velocity structure of the kapuskasing uplift northern ontario from seismic refraction studies a crustal scale seismic refraction experiment was conducted over the kapuskasing structural zone northern ontario in 1984 the zone cuts obliquely across the east west structural grain of the superior province in the canadian shield and has been proposed as a cross section of archean crust exposed by thrust faulting along the ivanhoe lake cataclastic zone during early proterozoic time five seismic refraction lines of 360 450 km were shot over the area there were 18 profile shots and two fan shots with a recorder spacing of 2 5 km we have modeled the travel times and amplitudes of the data from the profile lines and analyzed reflections from the crust mantle boundary on the fan shots we have imaged a low velocity zone under the abitibi greenstone belt ranging from 4 5 to 9 12 km depth that is underlain by a highly reflective zone there is a considerable deepening of the moho from 40 43 km to 50 53 km under and to the west of the southern end of the kapuskasing structural zone a high velocity anomaly of 6 6 6 7 km s has been imaged in the upper crust down to 20 km depth beneath the kapuskasing structure with a suggested dip of 15 2 to the west this corresponds well to the proposed location of a granulite zone thrust up from the middle or lower crust in the early proterozoic

quantifying climatic change through the last glacial interglacial transition based on lake isotope palaeohydrology from central turkey questions remain as to the nature of climatic change through the last glacial interglacial transition in the eastern mediterranean region particularly the relative contribution of evaporation and precipitation to regional water balance here changes in oxygen isotope values through this time period from eski acigol a crater lake in central turkey are investigated using hydrological and isotope mass balance models these allow changes in evaporation and precipitation to be quantified and their relative importance evaluated we show that it is the volumetric flux rate of water passing through the lake system and not the precipitation to evaporation ratio per se which controlled the stable isotope record in eski acigol early holocene precipitation is shown to be much greater than that during both the latter part of the last glaciation and the present day we test these calculated values against other records in the same region firstly with other lake records in anatolia the konya basin and lake van and secondly with isotope inferred palaeo precipitation data from soreq cave in israel this reveals a contrast between pre and post lgm precipitation values in turkey wetter and drier respectively and also suggests that during the last glacial interglacial transition there was a more marked precipitation gradient than at present between northern interior and southern coastal parts of the eastern mediterranean region

seismic reflection models of continental crust based on metamorphic terrains summary laboratory seismic velocity measurements on rock samples from metamorphic terrains coupled with geologic cross sections provide the basis for synthetic seismic reflection profiles for various types of continental crust results from greenstone belts mylonite zones and partial cross sections of continental crust indicate that lithologic heterogeneity and geometrical factors control crustal reflection characteristics

rise and fall of late pleistocene pluvial lakes in response to reduced evaporation and precipitation evidence from lake surprise california widespread late pleistocene lake systems of the basin and range province indicate substantially greater moisture availability during glacial periods relative to modern times but the climatic factors that drive changes in lake levels are poorly constrained to better constrain these climatic forcing factors we present a new lacustrine paleoclimate record and precipitation estimates for lake surprise a closed basin lake in northeastern california we combine a detailed analysis of lake hydrography and constitutive relationships describing the water balance to determine the influence of precipitation evaporation temperature and seasonal insolation on past lake levels at its maximum extent during the last deglaciation lake surprise covered 1366 km 2 36 of the terminally draining surprise valley watershed using paired radiocarbon and 230 th u analyses we dated shoreline tufa deposits from wave cut lake terraces in surprise valley california to determine the hydrography of the most recent lake cycle this new lake hydrograph places the highest lake level 176 m above the present day playa at 15 19 0 18 calibrated ka 14 c age this significantly postdates the last glacial maximum lgm when lake surprise stood at only moderate levels 65 99 m above modern playa similar to nearby lake lahontan to evaluate the climatic factors associated with lake level changes we use an oxygen isotope mass balance model combined with an analysis of predictions from the paleoclimate model intercomparison project 3 pmip3 climate model ensemble our isotope mass balance model predicts minimal precipitation increases of only 2 18 during the lgm relative to modern compared to an 75 increase in precipitation during the 15 19 ka highstand lgm pmip3 climate model simulations corroborate these findings simulating an average precipitation increase of only 6 5 relative to modern accompanied by a 28 decrease in total evaporation driven by a 7 c decrease in mean annual temperature lgm pmip3 climate model simulations also suggest a seasonal decoupling of runoff and precipitation with peak runoff shifting to the late spring early summer from the late winter early spring our coupled analyses suggest that moderate lake levels during the lgm were a result of reduced evaporation driven by reduced summer insolation and temperatures not by increased precipitation reduced evaporation primed basin and range lake systems particularly smaller isolated basins such as surprise valley to respond rapidly to increased precipitation during late heinrich stadial 1 hs1 post lgm highstands were potentially driven by increased rainfall during hs1 brought by latitudinally extensive and strengthened midlatitude westerly storm tracks the effects of which are recorded in the region9s lacustrine and glacial records these results suggest that seasonal insolation and reduced temperatures have been underinvestigated as long term drivers of moisture availability in the western united states

