surface microtextures of ice rafted quartz grains revealing glacial ice in the cenozoic arctic abstract ice rafted grains of the central arctic ocean sediments provide a reliable proxy for arctic palaeoenvironments and climatic conditions that prevailed at the time of their deposition to understand ice involvement and implications for environmental advancement it has proven necessary to ascertain whether these detrital grains were rafted on glacial ice or sea ice surface microtexture identification allows grain differentiation based on the processes and conditions in its environmental provenance here quartz sand grain surface microtextures are used to detect glacially crushed and reworked grains from the lomonosov ridge sediments obtained by the integrated ocean drilling program expedition 302 arctic coring expedition the data show that the most frequent distributions of glacial grains were deposited at the middle late miocene and during the pliocene and early pleistocene especially the middle miocene climatic cooling and the presence of glacial ice are well indicated at 13 5 ma sediment grains earliest finding of the high frequency occurrence of glacigenic microtextures represents the age of 56 ma this first sedimentological evidence for the late palaeocene glacial ice supports the existing hypothesis of ephemeral polar glaciations during times of marked global warmth however due to lack of uninterrupted sediment recovery and non continuous nature of sampling the glacially influenced samples recovered here should be treated as an estimate of the minimum frequency of glacier appearance in the arctic

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

a paleogene flora from the upper bonnet plume formation of northeast yukon territory canada palaeontological exploration of the bonnet plume basin in northwestern yukon territory canada has revealed a late paleocene to early eocene macrofloral assemblage from a channel fill deposit the flora is typified by cosmopolitan taxa and dominated by deciduous angiosperms with the notable presence of zizyphoides ettingshausenia and corylites floras with a similar composition are known from late cretaceous through early eocene deposits in alaska and the canadian arctic archipelago where they have been interpreted as evidence for warm equable temperatures this collection represents the most diverse known paleogene plant macrofossil assemblage from the yukon territory and helps to expand our knowledge of ancient high latitude floras

application of a seasonal climate model to cenozoic glaciation mathematical modelling of climate has matured as a discipline to the point that it can be useful in palaeoclimatology as an example a new two dimensional energy balance model is described and applied to several problems of current interest the model includes the seasonal cycle and the detailed land sea geographical distribution by examining the changes in the seasonal cycle when external perturbations are forced upon the climate system it is possible to construct hypotheses about the origin of mid latitude ice sheets and polar ice caps in particular the model predicts a rather sudden potential for glaciation over large areas when the earth s orbital elements are only slightly altered similarly the drift of continents or the change of atmospheric carbon dioxide over geological time can induce radical changes in continental ice cover with the advance of computer technology and our improved understanding of the individual components of the climate system it should be possible to test these ideas in far more realistic models in the near future

origin nature and world climate effect of arctic ocean ice cover during the cenozoic an open water arctic ocean changed to the modern permanently ice covered condition significant world climate modification accompanied this change but the precise role of the arctic ocean in major pleistocene climate events is controversial the present ice cover averages 3 m thickness but there are theories that during the pleistocene it was antarctic like several thousand metres thick the time of origin of the ice cover is placed as young as 0 7 myr ago and as old as the middle miocene any theory concerned with origin nature and climatic response of the arctic ice cover must consider the ocean s sediment record

vertebrate fossils dinosauria from the bonnet plume formation yukon territory canada dinosaurs and other terrestrial vertebrates are poorly documented in the mesozoic of the canadian polar region here we provide a complete review of the upper cretaceous maastrichtian vertebrate fauna of the bonnet plume formation in the northeastern yukon territory canada which includes the description of the first newly collected dinosaur bones from this unit in almost half a century previously reported fragmentary dinosaur remains collected in the early 1960 s pertain to an indeterminate hadrosaurid new material includes a poorly preserved forelimb bone and a pedal phalanx these new remains pertain to at least one species of non hadrosaurid ornithischian dinosaur and the humerus is tentatively referred to a small bodied basal ornithopod the new vertebrate fossils from the bonnet plume formation provide further evidence of vertebrates from this unit however directed field surveys in 2008 and 2009 suggest that vertebrate fossils are not abundant a review of the known localities of terrestrial mesozoic vertebrates from the canadian arctic indicate that it had a relatively diverse community of terrestrial vertebrates including dinosaurs during the late cretaceous but emphasizes our limited knowledge of the mesozoic arctic and considerable potential for future exploration and discovery

palaeoecology of late cretaceous polar vegetation preserved in the hansen point volcanics nw ellesmere island canada abstract mesozoic polar forests represent an extinct biome subject to a polar light regime and elevated atmospheric co2 levels in this paper new cretaceous fossil plant assemblages are reported from nw ellesmere island canada at a paleolatitude of 75 n these occur in a campanian maastrichtian aged interval of the hansen point volcanics a unit interpreted as a coastal plain peat mire complex within an active volcanic setting studies of palynomorphs sterile and fertile foliage and wood indicate that mire environments were dominated by amber producing taxodiaceous conifers with other conifers ginkgos cycads angiosperms ferns lycopsids and bryophytes occurring in subordinate numbers leaf physiognomic studies imply that most vegetation was deciduous occurrence of traumatic rings in the woods together with a high year to year variability in ring width indicates disturbed growing conditions possibly linked to a combination of frosts volcanic eruptions and flooding abundant charcoal remains indicate that an additional important disturbance process was wildfire results of this study compare closely with those from coeval circum arctic fossil sites and augment our knowledge of the community scale ecology of the cretaceous polar biome

a quantitative approach for identifying plant ecogroups in the romanian early jurassic terrestrial vegetation abstract community level ecology is considered to support significantly the recognition of the ecological status of plant taxa and the identification of plant ecogroups thus it generally provides extended data sets on the spatial and temporal changes of ecological factors since research based exclusively on plant structure and their supposed adaptation to the environment is now considered inadequate statistical methods can be used assuming that co occurrence of plant fossils on a single hand specimen in the case of autochthonous or parautochthonous floras is the result of their growth in the same phytocenosis quantitative ecological analysis on mesozoic materials would yield significant insights in this paper statistical and multivariate quantitative analyses of early jurassic plant fossil records from the steierdorf formation in anina south carpathians romania are presented four palaeoecological groups of taxa were distinguished by principal component analysis pca and interpreted as plant assemblages of various palaeobiotopes associated with the sedimentary facies of the enclosing formation a group of samples was analysed using the principal coordinate pco method and the statistical significance p less than or equal to 0 05 p 0 05 of individual binary responses of taxa along the first two pco ordination axes was tested by general linear model glm they revealed putative palaeoecological gradients axis 1 disturbance caused by water level fluctuations axis 2 temperature corresponding with the already assumed environmental and climatic change at the hettangian sinemurian boundary multivariate analyses enabled the identification of palaeoecological groups and thus inferring palaeogeographical conditions based on mesozoic materials

climatic implications of the variable obliquity explanation of cretaceous paleogene high latitude floras the record of high latitude cretaceous paleogene floras has been interpreted as indicative of warmth and climatic equability and has also been the basis for arguments of reduced obliquity climate model simulations suggest that a reduced obliquity will result in a substantial polar cooling that is incompatible with the interpretation for polar warmth paleobiologic adaptations to low light levels may be an alternative to a variable obliquity

