mobility of rhenium platinum group elements and organic carbon during black shale weathering this study investigates the effects of black shale weathering on the re os isotope system platinum group element concentrations and the degradation of organic matter samples from a weathering profile in late devonian 365 myr ohio shale show a pronounced decrease 77 in organic carbon corg near the present soil surface relative to the interior portion of the outcrop a similar trend is observed for total n 67 loss conversely organic phosphorus porg concentrations increase by 59 near the soil surface the decrease in corg is accompanied by a pronounced decrease in re 99 and to a lesser extent os 39 palladium and pt do not appear to be significantly mobile the effects of re and os mobility on the re os isotope system are significant none of the samples plots on a 365 myr isochron rather the samples define a trend with a slope corresponding to an age of 18 myr with an initial 187os 188os of 6 1 this indicates recent disturbance of the re os system isotope mass balance calculations imply that the labile fraction of os is significantly more radiogenic 187os 188os of 7 8 than the average of the unweathered samples 187os 188os of 6 4 based on data from this study the molar ratio of labile re to corg in ohio shale is estimated at 7 10 8 we estimate the present day riverine black shale derived re flux to seawater using literature data on re burial in anoxic marine sediments and assuming steady state between re release during black shale weathering and re burial in anoxic marine sediments then the labile re corg observed in this study implies that 0 5 tmol of corg is released annually from weathering of black shales a trace lithology in the continental crust this flux corresponds to 12 of the estimated annual co2 flux from oxidative weathering of sedimentary rocks the labile molar re os of 270 indicates that black shale weathering releases 130 mol os per year which accounts for 7 of the riverine os input to seawater the data from this study support the notion that the crustal cycles of labile corg re and os are tightly coupled gray shales which are less corg re and os rich but much more abundant in the continental crust than black shales are likely to be even more important continental sources of re and os to seawater

environmental significance of foraminiferal morphogroups in jurassic north sea deltas abstract the distribution of morphological groups of foraminifera has been analysed in toarcian and bajocian deposits of the northern north sea and the yorkshire coast the deposits are referred to prodeltaic lower delta front and interdistributary bay environments and contain mainly or entirely agglutinating assemblages of low to intermediate diversity a total of 33 agglutinating species are recognized in the studied material and these are arranged into eleven morphotypes composing seven subgroups and four morphogroups the categories are distinguished on the basis of main morphological features of the taxa combined with their life positions and micro habitats as inferred from modern analogues the prodelta deposits were formed in a normal saline and slightly stagnant depositional setting with foraminiferal faunas composed mainly of surficial and infaunal morphogroups the lower delta front and interdistributary bay sediments were deposited in shallow hyposaline waters strongly dominated by an epifaunal morphogroup with a partly phytal association a model of agglutinated morphotype distribution reveals increasing morphotype diversity and by inference ecological niche span from interdistributary bay through lower delta front to prodeltaic environments

marine 187os 188os isotope stratigraphy reveals the interaction of volcanism and ocean circulation during oceanic anoxic event 2 high resolution osmium os isotope stratigraphy across the cenomanian turonian boundary interval from 6 sections for four transcontinental settings has produced a record of seawater chemistry that demonstrates regional variability as a function of terrestrial and hydrothermal inputs revealing the impact of palaeoenvironmental processes in every section the 187os 188os profiles show a comparable trend radiogenic values in the lead up to oceanic anoxic event 2 oae 2 an abrupt unradiogenic trend at the onset of oae 2 an unradiogenic interval during the first part of oae 2 and a return to radiogenic values towards the end of the event above the cenomanian turonian boundary the unradiogenic trend in 187os 188os is synchronous in all sections previous work suggests that activity of the caribbean lip large igneous province was the source of unradiogenic os across the oae 2 and possibly an instigator of anoxia in the oceans here we assess this hypothesis and consider the influence of activity from other lips such as the high arctic lip a brief shift to high radiogenic 187os 188os values occurred in the western interior seaway before the onset of oae 2 we evaluate this trend and suggest that a combination of factors collectively played critical roles in the initiation of oae 2 differential input of nutrients from continental and volcanogenic sources coupled with efficient palaeocirculation of the global ocean and epeiric seas enhanced productivity due to higher nutrient availability which permitted penecontemporaneous transport of continental and lip derived nutrients to trans equatorial basins

early plate tectonics versus single plate tectonics on mars evidence from magnetic field history and crust evolution 1 the consequences of an early epoch of plate tectonics on mars followed by single plate tectonics with stagnant lid mantle convection on both crust production and magnetic field generation have been studied with parameterized mantle convection models thermal history models with parameterized mantle convection not being dynamo models can provide necessary but not sufficient conditions for dynamo action it is difficult to find early plate tectonics models that can reasonably explain crust formation as is required by geological and geophysical observations and allow an early magnetic field that is widely accepted as the cause for the observed magnetic anomalies dating of crust provinces and topography and gravity data suggest a crust production rate monotonically declining through the noachian and hesperian and a present day crust thickness of more than 50 km plate tectonics cools the mantle and core efficiently and the core may easily generate an early magnetic field given a sufficiently weak mantle rheology plate tectonics can explain a field even if the core is not initially superheated with respect to the mantle because the crust production rate is proportional to temperature however an early efficient cooling will frustrate later crust production and therefore cannot explain for example the absence of prominent magnetic anomalies in the northern crustal province and the northern volcanic plains in the early hesperian voluminous crust formation following plate tectonics is possible if plate tectonics heat transfer is inefficient but then the crust growth rate has a late peak about 2 ga b p which is not observed these models also require a substantial initial superheating of the core to allow a dynamo if one accepts the initial superheating then as we will show a simple thermal evolution model with monotonic cooling of the planet due to stagnant lid mantle convection underneath a single plate throughout the evolution can better reconcile early crust formation and magnetic field generation

