shear wave polarization anisotropy in the mantle wedge above the subducting pacific plate abstract research of azimuthal anisotropy in the mantle wedge above subduction zones opens up a new source of information about rising magma in the region because the physical property estimated from shear wave anisotropy is related to dynamic processes inside the earth regional variation in shear wave polarization is investigated from a teleseismic event and some local deep earthquakes using a spatially dense seismic array of the nied located in the central part of japan a characteristic pattern is found on the spatial distribution of shear wave polarization data obtained from scs waves large and small values of shear wave polarization anisotropy are observed at seismic stations located to the west and east of the volcanic front respectively the anisotropic zone with maximum velocity in n s direction is localized in the wedge portion between the surface and subducting slab using the data of the local deep events the location of the anisotropic zone corresponds with a low q zone obtained from seismic tomography data we conclude that the azimuthal anisotropic zone in the mantle wedge is caused by melt filled cracks which is consistent with models obtained by petrological studies

first report of wiwaxia from the cambrian chengjiang lagerstatte research was supported by the chinese academy of sciences kzzd ew 02 2 the national basic research program of china 2013cb835006 the national natural science foundation of china 41472012 the natural science foundation of jiangsu province bk2012893 and clare college cambridge

shear wave splitting and subcontinental mantle deformation splitting observations are interpreted in terms of the strain induced lattice preferred orientation of mantle minerals especially olivine we consider three hypotheses concerning the origin of the continental anlsotropy 1 strain associated with absolute plate motion as in the oceanic upper mantle 2 crustal stress and 3 the past and present internal deformation of the subcontinental upper mantle by tectonic episodes it is found that the last hypothesis is the most successful namely that the most recent significant episode of internal deformation appears to be the best predictor of q for stable continental regions this is interpreted as fossil anisotropy whereas for presently active regions such as alaska the anisotropy reflects present day tectonic activity in the stable portion of north america there is a good correlation between delay time and lithospheric thickness this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant the acceptance of this hypothesis has several implications for subcontinental mantle deformation first it argues for coherent deformation of the continental lithosphere crust and mantle during orogenies this implies that the anisotropic portion of the lithosphere was present since the deformational episode and rules out the addition of undeformed material to this layer by subsequent underplating or conductive growth of the thermal boundary layer one of the most important issues in the study of orogenies is the need to reconcile the formation of thickened lithosphere with the paradoxically high mantle temperatures often associated with orogenic episodes most efforts to date have focussed on modes of deformation whereby the cold lithospheric mantle is removed by convective instability or delamination and replaced by warm asthenosphere these models however are incompatible with the evidence for preserved coherent lithospheric deformation rather the deformed mantle appears to have been heated in place we suggest that the elevated mantle temperatures may be due to the strain heating accompanying the deformation

laboratory and seismological observations of lower mantle isotropy we have carried out seismological and mineral physics investigations to identify the extent and origin of elastic anisotropy in the lower mantle based on observations of shear wave splitting we conclude that the lower mantle is effectively isotropic this result is surprising since the lower mantle is composed of elastically anisotropic minerals silicate perovskite mgo sio 2 that have been extensively strained by geologic processes to reconcile the seismic observations we have measured texture development during deformation and high temperature recrystallization of mantle silicates we show that these experiments provide a direct explanation for the shear wave splitting measurements the lower mantle appears isotropic because silicate perovskite maintains an isotropic texture during deformation and recrystallization

sks splitting and the seismic anisotropy of the mantle beneath the hikurangi subduction zone new zealand abstract the analysis of 12 sks phases recorded on broadband stations above the hikurangi subduction zone in new zealand shows clear evidence of mantle anisotropy with the fast direction 28 5 almost parallel to the strike of subduction and the dominant geology of the region the slow shear wave delay times show a systematic change with the azimuth of the arrivals which if hexagonal symmetry is assumed indicates that either the axis of symmetry of the anisotropic volume beneath the subduction zone is not horizontal or that more than one anisotropic layer is present the magnitude of the delays 1 5 0 4s suggests that the anisotropy is most probably confined to the top 300 km of the mantle

