effective velocities in fractured media a numerical study using the rotated staggered finite difference grid the modelling of elastic waves in fractured media with an explicit finite difference scheme causes instability problems on a staggered grid when the medium possesses high contrast discontinuities strong heterogeneities for the present study we apply the rotated staggered grid using this modified grid it is possible to simulate the propagation of elastic waves in a 2d or 3d medium containing cracks pores or free surfaces without hard coded boundary conditions therefore it allows an efficient and precise numerical study of effective velocities in fractured structures we model the propagation of plane waves through a set of different randomly cracked media in these numerical experiments we vary the wavelength of the plane waves the crack porosity and the crack density the synthetic results are compared with several static theories that predict the effective p and s wave velocities in fractured materials in the long wavelength limit for randomly distributed and randomly orientated rectilinear non intersecting thin dry cracks the numerical simulations of velocities of p sv and sh waves are in excellent agreement with the results of the modified or differential self consistent theory on the other hand for intersecting cracks the critical crack density porosity concept must be taken into account to describe the wave velocities in media with intersecting cracks we propose introducing the critical crack density concept into the modified self consistent theory numerical simulations show that this new formulation predicts effective elastic properties accurately for such a case

ultrasonic moduli for fluid saturated rocks mavko jizba relations rederived and generalized mavko and jizba propose a quantitative model for squirt dispersion of elastic wave velocities between seismic and ultrasonic frequencies in granular rocks their central results are the expressions for the so called unrelaxed frame bulk and shear moduli computed under an assumption that the stiff pores are drained or dry but the soft pores are filled with fluid mavko jizba expressions are limited to liquid saturated rocks but become inaccurate when the fluid bulk modulus is small e g for gas saturated rocks we have derived new expressions for unrelaxed moduli of fluid saturated porous rocks using sayers kachanov discontinuity formalism the derived expressions generalize the established mavko jizba relations to gas saturated rocks reduce to mavko jizba results when the pore fluid is liquid and yield dry moduli when fluid bulk modulus tends to zero we tested this by comparing our model and the model of mavko and jizba against laboratory measurements on a sample of westerly granite

prominence of ichnologically influenced macroporosity in the karst biscayne aquifer stratiform super k zones a combination of cyclostratigraphic ichnologic and borehole geophysical analyses of continuous core holes tracer test analyses and lattice boltzmann fl ow simulations was used to quantify biogenic macroporosity and permeability of the biscayne aquifer southeastern florida biogenic macroporosity largely manifests as 1 ichnogenic macroporosity primarily related to postdepositional burrowing activity by callianassid shrimp and fossilization of components of their complex burrow systems ophiomorpha and 2 biomoldic macroporosity originating from dissolution of fossil hard parts principally mollusk shells ophiomorpha dominated ichnofabric provides the greatest contribution to hydrologic characteristics in the biscayne aquifer in a 345 km 2 study area stratiform tabular shaped units of thalassinidean associated macroporosity are commonly confi ned to the lower part of upward shallowing highfrequency cycles throughout aggradational cycles and in one case they stack vertically within the lower part of a high frequency cycle set broad continuity of many of the macroporous units concentrates groundwater fl ow in extremely permeable passageways thus making the aquifer vulnerable to long distance transport of contaminants ichnogenic macroporosity represents an alternative pathway for concentrated groundwater fl ow that differs considerably from standard karst fl ow system paradigms which describe groundwater movement through fractures and cavernous dissolution features permeabilities were calculated using lattice boltzmann methods lbms applied to computer renderings assembled from x ray computed tomography scans of various biogenic macroporous limestone samples the highest simulated lbm permeabilities were about fi ve orders of magnitude greater than standard laboratory measurements using air permeability methods which are limited in their application to extremely permeable macroporous rock samples based on their close conformance to analytical solutions for pipe fl ow lbms offer a new means of obtaining accurate permeability values for such materials we suggest that the stratiform ichnogenic groundwater fl ow zones have permeabilities even more extreme 2 5 orders of magnitude higher than the jurassic super k zones of the giant ghawar oil fi eld the fl ow zones of the pleistocene biscayne aquifer provide examples of ichnogenic macroporosity for comparative analysis of origin and evolution in other carbonate aquifers as well as petroleum reservoirs

