late miocene environmental change in nepal and the northern indian subcontinent stable isotopic evidence from paleosols neogene sediments belonging to the siwalik group crop out in the himalayan foothills along the length of southern nepal carbon and oxygen isotopic analyses of siwalik paleosols from four long siwalik sections record major ecological changes over the past 11 m y the carbon isotopic composition of both soil carbonate and organic matter shifts dramatically starting ca 7 0 ma marking the displacement of largely c3 vegetation probably semi deciduous forest by c4 grasslands by the beginning of the pliocene all the flood plains of major rivers in this region were dominated by monsoonal grasslands the floral shift away from woody plants is also reflected by the decline and final disappearance of fossil leaves and the decrease in coal logs in the latest miocene a similar carbon isotopic shift has been documented in the paleosol and fossil tooth record of pakistan and in terrigenous organic matter from the bengal fan showing that the floral shift was probably continentwide the latest miocene also witnessed an average change of 4 in the oxygen isotopic composition of soil carbonate as observed previously in pakistan the reasons for this are unclear if not diagenetic a major environmental change is indicated perhaps related to that driving the carbon isotopic shift recently described pollen and leaf fossils from the surai khola section show that evergreen forest was gradually displaced by semi deciduous and dry deciduous forest between 11 and 6 ma the gradual nature of this floral shift which culminated in the rapid expansion of c4 grasses starting 7 0 m y ago is difficult to explain by a decrease in atmospheric pco2 alone cerling et al 1993 but fits well with a gradual onset of monsoonal conditions in the late miocene in the northern indian subcontinent himalayan uplift driving both monsoonal intensification and consumption of co2 through weathering may be the common cause behind major late miocene environmental change globally however the decline of effective moisture associated with monsoon development has probably slowed not increased the rate of consumption of co2 by chemical weathering of himalayan sediments

modern and long term evaporation of central andes surface waters suggests paleo archives underestimate neogene elevations abstract central andean paleoelevations reconstructed from stable isotope and paleofloral data imply a large magnitude 2 km miocene to modern surface uplift however the isotopic relationships between precipitation surface waters and soil waters upon which these reconstructions are based remain poorly constrained for both past and in many cases modern conditions we quantify the relationships between central andean precipitation and surface waters by measuring the isotopic composition of 249 stream water samples 18o and d collected between april 2009 and october 2012 the isotopic compositions of stream waters match precipitation along the eastern flank in contrast altiplano surface waters possess a lower d 18o slope 4 59 vs 8 for meteoric waters not observed in precipitation which signals heavy isotope evaporative enrichment in surface waters paleoclimate models indicate that highly evaporative conditions have persisted on the plateau throughout andean uplift and that conditions may have been more evaporative when the andes were lower thus more ancient proxy materials may have a greater evaporative bias than previously recognized and paleoelevation reconstructions from stable isotope based central andean plateau proxy materials likely overstate miocene to present surface uplift we propose altiplano paleoelevations of 1 2 km at 24 5 ma 1 5 2 9 km by 11 45 ma and modern elevations by 6 ma based on the lightest isotopic compositions observed in altiplano proxy materials which are least likely to be influenced by evaporation these constraints limit total late miocene to modern uplift to

