2 d tomographic imaging of velocities in the wichita uplift anadarko basin region of southwestern oklahoma in january of 1985 a densely recorded wide aperture seismic experiment was performed by the university of texas at el paso and at dallas across the southwestern oklahoma aulacogen a two dimensional p wave velocity distribution is estimated for the wichita uplift the anadarko basin and the interface between them by iterative tomographic imaging of travel time picks from seven shots located near the 100 km long recording line the region that is imaged is roughly triangular in shape with depth 0 km at the ends of line and 15 km near its center the main features that are revealed are a high velocity 6 8 km sec central core in the wichita uplift and an asymmetrical anadarko basin with decreasing velocities toward the basin axis there are indications within the uplift of local high velocity sills and a local low velocity region that may be a remnant of normal crustal material

precambrian basement geology of the permian basin region of west texas and eastern new mexico a geophysical perspective because most of the permian basin region of west texas and southern new mexico is covered by phanerozoic rocks other means must be found to examine the precambrian upper crustal geology of the region we have combined geologic information on the precambrian from outcrops and wells with geophysical information from gravity and magnetic surveys in an integrated analysis of the history and structure of basement rocks in the region geophysical anomalies can be related to six precambrian events formation of the early proterozoic outer tectonic belt igneous activity in the southern granite rhyolite province an episode of pre grenville extension the grenville orogeny rifting to form the delaware aulacogen and eocambrian rifting to form the early paleozoic continental mar in two geophysical features were studied in detail the abilene gravity minimum and the central basin platform gravity high the abilene gravity minimum is shown to extend from the delaware basin across north central texas and is interpreted to be caused by a granitic batholith similar in size to the sierra nevada batholith in california and nevada this batholith appears to be related to formation of the southern granite rhyolite province possibly as a continental margin arc batholith because of this interpretation we have located the grenville tectonic front southward from its commonly quoted position closer to the llano uplift middle proterozoic mafic intrusions are found to core the central basin platform and the roosevelt uplift these intrusions formed at about 1 1 ga and are related in time to both the mid continent rift system and the grenville orogeny in texas because these features are likely to be rift related they suggest that the concept of a delaware aulacogen needs to be revised only to the extent that the rifting is proterozoic in age not eocambrian precambrian basement structures and changes in lithology have influenced the structure and stratigraphy in the overlying permian basin and thus have potential exploration significance interpretation of the gravity and magnetic data with geologic information also leads us to suggest the existence of pre ellenburger basins which may be extensive and of potential exploration interest

hydrological controls on the morphogenesis of low energy meanders cher river france summary river restoration is a key issue for european hydrosystems that were modified over centuries by human activities this is particularly true for numerous low energy rivers flowing in the plateaus of western europe because of this limited energy their potential in terms of autogenic restoration a priori appears strongly restricted this study examines the conditions under which the morphogenesis on one of these systems occurs in relation to various hydrologic conditions two complementary approaches are combined on three reaches of the meandering cher river france firstly we examine at a pluri decadal scale the control of duration frequency and intensity of floods on the planimetric erosion bank retreat mainly secondly we estimate the range of effective discharge for bedload transport the results show that the morphogenesis is controlled by low magnitude hydrological events two major controlling factors are suggested low differential of energy between small and large floods peculiar to low energy rivers of mid latitude and low critical discharges for lateral erosion and bedload mobilization for these reasons the ability of the alluvial cher river to self restore its fluvial dynamics seems to be relatively high

wave field processing of data from a large aperture seismic experiment in southwestern oklahoma data from a wide aperture survey performed in january 1985 in southwestern oklahoma have been processed using prestack imaging and the images are interpreted to reveal a new picture of the crustal structure in the wichita uplift and the anadarko basin as the data were in recording apertures of approximately 90 km it was necessary to develop new processing concepts and software a complete new imaging system based on common source gathers was conceived implemented tested and applied to these data the heart of the system consists of velocity estimation by slant stacking and acoustic prestack reverse time finite difference migration the migration produces reflectivity images in regions of 50 km 100 km has no dip restrictions and operates in an arbitrarily complicated two dimensional velocity distribution for comparison the data were also processed using standard common midpoint processing but this is a less valid approach for wide aperture data the main ambiguities and limitations in processing and interpretation are a consequence of the small number of shots processing and interpretation of the data provide a new picture of the subsurface structure of southwestern oklahoma the environment is clearly compressive with thrust faulting as the main accommodating mechanism in the upper and central crust beneath a possible detachment zone at 30 km depth the lower crust has responded to the compression by thickening by 50 the moho is interpreted to be 45 km in depth beneath the thrust zone shallowing to 40 km beneath the wichita uplift and the anadarko basin

evidence for late middle proterozoic extension in the precambrian basement beneath the permian basin through an integrated interpretation of gravity magnetic seismic reflection and well data we are able to define the geometry lateral extent and tectonic setting of late middle proterozoic mafic rocks the pecos mafic intrusive suite in the basement of the permian basin of west texas and eastern new mexico in this region seismic reflection data are characterized by subhorizontal layered reflectivity within basement that can be tied to compositional variation in a layered mafic intrusion through well cuttings and a synthetic seismogram in places the intrusion forms a sill and the base of the sill is imaged in the reflection data integration of the seismic interpretation with gravity models shows that the pecos mafic intrusive suite is 3 10 km thick and 50 100 km wide the overall structure of the suite is that of a sill with a locally dikelike keel north south trending gravity and magnetic anomalies associated with the pecos mafic intrusive suite suggest that it is composed of four large intrusive centers which cover a minimum area of 9200 km2 making it one seventh the size of the bushveld complex and one of the largest layered mafic intrusions in the world we interpret this massive intrusion to be associated with collisional rifting in the foreland of the grenville orogeny

flood plain and main channel flow interaction experimental results are presented concerning the discharge characteristics the boundary shear stress and boundary shear force distributions in a compound section comprising of one rectangular main channel and two symmetrically disposed flood plains equations are presented giving the shear force on the flood plains as a percentage of the total shear force in terms of two dimensionless parameters the experimental shear force results are used to derive ancillary equations for the lateral and vertical transfer of momentum within the cross section the apparent shear force acting on the vertical interface between one flood plain and the main channel is shown to increase rapidly for low relative depths and high flood plain widths equations are also presented giving the proportion of the total flow which occurs in the various sub areas the division of flow based on linear proportion of the areas is shown to be inadequate on account of the interaction between the flood plain and main channel flows

single hole imaging using borehole gravity gradiometry abstractwe study the feasibility of imaging density variations away from boreholes using gravity gradient measurements in a single borehole the objective is to develop numerical interpretation tools and to understand the utility and limitations of borehole gravity gradiometry in anticipation of the development of such instruments for the exploration and production of minerals oil and gas we develop an analytic solution for directly locating discrete off hole mass anomalies and apply a generalized inverse approach to image anomalous density distribution in the analytic approach we solve for the distance and direction angles to a point source using the multiple components of the gravity gradient tensor from a set of observations in a single borehole and then apply this approach to the scenarios of prismatic sources in the generalized inverse approach we invert multiple gradient tensor components to construct 3d density contrast distributions around the borehole as few as two independent gravity gr