a modeling study of oceanic nitrous oxide during the younger dryas cold period 1 the marine production cycling and air sea gas exchange of nitrous oxide n2o are simulated in a coupled climate biogeochemical model of reduced complexity the model gives a good representation of the large scale features of the observed oceanic n2o distribution and emissions to the atmosphere the transient behavior of the model is tested for the younger dryas y d cold period 12 700 11 550 bp which is simulated by releasing a freshwater pulse into the north atlantic causing a temporary collapse of the model s atlantic thermohaline circulation thc a temporary drop in atmospheric n2o of about 10 ppb results while ice core measurements show a total drop of 25 to 30 ppb this suggests that terrestrial changes have also contributed to the observed variations the main cause of the modeled reduction in atmospheric n2o is increased oceanic storage in the short term and a reduction of new production in the long term due to increased stratification

geometry of the kapuskasing structure from a lithoprobe pilot reflection survey a short 10 km pilot seismic reflection profile recorded in the kapuskasing structural zone near foleyet ontario reveals reflections with travel times of at least 5 0 s about 16 km depth an event dipping west from about 1 7 to 3 4 s probably corresponds to the ivanhoe lake cataclastic zone the true geologic dip on this boundary is calculated to be about 35 38 west northwest and is consistent with interpretations of this zone as a west dipping crustal scale thrust fault east dipping reflections are observed with longer travel times than the fault zone arrival and are likely from within the greenstone terrane of the abitibi subprovince

a direct comparison between the historical record of lake level and the δ18o signal in carbonate sediments from lake turkana kenya we compared oxygen isotopic profiles from authigenic calcite in nine freeze cores from lake turkana kenya with the historical record of lake levels for the past 105 years 210pb dating of the cores indicates that sediment in two of the cores spans the complete historical record we observed spatial variability in 6180 and 617c values between cores and an offset from expected isotopic equilibrium values in several of the cores both of these characteristics can be explained by proximity to river input in model calculations of lake level we muted the spatial variability of the s1 o dataset by using a normalized and stacked record there is good agreement between the lake level history modeled using the normalized and stacked record and the historical record of lake level the lake level record derived from the s180 data indicates that lake level fluctuated by 15 m during the last century our model calculations indicate that s o records can be used to generate quantitative lake level curves even using datasets with significant spatial variability the isotopic composition of carbonates has been used in numerous lacustrine studies to determine paleoclimatic information fluctuations in the isotopic record preserved in carbonates are created mainly by variations in the temperature and composition of the water in which the carbonate formed in turn these variations can be caused by climatic changes in the lake basin carbonates are therefore potentially an archive of the paleoenvironment of a lake basin in tropical or closed basin settings shifts in the oxygenstable isotopic composition s180 of carbonates are often attributed to shifts in the evaporation to input e z ratio of a lake previous workers have used the relationship between changes in the s180 value of carbonates and the e z ratio of a lake basin to discuss qualitative changes in paleo lake levels although the relationship between the o composition of lake water and the various inputs and outputs to a basin has been described quantitatively gat 1984 phillips et al 1986 benson and white 1994 only one quantitative comparison between a historical lake level record and lake level determined from the ai80 composition of carbonates has been attempted li 1995

evaporation and transport of water isotopologues from greenland lakes the lake size effect abstract isotopic compositions of evaporative flux from a lake are used in many hydrological and paleoclimate studies that help constrain the water budget of a lake and or to infer changes in climate conditions the isotopic fluxes of evaporation from a water surface are typically computed using a zero dimensional 0 d model originally conceptualized by craig and gordon 1965 such models generally have laminar and turbulent layers assume a steady state condition and neglect horizontal variations in particular the effect of advection on isotopic variations is not considered while this classical treatment can be used for some sections of large open surface water bodies such as an ocean or a large lake it may not apply to relatively small water bodies where limited fetch does not allow full equilibration between air from land and the water surface both horizontal and vertical gradients in water vapor concentration and isotopic ratios may develop over a lake these gradients in turn affect the evaporative fluxes of water vapor and its isotopic ratios which is not adequately predicted by a 0 d model we observed for the first time the vertical as well as horizontal components of vapor and isotopic gradients as relatively dry and isotopically depleted air advected over the surfaces of several lakes up to a 5 km fetch under winds of 1 5 m s in kangerlussuaq greenland we modeled the vapor and isotopic distribution in air above the lake using a steady state 2 d model in which vertical diffusive transport balances horizontal advection the model was verified by our observations and then used to calculate evaporative fluxes of vapor and its isotopic ratios in the special case of zero wind speed the model reduces to 1 d results from this 1 d model are compared with those from the 2 d model to assess the discrepancy in isotopic fluxes between advection and no advection conditions since wind advection above a lake alters the concentrations gradients and evaporative fluxes of water isotopes it alters the water balance and isotope ratios of the lake and the relationship between them these effects are greatest for small lakes if wind advection is neglected in the inference of water balance from lake isotopes an error is thus introduced the magnitude of which depends on lake size we refer to this as the lake size effect for lakes less than 500 m in length along the wind direction the average 18o and d of vapor flux are at least 2 lower than the corresponding flux values from the 1 d model the magnitude of the resulting relative error in water balance calculations is much greater if using 18o than d in mass balance calculations the former is about eight times the latter this result argues that water balance calculated with d is less sensitive to the difference in lake size and or its change over time the 1 d model result is also compared with that from a comparable 0 d model since vertical vapor and isotope gradients always exist even under no advection conditions one may not obtain correct flux values if the relative humidity and isotopic ratios in ambient air measured at an arbitrary height are used for the 0 d model calculation typically the standard meteorological measurements at 2 or 10 m would result in an underestimate of the 18o and d values of the vapor flux this work has provided the first quantification on the effect of advection on isotopic fluxes of evaporation the method of mobile vapor analysis combined with 2 d modeling can be applied to other environmental settings in which the size of advection effect on isotopic fluxes depends upon relationships among local meteorological and hydrological variables our results also suggest that incorporating isotopic vapor measurements can help constrain modeled evaporation rates which is worth exploring further in future studies

