mechanisms of flexural flow folding of competent single layers as evidenced by folded fibrous dolomite veins abstract flexural flow is thought unlikely to occur in naturally deformed competent isotropic single layers in this study we discuss a particular case of folded bedding parallel fibrous dolomite veins in shale in which the internal strain pattern and microstructural deformation features provide new insights in the mechanisms enabling flexural flow folding strain in the pre folding veins is accommodated by two main mechanisms intracrystalline deformation by bending and intergranular deformation with bookshelf rotation of dolomite fibres the initially orthogonal dolomite fibres allowed a reconstruction of the strain distribution across the folded veins this analysis shows that the planar mechanical anisotropy created by the fibres causes the veins to approximate flexural flow during folding synkinematic veins overgrow the pre folding fibrous dolomite veins microstructures and dolomite growth morphologies reflect growth during progressive fold evolution with evidence for flexural slip at fold lock up homogeneous flattening as evidenced by disjunctive axial planar cleavage subsequently modified these folds from class 1b to 1c folds our study shows that the internal vein fabric has a first order influence on folding kinematics moreover the fibrous dolomite veins show high viscosity contrasts with the shale matrix essential in creating transient permeability for subsequent mineralising stages in the later synkinematic veins during progressive folding

joint inversions of seismic and geodynamic data for models of three dimensional mantle heterogeneity the seismic models of three dimensional 3 d mantle heterogeneity may be interpreted in terms of the density perturbations which drive mantle flow and thus provide important predictions of flow related observables such as the nonhydrostatic geoid the current models of global scale shear velocity heterogeneity provide reasonably good fits to the long wavelength nonhydrostatic geoid data 60 70 variance reductions but rather poor fits to the corresponding free air gravity anomalies 30 40 variance reductions this major difference is due to two factors 1 the very different amplitude spectrum of the gravity anomalies which is nearly flat for degrees l 3 the largest mismatch between the pattern of predicted and observed gravity anomalies is in the southern hemisphere this observation suggests that one reason for the poor overall match between the two fields may be that the global seismic data are not resolving sufficiently well the heterogeneity in the southern hemisphere portion of the deep mantle in contrast the gravity data provide accurate and geographically uniform constraints on the vertically integrated heterogeneity in the mantle we therefore perform a series of experiments in which we simultaneously invert a large set of seismic data which includes long period waveforms ss s and scs s differential travel times and normal mode structure coefficients and the long wavelength gravity anomaly data we thus determine whether it is possible to derive new 3 d heterogeneity models which satisfy both data sets the gravity anomaly data are interpreted in the context of spherically symmetric viscous flow models of the mantle in these inversion experiments we test several radial viscosity and ln ln profiles and thereby assess their plausibility the joint seismic geodynamic inversions reveal that it is indeed possible to greatly improve the fit to the free air gravity anomalies with variance reductions of 80 90 readily accessible while preserving the fit to the seismic data this improvement is achieved with some adjustment to the heterogeneity in the depth range 1500 2500 km where the seismic data constraints appear to be weakest the joint inversions also reveal new structures in the southern hemisphere portion of the lower mantle which apparently are not resolved by the seismic data alone

implications of estimated magmatic additions and recycling losses at the subduction zones of accretionary non collisional and collisional suturing orogens

new global marine gravity model from cryosat 2 and jason 1 reveals buried tectonic structure gravity models are powerful tools for mapping tectonic structures especially in the deep ocean basins where the topography remains unmapped by ships or is buried by thick sediment we combined new radar altimeter measurements from satellites cryosat 2 and jason 1 with existing data to construct a global marine gravity model that is two times more accurate than previous models we found an extinct spreading ridge in the gulf of mexico a major propagating rift in the south atlantic ocean abyssal hill fabric on slow spreading ridges and thousands of previously uncharted seamounts these discoveries allow us to understand regional tectonic processes and highlight the importance of satellite derived gravity models as one of the primary tools for the investigation of remote ocean basins

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

the bonneville estates rockshelter rodent fauna and changes in late pleistocene middle holocene climates and biogeography in the northern bonneville basin usa abstract excavations at bonneville estates rockshelter nevada recovered rodent remains from stratified deposits spanning the past ca 12 500 14c yr bp 14 800 cal yr bp specimens from horizons dating to the late pleistocene and early holocene include species adapted to montane and moist and cool habitats including yellow bellied marmot marmota flaviventris and bushy tailed woodrat neotoma cinerea shortly after 9000 14c bp 10 200 cal yr bp these mammals became locally extinct or nearly so taxonomic diversity declined and the region became dominated by desert woodrats neotoma lepida and other species well adapted to xeric low elevation settings the timing and nature of changes in the bonneville estates rodent fauna are similar to records reported from nearby homestead and camels back caves and provide corroborative data on terminal pleistocene early holocene environments and mammalian responses to middle holocene desertification moreover the presence of northern pocket gopher thomomys talpoides at bonneville estates adds to a sparse regional record for that species and similar to homestead cave it appears that the ca 9500 14c yr bp 10 800 cal yr bp replacement of the northern pocket gopher by botta s pocket gopher in the great salt lake desert vicinity was also in response to climate change

late quaternary environmental change in the bonneville basin western usa abstract excavation and analyses of small animal remains from stratified raptor deposits spanning the last 11 5 ka together with collection and analysis of over 60 dated fossil woodrat midden samples spanning the last 50 ka provide a detailed record of changing climate in the eastern great basin during the late pleistocene and holocene sagebrush steppe dominated the northern bonneville basin during the full glacial suggesting that conditions were cold and relatively dry in contrast to the southern basin which was also cold but moister limber pine woodlands dominated 13 11 5 ka indicating increased dryness and summer temperatures 6 7 c cooler than present this drying trend accelerated after 11 5 ka causing lake bonneville to drop rapidly eliminating 11 species of fish from the lake from 11 5 8 2 ka xerophytic sagebrush and shadscale scrub replaced more mesophilic shrubs in a step wise fashion a variety of small mammals and plants indicate the early holocene was 3 c cooler and moister than at present not warmer as suggested by a number of climatic models the diversity of plants and animals changed dramatically after 8 2 ka as many species disappeared from the record some of the upland species returned after 4 ka and great salt lake became fresh enough at 3 4 and 1 2 ka to support populations of utah chub

preservation and detection of microstructural and taxonomic correlations in the carbon isotopic compositions of individual precambrian microfossils abstract here we present techniques for and new data from in situ carbon isotope 13c analysis of precambrian permineralized microscopic fossils with a reproducibility of 1 2 using secondary ion mass spectrometry sims individual microfossils selected for their excellent preservation were analyzed in petrographic thin sections of stromatolitic cherts from the proterozoic gunflint 1880 ma bitter springs 830 ma min yar 740 ma and chichkan 775 ma formations the range of 13c values 34 6 to 22 1 vpdb among the 46 individuals analyzed falls within that expected for photoautotrophic carbon fixation by ribulose bisphosphate carboxylase rubisco consistent with morphology based taxonomic assignments for these specimens microfossils classified as cyanobacteria from the gunflint bitter springs and min yar formations for which published carbonate carbon isotope data can be used to estimate the 13c of the original dissolved inorganic carbon substrate exhibit a consistent 19 total fractionation 13c of dissolved inorganic carbon 13c of biomass similar to that observed in living cyanobacteria over a wide range of 13ccarb values 2 9 to 3 4 in stromatolitic chert of the min yar formation morphologically diverse microfossils preserved in a 1 mm2 part of a microbial mat exhibit systematic isotopic differences among and within taxa that correlate with their morphologically inferred biological affinities and suggest that isotopic signatures of their original biosynthetic processes e g lipid and peptidoglycan synthesis are preserved isotopic offsets consistent with the different rubisco based fractionations typical of cyanobacteria and photosynthetic eukaryotes are documented by the differing 13c values of a colonial cyanobacterium 22 6 0 5 and a phytoplanktonic protistan acritarch 28 9 1 0 situated

calibration of the calcite water oxygen isotope geothermometer at devils hole nevada a natural laboratory abstract the 18 o of ground water 13 54 0 05 and inorganically precipitated holocene vein calcite 14 56 0 03 from devils hole cave 2 in southcentral nevada yield an oxygen isotopic fractionation factor between calcite and water at 33 7 c of 1 02849 0 00013 1000 ln calcite water 28 09 0 13 using the commonly accepted value of calcite water t of 0 00020 k 1 this corresponds to a 1000 ln calcite water value at 25 c of 29 80 which differs substantially from the current accepted value of 28 3 use of previously published oxygen isotopic fractionation factors would yield a calcite precipitation temperature in devils hole that is 8 c lower than the measured ground water temperature alternatively previously published fractionation factors would yield a 18 o of water from which the calcite precipitated that is too negative by 1 5 using a temperature of 33 7 c several lines of evidence indicate that the geochemical environment of devils hole has been remarkably constant for at least 10 ka accordingly a re evaluation of calcite water oxygen isotopic fractionation factor may be in order assuming the devils hole oxygen isotopic value of calcite water represents thermodynamic equilibrium many marine carbonates are precipitated with a 18 o value that is too low apparently due to a kinetic isotopic fractionation that preferentially enriches 16 o in the solid carbonate over 18 o feigning oxygen isotopic equilibrium

