tectonically driven underfilled overfilled cycles the middle cretaceous in the northern cordilleran foreland basin abstract it is shown that the middle cretaceous succession in the northern cordilleran foreland basin consists of several million year tectonically driven cycles comprising two components strata deposited in an underfilled basin with a prominent forebulge zone and strata deposited in an overfilled basin lacking evidence of a forebulge the episodic thrusting of the cordilleran orogenic wedge and its rich sediment supply to the basin are two main controlling factors for the formation of these cycles a qualitative model of several million year tectonically driven underfilled overfilled cycle for migration and stratigraphic fill in this basin is proposed during the early underfilled period orogenic loading period due to orogenic loading of emplaced thrust sheets flexural subsidence is created in the region proximal to the mountain belt and a prominent forebulge is developed during the late underfilled period early orogenic unloading period as the cratonward migration of the subsidence center of sediment loading in the foredeep zone forebulge zones and backbulge zones migrate cratonwards forming a diachronic erosion surface in the central basin during the overfilled period late orogenic unloading period a prominent erosion forms in the proximal basin and a peripheral sag develops above the forebulge area of the previous underfilled period this model may provide a pattern to subdivide sedimentary successions in the cordilleran foreland basin using this model alternative interpretations are suggested for some important but controversial stratigraphic phenomena in the cretaceous cordilleran foreland basin traditionally defined eustatic highstands wide sedimentation area of the basin erosion surfaces and widespread subtle topographic uplifts in the central basin high frequency coarsening up cycles extensively distributed erosive based sandstones and conglomerates enclosed in marine mudstones

potential analogues for paleoclimatic variations in eastern interior alaska during the past 14 000 yr atmospheric circulation controls of regional temperature and moisture responses the paleoclimatic history of a region can be viewed as a series of surface temperature and moisture anomalies through time the effects of changes in large scale climatic controls e g insolation major circulation controls can be mediated by the influence of smaller scale controls e g topographic barriers coastlines this may result in heterogenous surface climatic responses at the regional and sub regional scale divergent paleoclimatic trajectories between regions may be explainable in terms of such meso scale patterns using modern analogues for paleoclimate we examine how the sequence of climatic variations in eastern interior alaska during the interval 12 000 0 14c yr bp could have been generated by specific atmospheric circulation patterns fossil pollen and lake level records document the long term trends in temperature and effective moisture for the region water balance modelling provides additional estimates of paleoprecipitation synoptic climatological patterns are described using the modern instrumental record of upper level and sea level pressure surface temperature and precipitation at 12 000 14c yr bp eastern interior alaska was cooler and drier than present a situation generated today by a southward displacement of the jet stream conditions warmer and drier than present at 9000 14c yr bp may have been generated by increased ridging north of alaska and a weakened westerly circulation warmer wetter conditions than present possibly prevailed in the late middle holocene these might reflect ridging over alaska and troughing further west cool wet conditions feature enhanced westerly flow into alaska through an eastward shift in the east asian trough and positive pressure anomalies in the north pacific they may be analogous to cold periods of the little ice age the analogues demonstrate how surface conditions in other parts of beringia may sometimes be similar to while at other times different from those in the eastern interior these broader spatial patterns provide hypotheses about past climates that can be tested with paleoclimatological data for example the widespread positive temperature anomalies associated with the warm dry 9000 14c yr bp analogue fit with the expansion northward of the eastern siberian treeline the anomalously cool conditions in northeast siberia associated with the warm wet analogue may explain the continued late middle holocene treeline advance in alaska while there was retreat in siberia

the alberta foreland basin relationship between stratigraphy and cordilleran terrane accretion events a foreland basin sequence resulting from accretion of a terrane to a continental passive margin ideally should be unconformity bounded with a shallowing upward pattern like the classic flysch to molasse sequence of alpine foreland basins the basal unconformity is cut as the peripheral bulge associated with lithospheric flexure migrates cratonward ahead of the basin and the advancing overthrusts the shallowing occurs because sediment supply at first is low early stages of accretion near the continental slope generate little or no topography above sea level later stages result in significant tectonic uplift and much sediment is shed into the foreland filling the basin the upper unconformity is cut as lithospheric bending stresses are relaxed following overthrusting and reduction of the flexural load on the lithosphere through erosion and or tectonic denudation of the overthrusts causes regional uplift or basin rebound actual sequences show differences from this idealized version in that i

eastward tectonic migration and transition of the jurassic cretaceous andean type continental margin along southeast china abstract a mesozoic andean type active continental margin is believed to have developed along the southeast china continental margin which has been investigated in detail however the architecture and evolution of its retroarc arc forearc system which is important for us to understand the interaction or connection between continental and oceanic lithospheres are ambiguous using multiple disciplinary data comprising seismic profiles field observations and numerical paleo topographies this study synthetically focused on the jurassic cretaceous evolution and geodynamics of the andean type southeast china continental margin subduction of the paleo pacific plate was initiated during the early jurassic 200 ma generating a nne striking jurassic magmatic arc along the east china sea bounded by imbricate thrust faults on both sides and coinciding with a paleo topographic coastal mountain range while the jurassic arc erupted along an ene striking triassic suture zone in the northern south china sea dominated by the tethyan tectonic domain and overprinted by the pacific tectonic domain the jurassic coastal mountain range began to collapse and transited into a rift basin at 135 ma and then the andean type continental margin gradually switched to the western pacific type during the late cretaceous 100 72 ma accompanied by jurassic thrust faults inverting into cretaceous detachment faults and magmatic arc migrated eastward to the taiwan rukyu areas such eastward tectonic migration and transition is associated with the eastward retreat of the subducted paleo pacific slab then a regional latest cretaceous 72 66 ma compression prevailed southeast china probably related to ridge subduction when the pacific plate replaced the paleo pacific plate to subduct beneath east asia

late quaternary vegetation history of the fishhook bend area porcupine river alaska ped pond is a lake lying in a pleistocene scour channel of the porcupine valley the valley is considered to be a possible path of late quaternary species migrations between interior alaska and northwest canada pollen in the oldest lake sediments ca 13 000 years old indicates that shrub birch and willow probably occurred locally in a sparsely vegetated herb dominated landscape populus juniperus and typha latifolia increased about 10 000 years ago suggesting particularly warm temperatures during the early holocene picea glauca which is presently common in the surrounding forests first arrived near ped pond about 8500 years ago this arrival date together with existing evidence from other sites indicates that spruce expanded rapidly across far eastern beringia 8000 9000 years ago other boreal forest taxa picea mariana betula papyrifera and alnus spp became established locally between 7000 and 8000 years bp a date of ca 7500 years bp at ped pond suggests that the alnus rise in northeast

interglacial deposits at birch creek northeast interior alaska abstract a 12 m sequence of lake sediment and peat in a 45 m high exposure on birch creek northeast alaska contains pollen of picea betula alnus and populus and wood of picea and populus this sequence which may represent 10 000 yr of more of accumulation is beyond the limit of radiocarbon dating it lies between two units of loess the underlying loess lies above the old crow tephra recently dated at 149 000 13 000 yr b p the lake sediments probably were deposited during the last interglaciation isotope substage 5e and subsequently buried by wisconsinan loess analogs for the ancient lake may be deep long lived thaw lakes that are present in the modern landscape when birch creek is correlated with other sites across nonglaciated alaska and northwest canada there appears to be a common interglacial signal in sediments overlying the old crow tephra

