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

diagenetic origin of carbon and oxygen isotope compositions of permian triassic boundary strata bulk carbonate 13 c and 18 o compositions of profiles across permian triassic p t boundary sections in china italy austria and iran show wide varieties of trends the 13 c depletions occur in all sections and range from 2 to 8 pdb in magnitude these excursions take place over intervals ranging from less than 0 1 to more than 40 m the 18 o values may increase or decrease toward the p t boundary but decrease sharply by 2 9 pdb at or above the boundary cross plots of 13 c and 18 o values from all sections show positive covariance wide differences in magnitudes trends and position of the excursions relative to the boundary as well as the covariance patterns suggest that p t boundary 18 o and 13 c values are partially or entirely diagenetic in origin formed in association with exposure surfaces this interpretation implies that p t boundary sections studied till date were subaerially exposed before during and after the mass extinction resulting in the removal of strata containing key information about the extinction mechanism this inference is consistent with the paleontological studies that have shown the presence of gaps at the boundary and further supported by the sharp lithologic changes observed at virtually all p t boundary sections subaerial exposures are documented by detailed sedimentologic and isotopic studies from central tethyan sections in abadeh and shah reza in iran proposed p t boundary extinction models are based on isotopic values that are diagenetic in origin and stratigraphic sections that are incomplete leading to extinction mechanisms with little physical supporting evidence

on the physical structure of a front in the bellingshausen sea abstract the structure of a front observed at 67 s in austral spring in the bellingshausen sea is described the front extended to full depth and has been identified by read et al 1995 as the southernmost major front of the antarctic circumpolar current where circumpolar deep water cdw outcrops in this paper the structure of the front is examined on scales down to 10 km using a closely spaced ctd section and down to 3 km from underway surveys with seasoar and an accustic doppler current profiler adcp which resolved the density and velocity structure respectively in the top 400 m a seasonal halocline was present throughout the survey area on both sides of the front at the base of a mixed layer 50 70 m deep the signature of the previous winter s mixed layer depth could be seen in the weak stratification between 70 and 150 m the subsurface temperature minimum within the winter mixed layer was significantly colder south of the front 1 7 c than north of it 1 1 c the front defined by eastward velocities greater than 10 cm s 1 was 70 80 km wide with flow at speeds of up to 50 cm s 1 in the surface layer the zone within which water mass changes occurred was narrower about 40 km contained within the zone of eastward flow and extended down to 1000 m the strong velocities in the frontal jet caused differential advection of surface properties from upstream west of the survey area resulting in sharp cross frontal gradients of salinity and chlorophyll a chlorophyll was largest over 5 mg m 3 in a band barely 10 km wide that extended along front for well over 100 km and was tightly constrained along the southern flank of the front where isopycnals outcropped from the winter mixed layer into the surface layer across the seasonal halocline the large values of chlorophyll could only be maintained by advection into the survey area from an unknown source region upstream boyd et al 1995 patches of high chlorophyll were found only south of the front and it is hypothesised that productivity south of the front is a consequence either of some property of the upwelling cdw or of water that had been under ice identified by the 1 7 c subsurface temperature minimum temperature anomalies on the 27 4 kg m 3 isopycnal indicate that patches of water south of the front had broken off from the southern flank of the front so it is probable that the bloom was spreading southwards from the front within the survey area rather than northwards from the ice edge

on the causes of mass extinctions the temporal link between large igneous province lip eruptions and at least half of the major extinctions of the phanerozoic implies that large scale volcanism is the main driver of mass extinction here we review almost twenty biotic crises between the early cambrian and end cretaceous and explore potential causal mechanisms most extinctions are associated with global warming and proximal killers such as marine anoxia including the early middle cambrian the late ordovician the intra silurian intra devonian end permian and early jurassic crises many but not all of these are accompanied by large negative carbon isotope excursions supporting a volcanogenic origin most post silurian biocrises affected both terrestrial and marine biospheres suggesting that atmospheric processes were crucial in driving global extinctions volcanogenic atmospheric kill mechanisms include ocean acidification toxic metal poisoning acid rain and ozone damage and consequent increased uv b radiation volcanic darkness cooling and photosynthetic shutdown each of which has been implicated in numerous events intriguingly some of the most voluminous lips such as the oceanic plateaus of the cretaceous were emplaced with minimal faunal losses and so volume of magma is not the only factor governing lip lethality the missing link might be continental configuration because the best examples of the lip extinction relationship occurred during the time of pangaea many of the proximal kill mechanisms in lip extinction scenarios are also potential effects of bolide impact including cooling warming acidification and ozone destruction however the absence of convincing temporal links between impacts and extinctions other than the chicxulub cretaceous example suggests that impacts are not the main driver of extinctions with numerous competing extinction scenarios and the realisation that some of the purported environmental stresses may once again be driving mass extinction we explore how experimental biology might inform our understanding of ancient extinctions as well as future crises

mesoscale pigment fields in the gulf stream observations in a meander crest and trough in september october 1988 and april 1989 a series of hydrographic transects were completed across the gulf stream front in a meander crest and meander trough respectively one of the main experimental objectives was to relate the spatial distribution of chlorophyll to the physical fields of gulf stream meanders chlorophyll distributions are derived from conductivity temperature depth ctd fluorescence profiles calibrated with discrete pigment samples collected from bottles at several depths at various stations objective analysis oa maps and vertical sections in stream coordinates of chlorophyll on density surfaces show the chlorophyll distribution was strongly related to the structure of the gulf stream front in particular chlorophyll concentrations greater than 0 4 mg m 3 were at or inshore of the gulf stream north wall characteristic length scales of chlorophyll distribution determined from the horizontal and temporal correlation function are the same order 50 100 km as length scales of the physical variables the maximum chlorophyll concentrations in the vertical were from the surface to 50 m depth on the western flank of the meander crest and deepened to 75 to 100 m depth on the eastern flank this coincides with the deepening of the 24 4 25 7 surfaces from the western to the eastern flank of the meander crest although in the spring cruise the maximum chlorophyll concentrations were also found at depths between the surface and 100 m there were no clear distinctions in pigment distributions between the western and eastern transects of a relatively weak trough maximum chlorophyll concentrations 1 0 1 5 mg m 3 from the 1989 spring bloom in slope waters were about double those observed in the 1988 fall data the primary physical mechanisms influencing the mesoscale pigment distribution in gulf stream meanders observed in this study are 1 outcropping of nutrient bearing strata in the spring 2 meander induced upwelling of nutrients along sloping isopycnals and 3 gulf stream ring interactions

observations of gulf stream induced and wind driven upwelling in the georgia bight using ocean color and infrared imagery ocean color and infrared imagery from aircraft and satellite sensors are combined with in situ measurements of currents chlorophyll temperature salinity coastal winds and sea level to study upwelling events in the georgia bight where the gulf stream and continental shelf waters strongly interact these interactions were observed over an 8 day period in april 1980 during which five independent upwellings occurred the upwellings included a nearshore wind driven upwelling enhanced by topographic effects three gulf stream filament induced upwellings and what appears to have been a gulf stream meander induced event the chlorophyll distributions as inferred from the imagery are found to be reliable tracers which indicate filamentary circulation and propagation and advective routes by which nearshore water moves offshore the propagation of two of the filaments and the meander are studied in detail using the imagery and mooring array temperature time series both techniques yield nearly identical results for the phase speeds of each event there is evidence that one of the filaments accelerated as it entered into the charleston bump area where the gulf stream deflects offshore the other filament exhibited a steady deceleration as it moved past cape canaveral and eventually lost any semblance of wave motion also includedmore are data from april 1979 which offer corroborating evidence of filamentary structure and circulation intercomparisons of field measurements and the nimbus 7 coastal zone color scanner estimates of surface pigment concentrations show excellent agreement over the range of 0 1 7 0 mg m sup 3 54 references 22 figures 6 tables less

