the permo triassic transition in spitsbergen δ13corg chemostratigraphy fe and s geochemistry facies fauna and trace fossils new 13 c org analyses of two boundary sections between the late permian kapp starostin formation and the early triassic vardebukta formation of western spitsbergen confirm field evidence that their contact is a conformable one thus contrary to previous reports some spitsbergen sections contain a complete record of the environmental and faunal changes during the crisis interval of the end permian mass extinction no environmental deterioration is recorded in the late permian until near the end of the terminal changxingian stage whereupon the abundant siliceous sponge fauna of the kapp starostin formation disappears along with the deep burrowing fauna responsible for the zoophycus trace fossil a low diversity dysaerobic trace fossil assemblage is briefly developed before a transition to finely laminated pyritic facies immediately beneath the permo triassic boundary analysis of the s c ratios from the laminated strata suggests that free h 2 s was present in the water column euxinic conditions even in relatively nearshore settings subject to storm sandstone deposition the mass extinction crisis in spitsbergen is therefore coincident with the extensive development of oxygen poor conditions in the water column and compares closely both in timing and nature with the crisis seen in lower latitude tethyan settings however the subsequent aftermath and recovery in the boreal sections of spitsbergen was more rapid than in tethys thus a shoreface sandstone body within the dienerian stage contains an appreciable diversity of fauna by the standards of the early triassic including bryozoans calcareous algae and deep infaunal bivalves that suggests the marine ecosystem recovery began earliest in higher palaeolatitudes

timing of recovery from the end permian extinction geochronologic and biostratigraphic constraints from south china four volcanic ash beds bracket the early middle triassic boundary as defined by conodont biostratigraphy in a stratigraphic section in south china high precision u pb dates of single zircons allow us to place the early to middle triassic olenekian anisian boundary at 247 2 ma magnetic reversal stratigraphy allows global correlation the new dates constrain the early triassic interval characterized by delayed biotic recovery and carbon cycle instability to 5 m y this time constraint must be considered in any model for the end permian extinction and subsequent recovery

terrestrial and marine extinction at the triassic jurassic boundary synchronized with major carbon cycle perturbation a link to initiation of massive volcanism mass extinction at the triassic jurassic tr j boundary occurred about the same time 200 ma as one of the largest volcanic eruptive events known that which characterized the central atlantic magmatic province organic carbon isotope data from the uk and greenland demonstrate that changes in flora and fauna from terrestrial and marine environments occurred synchronously with a light carbon isotope excursion and that this happened earlier than the tr j boundary marked by ammonites in the uk the results also point toward synchronicity between extinctions and eruption of the first central atlantic magmatic province lavas suggesting a causal link between loss of taxa and the very earliest eruptive phases the initial isotopic excursion potentially provides a widely correlatable marker for the base of the jurassic a temporary return to heavier values followed but relatively light carbon dominated the shallow oceanic and atmospheric reservoirs for at least 600 k y

late guadalupian to lopingian permian carbon and strontium isotopic chemostratigraphy in the abadeh section central iran abstract the abadeh section well exposed in the hambast valley in central iran has long been one of the most extensively studied sections because of its continuous carbonate dominated strata from lower permian to lower triassic however biostratigraphy and correlation with the equivalent sequences in other regions remain controversial in this paper both carbon isotope excursion 13 c carb and strontium isotope ratio 87 sr 86 sr based on bulk carbonate samples have been measured to serve as chemostratigraphical proxies to estimate the three different chronostratigraphical boundaries in the lopingian at the abadeh section including the permian triassic event pteb the guadalupian lopingian glb and the wuchiapingian changhsingian boundaries wcb these three boundaries are important for understanding the marine biological evolution around this critical interval based on the 13 c excursions the rising trend of 87 sr 86 sr and the value around 0 7073 and the occurrence of microbialite beds the permian triassic event boundary bed 25 at the meishan section is suggested at 0 5 m below the base of the main microbialite bed the glb is suggested at 46 5 m based on the position of the minor 13 c carb negative depletion coupled with the values between 0 7069 and 0 7070 of 87 sr 86 sr and its beginning point of the rising trend which is above the lowest value 0 7068 of 87 sr 86 sr ratio in the paleozoic the relationship between section thickness and their high resolution depositional age projecting age is interpolated for the whole lopingian using locally weighted regression scatter plot smoother lowess of strontium isotopic ratio based on the negative 13 c excursion and the value 0 7072 of 87 sr 86 sr ratio the wcb is estimated at 1 m above the lithologic boundary between unit 6 and unit 7 much lower than the boundary defined by previous conodont biostratigraphy but similar to other index fossils this boundary is projected as ca 254 6 ma in 87 sr 86 sr age projecting model and is close to zircon u pb dating age from south china

constriction in a transpressive regime an example in the iberian branch of the ibero armorican arc abstract detailed strain analyses in the armorican quartzites have been performed in various places within the centro iberian zone of western europe the observed strain pattern shows that in the inner ibero armorican arc as well as near the hinge zone sinistral transpression produces constrictive ellipsoids in the outer arc away from the hinge zone the deformation regime produces plane strain to oblate strain ellipsoids some of these data clearly contradict existent kinematical models which associate constriction with transtension and consider transpression zones to generate oblate strain ellipsoids however newly developed models show that it is possible to obtain a wide range of finite strain ellipsoids in transpression zones if one takes account of lateral escape axial depression and volume change the geodynamic implications of the strain analyses suggest generation of constriction in a transpressive regime caused by lateral expulsion in front of the cantabrian indenter that produced the ibero armorican arc this mechanism was responsible for the variscan wrench component in western europe which was mainly sinistral in iberia and dextral in britanny in iberia the displacement by lateral escape was easily accommodated by subduction of the south portuguese terrane under the ossa morena zone of the iberian terrane

u pb zircon geochronology and tempo of the end permian mass extinction the mass extinction at the end of the permian was the most profound in the history of life fundamental to understanding its cause is determining the tempo and duration of the extinction uranium lead zircon data from late permian and early triassic rocks from south china place the permian triassic boundary at 251 4 0 3 million years ago biostratigraphic controls from strata intercalated with ash beds below the boundary indicate that the changhsingian pulse of the end permian extinction corresponding to the disappearance of about 85 percent of marine species lasted less than 1 million years at meishan a negative excursion in 13 c at the boundary had a duration of 165 000 years or less suggesting a catastrophic addition of light carbon

biogeochemical controls on photic zone euxinia during the end permian mass extinction geochemical biomarker and isotopic evidence suggests that the end permian was characterized by extreme oceanic anoxia that may have led to hydrogen sulfide buildup and mass extinction we use an earth system model to quantify the biogeochemical and physical conditions necessary for widespread oceanic euxinia and hydrogen sulfide release to the atmosphere greater than threefold increases in ocean nutrient content combined with nutrient trapping ocean circulation cause surface water h 2 s accumulation in the paleo tethys ocean and in areas of strong upwelling accounting for the presence of sulfide oxidizing phototrophs in the model suppresses but does not prevent widespread release of h 2 s to the atmosphere evidence from the geologic record is consistent with modeled geochemical distributions of widespread nutrient induced euxinia during the end permian suggesting h 2 s toxicity and hypercapnia may have provided the kill mechanism for extinction

