middle permian paleomagnetism of the sydney basin eastern gondwana testing pangea models and the timing of the end of the kiaman reverse superchron abstract paleomagnetic and geochronologic data from the eastern margin of gondwana have been obtained from the gerringong volcanics in the southern sydney basin australia the corresponding paleomagnetic pole at 56 9 s 154 8 e n 131 a95 9 1 has a 40ar 39ar plagioclase plateau age of 265 05 0 35 0 46 ma from the bumbo latite and overlaps with recent radio isotopic and paleomagnetic results published from western gondwana the long documented inconsistency between middle permian eastern and western gondwanan paleomagnetic datasets is most likely an artefact of a lack of reliable paleomagnetic data from eastern gondwana for this period a number of well dated and recently published ca 265 ma paleomagnetic results from gondwana and laurussia are shown to be consistent with the wegenerian pangea a configuration with a loose n s fit of the continents for the middle permian the lack of crustal overlap negates the need for a pangea b configuration which if valid must have been assembled to pangea a by ca 265 ma the reverse polarity bumbo latite was sampled from the kiaman type section located in the southern sydney basin three cases of normal polarity were detected in the overlying saddleback dapto and berkeley latites previously assigned to the kiaman reverse superchron krs we review krs aged magnetostratigraphic data and propose that an age assignment of 265 ma most likely represents the termination of the non reversing field with longer stable intervals of normal polarity recorded and able to be correlated globally

early permian pole evidence from the pictou red beds prince edward island canada the mid permian red beds of the upper pictou group retain a primary remanence in hematite that has been isolated by thermal step demagnetization above 600 c conglomerate contact and reversals tests show that the remanence is primary the pole position of let 42 1 n long 125 5 e dp 1 8 dm 3 6 falls on current apparent polar wander paths at older ages than expected there is also a significant difference between early permian poles from the northeastern united states canada and the southwestern united states the results suggest that postdepositional permian triassic remagnetization may have affected some units in the southwestern united states or that there has been about 9 of relative tectonic rotation between the two regions caused by the laramide orogeny

a cratonic middle jurassic paleopole callovian oxfordian stillstand j 2 cusp rotation of the colorado plateau and jurassic north american apparent polar wander 1 paleomagnetic results have been obtained from two sequences of the upper middle jurassic upper callovian summerville formation which are located on the north american craton north central new mexico the thicker of the two sections trujillo exhibits a well defined dual polarity remanence forming a magnetostratigraphy of at least 12 relatively short polarity intervals the high reversal frequency is consistent with that recorded by the oceanic crust at this time the second section romeroville is thin gypsiferous and poorly indurated consequently only a short interval 5 m was successfully sampled the characteristic magnetization was wholly normal polarity in the rapid reversals of the thicker section that thickness of normal polarity is unique and thus forms the basis of magnetostratigraphic correlation between the two sections a cratonic late middle jurassic paleomagnetic pole at 148 2 e 57 3 n k 30 3 95 6 0 was obtained from the larger trujillo sequence despite large confidence limits the small sample population of the romeroville sequence displayed the same pole throughout the western united states the summerville formation is overlain with little or no discordance by the morrison formation although the two stratigraphic units are commonly reported to be separated by an unconformity designated j 5 the new mexico paleopoles of the summerville and overlying lower morrison formations are statistically identical at the 95 confidence level a similar situation exists between summerville and lower morrison paleopoles of the colorado plateau the presence of the same geomagnetic field direction in both the summerville and the lower morrison formations suggests that the j 5 unconformity which separates them may encompass little time perhaps representing only a minor break in deposition the two newly investigated summerville sites are located east of the rio grande rift hence representative of the north american craton their paleopoles are displaced counterclockwise relative to those of the colorado plateau and in amounts consistent with other coeval craton colorado plateau pole pairs together six coeval paleopoles indicate that the colorado plateau has rotated clockwise by about 9 0 3 since late pennsylvanian time the cratonic summerville paleopole also removes the uncertainty over the jurassic north american apparent polar wander path the statistically identical summerville and lower morrison paleopoles form a substantial data set five paleopoles which indicate that na apw traced a path roughly along 60 latitude the five paleopoles stand in stark contrast to the paleopole from the slightly older 5 8 ma moat volcanics spreading rates in the central atlantic do not allow na plate motion that would include both paleopoles positions because the weight of the data five paleopoles from widely spaced localities and different tectonic blocks the moat volcanics pole cannot be representative of north america in the middle jurassic

