a new hexactinellid sponge from the cretaceous of devon island canadian high arctic over 20 specimens of the new genus and species nunavutospongia irregulara an irregular stump like to columnar or fan to blade shaped hexactinosid hexactinellid sponge have been recovered from exposures of the upper cretaceous upper kanguk formation on devon island nunavut territory in the canadian high arctic the species and genus are characterized by dermal surfaces with prominent radial irregularly vertical rib like flanges that have a single linear series of separated oscula perforating their rounded crests the thin but persistent dermal layer of fused hexactine based spicules has rays thicker than those of the similarly fused endosomal quadrangularly arranged hexactines of the principal skeleton ostia of coarse exhalant canals and finer inhalant canals are extensively and uniformly developed but irregularly placed in the dermal layer a thin less prominent gastral layer of thickened spicules lines the short internally tapered spongocoel openings the skeleton exposed in the commo

body wave inversion moment tensors and depths of oceanic intraplate bending earthquakes this paper develops a moment tensor inversion technique suited for analysis of long period body waves from distant shallow earthquakes in addition to the moment tensor the procedure resolves precise source depths 5 km and estimates the duration of faulting the technique is applied to digital sro dwwssn recordings of outer rise intraplate earthquakes these earthquakes result from bending of oceanic plates prior to subduction bending induces horizontal tension near the top of the lithosphere and horizontal compression near its base a neutral surface separates compressional from tensional regimes an examination of 11 bending earthquakes in the period january 1981 to july 1982 indicates that the depth to the neutral surface is not geographically uniform although the seismicity sample is very small the depth of the neutral surface appears to correlate with the position of the trench arc in the evolutionary sequence of uyeda and kanamori 1979 in particular neutral surfaces at strongly coupled chilean type plate boundaries are elevated as much as 15 km above those at weakly coupled mariana type boundaries this correlation implies that nonuniformities in neutral surface height are created by variations in regional compressive stress resulting from contrasts in plate plate coupling to account for the observed heights maximum interplate compressive stresses must be comparable with stresses derived from bending

latitudinal temperature gradient during the cretaceous upper campanian middle maastrichtian y18o record of continental vertebrates latitudinal variations in model biogenic apatite d18o values were calculated using fractionation equations of vertebrates and weighted rainfall y18o values along with mean annual air temperatures provided by iaea wmo meteorological stations the reference equation obtained was used to compute a continental temperature gradient for the late campanian middle maastrichtian interval by using published and new d18o values of phosphate from vertebrates samples are mainly tooth enamel from crocodilians and dinosaurs that lived at paleolatitudes ranging from 83 4 n alaska to 32 3 s madagascar the temperature gradient was less steep 0 4 0 1 c latitude than the present day one 0 6 c latitude with temperatures that decreased from about 30 c near the equator to about 5 c at the poles above 30 of paleolatitude air temperatures were higher than at present the validity of these results is discussed by comparison with climatic criteria inferred from paleontological paleobotanical and sedimentological data the latitudinal distribution of oxygen isotope compositions of continental vertebrates is potentially a powerful tool for quantifying mesozoic terrestrial climates

the effect of oceanic crustal structure on phase changes and subduction abstract recent numerical models for the thermal regime of subduction zones are in disagreement with observations of depth to formation of eclogite which require higher temperatures than those found in the models this discrepancy may be reconciled if more accurate geometric depictions of the subducted slab are incorporated in the modelling studies the transition from 15 dip along the thrust plane to 30 along the benioff zone starts at depths of about 40 km dehydration reactions and the gabbro eclogite phase change are presumed to increase the average density of the lithosphere and to cause the steepening of the subducted lithosphere the benioff zone seismicity which starts at about 40 km depth may itself be a result of stresses caused by the phase changes since the gabbro eclogite transformation occurs in gabbroic sections of the crust thickened crustal sections beneath oceanic plateaus will affect subduction first the width of the thrust zone is reduced due to the increased dip angle because of early transformation of lower and warmer crustal sections second incomplete conversion of the entire crustal thickness results in an average density intermediate between unsubducted oceanic lithosphere and fully transformed normal lithosphere the first effect leads to decreased thrust mechanism seismicity because the coupling between the plates is reduced the second effect leads to flat lying subcontinental subduction or arcward advance of the trench in suboceanic subduction