intermediate sodium potassium mica in hydrothermally altered rocks of the waterloo deposit australia a combined sem emp xrd tem study metastable intermediate na k mica represents a product of hydrothermal alteration in volcanic rocks from the alteration halo of the waterloo massive sulfide deposit australia the xrd pattern of this solid solution between paragonite and muscovite is characterized by a rational series of basal reflections with d values intermediate between the end members transmission electron microscopy revealed that the intermediate na k mica forms thick stacks that belong to a two layer polytype na rich intermediate na k mica typically occurs together with paragonite whereas k rich intermediate na k mica is intergrown with muscovite the intermediate na k mica is interpreted to have formed as a result of the incomplete transformation of k rich mica to na rich mica through dissolution and recrystallization processes driven by compositional changes of the hydrothermal fluids interacting with the volcanic rocks alteration must have proceeded under non equilibrium conditions because the composition of the solid solution falls into the miscibility gap separating paragonite and muscovite

the permo triassic extinction the end permian mass extinction brought the palaeozoic great experiment in marine life to a close during an interval of intense climatic tectonic and geochemical change improved knowledge of latest permian faunas coupled with recent advances in isotopic studies and biostratigraphy have greatly enhanced our understanding of the events of 250 million years ago and have begun to provide answers to many questions about the causes of extinction

on vertical motion divergence and the thermal wind balance in cold dome meanders a diagnostic study wavelike meanders are observed along the length of the florida current from the florida keys to cape hatteras these propagating meanders are three dimensional each has a cold dome and the meandering flow that overtakes the dome in a cyclonic turn is characteristically stronger when flowing offshore than when flowing onshore we focus on vertical motion as a key to understanding the interdependence of the downstream propagation the upwelling in the cold dome and the skewness in the strength of the meandering flow inferred from a composite of drogue and temperature observations the pattern of vertical motion is one of upwelling that extends throughout the water column formed by the forepart of the translating dome and its overlying on shore flow and a downwelling that similarly extends vertically through the rear part of the dome and its overlying offshore flow it is shown that the vertical motion and the translation of the meander are interrelated and both enter importantly in the acceleration of the water columns and hence in the skewness in the strength of the meandering flow component as the thermal wind changes with the divergence accompanying the vertical motion it also provides a twisting mechanism to help restore the thermal wind balance

permian gondwana boreal antitropicality with special reference to brachiopod faunas in a reconstructed global permian marine biogeographic framework antitropicality is defined as a biogeographic phenomenon whereby a taxon occurs only in the boreal and gondwanan realms and is lacking completely or nearly so in the intervening palaeoequatorial realm we recognise three types of antitropical distributions bipolar high latitude generally 50 latitude in each hemisphere bitemperate approximately between 30 and 50 latitudes in each hemisphere and a combination of both evidence of permian antitropicality has been reported from almost all major marine invertebrate groups both pelagic or benthic forms and is best known at the generic level although an increasing number of antitropical species have also been recognised antitropicality appears to have occurred throughout most of the permian but its strength varied from stage to stage judging by the number of brachiopod genera shared between the two hemispheres the phenomenon manifests itself most strongly from the sakmarian to the kazanian wordian suggesting a prolonged interval of enhanced biotic interchanges between the gondwanan and boreal realms possible migration pathways and mechanisms are reviewed and discussed among a number of existing scenarios invoked to explain the origin of both modern and geological antitropicality we here present data particularly supporting 1 a south to north stepping stone migratory mechanism via island terranes scattered in the eastern palaeotethys 2 a vicariance model exemplified by the spatio temporal distribution of tomiopsis and 3 a shelf north to south migration along the western coast of the palaeotethys as suggested by sowerbina in addition we also consider dispersal along the western coast of pangea facilitated at times by upwelling systems as an additional migration pathway for intercontinental biotic exchanges during the permian although corroborating data are required at present

phanerozoic shallow water diversity driven by changes in sea level shallow water 50 m marine diversity curves for the phanerozoic based on area changes due to sea level variation and continental movements are presented it is shown that a change in the degree of endemism can alter diversity more than the effect of sea level change or change in the number of faunal provinces the pattern produced for a constant degree of endemism shows some rapid but not periodic falls in diversity these occur in the middle cambrian at the end of the ordovician devonian permian cretaceous and eocene and in the messinian there is no recurring single cause for these falls

permian triassic boundary interval in the abadeh section of iran with implications for mass extinction part 1 sedimentology the uppermost permian strata of the abadeh section in iran consist of 56 m of skeletal limestone abadehian that grades upward into 18 m of grey bioturbated lime mudstone djulfian which in turn grades upward to 18 m of red nodular wackestone dorashamian containing an abundant pelagic fauna the overlying lowermost triassic includes two enigmatic layers at its base immediately above the boundary is a 1 m thick layer of inorganically precipitated synsedimentary carbonate cement the cement is composed of 10 20 cm long crystals oriented either perpendicular to the bedding or as dome shaped features resembling botryoids about 0 5 m of wackestone overlies the cement layer the second layer is a 1 5 m thick grainstone overlying the cement horizon and consists of recrystallised spherical grains ooids or peloids the remainder of unit a is composed of 100 m of grey bioturbated to nodular lime mudstone the lithofacies succession of the uppermost permian is interpreted to represent deposition under increasing water depth related to rising of relative sea level which led to drowning of the carbonate platform to below storm wave base sedimentologic characteristics lithology wide distribution and slow sedimentation rates indicate that strata immediately below the permian triassic p t boundary dorashamian interval were deposited in deep oxygenated waters the enigmatic lowermost triassic synsedimentary carbonate cement and grainstone layers are interpreted to have been deposited in shallow waters indicating a rapid and major drop in relative sea level at the end of permian time in this area followed by a relative sea level rise during the earliest triassic precipitation of synsedimentary cement immediately above the p t boundary in iran and elsewhere south china suggests a global change in ocean chemistry one possible explanation is that dissolved calcium and bicarbonate concentrations in seawater increased sufficiently to promote spontaneous carbonate precipitation a rare event in the phanerozoic but common during precambrian time alternatively a massive heating event could have resulted in co2 degassing and decreases in oceanic carbonate solubility both leading to inorganic synsedimentary carbonate precipitation inorganic precipitation of synsedimentary carbonate cement may indicate that biochemical production of carbonate was halted due to the p t boundary events our study indicates that shallow and moderately deep waters during the latest permian were well oxygenated in the open ocean setting of the central tethys sea in iran therefore p t mass extinction scenarios that invoke upon widespread marine anoxia should be viewed with caution

