early jurassic late pliensbachian co2 concentrations based on stomatal analysis of fossil conifer leaves from eastern australia the stomatal index a measure of stomatal density of an extinct australian early jurassic araucariacean conifer species allocladus helgei jansson is used to reconstruct the atmospheric carbon dioxide concentration pco 2 in the early jurassic the fossil leaves are preserved in a single bed palynologically dated to late pliensbachian similar to 185 183 mya atmospheric pco 2 is estimated from the ratios between the stomatal index of a helgei and the stomatal indices of three modern analogs nearest living equivalent plants co2 concentration in the range of similar to 750 975 ppm was calibrated from the fossil material with a best estimated mean of similar to 900 ppm the new average pco 2 determined for the late pliensbachian is thus similar to although similar to 10 lower than previously inferred minimum concentrations of similar to 1000 based on data from the northern hemisphere but may help constrain pco 2 during this period our results are the first pco 2 estimates produced using jurassic leaves from the southern hemisphere and show that i paleo atmospheric pco 2 estimates are consistent at a global scale though more investigations of southern hemisphere material are required and ii the stomatal proxy method can now be used without the context of relative change in pco 2 when applying the correct methodology c 2014 the authors published by elsevier b v on behalf of international association for gondwana research less

an ammonite zonation for the lower jurassic of canada and the united states the pliensbachian this is the first in a series of papers intended to establish a lower jurassic ammonite zonation that takes into account the biostratigraphic and biogeographic peculiarities of the north american succession its development has been spurred by the need for high resolution correlation between allochthonous terranes and the need for a standard to which microfossil sequences may be coupled in north america the lower boundary of the pliensbachian is drawn above the last echioceratids the lower pliensbachian is divided into in ascending order the imlayi whiteavesi and freboldi zones the upper pliensbachian into the kunae and carlottense zones the fannin bay section in the queen charlotte islands is designated the stratotype for the whiteavesi freboldi and kunae zones ideal stratotypes for the imlayi and carlottense zones are not presently known reference sections former illustrating the faunal associations that characterize all the zones are designated in western nevada the sunrise formation nor

magnetostratigraphy of the toarcian stage lower jurassic of the llanbedr mochras farm borehole wales basis for a global standard and implications for volcanic forcing of palaeoenvironmental change the lower jurassic toarcian stage c 183 174 ma is marked by one of the largest global exogenic carbon cycle perturbations of the phanerozoic which is associated with the early toarcian oceanic anoxic event t oae c 183 ma climatic and environmental change at the t oae is reasonably well constrained in the marine realm with marine anoxic or euxinic conditions developing locally across both hemispheres at the same time as the t oae negative carbon isotope excursion however high resolution stratigraphic comparison between different palaeo ocean basins and with the continental realm can be complicated palaeomagnetic reversals can provide a precise and accurate stratigraphic correlation tool between marine and continental sedimentary archives and even between sedimentary and igneous successions here we present a high resolution magnetostratigraphic record for the toarcian stage in the biostratigraphically complete and expanded llanbedr mochras farm borehole cardigan bay basin wales this study provides the first geomagnetic polarity reversal scale that is integrated with high resolution biostratigraphy and carbon isotope stratigraphy for the entire toarcian stage this stratigraphic framework also provides a new precise correlation with the basalt lava sequence of the karoo ferrar large igneous province linking the pliensbachian toarcian boundary and t oae climatic and environmental perturbations directly to this episode of major volcanic activity supplementary material details of the palaeomagnetic data and dip direction are available at https doi org 10 6084 m9 figshare c 4052720

faunal trends and sea level changes biogeographic patterns of kimmeridgian ammonites on the western european shelf the kimmeridgian series of the northern aquitaine margin is representative of the marine sedimentation on the western european shelf it has been used to demonstrate a fundamental relationship between relative sea level changes and the biogeographic dynamics of the kimmeridgian ammonites this synthesis based on comparative sedimentological and paleobiogeographical studies shows that the shelf was settled by submediterranean and or subboreal ammonites during transgressive phases and maximum sea level rises endemic lineages differentiated during the sea level highstands and the beginning of lowstands correlative with the long term sea level rise endemic elements have progressively taken a prominent role within the kimmeridgian ammonite faunas of the shelf the patterns of faunal changes have been deduced from studies of ammonite lineages from distinctive biogeographic origins rasenioides lithacosphinctes orthaspidoceras and gravesia compared with subboreal ammonites it seems that the submediterranean species were more tolerant of changing environments and adapted to new environments more easily therefore most of the endemic lineages which settled the western european area originated in submediterranean faunas

estimates of the amount and rate of sea level change across the rhaetian hettangian and pliensbachian toarcian boundaries latest triassic to early jurassic an attempt is made to determine the amount and rate of sea level change for two major events in the latest triassic to early jurassic both of which are associated with mass extinctions using the best available facies evidence and time scale the amount of marine deepening across the pliensbachian toarcian boundary based on analysis of the excellent yorkshire coast section is likely to have been a few tens of metres at a rate of between 1cm 1 2 ka 1 and 1cm 0 4 ka 1 the change across the rhaetian hettangian triassic jurassic boundary was different in that the sea level rise was immediately preceded by a sea level fall effectively a 9regression transgression9 couplet the earliest jurassic sea level rise is likely to have been much more rapid than that across the pliensbachian toarcian boundary at a rate of at least 1 cm 0 2 ka 1 whereas the speed of pliensbachian toarcian change is consistent with the growth of oceanic ridges the appreciably more rapid triassic jurassic change is suggestive of a different tectonoeustatic mechanism involving stress induced changes in plate density

an ammonite zonation for the toarcian lower jurassic of the north american cordillera this is the second in a series of papers intended to establish a lower jurassic ammonite zonation that takes into account the biostratigraphic and biogeographic peculiarities of the north american succession in north america the lower boundary of the toarcian is drawn at the first appearance of dactylioceras above the last occurrence of amaltheus and fanninoceras the lower toarcian is represented by the kanense zone the middle toarcian by the planulata and crassicosta zones and the upper toarcian by the hillebrandti and yakounensis zones section 5 on the yakoun river in the queen charlotte islands is designated the stratotype for the planulata crassicosta and hillebrandti zones section 3 on the yakoun river is designated the stratotype for the yakounensis zone an ideal stratotype for the kanense zone is not presently known reference sections further illustrating the faunal associations that characterize the zones are designated in eastern oregon snowshoe formation and northern british columbia

sequence stratigraphy of source rocks applied to the study of the kim meridgian tithonian in the north west european shelf dorset uk yorkshire uk and boulonnais france abstract in dorset and yorkshire england the sedimentation of kimmeridgianfrithonian age mutabilis to pallasioides zones shows ordered organic sequences the distribution of the organic matter content per cent total organic carbon petroleum potential hydrogen indices is not random but occurs as widespread primary organic rich cycles nested within each other these organic rich cycles with thicknesses of about 0 5 m show regular variations in organic carbon contents reaching a maximum value midway through the cycle they formed in response to widespread phenomena and can be correlated over long distances the cycles were deposited in marine environments mainly below the storm wave base they show little sedimentological evidence of sea level fluctuation either transgression or regression in the boulonnais france a more proximal setting the comparable strata show a greater lithological contrast and depositional environments corresponding to bathymetric changes are more easily determined a comparison of the distribution of organic matter through the sequence dated by ammonites in the three areas studied shows a good correlation between the distal dorset and yorkshire and the proximal boulonnais areas the main result of the biostratigraphic revision in the boulonnais france concerns the argiles de ch tillon which can be subdivided into two members these belong to the autissiodorensis zone autissiodorensis subzone and the gigas elegans zone respectively thus the kim meridgian tithonian boundary is located within this formation transgression does not appear to be the main factor determining the accumulation of autochthonous organic matter type ii not every major transgressive facies change seen in the kimmeridgian tithonian of the boulonnais is characterized by an enrichment in organic matter in the basinal area good source rocks with high petroleum potentials result from a conjunction between the physiography the transgression and the climate this last causes the variations in primary productivity which produce the organic rich cycles transgressions act mostly to reveal the climatic variations they are a necessary condition for the accumulation of the autochthonous organic matter but they are not sufficient by themselves as demonstrated by the transgressions in the autissiodorensis and elegans zones in the first instance the strata are depleted in organic matter in both the distal and proximal areas in the second instance type ii organic matter accumulated in both distal and proximal environments the vertical fluctuations in the total organic carbon contents the types of organic matter and the petroleum potentials of the organic rich cycles determine the oil potentials of transgressive sequences in sedimentary basins

diagenetic and catagenetic products of isorenieratene molecular indicators for photic zone anoxia a wide range of novel diagenetic and catagenetic products of the diaromatic carotenoid isorenieratene a pigment of the photosynthetic green sulphur bacteria chlorobiaceae has been identified in a number of sedimentary rocks ranging from ordovician to miocene compound identification is based on nmr mass spectrometry the presence of atropisomers and stable carbon isotopes atropisomers contain an axially chiral centre which in combination with other chiral centres results in two or more diastereomers that can be separated on a normal gc column chlorobiaceae use the reverse tca cycle to fix carbon so that their biomass is enriched in 13c high 13c contents of isorenieratene derivatives therefore support their inferred origins isorenieratene derivatives include c 40 c 33 and c 32 diaryl isoprenoids and short chain aryl isoprenoids with additional aromatic and or s containing rings c 33 and c 32 compounds are diagenetic products of c 33 and c 32 carotenoids formed from isorenieratene during early diagenesis through expulsion of toluene and m xylene respectively cyclisation of the polyene acyclic isoprenoid chain can proceed via an intramolecular diels alder reaction followed by aromatisation of the newly formed ring sulphurisation is also an important process during early diagenesis competing with expulsion and cyclisation sulphur bound isorenieratane is released during progressive diagenesis due to cleavage of relatively weak ss and cs bonds cleavage of c c bonds during aromatisation of newly formed rings and during catagenesis yields short chain compounds the inherent presence of a conjugated double bond system in carotenoids implies that similar diagenetic and catagenetic reactions can occur with all carotenoids chlorobiaceae live at or below the oxic anoxic boundary layer and require both light and h 2s the presence of isorenieratene or its diagenetic and catagenetic products in ancient sedimentary rocks and crude oils is therefore an excellent indication for photic zone anoxia in the depositional environment diagenetic and catagenetic products of isorenieratene are expected to find applications in reconstruction of palaeoenvironments and in oil oil and oil source rock correlation studies their presence in several petroleum source rocks suggests that anoxia is an important environmental parameter for the preservation of organic matter

carbon and oxygen isotope records of palaeoenvironmental and carbonate production changes in shallow marine carbonates kimmeridgian swiss jura carbon and oxygen isotope ratios are commonly used to correlate shallow and deep marine successions carbon and oxygen isotope analyses were performed on bulk carbonate samples from two kimmeridgian sections of the swiss jura platform in order to correlate them with biostratigraphically well dated coeval sections in the adjacent basin on the platform a general decrease in 13 c and 18 o values from the base to the top of the studied interval is measured whereas time equivalent pelagic hemipelagic carbonates record an increase in carbon and oxygen isotope ratios moreover the measured 13 c and 18 o values are generally lower than those indicated for the kimmeridgian open ocean and show high frequency variations superimposed on the general trend samples were screened for diagenetic alteration using optical and cathodoluminescence petrography and coupled carbon and oxygen isotope and trace element analyses some observations favour a role for diagenetic alteration but isotopic and elemental trends as well as sedimentological evidence suggest that the more negative values of 13 c and 18 o relative to kimmeridgian seawater are also due to local environmental conditions high frequency changes in 18 o and 13 c values most likely result from variations in salinity and carbonate production and accumulation rates these variations were produced by different water masses that were isolated from the open ocean and developed their own geochemical signatures repeated isolation was induced by high frequency sea level fluctuations and helped by irregular platform morphology consequently carbon and oxygen isotope records in shallow marine carbonates can be used for stratigraphic correlation only if their origin is well known

