tomographic imaging outside a seismic network application to the northeast japan arc the conventional local tomography can determine the 3d seismic velocity structure right beneath a seismic network but it cannot determine the 3d structure outside a seismic network in this study we show that such a limitation of tomography can be overcome if many earthquakes occur outside a seismic network in the northeast japan arc earthquakes occur actively from the japan trench to the pacific coast we detected and used sp depth phase to relocate the suboceanic earthquakes accurately and then used p and s wave arrival times from the relocated suboceanic events and the earthquakes under the northeast japan land area to determine the 3d p and s wave velocity and poisson s ratio structures of the entire northeast japan arc from the japan trench to the japan sea coast our results exhibit strong lateral heterogeneities under the forearc region the mainshock hypocenters of large interplate earthquakes m 7 0 8 2 mainly cluster near the boundaries of high and low velocity and poisson s ratio above the subducting pacific slab a few large earthquakes are located in areas with high velocity and low poisson s ratio these results suggest that lateral heterogeneities on the slab boundary can affect the rupture nucleation of large thrust earthquakes and the degree of interplate seismic coupling

paleomagnetic evidence for block rotations in central hokkaido south sakhalin northeast asia abstract the eocene to lower miocene strata in the bykov region of south sakhalin island far east russia show a mean paleomagnetic direction of dec 28 7 inc 55 7 95 6 7 and n 22 and a paleomagnetic pole at 66 3 n 245 7 e and a95 8 8 which shows that south sakhalin rotated 25 15 clockwise with respect to northeast asia since the early miocene this pole agrees with that of the eocene to middle miocene sedimentary rocks in central hokkaido japan it suggests that both south sakhalin and central hokkaido have rotated clockwise with respect to northeast asia since the early miocene these clockwise rotations can be interpreted as a vertical axis rotation of the blocks distributed in the north south direction more than 1000 km along the dextral hokkaido sakhalin shear zone considering the development of an en echelon structure of the basins in the shear zone we recognized five blocks each of which had rotated since the early miocene we conclude that this dextral shear is responsible not only for these block rotations but also for the opening of the kuril basin and the japan sea and that the shear motion was caused by oblique convergence between the eurasian and the okhotsk plates since the early miocene

morphology of the distorted subducted pacific slab beneath the hokkaido corner japan abstract the intersection of the japan and kurile arcs is expressed as a cuspate feature at the trench a bend in the japanese islands and a complex lithospheric structure and is known as the hokkaido corner the pacific plate is subducting beneath the two arcs in the northwest pacific at different velocities which has resulted in an arc arc collision and distortion of the subducting oceanic lithosphere using p and s wave tomographic images and seismicity the distorted shape of the subducted pacific plate beneath the hokkaido corner can be interpreted in three dimensions the pacific plate is imaged as continuous along the japan kurile arc with dip angle increasing from south to north but at the arc arc junction the geometry is complex and appears crumpled beneath the hokkaido corner there are two features in the tomography that are clearly imaged a region of low velocity at approximately 50 150 km depth between 142 5 145 e and 41 43 n and a distorted buckled lower slab boundary these two unusual characteristics in the slab morphology are likely to be related to deformation of the subducted pacific plate at the arc arc junction

cement stratigraphy of pennsylvanian holder formation sacramento mountains new mexico cyclic strata of the holder formation virgilian new mexico were deposited across a pennsylvanian shelf to basin transition during a time when sea level fluctuated over tens of meters cement stratigraphy studies indicate abundant calcite precipitation from low temperature fresh water within shelf shelf crest and shelf edge marine limestones freshwater cementation occurred during 15 periods of intraformational subaerial exposure these early cements are least abundant in basin and lagoon limestones the distribution of the early cement zones suggests that cementation was controlled by paleotopography stratigraphic position below subaerial exposure surfaces lithology and configuration of the paleoaquifer system distribution of early calcite cements provides new data for interpretation of cycles diagenetic systems and porosity evolution in petroleum reservoirs trace element analyses support a low temperature freshwater origin for the early cements cement stratigraphy studies fluid inclusion analyses and trace element analyses indicate a later cement that occluded remaining limestone porosity precipitated from a sodium and calcium rich brine at a temperature of about 100 c stratigraphic reconstruction dates this cementation as cretaceous or later fluorescent oil filled fluid inclusions were trapped along fractures in the late cement indicating oil migration during or after late stage cementation

p and s wave tomography and anisotropy in northwest pacific and east asia constraints on stagnant slab and intraplate volcanism we determined three dimensional p and s wave velocities and p wave azimuthal anisotropic tomography of the northwest pacific subduction zones by inverting 1 225 086 p wave and 335 117 s wave arrival times from 13 413 earthquakes our results show some differences between p and s wave images for the stagnant pacific slab in the mantle transition zone mtz beneath northeast china the stagnant slab looks thicker in the p wave image than that in the s wave image which may reflects the effects of both hydration and lower temperature in the mtz though differences in the resolution of p and s wave tomography may also have some effects the changbai intraplate volcanism is caused by hot and wet upwelling in the big mantle wedge above the stagnant pacific slab our p wave anisotropy tomography shows that the fast velocity direction fvd in the subducting philippine sea plate beneath the ryukyu arc is ne sw trench parallel which is consistent with the spreading direction of the west philippine basin during its initial opening stage suggesting that it may reflect the fossil anisotropy a striking variation of the fvd with depth is revealed in the subducting pacific slab beneath the northeast japan arc which may be caused by slab dehydration that changed elastic properties of the slab with depth the fvd in the mantle wedge beneath the northeast japan and ryukyu arcs is trench normal which reflects subduction induced convection beneath the kuril and izu bonin arcs where oblique subduction occurs the fvd in the mantle wedge is nearly normal to the moving direction of the downgoing pacific plate suggesting that the oblique subduction together with the complex slab morphology have disturbed the mantle flow