equivalent viscoelastic solids for heterogeneous fluid saturated porous rocks differenttheoreticalandlaboratorystudiesonthepropagation ofelasticwavesinrealrockshaveshownthatthepresenceofheterogeneities larger than the pore size but smaller than the predominant wavelengths mesoscopic scale heterogeneities may producesignificantattenuationandvelocitydispersioneffectson seismic waves such phenomena are known as mesoscopic effects and are caused by equilibration of wave induced fluid pressure gradients we propose a numerical upscaling procedure to obtain equivalent viscoelastic solids for heterogeneous fluidsaturated rocks it consists in simulating oscillatory compressibility and shear tests in the space frequency domain which enable us to obtain the equivalent complex undrained plane wave and shear moduli of the rock sample we assume that the behavior of the porous media obeys biot s equations and use a finiteelementproceduretoapproximatethesolutionsoftheassociated boundary value problems also because at mesoscopic scales rock parameter distributions are generally uncertain and of stochastic nature we propose applying the compressibility and sheartestsinamontecarlofashion thisfacilitatesthedefinition of average equivalent viscoelastic media by computing the moments of the equivalent phase velocities and inverse quality factors over a set of realizations of stochastic rock parameters described by a given spectral density distribution we analyzed the sensitivity of the mesoscopic effects to different kinds of heterogeneities in the rock and fluid properties using numerical examples also theapplicationofthemontecarloprocedureallowed us to determine the statistical properties of phase velocities and inverse quality factors for the particular case of quasi fractal heterogeneities

seismic attenuation and pore fluid viscosity in clay rich reservoir sandstones the frequency dependence of seismic attenuation in a suite of clay rich reservoir sandstones was investigated in the laboratory compressional and shear wave velocities vp and vs and quality factors qp and qs were measured as functions of pore fluid viscosity at an effective pressure of 50 mpa and at an experimental frequency of about 0 8 mhz using the pulse echo technique the experimental viscosity ranged from 0 3 to 1000 centipoise which gives equivalent frequencies for a water saturated sandstone of 2 6 mhz to 780 hz assuming a global flow loss mechanism two types of behavior were observed high permeability greater than 100 millidarcies sandstones tend to show variable qp and qs which are similar in magnitude to those predicted by the biot theory over the viscosity range 0 3 to about 20 centipoise equivalent frequency range 2 6 mhz to about 39 khz low permeability less than 50 millidarcies sandstones tend to show almost constant qp and qs over the experimental viscosity range that are

mechanisms associated with the erosion of sand dune cliffs magilligan northern ireland a fifteen year history of coastal dune recession at magilligan northern ireland has revealed both time and space contrasts in processes and morphology since 1968 storm frequency has increased while dune retreat reached a peak 5 4 m in 1978 1979 three types of dune eroding events are noted resulting from particular wave wind tide combinations the spatial variability in dune scarping is associated with vegetation and soil development and slope failures range from granular avalanches to retrogressive rotational slumps

computation of dynamic seismic responses to viscous fluid of digitized three dimensional berea sandstones with a coupled finite difference method the seismic response of saturated porous rocks is studied numerically using microtomographic images of three dimensional digitized berea sandstones a stress strain calculation is employed to compute the velocities and attenuations of rock samples whose sizes are much smaller than the seismic wavelength of interest to compensate for the contributions of small cracks lost in the imaging process to the total velocity and attenuation a hybrid method is developed to recover the crack distribution in which the differential effective medium theory the kuster toksoz model and a modified squirt flow model are utilized in a two step monte carlo inversion in the inversion the velocities of p and s waves measured for the dry and water saturated cases and the measured attenuation of p waves for different fluids are used by using such a hybrid method both the velocities of saturated porous rocks and the attenuations are predicted accurately when compared to laboratory data the hybrid method is a practical

sequence stratigraphy of the red river formation williston basin usa stratigraphic signature of the ordovician katian greenhouse to icehouse transition abstract the upper katian upper ordovician red river formation is a carbonate evaporite supersequence that formed in the epicratonic williston basin of western north america this study focuses on the upper part of the formation in the southern us part of the basin the studied succession is made up of three transgressive regressive sequences rr1 rr2 and rr3 each 0 5 1 m y in duration and composed of relatively few meter scale high frequency cycles parasequences sequence boundaries are characterized by intraclastic breccia laminated dolomite successions that have been truncated and capped by evaporite deposits subaqueous anhydrites within each sequence represent evaporite lowstand systems tracts lsts that formed during relative sea level lows that lead to the precipitation of gypsum later recrystallized into anhydrite in a quiet salina type environment transgressive tst and early highstand systems tracts hst are composed of subtidal facies of predominantly skeletal mudstone to wackestone packstone with abundant burrow mottling late hsts are predominantly composed of peritidal porous laminated dolomite the study illustrates how the sequence stratigraphic framework of carbonate evaporite deposits from the williston basin relates to the late ordovician glacio eustasy transitional climates and low basin subsidence in an arid setting

