natural free convection in porous media first field documentation in groundwater 1 natural free convection is a process of great importance in disciplines from hydrology to meteorology oceanography planetary sciences and economic geology and for applications in carbon sequestration and nuclear waste disposal it has been studied for over a century but almost exclusively in theoretical and laboratory settings despite its importance conclusive primary evidence of free convection in porous media does not currently exist in a natural field setting here we present recent electrical resistivity measurements from a sabkha aquifer near abu dhabi united arab emirates where large density inversions exist the geophysical images from this site provide for the first time compelling field evidence of fingering associated with natural free convection in groundwater

stepwise expansions of c4 biomass and enhanced seasonal precipitation and regional aridity during the quaternary on the southern chinese loess plateau abstract the expansion of c 4 plants is one of the most prominent vegetation changes in the global ecosystem during the cenozoic era although c 4 plant expansions in the latest miocene have been widely reported factors driving the expansions are still in debate and the details of vegetation changes during the quaternary have not been well studied here we present high resolution carbon isotope time series of both organic matter and bulk carbonates covering the past 2 58 ma derived from the loess soil successions on the southern chinese loess plateau the organic matter 13 c values indicate stepwise c 4 plant expansions initiated at 1 6 and at 0 43 ma respectively we conclude that such tectonic time scale c 4 plant expansions are controlled by enhanced seasonality of precipitation relatively more precipitation in the warm growing season as well as regional aridity and this long term fluctuation superimposes on the orbital scale variations of c 4 plants while the latter appears phase locked with cyclical changes of summer monsoon circulations

thermal convection dolomitization induced by the emeishan large igneous province abstract the mechanism of dolomitization has long been debated due to complex sedimentary and diagenetic conditions large scale dolomite bodies were recently discovered in the permian cisuralian qixia formation 284 273 ma in the northwestern sichuan basin providing an opportunity to understand the dolomitization associated with the emeishan large igneous province elip traditionally the dolomites in the sichuan basin have been interpreted as hydrothermal dolomitization because of the hydrothermal impacts from the elip here we report new petrographic and geochemical data on the permian dolomites which we grouped into two categories matrix dolomites or md1 md3 and cement dolomites or cd that support thermal convection dolomitization the petrographic and geochemical features 13c 18o ree mn sr ratios 87sr 86sr ratios suggest that md1 were formed in penecontemporaneous seawater whereas md2 md3 and cd were formed in fluids resembling permian seawater during shallow burial stage of which both dolomitizing fluids are non hydrothermal high formation temperature inferred from fluid inclusion is consistent with the low 18o values of the md2 md3 and cd suggesting that the elip event may have provided the heat for the dolomitization in the qixia carbonate platform the formation of the widespread dolomite bodies was facilitated by the rapid convection exchange between warm pore seawater in the qixia strata of the platform margin and cold water from outside the slope therefore we demonstrate that the dolomites in the northwestern sichuan basin are mainly due to thermal convection dolomitization in the shallow burial stage this study provides important implications for the mechanism of dolomite formation linked to abnormal geothermal activity

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

paleoclimatic significance of δd and δ13c values in pinon pine needles from packrat middens spanning the last 40 000 years we compared two approaches to interpreting dd of cellulose nitrate in pinon pine needles pinus edulis preserved in packrat middens from central new mexico usa one approach was based on linear regression between modern dd values and climate parameters and the other on a deterministic isotope model modified from craig and gordon s terminal lake evaporation model that assumes steady state conditions and constant isotope effects one such effect the net biochemical fractionation factor was determined for a new species pinon pine regressions showed thatdd values in cellulose nitrate from annual cohorts of needles 1989 1996 were strongly correlated with growing season may august precipitation amount and d 13 c values in the same samples were correlated with june relative humidity the deterministic model reconstructed dd values of meteoric water used by plants after constraining relative humidity effects with d 13 c values growing season temperatures were estimated via modern correlations with dd values of meteoric water variations of this modeling approach have been applied to tree ring cellulose before but not to macrofossil cellulose and comparisons to empirical relationships have not been provided results from fossil pinon needles spanning the last40 000 years showed no significant trend in dd values of cellulose nitrate suggesting either no change in the amount of summer precipitation based on the transfer function or dd values of meteoric water or temperature based on the deterministic model however there were significant differences in d 13 c values and therefore relative humidity between pleistocene and holocene published by elsevier science b v