oxygen and carbon isotope stratigraphy of the palaeogene and cretaceous limestones in the bottaccione gorge and the contessa highway sections umbria italy we have made oxygen and carbon isotope measurements on limestone samples of albian to eocene age recovered from the bottaccione gorge section in the umbrian apennines central italy additional measurements have been made on topmost maastrichtian and palaeocene sediments from the adjacent contessa highway section our data from the bottaccione gorge show 13c maxima at the cenomanian turonian boundary and during the palaeocene as well as a pronounced 13c minimum 7 metres above the clay layer at the k t boundary our data from the contessa highway show a 13c minimum 9 metres above the k t boundary clay these minima are probably diagenetic artifacts in the bottaccione gorge there is evidence for a hiatus in the early middle eocene the palaeocene of the bottaccione gorge appears to have been affected by slumping or faulting in addition to the diagenetic overprinting giving a spurious 13c recovery after the k t boundary the contessa highway section appears to be more complete the coniacian maastrictian is characterized by relatively stable 13c values our data indicate an increase in 18o and therefore possible cooling across the cretaceous tertiary boundary in both the bottaccione and contessa highway sections

the geologic record of climatic change this paper reviews the principal results from paleoclimate studies and includes background material slanted toward climate modelers the inferred temperature history of the last 4 6 billion years indicates major changes in the components of the earth s climate system a secular change in global insolation receipt is due to a 20 30 increase in solar luminosity since the formation of the earth a co2 h2o greenhouse effect may have offset the lower luminosity during early earth history inferred fluctuations of global temperature have occurred over a broad range of time scales on time scales of 106 108 years paleogeographic factors e g continental drift and sea level changes have contributed significantly to temperature changes associated with transitions between nonglacial and glacial states preliminary modeling efforts indicate that additional factors e g co2 changes in atmospheric circulation must also be considered in order to explain the origin of nonglacial climates the origin of polar ice caps may result from ocean circulation changes that were caused by plate tectonic processes fluctuations of ice volume on a time scale of 10 105 years correlate with insolation variations caused by orbital perturbations feedback interactions within the land sea air ice system e g ocean circulation changes and bedrock dynamics have been responsible for a significant modulation of the orbital signal ice ages may be due to orbitally induced temperature changes superimposed on a global cooling of terrestrial origin

paleofloristic and paleoenvironmental information from a late cretaceous maastrichtian flora of the lower cantwell formation near sable mountain denali national park alaska abstract the lower cantwell formation in denali national park alaska is a late cretaceous high latitude fluvial succession that contains dinosaur and bird footprints diverse invertebrate traces and plant fossils new fossil discoveries and stratigraphic descriptions in the sable mountain area allow for refined paleoenvironmental reconstructions and age interpretations the formation consists of well indurated conglomerate sandstone siltstone and shale interpreted as gravelly and sandy channel levee crevasse splay sheetflood lacustrine and floodplain sediments with interspersed debris flows the overall depositional environment is interpreted as a braided river floodplain that interfingered with distal alluvial fan sedimentation plant fossils include leaves branches cones and rare seeds of taxodiaceous and other conifer taxa fern fronds rhizomes and stem segments of equisetites linear and broad lanceolate monocot leaf fragments cf kenella and impressions of diverse angiosperm broad leaf morphotypes likely belonging to menispermoid platanoid and several late cretaceous hamamelid groups a sparse palynoflora extracted from the finer grained facies yielded the pollen taxa taxodiaceaepollenites aquilapollenites and alnipollenites monosulcate cycadophyte or ginkgophyte pollen grains bisaccate and monosaccate conifer pollen grains and a variety of trilete fern and psilate horsetail spores the middle to late maastrichtian pollen taxon aquilapollenites conatus provides a maximum age for the sable mountain deposits floral assemblages occur within distinct lithofacies deposited in a variety of depositional settings in the ancient floodplain angiosperm leaf fossils are dominant in channel and levee facies and were part of a mixed forest assemblage growing in floodplain and lake margin environments a variety of different types of conifers indicated by saccate pollen types and rare long thin leaf fragments probably inhabited distal floodplain realms and uplands frequent and abrupt changes in lithology and floral assemblages imply transitory habitats in a rapidly aggrading depositional setting a climate leaf analysis multivariate program clamp applied to a composite leaf collection yielded a mean annual temperature of 7 42 1 2 c a warmest monthly mean of 17 1 1 6 c and a coldest monthly mean of 2 3 1 9 c growing season precipitation is estimated at 229 4 334 5 mm over 4 8 0 7 months results are suggestive of a cool temperate and highly seasonal paleoclimate with short warm dry summers and long comparatively mild and probably wet winters temperature calculations are consistent with previous estimates from alaska s north slope and northeastern russia suggesting a low polar temperature gradient and a slight cooling trend during the middle to early late maastrichtian precipitation estimates for the growing season are low compared to overall wet climate predictions for the maastrichtian like other late cretaceous arctic floras the cantwell flora is classified herein as a polar broad leaved deciduous forest flora

high latitude meteoric δ18o compositions paleosol siderite in the middle cretaceous nanushuk formation north slope alaska siderite bearing pedogenic horizons of the nanushuk formation of the north slope alaska provide a critical high paleolatitude oxygen isotopic proxy record of paleoprecipitation supplying important empirical data needed for paleoclimatic reconstructions and models of greenhouse world precipitation rates siderite 18 o values were determined from four paleosol horizons in the national petroleum reserve alaska npr a grandstand 1 core and the values range between 17 6 and 14 3 peedee belemnite pdb with standard deviations generally less than 0 6 within individual horizons the 13 c values are much more variable ranging from 4 6 to 10 8 pdb a covariant 18 o versus 13 c trend in one horizon probably resulted from mixing between modified marine and meteoric phreatic fluids during siderite precipitation groundwater values calculated from siderite oxygen isotopic values and paleobotanical temperature estimates range from 23 0 to 19 5 standard mean ocean water smow minor element analyses show that the siderites are impure having enrichments in ca mg mn and sr minor element substitutions and mg fe and mg ca mg ratios also suggest the influence of marine fluids upon siderite precipitation the pedogenic horizons are characterized by gleyed colors rare root traces abundant siderite abundant organic matter rare clay and silty clay coatings and infillings some preservation of primary sedimentary stratification and a lack of ferruginous oxides and mottles the pedogenic features suggest that these were poorly drained reducing hydromorphic soils that developed in coal bearing delta plain facies and are similar to modern inceptisols model derived estimates of precipitation rates for the late albian of the north slope alaska 485 626 mm yr are consistent with precipitation rates necessary to maintain modern peat forming environments this information reinforces the mutual consistency between empirical paleotemperature estimates and isotope mass balance models of the hydrologic cycle and can be used in future global circulation modeling gcm experiments of greenhouse world climates to constrain high latitude precipitation rates in simulations of ancient worlds with decreased equator to pole temperature gradients

late cretaceous climate signal of the northern pekulney range flora of northeastern russia abstract plant bearing continental deposits from the northern pekulney mountain range in the anadyr koryak subregion of northeastern russia approximately 66 n 175 e represent a rich and diverse flora growing close to the late cretaceous north pole at a palaeolatitude of 78 n the early coniacian age of this flora is based on biostratigraphic correlation of the plant bearing beds with underlying and overlying marine units the northern pekulney range flora comprises two large plant macrofossil assemblages one from the tylpegyrgynai formation on the western slopes of the northern pekulney range and the other from the poperechnaya formation on its northeastern slopes the flora is dominated by angiosperms followed by conifers ferns cycadophytes ginkgophytes and sphenophytes in decreasing order of species diversity dicotyledonous angiosperm leaves 57 morphotypes from the northern pekulney range flora were subjected to a climate leaf analysis multivariate program clamp physiognomic analysis separate analyses of the constituent assemblages from the tylpegyrgynai and poperechnaya formations yielded 27 and 39 morphotypes respectively results suggest that the northern pekulney range flora experienced a mean annual temperature of 8 1 1 2 c a cold month mean temperature of 1 5 1 9 c a mean monthly growing season precipitation of 78 8 36 9 mm and a growing season of 5 3 0 7 months this suggests a warm temperate climate lacking pronounced drought in which the polar light regime constrained the length of the growing season clamp results for the tylpegyrgynai formation flora suggest slightly higher temperatures with a mean annual temperature of 9 4 1 2 c and a cold month mean temperature of 0 9 1 9 c whilst estimates for the poperechnaya formation flora are cooler with a mean annual temperature of 7 3 1 2 c and a cold month mean temperature of 2 7 1 9 c because the floras from the tylpegyrgynai and poperechnaya formations also exhibit differences in their taxonomy and physiognomy they should be considered as two distinct floras the overall taxonomic composition of these floras their foliar physiognomy and estimated palaeoclimate parameters suggest a deciduous phenology with a few evergreen elements comparisons with other arctic coniacian floras are consistent with the high latitudinal position of the northern pekulney range flora and its proximity to the northern proto pacific ocean

