origin of high mountains in the continents the southern sierra nevada active and passive seismic experiments show that the southern sierra despite standing 1 8 to 2 8 kilometers above its surroundings is underlain by crust of similar seismic thickness about 30 to 40 kilometers thermobarometry of xenolith suites and magnetotelluric profiles indicate that the upper mantle is eclogitic to depths of 60 kilometers beneath the western and central parts of the range but little subcrustal lithosphere is present beneath the eastern high sierra and adjacent basin and range these and other data imply the crust of both the high sierra and basin and range thinned by a factor of 2 since 20 million years ago at odds with purported late cenozoic regional uplift of some 2 kilometers

stable isotope compositions of waters in the great basin united states 3 comparison of groundwaters with modern precipitation 1 groundwater samples from wells and springs scattered over most of the great basin province were collected and analyzed for their isotopic makeup they were augmented by previously published isotopic data on groundwaters from southeast california and by several hundred unpublished isotopic analyses the ratio of 2h deuterium d to 1h in water samples from valleys in parts of california idaho nevada oregon and utah are here compared with the winter summer and annual isotopic compositions of precipitation falling in or near the sampled areas the main goal of this study was to identify basins where the groundwaters have isotopic compositions that are lighter depleted in the heavier isotope d relative to modern winter precipitation where these basins do not adjoin substantially higher terrain we consider those light groundwaters to be of pleistocene age and thus more than 10 000 years old where the groundwater is 10 to 19 lighter than local winter precipitation we consider it to be possibly an indication of pleistocene water where the d makeup is 20 lighter we consider it to be probably pleistocene water more than 80 sites underlain by waters of possible or probable pleistocene age were identified

isotopic analysis of tooth enamel carbonate from modern north american feral horses implications for paleoenvironmental reconstructions the accuracy of paleoenvironmental reconstructions based on isotope analyses of equid teeth is currently uncertain because the exact relationship between the isotope composition of modern feral equids and their environment has not been thoroughly studied we analyzed the carbon and oxygen isotope values 13c and 18o of tooth enamel carbonate and the 13c values of fecal samples from modern feral horses we compared those values with the 13c values of local vegetation and the 18o values of local waters herds were studied in two contrasting localities eastern oregon where grasslands consisted of 100 c3 species and new mexico where 95 of the grasses were c4 species carbon isotope analyses of fecal material and tooth enamel suggest that horses consumed primarily grass but some new mexico horses also consumed significant amounts of shrubs and or forbs microhistological analyses of fecal samples show that oregon horses consumed 95 grass and oregon enamel 13c values are consistent with a diet containing 100 c3 plants microhistological analyses of fecal samples from new mexico indicate a diet averaging 75 grass while enamel 13c values suggest that diets averaged 85 c4 plants range 72 97 thus reconstructions of the c3 c4 ratio of grasses in ancient grasslands that are based on the 13c values of fossil equid teeth may underestimate the abundance of c4 grasses the mean 18o values of tooth enamel paralleled the trends observed in the mean 18o values of precipitation however the mean 18o values of enamel carbonate from oregon and new mexico differed by only 3 3 which is less than the difference in the mean 18o values of precipitation 6 5 in addition the range of 18o values within new mexico enamel samples 6 5 was greater than the difference between mean enamel 18o values at each site calculated values for the 18o of water ingested by horses are 2 3 more positive than mean 18o values for corresponding precipitation suggesting that horses consumed waters that were enriched in 18o due to evaporation while our results confirm that local climatic and hydrological conditions can influence the 18o values of equid enamel they also show that the 18o values of equid teeth are not always a direct proxy for the isotope ratios of precipitation

pace of landscape evolution in the sierra nevada california revealed by cosmogenic dating of cave sediments we report 26 al 10 be based ages of sierra nevada caves that constrain detailed late pliocene and quaternary river incision his tories for five river canyons rapid incision of 0 2 mm yr from 2 7 to ca 1 5 ma slowed markedly to 0 03 mm yr thereafter likely reflecting the combined effects of a transient erosional re sponse to pliocene rock uplift and periodic mantling of riverbeds with glacially derived sediment in the late quaternary while 400 m of incision has occurred in the past 2 7 m y outpacing interfluve erosion and thereby increasing the local relief canyons as deep as 1 6 km existed prior to that time these new erosion rates strength en the case for tectonically driven late cenozoic uplift

geomorphically driven late cenozoic rock uplift in the sierra nevada california geologists have long accepted that the sierra nevada california experienced significant late cenozoic tectonically induced uplift a flexural isostatic model presented here shows however that a large fraction of the primary evidence for uplift could be generated by the lithospheric response to coupled erosion of the sierra nevada and deposition in the adjacent central valley and therefore requires less tectonic forcing than previously believed the sum of range wide erosion and the resultant isostatic rock uplift would have lowered sierra mean elevation by 200 to 1000 meters since 10 million years ago and could also have increased summit elevations during the current period of relief production

amount effect recorded in oxygen isotopes of late glacial horse equus and bison bison teeth from the sonoran and chihuahuan deserts southwestern united states stable oxygen isotopes from fossils both vertebrate and invertebrate or inorganic sedimentary minerals frequently have been used to make interpretations about ancient global climates oxygen isotope values measured from terrestrial vertebrates or sedimentary carbonates provide information about paleotemperature and amounts of precipitation at a particular site in general these inferences are made on the centennial to millennial scale serial i e ontogenetic sampling of equus and bison tooth enamel provides climatic data on the scale of months to a few years we present models showing how annual environmental patterns of d 18 o would be replicated in the tooth enamel of equus and bison changes in d 18 o due to shifts in temperature in terrestrial environments d 18 o increases with increased temperature and amount and timing of precipitation increased precipitation may result in a decrease in d 18 o a phenomenon called the amount effect are archived in both equus and bison teeth the input signal is better resolved in bison due to its more rapid enamel growth modeled patterns are compared with actual data from modern sites in the sonoran and chihuahuan deserts of the southwestern united states the isotopic patterns from modern teeth agree with that predicted from known variations in meteoric water known floral and faunal assemblages as well as computer models suggest summer rain for the chihuahuan desert of late glacial time 15 000 10 000 years ago but little summer rain for the sonoran desert at that same time serial data from fossil teeth show a clear pattern interpreted to represent the amount effect that includes increased summer rains in the chihuahuan desert and only minor summer rains in the sonoran desert d 2004 elsevier b v all rights reserved

oxygen and hydrogen isotopes in the hydrologic cycle changes of the isotopic composition of water within the water cycle provide a recognizable signature relating such water to the different phases of the cycle the isotope fractionations that accompany the evaporation from the ocean and other surface waters and the reverse process of rain formation account for the most notable changes as a result meteoric waters are depleted in the heavy isotopic species of h and o relative to ocean waters whereas waters in evaporative systems such as lakes plants and soilwaters are relatively enriched during the passage through the aquifers the isotope composition of water is essentially a conservative property at ambient temperatures but at elevated temperatures interaction with the rock matrix may perturb the isotope composition these changes of the isotope composition in atmospheric waters surface water soil and groundwaters as well as in the biosphere are applied in the characterization of hydrological system as well as indicators of paleo climatological conditions in proxy materials in climatic archives such as ice lake sediments or organic materials