late jurassic palaeoclimatic change from clay mineralogy and gamma ray spectrometry of the kimmeridge clay dorset uk abstract the late jurassic was a time of increasing aridity in nw europe here a new clay mineral dataset is presented from a 600 m thick composite core through the kimmeridge clay formation southern england clay mineral assemblages comprise mainly illite and kaolinite with minor randomly interstratified illite smectite mixed layer clays sem observations indicate that clay minerals are mainly detrital except in silty strata of late tithonian age which contain abundant pore filling kaolinite aggregates th k ratios determined from gamma ray spectrometry mirror palaeoclimatically significant variations in kaolinite illite ratios with notable exception where diagenetic kaolinite occurs comparison with age equivalent strata identifies regional cyclic variations in clay minerals at the 100 300 m scale small scale 10 20 m variations in clay minerals and th k also occur it is proposed that the region experienced progressively intense humidity through the kimmeridgian followed by a return to more arid conditions during the early tithonian following a mid tithonian peak in aridity the hudlestoni event9 more humid climatic conditions returned prior to the development of latest tithonian intense aridity late jurassic climate was apparently subject to synchronously cyclic changes across a broad area of the laurasian continent such changes could not have resulted from mountain building or continental rotations supplementary material clay data are available at http www geolsoc org uk sup18376

climatic ups and downs in a disturbed jurassic world the tropical warm and equable climate of the jurassic world is regularly challenged by geoscientists especially since oxygen isotopes 18 o of fossil hardparts have been used to reconstruct the paleotemperature history of seawater by applying the innovative sizer sig nifi cant zero crossings of the derivatives statistical approach to a newly compiled 18 o data base for the jurassic we demonstrate the occurrence of major and multiscale 18 o changes mainly related to climate disturbances for the fi rst time two long term anomalies in 18 o are identifi ed during the toarcian and the late jurassic in conjunction with intensive volcanism in large igneous provinces these results support a strong infl uence of repeated volcanic pulses on the modulation of pco 2 temperatures and polar ice cap volumes over protracted periods at shorter time scales 13 relatively rapid 0 5 1 m y and signifi cant warming and cooling events are identifi ed the causes of which include transient fl uctuations in greenhouse gas con centrations related to still debated mechanisms

210pb 230th and 10be in central indian basin seamount sediments signatures of degassing and hydrothermal alteration of recent origin 1 isotopic 210pb 238u 230th 10be major and trace elements and micromorphological and microchemical data were used to identify recent 100 yrs hydrothermal alteration of a 200 kyr sedimentary record from the flank of a seamount in the central indian basin located at the edge of the 75 30 e fracture zone alteration effects are also reflected in 1 the depleted sedimentary organic carbon 2 dissolution features of radiolarian skeletons 3 the presence of altered minerals such as smectite and zeolites and 4 distinctly different magnetic properties in the altered sediments we interpret a predominant influence of neutral chloride type hydrothermal fluids this is the first report of recently occurring sediment alteration by shallow circulating sub surface fluids along the indian ocean intra plate seamount environment

comparison between high resolution seismic and sequence stratigraphic approaches applied to the upper jurassic deposits of the dover strait area northern france abstract this study is an attempt to interpret very high resolution seismic data usually devoted to shallow marine surveys in terms of very high resolution seismic and sequence stratigraphy at the scale of the reservoir seismic data are compared with outcrop based observations in order to discuss the geometrical relationships between rock bodies and the nature of the seismic reflections in terms of seismic facies related to type lithologies two high resolution seismic surveys using a sparker were performed in the dover strait area some 100s of metres away from the boulonnais coastal cliffs the aim was to look to the 130 m thick mixed siliciclastic carbonate deposits of upper jurassic age kimmeridgian tithonian cropping out at the sea floor and to compare them to the coastal cliffs exposures the 100 m apart seismic profiles exhibit a 100 m deep penetration and 1 m in vertical resolution upper 30 ms part of the profiles four seismic facies are recognised on the seismic profiles they comprise ten seismic units which can be grouped into three broad families group 1 has a parallel aggradational reflection configuration and conformable boundaries which may correspond to the transgressive and highstand systems tracts the seismic facies exhibit either a high continuity high amplitude corresponding to clayey mudstone lithologies of the mid ramp environment or a high continuity low amplitude corresponding to shaly lithologies of the outer ramp environment group 2 has a sigmoid progradational reflection configuration bounded at the base by a downlap surface and at the top by a toplap surface these boundaries correspond respectively in the field to a marine regressive surface of erosion and a marine transgressive surface of erosion the seismic facies is cross layered and exhibits a moderate continuity low to moderate amplitude and moderate frequency group 2 corresponds to the bioclastic sand prone facies of the inner ramp environment it is interpreted as lowstand sharp based shorefaces group 3 exhibits a progradational complex to chaotic configuration it lies on an erosional unconformity with paleogullies the seismic facies shows discontinuous reflections with moderate amplitude and high to moderate frequency it corresponds in the field to cross bedded sandstones in channel fill arrangements of fluvial origin wealdian deposits marking the top of the section the different systems tracts sequence boundaries and depositional sequences identified onshore can be recognised as well on the seismic profiles but the comparison demonstrates that seismic data complement the onshore sequence stratigraphic analysis by providing the geometrical relationships between systems tracts onlap downlap toplap that cannot be observed onshore the maximum flooding surfaces however present no specific seismic signature on such a low angle ramp profile it can only be identified precisely in the field which also help to relate lithologies to seismic facies this study represents one of the first attempts to interpret very high resolution seismic data at the outcrop scale it will be improved again in the future by the collection of impedance logs and synthetic seismic traces from cored sections on the coastal cliffs for comparison with the seismic data

lower jurassic epicontinental carbonates and mudstones from england and wales chemostratigraphic signals and the early toarcian anoxic event sections through lower jurassic epicontinental carbonates from southern britain junction bed and equivalent show a positive carbon isotope excursion 13ccarbonate detectable in bulk rock in the falciferum zone of the lower toarcian isotopic data from organic matter in more clay rich sections from wales and north east england together with determinations on belemnite calcite indicate that highest 13c values are localized in the upper exaratum subzone of the falciferum zone levels of particular enrichment in organic carbon were developed in the early to mid exaratum subzone and hence pre date this 13c maximum these phenomena reflect the impact of the early toarcian oceanic anoxic event in the british area similar isotopic trends have been recorded in other toarcian sections from tethyan europe and are interpreted as reflecting the chemistry of sea water on the assumption of isotopic correlation between the english and tethyan sections the 13c maximum would be everywhere dated as latest exaratum subzone in terms of the north european ammonite scheme absolute oxygen isotope values in carbonates probably reflect both early diagenetic cementation and later temperature related burial diagenesis although a palaeotemperature maximum is tentatively identified as characterizing the early falciferum zone subsequent climatic deterioration may have been triggered by drawdown of co2 related to regional excess carbon burial during the oceanic anoxic event using the positive 13c excursion as a correlative level in sections from different faunal provinces britain italy and spain implies that lower toarcian zonal stratigraphy is diachronous between northern and southern europe there is evidence for partitioning of water masses between the north european shelf and the tethyan continental margin during the early jurassic

palaeobiogeographic patterns of the brachiopod assemblages of the iberian subplate during the late toarcian early aalenian jurassic abstract late toarcian aalenian brachiopod assemblages recorded in different basins located in and around iberia present a pattern of spatial and temporal distribution which enables two palaeobiogeographic biochoremas to be differentiated the iberian atlantic district iad which includes the lusitanian basin asturias and the basque cantabrian basin on one hand and the iberian mediterranean district imd the latter basically comprises the iberian range and the tortosa platform of the catalonian basin changes in the composition of the assemblages throughout the stratigraphical interval studied have enabled three main stages characterizing each palaeobiochorema to be recognized the first two assemblages reflect gradual individualization and isolation with frequent endemisms these two stages correspond to the iad1 iad2 imd1 and to the imd2 assemblages respectively as from the pseudoradiosa chronozone and during the aalensis and opalinum chronozones an increase in communication between the two districts can be observed as well as between these and other remote areas this stage is represented by the iad3 and the imd3 assemblages some of the brachiopods colonizing the districts are widely dispersed due to their capacity for expansion they have been found in other tethysian basins other species are exclusive to the district basins and appear to have originated in the areas close to them for the latter species the existence of two different evolutionary factories is proposed one that supplies species to the iad mainly from generic stocks as neozeilleria soaresirhynchia or praemonticlarella and another for the species reaching the basins of the imd clearly shared by other european and north african basins the atlantic evolutionary factory remains active until the aalenian and part of the early bajocian while the mediterranean is diluted since the aalenian

an attempt to constrain the age duration and eruptive history of the karoo flood basalt naude s nek section south africa we have carried out paleomagnetic sampling of a similar to 750 m sequence of the karoo large igneous province naude s nek pass south africa k ar dating cassignol gillot has been performed on four samples from the 650 m upper unit mean age 179 2 1 8 ma and a sample from the lower unit 184 8 2 6 ma a succession of two phases of volcanism is suggested the lower 25 flows 115 m thick have recorded a reversed polarity the next 23 flows 135 m thick are transitional and contribute a detailed record of the van zijl 1962 jurassic reversal the upper 38 flows 500 m thick have normal polarity directional groups dgs of lava flows with quasi identical remanence directions indicate eruption durations too short to have recorded geomagnetic secular variation and hence are interpreted as single eruptive events altogether 19 dgs and 10 sheet lobes yield a sequence of 29 distinct directions this could correspond to a total eruptive activity shorter than 3000 years less than one per mil of the total duration over which the section was emplaced we obtain a new paleomagnetic pole for south africa at similar to 180 ma lambda 75 2 degrees n phi 276 4 degrees e a 95 5 8 degrees n 19 which is consistent with earlier reports

recognition of diagenetic contribution to the formation of limestone marl alternations a case study from permian of south china abstract limestone marl alternations lmas have been extensively used in studies of sedimentology cyclostratigraphy and paleoclimatology however it has long been debated whether lmas are derived from primary sedimentation or from diagenetic alteration and the markers to distinguish one source from the other remain ambiguous in this study we investigate widespread permian lmas from various depositional settings in south china using traditional petrographic mineralogical and major element al2o3 vs tio2 methods as well as emerging trace and rare earth element ree analyses performed using solution based and in situ techniques the original depositional differences of the limestone and its coupled marl beds can be identified based on 1 the high volumes of siliciclastic minerals in the marls 2 unremarkable differential compaction 3 the recognizable signatures of the detrital admixture i e the al zr and th characteristics and 4 flattened shale normalized ree patterns diagenetic lmas are characterized by the compaction of fossils rare aragonite skeletons and abundant diagenetic clays sepiolite and talc preserved in the marl beds we also identified fully diagenetic lmas originating from primary carbonate sedimentation based on two almost completely consistent seawater like ree patterns with diagnostic positive la and negative ce anomalies la la sn 1 64 0 17 ce ce sn 0 73 0 05 superchondritic y ho 47 4 and depleted light rees relative to high rees pr yb sn 0 39 0 09 diagenesis also dominates the formation of lmas with limited terrigenous input in shallow water carbonate depositional environments it is likely that both the active metabolic processes in early diagenesis especially aerobic sulfide oxidation and the temporal palaeoceanographic conditions e g high levels of dissolved oxygen and sulfate play crucial roles in the genesis of the diagenetic lmas in the permian strata of south china

