions then hydrothermal alteration or metamorphism finally a well defined rb sr isochron of 158 5myr was obtained for these cherts and opens the possibility of determining absolute radiometric ages for similar cherts throughout the geologic record

overpressure development in sedimentary basins induced by chemo mechanical compaction of sandstones abstract mechanisms of overpressure build up resulting from chemically induced compaction are investigated by considering that intergranular pressure solution controlled by temperature and effective stresses is the dominant process of chemical deformation in sandstones the numerical simulations are performed using a thermo poro mechanical tool based on the finite element method specifically devised to deal with sedimentary basin modeling at the material level purely mechanical and chemo mechanical deformations are respectively addressed by means of plastic and viscoplastic constitutive components porosity data of the middle jurassic garn formation from the haltenbanken area of the mid norwegian continental shelf are taken as reference for calibration of the sandstone model to be used on synthetic cases of a siliciclastic basin in oedometric conditions two situations are proposed involving different depositional sequences of sandy and shaly sediments with the aim to assess the permeability effect in the numerical model the results have shown that early overpressure development in low permeability formations preserves sandstone porosities by reducing effective stresses and thus retarding pressure solution compaction whereas higher effective stresses associated with permeable depositional environments may lead to important chemo mechanical deformation resulting in low porosity sandstones and significant overpressure generation at later stages of basin history an additional case is finally analyzed to investigate the consequences of pressure solution inhibition due to diagenetic grain coating in a sandstone reservoir the simulation resulted in porosity preservation and lower overpressure values showing that a sedimentary basin submitted to an important level of chemo mechanical compaction can present substantially higher overpressure distribution than basins where this phenomenon did not take place the paper highlights the importance of integrating stresses fluid pressure and temperature to represent the porous material evolution in order to describe the geological state of sedimentary basins

temporal variation in the permeability anisotropy behavior of the malan loess in northern shaanxi province china an experimental study by analyzing a fresh soil section and soil samples from yan an new area northwest china an engineering shallow loess slope was investigated temporal variation in the saturated horizontal hydraulic conductivity kh and saturated vertical hydraulic conductivity kv of loess samples were measured using variable head permeability tests the kh and kv values indicate that the loess exhibited permeability anisotropy in space and time and kh and kv at different depths decreased as seepage time increased kh time showed an exponentially decreasing trend and kv time showed a linearly decreasing trend analysis of the initial state and micromorphological features of the loess indicate that the orientation of soil particles in the deposition process may be inherently anisotropic the kh and kv values of the loess tended to decrease with depth as described by an exponential decay model

field study of dispersion in a heterogeneous aquifer 3 geostatistical analysis of hydraulic conductivity observations of the spatial variability of hydraulic conductivity at a tracer test site located at columbus air force base in mississippi are presented direct measurements of hydraulic conductivity of the heterogeneous alluvial aquifer at the site were made using borehole flowmeter logging slug tests and a laboratory permeameter to test undisturbed soil cores indirect methods estimating hydraulic conductivity were also evaluated including soil grain size analyses surface geophysical surveys and mapping of sediment facies the spatial covariance of the 2187 hydraulic conductivity values obtained with the borehole flowmeter method was examined the log hydraulic conductivity variance ln2k and the horizontal and vertical correlation scales h and v of 4 5 12 8 m and 1 6 m respectively were estimated assuming second order stationarity of the conductivity field the covariance parameters are uncertain with bounding values that are 24 76 above or below the estimate covariance parameters estimated with more limited nonflowmeter data were within the same magnitude as those obtained using the extensive flowmeter data suggesting that data from a variety of methods may be used to provide approximate values of the autocovariance parameters nonstationarity of the ln k field was examined by removing three dimensional polynomial trend surfaces and calculating variograms of the residuals significantly lower estimates for ln2k h and v of 2 7 4 8 m and 0 8 m respectively were obtained from the third order log conductivity residuals after trend removal the bounding parameter values differ 15 44 from the estimated values accounting for unsteady flow and the uncertainty in the covariance parameters of the third order log conductivity residuals the calculated longitudinal and horizontal transverse macrodispersivities ranged from 1 5 m to 1 8 m and 0 3 m to 0 6 m respectively