haskell 1935 revisited the haskell 1935 value of 1021 pa s for mantle viscosity is a classic and enduring constraint on the rheology of the earth s interior we revisit this inference using spherically symmetric self gravitating maxwell viscoelastic earth models our inference is based on both forward and inverse analyses of decay times associated with uplift at two sites considered by haskell angerman river sweden and oslo norway rather than the raw relative sea level rsl data at these sites we demonstrate that predictions of the decay time associated with the angerman river data are insensitive to variations in both the late pleistocene ice load history and the lithospheric thickness of the earth model the predictions at oslo are sensitive to both these inputs and hence decay times at this site provide a remarkably robust constraint on mantle viscosity we derive a constraint on the average viscosity of the mantle of 0 65 1 10 1021 pa s where the average resolved by the data encompasses a region which extends from the base of the lithosphere to a depth of near 1400 km this indicates that many previous analyses which have invoked the haskell value of 1021 pa s as a constraint on the average upper mantle i e above 670 km depth viscosity alone have misinterpreted the resolving power of the inference furthermore our analysis indicates that a number of apparently contradictory inferences of viscosity based on fennoscandian data satisfy the new rigorous interpretation of the haskell constraint finally we demonstrate how the ambiguity in the upper mantle lower mantle viscosity contrast associated with the haskell average may be reduced by invoking decay time constraints estimated from rsl curves in hudson bay a preliminary inversion of decay times at angerman river and richmond gulf in hudson bay suggests a contrast of approximately an order of magnitude between the average viscosities of the upper mantle and the top 1000 km of the lower mantle however a conclusive analysis in this regard must await the determination of consistent decay time estimates for the hudson bay region

convection in a variable viscosity fluid newtonian versus power law rheology abstract a number of finite element calculations of convection in a variable viscosity fluid have been carried out to investigate the effects of non newtonian flow when rheology is also subject to a strong temperature and pressure influence a variety of cases has been studied in the range of effective rayleigh numbers between 104 and 106 including different modes of heating and a range of values for activation energy and activation volume power law creep with a stress exponent of 3 turns out to lead to considerably different flow pattern and heat transfer properties than newtonian rheology in general the effect is to reduce viscosity contrasts imposed by p t dependence which can lead in some circumstances to the mobilisation of otherwise stagnant regions within the cell the properties of non newtonian flow can be closely imitated by a newtonian fluid with a reduced value of the activation enthalpy bh with b 0 3 0 5 it appears possible that non newtonian rheology plays a key role in determining the convective style in a planetary mantle

thermal correction for moho depth estimations on west philippine basin a python code to calculate the gravitational effects of lithospheric cooling under oceanic crust the aim of this work is to present an easy to use python code to calculate the gravitational effect due to lateral variations in the thermal structure of oceanic lithospheric plates necessary to appropriately isolate the contribution of the variations in crustal thickness the model is applied to calculate the moho depth in the west philippine basin and the results are compared with seismic data the estimations of the moho depth taking into account the thermal correction presented a better fit with the seismic data and smoother geographical variations than the model without thermal correction

cretaceous oceanic anoxic event 2 triggered by a massive magmatic episode oceanic anoxic events oaes were episodes of widespread marine anoxia during which large amounts of organic carbon were buried on the ocean floor under oxygen deficient bottom waters oae2 occurring at the cenomanian turonian boundary about 93 5 myr ago is the most widespread and best defined oae of the mid cretaceous although the enhanced burial of organic matter can be explained either through increased primary productivity or enhanced preservation scenarios the actual trigger mechanism corresponding closely to the onset of these episodes of increased carbon sequestration has not been clearly identified it has been postulated that large scale magmatic activity initially triggered oae2 refs 4 5 but a direct proxy of magmatism preserved in the sedimentary record coinciding closely with the onset of oae2 has not yet been found here we report seawater osmium isotope ratios in organic rich sediments from two distant sites we find that at both study sites the marine osmium isotope record changes abruptly just at or before the onset of oae2 using a simple two component mixing equation we calculate that over 97 per cent of the total osmium content in contemporaneous seawater at both sites is magmatic in origin a approximately 30 50 fold increase relative to pre oae conditions furthermore the magmatic osmium isotope signal appears slightly before the oae2 as indicated by carbon isotope ratios suggesting a time lag of up to approximately 23 kyr between magmatism and the onset of significant organic carbon burial which may reflect the reaction time of the global ocean system our marine osmium isotope data are indicative of a widespread magmatic pulse at the onset of oae2 which may have triggered the subsequent deposition of large amounts of organic matter

