late quaternary arroyo formation and climate change in the american southwest arroyos entrenched ephemeral streams that form in desert environments first appeared in the arid and semiarid american southwest after 8000 14 c yr b p for at least 7 k y prior to that time climate vegetation and groundwater conditions were not conducive for arroyo formation along the floors of desert valleys after a hiatus in arroyo formation the frequency of arroyo cutting and filling increased dramatically after 4000 14 c yr b p the early holocene arroyos and increased frequency of arroyo incision after 4000 14 c yr b p are related to the establishment and changes in postglacial vegetation climate and groundwater conditions as a result arroyo sequences preserve a record of large scale climate change and small scale climatic perturbations that occurred during the holocene human modification of valley flood plains is an additional factor that contributed to mid nineteenth and early twentieth century arroyo cutting

oxygen and carbon isotopes in modern fresh water ostracod valves assessing vital offsets and autecological effects of interest for palaeoclimate studies abstract the isotopic composition of modern benthic ostracod and mollusc carbonate the oxygen isotope composition of lake water 18ow the carbon isotope composition of dissolved inorganic carbon 13cdic and water temperatures were monitored during a year at different water depths in two lakes ammersee and starnberger see southern germany the aim was to test whether the valves are built in isotopic equilibrium and how seasonal water temperatures are recorded in the shells we find systematic offsets between 18o of valve carbonate compared to 18o expected for a theoretical calcite formed in isotopic equilibrium offsets are higher than 2 for different species of the candona group 1 5 for cytherissa lacustris and around 0 8 for limnocythere inopinata and darwinula stevensoni they seem to be constant for all instars of a species and temperature independent mean water temperatures of the calcification period are readily reflected in the valve 18o if corrected for the offsets 13c of valve carbonate is mainly controlled by 13c of the dissolved carbonate in ambient lake water but seems to be biased by micro habitat effects and vital offsets the study provides information on the seasonality of valve formation thus potentially allowing the quantification of temporal and spatial water temperature gradients from specific 18o records

post tectonic landscape evolution of a coupled basin and range pinaleno mountains and safford basin southeastern arizona the pinaleno mountains and adjacent safford basin are a landscape defined by the extensional tectonics of the basin and range physiographic province however over the last 4 m y this coupled basin and range have been actively degrading in the absence of widespread regional extension while rates of relief generation and upland erosion during active subsidence ca 12 5 ma are reflected in the geometry of the basin s structure and the stratigraphy it contains rates of post tectonic landscape evolution from the pliocene to the present have been heretofore unknown we combined topographic analyses of the pinaleno mountains with cosmogenic nuclide derived catchment averaged erosion rates and burial dates of axial and piedmont deposits to quantify rates of post tectonic landscape evolution and define a chronology for the last stages of deposition and subsequent incision in safford basin in addition to constraining the timing of a deposit s formation cosmogenic nuclide burial dates provide paleo upland erosion rates at the time of deposition erosion rates in the pinaleno mountains have been generally moderate over the past 4 m y ranging between 30 and 60 m m y with no strong relationship to the drainage basins modern topography a potential acceleration of erosion rates to 100 250 m m y between 3 5 and 2 ma correlates with an inferred period of enhanced precipitation as well as the arrival from upstream of the gila river in safford basin sometime shortly before 2 8 ma widespread incision of safford basin was under way by ca 2 ma as recorded by the dissection of piedmont basin highstand deposits frye mesa and two intermediate gila river terraces on the northeast margin of safford basin dated to 1 8 ma and 0 64 ma gila river incision rates have ranged from 30 to 60 m m y over the past 3 m y paleo upland erosion rates and modern millennial scale upland erosion rates fall within the same range as incision rates of the gila river in safford basin suggesting that upland erosion rates are predominantly a function of base level fall driven by axial incision however based on similarities between catchment averaged erosion rates and topography from basins draining into the integrated safford basin and the still internally drained sulphur springs basin to the south it appears that upland erosion rates during the quaternary are not being driven exclusively by regional incision rates

a 22 000 year record of vegetation change in the north central sonoran desert abstract plant macrofossils from eleven packrat neotoma sp middens provide a history of vegetation change over the last 22 140 years at eagle eye mountain near the northern border of the sonoran desert in arizona this site is located in the arizona upland subdivision departures and arrivals of various perennial plant species during the holocene were similar to other records from more southerly sites and support earlier generalizations of van devender van devender t r 1990 late quaternary vegetation and climate of the sonoran desert united states and mexico in betancourt j l van devender t r martin p s eds packrat middens the last 40 000 years of biotic change university of arizona press tucson pp 134 165 regarding the tempo and mode of late quaternary changes in the arizona upland evergreen woodland containing pinus monophylla singleleaf pinyon juniperus osteosperma utah juniper and quercus turbinella shrub live oak occupied the site during full glacial times the latter two species but not p monophylla persisted into the early holocene and were joined by a limited number of desertscrub species including acacia greggii catclaw carnegiea gigantea saguaro and several other succulents with the arrival of many other species during the middle holocene a desertscrub community that differed considerably from the modern vegetation developed acacia greggii and cercidium floridum blue paloverde were the principal large woody species on exposed hillslopes assemblages similar in composition to the modern desertscrub did not appear until approximately 4000 years ago when the more xerophytic cercidium microphyllum foothills paloverde arrived and c floridum disappeared from hillslopes the delayed arrival of c microphyllum in comparison to other sonoran desertscrub species with similar climatic tolerances is attributed to the limited dispersal distance of its seeds by seed eating heteromyid rodents at 4540 and 6425 yr b p the cold intolerant shrub encelia farinosa was present on northeasterly aspect exposures where it is absent today suggesting slightly warmer winter conditions during the middle holocene the presence of the tree cercidium floridum and the perennial c 4 grass setaria leucopila on exposed slopes during the middle holocene indicates substantially moister conditions during that time than in the late holocene or today at sites on the xeric limits of the modern distributions of both species average annual precipitation is from 50 to 100 greater than that presently received at eagle eye mountain in particular the responses of s leucopila and cacti during the middle holocene indicate substantial increases in warm season precipitation

paleoclimatic significance of late quaternary lacustrine and alluvial stratigraphy animas valley new mexico lacustrine and alluvial stratigraphic sequences in the southern animas valley of new mexico allow reconstruction of late quaternary climates four separate stands of late quaternary lake cloverdale in the southern animas valley are recorded by lacustrine shoreline deposits soils and stratigraphic evidence show that three young lake highstands occurred during the holocene and that a higher lake stand occurred 18 000 to 20 00014c yr b p fluvial systems aggraded the southern animas valley during the middle to late holocene the late quaternary stratigraphy shows that several periods during the late holocene were characterized by higher effective precipitation than at any time since the last glacial maximum

limestone and the problem of radiocarbon dating of land snail shell carbonate in order to test the role of limestone in producing anomalously old radiocarbon ages in land snail shells 14 c analyses were performed on shell carbonate of modern land snails from limestone and nonlimestone areas of jamaica no anomaly was found in snails from the nonlimestone area implying that such material is suitable for radiocarbon dating snails from limestone areas produced variable anomalies of as much as 3 120 yr due to incorporation of 14 c free limestone into shell carbonate all rock scraping snails and most leaf litter feeding snails from limestone areas showed anomalous 14 c contents because of the variability in 14 c content even within species no standard correction factor for limestone anomaly can be applied however dating error can be minimized by selecting ecologically appropriate species or by comparison of analyses of several fossil species within a stratum to their modern counterparts

a 16 000 14c yr b p packrat midden series from the usa mexico borderlands abstract a new packrat midden chronology from playas valley southwestern new mexico is the first installment of an ongoing effort to reconstruct paleovegetation and paleoclimate in the u s a mexico borderlands playas valley and neighboring basins supported pluvial lakes during full and or late glacial times plant macrofossil and pollen assemblages from nine middens in the playas valley allow comparisons of two time intervals 16 000 10 000 and 4000 0 14c yr b p vegetation along pluvial lake margins consisted of open pinyon juniper communities dominated by pinus edulis juniperus scopulorum juniperus cf coahuilensis and a rich understory of c4 annuals and grasses this summer flowering understory is also characteristic of modern desert grassland in the borderlands and indicates at least moderate summer precipitation p edulis and j scopulorum disappeared or were rare in the midden record by 10 670 14c yr b p the late holocene is marked by the arrival of chihuahuan desert scrub elements and few departures as the vegetation gradually became modern in character larrea tridentata appears as late as 2190 14c yr b p based on macrofossils but may have been present as early as 4095 14c yr b p based on pollen fouquieria splendens one of the dominant desert species present at the site today makes its first appearance only in the last millennium the midden pollen assemblages are difficult to interpret they lack modern analogs in surface pollen assemblages from stock tanks at different elevations in the borderlands

