mechanical interactions between rigid particles in a deforming ductile matrix analogue experiments in simple shear flow abstract the mechanical interaction between two or more particles is investigated in newtonian simple shear flow the experimental models allow observation of both the particle rotation and the deformation pattern around the particles the finite and instantaneous strain patterns around rigid particles are strongly heterogeneous and asymmetric with high finite strain zones aligned to the direction of maximum finite stretch these correspond to local flow with low vorticity number heterogeneous strain patterns around rigid particles spread over a distance of 1 2 times the particle length and this distance increases with increasing bulk strain where rigid particles are more concentrated these patterns coalesce and the overall pattern is then strongly controlled by the particles and cannot be simply related to the external boundary conditions in rocks the characteristic asymmetric strain pattern around rigid isolated particles is a reliable shear criterion which becomes unreliable with high concentrations of rigid particles particle rotation is significantly disturbed when the distance between adjacent particles of equal size is shorter than their length that is only in very concentrated suspensions of rigid particles in a composite shape fabric the development of the sub fabric corresponding to the smaller minerals will be more disturbed

rheology of till beneath storglaciaren sweden in order to study in situ the rheology of a deforming subglacial till various instruments were emplaced in till beneath storglaciaren sweden boreholes were used to gain access to the till beneath about 100 m of ice tiltmeters provided an estimate of the shear strain rate in the till two other instruments yielded measures of till strength in addition water pressures were recorded in boreholes and in the till a computer controlled distance meter provided an effectively continuous record of the surface velocity and data from frequent surveys of a stake network were used to estimate the mean basal drag based on a force balance calculation tilt rates varied directly with effective pressure so decreases in water pressure apparently increased the coupling between the glacier and the bed surface speed was either out of phase with tilt or varied independently of tilt thus increases in speed were apparently a consequence either of longitudinal coupling or of reduced coupling between the glacier and the bed they were not a result of till deformation till strength varied directly with effective pressure which is consistent with it being a mohr coulomb or frictional material the devices measuring till strength are presumed to have been pulled through the till at a speed that varied in phase with the surface speed but till strength did not vary systematically with surface speed this implies that the residual strength of the till is insensitive to strain rate thus the appropriate constitutive equation for till rheology may be of the form e e k where k is a constant this is consistent with experimental data reported in the geotechnical literature

the interrelation of glaciotectonic and glaciodepositional processes within the glacial environment abstract in recent years it has been recognised that ice sediment coupling occurred beneath the quaternary ice sheets that advanced over the soft sediments of lowland areas this paper looks in detail at the effects of this coupling on the sediments which results in glaciotectonic deformation and also discusses the interaction of deformation and deposition within the subglacial environment two types of glaciotectonic deformation are discussed that are produced by the active movement of ice 1 proglacial tectonics at the margin which include compressive fold styles such as listric thrusts and faults and open folding 2 subglacial tectonics formed beneath the glacier which include fold styles resulting from simple shear and represent a soft rock purely dynamic shear zone styles of deformation associated with stagnant ice are also investigated we argue that glaciotectonic deformation is a common phenomenon and an integral part of geological record from continental ice sheets it is suggested that zones of deformation within the sediment are related to similar zones of strain in the ice sheet and complex deformation sequences are produced by the superimposition of these differing styles upon one another as the ice sheet advances and retreats it is also argued that subglacial deposition and deformation are related and that on soft beds underformed till is rare whilst deformed till is very common

seismic models of a prograding carbonate platform vercors south east france abstract the southern vercors area south east france displays superb exposures of a lower cretaceous prograding carbonate platform these exposures allow a geometrical sequence analysis to be combined with detailed outcrop observations two dimensional seismic modelling techniques were used to determine the seismic response of three of these exposures the montagnette the archiane valley and the rocher de combau the outcrops display prograding and retreating series of clinoforms interfingering with fine grained basinal sediments photographs from different angles of view combined with detailed field observations were used to construct lithological profiles with a resolution of f few metres p wave velocities and bulk densities were measured from cored hand specimens and selected values were assigned to lithostratigraphic units in each profile the vertical incidence modelling technique was then used to compute migrated time sections of reflectivity these were convolved with source wavelets of different frequencies to produce the final synthetic seismic profiles none of the modelled outcrop geometries is correctly portrayed seismically at 25 50 hz frequencies not only do the synthetic seismic profiles show less detail they also show misleading geometries in most seismic models for instance pseudo unconformities are present that correspond to rapid changes in dip and in facies in outcrop furthermore the seismic tool is not able to resolve between stratal patterns punctuated by unconformities and those with gradual shifts in facies belts accompanied by complex interfingering relationships this implies that an unconformity recognized on a real seismic line should not automatically be assumed to represent a true stratal unconformity large outcrops are often used to show the validity of sequence stratigraphy a concept mainly based on the analysis of seismic lines this study however shows that there is no one to one relationship between geometries observed in outcrop and in seismic lines seismic modelling of outcrops therefore provides a means for evaluating outcrop geometries in terms of seismic stratigraphy

sequence architecture and heterogeneities of a field scale vaca muerta analog neuquen basin argentina from outcrop to synthetic seismic abstract the quintuco vaca muerta system in the neuquen basin argentina has received much attention due to its potential as a major unconventional play this study combines field geology with satellite imagery interpretation to document the sequence architecture of the prograding mixed carbonate siliciclastic system over several kilometers from the shelf to the basin detailed sections allow the allocation of bed scale lithofacies changes within this sequence stratigraphic framework synthetic seismograms are constructed from the observed facies distribution and petrophysical properties in order to compare this architecture with subsurface seismic data the field area the sierra de la vaca muerta shows a prograding system along a 10 km long and 1 km thick cross section the studied interval can be subdivided into eight depositional sequences based on the facies distribution representing a very similar scale as the seven sequences documented in the global sea level chart in this time interval this suggests a eustatic control on the system the depositional sequences are dominated by calcareous shale and siliciclastics but have variable amounts of carbonates admixed both temporally and laterally leading to different motifs of cyclicity and geometry shales and calcareous silt and sandstones are the dominant facies pure carbonate or pure siliciclastic portions are very rare and restricted to sequence tops carbonate rich portions are characterized by abrupt lateral facies transitions and breaks within their steep depositional profile whereas siliciclastic rich intervals show gently inclined profiles with no breaks and more gradual facies changes in the temporal scale heterogeneities occur both as cycles and events meter scale alternations of pure shale with calcareous shale are the typical cyclic expressions which occur down slope of carbonate dominated systems mixed turbidites commonly follow just after carbonate sequences triggered by the steeper depositional gradients this distribution indicates that carbonate rich intervals offer both more brittle volumes for fracturing calc shales and silty wackestones and potential relatively permeable layers turbidites within the surrounding tight shale these sweet spots follow the sequence stratigraphic framework and typically occur in close relation with tops of carbonate dominated cycles these carbonate cycles prove to be easy to detect in the synthetic seismograms due to their strong acoustic impedance and geometrical expressions these findings could offer a way to identify sweet spots for unconventional exploration in the basinal transition since they are laterally related to carbonate sequence tops which have a distinct seismic signature

microfabric and microshear evolution in deformed till abstract the bed deformation model of glacier movement requires that ice masses shear their beds to high strains for homogeneous basal tills that can result from such deformation however there are no sedimentological criteria for estimating strain magnitude thus a large ring shear device was used to shear two basal tills and their particle fabrics and microshears were studied at various strains up to 108 sand particle fabrics in a longitudinal flow plane became steady at shear strains of 7 39 steady fabrics were moderately strong with s1 eigenvalues of 0 71 0 74 these values are smaller than those from experiments with pebble sized particles perhaps reflecting the greater probability of sand particles colliding with larger grains fabrics parallel to flow strengthened progressively indicating that particles did not reorient with their long axes transverse to flow r1 and r2 microshears developed and persisted to the highest strains attained r1 shears became more pervasive with strain and oriented closer to the shear plane movement along both sets of shears provides an explanation for the plunge of the steady state sand fabric approximately 10 upglacier these experiments provide a basis for estimating till deformation magnitude but results will require cautious application to the geologic record where deformation processes may be ambiguous