composition and structure of the central aleutian island arc from arc parallel wide angle seismic data new results from wide angle seismic data collected parallel to the central aleutian island arc require an intermediate to mafic composition for the middle crust and a mafic to ultramafic composition for the lower crust and yield lateral velocity variations that correspond to arc segmentation and trends in major element geochemistry the 3 d ray tracing 2 5 d inversion of this sparse wide angle data set which incorporates independent phase interpretations and new constraints on shallow velocity structure produces a faster and smoother result than a previously published velocity model middle crustal velocities of 6 5 7 3 km s over depths of 10 20 km indicate an andesitic to basaltic composition high lower crustal velocities of 7 3 7 7 km s over depths of 20 35 km are interpreted as ultramafic mafic cumulates and or garnet granulites the total crustal thickness is 35 37 km this result indicates that the aleutian island arc has higher velocities and thus more mafic compositions than average continental crust implying that significant modifications would be required for this arc to be a suitable building block for continental crust lateral variations in average crustal velocity below 10 km roughly correspond to trends in major element geochemistry of primitive mg 0 6 lavas the highest lower crustal velocities and presumably most mafic material are detected in the center of an arc segment between unmak and unalaska islands implying that arc segmentation exerts control over crustal composition

systematic variations in the carbon and oxygen isotopic composition of pedogenic carbonate along elevation transects in the southern great basin united states stable carbon and oxygen isotope variations in holocene soil carbonates that formed in the unsaturated zone were examined along several elevation transects in the southern great basin united states a region with a semi arid climate our intent was to study the relationship between the stable isotopic composition of pedogenic carbonates and climate ecological variations differences in parent material and soil depth 13 c of pedogenic carbonate in three different soil profiles from different elevations decreases with soil depth indicating a decrease in the ratio of atmospheric to plantderived co 2 downprofile pedogenic carbonate at the soil air interface approaches a 13 c value in equilibrium with atmospheric co 2 in all three soils observed 13 c profiles for pedogenic carbonate can be described using a one dimensional model for 12 co 2 and 13 co 2 assuming isotopic equilibrium between soil co 2 and soil carbonate the modeled best fit to observed isotopic profiles suggests that the profile differences in part result from differing soil respiration rates at each site 13 c in deep pedogenic carbonate 50 cm varies by about 12 per mil over a 2 440 m elevation range being enriched in 13 c at the lowest elevations the slope of 13 c for these carbonates versus elevation is very similar for soils developed on carbonate and on noncarbonate parent materials depletion by 4 6 to 4 7 per mil per 1 000 m increase in altitude between 300 to 2 740 m above mean sea level for the localities studied this concordance makes it likely that there has been complete isotopic exchange between hco 3 in solution and soil co 2 prior to carbonate precipitation soil co 2 and soil respiration rates increase systematically with elevation the plantderived component of soil co 2 indicates that c 3 plants dominate the biomass at most measured sites in agreement with plant surveys calculated equilibrium fractionation factors between soil co 2 and soil carbonate are very similar to those observed again indicating complete isotopic exchange between carbon species in all the soil co 2 and soil carbonate data suggest that the 13 c variation with elevation observed in the soil carbonates results from differing soil respiration rates at each site as well as from variations in the proportion of c 3 to c 4 and cam plants in each site9s surface biomass 18 o values in pedogenic carbonates are higher at lower elevations due in part to the more positive 18 o values for meteoric waters at lower elevations the average 18 o value of deep 50 cm pedogenic carbonate at all sites however is enriched 2 4 to 3 7 per mil with respect to values we predict should be in equilibrium with the isotopic composition of local meteoric waters this suggests that evaporative isotopic enrichment of soil waters may have occurred at all elevations prior to precipitation of carbonate or that seasonal differences in the isotopic composition of meteoric waters coupled with differential infiltration may be taking place one or both of these processes also may explain the 18 o decrease in soil carbonate with depth observed in two of three soil profiles

strain estimation from flattened buckle folds a simple and direct method of calculating the post buckle flattening strain of folds is proposed assuming that the folds have class 1b parallel shape before flattening the stretch of the layer at any position in the flattened fold is inversely proportional to the orthogonal thickness of the layer a polar graph showing inverse thickness as a function of layer orientation therefore yields directly the shape and orientation of the flattening strain ellipse the method can be applied to cases where flattening strains have been imposed obliquely to the fold s axial surface

intratest oxygen isotope variability in the planktonic foraminifer n pachyderma real vs apparent vital effects by ion microprobe abstract intratest oxygen isotope variations in the planktonic foraminifer neogloboquadrina pachyderma sinistral left coiling from north atlantic core top and multi net samples were assessed by ion microprobe analysis from 2 to 6 m spots with precision and accuracy better than 0 7 in 18 o 2 sd within a single foraminiferal test from a core top sample comprising both ontogenetic calcite and outer crust 18 o values vary from 0 5 to 3 7 pdb exceeding the range of equilibrium 18 o in the specimens habitat by a factor of three the isotopic difference between the ontogenetic calcite and the crust averages 1 8 neither of the two types of foraminiferal calcite precipitates in equilibrium with ambient seawater the ontogenetic calcite exhibits a negative vital effect 18 o m e 18 o measured 18 o equilibrium ranging from 0 5 to 1 the largest negative fractionation is associated to the inner walls of juvenile chambers in contrast a positive vital effect of about 0 8 was observed in the crust with respect to the highest equilibrium 18 o values at water depths below 200 m hence two vital effects that are opposite in sign are effective within a single foraminiferal test indicating that whole test values of this species are highly sensitive to the degree of encrustation and amplify or attenuate environmental signals the negative vital effect of the ontogenetic calcite was verified by ion microprobe analysis of four nonencrusted net sampled specimens reflecting three different depth intervals intra ontogenetic oxygen isotope ratios in these juvenile tests range from 0 6 to 3 0 and exhibit a negative vital effect even larger than that observed in core top samples based on these data the large range of apparent vital effects reported for this foraminiferal species can be assessed by a mass balance calculation assuming that the degree of encrustation is variable

strain analysis and vorticity of flow in the northern sardinian variscan belt recognition of a partitioned oblique deformation event abstract a field example of strain partitioning has been analysed along the nurra asinara transect of the nw sardinian variscan chain italy the section in the nurra asinara area is in a continuous sequence of tectono metamorphic complexes made of low to high grade metamorphic rocks affected by a polyphase tectonic history the principal fabric of the area is controlled by a d2 progressive deformation phase in which the strain is partitioned into folds and shear zone domains the d2 stretching lineation and shear sense show a clear change from south to north the principal meso and micro structures vorticity gauges and a quantitative kinematic analysis of local strain suggest that the d2 kinematic history could be envisaged as an oblique heterogeneous deformation similar to the transpressive systems described in ancient and modern settings elsewhere using a simple kinematic model we also propose that both a transpressive system followed by thrusting or a partitioned transpressive system could be responsible for the fabric distribution and strain accumulation described in the study transect

structure of an island arc wide angle seismic studies in the eastern aleutian islands alaska new seismic wide angle data from the eastern aleutian islands show a mafic composition and a 30 km thick island arc crust traveltimes of p and s refracted arrivals and prominent crustal and mantle reflectors observed to offsets of over 300 km were used to derive velocity models for the eastern aleutian arc between the islands of atka and unimak using a three dimensional finite difference modeling and tomography code we interpret the highest crustal p wave velocities of 7 2 7 4 km s between about 12 and about 22 km depth to the south and north of the main volcanic line as remainders of preexisting oceanic crust into which arc magma is intruded apart from the pieces of oceanic crust the velocities suggest an overall mafic composition for the arc composed mainly of metabasalts diorite and diabase in the upper crust and garnet granulite or amphibolite to hornblendite in the lower crust reflected arrivals from the subducting pacific plate at depths of 45 55 km beneath the fore arc together with pn show a mantle wedge with p wave velocities as low as 7 4 km s increasing with depth to about 8 1 km s with an average of about 7 7 km s a mantle composition that grades from mainly pyroxenite probably ultramafic cumulates near the moho to dunite at greater depths best explains these observed velocities

late quaternary temperature record from buried soils of the north american great plains we present the first comprehensive late quaternary record of north american great plains temperature by assessing the behavior of the stable isotopic composition 13 c of buried soils after examining the relationship between the 13 c of topsoil organic matter and july temperature from 61 native prairies within a latitudinal range of 46 38 n we applied the resulting regression equation to 64 published 13 c values from buried soils of the same region to construct a temperature curve for the past 12 k y estimated temperatures from 12 to 10 ka 1 k y 1000 14 c yr b p fluctuated with a periodicity of 1 k y with two cool excursions between 4 5 and 3 5 c and two warmer excursions between 1 and 0 c relative to modern early holocene temperatures from ca 10 7 5 ka were 1 0 to 2 0 c before rising to 1 0 c in the middle holocene between 6 0 and 4 5 ka after a cool interlude from 4 2 to 2 6 ka when temperatures dropped to slightly below modern another warm interval ensued from 2 6 to 1 ka as temperatures increased to 0 5 c a final decline in temperature to below modern occurred beginning ca 0 5 ka cooler than present temperatures in the great plains indicate telecommunications with cool water episodes in the gulf of mexico and north atlantic potentially governed by a combination of glacial meltwater pulses and low solar irradiance

using seismic waves to image earth s internal structure seismic waves generated in earth s interior provide images that help us to better understand the pattern of mantle convection that drives plate motions

