geology u pb geochronology and stable isotope geochemistry of the tunca semi massive sulfide mineralization black sea region ne turkey implications for ore genesis abstract upper cretaceous volcano sedimentary sequences of the eastern pontide orogenic belt ne turkey are host to significant vms mineralization including near tunca the initial stages of felsic volcanism within the mineralized area are marked by the eruption of dacitic lavas and breccias of the kizilkaya formation this was accompanied by the emplacement of domelike hematitic dacites autobrecciated and volcaniclastic rocks both in situ and resedimented were likely generated from extrusive portions of these dacite bodies basaltic volcanism is marked by the eruption of the lava flows and pillow lavas of the caglayan formation hiatuses in basaltic activity are marked by thin horizons of volcaniclastics and mudstones the uppermost felsic volcanic units were accompanied by resedimentation of autoclastic facies from previous volcanism and represent the latest phase of upper cretaceous volcanism in the area the semi massive sulfide mineralization is associated with a late stage of the initial felsic volcanism u pb la icp ms zircon dating of a dacitic tuff breccia yielded an age of 88 1 1 2 ma coniacian upper cretaceous which is interpreted to be the age of the sulfide occurrences a concentric zoned alteration pattern is observed in the footwall rocks the alteration pattern is considered to have formed by lateral migration of hydrothermal fluids which had ascended along the discharge conduit fluid inclusion data indicate precipitation or mobilization processes within a relatively narrow temperature range of 152 255 c avg 200 c the low salinity fluids in the fluid inclusions less than 5 9 wt nacl equivalent are consistent with typical modified seawater dominant hydrothermal vent fluids sulfur isotope analysis of the tunca sulfides yields a narrow range of 1 5 4 1 per mil these 34 s values are also typical of many vms deposits most of the recorded 18 o values 7 1 to 14 0 per mil are greater than 9 per mil the most intensely hydrothermally altered rocks tend to have lower 18 o values relative to the less altered rocks collectively the geologic relationships mineralization style and the lack of seafloor ore facies suggest that mineralization is principally of sub seafloor origin the most geologically reasonable interpretation of the genesis of the tunca mineralization is the continuous interaction between the host rocks and seawater derived fluids without significant involvement of a magmatic fluid

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

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

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

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

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

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

evolution and source of ore fluids in the stringer system hellyer vhms deposit tasmania australia evidence from fluid inclusion microthermometry and geochemistry the hellyer deposit is a classic large tonnage high grade mound style volcanic hosted massive sulphide vhms deposit in the cambrian mt read volcanic belt of western tasmania in the footwall directly underlying the deposit there is an extensively altered pipe which cootains a well developed and preserved stringer zone the vein paragenesis at hellyer indicates that premineralization stage i veins consist entirely of quartz and occur throughout the alteration pipe the synmineralization stage 2 veins are the most abundant veins in the stringer zone and consist of three sub stages stage 2a veins of crustiform quartz pyrite and carbonate with minor amounts of chalcopyrite sphalerite and galena stage 2b veins with abundant base metal sulphides minor quartz carbonate and barite gangue and stage 2c veins of coarsely crystalline barite with variable amounts of pyrite sphalerite galena and carbonate stages 3 6 veins are postmineralization veins and are related to the devonian tabberabberan orogeny textural petrographic and microthermometric investigations of fluid inclusions in the hellyer stringer system indicate that type i primary liquid vapour inclusions occur along growth planes of crustiform quartz crystals or within colour banding of zoned sphalerite these inclusions are 10 15 m in size and yielded homnogenisation temperatures of 170 220 c in early 2a veins 165 322 c in main stage 2b veins and 190 256 c io late stage 2c veins these data suggest a waxing and waning thermal history however the average salinity remained between 8 11 naci equiv wt in all stage 2 veins chalcopyrite bearing primary fluid inclusions have been recognised in the base metal rich stage 28 veins no evidence for presence of co2 e g formation of clathrates was recorded by rnicrothermometry however laser raman spectroscopic lrs analysis indicates the presence of co2 1 mole in the stage 2b veins and no detectable co2 in 2a and 2c vein stages semi quantitative sem wds microprobe analyses of fluid inclusion decrepitates indicate that the hellyer ore fluid was enriched in potassium and calcium but depleted in magnesium relative to seawater pixe microanalysis of fluid inclusions in quartz indicates that the stage 2b ore fluids have a significantly higher base metal concentration compared to the stage 2a veins the postmineralization stage 4 veins have a variable but lower base metal content in this study there was no fluid inclusion evidence of boiling cation composition higher salinities relative to seawater and the presence of co2 suggest that recycled seawater alone cannot be the sole source of the ore fluids this interpretation is in agreement with previous isotopic studies in the hellyer stringer system although direct input of bulk ore constituents from a magma chamber cannot be demonstrated from the present fluid inclusion data such a contribution of ore fluids from a magmatic source cannot be ruled out the possible input from the magmatic source may have occurred during the base metal rich stage 2b vein formation characterised by the intensifying temperature of deposition higher base metals and co2 contents

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

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

the spectrum of ore deposit types volcanic environments alteration halos and related exploration vectors in submarine volcanic successions some examples from australia variations in shape metal content alteration mineralogy and volcanic host rocks of the ore deposits in the two major volcanic hosted massive sulfide vhms districts of eastern australia the cambrian mount read volcanics and the cambro ordovician mount windsor subprovince strongly reflect their volcanic environment conditions of ore formation and hydrothermal alteration processes lens and sheet style polymetallic zinc rich deposits such as rosebery hellyer que river and thalanga are considered to have formed in moderate to relatively deep water environments 500 1 000 m these deposits probably formed either on the sea floor e g hellyer que river or by replacement of porous volcaniclastic units directly below the sea floor e g rosebery the footwall alteration associated with these polymetallic vhms deposits was controlled by host rock permeability and porosity which are in turn related to volcanic facies type degree of fracturing and synvolcanic structural architecture focusing of hydrothermal fluids along synvolcanic structures has resulted in well zoned chlorite sericite footwall alteration pipes within footwall lavas at hellyer on the other hand diffuse fluid flow through very thick pumice breccia at rosebery and hercules has resulted in strata bound sericite dominated footwall alteration zones parallel to the paleosea floor and the ore lenses massive and disseminated pyritic cu au deposits such as those in the mount lyell field and at highway reward formed by subsea floor replacement and are associated with only minor zinc lead massive sulfide ore these deposits formed from higher temperature fluids 300 degrees c in which copper transport is enhanced and are commonly located in felsic volcanic centers dominated by shallow porphyritic intrusions e g highway reward the cu au ore lenses may be strata bound e g mount lyell or crosscutting pipes e g highway reward depending on the structure and permeability characteristics of the felsic volcanic host rocks the presence of high sulfidation alteration minerals e g pyrophyllite zunyite in some of the cu au deposits e g mount lyell field indicates that fluids were relatively acidic and suggests the possibility of magmatic fluid input into the hydrothermal system alteration zonation associated with the cu au vhms deposits is more symmetrical than that of the zn rich deposits with sericite rich alteration extending into the hanging wall in keeping with the subsurface replacement origin of these deposits synvolcanic gold rich deposits with high gold base metal ratios are less common than the cu au and zn rich vhms ore types the gold rich ores e g henty south hercules are strata bound in nature have low sulfide contents and are associated with central zones of intense silicification surrounded by envelopes of sericite pyrite and carbonate alteration volcanological and geochemical studies at henty indicate the gold rich ore formed by the replacement of particular volcanic units deposited in a relatively shallow water environment dominated by volcaniclastic facies lavas and limestones this spectrum of cu au zn rich and au only deposits in the mount read volcanics and the mount windsor subprovince is interpreted to represent a continuum from classic sea floor vhms ores toward those with features more akin to porphyry cu au and epithermal au ag deposits this spectrum relates to the interplay between factors in the submarine volcanic environment and the character of the hydrothermal fluid as follows 1 proportions of volcaniclastic lava and subvolcanic intrusive facies 2 depth of seawater 3 permeability and porosity of volcanic host rocks 4 balance between magmatic components and seawater components in the ore fluid and 5 temperature and acidity of the ore fluid mineralogical lithogeochemical and isotopic studies have revealed a range of alteration vectors useful in exploration for both the zn rich and cu au vhms deposits carbonate and white mica compositional variations are highlighted as important mineralogical vectors thallium and antimony halos may be useful trace element vectors and oxygen and sulfur provide important isotope vectors toward the center of the hydrothermal system

