additional records of ichnogenus rhizocorallium from the lower and middle triassic south china implications for biotic recovery after the end permian mass extinction

crustal structure of accreted terranes in southern alaska chugach mountains and copper river basin from seismic refraction results seismic refraction data were collected along a 320 km long transect line in southern alaska crossing the prince william chugach peninsular and wrangellia terranes and along several shorter lines within individual terranes velocity structure in the upper crust less than 9 km depth differs among the four terranes in contrast layers in the middle crust 9 to 25 km depth in some cases extend across projected terrane boundaries the following observations can be made 1 an intermediate velocity layer 6 4 km s at 9 km depth extends across the deep projection of the suture between the chugach and peninsular terranes suggesting that the northern chugach and southern peninsular terranes are detached and rest on a deeper terrane of unknown origin 2 the top of a gently north dipping sequence of low and high velocity layers 5 7 7 8 km s more than 10 km thick extends from near the surface in the southern chugach terrane to more than 20 km depth beneath the southern peninsular terrane this sequence truncated by the suture between the prince william and chugach terranes is interpreted to be an underplated terrane made up of fragments of the kula plate and its sedimentary overburden that were accreted during subduction in the late mesozoic and or early tertiary during or between times of accretion of the prince william and chugach terranes 3 a thick crustal root with a laminated sequence at its top extends from a depth of 19 km to as much as 57 km beneath the northern peninsular and wrangellia terranes this root extends across the deep projection of the suture between the peninsular and wrangellia terranes although resolution of this apparent crosscutting relationship is relatively poor this root may represent tectonically or possibly magmatically emplaced rocks the lower crust beneath the prince william chugach and southern peninsular terranes includes a north dipping 3 to 8 km thick section of subducting oceanic crust

a newly discovered earliest triassic chert at gaimao section guizhou southwestern china abstract the permian triassic ptb boundary section at gaimao huaxi district guiyang guizhou province records a unique lithological transition between the permian and triassic in south china thus bioclastic limestones of the changxing formation are overlain by radiolarian bearing siliceous rocks of the dalong formation and ultimately limestone mudstone alternations of the shabaowan formation conodont sampling of the section revealed well preserved elements that enabled a conodont biostratigraphy to be established the occurrences of hindeodus julfensis and hindeodus typicalis in changxing formation bioclastic limestone indicate a late permian age four conodont zones have been established in dalong and shabaowan formations in ascending order those are the isarcicella isarcica zone neogondolella or clarkina planata zone neogondolella krystyni zone and neospathodus dieneri zone the presence of typical griesbachian conodonts i isarcica and isarcicella staeschei in upper dalong formation indicates that this formation s radiolarian bearing siliceous mudrocks are of earliest triassic age and not restricted to the permian as previously thought thin section analysis reveals that the upper dalong formation contains spheroidal radiolarians but not a diverse assemblage of permian holdover taxa the new data proves that following the end permian mass extinction of radiolarian the abundance of these siliceous planktons was maintained at least locally enabling chert deposition to persist thus the gaimao section provides an exception to the early triassic chert gap the first of its kind in palaeo tethys and indicates that the end of chert deposition does not always mark the end permian mass extinction

joint inversion of regional and teleseismic earthquake waveforms a least squares joint inversion technique for regional and teleseismic waveforms is presented the mean square error between seismograms and synthetics is minimized using true amplitudes matching true amplitudes in modeling requires meaningful estimates of modeling uncertainties and of seismogram signal to noise ratios this also permits calculating linearized uncertainties on the solution based on accuracy and resolution we use a priori estimates of earthquake parameters to stabilize unresolved parameters and for comparison with a posteriori uncertainties we verify the technique on synthetic data and on the 1983 borah peak idaho m 7 3 earthquake we demonstrate the inversion on the august 1954 rainbow mountain nevada m 6 8 earthquake and find parameters consistent with previous studies

ether lipids from the lower and middle triassic at qingyan guizhou province southern china abstract ether lipids such as non isoprenoid mono and dialkyl glycerol ethers mages and dages and archaeol have been found in carbonate rocks and mud rocks deposited during the early and middle triassic 250 240 ma the oldest previous discovery of ether lipids is from cretaceous black shale deposited during the albian 112 ma paleoenvironmental reconstruction using ether lipids has therefore not been conducted on pre cretaceous sediments archaeol derives from archaea e g methanogenic methanotrophic halophilic and thermophilic archaea the non isoprenoid dages and mages likely derive from sulfate reducing bacteria srb which are restricted to anaerobic environments the presence of ether lipids thus indicates that anoxic conditions expanded in the depositional and or water column environment in the qingyan area during the early middle triassic these ether lipids may be useful for the reconstruction of paleoredox conditions and paleoecosystems in the area furthermore their occurrence suggests that paleoenvironmental reconstruction using ether lipids may be possible throughout the mesozoic and cenozoic

early triassic conodont palynological biostratigraphy of the meishan d section in changxing zhejiang province south china the lower triassic consisting of the yinkeng fm helongshan fm and the lower part of the nanlinghu fm is well developed at the meishan d section of changxing county zhejiang province south china based on detailed study of the conodont biostratigraphy from the interval of the permian triassic boundary and the lower triassic in the meishan d section 8 conodont zones are recognized in ascending order as follows the neogondolella changxingensis yini hindeodus praeparvus zone beds 24a 24e top of the changxing fm the neogondolella meishanensis meishanensis hindeodus eurypyge zone beds 25 27b base of the yinkeng fm the hindeodus parvus zone beds 27c 27d first conodont zone of triassic the global index for the base of triassic the isarcicella staeschei zone beds 28 29a lower part of the yinkeng fm i isarcica zone beds 29b 51 lower part of the yinkeng fm the neogondolella tulongensis n planata zone beds 52 72 from upper part of the yinkeng fm to lower part of the helongshan fm the neospathodus kummeli zone beds 73 92 middle part of the helongshan fm and the neospathodus cristagalli n dieneri zone beds 93 111 from upper part of the helongshan fm to the base of the nanlinghu fm at the meishan d section the palynological biostratigraphy is also studied herein the palynological assemblage of lundbladispora taeniaesporites equisetosporites is found in the intervals which contain the conodont isarcicella isarcica zone and the lower part of the neogondolella tulongensis n planata zone

