the interrelation of glaciotectonic and glaciodepositional processes within the glacial environment abstract in recent years it has been recognised that ice sediment coupling occurred beneath the quaternary ice sheets that advanced over the soft sediments of lowland areas this paper looks in detail at the effects of this coupling on the sediments which results in glaciotectonic deformation and also discusses the interaction of deformation and deposition within the subglacial environment two types of glaciotectonic deformation are discussed that are produced by the active movement of ice 1 proglacial tectonics at the margin which include compressive fold styles such as listric thrusts and faults and open folding 2 subglacial tectonics formed beneath the glacier which include fold styles resulting from simple shear and represent a soft rock purely dynamic shear zone styles of deformation associated with stagnant ice are also investigated we argue that glaciotectonic deformation is a common phenomenon and an integral part of geological record from continental ice sheets it is suggested that zones of deformation within the sediment are related to similar zones of strain in the ice sheet and complex deformation sequences are produced by the superimposition of these differing styles upon one another as the ice sheet advances and retreats it is also argued that subglacial deposition and deformation are related and that on soft beds underformed till is rare whilst deformed till is very common

three dimensional deformation measured in an alaskan glacier measurements of movement along 28 boreholes reveal the three dimensional flow field in a 6 million cubic meter reach of worthington glacier a temperate valley glacier located in alaska sliding at the bed accounted for 60 to 70 percent of the glacier s surface motion strain rates in the ice were low from the surface to a depth of about 120 meters but then increased rapidly toward the bed ice deformation was not affected by temporal changes in the sliding rate the three dimensional pattern of motion indicates that plane strain which is often assumed by models is a poor approximation of this viscous flow

guadalupian lopingian conodont and carbon isotope stratigraphies of a deep chert sequence in japan abstract to improve international stratigraphic correlation of the lower guadalupian lower lopingian permian we examined the stratigraphies of conodonts and organic carbon isotopes from pelagic chert sequences in the gujo hachiman section gifu southwest japan age diagnostic conodonts such as jinogondolella nankingensis and jinogondolella shannoni were found in the study section the conodont stratigraphy in the gujo hachiman section was correlated with those in south china and west texas usa to date the study section from these correlations it was found that the study section was from the upper roadian lower guadalupian through wuchiapingian lower lopingian kerogen 13 c values were relatively high around 29 0 in the upper roadian wordian middle guadalupian decreasing over time to 29 4 a negative positive swing in 13 c values of around 1 magnitude was recognized in the middle capitanian upper guadalupian a similar negative positive swing was also found in the guadalupian lopingian g l transitional zone in the gujo hachiman section and is comparable to the isotopic change around the g l boundary in the penglaitan section south china subsequently 13 c values decreased to values below 30 0 above the g l transitional zone i e at the lower wuchiapingian overall 13 c values decreased from the lower capitanian to the lower wuchiapingian by over 1 4 a gradual increase in the 13 c values followed this long term negative trend these 13 c trends in the gujo hachiman section are comparable with time equivalent 13 c records in different sections suggesting that they record first order variations in atmospheric 13 c the high 13 c values during the upper roadian wordian interval could reflect high primary productivity in the surface water of the pelagic panthalassa ocean and imply global cooling in contrast the negative 13 c shift during the capitanian wuchiapingian interval implies global warming

styles of subglacial glaciotectonic deformation within the context of the anglian ice sheet a substantial proportion of the glacial sediments of east anglia england are chaotic and highly deformed this has been attributed to a direct glaciotectonic deformation or b slumping of glaciomarine sediments we show that interpretation a leads to a classification of subglacial glaciotectonic deposits into sites of constructional deformation where little or no erosion of the preglacial deposits has occurred and styles of deformation are preserved moving up in the sequence and excavational deformation where substantial erosion of preglacial sediments has occurred and deformational styles are superimposed on each other by using glaciological and geotechnical theory we show that the expression of these deformational styles in east anglia is a natural response to the stress fields imposed by the ice sheet and that in consequence their spatial relationships are explicable the depth of deformation is related to the geotechnical properties of till and substrate the stress and effective stress fields and found to be consistent with observations

a new magma chamber model based on structural studies in the oman ophiolite abstract structural mapping in the mafic ultramafic transition zone and in the overlying crustal section of the oman ophiolite has revealed the importance of magmatic flow in the formation of layering in the gabbros and the mechanical coupling between this flow and the asthenospheric flow of the underlying peridotites the crustal section near the spreading axis and in particular the magma chamber are fed by two independent melts a dominant gabbroic melt episodically injected from depth and a subordinate wehrlitic crystal mixture produced by compaction of the transition zone layering in the gabbros can be partly produced by tectonic transposition of the gabbroic and wehrlitic mixtures during magmatic flow whatever its origin the layering orientation in the newly created crust does not necessarily reflect its original attitude the final orientation of the layering is determined by the attitude of the magmatic flow plane at the time it was frozen a new magma chamber model is proposed which solves some of the physical difficulties of previous models and accounts for the seismic imaging of magma chambers beneath oceanic ridges

birth death and resurrection the life cycle of suprasubduction zone ophiolites 1 suprasubduction zone ssz ophiolites display a consistent sequence of events during their formation and evolution that suggests that they form in response to processes that are common to all such ophiolites this sequence includes the following 1 birth which entails the formation of the ophiolite above a nascent or reconfigured subduction zone this stage is typically characterized by the eruption of arc tholeiite lavas and the formation of layered gabbros and sheeted dike complex 2 youth during which is continued melting of refractory asthenosphere depleted during birth occurs in response to fluid flux from the subducting slab with extensional deformation of the older plutonic suite eruption of refractory lavas and the intrusion of wehrlite pyroxenite 3 maturity with the onset of semistable arc volcanism typically calc alkaline as the subduction zone matures and stabilizes and the intrusion of quartz diorite and eruption of silicic lavas and 4 death which is the sudden demise of active spreading and ophiolite related volcanism which in many cases is linked to collision with an active spreading center and the onset of shallow underthrusting of the buoyant spreading axis expressed as dikes and lavas with oceanic basalt compositions that crosscut or overlie rocks of the older suites 5 resurrection with emplacement by obduction onto a passive margin or accretionary uplift with continued subduction the early stages 1 3 may be diachronous and each stage may overlap in both time and space the existence of this consistent progression implies that ophiolite formation is not a stochastic event but is a natural consequence of the ssz tectonic setting

model for the origin of the troodos massif cyprus and other mideast ophiolites any comprehensive model for the origin of the troodos complex and other mideast ophiolite complexes must explain the geochemical evidence for subduction zone involvement the thin inferred oceanic crust the extensional environment indicated by sheeted dikes the existence of fault zones perpendicular to the inferred spreading axes and the discontinuous nature of ophiolite exposures around the arabian block the andaman sea region of the indian ocean may provide an actualistic model for the origin of these ophiolites there spreading takes place in short segments above a subduction zone in the region of active spreading the andaman sea model substantially accounts for the known geologic and geophysical data from the circum arabian ophiolite belt and it leads to some predictions about the structural and geophysical relationships to be expected in this important belt the model also predicts that andaman sea spreading center magmas may be similar in composition to those found in the mideast ophiolites

faunal evidence for a cool boundary current and decoupled regional climate cooling in the permian of western laurentia abstract deglaciation following the late paleozoic ice age was a complex climate transition marked by smaller glacial interglacial transitions superimposed on an overall permian warming trend in contrast to this growing recognition of a dynamic climate system few studies have investigated geographic variations in postglacial climate changes which may have been as dynamic as the temporal variations because temperature and ocean circulation are important controls on the biogeography of marine invertebrates many permian taxa were characteristic of either paleotropical or high latitude faunal realms this study takes advantage of that temperature sensitivity using a database of more than 5000 permian fossil collections from northwestern pangea to reconstruct spatial variations in permian climate changes throughout the region cluster analysis demonstrates that localities in the phosphoria basin nevada idaho wyoming were taxonomically distinct from coeval faunas in texas and occupied the transitional zone between paleoequatorial and boreal realms quantitative scoring of the faunal affinity of all taxa in 1 by 1 paleolatitudinal bins suggests that the western margin of laurentia was affected by a persistent southward flowing cool boundary current and that the effects of the current became more pronounced throughout the permian in conjunction with cooling in the boreal ocean the increasingly cool water nature of phosphoria basin faunas contrasted with warming in texas and implies that northern and northwest pangea were decoupled from the broader global warming trend following the late paleozoic ice age

mantle crust transition zone and origin of wehrlitic magmas evidence from the oman ophiolite abstract abundant exposure and well preserved outcrops in the oman ophiolite allow detailed observation of the transition from mantle to crust in an oceanic environment the mantle crust transition zone shows large lateral variations in thickness and composition but consists essentially of residual dunites and a magmatic component present as clinopyroxene and plagioclase impregnations and gabbro lenses compositionally the transition zone marks a gradational passage from mantle to crust the moho may be placed at the base of the continuous gabbroic crustal section structures both within the transition zone and near the base of the crust are nearly parallel to the moho however the dominant flow mechanisms differ from the upper mantle to the lower crust plastic flow dominates in the upper mantle while viscous flow resulting in strong magmatic fabrics dominates at crustal levels wehrlitic bodies within the crustal gabbro section are intruded from the transition zone into which they are rooted the parent magma of the wehrlitic instrusions is in fact a crystal melt mixture composed of olivine and chromite probably including a component of mantle xenocrysts and xenoliths and of reequilibrated basaltic melt