the late cretaceous environment of the arctic a quantitative reassessment based on plant fossils abstract late cretaceous megafossil floras from the palaeo arctic of northeastern russia and northern alaska are reviewed in respect of their age composition structure and floral dynamics palaeofloral correlations and comparisons are made between the two regions nine angiosperm rich predominantly cenomanian to coniacian floras from the palaeo arctic are re evaluated using climate leaf analysis multivariate program clamp calibrated using a global gridded 0 5 0 5 climate data set derived from that used in climate modelling additional floras from lower palaeolatitudes were used to derive latitudinal temperature gradients seven from n america five from around 30 n palaeolatitude in europe and one from kazakhstan the arctic climatic determinations similar to previous estimates support the existence of a northern pacific ocean cold gyre and a warm arctic ocean at palaeolatitudes greater than 80 n floras are insufficiently diverse in woody dicot taxa to use clamp but using clamp derived latitudinal temperature gradients arctic ocean coastal environments at 70 ma and 82 n and which supported a diverse dinosaur magafauna are predicted to have experienced a mean annual temperature of 6 3 2 2 c a warm month mean of 14 5 3 1 c and a cold month mean no colder than 2 0 3 9 c all uncertainties are 2 the new estimates are in good agreement with a wide range of non palaeobotanical climate proxies and render as an outlier warmer temperature estimates for the arctic ocean derived from the tex 86 proxy modelling however shows that land to ocean temperature gradients could have been steep the clamp estimates also suggest high values for humidity and precipitation consistent with sedimentological indicators and coupled with warm temperatures support the existence of a persistent polar cloud cap that helped maintain high terrestrial air temperatures throughout prolonged periods up to 5 months of winter darkness

geoid anomalies in the vicinity of subduction zones the regional geoid of the southwest pacific is matched reasonably well by results from a model of the upper mantle density structure including slabs associated with subduction zones of the region estimates of the geoid are obtained from geos 3 and seasat radar altimeter data these data are very well suited to the task of detecting intermediate wavelength 600 4000 km geopotential variations which contain the dominant signature of subducting slabs gravimetric profiles across trench island arc complexes resolve primarily short wavelengths the model represents subducting slabs as thin surfaces of anomalous mass per unit area these surfaces are positioned using published seismicity results which detail the configuration of the benioff zones crustal effects are ignored effects due to the contrast between the young thermal lithosphere of the behind arc regions marginal basins and the older lithosphere seaward of the trench are modeled results indicate that the new hebrides slab possesses an average areal density anomaly of about 3 105 g cm 2 this is about 3 times that which is estimated for the tonga kermadec slab both of these inferred density anomalies are somewhat less 10 and 65 than anomalies predicted by a thermal model consistent with the results of other studies additional modeling suggests that slabs worldwide may be an important source of large long wavelength gravity highs i e they may contribute substantially to geopotential power of harmonic degree as low as three or four subduction geoid anomalies slab lithosphere

stress and flow beneath island arcs summary the flow pattern stress distribution topography and gravity anomalies were computed from numerical models having density and viscosity distributions resemblant to the aleutian arc the results were compatible with the hypothesis that the excess density of the slab drives its descent and that hydrodynamic forces are responsible for topographic and gravity highs over the outer rise seaward of the trench and the frontal arc and lows over the trench in models with simple distributions of rheological parameters the force from the slab was transmitted directly upward producing a negative gravity anomaly over the arc material with low resistance to flow was needed along the fault plane above the slab or within the crust of the frontal arc and within the wedge of asthenosphere above the slab to reduce that force and to allow the horizontal lithosphere to move with the slab models with the resistance to flow thus reduced had outer rises deep trenches horizontal tension seaward of the trench horizontal compression under the trench and downdip tension in the slab free air gravity anomalies which are the sum of between deflections of the free surface due to hydrodynamic forces and direct attractions from the masses driving the flow were not fit excellently by any of the models in part because the coarse grid used precluded accurate representation of the fault zone above the slab and the frontal arc an alternate to the hypothesis that about 5 kb of stress on the fault plane is needed to produce an outer rise is offered by these models shear stress between the slab and the island arc was always below 700 bars in the more successful models if the density distribution was scaled to match the topography of the trench this is much less than the 2000 bars stresses needed if frictional heating causes island arc volcanism