upper permian and lower triassic conodonts high precision u pb zircon ages and the permian triassic boundary in the malay peninsula abstract conodont biostratigraphic and high precision u pb isotope data are presented for the permian triassic transition in three limestone hills gua bama gua panjang and gua sei in the malay peninsula gua bama yielded conodonts representating the clarkina orientalis clarkina wangi and clarkina subcarinata zones and the wuchiapingian changhsingian stage boundary is identified for the first time in malaysia the wuchiapingian subspecies hindeodus julfensis wardlawi kozur is elevated to species level h wardlawi and evolved to the changhsingian species hindeodus julfensis sweet and then hindeodus changxingensis wang distinguishing features and a new phylogeny of species of the genera hindeodus and isarcicella in the late permian early triassic are presented a new ca tims high precision u pb age of 253 70 0 06 ma for zircon from a tuff layer 6 5 m above the wuchiapingian changhsingian boundary and in the lower part of the clarkina subcarinata zone is reported conodont faunas from gua panjang represent the clarkina changxingensis hindeodus praeparvus clarkina yini clarkina zhangi and hindeodus parvus zones and the ptb is placed at approximately 12 m in the studied 19 m thick sequence three tuff layers in the lower part of gua panjang contain zircon grains with ca tims u pb ages of 252 23 0 07 ma 252 47 0 12 ma and 252 16 0 16 ma maximum age respectively conodont faunas from gua sei represent the upper permian changhsingian clarkina hauschei hindeodus latidentatus zone and the basal triassic lower induan griesbachian hindeodus parvus and isarcicella staeschei zones the ptb is placed at 30 m above the base of the gua sei sequence

tidal current effects on temperature in diffuse hydrothermal flow guaymas basin a twelve day record of temperature collected from the diffuse flow area of a guaymas basin hydrothermal site exhibits variations from a minimum of 3 05 c to a maximum of 4 87 c whose periodicity is correlated with tides measured at the nearby town of guaymas a simple model based on the hypothesis that temperature variations result as changes in tidal bottom currents induce changes in the height of the thermal boundary layer is in good quantitative agreement with observed temperatures for most of the record the success of this model illustrates that the effects of tidal currents can be strong enough to dominate the time variability of a temperature signal at a fixed point in hydrothermal flow therefore tidal currents must be taken into account when using temperature measurements to estimate time varying heat fluxes from hydrothermal diffuse flow regions

influence of asperities along subduction interfaces on the stressing and seismicity of adjacent areas abstract dmowska r and lovison l c 1992 influence of asperities along subduction interfaces on the stressing and seismicity of adjacent areas in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 23 43 we have investigated the influence of large scale fault inhomogeneities in large subduction earthquakes on the style of deformation and seismic behavior of the incoming oceanic plate and slab at intermediate depths during the earthquake cycle the zones of the large subduction events of rat islands 1965 alaska 1964 and valparaiso 1985 have been searched for earthquakes with m b 5 0 if available and for time periods as long as possible it has been found that in general the seismicity in the incoming oceanic plate clusters in front of asperities areas of highest seismic moment release and strongest locking and is positioned relative to them in the direction of plate motion it is usually lacking in areas adjacent to non asperities that is to zones that slip during the main event but with appreciably smaller seismic moment release and possibly slip seismically aseismically during the whole cycle similar behavior occurs in the downgoing slab at intermediate depths where seismicity during the cycle clusters but less strongly than in the oceanic crust next to asperities and down dip from them we infer that the locking of asperities causes higher stresses associated with the earthquake cycle itself to occur in areas adjacent to asperities both up dip and down dip from them along the direction of plate motion and that such stressing is much less pronounced in the areas adjacent to non asperities this opens the possibility of identifying the areas of highest seismic moment release in future subduction earthquakes and carries implications for where the highest deformation and possibly precursory phenomena and or nucleation of a future event might occur

seismicity of the wrangell and aleutian wadati benioff zones and the north american plate along the trans alaska crustal transect chugach mountains and copper river basin southern alaska the configuration of the aleutian and wrangell wadati benioff zones in southern alaska between longitudes 142 w and 148 w is determined from regionally recorded earthquakes from 1971 to 1986 the earthquakes are located with a simple velocity model calibrated with seismic refraction measurements conducted for the trans alaska crustal transect tact west of the transect meridian approximately 145 20 w and beneath the chugach mountains shocks in the depth range 25 60 km compose the shallow part of the northwest to north dipping aleutian zone this zone can be traced updip and seaward beneath prince william sound east of the transect meridian and north of 61 n latitude the weakly active north northeast dipping wrangell zone extends to a depth of at least 100 km beneath the wrangell volcanoes and along strike for at least 150 km the two zones appear to be continuous at least in the depth range 20 45 km and may define adjacent limbs of a buckle in the subducted oceanic lithosphere north of 61 n focal mechanisms in the shallow aleutian zone are compatible with a uniform stress field characterized by in plane least compressive stress directed toward the steeply dipping deeper part of the aleutian zone north of cook inlet stress orientation in the wrangell zone is unresolved because of the low level of seismicity no focal mechanisms corresponding to slip on a gently northward dipping megathrust have been observed along the transect meridian a change of focal mechanism with depth near the top of the dipping seismic zone is inferred to reflect the interplate boundary beneath the chugach mountains this boundary coincides with a band of strong reflectors imaged by tact vertical seismic profiling the overriding plate appears to be aseismic beneath the northern chugach mountains but minor shallow seismicity occurs beneath the copper river basin first motion patterns for these shallow shocks suggest the most compressive stress within the overriding plate is oriented subhorizontally and approximately north south

sutton alaska earthquake of 1984 evidence for activity on the talkeetna segment of the castle mountain fault system a magnitude 5 7 mb 5 2 ms earthquake occurred on 14 august 1984 14 km north of sutton in the vicinity of the mapped trace of the talkeetna segment of the castle mountain fault system the focal mechanism of the earthquake and the spatial distribution of well controlled aftershock hypocenters indicate that the shock involved dextral slip at 13 to 20 km depth on the talkeetna fault segment the depth of the shocks is consistent with the lack of observed surface breakage the sutton earthquake sequence plus recent small shocks recorded by the southern alaska seismograph network provide definitive evidence that the talkeetna segment of the fault system is active

latest permian to middle triassic redox condition variations in ramp settings south china pyrite framboid evidence a detailed 10 m y redox history of changhsingian to anisian latest permian to middle triassic oceans in ramp settings is reconstructed based on framboidal pyrite analysis from south china the result shows that the well established phenomenon of intense ocean euxinia anoxia is faithfully recorded in pyrite framboid data three major euxinia anoxia episodes namely the end changhsingian to end smithian middle to late spathian and early to middle anisian have been recognized from the ramp successions the first reducing episode is subdivided into four subepisodes permian triassic boundary griesbachian dienerian boundary earliest smithian and end smithian redox variations broadly track other oceanographic proxies euxinia anoxia episodes coincide with positive excursions of conodont ce anomalies negative excursions of 34scas carbonate associated sulfate increases in sea surface temperature and negative excursions of 13c in most cases however euxinia anoxia near the dienerian smithian boundary coincided with positive excursions of 13c and a general cooling period this exception may be the result of locally developed water column anoxia the permian triassic boundary subepisode witnessed two ephemeral euxinia anoxia events separated by a dysoxic to oxic period the former together with a rapid increase in sea surface temperature up to 8 c may have been responsible for the biodiversity crisis while the latter anoxic event destroyed ecosystem trophic structures in addition to the permian triassic boundary euxinia anoxia event which spread over habitats in all oceans the spathian and anisian euxinia anoxia episodes also prevailed in global oceans variation of the oxygen minimum zone are suggested as the driving mechanism that facilitated the movement of oxygen poor water columns in various paleogeographic settings over this critical period

