the lilliput effect in the aftermath of the end permian extinction event early triassic animal body fossils and trace fossils are small relative to those in older and younger intervals size decreases sharply through the end permian extinction event and permian triassic boundary and the smallest sizes are encountered in the parvus and isarcica zones of the earliest induan animals appearing within these two zones are also exceedingly small compared to younger congenerics and conspecifics temporary dramatic size decrease of surviving taxa in the immediate aftermath of the extinction event is an example of the lilliput effect coined by urbanek a 1993 biotic crises in the history of upper silurian graptoloids a palaeobiological model historical biology 7 29 50 body size increases somewhat from the carinata zone mid induan but remains depressed for the duration of the early triassic and pre extinction sizes are not commonly recorded until at least the middle triassic marine and terrestrial faunas appear to be similarly affected the lilliput effect and longer term size reduction could be the result of several factors environmental parameters such as marine anoxia due to low atmospheric concentrations of oxygen at this time coupled with sluggish ocean circulation in a greenhouse world and food shortage are the likely proximal causes for the early triassic lilliput effect no single cause can explain all the observations and a combination of factors are likely to be involved

ichnological record of the frasnian famennian boundary interval two examples from the holy cross mts central poland the frasnian famennian late devonian boundary interval within the carbonate siliciclastic series in the kowala and plucki sections holy cross mts central poland has been analysed to evaluate the influence of the kellwasser event on the macrobenthic tracemaker community the upper kellwasser event has a lithologically variable record as horizons of flints kowala and as a bed of bituminous black cephalopod limestone plucki both sections show mostly laminated unbioturbated beds of marlstones or shales just above the frasnian famennian boundary which point to events of anoxia on the sea floor however the first anoxic horizon occurs below the frasnian famennian boundary the trace fossils and bioturbational structures are uncommon and poorly diversified trichichnus and multina are the only frequent trace fossils in some beds moreover one horizon above the frasnian famennian boundary contains numerous multina and a single planolites such poorly diversified trace fossil assemblage suggests an unfavourable environment for most of burrowing organisms and fluctuations in oxygenation from anoxic to dysoxic conditions the occurrence of the trace fossils and bioturbational structures as spotted and mottled ichnofabrics from the 1 3 m above the frasnian famennian boundary is interpreted as an improvement in bottom water oxygen conditions after the upper kellwasser event

extinction survival and recovery of corals from the triassic to middle jurassic time recognizing extinction events and determining their cause at the triassic jurassic t j transition and near the pliensbachian toarcian lower jurassic boundary is a field of growing interest we provide arguments for these events through a literature based new evaluation of coral diversity from triassic to dogger and a new palaeobiogeographical map the t j extinction of corals is clearly related to the breakdown of reef environments origination curves show that hettangian the lowest jurassic stage was not only a survival phase but already rather a recovery phase post extinction evolution of reefs and their survival only in the northernmost margin of the tethys support the hothouse hypothesis for the t j extinction event during pliensbachian many new taxa appear but mostly solitary corals not really framebuilders many of these taxa do not occur anymore during the following stages the new increase in diversity is related to the development of bajocian middle jurassic reefs

ichnological characteristics of late cretaceous hemipelagic and pelagic sediments in a submarine high around the oae 2 event a case from the rybie section polish carpathians abstract the trace fossils alcyonidiopsis isp chondrites isp small and large palaeophycus isp planolites isp taenidium isp thalassinoides isp zoophycos isp and unnamed small spreite burrow structures have been found in the cenomanian turonian sediments in the rybie section they show significant stratigraphic variations in respect to the bonarelli level in the cenomanian from the base of the section up to just below the bonarelli level the fucoid marl in local lithostratigraphy a decrease in diversity and abundance of trace fossils and benthic foraminifers is present and related mainly to decreasing benthic food levels oxygenation changes have comparatively minor incidence but at least three thin anoxic layers occur about 2 m below the bonarelli level the bonarelli level shows the at least episodically anoxic sedimentation in the turonian part only small chondrites isp and planolites isp rarely occur the burial of organic matter and probably benthic food content was extremely low as revealed by red marls a gradual recovery of environmental conditions is marked by an increase in the diversity and abundance of trace fossils and benthic foraminifers by the turonian when grey marls egocina marl accumulated above the red marls the trends in ichnological record are confirmed by data on benthic foraminifers

trace fossils biology and taphonomy 1990 special topics in palaeontology 3 280 pp e17 95 pbk e40 00 hbk unwin hyman london isbn 004445 6867 pbk 3035 hbk

trace fossils after the k t boundary event from the agost section se spain palaeogene trace fossils penetrate the uppermost cretaceous sediments in the agost section betic cordillera se spain chondrites targionii zoophycos isp planolites isp a planolites isp b thalassinoides isp a thalassinoides isp b thalassinoides isp c alcyonidiopsis longobardiae and diplocraterion parallelum have been identified a well developed endobenthic tiering pattern is interpreted the uppermost tier a represents major benthic activity in the shallowest sediments at or just below the seafloor recorded as bioturbated background only discrete rare planolites the next upper tier b displays the highest trace fossil diversity with planolites in the shallow levels and thalassinoides and alcyonidiopsis at slightly deeper ones the intermediate tier c contains randomly distributed thalassinoides and alcyonidiopsis cross cut by zoophycos and large and medium sized chondrites the deepest tier d contains zoophycos cross cut by medium and mainly small sized chondrites two interpretations are proposed 1 vertical partitioning of a singled multi tiered community under steady stable conditions in well oxygenated water bottom reflecting gradual changes deep into the sediment with decreasing oxygen pore water and benthic food and increasing substrate consistency and 2 sequential colonization and community replacement reflecting the work of two successive communities the first community mainly represented by planolites alcyonidiopsis and thalassinoides was produced in a shallow oxygenated soft substrate probably related to decreasing oxygen content and benthic food availability this community was replaced by deeply burrowing organisms that produced zoophycos and chondrites this sequential colonization can be determined by changes in environmental parameters related to the cretaceous palaeogene k t event or may have resulted from normal ecological and early diagenetic processes

the trace fossil thalassinoides bacae in the cambrian zhangxia formation miaolingian series of north china abstract branched complex burrows with thick linings assigned to thalassinoides bacae are abundant in the cambrian zhangxia formation miaolingian series in southern north china these burrows occur in thinly layered micritic limestones which were formed in a restricted marine environment surrounded by oolitic shoals the macromorphological characteristics of the burrows observed in outcrop combined with microscopic burrow characteristics assessed using light microscopy and scanning electron microscopy were used to analyze the ethology of t bacae the complex geometric characters of horizontal branching tubes and subvertical shafts reflect t bacae is an agrichnical burrow system the horizontal tubes were used to cultivate microbes for food while the subvertical shafts provided openings to the sea floor organic material iron minerals and pyrite framboids just present in the margin of the fill indicate a special micro environment in the burrow system with a reducing environment and a high organic content and they may provide evidence for microbial garden the functions of the thick micrite lining may have included maintenancce of environmental conditions within the burrow and provision of suitable conditions for growing microbes dark colored irregular areas around the lining are identified as diagenetic halos the burrowers of t bacae built complex burrows system and thick lining for cultivating microbes to survive in a restricted marine environment that was oxygen poor and with low food availability reflecting adaptive behavioral evolution of the metazoan in the middle cambrian

ichnological record of deep sea palaeoenvironmental changes around the oceanic anoxic event 2 cenomanian turonian boundary an example from the barnasiowka section polish outer carpathians abstract trace fossil assemblages including planolites thalassinoides palaeophycus taenidium chondrites and trichichnus have been determined in the upper cenomanian turbiditic deep water succession corresponding to the pre oae 2 interval in the barnasiowka ostra gora section the skole nappe polish outer carpathians these assemblages indicate that oxygenation within sediment fluctuated from oxic to dysoxic zone the overlying uppermost cenomanian organic rich facies bonarelli equivalent horizon corresponding to the main interval of the oae 2 contains black shale layers devoid of trace fossils representing anoxic euxinic events and green shales that include chondrites planolites and thalassinoides recording dysoxic intervals three subintervals phases within the oae 2 sediments have been distinguished in the barnasiowka section based on trace fossil diversity ichnofabrics and chemical redox indices these phases correspond to intervals with various intensity of sea floor oxygenation ichnofabrics within the oae 2 succession was also controlled by consistency of sediment post oae 2 interval recorded by the earliest turonian red and green siliceous manganiferous shales and two fe mn layers represent sediments deposited in well oxygenated conditions under extremely low sedimentation rate most of the shales are parallel laminated and they do not include any benthic microfossils and trace fossils however some of the red and green layers display cryptic bioturbation these features are related to food scarcity cessation of gravity flows unfavorable characteristics of bottom water and a low consistency of substrate

impact of the paleocene eocene thermal maximum on the macrobenthic community ichnological record from the zumaia section northern spain article i nfo trace fossil assemblages from the latest paleocene to the earliest eocene were significantly affected by the environmental perturbation of the paleocene eocene thermal maximum petm high resolution ichnolo gical analysis shows well marked different ichnological features pre syn and post event a well developed normal tiered burrowing community is present in the sediments below the petm indicating oxic conditions and normal benthic food availability during the petm the record of trace fossil producers disappeared gradually but rapidly reflecting the global increase in temperature and the concentration of benthic food in the very shallow surface layer and probably the local depletion of oxygen within the sediments although probably not true anoxia the environmental perturbation significantly affected the whole benthic habitat as shown by the correspondence with the main phase of the benthic foraminiferal extinction after the petm the normal tiered burrowing community recovered gradually and slowly in a delayed return to pre petm environmental conditions the changes in the trace fossil assemblage thus document the impact of the petm on the macrobenthic community a decline in oxygen levels during the petm in a globally perturbed habitat due to global warming and the similarities and differences in the response of micro and macrobenthic communities to global phenomena thus ichnological analysis reveals as a very useful additional tool to understanding atmosphere ocean dynamic during petm and a potential way in future climate research 2011 elsevier b v all rights reserved