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

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

hydrogen isotopes in eocene river gravels and paleoelevation of the sierra nevada we determine paleoelevation of the sierra nevada california by tracking the effect of topography on precipitation as recorded in hydrogen isotopes of kaolinite exposed in gold bearing river deposits from the eocene yuba river the data compared with the modern isotopic composition of precipitation show that about 40 to 50 million years ago the sierra nevada stood tall 2200 meters a result in conflict with proposed young surface uplift by tectonic and climatic forcing but consistent with the sierra nevada representing the edge of a pre eocene continental plateau

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

paleobotanical evidence for high altitudes in nevada during the miocene leaf physiognomy provides estimates of environmental parameters including mean annual enthalpy which is a thermodynamic parameter of the atmosphere that varies with altitude analyses of 12 mid miocene floras from western nevada indicate that this part of the basin and range province stood 3 kilometers above sea level at 15 to 16 million years ago which is 1 to 1 5 kilometers higher than its present altitude much if not all of the collapse to present day altitudes seems to have been achieved by 13 million years ago the crust in much of this area has been extended and thinned throughout the past 40 to 50 million years and the isostatic balance of a thinning crust requires subsidence not uplift as suggested by previous paleobotanical work

the uplift of the sierra nevada and implications for late cenozoic epeirogeny in the western cordillera tilted cenozoic strata in the eastern great valley california record progressive late cenozoic uplift of the sierra nevada the magnitude of tilting is combined with other geologic data using a technique pioneered by grant and others to infer the rate and timing of post late miocene uplift between the kings river and the feather river angular unconformities of late neogene age have been reported throughout the east central great valley typically stratigraphic units of late oligocene through miocene pliocene age beneath the unconformities dip approximately 1 2 1 6 southwest middle to late pliocene units above the unconformities dip approximately 0 6 0 9 southwest and progressively overlap younger units from east to west these angular unconformities are interpreted to represent the onset of late cenozoic uplift of the sierra nevada due to westward tilting dated volcaniclastic units in the east central sacramento valley bracket the onset of tilting there between 3 4 and 8 4 ma stratigraphic and geologic relations from the stanislaus river area eastern san joa quin valley suggest that the late cenozoic tilting probably began approximately 5 ma previously published tilt data from the san joaquin valley combined with new work in the eastern sacramento valley indicate that the rate of post late miocene tilting has been approximately uniform in the east central great valley early to middle pleistocene units typically dip 0 5 0 7 southwest middle pleistocene units dip 0 2 0 4 middle to late pleistocene units dip 0 1 0 15 late pleistocene units dip 0 05 0 1 if it is assumed that major westward tilting began 5 ma these data indicate an approximately uniform tilting rate of 0 28 per million years these data have important implications for models of the uplift simultaneous inception of tilting in the east central great valley at approximately 5 ma does not support models that link uplift of the sierra nevada to the migration of the mendocino triple junction late cenozoic tilting of the sierra nevada block does not appear to coincide temporally with the onset of major basin and range extension the uplift may be due to thinning of the mantle lithosphere beneath the sierra nevada but the tilt data do not afford a direct test of this hypothesis post late miocene tilting of the sierra nevada is temporally associated with late cenozoic uplift of the northern basin and range uplift of the cascades uplift of the colorado plateau and uplift of the southern rocky mountains supporting the contention that tilting of the sierra nevada may have occurred as part of a cordillera wide uplift event

biomarker reconstruction of the early eocene paleotopography and paleoclimate of the northern sierra nevada we reconstruct ancient temperature and elevation gradients across the early eocene 52 49 ma northern sierra nevada california united states using organic molecular proxies that record atmospheric and ground level effects of topography paleoelevation was determined by reconstructing the change in the hydrogen isotopic composition of precipitation d precip and mean annual temperature t gdgt glycerol dialkyl glycerol tetraethers from the isotopic composition of fossil angiosperm leaf n alkanes and the distribution of microbially produced soil tetraethers preserved in leaf bearing sediments organic molecular data produce equivalent range scale d n alkane and channel t gdgt paleoelevation estimates that show the northern sierra nevada was a warm 6 8 c warmer than modern high elevation 2 km and moderate to low relief landscape at the eocene climatic optimum modern northern sierra nevada topography likely refl ects post paleocene reduction of mean surface elevation and late cenozoic increases in relief

evidence for rapid climate change in north america during the latest paleocene thermal maximum oxygen isotope compositions of biogenic phosphate from the bighorn basin wyoming oxygen isotope records of cenozoic sea water temperatures indicate that a rapid warming event known as the latest paleocene thermal maximum lptm occurred during the otherwise gradual increase in world temperatures during the late paleocene and early eocene oxygen isotope analysis of the carbonate and phosphate components of hydroxyapatite found in mammalian tooth enamel and body scales of river dwelling fish from the bighorn basin in wyoming were made to investigate corresponding changes in the terrestrial climate a comparison of carbonate and phosphate isotope data from modern and fossil material indicates that some diagenetic alteration of the fossil material has occurred although systematically larger intra tooth ranges in the oxygen isotope composition of carbonate indicate that it is more likely to have been affected than phosphate carbonate and phosphate from the ecologically diverse mammals and fishes both record a shift to higher oxygen isotope ratios at the same time and of the same duration as the lptm these shifts reflect a change in the isotopic composition of regional precipitation which in turn provides the first evidence for continental climate change during the lptm assuming the present day relation between the oxygen isotope composition of precipitation and temperature applies to conditions in the past and that animal physiology and behavior is relatively invariant over time the isotopic shift is equivalent to an increase of surface temperature in western north america of several degrees this result is consistent with the magnitude of high latitude ocean warming and provides a basis for relating marine and terrestrial oxygen isotope records to records of terrestrial biotic change 1998 elsevier science b v all rights reserved

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

geometric scale invariance genesis and self organization of polygonal fracture networks in granitic rocks abstract we documented polygonal fracture networks in the tuolumne intrusive suite sierra nevada batholith by collecting data on the size orientation and length of fractures and fracture bound polygons in nearly isotropic granitic rocks polygonal fracture networks are constrained to sheets of rock sub parallel to the underlying rock with the sheets bound above and below by fractures i e free surfaces data indicate that most geometric characteristics of the polygonal fracture networks are scale invariant large m scale networks exhibit the same geometry as small cm scale networks a linear correlation exists between sheet thickness and average polygon size polygons within the networks are anisotropic with the degree of anisotropy correlated with the degree of sheet curvature the preferred orientation of the polygons correlates with the inclination of the sheet with long axes of polygons parallel to sheet strike based on geometry we suggest that the polygonal fracture networks in granitic rocks observed in this study formed from temperature fluctuations that caused thermal expansion and contraction in the rock repeated cycles of expansion contraction led to the initiation and propagation of fractures within the network we propose that the observed fracture patterns are not a product of extrinsic conditions but rather a product of interactions between fractures implying that the polygonal fracture networks are self organizing systems

