climate stability across the eocene oligocene transition southern argentina fossil mammal teeth from mid latitude southern argentina 46 s that closely bracket the eocene oligocene transition show no resolvable change in oxygen isotope compositions in combination with paleofloral observations and geographic considerations this finding implies not only that climate was essentially constant despite interpretations elsewhere for major mid and high latitude cooling but also that evolution of hypsodonty did not coincide with climate change during the eocene oligocene transition one possible explanation for eocene oligocene transition climatic stability is that southern high latitude cooling increased latitudinal temperature gradients and strengthened ocean circulation gyres including the southward flowing brazil current in the western south atlantic regionally increased heat transport in the western atlantic offset global cooling producing a nearly constant temperature in southern south america a more radical interpretation supported by some marine data is that the paradigm of major global cooling at the eocene oligocene transition is largely false in that mean sea surface temperatures changed very little

palaeogene climate evolution in the paris basin from oxygen stable isotope δ18o compositions of marine molluscs the constraint of temperature evolution in coastal environments is an important factor in deciphering the earth s global climatic history in this study we reconstruct the evolution of sea surface palaeotemperatures from the oxygen stable isotope compositions in four marine molluscs families in the paris basin during the palaeogene the combination of several taxa living in different environments is used to limit uncertainties related to the influence of salinity variations on palaeotemperature estimations one family of bivalves oysters and three families of gastropods volutidae cerithiidae and turritellidae were sampled in the french part of the paris basin in belgium and in the isle of wight southern england maximum seawater temperatures were observed during the early eocene c 30 c which correspond to the early eocene climatic optimum and temperatures then decreased until the lutetian c 20 c a transient warming identified as the middle eocene climatic optimum occurred during the bartonian when temperatures reached 32 c temperatures decreased through the eocene oligocene boundary the coolest interval of the palaeogene c 12 c a final warming period occurred throughout the early oligocene with temperatures reaching 24 c the fossils analysed thus record the global climatic intervals of the palaeogene

synchronizing terrestrial and marine records of environmental change across the eocene oligocene transition records of terrestrial environmental change indicate that continental cooling and or aridification may have predated the greenhouse icehouse climate shift at the eocene oligocene transition eot by ca 600 kyr in north america marine terrestrial environmental change asynchronicity is inferred from a direct comparison between the astronomically tuned marine eot record and published 40ar 39ar geochronology of volcanic tuffs from the white river group wrg sampled at flagstaff rim wyoming and toadstool geologic park nebraska which are type sections for the chadronian and orellan north american land mammal ages we present a new age model for the wrg underpinned by high precision 206pb 238u zircon dates from 15 volcanic tuffs including six tuffs previously dated using the 40ar 39ar technique weighted mean zircon 206pb 238u dates from this study are up to 1 0 myr younger than published anorthoclase and biotite 40ar 39ar data calibrated relative to fish canyon sanidine at 28 201 ma giving consideration to the complexities strengths and limitations associated with both the 40ar 39ar and 206pb 238u datasets our interpretation is that the recalculated 40ar 39ar dates are anomalously old and the 206pb 238u zircon dates more accurately constrain deposition 206pb 238u calibrated age depth models were developed in order to facilitate a robust intercomparison between marine and terrestrial archives of environmental change and indicate that i early orellan terrestrial cooling recorded at toadstool geologic park was synchronous with the onset of early oligocene antarctic glaciation and ii the last appearance datums of key chadronian mammal taxa are diachronous by ca 0 7 myr between central wyoming and nw nebraska

stable isotope paleoecology of white river ungulates during the eocene oligocene climate transition in northwestern nebraska abstract we use the carbon and oxygen stable isotope content of mammalian tooth enamel to evaluate ancient biomes habitat partitioning and water use among 12 ungulate taxa from the white river group in nebraska the white river group spans an interval of climate change from the upper eocene to the lower oligocene when global climate cooled in a heterogeneous fashion we test whether changes in biome structure or mammalian ecology occurred during this interval we find that mean 13c values for both eocene and oligocene faunas are consistent with dry open biomes e g woodland savanna or woody scrubland a significant increase in mean faunal 13c values 0 4 occurs in the lower oligocene primarily from the loss of individuals feeding in wetter denser parts of the ecosystem in the upper eocene megacerops sp brontothere and perchoerus probus peccary have low mean 13c values consistent with feeding in wetter denser habitats presumably riparian whereas significantly higher mean values in the cursorial horse mesohippus spp and the clawed oreodont agriochoerus antiquus are consistent with feeding in more open drier habitats the extinctions of megacerops sp and trigonias sp a rhinocerotid with relatively low 13c values along with a decrease in the abundance of p probus and other taxa suggests reduction in the extent of wet habitats in the oligocene the rare tapir colodon sp is the only taxon sampled with a mean 13c value low enough to indicate consistent feeding in a wet habitat in the oligocene however range through taxa occupy the same relative positions in isotopic space in both the eocene and oligocene faunas suggesting stability in drier habitats a significant increase also occurs in mean faunal 18o values 1 0 in the oligocene primarily from the loss or reduction in abundance of water dependent species variance in 18o values increases significantly in the oligocene which is consistent with greater water stress in plants from drier conditions oxygen values increase in a antiquus 0 9 the most aridity sensitive species in both faunas as expected for drier conditions but values in another aridity sensitive taxon mesohippus spp are virtually unchanged together 13c and 18o enamel values generally suggest a shift to drier conditions in the early oligocene although 13c values yielded more consistent results the lack of a large negative shift in 18o values expected with a decrease in mean annual temperature suggests that any temperature changes in the early oligocene were relatively small in the continental interior of north america

nd sr isotopic constraints on the interactions of the intermontane superterrane with the western edge of north america in the southern canadian cordillera sr and nd isotopic compositions of the late paleozoic metavolcanics and late triassic to early tertiary granitoids from four magmatic episodes in the southern canadian cordillera from the kootenay arc to the fraser fault have been used to i identify the sources of these rocks ii constrain the compressive tectonic history from middle jurassic to paleocene and iii constrain the western boundary of the basement in this region the 215 190 ma old primitive granitoids end 3 1 to 8 7 87sr 86sr 0 7028 0 7043 of the late triassic and early jurassic magmatic episode were emplaced in the paleozoic oceanic crust of quesnellia end 2 9 to 9 3 prior to its obduction over the basement in contrast during the younger magmatic episodes middle late jurassic cretaceous and early tertiary the granitoids from western quesnellia show primitive isotopic compositions and those from eastern quesnellia show eastward increasing crust contaminated compositions the contaminated characters of the middle

discussion on the eocene oligocene boundary in the uk journal vol 163 2006 pp 401 415 jerry hooker margaret collinson stephen grimes nick sille david mattey write recognition of the eocene oligocene boundary in the hampshire basin uk has been debated since naming of the oligocene epoch in 1854 previously this was because the boundary itself had not been stabilized and because the strata concerned are largely non marine a global boundary stratotype and stratigraphic point gssp was established at massignano italy in 1993 in marine strata recognition of the boundary on extinction of the planktonic foraminiferan family hantkeninidae made boundary identification difficult in the continental realm correlation to marginal marine and non marine strata is nevertheless possible via magnetostratigraphic and sequence stratigraphic studies and importantly biostratigraphically via dinocyst zones at massignano brinkhuis biffi 1993 brinkhuis visscher 1995 therefore recent publication of the magnetostratigraphy sequence stratigraphy and orbital cyclicity of much of the hampshire basin solent group gale et al 2006 is welcomed and substantially increases the number of correlation tools available in this area such cyclical phenomena however rely on absolute dating or biostratigraphy for calibration no radiometric dates exist for the solent group so biostratigraphy remains the best means of dating the succession there are however problems with the way gale et al 2006 have interpreted biostratigraphic markers and therefore with their placement of the eocene oligocene boundary and associated events the organisms concerned are calcareous nannoplankton np zones and mammals mp reference levels thus the record by aubry 1985 of np22 in the argiles vertes de romainville paris basin was subsequently qualified by her aubry 1986 p 307 as zone np22 not younger possibly older np21 this dating was based solely on the presence of rare isthmolithus recurvus which ranges from np19 20 to np22 aubry 1992 this being the real level of dating for the argiles vertes de romainville

a multi proxy geochemical investigation of the early paleocene danian continental palaeoclimate at the fontllonga 3 site south central pyrenees spain chronologically well constrained non marine deposits across the cretaceous tertiary boundary ktb are exceptionally rare the fontllonga section tremp formation south central pyrenees lleida spain constitutes one of these rare global records stable isotope 18oco3 and 13c analyses have been performed on the carbonate fraction of 29 samples from diverse skeletal micro remains charophyte gyrogonites gastropod shells ostracod valves and isolated skeletal remains of lepisosteids and pycnodonts from the earliest danian site fontllonga 3 a mean ba ca water palaeotemperature of 28 0 6 7 c has been obtained from the ganoine of 25 lepisosteid scales this mean palaeotemperature is comparable with the temperature tolerance range for extant relatives of fossil osteoglossiform fish found at fontllonga 3 which require a temperature range of 24 35 c mean annual temperature 27 30 c to survive using the temperature range provided by the ba ca palaeothermometer 21 3 34 7 c it is possible to determine 18owater values from the isotopic content of charophyte gyrogonites gastropod shells ostracod valves and fish remains mean 18oco3 5 00 0 21 18owater values of between 4 01 and 0 95 vsmow are calculated which when combined with la yb n versus la sm n plots are in good agreement with the sedimentary interpretation of the site as an estuarine environment based upon a comparison with modern day meteorical conditions these isotopic values are relatively high for subtropical freshwaters suggesting a low precipitation rate amount effect high evaporation rate and or long residence time when combined with other isotopic palaeobotanical and mineralogical studies carried out in the pyrenean and tethys realms this first geochemical study of an early paleocene site is consistent with there being a subtropical seasonally dry climate in the south central pyrenees at this time