cenozoic paleoaltimetry of the se margin of the tibetan plateau constraints on the tectonic evolution of the region abstract an improved understanding of the elevation history of the tibetan plateau is crucial in discriminating among the various tectonic models for the evolution of the india asia continental collision we reconstruct the paleoelevation history for three cenozoic sedimentary basins from se tibet and yunnan china to provide more constraints on the tectonic processes for raising the se margin of the tibetan plateau the results presented here together with those of previous studies indicate that 1 the plateau margin of nw yunnan was near its elevation 2 6 km by the latest middle eocene 40 ma 2 the plateau margin of se yunnan reached its current elevation 1 6 km by the middle miocene 13 ma interpretations of the tectonic processes responsible for this inferred surface uplift of the region are made in the context of well documented surface geology we conclude that high landscape 2 6 km elevation in nw yunnan may represent the remnants of the eocene tibetan plateau that originally formed in the northeastern qiangtang block by crustal thickening associated with the india asia continental collision the near modern elevation of se yunnan since 13 ma probably reflects the initiation of lower crustal flow in this area by at least that time collectively our paleoaltimetric interpretations disagree with previously proposed models of middle miocene to pliocene crustal flow acting as a sole tectonic process for raising the se margin of the plateau but support a protracted history of surface uplift that most likely involved crustal thickening during the eocene southeastward extrusion of a portion of eocene tibetan plateau during the oligocene to early miocene and lower crustal flow beneath this region since at least the early miocene

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

clumped isotope paleotemperatures from mis 5 soil carbonates in southern hungary abstract quantitative paleotemperature reconstructions for the continents including east central europe over marine isotope stage 5 mis 5 and specifically the last interglacial lig mis 5e are scarce and mostly based on pollen assemblages here we provide soil and air temperature reconstructions for the summer season of mis 5e 5c using carbonate clumped isotope thermometry applied to soil carbonate concretions in the dunaszekcs loess paleosol record southern hungary the sediments making up the s1 pedocomplex investigated represent the mis 5 as demonstrated by bracketing k feldspar post ir irsl225 290 ages of 63 to 164 ka both the absolute ages and pedogenic susceptibility p curve indicate that all the subtages of mis 5 were found to be recorded in the sequence and soil carbonates found 1 m depth below the paleosurface of the s1 soil provide pristine undisturbed isotopic signals the soil carbonate concretions likely formed during mis 5e at a relatively shallow 20 50 cm depth but a later formation during mis 5c at 50 cm depth is also plausible clumped isotope based soil temperatures st 47sc ranged from 16 to 20 c and reconstructed summer season air temperatures sats for the lig are consistently lower than the modern values at the site by 1 5 c matching surprisingly well the soil bacteria membrane lipid based mis 5e air temperature estimates from a nearby serbian site at the same time the reconstructed sat values do not match the 2 4 c positive warm season anomalies modeled for east central europe between lig and present day in paleoclimate simulations st uncertainties of 1 6 c infiltration driven cooling of soil temperatures and the possibility of mis 5c formation of the investigated carbonates may account for this proxy model data discrepancy oxygen isotope compositions of summer season paleo rainwaters for mis 5e 5c as reconstructed using the st 47sc and 18osc data of soil carbonates were found in a range of 6 7 and 6 4 matching the modern mean summer season value of 6 2 0 94 within error

an oxygen isotope study of illite and calcite in three appalachian paleozoic vertic paleosols abstract the oxygen isotope compositions of pedogenic calcite and illite in three paleozoic vertic red bed paleosols record a complex history of pedogenic and diagenetic processes the paleosols are preserved in the upper mississippian chesterian mauch chunk pennsylvania hinton west virginia and pennington tennessee formations in the appalachian basin and were buried to 7 8 km 230 260 c 3 4 km 100 145 c and 1 5 3 km 70 100 c respectively the submicron size clay fractions of the paleosols are presently composed of r3 ordered illite smectite i s inferred from k ar dates and soil morphology to have been authigenically produced by the reaction of smectite to illite oxygen isotope fractionations calculated pore fluid compositions and k ar dates were used to constrain the conditions and timing of i s and pedogenic calcite re crystallization in each of the paleosols the data were interpreted in light of three possible end member environments for formation and recrystallization 1 the pedogenic environment 2 the burial diagenetic environment and 3 a burial environment dominated by hot tectonically driven fluid the 18o values of pedogenic calcite and authigenic i s in vertic red bed paleosols generally reflect recrystallization and exchange during burial diagenesis and are thus not suitable for interpretation of paleoenvironment or paleoclimate the involvement of orogenic fluids during burial cannot be ruled out but it is not required by any of the paleosols in the coastal margin pennington formation paleosol i s formation may have been initiated in the pedogenic environment in response to cyclical wetting and drying of the soil clay matrix continued smectite transformation and coarsening and ordering of i s during a long period of shallow burial led to its isotopic reequilibration with pore fluids at slightly elevated temperature but oxygen isotope compositions of pedogenic calcite in the paleosol are preserved