the late ordovician mass extinction abstract near the end of the late ordovician in the first of five mass extinctions in the phanerozoic about 85 of marine species died the cause was a brief glacial interval that produced two pulses of extinction the first pulse was at the beginning of the glaciation when sea level decline drained epicontinental seaways produced a harsh climate in low and mid latitudes and initiated active deep oceanic currents that aerated the deep oceans and brought nutrients and possibly toxic material up from oceanic depths following that initial pulse of extinction surviving faunas adapted to the new ecologic setting the glaciation ended suddenly and as sea level rose the climate moderated and oceanic circulation stagnated another pulse of extinction occurred the second extinction marked the end of a long interval of ecologic stasis an ecologic evolutionary unit recovery from the event took several million years but the resulting fauna had ecologic patterns similar to the fauna that had become e

permian diamictites in northeastern asia their significance concerning the bipolarity of the late paleozoic ice age despite a lack of detailed sedimentologic analyses diamictites in the middle permian atkan formation were previously interpreted as glaciomarine and glacially influenced marine deposits this interpretation allowed this unit to play a prominent role in paleoclimatic and biogeographical reconstructions associated with presumed bipolar glaciation during the late paleozoic ice age lpia in this sense the lpia is considered to be a close analog to bipolar glaciation and climate change during the cenozoic here results are presented that challenge the glacigenic interpretation for these strata and negate interpretations of the bipolar nature of the lpia the 400 to 1500 m thick atkan formation was deposited in back arc basins associated with activity of the okhotsk taigonos volcanic arc along the leading edge of pangea as it drifted across the north polar circle the occurrence of tuffs volcanic clasts and glass shards indicate derivation from a nearby arc cooling and solidification of some clasts during sedimentation is suggested by the occurrence of clasts with embayments and protrusions that extend into the surrounding matrix clasts with columnar like jointing and alteration of the matrix surrounding some clasts ca tims dating of tuff zircons indicate a late capitanian age which is consistent with fossils within the strata bedded diamictites deposited as debrites dominate these diamictites which occur as tens of m thick downlapping packages that thicken then thin upward were deposited as prograding and abandoning sediment gravity flow fans chaotic and folded strata formed as slumps graded sandstones and conglomerates were deposited as turbidites and mudstones were deposited as mudflows low density turbidites and hemipelagic deposits striated clasts and outsized clasts piercing bedding were not observed in the study area strata above and below the atkan formation contain abundant graded beds and deep water trace fossils indicating deposition as turbidites the combination of debrites turbidites slumps volcanic grains clasts glass and tuffs and an absence of glacigenic indicators suggest that atkan strata were deposited in deep water basins associated with the development of the volcanic arc rather than due to glacial activity these findings are significant as they require reconsideration of current views of lpia glaciation and suggest that ice sheets were limited to gondwana

phanerozoic large igneous provinces lips heatt haline euxinic acidic thermal transgression episodes and mass extinctions abstract the phanerozoic consists of three mutually exclusive climate states icehouse greenhouse and hothouse the greenhouse is the default state representing 70 of the phanerozoic it is characterized by a weak thermal mode pole driven deep water formation with little or no continental sea ice and weakly oxic cool water sinking near the poles nitrogen limitation characterizes greenhouse oceans in which ammonium may be the dominant bioavailable form of nitrogen the steady state greenhouse default must be forced to produce either of the other two states continent continent collision produces the intense chemical weathering that draws down atmospheric co2 and results in the icehouse state that comprises 20 25 of the phanerozoic icehouses have ice caps in contact with the ocean that produce icebergs and foster sea ice formation sea ice formation fills the ocean with highly oxic phosphorus limited icewater except for a thin layer of warm surface water in the tropics of the 23 most conspicuous mass extinctions of the phanerozoic including the late ediacaran 4 are associated with ice volume related regressions and 3 are problematic we suggest that the other 16 mass extinctions occurred when greenhouse climate was forced to hothouse climate large igneous provinces lips can trigger the heatt haline euxinic acidic thermal transgression mechanism which can force greenhouse climate to a hothouse climate state the rapid voluminous co2 emissions of lips cause a series of events that result in very slow but pronounced haline mode circulation mid latitude driven deep water formation that produces warm saline bottom water at very dry hot subtropical and middle latitudes this water upwells at the poles causing warm and moist equable climate hothouse development promotes deep sea anoxia that is generated in concert with co2 buildup and warming the spread of anoxia favors reduced nitrogen over nitrate and limited iron dust curtails nitrogen fixation this leads to dominance of primary productivity by primitive green algae and or cyanobacteria progression to euxinia that reaches the photic zone severely curtails primary productivity via poisoning even as availability of usable nitrogen plummets the result is eukaryotic mass extinction we suggest that the 16 phanerozoic mass extinctions referred to above resulted at least in part from the heatt process evidence for this relationship at 11 of the most severe extinctions is convincing data sets for the other 5 are strongly suggestive of heatt related mass extinction but do not yet have enough documentation to reliably characterize them as heatt episodes

alteration of felsic volcanics hosting the thalanga massive sulfide deposit northern queensland australia and geochemical proximity indicators to ore thalanga is an early ordovician stratiform zn pb cu ag rich massive sulfide deposit in northern queensland australia with a total resource of 6 6 mt of ore the host rock succession consists of variably altered rhyolite in the footwall and a dacite dominated volcano sedimentary sequence in the hanging wall the sulfide deposit and the enclosing volcanic sequence were metamorphosed under upper greenschist conditions a laterally continuous footwall alteration zone extends beneath the entire deposit 3 000 m and to a stratigraphic depth of at least 300 m below the ore lenses the bulk of this zone is occupied by feldspar destructive muscovite biotite chlorite rich mottled alteration facies with disseminated pyrite representing the metamorphic equivalent of phyllosilicate dominated hydrothermal alteration discordant zones of intense quartz pyrite alteration represent the principal fluid pathways during mineralizing hydrothermal activity locally quartz k feldspar alteration facies exist on the fringes of the system and calcareous alteration and chlorite pyrite alteration facies exist in the upper part of footwall rhyolite proximal to sulfide lenses quartz feldspar porphyritic rhyolite laterally surrounding the footwall alteration zone and feldspar porphyritic dacite in the hanging wall are unaltered or weakly altered the compositional diversity of altered footwall rhyolite implies that hydrothermal alteration at thalanga was a complex processes this paper presents a model for the evolution of the footwall alteration zone calcareous alteration probably represents the initial phase of hydrothermal activity this was followed by diffuse upwelling of acidic seawater dominated fluids causing destruction of primary feldspar precipitation of pyrite and formation of hydrothermal sericite chlorite and clay minerals subsequent intense quartz pyrite alteration was directly associated with mineralization the thalanga footwall alteration zone has several geochemical characteristics that show systematic changes with increasing proximity to ore these include na depletion and elevated mg s alteration index ai chlorite carbonate pyrite index ccpi mo bi and as furthermore the x mg of chlorite and biotite increases systematically from values of 0 45 to 0 5 in least altered rhyolite to values 0 9 immediately below ore these geochemical features can be used in exploration for massive sulfide deposits as vectors to ore at the prospect scale and in discrimination of prospective hydrothermal from unprospective diagenetic alteration systems at the regional scale

gulf stream meanders in the south atlantic bight 2 momentum balances gulf stream meanders and their associated frontal eddies have been numerically simulated using a model tuned to the southern portion of the south atlantic bight a run which produced events most similar to those observed in nature was identified and the dynamics of a particular meander event were examined in detail a complex array of momentum balances are obtained and they vary with position within the feature while the along isobath flow is predominantly in geostrophic balance several of the nonlinear advection terms in both horizontal momentum equations play important roles in the space time development of the flow in particular the vertical advection of horizontal momentum as well as frictional dissipation are now recognized as important contributors to the dynamical balances in the vicinity of the steep continental slope it would appear that the semigeostrophic equations constitute the simplest description of this system 10 refs 15 figs 3 tabs