increased effective moisture in northern vietnam during the little ice age abstract we present a 650 yr record of hydroclimate inferred from 18o values of lacustrine carbonate from ao tien fairy pond in northern vietnam ao tien occupies a collapsed karst basin that formed during the worst drought of the last millennium i e the angkor i drought which marks a dry transitional period between the medieval climate anomaly and the little ice age a multi centennial trend of increasing effective moisture spans the little ice age ending with aridity in the late 18th century that accompanied great societal turmoil across southeast asia after 1850 ce the ao tien record exhibits a drying trend that continues to the present over the last 650 years the 18o inferred hydroclimate is significantly correlated with the reconstructed southern oscillation index of precipitation soipr suggesting that a prolonged la nina like state existed during the little ice age generating overall wetter conditions in vietnam decadal scale droughts and pluvials from the ao tien record agree with a robust tree ring hydroclimate reconstruction from southern vietnam that identified the angkor i and ii droughts of the late 13th early 14th centuries and significant droughts during the early and late 17th century and latter half of the 18th century the decrease in effective moisture during the last 30 years is also evident in the tree rings and is consistent with a documented weakening of the pacific walker circulation major pluvials are indicated for the period between the two angkor droughts and the wettest period of the record is during the early 18th century comparison of the ao tien data with records from indonesia to china indicates regionally coherent climate during the little ice age however the overall wet conditions in easterly sites are difficult to ascribe to shifts in the itcz rather the pattern suggests that pacific walker circulation may have been the overriding control on precipitation

isotope sourcing of prehistoric willow and tule textiles recovered from western great basin rock shelters and caves proof of concept isotope and trace metal analyses were used to determine the origin of plants used to manufacture prehistoric textiles basketry and matting from archaeological sites in the western great basin research focused on strontium 87 sr 86 sr and oxygen 18 o 16 o isotope ratios of willow salix sp and tule schoenoplectus sp the dominant raw materials in great basin textiles the oxygen isotope data indicated that the willow and tule used to produce the textiles were harvested from the banks of rivers or in marshes characterized by flowing water and not from lakes or sinks the strontium isotope data were useful in showing which plants came from the humboldt river and which came from rivers headed in the sierra nevada published by elsevier ltd

progressive metamorphism of mafic rocks from greenschist to granulite facies in the dharwar craton of south india in the archean dharwar craton of southern india n s trending belts of metabasic rocks are exposed which underwent regional metamorphism at about 2 5 ga ago the progressive changes in the assemblages and mineral chemistry of metabasites was studied in a n s traverse covering the chitradurga and nagaman gala belts the sargur area and the nilgiri hills towards the south with increasing metamorphic grade greenschists chl act ab ep pm carb qtz give way to amphibolites hbl plag pm qtz gar cumm and mafic granulites pyx plag gar pm hbl qtz the amphibole composition changes from actinolite in the greenschist zone to tschermakitic hornblende in the amphibolite zone and pargasitic hastingsitic hornblende in the granulite zone the ti content of the amphiboles systematically increases in this direction the plagioclase composition changes from albite in the greenschist zone to oligoclase andesine in the amphibolite zone and andesine labradorite in the granulite zone almandin

the nature of seismic reflections from deep crustal fault zones deep seismic reflection profiles have recorded reflections from ductile shear zones within the crystalline basement perhaps the best example is the consortium for continental reflection profiling cocorp wind river line in wyoming which shows the wind river thrust fault to be a strong reflector from the surface to depths of about 30 km to identify the physical properties responsible for the seismic reflections from fault zones we report measurements of compressional wave velocity and velocity anisotropy in mylonites recovered from exhumed ductile shear zones these rocks are characterized by extensive ductile deformation of plastic minerals brittle deformation of the more rigid minerals grain size reduction and development of a strong fabric average velocity and density were not found to change significantly and systematically between the mylonites and the adjacent undeformed rock seismic anisotropy of 7 or greater is present in several mylonites dependent upon their composition and fabric using our data on mylonite properties and models for the crustal structure near the wind river line we compute true amplitude synthetic reflection seismograms and compare them to true amplitude plots of the cocorp wind river reflection data when anisotropy and the finely laminated structure of the fault zone are considered our modeling indicates fairly strong reflections from mylonite zones in most cases we also show that elevated pore pressure in shear zones may produce strong reflections however a permeability of the order of 10 16 darcy is required to maintain sufficient pore pressure to produce a velocity anomaly in a fault zone which has long been inactive