paleosols capping regressive carbonate cycles in the pennsylvanian black prince limestone arizona abstract the lower pennsylvanian morrowan to early derryan black prince limestone exposed in southeastern arizona consists of shallowing upward regressive carbonate cycles that accumulated on a shallow shelf platform a typical complete cycle from the base upward consists of the following fades mixed skeletal mudstones to grainstones subtidal shelf open circulation mixed skeletal to nonskeletal packstones and grainstones restricted shelf lagoon nonskeletal fenestral mudstones to grainstones intertidal nonskeletal cryptalgally laminated brecciated mudstones to wackestones supratidal and paleosol horizons terrestrial two paleosol types occur calcrete and terra rossa calcrete occurs as thin 5 10 cm profiles consisting of laminar micrite coated grains aggregate grains and vadose diagenetic features terra rossa paleosols consist of subspherical nodules derived from pedogenic alteration of parent limestones separated by a reddish insoluble accumulation ofclays iron oxides calcite skeletal debris and quartz silt the terra rossa paleosols occur as in situ preserved c horizons and as reworked soil residuum the first occurrence is marked by parent limestone in completely brecciated into nodules whereas reworked paleosols consist of nodules enveloped in red matrix both calcrete and terra rossa paleosols record subaerial exposure although the terra rossa paleosols suggest that signi icant amounts of limestone were removed during pedogenesis the terra rossa paleosols also favor an extrinsic versus anintrinsic mechanism for the origin of the cycles

p wave anisotropic tomography of the crust and upper mantle under hokkaido japan abstract we determined a 3 d anisotropic velocity structure beneath hokkaido in northern japan using a large number of first p wave arrival times the travel time inversion is parameterized with an isotropic component and two anisotropic parameters for each grid node by assuming p wave azimuthal anisotropy with hexagonal symmetry axis distributed horizontally the geometries of the conrad and moho discontinuities and the upper boundary of the subducting pacific plate are taken into account in the model our results show that low velocity zones exist beneath active arc volcanoes in the crust and in the central portion of mantle wedge above the high velocity pacific slab which are similar to the previous tomographic images p wave anisotropy is revealed in the crust mantle wedge and the subducting pacific slab in the upper crust the anisotropy is possibly caused by microcracks and cracks in the lower crust the anisotropic structure is different from that in the upper crust and it may be affected considerably by the plastic flow deformation in the mantle wedge the fast velocity direction fvd is generally trench normal in most of the study area while it becomes trench parallel in the pacific coast areas close to the trench which agrees with the shear wave splitting results beneath the volcanic front the fvd is also trench parallel which may suggest the existence of complex 3 d mantle flow in the mantle wedge the fvd in the subducting pacific slab is nearly north south which likely keeps the original fossil anisotropy of the pacific plate formed at the mid ocean ridge or is affected by the olivine fabric transition from a type to b type fabric due to the changes in water content stress and temperature

mantle wedge flow pattern and thermal structure in northeast japan effects of oblique subduction and 3 d slab geometry abstract we develop a 3 d thermal model for the northeast japan subduction margin using a realistic slab geometry for the subducting pacific plate and investigate the effects of oblique subduction and 3 d slab geometry on the mantle wedge flow pattern and the thermal structure in the tohoku region the mantle wedge flow pattern is nearly two dimensional resulting in a thermal structure similar to those obtained by a 2 d model owing to the simple slab geometry and subduction nearly perpendicular to the margin however in hokkaido oblique subduction leads to 3 d mantle wedge flow with northerly inflow and west northwestward outflow and also results in lower temperatures in the shallow part of the mantle wedge than in tohoku due to lower sinking rate of the slab between hokkaido and tohoku the slab has a hinge like shape due to a relatively sharp change in the dip direction in this hinge zone northerly mantle inflow from hokkaido and westerly mantle inflow from tohoku converge discouraging inflow from northwest and resulting in a cooler mantle wedge the model predicted mantle wedge flow patterns are consistent with observed seismic anisotropy and may explain the orientations of volcanic cross chains the predicted 3 d thermal structure correlates well with the along arc variations in the location of the frontal arc volcanoes and help to provide new insights into the surface heat flow pattern and the down dip extent of interplate earthquakes