tectonics and plate tectonics model for the variscan belt of europe abstract a plate tectonics model is presented to explain the tectonometamorphic characteristics of the european variscides after the closing of two oceanic domains by two sided subduction 500 420 ma and obduction 420 380 ma collision of the european and african continental plates occurred we propose that the subsequent complex intracontinental deformation 380 290 ma is the result of a double subduction of the continental lithosphere accompanied by crust mantle decollement this mechanism explains the progressive crustal thickening and migration of the deformation through time from the sutures toward the external parts of the variscan belt accounting for this model and for the relationships between the european variscides and the other paleozoic peri atlantic belts caledonides appalachian mauritanides and morocco we infer the relative positions of africa america and europe between the silurian and the permian

high resolution imaging an approach by incorporating stationary phase implementation into deabsorption prestack time migration abstractwe have improved the so called deabsorption prestack time migration pstm by introducing a dip angle domain stationary phase implementation deabsorption pstm compensates absorption and dispersion via an actual wave propagation path using effective q parameters that are obtained during migration however noises induced by the compensation degrade the resolution gained and deabsorption pstm requires more computational effort than conventional pstm our stationary phase implementation improves deabsorption pstm through the determination of an optimal migration aperture based on an estimate of the fresnel zone this significantly attenuates the noises and reduces the computational cost of 3d deabsorption pstm we have estimated the 2d fresnel zone in terms of two dip angles through building a pair of 1d migrated dip angle gathers using pstm our stationary phase qpstm deabsorption pstm was implemented as a two stage process first we used conventional pstm to obtain the fresnel zones then we p

carboniferous through jurassic paleomagnetic data and their bearing on rotation of the colorado plateau small yet systematic differences between paleomagnetic poles derived from strata on the colorado plateau and paleopoles determined from rocks on the north america craton have been interpreted to support the hypothesis of modest post late cretaceous clockwise rotation of the plateau as a quasi rigid body with respect to the craton using an iterative search for the best fit euler pole and rotation angle comparison of the best quality late carboniferous through late jurassic paleomagnetic poles from the colorado plateau and the north america craton gives a cumulative rotation estimate based on a rotation pole at 34 n 105 w of 7 4 3 8 95 confidence limits a similar comparison using subsets of the cratonic database from localities in 1 northeast north america and 2 the craton platform interior give larger 8 8 3 6 and smaller 5 1 3 8 estimates respectively reflecting the fact that poles from localities in northeast north america in particular those from triassic rift basins indicate a larger rotation as concluded in direct pole to pole comparisons the euler pole as determined by the paleomagnetic data only can lie anywhere within a relatively large area that encompasses locations in the western united states previously proposed from geological observations paleomagnetic data and geologic observations together or independently do not support the hypothesis of a large colorado plateau rotation of 11 to 15 if geologically reasonable previous estimates of significant 20 km dextral slip along the eastern margin of the plateau require a position for the euler pole east of the 105 w meridian

prestack time migration of nonplanar data improving topography prestack time migration with dip angle domain stationary phase filtering and effective velocity inversion abstractwe have developed a modified prestack time migration pstm approach that can directly image nonplanar data by using two effective velocity parameters above and below a datum the proposed extension improves the so called topography pstm by introducing a dip angle domain stationary phase migration or filtering and combining effective velocity inversion with the residual static corrections the stationary phase migration to constrain the imaging aperture within fresnel zones significantly improves the signal to noise ratio s n of the image gathers especially in the presence of steeply dipping structures this helps to extract an accurate residual moveout from the common shot and receiver image gathers and the surface consistent residual statics hidden in these image gathers can be simultaneously obtained from an inversion process as a result the final migrated images show higher s n and are better focused than the conventional topography pstm the proposed technique can handle rugged topogr