rudists as gregarious sediment dwellers not reef builders on cretaceous carbonate platforms abstract it has sometimes been claimed that rudist bivalves competitively displaced corals from reef frameworks during the cretaceous this hypothesis combines two assertions 1 that the autecology of rudists was convergent with that of reef building corals and 2 that rudist formations commonly developed as reefs we dispute both assertions and thus reject the hypothesis of competitive displacement we argue instead that mobile sediments rather than frameworks dominated the margins and tops of most of the extensive carbonate platforms of the period and that it was on these non reefal biotopes that the rudists flourished definitions of reefs tend to combine two major elements 1 a robust biogenic framework with accompanying sedimentary and diagenetic components and 2 topographical relief such definitions are clearly rooted in recent coral reefs in which endosymbiotic zooxanthellae permit the extensive growth of colonial coral frameworks in shallow but relatively nutrient poor waters coralline algae and cementation may contribute significantly to the growth of rigid structures and topography is largely the legacy of pleistocene changes in sea level in rudist formations in contrast individual rudist congregations are volumetrically limited relative to sediment they are often loosely constructed and they evidently showed little if any original relief tabular and small lenticular units predominate these differences in structure and palaeoenvironmental situation between rudist and modern coralgal associations reflect the different autecologies of the constituent organisms the clonal growth of corals predisposes them to the development of frameworks projecting above the sediment surface herein termed superstratal growth by contrast the aclonal development of rudists was better suited to the opportunistic occupation of a variety of temporarily available substrata by large numbers of individuals in particular elevator rudists in which the entire commissure exhibited upward growth evidently grew with their shells largely embedded in and supported by the ambient sediment herein termed constratal growth moreover the tolerances and growth responses of rudists to such factors as water turbidity nutrients and current regime were quite different from those of the majority of reef building corals despite repeated assertions in the literature that rudists possessed zooxanthellae only a few species show any evidence for such a symbiosis and other evidence suggests that most lacked them in view of these differences in their preferred biotopes competition between rudists and corals is doubtful even though members of both groups co occur in many areas the relative decline of coral frameworks in the cretaceous was thus probably independently caused

the formation of inertinite rich peats in the mid cretaceous gates formation implications for the interpretation of mid albian history of paleowildfire abstract image analysis and standard point count petrographic data are used to interpret the amount source and variation of inertinite in coal seams of the mid cretaceous gates formation rocky mountain foothills northeastern british columbia inertinite on average is abundant between 40 60 by seam by volume and higher in some zones and within seams fluctuates cyclically the inertinite is interpreted to be almost exclusively fire derived suggesting that fire was a relatively common occurrence in the original peat forming wetlands inertinite enrichment in the gates coals appears to have resulted from preferential destruction of vitrinite precursors by either low temperature decomposition processes or burning rather than by formation of inertinite by a microbial process the position of the gates formation depositional setting east of the rising canadian cordillera is interpreted to have resulted in overall drier conditions in the region and periodic drought in the wetland settings cyclic variation in inertinite vitrinite composition within some of the seams is primarily attributed to climatic variations although variation in subsidence rates could also have been responsible

late cretaceous early tertiary palaeoclimates of northern high latitudes a quantitative view analyses of plant community structure vegetational and leaf physiognomy and growth rings and vascular systems in wood provide qualitative and quantitative data that can be combined to define non marine palaeoclimatic parameters with better resolution than is available from other principally sedimentological methods application of these techniques to cenomanian through paleocene floras from high palaeolatitudes 75 85 n indicates a polar light regime similar to that of the present plant data suggests cenomanian sea level mean annual air temperatures mats of 10 c and mats of 13 c 5 c and 6 7 c in the coniacian maastrichtian and paleocene respectively evapotranspirational stresses at sea level were low and precipitation was in most part uniform throughout the growing season in the cenomanian with possible seasonal drying occurring by the maastrichtian maastrichtian winter freezing was likely but periglacial conditions did not exist at sea level permanent ice was likely above 1700 m at 75 n in the cenomanian and above 1000 m at 85 n in the maastrichtian these near polar data provide critical constraints on global models of late cretaceous to early tertiary climates

paleobotanical evidence for cool north polar climates in middle cretaceous albian cenomanian time mid cretaceous albian cenomanian floras are abundant and diverse on the north slope of alaska the older floras consist of conifers cycadophytes ferns ginkgophytes and sphenophytes horsetails angiosperms appeared in latest albian time and rapidly diversified the preserved floras consist entirely of deciduous plants with the exception of a microphyllous conifer ferns and sphenophytes deciduousness is evidence for strong seasonality which for these floras might be variations in either light or temperature or both cool temperatures are suggested by the prevalence of toothed leaves among the angiosperms and the presence of large leaved conifers the paleobotanical evidence points to a mid cretaceous climate that was no warmer than cool temperate on the north slope of alaska

jurassic savannah plant taphonomy and climate of the morrison formation upper jurassic western usa abstract the morrison formation contains six plant taphofacies wood whole leaf leaf mat root common carbonaceous debris and rare carbonaceous debris none of these taphofacies is common in the morrison particularly striking is the paucity of wood even in more reducing environments the flora of the morrison formation is distinct in the kimmeridgian and tithonian parts of the section the plant taphofacies are consistent with a predominantly herbaceous vegetation evidence from the plant taphofacies floras and sedimentology of the morrison is consistent with a warm seasonal semi arid climate throughout changing from dry semi arid to humid semi arid from the kimmeridgian to the tithonian parts of the formation

paleoclimate reconstruction of the prince creek formation arctic alaska during maastrichtian global warming abstract the upper cretaceous maastrichtian prince creek formation of arctic alaska 82 85 n paleolatitude preserves successions of alluvial paleosols that are used to estimate mean annual precipitation map mean annual temperature mat and meteoric water oxygen isotope composition for the prince creek formation the highest map estimates range between 1000 and 3900 mm yr and the lowest range between 350 and 1200 mm yr the precipitation variability derived from stable carbon isotope analysis occurs on a time scale of 104 years map values agree with previous interpretations from fossil pollen pedological features soil types vegetation composition sedimentological indicators and clamp estimates that suggest high precipitation amounts and high humidity despite the considerable uncertainty with mat proxies our values are consistent with warm month mean temperatures obtained previously from paleobotanical data the 18o of smectite from bentonite beds clusters around 5 0 vsmow the 18o of meteoric water calculated from bentonitic smectite is 23 vsmow assuming a mean annual temperature of 6 3 c which is slightly more 18o depleted than meteoric water calculated from pedogenic siderite in stratigraphically younger beds closer to the brooks range chronostratigraphic correlation with the lower cantwell formation denali national park alaska 64 n paleolatitude suggests higher precipitation rates and highly 18o depleted precipitation in the late cretaceous paleo arctic compared to central alaska these data are consistent with previous studies that suggest a warmer and moister greenhouse earth and an intensified hydrological cycle that enhanced latent heat transport resulting in increased rainout effects