intermediate and deep seismicity and lateral structure of subducted lithosphere in the circum pacific region in this paper we present a region by region review of the wadati benioff zone structure of most of the world s seismically active subduction zones focusing primarily on the intermediate and deep seismicity lateral changes in wadati benioff zone structure are common in every major subduction zone in this study we use these changes to define possible boundaries between portions or segments of lithosphere with differing subduction geometries although earthquake data seldom have the resolution to show conclusively whether these boundaries separate independent blocks of lithosphere the available data indicate that the active process at most of these segment boundaries is ductile deformation of the subducting plate rather than tearing we found the strongest evidence for the existence of tears where tears are geometrically necessary such as where a transform boundary terminates a trench as at the new hebrides tonga and south sandwich trenches weak evidence suggesting other tears does exist in some regions such as taiwan the japan izu bonin corner and the philippines the causes of these changes in structure are in most cases unclear only about 34 of the possible segment boundaries coincide with subducting bathymetric features some boundaries occur where there is apparent lateral strain caused by anomalous trench geometry we have designed a simple modeling procedure which incorporates published plate motion and the observed geometry of trenches and wadati benioff zones to estimate the lateral strain in subduction zones throughout the circum pacific region although no observed subduction zone has a perfectly strain free geometry there is a broad range of geometries for which the lateral strain is small indeed the observed geometry of most subduction zones involve relatively little lateral strain comparison with centroid moment tensor focal mechanisms indicates that in zones where the modeling predicted little lateral strain the mechanisms of intermediate and deep earthquakes show no effects of lateral stress and downdip stresses are clearly dominant in regions such as the mariana arc where the model predicts very large lateral extension lateral tension is very evident in the focal mechanisms in regions such as the hokkaido corner where the modeling predicts large compressional strains the plate appears to buckle and bending stresses parallel to the trench are evident in general this study finds that subducted lithosphere is remarkably cohesive and rigid and only rarely deforms by breaking or stretching

the rupture process and asperity distribution of three great earthquakes from long period diffracted p waves moment tensor source mechanisms for the largest twenty nine shallow earthquakes from 1981 m s 6 5 have been determined using long period rayleigh wave spectra and p wave first motions recorded by the international deployment of accelerograms ida global digital seismic network gdsn and world wide standardised seismic network wwssn these are compared with the centroid moment tensor mechanisms presented by dziewonski and woodhouse which were obtained in a contrasting manner in most cases the source is well represented by a single double couple mechanisms with good agreement of scalar moment and orientation between the two studies apparent mismatches for other cases may be interpreted in terms of source complexity we emphasise the objectivity of comparing moment tensor elements apparent discrepancies in the moment and orientation of double couple fault plane solutions are usually due to differences in the mxz and myz moment tensor elements which are poorly constrained by long period data

the 1964 prince william sound earthquake joint inversion of tsunami and geodetic data the 1964 prince william sound alaska earthquake mw 9 2 ruptured a large area beneath the continental margin of alaska from prince william sound to kodiak island a joint inversion of tsunami waveforms and geodetic data consisting of vertical displacements and horizontal vectors gives a detailed slip distribution two areas of high slip correspond to seismologically determined areas of high moment release the prince william sound asperity with average slip of 18 m and the kodiak asperity with average slip of 10 m the average slip on the fault is 8 6 m and the seismic moment is estimated as 6 3 1022 n m or over 75 of the seismic moment determined from long period surface waves

uppermost permian to lower triassic conodont successions from the enshi area western hubei province south china abstract we present recent study results of the lower triassic conodont succession from the ganxi and jianshi areas of enshi city western hubei province south china which were situated on a carbonate ramp at the northeastern margin of the upper yangtze platform therein the uppermost permian to lower triassic succession is well exposed and yielded abundant conodonts a total of nine conodont zones are differentiated 1 clarkina yini zone 2 clarkina meishanensis zone 3 hindeodus changxingensis zone 4 hindeodus parvus zone 5 hindeodus postparvus zone 6 clarkina planata zone 7 neoclarkina aff discreta zone 8 neospathodus dieneri zone and 9 novispathodus waageni zone the ns dieneri m1 ns dieneri m2 and ns dieneri m3 subzones have also been distinguished within the ns dieneri zone and the nv waageni eowaageni and nv waageni waageni subzones are recognizable within the nv waageni zone in jianshi most of the zones occur in succession but the c planata zone is a local ecozone reflecting deeper water biofacies during h postparvus zone time in the jianshi section the permian triassic boundary is placed at bed 136 2 based on the appearance of hindeodus parvus immediately above the disappearance of changhsingian taxa while the induan olenekian boundary iob is drawn at bed 225 40 cm based on the first appearance of nv waageni eowaageni within the upper range of the ns dieneri zone indices the enshi conodont zones overall correlate well with those recognized elsewhere in south china and worldwide

lower middle triassic conodont biostratigraphy of the mingtang section nanpanjiang basin south china abstract the well exposed stratigraphic sequences on the great bank of guizhou gbg in south china provide important information for the understanding of various environmental settings during the permian triassic mass extinction and the subsequent recovery including one of the oldest triassic marginal reef complexes which is viewed as an important indicator of biotic recovery following the end permian mass extinction here we report a systematic conodont study on a newly exposed lower middle triassic section the mingtang section at the margin of the gbg to provide more data for the time scale of the post extinction recovery twenty four species in 11 conodont genera are identified and assigned to hindeodus parvus neoclarkina discreta neospathodus dieneri novispathodus waageni neospathodus triangularis triassospathodus homeri chiosella timorensis nicoraella germanica and nicoraella kockeli zones in ascending order these zones correlate well with the conodont successions in south china and over the world the induan olenekian boundary can be well defined by the first occurrence of novispathodus waageni in the lower middle part of the luolou formation while the early middle triassic boundary was placed at 0 2 m below the top of the luolou formation according to the first occurrence of chiosella timorensis these conodont data suggest that the tubiphytes reef began to recover in the bithynian early middle triassic later than benthonic organisms such as foraminifers and calcareous algae

inversion of long period p waves from great earthquakes along subduction zones abstract long period p waves from subduction zone earthquakes in the moment range from 7 1027to 8 1029dyn cm are analyzed using an iterative deconvolution method in addition to discrete subevents which effectively contribute to the observed seismograms the long period component of the moment rate function is derived with the constraint that the total seismic moment is equal to the moment determined from long period surface waves it is shown that great earthquakes can be described by several subevents with a duration of about 10 s which changes little from earthquake to earthquake in the above moment range the long period component of the moment rate function becomes larger for a greater earthquake the greatest earthquakes of mw 9 additionally involve subevents with another duration scale much longer than 10 s it is also shown that the local stress drop is 1 order of magnitude larger than the stress drop averaged over the entire fault plane the constancy of the local stress drop as well as the average stress drop holds among various magnitudes of earthquakes these observations suggest an essential similarity in the mode of dislocation distribution