growth demise and dolomitization of miocene carbonate platforms on the marion plateau offshore ne australia abstract strontium isotope stratigraphy has been used to examine the timing of depositional events and dolomitization in two miocene carbonate platforms cored by ocean drilling program odp leg 194 just seaward of the great barrier reef the results provide firm constraints for correlating surfaces and depositional stages between the two platforms and thereby relating seismic sequences previously defined in the off platform sediments to the lithostratigraphic units described from cores in the seismically transparent platform top sites oyster bearing beds at the base of both platform successions yield early oligocene ages 29 31 ma thus dating initial transgression of the marion plateau s volcanic basement there followed a period of slow accumulation of shallow water grainstones rich in quartz and phosphate grains in late oligocene time 29 23 ma seismic megasequence a the main growth of the carbonate platforms took place in early to late miocene time 23 7 ma comprising five depositional sequences the first four of these seismic megasequence b are common to both platforms and terminated with a possible karst surface at 10 7 ma different sedimentologic expression of this megasequence in the two platforms reflects contrasting progradational versus aggradational geometries in the locations studied the final growth stage seismic megasequence c occurred only in the southern platform and terminated at 6 9 ma both platform demise events 10 7 and 6 9 ma approximately coincide with falls in global sea level combined with longer term trends of decreasing water temperature sr isotope ages of dolostones increase with depositional age and older dolostones in the southern platform have more coarsely crystalline and fabric destructive textures than overlying younger dolostones these relationships are consistent with dolomitization by normal seawater shortly after deposition and overprinting of multiple times of dolomite recrystallization and cementation in the deeper strata

carbonate systems along nutrient and temperature gradients some sedimentological and geochemical constraints research over the past several decades has clearly demonstrated that changes in the ocean environment have had major impacts on carbonate systems changes in climate ocean circulation and seafloor spreading rates have influenced temperature and seawater chemistry including carbonate saturation state and nutrient availability and thereby have determined boundary conditions for the biota that form carbonate platforms in turn the biota determine accumulation rates and facies zonations thus controlling platform geometry and facies dynamics in the first section of this paper we examine how nutrient availability influences carbonate facies associations we first discuss the role of temperature and nutrient gradients in the modern ocean and their influence on biotic associations then we discuss how carbonate sedimentation can be characterized along nutrient gradients in the second section we review proxies currently used to reconstruct paleoproductivity in open ocean environments and discuss their applicability to neritic carbonate systems we highlight the variety of existing proxies and their limitations and suggest that multiple lines of evidence are needed for valid interpretations our short review discusses sedimentological biogenic and geochemical proxies that can be used to reconstruct past nutrient fluxes and to constrain paleoceanographic controls over the distribution of carbonate associations however it also reveals that more data and case studies are needed that integrate shallow and deep water carbonate sequences and elucidate the links between temperature vs nutrient supplies changes and facies in ancient carbonate sequences

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

reconstruction of low temperature 100 c burial in sedimentary basins a comparison of geothermometer in the intracontinental paris basin abstract the thermal evolution of sediments in the shallowest part of sedimentary basins is challenging to investigate as most of the geothermometers are at their application limits this is typically the case of the callovian oxfordian claystones at the eastern border of the paris basin a recent 2000 m deep well penetrated the entire jurassic and triassic sedimentary series and permitted coring of sediments never reached by previous drilling in this part of the basin thanks to the use of several independent geothermometers apatite fission track thermochronology fluid inclusion microthermometry clay mineralogy and sedimentary organic matter evolution the burial history of the mesozoic series has been reconstructed modeled and calibrated using kinetic algorithms relevant to the various paleothermometers used in addition to these conventional methods an innovative approach was developed using the temperature dependence of the magnetic mineral assemblage within clay rich sediments mageval thermal modeling indicates that the callovian oxfordian and the lower triassic experienced maximum burial temperatures of 50 5 c and 90 10 c respectively i e about 25 c higher than present day this temperature offset implies the erosion of several hundred meters of sediments which depending on the thermal flux and conductivity considered most likely constituted upper cretaceous chalk deposits falling sea level resulted in the exposure and subsequent dismantling of the chalk cover at the beginning of cenozoic times the eastern border of the basin was then subjected to slow erosion and discrete tectonic deformation

the early toarcian anoxic event in the westernmost tethys subbetic paleogeographic and paleobiogeographic significance a positive delta 13 c excursion reveals an oceanic anoxic event in the subbetic corresponding to the westernmost end of the tethys during the early jurassic this positive delta 13 c excursion exists in five stratigraphic sections consisting of lower and middle toarcian pelagic sediments the positive delta 13 c excursion in the subbetic is located in the upper part of the early toarcian serpentinus approx falciferum biozone while in other tethyan regions alps apennines and dinarides it has been found in the lower part of the same biozone the most significant positive delta 13 c excursion detected in the subbetic is therefore about half a million years younger although other relative peaks had been detected this isotopic anomaly can be correlated with a maximum transgression that occurred earlier in the regions closer to the open sea of the tethys ocean other features of the anoxic event faunal crises and black shale deposits appear at different ages related t

tectonic and eustatic control on a mixed siliciclastic carbonate platform during the late oxfordian kimmeridgian la rochelle platform western france boreal and tethyan realms of western europe present significant sedimentological paleontological and stratigraphic differences the purpose of this study is to constrain regional versus global controls on the dynamics of a sedimentary system located at the interface of these two realms in order to better understand the origin of their differences detailed sedimentological palynofacies and calcareous nannofossil analyses were performed on two sections from the la rochelle platform western france the pas section includes part of the late oxfordian and early kimmeridgian and the rocher d yves section is assigned to the late kimmeridgian they correspond to monotonous marl argillaceous limestone alternations limestones are essentially mudstones with echinoderms bivalves and foraminifera that suggest low energy open marine conditions highly bioclastic and or peloidal deposits occur commonly and show wackestones to wacke pack grainstones textures these deposits indicate frequent high energy events and are interpreted as storm deposits marls dominate in the most proximal depositional environments while calcareous deposits are more important in more distal environments the rocher d yves section is globally more marly than the pas section suggesting a more proximal setting palynofacies are dominated by woody particles suggesting shallow water proximal depositional environments calcareous nannofossils are ascidian spicules coccoliths and schizospheres watznaueria britannica dominate calcareous nannofossil assemblages in the pas section the rocher d yves assemblages are quasi exclusively composed of cyclagelosphaera margerelii and indicate more proximal paleoenvironments than those of the pas section different orders of depositional sequences are defined with sequence boundaries corresponding to the most rapid relative sea level falls they are hierarchically stacked and correlate on the basis of ammonite zones with the sequences of contemporaneous sections from tethyan and boreal realms the stacking pattern of these sequences suggests an orbital control on sedimentation small medium and large scale sequences correspond to precession 20 ky cycles and to 100 ky and 400 ky eccentricity cycles respectively the elementary sequences have durations shorter than 20 ky the kimmeridgian was a period of global sea level rise that ended in the late kimmeridgian more proximal depositional environments in the rocher d yves section late kimmeridgian than in the pas section early kimmeridgian imply a progradation of the la rochelle platform during the kimmeridgian this progradation resulted from a slowdown of the subsidence in the aquitaine basin during the kimmeridgian corresponding to the first steps of atlantic ocean opening high frequency cycles on the la rochelle platform formed in sync with milankovitch orbital cycles while tectonics controlled the formation of the low frequency cycles

late oxfordian to late kimmeridgian carbonate deposits of nw switzerland swiss jura stratigraphical and palaeogeographical implications in the transition area between the paris basin and the tethys abstract geological sections of the shallow water carbonate dominated sedimentary system of the late jurassic reuchenette formation in northwestern switzerland have been studied between the southern jura mountains and the tabular jura the largest sections show a characteristic cyclic stacking pattern up to now the age of these sediments including the type section linking the boreal and tethyan realms was biostratigraphically poorly constrained in the tabular jura five 3rd order sequences can be assigned to the planula to eudoxus zone late oxfordian to late kimmeridgian using index fossils ammonites and ostracodes jank m 2004 new insights into the development of the late jurassic reuchenette formation of nw switzerland late oxfordian to late kimmeridgian jura mountains dissertationen aus dem geologisch palaontologischen institut der universitat basel 32 121 pp this time control and several new outcrops in combination with mineralostratigraphical and lithological marker beds allow the correlation and dating of the thickest sections of the reuchenette formation and thus serve to improve the previously estimated ages of their sequence boundaries the variability of stacking pattern and facies between sections also reveals distinctive changes in facies evolution related to late palaeozoic basement structures and synsedimentary subsidence these structures acted as important controlling factors for the sediment distribution of the reuchenette formation besides the sea level fluctuations the interplay of sea level changes and synsedimentary subsidence is outlined by lateral thickness variations and shifting depositional environments a close examination of these changes also sheds much light on the nature of platform topography in the transition area between the paris basin in the north and the tethys in the south or more generally between the boreal and tethyan realms during the planula to divisum time intervals the study area was a flat platform with a more or less uniform facies distribution which connected the above mentioned realms during the divisum to acanthicum time intervals this platform changed into a pronounced basin and swell morpoholgy with specific depositional environments and separated the paris basin from the tethys

a mesozoic time scale we present an integrated geomagnetic polarity and stratigraphic time scale for the triassic jurassic and cretaceous periods of the mesozoic era with age estimates and uncertainty limits for stage boundaries the time scale uses a suite of 324 radiomenc dates including high resolution 40 ar 39 ar age estimates this framework involves the observed ties between 1 radiometric dates biozones and stage boundaries and 2 between biozones and magnetic reversals on the seafloor and in sediments interpolation techniques include maximum likelihood estimation smoothing cubic spline fitting and magnetochronology

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

taphonomy and palaeoecology of high stress benthic associations from the upper jurassic of asturias northern spain abstract the late kimmeridgian terenes formation exposed on the coast of asturias northern spain displays a complex pattern of directed changes of grain size carbonate content and skeletal concentrations in its upper part here investigated the formation represents a protected shelf lagoon in which four major facies types are distinguished the nanogyra virgula mudstone 1 and the corbulomima concentrations 2 are characterized by concentrations of small bivalves the carbonate mudstone 3 contains pseudomorphs after gypsum crystals and thin crusts of gypsum occasionally in connection with thin microbial layers finally the silty to fine sandy marlstone and micrite and marly silt 4 is highly bioturbated and contains a moderately diverse benthic macrofauna these facies indicate a generally quiet environment punctuated by brief episodes of high water energy two low diversity macrobenthic assemblages can be recognized each of them strongly dominated by a single bivalve taxon the nanogyra virgula assemblage exhibits a higher diversity than the near monospecific corbulomima assemblage the former lived in well aerated waters of slightly reduced salinity and the latter in dysoxic waters of more strongly reduced salinity the environmental stress responsible for the extremely low species richness and evenness is thought to be multifactorial produced by reduced salinity dysoxic conditions and a soft substrate and resulted in simple food chains the eurytopic opportunist corbulomima was the only element of the shelly macrobenthos that was able to thrive in the shelf lagoon under these conditions it occurs in countless mm to cm thick pavements and shell beds which show evidence of winnowing influence of weak currents and occasionally of distal storms as can be deduced from the orientation pattern of shells these rhythmic corbulomima concentrations are explained as reflecting small scale climatic fluctuations between wetter stormier conditions leading to mixing of the water masses and enabling colonization of the lagoonal floor by the bivalve and drier more tranquil conditions the latter resulted in a stratified water mass and anoxia at the bottom superimposed on this rhythmic alternation are three higher orders of cycles which are partly climatic controlled partly reflect changes in relative sea level

numerical evaluation of mechanisms driving early jurassic changes in global carbon cycling the early jurassic early toarcian ca 183 ma carbon cycle perturbation is characterized by aabout 5 parts per thousand delta sup 13 c excursion in the exogenic carbon reservoirs a 1000 ppm rise in atmospheric co sub 2 and a 6 7 degrees warming two proposed explanations for this presumed global carbon cycle perturbation are the liberation of massive amounts of isotopically light ch4 from 1 gondwanan coals by heating during the intrusive eruption of the karoo ferrar large igneous province lip or 2 the thermal dissociation of gas hydrates carbon cycle modeling indicates that the release of ch4 from gondwanan coals synchronous with the eruption of the karoo ferrar lip fails to reproduce the magnitude or timing of the co sub 2 and delta sup 13 c excursions however sensitivity analyses constrained by a marine cyclostratigraphically dated delta sup 13 c record indicate that both features of geologic record can be explained with the huge input of about 15 340 24 750 gt c over about 220 k y a result possibly pointing to the involvement of hydrothermal vent complexes in the karoo basin the simulated release of 6000 gt c from gas hydrates also reproduces aspects of the early toarcian rock record but the large mass involved raises fundamental questionsmore about its formation storage and release less