the stable isotope composition of early ground water cements from sandstone in paleoecological reconstruction abstract the carbon isotope composition of soil carbonates in paleosols records the global expansion of cm4 biomass in the late miocene however soil carbonate is not present in many geological sections or if present is often difficult to distinguish from other carbonate cements here we report on the 13c values of sparry early ground water cements in sandstones from the siwalik group in pakistan that record like the soil carbonates from the same sections the dramatic late miocene expansion of c4 vegetation the early cements are confined to densely cemented nodules in the sandstones but can also be found reworked as nodules into adjacent paleo channels demonstrating their formation shortly after burial the early cements are isotopically distinct from later higher temperature calcite cements our results demonstrate that some early ground water cements can be used in a manner similar to soil carbonates to reconstruct vegetation and perhaps pco2 changes in the past

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

spatial and temporal uplift history of south america from calibrated drainage analysis a multi disciplinary approach is used to analyze the cenozoic uplift history of south america residual depth anomalies of oceanic crust abutting this continent help to determine the pattern of present day dynamic topography admittance analysis and crustal thickness measurements indicate that the elastic thickness of the borborema and altiplano regions is 10 km with evidence for sub plate support at longer wavelengths a drainage inventory of 1827 river profiles is assembled and used to investigate landscape development linear inverse modeling enables river profiles to be fitted as a function of the spatial and temporal history of regional uplift erosional parameters are calibrated using observations from the borborema plateau and tested against continent wide stratigraphic and thermochronologic constraints our results predict that two phases of regional uplift of the altiplano plateau occurred in neogene times regional uplift of the southern patagonian andes also appears to have occurred in early miocene times the consistency between observed and predicted histories for the borborema altiplano and patagonian plateaux implies that drainage networks record coherent signals that are amenable to simple modeling strategies finally the predicted pattern of incision across the amazon catchment constrains solid sedimentary flux at the foz do amazonas observed and calculated flux estimates match suggesting that erosion and deposition were triggered by regional andean uplift during miocene times

determining terrestrial paleotemperatures using the oxygen isotopic composition of pedogenic carbonate abstract quantifying terrestrial paleotemperatures has proven to be a challenging endeavor this paper explores the use of the oxygen isotopic composition of pedogenic calcite for terrestrial paleotemperature reconstructions we generate three paleotemperature equations two of them derived by simultaneous solution of equations that describe the fractionation of oxygen isotopes in the exogenic cycle while the third equation is derived using a linear regression through modern 18occ mat oxygen isotopic composition of pedogenic calcite versus mean annual temperature data we use the paleotemperature equations to evaluate climate change across the k t boundary by analyzing the oxygen isotopic composition of pedogenic carbonates from a series of stacked paleosols in west texas the fabrics in the calcite nodules were evaluated in order to identify soil carbonate components that have the best chance of containing isotopic information that represents ancient pedogenic conditions the average temperature for west texas during the time period studied is 18 0 5 c two temperature excursions are recognized prior to the k t boundary in which terrestrial temperatures increase by about 4 c for relatively short periods of time these short greenhouse events documented in west texas correlate with changes in marine temperatures as well as terrestrial temperatures in north dakota during the same time period latitudinal temperature gradients generated using the west texas and north dakota data indicate that the spatial simultaneous solution yields the most reliable temperature reconstructions of the three equations considered in this study