carbon isotopic excursions and detailed ammonoid and conodont biostratigraphies around smithian spathian boundary in the bac thuy formation vietnam abstract the smithian spathian boundary is indicated by the first occurrence of the ammonoid tirolites cf cassianus in the olenekian bac thuy formation northeastern vietnam the boundary is intercalated within organic rich dark gray mudstone that accumulated under anoxic to dysoxic conditions in the an chau and nanpanjiang basins on the south china block in lang son area three conodont zones novispathodus ex gr waageni novispathodus ex gr pingdingshanensis and icriospathodus collinsoni are recognized in the formation the smithian spathian boundary is intercalated within n ex gr pingdingshanensis conodont zone the positive excursion in 13c with values increasing from around 2 3 to 5 7 was recorded in the uppermost smithian xenoceltites variocostatus ammonoid beds and n ex gr pingdingshanensis conodont zone the 13c values decrease across the smithian spathian boundary these 13c isotopic patterns are correlated with well known positive excursions around the smithian spathian boundary globally

deformation of the kenai peninsula alaska crustal deformation on the kenai peninsula in southern alaska has been studied using data obtained from global positioning system gps measurements in 1993 and 1995 and leveling observations in 1964 immediately after the prince william sound earthquake this analysis shows that the kenai peninsula has experienced as much as 900 mm uplift during the past 3 decades and that the uplift forms an 125 km wide elongate dome with its major axis trending southwest to northeast following the trend of the major tectonic features of the region the averaged uplift rate between 1964 and 1995 is as high as 30 mm yr 1 although the current uplift rate may be substantially lower the gps measurements cast further doubt on previously suspect tide gauge data for nikiski alaska which indicated rapid postseismic uplift at this site located in northwest kenai peninsula adjacent to cook inlet examination of the three dimensional gps data indicates that the eastern kenai peninsula is currently undergoing significant sse to nnw contraction in response to north american pacific plate convergence the horizontal velocities are consistent with the predictions of an elastic half space model for the interseismic deformation this result taken in combination with the small changes in uplift between 1993 and 1995 suggests that most of the present deformation is due to steady plate convergence rather than transient postseismic rebound

a smithian early triassic ichnoassemblage from lichuan hubei province south china implications for biotic recovery after the latest permian mass extinction abstract a late smithian ichnoassemblage is reported from the lower triassic succession from the lichuan section western hubei province south china this ichnoassemblage comprises 13 ichnogenera which include simple horizontal traces cochlichnus cosmorhaphe didymaulichnus gordia circulichnis and planolites vertical traces arenicolites laevicyclus oblique or horizontal branching traces palaeophycus slightly complex burrow networks thalassinoides and treptichnus and grazing traces cosmorhaphe and gyrochorte these traces are also categorized into fodinichnia domichnia pascichnia and repichnia ethologic types suggesting a fairly high degree of behavioral complexity of these the fodinichnia traces are most abundant the ichnoassemblage horizons usually have rather high ichnofabric indices ii reaching ii 4 5 bedding plane coverage is up to 70 90 resulting in high bedding plane bioturbation index as well bpbi 4 5 the lichuan ichnoassemblage traces have mean and maximum diameters of 4 8 mm and 9 mm respectively n 342 the traces penetrate to a depth of up to 30 mm into the sediment with an average depth of penetration of 15 mm indicating third to fourth tiering levels 3 4 overall the lichuan ichnofauna shows an abrupt increase in ichnodiversity burrow width behavioral complexity and ecologic tiering level which are indicative of recovery stages of 2 3 in the late smithian when compared to five coeval ichnoassemblages from other sections in south china yashan susong daxiakou gaimao and tianshengqiao and coeval ichnoassemblages from elsewhere northern italy western australia western us the lichuan trace fossil assemblage reaches similar level of diversity during this time interval paleoenvironmental analysis indicates that the late smithian recovery pulse is typically confined to the offshore transition setting whereas more distal zones record much lower levels of recovery therefore time and environmental conditions were the two crucial factors controlling the rate and degree of recovery of trace making organisms in the aftermath of the latest permian mass extinction

the smithian spathian boundary late early triassic a review of ammonoid conodont and carbon isotopic criteria abstract the transition from the smithian substage to the spathian substage of the olenekian stage of the late early triassic was a critical time marked by a series of biological and environmental changes during the multimillion year recovery interval following the end permian mass extinction however the smithian spathian boundary ssb does not yet have an agreed definition a shortcoming that complicates high resolution analysis of events during the smithian spathian transition here we review key biostratigraphic i e ammonoid and conodont studies of the smithian and spathian substages in historically important regions e g the canadian arctic for the boreal realm western north america for the eastern panthalassic ocean and more recently re studied locations e g pakistan and india in the southern tethys south china in the eastern tethys as well as the carbon isotope chemostratigraphy of 29 major smithian spathian sections globally key ammonoid genera e g wasatchites anasibirites glyptophiceras and xenoceltites of the late smithian and bajarunia tirolites and columbites of the early spathian conodont species e g scythogondolella milleri novispathodus waageni and borinella buurensis of the late smithian and triassospathodus hungaricus neogondolella aff sweeti and icriospathodus spp of the early spathian and carbonate carbon isotope excursions provide appropriate markers for constraining the ssb use of the first occurrence of the conodont novispathodus pingdingshanensis as a potential marker of the ssb is also discussed based on correlations of biostratigraphic and carbon isotope data globally we propose to revise previous placements of the ssb transition in some sections finally we show that the smithian thermal maximum stm herein named was middle smithian in age and not correlative with the ssb as inferred in some earlier studies and that the ssb coincided with a subsequent major global cooling event

the rupture process and tectonic implications of the great 1964 prince william sound earthquake we have determined the rupture history of the march 28 1964 prince william sound earthquake m w 9 2 from long period wwssn p wave seismograms source time functions determined from the long period p waves indicate two major pulses of moment release the first and largest moment pulse has a duration of approximately 100 seconds with a relatively smooth onset which reaches a peak moment release rate at about 75 seconds into the rupture the second smaller pulse of moment release starts at approximately 160 seconds after the origin time and has a duration of roughly 40 seconds because of the large size of this event and thus a deficiency of on scale digitizable p wave seismograms it is impossible to uniquely invert for the location of moment release however if we assume a rupture direction based on the aftershock distribution and the results of surface wave directivity studies we are able to locate the spatial distribution of moment along the length of the fault the first moment pulse most likely initiated near the epicenter at the northeastern down dip edge of the aftershock area and then spread over the fault surface in a semi circular fashion until the full width of the fault was activated the rupture then extended toward the southwest approximately 300 km ruff and kanamori 1983 the second moment pulse was located in the vicinity of kodiak island starting at 500 km southwest of the epicenter and extending to about 600 km although the aftershock area extends southwest past the second moment pulse by at least 100 km the moment release remained low we interpret the 1964 prince william sound earthquake as a multiple asperity rupture with a very large dominant asperity in the epicentral region and a second major but smaller asperity in the kodiak island region