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

urucum neoproterozoic cambrian manganese deposits ms brazil biogenic participation in the ore genesis geology geochemistry and depositional environment abstract the urucum region mato grosso do sul brazil contains neoproterozoic cambrian manganese ore in the layers mn 1 mn 2 and mn 3 which are interbedded with iron formations ifs from the santa cruz formation jacadigo group and surrounded by carbonate rocks from the bocaina and tamengo formations corumba group these rocks fill an ancient graben with sediments from the santa cruz formation overlying fluvial deposits from the urucum formation and limestones from the bocaina and tamengo formations deposited in the shallow marginal regions as the graben deepened it was flooded with microbe rich seawater and hydrothermalism began iron and manganese precipitated within the pores in arkosic sandstones thereby forming the clastic lower mn 1 ore layer the remaining manganese was simultaneously deposited on the basin floor with clastic clay and silt from turbidity currents thereby forming the upper mn 1 clastic chemical ore layer the sedimentation of mn 1 and its host ifs was controlled by seawater saturation and homogeneous oxidation which caused manganese and iron sedimentation and the death of microorganisms generating mangano ferriferous sediments with high p co and ni contents mn 2 formed during periods of tectonic quiescence through water influxes that carried abundant microbes fe ii mn ii and sio 2 under uv radiation these microbes oxidized mn ii and fe ii to form hydroxides and died thereby forming biomass that was enriched in p co and ni and minor carbonate adjacent to and below the oxycline these microbes also formed kremydilites oblate structures that resemble manganese stromatolites within the biomass and produced ch 4 and or h 2 gas bubbles during early diagenesis wormlike organisms inhabited the biomass and probably separated iron from manganese to produce cryptomelane microbialites which agglutinated to form manganese micronodules that coalesced to form the massive layer mn 2 this process ended with the disappearance of microorganisms and the sedimentation of the ifs and a new water influx generated layer mn 3 via the same process the final seawater upwelling precipitated ifs in the basin depocenter whereas limestone from the tamengo formation was deposited along the basin s edges the diagenesis initially transformed the manganese oxides into cryptomelane and then into hollandite

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

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

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

high precision u pb zircon chronostratigraphy of the mount read volcanic belt in western tasmania australia implications for vhms deposit formation the middle cambrian mount read volcanics of western tasmania australia host several world class volcanic hosted massive sulfide vhms deposits representing a wide range of deposit styles although the deposits and their host sequences are variably deformed and locally preserve spectacular examples of primary textures and structures rapid lateral and vertical facies changes and faults with uncertain sense and magnitude of displacement have made it impossible to correlate stratigraphy across the belt previous dating studies in the area have yielded relatively imprecise crystallization ages we have employed the chemical abrasion isotope dilution thermal ionization mass spectroscopy id tims u pb zircon method to obtain highly precise crystallization ages for a total of 18 samples of volcanic and intrusive rock units from throughout the mount read volcanics and underlying mafic ultramafic complexes the new data permit detailed resolution of age relationships within the belt the study establishes an age of 516 0 0 9 ma for the mcivor hill gabbro which is part of a mafic ultramafic complex interpreted to underlie the mount read volcanics magmatism in the central mount read volcanics lasted at least 12 7 m y from 506 8 1 0 ma for a massive dacite unit in the lower part of the central volcanic complex to 496 0 0 9 ma for a welded ignimbrite in the lower tyndall group together with previous age constraints results of the study provide a precise chronostratigraphic framework for magmatism and vhms deposit formation within the mount read volcanics the precise age data indicate that north of the henty fault magmatism occurred in three discrete pulses at least two of which were separated by periods of sedimentation we demonstrate that vhms deposits in the mount lyell roseberry hercules and que hellyer districts comprising the majority of the known significant vhms deposits in the belt formed within a narrow time interval at 500 1 ma at a relatively late stage in the evolution of the belt some of the larger intrusions in the belt e g the bonds range porphyry 500 4 0 8 ma were emplaced contemporaneously with vhms deposit formation however other bodies such as the murchison granite 497 3 0 9 ma are younger than the deposits and are unlikely to have been involved in their genesis as has previously been suggested these conclusions will aid explorers in targeting vhms mineralization in the mount read volcanics

the paleoproterozoic aripuana zn pb ag au cu volcanogenic massive sulfide deposit mato grosso brazil geology geochemistry of alteration carbon and oxygen isotope modeling and implications for genesis aripuana is a paleoproterozoic 1 76 1 75 ga stratiform volcanogenic zn pb ag au cu massive sulfide deposit has an estimated resource of 11 6 million metric tons mt of ore and is located on the south southwest border of the amazon craton brazil aripuana resides in a caldera composed of strongly fractionated felsic metavolcanic rocks transitional between calc alkaline and tholeiitic compositions the entire region was metamorphosed into lower greenschist facies 1 68 1 63 ga and the deposit was subsequently thermally metamorphosed and metasomatized 1 56 1 53 ga the mineralized bodies are lenticular and elongated they are located at the base of a sequence of turbidites which overlie dacitic and rhyolitic ignimbrites the rocks of the footwall are silicified sericitized and chloritized and the hanging wall rocks are carbonate rhythmites and turbidites hydrothermal marbles carbonate breccias and breccia like rocks carbonate talc tremolite chlorite rock talc tremolite and biotite rich rocks and carbonate and fluorite bearing cherts the deposit was formed during at least four submarine exhalative hydrothermal cycles in which siliceous marbles and marls represent the initial phase of each cycle followed by the coprecipitation of pyrite pyrrhotite sphalerite argentiferous galenas chalcopyrite which were disseminated in clay carbonate breccias or formed massive lenses this phase was followed by fluoritic cherts and argillites which were followed by carbonate and fluorite rhythmites and turbidites to close the cycle the variation in total rare earth element ree contents and in the eu and ce anomalies indicates that the original sediments were mixtures of hydrothermal carbonate and smectitic clay and were deposited below a redoxcline isotopic analysis identified 18osmow values between 8 and 13 and 13cpdb values between 7 and 1 modeling isotopic data showed that mineralizing fluids were distinct based on the proportion of magmatic fluid that mixed with the seawater carbonate rocks and sulfide minerals precipitated while hydrothermal activity and volcanism evolved from an exhalative to an exhalative explosive character with temperatures increasing between 100 and 200 c the regional metamorphism of the deposit formed carbonate talc tremolite chlorite rocks tremolite biotite and talc rich rocks it recrystallized the minerals foliated and folded all of the rocks and caused limited decarbonation at the sites where carbonate rocks contained silica and smectite however the original isotopic signatures were maintained the thermal metamorphism erased the metamorphic foliation and the metasomatism generated veinlets of chlorite with sulfides

