differentiation of mesozoic basalts of the hartford basin connecticut the talcott oldest of the three basalts in the mesozoic hartford basin of connecticut contains abundant euhedral olivine and plagioclase phenocrysts and less common rounded augite plagioclase aggregates and orthopyroxene phenocrysts rimmed by augite and olivine the orthopyroxene which has a remarkably constant composition en 84 and is cr rich is believed to be a refractory residue from an upper mantle source region the holyoke basalt the middle unit is essentially aphyric with only minor plagioclase and olivine phenocrysts the hampden youngest of the three basalts contains abundant plagioclase and minor olivine and augite phenocrysts materials balance calculations using phenocryst compositions from the talcott basalt indicate that the holyoke can be derived from a talcott magma by addition of 7 8 orthopyroxene and removal of 7 9 olivine 15 clinopyroxene and 13 3 plagioclase the hampden basalt cannot be derived from a holyoke magma by any reasonable fractionation scheme but it can be derived from a talcott magma by removal of 4 4 olivine 12 0 clinopyroxene and 14 3 plagioclase one atmosphere melting experiments under controlled oxygen fugacities indicate successively lower liquidus temperatures for talcott holyoke and hampden basalts both the talcott and the holyoke have olivine and plagioclase on the liquidus simultaneously with augite and pigeonite appearing 15 c below the liquidus the hampden has plagioclase alone on the liquidus olivine and augite appear only 5 c below the liquidus orthopyroxene is not present in the low pressure experiments but is thought to have been stable on the liquidus at depths corresponding to pressures exceeding 8 kbar assimilation of orthopyroxene and crystallization of other phases necessary to produce the holyoke basalt from a talcott magma must have taken place at depth however because the low pressure phases obtained in the experiments are those required to produce the hampden from the talcott magma this fractionation likely occurred in a near surface magma chamber

rare earth element geochemistry of dolomites in the middle devonian presqu ile barrier western canada sedimentary basin implications for fluid rock ratios during dolomitization rare earth elements ree were determined in fine medium and coarse crystalline replacement dolomites and for saddle dolomite cements from the middle devonian presqu ile barrier from pine point and the subsurface of the northwest territories and north eastern british columbia ree patterns of the fine crystalline dolomite are similar to those of middle devonian limestones from the presqu ile barrier fine crystalline dolomite occurs in the back barrier facies and may represent penecontemporaneous dolomitization at or just below the sea floor medium crystalline dolomite is widespread in the lower southern and lower central barrier medium crystalline dolomite is slightly depleted in heavy ree compared with devonian marine limestones and fine crystalline dolomite and has negative ce and eu anomalies medium crystalline dolomites replaced pre existing limestones or were recrystallized from earlier fine crystalline dolomites during these processes the ree patterns of their precursors were modified late stage coarse crystalline replacement dolomite and saddle dolomite cements occur together in the upper barrier and have similar geochemical signatures coarse crystalline dolomites have negative eu anomalies and those from the pine point area also have positive la anomalies saddle dolomites are enriched in light ree and have positive la anomalies the ree patterns of coarse crystalline dolomite and saddle dolomite differ from those of marine limestones and fine and medium crystalline dolomites suggesting that different diagenetic fluids were responsible for these later dolomites although massive dolomitization requires relatively large volumes of fluids in order to provide the necessary amounts of mg2 dolomitization and subsequent recrystallization may not necessarily modify the ree signatures of the precursor limestones because of the low concentrations of ree in most natural fluids thus relative fluid rock ratios during diagenesis may be estimated from ree patterns in the diagenetic and precursor minerals fine crystalline dolomites retain the ree patterns of their limestone precursors in the medium and coarse crystalline dolomites the precursor ree patterns were apparently altered by large volumes of fluids involved during dolomitization this study suggests that ree compositions of dolomites and their limestone precursors may provide important information about the relative amounts of fluids involved during diagenetic processes such as dolomitization

the origin of coexisting carbonates in banded iron formations a micro mineralogical study of the 2 4 ga itabira group brazil this is the first petrographic and chemical study on the origin of co existing calcite dolomite ankerite and sideroplesite in the 2 4 ga itabira group brazil the itabira group hosts silicic and dolomitic bifs known as quartz itabirites and carbonate itabirites which are composed of micritic quartz and dolomite with inclusions of nano and micro hematite nanometric si bearing ferrihydrite clusters are observed in the micritic dolomite mineralogical and textural features indicate a primary oxidizing depositional environment for the itabira group at 2 4 ga limestones of the itabira group include early diagenetic hematite nodules intergrown with dolomite silica in the ferrihydrite structure increases its stability up to 500 c and the nano and micro hematite included in dolomite and quartz were partially protected from later transformation by being enclosed within the dolomite and quartz crystals positive eu and y anomalies and heavy rare earth element enrichments of all lithofacies along with their low terrestrial element abundance excluding the shales indicate their primary precipitation from a mixed hydrothermal marine environment in the case of the carbonate itabirites fluids were co2 rich dolomite precipitated abiotically due to higher temperatures 100 c and high mg ca ratios the facies changes from carbonate rich to quartz rich are attributed to transgression and regression episodes and or a change in the upwelling hydrothermal fluid composition post depositional reductive dissolution affected the quartz itabirites facilitating the precipitation of ankerite sideroplesite and magnetite sulphides from a reducing diagenetic solution rich in mn mg and fe either as lenses or disseminated in the quartz itabirites and shales the sideroplesite richest samples have the most negative 13c values quartz itabirite 9 49 shale 5 76 indicating that at least part of the c is of organic origin either through the oxidation of organic matter or introduced via the diagenetic fluids specularite is replacive and likely related to a post depositional hydrothermal event this study shows that careful mineralogical investigations combined with ree y and trace element geochemistry is necessary in order to decipher the depositional environments which are oxidizing mixed marine hydrothermal post depositional reductive diagenesis masks in part these primary conditions

time calibration of triassic jurassic microfloral turnover eastern north america abstract palynological data from the newark basin of the newark supergroup reveal a spike in the spore pollen ratio at the triassic jurassic boundary this spore spike is coincident with a 60 regional extinction of the palynoflora and approximately synchronous with terrestrial vertebrate extinctions orbitally controlled sedimentary cycles allow stratigraphic sections to be calibrated in time constraining the duration of the microfloral turnover to an interval of 21 ky the geologically brief palynofloral break is similar to cretaceous tertiary boundary fern spikes these data support a triassic jurassic boundary impact extinction scenario

in situ geochemistry of lower paleozoic dolomites in the northwestern tarim basin implications for the nature origin and evolution of diagenetic fluids lower paleozoic sedimentary rocks in the northwestern tarim basin were strongly altered by complicated geofluids which resulted in the occurrence of various diagenetic minerals e g dolomite here in situmajor trace and rare earth element geochemistry of lower ordovician diagenetic dolomite grains as well as petrography were performed to unravel the geochemical features the nature and origin of the diagenetic fluids the results indicate that different geochemical information can be detected within a single sample even within a single dolomite grain five generations of diagenetic dolomite have been identified based on geochemical signatures resulting from four distinct types of diagenetic fluids 1 hree enrichment paas normalized low rree no eu anomaly low mn ba moderate fe and high sr contents are probably due to early burial dolomitizing fluids 2 mree enrichment high rree high mn fe and low sr content are likely to be associated with devonian deep circulating crustal hydrothermal fluids 3 flat or lree enrichment pattern with obviously positive eu anomaly is inferred to be linked to permian magmatic hydrothermal fluids and 4 flat ree pattern moderate rree no eu anomaly low mn ba moderate fe and high sr contents are probably due to late burial dolomitizing fluids the significances of in situmethod demonstrated in this study compared with the whole rock analysis include not only contamination free analysis but also unraveling the internal geochemical variation within a single sample or a mineral grain thus for the geochemical study of complicated diagenetic process in situmethod should be preferentially considered

the late triassic extinction at the norian rhaetian boundary biotic evidence and geochemical signature abstract the latest triassic was an interval of prolonged biotic extinction culminating in the end triassic extinction ete the ete is now associated with a perturbation of the global carbon cycle just before the end of the triassic that has been attributed to the extensive volcanism of the circum atlantic magmatic province camp however we attribute the onset of declining latest triassic diversity to an older perturbation of the carbon cycle 13corg of global extent at or very close to the norian rhaetian boundary nrb the nrb appears to be the culmination of stepwise biotic turnovers that characterize the latest triassic and includes global extinctions of significant marine and terrestrial fossil groups these biotic events across the nrb have been largely under appreciated yet together with a coeval disturbance of the carbon cycle were pivotal in the history of the late triassic here we present new and published 13corg data from widespread sections italy greece odp australia new zealand usa canada these sections document a previously unknown perturbation in the carbon cycle of global extent that spanned the nrb the disturbance extended across the panthalassa ocean to both sides of the pangaean supercontinent and is recorded in both the northern and southern hemispheres the onset of stepwise late triassic extinctions coincides with carbon perturbation 13corg at the nrb indicating that a combination of climatic and environmental changes impacted the biota at a global scale the nrb event may have been triggered either by gas emissions from the eruption of a large igneous province pre dating the nrb by a bolide impact of significant size or by some alternative source of greenhouse gas emissions as yet it has not been possible to clearly determine which of these trigger scenarios was responsible the evidence is insufficient to decisively identify the causal mechanism and merits further study