quantitative stratigraphic correlation of the lower triassic in south china based on conodont unitary associations abstract unitary association method uam analyses of conodont faunas from 28 sections spanning the biggest phanerozoic end permian mass extinction and significant global environmental and ecosystem perturbations during the succeeding early triassic are presented based on 72 conodont species 26 unitary association zones uazs are established for the latest permian to earliest middle triassic of south china these uazs provide quantitative high resolution tools to correlate sequences in the early triassic of south china and to compare and test high resolution conodont biostratigraphy based on interval conodont zones developed over the past three decades our quantitative analyses provide insights on ongoing debates relating to the first appearance datum fad of the conodont hindeodus parvus which is used to place and subsequently correlate the golden spike defining the base of the triassic permian triassic boundary at the base of bed 27c at the gssp meishan d section previous proposals that suggested potential earlier occurrences of h parvus below its fad at meishan section are not supported by our results in deep water sections the first occurrence fo of h parvus lies at the base of uaz 5 at the bianyang section while it lies within uaz 6 at the meishan section this indicates that the earliest occurrence of h parvus in south china is in the bianyang section but this conclusion needs further testing due to the reliance on spot data by the uam anomalously high occurrences of hindeodus in the mingtang section close to the bianyang section further suggests that the bianyang mingtang area may have provided a temporally extended habitable zone for anchignathodontid conodonts stage boundaries currently proposed or established using interval conodont zones locate within or between uazs and are difficult to correlate with carbon isotope curves uazs are useful in helping to define gssps by recognizing which correlations are most robust and in the selection of the most appropriate species and level for gssps

stress pattern in the double seismic zone beneath cook inlet south central alaska abstract relocation of south central alaskan earthquakes recorded by the regional seismograph network using the joint hypocenter determination method revealed a double seismic zone in the underthrusting pacific plate beneath the cook inlet area the lower zone is separated from the upper one by a decrease in seismic activity within a 5 10 km wide band and extends from a depth of 50 km to about 90 km stress tensor inversion for earthquakes in the upper and lower zones shows different stress regimes in the upper zone minimum principal stress is oriented in the down dip direction and maximum principal stress is normal to the wadati benioff zone wbz in the lower zone both maximum and minimum principal stresses are horizontal and rotated by 40 60 from the down dip direction of the wbz below 80 90 km depth stress tensor inversion results show down dip orientation of the minimum principal stress and the maximum stress aligned in the direction of convergence of pacific plate

geochemical evidence from bio apatite for multiple oceanic anoxic events during permian triassic transition and the link with end permian extinction and recovery abstract a detailed 20 myr redox history of permian to triassic oceans changhsingian to carnian stages has been constructed using ce anomaly ce and th u ratios from conodont albid crown apatite material the results show that the well established phenomenon of intense ocean anoxia coincident with the end permian mass extinction is faithfully recorded in conodont ce and th u data extending this conodont redox record shows that end permian anoxia persisted possibly into the earliest dienerian stage and that two intense oceanic anoxic events also occurred later in the early triassic earliest smithian earliest spathian and middle spathian followed by a weaker manifestation of anoxia in the anisian stage seen in ce data marine benthic radiation following the end permian mass extinction began after the smithian earliest spathian anoxic event suggesting a suppression of evolution prior to this due to these inimical conditions the failure of the middle spathian anoxic event to retard the evolutionary rebound implies shallow shelf seas remained well ventilated at this time even if the oceans did not other attributes of the early triassic record also closely coincide with redox fluctuations phases of anoxia intensification saw the proliferation of microbial carbonates and major negative carbon isotope swings that can be attributed to chemocline shallowing causing alkalinity pulses and enrichment in light remineralised carbon and or indicate a trigger meachnaims related to increased fluxes of light c from siberian volcanic sources

lower triassic conodont sequence in chaohu anhui province china and its global correlation abstract the early triassic paleogeographical setting of the chaohu section in china was in a deep part of the yangtze platform and this has resulted in a rather complete lower triassic sequence with rich ammonoid and conodont successions three lower triassic sections west pingdingshan north pingdingshan and south majiashan have been sampled in detail for a systematic conodont study eight conodont zones are recognized in ascending order these are the zones of hindeodus typicalis neogondolella krystyni neospathodus kummeli neospathodus dieneri neospathodus waageni neospathodus pingdingshanensis neospathodus homeri and neospathodus anhuinensis these are correlated with the sequences in north america and other areas of the world the succession provides a good basis for the definition of the global stratotype of the induan olenekian boundary gssp which has been proposed at the base of the neospathodus waageni zone in west pingdingshan seven new species are introduced neospathodus chaohuensis n chii n concavus n eotriangularis n pingdingshanensis n posterolongatus n tongi a new subspecies n waageni eowaageni and three morphotypes of n dieneri

changes in crustal seismic deformation rates associated with the 1964 great alaska earthquake we calculated seismic moment rates from crustal earthquake information for the upper cook inlet region including anchorage alaska for the 30 yr prior to and 36 yr following the 1964 great alaska earthquake our results suggest over a factor of 1000 decrease in seismic moment rate in units of dyne centimeters per year following the 1964 mainshock we used geologic information on structures within the cook inlet basin to estimate a regional geologic moment rate assuming the structures extend to 30 km depth and have near vertical dips the geologic moment rates could underestimate the true rates by up to 70 since it is difficult determine the amount of horizontal offset that has occurred along many structures within the basin nevertheless the geologic moment rate is only 3 7 times lower than the pre 1964 seismic moment rate suggesting the 1964 mainshock has significantly slowed regional crustal deformation if we compare the geologic moment rate to the post 1964 seismic moment rate the moment rate deficit over the past 36 yr is equivalent to a moment magnitude 6 6 7 0 earthquake these observed differences in moment rates highlight the difficulty in using seismicity in the decades following a large megathrust earthquake to adequately characterize long term crustal deformation