cocorp profiling across the southern oklahoma aulacogen overthrusting of the wichita mountains and compression within the anadarko basin cocorp consortium for continental reflection profiling deep reflection profiles recorded across the wichita mountains and anadarko basin suggest that significant crustal shortening occurred in the final stages of the evolution of the southern oklahoma aulacogen the crystalline rocks of the wichita mountains were thrust in pennsylvanian time northeastward over sedimentary rocks of the anadarko basin along a series of faults with moderate average 30 to 40 and southwesterly dips these faults can be traced possibly as deep as 20 to 24 km listric thrust faults and hanging wall anticlines developed in the sedimentary rocks of the basin these features contrast with conventional interpretations of pennsylvanian structures as the result of predominantly vertical movements along high angle faults and they suggest that pennsylvanian downwarping of the anadarko basin was at least partially due to thrust loading truncations of reflections from cambrian ordovician rocks in the deepest part of the basin suggest normal faulting which would support ideas of an early extensional stage in the aulacogen cycle the distinctive precambrian layering seen on earlier cocorp data recorded south of the wichita mountains cannot be recognized under the anadarko basin and the proterozoic basin containing that layering may have been bounded on its north side by a precambrian fault this inferred fault was probably twice reactivated during formation of the southern oklahoma aulacogen once during late precambrian early cambrian extension and again during pennsylvanian compression the popular view that aulacogens originated from radial rifting of updomed homogeneous continental crust is probably too simplified and a more important constraint on their location and development may be the nature of pre existing lines of weakness

automatic interpretation of gravity gradiometric data in two dimensions vertical gradient1 the magnetic and gravity field produced by a given homogeneous source are related through poisson s equation starting from this consideration it is shown that some 2d interpretation tools widely applied in the analysis of aeromagnetic data can also be used for the interpretation of gravity gradiometric data vertical gradient this paper deals specifically with the werner deconvolution analytic signal and euler s equation methods after a short outline of the mathematical development synthesized examples have been used to discuss the efficiency and limits of these interpretation methods these tools could be applied directly to airborne gravity gradiometric data as well as ground gravity surveys after transformation of the bouguer anomalies into vertical gradient anomalies an example is given of the application of the werner deconvolution and euler s equation methods to a microgravity survey

nature of the eastern boundary of the rio grande rift from cocorp surveys in the albuquerque basin new mexico reprocessing and synthetic seismic modeling of cocorp profiles across the eastern margin of the rio grande rift at abo pass new mexico suggest that synthetic and antithetic cenozoic normal faults sole into or are truncated by a northwest dipping listric master fault which bounds the eastern side of the basin and reaches a depth of at least 10 km beneath the southern albuquerque basin this fault appears to project toward the surface position of the los pinos cenozoic normal fault which lies basinward of and trends parallel to a mapped laramide duplex thrust zone the los pinos fault may sole into the older thrust reactivating this preexisting compressional structure at depth a lateral change in reflection amplitude and frequency is conspicuous across the eastern rift margin analysis demonstrates that source coupling is the main cause of a much deteriorated signal below the rift basin although complex ray paths and attenuation by the graben fill may contribute

timing and chemistry of igneous events associated with the southern oklahoma aulacogen abstract igneous activity in the southern oklahoma aulacogen of north america was concentrated in the early rifting stages of aulacogen development the time span over which liquids rose may not have exceeded 50 m y and certainly terminated before the upper cambrian igneous activity began with three basaltic liquids stratigraphically identifiable but perhaps not all distinct genetically this was followed by one large rhyolitic granitic episode of a type character one final basaltic event ended the activity all the basaltic types seem to be tholeiitic showing more kinship with either the older proterozoic north american midcontinental rift or the northern part of the cenozoic rio grande rift than the cenozoic east african rift two major uplifts occurred one between the earlier basalts and the rhyolite and one much later after all igneous activity was over in the pennsylvanian

thermal structure of the anadarko basin the anadarko basin of oklahoma is a two stage paleozoic cratonic basin with as much as 12 km 7 5 mi or more of sedimentary fill we present a present day thermal model of the basin based on lithologic analysis at 3 m 10 ft intervals in 63 wells heat flow measurements at seven sites and in situ thermal conductivity calibration of the sediment section at two sites we do not use bht bottom hole temperature information in the process but we do at the end of the process compare the independently predicted temperatures to bht information the in situ calibration of thermal conductivity was accomplished using detailed temperature logs and represents a new practical application for evaluating basin thermal characteristics shale exerts the most control on the temperature distribution because it is the most abundant lithology and has the lowest thermal conductivity shale comprises 47 by volume of rock in the basin and represents 75 of total thermal resistance directly related to temperature gradient therefore shale dominates the thermal structure of the basin thus the problems in sampling and in characterizing the in situ thermal conductivity of shale from laboratory measurements represent a major limitation in basin thermal analysis we use the in situ calibration approach as a way to address the difficulty the temperatures calculated do not mimic the structure of the sediments i e the hottest area on a given age horizon in the lower paleozoic is not in the most deeply buried part of the anadarko basin the combination of decreasing heat flow toward the wichita mountains and the facies changes in the pennsylvanian units from marine shale low thermal conductivity in the basin to the granite wash high thermal conductivity toward the uplift results in the highest temperatures being displaced about 50 km 31 mi northward into the basin the pattern of vitrinite reflectance in the woodford shale is virtually identical to the present day reconstructed temperature pattern therefore we conclude that the thermal pattern is and has been dominated by conductive heat transport

paleoenvironmental and paleobiogeographic implications of a new ediacaran body fossil from the neoproterozoic carolina terrane stanly county north carolina new partial swartpuntiid from neoproterozoic age rocks of stanly county north carolina herein assigned to cf swartpuntia sp along with previously described pteridinium carolinaensis aspidella other metazoan trace fossils and previously reported radiometeric ages suggest nama assemblage type affinities for the carolina terrane the new specimen cf swartpuntia sp and associated radiometric ages add further information pertaining to proposed geographic linkages between the carolina terrane and the avalon terrane this new swartpuntiid may be evolutionarily convergent in terms of habitat preference to the infaunal or partially infaunal habitat preferred by other members of the nama type ediacaran biota such as pteridinium and rangea

late proterozoic to early palaeozoic supracrustal succession of sierra leone an aulacogen at the western margin of the west african craton three parallel zones of upper proterozoic to lower palaeozoic sedimentary volcanic cover rocks have been recognized in western sierra leone the kasila group m the sw ist metamorphosed to the granulite facies and grades into the marampa schist group and this in turn grades into the unmetamorphosed rokel river group in the ne prior to this investigation these rocks were thought to belong to different ages the most highly metamorphosed was thought to be the oldest and the unmetamorphosed the youngest this view is unrealistic since field mapping has failed to reveal any sharp contacts between them and all available age data indicate their involvement in the pan african ca 550 ma orogeny a model is proposed involving an intracontinental graben aulacogen extending from western sierra leone into the adjacent territories developed about 1000 ma ago during the pan african orogeny a portion of the aulacogen fill overlying the remobilized basement was subjected to a regional metamorphism and deformation the grade of metamorphism and the degree of deformation decreased steadily from the centre of the pan african domain to the contact with the west african craton the unmetamorphosed and mildly deformed to undeformed equivalent rests on the craton