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

simulation of foreland basin stratigraphy using a diffusion model of mountain belt uplift and erosion an example from the central alps switzerland foreland basin stratigraphy can be considered as the result of three interacting processes thrust deformation which builds the tectonic load sedimentary and erosional processes which redistribute that load and the flexural response of the lithosphere the resultant stratigraphy of foreland basins is commonly composed of a small number of shallowing and coarsening upward cycles bounded by regional unconformities to understand the development of these unconformities we present a simple model of these three processes coupling an evolving thrust wedge on a linear elastic plate with erosion and sedimentation defined by the diffusion equation applied to topography our model demonstrates the development of regional unconformities without recourse to either eustasy or complex viscoelastic models for the continental lithosphere the model describes the thrust wedge foreland basin system in terms of four parameters 1 the effective elastic thickness of the foreland plate te 2 the sediment transport coefficient k 3 the thrust wedge advance rate 4 the surface slope of the thrust wedge the model is applied to the oligocene miocene north alpine foreland basin nafb of eastern switzerland the stratigraphy of the nafb can be simplified into two large scale shallowing upward cycles separated by an unconformity at the base of the burdigalian 22 ma geological information is taken from the nafb to estimate suitable values for the parameters listed above assuming a linear elastic lithospheric rheology the te value is estimated at 10 5 km from decompacted sediment columns data to constrain the sequential development of the thrust wedge come from structural geology the early stages 40 24 ma of compression involved a relatively low angle thrust wedge with an advance rate of approximately 2 4 mm yr at about 24 ma the wedge advance slowed down and thickened by underplating crystalline basement of the foreland plate the value for the transport coefficient has been estimated from previous studies prior to attempting to simulate the broad scale geometry of the nafb the role of each parameter was assessed individually the values for te and k are held constant throughout the simulation of the nafb at 7 5 km and 500 m yr respectively the geometry of the base burdigalian unconformity is reproduced by variations in the parameters describing the thrust wedge the surface slope angle of the wedge is increased from 2 5 to 4 over 0 2 m y and the rate of thrust advance is decreased from 2 mm yr to 0 2 mm yr during the thickening event between 24 and 23 8 ma the rejuvenation of the internal parts of the thrust load causes backtilting of the foreland basin sediments and after a time lag erosion of the distal stratigraphy over the forebulge so simulating the base burdigalian unconformity

a 130 0 year history of vegetation and environmental change at jan lake east central alaska pollen stomates and macrofossils were analysed from a 3 63 m sediment core at jan lake eastcentral alaska in order to improve spatial resolution of patterns of vegetation history in this region the chronology was based on 19 ams 14c dates on plant macrofossils and concentrated pollen zone jan i 12400 11 600 yr bp records a unique herb tundra pollen assemblage particularly high in chenopodia ceae adding supporting evidence for a spatial mosaic of lateglacial vegetation in east central alaska unexpected pollen of picea betula and alnus in lateglacial sediments appears to arise from reworking of older pollen bearing deposits according to a radiocarbon date of 22180yr bp on a pollen sample shrub betula tundra dominates zone jan il 11 600 10000 yr bp with indications of climatic amelioration tree species populus picea glauca betula papyrifera began to arrive in zone jan illa 9200 6600 yr bp and the modern boreal forest including alnus and picea mariana became established during zone j

the cretaceous tertiary boundary in the central alberta foothills i stratigraphy the cretaceous tertiary boundary in the rocky mountain foothills occurs within a continental sequence carrying economic coal deposits and known as the coalspur formation this formation occurs between the fluvial brazeau below and paskapoo formations the exact position of the boundary is located at the base of the lowest coal mynheer within the coalspur formation the initiation of coal deposition in the coalspur formation is not a unique event as it is consistent with the cyclic pattern established within the underlying brazeau formation however the magnitude and lateral continuity of coal zone development far exceed those found in the underlying formation the classic shift from a diverse late maastrichtian flora within which angiosperm and especially aquiloid pollen are prominent to a low diversity early paleocene flora dominated by gymnosperm pollen and miospores is documented deviations from most previously recognized floral events at the cretaceous tertiary boundary include 1 san angio

lake morphometry sediment mixing and the selection of sites for fine resolution palaeoecological studies abstract palaeoecologists are increasingly using close interval or continuous sampling of lake sediments to construct fine resolution records of environmental change the degree of temporal resolution sought in these studies is typically decades or years the use of lake sediments for such fine resolution reconstructions assumes that temporal mixing of the sediments is negligible in this paper we examine the physical and biological processes that cause sediment mixing in small lakes we use physical models and empirical data to develop a set of heuristics relating lake depth and area to sediment mixing by slumping waves currents and bioturbation we also develop a heuristic that allows information on lake depth and area to be used to determine if the sediments of a lake will likely be massive or annually laminated in general the degree of sediment mixing likely to occur in a small lake is directly related to the depth and surface area of the lake however each of the agents of mixing has a different critical relationship with lake depth and surface area we present a series of equations and a summarizing figure that based on lake surface area and maximum depth allows the type of thermal stratification polymictic dimictic or meromictic and the degree of sediment mixing present in the lake to be inferred

