age and tectonic setting of the duke island ultramafic intrusion southeast alaska concordant u pb zircon ages on hornblende plagioclase pegmatites and a related granophyre from marginal and roof zones of the duke island ultramafic intrusion and from leucoquartz diorite internal to hornblende clinopyroxenite of nearby mary island cluster between 108 and 111 ma sm nd mineral and bulk rock data from pegmatite and granophyre zircon samples and from wehrlites and clinopyroxenites of the main duke island cumulate sequence are consistent with the consanguinity of the ultramafic cumulates and the zircon bearing feldspathic rocks and with an early cretaceous igneous age for the intrusion wall rocks for the intrusion consist of ordovician silurian amphibolite and greenschist grade metamorphosed plutonic volcanic and minor sedimentary rocks and crosscutting late triassic gabbro diorite of the alexander terrane the duke island ultramafic intrusion formed as a northwest trending elongate funnel shaped stratiform body commensurate with extensional brittle ductile faulting in its roof and adjacent wall rocks intrusion occurred in a basinal setting within the gravina volcanic arc along the cordilleran continental margin during the latter phases of intrusive activity the gravina basin began to close by regional thrust faulting which in the duke island region was west northwest directed the intrusion may have still had local intercumulate liquid upon initiation of thrust faulting it responded first by open folding with incipient crystal plasticity once completely solidified the intrusion behaved like a large augen with ductile deformation concentrated along its margins and within quartzo feldspathic and micaceous members of its wall rock complex much of the intrusion s northern margin behaved as a ductile shear zone serving as a tear fault between thrust plates to the northeast and an oblique thrust complex that roots beneath the southwest margin of the intrusion the intrusion may thus be tectonically transported relative to its original underpinnings north trending high angle faults and parallel fracture cleavage also cut the intrusion in response to axial loading as a result of its initial elongate shape and orientation relative to the thrust kinematics

end permian catastrophe by a bolide impact evidence of a gigantic release of sulfur from the mantle our studies in southern china have revealed a remarkable sulfur and strontium isotope excursion at the end of the permian along with a coincident concentration of impact metamorphosed grains and kaolinite and a significant decrease in manganese phosphorous calcium and microfossils foraminifera these data suggest that an asteroid or a comet hit the ocean at the end of permian time and caused a rapid and massive release of sulfur from the mantle to the ocean atmosphere system leading to significant oxygen consumption acid rain and the most severe biotic crisis in the history of life on earth

carbon isotope stratigraphy across the permian triassic boundary a review abstract the palaeozoic mesozoic transition is marked by distinct perturbations in the global carbon cycle resulting in a prominent negative carbon isotope excursion at the permian triassic p t boundary well known from a plethora of marine and continental sediments potential causes for this negative 13 c trend and their links to the latest permian mass extinction have been intensively debated in the literature in order to draw conclusions regarding causation a general 13 c curve was defined after consideration of all available datasets and with due reference to the biostratigraphic background the most important features of the p t carbon isotope trend are the following the 4 7 13 c decline lasting 500 000 years is gradual and began in the changhsingian at the stratigraphic level of the c bachmanni zone the decreasing trend is interrupted by a short term positive event that starts at about the latest permian low latitude marine main extinction event horizon eh indicating that the extinction itself cannot have caused the negative carbon isotope excursion after this short term positive excursion the 13 c decline continues to a first minimum at about the p t boundary a subsequent slight increase is followed by a second occasionally two peaked minimum in the lower and middle i isarcica zone the negative carbon isotope excursion was most likely a consequence of a combination of different causes that may include 1 direct and indirect effects of the siberian trap and contemporaneous volcanism and 2 anoxic deep waters occasionally reaching very shallow sea levels a sudden release of isotopically light methane from oceanic sediment piles or permafrost soils as a source for the negative carbon isotope trend is questionable at least for the time span a little below the eh and somewhat above the p t boundary

compaction corrected inclinations from southern california cretaceous marine sedimentary rocks indicate no paleolatitudinal offset for the peninsular ranges terrane paleomagnetic data have been used extensively to delineate the terrane displacement and accretion history of the western margin of north america however the anomalously shallow paleomagnetic inclinations used to indicate large scale northward translation might be alternatively interpreted as due to postmagnetization tilting of batholithic rocks and compaction of marine sediments to understand the magnitude of burial compaction effects on the post cretaceous motion history of the peninsular ranges baja borderlands terrane a rock magnetic compaction and paleomagnetic study of the ladd formation and the point loma formation from southern california was conducted the anhysteretic anisotropy of remanence of the characteristic remanence carrying grains and individual magnetic grain anisotropy were used to correct the inclinations of each formation individual magnetic grain anisotropy was determined by both compaction experiments and redeposition of a magnetic separate in a dc magnetic field standard paleomagnetic studies of the units indicated that previous ladd formation results could be reproduced and a correction was made at the sample level we were unable to adequately reproduce earlier results of the point loma formation so the average remanence anisotropy was used to correct the previously reported mean direction the mean inclination of the ladd formation was conected from 46 95 8 to 58 95 4 and the mean inclination of the point loma formation was conected from 39 5 5 4 normal and 36 4 16 6 reversed to 56 0 5 1 normal and 53 0 16 7 reversed these results suggest that the peninsular ranges baja borderland terrane has been part of the western north america since the late cretaceous and that clay containing sedimentary rocks may typically experience from 10 to 15 of inclination shallowing due to burial compaction

paleomagnetism magnetic anisotropy and mid cretaceous paleolatitude of the duke island alaska ultramafic complex we report paleomagnetic results from layered igneous rocks that imply substantial post mid cretaceous poleward motion of the insular superterrane western canadian cordillera and southeast alaska relative to north america the samples studied are from the stratiform zoned ultramafic body at duke island which intruded rocks of the alexander terrane at the south end of the southeastern alaska archipelago at about 110 ma thermal and alternating field demagnetization experiments show that the characteristic remanence of the ultramafic rocks has high coercivity and a narrow unblocking temperature range just below the curie temperature of magnetite this remanence is likely carried by low ti titanomagnetite exsolved within clinopyroxene and perhaps other silicate hosts the duke island intrusion exhibits a well developed gravitational layering that was deformed during initial cooling but below 540 c into folds that plunge moderately to the west southwest the characteristic remanence clearly predates this early folding and is therefore primary the fisher parameter describing the concentration of the overall mean remanence direction improves from 3 to 32 when the site mean directions are corrected by restoring the layering to estimated paleohorizontal all samples exhibit a magnetic anisotropy that is strong but nonuniform in orientation across the intrusion and we show that it has no significant or systematic effect on the site mean directions of remanence at least some of the anisotropy derives from secondary magnetite formed during partial serpentinization the mean paleomagnetic inclination 56 10 corroborates paleomagnetic results from five coeval silicic plutons of the canadian coast plutonic complex to the south and southeast and implies 3000 km 1300 km of poleward transport relative to the north american craton between mid cretaceous and middle eocene time the insular superterrane and coast plutonic complex shared a common paleolatitude history with more poleward transport than coeval inboard terranes