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

paleoenvironment and the oxygen isotope geochemistry of ironstone of the upper ordovician neda formation wisconsin usa geological evidence suggests that the goethite dominated oolitic ironstone of the upper ordovician neda formation in the north central united states was subaerially weathered in the late ordovician the oxygen isotope ratios of the goethites in the open quotes hard close quotes and open quotes soft close quotes ores of this deposit are rather uniform with a delta sup 18 o value of about minus 1 0 per thousand this delta sup 18 o value indicates the presence of meteoric water at the time of goethite formation and supports the idea that the goethites in hard and soft ores were formed in the same chemical weathering environment 440 million years ago the delta sup 18 o value of accessory phosphate in some soft ore goethite rich ooids was measured and combined with the goethite delta sup 18 o value to calculate a temperature of formation of about 23 degrees c the corresponding delta sup 18 o value of the ancient water was calculated to have been minus 7 3 per thousand the relatively open quotes cool close quotes temperature calculated for the low altitude tropical site occupied by the neda ironstone in the late ordovician is consistent with published evidence from fossil marine invertebrates for global cooling at that time the delta sup 18 o value of minus 7 3 per thousand for the ancient tropical precipitation could indicate intense rainfall ofmore a seasonal perhaps monsoonal character 27 refs 7 figs 3 tabs less

gulf stream meanders in the south atlantic bight 1 scaling and energetics as the gulf stream flows along the outer edge of the southeastern united states continental shelf it meanders on and offshore creating frontal eddies which influence the exchange of water between the shelf and the adjacent atlantic ocean on weekly timescales the dynamics controlling the development of such features in this region the open quotes south atlantic bight close quotes or sab is the subject of this pair of papers in the present paper the authors provide the background on the subject summarize the length time and velocity scales associated with these features and discuss meander energetics as simulated by a numerical model the scaling indicates that significant ageostgrophic dynamics may be crucial to the development of these flows and that the semigeostrophic equations may provide the simplest description of the system these nonlinear dynamics may permit complex interactions among meander modes and with topography resulting in the observed behavior of the gulf stream in the sab the princeton ocean model was tuned for conditions which prevail in the southern south atlantic bight and idealized numerical simulations of gulf stream meanders and associated frontal eddies were performed the system was found to be sensitive to both the amplitude and period of a small perturbationmore applied at the southern boundary the energetics indicate that the development of these features is controlled by a mixture of both baroclinic and barotropic instabilities of the mean gulf stream flow tantalizing hints of a period doubling phenomenon are present in the energy conversion time series 47 refs 12 figs 4 tabs less

the permian triassic palynological transition in the guryul ravine section kashmir india implications for tethyan gondwanan correlations this first palynological study of the permian triassic succession in the guryul ravine kashmir india reveals impoverished latest permian spore pollen assemblages in the uppermost zewan formation a rich palynoassemblage from the basal khunamuh formation characteristic of the permian triassic transition zone and depleted triassic assemblages from higher in the khunamuh formation the collective assemblages can be broadly correlated to the densipollenites magnicorpus and klausipollenites decipiens palynozones of peninsular india and to palynofloras spanning the permian triassic boundary elsewhere in gondwana generally low spore pollen yields and poor preservational quality of the studied assemblages hinder more precise correlations and are inferred to be a function of an offshore marine depositional setting on the margin of the neotethys ocean and thermal alteration associated with cenozoic collisional tectonism between india and asia

the effect of global warming and global cooling on the distribution of the latest permian climate zones abstract the end permian biotic crisis is commonly associated with rapid and severe climatic changes these climatic changes are commonly suggested to have originated from solid earth carbon degassing leading to global warming but aerosol and ash induced cooling induced by lava degassing has been suggested as well the application of an earth system model of intermediate complexity has enabled a visualisation of the major climatic shifts on the supercontinent pangaea caused by rapid temperature changes due to changed radiative properties from greenhouse gases the reconstructed reference climate was validated by latest permian climate indicative sediments to investigate the possible climatic shifts from a set of 22 reconstructions which varied with temperature a minimum global annual mean temperature of 18 2 c for the late permian climate prior to the climatic perturbation event was determined starting from this pre event setup global warming and global cooling scenarios were simulated the response of the end permian climate system to temperature increase and decrease show marked differences while global cooling is followed by major climatic changes in the high latitudes and replacement of boreal biomes by tundra and polar frost the changes during global warming are less pronounced with only locally increasing aridity compensated by humidisation in other regions the different behaviour of the climatic belts under warm and cold conditions is accompanied by different climate sensitivities caused by different strength of the snow cover albedo feedback thus changes in the energy balance of the latest permian surface troposphere system have a 30 higher perturbation potential during cold climate conditions than during warmhouse conditions therefore substantial global cooling resulting in coldhouse climate conditions and an annual global mean temperature below 18 c is more efficient in perturbing the earth palaeoclimate during the end permian warmhouse the results suggest that global cooling mechanisms as injection of sulphur aerosols and ash particles from the siberian traps large igneous province into the late permian palaeoatmosphere have a higher climate perturbation potential than a warming due to carbon greenhouse gases with a similar magnitude of radiative forcing

clean spectral analysis of long term sea level changes a new clean spectral technique has been applied for the first time to analyse a record of long term sea level fluctuation during the last 200 million year myr the technique is based on a one dimensional complex deconvolution algorithm and removes the effects of the data sampling as well as the artifacts arising from the choice of data window the analysis reveals a dominant periodicity of 33 myr in the sea level variations this periodicity compares well with the known half period of the sun s oscillation perpendicular to the galactic plane interestingly a 33 myr periodicity can also be correlated with the reported mass extinction cycles and other geological periodicities the results suggest galactic forcing as a possible driving mechanism for quasi periodic terrestrial processes

the largs high latitude oxygen isotope anomaly new zealand and climatic controls of oxygen isotopes in magma in northern fiordland the brook street terrane of new zealand consists of two units the predominantly basaltic plato and the predominantly andesitic largs terrane the permian plato terrane has normal to slightly enriched 18o values whereas the largs terrane which is of similar pre early triassic age has not yielded a single normal 18osmow result with all of 17 total rocks showing less than 3 2 seven less than 4 and two less than 9 these strongly anomalous data confirm an earlier suggested terrestrial character of largs deposition and demand the presence of permo triassic geothermal systems running on subantarctic to antarctic meteoric water the skewed data spectrum suggests a relatively immature flow system and likely values for the recharge water are 20 18o or less for a climate distribution similar to the present one including polar ice caps this would indicate over 70 of southern latitude rafts and xenoliths of largs rocks have been entrained within mackay intrusives in the early triassic on field evidence the mackay magmas have also intruded an early darran complex but this complex has been substantially reactivated in the cretaceous it has 18o values near 5 0 which is distinctly low for island arc magmas since the complex is isotopically homogeneous its 18o is unlikely to be a direct effect of the relatively shallow largs terrane more probable is a climate related slight depression of the 18o of magma sources in which other high latitude low 18o sediments and geothermal systems have been involved