kinematic significance of sediment filled fissures in the north mountain basalt fundy rift basin nova scotia canada abstract numerous sediment filled fissures are present near the upper surface of the north mountain basalt 202 ma of the fundy basin which formed during triassic jurassic rifting the fissures are infilled with the same clastic material comprising the basal parts of the overlying earliest jurassic age sedimentary formations which accumulated less than 200 k y after the cooling of the basalt nearly all of the 1368 fissures measured in this study are planar to sub planar and are sub vertical after correcting the basalt flows to paleo horizontal the fissures typically formed along preexisting columnar joints within the basalt northeast striking fissures generally define a preferred orientation and commonly are wider than other fissures the sediment filled fissures therefore indicate earliest jurassic age nw se extension this extension direction is consistent with that indicated by the ne striking shelburne diabase dike the attitude of mesoscopic faults and the geometry of the fundy rift basin thus sediment filled fissures by themselves can serve as useful kinematic indicators and place tight constraints on the relative timing of extension

post paleocene cooling in the southern canadian atlantic region evidence from apatite fission track models the traditional view of the geomorphic evolution of the southern canadian atlantic margin is one of gradual exhumation and peneplanation following triassic jurassic rifting thermal modelling of apatite fission track data from pre carboniferous granitic basement in nova scotia and from permian and triassic sandstones from nova scotia new brunswick and prince edward island suggest a more complex thermal evolution of the onshore part of the margin models clearly indicate significantly elevated regional paleotemperatures during jurassic time and as much as 30 c of post paleocene cooling model predicted paleogeothermal gradients for granitic samples from the digby d 1 well are normal ranging from 15 to 20 c km post paleocene cooling may be attributable to the combined effects of 13 c of exhumational cooling from erosion of approximately 700 m of post aptian sediments caused by decreased eustatic sea levels and 8 17 c of cooling from the propagation to depth of a 10 20 c decrease in paleo mean ann

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

stratigraphic record of the early mesozoic breakup of pangea in the laurasia gondwana rift system rift basins of the central atlantic margins cam of north america and morocco preserve largely continental sequences of sedimentary strata and less important minor basalt flows spanning much of the early mesozoic the best known is the newark basin of new jersey new york and pennsylvania where an astronomically calibrated magnetic polarity time scale is developed lacustrine cycles of milankovitch origin are commonly present in cam basins with the period changing from 10 ky paleoequator with coals to 20 ky 4 10n to perhaps 40 ky northward with evaporites cycles of100 ky 413 ky and2 my are also important four mostly unconformity bounded tectonostratigraphic sequences are present the anisian ts i is fluvial and eolian ts ii ts iv late triassic to early jurassic consist of tripartite lacustrine sequences caused by extension pulses the newark basin accumulation rate history allows comparison with quantitative rift basin models the north american plate s slow northward drift resulted in a relative shift of climate although the rapid humidification during the latest triassic and early jurassic is associated with a sea level rise the triassic jurassic mass extinction is of independent origin plausibly impact related

rare earth element geochemistry of late devonian reefal carbonates canning basin western australia confirmation of a seawater ree proxy in ancient limestones rare earth element and yttrium ree y concentrations were determined in 49 late devonian reefal carbonates from the lennard shelf canning basin western australia shale normalized sn ree y patterns of the late devonian samples display features consistent with the geochemistry of well oxygenated shallow seawater a variety of different ancient limestone components including microbialites some skeletal carbonates stromatoporoids and cements record seawater like ree y signatures contamination associated with phosphate fe oxides and shale was tested quantitatively and can be discounted as the source of the ree y patterns co occurring carbonate components that presumably precipitated from the same seawater have different relative ree concentrations but consistent ree y patterns clean devonian early marine cements n 3 display ree y signatures most like that of modern open ocean seawater and the highest y ho ratios e g 59 and greatest light ree lree depletion average nd sn yb sn 0 413 sd 0 076 however synsedimentary cements have the lowest ree concentrations e g 405 ppb non contaminated devonian microbialite samples containing a mixture of the calcimicrobe renalcis and micritic thrombolite aggregates in early marine cement n 11 have the highest relative ree concentrations of tested carbonates average total ree 11 3 ppm stromatoporoid skeletons unlike modern corals algae and molluscs also contain well developed seawater like ree patterns samples from an estuarine fringing reef have very different ree y patterns with lree enrichment nd sn yb sn 1 possibly reflecting inclusion of estuarine colloidal material that contained preferentially scavenged lree from a nearby riverine input source hence devonian limestones provide a proxy for marine ree geochemistry and allow the differentiation of co occurring water masses on the ancient lennard shelf although appropriate partition coefficients for quantification of devonian seawater ree concentrations from out data are unknown hypothetical devonian canning basin seawater ree patterns were obtained with coefficients derived from modern natural proxies and experimental values resulting devonian seawater patterns are slightly enriched in lree compared to most modem seawaters and suggest higher overall ree concentrations but are very similar to seawaters from regions with high terrigenous inputs our results suggest that most limestones should record important aspects of the ree geochemistry of the waters in which they precipitated provided they are relatively free of terrigenous contamination and major diagenetic alteration from fluids with high non seawater like ree contents hence we expect that many other ancient limestones will serve as seawater ree proxies and thereby provide information on paleoceanography paleogeography and geochemical evolution of the oceans copyright c 2004 elsevier ltd

accurate trace element analysis of speleothems and biogenic calcium carbonates by la icp ms the high spatial resolution of laser ablation inductively coupled plasma mass spectrometry la icp ms microanalysis of speleothems and biogenic calcium carbonates makes it possible to improve our understanding of past climatic conditions however there are analytical problems associated with this method such as molecular interferences elemental fractionation and mass load dependent matrix effects when using nist silicate reference glasses for calibration our study with a sector field icp ms shows that many masses are affected by interferences such as 24mg by 48ca or 31p by 15n16o elemental fractionation and mass load dependent matrix effects have been detected for both 213 and 193 nm nd yag lasers they are small for refractory lithophile elements in particular for the 193 nm laser 5 for chalcophile siderophile trace elements with low boiling points however these effects are large up to 40 and 20 for the 213 and 193 nm lasers respectively and variable for the nist glasses and carbonates in this paper a protocol for precise and accurate la icp ms analysis of calcium carbonates is established isotopes for interference free measurements at low m m 300 and medium m m 4000 mass resolution have been identified the nist glasses are suitable for calibration of refractory lithophile element concentrations however matrix matched calibration with carbonate reference materials such as usgs macs 1 or macs 3 is necessary for accurate analysis of chalcophile siderophile elements with low boiling points analytical reproducibility rsd is a factor of 2 better using the 193 nm laser than the 213 nm laser as shown by the analysis of macs 1 and macs 3 la icp ms analyses yield results that agree with the reference values within relative uncertainties of ca 5 10 at the 95 confidence level we have applied la icp ms for the determination of trace element concentrations in calcite and aragonite layers of a stalagmite and found large variations for mg zn sr and u in ostracod shells the concentrations of some trace elements e g sr and ba vary significantly indicating the potential for paleoclimate research

middle phanerozoic mass extinctions and a tribute to the work of professor tony hallam tony hallam s contributions to mass extinction studies span more than 50 years and this thematic issue provides an opportunity to pay tribute to the many pioneering contributions he has made to this field early work 1961 on the jurassic in europe revealed a link during the toarcian stage between extinction and the spread of anoxic waters during transgression the first time such a common leitmotif had been identified he also identified substantial sea level changes during other mass extinction intervals with either regression end triassic or early transgression end permian coinciding with the extinction phases hallam s 1981 study on bivalves was also the first to elevate the status of the end triassic crisis and place it amongst true mass extinctions changing previous perceptions that it was a part of a protracted period of turnover although debates on the duration of this crisis continue hallam 2002 conflicting views on the nature of recovery from mass extinctions have also developed especially for the aftermath of the end permian mass extinction these discussions can be traced to hallam s seminal 1991 paper that noted the considerable delay in benthic recovery during early triassic time and attributed it to the persistence of the harmful high stress conditions responsible for the extinction itself this idea now forms the cornerstone of one of the more favoured explanations for this ultra low diversity interval

origin and migration of brines from paleozoic strata in central tarim china constraints from 87sr 86sr δd δ18o and water chemistry chemistry of major and minor elements 87sr 86sr d and 18o of oilfield waters and 87sr 86sr of whole rock were measured from paleozoic strata in the central tarim basin nw china the aim is to elucidate the origin and migration of formation water and its relation to petroleum migration high salinity oilfield waters in carboniferous silurian and ordovician reservoirs have maintained the same na cl ratio as seawater indicative of subaerially evaporated seawater two possible sources of evaporitic water are carboniferous cii and cambrian both of which contain evaporitic sediments geographic and stratigraphic trends in water chemistry suggest that most of the high salinity water is from the cambrian strontium h and o isotopes as well as ion chemistry indicate at least 3 end member waters in the basin high salinity cambrian evaporitic water was expelled upward into ordovician silurian and carboniferous reservoirs along faults and fractures during compaction and burial meteoric water has likely invaded the section throughout its history as uplift created subaerial unconformities meteoric water certainly infiltrated silurian and older strata during development of the ciii unconformity and again in recent times modern meteoric water enters carboniferous strata from the west and flows eastward mixing with the high salinity cambrian water and to a lesser degree with paleometeoric water the third end member is highly radiogenic shale derived water which has migrated eastward from the awati depression to the west enrichment of ca and sr and depletion of k mg and so4 relative to the seawater evaporation trajectory suggest waters were affected by albitization of feldspars dolomitization illitization of smectite and so4 reduction the mixing of meteoric water occurred subsequently to seawater evaporation main water rock interactions and brine migration the direction of brine migration is consistent with that of petroleum migration suggesting water and petroleum have followed the same migration pathways