new wiwaxia material from the tsinghsutung formation cambrian series 2 of eastern guizhou china wiwaxia is an extinct early metazoan with uncertain affinities which is well represented in strata of cambrian series 2 3 age well preserved representatives of wiwaxia are known from the burgess shale biota and the kaili biota here new material of wiwaxia corrugata matthew 1899 is reported from the upper part of the tsinghsutung formation cambrian series 2 near balang village guizhou province china these specimens have a close evolutionary relationship to wiwaxia taijiangensis zhao qian lee 1994 from the overlying kaili formation new wiwaxia material from the tsinghsutung formation and observations of specimens with articulated individuals from the kaili formation suggest that wiwaxia taijiangensis should be a junior synonym of w corrugata a new study indicates that w corrugata has a wide geographic distribution a short geological history and evolutionary uniqueness and provides new data on taphonomy of this genus

cosmopolitan arthropod zooplankton in the ordovician seas abstract evidence is presented here for a zooplanktonic component in ordovician marine ecosystems namely the caryocaridid arthropods that add to other well documented midwater organisms such as graptolites cyclopygid and telephinid trilobites orthoconic cephalopods and the microphytoplankton e g acritarchs although the soft anatomy of caryocaridids is largely hypothetical their carapace design and ultrastructure and their phyllocarid like abdominal morphology flattened furcal rami telescopic segments indicate a swimming lifestyle in midwater niches both functional and ecological interpretations are supported by their palaeogeographical and facies distributions and by analogies with modern pelagic ostracods caryocaridids occur at numerous localities on the palaeo plates of laurentia baltica avalonia perunica gondwana and south china and are recurrent faunal components of graptolitic black shales mainly tremadoc to llanvirn typical faunal associates are the didymograptid and isograptid graptolites pelagic cyclopygid and deep sea benthic atheloptic trilobites their depositional environments suggest that the caryocaridids and their pelagic associates graptolites most probably thrived in waters above the distal shelf margins where upwelling controlled primary productivity possibly reached its maximum their exact bathymetrical range within the water column cannot be inferred from fossil evidence however their feeding strategies may have led them to exploit food resources across the mesopelagic epipelagic boundaries as do numerous midwater crustaceans in present day ecosystems caryocaridids represent a significant step in the post cambrian colonisation of midwater niches by arthropods and in the construction of complex modern foodwebs

widespread preservation of small carbonaceous fossils scfs in the early cambrian of north greenland the early cambrian ca 518 ma sirius passet lagerstatte of north greenland is one of the most celebrated sites bearing fossils of soft bodied organisms and provides key insights into the cambria

cambrian burgess shale type deposits share a common mode of fossilization although cambrian burgess shale type bst biotas are fundamental to understanding the radiation of metazoans the nature of their extraordinary preservation remains controversial there remains disagreement about the importance of the role of early mineral replication of soft tissues versus the conservation of primary organic remains most prior work focused on soft bodied fossils from the two most important bst biotas those of the burgess shale canada and maotianshan shale chengjiang china fossils from these two deposits do not provide ideal candidates for specimen level taphonomic study because they have been altered the burgess shale by greenschist facies metamorphism and the maotianshan shale by intensive subsurface weathering elemental mapping of soft bodied fossils from 11 other bst deposits worldwide demonstrates that bst preservation represents a single major taphonomic pathway that may share a common cause wherever it occurs the conservation of organic tissues and not early authigenic mineralization is the primary mechanism responsible for the preservation of bst assemblages early authigenic mineral replacement preserves certain anatomical features of some specimens but the preservation of non biomineralized bst fossils requires suppression of the processes that normally lead to the degradation of organic remains in marine environments

three dimensional p wave velocity structure beneath central japan low velocity bodies in the wedge portion of the upper mantle above high velocity subducting plates abstract the three dimensional 3 d p wave velocity structure beneath central japan has been investigated in detail by an inversion method 7490 p wave arrival times from 120 shallow and intermediate depth earthquakes that have occurred in this region are used to estimate velocity anomalies in 3 d subdivided blocks and hypocentral perturbations simultaneously the results reveal complex 3 d structures with low velocity zones in the wedge portion of the upper mantle above the high velocity philippine sea and pacific plates subducting beneath this region prominent low velocity bodies exist just beneath active volcanoes particularly in the hida mountain range low velocity bodies are spatially correlated with the low q zones estimated from seismic intensity data one low velocity body coincides with an anisotropic body detected from the study of shear wave splitting dome shaped low velocity masses seem to represent partially melted mantle diapirs no clear evidence on velocity contrast has been identified across the fossa magna which is a tectonic boundary between northeast and southwest japan