magnetic polarity stratigraphy and palynostratigraphy of the mississippian pennsylvanian boundary interval in eastern north america and the age of the beginning of the kiaman magnetic polarity data from the maritimes basin in eastern canada reveal patterns of magnetic reversal through 17 m y of late mississippian and early pennsylvanian time we collected samples from three sections on cape breton island a fourth that extends a section studied previously and a fifth from a deep cored well on prince edward island we compared the polarity data from these sections to previous results from lower parts of the joggins section of eastern canada all sections are constrained by new palynological data and collectively span the late mississippian brigantian pendleian and much of the arnsbergian substages a major unconformity at the pennsylvanian mississippian boundary makes correlation difficult the late mississippian arnsbergian substage is dominated by normal polarity whereas the pendleian and brigantian are characterized by normal and reversed polarity intervals in about equal proportions in the united states the mississippian pennsylvanian boundary is a major hiatus that juxtaposes strata of early pennsylvanian age on mississippian strata ranging in age from brigantian to mid to late arnsbergian data for the mauch chunk formation in the united states provide polarity reversal patterns for correlative sequences in the central appalachian basin field mapping and magnetic polarity data show closely comparable mississippian pennsylvanian relationships in the maritimes basin more than 1500 km northeast from the u s sections the eustatic event that coincides with the mississippian pennsylvanian boundary unconformity is late arnsbergian to yeadonian in both the central appalachians and maritime basins basal pennsylvanian strata of yeadonian to langsettian age on cape breton island reveal normal paleomagnetic polarity through several hundred meters of section these strata are overlain by a thick section showing only reversed polarity we believe that this polarity boundary is the base of the kiaman an early langsettian position ca 318 ma for the base kiaman superchron is indicated by these new data in eastern nova scotia and new brunswick the sedimentary rocks just above the unconformity are of reversed polarity it is clear that the sedimentation in the two areas is affected by the unconformity and no magnetic or palynological correlation is possible above the unconformity only saetosa zone sediments are present

pre drift extension of the atlantic margins of north america and europe based on paths of permo triassic apparent polar wander summary we reconstruct the relative configuration of north america and europe prior to separation using paths of apparent polar wander apw for the interval 300 to 200 ma the bullard et al 1965 reconstruction closely superimposes the 300 ma points on the two apw paths but leaves the 200 ma points far apart conversely anomaly based reconstructions for later times approximately superimpose the 200 ma ends of the paths but leave the older ends far apart this indicates that separation of the interiors of the two continents began during the interval 300 to 200 ma long before surficial rifting commenced in the late mesozoic this in turn requires pre rift extension in the two continental margins extension appears to have occurred in two phases of approximately equal magnitude but significantly different direction the change in direction occurred at about 200 ma the earlier 300 to 200 ma episode of extension appears to have involved a strong element of sinistral shear based on our preferred reconstruction the total amount of pre rift extension of the two continental margins may have been as much as 1400 km