subsurface deposition of cu rich massive sulphide underneath a palaeoproterozoic seafloor hydrothermal system the red bore prospect western australia the proterozoic bryah and yerrida basins of western australia contain important base and precious metal deposits here we present microtextural data trace element and s isotope analyses of massive sulphide mineralisation hosted in palaeoproterozoic subvolcanic rocks dolerite recently discovered at red bore the small scale high grade mineralisation which extends from the sub surface to at least 95 m down hole is dominated by massive chalcopyrite and contains minor pyrite and bi te se phases massive sulphide mineralisation is surrounded by discontinuous brecciated massive magnetite and a narrow 2 m alteration halo which suggests very focussed fluid flow laser ablation icp ms analyses indicate that chalcopyrite contains up to 10 ppm au and in excess of 100 ppm ag sulphur isotope analyses of pyrite and chalcopyrite indicate a narrow range of 34svcd 0 2 to 4 6 and no significant mass independent fractionation 0 1 33s 0 05 re os isotope analyses yield scattered values which suggests secondary remobilisation despite the geographical proximity and the common cu au ag association the mineralisation at red bore has significant differences with massive sulphide mineralisation at neighbouring degrussa as well as other massive sulphide deposits around the world these differences include the geometry sub volcanic host rocks extreme cu enrichment and narrow 34s ranges although a possible explanation for some of these characteristics is leaching of s and metals from the surrounding volcanic rocks we favour formation as a result of the release of a magmatic fluid phase along very focussed pathways and we propose that mixing of this fluid with circulating sea water contributed to sea floor mineralisation similar to neighbouring vhms deposits our data are permissive of a genetic association of red bore mineralisation with vhms deposits nearby thus suggesting a direct connection between magmatism and mineralising fluids responsible for vhms deposition at surface therefore the red bore mineralisation may represent the magmatic roots of a vhms system

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

a semipermeable interface model for the genesis of subseafloor replacement type volcanogenic massive sulfide vms deposits subseafloor replacement style volcanogenic massive sulfide vms deposits are a subset of vms deposits where sulfides have replaced unconsolidated volcanic volcano sedimentary and sedimentary material these deposits are anomalously large and are important global sources of metals they have distinct textures at the sulfide ore interface including bed by bed replacement of sedimentary layers and typically fill void space between unconsolidated volcaniclastic detritus or fractures in flows or intrusions at the microscale metalbearing sulfides have partially to fully replaced framboidal bacteriogenic sulfides or the framboidal sulfides have acted as nuclei upon which additional metalliferous massive sulfide is deposited the textures presented are reconciled within a semipermeable interface model for replacement in this model unconsolidated sediment volcaniclastic rocks or fractured coherent volcanic rocks provide a permeable to semipermeable interface that allowed ingress of cold seawater into the pore spaces of the stratigraphic sequence prior to and during lulls in hydrothermal activity seawater sulfate in the pore water is partially reduced by bacteria to provide reduced sulfur h2s as well as framboidal pyrite in the host sequence s the reduced sulfur and framboidal pyrite as well as the cool pore water provided a thermal redox and chemical gradient in which upwelling hydrothermal fluids interact in such an environment rising hydrothermal fluids mix with cold water not only at the seawater interface leading to exhalative sulfide deposition but also in the subseafloor leading to sulfide precipitation via replacement the upwelling hydrothermal fluids can also interact with bacterial h2s in the pore spaces of the unconsolidated material resulting in additional subseafloor precipitation of metal sulfides the fluids also result in replacement of framboidal pyrite nuclei pseudomorphous after the original framboidal masses this semipermeable interface also favors enhanced zone refining assuming the hydrothermal system is sufficiently long lived leading to upgrading of the tenor of the sulfides with well developed metal zoning as observed in many ancient replacement type deposits furthermore the precipitation of a significant subseafloor sulfide mineralization results in greater trapping of metals from upwelling fluids and larger tonnage deposits with greater contained metal this model may also be applicable to other replacement type deposits in broadly similar geologic and hydrothermal environments e g sediment hosted and irish type zn pb deposits additional critical tests are required to validate and refute the model and potential tests are presented herein

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

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

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

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

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

reply to the comments by marignac and cathelineau on the paper by sanchez espana et al source and evolution of ore forming hydrothermal fluids in the northern iberian pyrite belt massive sulphide deposits sw spain evidence from fluid inclusions and stable isotopes mineralium deposita 38 519 537

the precious metal rich south hercules mineralization western tasmania a possible subsea floor replacement volcanic hosted massive sulfide deposit south hercules is a newly delineated disseminated to semimassive base metal sulfide deposit with significant gold and silver grades the deposit lies a kilometer along strike south from the hercules mine a 2 0 mt polymetallic massive sulfide deposit in the mount read volcanics belt western tasmania the mineralization and alteration at the south hercules deposit has been divided into two major facies the mineralized sulfide facies and the carbonate facies the carbonate facies interfingers with and surrounds the upper part of the sulfide facies the mineralized sulfide facies includes three zones a massive pyrite or barite zone a siliceous or stringer sulfide zone and a sphalerite galena or pyrite zone the carbonate facies also consists of three zones a blebby carbonate chlorite zone a massive carbonate zone and a cherty carbonate zone the massive pyrite or barite zone contains significant gold grades and occurs mostly at the top of the sulfide facies this zone is characterized by colloform aggregates of pyrite and compact massive pyrite in chert the siliceous or stringer sulfide zone is a silicified and sericitized tuffaceous shale with disseminated to stringer pb zn mineralization the massive sphalerite galena or pyrite zone contains subordinate gold and silver and occurs as thin lenses toward the base of the sulfide facies significant zinc and lead values occur throughout the mineralized sulfide facies with the highest values occurring along stratigraphically controlled layers copper values are conspicuously low throughout the south hercules deposit rarely exceeding 0 5 percent the carbonate facies is conspicuous by its lack of significant precious metal and base metal grades mineragraphic investigations indicate that electrum occurs in two general associations with pyrite and with other sulfides such as sphalerite galena and tetrahedrite the electrum locked in the pyrite euhedra is generally fine grained 5 40 mu m whereas the electrum associated with other sulfides displays a range between 5 and 200 mu m microprobe analysis indicates that the fineness 1 000 au au ag wt for gold in the deposit ranges from 427 to 965 the delta 18 o isotope composition of the carbonate varies from 9 8 to 16 7 per mil and the delta 13 c values range from 3 5 to 0 6 per mil the calculated isotopic composition of the ore fluid at 150 degrees and 250 degrees c is consistent with derivation from evolved seawater sulfur isotope analyses of selected samples from the mineralized facies give delta 34 s values of 8 2 to 14 1 per mil which is in the same range as values from the rosebery deposit and consistent with values of sulfur derived from cambrian seawater the form texture mineralogy stable isotopes and fluid inclusion data for the south hercules deposit suggest that it was formed largely by a subsea floor replacement process from relatively low temperature 150 degrees 250 degrees c near neutral fluids the very low copper content and relatively high au ag pb zn ratio of the ores support a low temperature environment in which gold was transported as the au hs 2 super complex and pb and zn were transported as chloride complexes

