tectono sedimentary evolution of the bowland basin n england during the dinantian the bowland basin is a ne sw trending sedimentary basin lying between the askrigg bowland high to the n and nw and the central pennine high to the se the basin was initiated in late devonian tournaisian times sediment thickness and facies variations within the dinantian succession show marked asymmetry on both a basin wide and intra basin scale as a result of approximate nw se to n s extension across normal faults thickening of the sedimentary sequence from ne to sw over much of the basin resulted from fault controlled extension along the se margin of the basin with downthrow to the nw giving the basin a half graben character extension occurred in two distinct episodes marked by basin wide debris flow and sedimentary slide slump deposits during the late chadian early arundian the simple half graben became modified by a series of ne sw trending antithetic and nw se trending transfer faults associated with local unconformities and marked lateral thickness and facies variations this interval marks the transition from carbonate ramp to slope sedimentation and a temporary halt in carbonate supply to the basin the second episode of extension the late asbian early brigantian marks the break up of the northern basin margin ending major carbonate deposition within the basin reactivation of these structures at the end of the carboniferous created the ribblesdale fold belt as a result of nw se to n s compression transpression application of this research to areas surrounding the bowland basin has led to the recognition of additional shelf basins the orientation of which suggests control by normal and transfer fault systems discussion and

a coal depositional model for the durham coal measures of ne england the upper carboniferous westphalian coal measures of the durham coalfield were deposited on a broad flat deltaic plain in early westphalian a times a lower delta plain setting prevailed evolving through southward deltaic progradation into an upper delta plain by mid westphalian a detailed facies analysis of large opencast exposures supported by extensive subsurface data has shown that a hierarchy of depositional controls operated across the durham area during westphalian times i on the large scale depositional geometry was controlled by patterns of major delta progradation and switching ii on the medium scale by a combination of structurally and compactionally induced subsidence and iii on the small scale by local sedimentary processes and subsidence patterns these observations form the basis of a coal depositional model for the durham coal measures which predicts that the thickest coals are to be found in upper delta plain domains controlled by compactional subsidence and not underlain by substantial channel sandstones this model may also be applicable to other coalfields of northern england and to ancient delta plain sequences elsewhere in the world

overview of the influence of syn sedimentary tectonics and palaeo fluvial systems on coal seam and sand body characteristics in the westphalian c strata campine basin belgium

a physical explanation of the relation between flank uplifts and the breakup unconformity at rifted continental margins rift flank uplifts and the breakup or postrift unconformity are characteristic features of many rifted passive or atlantic type continental margins but are not predicted as primary features of simple lithospheric stretching models the explanations that have been proposed for their origin remain controversial either because they call upon special circumstances or because they are difficult to test plane strain finite element models are used in this paper to explore the dynamics of lithospheric necking during rifting and rupture the results agree with the conceptual interpretation that uplift of the rift boundaries to form flank mountains and uplift of the basin responsible for the breakup unconformity are related consequences of regional isostatic compensation of mass that is redistributed during the necking and rupture phases although the amplitudes of these uplifts depend on the model parameter values the relations between and relative signs of these two effects appear to be fundamental the explanation we propose may have been missed in recent studies because there has been a tendency to concentrate on kinematic stretching models which assume local isostatic equilibrium through out the rifting process such an approach is predicated on the assumption that the lithosphere has an insignificant strength or flexural rigidity during extension which is not true if our explanation is correct

grain boundary sliding and development of grain boundary openings in experimentally deformed octachloropropane abstract in situ observations of grain boundary sliding and associated accommodation mechanisms in experimentally pure and simple sheared octachloropropane at 75 85 of its absolute melting temperature and at strain rates of 10 5 10 6 s 1 are discussed discontinuities in the strain rotation and or translation components of deformation across the grain boundary induce grain boundary sliding the influence of crystallographic orientation of grains on grain boundary sliding is so strong that grains unfavorably oriented for basal slip contribute to deformation mainly by grain boundary sliding grain boundary diffusion and intragranular plastic deformation are observed to accommodate grain boundary sliding grain boundary diffusion also causes grain boundary migration types ii and iii that is different from conventional grain boundary migration type i in being non conservative and in the details of boundary movement with respect to material points within grains grain boundary openings filled with fluid octachloropropane vapor are strongly associated with grain boundary sliding openings develop preferentially along grain boundaries at low angles to the shortening direction once openings grow they are closed by thrusting of sliding grains and by diffusion in faster strain rate experiments and entirely by diffusion in slower strain rate experiments an approximately steady openings ratio of 0 5 3 of the sample volume persists without the development of any large scale fracture all grain boundary openings disappear during static readjustment of the microstructure after deformation

upper limits of power law creep of rocks at depths below a few kilometers most rocks probably flow in the steady state dominantly by diffusion assisted dislocation creep mechanisms whereby strain rate is proportional to a low power of deviatoric stress at high stress levels for metals ceramics and rocks the power law breaks down plb to some other strain rate stress functional relationship and this paper explores four methods by which the breakdown stress b may be estimated for metals alloys and ceramics b 10 3 for non silicate rocks b 5 10 3 and for silicates b 10 2 for silicates the low stress exponent power law breaks down at high stresses to an exponential dependence of strain rate upon stress or to a dorn law the governing flow mechanisms generally being lattice resistance controlled dislocation glide and mechanical twinning plb breakdown stresses for silicates are nearly strain rate insensitive and extrapolated values of b are so high as to suggest that low temperature high stress plasticity may be suppressed entirely in geological deformations plb for olivine rich rocks is discussed in some detail and new three dimensional deformation mechanism surfaces for wet and dry olivine polycrystals are presented

crustal kinematics and deep structure of the northern rhine graben germany surface and subsurface geological data unpublished information gleaned from industrial seismic surveys and results from a deep reflection seismic profile across the tertiary northern rhine graben indicate that crustal extension in excess of 6 km was achieved by asymmetric detachment of the upper crust at a depth of about 15 km comparison of a simple geometric kinematic cross sectional model and its depth extrapolation with the dekorp 9 n deep crustal reflection data suggests that extension below the graben was achieved by slip along a gently westward dipping shear zone which truncated and offset lower crustal planar fabrics and which continues into the uppermost mantle the planar lower crustal reflectors probably originated mainly during late variscan permocarboniferous crustal extension and or magmatic underplating

