constant elevation of southern tibet over the past 15 million years the uplift of the tibetan plateau an area that is 2 000 km wide to an altitude of about 5 000 m has been shown to modify global climate and to influence monsoon intensity mechanical and thermal models for homogeneous thickening of the lithosphere make specific predictions about uplift rates of the tibetan plateau but the precise history of the uplift of the plateau has yet to be confirmed by observations here we present well preserved fossil leaf assemblages from the namling basin southern tibet dated to approximately 15 myr ago which allow us to reconstruct the temperatures within the basin at that time using a numerical general circulation model to estimate moist static energy at the location of the fossil leaves we reconstruct the elevation of the namling basin 15 myr ago to be 4 689 895 m or 4 638 847 m depending on the reference data used this is comparable to the present day altitude of 4 600 m we conclude that the elevation of the southern tibetan plateau probably has remained unchanged for the past 15 myr

a new approach for palaeoaltitude estimates based on pollen records example of the mercantour massif southeastern france at the earliest pliocene the altitude of the mercantour massif southern alps france during the earliest pliocene has been estimated using a new quantification method instead of classical methods using geomorphologic criteria our method uses biogeographic and climatologic criteria composition of the modern vegetation belts in the european and peri mediterranean mountains and pliocene annual temperature estimates obtained from fossil pollen data the climatic transfer function indicates for the coastal earliest pliocene of the studied area a mean annual temperature of 16 5oc such a temperature today occurs at 38 5on latitude in the mediterranean region the relation established by ozenda between the present day vertical and latitudinal vegetation assemblages evidences a shift of on average in western europe 110 m in altitude per degree in latitude as a consequence it is possible taking into account that the pliocene lapse rate was almost similar to the modern one to estimate the minimum altitude of the massif at the earliest pliocene the so obtained palaeoaltitude estimate is close to that obtained with the geomorphological method the mercantour massif was almost 2000 meters high at the earliest pliocene

uplift history of the central and northern andes a review the elevation of the andean cordillera is a crucial boundary condition for both climatic and tectonic studies the andes affect climate because they form the only barrier to atmospheric circulation in the southern hemisphere and they intrigue geologists because they have the highest plateau on earth formed at a noncollisional plate margin the altiplano puna yet until recently few quantitative studies of their uplift history existed this study presents both 1 a review of the quantitative paleoelevation estimates that have been made for the central and colombian andes and 2 an examination of the source and magnitude of error for each estimate in the central andes paleobotanical evidence suggests that the altiplano puna had attained no more than a third of its modern elevation of 3700 m by 20 ma and no more than half its modern elevation by 10 7 ma these data imply surface uplift on the order of 2300 3400 m since the late miocene at uplift rates of 0 2 0 3 mm yr paleobotanical and geomorphological data suggest a similar uplift history for the eastern cordillera namely no more than half the modern elevation present by 10 ma no evidence exists for an exponential increase in uplift rate as has been interpreted from fissiontrack data these uplift rates mostly reflect mean surface uplift rather than rock uplift that is uplift of material points because little dissection of the western eastern cordillera has occurred south of lat 19 s and of the altiplano puna thus the central andean plateau appears to be young in the colombian andes paleobotanical data imply rapid uplift of the eastern cordillera between 2 and 5 ma at rates on the order of 0 6 3 mm yr however some of this uplift is likely rock uplift due to erosion driven isostatic rebound rather than mean surface uplift

model for the origin of the yakutat block an accreting terrane in the northern gulf of alaska a composite oceanic and continental terrane the yakutat block is currently colliding with and accreting to north america in the northern gulf of alaska marine geophysical data indicate that the block has moved with the pacific plate during pliocene and quaternary time but are indeterminant about its previous movement history a model that explains some observed geologic and structural features of the block is that it originated as a result of subduction of the kula farallon spreading center beneath north america in this model the spreading center that formed the basaltic basement of the yakutat block was offset from a spreading center to the south by a left lateral transform fault 400 500 km long subduction of the northern spreading center about 45 m y ago sliced off part of the north america continental margin attached it to the kula plate and initiated northward movement of the composite terrane as the yakutat block during eocene and oligocene time migration of the southern spreading center toward north america truncated the yakutat block on the south and left a fossil fracture zone that is now seen as the transition fault the southern spreading center subducted about 25 m y ago and the yakutat block has since traveled with the pacific plate to southern alaska

palaeoaltimetry from energy conservation principles a knowledge of past changes in the mean elevations of large continental areas is important for understanding both dynamic processes in the earth s mantle 1 and the evolution of the global climate 2 but virtually all methods for determining palaeoelevations are problematic in part because changes in either elevation or climate can give rise to the same observed geological phenomena 4 ideally palaeoelevations would be inferred directly from estimates of palaeopressure and it has recently been shown 5 that vesicles in basaltic lava flows preserve a record of atmospheric pressure at the altitude of emplacement however the elevations thus obtained have large errors 1 4 km and the method can at present be applied only to lavas that have had a simple emplacement history 5 palaeobotanical methods for estimating palaeoelevation have received much attention 6 12 but they rely on empirical temperature elevation relationships the uncertainties in which are difficult to evaluate for past climates here we describe an alternative palaeobotanical approach based on energy conservation in the atmosphere in which fossil leaf assemblages are used to infer enthalpy rather than temperature this approach is relatively insensitive to palaeoclimate with an expected error in palaeoelevation of 700 m