mapping the megathrust beneath the northern gulf of alaska using wide angle seismic data in the northern gulf of alaska and prince william sound we have used wide angle seismic reflection refraction profiles earthquake studies and laboratory measurements of physical properties to determine the geometry of the prince william and yakutat terranes the aleutian megathrust and the subducting pacific plate in this complex region the yakutat terrane is underthrust beneath the prince william terrane and both terranes are interpreted to be underlain by the pacific plate wide angle seismic reflection refraction profiles recorded along five seismic lines are used to unravel this terrane geometry modeled velocities in the upper crust of the prince william terrane to 18 km depth agree closely with laboratory velocity measurements of orca group phyllites and quartzofeldspathic graywackes the chief components of the prince william terrane to hydrostatic pressures as high as 600 mpa 6 kbar a landward dipping reflector at depths of 16 24 km is interpreted as the base of the prince william terrane this reflector corresponds to the top of the wadati benioff zone seismicity and is interpreted as the megathrust immediately beneath the megathrust is a 4 km thick 6 9 km s refractor which we infer to be the source of a prominent magnetic anomaly and which is interpreted by us and previous workers to be gabbro in eocene age oceanic crust of the underthrust yakutat terrane wide angle seismic data magnetic anomaly data and tectonic reconstructions indicate that the yakutat terrane has been underthrust beneath the prince william terrane for at least a few hundred kilometers wide angle seismic data are consistent with a 9 to 10 landward dip of the subducting pacific plate beneath the outer shelf and slope distinctly different from the inferred average 3 to 4 dip of the overlying 6 9 km s refractor and the wadati benioff seismic zone beneath the inner shelf our preferred interpretation of the geophysical data is that one composite plate composed of the pacific plate of a fairly uniform thickness and the yakutat plate of varying thickness is subducting beneath southern alaska

the lower triassic sulphur mountain formation in the wapiti lake area lithostratigraphy conodont biostratigraphy and a new biozonation for the lower olenekian smithian earth science sector ess contribution 20080714 the sulphur mountain formation in the wapiti area is subdivided into the phroso meosin mountain new and vega members which collectively span much of the lower triassic the smithian conodont faunas are particularly well developed and form the basis of three partly new conodont zones and two new subzones the lachrymiformis zone meeki zone and mosheri zone with the last subdivided into the phryna and milleri subzones an informal lowermost smithian nepalensis interval is introduced although it has yet to be found in the area the phroso member is latest griesbachian dienerian and in its uppermost part smithian specifically the lachrymiformis and meeki zones these are shown to be equivalent to the euflemingites romunduri ammonoid zone the meosin mountain member is assigned to the meeki zone in its lower part and the phryna subzone of the mosheri zone in its upper part at least the upper part of the mosheri zone is equivalent to the anawasatchites tardus ammonoid zone the mackenzie dolomit

coseismic slip in the 1964 prince william sound earthquake a new geodetic inversion the 1964 prince william sound earthquake march 28 1964 m w 9 2 caused crustal deformation over an area of approximately 140 000 km 2 in south central alaska in this study geodetic and geologic measurements of this surface deformation were inverted for the slip distribution on the 1964 rupture surface previous seismologic geologic and geodetic studies of this region were used to constrain the geometry of the fault surface in the kodiak island region 28 rectangular planes 50 by 50 km each oriented 218 with a dip varying from 8 nearest the aleutian trench to 9 below kodiak island define the rupture surface in the prince william sound region 39 planes with variable dimensions 40 by 50 km near the trench 64 by 50 km inland and orientation 218 in the west and 270 in the east were used to approximate the complex faulting prior information was introduced to constrain offshore dip slip values the strike slip component and slip variation between adjacent planes our results suggest a variable dip slip component with local slip maximums occurring near montague island up to 30 m further to the east near kayak island up to 14 m and trenchward of the northeast segment of kodiak island up to 17 m a single fault plane dipping 30 corresponding to the patton bay fault with a slip value of 8 m modeled the localized but large uplift on montague island the moment calculated on the basis of our geodetically derived slip model of 5 0 1029 dyne cm is 30 less than the seismic moment of 7 5 x 1029 dyne cm calculated from long pe riod surface waves kanamori 1970 but is close to the seismic moment of 5 9 1029 dyne cm obtained by kikuchi and fukao 1987

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

seismicity of the kodiak island region 1964 2001 and its relation to the 1964 great alaska earthquake earthquake relocation first motion and waveform modeling studies of m 5 5 earthquakes are used to examine the seismicity associated with the kodiak island region since the 1964 great alaska earthquake our results indicate that the most intense seismicity and moment release in this region occurred within the pacific plate and along the plate interface of the southwestern edge of the kodiak segment where slip during the 1964 mainshock was less than 5 m few earthquakes have occurred within the north american plate the intense seismicity correlates well with the northern edge of a zone of high plate interface coupling detected by global positioning system geodesy studies our studies suggest that during 1964 1974 faulting within the pacific plate was characterized by normal and normal oblique faulting however since 1974 reverse oblique faulting has become more common in the pacific plate seismic moment release has been over 6 times greater in the kodiak region than in the prince william sound cook inlet region during the past 37 years unlike the prince william sound region there is also a lack of down dip migration of seismicity since 1964 manuscript received 23 october 2001

recovery pattern of brachiopods after the permian triassic crisis in south china in south china the changhsingian brachiopods are extraordinarily abundant and diverse comprising 468 species in 144 genera however approximately 91 of brachiopod species were eliminated during the permian triassic p tr mass extinction event brachiopods in the aftermath of the p tr mass extinction were extremely rare with only one opportunistic taxon lingulida occasionally found in the griesbachian and smithian at a high abundance species diversity of articulated brachiopods in the early griesbachian late griesbachian dienerian and smithian are 35 3 2 and 0 respectively although a few of mesozoic type species occurred in the griesbachian dienerian and smithian a marked diversification of brachiopods occurred in the spathian and early anisian and was characterised by 9 and 17 mesozoic type species respectively the diversification of brachiopods in the spathian and early anisian coincides with the contemporaneous expansion of the refuge zone suggesting that the improvement of marine environmental conditions e g lethally hot temperature and anoxic seawater played a key role in brachiopod recovery after the p tr mass extinction

earthquakes in the pamplona zone yakutat block south central alaska the pamplona zone is a region of complex deformation and moderate seismicity located within the yakutat block a region that has been relatively aseismic since a series of large m 7 8 earthquakes in 1899 in 1970 a sequence of moderate to large sized earthquakes occurred within the pamplona zone largest event of mw 6 7 together with a mw 6 1 event in 1958 these events are the only m 5 5 events known to have occurred in the pamplona region since 1900 thus these events give important information on internal deformational processes within the yakutat block waveform modeling of three earthquakes in april 1970 showed rupture complexity along low angle thrust faults focal depths indicate that two of the events occurred above the wrangell aleutian megathrust while the largest event may have occurred on the megathrust events in 1958 and february 1970 indicate that deformation within the western pamplona zone is occurring along high angle 60 faults with reverse oblique motion we believe the pamplona spur the easternmost part of the pamplona zone may have behaved as an asperity during the 1899 sequence the location of the spur may be influenced by a north south trending fault zone in the subducting pacific plate that appears to be responsible for the 1987 1992 gulf of alaska sequence occurring 50 to 200 km south of the pamplona zone