carbonate filled channel complexes on carbonate ramps an example from the peerless park member keokuk limestone visean lower carboniferous mississippian st louis mo usa abstract the peerless park member keokuk limestone lower carboniferous visean mississippian exposed in the st louis mo area includes a carbonate filled channel complex with lithology and faunal elements distinct from under and overlying strata the complex is confined within a channel of 100 m apparent width that is under and overlain by cherty glauconitic crinoid bryozoan skeletal wackestone packstone and grainstone with abundant hardgrounds and little evidence for wave or current energy laterally the valley includes two subchannels separated by a subtle high the deeper subchannel truncates up to 5 m of strata the maximum thickness of the channel fill and associated deposits is 6 m the channel fill includes a matrix supported conglomerate locally at its base non cherty quartz silty foraminifer peloid crinoid bryozoan skeletal grainstone with spectacular lateral accretion foresets up to 5 m thick and cherty skeletal packstone a capping foraminifer skeletal grainstone is erosionally overlain by a 10 cm thick quartz siltstone that grades up into glauconitic crinoid bryozoan skeletal wackestone and packstone on the channel flanks correlative strata of the peerless park member are less than 1 m thick and include a lower non cherty crinoid foraminiferal skeletal grainstone a middle cherty packstone and an upper skeletal grainstone the upper grainstone is in turn erosionally overlain by the thin quartz siltstone that abruptly grades into the crinoid bryozoan skeletal wackestone and packstone of the upper part of the keokuk limestone the strata of the peerless park member are interpreted to be the result of a relative fall of sea level that places shallow water high energy inner ramp grainstone immediately above deeper water outer ramp packstone and grainstone there is no evidence for gradual downward or basinward migration of facies belts instead shallow water facies appear to have abruptly jumped downdip likewise no field or petrographic evidence for subaerial exposure has been recognized so the relative fall in sea level may not have subaerially exposed the area this occurrence of an isolated downdip carbonate grainstone filled channel complex not accompanied by progradational forced regressive deposits appears to be unique in carbonate ramp depositional systems and the channel includes fill with character different from many previously documented ramp carbonate filled channels

the potential failure of monte nuovo at ischia island southern italy numerical assessment of a likely induced tsunami and its effects on a densely inhabited area ischia is the emergent top of a large volcanic complex that rises more than 1 000 m above the sea floor at the north western end of the gulf of naples caldera resurgence in the central part of the island has resulted in the formation of differentially displaced blocks among which mt epomeo 787 m a s l is the most uplifted deformation and slope instability have been recognised as common features induced by a block resurgence mechanism that causes uplift and favours gravitational loading and flank failure the monte nuovo block a topographic high on the north western flank of mt epomeo has recently been interpreted as a block affected by deep seated gravitational slope deformation this block may undergo a catastrophic failure in the case of renewal of magmatic activity this paper investigates the potential failure of the monte nuovo block as a rockslide debris avalanche the consequent tsunami generation and wave propagation and discusses the catastrophic effects of such an event mobilization prone volume has been estimated at about 160 106 m3 and would move from a maximum elevation of 400 m a s l the landslide itself would sweep away a densely populated territory as large as 3 5 km2 the highest waves generated by the tsunami on which this paper is mainly focussed would hit the northern and western shores of ischia however the high coast would prevent inundation and limit devastation to beaches harbours and surrounding areas most of the tsunami energy would head towards the north east hitting the campania coast severe inundation would affect an area of up to 20 km2 around the mouth of the volturno river including the urban area of castel volturno in contrast less energy would travel towards the south and the gulf of naples would be perturbed by long persisting waves of limited damaging potential

the carbonate flysch transition late maastrichtian late palaeocene in the arachova sequence of the parnassus ghiona zone central greece the transition from the carbonate to the flysch facies in the arachova sequence of the parnassus ghiona zone is represented by argillaceous limestone beds with flaser structures deposited during latest maastrichtian palaeocene time in a pelagic carbonate environment with a periodic clastic influx deposition was continuous except for a short interruption during the k t boundary interval and the earliest palaeocene when the area was subaerially exposed this interruption gave rise to the development of a brecciated carbonate horizon through soil forming processes the mineralogical composition of the clastic influx i e quartz feldspars clay minerals amorphous iron oxides amorphous phosphatic compounds in particular the clay mineral assemblages i e illite chlorite irregularly interstratified illite vermiculite shows that the clastic supply represents erosional material that originated from a tectonically active continental setting of both carbonate and clastic rocks presumably the pelagonian zone as for the flysch of the beotian and sub pelagonian zones the arrival of the first clastic material in the arachova area as early as latest maastrichtian time its pelagonian origin and the persistence of pelagic conditions of sedimentation throughout the palaeocene indicate that the arachova area was situated along the northeastern margin of the parnassus platform and that it subsided into the beotian basin while the central areas of the platform remained tectonically stable during middle palaeocene times and there was an extensive development of stromatolites the northeastern marginal areas transitional to the beotian basin continued to subside allowing pelagic carbonate sedimentation with periods of clastic influx the total collapse of the platform in the late palaeocene gave rise to the deposition of the flysch over the entire zone

effect of water and stress on the lattice preferred orientation of olivine the influence of water and stress on the lattice preferred orientation lpo of olivine aggregates was investigated through large strain shear deformation experiments at high pressures and temperatures p 0 5 2 1 gpa t 1470 1570 k under both waterpoor and water rich conditions the specimens are hot pressed synthetic olivine aggregates or single crystals of olivine water was supplied to the sample by decomposition of a mixture of talc and brucite deformation experiments were conducted up to shear strain 6 using the griggs apparatus where water fugacity was up to 13 gpa at the pressure of 2 gpa the water content in olivine saturated with water increases with increasing pressure and the solubility of water in olivine at p 0 5 2 gpa was 400 1200 ppm h si several new types of lpo in olivine are found depending on water content and stress samples deformed in waterpoor conditions show a conventional lpo of olivine where the olivine 100 axis is subparallel to the shear direction the 010 plane subparallel to the shear plane type a however we identified three new types type b c and e of lpo of olivine depending on the water content and stress the type b lpo of olivine which was found at relatively high stress and or under moderate to high water content conditions is characterized by the olivine 001 axis subparallel to the shear direction the 010 plane subparallel to the shear plane the type c lpo which was found at low stress and under water rich conditions is characterized by the olivine 001 axis subparallel to the shear direction the 100 plane subparallel to the shear plane the type e lpo which was found under low stress and moderate water content is characterized by the olivine 100 axis subparallel to the shear direction the 001 plane subparallel to the shear plane observations by transmission electron microscopy tem and scanning electron microscopy sem show that the dislocations in water poor samples type a are curved and both b 100 and b 001 dislocations have a similar population numerous subgrains are seen in water poor samples in backscattered electron images in contrast water rich samples both type b and type c contain mostly b 001 dislocations and dislocations are straight and sub grain boundaries are rare compared to those in water poor samples these observations suggest that 1 dominant slip systems in olivine change with water fugacity and stress and 2 grain boundary migration is enhanced in the presence of water seismic anisotropy corresponding to the fabrics under water rich condition is significantly different from that under water poor condition consequently the relationship between seismic anisotropy and flow geometry in water rich regions is expected to be