three dimensional flow in the florida platform theoretical analysis of kohout convection at its type locality kohout convection is the name given to the circulation of saline groundwater deep within carbonate platforms first proposed by f a kohout in the 1960s for south florida it is now seen as an mg pump for dolomitization by seawater as proposed by kohout cold seawater is drawn into the florida platform from the deep straits of florida as part of a geothermally driven circulation in which the seawater then rises in the interior of the platform to mix and exit with the discharging meteoric water of the floridan aquifer system simulation of the asymmetrically emergent florida platform with the new three dimensional 3 d finite element groundwater flow and transport model sutra ms which couples salinity and temperature dependent density variations allows analysis of how much of the cyclic flow is due to geothermal heating free convection as opposed to mixing with meteoric water discharging to the shoreline forced convection simulation of the system with and without geothermal heating reveals that the inflow of seawater from the straits of florida would be similar without the heat flow but the distribution would differ significantly the addition of heat flow reduces the asymmetry of the circulation it decreases seawater inflows on the atlantic side by 8 and on the gulf of mexico side by half the study illustrates the complex interplay of freshwater saltwater mixing geothermal heat flow and projected dolomitization in complicated 3 d settings with asymmetric boundary conditions and realistic horizontal and vertical variations in hydraulic properties

advected glacial seawater preserved in the subsurface of the maldives carbonate edifice abstract analysis of both conservative and reactive geochemical tracers in pore fluids extracted from sediment cores from the maldives inner sea reveal extensive interstitial water masses whose origins lie in glacial intermediate water advected laterally through the maldives carbonate edifice these drillcores recovered during expedition 359 of the international ocean discovery program penetrate late oligocene to recent sediments including carbonate platform slope pelagic and drift facies combined shipboard and shore based analyses of the pore fluids show linearly co varying changes in the concentration of chloride and 18 o and d values of 25 mm 1 2 and 9 respectively additionally pore fluid strontium concentrations and calcium isotope ratios are strongly anti correlated with each other multiple reversals in these geochemical properties with depth indicate the existence of several distinct interstitial water masses these variations are interpreted as representing the different ages and reactive histories of young pleistocene and holocene waters advecting through the much older sedimentary formations in particular the elevated chloride concentrations and water isotope ratios suggest that seawater from the last glacial maximum is preserved in the subsurface where it occupies over 400 m of the sediment column within mid to late miocene sediments these pore fluids constrain the properties of an intermediate depth glacial water mass that had higher salinity and 18 o and d values than the average glacial ocean this system represents a unique archive yielding the most direct observations of glacial seawater to date as well as a demonstration of the long lasting potential for water rock interaction in carbonate platform systems

fresh and saline groundwater discharge to the ocean a regional perspective 1 studies of groundwater flow in coastal aquifers often focus strongly on freshwater and investigate flow in a narrow 5 km zone surrounding the coastline this work was designed to place coastal flow in a regional context and to compare fresh and saline submarine groundwater discharge sgd for regional flow systems numerical flow and transport models were developed to estimate sgd associated with topography driven flow seawater recirculation and geothermal convection in a passive margin setting simulations were based on two cross sections of north carolina and sensitivity studies were used to explore the impact of varying hydraulic and transport parameters results suggest that saline flow associated with seawater recirculation and geothermal convection should be considered in studies of sgd studies limited to shallow topography driven flow may be justified in using small study areas but flow systems contributing to sgd may span at least 20 km surrounding the coast and continental slope