thermal anomalies beneath the australian antarctic discordance abstract significant variations in shear wave velocity along the southeast indian ridge are delineated by ss s differential travel times the australian antarctic discordance shows ss s residuals that are 3 8 s faster than the adjoining segments 1500 2000 km away the large variability suggests that thermal structure in the upper mantle as opposed to crustal structure is the major cause of the velocity anomaly to quantify this inference we invert both geoid and topography into temperature perturbations beneath the ridge within specific depth extents assuming that the thermal sources and the geophysical observations are dynamically related in a viscous earth the joint inversion of these two sets of data is robust demanding a negative temperature anomaly of 80 and 250 c beneath the discordance for layers extending from the surface to depths of 300 and 100 km respectively in a forward sense the temperature so constrained predicts well the trend of the along axis variations in ss s residuals but with a smaller amplitude especially for the 8 s contrast between the discordance and the eastern end of the ridge where unusually high residuals sample a broad shallow region of ridge segments considering the proximity of the ss bounce points to the ridge axis and the possibility of sampling a partial melt zone the discrepancy in magnitude may be partially reconciled by deducting a presumed 2 3 s melt effect from the high residuals in the eastern end the resolved thermal perturbations drive asthenospheric flow along the ridge the flow converging and descending in the vicinity of the discordance this simple thermal viscous flow fmodel is consistent with the idea of pipe flow for the southeast indian ridge the source of the pipe flow may be the mantle plumes at the two ends of the ridge

small scale mantle flows and induced lithospheric stress near island arcs summary this paper explores the middle ground between complex thermallycoupled viscous flow models and simple corner flow models of island arc environments the calculation retains the density driven nature of convection and relaxes the geometrical constraints of corner flow yet still provides semianalytical solutions for velocity and stress a novel aspect of the procedure is its allowance for a coupled elastic lithosphere on top of a newtonian viscous mantle initially simple box like density drivers illustrate how vertical and horizontal forces are transmitted through the mantle and how the lithosphere responds by trench formation the flexural strength of the lithosphere spatially broadens the surface topography and gravity anomalies relative to the functional form of the vertical flow stresses applied to the plate base i find that drivers in the form of inclined subducting slabs cannot induce selfdriven parallel flow however the necessary flow can be provided by supplying a basal drag of 1 5mpa to the mantle from the oceanic lithosphere these basal drag forces create regional lithospheric stress and they should be quantifiable through seismic observations of the neutral surface the existence of a shallow elevated phase transition is suggested in two slab models of 300 km length where a maximum excess density of 0 2 g m was needed to generate an acceptable mantle flow a north new hebrides subduction model which satisfies flow requirements and reproduces general features of topography and gravity contains a high shear stress zone 75mpa around the upper slab surface to a depth of 150 km and a deviatoric tensional stress in the back arc to a depth of 70 km the lithospheric stress state of this model suggests that slab detachment is possible through whole plate fracture

middle late cretaceous climate of the southern high latitudes stable isotopic evidence for minimal equator to pole thermal gradients a detailed 18 o and 13 c stratigraphy has been generated from analysis of well preserved albian early maastrichtian foraminifera from deep sea drilling project dsdp sites 511 and 327 falkland plateau 58 s 62 s paleolatitude in the southern south atlantic and cenomanian and coniacian santonian foraminifera from dsdp site 258 naturaliste plateau 58 s paleolatitude in the southern indian ocean these results when combined with previously published maastrichtian stable isotope data from ocean drilling program odp site 690 weddell sea 65 s paleolatitude provide new insight into the climatic and oceanographic history of the southern high latitudes during middle late cretaceous time the planktonic foraminifer 18 o curves reveal a gradual warming of surface waters from the albian through the cenomanian followed by extremely warm surface waters from the turonian through the early campanian long term cooling of surface waters began in the late early campanian and continued through the end of the maastrichtian the benthic foraminifer 18 o record generally parallels changes in the oxygen isotopic curves defined by shallow dwelling planktonic foraminifera the vertical oxygen and carbon isotopic gradients were relatively low during the albian cenomanian high from the turonian early campanian and then low during the late campanian and maastrichtian foraminiferal oxygen isotopic data from published sources and this study are averaged for each site corrected for latitudinal changes in salinity based on modern day surface water values and plotted versus paleolatitude for the late albian coniacian santonian and late maastrichtian differences between lowand high latitude surface water paleotemperatures are estimated at 14 c during the late albian and late maastrichtian but the coniacian santonian reconstruction reveals only a 0 4 c latitudinal temperature gradient uncertainty regarding cretaceous salinity gradients and possible diagenetic alteration of 18 o values introduce error into our estimates of paleolatitudinal thermal gradients however apparent low equator to pole temperature differences could indicate much higher poleward heat transport than at present