temporal evolution of a long lived syenitic centre the kangerlussuaq alkaline complex east greenland abstract we present new mineral and whole rock compositions and sr nd hf pb o h isotope data on samples from the kangerlussuaq alkaline complex 1000 km2 in central east greenland part of the north atlantic igneous province this complex mainly consists of the kangerlussuaq intrusion but includes at least 13 separate satellite intrusions emplaced in the uppermost crust close to the unconformity between archaean gneisses and overlying palaeogene flood basalts the complex is divided into i older satellite intrusions 55 53 ma composed of multiple syenites and granites and minor gabbros and peridotites ii the voluminous kangerlussuaq intrusion 50 ma which displays a gradual transition from quartz syenites nordmarkites at the margin to nepheline syenites foyaites in the centre and iii younger satellite intrusions 47 45 ma of minor syenites granites and diorites concentrated southeast of the kangerlussuaq intrusion the complex displays a temporal evolution in which sio2 decreases 74 56 wt and total alkalis 6 16 wt amphibole na k content 206pb 204pbmeas endi and ehfi 3 to 11 increase from the older intrusions through the nepheline syenites this is followed by a reversal to higher silica 62 73 wt and lower total alkalis 9 12 wt amphibole na k content 206pb 204pbmeas endi and ehfi 13 to 2 in the younger satellite intrusions temporal changes in the location of magma plumbing systems and in magma production rates played a profound role in controlling silica content alkalinity and degree of crustal contamination during development of the complex phonolitic magma was only generated after prolonged magmatism had shielded the conduits from interaction with country rock the parental magmas were probably basanitic to alkali olivine basaltic in composition the older satellite intrusions and the kangerlussuaq intrusion have low 18o magma values 1 to 6 compared to the younger more crustally contaminated satellite intrusions 4 5 to 7 it appears that the magmas only had sufficient over pressure to intrude the basalt cover when larger volumes of less contaminated trachyte magma were produced resulting in the generation of low 18o magmas due to dehydration of hydrothermally altered basalt xenoliths

cool wet conditions late in the younger dryas in semi arid new mexico abstract a thick alluvial sequence in central new mexico contains the scholle wet meadow deposit that traces upstream to a paleospring the wet meadow sediments contain an abundant fauna of twenty one species of freshwater and terrestrial mollusks and ten species of ostracodes the mollusks and ostracodes are indicative of a local high alluvial water table with spring supported perennial flow but without standing water pollen analysis documents shrub grassland vegetation with sedges willow and alder in a riparian community stable carbon isotopes from the wet meadow sediments have 13c values ranging from 22 8 to 23 3 indicating that 80 of the organic carbon in the sediment is derived from c3 species the wet meadow deposit is ams dated 10 400 to 9700 14c yr bp corresponding to 12 300 to 11 100 cal yr bp and overlapping in time with the younger dryas event yd the wet meadow became active about 500 yr after the beginning of the yd and persisted 400 yr after the yd ended the scholle wet meadow is the only record of perennial flow and high water table conditions in the abo arroyo drainage basin during the past 13 ka

late quaternary vegetation history of rough canyon south central new mexico usa abstract south central new mexico usa at the junction of the rocky mountains high plains and chihuahuan desert is one of the better known regions in the late quaternary of north america plant macrofossils and pollen from a packrat midden series in rough canyon new mexico allows refinement of plant distributions and paleoclimates in this transitional area since full glacial times from 17 000 to 12 000 14c yr bp pinus edulis juniperus scopulorum woodlands dominated limestone substrates between 1800 and 1490 m with pseudotsuga menziesii and other mixed conifer species restricted to shady north facing slopes juniperus deppeana the dominant juniper today above 2000 m in southern new mexico is conspicuously absent from glacial middens and must have been displaced south of the us mexico border the minimum climatic conditions for p edulis j scopulorum woodlands are ca 20 wetter and 3 5 5 c cooler july mean maximum temperatures than the modern climate at rough canyon holocene warming drying may have started as early as 12 000 14c yr bp with the extirpation of j scopulorum from rough canyon and was completed by at least 10 54014c yr bp the record for arrivals of some desert species is confounded by traces of pollen and macrofossils in some of the glacial middens which could signify either earliest occurrence or temporal mixing contamination of assemblages ams 14c dating can discriminate between early arrival and contamination in midden macrofossils but not in pollen ams dates show that choisya dumosa presently near its northern cold limits at rough canyon endured late glacial winters possibly as clonal populations some larrea tridentata leaves and pollen occur in middens dominated by conifers and oaks no longer at the site an ams date of 3205 14c yr bp on larrea leaves from one midden indicates contamination evidence for some macrofossil contamination however does not rule out the possibility that pollen of desert elements e g larrea prosopis in late glacial early holocene middens indicates their presence in the tularosa basin well ahead of their local appearance in rough canyon finally the increasing dominance of desert elements after 5000 14c yr bp in the rough canyon series and elsewhere in the northern chihuahuan desert could reflect slow postglacial migration from the south and or progressive encroachment with gradual stripping of soils formed during the last glacial period

the ultramafic cumulate series gardiner complex east greenland the ultramafic cumulate series of the ultramafic alkaline and carbonatite bearing gardiner complex in east greenland is divided in 1 contact zone of plagio clase bearing alkaline rocks chilled to the surrounding gneisses and alkaline lavas 2 a banded sequence of dunites to mt pyroxenites 3 a zoned dunite cpx dunite ring and 4 in the centre of the complex ol pyroxenites and mt pyroxenites

thermoluminescence dating of sand dunes in rajasthan india we report here a new application of thermoluminescence tl for dating sand dunes this application assumes that exposure to sunlight causes bleaching of the geological tl of a sediment to a residual value and that tl accumulation starts again when the sediment is buried under fresh deposit and is thus shielded from the sun although the tl method has been applied to loess1 2 and ocean sediments3 4 the application of this technique to sand dunes provides the first reliable dating control for dune dynamics palaeoclimatology and spread of deserts

imaging the source region of the 2004 mid niigata prefecture earthquake and the evolution of a seismogenic thrust related fold 1 the velocity structure and accurate aftershock distributions of the 2004 mid niigata prefecture earthquake are elucidated by inverting the arrival times from 716 aftershocks using double difference tomography fourteen temporal seismic stations were immediately deployed in and around the source region within 46 h of the occurrence of mainshock the seismic velocities in a hanging wall are lower than those in a footwall and the velocity contrast extends to a depth of approximately 10 km the aftershocks associated with the mainshock are distributed around the clear boundary between the low and high velocity structures it is interpreted that the mainshock fault plane of the mid niigata prefecture earthquake was reactivated as a reverse fault since the crustal shortening initiated at 3 5 ma crustal stretching or shortening along the japan coastline has created complex structures such as low velocity zones which can potentially control the seismic activities around the source region

desert wetlands in the geologic record abstract desert wetlands support flora and fauna in a variety of hydrologic settings including seeps springs marshes wet meadows ponds and spring pools over time eolian alluvial and fluvial sediments become trapped in these settings by a combination of wet ground conditions and dense plant cover the result is a unique combination of clastic sediments chemical precipitates and organic matter that is preserved in the geologic record as ground water discharge gwd deposits gwd deposits contain information on the timing and magnitude of past changes in water table levels and therefore are a potential source of paleohydrologic and paleoclimatic information in addition they can be important archeological and paleontological archives because desert wetlands provide reliable sources of fresh water and thus act as focal points for human and faunal activities in some of the world s harshest and driest lands here we review some of the physical sedimentological and geochemical characteristics common to gwd deposits and provide a contextual framework that researchers can use to identify and interpret geologic deposits associated with desert wetlands we discuss several lines of evidence used to differentiate gwd deposits from lake deposits they are commonly confused and examine how various types of microbiota and depositional facies aid in reconstructing past environmental and hydrologic conditions we also review how late quaternary gwd deposits are dated as well as methods used to investigate desert wetlands deeper in geologic time we end by evaluating the strengths and limitations of hydrologic and climatic records derived from gwd deposits and suggest several avenues of potential future research to further develop and utilize these unique and complex systems