duality of magmatism in the plutonic sequence of the sumail nappe oman abstract detailed field mapping of the crustal sequence in several areas of the sumail ophiolite nappe mainly in the fizh the salahi and the haylayn blocks and comparisons with other well studied areas have shown that the crustal sequence was constructed by two distinct although nearly contemporaneous magmatic series the first a gabbroic series was emplaced during the accretion stage at an oceanic spreading centre which formed the layered gabbro unit the high level isotropic gabbro unit and their by products the sheeted dyke complex and the lower extrusives fine grained homogeneous planar laminated gabbros commonly occur at the top of the layered gabbro sequence in some specific areas wadi haymiliyah and wadi rajmi these are strongly differentiated fe ti rich gabbronorites and norites which coincide with large scale discontinuities within the plutonic sequence interpreted as axial discontinuities of the spreading magma chambers the second series an ultramafic wehrlitic series is locally rooted in the upper mantle i e the impregnated dunitic transition zone this has intruded the whole crustal sequence up to the pillow lavas countless discordant and concordant wehrlitic bodies intruded the plutonic sequence making up 20 40 of it in volume we describe the various settings and forms of these intrusions which were largely underestimated in previous studies we also describe their mineralogy and textures and show with chemical and mineralogical arguments that these bodies evolved as relatively closed systems independently from each other we infer from the study of the contacts that the gabbros were still hot and consolidated just at the moment of the wehrlitic intrusion at the base of the crust however indications of immiscibility between gabbros and wehrlites are common suggesting that both magmatic series were quite contemporaneous the wehrlites are commonly isotropic and may exhibit an internal layering of the dunite wehrlite clinopyroxenite type sometimes appearing at the upper or lower margins of the intrusions in this case the ultramafic layered cumulates show lobate intrusive contacts with the adjacent layered gabbros these plagioclase free ultramafic layered cumulates therefore are not interbedded within the gabbro cumulates but actually belong to the wehrlitic intrusive series picritic dykes radiating from the uppermost intrusions can be traced up to the upper extrusives which are for the main part cogenetic with the wehrlites the time of this second magmatic event coincides with the cessation of the accretion process and with the beginning of the intraoceanic detachment of the ophiolite at the spreading centre we believe that the compressive regime that initiated the detachment acted as an efficient filter press and helped the extraction and ascent of the wehrlitic magmas towards the uppermost levels of the crust

the effect of grain texture on the occurrence of microstructural properties in subglacial till in this paper we examine whether till grain size affects the range and occurrence of micromorphological features associated with subglacial shear our till samples were collected from two glaciers in iceland and varied in texture from a coarse sandy clast rich till fjallsjokull to a fine grained silty sandy till vestari hagafellsjokull we found a wide range of deformational microstructures that included skelsepic plasmic fabric intraclasts of pre existing eroded bedrock basalt and weathered clay and mini shear zones between clasts we classified our micromorphological data into three classes rotational intermediate and linear in addition to these observations we performed extensive microfabric analysis at different scales on all of our samples we found that the coarse grained till contained a greater number and variety of microstructures than the fine grained till in addition the fine grained till showed a distinct lack of rotational structures that we attribute to the lack of significantly sized clasts in the matrix we argue that the varied texture of the coarse grained till provides a greater degree of perturbation within the shearing layer and so more distinct microstructures form in a more fine grained till shearing is more homogeneous since there are less perturbations in the matrix and this leads to a more singular kind of microstructure our observations suggest that subglacial shear occurs within a multi layered patchwork of different grain sizes competence and pore water pressures it is these factors that are so crucial in determining the occurrence and type of microstructural evidence we see in subglacial tills

well documented travel history of mesozoic pelagic chert in japan from remote ocean to subduction zone the mino tanba belt in southwest japan a segment of the cordilleran type orogenic chain of jurassic east asia is composed mainly of a middle upper jurassic subduction accretion complex in which triassic and lower jurassic bedded radiolarian cherts occur as large allochthonous units structurally interlayered with middle upper jurassic clastic rocks high resolution microfossil conodont and radiolaria research has identified very low average sedimentation rates of about 0 5 g cm 1000 yr in the chert units similar to those of modern pelagic sediments accumulated in open ocean environments judging from the low average sedimentation rate high purity of biogenic silica long duration of continuous deposition 50 m y and wide along strike extent 1000 km the bedded radiolarian cherts in the mino tanba belt are best understood as ancient pelagic sediments that accumulated in open ocean environments accordingly the alleged origin in smaller marginal basins is untenable upward lithologic change from bedded chert to overlying siliceous mudstone in the uppermost portion of chert sequences suggests the gradual landward approach of the oceanic plate toward a trench the tectonic interlayering of these cherts and coarse grained terrigenous elastics is a secondary feature that was added through duplexing underplating in the subduction zone on the basis of the primary stratigraphy and field occurrence of triassic bedded chert in the mino tanba belt newly proposed are an idealized oceanic plate stratigraphy and a generalized travel history of a cordilleran type bedded chert from its birth at a mid oceanic ridge to its demise at a subduction zone

ring shear studies of till deformation coulomb plastic behavior and distributed strain in glacier beds a ring shear device was used to study the factors that control the ultimate steady strength of till at high shear strains tests at a steady strain rate and at different stresses normal to the shearing direction yielded ultimate friction angles of 26 3 and 18 6 for tills containing 4 and 30 clay sized particles respectively other tests at steady normal stresses and variable shear strain rates indicated a tendency for both tills to weaken slightly with increasing strain rate this weakening may be due to small increases in till porosity these results provide no evidence of viscous behavior and suggest that a coulomb plastic idealization is reasonable for till deformation however viscous behavior has often been suggested on the basis of distributed shear strain observed in subglacial till we hypothesize that deformation may become distributed in till that is deformed cyclically in response to fluctuations in basal water pressure during a deformation event transient dilation ofdiscrete shear zones should cause a reduction in internal pore water pressure that should strengthen these zones relative to the surrounding till a process called dilatant hardening consequent changes in shear zone position when integrated over time may yield the observed distributed strain

discrete element modeling of subglacial sediment deformation 1 the discrete element method dem is used in this study to explore the highly nonlinear dynamics of a granular bed when exposed to stress conditions comparable to those at the bed of warm based glaciers complementary to analog experiments the numerical approach allows a detailed analysis of the material dynamics and the shear zone development during progressive shear strain the geometry of the heterogeneous stress network is visible in the form of force carrying grain bridges and adjacent volumetrically dominant inactive zones we demonstrate how the shear zone thickness and dilation depend on the level of normal overburden stress and we show how high normal stress can mobilize material to great depths the particle rotational axes tend to align with progressive shear strain with rotations both along and reverse to the shear direction the results from successive laboratory ring shear experiments on simple granular materials are compared to results from similar numerical experiments the simulated dem material and all tested laboratory materials deform by an elastoplastic rheology under the applied effective normal stress these results demonstrate that the dem is a viable alternative to continuum models for small scale analysis of sediment deformation it can be used to simulate the macromechanical behavior of simple granular sediments and it provides an opportunity to study how microstructures in subglacial sediments are formed during progressive shear strain

pore water controlled grain fracturing as an indicator for subglacial shearing in tills genetic classification of glacial deposits still proves to be highly controversial in many cases it remains unclear whether a particular sediment has been sub glacially deformed in the present paper it is suggested that micromorphological research is helpful where current techniques fail to lead to unambiguous interpretations it is argued that the occurrence of fractured grains in glacial sediments is indicative of subglacial shearing and that such grains may be used as diagnostic evidence of glaciotectonism deformational mechanisms associated with the fracturing process are outlined and explained using a series of thin sections from wijnjewoude the netherlands

processes in magma chambers beneath spreading axes evidence from magmatic associations in the oman ophiolite ophiolite complexes where complete consist of tectonized ultramafic rocks overlain by layered gabbros and peridotites isotropic gabbros and plagiogranites a sheeted dyke swarm and pillowed volcanics this pseudo stratigraphy has been interpreted as oceanic crust and upper mantle dewey bird 1971 moores vine 1971 the base of the crust being drawn at the base of the layered series malpas 1978 in oman this succession is particularly well exposed in a 500 km long 14 km thick ophiolite nappe of upper cretaceous age glennie et al 1973 magmatic associations in its lower crustal and upper mantle portions oceanic layers 3 and 4 are currently being studied to determine the processes of magma supply and fractionation in oceanic magma chambers in the first section of this report we list the evidence for the greater part of the plutonic sequence of the ophiolite forming in a dynamic long lived open system magma chamber beneath a spreading axis in the second section the remainder of the plutonic sequence is described as a series of later short lived possibly closed system off axis plutons a fuller treatment of magma chamber processes during the spreading event is presented elsewhere smewing in press the earliest and volumetrically most significant magmatic event is represented by up to 3 5 km of layered gabbros and peridotites and an overlying unit of up to 200 m of isotropic gabbros and plagiogranites intruding the base of the sheeted dyke swarm the layered series rests with a sharp contact

contrasting microbial community changes during mass extinctions at the middle late permian and permian triassic boundaries abstract microbial communities are known to expand as a result of environmental deterioration during mass extinctions but differences in microbial community changes between extinction events and their underlying causes have received little study to date here we present a systematic investigation of microbial lipid biomarkers spanning 20 myr middle permian to early triassic at shangsi south china to contrast microbial changes associated with the guadalupian lopingian boundary glb and permian triassic boundary ptb mass extinctions high resolution analysis of the ptb crisis interval reveals a distinct succession of microbial communities based on secular variation in moretanes 2 methylhopanes aryl isoprenoids steranes n alkyl cyclohexanes and other biomarkers the first episode of the ptb mass extinction me1 was associated with increases in red algae and nitrogen fixing bacteria along with evidence for enhanced wildfires and elevated soil erosion whereas the second episode was associated with expansions of green sulfur bacteria nitrogen fixing bacteria and acritarchs coinciding with climatic hyperwarming ocean stratification and seawater acidification this pattern of microbial community change suggests that marine environmental deterioration was greater during the second extinction episode me2 the glb shows more limited changes in microbial community composition and more limited environmental deterioration than the ptb consistent with differences in species level extinction rates 71 vs 90 respectively microbial biomarker records have the potential to refine our understanding of the nature of these crises and to provide insights concerning possible outcomes of present day anthropogenic stresses on earth s ecosystems

a ring shear device for the study of till deformation tests on tills with contrasting clay contents abstract deformation of subglacial sediment may have had a profound influence on the geomorphic effects and dynamics of pleistocene ice sheets but data that bear on the rheology of such sediment are few and contradictory a means of studying systematically the mechanical properties of glacial tills is provided by a ring shear device that shears a large annular specimen to high strains at variable rates special features of the device allow continuous observation of the distribution of shear strain measurement of local stresses normal to the direction of shear and isolation of wall effects thus far a linear viscous putty and two tills with different clay contents 4 and 32 by weight have been tested the experiments with till indicate as expected that the presence of dispersed clay minerals reduces markedly both the residual strength and hydraulic diffusivity of till clay also reduces spatial variations in normal stress associated with grain bridges the walls bounding the specimen support only 9 17 of the total resistance to shearing strain was localized in both tills but not in the linear viscous putty strain localization in the tills indicates that their theology departs significantly from linear and bingham viscous models