on the compensation of geoid anomalies due to subducting slabs candidate models of the forces that oppose the sinking of slabs are all constrained to produce results consistent with the following observation relative geoid highs which one assumes are due to slabs characteristically occur over subduction zones however certain models of subduction induced flow such as one based on a newtonian half space mantle yield surface depressions and concomitant geoid lows that more than fully compensate the geoid highs due to the slab alone this study has extended a published model of viscous corner flow in subduction zones in order to demonstrate that it can in certain cases produce the requisite net geoid highs specifically the relative geoid highs are produced if mantle flow is distinctly non newtonian stress exponent n 2 results in the form of geoid slope or horizontal gravity disturbance profiles are computed for typical values of the slab parameters they are compared with a representative profile of geoid slopes derived from seasat altimeter data in order to show qualitative similarities it is concluded that the effect of non newtonian flow as opposed to newtonian is to spread out the induced surface deformation thereby stretching out the regional compensation to wavelengths transverse to the trench of many thousand kilometers

effects of bedding on the dynamic indirect tensile strength of coal laboratory experiments and numerical simulation abstract dynamic indirect tensile tests were carried out by using a split hopkinson pressure bar shpb for coal sampled from the datong mine in china the principal purpose was to explore the influence of bedding structure in the coal on its dynamic indirect tensile strength however to resolve some contradictions x ray micro ct high speed optical imaging and a discrete element based modelling approach were combined to analyze the test results the x ray micro ct was used to detect the actual bedding structure in the coal the high speed imaging captured failure patterns of the specimens with different bedding directions and the numerical modelling was utilized to investigate the influence of different bedding structures on dynamic strength the shpb and numerical results illustrate that dynamic indirect tensile strength reliably correlates with impact velocity in addition the dynamic indirect tensile strength is not only influenced by the bedding direction but also by the roughness and discontinuity of the bedding based on these findings a method is developed to further process the test data including a model to describe the dynamic indirect tensile strength of datong coal

hesperornis aves from ellesmere island and palynological correlation of known canadian localities a tarsometatarsus of hesperornis from the kanguk formation on ellesmere island is described and illustrated and constitutes the northernmost occurrence of the genus palynological evidence and stra

late cretaceous antarctic fish diversity new material from the santa marta formation late coniacian early maastrichtian of james ross island contributes significantly to the current knowledge of late cretaceous antarctic fish diversity the taxon list for the santa marta formation is extended and new records of neoselachians and teleosts are reported the stratigraphic ranges of some previously known taxa are enlarged and the palaeobiogeography and palaeoecology of late cretaceous antarctic fishes are discussed top predators that occupied the higher levels in the food chain along with marine tetrapods dominate the marine faunas from the santa marta and lopez de bertodano formations the only fish adapted to crushing hard shelled invertebrates were the chimeroids rays an important component of marine fish associations as well as fish from lower trophic levels remain unknown from the late cretaceous of antarctica