cosmogenic 3he exposure ages of pleistocene debris flows and desert pavements in capitol reef national park utah abstract the quaternary history of the capitol reef area utah is closely linked to the basaltic andesite boulder deposits that cover much of the landscape understanding the age and mode of emplacement of these deposits is crucial to deciphering the quaternary evolution of this part of the colorado plateau using cosmogenic 3 he exposure age dating we obtained apparent exposure ages for several key deposits in the capitol reef area coarse boulder diamicts capping the johnson mesa and carcass creek terraces are not associated with the bull lake glaciation as previously thought but were deposited 180 15 to 205 17 ka minimum age and are the result of debris flow deposition desert pavements on the johnson mesa surface give exposure ranging from 97 8 to 159 14 ka and are 34 96 kyears younger than the boulder exposure ages the offset between the boulder and pavement exposure ages appears to be related to a delay in pavement formation until the penultimate glacial interglacial transition or periodic burial and exposure of pavement clasts since debris flow deposition incision rates for the capitol reef reach of the fremont river calculated from the boulder exposure ages range from 0 40 to 0 43 m kyear 1 maximum rates and are some of the highest on the colorado plateau

crustal structure of the central nova scotia margin off eastern canada summary the central nova scotia margin off eastern canada is located at a transition from a volcanic margin in the south to a non volcanic margin in the north in order to study this transition a wide angle refraction seismic line with dense airgun shots was acquired across the central nova scotia margin the 500 km long transect is coincident with previous deep reflection profiles across the lahave platform and extending into the sohm abyssal plain a p wave velocity model was developed from forward and inverse modelling of the wide angle data from 21 ocean bottom seismometers and coincident normal incidence reflection profiles the velocity model shows that the continental crust is divided into three layers with velocities of 5 5 6 9 km s 1 the maximum thickness is 36 km a minor amount 5 km of thinning occurs beneath the outer shelf while the major thinning to a thickness of 8 km occurs over the slope region the seaward limit of the continental crust consists of 5 km thick highly faulted basement there is no evidence for magmatic underplating beneath the continental crust on the contrary a 4 km thick layer of partially serpentinized mantle 7 6 7 95 km s 1 begins beneath the highly faulted continental crust and extends 200 km seawards forming the lower part of the oceancontinent transition zone the upper part of the transition zone consists of the highly faulted continental crust and 4 to 5 km thick initial oceanic crust the continent ocean boundary is moved 50 km farther seawards compared to an earlier interpretation based only on reflection seismic data the oceanic crust in the transition zone consists of layer 2 and a high velocity lower crustal layer layer 2 is 1 3 km thick with velocities of 5 6 6 0 km s 1 the high velocity lower crustal layer is 1 2 km thick with velocities of 7 25 7 4 km s 1 suggesting a composite layer of serpentinized peridotite and gabbroic layer 3 oceanic crust with normal thickness of 5 7 km and more typical layer 3 with velocities of 6 95 7 3 km s 1 is observed at the seaward end of the profile

pedothem carbonates reveal anomalous north american atmospheric circulation 70 000 55 000 years ago our understanding of climatic conditions and therefore forcing factors in north america during the past two glacial cycles is limited in part by the scarcity of long well dated continuous paleoclimate records here we present the first to our knowledge continuous millennial resolution paleoclimate proxy record derived from millimeter thick pedogenic carbonate clast coatings pedothems which are widely distributed in semiarid to arid regions worldwide our new multiisotope pedothem record from the wind river basin in wyoming confirms a previously hypothesized period of increased transport of gulf of mexico moisture northward into the continental interior from 70 000 to 55 000 years ago based on oxygen and carbon isotopes determined by ion microprobe and uranium isotopes and u th dating by laser ablation inductively coupled plasma mass spectrometry this pronounced meridional moisture transport which contrasts with the dominant zonal transport of pacific moisture into the north american interior by westerly winds before and after 70 000 55 000 years ago may have resulted from a persistent anticyclone developed above the north american ice sheet during marine isotope stage 4 we conclude that pedothems when analyzed using microanalytical techniques can provide high resolution paleoclimate records that may open new avenues into understanding past terrestrial climates in regions where paleoclimate records are not otherwise available when pedothem paleoclimate records are combined with existing records they will add complimentary soil based perspectives on paleoclimate conditions

laminated soil carbonate rinds as a paleoclimate archive of the colorado plateau abstract recent work suggests that the c and o isotope composition of laminated soil carbonate rinds can provide high resolution 100 s yr sample information about hydrologic processes and vegetation over tens of thousands of years however while this archive can potentially provide quantitative reconstructions most interpretations have thus far been qualitative in this study we show how modern soil data and clumped isotope paleothermometry can be leveraged to constrain the conditions of rind formation for a sample from the western colorado plateau utah usa we can thus quantitatively interpret rind isotope values as vegetation composition c3 plants and soil water oxygen isotope composition 18osoil water over 35 5 ka we validate the approach by demonstrating consistency between our record and other paleoarchives from the western usa laminated soil carbonate rinds therefore represent a new avenue for sub millennial scale quantitative investigations of paleoclimatology paleoecology archeology and modeling questions down to the level of individual soils

water transportation from the subducting slab into the mantle transition zone using a recently developed petrogenetic grid for morb h2o we propose a new model for the transportation of water from the subducting slab into the mantle transition zone depending on the geothermal gradient two contrasting water transportation mechanisms operate at depth in a subduction zone if the geothermal gradient is low lawsonite carries h2o into mantle depths of 300 km with further subduction down to the mantle transition depth approximately 400 km lawsonite is no longer stable and thereafter h2o is once migrated upward to the mantle wedge then again carried down to the transition zone due to the induced convection at this depth hydrous phase olivine is stable and plays a role as a huge water reservoir in contrast if the geothermal gradient is high the subducted slab may melt at 700 900 c at depths shallower than 80 km to form felsic melt into which water is dissolved in this case h2o cannot be transported into the mantle below 80 km between these two endmember mechanisms two intermediate types are present in the high pressure intermediate type the hydrous phase a plays an important role to carry water into the mantle transition zone water liberated by the lawsonite consuming continuous reaction moves upward to form hydrous phase a in the hanging wall which transports water into deeper mantle this is due to a unique character of the reaction because phase a can become stable through the hydration reaction of olivine in the case of low pressure intermediate type the presence of a dry mantle wedge below 100 km acts as a barrier to prevent h2o from entering into deeper mantle 2006 published by elsevier b v on behalf of international association for gondwana research

the early origins of terrestrial c4 photosynthesis abstractthe c4 photosynthetic pathway is a series of structural and biochemical modifications around the more primitive c3 pathway that improve the photosynthetic efficiency under specific climatic conditions hence the origin and subsequent geographical expansion of the c4 plants likely reflects a record of climate change multiple paleoatmospheric pco2 proxies indicate a critical co2 threshold was breached 30 ma that potentially selected for co2 concentrating mechanisms to overcome photorespiratory stresses imposed on the basic c3 pathway details of the c4 pathway s earliest origins remain enigmatic given the paucity of the geologic record nonetheless 13c proxy records from paleosol carbonates ungulate teeth and plant derived compounds indicate c4 plants likely represented an important component of plant biomass by the early miocene low co2 levels appear to be a precondition for the development of the c4 photosynthetic pathway however comparisons of 13c proxy records indicate that the timin

atmospheric pco 2 control on speleothem stable carbon isotope compositions abstract the stable carbon isotope compositions of c3 plants are controlled by the carbon isotope composition of atmospheric co2 13ca and by the stomatal response to water stress these relationships permit the reconstruction of ancient environments and assessment of the water use efficiency of forests it is currently debated whether the 13c values of c3 plants are also controlled by atmospheric pco2 here i show that globally averaged speleothem 13c values closely track atmospheric pco2 over the past 90 kyr after accounting for other possible effects this coupling is best explained by a c3 plant 13c sensitivity of 1 6 0 3 100 ppmv co2 during the quaternary this is consistent with 20th century european forest tree ring 13c records providing confidence in the result and suggesting that the modest pco2 driven increase in water use efficiency determined for those ecosystems and simulated by land surface models accurately approximates the global average response the 13c signal from c3 plants is transferred to speleothems relatively rapidly thus the effect of atmospheric pco2 should be subtracted from new and existing speleothem 13c records so that residual 13c shifts can be interpreted in light of the other factors known to control spleleothem 13c values furthermore global average speleothem 13c shifts may be used to develop a continuous radiometric chronology for pleistocene atmospheric pco2 fluctuations and by correlation ice core climate records

a glacial chronology for the fish creek drainage of boulder mountain utah usa abstract boulder mountain located in south central utah is one of several mountain ranges on the colorado plateau that was glaciated during the late pleistocene using 3he exposure age dating corrected for non cosmogenic 3he with shielded samples we determined 3he exposure ages for boulders from the most well preserved moraines in the fish creek drainage of boulder mountain 3he exposure ages indicate a last glacial maximum lgm advance 23 100 1300 to 20 000 1400 yr ago and a later and smaller advance 16 800 500 to 15 200 500 yr ago this chronology is very similar to other cosmogenic glacial chronologies from the western u s and suggests that the timing of glacial advance and retreat on the colorado plateau was generally in phase with the rest of the western u s during the late pleistocene