correlation of eocene oligocene marine and continental records orbital cyclicity magnetostratigraphy and sequence stratigraphy of the solent group isle of wight uk the magnetostratigraphy clay mineralogy cyclostratigraphy and sequence stratigraphy of the estuarine and continental solent group isle of wight hampshire basin uk which is of late eocene early oligocene age were investigated a new magnetostratigraphy for the solent group is correlated to the chronostratigraphic standard using limited biostratigraphical data and it is concluded that the base of the oligocene falls close to the base of the bembridge limestone formation a long time series of clay mineral xrd data was generated which shows striking variation in illitic clay abundance illite is interpreted to have formed in gley palaeosols through repeated wetting and drying in response to high seasonality high illitic clay values are tuned to c 400 ka eccentricity maxima to develop an age model in addition to a very strong c 400 ka signal in the data spectral analysis of the clay data also confirms the influence of short eccentricity c 100 ka and obliquity c 40 ka cycles the succession displays seven conspicuous 10 20 m thick sequences which represent transitions from transgressive estuarine environments through highstand floodplains to freshwater lakes the sequences correspond exactly to the long eccentricity c 400 ka cycles a sea level curve is derived using the amount of incision as a minimum measure of eustatic fall but there is no evidence of a major eustatic drop of 30 90 m corresponding to the early oligocene glaciation of antarctica it is likely that incision was suppressed by rapid rates of subsidence

tightening the siberian connection to western laurentia newly available geological and geophysical data tighten the proterozoic connection between the rifted margins of the northern siberian craton and western laurentia and permit a siberia laurentia australia troika with northern australia connected to the southern margin of the siberian craton the continental assembly is linked by a prominent 2 0 1 8 ga collisional belt and the ca 1 3 1 0 ga grenville orogen the reconstruction also aligns a 1 5 1 45 ga dike sill swarm that extends from the wyoming province through the belt purcell basin into the northern siberian craton separation of australia and siberia may have occurred by the early neoproterozoic but separation of siberia and laurentia may not have been completed until the early cambrian continental extension began along the zigzag siberia laurentia rift zone in the early mesoproterozoic rift related igneous and sedimentary assemblages dated at ca 1 5 1 38 and 1 2 to 1 0 ga correlate across the reconstructed siberia laurentia rift zone renewed rifting in the neoproterozoic and vendian culminated with seafloor spreading and thermal subsidence of the conjugate rift shoulders correlative archeocyathan reefs endemic olenellid trilobite fauna and exchange of detritus between the cratons imply that the rift may have remained relatively narrow until the atdabanian stage black sulfidic shales buried the archeocyathan reefs on the rapidly subsiding rift margins during the botomian sinsk event

orogenic pulses in the alberta rocky mountains radiometric dating of major faults and comparison with the regional tectono stratigraphic record radiometric ages from regionally distributed thrust fault gouge show that the eastward propagation of the southern rocky mountain fold and thrust belt in canada occurred in four orogenic pulses that correlate with tectonic events of the cordilleran interior and with depositional patterns in the adjacent foreland in the main ranges the pyramid 163 0 ma simpson pass 161 7 ma and johnson creek 145 7 ma thrusts were related to the initiation of thin skinned deformation from jurassic terrane accretion and were partly contemporaneous with development of the first clastic wedge in the foreland basin in the front ranges the emplacement of the greenock thrust 103 1 ma and broadview snake indian thrust 99 2 ma was contemporaneous with development of cenomanian deltaic deposits in the immediate foreland three thrusts in the front ranges rocky pass 74 8 ma sulfur mountain 75 6 ma and clearwater 74 2 ma thrusts define a campanian phase of tectonic loading that led to the last major transgression in the southern portion of the alberta foreland along the eastern margin of the front ranges the mcconnell thrust 54 0 ma together with the muskeg 52 4 ma brule 53 9 ma and nikanassin 52 1 ma thrusts in the foothills recorded the last phase of regional contraction the late jurassic mid cretaceous late cretaceous and early eocene deformation pulses are separated by relatively long periods 40 m y 20 m y and 10 m y of tectonic quiescence these spatially and temporally restricted fault motion pulses contrast with gradual forward fault propagation while regional eastward progression of deformation is preserved

north american margin origin of quesnel terrane strata in the southern canadian cordillera inferences from geochemical and nd isotopic characteristics of triassic metasedimentary rocks new geochemical and nd isotopic data from triassic ca 220 ma clastic metasedimentary rocks assigned to the quesnel terrane quesnellia in southeastern british columbia show that detritus was derived from both primitive and evolved sources twenty four samples yield end 2 2 0 values between 9 1 and 5 6 independent of sample location these samples have eu anomalies between 0 6 and 1 0 la n yb n ratios between 3 8 and 11 4 la sc ratios ranging from 0 38 to 4 76 and th sc ratios between 0 09 and 1 62 this range of isotopic and geochemical values overlaps that of samples from upper paleozoic to mesozoic rocks of the north american miogeocline and upper triassic nicola group volcanic rocks of the quesnel terrane the range in nd isotopic and geochemical values supports the interpretation that detritus was derived from both continental north america evolved cratonic source and a volcanic arc primitive source developing on the continental margin these data do not support previous interpretations of the quesnel terrane as an intraoceanic arc the inferred depositional link between north america and the quesnel arc in triassic time is ca 40 ma older than the hypothesized obduction of the quesnel terrane onto the north american continental margin and when combined with existing geological information strongly supports a pericratonic nonexotic origin for the quesnel terrane in southeastern british columbia

taltson basement gneissic rocks upb and nd isotopic constraints on the basement to the paleoproterozoic taltson magmatic zone northeastern alberta the taltson magmatic zone is a 300 km long northerly trending belt of archean to paleoproterozoic granitic basement gneiss amphibolite supracrustal gneissic rocks and voluminous paleoproterozoi

beginning of foreland subsidence in the columbian sevier belts southern canada and northwest montana subsidence analysis and geometry of jurassic cretaceous foreland strata in northwestern montana and southern alberta and british columbia suggest that loading by the fold thrust belt in canada began as much as 40 m y earlier than in montana in canada early foreland basin deposits are late jurassic age thicken rapidly westward and are restricted to a narrow belt within 30 km of the thrust belt in western montana contemporaneous deposits are widespread and do not increase markedly in thickness toward the thrust belt the unconformity overlying these deposits also changes from canada where it is angular to a disconformity in western montana near great falls between these two areas foreland geometry is transitional over a distance of 250 km beyond the transition zone early foreland basin geometries are broadly consistent showing late jurassic foreland subsidence in southern canada and early cretaceous initial subsidence in the united states

equability continentality and tertiary climate the crocodilian perspective the distributions of fossil crocodilians are used to examine north american continental paleoclimates for four time periods in the cenozoic control groups provide a qualitative means of examining the completeness of the record and thus the validity of crocodilian patterns by analogy with the range of the extant american alligator alligator mississippiensis the patterns imply that mid to high latitude continental interiors during the eocene and miocene did not undergo seasonal temperature extremes as great as those observed in such areas today this is compatible with the paleobotanical data during both the late oligocene and the pleistocene times of major glaciation crocodilians were restricted to more maritime localities

the lower jurassic phosphorites of southeastern british columbia and terrane accretion to western north america sinemurian phosphorites in southeastern british columbia and southwestern alberta conform with the west coast type phosphorite depositional model the model indicates that they were deposited on or near the early jurassic western cratonic margin next to a sea or trough from which cold water upwelled this suggests that the allochthonous terrane quesnellia lay well offshore in sinemurian time the sea separating quesnellia from north america was partly floored by oceanic crust eastern terrane and partly by a thick sequence of rifted continental terrace wedge rocks comprising the purcell supergroup and overlying paleozoic sequence this sequence must have been depressed sufficiently that access of upwelling deep currents to the phosphorite depositional area was not impeded

new field evidence for an exposure of the appalachian decollement at the east end of the pine mountain terrane georgia detailed field mapping at the east end of the pine mountain terrane in central georgia indicates that the box ankle fault is an 4 km thick ductile shear zone separating grenvillian basement of laurentian affinity in the footwall from allochthonous accreted terranes in the hanging wall fabric data from the box ankle fault indicate that it is a gently southeast dipping northwest vergent thrust fault recently discovered structural relations together with geochronological data indicate that the box ankle fault is of late paleozoic age we argue that the box ankle fault is a surface exposure of the appalachian decollement the east end of the pine mountain terrane may be the only place in the entire orogen where this fundamentally important structure is exposed for study

analysis of the geochemical variability in lepisosteid scales from the fontllonga 3 site early danian tremp formation south central pyrenees spain implications for palaeoenvironmental studies rare earth element ree ba ca sr ca and 18opo4 analyses have been performed on the ganoine and isopedine of different types of isolated scales anterior middle posterior flank scales and dorsal body margin scales from juvenile lepisosteids from the fontllonga 3 site early danian tremp formation south central pyrenees spain with the aim of detecting the most suitable kind of scale to be used in palaeoclimate studies the ree flat shape patterns obtained in lepisosteid scales from fontllonga 3 are indicative of the absence of late stage diagenesis and recrystallization and have confirmed the identification of the palaeoenvironment where the fontllonga 3 lepisosteids inhabited to be that of an estuary the ba ca palaeothermometer shows that posterior flank scales record on average 4 52 c ganoine and 3 49 c isopedine higher temperatures when compared to middle flank scales which may be related to the fact that posterior flank scales grow preferentially during the warm season whilst middle flank scales which have the greatest number of layers of ganoine per unit of time and grow all year round record a greater amplitude with respect to palaeoenvironmental and palaeoclimatic variations temperature values obtained from anterior flank scales follow a pattern similar to that showed by middle flank scales whilst temperature values provided by dorsal scales resemble the pattern furnished by posterior flank scales the same relationship between scale position and temperature but to a lesser degree 1 48 c is also evident in the calculated 18opo4 temperatures the ba ca palaeothermometer was applied by considering ba ca ratios of the water for different types of environments and it has been found out that a ratio similar to that of marine waters yielded the best approximation to 18opo4 temperatures 29 82 3 76 c the mean ba ca temperature value obtained from the analysis of all the ganoine samples 26 96 5 72 c is also consistent with the temperature of the water in which extant relatives of osteoglossiform fish whose remains have been found in fontllonga 3 along with lepisosteid remains inhabit nowadays 24 40 c with mean values of 27 to 32 c the mean ba ca temperature values furnished by the isopedine are lower than that obtained on the ganoine which may be due to minor diagenetic alteration on account of these results it is recommended that a distinction should be made between different types of scales as this could provide information concerning the summer growth temperature posterior flank scales as well as the annual temperature range middle flank scales furthermore it is recommended that ganoine be used in all studies as it appears to be the most resistant tissue in lepisosteid scales to diagenetic alteration