fish tooth δ18o revising late cretaceous meridional upper ocean water temperature gradients the oxygen isotope composition of fossil fi sh teeth a paleo upper ocean temperature proxy exceptionally resistant to diagenetic alteration provides new insight on the evolution of the low to middlelatitude thermal gradient between the middle cretaceous climatic optimum and the cooler latest cretaceous period the new middle cretaceous low to middle latitude thermal gradient agrees with that previously inferred from planktonic foraminifera 18o recovered from deep sea drilling project and ocean drilling program drilling sites although the isotopic temperatures derived from 18o of fish teeth are uniformly higher by 3 4 c in contrast our new latest cretaceous thermal gradient is markedly steeper than those previously published for this period fish tooth 18o data demonstrate that low to middle latitude thermal gradients of the middle cretaceous climatic optimum and of the cooler latest cretaceous are similar to the modern one despite a cooling of 7 c between the two periods our new results imply that no drastic changes in meridional heat transport are required to explain the late cretaceous climate based on climate models such a cooling without any change in the low to middle latitude thermal gradient supports an atmospheric co2 decrease as the primary driver of the climatic evolution recorded during the late cretaceous

late cretaceous terrestrial vegetation a near polar temperature curve quantitative estimates of terrestrial paleotemperatures near the north pole were derived from the physiognomy of the vegetation including leaf margin analysis from rocks of latest albian and late cretaceous age of the north slope of alaska during the latest albian and cenomanian mean annual temperature was approximately 10 3 c during the coniacian mean annual temperature may have been 2 3 c warmer than during the albian cenomanian but no higher than 13 c during the campanian and maastrichtian mean annual temperature would have been about 2 8 c although the ranges for the individual estimates overlap differences among the floras indicate that the relative changes in mean annual temperature did occur

north american nonmarine climates and vegetation during the late cretaceous abstract analyses of physiognomy of late cretaceous leaf assemblages and of structural adaptations of late cretaceous dicotyledonous woods indicate that megathermal vegetation was an open canopy broad leaved evergreen woodland that existed under low to moderate amounts of rainfall evenly distributed through the year with a moderate increase at about 40 45 n many dicotyledons were probably large massive trees but the tallest trees were evergreen conifers megathermal climate extended up to paleolatitude 45 50 n mesothermal vegetation was at least partially an open broad leaved evergreen woodland perhaps a mosaic of woodland and forest but the evapotranspirational stress was less than in megathermal climate some dicotyledons were large trees but most were shrubs or small trees evergreen conifers were the major tree element some mild seasonality is evidenced in mesothermal woods precipitational levels probably varied markedly from year to year northward of approximately paleolatitude 65 n evergreen vegetation was replaced by predominantly deciduous vegetation this replacement is presumably related primarily to seasonality of light the southern part of the deciduous vegetation probably existed under mesothermal climate comparisons to leaf and wood assemblages from other continents are generally consistent with the vegetational climatic patterns suggested from north american data limited data from equatorial regions suggest low rainfall late cretaceous climates except probably those of the cenomanian had only moderate change through time temperatures generally appear to have warmed into the santonian cooled slightly into the campanian and more markedly into the maastrichtian and then returned to santonian values by the late maastrichtian the early eocene was probably warmer than any period of the late cretaceous latitudinal temperature gradients were lower than at present for the campanian and maastrichtian a gradient of about 0 3 c 1 latitude is inferred equability was high a mean annual range of temperature of about 8 c is inferred for paleolatitude 51 56 n during the campanian most late cretaceous plants evolved in a climate characterized by absence of freezing and low to moderate amounts of precipitation a brief low temperature excursion and a major long lasting increase in precipitation occurred at the cretaceous tertiary boundary in megathermal climates these events selected for plants that could exist in rainforest environments in mesothermal climates deciduousness and contamitant structural adaptations were selected the events at the cretaceous tertiary boundary had a major and long lasting impact on the evolution of land plants and their ecosystems low precipitation at low to middle late cretaceous latitudes is suggested to be the result of high levels of atmospheric co2 which in turn are probably related to inability of warm saline oceans to store large amounts of carbon conditions appear to have rapidly changed at the cretaceous tertiary boundary when oceanic circulation and stratification may have been fundamentally altered after the boundary the oceans were apparently able to store much greater amounts of carbon and the oceans withdrew large amounts of co2 from the atmosphere in turn more precipitation fell at low to middle latitudes the resulting high biomass vegetation formed a second major carbon reservoir to keep atmospheric co2 low relative to the late cretaceous changes in oceanic and atmospheric circulation probably resulted from some factor external to the ocean atmosphere system

early tertiary marine fossils from northern alaska implications for arctic ocean paleogeography and faunal evolution marine mollusks and ostracodes indicate a post danian paleocene to early eocene thanetian to ypresian age for a fauna from the prince creek formation at ocean point northern alaska that also contains genera characteristic of the cretaceous and neogene quaternary the life association of heterochronous taxa at ocean point resulted from an unusual paleogeographic setting the nearly complete isolation of the arctic ocean from about the end of the cretaceous until sometime in the eocene in which relict cretaceous taxa survived into tertiary time while endemic taxa evolved in situ these later migrated to the northern mid latitudes paleobiogeographic affinities of the ocean point association with mild temperate faunas of the london basin england denmark and northern germany indicate that a shallow intermittent paleocene seaway extended through the norwegian greenland sea to the north sea basin early tertiary arctic ocean paleogeography deduced from faunal evidence agrees with that inferred from plate tectonic reconstructions

general circulation of the northern adriatic sea results of long term measurements abstract residual sea currents of the northern adriatic were analysed in the sense of the general global circulation over a period of 42 months in one main and two control stations at the end of the summer season and the beginning of autumn in the so called inversion period residual surface 6 m sea currents at the main station showed characteristic seasonal behaviour a change of direction from the north nw n ne to the south east se the sequence with se directions lasted about 1 5 months after that directions changed again to the nw or n the direction of bottom residual currents 37 m in this inversion period had the same pattern as the surface ones this behaviour of the currents can be associated with the change of the cyclonic gyre into the anticyclonic in all other periods at the main station the surface residual sea currents have predominant north directions bottom residual currents mainly followed the pattern of surface currents for all stations and periods except during the periods from january to june 1990 and 1992 when they were of opposite direction at station b

cretaceous climate a comparison of atmospheric simulations with the geologic record abstract atmospheric simulations using realistic cretaceous geography 100 million years ago suggest that paleography is an important factor governing the nature of the circulation the simulated cretaceous atmospheric circulations are markedly different both from the present day atmospheric circulation and from the classical hypotheses of a weaker circulation and poleward displacement of circulation features e g the subtropical high therefore they pose specific questions which can be tested against the geologic record aspects of the cretaceous simulations are verified in comparisons with the geologic record the simulations serve to guide areas of future paleoclimatic research and to formulate better the nature of the problem of warm equable climates

middle turonian dinosaur paleoenvironments in the upper cretaceous kaskapau formation northeast british columbia the kaskapau formation is a mudstone dominated wedge up to 950 m thick that spans late cenomanian to middle turonian time the formation has a prominent wedge geometry and was deposited in the foredeep of the western canada foreland basin in outcrop in northeast british columbia nearshore sandstones are locally well developed and include rare wedges of nonmarine strata on quality creek near tumbler ridge 11 m of nonmarine strata contain abundant dinosaur tracks and the first in situ dinosaur bone reported from british columbia this site at a paleolatitude of about 67 n preserves a rare glimpse of turonian terrestrial environments during global eustatic highstand three main dinosaur habitats are recognized strandplain and beach ridge freshwater lake and brackish lagoon back beach sandstone has a relief of about 2 5 m interpreted as beach ridges sandy coals containing abundant dinosaur tracks represent inter ridge slough deposits overlying lake deposits comprising laminated muds with freshwa