structural development of an accretionary prism by thrust and strike slip faulting shumagin region aleutian trench a combination of seabeam swath bathymetric data closely spaced single channel seismic reflection profiles and multichannel seismic reflection profiles from the shumagin islands region indicates that the large scale deformation of the accretionary prism in this segment of the aleutian trench occurs progressively through several stages 1 folding along axes perpendicular to the plate convergence direction in the region 2 thrust faulting in the direction of plate convergence and 3 oblique strike slip faulting along conjugate west northwest trending right lateral and north northeast trending left lateral faults strike slip faults occur in distinct domains with right lateral oblique faults present west of a major transverse fault at long 161 w and left lateral oblique faults prevalent east of 161 w the structural development of the modern aleutian trench fore arc in this region is probably affected by pre eocene inherited structures that are still active in the present day stress regime a major domain boundary fault located at long 161 w is probably part of a strike slip fault system that also bounds sanak basin farther landward on the shumagin shelf this fault zone is nearly coincident with the mapped position of the western edge of the shumagin seismic gap these transverse structures in the shumagin fore arc probably influence the spatial distribution of stress buildup related to subduction and hence the locations of rupture zones of great interplate earthquakes along this segment of the aleutian trench

geophysical evidence for hydration of the crust and mantle of the nazca plate during bending at the north chile trench water transported in subducting oceanic plates plays a key role in a number of phenomena including intraslab seismicity and arc magmatism however the locus of plate hydration and water distribution in crust and mantle of plates entering subduction zones is debated we present evidence for anomalously low seismic velocities and densities of the crust and upper mantle of the nazca plate at the north chile trench crustal seismic velocities at the trench are lower than velocities of mature fast spreading crust and even lower than velocities of highly extended slow spreading crust in addition the nazca plate at the north chile trench may contain an 20 km thick upper mantle layer with 17 serpentine which implies 2 5 wt water these results document pervasive rock alteration by water percolation linked to bending related extensional faulting

magmatism of the westernmost komandorsky segment of the aleutian island arc abstract four magmatic associations are distinguished in the westernmost komandorsky segment of the aleutian island arc basalt plagiorhyolite 45 28 ma trachybasalt teschenite 27 16 ma diorite granitoid 12 5 8 5 ma and dacite rhyolite 0 7 0 ma the latter association is represented by the lavas of a recently discovered active submarine volcano piip volcano about 40 km north of the komandorsky islands and 700 km west of the quaternary center on buldir is detailed petrogeochemical data including ree and 143 nd 144 nd and 87 sr 86 sr isotopic ratios show that the parental melts of the komandorsky is were of mantle origin and their sources remained isotopically homogeneous during the whole geological history of the aleutian arc 10be concentrations in lavas of the piip volcano 2 7 106 at g indicate subduction related incorporation of young pelagic sediments in their magmatic sources or contamination of ascending melts by non solidified sedimentary material directly beneath the volcano the komandorsky segment of the aleutian arc evolved from a depleted arc tholeiitic series through a markedly alkaline series to later calc alkaline andesites and dacites and finally to late stage calc alkaline dacites and rhyodacites erupted inboard of the older volcanic centers

terrane accretion production and continental growth a perspective based on the origin and tectonic fate of the aleutian bering sea region orogenesis in the aleutian bering sea region would create an expansive new area of pacific rim mountain belts the region itself formed about 55 ma as a consequence of the suturing of a single exotic fragment of oceanic crust aleutia to the pacific s alaskan siberian margin a massive overlap assemblage of the igneous crust of the aleutian arc and the thick sedimentary masses of the aleutian basin have since accumulated above the captured basement terrane of aleutia future closure of the aleutian bering sea region either northward toward the continent or southward toward the aleutian arc would structurally mold new continental crust to the north american plate the resulting beringian orogen would be constructed of a collage of suspect terranes although some terranes would include exotic crustal rocks formed as far as 5000 km away most terranes would be kindred or cotetonic blocks composed of the overlap assemblage and of relatively local 100 1000 km derivation the aleutian bering sea perspective bolsters the common supposition that although disrupted and smeared by transcurrent faulting examples of kindred assemblages should exist and perhaps commonly in ocean rim mountain belts

solar forcing of holocene climate new insights from a speleothem record southwestern united states holocene climate change has likely had a profound infl uence on ecosystems and culture a link between solar forcing and holocene climate such as the asian monsoon has been shown for some regions although no mechanism for this relationship has been suggested here we present the fi rst high resolution complete holocene climate record for the north american monsoon region of the southwestern united states southwest in order to address the nature and causes of holocene climate change we show that periods of increased solar radiation correlate with decreased rainfall the opposite to that observed in the asian monsoon and suggest that a solar link to holocene climate is through changes in the walker circulation and the pacifi c decadal oscillation and el nino southern oscillation systems of the tropical pacifi c ocean given the link between increased warming and aridity in the southwest additional warming due to greenhouse forcing could potentially lead to persistent hyperarid conditions similar to those seen in our record during periods of high solar activity

the isogon rosette method for rapid estimation of strain in flattened folds abstract dip isogons drawn on the profile section of a fold by linking the points of equal dip on the inner and outer arcs can be arranged in a rosette by displacing the isogons without changing their orientation until the mid point of each isogon becomes the common point of intersection of all isogons the end points of isogons in the rosette trace a characteristic curve that defines the fold geometry this curve is a circle in parallel folds an ellipse in flattened parallel folds and it reduces to a pair of points in similar folds since isogons deform as material lines during flattening the characteristic curve namely the ellipse directly represents the strain ellipse in flattened parallel folds the method is tested successfully on several examples of natural flattened parallel folds the isogon rosette method allows representation of a given fold by a point on the r s plot where r s and are the two dimensional strain ratio and the angle between the maximum principal strain and the fold axial trace respectively

stable carbon and oxygen isotopes in quaternary soil carbonates as indicators of ecogeomorphic changes in the northern chihuahuan desert usa stable carbon and oxygen isotopes in soil carbonates provide an additional technique for investigating quaternary ecogeomorphic changes in arid and semiarid regions this study presents 13c and 18o values in surface and buried soils in a basin and range region of southern new mexico and west texas three landform categories were investigated for their isotopic content 1 middle piedmont slopes 2 a lower piedmont slope and adjacent playa depressions and 3 an intermontane basin floor soils of the middle piedmont slopes had greatest 13c variability ranging from 0 6 in buried soils to 11 1 pdb in surface soils soils of the basin floor had greatest variability in 18o values ranging from 0 6 to 7 6 pdb fossil pollen patterns roughly paralleled 13c shifts with cheno am pollen exhibiting greatest changes both isotope and pollen data across stratigraphic discontinuities suggest that a conversion from c4 grasses to c3 desert shrubs accompanied holocene erosion

crustal thickness anomalies in the north atlantic ocean basin from gravity analysis gravity derived crustal thickness models were calculated for the north atlantic ocean between 76 n and the chain fracture zone and calibrated using seismically determined crustal thickness about 7 of the ocean crust is 7 km thick and is interpreted to have been affected by excess magmatism thin crust probably reflects reduced melt production from relatively cold or refractory mantle at scales of up to hundreds of kilometers along the spreading axis by far the most prominent thick crust anomaly is associated with iceland and adjacent areas which accounts for 57 of total crustal volume in excess of 7 km much smaller anomalies include the azores 8 cape verde islands 6 canary islands 5 madeira 4 and new england great meteor seamount chain 2 all of which appear to be associated with hot spots hot spot related crustal thickening is largely intermittent suggesting that melt production is episodic on time scales of tens of millions of years thickened crust shows both symmetrical and asymmetrical patterns about the mid atlantic ridge mar axis reflecting whether melt anomalies were or were not centered on the mar axis respectively thickened crust at the bermuda and cape verde rises appears to have been formed by isolated melt anomalies over periods of only 20 25 myr crustal thickness anomalies on the african plate generally are larger than those on the north american plate this most likely results from slower absolute plate speed of the african plate over relatively fixed hot spots

aleutian island arc magma production rates and primary controlling factors abstract island arc magmatism is considered a major mechanism of continental crustal growth hence the variation in island arc magma production rates and its influencing factors are of great importance the along arc strike variation in the island arc magma production rate is important for elucidating whether the subduction zone temperature is a controlling factor on arc magmatism no back arc spreading or ridge subduction is occurring in the intraoceanic subduction region of the aleutian subduction zone and the along arc temperatures vary due to differences in the subducting plate age convergence rate and slab dip therefore this is an ideal region to study the correlation between magma production rates and subduction zone temperatures however previous studies estimated the magma production rates at only a few locations due to the insufficient coverage of seismic data here we employ the gravity inversion method based on density modelling and seismic data constraints to calculate the present day arc crustal thickness and then obtain the magmatic thickness by removing the pre existing crustal thickness from the present day arc crustal thickness finally the magma production rates along the main intraoceanic subduction region of the aleutian arc are mapped by estimating the island arc magmatic thickness and the most recent subduction inception dating result in addition the subduction zone temperatures and mantle melt amounts along five profiles across the aleutian arc are calculated the magma production rate variation is highly correlated with the mantle melt amount the slab temperature controls the extent of the slab dehydration which is essential for mantle wedge melting and the mantle wedge temperature controls the size of the hydrated mantle melting region and the melting fraction therein therefore as the subduction zone temperature controls the mantle melt amount we suggest that the subduction zone temperature is the first order controlling factor on the magma production rate