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

pliocene uplift of the massif central france constrained by the palaeoelevation quantified from the pollen record of sediments preserved along the cantal stratovolcano murat area the french massif central is a key basement relief this region experienced an intense period of alkaline volcanism beginning with the cantal stratovolcano at 11 ma and ending at 3 ma to quantify the palaeoelevation of the cantal stratovolcano and to replace it in the frame of the uplift history of the massif central we first reconstructed the vegetation and climate based on a pollen analysis of the murat diatomites which were deposited in a maar lake the vegetation was organized in three different belts a glyptostrobus swamp around the lake a mixed forest and at higher altitudes a conifer forest the climate estimated using the climatic amplitude method indicates temperatures between 11 4 and 17 c using these estimates and comparison with contemporaneous sites we infer a palaeoelevation for murat between 710 and 930 m a s l this site was therefore uplifted by 130 to perhaps 350 m during the early pliocene leading to a reorganization of the drainage pattern and the capture of rivers flowing from the northern edge of the massif central towards the atlantic ocean our study confirms that the cantal stratovolcano was a high volcano 2500 m before its progressive dismantling during glacial episodes in the pleistocene

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

using pre quaternary diptera as indicators of paleoclimate abstract many researchers have used fossilized insects to determine quaternary climates with great success however pre quaternary insect fossils have not been utilized as indicators of climate with the same frequency despite levels of preservation that are often equal to that of quaternary fossils in this study we use the mutual climate range mcr approach with fossil diptera from the florissant formation to examine the accuracy with which pre quaternary insect fossils can be used to determine paleoclimate a database of extant dipteran climate ranges was compiled and mcr analyses were performed on all fossil dipteran genera from florissant with extant representatives the analyses were performed using all fossil dipteran genera and then again with only non host specific taxa the estimates of paleoclimate from our analyses were then compared to previous estimates obtained from various paleobotanical studies of the florissant formation the paleobotanical studies utilize a variety of methods to determine paleoclimate including nearest living relative nlr modern analogues clamp palynalysis and leaf margin analysis we found that using a mcr approach with fossil diptera can provide an estimate of paleoclimate for pre quaternary assemblages that is consistent with estimates made by paleobotanists the analysis that included all diptera gave a less precise climate estimate 12 18 c than the analysis in which host dependent taxa were omitted our climate estimate based on only non host specific taxa was 12 14 c which is well within the range of estimates for florissant derived from floral material although approaches that use modern analogs are sometimes viewed with concern because of the necessary assumption that fossil taxa share the same environmental tolerances as their modern counterparts we believe that fossil insect assemblages especially when used in mcr analyses can be quite informative in estimating pre quaternary paleoclimate

paleoclimatic evidence for cenozoic migration of alaskan terranes chronostratigraphic and paleoclimatic comparisons of microfossils from deep sea cores from samples of an exploratory drill hole and from dredged rock of the gulf of alaska with coeval microfossil assemblages on the north american continent provide constraints on the northward migration of the yakutat block the prince william terrane and the pacific plate during tertiary time the comparative paleolatitudes of microfauna and flora provide three main constraints 1 the prince william terrane was in its present position with respect to north america at high latitudes 50 5 n by middle eocene time 40 42 ma consistent with models derived from paleomagnetic data 2 the adjacent yakutat block was 30 5 south of its present position in early eocene 50 ma 20 5 south in middle eocene 40 44 ma and 15 5 south in late eocene time 37 40 ma thus requiring a northward motion of about 30 since 50 ma moreover the yakutat block was at least 10 south of the prince william terrane during eocene time these data are consistent with migration of the yakutat block with the pacific and kula plates for at least the last 50 ma 3 site 192 on the pacific plate was at about 15 5 n latitude in the late cretaceous 68 ma at 30 5 n in early eocene 50 ma at 40 5 n in middle eocene 40 44 ma at 45 5 n in late eocene 37 40 ma and north of 50 5 n in latest eocene to early oligocene time 34 37 ma these paleolatitudes based on planktonic foraminiferal assemblages indicate northward drift consistent with the north america pacific plate reconstructions from about 68 ma to 40 ma engebretson 1982 however from cretaceous to early eocene time faunal data indicate significantly lower latitudinal positions and from oligocwne to early miocene time significantly higher latitudinal positions these discrepancies can be explained by the northward expansion of tropical faunas during the globally warm early tertiary and southward expansion of cold subarctic faunas as a result of global cooling during oligocene time