macrofossil magnetobiostratigraphy for the upper santonian lower campanian interval in the western interior of north america comparisons with european stage boundaries and planktonic foraminiferal zonal boundaries magnetostratigraphic samples were collected from the milk river and pakowki formations of southeastern alberta to determine the polarity chron 34 33r boundary this boundary was located in the upper half of the deadhorse coulee member and is below the first local occurrence of the western interior ammonite baculites obtusus comparison with the laterally equivalent eagle sandstone of montana and niobrara formation of colorado indicates that the 34 33r contact is within either the baculites sp smooth or baculites sp weak flank ribs ammonite zone in the western interior of north america direct correlation of the desmoscaphites erdmanni through baculites asperifomis western interior ammonite zones with magnetobiostratigraphic sections of the upper santonian lower campanian stages in europe suggests that i the santonian campanian boundary as defined in europe is within the lower baculites obtusus zone and ii the western interior appearance of some ammonites and crinoids scaphites hippocrepis trachyscaphites spiniger marsupites uintacrinus is profoundly time transgressive relative to the appearance of these same species in europe the date of 84 ma for the santonian campanian boundary is too old and a date of around 80 ma may be more accurate the santonian campanian boundary defined by ammonites crinoids and belemnites in europe is within the lower part of chron 33r and is younger than the santonian campanian boundary as determined by planktonic foraminifera at gubbio italy

strike variability of clastic depositional systems does it matter for sequence stratigraphic analysis current sequence stratigraphic models are two dimensional in nature and predict variability in depositional dip sections strike and dip variability of sediment supply to clastic depositional systems causes significant changes to sequence architecture so that contrasting yet coeval stacking patterns result these changes ultimately affect prediction potential based on fixed systems tract stacking patterns and relation to relative sea level curves identification of key surfaces in sequences rather than stacking patterns is the most reliable indicator of relative sea level history

concept and styles of reciprocal stratigraphies western canada foreland system the late cretaceous palaeocene western canada foreland system provides a record of high frequency cycles of reciprocal flexural tectonics superimposed on longer term changing dynamic subsidence initial dominance of dynamic subsidence during the deposition of the bearpaw marine succession resulted in continual subsidence with differential rates across the flexural hinge line subsequent dominance of flexural tectonics resulted in opposite base level changes between the proximal and distal reaches of the foreland system during the deposition of the post bearpaw nonmarine succession in both cases the contrasting base level changes generated out of phase stratigraphic sequences which defines the concept of reciprocal stratigraphies two styles of reciprocal stratigraphies have been identified in relation to the pattern of base level changes across the foreland system the bearpaw style consists of a conformable succession of correlative transgressive and regressive systems tracts suggesting continuous basin wide sedimentation with the rates within the range of variation of the rates of base level rise the post bearpaw style shows sequences correlative to age equivalent sequence boundaries related to coeval rising and falling base level respectively the succession of bearpaw and post bearpaw sequences corresponds to a cycle of marine to nonmarine foreland sedimentation controlled by changing ratios between dynamic subsidence and flexural tectonics the amount of sediment supply derived from the orogen to the foreland system may also reflect the rates of dynamic subsidence as a decrease in dynamic loading may lead to accelerated denudation of the sediment source areas

alluvial history of the porcupine river alaska role of glacial lake overflow from northwest canada the stratigraphy and morphology of alluvial terraces in the lower porcupine valley permit the definition of twelve river stages each marked by distinctive surface characteristics sediment composition and regional gradient terraces that exhibit characteristics suggestive of extremely high discharge such as coarse bouldery braided gravel surfaces and intense scouring formed at times when the porcupine river at the ramparts acted as an overflow outlet for glacial lakes in northern yukon territory which had been impounded by the lauren tide ice sheet terraces capped by sediment suggestive of relatively low discharge meandering streams and which were strongly affected by coleen river drainage probably formed when glacial lake overflow did not occur ten radiocarbon dates on alluvial sediments from the lower porcupine river range from greater than 35 000 to 2 350 55 yr b p when combined with geomorphologic interpretations on terraces in alaska and with radiocarbon dates from northern yukon territory these dates suggest repeated glaciolacustrine innundations of the old crow and bluefish basins during wisconsinan time

a late wisconsin and holocene vegetation history from the central brooks range implications for alaskan palaeoecology abstract five pollen diagrams reveal late wisconsin and holocene vegetation changes in the walker lake alatna valley region of the central brooks range approximately 100 km west of the area studied by d a livingstone 1955 ecology 36 587 600 new insights into the vegetation history of this region are provided by calculations of pollen influx and by the use of linear discriminant analysis to separate picea glauca and p mariana pollen three major pollen zones are identified 1 a basal herb zone characterized by high percentages of cyperaceae gramineae salix and artemisia and low total pollen influx 2 a shrub betula zone with increased total pollen influx and very high percentages of betula pollen predominantly in the size range of b nana and b glandulosa and 3 and alnus zone dominated by alnus pollen lakes currently within the boreal forest or near tree line show relatively high percentages of picea pollen in the alnus zone several striking vegetation changes occurred between ca 10 000 and 7000 yr b p between ca 11 000 and 10 000 yr b p populus balsamifera pollen percentages as great as 30 indicate that this species was present at low elevation sites near walker lake these populations declined abruptly ca 10 000 yr ago and have never regained prominence about 8500 yr b p picea glauca pollen reached 10 15 indicating the arrival of p glauca in or near the study area p glauca populations evidently decreased ca 8000 yr ago when picea pollen percentages and influx fell to low values about 7000 yr b p alnus pollen percentages and influx rose sharply as alder shrubs became established widely picea once more expanded ca 5000 yr ago but these populations were dominated by p mariana rather than p glauca which increased slowly at this time and may still be advancing northward some vegetation changes have been remarkably synchronous over wide areas of interior alaska and probably reflect responses of in situ vegetation to environmental changes but others may reflect the lagged responses of species migrating into new areas

cliff top eolian deposits and associated molluscan assemblages as indicators of late pleistocene and holocene environments in beringia abstract northern yukon cliff top eolian deposits are indicators of past climates and environments the deposits are located along the ramparts of the porcupine river near the international boundary these eolian deposits resulted from southwest wind regimes that operated at about 14 860 bp and more certainly at 11 640 8200 bp and from 4600 bp to present palynological analysis indicates that these three periods were marked by different vegetation covers the earliest one being dominated with cyperaceae the intermediate one by shepherdia canadiensis and the most recent one by spruce picea molluscs are particularly numerous and diversified which suggests that the cliff top deposits were important refuges for these animals molluscan assemblages indicate that the climate was wetter at about 14 860 bp than between 11 640 bp and 8200 bp the xeric regime that marked the latter period is also indicated by gypsum concretions it is suggested that the molluscs could have been introduced by migratory birds that in turn would also have been able to use the snail shells from the eolian deposits as an important dietary element it is also suggested that the molluscs are relicts of endemic fauna