astronomical timescale and palaeoclimatic implication of stacked 3 6 myr monsoon records from the chinese loess plateau abstract magnetic susceptibility and grain size records from two continuous red clay and loess palaeosol sequences on the chinese loess plateau have been generated to investigate the evolution and variability of the east asian monsoon eam during the late pliocene and pleistocene tuning the grain size records to orbital obliquity and precession yields an improved astronomical timescale for the loess palaeosol sequence 0 2 6 ma and an extended age model for the upper red clay formation 2 6 3 6 ma this timescale indicates older ages for a number of the magnetic polarity boundaries consistent with lock in depth offsets in loess sequences good site to site correlation enables generation of stacked grain size and susceptibility records spanning the last 3 6 myr these records indicate that monsoon evolution since the late pliocene can be subdivided into three phases 0 1 25 1 25 2 72 and 2 72 3 4 ma each phase is characterized by unique amplitude and frequency characteristics for both summer monsoon magnetic susceptibility and winter monsoon grain size spectral analyses of the stacked monsoon proxies indicate that characteristics of both the summer and winter monsoons are dominated mainly by variance in the eccentricity 410 and 100 kyr obliquity 41 kyr and precession 23 and 19 kyr bands over the past 3 4 myr implying a non linear response of the long term eam evolution to orbital and glacial forcing

timing of glaciation and last glacial maximum paleoclimate estimates from the fish lake plateau utah abstract the high plateaus of utah include seven separate mountain ranges that supported glaciers during the pleistocene the fish lake plateau located on the eastern edge of the high plateaus preserves evidence of at least two glacial advances four cosmogenic 3 he exposure ages of boulders in an older moraine range from 79 to 159 ka with a mean age of 129 39 ka and oldest ages of 152 3 and 159 5 ka these ages suggest deposition during the type bull lake glaciation and marine oxygen isotope stage mis 6 twenty boulder exposure ages from four different younger moraines indicate a local last glacial maximum lgm of 21 1 ka coincident with the type pinedale glaciation and mis 2 reconstructed pinedale age glaciers from the fish lake plateau have equilibrium line altitudes ranging from 2950 to 3190 m lgm summer temperature depressions for the fish lake plateau range from 10 7 to 8 2 c assuming no change in precipitation comparison of the fish lake summer temperature depressions to a regional dataset suggests that the fish lake plateau may have had a slight increase 1 5 modern in precipitation during the lgm a series of submerged ridges in fish lake were identified during a bathymetric survey and are likely bull lake age moraines

triple oxygen isotopes in biogenic and sedimentary carbonates abstract the 17 o anomaly 17 o of natural waters has been shown to be sensitive to evaporation in a way analogous to deuterium excess with evaporated bodies of water e g leaf waters lake waters animal body waters tending to have lower 17 o than primary meteoric waters in animal body water 17 o relates to the intake of evaporated waters evaporative effluxes of water and the 17 o value of atmospheric o 2 which itself carries signatures of global carbon cycling and photochemical reactions in the stratosphere carbonates have the potential to record the triple oxygen isotope compositions of parent waters allowing reconstruction of past water compositions but such investigations have awaited development of methods for high precision measurement of 17 o of carbonate we describe optimized methods based on a sequential acid digestion reduction fluorination approach that yield 17 o data with the high precision 0 010 1 needed to resolve subtle environmental signals we report the first high precision 17 o dataset for terrestrial carbonates focusing on vertebrate biogenic carbonates and soil carbonates but also including marine invertebrates and high temperature carbonates we determine apparent three isotope fractionation factors between the o 2 analyte derived from carbonate and the parent waters of the carbonate these in combination with appropriate temperature estimates from clumped isotope thermometry or known or estimated body temperatures are used to calculate the 18 o and 17 o of parent waters the clearest pattern to emerge is the strong 17 o depletion in avian dinosaurian and mammalian body water from analyses of eggshell and tooth enamel relative to meteoric waters following expected influences of evaporated water e g leaf water and atmospheric o 2 on vertebrate body water parent waters of the soil carbonates studied here have 17 o values that are similar to or slightly lower than global precipitation our results suggest that 17 o will have useful application to paleoenvironmental studies of continental environments where the effects of evaporation are important and where vertebrate body water may record an isotopic signal of evaporated water sources and atmospheric oxygen

radiocarbon dating of thin pedogenic carbonate laminae from holocene archaeological sites radiocarbon dating has been previously suggested to be applicable to pedogenic carbonate however until now the validity of radiocarbon dates from pedogenic carbonate remained poorly understood because of the relatively low resolution of chronological controls in this study we compared the radiocarbon dates a total of 21 of thin 0 2 0 3 mm in thickness laminae of pedogenic carbonate coatings on clasts from holocene archaeological sites in the eastern mediterranean and south siberia with independently estimated age ranges for these sites we obtained a high correlation between the oldest laminae of coatings with the site ages the 14 c ages of pedogenic carbonate were systematically younger by c 0 3 1 6 ka mean c 0 75 ka compared with archaeological sites this finding suggests that pedogenic carbonate despite potential complicating factors can be dated more accurately with 14 c than has been generally appreciated

revised age of aleutian island arc formation implies high rate of magma production radioisotopic dating of subaerial and submarine volcanic and plutonic rocks from the aleutian island arc provides insight into the timing of arc formation in the middle eocene twenty eight 40 ar 39 ar ages constrain the duration of arc magmatism to the last 46 m y basaltic lavas from the finger bay volcanics the oldest exposed rocks in the arc gave an isochron age of 37 4 0 6 ma which is 12 17 m y younger than a widely cited age of 55 50 ma three main pulses of arc wide magmatism occurred at 38 29 16 11 and 6 0 ma which coincide with periods of intense magmatism in other western pacific island arcs using the geochronology and volumetric estimates of crust generated and eroded over the last 46 m y we calculate a time averaged magma production rate for the entire arc that exceeds previous estimates by almost an order of magnitude

deep crustal structure in the eastern gulf of mexico we use air gun data recorded by ocean bottom seismometers to constrain the velocity structure along gulf of mexico basin opening line 4 a profile extending from the northwestern florida peninsula across the florida escarpment to the central gulf of mexico moderately thinned continental crust with a moho depth of 32 33 km average sediment thickness of 6 km and an average crustal thickness of 27 km is interpreted on the northeast end of the profile offshore florida thinned and intruded continental crust is identified over a horizontal distance of 225 km where the crustal layer thins from 25 km to 6 7 km mean seismic velocities of the crust in this region increase from 6 55 km s to 6 95 km s from northeast to southwest and are evidence for increased magmatic input as rifting developed oceanic crust with an average thickness of 5 6 5 7 km is observed over a distance of 175 km on the southwest end of the profile with an extinct spreading ridge with an axial valley morphology imaged on a coincident seismic reflection profile anomalously high upper oceanic crust velocities of 6 0 6 7 km s are interpreted as massive basalt flows and could reflect increased temperatures during emplacement integrating well seismic reflection and our seismic refraction data allow us to estimate a full spreading rate of 2 2 cm yr for seafloor spreading along the profile this indicates that oceanic crust was emplaced at a slow spreading center

paleogene history of the kula plate offshore evidence and onshore implications paleocene to middle eocene magnetic anomalies were mapped over oceanic crust that accreted at the kula pacific spreading center and is now obliquely entering the western aleutian trench between 179 e and 168 e the strike of anomalies and the pattern of abyssal hills and fracture zones changed abruptly during 56 55 ma when north south spreading veered to northwest southeast 310 130 kula pacific spreading ceased in 43 ma a 75 km long section of the fossil kula rift axis has avoided subduction although it now intersects the trench axis almost orthogonally near 171 5 e a narrow remnant of the former kula plate northwest of this fossil spreading center is bounded by a fossil kula pacific transform with a high transverse ridge alongside a sediment filled transform valley anomalies on this remnant show that eocene kula pacific spreading was highly asymmetric 2 1 the 56 55 ma change in kula plate rotation inferred from the change in spreading direction coincided with birth of the aleutian subduction zone and was probably a consequence of the resulting change in slab pull stresses on the oceanic lithosphere the change in direction of kula north american motion is a plausible explanation for the detachment of continental terranes from the pacific northwest and their migration around the gulf of alaska and for the early eocene demise of alaska range are volcanism the cessation of kula pacific spreading coincides with a major change in pacific plate rotation and the subsequent direction of convergence of the pacific plate with the aleutian arc was similar to the 55 43 ma direction of kula plate convergence

evidence for holocene environmental changes in the northern fertile crescent provided by pedogenic carbonate coatings abstract holocene environmental changes in the northern fertile crescent remain poorly understood because of the scarcity of local proxy records in the region in this study we investigated pedogenic soil formed carbonate coatings on stones at the pre pottery neolithic site gobekli tepe as an indicator of local early mid holocene environmental changes the 14c ages and stable isotopic composition of carbon and oxygen in thin 0 2 0 3 mm thick pedogenic carbonate lamina indicate two main periods of coating formation the early holocene ca 10000 6000 cal yr bp and the mid holocene ca 6000 4000 cal yr bp during the first period there was an inverse relationship between 13c and 18o curves a decrease in 13c values coincide with an increase in 18o values for this period a trend towards higher temperatures is suggested in the mid holocene the mean rate of coating growth was 2 3 times higher than in the early holocene both 13c and 18o reached their maximum values during this time and the direction of changes of the 13c and 18o curves became similar the combination of data suggests that this period was the most humid in the holocene and on average warmer than the early holocene at ca 4000 cal yr bp secondary accumulation of carbonate ceased presumably reflecting a shift to a more arid climate

