cenozoic topographic and climatic response to changing tectonic boundary conditions in western north america abstract this study presents an oxygen isotopic record from the paleocene to the pliocene based on the analysis of predominantly paleosol carbonate from intermontane basins in southwestern montana and eastern idaho 18 o values of calcite decrease by 7 to 10 between 50 and 47 ma in southwestern montana and idaho most likely as a result of an increase in elevation of 2 5 to 3 5 km this rise in elevation is roughly contemporaneous with the emplacement of the nearby challis volcanics and the formation of metamorphic core complexes in the hinterland of the sevier thrust belt moreover when compared to previous oxygen isotopic studies that show oxygen isotopic shifts of similar magnitude occurring later in the late eocene to early oligocene in northeastern nevada and late oligocene to miocene in southern nevada the results of this study add to a growing body of evidence for a spatial and temporal migration of high surface elevations from north to south in the great basin of western united states this surface uplift history supports tectonic models calling for north to south removal of the farallon slab or delamination of the mantle lithosphere

stable isotope paleoaltimetry and the evolution of landscapes and life abstract reconstructing topography of our planet not only advances our knowledge of the geodynamic processes that shape the earth s surface equally important it adds a key element towards understanding long term continental moisture transport atmospheric circulation and the distribution of biomes and biodiversity stable isotope paleoaltimetry exploits systematic decreases in the oxygen 18o or hydrogen d isotopic composition of precipitation along a mountain front when the interaction of topography and advected moist air masses induces orographic precipitation these changes in 18o or d can be recovered from the geologic record and recent geochemical and modeling advances allow a broad range of proxy materials to be evaluated over the last 10 yr stable isotope paleoaltimetry has witnessed rapidly expanding research activities and has produced a broad array of fascinating tectonic and geomorphologic studies many of which have concentrated on determining the elevation history of continental plateau regions these single site studies have greatly expanded what used to be very sparse global paleoaltimetric data the challenge now lies in disentangling the surface uplift component from the impact of climate change on 18o and d in precipitation the robustness of stable isotope paleoaltimetry can be enhanced when high elevation 18o or d data are referenced against low elevation sites that track climate modulated sea level 18o or d of precipitation through time approach analysis of central andean paleosols documents that differences in 18o of soil carbonate between the subandean foreland and the bolivian altiplano are small between 11 and 7 ma but rise rapidly to ca 2 9 after 7 ma corroborating the magnitude of late miocene change in 18o on the altiplano future advances in stable isotope paleoaltimetry will greatly benefit from addressing four key challenges 1 identifying topographically induced changes in atmospheric circulation and associated teleconnections in the global climate system that affect 18o or d of precipitation 2 evaluating on a case by case basis if temporal and spatial changes in isotope lapse rates influence interpretations of paleoelevation 3 interfacing with phylogenetic techniques to evaluate competing hypotheses with respect to the timing of surface uplift and the diversification of lineages 4 characterizing feedbacks between changes in surface elevation and atmospheric circulation as these are likely to be equally important to the diversification of lineages than changes in surface elevation alone tackling these challenges will benefit from the accelerating pace of improved data model comparisons and rapidly evolving geochemical techniques for reconstructing precipitation patterns most importantly stable isotope paleoaltimetry has the potential to develop into a truly interdisciplinary field if innovative tectonic paleoclimatic and evolutionary biology phylogenetic approaches are integrated into a common research framework it therefore opens new avenues to study the long term evolution of landscapes and life

the temperature dependence of hydrogen isotope fractionation between clay minerals and water evidence from a geopressured system abstract d values of water samples from two gulf coast geopressured fields vary linearly with temperature while the d values from the coexisting clays remain constant and are independent of temperature fluid how rates on the order of millimeters per year characteristic of gulf coast geopressured systems provide adequate residence time for hydrogen isotope equilibrium to be achieved between the extant porewaters and clay minerals since equilibrium is achieved these d values are used to calculate the temperature dependence of the hydrogen isotope fractionation factor between illite smectite and water clay waterh between 0 and 150 c 1000 in clay water h 45 3 10 3 t 94 7 this equation predicts values for clay waterh at 96 c which are equal to those predicted by a similar equation derived by yeh 1980 above and below 96 c this new equation predicts values which diverge from those predicted by the equation of yeh 1980 with a difference of 9 at 150 c and 25 at 0 c the possibility is raised that the very slow upward component of flow characteristic of gulf coast geopressured sediments combined with the slow downward subsidence of the clay rich sediments can result in a system which is rock dominated with respect to hydrogen

thrust structures in the eastern dauphinois zone french alps north of the pelvoux massif abstract an examination of thrust structures in the eastern part of the dauphinois zone of the external french alps referred to in the literature as the ultradauphinois zone shows that major basement thrusts climb up section to produce cover basement synclines these thrusts also climb laterally and are continuous with thrust in the cover rocks the external basement massifs are recognized as thrust sheets with variably deformed and thrust cover sequences the distinction made in the previous literature between the dauphinois and ultradauphinois zones is no longer tenable cover thrusting proceeded by both smooth slip and rough slip the latter producing a duplex of cover thrust slices restoration of this duplex indicates that a shortening of 70 km in the cover occured during its formation possible errors in this estimate include uncertainties in the original stratigraphic thickness and in the overall shape of the duplex another duplex is thought to have formed at a basement ramp created by the presence of an early basement normal fault partial footwall collapse of this basement ramp gave rise to a basement horse at the bottom of the duplex the overall relation between cover and basement thrusting is indicated using a hanging wall sequence diagram recent geophysical studies suggest that the basement thrusts developed from a mid crustal decollement which passes down dip to offset the moho model studies of thin skinned tectonics may not be appropriate to such thrust geometries

stable isotope compositions of herbivore teeth indicate climatic stability leading into the mid miocene climatic optimum in idaho u s a abstract the effects of global climate change are manifested at the regional level consequently evaluation of links between palaeoenvironmental change and turnover of past biotas must use regional scale climate data here we test whether climate change influenced faunal and floral patterns leading up to and during the mid miocene climatic optimum mmco based on datasets collected in the railroad canyon section rcs central eastern idaho u s a specifically we use isotope compositions of herbivore tooth enamel to investigate how mean annual precipitation map mean annual temperature mat cold month mean temperature cmmt and temperature seasonality varied through the rcs and how this local record compares to global climate reconstructions isotope compositions of teeth from the fossil equid merychippus and rhinocerotid diceratherium were compared across five time bins from c 23 to c 15 ma bulk 18o values of both taxa indicate that meteoric water compositions were unchanged through the study interval consistently c 15 6 but were c 1 9 higher than current regional meteoric water this difference points to warmer climates in central eastern idaho during the miocene post middle miocene topographic uplift in western north america and or shifts to air mass trajectories serial sampling of enamel shows seasonal fluctuations in water compositions and temperature bulk 13c values indicate an average map of 190 range 10 510 mm yr 1 with no significant change through the study interval comparable to today s map 236 mm yr 1 the reconstructed semi arid seasonal warm climate for the rcs agrees with phytolith assemblage data from the same strata indicating dominantly open grassy habitats however it is inconsistent with previously held ideas of warm wet mid miocene climates in the northern rocky mountains nrm based on paleosol analyses our inferred stable climate conditions for the mmco of the nrm contrast with coeval records from europe and asia indicating sustained or enhanced warm and wet climates these differences point to a decoupling of regional climate from global trends and highlight the necessity of studying regional variation to understand the biotic impacts of global climate change

a miocene to pleistocene climate and elevation record of the sierra nevada california orographic precipitation of pacific sourced moisture creates a rain shadow across the central part of the sierra nevada california that contrasts with the southern part of the range where seasonal monsoonal precipitation sourced to the south obscures this rain shadow effect orographic rainout systematically lowers the hydrogen isotope composition of precipitation dppt and therefore dppt reflects a measure of the magnitude of the rain shadow hydrogen isotope compositions of volcanic glass dglass hydrated at the earth s surface provide a unique opportunity to track the elevation and precipitation history of the sierra nevada and adjacent basin and range province analysis of 67 well dated volcanic glass samples from widespread volcanic ash fall deposits located from the pacific coast to the basin and range province demonstrates that between 0 6 and 12 1 ma the hydrogen isotope compositions of meteoric water displayed a large 40 decrease from the windward to the leeward side of the central sierra nevada consistent with the existence of a rain shadow of modern magnitude over that time evidence for a miocene to recent rain shadow of constant magnitude and systematic changes in the longitudinal climate and precipitation patterns strongly suggest that the modern first order topographic elements of the sierra nevada characterized the landscape over at least the last 12 million years

miocene tectonics and climate forcing of biodiversity western united states ungulate and carnivore diversity patterns since 30 ma in different regions of the western united states suggest abrupt increased diversification at 17 17 5 ma followed by decreases ca 11 ma and stasis thereafter although global climate change presumably affects evolution we hypothesize that widespread extensional tectonism in the western u s also helped drive diversity increases ca 17 5 ma through a topographically induced increase in floral and habitat diversity the decreases in diversities ca 11 ma as well as the rapid increase in c4 ecosystems rice worldwide at 7 8 ma may have responded to climate teleconnections and increased seasonality linked to global cooling and growth of orogenic plateaus particularly the tibetan plateau between 13 and 8 ma thus biodiversity complexly responds both to climate and to tectonics