the pliensbachian and tithonian extinction events the claim by raup and sepkoski1 that an approximately 26 myr mass extinction periodicity can be recognized on a global scale at family level over the past 250 myr has excited much attention and provoked speculation about an ultimate extraterrestrial cause2 10 while the purported periodicity can be challenged on grounds of both the inaccuracy of the geological timescale11 and the method of extinction analysis12 there can be no doubting the reality of at least some of the 12 proposed extinction events such as those at or near the end of the permian triassic and cretaceous others are less widely acknowledged further analysis by raup and sepkoski13 confirms the importance of two of these events within the jurassic at the end of the pliensbachian and tithonian stages i demonstrate here that marine invertebrate mass extinctions at approximately these times occurred on a regional not a global scale they can be related to severe reductions in habitat area provoked either by regression of epicontinental sea or by widespread anoxia

tracing of variabilities within a geological barrier by molecular organic geochemistry case of the callovo oxfordian sedimentary series in the east of the paris basin france abstract the callovo oxfordian claystones located at 500 m depth at bure meuse france are currently being investigated by andra the french national radioactive waste management agency for testing the feasibility of long term and deep geological nuclear waste disposal in order to evaluate its potential as a geological barrier it is very important to study assess and describe its physico chemical variability the molecular biomarker composition of 150 samples of these claystones and their surrounding limestones carry diverse information on the sources of the sedimentary organic matter the chemistry of the depositional environment the preservation and diagenesis conditions it also allows assessing the degree of lateral and vertical variability of the organic matter within these sedimentary series the abundance of unsaturated biomarkers the distribution of steroids and hopanoids and cpi values 2 prove the thermal immaturity of the organic matter the co occurrence of plankton bacteria and land plant biomarkers indicate that the organic matter is a mixture of marine and continental contributions the data also reveal that the organic matter was deposited under oxic and open sea conditions except for a brief event of photic zone anoxia at the beginning of the middle callovian in the claystones the geosynthesis of diasterenes is favored to the detriment of the formation of steranes especially in smectite rich levels and the organic matter is rapidly isolated from oxidizing then reducing conditions after the deposition due to the protective effect of clays on the scale investigated the claystones are characterized by a unique molecular facies and are thus homogenous from their organic content point of view yet detailed investigation of specific molecular families indicates changes related to major claystone limestone transitions the homogeneity of these claystones can be explained by the paleogeographic position of their depositional setting and the plane and sub horizontal paleotopography on which they were deposited this study demonstrates the efficiency of organic geochemistry in the assessment of the variability of geological barriers

the drowning of a carbonate platform an example from the devonian carboniferous of the southwestern holy cross mountains poland the broad middle devonian carbonate platform of the holy cross mountains was fragmented during the frasnian and afterwards submerged as isolated blocks and transformed into a topographic depression the section exposed in the ostrowka quarry illustrates a well documented drowning of the last small fragment seamount of this carbonate platform which submerged during late devonian and early carboniferous times the recognized facies succession reflects a progressive stepwise lowering of the sediment surface through time from a peritidal lagoonal environment to a deep water anoxic basin the frasnian shallow water carbonate platform is represented by lagoonal facies with peritidal sediments small scale deepening upward cycles punctuated with emersion surfaces are a feature of this stage they resulted from a combination and continuous balance between carbonate production subsidence and low order eustatic sea level fluctuations the carbonate platform aggraded at rates around 100 125 m ma the shallow water peritidal carbonates are separated from the post platform deposits by an unconformity surface developed during subaerial exposure the flooding of the faulted block of galezice in the pre late marginifera time and the subsequent initial drowning resulted primarily from a rapid sea level rise small dimension of the seamount and its cemented upper surface were the most important factors that facilitated the sediment removal and thus suppressed the sediment accumulation a condensed section was deposited on the top of the seamount its stratigraphic succession and rare cephalopod storm beds account for a model of redistribution of sediment over the swell disintegrated by small scale faulting during drowning the seamount traversed down through the photic zone at an average rate not higher than 20 25 m ma transformation of the swell into a basin accelerated in the late tournaisian anchoralis zone it is manifested by an increase of deposition rate and by a lithology of alternating limestones and clays with participation of fine grained calciturbidites the associated tephra deposits and syndepositional ferruginous hydrothermal mineralization were the result of extensional tectonics on the facies evolution the drowning was completed in the visean with deposition of black siliceous shales in the starved basin the death of the devonian carbonate platform in the galezice area illustrates well the famed paradox of drowned platforms as the subsidence rate was much slower during the drowning than during the phase of the platform aggradation

lowstand carbonates highstand sandstones the sedimentary facies sediment dynamics and sequence architecture of modern high energy shelves in the mid and high latitudes are largely governed by wave abrasion processes cool water carbonates may form there if the influx and or net accretion of siliciclastics is kept at a minimum little dilution of the carbonate produced in situ is generally promoted by a wide epicontinental shelf subdued topography of the adjacent mainland the predominance of limestone outcrops and an arid climate the aforementioned requirements are rarely met and thus will automatically lead to the formation of mixed siliciclastic cool water carbonates such an example is found in the early to mid miocene lagos portimao formation algarve s portugal which formed on a narrow high energy shelf of the atlantic ocean that was bounded by a mountain range the sediments of the formation consist of fossiliferous sandstone fs shell beds and rhodolith blankets along strike the stratification of the formation is monotonous for tens of kilometres and well exposed in coastal cliffs whereas no outcrops of dip sections exist the bulk skeletal composition of the sediments is typical for the warm temperate climatic zone various endo and epibenthic bivalves bryozoans coralline algae echinoderms gastropods and large foraminifers heterostegina in some very rare beds a few isolated not framework forming specimens of zooxanthellate corals porites tarbellastrea indicate temporally elevated surface water temperatures close to the lower threshold of the coral reef ecosystem in sandstones the fauna is well preserved and burrowing bivalves are commonly found in life position in limestone beds the state of preservation of the grains ranges from intact to disintegrated and abraded specimens we infer an accumulation of the shell beds through winnowing of fine materials siliciclastic sand and carbonate mud at wave abrasion depth and concentration of calcareous skeletons associated with the subsequent attraction of new epibiota in a complex shell bed the vertical alternation of fossiliferous sandstone and shell beds and in phase variations of the photo index photic biota vs bryozoans and bryozoan index bivalves vs bryozoans is envisaged to document variations of water depth and sea level sandstone units built up when wave abrasion depth wad rose above the sea floor during tst and early hst whereas the shell beds formed during lst when the wad for sand intersected with the sea floor clastic sediments were probably brought on the outer shelf during early transgression and by longshore currents sea level signatures inferred in the mixed siliciclastic cool water carbonate shelf setting of s portugal therefore significantly deviate from conventional concepts of carbonate sequence stratigraphy which were developed for flat topped platforms successful interpretations of ancient mixed sequences must therefore take into consideration the processes of production concentration and accretion of the carbonate sediments

biosedimentology of the early jurassic post extinction carbonate depositional system central high atlas rift basin morocco this study documents a liassic example of the long ranging effects of mass extinction on carbonate systems biohistoric constraints inherent in the liassic carbonate depositional system are deciphered from normal marine sub tidal deposits of the central high atlas rift basin morocco through hettangian sinemurian to early toarcian times the integration of results from the analysis of lithofacies depositional geometries microfacies macrobenthos carbonate build ups carbon and oxygen stable isotopes and rare earth element yttrium distribution patterns allows the intrinsic or biohistoric control on the central high atlas deposits to be separated from extrinsic factors such as basin development and palaeoclimate the survival interval in the aftermath of the end triassic mass extinction persisted until the early sinemurian indicated by a severely depleted carbonate system impoverished in skeletal organisms a tectonic pulse at the early to late sinemurian boundary interval caused a basin widening with immigration of a marine fauna however until the latest sinemurian macdonelli subzone of the raricostatum zone the deposits were dominated by filter feeding benthic heterotrophs sponges brachiopods polychaetes and crinoids during this stage primary production within the enlarged basin must have been largely planktonic and there was a net flux of organic matter to the sea floor oxygen minimum zone a regional radiation of organic walled phytoplankton is inferred to explain the selective success of the filter feeding community and the occurrence of sponge mounds thus significant effects of the end triassic mass extinction are still present during the late sinemurian through almost the entire pliensbachian a highly productive shoal rimmed carbonate platform existed it developed subsequent to tectonic reorganization and a marine recirculation event radiolarian facies 13c 1 1 strongly negative ce anomaly photosymbiotic sediment producers mainly large bivalves now state the success of specialists and environmental equilibrium conditions in the latest pliensbachian the climax stage was reached with the development of a coralgal reef rimmed carbonate platform the liassic carbonate depositional system experienced a terminal multicausal early toarcian drowning event during which most of the large bivalves became extinct

impact of basin burial and exhumation on jurassic carbonates diagenesis on both sides of a thick clay barrier paris basin ne france several diagenetic models have been proposed for middle and upper jurassic carbonates of the eastern paris basin the paragenetic sequences are compared in both aquifers to propose a diagenetic model for the middle and late jurassic deposits as a whole petrographic optical and cathodoluminescence microscopy structural fracture orientations and geochemical 18o 13c ree studies were conducted to characterize diagenetic cements with a focus on blocky calcite cements and their connection with fracturation events four generations of blocky calcite cal1 cal4 are identified cal1 and cal2 are widespread in the dominantly grain supported facies of the middle jurassic limestones about 90 of the cementation whereas they are limited in the oxfordian because grain supported facies are restricted to certain stratigraphic levels cal1 and cal2 blocky spars precipitated during burial in a reducing environment from mixed marine meteoric waters and or buffered meteoric waters the meteoric waters probably entered aquifers during the late cimmerian jurassic cretaceous boundary and late aptian early cretaceous unconformities the amount of cal2 cement is thought to be linked to the intensity of burial pressure dissolution which in turn was partly controlled by the clay content of the host rocks cal3 and cal4 are associated with telogenetic fracturing phases the succession of cal3 and cal4 calcite relates to the transition towards oxidizing conditions during an opening of the system to meteoric waters at higher water rock ratios these meteoric fluids circulated along pyrenean oligocene and alpine fractures and generated both dissolution and subsequent cementation in oxfordian vugs in mud supported facies and in poorly stylolitized grainstones however these cements filled only the residual porosity in middle jurassic limestones in addition to fluorine inputs fracturation also permitted inputs of sulphur possibly due to weathering of triassic or purbeckian evaporites or h2s input during paleogene times

early jurassic schizosphaerellid crisis in cantabria spain implications for calcification rates and phytoplankton evolution across the toarcian oceanic anoxic event 1 the toarcian oceanic anoxic event 183 myr ago represents a global perturbation marked by increasing organic carbon burial and a general decrease in calcium carbonate production likely triggered by elevated carbon dioxide levels in the atmosphere here we present quantitative analyses of calcareous nannofossil diversity and abundance from the castillo de pedroso section in cantabria northern spain we compare these data with geochemical data c and o isotopes obtained from biogenic and bulk carbonate records in order to highlight the response of calcareous phytoplankton to major climatic and paleoceanographic changes the pliensbachian toarcian boundary is characterized by an abrupt decrease in abundance of schizosphaerella punctulata the most important lithogenic contributor to hemi pelagic carbonates in the early jurassic the early toarcian nannofloral assemblages show an increase in abundance of mitrolithus jansae and small sized r selected taxa and a progressive decrease in s punctulata percentages the deep dwellers m jansae and s punctulata experienced a major crisis slightly prior to the deposition of the toarcian black shales that are characterized by high abundances of eutrophic taxa such as lotharingius spp and biscutum spp the return of s punctulata associated with lower percentages of eutrophic taxa was observed just above the toarcian black shales the toarcian episode reveals that high co2 levels and increasing primary productivity probably triggered a shift in abundance from highly calcified nannoliths such as s punctulata and m jansae to small sized r selected coccoliths that overall record a biocalcification crisis at the onset and during the toarcian episode

