basal ice facies and supraglacial melt out till of the laurentide ice sheet tuktoyaktuk coastlands western arctic canada glacially deformed massive ice and icy sediments mi is in the eskimo lakes fingerlands and summer island area of the tuktoyaktuk coastlands western arctic canada show in the same stratigraphic sequences features characteristic of both basal glacier ice and intrasedimental ice basal ice features comprise 1 ice facies and facies groupings similar to those from the basal ice layers of contemporary glaciers and ice sheets in alaska greenland and iceland 2 ice crystal fabrics similar to those from basal ice in antarctica and ice cored moraines on axel heiberg island canada and 3 a thaw or erosional unconformity along the top of the mi is buried by glacigenic or aeolian sediments intrasedimental ice consists of pore ice and segregated ice formed within pleistocene sands deposited before glacial overriding the co existence of basal and intrasedimental ice within the mi is records their occurrence within the basal ice layer of the laurentide ice sheet stagnation of the ice sheet and melt out of till from the ice surface allowed burial and preservation of the basal ice layer on a regional scale the widespread occurrence of supraglacial melt out till with clast fabrics similar to those in the underlying ice suggests that such till can be well preserved during partial thaw of a continental ice sheet in lowlands underlain by continuous permafrost

integrated climate model oxygen isotope evidence for a north american monsoon during the late cretaceous abstract during the late cretaceous western north america was characterized by a close geographic association between the sevier highlands and the western interior seaway in this paper an atmospheric general circulation model agcm is used to simulate the impact of this geographic association on surface pressure wind direction and precipitation and it is predicted that seasonal changes in these variables resulted in a strong monsoon along the eastern flank of the sevier highlands confirmation that these model simulations are accurate is provided by isotopic data from foreland basin sediments in particular oxygen isotope records from different environments large rivers small streams and ponds and proxies unionid bivalve shells and paleosol carbonates indicate that foreland basin streams were recharged by local precipitation with high oxygen isotope ratios while large trunk rivers were recharged by high elevation precipitation this hydrologic pattern is observed from alberta to utah and is consistent with east to west monsoonal air mass movements and associated seasonal rainfall recognition of a highland driven monsoon has implication in regard to studies of fossil taphonomy of water vapor transport and of links between climate and mountain uplift and exhumation in this region

lake stratigraphy implies an 80 000 yr delayed melting of buried dead ice in northern russia sediment cores from lakes kormovoye and oshkoty in the glaciated region of the pechora lowland northern russia reveal sediment gravity flow deposits overlain by lacustrine mud and gyttja the sediments were deposited mainly during melting of buried glacier ice beneath the lakes in lake kormovoye differential melting of dead ice caused the lake bottom to subside at different places at different times resulting in sedimentation and erosion occurring only some few metres apart and at shifting locations as further melting caused inversion of the lake bottom basal radiocarbon dates from the two lakes ranging between 13 and 9 ka match with basal dates from other lakes in the pechora lowland as well as melting of ice wedges this indicates that buried glacier ice has survived for ca 80 000 years from the last glaciation of this area at 90 ka until about 13 ka when a warmer climate caused melting of permafrost and buried glacier ice forming numerous lakes and a fresh looking glacial landscape copyright 2003 john wiley sons ltd

segregated intrusive ice of subglacial meltwater origin in retrogressive thaw flow headwalls richardson mountains nwt canada abstract extensive beds of icy sediments are exposed in the headwalls of active retrogressive thaw flows which developed on the aklavik plateau richardson mountains nwt sedimentary and isotopic characteristics defined two units debris rich ice overlain by icy diamicton these units originated from the same glacial sediment deposited during the late wisconsin westward expansion of the laurentide ice sheet the icy diamicton is a result of the development of thaw flows and mass movement processes during the early holocene warm interval which reworked the sediments the ice in the diamicton is characterized by average 18o and d values of 22 6 1 8 and 181 15 respectively which are similar to the modern isotropic composition of precipitation for that area the debris rich ice is more depleted in 18o and d with 18o ranging from 30 to 27 and d ranging from 230 to 210 air bubbles enclosed in the ice have 13c values ranging between 24 and 19 and a co2 concentration nine times higher than the expected concentration of air entrapped in modern glacier ice but similar to that of soil co2 both physical and isotopic properties of the debris rich ice suggest that it is segregated intrusive ice that formed after the retreat of the laurentide ice sheet during permafrost aggradation as sediment laden subglacial meltwater moved through a proglacial talik this article discusses the mechanism involved in the formation of massive segregated intrusive ice and how it differs from both buried glacier ice and holocene massive intrasedimental ice

robust multi proxy data integration using late cretaceous paleotemperature records as a case study abstract in paleoclimate studies multiple temperature records are often compared and combined to evaluate temperature trends yet no standardized approach for integrating proxy derived paleotemperature records exists in addition paleotemperature data are often reported without uncertainty estimates prediction errors and raw data are not always available this complicates the quantification of for example temperature trends and the magnitude of warming events here we propose a robust quantitative approach for multi proxy analysis in paleoclimate studies to demonstrate this we study the latest maastrichtian warming event lmwe in the odp 174ax bass river core new jersey and integrate five independent paleotemperature proxies covering the last million years of the cretaceous our integrated temperature reconstruction suggests that after a climatically stable period a latest cretaceous warming of 3 9 1 1 c occurred between 450 and 100 kyr before the k pg boundary the error on this reconstructed temperature should be considered the absolute minimum error as poorly constrained or unknown uncertainties cannot be fully propagated the warming event was followed by a gradual cooling to pre warming conditions towards the end of the cretaceous furthermore the record suggests multiple warming pulses during the lmwe the results of this integrated approach are consistent with other latest cretaceous temperature records suggesting that the trend described here represents a global signal

the end cretaceous in the southwestern tethys elles tunisia orbital calibration of paleoenvironmental events before the mass extinction an integrated study of magnetic mass susceptibility ms bulk stable isotopes and calcareous nannofossil paleoecological changes is undertaken on the late maastrichtian of the elles section tunisia spanning the last ca 1 myr of the cretaceous a cyclostratigraphic analysis reveals the presence of milankovitch frequencies and is used for proposal of two distinct orbital age models and to provide ages of important stratigraphic horizons relative to the age of the cretaceous paleogene boundary k pgb principal component analysis pca performed on the nannofossil assemblage reveal two main factors pca1 mostly representing fluctuations of d rotatorius p stoveri lithraphidites spp retecapsa spp staurolithites spp micula spp and pca2 mostly representing fluctuations of a regularis c ehrenbergii micula spp rhagodiscus spp w barnesiae and zeugrhabdotus spp variations in pca1 and pca2 match changes in bulk 13c and 18o respectively and suggest changes in surface water fertility and temperatures and associated stress the variations in abundances of high latitude taxa and the warm water species micula murus and in bulk 18o delineate fast changes in sea surface paleotemperatures as in many other sites an end maastrichtian greenhouse warming is highlighted followed by a short cooling and an additional warm pulse in the last 30 kyr of the maastrichtian which has rarely been documented so far orbital tuning of the delineated climatic events is proposed following the two different age models calcareous nannofossil assemblages highlight a decrease in surface water nutriency but their species richness remains high through the latest maastrichtian indicating in tunisia a weak impact of deccan volcanism on calcareous nannoplankton diversity before the mass extinction

late cretaceous restructuring of terrestrial communities facilitated the end cretaceous mass extinction in north america the sudden environmental catastrophe in the wake of the end cretaceous asteroid impact had drastic effects that rippled through animal communities to explore how these effects may have been exacerbated by prior ecological changes we used a food web model to simulate the effects of primary productivity disruptions such as those predicted to result from an asteroid impact on ten campanian and seven maastrichtian terrestrial localities in north america our analysis documents that a shift in trophic structure between campanian and maastrichtian communities in north america led maastrichtian communities to experience more secondary extinction at lower levels of primary production shutdown and possess a lower collapse threshold than campanian communities of particular note is the fact that changes in dinosaur richness had a negative impact on the robustness of maastrichtian ecosystems against environmental perturbations therefore earlier ecological restructuring may have exacerbated the impact and severity of the end cretaceous extinction at least in north america