paleomagnetism of the moenkopi and chinle formations in central new mexico implications for the north american apparent polar wander path and triassic magnetostratigraphy in central new mexico red sedimentary rocks unconformably overlying permian carbonates of the san andres formation have been correlated with the early middle triassic moenkopi and late triassic chinle formations of the colorado plateau paleomagnetic samples from triassic sections exposed on basement cored uplifts along both the east and west side of the rio grande rift near albuquerque yield upon thermal and chemical demagnetization well defined high unblocking temperature dual polarity magnetizations carried by hematite the characteristic magnetization is interpreted as an early acquired chemical remanent magnetization based on a positive intraformational microconglomerate test and bedding parallel magnetization polarity zonation the moenkopi and lowermost chinle formations produced paleomagnetic poles respectively at 57 6 n 100 3 e n 36 sites k 74 1 a95 2 8 and 60 8 n 88 9 e n 17 sites k 130 3 a95 3 1 these data plus previously published and additional results from the underlying permian strata suggest that portions of central new mexico have experienced a small clockwise rotation i e less than 10 similar to that of the colorado plateau with respect to the north american craton the paleomagnetic directions of the chinle formation and related strata in eastern new mexico document about 12 great circle distance of rapid apparent polar wander during mid carnian to late norian times along a track which contains other cratonic poles of similar age we present a preliminary magnetic polarity time scale for the triassic that incorporates the present new mexico data and previously published data mostly form continental red bed sequences this magnetic polarity scale provides a basic framework which can be tested with future data from triassic sections where additional biostratigraphic control exists

behavior of the paleosecular variation during the permian carboniferous reversed superchron and comparisons to the low reversal frequency intervals since precambrian times we investigated the paleo latitudinal dependence of angular dispersion sets of virtual geomagnetic poles vgps for the permian carboniferous reversed superchron pcrs 262 318 ma in order to analyze the paleosecular variation during this period we prepared different paleomagnetic datasets from scientific databases and recent literature based on selection criteria which provided high degree of refinement model g of mcfadden et al 1988 was fitted to the vgp dispersion data providing the shape parameters a and b which were further compared with similar results for the cretaceous normal superchron cns and other periods of different geomagnetic reversal rates throughout the last 3 ga our results indicate high similarity between the angular vgp dispersion from the pcrs and cns a low vgp dispersion at low paleolatitudes and strong paleolatitudinal dependence in contrasting difference for periods of higher reversal rates the last 5 ma despite the geodynamic differences related to both phanerozoic superchrons such evidence could point out similar heat flux conditions in the cmb which may favor compatible stability conditions throughout these magnetozones notably two additional observations which arose from the shape parameters relations for both phanerozoic superchrons and precambrian datasets demand further investigation i a pattern of increase for the b a ratio throughout the 0 5 1 6 ga interval was observed which could be partially explained by the maya superchron recently proposed by gallet et al 2012 ii the b a relationship for both phanerozoic superchrons and the 2 45 2 82 ga interval pointed to the presence of one or more long term magnetozones throughout the paleoproterozoic

the pictou red beds pennsylvanian pole could phanerozoic rocks in the interior united states be remagnetized the pennsylvanian red beds of the pictou group on prince edward island canada retain a stable remanence in hematite that gives a paleomagnetic pole position at 42 n 131 e dp 2 dm 4 positive conglomerate and contact tests along with dual polarities show that the remanence is primary and of stephanian age 286 306 ma for elongated pole distributions through time bingham statistics is more suitable than fisher statistics bingham statistics shows that there is a consistent discordance in the pennsylvanian to late triassic poles from the appalachian orogenic belt and interior craton of north america this discordance is most readily explained by younger partial remagnetization or possibly complete remagnetization in many rock units especially red beds of the interior craton bingham analysis also shows that there is a significant difference between the colorado plateau and interior craton that is most readily explained by a laramide 5 5 2 9 clockwise rotation of the plateau relative to the craton

scattering and dip angle decomposition based on subsurface offset extended wave equation migration abstractan angle dependent reflection coefficient is recovered by seismic migration in the angle domain we have developed a postmigration technique for computing scattering and dip angle common image gathers cigs from seismic images extended by the subsurface offset based on wave equation migration methods our methodology suggests a system of radon transform operators by introducing local transform relations between the subsurface offset image and the angle domain components in addition to the commonly used decomposition of the scattering angle the methodology associates the wave equation migration with dip domain images as well the same postmigration subsurface offset image is used to decompose scattering and dip angle cigs individually or to decompose a multiangle cig by showing simultaneously both angles on the gather s axis we show that the dip angle response of seismic reflections is a spot like signature focused at the specular dip of the subsurface reflector it differs from the well stu