pedogenic modification and structure evolution in palustrine facies as exemplified by the bembridge limestone late eocene of the isle of wight southern england abstract this paper considers the development and evolution of pedogenic structures within palustrine facies and their relationship with those of calcretes as exemplified by the bembridge limestone bl formation upper eocene of the isle of wight within this formation primary lacustrine facies mainly biomicrites have been modified by pedogenesis to varying degrees whilst such changes developed as part of an evolving continuum three structures are recognised to represent evolving stages in this process brecciated nodular clotted peloidal and peloidal ooidal structures a fourth structure laminar is sometimes intercalated with the other three and in places is seen to replace them they are particularly developed in the western outcrops of the formation which represent the palustrine fringes of the main lacustrine bodies the structures are thought to represent the progressive differentiation of the peloidal and ooidal elements from the original lacustrine sediment and appear to be a response to alternations of wetting and drying of the soil under fluctuating climatic conditions the vermiform fabric of the laminar structure is attributed to calcified root mats the general depletion in the heavy o and c isotopes of palustrine facies with respect to the original lacustrine ones is interpreted as being the result of repeated dissolution reprecipitation processes occurring during soil development the palustrine facies of the bl correlates well with an intermediate condition between semi arid and subhumid climates with extensive biological soil modification of freshwater carbonates

the signal and the noise forward modeling of allocyclic and autocyclic processes influencing peritidal carbonate stacking patterns recent carbonate sequence stratigraphic models suggest that the degree of order present in successions of carbonate parasequences is determined by temporal variations in eustatic amplitude and by varying levels of autocyclicity ordered parasequence stacking is suggested to occur during greenhouse periods dominated by low amplitude eustatic oscillations conversely disordered vertical successions are said to occur when amplitudes of eustatic oscillations are high or when autocyclic processes dominate and thus drown the periodic external signal these assertions of causal mechanism are tested here by application of a three dimensional stratigraphic forward model the three dimensional model generates parasequences via a ginsburg type mechanism of sediment transport and shoreline progradation parasequence stacking is controlled by a superimposed longer term eustatic oscillation and parasequences generated are analyzed using runs analysis and durbin watson autocorrelation results from the modeling suggest that autocyclic parasequences generated by shoreline progradation form ordered vertical successions when accommodation changes driven by a low amplitude relative sea level oscillation suggesting that partly autocyclic strata may not be inherently any less ordered than entirely allocyclic strata addition of stochastic processes such as mosaic carbonate production and fluctuations in regional sediment transport direction tend to decrease the level of measurable order present in the autocyclic strata increasing the frequency and amplitude of relative sea level oscillations also tends to decrease the measurable order in stacked autocyclic peritidal parasequence thicknesses these results suggest that controls on parasequence stacking patterns are likely to be more complex and varied than suggested by recent sequence stratigraphic models more outcrop and modeling investigation is required with appropriately circumspect interpretations applied

existence of interplane earthquakes and neutral stress boundary between the upper and lower planes of the double seismic zone beneath tohoku and hokkaido northeastern japan abstract using data from the recently constructed nationwide dense seismic network we determined the hypocenters and focal mechanisms of many intermediate depth intraslab earthquakes within the pacific slab beneath northeastern japan the results show that in addition to the upper and lower planes of the double seismic zone a considerable number of intraslab earthquakes also occur between the two planes this interplane earthquake activity is not homogeneously distributed in space being high beneath eastern hokkaido and the fore arc regions of southeast and central tohoku the focal mechanisms of the interplane earthquakes tend to be of the down dip compressional type dc in tohoku and the hokkaido corner but down dip tensional type de in eastern hokkaido upper plane earthquakes are characterized by dc type stress while lower plane earthquakes are de type in both tohoku and eastern hokkaido the existence of interplane earthquakes enables estimation of the position of the neutral plane between the upper plane dc stress and the lower plane de stress we did so by applying stress tensor inversions to focal mechanism data obtained in the present study and japan meteorological agency jma data the results show that the neutral plane is located about 22 km beneath the upper plate interface beneath tohoku but only about 10 km beneath the upper surface beneath eastern hokkaido this difference in the location of the neutral plane may be due to the difference in buoyancy force exerted by the less dense metastable olivine wedge that is a result of the oblique plate subduction beneath hokkaido comparison of large intraslab earthquakes beneath the two regions shows that their aftershock areas are limited by the neutral plane suggesting that large earthquake ruptures are confined to either the dc or de stress field and do not go beyond the neutral plane