a burial diagenesis origin for the ediacaran shuram wonoka carbon isotope anomaly marked negative 13c excursions in ediacaran age carbonate sediments have been identified in several sections globally but are not recognized in all sections of similar age the presence of 13ccarb values as low as 12 has been interpreted as recording fundamentally different processes in the global carbon cycle than those recognized today the 13ccarb anomalies are strongly correlated with 18ocarb values but are not represented in 13corg records while no primary depositional processes have been identified that can produce the correlated 18o 13c arrays simulations show that fluid rock interaction with high pco2 fluids is capable of producing such arrays at geologically reasonable pco2 and water rock ratios variations in the mg ca ratio and sulfate concentration of the altering fluid determine the extent of dolomite vs calcite and anhydrite in the resulting mineral assemblage incorporation of an initially aragonitic mineralogy demonstrates that high sr low mn sr and modest alteration of 87sr 86sr in ancient carbonates are all compatible with a burial diagenesis mechanism for generation of the 13c anomalies and do not necessarily imply preservation of primary values the profound ediacaran negative 13c anomalies can be adequately explained by well understood diagenetic processes conflated with the difficulty of correlating precambrian sections independently of chemostratigraphy they are not a record of primary seawater variations and need not have independent stratigraphic significance

thermochemical sulphate reduction in cambro ordovician carbonates in central tarim h2s and co2 are found in elevated concentrations in palaeozoic reservoirs in the tarim basin in china we have carried out analyses on gas petroleum mineral cement and bulk rock compositions and isotope ratios together with petrography and fluid inclusion to assess the origin of the h2s a deep crustal e g volcanic origin of the h2s and co2 is unlikely since the inert gases n2 and he have isotope ratios totally uncharacteristic of this source organic sources are also unlikely since the source rock has low a sulphur content and the sulphur isotope ratio of the petroleum correlates positively with the sulphur content the opposite of what would be anticipated from petroleum derived h2s bacterial sulphate reduction is unlikely because temperatures are too high for bacteria to have survived thermochemical sulphate reduction of petroleum fluids by anhydrite in lower ordovician and cambrian carbonate reservoirs is the most likely source of both the h2s and the co2 causing isotopically characteristic pyrite co2 gas and calcite cement h2s and possibly co2 migrated into silurian sandstone reservoirs by cross formational flow the h2s with the same sulphur isotope ratio as ordovician anhydrite was partially lost from the fluid phase by extensive growth of late diagenetic pyrite similarly the co2 was partially lost from the fluid phase by precipitation of late diagenetic calcite the h2s that resulted from tsr underwent reaction with the remaining petroleum resulting in locally elevated organic sulphur concentrations in the petroleum and the progressive adoption of the ordovician anhydrite sulphur isotope ratio

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

a geographical information system gis study of triassic vertebrate biochronology geographical information systems gis have been applied extensively to analyse spatial data relating to varied environmental issues but have not so far been used to address biostratigraphical or macroevolutionary questions over extended spatial and temporal scales here we use gis techniques to test the stability validity and utility of proposed middle and late triassic land vertebrate faunachrons lvfs a global biostratigraphical framework based upon terrestrial freshwater tetrapod occurrences a database of tetrapod and megafloral localities was constructed for north america and western europe that also incorporated information on relevant palaeoenvironmental variables this database was subjected to various spatial analysis techniques our gis analysis found support at a global level for eocyclotosaurus as an anisian index taxon and probably aetosaurus as a norian indicator other tetrapod taxa are useful biostratigraphical biochronological markers on a regional basis such as longosuchus and doswellia for late carnian time other potential index fossils are hampered however by taxonomic instability mastodonsaurus metoposaurus typothorax paleorhinus pseudopalatus redondasaurus redondasuchus and or are not clearly restricted in temporal distribution paleorhinus angistorhinus stagonolepis metoposaurus and rutiodon this leads to instability in lvf diagnosis we found only in the western northern hemisphere is there some evidence for an anisian ladinian biochronological unit amalgamating the perovkan and berdyankian lvfs and a possible late carnian unit integrating the otischalkian and adamanian megaplants are generally not useful for biostratigraphical correlation in the middle and upper triassic of the study area but there is some evidence for a carnian age floral assemblage that corresponds to the combined otischalkian and adamanian lvfs environmental biases do not appear to strongly affect the spatial distribution of either the tetrapods or megaplants that have been proposed as index taxa in biostratigraphical schemes though several examples of apparent environmental bias were detected by the analysis consequently we argue that further revision and refinement of middle and late triassic lvfs is needed before they can be used to support global or multi regional biostratigraphical correlations caution should therefore be exercised when using the current scheme as a platform for macroevolutionary or palaeoecological hypotheses finally this study demonstrates the potential of gis as a powerful tool for tackling palaeontological questions over extended timescales

transtensional arm of the early mesozoic fundy rift basin penecontemporaneous faulting and sedimentation formed as a major right lateral fault zone during paleozoic collisional orogenies and reactivated as a left oblique system during the early mesozoic the east striking minas fault zone of atlantic canada controlled adjacent sedimentation in the fundy rift basin producing a series of synsedimentary microbasins northeast striking boundary faults of the fundy basin underwent mostly early mesozoic normal slip and are reactivated paleozoic thrusts the adjacent basin has a much thicker section transverse folds and synthetic rider blocks contrasts in structural and stratigraphic styles are a response to local deformation controlled by reactivated fault zones of differing orientation under consistent northwest southeast early mesozoic extension rather than responses to a sequence of changing stress patterns

the nonmarine triassic jurassic boundary in the newark supergroup of eastern north america abstract for the last three decades the position of the triassic jurassic boundary tjb in nonmarine strata has largely been based on its palynostratigraphic placement just below the oldest basalts of the central atlantic magmatic province camp in the newark supergroup of eastern north america this boundary however is demonstrably older than the tjb as it is defined in marine strata thus the palynostratigraphic change used to place this tjb in the newark most resembles a late norian change in the european section and does not correspond to any palynological event at the marine defined tjb conchostracan biostratigraphy suggests that the tjb is in the newark extrusive zone above the oldest camp basalt and vertebrate biostratigraphy is consistent with this placement of the tjb radioisotopic ages indicate that the tjb defined in marine strata is no older than 200 ma but the oldest camp basalts of the newark supergroup consistently yield ages averaging about 201 ma magnetostratigraphic correlation of the newark section to the tjb section at st audrie s bay in england also indicates that the onset of camp volcanism in the newark supergroup is older than the marine tjb correlations based on carbon and osmium isotopes are also consistent with this correlation thus all data indicate that the tjb in the newark supergroup is above the lowest camp basalt in the newark extrusive zone correct placement of the tjb in the newark supergroup allows key nonmarine and marine events to be sequenced across the tjb indicating the following succession of events crurotarsan thecodont extinction the palynofloral turnover in the newark the first camp eruptions the extinctions of rhaetian ammonites and conodonts and the first appearance of jurassic psiloceratid ammonites

paleomagnetism and k ar isochron dates of early jurassic basaltic flows and dikes of atlantic canada k ar isochron dates of 193 2 189 3 and 191 2 ma are reported for the shelburne dike of nova scotia the avalon dike of newfoundland and the caraquet dike of new brunswick respectively these major tholeiitic dikes agree in radiometric date with the north mountain basalt of nova scotia and with other tholeiitic flows of the newark supergroup that have been paleontologically assigned to the hettangian however further work is needed to resolve the discrepancy between the triassic jurassic boundary date of 193 6 ma suggested by the newark supergroup flows and the boundary dates of 204 213 ma adopted in recent time scales the north mountain basalt flows at nine sites on the north shore of the bay of fundy are shown to have likely magnetized during initial cooling yielding an hettangian virtual paleopole at 66 n 72 e dp 9 dm 14 new paleomagnetic results are also reported for the caraquet and avalon dikes the virtual paleopoles from hettangian flows and dikes of atlantic canada lie on a