rainfall patterns and the distribution of coals and evaporites in the mesozoic and cenozoic abstract paleoclimatologists have adequately demonstrated over the last twenty years that the distribution of climatically sensitive sediments can be related to present day climatic zones that are roughly parallel to latitude for example coals were deposited at paleolatitudes that correspond to the present day rainy zones at the equator and at about 55 n and 55 s indicating that those zones were present in the past from this it can be concluded that atmospheric circulation has not been radically different from its present configuration despite some apparently great differences in some climatic parameters such as the equator to pole temperature gradient nevertheless the zonal model for predicting the distribution of climatically sensitive sediments is not wholly adequate although general atmospheric circulation may not have been radically altered from its present pattern it would have differed in some respects because the paleogeography was different from the present geography therefore we have constructed what we believe are more realistic maps of the distribution of rainfall through time these maps are based on maps of atmospheric circulation that have been successfully used to predict the distribution of some petroleum source beds and phosphorites we have compared the predicted distribution of rainfall to the distribution of coals and evaporites for each of seven geologic stages the circulation rainfall maps were more successful than the zonal model for predicting the distribution of evaporites and coals for times when the paleogeography would have maximized the development of a monsoonal circulation which most effectively disrupts the general zonal pattern for times when a monsoonal circulation would not have been important the zonal model adequately predicted the distribution of these rocks

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

plants and the palaeoatmosphere the effects of the development of terrestrial vegetation during devonian and carboniferous times is considered and it is concluded that the maximum possible global biomass in carboniferous times was equivalent to about 1 148 10 15 g c which is in excess of the current earth9s biomass 560 860 10 i5 g c global primary productivity however estimated at about 73 10 15 g c a 1 is of the same order as that of the present day the amount of carbon actually becoming stored as 9fossil fuel9 was a very small proportion of this productivity estimated here at only 0 00002 over 65 10 6 a thus the vegetation of carboniferous times cannot be regarded as a significant carbon sink the atmosphere of the mesozoic is discussed in relation to the evolution of angiosperms in particular the photosynthetic modifications in so called c 4 and cam plants are considered in relation to atmospheric and other environmental stresses taxonomic evidence indicates that the c 3 system is primitive in the angiosperms and that the modified systems have a polyphyletic origin physiological considerations suggest that their development relates more clearly to the demands of water balance rather than to lowered atmospheric co 2 or high atmospheric levels of oxygen it is not considered likely that the evolution of these mechanisms or of the angiosperms in general has had any profound effect upon the carbon content of the atmosphere

early palaeocene palaeoclimatic inferences from fossil floras of the western interior usa abstract twenty one early palaeocene floral assemblages were collected from a variety of alluvial depositional environments from sites in the williston powder river and raton basins of the western interior of the usa leaf fossils were assigned to morphotypes and their physiognomy was quantified for palaeoclimatic analysis two methods were used climate leaf analysis multi variate program clamp and leaf margin analysis lma temperature estimates and trends derived from clamp and lma indicate that early palaeocene palaeotemperatures decreased from the latest cretaceous particularly in northern areas of north america climatic zones shifted southwards from their latest cretaceous positions resulting in a steepened north south temperature gradient and decreased equability in the early palaeocene sub tropical conditions prevailed as far north as the raton basin with the 20 c mean annual temperature isotherm megathermal mesothermal boundary located at approximately 45 n palaeolatitude the 13 c mean annual temperature isotherm mesothermal microthermal boundary was located at approximately 55 n palaeolatitude to the south of the williston basin clamp estimates indicate that precipitation increased significantly in all areas sampled directly after the k t boundary event especially in the southern rockies precipitation levels decreased somewhat after this initial peak but remained high throughout the early palaeocene evidence from this and other studies suggests that seasonality increased from the latest cretaceous into the palaeocene and was most pronounced in central and northerly areas of the north american continent

testing for ice sheets during the mid cretaceous greenhouse using glassy foraminiferal calcite from the mid cenomanian tropics on demerara rise the mid cretaceous is widely considered the archetypal ice free greenhouse interval in earth history with a thermal maximum around cenomanian turonian boundary time ca 90 ma however contemporaneous glaciations have been hypothesized based on sequence stratigraphic evidence for rapid sea level oscillation and oxygen isotope excursions in records generated from carbonates of questionable preservation and or of low resolution we present new oxygen isotope records for the mid cenomanian demerara rise that are of much higher resolution than previously available taken from both planktic and benthic foraminifers and utilizing only extremely well preserved glassy foraminifers our records show no evidence of glaciation calling into question the hypothesized ice sheets and rendering the origin of inferred rapid sea level oscillations enigmatic simple mass balance calculations demonstrate that this cretaceous sea level paradox is unlikely to be explained by hidden ice sheets existing below the limit of 18 o detection

simple energy balance model resolving the seasons and the continents application to the astronomical theory of the ice ages a one level seasonal energy balance climate model which has explicit two dimensional land sea geography is introduced and its properties analyzed the model distinguishes land from sea surface strictly by the local thermal inertia employed the transport is governed by a smooth latitude dependent diffusion mechanism the model s seasonal cycle is solved for with and without ice feedback in each case good agreement with real data is accomplished with minimal tuning of the adjustable parameters the model sensitivity for small solar constant changes is in agreement with that of other accepted models however when the solar constant is lower a few percent the ice cap grows discontinuously from covering greenland and vicinity to a size three times larger and mostly into northern canada a similar discontinuous growth occurs when the orbital elements are changed to favor cool summers in the northern hemisphere this discontinuous sensitivity is discussed in the context of the milankovitch theory of the ice ages and the associated branch structure is shown to be analogous to the so called small ice cap instability known from simpler models although the discontinuity in sensitivity is somewhat conjectural both linear and nonlinear models have their largest sensitivity to orbital parameter changes in the northern portions of the large continents in the western hemisphere this also corresponds to the ice sheet boundary suggesting that the land sea configuration is crucial to large glacier growth irrespective of moisture budgets other experiments and implications are also discussed the remarkable paper by hays et al 1976 hereafter his presented compelling empirical evidence that continental ice sheet volume changes and sea surface temperature variations in the last 700 000 years are correlated with the changes in the earth s orbital elements theoretical arguments for such a connection date back to the last century but the most detailed and convincing arguments are due to milankovitch 1941 and the theory usually is associated with his name if the hypothesis is correct the theory and observations provide the cleanest experiment to determine the sensitivity of the earth s climate to truly external influences such a measure of climate sensitivity is of obvious importance considering the recent interest in estimating the change in climate due to other forcings such as the enhanced greenhouse effect due to increased levels of co2 in the atmosphere e g ramanathan 1981 hansen et al 1981 manabe and stouffer 1980 in effect climate models might be tested or calibrated by this natural experiment climate modeling has progressed dramatically in the last decade with the construction and testing of several general circulation models gcm s although some interesting ice age experiments have been done with these models gates 1976 manabe and hahn 1977 they still include only crude parameterizations of the slower components such as the oceans these numerical models are the ultimate tool that can be brought to bear upon the climate problem however they are almost as complicated as the climate itself hence experiments must be carefully designed and the interpretation is often difficult due to the expense of obtaining definitively long runs in parallel with gcm construction has been the development of x permanently at applied research corporation landover maryland 20785