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

mantle plume the invisible serial killer application to the permian triassic boundary mass extinction the earth experienced a severe mass extinction at the permian triassic boundary ptb about 252 million years ago this biological catastrophe was accompanied by major changes in geochemical composition of the atmosphere and ocean and the appearance of sedimentary features which had not occurred since the precambrian time the eruption of the largest continental flood basalt the siberian traps overlapped this mass killing many hypotheses have been proposed but no definitive conclusion currently exits here we present characteristics of three sections from iran and china and propose that an active mantle plume initiated a series of processes which led to the mass mortality and produced major sedimentological mineralogical and geochemical changes observed in the transition from the paleozoic to the mesozoic the injection of mantle plume related igneous dike swarms into the continental margin facilitated the release of massive amounts of ch 4 primarily from the dissociation of marine gas hydrates and secondarily from the maturation of organic rich sediments and fracturing of hydrocarbon reservoirs the bulk of the ch 4 was aerobically oxidized in the water column producing dissolved co 2 with low 13 c values this co 2 saturated seawater became acidic to the point of dissolution of shelf carbonates promoting precipitation of siliciclastic rich strata in the transition from the permian to the triassic methane derived co 2 also lowered carbon isotopic composition of seawater leading to the observed decline in 13 c composition of organic and inorganic marine carbon at the ptb gas charged oceans released large volumes of co 2 and ch 4 into the atmosphere which created a severe global warming the end permian inferno causing the release of additional ch 4 from the dissociation of polar gas hydrates these events lowered 13 c compositions of terrestrial carbon simultaneously feeder dikes from the mantle plume formed the siberian traps flood basalt marine mass extinction was the result of a change in seawater composition due to the injection and oxidation of ch 4 in the water column causing low ph high concentrations of co 2 ca 2 and hco 3 and low co 3 2 values combined with a hot seawater temperature these changes made calcification of marine organisms difficult and produced major physiological crisis including reduced metabolic rates high sensitivity to environmental stress and hampered growth and reproduction terrestrial mass extinction can be attributed to severe global warming and soil acidification produced by increased atmospheric co 2 acid rain that was generated by so 2 derived from the siberian trap eruption and loss of habitat cessation of the plume activity during early triassic stopped the release of ch 4 into the ocean and terminated continental flood basalt eruption ending the environment of death on land and in sea the cut off of co 2 production in the ocean instantly increased carbonate saturation of seawater resulting in extensive seafloor cementation it also resulted in the deposition of marine carbonates by microbial activities in the hostile post extinction environment from the trigger to recovery the perturbation which included the end permian mass mortality could have lasted for at least 2 myr several major mass extinctions of the phanerozoic are temporally accompanied by flood basalt eruptions so far these two events have been interpreted in a cause and effect relation flood basalt eruption causes mass extinction this study proposes that flood basalts and their time correlative biological crises are themselves the consequence of a complex perturbation caused by mantle plume activities if so major disturbances in the near surface of the earth are ultimately controlled by changes in the mantle the physical sedimentological observations presented here combined with previous paleontological evidence cast doubt on other interpretations which use geochemical variables numerical modeling biomarkers and ce anomaly to suggest that late permian ocean was anoxic all the way to the photic zone

migration origination and extinction of southern hemisphere brachiopods during the middle carboniferous abstract the migration patterns and latitudinal diversity gradients of early and middle carboniferous articulate brachiopod genera from the paleoequatorial zone and southern hemisphere are consistent with the paleoclimatic history of these intervals interpreted from the study of paleoequatorial and northern hemisphere forms both poles apparently became warmer between the middle and late visean south polar cooling associated with glaciation probably began in the late visean at this time 44 of 92 southern hemisphere nonequatorial genera migrated toward the equator the north pole remained warm into the namurian a and cooled during the namurian a to b both northern and southern hemisphere non equatorial genera reacted to high latitude warming with significant increases in percent origination genera from all latitudinal zones responded to high latitude cooling with significant increases in percent extinction during the namurian a to b when both poles were cool a small but statistically significant number of equatorial genera 8 out of 70 migrated out of the equatorial zone into the non equatorial northern hemisphere no similar migration into the southern hemisphere occurred at this time perhaps due to the steep latitudinal temperature gradient several lines of evidence suggest that the latitudinal temperature gradient was steeper in the southern hemisphere than in the northern hemisphere whereas percent origination in northern non equatorial latitudes rose significantly following north polar cooling origination rates in southern non equatorial latitudes did not rise significantly following south polar cooling southern hemisphere non equatorial brachiopods suffered a greater loss of diversity during the interval of polar cooling than either equatorial or northern hemisphere non equatorial brachiopods and there may be namurian tillites within 20 s of the paleoequator veevers and powell 1987

high productivity in the earliest triassic ocean black shales southwest japan abstract bedded cherts containing the permian triassic p t boundary exposed in the tanba and chichibu belts southwest japan contain interbedded organic rich black shales the organic carbon concentration of black shales before thermal maturation was evaluated to be about 3 average considering their maturity levels kerogens do not contain any debris of higher plant origins but are mostly composed of structureless amorphous kerogen black shales comprise organic matter derived mainly from plankton with additional organic matter derived from bacterial activity showing that the high primary production took place intermittently in the earliest triassic a stratified ocean with a well developed oxygen minimum layer rich in nutrients was intermittently disturbed due to tectonically and or climatically induced active ocean current systems in the earliest triassic resulting in upwelling causing remarkably high primary production to form organic rich black shales

some aspects of the permian triassic boundary ptb and of the possible causes for the biotic crisis around this boundary abstract the first appearance datum fad of hindeodus parvus is an excellent datum very close to the base of the otoceras woodwardi zone priority base of the triassic for the first time it allows an exact correlation of the ptb in all marine facies and faunal realms the following features of the extinction and recovery patterns near the ptb are most important for the search for causes of the ptb biotic crisis 1 most strongly affected were the siliceous plankton radiolarians and the warm water benthos and nekton 2 most of the cold water faunas were not significantly affected 3 the recovery of the warm water benthos and siliceous plankton occurred only after an unusually long time during the late olenekian and middle triassic 4 the productivity of the terrestrial plants dropped strongly and the recovery was mainly in the upper olenekian and in the middle triassic 5 several terrestrial extinction events occurred at different levels within the upper permian considerable before the marine ptb at or close to the fad of lystrosaurus no extinction event in the terrestrial faunas can be observed 6 terrestrial faunal elements that survived the dzhulfian dorashamian extinctions were able to survive some months of extreme climatic conditions by hibernation like life stages vertebrates or by dry and freezing resistant eggs conchostracans 7 about 50 of the genera that disappeared at the ptb re appeared in the olenekian middle triassic interval lazarus taxa or in this time interval genera appeared that had undoubtedly evolved from genera that had disappeared at the ptb and 8 the ptb is preceded by mass occurrences of marine and continental fungi and the fungal spike ends abruptly a little before the ptb a scenario for the ptb biotic crisis is elaborated that takes into consideration the real not interpolated diversity patterns of different marine and continental fossil groups the exact correlation of bioevents in different faunal realms and facies the strong biotic crisis in the tethyan warm water faunas in contrast to the much weaker biotic event in cold water faunas the severe dzhulfian dorashamian climate in many parts of the world caused by the continent ocean configuration and by siberian trap volcanism the cooling of the boreal area by the northward drift of pangaea that interrupted the exchange of warm water benthos between the tethys and western north america during the guadalupian the extinction event at the guadalupian lopingian boundary that restricted most of the affected warm water faunas to the tethys the importance of lower scythian anoxia that reached an unusually shallow level and above all the effects of the contemporaneous huge volcanic events about 250 m y ago on the siberian platform and in the eastern tethys that caused a 3 6 months lasting volcanic winter with strong cooling in low latitudes followed by a strong global warming

