3 d characterization of a clastic reservoir analog from 3 d gpr data to a 3 d fluid permeability model a three dimensional 3 d 100 mhz ground penetrating radar gpr data volume is the basis of in situ characterization of a fluvial reservoir analog in the ferron sandstone of east central utah we use the gpr reflection times to image the bounding surfaces via 3 d velocity estimation and depth migration and we use the 3 d amplitude distribution to generate a geostatistical model of the dimensions orientations and geometries of the internal structures from the surface down to 12 m depth each sedimentological element is assigned a realistic fluid permeability distribution by kriging with the 3 d correlation structures derived from the gpr data and which are constrained by the permeabilities measured in cores and in plugs extracted from the adjacent cliff face the 3 d gpr image shows that gpr facies changes can be interpreted to locate sedimentological bounding surfaces even when the surfaces do not correspond to strong gpr reflections the site contains two main sedimentary regimes the upper 5 m co

implementation of 3 d prestack kirchhoff migration with application to data from the ouachita frontal thrust zone a 3 d prestack kirchhoff migration is implemented and successfully applied to a 3 d data set from the ouachita frontal thrust zone in southeastern oklahoma the algorithm uses data decomposition and operates efficiently both in multiprocessor vector and parallel environments image time maps are precomputed once for each survey point regardless of how many times it is a source or receiver and stored in random access disk files these files and the data traces are read asynchronously during migration image time computation is done by two point ray tracing to avoid interpolation between irregularly spaced rays or points on wavefronts the same software can be used to depth migrate all input data geometries stacked sections common source or common receiver or common offset or common midpoint gathers the output images from the ouachita field data show structural closure on folded thrust sheets of wapanucka limestone and repetition of lithology caused by lateral displacement on the thrusts

modeling 3d porosity and permeability from gpr data in the ellenburger dolomite central texas three dimensional porosity and permeability were modeled in an ellenburger carbonate reservoir analog from 2d crosshole and 3d surface survey ground penetrating radar gpr data two dimensional gpr crosshole velocity tomography 3d migration of the gpr surface data and porosity and permeability calibration to gpr attributes results in 3d porosity and permeability predictions that provide a consistent model of the paleocave structures and facies distributions picking the maximum instantaneous amplitude of the direct arrival wavelet for velocity tomography reduces uncertainties caused by a low signal to noise ratio uncorrelated noise and the interference between reflections and critical refractions at the earth air interface the gpr velocity is anisotropic with an average vertical to horizontal velocity ratio of 0 93 which is attributed to the dominance of the relatively horizontal orientation of the maximum porosity and permeability porosity and permeability trends are influenced by regional northe

3d imaging of a reservoir analogue in point bar deposits in the ferron sandstone utah using ground penetrating radar most existing reservoir models are based on 2d outcrop studies 3d aspects are inferred from correlation between wells and so are inadequately constrained for reservoir simulations to overcome these deficiencies we have initiated a multidimensional characterization of reservoir analogues in the cretaceous ferron sandstone in utah detailed sedimentary facies maps of cliff faces define the geometry and distribution of reservoir flow units barriers and baffles at the outcrop high resolution 2d and 3d ground penetrating radar gpr images extend these reservoir characteristics into 3d to allow the development of realistic 3d reservoir models models use geometric information from mapping and the gpr data combined with petrophysical data from surface and cliff face outcrops and laboratory analyses of outcrop and core samples the site of the field work is corbula gulch on the western flank of the san rafael swell in east central utah the outcrop consists of an 8 17 m thick sandstone body which contains various sedimentary structures such as cross bedding inclined stratification and erosional surfaces which range in scale from less than a metre to hundreds of metres 3d depth migration of the common offset gpr data produces data volumes within which the inclined surfaces and erosional surfaces are visible correlation between fluid permeability clay content instantaneous frequency and instantaneous amplitude of the gpr data provides estimates of the 3d distribution of fluid permeability and clay content