shear wave polarization anisotropy in the upper mantle from a deep earthquake abstract shear wave polarization anisotropy in the upper mantle is investigated at the spatially dense seismic stations of the national research institute for earth science and disaster prevention located in central japan by the use of the scs wave of a deep earthquake which occurred beneath sakhalin island on 12 may 1990 a characteristic pattern is found small and large shear wave anisotropy values are observed at seismic stations located on the east and west sides of the volcanic front respectively

small carbonaceous fossils scfs a new measure of early paleozoic paleobiology use of a low manipulation hydrofluoric acid extraction procedure on cambrian mudstones reveals an unexpectedly abundant and diverse range of small carbonaceous fossils scfs primarily the disarticulated sclerites and cuticular fragments of animals relatively recalcitrant forms such as wiwaxia sclerites and priapulid like scalids are sufficiently common to yield a reasonably reliable biostratigraphic signal unlike their rare macroscopic counterparts molluscan radulae crustacean appendages and the carbonaceous components of originally mineralized metazoan sclerites provide further insights into the histology diversity and distribution of early metazoans the widespread occurrence of scfs is due in part to their enhanced biostratinomic potential for transport burial and preservation particularly in well aerated epicratonic settings not represented by burgess shale type macrofossils more generally the scf record represents a largely untapped measure of ecological and evolutionary dynamics through the early paleozoic

p and s wave travel time inversions for subducting slab under the island arcs of the northwest pacific we have observed slablike high p and s velocity anomalies around the wadati benioff zone under island arcs of the northwest pacific through travel time tomographic inversions nineteen years of international seismological centre travel time residuals for events and stations in this large region are used analyses of resolution and noise show that the images are generally well resolved the images illustrate that slab anomalies are continuous along strike in most parts of the upper mantle of the region and become contorted and generally broadened with depth near the bottom of the upper mantle fingering of the slabs including segmenting and spreading is indicated the fast anomalies associated with the japan izu bonin and mariana subduction zones tend to flatten to subhorizontal at depth while downward spreading may occur under parts of the mariana and kurile arcs the fast anomalies below 700 km are not in the shape of a single coherent sheet the principal compressional axes of focal mechanisms in the region consistently follow the downdip direction of the high velocity slab even when it bends to subhorizontal at depth the depth at which compression begins to dominate the downdip stress regime in the slab apparently depends on bending of the slab and its dip slab fingering and intense deep seismicity probably are the consequence of the slab encountering a barrier of some form around the 670 km discontinuity

shear wave polarization anisotropy beneath the north eastern part of honshu japan summary we have investigated the shear wave polarization anisotropy in the north eastern japan arc by using waveforms from many local earthquakes at various depths we used a cross correlation method to detect the shear wave splitting for intermediate depth and deep events the observed fast shear wave oscillation directions fsods are oriented parallel to the dip direction of the slab at the western stations while they are oriented perpendicular to the dip direction at the eastern stations these observations indicate that significant anisotropy exists in the mantle wedge and that its nature is quite different between the eastern and the western parts

origin of crustal anisotropy shear wave splitting studies in japan shear wave splitting manifested as leading shear wave polarization that is parallel alignment of leading shear wave particle motions from a variety of sources has been observed at a number of seismograph stations in japan detected on shear wave seismograms from crustal earthquakes over a wide range of source zones and source receiver azimuths the shear wave splitting can be attributed to crustal anisotropy this paper discusses the relation between leading shear wave polarization directions and tectonic features of japan to explain the observed shear wave splitting the author proposes that at least three phenomena should be taken into account stress induced microcracks primarily aligned in vertical or subvertical planes cracks or fractures in the vicinity of active faults having their orientation parallel to the fault planes and intrinsic rock anisotropy resulting from preferred orientation of minerals travel time differences between leading and slower split shear waves from crustal and upper mantle earthquakes analyzed for about one third of the stations suggest that the crustal anisotropy which causes the observed shear wave splitting may be limited to the upper 15 25 km this implies that the density of nonhorizontally aligned cracks or fractures below 15 25 km and into the upper mantle is muchmore smaller than that in the crust above 15 25 km less