3d inversion of airborne gravity gradiometry data in mineral exploration a case study in the quadrilatero ferrifero brazil abstractwe present a case study of applying 3d inversion of gravity gradiometry data to iron ore exploration in minas gerais brazil the ore bodies have a distinctly high density contrast and produce well defined anomalies in airborne gravity gradiometry data we have carried out a study to apply 3d inversion to a 20 km2 subarea of data from a larger survey to demonstrate the utility of such data and associated inversion algorithm in characterizing the deposit we examine multiple density contrast models obtained by first inverting tzz then txz tyz and tzz jointly and finally all five independent components to understand the information content in different data components the commonly discussed tzz component is sufficient to produce geologically reasonable and interpretable results while including additional components involving horizontal derivatives increases the resolution of the recovered density model and improves the ore delineation we show that gravity gradiometry data can be used to deli

interpretation of the reflections in the siljan ring area based on results from the gravberg 1 borehole abstract during 1985 about 80 km of surface multichannel seismic reflection data were collected across the meteorite impact in the siljan ring area in central sweden the area consists mainly of granitic and gneissic rock ranging in age from 1400 to 2000 million years with remnants of palaeozoic sedimentary rocks preserved by downfaulting after a meteorite impact at 360 ma thereby forming a circular ring about 40 km in diameter dolerite intrusions ranging in age from 850 to 1700 million years are also present the seismic data revealed several high amplitude laterally continuous sub horizontal reflections in the northern part of the structure the high amplitude reflections and a possible intermediate low velocity zone were contributing factors in choosing the site for the gravberg 1 deep earth gas test well drilling and vertical seismic profiling vsp found that the reflectors were associated with dolerite sills which had intruded into the granite and which range in thickness from a few metres up to 60 m and with a pre impact area extent of at least 800 km 2 studies of amplitude and frequency versus offset afvo show the observations are compatible with a model of simple granite dolerite granite layering

the thermal and mechanical evolution of the anadarko basin abstract during the late mississippian the style of subsidence and sedimentary facies in the anadarko basin changed significantly this marked an interval of rapid subsidence that was unrelated to the pre existing cambro ordovician trough referred to as the southern oklahoma aulacogen the sedimentary facies changed from black shales and carbonates to predominantly elastics of the mississippian springer series at the same time widespread deposition changed to deposition in a narrow geographically isolated trough during a span of close to 23 m y extending into the middle pennsylvanian nearly 3 5 km of these clastic sediments were deposited in the narrow trough on the south side of the basin during the latter half of this time interval reverse faulting and uplift of the wichita mountains accompanied subsidence in the basin the timing of the uplift indicates that north south shortening in the basin was not the primary cause of subsidence this early narrow phase was followed by a return to widespread deposition in late des moinesian time although with continued clastic sedimentation during the early permian elastics graded into evaporites subsidence slowed continuously throughout this final widespread phase of subsidence we model the formation of the anadarko basin in terms of elastic flexure of the lithosphere in order to accommodate the early narrow phase subsidence is attributed to crustal thinning accompanied by faulting we show that the final widespread phase of subsidence was accommodated by lithospheric flexure and that the flexural rigidity of the elastic lithosphere increased from d 4 1 10 30 dyne cm to d 1 9 10 31 dyne cm during this period this increase can be attributed to a decrease in heat flow with time these two phases of subsidence in the anadarko basin are consistent with crustal thinning followed by thermal subsidence

window constrained inversion of gravity gradient tensor data using dike and contact models we have developed a constrained inversion technique for interpretation of gravity gradient tensor data for dike and contact models striking in the y direction the measured g xz and g zz com

cocorp and the continental crust this is a speculative paper on the continental crust a major frontier of modern earth science seismic reflection profiling data from the cocorp project coupled with other kinds of geophysical and geological observations suggest some fresh perspectives on the crust for example there is evidence for great differences within the basement at a single site and from one cocorp site to another a simple layered model is surely not an adequate representation of the crust in most areas there is however the puzzling and rather common occurrence of limited zones of parallel though not always flat layered features at various depths in certain parts of the crust are the corresponding rocks metasedimentary or igneous or both there are transparent zones from which little or no coherent reflected seismic energy is detected are the corresponding rocks intrusions or highly deformed metasediments can degree of deformation suggest whether rocks were deformed in the hanging wall or footwall of a thrust there is evidence for large scale thrusting and related features that emphasizes the great importance of the wilson cycle to continental tectonics and that raises the possibility that water and rocks of sedimentary origin are trapped deep in the crust by the thrusting process and remain there for long periods with a variety of possible rheological and petrological consequences in some places the modern moho and adjacent rocks may correspond to parts of former oceanic or continental margin sections that have been emplaced at depth as a result of thrusting the widely held concept of the moho as a consistent boundary that is everywhere similar and that always separates the same kinds of rocks may be a major barrier to further progress in understanding the continental crust

two dimensional synthetic seismogram modeling of wide angle seismic data from the wichita uplift oklahoma abstract in conjunction with the 1979 cocorp wichita uplift survey wide angle reflection refraction data were recorded on a fixed array the object of the present study is to model and interpret these wide angle data to add independent constraints on the deep structure of the wichita uplift three common receiver profiles were extracted from the data recording apertures were 3 2 to 23 4 km to the north of the array 4 2 to 14 9 km to the east and 4 2 to 12 6 km to the west these profiles are modeled by iterative fitting of high frequency synthetic seismograms computed by asymptotic ray theory the model derived contains low velocity 2 0 to 2 16 km sec surficial sediments that vary in thickness these account for strong local travel time variations of 0 05 sec and for a small but persistent ghost arrival that follows all the main branches with a delay of 0 2 sec the basement granites rhyolites and gabbros are very near the surface throughout the study area both granite and gabbro outcrops are seen basement p wave velocities are therefore relatively high representative velocities are 4 7 km sec at 0 8 km depth 6 2 at 1 8 6 4 at 2 8 and 6 5 at 4 0 local velocities as high as 7 4 km sec may be present the basement is fairly transparent beneath the wichita uplift with only a few local reflectors present this is consistent with the cocorp results

optimum second vertical derivatives in geologic mapping and mineral exploration the second vertical derivative is often used in gravity interpretation to enhance localized near surface features since high frequency noise is amplified considerably in a true second derivative map some smoothing is always necessary one of the methods available to the interpreter is the optimum second derivative technique which utilizes wiener theory to design filters from an analysis of the power spectrum to suit the degree of noise in the data the power spectrum of the bouguer gravity field obtained from over 5100 gravity stations covering an area of approximately 21 000km2 in archean greenstone belts of northern ontario was computed the radially averaged spectrum decreased monotonically with frequency and flattened at the high frequency end the spectrum separated into its signal and noise components was used to design an optimum second vertical derivative filter which has a peak at 0 35 cycles grid interval with low and high frequency cut off at 0 12 and 0 44 cycles grid intervals respective

ediacarian fossils from the carolina slate belt stanly county north carolina discovery of metazoan fossils comparable to those of the late precambrian ediacarian fauna in the carolina slate belt stanly county north carolina extends the paleobiogeographic range of the ediacarian fauna into the southern piedmont of the southeastern united states these fossils provide paleontologic correlation with parts of the precambrian valdai series of the vendian system of the soviet union the nama group of south west africa and the pound quartzite of south australia in light of the recent discoveries north carolina fossil material previously described as the middle cambrian trilobite paradoxides carolinaensis st jean 1973 was re examined and identified as an element of the late precambrian ediacarian fauna

a review of gravity gradiometer survey system data analyses the gravity gradiometer survey system ggss was designed to measure the local and regional gravity field from a ground or airborne moving platform with the first and only airborne field test the ggss was able to recover five arcminute by five arcminute mean gravity anomalies to an accuracy of a few mgal these results were obtained by flying the system with an operational precision of about 10 eotvos ten second average on a grid of orthogonal tracks spaced 5 km apart at an altitude of about 700 m above the terrain despite perpetual navigation problems with the global positioning system and several periods of excessive system noise the results of a performance analysis on 19 out of 128 tracks demonstrated the potential accuracy and efficiency of the ggss as an airborne gravity mapping system the ground tests both road and railway suffering from undue vehicle vibrations and from a lack of ground truth data were correspondingly less successful but they also showed no surprises in the system corrupted by these adverse conditions unfortunately the ggss program has terminated and it is appropriate to reflect on its accomplishments without going into technical details this somewhat historical review summarizes the field tests the data reduction algorithms and the test results which together portray the breadth of expertise the program engendered in the area of gravity gradiometry