correlation between the oxygen isotope ratio of north american bison teeth and local waters implication for paleoclimatic reconstructions abstract the oxygen isotope ratios of tooth enamel carbonate from 64 north american bison bison bison from eleven locations were measured the mean enamel oxygen isotope ratios for bison populations ranged from 28 3 to 15 9 smow and correlated well with the annual mean oxygen isotope ratios of local surface waters and precipitation the standard deviation of oxygen isotope values among different individuals within each bison population averaged 1 0 and ranged from 0 7 to 1 4 the variability of enamel oxygen isotope ratios was not significantly different among different populations and did not correlate with changes in temperature precipitation or relative humidity these results demonstrate that the average oxygen isotope values of bison tooth enamel can be used for use as a quantitative proxy for reconstructing the values of surface waters and therefore may provide valuable paleoclimatic information this study provides a baseline comparison for analyses of the oxygen isotope ratios of bison and other large herbivores from across north america

dating topography of the sierra nevada california using apatite u th he ages the upward motion of rock masses relative to the earth s surface has been documented for most of the main mountain belts using thermochronological and petrological techniques more fundamental to the physical processes of mountain building however is the motion of the earth s surface itself which remains elusive here we describe a technique for estimating the age of topographic relief by mapping the low temperature thermal structure imparted by river incision using the ages of apatites determined from their uranium thorium and helium contents the technique exploits horizontal variations in temperature in the shallow crust that result from range normal river drainages because cooling beneath ancient river valleys occurs earlier than beneath intervening ridges our results from the sierra nevada california indicate that two of the modern transverse drainages the kings and the san joaquin had developed deep canyons by the late cretaceous period suggesting that the high topography of the range is 50 60 million years older than generally thought

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

atmospheric flow patterns around the southern alps of new zealand and implications for paleoaltimetry the development of relief may generate leeside rain shadows where precipitation 18o values are lower due to rainout on the windward side the magnitude of lowering in paleo 18o sampled from the leeside of a mountain range should at least in principle be related to the elevation of the mountain range in order for leeside proxies to record the highest elevations the majority of air masses need to travel up and over the ridge crest before raining out on the leeside if atmospheric flow patterns around the mountain range are dominated by flow deflection air masses that reach the leeside are less likely to record the highest elevations using the weather research and forecasting model and hybrid single particle lagrangian integrated trajectory hysplit model we demonstrate that modern atmospheric flow patterns in the southern alps of new zealand are not dominated by flow deflection the lack of flow deflection around the southern alps and the relatively low relief throughout the uplift history supports the use of leeside isotope records to constrain the timing of uplift and that uplift likely occurred 5 ma based on leeside isotope records in contrast orogens that are characterized by high elevations and strong flow deflection like the sierra nevada of california may not be good candidates for leeside isotope based paleoaltimetry studies ideal candidates for such studies should be characterized by relatively low elevations low atmospheric flow deflection and relatively low relief throughout the period of uplift

the chronology of cenozoic volcanism and deformation in the yerington area western basin and range and walker lane high precision 40 ar 39 ar isotopic ages obtained from cenozoic volcanic rocks and subvolcanic intrusions document the age of initiation and the temporal evolution of extensional and strike slip faulting in the western basin and range province in the northern wassuk range faulting began between ca 26 and 24 7 ma both normal and strike slip faults are bracketed between 23 1 and 22 2 ma and between 15 and 14 ma these ages document inception of the ancestral walker lane a northwest trending zone of right transtensional faulting in western nevada that separated extending crust on the east from the unextended sierra nevada block on the west at lat 39 n we speculate that the southwesterly migrating episodic oligocene early miocene east west extensional faulting in the basin and range thinned and weakened the crust allowing right slip faults to develop in the walker lane in response to san andreas right shear in california southwest of the walker lane there was no faulting prior to 15 ma here in the yerington district andesitic magmatism began at ca 15 ma and was followed by 150 east west extension along closely spaced 1 2 km normal faults with up to 4 km of offset each proffett 1977 these faults tilted older cenozoic rocks 35 40 w our new 40 ar 39 ar ages substantially revise earlier k ar ages of the timing of extension and establish that andesite lava flows cut by normal faults are 13 8 15 ma and that these faults are intruded by 12 6 13 0 ma dacites rapid extension is thus bracketed to a 0 7 1 7 m y interval at 95 confidence indicating local east west strain rates of 2 4 10 14 s 5 10 mm yr following this period lower rates of extension prevailed near yerington along more widely spaced normal oblique slip faults that localized clastic sedimentation of the wassuk group between 11 and 8 ma these faults and sedimentary rocks are more abundant southwest of yerington in a belt parallel to the walker lane in previously little extended crust from 7 ma to present normal right oblique slip faults with a lower rate of extension than the previous two periods produced the modern ranges near yerington and extend 100 km southwest of the walker lane which continues to be the locus of strike slip faulting thus since 15 ma the margin of the basin and range has moved progressively 100 km west creating the broad walker lane belt and lower strain rates near yerington

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

fossil isotope records of seasonal climate and ecology straight from the horse s mouth isotope analysis of a bulk fossil tooth gives a snapshot impression of paleoclimatic conditions a single point in time however hypsodont teeth grow over a period of a year or more so that stable carbon and oxygen isotope variations along their length are a tape recorder of short term seasonal variations from the distant past we have used a new in situ micro laser sampling method to determine submillimeter carbon and oxygen isotope variations in the enamel of individual fossil horse teeth to assess ancient annual meteoric water variations and feeding patterns the 18o values from a 6 8 ma fossil horse tooth astrohippus ansae from texas vary cyclically along the 6 cm length of the tooth with a smoothed amplitude of 4 similar to the monthly averaged amplitude measured in modern meteoric waters from the region the seasonal 18o values are 3 to 4 higher than those calculated from modern meteoric water data suggesting either a higher local meteoric water value in the miocene of texas or that the animal received a high proportion of its dietary water from plants or highly evaporated water a holocene horse tooth from the shores of glacial lake agassiz north dakota equus sp also has isotopic variations with the same 35 mm periodicity but a smoothed amplitude of only 2 this horse most likely had a buffered drinking supply the calculated 18o of the water in equilibrium with this tooth is the same as the modern measured annual average the variations within a single tooth can be as large as those generally observed in entire stratigraphic sections of fossil teeth analyzed by bulk methods the new method provides an important technique for evaluating fossil diagenesis conventional bulk analyses of teeth fragments may not be representative of the whole tooth thus explaining analytical scatter that has been previously attributed to diagenesis