retreat of northern margins of george vi and wilkins ice shelves antarctic peninsula the george vi and wilkins ice shelves are considered at risk of disinteg ration due to a regional atmospheric warming trend on the antarctic peninsula retreat of the northern margin of the george vi ice shelf has been observed previously but the wilkins ice shelf was thought to be stable we investigated the positions of the northern fronts of these shelves from the literature and looked for changes on 1974 landsat and 1992 and 1995 european remote sensing satellite ers synthetic aperture radar images our investigation shows that the northern george vi ice shelf lost a total of 906 km 2 between 1974 and 1992 and an additional 87 km2 by 1995 the northern margin of the wilkins ice shelf lost 796 km2 between 1990 and 1992 and another 564 km2 between 1992 and 1995 armadas of tabular icebergs were visible in front of this shelf in the ers images these two ice shelves mark the southern most documented conspicuous retreat of ice shelf margins

breakup and conditions for stability of the northern larsen ice shelf antarctica the breakup of ice shelves has been widely regarded as an indicator of climate change1 with observations around the antarctic peninsula having shown a pattern of gradual retreat associated with regional atmospheric warming and increased summer melt and fracturing processes2 3 4 5 6 7 8 9 the rapid collapse of the northernmost section of the larsen ice shelf larsen a over a few days in january 1995 indicated that after retreat beyond a critical limit ice shelves may disintegrate rapidly here we use a finite element numerical model that treats ice as a continuum without fracture10 to examine the breakup history2 between 1986 and 1997 of the two northern sections of larsen ice shelf larsen a and larsen b from which we establish stability criteria for ice shelves analysis of various ice shelf configurations reveals characteristic patterns in the strain rates near the ice front which we use to describe the stability of the ice shelf on larsen a only the initial and final ice front configurations show a stable pattern larsen b at present exhibits a stable pattern but if the ice front were to retreat by a further few kilometres it too is likely to enter an irreversible retreat phase

measurements of the cretaceous paleolatitude of vancouver island consistent with the baja british columbia hypothesis a previously unsampled outcrop of gently dipping or flat lying upper cretaceous sedimentary strata in the vancouver island region which contains unaltered aragonitic mollusk fossils yielded a stable remanent magnetization that is biostratigraphically consistent with cretaceous magnetochrons 33r 33n and 32r these results characterized by shallow inclinations indicate an upper cretaceous paleolatitude of about 25 3 degrees north which is equivalent to that of modern day baja california these findings are consistent with the baja british columbia hypothesis which puts the insular superterrane well south of the oregon california border in the late cretaceous

structural correction of paleomagnetic vectors dispersed about two fold axes and application to the duke island alaska ultramafic complex 1 a new analysis of paleomagnetic data from the mid cretaceous 110 ma ultramafic complex at duke island southeast alaska supports large poleward transport of the insular superterrane relative to north america consistent with the baja british columbia hypothesis previous paleomagnetic work has shown that the characteristic remanence of the ultramafic complex predates kilometer scale deformation of the very well developed cumulate layering but that the layering was not horizontal everywhere before the folding it is possible however to estimate paleohorizontal for the duke island ultramafic complex because the postremanence deformation of the intrusion occurred about two well defined and spatially separate fold axes in such a case the tectonically rotated paleomagnetic directions should be distributed along small circles centered on each of the two fold axes the ancient field direction will lie on both small circles and therefore will be identifiable as one of their two intersection points interpreted this way the tectonically rotated remanence of the duke island ultramafic complex defines a mid cretaceous i e ancient field direction that is within 2 of the paleomagnetic direction found by assuming the cumulate layering was initially horizontal despite the paleomagnetic evidence to the contrary and performing the standard structure correction the inferred mid cretaceous paleolatitude of duke island is 21 2 2350 km anomalous with respect to cratonic north america this result is concordant with southerly paleolatitudes determined by many other workers from bedded rocks of terranes farther inboard in the insular and intermontane superterranes

deciphering deformation in ultramafic intrusions via magnetic fabric ams and palaeomagnetic studies savannah ni pge camp nw australia abstract knowledge of the internal architecture of mafic ultramafic intrusions is critical to efficient targeting of magmatic ni pge mineralisation however the visual homogeneity of such rocks in drill core coupled with poor outcrop in many areas can make their structure difficult to decipher using standard techniques in this study we use measurements of anisotropy of magnetic susceptibility ams and remanent magnetisation to examine the structural history of four adjacent temporally equivalent ultramafic intrusions from the east kimberley province nw australia whilst temporally equivalent the intrusions have contrasting shape including bladed dyke sill and stock geometries and are hosted in rocks of contrasting rheology including mafic granulite and meta sedimentary migmatite early palaeomagnetic signatures present at savannah and savannah north originally had shallow nne to ene oriented inclinations consistent with acquisition at low palaeolatitudes at ca 1800 ma however these primary magnetisations were subsequently rotated during the ca 1810 ma mount stafford event and or ca 1400 1200 ma yampi orogeny demonstrating that significant deformation occurred post emplacement magmatic fabrics observed in ams data for savannah savannah north and dave hill all show evidence of ne or sw rotation during the same events however whilst there are similarities in the implied shortening directions across all four intrusions they each preserve a unique deformation style which is attributed to the unique shape of each intrusion coupled with the contrasting rheology of their respective host rocks each intrusion preserves a common dominant palaeomagnetic signature which is consistent with a high grade metamorphic overprint at ca 1200 ma during the latter stages of the yampi orogeny the lack of subsequent rotation of this dominant palaeomagnetic signature demonstrates that the majority of deformation pre dates the yampi event this study demonstrates that even where tectonic conditions are similar that intrusion shape and host rock rheology exert strong control on their deformation style

episodicity of mesozoic terrane accretion along the pacific margin of gondwana implications for superplume plate interactions a review of evidence for deformation and terrane accretion on the late triassic early jurassic margins of pangea and the mid cretaceous margins of the palaeo pacific ocean shows that deformation was global and synchronous with probable superplume events late triassic early jurassic deformation appears to be concentrated in the period 202 197 ma and was coeval with eruption of the central atlantic magmatic province onset of pangaea break up a period of extended normal magnetic polarity and a major mass extinction event all possible expressions of a superplume event mid cretaceous deformation occurred in two brief periods the first from approximately 116 to 110 ma in the west palaeo pacific and the second from roughly 105 to 99 ma in the east palaeo pacific with both events possibly represented in northeast siberia this deformation was coeval with eruption of major oceanic plateaus core complex formation and rifting of new zealand from gondwana the cretaceous normal polarity epoch and a major radiation of flowering plants and several animal groups all linked with the mid cretaceous superplume event a simple unifying mechanism is presented suggesting that large continental or oceanic plates when impacted by a superplume tend to break up reorganize associated with gravitational spreading away from a broad thermally generated topographic high and with a resulting short lived pulse of plate marginal deformation and terrane accretion