nature and origin of ground ice sandhills moraine southwest banks island western canadian arctic the sandhills moraine is a late wisconsinan lateral moraine complex on southwest banks island the occurrence of ice ablation landforms ground ice slumps kettle lakes and catastrophic lake drainage in winter suggests the presence of substantial bodies of massive ground ice the distinctive hummocky topography of the sandhills moraine is thought to reflect partial melt out of this ice stratigraphic observations indicate that the ice is overlain irregularly and unconformably by glacigenic sediments notably pebbly clay till and or sandy gravels outwash while the ice itself possesses numerous and variable mineral inclusions faults and foliations petrofabric analyses indicate a strongly preferred orientation to the ice crystals it is suggested that these characteristics are best explained if the ground ice is interpreted as relict glacier ice

crustal evolution in south india constraints from nd isotopes nd isotope analyses from a range of lithologies including charnockites metasediments and granitoids that comprise the high grade terrain of south india define contrasting age provinces north of the palghat cauvery shear zone the karnataka craton and the granulite blocks of nilgiri and madras are characterized by model nd ages from 3 4 to 2 4 ga with significant crustal growth during the late archean south of the palghat cauvery shear zone a pan african granulite facies event resulted in sm nd fractionation as observed in several incipient charnockite localities model nd age calculations that allow for sm nd fractionation at 550 ma yield ages in the range of 2 9 to 1 3 ga this range compares closely with published model nd ages from the high grade terrain of sri lanka mid proterozoic crustal growth 1 1 ga observed in the vijayan complex of sri lanka may have provided source material for metasediments characterized by young model nd ages in southern peninsular india the palghat cauvery shear z

high closure temperatures of the u pb system in large apatites from the tin mountain pegmatite black hills south dakota usa abstract the cores of several large 1 2 cm apatites from the early proterozoic tin mountain pegmatite black hills south dakota have concordant u pb ages the age uncertainties of these samples are less than 5 ma the lead isotopic compositions of muscovite and k feldspar coexisting with the apatites were used for initial lead isotopic corrections the resulting u pb concordia ages agree well with u pb and pb pb isochron ages based solely on multiple fragments from single apatites this agreement justifies the use of coexisting muscovite and k feldspar for initial lead corrections the precision of these u pb ages is comparable to those of the u pb systems of more commonly analyzed minerals such as zircon monazite and sphene the estimated u pb closure temperature t c of these apatites is about 620 c this t c is in close agreement with the t c calculated for 0 5 cm diffusion radii and published data for diffusivity and activation energy of lead diffusion in apatite apatite can therefore yield high precision u pb ages that are close to its crystallization age in igneous rocks

the chicxulub asteroid impact and mass extinction at the cretaceous paleogene boundary the cretaceous paleogene boundary similar to 65 5 million years ago marks one of the three largest mass extinctions in the past 500 million years the extinction event coincided with a large asteroid impact at chicxulub mexico and occurred within the time of deccan flood basalt volcanism in india here we synthesize records of the global stratigraphy across this boundary to assess the proposed causes of the mass extinction notably a single ejecta rich deposit compositionally linked to the chicxulub impact is globally distributed at the cretaceous paleogene boundary the temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations for example darkness and cooling lead us to conclude that the chicxulub impact triggered the mass extinction

u pb single zircon pb evaporation and sm nd isotopic study of a granulite domain in se madagascar madagascar is a poorly known precambrian domain at the eastern border of the mozambique belt strongly affected by the pan african orogeny this large island represents a key part of gondwanaland and the accurate dating of the major metamorphic event is critical for the reconstruction of that supercontinent in the southeastern zone of the island metamorphism has reached high temperature and low pressure conditions 850 c and 5 kbar with moderate retrogression a u pb conventional multigrain single zircon stepwise pb evaporation and sm nd geochronological study on meta felsic rocks has shown that basement of at least lower proterozoic age was strongly metamorphosed around 570 580 ma this tectometamorphic event nearly obliterated any pre pan african zircon isotopic memory the granulite facies metamorphism is associated with the syn metamorphic emplacement of the anosyan charnock ites and granites a strong channelized fluid contribution at 545 ma has produced the re crystallization of biotite apatite

carbon isotope δ13c differences between late cretaceous ammonites and benthic mollusks from antarctica abstract ammonites are one of the most common fossils of the mesozoic but there is little consensus on their mode of life isotopic studies have been used to reconstruct their preferred water temperature from 18 o measurements but 13 c values have more ambiguous interpretations previous studies have recorded population differences in 13 c values between ammonite and benthic organisms without explaining the cause in detail here we examine a molluscan community from seymour island antarctica and find a 4 carbon isotope offset between ammonites and other benthic mollusks the most likely cause of this anomaly is an increased metabolic carbon contribution to ammonite shell material when compared with other mollusks but we cannot rule out the possibility of a methane seep contribution increased respired co 2 production could be generated by a more active lifestyle and increased energy demands which may have increased the susceptibility of ammonites to the end cretaceous mass extinction

extinction patterns δ18 o trends and magnetostratigraphy from a southern high latitude cretaceous paleogene section links with deccan volcanism although abundant evidence now exists for a massive bolide impact coincident with the cretaceous paleogene k pg mass extinction event 65 5 ma the relative importance of this impact as an extinction mechanism is still the subject of debate on seymour island antarctic peninsula the lopez de bertodano formation yields one of the most expanded k pg boundary sections known using a new chronology from magnetostratigraphy and isotopic data from carbonate secreting macrofauna we present a high resolution high latitude paleotemperature record spanning this time interval we find two prominent warming events synchronous with the three main phases of deccan traps flood volcanism and the onset of the second is contemporaneous with a local extinction that pre dates the bolide impact what has been termed the k pg extinction is potentially the sum of multiple independent events at least at high latitudes

geochemistry of high grade supracrustal rocks from the kerala khondalite belt and adjacent massif charnockites south india abstract the kerala khondalite belt kkb comprises a suite of supracrustal rocks of probable proterozoic age that was metamorphosed to the granulite facies the kkb consists of an interlayered sequence of 1 garnet biotite orthopyroxene graphite gneisses 2 khondalites graphite garnet biotite sillimanite cordierite gneisses and 3 cordierite gneisses garnet biotite cordierite orthopyroxene as well as less abundant mafic granulites calc silicates and quartzites petrologic and geochemical data suggest that these rocks were originally arkosic and argillaceous sediments possibly accompanied by felsic volcanic rocks along with minor intercalations of basalts carbonates and quartz rich sandstones the ree patterns of the metasediments are typically lree enriched with large negative eu anomalies indicating a continental provenance the major and trace element compositions of some of the arkosic rocks of the kkb resemble those of the massif charnockites that bound the kkb to the north which suggests that the massif charnockites may have been the source of some of the kkb sediments modern day analogues of the pelite arkose lithologic association observed in the kkb occur in intracratonic rifts and rifted continental margins this association is clearly distinct from the graywacke mafic volcanic association found in the southern indian greenstone belts and many other lower grade archean sedimentary sequences the kkb supracrustals show both lithologic and chemical similarities to many proterozoic supracrustal successions

high temperature environments of human evolution in east africa based on bond ordering in paleosol carbonates many important hominid bearing fossil localities in east africa are in regions that are extremely hot and dry although humans are well adapted to such conditions it has been inferred that east african environments were cooler or more wooded during the pliocene and pleistocene when this region was a central stage of human evolution here we show that the turkana basin kenya today one of the hottest places on earth has been continually hot during the past 4 million years the distribution of 13c 18o bonds in paleosol carbonates indicates that soil temperatures during periods of carbonate formation were typically above 30 c and often in excess of 35 c similar soil temperatures are observed today in the turkana basin and reflect high air temperatures combined with solar heating of the soil surface these results are specific to periods of soil carbonate formation and we suggest that such periods composed a large fraction of integrated time in the turkana basin if correct this interpretation has implications for human thermophysiology and implies a long standing human association with marginal environments

cretaceous extinctions multiple causes figure 1 deccan plateau basalts lava from deccan volcanism formed distinct layering credit gsfc nasa in the review the chicxulub asteroid impact and mass extinction at the cretaceous paleogene boundary p schulte et al 5 march p 1214 2 the terminal cretaceous

abrupt deep sea warming at the end of the cretaceous climatic and oceanographic variations during the last 2 m y of the maastrichtian inferred from high resolution 10 k y stable isotope analysis of the mid latitude south atlantic deep sea drilling project site 525 reveal a major warm pulse followed by rapid cooling prior to the cretaceous tertiary boundary between 66 85 and 65 52 ma cool but fluctuating temperatures average 9 9 and 15 4 c in intermediate and surface waters respectively this interval is followed by an abrupt short term warming between 65 45 and 65 11 ma which increased temperatures by 2 3 c in intermediate waters and decreased the vertical thermal gradient to an average of 2 7 c this warm pulse may be linked to increased atmospheric pco 2 increased poleward heat transport and the switch of an intermediate water source from high to lowmiddle latitudes during the last 100 k y of the maastrichtian intermediate and surface temperatures decreased by an average of 2 1 and 1 4 c respectively compared to the maximum temperature between 65 32 and 65 24 ma