test of climate leaf physiognomy regression models their application to two miocene floras from kenya and 40ar 39ar dating of the late miocene kapturo site abstract to test multiple regression models developed to predict seven variables of climate from leaf margin and size characters leaf character data were collected from modern woodland and rainforest plant communities in uganda these localities were chosen for their structural similarity to two fossil sites for which climate values were desired the test indicated that for these communities the model accurately predicts mean annual temperature however the multiple regression models overestimate seasonality of temperature and mean annual and seasonal precipitation amounts for the two modern communities reasons for the models inaccuracies may include no african analog in the non african database on which the model is based too much intraspecific variability in leaf size an important character in precipitation models and relationships between leaf form and climate that may not be well defined by multiple regression mean annual temperatures were reconstructed for two miocene paleobotanical localities from the tugen hills of the eastern rift valley kenya using leaf form data primarily margin characters the results indicate that mean annual temperatures at kabarsero 12 6 ma and kapturo 6 7 7 2 ma were essentially equivalent to temperatures at those localities today and differed little from one another the kapturo paleofloral assemblage is a deciduous woodland interpreted as indicating less available or more seasonal moisture than the kabarsero paleofloral assemblage a wet forest with west african floral affinities laser fusion 40 ar 39 ar dating of volcanic materials at kapturo provides the first control of this paleoflora bracketed by a 7 2 ma trachyte at the base of the sedimentary sequence and an age of 6 7 ma on a reworked tuff overlying the fossiliferous horizon the chronologic data places the paleofloral assemblage in stratigraphic context relative to other tugen hills units containing paleofloras and abundant vertebrate remains including hominoids

a review of paleotemperature lapse rate methods for estimating paleoelevation from fossil floras one widely applied method for estimating paleoelevation from fossil floras uses the relation between vegetation and temperature to estimate mean annual temperature from two isochronous fossil assemblages one at elevation and one at or near sea level and the difference between these temperatures is multiplied by the reciprocal of a temperature lapse rate to estimate paleoelevation three fundamentally different approaches have been developed and these vary both in the method by which paleotemperatures are estimated and in the way by which modern lapse rates can be measured paleotemperature methodologies include the use of plant physiognomy or the use of nearest living relatives lapse rate methodologies use either a global terrestrial lapse rate as the world mean a regional terrestrial lapse rate that represents a large portion of a continent or a local terrestrial lapse rate for areas narrowly confined by latitude and longitude other variables and or corrective factors that should be considered in these applications include the thermal effects of continentality and elevated land surfaces in the continental interior and standardization to compensate for fluctuations or variability in sea level global climate change and paleolatitude these different methodologies can be contrasted by their common application to the late eocene florissant flora of colorado with results ranging from 455 to 4133 meters

the use of pollen floras as a tool to estimate palaeoaltitude of mountains the eastern pyrenees in the late neogene a case study northern hemisphere vegetation is generally zoned as a consequence of latitudinal and altitudinal gradients temperature reconstruction from three successive pollen floral assemblages of tortonian messinian and zanclean age from the eastern pyrenees has been used to estimate the altitudinal evolution of the uplifted cerdanya basin and its surrounding massifs a new method has been developed for the uplifted basins which completes that already applied to pollen floras from coastal marine deposits close to mountains in contrast to previous hypotheses it seems that the eastern pyrenees occurred at a lower altitude in the late miocene before continuous uplift began 10 ma ago the rate of this uplift ranged between 0 06 and 0 12 mm yr

late pleistocene c4plant dominance and summer rainfall in the southwestern united states from isotopic study of herbivore teeth abstract patterns of climate and c4plant abundance in the southwestern united states during the last glaciation were evaluated from isotopic study of herbivore tooth enamel enamel 13c values revealed a substantial eastward increase in c4plant consumption formammuthusspp bisonspp equusspp andcamelopsspp the 13c values were greatest inbisonspp 6 9 to 1 7 andmammuthusspp 9 0 to 0 3 and in some locales indicated c4 dominated grazing the 13c values of antilocaprids were lowest among taxa 12 5 to 7 9 and indicated c3feeding at all sites on the basis of modern correlations between climate and c4grass abundance the enamel data imply significant summer rain in parts of southern arizona and new mexico throughout the last glaciation enamel 18o values range from 19 0 to 31 0 and generally increase to the east this pattern could point to a tropical or subtropical source of summer rainfall at a synoptic scale the isotope data indicate that interactions of seasonal moisture temperature and lowered atmospheric pco2determined glacial age c4abundance patterns