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

production storage and output of particulate organic carbon waipaoa river basin new zealand 1 we compute the particulate organic carbon poc yield of the waipaoa river new zealand using sediment rating curves in conjunction with measurements of the carbon content of the suspended sediment to ascertain the source of the carbon and the extent to which the poc flux is tied to different erosion processes we determined the stable isotopic carbon composition 13c and carbon to nitrogen c n ratio of weathered bedrock soil and regolith most poc is derived from suspended sediment generated by gully erosion incision into weathered bedrock supplemented by landsliding during extreme events the specific yield of poc from the headwaters drainage area 1580 km2 is 55 g m 2 yr 1 which is very high by global standards and by comparison with other turbid steep land rivers the annual loss to floodplain storage is 4 3 6 kt of the mean annual poc yield 86 7 kt thus the waipaoa river is a very effective conduit for transporting poc to the ocean

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

geochemical model of δ18o of pedogenic calcite versus latitude and its application to cretaceous palaeoclimate abstract in the absence of a systematic global data base on the 18 o composition of modern soil calcite predicted isotopic values are calculated as a function of latitude between 60 and 20 using 18 o of summer and winter meteoric water ambient soil temperature equal to either measured values in asia or mean annual temperature and 0 10 20 and 30 evaporation of soil water the results show overall higher isotopic values for summer versus winter precipitation but steeper positive slopes for the winter precipitation curves where soil temperature is equated to mean annual temperature the summer precipitation curves are nearly flat at high latitudes and have a negative slope at low latitudes in all cases the 18 o values increase with increasing percent evaporation of soil water oxygen isotopic data for early aptian and late maastrichtian cretaceous palaeosol calcite as a function of palaeolatitude of the western interior of north america plot in the modern winter precipitation field which along with vertic features may suggest a winter wet palaeoclimate steeper positive slopes for the cretaceous curves compared to the modern curves may be attributable to greater latitudinal gradients in mean annual temperature and soil temperature in the cretaceous compared to today and or to a greater degree of evaporation in cretaceous soils at low latitudes compared to the modern earth distinguishing between these possibilities will require a more complete understanding of the variables that affect oxygen isotopes in pedogenic calcite as well as better cretaceous terrestrial palaeoclimate proxies with which to compare the isotopic data

expansion of c4 grasses in the late miocene of northern pakistan evidence from stable isotopes in paleosols stable isotopic clay mineralogic and bulk chemical analyses were conducted on paleosols of the neogene siwalik sections in northern pakistan in order to reconstruct floodplain environments over the past 17 ma the stable carbon isotopic composition of soil carbonate mean 13c pdb 10 2 and associated organic matter mean 13c pdb 24 1 in paleosols representing 17 7 3 ma reveal that floodplain vegetation was dominated by c3 plants at 7 3 ma a shift toward more positive carbon isotopic values began signaling the gradual expansion of c4 grasses onto the floodplain from 6 ma to present carbon isotopic values for paleosol carbonate mean 13c pdb 0 6 and organic matter mean 13c pdb 14 4 are uniformly enriched in 13c indicating the presence of nearly pure c4 grassland the scarcity of kaolinite and abundance of smectite and pedogenic carbonate in most paleosols suggest that rainfall in the region remained 1 0 1 25 m yr or less for the entire 17 ma of record paleosols in the lower portion of the section lack organic a horizons but have reddish b horizons often containing secondary iron oxide nodules leaching depths of soil carbonate in these older paleosols are typically greater than those in the plio pleistocene part of the section where organic a horizons are common and b horizons are markedly more yellow the combined evidence suggests that the mature paleosols in the pre 7 3 ma part of the record are dominantly calcareous alfisols or mollisols that once underlay nearly pure c3 vegetation perhaps trees and shrubs while calcareous mollisols underlying c4 grassland dominate the upper part of the record the carbon and oxygen isotopic trends in the paleosol record in pakistan are also evident in the diet of fossil mammals and in paleosols from nepal thus demonstrating that these paleoenvironmental changes in floodplain vegetation may be continent wide local effects such as the development or intensification of the asian monsoon driven by uplift of the tibetan plateau may have led to the expansion of c4 grasses if however the expansion of c4 grasses proves globally synchronous then a larger scale cause such as a marked decrease in co2 may be the driving mechanism