the nature and transport of the fine grained component of swift creek landslide northwest washington extreme sedimentation in swift creek located in the cascades foothills in nw washington 48 55 n 122 16 w results from erosion of the oversteepened unvegetated toe of a large 55 hectares active landslide deposition of landslide derived sediment has necessitated costly mitigation projects in the channel including annual dredging and temporary sediment traps in an attempt to reduce the risk of flooding and damage to man made structures downstream this study attempts to understand the process of sediment production along with the corresponding erosion rates of the sediment source to help with the development of mitigation plans and construction of optimal sediment reservoirs the bedload and suspended sediment in the creek are a direct result of the weathering process of the serpentinitic bedrock underlying the landslide the serpentinite does not weather to smectite clay as previously thought instead it weathers to asbestiform chrysotile with minor amounts of chlorite illite and hydrotalcite all of which occur in clay seeps on the unvegetated surface of the landslide the chrysotile fibers average 2 m in length and make up at least 50 by volume of the suspended load transported in swift creek this study does not address the environmental or health implications of the asbestiform chrysotile transport or deposition during the sampled time between february 2005 and february 2006 127 discrete suspended sediment samples were collected and discharge was measured 66 times the suspended sediment concentrations ranged from 0 02 g l 1 to 41 6 g l 1 and the discharge ranged from 0 0 m3 s 1 to 0 5 m3 s 1 a nonlinear functional model estimated the total suspended sediment flux from detailed precipitation records and discrete suspended sediment concentration and discharge measurements to be 910 t km 2 yr 1 when the suspended sediment flux is coupled with estimates of downstream deposition of coarse sediment the estimated erosion rate for the entire swift creek landslide is 158 mm yr 1 the majority of the material entering swift creek is presumed to originate on the unvegetated toe of the landslide for which the erosion rate is thus approximately 1 m yr 1 copyright 2010 john wiley sons ltd

seismic anisotropy in the fore arc region of the hikurangi subduction zone new zealand abstract shear waves from local earthquakes recorded on an array of nine broad band seismograph stations have been used to investigate the anisotropic structure within the crust of the overlying australian plate and within and below the subducting slab underlying the southern north island new zealand earthquakes near the plate interface were used to image the crustal anisotropy whereas deeper down dip subduction zone events were used to sample the subducting slab and the mantle below apart from a small amount of variable near surface anisotropy top few kilometres of the crust the measured fast shear wave directions of both the crust of the overlying plate 51 18 and the mantle 41 15 are similar and are nearly parallel to the strike of the subduction zone and the dominant geological features of the region sks measurements which mainly sample the mantle beneath the subducting plate give a value of 28 11 and measurements made elsewhere in the new zealand region using sks and scs2 produce similar results the measurements of crustal anisotropy are similar to those found further south on the wellington peninsula and confirm the presence of near surface anisotropy the maximum delay times for crustal earthquakes indicate a pervasive shear wave velocity anisotropy of 4 in the crust of the overlying plate and the increase in the delay times with depth for the subduction zone earthquakes translates to a shear wave velocity anisotropy of 1 4 in the mantle below the subducting slab these results when combined with the sks measurements suggest trench parallel flow in the mantle below the subducted slab and a coherence of the deformation processes in the crust of the overlying plate and the mantle beneath the subducting slab

three dimensional q structure beneath the kanto tokai district japan the q structure of the upper mantle beneath the kanto tokai district central japan where the eurasian pacific and philippine sea plates are converging is investigated from seismic p and s wave spectral ratios by means of a three dimensional 3 d inversion method it is found that the subducting philippine sea and pacific plates are characterized by high q zones a high q zone also exists between the philippine sea plate and the pacific plate to the east of the volcanic front on the other hand a low q zone in the uppermost mantle extends westward horizontally from the volcanic front under the philippine sea plate and appears to exist over the wedge mantle beneath the western tokai district a very low q value obtained here is roughly equal to the average qvalue in the low velocity layer derived from surface wave and free oscillation data a low q region that suggests a magma chamber under active volcanoes is not detected in the crust

evidence from shear wave splitting for the restriction of seismic anisotropy to the upper crust the existence of anistropy in the propagation speed of seismic waves through the earth s crust has been attributed to the non random alignment of microcracks in the crust1 for sparsely distributed parallel vertical cracks perturbation theory predicts the splitting of a shear wave into two orthogonally polarized waves2 4 here we present extremely clear evidence for shear wave splitting in three component seismograms from crustal and sub crustal microearthquakes recorded in the shikoku district of japan quantitative analysis of travel time differences between split shear waves leads to the conclusion that the observed anisotropy is limited to the upper crust shallower than 10 15 km this model is consistent with recent results from reflection seismology5 and implies that microcrack density or orientation changes from the upper to the lower crust