black shales on the basin margin a model based on examples from the upper jurassic of the boulonnais northern france abstract organic rich shales were deposited during two phases of relative sea level rise in the kimmeridgian late jurassic basin margin sections of the boulonnais n france pyrite framboid analysis indicates that bottom waters were euxinic during substantial periods of organic rich shale formation and th u ratios and degree of pyritisation of fe suggest severe oxygen restriction whilst palaeoecological and sedimentological evidence suggests that seafloor oxygenation events were frequent interbedded hummocky cross stratified sandstones indicate deposition above storm wave base correlation of lateral facies changes reveals that the black shales record deposition beneath a nearshore zone of oxygen poor waters that contracted in lateral extent during parasequence formation the boulonnais black shales are similar to other varieties of transgressive black shale in that they are developed upon surfaces of marine starvation but they differ in that they pass down dip into better oxygenated facies they are therefore classified as transgressive nearshore tn black shales that do not record the feather edge of basinal conditions deposition is interpreted to have occurred beneath a small volume of sub thermocline bottom waters that were readily de oxygenated whilst anoxia was less readily developed in more offshore settings due to the greater volume of sub thermocline water why such conditions should pertain only during initial stages of base level rise remains obscure

relative control of paleoceanography climate and eustasy over heterozoan carbonates a perspective from slope sediments of the marion plateau odp leg 194 in this paper we explore the relative control of paleocean ography eustasy and water temperature over the evolution of a car bonate slope system deposited on the marion plateau northeastern australia growth of several carbonate platforms started in the early miocene on this plateau and although they occurred in low latitude subtropical waters they are composed mainly of heterozoan organisms we investigated an upper to distal slope transect drilled during odp leg 194 and located close to the northern marion platform we re constructed mass accumulation rates of carbonate as well as the evo lution in the ratios of carbon and oxygen stable isotopes power spec trum analysis of the carbon isotope record revealed the existence of cycles with main frequencies centered around 409 kyr and 1800 kyr we interpret the 409 kyr cycle as being paced by changes in the ec centricity of the earth orbit and we suggest that the 1800 kyr cycle could be linked to long term eustatic changes finally on the basis of the timing of changes in mass accumulation rates of carbonate we infer that the strength and direction of oceanic currents affected sedimen tation on the marion plateau by shifting depocenters of slope sedi mentation a process probably further modulated by sea level changes we argue that the evolution and demise of the heterozoan carbonate systems present on the marion plateau were controlled mainly by the evolution of strong benthic currents and that eustasy and water tem perature alone did not account for the drowning of the platforms in the mid miocene

potassium argon dating of fine grained basalts with massive ar loss application of the 40ar39ar technique to plagioclase and glass from the kirkpatrick basalt antarctica 40ar39ar incremental heating measurements are reported for separated plagioclase and matrix fractions and a glass sample of the kirkpatrick basalt from victoria land antarctica these results are used to address the limitations of whole rock analyses of glassy or very fine grained basalts the use of plagioclase for determining ages of such rocks the ar behavior of matrix glass and feldspar components the use of k cl ratios in interpretation of step heating results and the age of the kirkpatrick basalt the precise age of the kirkpatrick basalt has been a long standing problem the wide range of reported k ar dates has been attributed to loss of ar despite massive ar loss from the matrix plagioclase is shown to yield good 40ar39ar plateaus plateaus are observed for increments above 700 c and are defined not only by consistent apparent ages but also appropriately low k ca and high k cl ratios cl relations help identify ar released from small amounts of matrix which can seriously contaminate a plagioclase separate an age of 176 8 1 8 ma defines the time of formation of the youngest lava at mt frustum in north victoria land a glass sample from south victoria land gives the same age indicating that terrestrial basaltic glasses as old as jurassic do not inherently lose ar the step heating profile of glass with very fine crystals shows discordance which is an artifact of ar recoil during irradiation

climatic fluctuations and seasonality during the kimmeridgian late jurassic stable isotope and clay mineralogical data from the lower saxony basin northern germany abstract in previous palaeoclimatic models the kimmeridgian stage has been defined as a typical greenhouse time interval with weak latitudinal gradients however palaeoclimatic information based on biogenic low mg calcite 18o for the kimmeridgian is still limited here shell materials n 81 precipitated by brachiopods oysters and trichites bivalves from the lower saxony basin northern germany are evaluated for their potential to act as archive for marine sea surface temperatures furthermore the associated clay mineral assemblages based on bulk materials are used to infer hinterland weathering patterns and overall climatic conditions simultaneously the established sea surface temperature curve reveals an overall slightly warming trend through the kimmeridgian weak seasonality 4 c in sea surface temperatures is documented by oxygen isotope variations measured along the growth lines of a large trichites shell distinctly higher 18o values observed in the lower kimmeridgian late baylei chron are interpreted to be related to the short term influx of cooler boreal water masses judging from the corresponding smectite dominated interval however the positive oxygen isotope anomaly may also be partly explained by a relatively drier climate causing enhanced 18oseawater values due to intensified evaporation the kaolinite illite chlorite ratio points to a slightly long term decrease in humidity through the kimmeridgian on the landmasses surrounding the lsb the short term fluctuations in humid arid conditions correlate significantly with sea level changes with humid climates accompanying high sea levels and arid climates accompanying low sea levels results from this study provide new insights into late jurassic climatic dynamics and help to establish a reliable subboreal late jurassic sea surface temperature curve

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

integrated stratigraphy of the kimmeridge clay formation upper jurassic based on exposures and boreholes in south dorset uk for the purposes of a high resolution multi disciplinary study of the upper jurassic kimmeridge clay formation two boreholes were drilled at swanworth quarry and one at metherhills south dorset uk together the cores represent the first complete section through the entire formation close to the type section we present graphic logs that record the stratigraphy of the cores and outline the complementary geophysical and analytical data sets gamma ray magnetic sus ceptibility total organic carbon carbonate 13 c org of particular note are the new borehole data from the lowermost part of the formation which does not crop out in the type area detailed logs are available for download from the kimmeridge drilling project web site at http kimmeridge earth ox ac uk of further interest is a mid eudoxus zone positive shift in the 13c org record a feature that is also registered in tethyan carbonate successions suggesting that it is a regional event and may therefore be useful for correlation the lithostratigraphy of the cores has been precisely correlated with the nearby cliff section which has also been examined and re described magnetic susceptibility and spectral gamma ray measurements were made at a regular spacing through the succession and facili tate core to exposure correlation the strata of the exposure and core have been subdivided into four main mudrock lithological types a medium dark dark grey marl b medium dark dark grey greenish black shale c dark grey olive black laminated shale d greyish black brownish black mudstone the sections also contain subordinate amounts of siltstone limestone and dolostone comparison of the type section with the cores reveals slight lithological variation and notable thick ness differences between the coeval strata the proximity of the boreholes and different parts of the type section to the purbeck isle of wight disturbance is proposed as a likely control on the thickness changes

sequence sequence stratigraphy sea level changes and depositional systems in the cambro ordovician of the north china carbonate platform abstract the cambro ordovician strata in north china were deposited over a very extensive craton extending some 1500 km east west and 1000 km north south the dominantly shallow water carbonate succession reaches up to 2000 m in thickness and two megasequences transgressive regressive cycles can be distinguished lower cambrian through lower ordovician strata and middle through upper ordovician strata separated by a major palaeokarst the first megasequence consists of nine sequences which are generally 50 150 m in thickness the lower cambrian sediments consist of phosphorites and phosphatic sandstones deposited during the flooding of the craton carbonates mudrocks and evaporites were deposited in the early cambrian under an arid climate laying the foundation for the subsequent long period of shallow water carbonate deposition which lasted some 70 m y the middle and lower upper cambrian sequences consist predominantly of mudrocks and storm deposits tempestites in the lower part and oolitic grainstones and tidal flat lime mudstones in the upper part these represent outer mid and mid inner ramp depositional systems respectively of the transgressive and highstand systems tracts these sequences have strong similarities with the grand cycles in the cambro ordovician successions of north america in the upper cambrian there is a distinctive unit of glauconitic purple red mudstone several metres thick which is interpreted as the deposits of the maximum flooding of the first megasequence in the upper cambrian there was a phase of tilting of the north china carbonate platform to the north and storm deposits especially intraclastic conglomerates and hummocky cross stratified grainstones packstones were very common at this time also common in upper middle and lower upper cambrian strata are stromatolitic thrombolitic bioherms several metres in diameter the upper upper cambrian through lower ordovician strata are dominantly fine grained limestones and dolomites deposited in shallow subtidal and inter to supra tidal environments on a low energy epeiric sea platform this part of the succession is the regressive part of the first megasequence so that overall the platform shows an evolution from platform initiation to platform foundation to a ramp depositional system and then an extensive epeiric platform on a small scale the succession is composed of metre scale shallowing upward cycles parasequences arranged into cycle sets of 10 30 m thick the middle upper ordovician megasequence consists mostly of shallow water carbonates with several thick evaporite units minor palaeokarsts and palaeosoils separate the sequences which are composed of metre scale cycles regional uplift affected the north china platform in the ordovician and sedimentation did not resume until the carboniferous there is a good correlation of the two transgressive regressive megasequences described here with the global 2nd order relative sea level curve for the cambro ordovician

correlation of reefal oxfordian episodes and climatic implications in the eastern paris basin france oxfordian reefal episodes of lorraine and burgundy have a long time been considered as contemporaneous biostratigraphic data and sequential evolutions peculiar to each region indicate their structural autonomy during oxfordian times a north south oriented well logging transect shows that during the middle oxfordian a shallow reefal platform developed in lorraine while thin deeper deposits occurred in burgundy in spite of their different ages reefal episodes of middle oxfordian in lorraine and upper oxfordian in burgundy exhibit a broadly similar vertical evolution of coral communities during the late oxfordian the contemporaneous occurrence of a diversified assemblage in the burgundy region a colder coral assemblage characterized by eurytopic genera and the decrease in seawater isotopic temperatures in lorraine can be explained by a shift in trophic conditions a climatic change related to structural rearrangements in this strategic place and a modification of oceanic circulations between the arctic and the tethyan regions

zircon upb and hornblende 40ar39ar ages for the dufek layered mafic intrusion antarctica implications for the age of the ferrar large igneous province abstract new high precision zircon u pb ages for the dufek intrusion establish the crystallization age for the only layered mafic intrusion sensu stricto known in the ferrar igneous province antarctica one of the largest igneous provinces in the world three concordant zircon fractions from the capping lexington granophyre yield an age of 183 9 0 3 ma 2 which we interpret as the crystallization age for the dufek intrusion concordant zircon fractions from a silicic dike crosscutting the upper layered gabbroic sequence yield a slightly younger crystallization age of 182 7 0 4 ma 2 for both samples agreement within errors between the two u pb and 207 pb 206 pb ages for three fractions each with a unique set of physical and chemical characteristics demonstrates that inheritance of older zircon components from the country rocks was imperceptible it also suggests that assimilation or anatexis of the lower paleozoic country rocks was not the dominant mechanism in the formation of the granophyre these new u pb dates agree within analytical errors with recent zircon and baddeleyite u pb ages for dolerite sills in both the ferrar and karoo igneous provinces which demonstrates the vastness of the rift axis along which simultaneous magmatic activity occurred contemporaneity between the dufek intrusion and other ferrar group rocks supports the possibility that this pluton acted as a conduit for magmas of the widely distributed ferrar sills and flows hornblende 40 ar 39 ar ages for the lexington granophyre 175 2 ma barely overlap with those for a silicic dike 179 2 ma in the layered gabbro section just below the granophyre the younger of the two hornblende ages may be explained by degassing of inclusions or by protracted hydrothermal alteration preventing the ar ar geochronometer form becoming a closed system in the higher level granophyre until after it had done so in the more deeply positioned silicic dike the 179 2 ma age of the dufek silicic dike is interpreted to represent cooling through the ar retention temperature for hornblende of about 500 c combining this cooling age with the u pb crystallization age of 182 7 0 4 ma yields a cooling rate for the dike of approximately 100 c m y inasmuch as this rate is not rapid it can be inferred that the bulk of the dufek intrusion was still fairly hot when the dated silicic dike was emplaced