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

a 16 ma record of paleodiet using carbon and oxygen isotopes in fossil teeth from pakistan abstract the siwalik sequence of northern pakistan contains a 16 ma record of paleosol carbonate and fossil teeth from which a record of paleovegetation can potentially be reconstructed and compared the carbon isotopic composition of paleosol carbonate and organic matter from siwalik strata reflects a major paleoecological change on the floodplains of major rivers beginning7 3 ma ago by 6 ma c 3 dominated plant communities probably composed of mostly trees and shrubs were displaced by nearly continuous c 4 grassland we find that the carbon isotopic ratios in herbivore tooth enamel reflect this dramatic ecologic shift carbonate in enamel older than 7 ma averages 11 in 13 c pdb consistent with a largely c 3 diet enamel from the plio pieistocene averages 1 9 in 13 c similar to the value displayed by modern c 4 grazers analysis of post burial carbonate cements and the concordance with isotopic evidence from paleosols argues strongly against major isotopic alteration of the enamel while coexisting bone may have been altered early in burial this study confirms that enamel apatite is useful for paleodietary reconstruction much further back in the geologic record than was previously thought

the effects of late quaternary climate and pco2 change on c4 plant abundance in the south central united states the late quaternary was a time of substantial environmental change with the past 70 000 years exhibiting global changes in climate atmospheric composition and terrestrial floral and faunal assemblages we use isotopic data and couple climate and vegetation models to assess the balance between c3 and c4 vegetation in texas during this period the carbon isotope composition of fossil bison mammoth and horse tooth enamel is used as a proxy for c3 versus c4 plant consumption and indicates that c4 plant biomass remained above 55 through most of texas from prior to the last glacial maximum lgm into the holocene these data also reveal that horses did not feed exclusively on herbaceous plants consequently isotopic data from horses are not reliable indicators of the c3 c4 balance in grassland biomes estimates of c4 percentages from coupled climate vegetation models illuminate the relative roles of climate and atmospheric carbon dioxide co2 concentrations in shaping the regional c4 signal c4 percentages estimated using observed modern climate vegetation relationships and late quaternary climate variables simulated by a global climate model are much lower than those indicated by carbon isotope values from fossils when the effect of atmospheric co2 concentration on the competitive balance between c3 and c4 plants is included in the numerical experiment however estimated c4 percentages show better agreement with isotopic estimates from late quaternary mammals and soils this result suggests that low atmospheric co2 levels played a role in the observed persistence of c4 plants throughout the late quaternary

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

changes in vegetation type on the chinese loess plateau since 75 ka related to east asian summer monsoon variation abstract floral communities in terrestrial habitats such as steppes are highly sensitive to regional climate changes here we generated carbon and nitrogen isotope profiles for soil organic matter som in the weinan loess paleosol section in order to investigate changes in floral communities on the chinese loess plateau clp and their relationship to climate variation since 75 ka 13csom at weinan ranges from 23 6 to 18 0 and 15nsom ranges from 3 4 to 5 5 modeling based on the 13csom record suggests that the proportion of c4 plants c4 has varied from lower during cold intervals with minima of 24 32 at 73 1 ka 20 9 ka lgm and 0 6 ka to higher during warm intervals with maxima of 62 64 at 53 0 ka and 8 2 ka the 13csom and 15nsom profiles are strongly correlated r 0 82 p

middle holocene bison diet and mobility in the eastern great plains usa based on δ13c δ18o and 87sr 86sr analyses of tooth enamel carbonate during the holocene bison bison bison were key components of the great plains landscape this study utilizes serial stable isotope analyses tooth enamel carbonate of 29 individuals from five middle holocene 7 8 5 ka archaeological sites to address seasonal variability in movement patterns and grazing behavior of bison populations in the eastern great plains stable carbon isotopes 13 c indicate a bison diet that is similar to the c3 c4 composition of modern tallgrass prairies while 87 sr 86 sr values generally indicate very little seasonal movement 50 km and relatively limited inter annual movement 500 km over the course of 4 5 yr analyses of variability in serial stable oxygen isotope samples 18 o further substantiate a model of localized bison herds that adhered to upland areas of the eastern plains and prairie forest border