late quaternary environmental changes in the upper las vegas valley nevada abstract five stratigraphic units and five soils of late pleistocene to holocene age crop out in dissected badlands on corn creek flat 30 km northwest of las vegas nevada and at tule springs nearer to las vegas the record is dominantly fluvial but contains evidence of several moister marsh forming periods the oldest unit b dates perhaps to the middle wisconsin and the more widespread unit d falls between 30 000 and 15 000 yr b p unit d therefore correlates with pluvial maximum lacustrine deposits elsewhere in the great basin standing water was not of sufficient depth or extent during either period to form lake strandlines between 14 000 and 7200 yr b p unit e standing surface water gradually decreased a trend also apparent in great basin pluvial lake chronologies during the same period groundwater carbonate cementation and burrowing by cicadas cicadae accompany the moist phase units after 7200 yr b p increased wind action decreased biotic activity and at least 25 m of water table lowering accompanied widespread erosion of older fine grained deposits based on pack rat midden and pollen evidence this coincides with major vegetation changes in the valley from sagebrush dominated steppe to lower mohave desertscrub

ubiquity of anomalous fading in k feldspars and the measurement and correction for it in optical dating anomalous fading rates were measured in k feldspars separated from 49 sediment samples mainly from north america the intensity of the optically stimulated luminescence was found to decrease linea

late quaternary lacustrine history and paleoclimatic significance of pluvial lake cochise southeastern arizona abstract during the latest quaternary freshwater pluvial lakes intermittently formed in the topographically closed willcox basin arizona a lacustrine sequence of six separate high stands of lake cochise is documented by stratigraphic studies 19 radiocarbon ages and supplementary evidence two stands of pluvial lake cochise older than 14 000 yr b p reached elevations above 1290 m the prominent 1274 m shoreline of lake cochise which circumscribes the basin was largely created during a high stand between 13 750 and 13 400 yr b p during the holocene water filled the willcox basin three times to an elevation slightly below the crest of the 1274 m shoreline this occurred once during the early holocene around or before 8900 yr b p and twice during the later part of the middle holocene since the middle holocene only shallow ephemeral lakes have occupied the deflated central portion of ancient lake cochise a depression known as the willcox playa the lacustrine sequence of lake cochise provides an independent evaluation of late quaternary paleoclimatic reconstructions for southern arizona and the american southwest

timing and extent of late quaternary paleolakes in the trans pecos closed basin west texas and south central new mexico abstract the trans pecos closed basin is a hydrographically closed region covering 20 000 km 2 centered on salt basin 160 km east of el paso texas geomorphic and limnetic evidence have been used to identify four major highstands for lake king during the last glacial maximum lgm additional geomorphic features from a second recently identified paleolake lake sacramento have been found in the beargrass subbasin a nested subbasin approximately 75 km northwest of salt basin radiocarbon ages of the organic material in lake king sediments date four abrupt climate changes and rapid lacustrine transgressions during the lgm with a quasi periodicity of 2000 yr geomorphic evidence in the beargrass subbasin identifies lake cycles contemporaneous with those in lake king the dates for these transgressions correlate with the dates of freshening events identified by researchers in paleolake basins elsewhere in new mexico the quasi periodicity of the events approximates that of dansgaard oeschger events identified from greenland ice cores the contemporaneity of the trans pecos transgressions with transgressive events in other basins in the region suggests that paleolakes in the region were in phase with respect to abrupt climate changes during the latter stages of the lgm

the micromorphology of younger dryas aged black mats from nevada arizona texas and new mexico abstract black mats are organic rich sediments and soils that form in wet environments associated with spring discharge micromorphological and geochemical analyses of 25 black mats dating to the younger dryas chronozone 12 9 11 7 ka and early holocene were conducted to determine their composition and depositional environment samples were collected from arizona new mexico texas and nevada micromorphological analyses were conducted on thin sections using polarized and blue fluorescent light these analyses determined that black mats contain humic acids fine 5 20 m plant fragments diatoms phytoliths and gastropods the dominant type of organic matter in black mats is derived from herbaceous plants contradicting previous studies that supported algal or charcoal sources differences in the micromorphological characteristics of the samples revealed that black mats formed as three different types organic horizons moist soils and ponded sediments depending on their topographic position in relation to the water table the microscopic evidence found in black mats supports the presence of widespread wet environments in nevada and arizona during the younger dryas chronozone clearly indicating a sustained period of greater effective moisture optimal for spring discharge and black mat formation

new optically stimulated luminescence ages provide evidence of mis3 and mis2 eolian activity on black mesa northeastern arizona usa abstract eolian deposition on the semiarid southern colorado plateau has been attributed to episodic aridity during the quaternary period however osl ages from three topographically controlled e g falling dunes on black mesa in northeastern arizona indicate that eolian sediments there were deposited in deep tributary valleys as early as 35 30 ka with most sand deposited before 20 ka in contrast the oldest osl ages for sand sheets fall within the pleistocene holocene climatic transition 12 8 ka thus most eolian sediment accumulated on black mesa under climatic conditions that were in general cooler moister and more variable than today not more arid pointing to a considerable increase in sediment supply

apparent synchroneity of submillennial scale climate events between greenland and santa barbara basin california from 30 10 ka abstract evidence is presented from odp hole 893a santa barbara basin for possible synchroneity between greenland and california margin submillennial climate change records during termination 1 and the last glacial maximum lgm planktonic foraminiferal isotope and faunal records are compared to the gisp2 18o records greenland for the interval between 30 and 10 ka using a new chronology based on 38 planktonic 14c dates apparent synchronous climatic events include interstadial is events 2 3 and 4 a broad warming trend between 21 and 19 ka and a broad cooling trend between 19 and 17 ka bolling and allerod warm episodes separated by the cooler older dryas event younger dryas cool episode and the preboreal the resulting tight correlation supports an intimate teleconnection between santa barbara basin surface waters and greenland air temperatures differences between greenland and santa barbara basin suggest that some regional variations were superimposed on the global pattern of climate change e g the pre bolling warming

paleoclimate simulations for north america over the past 21 000 years features of the simulated climate and comparisons with paleoenvironmental data maps of upper level and surface winds and of surface temperature and precipitation illustrate the results of a sequence of global paleoclimatic simulations spanning the past 21 000 years for north america we review a the large scale features of circulation temperature and precipitation that appear in the simulations from the ncar community climate model version 1 ccm 1 b the implications of the simulated climate for the past continental scale distributions of three plant taxa picea spp pseudotsuga menziesii and artemisia tridentata which are broadly representative of the vegetation across the continent and c the potential explanations in terms of atmospheric circulation or surface energy and water balance processes for mismatches between the simulations and observations most of the broad scale features of previous paleoclimatic simulations with the ncar ccm 0 for north america are present in the current simulations many of the elements of a conceptual model based on previous climate simulations that describes the controls of paleoclimatic variations across north america during the past 21 000 years are found in simulations reviewed here these include 1 displacement of the jet stream by the laurentide ice sheet to the south of its present position in both winter and summer 2 generation of a glacial anticyclone over the ice sheet at the lgm and the consequent induction of large scale sinking motions induced over eastern north america 3 changes in the strength of surface atmospheric circulation features through time including weakening of the aleutian low in winter and strengthening of the eastern pacific and bermuda high pressure systems in summer as the ice sheet decreased in size 4 development of a heat low at the surface and a strengthened ridge in the upper atmosphere over the continent at the time of the maximum summer insolation anomaly 5 increases in summer temperature earlier in regions remote from the ice sheet these increases appear earlier in the present ccm 1 simulations than in the previous ccm 0 ones however and 6 continuation of negative winter temperature anomalies into the middle holocene in general simulated surface conditions that are discordant with paleoenvironmental observations can be attributed to the simulation of particular atmospheric circulation patterns e g those that suppress precipitation or advect warm air into a region with these mismatches amplified in beringia and the southeastern united states by surface energy and water balance processes