environmental change across a terrestrial cretaceous paleogene boundary section in eastern montana usa constrained by carbonate clumped isotope paleothermometry the cretaceous paleogene k pg mass extinction has been attributed to the impact of a large bolide at the end of the cretaceous period although other potential causes have also been proposed most notably climate change caused by deccan traps india flood volcanism reconstructing paleoclimate particularly in terrestrial settings has been hindered by a lack of reliable proxies the recent development of carbonate clumped isotope paleothermometry has contributed to temperature reconstructions using geochemical proxies in terrestrial settings we employ this method along with new stratigraphic constraints in the hell creek cretaceous and overlying fort union paleogene formations montana usa to examine changes in temperature leading to and across the k pg boundary we demonstrate that well preserved ca 66 ma aragonitic bivalves serve as suitable paleoclimate archives although there are limitations in the stratigraphic availability of fossil bivalves for clumped isotope analysis we record an apparent 8 c decrease in summer temperatures over the last 300 k y of the cretaceous that corresponds broadly with patterns observed in other paleotemperature proxies this observed decrease plausibly could be explained by an absolute temperature decrease or by other environmental stresses on the organisms but in either case suggests changing living conditions over the interval previously documented declines in vertebrate and invertebrate biodiversity occur over the same stratigraphic interval at this study location these results are consistent with published models of the end cretaceous mass extinction in which destabilized ecosystems become more susceptible to an abrupt event like a bolide impact

massive ice of the tuktoyaktuk area western arctic coast canada the extensive coastal exposure of massive underground ice at peninsula point southwest of tuktoyaktuk northwest territories is believed to be intrasedimental ice the ice grew beneath a frozen d

a revised calibration of the clumped isotope thermometer abstract a growing number of materials and environmental settings are studied using the carbonate clumped isotope 47 thermometer the method has been applied in both biogenic and non biogenic carbonate systems in marine and terrestrial settings over a wide range of geological timescales the current 47 temperature calibration gives good temperature estimates for most biogenic materials however systematic biases are commonly observed at low temperatures in this study we report additional calibration data that covers a wider temperature range at more evenly distributed temperatures and are measured at higher analytical precision than the original calibration combining these data with the original calibration yields a 47 t relationship that is similar to the original calibration though slightly less steep 47 0 0526 0 0025 10 6 t 2 0 0520 0 0284 this revised calibration is in better agreement with biogenic carbonates including those grown at low temperatures the difference between the original and revised calibrations is significant for carbonates forming below 16 c or above 49 c 47 values of 0 68 and 0 56 additionally we include a comprehensive analysis of the sources of error associated with 47 measurements and estimated temperatures and recommend measurement strategies for obtaining the desired precision as an illustration we apply the revised calibration and uncertainty analysis to 3 previously published studies at low temperatures the revised calibration results in significant differences from the original calibration and hence affects the interpretation of the environmental signal recorded in light of our 47 errors analysis in cases where the temperature signals are small we find that replicate analyses are critical to identify a temperature signal

glaciotectonic deformation and reinterpretation of the worth point stratigraphic sequence banks island nt canada hill hole pairs comprising an ice pushed hill and associated source depression cluster in a belt along the west coast of banks island nt ongoing coastal erosion at worth point southwest banks island has exposed a section 6 km long and 30 m high through an ice pushed hill that was transported 2 km from a corresponding source depression to the southeast the exposed stratigraphic sequence is polydeformed and comprises folded and faulted rafts of early cretaceous and late tertiary bedrock a prominent organic raft quaternary glacial sediments and buried glacial ice three distinct structural domains can be identified within the stratigraphic sequence that represent proximal to distal deformation in an ice marginal setting complex thrust sequences interfering fold sets brecciated bedrock and widespread shear structures superimposed on this ice marginally deformed sequence record subsequent deformation in a subglacial shear zone analysis of cross cutting relationships within the stratigraphic sequence combined with osl dating indicate that the worth point hill hole pair was deformed during two separate glaciotectonic events firstly ice sheet advance constructed the hill hole pair and glaciotectonized the strata ice marginally producing a proximal to distal deformation sequence a glacioisostatically forced marine transgression resulted in extensive reworking of the strata and the deposition of a glaciomarine diamict a readvance during this initial stage redeformed the strata in a subglacial shear zone overprinting complex deformation structures and depositing a glaciotectonite 20 m thick outwash channels that incise the subglacially deformed strata record a deglacial marine regression whereas aggradation of glaciofluvial sand and gravel infilling the channels record a subsequent marine transgression secondly a later largely non erosive ice margin overrode worth point deforming only the most surficial units in the section and depositing a capping till the investigation of the worth point stratigraphic sequence provides the first detailed description of the internal architecture of a polydeformed hill hole pair and as such provides an insight into the formation and evolution of an enigmatic landform notably the stratigraphic sequence documents ice marginal and subglacial glaciotectonics in permafrost terrain as well as regional glacial and relative sea level histories the reinterpreted stratigraphy fundamentally rejects the long established paleoenvironmental history of worth point that assumed a simple layer cake stratigraphy including the type site for an organically rich preglacial interval worth point fm

the triangle shearzone zimbabwe revisited new data document an important event at 2 0 ga in the limpopo belt abstract the limpopo belt in southern africa has been used to demonstrate that modern style continent continent collision operated during the late archaean 2 6 2 7 ga we have studied the age and pt conditions of strike slip tectonism along the important right lateral triangle shearzone our results substantiate existing proterozoic metamorphic mineral age data of prior uncertain significance using the pb pb and sm nd garnet chronometers and the ar ar step heating technique for amphibole we have dated pre and syn tectonic metamorphic minerals at 2 2 and 2 0 ga thus the triangle shearzone can now be regarded as an important proterozoic suture examination of corresponding high grade pt conditions reaching 800 c at 9 kbar indicates a clockwise metamorphic evolution with pronounced isothermal uplift although the evidence that thrusting of the marginal zones of the limpopo belt over the adjoining cratons occurred during the late archaean clearly remains it is now very uncertain to which event the various pt paths obtained in the limpopo belt may be assigned therefore the question of whether the 2 6 2 7 ga tectonism fits on its own a modern style continental collision model remains open and has to be reassessed

temperature and salinity of the late cretaceous western interior seaway the western interior seaway wis was a shallow and expansive body of water that covered the central united states during the late cretaceous attempts to reconstruct temperatures in the seaway using the oxygen isotopic composition of biogenic carbonates have suffered from uncertainty in the oxygen isotopic composition of seawater 18 o w in the semi restricted basin we present new reconstructed temperature and 18 o w data from marine and estuarine environments in the wis and freshwater environments in wis source rivers derived from clumped isotope analyses of bivalve and gastropod shells we find temperatures of 5 21 c 18 o w values below contemporaneous gulf of mexico marine sites and a strong correlation between 18 o w and environmental setting we propose that decreasing 18 o w values reflect decreasing salinity driven by an increasing contribution of continental runoff using a two end member salinity 18 o w mixing model we estimate salinities of 29 35 psu practical salinity units for the deep marine 20 32 psu for the shallow marine and 11 26 psu for the estuarine environments of the wis new climate model simulations agree with reconstructed temperatures and salinities and suggest the presence of salinity driven stratification within the seaway

pbpb dating of apatite by a stepwise dissolution technique abstract apatites from different geologic settings have been dated by a new sequential dissolution method the procedure is based on stepwise exposure of apatite to weak intermediate acids a pegmatite sample from the kerala khondalite belt in southern india yielded an age of 509 25 ma apatites from an enderbite sample from the northern marginal zone of the limpopo belt in southern africa yielded an age of 1970 26 ma which is in agreement with the high grade metamorphism at around 2 0 ga reported from the triangle shear zone and amphibolite facies metamorphism in the transition zone apatites from an amphibolite facies gneiss from the transition zone south of the nmz yielded an age of 1878 18 ma this age is somewhat younger than a sphene age on the same rock of 1971 17 ma and is believed to reflect the time of retrograde metamorphism in the presence of a fluid phase the sequential dissolution method is a new tool that allows dating of apatites which have relatively unradiogenic pb ratios because the spread can be significantly increased and no correction for common lead is needed this study further demonstrates that apatites from magmatic and high grade metamorphic rocks yield ages very close to those of monazite zircon or garnet unless the rock subsequently interacted with a fluid phase