subduction zone stresses constraints from mechanics and from topographic and geoid anomalies abstract there are in principle direct relations between several important phenomena associated with subduction zones the depth of oceanic trenches the magnitude of the net force from trenches acting on subducting plates the distribution and fault plane orientations of earthquakes the magnitude of stresses on subduction faults the bathymetry of back arc regions and the magnitudes of gravity and geoid anomalies these phenomena are related through the stresses transmitted through surface and subducted lithosphere and are associated with the mass anomaly of the subducted lithosphere quantitative estimates suggest that observed trench depths imply a trench pull force on subducting plates which is comparable to the ridge push force but much less than the excess weight of the subducted lithospheric slab it is further suggested that either the mass anomaly of subducted lithosphere is much less than would be expected on the basis of conventional thermal and compositional models or that a a large resistance acts on the upper part of slabs due to high stress corner flow and b the mass anomaly of the slab is 70 90 compensated either by a broad 1 km deep back arc depression or a low density mantle wedge above the slab or both

high temperatures in the late cretaceous arctic ocean to understand the climate dynamics of the warm equable greenhouse world of the late cretaceous period it is important to determine polar palaeotemperatures the early palaeoceanographic history of the arctic ocean has however remained largely unknown because the sea floor and underlying deposits are usually inaccessible beneath a cover of floating ice a shallow piston core taken from a drifting ice island in 1970 fortuitously retrieved unconsolidated upper cretaceous organic rich sediment from alpha ridge a submarine elevated feature of probable oceanic origin a lack of carbonate in the sediments from this core has prevented the use of traditional oxygen isotope palaeothermometry here we determine arctic palaeotemperatures from these upper cretaceous deposits using tex86 a new palaeothermometer that is based on the composition of membrane lipids derived from a ubiquitous component of marine plankton crenarchaeota from these analyses we infer an average sea surface temperature of approximately 15 degrees c for the arctic ocean about 70 million years ago this calibration point implies an equator to pole gradient in sea surface temperatures of approximately 15 degrees c during this interval and by extrapolation we suggest that polar waters were generally warmer than 20 degrees c during the middle cretaceous approximately 90 million years ago

paleobiogeography of the cretaceous western interior seaway of north america the vertebrate evidence abstract distribution patterns of marine vertebrates of the cretaceous western interior seaway of north america are analysed in a biogeographical context the analysis is based on fossil vertebrate assemblages from the following lower campanian localities 1 anderson river fauna n w t 2 pembina fauna southern manitoba 3 sharon springs fauna south dakota wyoming 4 niobrara fauna kansas 5 mooreville fauna alabama due to the cosmopolitan nature of many marine vertebrates relative abundance is used in preference to presence absence data in identifying faunal distribution patterns the analysis demonstrates the presence of two faunal subprovinces in the seaway the northern interior subprovince is characterized by a low diversity in all groups and is dominated by plesiosaurs hesperornithiforms and the mosasaur platecarpus the southern interior subprovince is characterized by a high diversity in all groups and is dominated by sharks turtles and the mosasaur clidastes these biogeographical subdivisions support the hypothesis of warm temperature and cool temperate zones in the seaway that have been proposed on the basis of invertebrate faunas

new quantitative palaeocolimate data for the late cretaceous arctic evidence for a warm polar ocean abstract physiognomic analysis of four taphofloras one from the coniacian of n alaska one from the coniacian of kamchatka one from the turonian of kamchatka and one from the turonian of novaya sibir island using the clamp technique of wolfe 1993 yielded quantitative data on the mean annual warm month mean and cold month mean temperatures the length of the growing season mean annual precipitation mean growing season precipitation mean monthly growing season precipitation and the precipitation during the three consecutive driest months these new results represent the first application of multivariate statistical analysis of foliar physiognomy to determine palaeoclimatic parameters clamp to arctic cretaceous floras and demonstrate its robustness even in the context of vegetation which has no living analogues these new estimates were comparable to those from previous quantitative or qualitative sedimentological or palaeobotanical data where they were available but offer greater measurable precision the results also suggest that an arctic ocean with a winter surface temperature of approximately 6 c maintained n alaska coastal temperatures above freezing locally reversing the equator to pole temperature gradient a phenomenon not seen in the northern proto pacific this anomalously warm arctic ocean could have been produced by marine poleward heat transport precipitation in alaska kamchatka and novaya sibir island was predicted to have been high e g 1760 mm yr in the coniacian of n alaska reflecting a very weak polar high pressure cell and substantially different precipitation patterns to present