identifying storm impacts on an embayed high energy coastline examples from western ireland abstract large sections of the western irish coast are characterised by a highly compartmentalised series of headland embayment cells in which sand and gravel beaches are backed by large vegetated dune systems exposure to modally high energy swell renders most of these beaches dissipative in character a mesotidal range c 3 5 4 5 m exists along much of the coast analysis of instrumental wind records from three locations permitted the identification of a variety of storm types and the construction of storm catalogues few individual storms were recorded at all three stations indicating a lack of regional consistency in storm record of the total storms recorded only a small percentage are potentially damaging onshore directed and even fewer span a high tide and thus potentially induce a measurable morphological response at the coast through a combination of historical records meteorological records field observations and wave modelling we attempt to assess the impact of storms quantifiable records of coastal morphology maps air photos and beach profiles are few in number and do not generally record responses that may be definitely attributed to specific storms numerical wave simulations and observations at a variety of sites on the west irish coast however provide insights into instantaneous and medium term decadal storm responses in such systems we argue that beaches and dunes that are attuned to modally high energy regimes require extreme storms to cause significant morphological impact the varying orientation of beaches a spatially nonuniform storm catalogue and the need for a storm to occur at high water to produce measurable change impart site specific storm susceptibility to these embayments furthermore we argue that long period wave energy attenuation across dissipative shorefaces and beaches reduces coastal response to distant storms whereas short period locally generated wind waves are more likely to cause major dune and beach erosion as they arrive at the shoreline unrefracted this apparently variable response of beach and dune systems to storm forcing at a decadal scale over a coastline length of 200 km urges caution in generalising regarding regional scale coastal responses to climatic change

ca isotope study of ordovician dolomite limestone and anhydrite in the williston basin implications for subsurface dolomitization and local ca cycling abstract a difference of 0 61 is reported between dolomite 1 66 and its precursor limestone 1 05 in the yeoman formation red river equivalent of the williston basin southeastern saskatchewan the significance of the large difference found and the preference for light isotope enrichment in the dolomite is evaluated with assistance from 87 sr 86 sr ratios and dolomitization models previously proposed for the studied rocks in particular i explore the possibility that 44 ca values in dolomite reflect the 44 ca values of the dolomitizing fluids without any correction for mineral fluid fractionation this hypothesis is based on recent studies showing negligible isotopic fractionation between carbonates and ca 2 bearing waters at very low precipitation rates fantle and depaolo 2007 jacobson and holmden 2008 if correct calcium isotopes hold promise as a tool for discriminating among numerous hydrological models of dolomite formation as a case in point the 44 ca value of the yeoman dolomite 1 66 is too low to reflect ca derived from the following sources 1 the original limestone 1 05 2 overlying beds of anhydrite 1 28 or 3 evaporated seawater 0 25 paleozoic carbonates ranging as low as 1 7 appear to be the lightest source of ca in the basin succession suggesting that the mg containing dolomitizing fluid was a connate water with a previous history of water rock interactions with paleozoic carbonates possibly involving earlier episodes of dolomitization and light ca release into migrating basinal fluids the relatively high seawater 44 ca values inferred from measurements of yeoman limestone and lake alma anhydrite suggest that seawater in the williston basin 450 ma was 0 22 0 46 higher in 44 ca than the contemporaneous ocean based on globally distributed brachiopods farkas et al 2007 this finding suggests that 44 ca values preserved in the deposits of epeiric seas may bias the 44 ca reconstruction of the ocean secular record if local ca cycling effects are not taken into account equations describing the isotope balance of ca in an epeiric sea indicate that seawater 44 ca values may be higher lower or equal to the 44 ca value of the ocean depending on the sizes of local scale ca deposition and weathering fluxes in relation to seawater ca exchange fluxes