climatically induced retreat and collapse of northern larsen ice shelf antarctic peninsula the areal changes of the northern larsen ite shelf lis antarctic peninsula between march 1986 and march 1997 have been analyzed based on synthetic aperture radar images of the european remote sensing satellites ers 1 and ers 2 and on landsat images this analysis is complemented by data on ice motion and surface mass balance which have been obtained during several field campaigns since the early 1980s after a period of retreat coinciding with atmospheric warming and with decreasing net accumulation at the surface due to melt losses the two northernmost sections of lis disintegrated almost completely within a few days in january 1995 recent observations of the ice shelf section north of jason peninsula which is presently the northernmost section of lis show increased summer melt and intensification of the rifting processes probably causing accelerated retreat of this section in the near future the retreat and the disintegration event of lis indicate high sensitivity of ice shelves to prolonged perturbations of the mass balance

test for bias in paleomagnetically determined paleolatitudes from pacific plate deep sea drilling project sediments paleolatitudes determined from paleomagnetic study of azimuthally unoriented sediment cores recovered by deep sea drilling on the pacific plate have been previously used in determining reference poles for the pacific plate apparent polar wander apw path from discordant paleoinclinations and corresponding paleolatitudes determined from these data some workers have inferred tectonic tilting or large horizontal motion of some deep sea drilling sites relative to other parts of the pacific plate here the reliability of these paleolatitudes is evaluated by comparing them with paleolatitudes determined from a pacific plate reference apw path determined from seamount poles skewness and amplitudes of magnetic profiles across magnetically lineated seafloor and paleocolatitudes from azimuthally unoriented basalt cores and from equatorial sediment facies the reference apw path includes a new determination of the early cretaceous pole from several types of paleomagnetic data which agree well with one another sediment paleolatitudes are found to be systematically less southerly than those predicted from the reference apw path a discrepancy that corresponds to inclinations shallower than expected thus most deep sea drilling sediment paleomagnetic paleolatitudes are unreliable and should be omitted from the data used in determining reference apw paths inclination and paleolatitude discrepancies noted in prior studies may be due not to tectonic causes but to shallowly biased inclinations

oxygen isotopic variability associated with multiple stages of serpentinization duke island complex southeastern alaska abstract ultramafic rocks of the duke island complex in southeastern alaska crystallized in a supra subduction zone setting but the serpentinization of olivine bearing rocks involved the incursion of late stage meteoric waters three textural types of serpentine primarily lizardite have been identified which in part reflect progress in reactions during multiple stages of fluid infiltration the overall mesh texture of serpentine has been subdivided into a massive type found in dunites and wehrlites and a dendritic type found in wehrlites and olivine clinopyroxenites serpentine veins represent a late stage in the hydrothermal alteration process both feo contents and 18 o values of the three textural types of serpentine are variable at the centimeter scale magnetite abundance in association with serpentine is also variable with up to 5 vol of magnetite found in samples with dendritic serpentine continued reaction of feo bearing serpentine with fluid appears to control the formation of most magnetite oxygen isotope ratios of the three textural types of serpentine are distinct with the massive variety characterized by 18 o values between 3 and 3 the dendritic variety showing values between 2 and 6 and the veins having the highest values between 4 and 10 although the 18 o values may vary by as much as 5 on the centimeter scale d values tend to show relatively less variation with over 90 of the measured values between 100 and 120 the o and h isotopic values are consistent with the involvement of meteoric water that had undergone variable degrees of isotopic exchange with country rocks prior to reacting with olivine in the duke island complex small scale variability in both serpentine feo content and 18 o values suggests that chemical and isotopic equilibria may have not been attained at larger than centimeter scales oxygen isotopic variability in serpentine produced during relatively low temperature hydrothermal alteration is in large part a function of exchange mediated via fluid flow through microfractures

a compaction correction for the paleomagnetism of the nanaimo group sedimentary rocks implications for the baja british columbia hypothesis 1 a paleomagnetic and magnetic anisotropy study of the late cretaceous northumberland formation on hornby island british columbia was conducted to determine if burial compaction could have caused its anomalously shallow inclinations the shallow nanaimo group inclinations have been used to support the baja british columbia baja bc model of continental dynamics in which superterranes were transported thousands of kilometers northward along the active north american continental margin in the cretaceous a mean of the site means from the northumberland formation is d 5 8 i 50 9 95 7 9 n 8 anisotropy of magnetic susceptibility ams and anisotropy of anhysteretic remanence aar were measured to identify and correct for any inclination shallowing caused by depositional compactional processes both concretion and fine grained rock samples had typical depositional compactional ams and aar fabrics with bedding perpendicular minimum principal axes a revised correction equation was used to account for the effects of either triaxial magnetic fabrics or small angular deviations of principal axes from the bedding plane the average inclination was increased by 9 6 after the compaction correction d 6 1 i 60 5 95 7 1 n 8 and the mean inclination of concretion and fine grained rock sites was significantly steeper than ward et al s 1997 result i 42 5 placing hornby island and the insular superterrane at a paleolatitude of 41 n in the late cretaceous this paleolatitude indicates that baja bc did translate northward since the late cretaceous by about 1600 km but not by the 3500 km previously indicated

facies changes and diagenetic processes across the permian triassic boundary event horizon great bank of guizhou south china a controversy of erosion and dissolution the permian triassic boundary interval in shallow shelf seas of south china shows upper permian limestones overlain by lowermost triassic microbialites global sea level rose across the permian triassic boundary but an irregular top permian erosion surface across a 10 km north south transect of the great bank of guizhou contains evidence of sea level fluctuation the surface represents the event horizon of mass extinction below the biostratigraphic permian triassic boundary defined by first appearance datum of conodont hindeodus parvus an upper permian foraminiferal grainstone beneath this surface contains geopetal sediments etched grains and pendent and meniscus cements interpreted here as vadose however these latter diagenetic processes occurred before the event horizon and were followed by erosion of the final permian surface this erosion cuts previous fabrics but lacks evidence of weathering or bioerosion a few centimetres below is an earlier grainstone that was also eroded but lacks proof of sub aerial processes samples therefore reveal one or possibly two small scale relative sea level changes before the triassic transgression in this area and these may relate to local tectonics the final permian surface is subject to at least four interpretations i sub aerial physical erosion and dissolution by carbon dioxide enriched fresh water or carbon dioxide enriched mixed water prior to triassic transgression ii sub aerial physical erosion overprinted by dissolution related to carbon dioxide enriched sea water in the early triassic transgression iii submarine dissolution affected by acidified sea water due to rapid increase in volcanically derived carbon dioxide and oxidized methane released from marine clathrates iv submarine dissolution due to acid anoxic waters rising across the continental shelf unrelated to atmospheric carbon dioxide or oxidized methane field and petrographic evidence suggests that i is the simplest option and it is possible that ii and iii occurred but none are proved option iv is unlikely given the evidence and modelling of supersaturation of upwelled waters with respect to bicarbonate