multifractal analysis of the pore space of real and simulated sedimentary rocks it is well known that sedimentary rocks having same porosity can have very different pore size distribution the pore distribution determines many characteristics of the rock among which its transport properties are often the most useful multifractal analysis is a powerful tool that is increasingly used to characterize the pore space in this study we performed multifractal analysis of pore distribution on simulated sedimentary rocks using the relaxed bidisperse ballistic deposition model rbbdm the rbbdm can generate a 3 d structure of sedimentary rocks of variable porosity by tuning the fraction p of particles of two different sizes we also performed multifractal analysis on two samples of real sedimentary rock to compare with the simulation studies one sample an oolitic limestone is of high porosity 40 per cent while the other is a reefal carbonate of low porosity around 7 per cent 2 d sections of x ray microtomographs of the real rocks were stacked sequentially to reconstruct the real rock specimens both samples show multifractal character the results from analysis of real rock agree quite well with the simulated structure of low porosity the simulated rock of high porosity showed a weak multifractal nature though the real rock sample of similar porosity was found to be strongly multifractal we propose a structure parameter which is a function of porosity and the generalized dimensions and controls the transport properties of the rock

fractal measurements of sandstones shales and carbonates measurements were made of the fractal properties of sandstones shales and carbonates using a statistical analysis of structural features on fracture surfaces fractal behavior is associated with power law behavior for the number of features as a function of the feature size on the pore rock interface only one sedimentary rock a novaculite was found not to have a fractal structure the fractal dimensions range from 2 27 to 2 89 and the long length limits to the fractal regime range from 2 m to over 50 m in all cases the fractal behavior extends to less than 0 2 m which is the measurement resolution the porosity associated with the fractal pore rock interface can be calculated from the fractal parameters some of the samples have additional porosity not associated with power law behavior photographs and other evidence are used to show that the fractal structures are the result of diagenesis fractal diagenetic structures include euhedral quartz overgrowths druse quartz calcite dolomite clays and chert

porosity and permeability changes in sedimentary rocks induced by injection of reactive fluid a simulation model summary numerical programs for simulating flow and reactive transport in porous media is essential for predicting reservoir properties related to co 2 sequestration performance subsurface storage and risk assessment in this paper we solve the navier stokes equation using finite difference method on a simulated porous rock structure to study the velocity distribution of fluid flowing through it under a constant pressure gradient a reactive solute carried through the fluid is allowed to interact with the minerals in the rock this chemical reaction dissolves the mineral which changes the rock structure thus affecting its flow properties these changes of flow properties are studied with variation in reactive solute concentration and pressure field the different mechanisms of dissolution responsible for the variation of flow properties for the different parameters is predicted before the onset of homogeneous dissolution variation in porosity follows a power law behaviour with change in permeability when the latter is scaled by the concentration of the reactive species the simulation results are compared with available experimental data and found to give a reasonable match

relationships between dynamically recrystallized grain size and deformation conditions in experimentally deformed olivine rocks new microstructural data on experimentally deformed wet and dry natural olivine rocks anita bay and aheim dunite together with the other reliable experimental data indicate that the experimental stress recrystallized grain size relationship in olivine rocks is largely independent of water content and temperature and is only slightly dependent on the flow properties of the material the experimental data cover a stress range of 30 300 mpa water contents from 30 ppm to 300 ppm and temperatures in the range 1100 1650 c local melt contents of up to 10 volume cannot be demonstrated to have a significant effect on the stress grain size relationship

3d digital rock modeling of the fractal properties of pore structures abstract fractal parameters of porous media have been a focus of study in petroleum engineering and hydrogeology for several decades because they provide an effective way to describe the complexity of pore structure across a wide range of scales this paper combines 3d process driven digital rock modeling with fractal analysis in order to understand the effect of varying sorting compaction cementation and the fine grain fraction of binary models on the fractal parameters and specific surface area of porous media digital rock models drms were constructed to simulate sandstone using a process driven modeling technique which simulates sedimentation the fractal parameters of the resulting pore geometry were calculated using the box counting method on 2d and 3d representations of the drms our simulations indicate that increasing compaction or cementation lead to significant decreases in fractal dimension specific surface area ssp and porosity showing that these two diagenetic processes can affect the pore microstructure of the rock significantly while interface fractal dimension di and ssp both increase slightly with decreases in sorting grain size variety and porosity decreases slightly examining the behavior of binary models the porosity of our digital models shows a v shaped curve as fine grain fraction increases from 0 to 1 consistent with but higher than the theoretical values which we attribute to incomplete packing of the grains arising from the simplified packing algorithm and finite boundary of models the value of both ssp and di increase as the fine grain fraction increases however we must notice that the porosity may be underestimated and the fractal dimension may be overestimated when we use models consisting of very fine spherical grains due to the effect of image resolution

reflections from mantle fault zones around the british isles british institutions reflection profiling syndicate birps deep seismic reflection surveys show that the upper mantle around the british isles is reflective exhibiting discrete isolated reflecting zones within an otherwise seismically transparent mantle there are 20 known occurrences of reflectors within the upper mantle across the continental shelf of the british isles many delimited by intersecting or closely spaced profiles most of the mantle reflectors have similar reflection characteristics they dip 10 degree to 30 degree and are thin approximately 0 5 s approximately 2 km and discrete the geologic history of the continental shelf around the british isles an area 1000 x 1000 km is complex and the tectonic settings of these reflectors very each mantel reflector is associated with a major zone of deformation in the crust this association the dips of the reflectors and their high reflectivity all indicate a structural origin the birps mantle reflectors include probable early paleozoic thrusts and mesozoic normal faults in contrast to birps data deep reflection profiles in other areas of the world in a variety of geologic settings have only rarely imaged reflectors within the upper mantle

experimental deformation of a synthetic dunite at high temperature and pressure i mechanical behavior optical microstructure and deformation mechanism abstract we have performed a series of 27 deformation experiments on a very dry synthetic dunite using the griggs solid medium apparatus strain rates ranged from 1 10 4 to 1 10 7 sec 1 temperatures varied from 1100 to 1300 c and the confining pressure was maintained at 10 or more usually 15 kbar macor im a commercially available anhydrous machinable glass ceramic with a low melting point was used in many of the experiments we find that strength measurements performed using macor as a confining medium are similar to results obtained using sodium chloride as the confining solid tests performed in undried sample assemblies using air dried dunite specimens resulted in creep strengths greater than those found in any earlier studies except those of post 1973 1977 a single test on a sample for which both sample and assembly were dried at a temperature sufficiently high to drive off any adsorbed water resulted in a creep strength comparable to that determined by post 1973 1977 for very dry mt burnett dunite despite our experimental difficulties we are led to believe that our synthetic dunite exhibits mechanical behavior consistent with that determined in other experimental studies in which natural dunites and peridotites were used furthermore we conclude that dry dunite is very probably as strong as the oft disputed results of post earlier indicated finally we show that the optical textures of our highly recrystallized experimental specimens are essentially identical to naturally produced porphyroclastic textures and that the deformation mechanism in both the experimental and natural specimens is probably dislocation creep with recovery by dynamic recrystallization