impacts of climate change on the formation and stability of late quaternary sand sheets and falling dunes black mesa region southern colorado plateau usa abstract detailed geomorphic mapping and analysis of soil stratigraphy and optically stimulated luminescence osl dating of eolian sand dunes on black mesa arizona reveal eolian sediment deposition occurred from 30 to 16 ka followed by a period of widespread dune stabilization from 12 to 8 ka localized reactivation of the previously stabilized dune forms or local changes in sediment supply have occurred in the middle to late holocene in this region cooler wetter and more variable climatic conditions during mis 3 and 2 led to increased channel and floodplain sediment supply eolian sediment derived from these sources was transported up to 60 km deposition of this material has reduced regional topographic roughness by filling tributary canyon traps oriented perpendicular to the dominant wind and sediment transport direction topographically controlled falling dunes and sand ramps in this region are preserved because of their geomorphic position and provide evidence of the paleoenvironmental state of the fluvial and eolian systems before during and immediately after the last glacial maximum on the southern colorado plateau widely used predictive models of eolian system dynamics are typically based entirely on climatic variables and do not account for landscape complexity and geomorphic history climate only assumptions fail to give accurate predictions of the dynamics of this and many other dune fields a growing body of work suggests that eolian deposits in wind driven semiarid climates may be more strongly related to increases in sediment supply than to increases in aridity

evidence for younger dryas global climate oscillation and human response in the american southwest whether or not abrupt younger dryas climate change affected regional paleoenvironments and late pleistocene hunter gatherer populations is an important topic in the archaeology of the american southwest this paper reviews multiple age resolved proxy evidence to gauge the magnitude and direction of younger dryas chronozone ydc environmental changes in different settings and systems there is no record of ydc pluvial lake highstands in arizona or new mexico but there are impressive records of vegetation faunal stable isotope and geomorphological change coincident with the ydc these correlate with important adaptive changes in human hunting and land use as revealed in the analysis of the spatiotemporal distribution of late pleistocene hunting technologies clovis and folsom projectile point distributions do not support extant models of paleoenvironmental conditions in these interpretations significant cultural changes that coincide with the ydc include the clovis to folsom transition the demise of mammoth hunting and the development of a highly successful emphasis on bison increased regionalization and the abandonment of the northwestern chihuahuan and the sonoran deserts by mobile big game hunters

a continuous high resolution record of late pleistocene climate variability from the estancia basin new mexico lake sediments that accumulated in the estancia basin central new mexico provide a detailed record of submillennial latest pleistocene climatic oscillations sedimentologic biologic and geochemical proxies for changes in salinity and lake level were used to identify episodes of wet and dry climate that occurred between 24 and 12 k y b p as dated by 14c by means of accelerator mass spectrometry from shoreline and basin center deposits these dates determine the timing and duration of the episodes of wet and dry climate the lake expanded and contracted repeatedly during the last glacial maximum and fluctuated near its highest elevation several times during the interval ca 20 to 15 k y b p a pronounced lowstand lasting 1 k y occurred between ca 15 and 14 k y b p followed by two more highstands of the lake between ca 14 and 12 5 k y b p desiccation of the perennial lake after 12 k y b p was followed by a final poorly dated highstand at ca 10 k y b p the record of lake level fluctuations from the estancia basin provides a high resolution record of changes in water budget in a basin the comparatively simple physiography and hydrogeology of which ensured a direct response to the strong climatic fluctuations that occurred during the last glacial maximum and termination

geochronology and stratigraphy of late pleistocene lake cycles on the southern bolivian altiplano implications for causes of tropical climate change large paleolakes 33 000 60 000 km2 that once occupied the high altitude poopo coipasa and uyuni basins in southern bolivia 18 22 s provide evidence of major changes in low latitude moisture in these now dry or oligosaline basins extensive natural exposure reveals evidence for two deep lake and several minor lake cycles over the past 120 k y fifty three new u th and 87 new 14c dates provide a chronologic framework for changes in lake level deposits from the ouki deep lake cycle are extensively exposed in the poopo basin but no deep lakes are apparent in the record between 98 and 18 1 ka the ouki lake cycle was 80 m deep and nineteen u th dates place this deep lake cycle between 120 and 98 ka shallow lakes were present in the terminal uyuni basin between 95 and 80 ka salinas lake cycle at ca 46 inca huasi lake cycle and between 24 and 20 5 ka sajsi lake cycle the tauca deep lake cycle occurred between 18 1 and 14 1 ka resulting in the deepest 140 m and largest lake in the basin over the past 120 ka multiple 14c and u th dates constrain the highest stand of lake tauca along a topographically conspicuous shoreline between 16 4 and 14 1 ka a probable post tauca lake cycle the coipasa produced a 55 m deep lake that is tentatively dated between 13 and 11 ka we suggest that paleolakes on the bolivian altiplano expanded in response to increased moisture in the amazon and enhanced transport of that moisture onto the altiplano by strengthened trade winds or southward displacement of the intertropical convergence zone itcz pole to equator sea surface temperature sst and atmospheric gradients may have influenced the position of the itcz affecting moisture balance over the altiplano and at other locations in the amazon basin links between the position of the itcz and the ca 23 ka precessional solar cycle have been postulated march insolation over the altiplano is a relatively good fit to our lake record but no single season or latitude of solar cycling has yet to emerge as the primary driver of climate over the entire amazon basin temperature may influence altiplano lake levels indirectly as potentially dry glacial periods in the amazon basin are linked to dry conditions on the altiplano intensification of the trade winds associated with la nina like conditions currently brings increased precipitation on the altiplano and deep lake development during the tauca lake cycle coincided with apparently intense and persistent la nina like conditions in the central pacific this suggests that sst gradients in the pacific are also a major influence on deep lake development on the altiplano

infra red stimulated luminescence dating of holocene reworked silty sediments abstract infra red stimulated luminescence irsl ages are reported for holocene colluvial lacustrine and alluvial sediments and late glacial loess for colluvial sediments irsl ages concur with independent ages age overestimation occur in the case of very poorly bleached sediments such as young less than 2000 years floodloams for which a high suspended sediment load was deduced from sedimentation rates and actually observed floods age underestimates are observed for late glacial loess probably due to inadequate preheat procedures

early to mid holocene lake high stand sediments at lake donggi cona northeastern tibetan plateau china comment to the paper published by dietze et al quaternary research 79 2013 325 336

late pleistocene paleohydrology near the boundary of the sonoran and chihuahuan deserts southeastern arizona usa abstract ground water discharge gwd deposits form in arid environments as water tables rise and approach or breach the ground surface during periods of enhanced effective precipitation where preserved these deposits contain information on the timing and elevation of past ground water fluctuations here we report on the investigation of a series of gwd deposits that are exposed in discontinuous outcrops along a 150 km stretch of the san pedro valley in southeastern arizona near the boundary of the sonoran and chihuahuan deserts chronologic isotopic geochemical faunal assemblage ostracodes and gastropods and sedimentological evidence collectively suggest that the elevation of the regional water table in the valley rose in response to a change in climate 50 ka ago and remained relatively high for the next 35 ka before falling during the bolling allerod warm period rebounding briefly during the younger dryas cold event and falling again at the onset of the holocene the timing of these hydrologic changes coincides closely with variations in 18o values of calcite from a nearby speleothem to the west and changes in lake levels at pluvial lake cochise to the east thus in southeastern arizona the assumption that changes in climate are reflected in all aspects of the hydrologic cycle of a region simultaneously is validated the timing of these changes also broadly coincides with variations in the gisp2 18o record which supports the hypothesis that atmospheric teleconnections existed between the north atlantic and the deserts of the american southwest during the late pleistocene

interstadial climatic cycles a link between western north america and greenland during the interval 33 6 to 26 1 ka searles lake in southeastern california went through six major cycles of expansion and contraction a comparison of u th ages for these events with the chronologies for quasi cyclic interstadial episodes in the ice core from summit greenland suggests that the episodes of low water at searles lake are synchronous with the interstadial episodes at summit the two phenomena may be linked by variations in the strength of the global hydrological cycle driven by oscillations in the atlantic ocean thermohaline circulation