global versus local processes during the pliensbachian toarcian transition at the peniche gssp portugal a multi proxy record abstract the toarcian oceanic anoxic event t oae 183 ma was an episode of extreme warmth environmental changes and carbon cycle perturbation we present a high resolution study of the peniche section lusitanian basin portugal recently defined as the toarcian global stratotype section and point to provide a review of the pliensbachian toarcian pl to environmental and climatic changes a large 7 negative carbon isotope excursion cie is recorded within the t oae interval in bulk organic matter distinct small scale 13c negative shifts modulating the t oae carbon isotope signal are correlated across different european basins which have implications on the estimation of the t oae duration the increase in kaolinite content and chemical index of alteration from the pl to boundary up to the t oae interval is interpreted as reflecting a shift towards warmer and wetter climate conditions the common occurrence of coarse grained turbidites within the t oae interval is possibly linked with changes of the hydrological cycle and storm intensity low total organic carbon contents together with the absence of redox sensitive trace element enrichments indicate oxygen deficient conditions unfavourable for organic matter preservation mercury data show a clear increase at the base of the t oae cie followed by a return to background values providing further evidence that karoo ferrar volcanism might have triggered the series of environmental disturbances during the early toarcian however the highest mercury values are recorded in samples containing abundant pyritized wood fragments highlighting the influence of local chemical processes on mercury enrichments which should be considered before any interpretation of the hg records

large burrow systems in marine miocene deposits of the betic cordillera southeast spain abstract large burrow systems occur in the miocene marine deposits of the almeria nijar basin betic cordillera southeast spain they consist of galleries of dense burrow segments locally forming irregular networks cylindrical branched y shaped structures with diameters ranging from 8 to 22 cm and minimum lengths of 30 60 cm are abundant in addition galleries longer than 70 80 cm are common and burrow segments larger than 200 cm are locally present burrows have smooth walls without pellet reinforcements but locally possible scratch marks are present burrow fill is structureless and has a similar composition to the host rock these structures are assigned to the ichnogenus thalassinoides ehrenberg displaying similarities with t suevicus identification of the possible tracemaker is not straightforward but decapod crustaceans probably shrimp or shrimp like organisms are the most likely candidates

numerical paleoceanographic study of the early jurassic transcontinental laurasian seaway the forces governing marine circulation of a meridional transcontinental seaway is explored with the princeton ocean model the jurassic laurasian seaway which connected the low latitude tethys ocean with the arctic sea is modeled quantitatively the global ocean is found to have a profound influence on seaway dynamics a north south density difference and hence sea level difference of the global ocean was probably the main factor in forcing the seaway flow when the tethys waters were the denser water the net seaway flow was southward and conversely it was northward for denser arctic waters marine bioprovincial boundaries and sediment data indicate that the seaway probably was dominated by boreal faunal groups and reduced salinities several times in the jurassic the model results suggest that this can be explained by southward flowing seaway currents which may have been related to an oceanic thermohaline circulation where no northern high latitude deep convection occurred

evidence of terrestrial organic matter deposition across the early toarcian recorded in the northern lusitanian basin portugal abstract the pliensbachian toarcian lower jurassic in the lusitanian basin portugal is particularly well exposed through marl limestone alternations very rich in nektonic and benthonic macrofauna in the general context of toarcian oceanic anoxic event t oae the lower toarcian polymorphum and levisoni ammonite zones marks important sedimentological changes in the marine paleoenvironment to better understand the paleoenvironmental changes that occurred during the latest pliensbachian early toarcian a high resolution study of organic matter was undertaken in the alcabideque section in the northern sector of the basin based on the analysis of 14 samples from a section 20 m thick this study involved organic geochemistry total organic carbon toc sulfur and biomarkers and palynofacies the results confirm that sediments are particularly poor in organic matter with the highest toc values reaching 0 41 wt around the top of polymorphum zone the palynofacies analysis provides evidence that the organic matter largely consists of particles belonging to phytoclasts and palynomorphs groups the phytoclasts present were generally degraded and oxidized with significant representation in the emaciatum and polymorphum zones the palynomorphs were mainly composed by sporomorphs with a sporadic increase in marine palynomorphs mainly dinocysts at the top of the emaciatum and polymorphum zones continental organic matter was predominant at the base of levisoni zone t oae through the deposition of brownish marls chocolate marls which was confirmed by the occurrence of tetrads and polyads pollen grain agglomerates and by biomarkers with the major presence of long chain n alkanes n alkane c17 c20 tricyclic terpane c24 tetracyclic terpane and c29 regular sterane the gammacerane index shows a peak at the top of polymorphum zone clearly associated with the increase of marine palynomorphs and the maximum marine influence in the series

terrestrial evidence for the lilliput effect across the cretaceous paleogene k pg boundary abstract recent research has demonstrated that the lilliput effect reduction of body size in biota associated with the aftermath of mass extinctions affected all trophic levels in the marine realm following the cretaceous paleogene k pg event however it is unclear if this size change was strictly a marine signal or a global phenomenon that also affected continental ecosystems herein we present the results of an ichnological proxy for body size of soil dwelling insects across the k pg boundary in big bend national park texas u s a quantitative efforts focused on naktodemasis bowni which are characterized as unbranching burrows composed of ellipsoidal packets of backfill menisci these traces were likely produced by beetle larvae or cicada nymphs based on previous comparison with structures generated in modern soils and laboratory experiments as an approximation for the body size of the subterranean insects this dataset indicates that a smaller n bowni diameter dn is statistically correlated

use of high resolution ichnological and stable isotope data for assessing completeness of a k p boundary section agost spain high resolution ichnological analysis has been performed at the agost section betic cordillera southeast spain in order to assess the completeness of the k p boundary transition below the biostratigraphic resolution intrasubzone high resolution planktonic foraminifera biozonation revealed that the first appearance of the palaeogene index species does not coincide with the k p boundary but is located a few centimetres above and calibrated 65 7 6 7 ky later the k p boundary to establish the continuity of this first interval of the lowermost danian hedbergella holmdelensis subzone and the existence of any hiatus below biostratigraphic resolution trace fossil analysis was revealed to be a useful tool planolites thalassinoides and alcyonidiopsis structures belonging to the upper tiers colonizing at or immediately after the k p boundary event were studied focusing on the isotopic composition of the filling materials and the genesis of thalassinoides rapid firmground generation and thalassinoides tracemaker colonization is mainly attributed to cessation of precipitation and or deposition of calcium carbonate but an incipient lithification is not disregarded the d 13 c data obtained from trace fossils fit well with those corresponding to a the k p boundary layer from 1 00x to 1 30x b the stratigraphic interval between 2 5 and 5 0 cm above the k p boundary between 0 32x and 0 47x and c the interval between 7 0 and 11 0 cm above the k p boundary between 0 69x and 0 79x revealing continuity in the colonization from the k p boundary event to the dark clay deposition above this macrobenthic colonization occurred continuously during the dark layer deposition from the k p boundary layer including the first centimetres evidencing completeness and the absence of hiatuses below biostratigraphic resolution intrasubzone at the agost section d 2005 elsevier b v all rights reserved

high resolution dynamics of early jurassic marine extinctions the case of pliensbachian toarcian ammonites cephalopoda abstract the pliensbachian toarcian interval was marked by major environmental disturbances and by a second order mass extinction here we reappraise the taxonomic spatiotemporal and selective dynamics of extinctions over the whole interval by analysing a high resolution dataset of 772 ammonite species from nw tethyan and arctic domains on average 40 65 of ammonite species disappeared during each subchronozone but higher extinction pulses reaching 70 90 prevailed from the margaritatus to the dispansum chronozone the main extinctions corresponding to the gibbosus pliensbachian toarcian boundary semicelatum bifrons variabilis and dispansum events differed in their dynamics suggesting episodes of ecological stress related to climate change regression disturbance in the carbon cycle or anoxia the multi pulsed volcanic activity in the karoo ferrar province could well have triggered these ecological changes in addition ammonites experienced a morphological bottleneck during the gibbosus event 1 ma before the early toarcian diversity collapse typically drops in richness were related both to high extinctions and to declines in origination rates this feature could result from strengthened ecological stresses related to the temporal overlap of environmental disturbances after the early toarcian crisis the recovery of ammonites was rapid 2 ma and probably influenced by a coeval marine transgression supplementary material figures showing a comparison of extinction and origination patterns based on different datasets and variations of the morphospace occupation are available at http www geolsoc org uk sup18381

structural analysis using thrust fault hanging wall sequence diagrams ogden duplex wasatch range utah detailed mapping and cross section traverses provide the control for structural analysis and geometric modeling of the ogden duplex a complex thrust system exposed in the wasatch mountains east of ogden utah the structures consist of east dipping folded thrust faults basement cored horses lateral ramps and folds and tear faults the sequence of thrusting determined by means of lateral overlap of horses thrust splay relationships and a top to bottom piggyback development is willard thrust ogden thrust weber thrust and taylor thrust major decollement zones occur in the cambrian shales and limestones the tintic quartzite is the marker for determining gross geometries of horses this exposed duplex serves as a good model to illustrate the method of constructing hanging wall sequence diagram a series of longitudinal cross sections that move forward in time and space and show how a thrust system formed as it moved updip over various footwall ramps a hanging wall sequence diagram also shows the complex lateral variations in a thrust system and helps to locate lateral ramps lateral folds tear faults and other features not shown on dip oriented cross sections