strain determination from concentric folds abstract a new technique to determine flattening strain from initially concentric folds is described in this paper the proposed method is simple and involves direct measurements on fold profiles it requires measurement of the distance between the center of the fold to the middle of the layer and this is plotted as a function of line orientation the method needs few measurements at fixed angular spacing resulting in quick estimation of strain

bowers ridge bering sea an oligocene early miocene island arc bowers ridge is an similar to 700 km long arcuate ridge behind the central aleutian arc in the bering sea the lack of age and geochemical data for the ridge has hampered the development of geodynamic models for the evolution of the north pacific and the aleutian bering sea region here we present the first geochemical and ar 40 ar 39 age data for the volcanic basement of bowers ridge and a seamount from the western end of the ridge sampled during r v sonne cruise so201 1b the northern bowers ridge basement 26 32 ma consists of mafic to intermediate calc alkaline rocks with adakite like sr y 33 53 la n yb n 3 3 7 8 high field strength element hfse depleted e g nb n la n 0 07 0 31 trace element patterns and sr nd pb isotope compositions within the western aleutian arc array implying magma generation above an obliquely subducting slab the seamount samples 22 24 ma are hfse rich alkaline olivine basalts la n yb n 3 3 3 9 nb n la n 1 0 1 4 with minor arc type trace element signatures pb n ce n 1 4 1 6 k n nb n 1 7 1 9 but with pacific mid oceanic ridge basalt morb like isotopic compositions pointing to an origin by small degree decompression melting from slightly subduction modified mantle the geochemistry of the recovered rocks can be explained by highly oblique subduction along the northern part of bowers ridge in its present day configuration consistent with an in situ origin of bowers ridge as a cenozoic island arc

gravity effect of sediment compaction examples from the north sea and the rhine graben abstract a fourier domain expression for calculating the gravity effect of a continuously varying density structure is used to investigate the way in which sediment compaction modifies the shape of the gravity anomaly across a sedimentary basin in general sediment density increases with depth in a basin as the overburden thickness increases the effect of the increase in sediment density is to reduce the gravity contribution from the density contrasts in the deeper parts of the basin relative to near surface contributions for a theoretical uncompensated basin the gravity effect of the sediments is calculated for a density depth variation described by 1 a simple exponential increase in sediment density with depth and 2 an exponential modified to include a local density inversion representative of sediment overpressuring it is shown that for both cases the calculated gravity does not necessarily reflect the morphology of the sediment basement interface the gravity effect is most sensitive to the distribution of the youngest stratigraphic units within the basin results of modeling observed gravity anomalies across the viking and rhine graben show that the small peak to trough amplitude of the gravity anomalies across these basins can be attributed to the increase in sediment density with depth rather than the compensation of the basin for the rhine graben it is further shown that the wavelength of the gravity anomaly is strongly controlled by the flexural strength of the lithosphere together these results suggest that while the amplitude of gravity anomalies across extensional basins may be primarily reflecting compaction of the sediment infill the anomaly wavelength is more sensitive to the compensation mechanism

middle and late wisconsin paleobotanic and paleoclimatic records from the southern colorado plateau usa the colorado plateau is a distinct physiographic province in western north america which presently straddles the transition between summer wet and summer dry climatic regimes to the south and northwest respectively in addition to climate the diversity of environments and plant communities on the colorado plateau has resulted from extreme topographic diversity desert lowlands as low as 360 m elevation are surrounded by forested plateaus and even higher peaks greater than 3800 m elevation this environmental diversity provides a unique opportunity to study the history of biotic communities in an arid region of north america although the colorado plateau harbours numerous potential sites the paleoecological record of the plateau is poorly known potential deposits for analysis include packrat middens alluvial and cave sites at lower elevations and lake bog and wetland sites at higher elevations forty six sites have been analysed across the nearly 337 000 km2 region of which 27 contain records that span marine oxygen isotope stage is 2 data with is 3 information coming from only 12 sites most is 2 and 3 sites are clustered along the lowland regions of the colorado river corridor and the uplands of the mogollon rim area we compiled selected data from long paleoecological records to examine patterns of vegetation and climate change across the southern colorado plateau for the middle and late wisconsin during the middle wisconsin mixed conifers covered middle elevations presently dominated by ponderosa pine pinus ponderosa and juniper juniperus woodland grew at elevations today covered by blackbrush coleogyne and sagebrush artemisia desert during the late wisconsin boreal conifers primarily engelmann spruce picea engelmannii replaced the mixed conifer association estimates of mean annual temperatures mat during is 3 were at least 3 4 c cooler than today whereas is 2 mat estimates are at least 5 c colder our investigation of millennial scale climatic variability within the region provided equivocal results the packrat midden sequence could not distinguish vegetation changes that might be associated with heinrich events in the north atlantic from the lake records however many heinrich events were associated with generally drier intervals often with elevated sagebrush pollen concentrations future paleoecological investigations should concentrate on the northern colorado plateau as well as the eastern and western margins additional sites along with closer spaced sampling in regions already studied will be important in determining the history of important climatic phenomena such as the timing of the arizona monsoon

evolution of the stable carbon isotope composition of atmospheric co2 over the last glacial cycle we present new c measurements of atmospheric co covering the last glacial interglacial cycle complementing previous records covering terminations i and ii most prominent in the new record is a significant depletion in c atm of 0 5 occurring during marine isotope stage mis 4 followed by an enrichment of the same magnitude at the beginning of mis 3 such a significant excursion in the record is otherwise only observed at glacial terminations suggesting that similar processes were at play such as changing sea surface temperatures changes in marine biological export in the southern ocean so due to variations in aeolian iron fluxes changes in the atlantic meridional overturning circulation upwelling of deep water in the so and long term trends in terrestrial carbon storage based on previous modeling studies we propose constraints on some of these processes during specific time intervals the decrease in c atm at the end of mis 4 starting approximately 64 kyr b p was accompanied by increasing co this period is also marked by a decrease in aeolian iron flux to the so followed by an increase in so upwelling during heinrich event 6 indicating that it is likely that a large amount of c depleted carbon was transferred to the deep oceans previously i e at the onset of mis 4 apart from the upwelling event at the end of mis 4 and potentially smaller events during heinrich events in mis 3 upwelling of deep water in the so remained reduced until the last glacial termination whereupon a second pulse of isotopically light carbon was released into the atmosphere

steering of westerly storms over western north america at the last glacial maximum the last glacial maximum hydroclimate over western north america differed from the modern climate a proxy model comparison suggests that the glacial storm track was squeezed and steered by atmospheric high pressure systems

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

comparison of δ18o analyses on individual planktic foraminifer orbulina universa shells by sims and gas source mass spectrometry author s wycech jb kelly dc kozdon r orland ij spero hj valley jw abstract 2018 elsevier b v the oxygen isotope 18o compositions of final chamber fragments of individual shells of the planktic foraminifer orbulina universa were measured in situ via secondary ion mass spectrometry sims and by traditional gas source mass spectrometry gsms entailing acid digestion of sampled calcite the paired sims gsms analyses were performed on final chamber fragments of fossil shells taken from the top of a sediment core holocene as well as shells grown in laboratory culture multiple iterations of sims gsms analyses were conducted on final chamber fragments treated with a variety of cleaning protocols the series of paired analyses yielded an average sims gsms 18o offset 18osims gsms of 0 9 0 1 2 se the volume of material analyzed in 10 m sims spots is 105 times smaller than that analyzed by gsms hence the extent to which these 18osims gsms values represent real differences in analyte vs instrumental factors remains unclear possible contributing factors to the sims gsms 18o difference include sample standard mismatch by sims differences in standardization of sims and gsms and non calcite contaminants in samples although the two datasets are consistently offset sims values reproduce inter shell 18o variability delineated by shell fragment gsms values this strong positive covariance proved useful for bringing the two datasets into agreement i e 18osims gsms 0 and confirms that sims based foraminifer 18o values record changes in calcification temperature and or 18o of seawater whether shells of foraminifer taxa with differing microcrystalline structures chemical composition and or preservation histories register a similar 18osims gsms value is a subject of ongoing testing

response of the north american monsoon to regional changes in ocean surface temperature 1 the north american monsoon nam an onshore wind shift occurring between july and september has evolved in character during the holocene largely due to changes in northern hemisphere insolation published paleoproxy and modeling studies suggest that prior to 8000 cal years bp the nam affected a broader region than today extending westward into the mojave desert of california holocene proxy sst records from the gulf of california goc and the adjacent pacific provide constraints for this changing nam climatology prior to 8000 cal years bp lower goc ssts would not have fueled northward surges of tropical moisture up the goc which presently contribute most of the monsoon precipitation to the western nam region during the early holocene the north pacific high was further north and ssts in the california current off baja california were warmer allowing monsoonal moisture flow from the subtropical pacific to take a more direct northwesterly trajectory into an expanded area of the southwestern u s west of 114 w a new upwelling record off southwest baja california reveals that enhanced upwelling in the california current beginning at 7500 cal year bp may have triggered a change in nam climatology focusing the geographic expression of nam in the southwest usa into its modern core region east of 114 w in arizona and new mexico holocene proxy precipitation records from the southwestern u s and northwestern mexico including lakes vegetation pollen and caves are reviewed and found to be largely supportive of this hypothesis of changing holocene nam climatology