coastal and baja california paleomagnetism reconsidered systematic reappraisal of paleomagnetic data from upper mesozoic and lower cenozoic sedimentary rocks and igneous rocks of late mesozoic age in coastal and baja california indicates that pluton tilt and shallowing of paleomagnetic directions by sedimentary compaction resolve observed discordances with the north american apparent polar wander apw path when the best available reference paleopoles are used for comparison the hypothesis of major tectonic transport in excess of distances inherent in current models for evolution of the san andreas transform system is unnecessary and in conflict with geologic observations fresh insights derived from recent data sets and improved analysis include the following 1 the limited paleomagnetic data recording primary remanence for upper jurassic and lower cretaceous volcanic rocks in coastal california are concordant with the north american apw path 2 the tilt of the peninsular ranges batholith inferred from paleobarometric data eliminates its declination discordance and reduces its inclination discordance to a level where ovals of confidence for observed and expected paleomagnetic directions overlap 3 key cretaceous and paleogene red bed successions on the salinian block of coastal california and in baja california have yielded concordant paleolatitudes 4 the discordances of different apparent paleolatitudes inferred from cretaceous and paleogene marine sedimentary strata lie within a range that can be attributed to compaction shallowing on the basis of both experimental information and observations from elsewhere 5 turbidites are more susceptible to compaction shallowing than shelf and deltaic strata 6 the uniform rotation of paleomagnetic directions inferred previously for peninsular california is not supported by the full array of data now available from multiple localities 7 basement ties of the salinian block in california and of the baja california peninsula to the continental interior preclude any hypothesis for tectonic transport much in excess of san andreas transform slip

extent and duration of antarctic surface melting the extent and duration of surface melting on the antarctic ice shelves and margins of the antarctic ice sheet are derived from satellite passive microwave data for 1978 87 the occurrence of surface melting in daily maps of t b is indicated by a marked increase in microwave brightness temperature t b which is caused by moisture in the near surface firn t b increases of more than 30 deg above the annual mean t b are chosen to indicate melting most antarctic surface melting occurs during december and january the observed melting is correlated with regional air temperatures but some melt patterns also appear to be related to katabatic wind effects the correlations suggest that the surface melting in antarctica increases about 3 5 10 6 d km 2 per degree of summer temperature increase the surface melt index duration times area of melting calculated for antarctica is 24 10 6 d km 2 averaged over nine summers the observed inter annual and regional variability is large surface melting was most extensive during the 1982 83 summer 36 10 6 d km 2 and least extensive during the 1985 86 summer 15 10 6 d km 2 the data indicate a decline in surface melting over the 9 years but meaningful inferences regarding trends in surface melting are precluded by the large inter annual variability

understanding antarctic peninsula precipitation distribution and variability using a numerical weather prediction model daily precipitation fields and annual means from the european centre for medium range weather forecasts re analysis exercise are used to examine the distribution and variability of precipitation across the antarctic peninsula the annual mean precipitation field from the model agrees well with the available ice core data and suggests that the maximum accumulation for the area is on the western side of the barrier at about the 200 m level where the annual total is close to 1 3 m w e the peninsula is shown to be a very effective barrier to the zonal movement of precipitati ng weather systems which results in quite different atmospheric flow regimes being responsible or significant precipitation events on either side of the divide frontal depressions are the primary source of large daily snowfall totals on both sides of the peninsula on the southern coast of the bellingshausen sea major snowfall events are often linked to strong northerly flow when the atmospheric circulation is blocked predominantly northerly flow is also responsible for significant snowfall on the ronne ice shelf which often occurs in association with lee cyclogenesis events to the east of the peninsula

the prelude of the end permian mass extinction predates a postulated bolide impact the mass extinction at the permian triassic boundary ptb is said to have been abrupt and probably caused by an extraterrestrial impact however evidence from the global stratotype section and point gssp of the base of the induan at meishan china shows that the biotic crisis began prior to the level in beds 25 and 26 at which the postulated impact event occurred evidence of such an earlier biotic crisis occurs in other sections in south china and in central and western tethyan regions this event is characterized by the extinction of a range of faunas including corals deep water radiolarians most fusulinids and pseudotirolitid ammonoids and many permian brachiopods in all sections this extinction level is usually a few decimeters to meters below that of the main mass extinction in the event beds 25 and 26 at meishan and their correlatives elsewhere this earlier extinction event happened before the postulated bolide impact at the level of beds 25 and 26 and constrains interpretation of the mechanisms that brought about this greatest mass extinction

size variation of conodont elements of the hindeodus isarcicella clade during the permian triassic transition in south china and its implication for mass extinction abstract based on the analysis of thousands of conodont specimens from the permian triassic p t transition at meishan the gssp of p t boundary and shangsi sections in south china this study investigates the size variation of hindeodus and isarcicella p1 elements during the mass extinction interval the results demonstrate that hindeodus isarcicella underwent 4 episodes of distinct size reduction during the p t transition at the meishan section and 2 episodes of size reduction in the earliest triassic at shangsi the size reductions at meishan took place at the junctions of beds 24d 24e 25 26 27b 27c and 28 29 and at the junctions of beds 28 29c and 30d 31a at shangsi the two earliest triassic size reduction episodes were correlative between the two sections these changes coincide with some important geological events such as eustatic sea level changes anoxic events carbon isotope oscillations miniaturization of brachiopods and microbial changes through detailed investigation of the palaeoenvironment and the palaeoecology of hindeodus isarcicella the authors propose that the main causes of the size reduction was a sharp decline of food availability because of the mass extinction and the anoxic event during the p t transition the pattern of size reduction supports suggestions that the end permian mass extinction was multi episodal consisting of 3 extinction events rather than a single catastrophic event

major dextral transcurrent displacements along the northern rocky mountain trench and related lineaments in north central british columbia the northern rocky mountain trench and a number of other prominent lineaments along and east of the eastern margin of the intermontane belt mark faults along which dextral transcurrent movements have been dominant offsets of shelf to off shelf facies boundaries in lower paleozoic rocks indicate a cumulative displacement of at least 750 km and probably 900 km within the system of faults related to those in the northern rocky mountain and the tintina trenches farther west another system of faults appears to offset plutons and stratigraphic assemblages along the eastern margin of the intermontane belt by as much as 300 km these faults including the kutcho and the pinchi connect in part with the teslin suture zone in yukon territory and probably with the fraser river straight creek fault zone in southern british columbia although dextral transcurrent faulting may have taken place between the middle jurassic and early cenozoic the most convincing evidence points to middle cretaceous and particularly to early cenozoic eocene displacements the eocene movements were temporally related to plutonism volcanism lamprophyre dike emplacement high heat flow sedimentation in grabens and rapid uplift of northwesterly trending elongate ranges climactic episodes of granite emplacement particularly in and near the northern omineca crystalline belt at 100 m y 70 m y and 50 m y ago may have been facilitated by changes from dominantly compressional to dominantly transcurrent and related tensional strain