empirical relationships between elevation and the stable isotope composition of precipitation and surface waters considerations for studies of paleoelevation change a compilation of 68 studies from throughout many of the world s mountain belts reveals an empirically consistent and linear relationship between change in elevation and change in the isotopic composition of precipitation along altitudinal transects the isotopic composition of precipitation decreases linearly with increasing elevation in most regions of the world except in the himalayas and at elevations 5000 m there are no significant differences in isotopic lapse rates from most regions of the world 0 28 permil 100 m except at the extreme latitudes where isotopic lapse rates are higher given information on past changes in the isotopic composition of precipitation preserved in pedogenic or authigenic minerals this global isotopic lapse rate can be used to place numerical constraints on the topo graphic development of some ancient mountain belts or plateaus there are many complicating factors that can confound interpretation of paleoel evation change based on stable isotopes and many of these are unique to specific mountain belts or time periods relevant to all stable isotope based paleoelevation change studies is the temperature dependent isotope fractionation between a pedo genic or authigenic mineral and the water from which it forms in cases where isotopic proxy minerals are sampled from localities where temperature will change simulta neously with elevation change the apparent change in the isotopic composition of precipitation may be dampened by several permil this suggests that samples taken from the rainshadow side of an emerging orographic barrier may be more likely to preserve isotopic changes resulting from mountain uplift than samples taken from atop a rising mountain range or plateau

geochemical and isotopic evolution of groundwater in the wadi watir watershed sinai peninsula egypt the wadi watir delta in the wadi watir watershed is a tourist area in the arid southeastern part of the sinai peninsula egypt where development and growth of the community on the delta are constrained by the amount of groundwater that can be withdrawn sustainably to effectively manage groundwater resources in the wadi watir delta the origin of groundwater recharge groundwater age and changes in groundwater chemistry in the watershed needs to be understood mineral identification rock chemistry water chemistry and the isotopes of hydrogen oxygen and carbon in groundwater were used to identify the sources mixing and ages of groundwater in the watershed and the chemical evolution of groundwater as it flows from the upland areas in the watershed to the developed areas at the wadi watir delta groundwater in the wadi watir watershed is primarily from recent recharge while groundwater salinity is controlled by mixing of chemically different waters and dissolution of minerals and salts in the aquifers the el shiekh attia and wadi el ain areas in the upper wadi watir watershed have different recharge sources either from recharge from other areas or from different storm events the downgradient main channel area receives groundwater flow primarily from the el shiekh attia area groundwater in the main channel area is the primary source of groundwater supplying the aquifers of the wadi watir delta

cenozoic migration of topography in the north american cordillera continental topography is the result of complex interactions among mantle convection continental dynamics and climatic and erosional processes therefore topographic evolution of mountain belts and continental interiors reflects directly upon the coupling between mantle and surface processes it has recently been proposed that the modern topography of western north america is partly controlled by the removal of the subducting farallon plate and replacement of lithospheric mantle by hot asthenosphere creating surface uplift of the colorado plateau the southwestern united states and northern mexico while concomitant subsidence characterizes the central united states how the topography of the cenozoic north american cordillera evolved in the past is largely unknown yet currently debated tectonic models each have a predictable topographic response here we examine cenozoic surface uplift patterns of western north america based on a record of 3000 stable isotope proxy data this data set is consistent with eocene north to south surface uplift in the cordillera culminating in the assembly of an eocene oligocene highland 3 4 km in elevation the diachronous record of surface uplift and associated magmatism further supports tectonic models calling for the convective removal of mantle lithosphere or removal of the farallon slab by buckling along an east west axis the eocene oligocene development of rainout patterns similar to present day patterns along the flanks of the cordilleran orogen is therefore unlikely to be the result of late mesozoic crustal thickening and associated development of an andean style altiplano

geomorphic controls on lacustrine isotopic compositions evidence from the laney member green river formation wyoming oxygen isotope values from lacustrine carbonate in the laney member of the green river formation wyoming exhibit a sudden basinwide 6 upsection decrease in 18 o at ca 49 ma 40 ar 39 ar geochronology constrains the duration of the isotopic shift to 200 000 years this change coincides with a sudden change in lake type from balancedfi lled in the lower laclede bed to overfi lled in the upper laclede bed as well as an increase in the proportion of calcitic 80 calcite out of total carbonate by x ray diffraction xrd samples from 32 to 73 the 18 o shift is correlatable through several locations across the greater green river basin and also coincides with a previously observed shift to less radiogenic 87

oxygen isotope evidence of climate change from pedogenic clay minerals in the himalayan molasse abstract in this study we examine the oxygen isotope ratios of smectite and kaolinite in a stratigraphic sequence of paleosols in the siwalik himalayan molasse on the potwar plateau northern pakistan there is a 3 4 o increase in the smectite 18 o values synchronous with a 3 5 o increase in 18 o values of pedogenic calcite at 8 5 6 5 ma previously observed by quade et al 1989 the covariation of the 18 o values of smectite with calcite gd 18 o values through time strongly suggests a pedogenic origin of smectite and that its 18 o values reflect the oxygen isotope ratio of the soil water present during pedogenesis these data show that the 18 o values of clay minerals in paleosols in aggrading sedimentary sequences are viable paleoclimate indicators kaolinite 18 o values are similar to smectite 18 o values as would be expected for pedogenic kaolinite but there is greater variation in these data which we attribute to incomplete mineral separation the measured permil oxygen isotope fractionation between calcite and smectite within individual paleosols is on average 3 o higher than the equilibrium fractionation this isotopic disequilibrium can be explained by the calcite forming predominantly during the dry winter season and the smectite forming predominantly during the wet summer season the synchronous 3 5 o increase in oxygen isotope ratios of smectite and calcite at 8 5 6 5 ma indicates that this 18 o 16 o increase is not due to diagenesis but rather results from a climate change the most likely causes of the 18 o 16 o increase in smectite and calcite are either increased aridity resulting in increased soil water evaporation thus 18 o enrichment and or a change from more continental to more marine sourced precipitation the tibetan plateau which is suggested to have undergone rapid uplift around 8 ma e g harrison et al 1992 may have acted as an effective orographic barrier to low 18 o precipitation originating from central asia causing higher 18 o values of the precipitation falling on the potwar plateau currently it is impossible to distinguish between these two potential causes of the 18 o 16 o increase at 8 5 6 5 ma but these clay mineral 18 o values support that there was a significant climate change in this region

capture of high altitude precipitation by a low altitude eocene lake western u s sedimentary facies of the eocene green river formation refl ect a rapid increase in water supply to lake gosiute ca 49 ma marked by a stratigraphic fi ll to spill surface deposits below this surface constitute repetitive lacustrine expansion desiccation cycles whereas those above consist of continuous profundal lacustrine mudstone grading upward into volcaniclastic deltaic sandstone above the fi ll to spill surface calcitic mudstone 18 o decreases from 26 to 20 over an interval representing 100 k y we interpret this shift to have resulted from capture of a foreland river or rivers that drained higher topography north of lake gosiute most likely in north central idaho accurate paleoelevation estimates derived from stable isotopic records in intermontane basins thus may require detailed knowledge of regional drainage systems

groundwater recharge and salinization in the arid coastal plain aquifer of the wadi watir delta sinai egypt abstract the quaternary coastal plain aquifer down gradient of the wadi watir catchment is the main source of potable groundwater in the arid region of south sinai egypt the scarcity of rainfall over the last decade combined with high groundwater pumping rates have resulted in water quality degradation in the main well field and in wells along the coast understanding the sources of groundwater salinization and amount of average annual recharge is critical for developing sustainable groundwater management strategies for the long term prevention of groundwater quality deterioration a combination of geochemistry conservative ions cl and br and isotopic tracers 87 86 sr 81 br 37 cl in conjunction with groundwater modeling is an effective method to assess and manage groundwater resources in the wadi watir delta aquifers high groundwater salinity including high cl and br concentrations is recorded inland in the deep drilled wells located in the main well field and in wells along the coast the range of cl br ratios for shallow and deep groundwaters in the delta 50 97 fall between the end member values of the recharge water that comes from the up gradient watershed and evaporated seawater of marine origin which is significantly different than the ratio in modern seawater 228 the 87 86 sr and 81 br isotopic values were higher in the recharge water 0 70 723 87 86 sr 81 br 87 86 sr 81 br 37 cl isotopic values were lower in the recharge water 0 48 37 cl 37 cl a three dimensional variable density flow and transport seawat model was developed using groundwater isotopes 87 sr 86 sr 37 cl and 81 br and calibrated using historical records of groundwater level and salinity 18 o was used to normalize the evaporative effect on shallow groundwater salinity for model calibration the model shows how groundwater salinity and hydrologic data can be used in seawat to understand recharge mechanisms estimate groundwater recharge rates and simulate the upwelling of deep saline groundwater and seawater intrusion the model indicates that most of the groundwater recharge occurs near the outlet of the main channel average annual recharge to delta alluvial aquifers for 1982 to 2009 is estimated to be 2 16 10 6 m 3 yr the main factors that control groundwater salinity are overpumping and recharge availability

seismic evidence of a crustal overthrust in the western alps seismic data provided by the alp75 experiment in the northwestern part of the alpine arc has been re evaluated using ray tracing techniques in a laterally inhomogeneous medium thus improving a previous interpretation the structure of the crust definitely appears to be different in the northern subalpine chains where it is layered with an ese mean dip of 30 and in the inner part of the alpine are where no clear stratification can be derived from the available data

stable isotopic evidence for neogene surface downdrop in the central basin and range province authigenic calcite and smectite stable isotopic records were determined for five neogene terrestrial stratigraphic sections from the central basin and range province and surrounding regions we recognized a general pattern of increasing authigenic mineral 18 o values with decreasing age since the middle miocene throughout the region we suggest this pattern results from regional elevation decrease and associated changes in atmospheric circulation patterns an anomalous pattern of decreasing 18 o values with decreasing age is observed in the miocene horse spring formation exposed in the lake mead basin which is contemporaneous with local magmatic activity we suggest this pattern results from surficial uplift of local highlands feeding water into the horse spring depositional system the topographic histories suggested here provide insight into the response of the land surface to crustal processes neogene extensional deformation in the central basin and range province resulted in a net regional elevation decrease