evolution of a plume influenced source to sink system an example from the coupled central emeishan large igneous province and adjacent western yangtze cratonic basin in the late permian sw china abstract source to sink paleogeography in a time constrained sequence stratigraphic framework has been reconstructed for the non marine to marine transitional lopingian strata late permian in the western yangtze cratonic basin wycb and the adjacent inner zone of the emeishan large igneous province elip in order to reveal the evolution of a mantle plume influenced cratonic basin the lopingian coal bearing strata can be subdivided into seventeen 4th order sequences and three 3rd order composite sequences representing 6 76 myr paleogeographic reconstructions of the wycb demonstrate the existence of n s trending terrestrial transitional and marine facies belts distributed west to east away from the central elip geomorphological analysis indicates that the western boundary of the source area coincided with the major axis of the uplifted central elip based on sediment flux estimates and modeling bqart model relief of the central elip increased from near sea level in the earliest late permian and reached equilibrium at about 200 m in the latest permian sediment volume backfilling analysis indicates that total tectonic uplift of the central elip in the late permian was more than 500 m evolution of the coupled central elip and wycb can be subdivided into three stages pre eruptive uplift stage pre and syn eruptive subsidence stage and syn and post eruptive uplift stage post eruptive basin filling was controlled by sediment supply that was related to tectonic uplift drainage topography and climate change and basin accommodation that was related to sea level fluctuations and plume induced syn sedimentary tectonics

new northwest pacific radiolarian data as a tool to estimate past sea surface and intermediate water temperatures a new radiolarian data set for transfer function estimates of past sea surface temperature sst and intermediate water temperature was developed in this study for the northwestern pacific ocean covering a region from 1 to 50 n and 120 to 167 e we analyzed 87 sediments surface samples selected 30 species and or species group found in shallow water for estimating past summer sst and 17 species and or species group found in the intermediate water for estimating past intermediate water temperature since the intermediate water temperature changes greatly between 200 and 500 m our estimates provide values at 500 m because temperatures are relatively stable between 500 and 1000 m in this context we estimated past summer sst and intermediate water at 500 m temperature within an error margin of 0 9 and 1 2 c respectively a test of the accuracy of our transfer functions conducted on core samples provided by iodp expedition 346 site u1429 in the northern east china sea showed that the reconstructed summer ssts fluctuated between 17 2 and 26 5 c in selected late pleistocene sequences these temperatures corresponded to modern winter and summer sst respectively which highlights the ability of our new database to accurately reconstruct summer sst the reconstructed intermediate water temperature fluctuates between 3 and 8 c which corresponds to the observed temperature range at depths of 500 m at high and midlatitudes respectively

low latitudinal standard permian radiolarian biostratigraphy for multiple purposes with unitary association graphic correlation and bayesian inference methods abstract the ideal goal of biostratigraphic studies is to make stratigraphic ranges of all species clear and to fix globally synchronous biohorizons as age controls however it is difficult to achieve this goal in simple traditional ways and so a new solution is proposed for permian radiolarian biostratigraphy to achieve this goal including to establish a globally applicable biostratigraphy to estimate the numerical age of biohorizons and to determine stratigraphic ranges at species level all 400 known permian radiolarian species approximately 70 stratigraphic sections and 1560 samples from 350 previously published papers about the low latitude tethys and panthalassa oceans were analyzed issues of permian studies are summarized and a solution is proposed from the cenozoic point of view considering traditional methods as well as successful methods in cenozoic radiolarian studies here we implement newly proposed methods that have never been used for permian radiolarian studies unitary association method uam minimum disordered biohorizon algorithm mdba graphic correlation gc and reiteration estimation rounds rer of these our proposed rer is a new method to predict the probability of the estimated age for a sample by bayesian inference and joint probability both statistical methods as these four methods are applicable to any biostratigraphic study the principals and practical applications of these methods are carefully explained so non specialists can understand the logical procedure as a result 15 unitary association zones uazs are established for the entire permian biostratigraphic scheme by uam the numerical ages of 42 first occurrences fos are estimated from non parametric data from the middle guadalupian middle permian to the uppermost lopingian uppermost permian by mdba and gc and the statistical likelihood uaz ranges of 165 species in the entire permian were obtained using the rer procedure a usability test of our uazs shows that 97 96 of the 933 tested samples from previously published papers are well correlated and without contradiction within the statistical error of cenozoic synchronous biohorizons at 1 4 myr 23 of 42 fos are potentially regarded as synchronous events as the statistical likelihoods of uaz ranges are estimated by bayesian inference these ranges can be updated by anyone

ocean plate stratigraphy in east and southeast asia abstract ancient accretionary wedges have been recognised by the presence of glaucophane schist radiolarian chert and melange recent techniques for the reconstruction of disrupted fragments of such wedges by means of radiolarian biostratigraphy provide a more comprehensive history of ocean plate subduction and successive accretion of ocean floor materials from the oceanic plate through offscraping and underplating reconstructed ocean floor sequences found in ancient accretionary complexes in japan comprise from oldest to youngest pillow basalt limestone radiolarian chert siliceous shale and shale and sandstone similar lithologies also occur in the melange complexes of the philippines indonesia thailand and other regions this succession is called ocean plate stratigraphy ops and it represents the following sequence of processes birth of the oceanic plate at the oceanic ridge formation of volcanic islands near the ridge covered by calcareous reefs sedimentation of calcilutite on the flanks of the volcanic islands where radiolarian chert is also deposited deposition of radiolarian skeletons on the oceanic plate in a pelagic setting and sedimentary mixing of radiolarian remains and detrital grains to form siliceous shale in a hemipelagic setting and sedimentation of coarse grained sandstone and shale at or near the trench of the convergent margin radiolarian biostratigraphy of detrital sedimentary rocks provides information on the time and duration of ocean plate subduction the ages of detrital sediments becomes younger oceanward as younger packages of ops are scraped off the downgoing plate ops reconstructed from ancient accretionary complexes give us the age of subduction and accretion direction of subduction and ancient tectonic environments and is an important key to understanding the paleoenvironment and history of the paleo oceans now represented only in suture zones and orogenic belts

conodont biostratigraphy across the permian triassic boundary at chaotian in northern sichuan china abstract detailed conodont biostratigraphy of the permian triassic boundary ptb interval was analyzed at the fossiliferous chaotian section in northern sichuan china the ptb interval at chaotian is composed of the uppermost permian mudstone limestone of the dalong formation and the lowermost triassic marl limestone of the feixianguan formation both representing deep basinal facies the ptb interval is enriched in ammonoids and conodonts and is divided into 6 conodont zones including 1 clarkina changxingensis changxingensis c subcarinata assemblage zone 2 c postwangi c sp b assemblage zone 3 c taylorae c zhejiangensis c changxingensis yini assemblage zone 4 barren intra zone 5 hindeodus parvus zone and 6 isarcicella zone in ascending order the first four zones correspond to the changhsingian whereas the latter two to the lower induan griesbachian the first occurrence fo of h parvus in the lowermost feixianguan formation is regarded as the conodont biostratigraphic boundary from the uppermost dalong formation various taxa of the genus clarkina occurred abundantly and suddenly disappeared at the top of the dalong formation therefore the top of the dalong formation is interpreted as a horizon of the eventostratigraphic boundary on the basis of conodont zones the chaotian section is correlated with the shangsi and meishan gssp of the ptb sections in south china and the zal section in iran

till fabric associated with deformable beds this paper investigates the development of till fabric associated with glaciers overlying deformable beds first the till fabrics from both modern and ancient soft bed and hard bed subglacial environments are investigated and then soft bedded sites with specific strain histories are examined the results indicate that lodgement tills had a strong fabric whilst there is a wide range of much weaker fabric strengths associated with soft bed tills it is suggested from a theoretical study of soft bed till deposition that longitudinal and vertical processes in the subglacial deforming layer are important in fabric development field sites were chosen to isolate these two factors and fabrics investigated in areas of known relative shear strain and known relative thickness of the deforming layer the results indicate that 1 for a fixed deforming layer fabric strength does increase with increasing deformation except at very high strains where the development of a transverse fabric can lead to a reduction in the overall fabric strain and 2 lodgement tills and soft bed tills associated with a thin deforming layer have a high fabric strength whilst soft bed tills associated with a thick deforming layer have a low fabric strength where the deforming layer is thin clasts are oriented parallel with the glacier direction either by lodging against a hard bed or ploughing against a soft bed however where the deforming layer is thicker and shear strains are high melt out processes encourage a parallel fabric but the increased shear strain and changes in the deforming layer thickness cause the clasts to develop both a parallel and transverse fabric these processes combine to reduce the overall fabric strength till fabric studies are a further sedimentological technique to separate the depositional processes associated with a homogeneous till

volcanic glass compositions of the troodos ophiolite cyprus fresh volcanic glass is preserved throughout the extrusive section of the troodos ophiolite which indicates that the lavas have not been pervasively metamorphosed glass compositions reveal the existence of two major magma suites apparently corresponding to distinct stratigraphic intervals the basal 400 500 m of the sequence consists of an andesite dacite rhyolite assemblage containing abundant hyaloclastites the remainder of the section comprises a basalt basaltic andesite assemblage with high mgo and low tio 2 and total iron the lower sequence is interpreted as an evolved arc tholeiite suite the upper has some similarities to boninitic lavas the close association in time and space of these two suites is similar to that observed in the mariana and bonin arcs and suggests that all of the troodos lavas were erupted in a subduction zone environment most probably in an incipient arc or fore arc

influence of the glacier bed lithology on the formation of a subglacial till sequence ring shear experiments as a tool for the classification of subglacial tills abstract a glaciogenic sediment sequence deposited by a local glacier in the rhine catchment area near sargans eastern swiss alps was investigated in order to examine the shear behaviour of two different tills in addition to ring shear experiments examination of clast lithology clay mineralogy and physical properties of all samples were determined sem analyses of artificially produced deformation patterns in the till samples show only a very thin shear zones of 2 3 m thickness despite long shear distances of up to 145 mm a clear relationship between local bedrock and the formation of a thin basal layer of heavily deformed till can be demonstrated this locally derived till layer exhibits distinctly different shearing properties compared to the massive overlying till unit that is composed of more distantly transported lithic material from the upper catchment area of the glacier the difference in the angle of internal friction between the two tills is 10 at residual shear strength although the clay mineralogy of both tills is similar it can further be demonstrated that after the deposition of a 10 15 cm thin till layer directly on bedrock the flow dynamics of the glacier tongue may have changed due to differences in glacier bed debris lithology differences in the shear behaviour of the sediments allied to microscopic analyses point to an important environmental change from a deformation till to an overlying non deformed till