headwall retreat of ground ice slumps banks island northwest territories the relationship between ice face ablation and headwall retreat is described for three ground ice slumps in the sand hills moraine southwest banks island retreat exceeds ablation by a geometric factor that depends on the slope of the ice and the gradient of the surrounding terrain amounts of retreat predicted from ice ablation calculations compare favourably with field measurements except at the start of thermokarst activity in the spring or when the ground ice remains covered by debris for long periods long term headwall retreat for slumps in southern banks island with different orientations and ice contents can be estimated using a model based on meteorological information the model predicts headwall recession of 11 m a for a ground ice slump facing south and 8 8 9 3 m a for one facing north with inputs of a 35 ice face a ground slope of 5 and a volumetric latent heat of 270 mj m3 these predictions are close to the maximum rates of retreat over a 10 year period as measured from air photographs

modeling climatic effects of carbon dioxide emissions from deccan traps volcanic eruptions around the cretaceous paleogene boundary abstract warming events observed in paleotemperature proxy records within 500 kyr of the cretaceous paleogene k pg boundary have often been attributed to atmospheric co 2 increases due to deccan traps flood volcanism currently there is uncertainty in the size nature and timing of the deccan eruptions all of which lead to uncertainty in the likely climatic effects modeling the impact of deccan traps eruption on climate is complicated by the discrepancy between the lifetimes of emitted gasses and the length of the total eruptive sequence though so 2 emissions can have important climatic effects the short atmospheric lifetimes of so 2 and resulting aerosols mean these effects are unlikely to be recognized in the proxy record here we focus on the co 2 emissions and attempt to match paleotemperature proxy records with plausible emissions scenarios we also test the relevance for climate of the number length and arrangement e g increasing or decreasing size of individual eruptions as well as the total duration and size of the overall eruptive sequence we find that the number and length of individual eruptions are largely unimportant to co 2 based based climate effects but that the pattern and duration of eruption have measureable effects unsurprisingly the total emitted co 2 from the deccan traps exerts a strong control on climatic effects and better constraints on the volume of emitted gas are necessary at the high end of the uncertainty range the deccan traps eruptions are capable of generating warming events recorded in the proxy record but rates of silicate weathering above modern rates are necessary to draw down co 2 in accordance with those records

high resolution hg chemostratigraphy a contribution to the distinction of chemical fingerprints of the deccan volcanism and cretaceous paleogene boundary impact event abstract there is a renewed interest in volcanism as the major trigger for dramatic climatic changes at the cretaceous paleogene transition ktb which were accompanied by a decrease in biodiversity and mass extinction we have used hg contents as proxy for volcanic activity at the classical localities of gubbio italy and stevns klint denmark where the ktb layer is easily recognizable and at a near complete succession exposed at the bajada del jaguel locality in the neuquen basin argentina these three localities display similar 13ccarb trends with markedly negative excursion at the ktb layer bulk rock oxygen isotopes yielded similar pathways across the ktb layers in these localities and if considered near primary the negative 18o excursion at the ktb in gubbio and bajada del jaguel suggest warming temperatures during this transition whereas the negative excursion immediately followed by positive one at stevns klint points to a cycle of warm followed by colder climate at stevns klint hg contents reach 250 ng g 1 within the ktb layer fiskeler member and 45 ng g 1 at 1 5 m above that while within the scaglia rossa formation at gubbio three hg peaks across the ktb are observed one of them within the ktb layer 5 3 ng g 1 hg shows several peaks across the ktb in the neuquen basin with up to 400 ng g 1 in the jaguel formation the phenomena that caused dramatic changes at the ktb probably expelled huge amounts of hg into the atmosphere as recorded by these high hg levels a co variation between hg and al2o3 in the studied sections suggest that hg is adsorbed onto clays hg concentrations and also hg isotopes are perhaps a powerful tool in the assessment of the role of volcanic activity during extreme climatic and biotic events and in assessing the role of meteorite impact versus volcanism as the predominant cause of past global catastrophes and mass extinction

environmental effects of deccan volcanism across the cretaceous tertiary transition in meghalaya india the um sohryngkew section of meghalaya ne india located 800 1000 km from the deccan volcanic province is one of the most complete cretaceous tertiary boundary ktb transitions worldwide with all defining and supporting criteria present mass extinction of planktic foraminifera first appearance of danian species 13c shift ir anomaly 12 ppb and ktb red layer the geochemical signature of the ktb layer indicates not only an extraterrestrial signal ni and all platinum group elements pges of a second impact that postdates chicxulub but also a significant component resulting from condensed sedimentation p redox fluctuations as co fe pb zn and to a lesser extent ni and cu and volcanism from the late maastrichtian c29r into the early danian a humid climate prevailed kaolinite 40 60 detrital minerals 50 80 during the latest maastrichtian periodic acid rains carbonate dissolution cia index 70 80 associated with pulsed deccan eruptions and strong continental weathering resulted in mesotrophic waters the resulting super stressed environmental conditions led to the demise of nearly all planktic foraminiferal species and blooms 95 of the disaster opportunist guembelitria cretacea these data reveal that detrimental marine conditions prevailed surrounding the deccan volcanic province during the main phase of eruptions in c29r below the ktb ultimately these environmental conditions led to regionally early extinctions followed by global extinctions at the ktb

the eruptive tempo of deccan volcanism in relation to the cretaceous paleogene boundary late cretaceous records of environmental change suggest that deccan traps dt volcanism contributed to the cretaceous paleogene boundary kpb ecosystem crisis however testing this hypothesis requires identification of the kpb in the dt we constrain the location of the kpb with high precision argon 40 argon 39 data to be coincident with changes in the magmatic plumbing system we also found that the dt did not erupt in three discrete large pulses and that 90 of dt volume erupted in 1 million years with 75 emplaced post kpb late cretaceous records of climate change coincide temporally with the eruption of the smallest dt phases suggesting that either the release of climate modifying gases is not directly related to eruptive volume or dt volcanism was not the source of late cretaceous climate change

basal glacier ice and massive ground ice different scientists same science whilst glaciologists and permafrost researchers investigate ice bodies using similar techniques there has been surprisingly little collaboration between the two communities this paper examines the potential benefits of interdisciplinary research into the formation of basal ice beneath glaciers and the origin of massive ice in glaciated permafrost regions active collaboration in these areas has already improved our understanding of the formation of basal ice beneath cold based glaciers the critical role played by basal freezing in controlling the dynamic behaviour of stagnating ice streams and the significance of glacier permafrost interactions at the margins of pleistocene ice sheets however in order to promote future collaboration certain obstacles need to be overcome the contrasting ice classification schemes employed by glaciologists and permafrost scientists for example need to be unified in order to allow detailed comparisons of ice rich sequences in both environments this could in turn enable exciting research advances most notably by facilitating the identification of preserved remnants of pleistocene ice sheets within permafrost regions that provide a potentially invaluable and currently largely untapped source of palaeoglaciological information

high elevation of jiaolai basin during the late cretaceous implication for the coastal mountains along the east asian margin abstract a large body of evidence suggests that there were extensive coastal mountains along the east asian margin during the late cretaceous however current knowledge of the paleo mountains the period range and elevation is limited therefore direct paleoaltimetry is needed to validate and evaluate the paleo mountains in east asia our study area is jiaolai basin which is located at the east asian continental margin we estimate the paleoelevation of jiaolai basin during the late cretaceous using carbonate clumped isotope paleothermometry after correcting for seasonal preference latitudinal difference and secular climate change we conclude that the paleoelevation of jiaolai basin was almost certainly 2 0 km at 80 ma combined with the evidence from stratigraphy paleogeography and paleoclimatology our results suggest that the existence of coastal mountains along east asia during the late cretaceous is likely and the model of okhotomorsk east asia collision is preferred

single mineral pbpb dating a new stepwise leaching procedure applied to ca bearing silicates enables the selective recovery of radiogenic and common pb from a mineral and thus makes single phase pbpb dating possible this permits independent dating of rock forming minerals within a paragenetic sequence and the direct combination of age data with petrological results furthermore the stepwise leaching technique has the advantage over multi phase pbpb dating in that it does not require initial pb isotope equilibrium among the phases but may be used to test it the presence of microscopic solid inclusions which complicate dating of single phases if they are not in equilibrium with the host can be traced via the behaviour of the 208pb 204pb ratio through the various leaching steps this constitutes a major advantage over conventional bulk phase pbpb dating in addition the precision of an isochron age can be improved relative to that of the bulk mineral approach since the 207pb 204pb and 206pb 204pb data spread is significantly enhanced therefore the technique may both be used to date younger phases and or minerals with less favourable u pb ratios and to extend the applicability of self consistent p t t modelling