chronology sedimentology and microfauna of groundwater discharge deposits in the central mojave desert valley wells california during the late pleistocene emergent groundwater supported persistent and long lived desert wetlands in many broad valleys and basins in the american southwest when active these systems provided important food and water sources for local fauna supported hydrophilic and phreatophytic vegetation and acted as catchments for eolian and alluvial sediments desert wetlands are represented in the geologic record by groundwater discharge deposits which are also called spring or wetland deposits groundwater discharge deposits contain information on the timing and magnitude of past changes in water table levels and thus are a source of paleohydrologic and paleoclimatic information here we present the results of an investigation of extensive groundwater discharge deposits in the central mojave desert at valley wells california we used geologic mapping and stratigraphic relations to identify two distinct wetland sequences at valley wells which we dated using radiocarbon luminescence and uranium series techniques we also analyzed the sediments and microfauna ostracodes and gastropods to reconstruct the specifi c environments in which they formed our results suggest that the earliest episode of high water table conditions at valley wells began ca 60 ka thousands of calendar yr b p and culminated in peak discharge between ca 40 and 35 ka during this time cold 4 12 c emergent groundwater supported extensive wetlands that likely were composed of a wet sedge rush tussock meadow mixed with mesic riparian forest after ca 35 ka the water table dropped below the ground surface but was still shallow enough to support dense stands of phreatophytes through the last glacial maximum lgm the water table dropped further after the lgm and xeric conditions prevailed until modest wetlands returned briefl y during the younger dryas cold event 13 0 11 6 ka we did not observe any evidence of wet conditions during the holocene at valley wells the timing of these fl uctuations is consistent with changes in other paleowetland systems in the mojave desert the nearby great basin desert and in southeastern arizona near the border of the sonoran and chihuahuan deserts the similarities in hydrologic conditions between these disparate locations suggest that changes in groundwater levels during the late pleistocene in desert wetlands scattered throughout the american southwest were likely driven by synopticscale climate processes

bonneville basin shoreline records of large lake intervals during marine isotope stage 3 and the last glacial maximum abstract lacustrine shoreline depositional features in the bonneville basin western north america were investigated to chronicle paleolake expansion and contraction in response to climate change based on stratigraphy sedimentology geomorphology and radiocarbon dating this study identifies multiple intermediate to large lake intervals during marine isotope stage 3 and the last glacial maximum timing and magnitude of the bonneville basin lake size change are compared with those of hemispheric scale climate change events reported from the greenland ice sheet southwestern north america winter precipitation and east asian monsoon 18 o records the amount of precipitation received by surface water systems in the bonneville basin appears to have increased significantly during the greenland stades throughout the last half of mis 3 and early mis 2 the lake also underwent rapid large amplitude oscillations during the last glacial maximum

accumulation of impact markers in desert wetlands and implications for the younger dryas impact hypothesis the younger dryas impact hypothesis contends that an extraterrestrial object exploded over north america at 12 9 ka initiating the younger dryas cold event the extinction of many north american megafauna and the demise of the clovis archeological culture although the exact nature and location of the proposed impact or explosion remain unclear alleged evidence for the fallout comes from multiple sites across north america and a site in belgium at 6 of the 10 original sites excluding the carolina bays elevated concentrations of various impact markers were found in association with black mats that date to the onset of the younger dryas black mats are common features in paleowetland deposits and typically represent shallow marsh environments in this study we investigated black mats ranging in age from approximately 6 to more than 40 ka in the southwestern united states and the atacama desert of northern chile at 10 of 13 sites we found elevated concentrations of iridium in bulk and magnetic sediments magnetic spherules and or titanomagnetite grains within or at the base of black mats regardless of their age or location suggesting that elevated concentrations of these markers arise from processes common to wetland systems and not a catastrophic extraterrestrial impact event

latest pleistocene holocene debris flow activity santa catalina mountains arizona implications for modern debris flow hazards under a changing climate abstract hazard mitigation for extreme events such as debris flows requires geologic mapping and chronologic information particularly for alluvial fans near mountain fronts in the southwestern united states in july 2006 five consecutive days of monsoonal storms caused hundreds of debris flows in southeastern arizona particularly in the southern santa catalina mountains north of tucson before 2006 no historical debris flows from the santa catalina mountains reached the populated mountain front although abundant evidence of prehistoric debris flows is present on downslope alluvial fans we used a combination of surficial geologic mapping and 10 be exposure dating to produce a debris flow history for pima and finger rock canyons the largest debris flows of latest pleistocene to early holocene age covered much of the apices of alluvial fans formed at the mouths of these canyons and extended up to 3 km downslope these debris flow deposits were inset against higher and older alluvial surfaces with few debris flow deposits of late pleistocene age the 10 be ages in this study have considerable scatter for surfaces believed to be of uniform age indicating the dual possibilities of inheritance from previous cosmic ray exposure as well as the potential for composite deposits derived from numerous debris flows we then used an empirical inundation model laharz to assess probable magnitudes of the older debris flows to evaluate possible initiation mechanisms in channel and terrace storage within the canyons is not sufficient to generate volumes likely needed to produce the larger late pleistocene to early holocene debris flow deposits the abundance of latest pleistocene and early holocene deposits suggests that large debris flows were generated during the instability associated with climate and vegetation changes at the pleistocene holocene transition under present watershed conditions with limited sediment supplies modern debris flow hazards are generally limited to within mountains and near mountain fronts

luminescence dating of loess from the northwest united states thermoluminescence tl and infra red stimulated luminescence irsl ages have been determined for loess from the columbia plateau region of southeast washington and northeast oregon u s a the irsl ed values and ages appear to be tending towards a maximum level lower than that of the tl ed values and ages in general the tl ages are in stratigraphic order and agree well with the age control in the form of 14c and tl dated tephra units derived from various eruptions of mount st helens

nearly synchronous climate change in the northern hemisphere during the last glacial termination the climate of the north atlantic region underwent a series of abrupt cold warm oscillations when the ice sheets of the northern hemisphere retreated during the last glacial termination 17 7 11 5kyr ago evidence for these oscillations which are recorded in european terrestrial sediments as the oldest dryas bolling older dryas allerod younger dryas vegetational sequence1 2 has been found in greenland ice cores3 4 the geographical extent of many of these oscillations is not well known5 6 but the last major cold event the younger dryas seems to have been global in extent7 8 9 10 here we present evidence of four major oscillations in the hydrological balance of the owens basin california that occurred during the last glacial termination dry events in western north america occurred at approximately the same time as cold events recorded in greenland ice with transitions between climate regimes in the two regions taking place within a few hundred years of each other our observations thus support recent climate simulations which indicate that cooling of the north atlantic ocean results in cooling of the north pacific ocean11 which in turn leads to a drier climate in western north america12

geoarchaeological and paleohydrological evidence for a clovis age drought in north america and its bearing on extinction abstract at the murray springs clovis site in southeastern arizona stratigraphic and geomorphic evidence indicates that an abnormally low water table 10 900 yr b p was followed soon thereafter by a water table rise accompanied by the deposition of an algal mat the black mat that buried mammoth tracks clovis artifacts and a well this water table fluctuation correlates with pluvial lake fluctuations in the great basin during and immediately following clovis occupation of that region many elements of pleistocene megafauna in north america became extinct during the dry period oxygen isotope records show a marked decrease in 18o correlated with the younger dryas cold dry event of northern europe which ended 10 750 yr b p essentially the same time as the water table began to rise in southeastern arizona clovis hunters may have found large game animals easier prey when concentrated at water holes and under stress if so both climate and human predation contributed to pleistocene extinction in america

isotopic paleoecology of clovis mammoths from arizona the causes of megafaunal extinctions in north america have been widely debated but remain poorly understood mammoths mammuthus spp in the american southwest were hunted by clovis people during a period of rapid climate change just before the regional onset of younger dryas cooling and mammoth extirpation thus these mammoths may provide key insights into late pleistocene extinction processes here we reconstruct the seasonal diet and climatic conditions experienced by mammoths in the san pedro valley of arizona using the carbon 13c 12c and oxygen 18o 16o isotope compositions of tooth enamel these records suggest that clovis mammoths experienced a warm dry climate with sufficient summer rainfall to support seasonal c4 plant growth monsoon intensity may have been reduced relative to the preceding time period but there is no isotopic evidence for severe drought however it is possible that the clovis drought inferred from stratigraphic evidence occurred suddenly at the end of the animals lives and thus was not recorded in the enamel isotopic compositions unlike mammoths that lived before the last glacial maximum clovis mammoths regularly increased c4 grass consumption during summer probably seeking seasonally green grasslands farther from the river valley this predictable seasonal behavior may have made mammoths easier to locate by clovis hunters furthermore clovis mammoths probably had no previous experience of such sudden climatic change as is believed to have occurred at the time of their extinction