till beneath ice stream b 3 till deformation evidence and implications most of the velocity of ice stream b near the upstream b camp upb west antarctica appears to arise from deformation of a seismically detected subglacial till layer that averages 6 m thick available evidence indicates that the entire thickness of this till layer is deforming and is eroding subjacent bedrock into flutes parallel to ice flow and hundreds of meters across the resulting till flux beneath upb is equivalent to an average erosion rate of about 0 4 mm yr 1 in the catchment area and suggests that till deltas tens of kilometers long have been deposited at the grounding line during the holocene such deltas should be characterized by partial ice till decoupling across a water film and by a small ice air surface slope they may have been discovered by recent geophysical work

high organic carbon content and a decrease in radiolarians at the end of the permian in a newly discovered continuous pelagic section a coincidence article i nfo the greatest mass extinction occurred at the end of the permian most records of the mass extinction are not from pelagic sediments but from shallow marine and terrestrial sediments although several pelagic sections that span the end permian mass extinction have been found these sections contain few index fossils and are often discontinuous because of small faults we found the index fossils albaillella cf triangularis radiolaria in siliceous claystone beds hindeodus parvus conodont in the overlying black claystone beds and neospathodus cf cristagalli and ns waageni conodont in the subsequent siliceous claystone beds in akkamori section 2 in northern japan these fossils suggest that this section ranges from the late permian to the early triassic including the early induan and olenekian stages furthermore the lithological changes in the section i e starting from bedded chert through siliceous claystone and black claystone to siliceous claystone are concordant with those of well known permian triassic pelagic sequences in japan there is no gap between each lithofacie of the akkamori section 2 critical lithological continuity between upper permian siliceous claystone beds and uppermost permian to lowermost triassic black claystone beds of the akkamori section 2 was recognized by observing hand polished specimens and thin sections such paleontological and sedimentological evidence implies that the akkamori section 2 is a continuous pelagic section that records the end permian mass extinction event the carbonaceous black claystone beds have high total organic carbon toc concentrations 1 06 3 31 wt suggesting oceanic anoxia at least deep and probably stable primary productivity a decrease in radiolarian abundance from 26 563 to 0 27 20 specimens cm 2 coincided with an increase in toc content from 0 01 0 16 to 1 06 3 31 wt at the boundary of the siliceous claystone and the overlying black claystone beds near the top of the permian implying that radiolarian extinction occurred at the end of the permian coinciding with oceanic anoxia although toc contents decreased in the early olenekian smithian radiolarian abundance did not increase at that time indicating that radiolarian recovery was delayed by n1 5 m y

approaches to the study of glacier bed deformation investigation of glacier bed conditions and subglacial processes is an obligatory requirement for the modelling and understanding of contemporary glacier behaviour past glacier behaviour glacier response to both spatial and temporal variations in bed material and glacier response to external forcing factors such as climate change the recognition of the importance of coupling between the glacier and its bed resulted in a paradigm shift in the subject and drew attention to the critical importance of subglacial deformation as opposed to simply subglacial deposition and sliding a number of methods have been adopted to measure glacier bed deformation ranging from direct observation and instrumentation the interpretation of macroscale and microscale sedimentary structures to the interpretation of glacier bedforms and glacier bed modelling this paper is concerned to describe the methods used by the two authors and co workers and attention is given to field methods the type and arrangement of sedimentary structures thin section micromorphology and microfabric and clast microfabric and glacier bedform morphology as evidence of subglacial deformation sedimentary structures macro and mesoscale are used to identify constructional deformation where deformational units are preserved one on top of another due to the formation of a thin deforming layer by low basal stresses and excavational deformation in which the deformational style is superimposed on pre existing styles due to increasing thicknesses of glacier deformation caused by increasing basal shear stresses thin section micromorphology has been used to define a range of glacial processes of which subglacial deformation is just one but has drawn attention to critical criteria such as discrete microscale shears orientated matrix kink structures and fractured grains as well as deformed intraclasts that can be used to recognise deformational processes more recently individual aggregates taking the form of rounded pebbles within till matrix have been shown to reflect rotational processes during glacial deformation and provide an additional mechanism to discrete shear within subglacial deformation and an explanation for the transport paths of subglacial materials finally measurements of sediment flow directions using clast macrofabric characteristics coupled with measurement of quantities of sediment transfered and detailed palaeoglacial properties have been used to determine the rates and scales of subglacial deformation associated with the formation of small scale glacier bedforms

evidence against pervasively deformed bed material beneath rapidly moving lobes of the southern laurentide ice sheet abstract during the wisconsin glaciation the ice lobes of the southern part of the laurentide ice sheet moved rapidly as the result of elevated subglacial water pressure the rapid movement was probably not accompanied by wide spread pervasive deformation of unfrozen material under the ice the till stratigraphy of much of this area is well known and it is clear that the stratigraphic sequence is generally intact therefore such deformation if it occurred would have been restricted to the till sheet that was currently being deposited however this seems unlikely as well because the till of the region commonly contains lenses and clasts of unlithified bedded sand that should have been destroyed by pervasive shearing if unfrozen deformed till layers were widely present they must have been confined to the thin upper parts of till sheets

radiolarian distribution in the water column southern gulf of california and its implication in thanatocoenose constitution abstract the geographical and depth distributions of five radiolarian plankton assemblages defined through q mode factor analysis of 24 plankton samples demonstrate a direct correspondence to the distribution of oceanographic water masses in the southern gulf of california two assemblages are associated exclusively with water masses of the mixed layer two represent only subsurface water masses and one is important in both surface and subsurface environments the lithomelissa thoracites group and peridium spinipes are predominant species in water that is formed at the surface of the guaymas basin and subsequently is subducted southward into the carmen basin plagiocantha panarium is the predominant species in upwelled surface water at the carmen basin while tetrapyle octhacanta and botryostrobus scutum follow the incursion of the subtropical water mass into the gulf of california through the pescadero and farallon basins druppatractus variabilis and porodiscus sp b occur conspicuously in the upper layer of the pacific intermediate water between approximately 400 and 700 m water depth statistical correlation between plankton and sediment assemblages supports previous evidence that the radiolarian thanatocoenose in the gulf of california is composed primarily of species from the surface mixed layer two exceptions to this are observed in the data first the upwelling plankton assemblage was not well correlated to the sediment assemblage and second input to the sediment during glacial stages appears to be dominated by subsurface forms

new insight into a subduction related orogen a reappraisal of the geotectonic framework and evolution of the japanese islands abstract the geotectonic framework and the evolutionary history of the japanese islands need revision in accordance with the various geophysical geological evidence gathered by new methodologies in the recent years including seismic tomography vibroseis ground breaking seismic experiments and detrital zircon chronology these investigations have addressed various themes such as 1 seismic profile of the crust and mantle beneath the japanese islands 2 high precision ages of the protoliths of high p t metamorphic rocks and 3 provenance of terrigenous clastics the results have led to a number of important findings including 1 detection of a large mass of slab around the mantle boundary layer suggesting the long term oceanic subduction beneath japan 2 confirmation of the subhorizontal piled nappe structure for the entire crust of japan 3 finding a new high p t metamorphosed accretionary complex unit that represents the youngest blueschist in japan 4 finding of the oldest early cambrian arc batholith and cover sediments and 5 the identification of plural arc batholiths which have already been erased from the surface based on a synthesis of these new data this article presents a re evaluation of the conventional geotectonic subdivision of the subduction related orogen in japan re definition of the elements and their mutual boundaries and re consideration of the geotectonic evolution of the japanese islands in particular the historical change in provenance suggests that proto japan has experienced large scale tectonic erosion in multiple stages and the corresponding large amounts of continental crust materials were subducted for understanding the orogenic growth of japan during the last ca 500 million years the significance of tectonic erosion coupled with continental contraction as well as the oceanward accretionary growth requires further attention

paleoceanographic history of the northwest pacific ocean over the past 740kyr discerned from radiolarian fauna abstract the northwest pacific ocean is characterized by a strong mixing of water masses due to the interplay of three distinct currents i e the kuroshio the tsugaru and the oyashio the c9001c drill core site located east of the shimokita peninsula and directly influenced by the tsugaru warm current and the oyashio subarctic current was used here to reconstruct the paleoceanographical history of this region especially focusing on the mid brunhes event mbe and its consequences this core provides a continuous record from marine isotope stage mis 18 740 ka to the present polycystine radiolarian assemblages were analyzed to highlight paleoceanographic and sea surface temperature changes at this site based on the radiolarian fauna seven time periods are defined which coincide with changes in the dynamics of the tsugaru and oyashio currents respectively the oldest time interval covered by our analysis i e vii 740 621 ka was marked by generally sluggish ocean circulation the tsugaru current influence increased during the following interval vi 621 478 ka which encompasses interglacials mis 15 and 13 while the oyashio current strengthened during the interval v 478 337 i e from glacials mis 12 to 10 these latter intervals vi to v constitute a long climatic transitional period where tsugaru current and oyashio current influences are strengthened in the time period from interval iv to interval i 0 337 ka the warming intensity of interglacials mis 9 mis 5 appears to be close to the modern one however several unusually warm glacials associated with a relatively strong tsugaru current flow were identified during this interval e g mis 8 and mis 6 radiolarian productivity data suggest that during intervals vii to v deep water masses are rich in nutrient content however a high vertical mixing event is recorded after interval iv when high nutrient concentrations appear to shift to the surface layer