northward translation of baja british columbia along the late cretaceous to paleocene margin of western north america paleomagnetic data suggest that a large part of british columbia and southern alaska was at the latitude of baja california mexico in early late cretaceous time this allochthonous block baja bc includes the insular talkeetna in alaska and intermontane composite terranes the miniterranes between them and possibly part of the omineca metamorphic belt assuming that baja bc was adjacent to north america by middle cretaceous an analysis using plate kinematics of the pacific basin produces a model of northward movement of baja bc which is compatible with the known geology of the reconstructed margin of western north america baja bc moved north 2400 km as part of the kuia plate along a transform margin with north america from 85 to 66 ma this time interval is marked by the cessation of igneous activity in the sierra nevada development of wrench faults and basins along coastal california and initiation of laramide style tectonics to the east within baja bc diminished igneous activity to the west was coeval with possible wrench tectonic basins along its eastern margin by the end of the cretaceous baja bc was positioned from oregon to northern british columbia between 66 and 56 ma baja bc became attached to north america in a dextral transpressive stage during which the kula north america plate boundary expanded to encompass the whole block with a series of northwest trending strike slip faults a fold and thrust belt in the east and large scale uplifts and the formation of an incipient volcanic arc on the west southern alaska was the site of convergence during the whole of the period of northward translation of baja bc a late cretaceous subduction zone in alaska evolved into a major compressional belt as the basin and miniterranes on the northern margin of baja bc collided with interior alaska the collision culminated in the paleocene with formation of the mckinley granites and coeval dextral slip on the denali fault system

a refined succession of changhsingian and griesbachian neogondolellid conodonts from the meishan section candidate of the global stratotype section and point of the permian triassic boundary abstract a detailed study of new conodont collections from the changxing formation at the meishan section has resulted in taxonomic refinement of several important neogondolellid species most of the previously erected species are much more strictly redefined mainly based on the denticulation of the holotypes and the stratigraphic ranges attributed to key conodont taxa are modified three new species and two new subspecies all of which are form species are tentatively erected and described mainly for the purpose of taxonomic explanation as a result of the taxonomic refinement six neogondolellid conodont zones are recognized for the changxing formation and the permian triassic boundary interval

discordant paleomagnetic poles from the canadian coast plutonic complex regional tilt rather than large scale displacement stratigraphic petrologic and isotopic data indicate that parts of the coast plutonic complex and the north cascade range have been tilted northeast side up by angles of approximately 30 degree about north northwest trending axes these tilts can account for discordant paleomagnetic directions observed in mid cretaceous plutons from these regions without large scale displacement relative to north america

relationships between carbon isotope evolution and variation of microbes during the permian triassic transition at meishan section south china this paper investigates kerogen carbon isotopes the difference between carbonate and kerogen carbon isotopes 13ccarb kero 13ccarb 13ckero and the difference between carbonate and n c19 alkane compound specific carbon isotopes 13ccarb n c19 13ccarb 13cn c19 during the permian triassic transition at meishan south china the results show that kerogen carbon isotopes underwent both gradual and sharp shifts in beds 23 25 and 26 29 respectively the differences between carbonate and organic carbon isotopes both the 13ccarb kero and 13ccarb n c19 which are mainly affected by co2 fixing enzyme and pco2 oscillated frequently during the permian triassic transition both the variations of 13ccarb n c19 and 13ccarb kero coupled with the alternation between cyanobacteria and green sulfur bacteria indicated by biomarkers the episodic low values of 13ccarb n c19 corresponded to episodic blooms of green sulfur bacteria while the episodic high values of 13ccarb n c19 corresponded to episodic blooms of cyanobacteria the relationships between the variation of carbon isotopes and biota show that the microbes which flourished after the extinction of macroorganism affected the carbon isotope fractionation greatly combining the carbon isotope compositions and the pattern of size variation of the conodont neogondolella this paper supposes that anoxia of the photic zone at bed 24 was episodic and it would be caused by the degradation of terrigenous organic matters by sulfate reducing bacteria in the upper water column considered together with results from previous research the high resolution variation of the biogeochemistry presents the sequence of the important geo events during the permian triassic crisis

statistical significance of the fold test in palaeomagnetism summary the significance of the change in direction dispersion on applying the fold test in palaeomagnetism is used as the criterion for deciding whether or not the fold test has statistical significance a set of tables is compiled which can be used for quick application of the test

concordant paleolatitudes for neoproterozoic ophiolitic rocks of the trinity complex klamath mountains california 1 new paleomagnetic results from the eastern klamath mountains of northern california show that neoproterozoic rocks of the trinity ophiolitic complex and overlying middle devonian volcanic rocks are latitudinally concordant with cratonal north america combining paleomagnetic data with regional geologic and faunal evidence suggests that the trinity complex and related terranes of the eastern klamath plate were linked in some fashion to the north american craton throughout that time but that distance between them may have varied considerably a possible model that is consistent with our paleomagnetic results and the geologic evidence is that the trinity complex formed and migrated parallel to paleolatitude in the basin between laurasia and australia east antarctica as the rodinian supercontinent began to break up it then continued to move parallel to paleolatitude at least through middle devonian time although the eastern klamath plate served as a nucleus against which more western components of the klamath mountains province amalgamated the klamath superterrane was not accreted to north america until early cretaceous time index terms 1525 geomagnetism and paleomagnetism paleomagnetism applied to tectonics regional global 5475 planetology solid surface planets tectonics 8149 8157 tectonophysics evolution of the earth plate motions past 3040 9350 information related to geographic region north america 9619 information related to geologic time precambrian

paleomagnetism of the duke island alaska ultramafic complex revisited the duke island ultramafic intrusion was emplaced into the alexander terrane immediately preceding development of a regional mid cretaceous thrust belt paleomagnetic samples were collected from exposures of ultramafic rock with cumulate layering northwest of judd harbor and northwest of hall cove thermal demagnetization results were analyzed using principal component analysis to isolate the characteristic remanent magnetization site mean characteristic directions determined from 16 sites fail the fold test at 95 confidence indicating that cumulate layering attitudes were highly contorted at the time of magnetization at least on a scale of tens of meters variations in cumulate layering attitudes probably resulted from the combined effects of thermal convection phenomena during crystallization and deformation following crystallization but prior to magnetization analysis of cumulate layering over larger structural domains indicates that kilometer scale deformation produced southwest plunging folds within the hall cove and judd harbor bodies bogue et al 1995 proposed that a compound structural correction involving unplunging of fold axes followed by unfolding of average cumulate layering could restore cumulate layering to horizontal however using the full set of 21 site mean paleomagnetic directions from duke island 16 from the current study and 5 from bogue et al 1995 the compound structural correction yields mean paleomagnetic directions from the judd harbor and hall cove areas that are statistically distinguishable at 99 confidence this result indicates that even on the kilometer scale cumulate layering within the duke island ultramafic intrusion was neither coplanar nor horizontal at the time of magnetization observations of cumulate layering in other ultramafic intrusive rocks indicate that this layering can significantly depart from horizontal by 10 20 even on the kilometer scale therefore use of cumulate layering of ultramafic rocks as a proxy for paleohorizontal is not justified and paleomagnetic directions from the duke island ultramafic intrusion cannot be used to infer the cretaceous paleolatitude of the insular superterrane