estimation of the spatial distribution of fluid permeability from surface and tomographic gpr data and core with a 2 d example from the ferron sandstone utah reservoir analogs provide detailed information that is applicable to fluid transport simulations but that cannot be obtained directly from reservoirs because of inaccessibility the ferron sandstone of east central utah is an analog for fluviodeltaic reservoirs its excellent outcrop exposures are ideal for detailed study ground penetrating radar gpr data were collected in and between two cored boreholes and are used to build a 2 d fluid permeability model in four steps first an anisotropic gpr propagation velocity model is obtained from traveltime tomography between two boreholes and between each borehole and the earth s surface second the geometry of the sedimentological features is imaged by prestack kirchhoff depth migration of constant offset gpr data acquired along a line between the two holes at the earth s surface third a background permeability is assigned to each layer by interpolating the geometrical average of the measured permeabilities in each sedimentological element finally the

the brittle plastic transition and the depth of seismic faulting a simple rheological model of shearing of the lithosphere that has gained wide acceptance is a two layer model with an upper brittle zone in which deformation takes place by frictional sliding on discrete fault surfaces and a lower plastic zone in which deformation takes place by bulk plastic flow the two are separated by an abrupt brittle plastic transition which is assumed to be indicated by the lower limit of seismicity experimental studies however as well as the deformation structures of mylonites indicate that a broad transitional field of semi brittle behavior lies between these extremes this is a field of mixed mode deformation with a strength that can be expected to be considerably higher than that predicted from the extrapolation of high temperature flow laws for quartzofeldspathic rocks the semi brittle field lies between t1 the onset of quartz plasticity at about 300 c and t2 feldspar plasticity at about 450 c a model is presented in which the transition t1 does not correspond to a transition to bulk flow but to a change from unstable velocity weakening friction to stable velocity strengthening friction t1 thus marks the depth limit of earthquake nucleation but large earthquakes can propagate to a greater depth t3 t3 t2 which corresponds to the lower limit of dynamic frictional behavior in the semi brittle field and approximately to the peak in strength the zone between t1 and t3 is one of alternating behavior with flow occurring m the interseismic period and with co seismic dynamic slip occurring during large earthquakes this zone is characterized by mylonites interlaced by pseudotachylytes and other signs of dynamic faulting the transition t1 is also marked by a change in the generation mechanism of fault rocks from abrasive wear above which produces cataclastites to adhesive wear below which is proposed as an important generation mechanism of mylonites in the upper part of the semi brittle field

crustal structure and domain tectonics of the dharwar craton india insight from new gravity data abstract the precambrian dharwar craton of peninsular india comprises three distinct crustal domains namely the western dharwar craton wdc the eastern dharwar craton edc and the eastern ghats mobile belt egmb the domain boundaries are demarcated by bipolar positive and negative gravity anomalies measured along a 600 km long udipi kavali seismic line the two and half dimensional modelling of the gravity anomalies well constrained by available seismic depth sections identified the two contact zones one occurs between the wdc relatively low density and the edc intermediate density to the east of the chitradurga schist belt and the second occurs between the edc and the egmb high density to the east of cuddapah basin as west verging thrust faults the three layer crustal structure is up to 41 km thick beneath the wdc thinning to 37 km beneath the west coast under the edc the depth of the moho varies from 38 km towards the west to 40 km beneath the cuddapah basin and decreases to a depth of 35 km beneath the egmb a high density steeply inclined ridge like body is modelled between 5 and 20 km depth beneath the closepet granite and a similar body is modelled under the egmb it is suggested that the three domains of the dharwar craton were brought and welded together at the suture zones in the period from late archaean to late proterozoic through collisional tectonics the apparent offsets in the moho depth may be the imprint of the relative domain movement that probably was initiated by the convergent plate motion the steeply inclined ridge like high density bodies are interpreted as stacked lower crustal blocks from the convergent tectonic setting the cuddapah basin with a 10 km thick shelf marine sedimentary sequence is interpreted as a peripheral foreland basin abutting the egmb a lopolith of likely mafic composition is modelled at 10 km depth and is interpreted as a product of juvenile magmatism beneath the edc

