tertiary tectonics of the border ranges fault system chugach mountains alaska deformation and uplift in a forearc setting the border ranges fault system brfs locally separates supracrustal upper cretaceous tertiary rocks of the cook inlet matanuska valley forearc basin on the peninsular terrane from metamorphosed cretaceous subduction complex rocks of the chugach terrane to the south this 5 to 10 km wide zone of concentrated deformation along the inboard edge of southern alaska s accretionary prism has suffered a protracted history beginning with its inception as a megathrust by early cretaceous time and continuing into early tertiary time when it was transected by a system of steeply arcward dipping normal and dextral slip faults based on detailed geologic mapping structural analysis metamorphic mineral assemblage data and k ar and fission track geochronology the tertiary history of displacements along a central part of this forearc fault system has been divided into several phases of deformation these include a paleocene phase of regional uplift of the forearc basin together with block faulting along the brfs to rapidly uplift and subaerially expose low grade metamorphic rocks of the subduction complex upper cretaceous valdez group within 15 ma of their inferred underplating at deep structural levels of the accretionary prism continued normal separation faulting along the brfs in late paleocene early eocene time to further uplift the subduction complex was recorded by deposition of a syntectonic alluvial fan system chickaloon formation across the brfs and along the southern margin of the forearc basin a third mid eocene increment of normal separation faulting along the brfs juxtaposed greenschist facies fabrics of early eocene age in the subduction complex against the chickaloon formation this latter uplift event predated intrusion of early late eocene 43 48 ma zircon fission track minimum ages felsic dikes into the present terrane bounding fault and was accompanied by no more than a few tens of kilometers of dextral slip faulting along the brfs a conclusion that does not accord with recent suggestions for thousands of kilometers of displacement along that fault system in early middle tertiary time based on paleomagnetic data field observations in the study area indicate that the great oroclinal bend of southern alaska is postearly eocene and possibly prelate oligocene in age a final period of deformation in middle to late tertiary time was marked by periods of minor north south contraction of the forearc basin and by local reverse slip reactivation of earlier faults fission track age data on apatite indicate rapid cooling and probably uplift of both subduction complex and adjacent parts of the forearc basin in miocene time 17 24 ma episodic uplift of the subduction complex either locally by normal separation faulting along its backstop or by a more regional uplift also affecting the adjacent forearc basin overlapped in time or closely followed discrete pulses of large scale sediment underplating along the gulf of alaska subduction margin this coincidence suggests that major pulses of sediment underplating along southern alaska s convergent margin may have led to isostatic uplift of its critical taper accretionary prism an uplift that was in part accommodated by normal separation faulting along its mechanical backstop

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

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

rapid uplift of the altiplano revealed through 13c 18o bonds in paleosol carbonates the elevation of earth s surface is among the most difficult environmental variables to reconstruct from the geological record here we describe an approach to paleoaltimetry based on independent and simultaneous determinations of soil temperatures and the oxygen isotope compositions of soil waters constrained by measurements of abundances of 13 c 18 o bonds in soil carbonates we use this approach to show that the altiplano plateau in the bolivian andes rose at an average rate of 1 03 0 12 millimeters per year between 10 3 and 6 7 million years ago this rate is consistent with the removal of dense lower crust and or lithospheric mantle as the cause of elevation gain

exhumation along the fairweather fault southeastern alaska based on low temperature thermochronometry 1 the southern alaskan syntaxis marks the spectacular junction between the 1000 km long pacific north america transform margin and the chugach st elias belt where subduction and terrane accretion drive rapid convergent deformation and rock uplift new low temperature thermochronometry reveals that intense orogenic deformation is not restricted to one side of the syntaxis but extends nearly 300 km south along the dextral fairweather fault apatite and zircon u th he ages as young as 0 9 and 2 0 ma suggest maximum exhumation rates of nearly 2 mm a in close proximity 0 5 mm a along the entire plate margin we estimate that long term rock uplift accommodates 3 mm a of fault normal convergence in this area this suggests that the fairweather fault is slightly transpressive and highly partitioned analogous to the central san andreas fault this convergence only accounts for 1 5 of the obliquity between pacific plate motion and the continental margin however implying the deficit is taken up by 1 2 cm a thrust sinistral motion along the offshore transition fault additionally thermochronometry shows a marked increase in bedrock cooling coincident with onset of heavy glaciation similar to what has been observed in other parts of the pacific northwest the tectonically active fairweather corridor is distinguished however by the magnitude of the acceleration and the depth of exhumation since pliocene climate change

oxygen isotope systematics in a multiphase weathering system in haiti abstract physical and chemical partial dissolution techniques have been applied to a suite of young karst bauxite and laterite samples from the southern peninsula of haiti the 18o values have been obtained for nine mineral species and range from 1 0 for anatase rutile to 33 4 for authigenic quartz on one hand results for quartz calcite kaolinite gibbsite and boehmite compare favourably with 18o values predicted from accepted mineral water fractionation factors assuming modern temperatures 25 2 c and water 18o values 3 1 0 5 on the other hand the 18o values measured for anatase illite smectite chlorite smectite and some iron oxide samples do not compare favourably with predicted values departures from expected values for these minerals may be related to crystallization from water with a different 18o value than modern water an imprecise knowledge of some mineralwater fractionation factors under surficial conditions or nonattainment of isotopic equilibrium between mineral and water during formation partial dissolution techniques hold considerable promise for obtaining quantitative 18o values of individual minerals in single samples of complex fine grained regolith material

orographic precipitation isotopic ratios in stratified atmospheric flows implications for paleoelevation studies an idealized fully nonlinear atmospheric model was used to evaluate the effects of stratified atmospheric flows on orographic precipitation isotopic ratios with the aim of improving the foundation for interpreting proxy records used for paleoelevation studies orographic precipitation isotopic ratios can be understood in terms of two nondimensional parameters the flow parameter nh u where n is the moist brunt vaisala frequency a measure of atmospheric stratification h is the large scale relief and u is the upstream horizontal wind speed perpendicular to the orogen and the horizontal aspect ratio the ratio of the along strike length of the orogen to its across strike width existing rayleigh condensation models for paleoaltimetry studies are only strictly applicable when nh u 0 much of the time high values of both nh u and favor precipitation upstream of the terrain leading to isotopic ratios that are more depleted than predicted by the rayleigh model high nh u and low favor low level deflection of winds around the terrain which substantially reduces lifting and condensation leading to precipitation isotopic ratios in that are less depleted than predicted by the simple rayleigh model changes in climate or the horizontal terrain aspect ratio can change precipitation isotopic ratios at least as much as changes in surface elevation and surface uplift need not always affect precipitation isotopic ratios suggesting that proxy records must be interpreted within a broad context of climate variability and landscape evolution