origin of reflections from the brevard fault zone the brevard fault zone is a belt of mylonitic metamorphic rocks that extends northeast over 700 km from alabama into virginia seismic reflection studies show that the fault zone produces excellent reflections which dip gently to the southeast and sole at depth the origin of these reflections has been investigated by measuring compressional wave velocities to 800 mpa confining pressure in 127 samples obtained from drill core which continuously sampled the fault zone to a depth of over 300 m densities are reported as well as chemical analyses at selected depths anisotropy at elevated pressures ranges within the fault zone from less than 5 to over 26 similarly the fault zone rocks show significant chemical variability with sio2 ranging from 58 0 to 70 4 by weight synthetic seismograms generated from the velocity and density measurements show that the reflections originate within the brevard fault zone from the complex interaction of compositional variations and seismic anisotropy resulting from ductile strain essential to this study has been the continuous coring of a major section of the brevard fault zone which has provided the necessary stratigraphic control as well as unweathered samples for laboratory studies

climate change in the turkana basin as deduced from a 4000 year long δo18 record abstract a model of the oxygen isotopic composition of lake turkana waters sheds insight into the paleoclimatic interpretation of a 18 o profile of inorganic calcite from a core taken from the lake the model indicates that high frequency fluctuations seen in the isotopic record are probably due to shifts in lake level while the long term increase of 1 4 seen from 4 to 2 kyr bp cannot be due solely to lake level change it must be due to changes in other climatic parameters such as the isotopic composition of the inflow these findings suggests that the abrupt change observed in lake turkana and many other african lakes at 4 ka was the precursor to a 2000 year long adjustment in the climate over the ethiopian plateau the isotopic record from lake turkana agrees with other paleoclimate records from the basin including the diatom stratigraphy and radiocarbon dates on exposed shoreline deposits

archean crust as revealed in the kapuskasing uplift superior province canada in the central superior province of the canadian shield a 120 km wide transition from the low grade michipicoten greenstone belt to the high grade kapuskasing structural zone represents an oblique section through some 20 km of archean crust uplifted along a northwest dipping thrust fault the restored vertical section through the upper and middle crust consists of three megalayers with undulating boundaries 1 0 to 25 km a high grade heterogeneous gneissic assemblage in part older than the upper supracrustal succession

quantifying closed basin lake temperature and hydrology by inversion of oxygen isotope and trace element paleoclimate records lake systems are important paleoclimate archives that preserve ecosystem and hydrologic responses to critical periods in earth history such as carbon cycle perturbations and glacial interglacial cycles geochemical measurements of biogenic carbonate for example 18o 13c 87sr 86sr li u sr and mg are indicators of hydrologic variability in lake systems throughout the geologic record in this study we present a new closed basin lake modeling approach hybim the hydrologic balance inverse model that employs a system of total differential equations and uses the measured 18o sr ca and mg ca of biogenic carbonate to determine changes in temperature runoff and lake evaporation using equally spaced time steps these equations are simultaneously solved to constrain the hydrologic parameters of the lake as recorded in biogenic carbonate we use a monte carlo approach to account for uncertainty in the input parameters such as 18o temperature relationships partition coefficient uncertainty and watershed solute chemistry for illustrative purposes we apply the model to two ostracod valve datasets covering different timescales 1 the cretaceous songliao basin northeast china and 2 holocene lake miragoane haiti modern water measurements of water isotopes and cation concentrations from each location are required as model inputs we compare our modeling results with author interpretations and geologic observations the modeling approach presented in this study can be applied to other closed basin lake records can be modified for other calcifying species for example gastropods or mollusks or with calibration to inorganic lacustrine carbonate in addition this approach holds promise for extension with additional proxy measurements that is d u ca or li ca and changing source area on tectonic timescales using proxies that reflect changing source lithology that is sr and pb isotopes future incorporation of age model uncertainty in the monte carlo approach will also provide utility by quantifying temporal uncertainty on the hydrologic response recorded by lake sediments

carbonate deposition pyramid lake subbasin nevada 4 comparison of the stable isotope values of carbonate deposits tufas and the lahontan lake level record abstract in this paper the fundamental importance of changes in hydrologic balance and hydrologic state on the 18o and 13c values of water and dissolved inorganic carbon dic in lakes of the lahontan basin is illustrated abrupt changes in 18o and 13c values of carbonate deposits tufas from the pyramid lake subbasin nevada coincide with abrupt changes in lake level and hydrologic state minima in lake level at 26 000 15 500 and 12 000 yr b p are associated with relatively heavy 18o and 13c values maxima in the lake level record at 14 000 and 10 500 yr b p are associated with relatively light 18o and 13c values we believe that the correlation between maxima and minima in the lake level and 18o records reflect the fundamental effect of lake level dynamics on the 18o value of lake water evaporation increases the 18o value of lake water whereas streamflow discharge and on lake precipitation decrease the 18o value variation in the 18o value of lake water therefore indicates change in the hydrologic balance increases in 18o accompany decreases in lake volume and decreases in 18o accompany increases in lake volume covariance of 13c and 18o indicates that change in 13c values of dic also accompany change in lake volume we offer the hypothesis first put forward by j a mckenzie that change in the productivity photosynthesis respiration balance is responsible for much of the observed variation in 13c most great basin lakes including lake lahontan experienced changes in hydrologic state during the late wisconsin when a lake becomes hydrologically open the residence time of water decreases the greater the rate of spill the greater the volume of evaporated 18o enriched water removed from the spilling lake and the more negative the 18o value of water remaining in the spilling lake the concentration of dic as well as the concentrations of photosynthesis limiting nutrients e g phosphorus nitrogen silica molybdenum decrease as spill increases increasing rates of spill therefore lead to overall decreases in photosynthetic rates relative to respiration rates and as a consequence the 13c values of dic become more negative