paleovalley morphology and fluvial system evolution of eocene oligocene sediments auriferous gravels northern sierra nevada california implications for climate tectonics and topography in the northern sierra nevada california eocene oligocene fluvial sediments the auriferous gravels rest unconformably in well defined basement incised paleovalleys providing a record of paleolandscape geomorphology and drainage system evolution paleovalley surface mapping shows that local topography and bedrock lithology controlled the location of broad terraced paleovalley segments which formed in the central and eastern metamorphic bedrock belts and subsequently became areas of significant fluvial deposition high gradient high energy deposits are present near the edges of these areas suggesting that tributaries and outlets resided in steeper narrow paleovalleys multiple strath terraces are common in broad paleovalleys indicating that incision events occurred both before deposition and during paleovalley widening followed by periods of aggradation broad paleovalley deposits contain predominantly braided stream facies deposited in an energetically variable system multiple upward fining cycles bounded by erosional surfaces are composed of alternating coarse grained channel belt and fine grained floodplain packages an overall upward fining succession suggests that the locus of fluvial deposition shifted and depositional energy waned over time as the system backfilled successive broad paleovalleys paleochannel slope estimates of 0 004 0 055 were obtained based on average grain sizes of coarse channel fills anomalously thick up to 11 m laterally continuous 1 3 km floodplain units containing kaolinite rich clay and oxisol intervals record high fine grained sediment supply driven by high rates of chemical weathering in the warm eocene climate based on sedimentary characteristics combined with floral and detrital zircon data braided stream deposition within the basin occurred from the late early eocene through late eocene and aggradation primarily occurred in broad lower gradient reaches behind a major bedrock knickpoint created in the late mesozoic early cenozoic possibly due to asymmetric batholith unroofing the diachronous localized nature of paleovalley incision and braided stream aggradation within the northern sierra nevada invalidates previous estimates of the timing and amount of range uplift based on paleochannel reconstructions and gradients both internal and external drivers influenced the evolution of the fluvial system through 1 the pattern of basin filling as the locus of deposition migrated east to west 2 the warm eocene climate which increased chemical weathering and contributed a high sediment supply and 3 changes in base level due to eustasy and or laramide tectonism this record of laramide tectonics in the sierra nevada and basin and range is important for the timing of sierra nevada uplift for tectonic reconstructions of western north america and for studies of landscape evolution in tectonically active orogens

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

regional variations in bulk chemistry mineralogy and the compositions of mafic and accessory minerals in the batholiths of california we define regional variations in mafic and accessory mineral assemblages and compositions and expand the current understanding of spatial variations in whole rock geochemistry in the batholiths of california in so doing we gain new insights into the nature of magmatic source rocks and mechanisms of magma generation in volcano plutonic arcs of active continental margins little studied metaluminous to strongly peraluminous granites containing fe rich biotite with log x mg x fe f oh and mn in biotite and amphibole increase on a regional scale from western i wc types to eastern i mc and i sc types parallel to eastward increases in incompatible elements and decreases in compatible elements in the plutons in contrast the belts of western i scr granites and eastern i wc quartz diorites and granodiorites disrupt the regional west to east systematics in both mineral and whole rock geochemistry spatial variations in the al content of amphibole are regional in scale and reflect pressures of pluton crystallization we conclude that significant previously unrecognized complexity exists in regional geochemical systematics in the california batholiths

spatial and temporal variations in the isotopic composition of bison tooth enamel from the early holocene hudson meng bone bed nebraska the hudson meng bone bed in northwestern nebraska is an early holocene deposit of hundreds of bison of divering ages that were killed in a catastrophic event of unknown origin the m 1 m 2 and m 3 molars of individuals ranging from ca 1 to 7 years of age at the time of their death were examined to determine inter and intra tooth isotopic variability and to link this variability to time in order to better understand the environments that existed prior to the mass death event the d13c value of molar structural carbonate increases by 2 3 from the m 1 to m 3 molars reflecting increasing direct forage signals and decreasing maternal influences the d18o value of molar structural carbonate in a given individual shows no consistent trend with time from birth indicating a fairly direct linkage to dietary water regardless of tooth ontogeny detailed down tooth isotopic measurements indicate a small seasonal signal in the d13c value of forage maternal milk which appeared to have been largely dominated by c 4 flora in contrast there was almost a 10 range in the isotopic composition of dietary water a range that is within present day summer versus winter precipitation in the region the d18o value of bulk tooth enamel arranged by approximate time prior to the death event indicate a consistent increase in the d18o value of body water 2 3 suggesting a long term decrease in winter spring precipitation and or drought the d18o trend with time coupled with the high c 4 grass abundance suggest environmental stresses on the herd preceding the catastrophic death event 2000 elsevier science b v all rights reserved

stable isotope constraints on the elevation history of the sierra nevada mountains california research on the uplift history of the sierra nevada mountain range has yielded seemingly conflicting results some studies argue for substantial uplift within the past 3 5 m y others suggest that high elevations may have existed since the cretaceous the rain shadow across the sierra nevada is associated with a strong isotopic gradient with lower 18o values in precipitation on the leeward side of the range reconstruction of the 18o value of meteoric water as a monitor of paleoelevation has focused mainly on the leeward side of the sierras but interpretation of the results of these studies may be complicated by shifts in global climate and regional moisture sources we address these concerns by analyzing the 18o value of tooth enamel bioapatite from contemporaneous mammalian fossils on either side of the present sierra range by sampling across the range 18o differences induced by a rain shadow can be isolated from other complicating factors our results indicate that the sierra rain shadow has existed since at least 16 ma which is an important constraint on models for the tectonic evolution of the western united states unfortunately temporal resolution for localities is too coarse to differentiate between glacial and interglacial localities during the past 2 m y so we cannot evaluate if there was a latest cenozoic pulse of uplift or elevation loss

paleobotanical evidence of eocene and oligocene paleoaltitudes in midlatitude western north america comparisons of the physiognomy of leaves from modern vegetation of known climates with that of eocene and oligocene fossil leaf assemblages from middle latitudes of western north america indicate paleoaltitudes comparable or higher than those at present using canonical correspondence analysis a multivariate statistical approach that includes nonlinear relationships between characters and environmental parameters we relate leaf physiognomy of fossil samples to modern vegetation of known environmental parameters including moist enthalpy of the atmosphere a thermodynamically conserved quantity of the atmosphere that varies with altitude by estimating enthalpy values for both lowland leaf assemblages and coeval interior leaf assemblages altitudes for the interior assemblages can be estimated to 890 m in northeastern washington and southern british columbia the high eocene altitudes indicate subsidence or collapse of an area undergoing crustal extension and may reflect an immediately preceding period of uplift that triggered the extension similarly other areas that have undergone cenozoic crustal extension appear to have been at least as high as they are at present three sites from the rocky mountains also indicate elevations at least as high as at present and therefore suggest subsidence either resulting from cooling of a hot upper mantle or erosion and isostatic compensation of surrounding terrain high altitudes during eocene and oligocene time in western north america appear to have been normal even in areas such as the green river basin and therefore cast doubt on the commonly inferred late cenozoic uplift of that region

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

old neogene summer dry soils with ultramafic parent materials abstract old strongly weathered soils that have developed from ultramafic or serpentine parent materials in summer dry temperate climates are sparse five serpentine soils with kandic horizons have been described and sampled in summer dry coniferous forests of northern california and southwestern oregon although the dispersion of clay in the subsoils is difficult and they are neither very sticky nor very tough 1 5 mpa water retention indicates that all but one have at least 50 clay and two of them have subsoils with about 85 clay thus the effective cecs in the bt horizons are much kg of clay and at ph 7 cecs are much kg of clay the kandic horizons are moderately to slightly acid and net positive charges occur in four of them in all of the soils the kcl extractable acidity is negligible variable charge ph 7 0 to 8 2 in the subsoils is closely related to free iron contents that range from 14 to 33 fe 0 33 g g even though all five of the soils have kandic horizons only in three of them have basic cations been leached deeply enough for the soils to be ultisols rather than alfisols magnesium is the dominant basic cation in the soil parent materials and it remains the dominant cation in the subsoils although ca has replaced it as the dominant exchangeable cation in surface soils intensive weathering to develop kandic horizons appears to be more prevalent than intensive deep leaching of basic cations in these summer dry soils with mesic soil temperature regimes because the major minerals in serpentinized peridotite are highly susceptible to weathering kandic horizons may form in them within one or two million years