influence of the high arctic igneous province on the cenomanian turonian boundary interval sverdrup basin high canadian arctic abstract emplacement of large igneous provinces lips had a major effect on global climate ocean chemistries as traced in sedimentary records and biotic turnovers the linkage between lips and oceanic anoxic events has been documented with the cenomanian turonian boundary event and oceanic anoxic event 2 oae2 the caribbean lip and high arctic large igneous province halip are regarded as possible triggers the pericratonic arctic sverdrup basin is the partial location of the halip where little is known about sedimentary geochemical and biotic responses to the halip phases sedimentary strata at glacier fiord axel heiberg island exhibit a dynamic cretaceous polar carbon burial history within the lower to middle cenomanian bastion ridge formation and upper cenomanian to turonian part of the kanguk formation we present the first initial 187os 188os osi composition profile for a polar cenomanian turonian boundary interval 100 93 9 ma linked to recently dated magmatic phases of the strand fiord formation part of the halip the carbon isotope record coupled with the osi profile show two events in the upper cenomanian interval marked by positive carbon perturbations and shifts to more non radiogenic osi compositions the earlier short lived event is interpreted as result of weathering of the surrounding strand fiord volcanics causing a local non radiogenic osi signal coinciding transgressive shorelines let to an increase in marine and terrestrially derived organic matter subsequently injection of mantle derived basalts into organic rich sediments is credited with causing the release of methane documented in a distinct negative carbon isotope excursion we speculate that the methane release of the halip was an important contribution for rapid global warming caused by increasing atmospheric co2 levels associated with the oae2 event likewise recognized in the sverdrup basin as climate cooled in the middle and late turonian carbon burial decreased under increasingly oxygenated benthic conditions epifaunal foraminiferal species adapted to low oxygen conditions persisted during the oae2 our cenomanian to turonian multiproxy record of the sverdrup basin distinguishes between local and global signals within a restricted high arctic basin our results demonstrate the interplay between basin tectonism and sea level change increased weathering during transgressive phases seafloor processes such as hydrothermal activity and methane release and biotic response to a complex paleoceanography with future reliable dated frameworks this unique polar record will facilitate correlations to other polar basins and records of lower paleolatitudes

an improved jpl mars gravity field and orientation from mars orbiter and lander tracking data abstract the mars gravity field resolution is mostly determined by the lower altitude mars reconnaissance orbiter mro tracking data with nearly four years of additional mro and mars odyssey tracking data since the last jpl released gravity field mro110c and lander tracking from the mer opportunity rover the gravity field and orientation of mars have been improved the new field mro120d extends the maximum spherical harmonic degree slightly to 120 improves the determination of the higher degree coefficients as demonstrated by improved correlation with topography and reduces the uncertainty in the corresponding mars orientation parameters by up to a factor of two versus previously combined gravity and orientation solutions the new precession solution is 7608 3 2 1 mas yr and is consistent with previous results but with a reduced uncertainty by 40 the love number solution k2 0 169 0 006 also shows a similar result to previous studies

accretion of phobos and deimos in an extended debris disc stirred by transient moons mars has two small moons that may have formed in the aftermath of a giant impact simulations suggest that phobos and deimos accreted from the disperse outer region of the debris disc that was stirred up by short lived larger moons

onset of solid state mantle convection and mixing during magma ocean solidification energy sources involved in the early stages of planetary formation can cause partial or even complete melting of the mantle of terrestrial bodies leading to the formation of magma oceans upon planetary cooling solidification is expected to take place from the bottom upwards because of the steeper slope of the liquid adiabat with respect to the liquidus elkins tanton 2012 solomatov 2015 fractional solidification in particular can lead to the formation of a compositional layering that can play a fundamental role for the subsequent long term dynamics and evolution of the interior tosi et al 2013 plesa et al 2014 in order to assess to what extent primordial compositional heterogeneities generated upon magma ocean solidification can be preserved we investigate the cooling and solidification of a whole mantle magma ocean along with the conditions that allow solid state convection to start mixing the mantle before solidification has completed to this end we run 2 d numerical simulations in cylindrical geometry using the finite volume code gaia huttig et al 2013 we treat the liquid magma ocean in a parametrized fashion while we self consistently solve the conservation equations of thermochemical convection in the growing solid mantle accounting for pressure temperature and melt dependent rheology we consider two end member cases fractional crystallization where melt is instantaneously extracted into the overlying liquid leaving beneath a differentiated mantle and batch crystallization where melt remains in contact with the silicate matrix throughout solidification causing no differentiation by testing the effects of different cooling rates and rayleigh numbers we show that for a lifetime of the liquid magma ocean between 1 and 10 myr lebrun et al 2013 the onset of solid state convection prior to complete mantle crystallization is possible and that part or even all of the compositional heterogeneities generated upon fractionation can be erased by efficient mantle stirring figure 1 we discuss the consequences of our findings in relation to the early and long term evolution of compositional heterogeneities generated via fractional crystallization of magma oceans in terrestrial bodies with emphasis on mars thermochemical history

evidence for recent volcanism on mars from crater counts impact craters help characterize the age of a planetary surface because they accumulate with time they also provide useful constraints on the importance of surface erosion as such processes will preferentially remove the smaller craters earlier studies of martian crater populations revealed that erosion and dust deposition are important processes on mars they disagreed however on the age of the youngest volcanism these earlier studies were limited by image resolution to craters larger than a few hundred metres in diameter here we report an analysis using new images obtained by the mars global surveyor spacecraft of crater populations that extend the size distribution down to about 16 m our results indicate a wide range of surface ages with one region lava flows within the arsia mons caldera that we estimate to be no older than 40 100 million years we suggest that volcanism is a continuing process on mars