organic facies of the asbian early carboniferous queensferry beds lower oil shale group south queensferry scotland and a brief comparison with other carboniferous north atlantic oil shale deposits abstract the 71 m foreshore exposure of the queensferry beds at south queensferry is currently the best accessible section of the oil shale group of the midland valley of scotland a combination of bulk organic geochemistry and kerogen microscopy palynofacies organic petrology is used to define four organic facies and one variant organic facies 1 occurs in silty mudstones has a mean toc of only 2 and type iii iv gas prone or inert kerogen hi 800 variant 3a is additionally characterised by an abundance of small 4 m spherical cells of possible cyanobacterial origin occurring in one sample adjacent to a stromatolitic limestone organic facies 2 is transitional between 1 and 3 organic facies 4 has atypically low c s ratios and corresponds to the pumpherston marine band these organic facies can also be distinguished using biomarker parameters pr ph oep c25 c15 predominant carbon number etc the hi is very strongly correlated with the relative fluorescence of the organic matter and strongly correlated with the aom phytoclast ratio and the botryococcus and total alginite contents it is inversely correlated with the diameter of black equant phytoclasts the organic rich shales thus correspond to distal lower energy anoxic conditions during periods of meromixis high preservation low dilution similar carboniferous lacustrine source rocks occur in eastern canada and east greenland all are characterised by large lateral extents 500 2 000 km2 a geographic and temporal association with strong syndepositional subsidence generally low botryococcus contents and a dominance of amorphous type ii kerogen

heat flow and heat generation in the archaean dharwar cratons and implications for the southern indian shield geotherm and lithospheric thickness abstract we report terrestrial heat flow density measurements from 11 new sites in the archaean eastern and western dharwar cratons of the southern indian shield the new values together with already published data have yielded a mean heat flow of 40 3 4 s d mw m 2 n 11 for the eastern dharwar craton which is a predominantly gneiss granite terrain the mean heat flow in the archaean supracrustal belts of western dharwar craton which is a granite greenstone terrain is 31 4 1 s d mw m 2 n 4 the observed difference in surface heat flow between the two cratons is ascribed to differences in radiogenic heat production in upper crustal layers inferred to be related to different crust forming processes it has been argued that low heat production appears to be an inherent characteristic of the crust similar to that of the western dharwar craton which evolved during the early archaean and suffered depletion of the lithophile elements of its lower crust prior to the late archaean radiogenic heat production measurements were carried out on borehole core samples for one heat flow site sortur and data have been compiled from the literature on three other sites and on a variety of rocks of the southern indian shield heat flow and radiogenic heat production for sortur when combined with the published data define a linear relation r 0 97 with a slope of 11 5 km and an intercept of 23 mw m 2 the thickness of the thermal lithosphere beneath the dharwar cratons is over 200 km thereby indicating beneath the cratons the existence of deep continental roots a concept which is also supported by teleseismic p wave travel time data the geothermal data has clearly demonstrated that the archaean dharwar cratons of the indian landmass are associated with low mean surface heat flow 37 7 mw m 2 reduced heat flow moho heat flux 12 17 mw m 2 and a cool and thick lithosphere all characteristics of many archaean early proterozoic terrains of other shields it is inferred that the thermal structure of the south indian lithosphere is identical with that of other cratons

3 d prestack kirchhoff depth migration from prototype to production in a massively parallel processor environment portable production scale 3 d prestack kirchhoff depth migration software capable of full volume imaging has been successfully implemented and applied to a six million trace 46 9 gbyte marine data set from a salt subsalt play in the gulf of mexico velocity model building and updates use an image driven strategy and were performed in a sun sparc environment images obtained by 3 d prestack migration after three velocity iterations are substantially better focused and reveal drilling targets that were not visible in images obtained from conventional 3 d poststack time migration amplitudes are well preserved so anomalies associated with known reservoirs conform to the petrophysical predictions prototype development was on an 8 node intel ipsc860 computer the production version was run on an 1824 node intel paragon computer the code has been successfully ported to cray t3d and unix workstation pvm environments