anisotropy and depth related heterogeneity of hydraulic conductivity in a bog peat i laboratory measurements anisotropy and heterogeneity of hydraulic conductivity k are suspected of greatly affecting rates and patterns of ground water seepage in peats a new laboratory method termed here the modified cube method was used to measure horizontal and vertical hydraulic conductivity kh and kv of 400 samples of bog peat the new method avoids many of the problems associated with existing field and laboratory methods and is shown to give relatively precise measurements of k in the majority of samples tested kh was much greater than kv indicating that the bog peat was strongly anisotropic log10kh log10kv and log10 kh kv were found to vary significantly with depth although none of the relationships was simple we comment on the scale dependency of our measurements

enhanced porosity preservation by pore fluid overpressure and chlorite grain coatings in the triassic skagerrak central graben north sea uk current understanding of porosity preservation in deeply buried sandstone reservoirs tends to be focused on how diagenetic grain coatings of clay minerals and microquartz can inhibit macroquartz cementation however the importance of overpressure developed during initial shallow burial in maintaining high primary porosity during subsequent burial has generally not been appreciated where pore fluid pressures are high and the vertical effective stress is low the shallow arrest of compaction can allow preservation of high porosity and permeability at depths normally considered uneconomic the deeply buried fluvial sandstone reservoirs of the triassic skagerrak formation in the central graben north sea show anomalously high porosities at depths greater than 3500 metres below sea floor mbsf pore pressures can exceed 80 mpa in the upper part of the skagerrak formation at depths of 4000 5000 mbsf where temperatures are above 140 c the skagerrak reservoirs commonly have high primary porosities of up to 35 little macroquartz cement and variable amounts of diagenetic chlorite grain coats this research sheds light on the complex controls on reservoir quality in the fluvial sandstones of the skagerrak formation by identifying the role of shallow overpressure in arresting mechanical compaction and the importance of chlorite detrital grain coatings in inhibiting macroquartz cement overgrowth as temperature increases during progressive burial

an analysis of the roles of stress temperature and ph in chemical compaction of sandstones abstract chemical compaction also known as pressure solution involves dissolution along grain contacts and transport of solute to the adjacent pore space by diffusion the driving force for diffusion is a gradient in chemical potential therefore chemical compaction requires persistent gradients in chemical potential along grain contacts in order to drive diffusion continuously such gradients exist in porous rocks because of the heterogeneous distribution of stress over the grain surfaces the rate of chemical compaction depends on stress fluid pressure temperature and the composition of the pore fluid which itself depends on various processes that add or remove solute an alternative model of chemical compaction invokes the effect of sheet silicates on ph to account for localized dissolution of grains adjacent to stylolites or where sheet silicates are present along grain contacts in this model the rate of chemical compaction is independent of stress and fluid pressure depending only on temperature this model is untenable because the proposed mechanism cannot give rise to the persistent gradient in chemical potential required to drive diffusion however sheet silicates may increase the rate of chemical compaction because of their influence on dissolution and diffusion rates the development of anisotropic fabrics as a result of chemical compaction and the widespread occurrence of stylolites in carbonates as well as sandstones are inconsistent with the ph model and provide strong support for the role of stress in chemical compaction

importance of vertical effective stress for reservoir quality in the skagerrak formation central graben north sea abstract the complex fluvial sandstones of the triassic skagerrak formation are the host reservoir for a number of high pressure high temperature hpht fields in the central graben north sea all the reservoir sandstones in this study comprise of fine grained to medium grained sub arkosic to arkosic sandstones that have experienced broadly similar burial and diagenetic histories to their present day maximum burial depths despite similar diagenetic histories the fluvial reservoirs show major variations in reservoir quality and preserved porosity reservoir quality varies from excellent with anomalously high porosities of up to 35 at burial depth of 3500 m below seafloor to non economic with porosities this study has combined detailed petrographic analyses core analysis and pressure history modelling to assess the impact of differing vertical effective stresses ves and high pore fluid pressures up to 80 mpa on reservoir quality it has been recognised that fluvial channel sandstones of the skagerrak formation in the uk sector have experienced significantly less mechanical compaction than their equivalents in the norwegian sector this difference in mechanical compaction has had a significant impact upon reservoir quality even though the presence of chlorite grain coatings inhibited macroquartz cement overgrowths across all skagerrak formation reservoirs the onset of overpressure started once the overlying chalk seal was buried deeply enough to form a permeability barrier to fluid escape it is the cumulative effect of varying amounts of overpressure and its effect on the ves history that is key to determining the reservoir quality of these channelised sandstone units the results are consistent with a model where vertical effective stress affects both the compaction state and subsequent quartz cementation of the reservoirs