hydrolytic weakening of olivine at mantle pressure evidence of 100 010 slip system softening from single crystal deformation experiments abstract to date most of the experiments performed to quantify the hydrolytic weakening of olivine single crystals have been performed at low confining pressure and low water fugacities in order to determine if the degree of hydrolytic weakening changes at higher water fugacities higher water contents we have performed a series of high pressure p and high temperature t deformation experiments in hydrous condition on san carlos olivine fo92 and forsterite fo100 single crystals in a deformation dia apparatus d dia deformation was carried out in axial compression along the 1 1 0 c crystallographic reference frame direction in order to activate 1 0 0 0 1 0 dislocation slip system alone at p ranging from 4 to 7 gpa and t 1200 c water was supplied during the experiments through dehydration of a talc sleeve talc enstatite coesite h 2 o around the sample while the differential stress and strain rate of the specimen were calculated from in situ x ray diffraction and time resolved imaging respectively run products were investigated using fourier transform infrared ftir spectroscopy and optical electron microscopy sem and tem structurally bound hydroxyl content c oh derived from absorbance in ftir spectra based on the paterson 1982 relation were typically between 290 and 720 ppm h si in the run products and the majority of these hydroxyls were observed as distinct peaks in the range of wavenumber from 3620 to 3500 cm 1 tem reveals that the 1 0 0 0 1 0 slip system was effectively activated and responsible for crystal deformation and that dislocation glide was significantly assisted by recovering processes such as dislocation climb and dipole annihilation combining the experimental data from this study and mackwell et al 1985 we estimate the activation volume v 110 c for san carlos olivine in order to produce a reasonable water fugacity exponent r in the flow law and obtain v 110 c 12 1 cm 3 mol for r 0 and v 110 c 17 3 cm 3 mol for r 1 2 comparisons of the strengths of the wet single crystals to the strengths of dry single crystals calculated from the rheological laws bai et al 1991 darot and gueguen 1981 raterron et al 2009 indicate that the wet single crystal cylinders were between 1 3 and 1 6 times weaker than their dry counterpart at same conditions which is consistent with previous studies of 1 0 0 0 1 0 olivine rheology performed at low confining pressure 300 mpa

cenomanian to campanian carbon isotope chemostratigraphy from the western interior basin u s a abstract late cretaceous carbon isotope curves generated for localities in europe asia and the deep sea records have provided the foundation for development of a contiguous intercontinental chemostratigraphic framework despite the development of carbon isotope records from selected stratigraphic intervals in the western interior basin however a comprehensive 13c record comparable to those developed in europe and asia and from odp sites had not yet been completed this study reports a new high resolution cenomanian to campanian carbon isotope record for the central western interior basin of north america that makes a key contribution to the intercontinental correlation the curve is correlated to the well developed molluscan biostratigraphic framework for the western interior basin as well as a revised geochronology based on integration of new radioisotopic dating and astrochronology developed in the same core records from where the 13c data were derived the new 13c record reflects not only major perturbations in the global carbon cycle such as the mid cenomanian event and the cenomanian turonian ocean anoxic event 2 but also smaller excursions that have been recognized in records from europe and asia this shows that the western interior shallow epeiric sea was not isolated for any appreciable part of cenomanian to early campanian time it consistently recorded changes in the global marine carbon cycle observed elsewhere a critical attribute of the chemostratigraphic dataset produced in this study is its linkage with a revised late cretaceous time scale assignment of revised ages to western interior carbon isotope events that are globally expressed will allow export of the improved time scale to localities within and outside the western interior where similar carbon isotope records have been generated this chronostratigraphic tool will allow a number of stratigraphic and geochemical hypotheses to be more rigorously tested

a perturbed hydrological cycle during oceanic anoxic event 2 the late cretaceous oceanic anoxic event 2 oae2 ca 94 ma was one of the largest global carbon cycle perturbations during the phanerozoic oae2 represents an important although extreme case study for modern trends because widespread anoxia and enhanced organic carbon burial during oae2 were linked to exceptionally warm climates and high atmospheric co 2 concentrations however the consequences of this warmth for the hydrological cycle remain poorly understood hampering our understanding of its impact on biogeochemical cycles during this greenhouse episode here we show evidence for changes in the hydrological cycle during oae2 based on combined geochemical and palynological data for the stratigraphically expanded coastal oae2 succession at bass river located on the new jersey shelf ocean drilling program leg 174ax eastern united states paleothermometry based on tex86 indicates sea surface warming at the onset of oae2 and a subsequent pronounced cooling event palynological data show that these changes in temperature were associated with strong variations in precipitation and runoff we suggest that an acceleration of the hydrological cycle during oae2 played a key role in supplying nutrients to coastal waters and enhancing stratification thus contributing to the development of ocean anoxia

tropical warming and intermittent cooling during the cenomanian turonian oceanic anoxic event 2 sea surface temperature records from the equatorial atlantic oceanic anoxic event 2 oae 2 occurring during the cenomanian turonian c t transition is evident from a globally recognized positive stable carbon isotopic excursion and is thought to represent one of the most extreme carbon cycle perturbations of the last 100 myr however the impact of this major perturbation on and interaction with global climate remains unclear here we report new high resolution records of sea surface temperature sst based on tex86 and 18o of excellently preserved planktic foraminifera and stable organic carbon isotopes across the c t transition from black shales located offshore suriname french guiana demerara rise ocean drilling program leg 207 site 1260 and offshore senegal cape verde basin deep sea drilling project leg 41 site 367 at site 1260 where both sst proxy records can be determined a good match between conservative sst estimates from tex86 and 18o is observed we find that late cenomanian ssts in the equatorial atlantic ocean 33 c were substantially warmer than today 27 29 c and that the onset of oae 2 coincided with a rapid shift to an even warmer 35 36 c regime within the early stages of the oae a marked 4 c cooling to temperatures lower than pre oae conditions is observed however well before the termination of oae 2 the warm regime was reestablished and persisted into the turonian our findings corroborate the view that the c t transition represents the onset of the interval of peak cretaceous warmth more importantly they are consistent with the hypotheses that mid cretaceous warmth can be attributed to high levels of atmospheric carbon dioxide co2 and that major oaes were capable of triggering global cooling through the negative feedback effect of organic carbon burial led co2 sequestration evidently however the factors that gave rise to the observed shift to a warmer climate regime at the onset of oae 2 were sufficiently powerful that they were only briefly counterbalanced by the high rates of carbon burial attained during even the most extreme interval of organic carbon burial in the last 100 myr