strontium isotopes in early jurassic seawater abstract the analysis of well preserved well dated belemnites and oysters from the jurassic of great britain has resulted in a well constrained detailed seawater strontium isotope curve for the early jurassic the preservation of fossil low mg calcite was monitored using mn fe 13 c and 18 o iron was the most useful indicator with about 75 of the samples containing more than 150 ppm fe showing 87 sr 86 sr ratios elevated relative to adjacent points on the curve high mn concentrations less often correlated with elevated 87 sr 86 sr ratios however low mn concentrations 87 sr 86 sr 13 c and 18 o proved to be insensitive to diagenesis as it affects 87 sr 86 sr the principal features of the strontium isotope curve include a rise to about 0 70772 in the latest triassic and earliest jurassic hettangian from the hettangian the curve begins a roughly linear descent through the sinemurian and pliensbachian following a small levelling off and increase in the late pliensbachian the curve falls rapidly to its early jurassic minimum of 0 70706 it then gently increases through the toarcian until the falciferum zone where it shows an apparently abrupt increase to 0 70719 before continuing its slow increase to 0 70728 in the aalenian bajocian middle jurassic this reversal of the downwards trend established in the sinemurian and pliensbachian had not been previously identified the sinemurian and pliensbachian section of the curve potentially allows correlation and dating to within 1 or 2 ammonite subzones 0 5 to 1 ma

a u pb and 40ar 39ar time scale for the jurassic published time scales provide discrepant age estimates for jurassic stage boundaries and carry large uncer tainties the u pb or 40 ar 39 ar dating of volcaniclastic rocks with precisely known stratigraphic age is the preferred method to improve the calibration a radiometric age database consisting of fifty u pb and 40 ar 39 ar ages was com piled to construct a revised jurassic time scale accepted ages have a precision of 5 ma 2 or better and are con fined to no more than two adjacent stages the majority of these calibration points result from integrated bio and geochronologic dating in the western north american cordillera and have not been previously used in time scales di rect dates are available only for the triassic jurassic boundary and the initial boundary of the crassicosta chron and the callovian stage the chronogram method was used to estimate all early and early middle jurassic zone boundaries attempted here for the first time late middle jurassic substage boundaries and late jurassic stage boundaries signif icant improvement is achieved for the pliensbachian and toarcian where six consecutive zone boundaries are deter mined the derived zonal durations are disparate varying between 0 4 and 1 6 ma the latest jurassic isotopic database remains too sparse therefore chronogram estimates are improved using interpolation based on magnetochronology the initial boundaries of jurassic stages are proposed as follows berriasian jurassic cretaceous 1418 18

climatic fluctuations and seasonality during the late jurassic oxfordian early kimmeridgian inferred from δ18o of paris basin oyster shells abstract oxygen isotope data from biostratigraphically well dated oyster shells from the late jurassic of the eastern paris basin are used to reconstruct the thermal evolution of western tethyan surface waters during the early oxfordian early kimmeridgian interval seventy eight oyster shells were carefully screened for potential diagenetic alteration using cathodoluminescence microscopy isotope analyses were performed on non luminescent parts of shells n 264 intra shell 18 o variability was estimated by microsampling along a transect perpendicular to the growth lines of the largest oyster shell the sinusoidal distribution of the 18 o values along this transect and the dependence of the amplitude of variations with bathymetry suggest that intra shell variability reflects seasonal variations of temperature and or salinity average amplitudes of about 5 c in shallow water environments and of about 2 3 c in deeper offshore environments are calculated these amplitudes reflect minimum seasonal temperature variation our new data allow to constrain existing paleotemperature trends established from fish tooth and belemnite 18 o data and are in better agreement with paleontological data more specifically a warming trend of about 3 c is reconstructed for oceanic surface waters during the early to middle oxfordian transition with maximum temperatures reaching 24 c in the transversarium zone late middle oxfordian from the transversarium zone to the bimmamatum zone a cooling of about 7 c is indicated whereas from the bimmamatum zone temperatures increased again by about 7 c to reach 24 c in average during the cymodoce zone early kimmeridgian

upper cambrian carbonate platform evolution elvinia and taenicephalus zones pterocephaliid ptychaspid biomere boundary northwestern wyoming abstract the pterocephaliid ptychaspid biomere boundary is an upper cambrian extinction horizon that can be used to correlate mixed carbonate siliciclastic strata in northwestern wyoming the biomere boundary is defined by the change between the elvinia and taenicephalus zones of the standard north american trilobite zonation it is also signaled chemostratigraphically by a positive trend in carbon isotope ratios thus both biostratigraphic horizons and carbon isotope data are used to constrain the position of the biomere boundary in northwestern wyoming study of 21 stratigraphic sections reveals the presence of distinct facies belts for the middle and upper elvinia zone and lower taenicephalus zone these are interpreted to reflect deposition in three distinct paleoenvironments 1 oolitic shoal 2 intrashelf basin and 3 inner platform margin following a major hiatus in sedimentation in wyoming during much of pterocephaliid biomere time a healthy shallow water carbonate factory was reestablished during elvinia zone time this produced abundant deposits of oolitic and skeletal packstone in the shoal environment and an areally extensive thrombolite boundstone facies in the intrashelf basin setting approximately coincident with the biomere boundary extinction event irvingella major time ooid production was terminated and the thrombolites were drowned the correlation of this major change in the pattern of sedimentation allows for the recognition of parts of two depositional sequences in the study area this drowning event sequence boundary may also be coeval with the accumulation of transported shallow water carbonate deposits in an inner platform margin environment during early taenicephalus zone time sedimentation rates were apparently reduced and the entire study area is marked by thin concentrations of trilobite and brachiopod shells the nonskeletal carbonate factory was never reestablished in the former shoal environment where thick successions of homogeneous lime mud accumulated during the rest of taenicephalus zone time flat pebble conglomerate and shale accumulated in the storm influenced intrashelf basin during this time sea level change and changes in seawater chemistry likely both played roles in the drowning event across the elvinia taenicephalus boundary a positive trend in carbon isotope values across the pterocephaliid ptychaspid biomere boundary is observed in the six sections analyzed this is consistent with previous studies that indicated that the mass extinction occurs within a regional shift towards positive values and this may reflect the development of low oxygen conditions on the shelf the global significance of these isotopic trends changes in relative sea level and the mass extinction has not been confirmed although recent study of the extinction event at the base of the pterocephaliid biomere has revealed a similar trend towards positive carbon isotope values that is worldwide

the oldest deep sea ophiomorpha and scolicia and associated trace fossils from the upper jurassic lower cretaceous deep water turbidite deposits of sw bulgaria deep sea trace fossils of the nereites ichnofacies occur in the uppermost kimmeridgian berriasian deep water turbidite deposits of the kostel formation in sw bulgaria the trace fossil assemblage contains tithonian ophiomorpha isp and ophiomorpha annulata which are the oldest deep sea representatives of this ichnogenus they indicate much older invasion of ophiomorpha into deep sea which was hitherto dated as to mid cretaceous it is not clear whether the invasion failed or ophiomorpha survived in deep sea refuge and became widespread after improving oxygenation of the deep seas after the cenomanian turonian anoxic event tithonian scolicia produced by irregular echinoids exhibits a similar distribution pattern

a sequence stratigraphy of the kimmeridgian and bolonian stages late jurassic wessex weald basin southern england a sequence stratigraphic framework for the late jurassic kimmeridgian and bolonian stages of the wessex weald basin southern england is proposed based on the integration of sedimentological geophysical and geochemical data the nerc funded rapid global geological events rgge boreholes of swanworth quarry 1 and 2 and metherhills 1 are used as reference sections eleven complete depositional sequences and their component systems tracts are recognized within the kimmeridge clay formation bounded by 12 sequence boundaries km1 12 seventy four boreholes have been used in this study during the kimmeridgian a major transgression associated with tectonic movements led to a marked change in basin geometry major deepening of the sea during the late kimmeridgian eudoxus zone led to a change from unconformities of basinwide extent to those confined to the basin margins the progressive deepening of the basin towards a highstand in the mid bolonian wheatleyensis to pectinatus zones was associated with a broad scale change in sedimentary faunal and geochemical characters the layer cake basin architecture and thickening of the kimmeridge clay formation towards the basin centre suggests a dominantly aggradational system the partially enclosed nature of the kimmeridgian and bolonian seas generated basin dynamics more analogous to those of modern day meromictic lakes consequently sequence stratigraphic approaches derived from continental shelf margins are inappropriate in epicontinental basins of this type

organic facies variability during the toarcian oceanic anoxic event record of the grands causses and quercy basins southern france abstract the early toarcian is marked worldwide by major environmental changes that resulted in organic rich black shale deposition the toarcian oceanic anoxic event t oae this organic rich sedimentation is particularly recorded in the grands causses gcb and quercy qb basins the main objectives of this study are the characterization through organic petrology and geochemistry techniques of the organic matter om of the late pliensbachian early toarcian sedimentary successions of these basins and the definition of the organic facies assessing their implications in the evolution of depositional paleoenvironments in the gcb sedimentation occurred during the late pliensbachian in a well oxygenated water body total organic carbon toc 0 6 wt and low amorphous organic matter aom proximal to the terrestrial source area high terrestrial contribution with marine influence in the lattermost pliensbachian a shallowing of the water column is observed with decrease of marine influence and separation from the terrestrial source area toc 0 9 wt aom and zooclasts co dominate under an arid climate classopollis ssp from the tenuicostatum to early serpentinum chronozones a restricted and stagnated environment toc 5 7 wt aom dominates is implemented from middle to late serpentinum chronozone the reestablishment of the oxygen levels decrease in toc and aom takes place as well as paleoceanographic circulation patterns in the qb the late pliensbachian to earliest toarcian is characterized by low toc 0 2 wt with sedimentation occurring in a shallow oxygenated proximal water body amorphous hydrozoans dominate separated from the terrestrial source area with arid climate classopollis ssp and with episodes of emersion from the semicelatum subchronozone to serpentinum chronozone the development of dysoxic to anoxic conditions toc 4 2 wt takes place associated with water column stratification and more effective non carbonate sedimentation and with an increase in water level for the lattermost serpentinum chronozone shallowing of a more oxidizing water body with some oxygen depletion still present is proposed the differences in these paleoenvironmental depositional contexts further demonstrate that although the t oae has a global character local control mechanisms in these basins play a pivotal role furthermore the first occurrence of hydrozoans namely its free swimming medusoid forms is described in organopalynological preparations of sediments from the pliensbachian toarcian and their first paleoenvironmental application in a palynofacies based study is made

benthic foraminiferal morphogroups of mid to outer shelf environments of the late jurassic prebetic zone southern spain characterization of biofacies and environmental significance abstract benthic foraminiferal assemblages belonging to a mixed carbonate siliciclastic shelf succession of the oxfordian upper jurassic in the prebetic southern spain were analyzed the faunal data obtained on thin sections of strongly lithified sediments allowed the detailed differentiation of a foraminiferal morphogroups system to be applied to the interpretation of paleoenvironmental conditions eleven morphogroups were differentiated according to shell composition general morphology number of chambers and mode of coiling paleoenvironmental analysis combines these features with inferred life style epifaunal shallow infaunal and deep infaunal and feeding strategy suspension feeder deposit feeder herbivores etc of the foraminifera analogies and differences regarding previously established morphogroup systems could be outlined accordingly in the prebetic oxfordian distribution trends of foraminiferal morphogroups allow for a comparison of mid to outer shelf environments occupying the south iberian paleomargin indicating that nutrient supply was the most important factor controlling morphogroup development the mid shelf settings are dominated by epifaunal active herbivores phytodetritivores in shallow to deep substrate position of the redox boundary the outer shelf is dominated by agglutinated and infaunal detritivore bacterial scavenger morphogroups revealing a deep substrate position of the redox boundary particularly favorable trophic conditions in mid shelf environments are related with higher phytodetritus input from more proximal and shallower shelf areas