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

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

microstructural timing of the rosebery massive sulphides tasmania evidence for a metamorphic origin through mobilization of disseminated base metals microstructural timing relationships indicate that the rosebery massive sulphide ore western tasmania australia formed by metasomatic replacement of sericite schist during a devonian deformation event d3 this interpretation is contrary to earlier volcanogenic based interpretations but accords with the discordant position and inferred structurally controlled emplacement of the orebody the main timing criteria are overprinting of s3 by the late ore minerals replacement textures in undeformed mineral parageneses and a d3 structural control from the microscopic to the macroscopic scales the consistent observation of these criteria in the orebody and the complete lack of pre d3 ore argue against in situ dissolution of a primary orebody and local redeposition of sulphides by replacement d3 deformation at rosebery is inferred to have been characterized by heterogeneous cleavage parallel extension which resulted in localized microfracturing and selective replacement of zones of maximum strain rate continuous shifts in the strain rate distribution pattern during progressive mineralization led to the compositional ore banding published pb isotope data point towards a cambrian source rock for the orebody this suggests a metamorphogenic origin by regional scale dissolution of dispersed volcanogenic metals focused solution transfer and concentrated redeposition in a structural trap

alteration of felsic volcanics hosting the thalanga massive sulfide deposit northern queensland australia and geochemical proximity indicators to ore thalanga is an early ordovician stratiform zn pb cu ag rich massive sulfide deposit in northern queensland australia with a total resource of 6 6 mt of ore the host rock succession consists of variably altered rhyolite in the footwall and a dacite dominated volcano sedimentary sequence in the hanging wall the sulfide deposit and the enclosing volcanic sequence were metamorphosed under upper greenschist conditions a laterally continuous footwall alteration zone extends beneath the entire deposit 3 000 m and to a stratigraphic depth of at least 300 m below the ore lenses the bulk of this zone is occupied by feldspar destructive muscovite biotite chlorite rich mottled alteration facies with disseminated pyrite representing the metamorphic equivalent of phyllosilicate dominated hydrothermal alteration discordant zones of intense quartz pyrite alteration represent the principal fluid pathways during mineralizing hydrothermal activity locally quartz k feldspar alteration facies exist on the fringes of the system and calcareous alteration and chlorite pyrite alteration facies exist in the upper part of footwall rhyolite proximal to sulfide lenses quartz feldspar porphyritic rhyolite laterally surrounding the footwall alteration zone and feldspar porphyritic dacite in the hanging wall are unaltered or weakly altered the compositional diversity of altered footwall rhyolite implies that hydrothermal alteration at thalanga was a complex processes this paper presents a model for the evolution of the footwall alteration zone calcareous alteration probably represents the initial phase of hydrothermal activity this was followed by diffuse upwelling of acidic seawater dominated fluids causing destruction of primary feldspar precipitation of pyrite and formation of hydrothermal sericite chlorite and clay minerals subsequent intense quartz pyrite alteration was directly associated with mineralization the thalanga footwall alteration zone has several geochemical characteristics that show systematic changes with increasing proximity to ore these include na depletion and elevated mg s alteration index ai chlorite carbonate pyrite index ccpi mo bi and as furthermore the x mg of chlorite and biotite increases systematically from values of 0 45 to 0 5 in least altered rhyolite to values 0 9 immediately below ore these geochemical features can be used in exploration for massive sulfide deposits as vectors to ore at the prospect scale and in discrimination of prospective hydrothermal from unprospective diagenetic alteration systems at the regional scale

geochemical characteristics of pyrite in the dabaozhuang deposit in the middle lower yangtze river metallogenic belt eastern china abstract dabaozhuang is a pyrite deposit in the luzong volcanic basin eastern china and has similar exhalation sedimentary features to volcanic massive sulfide deposits vms which commonly form in seawater to better understand the ore forming process of this special type of deposit we employed shrimp si and la icp ms to measure sulfur isotope and trace element compositions of anhydrite and four types of pyrite from the dabaozhuang deposit shrimp in situ sulfur isotope analysis indicates a narrow range in 34s of anhydrite 21 0 21 7 and variable ranges for pyrite 9 9 10 7 for pyrite vein in the deep py i 9 2 to 2 0 for cyclic annular and oval shaped pyrite in massive ore py ii 3 1 5 3 for massive or disseminated pyrite in the footwall tuff and hematite py iii and 29 7 to 30 4 for euhedral and coarse pyrite in the carbonate cement py iv 33s and 36s in four types of pyrite have no abnormal values indicating that sulfur isotope fractionation is mainly controlled by thermochemical sulfate reduction tsr the higher 34s values in type i pyrite and anhydrite indicate a mixing process of magmatic fluid and evaporates at depth py ii and iv have negative 34s data indicating the formation temperature of pyrite decreases because of the mixing of lake water 34s values in py iii are close to magmatic sulfur which shows the igneous sulfur tuff is an important sulfur source for the disseminated mineralization cobalt and ni content also show that the formation temperature of py i is highest and py iv is lowest this research indicates that the vms like deposits could be formed in continental volcanic lakes and are genetically related to so42 rich ioa iron oxide apatite deposits