the early toarcian oceanic anoxic event in the external subbetic southiberian palaeomargin westernmost tethys geochemistry nannofossils and ichnology abstract the analysis of macroinvertebrates trace fossils calcareous nannofossils and geochemistry from pliensbachian to lower toarcian deposits of the subbetic southern spain allows us to interpret the incidence of the toarcian oceanic anoxic event t oae in the boundary between the tethys and the hispanic corridor trace fossils from the marl limestone rhythmite upper pliensbachian to lower toarcian indicate an oxygenated bottom a dark marly interval occurs above a fossil rich condensed surface with a negative excursion of 18o interpreted as evidence of the early toarcian transgression and a climate warming the carbon cycle perturbation is recorded by decreasing caco3 content and the negative excursion of 13c at the base of the serpentinum zone njt 6 nannofossil zone the barren interval for nektonic and benthic organisms at the beginning of the serpentinum zone confirms the oxygen restricted conditions in the sea floor environmental conditions were unfavourable for the development of calcareous nannoplankton as attested by the drop in absolute abundances the deep photic zone seemed to be particularly hostile to phytoplankton as shown by the decrease in relative abundance of the deep dweller mitrolithus jansae related to shoaling of the oxygen minimum zone in the water column increasing values of redox sensitive elements and total organic carbon as well as the record of pyrite framboids

nutrient spatial variation during intrabasinal upwelling at the cenomanian turonian oceanic anoxic event in the westernmost tethys an ichnological and facies approach abstract facies and ichnofabrics of two sections of the cenomanian turonian boundary interval are correlated and compared to evaluate changes in palaeoceanographic conditions controlled by palaeogeography in the distal zone of the westernmost tethys southern iberian continental palaeomargin the oceanic anoxic event oae 2 was interrupted by short aerobic or dysaerobic sub events with slight differences in facies and ichnofabrics these sub events display a tendency to expansion from the more distal section hedionda towards the proximal one el chorro the anoxia spread out from the open sea probably from slope upwellings higher diversity and abundance of trace fossils in comparatively distal position during the pre and post event intervals can be caused by a higher abundance of food available for tracemakers shape of the correlation bands of the oae 2 event suggests that the event started earlier by about a few tens of thousands years in the most distal areas than in proximal slightly higher bottom settings

ichnological analysis of the bidart and sopelana cretaceous paleogene k pg boundary sections basque basin w pyrenees refining eco sedimentary environment abstract ichnological analysis of two cretaceous paleogene boundary sections at bidart se france and sopelana n spain has been conducted in order to refining eco sedimentary environment and to a make comparison with previous interpretations based on microfossils in both sections trace fossil assemblage is low diverse consisting of chondrites planolites thalassinoides trichichnus zoophycos and phycosiphon ascribed to the zoophycos ichnofacies however with distinct differences in the bidart section early danian dark filled trace fossil assemblage is more abundant in large thalassinoides zoophycos and larger chondrites and less abundant in trichichnus and small chondrites in comparison to the sopelana section sopelana is thus interpreted as a more offshore deeper section than bidart although both were located in the upper bathyal zone of the basin oxygenation below the sediment water interface was enough to favour a generalized total bioturbation of sediments the presence of chemichnia and trace fossils which tracemakers sequestered sediments from the sea floor in deep burrows zoophycos suggests at least periodical food deficiency the distribution and content of trace fossils across the k pg boundary do not change significantly revealing minor incidence of the k pg boundary event on the macrobenthic environment the k pg boundary transition including the boundary layer is nearly totally bioturbated hence a redistribution of microbiotic and abiotic components by tracemakers is possible

sample preparation for determination of comminution ages in lacustrine and marine sediments abstract the uranium isotope composition 234u and 238u of detrital matter has become an essential tool for evaluating the response of erosion and catchment dynamics to climate variability on geological time scales relative variability of the 234u 238u activity ratio can be used as an estimate of the time that has elapsed since physical and chemical weathering has formed grains combined u isotopes and gas adsorption surface area analyses on two sediment samples from the mediterranean sea yield comminution ages up to 5 times older after sample treatment which highlights the importance of a comprehensive removal of non detrital matter from the bulk sediment composition moreover gas sorption analysis allowed determining whether a fractal correction for calculation of the recoil fraction should be applied precise estimates of the recoil fraction are crucial for calculating the comminution ages as it governs the loss of 234u from detrital matter samples analyzed in this study display type ii isotherms suggesting a non porous or macroporous surface micro and mesopores which increase the surface area during gas adsorption analyses but do not contribute to the loss of 234u are absent thus a fractal correction to account for micro and mesopores is not required

toarcian oceanic anoxic event induced unusual behaviour and palaeobiological changes in thalassinoides tracemakers abstract the early toarcian early jurassic global marine mass extinction is associated with one of the most important environmental perturbations of the mesozoic the toarcian oceanic anoxic event t oae usually interpreted as a global oceanic anoxic event in the lusitanian basin lb one of the reference areas for the study of the t oae despite an elevated extinction rate among marine invertebrates the anoxia hypothesis has been discarded based on geochemical and isotopic data in the fonte coberta section the t oae is characterised by the extinction of the previously well represented brachiopod taxa a decreased abundance of ammonoids and the establishment of a well developed endobenthic community mainly composed by thalassinoides tracemaker which indicates favourable environmental parameters at least for this community thus the palaeoenvironmental changes associated with the t oae event bear a minor incidence on the macrobenthic tracemaker community at the level of extinctions and changes in diversity or abundance yet they exert a major effect on the behaviour and palaeobiology of tracemakers the thalassinoides specimens show an exclusively horizontal development and unusual architectural features during the extinction interval tied to behavioural adaptations to nutrient availability and or substrate firmness smaller burrow diameters are registered at the base of the t oae and then an increase is observed during the t oae this could be associated with a palaeobiological response lilliput effect to palaeoecological changes at the beginning of the t oae followed by a progressive change to pre event environmental parameters this study therefore sheds light on how environmental alterations can determine specific behavioural and palaeobiology changes of the producer as reflected by variations in significant features of thalassinoides architecture

early jurassic mass extinction a global long term event the end pliensbachian extinction event 187 ma has been interpreted either as one of 10 global periodically recurring mass extinctions of the past 250 m y or as a minor localized european event elevated levels of family extinction spanned five ammonite zones during the late pliensbachian and the early toarcian an interval of 7 5 m y and were distributed unequally in the boreal tethyan and austral realms detailed sampling of invertebrate macrofaunas through complete expanded sequences in northwest europe shows that most species extinctions occurred in the early toarcian following a regional anoxic event the early jurassic mass extinction event took place over a long time scale and it was global in extent

duration of the early toarcian carbon isotope excursion deduced from spectral analysis consequence for its possible causes abstract the marked 3 8 negative carbon isotope excursion associated with the early toarcian oceanic anoxic event oae 183 myr ago in the early jurassic period is thought to represent one of the most important perturbations of the c cycle in the last 200 myr however the origin of this excursion remains strongly debated primarily due to uncertainties in the estimation of its duration which ranges from 200 kyr to 1 myr here we present a new orbital calibration of the early toarcian carbon isotope excursion based on spectral analyses of two independent datasets generated from the sedimentary record of two hemipelagic sections from portugal peniche and sw germany dotternhausen in order to better constrain the timescale and hence the origin of this excursion these analyses reveal that orbital cycles exert a strong influence on both the calcium carbonate content in portugal and on the greyscale of black shales in germany which allow us to propose a duration of 1 9 myr for the early toarcian and of 900 kyr for the entire carbon isotope excursion the shift towards lower carbon isotope values lasted 150 kyr and carbon isotope values remained low for 450 kyr the subsequent increase of carbon isotope values lasted 300 kyr this calibration suggests that the sustained input of isotopically light carbon at the origin of the excursion occurred over 600 kyr and thus dismisses causal mechanisms implying relatively small source reservoirs such as the massive dissociation of methane hydrates in the light of our new cyclostratigraphic timescale the massive input of isotopically light carbon associated with the emplacement of the karoo ferrar basaltic province appears as the most likely cause of the toarcian global carbon isotope excursion we also show that the c isotope perturbation coincided with a transition from precession eccentricity dominated cycles to obliquity eccentricity dominated cycles suggesting that the oae was marked by a fundamental change in the response of the climate system which allowed the obliquity signal normally better recorded at high latitudes to be a dominant forcing factor of short term sedimentary cycles at tropical latitudes

secular environmental precursors to early toarcian jurassic extreme climate changes the early toarcian oceanic anoxic event t oae about 183 myr ago was a global event of environmental and carbon cycle perturbations which deeply affected both marine biota and carbonate production nevertheless the long term environmental conditions prevailing prior to the main phase of marine extinction and carbonate production crisis remain poorly understood here we present a similar to 8 myr long record of early pliensbachian middle toarcian environmental changes from the lusitanian basin portugal in order to address the long term paleoclimatic evolution that ultimately led to carbonate production and biotic crises during the t oae paleotemperature estimates derived from the oxygen isotope compositions of well reserved brachiopod shells from two different sections reveal a pronounced similar to 5 degrees c cooling in the late pliensbachian margaritatus spinatum ammonite zones boundary this cooling event is followed by a marked similar to 7 10 degrees c seawater warming in the early toarcian that after a second cooling event in the mid polymorphum zone culminates during the t oae calcium carbonate caco3 contents the amount of nannofossil calcite and the mean size of the major pelagic carbonate producer schizosphaerella all largely covary with paleotemperatures indicating a coupling between climatic conditions and both pelagic and neritic caco3 production furthermore the cooling and warming episodes coincided with major marine regressions and transgressions respectively suggesting that the growth and decay of ice caps may have exerted a strong control on sea level fluctuations throughout the studied time interval this revised chronology of environmental changes shows important similarities with neogene and paleozoic episodes of deglacial black shale formation and thus prompts the reevaluation of ice sheet dynamics as a possible agent of mesozoic events of extinction and organic rich sedimentation c 2010 elsevier b v all rights reserved