a late miocene subtropical dry flora from the northern altiplano bolivia abstract a variety of evidence suggests that the altiplano of the central andes the second highest and largest plateau on earth underwent significant uplift in the late miocene pliocene the most important datum supporting recent uplift is a collection of the 10 66 0 06 ma jakokkota flora from west central bolivia which implies a paleoelevation no more than 1600 1200 m today the site has an elevation of almost 4000 m in order to test the reliability of this estimate the present study analyzes a new collection of the jakokkota flora from a lacustrine unit that is 0 2 0 5 myr younger than the previously analyzed collection from a fluvial unit climate estimates based on leaf morphology for the two collections are statistically indistinguishable the combined flora has a mean annual temperature of 21 5 2 0 c and a mean annual precipitation of 550 180 mm the similarity of the climate estimates for the two floras suggests that there was not a significant climate change between them nor a significant bias in the leaf morphology due to differing taphonomic processes the climate estimate for the combined flora thus presents a representative picture of the late miocene climate of the northern altiplano if one assumes that the climate of the tropics has not changed significantly since the late miocene as is suggested by marine isotopic data then the paleoclimate of the jakokkota flora implies a paleoelevation of 1160 600 m thus the jakokkota flora supports the hypothesis of a young age for the altiplano

the el abra stadlal in the eastern cordillera of colombia south america abstract the el abra stadial is a climatic cooling event defined in the eastern cordillera of colombia which corresponds both in timing and intensity to the younger dryas climatic oscillation of the northern north atlantic region the stadial was preceded by the relatively warm guantiva interstadial and followed by the warm holocene colder climatic conditions during the el abra stadial caused a 400 m lowering of the upper andean forest limit below its altitudinal location during the preceding guantiva interstadial translated in temperature change this represents a drop in mean annual temperature of approximately 2 to 3 c the lowering of the upper forest limit and inferred temperature change for the el abra stadial compared to late holocene conditions are in the order of 600 m and 4 c respectively the transition of the guantiva interstadial to the el abra stadial has been radiocarbon dated at 11 210 90 bp and 10 820 60 bp climatic warming may have started shortly after 10 380 90 bp and near present day temperatures were reached at least as early as 8920 100 bp maximum cooling was probably attained between 10 800 bp and 10 300 bp further ams radiocarbon dating is planned to establish more exactly the timing of the el abra stadial a glacial advance of el abra age the bocatoma stade has been recognized in the highest part of the colombian eastern cordillera the sierra nevada del cocuy during this advance glaciers extended some 700 m lower than at present a climatic cooling event of el abra age associated with shifts of the upper andean forest limit and glacial advances has also been recognized in other parts of andean colombia including the central cordillera and the sierra nevada de santa marta

climate independent paleoaltimetry using stomatal density in fossil leaves as a proxy for co2 partial pressure existing methods for determining paleoelevation are primarily limited by 1 large errors 450 m 2 a reliance on incorrect assumptions that lapse rates in terrestrial temperature decrease with altitude in a globally predictable manner and or 3 are inherently climate dependent here i present a novel paleoelevation tool based on a predictable globally conserved decrease in co 2 partial pressure p co 2 with altitude as indicated by increased stomatal frequency of plant leaves the approach was validated using historical populations of black oak quercus kelloggii these analyses demonstrate highly significant inverse relationships between stomatal frequency and p co 2 r 2 0 73 independent of ecological or local climatic variability as such this is the first paleobotanical method to be globally applicable and independent of long term cenozoic climate change further tests on modern leaves of known elevations indicate that species specific application to the fossil record of q kelloggii q pseudolyrata will yield paleoelevation estimates within average errors of 300 m representing a significant improvement in accuracy over the majority of existing methods

the effect of holocene temperature fluctuations on the evolution and ecology of neotoma woodrats in idaho and northwestern utah abstract animals respond to climatic change by adapting or by altering distributional patterns how an animal responds is influenced by where it is positioned within its geographic range the probability of extirpation is increased near range boundaries here we examine the impact of holocene climatic fluctuations on a small mammalian herbivore the bushy tailed woodrat neotoma cinerea at five locations within south central idaho and northwestern utah previous work demonstrated that woodrats adapt to temperature shifts by altering body size we focus here on the relationship between body mass temperature and location within the geographic range body mass is estimated by measuring fossil fecal pellets a technique validated in earlier work overall we find the predicted phenotypic response to climate change animals were larger during cold periods and smaller during warmer episodes however we also identify several time periods when changes in environmental temperature exceeded the adaptive flexibility of n cinerea a smaller bodied species the desert woodrat n lepida apparently invaded lower elevation sites during the mid holocene despite being behaviorally and physically subordinate to n cinerea analysis of contemporary patterns of body size and thermal tolerances for both woodrat species suggests this was because of the greater heat tolerance of n lepida the robust spatial relationship between contemporary body size and ambient temperature is used as a proxy to reconstruct local climate during the holocene