assessing the record and causes of late triassic extinctions accelerated biotic turnover during the late triassic has led to the perception of an end triassic mass extinction event now regarded as one of the big five extinctions close examination of the fossil record reveals that many groups thought to be affected severely by this event such as ammonoids bivalves and conodonts instead were in decline throughout the late triassic and that other groups were relatively unaffected or subject to only regional effects explanations for the biotic turnover have included both gradualistic and catastrophic mechanisms regression during the rhaetian with consequent habitat loss is compatible with the disappearance of some marine faunal groups but may be regional not global in scale and cannot explain apparent synchronous decline in the terrestrial realm gradual widespread aridification of the pangaean supercontinent could explain a decline in terrestrial diversity during the late triassic although evidence for an impact precisely at the boundary is lacking the presence of impact structures with late triassic ages suggests the possibility of bolide impact induced environmental degradation prior to the end triassic widespread eruptions of flood basalts of the central atlantic magmatic province camp were synchronous with or slightly postdate the system boundary emissions of co2 and so2 during these eruptions were substantial but the contradictory evidence for the environmental effects of outgassing of these lavas remains to be resolved a substantial excursion in the marine carbon isotope record of both carbonate and organic matter suggests a significant disturbance of the global carbon cycle at the system boundary release of methane hydrates from seafloor sediments is a possible cause for this isotope excursion although the triggering mechanism and climatic effects of such a release remain uncertain d 2003 elsevier b v all rights reserved

regional and global changes around the triassic jurassic boundary reflected in the late norian hettangian history of the apennine basins abstract palaeogeographic restorations for the late triassic and early jurassic of the west mediterranean area show that significant facies changes occurred in this period the study of three basinal successions in the northern central and southern apennines indicates that changes in ecological conditions occurred at the same time in different palaeogeographic and geodynamic domains the early mesozoic evolution of the apennines is controlled by the opening of two oceans the ionian east mediterranean tethys to the south east and the alpine ocean to the north west the lagonegro basin in the southern apennines was the northern continental margin of the ionian tethys from the triassic while the la spezia basin in the northern apennines became part of the south eastern continental margin of the alpine ocean in the middle late jurassic the third studied basin mt camicia basin in the gran sasso central apennines was an intra platform basin from the early norian up to the late hettangian early sinemurian during the norian hettangian period these basins were not directly connected to each other being separated by wide carbonate platforms and show different evolutionary trends stratigraphic studies in these successions place the triassic jurassic boundary in 6 8 m thick intervals with anoxic facies in the three basins relevant facies changes are also recorded in the late norian in the northern apennines the sedimentation of sulphate evaporites ended being replaced by the rhaetavicula contorta facies whilst in the southern apennines lagonegro basin the deposition of radiolarites began the end of evaporite accumulation can be explained by a climate change from arid to humid conditions and it is also probably linked to an extensional phase preceding the jurassic rifting of the alpine ocean and may therefore have a regional significance nevertheless it corresponds to the spread of the r contorta facies into other parts of southern europe from france to germany and austria the beginning of radiolaritic sedimentation in the lagonegro basin could be related to the rise of atmospheric co2 content linked to volcanic activity in the ionian ridge these facies changes reflect changes of environmental conditions that caused the decline of some fossil associations favoring the development of opportunistic forms e g triasina hantkeni the end triassic extinction coupled with an anoxic episode in all the examined basins immediately preceded a new environmental change documented by the recovery of the carbonate platforms with oolitic facies and different associations the evolution of all these basins suggests that geodynamics were probably responsible for regional events and that at certain moments development reflected global effects as a response to new connections between formerly different domains the central atlantic magmatic province camp volcanism considered as one of the possible causes for the end triassic mass extinction would have had even greater importance if coupled with the volcanism linked to the rifting of the ionian tethys

did paleo tethyan anoxia kill arc magma fertility for porphyry copper formation the tethyan orogen is host to numerous porphyry cu mo au deposits but the majority formed during subduction of the neo tethyan ocean basin in the late mesozoic cenozoic very few deposits have been found associated with paleo tethyan subduction we propose that this sparsity is due to widespread anoxia in the paleo tethyan ocean basin leading to the generation of relatively reduced arc magmas that were infertile for porphyry cu formation a compilation of published geochemical data indicates that neo tethyan arc rocks have higher average cu contents and v sc and sr y ratios compared to paleo tethyan rocks indicating higher magmatic oxidation states and greater fertility for ore formation during neo tethyan subduction subduction of relatively reduced oceanic lithosphere or reduction of normal moderately oxidized arc magmas by interaction with reduced lithosphere can therefore destroy the ore forming potential of arc magmatic suites

finite strains within recumbent folds of the kishorn nappe northwest scotland abstract this study is based on the torridonian and cambro ordovician rocks of the kishorn nappe on the isle of skye and the adjacent mainland of scotland grain shape fabric skolithos pipe shape analysis and palaeomagnetic techniques have been used to give an indication of the strain distribution and possible mechanisms involved in the generation of the recumbent folds within the kishorn nappe results indicate that recumbent folding has occurred without internal deformation

finite strain analysis in a transpressive regime variscan autochthon northeast portugal abstract we apply a method of estimating finite strain that can be widely used in armorican quartzites affected by transpressive regimes the method proposed uses data from skolithos which are quite common in these rocks the main assumption is that the orientation of the finite strain ellipsoid can be represented by the cleavage and the stretching lineation observed in the rocks this method was tested in a macroscopic fold in the moncorvo region northeast portugal

a coupled marine ice stream ice shelf model theorie des variations climatiques du pleistocene a aujourd hui liees a la dynamique des couvertures marines de glace couplee aux glaces libres flottantes on neglige les effets thermodynamiques et on etudie les processus de flottaison en relation avec les rapports de densite entre la place et l eau de mer

carbon and nitrogen isotope disturbances and an end norian late triassic extinction event major perturbations of organic carbon and nitrogen isotope ratios from a norian rhaetian late triassic boundary section in british columbia coincide with an extinction of the dominant deep water invertebrate fauna of the late triassic monotids and most ammonoids the carbon isotope excursion is attributed to the development of widespread oceanic stagnation that favored organic rich shale deposition the coincident nitrogen isotope excursion suggests that progressively more nitrate limited productivity forced a change to nitrogen fixing cyanobacteria populations as ocean stagnation created nutrient starved conditions the biotic crisis and geochemical events of the norian rhaetian boundary predate the latest rhaetian end triassic mass extinction thus the late triassic interval was marked by more than one extinction event