late triassic ecosystem variations inferred by palynological records from hechuan southern sichuan basin china the late triassic deposits of the sichuan basin southwestern china are significant for hosting abundant and diverse fossil assemblages including plants containing spores and pollen bivalves and insects however the late triassic palaeoecological variations are still poorly documented in this region here we present results from a palynological study from the upper triassic xujiahe formation in hechuan of chongqing southern sichuan basin the palynological analysis revealed a well preserved terrestrial palynoflora of high diversity comprising 184 species in 75 genera of spores and pollen three palynological assemblages were recognized reflecting terrestrial successions throughout the entire interval with significant changes in the vegetation cycads bennettites ginkgophytes and conifers show an increasing trend into younger deposits while ferns and lycopsids decrease in relative abundance the late triassic vegetation underwent changes from lowland fern forest to a mixed forest with more canopy trees we applied the spore pollen morphological group smg method and sporomorph ecogroup seg model to interpret the palaeoclimate features the results reveal that the lower part of the xujiahe formation was deposited under relatively warm and humid conditions with an overall cooling and drying trend from latest norian to rhaetian time accompanied by a general decrease of ferns and simultaneous increase of gymnosperms and a decline in diversity of miospores this study presents data on variations within the terrestrial ecosystem prior to the end triassic extinction event in the sichuan basin and therefore provides important information for understanding the changes in the vegetation preceding the end triassic event

paleomagnetism of the moenkopi and chinle formations in central new mexico implications for the north american apparent polar wander path and triassic magnetostratigraphy in central new mexico red sedimentary rocks unconformably overlying permian carbonates of the san andres formation have been correlated with the early middle triassic moenkopi and late triassic chinle formations of the colorado plateau paleomagnetic samples from triassic sections exposed on basement cored uplifts along both the east and west side of the rio grande rift near albuquerque yield upon thermal and chemical demagnetization well defined high unblocking temperature dual polarity magnetizations carried by hematite the characteristic magnetization is interpreted as an early acquired chemical remanent magnetization based on a positive intraformational microconglomerate test and bedding parallel magnetization polarity zonation the moenkopi and lowermost chinle formations produced paleomagnetic poles respectively at 57 6 n 100 3 e n 36 sites k 74 1 a95 2 8 and 60 8 n 88 9 e n 17 sites k 130 3 a95 3 1 these data plus previously published and additional results from the underlying permian strata suggest that portions of central new mexico have experienced a small clockwise rotation i e less than 10 similar to that of the colorado plateau with respect to the north american craton the paleomagnetic directions of the chinle formation and related strata in eastern new mexico document about 12 great circle distance of rapid apparent polar wander during mid carnian to late norian times along a track which contains other cratonic poles of similar age we present a preliminary magnetic polarity time scale for the triassic that incorporates the present new mexico data and previously published data mostly form continental red bed sequences this magnetic polarity scale provides a basic framework which can be tested with future data from triassic sections where additional biostratigraphic control exists

the terminal triassic catastrophic extinction event in perspective a review of carboniferous through early jurassic terrestrial vertebrate extinction patterns abstract a catastrophic terminal triassic extinction event among terrestrial vertebrates is not supported by available evidence the current model for such an extinction is based on at least eight weak or untenable assumptions 1 a terminal triassic extinction inducing asteroid impact occurred 2 a terminal triassic synchronous mass extinction of terrestrial vertebrates occurred 3 a concurrent terminal triassic marine extinction occurred 4 all terrestrial vertebrate families have similar diversities and ecologies 5 changes in familial diversity can be gauged accurately from the known fossil record 6 extinction of families can be compared through time without normalizing for changes in familial diversity through time 7 extinction rates can be compared without normalizing for differing lengths of geologic stages and 8 catastrophic mass extinctions do not select for small size these assumptions have resulted in unsupportable and or erroneous conclusions carboniferous through early jurassic terrestrial vertebrate families mostly have evolution and extinction patterns unlike the vertebrate evolution and extinction patterns during the terminal cretaceous event only the serpukhovian mid carboniferous extinction event shows strong analogy to the terminal cretaceous event available data suggest no terminal triassic extinction anomaly but rather a prolonged and nearly steady decline in the global terrestrial vertebrate extinction rate throughout the triassic and earliest jurassic

environmental changes across the triassic jurassic boundary and coeval volcanism inferred from elemental geochemistry and mineralogy in the kendlbachgraben section northern calcareous alps austria the end triassic extinction ete one of the five largest phanerozoic mass extinctions is associated with rapid and severe environmental change but existing data permit alternative models of causation volcanism in the central atlantic magmatic province camp has been proposed as the main trigger but direct evidence for this linkage is scarce to help constrain scenarios for the ete and other triassic jurassic boundary tjb events we obtained a temporally highly resolved multidisciplinary dataset from the kendlbachgraben section in the northern calcareous alps in austria the section belongs to the same paleogeographic unit eiberg basin and share similar stratigraphy with the recently selected base jurassic global stratotype section and point at kuhjoch micromineralogic study of the topmost bed of the rhaetian k ossen formation revealed pseudomorphs of altered euhedral pyroxene and amphibole crystals their well faceted morphology is consistent with their origin from distal mafic volcanic ash fallout spherical grains were also observed in the same bed likely representing clay altered volcanic glass clay minerals of this bed include lowto medium charged smectite and mg vermiculite both typical alteration products of mafic rocks the same bed yielded a rare earth element pattern that differs from all other levels in an enrichment of heavy rees hinting at some minor contribution from mafic magmatic material these features from a layer that was deposited very near to the tjb are interpreted as direct evidence of camp volcanism coeval or immediately preceding the ete and the initial negative carbon isotope anomaly the kaolinite dominated clay mineral spectrum of the overlying boundary mudstone records intensive weathering under hot and humid greenhouse conditions redox sensitive minor and trace elements do not support the development of widespread anoxia in the studied section although pyrite is common in several layers framboid size indicates formation within a reductive zone below the sediment water interface rather than in an anoxic water column our data provide a direct link between uppermost triassic marine strata and camp derived material they support scenarios where camp volcanism induced climate and other environmental change which in turn triggered the ete and that is also reflected in the carbon isotope anomalies 2012 elsevier b v all rights reserved

ree systematics in hydrothermal fluorite abstract ree patterns of fluorite from 63 post variscan hydrothermal veins of the schwarzwald area germany can be divided into two major groups type a fluorite shows roof shaped paas normalized patterns with enriched mree the turning point of the curvature is at ho or er position all patterns of type a show a distinct positive eu anomaly type b fluorite shows roof shaped patterns with enriched mree and strongly depleted hree and a characteristic steep slope between nd and sm the turning point of the curvature is at gd to dy all patterns of type b show negative or no eu anomalies laser ablation icp ms traverses through single grains combined with cathodoluminescence imagery revealed either i identical ree patterns and total ree concentrations from core to rim ii identical ree patterns but concentration gradients or iii variable ree patterns and concentration gradients from core to rim these features are explained by different degrees of supersaturation or different fluid fluorite ratios during crystallization and by complexly controlled precipitation processes under closed system conditions petrographically late fluorites from several deposits show the characteristics of new fluid batches rather than the expected remobilization features lree enrichment close to the crystal faces in some grains may result from the copreciptiation of a submicrometer sized lree enriched phase or from lree clustering in late cool fluids by comparison with literature data on natural waters from gneissic and granitic aquifers and of leachates of granites and gneisses we show that the hydrothermal vein fluorite preserves the characteristic source related ree feature of the hydrothermal fluid that migrated through either gneissic type a or granitic type b host rocks the immediate host rocks of the veins however are not the source rocks of the ree which indicates large scale fluid convection in the basement gneiss related type a fluorite shows tb ca tb la trends of primary hydrothermal crystallization whereas granite related type b fluorite indicates remobilization of possibly pegmatitic or variscan fluorite

mesozoic fluorite veins in ne spain record regional base metal rich brine circulation through basin and basement during extensional events abstract basinal brines are commonly involved in the formation of hydrothermal base metal ore deposits in sedimentary basins although in many instances the source of metals is often thought to be the underlying basement rocks the evidence of brine infiltration through the basement is sometimes directly found in vein systems in fracture zones crosscutting the basement that is the case of the fluorite barite base metal veins found throughout the hercynian basement of europe north africa and the appalachians a geochemical study of brines trapped in these veins can reveal their origin and evolution but also their mineralizing potential and coupled with the timing of fluid circulation can give clues to elucidate the role of these or similar brines in the genesis of base metal mineralizations together with their possible links to tectonic events the sm nd dating of fluorite samples from one of these veins in ne spain the rigros fluorite vein has yielded an age of 137 25 ma 2 mswd 0 40 the vein formation took place during the late jurassic early cretaceous rifting event in the western european basins which is related to the opening of the atlantic inclusion fluids in samples from rigros and another vein system from the same region the berta fluorite vein have been studied with microthermometry crush leach and la icp ms the brines trapped in the two studied vein systems are na ca cl k mg brines with homogenization temperatures 120 c and salinities up to 25 equiv mass nacl the source of this salinity is related to evaporated seawater at least in the halite precipitation field and to the leaching of mesozoic halite and gypsum sequences by seawater and or meteoric water the basinal brines later evolved through water rock interaction with the crystalline basement resulting in some sodium loss and potassium calcium strontium the latter inferred from isotope data and barium enrichment the analyzed brines have concentrations of zn between 3 and 790 ppm of pb between 3 and 995 ppm and of fe between 27 and 2639 ppm which are similar to those reported in comparable hydrothermal veins and mississippi valley type deposits but higher than in most present day sedimentary brines despite the fact they were able to transport large amounts of metals no significant precipitation of sulfides occurred in the veins and consequently the mineralizing potential of these brines was still preserved after fluorite vein formation