recent foraminifera tracers of oceanic water movements in the southwestern lagoon of new caledonia abstract water movements in the southwestern lagoon of new caledonia are controlled mainly by tidal currents and by a wind driven surface current to the northwest balanced by a subsurface return current to the southeast during each rising tide oceanic water inflows over the barrier reef through the passes and between the scattered reefs of the southeast the distribution of planktonic foraminiferal tests shows that most of the superficial oceanic water is pushed by the southeast trade winds to the inner part of the bay de boulari the distribution of some benthic species especially gypsina globula reuss and pyrgo denticulata brady is also related to an oceanic inflow the distribution of their tests follows the trajectory of subsuperficial oceanic water penetrating into the lagoon through the passes and gives a clear picture of these water movements this image based on thanatocoenoses can be preserved after diagenesis therefore its possible utilization in similar paleoenvironments can be considered

crustal structure of the continent ocean transition off the cote d ivoire ghana transform margin implications for thermal exchanges across the palaeotransform boundary summary crustal structure of the continent ocean transition off the cote d ivoire ghana transform margin is determined by 2 d modelling of wide angle seismic data and gravity data the resulting models together with geological data recently collected by drilling on the margin are compared with available thermomechanical models of transform margins in particular we test the predicted effects on the transform margin crust of continental heating by the adjacent oceanic lithosphere these effects include i ductile flow of the lower continental crust either parallel to the transform direction or perpendicular to it from the continent towards the ocean and ii thermal uplift of the transform margin in the region of the cote d ivoire ghana transform margin the seismic and gravity data indicate that the continental crust remains uniform in thickness as the continent ocean boundary is approached the interpreted models lack a transitional domain between continental and oceanic crusts and abnormally thin oceanic crust is found along the margin these results exclude large scale ductile flow of lower continental crust during the margin formation the geological data are moreover not consistent with thermal uplift of the margin during the period of contact between the transform margin and the spreading centre our geophysical and geological data thus infer only moderate heating of the transform continental margin by the adjacent oceanic lithosphere moderate heating of the cote d ivoire ghana transform margin during margin formation implies that the thermal exchange between the transform margin and the adjacent spreading centre were lower than predicted by available thermal models two main factors may have contributed to reduce thermal exchanges across the continent ocean boundary the first factor is that the oceanic edge may have been colder than assumed by thermal models an abnormally cold spreading axis along the transform margin when the oceanic crust was emplaced is supported by the atypical structure of the oceanic crust along the cote d ivoire ghana transform margin the oceanic crustal structure is similar to that found along oceanic fracture zones where oceanic crust is also emplaced near a ridge transform intersection in both cases abnormally low thermal gradients at the spreading centre along the transform margin may be explained by the cumulative effect of i a cold edge effect of the adjacent continental lithosphere ii accretion at the end of a ridge segment away from the main magma supply point along the spreading axis and iii an efficient upward cooling of the oceanic lithosphere owing to deep hydrothermal circulation within the faulted lithosphere the second factor causing moderate thermal exchanges is the possibility of large amounts of water in oceanic lithospheric faults which reduces the lateral thermal conduction in the lithosphere since water is much less conductive than rock during the margin formation the oceanic edge thus seems to have acted as a thermal buffer between the cold continental margin and the hot spreading centre we propose that this thermal buffer hypothesis may be generalized to most transform margins implying a lower amount of continental heating than assumed by the available thermomechanical models

investigating a symmetry in a small mammal s response to warming and cooling events across western north america over the late quaternary many mammalian populations conform spatially and temporally to bergmann s rule this ecogeographic pattern is driven by selection for larger body masses by cooler temperatures and smaller ones by warming temperatures however it is unclear whether the response to warming or cooling temperatures is a symmetrical studies of the evolutionary record suggest that mammals evolve smaller body sizes more rapidly than larger ones suggesting that it may be easier to adapt to warming climates than cooling ones here we examine the potential asymmetrical response of mammals to past temperature fluctuations we use the fossil midden record of the bushy tailed woodrat neotoma cinerea a well studied animal that generally conforms to bergmann s rule to test the ability of populations to respond to warming versus cooling climate throughout its modern range in western north america over the late quaternary we quantified the response to temperature change as characterized by the greenland ice sheet project 2 temperature record using n cinerea presence absence and darwins our results show that populations within the modern range of n cinerea show little difference between warming and cooling events however northern peripheral populations are absent during older cooler periods possibly due to climate or taphonomy our study suggests adaptation in situ may be an underestimated response to future climate change