composition of soils and ground waters at the pampa del tamarugal chile anatomy of a fossil geochemical anomaly derived from a distant porphyry copper deposit the pampa del tamarugal in northern chile is a gravel plain part of the hyperarid atacama desert soil geochemical surveys over the pampa using partial extraction analyses identified a large 100 km2 geochemical anomaly for cu subsequent analyses showed unusually high concentrations of elements that are associated with copper porphyry deposits mo as and se the soils are saline nacl and contain high concentrations of br and i which are abundant in ground waters from northern chile the anomaly lies west of one of the world s most important copper porphyry districts which includes the chuquicamata radomiro tomic and el abra deposits follow up drilling in the center of the anomaly through 300 m of piedmont gravel cover revealed barren andesitic basement rocks the soil anomalies were caused by ground water reaching the surface then evaporating both ground waters and soils share a common element assemblage with higher concentrations of mo as and se than cu the former dissolve as anions in ground water which can travel far from their source whereas dispersion of cu2 is restricted by adsorption the soil anomaly is interpreted to be a fossil anomaly preserved by the hyperarid climate to the south the anomaly is cut by an alluvial fan another nearby fan has been dated at 7 ma to the west the anomaly was eroded in the flood plain of the rio loa prior to the present 50 m deep incision of the rio loa the water table in the area of the anomaly may have been higher than the present depth of 33 to 55 m facilitating capillary rise of water to the surface we suggest that the source for the anomaly was the el abra deposit 75 km east and updrainage from the anomaly

a catalogue of late cenozoic tephra beds in the klondike goldfields and adjacent areas yukon territory preece s j westgate j a froese d g pearce n j g perkins w t 2011 a catlogue of late cenozioc tephra beds in the klondike goldfields and adjacent areas yukon canadian journal of earth sciences 48 10 1386 1418

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

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

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

deformation during terrane accretion in the saint elias orogen alaska the saint elias orogen of southern alaska and adjacent canada is a complex belt of mountains formed by collision and accretion of the yakutat terrane into the transition zone from transform faulting to subduction in the northeast pacific the orogen is an active analog for tectonic processes that formed much of the north american cordillera and is also an important site to study 1 the relationships between climate and tectonics and 2 structures that generate large to great magnitude earthquakes the yakutat terrane is a fragment of the north american plate margin that is partly subducted beneath and partly accreted to the continental margin of southern alaska interaction between the yakutat terrane and the north american and pacific plates causes significant differences in the style of deformation within the terrane deformation in the eastern part of the terrane is caused by strike slip faulting along the fairweather transform fault and by reverse faulting beneath the coastal mountains but there is little deformation immediately offshore the central part of the orogen is marked by thrusting of the yakutat terrane beneath the north american plate along the chugach saint elias fault and development of a wide thin skinned fold and thrust belt strike slip faulting in this segment may be localized in the hanging wall of the chugach saint elias fault or dissipated by thrust faulting beneath a north northeast trending belt of active deformation that cuts obliquely across the eastern end of the fold and thrust belt superimposed folds with complex shapes and plunging hinge lines accommodate horizontal shortening and extension in the western part of the orogen where the sedimentary cover of the yakutat terrane is accreted into the upper plate of the aleutian subduction zone these three structural segments are separated by transverse tectonic boundaries that cut across the yakutat terrane and also coincide with the courses of piedmont glaciers that flow from the topographic backbone of the saint elias mountains onto the coastal plain the malaspina fault pamplona structural zone separates the eastern and central parts of the orogen and is marked by reverse faulting and folding onshore most of this boundary is buried beneath the western or agassiz lobe of the malaspina piedmont glacier the boundary between the central fold and thrust belt and western zone of superimposed folding lies beneath the middle and lower course of the bering piedmont glacier

geochemical and isotopic studies of bauxitization in the tatun volcanic area northern taiwan the tatun volcanic area in the northern tip of taiwan is composed of pleistocene andesite and andesitic tuff its high relief causes extraordinarily heavy rainfall 3000 mm yr 1 especially during the winter monsoon season bauxite deposits were formed on the windward northern slopes soil samples from two profiles in the bauxite deposits were studied by chemical analysis x ray diffraction differential thermal analysis and hydrogen and oxygen isotopic analyses the soil profiles can be divided into two zones by chemical characteristics in the upper zone zone a the chemical composition of the soil samples undergoes little change except depletion of na and ca due to leaching the major minerals are quartz chlorite and illite in the lower zone zone b all major elements suffer rapid dissolution except al2o3 gibbsite grows drastically at the expense of clays while quartz diminishes sharply fe2o3 and tio2 are enriched at the boundary between the two zones due to coprecipitation of fe and ti as hematite and goethite probably as a result of increasing oxygen fugacity mobilization of fe in zone b is attributed to its low eh thus zone a is inferred as a permeable layer and zone b as an aquifer the weathering rate in this area is estimated to be 12 cm ka 1 the most thoroughly leached soil samples contain up to 80 gibbsite the high gibbsite contents and the analyses of coexisting waters allow hydrogen and oxygen isotopic fractionation factors between gibbsite and water to be calculated as 0 992 0 002 and 1 016 0 001 respectively

oxygen and hydrogen isotope compositions in clay minerals a potential single mineral geothermometer the opposite slopes of the isotopic fractionation of hydrogen and oxygen in the clay water system and the well known relationship between d and 18o in meteoric waters allow the isotopic composition of clay minerals to be used as a single mineral geothermometer equations can be derived which are valid for continental systems where meteoric waters are common the following equation was derived for smectite 3 54 106t 2 18osm 0 125 dsm 8 95 0 150 this equation was used to determine the isotopic composition and temperature of the waters involved in the transformation of volcanic rock to bentonite at the cortijo de archidona southeastern spain site the values obtained 6 t 21 c i e environmental temperatures confirm the reliability of this equation