forward seismic modeling as a guide improving detailed seismic interpretation of deltaic systems example of the eocene sobrarbe delta outcrop south pyrenean foreland basin spain as a reference to the analogous subsurface albian cenomanian torok nanushuk delta of the colville basin npra usa abstract a forward seismic model of the middle eocene sobrarbe delta outcrop south pyrenees spain has been made to investigate its seismic signature the sobrarbe delta complex corresponds to a syntectonic sedimentary wedge locally thicker than 1000 m this 15 km long highly progradational and moderately aggradational sedimentary system presents sigmoid and oblique clinoforms characterized by slopes ranging from 0 2 to 5 7 along the clinoforms the classical deltaic depositional environments grade progressively from one to the other alluvial plain delta plain delta front and prodelta locally specific carbonate deposits occur corresponding to transgressive pulses the transition from delta front to prodelta is locally marked by large slide scars affecting clinoform morphology a detailed outcrop transect of the sobrarbe delta was converted to an acoustic impedance model by assigning petrophysical properties to each geological facies this model was then used to create synthetic seismic lines characterized by various input wavelets the resulting various peak frequency synthetic seismic lines have been interpreted and the seismic interpretation compared to the outcrop description to calibrate the seismic interpretation and assess the limits of that interpretation this work shows that the seismic stratigraphy methodology is consistent and allows the correct interpretation of most seismic sequences however composite reflections from rapid lateral facies transitions and higher frequency sequence boundaries can clearly lead to seismic interpretation mistakes the seismic facies of seven facies associations have been described providing guidelines to recognize them on actual seismic lines the synthetic seismic image of four selected systems tracts comprising good reservoir bodies has been analyzed to highlight recognition criteria which can be used to interpret analog deltaic systems in the subsurface and therefore enhance the prediction and characterization of the reservoir bodies that they hold these guidelines were systematically applied to a direct subsurface analog the torok nanushuk delta colville basin npra usa

in search of ice stream sticky spots the form drag of large bedrock bumps sticking into the base of an ice stream can produce effective sticky spots supporting large basal shear stress bedrock regions surrounded by lubricating till at the same topographic level can cause sticky spots but tend to collect lubricating water and thus are unlikely to support a shear stress of more than a few tenths of a bar unless they contain abundant large bumps raised regions on the ice air surface also can cause moderate increases in the shear stress supported on the bed beneath surveys of large scale bedrock roughness strain grids across the margins of ice surface highs and possibly water pressure measurements in regions of thin or zero till would help identify and characterize sticky spots

impact of carbonate producing biota on platform architecture insights from miocene examples of the mediterranean region abstract different types of carbonate platforms formed in the mediterranean during the miocene low angle homoclinal types of ramp distally steepened ramps flat topped platforms and reef rimmed shelves the critical differences between these platforms result from differences in the capacities of the carbonate systems to accumulate sediments above hydrodynamic base level ecologically controlled accommodation the various depositional profiles and facies belt distributions resulted from the interplay between different sediment production and redistribution processes and the internal architectures resulted from the response of each type of platform to changes in accommodation heterogeneities driven by high frequency sea level cycles are maximized in platforms ruled by shallow water euphotic framework dominated production and minimized in low angle ramps where sediment resulted from aphotic and oligophotic carbonate production in the mediterranean region there is no direct relationship between type of platform and global temperature as shown by the coeval occurrence of different platforms in similar latitudinal settings although temperature is a key limiting factor other paleoceanographic factors such as trophic resources may have also been along with biological evolution important factors influencing different types of carbonate producing biotas

controls on sonic velocity in carbonates compressional and shear wave velocities v p and v s of 210 minicores of carbonates from different areas and ages were measured under variable confining and pore fluid pressures the lithologies of the samples range from unconsolidated carbonate mud to completely lithified limestones the velocity measurements enable us to relate velocity variations in carbonates to factors such as mineralogy porosity pore types and density and to quantify the velocity effects of compaction and other diagenetic alterations

seismic characterization of switching platform geometries and dominant carbonate producers miocene las negras spain the primary goals of seismic interpretation and quantification are to understand and define reservoir architecture and the distribution of petrophysical properties since seismic interpretation is associated with major uncertainties outcrop analogues are used to support and improve the resulting conceptual models in this study the miocene carbonates of cerro de la molata las negras south east spain have been selected as an outcrop analogue the heterogeneous carbonate rocks of the cerro de la molata platform formed by a variety of carbonate producing factories resulting in various platform morphologies and a wide range of physical properties based on textural thin sections and petrophysical porosity density carbonate content and acoustic properties analyses of the sediment s eleven individual facies types were determined the data were used to produce synthetic seismic profiles of the outcrop the profiles demonstrate that the spatial distribution of the facies and the linked petrophysical properties are of key importance in the appearance of the synthetic seismic sections they reveal that carbonate factory and facies specific reflection patterns are determined by porosity contrasts diagenetic modifications and the input of non carbonate sediment the reflectors of the seismograms created with high frequency wavelets are coherent with the spatial distribution of the predefined facies within the depositional sequences the synthetic seismograms resulting from convolution with lower frequency wavelets do not show these details the major reflectors coincide with i the boundary between the volcanic basement and the overlying carbonates ii the platform geometries related to changes in carbonate factories thus sequence boundaries and iii diagenetic zones changes in seismic response related to diagenesis switching carbonate producers and linked platform geometries are an important finding that needs to be considered when interpreting seismic datasets this article is protected by copyright all rights reserved

glacier motion dominated by processes deep in underlying till black rapids glacier is a 40 km long surge type glacier in the central alaska range in spring 1997 a wireline drill rig was set up at a location where the measured surface velocities are high and seasonal and annual velocity variations are large the drilling revealed a layer of subglacial till up to 7 m thick that is believed to be water saturated at one location a string of instruments containing three dual axis tiltmeters and one piezometer was successfully introduced into the till the tiltmeters monitored the inclination of the borehole at the ice till interface and at 1 and 2 m into the till for 410 days they showed that no significant deformation occurred in the upper 2 m of the till layer and no significant amount of the basal motion was due to sliding of the ice over the till the measured surface velocity at the drill site is about 60 m a 1 of which 20 30 m a can be accounted for by ice deformation almost the entire amount of basal motion 30 40 m a 1 was taken up at a depth of 2 m in the till possibly in discrete shear layers or as sliding of till over the underlying bedrock we propose that the large scale mobilization of such till layers is a key factor in initiating glacier surges

finite difference calculation of travel times the travel times of the first arriving seismic waves through any velocity structure can be rapidly computed on a two or three dimensional numerical grid by finite difference extrapolation from point to point wavefronts rather than the traditional rays are tracked head waves are properly treated and shadow zones are filled by the appropriate diffractions differences of less than 0 03 per cent are found between the results of this technique and raytracing for a complex two dimensional model this scheme is useful for the windowing of finite difference calculations to increase computing speed and promises to aid in earthquake location tomographic inversion and kirchhoff migration in structures that have strong lateral velocity gradients

subglacial clast behaviour and its implication for till fabric development new results derived from wireless subglacial probe experiments this study has investigated the three dimensional movement of clasts within deformation till using embedded wireless probes these probes were part of an environmental sensor network which measured subglacial properties temperature water pressure resistivity case strain and tilt six times a day and relayed that data via radio to the glacier surface where they were forwarded and broadcast on line the systemwas installed at briksdalsbreen norway and operated from august 2004 until august 2006 approximately 2000 probe days worth of data were collected with an increase in performance 41 more readings during the second year the probes showed similar patterns of water pressure rises throughout the two years but with slightly different magnitudes and timings these changes in water pressure could be related to clast behaviour the probes decreased their dip over the year and the rate of change was related to an increase in glacier velocity after initial changes in dip the probes experienced changes in orientation followed by rotation about the a axis this continuous rotation was similar to the motion suggested by jeffery 1922 the motion of ellipsoidal particles immersed in a viscous fluid proceedings of the royal society of london series a 102 161 179 for the behaviour of clasts within a viscous material in addition some probes also showed short frequent dip oscillations in spring and autumn which were interpreted to reflect stick slip events similar to lodging and demonstrated how local conditions can interrupt the predicted rotation pattern overall it is demonstrated that when water pressures were high decoupling occurred associated with basal sliding and dip oscillations and when water pressures fell the ice and sediment were coupled and till deformation occurred these events happened during summer and autumn it is this combination of lodgement and deformation that builds up both a complex but predictable fabric and a resultant composite till sedimentology

accommodation and supply a dual control on stratigraphic sequences abstract it is widely accepted that both eustatic and tectonically controlled regional changes of sea level have contributed to the record of stratigraphic sequences i suggest that environmental change be added as a third autonomous control sedimentologic principles clearly indicate that sequences and their systems tracts are controlled by the interplay of two rates the rate of change in accommodation space available for sedimentation and the rate of sediment supply sea level has direct control on accommodation but its influence on sediment supply is remote and easily overshadowed by environmental factors for instance the record of the most recent sea level rise is a transgressive systems tract where supply is low it is a prograding highstand systems tract in deltas where the supply is high examples of sequence boundaries generated by changes in sediment supply include tectonically driven shifts in sediment input into basins changes in ocean currents pulsating supply from failure of submarine slopes and drowning of carbonate platforms by environmental stress furthermore the stratigraphic sequences in fluviatile continental basins are physically removed from sea level induced changes in accommodation and must have formed by changes in the rate and pattern of supply subaerial exposure of marine sediments at the sequence boundary is a most important criterion for recognizing sea level cycles as opposed to supply cycles other criteria include downstepping of shelf breaks and characteristic patterns in the spacing of time lines within sequences some third order cycles ca 0 5 3 ma duration meet these criteria others do not cycle stacking patterns and the shifting facies belts on cratons indicate that many second and third order cycles lack pronounced exposure unconformities and represent gradual changes superimposed on more rapid shorter oscillations seismic data yield poor images of these gradational changes because they lack resolution seismic models of outcrops show that near the limits of resolution the seismic tool tends to portray rapid changes in facies and bed thickness i e lateral variations in supply as unconformities seismic unconformities do not necessarily correspond to unconformities in outcrop the succession of stratigraphic sequences is best considered a composite record of sea level and environmental change separating the various controls requires carefully planned experiments work on the oxygen isotope curve another proxy for sea level has set an example in this respect