analysis of vesicular basalts and lava emplacement processes for application as a paleobarometer paleoaltimeter abstract we have developed a method for determining paleoelevations of highland areas on the basis of the vesicularity of lava flows vesicular lavas preserve a record of paleopressure at the time and place of emplacement because the difference in internal pressure in bubbles at the base and top of a lava flow depends on atmospheric pressure and lava flow thickness at the top of the flow the pressure is simply atmospheric pressure while at the base there is an additional contribution of hydrostatic lava overburden thus the modal size of the vesicle bubble population is larger at the top than at the bottom this leads directly to paleoatmospheric pressure because the thickness of the flow can easily be measured in the field and the vesicle sizes can now be accurately measured in the lab because our recently developed technique measures paleoatmospheric pressure it is not subject to uncertainties stemming from the use of climate sensitive proxies although like all measurements it has its own sou

a numerical study of the climate response to lowered mediterranean sea level during the messinian salinity crisis abstract roughly six million years ago tectonic movements isolated the mediterranean sea ms from the atlantic ocean an event known as the messinian salinity crisis msc subsequent evaporative drawdown of the ms resulted in a subaerial depression with a depth between 1500 and 2500 m in this study five simulations are run using the national center for atmospheric research ncar community atmosphere model version 3 cam3 configured with the slab ocean model three simulations have been performed to test the climate impacts to desiccation and to changing the ms base level in this study the ms base level is reduced 750 m in the half land simulation hl and 1500 m in the lowered sea ls and lowered land ll simulations the hl and ll simulations differ from the ls in that the surface is converted to land representing the complete desiccation of the ms the substantial ms depression generates planetary scale atmospheric waves responsible for significant climate effects throughout the northern hemisphere a notable deepening of the aleutian low and a significant equatorward shift in the atlantic jet stream are evident in djf vertical ascent at the northern margin of the ms results in a 1 5 2 5 mm day 1 precipitation anomaly in the ls run over the alps consistent with proxy data annual mean area averaged ms evaporation is slightly higher than control conditions except when salinity is a substantial barrier to evaporation our results suggest that a partially filled basin cannot exist in equilibrium and the ms must either be partly connected to the atlantic ocean or completely desiccated base level lowering which alters the water budget must be taken into account when considering the freshwater budget during the msc

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

response of bushy tailed woodrats neotoma cinerea to late quaternary climatic change in the colorado plateau abstract temperature profoundly influences the physiology and life history characteristics of organisms particularly in terms of body size because so many critical parameters scale with body mass long term temperature fluctuations can have dramatic impacts we examined the response of a small mammalian herbivore the bushy tailed woodrat neotoma cinerea to temperature change from 20 000 yr b p to present at five sites within the colorado plateau our investigations focused on the relationship between temperature plant composition and abundance and woodrat size body size was estimated by measuring fossil fecal pellets a technique validated in earlier work we found significant and highly covariable patterns in body mass over the five locations suggesting that responses to temperature fluctuations during the late quaternary have been very similar although woodrat mass and the occurrence of several plant species in the fossil record were significantly correlated in virtually all instances changes in woodrat size preceded changes in vegetational composition these results may be due to the greater sensitivity of woodrats to temperature or to the shorter generation times of woodrats as compared to most plants an alternative hypothesis is that winter temperatures increased before summer ones woodrats are highly sensitive to warmer winters whereas little response would be expected from forest woodland plants growing at their lower limits our work suggests that woodrat size is a precise paleothermometer yielding information about temperature variation over relatively short term temporal and regional scales

middle to late cenozoic cooling and high topography in the central rocky mountains constraints from clumped isotope geochemistry abstract the timing and mechanism of the formation of the high elevations of the central rocky mountains rockies in the western interior of north america remain controversial we examine the middle and late cenozoic paleorelief between the great plains and the central rockies using clumped isotope geothermometry of carbonate cements of fluvial and eolian sandstones our petrographic observations suggest that the studied carbonate cements were formed primarily during eodiagenesis in near surface conditions and retain primary paleoclimate and paleoelevation signals carbonate clumped isotope temperatures decrease 10 c and calculated water o 18 values decrease 4 from 35 ma to 5 ma in both the central rockies and the western great plains following middle and late cenozoic global cooling trend a persistent longitudinal gradient in temperature and o 18 value existed between the central rockies and the great plains during the oligocene and miocene with temperatures 4 8 c higher and calculated water o 18 values 3 6 higher in the great plains these observations suggest the mean elevation of the central rockies was 1 km higher than the western great plains during the middle and late cenozoic similar to the present day regional relief when placed in the context of other paleoaltimetry studies and geological observations our findings support the hypothesis that the high mean topography of the rockies was developed during the late eocene possibly related to isostatic adjustment or dynamic uplift caused by foundering of lower mantle lithosphere or the farallon slab or both