low stable isotope ratios of tropical cyclone rains tropical cyclone rains have distinctly lower stable isotope ratios than rains in other tropical and summer precipitation systems with a mean value slightly above that of water vapor near the sea surface the isotope ratios also decrease radially inward to the eye wall but appear to be anomalously low even near the periphery of the rain shield these findings indicate that tropical cyclones are highly efficient precipitation systems and suggest the use of stable isotope ratios as dynamic tracers of a tropical cyclone s water and energy budgets

seasonal migration of bison antiquus from rancho la brea california abstract evidence for annual seasonal migration of extinct bison antiquus in the late pleistocene fossil assemblage from rancho la brea california is demonstrated for the first time the maturation of individuals from the b antiquus sample was analyzed using the cheek tooth eruption sequence and occlusal wear patterns in juvenile and young adult inferior dentitions individual age of the specimens was established by comparison with wear stages observed in modern b bison dentitions of known age assuming that reproductive behavior was restricted to a specific annual cycle similar to modern b bison b antiquus was seasonally present at rancho la brea during the late spring an annual migratory pattern is indicated by the presence in the assemblage of yearly groups of young individuals of the same age

the occurrence and chemical implications of geothermal convection of seawater in continental shelves 1 geothermal convection is an important driving force for fluid flow and diagenesis in carbonate platforms and the similar shape of continental shelves in general suggests that geothermal convection could occur in continental shelves around the world numerical models based on seven transects of the shelf off the east coast of north america were developed to bracket possible fluxes simulations assuming relatively permeable sediments medium grained carbonates failed to produce significant thermal variations suggesting that chemical tracers will be required to detect this flow in the field fluxes calculated assuming lower permeabilities fine grained carbonates between cape fear and the savannah river were approximately 3 orders of magnitude smaller than river discharge for the area a difference similar to that between global river discharge and hydrothermal convection at mid ocean ridges sediment diagenesis during geothermal convection in continental shelves thus has the potential to affect ocean chemical budgets including potassium calcium and magnesium

early dolomitization and partial burial recrystallization a case study of middle triassic peritidal dolomites in the villany hills sw hungary using petrography carbon oxygen strontium and clumped isotope data

the isotopic ecology of late pleistocene mammals in north america part 1 florida abstract mammoths and mastodons are common in pleistocene deposits yet these proboscideans and many other animals disappeared suddenly 10 000 years ago in this study we reconstruct the diets of proboscideans and associated mammals through isotopic analysis of carbonate in tooth enamel apatite in order to test nutritional hypotheses for late pleistocene extinction we analyzed specimens from six sites in florida ranging from full glacial 21 000 bp to late glacial 14 750 to 10 000 bp age the oxygen isotope composition of mammalian apatite covaries with meteoric water composition which in turn varies with climate consequently oxygen isotope analysis can be used to assess the potential for time averaging or mixing of specimens from different geographic regions within fossil assemblages the carbon isotope composition of an herbivore is controlled by the isotopic composition of the plants that it ingests carbon isotope analysis reveals that mastodons ate chiefly c3 plants presumably trees shrubs and herbs whereas mammoths consumed chiefly c4 grass several nutritional hypotheses for late pleistocene extinction entail the assumption that extinct taxa had specialized diets the resource partitioning and focused feeding preferences of florida s proboscideans corroborate this assumption but they do not in themselves prove that nutritional stress was the cause of the late pleistocene extinction

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

dietary controls on extinction versus survival among avian megafauna in the late pleistocene the late pleistocene extinction decimated terrestrial megafaunal communities in north america but did not affect marine mammal populations in coastal regions marine megafauna may have provided a buffer that allowed some large predators or scavengers such as california condors gymnogyps californianus to survive into the holocene to track the influence of marine resources on avifaunas we analyzed the carbon nitrogen and hydrogen isotope composition of collagen from late pleistocene vultures and raptors including species that survived the extinction condor bald eagle golden eagle and extinct species teratorn black vulture at the rancho la brea and mckittrick tar pits of southern california isotope values for extinct teratorns teratornis merriami n 10 and black vultures coragyps occidentalis n 8 show that they fed entirely in a terrestrial c3 ecosystem in contrast la brea condors cluster into two groups one with a terrestrial diet n 4 and the other with a strong marine influence n 5 at localities in the american southwest texas and florida where condors became extinct they have isotope values indicating entirely terrestrial diets n 10 our results suggest that dependence upon terrestrial megafaunal carrion as a food source led to the extinction of inland california condor populations and coastal populations of teratorns and black vultures at the pleistocene holocene boundary whereas use of marine foods allowed coastal condor populations to survive