high resolution chronostratigraphy of the terrestrial cretaceous paleogene transition and recovery interval in the hell creek region montana detailed understanding of ecosystem decline and recovery attending the cretaceous paleogene boundary kpb mass extinctions is hindered by limited constraints on the pace and tempo of environmental events near the boundary to mitigate this shortcoming high resolution 40ar 39ar geochronology was performed on tephras intercalated between fossiliferous terrestrial sediments of the upper hell creek and lower fort union formations in the western williston basin of northeastern montana usa tephra samples were collected from 10 stratigraphic sections spanning an area of 5000 km2 several distinctive tephras can be correlated between sections separated spatially by as much as 60 km the tephras are thin distal deposits generally preserved only in lignite beds which are interbedded with clastic deposits yielding vertebrate faunas of lancian late maastrichtian to torrejonian early danian north american land mammal ages sanidine from 15 tephra samples was analyzed in 1649 total fusion experiments 1597 on single crystals and 12 incremental heating analyses of multigrain aliquots ages were determined for 13 distinct tephras ranging from 66 289 0 051 to 64 866 0 023 ma including only analytical uncertainties this level of precision is sufficient to resolve the ages of all of the coal beds that have served as a basis for a regional stratigraphic framework the data confirm that the hell creek fort union formational contact is diachronous and further support the age of the kpb impact layer at 66 043 0 010 ma or 0 043 ma considering systematic uncertainties application of the new results to previous magnetostratigraphic data indicates an appreciably compressed time interval between the base of chron c29r and the top of chron c28r with a maximum duration estimate of 1 421 0 066 ma most notable is the implied brevity of chron c29r with a maximum estimate of 457 54 ka and possibly as brief as 345 38 ka compared to the 710 ka estimate from the geologic time scale 2012 gts2012 further application of new results to terrestrial biostratigraphy adds higher precision to the timing and tempo of biotic change before and after the kpb our results indicate that the timing of pre kpb ecological decline is constrained to the last 200 ka of the cretaceous adding further support to the press pulse extinction hypothesis additionally the duration of the depauperate basal paleogene puercan 1 disaster fauna is confined to a 70 ka interval faunal recovery in this region indicated by the appearance of primitive members of the placental mammal radiation and the restoration of taxonomic richness and evenness occurred within 900 ka after the kpb these results show that biotic recovery after the mass extinction in the terrestrial realm was more rapid than in the marine

the evolution of latitudinal temperature gradients from the latest cretaceous through the present abstract latitudinal temperature gradients are a defining characteristic of the climate system using thermometric indicators including 18o plant and animal fossils glycerol dialkyl glycerol tetraether gdgt proxies and clumped isotope estimates we document marine and terrestrial temperature gradients for the latest cretaceous late paleocene early eocene early oligocene pliocene and recent the changes in gradients reflect the transition greenhouse to icehouse conditions the evolution of latitudinal temperature gradients in marine and terrestrial realms are similar but has some distinctive differences marine temperatures are generally warmer than those on land except for the late paleocene early eocene the marine records show distinct inflection points at 30 and 50 latitude indicating the existence of frontal systems in the ocean except for the late paleocene early eocene the marine records show an increasingly steeper trend from latest cretaceous through recent being most pronounced after the early oligocene greenhouse icehouse transition this trend reflects the increasing intensity of high latitude and polar cooling as the icehouse state developed during the late paleocene early eocene the oceans were characterized by slightly warmer tropics and much warmer higher latitudes than at present the continents have generally had tropical temperatures like those of today varying by

massive ground ice and ice cored terrain near sabine point yukon coastal plain massive ground ice 5 6 m in thickness is exposed within retrogressive thaw flow slides near sabine point yukon territory the ice is present near the upper surface of buckland till and is overla

upb geochronology of the sri lankan basement abstract u pb ages of zircons and monazites from ortho and paragneisses representing the major crystalline basement units of sri lanka establish a new geochronological framework which is consistent with previously published work on sm nd model ages rb sr whole rock ages and u pb mineral ages in the highland complex three newly dated orthogneisses one previously dated by baur et al 1991 and one dated by kroner and williams 1992 all intruded 1 85 to 1 9 ga ago this widespread intrusion event occurred soon after the end of sediment deposition which is estimated at 1 9 to 2 0 ga using upper intercept ages of zircons from metapelites in the highland complex within the boundaries of this complex established by sm nd model age mapping milisenda et al 1994 only one orthogneiss has been found which is substantially younger than 1 8 ga this is the metatonalite from polonnaruwa which intruded 670 ma ago baur et al 1991 three orthogneisses from the vijayan complex which lies to the east of the highland complex yield similarly consistent crystallization ages of 1023 8 1016 28 and 1033 121 ma in the wanni complex which lies to the west of the highland complex a sillimanite bearing gneiss which is apparently of metasedimentary origin but contains zircons of igneous appearance yields a primary crystallization age of 793 4 ma consistent with a previously dated orthogneiss from kurunegala of 770 ma baur et al 1991 in addition single zircon data by kroner et al 1994 indicate primary crystallization ages of 1 0 to 1 1 ga for orthogneisses from the vavuniya charnockite province which is considered to be part of the wanni complex these results confirm the age contrast between the highland complex on the one hand and the vijayan complex and wanni complex on the other as previously inferred from sm nd model ages milisenda et al 1988 1994 post tectonic granitoids and pegmatites intruded throughout all three complexes 550 ma ago the age of regional high grade metamorphism mostly granulite facies in the highland complex mostly amphibolite facies in the vijayan complex and both granulite and amphibolite facies in the wanni complex is constrained to be less than 670 ma the primary crystallization age of the polonnaruwa metatonalite it is more closely defined by lower intercept zircon ages which include one concordant age of 608 4 ma and one discordant but well defined age of 611 23 ma and by a nearly concordant monazite age of 592 2 ma this indicates that peak metamorphic conditions occurred 610 ma ago numerous other lower intercept ages between 590 and 550 ma and post tectonic intrusion ages of 550 ma set a lower age limit for high grade conditions and deformation the temperature history between 610 and 550 ma is not yet well resolved and it is not clear whether there was a separate thermal event 550 ma ago previously published whole rock rb sr and sm nd isochrons for gneisses from the highland complex yielding ages of 2 ga and greater and previously interpreted to date the time of granulite grade metamorphism must be reinterpreted in the light of the new data presented here as well as other recently published results e g burton and o nions 1990b baur et al 1991 and in view of the accumulated evidence for very limited element mobility during high grade metamorphism these whole rock ages are in fact identical or close to the ages of primary granitoid emplacement rather than the age of granulite facies metamorphism

metamorphic p t conditions of the kerala south india khondalite belt a granulite facies supracrustal terrain the khondalite belt of southernmost india is an immense section of granulite facies metasediments of probable early proterozoic age dominant rock types are migmatized khondalites garnet sillimanite pm cordierite metapelites acid biotite garnet graphitic gneisses and charnockites quartzofeldspathic gneisses with orthopyroxene throughout much of southern kerala the biotite gneisses are in a state of arrested conversion to charnockite partially decrepitated co 2 inclusions in quartz at the ponmudi mixed biotite gneiss charnockite quarry have significant ch 4 and or n 2 and are texturally late the probable sequence of events in metasediments was 1 migmatization 2 charnockite formation 3 symplectitic cordierite formation and 4 late co 2 entrapment phase equilibrium diagrams of anatexis in aluminous systems and fe mg exchange between garnet and biotite indicate metamorphic temperatures of 650 850 c for the khondalites temperatures based on garnet orthopyroxene

westward continuation of the craton limpopo belt tectonic break in zimbabwe and new age constraints on the timing of the thrusting the umlali thrust zone has been mapped between the granite greenstone rocks of the zimbabwe craton and the granulite facies rocks of the limpopo belt a tectonic break had not been previously recognized in the southwest because of the intrusion of syn to post kinematic porphyritic granites these intrusions locally obliterate evidence for the tectonic break although in some localities the associated mylonites are preserved as xenoliths within the intrusive porphyritic granite bodies the porphyritic granite bodies were emplaced during and after the main regional fabric forming event a u pb zircon age of 2627 7 ma obtained from a late kinematic microgranite is interpreted to be the minimum time of thrusting a whole rock rb sr age of 2583 52 ma obtained from plutonic rocks and retrogressed zones within the north marginal zone falls within error of the zircon age suggesting widespread magmatic and hydrothermal activity coeval with the thrusting