the cenozoic climatic and topographic evolution of the western north american cordillera herein we present oxygen isotope records from cretaceous to recent terrestrial sediments in the western north american cordillera the purpose of this analysis is to use oxygen isotope records to understand the coupled surface elevation and climate histories of this region through the cenozoic to do this we constructed 18o maps of surface waters for time intervals that trace the development of topography of western north america these maps are based on 4861 oxygen isotope analyses from both published 4478 and new 383 data we determined the 18o values of surface waters using paleotemperatures derived previously from floral assemblages and the appropriate isotope fractionation factors these data suggest that in the late cretaceous to early eocene the sevier hinterland formed a plateau of unknown height around 50 ma a topographic wave developed in british columbia and eastern washington that swept southward reaching northeastern nevada at 40 to 38 ma and southern nevada 23 ma this southward encroachment of an eocene plateau sweep caused reorganization of drainage patterns such that the intraforeland basins of wyoming and utah drainages extended deep within the sevier hinterland as the wave swept southward the landscape within the sevier hinterland developed into a rugged and high mountain range with the hypsometric mean elevation of 4 km and relief of 1 5 km this eocene highland was bordered on the west by a high sierra nevada ramp and on the east by the intraforeland basins that captured water draining these growing highlands the spatial and temporal evolution of this highland correlates with the timing of volcanism and extension these observations support tectonic models that call for north to south removal of the farallon slab or piecemeal removal of mantle lithosphere the isotopic data show that prior to growth of this highland the north american monsoon nam penetrated much farther north in the paleocene eocene than today the combined effects of global cooling increasing latitudinal temperature gradients and the generation of the orographic barrier created by the growing north to south highland produced a southward migration of the nam front by the oligocene the hydrologic regime that we observe today was in place it has been modified since then as a result of basin and range extension and collapse of the highlands in the mid miocene this collapse allowed the nam to penetrate farther north into the great basin of nevada and utah

a hydrogeochemistry and multi isotope sr o h and c study of groundwater salinity origin and hydrogeochemcial processes in the shallow confined aquifer of northern yangtze river downstream coastal plain china abstract economically developed coastal areas have a high water demand and their groundwater resources can be threatened by salinization many methods and tracers have been used to discriminate the source of salinization because a single method does not yield reliable results in this paper the shallow confined coastal plain aquifer north of the downstream yangtze river in china is used as a case study to investigate the origin of the salinity and the relevant geochemical processes for this aquifer multiple environmental tracers of major ions minor ions br i and isotopes 18 o 2 h 13 c 87 sr 3 h 14 c were used so as to provide reliable conclusions the tds distribution of the aquifer has an increasing trend from below 500 mg l in the inland areas to more than 20 000 mg l around the southeast coastline the water chemical type evolves from hco 3 ca to cl na as the tds increases the results suggest that the groundwater salinity is influenced by seawater intrusion the seawater proportions in the groundwater samples range from 0 07 to 94 41 and show the same spatial distribution pattern as tds the 3 h and 14 c values show that the highest salinity was mainly caused by a seawater transgression around 6000a b p the aquifer is also affected by other hydrogeochemical processes base exchange has enriched ca 2 and depleted k and na sulfate reduction has reduced the concentration of so 4 2 and enriched hco 3 and iodine rich organic matter decomposition has enriched the concentration of i the iodine enrichment also suggests paleo seawater intrusion in addition the precipitation of carbonate minerals has decreased the concentration of ca 2 mg 2 and hco 3 albeit to a limited extent

thrust tectonics a personal view the structure of fold and thrust belts has been studied for just over one hundred years and has been the subject of a recent international conference at toulouse in may 1984 this article reviews some of the recent advances in thrust tectonics from a personal viewpoint in the light of the toulouse meeting key tools in correctly interpreting thrust systems are the use of balanced restorable cross sections and the resolution of three dimensional fault systems these analytical methods are now being widely developed and applied to numerous orogenic belts with many surprising results while our understanding of foreland thrust belts is now probably better than any other structural environment there is still great uncertainty as to the emplacement driving mechanisms of these belts future work will try to solve these and other outstanding problems and apply the new analytical methods to the interior parts of thrust belts in efforts to restore entire orogens

high times on the tibetan plateau paleoelevation of the thakkhola graben nepal east west extension in the tibetan plateau is generally assumed to have resulted from gravitational collapse following thickening and uplift on the basis of this assumption several studies have dated east west extensional structures to determine when the plateau attained its current high elevation however independent estimates of elevation are needed to determine whether extension occurred before during or after the plateau achieved its current elevation because the isotopic composition of meteoric water decreases with increasing elevation significant change in local elevation throughout the thakkhola graben depositional history should be recorded by change in 18 o values of fluvial and lacustrine carbonates the 18 o values of 16 to 23 of thakkhola graben carbonates reflect meteoric water values similar to modern values and suggest that the southern tibetan plateau attained its current elevation prior to eastwest extension initiation of thakkhola graben extension is constrained between 10 and 11 ma based on magnetostratigraphy of the older tetang formation the 13 c values of soil carbonates suggest an age younger than 8 ma for the base of the thakkhola formation

oxygen isotope evidence for the late cenozoic development of an orographic rain shadow in eastern washington usa topographic development of the southern washington cascade range and its influence on regional climate on the leeward side of the range for the past 15 6 m y are evaluated using oxygen isotope ratios d 18 o of ancient meteoric water recorded in authigenic smec tites the d 18 o values of authigenic smectites from paleosols and altered tuffs on the east side of the range exhibit a temporal and continuous decrease of 3 4 from 15 6 ma to the present taking into account a regional temperature change in eastern washington since the middle miocene the calculated d 18 o values of regional meteoric water show a negative shift of 3 5 4 5 over the same interval such a decrease is similar to the change in the d 18 o values of modern precipitation from the coastal side to a region down wind of the washington cascades this negative shift of the calculated d 18 o values on the east side of the range is best explained by the development of a rain shadow due to the tectonic rock uplift of the cascades during the late cenozoic based on the empirically calculated relationship between change in elevation and change in the d 18 o value of pre cipitation paleorelief of the southern washington cascades since 15 6 ma is estimated to be 1 2 1 7 km

ages and stratigraphy of lower and middle tertiary sedimentary and volcanic rocks of the central cascades washington application to the tectonic history of the straight creek fault in the central cascade range of washington three structural blocks of early tertiary sedimentary and volcanic rocks help to define the position and history of the southern segment of the straight creek fault east of the fault in the teanaway river block the early eocene fluviatile feld spathic sandstone of the swauk formation is interbedded with largely dacitic volcanic rocks of the silver pass volcanic member zircon fission track ages on the silver pass are about 52 m y overlying the tightly folded swauk and silver pass is the teanaway formation a gently dipping accumulation of basalt andesite rare dacite and rhyolite that yields middle eocene about 47 m y whole rock k ar ages conformably overlying the teanaway is the roslyn formation a coal bearing fluviatile feld spathic sandstone of probable middle to late eocene age the late eocene and oligocene naches formation exposed west of the straight creek fault in the cabin creek block is rich in fluviatile feldspathic sandstone and rhyolite flows and tuffs in its lower part but grades upward into a sequence dominated by basalt but with some andesite the basal guye sedimentary member of the naches formation underlies and is interbedded with the mount catherine rhyolite member in the snoqualmie pass area on the basis of zircon fission track ages on silicic tuffs and whole rock k ar ages on basalt the basal part of the naches is about 40 to 44 m y old the formation is tightly folded and complexly faulted along the straight creek fault the straight creek fault intersects the olympic wallowa lineament in the strongly deformed manastash river block in this block fluviatile coal bearing feldspathic sandstone of the manastash formation is overlain by principally dacitic volcanic rocks of the taneum formation overlying the taneum is the basalt of frost mountain we correlate this threefold sequence feldspathic sandstone dacite basalt with the sequence in the teanaway river block small patches of rhyolitic ash flow tuff dated at 33 m y late oligocene and interbedded feldspathic sandstone overlie the roslyn and teanaway formations in the teanaway river block and are probably correlative with the late oligocene wenatchee formation exposed in the chiwaukum graben east of the teanaway river block as well as with the late oligocene volcanic rocks 30 m y along the cascade crest to the southwest these latter rocks are little deformed and unconformably overlie the naches formation the ages and depositional record in the three blocks indicate a tertiary history of dominantly vertical movement along the straight creek fault and its southeasterly splays that merge with the olympic wallowa lineament the horst and graben structure of the blocks as well as enechelon fold axes in the swauk formation suggests some post early eocene right lateral shear along the fault although there is no direct evidence of lateral offset vertical movement significant since early eocene swauk deposition followed late eocene naches deposition but tapered off by late oligocene time and ceased by miocene time when the fault was intruded by the 25 m y old snoqualmie batholith and other plutons however structures with olympic wallowa lineament trends appear to have influenced folding of the miocene yakima basalt subgroup

stable isotopic evidence for a pre middle miocene rain shadow in the western basin and range implications for the paleotopography of the sierra nevada 1 a recently proposed method for approximating the paleorelief of mountain belts makes use of the predictable relationship between the isotopic depletion of precipitation and the net elevation of an orographic barrier over which an air mass rises this rain shadow effect often creates desert regions on the lee side of mountain belts in which precipitation is isotopically light changes in the isotopic composition of precipitation can be estimated from the isotopic composition of authigenic or pedogenic minerals which can then be used to infer both the development of relief during orogenesis as well as the stability of a rain shadow formed by developing mountains the 18o of smectites formed from the weathering of middle miocene to late pliocene volcanic ashes currently exposed in the rain shadow of the modern sierra nevada of california show no indication of large scale late cenozoic surface uplift of the sierra and corresponding regional rain shadow development rather smectite isotope data tentatively suggest that elevations may have decreased over this time by as much as 2000 m toward the southern end of the range and 700 m in regions farther north this suggests that the modern rain shadow cast over the western basin and range has been in existence since pre middle miocene and that the sierra nevada have been a prominent orographic barrier since before this time these interpretations are in accord with several recent studies also suggesting a possible cenozoic elevation loss of an already developed sierra nevada mountain range