carbon sulfur oxygen and strontium isotope records organic geochemistry and biostratigraphy across the permian triassic boundary in abadeh iran pelagic deposits at abadeh represent a complete biostratigraphic record across the permian triassic boundary ptb the presumed water depth during deposition of these sediments was between 60 and 90 m similar to other permian triassic boundary sections the succession at abadeh is characterised by a negative carbon isotope shift of approximately 4 the values start to decrease in the lower c changxingensis c deflecta s l zone reach 0 12 v pdb in the uppermost permian just below the ptb remain low to the early i isarcica zone 0 32 and increase subsequently in the upper i isarcica zone for the time interval of the ptb negative carbon isotope excursion between the c iranica and the i isarcica zones no correlation exists between the 13ccarb and the 18ocarb the above observations argue against the conclusion of heydari et al 2001 that the carbon isotope event at the p t transition is an alteration artefact and not a global signal the decrease in 13ccarb is accompanied by a 5 and potentially up to 10 increase in 34ssss together these features are thought to reflect a complex global event notably the development of widespread anoxic oceans with anoxic bottom layers rising onto the shelves for the carbon isotope drop other factors such as the collapse of ocean primary productivity may also have played a role the 87sr 86sr ratios of dzhulfian seawater show only a minor increase from 0 70705 to 0 70710 reaching 0 70720 in the dorashamian the increase becomes steeper in the early triassic reaching 0 70754 in the n dieneri zone the rise of the strontium isotope values is thought to be related to enhanced continental weathering under humid climatic conditions in the uppermost permian c meishanensis h praeparvus zone and the lack of a dense land vegetation in the early triassic prior to the spathian upper olenekian

chondritic meteorite fragments associated with the permian triassic boundary in antarctica multiple chondritic meteorite fragments have been found in two sedimentary rock samples from an end permian bed at graphite peak in antarctica the ni fe co ni and p fe ratios in metal grains the fe mg and mn fe ratios in olivine and pyroxene and the chemistry of fe ni p and s bearing oxide in the meteorite fragments are typical of cm type chondritic meteorites in one sample the meteoritic fragments are accompanied by more abundant discrete metal grains which are also found in an end permian bed at meishan southern china we discuss the implications of this finding for a suggested global impact event at the permian triassic boundary

permian circumpacific deep water faunas from the western tethys sicily italy new evidences for the position of the permian tethys abstract circumpacific deep water faunas characterized mainly by radiolarians paleopsychrospheric ostracods and conodonts were found in the early middle and late permian deposits pertaining to the sicanian paleogeographic domain of western sicily near the western end of the eurasiatic tethys similar permian deep water faunas are known from the phyllite unit of crete and from oman in the latter area partly above oceanic crust all these occurrences indicate the presence of a late paleozoic tethys ocean immediately north of gondwana

paleomagnetism of the upper cretaceous strata of mount tatlow evidence for 3000 km of northward displacement of the eastern coast belt british columbia this study contributes the first paleomagnetic data from dated cretaceous units of the coast belt 51 3 n 123 8 w in which paleohorizontal bedding surfaces can be identified with certainty we sampled 38 sites through a 1 5 km stratigraphic interval of cenomanian silverquick sedimentary strata and cenomanian to campanian powell creek volcanics in the tatlow syncline in the tyaughton methow basin magnetizations at 21 sites have high unblocking temperatures tub and pass the tilt test precision k 5 before untilting maximum k 48 after 100 untilting magnetic minerals of volcanics show original textures mean declinations in volcanic and sedimentary rocks are statistically identical and polarity is consistently normal the mean inclination 55 4 3 4 probability p 0 05 of this pretilting magnetization is 20 1 4 0 shallower than that expected if the rocks were deposited in their present position relative to cratonic north america field and laboratory observations rule out other causes for these anomalous shallow inclinations these rocks therefore have been displaced northward by 3000 500 km relative to cratonic north america since mid cretaceous time this displacement is almost 3 times greater than that estimated from mid cretaceous volcanics in the now adjacent intermontane belt evidently the two belts were not amalgamated until latest cretaceous or early tertiary time these results are inconsistent with all previous geologically based tectonic reconstructions of the cordillera magnetizations at eight sites in silverquick and powell creek beds have low tub and directional characteristics similar to those in three younger diorite intrusions reversed and normal polarities occur the rocks are commonly highly altered and maximum precision occurs after 40 untilting the magnetizations therefore are interpreted as overprints of latest cretaceous age acquired during folding

paleomagnetic evidence for displacement from the south of the coast plutonic complex british columbia the mid cretaceous spuzzum and porteau plutons of the coast plutonic complex of british columbia have two magnetizations a and b the a magnetization eight sites 83 specimens d 30 3 i 56 7 95 4 9 paleolatitude 37 5 n paleopole 65 0 n 14 9 w a95 6 2 is considered to have been acquired in the age range 105 90 ma this result differs from the field established for cratonic north america in this time range the difference could be caused either by previously undetected tilting about a horizontal axis of the plutons or by their rotation about a vertical axis and lateral displacement relative to the craton previously observed mid cretaceous magnetizations from other rock units from the western canadian cordillera and the cascades of washington united states are similarly discordant with respect to the craton this similarity over such a large area indicates that although local undetected tilting could be partly responsible it is unlikely to be the prime cause and we argue ther

paleomagnetic evidence for a post cretaceous accretion of wrangellia in order to test the various estimates of the accretion age of some of the southern alaska terranes a paleomagnetic investigation of the maccoll ridge formation latest cretaceous age in the wrangell mountains wrangellia was undertaken the data pass the fold test and reversal test thus affirming the primary nature of the magnetic remanence the mean paleomagnetic direction corresponds to a paleolatitude of 32 9 which is far south of the predicted paleolatitude assuming a north american paleogeography therefore these results apparently rule out a pre cenozoic accretion age of wrangellia and its associated terranes composing the southern alaska superterrane the data also imply about 130 counterclockwise rotation which is the opposite sense of rotation usually observed in western north america

rheological conditions for emplacement of ural alaskan type ultramafic complexes article i nfo ural alaskan or alaskan type complexes correspond to a particular class of ultramafic intrusions that attract particular attention due to their deep mantle origin and their platinum group element pge mineralization when defined as massifs of dunite clinopyroxenite only forty six complexes are reported in the literature these large scale dunite pipe like structures are rarely isolated and they even can appear in clusters to better understand genesis of these relatively young b460 ma complexes a worldwide compilation has been built and three categories have been defined single circular or elliptical bodies twin bodies with similar shapes and dismembered dunite bodies pge enrichment in alaskan type complexes is highest for the second category where twin bodies are interpreted as horizontal sections of y shaped dunite pipes to constrain mechanical properties of the lithosphere allowing emplacement of the alaskan type complexes the forceful diapiric ascent hypothesis is investigated through numerical thermo mechanical models one hundred high resolution experi ments accounting for realistic phase changes and softening mechanisms have been performed the experiments show that with no rheological softening of the host rock and in case of a relatively weak ductile lower crust the uprising magma tends to spread laterally without reaching the surface to account for the forceful ascent of deep magmas it is hence necessary to assume a strong lower crust rheology and strong local softening mechanisms besidesreproducingtheclustereddistributionoftheweaknesszonesrepresentingmagmapathways theselatter experiments reproduce large scale pipe like cylindrical structures y shaped and funnel shaped bodies and laterally shifted structures interestingly zones of highest strain rates are located at the bottom parts of the inclined edges of y shaped and funnel shaped bodies the restricted age range of alaskan type complexes b460 ma would mean that prior to this time the lower crust was less resistant due to the hotter geotherm prohibiting the possibility of alaskan type magmatism