stable isotopic results from paleosol carbonate in south asia paleoenvironmental reconstructions and selective alteration article i nfo we measured 18 o and 13 c values of paleosol carbonate nodules from a variety of sedimentary units in southern asia in order to reconstruct paleoenvironmental conditions and to evaluate for possible diagenetic alteration paleosol carbonate nodules were collected from lower to upper cretaceous strata exposed in two locations in southern tibet and from lower to middle miocene strata in northern india and nepal additional samples were collected from stratigraphically adjacent marine carbonate units to test for possible resetting of stable isotope values based on the implausibly low 18 o values 13 of most of the marine carbonate samples we interpret the 18 o values of the associated paleosol carbonate nodules as being reset and therefore unreliable for paleoenvironmental or paleoelevation reconstruction importantly the 18 o values of 13 c values of marine carbonate rocks fall within the expected primary

clumped isotope geochemistry the study of naturally occurring multiply substituted isotopologues clumped isotope geochemistry is concerned with the state of ordering of rare isotopes in natural materials that is it examines the extent to which rare isotopes d 13 c 15 n 18 o etc bond with or near each other rather than with the sea of light isotopes in which they swim abundances of isotopic clumps in natural materials are influenced by a wide variety of factors in most cases their concentrations approach within ca 1 relative the amount expected for a random distribution of isotopes deviations from this stochastic distribution result from enhanced thermodynamic stability of heavy isotope clumps slower kinetics of reactions requiring the breakage of bonds between heavy isotopes the mass dependence of diffusive and thermo gravitational fractionations mixing between components that differ from one another in bulk isotopic composition biochemical and photochemical fractionations that may reflect combinations of these simpler physical mechanisms and in some cases other processes we do not yet understand although clumped isotope geochemistry is a young field several seemingly promising applications have already emerged most importantly it appears that proportions of 13 c 18 o bonds in carbonate minerals are sensitive to their growth temperatures independent of bulk isotopic composition thus clumped isotope analysis of ancient carbonates can be used as a quantitative paleothermometer that requires no assumptions about the 18 o of waters from which carbonates grew this approach has been used to reconstruct marine temperatures across the phanerozoic reaching back to the silurian terrestrial ground temperatures across the cenozoic thermal histories of aqueously altered meteorites among other applications clumped isotope geochemistry is also placing new constraints on the atmospheric budget and stratospheric photochemistry of co 2 and should be capable of placing analogous new constraints on the budgets of other atmospheric gases finally this field could be extended to encompass sulfates volatile hydrocarbons organic moieties and other materials

response to comment on rapid uplift of the altiplano revealed through 13 c 18 o bonds in paleosol carbonates clumped isotope thermometry measurements of carbonate samples deposited in the bolivian altiplano as early as 28 5 million years ago and buried up to 5000 meters deep exhibit no relationship between burial depth and apparent temperature and largely yield temperatures within error of plausible earth surface conditions these results counter the predictions of sempere et al and support our previous conclusions regarding the uplift of the altiplano