cooler winters as a possible cause of mass extinctions at the eocene oligocene boundary the eocene oligocene boundary at about 33 7 myr ago marks one of the largest extinctions of marine invertebrates in the cenozoic period1 for example turnover of mollusc species in the us gulf coastal plain was over 90 at this time2 3 a temperature change across this boundary from warm eocene climates to cooler conditions in the oligocene has been suggested as a cause of this extinction event4 but climate reconstructions have not provided support for this hypothesis here we report stable oxygen isotope measurements of aragonite in fish otoliths ear stones collected across the eocene oligocene boundary palaeotemperatures reconstructed from mean otolith oxygen isotope values show little change through this interval in agreement with previous studies5 6 from incremental microsampling of otoliths however we can resolve the seasonal variation in temperature recorded as the otoliths continue to accrete new material over the life of the fish these seasonal data suggest that winters became about 4 c colder across the eocene oligocene boundary we suggest that temperature variability rather than change in mean annual temperature helped to cause faunal turnover during this transition

a re examination of the type area of the devono mississippian cariboo orogeny central british columbia three tectonostratigraphic successions are established from remapping of the area near barkerville and cariboo river the first of late proterozoic to cambrian sediments was deposited on the shallow to moderately deep platformal shelf west of and derived from the exposed north american craton the second is an unconformably overlying ordovician to permian sequence of sedimentary and volcanic rocks representing a basinal environment with periodic highs these packages of sediments were deposited on the north american craton and its western transitional extensions the third succession composed of oceanic chert and basalt of the permo pennsylvanian antler formation was thrust eastward over the other two during the early mesozoic the three successions were folded faulted and metamorphosed during the mid mesozoic columbian orogeny the devono mississippian cariboo orogeny which was thought to have affected all of the first sequence and part of the second could not be documented in its type locality

eocene oligocene transition in central asia and its effects on mammalian evolution the eocene oligocene boundary eob marks a period of dramatic global climatic change correlated with pronounced mammalian faunal change the timing of these events is well constrained in north america and europe but the asian record has yet to produce a synthetic section linking environmental change mammalian fossils and precise geochronological dates here we present the first magnetostratigraphic section for the hsanda gol formation mongolia which yields significant oligocene fossils and also marks a pattern of aridification that is tightly correlated to the eob 33 9 ma supporting a broader pattern of aridification in the central asian plateau across the eob oligocene faunas of asia can now be confidently correlated to those of north america europe and africa these results suggest that mammalian faunal turnover within asia occurred slightly later than similar events within europe and question the influence of asian immigrants on the grande coupure faunal turnover

eocene oligocene latitudinal climate gradients in north america inferred from stable isotope ratios in perissodactyl tooth enamel abstract the eocene oligocene transition 34 ma was one of the most pronounced episodes of climate change of the cenozoic in order to investigate this episode of global climate cooling in north america we analyzed the carbon and oxygen stable isotope composition of the carbonate component of 19 perissodactyl horse and rhino tooth enamel samples from the eocene oligocene rocks of the cypress hills formation southwestern saskatchewan canada we then compared the results with previously published data from the us great plains nebraska south dakota and wyoming average 1 perissodactyl enamel 13 c values vs v pdb in the eocene 8 8 0 3 and oligocene 9 0 0 3 are indistinguishable suggesting no major change in mean annual precipitation in saskatchewan across the transition the 13 c values in saskatchewan indicate the presence of arid ecosystems and are slightly higher than those in the us great plains suggesting drier conditions at higher latitudes with respect to oxygen isotopes average 1 perissodactyl enamel 18 o values vs v smow in the eocene 19 8 2 0 and oligocene 20 1 3 6 are also indistinguishable suggesting no change in the 18 o of meteoric precipitation across the transition in saskatchewan enamel 18 o variability is much larger in the oligocene vs eocene indicating a large increase in temperature seasonality this increase in enamel 18 o variability is much larger than that recorded in the us great plains suggesting that higher latitudes are more sensitive to major episodes of climate change with respect to temperature seasonality finally our data indicate no major change in the oligocene vs eocene latitudinal gradient in local water 18 o in north america which suggests no change in mean annual temperature gradients across the transition this result supports the hypothesis that ascribes the climate change of the transition to a drop in atmospheric p co 2 because climate models show that this mechanism produces uniform cooling at mid latitudes

northward translation of baja british columbia along the late cretaceous to paleocene margin of western north america paleomagnetic data suggest that a large part of british columbia and southern alaska was at the latitude of baja california mexico in early late cretaceous time this allochthonous block baja bc includes the insular talkeetna in alaska and intermontane composite terranes the miniterranes between them and possibly part of the omineca metamorphic belt assuming that baja bc was adjacent to north america by middle cretaceous an analysis using plate kinematics of the pacific basin produces a model of northward movement of baja bc which is compatible with the known geology of the reconstructed margin of western north america baja bc moved north 2400 km as part of the kuia plate along a transform margin with north america from 85 to 66 ma this time interval is marked by the cessation of igneous activity in the sierra nevada development of wrench faults and basins along coastal california and initiation of laramide style tectonics to the east within baja bc diminished igneous activity to the west was coeval with possible wrench tectonic basins along its eastern margin by the end of the cretaceous baja bc was positioned from oregon to northern british columbia between 66 and 56 ma baja bc became attached to north america in a dextral transpressive stage during which the kula north america plate boundary expanded to encompass the whole block with a series of northwest trending strike slip faults a fold and thrust belt in the east and large scale uplifts and the formation of an incipient volcanic arc on the west southern alaska was the site of convergence during the whole of the period of northward translation of baja bc a late cretaceous subduction zone in alaska evolved into a major compressional belt as the basin and miniterranes on the northern margin of baja bc collided with interior alaska the collision culminated in the paleocene with formation of the mckinley granites and coeval dextral slip on the denali fault system

is small beautiful a review of the advantages and limitations of using small mammal teeth and the direct laser fluorination analysis technique in the isotope reconstruction of past continental climate change abstract oxygen isotopes in mammalian tooth enamel have become a widely used proxy for reconstructing past continental climate change however owing to sample size constraints in the chemical separation and precipitation of the phosphate prior to oxygen isotope analysis this technique has been until recently limited to relatively large mammal teeth as the result of recent developments in chemical and analytical techniques including the development of a novel pre treatment technique and a direct laser fluorination methodology of analysis small mammal teeth rodents which are relatively more abundant in the fossil record than large mammal teeth can now be used published examples from the recent literature are provided with the aim of examining the advantages and limitations of using small mammal teeth in palaeoclimate reconstruction studies issues that are addressed include 1 the rationale behind the calculation of the mean oxygen isotope composition of local water and the problems associated with the intake of 18 o enriched water from plant food and from small water bodies fractionated as a result of evaporation 2 the methodology justification and limitations in determining mean annual temperatures mats from calculated 18 o local water values and also combining the 18 o local water values with 18 o values from freshwater biota to calculate using established thermometry equations multiple palaeotemperatures of differing climatic significance 3 specific published examples of how the phosphate oxygen isotope composition of small mammal teeth are being used in studies of continental climate change

link between global cooling and mammalian transformation across the eocene oligocene boundary in the continental interior of asia evidence in the world s ocean current system indicates an abrupt cooling from 34 1 to 33 6 ma across the eocene oligocene boundary at 33 9 ma the remarkable cooling period in the ocean called the eocene oligocene transition eot is correlated with pronounced mammalian faunal replacement as shown in terrestrial fossil records for the first time within asia a section is magnetostratigraphically dated that also produces mammalian fossils that span the late eocene early oligocene transition three fossil assemblages revealed through the eot 34 8 33 7 and 30 4 ma demonstrate that perissodactyl faunas were abruptly replaced by rodent lagomorph dominant faunas during climate cooling and that changes in mammalian communities were accelerated by aridification in central asia three fossil assemblages 34 8 33 7 and 30 4 ma within the north junggar basin burqin section tied to this magnetostratigraphically dated section reveal that perissodactyl faunas were abruptly replaced by rodent lagomorph dominant faunas during climate cooling and that changes in mammalian communities were accelerated by aridification in central asia the biotic reorganization events described in the burqin section are comparable to the grande coupure in europe and the mongolian remodeling of mammalian communities that is the faunal transition was nearly simultaneous all over the world and mirrored global climatic changes with regional factors playing only a secondary role

palaeogeographic palaeoclimatic palaeohydrological and chemical biochemical controls on accumulation of late eocene coastal lacustrine palustrine limestones southern england abstract the shallow lacustrine to palustrine hatherwood limestone member of the late eocene headon hill formation southern england is in a succession of fluvio estuarine and laguno lacustrine siliciclastic sediments it is up to 8 0 m thick and is subdivided by metric scale palaeotopographic erosion surfaces one of which underlies lenticular humic siliciclastic mudstones the limestone lithologies are 1 biocalcilutites biocalcisiltites 2 biocalcarenites 3 calcirudites and 4 laterally discontinuous laminar and fenestral crusts lithology 1 accumulated in a low energy shallow lacustrine depositional environment indicated by the predominance of pulmonate pond snails in the mollusc assemblage in contrast lithologies 2 and 3 are the coarse grained fills of shallow palaeotopographic lows and also form basal lags and palaeokarst fills lithology 3 comprises remnant autochthonous lags that resulted from selective erosion during lacustrine transgressions brecciation and proto intraclast to nodular differentiation in lithology 2 suggests derivation of the intraclasts from subaerially and pedogenically modified shallow lacustrine muds laminar crusts 4 0 5 6 0 cm in thickness display irregularly undulose and anastamosing laminations 150 400 m thick that display differential staining by iron oxide the abundance of rootlet traces and calcitised parenchymatic root tissues in the fenestral crusts suggests a palustrine depositional environment for these lithologies the siliciclastic mudstone lithologies are 1 black humic muds and 2 blue green silty muds and marls the high c n molar ratio of the black muds suggests derivation of the humic content mainly from vascular plants in local wetlands the mollusc assemblage of the blue green siliciclastic muds resembles floodplain lake assemblages from the regional palaeogene succession mean stable isotopic values for limestone samples of 4 75 1 53 for 13 c and 2 77 1 47 for 18 o indicate a relatively heavy tendency within published spectra for tertiary lacustrine carbonates the 18 o isotope results agree with published subtropical surface water palaeotemperatures for this succession the total characteristics of the member therefore suggest a shallow lacustrine to palustrine depositional environment pedogenic overprinting and mechanical reworking displayed by the limestones are attributable to seasonal fluctuations of water level during lake highstands but in this marine influenced setting major long term lake lowstands resulting in deep erosion and palaeokarsting of the limestones may be attributable to falls in relative sea level the biocalcilutites and humic muds accumulated during the ensuing lake transgressions