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

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

subsea floor replacement in volcanic hosted massive sulfide deposits abstract recent research on volcanic hosted massive sulfide vms deposits indicates that syngenetic subsea floor replacement ores form an important component of many deposits in the context of vms deposits subsea floor replacement can be defined as the syn volcanic formation of sulfide minerals within pre existing volcanic or sedimentary deposits by infiltration and precipitation in open spaces fractures inter and intra granular porosity as well as replacement of solid materials there are five criteria for distinguishing subsea floor replacement in massive sulfide deposits 1 mineralized intervals are enclosed within rapidly emplaced volcanic or sedimentary facies lavas intrusions subaqueous mass flow deposits pyroclastic fallout 2 relics of the host facies occur within the mineral deposit 3 replacement fronts occur between the mineral deposit and the host lithofacies 4 the mineral deposit is discordant to bedding and 5 strong hydrothermal alteration continues into the hanging wall without an abrupt break in intensity criteria 1 3 are diagnostic of replacement whereas criteria 4 and 5 may suggest replacement but are not alone diagnostic because clastic sulfide ores contain accessory rock fragments collected by the parent sediment gravity flow s during transport criteria 2 can only be applied to massive semi massive disseminated or vein style deposits and not clastic ores the spectrum of vms deposit types includes deposits that have accumulated largely subsea floor and others in which sedimentation and volcanism were synchronous with hydrothermal activity and precipitation of sulfides occurred at and below the sea floor over the life of the hydrothermal system deposits that formed largely subsea floor are mainly hosted by syn eruptive or post eruptive volcaniclastic facies gravity flow deposits water settled fall autoclastic breccia however some subsea floor replacement vms deposits are hosted by lavas and syn volcanic intrusions sills domes cryptodomes burial of sea floor massive sulfide by lavas or sediment gravity flow deposits can interrupt sea floor mineralization and promote subsea floor replacement and zone refining the distance below the sea floor at which infiltration and replacement took place is rarely well constrained with published estimates ranging from less than 1 to more than 500 m but mainly in the range 10 200 m the upper few tens to hundreds of metres in the volcano sedimentary pile are the favoured position for replacement as clastic facies are wet porous and poorly consolidated in this zone and at greater depths become progressively more compacted dewatered altered and less amenable to large scale infiltration and replacement by hydrothermal fluids furthermore sustained mixing between the upwelling hydrothermal fluid and cold seawater is regarded as a major cause of sulfide precipitation in vms systems and this mixing process generally becomes less effective with increasing depth in the volcanic pile the relative importance of subsea floor replacement in vms systems is related principally to four factors the permeability and porosity patterns of host lithofacies sedimentation rate the relative ease of replacement of host lithofacies especially glassy materials and early formed alteration minerals during hydrothermal attack and physiochemical characteristics of the hydrothermal fluid

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

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

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

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

drilling shallow water massive sulfides at the palinuro volcanic complex aeolian island arc italy a subseafloor replacement style barite and sulfide occurrence was drilled in shallow waters at the palinuro volcanic complex the northernmost aeolian arc volcano in the tyrrhenian sea italy using a lander type drilling device 11 successful drill holes yielded a total of 13 5 m of core from a sediment filled depression located at a water depth of 630 to 650 m the longest continuous drill core recovered consists of 4 84 m of massive to semimassive barite and sulfides with abundant late native sulfur overprint seafloor observations suggest that the hydrothermal system associated with the formation of the subseafloor barite and sulfide ore zone is still active although black smoker activity does not occur on the seafloor the recovered drill core shows that the subseafloor deposit is zoned with depth the top of the mineralized zone is comprised of a variably silicified vuggy barite sulfide facies that shows notable polymetallic metal enrichment while the deeper portion of the mineralized zone is dominated by massive pyrite having distinctly lower base and precious metal grades metal zonation of the barite and sulfide deposit is related to the evolution of the hydrothermal fluids in space and time the barite cap and the massive pyrite present in the deeper portion of the mineralized zone appear to have formed early in the paragenesis during the main stage of the mineralization the barite cap was brecciated and cemented by a polymetallic assemblage of barite and pyrite with minor chalcopyrite and tetrahedrite trace famatinite and rare cinnabar lower temperature precipitates formed during the main stage of mineralization include sphalerite galena pyrite opal a and barite which are associated with traces of pb sb as sulfosalts such as bournonite seligmannite or semseyite a distinct mineral assemblage of fine grained anhedral enargite hypogene covellite chalcopyrite and galena is commonly associated with colloform sphalerite galena and pyrite as a late phase of this main stage colloform pyrite and marcasite are the last sulfides formed in the paragenetic sequence the deposit is interpreted to have formed from fluids having an intermediate sulfidation state although excursions to high and very high sulfidation states are indicated by the presence of abundant enargite and hypogene covellite laser ablation and conventional sulfur isotope analyses show that pyrite formed close to the seafloor within the zone of polymetallic metal enrichment has a variable sulfur isotope composition 34s 39 to 3 whereas a more narrow range is observed in the massive pyrite at depth 34s 10 to 0 similar variations were also documented for the late native sulfur overprint overall the negative sulfur isotope ratios at depth the intermediate to very high sulfidation conditions during mineralization and the abundance of native sulfur suggest contributions of magmatic volatiles to the mineralizing fluids from a degassing magma chamber at depth biological processes are interpreted to have played a major role during late stages of ore formation the combination of a subseafloor replacement deposit with a massive to semimassive barite cap rock overlying massive pyrite the intermediate to high sulfidation characteristics and the strong biological influence on the late stages of mineralization are distinct from other modern seafloor massive sulfide deposits and represents a style of submarine mineralization not previously recognized in a modern volcanic arc environment the barite and sulfide occurrence at palinuro shares many characteristics with porphyry related base metal veins and intermediate sulfidation epithermal deposits suggesting that metallogenic processes associated with arc related magmatic hydrothermal systems are not restricted to the subaerial environment

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

hydrothermal alteration and mineralization in the neves corvo volcanic hosted massive sulfide deposit portugal ii oxygen hydrogen and carbon isotopes the oxygen hydrogen and carbon isotope compositions of hydrothermally altered rocks and minerals from massive and stockwork ores of the neves corvo volcanic hosted massive sulfide deposit have been used to infer its thermal history and the origins of the hydrothermal fluids quartz and cassiterite separated from the stringer and massive cassiterite ores of the corvo orebody tin corridor have 18o values of 12 5 to 13 6 and 1 4 to 0 4 per mil respectively quartz cassiterite oxygen isotope fractionation indicates temperatures of 174 to 207 c avg 191 c for precipitation of this mineral pair the calculated oxygen isotope composition of the fluid 18oh2o 0 4 to 0 7 avg 0 1 suggests that cassiterite precipitation resulted from extensive mixing of a tin bearing fluid with seawater at sea floor hydrothermal vents the whole rock oxygen isotope composition of the hydrothermally altered felsic volcanic rocks hosting the sulfide stockwork of the corvo orebody varies from the central stockwork chloritic alteration zone i 18o 8 7 9 6 to the peripheral zones sericitic and paragonitic alteration zones iia 18o 11 6 13 1 and iib 18o 11 0 14 1 the 18o values of quartz also increase from alteration zone i avg 13 9 to alteration zone iia avg 14 4 to alteration zone iib avg 15 0 quartz from the hanging wall jasper unit yielded higher 18o values of 15 5 to 17 9 per mil chlorite from alteration zone i has 18o values of 6 1 to 8 4 per mil avg 7 4 sericite has 18o and d values that vary slightly from 18o 9 3 to 10 1 per mil avg 9 9 and d 59 to 47 per mil avg 53 in alteration zone i to 18o 9 8 to 11 4 per mil avg 10 5 and d 50 per mil in alteration zone iia to 18o 9 4 to 11 7 per mil avg 10 6 and d 61 to 36 per mil avg 45 in alteration zone iib siderite associated with waning hydrothermal activity has low 13c values 11 1 to 5 8 suggesting the incorporation of oxidized organic carbon from the footwall sequence and or the addition of magmatic carbon in alteration zone i quartz chlorite fractionation indicates temperatures of 249 to 402 c avg 335 c and 18oh2o values of 6 1 to 10 2 per mil avg 8 3 quartz sericite pairs gave isotopic equilibrium temperatures of 250 to 289 c avg 269 c and 18oh2o values of 5 8 to 7 0 per mil avg 6 4 in alteration zone iia and 170 to 318 c avg 223 c and 18oh2o 1 4 to 8 3 per mil avg 4 5 in alteration zone iib the oxygen isotope data show that in the core of the feeder system alteration zone i the temperature and the 18oh2o values were very high the d values calculated for the ore fluids d 37 to 11 are also significantly lower than seawater outward from the central stockwork alteration zones iia and iib the ore fluid was depleted in 18o and the temperatures were lower the oxygen hydrogen and carbon isotope signatures of the neves corvo ore fluids are best explained by incorporation of magmatic and or metamorphic fluids into a seawater dominated hydrothermal system magmatic fluids in particular were a likely source for the tin and much of the copper in the neves corvo ores