late devonian glacial deposits from the eastern united states signal an end of the mid paleozoic warm period abstract a late devonian polymictic diamictite extends for more than 400 km from northeastern pennsylvania across western maryland and into east central west virginia the matrix supported unbedded locally sheared diamictite contains subangular to rounded clasts up to 2 m in diameter the mostly rounded clasts are both locally derived and exotic some exhibit striations faceting and polish the diamictite commonly is overlain by laminated siltstone mudstone facies associations laminites the laminites contain isolated clasts ranging in size from sand and pebbles to boulders some of which are striated the diamictite laminite sequence is capped by massive coarse grained pebbly sandstone that is trough cross bedded a stratigraphic change from red calcic paleo vertisols in strata below the diamictite to non calcic paleo spodosols and coal beds at and above the diamictite interval suggests that the climate became much wetter during deposition of the diamictite the diamictite deposit is contemporaneous with regressive facies that reflect fluvial incision during the late devonian of the appalachian basin these deposits record a late devonian episode of climatic cooling so extreme that it produced glaciation in the appalachian basin evidence for this episode of climatic cooling is preserved as the interpreted glacial deposits of diamictite overlain by glaciolacustrine varves containing dropstones and capped by sandstone interpreted as braided stream outwash the appalachian glacigenic deposits are contemporaneous with glacial deposits in south america and suggest that late devonian climatic cooling was global this period of dramatic global cooling may represent the end of the mid paleozoic warm interval that began in the middle silurian

greenschist facies regional and contact metamorphism of the thalanga volcanic hosted massive sulfide deposit northern queensland australia the conditions of two separate greenschist facies metamorphic events have been reconstructed at the syn genetic thalanga massive sulfide deposit northern queensland australia using scarce garnet biotite and garnet chlorite bearing samples from the felsic volcano sedimentary host rock succession regional metamorphism peak temperature 440 to 480 c generated a foliation defined by aligned chlorite muscovite and biotite and rare euhedral spessartine almandine grossular rich garnets the emplacement of a post tectonic diorite pluton was associated with contact metamorphism and scarce anhedral spessartine almandine rich garnet poikiloblasts crystallized within a 650 m wide aureole at temperatures of 500 c both metamorphic stages occurred under pressure conditions of 3 5 kbar our study documents a useful method for geothermobarometric reconstruction of metamorphosed syn genetic ore deposits where calculations based on sulfide assemblages failed to produce unequivocal constraints furthermore we show that hydrothermally altered footwall rhyolite have higher rm x rm mg rm chlorite rm and rm x rm mg rm biotite than unaltered rocks which may help to identify fossil metamorphosed hydrothermal systems associated with massive sulfide deposits similar to thalanga

vertical velocities and dynamical balances in gulf stream meanders a triangular array of current meter moorings was deployed within the cyclonic flank of the gulf stream in the south atlantic bight from september 1981 to april 1982 using velocity and temperature data and the nondiffusive heat equation a time series of vertical velocity was derived a mean vertical velocity of 0 013 cm s 1 and standard deviation of 0 078 cm s 1 were obtained to better understand the subsurface structure of gulf stream meanders the time series of horizontal and vertical velocities and temperature were examined at times when events were passing through the array the flow along the trailing edge of a gulf stream meander and within the leading portion of a cold core frontal eddy was found to have an upward component positive w while that within the trailing portion of the frontal eddy and along the leading edge of a meander had a downward component negative w using the horizontal and vertical velocity time series cross stream and along stream momentum balances were calculated the downstream flow was found to be in geostrophic balance in contrast the coriolis and nonlinear terms were found to contribute equally to the determination of the cross stream flow

thermal barriers and the fate of perched faunas thermal barriers provide an explanation for the geologically sudden extinction of benthic faunas of epeiric seas when these seas disappeared by contracting to the open ocean biotic interactions could not have caused the sudden extinctions and neither could reduction of the regional area of seafloor because substantial areas of shallow seafloor remained along neighboring continental shelves when epeiric seas drained instead temperature contrasts must have been responsible epeiric seas had strongly seasonal climates and when some receded to continental margins many of their species would have encountered waters that failed to provide the maximum or minimum temperature required for reproduction when epeiric seas receded poleward equatorward or into coriolis driven currents many species faced lethal temperatures the history of the jurassic sundance sea provides a striking example of the fate of a warm adapted fauna driven westward into an area dominated by a cool coriolis driven current

climate change and the selective signature of the late ordovician mass extinction selectivity patterns provide insights into the causes of ancient extinction events the late ordovician mass extinction was related to gondwanan glaciation however it is still unclear whether elevated extinction rates were attributable to record failure habitat loss or climatic cooling we examined middle ordovician early silurian north american fossil occurrences within a spatiotemporally explicit stratigraphic framework that allowed us to quantify rock record effects on a per taxon basis and assay the interplay of macrostratigraphic and macroecological variables in determining extinction risk genera that had large proportions of their observed geographic ranges affected by stratigraphic truncation or environmental shifts at the end of the katian stage were particularly hard hit the duration of the subsequent sampling gaps had little effect on extinction risk suggesting that this extinction pulse cannot be entirely attributed to rock record failure rather it was caused in part by habitat loss extinction risk at this time was also strongly influenced by the maximum paleolatitude at which a genus had previously been sampled a macroecological trait linked to thermal tolerance a model trained on the relationship between 16 explanatory variables and extinction patterns during the early katian interval substantially underestimates the extinction of exclusively tropical taxa during the late katian interval these results indicate that glacioeustatic sea level fall and tropical ocean cooling played important roles in the first pulse of the late ordovician mass extinction in laurentia