nd isotopic composition of jurassic tethys seawater and the genesis of alpine mn deposits evidence from sr nd isotope data jurassic metabasalts metasediments and mn ores from the pennine realm of the alps were examined in order to establish the nd isotopic composition of the jurassic tethys seawater and to elucidate the genesis of the mn deposits the highly positive initial epsilon sub nd values 7 to 9 8 of the metabasalts and their low sup 87 sr sup 86 sr ratios 0 7028 to 0 7049 indicate that they originated from a depleted mantle the initial epsilon sub nd values of the cherts range between minus 5 and minus 9 the sm nd isotope data indicate that they are primary mixtures of basalt and continental detritus the smaller than 2 mu m fractions of the cherts and of a marble which probably represent the formerly authigenic material show initial epsilon sub nd values ranging between minus 5 9 and minus 6 6 the average initial sr isotopic composition of five mn ores is 0 70730 plus minus 22 identical to that of contemporaneous jurassic seawater the initial nd isotopic composition values of the mn ores are very homogeneous the average value of five ores a leachate and residue of one of them calculated for an age of 170 ma is 0 512082 plus minus 19 it is suggested that the ores together with the smaller than 2 mu mmore fractions of the sediments define the jurassic tethys seawater isotopic composition the resulting average sup 143 nd sup 144 nd initial value is 0 512089 plus minus 17 epsilon sub nd minus 6 5 plus minus 0 6 less

the effect of oil saturation on the mechanism of compaction in granular materials higher oil saturations lead to more grain fracturing and less pressure solution abstract whether addition of oil to sandstones slows stops or has no influence upon pressure solution and quartz cementation has long been disputed despite having major implications for petroleum exploration and appraisal strategies to elucidate the effect of addition of oil to compaction pressure solution and cementation processes this study utilizes an experimental approach simulating isochemical volumetric compaction using granular halite in the presence of variable brine oil mixtures each experiment at 500 kpa effective stress lasted 48 hours and involved repeated measurements of volumetric strain the lithified products of experiments were examined using sem techniques after 30 hours approximately 4 volumetric strain occurs when the brine oil ratio is 100 0 pure brine fractures are rare in samples from experiments undertaken with pure brine so that pressure solution and concomitant cementation must be the compaction mechanism when the brine oil ratio is decreased from 100 0 to 40 60 the volumetric strain remains about 4 but there are more fractures as quantified from sem image analysis these observations suggest that although pressure solution has occurred some of the volumetric strain is the result of fracturing implying that pressure solution has been less effective in the presence of some oil than it is in the presence of pure brine when the brine oil ratio is decreased further from 40 60 to 5 95 the volumetric strain increases up to 7 3 sem image analysis reveals that the strain is predominantly due to grain fracturing this change from pressure solution to grain fracturing is likely due to heterogeneous pressure solution resulting from heterogeneous distribution of stresses brine coated grain contacts undergo pressure solution but oil coated grain contacts experience increasing stress up to the point of failure as the surrounding grain pack compacts when the brine oil ratio is decreased to less than 5 95 volumetric strain decreased to about 1 with few induced fractures and little pressure solution compaction is negligible when the brine oil ratio is 0 100 only oil in the pores and fractures are negligible halite is more water soluble and more hygroscopic than quartz so that water will cling to halite surfaces more tenaciously than to quartz since even halite has its mechanism of volumetric strain affected when the brine oil ratio is less than 40 60 quartz pressure solution and subsequent cementation is even more likely to be affected by oil filling this experimental study suggests that the mechanism and extent of compaction and subsequent cementation in sandstones is strongly affected by the addition of oil