jurassic onset of foreland basin deposition in northwestern montana usa implications for along strike synchroneity of cordilleran orogenic activity stratigraphic provenance and subsidence analyses suggest that by the middle to late jurassic a foreland basin system was active in northwestern montana united states u pb ages of detrital zircons and detrital modes of sandstones indicate provenance from accreted terranes and deformed miogeoclinal rocks to the west subsidence commenced ca 170 ma and followed a sigmoidal pattern characteristic of foreland basin systems thin jurassic deposits of the ellis group and morrison formation accumulated in a backbulge depozone a regional unconformity and or paleosol zone separates the morrison from early cretaceous foredeep deposits of the kootenai formation the model presented here is consistent with regional deformation events registered in hinterland regions and challenges previous interpretations of a strongly diachronous onset of cordilleran foreland basin deposition from northwestern montana to southern canada

unexpected values of qs in the unconsolidated sediments of the mississippi embayment we studied the attenuation of shear waves at three sites in the mississippi embayment using data recorded in boreholes drilled to depths of up to 60 m the source was a highly repeatable compressed air driven hammer to estimate attenuation we used a spectral ratio technique for fixed depth and variable frequency the best fit line for each depth z gives a measure of the cumulative attenuation indicated by z then we fit a straight line to z for a range of values of z the slope of this line gives an estimate of the average attenuation per distance and was used to determine an average q s for one of the sites newport northeastern arkansas q s ranges between 34 1 5 m z 44 2 m and 44 1 5 m z 51 8 m these values are significantly higher than the more typical value of about 10 determined for unconsolidated sediments by other authors in addition these high values correspond to sediments with low average shear wave velocity about 300 m sec in contrast average q s and velocity for sediments in shelby forest near memphis tennessee are 22 and 348 m sec 22 6 m z 60 1 m respectively therefore these results go against the conventional wisdom that low velocity implies low q for the third site marked tree northeastern arkansas average q s and velocity are 18 and 251 m sec 9 8 m z 33 6 m respectively this site is about 75 km from newport and the differences in attenuation appear related to differences in lithology manuscript received 5 april 2001

orogeny forced terrestrial climate variation during the late eocene early oligocene in europe terrestrial climatic data reflect variable and often conflicting responses to the global cooling event at the eocene oligocene transition ca 34 ma stable isotopic compositions of the tooth enamel of large water dependent herbivorous terrestrial mammals are investigated here to better understand the european continental climate during the late eocene early oligocene high 18opo4 and 13c values reflect a semiarid climate and ecosystem in the late eocene in the west southwest region of europe these conditions prevailed until at least 33 ma after which it became more humid a similar change was recorded north of the alpine thrust but it occurred 2 m y earlier the north and west southwest regions show a significant offset in 18opo4 composition between 35 and 31 ma indicating the influence of different air trajectories with different moisture sources atlantic versus tethys this also marks the presence of an orographic height in central europe from the latest eocene after 31 ma a large drop in 18opo4 is registered explained by altitude induced fractionation on meteoric water isotopic composition the related paleoaltitude change is estimated to be 1200 m and the uplift could have taken place along the alpine dinaridic orogenic system

triple oxygen isotope analysis of bioapatite as tracer for diagenetic alteration of bones and teeth abstract the detection of diagenetic alteration is critical for palaeoclimate reconstruction that is based on the oxygen isotope composition of fossil bones and teeth so far no direct chemical proxy has been found to track diagenetic modification of the oxygen isotope ratios here a new approach to identify diagenetic changes of 18opo4 values in skeletal apatite of small mammals by means of triple oxygen isotope analysis 16o 17o and18o is presented our method is based on the fact that inhaled air oxygen o2 has an isotope anomaly on its rare isotope 17o inhaled air o2 is a major source of oxygen in small land living mammals a fraction of the anomaly is transferred via body water to skeletal apatite where it can be detected by means of 17o and 18o analyses the approach considering the current analytical uncertainty is restricted to small mammals with body masses 1 kg this is due to the low specific metabolic rates of large mammals resulting in a lower fraction of oxygen inhaled via breathing relative to oxygen from other sources in their body water remnant negative 17o anomalies derived from in vivo inhaled o2 have been detected in enamel bioapatite of eocene to miocene rodent teeth while dentine of the same teeth lacks significant 17o anomalies this suggests preservation of the original phosphate oxygen isotope composition in enamel of these small mammal teeth in contrast 17o anomalies in dentine have been erased due to diagenetic alteration with isotopically normal diagenetic fluids triple oxygen isotope analysis of bioapatite thus seems to be a useful new proxy to directly detect diagenetic alterations of the 18opo4 values of small mammal teeth

infrasound from thunder a natural seismic source 1 a small array consisting of five three component short period surface seismometers a three component borehole seismometer and five infrasound microphones was built to investigate thunder induced ground motions data from two thunder events with similar n wave waveforms but different horizontal slownesses are chosen as examples of data collected by the array these impulsive acoustic waves excited p and s reverberations in the near surface that depend on both the incident wave horizontal slowness and the velocity structure in the upper 30 meters at the site although the depth of the borehole is relatively shallow compared to a seismic wave wavelength velocity amplitude in the radial component decays as much as 63 percent with depth but vertical component amplitudes are unaffected consistent with air coupled rayleigh wave excitation naturally occurring thunder appears to be a useful seismic source to empirically determine site resonance characteristics for hazards assessments

bulk sediment qp and qs in the mississippi embayment central united states we have estimated p wave ands wave anelastic attenuation coefficients for the thick unconsolidated sediments of the mississippi embayment central united states using the spectral distance decay of explosion p and rayleigh waves the sediment trapped p wave psed is observed to ranges of 80 km at 10 hz and 1 hz rayleigh waves are observed out to 130 km from a 5000 lb borehole explosion in the northern part of the embayment rayleigh waves of 4 hz are seen to distances of 3 km from a smaller 50 lb explosion analysis of the group velocity and amplitude distance decay of both waves yields an average qs of 100 and qp of 200 for embay ment sediments that are independent of frequency scatter in the q estimates comes from interference of multiple p wave reverberations and rayleigh wave modes the attenuation model is self consistent in that it is the same as obtained by the analysis of synthetic seismograms using the inferred q values inferred qp and qs values are more than three times higher than previous estimates and imply that unconsolidated sediments of the embayment do not significantly attenuate small strain earthquake ground motions these estimates represent a lower bound to q of the sediments since significant scattering is observed in the waveform data that contributes to the distance decay of wave amplitude higher q values also imply that the unconsolidated sedi ments of the embayment will form an efficient wave guide for surface waves radiated from shallow earthquakes or large earthquakes that rupture into the sediments pro ducing high amplitude long duration wave trains that should be considered in earth quake hazard assessments

mechanisms of mass and heat transport during barrovian metamorphism a discussion based on field evidence from the central alps switzerland northern italy 1 tectonic and metamorphic data for the central alps switzerland italy are used to discuss this classic example of a barrovian metamorphic terrain notably the evolution of its thermal structure in space and time available p t t data indicate variable contributions of advective and conductive heat transport during collision and subsequent cooling and exhumation some areas experienced a prolonged period of partial melting while other areas at the same time show but moderate heating the barrow type metamorphic field gradient observed in the final orogen is the result of two distinct tectonic processes with their related advective and conductive heat transport processes the two tectonic processes are 1 accretion of material within a subduction channel related to decompression and emplacement of high pressure units in the middle crust and 2 wedging and related nappe formation in the continental lower plate the second process postdates the first one wedging and underthrusting of continental lower plate material produces heat input into lower crustal levels and this process is responsible for predominantly conductive heat transport in the overlying units the interacting processes lead to different maximum temperatures at different times producing the final barrovian metamorphic field gradient the south experienced rapid cooling whereas the north shows moderate cooling rates this discrepancy principally reflects differences in the temperature distribution in the deeper crust prior to cooling differences in the local thermal gradient that prevailed before the cooling also determined the relationships between cooling rate and exhumation rate in the different areas citation berger a s m schmid m engi r bousquet and m wiederkehr 2011 mechanisms of mass and heat transport during barrovian metamorphism a discussion based on field evidence from the central alps switzerland northern italy tectonics 30 tc1007 doi 10 1029 2009tc002622

coupling of marine and continental oxygen isotope records during the eocene oligocene transition while marine records of the eocene oligocene transition indicate a generally coherent response to global cooling and the growth of continental ice on antarctica continental records indicate substantial spatial variability marine eocene oligocene transition records are marked by an 1 1 foraminiferal 18o shift but continental records rarely record the same geochemical signature making both correlation and linking of causal mechanisms between marine and continental records challenging here a new high resolution continental 18o record derived from the freshwater gill breathing gastropod viviparus lentus is presented from the hampshire basin uk the solent group records marine incursions and has an established magnetostratigraphy making it possible to correlate the succession directly with marine records the v lentus 18o record indicates a penecontemporaneous higher magnitude shift 1 4 than marine records which reflects both cooling and a source moisture compositional shift consistent with the growth of antarctic ice when combined with clumped isotope measurements from the same succession about half of the isotopic shift can be attributed to cooling and about half to source moisture change proportions similar to marine foraminiferal records thus the new record indicates strong hydrological cycle connections between marine and marginal continental environments during the eocene oligocene transition not observed in continental interior records

paleogene paleoclimate reconstruction using oxygen isotopes from land and freshwater organisms the use of multiple paleoproxies abstract understanding past climate change is critical to the interpretation of earth history even though relative temperature change has been readily assessed in the marine record it has been more difficult in the terrestrial record due to restricted taxonomic distribution and isotopic fractionation this problem could be overcome by the use of multiple paleoproxies therefore the 18o isotopic composition of five paleoproxies rodent tooth enamel 18ophosphate 17 7 2 0 n 74 vsmow fish scale ganoine 18ophosphate 19 7 0 7 n 20 vsmow gastropod shell 18ocalcite 1 7 1 3 n 50 vpdb charophyte gyrogonite 18ocalcite 2 4 0 5 n 20 vpdb fish otolith 18oaragonite 18o 3 6 0 6 n 20 vpdb from the late eocene priabonian osborne member headon hill formation solent group hampshire basin uk were determined because diagenetic alteration was shown to be minimal the phosphate oxygen component of rodent tooth enamel as opposed to enamel carbonate oxygen was used to calculate an initial 18olocal water value of 0 0 3 4 however a skewed distribution most likely as a result of the ingestion of evaporating water necessitated the calculation of a corrected 18olocal water value of 1 3 1 7 n 62 this 18olocal water value corresponds to an approximate mean annual temperature of 18 1 c four other mean paleotemperatures can also be calculated by combining the 18olocal water value with four independent freshwater paleoproxies the calculated paleotemperature using the fish scale thermometry equations most likely represents the mean temperature 21 2 c of the entire length of the growing season this should be concordant with the paleotemperature calculated using the lymnaea shell thermometry equation 23 2 c the lack of concordance is interpreted to be the result of diagenetic alteration of the originally aragonitic lymnaea shell to calcite the mean paleotemperature calculated using the charophyte gyrogonite thermometry equation 21 2 c on the other hand most likely represents the mean temperature of a single month toward the end of the growing season the fish otolith mean paleotemperature 28 2 c most likely represents the mean temperature of the warmest months of the growing season an approximate mean annual temperature of 18 1 c in addition to a mean growing season paleotemperature of 21 2 c using fish scale only with a warmest month temperature of 28 2 c and high associated standard deviations suggest that a subtropical to warm temperate seasonal climate existed during the deposition of the late eocene osborne member