proterozoic transpressive deformation in the northern marginal zone limpopo belt zimbabwe a major tectono metamorphic event affected the southern half of the northern marginal zone of the limpopo belt at 2 0 ga structural analysis along a 43 km long profile perpendicular to strike shows extension inclined toward the northeast extension parallel to axes of folds that uplift the southeast of the section i e the central zone of the limpopo belt and dextral shear these deformation patterns developed coevally the lineations form distinct tightly clustered groups that occur together in the profile there is no evidence for superimposed deformation or deformed lineations nor are lineations observed cross cutting each other this single episode of deformation can therefore be called transpression petrographic and thermobarometric evidence support this kinematic picture in that decreases of both pressure 2 5 kb and temperature 150 c are documented from southeast to northwest across strike 39 ar 40 ar step heating of metamorphic hornblende from amphibolites has yielded ages of

shear zones of the limpopo belt and adjacent granitoid greenstone terranes implications for late archaean collision tectonics in southern africa abstract granulite metamorphism in the 2 65 ga limpopo belt of southern africa is related to crustal thickening due to late archaean collision tectonics the central zone of the belt is a major thrust sheet of distinctive lithological structural and isotopic character separated from adjacent terranes by crustal scale shear zones and the northern and southern marginal zones are up thrust deep level granulite facies terranes of the adjacent cratons geometrically the marginal zones are mirror images and the limpopo belt is essentially symmetrical in n s section conventionally regarded as a n s collisional orogeny the gross structural and lithological differences between the central zone and the marginal zones kinematic data from shear zones and geophysical data showing the three dimensional geometry of the central zone are here used to suggest that the direction of emplacement of the central zone was also the collision direction this was from northeast to southwest with the upthrust outwardly directed marginal zones developing in mechanical response to this collision

dating a variscan pressure temperature loop with staurolite staurolite with a complex internal metamorphic and structural relationship occurs in metapelite from the silvretta thrust sheet eastern alps stepwise leaching of a core and rim fraction of a single staurolite crystal resulted in a total pb pb isochron of 308 28 ma the variscan metamorphism has been confirmed by a further single bulk staurolite pb pb age of 298 42 ma which is in accordance with u pb ages of 306 8 ma and 304 6 ma respectively obtained from combined u pb leaching of the same crystals direct dating of the staurolite in reaction isograd was therefore successful our results date the prograde part of a variscan counterclockwise pressure temperature path in the silvretta thrust sheet proximity with white mica rb sr and k ar cooling ages suggests that the whole variscan episode was fast and took place within a few million years

paleoclimate reconstruction using carbonate clumped isotope thermometry carbonate clumped isotope thermometry is a relatively new paleotemperature proxy based on measurements of the degree of ordering of 13 c and 18 o into bonds with each other making the 13 c 18 o 16 o 2 2 ion group in lattices of carbonate minerals this technique has several unusual properties that complement existing methods of paleoclimate reconstruction most importantly it is based on a homogeneous isotope exchange equilibrium and thus constrains temperature independent of the isotopic composition of waters from which carbonates grew this method also appears to be generally insensitive to vital effects that compromise many other paleothermometers based on the chemical properties of biominerals or organic matter at least for those organisms that have been subjected to systematic study to date corals and foraminifera however discrepancies among some calibrations particularly at low temperatures may point toward the existence of vital effects in mollusks and other organisms this review discusses the principles and calibrations of the technique its uses in combination with conventional stable isotope measurements to constrain the 18 o of past waters preservation of paleotemperatures in ancient materials as well as current problems in our understanding of calibrations and interlaboratory data comparisons

intercrystalline stable isotope diffusion a fast grain boundary model we formulated a numerical model for stable isotope interdiffusion which predicts the temperatures recorded between two or more minerals and the intragranular distribution of stable isotopes in each mineral as functions of mineral grain sizes and shapes diffusivities modes equilibrium isotopic fractionations and the cooling rate of a rock one of the principal assumptions of the model is that grain boundaries are regions of rapid transport of stable isotopes this fast grain boundary fgb model describes interdiffusion between any number of mineral grains assuming that local equilibrium and mass balance restrictions apply on the grain boundaries throughout the volume modeled the model can be used for a rock containing any number of minerals and number of grain sizes of each mineral several grain shapes and any thermal history or domain size desired previous models describing stable isotope interdiffusion upon cooling have been based on dodson s equation or an equivalent numerical analogue the closure temperature of dodson is the average bulk temperature recorded between a mineral and an infinite reservoir by using dodson s equation these models have treated the closure temperature as an innate characteristic of a given mineral independent of the amounts and diffusion rates of other minerals such models do not accurately describe the mass balance of many stable isotope interdiffusion problems existing models for cation interdiffusion could be applied to stable isotopes with some modifications but only describe exchange between two minerals under specific conditions the results of fgb calculations differ considerably from the predictions of dodson s equation in many rock types of interest actual calculations using the fgb model indicate that closure temperature and diffusion profiles are as strongly functions of modal abundance and relative differences in diffusion coefficient as they are functions of grain size and cooling rate closure temperatures recorded between two minerals which exchanged stable isotopes by diffusion are a function of modal abundance and differences in diffusion coefficient and may differ from that predicted by dodson s equation by hundreds of degrees c either or both of two minerals may preserve detectable zonation which may in some instances be larger in the faster diffusing mineral rocks containing three or more minerals can record a large span of fractionations resulting from closed system processes alone the results of fgb diffusion modeling indicate that the effects of diffusive exchange must be evaluated before interpreting mineral fractionations concordant or discordant recorded within any rock in which diffusion could have acted over observable scales the predictions of this model are applicable to thermometry evaluation of open or closed system retrogression and determination of cooling rates or diffusion coefficients

controlled moraines origins characteristics and palaeoglaciological implications abstract controlled moraines are supraglacial debris concentrations that become hummocky moraine upon de icing and possess clear linearity due to the inheritance of the former pattern of debris rich folia in the parent ice linearity is most striking wherever glacier ice cores still exist but it increasingly deteriorates with progressive melt out as a result moraine linearity has a low preservation potential in deglaciated terrains but hummocky moraine tracts previously interpreted as evidence of areal stagnation may instead record receding polythermal glacier margins in which debris rich ice was concentrated in frozen toe zones recent applications of modern glaciological analogues to palaeoglaciological reconstructions have implied that a controlled moraine development can be ascribed to a specific process e g englacial thrusting or supercooling and b controlled moraine preservation potential is good enough to imply the occurrence of the specific process in former glacier snouts e g ancient polythermal or supercooled snouts these assumptions are tested using case studies of controlled moraine construction in which a wide range of debris entrainment and debris rich ice thickening mechanisms are seen to produce the same geomorphic features polythermal conditions are crucial to the concentration of supraglacial debris and controlled moraines in glacier snouts via processes that are most effective at the glacier permafrost interface end moraines lie on a process form continuum constrained by basal thermal regime the morphological expression of englacial structures in controlled moraine ridges is most striking while the moraines retain ice cores but the final deposits landforms tend to consist of discontinuous transverse ridges with intervening hummocks preserving only a weak impression of the former englacial structure these are arranged in arcuate zones of hummocky moraine up to 2 km wide containing ice walled lake plains and lying down flow of streamlined landforms produced by warm based ice a variety of debris entrainment mechanisms can produce the same geomorphic signature spatial and temporal variability in process form relationships will lead to the sequential development of different types of end moraines during the recession of a glacier or ice sheet margin

fourier analysis and the extinction of unionoid bivalves near the cretaceous tertiary boundary of the western interior usa pattern causes and ecological significance abstract the williston basin in the western interior of the usa is known for its highly diverse and well preserved fauna of unionoid bivalves this fauna undergoes a significant turnover near the cretaceous tertiary k t boundary a quantitative study based on multivariate morphometrics has been carried out to better understand the pattern and causes of the extinction of unionoid bivalves in the k t transition the decrease in taxonomic diversity in the interval spanning the k t boundary is associated with a significant shift in morphospace occupation this shift indicates a major decrease in habitat stability four events and processes are discussed as possible causes of this change in habitat stability 1 the chicxulub impact on the yucatan peninsula 2 global climate changes to some extent due to deccan volcanism 3 tectonic changes in the emerging rocky mountains and 4 eustatic changes in the western interior seaway we conclude that the bolide impact was not the major killing agent for unionoid bivalves the tectonic and eustatic processes are much more important to explain the unionoid faunal turnover at the end of the cretaceous the results and conclusions of the study are considered to be helpful to better understand the present day distribution of unionoid bivalves