rare earth element geochemistry of oceanic ferromanganese nodules and associated sediments abstract analyses have been made of ree contents of a well characterized suite of deep sea 4000 m principally todorokite bearing ferromanganese nodules and associated sediments from the pacific ocean ree in nodules and their sediments are closely related nodules with the largest positive ce anomalies are found on sediments with the smallest negative ce anomalies in contrast nodules with the highest contents of other rare earths 3 ree are found on sediments with the lowest 3 ree contents and vice versa 143 nd 144 nd ratios in the nodules 0 51244 point to an original seawater source but an identical ratio for sediments in combination with the ree patterns suggests that diagenetic reactions may transfer elements into the nodules analysis of biogenic phases shows that the direct contribution of plankton and carbonate and siliceous skeletal materials to ree contents of nodules and sediments is negligible inter element relationships and leaching tests suggest that ree contents are controlled by a p rich phase with a ree pattern similar to that for biogenous apatite and an fe rich phase with a pattern the mirror image of that for sea water it is proposed that 3 ree concentrations are controlled by the surface chemistry of these phases during diagenetic reactions which vary with sediment accumulation rate processes which favour the enrichment of transition metals in equatorial pacific nodules favour the depletion of 3 ree in nodules and enrichment of 3 ree in associated sediments in contrast ce appears to be added both to nodules and sediments directly from seawater and is not involved in diagenetic reactions

large scale natural gradient tracer test in sand and gravel cape cod massachusetts 3 hydraulic conductivity variability and calculated macrodispersivities hydraulic conductivity k variability in a sand and gravel aquifer on cape cod massachusetts was measured and subsequently used in stochastic transport theories to estimate macrodispersivities nearly 1500 k measurements were obtained by borehole flowmeter tests and permeameter analyses of cores the geometric mean for the flowmeter tests 0 11 cm s is similar to that estimated from other field tests the mean for the permeameter tests 0 035 cm s is significantly lower possibly because of compaction of the cores the variance for the flowmeter 0 24 is also greater than that for the permeameter 0 14 geostatistical analyses applying negative exponential models with and without nuggets reveal similar spatial correlation structures for the two data sets estimated correlation scales range from 2 9 to 8 m in the horizontal and from 0 18 to 0 38 m in the vertical estimates of asymptotic longitudinal dispersivity b 35 0 78 m are similar in magnitude to that observed in the natural gradient tracer test 0 96 m previously conducted at this site

nd isotope evidence for the evolution of the paleocurrents in the atlantic and tethys oceans during the past 180 ma the nd isotopic composition of atlantic and tethys seawater as deduced from marine phosphorites varied considerably during the past 180 ma the early tethys and central atlantic seawater from 180 to 160 ma ago early middle jurassic had a nd isotopic signature identical to that of the pacific end 6 suggesting that pacific seawater entered the newly forming tethys basin however with time continental runoff draining into the young basin became more important and led to a decrease in the nd isotopic composition and finally a decoupling from the pacific ocean during the late early cretaceous 120 90 ma ago atlantic and tethys seawater reached continental crust like nd isotopic composition values end 10 which could reflect high weathering rates induced by the warm and humid climate at that time in the time span between 80 and 50 ma late cretaceous early tertiary the nd isotopic composition of both tethys and atlantic seawater strongly increased towards pacific seawater values in the case of the atlantic ocean this change has been correlated with the opening of the south atlantic which enabled the more radiogenic pacific seawater to travel westwards around the southern edge of africa into the south and finally the north atlantic in the case of tethys seawater we have to assume that during this period large masses of pacific seawater entered the tethys again directly through the indian tethys seaway the renewed importance of this seaway might be related to the late cretaceous early tertiary first order global sea level highstand the most abrupt change towards lower more crust like values occurred in the early miocene 25 17 ma ago in the south and north atlantic as well as in the tethys during this period the143nd 144nd isotope ratios dropped from 0 5124 end 4 2 down to 0 5122 end 8 this change indicates a diminishing influx of pacif seawater into the atlantic and tethys oceans and can be correlated with the breakdown of the circum equatorial circulation patterns of the world oceans due to plate tectonics from 20 to 17 ma ago miocene the nd isotopic composition of the atlantic ocean increased again and reached values as high as 0 5123 end 6 6 whereas tethys seawater remained at low values this decoupling can be correlated with the incipient complete isolation of the tethys the nd isotopic composition was henceforth controlled by the continental runoff from surrounding land masses the major increase in the nd isotopic composition observed in the atlantic can be related to the opening of the drake passage and establishment of the circum antarctic current system this allowed pacific seawater to enter directly the south atlantic around antarctica a renewed drop in the nd isotopic composition of atlantic seawater during the late miocene can be related to the onset of north atlantic bottom water formation and its subsequent upwelling