image enhancement by multi parameter characterization of common image gathers we present an innovative approach for seismic image enhancement using multiparameter angle domain characterization of common image gathers a special subsurface angle domain imaging system is used to generate the multi parameter common image gathers in a summation free image space the imaged data associated with each common image gathers depth point contain direction dependent opening angle image contributions from all the available incident and scattered wave pairs at this point each direction dependent opening angle data can be differently weighted according to its coherency measure once the optimal migration velocity is used it is assumed that in the actual specular direction the coherency measure semblance along reflection events from all available opening angles and opening azimuths is larger than that along non specular directions the computed direction dependent semblance attribute is designed to operate as an imaging filter which enhances specular migration contributions and suppresses all others in the final migration image the ability to analyse the structural properties of the image points by the multi parameter common image gather allows us to better handle cases of complicated wave propagation and to improve the image quality at poorly illuminated regions or near complex structures the proposed method and some of its practical benefits are demonstrated through detailed analysis of synthetic and real data examples

widespread inclination shallowing in permian and triassic paleomagnetic data from laurentia support from new paleomagnetic data from middle permian shallow intrusions in southern illinois usa and virtual geomagnetic pole distributions abstract recent paleomagnetic work has highlighted a common and shallow inclination bias in continental redbeds the permian and triassic paleomagnetic records from laurentia are almost entirely derived from such sedimentary rocks so a pervasive inclination error will expectedly bias the apparent polar wander path of laurentia in a significant way the long standing discrepancy between the apparent polar wander paths of laurentia and gondwana in permian and triassic time may be a consequence of such a widespread data pathology here we present new middle permian paleomagnetic data from igneous rocks and a contact metamorphosed limestone from cratonic laurentia the exclusively reversed middle permian magnetization is hosted by low ti titanomagnetite and pyrrhotite and yields a paleomagnetic pole at 56 3 s 302 9 e a95 3 8 n 6 this pole which is unaffected by inclination shallowing suggests that a shallow inclination bias may indeed be present in the laurentian records to further consider this hypothesis we conduct a virtual geomagnetic pole distribution analysis comparing theoretical expectations of a statistical field model tk03 gad against published data sets this exercise provides independent evidence that the laurentian paleomagnetic data is widely biased likely because of sedimentary inclination shallowing we estimate the magnitude of this error from our model results and present and discuss several alternative corrections

paleomagnetism of the distal member of the new glasgow formation nova scotia canada new constraints on magnetic polarity stratigraphy near the base of the kiaman superchron abstract the ca 315 260 ma kiaman reversed permo carboniferous magnetic superchron is an important time marker that can be used for correlation of stratigraphic sequences from a local to a global scale earlier workers from a paleomagnetic study of the joggins stratigraphic section of the western cumberland basin of nova scotia demonstrated that the base of the superchron lies above redbeds of the lowermost portion of the late namurian westphalian a boss point formation although a detailed sequence of reversals was observed below this point no normal magnetic polarity zones were recognized above it in our study samples were collected from redbeds of the distal member of the westphalian a new glasgow formation of the eastern cumberland basin which directly overlie the gray sandstones of the boss point formation most sampling sites carry a normal polarity magnetization probably acquired at about the time of deposition therefore the base of the kiaman reversed superchron lies within or above th

specular ray parameter extraction and stationary phase migration the kirchhoff type prestack depth migration operator is a diffraction stack of seismic reflection energies over seismic traces typically the diffraction stack is carried out over the full data aperture producing not only images of reflectors but also aliasing artifacts aliasing artifacts often break reflector continuity in images the stationary phase approximation to the migration operator shows that for image points on reflectors traces within the neighborhood of specular rays contribute most to the diffraction stack traces outside this vicinity introduce aliasing artifacts into the image especially in the case of coarse trace spacing and aperture truncation a new migration algorithm denoted as stationary phase migration is proposed to find the specular ray parameters and then to migrate the specular ray energies and reject nonspecular ray energies to yield images with less aliasing