tectonic forcings of maastrichtian ocean climate evolution a global compilation of deep sea isotopic records suggests that maastrichtian ocean climate evolution tvas tectonically driven during the early maastrichtian the atlantic intermediate deep ocean was isolated from the pacific indian and southern oceans deep water formed in the high latitude north atlantic and north pacific at the early late maastrichtian boundary a major reorganization of oceanic circulation patterns occurred resulting in the development of a thermohaline circulation system similar to that of the modem oceans a combination of isotopic and plate kinematic data suggests that this event was triggered by the final breaching of tectonic sills in the south atlantic and the initiation of north south flow of intermediate and deep water in the atlantic the onset of laramide tectonism during the mid maastrichtian led to the concurrent draining of major epicontinental seaways together these events caused cooling increased latitudinal temperature gradients increased ventilation of the deep ocean and affected a range of marine biota

a long marine history of carbon cycle modulation by orbital climatic changes pacing of the marine carbon cycle by orbital forcing during the pliocene and pleistocene ice ages past 2 5 million years myr is well known as older deep sea sediment records are being studied at greater temporal resolution it is becoming clear that similar fluctuations in the marine carbon system have occurred throughout the late mesozoic and tertiary despite the absence of large continental ice sheets over much of this time variations in both the organic and the calcium carbonate components of the marine carbon system seem to have varied cyclically in response to climate forcing and carbon and carbonate time series appear to accurately characterize the frequency spectrum of ancient climatic change for the past 35 myr much of the variance in carbonate content carries the polar signal of obliquity 41 000 years 41 kyr forcing over the past 125 myr there is evidence from marine sediments of the continued role of precessional 21 kyr climatic cycles repeat patterns of sedimentation at about 100 400 and 2 400 kyr the modulation periods of precession persistently enter into marine carbon cycle records as well these patterns suggest a nonlinear response of climate and or the sedimentation of organic carbon and carbonates to precessional orbital perturbations nonlinear responses of the carbon system may help to amplify relatively weak orbital insolation anomalies into more significant climatic perturbations through positive feedback effects nonlinearities in the carbon cycle may have transformed orbital climatic cycles into long wavelength features on time scales comparable to the residence times of carbon and nutrient elements in the ocean

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 guide to phanerozoic cold polar climates from high latitude ice rafting in the cretaceous the high latitude extent of warm climate indicators at certain times in earth history has been considered as evidence that the globe was ice free for long intervals despite theoretical considerations and results from numerical modelling experiments1 2 indicating that this was unlikely one of the warmest periods the cretaceous displays faunal and floral evidence for cool temperate to sub tropical conditions very near to the poles however our studies of lower cretaceous mudstones of central australia that contain outsized exotic blocks have led to the conclusion that the blocks were emplaced by ice rafting implying that high latitude ice was present at sea level strata of a similar origin of mid jurassic to mid cretaceous age occur on other continents that were positioned between 65 and 78 palaeolatitude indeed there is a record of high latitude ice rafting throughout the phanerozoic suggesting that ice was present on earth for much of its history and that ice free conditions could have been at most only episodic over the past 600 myr

early history of the arctic ocean the lomonosov ridge divides the arctic ocean into two basins with different histories the older amerasian basin consists of a ridge basin complex reflecting multiple tectonic cycles that are poorly understood the younger eurasian basin includes the present arctic mid ocean ridge its origin is linked to cenozoic spreading the entire older sediment record of the arctic ocean is known from only four short piston cores all recovered from the alpha ridge of the amerasian basin the oldest sediment recovered is a single core of black mud consisting of abundant terrestrial plant material deposited in a marine environment dinoflagellates are late campanian the black mud resulted from rapid accumulation of organic matter rather than from any of the well known cretaceous anoxic events two cores taken 100 to 200 km from the black mud consist of late maastrichtian siliceous ooze of diatoms and silicoflagellates this sediment has been interpreted to represent oceanic upwelling and high productivity in the late cretaceous arctic ocean a paleogene core consisting of similar biogenic silica has been recovered approximately 100 km from the cretaceous cores silicoflagellates of this core are either paleocene or middle to late eocene the sediment like that of the maastrichtian cores has been interpreted to represent oceanic upwelling and high productivity the older arctic cores were recovered as a result of fortuitous sampling in areas of thin late cenozoic sediment all other arctic cores consist of late cenozoic sediment the older sediment record is strong evidence of a late cretaceous to early paleogene arctic ocean with no perennial ice and with high productivity of dinoflagellates or siliceous organisms in water that circulated with lower latitude oceans recent modeling predicts some of the same climatic and oceanographic events recognized in the oldest sediment of the arctic ocean the sequence of events from a warm arctic ocean to an ice covered condition involved circulation changes seasonality and uneven spreading rates that increased north atlantic arctic ventilation

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

southern polar forests the early cretaceous floras of victoria and their palaeoclimatic significance abstract a diverse fossil flora including cryptogams pteridosperms cycadales bennettitales ginkgoales coniferales and angiosperms occurs in early cretaceous fluvial and lacustrine strata in the otway and gippsland basins in southern victoria both evergreens e g araucarians cycads ferns and deciduous or semi deciduous forms e g certain pteridosperms and ginkgoales seem to have been represented certain ferns ginkgos and conifers grew to a large size overall the assemblages are typical of early cretaceous floras the associated fauna includes dinosaurs hypsilophodontids allosaurs lepidosaurs chelonians birds fish including the lungfish ceratodus and insects the evidence of the biota as a whole suggests a warm to cool temperate relatively equable climate of moderate seasonality with no widespread winter freezing the complex mesozoic apparent polar wander path apw indicated for australia places victoria in high to polar palaeolatitudes ca 70 85 s during the early cretaceous this apw path is supported by paths for other gondwana continents the existence of the victorian early cretaceous forest and biotic communities through polar nights of about two to five months duration is difficult to accept evergreen species would have required relative equability of light whatever the temperature the dinosaurs foliage throughout the year and the lungfish warm to temperate conditions without freezing in view of the consistency of mesozoic palaeomagnetic results for gondwanaland and the enigmatic presence of mesozoic and early cenozoic fossil floras and faunas in very high northern palaeolatitudes the possibility of a reduced obliquity of the ecliptic in mesozoic early cenozoic time should be considered

do fossil plants give a climatic signal the agreement in the pattern of major biomes with that of climatic zonation of the earth gives a strong indication that climate is the overriding influence controlling the distribution of plant communities three aspects of plants which may be preserved in the fossil state give a signal of the climatic conditions under which they grew 1 the present climatic association of their 9nearest living relative9 2 leaf physiognomy of arborescent plants 3 the character of their secondary xylem 9wood9 of ordinary usage reflecting by the presence or absence of growth rings the seasonality or lack of it in their environment and the potential for tree growth that it offered the significance and limitations of these 9palaeoclimatic signals9 as they may be read from the fossil plant record are reviewed and evaluated the recent demonstration that stomatal frequency of leaves is responsive to changes in ambient carbon dioxide partial pressure offers promise for direct palaeobotanical evidence for past changes in the level of this climatically significant atmospheric constituent