illawarra reversal the fingerprint of a superplume that triggered pangean breakup and the end guadalupian permian mass extinction abstract the permian magnetostratigraphic record demonstrates that a remarkable change in geomagnetism occurred in the late guadalupian middle permian ca 265 ma from the long term stable kiaman reverse superchron throughout the late carboniferous and early middle permian to the permian triassic mixed superchron with frequent polarity changes in the late permian and triassic this unique episode called the illawarra reversal probably reflects a significant change in the geodynamo in the outer core of the planet after a 50 million years of stable geomagnetism the illawarra reversal was likely led by the appearance of a thermal instability at the 2900 km deep core mantle boundary in connection with mantle superplume activity the illawarra reversal and the guadalupian lopingian boundary event record the significant transition processes from the paleozoic to mesozoic modern world one of the major global environmental changes in the phanerozoic occurred almost simultaneously in the latest guadalupian as recorded in 1 mass extinction 2 ocean redox change 3 sharp isotopic excursions c and sr 4 sea level drop and 5 plume related volcanism in addition to the claimed possible links between the above listed environmental changes and mantle superplume activity i propose here an extra explanation that a change in the core s geodynamo may have played an important role in determining the course of the earth s surface climate and biotic extinction evolution when a superplume is launched from the core mantle boundary the resultant thermal instability makes the geodynamo s dipole of the outer core unstable and lowers the geomagnetic intensity being modulated by the geo and heliomagnetism the galactic cosmic ray flux into the earth s atmosphere changes with time the more cosmic rays penetrate through the atmosphere the more clouds develop to increase the albedo thus enhancing cooling of the earth s surface the illawarra reversal the kamura cooling event and other unique geologic phenomena in the late guadalupian are all concordantly explained as consequences of the superplume activity that initially triggered the breakup of pangea the secular change in cosmic radiation may explain not only the extinction related global climatic changes in the end guadalupian but also the long term global warming cooling trend in earth s history in terms of cloud coverage over the planet

bryozoan paleoecology indicates mid phanerozoic extinctions were the product of long term environmental stress we compiled the global onshore offshore distribution of marine bryozoans within 396 permian early jurassic bryozoan assemblages and show that bryozoan assemblage generic richness declined significantly in advance of the end permian and end triassic mass extinctions starting as early as the capitanian prior to the end permian and the norian prior to the end triassic we also show that offshore settings were affected first prior to both extinctions suggesting that environmental stress resulted from the gradual encroachment of some deep water phenomenon onto the shelves these patterns support long term oceanographic rather than extraterrestrial extinction mechanisms such as widespread euxinia triggered by massive volcanism and global warming tracking the onshore offshore environmental distribution of these marine invertebrates provides a unique approach to assessing prolonged environmentally induced stress through this 120 m y time interval

palaeoenvironmental trends in the history of trace fossils tracks trails and burrows made by organisms are commonly preserved in phanerozoic sedimentary rocks these biogenic sedimentary structures or trace fossils have been most intensively studied from rocks deposited in marine environments and have proven to be extremely useful in palaeoenvironmental reconstruc tions our systematic analysis of occurrences in the stratigraphic record of two of the most common trace fossils zoophycos and ophiomorpha indicates that occurrences for each show an environmentally linked directional pattern through time zoophycos is commonly reported from palaeozoic strata deposited from nearshore to deep sea environments whereas in post palaeozoic stratait is generally reported only from rocks deposited in deeper water environments ophiomorpha first appeared in permian shallowwater environments and was common in deep sea fan environments by the cretaceous and has been distributed from nearshore to deep sea environments since then these onshore offshore trends which are similar to those previously reported for phanerozoic benthic macroinvertebrate assemblages and individual higher taxa require integration into future palaeoenvironmental reconstructions that use trace fossils

a review of the arcuate structures in the iberian variscides constraints and genetic models abstract in the iberian variscides several first order arcuate structures have been considered in spite of being highly studied their characterization formation mechanisms and even existence is still debatable the main ibero armorican arc iaa is essentially defined by a predominant nw se trend in the iberian branch and an e w trend in the brittany one however in northern spain it presents a 180 rotation sometimes known as the cantabrian arc ca the relation between both arcs is controversial being considered either as a single arc due to one tectonic event or as the result of a polyphasic process according to the last assumption there is a later arcuate structure ca overlapping a previous major one iaa whatever the models they must be able to explain the presence of a variscan sinistral transpression in iberia and a dextral one in armorica and a deformation spanning from the devonian to the upper carboniferous another arcuate structure in continuity with the ca the central iberian arc cia was recently proposed mainly based upon on magnetic anomalies geometry of major folds and ordovician paleocurrents the critical review of the structural stratigraphic and geophysical data supports both the iaa and the ca but as independent structures however the presence of a cia is highly questionable and could not be supported the complex strain pattern of the iaa and the ca could be explained by a devonian carboniferous polyphasic indentation of a gondwana promontory in this model the ca is essentially a thin skinned arc while the iaa has a more complex and longer evolution that has led to a thick skinned first order structure nevertheless both arcs are essentially the result of a lithospheric bending process during the iberian variscides

strains and folds within thrust sheets an analysis of the heilam sheet northwest scotland abstract the changes of shape and orientation of fossil worm burrows have been used to carry out a detailed strain analysis of the heilam thrust sheet in the moine thrust zone northwest scotland the strains have been factorised into components of layer parallel shear 1 layer normal shear 2 and layer parallel shortening or elongation variations in the 1 shear are largely lithologically controlled some strain is due to flexural processes as the thrusts and overlying beds change dip over thrust ramps or are tightened by later deformation while there may also be a component of drag which increases towards the overlying thrust this predating the shear due to flexure a contoured map of the values suggests that major folds within the thrust sheet developed as a result of stick or drag on the floor thrust prior to ramp climb this led to differential movement in the transport direction causing layer parallel shortening accompanied or followed by buckling of the layers a map showing layer normal shear strains 2 suggests that the heilam sheet forms a major surge zone the central part having moved further wnw than the northern and southern parts this has led to components of lateral shear along parts of the sheet especially in the north producing curvature of the imbricate faults

age and timing of the permian mass extinctions u pb dating of closed system zircons the age and timing of the permian triassic mass extinction have been difficult to determine because zircon populations from the type sections are typically affected by pervasive lead loss and contamination by indistinguishable older xenocrysts zircons from nine ash beds within the shangsi and meishan sections china pretreated by annealing followed by partial attack with hydrofluoric acid result in suites of consistent and concordant uranium lead u pb ages eliminating the effects of lead loss the u pb age of the main pulse of the extinction is 252 6 0 2 million years synchronous with the siberian flood volcanism and it occurred within the quoted uncertainty