an investigation of subglacial processes at the microscale from briksdalsbreen norway the subglacial processes at briksdalsbreen norway are examined by a combination of sedimentology thin section and scanning electron microscope sem analysis of till samples from an exposed subglacial surface and from beneath the glacier studies of a fluted surface indicate that subglacial deformation is occurring on a field scale with flutes forming behind most clasts 0 6 m high at the thin section scale 0 014 2 0 mm it is seen that deformation is by rotation and attenuation and is dependent on till texture at the sem scale 0 1 0 4 mm it is seen that erosion is controlled by abrasion and percussion which produces distinct grain styles as part of an erosional continuum overall it is shown that rotation and attenuation is a dominant process at all scales and that the clast interactions associated with different scale perturbations within the shear zone control erosion and deposition as well as landform and fabric production

building the 3 d jigsaw puzzle applications of sequence stratigraphy to 3 d reservoir characterization permian basin reservoir characterization involves the quantification integration reduction and analysis of geological petrophysical seismic and engineering data this is no small task a principal goal of reservoir characterization is to derive a spatial understanding of interwell heterogeneity traditionally geologic attempts to characterize interwell heterogeneity have been done using hand drawn or computer generated two dimensional 2 d maps and cross sections results can be improved dramatically using three dimensional 3 d interpretation and analysis techniques three dimensional reservoir characterization requires the same input data used in 2 d approaches and the cost is equal to and commonly lower than traditional 2 d methods the product of 3 d reservoir characterization is a 3 d reservoir model the language used to communicate the results of a 3 d reservoir model is visualization i e visual images of numerical data all of the available log and core data in a model area are incorporated in a 3 d model but the data are depicted as colored cells rather than as log traces the integrity of the 3 d reservoir model is largely a function of the stratigraphic framework interpreting the correct stratigraphic framework for a subsurface reservoir is the most difficult and creative part of the 3 d modeling process sequence and seismic str tigraphic interpretation provide the best stratigraphic framework for 3 d reservoir modeling the purpose of this paper is to discuss the process of 3 d deterministic reservoir modeling and to illustrate the advantages of using a sequence stratigraphic framework in 3 d modeling mixed carbonate and siliciclastic sediment outcrop and subsurface examples from the permian basin of west texas and new mexico will be used as examples but the concepts and techniques can be applied to reservoirs of any age three dimensional reservoir modeling results in an improved geologic interpretation provides a means of integrating geological petrophysical geophysical and engineering data and allows for immediate model updates as new data are acquired as a result of 3 d reservoir characterization reservoir management decisions data quality control volumetric calculations numerical sim lation input and communication between disciplines are improved

modeling dolomitized carbonate ramp reservoirs a case study of the seminole san andres unit part i petrophysical and geologic characterizations major issues in characterizing carbonate ramp reservoirs include geologic framework seismic stratigraphy interwell heterogeneity including rock fabric facies and permeability structure and factors affecting petrophysical properties and reservoir simulation the seminole san andres unit gaines county west texas and the san andres outcrop of permian age in the guadalupe mountains new mexico were selected for an integrated reservoir characterization to address these issues the paper is divided into two parts part i covers petrophysical and geologic characterization and part ii describes seismic modeling reservoir geostatistics stochastic modeling and reservoir simulation in dolomitic carbonates two major pore types are interparticle includes intergranular and intercrystalline and vuggy for nonvuggy carbonates the three important petrophysical rock fabric classes are i grainstone ii grain dominated packstone and medium crystalline dolostone and iii mud dominated packstone wackeston

clast collision frequency as an indicator of glacier sliding rate the mechanical interaction between a glacier and subglacial sediment can be observed using an instrumented rod that we refer to as the ubc ploughmeter for clast rich sediments the rate of collision between clasts and a rod dragged through these sediments should be related to the glacier sliding rate by assuming that proglacial measurements of sediment granulometry represent the subglacial granulometry of trapridge glacier yukon territory canada we have used ploughmeter results to obtain an estimated sliding rate of 45 mm d 1 in good agreement with known rates in addition for a subglacial material treated as a solid liquid dispersion having a linear viscous rheology the force of collision experienced by the rod should be proportional to the effective sediment viscosity our estimate of 2 0 x 10 10 pa s agrees well with previously derived values

clast fabric development in a shearing granular material implications for subglacial till and fault gouge elongate clasts in subglacial till and in fault gouge align during shearing but the relation between clast fabric strength and cumulative shear strain for such materials is effectively unknown this relation was explored in experiments with a large ring shear device in which a till and a viscous putty that contained isolated clasts were sheared to high strains as expected rotation of clasts in the putty is closely approximated by the theory of g b jeffery who derived the orbits of rigid ellipsoids in a slowly shearing fluid clast rotation in the till however is strikingly different rather than orbiting through the shear plane as predicted by jeffery most clasts rotate into the shear plane and remain there resulting in strong fabrics regardless of the aspect ratios and initial orientations of clasts this divergent behavior is likely due to slip of the till matrix along the surfaces of clasts which is a natural expectation in a granular material but violates the no slip condition of jeffery9s model these results do not support the widespread belief that subglacial till deformation results in weak clast fabrics thus many tills with weak fabrics thought to have been sheared subglacially to high strains like many basal tills of the laurentide ice sheet may have been sheared only slightly with little effect on either ice sheet dynamics or sediment transport in addition these results indicate that in simple shear the rotation of clasts in till and in fault gouge is best analyzed with the model of a march who treated inclusions as passive markers

rotation of rigid elliptical cylinders in viscous simple shear flow analogue experiments we used experiments to investigate the behaviour of rigid elliptical cylinders embedded in a viscous fluid of finite thickness and for very small ratios s between shear zone width z and the shortest principal axis e2 of the ellipse that constitutes the base of the elliptical cylinder 3 5 s z e2 1 2 former theoretical and experimental work on the rotation of rigid inclusions immersed in a viscous matrix considered infinite shear zone thickness and or a very large ratio between shear zone thickness and inclusion size s 1 and concluded that inclusions rotate continuously and synthetically with the applied bulk simple shear flow except for inclusions with infinite axial ratio our results depart greatly from the analytical predictions experiments were carried out at constant shear zone thickness but variable s and degree of coupling at the inclusion matrix interface the results show that 1 confined inclusion rotation always deviates from theoretical predictions for infinite shear zone thickness even for synthetic rotation 2 the deviation in the angular velocity and or in the sense of rotation increases as s approaches 1 and antithetic rotation is possible from a position with ellipse longest axis parallel to the shear plane and 3 a slipping inclusion matrix interface greatly enhances deviation from theoretical predictions with antithetic rotations to as much as 20

seismic expressions of a miocene prograding carbonate margin mut basin turkey the detailed stratigraphic architecture of a miocene intraplatform prograding carbonate margin outcropping in mut basin turkey was used to build two dimensional synthetic seismograms by normal ray tracing and finite difference exploding reflector methods the synthetic seismic models at various frequencies display the overall prograding architecture of the 1 5 km 0 95 mi 250 m 820 ft prograding margin even at 40 hz frequency however most of the complex stratigraphic architecture is below standard seismic resolution sigmoidal outcrop geometries create complex shingled seismic reflections that contain pseudodownlap pseudotoplap and various truncations at 40 hz frequency in addition reflections that do not correspond to any impedance contrast are generated by a tuning effect within the clinoform interference patterns created by the complex impedance distribution create reflections that change phase laterally and cross stratigraphic timelines several high impedance coral buildups at the slope break and on the platform top cause reflections to change phase and amplitude along the timeline in addition lateral impedance variations generate mounded reflections that in places cross timelines and resemble seismic images for buildups or anticlinal structures several of these resolution problems and interference patterns are reduced by an increase of the frequency for example at 80 hz peak frequency the sigmoidal geometries are better imaged improved resolution was also achieved on the synthetic seismic data simply by dividing trace spacing from 25 to 12 5 m 82 to 39 ft but keeping the modeling frequency constant indicating that for stratigraphic interpretation horizontal seismic resolution is at least as important as vertical seismic resolution this implies that adjusting the acquisition geometries would improve the seismic resolution without compromising depth by increased frequency for seismic interpretation this study shows how little of a complex stratigraphic architecture is truly imaged on seismic data and how complex impedance distribution can create false seismic reflection geometries that impede a correct seismic facies and sequence stratigraphic interpretation