topographic development of the southern alps recorded by the isotopic composition of authigenic clay minerals south island new zealand abstract the southern alps are developing as a consequence of oblique collision between the pacific and australian plates the southern alps lie on the west side of the south island of new zealand and create a massive rain shadow where greater than 12 m year of rain falls on the west coast and semiarid conditions exist to the east the rain out effect across the mountains causes precipitation west of the southern alps to have d and 18 o values averaging 30 and 5 5 whereas precipitation in the rain shadow to the east is isotopically lighter d 72 and 18 o 9 8 such large differences in the isotopic composition of precipitation would not have existed prior to the development of significant topography we have examined the topographic evolution of the southern alps using oxygen isotope analyses of authigenic kaolinites formed in the rain shadow to the east of the mountains between the cretaceous low topography and the pleistocene changes in the isotopic composition of authigenic clay minerals forming in equilibrium with meteoric water in the stratigraphic sequence record the development of southern alps topography and the resultant rain shadow our oxygen isotope analyses of authigenic kaolinites show a 5 6 decrease in the early pliocene from 18 2 in older rocks to 12 3 in younger rocks in addition smectite is abundant in all samples from the late miocene to recent but is conspicuously absent in most older rocks suggesting a change to a generally drier climate roughly coincident with the isotopic shift in kaolinites this method may be useful in unraveling timing of development of mountain belts elsewhere in the world

onset of convective rainfall during gradual late miocene rise of the central andes a decrease in the ratio of 18o to 16o 18o of sedimentary carbonate from the bolivian altiplano has been interpreted to indicate rapid surface uplift of the late miocene andean plateau ap here we report on paleoclimate simulations of andean surface uplift with an atmospheric general circulation model gcm that tracks oxygen isotopes in vapor the gcm predicts changes in atmospheric circulation and rainfall that influence ap isotopic source and amount effects on eastern ap slopes summer convective precipitation increases by up to 6 millimeters per day 500 for plateau elevations that are greater than about 2000 meters high precipitation rates enhance the isotope amount effect leading to a decrease in precipitation 18o at high elevations and an increase in 18o lapse rate our results indicate that late miocene 18o depletion reflects initiation and intensification of convective rainfall

miocene paleotopography of the central alps abstract reconstructing surface elevation surface uplift and relief histories is fundamental to understanding the growth of mountain ranges to explore their topographic limits and relate these to the interplay between geodynamic and earth surface processes here we aim to quantify miocene paleoelevation of the central european alps through stable isotope paleoaltimetry the novelty of our approach which renders our analysis less sensitive to past climate change is that stable isotope proxies of identical age are analyzed from both the high internal parts of the alpine orogen and the adjacent foreland basin whereas the foreland basin was at or near sea level and traces the combined effects of upstream changes in rainfall amount and composition the high alpine site additionally records the effect of elevation on stable isotopes in precipitation we compare hydrogen isotopic ratios d in mica and chlorite that interacted with meteoric water along the simplon detachment a major normal fault that developed at high elevations with meteoric water compositions deduced from carbonate bearing paleosols of the north alpine foreland basin d values of muscovite 126 and chlorite 135 from the brittle hanging wall and of recrystallized muscovite 108 and biotite 140 from adjacent footwall mylonites provide unequivocal evidence for localized syntectonic meteoric water interaction along the simplon detachment detailed 40 ar 39 ar and fission track geochronology constrains the timing of isotopic exchange to ca 14 5 ma when the footwall mylonites passed through the ductile to brittle transition age equivalent oxygen isotope ratios 18 o measured within pedogenic carbonate from north alpine foreland paleosols that developed near miocene sea level serve as our low elevation point of reference 18 o values in these paleosols dated with ca 100 ka precision vary between 19 and 25 smow with average values of 20 at ca 14 5 ma using the relative differences between meteoric water compositions in the foreland basin and the high alpine simplon detachment our isotope data are consistent with a mid miocene minimum average elevation difference of 2350 700 500 m for the simplon region our results indicate that miocene alpine elevations were at least comparable to those of today and are likely to have acted as an important barrier to atlantic derived moisture transport into central europe and eurasia since that time

a new approach to stable isotope based paleoaltimetry implications for paleoaltimetry and paleohypsometry of the high himalaya since the late miocene the change in oxygen isotopic composition of precipitation is modeled using equilibrium fractionation during rayleigh distillation linked to the thermodynamics of atmospheric ascent and water vapor condensation the primary controllers of the vertical variation in isotopic composition with elevation are the low elevation temperature and relative humidity as these control the vertical distribution of condensation an empirical fit of precipitation versus model condensation based on alpine stations is derived this fit is represented in the model as the weighted mean composition of condensation within a 1000 m thick air parcel 1500 500 m above the ground surface and is used for all other regions comparison of model versus observed modern precipitation reveals a close fit particularly of more highly elevated sites comparison of modern waters in the himalayas and southern tibet with model predictions particularly as revealed by comparison of observed and predicted hypsometry provides additional support to the validity of the model finally application of this model to estimates of paleo waters in the himalayas and southern tibet reveals that this region had already achieved its present hypsometry by the late miocene about 10 ma ago fl 2001 published by elsevier science b v

grassland expansion as an instrument of hydrologic change in neogene western north america abstract the evapotranspiration et flux accounts for approximately two thirds of terrestrial precipitation worldwide and in grassland regions et is equivalent in magnitude to precipitation regional contributions to the terrestrial hydrologic budget however have been far from constant in the past as distribution of vegetation changed dramatically the rise of grass dominated ecosystems is one of the most profound paleoecological changes in the cenozoic why then would grassland expansion not feature prominently in the record of neogene hydrologic change despite numerous stable isotope paleoenvironmental studies in neogene north america the contributions of land cover change have been largely ignored we present a compilation of 16 oxygen isotope studies of pedogenic carbonate and smectite from western north america including 4 new records nearly all records from california the basin and range the rocky mountains and the great plains show increases in o 18 on the order of 2 6 in order to assess the role of et in the hydrologic cycle we developed an isotopic water vapor transport model wherein we manipulated et parameters along a specified air mass trajectory grasslands lead to o 18 of precipitation o p 18 values that are up to 5 greater than broadleaf and needleleaf vegetation at inland study sites these results demonstrate that changes in vegetation played a critical role in establishing the modern hydrologic regime in western north america we suggest that this isotopic increase is due to three primary reasons 1 increased evaporation and transpiration fluxes in grassland regions affect water balance 2 shallower rooting depths of grasses lead to the transpiration of soil water enriched in o 18 due to evaporation and 3 grasslands transpire o 18 rich waters during a shorter more punctuated growing season we argue that the observed isotope signals are indicative of a feedback mechanism wherein grasslands not only respond to regional and global climatic trends but also act as a driver of hydrologic change by enhancing seasonality and aridity grasslands transmit hydrologic disturbances downstream engineering climatic conditions favorable for their expansion