usarray shear wave splitting shows seismic anisotropy from both lithosphere and asthenosphere north america provides an important test for assessing the coupling of large continents with heterogeneous archean to cenozoic aged lithospheric provinces to the mantle flow we use the unprecedented spatial coverage of the usarray seismic network to obtain an extensive and consistent data set of shear wave splitting intensity measurements at 1436 stations overall the measurements are consistent with simple shear deformation in the asthenosphere due to viscous coupling to the overriding lithosphere the fast directions agree with the absolute plate motion direction with a mean difference of 2 with 27 standard deviation there are however deviations from this simple pattern including a band along the rocky mountain front indicative of flow complication due to gradients in lithospheric thickness and variations in amplitude through the central united states which can be explained through varying contributions of lithospheric anisotropy thus seismic anisotropy may be sourced in both the asthenosphere and lithosphere and variations in splitting intensity are due to lithospheric anisotropy developed during deformation over long time scales

inversion of airborne gravity gradient data southwestern oklahoma the diagonal elements of the gravity gradient tensor as recorded by the bell airborne gravity gradient survey system ggss are used to determine the basement topography in southwestern oklahoma this determination is accomplished through a nonlinear inverse procedure based on the conjugate gradient algorithm the resulting model contains a ridge of shallow basement material or 3 0 km deep trending east southeast this ridge is bounded on the north and the south by basement troughs the northern trough extends as deep as 10 0 km the gradient field which results from this model fits most of the ggss observations within their estimated errors of 12 0 e 1 eotvos 10 super 6 mgal cm the model is in general agreement with a set of available oil well depths to the basement and with inferred faults in these igneous rocks to assess the derived solution the problem was linearized about the final model and the linear parameter resolution and parameter covariances were computed generally the basement depths are well resolved and the resolution matrix is diagonally dominant furthermore the parameter standard errors are small 72 parameters out of 98 have errors less than 1 0 km

sediment transport in river models with overbank flows some laboratory sediment transport experiments are described in which a compound channel with a mobile bed composed of uniform sand with a d50 of 0 88 mm was subjected to overbank flows the main river channel was monitored to determine the effect of floodplain roughness on conveyance capacity bed form geometry resistance bed load transport and dune migration rate the floodplain roughness was varied to simulate a wide range of conditions commensurate with conditions that can occur in a natural river for a given discharge the main river channel bed was found to adjust itself to a quasi equilibrium condition governed by the lateral momentum transfer between the floodplain and main channel flows and the local alluvial resistance relationship appropriate for the proportion of total flow in the main river channel the sediment transport rate was found to reflect all these influences the data are summarized in equation form for comparison with other experimental studies and for checking numerical river simulation models

tectonic cycles in southern africa abstract the recurrence of major geological events within the 3600 ma stratigraphic record of southern africa suggests a periodicity of320 25ma for at least the last 3200 ma this periodicity is reflected in major episodes of continental volcanism granitoid plutonism orogeny reciprocity of terrestrial and marine dominated sequences platform carbonate sedimentation glaciation and first order changes in sea level these serve to define 11 completed megacycles each introduced by a major rifting event accompanied by listric faulting alluvial sedimentation in restricted fault bound troughs volcanism and a type granitoid plutonism prior to 3200 ma continental rift magmatism occurred subaqueously due to very high early archean sea levels resulting in pillow lavas and a lack of interbedded terrigenous siliciclastics the long term reciprocity of terrestrial and marine dominated sequences records eustatic first order changes in sea level with highstands characterized by generally humid warm continental climates low relief and tropical afforestation on the other hand lowstand climates were hot and arid with high relief and widespread desertification thick marine sequences accumulate in areally extensive epeirogenic basins without significant volcanism or faulting and commonly are divided into an early phase of open shelf sedimentation followed by deposition in a brackish marine foreland basin within openshelf environments an early phase of biochemical precipitation and or siliciclastic reworking along linear shorelines is separated from a later phase involving rapid deposition of immature siliciclastics along lobate shorelines evolution of the foreland basin is related to orogenic activity and the isolation of an epeiric sea which sometimes developed the characters of a barred basin marine dominated sequences display a deterministic stacking of lithofacies important glacial epochs commonly occur midway through first order regression sometimes with lesser events closely following peak transgression potentially they display 320 ma periodicity but with an unexplained mid proterozoic gap glaciation is related to the combined effect of climatic cooling associated with first order regression and depletion of atmospheric co2 by biological uptake associated with platform carbonate development terrestrial volcanism is believed to be the main contributor of atmospheric co2 climatic change is accompanied by cyclical patterns of cratonic weathering and pedogenesis

the problems and potential of using animal fossils and trace fossils in terminal proterozoic biostratigraphy abstract despite the discovery of soft bodied megascopic fossils of late neoproterozoic age at numerous localities world wide there has been slow acceptance of their potential for intercontinental correlation the stratigraphic thickness of sediments separating individual occurrences of such fossils from the base of the cambrian is very varied basic questions have also been posed as to the classification of the organisms represented and hence their likely time significance recent geochronological studies support notions of a narrow time distribution well studied neoproterozoic sequences in eurasia eastern and western north america and southern australia show strikingly similar patterns of increase in the numbers and diversity of trace fossils and soft bodied megascopic remains up section though strata immediately preceding the cambrian are relatively barren other than for a sparse palynoflora and compressions of primitive plants trace fossils from australian sections relating to an early part of the ediacaran apparently overlap a time of abundance of large process bearing acritarchs and big leiosphaerids this overlap of early animal traces and distinctive acritarchs may prove to be of significant biostratigraphic importance rare discoveries of forms resembling rangea gurich in the flinders ranges of south australia precede the classical ediacara assemblage and may provide a possible correlation with occurrences of this genus in namibia the distinctive remains and trace fossils at this level constituting the rangeid hiemalora assemblage zone resemble a biota from the podolia region of the ukraine and show a similarity to finds in parts of the windermere supergroup of the northwest territories canada similarly the offshore frondose assemblage of newfoundland is comparable with the biota of charnwood forest england the type ediacara assemblage of the flinders ranges characterizing the dickinsonia costata assemblage zone is a climax biota with diverse taxa and large individual species as well as some 20 ichnogenera it closely correlates with a late redkinian or early kotlinian assemblage in the upper part of the section on the zimny gory coast of the white sea northern russia the trace fossils of these levels show that significant diversification began before the cambrian

gravity field approximation using airborne gravity gradiometer data a set of airborne gravity gradiometer survey system ggss data was used in combination with the osu89b geopotential model to predict gravity anomalies and deflections of the vertical the gradiometer data were collected during an airborne survey of the ggss in the texas oklahoma area nineteen flight tracks were in our disposal for further analysis these tracks resulted from 54 initial distinct tracks from which a processing was performed by the analytic sciences corporation in order to assess the quality of the ggss measurements a first crossover analysis was carried out the results showed large discrepancies at the crossing points between east west ew and north south ns tracks the least squares collocation method and the fast fourier transform technique were used to produce gravity anomalies and deflections of the vertical referred to geoid surface from second order derivatives measured at the flight level the predicted gravity values were then compared to truth based point free air gravity anomalies with a standard deviation s d of the differences at the level of 3 mgal in the best cases presumably improved ggss data would have given improved predictions of surface gravity values the predicted deflections of the vertical were compared to truth based values at a small number of ground stations the very low accuracy of this prediction s d 5 62 arc sec for and 6 78 for should be studied in combination with the inherent characteristics of the gravity field and the validation of ggss data in the test area