basal friction of ice stream e west antarctica we use surface velocity derived from sequential landsat imagery and a control method to estimate the basal friction distribution of a major west antarctic ice stream the area averaged basal stress is approximately 1 4 10 4 pa or about 29 of the area averaged driving stress of 4 9 10 4 pa uncertainty of the derived area averaged basal stress is difficult to assess and depends primarily on spatial variation of the flow law rate factor in the constitutive law spatial variation associated with depth averaged temperature variation gives an uncertainty of approximately 10 3 pa approximately 60 of the ice stream has a basal stress magnitude less than 10 4 pa and approximately 30 has less than 10 3 pa these characteristics suggest the presence of a mechanically weak water charged subglacial till small scale sticky spots where basal friction exceeds the area averaged driving stress are scattered irregularly across the subglacial regime and comprise approximately 15 of the ice stream area sticky spots cluster in regions where landsat imagery suggests structural features in the underlying bedrock

scales of lateral petrophysical heterogeneity in dolomite lithofacies as determined from outcrop analogs implications for 3 d reservoir modeling petrophysical data from dolomite outcrops of the mississippian madison formation at sheep canyon wyoming exhibit three scales of lateral variability in single rock fabric units these include a near random component nugget effect a short range structure and a long range cyclic trend hole effect the nugget effect is high and accounts for 31 39 and 48 50 of the variance in porosity and permeability respectively short range lateral variability is reflected by correlation lengths of 6 5 16 ft 2 5 5 m laterally long range periodicities are equivalent to approximately 10 of the petrophysical variance and have wavelengths of 31 and 140 ft 9 5 and 42 6 m for porosity and permeability 55 ft 16 8 m for log10 permeability respectively cross sectional and plan view petrophysical models and streamline simulations explore the effects of these scales of heterogeneity on fluid flow although short range variability accounts for most of the petrophysical heterogeneity the longer range trends can significantly affect fluid flow behavior results indicate that breakthrough time and sweep efficiency vary depending on the magnitude of the lateral long range petrophysical variability that exists in a dolomite reservoir as the component of the long range periodicity hole effect increases from approximately 0 to 25 of the total petrophysical variability a corresponding increase in breakthrough time and sweep efficiency occurs however as the magnitude of the lateral long range petrophysical variability increases beyond 25 of the total petrophysical variability e g from 25 to 50 a corresponding reduction in breakthrough time occurs because the spatial continuity of permeability is greater results indicate that heterogeneity caused by lateral petrophysical cyclicity should be incorporated into dolomite reservoir models for hole effect magnitudes that are greater than 10 of the petrophysical variance to properly characterize and model these scales of variability in a petroleum reservoir outcrop analogs are essential to provide accurate quantitative descriptions of lateral variability in dolomite rock fabrics

analogue modelling of the influence of shape and particle matrix interface lubrication on the rotational behaviour of rigid particles in simple shear abstract the rotational behaviour of a rigid particle embedded in a linear viscous matrix undergoing cylindrical simple shear couette flow was studied in 2d rock analogue experiments the influence of particle shape elliptical vs monoclinic aspect ratio and the nature of the matrix particle interface lubricated vs unlubricated was investigated both matrix pdms and lubricant liquid soap were linear viscous with a viscosity ratio of ca 10 4 without lubricant the rotational behaviour of all particles closely approximates the jeffery theory lubricated monoclinic particles with the long diagonal initially parallel to the shear direction show back rotation and approach a stable position lubricated elliptical particles initially parallel to the shear direction also show back rotation but only transiently stabilize weak planar zones in the matrix adjacent to unlubricated elliptical particles do not induce backward rotation in general for elliptical particles rotation rate as a function of orientation depends on axial ratio and thickness of the lubricant mantle for thick mantles initially 10 of the volume of the particle rotation rates are faster than jeffery theory for very thin mantles they are markedly slower compared with thick mantles particularly when the long axis is nearly parallel to the shear direction rotation rates are never strictly zero so true stabilization does not occur however for more elongate particles axial ratio 6 rotation rates are so slow that a very strong shape preferred orientation would develop in a lubricated elliptical particle population in experiments the volume of lubricant is constant and the thickness adjacent to the long side of the particle progressively decreases with increasing strain in natural examples of porphyroclast systems the weak mantle continually develops by recrystallization and or cataclasis of the rigid clast core and a steady state between production and thinning could be attained potentially leading to true stabilization for particles with a high axial ratio

ice stream sticky spots a review of their identification and influence beneath contemporary and palaeo ice streams rapidly flowing ice streams are the arterial drainage routes in continental ice sheets and exert a major influence on ice sheet mass balance recent observations have revealed that ice stream flow exhibits considerable variability with relatively rapid changes taking place in speed and direction this spatial and temporal variability is intimately linked to the conditions at the base of the ice streams and the distribution of localised patches of basal friction known as sticky spots in this paper we provide a detailed review of sticky spot observations from both contemporary and palaeo ice stream beds in order to better understand their nature and influence observations and theoretical considerations reveal four primary causes of stickiness i bedrock bumps ii till free areas iii areas of strong well drained till and iv freeze on of subglacial meltwater these may act together in one location or in isolation and a progressive increase in their distribution could lead to ice stream shut down bedrock bumps are influential under active ice streams where they provide form drag and can create thinner ice which increases the likelihood of basal freeze on increased bed roughness may prevent the lateral migration of some ice streams but bedrock bumps are unlikely to cause ice stream shut down because over long time scales ice stream erosion might be expected to reduce their amplitude the influence of till free areas beneath an ice stream will depend critically on the amount of water that might be drawn out of the surrounding till to lubricate such areas they are likely to be most important in ice stream onset zones but their identification has proved difficult beneath active ice streams if an ice stream operates solely by till deformation it is conceivable that a progressive increase in the exposure of till free areas could lead to shut down through a process of sediment exhaustion areas of strong well drained till have been identified beneath both active and ancient ice streams and are most likely to result from the reorganisation of subglacial meltwater the collapse of an inefficient cannalised system to a more efficient channelised system can occur rapidly and this mechanism has been hypothesised as a candidate for ice stream shut down in both contemporary and palaeo settings basal freeze on has also been observed and inferred from beneath modern and palaeo ice streams and a reduction in basal meltwater supply coupled with ice stream drawdown and the advection of cold ice increases the likelihood of switching off an ice stream a paucity of data from ice stream sticky spots limits a better understanding of their nature distribution and evolution beneath ice streams future technological advances are likely to improve the resolution of the data collected from the beds of modern ice streams but well preserved palaeo ice stream beds also hold potential for investigating their influence on ice stream flow and we present simple landsystems models to aid their identification such data will considerably enhance the basal boundary condition in ice stream models which will ultimately refine our predictions of the response of contemporary ice sheets to future changes in climate

discriminating between onlap and lithologic interfingering in seismic models of outcrops seismic models of outcrops have shown that near the limits of resolution the seismic reflection tool records rapid facies changes as false lap outs we examined one such outcrop the triassic platform flank of picco di vallandro durrenstein in northern italy to develop criteria for recognizing false lap out patterns using measured sections photo mosaics of the continuous outcrop and petrophysical measurements on samples two contrasting impedance models were constructed one model supported by field observation shows interfingering between basin marls and slope carbonates the second model shows onlap of basin marls against slope carbonates but with similar overall geometries to the first model vertical incidence seismic models were produced at frequencies between 50 and 150 hz and with displays of seismic amplitude as well as two seismic attributes instantaneous phase and reflection strength at 50 hz the two lithologic models are seismically indistinguishable both showing onlap of basin units onto the slope at 90 hz displays of instantaneous phase begin to reveal the stratigraphic interfingering whereas seismic amplitude displays require frequencies of 150 hz to do so reflection strength accurately portrays the distribution of the two major facies in the entire range of examined frequencies but does not show sufficient detail to reveal interfingering vs onlap the same trends were visible with finite difference modeling of the full waveform here the differences between interfingering and onlap become visible at 150 hz in the phase model where seismic amplitude displays at this frequency are still ambiguous the phase model however fails to differentiate between slope dip and the basin sediment wedge whereas this wedge is clearly mapped by the reflection strength a combination of instantaneous phase and reflection strength provides a decisive advantage over conventional amplitude displays in recognizing rapid facies changes in seismic reflection data