deev jahi model of the permian triassic boundary mass extinction a case for gas hydrates as the main cause of biological crisis on earth the smoking gun revealing the secrets of the end permian mass mortality is a unique 1 2 m thick layer consisting of 5 20 cm long crystals of calcite that occurs precisely at the permian triassic boundary ptb in iran armenia turkey and china this layer is interpreted as synsedimentary abiotic seafloor cement indicative of precipitation from a highly carbonate supersaturated seawater its 13 c composition 13 c 0 pdb is 4 to 5 pdb lower than the typical upper permian values 4 to 5 pdb suggesting the involvement of massive amounts of gas hydrate ch 4 13 c 60 pdb the temporal coincidence of the cement layer with the ptb suggests that the process that promoted seafloor cementation was also responsible for the biological crisis a cementation model is developed based on accumulation dissociation cycle of gas hydrates which also explains the mass extinction at the ptb the upper permian accumulation period of gas hydrates ended abruptly adjacent to the ptb and the dissociation event began releasing 3 2 to 4 7 10 18 g ch 4 into the ocean oxidation of ch 4 in the water column created a seawater that was charged with co 2 an oceanic acid bath and had lower than normal o 2 content but not anoxic this oceanic acid bath first dissolved suspended fine grained carbonate particles and small calcareous organisms followed by extensive dissolution of platform carbonates raising ca 2 and hco 3 concentrations of seawater when the release of ch 4 declined the acid bath ocean became a soda ocean precipitating massive amount of seafloor cements observed globally at the ptb the study suggests that prior to cement precipitation the ptb ocean was charged with co 2 warm had low oxygen high ca 2 and high hco 3 concentrations these conditions collectively created stressful conditions causing the marine mass mortality the leakage of ch 4 to the atmosphere produced a super hot climate resulting in the biological devastation on land the proposed kill mechanism is developed on the basis of the physical clue the cement layer left behind by the killing process the change in ocean chemistry the accumulation dissociation cycles of gas hydrates also explain the 13 c pattern of marine carbonates and the periodicity of mass extinction events during the phanerozoic accumulation periods were long 5 to 20 my providing favorable conditions for ecosystem development pardeess phase the dissociation events were short and catastrophic 10 to 500 ky causing low oxygenation super hot climate and biological devastation doozakh phase it appears that most mass extinctions of the phanerozoic have been related to the internal working of the earth system during the phanerozoic methane has played the role of the deev jahi a female demon in persian mythology whose task is to attack the earth every so often to kill life on land and in sea

gulf stream fluctuations and meanders over the onslow bay upper continental slope abstract gulf stream fluctuations observed over the 200 and 400 m isobaths off onslow bay north carolina have a prominent weekly time scale the principal fluctuations observed during the 4 month winter experiment are consistent with webster s 1961a description of downstream propagating skewed lateral meanders of the gulf stream over the upper continental slope the subtidal velocity fluctuations were highly coherent over the vertical extent 120 m and over the horizontal extent 64 km of our array the implied downstream propagation speed was 30 km day 1 for the weekly period meanders concurrent satellite images of a sea surface temperature sst meander pattern indicate that subsurface temperature salinity velocity and relative vorticity maxima occurred as meander crests shoreward sst front excursions passed over the experiment site the meandering currents were not coherent with nearby wind stress or coastal sea level fluctuations eddy flux estimates indicate energy conversion from the f

a numerical study of the seasonal variability in the circulation off central chile the princeton ocean model is used to study the coastal ocean circulation off central chile between 30 and 45 s and its seasonal transitions in response to monthly mean climatological wind stress and surface heat flux the model reproduces many of the dominant circulation features including an equatorward coastal current coastal upwelling and a poleward undercurrent to get the correct seasonal variability in the undercurrent it was necessary to prescribe the inflow of the undercurrent on the northern model boundary meanders and eddies form throughout the simulation period seaward of the coastal current in response to baroclinic instability of the flow the flow associated with the meanders shows upwelling in the shoreward flow and downwelling in the seaward flow this upwelling downwelling pattern is explained by conservation of relative vorticity in the flow the upwelling velocity associated with the meanders corresponds to a vertical migration of 15 30 m over a typical timescale of the meanders of 1 2 months it is argued that this upwelling may be important for maintaining observed high phytoplankton biomass and primary production seaward of the coastal zone directly affected by wind driven upwelling

causes and consequences of extreme permo triassic warming to globally equable climate and relation to the permo triassic extinction and recovery permian waning of the low latitude alleghenian variscan hercynian orogenesis led to a long collisional orogeny gap that cut down the availability of chemically weatherable fresh silicate rock resulting in a high co2 atmosphere and global warming the correspondingly reduced delivery of nutrients to the biosphere caused further increases in co2 and warming melting of polar ice curtailed sinking of o2 and nutrient rich cold brines while pole to equator thermal gradients weakened wind shear and associated wind driven upwelling lessened further diminishing productivity and carbon burial as the earth warmed dry climates expanded to mid latitudes causing latitudinal expansion of the ferrel circulation cell at the expense of the polar cell increased coastal evaporation generated o2 and nutrient deficient warm saline bottom water wsbw and delivered it to a weakly circulating deep ocean warm deep currents delivered ever more heat to high latitudes until polar sinking of cold water was replaced by upwelling wsbw with the loss of polar sinking the ocean was rapidly filled with wsbw that became increasingly anoxic and finally euxinic by the end of the permian rapid incursion of wsbw could have produced 20 m of thermal expansion of the oceans generating the well documented marine transgression that flooded embayments in dry hot pangaean mid latitudes the flooding further increased wsbw production and anoxia and brought that anoxic water onto the shelves release of co2 from the siberian traps and methane from clathrates below the warming ocean bottom sharply enhanced the already strong greenhouse increasingly frequent and powerful cyclonic storms mined upwelling high latitude heat and released it to the atmosphere that heat trapped by overlying clouds of its own making suggests complete breakdown of the dry polar cell resulting rapid and intense polar warming caused or contributed to extinction of the remaining latest permian coal forests that could not migrate any farther poleward because of light limitations loss of water stored by the forests led to aquifer drainage adding another 5 m to the transgression non peat forming vegetation survived at the newly moist poles climate feedback from the coal forest extinction further intensified warmth contributing to delayed biotic recovery that generally did not begin until mid triassic but appears to have resumed first at high latitudes late in the early triassic current quantitative models fail to generate high latitude warmth and so do not produce the chain of events we outline in this paper future quantitative modeling addressing factors such as polar cloudiness increased poleward heat transport by deep water and its upwelling by cyclonic storms and sustainable mid latitude sinking of warm brines to promote anoxia warming and thermal expansion of deep water may more closely simulate conditions indicated by geological and paleontological data

a sulfidic driver for the end ordovician mass extinction the end ordovician extinction consisted of two discrete pulses both linked in various ways to glaciation at the south pole the first phase starting just below the normalograptus extraordinarius zone particularly affected nektonic and planktonic species while the second pulse associated with the normalograptus persculptus zone was less selective glacially induced cooling and oxygenation are two of many suggested kill mechanisms for the end ordovician extinction but a general consensus is lacking we have used geochemical redox indicators such as iron speciation molybdenum concentrations pyrite framboid size distribution and sulfur isotopes to analyze the geochemistry in three key hirnantian sections these indicators reveal that reducing conditions were occasionally present at all three sites before the first pulse of the end ordovician extinction and that these conditions expanded towards the second pulse even though the n extraordinarius zone appears to have been a time of oxygenated deposition pyrite is significantly enriched in 34s in our sections as well as in sections reported from south china this suggests a widespread reduction in marine sulfate concentrations which we attribute to an increase in pyrite burial during the early hirnantian the s isotope excursion coincides with a major positive carbon isotope excursion indicating elevated rates of organic carbon burial as well we argue that euxinic conditions prevailed and intensified in the early hirnantian oceans and that a concomitant global sea level lowering pushed the chemocline deeper than the depositional setting of our sites in the n persculptus zone an interval associated with a major sea level rise our redox indicators suggests that euxinic conditions and ferruginous in some places encroached onto the continental shelves in our model the expansion of euxinic conditions during the n extraordinarius zone was generated by a reorganization of nutrient cycling during sea level fall and we argue overall that these dynamics in ocean chemistry played an important role for the end ordovician mass extinction during the first pulse of the extinction euxinia and a steepened oxygen gradient in the water column caused habitat loss for deep water benthic and nektonic organisms during the second pulse the transgression of anoxic water onto the continental shelves caused extinction in shallower habitats