the holocene paleolimnology of lake issyk kul kyrgyzstan trace element and stable isotope composition of ostracodes the stable isotope and trace element geochemistry of ostracode shells from lake issyk kul kyrgyzstan provide an important new paleoclimate record for central asia the n 18 o n 13 c sr ca mg ca and u ca composition of shells from the species candona neglecta found in two piston cores constrains the paleohydrology of the lake from 8700 to 1000 calendar yr before present these data combined with robust chronologies based on 16 ams 14 c dates suggest that the region went from a relatively moist climate in the early holocene to a more arid climate in the late holocene intense freshwater input presumably glacial runoff flowed into the lake from 8700 to 8300 cal yr bp as evident from the n 18 o and n 13 c values from 8300 to 6900 cal yr bp n 18 o and sr ca values indicate that the lake was relatively fresh and an open basin and u ca values suggest that the lake was well mixed with well oxygenated bottom waters there is a transition zone between 6900 and 4900 cal yr bp when n 18 o and sr ca values rapidly increase and mg ca and u ca values rapidly decrease during this period the lake evolved from an open freshwater well mixed lake to a closed more saline less well mixed lake for the remainder of the record n 18 o sr ca mg ca and u ca are relatively constant implying conditions similar to modern conditions although the slight increasing trend in sr ca may suggest an increase in salinity over this period the n 13 c values were approximately in equilibrium with atmospheric co2 in the early part of the record but became relatively negative in the later part of the record this indicates that the dominant mechanism controlling the isotopic composition of dissolved inorganic carbon shifted from exchange with the atmosphere to variations in biological productivity fl 2001 elsevier science b v all rights reserved

stable isotopes of oxygen and hydrogen in the truckee river pyramid lake surface water system 3 source of water vapor overlying pyramid lake during 1988 and 1989 a series of water vapor extractions were conducted in the pyramid lake basin to determine the source of moisture that overlies the lake calculations of the isotopic and water vapor balances were made from isotopic and meteorological data from the pyramid lake and reno nevada areas the results indicate that in the warm season most of the moisture that overlies the lake is derived from evaporation as opposed to advected moisture isotopic fluxes at the lake surface can be approximated by climatic data from the lake site which simplifies the calculation of this input in numerical simulations of the isotopic evolution of the lake the stable isotopic composition of a lake is a function of the volume weighted isotopic values of each component of the lake s hydrologic balance researchers have used the stable isotope history of a lake together with the volume weighted isotopic composition of easily measured components of the hydrologic balance to estimate the stable isotope values or amounts of less easily measured components of the hydrologic balance see iaea 1970 1979 it is usually relatively simple to quantify the amounts and isotopic compositions of components of the surface water system and the isotopic composition of groundwater it is often more difficult to quantify the amount and direction of groundwater transport across the sediment water interface and the amount and isotopic composition of lake surface evaporation the isotopic value of water evaporated from a lake is highly dependent on the isotopic value acknowledgments we express our appreciation to those who assisted in sampling including jim davis dan mosley and nancy vucinich special thanks to irving friedman who loaned us the copper traps used for water vapor extraction to carol kendall and tyler coplen who oversaw the isotopic analyses to james ashby who maintained the weather stations and to steve hostetler who extracted the meteorological data from the weather station database and stratified the wind data for the sutcliffc and northshore sites we also thank zell peterman steve hostetler and pieter tans for reviews of earlier versions of this manuscript

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

a 1200 year record of hydrologic variability in the sierra nevada from sediments in walker lake nevada 1 measurements of the oxygen isotopic composition 18o of the total inorganic carbon tic fraction from cored sediments of walker lake nevada were conducted at an average resolution of 3 years per sample over the last 1200 years on the basis of radiocarbon analysis on the total organic carbon toc fraction a 18o time series was created to reconstruct changes in hydrologic conditions back to ad 800 the timings of variations in the tic 18o record are generally consistent with the tree ring based sacramento river flow record spanning ad 869 to 1977 indicating that walker lake 18o contains information about past changes in at least regional hydrologic conditions comparison with the 18o record from pyramid lake sediments indicates that both basins have recorded five century scale oscillations in regional hydrologic conditions since ad 800 several of these changes in hydrologic conditions appear synchronous with century scale california current water temperature changes derived from analysis of sediment cores from the santa barbara basin also attesting to the regional extent of these climatic fluctuations nearly synchronous oscillations in the sierra wetness and the california current suggest that regional changes in atmospheric circulation may have played an important role in century scale climate variability over the last millennium