pattern of marine mass extinction near the permian triassic boundary in south china the meishan section across the permian triassic boundary in south china is the most thoroughly investigated in the world a statistical analysis of the occurrences of 162 genera and 333 species confirms a sudden extinction event at 251 4 million years ago coincident with a dramatic depletion of 13ccarbonate and an increase in microspherules

platinum group element geochemistry of sulfide rich horizons in the ural alaskan type ultramafic complex of duke island southeastern alaska the duke island ultramafic complex in southeastern alaska is a ural alaskan type complex that hosts sulfide rich horizons primarily in the olivine clinopyroxenite unit although placer deposits hosting platinum group elements pges have been found in association with ural alaskan type complexes in several locations around the world these ultramafic complexes have traditionally been viewed as sulfide poor systems and therefore unlikely hosts of economic ni cu sulfide deposits sulfide mineralization in the duke island complex consists of massive net textured and disseminated assemblages that formed as a result of the interaction between magma and sulfidic graphitic country rocks the sulfide mineralization at duke island is characterized by strong depletion in ir os and ru ipges and relative enrichment in pt pd and cu the sulfide bearing olivine clinopyroxenites formed from a derivative magma produced as a result of the fractional crystallization of olivine and chromite although ipges may be compatible within olivine and chromite fractional crystallization of up to 20 cannot explain the observed ipge depletion we propose that early crystallization of laurite and ir alloys accompanied the accumulation of olivine and chromite r factor modeling indicates that much of the inter element variation in the sulfide mineralization can be attributed to variations in the degree of equilibration between sulfide and silicate liquids mixing between monosulfide solid solution and fractionated sulfide liquid may also have contributed to the variability the modeling suggests that the pre sulfide saturation concentrations of os pt and pd in the magmas were approximately 0 03 2 and 3 ppb respectively the concentration of pd is near that of primitive mantle and the low pt concentration can be explained by the crystallization of pt alloy with early formed dunites and chromitites this is consistent with models for pt rich placers in the urals that have been derived from chromitites and dunites the relative enrichments in pd and cu are the results of fractional crystallization before sulfide saturation was achieved taken together the ni cu pge elemental characteristics at the duke island complex are similar to those shown by flood basalt related sulfide deposits and cu rich sulfide veins studied in different locations around the world

included blocks and blocks within blocks in the skaergaard intrusion geologic relations and the origins of rhythmic modally graded layers the early eocene skaergaard intrusion of greenland includes enormous numbers of rocks of both exotic and cognate origins the lower parts of the marginal border series contain abundant fragments of feldspathic peridotite that are possibly autoliths intermixed with occasional xenoliths of precambrian gneiss and metasomatized cretaceous paleocene sediments derived from adjoining country rocks the upper border series includes one exceptionally large block of gneiss several hundred meters across and numerous smaller fragments these originating from the intrusion9s footwalls plus a few pieces of peridotite the layered series contains countless autoliths of troctolite gabbroic anorthosite and oxide magnetite ilmenite gabbro broken from parts of the upper border series that have otherwise been lost to erosion at the upper midlevel of its western half it contains a few xenoliths of basalt derived probably from the now eroded eocene roof of the intrusion a distinctive postintrusion composite basaltic dike at one place contains 40 or more xenoliths of troctolite olivine gabbro and gabbroic anorthosite that may represent parts of the layered series still hidden at depth the layered series autoliths range from fragments a few centimeters on a side to blocks more than 400 m across and they typically are coarser grained than their host cumulates being in this respect more like upper border series rocks the autoliths are spread stratigraphically through the lower 70 of the exposed 2500 m thickness of the layered series and are generally concentrated in three broad stratigraphic zones their physical relationships to their host rocks particularly the way they indent older layers beneath and are covered by younger layers above provide abundant evidence that there was generally a sharp well defined interface between the top of the cumulate pile and the main body of magma in the intrusion while the layered series was forming the distribution of the autoliths between and through the well known rhythmic thin modally graded layers shows that these layers were spread by magmatic currents and their relations to the more extensive macrorhythmic layering suggest that it too was significantly shaped by currents many of the larger autoliths are crudely layered internally and in places it is evident that their stratification existed before they broke loose therefore it must have formed in the upper border series one particularly large block of oxide gabbro exhibits extraordinarily well developed modal and textural layering and includes small troctolitic autoliths of an earlier generation and it provides evidence that currents also spread crystalline materials across the top of the magma body many of the very small autoliths in the layered series are highly anorthositic in composition apparently because they were leached of mafic minerals and some of the larger blocks show local patchy internal replacement by anorthosite most large blocks show little sign of postaccumulation modification and some have thin fine grained augite rich rims or rinds demonstrating that even though they were out of thermal and chemical equilibrium with their host cumulates they still were effectively armored against extensive chemical change also documented is a large block that was cut by several early basaltic dikes before it broke free from the top of the intrusion these early dikes transgress small anorthositic replacement pipes in the block showing that the replacement process also occurred in the upper border environment two mechanisms are described whereby graded cumulate layers can be sorted and deposited by magmatic crystal liquid suspension currents one involving density surge currents has been advocated previously the other is a new concept based on boundary flow separation and reattachment vortex cells the two mechanisms are used in complementary ways to illustrate the formation of 1 some of the principal skaergaard structures involving blocks and layers 2 modally graded layers in the layered series that rhythmically alternate with uniform layers and 3 modally sorted layers in the upper border series featuring underside draping beneath small included blocks explanations are provided for 1 why plagioclase did not float away from the tops of graded layers even though it was less dense than the liquid and 2 how the liquid part of a current was fractionated away from the crystalline materials modal and grain size data from skaergaard intrusion graded layers are shown to be in excellent accord with characteristics predicted for layers sorted by currents a synthesis diagram is presented illustrating how all the above processes may have functioned in concert in the intrusion

absolute inclination values from deep sea sediments a reexamination of the cretaceous pacific record new data are used to examine anomalously shallow paleomagnetic inclinations derived from previous analyses of cretaceous dsdp sediments of the central western pacific ocean while viscous remanent magnetizations vrms are shown to produce a similar effect the bias toward shallow values is still present with thoroughly demagnetized data superimposed upon this bias is a trend towards maximum flattening at an expected inclination of approximately 55 degree with the flattening falling to zero at the equator and pole flattening due to sediment compaction or inclination error is proposed to explain these observations