the mesozoic return of paleozoic faunal constituents a decoupling of taxonomic and ecological dominance during the recovery from the end permian mass extinction abstract phanerozoic diversity curves illustrate that the transition from taxonomic dominance of the paleozoic fauna to taxonomic dominance of the modern fauna is coincident with the permo triassic boundary although a corresponding transition in ecological dominance must have occurred its timing is unclear one way to assess ecological dominance during the early middle triassic recovery interval is through the study of bioclastic accumulations bioclastic accumulations from the early triassic are largely dominated by constituents of the modern fauna in this study we examined bioclastic accumulations from the middle triassic the interval after the environmental stress associated with the end permian extinction abated bioclastic accumulations from panthalassan deposits ladinian portion of the liard formation at williston lake canada and tethyan deposits anisian ladinian muschelkalk group germany were examined although the most common shell bed producer differed between the two sites bivalves constituents of the modern fauna in germany and brachiopods constituents of the paleozoic fauna in canada both sites though geographically disparate contained significant crinoidal bioclastic accumulations encrinites crinoids like many constituents of the paleozoic fauna suffered drastic diversity losses at the end permian mass extinction and maintained relatively low diversity through the middle triassic despite reduced diversity bioclastic accumulations show that crinoids regained some measure of ecologic dominance in the middle triassic in addition brachiopods another constituent of the paleozoic fauna that suffered severe diversity losses at the end permian extinction regained at minimum local ecological dominance in the middle triassic of panthalassa these data demonstrate that the transition to modern faunal taxonomic dominance was decoupled from the transition to modern faunal ecological dominance

co2 forced climate and vegetation instability during late paleozoic deglaciation the late paleozoic deglaciation is the vegetated earth9s only recorded icehouse to greenhouse transition yet the climate dynamics remain enigmatic by using the stable isotopic compositions of soil formed minerals fossil plant matter and shallow water brachiopods we estimated atmospheric partial pressure of carbon dioxide pco2 and tropical marine surface temperatures during this climate transition comparison to southern gondwanan glacial records documents covariance between inferred shifts in pco2 temperature and ice volume consistent with greenhouse gas forcing of climate major restructuring of paleotropical flora in western euramerica occurred in step with climate and pco2 shifts illustrating the biotic impact associated with past co2 forced turnover to a permanent ice free world

the role of initial fabric on strain determination from deformed ellipsoidal objects abstract twenty one samples of undeformed conglomerates sandstones tuffs oolites and pisolites from precambrian to pleistocene in age were collected from a variety of geologic environments each sample was sectioned on three mutually perpendicular faces with one face parallel to bedding selected samples were also sectioned at 60 and 30 degrees to the bedding plane the shape and orientation of at least 100 particles were measured on each section particle shape ranges from nearly circular in some samples to highly eccentric in others sections parallel with bedding have essentially random fabrics no preferred orientation of particles sections not parallel with bedding have a preferred orientation of particles along the bedding trace but particles with all orientations do exist the fabric distributions on the polar plot elliott 1970 are often irregular in shape and the initial circle point lies well within the distribution in all cases transformation equations for the final shape and orientation of an individual particle using known shapes and orientations of the initial particle and the strain ellipse are used to construct the resultant fabrics after homogeneous simulated strains of several directions and magnitudes the resultant fabrics can be used as a test of utility and accuracy of strain determination methods a simple algebraic method of strain determination is found to be fairly accurate if the initial fabrics measured in this study are representative the accuracy of the method can be increased with the use of an error function introduced herein

biogenic structures in modern slope to deep sea sediments in the sulu sea basin philippines abstract slowly accumulated slope and rise sediments 5 20 cm 1000 yr are totally bioturbated as compared to only 10 30 in rapidly deposited abyssal plain sediments 100 200 cm 1000 yr in contrast to a decrease in degree of bioturbation biogenic trace diversity increases with water depth all ichnocoenoses are clearly influenced by the low oxygen content of the bottom water caused by minimal circulation and restricted water exchange oxygen deficiency and relatively high sedimentation rates have created nutrient rich sediments thus there is no need for optimal fractionation into individual ecological niches and behavioral programs are not highly developed 1 in slope and rise sediments animal traces are associated with biodeformational structures 2 in slope to abyssal plain sediments trace assemblages are dominated by burrows with open tubes for circulation of respiration water 3 in abyssal plain sediments small diameter biogenic traces common in turbidite sequences graphoglyptids e g paleodictyon are absent this may be due to rapid sedimentation leading to inefficiency of graphoglyptid behavior where graphoglyptids are lacking ichnocoenoses are dominated by forms like phycosiphon in slope and rise sediments graphoglyptids may have been destroyed by deeper burrowing organisms

bryozoans in transition the depauperate and patchy jurassic biota bryozoans were profoundly affected by the end permian and probably also by the end triassic mass extinction events their recovery in terms of diversity and disparity during the jurassic was slow and geographically patchy critical compilation of data from the published literature reveals only 172 valid species 160 cyclostomes 10 ctenostomes and 2 cheilostomes some as yet not formally named however the rate of description of new jurassic bryozoan species during the last two hundred years implies that many more species remain to be discovered and described the jurassic is the only geological period during which cyclostomes were the dominant order and is also important in having the oldest cheilostome bryozoan the first representative of the order that dominates the modern bryozoan biota species diversity peaked in the bathonian where local assemblages may contain up to 33 species encrusters account for 124 73 of the 172 jurassic species among which small sheet like forms especially those assigned to the form genus berenicea are the most numerous the overwhelming predominance in the jurassic of weeds with runner ribbon or sheet colony forms is striking unlike the triassic and cretaceous large tree like or frondose erect colonies are uncommon and species with fenestrate articulated and free living colonies are unknown of 92 geographically categorized entries for jurassic bryozoans in the zoological record 1937 2003 80 87 are european records outside europe diversity appears to have remained low throughout the jurassic and non weedy species are particularly scarce compared with the cretaceous jurassic bryozoans show no adaptations that can be interpreted as related to the increased predation pressure associated with the mesozoic marine revolution the jurassic bryozoan biota shares characteristics with both the stenolaemate dominated palaeozoic triassic biota and the cheilostome dominated cretaceous recent biotas

rising atmospheric co2 as a possible trigger for the end triassic mass extinction the end triassic mass extinction one of the five largest extinctions in earth history was a severe catastrophe in which 80 of all species were wiped out the cause of the extinction is controversial but any mechanism must account for mass extinction in both marine and terrestrial environments one smoking gun the eruption of the central atlantic magmatic province camp has prompted the hypothesis that co2 degassing to the atmosphere may have induced an environmental catastrophe at the end triassic in this study we use a numerical coupled ocean atmosphere climate model of the late triassic to determine environmental stresses associated with a rapid increase in atmospheric co2 a series of sensitivity experiments with co2 levels that bracket estimated end triassic pco2 estimates 2 8 pre industrial levels predict extreme environmental conditions on land increasing co2 from 2 to 8 pre industrial levels causes an increase in the number and severity of hot days and days without precipitation an exponential increase in continental area experiencing hot days and enhanced seasonal fluctuation in the ocean wind driven circulation decreases and meridional overturning diminishes by a factor of 4 leading to enhanced ocean stratification a three box model of the deep ocean predicts a decline of 85 mol l in deep ocean oxygen concentration with a 4 fold increase in atmospheric co2 consequently while terrestrial organisms would have been subject to severe heat and water stress marine fauna would have experienced oxygen deprivation additional sensitivity experiments indicate that variations in milankovitch orbital parameters may further contribute to faunal stress by intensifying continental heating and seasonal fluctuations in sum model results predict that rising atmospheric co2 would have significantly impacted both marine and continental environments providing a link between turnover on land and ocean during the late triassic