thermotectonic history of mt logan yukon territory canada implications of multiple episodes of middle to late cenozoic denudation abstract the extreme relief of the st elias mountains including mt logan is suggestive of a young mountain belt new apatite fission track data indicate that the mt logan massif experience rapid low temperature cooling during three distinct periods during the middle eocene middle miocene and pliocene each cooling episode the magnitude of which varies due to temporal variations in recorded paleogeothermal gradients can be tentatively linked to a tectonic cause eocene cooling may be due to re equilibration of isotherms following normal faulting caused by a combination of thermal weakening of the crust and a decrease in regional compressional stress due to the 43 ma change in relative motions between the pacific and north american plates the cause of miocene cooling is problematic and could reflect denudation in response to initial underplating of the yakutat terrane or a recorded change in heat flow unrelated to denudation pliocene cooling reflects erosion due to surface uplift that produced the spectacular present day topography of the st elias mountians this surface uplift is probably related to the coeval significant change in relative motion between the north american and pacific plates and or resistance to subduction by the yakutat terrane

oxygen and hydrogen isotope compositions of permian pedogenic phyllosilicates development of modern surface domain arrays and implications for paleotemperature reconstructions abstract mineralogic chemical and oxygen and hydrogen isotope compositions of 15 different phyllosilicate samples from permo pennsylvanian age paleosols of the eastern shelf of the midland basin of texas and the southern anadarko basin are presented mixtures of 2 1 phyllosilicates and kaolinite dominate most samples although some samples consist of relatively pure 2 1 phyllosilicates chemical and mineralogic data are used in conjunction with published thermodynamic data to calculate hydrogen and oxygen isotope fractionation factors for each sample in turn application of measured oxygen and hydrogen isotope compositions of the phyllosilicates to temperature dependent fractionation equations are used to calculate paleotemperatures of crystallization the d values of the phyllosilicates range from 69 to 55 the 18 o values range from 19 5 to 22 7 if these samples preserve a record of equilibrium with paleo meteoric waters the isotopic compositions of the phyllosilicates correspond to paleotemperatures of phyllosilicate crystallization ranging from 22 3 c to 35 3 c in particular the stratigraphic trend of calculated temperatures from midland basin samples suggests that early permian surface temperatures may have been up to 10 c warmer than those of the latest pennsylvanian

the impact of topography on isotopes in precipitation across the central anatolian plateau turkey paleoelevation reconstructions of mountain belts and orogenic plateaus based on stable isotope climate and precipitation records benefit greatly from present day calibrations that relate the fractionation of hydrogen d and oxygen 18o isotopes in precipitation to orographic rainfall here we establish a first order template of d and 18o of modern meteoric waters across the central anatolian plateau cap and its bordering pontic and taurus mountains we identify key regions in the plateau interior and along the plateau margins that have the potential to reliably record topography related paleotemperature and paleoprecipitation changes as recovered from stable isotope paleosol fossil teeth or lipid proxy data based on d and 18o data of more than 480 surface water samples from small catchments and springs we characterize moisture sources affecting the net isotopic budget of precipitation over the cap and analyze how orographic rainout and plateau aridity shape modern patterns of d and 18o in precipitation the taurus mountains bordering the cap to the south act as a major orographic barrier for transport of predominantly winter moisture and exhibit isotopic lapse rates of approximately 20 km for d and 2 9 km for 18o across an elevation range of nearly 3000 m the pontic mountains at the northern margin of the cap force perennial moisture to ascend and condensate revealing lapse rates of 19 km for d and 2 6 km for 18o the difference in the predominant moisture source for the southern and northern margins of the cap north african versus atlantic air masses is manifested in systematic north south differences in near sea level meteoric water compositions of dn s 20 permil and 18on s 3 permil in a swath across the central part of the plateau stable isotope data from the semi arid plateau interior with rainfall as low as 300 to 500 mm yr and mean summer temperatures attaining 23 c provide clear evidence for an evaporative regime that drastically affects surface water and runoff compositions and results in a local meteoric water line for the plateau interior that follows d 4 0 18o 29 3 strongly evaporitic conditions contrast rainfall patterns along the plateau margins including their immediate leeward flanks where d and 18o elevation relationships are reliable predictors of modern topography

erosional processes as a control on the structural evolution of an actively deforming fold and thrust belt an example from the pamir tien shan region central asia the foreland of the pamir mountains displays an unusual orogenic topography in which an active north vergent thin skinned fold and thrust belt shows no topographic foredeep in advance of the thrust sheets instead the thrusts are impinging on a topographic barrier formed by the southern edge of the tien shan the deformation front of this thrust belt is coincident with a deeply incised river valley occupied by a large river the surkhob we suggest that this river played a key role in the evolution of this orogenic system by acting as a lateral conveyor belt for the transport of mass delivered to the deformation front by thrusting on the basis of reconnaissance geologic mapping it is clear that the present system developed in the late miocene or pliocene when the tien shan were uplifted within an existing foreland basin as the tien shan highland developed a longitudinal river within the foreland basin was trapped between the north directed thrusts and the tien shan highland with continued deformation the river was squeezed into a narrow canyon and since that time the system has been in an unusual equilibrium where thrusting acts to push the deformation front northward toward the tien shan but fluvial erosion and transport act to keep it in a constant position geologic relationships indicate that the vakhsh thrust the frontal thrust of the north directed system is now emerging on an erosion surface beneath a thin quaternary cover throughout the canyon suggesting that the river has been unable to keep pace with the tectonic mass flux and the thrust front as well as the river have been pushed northward across the beveled edge of what was originally the southern edge of the tien shan we suggest that the original deformation front of the tien shan now lies 10 km south of the present day topographic front of the tien shan beneath the north vergent vakhsh thrust as indicated by 1 a near vertical zone of intense basement seismicity the petrovsky seismic zone 2 an en echelon array of backthrusts along the south flank of the peter the first range and 3 footwall cutoff relationships of the vakhsh thrust system order of magnitude mass balance considerations based on sediment budgets support this conclusion but suggest that the mass imbalance may be small thus large volumes of material may have passed through the thrust fron and been carried out of the system by erosion a relationship that may account for the narrow 30 50 km wide band of deformed sedimentary rock between the pamir salient and the tien shan the present near equilibrium is maintained by long term tectonic transport rates and fluvial transport rates the latter closely linked to climate particularly precipitation thus although there is apparently a mass pile up within this system other systems of this type might show grossly different structural and stratigraphic relationships depending on the amount of rainfall and corresponding variations in rates of fluvial sediment transport similar settings can be recognized in the active thick skinned thrust systems of the tien shan and ancient systems like the laramide belt of western north america