eigenvector analysis of gravity gradient tensor to locate geologic bodies we have developed a new method to locate geologic bodies using the gravity gradient tensor the eigenvectors of the symmetric gravity gradient tensor can be used to estimate the position of the source body as well as its strike direction for a given measurement point the eigenvector corresponding to the maximum eigenvalue points approximately toward the center of mass of the causative body for a collection of measurement points a robust least squares procedure is used to estimate the source point as the point that has the smallest sum of square distances to the lines defined by the eigenvectors and the measurement positions it s assumed that the maximum of the first vertical derivative of the vertical component of gravity vector gzz is approximately located above the center of mass observation points enclosed in a square window centered at the maximum of gzz are used to estimate the source location by increasing the size of the window the number of eigenvectors used in the robust least squares and

trace fossils in the ediacaran cambrian transition behavioral diversification ecological turnover and environmental shift abstract after taxonomic revision trace fossils show a similarly explosive diversification in the ediacaran cambrian transition as metazoan body fossils in shallow marine deposits of ediacaran age trace fossils are horizontal simple and rare and display feeding strategies related to exploitation of microbial matgrounds equally notable is the absence of arthropod tracks and sinusoidal nematode trails this situation changed in the early cambrian when a dramatic increase in the diversity of distinct ichnotaxa is associated was followed by the onset of vertical bioturbation and the disappearance of a matground based ecology agronomic revolution on deep sea bottoms animals have been present already in the ediacaran but ichnofaunas were poorly diverse and dominated by the horizontal burrows of undermat miners as shown by the ichnogenus oldhamia this life style continued to be predominant into the early and to a lesser extent middle cambrian nevertheless there was an explosive radiation of behavioral programs during the early cambrian when exactly the bioturbational revolution arrived in the deep sea is uncertain in any case the nereites ichnofacies was firmly established in the early ordovician the rich ichnofauna in the early cambrian guachos formation of northwest argentina probably marks a first step in this ecological onshore offshore shift

the a type mount scott granite sheet importance of crystal magma traps the presence of rapakivi feldspar and of distinctive porphyritic texture of mount scott granite indicates a period of crystallization prior to final emplacement beneath an extensive penecontemporaneous rhyolite volcanic pile final crystallization conditions are interpreted to have been 50 mpa at depths 1 4 km based on stratigraphic constraints however geobarometry based on the al content of amphibole phenocrysts and comparison of granite compositions with phase relations in the sio2 naalsi3o8 kalsi3o8 ternary system both yield pressure estimates of 200 mpa these pressure estimates are interpreted as plumbing the depth of a temporary storage chamber at 7 8 km this depth coincides in this case both with the probable proterozoic basement cover contact and with the calculated brittle ductile transition at time of ascent of mount scott magma although rising magma that fed the preceeding voluminous carlton rhyolite apparently rose unimpeded past these horizontal anisotropies rising magma that formed mount scott granite temporarily paused at this depth based on magmastatic calculations we suggest that horizontal anisotropies e g brittle ductile transition become crustal magma traps where the magma driving pressure exceeds the lithostatic load when the anisotropy is encountered during rifting initial large influxes of magma may proceed passed crustal anisotropies but have the effect of increasing the relative magma driving pressure through reducing horizontal stress thus magma driving pressure may eventually exceed the lithostatic load at the depth of the brittle ductile transition thereby activating this crustal magma trap ponding of magma at the brittle ductile transition chokes the eruption such a pause in magma supply rate may permit a return to initial stress conditions and deactivate the crustal magma trap once again magma will rise to the surface initiating a new magmatic cycle

the role of rifting in the tectonic development of the midcontinent u s a abstract recent studies have proposed the existence of several major ancient rift zones in the midcontinent region of north america although the dating of some of these rifts and even the rift interpretations are subject to question an analysis of these paleo rifts reveals three major episodes of rifting keweenawan 1 1 b y b p eocambrian 600 m y b p and early mesozoic 200 m y b p the extent of these events documents that rifting has played a major role in the tectonic development of the midcontinent region this role goes well beyond the initial rifting event because these features display a strong correlation with paleozoic basins and a strong propensity for reactivation for example the eocambrian reelfoot rift was reactivated in the mesozoic to form the mississippi embayment and is the site of modern seismicity which suggests reactivation in a contemporary stress field of ene compression even though the importance of rifting can be established recognition of rifts and delineation of their complexities remain a major problem which requires more study

cambrian extensional tectonics and magmatism within the southern oklahoma aulacogen abstract the tectonic evolution of the southern oklahoma aulacogen is partially constrained by the petrological consequences of a bimodal igneous suite associated with the cambrian rift mineralogical and compositional layers and erosional surfaces are recognized as initially subplanar subhorizontal markers the progressive rotation of these horizons can be explained by uniform sense normal faulting magmatism confined to the aulacogen trend elevated the thermal gradient producing a crustal strength anisotropy this ensured the localization of the extension throughout the cambrian rifting event the presence of a substantial volume of mafic igneous rocks within the crust along the aulacogen s trend suggests that crustal attenuation was compensated for by the addition of mantle derived material during extension

aulacogens of ancient platforms problems of their origin and tectonic development abstract riphean and palaeozoic linear graben like platform depressions aulacogens jointly with linear swell uplifts in a platform cover intraplatform folded zones and meso cenozoic epi platform rift zones are different morphological manifestations of a single group of linear platform structures aulacogens are characterized by the long duration of their development and ability for regeneration their existence is certain mainly since the late proterozoic riphean usually they inherit more ancient linear attenuated tectonic zones of platform basement or adjust to them aulacogens pass through common stages of development forming a single cycle or in many cases even several similar though not identical cycles the cycle starts with the incipience or regeneration of a linear graben like depression limited by normal faults and after a more or less deep and long subsidence accompanied often by basic or alkaline basic volcanism it is completed in many cases by an inversion stage at this stage horst like uplifts appear limited by thrust and overthrusts in the aulacogen basement while linear swell like uplifts or their systems and even linear folded structures occur in its cover the early stages of an aulacogen evolution occur under horizontal extension conditions whereas the inversion stage takes place under a compressional regime cycles of aulacogen development resemble in attenuated miniature form the development cycle of adjacent geosynclinal areas coincide with them in time and many through and penetrating aulacogens are their direct offsets the late proterozoic cycle of aulacogen evolution corresponds to a pre plate stage of the platform history aulacogen stage by bogdanov and is characterized by the widest development of a network of differently oriented aulacogens over the whole area of ancient platforms which have been subjected to some general horizontal extension crawling away and only partially compensated by compression during the inversion stage the subsequent aulacogen development in palaeozoic and on laurasian platforms partly in meso cenozoic was spatially and genetically connected with the history of geosynclinal later orogenic belts bordering these platforms with regard to gondwana platforms and later the north american and siberian the mesozoic saw the development of many aulacogens or rift zones ranging parallel to transversally with respect to the recent margins of platforms this process was connected with the break up of the gondwana supercontinent and the formation of secondary oceanic depressions as a rule it has not been completed by inversion but took place under extension conditions and probably some general expansion of the earth activated during the meso cenozoic

enhancement and sharpening the migration images of the gravity field and its gradients potential field migration represents a rapid technique for imaging the subsurface based on gravity data however migration transformation usually produces a smooth and unfocused image of the targets due to the diffusive nature of the potential fields in this paper we introduce a method of the migration image enhancement and sharpening based on the application of the hybrid focusing stabilizer which combines the edge preserving smoothing filter with the minimum support functional the method is based on the model resolution matrix of the migration operator we also improve the migration image with a novel target oriented migration method the developed method of migration image enhancement and sharpening is illustrated by synthetic model studies and case studies the case study involves imaging the full tensor gravity gradient data collected in the nordkapp basin of the barents sea