sequence stratigraphy and cyclicity in the middle eocene of the fayoum ranges western desert egypt implications for regional sea level changes abstract the middle eocene deposits in the fayoum ranges are composed of complex alternative clastic claystone and sandstone and carbonate limestone and dolostone facies and dominated carbonate limestone facies facies are arranged mainly in regression and shallowing upward emergence cycles and sequences field stratigraphic and microfacies analysis of the study area permits recognition of four major sequences reflecting 3rd order cycles depositional sequences and cycles are bounded by subaerial erosive surfaces or caliche deposits ferruginous crust and by their correlative conformities sequence 1 consists of two shallowing upward cycles dominate carbonate facies each of which starts with nummulitic wackestone capped with nummulitic packstone including globigerinatheka subconglobata subconglobata biozone these cycles were deposited under tropical to subtropical conditions as evidenced by the carbonate nature of the rocks and the abundance of nummulites which need warm conditions for their flourishing sequence 2 consists of four emergence cycles based with claystone and capped with wackestone including morozovella lehneri biozone the duration ma of sequence 2 morozovella lehneri zone is 3 05 ma 44 25 ma for the upper of ta3 3 3 to 41 2 ma for the lower of ta3 3 5 sequence 3 includes three rock units includes trucorotaloides rohri biozone the lower unit involves lowstand systems tract the middle unit contains transgressive systems tract and the upper rock unit includes highstand systems tract the lowstand systems tract consists of emergence cycles of mixed clastic carbonate facies clays at the base and capped with wackestone and packstone facies the transgressive systems tract consists of dominant carbonate facies wackestone at the base and capped with packstone facies sequence 4 involves transgressive systems tract the duration of both sequence 3 and sequence 4 has been estimated as 1 8 ma

melting and seismic structure beneath the northeast japan arc transportation of h2o associated with subduction of the pacific plate beneath the northeast japan arc is modeled to predict distribution of aqueous solution and melt and the consequent p wave velocity structure the observed velocity structure coincides well with the model for equilibrium transport of h2o most of h2o subducted is brought down to 150 200 km depth along the slab then the aqueous fluid generated ascends to initiate melting which explains the low velocity regions 6 reduction observed beneath the backarc rather than beneath the volcanic front if equilibrium transport of h2o occurs initiation of melting beneath the backarc with deep subduction of h2o is likely to be the case also for other subduction zones with slabs older than several tens of m y cold enough to stabilize serpentine to a great depth

detailed seismic attenuation structure beneath hokkaido northeastern japan arc arc collision process arc magmatism and seismotectonics in this study we imaged a detailed seismic attenuation structure frequency independent q 1 beneath hokkaido japan by merging waveform data from a dense permanent seismic network with those from a very dense temporary network corner frequency of each event used for t estimation was determined by the s coda wave spectral ratio method the seismic attenuation qp 1 structure is clearly imaged at depths down to about 120 km for the fore arc side of hokkaido high qp zones are imaged at depths of 10 to 80 km in the crust and mantle wedge above the pacific slab low qp zones are clearly imaged in the mantle wedge beneath the back arc areas of eastern and southern hokkaido these low qp zones extending from deeper regions extend to the moho beneath volcanoes the locations of which are consistent with those of seismic low velocity regions these results suggest that the mantle wedge upwelling flow occurs beneath hokkaido except in the area where there is a gap in the volcano chain in contrast an inhomogeneous seismic attenuation structure is clearly imaged beneath the hokkaido corner a broad low qp zone is located at depths of 0 60 km to the west of the hidaka main thrust the location almost corresponds to that of the seismic low velocity zone in the collision zone the fault planes of the 1970 m6 7 and 1982 m7 1 earthquakes are located at the edges of this broad low qp zone observations in this study indicate that our findings contribute to understanding the detailed arc arc collision process magmatism and seismotectonics beneath hokkaido

paleomagnetic and petrographic evidence for early magnetizations in successive terra rosa paleosols lower pennsylvanian black prince limestone arizona an early synsedimentary chemical remanent magnetization crm is found in and below terra rosa paleosols which cap regressive carbonate cycles in the pennsylvanian morrowan black prince limestone in southeastern arizona authigenic hematite occurring in fractures between soil nodules in liesegang bands and replacing allochems is abundant in specific horizons and is related to soil forming processes paleomagnetic analysis of many specimens from the paleosol horizons reveals both northwesterly and shallow and southeasterly and shallow directions these unidirectional northwesterly and southeasterly magnetizations are interpreted to be antipodal equivalents and show a stratigraphic distribution with at least three reversals the mean direction declination 308 inclination 9 corresponds to a pole position at latitude 34 n longitude 143 e similar to other pre kiaman carboniferous poles some specimens also contain multicomponent magnetizations those with dual polarities or with curved thermal demagnetization trajectories and are interpreted to be the result of remagnetization after a reversal in the earth s field demagnetization and rock magnetic results for the reddened rocks confirm that hematite is the primary magnetic carrier in contrast to the paleosol zones the magnetization in the interbedded gray marine limestones resides in magnetite and does not exhibit stable decay terra rosa paleosols are likely to have preserved the hematite and associated magnetizations that formed as a result of soil forming processes these paleosols therefore may contain data that are useful in determining pole positions and validating polarity zonations