anisotropic loci in the mantle beneath central peru abstract seismic anisotropy of the upper mantle beneath the central part of peru is examined by analyzing shear waves observed at broad band stations and a temporary array of short period stations shear wave splitting is seen on various shear phases such as direct s waves from local intermediate to deep earthquakes scs waves from regional deep earthquakes and sks waves from teleseismic earthquakes it is inferred that the shear wave anisotropy in the uppermost 100 km of the subcontinental mantle overlying the subducted nazca plate is 0 5 at most while the anisotropy in the subslab asthenosphere depth range of about 150 350 km is 2 or greater the fast shear wave polarization direction in this depth range as observed at two broad band stations is 30 40 different from the absolute motion of the nazca plate this does not fit simple two dimensional 2 d models of olivine alignment caused by slab induced mantle flow and implies either the existence of a complex flow pattern in the asthenosphere underneath the nazca plate or the presence of an unknown mechanism for the anisotropy formation the lower mantle beneath central peru is found to be effectively isotropic for nearly vertically propagated shear waves

crustaceans and the cambrian explosion we noted with interest the report by siveter et al 1 1 of new phosphatocopid specimens showing soft part preservation from the lower cambrian comley limestones but we question some of the interpretations both in the report and in the accompanying perspective by fortey 2 2 first

seismic anisotropy in the wedge above the philippine sea slab beneath kanto and southwest japan derived from shear wave splitting abstract we conduct shear wave splitting measurements on waveform data from the hi net and the broadband f net seismic stations in kanto and sw japan generated by shallow and intermediate depth earthquakes occurring in the subducting philippine sea and pacific slabs we obtain 1115 shear wave splitting parameter pairs the results are divided into those from the shallow depth 50 km events the deep events beneath kanto are further divided into phs1 and phs2 upper and lower planes of the double seismic zone in the philippine sea slab respectively pac1 and pac2 western and eastern pacific slab respectively events the results from the shallow events represent the crustal anisotropy and their fast directions are more or less aligned in the hmax directions implying that the anisotropy is produced by the alignment of the vertical cracks in the crust induced by the compressive stresses in kanto kii peninsula and kyushu regions the results from the deep events suggest a contribution from the mantle wedge anisotropy events from all groups beneath kanto show nw ne and ew fast directions this complex pattern seems to be produced by the corner flows induced by both the wnw pac plate subduction and the oblique nnw phs slab subduction with the associated olivine lattice preferred orientations lpos and the anisotropy frozen in the phs slab the deep events beneath kii peninsula show ne and nw fast directions and may be produced by the corner flow produced by the nnw phs slab subduction with the associated olivine lpos the ne directions might also be produced by the segregated melts in the thin layers parallel to the phs slab subduction the deep events beneath n kyushu show nnw fast directions which may result from the southeastward flow in the upper mantle inferred from the stresses in the upper plate results from the deep events beneath middle south kyushu show dominantly e w fast directions in both the fore and back arcs they may be produced by the corner flow of the westward phs slab subduction with the olivine lpos because the source regions with multiple fast directions are not resolved in this study further detailed analyses of shear wave splitting are necessary for a better understanding of the stress state the induced mantle flow and the melt segregation processes

burgess shale type faunas in the context of the cambrian explosion a review burgess shale type faunas are now known from almost 40 lower and middle cambrian localities although those from british columbia canada yunnan china and peary land greenland are of paramount significance the diverse faunas are dominated by animals with an otherwise negligible fossilization potential and their stratigraphical position makes them of unique importance in documenting the major adaptive radiations at this time cambrian explosion important features of these faunas include the presence of taxa surviving from the late precambrian ediacaran faunas the discovery of articulated material that throws new light on scleritome organization in various cambrian skeletal taxa and the significance of the degree of anatomical disparity among cambrian animals in addition these soft bodied faunas offer some hope of reconciling soft part data with trace fossil occurrences new discoveries of burgess shale type faunas are inevitable and such finds will continue to enhance our under standing of early animal evolution