stable carbon isotopes c3 c4 vegetation and 12 800years of climate change in central new mexico usa abstract a thick sequence of fine textured alluvium in central new mexico has provided an opportunity to reconstruct vegetation type and climate at the western edge of the great plains grassland the analysis of thirty eight ams radiocarbon ages 13 c values and modern weather data has produced a 12 800 cal yr record of changing c 3 c 4 vegetation temperature and precipitation the record begins with the younger dryas that was characterized by c 3 plants and was about 2 4 c cooler with over 100 mm rainfall than today after 11 000 cal yrs bp the climate became less cool and less wet reaching present day conditions by 9000 yrs the middle holocene was c 4 warm and dry although the 13 c record is incomplete for this interval from 3300 to 1400 cal yrs bp the climate was cool and wet with c 3 plants averaging 0 5 c cooler and 22 mm greater rainfall than today matching other records in the region for a wetter climate after 1400 cal yrs bp the local climate became warm and dry shifting to c 4 vegetation the severe second century drought first observed in tree rings in southern colorado is supported by the 13 c data and occurred during the interval a d 40 to a d 180 hiatuses in the local alluvial and 13 c record extend from 9000 to 6000 cal yrs bp and from 1000 cal yrs bp to present

late quaternary stratigraphy and luminescence geochronology of the northeastern mojave desert abstract the chronology of the holocene and late pleistocene deposits of the northeastern mojave desert have been largely obtained using radiocarbon ages our study refines and extends this framework using optically stimulated luminescence osl to date deposits from valjean valley silurian lake playa red pass and california valley of particular interest are eolian fine silts incorporated in ground water discharge gwd deposits bracketed at 185 140 and 20 50 ka alluvial fan deposits proved amenable for osl by dating both eolian sand lenses and reworked eolian sand in a matrix of gravel that occurs within the fan stratigraphy lacustrine sand in spits and bars also yielded acceptable osl ages these osl ages fill gaps in the geochronology of desert deposits which can provide data relevant to understanding the responses of several depositional systems to regional changes in climate this study identifies the most promising deposits for future luminescence dating and suggests that for several regions of the mojave desert sediments from previously undated landforms can be more accurately placed within correct geologic map units

moisture variability in the southwestern united states linked to abrupt glacial climate change the atmospheric response to millennial scale circulation changes in the north atlantic ocean during the last glacial period has been difficult to constrain cave deposits from southwestern north america reveal that atmospheric moisture in this region increased in response to slowdowns of the atlantic meridional overturning circulation

the e greenland continental margin a transition between oceanic and continental magmatism the e greenland continental margin differs from typical margins in having a superimposed regional uplift which has exposed the early rift products for direct examination most of the igneous rocks in this region find counterparts in the oceanic setting with the proviso that the area is part of an aseismic ridge thus picrites basalts sheeted dyke swarms and layered gabbros are present and these can be used to shed light on oceanic magmatic events nephelinitic rocks are products of off axis volcanism and find no counterparts in the present oceanic rift system although they occur in marginal regions of the ocean basins and were generated in distal regions at the initiation of rifting in icelandic anomaly voluminous salic rocks in the area owe their generation largely to continental crust which has undergone extensive melting they find no direct counterparts in oceanic areas the outstanding degree of exposure in this area combined with its transitional nature and wide spectrum of rock types make it a unique laboratory for the elucidation of a variety of problems regarding both oceanic and continental volcanism together with the nature of rifted continental margins in general

late pleistocene woodlands in the bolson de mapimi a refugium for the chihuahuan desert biota abstract packrat middens radiocarbon dated at 12 280 345 and 12 700 165 yr b p record expansions of junipers and papershell pinyon pinus remota into the desert lowlands of durango and coahuila mexico 26 n extralocal trees and shrubs presently occur 24 580 km in nearly all directions including more subtropical areas to the northeast and southeast an equable late wisconsin climate marked by mild winters with increased precipitation and by cool summers with reduced summer monsoons is proposed the extensive playas of the bolson de mapimi probably held water at that time the bolson de mapimi was not a geographical refugium unaffected by glacial climates although many chihuahuan desert plants and animals probably remain in situ as members of equable woodlands equable climates low extinction rates and repeated rapid glacial interglacial climatic fluctuations may have been important in the evolution and accumulation of species at lower latitudes

late quaternary spring fed deposits of the grand canyon and their implication for deep lava dammed lakes one of the most intriguing episodes in the quaternary evolution of the grand canyon of the colorado river arizona was the development of vast lakes that are thought to have backed up behind lava erupted into the gorge stratigraphic evidence for these deep lava dammed lakes is expectedly sparse possible lacustrine deposits at six areas in the eastern canyon yielded no compelling evidence for sediment deposited in a deep lake at two of the sites the sediment was associated with late quaternary spring fed pools and marshes water lain silt and sand at lower havasu creek was deposited 3000 cal yr ago the deposit contains an ostracode assemblage similar to that living in the modern travertine dammed pools adjacent to the outcrop the second deposit at lees ferry formed in a spring fed marsh 43 000 cal yr ago as determined by 14 c and amino acid geochronology it contains abundant ostracode and mollusk fossils the richest assemblages reported from the grand canyon to date our interpretation of these sediments as spring fed deposits and their relative youth provides an alternative to the conventional view that deposits like these were formed in deep lava dammed lakes that filled the grand canyon c 2002 university of washington

fossil spring deposits in the southern great basin and their implications for changes in water table levels near yucca mountain nevada during quaternary time fossil spring deposits are common in the southern great basin and their distribution provides important constraints on the hydrologic response of the regional water table to climate change this information is crucial because the proposed high level nuclear waste repository at yucca mountain will be located 200 400 m above the modern water table water tables will rise in response to a future return to glacial climates but the magnitude of the change and the consequences for radionuclide travel times and overall repository integrity are key uncertainties increased recharge during past pluvial periods in the spring mountains and sheep range caused water tables to rise and ground water to discharge over broad expanses of the las vegas valley system and in nearby pahrump sandy and coyote springs valleys in contrast other valleys in the region contain only small areas of pleistocene discharge resulting from local damming of ground water by faults that cut valley alluvium in these instances which include the valley wells area and piute and northern coyote springs valleys smaller ranges such as the clark and new york mountains supplied the moisture the change in water table levels since the last full glacial period varies between and within valleys from as little as 10 m in several areas to 95 m in the coyote springs valley at yucca mountain the water table has probably changed by 115 m in response to climate change the spring deposits and the mollusk faunas found with them often misinterpreted as lacustrine in origin share many essential features with active spring systems in northeast nevada deposits associated with discharge mainly consist of pale brown silt and sand that is entrapped by dense stands of phreatophytes covering valley bottoms when water tables are high pale green mud containing a mix of aquatic semiaquatic and moist terrestrial mollusks accumulates in wet meadows and marshes associated directly with spring discharge the record in subbasins of the las vegas valley system is dominated by late wisconsin age sediments although pond sediments and alluvium belonging to at least one older pre wisconsin pluvial period are also locally exposed deposits from two even earlier episodes of spring discharge both of which also occurred during rancholabrean time 10 to 450 ka are exposed in the pahrump chicago piute and coyote springs valleys and in the valley wells the records from the pahrump and coyote springs valleys are especially well exposed and likely extend back to at least early pleistocene time

active tectonics of northeastern sonora mexico southern basin and range province and the 3 may 1887 mw 7 4 earthquake north south striking and west dipping basin and range province normal faults form the western edge of the sierra madre occidental plateau in northeastern sonora these faults and associated half grabens extend over a distance of more than 300 km between the san bernardino basin in the north and the sahuaripa basin in the south an earthquake in 1887 ruptured three neighboring segments of this major fault zone our field mapping in this region indicates that the surface rupture of the 1887 earthquake extends farther to the south and is considerably longer 101 4 km end to end length than previously reported a compilation of the seismicity in the epicentral region of the 1887 earthquake shows the epicenters to be distributed in well defined clusters at the northern end of the 1887 surface rupture in the step overs between the three rupture segments on a neighboring fault in the west fronteras fault and on fault segments farther south along the same fault zone granados region the distribution of seismicity correlates well with calculated changes in coulomb failure stress resulting from the 1887 earthquake