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

patterns of faunal turnover and diversity in the neogene siwaliks of northern pakistan abstract the fluvial neogene siwalik formations of northern pakistan contain a long and richly fossiliferous sequence of terrestrial vertebrate faunas in which patterns of faunal turnover and changes in diversity can be documented and analyzed for intervals having durations of 0 5 m y the complete sequence extends from circa 18 5 to 1 ma but the part between 18 5 and 5 5 ma is best sampled and most intervals within it are well represented thirteen orders of siwalik mammals have been identified with well sampled intervals having 50 or more species most siwalik mammals however are either rodents or artiodactyls bovids are the most common and most speciose of the larger mammals while murid and cricetid rodents dominate the small mammal assemblages between 18 5 and 5 5 ma species diversity varied considerably among artiodactyls and rodents the number of species first increased between 15 and 13 ma and then fell data on stratigraphic ranges of rodents and artiodactyls show that faunal change in the siwaliks was episodic occurring during short intervals with high turnover followed by longer periods with considerably less change maxima of first appearances occurred at approximately 13 5 and 8 5 ma while maxima of last occurrences were at 12 5 and 8 0 ma some of the observed faunal events can be correlated to climatic and environmental changes the middle miocene diversification occurred during a period of global cooling while the latest miocene decline in diversity and increased turnover accompanied oxygen and carbon isotopic changes that correlate to globally increasing seasonality and aridity other correlations are ambiguous the marked decrease in diversity and the major turnover events between 13 and 8 ma do not correspond to known local or global events the neogene siwaliks and paleogene bighorn crazy mountains sequence in wyoming and montana share many similarities they have equivalent levels of temporal resolution and similar levels of completeness of their fossil records siwalik ordinal abundance and diversity patterns differ markedly from those of the paleogene but generic and probably species diversity was approximately the same although the siwalik faunas may have been slightly less diverse over time changes in diversity were of comparable magnitude with monotonic trends persisting for more than 5 million years the magnitude of faunal turnover was also similar ranging from less than half to 3 5 times that expected in both sequences faunal change appears to have been episodic with strong pulses between intervals of low turnover the siwaliks in contrast to the paleogene sequence may have had more distinct pulses and longer intervals between pulses neither sequence has peaks of first occurrences coinciding with peaks of last occurrences

gravity anomalies and flexure of the lithosphere at mountain ranges the bouguer gravity anomaly over the himalayan alpine and appalachian mountains is characterized by a generally asymmetric gravity low which spans the mountains and associated foreland basins the minimum of the gravity low is generally systematically displaced from the region of greatest topographic relief and shows no obvious relationship to surface geology in addition the alps and appalachians are associated with a generally symmetric gravity high that is unrelated to the topographic relief together the gravity low and high form a characteristic positive negative anomaly couple the steep gravity gradient between the positive and negative couple correlates with the insubric line and its equivalents in the alps and the brevard zone in the southern appalachians this gravity anomaly couple is interpreted as evidence for flexure of the continental lithosphere by subsurface buried and surface topographic loading the magnitude of the subsurface load is estimated from the integrated excess mass represented by the positive anomaly and the magnitude of the surface load from the topography by combining these loads the flexure of the lithosphere and the associated bouguer gravity anomaly are calculated for different assumed values of the elastic thickness te of continental lithosphere the best fitting value of te for the himalayas is 80 100 km for the alps 25 50 km and for the appalachians 80 130 km the model calculations suggest that the main contribution to the gravity couple in the alps and appalachians arises not from surface loads such as thrust sheets and nappes but from subsurface loads however in the case of the himalayas the topography appears to be a sufficient load to explain the observed asymmetric gravity low when subsurface loads do exist therefore we would not expect a close correlation between mountain topographic relief and depth to the m discontinuity as required by classical models of isostasy rather the m discontinuity is expected to relate to the center of mass of all the loads acting on the lithosphere the surface and subsurface loads inferred from the gravity anomaly play a major role in the development of mountains and foreland basins the emplacement of large subsurface loads represents the primary event in the alps and appalachians while in the himalayas the emplacement of the surface load is the primary event the emplacement of the subsurface load probably marks the initiation of foreland basin development the regional characteristics of the basin are controlled by the primary load while local variations are controlled by the secondary thrust sheet loads subsequent movement of either load will produce migration of the basin depocenter the origin of the subsurface load is not clear but its association with the insubric line in the alps and the brevard zone in the appalachians suggests that it may be related to the obduction of crustal blocks flakes onto the underlying plate during continental collision or possibly to the preloaded crustal structure of the underlying plate

the clumped isotope geothermometer in soil and paleosol carbonate we studied both modern soils and buried paleosols in order to understand the relationship of temperature t c 47 estimated from clumped isotope compositions 47 of soil carbonates to actual surface and burial temperatures carbonates from modern soils with differing rainfall seasonality were sampled from arizona nevada tibet pakistan and india t c 47 obtained from these soils shows that soil carbonate forms in the warmest months of the year in the late morning to afternoon and probably in response to intense soil dewatering t c 47 obtained from modern soil carbonate ranges from 10 8 to 39 5 c on average t c 47 exceeds mean annual temperature by 10 15 c due to summertime bias in soil carbonate formation and to summertime ground heating by incident solar radiation secondary controls on t c 47 are soil depth and shading site mean annual air temperature maat across a broad range 0 30 c of site temperatures is highly correlated with t c 47 from soils following the equation maat c 1 20 t c 47 0 21 72 r 2 0 92 where t c 47 0 is the effective air temperature at the site estimated from t c 47 the effective air temperature represents the air temperature required to account for the t c 47 at each site after consideration of variations in t c 47 with soil depth and ground heating the highly correlated relationship in this equation should now permit mean annual temperature in the past to be reconstructed from t c 47 in paleosol carbonate assuming one is studying paleosols that formed in environments generally similar in seasonality and ground cover to our calibration sites t c 47 0 decreases systematically with elevation gain in the himalaya following the equation elevation m 229 t c 47 0 9300 r 2 0 95 assuming that temperature varied similarly with elevation in the past this equation can be used to reconstruct paleoelevation from clumped isotope analysis of ancient soil carbonates we also measured t c 47 from long sequences of deeply buried 5 km paleosol carbonate in the himalayan foreland in order to evaluate potential diagenetic resetting of clumped isotope composition we found that paleosol carbonate faithfully records plausible soil t c 47 down to 2 5 4 km burial depth or 90 125 c deeper than this and above this temperature t c 47 in paleosol carbonate is reset to temperatures 40 c we observe 40 c as the upper limit for t c 47 in modern soils from soil depths 25 cm and therefore that t c 47 40 c obtained from ancient soil carbonate indicates substantially warmer climate regimes compared to the present or non primary temperatures produced by resetting during diagenesis if representative this limits the use of t c 47 to reconstruct ancient surface temperature to modestly buried 3 4 km paleosol carbonates despite diagenetic resetting of 47 values 18 o and 13 c values of the same deeply buried paleosol carbonate appear unaltered we conclude that solid state reordering or recrystallization of clumping of carbon and oxygen isotopes can occur in the absence of open system exchange of paleosol carbonate with significant quantities of water or other phases

successive approximations of diversity curves ten more years in the library traditional paleontological diversity curves are based on tallies of all taxa appearing in formally defined time units these tallies are thought to be robust to further data collection thus they supposedly do not reflect nuisance factors like variable time unit lengths and sampling intensity biases a comparison of a decade old north american cenozoic mammal diversity curve and a newer database shows major differences at least three major factors differentiate the two use of shorter fixed length time intervals restriction of counts to taxa that cross boundaries between intervals and correction for variation in sampling intensity the difference between genus and species level data also was examined but appears to be minor by comparison because at best only one pattern can be close to the true historical trajectory the analyses suggest that the new data and protocols together have yielded a curve that is converging on an accurate signal

sensitivity of eurasian climate to surface uplift of the tibetan plateau experiments with climate models are used to illustrate how earth s climate could be expected to change if surface uplift occurred the experiments contrast two climate simulations one with all continents at sea level and one with present day mountains and plateaus the simulations in the eurasia sector show that surface uplift increased elevation produces marked increases in the intensity of summer and winter monsoons of asia with development of wetter climates to the south and east of the tibetan plateau and drier climates to the north and west of the plateau there is a general cooling in northern polar latitudes comparison of simulations from two different models shows that the magnitude of the simulated changes depends upon how the models calculate the land surface hydrology and the ocean temperature the simulated changes produced by surface uplift agree in a general way with many geologic indicators of late cenozoic climate change the results suggest that surface uplift of mountains and platea

assessment of submarine groundwater discharge in the intertidal zone of laizhou bay china using electrical resistivity tomography abstract coastal zones are the most sensitive and vulnerable ecological environments in the world submarine groundwater discharge sgd is an important pathway for material transport between land and sea in the low lying coastal plains of coastal zones in the present study electrical resistivity tomography was used to monitor submarine groundwater discharge in the intertidal zone the salinity change ratio was derived using archie s law and manheim s equation and was used as an index to describe the dynamic discharge process a model of the seawater circulation process in the multilayer coastal aquifer system was established the model contains a window area between the upper unconfined and lower confined aquifer and a highly permeable channel in the upper silt layer the results of the study provide a theoretical basis and technical support for the rapid assessment of sgd in low lying coastal plains and will assist in the management of coastal zone environments