assimilation of simulated polarimetric radar data for a convective storm using the ensemble kalman filter part i observation operators for reflectivity and polarimetric variables abstract a radar simulator for polarimetric radar variables including reflectivities at horizontal and vertical polarizations the differential reflectivity and the specific differential phase has been developed this simulator serves as a test bed for developing and testing forward observation operators of polarimetric radar variables that are needed when directly assimilating these variables into storm scale numerical weather prediction nwp models using either variational or ensemble based assimilation methods the simulator takes as input the results of high resolution nwp model simulations with ice microphysics and produces simulated polarimetric radar data that may also contain simulated errors it is developed based on calculations of electromagnetic wave propagation and scattering at the s band of wavelength 10 7 cm in a hydrometeor containing atmosphere the t matrix method is used for the scattering calculation of raindrops and the rayleigh scattering approximation is applied to snow and ha

comparison of disdrometer and x band mobile radar observations in convective precipitation abstractmicrophysical data from thunderstorms are sparse yet they are essential to validate microphysical schemes in numerical models mobile dual polarization x band radars are capable of providing a wealth of data that include radar reflectivity drop shape and hydrometeor type however x band radars suffer from beam attenuation in heavy rainfall and hail which can be partially corrected with attenuation correction schemes in this research the authors compare surface disdrometer observations to results from a differential phase based attenuation correction scheme this scheme is applied to data recorded by the national oceanic and atmospheric administration noaa x band dual polarized noxp mobile radar which was deployed during the second verification of the origins of rotation in tornadoes experiment vortex2 results are presented from five supercell thunderstorms and one squall line 183 min of data the median disagreement radar disdrometer in attenuation corrected reflectivity z and

temporal significance of sequence boundaries abstract this paper analyses the temporal significance of stratigraphic surfaces bounding the marine portions of the depositional sequence genetic stratigraphic sequence and transgressive regressive sequence these bounding surfaces known as the correlative conformity c c maximum flooding surface mfs and conformable transgressive surface cts respectively may either be defined on the basis of stratal stacking patterns which we call type a surfaces or on the basis of water depth changes and relative sea level changes which we call type b surfaces the type a mfs and cts are time lines in a depositional dip section corresponding to the turnaround points from shoreline transgression to regression and vice versa they separate prograding coarsening upward from retrograding fining upward geometries with a timing determined by the interplay between the rates of sedimentation and relative sea level rise in the shoreline area the timing of type a mfs and cts is not affected by the offshore variations in sedimentation and subsidence rates but it is only controlled by the shoreline movements and the associated facies shifts the type a c c separates rapidly prograding and offlapping forced regressive strata from the overlying lower rate prograding and aggrading normal regressive strata this surface is diachronous younger basinward with the rate of offshore sediment transport the timing of the type a c c in the shoreline area corresponds to the end of relative sea level fall but it develops under relative sea level rise conditions offshore the timing of the type b mfs and cts depends on the offshore variations in the sedimentation and subsidence rates these surfaces defined on the basis of bathymetric changes become younger and older seaward respectively tending to merge together offshore the type b c c marks the end of relative sea level fall in any point along a depositional dip section it is diachronous older basinward as its timing depends on the offshore variations in subsidence rates the diachroneity of type b surfaces reaches a quarter of the period of the highest frequency variable whichever that is among the eustasy tectonics or sedimentation controls types a and b surfaces merge together in the shoreline area but they become temporally divergent offshore deepening upward and shallowing upward facies should not be confused with transgressive and regressive systems tracts the latter are strictly controlled by the shoreline movements which determine the direction of facies shifts and the stratal stacking patterns

origin of last glacial loess in the western yukon tanana upland central alaska usa loess is widespread over alaska and its accumulation has traditionally been associated with glacial periods surprisingly loess deposits securely dated to the last glacial period are rare in alaska and paleowind reconstructions for this time period are limited to inferences from dune orientations we report a rare occurrence of loess deposits dating to the last glacial period 19 ka to 12 ka in the yukon tanana upland loess in this area is very coarse grained abundant coarse silt with decreases in particle size moving south of the yukon river implying that the drainage basin of this river was the main source geochemical data show however that the tanana river valley to the south is also a likely distal source the occurrence of last glacial loess with sources to both the south and north is explained by both regional synoptic scale winds from the northeast and opposing katabatic winds that could have developed from expanded glaciers in both the brooks range to the north and the alaska range to the south based on a comparison with recent climate modeling for the last glacial period seasonality of dust transport may also have played a role in bringing about contributions from both northern and southern sources

polarimetric radar modeling of mixtures of precipitation particles with the advances of dual polarized radar techniques in meteorology it is now possible to deduce precipitation microphysical characteristics in far more detail than possible with reflectivity measurements alone radar parameters such as differential reflectivity and differential phase between horizontal and vertical polarizations have been studied in detail as well as linear depolarization ratio copolar correlation coefficient and backscatter differential phase while these parameters can be linked to certain microphysical properties of specific classes of precipitation such as raindrops or hail very little study has been directed at the practically important cases of mixtures of different types of precipitation particles such as rain hail graupel ice crystals and snow each type can have different size shape orientation and dielectric constant distributions the present treatment is rigorous and is based on the mueller matrix formulation radar parameters are derived from the averaged mueller matrix computations careful consideration is given to the orientation and size distributions of the different particle types after calculating single particle scattering characteristics some simple two component mixtures such as rain hail and ice crystals snow are considered finally a 2d numerical cloud model is used to simulate the rain hail graupel and snow fields of an evolving convective storm from which the radar parameters are derived for the initial peak and dissipating stages of the storm model computations are performed at c and s band frequencies

ostracode geochemical record of holocene climatic change and implications for vegetational response in the northwestern alaska range abstract trace element analysis of the calcareous shells of ostracodes in a sediment core from farewell lake provides the first limno geochemical record for climatic reconstructions in alaska when compared with pollen data from the same site this record offers new insights into climatic controls over vegetation dynamics during the holocene the low mg ca ratios and high sr ca ratios suggest that a relatively cold dry climate prevailed in this region between 11 000 and 9000 yr b p uncalibrated14c ages are used throughout the paper this result contrasts with previous interpretations of a thermal maximum at this time corresponding to the widespread establishment ofpopuluswoodland forest the trace element record suggests instead that the warmest period of the early holocene at farewell lake was between 8500 and 8000 yr b p during the decline ofpopulus marked decreases in sr ca and mg ca suggest a major increase in effective moisture around 6500 yr b p which coincided with the establishment ofpiceaboreal forests in the farewell lake region this climatic change was probably widespread throughout much of alaska and adjacent canada and might have induced the rapid spread ofalnusand the shift frompicea glaucatop marianadominance across that region our geochemical record also suggests that the late holocene climate history was more complex than previously thought on the basis of palynological studies according to this record growing season temperatures increased 6000 4500 yr b p decreased 4500 1500 yr b p and increased with fluctuations afterward after 6000 yr b p stratigraphic changes in pollen percentages ofpiceaappear to be positively related with those of mg ca this relationship implies that once the threshold of effective moisture was crossed for the establishment ofpiceaforests temperature was the primary control ofpiceapopulation density