groundwater hydrology coastal flow how groundwater flow varies when long term external conditions change is little documented geochemical evidence shows that sea level rise at the end of the last glacial period led to a shift in the flow patterns of coastal groundwater beneath florida

permeability loss with depth in the cenozoic carbonate platform of west central florida relationships between matrix permeability and depth in shallow buried 500 m cenozoic limestones of florida were investigated using more than 12 000 minipermeameter measurements on 1210 m of slim hole core these data are considered representative of the matrix permeability reduction that accompanies early burial of shallow water subtidal to peritidal nonreefal carbonates of sta ble cratonic margins platforms shelves and ramps measured matrix permeabilities range from less than 4 0 to 6450 md for both limestones and dolostones although the median permeability of limestones 88 md exceeds that for dolostones 15 md sucrosic dolostones which have high intercrystalline po rosities have median matrix permeabilities of 1000 md non sucrosic dolostones which are much less porous have median matrix permeabilities of only 13 md neither population of dolostones exhibits a permeability with depth trend low permeability limestones consist of mudstones wackestones tidal laminites pedogenetically altered limestone lime mud rich breccia and well cemented grain supported rocks these low permeability limestones all exhibit median matrix permeabilities less than 35 md and none exhibit permeability with depth trends in contrast high mud packstones low mud packstones very low mud packstones and grainstones exhibit larger median matrix permeabilities 69 129 181 and 418 md respectively and a systematic reduction with depth in their mean and maximum permeabilities least squares exponential regressions indicate that burial depth explains 22 31 of the permeability variance in these grain supported rocks the balance of the variability within each textural class is attributed to variation in facies grain types grain sizes sorting etc and the amount of early preburial cementation in the absence of permeability enhancement by deep subsurface diagenesis or fracturing extrapolation of the permeability with depth trends suggests that the limestones that have the best reservoir potential in the deeper subsurface are grain supported limestones that have higher than begin page 1254 average matrix permeabilities in the near surface realm petrographic analyses and consideration of diagenetic histories suggest that matrix permeability of the dolostones and low permeability limestones was determined by early near surface dolomitization and cementation respectively and has yet to be affected by burial processes petrographic observations also suggest that the depth signal in grain supported limestones results from mechanical compaction and the onset of grain to grain pressure solution extrapolation of the matrix permeability data indicates that permeability loss with burial occurs faster than the documented burial related porosity loss for the same group of rocks this indicates that limestone permeability is more sensitive to burial compaction than limestone porosity thus preservation of reservoir quality rock during burial is more dependent on permeability preservation than on porosity preservation

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

dung of mammuthus in the arid southwest north america abstract the discovery of a unique organic deposit in a dry cave on the colorado plateau southern utah permits the first comparison of the physical characteristics and the diet of the dung of the extinct mammoths from the arid southwest north america with that of mammoths from siberia and northern china the only other known locations of such remains the deposit buried beneath sand and rockfall is composed primarily of mammoth dung estimated at over 300 m3 radiocarbon dates on dung boluses indicate that the mammoths frequented the cave between approximately 14 700 and 11 000 yr b p the range of ages at 2 the desiccated boluses measuring approximately 230 170 85 mm are nearly identical in size to dung from extant elephants the largest contents in the dung are stalks measuring 60 4 5 mm grasses and sedges dominated the diet although woody species were commonly eaten