stability of atmospheric co2 levels across the triassic jurassic boundary the triassic jurassic boundary 208 million years ago is associated with widespread extinctions in both the marine and terrestrial biota the cause of these extinctions has been widely attributed to the eruption of flood basalts of the central atlantic magmatic province this volcanic event is thought to have released significant amounts of co2 into the atmosphere which could have led to catastrophic greenhouse warming but the evidence for co2 induced extinction remains equivocal here we present the carbon isotope compositions of pedogenic calcite from palaeosol formations spanning a 20 myr period across the triassic jurassic boundary using a standard diffusion model we interpret these isotopic data to represent a rise in atmospheric co2 concentrations of about 250 p p m across the boundary as compared with previous estimates of a 2 000 4 000 p p m increase the relative stability of atmospheric co2 across this boundary suggests that environmental degradation and extinctions during the early jurassic were not caused by volcanic outgassing of co2 other volcanic effects such as the release of atmospheric aerosols or tectonically driven sea level change may have been responsible for this event

depositional facies paleogeography and palaeoclimatology of the lower jurassic mccoy brook formation fundy rift basin nova scotia the mccoy brook formation is a 230 m sequence of redbeds of early jurassic age that accumulated in the subtropical fundy rift basin the basin was asymmetrical bordered on the northern side by the cobequid fault system and adjacent highlands the formation is a mosaic of terrestrial facies a multi and single storey fluvial sandstones were deposited by rivers that collected drainage from the norhern highlands and flowed southwest across the valley floor b graded bed sequences of sandstone mudstone were deposited by flood events on the fluvial floodplains and the margins of playas c interbedded sandstones and finely laminated to disrupted red mudstones represent deposits of interfingering sandflats at the toes of alluvial fans and playas respectively the fabrics of both lithologies are commonly disrupted by desiccation and intrastratal precipitation of calcite and minor gypsum d plane bedded conglomerate and pebbly sandstone record deposition in shallow channels that traversed alluvial fans e non bedded breccias of basalt boulders up to 8 m in size in a sand to mud matrix formed as talus against palaeocliffs of the lower jurassic north mountain basalt the palaeocliffs resulted from synsedimentary faulting within the basin f basalt conglomerate beds with matrix to clast supported fabrics comprise sequences deposited by debris flows probably generated by remobilization of talus g a thin sequence of limestone siltstone and muddy sandstone containing fish scales and bones formed in a shallow lake on a basalt flow h sandstones containing m scale crossbeds and a three fold hierarchy of erosional surfaces accumulated as barchans and barchanoid transverse ridges that moved southwest in the valley all of these facies occur within an area of 18 km2 located south of the fault bounded highlands synsedimentary faulting within the basin during early deposition of the mccoy brook formation created palaeocliffs of north mountain basalt talus and debris flow deposits accumulated adjacent to these cliffs interfingering with eolian fluvial and lacustrine sediments during later deposition of the mccoy brook formation the early fault controlled topography was buried as alluvial fans prograded southward from the highlands broad sandflats extended basinward from the toes of the fans interfingering with playa mudflats on the valley floor the palaeoclimate was semi arid as evidenced by gypsum bearing playa redbeds eolian sandstones and caliche palaeosols

palaeoenvironmental interpretation of a triassic jurassic boundary section from western austria based on palaeoecological and geochemical data a section spanning the triassic jurassic boundary is described from near the village of loruns in the vorarlberg region of western austria at loruns the uppermost triassic is characterised by bedded carbonates of the kossen formation supporting a stenotopic fauna indicative of a shallow sub tidal environment of normal marine salinity the triassic jurassic boundary may be represented as a sequence boundary developed on top of a 1 1 m thick red mudstone of the lower schattwald shale which is interpreted to have been deposited in a marginal marine environment possibly a mud flat above the boundary beds the upper schattwald shale is characterised by thin bedded marl and dark limestone beds with an earliest hettangian macrofauna dominated by epifaunal filter feeding bivalves including ostreids mytilids and oxytomids which suggest a shallow subtidal salinity controlled environment typical of an interplatform lagoon carbonate production rejuvenated in the later early hettangian with development of the loruns oolite a shallow subtidal oolitic and oncolitic unit bearing echinoderms indicative of normal marine conditions low thu ratios from the remainder of the section are a result of reduced thorium in carbonate rich sediments and not from authigenic uranium in anoxic sediments in the boundary beds evidence for marine anoxia or dysoxia is absent where thu values determined by gamma ray spectrometry are above 5 the negative excursion in 13c and positive excursion in 18o in the boundary beds may be due to secondary geochemical effects due to organic diagenesis or the precipitation of caliche during paleosol development alternatively the excursions may reflect a primary geochemical signal recording short term decline in primary productivity comparison in 18o and 13c values between the kossen formation and lorfus oolite indicate no significant long term geochemical changes are evident in the section and suggest that any environmental perturbations were restricted to the boundary beds and possible sequence boundary

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

provenance of tertiary sandstone in the northern qaidam basin northeastern tibetan plateau integration of framework petrography heavy mineral analysis and mineral chemistry abstract an exceptionally thick cenozoic sedimentary succession has developed in the qaidam basin of the northeastern tibetan plateau the provenance remains enigmatic thus more precise investigations are needed an integrated study of sandstone framework petrography heavy mineral analysis and mineral chemistry was adopted to perform provenance analysis of the tertiary sandstones in the northern qaidam basin no individual method exists that can provide comprehensive provenance interpretations on spatial and temporal variations based on three types of data three depositional areas can be distinguished sandstones of area a exhibit relatively high abundances of quartz garnet and zircon as well as relatively high textural maturity implying long distance sources multi composition garnets and tourmalines reveal derivations of metasedimentary rocks and intermediate acidic igneous rocks sandstones of area b are rich in metamorphic lithic fragments epidote and garnet a dominance of fe rich garnets with low mg low mn and variable ca contents and dravites demonstrates predominant derivation of metasedimentary rocks therefore the north qaidam and south qilian terranes are potential source areas for these two depositional areas additionally high metamorphic heavy mineral abundances in the upper formations imply increasing contributions of these two metamorphic belts during the tertiary tectonic uplift however sandstones of area c are characterized by relatively high abundances of feldspar igneous heavy minerals and high fe mn garnet which suggest a main source of igneous rocks the altun and qilian mountains are potential source regions furthermore increasing amounts of feldspar and igneous heavy minerals in the upper formations indicate a significant presence of igneous parent rocks which are most likely a response to the multi stage uplift events in the altun mountains since the early eocene

new early jurassic tetrapod assemblages constrain triassic jurassic tetrapod extinction event the discovery of the first definitively correlated earliest jurassic 200 million years before present tetrapod assemblage fundy basin newark supergroup nova scotia allows reevaluation of the duration of the triassic jurassic tetrapod extinction event present are tritheledont and mammal like reptiles prosauropod theropod and ornithischian dinosaurs protosuchian and sphenosuchian crocodylomorphs sphenodontids and hybodont semionotid and palaeonisciform fishes all of the families are known from late triassic and jurassic strata from elsewhere however pollen and spore radiometric and geochemical correlation indicate an early hettangian age for these assemblages because all typical triassic forms are absent from these assemblages most triassic jurassic tetrapod extinctions occurred before this time and without the introduction of new families as was previously suggested by studies of marine invertebrates this pattern is consistent with a global extinction event at the triassic jurassic boundary the manicouagan impact structure of quebec provides dates broadly compatible with the triassic jurassic boundary and following the impact theory of mass extinctions may be implicated in the cause

the end of the cretaceous sharp boundary or gradual transition evidence indicates that the cretaceous tertiary boundary is very sharp and within the limits of resolution it is apparently synchronous at the various boundary localities arguments to the contrary particularly those of officer and darke are shown to invalid

a search for shocked quartz at the triassic jurassic boundary in the fundy and newark basins of the newark supergroup triassic jurassic rift basins associated with the breakup of pangea preserve key geological elements of a defining interval in earth history in eastern north america the fundy basin is the largest and deepest of nine major early mesozoic basins of the newark supergroup overall the stratigraphic succession is that of continental sediments primarily fluvial eolian and playa lacustrine facies in the fundy basin the triassic jurassic boundary as palynologically defined is located within a few metres of the base of the north mountain basalt in the jacksonwald syncline of the newark basin the boundary is precisely correlated to a fern spike coincident with geologically rapid late triassic extinctions if meteorite impact is held to account for extinctions at the triassic jurassic boundary then shocked quartz the most important and unequivocal evidence of terrestrial impact should be preserved in strata of the appropriate time interval quartz bearing rocks below the north mountain basalt displ