geology fluid inclusions and oxygen isotope geochemistry of the baiyinchang pipe style volcanic hosted massive sulfide cu deposit in gansu province northwestern china the baiyinchang massive sulfide cu deposit zheyaoshan and huoyanshan mines is hosted by an early cambrian submarine felsic volcanic succession within an extrusive cryptodome associated with an overlying basaltic flow in a late proterozoic early paleozoic submarine volcanic belt in the north qilian orogen northwestern china the deposit is comprised of two mineralized zones a 30 cm thick strata bound zn rich sulfide lens associated with hematitic fe mn cherts and an underlying discordant massive ore dominated sulfide zone enveloped by a hydrothermal alteration pipe that is zoned from chlorite in the center to quartz sericite at the margin the discordant sulfide zone accounts for 90 percent of the cu reserves of the zheyaoshan mine it consists of four main ore types 1 pipelike pyrrhotite pyrite chalcopyrite ore 2 massive sulfide ore 3 a disseminated ore halo and 4 footwall stringer ore the pyrrhotite pyrite chalcopyrite pipe has an elliptical shape in plan and is 30 50 m across the pipe partially replaces the overlying massive pyrite lens and extends downward at least 150 m to be gradually replaced by chalcopyrite rich stringer veins and chalcopyritebearing quartz veins surrounded by a discordant hydrothermal alteration envelope massive chalcopyrite pyrite lenses discordant to volcanic bedding containing relict patches of felsic volcanic host rocks are commonly enveloped by a disseminated sulfide halo within a chloritized volcanic unit these features suggest that zheyaoshan is a pipe style deposit that formed mainly by subsea floor replacement of volcanic host rocks studies of fluid inclusions indicate that there are four types 1 type i two phase aqueous fluid inclusions 2 type ii daughter mineral bearing multiphase fluid inclusions 3 type iii co2 rich fluid inclusions and 4 type iv ch4 rich fluid inclusions type ii inclusions have high homogenization temperatures th ranging from 320 to 430 c contain high salinity fluids 31 38 wt nacl equiv and coexist with co2 rich fluids found in vapor rich high th up to 487 c moderate salinity 10 16 wt nacl equiv inclusions in the discordant sulfide zone and associated altered rocks suggesting a possible contribution of a magmatic fluid to the hydrothermal system the coexistence of vapor rich high th 300 c and aqueous low th 220 c type i fluid inclusions in the stringer zone suggests that heated seawater mixed with magmatic fluid gas in the feeder zone most type i fluid inclusions in the massive chalcopyrite pyrite body and in the strongly chloritized pipe have a low th 62 225 c and high salinities 15 0 23 0 wt nacl equiv suggesting that a dense brine zone developed in fractures in the subsea floor where sulfides accumulated by open space filling and replacement of host volcanic rocks eleven quartz samples from the overlying discordant sulfide zone yielded a restricted range of 18o values between 8 8 and 11 1 per mil from which we calculate that the corresponding hydrothermal fluids had 18o values ranging from 5 3 to 3 1 per mil over a temperature range of 160 to 278 c whole rock 18o values

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

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

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

sources of strontium and calcium in desert soil and calcrete the carbon cycle significance of soil carbonate fluxes is subject to large uncertainties because it is not clear precisely how much calcium is derived from atmospheric sources compared with that from the chemical weathering of silicate minerals in the petrocalcic horizon calcrete of a pleistocene soil from the usda scs desert project area near las cruces nm approximately 1 5 g ca cm 3 has been added with an associated expansion of the profile of200 strontium isotope values for the labile cations and carbonate from the a b and k soil horizons have 87 sr 86 sr values that range from 0 7087 to 0 7093 similar to the values for easily soluble local dust and rain the parent material non calcareous camp rice alluvial sediment has a 87 sr 86 sr ratio of0 7165 mixing calculations indicate a minimum atmospheric contribution to soil carbonate calcium of 94 the more likely scenarios indicate at least 98 of the ca originated from atmospheric input the variations in 87 sr 86 sr ratios of soil silicate 0 7131 to 0 7173 are consistent with weathering of volcanogenic sediments and neoformation of clay minerals in the petrocalcic horizon moreover the sr isotope data suggest that 50 70 of silicate in the uppermost 25 cm of the profile could be atmosphere derived the isotopic composition of labile strontium in the a horizon and the mass distribution of silicon and calcium indicate that the uppermost portion of the profile is the present zone for the release of cations due to silicate weathering steady state models of the whole profile yield a sr weathering flux ranging from200 to 400 m gc m 2 ma 1 the results indicate that both the present day and long term contribution of calcium from silicate weathering is less than 2 of that supplied from the atmosphere and confirm that desert soil formation is not a significant sink for atmospheric carbon 1999 elsevier science b v all rights reserved