deccan volcanism caused coupled pco2 and terrestrial temperature rises and pre impact extinctions in northern china evaluating the terrestrial climate record provides a critical test of the roles of chicxulub impact and deccan traps volcanism during the cretaceous paleogene k pg mass extinction most evidence came from marine records but our new clumped isotopes data from paleosol carbonates in the songliao basin provide a terrestrial climate history from northern china this reveals there was a pre impact warming caused by the onset of deccan traps volcanism whereas the following short term cooling then another warming episode were likely caused by chicxulub impact and post boundary volcanism our study suggests that the pco levels were probably the main control on the latest cretaceous cooling and the climatic fluctuations across the k pg boundary interval in northern china in the songliao basin the pre impact deccan traps volcanism links to losses of half of the lacustrine algae species charophytes and almost all of the lacustrine ostracodes this suggests that the deccan traps volcanism had already destabilized the ecosystem and caused extinctions prior to the chicxulub impact

depositional history of the north taymyr ice marginal zone siberia a landsystem approach the sediment landform associations of the northern taymyr peninsula in arctic siberia tell a tale of ice sheets advancing from the kara sea shelf and inundating the peninsula probably three times during the weichselian in each case the ice sheet had a margin frozen to its bed and an interior moving over a deforming bed the north taymyr ice marginal zone ntz comprises ice marginal and supraglacial landsystems dominated by thrust block moraines 2 3 km wide and large scale deformation of sediments and ice large areas are still underlain by remnant glacier ice and a supraglacial landscape with numerous ice walled lakes and kames is forming even today the proglacial landsystem is characterised by subaqueous e g deltas or terrestrial e g sandar environments depending on location altitude and time of formation dating results osl c 14 indicate that the ntz was initiated ca 80 kyr bp during the retreat of the early weichselian ice sheet and that it records the maximum limit of a middle weichselian glaciation ca 65 kyr bp during both these events proglacial lakes were dammed by the ice sheets part of the ntz was occupied by a thin late weichselian ice sheet 20 12 kyr bp resulting in subaerial proglacial drainage copyright c 2002 john wiley sons ltd

the extension of the late weichselian late devensian ice sheets in the north sea basin the distribution of large channel like features comprising weichselian devensian incisions in the western north sea provides evidence for a much larger extension of the last ice sheet than currently assumed morphological comparison of the incisions with those in north germany and poland reveals a striking similarity in shape and distribution the features on the north sea floor are interpreted as being formed by meltwater erosion within the margin of the ice sheet the widespread absence of weichselian devensian till in the area under consideration may be attributed to later erosion large scale reworking and redistribution of sediments is indicated by the complete sediment infill of the majority of the incisions

cryostructures in permafrost tuktoyaktuk coastlands western arctic canada the shape and distribution of ice and sediment within frozen ground constitute its cryostructure observations on perennially frozen sediments in the tuktoyaktuk coastlands enable six cryostructures to be identified 1 structureless 2 lenticular 3 layered 4 reticulate 5 crustal and 6 suspended these cryostructures can be transitional or composite five cryofacies types can also be identified according to volumetric ice content and grain size they can be grouped into cryofacies assemblages the utility of the descriptive classification of ice rich sediments is illustrated from a palaeothaw layer at crumbling point

burial and preservation of a 30 000 year old perennial snowbank in red creek valley ogilvie mountains central yukon canada this study describes the origin and age of a body of massive ground ice exposed in the headwall of a thaw slump in the red creek valley central yukon canada the site is located beyond the limits of pleistocene glaciation in central yukon and within the southern limit of the modern continuous permafrost zone the origin of the massive ground ice which is preserved under a fine grained diamicton containing thin layers of tephra was determined through ice petrography stable o h isotope composition of the ice and gas composition of occluded air entrapped in the ice the age of the massive ground ice was established by identifying the overlying tephra and radiocarbon dating of a muck deposit preserved within the ice collectively the results indicate that the massive ground ice formed by snow densification with limited melting refreezing and is interpreted as being a buried perennial snowbank the muck deposit within the ice which yielded an age of 30 720 340 14 c a bp and the dawson tephra 25 300 14 c a bp overlying the perennial snowbank indicates that the snowbank accumulated at roughly the transition between marine isotope stages 3 and 2 dry climatic conditions at this time and possibly high winds enabled the snowbank to accumulate in the absence of extensive local valley glaciation as occurred in the mountains to the south in addition to documenting the persistence of relict permafrost and ground ice to warming climate in regions where they are predicted to disappear by numerical models this study presents evidence of an isotopic biosignature preserved in a body of massive ground ice

a paleoclimatic and paleoatmospheric record from peatlands accumulating during the cretaceous paleogene boundary event western interior basin canada petrological and 13 c analyses were undertaken on contiguous specimens of coal and intercalated minor organic rich clastic sediments collected from coal seams spanning the cretaceous paleogene boundary in the alberta and saskatchewan portions of the western interior basin the generally high smectite content of the coal suggests that the original mires were largely small disconnected and rheotrophic readily receiving abundant waterborne detrital clastic material of largely volcanic origin nevertheless using the distinctive claystone that marks the cretaceous paleogene boundary as a regional datum it is possible to correlate cycles in the vitrinite and inertinite composition of the coals over 500 km estimates of peat accumulation rates suggest that the cycles in vitrinite and inertinite composition represent regional cyclic fluctuations in wildfire and oxidation of the peatlands and overlying canopy at a frequency of hundreds to thousands of years the likely causes of these fluctuations were cyclic regional scale changes in temperature the cretaceous paleogene boundary event occurred early during a phase of gradually increasing temperature and or decreasing rainfall but peak wildfire and desiccation of peat occurred up to 14 000 yr later than the cretaceous paleogene boundary and the mires did not experience significant water stress in the immediate aftermath of the extinction event a persistent 1 5 3 0 negative 13 c excursion occurs across the cretaceous paleogene boundary but it cannot be readily separated from four further negative excursions later in the earliest danian the negative carbon isotope excursion linked to the cretaceous paleogene boundary began a few hundred years before the event itself and recovery occurred within 21 k y and possibly in as little as just a few thousand years consistent with recently calibrated shallow marine 13 c records hence the atmospheric and surface ocean carbon pools were coupled at this time the absence of evidence for catastrophic change in the climatic regime at the time of the cretaceous paleogene extinction in these mires supports the notion that the negative shift in atmospheric 13 c was brought about by changes in the 13 c composition of the surface ocean this is consistent with the greater magnitude of extinction experienced by marine fauna relative to the terrestrial realm

mid latitude terrestrial climate of east asia linked to global climate in the late cretaceous reply the late cretaceous late campanian to maastrichtian was characterized by a variable greenhouse climate with evidence for cooling and or glaciation and warming events most of these climatic signals are derived from marine records and knowledge of the terrestrial climate especially in the mid latitudes is limited due to fragmentary geological records on continents here we report mid latitude terrestrial stable oxygen and carbon isotope data from pedogenic carbonates in the nearly continuous late cretaceous age sk 1 core drilled in the songliao basin northeastern china our data indicate a punctuated mid latitude terrestrial climate in the late cretaceous we interpret the negative excursion of pedogenic carbonate 18o in the early maastrichtian to be the result of decreasing temperature and or strengthened westerlies during global cooling and possible glaciation providing valuable mid latitude terrestrial evidence for this event the negative 13c isotopic excursion ca 66 ma is modeled as higher primary productivity caused by increasing temperature and precipitation in response to a warming climate in the latest cretaceous our continuous stable isotopic records in the songliao basin are in accordance with previously published global late cretaceous records of climate variability from marine and terrestrial regions and demonstrate the sensitivity of mid latitude terrestrial climate in a greenhouse world