shear wave polarization anisotropy in the upper mantle beneath honshu japan shear wave polarization anisotropy in the wedge portion of the upper mantle between a subducting plate and the earth s surface is investigated using three component seismograms of intermediate depth and deep earthquakes recorded at 14 local stations in honshu japan eighty nine high quality seismograms were selected from a period of 3 years the data used in this study are restricted such that incidence angles are smaller than the critical angle of 30 to the earth s surface in order to avoid phase shifts in the shear wave train to find directions of the maximum and minimum velocities in split shear waves where shear waves are resolved into two phases with the maximum time separation each set of the two horizontal component seismograms is rotated in the horizontal plane the split shear waves thus obtained are again recombined after the correction of anisotropy and the anisotropy corrected particle motion is compared with the focal mechanism for a cross check of the observed anisotropy directions of the maximum axes are plotted on azimuthincidence angle stereograms at each station the stereograms and the cross sections of seismic ray paths show that 1 the anisotropic material is distributed at intermediate location between earthquake sources and receiving stations and 2 the anisotropic region is separated into two parts one in the north of the present study area with the polarization of the maximum velocity shear wave trending 0 to 30 from the north north anisotropy and the other in the south with it trending 90 to 120 south anisotropy the maximum time delays between the two shear waves along a vertical seismic ray is about l s for both the anisotropic regions the horizontal extent of the anisotropic area in the north is 50 km at depths of 50 to 150 km perhaps prevalent in west honshu however the depth of anisotropic material is not well constrained because of insufficient coverage of seismic ray paths and angles if we assume the vertical extent of the anisotropic material to be 100 km the maximum velocity contrast would be 4 if we adopt a crack alignment model for the observed anisotropy cracks are inferred to be distributed vertically trending 0 to 30 in the north and 90 to 120 in the south if we assume an olivine alignment model olivine crystals are inferred to be aligned in the north with the a axis of the slip direction trending 0 to 30 and the slip plane normal to the b axis being vertical and in the south anisotropy with the axis trending 90 to 120 and the slip plane being horizontal

a burgess shale like fauna from the lower cambrian of north greenland the cambrian explosion refers to the major adaptive radiation of the metazoans during the earliest phanerozoic an event that is best known by the abrupt appearance of hard parts near to the precambrian cambrian boundary 550 myr bp 1 deciphering this important evolutionary episode depends largely on the study of these skeletal remains2 3 together with trace fossils that include burrows and trackways4 5 many of these latter fossils evidently represent the activities of soft bodied organisms such as worms and lightly sclerotized arthropods whose exact identity is seldom known not least because they can be fossilized only in exceptional circumstances6 however documenting the soft bodied representatives of early metazoan communities cannot be neglected if they accounted for a substantial fraction of these early biotas7 here we report a new soft bodied fauna from the lower cambrian of north greenland this assemblage has highly significant similarities with the younger burgess shale and provides additional evidence for the geological longevity of this faunal type and its widespread distribution in deeper waters of cambrian oceans

sediment ingestion by worms and the production of bio clays a study of macrobiologically enhanced weathering and early diagenetic processes the experiments reported here show that a range of early diagenetic clay minerals can develop within ingested sand in the guts of creatures at a rate that is at least 2 or 3 orders of magnitude greater than in an abiotic environment early diagenesis in marine environments may be strongly influenced by the occurrence of sediment ingestion and excretion by animals using a set of artificial marine experiments and the common lugworm arenicola marina i t is shown that sediment ingestion by macrobiota represents a new way in which to precipitate clay minerals or bio clays significant quantities of clay minerals can be the product of biological interaction within sediment tanks were constructed with artificially layered sediment and natural seawater the experiments were conducted at room temperature for a total duration of 9 months the silicate material fed to the worms was an unweathered and thus clay mineral free basalt from iceland less than 2 lm fractions from original control and faecal samples were periodically analysed using x ray diffraction xrd and fourier transform infrared spectroscopy ftir faecal casts underwent mineral alteration as denoted by loss of primary minerals especially plagioclase new minerals in faecal casts from the lugworms included kaolinite illite quartz and possibly chlorite inorganic weathering of similar parent basalt would probably produce an identical mineral assemblage but many more times slowly than with the macrobiotic mechanism demonstrated here