terrestrial isotopic evidence for a middle maastrichtian warming event from the lower cantwell formation alaska abstract carbon stable isotope data 13c and new radiometric dates indicate that the non marine late cretaceous lower cantwell formation central alaska registers the middle maastrichtian event mme a global warming episode a stratigraphic section measured at the east fork of the toklat river in denali national park preserve includes a bentonite layer that we have dated to 69 5 0 7 ma using u pb isotope analysis of zircons the new depositional age confirms that dinosaur tracks from the lower cantwell formation are coeval with dinosaur bones from outcrops of the prince creek formation on alaska s north slope 13c data from fossil wood recovered from the lower cantwell formation records an 3 positive excursion correlative with positive excursions from terrestrial and marine sections in west texas usa and gubbio italy respectively the similarity between marine and terrestrial records suggests that this excursion is the result of a major perturbation in the global carbon cycle known as the middle maastrichtian event mme mean annual precipitation map estimates calculated from 13c data yield a range of 168 470 mm yr during the mme 353 1050 mm yr before and 475 1451 mm yr after the warming event the 13c record from the lower cantwell formation provides the first terrestrial high latitude evidence for the mme while map estimates for the coeval prince creek formation suggest that the arctic coast may have been more humid than southern interior alaska during the middle maastrichtian

structural styles and deformation fabrics of accretionary complexes intricately deformed stratally disrupted and mixed rocks produced at subduction zones have been considered structurally intractable however marine geophysical studies deep sea drilling analyses of subaerially exposed complexes and theoretical advances have recently produced breakthroughs in elucidating the structural enigmas of these accretionary complexes the penrose conference structural styles and deformational fabrics of accretionary complexes assembled specialists from the above and related research areas and addressed the research frontiers of this dynamic topic this conference in eureka california in may 1984 drew participants from great britain france canada japan and new zealand

late paleocene arctic ocean shallow marine temperatures from mollusc stable isotopes late paleocene high latitude 80 n arctic ocean shallow marine temperatures are estimated from molluscan 18o time series sampling of individual growth increments of two specimens of the bivalve camptochlamys alaskensis provides a high resolution record of shell stable isotope composition the heavy carbon isotopic values of the specimens support a late paleocene age for the youngest marine beds of the prince creek formation exposed near ocean point alaska the oxygen isotopic composition of regional freshwater runoff is estimated from the mean 18o value of two freshwater bivalves collected from approximately coeval fluviatile beds over a 30 34 range of salinity values assumed to represent the tolerance of c alaskensis the mean annual shallow marine temperature recorded by these individuals is between 11 and 22 c these values could represent maximum estimates of the mean annual temperature because of a possible warm month bias imposed on the average 18o value by slowing or cessation of growth in winter months the amplitude of the molluscan 18o time series probably records most of the seasonality in shallow marine temperature the annual temperature range indicated is approximately 6 c suggesting very moderate high latitude marine temperature seasonality during the late paleocene on the basis of analogy with modern chlamys species c alaskensis probably inhabited water depths of 30 50 m the seasonal temperature range derived from 18o is therefore likely to be damped relative to the full range of annual sea surface temperatures high resolution sampling of molluscan shell material across inferred growth bands represents an important proxy record of seasonality of marine and freshwater conditions applicable at any latitude if applied to other regions and time periods the approach used here would contribute substantially to the paleoclimate record of seasonality

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

the climate of the eocene ocean oxygen isotope palaeotemperature estimates are presented for a number of deep sea sediment samples of eocene age covering a wide geographical area these are plotted on a geographical reconstruction for 50 ma the latitudinal temperature gradient at that time was less than half its present value surface temperature at high latitudes was about 10 c and at low latitudes little over 20 c it is concluded that ocean currents must have contributed a greater proportion of the poleward transport of heat than they do at present

campanian maastrichtian cretaceous stratigraphy of the james ross island area antarctica one of the most important outcrops of uppermost cretaceous campanian maastrichtian sedimentary rocks in the southern high latitudes occurs within the james ross island group northeastern antarctic peninsula these rocks comprise a 1500 2000 m thick sequence of predominantly shallow marine clastic sediments that were deposited within a retro arc basin they are virtually undeformed and have yielded prolific invertebrate and vertebrate faunas and a wide range of plant taxa campanian maastrichtian strata are contained within two component formations of the upper cretaceous lower tertiary marambio group the lower santa marta formation is approximately 1100m thick and has three constituent members ammonites within the santa marta formation indicate an early to late campanian age assignment dinoflagellates suggest that the lower levels of the formation may range into the santonian stage in the northern james ross island to vega island region there is a conformable transition into the overlying lopez de bertodano formation here the basal cape lamb member is unconformably overlain by the sandwich bluff member although there are some lithological and fauna1 discrepancies which are attributed to marked lateral facies changes across the basin it is believed that the cape lamb member can be correlated with the lower to middle regions of the 1200 m thick sequence of undifferentiated lopez de bertodano formation lithologies exposed on seymour island molluscan data indicate a late campanian palaeocene age range for this upper formation dinoflagellates again suggest that the lowest beds may be slightly older the correlation presented provides the basis for a formal subdivision of the campanian and maastrichtian stages in the southern high latitudes it has also revealed two major basin shallowing events in the late campanian early maastrichtian and latest maastrichtian respectively and the existence of a major fault fault zone across southeastern james ross island the improved temporal framework will aid late cretaceous palaeoclimatic and palaeobiological studies in antarctica

late quaternary vegetation changes around lake rutundu mount kenya east africa evidence from grass cuticles pollen and stable carbon isotopes woody subalpine shrubs and grasses currently surround lake rutundu mount kenya multiple proxies including carbon isotopes pollen and grass cuticles from a 755 cm long core were used to reconstruct the vegetation over the past 38 300 calendar years stable carbon isotope ratios of total organic carbon and terrestrial biomarkers from the lake sediments imply that the proportion of terrestrial plants using the c4 photosynthetic pathway was greater during the late pleistocene than in the holocene pollen data show that grasses were a major constituent of the vegetation throughout the late pleistocene and holocene the proportion of grass pollen relative to the pollen from other plants was greatest at the last glacial maximum lgm grass cuticles confirm evidence that c4 grass taxa were present at the lgm and that the majority followed the cold tolerant nadp mec4 subpathway copyright 2003 john wiley sons ltd

upper cenozoic history of the labrador sea baffin bay and the arctic ocean a paleoclimatic and paleoceanographic summary foraminifera palynomorphs and stable isotopes in planktonic foraminifera have been studied in piston cores from the northern labrador sea southern baffin bay and the alpha ridge region of the central arctic ocean foraminifera in cores from the labrador sea and southern baffin bay show glacial interglacial 18o values similar to those reported from the norwegian and greenland seas in contrast to the eastern north atlantic ocean however peaks of subarctic foraminifera and dinoflagellates in the western north atlantic cores show that relatively warm atlantic surface water continued to flow into the northern labrador sea during the early glaciation growth phases of isotopic stages 2 4 6 and 8 boreal and subarctic pollen suggest that warm atlantic air flowed into the northern labrador sea and baffin bay during the ice sheet growth phases the advection of warm air masses and the presence of open waters during the summer probably provided moisture for the growth of the laurentide innuitian and greenland ice sheets isotopic and microfossil records in arctic cores can also be tentatively correlated with major high latitude north atlantic glacial interglacial events magnetostratigraphic palynological and amino acid dating however shows that sedimentation on the alpha ridge has been very slow during the past 0 73 m y therefore events of less than 20 000 years duration cannot be clearly discerned interpretation of pre pleistocene paleoenvironments is further limited by the sparseness of calcareous and siliceous microfossils

explanations of the tertiary global cooling trend abstract a series of general circulation model experiments are performed to examine the role of paleogeography as an explanation of the tertiary global cooling trend systematic long term variations in topography and land sea distribution are potential causes of long term climate change however climate model sensitivity experiments indicate a geographically related cooling during the last 20 million years but not a long term cenozoic trend coarse resolution changes in geography throughout the tertiary may not be the explanation of the tertiary global cooling trend either a series of events some geographically related or another forcing factor most probably atmospheric co2 concentration are offered as alternative explanations of the tertiary global cooling trend