holocene multidecadal and multicentennial droughts affecting northern california and nevada abstract continuous high resolution 18 o records from cored sediments of pyramid lake nevada indicate that oscillations in the hydrologic balance occurred on average about every 150 years yr during the past 7630 calendar years cal yr the records are not stationary during the past 2740 yr drought durations ranged from 20 to 100 yr and intervals between droughts ranged from 80 to 230 yr comparison of tree ring based reconstructions of climate change for the past 1200 yr from the sierra nevada and the el malpais region of northwest new mexico indicates that severe droughts associated with anasazi withdrawal from chaco canyon at 820 cal yr bp calendar years before present and final abandonment of chaco canyon mesa verde and the kayenta area at 650 cal yr bp may have impacted much of the western united states during the middle holocene informally defined in this paper as extending from 8000 to 3000 cal yr bp magnetic susceptibility values of sediments deposited in pyramid lake s deep basin were much larger than late holocene 3000 0 cal yr bp values indicating the presence of a shallow lake in addition the mean 18 o value of caco 3 precipitated between 6500 and 3430 cal yr bp was 1 6 less than the mean value of caco 3 precipitated after 2740 cal yr bp numerical calculations indicate that the shift in the 18 o baseline probably resulted from a transition to a wetter 30 and cooler 3 5 c climate the existence of a relatively dry and warm middle holocene climate in the truckee river pyramid lake system is generally consistent with archeological sedimentological chemical physical and biological records from various sites within the great basin of the western united states two high resolution holocene climate records are now available from the pyramid and owens lake basins which suggest that the holocene was characterized by five climatic intervals tic and 18 o records from owens lake indicate that the first interval in the early holocene 11 600 10 000 cal yr bp was characterized by a drying trend that was interrupted by a brief 200 yr wet oscillation centered at 10 300 cal yr bp this was followed by a second early holocene interval 10 000 8000 cal yr bp during which relatively wet conditions prevailed during the early part of the middle holocene 8000 6500 cal yr bp high amplitude oscillations in tic in owens lake and 18 o in pyramid lake indicate the presence of shallow lakes in both basins during the latter part of the middle holocene 6500 3800 cal yr bp drought conditions dominated owens lake desiccated and lake tahoe ceased spilling to the truckee river causing pyramid lake to decline at the beginning of the late holocene 3000 cal yr bp lake tahoe rose to its sill level and pyramid lake increased in volume

climatic and hydrologic oscillations in the owens lake basin and adjacent sierra nevada california oxygen isotope and total inorganic carbon values of cored sediments from the owens lake basin california indicate that owens lake overflowed most of the time between 52 500 and 12 500 carbon 14 14 c years before present b p owens lake desiccated during or after heinrich event h1 and was hydrologically closed during heinrich event h2 the magnetic susceptibility and organic carbon content of cored sediments indicate that about 19 sierra nevada glaciations occurred between 52 500 and 23 500 14 c years b p most of the glacial advances were accompanied by decreases in the amount of discharge reaching owens lake comparison of the timing of glaciation with the lithic record of north atlantic core v23 81 indicates that the number of mountain glacial cycles and the number of north atlantic lithic events were about equal between 39 000 and 23 500 14 c years b p

exposed cross sections through the continental crust implications for crustal structure petrology and evolution abstract the continental crust is exposed in cross section at numerous sites on the earth s surface these exposures which appear to have formed by obduction along great faults during continental collision may be recognized by exposures of deep crustal rocks exhibiting asymmetric patterns of metamorphic grade and age across the faults and by distinctive bouguer anomaly patterns reflecting dipping basement structure and an anomalously deep mantle from an examination of five complexes which meet these criteria it is concluded that the most prominent layering in the crust is not compositional but metamorphic the lower crust consists of granulite facies rocks of mafic to intermediate composition while the intermediate and shallow levels consist predominantly of amphibolite facies gneisses and greenschist facies supracrustal rocks respectively post metamorphic granitic intrusions are common at intermediate to shallow levels position of discontinuities in refraction velocity where present commonly correspond to changes in composition or metamorphic grade with depth the continental crust is characterized by lateral and vertical heterogeneities of varying scale which are the apparent cause of the complex seismic reflections recorded by cocorp field observations coupled with geochemical data indicate a complex evolution of the lower crust which can include anatexis multiple deformation polymetamorphism and reworking of older crustal material the complexity of the crust is thus the result of continuous evolution by recycling and metamorphism through time in a variety of tectonic environments

isotopic and hydrologic responses of small closed lakes to climate variability hydroclimate reconstructions from lake sediment oxygen isotope records and mass balance models abstract hydroclimate sensitivity simulations were conducted with a lake catchment hydrologic and isotope mass balance model adapted to two small closed lakes castor and scanlon located in the pacific northwest model simulations were designed to investigate the combined influences of persistent disequilibrium reddening and equifinality on lake water and sediment i e biogenic and endogenic carbonate mineral oxygen isotope 18 o values and to provide a basis for quantitative probabilistic climate reconstructions using lake sediment 18 o records simulation results indicate that within closed basin lakes changes in long term i e multi decadal precipitation amounts produce inconsistent responses in lake water and sediment 18 o values that are strongly influenced by lake basin outseepage and morphometry simulations of variable initial conditions in which randomly generated monthly climate data i e precipitation temperature and relative humidity were used to force the model during the equilibration period which precedes the application of instrumental climate data demonstrate that castor lake and scanlon lake have a somewhat limited isotopic memory of 10 years additional tests conducted using a monte carlo ensemble in which random climate data were used to force the model combined with 18 o analyses of water samples collected from 2003 to 2011 ad indicate that within small closed lakes in the pacific northwest november february precipitation is the strongest seasonal climatic control on sediment oxygen isotope values further a monte carlo based reconstruction of 20 year average november february precipitation amounts strongly correlates r 2 0 66 to instrumental values from the 20th century with all observed values falling within modeled 95 prediction limits indicating that probabilistic quantitative paleoclimate interpretations of lake sediment 18 o records are attainable