evidence from core reflected shear waves for anisotropy in the earth s mantle seismologists have begun to recognize that the upper mantle at depth is anisotropic and that seismological data are not fully explicable if anisotropy is ignored1 5 on entering an anisotropic zone a plane shear wave splits into two orthogonally polarized phases6 an effect observed by several researchers7 notably by ando et al 5 8 9 the near vertical scs wave an s wave reflected once at the core mantle boundary is one of the most suitable phases to study the phenomenon of shear wave birefringence because it is isolated from other phases and because its particle motion is nearly horizontal and thus free from s to p conversion the split scs shear waves travel with different velocities in the anisotropic zone and consequently there is a time delay between their arrival at stations my aim was to determine this time delay and the azimuth of polarization using the scs records of two horizontal components from the japanese islands for a deep shock beneath the sea of okhotsk from the total of 41 stations 34 show a polarization of the maximum velocity phase in the nnw sse direction with an average time advance of 0 8s from the minimum velocity phase the relevant anisotropic zone seems to be deep seated

global patterns of azimuthal anisotropy and deformations in the continental mantle summary we present a summary of measurements of azimuthal anisotropy in the continental mantle based on the sks technique and performed mostly with the active participation of the authors the directions of polarization of the fast quasi shear wave and the time delays between the quasi shear waves are obtained at nearly 70 locations in all continents except antarctica these data are interpreted in terms of lattice preferred orientation of olivine which is caused by deformations in the mantle the depth interval responsible for anisotropy is unknown but the data suggest that it may reach at least 300 km the fast directions in sks do not show clear correlation with the fast directions of the teleseismic p at the same seismograph stations in the regions of present day convergence the fast direction of anisotropy usually aligns with the plate boundary this correlation implies that the direction of shortening is the same in the crust and the upper mantle in the regions of rifting the inferred direction of mantle flow usually aligns with the direction of extension in the crust outside the regions of recent tectonic activity we most likely observe a combined effect of frozen anisotropy in the subcrustal lithosphere and of recently formed anisotropy in the asthenosphere on a global scale in these regions there is a positive correlation between the absolute plate velocity directions and the fast directions of anisotropy the correlation is especially strong in central and eastern parts of north america a clear absence of any evidence of large scale azimuthal anisotropy in the data of long range refraction profiling for the upper 100 km of the mantle of that region implies that the effect in sks is generated mainly at greater depths in the asthenosphere orientation of olivine at these depths reflects recent and present day flow in the mantle rather than processes of a distant geologic past

mantle anisotropy beneath northwest pacific subduction zones to assess the location strength and orientation of seismic anisotropy in the southern kuril japan and izu bonin subduction zones we analyzed shear wave splitting in local s phases and teleseismic sks phases fast directions from these phases are roughly parallel to the direction of absolute pacific plate motion wnw in izu bonin roughly parallel to the strike of the trench nne in central honshu and roughly n in the southern kuril back arc in the vicinity of sakhalin island assuming that the orientation and strength of anisotropy does not vary with depth modeling of splitting times from local s and teleseismic phases recorded at sakhalin island requires that the maximum depth of anisotropy lies between 480 km and 950 km in contrast splitting times for local s phases from events in izu bonin rule out anisotropy in the transition zone all the data are consistent with a model in which the lower transition zone 520 660 km and lower mantle are largely isotropic and in which anisotropy occurs intermittently in the upper transition zone 410 520 km possibly due to preferred orientation of spinel assuming that splitting in the upper mantle is produced by preferred orientation of olivine the observed fast directions indicate that the geometry of back arc strain varies systematically between subduction zones the relationship of fast directions and plate motions suggests that the subducting slab exerts significant control on back arc flow but that flow correlated with upper plate deformation must also exist