seismic models of a shelf margin depositional sequence upper san andres formation last chance canyon new mexico abstract the seismic resolution of stratal geometries and facies distributions observed in san andres formation permian outcrops in last chance canyon guadalupe mountains new mexico is studied by seismic modeling of a published detailed stratigraphic cross section the outcrops in last chance canyon are composed of two fourth order depositional sequences an aggrading carbonate bank upper san andres 3 usa3 followed by a strongly progradational offlapping mixed carbonate siliciclastic succession upper san andres 4 usa4 each sequence comprises a number of subsidiary high frequency sequences fifth order two alternative impedance models were used model a in which all facies transitions are reflecting boundaries and model b in which only time significant surfaces act as reflectors and lateral facies transitions are represented by horizontal velocity gradients the vertical incidence modeling technique was used to compute perfectly migrated time and depth sections with different frequencies using a low frequency wavelet 25 hz the sequence boundary separating the two fourth order cycles usa3 and usa4 is poorly imaged instead one is tempted to incorrectly interpret an onlap pattern generated by a high frequency cycle within usa4 as this major sequence boundary in addition the 25 hz runs show toplap and downlap lap out patterns in an overly oblique fashion obscuring true asymptotic stratal relationships both at 35 hz and 50 hz profiles based on model b image the genetic structure of both usa3 and usa4 relatively well at 50 hz model a incorrectly shows a transition from a ramp to a rimmed margin within usa4 the 35 hz models are qualitatively compared with a published exxon production research co seismic line located approximately 50 km along depositional str ke to the northeast model a shows an unexpected good match with the exxon seismic line whereas model b comes much closer to the depositional anatomy observed in outcrop our results show that the resolution of stratal geometries and facies distributions in last chance canyon is strongly related to carbonate sandstone alternations and the way impedance contrasts at carbonate sandstone transitions are represented

basal sliding of ice stream b west antarctica a tethered stake apparatus is used to measure basal sliding in a borehole on ice stream b west antarctica about 300 km upstream east from its grounding line near the head of the ross ice shelf a metal stake emplaced at the top of a layer of unfrozen till underlying the ice is connected by a tether line to a metering unit that measures the tether line as it is pulled out from the borehole by the stake as a result of basal sliding the measured sliding motion includes any actual slip across the ice till interface and may include in addition a possible contribution from shear deformation of till within about 3 cm of the interface this 3 cm figure follows from a qualitative model of the movements of the stake in the course of the experiment based on features of the record of apparent sliding alternative but less likely models would increase the figure from 3 cm to 10 cm or 25 cm in any case it is small compared to the seismically inferred till thickness of 9 m measured apparent sliding averages 69 of the total motion of 1 2 m d 1 over 26 days of observation if a 3 5 day period of slow apparent sliding 8 of the total motion is included in the average the occurrence of the slow period raises the possibility that the sliding motion switches back and forth between c 80 and c 8 of the total motion on a time scale of a few days however it is likely that the period of slow apparent sliding represents instead a period when the stake got caught on the ice sole if the slow period is therefore omitted the indicated average basal sliding rate is 83 of the total motion in either case basal sliding predominates as the cause of the rapid ice stream motion in the last 2 days of observation the average apparent sliding rate reached 1 17 m d 1 essentially 100 of the motion of the ice stream if till deformation contributes significantly to the ice stream motion the contribution is concentrated in a shear zone 3 cm to possibly 25 cm thick at the top of the 9 m thick till layer these observations if applicable to the west antarctic ice sheet in general pose complications in modeling the rapid ice streaming motion

rotation behaviour of rigid inclusions in multiple association insights from experimental and theoretical models many rocks are representative of inclusion matrix systems where rigid inclusions float on a ductile matrix the geological analogues of such inclusion matrix systems are theoretically modelled with the help of jeffery s 1922 theory in recent years there have been a number of reinvestigations on the rotational motion of rigid inclusions to account for some geological observations that are not yet predicted in models based on jeffery s theory adding to this effort this paper investigates the effects of 1 inclusion concentration and 2 the degree of coherence at the inclusion matrix interface on the rotation behaviour of rigid inclusions in a multiple inclusion system during simple shear deformation shear box experiments were run on models containing multiple identical elliptic cylinders of wax mimicking rigid inclusion embedded within putty representing ductile matrix two sets of experiments were performed with and without lubrication at the inclusion matrix interfaces each model had an isolated inclusion to reveal the variation of rotations of single and multiple inclusions increase in inclusion concentration results in contrasting rotation behaviour of isolated and multiple inclusions initially oriented parallel to the shear direction when the interfaces were not lubricated inclusions in multiple association rotated antithetically whereas the isolated one almost remained stationary in models wherein the inclusion matrix interfaces were lubricated with liquid soap both isolated and multiple inclusions rotated antithetically but the isolated inclusion rotated at a lower rate with increasing inclusion concentration the difference in the rates of antithetic rotation between isolated and multiple inclusions tended to be larger in both lubricated and non lubricated conditions the sense of rotation of isolated as well as multiple inclusions initially oriented perpendicular to the shear direction was always synthetic irrespective of the nature of the interface lubricated or non lubricated however the instantaneous rotation rates of inclusions in multiple association were higher than that of the isolated inclusions disposed in the same orientation rotation of inclusion in an inclusion matrix system is basically induced by the traction exerted by the flowing matrix on the surface of the inclusion during deformation employing a hydrodynamic model it is shown that mutual mechanical interaction among inclusions which is a function of inclusion concentration modifies the stresses at the inclusion matrix interface to a large extent moment calculations reveal that inclusions oriented parallel to the shear direction experience an antithetic moment in response to the normal stress components the magnitude of which increases with increasing inclusion concentration this implies that rotation of shear parallel inclusions in antithetic sense is favoured by higher inclusion concentration on the other hand inclusions oriented perpendicular to shear direction experience a moment that induces synthetic rotation the magnitude of the synthetic moment is larger for larger inclusion concentration leading to increase in the rate of synthetic rotation using the theoretical model the moments are calculated as a function of the aspect ratio of inclusions and the inferences based on this moment calculation are complemented with experimental findings

mut basin turkey miocene carbonate depositional styles and mixed systems in an icehouse setting the mut basin in southcentral turkey contains a rich variety of cenozoic carbonate deposits that developed on a complex pre miocene topography and can be studied in seismic scale three dimensional outcrops these include open and rimmed carbonate shelves with steep slopes small isolated platforms and mixed carbonate siliciclastic systems showing reciprocal sedimentation the exceptional preservations of the stratal geometries make it possible to easily link large scale depositional geometry to depositional facies in a variety of platform types and depositional environments the mut basin provides a better understanding of 1 the control of antecedent topography on carbonate platform development 2 the influence of icehouse conditions e g high amplitude high frequency sea level fluctuations on the carbonate system 3 the link between faunal evolution and the style of carbonate platforms and stratigraphic architecture 4 lateral and reciprocal carbonate and siliciclastic sedimentation 5 platform asymmetry and local controls on stratal geometries and 6 the architecture of steep carbonate margin and associated gravitational collapse deposits these concepts are directly applicable to time equivalent cenozoic carbonate reservoir systems in southeast asia the southern caribbean and the eastern mediterranean

deformation around rigid particles the influence of slip at the particle matrix interface abstract theoretical and previous experimental studies of rigid particle structures have only considered the behaviour of rigid particles for which the interface between particle and matrix is coherent in natural rocks the boundary behaviour may cover the whole range from free slip to complete coherence examples where slip may be promoted include crack seal deformation during the development of pressure shadows core mantle structures where the mantle is composed of much weaker fine recrystallized material and crystallizing magmas or partially molten rocks where grain boundaries are lubricated by the melt phase analogue scale model experiments have been performed under pure shear and simple shear conditions to compare the particle rotation and the flow in the matrix for both slipping and non slipping particle matrix interfaces when slip does occur particles rotate faster in pure shear and slower in simple shear than for non slip leading to the more rapid development of a shape preferred orientation the preferred orientation tends to be bimodal in simple shear flow the flow and finite strain patterns in the matrix are also strongly influenced by slip at the interface and porphyroclast systems can develop geometries with ambiguous or contradictory shear senses dependent on the original particle orientation in multi particle experiments slip on the interfaces enhances strong strain localization in non linear viscous material to produce patterns very similar to natural s c fabrics

integrated characterization of carbonate ramp reservoirs using permian san andres formation outcrop analogs the san andres formation permian guadalupian of the permian basin is representative of carbonate ramp reservoirs in that it has highly stratified character complex facies and permeability structure and generally low recovery efficiencies of 30 of original oil in place the approach used here to describe carbonate ramp reservoirs such as the san andres formation produces detailed reservoir models based on integration of sequence stratigraphic analysis petrophysical quantification through definition of rock fabric flow units and fluid flow simulation synthesis of these subdisciplines clarifies which aspects of the geologic petrophysical model are most significant in predicting reservoir performance and ultimately in understanding the location of remaining oil satur tion the san andres formation crops out along the algerita escarpment a long oblique dip continuous shelf to basin exposure in the central guadalupe mountains these outcrops provide a unique opportunity to study lateral relationships in geologic and petrophysical structure analogous to those occurring between wells in subsurface reservoirs on the basis of sequence stratigraphic analysis three scales of cyclicity are recognized depositional sequences high frequency sequences and cycles examination of the cycles in two detailed window areas provides a practical scale for petrophysical quantification and fluid flow simulation an understanding of cycle position within the high frequency sequence framework also provides predictive information petrophysical analysis revealed six rock fabric groups dominated by intergranular separate vug or dense intercrystalline pore types comparison of these rock fabric groups with facies descriptions produced a rock fabric flow unit model that honors the geologic structure of the cycle and sequence framework permeability data were averaged within rock fabric flow units using a geometric mean approach based on fine scale fluid flow modeling of deterministic and stochastically generated permeability fields two dimensional black oil fluid flow models illustrate that 1 major differences in sweep efficiency and fluid flow performance are predicted when linear interwell interpolations are compared with actual interwell scale geologic structure as determined by outcrop geologic and petrophysical mapping 2 an understanding of static geologic petrophysical conditions provides only a partial understanding of reservoir performance defined by the interaction of these static properties and dynamic properties of fluid flow interaction within the flow unit architecture and 3 because of the orderly distribution of high and low permeability facies within cycle stacks of high frequency sequences this larger scale of geologic description can give a reasonable first order approximation of fluid flow patterns and early breakthrough end page 181