stable isotope composition of precipitation across the southern patagonian andes 1 a surface water and precipitation transect across the southern patagonian andes at 47 48 s was conducted to assess how mountains affect the isotopic composition of precipitation this westerly wind region derives its moisture that falls as precipitation from the pacific orographic uplift of air over the andes causes pseudoadiabatic cooling and orographic precipitation on the western side and a strong rain shadow on the eastern side of the mountains these processes also produce a profound isotopic rain shadow with 18o values 4 lower in the east compared to the west on the windward western side of the andes the isotope values of precipitation and surface waters show weak although systematic trends with elevation but a pronounced correlation with distance from the main source of moisture pacific ocean a rayleigh simulation of precipitation 18o values as a function of condensation altitude matches our data well suggesting that other processes such as mixing of water sources and postcondensation evaporation are negligible and that topography is the dominant control on the isotope ratio of precipitation in contrast isotope ratios of waters on the leeward eastern side of the southern patagonian andes vary neither with elevation nor with distance from the mountains consistent with much of the precipitation on the leeward side being derived from precipitation carried over the andes by winds thus paleoprecipitation isotopic composition on the leeward side of orogens in similar climatic settings single moisture source and cool climate yield useful estimates of the elevation of these orogens but not local elevation

response of meteoric δ18o to surface uplift implications for cenozoic andean plateau growth abstract the timing and magnitude of surface uplift provide important constraints on geodynamic models of orogen formation oxygen isotope 18 o and mass 47 isotopolog 47 compositions from terrestrial carbonate sediments have been used with modern isotope and temperature lapse rates to infer past surface elevations of the andes however these paleoaltimetry interpretations are contentious because variations in the oxygen isotope composition in meteoric water 18 o p are caused by changes in elevation orographic and regional climate here we use a limited domain isotope tracking general circulation model to simulate changes in 18 o p and isotopic lapse rates in response to andean surface uplift and to re evaluate 18 o and 47 changes in late miocene carbonates previously associated with rapid andean growth results indicate that andean surface uplift leads to changes in low level atmospheric circulation and an increase in precipitation along the eastern andean flank which influences isotopic source and amount effects simulated changes in andean 18 o p are not systematic with an increase in surface elevation but are instead a function of orographic thresholds that abruptly change regional climate a 18 o p decrease of 5 over the central andes and an increase in isotopic lapse rates up to 0 8 km 1 coincide with andean surface uplift from 75 to 100 of modern elevation these changes in the isotopic signature could account for the entire 3 4 18 o depletion in late miocene carbonate nodules and suggest an andean paleoelevation of 3000 m 75 of modern elevations before 10 ma

18o 16o and d h in goethite from a north american oxisol of the early eocene climatic optimum abstract an early eocene oxisol in the ione formation of california formed in a coastal continental weathering environment at a paleolatitude of 38 n the dominant minerals in the oxisol are goethite quartz and kaolinite material balance calculations were applied to new measurements of chemical composition d h and 18 o 16 o ratios of oxisol samples to determine the d 150 3 and 18 o 2 4 0 3 values of the goethite feooh these data in combination with the global meteoric water line mwl yielded an isotopic temperature of 21 4 c the nominal value of 21 c contrasts with the modern mean annual temperature mat of 16 c in that area the warmer temperature is consistent with formation of the goethite during the early eocene climatic optimum the isotopic composition of the goethite and a temperature of 21 c imply ancient water with a d value of 61 4 and a 18 o value of 8 9 0 5 this early eocene 18 o or d value is more negative than values in the range of isotopic scatter observed for modern global precipitation at sites with a mat of 21 c at times of warm global climates the location of a near surface atmospheric isotherm would generally shift relative to its location under modern climatic conditions a simple rayleigh type condensation model indicates that if one follows the isotherm the associated scatter in d and 18 o of precipitation in very warm global climates should shift for a given isotherm to more negative values that may be detectable in proxy records the isotopic results from the goethite of the early eocene oxisol appear to add to evidence in support of this idea

late cenozoic uplift of denali and its relation to relative plate motion and fault morphology apatite fission track analysis of samples that cover a 4 kilometer vertical section from the western flank of denali mount mckinley north america9s highest mountain suggests that the mountain massif was formed by rapid uplift 1 kilometer per million years beginning 6 million years ago ma uplift was a result of the morphology of the denali fault and a change in motion of the pacific plate with respect to north america at 5 ma which created opposing tangential vectors of relative movement along the fault and forced the intervening crustal blocks upward

late pliocene dawson cut forest bed and new tephrochronological findings in the gold hill loess east central alaska thick loess deposits in the fairbanks region of interior alaska are a rich source of information on past climates and environments during the late cenozoic and the numerous distal silicic tephra beds preserved within them offer the potential for good chronological control the dawson cut forest bed lies in the lower part of this loess cover plant macrofossils consist of picea glauca picea mariana betula papyrifera and populus balsamifera but no pinus these fossils together with the abundance and size of spruce remains pollen tree ring characteristics and 13 c values of spruce wood demonstrate that the boreal forest represented by the dawson cut forest bed was similar to the modern boreal forest of central alaska warming conditions during the early part of the dawson cut interglaciation initiated thawing of permafrost and melting of ground ice as evidenced in the presence of ice wedge casts and major erosion of the lower gold hill loess tephrochronological magnetostratigraphic and glass fission track dating studies in the fairbanks area and at the palisades site on the yukon river in central alaska suggest an age for the dawson cut forest bed of ca 2 ma hence the northern boreal forest of northwestern north america as we know it today has a long history that probably extends back to at least 2 ma

alternating asymmetric topography of the alaska range along the strike slip denali fault strain partitioning and lithospheric control across a terrane suture zone contrasting lithospheric strength between terranes often results in the concentration of strain and deformation within the weaker material dramatic alternating asymmetric topography of the central and eastern alaska range along the active denali fault is due to contrasting lithospheric strength between terranes and a suture zone controlled by fault location with respect to the irregular boundary of a relatively stronger terrane backstop highest topography and greatest neogene exhumation in the central alaska range occur on the concave side of the arcuate denali fault yet to the north and on the convex side of the fault in the eastern alaska range the denali fault largely lies along a mesozoic suture zone between two large composite terranes yukon and wrangellia composite terranes yct and wct but the mckinley strand of the fault cuts across an embayment of weaker suture zone rocks alaska range suture zone arsz within the irregular southern boundary of the yct hines creek fault deformation and uplift of the alaska range is driven by slip and partitioning of strain along the denali fault occurring preferentially in weaker rocks of the arsz against the stronger yct where the yct lies well north of the mckinley strand deformation is primarily to the north of the fault eastern alaska range where the yct is close to the fault deformation is primarily to the south central alaska range while the trace of the mckinley strand approximates a small circle two restraining bends mckinley and hayes pinned equidistant from the ends of this strand localize uplift and exhumation