a simple hydromechanical approach for simulating squirt type flow abstractthe deformations caused by an acoustic wavefield in subsurface rock can induce fluid flow within hydraulically interconnected mesoscopic fractures from one fracture into the other the viscous friction associated with this squirt type fluid flow parallel to the fracture walls results in energy dissipation and velocity dispersion we have developed a quasi static hydromechanical approach that is suitable for simulating squirt type flow in the mesoscopic scale range and microscopic squirt flow our approach couples navier stokes equation with hooke s law to describe the laminar flow of a viscous compressible fluid in conduits embedded in an elastic solid background results from the proposed method were compared with those obtained with biot s equations for a model containing interconnected mesoscopic fractures embedded in a background of very low porosity and permeability despite significant differences in the flow and dissipation spatial patterns we have observed an essentially perfect agreemen

elastohydrodynamic lubrication of faults the heat flow paradox provides evidence that a dynamic weakening mechanism may be important in understanding fault friction and rupture we present here a specific model for dynamic velocity weakening that uses the mechanics of well studied industrial bearings to explain fault zone processes an elevated fluid pressure is generated in a thin film of viscous fluid that is sheared between nearly parallel surface this lubrication pressure supports part of the load therefore reducing the normal stress and associated friction across the gap the pressure also elastically deforms the wall rock the model is parameterized using the sommerfeld number which is a measure of the lubrication pressure normalized by the lithostatic load for typical values of the material properties slip distance and velocity the sommerfeld number suggests that lubrication is an important process if the lubrication length scales as the slip distance in an earthquake the frictional stress during dynamically lubricated large earthquakes is 30 less than the friction with only hydrostatic pore pressure elastohydrodynamic lubrication also predicts a decrease in high frequency 1 hz radiation above a critical slip distance of a few meters this prediction is well matched by the strong motion data from the 1999 taiwan earthquake the observed 2 orders of magnitude variation in scaled radiated energy between small m w 6 is also predicted by the lubrication model

shoreline evolution of the holland coast on a decadal scale the decadal evolution of the dunefoot position along 120 km of the holland coast is analysed firstly a new definition of dunefoot is introduced based on hydrodynamic and morphologic considerations which is not affected by local and instantaneous processes occurring immediately before the bathymetric survey the dunefoot evolution over decadal scales indicates the existence of spatial and temporal oscillations in the shoreline position with magnitudes of 2 3 km length and a periodicity of 4 15 years two main controlling factors of this behaviour are identified 1 influence of sub aqueous bar systems and 2 changes in the storm wave conditions reaching the coast although the precise controlling processes of the relation between the dunefoot and the subaqueous profile still remain unclarified we introduce the concept that the development of a morphological bar cycle requires a fixed amount of time integrated forcing that is proportional to the cumulative effect of storm waves beach mobility along the holland coast on decadal scales 10 20 m is similar or lower than mobility introduced by storms or by seasonal cycles however it is important to consider these changes for the possible implications on the local vulnerability of the coast to extreme events copyright 1999 john wiley sons ltd

geothermics of the williston basin in canada in relation to hydrodynamics and hydrocarbon occurrences over 8 400 bottom hole temperature bht values from the canadian part of the williston basin were analyzed and a temperature high was discovered in the weyburn area of southeastern saskatchewan geothermal gradients thermal conductivities and heat flow have been investigated for most of the mesozoic cenozoic clastic unit as well as the upper paleozoic carbonate evaporite unit regional heat flow variations with depth occur which are closely related to the hydrodynamics governed by the topography and geology the blanketing effect of low conductivity shaly formations may cause a temperature anomaly in the south where the thickest phanerozoic cover exists however the weyburn high can be explained only partially in this way hydrodynamics has also contributed to formation of the temperature anomaly there the process of forming the anomaly by the blanketing effect and hydrodynamics also contributed to oil deposition there is a correlation between mississippian oil occurrences in the southeastern part o