efficient 3 d viscoelastic modeling with application to near surface land seismic data three dimensional viscoelastic modeling is implemented by reparameterizing the viscoelastic wave equation for a standard linear solid the formulation uses weighting factors corresponding to relaxation frequencies and composite memory variables this novel 3 d formulation requires less computer memory than the traditional relaxation time formulation because one set of relaxation frequencies can be used for all mechanisms for all parts of a model and only three sets of composite memory variables are needed rather than the seven used in the standard implementation giving a net reduction of 40 in the total required memory computational time is also reduced approximately 25 because of reduced input output i o the algorithm is applied to 3 d modeling of the viscoelastic response of the near surface structure beneath a 3 d reflection survey in the ouachita frontal thrust zone of southeast oklahoma comparison of the 3 d field data with both viscoelastic and elastic response clearly demonstrates the importance of inclusion of viscoelasticity when accurate amplitude fitting is desired observed amplitude and traveltime variations can be explained by shallow velocity and q distributions obtained independently by 3 d tomography

teleseismic tomographic evidence for contrasting crust and upper mantles in south indian archaean terrains abstract we compare the velocity structure of the crust and upper mantle of the archaen granulite terrain of southernmost india with that of the archaean granite greenstone dharwar craton terrain just to the north through p wave teleseismic travel time measurements the teleseismic rays recorded by a coarse network of 11 portable seismic stations show an anomalous pattern of late arrivals delays over the granulite terrain in contrast to fast arrivals on the dharwar craton such a pattern of time residuals amongst these archaean terrains which have remained inert in the last 2 ga may indicate the presence of compositional heterogeneity within the crust and upper mantle beneath them three dimensional p wave velocity tomography using teleseismic rays from a variety of azimuths indicates the existence of contrasting p wave crust and upper mantle velocity patterns 1 in the crust 0 40 km the western dharwar craton and the granulite terrain have lower velocity up to 3 compared with the higher velocity 1 3 observed over the eastern dharwar craton and 2 in the upper mantle 40 177 km there is 2 3 lower velocity beneath the granulite terrain compared with the western dharwar craton the existence of such lateral velocity variation in the crust and upper mantle and its preservation since late archaean times points to the presence of possibly thick and chemically distinct lithospheres that did not participate in mantle convection

prediction of 3 d fluid permeability and mudstone distributions from ground penetrating radar gpr attributes example from the cretaceous ferron sandstone member east central utah a 3 d fluid permeability distribution is estimated inside a channel sandstone reservoir analog in the cretaceous ferron sandstone fluvio deltaic complex in east central utah from ground penetrating radar gpr attributes fluid permeability measurements at 5 cm spacing along four boreholes and one pseudohole section at the adjacent cliff face are used together with instantaneous amplitude and frequency attributes of gpr data to predict fluid permeabilities away from the measured vertical transects and to delineate the distribution and geometry of mudstone layers inside the reservoir analog statistically significant relationships are determined between the well data fluid permeability and mudstone content and the gpr attributes these calibrations are applied to the entire gpr volume to estimate the 3 d fluid permeability variation and the lateral development of mudstone units measured and predicted fluid permeabilities range from 0 1 to 290 md one of the five units considered contained no mudstone lay

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

thickness composition and evolution of the indian precambrian crust inferred from broadband seismological measurements abstract we present seismological constraints to model the evolution of indian precambrian crust through receiver function analysis of teleseismic waveforms recorded on 22 broadband seismographs along a n s corridor from southern granulite terrain to delhi on the aravalli craton archean terrains eastern dharwar bastar bundelkhand and aravalli cratons are underlain by crust with felsic intermediate composition vp vs 1 65 1 75 in contrast to mafic composition vp vs 1 78 of crust beneath vindhyan basin godavari basin and the narmada son lineament nsl of proterozoic age the moho depth varies between 33 and 43 km with no definite relationship with age of the crust duplex moho with highly mafic underplated lower crust is characteristic feature of the nsl signifying its paleo rift character present day felsic character of the indian archean crust could be a consequence of post formation modification of the initial mafic lower crust through the process of lithospheric delamination this major tectonic event also created layered lithosphere beneath parts of india imprinted as positive velocity contrast at a depth of 80 km usually referred to as hales discontinuity the upper part of the lithosphere has shear velocity vs 4 52 km s and the lower one 4 77 km s we speculate that such a layered lithosphere could be due to a low density depleted spinel peridotite with archean affinity lying over higher density fertile garnet peridotite of proterozoic age