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

isotopic reconstruction of past continental environments abstract vertebrate fossils and continental sediments provide a rich record of variations in the isotopic composition of surface environments to interpret these records a greater understanding of isotopic sources as well as fractionations associated with animal physiology soil geochemistry and diagenesis has been essential tooth enamel and fish otoliths yield subannual records of surface environments whereas soil minerals may integrate signals over many thousands of years carbon isotope variations in fossil vertebrates and soils record changes in the structure of vegetation and the isotope composition and concentration of atmospheric co2 oxygen isotope variations may be indirectly related to climate through reconstruction of the oxygen isotope composition of meteoric water or directly related to temperature through application of oxygen isotope paleothermometry to soil minerals or otoliths in africa nitrogen isotope variations show promise as a proxy for rainfall abundance though the gen

microplate capture rotation of the western transverse ranges and initiation of the san andreas transform as a low angle fault system tectonic rotation of the western transverse ranges block is explained by capture of the partially subducted monterey microplate by the pacific plate at about anomaly 6 time ca 20 ma as pacific monterey spreading slowed and eventually ceased the slip vector along the gently northeast dipping subduction interface beneath the california margin changed from slightly oblique subduction to transtensional dextral transform motion this change in slip vector and a shift of pacific plate motion eastward along the already subducted monterey plate interface imply that the san andreas transform began as a system of low angle faults that locally subjected the overriding continental margin to distributed basal shear and crustal extension this basal shear produced the rotated western transverse ranges this model helps explain the timing of initial rotation and basin formation the sudden appearance of widely distributed transform motion well inland of the margin in early miocene time why the western transverse ranges uniquely rotated as a large coherent crustal block and several fundamental structural characteristics of central and southern california the model also provides major constraints on the amount of pacific north america strike slip motion the position through time of offshore oceanic plates relative to onshore geology and a general explanation for what may happen as a spreading ridge approaches a trench and the subduction zone evolves into a transform system

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

andean scale highlands in the late cretaceous cordillera of the north american western margin from the late jurassic through the cretaceous collision between the north american and farallon plates drove extensive thin skinned thrusting and crustal shortening that resulted in substantial relief in the north american cordillera the elevation history of this region is tightly linked to the tectonic climatic and landscape evolution of western north america but is not well constrained here we use an atmospheric general circulation model with integrated oxygen isotope tracers isocam3 to predict how isotope ratios of precipitation would change along the north american cordillera as the mean elevation of orogenic highlands increased from 1200 m to 3975 m with increases in mean elevation highland temperatures fall monsoonal circulation along the eastern front of the cordillera is enhanced and wet season generally spring and summer precipitation increases simulated oxygen isotopic ratios in that precipitation are compared to those obtained from geologic materials e g fossil bivalves authigenic minerals quantification of match between model and data derived 18o values suggests that during the late cretaceous the best approximation of regional paleoelevation in western north america is a large orogen on the scale of the modern andes mountains with a mean elevation approaching 4000 m and a north south extent of at least 15 of latitude

rates of erosion and topographic evolution of the sierra nevada california inferred from cosmogenic26al and10be concentrations concentrations of cosmogenic 26 al and 10 be in cave sediments and bedrock surfaces combined with studies of landscape morphology elucidate the topographic history of the southern sierra nevada over the past 5 ma caves dated by 26 al 10 be in buried sediments reveal that river incision rates were moderate to slow between c 5 and 3 ma 0 07 mm a 1 accelerated between 3 and 1 5 ma c 0 3 mm a 1 and then have subsequently become much slower c 0 02 mm a 1 although the onset of accelerated incision coincides in time with both postulated pliocene tectonism and pronounced global climate change we argue that it primarily represents the response to a discrete tectonic event between 3 and 5 ma dated cave positions reveal that prior to 3 ma river canyons displayed up to 1 6 km of local relief suggesting that pliocene rock uplift elevated pre existing topography renewed incision beginning c 3 ma deepened canyons by up to 400 m creating narrow inner gorges tributary streams exhibit strong convexities indicating that the transient erosional response to pliocene uplift has not yet propagated into upland surfaces concentrations of 26 al and 10 be in bare bedrock show that upland surfaces are eroding at slow rates of c 0 01 mm a 1 over the past c 3 ma upland surfaces eroded slowly while adjacent rivers incised rapidly increasing local relief although relief production probably drove at least modest crestal uplift considerable prepliocene relief and low spatially averaged erosion rates suggest that climatically driven rock uplift is not sufficient to explain all uplift implied by tilted markers at the western edge of the range despite the recent pulse of erosion spatially averaged erosion rates are low and have probably acted to preserve the broad topographic form of the sierra nevada throughout much of the late cenozoic copyright 2005 john wiley sons ltd

investigation of early eocene water vapor transport and paleoelevation using oxygen isotope data from geographically widespread mammal remains the oxygen isotope composition 18 o of apatite from mammalian tooth enamel can be used to infer the 18 o value of ingested water which is in turn related to that of precipitation stored in surface reservoirs therefore the 18 o value of phosphate from fossil tooth enamel can be used to infer the 18 o value of these reservoirs in the past in this paper tooth enamel from a semiaquatic mammal taxon coryphodon collected from five early eocene localities in north america is used to construct patterns in 18 o values of river water for this time period at all localities the 18 o value of river water 18 o r is estimated to have been higher during the early eocene relative to present day north american rivers although the 18 o vs latitude gradient was shallower during the eocene higher 18 o r values are consistent with warmer eocene air masses being able to hold more water vapor and with an increase in the poleward transport of both moisture and latent heat the regular decrease in 18 o r with latitude indicates that global atmospheric circulation patterns and hydrological transport were not much different from those of the present although the shallower 18 o vs latitude gradient during the eocene may reflect regional differences in precipitation evaporation and river recharge at a more regional scale the 18 o value of river water can provide insight into topographic relief during the early eocene in the case of intermontane basins of wyoming differences in average 18 o r values between basins indicate that laramide mountain relief was on the order of 475 m it is suggested that anomalously low 18 o r values reported previously do not provide unambiguous evidence for permanent snow at higher elevations and may instead reflect brief episodes of cooler winters and or altered atmospheric circulation patterns