spatial distribution pattern of living polycystine radiolarian taxa baseline study for paleoenvironmental reconstructions in the southern ocean atlantic sector the horizontal and vertical distribution of living polycystine radiolarian taxa was investigated at seven locations on a n s transect between the antarctic zone 54 s in the southern ocean and the subtropical zone 30 s in the southeastern south atlantic during austral autumn four to five depth intervals from 0 to 1000 m depth were sampled with 55 m mesh opening closing nets in combination with a hydrographic ctd survey a factor analysis for the delineation of specific assemblages and the relation between different taxa and taxa groups resulted in eight factors of which five represent surface and subsurface factors and three deep water factors the spatial distribution pattern of the factors shows that distinct radiolarian assemblages are closely related to water depth distribution of water masses hydrographic boundaries such as frontal systems and nutrients this documents that the distribution of individual radiolarian assemblages is controlled by specific hydrographic conditions and water depth and allows the definition and consolidation of the autecological demands these data are crucial for the paleoenvironmental interpretation of fossil polycystine radiolarian assemblages the comparison of living polycystine radiolarian taxa with those preserved in surface sediments shows general similarities this study includes the first documentation on the distribution of living cycladophora davisiana in circumpolar deep water and supports previous studies stating that c davisiana also lives in deep water masses

anomalous oceanic lithosphere formed in a leaky transform fault evidence from the western limassol forest complex cyprus detailed studies in the western limassol forest complex cyprus have revealed plutonic and structural histories that differ markedly from the penrose type ophiolite of the troodos massif to the north a tectonized harzburgite of upper mantle origin acts as host to multiple mafic and ultramafic intrusions forming a plutonic core complex mafic and picrite dykes cut and are cut by e w trending shear zones demonstrating syn tectonic magmatism a retrogressive metamorphic and progressive cooling history of the intrusive suite indicates uplift of the host mantle harzburgite while in a sea floor setting it is suggested here that the geological evolution of the western limassol forest complex indicates formation of anomalous oceanic lithosphere in the active domain of an upper cretaceous leaky transform fault

high porosity of basal till at burroughs glacier southeastern alaska debris rich basal ice at burroughs glacier southeastern alaska has 60 vol to 70 vol debris recently deposited basal till exceeds 60 vol sediment with 30 to almost 40 porosity where basal ice is very rich in debris basal till is deposited through melt out with only slight compaction of the debris porosity this high in till is commonly associated with subglacially deforming and dilated sediment however the recently deposited basal melt out till at burroughs glacier has not been deformed after deposition but has porosity values similar to tills elsewhere interpreted to be subglacially deforming and dilated in an unfrozen state high porosity can occur in basal melt out till deposited directly by basal melt out

the spatial nearshore offshore distribution of latest permian phytoplankton from the yangtze block south china abstract in order to analyze the spatial paleoecological distribution of the organic walled microphytoplankton in the late permian five sections from the yangtze block south china displaying different sediment facies types from neritic to offshore paleoenvironments including basinal facies have been investigated palynologically based on the diversity and relative abundance of acritarch species and genera the new data from the permian provide similar patterns as those described from other geological periods 1 low diversities with 2 to 4 acritarch species occur in nearshore environments whereas the higher diversities more than ten acritarch species appear in the offshore environments 2 at the generic level the genera leiosphaeridia reduviasporonites and micrhystridium are distributed widely from nearshore facies corresponding to shallow water environments to offshore facies corresponding to deeper water settings whereas some genera such as dictyotidium and veryhachium have a narrower distribution occurring on the continental shelf and towards the basin indicating open marine environments 3 the genus schizosporis only occurs around the permian triassic boundary ptb when the sea level declined probably indicating nearshore environments with shallow water settings 4 at the specific level the species micrhystridium breve displaying short spines and leiosphaeridia minutissima are indicative of neritic facies whereas the other species of micrhystridium and veryhachium with longer spines e g micrhystridium stellatum and veryhachium hyalodermum and leiosphaeridia microgranifera indicate more open marine environments big spherical acritarch species over 80 m in diameter such as dictyotidium reticulatum indicate shallow water environments and 5 in the ptb strata the relative abundance of the enigmatic reduviasporonites interpreted by some authors as a fungal spore is not higher than 14 in every sample indicating that a spike of reduviasporonites does not occur in the yangtze area reduviasporonites chalastus 40 m in length obviously dominates in shelf environments of shallow water whereas the smaller reduviasporonites catenulatus 15 m in length are more common in deeper water

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

intrusive suite documented in the troodos ophiolite plutonic complex cyprus two definable magmatic suites occur within the plutonic complex in the caledonian falls area of the troodos ophiolite cyprus an early suite of generally well layered and structurally concordant gabbros and pyroxenites is intruded by a later suite of poikilitic wehrlites and gabbro norites discordant structural relations can be demonstrated between units belonging to the two magmatic suites xenoliths near the contacts prove relative age relations differences in mineral chemistry between the two suites indicate that the parent magmas of the two suites were of different compositions the petrogenesis of the two cumulate suites may be explained by a second stage melting of a mantle diapir or by compaction of a zone of crystal mush below the moho

the guadalupian lopingian boundary permian in a pelagic sequence from panthalassa recognized by integrated conodont and radiolarian biostratigraphy abstract guadalupian lopingian sedimentary rocks are widely distributed in accretionary complexes in japan but the guadalupian lopingian boundary g lb is not well documented from these pelagic sediments to identify the g lb and to better correlate an extinction event that occurred around the guadalupian lopingian boundary we examined the conodont biostratigraphy from a permian pelagic chert sequence in the gujo hachiman section gifu southwest japan age diagnostic conodonts including clarkina postbitteri postbitteri were found in this section the biostratigraphic occurrences of these age diagnostic conodonts can pinpoint the g l transitional zone in the gujo hachiman section by comparison with well studied sections from south china including the gssp section the transitional zone was recognized by the first occurrence horizons of both clarkina postbitteri hongshuiensis and c p postbitteri the g lb has been placed at or above the first occurrence horizon of the radiolarians albaillella yamakitai or albaillella cavitata in previous studies from china and japan we detected the first occurrence horizon of a yamakitai below the base of the g l transitional zone in the upper capitanian the conodont biostratigraphy is consistent with the radiolarian biostratigraphy in this section which can be correlated to relevant sections in china

high resolution δ13ccarb chemostratigraphy from latest guadalupian through earliest triassic in south china and iran large carbon cycle perturbations are associated with the end permian mass extinction and subsequent recovery but late permian lopingian carbon cycle dynamics prior to the mass extinction event remain poorly documented here we present a high resolution 13ccarb chemostratigraphic framework from latest guadalupian to earliest triassic time calibrated with high resolution conodont biostratigraphy and high precision geochronology we observe two large negative excursions in 13ccarb the first in uppermost guadalupian strata and the second at the end of the changhsingian stage and between these events distinctive excursions from the middle wuchiapingian to the early changhsingian the end changhsingian excursion represents a major reorganization of the global carbon cycle associated with the end permian mass extinction however the extent to which the end guadalupian and wuchiapingian changhsingian boundary excursions result from local versus global controls remains unresolved regardless of their underlying causes these three excursions provide chemostratigraphic markers for global correlation of lopingian strata

intra panthalassa ocean subduction zones revealed by fossil arcs and mantle structure the vast panthalassa ocean once surrounded the supercontinent pangaea subduction has since consumed most of the oceanic plates that formed the ocean floor so classic plate reconstructions based on magnetic anomalies can be used only to constrain the ocean s history since the cretaceous period 1 2 and the triassic jurassic plate tectonic evolution of the panthalassa ocean remains largely unresolved 3 4 geological clues come from extinct intra oceanic volcanic arcs that formed above ancient subduction zones but have since been accreted to the north american and asian continental margins 4 here we compile data on the composition the timing of formation and accretion and the present day locations of these volcanic arcs and show that intra oceanic subduction zones must have once been situated in a central panthalassa location in our plate tectonic reconstructions 5 7 to constrain the palaeoposition of the extinct arcs we correlate them with remnants of subducted slabs that have been identified in the mantle using seismic wave tomographic models 8 9 we suggest that a series of subduction zones together called telkhinia may have defined two separate palaeo oceanic plate systems the pontus and thalassa oceans our reconstruction provides constraints on the palaeolongitude and tectonic evolution of the telkhinia subduction zones and panthalassa ocean that are crucial for global plate tectonic reconstructions and models of mantle dynamics the spatial uncertainty in reconstructions of oceanic basins increases the further we go back in time because oceanic plates subduct plate reconstructions for the triassicjurassic history of the panthalassa ocean once surrounding the pangaea supercontinent are based on the premise that the pacific plate formedinthemiddlejurassicasatriangle 2 originatingfromatriple junction between the farallon phoenix and izanagi plates fig 1 the preserved area of jurassic palaeoplates represents only a small portion 10 of the oceanic crust of the jurassic panthalassa ocean the remaining part along with pre jurassic oceanic plate configurations is entirely unconstrained however the geology of the circum panthalassa continental margins provides evidence that early mesozoic subduction related volcanism occurred in the panthalassa ocean 4 10 on subduction continental fragments volcanic arcs ophiolites and ocean floor sediments collided with or accreted to the continental margins of in particular western north america far east asia and japan marine microfossils in these sediments and palaeomagnetic data constrain their age and palaeolatitude but their palaeolongitudes remain undetermined palaeogeographic reconstructions therefore show uncorrelated intra panthalassa exotic terranes essentially

a dolomitization event at the oceanic chemocline during the permian triassic transition the permian triassic boundary ptb crisis caused major shortterm perturbations in ocean chemistry as recorded by the precipitation of anachronistic carbonates here we document for the first time a global dolomitization event during the permian triassic transition based on mg mg ca data from 22 sections with a global distribution representing shallow to deep marine environments ten of these sections show high mg mg ca ratios bracketing the ptb recording a short term spike in dolomite formation the dolomite consists mainly of micron scale anhedral to subhedral crystals that are associated with abundant fossilized bacterial bodies and extracellular polymeric substances suggesting that dolomite precipitation was induced by microbial metabolic activity sections showing a dolomite spike at the ptb are widely distributed geographically but mostly encountered in mid shelf to upper slope settings because the dolomitization event coincided with a rapid expansion of oceanic anoxia and high rates of sulfate reduction we hypothesize that it was triggered by enhanced microbial sulfate reduction within the oceanic chemocline