growth ring analysis of early tertiary conifer woods from the canadian high arctic and its paleoclimatic interpretation abstract fossil forests where petrified stumps were preserved in growth position have been found within early tertiary sediments near strathcona fiord ellesmere island canadian arctic archipelago these fossil forests are obvious evidence for early tertiary climate much warmer than that of today we analyzed the growth rings of petrified woods from two fossil forest sites one in middle paleocene and the other in late early eocene to extract information on climate change the woods consist most abundantly of metasequoia and cf glyptostrobus suggesting that these forests grew in similar environments of warm to cool temperate climates mean ring width mean sensitivity and power spectrum were calculated for ring width sequences although significant difference in the mean ring width between the two forests was found a comparison with living trees suggests that the difference can be attributed to the specific difference between the forests so that a significant climate change may not necessarily be invoked we found little significant difference in the mean sensitivity and power spectrum between the forests neither did we find any strong indication of periodicities consideration of all features suggests that there was no significant difference in climate of middle paleocene and late early eocene time in the high arctic however the mean ring widths of these forests were significantly smaller than that reported for mid cretaceous high arctic fossil forest

quantitative palaeoclimate gcm validation late jurassic and mid cretaceous case studies using quantitative proxy models of peat and bauxite formation based upon modern analogues predictions of the distribution of peats coals and bauxites for both the late jurassic kimmeridgian and mid cretaceous cenomanian have been made using a general circulation model gcm the predictions have been compared with the known distribution of these deposits such an approach provides a means of identifying and isolating which components of the gcm accurately reflect palaeoclimate the prediction of peats and bauxites for the jurassic and cretaceous show good correspondence with known coals and bauxites and provides otherwise elusive quantitative estimates of high latitude climate the gcm is thus successfully replicating precipitation and mean annual temperatures for both the kimmeridgian and cenomanian investigations of mesozoic palaeoclimate using general circulation models gcms have often focused on qualitative evaluation of results e g barron washington 1982 valdes et al 1995 chandler et al 1992 a number of recent studies have however highlighted the need for gcm predictions to be quantitatively validated against the sedimentological and palaeobiological record e g poore chandler 1994 pollard schulz 1994 price et al 1995 quantitative estimates of terrestrial climate have been produced by physiognomic analysis of floras e g herman spicer 1996 wolfe upchurch 1987 and have also been derived from organisms such as crocodiles e g markwick 1994 comparable results have been used effectively for validating gcm predictions e g sloan barron 1992 but data tend to be restricted to north america and are often latest cretaceous or younger in age

modelling equable climates of the late cretaceous can new boundary conditions resolve data model discrepancies late cretaceous maastrichtian climate and vegetation is modelled using the hadcm3l fully coupled atmosphere ocean model and the triffid dynamic vegetation model we investigate data model inconsistencies in the high latitudes and continental interiors by exploring the sensitivity of modelled terrestrial climate to vegetation treatment changing atmospheric pco2 levels and the representation of arctic seaway connections we expand on previous work by using millennial scale gcm runs with dynamic vegetation to allow for improved representations of ocean heat transport and terrestrial boundary conditions incorporating realistic vegetation drives high latitude warming particularly during summer through reductions in surface albedo and induced atmosphere ocean feedbacks resulting regional warming can exceed 10 c as pco2 rises some regions cool as deciduous to evergreen change increases albedo incorporating enhanced arctic connectivity reconfigured ocean heat transport drives widespread terrestrial warming of 3 c and 5 c regionally applying sensitivities in combination significant palaeobotanical data model inconsistencies in the northern high latitudes and continental interiors remain further work is required to resolve climate and vegetation model deficiencies and improve the interpretation and geographic distribution of quantitative climate sensitive geological proxies

thermal evolution of cretaceous tethyan marine waters inferred from oxygen isotope composition of fish tooth enamels 1 the evolution of subtropical 30 35 n upper ocean temperatures through the cretaceous is inferred from the oxygen isotope compositions of 64 fish teeth enamel coming from the western tethyan platform mean 18o values of 22 at the berriasian valanginian boundary decrease with oscillations to 18 5 around the cenomanian turonian boundary and progressively increase to 21 5 by the end of the cretaceous the similarity of this oxygen isotope curve for bioapatites from platform environments with those for foraminifera and bulk carbonates that were deposited in deeper waters and at other paleolatitudes indicates that they record global climatic signals major cooling events at the million year scale can be distinguished 1 at the berriasian valanginian boundary and 2 during the earliest late valanginian a third cooling event is detected during the earliest aptian these events already proposed as icehouse interludes during the lower cretaceous are also recorded at subtropical latitudes a progressive warming is identified from the aptian to the cenomanian turonian interval that corresponds to a thermal optimum and then upper ocean temperatures decreased to the maastrichtian minimum isotopic temperatures range from 15 c to 28 c assuming a 18oseawater of 1 for an ice free world taking more realistic 18oseawater values of 0 for tropical waters during glacial periods within the berriasian valanginian interval and earliest aptian or with above average salinities possibly the maastrichtian temperatures are increased by 4 5 c temperature differences between climatic extremes of the valanginian and cenomanian turonian are estimated to have been 10 c latitudinal thermal gradients for the albian cenomanian turonian and maastrichtian were 0 2 0 3 c latitude and thus weaker than modern oceanic values at about 0 4 c latitude

floodplain palaeosols of the cenomanian dunvegan formation alberta and british columbia canada micromorphology pedogenic processes and palaeoenvironmental implications

three growth in the mesozoic and early tertiary and the reconstruction of palaeoclimates abstract evidence from the distribution and characteristics of fossil wood in the mesozoic and early tertiary indicates that a much warmer global climate prevailed in those times there appears to have been a broad zone of largely non seasonal climate stretching from about 32 n to 32 s palaeolatitudes in addition to this low latitude zone forest growth extended into very high palaeolatitudes where trees cannot grow at the present day a number of theories have been proposed to account for the palaeoclimate responsible for this distribution of forests most notable have been those involving changes in the amount of carbon dioxide in the atmosphere in the positions of the continents or in the obliquity of the earth s axis of rotation evidence from fossil forests indicates that a combination of the effects of an increased quantity of carbon dioxide in the atmosphere and the palaeopositions of the continents in the mesozoic and early tertiary appears at the moment to be the simplest explanation for the climate of those geological times without the need to invoke axial movement

atmospheric circulation during warm geologic periods is the equator to pole surface temperature gradient the controlling factor paleoclimatologists have hypothesized that the equator to pole surface temperature gradient is a dominant control on the paleocirculation of the oceans and the atmosphere atmospheric simulations using realistic cretaceous 100 m y ago geography are used to examine quantitatively the relationships between paleogeography surface temperature gradients and the nature of the atmospheric circulation these results raise questions concerning the classical theories and interpretations of warm paleoclimates and suggest that paleogeography is an important factor governing the nature of the circulation

palynology of maastrichtian and paleocene rocks lower colville river region north slope of alaska outcrops of maastrichtian rocks are rare on the north slope of alaska and it is even more unusual to find outcrops of maastrichtian and paleocene age in the same vicinity in general late cretaceous and paleogene rocks have not been well dated in published papers pertaining to northern alaska in this article we describe palynomorph assemblages from 20 outcrop samples taken from nine localities along the lower colville river and nearby areas the latest cretaceous palynomorph assemblages that are from marine rocks contain late campanian or maastrichtian dinoflagellate cysts however these cysts and other marine fossils are absent from the tertiary samples indicating that the tertiary strata are nonmarine our latest cretaceous and early tertiary samples contain abundant spores and pollen grains and can be readily dated by reference to well known pollen assemblages from the northern great plains and northwestern canada by dating each sampled outcrop we can approximate the position of the cretaceous