weathering fluxes of arsenic from a small catchment in slovak republic inputs of as to a small catchment due to chemical weathering of bedrock mechanical weathering of bedrock and atmospheric precipitation were 71 53 23 98 and 0 02 g ha 1 year 1 respectively the output fluxes of as due to mechanical erosion of soil biological uptake stream discharge and groundwater flow were 6 32 4 77 0 37 and 0 02 g ha 1 year 1 respectively the results indicate that arsenic accumulates in soil and regolith with a very high rate this is attributed to the selective weathering and erosion with respect to arsenic and fixation of arsenic in the secondary solids produced by weathering the output fluxes of as in stream and groundwater in vydrica catchment in slovak republic 0 39 g ha 1 year 1 based on muscovite biotite granites and granodiorites were much lower compared to catchments in a gold district in the czech republic these results may be ascribed to the low levels of arsenic pollution measured in vydrica catchment the arsenic fluxes were estimated by calculation of mechanical and chemical weathering rates of the bedrocks in vydrica catchment from mass balance data on sodium and silica the justification of the steady state of na and si is that neither of the elements is appreciably accumulated in plants and in exchangeable pool of ions in soil

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

a 164 ka record of environmental change in the american southwest from a carlsbad cavern speleothem abstract a horizontal core 2 8 m in length drilled from the georgia giant column in carlsbad cavern provides climate information for the last 164 ka forty six alpha spectrometric u series ages determined at intervals of 7 6 cm along the core indicate five periods of deposition and five hiatuses the longest from 136 to 110 ka variations in growth rate 0 to 70 mm ka in the abundance of aragonite chalcedony and fe bearing phases and in 13c indicate that glacial intervals of the last 164 ka ois 6 4 and 2 were much wetter than today as were the colder substages 5d and 5b of ois 5 by contrast during the two warmest periods of the past 164 ka namely ois 5e and 1 there was no deposition on either side of the speleothem suggesting conditions as dry or drier than today the record from carlsbad parallels data from many other sites in the southwestern usa and northern mexico and data from marine sediments and ice cores demonstrating the extent to which ice sheet fluctuations influenced conditions in southern new mexico detailed correlation of 13c values in the georgia giant which range from 6 6 to 0 9 relative to pdb with distant speleothem records and with data from ice cores further documents the linkage of southwestern climate with global scale extent of glaciation values of 18o in the georgia giant core range from 9 7 to 4 7 relative to pdb and average 6 6 18o depleted carbonate in the georgia giant during ois 6 at a time when the world s oceans were enriched in 18o suggests that precipitation during cold intervals was brought largely by pacific air masses in fall winter and spring as a result of the southward displacement of the polar jet stream by the growth of the laurentide ice sheet termination ii marking the end of the penultimate glaciation is well defined in the core s 18o data analytical uncertainties in the radiometric ages do not preclude a start of termination ii as late as 128 ka as suggested by specmap data however data from the georgia giant core are more compatible with an earlier start like that obtained from devils hole and vostok data raising the possibility that early warming was widespread in the u s southwest region by 145 ka

late quaternary vegetation and climate changes in central texas based on the isotopic composition of organic carbon stable carbon isotope analysis of organic carbon in alluvial deposits and soils of three streams in central texas reveals significant shifts in the ratio of c3 to c4 plant biomass production during the past 15 000 yr these temporal changes in vegetation appear to be in response to changes in climate during the late pleistocene c4 plants comprised only about 45 to 50 of the vegetative biomass in this area suggesting that conditions were cooler and wetter than at any time during the past 15 000 yr the time between 11 000 and 8000 yr b p is interpreted as transitional between late pleistocene conditions and warmer and drier holocene conditions based on a slight increase in the abundance of c4 plant biomass during the middle holocene between approximately 6000 and 5000 yr b p mixed c3 c4 plant communities were replaced almost completely by c4 dominated communities indicating prairie expansion and warmer and drier climatic conditions by 4000 yr b p the abundance of c4 plant biomass decreased to levels similar to the early holocene transitional period suggesting a return to cooler and wetter climatic conditions no significant shift in the ratio of c3 to c4 productivity has occurred during the last 4000 yr except for a slight increase in the abundance of c4 plant biomass around 2000 yr b p the results of this investigation correlate well with other regional late quaternary climatic interpretations for central and north texas the southern plains region and with other portions of the great plains