the magnitude symmetry and origin of upper mantle anisotropy based on fabric analyses of ultramafic tectonites summary seismic anisotropy within the upper mantle originates from the preferred orientation of highly anisotropic single crystals the symmetry and magnitude of anisotropy depend upon 1 the volume percentages of the minerals constituting the upper mantle 2 the degree and symmetry of preferred orientation of each mineral and 3 the alignment of the minerals crystallographic axes relative to one another the nature of upper mantle anisotropy can be examined by studying mineral orientations within ultramafic rocks which were once part of the mantle petrofabric data for olivine and pyroxene have been used to obtain velocity anisotropy patterns over large regions of ultramafic rocks from the samail ophiolite oman the troodos ophiolite cyprus the bay of islands ophiolife newfoundland the twin sisters ultramafic washington usa the dun mountain ophiolite new zealand the red hills ophiolite new zealand and the red mountain ophiolite new zealand the compressional wave anisotropy calculated for these massifs ranges from 3 to 8 per cent in excellent agreement with observed seismic anisotropy in the upper continental and oceanic mantle the symmetry varies from orthorhombic to axial with the axial symmetry axis corresponding to the olivine a axes maxima and subparallel to spreading directions in oceanic upper mantle pyroxene a b and c axes maxima generally parallel olivine b c and a axes respectively and anisotropy decreases with increasing pyroxene content shear wave splitting is predicted for all propagation directions within the upper mantle symmetry is also orthorhombic or axial with the minimum difference in velocity between the two shear waves parallel to the maximum compressional wave velocity

uplands lowlands and climate taphonomic megabiases and the apparent rise of a xeromorphic drought tolerant flora during the pennsylvanian permian transition abstract the late mississippian and pennsylvanian have been referred to as the coal age due to enormous paleotropical peat accumulations coal beds numerous fossil floras have been collected from these coals and their associated seat earth paleosols and roof shales over more than two centuries leading to the inference of vast swampy wetlands covering the pangean tropics during the pennsylvanian in contrast the permian tropics are characterized as more arid with sparser and more heterogeneous vegetation than inferred for the pennsylvanian in the tropics the pennsylvanian to permian transition has been described as a changeover from a pteridophyte dominated paleophytic flora to a seed plant dominated mesophytic flora this view notwithstanding floras dominated by xeromorphic seed plants also are well known from the pennsylvanian tropics some authors have characterized these plants as being occupants of uplands subsequently transported into basinal lowland preservational environments in this model uplands are well drained causing areas of drought under otherwise everwet climates in this paper we present an alternative interpretation that the apparent transition in pennsylvanian permian tropical vegetation reflects two types of taphonomic megabias first is a preservational megabias strongly favoring the vegetation of humid climates over that of seasonally dry climates accordingly tropical plant preservational potential fluctuated in concert with late paleozoic ice age glacial interglacial oscillations and contemporaneous sea level and climatic changes second is an analytical megabias strongly favoring the discovery and collection of the wetland biome from pennsylvanian strata overlooking the less frequently and more poorly preserved drought tolerant biome by permian times vast wetlands and their fossil record had largely disappeared from central pangea although continuing in cathaysia making drought tolerant vegetation more visible to searchers without changing its preservational circumstances we demonstrate that the upland model is untenable being inconsistent with the principles of plant biogeography and with geological aspects of the fossil record

tomographic imaging of the alaska subduction zone the alaska subduction zone is characterized by the pacific plate descending beneath the north american plate causing abundant seismic activity in the crust and along the wadati benioff zone down to a depth of approximately 200 km we have used 142 908 p wave arrival times from 12 237 shallow and intermediate depth earthquakes recorded by the alaska earthquake information center jointly run by the geophysical institute university of alaska fairbanks and u s geological survey in the period from january 1977 to november 1991 to investigate the three dimensional 3 d p wave velocity structure beneath central and southern alaska travel times and ray paths are accurately calculated by using an efficient 3 d ray tracing technique the nonlinear tomographic problem is solved by iteratively conducting linear inversions and the velocity structure and hypocentral locations are simultaneously determined we conducted two types of inversions one is an inversion with a laterally homogeneous starting model the others are what we call slab inversions in which we introduce into the initial model the high velocity subducting pacific plate as a priori information we found that the slab inversions gave a seismologically more plausible result and a final root mean square travel time residual significantly smaller than that of the inversion with the homogeneous starting model detailed p wave tomographic images are obtained for the crust and upper mantle down to a depth of 200 km with spatial resolutions of 30 60 km the tomographic image of the upper crust correlates well with the major surface geological features such as slow sedimentary basins and fast ultramafic bodies prominent low velocity anomalies exist in the crust and upper mantle beneath active volcanoes in the mantle wedge the low velocity anomalies dip toward the continental side and extend to a depth of about 150 km which are considered to be associated with the active volcanism in the alaska subduction zone the results suggest that the subducting pacific plate has a thickness of 45 55 km and a p wave velocity 3 6 higher than that of the surrounding mantle