40ar 39ar dating of penninic front tectonic displacement w alps during the lower oligocene 31 34 ma direct absolute dating of the penninic frontal thrust tectonic motion is achieved using the 40 ar 39 ar technique in the pelvoux crystalline massif western alps the dated phengites were formed syn kinematically in shear zones they underline the brittle ductile stretching lineation pressure shadow fibres and slickensides consistent with underthrusting of the european continental slab below the propagating penninic thrust chlorite phengite thermobarometry yields 10 15 km and t 280 c while 40 ar 39 ar phengite ages mainly range between 34 and 30 ma with one younger age at 27 ma this early oligocene age range matches a major tectonic rearrangement of the alpine chain preservation of prograde 40 ar 39 ar ages is ascribed to passive exhumation of the pelvoux shear zone network sandwiched between more external thrusts and the penninic front reactivated as an e dipping detachment fault partial resetting in the low temperature part of argon spectra below 24 ma is ascribed to brittle deformation and alteration of phengites

the use of strontium isotopes in determining groundwater mixing and brine fingering in a playa spring zone lake tyrrell australia j hydrol 167 225 239 playas in arid and semi arid regions can be important regional groundwater discharge zones located in the northwestern portion of victoria australia lake tyrrell is a large playa that serves as a major discharge zone of regional groundwater the chemistry of the regional groundwater is unique having salinities of approximately 30 g 1 1 and ph values as low as 2 8 as the regional groundwater is discharged along the western edge of the playa in the spring zone it is evapo concentrated into a dense brine which sinks through the playa sediments macumber s pioneering work on the geohydrology of this region established that this denser reflux brine below the playa surface has evolved from the evaporation of regional groundwaters we have measured the 87sr 86sr ratio of a number of groundwater samples taken at shallow depths along the spring zone at the playa edge and compared them with the regional groundwaters and the reflux brine our data reveal a rather complex pattern of mixing of the various water masses associated with the playa system most probably the result of density driven convective plumes two types of regional groundwater can be identified based on their 87sr 86sr values with groundwater from the south being less radiogenic than that flowing from the north i e 0 7108 vs 0 7142 vertical variations in 87sr 86sr in the regional groundwaters observed in wells adjacent to the spring zone can also be identified along a vertical gradient in the spring zone besides the hydrogeological information provided by these measurements the strontium isotope variations allow us to evaluate the source of strontium to these waters the regional groundwaters south of the lake are very similar in 87sr 86sr ratio to the reflux brines whereas the northern regional groundwaters are comparatively enriched in 87sr this enhanced 87sr signature indicates the addition of sr along the flow path via the weathering of the aquifer material the miocene parilla sand the southern waters have 87sr 86sr values closer to that of present day seawater and or miocene seawater indicating that the major source of sr to the system is from one or both of these sources our results demonstrate that strontium isotopes can be extremely useful in studying the dynamics as well as the geochemistry of surface water groundwater interactions

microfabrics of calcite ultramylonites as records of coaxial and non coaxial deformation kinematics examples from the rocher de l yret shear zone western alps microfabrics were analysed in calcite mylonites from the rim of the pelvoux massif western alps france wnw directed emplacement of the internal penninic units onto the dauphinois domain produced intense deformation of an eocene age nummulitic limestone under lower anchizone metamorphic conditions slightly below 300 c two types of microfabrics developed primarily by dislocation creep accompanied by dynamic recrystallisation in the absence of twinning coaxial kinematics are inferred for samples exhibiting grain shape fabrics and textures with orthorhombic symmetry their texture crystallographic preferred orientation cpo is characterised by two c axis maxima symmetrically oriented at 15 from the normal to the macroscopic foliation non coaxial deformation is evident in samples with monoclinic shape fabrics and textures characterised by a single oblique c axis maximum tilted with the sense of shear by about 15 from the analysis of suitably oriented slip systems for the main texture components under given kinematics it is inferred that the orthorhombic textures which developed in coaxial kinematics favour activity of b10 11n and b02 21n slip along the f and r planes respectively with minor contributions of basalban slip in contrast the monoclinic textures which developed during simple shear are most suited for duplex ban slip along the basal plane the transition between the dominating slip systems for the orthorhombic and monoclinic microfabrics is interpreted to be due to the effects of dynamic recrystallisation upon texture development since oblique c axis maxima documented in the literature are most often rotated not with but against the shear sense calcite textures alone should not be used as unequivocal shear sense indicators but need to be complemented by microstructural criteria such as shape preferred orientations grain size estimates and amount of twinning

structural implications of paleomagnetic data from pelvoux belledonne area french alps abstract paleomagnetic studies were carried out in triassic lias lavas from five new sites of the external zone of the french alps pelvoux belledonne area and compared with previous data in two sites magnetization seems to have been disturbed during alpine deformation but the paleomagnetic directions obtained in the other sites allow one to define the eastern boundary of the anticlockwise rotated taillefer block and the importance of local rotation along the aspres les corps faults the major anticlockwise rotation of taillefer is probably of ante nummulitic age but other rotations in the pelvoux belledonne area could have occurred during this same period or be of more recent age

spatial and temporal variation of cenozoic surface elevation in the great basin and sierra nevada the surface uplift of mountain belts caused by tectonism plays an important role in determining the long term climate evolution of the earth however the general lack of information on the paleotopography of mountain belts limits our ability to identify the links and feedbacks between topography tectonics and climate change on geologic time scales here we present a 1 8 o and d record of authigenic minerals for the northern great basin that captures the timing and magnitude of regional surface uplift and subsidence events in the western united states during the cenozoic authigenic calcite smectite and chert 1 8 o values suggest the northern great basin region experienced 2km of surface uplift between the middle eocene and early oligocene followed by 1 to 2km of surface subsidence in the southern great basin and or sierra nevada since the middle miocene these data when combined with previously published work show that the surface uplift history varied in both space and time surface uplift migrated from north to south with high elevations in southern british columbia and northeastern washington in the middle eocene and development of surface uplift in north and central nevada in the oligocene this pattern of north to south surface uplift is similar to the timing of magmatism in the western cordillera a result that supports tectonic models linking magamtism with removal of mantle lithosphere and or a subducting slab

seasonal bias in the formation and stable isotopic composition of pedogenic carbonate in modern soils from central new mexico usa in order to better calibrate pedogenic carbonate as a proxy for past environments we compared the stable isotopic composition of soil co 2 soil water and pedogenic carbonate in young soils from central new mexico usa seasonal changes in the 13 c value of soil co 2 the 18 o value of soil water and the soil temperature were monitored to establish the timing of isotopic equilibrium with the carbonate calcite solubility was calculated from measured temperatures and co 2 concentrations in the soil this approach allowed us to determine the conditions associated with pedogenic carbonate formation carbon isotope equilibrium oxygen isotope equilibrium and minimum calcite solubility all occurred simultaneously during warm dry conditions in may 2008 when soil co 2 concentrations were low it is therefore concluded that pedogenic carbonate forms during warm dry periods and does not record mean growing season conditions as typically assumed the seasonal bias in pedogenic carbonate formation may explain the occurrence of pedogenic carbonate in monsoon climates and its absence in regions where annual precipitation is more uniformly distributed the implications of the seasonal bias for stable isotope based paleoenvironmental reconstructions are that paleoelevations may have been previously over or underestimated paleoatmospheric co 2 concentrations likely have been signifi cantly overestimated and pedogenic carbonate provides a c 4 biased record of paleovegetation especially in dry soils

the effect of drainage reorganization on paleoaltimetry studies an example from the paleogene laramide foreland abstract using multiple isotope systems we examine the complex effects of drainage reorganization in the laramide foreland in the context of stable isotope paleoaltimetry strontium oxygen and carbon isotopic data from lacustrine carbonates formed in the southwestern uinta basin utah between the late cretaceous and late middle eocene reveal a two stage expansion in the drainage basin of lake uinta beginning at 53 ma culminating in the mahogany highstand at 48 6 ma a marked increase in 87 sr 86 sr ratios of samples from the main body of the green river formation is interpreted as the result of water overflowing the greater green river basin in wyoming and entering lake uinta from the east via the piceance creek basin of northwestern colorado this large new source of water caused a rapid expansion of lake uinta and was accompanied by a significant and rapid increase in the o isotope record of carbonate samples by 6 the periodic overspilling of lake gosiute probably became continuous at 49 ma when the lake captured low 18 o water from the challis and absaroka volcanic fields to the north however evaporation in the greater green river and piceance creek basins meant that the waters entering lake uinta were still enriched in 18 o by 46 ma inflows from the greater green river basin ceased resulting in a lowstand of lake uinta and the deposition of bedded evaporites in the saline facies of the green river formation we thus show that basin development and lake hydrology in the laramide foreland were characterized by large scale changes in cordilleran drainage patterns capable of confounding paleoaltimetry studies premised on too few isotopic systems samples or localities in the case of the north american cordillera of the paleogene we further demonstrate the likelihood that 1 topographic evolution of distal source areas strongly influenced the isotopic records of intraforeland basins and 2 a pattern of drainage integration between the hinterland and foreland may correlate in space and time with the southward sweep of hinterland magmatism

hot or not impact of seasonally variable soil carbonate formation on paleotemperature and o isotope records from clumped isotope thermometry quantifying the timing and temperature of soil carbonate formation is important for interpreting isotopic records of earth surface temperature and soil water composition from paleosols pedogenic carbonates typically have been assumed to form at mean annual temperature but recent work suggests warm season bias in carbonate formation could impact the interpretation of d 18 o values and carbonate

oxygen isotope evidence for progressive uplift of the cascade range oregon oxygen isotope compositions of fossil equid teeth in the cascade rainshadow reveal a v5x decrease in mean n 18 o since 27 ma isotopic changes are inconsistent with expected effects from global climate change because a the expected isotopic shift to tooth n 18 o values due to global climate change v1x is much smaller than the observed shift b predicted and observed isotopic trends are opposite for oligocene vs miocene samples and c average compositions and ranges in compositions remained unchanged for samples from before and after major global cooling in the mid miocene accounting for a decrease in relative humidity of at least 15 we infer a topographically driven secular shift in the n 18 o value of rainwater of 6 8x since the late oligocene which is approximately equivalent to the modern day difference in n 18 o values of precipitation and surface waters across the central cascades rise of the central cascades apparently occurred monotonically over the last 27 ma with a hiatus between v15 4 and 7 2 ma possibly related to eruption of the columbia river basalts progressive volcanic accumulation over tens of millions of years best explains the data rather than a short lived uplift event paleoseasonality as inferred from isotope zoning and intertooth variability decreased dramatically from 7 9x at 15 4 7 ma to v3x at 3 ma then increased to 6 8x today the cause of the decrease in seasonality at 3 ma may reflect either brief warming during the mid pliocene within the context of global tectonic reorganization or consumption by equids of water from an isotopically buffered lake idaho 2002 elsevier science b v all rights reserved