evolution of oceanic redox conditions during the permo triassic transition evidence from deepwater radiolarian facies abstract the 90 biodiversity loss among marine invertebrate species during the end permian mass extinction the most severe phanerozoic biocrisis has been attributed to widespread oceanic anoxia superanoxia recent studies of the lithofacies inorganic geochemistry and biomarkers of permian triassic boundary ptb sections have yielded an inferred pattern of oceanic redox changes that is complex and sometimes inconsistent in this contribution we review the ecology of radiolarians an important microzooplankton group during the permo triassic transition and consider its implications for contemporaneous changes in paleoceanographic conditions our analysis shows that 1 late permian radiolarian faunas were cosmopolitan with different orders having specific depth preferences i e albaillellarians favoring deeper waters and spherical forms entactinarians and spumellarians shallower waters 2 deep water taxa declined earlier than shallow water taxa 3 many paleozoic type taxa survived into the early triassic but went extinct during a second crisis in the dienerian dead clade walking followed by the appearance or expansion of mesozoic type taxa during the olenekian and 4 the survival of paleozoic type taxa during the early triassic was greater at higher paleolatitudes than in the tropics these observations are consistent with a first order redox control on radiolarian faunal distributions specifically a shallowing and poleward expansion of the oceanic oxygen minimum zone during the ptb crisis the consequent adaptation of some deepwater taxa to shallower environments resulted in early triassic radiolarian faunas in continental basins becoming more similar to those in pelagic settings enhanced survival of paleozoic type taxa in high latitude regions indicates that the main stressor on permo triassic radiolarian communities was reduced oceanic oxygen levels stronger in the tropics rather than climatic warming stronger at the poles

the 3d microscopic signature of strain within glacial sediments revealed using x ray computed microtomography abstract x ray computed microtomography ct a non destructive analytical technique was used to create volumetric three dimensional 3d models representing the internal composition and structure of undisturbed pro and subglacial soft sediment sample plugs for the purposes of identifying and analysing kinematic indicators the technique is introduced and a methodology is presented addressing specific issues relating to the investigation of unlithified polymineralic sediments six samples were selected based on their proximity to type brittle and ductile deformation structures or because of their perceived suitability for successful application of the technique analysis of a proglacial ideal specimen permitted the 3d geometry of a suite of micro faults and folds to be investigated and the strain history of the sample reconstructed the poor contrast achieved in scanning a diamicton of glaciomarine origin is attributable to overconsolidation under normal loading the sediment demonstrated to have undergone subsequent subglacial deformation another overconsolidated diamicton contains an extensive small scale the subglacial sample evidence indicates that complex polyphase brittle ductile deformation histories are common in such diamictic soft sediments and that the local micro scale environment composition structure shear forces and effective pressure controls rheology the sediment void ratio is a key indicator of strain three of the samples are tentatively placed at different points on the strain cycle for subglacially deforming soft sediment based on their void ratio characteristics and distribution it has been demonstrated that ct offers significant potential for elucidating glacial soft sediment kinematics the ability of the technique to both test a variety of hypotheses pertaining to mechanisms operating within the subglacial environment and evaluate efforts to replicate those processes under controlled laboratory conditions is therefore discussed along with solutions to the problems encountered within this project ct also permits the seamless linking of analytical techniques applied at the hand specimen mm micromorphological m mm scanning electron microscopy and x ray diffraction fluorescence nm m scales and the archiving duplication and dissemination of sample volumetric 3d data

carbon isotopic evidence for chemocline upward excursions during the end permian event abstract a negative shift in marine inorganic carbon isotope composition 13 c carb during the end permian mass extinction has been used as evidence for several different extinction mechanisms changes to the 13 c of organic matter and the difference between it and 13 c carb 13 c 13 c carb 13 c org have been examined at few locations with conflicting interpretations we examine the changes to both organic and inorganic carbon isotopes across the permian triassic boundary at two marine sections from south china meishan and shangsi and compare these to data from other previously published sections through these analyses we demonstrate that a decrease in 13 c occurred during the extinction event throughout the paleo tethys ocean the extent and intensity of the decrease varies by location averaging a negative shift of 5 several possibilities as to the cause of this shift exist including siberian trap volcanism a change in the terrestrial marine organic carbon input to the system or a change in the dominant marine biota brought about through environmental changes such as widespread ocean anoxia euxinia the decrease in 13 c observed at many of these sections across the event horizon is here interpreted to represent a shift from algae cyanobacteria to less fractionating phototrophic sulfur bacteria in marine shelf environments resulting from upward excursions of the chemocline these chemocline upward excursions would release euxinic water to the photic zone allowing phototrophic sulfur bacteria to thrive the limited available biomarker data are consistent with this interpretation

the end permian regression in south china and its implication on mass extinction abstract records of more than 20 permian triassic boundary ptb sections from south china show that widespread end permian regression took place in whole south china timing of the low ebb of this regression was pinpointed to the clarkina meishanensis and hindeodus changxingensis zones biostratigraphic and paleogeographic studies at conodont zonation level reveal that the yangtze carbonate platform and isolated small carbonate platforms in the hunan guizhou guangxi hgg basin experienced sedimentary hiatus during these two zones which lasted about 50 100 kya meanwhile the basinal areas namely the northern marginal basin of yangtze platform and the hunan guizhou guangxi basin have continuous conodont zonation with silicious and ashbed deposits the basinal areas show two negative 13c shifts during the ptb interval from clarkina yini zone to isarcicella isarcica zone while on the platforms there is usually only one negative shift because the early shift at c meishanensis zone was lost during hiatus the end permian regression and successive rapid transgression taking place at the ptb casted important effects to the pattern and process of the ptb mass extinction the depositional hiatus hitherto underestimated will necessitate reassessment of some interpretations on the causes and results of that extinction

theory of glacial erosion transport and deposition as a consequence of subglacial sediment deformation a theory of erosion transport and deposition of unlithified sediments by glaciers is presented it predicts the large scale areal distribution of zones and rates of erosion and deposition in time and space through a complete glacial cycle together with the resultant intensity of large scale lincations drumlins which will be incised in the landscape the theory also predicts the dispersal patterns of subglacial lithologies together with the form of dispersal trains derived from distinctive sources and the vertical and horizontal distribution of lithologies within a till it predicts major erosional discontinuities within tills and the formation of boulder pavements it suggests that the dominant proportion of the lowland tills produced by pleistocene mid latitude ice sheets was generated by subglacial deformation and explains why they are predominantly fine grained the theory is based on an analysis of glacier dynamic processes and therefore can be used to infer the dynamic behaviour of former ice sheets from the distribution of tills and their lithologic composition

growth and demise of permian biogenic chert along northwest pangea evidence for end permian collapse of thermohaline circulation abstract the permian chert event pce was a 30 ma long episode of unusual chert accumulation along the northwest margin of pangea and possibly worldwide the onset of the pce occurred at about the sakmarian artinskian boundary in the sverdrup basin canadian arctic where it coincides with a maximum flooding event the ending of high frequency high amplitude shelf cyclicity the onset of massive biogenic chert deposition in deep water distal areas and a long term shift from warm to cool water carbonate sedimentation in shallow water proximal areas a similar and coeval shift is observed from the barents sea to the northwestern usa a landward and southward expansion of silica factories occurred during the middle and late permian at which time warm water carbonate producers disappeared completely from the northwest margin of pangea biotically impoverished and increasingly narrow cold water carbonate factories characterised by non cemented bioclasts of sponges bryozoans echinoderms and brachiopods were then progressively replaced by silica factories by late permian time little carbonate sediments accumulated in the barents sea and in the sverdrup basin where the deep to shallow water sedimentary spectrum was occupied by siliceous sponge spicules by that time biogenic silica sedimentation was common throughout the world silica factories collapsed in the late permian abruptly bringing the pce to an end in northwest pangea the end permian collapse of the pce was associated with a major transgression and with a return to much warmer oceanic and continental climatic conditions chert deposition resumed in the distal oceanic areas during the early middle triassic anisian after a 8 10 ma interruption early triassic chert gap the conditions necessary for the onset expansion and zenith of the pce were provided by the thermohaline circulation of nutrient rich cold waters along the northwestern and western margin of pangea and possibly throughout the world oceans these conditions provided an efficient transportation mechanism that constantly replenished the supply of silica in the area created a nutrient and oxygen rich environment favouring siliceous biogenic productivity established cold sea floor conditions hindering silica dissolution while increasing calcium carbonate solubility and provided conditions adverse to organic and inorganic carbonate production the northwest margin of pangea was for nearly 30 ma bathed by cold waters presumably derived from the seasonal melting of northern sea ice the assumed engine for thermohaline circulation this process started near the sakmarian artinskian boundary intensified throughout middle and late permian time and ceased suddenly in latest permian time it led to oceanic conditions much colder than normally expected from the palaeolatitudes and the influence of cold northerly derived water was felt as far south southern nevada the demise of silica factories was caused by the rapid breakdown of these conditions and the establishment of a much warmer marine environment accompanied by sluggish circulation and perhaps a reduced input of dissolved silica to the ocean complete thawing of northern sea ice would have ended thermohaline circulation and led to warm and sluggish oceanic conditions inimical to the production accumulation and preservation of biogenic silica

depth related radiolarian assemblage in the water column and surface sediments of the japan sea plankton tows and surface sediments from the japan sea a marginal sea of the northwestern pacific were examined to study the depth distribution of modern radiolarians the depth distribution patterns between the living assemblage in the water column and the thanatocoenose in surface sediments are similar to each other indicating that the depth related assemblage in sediments is closely related to the living depths of major species four clear restrictions of many species to discrete depth zones are recognized in the water column from the surface down to 2000 m 1 upper subsurface water species which are abundant from 40 to 120 m larcopyle butschlii juvenile form spirocyrtis subscalaris spongodiscus resurgens and lipmanella virchowii 2 lower subsurface water species which are abundant from 40 to 300 m larcopyle butschlii adult form ceratocyrtis histricosa and spongotrochus glacialis 3 intermediate water species which have population maxima from 160 to 300 m ceratospyris borealis and 4 deep water species which have maxima between 1000 and 2000 m cycladophora davisiana and actinomma boreale only a few specimens of a boreale were found in the water column ranging from 1000 to 2000 m depth although this is a dominant species in surface sediments from depths below 2000 m of which the dominance increases with water depth a boreale may live mainly in the bottom water cycladophora davisiana and a boreale which characterize the japan sea deep assemblage are naturally shallow or intermediate dwellers in other oceans on the other hand the typical deep dwellers e g cornutella profunda cyrtopera languncula and peripyramis circumtexta of other oceans have not been found in the japan sea such a peculiar deep assemblage is a result of the deep circulation system in the japan sea and the shallow depths of the sills around it