tectonics of pliocene removal of lithosphere of the sierra nevada california pliocene ca 3 5 ma removal of dense eclogitic material under the sierra nevada has been proposed from variations in the petrology and geochemistry of neogene volcanic rocks and their entrained xenoliths from the southern sierra the replacement of eclogite by buoyant warm asthenosphere is consistent with present day seismologic and magnetotelluric observations made in the southern sierra a necessary consequence of replacing eclogite with peridotite is that mean surface elevations and gravitational potential energy both increase an increase in potential energy should increase extensional strain rates in the area if these forces are insuffi cient to signifi cantly alter pacifi c north american plate motion then increased extensional strain rates in the vicinity of the sierra must be accompanied by changes in the rate and style of deformation elsewhere changes in deformation in california and westernmost nevada agree well with these predictions existing geologic evidence indicates that a period of rapid uplift along the sierran crest of more than 1 km occurred between 8 and 3 ma most likely as a consequence of removal of lower lithosphere about this same time extensional deformation was initiated within 50 km of the eastern side of the sierra 5 3 ma and regional shortening began to produce the california coast ranges 5 3 ma we suggest that these events were induced by the 1 2 10 12 n m increase of gravitational potential energy generated by the sierran uplift evidence for pliocene uplift adjoining crustal extension and shortening in directly opposing parts of the coast ranges is found along nearly the entire length of the sierra nevada and implies that lithosphere was removed beneath all of the presentday mountain range the uplifted area lies between two large upper mantle high pwave velocity bodies under the south end of the san joaquin valley and the north end of the sacramento valley these high velocity bodies plausibly represent the present position of material removed from the base of the crust lithospheric removal may also be responsible for shifting of the distribution of transform slip from the san andreas fault system to the eastern california shear zone a prediction that awaits better defi ned slip histories on both faults overall the late cenozoic deformational history of the sierra nevada and vicinity illustrates that locally derived forces can infl uence deformation kinematics within plate boundary zones

influences of dolomite precipitation on quartz surface textures abstract scanning electron microscopic examination of surface textures of quartz grains digested from dolomite cemented sandstones and sandy dolostones revealed that dolomite precipitation can affect quartz surfaces by 1 impeding syntaxial quartz overgrowth precipitation and 2 causing detrital quartz dissolution both of these processes resulted in the formation of dolomite rhombohedron shaped molds on quartz grain surfaces which are diagnostic for the recognition of secondary porosity formed by cement dissolution precipitation controlled dolomite replacement of quartz along euhedral dolomite crystal faces is consistent with the force of crystallization controlled replacement model some dolomite cement precipitation occurs without noticeable alteration of quartz grain surfaces dolomite c mentation is also associated with surface reaction controlled dissolution textures that may have formed by either 1 host grain controlled replacement of quartz by dolomite or 2 void filling dolomite precipitation into etch pits formed by earlier quartz dissolution in undersaturated bulk pore waters

stream incision tectonics uplift and evolution of topography of the sierra nevada california abstract stream incision faulting thermochronologic and geobarometric data suggest that sierra nevada topography is a consequence of two periods of uplift stream incision of up to 1 km has occurred since 5 ma maximum eocene miocene incision was 150 m uplift of the sierra nevada westward tilting stream incision and east down normal and dextral faulting along the present eastern escarpment of the range began at 5 ma estimates of late cenozoic crestal rock uplift for different areas in the sierra nevada range from 1440 to 2150 m low summit erosion rates suggest that the rock uplift approximates the surface uplift of crestal summits tertiary stream gradients were lower than modern ones suggesting that the bottoms of the canyons have been uplifted in the late cenozoic and that the mean elevation of the sierra nevada has increased the elevation of pre cenozoic basement rocks above the base of tertiary paleochannels ranges from 1000 m in the south and

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

oxygen isotopic composition of fossil equid tooth and bone phosphate an archive of difficult interpretation abstract variation in the concentration of the stable isotopes of hydrogen oxygen and carbon have been tested in continental records as tools for quantitative or semi quantitative paleoclimatological studies among the different methods the potential use of oxygen isotopes in mammal bone and tooth phosphate has recently been recognized measurements carried out on fossil mammal bones of holocene age and their paleoclimatological interpretation corresponded well with paleontological and paleobotanical records in the case of considerably older fossils diagenetic processes may change the primary oxygen isotopic composition of phosphate fossil horse bones and teeth principally of the species equus stenonis were studied to ascertain how far back in time fossil mammal remains may be considered reliable material for paleoclimatological studies the samples come from 13 different locations in southeastern spain their age ranging from maspinian late pleistocene to middle villafranchian pliocene apart from the variations of the 18o po43 values which may be related to climatic changes it is apparent that the isotopic composition of bones and teeth from the same deposit are frequently rather different from one another the isotopic differences range from a few tenths of one to several this suggests a strong influence of taphonomy over the measured isotopic values of fossils in each deposit time can be considered neither the only variable nor the most important one responsible for the change of the primary isotopic composition of fossils under these conditions it is rather difficult to establish lower or upper limits for the age of fossils to be studied for reliable paleoclimatological information since the limits are directly related to taphonomic history this in turn is related to local environmental conditions and not only to the age of fossils

deep structure and structural inversion along the central california continental margin from edge seismic profile ru 3 deep penetration seismic reflection profile ru 3 crosses the central california continental margin revealing a subducted oceanic plate a modified accretionary prism and complex structures of the overlying sedimentary basins this structural framework was established by subduction processes during paleogene and earlier time and subsequently was modified by neogene transform motion combined with apparent components of extension and compression subducted rocks are indicated by deep gently dipping reflectors that extend beneath the continental margin for at least 38 km at a depth of about 15 km we interpret the subducted crust as either a part of the pacific plate or more likely a subducted fragment derived from the farallon plate a set of more steeply dipping deep events may indicate faulting within the subducted plate or its boundary with a no slab zone the overlying largely nonreflective layer of accreted material rapidly reaches 10 km in thickness landward of the paleotrench and increases to 15 km in thickness near the coast the santa lucia basin landward of the steep continental slope originated as a slope basin during paleogene subduction the lower strata of this basin were deposited onto and partially incorporated into the accretionary complex the offshore santa maria basin exhibits a variety of compressional structures that formed in the last 3 5 m y and whose locations correspond to an earlier framework of extensional faults structural inversion has occurred in miocene depocenters adjacent to the santa lucia bank fault and at the queenie structure miocene and lower pliocene strata also thicken toward the hosgri fault zone where subsequent compression is characterized by low angle thrusts and folding

a model of fossil tooth and bone diagenesis implications for paleodiet reconstruction from stable isotopes abstract diagenesis of structural carbonate in biogenic apatite in the postmortem environment is modeled as a process of water mineral interaction both closed and open system model calculations suggest that 13 c of structural carbonate in biogenic apatite is much more resistant to diagenetic modification than 18 o apatite structural carbonate retains an original 13 c signal in closed system diagenesis for open systems 13 c of biogenic apatite with very low porosity such as tooth enamel can survive most diagenesis and retain a primary isotopic signature on the hand 18 o of structural carbonate in biogenic apatite may not be a reliable indicator of the original isotopic ratios except in a diagenetic system with low temperature and very low water biomineral ratio application of the model to teeth and carbonate cement in sediments from the badlands south dakota illustrates that 13 c values of enamel samples preserve the original signal whereas 13 c values of dentine represent varying extents of diagenesis 18 o values of fossil teeth may record an early or late part of their water biomineral interaction history during diagenesis