temporal variations in lake water temperature paleoenvironmental implications of lake carbonate δ18o and temperature records abstract 18 o and clumped isotope measurements of lacustrine carbonates provide important records of past terrestrial climate and paleoelevation however one of the primary challenges interpreting these data is constraining the relationship between mineral formation temperature and seasonal and mean annual climate we examined surface water temperature records from 88 lakes across the globe to develop transfer functions that relate seasonal water surface temperature to mean annual air temperature these transfer functions provide a means of reconciling proxy measures of water temperature with annual climatic conditions mean annual surface water temperature is related to mean annual air temperature maat 0 0318 t water 2 2 195 t water 12 607 r 2 0 96 independent of lake size with consistently higher mean water temperatures than air n hemisphere spring april june mean lake surface temperatures maat 0 0097 t water 2 1 379 t water 8 227 r 2 0 94 are only slightly warmer than maat for lakes in all climate zones while summer water temperatures jja maat 0 0055 t water 2 1 476 t water 18 915 r 2 0 90 may be 10 20 c warmer than maat for cold climate lakes comparison of carbonate stable isotopic data from sites with different timescales of carbonate formation such as found along latitude or elevation gradients can lead to large over or underestimates of past temperature accurate paleoclimatic interpretation of isotopic proxies or use of temperature proxy constraints i e fossil leaves to estimate lake temperature and calculate water 18 o thus requires appropriate application of water temperature air temperature transfer functions particularly when considering ancient cool high elevation lake systems

palaeoenvironment and palaeoclimate of the middle miocene lake in the steinheim basin sw germany a reconstruction from c o and sr isotopes of fossil remains a differentiated reconstruction of palaeolimnologic environmental and climatic conditions is presented for the middle miocene long term freshwater lake 14 3 to 13 5 ma of the steinheim basin on the basis of a combined c o and sr isotope study of sympatric skeletal fossils of aquatic and terrestrial organisms from the lake sediments the oxygen isotope composition for lake water of the steinheim basin 18oh2o 2 0 0 4 vsmow n 6 was reconstructed from measurements of 18opo4 of aquatic turtle bones the drinking water calculated from the enamel of large mammals proboscideans rhinocerotids equids cervids suids has 18oh2o values 18oh2o 5 9 1 7 vsmow n 31 typical for middle miocene meteoric water of the area this 18oh2o value corresponds to a mean annual air temperature mat of 18 8 3 8 c calculated using a modern day 18oh2o mat relation hence large mammals did not use the lake water as principal drinking water in contrast small mammals especially the then abundant pika prolagus oeningensis drank from 18o enriched water sources 18oh2o 2 7 2 3 vsmow n 7 such as the lake water differences in sr and o isotopic compositions between large and small mammal teeth indicate different home ranges and drinking behaviour and support migration of some large mammals between the swabian alb plateau and the nearby molasse basin while small mammals ingested their food and water locally changes in the lake level water chemistry and temperature were inferred using isotopic compositions of ostracod and gastropod shells from a composite lake sediment profile calcitic ostracod valves ilyocypris binocularis 18o 1 7 1 2 vpdb 13c 0 5 0 9 vpdb n 68 and aragonitic gastropod shells gyraulus spp 18o 2 0 1 3 vpdb 13c 1 1 1 3 vpdb n 89 have 18o and 13c values similar to or even higher than those of marine carbonates 13c values of the biogenic carbonates parallel lake level fluctuations while 18o values scatter around 2 2 and reflect the short term variability of meteoric water inflow vs longer term evaporation 87sr 86sr ratios of aragonitic gyraulus spp gastropod shells parallel the lake level fluctuations reflecting variable inputs of groundwater and surface waters using a water 18oh2o value of 2 0 vsmow water temperatures calculated from skeletal tissue 18o values of ostracods are 16 7 5 0 c gastropods 20 6 5 6 c otoliths 21 8 1 4 c and fish teeth 17 0 2 7 c the calculated mat 19 c lake water temperatures 17 to 22 c and the 18o enriched water compositions are indicative of warm temperate climatic conditions possibly with a high humidity during this period vegetation in the area surrounding the basin was largely of the c3 type as indicated by carbon isotopic compositions of tooth enamel from large mammals 13c 11 1 1 1 vpdb n 40

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

clay mineral changes across the eocene oligocene transition in the sedimentary sequence at xining occurred prior to global cooling abstract during the cenozoic high quality long term sedimentary sequences formed in xining basin at the northeastern margin of the tibetan plateau which are characterized by alternating gypsiferous layers and reddish mudstone beds the tashan section was previously dated in detail by magnetostratigraphy which yielded an age span of 16 to 35 7 ma in this study bulk and clay mineral assemblages and magnetic parameters of the 33 1 35 7 ma portion were analyzed using x ray diffraction and magnetic methods to determine the behavior of the eocene oligocene climate transition quartz calcite feldspar and clay fractions in sediments that are mainly derived from the surrounding catchments gypsum and dolomite are authigenic minerals illite chlorite irregular mixed layer illite smectite and smectite are the four main clay sized fractions

faster better shear wave velocity to 100 meters depth from refraction microtremor arrays current techniques of estimating shallow shear velocities for assessment of earthquake site response are too costly for use at most construction sites they require large sources to be effective in noisy urban settings or specialized independent recorders laid out in an extensive array this work shows that microtremor noise recordings made on 200 m long lines of seismic refraction equipment can estimate shear velocity with 20 accuracy often to 100 m depths the combination of commonly available equipment simple recording with no source a wavefield transformation data processing technique and an interactive rayleigh wave dispersion modeling tool exploits the most effective aspects of the microtremor spectral analysis of surface wave sasw and multichannel analysis of surface wave masw techniques the slowness frequency wavefield transformation is particularly effective in allowing accurate picking of rayleigh wave phase velocity dispersion curves despite the presence of waves propagating across the linear array at high apparent velocities higher mode rayleigh waves body waves air waves and incoherent noise two locations illustrate the application of this technique in detail coincident with a large accelerometer microtremor array in reno nevada and atop a borehole logged for shear velocity in newhall california refraction equipment could duplicate microtremor results above 3 hz but could not estimate velocities deeper than 100 m refraction microtremor cannot duplicate the detail in the velocity profile yielded by a suspension logger but can match the average velocity of 10 to 20 m depth intervals and suggest structure below the 100 m logged depth of the hole eight additional examples from southern california and new zealand demonstrate that the refraction microtremor technique quickly produces good results from a wide range of hard and soft sites

thunder induced ground motions 2 site characterization 1 thunder induced ground motion near surface refraction and rayleigh wave dispersion measurements were used to constrain near surface velocity structure at an unconsolidated sediment site we employed near surface seismic refraction measurements to first define ranges for site structure parameters air coupled and hammer generated rayleigh wave dispersion curves were used to further constrain the site structure by a grid search technique the acoustic to seismic coupling is modeled as an incident plane p wave in a fluid half space impinging into a solid layered half space we found that the infrasound induced ground motions constrained substrate velocities and the average thickness and velocities of the near surface layer the addition of higher frequency near surface rayleigh waves produced tighter constraints on the near surface velocities this suggests that natural or controlled airborne pressure sources can be used to investigate the near surface site structures for earthquake shaking hazard studies

glacial eustasy during the cenozoic sequence stratigraphic implications a newly constructed composite oxygen isotope record is a proxy for eustasy that extends back to the cretaceous tertiary boundary and provides an independent test of sequence stratigraphic based eustatic curves the isotope record shows several eustatic episodes that are consistent with the geological record of ice sheet evolution the first evidence for the existence of an ice sheet in east antarctica occurs near the lower middle eocene boundary base of the lutetian stage there is no evidence for a large ice sheet on antarctica prior to this time however strata of this age are lacking over most of the continent the isotope curve also indicates that the ice sheet experienced phases of growth during the late eocene and middle oligocene followed by a decrease in volume in the early miocene the ross sea stratigraphic record indicates initial evolution of the west antarctica ice sheet during the early miocene by the middle miocene the ice sheet spread across the ross sea weddell sea and antarctic peninsula continental shelves the pliocene pleistocene record of glaciation in antarctica includes numerous glacial erosion surfaces on the continental shelf indicating repeated advance and retreat of both east and west antarctica ice sheets these volume changes in the antarctica ice sheet were in response to the rise and fall of sea level caused by expanding and contracting northern hemisphere ice sheets there is a reasonable correlation between eustatic curves derived from sequence stratigraphic studies and the composite oxygen isotope record since the middle eocene this correlation indicates that glacial eustasy has been the principal factor regulating stratal stacking patterns on a global scale since the middle eocene

stratigraphy and deformational history of the scrip nappe monashee mountains british columbia the scrip nappe a large recumbent anticline that occupies the northern selkirk and northern monashee mountains has an inverted lower limb some 50 km in length across strike and comprises stratigraphic divisions of the hadrynian horsethief creek group which can be traced southward with decreasing metamorphic grade through the selkirk mountains to the northern purcell mountains the scrip nappe has a southwesterly vergence and it formed that way during the first folding phase of the mesozoic columbian orogeny metamorphism no greater than biotite zone accompanied that first deformation the nappe was subsequently refolded into tight northeast verging folds metamorphism rose to upper amphibolite facies late in the second deformation phase after the metamorphic climax northeast verging buckle folds and associated crenulation cleavage formed locally during a third folding episode the entire nappe complex was then carried northeastward on the purcell thrust over the folds and thrusts of the western r