brachiopod miniaturization and its possible causes during the permian triassic crisis in deep water environments south china abstract brachiopod miniaturization is both the reduction in size of individuals of a species over time and where one brachiopod fauna dominated by larger individuals was replaced by a brachiopod fauna dominated by smaller individuals over time this paper investigates this phenomenon prior to and during the end permian crisis in a deep water setting in south china based on precise measurements of brachiopod body size and on the abundance and diversity of brachiopod species the process of miniaturization near the permian triassic boundary in deep water environments is characterized by 1 larger species including martinia sp costatumulus dongpanensis and anidanthus mucronata reduced in average body size and abundance over time towards the end permian brachiopod extinction event 2 small species including attenuatella mengi and spinomarginifera semicircridge showed a mixed response with either no size change or a reduction in average body size while these species increased in abundance over time indicating they were less sensitive to the stressed environmental setting 3 both the total abundance and the diversity of this brachiopod fauna decreased over time towards the end permian crisis regression an increased input of terrestrial material and productivity decline are considered to all have contributed to brachiopod miniaturization based on the biotic replacement and changes in sea water chemistry among these factors the fall in sea level is perhaps the primary factor and led to a decline in productivity and an increased input of terrestrial material into the marine setting

changes in productivity and redox conditions in the panthalassic ocean during the latest permian the gujo hachiman section in central japan provides a rare window into environmental conditions within the panthalassic ocean which encompassed more than half the earth s surface at 251 ma the section is characterized by a sharp transition from green gray organicpoor cherts to black siliceous shales in the uppermost permian normalization to the clay fraction demonstrates that apparent increases in the concentrations of organic matter and trace metals above this transition were due primarily to the loss of a diluent biogenic radiolarian silica fl ux and only secondarily to a small shift toward more reducing bottom waters in the black shale pyrite abundance increases by a factor of 30 and is dominated by framboidal grains of probable syngenetic origin these observations suggest that the expansion of lowoxygen conditions within the panthalassic ocean was focused within the oxygen minimum zone rather than at the seafl oor such a pattern implies that 1 changes in nutrient fl uxes and primary productivity rates rather than stagnation of oceanic circulation were a key factor infl uencing oceanic redox conditions around the permian triassic boundary and 2 large regions of the panthalassic ocean underwent only limited redox changes providing potential refugia for marine taxa that survived into the triassic

end permian extinction and volcanism induced environmental stress the permian triassic boundary interval of lower slope facies at chaotian south china abstract in order to reveal environmental changes across the permo triassic boundary ptb the detailed lithostratigraphy of the ptb interval is analyzed at chaotian in northern sichuan china the studied section is composed of the changhsingian upper permian dalong formation and the induan lower triassic feixianguan formation of a lower slope facies deposited on the northwestern margin of the yangtze carbonate platform the 12 m thick interval across the ptb consists mainly of bedded carbonates and mudstone and is lithologically divided into 7 units i e units a to g in ascending order the main extinction horizon of permian taxa is recognized at the unit d e boundary where various fossil metazoans and protists such as ammonoids brachiopods bivalves conodonts and radiolarians rapidly disappeared or became scarce the complete disappearance of radiolarians at the unit d e boundary emphasizes that the ptb extinction affected not only various late permian benthic and free swimming metazoans but also planktonic protozoans the lowest induan index conodont hindeodus parvus first occurs at the base of unit f marking the biostratigraphically defined ptb horizon unit e composed of unique bedded marl between the main extinction horizon and the first occurrence of triassic taxon represents a period of strong environmental stresses that suppressed productivity both of silica and carbonate secreting organisms by changing their size radiolarians reacted most sensitively to the environmental change that already started in the late changhsingian appreciably before the final extinction event the frequent intercalation of rhyo dacitic tuff beds particularly in unit d and the lower part of unit e across the main extinction horizon suggests that intermittent felsic volcanism and relevant environmental change may have been responsible for the mass extinction of the permian taxa and for the prolonged post extinction lag time before the initial recovery the frequent ash falls during the late changhsingian indicate that the volcanism induced environmental change had already started earlier than the main extinction all the biological production carbonate silica and organic matter collapsed at the unit d e boundary when the environmental stresses may have passed a critical threshold for maintaining ecological stability the ptb interval between the extinction and the first appearance of triassic taxon at chaotian is ca 1 4 m thick apparently almost eight times thicker than that at the global stratotype section and point of ptb in meishan 19 cm the chaotian section as well as the neighboring shangsi section in northern sichuan may provide a better chance for high resolution chemostratigraphic analyses that may allow detection and correlation of subtle environmental changes across the ptb

marine productivity changes during the end permian crisis and early triassic recovery abstract the latest permian mass extinction lpme coincided with major changes in the composition of marine plankton communities yet little is known about concurrent changes in primary productivity earlier studies have inferred both decreased and increased productivity in marine ecosystems immediately following the end permian crisis here we assess secular and regional patterns of productivity variation during the crisis through an analysis of the burial fluxes of three elemental proxies total organic carbon toc phosphorus p and biogenic barium babio primary productivity rates appear to have increased from the pre crisis late permian through the early triassic in many parts of the world although the south china craton is unusual in exhibiting a pronounced decline at that time most of the 14 permian triassic study sections show concurrent increases in sediment bulk accumulation rates suggesting two possible influences linked to subaerial weathering rate changes 1 intensified chemical weathering resulting in an increased riverine flux of nutrients that stimulated marine productivity and 2 intensified physical weathering leading to higher fluxes of particulate detrital sediment to continental shelves thus enhancing the preservation of organic matter in marine sediments an additional factor especially in the south china region may have been the intensified recycling of bacterioplankton derived organic matter in the ocean surface layer reducing the export flux rather than primary productivity per se the ecosystem stresses imposed by elevated fluxes of nutrients and particulate sediment as well as by locally reduced export fluxes of organic matter may have been important factors in the 2 to 5 million year long delay in the recovery of early triassic marine ecosystems

sulfur isotopic evidence for chemocline upward excursions during the end permian mass extinction the latest permian was a time of major change in ocean chemistry accompanying the greatest mass extinction of the phanerozoic to examine the nature of these changes samples from two well studied marine sections that span the permian triassic boundary have been analyzed the meishan and shangsi sections located in southern china isotopic analysis of the carbonate associated sulfate in these samples provides a detailed record of several isotopic shifts in 34scas approaching and across the ptb ranging from 30 to 15 vcdt with repeated asynchronous fluctuations at the two locations we interpret the patterns of isotopic shifts in conjunction with other data to indicate a shallow unstable chemocline overlying euxinic deep water which periodically upwelled into the photic zone these chemocline upward excursion events introduced sulfide to the photic zone stimulating a bloom of phototrophic sulfur oxidizing bacteria we hypothesize that elemental sulfur globules produced by these organisms and 34s depleted pyrite produced in the euxinic water column were deposited in the sediment later oxidation led to incorporation as cas this created the large changes to the 34scas observed in the latest permian at these locations

constraining paleo latitude of a biogeographic boundary in mid panthalassa fusuline province shift on the late guadalupian permian migrating seamount abstract the guadalupian paleo atoll limestone iwato formation in sw japan was primarily formed in low latitude mid panthalassa and was later tectonically accreted to south china japan margin during the jurassic the present biostratigraphic study clarified that the iwato formation consists of 5 biostratigraphical intervals i e four fusuline assemblage zones assemblage zones 1 to 4 and a barren interval on the top assemblage zones 1 to 4 correspond to the neoschwagerina craticulifera zone n margaritae zone yabeina globosa zone and lepidolina multiseptata zone of the conventional tethyan fusuline stratigraphy respectively the present study newly clarified the following significant aspects of paleobiogeography of the permian fusulines as to the extinction of large tested taxa in the latest guadalupian 1 the long unknown stratigraphic relationship was documented for the first time between the yabeina dominant interval and the overlying lepidolina dominant one within a single limestone unit 2 the occurrence of lepidolina cf kumaensis kanmera the unique last runner of large tested fusuine was detected for the first time in mid oceanic paleo atoll limestones 3 with respect to the northbound migration history of the paleo seamount capped by the iwato formation the development of the two coeval fusuline biogeographic territories in the low latitude panthalassa i e the yabeina territory on the south and the lepidolina territory on the north was confirmed 4 the paleo latitude of the biogeographic boundary between the yabeina and lepidolina territories is constrained around 12 in the southern hemisphere on the basis of the latest geomagnetic data from the same limestone this new approach utilizing biostratigraphy on ancient migrating seamounts coupled with geomagnetic paleo latitude data is applicable to other cases in different time space co ordinates and of other fossil groups for constraining position of ancient biogeographic boundaries within lost oceanic domains of deep past

radiolarian assemblages in surface sediments along longitude 175 e in the pacific ocean abstract this study of 24 surface sediment samples along longitude 175 e between latitudes 48 n and 14 s in the western pacific ocean documents the relationship between the modern distribution of radiolarian assemblages and present oceanographic conditions ninety two species were classified into eight clusters by using r mode cluster analysis q mode cluster analysis was used to distinguish five geographical zones which were interpreted to represent the tropical southern subtropical northern subtropical transitional and subarctic climatic zones species richness diversity and equitability are highest in the tropical and transitional zones we attempted to formulate new regression equations considering ecological information on the vertical distribution of radiolarian species transfer functions were derived from regression analysis of radiolarian assemblages to observed sea surface temperature sst values the transfer functions have a standard error of 1 16 c in the estimate of winter sst 0 81 c in that of summer sst

soft lodgement till deposition and syndepositional deformation anielinek the polish lowlands the paper presents a case study of sediment termed soft lodgement till a product of subglacial deposition by active ice described previously on the basis of macro evidence from poland and canada but not yet studied in detail in one particular site the till at anielinek about 7 m thick was examined by macroscopic observation thin section description and qualitative and quantitative scanning electron microscopy sem analyses it shows a macroscopic massive structure and overlies a flat top of glaciolacustrine sediments these sediments form upward intrusions within the till owing to the existence of reversed density gradients among the deposits and the upper parts of the intrusions are tilted in consistent directions within the successive parts of the till moreover sem images also record uniformly oriented microintrusions within this diamictic material the occurrence of these macro and microstructures within the successive parts of the till point to an almost continuous process of intrusion du