deep reflection seismics in the precambrian of sweden summary a total of 161 km of deep seismic profiles have been shot in the region one profile crosses the protogine zone in sw sweden over most of the profile short weak reflectors are seen the only area with a concentration of reflectors is in the upper two seconds between the two tectonic zones a nearly transparent area east of the protogine zone is interperted as a deep granite intrustion in the siljan impact structure where four profiles were shot the ne part of the structure is dominated by upper crustal high amplitude reflectors possible causes are discussed

robust 3d gravity gradient inversion by planting anomalous densities we have developed a new gravity gradient inversion method for estimating a 3d density contrast distribution defined on a grid of rectangular prisms our method consists of an iterative algorithm that does not require the solution of an equation system instead the solution grows systematically around userspecified prismatic elements called seeds with given density contrasts each seed can be assigned a different density contrast value allowing the interpretation of multiple sources with different density contrasts and that produce interfering signals in real world scenarios some sources might not be targeted for the interpretation thus we developed a robust procedure that neither requires the isolation of the signal of the targeted sources prior to the inversion nor requires substantial prior information about the nontargeted sources in our iterative algorithm the estimated sources grow by the accretion of prisms in the periphery of the current estimate in addition only the columns of the sensitivity matrix corresponding to the prisms in the periphery of the current estimate are needed for the computations therefore the individual columns of the sensitivity matrix can be calculated on demand and deleted after an accretion takes place greatly reducing the demand for computer memory and processing time tests on synthetic data show the ability of our method to correctly recover the geometry of the targeted sources even when interfering signals produced by nontargeted sources are present inverting the data from an airborne gravity gradiometry survey flown over the iron ore province of quadrilatero ferrifero southeastern brazil we estimated a compact iron ore body that is in agreement with geologic information and previous interpretations

hydrothermally induced changes in mineralogy and magnetic properties of oxidized a type granites abstract the changes in magnetic mineralogy due to the hydrothermal alteration of a type granitic rocks have been thoroughly investigated in samples from the granite of tana corsica france and compared with other a type granites meruoca ne brazil bushveld south africa mount scott wichita mountains oklahoma usa and the stratoid hypersolvus granites of madagascar the altered red colored samples and their non altered equivalents were magnetically characterized by means of magnetic susceptibility measurements hysteresis loops remanent coercivity spectra and lowrie test it is shown that hydrothermalization in magnetite bearing granites is related to the formation of fine grained magnetite and hematite and to coeval depletion in the content of primary low coercive coarse grained magnetite these mineralogical changes give typical rock magnetic signatures namely lower susceptibility magnitudes and anisotropy degrees prolate ams anisotropy of magnetic susceptibility fabrics and increased coercivities optical microscopy and sem scanning electronic microscopy images suggest that the orientation of the secondary magnetic minerals is related to fluid pathways and micro fractures formed during the hydrothermal event and therefore may be unrelated to magma emplacement and crystallization fabrics changes in magnetic mineralogy and grain size distribution have also to be considered for any paleomagnetic and iron isotope studies in granites

from trash to treasure three dimensional basement imaging with excess data from oil and gas explorations modern oil and gas seismic surveys commonly use areal arrays that record continuously and thus routinely collect excess data that are not needed for the conventional common reflection point imaging that is the primary goal of exploration these excess data have recently been recognized to have utility not only in resource exploration but also for addressing a diverse range of scientific issues here we report processing of such discarded data from recent exploration surveys carried out in southeastern new mexico these have been used to produce new three dimensional 3 d seismic reflection imagery of a layered complex within the crystalline basement as well as elements of the underlying crust this enigmatic basement layering is similar to that found on industry and academic seismic reflection surveys at many sites in the central united states correlation of these reflectors with similar features encountered by drilling in northwestern texas suggest that they may be part of an extensive continental scale network of tabular mafic intrusions linked to keweenawan rifting of the igneous eastcentral unites states during the late proterozoic more importantly this analysis clearly demonstrates that the new generation of continuously recorded 3 d exploration datasets represent a valuable source of fresh information on basement structure that should be examined rather than discarded such basement information is not only important to understanding crustal evolution it is directly relevant to assessing risks associated with fossil fuel extractions such as induced seismicity related to waste water injection

resolution and variance operators of gravity and gravity gradiometry gravity gradiometry represents a new potential field data set which may better constrain the density structure of the earth using singular value spectral decomposition of the gravity and gravity gradient kernels the model parameter resolution and model parameter variance of the two data types are compared using data from the defense mapping agency and a recently acquired collection of airborne gradient measurements from bell aerospace textron s gravity gradient survey system ggss the ggss was flown over a portion of southwestern oklahoma where the gravitational anomaly from the buried wichita basement rocks is over 60 mgal the corresponding maximum vertical gravity gradient was found to be 46 2 eotvos the determination of the subsurface density structure is cast as a linear inverse problem and for comparison a nonlinear inverse problem for both the linear and nonlinear inversions the gravity gradients improve the resolution and result in smaller variances than the vertical component of gravi

seismic studies of crustal structure during the past four years seismology has continued its role as the key technique for determination of the structure of the continental and oceanic crust by and large however the field and analysis methods used bear little resemblance to those of ten years ago a continued push to increase the number of recording channels has led to the routine use of ocean bottom seismometers sonobuoys and multichannel streamers in oceanic studies and to the use of large sets of portable instruments and multichannel seismic reflection strings on land in studies using earthquakes as sources local and regional arrays provide a capability for obtaining geologically useful two and three dimensional information about the crust

puncoviscana folded belt in northwestern argentina testimony of late proterozoic rodinia fragmentation and pre gondwana collisional episodes stratigraphic correlations and tectonic analysis suggest that the puncoviscana fold belt of northwestern argentina was an intracontinental basin with bimodal igneous suites that formed in connection with the breakup of the rodinia supercontinent at 800 ma several lines of evidences point to an initial lithosphere rupture possibly induced by a rising mantle plume the earliest synrift igneous products are represented by ultra potassic dykes and alkaline lava flows of high lree hree and low zr nb y nb ratios the dyke emplacements and the initiation of rifting were probably synchronous they pass laterally and upwards middle part of the puncoviscana succession into basalts of alkaline transitional character oib like source the distinctive chemical feature of these lavas are very similar to the source of oceanic island basalts thus they are thought to represent a magmatism associated with the rift and rift drift transition stage during this stage of rifting probably true oceanic crust was formed the upper part of the puncoviscana sequence late precambrian lower cambrian in age comprises a thick and monotonous sequence of pillow lavas massive basaltic flows and minor volcanic breccias and hyaloclastites these lavas exhibit morb trace element characteristics with high feot and tio2 low k2o and p2o5 flat light ree spectra little or no depletion in nb and ta this volcanism consists of the major and latest effusive episode from the puncoviscana basin which was slightly modified by subduction processes the geodynamical model proposed for the generation of these volcanic rocks could have been developed in two stages in the first stage the volcanic event is compatible with a progressive opening of a continental rift leading to formation of a mature oceanic basin in contrast the second stage shows the effects of a completed wilson cycle including a primitive volcanic arc which continued until the accreted cuyania arequipa belen antofalla caba terrane against the proto gondwana western borderland of the amazonian shield 535 ma