experimentally based water budgets for dehydrating slabs and consequences for arc magma generation phase diagrams of hydrous mid ocean ridge mor basalts to 330 km depth and of hydrous peridotites to 250 km depth are compiled for conditions characteristic for subduction zones a synthesis of our experimentally determined phase relations of chlorite lawsonite epidote zoisite amphibole paragonite chloritoid talc and phengite in basalts and of phase relations from the literature of serpentine talc chlorite amphibole and phase a in ultramafics permits calculation of h2o contents in hydrous phase assemblages that occur in natural compositions this yields the information necessary to calculate water budgets for descending slabs starting from low grade blueschist conditions 10 20 km depth with h2o contents between 5 and 6 wt for hydrated oceanic crust complete dehydration is achieved between 70 and 300 km depth as a function of individual slab geotherms hydrous phases which decompose at depth below volcanic arcs are lawsonite zoisite chloritoid and talc phengite in mafic compositions and chlorite and serpentine in peridotite approximately 15 35 of the initially subducted h2o are released below volcanic arcs the contribution of amphibole dehydration to the water budget is small 5 20 and occurs at relatively shallow depth 65 90 km in any predicted thermal structure dehydration is a combination of a stepwise and a continuous process through many different reactions which occur simultaneously in the different portions of the descending slab such a dehydration characteristic is incompatible with single phase dehydration models which focus fluid flow through a unique major dehydration event in order to explain volcanic fronts as a consequence of continuously progressing dehydration water ascending from the slab will be generally available to depth of ca 150 200 km the fluid rising from the subducting lithosphere will cause partial melting in the hot portion of the mantle wedge we propose that the volcanic front simply forms above the mantle wedge isotherm where the extent of melting is sufficient to allow for the mechanical extraction of parental arc magmas thermal models show that such an isotherm ca 1300oc locates below volcanic fronts slab surface depths below such an isotherm are compatible with the observed depths of the slab surface below volcanic fronts 1998 elsevier science b v all rights reserved

gravity modelling of the hellenic subduction zone a regional study abstract the hellenic subduction zone is clearly expressed in the arc shaped distribution of earthquake epicenters and gravity anomalies which connect the peloponnesos with crete and anatolia in this region oceanic crust of the african plate collides northward with continental crust of the aegean microplate which itself is pushed apart to the south west by the anatolian plate and at the same time is characterised by crustal extension the result is an overall collision rate of up to 4 cm year and a retreating subduction process recent passive and active seismic studies on and around crete gave first but not in all details consistent structural results useful for supporting gravity modelling this was undertaken with the aim of presenting the first 3d density structure of the entire subduction zone gravity interpretation was based on a bouguer map newly compiled using data from land marine and satellite sources the anomalies range from 170 mgal cretan sea to 10 mgal mediterranean ridge 3d gravity modelling was done applying the modelling software igmas the computed bouguer map fits the low frequency part of the observed one which is controlled by variations in moho depth less than 20 km below the cretan sea and extending 30 km below crete and the extremely thick sedimentary cover partly up to 18 km of the mediterranean ridge the southernmost edge of the eurasian plate with its more triangular shaped backstop area was traced south off crete only 50 to 100 km further to the south the edge of the african continent was traced as well in between these boundaries there is african oceanic crust which has a clear arc shaped detachment line situated at the eurasian continental edge the subduction arc is open towards the north its slab separates hotter mantle material lower density below the updoming moho of the cretan sea from colder one higher density in the south subjacent to the upper continental crust of crete is a thickened layer of lower crust followed by the subducted oceanic crust with some mantle material as intermediate layer the depth of the oceanic moho below crete is 50 km the presence and structure of subducted or underplated sediments remains uncertain

stable carbon and oxygen isotopes of pedogenic carbonates ajo mountains southern arizona implications for paleoenvironmental change abstract in this study we compare the stable isotope composition of late holocene pedogenic carbonate from a late holocene soil developed on the pediment below the ajo mountains in southern arizona usa with measurements of the 18 o of the soil water throughout the seasonal cycle and with 18 o and 13 c measurements on older dated soils the comparison with the soil water composition shows that the pedogenic carbonate is forming in equilibrium with highly evaporated soil water at the highest summer temperatures the 13 c of the carbonate apparently reflects equilibrium with co 2 of an isotopic composition consistent with the present mixture of c3 desert shrubs and cam cactus comparison with glacial period soil carbonates shows that there has been little change in the 18 o but that the 13 c was about 4 5 heavier independent evidence indicates that glacial period summer temperatures were probably much cooler and that the 18 o of precipitation was also lighter the increase in the carbonate water fractionation factor with decreasing temperature probably counteracted the decrease in the 18 o of precipitation producing little net change in the 18 o of the soil carbonate we attribute the decrease in the 13 c to replacement of a glacial period c4 grassland by holocene c3 cam desert shrubs and succulents this replacement was probably in response to an increase in temperature and reduction in summer precipitation at the end of the last glacial period the 13 c of older soil carbonates indicates that landscape was dominated by grassland for most of the past 700 ka and that the present vegetation likely represents a relatively brief anomaly

patterns of hydroclimatic change in the rocky mountains and surrounding regions since the last glacial maximum abstract the paleohydrologic record of western north america since the last glacial maximum reveals a wide range of hydroclimatic variability in time and space to improve the understanding of abrupt hydroclimatic shifts and millennial scale hydrologic changes in the central rocky mountains we reconstruct the lake level histories of two small lakes in the beartooth and bighorn mountains in northern wyoming over the past 17 ka to do so we use ground penetrating radar gpr and sediment cores to track the elevations of shoreline sediments within the lakes through time we compare the stratigraphies with those from four other lakes in wyoming and colorado and find widespread evidence for a terminal pleistocene drought from 15 to 11 ka an early holocene humid period from 11 to 8 ka and mid holocene aridity from 8 to 5 5 ka the northern wyoming lakes also provide evidence of high levels in the pleistocene possibly before ca 15 ka and rapid hydroclimatic changes that may have correlated with heinrich event 1 ca 16 8 ka we place the changes in a broad context by summarizing and mapping water level changes from 107 additional previously studied lakes important patterns include 1 extensive drying across the western u s after 15 ka 2 sub regional differences during the pleistocene holocene transition 3 a north south contrast from 9 to 6 ka consistent with a northward shift in storm tracks as the influence of the laurentide ice sheet diminished and 4 rapid increases in effective moisture across much of western north america from 6 to 4 ka

climate controls on spatial and temporal variations in the formation of pedogenic carbonate in the western great basin of north america pedogenic carbonate is common in arid and semiarid soils and though its stable c and o isotope composition has been shown to reflect local environmental conditions questions remain about the quantitative nature of this relationship and the implications for paleoclimate applications to further address these questions a climosequence of four holocene soils in fish lake valley nevada western united states was instrumented and examined over the course of more than a year the annual precipitation along the transect ranges from 80 mm yr 1 to 220 mm yr 1 results show that the c and o stable isotope compositions of soil co 2 h 2 o and carbonate change systematically with elevation and climate however there was considerable temporal variability in the conditions that affected carbonate isotope values at the lowest elevation co 2 13 c and h 2 o 18 o values were similar to that in equilibrium with carbonate nearly year round at the midelevation sites spring through summer co 2 13 c and h 2 o 18 o values appeared to most closely match the 13 c and 18 o values of pedogenic carbonate at the highest elevation the c and o isotopes of carbonate did not reflect the soil co 2 13 c and h 2 o 18 o values measured during the period of study but they did appear to reflect soil respiration rates during the late spring the transect shows that arid soil carbonate 13 c values strongly reflect variations in soil respiration rates and the resulting concentrations of soil co 2 these results also indicate that depth profile sampling may be required to adequately constrain respiration rates which affect the interpreted atmospheric co 2 concentrations

total bulk strain in flattened parallel folds a new simple method is proposed to analyse the total bulk shortening in flattened parallel folds application of the method requires determining first the amount of flattening using any of the available techniques or by using a new method proposed in this paper then some shape information must be obtained from the fold such as the interlimb angle or the aspect ratio as well as the eccentricity of the conic section that gives the best fit to the midline of the folded layer the latter parameter can be obtained using the program fold profiler finally the flattening and the shape data are used to obtain the total bulk shortening of the folded layer a computer code is provided that performs these calculations the method does not consider the initial layer shortening prior to buckling and therefore gives an estimate of the minimum bulk shortening associated with the fold the strain data obtained with this method are not point values from selected locations inside the folded structure but an overall evaluation of its bulk strain that can be advantageously used in the regional interpretation the analysis is two dimensional and only considers deformation in the fold profile plane the study is completed with an example of the application of the method to natural folds

influence of parent material and grain size on carbonate coatings in gravelly soils palo duro wash new mexico abstract close examination of carbonate coatings found on the bottoms of pebbles from gravelly soils indicates that soil hydraulic conductivity and respiration rate have a strong influence on the carbonate morphology of aridic soils clast size and lithology strongly correlate with coating thickness because of the nature of unsaturated flow within macropores of gravelly soils thicker coatings are found at the bottom of larger clasts coatings are thickest on limestone pebbles that commonly display dissolution features at their tops model values for soil co 2 based on gas diffusion predict soil atmospheric condition where soil water can remain undersaturated with respect to calcite and dissolve calcareous pebbles throughout the depth of the soil profile this coupled with soil hydrology creates a microenvironmental condition where the largest limestone clasts have the thickest coating a second phenomenon that is apparent from close observation of coatings is that soils containing abundant fines and translocated dust in the matrix have continuous coatings continuous coatings are absent however in soils that do not neighbor a dust source or do not have sufficient fines in the matrix in these soils coatings are almost completely absent from sand and granule size particles suggesting that zones of preferential flow in the soil inhibit carbonate precipitation in parts of the soil profile these inconstancies in the continuity and thickness of coatings suggest that stage iii morphology may not develop at the same rate even locally