contact metamorphic devolatilization of shales in the karoo basin south africa and the effects of multiple sill intrusions abstract quantification of fluid generation during contact metamorphism of shale is important for the understanding of metamorphic processes fluid flow in sedimentary basins and perturbations of the global carbon cycle in this study we provide geochemical and numerical analyses from the organic rich ecca group in the karoo basin south africa which was affected by contact metamorphism from multiple sill intrusions in the early jurassic organic matter was efficiently converted to hydrocarbons during contact metamorphism and complete loss of organic carbon in the innermost aureole is common mineral dehydration reactions are evident from the occurrence of metamorphic minerals like biotite and loss of the clay fraction towards the intrusive contact we have developed a numerical model in order to quantify fluid production from both inorganic and organic reactions during contact metamorphism the modelling results are constrained by data from two case studies in the karoo basin in order to obtain reliable estimates of the carbon loss from metamorphism of shale we show that single thin 15 m thick sills have a gas production potential of several gigatons of methane ch4 if emplaced over a 1000 km2 area furthermore the vertical spacing between simultaneously emplaced sills has an important influence on the gas generation potential when two sills are emplaced with a vertical spacing of 7 times the intrusion thickness the total ch4 generation is up to 35 more than for two separate sills data and modelling from five sills emplaced within the ecca group show hydrocarbon generation throughout the organic rich section with total carbon loss next to the sills this has implications for the fluid production and metamorphism in volcanic basins where multiple sills are common

pacific 187 os 188 os isotope chemistry and u pb geochronology synchroneity of global os isotope change across oae 2 studies of oae 2 sections beyond the atlantic ocean western interior seaway wis and european pelagic shelf are limited here we present initial osmium isotope stratigraphy 187os 188os osiosi from two proto pacific sites that span the cenomanian turonian boundary interval ctbi the yezo group yg section hokkaido japan and the great valley sequence gvs california usa to evaluate the 187os 188os seawater chemistry of the proto pacific additionally we combine new 206pb 238u zircon ca id tims geochronology from five volcanic tuff horizons of the yezo group section to test and facilitate inter basinal integration with the wis using radio isotopically constrained age depth models for both sections and quantitatively constrain the absolute timing and duration of events across the ctbi the yg shows an almost identical osiosi profile to that of the wis and very similar to that of other sites of the proto atlantic and european pelagic oceans turgeon and creaser 2008 and du vivier et al 2014 the characteristics of the osiosi profile are radiogenic and heterogeneous 0 55 0 85 prior to the oae 2 and synchronous with the inferred oae 2 onset the osiosi abruptly become unradiogenic and remain relatively homogeneous 0 20 0 30 before showing a gradual return to more radiogenic view the mathml sourceosi 0 70 throughout the middle to late oae 2 a206a206pb 238u zircon age of an interbedded tuff hk017 in the adjacent horizon to the first unradiogenic osiosi value constrains the age of the osiosi inflection at 94 44 0 14 ma94 44 0 14 ma this age including uncertainty agrees with the interpolated age of the same point in the osiosi profile 94 28 0 25 ma94 28 0 25 ma in the only other dated oae 2 section the wis indicating a coeval shift in seawater chemistry associated with volcanism at the oae 2 onset at the levels of temporal resolution ca 0 1 myr further prior to the onset of oae 2 an enhanced radiogenic inflection in the osiosi profile of the yg is correlative within uncertainty with a similar trend in the wis based on the u pb age depth model the interpolated ages 94 78 0 12 ma94 78 0 12 ma and 94 66 0 25 ma94 66 0 25 ma for this osiosi inflection in the yg and wis respectively indicate that palaeocirculation was sufficient to simultaneously influence transbasinal seawater chemistry in contrast the pre oae 2 osiosi profile for the gvs is disparate to that of the yg and those of the proto atlantic and european pelagic shelf locations we interpret the pre oae 2 heterogeneous osiosi values 0 30 0 95 to record a palaeobasin that was regionally influenced interchangeably by both unradiogenic hydrothermal flux and radiogenic continental flux os we conclude that the osiosi profiles from the proto pacific sections record both trends that are consistent globally oae 2 onset syn and post oae 2 but also show regional differences pre oae 2 between oae 2 sections worldwide as such the osiosi profiles coupled with u pb geochronology facilitate the correlation of oae 2 stratigraphy and demonstrate both regional and global ocean dynamics