foraminiferal assemblages extinctions and appearances associated with the early toarcian oceanic anoxic event in the llanbedr mochras farm borehole cardigan bay basin united kingdom abstract the uppermost pliensbachian lower toarcian sediments recovered from llanbedr mochras farm borehole north wales uk were deposited in the cardigan bay basin and mainly consist of alternating marls and marly limestones the current study analyses the foraminiferal assemblages from the cored interval 143 m that has been assigned to the spinatum zone upper pliensbachian to the lower part of the bifrons zone middle toarcian the foraminiferal assemblages are dominated by the suborders lagenina and robertinina four main ecostratigraphic intervals have been identified based on changes in the foraminiferal assemblages that occurred before during and after the toarcian oceanic anoxic event t oae ecostratigraphic interval i upper part of the spinatum zone is characterized by a diverse assemblage with specialist opportunist and intermediate forms this assemblage is interpreted to represent a phase that pre dates the biotic crisis the ecostratigraphic interval ii tenuicostatum zone shows an abrupt increase in opportunist forms such as the genus reinholdella and a facultative opportunist such as paralingulina tenera which was tolerant to oxygen depleted conditions this second interval represents the initial biotic crisis phase in response to decreasing oxygenation the ecostratigraphic interval iii is considered the peak of the biotic crisis coincident with the negative carbon isotopic excursion at the base of the serpentinum zone and characterized by the dominance of the opportunist reinholdella 87 97 of the assemblage and low diversity the ecostratigraphic interval iv upper part of serpentinum zone and lower part of bifrons zone is characterized by an increase of diversity and an abrupt decrease in reinholdella this assemblage is interpreted to reflect the increased availability of oxygen from deep infaunal to epifaunal microhabitats and the return to normal conditions at the sea bottom ecostratigraphic fluctuations in the mochras foraminiferal assemblages across the t oae event are comparable with those from other parts of the uk the lusitanian basin portugal the umbria marche basin italy and the atlassic basin north africa in addition a foraminiferal turnover is evident across the pliensbachian toarcian boundary and the t oae and reflects the effects of the early jurassic biotic crisis on benthic foraminifera controlling factors of the biotic crisis are discussed regarding that anoxic conditions do not necessarily have a lethal effect on all foraminiferal species and other oceanographic and environmental factors need consideration fragmentation of epicontinental platforms sea level changes crisis of carbonate productivity and temperature changes

sr and nd isotopes at the prmian triassic boundary a record of climate change abstract we present a detailed curve of seawater 87sr 86sr for the middle permian to triassic based on analyses of conodonts from overlapping sections in the u s a pakistan correlated using conodont biostratigraphy the isotope ratio decreased in the middle permian at an average rate of 0 000062 ma 1 reached a minimum in the capitanian 257 258 ma and increased in the late permian at an average rate of 0 000097 ma 1 the late permian rate of increase was roughly two and a half times greater than the average increase over the past 40 ma and approximately equal to the highest cenozoic rates which occurred over much shorter time intervals modeling results suggest that decreasing middle permian 87sr 86sr ratios were driven by changes in the riverine sr flux to the oceans while increasing ratios in the late permian triassic are attributed to both increased riverine 87sr 86sr and flux the reduced middle permian riverine flux coincides with extreme continental aridity associated with the formation of pangea and recorded by massive evaporite deposits in addition mountains in the equatorial region of pangea may have created a rain shadow thereby minimizing precipitation in regions that currently contribute the bulk of chemical weathering products to the ocean increasing riverine 87sr 86sr in the late permian is suggested by the observation that 143nd 144nd values decrease at the same time however the source of radiogenic sr is not known frequently cited mechanisms for increasing 87sr 86sr in runoff such as glaciations and continent to continent collisions coincide instead with decreasing seawater 87sr 86sr in the middle permian one possible source may have been deep erosion into older orogens associated with a dramatic increase in chemical weathering in the late permian the cause of enhanced weathering appears to have been increased levels of atmospheric co2 with associated global warming and increased humidity proposed sources of co2 include dissociation of gas hydrates and oxidation of organic matter during extreme sea level regression as well as volcanic emissions from siberian traps eruptions continental floral and faunal distributions are consistent with this interpretation as are oceanic 13c patterns and variations in shallow water sediment lithologies

a short interval of jurassic continental flood basalt volcanism in antarctica as demonstrated by 40ar39ar geochronology a continental flood basalt province the ferrar group kirkpatrick basalt and ferrar dolerite crops out along 3000 km of the transantarctic mountains in antarctica and is temporally related to the break up of gondwanaland although a wide range of dates between 90 and 193 ma have been published for the kirkpatrick basalt it is now recognized that the young dates reflect non ideal behavior of ar in the matrix in order to refine the geochronology feldspar separates have been analyzed by the 40ar39ar incremental heating method the main objectives are to constrain the duration of extrusive activity and the timing of volcanism along the outcrop belt basalt samples have been studied from the three principal outcrop areas yielding the following apparent ages central transantarctic mountains 176 8 0 5 ma south victoria land 176 4 0 4 ma north victoria land 176 6 0 7 ma ages from different stratigraphic levels within each area and from the three different areas are not analytically distinct the data imply that the eruptive activity which produced the kirkpatrick basalt occurred within a short interval of less than about 1 m y at 176 6 1 8 ma over an area which included more than 1200 km of the transantarctic mountains the jurassic volcanism in antarctica represents a short episode of magmatism comparable in duration with other well dated continental flood basalt provinces the linearly extensive outcrop of the ferrar province and the rapid eruption of the lavas suggests that lithospheric stretching exerted a major control on magmatism the poorly constrained age of the bajocian bathonian boundary makes the previously suggested connection between ferrar volcanism and an extinction event at that boundary uncertain

sequence stratigraphy and biological signals statistical studies of benthic foraminifera from liassic series abstract a study of benthic foraminifera from the toarcian in quercy aquitaine basin france shows that micropaleontological assemblages are influenced by sea level changes the percentages of coiled and straight nodosarridae lenticulina citharina differ during periods of low sea level to high sea level statistical analysis of all the taxa in the successive levels of a section multiple factorial analysis of correspondences methods of automatic clustering show that there is a perfect distribution of the samples into groups corresponding to the type of systems tract differences within the foraminiferal benthic biocoenosis allow the successive systems tracts to be separated the first axis in the multiple analysis of correspondences coincides with a gradient of biotic capacity and seems to be connected with the sea level changes the second axis could be linked with depth the renewal rate of taxa and the factorial diversity of the sampling levels show fluctuations associated with 4th 3rd and 2nd order variations of the sea level these connections are caused by intricate processes with ecological biogeographical and bioevolutionary influence however the micropaleontological assemblages can be good indicators of systems tracts and unconformities this is particularly important within deposits that have homogeneous lithology

subtropical to temperate facies from a transition zone mixed carbonate siliciclastic system palaeogene north carolina usa palaeogene passive margin sediments on the us mid atlantic coastal plain provide valuable insight into facies interaction and distribution on mixed carbonate siliciclastic shelves this study utilizes well cuttings outcrop core and seismic data to document temporal and spatial variations in admixed bryozoan rich skeletal carbonates and sandy siliciclastic units that were deposited on a humid passive margin located in the vicinity of a major marine transition zone this zone was situated between north flowing warm waters of the ancestral gulf stream carbonate dominated settings and south flowing cold waters of the ancestral labrador current siliciclastic dominated settings some degree of mixing of carbonates and siliciclastics occurs in all facies however siliciclastic prone sediments predominate in nearshore settings while carbonate prone sediments are more common in more open marine settings of the inner shelf break and deep shelf a distinctive dual break shelf depositional profile originated following a major late cretaceous to palaeocene transgression that drowned the earlier shallow platform this profile was characterized by prominent mid shelf break dividing the shallow shelf from the deep shelf and a major continental shelf slope break incomplete filling of available accommodation space during successive buildup of the shallow shelf preserved the topographic break on this passive margin storm wave base also contributed to the preservation of the dual break shelf geometry by beveling shallow shelf sediments and transporting them onto and seaward of the mid shelf break sediment fines in deep shelf facies were produced in place transported downdip from the shallow shelf by storm ebb currents and boundary currents and reworked from adjacent areas of the deep shelf by strike parallel boundary currents regional climate and boundary currents controlled whether carbonate or siliciclastic material was deposited on the shelf with warmer waters and more humid climates favouring carbonate deposition and cooler more arid conditions favouring glaucony and siliciclastic dominated deposition continuous wave and current sweeping of the shallow shelf favoured deposition of mud lean facies across much of the shallow shelf skeletal components in much of the carbonate rich strata formed in warm nutrient rich subtropical waters as indicated by widespread occurrences of larger benthic foraminifera and molluscan assemblages these indicators of warm water deposition within the bryozoan mollusk rich carbonate assemblage on this shelf provide an example of a warm water bryomol assemblage such facies generally are associated with cooler water depositional settings

timing the end triassic mass extinction first on land then in the sea the end triassic marks one of the five biggest mass extinctions but current geologic time scales are inadequate for understanding its dynamics a tuff layer in marine sedimentary rocks encompassing the triassic jurassic transition yielded a u pb zircon age of 199 6 0 3 ma the dated level is immediately below a prominent change in radiolarian faunas and the last occurrence of conodonts additional recently obtained u pb ages integrated with ammonoid biochronology confirm that the triassic period ended ca 200 ma several million years later than suggested by previous time scales published dating of continental sections suggests that the extinction peak of terrestrial plants and vertebrates occurred before 200 6 ma the end triassic biotic crisis on land therefore appears to have preceded that in the sea by at least several hundred thousand years

deciphering the history of climate and sea level in the kimmeridgian deposits of bure eastern paris basin abstract an integrated stratigraphic study was conducted on a kimmeridgian succession of 3rd order cycles including marls and limestones in a shelf context at bure paris basin the study was possible due to the exceptional opportunity provided by well boring activities related to the construction of an underground laboratory of the french national agency for radioactive waste management andra studies of macrofossils microfossils sedimentology clay mineralogy isotopic composition c o of shells and organic molecular geochemistry lead to a detailed description of the stratigraphic column which allows us to address the history of sea level and climate changes six transgressive regressive cycles are recognised in the studied kimmeridgian succession in these 3rd order cycles the deepest environments are systematically represented by marls and organic rich sediments whilst the shallowest are represented by limestones these cycles do not correspond to changes in temperatures or carbonate production rates at a regional or global scale on the contrary long term palaeontological sedimentological and geochemical changes during the early kimmeridgian are interpreted as climatically induced these climatic changes are considered as responsible for bringing significant granular carbonate production to an end in contrast to carbonate mud that was deposited in alternation with marls throughout the late kimmeridgian