geology and volcanic facies architecture of the lower ordovician waterloo massive sufide deposit australia the waterloo massive sulfide deposit occurs in the cambro ordovician seventy mile range group in the charters towers district in northern queensland one of the principal submarine successions in eastern australia that contains abundant volcanic hosted base metal deposits the deposit consists of several small dismembered stratiform blanketlike pyrite chalcopyrite sphalerite galena massive sulfide lenses hosted by intensely altered volcanic rocks the deposit and its host rocks have been deformed during regional deformation of the middle to late ordovcian and were affected by two subsequent events of brittle deformation the waterloo deposit formed on top of a lava dominated andesite succession comprising coherent volcanic units and related juvenile volcaniclastic rocks the hydrothermal activity leading to the deposition of massive sulfides commenced during the waning stages or after the cessation of the andesite volcanism the blanketlike mineralization is interpreted to have formed largely at or very close to the sea floor in a moderately deep to deep marine environment formation of the massive sulfides was accompanied by the mass flow deposition of coarse quartz feldspar crystal rich volcanic debris that records broadly contemporaneous probably explosive rhyolitic volcanism occurring outside the immediate study area this resedimented volcaniclastic unit retains a record of hanging wall alteration indicating that the waterloo hydrothermal system was operative during and after burial by the coarse volcaniclastic material the deposition of the coarse volcaniclastic rocks was followed by the intrusion of a feldspar porphyritic dacite cryptodome that was also subject to hydrothermal alteration associated with the massive sulfide formation facies relationships suggest that the cryptodome locally breached the wet and unconsolidated coarse volcaniclastic material to emerge on the sea floor the emplacement of the partially extrusive dacite cryptodome coincided with the waning of the waterloo hydrothermal system the subsequent period of relatively quiet sedimentation was occasionally interrupted by the emplacement of synsedimentary basalt and andesite sills as volcanism at waterloo shifted back to more mafic compositions this period was followed by the mass flow deposition of coarse feldspar quartz vitric volcanic debris and the onset of another period of intense basalt to andesite dominated volcanism geochemical analyses of volcanic rocks from the host rock succession of the waterloo deposit and correlation with regional data suggest that the massive sulfide deposits in the charters towers district formed during a specific period of cambro ordovician back arc basin development dominated by mantle derived volcanism comparison with the volcanic architecture of other known massive sulfide deposits in the district indicates that massive sulfide mineralization at charters towers is mainly associated with silicic shallow intrusion dominated volcanic centers and occurrences of this volcanic facies should be considered prospective for other deposits in the belt

changing transport and curvature bias a new type of meandering in the florida straits meanders in strong inertial flows are generally asymmetric florida current meanders with periods of 7 10 days and flows that tend to meander offshore when strong and onshore when weak which we call type a have been widely documented we find a countertrend in the florida current data collected under the aegis of subtropical atlantic climate studies a type b meandering where flows tend to meander offshore when weak and onshore when strong on time scales of several months and depending on the strength of the flow the tendency displays a largely one sided preference for either the onshore or the offshore component of the meander in particular the data reveal a negative curvature bias during the generally higher transports in spring and summer when most of the speed cores were inshore and a positive curvature bias during lower transports in fall and winter when most speed cores were offshore the data show that any use of cross channel sea level slope to estimate the transport would generally overestimate the weaker but underestimate the stronger flows type b meander is interpreted as one of three types embodied in a meandering equation in which curvature changes are controlled primarily by the coriolis effect of downstream acceleration and hence by that of changing transport in this light the bimodal paths of the kuroshio south of japan is a type b meander

18o16o and 13c12c in lower paleozoic articulate brachiopods implications for the isotopic composition of seawater three hundred and eleven articulate brachiopods with extensive geographic coverage spanning the cambrian to silurian stratigraphic interval were analyzed for oxygen and carbon isotopic composition cambrian samples have 18o 7 ordovician samples 2 4 and silurian samples 1 9 confirming the previously established trend towards lighter isotopic compositions with increasing age throughout the lower paleozoic forty nine best preserved ordovician and silurian samples were identified based on scanning electron microscopy and trace element analysis they were found to bracket the isotopic compositions of over 85 of specimens from these stratigraphic intervals supporting widespread preservation of the isotopic signal some latest ordovician and lower ludlovian samples associated with shale sequences are apparently enriched in 18o these are interpreted as an environmental phenomenon perhaps related to water temperature and glaciation a number of silurian samples of varying genera and stratigraphic levels are highly enriched in 13c up to 6 some are shale related but some are associated with carbonate bearing basins these are also thought to represent near original compositions but a single environmental cause is unknown the present data show that luminescence is not a decisive criterion for evaluating the degree of brachiopod preservation whole shell values were isotopically similar to their nonluminescent portions for both oxygen and carbon

did the amalgamation of continents drive the end ordovician mass extinctions abstract global biodiversity has been punctuated throughout the phanerozoic by extinction events that vary in their degree of intensity and devastation the mass extinction event that occurred at the end of the ordovician period rapidly removed a wide range of species because taxonomic loss occurred during an ice age this is believed to have initiated the extinctions and thus these extinctions have often been viewed as a deep time analogue to the loss in species diversity during the present day glacial interval the current study however indicates that temperature though arguably being a trigger was not the sole reason for the crisis based on a large bibliographic database of rhynchonelliform brachiopods that specifically operates within very narrow time slices where every locality has been precisely georeferenced for the upper ordovician lower silurian interval we show that the extinctions were not uniformly distributed nor was the succeeding recovery here we argue that changing plate tectonic configurations during the ordovician silurian interval may have exerted a primary control on biotic extinction and recovery in particular the proximity and ultimate loss of microcontinents and associated smaller terranes around laurentia may have restricted shelf and slope habitats during the latest ordovician but nevertheless in a contracted iapetus ocean provided migration routes to help drive a diachronous early silurian recovery the conclusion that plate tectonics was a primary factor controlling the extent of the extinctions and the subsequent diversity rebound demonstrates that a reduction in diversity was perhaps the most important manifestation of the end ordovician crisis and further raises the question whether this could be applied to other large phanerozoic perturbations in biodiversity levels

flow modification and shelf slope exchange induced by a submarine canyon off the northeast spanish coast we present results from a study of the modifications induced by the short timescale response of a shelf break baroclinic jet to the presence of a downstream canyon the field site was the canyon of palamos located in the northeastern edge of spain to determine the short time scale variability of the area three intensive surveys were carried out at approximately 10 day intervals data indicate that the jet s location usually over the slope is subjected to significant onshore offshore displacements analysis of the data has shown the importance of a small scale temporal variability induced by river runoff and the climatology of the area this variability generates on off shore displacements of the jet which interacts with the head mouth of the canyon the different interactions with the canyon induced by these displacements produce different regimes of shelf slope exchange in the canyon domain that strongly modify the biomass patterns in the area