debris ridges along the southern drakensberg escarpment as evidence for quaternary glaciation in southern africa considerable geomorphological work has been undertaken on periglacial and possible glacial landforms found in the eastern lesotho highlands however the origin of several of these landforms remains controversial and differences in opinion concerning their original process mechanisms and associated climatic implications is unresolved debris ridges were recently found on south facing slopes along the tsatsa la mangaung and leqooa ranges in the southern drakensberg the objective is to use a variety of approaches to test a number of possible hypotheses to their origin these include an analysis of topographic and spatial positioning geomorphology sedimentology ams dating and palaeo climatological extrapolations a variety of possible geomorphological process origins for particular deposits are tested against the results of the above mentioned approaches the possible origins considered include debris flows water flow pronival ramparts seasonal perennial snow patches glacial moraine permanent glacier ice and variations in landscape denudation i e erosional remnant e g valley fill the results support the contention that the ridges are moraines which relate to the former presence of small glaciers

quantification of large uncertainties in fossil leaf paleoaltimetry 1 estimates of paleoelevation potentially constrain geodynamic models of continental deformation and inform interpretations of landscape and climate evolution one widely used paleobotanical approach reconstructs paleoelevation from the difference in estimated atmospheric enthalpy between a known sea level and a targeted coeval elevated fossil floral site enthalpy is estimated using climate leaf analysis multivariate program clamp on 31 leaf size and shape variables that have been calibrated in living forests errors related to clamp are significantly greater than often reported and there are many sources of large potential error related to this method that are either difficult to quantify or unquantifiable and are thus not documented here we quantify one significant bias toward underestimation of leaf area in the clamp data set 50 that affects all clamp climate estimates including enthalpy crucially errors in paleoelevation when the leaf size bias is included are in the range of 2 km or more at least 2 times the previous estimates and exceeding the plausible paleoelevations of many fossil sites previously published paleoelevations derived from this technique are unlikely to be accurate either in magnitude or in estimated error

surface uplift uplift of rocks and exhumation of rocks uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges rates of uplift of the surfaces of mountain ranges have not however been quantified sufficiently well that they provide useful constraints on those processes many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift and provide no information whatsoever on the rates of surface uplift

basalt vesicularity as a measure of atmospheric pressure and palaeoelevation the pressure in and thus the size of a bubble in a lava flow is determined by the atmospheric pressure and the hydrostatic pressure of the overlying lava if atmospheric sea level pressure is known or assumed vesicle size distributions in basalt flows can thus be used as an indicator of the palaeoelevation of emplacement1 here we show by analysis of the vesicle size distribution of basalt samples collected from the summit and base of mauna loa volcano in hawaii that the technique provides estimates of ambient pressure that are accurate to within 0 1 bar and thus estimates of elevation with a resolution of about 1 400m this palaeoaltimetric technique should find useful application in palaeogeographical reconstruction2 for times when sea level pressure was similar to the present value conversely if the elevation of emplacement is known our technique should be able to provide a measure of sea level palaeopressure unlike palaeo botanical methods for estimating elevations3 6 this method does not have to assume a relationship between temperature and altitude on the other hand its use is restricted to lava flows that have had a simple emplacement history

paleoaltimetry incorporating atmospheric physics and botanical estimates of paleoclimate we present a method for deducing paleoaltitudes that incorporates basic physical principles of atmospheric science and inferences of paleoclimates from plant leaf physiognomy we exploit the average west to east flow of the atmosphere at mid latitudes and a thermodynamically conserved variable in the atmosphere moist static energy the combined internal latent heat and gravitational potential energy of moist air to develop a method that relies on a parameter that varies with height in the atmosphere in a predictable fashion because the surface distribution of moist static energy is constrained by atmospheric dynamics and thermodynamics the combined internal and latent heat energies also known as the moist enthalpy should only vary with altitude provided we know the distribution of moist static energy thus we avoid having to make assumptions about the mean annual temperature lapse rate which varies spatially and temporally owing to unpredictable variations in atmospheric water vapor to estimate a paleoaltitude therefore we require 1 a priori knowledge of the spatial distribution of moist static energy for the paleoclimate and 2 the ability to estimate paleoenthalpy for two isochronous locations one at sea level the other at some unknown elevation to achieve this we investigated the spatial distribution of moist static energy for the present day climate of north america to estimate the deviations in moist static energy from zonal invariance in parallel we quantified the relation between moist enthalpy and plant leaf physiognomy of modern forests assuming that such deviations from zonal invariance and such relationships between physiognomy and enthalpy apply to ancient climates and fossil leaves these investigations yield an uncertainty estimate of 910 m in the paleoaltitude difference between two isochronous fossil assemblage locations

determining the paleoclimate and elevation of the late eocene florissant flora support from the coexistence approach published estimates on the paleoclimate of the florissant fossil beds site of colorado 34 1 ma have led to extremely different estimates of paleoelevation the purpose of this paper is to review the paleoclimate methods used and to add the coexistence approach ca method to estimate paleotemperature for the florissant site the basis of the ca method is the dependence on overlapping climatic requirements for different taxa in the flora and their nearest living relatives these relationships tie the fossil identities to the actual plant habitats and climatic requirements of close relatives based on the ca method we conclude that the mean annual temperature ranged between 14 3 and 18 2 c these results support the conclusions offered by several other studies that the florissant was a warm temperate to subtropical flora and they are consistent with recent conclusions by structural geologists as well as other studies indicating that the florissant site was deposited at a relatively low elevation prob