isotopic evidence for an anomalously low oceanic sulfate concentration following end permian mass extinction abstract the cataclysmic end permian mass extinction was immediately followed by a global expansion of microbial ecosystems as demonstrated by widespread microbialite sequences disaster facies in shallow water settings here we present high resolution carbonate carbon 13 c carb and carbonate associated sulfate sulfur isotope 34 s cas records from the microbialite in the cili permian triassic p tr section in south china a stepwise decline in 13 c carb begins in the underlying skeletal limestone predating the main oceanic mass extinction and the first appearance of microbialite and reaches its nadir in the upper part of the microbialite layer the corresponding 34 s cas in the range of 17 4 to 27 4 is relatively stable in the underlying skeletal limestone and increases gradually from 2 m below the microbialite rising to a peak at the base of the microbialite two episodes of positive and negative shifts occurred within the microbialite layer and exhibit a remarkable co variance of sulfur and carbon isotope composition the large amplitude of the variation in 34 s cas as high as 7 per 100 kiloyears suggests a small oceanic sulfate reservoir size at this time furthermore the 13 c carb and 34 s cas records co vary without phase lag throughout the microbialite interval implying a marine driven c cycle in an anoxic ocean with anomalously low oceanic sulfate concentrations on the basis of a non steady state box model we argue that the oceanic sulfate concentration may have fallen to less than 15 perhaps as low as 3 of that in the modern oceans low oceanic sulfate concentration likely was the consequence of evaporite deposition and widespread anoxic sulfidic conditions prior to the main mass extinction by promoting methanogenesis and a build up of atmospheric ch 4 and co 2 low oceanic sulfate may have intensified global warming exacerbating the inimical environmental conditions of the latest permian

δ13c depth profiles from paleosols across the permian triassic boundary evidence for methane release stable carbon isotopic analyses of organic carbon 13 c in individual paleosol profiles from permian triassic sequences of antarctica reveal systematic isotopic variations with profile depth these variations are in many cases analogous to those in modern soils which are functions of redox conditions soil development and degree and type of microbial decay in modern soils these isotopic depth functions develop independently from vegetation changes c 3 versus c 4 vegetation and can be diagnostic of soil orders this study shows that soil intrinsic functions can be preserved in the 13 c values of paleosols as old as 260 ma and constitute valuable data for paleoecological interpretations a large carbon isotopic offset of as much as 10 in whole paleosol profiles across the permian triassic boundary indicates significant changes in the soil biogeochemistry and the soil atmosphere system early triassic paleosols are distinctive in their extremely low 13 c values to 42 and often show an anomalous 13 c depth distribution compared to both permian paleosols and modern soils highly depleted 13 c values as the ones in early triassic paleosols are suggested to be associated with microbial methane oxidation methanotrophy this hypothesis implies increased methane concentrations in the early triassic soil atmosphere system increased atmospheric methane was probably partly responsible for the global carbon isotopic shift documented in marine and terrestrial sediments across the permian triassic boundary

isotopic evidence bearing on late triassic extinction events queen charlotte islands british columbia and implications for the duration and cause of the triassic jurassic mass extinction stable isotope analyses of late triassic to earliest jurassic strata from kennecott point in the queen charlotte islands british columbia canada shows the presence of two distinct and different organic carbon isotope anomalies at the norian rhaetian and rhaetian hettangian triassic jurassic stage boundaries at the older of these boundaries which is marked by the disappearance of the bivalve monotis the isotope record shows a series of short lived positive excursions toward heavier values strata approaching this boundary show evidence of increasing anoxia at the higher boundary marked by the disappearance of the last remaining triassic ammonites and over 50 species of radiolarians the isotopic pattern consists of a series of short duration negative anomalies the two events separated by the duration of the rhaetian age comprise the endtriassic mass extinction while there is no definitive evidence as to cause the isotopic record does not appear similar to that of the impact caused cretaceous tertiary boundary extinction d 2004 published by elsevier b v

nitrogen isotope chemostratigraphy across the permian triassic boundary at chaotian sichuan south china abstract nitrogen isotopic compositions of upper permian to lowermost triassic rocks were analyzed at chaotian in northern sichuan south china in order to clarify changes in the oceanic nitrogen cycle around the permian triassic boundary p tb including the entire changhsingian late late permian prior to the extinction the analyzed ca 40 m thick interval across the p tb at chaotian consists of three stratigraphic units the upper wujiaping formation the dalong formation and the lowermost feixianguan formation in ascending order the upper wujiaping formation ca 10 m thick is mainly composed of dark gray limestone with diverse shallow marine fossils such as calcareous algae and brachiopods deposited on the shallow shelf in contrast the overlying dalong formation ca 25 m thick is mainly composed of thinly bedded black mudstone and siliceous mudstone containing abundant radiolarians deposited on the relatively deep slope basin absence of bioturbation substantially high total organic carbon contents up to 15 and abundant occurrence of pyrite framboids in the main part of the dalong formation indicate deposition under anoxic condition the lowermost feixianguan formation ca 5 m thick is composed of thinly bedded gray marl and micritic limestone with minor fossils such as ammonoids and conodonts deposited on the relatively shallow slope 15ntn values are in positive values around 1 to 2 in the upper wujiaping formation implying denitrification and or anammox in the ocean 15ntn values gradually decrease to 1 in the lower dalong formation and are consistently low around 0 in the middle dalong to lowermost feixianguan formation no clear 15ntn shift is recognized across the extinction horizon the consistently low 15ntn values suggest the enhanced nitrogen fixation in the ocean during the changhsingian at chaotian composite profiles based on previous and the present studies demonstrate the substantial 15n variation on a global scale in the late permian to earliest triassic a systematic 15n difference by low and high latitudes is particularly clarified although the enhanced nitrogen fixation throughout the changhsingian at chaotian was likely a regional event in northwestern south china the composite 15n profiles imply that the sea area in which fixed nitrogen is depleted has gradually developed worldwide in the changhsingian possibly acting as a prolonged stress to shallow marine biota

evidence for sulfidic deep water during the late permian in the east greenland basin a detailed study of the size distribution of framboidal pyrites in the black shales of the upper permian ravnefjeld formation was performed to evaluate the redox state of the late permian ocean in contrast to framboidal pyrites in bioturbated sediments the smaller and less variable size distribution of pyrite framboids in the laminated shales of the ravnefjeld formation provides persuasive evidence for sulfidic h 2 s rich bottom water conditions in the east greenland basin however the s isotope compositions of both pyrite populations show a similar distribution the widespread 3 4 s values of pyrites 41 2 to 28 2 in the black shales of the ravnefjeld formation indicate a large fractionation up to 52 7 relative to seawater sulfate and may record different pathways of sulfur cycling in sulfidic water columns as well as within sediments the new data from the east greenland basin indicate that environmental stress such as widespread sulfidic conditions could have caused the biotic crisis in the late permian