diffraction imaging in depth high resolution imaging is of great value to an interpreter for instance to enable identification of small scale faults and to locate formation pinch out positions standard approaches to obtain high resolution information such as coherency analysis and structure oriented filters derive attributes from stacked migrated images since they are image driven these techniques are sensitive to artifacts due to an inadequate migration velocity in fact the attribute derivation is not based on the physics of wave propagation diffracted waves on the other hand have been recognized as physically reliable carriers of high or even super resolution structural information however high resolution information encoded in diffractions is generally lost during the conventional processing sequence indeed migration kernels in current migration algorithms are biased against diffractions we propose here methods for a diffraction based data oriented approach to image resolution we also demonstrate the different behaviour of diffractions compared to specular reflections and how this can be leveraged to assess characteristics of subsurface features in this way a rough surface such as a fault plane or unconformity may be distinguishable on a diffraction image and not on a traditional reflection image we outline some characteristic properties of diffractions and diffraction imaging and present two novel approaches to diffraction imaging in the depth domain the first technique is based on reflection focusing in the depth domain and subsequent filtering of reflections from prestack data the second technique modifies the migration kernel and consists of a reverse application of stationary phase migration to suppress contributions from specular reflections to the diffraction image both techniques are proposed as a complement to conventional full wave pre stack depth migration and both assume the existence of an accurate migration velocity

true amplitude angle domain common image gathers from one way wave equation migrations true amplitude wave equation migration provides a quality migrated image of the earth s interior in addition the amplitude of the output provides an estimate of the angular dependent reflection coefficient similar to the output of kirchhoff inversion recently true amplitude wave equation migration for common shot data has been proposed to generate amplitude reliable shot domain common image gathers in heterogeneous media we present a method to directly produce angle domain common image gathers from both common shot and shot receiver wave equation migration generating true amplitude shot domain common image gathers requires a deconvolution type imaging condition using the ratio of the upgoing and downgoing wavefield each downward projected to the image point producing true amplitude angle domain common image gathers requires instead the product of the upgoing wavefield and the complexconjugate of the downgoing wavefield in the imaging condition since multiplication is a more stable comput

a geomagnetic polarity timescale for the permian calibrated to stage boundaries the reverse polarity kiaman superchron has strong evidence for at least three or prob ably four normal magnetochrons during the early permian normal magnetochrons are during the early asselian base ci1r 1n at 297 94 0 33 ma late artinskian ci2n at 281 24 2 3 ma mid kungurian ci3n at 275 86 2 0 ma and roadian ci3r an at 269 54 1 6 ma the mixed polarity illawarra superchron begins in the early wordian at 266 66 0 76 ma the wordian capitanian interval is biased to normal polarity but the basal wuchiapingian begins the beginning of a significant reverse polarity magnetochron lp0r with an overlying mixed polarity interval through the later lopingian no significant magnetostratigraphic data gaps exist in the permian geomagnetic polarity record the early cisuralian magnetochrons are calibrated to a succession of fusulinid zones the later cisuralian and guadalupian to a conodont and fusulinid biostratigraphy and lopingian magnetochrons to conodont zonations age calibration of the magnetochrons is obtained through a bayesian approach using 35 radiometric dates and 95 confidence intervals on the ages and chron durations are obtained the dating control points are most numerous in the gzhelian asselian wordian and changhsingian intervals this significant advance should provide a framework for better correlation and dating of the marine and non marine permian