selective extinction among early jurassic bivalves a consequence of anoxia analyses of taxonomically standardized data sets demonstrate several statistically robust extinction patterns in early jurassic bivalve species from northwest europe and the andean basins of south america in both regions extinction intensities were significantly enhanced in late pliensbachian and early toarcian time as compared to all other time intervals the same intervals except for the early toarcian of south america also represent times of unusual extinction selectivity with infaunal taxa suffering distinctly more than epifaunal forms as infaunal suspension feeders are extremely rare components of early jurassic oxygen controlled macrofaunas these results are entirely compatible with sedimentological and geochemical data suggesting that widespread anoxia was a principal cause of the diversity crisis although many biotic traits that enhance survivorship during background times seem to be irrelevant during major mass extinctions patterns of survivorship selectivity may provide more distinct clues to the causes of less severe mass extinctions

changes in foraminiferal assemblages and environmental conditions during the t oae early jurassic in the northern lusitanian basin portugal abstract the foraminiferal assemblages and other microfossils from the rabacal area maria pares section in the lusitanian basin portugal provide new insights regarding the toarcian oceanic anoxic event t oae complementary analysis of the 13c total organic carbon toc and geochemical redox and palaeoproductivity proxies reflect environmental changes that affected the microfossil assemblages detailed analyses of foraminiferal assemblages their diversity abundance morphogroups and lifestyle and geochemistry led us to discern phases of the biotic crisis and subsequent stages of recovery environmental instability which began in the lattermost part of the polymorphum zone is marked by a lesser abundance of foraminifera and ostracods increased opportunist foraminifera fluctuations in toc values and the enrichment factor of phosphorous pef as well as the onset of a negative carbon isotopic excursion cie the peak phase of the biotic crisis corresponds with the lowest values for foraminiferal diversity and abundance including a barren sample for benthic microfossils the abundance and diversity of echinoderms brachiopods dinoflagellate cysts and calcareous nannofossils dropped sharply during the peak phase this biotic crisis also entails extinction of the order metacopina and a local disappearance of echinoderms and brachiopods anoxic conditions at sea bottom did not develop given the almost continuous record of foraminifera and trace fossils yet oxygen depleted conditions occurred the lower part of the levisoni zone contains thin nodular limestones corresponding to a tempestitic turbiditic facies in this context the re oxygenation of bottom waters was favoured as indicated by the presence of thalassinoides and the low values of toc and redox sensitive elements mo ni and u the survival phase in the wake of the biotic crisis is characterized by greater diversity and abundance of foraminifera and echinoderms holothuroids and ophiuroids the lowest 13c values are recorded during this phase with a dominance of opportunist eoguttulina and facultative opportunist paralingulina tenera foraminifera finally recovery after the biotic crisis is evidenced by high values for specialists and potentially deep infaunal foraminifera indicating oxic conditions in the sediment

evidence for variations in magma production along oceanic spreading centers a critical appraisal recent geologic geophysical and geochemical studies of the oceanic lithosphere near fracture zones have resulted in the proposal that the magma budget defined as the amount of magma delivered to magma chambers or conduits beneath a spreading center for a given amount of spreading decreases as fracture zones are approached seismic reflection and refraction studies indicate that the crust becomes anomalously thin near fracture zones but reference must be made to the boundary between residual upper mantle peridotites and overlying cumulate rocks in order to assess potential variations in the magma budget the position of this interface however generally is not constrained by geophysical studies geochemical variations in basaltic glasses collected near fracture zones are consistent with a decrease in partial melting as fracture zones are approached but they could also be produced by variations in open system mag matic processes with no change in the extent of partial melting although a decrease in the magma budget as fracture zones are approached is consistent with these data so are alternative models that incorporate a constant magma budget

environmental controls on jurassic marine ecosystems during global warming the fossil record has the potential to provide valuable insights into species response to past climate change if paleontological data are combined with appropriate proxies of environmental change here we use a novel multivariate approach that combines a suite of geochemical proxies with high resolution quantitative macroinvertebrate fossil data to study responses to early toarcian warming ca 183 ma we show that benthic and nektonic ecosystems became decoupled during warming and were driven by different environmental variables benthic turnover was mostly driven by variations in seawater dissolved oxygen concentration whereas turnover among the nektonic cephalopods was primarily controlled by variations in weathering nutrient runoff and primary productivity although rapid warming has been invoked as the main trigger of this event the paleotemperature proxy was a poor predictor of marine community dynamics and abiotic factors indirectly linked to temperature were more important given that similar environmental changes characterize other episodes of global warming and are impacting present day marine communities we predict that similar ecological responses occurred during other past events and are a probable outcome of current changes

fe oxide spherules infilling thalassinoides burrows at the cretaceous paleogene k p boundary evidence of a near contemporaneous macrobenthic colonization during the k p event a detailed ichnological analysis focused on thalassinoides structures recorded just below the cretaceous paleogene k p boundary layer of the agost section southeast spain aimed to evaluate macrobenthic colonization during the k p boundary event stereomicroscopy and field emission scanning electron microscopy analyses conducted on material filling in thalassinoides trace fossils reveal the presence of dark infill material that includes spherule like elements similar to those previously differentiated in the k p boundary layer energy dispersive x ray spectrometry indicates a ferruginous composition goethite spherules this represents the first record of spherules related to the k p boundary event within trace fossil infilling material the passive filling of this material into the thalassinoides bioturbation allows interpretation of the gravitational deposition just after thalassinoides trace maker colonization the absence of erosive sedimentary structures or other material deposited between the thalassinoides trace maker colonization and the spherule deposition is interpreted as evidence of rapid colonization during the k p boundary event nearly contemporary with the spherule layer deposition

mass extinction and recovery of the early toarcian early jurassic brachiopods linked to climate change in northern and central spain abstract the early toarcian mass extinction event represented the most important mesozoic and cenozoic turnover of the population of brachiopods and severely affected other benthic fauna two main hypotheses have been proposed to explain the synchronous and global mass extinction an oceanic anoxic event or a warming episode to test both hypotheses the dynamics of the brachiopod assemblages below and above the extinction boundary are analyzed and compared with the seawater paleotemperature variations calculated from the 18 o data recorded in belemnite rostra five sections from northern and central spain well dated with ammonites have been selected for this study the sections show no indication of sedimentary breaks and contain abundant brachiopods which have been grouped into four assemblages the changes observed in the brachiopod assemblages show a close correlation with the changes in the seawater paleotemperatures the oldest assemblage assemblage 1 coincides with a cooling interval recorded to have taken place in the latest pliensbachian paleobiogeographical reconstruction shows that this assemblage was distributed at paleolatitudes between 30 and 45 n with a preference for relatively cool waters with the rise of temperatures that took place during the earliest toarcian tenuicostatum zone assemblage 1 was substituted by assemblage 2 which composed of different species of the same genera but considerably restricted to the warmer waters of lower paleolatitudes between 28 and 35 n coinciding with the rapid and pronounced increase in seawater temperature recorded at the tenuicostatum serpentinum zonal boundary all of these brachiopod species disappeared in the studied localities marking clearly the extinction boundary predominant southward currents through the laurasian seaway precluded the possible migration of the brachiopods to cooler northern waters the brachiopods disappearance is independent from the oxygenation degree of the sea bottom and therefore the rapid warming seems to be the most plausible cause of the mass extinction after the extinction event the recovery of the brachiopods was uneven subsequent to a brief pause recovery was rapid in central spain and in other southern areas of western tethys whereas in northern spain and in the whole of europe north of the french central massif brachiopods did not recover until the mid to late toarcian times

evidence for major environmental perturbation prior to and during the toarcian early jurassic oceanic anoxic event from the lusitanian basin portugal the timing and causal relationships between the pronounced negative c isotope excursion and paleoenvironmental perturbations associated with the toarcian oceanic anoxic event early jurassic remain unclear particularly because biotic crises and carbonate production decrease appear to have been initiated earlier than the main c isotope anomaly here we present a new quantification of late pliensbachian early toarcian calcareous nannofossils abundance and size from the peniche reference section portugal together with o and c isotope records of well preserved brachiopod shells from the same section the brachiopod shell 13c curve parallels that of bulk carbonate and records two pronounced negative isotopic excursions close to the pliensbachian toarcian boundary 2 and during the toarcian oceanic anoxic event 3 5 our results indicate that both c isotope negative excursions were characteristic of benthic and shallow water environments suggesting that these two carbon cycle perturbations affected all epioceanic reservoirs coeval shifts toward lower values of brachiopod oxygen isotope compositions and closely correlated northward migrations of mediterranean ammonite fauna suggest that both events coincided with major rises in seawater temperatures probably as a result of increased co2 levels and enhanced greenhouse conditions co2 induced changes in seawater chemistry likely affected the calcification potential of both neritic and pelagic systems as evidenced by synchronous drops of platform derived carbonate accumulation and drastic reductions in size 3 m of the main pelagic carbonate producer schizosphaerella we suggest that the early toarcian paleoenvironmental crisis occurred in two distinct episodes that were most likely related to two successive phases of intense volcanic degassing in the karoo ferrar province