the problem of heat flow density determination from inaccurate data abstract we present an inverse method for processing rough data from oil wells in order to evaluate the heat flow density assuming that the evaluations of temperatures and thermal resistivities present gaussian uncertainties we give formulas for computing the optimal value of the heat flow density and its standard deviation a synthetic example using likely assumptions on various uncertainties leads to the prediction that a standard deviation of about 10 mw m 2 could apply to heat flow estimates from oil well data for typical situations

the arsikere granite of southern india magmatism and metamorphism in a previously depleted crust abstract the arsikere granite is a small diapiric potassic pluton intruded into archean gneisses of the western part of the dharwar craton of southern india a rb sr age of 2563 ma indicates that the granite was formed during a period of granulite development at lower crustal levels at least to the south of the dharwar craton schist belts in the craton were metamorphosed to greenschist or amphibolite facies at this time but gneisses underwent no isotopic or other geochemical effects the arsikere granite contains quartz oligoclase highly perthitic alkali feldspar originally precipitated as a single phase f rich biotite plus primary epidote fluorite and f rich muscovite sphene forms large euhedrons which incorporate nearly all of the ti in the rock leaving pure magnetite as the only opaque phase equilibration parameters include temperatures of 700 from feldspars f o 2 10 12 bar biotite and opaques and f oh 10 3 biotite nearby schist belts were metamorphosed at 5 kbar pressure at the same time as granite emplacement if the granite was emplaced at 5 kbar the magma could not have been water saturated perthite an initial 87 sr 86 sr ratio of 0 7021 in the arsikere granite is too low for the magma to have formed by partial melting of rocks with the rb sr ratios of gneisses currently exposed in the craton apparently the magma formed in a lower crust that had been depleted in rb and probably other lithophilic elements several hundred million years earlier at this time the craton also became water poor and inert to further geochemical activity such as resetting isochrons during later metamorphism

parsimonious 3d post stack kirchhoff depth migration parsimonious post stack migration is extended to three dimensions by tracing single rays back along each incident wave direction as determined by a local slant stack at the receivers the ray tracing can be embedded in the migration this approach significantly reduces the computer time and disk space needed because it is not necessary to build and save image time maps 3d migration can be performed on a workstation or personal computer rather than using a supercomputer or cluster the location of a reflector in the output image is defined by tracing a zero offset ray to the one way traveltime the image condition the orientation of the reflector is defined as a surface perpendicular to the raypath the migration impulse response operator is confined to the first fresnel zone around the estimated reflection point which is much smaller than the large isochronic surface in traditional kirchhoff depth migration additional efficiency is obtained by applying an amplitude threshold to reduce the amount of data to be migrated tests on synthetic data show that the proposed implementation of parsimonious 3d post stack kirchhoff depth migration is at least two orders of magnitude faster than traditional kirchhoff migration at the expense of slightly degraded migration image coherence the proposed migration is expected to be a useful complement to conventional time migrations for fast initial imaging of subsurface structures and for real time imaging of near offset sections during data acquisition for quality control