13c18o clumping in speleothems observations from natural caves and precipitation experiments the oxygen isotope composition of speleothems is an important proxy of continental paleoenvironments because of its sensitivity to variations in cave temperature and drip water 18 o interpreting speleothem 18 o records in terms of absolute paleotemperatures and 18 o values of paleo precipitation requires quantitative separation of the effects of these two parameters and correcting for possible kinetic isotope fractionation associated with precipitation of calcite out of thermodynamic equilibrium carbonate clumped isotope thermometry based on measurements of 47 a geochemical variable reflecting the statistical overabundance of 13 c 18 o bonds in co 2 evolved from phosphoric acid digestion of carbonate minerals potentially provides a method for absolute speleothem paleotemperature reconstructions independent of drip water composition application of this new technique to karst records is currently limited by the scarcity of published clumped isotope studies of modern speleothems the only modern stalagmite reported so far in the literature yielded a lower 47 value than expected for equilibrium precipitation possibly due to kinetic isotope fractionation here we report 47 values measured in natural speleothems from various cave settings in carbonate produced by cave precipitation experiments and in synthetic stalagmite analogs precipitated in controlled laboratory conditions designed to mimic natural cave processes all samples yield lower 47 and heavier 18 o values than predicted by experimental calibrations of thermodynamic equilibrium in inorganic calcite the amplitudes of these isotopic disequilibria vary between samples but there is clear correlation between the amount of 47 disequilibrium and that of 18 o even pool carbonates believed to offer excellent conditions for equilibrium precipitation of calcite display out of equilibrium 18 o and 47 values probably inherited from prior degassing within the cave system in addition to these modern observations clumped isotope analyses of a flowstone from villars cave france offer evidence that the amount of disequilibrium affecting 47 in a single speleothem can experience large variations at time scales of 10 kyr application of clumped isotope thermometry to speleothem records calls for an improved physical understanding of dic fractionation processes in karst waters and for the resolution of important issues regarding equilibrium calibration of 47 in inorganic carbonates

rise of the andes the surface uplift of mountain belts is generally assumed to reflect progressive shortening and crustal thickening leading to their gradual rise recent studies of the andes indicate that their elevation remained relatively stable for long periods tens of millions of years separated by rapid 1 to 4 million years changes of 1 5 kilometers or more periodic punctuated surface uplift of mountain belts probably reflects the rapid removal of unstable dense lower lithosphere after long term thickening of the crust and lithospheric mantle

use of clumped isotope thermometry to constrain the crystallization temperature of diagenetic calcite we describe an approach to estimating the crystallization temperatures of diagenetic calcites using clumped isotope thermometry a paleothermometer based on the 13 c 18 o bond enrichment in carbonates application of this thermometer to calcified gastropod shells and calcite cements in an early eocene limestone from the colorado plateau reveals a record of calcite precipitation and replacement at temperatures varying from 14 to 123 c the early eocene host sediments were never deeply buried but they experienced a significant thermal pulse associated with the emplacement of a late miocene basalt flow the combination of independent constraints on thermal history with clumped isotope thermometry petrographic including cathodoluminescence observations and oxygen isotopic data provides an improved basis for estimation of the temperature and timing of diagenetic events and fluid sources the petrography and calcite 18 o values taken alone suggest that the aragonite to calcite transformation of gastropod shell material occurred simultaneously with early formation of cements and lithification of the matrix in the same sample however addition of clumped isotope thermometry demonstrates that this phase transformation of shell material occurred at temperatures of 94 123 c in a highly rock buffered microenvironment i e with the isotopic composition of fluid buffered by coexisting carbonate millions of years after lithification of the matrix and formation of initial low temperature 14 19 c calcite cements within shell body cavities clumped isotope temperatures in excess of reasonable earth surface conditions recorded by later formed cements demand that cement growth occurred in association with the lava emplacement our results illustrate the potential for clumped isotope thermometry to constrain conditions of diagenesis and guide interpretations that would not be possible on the basis of conventional stable isotopic and petrographic data alone and demonstrate how petrographic characterization of clumped isotope thermometry samples can benefit paleoclimate studies