new time constraints on lithospheric scale oroclinal bending of the ibero armorican arc a palaeomagnetic study of earliest permian rocks from iberia abstract the palaeozoic variscan orogeny was a large scale collisional event that involved amalgamation of multiple continents and microcontinents previous palaeomagnetic and structural analyses of the western variscan orogen notably the ibero armorican arc suggest that this region underwent oroclinal bending of an originally near linear orogen during the latest stages of variscan deformation in the late palaeozoic these analyses necessitate a two stage tectonic history with east west compression forming a linear belt in the carboniferous followed by a change in regional compression directions resulting in crustal block rotation and formation of the present day arc this study presents new palaeomagnetic analyses of early permian samples from the sotres and cabranes formations 41 3 n 222 5 w 95 13 1 in the northern inner limb and the viar basin 51 8 n 199 2 w 95 6 7 in the southern outer limb of the arc both locations yield expected early permian palaeomagnetic pole positions for stable iberia implying that measured magnetizations have undergone no significant vertical axis rotation since acquisition and thus were acquired subsequent to oroclinal bending this new result places a time constraint of about 10 ma for oroclinal bending of the ibero armorican arc which agrees well with recent geodynamical models that relate oroclinal bending to lithospheric delamination in this region

paleogeographical significance of the rot anisian triassic facies marines clays muds and marls fm in the iberian ranges eastern spain abstract the marines clays muds and marls formation consists of fine grained sediments recording the transition from distal fluvial facies to shallow marine sediments representing the onset of the first marine transgression of the tethys sea in the iberian basin muds show irregular parallel lamination of possible cryptalgal origin wave ripples linsen bedding mud cracks vertical burrows and halite pseudomorphs and contain anisian palynomorphs the carbonate content increases towards the se the deposition of the marines formation took place in a rift the iberian basin during a period of distensive tectonics and probably during a marine transgression of eustatic origin but the relative importance of the tectonic and eustatic factor is a matter of speculation in the area up to now

frequency selective design of the kirchhoff migration operator1 integral migration techniques perform a sum over an aperture of input traces to obtain output at a single point the length of the aperture is limited by a spatial nyquist criterion which typically prohibits imaging very steep dips at very high frequencies without generating severe migration artifacts migration operator aliasing for time domain kirchhoff migration this can be a fatal shortcoming the standard way to address this problem is to interpolate traces spatially before migration this reduces the trace spacing thereby increasing the frequency content which can be migrated without aliasing at steep dips an alternative remedy to the operator aliasing problem is to modify the phase response of the kirchhoff migration operator this operator is frequency selective across the migration aperture it passes all temporal frequencies of the input traces in the innermost portion of the aperture referring to the shallow dips and gradually cuts out the higher frequencies as it approaches the outer portion of the aperture thus while all frequencies of the input data contribute to the shallow dip portion of the migrated image only the permissible low frequencies of the input data contribute to imaging the steepest dips using a simple realization of a frequency selective kirchhoff migration operator this technique is illustrated on a synthetic data set involving greater than vertical dips

magnetic polarity stratigraphy and carboniferous paleopole positions from the joggins section cumberland structural basin nova scotia one hundred seventy seven samples were taken in stratigraphic sequence in redbeds from approximately 2100 m of namurian westphalian strata from the shepody enrage boss point and lower joggins formations between minudie and joggins nova scotia for the purpose of constructing a magnetic polarity stratigraphy in addition five samples from each of four sites were taken from north dipping strata of the cumberland group for the purpose of conducting a fold test for the joggins formation this yields a total coverage of 412 samples from approximately 2400 m of south dipping strata in the composite section when combined with previous results from the maringouin peninsula divenere and opdyke 1990 and 88 samples from north dipping strata collected for the purpose of conducting fold tests two components of magnetization are identified in these sediments a prefolding component termed c and a synfolding component termed b the present results extend the mid carboniferous magnetic polarity stratigraphy to include eight normal and eight reversed magnetozones in the namurian a through early westphalian a interval the results are dominantly to completely reversed in samples from the remainder of the westphalian a and the westphalian b but because of the complication of varying degrees of remagnetization and an 800 m sampling gap it is not possible to verify the base of the permo carboniferous reversed superchron in this time period northward plate motion is inferred from an observed shallowing of inclinations upsection a 5 7 cm yr average poleward drift rate is calculated for this time period from these results yielding a low latitude southern hemisphere paleogeographic position