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

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

a upb age from the toarcian lower jurassic and its use for time scale calibration through error analysis of biochronologic dating abstract the early jurassic is the most poorly constrained part of the geochronologic scale within the mesozoic owing to the scarcity of calibration points we report a new u pb zircon age of 181 4 1 2 ma 2 from an ash layer within the type section of crassicosta zone a north american regional standard ammonite zone in the middle toarcian for time scale calibration the isotopically dated level needs to be tied to the jurassic chronostratigraphic framework established in northwest european successions three major contributing factors difference between local observed and true ranges uncertainties of correlation and taxonomic noise are assessed to determine the maximum biochronologic dating error the local ammonite distribution data are robust in that 95 confidence level extensions of observed ranges of common ammonite taxa would not significantly modify the zonal assignment the computer assisted unitary association ua method is used for world wide biochronologic correlation representative north and south american western tethyan and northwest european sections were selected to establish the global maximum ranges for 103 middle toarcian ammonite taxa and a sequence of 40 ua maximum permissible correlatives of the crassicosta zone lie between the northwest european standard semipolitum subzone late bifrons zone and bingmanni subzone early thouarsense zone in particular the dated tuff layer cannot be older than the semipolitum subzone or younger than the illustris subzone variabilis zone taxonomic inconsistencies are present in the source data but their effect in corrupting ua based correlation is shown to be negligible the precise u pb age 2 error

tethyan to boreal correlation in the kimmeridgian using high resolution sequence stratigraphy vocontian basin swiss jura boulonnais dorset ammonite biostratigraphy plays a central role in the definition of jurassic stratigraphy nevertheless the strong provincialism of european ammonite species during the kimmeridgian is a long standing problem in correlation attempts between the boreal and tethyan faunal realms moreover the sequence stratigraphic interpretations for northern and southern europe given in the jurassic chronostratigraphic chart of hardenbol et al in sepm publ 60 chart 1998 are different the present study aims to resolve this correlation problem in order to better understand the connections between the boreal and the tethyan realms during the kimmeridgian a sedimentological and high resolution sequence stratigraphic interpretation is presented for two unpublished sections cras d hermont and roche de mars in the northern swiss jura where recently discovered ammonites display both boreal and tethyan influences then these sections are correlated with the same time interval in the central swiss jura and vocontian basin which belong to the tethyan realm lastly a long distance transect is constructed between the vocontian basin swiss jura northern france and southern england the last two areas being part of the sub boreal realm the main results of this work are that 1 third order depositional sequences and also higher frequency sequences can be correlated from the tethyan to the boreal realm 2 the sequence stratigraphic interpretation given by hardenbol et al in sepm publ 60 chart 1998 for northern europe seems to be accurate and agrees with the sequence stratigraphic framework established in the swiss jura 3 the late kimmeridgian of the swiss jura displays boreal influences 4 integrated high resolution sequence stratigraphic and cyclostratigraphic studies are a valuable approach for bridging the correlation gap between northern and southern europe

influence of differential diagenesis on primary depositional signals in limestone marl alternations an example from middle permian marine successions south china abstract the diagenetic alteration of rhythmic successions remains one of the main challenges in paleoclimatology and cyclostratigraphy to address this very important problem thin sections and geochemical data of the limestone marl alternations from middle permian carbonate successions in south china are examined to identify differential diagenetic effects in the petrography organic and inorganic compositions strontium concentrations and stable isotopic compositions of limestone beds and marl interlayers in the lengshuixi outcrop and the jy66 1 drill core the most conspicuous features are that the limestone beds exhibit dense cementation high strontium concentrations negative oxygen isotopic values and positive carbon isotopic values in contrast the marl interlayers contain talc and exhibit strongly deformed and oriented bioclasts low strontium concentrations positive oxygen isotopic values and negative carbon isotopic values although differential diagenesis has occurred some paleoclimate proxies e g computed gamma ray values still preserve their primary signals and thus are suitable for cyclostratigraphic research eccentricity rhythm and millennial scale rhythm are obviously recorded in middle permian limestone marl alternations in south china the variations in the oxygen and carbon isotopic values of limestone marl alternations from different basins represent responses to different processes of differential diagenesis this knowledge assumes that differential diagenesis occurs in diagenetically closed systems under the deep sea floor however this assumption may not be valid in diagenetically open systems where exotic fluids may add unexpected disturbances hence it is crucial to understand diagenetic systems by determining the variations in strontium concentrations which are as important as variations in carbon and oxygen isotopic values

are oxygen and carbon isotopes of mollusc shells reliable palaeosalinity indicators in marginal marine environments a case study from the middle jurassic of england stable isotope analyses of non luminescent texturally pristine oyster calcites praexogyra hebridica are presented from bathonian inner ramp limestones in central eastern england a relatively large range of values 18 o 2 0 to 2 3 pdb 13 c 0 9 to 3 7 pdb define a crude positive covariance which can be regionally correlated with an offshore tonearshore increase in faunal restriction this palaeoenvironmental stress gradient has previously been interpreted as a consequence of fluctuating nearshore palaeo salinities due to episodic or seasonal runoff from surrounding hinterlands covariant 18 o 13 c trends from euryhaline bivalves are commonly ascribed to regional salinity gradients the most isotopically depleted examples representing the greatest influence of fresh water however bathonian palaeogeography indictates that the most isotopically depleted oysters inhabited relatively offshore settings assuming an average growth temperature of 25 c these shells were secreted in near normal sea water 18 o 0 4 smow in contrast isotopically heavy oyster calcites were produced in highly evaporated nearshore lagoonal waters 18 o up to 4 8 smow modelling the oxygen isotope and chemical evolution of residual waters during evaporation suggests that up to 65 of the nearshore water mass was lost probably in a complex of hydrodynamically choked lagoons evaporites were not precipitated in the sediment and geochemical modelling suggests that the lagoon waters may have been brackish rather than marine in origin the regional 13 c trend is contrary to that predicted on the basis of palaeosalinity and may have resulted from variations in organic carbon production decay and fixation in early diagenesis

evolution and demise of a mid cretaceous carbonate shelf the altamira limestones cenomanian of northern cantabria spain abstract in northern cantabria the cenomanian transgression is pulsatory in character and progressively onlaps onto deltaic siliciclastics of latest albian to earliest cenomanian age this pronounced 2nd order sea level rise can be subdivided into an earlier constructive phase and a later destructive phase separated by a significant low sea level stand at the early mid cenomanian boundary in the first phase the flooding of the north iberian continental margin in the early early cenomanian caused the sources of terrigenous sediments located on the iberian meseta to retreat thus promoting the development of a carbonate ramp this ramp evolved into a shelf attached platform altamira platform during the course of the early cenomanian pronounced sea level fall in the early mid cenomanian boundary interval exposed the platform increased fluvial input and terminated the constructive phase the destructive phase started in the early mid cenomanian and lasted until the late cenomanian carbon and oxygen stable isotopes microfacies analysis palaeontological criteria and sequence stratigraphy are used to elucidate the complex interplay of climatic changes sea level history nutrient supply and platform drowning three 3rd order sea level rises early and late mid cenomanian early late cenomanian resulted in a westward backstepping and final drowning of the altamira platform the drowning succession is accompanied by a negative shift of 18 o and a positive 13 c excursion interpreted to reflect progressive climatic warming and elevated nutrient levels the resulting eutrophication is represented by the biotic community of the drowning succession and negatively influenced the carbonate budget of the depositional system as a result the stressed platform was readily drowned during the mid and earliest late cenomanian 3rd order sea level rises

facies cycles and controls on the evolution of a keep up carbonate platform kimmeridgian swiss jura during the late jurassic accelerated ocean floor spreading and associated sealevel rise were responsible for a worldwide transgression which reached its maximum in the late kimmeridgian in many western european basins this major sea level rise led to the formation of marly and condensed sections in the swiss jura however a shallow carbonate platform kept growing and only subtle changes in the stratigraphic record suggest an increasingly open marine influence field observations and thin section analyses reveal that the central swiss jura was at that time occupied by tidal flats and by more or less open marine lagoons where shoals and bioherms developed the evolution through time of sedimentary facies and bed thicknesses permits the definition of small medium and large scale depositional sequences the diagnostic features of these sequences are independent of scale and seem largely controlled by the kimmeridgian second order transgression a high resolution sequencestratigraphic correlation with biostratigraphically well dated hemipelagic and pelagic sections in the vocontian basin in france reveals that i the most important increase in accommodation recorded in the kimmeridgian of the central swiss jura occurs in the eudoxus ammonite zone late kimmeridgian and corresponds to the second order maximum flooding recognized in many sedimentary basins ii the small and medium scale sequences have time durations corresponding to the first and second orbital eccentricity cycle i e 100 and 400 ka respectively suggesting that sedimentation on the platform and in the basin was at least partly controlled by cyclic environmental changes induced by insolation variations in the milankovitch frequency band the comparison of the high resolution temporal framework defined in the swiss jura and vocontian basin with the sequencestratigraphic interpretation realized in other western european basins shows that the large scale sequence boundaries defined in the kimmeridgian of the swiss jura appear in comparable biostratigraphic positions in most western european basins discrepancies that occur are probably because of local or regional tectonics

calcareous nannofossils and mesozoic oceanic anoxic events abstract twenty five years ago mesozoic oceanic anoxic events oaes were documented and formalised as intervals of widespread to global deposition of organic matter the toarcian early aptian oae1a and latest cenomanian oae2 oaes are truly global in nature commonly carbonate poor and typically represented by organic carbon rich black shales in some areas these oaes are also characterised by abundant radiolarian sands and silts they are associated with negative and positive excursions in the 87sr 86sr record in addition to large global carbon isotope anomalies in carbonate and or organic matter caused by a major perturbation of the global carbon budget increased rates of volcanism during the formation of the ontong java and manihiki and caribbean plates and the karoo ferrar traps are believed to have caused the geological responses associated with oae1a oae2 and the toarcian oae respectively excess volcanogenic co2 in the atmosphere most probably turned the climate into a greenhouse mode accelerating continental weathering and increasing nutrient content in oceanic surface waters via river run off higher fertility in the global ocean was also probably triggered directly by submarine igneous events that introduced enormous quantities of biolimiting metals within hydrothermal plumes because mesozoic oaes are often represented by carbonate poor sediments quantitative studies of calcareous nannofossils have been applied to explore a the causes and effects of igneous tectonic events and climate changes relative to nannofloral increases and crises as well as b dissolution events and c diagenetic modifications characterization of calcareous nannofloras in oae intervals can improve our understanding of the marine ecosystem and biological processes such as photosynthesis biological pump and biomineralisation carbonate pump that affect the organic and inorganic carbon cycle as well as adsorption of atmospheric co2 in the oceans types and rates of nannoplankton production and evolution are interpreted to trace the impact of major palaeoceanographic and palaeoclimatic events in selected sections it has been documented that calcareous nannofloras rapidly reacted to new conditions of fertility and higher pco2 by drastically reducing calcification as in the modern oceans during oaes the increase of nutrients and atmospheric co2 induced higher abundances of nannoplankton producing small placoliths and inhibited the deep photic zone nannoconids and schizosphaerellids similarly to the nannoconid crisis preceding deposition of the early aptian oae1a black shales a schizosphaerellid crisis is detected prior to the toarcian oae both oaes are further characterised by a rapid nannofloral speciation beginning approximately 1 5 myr before the oae but without extinctions global changes during the latest cenomanian oae 2 exerted different influences on calcareous nannoplankton that experienced a turnover due to most extreme environmental conditions this event in fact was a time of extinctions followed by originations within calcareous nannofossils precise timing of the events before during and after oae1a oae2 and the toarcian oae indicates that they were intervals of enhanced oceanic productivity and that anoxia dysoxia post dated biotic changes

strontium isotope profile of the early toarcian jurassic oceanic anoxic event the duration of ammonite biozones and belemnite palaeotemperatures we profile 87sr 86sr 13c 18o sr ca mg ca and na ca in belemnites through pliensbachian and toarcian strata on the yorkshire coast uk which include the early jurassic oceanic anoxic event the 87sr 86sr profile shows that the relative duration of ammonite subzones differ by a factor of up to 30 the lower jurassic exaratum subzone is 30 times longer than the clevelandicum subzone because the exaratum subzone in yorkshire which contains the anoxic event is condensed by a factor of between 6 5 and 12 2 times relative to adjacent strata using our 87sr 86sr profile the resolution in correlation and dating attainable in the interval is between 1 5 m and 15 m of section and better than 0 25 myr in parts of the sequence this stratigraphic resolution equals that attainable with ammonites a new age model is provided for late pliensbachian and early toarcian time that is based on the 87sr 86sr profile through the sequence the sr ca mg ca na ca and 18o of belemnite carbonate covary suggesting that elemental ratios may be useful for palaeotemperature measurement our 13cbelemnite data splits into three the previously reported positive isotope excursion to 6 5 in the early toarcian we speculate that the excursion s resulted from addition to surface waters of isotopically heavy co2 via ebullition of methanogenic co2 from the sediment during early burial of organic rich 10 toc sediments