diversity and morphological evolution of jurassic belemnites from south germany abstract belemnites are extinct cephalopods whose evolutionary history is representative of successful adaptive radiations during the mesozoic nevertheless a detailed understanding of the dynamics and palaeoenvironmental drivers of this evolution is still lacking in order to fill this gap we analyze the diversity and morphological disparity of jurassic rostra from south germany and compare these patterns with other euro boreal trends we show that after an early apparition of few dissimilar groups during the hettangian sinemurian interval belemnites experienced four periods of diversification i e early pliensbachian middle late toarcian early bajocian and oxfordian marked by morphological disparifications of rostra towards forms potentially optimized for different hydrodynamic properties these adaptive radiations were interrupted at regional scale by four biological crises corresponding to morphological bottlenecks i e pliensbachian toarcian aalenian late bajocian and kimmeridgian most of them were morphoselective except the aalenian extinction which could be related to a prominent sea level fall by comparing our results to palaeoenvironmental data we show that warm temperate seawater temperatures might have favoured the diversification of belemnites potentially by accelerating their metabolic rates the population turnovers and the evolutionary rates on the long term conversely cooling or hyperthermal events correspond with biological crises migrations towards refuge areas located in the arctic and mediterranean domains could have been key factors for rapid post crisis recoveries finally the available data suggest a trend towards increased streamlining of the rostrum through the jurassic

carbon isotope evidence for the timing of the cretaceous palaeogene macrobenthic colonisation at the agost section southeast spain abstract the cretaceous palaeogene k t boundary section of agost southeast spain one of the most complete sections existing contains a well developed trace fossil assemblage composed of dark and light filled trace fossils registered in the uppermost cretaceous maastrichtian plummerita hantkeninoides biozone sediments the trace fossil assemblage reveals that significant macrobenthic colonisation occurred around the k t boundary interval however difficulties in recognising trace fossils affecting the k t boundary layer as well as in biostratigraphically characterising these trace fossils hindered a conclusive interpretation on the timing of this macrobenthic colonisation with the aim of this characterisation we determined the 13c of the carbonate fraction of dark and light filling materials from the trace fossils since the carbon isotope compositions of uppermost cretaceous and lowermost palaeogene materials are clearly different the data compiled provide evidence for a significant distinction between light filled trace fossils with 13c values higher than 1 6 peedee belemnite pdb and dark filled trace fossils with 13c values between 0 21 and 1 2 pdb most of these being lower than 0 7 pdb the comparison of these values with those from the uppermost maastrichtian to the lowermost danian sediments reveals that the macrobenthic colonisation occurred in different phases across the k t boundary interval

carbon isotope record of the early jurassic toarcian oceanic anoxic event from fossil wood and marine carbonate lusitanian basin portugal thetoarcianoceanicanoxicevent oae intheearlyjurassic 183maago wascharacterizedbywidespreadnear synchronous deposition of organic rich shales in marine settings as well as perturbations to several isotopic systems characteristically two positive carbon isotope excursions in a range of materials are separated by an abrupt negative shift carbon isotope profiles from toarcian fossil wood collected in england and denmark have previously been shown to exhibit this large drop 7 i n 13 c values interpreted as due to an injection of isotopically light co2 into the ocean atmosphere system however the global nature of this excursion has been challengedonthebasisofcarbon isotopedatafromnektonicmarinemolluscs belemnites whichexhibitheavierthanexpectedcarbonisotope values here we present new data principally from fossil wood and bulk carbonate collected at centimetre scale from a hemipelagic section at peniche coastal portugal this section is low in organic carbon average toc 0 5 and the samples should not have suffered significant diagenetic contamination by organic carbon of marine origin the carbon isotope profile based on wood shows two positive excursions separated by a large and abrupt negative excursion which parallels exactly the profile based on bulk carbonate samples from the same section albeit with approximately twice the amplitude 8 in wood versus 3 5 in carbonate these data indicate thatthe negative carbon isotope excursion affected the atmosphereand by implication the global ocean as well the difference in amplitude between terrestrial organic and marine carbonate curves can be explained by greater water availability in the terrestrial environment during the negative excursion for which there is independent evidence from marine osmiumisotope records and plausibly changes in atmospheric co2 content for which independent evidence is also available the peniche succession is also notable for the occurrence of re deposited sediments their lowest occurrence coincides with the base of the negative excursionandtheirhighestoccurrencecoincideswithitstop thus slopeinstabilityandsedimentsupplycouldhavebeenstronglylinked to the global environmental perturbation an association that may misleadingly simulate the effects of sea level fall

benthic foraminiferal assemblages record major environmental perturbations during the late pliensbachian early toarcian interval in the peniche gssp portugal abstract this is the first ecostratigraphic and palaeoecological analysis of the benthic foraminiferal assemblages defined as morphogroups in the pliensbachian toarcian transition and the toarcian oceanic anoxic event t oae of the peniche section the toarcian global boundary stratotype section and point foraminiferal assemblages from the uppermost pliensbachian emaciatum zone reveal the presence of a stable benthic environment with good oxygen and availability of trophic resources as evidenced by the high diversity of specialists the pliensbachian toarcian transition reveals high foraminifera abundance mainly specialists although it is considered a slightly condensed interval the base of the levisoni zone shows dramatic changes in life style of foraminifera increase of epifauna and potentially deep infauna an increase in opportunistic forms and a decrease in diversity these changes suggest unfavourable conditions related to food availability diminution and depleted oxygenation corresponding to the beginning of the 13c negative excursion palaeoenvironmental conditions become severe in the lower to middle levisoni zone where there is a barren interval for foraminifera coincident with the highest values of total organic carbon after this interval foraminiferal assemblages experienced a recovery with increasing diversity and occurrence of specialists consistent with a well oxygenated environment and good food availability these changes observed in benthic foraminiferal fauna from the peniche section through the uppermost pliensbachian lower toarcian are comparable to what was reported previously on ostracods brachiopods and calcareous nannofossils foraminiferal assemblages from peniche section are comparable to other tethyan spain italy north africa and nw european sections england from the same stratigraphic interval with the suborder lagenina dominating the assemblages

trace fossils in the ediacaran cambrian transition behavioral diversification ecological turnover and environmental shift abstract after taxonomic revision trace fossils show a similarly explosive diversification in the ediacaran cambrian transition as metazoan body fossils in shallow marine deposits of ediacaran age trace fossils are horizontal simple and rare and display feeding strategies related to exploitation of microbial matgrounds equally notable is the absence of arthropod tracks and sinusoidal nematode trails this situation changed in the early cambrian when a dramatic increase in the diversity of distinct ichnotaxa is associated was followed by the onset of vertical bioturbation and the disappearance of a matground based ecology agronomic revolution on deep sea bottoms animals have been present already in the ediacaran but ichnofaunas were poorly diverse and dominated by the horizontal burrows of undermat miners as shown by the ichnogenus oldhamia this life style continued to be predominant into the early and to a lesser extent middle cambrian nevertheless there was an explosive radiation of behavioral programs during the early cambrian when exactly the bioturbational revolution arrived in the deep sea is uncertain in any case the nereites ichnofacies was firmly established in the early ordovician the rich ichnofauna in the early cambrian guachos formation of northwest argentina probably marks a first step in this ecological onshore offshore shift

palaeoecological insights on toarcian and lower aalenian calcareous nannofossils from the lusitanian basin portugal abstract a comprehensive and detailed account is presented of the calcareous nannofossil evolution across the toarcian and early aalenian from the strategically located lusitanian basin in portugal the basin connected nw tethys and mediterranean water masses during the toarcian and thus the in situ nannoplankton community responded to this double influence biostratigraphic control by ammonites from two well calibrated and continuous sections was compared to an intermediate section which rendered a complete 286 m of toarcian and lower aalenian succession quantification of calcareous nannofossils factor analysis stable carbon and oxygen isotope analysis from brachiopods shells was performed temperature water masses exchanges and primary productivity were highlighted by three extracted factors three major ecological events were identified in this work throughout the early toarcian during the onset of a warming transgressive period with an intensified hydrological cycle where calcareous nannoplankton thrived nw tethys waters started flooding the lusitanian basin which became dominated by mediterranean taxa such as m jansae and schizosphaerella water mixing between nw european and mediterranean water masses occurred as recorded by nannofossil assemblages typical of the two provinces across the middle and part of the late toarcian as climatic conditions stabilized during the long term regressive period that had just begun nw european connections were still effective waters became more stratified and primary productivity decreased as indicated by the 13 c data the coeval decrease in total nannofossil abundances and increase in diversity from part of the late toarcian the connection between north and south water masses was diminutive and mediterranean waters filled and dominated the basin as inferred from the steady increase in schizosphaerella and the near disappearance of crepidolithus crassus the calcareous nannoplankton increase in abundance and decrease in diversity show that under a humid climate environmental conditions in such a shallow basin would tend to be more meso eutrophic

synchrony between early jurassic extinction oceanic anoxic event and the karoo ferrar flood basalt volcanism a well known second order mass extinction took place during the pliensbachian and toarcian stages of the early jurassic first recognized as a minor pliensbachian peak in the global extinction rate it has alternatively been interpreted as a regional response to the early toarcian oceanic anoxic event detailed studies established it as a global long term event spanning five successive ammonoid zones here we present a revised time scale based on highprecision u pb ages resolved to the zone level which suggests that elevated extinction rates were sustained for about 4 m y and peak extinction occurred at 183 ma recent isotopic dating of flood basalts from the southern gondwanan karoo and ferrar provinces documents a culmination in volcanic activity ca 183 ma the onset of volcanism is recorded as an inflection and start of a rapid rise of the seawater 87 sr 86 sr curve the synchrony of voluminous flood basalt eruptions and biotic crises as already noted for three of the major mass extinctions permits a causal relationship which in this case may be mediated by widespread oceanic anoxia