testing the analytical protocols and calibration of volcanic glass for the reconstruction of hydrogen isotopes in paleoprecipitation in this study we investigate the foundations of the hydrated volcanic glass paleoelevation paleoenvironment proxy by testing 1 the sensitivity of volcanic glass d values to laboratory procedures 2 the reliability of young glass reconstructions of observed meteoric water values and 3 the paleoenvironmental reconstructions based on volcanic glass in comparison to those of other proxies volcanic glass d values are insensitive to variations in laboratory pretreatments displaying no signifi cant shift in d values with variations in duration of drying rinsing the temperature at which glass is dried or with the grain size that is analyzed however clay adhering to the glass particles may skew d results by 10 and hf acid pretreatment can cause signifi cant isotopic shifts parent water d values calculated from young 0 3 ma glass d values are in close accord with modern surface water d values across 3000 m of elevation in the central andes combined glass d values pedogenic carbonate 18 o values and clumped isotope paleothermometry from the 16 3 ma los cristales tuff provide a key test of resistance to resetting of d values in ancient glass hydration layers these proxies indicate hydrated volcanic glass preserves its stable isotopic information over geologic time and that the climatic patterns of the high and dry puna plateau were already in place by 16 3 ma

widespread hillslope gullying on the southeastern tibetan plateau human or climate change induced many drainage basins adjacent to the upper tsangpo valley on the southeastern tibetan plateau are pervasively gullied these gullies expose a stratigraphic record alternating between slow aggradation and stability i e soil development for much of the quaternary suggesting that gullying is recent and unprecedented within at least the past 10 100 k y in this paper we date the initiation of gullying at five sites in the region using optically stimulated luminescence osl we also test alternative hypotheses for gully initiation using numerical landform evolution modeling osl ages constrain the initiation of gullying to be mid to late holocene in age this period coincides with the onset of pastoralism in the upper tsangpo valley numerical modeling suggests that a reduction in vegetation density during the colder drier conditions of pleistocene glacial intervals did not trigger gullying because the reduction in vegetation density and hence rates of colluvial deposition in valleys coincided with an unusually dry period less capable of significant fluvial erosion from valleys as such low order valleys most likely did not incise prior to the mid to late holocene because an approximate balance was maintained between colluvial deposition and fluvial erosion vegetation changes associated with the onset of pastoralism however may have triggered gullying because such changes lowered the rate of colluvial deposition in valleys and or increased the rate of fluvial erosion in valleys the results of this paper provide insight into the ways in which drainage basins respond to climatic and anthropogenic perturbations in semiarid climates of moderate relief and underscore the dramatic landscape responses that can occur when geomorphic thresholds are crossed

δ13c of organic carbon in the bengal fan source evolution and transport of c3 and c4 plant carbon to marine sediments carbon isotopic measurements on organic carbon oc in sediment cores from the bengal fan odp leg 116 show a dramatic 10 increase beginning ca 7 ma ago and a rapid decrease after 0 9 ma these shifts reflect changes in the mixing ratio of terrigenous carbon derived from c3 and c4 plants the rapid increase in 13c of bengal fan oc at 7 ma shows that late miocene expansion of c4 plants already documented in the siwaliks was widespread over all the himalayan foreland after 7 ma relations of 13c with sedimentological parameters show that c4 plants dominate in the foreland whereas c3 plants remain abundant in the mountain range variations in the source of the sediments and of the oc appear to be sensitive to climate hydrologic conditions in the basin major changes in the isotopic composition of the carbon flux in one of the worlds largest river systems modify the isotopic budgets of both marine dissolved carbon and the sedimentary carbon mass

paleomagnetic chronology fluvial processes and tectonic implications of the siwalik deposits near chinji village pakistan a 2800 m section of siwalik strata containing the stratotypes for both the chinji and nagri formations has been dated by magnetic polarity stratigraphy and the observed polarity zonation has securely been correlated with the chron 17 7 segment of the time scale the base of the section is the base of the kamlial formation which occurs near the top of chron 17 18 3 m y the kamlial chinji formation boundary occurs in the middle of chron 15 14 3 m y the chinji nagri boundary near the bottom of chron 10 10 8 m y and the nagri dhok pathan boundary at the chron 8 9 boundary 8 5 m y the siwalik deposits near chinji village consist of four distinct classes of fluvial cycles each with a characteristic periodicity a first order of 10 7 years a second order of 10 6 years a third order of 10 4 10 5 years and a fourth order of 10 0 10 4 years the river system responsible for siwalik sedimentation flowed from west to east and had properties much like the modern ganges river syste