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

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

topographic evolution of the sierra nevada measured directly by inversion of low temperature thermochronology at present there are at least two competing ideas for the topographic evolution of the sierra nevada one idea is that the sierra nevada was formed as a monocline in the cretaceous marking the transition from the great valley forearc basin to the west and a high nevadaplano plateau to the east similar to the west flank of the modern altiplano of the andes both the thermochronologic imprint of local relief and the stable isotopic evidence of a topographic rain shadow support this hypothesis a second idea supported by geomorphic observations suggests that the sierra gained a large fraction of its present elevation as recently as the pliocene this recent surface uplift could have been driven by convective removal of the lower part of the lithosphere the isostatic response to basin and range faulting and or by changes in dynamic topography associated with deep subduction of the farallon plate here we present the first comprehensive analysis of low temperature thermochronology in the sierra nevada which indicates that both ideas are likely correct we show that thermochronology can resolve surface uplift as well as exhumation by measuring long wavelength topographic evolution relative to sea level uplift measurements are possible whenever there is sufficient constraint on vertical rock velocity the tilting of isochrones defined as surfaces of equal cooling age provide this constraint in the sierra nevada three new factors further distinguish our analysis the first is that we allow for the local relief and the long wavelength topography to evolve independently second we use al in hb barometry to constrain the initial depth of emplacement for the sierra nevada plutons third our analysis is tied to a sea level datum by using the paleo bathymetric record of the great valley basin where it transitions to the sierra nevada batholith results indicate that westward tilting of the sierra nevada accounts for 2 km of uplift since 20 ma topographic relief increased by a factor of 2 these findings suggest that the sierra nevada lost elevation through most of the tertiary but regained much of its initial elevation following the onset of surface uplift in the miocene

southern california earthquake center geologic vertical motion database the southern california earthquake center geologic vertical motion database vmdb integrates disparate sources of geologic uplift and subsidence data at 104 to 106 year time scales into a single resource for investigations of crustal deformation in southern california over 1800 vertical deformation rate data points in southern california and northern baja california populate the database four mature data sets are now represented marine terraces incised river terraces thermochronologic ages and stratigraphic surfaces an innovative architecture and interface of the vmdb exposes distinct data sets and reference frames permitting user exploration of this complex data set and allowing user control over the assumptions applied to convert geologic and geochronologic information into absolute uplift rates online exploration and download tools are available through all common web browsers allowing the distribution of vertical motion results as html tables tab delimited gis compatible text files or via a map interface through the google maps web service the vmdb represents a mature product for research of fault activity and elastic deformation of southern california

tooth enamel biomineralization in extant horses implications for isotopic microsampling abstract isotopic analyses of tooth enamel from fossil equids are increasingly being used to reconstruct paleoclimatic and paleoenvironmental conditions however the accuracy of these reconstructions is currently limited partly because the precise timing and spatial patterns of enamel mineralization in equids have not been documented we used radiographic analyses of mandibles collected from modern juvenile and adult domestic horses equus caballus to document the timing of enamel mineralization in equid cheek teeth premolars and molars optical and radiographic analyses of thin sections of mature and developing teeth were used to document the spatial pattern of enamel mineralization in each tooth we found that the enamel layers in equine cheek teeth took longer to mineralize than had been previously assumed largely because the enamel continued to mineralize for approximately 6 to 12 months after each tooth had begun to erupt total enamel mineralization times for individual teeth ranged from 1 5 to 2 8 years examination of thin sections revealed that retzius striae extend outward from the enamel dentin junction at an angle of 5 to 10 and run near parallel to the nonocclusal surface of the tooth daily cross striations average 5 m in width suggesting that during the initial phase of enamel mineralization matrix formation new material is added at a rate of 5 m day radiographic analyses demonstrate that the secondary mineralization front enamel maturation front is orientated approximately parallel to the retzius striae but complete maturation i e full mineralization lags behind matrix formation by several weeks to months

development of a fracture network in crystalline rocks during weathering study of bishop creek chronosequence using x ray computed tomography and 14c pmma impregnation method the progressive development of porosity during subsoil weathering of granodiorite clasts was studied at the bishop creek moraine chronosequence in east central california fractures and other pores were examined using two complementary imaging techniques x ray computed tomography xrct and a 14c pmma 14c polymethylmethacrylate method the well known xrct method allows the investigation of three dimensional 3 d pore space 14c pmma is a less known method based on the complete impregnation of pore space with 14c doped pmma and subsequent autoradiograph of a rock section these imaging methods allow us to decipher the evolution of pore space in the granodiorite during the 120 k y weathering period the 14c pmma imaging technique was found to be more suitable for following the evolution of the whole sequence from intact bedrock to saprock in terms of crack density porosity and aperture working with hand specimens this method was adapted to detect both the low aperture fractures microcracks and macrocracks only a slight and progressive increase in total fracture density was observed during the whole weathering period however this trend does not hold if macrocracks and microcracks are separated microcrack density slightly decreases whereas macrocrack density increases due to a progressive expansion of microcracks the total porosity of the rock increases during weathering and is correlated to the progressive aperture increase of all types of cracks this evolution is accompanied by a change of crack morphology and connectivity and an overall increase in intragranular porosity of biotite and plagioclase aggregates

stable isotope composition of waters in the great basin united states 1 air mass trajectories 1 isentropic trajectories calculated using the noaa climate monitoring and diagnostics laboratory s isentropic transport model were used to determine air parcel origins and the influence of air mass trajectories on the isotopic composition of precipitation events that occurred between october 1991 and september 1993 at cedar city utah and winnemucca nevada examination of trajectories that trace the position of air parcels backward in time for 10 days indicated five distinct regions of water vapor origin 1 gulf of alaska and north pacific 2 central pacific 3 tropical pacific 4 gulf of mexico and 5 continental land mass deuterium d and oxygen 18 18o analyses were made of precipitation representing 99 of all cedar city events similar analyses were made on precipitation representing 66 of the precipitation falling at winnemucca during the same period the average isotopic composition of precipitation derived from each water vapor source was determined more than half of the precipitation that fell at both sites during the study period originated in the tropical pacific and traveled northeast to the great basin only a small proportion traversed the sierra nevada the isotopic composition of precipitation is determined by air mass origin and its track to the collection station mechanism of droplet formation reequilibration within clouds and evaporation during its passage from cloud to ground the rayleigh distillation model can explain the changes in isotopic composition of precipitation as an air mass is cooled pseudo adiabatically during uplift however the complicated processes that take place in the rapidly convecting environment of cumulonimbus and other clouds that are common in the great basin especially in summer require modification of this model because raindrops that form in the lower portion of those clouds undergo isotopic change as they are elevated to upper levels of the clouds from where they eventually drop to the ground

diagenesis and the reconstruction of paleoenvironments a method to restore original δ18o values of carbonate and phosphate from fossil tooth enamel abstract intra tooth 18 o variations within the carbonate 18 oc and phosphate 18 op components of tooth apatite were measured for miocene and pliocene hypsodont mammals from afghanistan greece and chad in order to evaluate the resistance of enamel to diagenetic alteration application of water apatite interaction models suggest that the different kinetic behaviours of the phosphate water and carbonate water systems can be used to detect subtle oxygen isotope disequilibria in fossil enamel when intra individual variations are considered selective alteration of the oxygen isotope composition from the carbonate component of afghan and greek enamels suggests inorganic isotopic exchange processes microbially induced isotopic exchange for phosphate is demonstrated for the first time in enamel samples from chad in association with extensive recrystallization in chad 18 op values were derived from partial isotopic exchange with fossil groundwater during early diagenesis mass balance calculations using average carbonate content in enamel as a proxy for recrystallization and the lowest 18 op value of dentine as a proxy for the isotopic composition of the diagenetic fluid indicate that diagenesis can alter 18 op by as much as 3 in some enamel samples this diagenetic alteration is also responsible for a decrease in intra individual variations of up to 1 in affected specimens the effects of diagenesis on 18 op values of fossil enamel are not systematic however and can only be estimated if sequential 18 op and 18 oc analyses are performed on fossil enamel and dentine reconstruction of large temporal or spatial scale paleoclimates based on 18 op analyses from mammalian teeth cannot be considered valid if enamel has been affected by bacterial activity or if the data cannot be corrected for diagenetic effects