uk onshore oil exploration 1930 1964 abstract the earliest attempts to find oil in britain dating from 1918 1922 based on anticlines flanking the pennines were largely unsuccessful renewal of exploration in the 1930s aimed at a broader range of prospects met with much criticism but went ahead after nationalization of the unknown and undiscovered oil resources 1934 the south of england ranked as first priority but the initial drilling of the new campaign carried out in 1935 1937 yielded only minor quantities of oil and gas attention was transferred in 1938 to upper palaeozoic prospects in the midlands and north resulting in small gas and oil discoveries in scotland and yorkshire and discovery of a series of commerical oilfields in the upper carboniferous of nottinghamshire in the 1950s the first commercial discovery in the jurassic was made at kimmeridge in dorset further carboniferous discoveries were made in nottinghamshire and lincolnshire and a series of fresh objectives defined by seismic reflection were drilled in the mesozoic basin of southern england this phase of exploration was terminated at the end of 1964 by adverse fiscal changes continuation of effective exploration operations remained uneconomic until the oil price rise in 1973

geophysical evidence for thick skinned crustal deformation in central australia until now there has been no clear evidence from deep seismic reflection profiles of crustal faults that displace the moho new data from central australia show such a structure in a region characterized by large thrust structures large gravity anomalies and abrupt changes in teleseismic travel times here the principal thrust the redbank deformed zone cuts through the crust and the moho is significantly displaced across it the geological and geophysical evidence leads to a model of thick skinned crustal deformation which occurred in an intra cratonic environment in late devonian time

late yeadonian upper sandstone group incised valley supply and depositional systems in the south wales peripheral foreland basin implications for the evolution of the culm basin and for the silesian hydrocarbon plays of onshore and offshore uk abstract the upper sandstone group of south wales has previously been interpreted as a simple nnw sse trending incised valley that was filled during the late yeadonian namurian g1b data presented in this study indicate a far more complex scenario the group is well developed in the pembrokeshire sub basin but it is absent from the main part of the south wales basin located to the east of the penlan axis the principal source area for sediment flux was the forebulge of the basin located to the north in lower palaeozoic foreland strata variscan flexural uplift of this source area and an accompanying rapid high magnitude fall in sea level produced a very high sediment budget thus during the late yeadonian lowstand of sea level massive amounts of sediment were being generated and transported via an incised valley system across the western part of the south wales peripheral foreland basin the location and orientation of the incised supply system and its related interfluves were controlled by intrabasinal synsedimentary variscan structures many of which were reactivated caledonian extensional faults during the succeeding sea level rise the incised valley was filled initially by fluvio deltaic sands and later by estuarine argillaceous sediments the implications of this combined tectonic sedimentological high resolution sequence stratigraphic model for the evolution of the late namurian crackington formation turbidites of the culm basin are discussed examples of silesian incised valley fill sandstone reservoirs developed in the east midlands oilfield and the southern gas basin are briefly summarised and their spatial and temporal distributions are appraised data generated from these case studies are assessed in terms of their use for the modelling of incised valley fill sequences in foreland basins and other tectonic settings

microscopic pore structures of tight sandstone reservoirs and their diagenetic controls a case study of the upper triassic xujiahe formation of the western sichuan depression china abstract the study of microscopic pore structures is of central significance to the evaluation of the reservoir quality and well productivity of tight gas sandstone the second and fourth members abbreviated as t3x2 and t3x4 respectively of the upper triassic xujiahe formation of the western sichuan depression were used as cases to analyze microscopic pore structures and diagenetic controls in consideration of the disparities in reservoir quality and well productivity optical microscopy of thin sections micro ct scanning scanning electron microscopy sem high pressure mercury injection hpmi and apex methods based on the hpmi results were used to determine the pore and throat geometries and the types and pore size distributions in terms of the quantity and levels of pore connectivity tight sandstone reservoirs of the study area are characterized by poor physical properties with the t3x2 reservoirs presenting relatively higher levels of permeability and lower porosity levels than those of the t3x4 reservoirs the pore spacing configurations sizes and distributions and throat geometries reveal significant disparities primary pores and micro fractures were found to be more developed in the t3x2 reservoirs with bending and narrow pore throats measured as smaller than 0 5 m compared to those of the t3x2 reservoirs secondary pores including moldic and intracrystalline pores were more developed in the t3x4 reservoirs with relatively larger straighter and wider throats of 0 5 1 0 m an evaluation of the pore connectivity levels shows that only 26 86 and 28 90 pores are closely connected to the whole for t3x2 and t3x4 reservoirs respectively four major diagenetic processes were found to control reservoir quality and the microscopic pore structure mechanical compaction is the primary cause of the densification of reservoirs in the study area compared to that observed in the t3x4 reservoirs more intensive mechanical compaction was observed in the t3x2 reservoirs changing the configuration of the throats present reducing the pore throat radii and ultimately lowering the porosity of t3x2 reservoirs as a whole quartz overgrowth and late period carbonate cements were observed in partly filled pore spaces narrowing throats and reducing pore connectivity but eogenetic cementation and chlorite cements can increase the pressure resistance of sandstone and inhibit compaction quartz overgrowth thus t3x4 reservoirs are relatively more porous as a result of eogenetic calcite cementation and primary pores are more developed in t3x2 reservoirs with chlorite cements dissolution is a major factor that improves the tight sandstone reservoir quality because it generates a large volume of secondary pores the more intensive levels of dissolution in t3x4 reservoirs not only creates more intergranular intragranular moldic and intracrystalline pores but also further increases the porosity of t3x4 reservoirs fracturing effects have developed in the study area to improve pore connectivity levels and thus the permeability of tight sandstone reservoirs potentially explaining the pore connectivity and permeability of certain t3x2 reservoirs this work may be able to be used as a useful reference for the reservoir quality evaluation and exploration of tight gas sandstone reservoirs for similar oil fields worldwide