recognition of forebulge unconformities associated with early stage foreland basin development example from the north alpine foreland basin the peripheral upwarp forebulge associated with early foreland basin evolution may be recorded as an unconformity at the base of the foreland basin fill a forebulge unconformity represents a distinctive type of megasequence boundary forward modeling of foreland flexure illustrates the expected geometry of an unconformity cut by erosion of the forebulge during the early stages of foreland basin development internal conformity a zone of rapid increase in the depth of erosion and an external zone of steady state stratigraphic gap this geometry is modified by the preexisting bathymetry and by eustatic sea level changes which result in the formation of a composite unconformity however the geometry of the unconformity and the onlap of the overlying sediments are fund mentally different from those associated with a major eustatic sea level fall and represent a distinctive assemblage of petroleum play components producing hydrocarbon accumulations are associated with both forebulge arching and truncational unconformity traps modeling achieves an accurate simulation of the geometry and stratigraphic gap of the basal unconformity of the north alpine foreland basin switzerland further support for the flexural forebulge interpretation is provided by facies patterns in the overlying sediments suppression and smothering of forebulges during the late molasse stage of foreland basin development coupled with the cannibalization of the early flysch stage stratigraphy by the advancing orogenic wedge may limit the formation and recognition of forebulge unconformities model results may be helpful in predicting the timing duration and amount of uplift associated with flexural forebulges and thereby aid in assessing petroleum play potential particularly the formation of traps and the development of enhanced porosity

tectonic control on fluvial styles the balfour formation of the karoo basin south africa abstract the balfour formation represents a fully fluvial succession of late late permian earliest triassic age which accumulated in the foredeep of the karoo basin during the overfilled phase of the foreland system the lack of a coeval marine environment within the limits of the preserved karoo basin provides an opportunity to study the stratigraphic cyclicity developed during a time when accommodation was solely controlled by tectonics the balfour stratigraphy is composed of a succession of six third order fluvial depositional sequences separated by subaerial unconformities they formed in isolation from eustatic influences with a timing controlled by orogenic cycles of loading and unloading sediment accumulation took place during stages of flexural subsidence whereas the bounding surfaces are related to stages of isostatic uplift the vertical profile of all sequences displays an overall fining upward trend related to the gradual decrease in topographic slope during orogenic loading at the same time an upward change in fluvial styles can be observed within each sequence from initial higher to final lower energy systems the actual fluvial styles in each location depend on paleoslope gradients and the position of the stratigraphic section relative to the orogenic front proximal sequences show transitions from braided to meandering systems whereas more distal sequences show changes from sand bed to fine grained meandering systems the average duration of the balfour stratigraphic cycles was 0 66 my i e six cycles during 4 my no climatic fluctuations are recorded during this time with the long term climatic background represented by temperate to humid conditions

palynostratigraphic zonation of paleocene strata in the central and south central alberta plains paleocene strata of the scollard and paskapoo formations in the central and south central alberta plains can be subdivided into five formal biostratigraphic zones based in part on a momipites cary

a unique lower paleocene shelf sea chalk in the eastern u s gulf coastal plain clayton formation western alabama implications for depositional environment sea level dynamics and paleogeography abstract the deposition of carbonate oozes in shelf sea settings so prevalent during the cretaceous generally ceased by the onset of the paleogene in response to sea level fall however the lower paleocene danian clayton formation exposed at moscow landing in western alabama u s a contains a thin chalk bed the clayton chalk that records a later final phase of shelf sea carbonate ooze deposition in the u s eastern gulf coastal plain sedimentologic character ichnology and foraminiferal assemblages indicate deposition in an outer shelf setting comparable to that for cretaceous chalks exposed in the gulf region i e campanian demopolis chalk at depths of 90 m or more during a brief transgressive pulse peaking circa 63 8 63 2 ma this transgression occurred 1 myr after the maximum expansion of the danian cannonball sea in the north american western interior presumably reflecting different controls on sea level dynamics eustasy vs laramide tectonism and isostasy although regional paleogeography for the early paleocene is poorly constrained deposition of the clayton chalk suggests that the eastern gulf seaway at times extended much further north than implied by the presently mapped updip limit of preserved paleocene marine strata the apparent geographic restriction of this unique paleocene shelf sea chalk indicates that relative sediment starvation and associated carbonate ooze deposition may have been influenced by local structural controls operating along the eastern margin of the mississippi embayment

thrust loads and foreland basin evolution cretaceous western united states two dimensional modeling of loading during the formation of the idaho wyoming thrust belt shows that regional isostatic compensation by flexure of an elastic lithosphere is sufficient to control the formation of a foreland basin the flexural rigidity of the lithosphere is inferred to have been approximately 1023 nm 1030 dyne cm on the basis of palinspastic comparison of predicted downwarping due to the thrust plate loads to the shape of the sedimentary wedge on the west side of the cretaceous western interior seaway erosion of part of the uplifted thrust plates redistributed the load depositing it farther to the east thereby causing subsidence over a much wider area than could have been accomplished only by the loading by thrust plates paleotopography after major cretaceous thrust events was calculated the resulting mountainous terrain gentle alluvial plain and flat sea floor correspond well with the topography of the modern foreland thrust belt and basin system in the andes of south america and to paleogeographic reconstructions in the western united states thrust belt topography is controlled by the subsurface geometry of the thrust faults particularly the positions of ramp zones and by isostatic subsidence

late quaternary lake records from the anadyr lowland central chukotka russia abstract three lake cores provide insight into the vegetation and climate history of the past 45 000 14c yr in the anadyr lowland a key paleogeographic link between the bering land bridge blb and interior western beringia wb although not without chronological issues these records suggest that the late pleistocene interstade approximating oxygen isotope stage ois 3 was a time of unstable environments consistent with previous interpretations for southern areas of wb and in contrast to more stable conditions inferred for northern wb a hiatus in the records during ois2 implies dry frigid environments in the anadyr lowland previous research suggested that chuktoka was a westward extension of relatively mesic environments of the blb which acted as a filter to intercontinental migrations the lowland data indicate that chukotka may have been more of a transitional zone between mesic blb and more xeric regions of western wb a structurally novel biome dominated by deciduous forest and high shrub tundra was proposed as occupying much of beringia between 11 000 and 9000 14c yr bp the unusual pollen assemblage that characterizes the lowland suggests that perhaps a second biome was also present in beringia one that was dominated by meadows with betula shrub thickets