late miocene climate variability and surface elevation in the central andes abstract temporal and spatial variations in topography and oxygen stable isotope ratios in precipitation in the central andes have stimulated widespread discussion about the competing roles of mantle and crustal processes and their feedbacks with global scale climatic change in uplifting and shaping the central andes in general one of the major obstacles in assessing the relative contributions of long term 10 5 10 6 a tectonic processes and precipitation as a proxy for climate to the uplift history of the andean orogen is the lack of integrated data sets that record late miocene patterns of uplift and climate radiogenic 87 sr 86 sr sedimentologic and stable isotope 18 o data from subandean foreland deposits of the chaco basin bolivia show a rapid 18 o and 87 sr 86 sr values at 8 5 ma that we interpret to reflect a change in precipitation patterns along the eastern cordillera and the subandean fold thrust belt in agreement with 13 c studies on paleosol carbonates we attribute this change to a southward deflection of the south american low level jet llj that currently exerts the dominant control over the seasonality and amount of precipitation along the eastern flanks of the andes deflection of the llj occurred most likely as the combined effects of readjustment of relief and topography within the eastern cordillera at 20 22 s and possibly associated surface uplift of the altiplano contemporaneous rapid positive shifts in 18 o and 87 sr 86 sr of pedogenic carbonate in fluvial foreland deposits are consistent with a transition to more seasonal precipitation conditions and critical threshold elevations being attained that affected south american atmospheric circulation patterns a four fold increase in sedimentation rates in the foreland together with a shift to strongly radiogenic 87 sr 86 sr ratios in paleo river water and sediment load as well as river incision into the well preserved san juan del oro paleo surface directly reflects a rapid change in moisture distribution along the eastern flank of the central andes at 8 5 ma and associated rearrangement of the drainage systems collectively the data presented here strongly suggest that between 12 and 8 ma the amount oxygen isotopic composition spatial distribution and seasonality of precipitation along the eastern flank of the bolivian andes changed dramatically which in turn require changes in trans andean moisture flux and isotopic composition of precipitation on the uplifting plateau region

tertiary climatic changes at middle latitudes of western north america abstract a new multivariate analysis of leaf physiognomy provides the basis for estimating various climatic parameters for angiosperm leaf assemblages estimates from this climate leaf analysis multivariate program clamp are both accurate valid and precise repeatable application of clamp to fossil leaf assemblages from western north america confirms that eocene mean annual temperature mat was generally high early eocene mat 19 c at paleolat 70 n and 27 c at paleolat 45 n significant fluctuations 5 8 in mat occurred during the eocene each successive warm period was cooler than the preceding warm period mean annual range of temperature mart was generally low during the eocene especially at middle latitudes but then markedly increased by 12 13 c at 33 ma as mat decreased by 7 8 c these changes at 33 ma largely involved a decrease in cold month mean temperature which continued to decline into the early miocene but then increased significantly into the mid miocene thermal optimum warm month mean temperature changed little from the eocene through the early miocene this parameter however markedly decreased at 13 ma which coincides with the growth of the east antarctic ice sheet clamp also indicates that the coastal region of western north america had significantly higher mat than interior regions such as the great basin and rocky mountains these differences in mat appeared by or during the eocene and indicate that much of the interior had high altitudes in the paleogene these inferences have a significant bearing on global circulation models proposed for tertiary climates

the restoration of thrust systems and displacement continuity around the mont blanc massif nw external alpine thrust belt abstract foreland propagating external thrust belts may be considered as essentially plane strain phenomena so that displacements can be correlated throughout their linked three dimensional fault geometry this approach has been applied to part of the northwest external french swiss alps around the mont blanc basement massif imbricates of basement and cover sequences on the sw margin of this massif restore to a width in excess of 77 km with an implicit shortening of at least 67 km these displacements can be correlated with those in the neighbouring helvetic nappes by transferring movements via lateral branch lines onto the mont blanc thrust by reappraising thrust geometries the helvetic ultrahelvetic nappe complex has been restored to a width of 114 km to the ese of the aiguilles rouges basement massif displacements on the internal se margin of the mont blanc massif estimated by balanced sections and a restoration of the ultrahelvetic klippen in the sub alps exceed 59 km thrust continuity incorporating the restorations of nappes and imbricate geometries around the mont blanc massif is illustrated on a crude restored branch line map which also serves as a preliminary palaeogeographic reconstruction external thrust systems to the east of the external belledonne aiguilles rouges massif restore to a width of at least 140 km in the footwall to the frontal pennine thrust

genesis of salinized groundwater in quaternary aquifer system of coastal plain laizhou bay china geochemical evidences especially from bromine stable isotope abstract in the south coast of laizhou bay due to intensive groundwater extraction since the 1970s salt water intrusion has occurred seriously which increased the stress on regional fresh water resources it is of great importance to understand origin of salinity and salinization process in coastal aquifers to trace source and transport of dissolved bromide as a perfect representative of salinity and reveal genesis of salinized groundwater in regional aquifer system br stable isotopes of the sampled waters were surveyed coupled with hydrochemistry and stable h o isotopes along the direction from inland to shore the results show that groundwater salinity hydrochemistry and stable isotopes exhibit regular variation from inland to shore the tds values of the groundwater increase gradually ranging from 0 52 to 133 74 g l the chemical types transform from cl ca and hco 3 ca to cl na 2 h and 18 o are getting more and more enriched and the 81 br values decrease gradually from inland to shore trends of major ions versus bromide and br isotope signatures for brine indicate brine originated from seawater evaporation followed by some water rock interaction processes the hydrogen and oxygen isotope signatures of the brine indicate the dilution by fresh water of meteoric origin was a probable process during or after brine formation the 81 br values of brine samples show good anticorrelation to both 2 h and 18 o values probably confirming the addition of fresh water the potential contribution of evaporate dissolution as a primary process to the brine was ruled out based on their br isotope signatures trends of major ions versus bromide and h o stable isotopes for brackish water reveal brine intrusion has occurred and mixed with fresh water inland and br stable isotopic composition of brackish water indicates that marine aerosol input could enrich the dissolved bromide in brackish water except for brine intrusion other processes such as diffusion subaerial evaporation and anthropogenic activities may change the budget of dissolved br but are not primary processes responsible for behavior of br stable isotope in shallow brackish water major contribution of meteoric water in deep fresh water and more influence by brine in deep saline water were revealed based on the br isotopic results

coupled hydrogeochemical modelling using kirmat to assess water rock interaction in a saline aquifer in central eastern tunisia abstract to quantify water rock interactions and forecast their spatiotemporal evolution in the shallow aquifer of sidi el hani located in central eastern tunisia the numerical code kirmat was used based on available geological mineralogical thermodynamic kinetic and hydrodynamic data the model was built and calibrated on two transects of the aquifer oriented along the flow lines of groundwater the numerical results show that the interactions between water and rock are responsible for groundwater salinity which is strongly dominated by chlorides sodium and sulphates the variations of dissolved species in space and time are the result of halite dissolution anhydrite and gypsum dissolution and precipitation calcite dissolution and dolomite precipitation the precipitation of dolomite can locally induce a reduction in permeability and further enhance an increase in leaching because the residence time between rock and water will be amplified three numerical sensitivity studies have been conducted to evaluate the influence of water rock interactions on groundwater salinization the study highlights the finding that the modelled fate of dissolved species in the unconfined aquifer is rather sensitive to the darcy velocity but not very sensitive to the initial volume fractions of minerals in the two transects and the composition of groundwater injected at the upstream boundary

combined use of tracer approach and numerical simulation to estimate groundwater recharge in an alluvial aquifer system a case study of nasunogahara area central japan summary in this study we simulate the spatial and temporal distribution of groundwater recharge in an alluvial aquifer system in the nasunogahara area of japan natural stable isotopes 18 o d were considered as additional calibration targets in a numerical model the reliability of the model outputs was further validated by comparing the results from the numerical simulation and an independent tracer approach the results indicated that the calibrated model can effectively simulate the spatial and temporal characteristics of the contribution ratios of recharge sources to groundwater in the nasunogahara area however the tracer approach i e end member mixing analysis provided more reliable results at point scale particularly for the estimated contribution ratios of paddy field water the precipitation in the nasunogahara area is the major recharge source its mean contribution ratio is 58 for a one year period over the entire alluvial fan river seepage is significant in the upstream area of the alluvial fan and the contribution ratio of river waters along the river channels in the upstream area increases during the wet season paddy field water is a highly important recharge source in the midstream and downstream areas of the alluvial fan and the contribution ratio of paddy field water obviously increases from dry season to wet season because of irrigation this study demonstrates that combined use of the tracer approach and numerical simulation with stable isotopes as additional calibration targets can eliminate their respective limitations and can assist in better understanding the groundwater recharge mechanism in alluvial aquifer systems