terrestrial marine teleconnections in the collapse and rebuilding of early triassic marine ecosystems abstract the latest permian mass extinction lpe just prior to the permian triassic boundary at 252 ma resulted in the disappearance of 90 of skeletonized marine taxa and the replacement of the paleozoic fauna by the modern fauna in the immediate aftermath of the extinction shallow marine ecosystems were dominated by microbial communities and diminutive disaster taxa lilliput faunas and the post crisis period in general was characterized by high abundance low diversity marine communities occupying a reduced ecological space the recovery of marine ecosystems was a protracted process lasting throughout the 5 myr long early triassic some clades failed to recover and subsequently went extinct dead clades walking while others recovered only to suffer secondary crises during the early triassic profound environmental changes accompanied these biotic developments deep oceans experienced sustained hypoxia or anoxia for at least several million years following the boundary event anoxia was also widespread in shallow marine areas especially at the time of the lpe but it was more episodic and abated more rapidly than in the deep ocean making it an unlikely factor in the delayed recovery of early triassic marine ecosystems the development of anoxia was due at least in part to a sharp temperature rise following the lpe but may have been stimulated by changes in marine nutrient inventories and productivity rates as well these conditions may have been the result of a concurrent increase in subaerial weathering rates that was sustained into the early triassic in addition to increasing nutrient fluxes to marine areas rapid weathering caused a massive influx of sediment to shallow marine systems subjecting marine biotas to siltation stress this scenario implies close teleconnections between terrestrial and marine environments during the permian triassic boundary crisis with perturbations of the terrestrial realm contributing to the marine crisis

crustal structure beneath exposed accreted terranes of southern alaska summary the crustal structure beneath the exposed terranes of southern alaska has been explored using coincident seismic refraction and reflection profiling a wide angle reflector at 8 9 km depth at the base of an inferred low velocity zone underlies the peninsular and chugach terranes appears to truncate their boundary and may represent a horizontal decollement beneath the terranes the crust beneath the chugach terrane is characterized by a series of north dipping paired layers having low and high velocities that may represent subducted slices of oceanic crust and mantle this layered series may continue northward under the peninsular terrane earthquake locations in the wrangell benioff zone indicate that at least the upper two low high velocity layer pairs are tectonically inactive and that they appear to have been accreted to the base of the continental crust the refraction data suggest that the contact fault between two similar terranes the chugach and prince william terranes is a deeply penetrating feature that separates lower crust deeper than 10 km with paired dipping reflectors from crust without such reflectors

a comprehensive study of the seismicity of the kenai peninsula cook inlet region south central alaska abstract we compare 30 yr of background seismicity of the kenai peninsula cook inlet region extending from eastern prince william sound kayak island to west of the cook inlet volcanic arc to potential field gravity magnetics tomographic global positioning system geodesy and geologic information to better determine factors controlling seismicity we also compare the occurrence of m w 5 events over the past 80 100 yr to background seismicity in an effort to determine how reflective background seismicity is of the regional seismic hazard our results indicate that contrasts in upper plate rheology leading to changes in density magnetic susceptibility and velocity of the upper plate serve to concentrate seismicity the southwestern edge of the subducting yakutat microplate has a strong influence on both upper and lower plate seismicity density and velocity contrasts also indicate changes in lower plate rheology that influence the location of deeper 30 km seismicity and the occurrence of a double seismic zone within the subducting pacific plate

middle triassic anisian diversified bivalves depositional environments and bivalve assemblages in the leidapo member of the qingyan formation southern china abstract the middle triassic anisian leidapo member of the qingyan formation which crops out in southwestern china consists of basin floor and slope deposits with abundant benthic fossils and records two transgressions and one regression the well preserved bivalves are grouped into four assemblages the allochthonous cassianella elegantinia and protostrea cassianella assemblages as well as the autochthonous palaeonucula assemblage are found in slope deposits the allochthonous assemblages exhibit several modes of occurrence in sediment gravity flow deposits the parautochthonous posidonia assemblage is preserved in slope and basin deposits the genus level compositions of these bivalve assemblages are similar to those from the early carnian of tethyan europe it is probable that a significant diversification of bivalves took place in the anisian

seismic potential of the queen charlotte alaska aleutian seismic zone the 5000 km long queen charlotte alaska aleutian seismic zone is subdivided into 17 unequally sized segments their boundaries are delineated based on the prior distribution of large and great earthquakes the 17 segments are chosen to represent areas likely to be ruptured by characteristic earthquakes this term usually implies repeated breakage of a plate boundary segment by either a large or great earthquake whose source dimensions remain consistent from cycle to cycle this definition does not exclude the possibility that occasionally adjacent characteristic earthquake segments may break together in a single giant event that is larger than the characteristic size outlined conversely a segment can also sometimes break in a series of smaller ruptures formal computations of the conditional probabilities for future large and great earthquakes in the 17 segments of the queen charlotte alaska aleutian seismic zone are based on the following data sets and findings 1 recurrence intervals from historic and geologic data 2 direct recurrence time estimates based on rates of relative plate motion and the size or displacement of the most recent characteristic event in each segment and 3 the application of a lognormal distribution of recurrence times for large and great earthquakes results of these computations indicate seven areas that have high i e 60 conditional probabilities for the recurrence of either large or great earthquakes within the next 20 years 1988 2008 these areas include cape st james yakataga the shumagin islands unimak island and the fox delarof and near islands segments of the aleutian arc when a shorter time interval is considered 1988 1998 those segments more likely to rupture in large ms 7 7 7 rather than great earthquakes have a high conditional probability these areas include the unimak fox and delarof islands segments the largest uncertainties in these forecasts stem from the short historic record providing a single recurrence time estimate for some segments or widely varying estimates for others from the unknown importance of aseismic slip and from a vague definition of characteristic earthquake size in fact characteristic earthquake size may not be a time invariant quantity

relocation of earthquakes in the cook inlet area south central alaska using the joint hypocenter determination method abstract the joint hypocenter determination jhd method was used to relocate 1604 earthquakes that occurred during 1988 to 1993 in the wadati benioff zone wbz beneath the cook inlet in south central alaska the study utilizes both p and s wave arrivals recorded by a recently improved regional seismic network and it provides an improvement over previous studies the jhd locations of the events allowed improved delineation of the geometry of the subducted slab and the detection of a double seismic zone within the wbz in the 40 to 100 km depth range the jhd station corrections obtained correlate with the major surface geological features in the study area slow velocity sedimentary basins as well as with crustal and mantle structure high velocity subducting slab and low velocity anomalies beneath the active volcanoes to investigate the dependence of the jhd relocation procedure on factors such as the hypocentral depths of the events used the velocity model the p s ratio and random and systematic errors in travel time readings synthetic travel times were calculated using an exact raytracing technique a three dimensional tomographic p wave velocity model the present network configuration and the actual seismicity distribution then the synthetic events were located with the jhd algorithm the synthetic experiments showed that the jhd procedure is rather insensitive to the choice of plane layered velocity model and p s ratio preserves relative hypocenter locations well and can handle systematic and large random reading errors effectively