the structure and evolution of the northumberland trough from new seismic reflection data and its bearing on modes of continental extension an 18 km long n s seismic reflection profile has been acquired across the faulted boundary between the alston block and the northumberland trough a nw se geological cross section has been constructed across the trough by integrating this line with other data and a tricentrol seismic profile confirms the suitability of this model the trough has a markedly asymmetric form with a thickness of more than 4 2 km of dinantian strata adjacent to its faulted southern margin the present day surface faults stublick ninety fathom are related to variscan and later inversion and transpression and do not everywhere correspond precisely to the earlier syn depositional normal faults the basin is believed to have formed in response to reactivation of the iapetus suture in a dominantly n s extensional stress field basin evolution has been analysed by fault restorations and subsidence modelling the fault restorations indicate an upper crustal extension factor of 1 15 to 1 19 subsidence modelling indicates a whole crustal extension factor of 1 30 with similar sub crustal lithospheric extension it is possible that the difference between the inferred extension factors is due to non uniform increasing downwards lithospheric extension but the uncertainties inherent in both methods are such that this cannot yet be confirmed

the experimental deformation of dunite deformation experiments have been carried out on two dunites anita bay of 100 m grain size and aheim of 900 m grain size at strain rates from 10 3 to 10 6 s 1 and temperatures from 1000 c to 1300 c in a gas medium deformation apparatus at 300 mpa confining pressure most of the tests were under wet conditions defined by the presence of small amounts of water from hydrous minerals initially present constant strain rate and relaxation experiments covering ranges of flow stress down to about 70 mpa and 7 mpa respectively show that there is a change in flow law in going below about 100 mpa differential stress and that the coarser grained rock is stronger than the finer grained one power law parameters above the transition are n 4 48 0 31 and q 498 38 kj mol 1 for aheim dunite and n 3 35 0 17 and q 444 24 kj mol 1 for anita bay dunite while below the transition relaxation tests on anita bay dunite give n 2 44 0 18 and q 386 27 kj mol 1 it is concluded that there is a weakening effect of water that this effect is mainly in the grain boundaries and that grain boundary sliding is probably a significant deformation mechanism at the lower stresses under wet conditions

simulation of diagenesis and permeability variation in two dimensional rock structure summary a model is suggested to simulate the physical aspect of diagenesis in porous rocks a bidisperse ballistic deposition model with relaxation of deposited grains is used to generate the porous structure sedimentation and erosion are allowed to restructure the pore space as a fluid flows through the rock the effect of this restructuring of the pore space on permeability is studied the navier stokes equation is solved numerically by the finite difference method to determine the pressure and velocity distributions in the pore space we find that though deposition is the dominant process in our model of diagenesis reducing the porosity the permeability may increase dramatically in some cases these are when the erosion takes place at a single narrow constriction in the pore channel

the vibroseis system a high frequency tool exploration methods are extended to their limits as we continue the search for energy resources successful application of high frequency seismic method requires evaluating each element in the seismic acquisition system and ensuring that each part of the system contributes to the success of the method this extends from seismic signal generation through data processing where good equipment performance and correct parameter selections are required the vibroseis system depends upon the ability of vibrators to generate synchronous repeatable sweeps over the frequency range of interest to support our high frequency seismic efforts conoco inc has developed and built a new high frequency vibrator this paper includes some of the consideration used in building the vibrator along with typical baseplate responses showing excellent drive levels to the design goal of 200 hz with an excellent source available correct application is essential to assure retention of high frequency data recording offsets ar

fractal geometry of sedimentary rocks simulation in 3 d using a relaxed bidisperse ballistic deposition model several studies both theoretical and experimental show that sedimentary rocks have a fractal pore grain interface in this paper a computer simulated 3 d sedimentary rock structure generated by the relaxed ballistic bidisperse deposition model rbbdm is investigated to characterize the micro structure of its pores the pore volume and the rock pore interface show the same fractal dimension indicating that the pore volume is a fractal the two point density correlation is computed for the pore space and the results compare favourably with the range reported from experiments an array of 2 d x ray tomography micrograph sections of a real sedimentary rock an oolitic limestone pure calcite from the mondeville formation of middle jurassic age paris basin france was used to generate a 3 d bitmap the 3 d real rock sample generated in this manner was analysed for similar studies as the simulated structure the results were compared with those obtained from simulation the simulation results agree qualitatively with the real rock sample diffusion through the connected pore space of the simulated structure was studied using a random walk algorithm and the results compared with the similar simulation study done on the 3 d oolitic limestone specimen in both cases diffusion was found to be anomalous indicating that the sedimentary rock has a fractal geometry the favourable comparability of results between the simulated and real rock supports the usefulness of the model of sedimentary rock generation which can be applicable to transport phenomena

flow behavior of fine grained synthetic dunite in the presence of 0 5 wt h2o the deformation behavior of synthetic dunite mg forsterite plus 2 5 vol enstatite with a grain size of 1 m has been investigated in combined constant displacement rate and temperature stepping experiments at temperatures of 850 to 1000 c strain rates of 10 7 to 10 5 s 1 and a confining pressure of 600 mpa nominally dry material behaved purely elastically in contrast samples with 0 5 wt added water flowed at stresses between 9 and 81 mpa reaching strains up to 12 fitting a dorn type power law to the wet data yielded stress exponents n of 1 7 0 4 and apparent activation energies in the range 302 22 kj mol 1 the wet deformed samples showed polygonal grains no crystallographic preferred orientation no subgrains low dislocation densities and evidence for grain boundary cavitation grain growth was minor it is concluded that the wet samples probably deformed by a grain size sensitive grain boundary sliding dominated mechanism though the nature of the accommodation process remains unclear and the possibility of transitional behavior between dislocation creep and diffusion creep cannot be eliminated application of the results to upper mantle shear zones supports previous speculation that the presence of such zones can lead to a significant weakening of the top 10 to 20 km of the upper mantle during extension of the continental lithosphere

seismic facies analysis of westphalian sequences of the southern north sea abstract differing seismic facies are observed from within the westphalian sequences of the southern north sea a review of published synthetic seismograms and seismic data from known coal bearing basins establishes seismic facies types and their relationships similar reflection character is recognized from westphalian sequences in the southern north sea and lithologies confirmed by borehole information probable sand silt or clastic prone upper coal measures westphalian c d stages and coal prone lower and middle coal measures westphalian a b and part c stages can be defined and mapped providing information on the regional distribution of source and reservoir rocks and stratigraphic plays it is suggested that sand prone channel complexes or clastic dominated areas within the mainly a b stages can be recognized and mapped providing information on migration pathways and stratigraphic plays

short paper evidence of negative structural inversion beneath central england from new seismic reflection data a major seismic reflection transect acquired by the british geological survey between 1984 and 1986 has elucidated the deep geology and structure of some well known surface features of central england the worcester basin a mesozoic extensional graben system is bounded to west and east by major sub planar normal faults which formed by the extensional reactivation of much older structures respectively the malvern axis and a similar though concealed structure forming its mirror image to the east within the worcester basin a thick permo triassic sequence rests directly upon precambrian basement rocks to the west and east permo triassic rocks are thin or absent but relatively thick palaeozoic sequences are preserved above the precambrian these strikingly different successions together with the fault geometry suggest that the worcester basin lies within a major inverted oblique slip fault system or flower structure in palaeozoic times transpressivt stresses led to reverse faulting along the malvern axis and its complementary structure to the east with consequent regional uplift of the intervening tract and the formation of a positive flower structure in permian and early mesozoic times transtensional stresses caused collapse and negative inversion of the flower structure and consequent subsidence of the worcester basin