middle to late miocene middle eastern climate from stable oxygen and carbon isotope data southern alborz mountains n iran abstract the alborz mountains of northern iran intercept and divert the northern hemisphere westerlies carrying moisture from the mediterranean and black sea and form an orographic barrier to moisture sourced to the north in the caspian sea this implies that terrestrial deposits along the southern alborz mountains leeward side of northerly winds and windward side of westerlies with the respect to tibet and other mountainous terrain in the himalayan karakoram realm potentially track changes in past moisture and erosional regimes and mirror rainfall patterns here we present results of a stable isotope analysis and clay mineral study of the miocene ca 17 5 7 6 ma upper red formation in the foreland of the southern alborz mountains the changes recorded by stable oxygen and carbon isotope data from pedogenic and lacustrine palustrine carbonate in the southern alborz mountains suggest 1 an increase in aridity possibly related to the evolution of the alborz orographic rain shadow which became more efficient between 17 5 and 13 2 ma 2 a steady increase in precipitation between 13 2 and 10 3 ma with a significant increase in rainout along the southern slope of the alborz mountains between 11 and 10 3 ma possibly related to perturbations in atmospheric circulation pattern in the northern hemisphere as suggested by coeval wetter phases in southern europe and 3 a decrease in aridity from ca 9 6 to 7 6 ma possibly reflecting an increase in the seasonality of precipitation based on environmental and climatic changes observed across southern asia and india starting from ca 10 ma we speculate that the topographic evolution of the himalayan tibetan system might have affected the late miocene climate in middle east

strontium isotopic composition of some brines from the precambrian shield of canada abstract twenty four groundwater samples from seven operating mines at sudbury yellow knife and thompson ontario north west territories and manitoba resp all from depths greater than 1 km and ranging in total dissolved solids tds from 1900 to 250 000 mg l 1 were measured for their 87 sr 86 ar values each geographic location gives a limited range in values and each location is distinct from the others this is interpreted as the result of extensive water rock interaction on a local scale for most of the time these brines were isolated and only recently have been exposed to surface water as a result of the mining operations the extent of the isolation is shown by the contrasting isotopic values of two pockets of water 0 711 vs 0 716 located on opposite sides of the same fault system on the north range at sudbury the exchange at all sites probably has continued until the present as indicated by the close agreement between water and present day 87 sr 86 sr whole rock values if so it suggests that there is no single age for such brines but it may be possible to date stages in the water s evolution by determining the age of secondary minerals that equilibrated with the water

hydrodynamic analysis of a mediterranean aquifer system with the use of hydrochemical and isotopical analysis as supporting tools the management of groundwater resources in coastal environments within the mediterranean basin has become of paramount importance especially in the light of global changes a typical example of such a hydrosystem is the lavrio basin in greece this research site involves two aquifer types granular and karstic formations that are hydraulically interconnected furthermore the proximity to the sea and the abstractions for irrigation and drinking water supply have led to the phenomenon of seawater intrusion the present study aims at analyzing the hydraulic hydrological and hydrogeological conditions of the area by means of hydrochemical and isotopical data interpretation as supporting tools which will inform and support the development of an integrated conceptual hydrogeological model of the area field investigations were conducted in order to collect piezometric and chemical data and use them to retrieve the quantitative and qualitative status of the local aquifer units new interpretation of an older dataset gave an insight into how the karstic aquifer behaves in terms of hydraulics the results have also demonstrated that there is a hydraulic connection between the different aquifers and the mediterranean sea while natural recharge was quantified for both aquifer types

stable isotopic constraints on the tectonic topographic and climatic evolution of the northern margin of the tibetan plateau abstract this study presents oxygen and carbon isotopic records from lacustrine paleosol alluvial and fluvial carbonate sampled in thirteen cenozoic sedimentary sections that span the northern margin of the tibetan plateau isotopic analyses of 1475 carbonate samples yield 18 o values that range from 13 1 to 38 9 smow and 13 c values range from 11 5 to 3 7 pdb based on these analyses we see two isotopic trends regionally we interpret a paleogene decrease in average oxygen isotope values to result from an increase in the mean elevation of the study region s drainages as they tapped waters from a growing tibetan plateau to the south of the study area we interpret a neogene increase in both carbon and oxygen isotope values to result from the initiation of local mountain building in the study area and the withdrawal of marine waters which increased basin isolation aridity and temperatures the timing of inferred initiation of uplift in this region is consistent with structural thermochronological and sedimentological evidence for a tectonic transition in the early and middle miocene from accommodation of india eurasia convergence through extrusion along the altyn tagh fault to accommodation of convergence through active shortening and mountain building in this region this study also supports tectonic models for the differential uplift of the tibetan plateau in that mountain building in this study region significantly postdates estimates for the attainment of high elevation from isotopic studies of the central tibetan plateau

late proterozoic rift faults and basement cover relationships within the ben more thrust sheet nw scotland recently proposed models for the tectonic evolution of northern scotland involving lithospheric extension during the late precambrian are supported by new discoveries and interpretations of early normal faults within the moine thrust belt such structures control the preser vation of torridonian sediments beneath the sub cambrian unconform ity the ben more thrust ramp from basement into the cambrian cover may have been controlled by the early faults major synclines within the ben more thrust sheet appear as tightenedhalf grabens and thus are composite structures this may require a re examination of the field relationships between these folds and the apparently syn tectonic alkaline intrusions that have been used to date thrust activity the ben more thrust sheet of the moine thrust belt contains the most easterly outcrops of torridonian supergroup late proterozoic in scotland fig 1 these sediments and their lewisian basement are unconformably overlain by the cambrian quartzites of the eriboll sandstone group the stratigraphic relationships of these units with the two un conformities cambrian on torridonian torridonian on lewisian discordant so that the cambrian sediments overstep from toridonian onto lewisian basement have been known for over a century however the nature of the overstep and its implications for the precambrian arrangement of torridonian and lewisian rocks is less established soper barber 1979 inferred the presence of major upright folds with wavelength in excess of 30 km so that torridonian sediments lie preserved in synclines while the crests of the anticlines are eroded beneath the sub cambrian unconformity this model for precambrian basement cover relationships has

regional paleoprecipitation records from the late eocene and oligocene of north america abstract the marine 18o record indicates precipitous cooling or significant expansion of antarctic ice volume across the eocene oligocene epoch boundary at 33 7 ma this climatic step is also found in estimates of decreased paleoprecipitation from paleosols in oregon montana and nebraska but is only a part of a long term decline across the eocene oligocene transition rather than a sudden shift this suggests that climate was driven by a gradual process rather than a single perturbation paleoprecipitation levels stabilized during the oligocene coincident with a stabilization in 18o values possibly indicating a new climatic steady state

stable chlorine isotopes in phanerozoic evaporites abstract modern seawater has a uniform 37cl value 0 0 with an exception in the upper current of the bosphorus 0 4 marine halite ranging in age from cambrian to miocene has 37cl values of 0 0 0 9 with most of the data in the range 0 0 0 5 mean 37cl values differ measurably between basins with no evident relationship to basin size or to age smaller evaporite bodies have the largest 37cl ranges potash facies halite has mean 37cl values lower than those of halite facies salt in the east siberia and zechstein basins the bulk 37cl of bedded halite preserving sedimentary textures cannot be shifted measurably after deposition under plausible natural conditions during the phanerozoic a detectable change in the 37cl values of the oceans is unlikely as a result of cl fluxes to and from the mantle and evaporites in halite the values of 37cl that cannot be explained by fractionation occurring on crystallization are best explained by the addition of non marine cl with 37cl 0 0 to evaporite brine

palaeo altimetry of the late eocene to miocene lunpola basin central tibet the elevation history of the tibetan plateau provides direct insight into the tectonic processes associated with continent continent collisions here we present oxygen isotope based estimates of the palaeo altimetry of late eocene and younger deposits of the lunpola basin in the centre of the plateau which indicate that the surface of tibet has been at an elevation of more than 4 kilometres for at least the past 35 million years we conclude that crustal but not mantle thickening models combined with plate kinematic solutions of india asia convergence are compatible with palaeo elevation estimates across the tibetan plateau

budget of crustal shortening and subduction of continental crust in the alps the stratigraphy surface structure and deep structure of the alps permit but do not require that a significant amount of european continental crust was subducted into the mantle beneath adria the fragment of continental lithosphere now comprising much of italy and the adriatic sea floor the present thin crust in much of europe suggests that the crust that was stretched in mesozoic time to form the southern margin of europe was initially thinner than normal the stratigraphic history of sediment deposited on that margin before its collision with adria suggests that the crustal basement on which much of this material was deposited had become particularly thin during the formation of the margin most of the crustal basement underlying the european margin and involved in the collision and the formation of the chain probably was thinner than 20 km and much of it may have been thinner than 10 km profiles of the present deep structure of the alps yield a range of possible values for the the average cross sectional area of crust involved in the collision that permit as much as 280 km of crustal shortening if this crust was as thin as implied by the stratigraphy thus although subduction of hundreds of kilometers of continental crust into the mantle beneath adria could have occurred the budget of crustal material involved in the formation of the alps does not require such crustal subduction

possible regional tectonic controls on mammalian evolution in western north america abstract previous work has suggested that tectonically active regions act as speciation pumps for mammals and plant species but little is known about how fast or widespread tectonism must be in order to directly influence evolution here we use oxygen and hydrogen isotopic data from miocene sedimentary deposits to characterize the topographic evolution of the southern columbia plateau snake river plain and northern rocky mountain regions during the yellowstone hotspot passage with the ultimate goal of understanding whether topographic changes caused by the hotspot influenced mammalian evolution within those regions we conducted oxygen isotope analyses of 130 samples of lacustrine and paleosol carbonate from miocene stratigraphic sections that span much of the northern rocky mountain region and combined these data with previously published isotopic records collectively these isotopic data show that caldera formation associated with the yellowstone hotspot has modified regional topography and rearranged drainages along the track of the hotspot and that the hotspot has left a topographic depression in its wake we explore the extent to which these topographic changes influenced or are decoupled from diversity changes exhibited by the local mammal faunas and conclude that the passage of the hotspot and consequent surface uplift created rainshadows in the lee of high elevation calderas and or generated large volumes of volcanic materials influencing soils and vegetation collectively that may explain a possible rise in mammal diversity in the cp srp region at 14 ma coincident with a drop in diversity in the nrm it is still unclear however how different taphonomic pathways and sample standardization problems are influencing apparent diversity peaks at this temporal and geographic resolution