seismicity of the prince william sound region for over thirty years following the 1964 great alaskan earthquake in this paper we present results of body wave form modeling of 19 earthquakes generally m b 5 7 occurring from 1964 to 1983 in the vicinity and down dip of the large asperity within the prince william sound region that ruptured in 1964 these data are supplemented with source parameters from studies of more recent post 1980 events our results suggest that moderate earthquakes which occurred in the region between 1964 and 1984 were predominantly located in the vicinity of the prince william sound asperity and could be assigned to two groups the first group consists of events occurring above the plate interface within prince william sound along reverse faults or low angle thrusts the second group occurs at 35 to 60 km depth in the region north of prince william sound and represents normal to normal oblique faulting within the subducted pacific crust or upper mantle these earthquakes occur below the northern edge of the 1964 asperity in a region where the subducting plate undergoes a rapid change in strike and dip a third group of events occurs in cook inlet well down dip of the 1964 asperity and below the plate interface these events exhibit a variety of mechanisms and many at depths of 50 to 70 km may be associated with complexities in the shape of the downgoing slab most of the cook inlet events occurred after 1984 whereas a few events of similar magnitude have occurred in the vicinity of the prince william sound asperity since 1984

cisuralian guadalupian conodont sequence from the shaiwa section ziyun guizhou south china abstract a sequence of successive conodont datums and zones for the cisuralian and guadalupian series for the south china region of the equatorial warm water province is proposed based on the shaiwa section ziyun guizhou the seven conodont zones in ascending order are sweetognathus aff whitei zone of artinskian stage a set of three new kungurian zones of sweetognathus guizhouensis zone sweetognathus subsymmetricus zone mesogondolella nashuiensis zone the mesogondolella idahoensis lamberti zone of uppermost kungurian the guadalupian zones of jinogondolella aserrata followed by jinogondolella postserrata the base of the kungurian stage is tentatively defined by the first occurrence of s guizhouensis 174 5 m above the base of the sidazhai formation this suite of conodont datums and zones will help to improve the global correlations of permian strata of the kungurian stage

a proposed ontogenesis and evolutionary lineage of conodont eurygnathodus costatus and its role in defining the base of the olenekian lower triassic abstract the early triassic is a critical interval recording episodic climatic environmental and biotic events after the end permian mass extinction a precise global timescale for this epoch is essential to understand the sequence of events during this crisis the undefined induan olenekian stage boundary iob long disputed is a crucial element in providing a high resolution chronostratigraphic framework for the lower triassic here we report new conodont lineages from the jianshi section south china that may contribute to the definition of the iob in jianshi within a succession of nine conodont zones a possible iob is placed at bed 225 40 cm based on the first occurrence fo of conodont subspecies novispathodus waageni eowaageni new collections include a total of 99 well preserved eurygnathodus costatus specimens from bed 225 to bed 241 and a single occurrence of eu hamadai from bed 226 the fo of eu costatus occurs in bed 225 10 cm 30 cm below n w eowaageni the reconstructed ontogenetic series of eurygnathodus costatus involves four growth stages a b c d based on characteristics of the denticles nodes or ridges platform basal cavity margin profile and crimp these preserve ancestral characters that suggest a novel origin for the evolutionary lineage of the genus namely from sweetospathodus kummeli eurygnathodus costatus eu sp d eurygnathodus hamadai seven additional informal species of eurygnathodus are differentiated as potential biostratigraphic markers the fo of eu costatus may serve as an auxiliary marker for the iob

lower middle triassic conodont biostratigraphy of the qingyan section guizhou province southwest china abstract the middle triassic qingyan formation at its type section the qingyan section of guizhou southwest china yields more than 300 species belonging to 17 fossil groups which mark the radiation of benthic organisms following the end permian mass extinction this study intends to establish a primary conodont biostratigraphical succession through the lower and middle triassic sequence at qingyan to provide a time framework for the understanding of the recovery and radiation process from the mass extinction a total of 30 species in 8 conodont genera are stratigraphically significant and assigned to the neospathodus dieneri neospathodus cristagalli neospathodus waageni neospathodus homeri chiosella timorensis and neogondolella cf bulgarica zones in ascending order most conodont zones correlate well with their counterparts recognized from elsewhere in china and even worldwide the first appearance of ns waageni marks the induan olenekian boundary which is placed at the lower middle part of the luolou formation 121 47 m above the permian triassic boundary the olenekian anisian early middle triassic boundary is here defined by the first occurrence of chiosella timorensis at the base of the qingyan formation although no conodonts retrieved from the upper qingyan formation containing the extraordinarily diverse biota i e the qingyan biota stratigraphical correlation with the neighbouring conodont bearing sections in guizhou and the ammonoid zones suggest that the qingyan biota has an age of early late anisian early middle triassic

three dimensional elastic dislocation modeling of the postseismic response to the 1964 alaska earthquake 1 gps velocity observations from the kenai peninsula and kodiak island alaska display a pattern of spatial variability suggesting the presence of multiple active processes on the underlying pacific north american plate interface velocities of sites on the eastern kenai peninsula and kodiak island are consistent with elastic strain accumulation at the plate interface whereas velocities of sites on the western kenai peninsula and cook inlet are oriented in the opposite direction and suggest an ongoing postseismic response to the 1964 alaska earthquake we can reproduce the observed velocities using a three dimensional elastic dislocation model to estimate the variation in coupling between the pacific and north american plates two different inversion schemes are examined to check the robustness of the results we find that the gps data can be satisfied by the presence of a locked area near southwest prince william sound a locked area near southwest kodiak island and an area of postseismic reverse slip beneath and north of the western kenai peninsula the shallow plate interface trenchward of the western kenai peninsula does not appear to be locked the locked areas correspond to the prince william sound and kodiak island asperities that ruptured in 1964 and the area of postseismic slip lies downdip of the 1964 rupture area the correspondence between the present shallow coupling distribution and the 1964 slip distribution suggests that the locked regions repeat from one earthquake cycle to another

recurrent biotic rebounds during the early triassic biostratigraphy and temporal size variation of conodonts from the nanpanjiang basin south china eleven conodont zones are established for the lower triassic of the motianling section in the nanpanjiang basin south china detailed size measurements on 2244 p1 conodont elements demonstrate dynamic size variation patterns during the early triassic that are calibrated to the early triassic timescale and conodont zonation correlation of conodont size variation with various environmental indicators shows that these size changes are primarily controlled by rapidly changing and episodic environmental conditions and ecological recovery in the aftermath of the end permian mass extinction decreasing size trends occur in the early griesbachian late griesbachian and at the smithian spathian boundary episodes of size increase rebounds occur in the middle griesbachian induan olenekian boundary and middle late spathian the observed temporal size variations indicate that conodont animals were significantly affected by rapidly changing environmental conditions mainly temperature and redox conditions during the early triassic and recurrent size increases rebounds occurred during periods of environmental and climatic amelioration climatic cooling and oxygenation demonstrating a complicated recovery history of marine ecosystems in the aftermath of the largest phanerozoic biotic crisis supplementary material data for all species are available at https doi org 10 6084 m9 figshare c 4528616