cenozoic long term terrestrial climatic evolution in germany tracked by δ18o of rodent tooth phosphate even though the cenozoic has been recognized as a period of important climate change long term climatic changes that took place in the continental domain are still questioned for an area southern germany for which other long term palaeoclimatic records exist analysis of oxygen isotope composition of small mammal teeth has been carried out for localities ranging in age from the late eocene c 36 ma to the middle miocene c 10 ma comparison of this long term continental 18o record with the marine record reveals comparable trends the major cenozoic climatic events are thus recognized in the continental oxygen isotope record through comparison with other quantitative palaeoclimatic reconstructions available for the studied area temperatures in southern germany are broadly estimated to have fluctuated between 12 c and 25 c from late eocene to early late miocene according to the different available chronological frameworks either a 2 c considering the classical biostratigraphy or a 6 c considering a revised biostratigraphy decrease in mean air temperature is estimated for the eocene oligocene boundary

increased seasonality through the eocene to oligocene transition in northern high latitudes a profound global climate shift took place at the eocene oligocene transition approximately 33 5 million years ago when cretaceous early palaeogene greenhouse conditions gave way to icehouse conditions during this interval changes in the earth s orbit and a long term drop in atmospheric carbon dioxide concentrations resulted in both the growth of antarctic ice sheets to approximately their modern size and the appearance of northern hemisphere glacial ice however palaeoclimatic studies of this interval are contradictory although some analyses indicate no major climatic changes others imply cooler temperatures increased seasonality and or aridity climatic conditions in high northern latitudes over this interval are particularly poorly known here we present northern high latitude terrestrial climate estimates for the eocene to oligocene interval based on bioclimatic analysis of terrestrially derived spore and pollen assemblages preserved in marine sediments from the norwegian greenland sea our data indicate a cooling of approximately 5 degrees c in cold month winter mean temperatures to 0 2 degrees c and a concomitant increased seasonality before the oi 1 glaciation event these data indicate that a cooling component is indeed incorporated in the delta 18 o isotope shift across the eocene oligocene transition however the relatively warm summer temperatures at that time mean that continental ice on east greenland was probably restricted to alpine outlet glaciers

multiproxy reconstruction of the palaeoclimate and palaeoenvironment of the middle miocene somosaguas site madrid spain using herbivore dental enamel profound palaeoclimatic changes took place during the middle miocene the miocene climatic optimum 20 to 14 13 5 ma was followed by a sudden 200 ka decrease in temperature and an increase in aridity around the world as a consequence of the reestablishment of the ice cap in antarctica somosaguas palaeontological site madrid basin spain has provided a rich record of mammal remains coincident with this global event middle miocene biozone e 14 1 13 8 ma it contains four fossiliferous levels t1 t3 1 t3 2 and t3 3 with t1 being the oldest that span an estimated time of 105 125 ka scanning electron microscope sem and rare earth element ree analyses performed on herbivore tooth enamel gomphotherium angustidens anchitherium cf a cursor conohyus simorrensis prosantorhinus douvillei and ruminants indicate that diagenetic processes have not been intense enough as to obscure the original geochemical signal stable isotope 18oco3 13cco3 and 18opo4 analyses have been measured on the herbivore tooth enamel across these levels with the aim of determining to what extent the global cooling and aridity pattern is recorded at this site a decrease in 18oco3 and 18opo4 has been detected from t1 to t3 3 and t3 1 to t3 3 respectively indicating a progressive drop of about 6 c from around 18 c to 12 c in mean annual temperatures within t3 tooth enamel 13c values experience an increase from t3 1 to t3 3 suggesting an increase in aridity ba ca analyses have also been performed on the tooth enamel in order to detect changes in the palaeoecology of the studied taxa this ratio allows the establishment of particular feeding patterns such as a more browsing habit in the case of gomphotherium angustidens compared to anchitherium cf a cursor as suggested by higher ba ca values in the latter trace elements do not support any significant change across the succession in the dietary behaviour of the species analyzed despite the stable isotopes evidence of an important palaeoclimatic shift from t1 to t3 3

new bathonian middle jurassic ammonite faunas from the fernie formation southern alberta lateral impressions of ammonites are described from three levels in shales of the ribbon creek member fernie formation at adanac pass southern alberta the occurrence of kepplerites cf costidensus imlay and kepplerites subitus imlay with east pacific forms belonging to xenocephalites and lilloettia indicates correlation with the upper bathonian of the boreal sequence

two phase stratigraphic model of foreland basin sequences application of flexural models to nonmarine foreland basin evolution indicates that two different stratigraphic styles of basin fill may develop over time basin subsidence is most rapid during times of thrust load emplacement associated sedimentation is coarse grained immediately adjacent to the thrust front and grades rapidly into fine grained deposits that cover most of the basin the distal part of the basin may also contain deposits derived from streams that flow from beyond the basin toward the thrust belt subsequent removal of the thrust load by erosion and other processes results in flexural rebound of the thrust belt and adjacent foreland basin during this postorogenic phase of adjustment a regional unconformity develops in the proximal part of the foreland basin proximal deposits along with thrust derived sediment are redeposited in the distal foreland basin and beyond this two phase model of foreland sedimentation predicts that coarsening upward sequences in the proximal and distal parts of the basin have reciprocal significance the proximal sequence represents thrust belt advance whereas the distal sequence represents thrust belt cessation

cordilleria a newly defined canadian microcontinent palaeomagnetic data and geological field evidence indicate that most of the western canadian cordillera lay 1 500 km south of its present position in the early cretaceous we suggest that this region comprised a microcontinent termed cordilleria which moved on the kula plate and collided with the craton 100 myr ago to form first the mackenzie mountains and then the rockies

extending the ancient margin outboard in the canadian cordillera record of proterozoic crust and paleocene regional metamorphism in the nicola horst southern british columbia the nicola horst exposes plutonic and amphibolite grade metamorphic rocks and is surrounded by low grade arc rocks of the late triassic nicola group we present new geological mapping and u pb nd and metamorphic data for the nicola horst near bob lake 40 km south of kamloops british columbia the bob lake assemblage includes felsic to intermediate metavolcaniclastic rocks metaconglomerate schist phyllite and other rock types from u pb zircon analysis a felsic metaporphyry clast in metaconglomerate is 1 04 ga old the oldest detrital zircons in metaconglomerate and schist are also near 1 ga the bob lake assemblage was intruded by 230 ma tonalite 219 ma diorite and 64 ma leucogranite and includes 161 ma felsic porphyry and 157 ma rhyodacite amphibolite grade metamorphism and ductile flattening and stretching affected all rocks except crosscutting paleocene granite and granodiorite the high grade rocks may be exposed as a result of latest cretaceous eocene extensional ductile flow beneath a thin brittle upper crust a thickness of 20 km of juvenile crust beneath the proposed quesnel terrane is inconsistent with the evidence of proterozoic source rocks at surface we infer that most of the crustal lithosphere in this part of the intermontane belt is continental which does not preclude possibly thick arc rocks in other parts the local thinness of the nicola group however is inconsistent with emplacement as a regional allochthon and thus with their inclusion in a quesnel terrane the nicola arc succession appears to have been built on the ancient continental margin

early oligocene ice sheet expansion on antarctica stable isotope and sedimentological evidence from kerguelen plateau southern indian ocean sedimentological and stable isotope data from a pelagic sequence recovered from the southern indian ocean provide the most convincing evidence to date for short term expansion of a large ice sheet on antarctica during the earliest oligocene 36 ma terrigenous debris identified as ice rafted in origin on the basis of textural compositional and size criteria is present at the same stratigraphic level as the ubiquitous early oligocene oxygen isotope shift the highest benthic foraminiferal 18o values 3 0 of the paleogene occur in samples from within the ice rafted debris interval these values are similar to those recorded by holocene benthic foraminifera implying that the ice sheet may have attained a volume similar to that of the present day ice sheet on antarctica the stratigraphic distribution of ice rafted debris and high oxygen isotope values indicate that these conditions persisted for roughly 100 ka

orogenic remagnetizations in the front ranges and inner foothills of the southern canadian cordillera chemical harbinger and thermal handmaiden of cordilleran deformation abstract paleomagnetic studies of carbonate rocks in mountain belts have been helpful to the understanding of orogenic mational origin with only one exception the a component has normal polarity in the front ranges and reverse processes the timing of deformation and the nature of fluid flow in actively deforming foreland basins most studies on shallow water carbonates indicate that their remanence is not primary but rather they record remagnetization events contemporaneous with orogeny by considering the remanent directions fold test results and rock magnetic properties and tying these results to complementary structural geochronological and geochemical studies we are able to interpret deformation history hydrological environment and orogenic diagenesis we study the relationship between remagnetization and deformation of paleozoic carbonates of the front ranges and inner foothills of the southern canadian rockies the magnetic properties are remarkably constant along 500 km strike length as sampled at 124 sites through 4 transects primary paleozoic remanent directions which would have shallow inclination are never observed rather the paleomagnetic signal is dominated by geographically persistent remagnetizations characterized by steep inclination as well as a soft present field overprint we observed two distinctive secondary magnetizations named the a and b components carried by fine grained magnetite pervasive diagenesis induced the a component a total chemical remanent remagnetization poles for the a component are better concentrated after bedding correction indicating a pre or early syndefor polarity in the inner foothills pole positions polarity and geological and thermal constraints indicate that the a component was acquired diachronously in advance of the eastward migrating cordilleran tectonic wedge subsequently an intermediate temperature partial thermo remanent remagnetization the b component was superimposed on large regions of the front ranges and inner foothills b component directions are brought into optimal concentration by differential untilting of 0 to 50 indicating that the component was acquired after the rocks were incorporated into the orogenic wedge but before the end of contractional deformation the b component is strongest within a couple of kilometers of the frontal thrust of the front ranges the relative magnitude of the b to a components and the maximum unblocking temperature of the b component decrease away from the frontal thrust over about 30 km both to the west and to the east the b component thermal overprint was attained by 250 c heating in response to tectonic or possibly sedimentary loading it was preserved by a rapid cooling accompanying a differential uplift and erosion of up to 8 km in the vicinity of the frontal thrust late in or post dating its local tilting history the likely cause was uplift of the exposed structural panel by contraction of younger underlying thrust structures