intercalibration of radioisotopic and astrochronologic time scales for the cenomanian turonian boundary interval western interior basin usa we develop an intercalibrated astrochronologic and radioisotopic time scale for the cenomanian turonian boundary ctb interval near the global stratotype section and point in colorado usa where orbitally influenced rhythmic strata host bentonites that contain sanidine and zircon suitable for 40ar 39ar and u pb dating paired 40ar 39ar and u pb ages are determined from four bentonites that span the vascoceras diartianum to pseudaspidoceras flexuosum ammonite biozones utilizing both newly collected material and legacy sanidine samples of j obradovich comparison of the 40ar 39ar and u pb results underscores the strengths and limitations of each system and supports an astronomically calibrated fish canyon sanidine standard age of 28 201 ma the radioisotopic data and published astrochronology are employed to develop a new ctb time scale using two statistical approaches 1 a simple integration that yields a ctb age of 93 89 0 14 ma 2 total radioisotopic uncertainty and 2 a bayesian intercalibration that explicitly accounts for orbital time scale uncertainty and yields a ctb age of 93 90 0 15 ma 95 credible interval total radioisotopic and orbital time scale uncertainty both approaches firmly anchor the floating orbital time scale and the bayesian technique yields astronomically recalibrated radioisotopic ages for individual bentonites with analytical uncertainties at the permil level of resolution and total uncertainties below 2 using our new results the duration between the cenomanian turonian and the cretaceous paleogene boundaries is 27 94 0 16 ma with an uncertainty of less than one half of a long eccentricity cycle

the rheology and thermal history of mars revealed by the orbital evolution of phobos the evolution and internal structure of mars are by comparison to its present day surface poorly known although evidence of recent volcanic activity1 suggests that its deep interior remains hot and convectively cooling the cooling rate of mars is related to its early thermal state and to its rheology which determines its ability to deform and to dynamically evolve2 attempts to reconstruct the dynamic history of mars and reveal its present day structure by combining the study of thermal evolution with surface observations are limited by the interplay between several key quantities including temperature composition and rheology here we show that by considering phobos the closest satellite of mars the orbital evolution of which is governed by the thermochemical history of mars through tidal interactions we can gain insight into the thermal history and rheology of the planet we investigated the long term evolution of the main envelopes of mars these comprise a liquid metallic core that is overlain by a homogeneous silicate convecting mantle underneath an evolving heterogeneous lithospheric lid that includes a crust enriched in radiogenic elements by exploiting the relationship between mars and phobos within an established in situ scenario for the early origin of the moons of mars3 we find that initially mars was moderately hotter 100 to 200 kelvin than it is today and that its mantle sluggishly deforms in the dislocation creep regime this corresponds to a reference viscosity of 1022 2 0 5 pascal seconds and to a moderate to relatively weak intrinsic sensitivity of viscosity to temperature and pressure our approach predicts a present day average crustal thickness of 40 25 kilometres and a surface heat flow of 20 1 milliwatts per square metre we show that combining these predictions with data from future and ongoing space missions such as insight could reduce uncertainties in martian thermal and rheological histories and help to uncover the origin of phobos insights into the thermal and rheological history of mars are generated by considering the interplay between the thermochemistry of the planet and the orbital evolution of its closest satellite phobos

cenomanian to santonian radiolarian biostratigraphy carbon isotope stratigraphy and paleoenvironments of the sverdrup basin ellef ringnes island nunavut canada abstract an upper albian to santonian sedimentary record on ellef ringnes island canadian arctic archipelago records variable paleoenvironmental conditions within the cretaceous polar sea and sverdrup basin the upper albian to lower cenomanian uppermost christopher and hassel formations represent a regressive system tract from offshore to shoreface terrestrial paleoenvironments the upper cenomanian to santonian shales of the kanguk formation signify a distal offshore basin setting controlled by increased subsidence and high global sea levels siliceous pelagic faunas and floras dominate the basin and herein three informal radiolarian partial range zones are proposed for the polar sea alternating diversity and abundance patterns are interpreted as a response to sea level controlled productivity systems transgressive phases correspond to low diversity shallow dwelling radiolarian taxa with an expanded oxygen minimum zone omz regressive phases are coupled with radiolarian radiations of deeper dwelling species and a depressed omz the upper cenomanian to turonian was marked by increased preservation of marine type organic matter and organic carbon isotope excursions indicate the presence of the oceanic anoxic event 2 oae 2 at the base of the kanguk formation rock eval data suggest that an increasing terrestrial influence prevailed during the coniacian to campanian time covering the oae 3 benthic environments are dominated by anoxic conditions as suggested by the near lack of benthic foraminifera and extensive intervals of fine platy shale lacking bioturbation only the upper coniacian records a return to dysoxic benthic conditions radiolarian faunal comparisons to more southern localities suggest migration routes from the east through a narrow north atlantic pathway and from the pacific through the alaskan asian pathway

a new look at modern agglutinated benthic foraminiferal morphogroups their value in palaeoecological interpretation morphogroups offer a way of overcoming taxonomic differences and thereby making comparisons between assemblages of different geological ages relating morphogroups to environments has proved useful in palaeoecological interpretations the model proposed by jones and charnock in 1985 has subsequently been adapted and still serves as the main reference for such palaeoecological interpretations new data from 400 samples from marsh to deep sea off nw europe are used here to refine the model by providing the range of abundance of each morphogroup in each environment it is shown that this range of variation is great so that there is considerable overlap between environments nevertheless the mean values show patterns of distribution tubular forms morphogroup a are characteristic of slope environments especially those under the influence of geostrophic currents morphogroup b is not common in marginal marine environments but is an indicator of shallow fjord to deep sea the elongate forms of morphogroup c are widely distributed but c1 is especially common in marginal marine and shelf to upper slope settings the quinqueloculine coiled c2 subgroup is characteristic of marsh and marginal marine environments in the temperate zone but around antarctica this form is common down to 2000 m the plano convex low trochospiral trochamminids of morphogroup d are typical of marshes therefore these trends have application to palaeoecology of similar well oxygenated temperate environments