volcanism in an arc transform transition zone the stratigraphy of the st clare creek volcanic field wrangell volcanic belt yukon canada the st clare creek volcanic field in the southwestern yukon overlies a tectonic transition in the wrangell volcanic belt between subduction to the northwest in alaska and transform faulting along the duke river fault in the southeast two large polygenetic volcanic centres dominated the miocene landscape of the st clare creek field the 18 16 ma wolverine centre and the 16 10 ma klutlan centre the wolverine centre evolved from a small alkaline shield volcano at 18 ma from which alkaline basalts hawaiites and mugearites erupted to a larger composite volcano between 18 and 16 ma composed of transitional basalt basaltic trachyandesite trachyte and rhyolite lavas and pyroclastic rocks the youngest wolverine lavas are calc alkaline basaltic andesites andesites and hybrid lavas transitional calc alkaline this temporal progression from alkaline through transitional to calc alkaline volcanism is accompanied by a systematic increase in the degree of silica saturation and decrease in fe si nb y and

the relationship between overshooting tops in a tornadic supercell and its radar observed evolution abstractthis is a study of a tornadic supercell in kansas on 14 may 2018 in which data of relatively high spatiotemporal resolution from a mobile polarimetric x band doppler radar were integrate

tracking the influence of a continental margin on growth of a magmatic arc fiordland new zealand using thermobarometry thermochronology and zircon u pb and hf isotopes 1 geothermobarometric radiogenic isotopic and thermochronologic data are used to track the influence of an ancient continental margin western province on development of an adjacent carboniferous cretaceous magmatic arc outboard median batholith in fiordland new zealand the data show a record of complicated mesozoic gondwana margin growth paragneiss within the outboard median batholith is of carboniferous to jurassic age and records burial to middle crustal depths in late jurassic early cretaceous during subduction related plutonism and arc thickening in contrast western province metasedimentary rocks in the area of study immediately west of the outboard median batholith are late cambrian early ordovician in age recrystallized at the amphibolite facies in the late devonian early carboniferous and exhibit no evidence for mesozoic textural or isotopic reequilibration a phase of deformation between 128 and 116 ma deformed exhumed and cooled the outboard median batholith to greenschist facies temperatures while large parts of the western province underwent 9 kbar metamorphic conditions zircon grains from mesozoic inboard plutons are isotopically more evolved hf t 2 3 to 4 0 than those in the outboard median batholith hf t 9 4 to 11 1 the contrasting zircon hf isotope ratios absence of s type plutons or proterozoic early paleozoic inherited zircon and the apparent absence of early paleozoic metasedimentary rocks indicates that the outboard median batholith is unlikely to be underlain by the western province continental lithosphere the new data are consistent with the outboard median batholith representing an allochthonous although not necessarily exotic arc that was juxtaposed onto the gondwana continental margin along the intervening grebe mylonite zone

architecture kinematics and exhumation of a convergent orogenic wedge a thermochronological investigation of tectonic climatic interactions within the central st elias orogen alaska abstract the kinematics and architecture of orogenic systems along the leading edges of accreting terranes may be heavily influenced by climate but little research has been devoted to the long term effects of glacial erosion on orogenesis here we use low temperature apatite and zircon u th he and fission track thermochronometry along with subsidiary structural relationships and seismicity to develop a new architectural model of the st elias orogen in southern alaska which is one of the best examples of a glaciated orogenic wedge worldwide these data illustrate that the orogen consists of a deformational backstop on the leeward flank and a rapidly deforming and eroding thin skinned fold and thrust belt on the windward flank a structure beneath the bagley ice field separates these distinct deformational domains which we propose is a backthrust that makes the orogen doubly vergent thermochronometry within the orogenic wedge suggests that denudation and deformation are strongly influenced by glacial erosion long term exhumation at rates of up to 4 mm yr is concentrated within a narrow zone along the windward flank where glacier equilibrium lines intersect the orogenic wedge the onset of enhanced glaciation also coincided with a marked acceleration in exhumation across the orogenic wedge accelerated backthrust motion and a major shift in deformation away from the north american yakutat terrane suture chugach st elias fault we propose that accelerated glacial erosion forced the redistribution of strain along the backthrust and an en echelon array of forethrusts that lie beneath the zone of heaviest glaciation which in turn are systematically truncated by the backthrust this focusing of deformation matches predictions from analytical models of orogenic wedges and implies a high degree of coupling between climate and tectonics in this glacially dominated orogen

the thermochronological record of tectonic and surface process interaction at the yakutat north american collision zone in southeast alaska we investigate the material fluxes in space and time as a result of exhumation and erosion processes at the ongoing yakutat north american collision in southeast alaska many thermochronologic studies using a variety of sampling strategies are challenged by the widespread ice cover that limit field observations and accessibility this paper reviews new and published low temperature thermochronological data from southeast alaska to give a comprehensive interpretation of the exhumation patterns through time and how they are influenced by surface processes and climate change we find that the southeastern margin of alaska was exhumed and eroded long before the late miocene pliocene yakutat collision but since the beginning of the subduction of the yakutat lithosphere in the oligocene early miocene today there is a distinct pattern of exhumation in southeast alaska with a localized very rapid and deep seated exhumation at the yakutat plate corner st elias syntaxis where strike slip motion changes to convergence exhumation is also rapid but less deep along the dextral fairweather fault and in the evolving fold and thrust belt we present a re interpretation of the exhumation pattern in the fold and thrust belt and suggest that mass transport by exhumation is parallel to the observed active thrust faults and oblique to the suture zone and orogenic strike the locus of most rapid exhumation migrated from northwest to southeast with recent exhumation occurring near the st elias syntaxis exhumation of the chugach terrane rocks is still active however to a lesser degree than on the south side of the orogen where precipitation rates are much higher the wrangellia terrane to the north has experienced little exhumation and has essentially formed the backstop for terrane accretion in southeast alaska since the early cretaceous apatite u th he ages give the first evidence that rocks of the wrangell range have only been recently uplifted and eroded as a consequence of the continuing yakutat collision in general the thermochronology in southeast alaska reveals that climate variations across the region as well as changes through time have a limited influence on the pattern of erosion and that the location of deep exhumation is primarily influenced by tectonic processes