the timing and pattern of biotic recovery following the end permian mass extinction the aftermath of the great end permian period mass extinction 252 myr ago shows how life can recover from the loss of 90 species globally the crisis was triggered by a number of physical environmental shocks global warming acid rain ocean acidification and ocean anoxia and some of these were repeated over the next 5 6 myr ammonoids and some other groups diversified rapidly within 1 3 myr but extinctions continued through the early triassic period triassic ecosystems were rebuilt stepwise from low to high trophic levels through the early to middle triassic and a stable complex ecosystem did not re emerge until the beginning of the middle triassic 8 9 myr after the crisis a positive aspect of the recovery was the emergence of entirely new groups such as marine reptiles and decapod crustaceans as well as new tetrapods on land including eventually dinosaurs the stepwise recovery of life in the triassic could have been delayed either by biotic drivers complex multispecies interactions or physical perturbations or a combination of both this is an example of the wider debate about the relative roles of intrinsic and extrinsic drivers of large scale evolution from a much more devastated planet and biota than the others with only some 10 of species surviving the epme was much harsher than the other mass extinctions during which global species diversity reduced to only about 50 of the pre extinction total 1 2 24 26 this means that the triassic recovery has two profound implications first it may show qualitative as well as quantitative differences from the other post extinction recoveries and second it can act as an exemplar of what to expect at its most extreme when global biodiversity is pushed to the brink there are obvious implications for current concerns about biodiversity loss and recovery resulting from human impacts 27 28 in the past ten years attention has focused on the sedimentary successions in south china these are enormously laterally extensive with some formations extending more than 2 000 km from the zhejiang to yunnan provinces the huge exposures length of the sections and improving dating open up the opportunity to explore physical environmental and biotic changes through the extinction and recovery times in varied marine habitats and compare these with patterns elsewhere in the world fig 1 a fine scale forensic analysis of this extraordinary time in earth s history now becomes possible the end permian mass extinction the epme killed 80 96 of marine animal species and 70 of terrestrial vertebrate species

tempo of the end permian event high resolution cyclostratigraphy at the permian triassic boundary the permian triassic p t boundary is marked by the most severe mass extinction in the geologic record high resolution cyclostratigraphy on a 10 4 yr scale across the p t boundary in a core from the carnic alps austria revealed significant cycles in the ratio 40 10 4 7 2 3 m identified with milankovitch cycles of 412 100 40 20 k y eccentricity 1 and 2 obliquity and precession wavelet analysis indicates continuity of deposition across the boundary with an average accumulation rate of 10 cm k y the dramatic faunal changes at the p t boundary can be constrained within an interval of 60 k y possibly 8 k y with the accompanying sharp negative global carbonisotope shift within 30 k y suggesting a catastrophic cause

photic zone euxinia during the permian triassic superanoxic event carbon and sulfur isotopic data together with biomarker and iron speciation analyses of the hovea 3 core that was drilled in the perth basin western australia indicate that euxinic conditions prevailed in the paleowater column during the permian triassic superanoxic event biomarkers diagnostic for anoxygenic photosynthesis by chlorobiaceae are particularly abundant at the boundary and into the early triassic similar conditions prevailed in the contemporaneous seas off south china our evidence for widespread photiczone euxinic conditions suggests that sulfide toxicity was a driver of the extinction and a factor in the protracted recovery

carbon isotope excursions and microfacies changes in marine permian triassic boundary sections in hungary abstract several permian triassic boundary sections occur in various structural units within hungary these sections represent different facies zones of the western palaeotethys margin the gardony core in the ne part of the transdanubian range typically represents the inner ramp while the balvany section in the bukk mountains of northern hungary represents an outer ramp setting the two sections have different patterns for their 13 c values the balvany section shows a continuous change towards more negative 13 c values starting at the first biotic decline followed by a sharp quasi symmetric negative peak at the second decline the appearance of the 13 c peak has no relationship to the lithology and occurs within a shale with low overall carbonate content indicating that the peak is not related to diagenesis or other secondary influences instead the shift and the peak reflect primary processes related to changes in environmental conditions the continuous shift in 13 c values is most probably related to a decrease in bioproductivity whereas the sharp peak can be attributed to an addition of c strongly depleted in 13 c to the ocean atmosphere system the most plausible model is a massive release of methane hydrate the quasi symmetric pattern suggests a rapid warming cooling cycle or physical unroofing of sediments through slope failure and releasing methane hydrate the gardony 1 core shows a continuous negative 13 c shift starting below the p t boundary however the detailed analyses revealed a sharp 13 c peak in the boundary interval just below the major biotic decline although its magnitude doesn t reach that observed in the balvany section based on careful textural examination and high resolution stable isotope microanalyses we suggest that the suppression of the 13 c peak that is common in the oolitic boundary sections is due to combined effects of condensed sedimentation sediment reworking and erosion as well as perhaps diagenesis

paleomagnetism and tectonics of the cretaceous mt stuart batholith of washington translation or tilt abstract the mt stuart batholith is a composite pluton of late cretaceous age that intrudes the crystalline north cascades terrane of northwestern washington its paleomagnetic direction d 10 0 i 45 5 95 4 9 is markedly different from the direction expected for cretaceous rocks from northwestern washington d 330 5 i 73 0 which means that the mt stuart batholith either has moved relative to the north american interior or has been tilted through a substantial angle or both since it acquired its magnetism either tilt or translation are possible geometrically but translation is more likely because 1 local geology apparently does not support tilt in the required direction 2 it probably is not possible for a panel of rock the size of the mt stuart batholith to tilt through the necessary angle ca 35 after its deeper parts have cooled sufficiently to retain remanent magnetization 3 the sense of paleomagnetic discordance found in the mt stuart batholith clockwise rotation of declination flattened inclination is identical to that found in nearly every other allochthonous terrane in the western north american cordillera including every other cretaceous batholith studied except the sierra nevada

the link between climate warming and break up of ice shelves in the antarctic peninsula a review of in situ and remote sensing data covering the ice shelves of the antarctic peninsula provides a series of characteristics closely associated with rapid shelf retreat deeply embayed ice fronts calving of myriad small elongate bergs in punctuated events increasing flow speed and the presence of melt ponds on the ice shelf surface in the vicinity of the break ups as climate has warmed in the antarctic peninsula region melt season duration and the extent of ponding have increased most break up events have occurred during longer melt seasons suggesting that meltwater itself not just warming is responsible regions that show melting without pond formation are relatively unchanged melt ponds thus appear to be a robust harbinger of ice shelf retreat we use these observations to guide a model of ice shelf flow and the effects of meltwater crevasses present in a region of surface ponding will likely fill to the brim with water we hypothesize building on weertman 1973 hughes 1983 and van der veen 1998 that crevasse propagation by meltwater is the main mechanism by which ice shelves weaken and retreat a thermodynamic finite element model is used to evaluate ice flow and the strain field and simple extensions of this model are used to investigate crack propagation by meltwater the model results support the hypothesis