shear localisation in upper mantle peridotites upper mantle peridotite bodies at the earth s surface contain relict structures and microstructures which provide direct information on the role and the mechanisms of shear localisation in the upper mantle deformation which occurred at high temperatures t 950 50 c is relatively homogeneous within domains ranging in scale from a few kilometres to a few tens of kilometres below 950 50 c strain is localised into centimetre to several hundred metre wide shear zones which commonly contain hydrated mylonitic peridotites the microstructures developed in the peridotites suggest there is a correlation between the occurrence of shear localisation and the occurrence of strain softening and brittle deformation processes the most important strain softening processes are inferred to be structural and reaction induced softening structural softening processes include dynamic recrystallisation and strain induced transitions from dislocation creep to some form of grain size sensitive gss creep reaction induced softening is related to the formation of fine grained polyphase reaction products which deform by gss creep and the formation of weak sheet silicates such as phlogopite chlorite talc and antigorite from experimental studies these softening processes and brittle deformation processes are inferred to occur mainly at temperatures less than about 910 160 c this temperature range is inferred to be a significant rheological transition in the upper mantle below 910 160 c deformation during orogenesis may be accommodated by an anastomosing network of hydrated mylonitic shear zones with a distinct perhaps weak rheology at higher temperatures strain is accommodated in much wider deformation zones

a simulation study of reactive flow in 2 d involving dissolution and precipitation in sedimentary rocks in this paper we solve the navier stokes equation using finite difference method on a simulated porous rock structure in 2 d to study the velocity distribution of fluid flowing through it under a constant pressure gradient a reactive solute carried through the fluid is allowed to interact with the minerals in the rock depending on the rock composition both dissolution and precipitation reactions may occur however precipitation occurs only through the cations that are released in the solution due to dissolution these combined dissolution precipitation reactions change the porosity permeability and pore geometry of the sedimentary rock we study the temporal changes of these properties as functions of peclet number concentration of the reactive solute and ratio of damkholer numbers of dissolution to precipitation the final flow property is decided by a combination of these parameters

detachment faulting and the evolution of passive continental margins major detachment faults play a key role in the lithospheric extension process in the basin and range province and may also be important in other continental extension terranes such detachment faulting leads to an inherent asymmetry of extensional structure and of uplift subsidence patterns detachment models developed for the formation of metamorphic core complexes can also be applied to the formation of passive continental margins we therefore suggest the existence of upper plate and lower plate passive margins these give rise to a complementary asymmetry of opposing margins after continental breakup transfer faults offset marginal features and allow margins to switch from upper plate to lower plate characteristics along strike

simple kinetic models of petroleum formation part i oil and gas generation from kerogen modern basin analysis uses kinetic models to predict the extent of petroleum generation within potential source rocks the global kinetic model presented here assigns kinetic parameters based on gross depositional environment and stratigraphic age this is useful in areas of low geochemical knowledge including exploration frontiers five kerogen kinetic organofacies each characterized by a specific organic matter input and early diagenetic overprint can broadly be related to sedimentary facies age associations even using seismic sequence stratigraphy alone a aquatic marine siliceous or carbonate evaporite any age b aquatic marine siliciclastic any age c aquatic non marine lacustrine phanerozoic d e terrigenous non marine ever wet coastal mesozoic and younger and f terrigenous non marine coastal late palaeozoic and younger routine pyrolysis data allow partitioning of organic carbon in the immature source rock into four initial components oil oil generative gas generative and inert separate kinetic parameters for the oil and gas generative fractions allow computation of the evolving concentration and composition of the products it was assumed that the activation energy distributions for each fraction were normally distributed non linear regression of large combined laboratory and field data sets varying by up to 12 orders of magnitude in heating rate established optimum values for the required ten 5 2 kinetic parameter sets a emean e differences in kinetic parameters can be reconciled with known chemical properties although our knowledge base is still inadequate to construct kinetic models from first principles mean activation energies governing oil generation increase systematically in the order a f causing a corresponding increase in generation temperature at a reference heating rate 2 c ma 1 the oil generation window 10 90 oil generative kerogen degraded increases from ca 95 135 c to 145 175 c organofacies c has the tightest energy distribution and narrowest oil generation window the gas generation window ranges from ca 105 155 c to 175 220 c thermal stress results from a combination of temperature and time an order of magnitude increase decrease in heating rate elevates depresses reaction temperatures by ca 15 c heating rates in subsiding sedimentary basins can vary by two orders of magnitude dramatic differences in generation temperature can result if the heating rate and organofacies effects compound thus global oil and gas generation temperature thresholds constitute blunt instruments with which to screen the petroleum potential of sedimentary basins because unexpelled oil provides a potential feedstock for oil to gas cracking in the source rock quantitative models of petroleum generation become really useful only when coupled with models of oil gas cracking and expulsion for example the frequently observed association between gas provinces and coals cannot be explained solely by their generation behaviour

the seismic attenuation structure of a fast spreading mid ocean ridge the two dimensional p wave attenuation structure of the axial crust of the east pacific rise was obtained from an inversion of waveform spectra collected during an active source seismic tomography experiment the structure shows that attenuation near the surface is high everywhere but decreases markedly within 1 to 3 kilometers of the rise axis the near axis variation is attributed to the thickening of the surface basalt layer and possibly to in situ changes in porosity related to hydrothermal circulation high attenuation is also observed beneath the rise axis at depths ranging from about 2 kilometers less than 1 kilometer beneath the axial magma lens to the base of the crust the levels of attenuation in this deeper region require at most only a small fraction of partial melt

upper palaeozoic basins of the british isles caledonide inheritance versus hercynian plate margin processes hypotheses to explain the origin and location of upper palaeozoic sedimentary basins are presented group a basins were those old red sandstone basins whose location and subsidence were controlled by caledonide features including active and remnant fore arc basins midland valley and major transcurrent movements orcadian basin newer granite plutonic magmas in the southern uplands subduction complex post dated subduction and resulted from post collision cratonization processes as yet little understood group b basins were those whose initial positions in space were controlled by palaeo plate factors in particular the location of granitoid plutons but whose subsidence was controlled by active hercynian neoplate processes some group a basins were regenerated by this process midland valley a new hypothesis is presented to account for the origin of a carboniferous rift to sag trend similar to that proven in modern continental margin basins such as the north sea the hypothesis is an adaptation of mckenzie9s lithospheric stretching model some of whose major features are well shown in the carboniferous history of the north and central british isles group b processes were controlled by ligurian bretonic plate consumption in the s brittany massif central vosges areas group c basins in the rheno hercynian zone also owe their location and origin to back arc rifting and continental crustal oceanization processes caused by liguro bretonic subduction