stable isotope compositions of mammoth teeth from niederweningen switzerland implications for the late pleistocene climate environment and diet abstract oxygen and carbon isotope compositions of well preserved mammoth teeth from the middle wurmian 40 70 ka peat layer of niederweningen the most important mammoth site in switzerland were analysed to reconstruct late pleistocene palaeoclimatic and palaeoenvironmental conditions drinking water 18o values of approximately 12 3 0 9 were calculated from oxygen isotope compositions of mammoth tooth enamel apatite using a species specific calibration for modern elephants these 18 o h 2 o values reflect the mean oxygen isotope composition of the palaeo precipitation and are similar to those directly measured for late pleistocene groundwater from aquifers in northern switzerland and southern germany using a present day 18 o h 2 o precipitation air temperature relation for switzerland a mean annual air temperature mat of around 4 3 2 1 c can be calculated for the middle wurmian at this site this mat is in good agreement with palaeotemperature estimates on the basis of middle wurmian groundwater recharge temperatures and beetle assemblages hence the climatic conditions in this region were around 4 c cooler during the middle wurmian interstadial phase around 45 50 ka bp than they are today during this period the mammoths from niederweningen lived in an open tundra like c3 plant dominated environment as indicated by enamel 13c values of 11 5 0 3 and pollen and macroplant fossils found in the embedding peat the low variability of enamel 13c and 18o values from different mammoth teeth reflects similar environmental conditions and supports a relatively small time frame for the fossil assemblage

eocene oligocene mammalian faunal turnover in the hampshire basin uk calibration to the global time scale and the major cooling event a new high resolution c 1 ma mammalian record in continental eocene oligocene strata in the hampshire basin is used to investigate the nature and timing of the major europe wide mammalian faunal turnover termed the grande coupure whether this was caused by climate change or by competition with taxa dispersing from asia is controversial the mammalian faunas in this record after rarefaction analysis show a sharp reduction in diversity only after the grande coupure improved correlation of nw european successions to global events confirms the grande coupure as earliest oligocene it shows that a c 350 ka hiatus interrupts the hampshire and paris basin sequences prior to the first record of post grande coupure asian taxa hiatus bridging faunas from elsewhere in europe record mainly post grande coupure taxa suggesting that the turnover occurred early in the hiatus minimizing bias to the turnover pattern a previously unrecorded second smaller turnover involving european mammals only immediately precedes the grande coupure in the hampshire basin coinciding with vegetational change this turnover is judged not to represent cooling it is concluded that the grande coupure coincides with the earliest oligocene oi 1 glaciation and that climate change combined with competition to produce the turnover

thunder induced ground motions 1 observations 1 acoustic pressure from thunder and its induced ground motions were investigated using a small array consisting of five three component short period surface seismometers a three component borehole seismometer and five infrasound microphones we used the array to constrain wave parameters of the incident acoustic and seismic waves the incident slowness differences between acoustic pressure and ground motions suggest that ground reverberations were first initiated somewhat away from the array using slowness inferred from ground motions is preferable to obtain the seismic source parameters we propose a source equalization procedure for acoustic seismic deconvolution to generate the time domain transfer function a procedure similar to that of obtaining teleseismic earthquake receiver functions the time domain transfer function removes the incident pressure time history from the seismogram an additional vertical to radial ground motion transfer function was used to identify the rayleigh wave propagation mode of induced seismic waves complementing that found using the particle motions and amplitude variations in the borehole the initial motions obtained by the time domain transfer functions suggest a low poisson s ratio for the near surface layer the acoustic to seismic transfer functions show a consistent reverberation series at frequencies near 5 hz this gives an empirical measure of site resonance that depends on the ratio of the layer velocity to layer thickness for earthquake p and s waves the time domain transfer function approach by transferring a spectral division into the time domain provides an alternative method for studying acoustic to seismic coupling

eocene oligocene extinction and paleoclimatic change near eugene oregon thick ash fl ow tuffs provide marker beds through fossiliferous eocene and oligocene marine and non marine sedimentary rocks near eugene oregon new mapping radiometric dating and paleomagnetic stratigraphy of these tuffs and rocks now allow dating of local fossil fl oras the comstock goshen rujada and willamette fl oras have been widely used as evidence for eocene oligocene climatic cooling and drying eocene leaves from comstock and hobart butte included such thermophilic taxa as liquidambar the early oligocene goshen fl ora lacked liquidambar but retained many thermophilic species with large leaves that have entire margins and acuminate apices drip tips in contrast fossil leaves from later oligocene rujada and willamette fl oras are small and serrate and most lack drip tips marine faunas also indicate climatic cooling and local disappearance of thermophilic molluscs such as anadara ficus and conus our dating and compilation of plant and molluscan fossil occurrences indicate a steady rise in species diversity from 46 ma to maximal diversity of thermophilic taxa at 35 34 ma then extinctions of 60 of plant species after 33 4 ma and 32 of marine invertebrates after 33 2 ma both signifi cantly postdating the eocene oligocene boundary at 33 7 ma plant diversity rebounds during the early oligocene but marine invertebrates continue to decline into the oligocene in part due to the retreat of fully marine environments from the eugene area neither these data nor evidence from coeval fossil plants and soils in central oregon support the notion of a terminal eocene event nor any other single abrupt paleoclimatic shift or extinction the eocene oligocene biotic and climatic transition was drawn out over some 6 m y abrupt forcings such as meteorite impacts or volcanic eruptions are less likely explanations for cooling and diversity decline than long term processes such as mountain building changing ocean currents or reorganization of the carbon cycle by coevolution of grasses and grazers

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

the arctic forest of the middle eocene abstractlush forests dominated by deciduous conifers existed well north of the arctic circle during the middle eocene 45 ma the fossil forest site located on axel heiberg island canada has yielded a particularly rich assemblage of plant macro and microfossils as well as paleosols all exquisitely preserved methods ranging from classical paleobotany to stable isotope geochemistry have been applied to materials excavated from the fossil forest and have revealed layers of diverse conifer forests with a rich angiosperm understory that successfully endured three months of continuous light and three months of continuous darkness paleoenvironmental reconstructions suggest a warm ice free environment with high growing season relative humidity and high rates of soil methanogenesis methods to evaluate intraseasonal variability highlight the switchover from stored to actively fixed carbon during the short annual growing season

multiproxy record of abrupt sea surface cooling across the eocene oligocene transition in the gulf of mexico the eocene oligocene transition eot ca 33 34 ma was a time of pronounced climatic change marked by the establishment of continental scale antarctic ice sheets the timing and extent of temperature change associated with the eot is controversial here we present multiproxy eot climate records 15 34 k y resolution from st stephens quarry alabama usa derived from foraminiferal mg ca d18o and tex86 we constrain sea surface temperatures ssts in the latest eocene and early oligocene and address the issue of climatic cooling during the eot paleotemperatures derived from planktic foraminifera mg ca and tex86 are remarkably consistent and indicate late eocene subtropical ssts of 28 c there was substantial and accelerated cooling of ssts 3 4 c through the latest eocene precursor d18o shift eot 1 prior to oligocene isotope 1 oi 1 our multispecies planktic foraminiferal d18o records diverge at the e o boundary 33 7 ma signifying enhanced seasonality in the earliest oligocene in the gulf of mexico

terrestrial cooling in northern europe during the eocene oligocene transition geochemical and modeling studies suggest that the transition from the greenhouse state of the late eocene to the icehouse conditions of the oligocene 34 33 5 ma was triggered by a reduction of atmospheric pco2 that enabled the rapid buildup of a permanent ice sheet on the antarctic continent marine records show that the drop in pco2 during this interval was accompanied by a significant decline in high latitude sea surface and deep ocean temperature and enhanced seasonality in middle and high latitudes however terrestrial records of this climate transition show heterogeneous responses to changing pco2 and ocean temperatures with some records showing a significant time lag in the temperature response to declining pco2 we measured the 47 of aragonite shells of the freshwater gastropod viviparus lentus from the solent group hampshire basin united kingdom to reconstruct terrestrial temperature and hydrologic change in the north atlantic region during the eocene oligocene transition our data show a decrease in growing season surface water temperatures 10 c during the eocene oligocene transition corresponding to an average decrease in mean annual air temperature of 4 6 c from the late eocene to early oligocene the magnitude of cooling is similar to observed decreases in north atlantic sea surface temperature over this interval and occurs during major glacial expansion this suggests a close linkage between atmospheric carbon dioxide concentrations northern hemisphere temperature and expansion of the antarctic ice sheets

air humidity and lake δ18o during the latest paleocene earliest eocene in france from recent and fossil fresh water and marine gastropod δ18o δ13c and 87sr 86sr detailed isotopic 18 o 13 c 87 sr 86 sr analyses have been performed on aragonitic fresh water brackish water and marine gastropod shells of latest paleocene earliest eocene age from northwestern europe fresh water shells e g viviparus lymnaea from sparnacian deposits in the paris basin show relatively high 18 o values in the range 4 to 0 1 large intrashell 18 o variability typically 3 is consistent with significant seasonal variation in precipitation and or temperature we also present intrashell isotopic profiles for 22 recent fresh water shells mainly viviparidae representing the major middle to low latitude climate zones e g sweden france portugal lake chad ceylon gambia congo lake victoria new guinea distinct isotopic patterns reflecting humidity and temperature characterize each of the climate zones comparing the results for recent and fossil shells suggests that the climate in northern france during sparnacian time was warm subtropical with a pronounced seasonal drought the 18 o composition of sparnacian lake water has been estimated from the fossil fresh water shell 18 o and by using seasonal temperatures derived from 18 o profiles of fully marine shells the best estimate of the 18 o composition of sparnacian lake water compared with eocene mean ocean water is 1 this is consistent with paleorain 18 o values of 3 to 5 similar to present mean rain 18 o standard mean ocean water values close to 4 in portugal at 40 n the paleolatitude of the paris basin during earliest eocene time the evaporated nature of sparnacian lake water contradicts hypotheses of globally equable humid conditions in the warm early eocene and instead suggests that dry subtropical highs occurred over the eastern parts of the oceans similar to today the results of this study demonstrate the potential of fossil fresh water carbonates to reconstruct the development of subtropical highs and hadley cell circulation in the past

significance of shallow marine and non marine algae stable isotope δ18o compositions over long periods example from the palaeogene of the paris basin in this study we test the potentiality of using dasycladales and charophytes calcareous shallow marine and non marine algae respectively as palaeoclimatic recorders these algae mineralize their carbonate during short periods in summer throughout the palaeogene we compare the 18o variation of these two taxa to identify a possible common factor influencing their isotopic composition i e temperatures variations from a local environmental signal we sampled and isotopically analyzed eight species of charophytes and seven species of dasycladales from 23 formations ranging from the palaeocene to the oligocene series of the paris basin by comparing the 18o of these two groups living in different environment with that of shallow marine mollusks from a previous study we show that temperature variations are the main factor influencing their 18o compositions and that local environmental effects do not screen the global thermal signal maximum annual palaeotemperatures are calculated from the 18o of the dasycladales and indicate by comparison with the data from mollusks previously analyzed that dasycladales species used probably mineralized their carbonate in equilibrium with sea water dasycladales recorded the global climatic events already known for the palaeogene with high temperatures reached during the early eocene and middle eocene climatic optimums and relative cooling intervals during the lutetian the priabonian and the rupelian charophyte gyrogonites also recorded temperature variations in their 18o compositions but reconstituting reliable temperature values in non marine environments is not directly possible and requires constraining 18o of local continental water using other proxies these promising results show that carbonates mineralized from algae constitute a reliable support for palaeoclimatic information and should be more widely used in the fossil record