late paleocene high laramide ranges in northeast wyoming oxygen isotope study of ancient river water abstract the distribution and initial timing of the establishment of high surface elevations in the rocky mountains during the early cenozoic remain controversial despite the importance of these data in testing tectonic models for this region we track the timing and distribution of high elevation in the rocky mountains during the late cretaceous early eocene by examining annual and seasonal 18o values of the ancient river water which are calculated from the 18o values of well preserved freshwater bivalve shells in the powder river basin of the eastern laramide province the 18o values of the ancient river water vary between 23 0 and 8 0 smow in both seasonal and annual records in the late paleocene early eocene the large variation suggests that the ancient rivers were fed yearly or seasonally by snowmelt from highlands of 4 5 1 3 km this can be explained by the existence of the bighorn mountains and black hills with a drainage pattern similar to the present in northeast wyoming the 18o values of ancient river water along the front of the sevier thrust belt generally follow a trend from lower values in north 14 2 1 4 in the early paleocene crazy mountains basin to higher values in south 11 1 0 8 in the late paleocene bighorn basin and 7 1 1 6 in the early eocene washakie basin the variations within each basin are relatively small these rivers most likely rise in the sevier thrust belt and may reflect highland elevation of 1 2 km the 18o values in the alberta foreland and williston basin are very low 20 5 in the late cretaceous indicating the rivers were fed by snowmelt from the canadian rocky mountains of 4 3 1 0 km high the attainment of high elevation in the eastern laramide province prior to the western province could be explained by southwestward progression of back thrusts soled into an earlier east directed master detachment which may be formed by the westward rollback of subducted shallow slab

initial isotopic heterogeneity and secondary disturbance of the smnd system in fluorites and fluid inclusions a study on mesothermal veins from the central and western swiss alps abstract this paper presents sm nd data on hydrothermal fluorites fluid inclusions and leach experiments on samples from the mont blanc and gotthard units swiss alps both areas have experienced alpine greenschist facies overprint 350 and 450 c respectively mont blanc samples represent late variscan fluorites from three individual veins whereas gotthard samples were taken from one hand specimen of probable late variscan age nd concentrations of fluorites range from 3 6 to 23 ppm 147 sm 144 nd ratios from 0 12 to 0 35 none of the samples sets yielded an isochron relationship imperfect correlations indicate apparent ages between late variscan and alpine reflecting neither the formation nor the age of metamorphic overprint reasons are wall rock influence during formation and post formation disturbance secondary fluorite gotthard shows the highest nd concentration and a low sm nd ratio close to that of fluid inclusion fractions a leach experiment showed the same trend even more pronounced 7 of nd and 2 of sm were removed from fluorite by 0 18 n hcl at 100 c hence secondary fluids are likely to leach and fractionate sm and nd and may easily cause dissolution and reprecipitation of fluorite consequently the system is highly suspicious if secondary fluid flow cannot totally be ruled out this is in sharp contrast to previously published conclusions however evidence for rejuvenation of the sm nd system in fluorites is also found in published data sets

pingo ice of the western arctic coast canada a field study of pingo ice exposures shows that all pingos contain pore ice and varying proportions of intrusive ice segregated ice dilation crack ice and ice wedge ice the intrusive ice is derived from water in a subpingo water lens the ice is usually pure and columnar grained with c axes normal to the direction of heat flow the columnar grains tend to develop parallel lines normal to the c axis upon exposure to radiation precise surveys of pingo growth for the 1973 1983 period show that displacement vectors are upward and radially outward and that radial dilation cracks are produced by circumferential stretching the dilation cracks which can open at any time of the year become infilled with surface water and also with soil from the pingo overburden the cumulative width of the dilation crack ice approximates the stretch of the pingo overburden as it is domed by pingo growth dilation crack ice is vertically banded the bands are much wider than those in ice wedge ice and have less vertical tap

mesozoic climates general circulation models and the rock record abstract general circulation models gcms use the laws of physics and an understanding of past geography to simulate climatic responses they are objective in character however they tend to require powerful computers to handle vast numbers of calculations nevertheless it is now possible to compare results from different gcms for a range of times and over a wide range of parameterisations for the past present and future e g in terms of predictions of surface air temperature surface moisture precipitation etc gcms are currently producing simulated climate predictions for the mesozoic which compare favourably with the distributions of climatically sensitive facies e g coals evaporites and palaeosols they can be used effectively in the prediction of oceanic upwelling sites and the distribution of petroleum source rocks and phosphorites models also produce evaluations of other parameters that do not leave a geological record e g cloud cover snow cover and equivocal phenomena such as storminess parameterisation of sub grid scale processes is the main weakness in gcms e g land surfaces convection cloud behaviour and model output for continental interiors is still too cold in winter by comparison with palaeontological data the sedimentary and palaeontological record provides an important way that gcms may themselves be evaluated and this is important because the same gcms are being used currently to predict possible changes in future climate the mesozoic earth was by comparison with the present an alien world as we illustrate here by reference to late triassic late jurassic and late cretaceous simulations dense forests grew close to both poles but experienced months long daylight in warm summers and months long darkness in cold snowy winters ocean depths were warm 8 c or more to the ocean floor and reefs with corals grew 10 of latitude further north and south than at the present time the whole earth was warmer than now by 6 c or more giving more atmospheric humidity and a greatly enhanced hydrological cycle much of the rainfall was predominantly convective in character often focused over the oceans and leaving major desert expanses on the continental areas polar ice sheets are unlikely to have been present because of the high summer temperatures achieved the model indicates extensive sea ice in the nearly enclosed arctic seaway through a large portion of the year during the late cretaceous and the possibility of sea ice in adjacent parts of the midwest seaway over north america the triassic world was a predominantly warm world the model output for evaporation and precipitation conforming well with the known distributions of evaporites calcretes and other climatically sensitive facies for that time the message from the geological record is clear through the phanerozoic earth s climate has changed significantly both on a variety of time scales and over a range of climatic states usually baldly referred to as greenhouse and icehouse although these terms disguise more subtle states between these extremes any notion that the climate can remain constant for the convenience of one species of anthropoid is a delusion although the recent rate of climatic change is exceptional

arrested charnockite formation at kottavattam southern india at kottavattam southern kerala india late proterozoic homogeneous leptynitic garnet biotite gneisses of granitic composition have been transformed on a decimetric scale into coarse grained massive charnockite sensu stricto along a set of conjugate fractures transecting the gneissic foliation charnockitization post dates the polyphase deformation regional high grade metamorphism and anatexis and evidently occurred at a late stage of the pan african tectonothermal history geothermobarometric and fluid inclusion data document textural and chemical equilibration of the gneiss and charnockite assemblages at similar p lith t conditions 650 700 degrees c 5 6kbar in the presence of carbonic fluids internally buffered by reaction with graphite and opaque mineral phases x co2 0 7 0 6 x h2o 0 2 0 3 x n2 0 1 logf o2 l7 5 mineralogical zonation indicates that charnockitization of the leptynitic gneiss involved first the breakdown of biotite and oxidation of graphite in narrow outward migrating transition zones adjacent to the gneiss followed by the breakdown of garnet and the neoblastesis of hypersthene in the central charnockite zone compared to the host gneiss the charnockite shows higher concentrations of k na sr ba and zn and lower concentrations of mg fe ti v y zr and the hree with a complementary pattern in the narrow transition zones of biotite breakdown the p lith t x h2o data and chemical zonation patterns indicate charnockitization through subsolidus dehydration reaction in an open system subsequent residence of the carbonic fluids in the charnockite resulted in low grade alteration causing modification of the syn charnockitic elemental distribution patterns and the properties of entrapped fluids we favour an internally controlled process of arrested charnockitization in which during near isothermal uplift the release of carbonic fluids from decrepitating inclusions in the host gneiss into simultaneously developing fracture zones led to a change in the fluid regime from fluid absent in the gneiss to fluid present in the fracture zones and to the development of an initial fluid pressure gradient triggering the dehydration reaction

oxygen isotope evidence for high altitude snow in the laramide rocky mountains of north america during the late cretaceous and paleogene the 18 o values of river waters in late cretaceous and paleogene basins of alberta montana wyoming and colorado are calculated from the isotopic composition of unaltered aragonite mollusk fossils the isotopic composition of these river waters has significant implications for the uplift and climate history of the mountains surrounding the basins our data show that the 18 o values of river water varied dramatically ranging from 23 to 5 relative to vienna standard mean ocean water with an uncertainty of 2 close stratigraphic association of river deposits with very different isotopic values indicates two different water sources rainfall in the warm low elevation basins and snowfall in surrounding mountains the 18 o difference between basinal and highland precipitation suggests that local relief was similar to today9s on the order of 2 5 3 km seasonal variation in shell 18 o values also indicates that there are times when large snow fields in the maastrichtian and paleocene mountains of montana and wyoming survived summer melting and were multiannual features

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