short term environmental changes in the cretaceous tethyan ocean micropalaeontological evidence from the early albian oceanic anoxic event 1b to better understand the linkage between climate and ocean circulation under greenhouse conditions we have studied calcareous nannofossils palynomorphs and benthic foraminifera from the early albian oceanic anoxic event 1b black shale oae 1b in the vocontian basin se france we propose that monsoonal activity resulting from precessional forcing and modulated by eccentricity driven temperature changes represents the driving factor of oae 1b formation in low latitudes with the onset of oae 1b increasingly warm and humid conditions stronger winds and enhanced terrestrial input led to higher surface water productivity therefore increased productivity is an important factor for oae 1b formation in the vocontian basin however monsoonally forced productivity changes are a regional climate signal only the supraregional occurrence of the oae 1b is probably due to a reduction of deep water formation in the low latitudes under extremely warm and humid conditions leading to enhanced preservation of organic matter

an ongoing satellite ring cycle of mars and the origins of phobos and deimos the martian moons phobos and deimos may have accreted from a ring of impact debris but explaining their origin from a single giant impact has proven difficult one clue may lie in the orbit of phobos that is slowly decaying as the satellite undergoes tidal interactions with mars in about 70 million years phobos is predicted to reach the location of tidal breakup and break apart to form a new ring around the planet here we use numerical simulations to suggest that the resulting ring will viscously spread to eventually deposit about 80 of debris onto mars the remaining 20 of debris will accrete into a new generation of satellites furthermore we propose that this process has occurred repeatedly throughout martian history in our simulations beginning with a large satellite formed after a giant impact with early mars we find that between three and seven ring satellite cycles over the past 4 3 billion years can explain phobos and deimos as they are observed today such a scenario implies the deposition of significant ring material onto mars during each cycle we hypothesize that some anomalous sedimentary deposits observed on mars may be linked to these periodic episodes of ring deposition the moon phobos is spiralling inwards towards its disintegration to eventually form a ring around mars from which new moons may form simulations suggest that this is just the latest of multiple ring moon cycles over the history of mars

water undersaturated mantle plume volcanism on present day mars based on meteorite evidence the present day martian mantle has a combined abundance of up to a few hundred ppm of h2o cl and f which lowers the solidus and enhances the magma production rate adiabatic decompression melting in upwelling mantle plumes is the best explanation for young last 200 myr volcanism on mars we explore water undersaturated mantle plume volcanism using a finite element mantle convection model coupled to a model of hydrous peridotite melting relative to a dry mantle the reduction in solidus temperature due to water increases the magma production rate by a factor of 1 3 1 7 at 50 ppm water and by a factor of 1 9 3 2 at 200 ppm water mantle water also decreases the viscosity and increases the vigor of convection which indirectly increases the magma production rate by thinning the thermal boundary layer and increasing the flow velocity at conditions relevant to mars these indirect effects can cause an order of magnitude increase in the magma production rate using geologic and geophysical observations of the late amazonian magma production rate and geochemical observations of melt fractions in shergottite meteorites present day mars is constrained to have a core mantle boundary temperature of 1750 to 1800 c and a volume averaged thermal rayleigh number of 2 106 to 107 indicating that moderately vigorous mantle convection has persisted to the present day melting occurs at depths of 2 5 6 gpa and is controlled by the rayleigh number at the low pressure end and by the mantle water concentration at high pressure

grain size sensitive seismic wave attenuation in polycrystalline olivine 1 in order to investigate the processes responsible for the attenuation of seismic shear waves in the earth s upper mantle four olivine polycrystals ranging in mean grain size d from 3 to 23 m have been fabricated characterized and mechanically tested in torsion at high temperatures and seismic frequencies both the shear modulus which governs the shear wave speed vs and the dissipation of shear strain energy q 1 have been measured as functions of oscillation period to temperature t and for the first time grain size at sufficiently high t all four specimens display similar absorption band viscoelastic behavior adequately represented for 1000 t 1200 or 1300 c and 1 to 100 s by the expression q 1 a tod 1 exp e rt with a 7 5 102 s m 0 26 and e 424 kj mol 1 this mildly grain size sensitive viscoelastic behavior of melt free polycrystalline olivine is attributed to a combination of elastically and diffusionally accommodated grain boundary sliding the latter becoming progressively more important with increasing t and or to extrapolation to the larger mm cm grain sizes expected in the earth s upper mantle yields levels of dissipation comparable with those observed seismologically implying that the same grain size sensitive processes might be responsible for much of the observed seismic wave attenuation the temperature sensitivity of vs is increased substantially by the viscoelastic relaxation allowing the lateral variability of wave speeds to be associated with relatively small temperature perturbations

trace element abundances in the rock canyon anticline pueblo colorado marine sedimentary section and their relationship to caribbean plateau construction and oxygen anoxic event 2 1 rapid eruption of submarine lava flows during formation of the caribbean plateau correlates closely with ocean anoxic event 2 oae2 which bracketed the cenomanian turonian boundary 93 5 ma these events also correspond with a positive excursion in carbon isotopic composition of seawater hydrothermal activity associated with large scale submarine volcanism may have been responsible for this abrupt change in ocean chemistry we determined the distribution of major minor and trace element abundances in the rock canyon marine sedimentary section pueblo colorado after normalizing element concentrations to zr to remove the variable contribution of terrigenous material to these sediments we detected an interval of concentrated metal abundance anomalies that coincides with the abrupt beginning of the positive 13c isotope excursion the metal abundance anomalies indicate that intermittent hydrothermal activity in the form of both water rock exchange and magmatic degassing introduced large concentrations of trace metals into the cretaceous ocean at the same time that extinctions of benthic species turnover in plankton communities and increases in isotopically light organic carbon burial occurred the stratigraphic position of this interval of trace metal anomalies matches events associated with oae2 and indicates that intermittent hydrothermal activity on a massive scale triggered abrupt changes in carbon burial and deep ocean oxygen contents