changes in surfzone morphodynamics driven by multi decadal contraction of a large ebb tidal delta abstract the impact of multi decadal large scale deflation 76 million m 3 of sediment loss and contraction 1 km of a 150 km 2 ebb tidal delta on hydrodynamics and sediment transport at adjacent ocean beach in san francisco ca usa is examined using a coupled wave and circulation model the model is forced with representative wave and tidal conditions using recent 2005 and historic 1956 ebb tidal delta bathymetry data sets comparison of the simulations indicates that along north south trending ocean beach the contraction and deflation of the ebb tidal delta have resulted in significant differences in the flow and sediment dynamics between 1956 and 2005 the transverse bar the shallow attachment point of the ebb tidal delta to the shoreline migrated northward 1 km toward the inlet while a persistent alongshore flow and transport divergence point migrated south by 500 m such that these features now overlap a reduction in tidal prism and sediment supply over the last century has resulted in a net decrease in offshore tidal current generated sediment transport at the mouth of san francisco bay and a relative increase in onshore directed wave driven transport toward the inlet accounting for the observed contraction of the ebb tidal delta alongshore migration of the transverse bar and alongshore flow divergence have resulted in an increasing proportion of onshore migrating sediment from the ebb tidal delta to be transported north along the beach in 2005 versus south in 1956 the northerly migrating sediment is then trapped by pt lobos a rocky headland at the northern extreme of the beach consistent with the observed shoreline accretion in this area conversely alongshore migration of the transverse bar and divergence point has decreased the sediment supply to southern ocean beach consistent with the observed erosion of the shoreline in this area this study illustrates the utility of applying a high resolution coupled circulation wave model for understanding coastal response to large scale bathymetric changes over multi decadal timescales common to many coastal systems adjacent to urbanized estuaries and watersheds worldwide

pool characterization of ordovician midale field implication for red river play in northern williston basin southeastern saskatchewan canada the upper ordovician midale field is located in the northern williston basin in southeast saskatchewan canada hydrocarbons are hosted mainly in the dolomite reservoirs with burrowed textures in the upper yeoman formation these reservoirs are characterized by intercrystalline porosity in the dolomitized matrix with variable amounts of vugs and fractures and can be divided into four zones reservoir zones 1 and 2 typically 6 10 m 20 33 ft thick in total are situated in the upper part of the traps and commonly bear oil although the underlying zones 3 and 4 are thicker they commonly contain only water because they are located below the spillpoint of the hydrocarbon traps the seismic reflection of the red river reservoirs in the midale field is characterized by a weak to medium amplitude trough immediately above the positive reflection of the winnipeg shale where all four zones are present an additional peak occurs on the seismic profile above the original reservoir reflection this additional peak however disappears where reservoir zones 3 and 4 pinch out where there is an increase in the thickness of reservoir zones 1 and 2 or amalgamation of zone 1 with zone 2 the red river reservoirs are characterized by high amplitude and high frequency reflections on seismic profiles the ordovician oil pools in the midale area are associated with low relief anticline structures these low relief structures are interpreted as the compactional drape of red river strata over local precambrian basement highs the source of hydrocarbons in the red river reservoirs is ordovician kukersites a wide range of api fractions for the oils from the midale pools suggests a mixing of low maturity oils sourced from local kukersite beds and high maturity oils that migrated over a long distance from the south the hydrocarbon production from red river midale pools is characterized by the fast rise of water cut and high water output which can be attributed to the small pool size and the fracture systems connecting oil and water zones

the squirt flow mechanism macroscopic description we introduce a poroelasticity model that incorporates the two most important mechanisms of solid fluid interaction in rocks the biot mechanism and the squirt flow mechanism this combined biot squirt bisq model relates compressional velocity and attenuation to the elastic constants of the drained skeleton and of the solid phase porosity permeability saturation fluid viscosity and compressibility and the characteristic squirt flow length squirt flow length is a fundamental rock property that does not depend on frequency fluid viscosity or compressibility and is determined experimentally we find that the viscoelastic response of many sandstones is dominated by the squirt flow component of the bisq mechanism and that the viscoelastic properties of these rocks can be expressed through a single dimensionless parameter omega r 2 kappa where omega is angular frequency r is the characteristic squirt flow length and kappa is hydraulic diffusivity the biot mechanism alone does not give an adequate explanation of the observed velocity dispersion and attenuation and the viscoelastic behavior of many sandstones