a simple global model of plate dynamics and mantle convection cooling and thickening of lithospheric plates with age and subduction result in large scale horizontal density contrasts tending to drive plate motions and mantle flow we quantify the driving forces associated with these density contrasts to determine if they can drive the observed plate motions first two dimensional models are computed to evaluate the effects of assumed rheologies and boundary conditions we are unable to obtain platelike behavior in viscous models with traction free boundary conditions the piecewise uniform velocities distinctive of plate motion can be imposed as boundary conditions and the dynamic consistency of the models evaluated by determining if the net force on each vanishes if the lithosphere has a newtonian viscous rheology the net force on any plate is a strong function of the effective grid spacing used leading to ambiguities in interpretation incorporating a rigid plastic lithosphere which fails at a critical yield stress into the otherwise viscous model removes these ambiguities the model is extended to the actual three dimensional spherical plate geometry the observed velocities of rigid plastic plates are matched to the solution of the viscous stokes equation at the lithosphere asthenosphere boundary body forces from the seismically observed slabs from the thickening of the lithosphere obtained from the actual lithospheric ages and from the differences in structure between continents and oceans are included interior density contrasts such as those resulting from upwellings from a hot bottom boundary layer are assumed to occur on a scale small compared to plate dimensions and are not included the driving forces from the density contrasts within the plates are calculated and compared to resisting forces resulting from viscous drag computed from the three dimensional global return flow and resistance to deformation at converging boundaries the rms residual torque is 30 of the driving torque the density contrasts within the plates themselves can reasonably account for plate motions body forces from convection in the interior may provide only a small net force on the plates at converging boundaries the lithosphere has a yield stress of 100 bars drag at the base of the plates is 5 bars and resists plate motion the net driving forces from subducting slabs and collisional resistance are localized and approximately balance driving forces from lithospheric thickening are distributed over the areas of the plates as is viscous drag the approximate balance of these two forces predicts plate velocities uncorrelated with plate area as observed the model represents a specific case of boundary layer convection the dynamical results are consistent with either upper mantle or mantle wide convection

regional compensation of subducted lithosphere effects on geoid gravity and topography from a preliminary model abstract it is proposed that the anomalous mass of subducted lithospheric slabs is partially compensated by two mechanisms a by stresses transmitted up the slab to the surface lithosphere causing the trench and b by stresses transmitted through the mantle wedge overlying the slab which cause a broad shallow depression results calculated from a preliminary two dimensional model show that it can give a first order account of observed topography gravity and geoid anomalies in particular the model can reconcile the large mass anomaly predicted for the slab by thermal conduction theory with the smaller than expected gravity and geoid anomalies preliminary results indicate substantial compensation by mechanism a implying rather large stresses at the top of the slab these could be important for theories of earthquake mechanisms and plate driving mechanisms roughly 50 of the possible compensation by mechanism b is indicated the resulting depression the order of 500 m deep and over 500 km wide could explain anomalously deep marginal basins and some marine transgressions of continents

subducted slabs and the geoid constraints on mantle rheology and flow geoid anomalies are primarily the result of the density contrasts driving mantle convection and plate motion the total geoid anomaly resulting from a given density contrast in a convecting earth is affected by the mass anomalies associated with the flow induced deformation of the upper surface and internal compositional boundaries as well as by the density contrast itself these boundary deformations and hence the total gravity field depend on the radial distribution of effective viscosity if the internal density contrasts can be estimated as is the case for subducted slabs useful constraints can be placed on the depth and on the variation of viscosity with depth of the convecting system the degree 4 9 components of the observed long wavelength geoid are highly correlated with those predicted by a density model for seismically active subducted slabs the positive sign of the correlation requires that the effective viscosity increases with depth by a factor of 30 or more the amplitude of the correlation cannot be explained by the density contrasts associated with just the seismically active parts of subducted slabs however the amplitude can be explained if the density contrasts associated with subduction extend into the lower mantle or if old lithosphere is piled up at the base of the upper mantle beneath subduction zones to a thickness in excess of 350 km over horizontal distances of thousands of kilometers mantlewide convection in a mantle that has a viscosity increasing with depth provides a simple explanation of the long wavelength geoid anomalies over subduction zones