the terrestrial impact cratering record approximately 130 terrestrial hypervelocity impact craters are currently known due to variations in preservation and in geologic knowledge this sample is biased towards young x 20 km craters on the cratons of australia europe including the former u s s r and north america the rate of discovery of new craters is 3 5 craters per year although modified by erosion terrestrial impact craters exhibit the range of morphologies observed for craters on other terrestrial planetary bodies such as the moon terrestrial craters provide essential ground truth data on the geologic effects of impact and the subsurface structure of impact craters which can be used to constrain interpretations of lunar samples and models of crater formation due to erosion and its effects on form terrestrial craters are recognized primarily by the occurrence of shock metamorphic effects these include shatter cones microscopic planar deformation features solid state and fusion glasses high pressure polymorphs and whole rock melting and vaporization shock recovery experiments indicate that these features occur over shock pressures of 5 gpa to x 100 gpa terrestrial craters have a set of geophysical characteristics which are largely the result of the passage of a shock wave and impact induced fracturing they include gravity and magnetic lows and reductions in seismic velocity the gravity anomalies are seldom greater than 30 mgal due to the limiting effects of lithostatic pressure on fracturing at large complex craters the gravity signature may include a central relative gravity high due to uplift and short wavelength central magnetic anomalies due to a variety of processes much current work is focused on the effects of impact on earth evolution previous work on shock metamorphism and the contamination of impact melt rocks by meteoritic siderophile elements provides a basis for the interpretation of the physical and chemical evidence from cretaceous tertiary boundary sites as resulting from a major impact suggestions that other biological boundaries in the stratigraphie record are due to periodic impacts are not supported by time series analysis of the terrestrial cratering record by analogy with the lunar record and modelling of the effects of very large impacts it has been proposed that biological and atmospheric evolution of the earth could not stabilize before the end of the late heavy bombardment 3 8 ga ago the present terrestrial cratering rate is 5 4 2 7 10 15 km 2a 1 for a diameter 20 km this represents a local threat on historic time scales on a global scale a major impact sufficient to cripple human civilization severely will occur on time scales of 106 a

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

occurrence and distribution of high molecular weight hydrocarbons in selected non marine source rocks from the liaohe qaidam and tarim basins china abstract extracts of 18 potential source rocks from the qaidam liaohe and tarim basins china have been characterized by high temperature gas chromatography htgc and found to contain high molecular weight hydrocarbons hmwhcs above c40 these rocks were originally formed in freshwater lacustrine saline lacustrine and terrigenous bog environments with mudstone calcareous mudstone coaly shale and coal lithologies their ages range from triassic to miocene and maturities from immature to mature covering a vitrinite reflectance range ro for the liaohe and tarim samples of 0 54 0 84 the combined distributions of the n alkane and alkylcyclopentane homologues in the extracts can be used to characterize the nature of the original depositional environment in certain samples the carbon number predominance of the n alkanes changes from an odd even predominance to even odd predominance above c40 possibly suggesting different precursors for the n alkanes above and below c40 concentrations of the hmwhcs were also observed to increase with maturity of the source rocks this is the first comprehensive report on the occurrence of hmwhcs in source rocks and their discovery introduces the possibility of using these compounds for oil source rock correlation purposes in future studies along with the more conventional biomarkers

mass extinctions the view of a sceptic the concept of periodic mass extinctions by extraterrestrial impacts has contributed very strongly to the current revival of interest in the problem of mass extinctions in this context several radical claims have been made asserting that the newly emerging picture of mass extinctions as a separate class of biological phenomena caused by a separate class of processes demands a far reaching revision of the the neodarwinian paradigm of evolution and implies a vindication of the cuvierian perspective on earth9s history the validity of these claims however is questionable at all levels from the interpretation of particular events to the concept of mass extinctions as a special class of phenomena to their proposed causation by impacts and to their alleged historical pedigree and implications for current evolutionary theory mass extinctions may actually be clusters of more or less accidentally aggregated in time but causally distinct extinction episodes

events around the triassic jurassic boundary in northern and eastern spain a review abstract more than 20 successions containing the triassic jurassic t j boundary were studied in five of the major geological units of spain the data are from outcrop cored boreholes and interpreted well logs a consistent 3 4 13 c org isotope excursion starting in the rhaetian and continuing in the hettangian was recorded in asturias climate changes in the t j transition show a warming episode in the early hettangian other climate changes are indicated by an increase in hygrophytic miospores above the t j boundary this reflects a more humid episode at the beginning of the hettangian the messejana dyke in southeastern iberia is part of the central atlantic magmatic province camp co 2 outgassing related to extensive magmatic activity in the camp is thought to be one of the possible factors responsible for the end triassic mass extinction no major sea level changes or unconformities were recorded at the t j boundary only in the asturias area was there a well defined shallow carbonate platform during the t j transition the other areas of eastern and northern spain were occupied by coastal playas and sabkhas that developed in arid climatic conditions the biotic crisis around the t j boundary is reflected in the palynomorph record in asturias seven species do not persist beyond the late rhaetian and only six appeared in the triassic jurassic transition however 22 taxa appeared in the early hettangian

structural stratigraphic and sedimentological characterisation of a wide rift system the triassic rift system of the central atlantic domain abstract the extension driven break up of the pangean supercontinent in the present day central and north atlantic domains commenced during permo triassic times permian rift processes in this region are generally attributed to crustal collapse during the latter part of the hercynian variscan orogeny but the triassic rifting style is more complex and the presence of a single over riding first order control is equivocal basement terrane structures and boundaries provide pre existing zones of weakness that had significant influences on the location timing orientation and extent of triassic rifting the 201 ma central atlantic magmatic province camp a large igneous province lip increased lithospheric heat flow at the end of rifting produced uplift and doming and also contributed to deformation and subsequent continental breakup analysis of the triassic basin structures in the central atlantic and north atlantic domains respectively georgia to nova scotia and conjugate margin and newfoundland iberia shows that four main basin types are geographically distributed 1 southern basins georgia to virginia small to medium size with limited growth structures 2 basins in the central east domain new jersey nova scotia wide basins with growth structures along long lived inherited bounding faults 3 basins in the central west domain offshore ns and morocco that comprise numerous half graben sub basins in a lower unit and an upper very wide tabular unit and 4 northern basins newfoundland portugal that are tabular and extremely wide basin architectures suggest that subsidence was regional in extent and not necessarily controlled by main faults variations in crustal characteristics are considered to have led to the development of the four main basin types stratigraphic data show that the onset of deposition in the central and southern north atlantic domain was restricted to a central segment between two main structural lineaments overall crustal rheology and inheritance exhibited first order controls on subsidence and basin development triassic basins in the central and north atlantic domain were all filled by continental deposits in various palaeo environments such as alluvial fan mega fluvial systems terminal fluvial systems fan delta fluvial systems permanent oxic and anoxic lakes playa lakes and saline lakes some of them interbedded with aeolian and volcanic deposits most basins were far from any marine domain but marine ingressions from the tethys domain are inferred from dolomite and marine fauna in portugal and from thick salt deposits in morocco and offshore canada during the late rhaetian a series of palaeogeographic maps are presented utilising plate reconstructions based on sahabi et al 2004 in order to summarize continental scale palaeo environment distribution our tectono stratigraphic model suggests that initial strain was accommodated in a central segment by inherited faults during the early and middle triassic during the carnian the rift domain was increasingly extended with the development of half graben basins in the central segment and some in the northern segment in both segments the initial strain re activated inherited faults and later the rift zones evolved towards significantly wider basins marked by the presence of a major erosional truncation surface across the basins and followed by lacustrine sedimentation that eventually overlapped paleo topographic highs subsidence of such regional extent is likely driven by thermal processes following a phase of extreme lithospheric thinning and lower crustal removal associated with mantle uplift the architecture of the triassic rifting has the characteristics of the wide rift mode very large basins with some active faults for which subsidence is driven by lower crustal flow within a high heat flow region nevertheless some faults were active during late triassic sedimentation but accounted for a relatively minor part of the overall subsidence pulses of active subsidence and topographic rejuvenation led to fluvial dominated deposition within basins non rejuvenation of hinterland led to more lacustrine dominated sedimentation and eventual connection of basins across topographic highs due to regional thermal subsidence during the latest rhaetian basins with the lowest elevations were possibly flooded by marine waters resulting in precipitation of thick salt deposits

deep sea record of impact apparently unrelated to mass extinction in the late triassic the 34 million year my interval of the late triassic is marked by the formation of several large impact structures on earth late triassic impact events have been considered a factor in biotic extinction events in the late triassic e g end triassic extinction event but this scenario remains controversial because of a lack of stratigraphic records of ejecta deposits here we report evidence for an impact event platinum group elements anomaly with nickel rich magnetite and microspherules from the middle norian upper triassic deep sea sediment in japan this includes anomalously high abundances of iridium up to 41 5 parts per billion ppb in the ejecta deposit which suggests that the iridium enriched ejecta layers of the late triassic may be found on a global scale the ejecta deposit is constrained by microfossils that suggest correlation with the 215 5 mya 100 km wide manicouagan impact crater in canada our analysis of radiolarians shows no evidence of a mass extinction event across the impact event horizon and no contemporaneous faunal turnover is seen in other marine planktons however such an event has been reported among marine faunas and terrestrial tetrapods and floras in north america we therefore suggest that the manicouagan impact triggered the extinction of terrestrial and marine organisms near the impact site but not within the pelagic marine realm