upper and middle crustal deformation of an arc arc collision across hokkaido japan inferred from seismic refraction wide angle reflection experiments abstract the hidaka collision zone hcz central hokkaido japan is a good target for studies of crustal evolution and deformation processes associated with an arc arc collision the collision of the kuril arc ka with the northeast japan arc nja which started in the middle miocene is considered to be a controlling factor for the formation of the hidaka mountains the westward obduction of middle lower crustal rocks of the ka the hidaka metamorphic belt hmb and the development of the foreland fold and thrust belt on the nja side the hokkaido transect project undertaken from 1998 to 2000 was a multidisciplinary effort intended to reveal structural heterogeneity across this collision zone by integrated geophysical geological research including seismic refraction reflection surveys and earthquake observations an e w trending 227 km long refraction wide angle reflection profile found a complicated structural variation from the ka to the nja across the hcz in the east of the hcz the hinterland region is covered with 4 4 5 km thick highly undulated neogene sedimentary layers beneath which two eastward dipping reflectors were imaged in a depth range of 10 25 km probably representing the layer boundaries of the obducting middle lower crust of the ka the hmb crops out on the westward extension of these reflectors with relatively high vp 6 0 km s and vp vs 1 80 consistent with middle lower crustal rocks beneath these reflectors more flat and westward dipping reflector sequences are situated at the 25 27 km depth forming a wedge like geometry this distribution pattern indicates that the ka crust has been delaminated into more than two segments under our profile in the western part of the transect the structure of the fold and thrust belt is characterized by a very thick 5 8 km sedimentary package with a velocity of 2 5 4 8 km s this package exhibits one or two velocity reversals in paleogene sedimentary layers probably formed by imbrication associated with the collision process from the horizontal distribution of these velocity reversals and other geophysical geological data the rate of crustal shortening in this area is estimated to be greater than 3 4 mm year which corresponds to 40 50 of the total convergence rate between the nja and the eurasian plate this means that the fold and thrust belt west of the hcz is absorbing a large amount of crustal deformation associated with plate interaction across hokkaido island

mantle flow in subduction systems the mantle wedge flow field and implications for wedge processes 1 the mantle wedge above subducting slabs is associated with many important processes including the transport of melt and volatiles our understanding of mantle wedge dynamics is incomplete as the mantle flow field above subducting slabs remains poorly understood because seismic anisotropy is a consequence of deformation measurements of shear wave splitting can constrain the geometry of mantle flow in order to identify processes that make first order contributions to the pattern of wedge flow we have compiled a data set of local s splitting measurements from mantle wedges worldwide there is a large amount of variability in splitting parameters with average delay times ranging from 0 1 to 0 3 s up to 1 0 1 5 s and large variations in fast directions we tested for relationships between splitting parameters and a variety of parameters related to subduction processes we also explicitly tested the predictions made by 10 different models that have been proposed to explain splitting patterns in the mantle wedge we find that no simple model can explain all of the trends observed in the global data set mantle wedge flow is likely controlled by a combination of downdip motion of the slab trench migration ambient mantle flow small scale convection proximity to slab edges and slab morphology with the relative contributions of these in any given subduction system controlled by the subduction kinematics and mantle rheology there is also a likely contribution from b type olivine and or serpentinite fabric in many subduction zones governed by the local thermal structure and volatile distribution

new type of olivine fabric from deformation experiments at modest water content and low stress a new type of olivine fabric was found by high strain simple shear deformation experiments in the presence of trace amounts of water at 0 5 2 2 gpa and 1470 1570 k in this fabric called e type fabric the olivine 100 axis is subparallel to the shear direction and the 001 plane is parallel to the shear plane this geometry suggests that the 100 001 slip system makes the dominant contribution to total strain this fabric is dominant at a modest water content 200 coh 1000 h 10 6 si at low stresses and high temperatures some mylonites from peridotite massifs show this type of olivine fabric which suggests the presence of water during the shear localization the seismic anisotropy caused by this fabric is qualitatively similar to that by dry fabric a type but the magnitudes of anisotropy are different between the two types for horizontal flow the amplitude of vsh vsv anisotropy is weaker but the amplitude of shear wave splitting is stronger for the e type fabric than for the a type dry fabric seismic anisotropy in the oceanic upper mantle may be due to the olivine e type fabric

double seismic zone beneath the middle of hokkaido japan in the southwestern side of the kurile arc abstract the vertical section of microearthquakes determined accurately by using the hokkaido university network shows two dipping zones the double seismic zone 25 30 km apart in the depth range of 80 150 km beneath the middle of hokkaido in the southwestern side of the kurile arc hypocentral distribution of large earthquakes m b 4 based on the isc international seismological centre bulletin also shows the double seismic zone beneath the same region the hypocentral distribution indicates that the frequency of events occurring in the lower zone is four times greater than that in the upper zone the difference in seismic activity between the two zones beneath hokkaido is in contrast with the region beneath northeastern honshu in the northeastern japan arc composite focal mechanisms of microearthquakes and individual mechanisms of large events mainly characterize the down dip extension for the lower zone as is observed beneath northeastern honshu for the upper zone however the stress field is rather complex and not necessarily similar to that beneath northeastern honshu this may be considered to indicate the influence of slab contortion or transformation in the hokkaido corner between the kurile and the northeastern japan arcs

deformation fabrics of olivine in val malenco peridotite found in italy and implications for the seismic anisotropy in the upper mantle abstract an exhumed huge body of ultramafic rocks is preserved in val malenco italy in this study petrofabrics and deformation microstructures of olivine in the val malenco peridotite were examined and new observations of lattice preferred orientation lpo of olivine such as type b and type e lpo in the peridotite are reported three types depending on the grain size of olivine fabrics were observed type a fabric exhibiting the 010 100 slip system in the large relic grain area and type b and type e fabrics exhibiting the 010 001 and 001 100 slip systems respectively in the widely distributed recrystallized grain area the slips occurred mainly on 010 001 and the 001 100 slip system has only rarely been reported to be the dominant slip system of olivine found in natural rocks further seismic velocities and seismic anisotropies were calculated for the three types of fabrics found the seismic anisotropies in the upper mantle can be attributed to the type b type e or type a lpos of olivine moreover the anomaly in seismic low velocity in the mantle wedge can be attributed to the serpentinization as well as the mixed fabrics of the type a type b and type e