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

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

glacial interglacial temperature variations in soreq cave speleothems as recorded by clumped isotope thermometry clumped isotope thermometry is based on analyzing mass 47 in co2 extracted from carbonates and uses the tracer mass 47 anomaly 47 47 is defined as the deviation of r47 from that expected for a random distribution of isotopologues and reflects a temperature dependent preference of 13c and 18o to create a bond with each other in co2 or in the carbonate lattice being an internal characteristic of the carbonate mineral it is independent of the isotopic composition of the water in which equilibrium precipitation of the carbonate occurs and can therefore be used to independently determine carbonate growth temperatures this work provides a first examination of the applicability of clumped isotopes thermometry to reconstructing the growth temperatures of speleothems by examining the glacial interglacial variations of the 47 values of speleothem carbonates from soreq cave israel the results indicate that the last glacial maximum temperatures were 6 7 c colder than modern day temperature and a sample at 56 ky bp was 3 c colder than the modern early holocene temperatures were slightly above modern day and late holocene temperatures were slightly below modern day these temperature variations are similar to those previously estimated for eastern mediterranean sea surface water cave water was 18o depleted in the holocene compared to modern day by 0 6 1 and 1 1 more enriched in the last glacial maximum comparison of these cave water 18o values with fluid inclusion d values indicated a late holocene d excess value within the range of modern rainfall implying not vert similar45 relative humidity last glacial maximum and early holocene d excess values were significantly lower suggesting relative humidity of not vert similar60 and not vert similar70 respectively the temperatures reported in this study were empirically corrected for a non equilibrium artifact observed in a modern speleothem the similarity of the temperature variations obtained here to other independent records in the region suggests that the 47 temperature calibration slope observed in inorganic synthetic calcite and marine organisms may also be applied in speleothems but the offset observed in modern temperature suggests that the intercept is different so that a separate calibration is needed for accurate absolute temperature reconstruction using speleothem clumped isotopes similar examination of additional caves would be necessary to determine whether such empirical correction can be generally applied or is it a unique characteristic of soreq cave

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

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

the paleoaltimetry of tibet an isotopic perspective stable isotopes provide a valuable perspective on the timing of elevation change of the tibetan plateau we begin our paper by looking in depth at isotopic patterns in modern tibet we show that the 18 o value of surface waters decreases systematically up the himalayan front in central nepal by about 2 8 km in agreement with the patterns documented and modeled by previous research on the tibetan plateau itself there is no apparent correlation between elevation and the 18 o value of flowing surface waters both surface waters and soil carbonates display a northward increase in 18 o values of about 1 5 north of the himalayan crest even though elevation increases modestly the isotopic increase with latitude reduces the isotope elevation gradient for water in the northernmost plateau to 1 to 2 km carbonates in both soils and lakes form at higher temperatures than assumed by previous studies on the plateau temperature estimates from clumped isotope 47 analyses of modern soil carbonates significantly exceed mean annual air t and modeled maximum summer soil temperatures by 15 8 2 8 and 9 7 2 5 c respectively similarly elevated temperatures best account for the 18 o values observed in modern soil and lake carbonates we recalculated paleoelevations from previous studies on the plateau using both higher formation temperatures and latitude corrected isotopic values with one notable exception our revised model produces paleoelevation estimates very close to previous estimates the exception is the reconstruction from late eocene age deposits at xoh xil for which we calculate elevations that are higher and much closer to the current elevation than previously reconstructed therefore there is no evidence for northward progression through time of tibetan elevation change instead the available but admittedly very scanty evidence suggests that much of tibet attained its modern elevation by the mid eocene a truly robust test of the various geodynamic models of uplift await expansion and replication of isotopic records all across tibet especially in the center and north and for 15 ma