holocene sedimentary and environmental history of an in channel wetland along the ecotone of the sonoran and chihuahuan desert grasslands abstract the paleoenvironmental record of sedimentation and development of an in channel wetland that spans the border of southeast arizona usa and northeast sonora mexico suggests a complex history between climate change and regional groundwater levels from the late pleistocene to early holocene the channel occupied by the san bernardino cienega was largely aggradational with cobbles to sands being deposited in the oldest and deepest sediments changes in grain size indicate lowered stream power through the early to middle holocene around 7200 years ago sediments changed from sand and cobble dominance to significant proportions of silts and clays suggesting standing or still waters along with changes in sediment texture preservation of organic material initiated providing a record of regional and local vegetation change the upland transitioned from woody grassland co dominance between 7000 and 5400 cal bp to grassland dominated conditions after 5400 cal bp locally wetland vegetation established within the stream channel after 7000 cal bp and persisted until ca 4100 cal bp from 4100 to 2400 cal bp the cienega remained stabilized but was covered with grasses and forbs wetland vegetation returned after 2400 cal bp the change in sediment characteristics and inferred establishment of wetland vegetation is interpreted as increased importance of regional groundwater hydrology from the middle holocene to present the timing of this change is coincident with increasing el nino variability and suggests a causal mechanism for increasing regional groundwater namely increase in winter precipitation in the american southwest

radiocarbon calibration curve spanning 0 to 50 000 years bp based on paired 230 th 234 u 238 u and 14 c dates on pristine corals abstract radiocarbon dating is the most widely used dating technique in the world recent advances in accelerator mass spectrometry ams and sample preparation techniques have reduced the sample size requirements by a factor of 1000 and decreased the measurement time from weeks to minutes today it is estimated that more than 90 percent of all measurements made on accelerator mass spectrometers are for radiocarbon age dates the production of 14 c in the atmosphere varies through time due to changes in the earth s geomagnetic field intensity and in its concentration which is regulated by the carbon cycle as a result of these two variables a radiocarbon age is not equivalent to a calendar age four decades of joint research by the dendrochronology and radiocarbon communities have produced a radiocarbon calibration data set of remarkable precision and accuracy extending from the present to approximately 12 000 calendar years before present this paper presents high precision paired 230 th 234 u 238 u and 14 c age determinations on pristine coral samples that enable us to extend the radiocarbon calibration curve from 12 000 to 50 000 years before present we developed a statistical model to properly estimate sample age conversion from radiocarbon years to calendar years taking full account of combined errors in input ages and calibration uncertainties our radiocarbon calibration program is publicly accessible at http www radiocarbon ldeo columbia edu along with full documentation of the samples data and our statistical calibration model

a 20 000 year record of ocean circulation and climate change from the santa barbara basin much of the evidence for climate driven fluctuations in ocean circulation during the past 20 000 years has come from studies of the north atlantic region1 6 the extent to which such interactions have occurred in other ocean basins and any associated teleconnec tions between basins is poorly understood here we present high resolution palaeoclimate and palaeoceanographic records from a 20 000 year sedimentary sequence from the santa barbara basin on the eastern margin of the north pacific ocean the sequence shows oscillations of the benthic environment between low oxygen conditions laminated sediments during periods of warm climate and higher oxygen conditions non laminated bioturbated sediments during cool intervals age differences between coexisting benthic and planktonic foraminifers indicate climate related changes in the age and source and hence oxygen content of basin bottom waters relatively young bottom waters are associated with the cooler intervals and are considered to reflect high proportions of intermediate waters derived from proximal sources conversely older bottom waters are associated with the warmer intervals and were derived from more distal sources these climate driven variations in ocean circulation appear to be synchronous with the main ocean climate fluctuations in the north atlantic region1 6 suggesting that a tight coupling mechanism operates between the two basins

prolonged wet period in the southwestern united states through the younger dryas the younger dryas was one of the more dramatic climatic transitions ever recorded how these types of climatic shifts are expressed in continental interiors is of primary scientific interest and of vital societal concern here we present a speleothem based absolutely dated record using uranium series data of climate change for the southwestern united states from growth chronology of multiple speleothems the stalagmite growth represents the onset of wetter climate 12 500 yr b p soon after the start of the younger dryas the wetter climate persisted a millennium beyond the termination of the younger dryas this wet cycle is likely related to a more southern positioning of the polar jet stream in response to cooler northern hemisphere climate the end of the wet period coincides with the peak of the holocene summer insolation maximum ca 10 500 yr b p the allerod prior to the younger dryas which corresponds to clovis occupation in the southwestern united states was drier in comparison and seems in line with a climatic contribution to megafauna extinction

late wisconsin groundwater discharge environments of the southwestern indian springs valley southern nevada abstract badland exposures in the indian springs valley southern nevada contain evidence of formerly widespread spring and seep discharge the stratigraphic position and appearance of most of these deposits suggests correlation with late wisconsin 30 000 to ca 10 000 yr b p marsh sediments in nearby las vegas valley previously all these deposits have been loosely described as lacustrine because of the presence of extensive green mudstones associated with aquatic mollusks however this association also typifies modern groundwater discharge environments in many basins of northeast nevada such as the steptoe valley basins often without hydrographic closure such analogs best explain the origin of late wisconsin fine grained deposits in the unclosed southwestern arm of the indian springs valley key features of these depositional systems are the lack of shoreline deposits the presence of a broad belt of subaerially deposited plae brown silts surrounding spring wet meadow and marsh deposits and the intermixture of terrestrial and aquatic mollusks in most horizons where mollusks occur

a 36 000 yr vegetation history from the peloncillo mountains southeastern arizona usa a 36 200 cal yr b p vegetation history was developed from macrofossils and pollen from 55 packrat middens from 1287 to 1442 m elevation in the peloncillo mountains of southeasternmost arizona usa today these elevations are dominated by semidesert grassland with a mixture of chihuahuan and sonoran desert shrubs including an eastern disjunct population of jojoba simmondsia chinensis from 36 200 to 15 410 cal yr b p rocky areas just above large pluvial lakes that occupied what are now dry playas supported pinus edulis juniperus osteosperma juniperus cf coahuilensis quercus cf turbinella and a rich understory of summer flowering c4 annuals and grasses indicating abundant summer rains and mild winters after 15 410 cal yr b p p edulis declined in abundance and disappeared briefly at 13 925 cal yr b p coincident with expansion of more xeric species and paleohydrological evidence for regional aridity during the bolling allerod warm interval p edulis rebounded briefly during the younger dryas at 12 405 cal yr b p before disappearing along with other mesic woodland species sometime after 12 100 cal yr b p the few middens dating from the early to middle holocene 10 000 4000 yr b p indicate wetter conditions than today at 7790 cal yr b p followed by a general drying trend the 35 middens from the late holocene detail the sequential arrival of desertscrub species as vegetation became more modern in character

the younger dryas black mat from ojo de agua a geoarchaeological site in northeastern zacatecas mexico abstract new explorations in the desert of northeastern zacatecas in central northern mexico revealed dozens of archaeological and geoarchaeological sites one of them ojo de agua contains the remains of a pleistocene spring fed hydrographic system located at the southeastern end of a large elongated endorheic basin the locality yielded a particularly dark highly organic stratigraphic layer commonly known in the americas as black mat bm exposed on the natural profiles of a creek but not associated with cultural materials several radiocarbon assessments confirmed the formation of the ojo de agua black mat during the younger dryas chronozone with ten calibrated results clustering between 12 700 12 100 cal bp this multi proxy study confirmed the peculiarity of the deposit and found similarities and differences with other contexts of younger dryas age the ojo de agua black mat stratum c2 is far richer in charcoal specks than the related strata but lacks phytoliths diatoms or ostracods no further biological remains were found in it except for intrusive capillary roots clearly water lain in a shallow pond the stratum qualifies as a clayey silt with an acidic to neutral ph rich in heavy metals and with high contents of titanium the ojo de agua black mat yielded significant indicators of intense wildfires during the younger dryas but produced no carbon spherules or nanodiamonds supposedly linked to the impact theory