anisotropic pn tomography in the western united states pn travel times are affected not only by lateral variations in crust and mantle velocity but also by significant amounts of laterally varying anisotropy to investigate uppermost mantle anisotropy a tomography algorithm was reformulated to include lateral variations in both velocity and horizontal anisotropy and it was applied to pn travel time data from the western united states results show that anisotropy is as important in explaining the travel time residuals as are the velocity variations a detailed resolution study examined the trade off between the velocity variations and the anisotropy variations and showed that both could be resolved for regions with good ray path coverage pn anisotropy beneath the western united states has maximum amplitudes of 0 3 km s 7 5 when resolved on a length scales of around 3 the orientations of pn anisotropy often correlate well with those inferred from shear wave splitting results this correlation suggests that orientation of mantle anisotropy does not change significantly with depth for many regions the orientation of the pn anisotropy can be correlated with some of the tectonic processes which occur within the western united states for example the fast direction of pn anisotropy parallels the northeast direction of subduction of the juan de fuca plate beneath the northwest pacific coast suggesting that there the anisotropy is related to subduction driven deformation the fast direction of pn anisotropy also parallels the strike of the san andreas fault system in central california indicating that shear strains along the plate boundary may be responsible for the anisotropy there within the great basin the pn anisotropy varies substantially and both partial melting and small scale convection within the uppermost mantle could be responsible for these anisotropy variations

upper pennsylvanian permian naco group paleosols north central arizona field and isotopic evidence deposits of the upper naco group upper pennsylvanian permian north central arizona include features consistent with multiple episodes of soil formation the preserved paleosols are developed on shallowing upward regressive carbonate cycles that accumulated on the margins of a shallow shelf platform field evidence of paleosols consist of a monopodial taproot like and branching root and rootlet trace fossils b cylindrical carbonate nodules rhizoliths c subspherical carbonate nodules that occur as discrete entities in the paleosol and d an accumulation of red clay and quartz silt petrographic evidence consists of a plasmic fabrics analogous to those found in some modern soils cf brewer 1976 b microscopic carbonate nodule accumulations c soil nodule spar crystallaria and d alveolar septal structures paleosol profiles occur as a lithified in situ partly eroded clay rich horizons that commonly grade into unmodified parent material at depth below the disconformity and b reworked pedogenic carbonate nodule horizons oxygen and carbon stable isotope ratios of pedogenic carbonate are depleted relative to local marine carbonate this suggests that isotopically light soil co2 and meteoric water were present during pedogenic carbonate precipitation the depleted stable isotope ratios are consistent with an interpretation of soil carbonate precipitated under near surface conditions the presence of well developed calcareous rhizoliths and soil nodules in a red bed matrix and desiccation like crystallaria in host rhizoliths may qualitatively signify seasonally dry paleoclimatic conditions alteration of the underlying limestone units and development of multiple albeit truncated paleosols record a cyclical shift between marine and terrestrial paleoenvironmental conditions near the pennsylvanian permian boundary 280 m y ago

paleosols in shallow marine carbonate sequences abstract shallow water carbonate sequences in the geological record commonly exhibit numerous exposure surfaces reflecting emersion of sediment due to progradation processes and sealevel oscillations some ancient platform sequences contain hundreds of such surfaces associated with paleosols fossil soils typically calcretes a wide range of macro and microstructures are associated with these calcretes which are reviewed profile types and stages in profile development can be defined the nature of the exposure surface and associated paleosols can be used to identify the nature of the prevailing climate although hydromorphic effects related to marine flooding of the platforms can modify the paleosols a potentially important use of paleosols is to define the nature of sequence boundaries several studies have identified sets of paleosols with varying maturities reflecting changes in rates of accommodation space creation during sealevel rises and falls

deep structure of the japan subduction zone abstract we determined 3 d p wave velocity structure down to 700 km depth under the japan islands using a large number of arrival time data from local and teleseismic events simultaneously we collected 207 000 arrival times from 7743 shallow and deep earthquakes occurred in and around japan and 34 148 data from 333 teleseismic events which were recorded by over 1000 seismic stations on the japan islands our tomographic model revealed some new features the philippine sea slab is found to subduct down to 500 km depth under southwest japan though the seismicity within the slab ends at 150 200 km depth significant low velocity anomalies are found to exist in the deep portion of the mantle wedge above the pacific slab which may be caused by the deep dehydration process of the slab slow anomalies are detected in the mantle beneath the pacific slab which may be caused by a mantle plume or upwelling of hot mantle materials associated with the deep subduction of the pacific slab and its collapsing down to the lower mantle

shear wave splitting beneath the southwestern kurile arc and northeastern japan arc a new insight into mantle return flow 1 shear wave splitting in the southwestern part of the kurile arc and the northeastern ne japan arc is investigated using the waveforms from local earthquakes for both arcs observed shear wave splitting shows clear evidence for a striking rotation of fast direction across the arc suggesting the different feature of anisotropy between the fore arc and back arc sides trench parallel fast directions are observed in the fore arc side which is consistent with the anisotropy expected from the deformation of the b type olivine fabric as well as the anisotropy in the slab fast directions observed in the back arc side show approximately e w and ese wnw in the ne japan arc and n s in the southwestern kurile arc which are characterized by the local maximum dip direction of the subducted pacific plate not by the direction of plate convergence this relationship suggests that the direction of the mantle return flow is governed by the local slab geometry