sedimentology and ichnology of the cretaceous tertiary boundary in denmark implications for the causes of the terminal cretaceous extinction abstract trace fossils and other sedimentologic evidence of bioturbation in latest cretaceous and earliest tertiary marine deposits in denmark provide important clues to understanding the ecology of the sea bottom immediately before during and after the terminal cretaceous boundary event trace fossil associations at all the onshore danish boundary sites indicate a general upward shoaling of the late maastrichtian chalk sea which was accompanied by an abrupt shift from a carbonate ooze sea floor to a marly clay rich unstable substrate at the boundary although the substrate condition may have become more stable in the early danian water depths never did return to their former deep level there is evidence of localized anoxia during the deposition of some boundary sediments in the fish clay in shallow parts of the danish maastrichtian sea but no clear evidence of anaerobic conditions occurring at the era boundary was observed in boundary strata deposited in deeper water near the center of the basin in fact earliest danian marl there is totally bioturbated a pulse of calcite dissolution in shallow water coincided precisely with the era boundary and this event played a major role in the formation of the fish clay in eastern denmark which is a condensed series of smectitic clay rich layers from which much calcite has dissolved the effects of this dissolution episode however were not so extreme in the marl that was deposited at the same time in slightly deeper water in northwestern denmark evidence from cretaceous tertiary boundary sequences in denmark and elsewhere suggests that no single catastrophe can account for the major biotic extinctions that occurred at the end of the cretaceous period the primary causal factors of the terminal cretaceous extinction event appear to be drastic global sea level regression occurring simultaneously with extensive volcanism on land and a strong pulse of calcite dissolution in ocean surface waters

massive dissociation of gas hydrate during a jurassic oceanic anoxic event in the jurassic period the early toarcian oceanic anoxic event about 183 million years ago is associated with exceptionally high rates of organic carbon burial high palaeotemperatures and significant mass extinction heavy carbon isotope compositions in rocks and fossils of this age have been linked to the global burial of organic carbon which is isotopically light in contrast examples of light carbon isotope values from marine organic matter of early toarcian age have been explained principally in terms of localized upwelling of bottom water enriched in 12c versus 13c refs 1 2 5 6 here however we report carbon isotope analyses of fossil wood which demonstrate that isotopically light carbon dominated all the upper oceanic biospheric and atmospheric carbon reservoirs and that this occurred despite the enhanced burial of organic carbon we propose that as has been suggested for the late palaeocene thermal maximum some 55 million years ago the observed patterns were produced by voluminous and extremely rapid release of methane from gas hydrate contained in marine continental margin sediments

calcareous nannoplankton changes across the early toarcian oceanic anoxic event in the western tethys 1 calcareous nannoplankton were profoundly affected by environmental perturbations coincident with the early toarcian oceanic anoxic event t oae we quantify the abundance of nannofossils across the t oae at three locations in western europe where the event is marked by a prominent negative carbon isotope excursion cie data were treated by statistical analysis and the shannon diversity index was applied in order to describe nannofossil assemblage changes related to paleoenvironmental evolution in the basal toarcian before the t oae high proportions of taxa with an affinity for low temperature e g p liasicus t patulus bussonius occurred this observation is consistent with interpretations of published oxygen isotope records during the t oae the lowest abundance of nannofossils is observed but there is a peak of a coccolith calyculus from an organism that probably thrived in low saline surface waters depleted of nitrate at the end of the perturbation the lowest diversities of nannofossils occurred and assemblages are dominated by crepidolithus crassus a deep dweller this interval corresponded to progressive reoxygenation of deep water and the reoccupation of the deep photic zone by nannoplankton the highest abundance of nannofossils is recorded above the cie and testifies to the recovery of the entire nannoplankton community the t oae was widespread perhaps global and probably linked to major changes in the atmosphere and hydrosphere however the record of this event varies in the basins surrounding the western tethys suggesting regional imprints on the global signal the regional variability may attest to establishment of effective connections between the arctic and tethys oceans which allowed cool low saline water formed at high latitudes to stream toward the western tethys

how bioturbation obscured the cretaceous palaeogene boundary record the cretaceous palaeogene k pg boundary interval is often penetrated by burrows which may obscure stratigraphic and micropalaeontological records leading to misinterpretations of the sequence of events spanning the k pg boundary here we assess the role of burrowing organisms in the redistribution of benthic foraminifera across the boundary at bidart france and report a strong relationship between the behaviour represented by pre and post k pg trace fossils and their benthic foraminiferal content we further infer a brief interval of eutrophic conditions at the seafloor as reported from other locations which disappeared from the lowermost danian stratigraphic record and is represented only inside post k pg trace fossils hosted in cretaceous strata the combined study of trace fossils and microfossils is a powerful tool in eco stratigraphy and event stratigraphy and can yield important insights into the completeness of the k pg record especially at locations such as bidart where this interval has traditionally been assumed to be complete

seawater temperature and carbon isotope variations in belemnites linked to mass extinction during the toarcian early jurassic in central and northern spain comparison with other european sections the early toarcian mass extinction marks one of the critical events in the history of the earth many of these events have been linked to important climate changes two sections of the toarcian showing high resolution ammonite based biostratigraphy are studied in central and northern spain stable isotope datasets based on the analysis of 192 diagenetically screened belemnite calcite and 41 bulk carbonates allowed the construction of 13c curves and a 18o based palaeotemperature comparison of the extinction pattern with other sections in europe and northern africa shows that the early toarcian mass extinction boundary occurred at the tenuicostatum serpentinum transition and that the organic rich facies linked to the oceanic anoxic event and the associated negative 13c excursion are diachronous from a latest pliensbachian cooling interval a first increment of seawater temperature averaging about 4 5 c started around the pliensbachian toarcian boundary and developed during the earliest toarcian tenuicostatum biochron marking the beginning of the main extinction interval from the tenuicostatum serpentinum transition up to the bifrons biochron a rise in seawater temperature averaging 5 7 c to 7 8 c was recorded this warming interval which started rapidly and which seems to be synchronous at least in western europe is considered one of the main factors responsible for mass extinction for some authors this rapid warming was probably due to a massive injection of greenhouse gases into the atmosphere but it does not seem to be recorded in belemnite calcite and the origin of these possible gases is largely debated in the literature additional isotope excursions were found in the studied sections in spain during the middle and late toarcian a negative 13cbel excursion has been recorded at the latest bifrons biochron above this shift the illustris vitiosa subzones thermal peak which represents a 2 3 c t could be linked to one of the tectonomagmatic activity peaks recorded in the karoo basin a renewal in the ammonite and brachipod faunas coincident with this climatic change has been recognized in nw europe and western tethys an interesting thermal peak has also been detected in belemnites of the insigne subzone t is in the order of 3 c and in both sections the thermal peak is included into a 13cbel negative excursion of about 1 5 relative synchrony with the new age for the karoo main magmatic activity 178 180 ma indicates that the 13c negative anomaly and the warming interval could be caused by the release of volcanogenic greenhouse gases at this short interval noteworthy changes in the abundance and diversity of the recorded assemblages in several faunal groups of nw europe and tethys are observed the uppermost levesquei subzone thermal peak has only been recognized in the deposits of the section located in central spain and coincides with a positive 13c excursion

nitrogen isotope evidence for water mass denitrification during the early toarcian jurassic oceanic anoxic event bulk sedimentary nitrogen isotope 15ntot data have been generated from lower jurassic black carbon rich shales in the british isles and northern italy deposited during the early toarcian oceanic anoxic event a pronounced positive 15ntot excursion through the exaratum subzone of the falciferum zone defined by characteristic ammonites in the british isles broadly correlates with a relative maximum in weight percent total organic carbon and in some sections with a negative 13corg excursion upwelling of a deoxygenated water mass that had undergone partial denitrification is the likely explanation for relative enrichment of 15ntot and parallels may be drawn with quaternary sediments of the arabian sea gulf of california and northwest mexican margin the development of early toarcian suboxic water masses and consequent partial denitrification is attributed to increases in organic productivity approximately coincident phenomena include the following a relative climatic optimum realignment of major oceanic current systems and a possible release of methane gas hydrates from continental margin sediments early in the history of the oceanic anoxic event

two pulses of extinction of larger benthic foraminifera during the pliensbachian toarcian and early toarcian environmental crises abstract the early toarcian early jurassic 183 ma was characterized by a pronounced oceanic anoxic event oae global warming major changes in hydrological cycling and a second order mass extinction most studies of early toarcian geobiology have focused on the northern hemisphere and only a few studies have been carried out on strata from the southwestern tethys ocean and southern hemisphere this limits our understanding of the geographic extent of the early toarcian mass extinction etme to address this issue in this study we have analyzed foraminiferal assemblages from the east selong and nianduo sections of south tibet china our results show that 14 species disappeared during the etme accounting for 21 9 14 64 of overall taxonomic richness of these nine of the victims were larger benthic foraminifera lbf accounting for 75 9 12 of lbf species we also find that close to the pliensbachian toarcian boundary six species of foraminifera disappear and five of these victims were lbf 5 17 our work thus demonstrates two extinction pulses of lbf in south tibet i e at the pliensbachian toarcian boundary and coeval the early toarcian oae the results suggest lbf were more vulnerable to environmental stress than smaller foraminifera which is consistent with other mass extinctions such as the permian triassic extinction our findings confirm that the southern hemisphere like the northern hemisphere was severely affected by environmental changes across the late pliensbachian to early toarcian interval and that extinctions were synchronous with the northern hemisphere

the timing of paleoenvironmental change and cause and effect relationships during the early jurassic mass extinction in europe the early jurassic marine mass extinction is one of several crises thought to coincide with anoxia transgression and warming caused by catastrophic release of gas hydrates however high resolution study of expanded sections in yorkshire england reveal that only the first of these factors is truly coincidental with extinction the well known transgression and large negative carbon isotope perturbation attributed to massive release of methane from gas hydrates occur after these events the anoxic event is developed diachronously in the european area with anoxia developing and fading away earlier in the mediterranean region compared with the nw european record however for a brief interval in the mid semicelatum subzone anoxia was simultaneously developed throughout the european region and it is this time that is marked by extinction of both benthic and pelagic marine fossils the sea level curve is also more complex than hitherto assumed with a minor regression occurring late in the semicelatum subzone shortly after the extinction the toarcian crisis occurred during a phase of global warming but the postulated release of methane from gas hydrates is too late to be implicated in the extinction mechanism as indeed is a recently reported cooling event from within the warming trend