gulf stream structure transport and recirculation near 68 w an analysis of the structure and transport of the gulf stream is undertaken using direct current meter observations from a 13 mooring array deployed near 68 w from june 1988 to august 1990 the analysis is based on a stream coordinate approach in which velocities are rotated into a local downstream coordinate frame and averaged according to their relative cross stream location within the current the picture so obtained represents the average synoptic structure of the gulf stream rather than the eulerian averaged structure in which the current is weakened and broadened by lateral meandering of the current and adjacent recirculations many familiar features of the gulf stream are reproduced in the analysis including an asymmetric velocity profile with larger shear on the cyclonic shoreward side of the current an offshore displacement of the velocity core with depth and a subsurface velocity maximum on the offshore side of the current westward recirculations are also seen on both sides of the gulf stream maximum downstream speeds at the axis of the gulf stream reach approximately 2 0 m s at the surface and 0 7 m s at 1000 m roughly twice the corresponding eulerian averaged values the analysis also reveals a deep extension of the gulf stream at 3500 m depth with a width of 130 km and average speeds of 3 4 cm s the transport of the gulf stream in the stream coordinate frame is 113 8 sv approximately 30 larger than the eulerian averaged transport of 88 sv on the basis of these results and other recent studies the downstream transport increase of the gulf stream and the inflow structure to the gulf stream are reconsidered it is concluded that approximately 30 sv or over half of the transport increase between cape hatteras and 68 w is fed by inflow from the northern side of the gulf stream and that this inflow is concentrated near cape hatteras and 68 w where the gulf stream flows steeply across isobaths converging from the north

multiple ir anomalies in uppermost triassic to jurassic age strata of the blomidon formation fundy basin eastern canada article i nfo a detailed profile of ir concentrations in continental strata of the blomidon formation ostensibly spanning the triassic jurassic boundary confirms the existence of multiple anomalies with a peak ir concentration of 450 pg g the total amount of ir deposited exceeds 4 ng cm 2 a value that requires an external source other than typical terrestrial sediment of the 10 other elements measure only zn and organic carbon are correlated to ir the organic carbon appears to be concentrated in mm thick kerogenous laminae in greenish grey to dark grey sediment layers that also host the ir anomalies the stratigraphic distribution of ir and probably zn appears to be controlled largely by redox boundaries conditions with ir probably forming organo metallic complexes we find no specific geochemical or sedimentological evidence for an extraterrestrial source for this enrichment although we cannot exclude an impact origin however the close spatial and temporal relationship of the ir anomalies in the fundy and newark basins to the basalts of the central atlantic magmatic province suggests alternative working hypotheses potentially the volcanic rocks sourced the ir through post eruptive fluid mobilization into the surrounding sediments conversely mantle outgassing and aerosol deposition during early stages of the eruptions may have been the source for the ir anomalies at this time the data are insufficient to eliminate any of these hypotheses conclusively 2008 elsevier b v all rights reserved

shocked quartz at the triassic jurassic boundary in italy quartz grains that appear to have been shock metamorphosed occur within three closely spaced shale beds from the uppermost triassic rhaetian calcare a rhaetavicula in the northern apennines of italy the upper shale coincides with the abrupt termination of the distinctive uppermost triassic rhaetavicula fauna and is overlain by the hettangian lower jurassic calcare massiccio no extinctions appear to be associated with the two lower layers which occur 1 2 and 2 4 meters below the boundary shale approximately 5 to 10 of the quartz grains within these layers exhibit one or more sets of planar deformational features whose orientations cluster around the rational crystallographic planes basal and most commonly observed in shocked quartz textural and stratigraphic observations support an interpretation of at least three closely spaced impacts at the end of the triassic

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

on the edge of camp geology and volcanology of the jurassic north mountain basalt nova scotia abstract the north mountain basalt nmb is a sequence of continental tholeiitc basalts that are part of the larger 200 ma central atlantic magmatic province camp the nmb occur within the fundy basin one of several mesozoic extensional basins that formed during the incipient rupture of pangea in addition to the nmb the fundy basin was also filled by fluvial alluvial playa lacustrine and aeolian sediments under arid to semi arid conditions mapping of a 200 km long segment of the nmb along the southern coast of the bay of fundy indicates for the first time the lateral continuity of the three recognized lava units the east ferry margaretsville and brier island members efm mm bim respectively that comprise the nmb the efm 150 m are massive and characterized by pervasive development of columnar jointing both colonnade and entablature in addition whereas the efm contains abundant layers of mafic pegmatite the bim is characterized by abundant mesostasis possibly reflecting widespread quenching of this flow and locally abundant segregation pipes due to mobilization of a late stage felsic liquid these two units represent expansive eruption of low viscoity flows onto a low slope surface which encouraged uniform thickness and their massive nature but the role of faulted basins cannot be ruled out in contrast the mm 170 m consists of numerous 16 inflated pahoehoe sheet flow lobes evidence that these flows formed as pahoehoe flows is represented by exceptional development of the vesicle zonation i e upper crust vesicle sheets vesicle cylinders pipe vesicles as observed in modern hawaiian flows historical icelandic flows and ancient flows of the columbia river basalt group the thickness of upper crust zones indicates that the individual flows formed over months to years whereas inclined basal pipe vesicles indicate the mm and bim flowed to the south the similar age and nature of the nmb to other basalt sequences in camp suggest that similar processes operated throughout this lip thereby having implications for such phenomena as atmospheric contamination and extinction events caused by eruption of these voluminous basaltic lava flows

paleomagnetism of the chinle and kayenta formations new mexico and arizona paleomagnetic data were obtained from 22 sites 6 10 samples site in the upper shale member of the chinle formation 43 sites in the owl rock member of the chinle formation and 35 sites in the kayenta formation thermal demagnetization and data analyses indicate that within site dispersion is an important criterion for selecting sites which retain a high unblocking temperature characteristic remanent magnetization chrm site mean directions define at least four antipodal polarity zones within each member formation suggesting the chrm was acquired soon after deposition fifteen site mean virtual geomagnetic poles vgps from the upper shale member of the chinle formation yield an early norian paleomagnetic pole position of 57 4 n 87 8 e k 60 a95 5 0 eighteen site mean vgps from the owl rock member of the chinle formation yield a middle norian paleomagnetic pole position of 56 5 n 66 4 e k 183 a95 2 6 twenty three site mean vgps from the kayenta formation yield a pliensbachian pole position of 59 0 n 66 6 e k 155 a95 2 4 combined with paleomagnetic poles from the moenave formation and the shinarump member of the chinle formation these data record 30 m y of north american apparent polar wander apw within a regional stratigraphic succession during the camian and norian stages of the late triassic chinle poles progress westward during the hettangian through pliensbachian stages of the early jurassic the pattern of apw changed to an eastward progression even after correction for 4 clockwise rotation of the colorado plateau a sharp comer in the apw path j1 cusp is resolved near the pole from the hettangian sinemurian 200 ma moenave formation 59 4 n 59 2 e amongst other implications the sharp change in the apw path at the j1 cusp implies an abrupt change from counterclockwise rotation of pangea prior to 200 ma to clockwise rotation thereafter

cycles of sand flat sandstone and playa lacustrine mudstone in thetriassic jurassic blomidon redbeds fundy rift basin nova scotia implications for tectonic and climatic controls the redbeds of the 220 m blomidon formation comprise more than 100 pairs of i sand flat sandstone distal alluvial fan and ii playa sandy mudstone and or lacustrine claystone these pairs are tectonic autocycles generated by rift basin subsidence and sagging along the glooscap fault zone that shifted loci of active fan sedimentation toward and away from the playa surface as fan lobes migrated into topographically low areas intervals of intense and prolonged aridity are recorded in many of the sand flat sandstones and playa sandy mudstones by evaporite minerals principally gypsum precipitated by subsurface evolution of a caso4 nacl brine aridity is further demonstrated by intense disruption of sediment fabrics beneath evaporite crusts deep mudcracks eolian sandstone layers and patches and the presence of authigenic ca mg rich illite smectite and analcime during relatively wetter intervals claystone beds accumulated in shallow lakes that filled the playa depression lapping onto the sand flat

platinum group element anomalies and bioevents in the triassic jurassic deep sea sediments of panthalassa abstract micropalaeontological and geochemical analyses were performed on samples from a continuous sequence of bedded chert from the kurusu ku section inuyama area southwest japan the sequence contains the triassic jurassic t j boundary and is representative of deep sea sediments from panthalassa the succession records a rapid stepwise extinction pattern of radiolarian faunas and the disappearance of conodonts at the t j boundary comparison of micropalaeontological results and geochemical data reveals anomalously high abundances of platinum group elements pges in the latest rhaetian at the beginning of the radiolarian extinction at the t j boundary the pge anomaly suggests that the radiolarian ooze of panthalassa was contaminated by siderophile rich materials during the late rhaetian the rare earth element ree pattern shows no distinct change across the t j boundary except for one significant positive ce anomaly immediately below the pge anomaly these geochemical signatures imply the anomalous input of pge rich materials but no obvious anoxic event in deep sea sediments during latest triassic time the pge anomaly at the end of the triassic may be linked to the first phase of marine plankton extinction but would not have been directly connected with the main radiolarian extinction at the t j boundary