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

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

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

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

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 archean cu zn magnetite rich gossan hill volcanic hosted massive sulfide deposit western australia genesis of a multistage hydrothermal system the gossan hill volcanic hosted massive sulfide vhms deposit is an archean cu zn magnetite rich deposit located in the warriedar fold belt of the yilgarn craton western australia the deposit is hosted by redeposited rhyodacitic tuffaceous volcaniclastics of the golden grove formation and is overlain by felsic volcanic rocks of the scuddles formation the deposit consists of two separate subvertical ore zones the stratigraphically lower cu rich ore zone 7 0 mt 3 4 cu is strata bound and varies from podiform massive pyrite chalcopyrite pyrrhotite magnetite to sheetlike massive magnetite carbonate chlorite talc the upper zn cu ore zone 2 2 mt 11 3 zn 0 3 cu 1 5 g t au and 102 g t ag contains strata bound massive sphalerite pyrite chalcopyrite that overlies discordant moundlike massive pyrite pyrrhotite chalcopyrite magnetite sulfide stockwork connects the upper and lower ore zones metal zonation varies from cu au in the lower ore zone to zn cu at the base of the upper ore zone which grades upward and laterally to zn ag au cu pb multiphase deformation and greenschist facies metamorphism overprint the deposit the relationship between host rocks and sulfide indicates that mineralization was broadly codepositional with sedimentation of the golden grove formation however gradational and interdigitating contacts between these volcaniclastic rocks and magnetite support the formation of massive magnetite by subsea floor replacement sulfides replace and vein the massive magnetite with inferred synchronous formation of the upper and lower sulfide ore zones although these sulfide ore zones formed mainly by subsea floor replacement stratiform hydrothermal chert sulfide sediment layers within and adjacent to the upper zn rich ore zone attest to some local exhalation the thickest development of massive magnetite massive sulfide and stringer stockwork occurs in the north of the deposit and supports a common feeder during massive magnetite and sulfide formation furthermore local chlorite quartz hydrothermal alteration massive magnetite massive sulfide and stockwork all form asymmetric zones that thin southward these attributes indicate strong synvolcanic structural control during mineralization the relict synvolcanic growth structure is obscured and probably occupied and by a dacite dome of the hanging wall scuddles formation thermodynamic considerations suggest that massive magnetite and sulfide formed from similar high temperature 300 degrees celsius slightly acidic low fo2 hydrothermal fluids massive magnetite formed from h2s poor fluids whereas massive sulfide formed from relatively rich h2s fluids physicochemical changes associated with interaction between upwelling h2s bearing fluids and preexisting massive magnetite may have resulted in the subsea floor precipitation of sulfide in the lower cu rich ore zone the gossan hill vhms deposit represents a multistage hydrothermal system within an environment characterized by rapid volcaniclastic sedimentation and changing structural and magmatic processes the six main stages were as follows 1 initiation of the hydrothermal system 2 sedimentation metasomatism and progressive heating of convecting fluids 3 deposition of massive magnetite from h2s poor fluids by subsea floor replacement above a buried synvolcanic conduit 4 structural reactivation tapping deeper h2s and metalbearing fluids 5 subsea floor replacement and minor exhalative sulfide mineralization with 6 burial and preservation of the deposit resulting from proximal felsic volcanism

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

lithostratigraphic hydrothermal and tectonic setting of the boundary volcanogenic massive sulfide deposit newfoundland appalachians canada formation by subseafloor replacement in a cambrian rifted arc the boundary volcanogenic massive sulfide vms deposit 0 5 mt 3 5 cu 4 zn 1 pb 34 0 g t ag in the tally pond group central newfoundland represents one of the best preserved subseafloor replacement style vms deposits in the northern appalachian orogen the deposit is hosted within a late cambrian 510 ma volcanic sequence consisting predominantly of rhyolitic flows and associated volcaniclastic rocks footwall strata are dominated by rhyolitic lapilli tuff tuffs lesser rhyolite flows and in situ rhyolite breccias the hanging wall consists of massive quartz bearing flow banded lobe and breccia facies rhyolite the deposit occurs at and below the contact between these two units and comprises pyrite chalcopyrite and lesser sphalerite and other minerals massive mineralization contains abundant clasts of the surrounding host rocks including chlorite sericite quartz altered rhyolite lapilli and ash hydrothermally altered rocks consist of variably intense chlorite with lesser sericite and quartz chlorite alteration occurs in a discordant geometry likely representing hydrothermal upflow zones and chlorite sericite quartz occur as blankets that are parallel to the volcanic stratigraphy likely representing alteration associated with replacement the hanging wall rhyolite flows also contain moderate to intense pervasive quartz and sericite alteration both the hanging wall and footwall are characterized by strong na2o sr depletions k2o mgo fe2o3 ba enrichments high alteration index values e g ba sr chlorite carbonate pyrite index ccpi alteration index ai and enrichments in base metals and volatile metals e g cu zn pb hg the presence of abundant remnant wall rock and host rock clasts within the ore intricate sulfide replacement of laminated porous tuff and sand dikes replacement fronts in host lithofacies and intense alteration in both the footwall and hanging wall where the hanging wall is preserved are all features consistent with formation of the bulk of the boundary deposit via subseafloor replacement the deposit likely formed as a result of cooling of metal bearing hydrothermal fluids mixing with ambient seawater and pore water entrained seawater within the volcanic rocks at a permeability interface between young unlithified highly permeable footwall volcaniclastic rocks and relatively impermeable hanging wall rhyolitic flows in our model this permeability boundary was an important feature that promoted subseafloor replacement within the deposit immobile element systematics of rhyolitic rocks from the boundary deposit lack major differences in primary petrochemistry between hanging wall and footwall strata all rocks from the deposit area are subalkalic with transitional zr y ratios 2 8 4 5 la sm ratios 1 normalized to upper crust and primitive mantle normalized signatures with slightly light rare earth element lree enriched patterns with flat heavy ree hree and negative nb ti and eu anomalies these geochemical features coupled with existing nd pb isotope data zircon inheritance patterns and geologic information are consistent with rhyolitic rocks at the boundary deposit having formed by re melting of arc basement with continental crust or recycled continental crust present in the source region it is likely that the deposit and its associated rhyolitic host rocks formed within a cambrian continental or pericontinental rifted arc along the margin of ganderia within the iapetus ocean

source and evolution of ore forming hydrothermal fluids in the northern iberian pyrite belt massive sulphide deposits sw spain evidence from fluid inclusions and stable isotopes a fluid inclusion and stable isotopic study has been undertaken on some massive sulphide deposits aguas tenidas este concepcion san miguel san telmo and cueva de la mora located in the northern iberian pyrite belt the isotopic analyses were mainly performed on quartz chlorite carbonate and whole rock samples from the stockworks and altered footwall zones of the deposits and also on some fluid inclusion waters homogenization temperatures of fluid inclusions in quartz mostly range from 120 to 280 c salinity of most fluid inclusions ranges from 2 to 14 wt nacl equiv a few cases with th 80 110 c and salinity of 16 24 wt nacl equiv have been also recognized in addition fluid inclusions from the soloviejo mn fe jaspers 160 190 c and 6 wt nacl equiv and some late to post hercynian quartz veins 130 270 c and 4 wt nacl equiv were also studied isotopic results indicate that fluids in equilibrium with measured quartz 18ofluid 2 to 4 chlorites 18ofluid 8 14 dfluid 45 to 27 whole rocks 18ofluid 4 7 dfluid 15 to 10 and carbonates 18oankerite 14 5 16 13cfluid 11 to 5 evolved isotopically during the lifetime of the hydrothermal systems following a waxing waning cycle at different temperatures and water rock ratios the results fluid inclusions 18o d and 13c values point to a highly evolved seawater along with a variable but significant contribution of other fluid reservoirs such as magmatic and or deep metamorphic waters as the most probable sources for the ore forming fluids these fluids interacted with the underlying volcanic and sedimentary rocks during convective circulation through the upper crust