water depths of the latest permian changhsingian radiolarians estimated from correspondence analysis abstract this paper briefly summarizes current knowledge on water depth indicators in permian radiolarians and compares this knowledge with observational evidence for water depth indicators in living radiolarians studies on modern radiolarians demonstrate the feasibility of estimating floating depths at the species level but not at higher taxonomic levels this apparently contradicts the common assumption that the subfamily copicyntrinae indicates shallow water and the order albaillellaria deep water in the permian we approach this contradiction in water depth distributions by using a statistically driven correspondence analysis ca which so far has never been used for permian radiolarian studies ca was applied to multivariate meta datasets of the changhsingian dalong formation of south china and of pelagic deep cherts from japan because the depositional water depths from these successions have been well studied and the evidence is reliable these two regions belonged to the same low latitude region in the lopingian late permian based on fusulinids and tectonic reconstructions the ca results indicate that the output dimension 1 largely represents depositional water depths from very shallow positive value to deep negative value and dimension 2 seems to be closely related with siliciclastic input following the scores along dimension 1 the nine examined sections were categorized into five water depth zones very shallow xinmin and shangsi shallow pingdingshan and hushan upper intermediate rencunping middle intermediate dongpan and lower intermediate pelagic deep gujo hachiman itsukaichi and shikoku this order roughly agrees with empirical water depths based on palaeontological and geological evidence based on this water depth order species were categorized into five water depth zones 14 very shallow water species 18 shallow water species 14 upper intermediate water species 39 middle intermediate water species and seven lower intermediate to deep water species for the first time our data also statistically prove that entactinaria and spumellaria did not live in very deep water and that most latentifistularia and albaillellaria species are upper intermediate to deep water species this result partly supports the utility of water depth indicators at the taxonomic order level in the late permian

microscopic evidence of subglacial deformation abstract subglacial deformation is by now a well established process however recognition of this process in pleistocene tills is not always clear studies of thin sections of pleistocene tills show that there are a variety of microscopic features caused by deformation this paper gives a review of microscopic evidence for subglacial deformation and starts with a case where deformation could be established macroscopically then traces the microscopic features through planar and rotational movements which are described and separated accordingly attention is also given to features caused by crushing of grains and sediment dewatering these studies indicate that almost all basal tills show evidence of subglacial deformation rather than sedimentary derivation this implies that if we want to understand subglacial processes such tills should be described in tectonic rather than sedimentary terminology

spatial variation in sediment fluxes redox conditions and productivity in the permian triassic panthalassic ocean abstract two permian triassic boundary sections in central japan provide a rare window into environmental conditions within the panthalassic ocean which encompassed more than half the earth s surface at 252 ma integration of petrographic geochemical and time series data provides new insights regarding the fluxes of major and trace components to the sediment as well as environmental conditions in both the deep and intermediate water masses at each study site the ubara section was located in a high productivity peri equatorial location whereas the gujo hachiman section was located in a moderate productivity location at some distance from the paleoequator an upward transition from gray organic poor cherts to black siliceous mudstones at both sites occurred in conjunction with increased primary productivity intensified euxinia within the oxygen minimum zone omz and decimation of the radiolarian zooplankton community euxinia in the omz of the equatorial panthalassic ocean developed episodically for a 200 250 kyr interval during the late permian followed by an abrupt intensification and lateral expansion of the omz around the permian triassic boundary throughout the study interval bottom waters at both sites remained mostly suboxic a finding that counters hypotheses of development of a superanoxic permo triassic deep ocean as a consequence of stagnation of oceanic overturning circulation

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

the effect of severe storms on the ice cover of the northern tatarskiy strait the tatarskiy strait is the northernmost region of the japan sea with an ice covered area in winter of about 4 104 km2 this study uses the daily passive microwave images of the region from the special sensor microwave imager ssm i which was launched in 1987 to estimate the production of ice and japan sea bottom water in winter the prevailing winds in the strait are northerly and cold these conditions create a region of reduced ice concentration in the northern strait which leads to an enhanced ice production throughout the season in addition to these prevailing winds each winter one or two severe storms generate very strong northerly winds and cold temperatures in the strait these storms create a large transient polynya in the strait at a time simultaneous with the greatest heat flux out of the open water calculation of the ice growth from open water in the northern strait yields about 25 km3 of ice per season of which severe storms provide about 25 the total ice production is sufficient to form about 5 12 102 km3 of the japan sea bottom water which is about 50 100 of the renewal rate required from 14c data because the oxygen bottom layer thickness decreased between 1969 and 1984 the study also investigates the frequency of the severe storms in the northern strait during 1966 1990 and finds that these storms are about 3 times as frequent at the beginning of this period than at the end this suggests the storms may play a role in the generation of the japan sea bottom water

vertical distribution of polycystine radiolarians in the northern east china sea abstract the east china sea ecs is a marginal sea influenced by the kuroshio current kc and by freshwater discharged by the changjiang river in this study the vertical distribution of polycystine radiolarians in the northern ecs was investigated we collected plankton tow samples from the water column at five stations in the northern ecs stations 11 and 11 were on the ecs continental shelf and stations 1 8 and 12 were in the northeastern ecs which is influenced by the kc we identified six distinct depth intervals by a q mode cluster analysis at stations 1 8 and 12 radiolarians were abundant and species diversity was high in the surface waters standing stocks of subtropical species such as didymocyrtis tetrathalamus phorticium pylonium pterocanium praetextum spongaster tetras tetras and the tetrapyle octacantha groups were high reflecting the influence of the warm kc in contrast at intermediate water depths standing stocks of subarctic radiolarians such as actinomma leptodermum cycladophora bicronis haliommetta miocenica pseudodyctiophimus gracilipes and lithelius minor were relatively high which may reflect the influence of a subarctic water mass that probably originated in the north pacific at stations 11 and 11 on the shelf the influence of freshwater from the changjiang river is high and radiolarians were absent in the upper 20 m of the water column and scarce at depths of 20 100 m where three species dominated archipera triclavigera pseudocubus obeliscus and cryptogyrus calvatus

mercury anomalies across the end permian mass extinction in south china from shallow and deep water depositional environments abstract life on earth suffered its greatest bio crisis since multicellular organisms rose 600 million years ago during the end permian mass extinction coincidence of the mass extinction with flood basalt eruptions in siberia is well established but the exact causal connection between the eruptions and extinction processes in south china is uncertain due to their wide spatial separation and the absence of direct geochemical evidence linking the two the concentration and stable isotope analysis of mercury provides a way to test these links as its concentration is thought to be tied to igneous activity mercury total organic carbon ratios from three permian triassic boundary sections with a well resolved extinction record in south china show elevated values up to 900 ppb wt relative to a background of 199 hg with sustained positive values indicate a predominant atmospheric derived signature of volcanic hg in deep shelf settings of the daxiakou and shangsi sections in contrast the nearshore environment of the meishan section displays a negative 199 hg signature interpreted to be related to terrestrial hg sources such temporal differences in 199 hg values shed new light on hg geochemical behavior in marine settings and also on the kill mechanisms associated with volcanism that were responsible for biotic mortality at the end of the permian

rapid biotic rebound during the late griesbachian indicates heterogeneous recovery patterns after the permian triassic mass extinction new fossil data from two early triassic griesbachian to dienerian sections from south china show unusually high levels of both benthic and nektonic taxonomic richness occurring in the late griesbachian in total 68 species including 26 newly originated species representing mollusks brachiopods foraminifers conodonts ostracods and echinoderms occur in the late griesbachian indicating well established and relatively complex marine communities furthermore the nekton shows higher origination rates than the benthos analyses of the sedimentary facies and size distribution of pyrite framboids show that this high diversity interval is associated with well oxygenated environments in contrast to the previously suggested scenario which inferred that persistently harsh environmental conditions impeded the biotic recovery during the early triassic our new findings combined with recent work indicate a fitful regional recovery pattern after the permian triassic crisis resulting in three main diversity highs late griesbachian early dienerian early middle smithian and spathian the transient rebound episodes were therefore influenced by both extrinsic local e g redox condition temperature and intrinsic e g biological tolerances origination rates parameters

deformation till in the great lakes region implications for rapid flow along the south central margin of the laurentide ice sheet structural and lithologic data indicate that while deposited under actively moving ice considerable portions of three muddy calcareous subglacial tills in the great lakes region probably experienced some component of ductile deformation viscous till flow and ductile shear are invoked to explain a combination of features such as recumbent isoclinal folds unlithified sediment clasts mixed ostracode shells reversed stone lee ends girdle and transverse fabrics irregular stone pavements fine striae following stone curves and inconsistent stone striae and a axes deforming fine textured subglacial till is considered as a subhorizontal shear zone rheologically layered with associated structures in descending order ductile e g isoclinal folds brittle ductile e g fissility and brittle e g till wedges rheology would be controlled mainly by till pore water content matrix texture and stone content spatial and temporal superposition of rheologies and subglacial processes probably occur

mantle flow at oceanic spreading centers models derived from ophiolites abstract the internal structures of eleven ophiolite complexes have been structurally investigated the attitude of the foliation and the lineation in the peridotites is related to asthenospheric flow in the uppermost mantle at an oceanic spreading center from the orientation of these structures with respect to the paleohorizontal plane two oceanic situations are distinguished the horizontally spreading asthenosphere illustrated by the table mountain massif newfoundland is characterized by 1 a homogeneous regular and sub horizontal plastic flow pattern over large distances 2 b flat paleo mono and absence of large scale folding 3 c rare economical chromite deposits and depleted mantle the diapirically spreading asthenosphere illustrated by the acoje type philippines displays 1 a inhomogeneous and sub vertical plastic flow pattern 2 b deformed paleo moho and large scale folds 3 c important economical chromite deposits and less depleted mantle presumably due to secondary magmatic impregnation this leads to vogt s model of asthenospheric flow beneath an oceanic ridge the direction of which being equated with the dike swarm in this model the horizontally spreading asthenosphere is derived from the diapirically spreading one in the following way the vertical mantle flow at the diapir center diverges horizontally in every direction including that parallel to the ridge at about 50 km from the diapir center the mantle flow becomes progressively perpendicular to the ridge due to the damming effect of transform faults an important economical consequence of this model is that large chromite deposits are expected preferentially in the diapiric type of ophiolite because chromite is preferentially precipitated at the diapir center from pristine magma