recurring middle pleistocene outburst floods in east central alaska abstract recurring glacial outburst floods from the yukon tanana upland are inferred from sediments exposed along the yukon river near the mouth of charley river in east central alaska deposits range from imbricate gravel and granules indicating flow locally extending up the yukon valley to more distal sediments consisting of at least 10 couplets of planar sands granules and climbing ripples with up valley paleocurrent indicators overlain by massive silt an interglacial organic silt occurring within the sequence indicates at least two flood events are associated with an earlier glaciation and at least three flood events are associated with a later glaciation which postdates the organic silt a minimum age for the floods is provided by a glass fission track age of 560 000 80 000 yr on the gi tephra which occurs 8 m above the flood beds a maximum age of 780 000 yr for the floods is based on normal magnetic polarity of the sediments these age constraints allow us to correlate the flood events to the early middle pleistocene and further the outburst floods indicate extensive glaciation of the yukon tanana upland during the early middle pleistocene likely representing the most extensive pleistocene glaciation of the area

stable isotope paleoaltimetry a critical review stable isotope paleoaltimetry makes use of systematic trends in the distribution and isotopic composition of modern precipitation with climate and topography and of the potential to estimate the isotopic composition of paleoprecipitation from authigenic in situ formed minerals to illustrate the usefulness as well as potential limitations of this method we review 1 processes controlling the isotopic composition of modern precipitation 2 stable isotope data from modern precipitation across regions of high topography and 3 stable isotope data from authigenic minerals that have been used to infer paleotopography from this we conclude that stable isotope studies of authigenic minerals can permit useful inferences on paleotopography with uncertainties that critically depend on a detailed understanding of local to global scale paleoclimate during the time interval of interest

reconstructing the paleotopography of mountain belts from the isotopic composition of authigenic minerals the paleorelief of mountain belts can be estimated from the 18 o value of authigenic minerals development of relief during mountain building often creates lee side rain shadows in which precipitation is depleted in 18 o and d the magnitude of this rain shadow effect is strongly correlated to relief a compilation of 18 o data from surface waters throughout the globe shows a linear relationship between net elevation change and 18 o r 2 0 79 through the use of this relationship we investigated the timing and magnitude of elevation change in the southern alps of new zealand and the sierra nevada of california the 18 o values of kaolinites from new zealand show an 6 decrease in the early pliocene that corresponds to an 2 km elevation change in the southern alps the 18 o of smectites from the sierra nevada show little change since 16 ma suggesting that these mountains have been a long standing topographic feature

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

a 3 m y record of pliocene pleistocene loess in interior alaska many distal tephra beds exist in the thick fossiliferous loess deposits near fairbanks interior alaska isothermal plateau fission track ages determined on glass shards from tephra beds in conjunction with tephrostratigraphic and magnetostratigraphic techniques indicate that loess deposition began in the late pliocene an antiquity previously unsuspected hence there is the opportunity now to reconstruct a detailed well dated record of environmental changes in interior alaska during the past 3 m y

stable isotope records of hydrologic change and paleotemperature from smectite in cenozoic western north america abstract the oxygen and hydrogen isotopic composition of soil water 18ow and dw hereafter reflect the history of water through processes such as source evaporation precipitation and vapor recycling temperature humidity evaporation and post condensation processes can affect 18ow and dw as such isotope proxy records are often limited in their ability to constrain paleoclimate paleoecology or paleoelevation without independently corroborating data smectite preserves both the hydrogen and oxygen isotope signature of parent water and therefore provides critical insight into meteoric water line relationships and paleotemperature here we use in situ pedogenic smectite 18o and d records to characterize the evolution of the hydrologic cycle in cenozoic western north america we incorporate 192 samples 119 of which are previously unpublished from 11 cenozoic basins representing a range of environments in the basin and range rocky mountains and great plains our results indicate that the processes controlling smectite isotopic compositions vary both regionally and temporally in some localities such as oligocene to pleistocene western nebraska change in temperature is the primary control on smectite isotopic composition in other basins such as in miocene trapper creek id isotope values lie along the meteoric water line suggesting change in meteoric water composition is responsible for the variation in most basins especially those in the neogene basin and range smectite line slope suggests either evaporation of previously meteoric water or a combination of change in paleotemperature and meteoric water composition smectite geothermometry suggests mineral formation temperatures of 30 40 c in the middle miocene in the rocky mountains great plains and basin and range and a decrease of 10 15 c since the middle miocene climatic optimum consistent with clumped isotope and paleofloral temperature estimates

neogene and quaternary rollback evolution of the tyrrhenian sea the apennines and the sicilian maghrebides reconstruction of the evolution of the tyrrhenian sea shows that the major stage of rifting associated with the opening of this basin began at similar to10 ma it involved two episodes of back arc extension which were induced by the rollback of a west dipping subducting slab the first period of extension 10 6 ma was prominent in the northern tyrrhenian sea and in the western part of the southern tyrrhenian sea the second period of extension mainly affected the southern tyrrhenian sea began in the latest messinian 6 5 ma and has been accompanied by subduction rollback at rates of 60 100 km myr 1 slab reconstruction combined with paleomagnetic and paleogeographic constraints indicates that in the central apennines the latest messinian 6 5 ma arrival of a carbonate platform at the subduction zone impeded subduction and initiated a slab tear and major strike slip faults these processes resulted in the formation of a narrow subducting slab beneath the ionian sea that has undergone faster subduction rollback and induced extreme rates of back arc extension

exhumation rates in the st elias mountains alaska abstract reprocessing and interpretation of seismic profiles from the gulf of alaska in the vicinity of the st elias mountains indicate that over 3000 km 3 of sediment were deposited on the ocean shelf since the end of the last glacial epoch approximately 10 000 years ago this estimate of the sediment volume does not include material moved out of the region by long shore currents transportation from the shelf to deeper waters or material trapped in fiords and basins on and near land thus an estimated sedimentation rate offshore of 7 9 mm year and the average erosion rate of 5 1 mm year from the st elias mountains derived from the estimated sedimentation rate represent minimum estimates we infer that these estimated rates are not typical of the approximately 5 m y history of mountain building in the area but rather they represent the result of efficient erosion by glaciers during this interglacial period