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

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

carbonic fluid overprints in volcanogenic massive sulfide deposits examples from the kelan volcanosedimentary basin altaides china the tiemurte and the dadonggou zn pb cu volcanogenic massive sulfide vms deposits situated in the devonian kelan volcanosedmentary basin of the south margin of the chinese altaides were metamorphosed and overprinted by metamorphic sulfide quartz veins during early carboniferous to early permian two mineralizing periods of ore mineral growth can be identified 1 disseminated banded and massive sulfide ores related to a primary depositional sea floor volcanic hydrothermal activity and 2 the foliated sulfide quartz veins q1 related to synorogenic metamorphism and late chalcopyrite bearing quartz veins q2 cutting the schist related to a younger metamorphic overprinting event carbonic co 2 ch 4 n 2 fluid inclusions are ubiquitous in q1 and q2 veins a few carbonic fluid inclusions may be primary and some may be pseudosecondary whereas the vast number of carbonic fluid inclusions are secondary representing later events a microthermometry study shows that primary carbonic fluid inclusions in q1 and q2 have tm co2 ranging from 64 5 to about 59 4 c with th co2 13 4 to about 18 6 c the secondary carbonic fluid inclusions exhibit two behaviors when cooling and heating the tm co2 of the first group l co2 ranges from 63 3 to 57 7 c and that of the second group l co2 ch4 n2 ranges from 83 4 to 61 c the second group of carbonic fluids has much higher ch 4 and or n 2 proportions than the first group the trapping temperatures for the carbonic inclusions have been estimated to be 243 1 to 412 1 c for tiemurte and 216 to 430 c for dadonggou on the basis of some l co2 l h2o inclusions associated with carbonic inclusions and the trapping pressures have been estimated to be 120 to 340 mpa which are consistent with deformation p t conditions of quartz and slightly less than the p t conditions of the biotite and garnet metamorphic zones these abundant carbonic inclusions at the tiemurte and the dadonggou deposits were not a part of a volcanogenic ore producing system but represent a much younger event possibly having originated from a synorogenic metamorphism which may have contributed to orogenic gold

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

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

the origin of chlorite tremolite carbonate rocks associated with the thalanga volcanic hosted massive sulfide deposit north queensland australia the thalanga polymetallic massive sulfide deposit is hosted by felsic volcanics of the cambro ordovician mount windsor subprovince in north queensland the sheetlike sulfide deposit consists of several semiconnected lenses totaling 6 6 million metric tons mt which lie at a single stratigraphic level between underlying subaqueously emplaced rhyolite and overlying dacitic to andesitic lavas sills and volcaniclastic rocks the ores and host rocks have been deformed and metamorphosed to upper greenschist facies associated with the west thalanga orebody are strata bound lenses composed of chlorite tremolite dolomite and calcite that previously have been interpreted as exhalites they extend up to a few hundred meters along the mineralized horizon and locally also exist in the stratigraphic footwall around the fringes of the deposit rhyolitic volcanics beneath the deposit are extensively altered a pervasive sericite chlorite pyrite zone that extends greater than 200 m into the footwall envelops semistratiform proximal quartz pyrite chlorite stringer zones major and trace element geochemical data indicate that zr ti and al remained essentially immobile in the footwall rocks despite intense hydrothermal alteration involving significant mass transfers of mobile elements the chlorite tremolite carbonate assemblages associated with ore lenses have immobile element ratios identical to those of the altered rhyolites carbonate rich assemblages retain some relict spheroidal and rhombic textures in dolomite which suggest formation at an early hydrothermal stage in a matrix of chlorite or in open spaces the chlorite tremolite carbonate rocks probably represent metamorphic equivalents of hydrothermal chlorite quartz dolomite calcite or mg smectite quartz dolomite calcite assemblages the formation of tremolite by metamorphic reaction of quartz and dolomite is consistent with regional metamorphic conditions with allowance for metamorphic decarbonation carbon and oxygen isotope data from dolomite and calcite are consistent with precipitation of primary dolomite at 170 to 250 c from seawater dominated fluid the chlorite tremolite carbonate rocks at thalanga are consequently reinterpreted as altered rhyolitic volcaniclastics containing variable proportions of hydrothermal carbonate they probably formed in a zone of mixing of hydrothermal fluid and seawater in a permeable substrate close to the paleosea floor siliceous ironstones that are present in distal parts of some thalanga ore lenses have very low immobile element contents and are probably true exhalites

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

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

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

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

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

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

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

erratum to variations of sulphur isotope signatures in sulphides from the metamorphosed ming cu au volcanogenic massive sulphide deposit newfoundland appalachians canada the ming deposit is an early ordovician bimodal mafic cu au volcanogenic massive sulphide vms deposit in the newfoundland appalachians that was metamorphosed to upper greenschist lower amphibolite facies conditions and deformed in the silurian and devonian the ming deposit consists of several spatially proximal ore bodies of which the 1806 zone 1807 zone ming south up plunge and down plunge and the lower footwall zone are the focus of this paper the ore bodies have similar stratigraphic sequences the ore bodies can be divided into 1 a silicified horizon that caps the massive sulphides 2 semi massive to massive sulphides and 3 sulphide mineralization in a rhyodacitic footwall sulphide mineralization in a rhyodacitic footwall includes a sulphide stringers immediately below the semi massive to massive sulphides and b chalcopyrite pyrrhotite pyrite stringers distally from semi massive to massive sulphides in the lower footwall zone pyrite chalcopyrite pyrrhotite arsenopyrite and galena were analysed by in situ secondary ion mass spectrometry sims for sulphur isotope compositions the isotopic signatures of pyrite chalcopyrite pyrrhotite and arsenopyrite fall within a limited range of 2 8 to 12 0 for semi massive to massive sulphides and sulphide mineralization in the footwall the silicified horizon capping the semi massive to massive sulphides has higher 34s 5 8 19 6 especially for pyrrhotite mean 17 2 2 2 n 8 the sulphur isotope composition of galena is more heterogeneous especially within semi massive to massive sulphides and sulphide stringers ranging from 0 8 to 17 3 mean 6 1 4 3 n 35 and 7 6 to 17 1 mean 13 7 5 3 n 3 respectively geothermometric calculations give insufficient formation and metamorphism temperatures for neighbouring mineral pairs because sulphides were not in isotopic equilibrium while deposited in early ordovician or re equilibrated during silurian devonian metamorphism respectively therefore original isotopic compositions of sulphides at the ming deposit have been preserved modelling of the source of sulphur shows that 1 reduced seawater sulphate and 2 sulphur leached from igneous wall rock and or derived from magmatic fluids are the main sources of sulphur in the ming deposit the influence of igneous sulphur igneous wall rock magmatic fluids increases with temperature and is an important sulphur source for the semi massive to massive sulphides and footwall mineralization in addition to a contribution from thermochemical sulphate reduction tsr of seawater it is difficult to distinguish between sulphur leached from igneous rocks and magmatic fluid related sulphur and it is possible that both sources contributed to the ores at the ming deposit in addition to igneous sulphur the heavy isotopes of the silicified horizon are consistent with the sulphur in this horizon being derived only from thermochemical sulphate reduction of early ordovician seawater sulphate

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