barguzin rift valley sedimentogenesis and paleogeography baikalian area russia abstract research on subdivision of sediments in the barguzin rift valley based on paleofluvial studies and paleogeographic reconstructions showed that the deposits of high terraces vii iv formed mostly in alluvial lacustrine environments whereas the lower terraces iii i are essentially fluvial the late cenozoic activation of the tectonic movements was marked by the rise of the baikal lake level and the lake water inundation into river valleys and dry depressions during the late pleistocene the flood water flowed gradually a set of low terraces being formed in the process

pliocene change in pacific plate motion the absolute motion of the pacific plate has been nearly constant during the past 15 myr but epp1 recognized that some change took place between 15 myr and the present and tentatively chose 1 myr for the time of the change cox and engebretson2 found a change in pacific absolute motion based on hotspot tracks and a change in pacific antarctic relative motion the pliocene deformation in california and the juan de fuca rotations led them to postulate a 5 myr age for the change the manner and timing of the change are explored more thoroughly here and we put the time for the change in motion of the pacific plate at between 5 and 3 2 myr basing the younger limit on the correlation of computed hotspot tracks with pacific and nazca hotspot traces the change may explain several observations on the neighbouring continental and oceanic plate boundaries including direct adjustments at the pacific spreading ridges a likely mechanism for the change is a large clockwise torque caused by acceleration of the sinking slab beneath the kurile trench where a fossil spreading ridge is inferred to have been subducted

deuterium and oxygen isotopes paleoelevations of the sierra nevada and cenozoic climate although geomorphic observations suggest that the sierra nevada has tilted so that the crest has risen 1 2 km since late miocene time deuterium and oxygen 18 isotope concentrations in cenozoic geologic materials decrease eastward across california and nevada similarly to those in modern orographically induced precipitation as if little change in sierra nevadan elevations has occurred since eocene time orographic precipitation however depends on the amount of moisture in the atmosphere which in turn can be much larger in warm air as in eocene or oligocene time and in summer than in the cooler air characteristic of present day dominantly winter precipitation moreover the integrated rainout of vapor and hence presumably in stable isotope concentrations in the remaining vapor depends largely on the difference in heights traversed by air masses not slopes of mountain ranges thus if due simply to orographically induced rainout both eocene and oligocene variations in deuterium isotopes across the sierra nevada and miocene quaternary differences in deuterium and oxygen isotopes between the great valley of california and the basin and range place only weak constraints on the slope or past elevations of the sierra nevada they do not necessarily contradict the inference that the crest of the sierra nevada has risen 1000 m or more since late miocene time

present tectonic motion across the coast ranges and san andreas fault system in central california geodetic results from very long baseline interferometry vlbi satellite laser ranging slr and the global positioning system gps are used to estimate angular velocities between the sierran microplate pacific plate and north american plate the sierra pacific pole of rotation lies nearer to the san andreas fault than does the pacific north america pole of rotation and leads to different tectonic implications than if the latter is used the angular velocities show that the san andreas fault system and central california coast ranges accommodate motion of 39 2 mm yr mainly by strike slip faulting all confidence limits following signs in this paper are 95 confidence limits fault normal motion is small is mainly convergent at rates up to 3 3 1 0 mm yr and varies along the coast but is divergent at 2 6 1 2 mm yr across san pablo bay and associated topographic lows across which the sierran and central valley watershed drains to the pacific ocean the mountain ranges tend to be larger where the fault normal convergence rates are larger the low convergence rate 0 5 1 8 mm yr normal to the san andreas fault in the carrizo plain differs sharply from that previously inferred 8 2 1 2 mm yr and 4 9 1 6 mm yr by feigl et al 1993 the difference is due to differences between their and our elastic strain accumulation models and between how their and our pacific plate reference frames are defined the ranges in most places require a minimum of 4 2 1 m y of fault normal convergence at the present rate to attain their present cross sectional area if erosion is neglected more if it is not the amount of convergence previously estimated from a balanced cross section across the diablo range in central california requires 10 8 3 m y of convergence at the present rate the former is consistent with widely held views about the onset of the coast range orogeny but the latter is not both are consistent however with the recent plate reconstructions by s cande j stock and colleagues which indicate that pacific plate motion relative to north america changed to a more convergent direction 20 25 clockwise of its prior direction at ca 8 to 6 ma and not at 3 5 ma as had been previously inferred the inferred change in direction of plate motion is large compared with the present angle of convergence across the straight and narrow segment of the san andreas fault of 0 7 4 7 from which we infer that the sierran microplate changed motion relative to north america at the same time ca 8 to 6 ma as did the pacific plate we further infer that the motion accommodated across the great basin must also have changed at the same time we also examine the hypothesis that stable sliding occurs along the san andreas fault and other northwest striking strike slip faults in central california where the fault normal convergence rate is low or negative and that these faults are unstable where the fault normal convergence rate is high such a relationship appears to hold in general but fails in detail in particular there are substantial sections of fault with small inferred rates of fault normal convergence across which the san andreas fault is locked moreover the creeping section of the san andreas fault i e the section between parkfield and the calaveras junction is the locus of greater fault normal convergence 3 2 1 4 mm yr than is the locked part of the fault 0 5 1 8 mm yr south of parkfield thus this hypothesis is at best a partial explanation for the observed distribution of locked and nonlocked sections of the fault

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

paleo geomorphology of the sierra nevada california from u th he ages in apatite new apatite u th he ages from the central sierra nevada california place limits on the morphology and evolution of longitudinal profiles of major transverse river drainages developed in the late cretaceous helium ages from a new orogen parallel constant elevation sample transect are relatively uniform 60 ma and not correlated with topography unlike those from a similar lower elevation transect approx 15 km to the west we interpret the marked difference in the two orogen parallel profiles to reflect a headward decrease in long wavelength transverse relief at the time of cooling consistent with either a concave up stream gradient typical of those observed near the headwaters of modern sierran trunk streams or a convex gradient like those found along slope breaks of eroding plateau edges from the san joaquin drainage we obtained a new helium age versus elevation profile which has a comparable slope to those previously reported for the yosemite valley kings canyon and mt whitney areas this new profile yields slightly older ages at a given elevation as expected from its position adjacent to the largest major drainage the age versus elevation profiles imply that the mean denudation rate of the region in the cenozoic was about 0 04 to 0 05 mm yr we show that long wavelength 70 km relief inferred from longitudinal helium age variations is a strong function of erosion rate such that even relatively subdued relief is detectable with helium age profiling provided that denudation rates were low using the rate implied by sierran age versus elevation profiles we infer long wavelength relief of 1500 500 m in the late cretaceous by analogy with modern orogenic plateaus this value of long wavelength relief suggests a cretaceous interior cordilleran plateau lay at an elevation of at least 3000 m

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