two dimensional elastic pseudo spectral modeling of wide aperture seismic array data with application to the wichita uplift anadarko basin region of southwestern oklahoma abstract full wave field modeling of wide aperture data is performed with a pseudospectral implementation of the elastic wave equation this approach naturally produces three component stress and two component particle displacement velocity and acceleration seismograms for compressional shear and rayleigh waves it also has distinct advantages in terms of computational requirements over finite differencing when data from large scale structures are to be modeled at high frequencies the algorithm is applied to iterative two dimensional modeling of seismograms from a survey performed in 1985 by the university of texas at el paso and the university of texas at dallas across the anadarko basin and the wichita mountains in southwestern oklahoma the results provide an independent look at details of near surface structure and reflector configurations near surface 70 per cent of the energy in the observed seismograms the interpretation of the data is consistent with the results of previous studies of these data but provides considerably more detail overall the p wave velocities in the wichita uplift are more typical of the middle crust than the upper crust 5 3 to 7 1 km sec at the surface the uplift is either exposed as weathered outcrop 5 0 to 5 3 km sec or is overlain with sediments of up to 0 4 km in thickness ranging in velocity from 2 7 to 3 4 km sec generally increasing with depth the core of the uplift is relatively seismically transparent a very clear coherent reflection is observed from the mountain view fault which dips at 40 to the southwest to at least 12 km depth velocities in the anadarko basin are typical of sedimentary basins there is a general increase from 2 7 km sec at the surface to 5 9 km sec at 16 km depth with discontinuous reflections at depths of 8 10 12 and 16 km

a new isostatic residual gravity map of the conterminous united states with a discussion on the significance of isostatic residual anomalies to display more clearly the gravity anomalies caused by geologic bodies in the upper parts of the crust a new colored isostatic residual gravity map of the conterminous united states has been prepared using the gravity data set compiled for the gravity anomaly map of the united states society of exploration geophysicists 1982 the new isostatic residual gravity map is based on an airy heiskanen model of local compensation in which the surface load requiring compensation is defined by 5 min topographic and bathymetric data sets a colored first vertical derivative map of isostatic residual gravity further enhances the short wavelength anomalies produced by bodies at or near the surface and emphasizes the regional fabrics and trends in the gravity field for the purpose of displaying gravity anomalies caused by shallow bodies of geologic significance the nature of the isostatic model and the values of its parameters are of lesser importance than the application of an isostatic correction of some sort most isostatic models result in residual gravity maps that appear nearly identical in their main patterns and features anomalies on isostatic residual gravity maps should not be casually interpreted in terms of undercompensation or overcompensation because large amplitude anomalies can be produced by crustal bodies in complete local isostatic equilibrium many isostatic residual gravity anomalies less than several hundred kilometers wide can be related to known geologic bodies we present here a classification scheme that attempts to categorize such anomalies on the basis of tectonic environment in general highs correlate with intruded or accreted mafic material or with upthrusted crustal sections whereas lows occur over low density sedimentary or volcanic sections felsic intrusive bodies or down warped crustal sections although some longer wavelength anomalies such as the broad gravity high centered over montana could be manifestations of density contrasts deep in the mantle many such anomalies can also be modeled by geologically reasonable density contrasts that are isostatically compensated and confined to depths of less than several hundred kilometers so that their source bodies need not be deep the fact that certain of these broader anomalies have well defined boundaries which correlate with near surface geologic features increases the likelihood that their sources lie entirely within the lithosphere if so then the density contrasts required to explain the gravity data imply fundamental anomalies in chemical composition or thermal state for the crustal and upper mantle columns under these regions we have investigated spectral analysis as a method to quantitatively characterize regional anomaly patterns contoured plots of normalized amplitude spectra were prepared for various areas of the isostatic residual gravity field of the united states these fourier domain representations show characteristic patterns that can be interpreted in terms of the trends and wavelengths of anomalies and may help to more objectively distinguish geologic basements with different origins or tectonic histories

thermal maturation by vitrinite reflectance of woodford shale anadarko basin oklahoma the woodford shale upper devonian lower mississippian a black shale widely regarded as an important hydrocarbon source rock has attained thermal maturity to postmaturity with respect to the generation of liquid hydrocarbons in most of the anadarko basin in western oklahoma untreated whole rock well cuttings and core material from selected 10 ft intervals of the woodford shale in 28 wells were examined under reflected white light thermal maturation was determined by measuring the reflectance in oil immersion ro of first generation vitrinite particles a minimum of 45 reflectance measurements were recorded for each well representing one or more sample intervals the woodford shale was sampled at depths from 5 060 ft 1 542 m in the northeastern shelf to 25 115 ft 7 655 in the deepest part of the basin a systematic increase in mean vitrinite reflectance meanro with depth was observed over much of the anadarko basin from northeast to southwest across the basin mean ro increases from 0 48 to 2 61 high temperatures have raised the woodford shale to anthracite rank in two wells 4 29 and 4 89 ro in the deep anadarko basin an isoreflectance map for the woodford shale indicates those areas of the basin where the thermal history of the shale is optimum for preserving liquid hydrocarbons mean ro of 0 5 to 2 0 computer generated plots of vitrinite reflectance versus depth provide a regression equation that predicts the vitrinite reflectance of the woodford shale at any depth in the anadarko basin and determines the amount of erosion

ordovician docking of the carolina slate belt paleomagnetic data paleomagnetic results from eight sites in argillaceous metasediments from union county north carolina in the central carolina slate belt yield a consistent high blocking temperature magnetization component the precision of the mean declination and inclination of all site means is maximized at 50 tilt correction and the improvement in grouping relative to 0 and 100 tilt correction is significant at the 95 confidence level this tends to indicate that the high blocking temperature component was acquired during folding the metamorphism and deformation in this area are rather well constrained by recent 40ar 39ar data to the late ordovician 450 ma we therefore interpret the computed pole position 29 6 n 122 1 e 95 5 11 as late ordovician in age and note that it lies close to some of the late ordovician poles for cratonic north america the paleolatitude 22 2 s of the sampling site is certainly unlike those derived from armorica and gondwana for this time interval and is rather similar to that proposed for the iapetus coast of laurentia during the late ordovician indeed the magnetization and deformation may be contemporaneous with the docking of the carolina slate belt onto the laurentian continent

shallow seismic reflection profile of the meers fault comanche county oklahoma this is the publisher s version also available electronically from http onlinelibrary wiley com

how well do fossil assemblages of the ediacara biota tell time comment gehling and droser s 2013 1 conclusion that ediacaran fossils are not useful for biostratigraphy is an artifact of their lumping of all frond fossils into one indeterminate category because there are potential biostratigraphic zones based on successive appearance of fronds of trepassia

results of airborne vector 3 d gravimetry gravity field modeling using airborne vertical component gravimetry has made significant strides over the last decade we demonstrate the feasibility of extending this to three dimensions using data from inertial navigation systems ins and the global positioning system gps a significant advantage of measuring the horizontal gravity components is that the geoid can be determined in profiles by direct along track integration thus not only adding strength to conventional methods but reducing the required area of survey support especially along model boundaries as such the ultimate limitation of the method is in the quality of the ins and gps sensors in our test case all three components of the gravity vector were determined over a profile in the canadian rocky mountains differences between available truth data and the computed gravity components have standard deviations of 7 8 mgal horizontal and 3 mgal vertical these standard deviations include uncertainties in the truth data 5 mgal for horizontal 1 3 mgal for vertical the resolution in the computed values is about 10 km these analyses have demonstrated for the first time that the total gravity vector can be determined from airborne ins and gps to reasonable accuracy and resolution without any external orientation information nor prior statistical hypothesis on the gravity signature using medium accuracy ins and geodetic quality gps receivers

kinematic wave model for transient bed profiles in alluvial channels under nonequilibrium conditions 1 transient bed profiles in alluvial channels are generally modeled using diffusion or dynamic waves and assuming equilibrium between detachment and deposition rates equilibrium sediment transport can be considerably affected by an excess or deficiency of sediment supply due to mostly flows during flash floods or floods resulting from dam break or dike failure in such situations the sediment transport process occurs under nonequilibrium conditions and extensive changes in alluvial river morphology can take place over a relatively short period of time therefore the study and prediction of these changes are important for sustainable development and use of river water this study hence developed a mathematical model based on the kinematic wave theory to model transient bed profiles in alluvial channels under nonequilibrium conditions the kinematic wave theory employs a functional relation between sediment transport rate and concentration the shear stress approach for flow transport capacity and a relation between flow velocity and depth the model satisfactorily simulated transient bed forms observed in laboratory experiments