effects of mineral spatial distribution on reaction rates in porous media 1 this study examined the effects of variations in mineral spatial distributions on reaction rates in porous media pore scale network models were constructed to represent sandstones with anorthite and kaolinite present in various amounts and in different spatial patterns simulation conditions corresponded to geological sequestration of carbon dioxide to examine scaling effects arising from pore scale heterogeneities reaction rates from network models were compared to rates from continuum models that use uniform concentrations with small percentages of reactive minerals the scaling effects are large and the effect of spatial distribution is significant scaling effects are largest when reactive minerals are closely clustered and oriented parallel to flow conversely spatial distributions that enhance mass transport to and from reactive minerals such as small mineral clusters or elongated clusters oriented transverse to flow result in reaction rates that are well represented by the continuum model

initiation of asymmetric extension in continental lithosphere govers r and wortel m r 1993 initiation of asymmetric extension in continental lithosphere in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 x 96 the physical conditions are investigated under which the lithospheric scale style of extension is pure shear or simple shear we focus on the initial stages of continental extension to monitor how symmetric or asymmetric modes of extension evolve from specific tectonic conditions continental collision magma intrusions and interaction between the lithosphere and the underlying mantle are investigated as sources for extension we use a finite element method to model the thermo mechanical evolution of continental lithosphere experimental flow laws are used to model the elastic hutle power law creep or diffusion creep rheology of lithospheric rocks our results indicate that if in plane forces change from compressive to tensile immediately after a rapid mountain building phase initiation of a lithosphere scale detachment fault is possible we find a strong dependence of the extensional style on the distribution with depth of residual stresses from the collision phase this result is consistent with observations of gravitational collapse in regions like the aegean and the basin and range province where detachment faults have exhumed lower crustal rocks the predicted dip direction of the fault also agrees with observations in these areas intrusion of magma into continental lithosphere which is subject io in plane tensile forces will cause localization of pure shear deformation the style of deformation resulting from mantle plumes impinging to the base of the lithosphere is symmetric delamination of lithospheric mantle may initiate detachment faults if delamination occurs at the end of a collision phase when in plane forces change sign from compressive to tenstle this result also strongly depends on the assumed residual stress distribution if delamination occurs during the mountam huilding phase the style of deformation will be pure shear another interesting outcome from our modeling is that dramatic strain weakening as a result of a deformation mechanism change from dislocation creep to diffusion creep reduces the tendency to strain localization a large volume of the published work on continental extension has been concentrated on quantifying the stretching factor p of the pure shear model of mckenzie 1978a in some basins it was found that the kinematics of deformation could be more accurately described by depth dependent stretching factors royden and keen 19801 which introduced asymmetry near basin edges in the simple shear model of wemicke

a joint interpretation of electromagnetic and seismic tomography models suggests the mantle transition zone below europe is dry abstract the three dimensional 3d electrical conductivity distribution in the mantle transition zone mtz below europe is resolved by directly inverting geomagnetic response functions from 12 selected european observatories comparison of the conductivity image with the results of global seismic tomography reveals a good correlation between low conductivity and high velocity anomalies at depths of 400 700 km beneath the mediterranean subduction zone in central europe interpretation of the 3d conductivity model combined with seismic tomography indicates that the european mtz is drier than the mtz beneath the western pacific subduction zone even though the subducted slab material is stagnating similarly in both regions

experimental sytectonic dehydration of serpentinite under conditions of controlled pore water pressure we have studied the mechanical behavior of serpentinite under conditions favouring dehydration to olivine talc water at temperatures ranging between 300 and 600 and at total pressures from 100 to 300 mpa constant stress stress relaxation and constant displacement rate testing techniques permitted a wide range of deformation rates and paths to be accessed effective confining pressure was held constant during the dehydration process by means of a controlled pore water pressure system stress supported by the samples was almost independent of deformation rate at temperatures below those required for the onset of the breakdown reaction at 500 and 600 c however the strength was linearly dependent on the inverse of the deformation rate and independent of effective confining pressure over the range investigated microstructural studies revealed that the weakening was associated with sliding in narrow shear zones containing ultrafine grained 0 1 m olivine produced in the breakdown reaction the enhanced deformability is interpreted in terms of flow of the olivine in these shear zones by diffusion accommodated grain boundary sliding these experimental results suggest that metamorphic transformations affect the deformability of rocks and demonstrate enhancement of deformability through the transient existence of fine grained reaction products the results may also be applicable to the mechanics of deformation processes in oceanic transform faults and give some indication of the degree of weakening that might be expected from grain size reduction by dynamic recrystallization in plastically deforming rocks

the silkstone rock westphalian a from the east pennines england implications for sand body genesis the silkstone rock westphalian a langsettian is a major multistorey channel sandstone formed in a delta plain environment with minimal marine influence it occupies up to three interseam intervals in the east pennine coalfield england and exceeds 50 m in thickness and 15 km in width at its maximum development which is larger than many westphalian channel sand bodies the high ash content of coal adjacent to the channel belt indicates that regional peat accumulation took place contemporaneously with the existence of the channel system the major channel system fed a number of minor channels during different interseam intervals and conducted sediment and water into nearby delta plain lakes via lacustrine delta and crevasse splay systems these minor channels which show a range of fills are sub parallel and show lateral offset stacking suggesting that differential compaction was an important control on their location the major channel belt acted as a long lived distributary system that flowed towards the east away from the overall basin depocentre with its position being controlled mainly by deltaic processes

shallow seismic reflection investigations of coal in the sydney basin surface reflection profiling with the mini sosie technique successfully mapped shallow coal seam structure in the western sydney basin new south wales several minor faults and zones of fracturing were detected in regions of thick triassic sandstone cover data quality was poor and unsuitable for geologic interpretation synthetic seismograms based on nearby borehole and petrophysical control show excellent agreement with the mini sosie sections and illustrate the deleterious filtering effects of coal seams and sequences to establish a phenomenological basis for seismic wave propagation in shallow coal measures two vertical seismic profiles vsps which used small explosive charges were recorded with high spatial and temporal sampling numerous multiple reflections were observed in the downgoing wave display the isolated upgoing waves were migrated to yield blurred images of the main coal seams the subsurface velocity function also deduced from the vsp shows broad correlation with the geologic log