permian bimodal dyke of tarim basin nw china geochemical characteristics and tectonic implications abstract this study reports for the first time the occurrence of bimodal dyke in the shuigongtuan area of bachu county tarim basin nw china here quartz syenite porphyry and diabase dykes occur in direct contact showing bimodal feature the quartz syenitic porphyry is metaluminous enriched in k2o na2o 10 11 wt and total rare earth elements ree with low mg mg fe ratios high lree hree and negative eu anomalies the chemical characteristics and tectonic discriminative diagrams show that the rocks have geochemical affinity with a type granites the diabase dyke shows 45 52 wt sio2 and mg mg fe ratio in the range of with high total ree high lree hree ratios and lack of eu anomalies broadly corresponding to tholeiitic composition based on low y nb as low as 0 4 and less than 1 2 enrichment in lile and hfse and uniform nb enrichment patterns in spider diagram for the quartz syenitic porphyry together with the geochemical patterns of the diabases this biomodal association is interpreted to be derived from a mantle source and formed under typical within plate environment the quartz syenitic porphyry and diabase have daly gap of 46 wt 67 wt in sio2 which is explained through formation under bimodal rifting the quartz syenitic dyke probably formed during early permian 277 ma and has geochemical affinity with the xiaohaizi syenitic body we propose that magmas sourced from the mantle intruded into middle upper crust and were emplaced as dykes which indicate large scale extension during the permian in tarim basin the bimodal dyke has genetic affinity with the huge volume of permian basalts and igneous rocks 248 292 ma that occur in the tarim basin the magmatism manifests the culmination of the major thermal event in the tarim basin

mercury evidence for pulsed volcanism during the end triassic mass extinction the central atlantic magmatic province camp has long been proposed as having a causal relationship with the end triassic extinction event 201 5 ma in north america and northern africa camp is preserved as multiple basaltic units interbedded with uppermost triassic to lowermost jurassic sediments however it has been unclear whether this apparent pulsing was a local feature or if pulses in the intensity of camp volcanism characterized the emplacement of the province as a whole here six geographically widespread triassic jurassic records representing varied paleoenvironments are analyzed for mercury hg concentrations and hg total organic carbon hg toc ratios volcanism is a major source of mercury to the modern environment clear increases in hg and hg toc are observed at the end triassic extinction horizon confirming that a volcanically induced global hg cycle perturbation occurred at that time the established correlation between the extinction horizon and lowest camp basalts allows this sedimentary hg excursion to be stratigraphically tied to a specific flood basalt unit strengthening the case for volcanic hg as the driver of sedimentary hg toc spikes additional hg toc peaks are also documented between the extinction horizon and the triassic jurassic boundary separated by 200 ky supporting pulsatory intensity of camp volcanism across the entire province and providing direct evidence for episodic volatile release during the initial stages of camp emplacement pulsatory volcanism and associated perturbations in the ocean atmosphere system likely had profound implications for the rate and magnitude of the end triassic mass extinction and subsequent biotic recovery

a comparative study of the rare earth element ree distributions within the lower cretaceous dolomites and limestones of central tunisia ree distribution strontium content and oxygen isotopic composition have been studied in the lower cretaceous dolomites and their interbedded and or parental limestones of central tunisia dolomites as indicated by previous sedimentologic geochemical and isotopic study are different in origin environments of dolomite formation include evaporitic sabkha deep phreatic karst and lacustrine with the exception of the sabkha environment dolomitizing fluids presumably have been essentially meteoric the comparison between ree distributions in dolomites and limestones clearly suggests that the general shapes of the ree patterns are preserved during dolomitization nevertheless the total ree amounts are somewhat lowered in dolomites comparatively to parental limestones moreover within the dolomites the total ree contents are positively correlated to the sr and 18o contents thus indicating that the decrease in ree sr and 18o contents is related to a decrease in the salinity of dolomitizing fluids in addition dolomites associated with emergence surfaces karst are the most impoverished in ree furthermore they are relatively enriched in light ree indicating a more or less important fractionation with the ree distributions this enrichment has been related to the influence of the inorganic complexes which favours the greatest solubility of the heavy ree in basic solution with respect to the lightest members of the ree group

distribution and interpretation of rare earth elements and yttrium in cenozoic dolostones and limestones on cayman brac british west indies abstract the cenozoic carbonate succession on cayman brac a small island 19 km long and 1 5 to 3 km wide located in the caribbean sea has been dolomitized to varying degrees the rare earth element ree and yttrium y concentrations ree y of 134 carbonate samples 127 from cayman brac and 7 supplementary samples from grand cayman vary from 0 2 to 7 5 ppm average 2 8 ppm n 134 the shale normalized ree y patterns of the carbonate samples akin to those of oxygenated seawater are characterized by 1 lree depletion relative to hree average dy n sm n 1 7 n 125 2 positive la anomalies 3 negative ce anomalies average ce ce 0 4 n 133 and 4 superchondritic y ho molar ratios average y ho 85 n 86 the lack of correlation between the dolomite content of the samples and their ree y dy n sm n la n nd n ce ce or y ho indicates that dolomitization did not have a major impact on ree y signatures and that dolomitization was probably mediated by seawater like fluids the shale normalized patterns e g dy n sm n la n nd n ce ce and y ho vary from formation to formation for samples from the cayman formation the pedro castle formation and the ironshore formation there are subtle but gradual changes in dy n sm n la n nd n ce ce with depth in contrast there are marked changes in la n nd n ce ce y ho and sm nd across the brac unconformity which forms the boundary between the lower oligocene brac formation and the overlying miocene cayman formation variations in the ree y patterns reflect diagenetic processes e g dy n sm n and possibly secular changes in the ree y composition of seawater e g la n nd n y ho and sm nd

new record of fossil wood xenoxylon from the late triassic in the sichuan basin southern china and its paleoclimatic implications abstract fossil wood is one of the significant proxies for terrestrial paleoclimate and paleogeographical reconstruction in earth history abundant and diversified mesozoic fossil woods are well recorded in china however triassic fossil wood is very scarce here we report a new fossil wood from the late triassic xujiahe formation norian to rhaetian in guangyuan of northern sichuan basin southwestern china the fossil wood material consists of two well preserved specimens yielding secondary xylem with distinct growth rings bordered pits on the radial tracheid walls are mostly contiguous biseriate alternate locally uniseriate and strongly flattened cross fields show a large window like pore this anatomy is typical for the important fossil wood morphogenus xenoxylon gothan and based on a novel combination of radial and cross field pitting type and ray height a new species xenoxylon guangyuanense sp nov is recognized the finding of this new fossil wood taxon contributes to a better understanding of the yet poorly documented xenoxylon early radiation during the late triassic as well as of the origin of x meisteri group a peculiar endemic group which diversified in far east asia from the triassic to the early cretaceous xenoxylon is a paleobiogeographically significant genus being bound to cooler and or wetter climates of northern hemisphere throughout its late triassic late cretaceous range the occurrence of xenoxylon in the sichuan basin of southern china may indicate a short term cooling event sandwiched within a period during which warm and wet climate conditions largely prevailed over lower latitude regions of the northern hemisphere such a cooling event in the sichuan basin which was located at a low paleolatitude on the eastern rim of tethys may be in accordance in time with the temperature decline event in norian rhaetian boundary uncovered by oxygen isotope 18 o record in italy of the western rim of tethys

petrography and geochemistry of early stage fine and medium crystalline dolomites in the middle devonian presqu ile barrier at pine point canada the petrography and geochemistry of fine and medium crystalline dolomites of the middle devonian presqu ile barrier at pine point western canada sedimentary basin are different from those of previously published coarse crystalline and saddle dolomites that are associated with late stage hydrothermal fluids fine crystalline dolomite consists of subhedral to euhedral crystals ranging from 5 to 25 m mean 8 m the dolomite interbedded with evaporitic anhydrites that occur in the back barrier facies in the elk point basin fine crystalline dolomite has 18 values between 1 6 to 3 8 pdb and 87sr 86sr ratios from 0 7079 0 7081 consistent with derivation from middle devonian seawater its sr concentrations 55 225 p p m mean 105 p p m follow a similar trend to modern little bahama seawater dolomites its rare earth element ree patterns are similar to those of the limestone precursors these data suggest that this fine crystalline dolomite formed from middle devonian seawater at or just below the sea floor medium crystalline dolomite in the presqu ile barrier is composed of anhedral to subhedral crystals 150 250 m mean 200 m some of which have clear rims toward the pore centres this dolomite occurs mostly in the southern lower part of the barrier medium crystalline dolomite has 18o values between 3 7 to 9 4 pdb mean 5 9 pdb and 87sr 86sr ratios from 0 7081 0 7087 mean 0 7084 sr concentrations from 30 to 79 p p m mean 50 p p m and mn content from 50 to 253 p p m mean 161 p p m and negative ce anomalies compared with those of marine limestones the medium crystalline dolomite may have formed either 1 during shallow burial at slightly elevated temperatures 35 40 c from fluids derived from burial compaction or more likely 2 soon after deposition of the precursor sediments by middle devonian seawater derived from the elk point basin these results indicate that dolomitization in the middle devonian presqu ile barrier occurred in at least two stages during evolution of the western canada sedimentary basin the geochemistry of earlier formed dolomites may have been modified if the earlier formed dolomites were porous and permeable and water rock ratios were large during neomorphism