facies heterogeneity at interwell scale in a carbonate ramp upper jurassic ne spain abstract the well exposed upper kimmeridgian carbonate ramp near arroyo cerezo iberian basin eastern spain provides an excellent analog to stratigraphically equivalent subsurface reservoirs such as the carbonate ramps of the arab d of the middle east and the smackover of the gulf of mexico critical questions regarding interwell scale heterogeneity and correlation motifs for low angle ramp systems can be addressed using continuous exposures that encompass a full range of inner to outer ramp facies outcrops in this area provide a complete exposure of the ramp succession in depositional dip direction at arroyo cerezo a 40 m thick and 1 3 km long dip oriented continuous outcrop has been studied lithofacies and bounding surfaces have been mapped on a continuous photomosaic to build a detailed 2d cross section complemented by five stratigraphic sections 300 m apart and petrographic analysis the reconstructed section shows the facies transition from relative proximal to distal carbonate ramp settings carbonate facies associations are grouped according to the dominant carbonate types buildup dominated systems and coated grain dominated systems detailed mapping of facies and bounding surfaces documents distinct ramp depositional units with downdip facies changes occurring within the 1 3 km length of the outcrop the arroyo cerezo outcrop indicates that the ramp facies continuity when based on a 5 10 km distance well log correlation is mostly apparent use of detailed spatial and temporal analysis of high quality outcrop analogs promotes more realistic models for understanding the interwell meter scale heterogeneity and the scale of these depositional heterogeneities although being below resolution of subsurface tools governs in fact along with diagenetic modifications the fluid flows within a reservoir the scale of these stratigraphic heterogeneities needs to be considered in order to optimize and enhance hydrocarbon production and last recovery

basal conditions beneath a soft bedded polythermal surge type glacier bakaninbreen svalbard original article can be found at http www sciencedirect com science journal 10406182 copyright elsevier ltd and the international union for quaternary research inqua doi 10 1016 s1040 6182 01 00053 2 full text of this article is not available in the uhra

warm humid paleoclimate control of salinized lacustrine organic rich shale deposition in the oligocene hetaoyuan formation of the biyang depression east china abstract lacustrine organic rich shales are widely developed within the oligocene biyang depression in the nanxiang basin in east china and across southeast asia these shales have been proven as hydrocarbon source rocks of crude oil as well as sources and reservoirs of shale oil understanding the deposition of these shales is essential to reconstruct the paleoenvironment and paleoclimate during the oligocene in east china as well as target the potential shale oil resources based on x ray diffraction organic and inorganic petrologic organic and inorganic geochemical and stable isotopic analyses paleoenvironment paleoclimate and hydrocarbon potential of the lacustrine organic rich shales in the oligocene hetaoyuan formation were investigated the mineral composition of hetaoyuan formation organic rich shales is dominated by clay minerals followed by quartz plagioclase calcite dolomite pyrite and gypsum six lithotypes are identified including siltstone silty shale clay shale calcareous shale dolomite shale and massive mudstone the organic matter om of the organic rich shales is dominated by type i kerogen lamalginite maturity parameters tmax biomarker ratios and calculated vitrinite reflectance suggest that the om enters the oil window maturity high toc and generative potential together with high contents of brittle minerals including quartz plagioclase and carbonates reveal the oligocene hetaoyuan formation hold good to very good potential of shale oil exploitation six organic rich shale layers have been identified in the hetaoyuan formation shale layer 1 to 6 from top to bottom among them shale layers 5 and 3 hold the best shale oil potential and therefore be investigated in the present paper shale layer 5 was deposited in a semi deep lacustrine environment under the moderately warm humid paleoclimate further dividing into lower middle and upper units relatively low toc contents av 2 6 wt in the lower unit are probably caused by high sedimentation rate high bioproductivity under favorable preservation conditions led to relatively high toc contents av 3 6 wt in the middle unit less reducing conditions together with moderate low bioproductivity resulted in relatively low toc contents av 2 6 wt in the upper unit warm humid paleoclimate prevailed during deposition of shale layer 3 deepened water depth and formed a deep lacustrine environment the stratified water column led to stable anoxic condition and photic zone euxinia in the saline deep lacustrine environment which enabled the accumulation of high amounts of om av 4 9 wt toc under excellent preservation av hi 710 mg hc g toc the results of core scanning analysis indicate that formation of the laminated shales probably controlled by seasonal fluctuations of paleoclimate

reef building and carbonate production modes in the west central tethys during the cenozoic abstract changing components rock textures lithofacies platform types and architecture throughout time are unique characteristics of carbonate rocks characterizing these attributes has been approached by 1 building reference models for specific phanerozoic intervals 2 recognizing the climatic impact in modulating carbonate production and 3 analyzing the influence of changing bio geochemical conditions the reference model approach is mostly based on biological evolution the climatic impact approach emphasizes temperature and the bio geochemical approach considers the changes in mg ca ratios and ca concentrations in the oceans to date however an analysis integrating all of these factors is still missing the analysis presented here includes all these factors but also co 2 which is fundamental for both photosynthesis and caco 3 precipitation here we analyze the waxing and waning of cenozoic reef limestones from the central tethys region through several steps 1 on the basis of rock volume rock textures associated sediments and light dependent skeletal components as records of light penetration and wave energy depth 2 on global environmental conditions 13 c 18 o p co 2 temperature and 3 on the basis of functionality nutritional requirements and available resources through the cenozoic water motion whether induced by surface or internal waves or by currents increased as the thermal gradients strengthened both with depth and with latitude active water motion is essential for plankton catchers such as corals but less so for many larger benthic foraminifers lbf pycnoclines in the meso oligophotic zone would then favor the benthic plankton catchers such as corals but would be detrimental for many lbf warm temperatures favored lbf the eocene lbf families predominated during lowering of atmospheric p co 2 by using respiratory co 2 to enhance the symbiont production of photosynthates under oligotrophic conditions and limited turbulence whereas the miocene families had to adapt to a progressive increase in turbulence the eurythermal coralline red algae however became preponderant producers in the mesophotic zone during times when the 13 c was relatively high this explains two apparent paradoxes 1 corals thrive best when the earth s high latitudes cool and 2 the dominance of corals and lbf is inversely correlated despite they both require tropical conditions and have similar trophic strategies mixotrophy

an investigation of subglacial shear zone processes from weybourne norfolk uk abstract the glacial sediments of north norfolk are a type site for subglacial deforming bed sediments this investigation focussed on subglacial shear zone process at the field and thin section scale in order to understand subglacial processes as well as considering the implications for regional stratigraphies the sandy and chalky tills from three sites within 1 km at weybourne norfolk showed evidence for subglacial deformation associated with simple shear producing extension compression and rotation it was demonstrated how these processes interacted to cause chalk fragmentation and predictable fabric strengths dependant on sorting and grain size it is suggested that the marly drift is a diachronous unit and the resultant stratigraphy at weybourne reflects one deformation till resulting from a series of ice advances but with a lithology derived from the local chalk bed rock with some far travelled erratics which have undergone different degrees of chalk fragmentation reflecting the nature and duration of the subglacial deformation

experimental observations on the effect of interface slip on rotation and stabilisation of rigid particles in simple shear and a comparison with natural mylonites for axial ratios r not vert similar3 porphyroclasts from three mylonites all show a very strong spo with the long axis of the best fit ellipse at an antithetic angle of 5 10 to the shear direction this is more consistent with a stable end orientation than with the transient fabrics predicted by theory for elliptical rigid particles in simple shear the cause of this divergence is investigated in a series of high simple shear strain 15 analogue experiments performed in a ring shear machine couette flow using a linear viscous matrix pdms the rotational behaviour of elongate r not vert similar5 rigid particles with elliptical and rhomboidal shapes comparable with the natural examples is modelled for both coherent and slipping particle matrix interfaces interface slip causes a dramatic reduction in the rotation rate of the elliptical particle compared with theory when the long axis is close to the shear direction but not stabilisation interface slip does result in stabilisation of the rhomboidal particle with the long diagonal oriented at a small antithetic angle to the shear direction for monoclinic particles mirror image shapes referred to here as types 1 and 2 show different rotational behaviour for the type 1 particle with a shape comparable to porphyroclast systems and mica fish the long side rotates asymptotically into parallelism with the shear direction natural examples of type 1 particles such as hornblende and olivine porphyroclasts measured from the finero mylonites southern alps show a very strong preferred orientation for r not vert similar3 with the long side parallel or at a small 5 antithetic angle to the mylonitic foliation for type 2 particles the short side stabilises close to the shear direction or at a small synthetic angle as also observed for sillimanite porphyroclasts from the mont mary mylonites western alps in this natural case stabilisation of the short sides is against an extensional crenulation cleavage rather than the mylonitic foliation the analogue experiments establish that interface slip is one mechanism for stabilisation of elongate rhomboidal particles in natural examples decoupling from the matrix may be affected by extensional crenulation cleavage or c planes in s c fabrics