the late variscan fault network in central northern portugal nw iberia a re evaluation abstract the fault network in central northern portugal especially the fault system with mean strike n25 has been used to help deduce the late palaeozoic dynamics of western europe on the other hand the n80 strike slip fault system was recognized in previous works as late variscan and left lateral but was scarcely mapped and its importance neglected this study shows that the n25 faults were dextral in the late stages of the variscan orogeny and sinistral during the alpine cycle due to pervasive reactivation fault rocks and intrusions are clearly different according to age mostly high temperature quartz infillings but locally muscovite tourmaline and aplite dykes in late variscan times and low temperature cataclasites fault gouges and mesozoic mafic dykes in younger alpine times we dated dextral n45 segments of the n25 fault system because they are less prone to reactivation by the nnw sse alpine compression and can thus preserve the variscan record we used k ar in muscovite concentrates and obtained a minimum age of the analysed faults of ca 312 ma which sets a lower limit to the so called late variscan wrench faulting period the present study shows that the n80 fault set is pervasive and sinistral in central northern portugal and therefore that it only admits one brittle dextral conjugate the n25 fault system both were generated by a maximum compressive stress bearing between n50 and n55 in azimuth we did not find evidence of a variscan sinistral strike slip movement in the n25 fault system and therefore this kinematics is believed to represent only the displacements accommodated during the alpine cycle

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

rheologically induced structural anomalies in transpressive regimes abstract local structural anomalies are sometimes found in transpressive regimes they can be related to strain partitioning processes but in some cases other types of heterogeneities could affect the deformation style this paper shows that rheological heterogeneities can radically influence the geometry of faults in transpression zones and cause them to be markedly non planar in the marao region of northern portugal a zone in which variscan structures are sw facing is found within the regional ne facing geometry this anomaly is adjacent to a complex shear zone mina ribeira das cestas where the fault plane is curved however the surrounding material does not show any signs of a related folding event detailed field studies mainly concerning the rheological contrasts between the deformed lithostratigraphic units show a close relationship between the structural anomaly and the movement along rheological anisotropies these observations complemented by experimental deformation of multilayers composed of analogue materials allow the construction of a generic model strain partitioning during the initial stage of the sinistral transpressive variscan deformation produced the juxtaposition of lithostratigraphic units with strongly different rheological contrasts subsequent flattening deformation induced heterogeneous indentation phenomena producing the non planar geometry of the complex shear zone the structural heterogeneities caused could have an important role in the evolution of a transpressive domain

bryozoan distribution and growth form associations as a tool in environmental interpretation tasmania australia abstract the cool temperate carbonate sediments of eastern and western tasmania and bass strait composed of 29 50 of bryozoan skeletal grains two hundred and eighty three bryozoan bulk sediments around tasmania were studied to determine the relationship between bryozoan zoarial growth form association and their depth zone bryozoans skeletons are grouped into 11 morphotypes according to architecture and style of disarticulation fragmentation encrusting forms erect flexible cellariiform and erect rigid robust branching adeoniform cheilostomes are consistently the most widespread with delicate branching cyclostomes the next most common growth form associations were grouped into four depth related settings strand line shallow shelf middle shelf and deep shelf this study demonstrates that bryozoan morphotype associations occupying different depth zones are valuable for providing fundamental paleo environmental information morphotype associations are related mainly to water depth water energy sedimentation rate and substrate in the strand line setting encrusting unilaminar and erect flexible articulated branching are abundant while in the shallow shelf erect flexible encrusting multilaminar erect rigid robust fenestrate and delicate branching are major growth forms the above associations indicate high to moderate energy levels moderate to high sedimentation rates and flexible to hard substrates in middle shelf areas erect rigid fenestrate robust and delicate branching cheilostomes and cyclostomes are the most common growth forms these associations indicate decreasing water energy lower sedimentation rate and presence of stable hard to soft substrates in the deep shelf setting the dominance of erect rigid robust fenestrate and foliose forms indicate deep quiet water low sedimentation rate and hard substrate

end triassic calcification crisis and blooms of organic walled disaster species the triassic jurassic t j mass extinction event is marked by isotope anomalies in organic 13 corg and carbonate carbon 13 ccarb reservoirs these have been attributed to a rapid 4 fold rise in pco2 as a result of massive flood basalt volcanism and or methane hydrate dissociation here we examine the response of marine photosynthetic phytoplankton to the proposed perturbation in the carbon cycle our high resolution micropalaeontological analysis of t j boundary beds at st audrie s bay in somerset uk provides evidence for a bio calcification crisis that is characterized by 1 extinction and malformation in calcareous nannoplankton and 2 contemporaneous blooms of organic walled green algal disaster species which comprise in one case n70 of the total palynomorph fraction blooms of prasinophytes and acritarchs occur at the onset and in association with a prominent negative shift in 13 corg values close to the first appearance of the early jurassic ammonite psiloceras planorbis across the same interval we obtained palaeotemperature and palaeosalinity estimates from oyster low mg calcite based on mg ca sr ca and 18 o records the results of our palynological and geochemical analyses strongly suggest that shallow marine basins in nw europe during this period became salinity stratified inducing anoxic conditions the t j boundary event shows similarities with the permian triassic p t mass extinction event which was also marked by extensive flood basalt volcanism negative excursions in carbon isotope records a bio calcification crisis the development of shallow marine anoxia and mass abundances of acritarchs in the early triassic this leads us to suggest that the proliferation of green algal phytoplankton may be symptomatic of elevated carbon dioxide levels in the atmosphere and oceans during mass extinction events 2007 published by elsevier b v

fry and rf ϕ strain methods constraints and fold transection mechanisms in the nw iberian variscides abstract apulia is a small portuguese sector in nw of central iberian zone that have been deformed in a non coaxial sinistral transpressive regime during the first and main variscan tectonic event d1 this deformation give rise to a major nw se anticline where the s1 n s cleavage transect the inverted short ne limb two and three dimensional strains analysis have been done in the low metamorphic grade ordovician quartzites of this limb using fry and rf methods the data show that most deformation was due to intergranular deformation mechanisms the intragranular deformation leading to the distortion of strain markers and to cleavage was very incipient and a latter event in the d1 phase the apparent plane strain ellipsoids if no volume change is assumed related to the intragranular mechanisms contrast with the more prolate strain ellipsoids related to the bulk deformation of apulia quartzites this constrictional bulk strain fabrics are characteristic of the sinistral transpressive regimes dominant in the northern sectors of the central iberian zone

synchrony and causal relations between permian triassic boundary crises and siberian flood volcanism the permian triassic boundary records the most severe mass extinctions in earth9s history siberian flood volcanism the most profuse known such subaerial event produced 2 million to 3 million cubic kilometers of volcanic ejecta in approximately 1 million years or less analysis of 40 ar 39 ar data from two tuffs in southern china yielded a date of 250 0 0 2 million years ago for the permian triassic boundary which is comparable to the inception of main stage siberian flood volcanism at 250 0 0 3 million years ago volcanogenic sulfate aerosols and the dynamic effects of the siberian plume likely contributed to environmental extrema that led to the mass extinctions