lapse rates and other variables applied to estimating paleoaltitudes from fossil floras abstract a previous method for determining paleoaltitude from fossil floras has used the difference between sea level and upland paleotemperatures which is then multiplied by the reciprocal of a normal lapse rate the present study examines other variables that can significantly influence such results terrestrial lapse rates have been calculated for 39 areas of the world based upon mean annual temperature mat mean warm month temperature mat and mean cold month ttemperature cmt these show regional and seasonal variability that is explained by factors including continentality elevation of large massifs or high base levels cold air drainage fog mountain barrier effects and the location of the subtropical high pressure zone lapse rates and projected sea level temperatures based on data from the western united states show distinct regional patterns these indicate that within this region the highest lapse rate and temperature values are correlated with 1 continental climates in the subtropical high pressure zone and 2 areas having relief where the lowest elevation land surfaces base levels occur at high altitude the data are applied to evaluate and revise the methodology for estimating paleoaltitudes variables of climatic change sea level fluctuation and paleogeography are also considered limitations in application of the method are emphasized the method is exemplified by application to the latest eocene florissant flora of colorado u s a although the results are conjectural they strongly suggest that the late eocene erosion surface in the southern rocky mountains occurred at a much higher paleoaltitude than previously thought this high elevation may have resulted from earlier laramide crustal thickening

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

paleoclimate and paleoecology of the latest eocene florissant flora of central colorado u s a abstract the uppermost eocene florissant formation of central colorado u s a contains a diverse flora and fauna preserved in lacustrine facies and represents a key episode in earth history immediately preceding the eocene oligocene boundary laminated shales contain impressions of non monocot angiosperm leaves that were used to estimate paleoecological and paleoclimatic parameters using leaf physiognomic methods including leaf mass per area ma digital leaf physiognomy dilp leaf margin analysis lma and leaf area analysis laa the majority 58 of the morphotypes analyzed for ma suggested a semi evergreen leaf lifespan whereas another 27 indicated a deciduous habit and 15 an evergreen habit there was no significant relationship between ma and insect damage based on a small subset of florissant s leaves higher ma values 73 of leaves one year lifespan coupled with a tendency toward long and narrow leaf shapes and small leaf areas indicate the existence of sclerophyllous vegetation using the global regression for mean annual temperature mat the dilp estimate of mat was anomalously cold 5 5 4 c however using a northern hemisphere regression the dilp mat estimate of 11 6 3 3 c was more plausible using dilp mean annual precipitation map was estimated at 740 608 334 mm yr 1 which supports dry conditions estimates for mat and map using the univariate lma and laa methods overlapped within uncertainty of the dilp results in addition those taxa classified as growing in wet areas riparian had significantly more teeth than non riparian taxa these paleoclimatic and paleoecological results suggest that outside the riparian forest the florissant flora sampled a seasonally dry temperate sclerophyllous shrubland to woodland perhaps similar to modern chaparral forests in the western interior of the u s a just before the transition into the cooler oligocene

a hot and high eocene sierra nevada despite broad interest in determining the topographic and climatic histories of mountain ranges the evolution of california s sierra nevada remains actively debated prior stable isotope based studies of the sierra nevada have relied primarily on hydrogen isotopes in kaolinite hydrated volcanic glass and leaf n alkanes here we reconstruct the temperature and elevation of the early eocene sierra nevada using the oxygen isotope composition of kaolinitized granite clasts from the ancestral yuba and american rivers that drained the windward pacific flank of the sierra nevada first we evaluated the possible contributions of hydrogen isotope exchange in kaolinite by direct comparison with oxygen isotope measurements next we utilized differences in the hydrogen and oxygen isotope fractionation in kaolinite to constrain early eocene midlatitude weathering temperatures oxygen isotope geochemistry of in situ kaolinites indicates upstream eastward depletion of 18o in the northern sierra nevada the 18o values ranging from 11 4 to 14 4 at the easternmost localities correspond to paleoelevations as high as 2400 m when simulating the orographic precipitation of moisture from a pacific source using eocene boundary conditions this result is consistent with prior hydrogen isotope studies of the northern sierra but oxygen isotope based paleoelevation estimates are systematically 500 1000 m higher than those from hydrogen based estimates from the same samples kaolinite geothermometry from 16 samples produced early eocene weathering temperatures of 13 0 36 7 c with an average of 23 2 6 4 c 1 these kaolinite temperature reconstructions are in general agreement with paleofloral and geochemical constraints from eocene california localities and climate model simulations our results confirm prior hydrogen isotope based paleoelevation estimates and further substantiate the existence of a hot and high eocene sierra nevada