detailed internal architecture of a fluvial channel sandstone determined from outcrop cores and 3 d ground penetrating radar example from the middle cretaceous ferron sandstone east central utah ideally characterization of hydrocarbon reservoirs requires information about heterogeneity at a submeter scale in three dimensions detailed geologic information and permeability data from surface and cliff face outcrops and boreholes in the alluvial part of the ferron sandstone are integrated here with three dimensional 3 d ground penetrating radar gpr data for analysis of a near surface sandstone reservoir analog in fluvial channel deposits the gpr survey covers a volume with a surface area of 40 x 16 5 m and a depth of 12 m five architectural elements are identified and described in outcrop and well cores using a sixfold hierarchy of bounding surfaces internally the lower four units consist of fine grained parallel laminated sandstone and the upper unit consists of medium grained trough cross bedded sandstone the same sedimentary architectural elements and associated bounding surfaces are distinguished in the gpr data by making use of principles developed in seismic stratigraphic analysis to facilitate comparison of geologic features in the depth domain and radar reflectors in the time domain the radar data are depth migrated the gpr interpretation is carried out mainly on migrated 100 mhz data with a vertical resolution of about 0 5 m measures of the spatial continuity and variation of the first and second order bounding surfaces are obtained by computing 3 d experimental variograms for each architectural element each radar begin page 1584 facies the maximum correlation length of the dominant internal features ranges between 4 and 6 m and the anisotropy factor ranges between 0 6 and 0 95

low shear velocities in the sub lithospheric mantle beneath the indian shield 1 ever since its breakup from the gondwanaland 140 myr ago the indian plate was ravaged by four hot spots although the surface manifestations of such deep processes are evident in terms of large igneous provinces like the deccan and the fast drift of the indian plate the modifications to the deep structure remain to be grasped in this study we investigate the mantle transition zone tz structure beneath the indian shield region using 14 000 teleseismic receiver functions from 77 broadband stations sited on diverse geologic terrains the arrival times of the p to s ps conversions from the 410 km discontinuity at most cratonic stations appear to be delayed by 2 s in comparison with the times observed for other precambrian shield regions like africa australia and canada such delays in the conversions from the 410 km discontinuity below the indian shield suggest low shear wave speeds in the lithospheric and sub lithospheric mantles due to higher temperatures together with a thinner high velocity lid that contrasts with a thicker one found beneath most archean cratons a thin transition zone beneath most of the cratonic stations lends support to the enhanced temperatures within the tz itself also a further delay of the tz discontinuities is observed for stations on the southern granulite terrain which was under the influence of the marion plume that is responsible for the separation of madagascar from india although the data do not conclusively show evidence for a 520 km discontinuity an lvl atop the 410 cannot be ruled out beneath certain geological provinces of the indian shield

3 d architecture and sequence stratigraphic evolution of a forced regressive top truncated mixed influenced delta cretaceous wall creek sandstone wyoming u s a abstract ground penetrating radar gpr is used to delineate the 3 d facies architectural elements and examine the evolution of a top truncated forced regressive mixed influenced delta front in the cretaceous wall creek member of the frontier formation wyoming the gpr data provide a bridge between outcrop facies architecture and recently published high resolution 2 d seismic studies of quaternary delta systems the gpr data were integrated with outcrops photomosaics cores and gps data two orthogonal grids of 2 d gpr profiles provide information on the 3 d facies architecture and stratigraphy of the deltaic deposits three main gpr architectural elements are identified within the delta front 1 mouth bars are characterized by seaward dipping reflections foreset beds in dip view and mounded bidirectionally downlapping reflections in strike view 2 shallow delta slope channels show truncation and onlap and also show low angle landward northwest dipping reflections the mouth bars are locally interrupted by 3 sub horizontal radar reflections that are interpreted as tidally modulated bars within the mouth bar radar facies both top preserved proximal and top truncated distal examples are observed top preserved proximal bars show evidence of mounded bar crests and landward accretion as is observed in the upstream end of mouth bars on the modern atchafalaya delta in the gulf of mexico distal bar deposits primarily comprise the top truncated seaward dipping foresets the gpr interpretation shows two laterally overlapping delta lobes interpreted to represent autocyclic delta switching the older lower lobe forms a fan shaped delta lobe composed of top truncated coalesced mouth bars the second phase of bars is largely top preserved building over the older bars the presence of thicker bedsets and upstream accretion suggests that the younger lobe was quickly abandoned as seen in the overlying transgressive ravinement although marine erosion during transgression was less effective on these later stage bar deposits ravinement increased landward a comparison of the architectural elements at a more regional scale in two separate wall creek delta lobes murphy creek and raptor ridge 30 km apart indicates that the bar complexes were deposited on the delta fronts as accretionary forced regressive deposits during a relative sea level fall the older river dominated deltaic deposits at the murphy creek site prograded southeastward 124 whereas the younger and more tidally influenced raptor ridge bar deposits expanded southward 171 before final abandonment and regional transgression the most distal lowstand lobe sediments within the offlapping parasequence at raptor ridge are more completely preserved and also show the greatest tidal influence compared to the more severely top truncated murphy creek which is in an otherwise more landward location this challenges the notion that tidal facies are predominantly associated with transgressive or highstand systems tracts greater preservation of deltaic facies in forced regressive and lowstand deltas as shown here has also been documented in quaternary shelf edge deltas such as the lagniappe in the gulf of mexico and the mahakham in kalimantan