climate change and arctic ecosystems 1 vegetation changes north of 55 n between the last glacial maximum mid holocene and present a unified scheme to assign pollen samples to vegetation types was used to reconstruct vegetation patterns north of 55 n at the last glacial maximum lgm and mid holocene 6000 years b p the pollen data set assembled for this purpose represents a comprehensive compilation based on the work of many projects and research groups five tundra types cushion forb tundra graminoid and forb tundra prostrate dwarf shrub tundra erect dwarf shrub tundra and low and high shrub tundra were distinguished and mapped on the basis of modern pollen surface samples the tundra forest boundary and the distributions of boreal and temperate forest types today were realistically reconstructed during the mid holocene the tundra forest boundary was north of its present position in some regions but the pattern of this shift was strongly asymmetrical around the pole with the largest northward shift in central siberia 200 km little change in beringia and a southward shift in keewatin and labrador 200 km low and high shrub tundra extended farther north than today at the lgm forests were absent from high latitudes graminoid and forb tundra abutted on temperate steppe in northwestern eurasia while prostrate dwarf shrub erect dwarf shrub and graminoid and forb tundra formed a mosaic in beringia graminoid and forb tundra is restricted today and does not form a large continuous biome but the pollen data show that it was far more extensive at the lgm while low and high shrub tundra were greatly reduced illustrating the potential for climate change to dramatically alter the relative areas occupied by different vegetation types

large scale stratigraphic architecture eustatic variation and unsteady tectonism a theoretical evaluation we incorporate a process based depositional model with basin subsidence models to predict stratigraphic records this allows us to investigate the importance of subsidence geometry on coastal stratigraphy and thus to characterize and compare the stratigraphic architecture of two categories of tectonic basins the models demonstrate that the correlation of stratigraphic sequences to eustatic cycles is not the same in passive margin basins as in foreland basins and that in a foreland basin the record of episodic tectonism is distinct from that of eustatic sea level change in the model sediment transport is approximated by slope controlled diffusion nonmarine transport is treated as more efficient diffusion than marine transport three different subsidence and sediment supply models are examined a simple passive margin basin a simple foreland basin and then a foreland basin for which vertical motions are driven by thrust shortening that is compensated flexurally and for which sediment supply is related to relief predicted passive margin stratigraphies for cases of varying eustatic sea level are similar to those of natural basins and include progradational packages and subaerial unconformities which are used to define sequence boundaries that form during sea level fall we explore the timing relationships between stratigraphic features and a sinusoidal sea level history showing that the phase relationship depends on subsidence sediment flux efficiency of sediment transport and period and amplitude of sea level when the basic geometry of the basin is inverted placing the sediment supply on the side with maximum subsidence as is the case in foreland basins the sequence character changes markedly subaerial erosion does not generate unconformities in the models of a dynamic foreland basin sediment supply and subsidence are linked to the structure of the flanking thrust belt and are not necessarily constant for steady thrusting and variable sea level unconformities that define sequence boundaries form only on the distal or forebulge side of the basin and the ages of the sequence boundaries correlate to limes of rising sea level in cases of constant sea level but variable thrusting subaerial unconformities are cut locally on both the proximal margin of the basin and the distal margin of the basin yet the ages of the proximal margin and distal margin unconformities are out of phase in the tectonic cycle erosion is most pronounced during quiescence on the proximal side and during thrusting on the distal side

notes and correspondence polarimetric radar observation of multiple freezing levels abstract an unusual multiple freezing level event observed with polarimetric radar during the second phase of the improvement of microphysical parameterization through observational verification experiments improve 2 field program is described the event occurred on 28 november 2001 when a warm front moved over the oregon cascade mountains as the front approached an elevated melting layer formed above a preexisting melting layer near ground continued warming of the lower atmosphere eventually dissipated the lower melting layer the polarimetric measurements are used to estimate the height of the freezing levels document their evolution and deduce hydrometeor habits the measurements indicate that when the two freezing levels were first observed melting was incomplete in the upper melting layer and characteristics of particles that passed through the two melting layers were similar as warming progressed the character of particles entering the lower melting layer changed possibly becoming ice pell

time place and mode of propagation of foreland basin systems as recorded by the sedimentary fill examples of the late cretaceous and eocene retro foreland basins of the north eastern pyrenees the relationship between tectonics and sedimentary fill has been studied in two syncontractional basins of the western corbieres eastern north pyrenean retro foreland basin the late cretaceous basin formed during c 10 12 ma as a result of left lateral transpressional deformation and is composed of forward younging sub basins characterized by reworking of the forelimbs of growing fold propagation folds thrust wedge advance and cratonward migration of the platform are recorded by a deepening upward stacking pattern indicating increased regional subsidence with a limited contribution of the submarine orogen tectonic quiescence and erosional unloading lasting 29 30 ma are recorded by a shallowingupward stacking pattern and fluvial sedimentation issued from widespread sources in the emerging inner orogen the early to middle eocene basin formed as a result of pure shortening normal to the range the marine early eocene basin developed during c 2 ma by widening of a single basin provoked by the two step propagation of a basement duplex this is recorded by growth stratal patterns and coarsening upward depositional sequences indicating the increasing contribution of the emerged orogen the middle eocene continental deposits infilled two sub basins working synchronously and were transported by alluvial fans with a provenance in the inner orogen during decreasing thrust wedge advance and increasing erosional unloading

consequences of thrusting and intraplate stress fluctuations for vertical motions in foreland basins and peripheral areas summary we present a conceptual model for short term and long term alternations in subsidence and uplift in foreland basins convergence of lithospheric plates produces forces at the plate boundaries generating stresses in the accretionary wedge the underthrusted crust and the lithosphere when the stresses reach the shear strength of the rocks in these units deformation which results in the redistribution of mass takes place contemporaneously with reduction of the stress level modelling of both the effects of this alternating building up and relaxation of stress and the effects of the resulting mass redistribution on foreland basin geometry employing an elastic rheology of the lithosphere demonstrates that these processes exert an important control on the shape of foreland basins vertical motions take place on different time scales dependent on the scale of thrusting and the style of deformation short term 10 104 yr vertical motions are related to small scale thrust events while long term vertical motions are induced by larger scale deformation in the overriding thrust wedge furthermore the geometry of faults influences the duration of the magnitude of stress fluctuations stress induced alternations of subsidence may lead to the deposition of alternating sequences in foreland basins on scales of centimetres e g cyclothems to scales of several hundreds of metres on lap and off lap sequences in this respect the mechanical coupling between convergent zones and peripheral areas is of particular importance as it induces simultaneous alternations in regional facies patterns the model also provides an explanation for vertical motions in the foreland basin previously attributed to visco elastic relaxation processes