scs wave splitting of deep earthquakes around japan summary scs wave splitting of five deep earthquakes in subduction zones near japan is investigated using horizontal seismograms recorded al jma stations for each earthquake we clearly observe uniform scs wave splitting in all stations over japan especially for the events located south of honshu in 1982 1984 and 1993 however the directions of fast polarized waves of these events differed by a maximum of about 50 from one another the orientation of fast polarized waves in the 1982 event was nnw sse those in the two later events wnw ese we also recognize this discrepancy in the results of the analysis of the 1971 sea of okhotsk event reported by fukao 1984 the sakhalin islands event in 1990 reveals a linear particle motion without such a change in direction of the second arrivals implying no anisotropy these observations are interpreted as indicating an anisotropic region within the slab near the earthquake sources but not beneath the receivers since the orientations of fast polarized waves recorded at each station are not common to all the earthquakes furthermore we consider that anisotropy exists non uniformly within the slab the event in 1982 which occurred in almost the same area as those in 1984 and 1993 showed a fast direction different from the events in 1984 and 1993 the 1982 event was 179 km deep but the two later events were at 398 km and 360 km respectively the fast direction observed from the 1982 event is parallel to the fossil plate motion whereas those from the events in 1984 and 1993 are parallel to the compression axis within the subducting slab the depth of 400 km is a phase boundary where olivine changes to spinel we consider that the most likely cause of the change in anisotropy direction is the re orientation of crystals associated with the phase change of olivine to spinel due to subduction of the slab

seismic anisotropy of the pacific slab and mantle wedge beneath the japanese islands 1 the mantle beneath the japanese islands is complex because of subduction of the pacific and philippine sea plates and the deformation associated with it detection of seismic anisotropy should be useful for understanding the processes occurring in such mantle here we resolve seismic anisotropy of the mantle wedge from that of the underlying subducted pacific slab using a large number of measurements of shear wave splitting for a family of core reflected shear phases scs sscs scs2 and sscs2 the anisotropy of the mantle wedge changes sharply across the volcanic front on the pacific side of the volcanic front a vertically propagating shear wave is polarized with the fast direction approximately parallel to the trench whereas on the back arc side it is polarized with the fast direction approximately parallel to the plate convergence direction the pacific slab is uniformly anisotropic with the nnw fast direction consistent with the paleospreading direction of the northwestern pacific seafloor the preferential alignment of anisotropic crystals frozen in the plate at the time of its formation appears to be preserved down to depths beyond 400 km within the slab

burgess shale type fossils from a lower cambrian shallow shelf sequence in northwestern canada fossil lagerstatten comparable to that of the burgess shale potentially provide the detail necessary to resolve and assess the so called cambrian explosion of multicellular life1 2 distributional and taphonomic biases however often limit the generalizations that can be drawn here i report widespread occurrences of burgess shale type fossils in shallow shelf sediments of the lower cambrian mount cap formation district of mackenzie northwest territories canada these borehole assemblages significantly expand the known geographical and ecological range of such fossil biotas and document the early appearance of both wiwaxiid polychaetes and filter feeding crustaceans the ability of this latter group to exploit microplanktic primary productivity marks a fundamental shift in trophic structuring and may distinguish phanerozoic from pre phanerozoic ecosystems

exceptionally preserved fossil assemblages through geologic time and space abstract geologic deposits containing fossils with remains of non biomineralized tissues i e konservat lagerstatten provide key insights into ancient organisms and ecosystems such deposits are not evenly distributed through geologic time or space suggesting that global phenomena play a key role in exceptional fossil preservation nonetheless establishing the influence of global phenomena requires documenting temporal and spatial trends in occurrences of exceptionally preserved fossil assemblages to this end we compiled and analyzed a dataset of 694 globally distributed exceptional fossil assemblages spanning the history of complex eukaryotic life 610 to 3 ma our analyses demonstrate that assemblages with similar ages and depositional settings commonly occur in clusters each signifying an ancient geographic region up to hundreds of kilometers in scale which repeatedly developed conditions conducive to soft tissue preservation using a novel hierarchical clustering approach we show that these clusters decrease in number and shift from open marine to transitional and non marine settings across the cambrian ordovician interval conditions conducive to exceptional preservation declined worldwide during the early paleozoic in response to transformations of near surface environments that promoted degradation of tissues and curbed authigenic mineralization potential we propose a holistic explanation relating these environmental transitions to ocean oxygenation and bioturbation which affected virtually all taphonomic pathways in addition to changes in seawater chemistry that disproportionately affected processes of soft tissue conservation after these transitions exceptional preservation rarely occurred in open marine settings excepting times of widespread oceanic anoxia when low oxygen levels set the stage with these patterns non marine cluster count is correlated with non marine rock quantity and generally decreases with age this result suggests that geologic processes which progressively destroy terrestrial rocks over time limit sampling of non marine deposits on a global scale future efforts should aim to assess the impacts of such phenomena on evolutionary and ecological patterns in the fossil record