natural bathymetric change as a control on century scale shoreline behavior identification of the relevant forcing factors behind coastal change is a major societal demand in the face of rising sea level changes in the patterns of coastal erosion and accretion at a century scale in dundrum bay northern ireland are here attributed to natural changes in the nearshore bathymetry of sufficient magnitude to alter incident wave energy dispersal simulations of wave propagation across the nearshore reveal a marked change in the nearshore patterns of energy dispersal and related sediment transport pathways between 1861 and 1968 the 1861 bathymetry is associated with a simulated longshore drift divide in the middle of the bay and with sediment dispersal to the southeast and northeast whereas the 1968 bathymetry is associated with a consistent northeastward drift throughout the bay these changes are consistent with recorded shoreline changes sediment accumulation and foredune accretion in the northeast and northeastward spit elongation across a tidal inlet this study reveals a case in which purely natural changes in the seafloor at a century scale can be related to long term shoreline changes similar changes during relative sea level rise during the holocene were potentially capable of significant modification of shoreline morphology and dynamics near shore extraction of sand for beach nourishment purposes may have consequences of similar magnitude for adjacent beaches

seismic attenuation effects of pore fluids and frictional sliding seismic wave attenuation in rocks was studied experimentally with particular attention focused on frictional sliding and fluid flow mechanisms sandstone bars were resonated at frequencies from 500 to 9000 hz and the effects of confining pressure pore pressure degree of saturation strain amplitude and frequency were studied observed changes in attenuation and velocity with strain amplitude are interpreted as evidence for frictional sliding at grain contacts since this amplitude dependence disappears at strains and confining pressures typical of seismic wave propagation in the earth we infer that frictional sliding is not a significant source of seismic attenuation in situ partial water saturation significantly increases the attenuation of both compressional p and shear s waves relative to that in dry rock resulting in greater p wave than s wave attenuation complete saturation maximizes s wave attenuation but causes a reduction in p wave attenuation these effects can be interpreted in term

sub tidal ebb shoal control of shoreline erosion via wave refraction magilligan foreland northern ireland abstract a wave refraction model is used to examine the effects of sub tidal ebb shoal elongation on the erosion of the adjacent coast at magilligan northern ireland as deep water wave approach angles are stepped at 10 intervals from nw to ne so the shoal controls the position of breaker convergence zones which migrate nw along the shore but at a decreasing rate prolonged refraction of unidirectional swell is thought to be responsible for the formation of inshore sandwaves which are known from previous studies carter 1978 to promote differential erosion of the dune cliffs however longer term changes in shoal geometry lead to shifts in the pattern of convergence and a general uniformity in erosion rates it is surmised that the gradual development of the ebb shoal and its consequential role in local wave refraction may have been a factor in the cessation of holocene beach ridge formation

application of the bisq model to clay squirt flow in reservoir sandstones 1 an understanding of the variations of compressional wave velocity and attenuation in sandstones as a function of pore fluid properties is important for the identification and monitoring of hydrocarbon reservoirs in order for seismic inversion to be well constrained a rock physics model that describes accurately the observed behavior is required a number of such models have been proposed but have not been extensively tested against laboratory data the unified biot and squirt flow model was applied to data obtained from ultrasonic experiments conducted on a wide range of sandstone types when saturated with different pore fluids with viscosities ranging from 0 3 to 1000 cp this model was seen to match well all the observed velocity and attenuation values as opposed to the biot model which was only successful for clean sandstones saturated with low viscosity fluids this has led to the conclusion that a squirt flow mechanism is important at the grain scale in addition an increase in the dynamic uniaxial strain modulus of the dry frame with increasing pore fluid viscosity was observed in the absence of free gas or grain contact microcracks the laboratory data were collected at 60 mpa effective pressure this can be linked to decreasing local flow and decreasing relaxation in the soft pore space of the sandstone the extent of which is in turn connected to the clay content and pore structure of the sandstone these results imply that at ultrasonic frequencies the squirt flow is due to the presence of clay