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

a squall line in southern germany kinematics and precipitation formation as deduced by advanced polarimetric and doppler radar measurements abstract a multiscale analysis of a squall line system is reported in this paper it is shown that the squall line was initiated as part of a synoptic scale frontal zone the main emphasis then is on the polarimetric and doppler radar measurements which give insight into the meso and microscale structure of the kinematics and the precipitation microphysics especially within the new cells growing ahead of the squall line and within the main precipitation system the principal polarimetric measurements considered are the differential reflectivity zdr and a related new derived parameter termed the difference reflectivity or zdp which is useful in detection of rain ice mixed phase precipitation a limited amount of time series data have been analyzed to derive the specific differential phase kdp and the backscatter differential phase between horizontal and vertical polarizations a brief overview of the microphysical interpretation of these parameters is provided the newly grown clouds are identifi

postglacial vegetation and climate change in the northern bristol bay region southwestern alaska pollen analysis of sediment cores from grandfather and ongivinuk lakes reveals a record of postglacial vegetation and climate change in the northern bristol bay region the chronology is based on six conventional 14c dates of bulk organic matter from the grandfather core a mesic herb tundra dominated the landscape 13 000 9800 yr b p betula shrubs probably first appeared in the region 11 300 yr b p but were restricted to favorable microhabitats until 9800 yr b p the later establishment of betula shrubs and relatively low betula pollen abundance in these records compared to other areas of eastern beringia suggest that postglacial warming in southwestern alaska was dampened by regional climatic controls possibly low sea surface temperatures of the north pacific ocean between 10 800 and 9800 yr b p diminished betula shrub cover along with decreased aquatic productivity as recorded by pediastrum cell nets and biogenic silica suggest a brief reversion to colder and drier climatic conditions possibly associated with the younger dryas event around 9800 yr b p betula shrub tundra and meadow communities expanded probably in response to increased temperature and precipitation alnus arrived and formed extensive thickets within the region ca 7400 yr b p the establishment of the modern boreal forest tundra ecotone is marked by the arrival of picea glauca at grandfather lake ca 4000 yr b p and the subsequent increase to present population densities ca 2000 yr b p the unique features of these pollen records emphasize the spatial complexity of late quaternary vegetation and climate history in eastern beringia

sedimentological and palynological evidence of regional climatic changes in the campanian to paleocene sediments of the rocky mountain foothills canada abstract evidence of paleoclimatic variations in the upper campanian to lower paleocene post wapiabi sequence of strata is visible both laterally between the central and southern foothills and vertically in the stratigraphic record these differences are expressed by the distribution of climatically sensitive sediments i e coal and caliche and associated palynological assemblages within floodplain facies as well as by changes in the style of fluvial channels the interpretation of a semi arid environment for mature caliche paleosols is supported by the impoverished character of the associated palynological assemblages both in terms of diversity and the number of specimens recovered and by the conspicuous presence of classopollis the lateral extent of the semiarid floodplain facies and associated broad and mobile channel deposits is limited to the southern part of the basin no signs of a caliche facies have been found in the post wapiabi strata of the central foothills instead some of the floodplain deposits associated with meandering streams in this part of the basin contain numerous thick coal bearing intervals the relative climatic differences between the more humid central part and the drier southern part of the basin prevailed throughout the entire post wapiabi interval as this cannot be satisfactorily explained by the position of the sea shore or by orographic influences alone there was probably another external factor this could have been the pattern of atmospheric circulation such as that responsible for the present day climatic differences existing between the southern and central foothills semiarid floodplain facies occur at two levels in the stratigraphic column of the southern foothills in the late campanian belly river formation and in the upper maastrichtian to lower paleocene willow creek formation they correspond to regressive episodes of the epicontinental seaway intervening between these semiarid floodplain facies are the marine shales of the bearpaw formation and both overlying and underlying them thin coal beds these represent recurrent periods of swamp growth and peat accumulation in back barrier environments lagoon fill and supratidal marsh respectively because of the proximity of these swamps to the sea shore it is difficult to assess the influence of climate on the relative humidity of these settings on strictly sedimentological grounds however the terrestrial components of the palynological assemblages recovered from these marginal marine settings and correlative lacustrine sediments containing fresh water stromatolites but no coal in the central foothills are in sharp contrast with the impoverished assemblages known from the caliche facies the former are prolific diverse and contain a number of triprojectate pollen species which indicate a relatively humid climate during the latest campanian time

late quaternary vegetational change in the kotzebue sound area northwestern alaska abstract two sediment cores from kaiyak and squirrel lakes in northwestern alaska yielded pollen records that date to ca 39 000 and 27 000 yr b p respectively between 39 000 and 14 000 yr b p the vegetation around these lakes was dominated by gramineae and cyperaceae with some salix and possibly betula nana glandulosa forming a local shrub component of the vegetation betula pollen percentages increased about 14 000 yr b p indicating the presence of a birchdominated shrub tundra alnus pollen appeared at both sites between 9000 and 8000yr b p and picea pollen mostly p mariana arrived at squirrel lake about 5000 yr b p the current foresttundra mosaic around squirrel lake was established at this time whereas shrub tundra existed near kaiyak lake throughout the holocene when compared to other pollen records from north western north america these cores 1 represent a meadow component of lowland beringian tundra between 39 000 and 14 000 yr b p 2 demonstrate an early holocene arrival of alnus in northwestern alaska that predates most other alnus horizons in northern alaska or northwestern canada and 3 show an east to west migration of picea across northern alaska from 9000 to 5000 yr b p

late quaternary pollen records from the kobuk and noatak river drainages northwestern alaska abstract pollen diagrams from joe and niliq lakes date to ca 28 000 and 14 000 yr b p respectively mesic shurb tundra grew near joe lake ca 28 000 to 26 000 yr b p with local populus populations prior to ca 27 000 yr b p shrub communities decreased as climate changed with the onset of itkillik ii glaciation 25 000 to 11 500 yr b p and graminoid dominated tundra characterized vegetation ca 18 500 to 13 500 yr b p herb tundra was replaced by shrub betula tundra near both sites ca 13 500 yr b p with local expansion of populus ca 11 000 to 10 000 yr b p and alnus ca 9000 yr b p mixed picea glauca p mariana woodland was established near joe lake ca 6000 yr b p these pollen records when combined with others from northern alaska and northwestern canada indicate 1 mesic tundra was more common in northwestern alaska than in northeastern alaska or northwestern canada during the duvanny yar glacial interval 25 000 to 14 000 yr b p 2 with deglaciation shrub betula expanded rapidly in northwestern alaska but slowly in areas farther east 3 an early postglacial thermal maximum occurred in northwestern alaska but had only limited effect on vegetation and 4 pollen patterns in northern alaska and northwestern canada suggest regional differences in late quaternary climates