radiocarbon dating of minute gastropods and new constraints on the timing of late quaternary spring discharge deposits in southern arizona usa abstract gastropod shells are commonly preserved in quaternary sediments but are often avoided for radiocarbon dating because some taxa incorporate 14 c deficient carbon during shell formation recently brennan and quade 1997 quat res 47 329 336 found that some minute taxa vallonia pupilla and succineidae appear to yield reliable 14 c ages for late pleistocene samples a more rigorous evaluation of the 14 c inventory of minute gastropods is presented here which involved measuring the 14 c activity of specimens collected live in two geologic settings that maximize the potential for ingestion of old carbon 1 alluvium dominated by paleozoic carbonate rocks and 2 adjacent to extant springs with highly 14 c deficient water present at the surface we found that several minute taxa including vallonia incorporate significant and variable amounts of old carbon 2 to 30 during shell formation the 14 c activities of the land snails pupilla blandi and euconulus fulvus however are indistinguishable from the 14 c activity of live plants the 14 c activity of the semi aquatic gastropod catinella sp family succineidae deviates from modern values in the presence of 14 c deficient water by an amount equivalent to 10 of the local carbon reservoir effect these results imply that at least some minute gastropods can provide reliable 14 c ages even when 14 c deficient carbon is readily available to demonstrate an application of our findings we 14 c dated shells from p muscorum e fulvus and succinea sp family succineidae recovered from the coro marl a late pleistocene spring fed marsh deposit exposed at the murray springs paleoindian site in the san pedro valley of southern arizona usa radiocarbon ages obtained from the minute gastropods show that the unit was deposited between 25 000 and 13 000 14 c years ago the marl is situated 15 m above the modern water table at murray springs and is similarly positioned in discontinuous outcrops along a 150 km stretch of the san pedro valley thus the 14 c ages of minute gastropods presented here may be used to infer the timing of high water table levels throughout the valley

pollen record of precipitation changes during the younger dryas and early holocene in the north china plain abstract the younger dryas event which was the most recent millennial scale cold event had a major impact on the global environment however there were substantial regional differences in precipitation during the younger dryas ningjinpo lake was formed at the end of late pleistocene and was formerly the largest lake in the north china plain its sedimentary record is well suited for studying environmental changes during the younger dryas we used pollen and grain size analyses of 69 lake sediment samples combined with 1190 modern surface samples and a radiocarbon chronology to characterize the processes of vegetation succession and precipitation change during the younger dryas and early holocene in the ningjinpo area of north china plain the results show that during the younger dryas the sediments were relatively coarse grained and the pollen assemblages were dominated by herb taxa such as poaceae artemisia and asteraceae indicating that the vegetation was mainly meadow steppe or forest meadow and that the climate was generally dry the annual average precipitation was 510 mm which was 100 mm lower than today however four events of enhanced centennial scale precipitation are evident in the record characterized by increases in tree pollen representation during 12 350 12 250 12 200 12 100 11 900 11 800 and 12 650 12 550 cal yr b p during these events precipitation was 50 mm higher than before and afterwards in the late part of the younger dryas after 12 100 cal yr b p the representation of tree pollen increased indicating an increase in forest dominated by pinus and betula and precipitation increased to 560 mm after 11 440 cal yr b p at the beginning of the holocene the arboreal pollen percentages exceeded 60 indicating that the regional vegetation was dominated by pinus ulmus and quercus forest and the annual average precipitation was 620 mm which was close to that of today

late quaternary environmental dynamics in the atacama desert reconstructed from rodent midden pollen records in the past two decades much has been learned about the late quaternary climate history of the atacama desert with some details still unclear about the seasonality timing and extent of wet and dry phases modern climate studies reveal that far from exhibiting a unique pattern seasonal precipitation originates from many sources and mechanisms for the last 16 ka we attempt to sort out these complexities in pollen records from four fossil rodent midden series spanning 22 25 s in northern chile widespread wet conditions prevailed during the late pleistocene and early holocene particularly between 13 and 9 ka evidenced by 400 m lowering of pollen zones plant communities compared to today regional differences in the timing and magnitude of this displacement may be related to the prevailing source tropical extra tropical or mode nnw se of tropical precipitation through time wet conditions persisted well into the early holocene lasting 1 1 5 ka longer than previously suggested the pollen record suggests extreme drying 8 ka possibly associated with a northward shift of the inter tropical convergence zone tracking minimum insolation values at subtropical latitudes during the austral summer the establishment of conditions similar to today happened 4 ka copyright 2017 john wiley sons ltd

an enhanced role for the tropical pacific on the humid pleistocene holocene transition in southwestern north america abstract climate effects on landscape evolution during the late pleistocene holocene transition 14 6 8 ka in southwestern north america traditionally are linked to the activity of the north american monsoon and to vegetation change related to a decrease in winter precipitation acting in response to orbital cyclicity we performed an integrated analysis of regional alluvial fan lacustrine and paleobotanical records for the area comparing them with hemispheric and regional paleoclimate proxies our focus was on the potential role the tropical pacific has as a synoptic pattern modulator and moisture source for hydrogeomorphic activity in the region our analysis indicates that the onset of alluvial fan aggradation in most of the region at 13 5 ka could have been a response to semi permanent el nino like conditions in the tropical pacific which enhanced the frequency of winter frontal storms as well as increased penetration of tropical cyclones in the region the north american monsoon was restricted in extent and intensity until 7 ka and probably was not a major factor in alluvial fan aggradation a second stage of alluvial fan aggradation from 11 5 to 9 ka was dominated by hyper concentrated flows and sheet flood sedimentation along with deposition in fluvial settings storms were probably were linked to landfall of enhanced water vapor bands in the leading edge of winter extra tropical cyclones with moisture advected directly from the tropical pacific at 8 ka favorable conditions for the occurrence of these storms waned and storm tracks shifted northward analysis of modern analogs for storm types described above as prevalent during this period indicates that changes in circulation patterns across the tropical pacific can affect storm properties enough to explain the observed geomorphic effects regardless of other factors traditionally considered of large impact like vegetation change our results suggest that the tropical pacific plays a larger role than currently thought in landscape evolution of the region

noble gas signatures of high recharge pulses and migrating jet stream in the late pleistocene over black mesa arizona united states many semiarid and arid regions of the world are almost entirely dependent on groundwater for water supply yet many of these aquifers were primarily recharged during the late pleistocene here we show that new noble gas data record the high pulses of recharge to the navajo sandstone aquifer at black mesa arizona between 14 and 17 ka which was associated with the passing of the southern branch of the jet stream higher excess neon coincided with high water levels independently deduced from numerical modeling of groundwater fl ow and 14 c data in previous studies this development allows the use of noble gases not only as a tool to reconstruct paleotemperatures but also as a new tool to reconstruct paleohydraulic conditions and to verify the conceptual and hydraulic assumptions of existing groundwater models

black mats spring fed streams and late glacial age recharge in the southern great basin black mats are prominent features of the late pleistocene and holocene stratigraphic record in the southern great basin faunal geochemical and sedimentological evidence shows that the black mats formed in several microenvironments related to spring discharge ranging from wet meadows to shallow ponds small land snails such asgastrocopta tappanianaandvertigo berryiare the most common mollusk taxa present semiaquatic and aquatic taxa are less abundant and include catinellids fossaria parva gyraulus parvus and others living today in and around perennial seeps and ponds the ostracodescypridopsis okeechobiandscottia tumida typical of seeps and low discharge springs today as well as other taxa typical of springs and wetlands are common in the black mats several new species that lived in the saturated subsurface also are present but lacustrine ostracodes are absent the 13c values of organic matter in the black mats range from 12 to 26 reflecting contributions of tissue from both c3 sedges most shrubs and trees and c4 saltbush saltgrass plants carbon 14 dates on the humate fraction of 55 black mats fall between 11 800 to 6300 and 230014c yr b p to modern the total absence of mats in our sample between 6300 and 230014c yr b p likely reflects increased aridity associated with the mid holocene altithermal the oldest black mats date to 11 800 11 60014c yr b p and the peak in the14c black mat distribution falls at 10 00014c yr b p as the formation of black mats is spring related their abundance reflects refilling of valley aquifers starting no later than 11 800 and peaking after 11 00014c yr b p reactivation of spring fed channels shortly before 11 20014c yr b p is also apparent in the stratigraphic records from the las vegas and pahrump valleys this age distribution suggests that black mats and related spring fed channels in part may have formed in response to younger dryas yd age recharge in the region however the inception of black mat formation precedes that of the yd by at least 40014c yr and hydrological change is gradual not rapid

late archaic wells on the gila river indian community arizona eight prehistoric wells dug to a depth of 2 m below the modern ground surface were found in the alluvial sediments of mcclellan wash on gila river indian community in southern arizona charcoal from the sediments filling the wells yielded radiocarbon ages of 1000 b c the time in which wells were dug coincides with a period of general regional aridity and high enso activity in the american southwest digging to access water may have occurred in response to period s of resource uncertainty or as a logistical activity that engaged increasingly resource tethered late archaic early agricultural populations these activities laid the foundation for agricultural practices that eventually became the dominant mode of subsistence in the low lying areas of the sonoran desert