u pb zircon geochronology of the kapuskasing structural zone and vicinity in the chapleau foleyet area ontario geological development of the archean abitibi and wawa greenstone granite subprovinces of the superior province occurred in three main stages 1 a volcanic sedimentary depositional stage 2750 2696 ma ago 2 a metamorphic tectonic event 2700 2685 ma ago and 3 a late plutonic event at 2685 2668 ma the area between wawa in the west and ivanhoe lake in the east represents an oblique section through some 20 km of the crust where geochronological relationships can be examined at different structural levels much of the eastern wawa subprovince is characterized by tonalite granodiorite gneiss containing abundant mafic xenoliths and represents a crustal level intermediate between high level metavolcanic rocks near lake superior and the deep seated gneisses of the kapuskasing structural zone a tonalitic phase of the complex gneiss of the wawa subprovince has a minimum u pb zircon date of 2707 ma but the fine zircons are partly reset possibly in response to lit par lit injections of gneissic to foliat

amplification of ground motion and waveform complexity in fault zones examples from the san andreas and calaveras faults summary p wave seismograms at ranges less than 10 km are synthesized by asymptotic ray theory and by summation of gaussian beams for point sources located in a low velocity wedge surrounding a fault the computations are performed using models of the wedge inferred from the analysis of reflection and refraction experiments across the san andreas and haywardcalaveras faults calculations in these models show that the 10 20hz vertical displacements of earthquakes located at 3 10 km depth are amplified by up to an order of magnitude in a 1 2 km wide region centred on the fault trace compared to displacements predicted by laterally homogeneous models of the crust this amplification is not cancelled by high attentuation in the fault zone and compensates for the reduction in amplitudes directly above the source predicted from the radiation pattern of a strike slip earthquake depending on the source depth of the earthquake and the structure and velocity contrast of the wedge multiple triplications in the travel time curve of direct p and s waves will occur at stations in the fault zone a wedge model successfully predicts the triplications observed in the p waveforms of aftershocks of the coyote lake earthquake recorded in the fault zone showing that body waves from microearthquakes can be used to determine the three dimensional velocity structure of the fault zone the amplification waveform complexity and distortion of ray paths introduced by the lowvelocity wedge suggest that its effects should be included in the interpretation of strong ground motions and travel times observed in the fault zone for realistic models of the wedge asymptotically approximate methods of calculating the body waveforms are strictly valid for frequencies greater than 20hz numerical methods may be necessary to calculate accurately the wavefield at lower frequencies

regionalization of crustal coda q in the continental united states a contour map of crustal q sub 0 values for the entire united states is presented based on a scattering model to explain the coda waves of local and near regional earthquakes these coda q sub 0 values are in good agreement with q of lg waves data are obtained from over 250 local earthquakes with most magnitudes between 3 0 and 5 0 recorded by 25 wwssn and 27 lrsm stations throughout the continental united states these two sets of data provide a range of frequencies from 0 5 to 3 5 hz a frequency dependence of q is observed in the range of frequencies considered a power law dependence of the form q q sub 0 f f sub 0 sup eta is assumed the value of frequency dependence eta is found to be maximum in the tectonically active western united states and least in the stable regions of the central and south central united states the lowest q sub 0 values are obtained in the western united states with values ranging from 140 to 200 in the coastal plains average crustal q sub 0 values for the basin and range province vary from 200 to 300 increasing gradually to 400 in the colorado plateau region q sub 0 valuesmore in the columbia plateau vary from 200 to 400 q sub 0 values increase very rapidly along the central and southern rocky mountains from 400 to 800 east of the rocky mountains q sub 0 values increase gradually in the interior plains to a maximum value of around 1300 in the mississippi embayment region farther east q sub 0 values decrease gradually to an almost constant value of 1000 along the appalachian mountains coastal regions of eastern and northeastern united states have a crustal q sub 0 value between 900 to 700 regions of north central and gulf coastal plains show low q sub 0 values ranging from 600 to 400 and less the source factor b f sub p a measure of the intensity of scattering was obtained for several different regions of the continental united states regions of high q sub 0 values exhibit low intensity of scattering less

the 1982 cocrust seismic experiment across the ottawa bonnechere graben and grenville front in ontario and quebec summary during the summer of 1982 the canadian consortium for crustal reconnaissance using seismic techniques cocrust conducted a major long range seismic refraction and wide angle reflection experiment across the grenville province of the canadian shield three seismic lines each approximately 300 km in length were located i along the ottawa bonnechere graben ii perpendicular to the graben and iii perpendicular to the crenville front geological evidence indicates that the graben may have originated from a failed arm of the st lawrence rift system and the grenville front marks the boundary between the grenville province and the much older superior province other geological features of the grenville province that were traversed by the profiles were the central metasedimentary belt and the central gneiss belt analysis of the data involved conventional traveltime procedures coupled with the use of synthetic seismogram analysis using programs that were written to handle laterally heterogeneous structures results from the survey indicate a variation in near surface seismic velocity