stratigraphic classification of ancient lakes balancing tectonic and climatic controls lakes and lake deposits present two fundamental paradoxes 1 modern lakes are vastly complicated but the rock records of lakes are relatively simple extensive observations reveal three distinct facies associations of common and widespread occurrence these are referred to here as fluvial lacustrine fluctuating profundal and evaporative facies associations 2 most explanations of modern and ancient lakes attribute their nature to climate but neither modern lake parameters lake size depth and salinity nor the character of ancient lake strata thickness extent lithology correlate with measured or inferred climatic humidity we propose that it is the relative balance of rates of potential accommodation mostly tectonic with sediment water fill mostly a function of climate that controls lake occurrence distribution and character lake basins may be termed overfilled balanced fill or underfilled depending on the balance between these rates we conclude that climate and tectonics exert coequal influence on lake deposits at both mesoscales 1 m to hundreds of meters and macroscales hundreds to thousands of meters

seawater 87sr 86sr ratios along continental margins patterns and processes in open and restricted shelf domains abstract to better constrain the sr isotope budget in marginal domains without any fluvial inputs we analyzed the chemical composition and 87sr 86sr ratio of waters and shells from four locations two coastal lagoons one hemipelagic platform and one open marine shelf our results highlight homogeneous 87sr 86sr ratios typical of oligotrophic oceanic waters oow i e 0 709172 0 000023 in the pacific tatakoto atoll and along a mediterranean shore to offshore transect 25 km off banyuls sur mer bsm this attests that oceanic inputs from oligotrophic areas remain the main sr source in open shelf areas compared with submarine groundwater discharges sgd or particulate dissolution influences in bsm only foreshore data are more radiogenic possibly due to rainwater mixing local groundwater springs or more efficient particle dissolution in the intertidal zone in restricted areas we report variable 87sr 86sr ratios between the salses leucate france and oualidia morocco lagoons the first one has homogeneous 87sr 86sr ratio typical of oow except close to sgd in oualidia 87sr 86sr ratios decrease by 1 2 10 3 from oow values close to the atlantic inlet to progressively less radiogenic ones upstream within the interior of the lagoon these differences depend on several factors including the leaky restricted or choked morphology of lagoons modulating the oceanic sr inputs but also sgd fluxes whose 87sr 86sr ratios and sr concentrations are highly variable according to the nature of rocks leached in karstic aquifer in oualidia the low 87sr 86sr ratios correspond to high sr concentrations up to 150 mol l 1 issued from the dissolution of mesozoic evaporites leading to sgd fluxes accounting for 60 of the local sr budget through data compilation we show that similar 87sr 86sr gradients and processes prevail at the whole mediterranean scale finally we postulate that high coastal water retention times can also account for anomalous coastal 87sr 86sr ratios and that the combination of water mass restriction sgd bioadsorption and early diagenetic processes could decrease seawater sr concentrations in some marginal areas

assessment of saltwater contamination extent in the coastal aquifers of chaouia morocco using the electric recognition abstract the coastal chaouia located on the moroccan atlantic coast comports three aquifers a first plio quaternary constitutes the cover a second cretaceous located at sw in the zone of azemmour tnine chtouka and a third primary located at se in the zone of tnine chtouka casablanca these reservoirs constitute the only exploitable water resource for the social and economic development of the region between azemmour and casablanca these aquifers are unconfined pellicular and discontinuous they feed by infiltration of rainwater and discharge at sea agricultural irrigation is carried out exclusively from the groundwater which causes a drop of the piezometric surface and the intrusion of saltwater into the aquifer at the coast the consequence is the abandonment of some wells contaminated by seawater leading to conflict situations and significant economic losses therefore delineation of the freshwater saltwater interface is very important in order to build a sustainable groundwater management system and to implement appropriate regulatory policies the purpose of this study is to determine the extent and the geometric characteristics of the saltwater contamination extent in the coastal aquifers of the coastal chaouia to achieve this 399 vertical electric soundings and 48 electrical resistivity tomography profiles were performed perpendicular to the ocean furthermore the electrical conductivity and the piezometry were measured in 344 wells distributed over the study area the study demonstrated the effectiveness of electrical methods for mapping seawater intrusion into coastal aquifers in fact the results of the interpretation of the ves and erts after calibration with the lithological data of the boreholes as well as the values of the electrical conductivity have shown that the length of the saltwater wedge penetration inland depends on the lithological nature of the aquifer formations thus in the zone of azemmour tnine chtouka characterized by the presence of cretaceous terrains the extension of the saltwater wedge exceeds 2 km towards the continent and its depth reaches 45 m on the other hand in the zone of tnine chtouka casablanca characterized by the rise of the schists surmounted by the altered schists the seawater intrusion remains limited at 700 m from the coast and at 20 m of depth

tropical circulation intensification and tectonic extension recorded by neogene terrestrial δ18o records of the western united states terrestrial water isotope records preserve a history of hydrological cycling that is influenced by past climate and surface topography 18o and d records from authigenic minerals of the western united states display a long term increase during the neogene in the vicinity of the sierra nevada and the central rocky mountains rockies but a smaller increase or decrease in the northern great basin interpretations of these isotopic trends require quantitative estimates of the influence of climatic and environmental changes on 18o and d of soil water here we use a coupled atmosphere land model with water isotopologue tracking capabilities echam5 jsbach wiso to simulate precipitation and 18o responses to elevation independent changes in neogene geography equator to pole temperature gradient epgrad grassland expansion and tropical pacific sea surface temperatures both precipitation and soil water 18o 18osw respond strongly to neogene strengthening of the epgrad but weakly to other forcings an increase in epgrad leads to significant drying and 18o enrichment 3 5 of soil water over the northern sierra nevada and central rockies as a result of hadley circulation strengthening and enhanced coastal subtropical subsidence these large scale circulation changes reduce inland moisture transport from the pacific ocean and gulf of mexico our simulated 18osw responses could explain 50 100 of the proxy 18o increases over the sierra nevada and central rockies suggesting that climate change rather than surface subsidence may have been the dominant climate signal in 18o records in these regions on the contrary 18o responses to climate changes are small in the great basin indicating that the observed 18o increase over this region was likely a direct response to surface subsidence with elevation losses of 1 1 5 km adding this elevation loss to current great basin elevations reveals the former existence of a uniformly high plateau extending from the sierra nevada to the central rockies prior to neogene extension this revised elevation history brings neogene 18o and d paleoaltimetry of the western united states in accordance with independent lines of structural evidence and early cenozoic elevation reconstructions

extension analysis of stretched belemnites a comparison of methods abstract stretched belemnites and other fragmented rigid brittle inclusions offer great potential for estimating true extensions in deformed rocks in the standard ramsay method of analysis the elongation is calculated as 1 e l l o where l is the final end to end length of the fragmented belemnite and l o is the original length sum of the individual fragment lengths this method always underestimates the true extension usually by a substantial amount an apparently trivial modification of the standard method as used by hossain gives much improved extension estimates without any additional cost in time or effort the strain reversal method proposed by ferguson is the most accurate method currently available but involves more laborious data collection and subsequent computer processing the three methods were applied to 120 stretched belemnites in the external french alps the different extension values calculated by the three methods arise because ferguson s method is sensitive to the entire fracture and separation history hossain s method is sensitive to only part of that history and ramsay s method is history insensitive if strain history is of prime interest ferguson s method should be used but the ease speed and relatively good performance of hossain s method will make it attractive to many field geologists

plio pleistocene climatic transition and the lifting of the teton range wyoming abstract fine grained lacustrine riverine and ash fall sediments of the shooting iron formation whose late pliocene age is established by blancan gastropods and vertebrates yield a pollen flora that is essentially similar in composition to the modern pollen rain in the jackson hole area the pliocene assemblage suggests a climate like that of the jackson valley and foothills today these spectra also resemble a pliocene pollen flora from yellowstone park dated at 2 02 ma however the underlying miocene teewinot sediments differ by containing pollen of four exotic deciduous hardwoods tertiary relicts that suggest a summer moist climate unlike that of today the shooting iron sediments lie with an angular unconformity on and above the miocene lake sediments of the teewinot formation both of these deposits probably preceded the main uplift of the teton range based on the absence of precambrian clasts in the tertiary valley deposits because the pliocene floras were modern in aspect a plio pleistocene transition would be floristically imperceptible here the sequence denotes a protracted period of relative stability of climate during teewinot time and a shift in vegetational state summer wet trees drop out sometime between the latest miocene and latest pliocene the pliocene spectra suggest a dry cooler climate toward the end of shooting iron time

high and dry in central tibet during the late oligocene the time at which the tibetan plateau rose to its present high elevation remains controversial with estimates ranging from 40 ma to more recent than 7 ma new stable isotope analyses of modern and accurately dated ancient paleosol carbonate in the nima basin of central tibet point to an arid climate and high paleoelevation 4 5 5 km comparable to today s setting by 26 ma oxygen isotope values of ancient 26 ma soil carbonate are both very negative and indistinguishable after modest corrections for changes in global climate from the lowest least evaporated oxygen isotope values of modern soil carbonates in the area substantial enrichments in oxygen 18 in paleolacustrine carbonates as well as high carbon isotope values from paleosol carbonates indicate considerable lake evaporation and low soil respiration rates respectively and both are consistent with the present arid climate of the nima area blockage of tropical moisture by the himalaya and perhaps the gangdese shan probably has contributed strongly to the aridity and very negative oxygen isotope values of soil carbonate and surface water in the nima area since at least the late oligocene the maintenance of high elevation since at least 26 ma suggests that any flow of lower crust from beneath central tibet must have been balanced by coeval northward insertion of indian crust beneath the plateau