syn collisional extensional collapse parallel to the orogenic trend in a domain of steep tectonics the salamanca detachment zone central iberian zone spain the area south of the town of salamanca is a zone of the spanish variscan belt characterized by a first compressional event which gave rise to steep structures followed by the development of an extensional ductile shear zone more than 4 km thick that is described as the salamanca detachment zone the strain associated to the detachment is analyzed using quartz pebbles in conglomerates comparing the measured strain values with theoretical strain paths leads to the conclusion that the deformation was approximately of plane strain type quartz c axis fabrics and kinematic criteria indicate that simple shear was a very important component of the deformation though coaxial components were probably involved the extensional character of the detachment is indicated by the geometry of the metamorphic zones and the metamorphic evolution taken together the data indicate that the extensional event was related to gravitational collapse induced by the thickening of the continental crust and that it was syn collisional the movement of the hangingwall unit was to the southeast parallel to the trend of the fold belt and the translation was of the order of one to a few dozens of km though important this is not exceedingly large and allowed the preservation of low grade metamorphic conditions in the hangingwall preventing it from being affected by extensive brittle tectonic processes

new geochemical evidence for the onset of volcanism in the central atlantic magmatic province and environmental change at the triassic jurassic boundary the late triassic early jurassic was a time of major global change however the fundamental processes driving these changes are less than clear we have determined the re and os abundances and os isotope compositions of marine mudrock samples that span the triassic jurassic boundary in the uk and have established that major isotopic and geochemical shifts in the composition of seawater took place in the latest triassic we argue that these shifts were caused by the sudden initiation of widespread igneous activity within the central atlantic magmatic province associated with rifting of the supercontinent pangea the os isotope composition of seawater responded rapidly to these events demonstrating that the seawater os isotope system has great potential in identifying the nature and precise timing of major environmental change

geocarbsulf a combined model for phanerozoic atmospheric o2 and co2 abstract a model for the combined long term cycles of carbon and sulfur has been constructed which combines all the factors modifying weathering and degassing of the geocarb iii model berner r a kothavala z 2001 geocarb iii a revised model of atmospheric co2 over phanerozoic time am j sci 301 182 204 for co2 with rapid recycling and oxygen dependent carbon and sulfur isotope fractionation of an isotope mass balance model for o2 berner r a 2001 modeling atmospheric o2 over phanerozoic time geochim cosmochim acta 65 685 694 new isotopic data for both carbon and sulfur are used and new feedbacks are created by combining the models sensitivity analysis is done by determining 1 the effect on weathering rates of using rapid recycling rapid recycling treats carbon and sulfur weathering in terms of young rapidly weathering rocks and older more slowly weathering rocks 2 the effect on o2 of using different initial starting conditions 3 the effect on o2 of using different data for carbon isotope fractionation during photosynthesis and alternative values of oceanic 13c for the past 200 million years 4 the effect on sulfur isotope fractionation and on o2 of varying the size of o2 feedback during sedimentary pyrite formation 5 the effect on o2 of varying the dependence of organic matter and pyrite weathering on tectonic uplift plus erosion and the degree of exposure of coastal lands by sea level change 6 the effect on co2 of adding the variability of volcanic rock weathering over time berner r a 2006 inclusion of the weathering of volcanic rocks in the geocarbsulf model am j sci 306 in press results show a similar trend of atmospheric co2 over the phanerozoic to the results of geocarb iii but with some differences during the early paleozoic and for variable volcanic rock weathering lower co2 values during the mesozoic atmospheric oxygen shows a major broad late paleozoic peak with a maximum value of about 30 o2 in the permian a secondary less broad peak centered near the silurian devonian boundary variation between 15 and 20 o2 during the cambrian and ordovician a very sharp drop from 30 to 15 o2 at the permo triassic boundary and a more or less continuous rise in o2 from the late triassic to the present

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

permo triassic boundary superanoxia and stratified superocean records from lost deep sea pelagic cherts of japan and british columbia canada recorded a long term and worldwide deep sea anoxic oxygen depleted event across the permo triassic or paleozoic and mesozoic boundary 251 2 million years ago the symmetry in lithostratigraphy and redox condition of the boundary sections suggest that the superocean panthalassa became totally stratified for nearly 20 million years across the boundary the timing of onset climax and termination of the oceanic stratification correspond to global biotic events including the end guadalupian decline the end permian extinction and mid triassic recovery

a global marine sedimentary response to the end permian mass extinction examples from southern turkey and the western united states the end permian mass extinction greatly diminished marine diversity and brought about a whole scale restructuring of marine ecosystems these ecosystem changes also profoundly affected the sedimentary record data presented here attained through facies analyses of strata deposited during the immediate aftermath of the end permian mass extinction southern turkey and at the close of the early triassic southwestern united states in combination with a literature review show that sedimentary systems were profoundly affected by 1 a reduction in biotic diversity and abundance and 2 long term environmental fluctuations that resulted from the end permian crisis lower triassic strata display widespread microbialite and carbonate seafloor fan development and contain indicators of suppressed infaunal bioturbation such as flat pebble conglomerates and wrinkle structures facies considered unusual in post cambrian subtidal deposits our observations suggest that depositional systems too respond to biotic crises and that certain facies may act as barometers of ecologic and environmental change independent of fossil assemblage analyses close investigation of facies changes during other critical times in earth history may serve as an important tool in interpreting the ecology of metazoans and their environment

permian marine paleoecology and its implications for large scale decoupling of brachiopod and bivalve abundance and diversity during the lopingian late permian abstract the transition during the permian triassic interval from brachiopod rich benthic marine assemblages to communities with diverse molluscs has been well constrained by measures of global taxonomic richness but its ecological context has not been studied using quantitative relative abundance data new relative abundance data from early middle and late permian silicified fossil assemblages from offshore shelf carbonate environments indicate that molluscs increased significantly in relative abundance from 0 8 in the middle permian guadalupian to 65 4 in the late permian lopingian these numerical changes are accompanied by increases in the abundance of infaunal bivalves and motile gastropods in the late permian although this ecological change was coincident with the end guadalupian extinction a new global diversity compilation indicates that the overall genus level severity of that biotic crisis was substantially lower than previous estimates the pronounced ecological shift was instead concurrent with the onset of deep marine anoxic or euxinic conditions around the guadalupian lopingian boundary suggesting that increased environmental variability in proximity to the deep water mass may have given eurytopic molluscs a competitive advantage over more stenotopic brachiopods however the lack of global changes in relative genus richness implies dramatic decoupling of global taxonomic and local ecological processes the pronounced increase in molluscan abundance and alpha diversity in the silicified assemblages contrasts with their unchanged global taxonomic richness and may also have resulted from increased environmental stress in offshore shelf environments these results demonstrate that the ecological transition from the brachiopods to molluscs was more complex than inferred from global measures of taxonomic richness and imply that initial stages of permo triassic environmental deterioration may have been responsible for the decoupling of local ecological from global taxonomic processes during the dramatic late permian rise of the modern fauna