effect of a jurassic oceanic anoxic event on belemnite ecology and evolution the toarcian oceanic anoxic event t oae 183 million y ago is possibly the most extreme episode of widespread ocean oxygen deficiency in the phanerozoic coinciding with rapid atmospheric pco2 increase and significant loss of biodiversity in marine faunas the event is a unique past tipping point in the earth system where rapid and massive release of isotopically light carbon led to a major perturbation in the global carbon cycle as recorded in organic and inorganic c isotope records modern marine ecosystems are projected to experience major loss in biodiversity in response to enhanced ocean anoxia driven by anthropogenic release of greenhouse gases potential consequences of this anthropogenic forcing can be approximated by studying analog environmental perturbations in the past such as the t oae here we present to our knowledge the first organic carbon isotope record derived from the organic matrix in the calcite rostra of early toarcian belemnites we combine both organic and calcite carbon isotope analyses of individual specimens of these marine predators to obtain a refined reconstruction of the early toarcian global exogenic carbon cycle perturbation and belemnite paleoecology the organic carbon isotope data combined with measurements of oxygen isotope values from the same specimens allow for a more robust interpretation of the interplay between the global carbon cycle perturbation environmental change and biotic response during the t oae we infer that belemnites adapted to environmental change by shifting their habitat from cold bottom waters to warm surface waters in response to expanded seafloor anoxia

warming driven mass extinction in the early toarcian early jurassic of northern and central spain correlation with other time equivalent european sections abstract causes of the major mass extinction recorded during the early toarcian early jurassic are controversial many authors have concluded that the mass extinction is caused by the widespread oceanic anoxia derived from a postulated early toarcian oceanic anoxic event etoae supposedly synchronous in all basins and global in extent another group of papers links the mass extinction with a major climate change that occurred synchronously with the mass extinction the results of the study of five sections of the uppermost pliensbachian and lower middle toarcian deposits located in northern and central spain are presented detailed ammonite based biostratigraphy coupled with stable isotope analysis of belemnite calcite and bulk carbonates as well as total organic carbon toc analyses have been performed in all sections records of the vertical distribution of mainly benthic fossils have been compiled in four of the studied sections results obtained in the spanish outcrops have been compared and correlated with other european sections the excellent mutual relation between the patterns of the early toarcian progressive warming and the concomitant progressive losses of species evidences a cause and effect relationship between the increase of temperature and the mass extinction from an uppermost pliensbachian cooling interval warming started at the lower toarcian tenuicostatum zone increase of average seawater palaeotemperature is associated with a progressive and substantial drawdown in the number of species of nektonic planktonic and benthic organisms representing the extinction interval a prominent increase in seawater temperature occurred around the lower toarcian tenuicostatum serpentinum zonal boundary average temperatures at the serpentinum zone increased about 7 c marking the extinction boundary the high temperatures continued during the middle toarcian bifrons chronozone representing the repopulation interval the anoxia linked to the postulated etoae cannot be the responsible for the mass extinction because it has been synchronously recorded in the oxygenated environments of many european and northern african platforms deposition of laminated organic rich black shale facies above 5 wt toc indicating anoxic environments was mostly confined geographically to the western europe euxinic basin and mainly deposited after the extinction event during the interval of faunal recovery

polar record of early jurassic massive carbon injection abstract the toarcian oceanic anoxic event t oae ca 182 myr early jurassic represents one of the best recognized examples of greenhouse warming decreased seawater oxygenation and mass extinction the leading hypothesis to explain these changes is the massive injection of thermogenic or gas hydrate derived 13 c depleted carbon into the atmosphere resulting in a 3 per mil negative carbon isotope excursion cie accelerated nutrient input and dissolved oxygen consumption in the oceans nevertheless the lack of a precisely dated record of the t oae outside low latitudes has led to considerable debate about both its temporal and spatial extent and hence concerning its underlying causes here we present new isotopic and lithological data from three precisely dated n siberian sections which demonstrate that mass extinction and onset of strong oxygen deficiency occurred near synchronously in polar and most tropical sites and were intimately linked to the onset of a marked 6 negative cie recorded by bulk organic carbon rock eval pyrolysis data from siberia and comparisons with low latitudes show that the cie cannot be explained by the extent of stratification of the studied basins or changes in organic matter sourcing and suggest that the negative cie reflects rapid 13 c depleted carbon injection to all exchangeable reservoirs sedimentological and palynological indicators show that the injection coincided with a change from cold abundant glendonites and exotic boulder sized clasts to exceptionally warm conditions dominance of the thermophyllic pollen genus classopollis in the arctic which likely triggered a rapid possibly partly glacioeustatic sea level rise comparisons with low latitude records reveal that warm climate conditions and poor marine oxygenation persisted in continental margins at least 600 kyr after the cie features that can be attributed to protracted and massive volcanic carbon dioxide degassing our data reveal that the t oae profoundly affected arctic climate and oceanography and suggest that the cie was a consequence of global and massive 13 c depleted carbon injection

ichnological analysis of the cretaceous palaeogene boundary interval at the caravaca section se spain abstract ichnological analysis of the cretaceous palaeogene k pg boundary at caravaca betic cordillera southeast spain reveals significant data for the interpretation of the k pg boundary event the uppermost maastrichtian marls below the cretaceous palaeogene k pg boundary at caravaca contains the dark coloured trace fossils chondrites targionii planolites thalassinoides zoophycos and alcyonidiopsis the composition of trace fossil associations in the upper maastrichtian and lower danian marls is generally the same yet much more poorly preserved in the latter showing in general no ichnological evidence of a severe macroinfaunal crisis at the k pg boundary the dark coloured trace fossils penetrate from two bioturbated horizons in the dark boundary layer separated by two horizons with primary lamination the ichnofauna rapidly recovered after the k pg event following deposition of the lower parallel laminated bed 14 mm thick that occurs in the dark boundary layer above the k pg boundary zoophycos is the deepest trace fossil penetrating as far as 90 cm below the k pg boundary probably in stiff or partly firm substrate which was dewatered to some extent during the slow accumulation of the danian dark boundary layer the firmness probably prevented the chondrites trace maker from deeper burrowing the maastrichtian sediments may be contaminated with danian microfossils due to bioturbation

a carbon isotope perturbation at the pliensbachian toarcian boundary evidence from the lias group ne england a perturbation in the carbon isotope record at the time of the pliensbachian toarcian boundary 184 ma in the early jurassic is reported based on new data from yorkshire england two sharp 13 c org negative excursions each with a magnitude of 2 5 and reaching minimum values of 28 5 are recorded in the bulk organic matter record in sediments of latest pliensbachian to earliest toarcian age a similar pattern of negative carbon isotope excursions has been observed at the stage boundary in the sw european section at peniche portugal in 13 c carbonate 13 c wood and 13 c brachiopod records the isotopic excursion is of interest when considering the genesis and development of the later toarcian oceanic anoxic event oae as well as the second order global extinction event that spans the stage boundary furthermore the isotope excursion potentially provides a chemostratigraphic marker for recognition of the stage boundary which is currently achieved on the basis of different ammonite faunas in the nw european and tethyan realms

trace fossil evidence suggests widespread dwarfism in response to the end cretaceous mass extinction braggs alabama and brazos river texas as a proxy for the body size of the tracemaker burrow diameter provides information on fundamental characteristics such as organism biology and behavior furthermore changes in this endobenthic parameter provide insight into the timing and recovery of burrowing organisms in response to large scale processes operating in ancient trophic systems we herein report a decrease in burrow size in thalassinoides dominated ichnoassemblages across the cretaceous paleogene k pg boundary in well studied shallow marine sections along the brazos river and cottonmouth creek texas and at braggs alabama at the cottonmouth creek and brazos river localities thalassinoides isp occurring above the previously reported negative 13c shift and the first occurrence of unequivocal danian planktonic foraminifera are 17 smaller in short axis diameter and 22 smaller when diameters are corrected for sediment compaction mean k 27 15 7 12 mm mean pg 21 13 6 88 mm n 53 than those excavated and filled prior to deposition of a hummocky cross bedded ejecta bearing sandstone complex commonly interpreted as the chicxulub event deposit across the k pg boundary at braggs diameters dth of simple maze thalassinoides structures from similar recurring depositional facies abruptly decrease by 22 mean k 13 08 1 86 mm mean pg 10 21 1 87 mm n 26 the cretaceous and paleogene burrows were preserved in beds of similar lithology suggesting that the reduction in size is not attributed to sedimentological factors at both localities up section trends in dth are statistically significant 0 05 equal variance t test non parametric mann whitney u test a reduction in dth above the k pg boundary reflects dwarfing within the post extinction endobenthic community these ichnological trends are similar to those recently documented at more impact distal sites along the new jersey coastal plain dwarfing during the early recovery stages of the end cretaceous mass extinction as recorded by trace fossils was widespread and occurred within siliciclastic carbonate and glauconite producing depositional environments since this ichnological signal in shallow marine successions appears to be a general phenomenon across the crisis interval trace fossil analysis provides a potential in situ field method for constraining and correlating the stratigraphic position of the event particularly in the absence of other macroscopic microscopic and geochemical indicators

paleoethologic interpretation of complex thalassinoides in shallow marine limestones lower ordovician southern sweden abstract lower ordovician thalassinoides t bacae isp nov from oland sweden is characterized by irregularly anastomosing horizontal tunnel mazes with highly variable branching angles accompanied by numerous closely spaced short vertical shafts that must have provided a large number of burrow openings to the sea floor these complex trace fossils appear to be agrichnial burrow systems that represent chemosymbiotic feeding behavior by infaunal animals they occur profusely in thin bedded fossiliferous lime mudstone and wackestone that were deposited on a shallow marine carbonate platform