50 000 years of vegetation and climate history on the colorado plateau utah and arizona usa sixty packrat middens were collected in canyonlands and grand canyon national parks and these series include sites north of areas that produced previous detailed series from the colorado plateau the exceptionally long time series obtained from each of three sites n48 000 14 cy r bp to present include some of the oldest middens yet discovered most middens contain a typical late wisconsinan glaciation mixture of mesic and xeric taxa evidence that plant species responded to climate change by range adjustments of elevational distribution based on individual criteria differences in elevational range from today for trees and shrubs ranged from no apparent change to as much as 1200 m difference the oldest middens from canyonlands np however differ in containing strictly xeric assemblages including middens incorporating needles of arizona single leaf pinyon far north of its current distribution similar aged middens from the eastern end of grand canyon np contain plants more typical of glacial climates but also contain fossils of one seed juniper near its current northern limit in arizona holocene middens reveal the development of modern vegetation assemblages on the colorado plateau recording departures of mesic taxa from low elevation sites and the arrival of modern dominant components much later published by university of washington

the dynamics of big mantle wedge magma factory and metamorphic metasomatic factory in subduction zones abstract the east asian continental margin is underlain by stagnant slabs resulting from subduction of the pacific plate from the east and the philippine sea plate from the south we classify the upper mantle in this region into three major domains a metasomatic metamorphic factory mmf subduction zone magma factory szmf and the big mantle wedge bmw whereas the convection pattern is anticlockwise in the mmf domain it is predominantly clockwise in the szmf and bmw along a cross section from the south here we define the mmf as a small wedge corner which is driven by the subducting pacific plate and dominated by h 2 o rich fluids derived by dehydration reactions and enriched in large ion lithophile elements lile which cause the metasomatism the szmf is a zone intermediate between mmf and bmw domains and constitutes the main region of continental crust production by partial melting through wedge counter corner flow large hydrous plume generated at about 200 km depth causes extensive reduction in viscosity and the smaller scale hydrous plumes between 60 km and 200 km also bring about an overall reduction in the viscosity of szmf more fertile and high temperature peridotites are supplied from the entrance to this domain the domain extends obliquely to the volcanic front and then swings back to the deep mantle together with the subducting slab the bmw occupies the major portion of upper mantle in the western pacific and convects largely with a clockwise sense removing the eastern trench oceanward sporadic formation of hydrous plume at the depth of around 410 km and the curtain flow adjacent to the trench cause back arc spreading we envisage that the heat source in bmw could be the accumulated ttg tonalite trondhjemite granodiorite crust on the bottom of the mantle transition zone the ongoing process of transportation of granitic crust into the mantle transition zone is evident from the deep subduction of five intra oceanic arcs on the subducting philippine sea plate from the south in addition to the sediment trapped subduction by the pacific plate and philippine sea plate the dynamics of mmf szmf and bmw domains are controlled by the angle of subduction a wide zone of mmf in sw japan is caused by shallow angle subduction of the philippine sea plate and the markedly small mmf domain in the mariana trench is due to the high angle subduction of pacific plate the domains in ne japan and kyushu region are intermediate between these two during the tertiary a series of marginal basins were formed because of the nearly 2000 km northward shift of the subduction zone along the southern margin of tethyan asia which may be related to the collision of india with asia and the indentation the volume of upper mantle under asia was reduced extensively on the southern margin with a resultant oceanward trench retreat along the eastern margin of asia leading to the formation of a series of marginal basins the western pacific domain in general is characterized by double sided subduction from the east by the oldest pacific plate and from the south by the oldest indo australian plate the old plates are hence hydrated extensively even in their central domains and therefore of low temperature the cracks have allowed the transport of water into the deeper portions of the slab and these domains supply hydrous fluids even to the bottom of the upper mantle thus a fluid dominated upper mantle in the western pacific drives a number of microplates and promote the plate boundary processes

mid holocene drying of the u s great basin recorded in nevada speleothems lake level records point to dramatic changes in great basin water balance over the last 25 ka but the timing and pace of holocene drying in the region remains poorly documented here we present stable isotope and trace metal data from two lehman caves nv speleothems that provide a well dated record of latest pleistocene to mid holocene hydroclimate in the u s great basin together the stalagmites span the interval between 16 4 ka and 3 8 ka with a hiatus from 15 0 ka to 12 7 ka mg ca and d 13 c covary throughout the records consistent with control by the extent of degassing and prior calcite precipitation pcp measurements of modern cave and soil waters support pcp as the primary control on drip water trace element composition we therefore interpret mg ca and d 13 ca s reflecting infiltration rates with higher values corresponding to drier periods both mg ca and d 13 c indicate a wet period at the beginning of the record 12 7e8 2 ka followed by pronounced drying after 8 2 ka this mid holocene drying is consistent with records from around the western united states including a new compilation of great basin lake level records the strong temporal correspondence with the collapse of the laurentide ice sheet over hudson bay suggests that this drying may have been triggered by northward movement of the winter storm track as a result of ice sheet retreat however we cannot rule out an alternative hypothesis that wet early holocene conditions are related to equatorial pacific sea surface temperature regardless our results suggest that great basin water balance in the early holocene was driven by factors other than orbital changes

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

holocene vegetation and fire reconstructions from the aquarius plateau utah usa micropaleontological assemblages from two lakes located on the aquarius plateau in southern utah were investigated to evaluate changes in vegetation fire disturbance and paleoclimate over the last 8600 years this paper presents reconstructions of holocene landscape conditions and wildfire dynamics in the subalpine zone of the colorado plateau during the early holocene forests on the aquarius plateau were dominated by spruce and pine at upper elevations and mixed conifer forests at mid elevation sites fire return intervals were the most frequent of the record averaging 250 years between burning episodes proxy based reconstructions of the middle holocene suggest warmer climate conditions relative to present with variable moisture availability during the middle holocene the forest zone on the aquarius plateau contracted where both lower and upper timberline retreated upslope and downslope respectively fire frequency was similar to early holocene though overall charcoal accumulations were reduced in the late holocene forests in the subalpine zone became dominated by spruce fir and aspen while at mid elevation forests dominated by douglas fir spruce and pine established the most striking result indicates that evidence of fire was essentially absent from the aquarius plateau during the late holocene until the arrival of european settlers to the region c 1850

revision of the epica dome c co2 record from 800 to 600 kyr before present the european project for ice coring in antarctica dome ice core from dome c edc has allowed for the reconstruction of atmospheric co2 concentrations for the last 800 000 years here we revisit the oldest part of the edc co2 record using different air extraction methods and sections of the core for our established cracker system we found an analytical artifact which increases over the deepest 200 m and reaches 10 1 2 4 ppm in the oldest deepest part the governing mechanism is not yet fully understood but it is related to insufficient gas extraction in combination with ice relaxation during storage and ice structure the corrected record presented here resolves partly but not completely the issue with a different correlation between co2 and antarctic temperatures found in this oldest part of the records in addition we provide here an update of 800 000 years atmospheric co2 history including recent studies covering the last glacial cycle

990 and 1100 ma grenvillian tectonothermal events in the northern oaxacan complex southern mexico roots of an orogen inliers of f1 0 1 3 ga rocks occur throughout mexico and form the basement of the oaxaquia microcontinent in the northern part of the largest inlier in southern mexico rocks of the oaxacan complex consist of the following structural sequence of units from bottom to top which protolith ages are 1 huitzo unit a 1012f12 ma anorthosite mangerite charnockite granite amcg suite 2 el catro n unit z1350 ma orthogneiss migmatized at 1106f6 ma and 3 el marquez unit z1140 ma para and orthogneisses these rocks were affected by two major tectonothermal events that are dated using u pb isotopic analyses of zircon a the 1106f6 ma olmecan event produced a migmatitic or metamorphic differentiation banding folded by isoclinal folds and b the 1004 978f3 ma zapotecan event produced at least two sets of structures z1 recumbent isoclinal class 1c 3 folds with gently nw plunging fold axes that are parallel to mineral and stretched quartz lineations under granulite facies metamorphism and z2 tight upright subhorizontal wnw to nne trending folds accompanied by development of brown hornblende at upper amphibolite facies metamorphic conditions cooling through 500 jc at 977f12 ma is documented by 40 ar 39 ar analyses of hornblende fold mechanisms operating in the northern oaxacan complex under zapotecan granulite facies metamorphism include flexural and tangential longitudinal strain accompanied by intense flattening and stretching parallel to the fold axes subsequent phanerozoic deformation includes thrusting and upright folding under lower grade metamorphic conditions the zapotecan event is widespread throughout oaxaquia and took crustal rocks to a depth of f25 30 km by orogenic crustal thickening and is here designated as zapotecan orogeny modern analogues for zapotecan granulite facies metamorphism and deformation occur in middle to lower crustal portion of subduction and collisional orogens contemporaneous tectonothermal events took place throughout oaxaquia and in various parts of the genvillian orogen in laurentia and amazonia d 2003 elsevier science b v all rights reserved