the role of membrane like stresses in determining the stability and sensitivity of the antarctic ice sheets back pressure and grounding line motion membrane stresses act along thin bodies which are relatively well lubricated on both surfaces they operate in ice sheets because the bottom is either sliding or is much less viscous than the top owing to stress and heat softening of the basal ice ice streams flow over very well lubricated beds and are restrained at their sides the ideal of the perfectly slippery bed is considered in this paper and the propagation of mechanical effects along an ice stream considered by applying spatially varying horizontal body forces propagation distances depend sensitively on the rheological index and can be very large for ice type rheologies a new analytical solution for ice shelf profiles and grounded tractionless stream profiles is presented which show blow up of the profile in a finite distance upstream at locations where the flux is non zero this is a feature of an earlier analytical solution for a floating shelf the length scale of decay of membrane stresses from the grounding line is investigated through scale analysis in ice sheets such effects decay over distances of several tens of kilometres creating a vertical boundary layer between sheet flow and shelf flow where membrane stresses adjust bounded physically reasonable steady surface profiles only exist conditionally in this boundary layer where bounded steady profiles exist adjacent profile equilibria for the whole ice sheet corresponding to different grounded areas occur neutral equilibrium if no solution in the boundary layer can exist the ice sheet profile must change the conditions for existence can be written in terms of whether the basal rate factor sliding or internal deformation is too large to permit a steady solution the critical value depends extremely sensitively on ice velocity and the back stress applied at the grounding line high ice velocity and high stress both favour the existence of solutions and stability changes in these parameters can cause the steady solution existence criterion to be traversed and the ice sheet dynamics to change a finite difference model which represents both neutral equilibrium and the dynamical transition is presented and preliminary investigations into its numerical sensitivity are carried out evidence for the existence of a long wavelength instability is presented through the solution of a numerical eigenproblem which will hamper predictability

physical modelling of lithosphere subduction in collision zones abstract physical mechanical modeling of continental collision is performed with a 4 layered mantle model compositionally distinct layers of hydrocarbons are used to model a lithosphere which consists of two crustal layers the upper one quasi brittle the lower one plastic and a plastic mantle layer the lower crustal layer the crustal asthenosphere has a low yield limit a low viscosity liquid water represents the asthenosphere under the lithosphere lateral compression of the model plate by a piston is the driving mechanism of collision similarity criteria are satisfied in the modeling the collisional process was investigated with various boundary conditions and values of the model parameters the yield limit and the thickness of the crustal asthenosphere were varied as well as the action of the piston on the plate the force was applied either throughout the plate section or on its mantle layer only in the latter case this layer slipped relative to the upper crust hence different results were obtained a more realistic pattern seems to occur when the yield limit of the crustal asthenosphere is not too small and free sliding of the crustal layers over the mantle lithosphere is not possible the upper crustal layer then experiences failure in the collision zone and thrusting develops there intensive thickening of the lower crust was observed the mantle layer being subducted like oceanic lithosphere in a subduction zone

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

elevated atmospheric co2 and the delayed biotic recovery from the end permian mass extinction excessive co2 in the earth ocean atmosphere system may have been a significant factor in causing the end permian mass extinction co2 injected into the atmosphere by the siberian traps has been postulated as a major factor leading to the end permian mass extinction by facilitating global warming widespread ocean stratification and development of anoxic euxinic and co2 rich deep waters a broad incursion of this toxic deep water into the surface ocean may have caused this mass extinction although previous studies of the role of excessive co2 have focused on these bottom up effects emanating from the deep ocean top down effects of increasing atmosphere co2 concentrations on ocean surface waters and biota have not previously been explored passive diffusion of atmospheric co2 into ocean surface waters decreases the ph and caco3 saturation state of seawater causing a physiological and biocalcification crisis for many marine invertebrates while both bottom up and top down mechanisms may have contributed to the relatively short term biotic devastation of the end permian mass extinction such a top down physiological and biocalcification crisis would have had long term effects and might have contributed to the protracted 5 to 6 million year long delay in biotic recovery following this mass extinction earth s modern marine biota may experience similar top down co2 stresses if anthropogenic input of atmosphere ocean co2 continues to rise

behavior of lophophorates during the end permian mass extinction and recovery abstract the end permian mass extinction devastated most marine communities and the recovery was a protracted event lasting several million years into the early triassic environmental and biological processes undoubtedly controlled patterns of recovery for marine invertebrates in the aftermath of the extinction but are often difficult to single out the global diversity and distribution of marine lophophorates during the aftermath of the end permian mass extinction indicates that stenolaemate bryozoans rhynchonelliform brachiopods and lingulid brachiopods displayed distinct recovery patterns bryozoans were the most susceptible of the lophophorates experiencing relatively high rates of extinction at the end of the permian and becoming restricted to the boreal region during the early triassic the recovery of bryozoans was also delayed until the late triassic and characterized by very low diversity and abundance following the final disappearance of permian rhynchonelliform brachiopod survivors early triassic rhynchonelliform brachiopod abundance remained suppressed despite a successful re diversification and a global distribution suggesting a decoupling between global taxonomic and ecological processes likely driven by lingering environmental stress in contrast with bryozoans and rhynchonelliforms lingulid brachiopods rebounded rapidly colonizing shallow marine settings left vacant by the extinction lingulid dominance characterized by low diversity but high numerical abundance was short lived and they were once again displaced back into marginal settings as environmental stress changed through the marine recovery the presence in lingulid brachiopods of the respiratory pigment hemerythrin known to increase the efficacy of oxygen storage and transport when coupled with other morphological and physiological adaptations may have given lingulids a survival advantage in environmentally stressed early triassic settings

evolution in a cold climate abstract a brief appraisal of marine fossils from high latitudes and episodically cold climate especially in east australia and new zealand during late palaeozoic and early mesozoic times shows patterns of evolution and survival that differ from those adduced for the palaeotropics and northern hemisphere examples taken from amongst phyla scyphozoa bryozoa brachiopoda and classes bivalvia and class cephalopoda suggest these attributes 1 evolution and demise of species and genera proceeded at a rate close to that known for palaeotropical and northern hemisphere macro invertebrates but involved fewer families and orders 2 possibly intraspecific variation was greater amongst southern palaeohemisphere permian species than in those of the permian palaeotropics 3 there was no proven diminution of life at the end of the guadalupian middle permian at southern high latitudes where however the fossil record is meagre for this interval younger wuchiapingian and changhsingian faunas were moderately diverse 4 there is no evidence for a high latitude southern hemisphere anoxic event in the early triassic despite claims of a world wide anoxic interval nor has any substantial volcanic eruption or bolide impact left any marked traces in the sedimentary record 5 as a consequence some major groups such as bryozoa and conulariida staurozoa survived the end permian extinction shock in the southern hemisphere 6 other major groups appear to have survived better in the south than in the north notably mollusc bivalvia and cephalopoda it therefore appears likely that triassic seas were restocked substantially from the southern hemisphere and that the permian extinction shock was asymmetric with respect to latitudes in its distribution and affect