the early toarcian jurassic anoxic event stratigraphic sedimentary and geochemical evidence detailed paleogeographic studies in the southern alps suggest that an oxygen minimum model is appropriate for interpreting conditions on tethyan continental margins advection of manganese in this low oxygen layer may explain the local occurrence of carbonate ores of this element carbon sulfur and iron sulfur ratios although showing considerable scatter suggest that bottom waters at this time were locally euxinic containing free hydrogen sulfide this oceanic anoxic event was preceded by significant faunal turnover of ammonites in tethys and accompanied by widespread extinction of benthos in northern europe in response to the lateral spread of anoxic bottom waters during transgression similar changes may be recognized in other parts of the world other anoxic events may have taken place during the jurassic but documentation is as yet meagre furthermore models for such phenomena remain largely speculative although upwelling and increased planktonic productivity commencing in pre toarcian time are favored for the falciferum zone event documented here from author

sedimentary organic matter and early toarcian environmental changes in the lusitanian basin portugal abstract the objective of this study is to investigate the relationship between early toarcian climatic events and the composition of kerogen assemblages in the lusitanian basin portugal in particular we aim to understand how the pliensbachian toarcian event pl toa event and toarcian oceanic anoxic event toae affected the continental areas of the western iberian margin and how possible variations in continental sources of organic matter om were expressed in marginal marine and hemipelagic depositional environments during the early toarcian we present here a characterisation total organic carbon toc total sulphur ts 13c in kerogen concentrate 13ckerogen and palynofacies of kerogen assemblages from several uppermost pliensbachian emaciatum ammonite zone lower toarcian sections in the lusitanian basin western iberian margin including the peniche section which contains the toarcian gssp in all sections toc concentration is low average 0 4 wt with the highest values reaching up to 2 1 wt in a discrete level located approximately 10 5 m above the base of the levisoni zone at peniche the toae negative carbon isotope excursion is observed in kerogen concentrate at the base of the levisoni zone throughout the basin palynofacies analysis demonstrates that the kerogen assemblages are mostly of terrestrial affinity with the dominance of the phytoclast group and terrestrial palynomorphs and with punctual increases in amorphous organic matter freshwater e g botryococcus sp and marine microplankton dinoflagellate cysts acritarchs and prasinophyte algae in specific stratigraphic intervals a change in palynofacies assemblages associated with the toae is observed around the base of levisoni zone although with slight differences between sections the toae interval records an increase in non opaque translucent phytoclasts nop and cuticle fragments and is also associated with an increased contribution of terrestrial palynomorphs increase in sporomorphs and classopollis in tetrads and agglomerates and decrease in marine palynomorphs the increases in nop and terrestrial palynomorphs support the postulated enhancement of the hydrological cycle and increased export of terrestrial om into marine environments during the early toarcian especially during the toae in the western iberian margin understanding the impact of the early toarcian climatic events on land based ecosystems may provide important insights into current climate change

rapid warming and ostracods mass extinction at the lower toarcian jurassic of central spain abstract here we present the results of the study of two lower toarcian carbonate sections located in the iberian range of central spain analyses of stable isotope on belemnite calcite allowed calculation of seawater palaeotemperature variations which were compared with the stratigraphical distribution of ostracods these organisms are particularly sensitive to ratios of temperature and salinity variations and hence are good indicators of climate changes from a cooling interval with seawater temperatures of 13 2 c recorded at the pliensbachian toarcian transition seawater temperature began to rise in the lowermost toarcian tenuicostatum zone reaching average temperatures between 14 6 c and 16 3 c during the time of deposition of this zone coinciding with this seawater warming up to 85 of the ostracods species progressively disappeared during a period of approximately 300 kyr marking the extinction interval the extinction boundary located around the tenuicostatum serpentinum zonal boundary coincides with a marked increase in temperature in the serpentinum zone on which average seawater temperatures of 22 c have been calculated warming continued through part of the middle toarcian bifrons zone reaching average temperatures of 24 7 c readjustment of the ostracod population allowed recovery of these faunas in the upper serpentinum zone although the extinction of a major ostracod group the healdioids was also recorded the correlation between mass extinction and warming infers a causal relationship comparison of the results with the records of stable isotopes in belemnites and in bulk carbonates as well as toc and facies analysis suggests that the anoxia linked to the early toarcian oceanic anoxic event was not the main responsible for the ostracod mass extinction

danian lower selandian microcodium rich calcarenites of the subbetic zone se spain record of nereites ichnofacies in a deep sea base of slope system abstract the olivares formation a lower paleogene unit of the subbetic zone in southern spain is mostly composed of calcarenites comprising 60 90 of resedimented microcodium remains which are intercalated in hemipelagic marls rich in planktonic foraminifera microcodium is formed on the roots of terrestrial plants adapted to live on carbonate rich substrates its occurrence in the olivares formation entailing a massive resedimentation from a subaerially exposed carbonate source area new field observations demonstrate that the unit was deposited at the base of a faulted slope within a graben flanked by massifs of mostly jurassic carbonates while an ichnological analysis shows an abundant and moderately diverse trace fossil assemblage consisting of 30 ichnospecies belonging to 21 ichnogenera the nongraphoglyptid assemblage 24 ichnospecies 16 ichnogenera is dominated by chondrites ophiomorpha planolites and scolicia zoophycos isp is common while cladichnus gordia helminthopsis multina nereites parahaentzscheliana polykampton spirophycus strobilorhaphe and thalassinoides isp are scarce or rare in the graphoglyptid assemblage 6 ichnospecies 5 ichnogenera helminthorhaphe is common scarce and belorhaphe desmograpton paleodictyon and urohelmintoida are scarce rare this trace fossil assemblage with abundant scolicia and nereites and frequent graphoglyptids can be assigned to the deep sea nereites ichnofacies within the nereites ichnofacies the ophiomorpha rudis and paleodictyon subichnofacies are readily differentiated and the nereites subichnofacies probably also occurs pointing to vertical changes in the turbiditic system most likely related to a coeval sea level rise that eventually resulted in the flooding of the emergent microcodium producing carbonate massifs

basinal restriction black shales re os dating and the early toarcian jurassic oceanic anoxic event 1 profiles of mo total organic carbon toc through the lower toarcian black shales of the cleveland basin yorkshire united kingdom and the posidonia shale of germany and switzerland reveal water mass restriction during the interval from late tenuicostatum zone times to early bifrons zone times times which include that of the putative early toarcian oceanic anoxic event the degree of restriction is revealed by crossplots of mo and toc concentrations for the cleveland basin which define two linear arrays with regression slopes ppm of 0 5 and 17 the slope of 0 5 applies to sediment from the upper semicelatum and exaratum subzones this value which is one tenth of that for modern sediments from the black sea mo toc regression slope 4 5 reveals that water mass restriction during this interval was around 10 times more severe than in the modern black sea the renewal frequency of the water mass was between 4 and 40 ka the mo toc regression slope of 17 applies to the overlying falciferum and commune subzones the value shows that restriction in this interval was less severe and that the renewal frequency of the water mass was between 10 and 130 years the more restricted of the two intervals has been termed the early toarcian oceanic anoxic event but is shown to be an event caused by basin restriction local to nw europe crossplots of re os and mo against toc show similar trends of increasing element concentration with increase in toc but with differing slopes together with modeling of 187 os 188 os and d 98 mo the element toc trends show that drawdown of re os and mo was essentially complete during upper semicelatum and exaratum subzone times mo toc regression slope of 0 5 drawdown sensitized the restricted water mass to isotopic change forced by freshwater mixing so that continental inputs of re os and mo via a low salinity surface layer created isotopic excursions of up to 1 3 in d 98 mo and up to 0 6 for 187 os 188 os restriction thereby compromises attempts to date toarcian black shales and possibly all black shales using re os chronology and introduces a confounding influence in the attempts to use d 98 mo and initial 187 os 188 os for palaeo oceanographic interpretation

early toarcian early jurassic oceanic anoxic event recorded in the shelf deposits in the northwestern panthalassa evidence from the nishinakayama formation in the toyora area west japan abstract the early toarcian oceanic anoxic event t oae was marked by the worldwide burial of organic rich black shales and a coincident pronounced negative carbon isotope excursion of carbonates organic matter and fossil wood this characteristic carbon isotope perturbation and other geochemical records have been recognized in many sections in the european domain and in selected sections in the central and eastern panthalassa but not in the western panthalassa we present herein for the first time data of carbon isotope ratios of organic carbon total organic carbon toc contents and sedimentary fabrics from the uppermost pliensbachian to the lower toarcian sequence in the sakuraguchi dani valley toyora area west japan that was deposited in the shelf basin of the northwestern panthalassa the carbon isotope profile displays a similar trend to those in contemporaneous strata in the tethys and in the eastern and central panthalassic regions which is characterized by a distinct negative excursion around the tenuicostatum falciferum zone boundary in the early toarcian this evidence suggests that the widely recognized negative carbon isotope excursion represents a nature of the global carbon cycle perturbation analyses of total organic carbon contents and sedimentary fabrics in the study section reveal that accumulation of organic carbon occurred and anoxic bottom water was prevalent during the early toarcian the most organic rich strata and bottom water anoxia described in the study section however exist in the interval showing the carbon isotope positive recovery after the abrupt negative shift and this fact suggests that the accumulation of organic matters and development of marine anoxia were globally diachronous even though the negative cie was interpreted as a synchronous event our study also demonstrates that the early toarcian anoxia in the northwestern panthalassic basin was not a single and continuous anoxic event but was interrupted by episodic short term oxygenation events