the role of recrystallization in the preferred orientation of olivine abstract the effects of recrystallization on the preferred orientation in olivine have been studied the recrystallization mechanisms studied include grain growth the deformation induced grain boundary migration digbm and subgrain rotation sgr grain boundary migration is involved in the first two but not in sgr significant preferred orientation was found only in the latter two where dislocations are involved the combined microstructural and fabric preferred orientation observations indicate that the grain boundary migration produces strong preferred orientation when the driving force is the dislocation energy but not when the grain boundary energy is the driving force the nature of preferred orientation due to dislocation related recrystallization digbm or sgr was found to depend on the mechanism of recrystallization the digbm produces preferred orientation in which the low dislocation density grains with unfavourable orientation for easy slip dominate thereby significantly altering the preferred orientation formed by dislocation glide in contrast sgr does not essentially alter the deformation fabric and therefore the fabric associated with sgr recrystallization is related to the geometry of flow the present results demonstrate that the existence of seismic anisotropy in the upper mantle is strong evidence for the dislocation mechanism s of deformation and suggest that care must be exercised in applying the results of laboratory fabric studies made for a particular mechanism of recrystallization to the earth s interior where the dominant mechanism s of dynamic recrystallization can be different

upper carboniferous and lower permian tectonostratigraphy on the southern margin of the central north sea hydrocarbon exploration in uk licence blocks 31 26 and 39 2 on the southern margin of the central north sea in 1996 and 1997 proved the presence of a palaeozoic sedimentary succession previously undescribed in the area biostratigraphic data from the sediments and radiometric dating of interbedded basaltic lavas indicate that the succession spans the upper carboniferous westphalian b to lower permian asselian interval this has been informally split into three sedimentary units the lower flora sandstone is of westphalian b c age this clastic interval is overlain by the first of two main lavas which is in turn overlain by the westphalian c d to stephanian upper flora sandstone the flora sandstones are interpreted to be lithostratigraphic equivalents to the schooner formation of the southern north sea the flora sandstones are separated from the grensen formation by an angular unconformity possibly related to variscan asturic inversion the grensen formation is in turn overlain by a second basaltic lava flow both basaltic units are assigned to the inge volcanics formation rotliegend group petrographic data indicate that the grensen formation also forms part of the rotliegend group a major extensional event of permian age post dates all of these strata extensional faults are planed by a regional unconformity saalian unconformity that is overstepped by permian to cretaceous strata

pore scale simulation of carbonate dissolution in micro ct images we present a particle based method to simulate carbonate dissolution at the pore scale directly on the voxels of three dimensional micro ct images the flow field is computed on the images by solving the incompressible navier stokes equations rock fluid interaction is modeled using a three step approach solute advection diffusion and reaction advection is simulated with a semianalytical pore scale streamline tracing algorithm diffusion by random walk is superimposed while the reaction rate is defined by the flux of particles through the pore solid interface we derive a relationship between the local particle flux and the independently measured batch calcite dissolution rate we validate our method against a dynamic imaging experiment where a ketton oolite is imaged during co2 saturated brine injection at reservoir conditions the image calculated increases in porosity and permeability are predicted accurately and the spatial distribution of the dissolution front is correctly replicated the experiments and simulations are performed at a high flow rate in the uniform dissolution regime pe 1 and peda 1 thus extending the reaction throughout the sample transport is advection dominated and dissolution is limited to regions with significant inflow of solute we show that the sample averaged reaction rate is 1 order of magnitude lower than that measured in batch reactors this decrease is the result of restrictions imposed on the flux of solute to the solid surface by the heterogeneous flow field at the millimeter scale

oxidation softens mantle rocks seismic waves that propagate through a layer of earth s upper mantle are highly attenuated contrary to general thinking this attenuation seems to be strongly affected by oxidation conditions rather than by water content seismic waves that propagate through a layer of earth s upper mantle are highly attenuated contrary to general thinking this attenuation seems to be strongly affected by oxidation conditions rather than by water content

fluvial channel and overbank deposits from the westphalian of the durham coalfield ne england the westphalian upper carboniferous coal measures of the durham coalfield in ne england were deposited in lower and upper delta plain environments distributary channels crossed the plain and were separated by shallow interdistributary lakes and bays detailed observation of three dimensional 3 d opencast surface mine exposures in collaboration with subsurface borehole analysis has revealed the existence of five varieties of channel deposits and two associated overbank facies within the durham coal measures major distributary channels were the major avenues of sediment transport across the coal measures plain were variably sinuous mostly 1 2 km wide and deposited elongate belts of sand mostly up to 5 km wide proximal major crevasse splay channels formed by the breaching of major channel banks during flood events were straight sand filled and up to 400 m wide minor distributary channels formed by the sustained operation of such crevasses varied from straight to highly sinuous and deposited shoestring sand mud belts up to a few hundred metres wide minor crevasse channels generally straight and up to 50 m wide were formed through bank breaching of minor and in a few cases major distributaries distal feeder channels formed down palaeocurrent extensions of minor distributaries which supplied interdistributary minor delta subsystems were generally straight and up to 200 m wide of the two types of channel overbank levee deposits recognized one comprising thinly interbedded fine grained sandstone and siltstone claystone is mostly though not exclusively associated with major distributary channels the other consisting of massive siltstones with regularly spaced thin claystone bands is uniquely developed at the margins of minor distributary channels the lower part of the westphalian a succession in the northern pennines records a change in the depositional environment upwards from a lower to upper delta plain through this transition major channel deposits show evidence of having evolved from being of dominantly low sinuosity to being more variable in morphology channel sedimentation was profoundly influenced by regular possibly seasonal variations in flow stage and sediment load