stochastic modeling of the thermal structure to decipher the lithospheric thickness application to dharwar craton a wide range of speculation regarding lithospheric thermal thickness in a region calls for quantifying the uncertainties associated with model parameters in this paper we present an attempt to decipher it by solving the differential equations governing the heat transfer through the lithosphere adequately quantifying the temperature field is very important since it is highly dependent on the controlling thermal parameters thermal conductivity is modeled as a random parameter with a known mean value and correlation structure we compute the temperatures in the crust and lithospheric mantle along with their error bounds using an analytical solution to the steady state heat equation and the adomian method of decomposition we apply these solutions in the archean dharwar craton which is divided into western dharwar craton wdc and eastern dharwar craton edc we obtain a moho temperature estimate of 304 58 c in wdc whilst in edc it is 375 74 c for a 20 coefficient of variability in thermal conductivity the range of lithospheric thickness obtained for wdc is 150 280 km and 110 160 km for the edc these values are in agreement with other geophysical and geological findings in the region the thermal lithosphere obtained from this study is based on the mantle solidus and the surface wave seismological studies considering radial anisotropy reveal that the lithosphere is characterized by higher shear wave velocities and decrease at the lithosphere asthenosphere boundary average shear velocity model for two different cratonic blocks edc and wdc is used to show the lab thickness for the eastern and western dharwar craton the two independent studies show a correlation in the lithospheric thickness

a ground penetrating radar survey of a delta front reservoir analog in the wall creek member frontier formation wyoming ground penetrating radar gpr measurements in conjunction with outcrop sedimentology were carried out at murphy creek reservoir in the upper cretaceous turonian wall creek member of the frontier formation in wyoming the objectives were to apply gpr to map geometrical details of a top truncated lowstand delta front and to estimate the volumes of the prograding bar deposits of the delta lobe eleven gpr profiles totaling about 4400 m 14 435 ft were acquired using 50 mhz antennas on a coarsely spaced two dimensional grid of lines lying parallel and perpendicular to the average depositional dip ground penetrating radar reflections were detected from within the outcrop to a depth of about 10 15 m 33 49 ft four southerly dipping major surfaces identified in the gpr data are correlated with the boundaries of progradational delta front facies stacked as distal mouth bar deposits in the outcrop the major boundaries correspond to lithological changes between relatively clean sandstones that are interpreted to have been deposited during floods with high sediment supply alternating with bioturbated sandstones and mudstones deposited during interflood periods with correspondingly low sedimentation rates these two lithological units which also correspond to the two main gpr facies repeat at least three times with no change in dominant average sand grain size subsequent erosion by transgressive ravinement caused the significantly truncated lowstand delta long after the sandstones were deposited the bar assemblage volume at successive stages of growth is estimated using measurements from the outcrop and the gpr data the migrating bars have an estimated average half length of 650 m 2132 ft a lower bound on the average volume of the bar is 3 9 106 m3 1 37 108 ft3 as the volume of the bars increases the bar deposits appear to have a landward as well as a basinward component of accretion