a stable isotope record of late cenozoic surface uplift of southern alaska abstract although the timing of an acceleration in late cenozoic exhumation of southern alaska is reasonably well constrained as beginning 5 6 ma the surface uplift history of this region remains poorly understood to assess the extent of surface uplift relative to rapid exhumation we developed a stable isotope record using the hydrogen isotope composition d of paleo meteoric water over the last 7 ma from interior basins of alaska and yukon territory our record which is derived from authigenic clays dclay in silicic tephras documents a 50 60 increase in d values from the late miocene 6 7 ma through the plio pleistocene transition 2 3 ma followed by near constant values over at least the last 2 ma although this enrichment trend is opposite that of a rayleigh distillation model typically associated with surface uplift we suggest that it is consistent with indirect effects of surface uplift on interior alaska including changes in aridity moisture source and seasonality of moisture we conclude that the dclay record documents the creation of a topographic barrier and the associated changes to the climate of interior alaska and yukon territory

climatic hydrologic oscillations since 155 000 yr b p at owens lake california reflected in abundance and stable isotope composition of sediment carbonate abstract sediment grain size carbonate content and stable isotopes in 70 cm long 1500 yr channel samples from owens lake core ol 92 record many oscillations representing climate change in the eastern sierra nevada region since 155 000 yr b p to first order the records match well the marine 18o record at owens lake however the last interglaciation appears to span the entire period from 120 000 to 50 000 yr b p according to our chronology and was punctuated by numerous short periods of wetter conditions during an otherwise dry climate sediment proxies reveal that the apparent timing of glacial interglacial transitions notably the penultimate one is proxy dependent in the grain size and carbonate content records this transition is abrupt and occurs at 120 000 yr b p in contrast in the isotopic records the transition is gradual and occurs between 145 000 and 120 000 yr b p differences in timing of the transition are attributed to variable responses by proxies to climate change

δ18o and δd of streamwaters across the himalaya and tibetan plateau implications for moisture sources and paleoelevation reconstructions abstract this study presents new 18o and d data from 191 streams across the himalaya and tibetan plateau to better constrain the spatial variability of stable isotopes in modern precipitation over this region moisture penetrating into the southeastern tibetan plateau is predominantly derived from monsoonal airmasses originating from the bay of bengal and transported into the eastern himalayan syntaxis along the brahmaputra river progressive rainout during orographic lifting and cooling results in clear relationships between 18o and d and catchment hypsometric elevation on the plateau margin however monsoonal derived moisture is progressively mixed with central asian airmasses in more western and northern parts of the tibetan plateau as a result predicted isotope elevation relationships that are based on empirical lapse rates or thermodynamic models of the isotopic evolution of an airmass produce large 1 3 km misfits between measured and predicted catchment elevations for much of the tibetan plateau including some areas directly north of the central himalayan crest this suggests that changes in the 18o or d of paleoprecipitation on the central and southwestern tibetan plateau may reflect surface uplift along moisture transport pathways or changes in the penetration of monsoonally derived moisture rather than regional surface uplift histories

mesozoic history of the fairway aotea basin implications for the early stages of gondwana fragmentation the fairway ridge is a buried continental structure that separates the fairway basin from the new caledonia basin the proposed cretaceous age of the fairway basin has remained highly hypothetical to date deep offshore petroleum exploration wells revealed well dated mesozoic carbonaceous sedimentary rocks in the taranaki basin at the southern end of the aotea basin in this paper we use geophysical data to confirm the continuity of the 2000 km long fairway aotea basin connecting new caledonia to new zealand and prove its early late cretaceous age analysis of seismic reflection profiles together with newly compiled gravity and magnetic maps reveals late cretaceous ne sw trending lineaments projecting northeastward from major tasman sea fracture zones and the bellona trough which demonstrate that the opening of the fairway aotea basin predates the opening of the tasman sea this result combined with observations of the mesozoic regional geology suggests that the lord howe fairway and norfolk ridges are part of a remnant late early cretaceous continental arc which was fragmented into three pieces by the late early to early late cretaceous this event might be contemporaneous with a plate motion change between the gondwana and pacific plates and or the arrival of the hikurangi plateau in the subduction zone around 105 ma which caused the cessation of subduction along this plate boundary we interpret either of those two events as being possible trigger events for the post early cretaceous fragmentation of the eastern gondwana margin in a slab retreat process

influence of andean uplift on climate and paleoaltimetry estimates article i nfo article history recent elevation reconstructions of the andean plateau suggest a rapid 2 5 1 0 km rise of the central andes between 10 and 6 ma this rapid rise has been attributed to a catastrophic removal of a dense lithospheric mantle root beneath the andes however these findings are based on the assumption that climate did not change during deposition of paleoaltimetry proxies here we evaluate south american climate change due to andean uplift and its influence on interpretations of plateau elevation from climate sensitive paleoaltimetry data a series of experiments are presented using the regcm3 regional general circulation model rcm to characterize changes in andean precipitation amount surface temperature and wind direction vapor source as a function of changing plateau elevation results indicate that south american and andean climate changed significantly in response to plateau growth more specifically rising of the plateau results in up to a 900 mm increase in rainy season december january february precipitation over the plateau plateau uplift also results in a decrease in non adiabatic surface temperature of up to 6 5 c in addition to adiabatic cooling directly related to elevation change through the lapse rate finally the prevailing wind direction and the vapor source for precipitation switches from the south pacific ocean to the equatorial atlantic as plateau elevation increases above of its present day elevation taken together these changes in paleoclimate would have substantially depleted the oxygen isotopic concentration of paleoprecipitation through the cenozoic unless this climatic effect is taken into consideration paleoaltimetry reconstructions based on stable isotope methods may overestimate the rapid rise of the andes by up to several kilometers we conclude that some or all of the apparent rapid rise of the andean plateau from paleoaltimetry data could be an artifact of large changes in paleoclimate

the impact of neogene grassland expansion and aridification on the isotopic composition of continental precipitation the late cenozoic was a time of global cooling increased aridity and expansion of grasslands in the last two decades numerous records of oxygen isotopes have been collected to assess plant ecological changes understand terrestrial paleoclimate and to determine the surface history of mountain belts the 18o values of these records in general increase from the mid miocene to the recent we suggest that these records record an increase in aridity and expansion of grasslands in midlatitude continental regions we use a nondimensional isotopic vapor transport model coupled with a soil water isotope model to evaluate the role of vapor recycling and transpiration by different plant functional types this analysis shows that increased vapor recycling associated with grassland expansion along with biomechanistic changes in transpiration by grasses themselves conspires to lower the horizontal gradient in the 18o of atmospheric vapor as an air mass moves into continental interiors the resulting signal at a given inland site is an increase in 18o of precipitation with the expansion of grasslands and increasing aridity matching the general observed trend in terrestrial cenozoic 18o records there are limits to the isotopic effect that are induced by vapor recycling which we refer to here as a hydrostat in the modern climate this hydrostatic limit occurs at approximately the boundary between forest and grassland ecosystems