deformation of till beneath ice stream b west antarctica the behaviour and possible instability of the west antarctic ice sheet depend fundamentally on the dynamics of the large ice streams which drain it model calculations show that most ice stream velocity arises at the bed1 2 and radar sounding has shown the bed to be wet3 but the basal boundary condition is not well understood seismic evidence from the upstream b camp upb on the siple coast of west antarctica4 shows that the ice stream there rests on a layer of unconsolidated sediment averaging 5 or 6 m thick in which the water pressure is only 50 kpa less than the overburden pressure because this thin layer occurs well inland beneath an active ice sheet and rests on a surface showing flutes4 characteristic of glacial erosion5 we presume that it is glacial till we propose here that deformation within the till is the primary mechanism by which the ice stream moves and we discuss implications of this hypothesis

seismic model of a progradational carbonate platform picco di vallandro the dolomites northern italy we present a seismic model of a well exposed carbonate platform to basin transition from the triassic succession at picco di vallandro the dolomites northern italy the core of this model is a detailed lithologic cross section that represents 1500 m of stratigraphic section over a distance of 3 5 km the cross section is based on detailed measured sections photo interpretation and careful projection of surface mapping into the plane of section samples from the measured sections provide control on velocity and density distribution and these data were used to generate an impedance model from the cross section the impedance model was convolved with a zero phase 25 hz peak frequency wavelet to produce the seismic model the results illustrate how the platform to basin transition might be imaged by conventional seismic reflection data how the reflections relate to the distribution of lithology and through going geological surfaces and how constructive and destructive interference and seismic resolution combine to produce individual reflections the picco di vallandro section displays several scales of progradation and retrogradation ranging from stacked buildups that are several hundreds of meters thick to the interfingering of individual beds the seismic model displays this complexity with varying degrees of success the individual buildups are well imaged but as expected smaller features are not as clearly reproduced by the model intermediate scale sections that represent platform retrogradation are shown as surfaces of onlap in the seismic model but field work shows that the platform was still shedding sediment while retreating and that no simple onlap surface exists in the outcropping section a similar lack of stratigraphic resolution is shown by the model at the downlapping clinoforms which do not correspond to iscrete stratal surfaces but to the toe of slope position where major bedding units thin below seismic resolution smaller features such as the position of downslope terminations of carbonate breccia wedges are not resolved by the model toe of slope packages of limestone turbidites are represented only by reflection segments of higher amplitude the decreasing seismic resolution is caused by limited seismic bandwidths and by the effects of constructive and destructive interference interference has the largest effects at the complexly interfingering buildup to basin transition or at the most detailed part of our model an understanding of these types of seismic limitations and their controls is important as we try to extract more and more stratigraphic information from seismic data p

seismic models of a carbonate foreslope to basin transition picco di vallandro dolomite alps northern italy detailed geologic cross sections augmented by laboratory calibration of lithology and acoustic impedance have been used to produce synthetic reflection seismic sections of a carbonate foreslope to basin transition two areas from the picco di vallandro region of the dolomite alps were modeled a progradational section and a retrogradational backstepping section the resulting models show how these complex areas of strata interfingering might be displayed on conventional reflection seismic lines in the area of progradation rapid stratigraphic thinning below seismic detectibility coupled with abrupt impedance changes produces a reflection discontinuity between steeply dipping reflections of the foreslope and gently dipping parallel reflections of the basin section this apparent downlap surface marks the toe of slope for successive clinoforms but does not correspond to a discrete stratigraphic surface in the backstepping example similar stratigraphic thinning and impedance changes create an apparent onlap surface wavelet interference causes complications in both examples these models indicate how stratigraphic complexity can be simplified by the seismic reflection process and suggest that caution should be exercised when using seismic data to construct general models in areas of complex depositional geometries and rapidly changing facies

seismic interpretation of carbonate depositional environments most seismic stratigraphic or seismic lithologic interpretations have been applied to clastic depositional systems because of their unique sedimentologic and mineralogic characteristics carbonate rocks are more difficult to study using seismic data increased knowledge of carbonate deposits and their petrophysical parameters and higher quality geophysical tools now permit a better understanding of carbonate rocks using seismic images in this paper seismic facies of carbonate rocks are characterized step by step from the basin to the supratidal environment 1 pelagic deposits shales and micritic limestone layers exhibit continuous parallel reflections with an apparently high frequency chalk deposits display continuous high amplitude reflections at the top and base with an internal reflection free zone 2 talus deposits are characterized by discontinuous oblique reflections of high amplitude carbonate debris flow generates chaotic reflections with hummocky surfaces channels exhibit erosional truncations 3 reef barriers are mound shaped biogenic deposits that display marginal onlapping reflections overlying reflections drape the reefs and underlying reflections exhibit pull up or pull down effects hyperbolic diffractions also may occur 4 platform border sands are mound shaped oblique reflections of moderately high amplitude 5 inner shelf strata are characterized by parallel continuous reflections typically displaying low frequency patch reefs may be distinguished within the inner shelf system mound shape drape of overlying reflections velocity anomalies and spurious events 6 where dolomitized the intertidal to supratidal facies exhibit a marbled zone a practically reflection free zone with a few discontinuous reflections diagenetic events such as paleokarst zones may be delineated using special analyses involving amplitude offset variations the study of carbonate depositional environments and petrophysical characteristics provides a more complete geologic insight including relative changes in sea level within a sedimentary basin such studies are fundamental in analyzing carbonate reservoirs and their paleogeographic settings

rapid soft bed sliding of the puget glacial lobe the puget lobe of the late pleis inferred to be lodgment till based on the tocene cordilleran ice sheet advanced into presence of oriented stones oriented stria western washington over a thick sequence of tions on stones overconsolidation and unlithified sediments the basal drag due to deformation features sliding over this surface was calculated by 1 this paper investigates the rapid motion of idealizing the sediment bed as a rigid planar the puget lobe over its bed of deformable sedi surface scattered with roughness elements cor ment studies of large vanished glaciers com responding to individual sedimentary particles plement basal motion studies of modern glaci and 2 taking the minimum reconstructed slid ers in which the glacier geometry and velocity ing velocity to be 500 m yr 1 the calculated are well constrained but the characteristics of basal drag minimized by choices of parameters the bed can only be inferred from observations is 400 kpa much higher than the reconstructed over very limited areas kamb et al 1985 gravitational driving stress of 40 kpa indi seismic measurements blankenship et al 1986 cating that a rigid bed and low water pressure or modelling lingle and brown 1987 obser are not consistent with the glacierfs rapid vations on glacier beds recently exposed by motion high subglacial water pressure aver glacial retreat can provide information about aging 90 of the ice overburden 10 mpa is conditions during a somewhat greater time span inferred from overconsolidation of subglacial but are restricted to the marginal environ clays the occurrence and deformation of ment in addition inferences about the bed of water deposited sediments within the till and modern glaciers are limited by the short dura the requirement to drain large quantities of tion and seasonality of the observations a water from the interface suggest that water notable benefit of studying the beds of pieis pressure reached 99 of the ice overburden tocene glaciers is that they record basal ploughing of till by ice entrained clasts per conditions for intervals spanning entire glaci vasive shearing and finally ice bed separa ations and accessible far from the glacier tion become possible as water pressure margins increases at the low inferred effective nor after a brief summary of data available from mal stress the basal drag is reduced from the previous reconstructions of the puget lobe the rigid bed case by water layers which decouple basal conditions of the lobe are explored along the smallest particles from the glacier sole two complementary lines we first present cal and ploughing which reduces the resistance culations of basal drag due to glacier sliding offered by the largest particles the limited for different models of till bed roughness that shear strain observed in much of the till indicate that rapid sliding requires very low implies pervasive shearing did not contribute effective stresses and extensive ice bed significantly to ice motion basal motion was decoupling or ploughing second we summarize confined to the ice bed interface or to dis geological and geotechnical data that indicate tinct faults within the substrate