secular variation in late cretaceous carbon isotopes a new δ13c carbonate reference curve for the cenomanian campanian 99 6 70 6 ma carbon stable isotope variation through the cenomanian santonian stages is characterized using data for 1769 bulk pelagic carbonate samples collected from seven chalk successions in england the sections show consistent stratigraphic trends and 13c values that provide a basis for highresolution correlation positive and negative 13cexcursions and inflection points on the isotope profiles are used to define 72 isotope events key markers are provided by positive 13c excursions of up to 2 the albian cenomanianboundary event mid cenomanian event i thecenomanian turonian boundary event the bridgewick hitch wood and navigation events of late turonian age and the santonian campanian boundary event isotope events are isochronous within a framework provided by macrofossil datum levels and bentonite horizons an age calibrated composite 13c reference curve and an isotope event stratigraphy are constructed using data from the english chalk the isotope stratigraphy is applied to successions in germany france spain and italy correlation with pelagic sections at gubbio central italy demonstrates general agreement between biostratigraphic and chemostratigraphic criteria in the cenomanian turonian stages confirming established relationships between tethyan planktonic foraminiferal and boreal macrofossil biozonations correlation of the coniacian santonian stages is less clear cut magnetostratigraphic evidence for placing the base of chron 33r near the base of the upper santonian is in good agreement with the carbon isotope correlation but generates significant anomalies regarding the placement of the santonian and campanian stage boundaries with respect to tethyan planktonic foraminiferal and nannofossil zones isotope stratigraphy offers a more reliable criterion for detailed correlation of cenomanian santonian strata than biostratigraphy with the addition of campanian 13c data from one of the english sections a composite cenomanian campanian age calibrated reference curve is presented that can be utilized in future chemostratigraphic studies the cenomanian campanian carbon isotope curve is remarkably similar in shape to supposedly eustatic sea level curves increasing 13c values accompanying sea level rise associated with transgression and falling 13c values characterizing sea level fall and regression the correlation between carbon isotopes and sea level is explained by variations in epicontinental sea area affecting organic matter burial fluxes increasing shallow sea floor area and increased accommodation space accompanying sea level rise allowedmore efficient burial ofmarine organic matter with the preferential removal of 12c from the marine carbon reservoir during sea level fall reduced seafloor area marine erosion of previously deposited sediments and exposure of basin margins led to reduced organiccarbon burial fluxes and oxidation of previously deposited organic matter causing falling 13c values additionally drowning of carbonate platforms during periods of rapid sea level rise may have reduced the global inorganic relative to the organic carbon flux further enhancing 13c values while renewed platform growth during late transgressions and highstands prompted increased carbonate deposition variations in nutrient supply changing rates of oceanic turnover and the sequestration or liberation of methane from gas hydrates may also have played a role in controlling carbon isotope ratios

siberian gas venting and the end permian environmental crisis abstract the end of the permian period is marked by global warming and the biggest known mass extinction on earth the crisis is commonly attributed to the formation of the siberian traps large igneous province although the causal mechanisms remain disputed we show that heating of tunguska basin sediments by the ascending magma played a key role in triggering the crisis our conclusions are based on extensive field work in siberia in 2004 and 2006 heating of organic rich shale and petroleum bearing evaporites around sill intrusions led to greenhouse gas and halocarbon generation in sufficient volumes to cause global warming and atmospheric ozone depletion basin scale gas production potential estimates show that metamorphism of organic matter and petroleum could have generated 100 000 gt co2 the gases were released to the end permian atmosphere partly through spectacular pipe structures with kilometre sized craters dating of a sill intrusion by the u pb method shows that the gas release occurred at 252 0 0 4 million years ago overlapping in time with the end permian global warming and mass extinction heating experiments to 275 c on petroleum bearing rock salt from siberia suggests that methyl chloride and methyl bromide were significant components of the erupted gases the results indicate that global warming and ozone depletion were the two main drivers for the end permian environmental crisis we demonstrate that the composition of the heated sedimentary rocks below the flood basalts is the most important factor in controlling whether a large igneous provinces causes an environmental crisis or not we propose that a similar mechanism could have been responsible for the triassic jurassic 200 ma global warming and mass extinction based on the presence of thick sill intrusions in the evaporite deposits of the amazon basin in brazil

release of methane from a volcanic basin as a mechanism for initial eocene global warming a 200 000 yr interval of extreme global warming marked the start of the eocene epoch about 55 million years ago negative carbon and oxygen isotope excursions in marine and terrestrial sediments show that this event was linked to a massive and rapid approximately 10 000 yr input of isotopically depleted carbon it has been suggested previously that extensive melting of gas hydrates buried in marine sediments may represent the carbon source and has caused the global climate change large scale hydrate melting however requires a hitherto unknown triggering mechanism here we present evidence for the presence of thousands of hydrothermal vent complexes identified on seismic reflection profiles from the voring and more basins in the norwegian sea we propose that intrusion of voluminous mantle derived melts in carbon rich sedimentary strata in the northeast atlantic may have caused an explosive release of methane transported to the ocean or atmosphere through the vent complexes close to the palaeocene eocene boundary similar volcanic and metamorphic processes may explain climate events associated with other large igneous provinces such as the siberian traps approximately 250 million years ago and the karoo igneous province approximately 183 million years ago