pseudobreccias revealed as calcrete mottling and bioturbation in the late dinantian of the southern lake district uk two types of pseudobreccia one with grey and the other with brown mottle fabrics occur in shoaling upward cycles of the urswick limestone formation of asbian late dinantian carboniferous age in the southern lake district uk the grey mottle pseudobreccia occurs in cycle base packstones and developed after backfilling and abandonment of thalassinoides burrow systems burrow infills consist of a fine to coarse crystalline microspar that has dull brown to moderate orange colours under cathodoluminescence mottling formed when an early diagenetic aerobic decay clock operating on buried organic material was stopped and sediment entered the sulphate reduction zone this probably occurred during progradation of grainstone shoal facies after which there was initial exposure to meteoric water microspar calcites then formed rapidly as a result of aragonite stabilization the precipitation of the main meteoric cements and aragonite bioclast dissolution post date this stabilisation event the brown mottle pseudobreccia fabrics are intimately associated with rhizocretions and calcrete which developed beneath palaeokarstic surfaces capping cycle top grainstones and post date all depositional fabrics although they may also follow primary depositional heterogeneities such as burrows they consist of coarse inclusion rich microspar calcites that are always very dull to non luminescent under cathodoluminescence sometimes with some thin bright zones these are interpreted as capillary rise and pedogenic calcrete precipitates the d 18 o values 5 to 8 pdb and the d 13 c values 2 to 3 pdb of the pseudobreccias are lower than the estimated d 18 o values 3 to 1 pdb and d 13 c values of 2 to 4 pdb of normal marine calcite precipitated from late dinantian sea water reflecting the influence of meteoric waters and the input of organic carbon

stratigraphic and geochemical investigation of kukersites petroleum source beds within the ordovician red river formation williston basin abstract the upper ordovician red river formation has been a prolific producer of oil and gas in the williston basin where it has cumulatively produced more than 750 million bbl of oil equivalent over the past half century previous studies have recognized petroleum source beds referred to as kukersites in the red river formation but have not determined their complete extent or hydrocarbon generation significance examination and analysis of 28 cores and greater than 300 wireline logs have revealed 10 distinct kukersites in the red river d zone that can be correlated individually for tens to hundreds of miles tens to hundreds of kilometers across the western quarter of north dakota although each red river kukersite is typically thin 1 2 ft 0 3 0 7 m thick they combine to reach net thicknesses of greater than 12 ft 3 7 m with average present day total organic carbon toc values of typically 3 6 wt hydrogen index hi values from kukersite samples range from primarily greater than 800 mg hydrocarbons hc g toc within the northern flank of the basin to systematically decreasing to less than 100 mg hc g toc within the basin center this systematic decrease in hi is interpreted to be a function of increased thermal maturity where hydrocarbon generation has depleted kukersite organic richness preliminary calculations of hydrocarbon volumes generated from red river kukersites based on a previously developed method that calculates the volumetric decrease in original to present day kerogen content total approximately 66 billion bbl 1 05 10 10 m 3 of oil equivalent this approximate generation total is more than enough to account for cumulative red river production and supports the idea that the red river is a self sourced petroleum system with potentially significant remaining exploration potential

anthropogenic influences on shoreline and nearshore evolution in the san francisco bay coastal system abstract analysis of four historical bathymetric surveys over a 132 year period has revealed significant changes to the morphology of the san francisco bar an ebb tidal delta at the mouth of san francisco bay estuary from 1873 to 2005 the san francisco bar vertically eroded an average of 80 cm over a 125 km 2 area which equates to a total volume loss of 100 52 million m 3 of fine to coarse grained sand comparison of the surveys indicates the entire ebb tidal delta contracted radially with the crest moving landward an average of 1 km long term erosion of the ebb tidal delta is hypothesized to be due to a reduction in the tidal prism of san francisco bay and a decrease in coastal sediment supply both as a result of anthropogenic activities prior research indicates that the tidal prism of the estuary was reduced by 9 from filling diking and sedimentation compilation of historical records dating back to 1900 reveals that a minimum of 200 million m 3 of sediment has been permanently removed from the san francisco bay coastal system through dredging aggregate mining and borrow pit mining of this total 54 million m 3 of sand sized or coarser sediment was removed from central san francisco bay with grain sizes comparable to the ebb tidal delta and its direct connection to the bay mouth removal of sediments from central san francisco bay may limit the sand supply to the delta and open coast beaches swan wave modeling illustrates that changes to the morphology of the san francisco bar have altered the alongshore wave energy distribution at adjacent ocean beach and thus may be a significant factor in a persistent beach erosion hot spot occurring in the area shoreline change analyses show that the sandy shoreline in the shadow of the ebb tidal delta experienced long term 1850s 1890s to 2002 and short term 1960s 1980s to 2002 accretion while the adjacent sandy shoreline exposed to open ocean waves experienced long term and short term erosion therefore the recently observed accelerating rates of bay sediment removal ebb tidal delta erosion and open coast beach erosion are all correlated temporally