seismic models of a mixed carbonate siliciclastic shelf margin permian upper san andres formation last chance canyon new mexico seismic models based on randomly distributed samples from the permian upper san andres formation last chance canyon new mexico verify that the most prominent seismic reflections are related to stratal geometry however at least some reflections arise from lateral facies transitions that are commonly associated with highly prograding mixed carbonate siliciclastic sediments understanding seismic reflections and reflection terminations in sedimentary rocks requires simulation of at least 2 d cross sections of the impedance distribution to investigate the cause of reflections in strongly prograding mixed carbonate siliciclastic shelf margins acoustic velocity and bulk density were measured on more than 60 plugs that spatially cover one higher order genetic sequence the resulting impedance values were gridded and contoured and the genetic sequence was repeated to create a cross section averaging impedance values for each lithofacies zone generated a second impedance cross section seismic models of both impedance cross sections revealed the following observations 1 reflections associated with the sequence boundaries are subject to amplitude and polarity phase changes and 2 at least one reflection within the high order sequences is related to subhorizontal facies changes and is associated with two pseudounconformities the contoured impedance model is suggested to closer resemble the true impedance function in outcrop and shows subtle vertical shifts and significantly higher impedance contrasts

synthetic seismic model of a permian biosiliceous carbonate carbonate depositional system spitsbergen svalbard archipelago abstract the non unique correspondence between seismic and subsurface geology is a fundamental problem when interpreting seismic data sets synthetic seismic models of outcrop analogs are commonly constructed to cover the gap between the small scale outcrop observations and low resolution seismic data the permian biosiliceous carbonate carbonate sediments on spitsbergen are characterized by a wide variability in lithologies and microfacies determining the petrophysical properties e g porosity acoustic properties that consequently complicate seismic interpretation this study uses 1d and 2d synthetic seismic modelling techniques at different resolutions to gain an understanding of how seismic reflectors are expressed with respect to the sediment distribution aiming to facilitate real seismic interpretation in the study area nine microfacies were defined that were used to produce a geological model displaying small scale microfacies variations within a well defined sequence stratigraphic framework laboratory derived petrophysical properties vp bulk and ai were assigned to each predefined microfacies body in the geological models in order to construct acoustic impedance models that were used to produce synthetic seismograms the appearance of the seismic reflectors in the synthetic seismic profiles is primarily controlled by changes in mineral composition and link to spatial microfacies distributions within the depositional sequences differences in acoustic impedance and the origin of synthetic seismic reflections within a single microfacies type are mainly caused by porosity contrasts varying between 5 and 20 and diagenetic modifications such as chertification and cementation this detailed information cannot be derived from the low frequency seismograms 25 100 hz resulting in changes in seismic expression when seismic resolution diminishes comparison with time equivalent real and synthetic seismic data of the finnmark platform reveals similarities with the synthetic seismic reflection patterns of spitsbergen in both areas the pronounced seismic traces follow abrupt microfacies transitions which are coherent with cycle boundaries and timelines

pseudo unconformities in seismic models of large outcrops traditionally seismic modeling has concentrated on one dimensional borehole modeling and two dimensional forward modeling of basic structural stratigraphic schemes which are directly compared with real seismic data two dimensional seismic models based on outcrop observations may aid in bridging the gap between the detail of the outcrop and the low resolution of seismic lines examples include the dolomites north italy the vercors se france and the high atlas morocco the seismic models are generally constructed using the following procedure a construction of a detailed lithologic model based on direct outcrop observations b division of the lithologic model into lithostratigraphic units c assignment of petrophysical properties to these lithostratigraphic units d ray tracing to compute time or depth sections of reflectivity e convolution of the reflectivity sections with source wavelets of different frequencies the lithologic detail modeled in the case studies led to some striking results particularly the discovery of pseudo unconformities pseudo unconformities are unconformities in seismics but correspond to rapid changes of dip and facies in outcrop none of the outcrop geometries studied were correctly portrayed seismically at 25 hz peak frequency however in some instances the true relationship would gradually emerge at peak frequencies of 50 100 hz the examples given in this study demonstrate that detailed outcrop derived seismic models can reveal what stratigraphic relationships and features are likely to be resolved under ideal or less ideal conditions and what pitfalls may befall the interpreter of real seismic data

subglacial till formation sedimentary characteristics and classification we review the major subglacial till forming processes as presently understood by glacial researchers and define the parameters within which tills are produced and reconcile them with sedimentary end members processes of deformation flow sliding lodgement and ploughing coexist at the base of temperate glacier ice and act to mobilize and transport sediment and deposit it as various end members ranging from glacitectonically folded and faulted stratified material to texturally homogeneous diamicton the dominance of any one subglacial process varies both spatially and temporally giving rise to the possibility that a till or complex till sequence contains a superimposed signature of former transportation deposition at the ice bed interface we recommend that while glacial geologists and geomorphologists should be able to recognize the sedimentary imprints of various subglacial processes genetic fingerprinting of subglacial tills should be less process specific and till classification must reflect the range of products encompassed by the subglacial till production continuum glacial geologists can presently unequivocally identify a glacitectonite rock or sediment that has been deformed by subglacial shearing deformation but retains some of the structural characteristics of the parent material b subglacial traction till sediment deposited by a glacier sole either sliding over and or deforming its bed the sediment having been released directly from the ice by pressure melting and or liberated from the substrate and then disaggregated and completely or largely homogenised by shearing and support the theoretical case for c melt out till sediment released by the melting of stagnant or slowly moving debris rich glacier ice and directly deposited without subsequent transport or deformation because observations on contemporary glaciers reveal that their beds are most likely to be mosaics of deformation and sliding and warm based and cold based conditions the patterns of which change temporally and spatially it is extremely unlikely that subglacial till end members in the geological record will be anything but hybrids produced by the range of processes operative in the subglacial traction zone

modeling reservoir heterogeneity within outer ramp carbonate facies using an outcrop analog san andres formation of the permian basin variably cyclic fusulinid rich outer ramp facies of the permian san andres formation are exposed along the algerita escarpment guadalupe mountains new mexico we have used the outcrop exposures and cored wells drilled adjacent to the outcrop to assess reservoir and interwell scale variability of permeability as a potential analog for carbonate reservoirs in the permian basin and elsewhere permeability distribution was evaluated using a field permeameter and conventional measurements on small core plugs taken along vertical and horizontal outcrop traverses and from the slim hole cores permeability is related to the variable development of depositional cycles within a small scale sequence and also to diagenetic overprinting geostatistical models of permeability variation honoring the geologic and petrophysical data were constructed and input into a waterflood simulator to understand the interactions between heterogeneity and flow variograms constructed from conventional plug analyses of permeability for a vertical outcrop transect contain a significant small scale signal noise as seen in the high nugget effect approximately 50 of the overall sample variance and have correlation ranges of less than 4 5 m 15 ft different vertical variogram characteristics are displayed by cyclic and less distinctly cyclic parts of the san andres variograms constructed for horizontal transect data from three distinct stratigraphic units have nearly identical properties overall the ranges of correlation are short 3 3 5 m 10 12 ft when compared to typical interwell distances supporting a nearly uncorrelated and highly variable permeability model using observed short ranges of vertical and horizontal correlation and honoring the vertical transect data cross sectional conditionally simulated permeability fields were generated and used in simulated waterfloods to investigate the sensitivities to an oil recovery model and overall fluid injection rate for this style of stratigraphy and cyclicity cyclic parts of the section are characterized by a potential for early water breakthrough and relatively high vertical sweep efficiencies within the less distinctly cyclic section waterflood fronts have a fingerlike profile and vertical sweep efficiency is generally poorer

subglacial till a physical framework for its properties and processes the continuum theory of mixtures provides a framework around which present knowledge of subglacial till can be organized the proposed framework is provisional in two senses the constitutive description of till will require improvement and not all potentially significant processes have been included till is treated as a three component mixture of water clasts coarse grained solids and fine grained matrix solids these components obey mass balance equations and their behavior is subject to constitutive relations that describe such processes as darcian water transport fine grained sediment transport consolidation shear deformation dilatancy and comminution five state variables uniquely determine the compressibility permeability shear strength and other physical properties numerical solutions of the state evolutions equations illustrate that the properties of till are highly responsive to changes in the subglacial environment

effect of mechanical interactions on the development of shape preferred orientations a two dimensional experimental approach abstract modifications in the development of preferred orientations of rigid particles due to mechanical interactions between particles are studied experimentally in two dimensions experiments in both pure shear and simple shear were performed and the results analysed using an easy and fast new automatic method for increased concentration of rigid particles the rotation of individual particles may be slowed down or even stopped due to collisions or disturbance of the flow in the matrix caused by neighbours in coaxial flow the fabric intensity is consequently reduced in simple shear flow the fabric evolution is no longer cyclic the intensity is on average weaker and the fabric axis rotates asymptotically toward the shear plane in the case of preferred orientations of particles having a low aspect ratio 2 5 the fabric rotates through the shear plane then undergoes a reverse rotation and rotates toward the shear plane again in the light of these experimental results we emphasize that quantification of finite strain based on such fabrics may lead to significant underestimates and calculated values should be taken as minimum estimates the kinematic significance of concentrated rigid particle preferred orientations in rocks is modified by interactions between particles techniques for qualitative or quantitative kinematic analysis may become unreliable for simple shear flows the concentrated population fabrics show an angular behaviour close to that of passive markers they tend to align parallel to the shear plane in simple shear flow