low and high frequency climate variability in eastern beringia during the past 25 000 yearsthis article is one of a series of papers published in this special issue on the theme polar climate stability network we present new temperature and precipitation reconstructions for the past 25 000 cal years bp from across eastern beringia based on a network of pollen diagrams an updated modern pollen calibration database and an improved methodology using the modern analogue technique mat time series show july temperatures were around 4 c lower during full glacial and january temperatures were about 2 c lower than present annual temperatures rose beginning around 16 000 cal years bp reaching a maximum around 12 000 cal year bp the warming was more rapid in southern beringia annual precipitation varied by 250 mm during the past 25 000 cal years bp maps of reconstructed precipitation patterns show increasingly drier conditions since 12 000 cal years bp that vary regionally suggesting holocene atmospheric circulation changes at multiple time and space scales orbitally forced seasonality changes during the late glacial and early holocene resulted in reversed seasonal temperature reconstructions due to me

reciprocal stratigraphy of the campanian paleocene western interior of north america abstract the claggett bearpaw and cannonball successions campanian paleocene of the western interior foreland system were deposited during a series of regional second and third order transgressions and regressions locally modulated by fourth and lower order cycles the reciprocal flexural behaviour of the foreland lithosphere in response to orogenic cycles of loading and unloading results in out of phase sequences on opposite sides of the basin which defines the concept of reciprocal stratigraphies the proximal and distal regions of the basin are separated by a few kilometre wide hinge zone of proximal to distal facies change with the mid point taken as a stratigraphic hinge line which defines the boundary between coeval marine transgressive and regressive systems tracts or between nonmarine sequences and correlative sequence boundaries hinge lines have been mapped in alberta saskatchewan montana and wyoming for consecutive time slices during the campanian paleocene interval areally the hinge line traces a semielliptical pattern outlining the region of maximum foreland basin subsidence it migrated at 10 km ma to the north in response to late cretaceous paleocene orogenic dextral transpression the hinge line also migrated eastward during the campanian and maastrichtian in response to thrust sheet advance and westward during the paleocene in response to the redistribution of orogenic load associated with a transition from transpression to transtension possibly accompanied by a visco elastic deepening and narrowing of the foredeep

a re evaluation and spatial analysis of evidence for a younger dryas climatic reversal in beringia abstract an objective classification of paleoclimatic proxies from 75 lake and peat records is used to re evaluate data quality and inferred climatic patterns in beringia during the younger dryas mapped data reveal coherent but spatially complex regional patterns suggesting the younger dryas was characterized by 1 cooling in southern alaska eastern siberia and portions of northeastern siberia and 2 uniform to warmer than present conditions through most of central alaska northeastern siberia and possibly the russian far east and northern alaska the beringian patterns correspond to distinctive large scale climatic forcings although in some locations further modified by more local influences such as topography general circulation models and modern synoptic climatology provide a conceptual framework for exploring possible mechanisms responsible for the observed changes forcings and associated climatic responses consistent with the proxy data include 1 lowered sea surface temperatures in the north atlantic and pacific reducing temperature and precipitation in eastern siberia 2 intensified aleutian low and lowered sea surface temperatures causing cooler summers and higher winter precipitation in southern alaska 3 stronger pacific subtropical high and an eastward shift of the east asian trough reducing summer temperatures in southern alaska and causing relative warmth in northeastern siberia and 4 strong high pressure system producing warm dry conditions in interior alaska

late cretaceous to early tertiary magnetostratigraphy of a continental sequence red deer valley alberta canada the red deer valley exposes a conformable 350 m thick late campanian to early paleocene fluvial deltaic coal bearing sequence named the edmonton group systematic sampling and paleomagnetic analysis of the dominant lithologies mudstones sandstones and shales were carried out over five sections correlated by coal seams to provide some 500 sites stratigraphic levels primary detrital remanent magnetization directions after alternating field cleaning produce a polarity reversal pattern correlatable to sea floor magnetic anomalies 29 33 the campanian maastrichtian boundary based upon the first appearance of wodehouseia and the maastrichtian paleocene cretaceous tertiary boundary based upon an ir anomaly associated with dinosaur and cretaceous palynofloral extinctions correlate closely magnetostratigraphically with the marine foraminiferal section at gubbio italy radiometric dating of bentonites has indicated the ages of these boundaries to be approximately 71 and 64 ma respectively

climate and vegetation in northeastern alaska 18 000 yr b p present changing abundances of taxa in the pollen record of northeastern alaska contain a climate signal and may be compared with gcm simulations of paleoclimates cold dry conditions indicated by full glacial pollen spectra are in broad agreement with model simulations successive expansion of betula and salix and later populus during the deglacial period 14 000 11 000 yr b p are likely correlated with the crossing of temperature thresholds determined largely by the size and position of the laurentide ice a degree of asynchroneity between sites probably reflects differential site responses to regional effects plus inaccuracies of radiocarbon dating the early holocene was probably the warmest period of the present interglacial as summer climate was influenced by a strong positive insolation anomaly picea glauca expanded in majorr river valleys ca 9000 yr ago and slightly later at upland sites in the brooks and alaska ranges at some sites a juniperus subzone which suggests particularly warm and dry conditions occurs between ca 10 000 and 8000 yr b p early mid holocene expansions of alnus 8500 7000 yr b p and picea mariana 7500 5000 yr b p suggest the subsequent development of moister conditions which have continued to the present temporal patterns in picea treeline position during the holocene are different in northern alaska northwestern canada and central canada in alaska the treeline is currently at its furthest holocene extent in northwestern canada the treeline has retreated since the mid holocene and in central canada a mid holocene advance and retreat occurred such differences between regions suggest a complex response of this taxon to climatic controls and underscore the need to interpret vegetation changes in relation to regional scale climate phenomena if the pollen chronology is calibrated with reference to u th dates the relationship of vegetational events to the insolation maximum at ca 10 000 yr b p is significantly altered the changed chronology also affects the interpretation of pollen records in relation to gcm simulations which are partly keyed to calendar years