deep sea paleotemperature record of extreme warmth during the cretaceous oxygen isotope analyses of well preserved foraminifera from blake nose 30 n paleolatitude north atlantic and globally distributed deep sea sites provide a long term paleotemperature record for the late albian maastrichtian interval that is difficult to reconcile with the existence of significant cretaceous ice sheets given reasonable assumptions about the isotopic composition of cretaceous seawater our results suggest that middle bathyal water temperatures at blake nose increased from 12 c in the late albian through middle cenomanian to a maximum of 20 c during the latest cenomanian and earliest turonian bottom waters were again 12 c during the middle campanian and cooled to a minimum of 9 c during the maastrichtian correlative middle bathyal foraminifera from other ocean basins yield paleotemperature estimates that are very similar to those from blake nose comparison of global bottom water temperatures and latitudinal thermal gradients suggests that global climate changed from a warm greenhouse state during the late albian through late cenomanian to a hot greenhouse phase during the latest cenomanian through early campanian then to cool greenhouse conditions during the mid campanian through maastrichtian

a warm equable cretaceous the nature of the problem abstract the nature of the problem of warm equable paleoclimates is defined by investigating the mid cretaceous period the problem consists of three components 1 defining precisely the climatic state during any specified interval of geologic time 2 specifying the external climatic forcing factors which may have been important and 3 understanding the climatic response to any specific modifying influence these components are characterized by limitations of critical importance in understanding paleoclimates the nature of the problem of a warm cretaceous is defined both qualitatively and quantitatively within these limits

a new hesperornithiform aves specimen from the late cretaceous canadian high arctic with comments on high latitude hesperornithiform diet here we describe a new hesperornithiform specimen from the upper cretaceous kanguk formation of devon island nunavut canada this specimen nuvf 286 is referred to cf hesperornis sp based on size and shape of femora and teeth preserved with other skeletal elements previous osteohistologic analyses indicate a subadult ontogenetic stage at the time of death this new cf hesperornis specimen includes the first teeth associated with a high latitude hesperornithiform allowing for comments on the trophic behavior of these birds paleoecological reconstructions based on current knowledge of polar assemblages and comparisons to modern birds suggest that high latitude hesperornithiform birds may have had more varied diets than previously assumed

the climate of the late cretaceous new insights from the application of the carbonate clumped isotope thermometer to western interior seaway macrofossil abstract we apply the carbonate clumped isotope thermometer 47 to macrofossils from the baculites compressus 73 5 ma and the hoploscaphites nebrascensis 67 ma ammonite zones of the western interior seaway wis of north america and nearby coeval terrestrial and open marine environments the carbonate clumped isotope thermometer is based on a single phase isotope exchange equilibrium that promotes the clumping of two heavy isotopes together within a single carbonate molecule as temperature decreases due to the thermometer s isotopic independence from water coupled measurements of 47 and the bulk oxygen isotopic composition of a carbonate 18 o c enable the reconstruction of both paleotemperature and the isotopic composition of the water in which the organisms grew before applying the technique to the aragonite shells of fossil marine organisms mostly ammonites but also some gastropods bivalves and one belemnite we measure the clumped isotopic composition of modern nautilus and cuttlefish two of the nearest living relatives to the cretaceous ammonites modern cephalopods exhibit disequilibrium isotope effects with respect to 47 but not 18 o c therefore a simple correctional scheme is applied to the late cretaceous macrofossil data before reconstructing paleotemperatures diagenesis is also assessed by visual preservation and previously measured sr concentrations cochran et al 2003 temperatures reconstructed for the late cretaceous western interior seaway range from 16 4 3 5 c for an offshore interior seaway environment from the h nebrascensis zone to 24 2 0 4 c for the b compressus ammonite zone the seaway itself has an isotopic composition of approximately 1 relative to vsmow the expectation for an ice free global ocean average while a nearby freshwater environment has an isotopic composition approaching 20 we compare the attributes of the reconstructed climate to predictions based on late cretaceous climate models and previous reconstructions of the seaway and also assess the sensitivity of our results to the modern cephalopods correction by comparisons to suitable modern analogs finally our clumped isotope data are consistent with cooling between the late campanian and maastrichtian as also seen in benthic foraminfera 18 o