cyclical evolution of a modern transgressive sand barrier in northwestern spain elucidated by gpr and aerial photos abstract the internal structure of a modern baymouth barrier is analyzed in detail including its historical evolution and the factors controlling it historical evolution was reconstructed using available aerial photographs from 1956 to 2003 detailed geophysical data were acquired using ground penetrating radar gpr and analyzed along with airphotos to reconstruct the recent evolution of a barrier located in northwestern spain the gpr data reveal the internal architecture of the barrier which consists of two main radar facies 1 washover deposits associated with landward barrier migration and vertical aggradation and 2 beach deposits associated with seaward barrier progradation the reconstruction of the stratigraphic sequence indicates the occurrence of two erosive periods followed by an accretionary period the erosion along the barrier is outlined by the presence of three well defined bounding surfaces the stratigraphic record of the subsequent recovery phase depends on the impact level of the erosive phase which is controlled by the presence of ephemeral inlets along the barrier this alternating behavior implies a discontinuous shoreline trajectory in spite of a net landward migration this trend is consistent with regional sea level rise albeit being intensified locally by the interplay of sediment starvation and storm regime landward barrier retreat occurs by overwash and inlet breaching which permits barrier preservation of volume due to a continuous constructive destructive cycle the results acquired from this example expand our understanding of the internal structure and evolutionary trends of transgressive sand barriers

dynamic poroelasticity a unified model with the squirt and the biot mechanisms the velocities and attenuation of seismic and acoustic waves in rocks with fluids are affected by the two most important modes of fluid solid interaction 1 the biot mechanism where the fluid is forced to participate in the solid s motion by viscous friction and inertial coupling and 2 the squirt flow mechanism where the fluid is squeezed out of thin pores deformed by a passing wave traditionally both modes have been modeled separately with the biot mechanism treated in a macroscopic framework and the squirt flow examined at the individual pore level we offer a model which treats both mechanisms as coupled processes and relates p velocity and attenuation to macroscopic parameters the biot poroelastic constants porosity permeability fluid com pressibility and viscosity and a newly introduced microscale parameter a characteristic squirt flow length the latter is referred to as a fundamental rock property that can be determined experimentally we show that the squirt flow mechanism dominates the biot mechanism and is responsible for measured large velocity dispersion and attenuation values the model directly relates p velocity and attenuation to measurable rock and fluid properties therefore it allows one to realistically interpret velocity dispersion and or attenuation in terms of fluid properties changes e g viscosity during thermal enhanced oil recovery eor or to link seismic measurements to reservoir properties as an example of the latter transformation we relate permeability to attenuation and achieve good qualitative correlation with experimental data

velocity and attenuation in sandstone at elevated temperatures and pressures new measurements of seismic velocity and attenuation have been made in the kilohertz frequency range to temperatures of 120 c confining and pore pressure to 200 bars in berea sandstone with increasing temperature shear velocity and attenuation decrease at all pressures in a fully saturated rock the data suggest that thermal relaxation is not a significant loss mechanism under these conditions we propose that dissipation is controlled by a viscous fluid flow mechanism in which a sharp frequency peak in attenuation is shifted from 2khz at room temperature to 8 khz at 120 c as the pore fluid viscosity is decreased with increasing temperature however the velocity decrease is too great to be accounted for by a change of relaxation times a non dispersive temperature softening in shear may control the velocities

fluid mobility and frequency dependent seismic velocity direct measurements the influence of fluid mobility on seismic velocity dispersion is directly observed in laboratory measurements from seismic to ultrasonic frequencies a forceddeformation system is used in conjunction with pulse transmission to obtain elastic properties at seismic strain amplitude 10 7 from 5 hz to 800 khz varying fluid types and saturations document the influence of pore fluids the ratio of rock permeability to fluid viscosity defines mobility which largely controls pore fluid motion and pore pressure in a porous medium high fluid mobility permits pore pressure equilibrium either between pores or between heterogeneous regions resulting in a low frequency domain where gassmann s equations are valid in contrast low fluid mobility can produce strong dispersion even within the seismic band here the low frequency assumption fails since most rocks in the general sedimentary section have very low permeability and fluid mobility shales siltstones tight limestones etc most rocks are not in the lowfrequency domain even at seismic frequencies only those rocks with high permeability porous sands and carbonates will remain in the low frequency domain in the seismic or sonic band