3d inversion of airborne gravity gradiometry data using cokriging abstractwe developed a new method for interpretation of airborne gravity gradiometry data based on cokriging inversion the cokriging method that we evaluated minimized the theoretical estimation error variance by using auto and crosscorrelations of several variables it does not require iterations and can easily include complex a priori information moreover the smoothing effects in the inverted density structure model can be reduced to a certain extent due to the anisotropy constrain in the covariance model we compared the recovered models obtained by inverting the different combinations of gravity gradient components to understand how different component combinations contributed to the resolution of the recovered model the results indicated that including multiple components for inversion increased the resolution of the recovered density model and improved the structure delineation moreover in the case in which the parameters of the variogram model are not well chosen cokriging with multicompon

the gradient tensor of potential field anomalies some implications on data collection and data processing of maps the full gradient tensor is presently not measured routinely onboard airplanes or on land this paper describes some improvements that can be made in strategies of data collection and in processing of potential field maps if such tensor measurements were available we suggest that in addition to producing for example standard total field anomaly maps the invariants of the tensor be mapped strikes of magnetic or gravimetric structures may be determined from minimizing the power in the first row and column of the tensor invariants can be looked upon as nonlinear filters enhancing sources with big volumes their lateral resolution is superior to that of the field proper and for a given resolution the flight altitude and separation between flight lines can be increased compared with the standard mode of operation in airborne surveys the distance between flight lines is normally much larger than the height above the ground this may introduce severe aliasing effects in the direction perpendicular to the

proterozoic basin in the southern midcontinent of the united states revealed by cocorp deep seismic reflection profiling cocorp deep crustal seismic profiles in southwestern oklahoma show strong persistent continuous and undeformed layering in the basement over an area probably very much greater than 2 500 km 2 such layering is very unusual judging by cocorp experience with basement rocks elsewhere in the united states the data can be interpreted as representing a proterozoic basin filled with clastic sedimentary and felsic volcanic rocks 7 to 10 km thick whose base lies 10 to 13 km deep these rocks are believed on the basis of sparse evidence from regional geology to have been deposited or extruded about 1 200 to 1 400 m y ago and some of them may now be metamorphosed this basin lies on the south side of the wichita mountains under the paleozoic hardeman basin and is similar in depth to the paleozoic anadarko basin north of the mountains the deep basement layering is truncated on the south side of the wichita mountains probably by precambrian faults in conjunction with granitic intrusions pennsylvanian compression probably reactivated these precambrian trends extensive precambrian basin deposits in this area were unexpected on the basis of evidence from sparse well control and reports of other layered basement reflections elsewhere in the southern midcontinent suggest that precambrian basins may be an important feature of this region simple models for the evolution of southwestern oklahoma as an aulacogen must be reformulated in the light of these new data

intraplate magmatism related to opening of the southern iapetus ocean cambrian wichita igneous province in the southern oklahoma rift zone abstract southern oklahoma and adjacent parts of texas contain an extensive igneous province emplaced during early cambrian rifting within the southern oklahoma rift zone the rift zone was initiated in association with the opening of the southern iapetus ocean during rodinia supercontinent breakup and later became the site of a series of linked uplifts and basins as a result of late paleozoic inversion igneous rocks within the rift are referred to as the wichita province and are present mostly in the subsurface although critical exposures occur in the wichita and arbuckle mountains in southwestern and southern oklahoma wells drilled into basement in the region provide a wealth of information on the distribution and relations of the major igneous units in the upper crust and geophysical data provide important constraints on deeper levels of the rift zone the upper parts of the igneous rift fill comprise the carlton rhyolite group which has an estimated subsurface areal extent of 40 000 km 2 and the related wichita sheet granites which intrude the lower parts of the rhyolite succession these rocks have a type characteristics and were emplaced after intrusion tilting and uplift of a large tholeiitic layered mafic complex smaller bodies of gabbro also intruded the layered complex after it was tilted u pb zircon and 40 ar 39 ar geochronology indicates the felsic rocks and at least some of the mafic units were emplaced in a relatively narrow time frame at 539 530 ma basalts and intermediate lavas are present only in the subsurface our new work shows these lavas to have tholeiitic to mildly alkaline compositions and to be more extensive than previously realized forming thick successions that both underlie and are intercalated with the rhyolites diabase dikes were intruded into older crust during initial opening of the rift and a suite of late diabase intrusions also cuts the rhyolites and granites indicating that mafic magma was supplied to the rift throughout its igneous history geophysical data show that an enormous mass of mafic rock occupies deeper parts of the rift extending to depths of at least 10 km beneath the surface the total volume of igneous rock emplaced within the rift is estimated to be in excess of 250 000 km 3 detailed studies of carlton rhyolite exposures in the wichita mountains complemented by work on drill cuttings from basement wells indicate that lava flows up to 400 m thick make up major parts of the rhyolitic succession the generally limited exposures of these rhyolite lavas in the wichita mountains are interpreted to be remnants of laterally extensive flow units similar to those documented from other a type felsic provinces trace element abundances define three distinct geochemical groups of rhyolite suggesting derivation from three different sources or magma reservoirs flows belonging to the different geochemical groups are intercalated in the wichita mountains exposures which may indicate that laterally extensive flows from separate magma chambers came to rest on top of one another during accumulation of the rhyolitic volcanic pile

the hsi bright reflector further evidence for extensive magmatism in the precambrian of western canada abstract seismic reflection lines acquired in 1995 as part of lithoprobe canada s national geoscientific research program revealed unusually bright reflectors of extensive lateral scale in the archaean medicine hat block of southern alberta the herein named head smashed in hsi reflector is imaged over an area of at least 6000 km 2 in the upper half of the crust the reflector appears as a mostly horizontal to subhorizontal feature although continuous it has a complex and laterally variable internal structure comparison with a reflector of known impedance contrast in the overlying western canadian sedimentary basin indicates a high impedance structure to cause the reflections dense one dimensional modelling is consistent with the reflector being a multilayered structure with layer thicknesses in the range of tens to hundreds of metres and lateral scales of discrete reflecting elements between tens of metres and hundreds of metres polarity constraints overall geometry and reflection character strongly suggest that mafic ultramafic horizontal sheets are the cause of hsi reflectivity the hsi is the third major sequence of strong crustal reflectivity imaged by lithoprobe deep seismic data in the precambrian crust of western canada all three features are very similar in overall geometry reflector strength and character and have been interpreted as horizontal sheetlike intrusions small scale variations of the reflectivity signatures suggest a pronounced rheological heterogeneity in the upper crustal rocks within the host tectonic domains

reflection seismic investigations of the siljan impact structure sweden reflection seismic measurements were carried out during 1985 in the area of the siljan impact structure of sweden a total profile length of 80 km was shot to get a clearer picture of the subsurface geometry of impact structures and the processes that formed them than could be obtained from surface observations or theoretical modeling studies standard stacked sections have been interpreted in terms of current impact models the transient crater diameter is found to be approximately 22 km considerably smaller than current estimates based on interpretation of surface geology the structural uplift is estimated to be 3 km at the 5 to 8 km level and the material flow necessary to support the uplift is mainly horizontal rather than vertical