comparison of phase velocities from array measurements of rayleigh waves associated with microtremor and results calculated from borehole shear wave velocity profiles shear wave velocities vs are widely used for earthquake ground motion site characterization vs data are now largely obtained using borehole meth ods drilling holes however is expensive nonintrusive surface methods are inex pensive for obtaining vs information but not many comparisons with direct borehole measurements have been published because different assumptions are used in data interpretation of each surface method and public safety is involved in site character ization for engineering structures it is important to validate the surface methods by additional comparisons with borehole measurements we compare results obtained from a particular surface method array measurement of surface waves associated with microtremor with results obtained from borehole methods using a 10 element nested triangular array of 100 m aperture we measured surface wave phase veloci ties at two california sites garner valley near hemet and hollister municipal air port the garner valley site is located at an ancient lake bed where water saturated sediment overlies decomposed granite on top of granite bedrock our array was deployed at a location where seismic velocities had been determined to a depth of 500 m by borehole methods at hollister where the near surface sediment consists of clay sand and gravel we determined phase velocities using an array located close to a 60 m deep borehole where downhole velocity logs already exist because we want to assess the measurements uncomplicated by uncertainties introduced by the inversion process we compare our phase velocity results with the borehole vs depth profile by calculating fundamental mode rayleigh wave phase velocities from an earth model constructed from the borehole data for wavelengths less than 2 times of the array aperture at garner valley phase velocity results from array measure ments agree with the calculated rayleigh wave velocities to better than 11 mea surement errors become larger for wavelengths 2 times greater than the array aper ture at hollister the measured phase velocity at 3 9 hz near the upper edge of the microtremor frequency band is within 20 of the calculated rayleigh wave veloc ity because shear wave velocity is the predominant factor controlling rayleigh wave phase velocities the comparisons suggest that this nonintrusive method can provide vs information adequate for ground motion estimation

summer temperatures of late eocene to early oligocene freshwaters the marine foraminiferal isotope record displays a positive 18o shift early in the oligocene which has been identified as the onset of the antarctic oi 1 glaciation reported here are the first oxygen isotope derived summer paleotemperatures for continental freshwater in the northern hemisphere hampshire basin isle of wight uk leading up to and across this event these paleotemperatures are derived from multiple paleoproxies rodent tooth enamel gastropod shells charophyte gyrogonites and fish otoliths and are independent of freshwater evaporation effects and changes in ice volume we conclude that a fluctuating mesothermal climate existed but that there was no significant decrease in summer temperatures across the oi 1 glaciation this result is concordant with several other studies in suggesting that the majority of the isotopic shift in the marine realm across the oi 1 glaciation is linked to changes in antarctic ice volume and not to global temperature change our new approach has allowed us to derive numerical values for summer temperatures as well as to reconstruct relative temperature change across this key interval of the eocene oligocene transition

tibetan plateau aridification linked to global cooling at the eocene oligocene transition the eocene oligocene transition about 33 5 million years ago was a major global climate event the end of the eocene was unusually warm with no significant ice on antarctica but the oligocene saw the arrival of a permanent antarctic ice sheet two papers this week relate to the continental effects of this global change dupont nivet et al examined sedimentary records from the tibetan plateau and find a drop in atmospheric water which caused cooling and aridification coincident with antarctic cooling previous studies attributed this phenomenon to the rapid uplift of the tibetan plateau but this new work suggests that regional tibetan climate was influenced by global events in an unrelated paper on the same climate transition zanazzi et al explore the cooling in north america at the time using stable isotope measurements from fossil teeth and bones to create a proxy temperature record they find a large drop in mean annual temperature of 8 2 c a greater fall than seen in the oceans this continental transition may explain why many cold blooded reptiles and amphibians became extinct whereas mammals able to regulate their body temperature escaped relatively unscathed precisely dated evidence details that aridification on the tibetan plateau occurred at the time of the eocene oligocene transition in the marine records this suggests a direct link between the palaeontological and palaeoenvironmental changes recorded in continental asia at the time and global climate cooling continental aridification and the intensification of the monsoons in asia are generally attributed to uplift of the tibetan plateau and to the land sea redistributions associated with the continental collision of india and asia1 2 3 whereas some studies suggest that past changes in asian environments are mainly governed by global climate4 5 6 the most dramatic climate event since the onset of the collision of india and asia is the eocene oligocene transition an abrupt cooling step associated with the onset of glaciation in antarctica 34 million years ago7 8 9 however the influence of this global event on asian environments is poorly understood here we use magnetostratigraphy and cyclostratigraphy to show that aridification which is indicated by the disappearance of playa lake deposits in the northeastern tibetan plateau occurred precisely at the time of the eocene oligocene transition our findings suggest that this global transition is linked to significant aridification and cooling in continental asia recorded by palaeontological and palaeoenvironmental changes10 11 12 and thus support the idea that global cooling is associated with the eocene oligocene transition13 14 15 we show that with sufficient age control on the sedimentary records global climate can be distinguished from tectonism and recognized as a major contributor to continental asian environments

selkirk fan structure southeastern canadian cordillera tectonic wedging against an inherited basement ramp a revised cross section through the selkirk fan structure provides the basis for a new model for the middle jurassic tectonic evolution of the southern omineca belt canadian cordillera palinspastic restoration of this cross section shows that the southwest verging structures along the west flank of the selkirk fan structure formed as a result of tectonic wedging of distal north american strata clachnacudainn complex beneath more proximal north american strata and that the selkirk fan structure developed outboard from a crustal ramp dogtooth high inherited from late proterozoic early paleozoic rifting along the western margin of north america the first episode of mesozoic deformation in southeastern british columbia occurred between 187 and 173 ma and involved the northeastward juxtaposition of the intermontane superterrane over the outer part of the north american continental terrace wedge it resulted in deep burial 20 25 km of the outer margin of north america a crustal ramp localized along the western edge of the late proterozoic early paleozoic dogtooth high impeded the northeastward propagation of the orogenic wedge comprising the intermontane superterrane and the imbricate underlying northeast verging thrust sheets of north american supracrustal rocks tectonic wedging involving southwest verging deformation occurred within the orogenic wedge and the resulting crustal thickening established sufficient topography and gravitational potential to drive the propagation of the deformation eastward into the dogtooth range and the rocky mountains the southwest verging structures along the west flank of the selkirk fan developed between approximately 173 and 168 ma concurrent with synorogenic extension and 10 km of exhumation the initial subsidence of the foreland basin during kimmeridgian time ca 154 ma provides the first indication of tectonic loading and lithospheric flexure of the north american plate it is interpreted to mark the time at which the orogenic wedge overrode the crustal ramp of the dogtooth high and advanced onto relatively thick and rigid continental lithosphere the tectonic model proposed for the selkirk fan structure illustrates how the configuration of the rifted margin influenced the style of crustal thickening during subsequent compressional deformation

cenozoic deep sea temperatures and global ice volumes from mg ca in benthic foraminiferal calcite a deep sea temperature record for the past 50 million years has been produced from the magnesium calcium ratio mg ca in benthic foraminiferal calcite the record is strikingly similar in form to the corresponding benthic oxygen isotope 18o record and defines an overall cooling of about 12 c in the deep oceans with four main cooling periods used in conjunction with the benthic 18o record the magnesium temperature record indicates that the first major accumulation of antarctic ice occurred rapidly in the earliest oligocene 34 million years ago and was not accompanied by a decrease in deep sea temperatures

seismic ground motions from a bolide shock wave 1 an intensely brilliant bolide accompanied by an audible sonic boom occurred on the night of 3 november 2003 2150 lt or 4 november 2003 0350 ut in northeastern arkansas the sonic boom was well recorded by 22 three component stations of the center for earthquake research and information cooperative seismic network arrival times and wave polarizations were used to reconstruct the acoustic wave front propagating across the network and to estimate trajectory parameters of the bolide a grid search location technique constrains the trajectory and gives a reference height of 50 100 km above the southern edge of the network an azimuth of propagation of 270 290 toward the northwest and a plunge of 38 48 downward the trajectory and date of the bolide event are consistent with a taurid shower meteor transient ground motions from the sonic boom were studied using plane wave cagniard dehoop and propagator matrix theory for an incident pressure pulse impinging on a layered elastic earth model general characteristics of the vertical and radial polarization and wave frequency content require acoustic coupling within a thin 10 m near surface layer with low p wave 0 25 km s and s wave 0 125 km s velocities ground motions are generally confined to this near surface layer are not sensitive to deeper earth structure within the mississippi embayment unconsolidated sediments and display both leaky mode pl a type of dispersed p type seismic wave and locked mode rayleigh wave propagation acoustic wave ground motion coupling studies may be a useful way to analyze near surface site responses to determine velocity structure in earthquake shaking hazard studies

reevaluation of conflicting eocene tropical temperature estimates molluskan oxygen isotope evidence for warm low latitudes oxygen isotope data from planktonic foraminifera for the warm eocene epoch suggest that tropical sea surface temperatures ssts may have been cooler than at present such data have stimulated various explanations involving e g major changes in ocean heat transport however the planktonic data disagree with terrestrial climate proxies which suggest significantly warmer low latitude temperatures we examined this discrepancy by analyzing seasonal oxygen isotope variations in shallow marine mollusks from the mississippi embayment results indicate that mean annual ssts decreased from 26 27 c in the early eocene to 22 23 c in the oligocene agreeing well with temperatures inferred from terrestrial climate proxies these cooling trends with more significant winter cooling 5 c than summer cooling 3 c are consistent with the predicted consequences of decreasing atmospheric co 2 concentration through the paleogene suggesting that atmospheric co 2 change was a major controlling factor for paleogene climate change that winter sst estimates from the mollusks agree well with the foraminiferal sst estimates suggests that planktonic foraminiferal growth in low latitudes occurred mainly during the cooler winter months throughout the eocene we hypothesize that the unusual hydrography of eocene oceans shifted foraminiferal productivity primarily to winter biasing foraminiferal sst estimates of mean annual ssts