high temperature creep of olivine single crystals 2 dislocation structures dislocation structures and densities in experimentally deformed single crystals of san carlos olivine were examined using the oxidation decoration technique the high temperature deformation experiments were conducted at various temperatures t differential stresses and oxygen fugacities o2 the samples were buffered against either orthopyroxene opx or magnesiowustite mw solid state powders and compressed along one of the three 45 orientations in samples that were deformed and subsequently quenched under load seven distinct dislocation structures were observed a for samples compressed parallel to 110 c at 16 50 mpa and o2 10 6atm two different dislocation arrangements were identified for opx buffered samples at 1400 t 1475 c the dislocation structure was composed of curved screw segments that had usually cross slipped and straight edge segments of comparable length at 1300 t 1350 c for opx buffered samples and at 1350 t 1500 c for mw buffered samples the dislocation structure is dominated by arrays of very long edge or mixed dislocations with only a few screw dislocations b for both opx buffered and mw buffered samples compressed parallel to 101 c at 1340 t 1400 c and 30 60 mpa the dislocation configurations are characterized by zigzag near edge dislocations at o2 10 5atm and by straight cross slipped screw dislocations plus pinned edge dislocations at o2 10 9atm c for samples compressed parallel to 011 c at t 1400 c and 70 150mpa the primary dislocations change from long straight edge dislocations for o2 10 4atm and opx buffer to a combination of straight edge dislocations and polygon shaped half loops for o2 10 4atm and mw buffer to gently curved near edge dislocations for o2 10 9atm for both solid state buffers abundant long straight screw dislocations were present in each case for the 011 c samples all of the above variations in dislocation structure are paralleled by changes in the measured power law equation that describes the behavior of creep mechanisms of olivine thus the different dislocation structures are associated with different rate controlling creep mechanisms for all of the dislocation structures the dislocation density increases with differential stress according to the relation 1 4 dislocation structures in samples that were deformed and then statically annealed have also been studied for both 110 c and 011 c samples deformed over a wide range of experimental conditions the dislocation structures on the slip planes generally consist of short curved edge or mixed dislocation segments in 101 1 samples deformed at low o2 50 mpa and 1400 c the dislocation structure was much less altered by annealing than the dislocation structures in 110 c and 011 c samples the density of dislocations decreased much less for these 101 c samples than for the 110 c and 011 c samples due to climb of the edge segments the straight screw segments found in quenched samples became curved and many low angle 100 tilt boundaries connected by straight 100 screw dislocations developed during the annealing process

the global attenuation structure of the upper mantle 1 a large data set of fundamental mode rayleigh wave amplitudes is analyzed to derive a new global three dimensional model of shear wave attenuation in the upper mantle the amplitude observations span a range of periods between 50 and 250 s and are derived from earthquakes with mw 6 0 that occurred between 1993 and 2005 four separate factors may influence an amplitude anomaly intrinsic attenuation along the raypath elastic focusing effects along the raypath uncertainties in the strength of excitation and uncertainties in the response at the station in an earlier paper dalton and ekstrom 2006a dependence of the retrieved attenuation structure on these terms was shown to be significant and an approach was developed to invert the amplitudes simultaneously for each term the new three dimensional attenuation model qrfsi12 which is the subject of this paper is derived using this method the model contains large lateral variations in upper mantle attenuation 60 to 100 and exhibits strong agreement with surface tectonic features at depths shallower than 200 km at greater depth qrfsi12 is dominated by high attenuation in the southeastern pacific and eastern africa and low attenuation along many subduction zones in the western pacific resolution tests confirm that the change in pattern of attenuation above and below 200 km depth can be determined with confidence using the fundamental mode data set the new model is highly correlated with global models of shear wave velocity particularly in the uppermost mantle suggesting that the same factors may control both seismic attenuation and velocity in this depth range however forcing the lateral perturbations in attenuation to match those found in global velocity models decreases the data variance reduction which suggests that subtle differences between patterns of attenuation and velocity are robust

aspects of seismic character and extent of upper carboniferous coal measures gulf of st lawrence and sydney basins abstract a seismic facies related to upper carboniferous coal measures has been mapped in the gulf of st lawrence sydney basin region of atlantic canada the inferred original extent of this area of coal deposition is over 100 000 km 2 which is two to three orders of magnitude larger than the fault bounded terrestrial coal basins on the surrounding landmass the depositional continuity of this seismic sequence is on the scale of cyclothem deposition in the illinois basin and mid continent basin region of the united states and suggests an analogous stable cratonic shelf setting for the gulf of st lawrence sydney basin region in paleogeographic reconstructions for the late carboniferous cyclothems in a paleoequatorial setting in the mid continent basin of euramerica have been correlated with cyclothems in a similar setting on the russian platform the gulf of st lawrence and sydney basins lie midway between these two regions it will be an interesting test of these correlations to determine the exact age and environment of the coal measures seismic facies

the role of water in the deformation of dunite specimens of two natural dunites anita bay of 100 m grain size and aheirn of 900 m grain size have been deformed in experiments at temperatures between 1200 and 1400 c and constant strain rates between 10 4 and 10 6 s 1 in a gas medium deformation apparatus at 300 mpa confining pressure prior to these experiments the specimens were given a heat treatment in a controlled oxygen fugacity furnace at 1200 c for 60 hours to dehydrate the trace layer silicate minerals present and drive off adsorbed water the predried specimens are much stronger than specimens tested under wet conditions in an earlier study the predried specimens also do not show the apparent grain size dependence seen under wet conditions infrared absorption measurements on the present specimens and those of the earlier study indicate that for a given rock flow stress can be correlated with the intensity of a residual water related broad absorption the addition of water to a predried specimen results in both a mechanical reweakening and an intensifying of the broadband infrared component the weakening of the dunites under wet conditions is probably strongly influenced by the presence of small amounts of a water related species in the grain boundaries but intragranular weakening may also be contributing it is suggested that the concentration of the water related species in the grain boundaries is governed by its concentration in the small melt fraction present the amounts of water that have been found to be of importance for the strength of these dunites are of the order of 0 01 wt amounts much less than most estimates of the water content of the earth s undepleted upper mantle such water may have an important role in determining upper mantle flow behavior stress strain curves for all experiments are available with entire manuscript on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b84 008 2 50 payment must accompany order

can thin coals be resolved in seismic data an example of the challenges for carboniferous visean to westphalian source rock definition across the elbow spit platform netherlands and the mid north sea high uk through well synthetic modelling

multi scale x ray tomography analysis of carbonate porosity the porosity from values of 1 up to more than 50 with a mean value of 36 5 and permeability from very low values to 20 4 d with a mean value around 800 md of 38 plugs with a diameter 40 mm have been measured these plugs were taken approximately every 1 5 m along a 100 m long core sampling a series of reefal carbonate platform lithofacies a non unique relationship between porosity and permeability is obtained in addition the porosity was measured from processing x ray micro tomography images with resolutions ranging from 0 42 to 190 0 m and sampling volumes ranging from less than 1 m3 to few cm3 depending on the structure of the pore network the computed porosity is in some cases controlled by the x ray image resolution and the sampled volume while high resolution is required to image micro porous material large samples with lower resolution images are necessary for identifying distributed vugs and millimetre scale structures this study shows that multi resolution x ray micro tomography is an effective tool for characterizing the multi scale pore structure of carbonate rocks and understanding how it may control key petrophysical parameters such as porosity and permeability