triple oxygen isotope signatures of evaporation in lake waters and carbonates a case study from the western united states abstract evaporation can increase the 18 o values of lake waters and carbonates by several per mil if not accounted for in geological studies this can lead to substantial misinterpretation of 18 o values in terms of paleoclimate and paleoelevation evaporation also leads to a lowering in residual waters of 17 o a measure of the departure of 17 o from a characteristic relationship with 18 o we present new triple oxygen isotope data from waters and carbonates from lakes and their source rivers in the western united states bear lake great salt lake lake tahoe mono lake and pyramid lake consistent with predictions from steady state isotopic mass balance models the data illustrate marked lowering of 17 o in closed basin lakes and freshwater lakes relative to their source rivers the evaporation slope in triple oxygen isotope space lake is similar for these lakes averaging 0 5229 and ranging between 0 5219 and 0 5239 moreover models and data both show that the evaporation slope correlates with 17 o meaning that the slope can be estimated on the basis of the measured 17 o value of the carbonate we show how triple oxygen isotopes in lake waters and carbonates and clumped isotopes 47 in carbonates can be combined to reconstruct the 18 o values of primary unevaporated catchment precipitation 18 orucp we use our lacustrine carbonate data as a test case for this approach and find that 18 orucp values closely approximate independently measured 18 o values of catchment precipitation however the 18 orucp values are consistently higher than 18 o of catchment precipitation by 2 which may reflect present incomplete understanding of a number of triple oxygen isotope parameters used in the calculation such as the fractionation exponent for carbonate water equilibrium the evaporation slope lake and the 17 o values of unevaporated meteoric waters in conclusion triple oxygen isotope analysis of lake waters and lacustrine carbonates is a promising new method for studying evaporation in fossil lake systems but will benefit from additional research into triple oxygen isotope systematics relevant to meteoric waters lake systems and carbonate water fractionation

paleomagnetism of the hearst dike swarm and implications for the tectonic history of the kapuskasing structural zone northern ontario prominent north to northwest trending dikes herein termed the hearst swarm west of the kapuskasing structural zone ksz in northern ontario yield a paleomagnetic pole position of 48 6 n 69 0 e dm 6 9 dp 3 6 60 samples from 12 dikes using paleomagnetic petrographic and structural criteria the hearst swarm is correlated with the 2 6 ga matachewan swarm east of the ksz a positive correlation is observed between the trend and paleomagnetic declination of hearst matachewan dikes and may result from an 15 post 2 6 ga rotation of terranes across the ksz paleomagnetic and structural data from the hearst dikes are consistent with the regional westward tilting of the crust near the southern ksz as first proposed in 1983 by percival and card

radiocarbon ages and environments of deposition of the wono and trego hot springs tephra layers in the pyramid lake subbasin nevada abstract uncalibrated radiocarbon data from core plc92b taken from wizards cove in the pyramid lake subbasin indicate that the trego hot springs and wono tephra layers were deposited 23 200 300 and 27 300 300 14 c yr b p uncorrected for reservoir effect sedimentological data from sites in the pyramid lake and smoke creek black rock desert subbasins indicate that the trego hot springs tephra layer was deposited during a relatively dry period when pyramid lake was at or below its spill point 1177 m to the winnemucca lake subbasin the wono tephra layer was deposited when lake depth was controlled by spill across emerson pass sill 1207 m to the smoke creek black rock desert subbasin 18 o data from core plc92b also support the concept that the trego hot springs tephra fell into a relatively shallow pyramid lake and that the wono tephra fell into a deeper spilling lake

depth migration and interpretation of the cocorp wind river wyoming seismic reflection data to better understand laramide deformation deep seismic reflection data have been depth migrated focused or imaged in order to more clearly reveal structural features associated with the wind river thrust wyoming major structural features displayed in the migrated data are the wind river fault zone and the pacific creek anticline the wind river fault zone is seen to a depth of at least 25 km and interpretively to 32 km it is a complex zone that includes numerous splays flattening with depth the wind river range was tilted along these arcuate splays as it was compressionally thrust up the pacific creek anticline is asymmetric and thrust cored with the top of basement offset 600 m the pacific creek thrust is viewed as an embryonic wind river thrust

deep crustal structure and tectonic history of the northern kapuskasing uplift of ontario an integrated petrological geophysical study the northeast trending kapuskasing uplift transects the east west belts of the central superior province over a distance of some 500 km granulite to upper amphibolite facies rocks of the uplift form three distinct geological geophysical entities from south to north the chapleau groundhog river and fraserdale moosonee blocks uplift of the granulites along a moderately northwest dipping crustal scale thrust fault is attributed to an early proterozoic compressional event major northeast striking faults that bound the kapuskasing zone on the west were examined by modelling of geophysical anomalies to determine dip and by geobarometry of garnet orthopyroxene plagioclase quartz assemblages to determine vertical displacement granulites in the kapuskasing zone have 7 to 9 kbar signatures whereas those in the quetico belt to the west indicate metamorphic pressure of 4 6 kbar individual calibrations of the barometer yield consistent pressure differences of 2 3 kbar suggesting 7 10 km of west side down movement on the faults modelling of gravity and aeromagnetic gradients indicates westerly dips of 60 65 with west side down offset of up to 14 km these major normal faults probably formed as collapse structures in response to crustal thickening which occurred during the preceding compressional uplift stage differences in the configuration of individual blocks of the kapuskasing zone can be related to variable fault slip and intersection angles between normal and reverse faults thus the groundhog river and southern fraserdale moosonee blocks are perched thrust tips analogous to the sangre de cristo range of the laramide uplift province whereas the southern chapleau block is a tilted slab with similar configuration to the laramide wind river range pop up geometry deduced for the northern fraserdale moosonee block resembles the structure of the laramide uinta mountains a normal fault crosses the surface trace of the basal thrust fault between the groundhog river and fraserdale moosonee blocks and causes a 65 km gap without granulites this article contains supplementary material