reactive transport modeling of brine reflux dolomitization anhydrite precipitation and porosity evolution abstract both geothermal convection and brine reflux drive circulation of sea water derived fluids through carbonate platforms during early burial but dynamic interactions between heat and solute transport and resulting diagenesis are at present poorly understood this paper describes high resolution reactive transport model rtm simulations that suggest that reflux of 85 ppt brines rapidly restricts geothermal convection to the platform margin with flow focused in the more permeable shallow carbonates in a baseline simulation involving an elongate 25 km wide grain dominated packstone platform brine reflux resulted in complete dolomitization beneath the 5 km wide brine pool in 335 ky the dolomite body then extends downward at c 22 m 100 ky into an underlying broad area of partial dolomitization this process enhances porosity at shallow depth but beneath the dolomite body precipitation of anhydrite occludes porosity and limits the depth of reflux in contrast geothermal convection at the platform margin forms a smaller partially dolomitized body over a longer time 60 dolomite after 1 my with very minor associated anhydrite cementation reflux diagenesis is sensitive to platform geometry with higher rates of fluid flow increasing the depth of alteration beneath the brine pool for a circular platform compared to the linear baseline fluid flow across thermal gradients enhances reaction rates and ignoring heat transport by 85 ppt brine reflux underestimates the extent of reflux dolomite by 25 and associated anhydrite by 90 the depth and rate of anhydritization is sensitive to the geothermal heat flux whereas platform top temperatures affect dolomitization rate reflux diagenesis is also sensitive to brine density which affects both fluid flow and reaction rates sediment permeability and reactive surface area rsa are key intrinsic controls on diagenesis where the permeability structure permits sufficient fluid flow diagenesis preferentially affects more reactive fine grained sediments however as flow rates decline reactions become focused in the more permeable but less reactive sediments simulations thus shed light on why in some settings reflux preferentially dolomitizes muddy sediments but elsewhere favors grainstones once active reflux ceases brines continue to flow in the subsurface but this latent reflux causes only minor dolomitization due to prior mg2 consumption at shallow depth

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

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

groundwater reorganization in the floridan aquifer following holocene sea level rise sea level fluctuations can have a profound impact on coastal groundwater circulation the geochemistry of groundwater in the floridan aquifer system suggests that the fresh water in the upper aquifer was emplaced primarily during the last glacial period when sea level was more than 100 m lower than at present

holocene environmental change and vegetation contraction in the sonoran desert abstract two types of microtopographic features plant scar mounds and plant scar depressions on surfaces of barren desert pavements provide a unique record of the former presence of large perennial plants evidence of bioturbation by burrowing animals extends more than 1 m beneath each type of plant scar indicating that both features originated as large bioturbation mounds formation of bioturbation mounds in desertscrub environments is generally restricted to areas beneath widely separated large perennial plants the contrasting forms of plant scars mounds vs depressions represent time dependent changes following disappearance of the large plants and eventual cessation of bioturbation plant scar mounds represent a geologically recent episode of plant mortality whereas plant scar depressions represent the disappearance of plants at a considerably earlier time possibly at the pleistocene holocene transition contrasting spatial distributions of the two kinds of plant scars indicate that vegetation on alluvial fans has progressively contracted from a more diffuse former vegetation cover yielding the wide barren pavement surfaces present today in less arid portions of the sonoran desert spatial distribution of recent plant mortality due to persistent severe drought provides an analog of the progressive loss of plants from different parts of the landscape in the past

a review of the source behaviour and distribution of arsenic in natural waters the range of as concentrations found in natural waters is large ranging from less than 0 5 g l 1 to more than 5000 g l 1 typical concentrations in freshwater are less than 10 g l 1 and frequently less than 1 g l 1 rarely much higher concentrations are found particularly in groundwater in such areas more than 10 of wells may be affected defined as those exceeding 50 g l 1 and in the worst cases this figure may exceed 90 well known high as groundwater areas have been found in argentina chile mexico china and hungary and more recently in west bengal india bangladesh and vietnam the scale of the problem in terms of population exposed to high as concentrations is greatest in the bengal basin with more than 40 million people drinking water containing excessive as these large scale natural as groundwater problem areas tend to be found in two types of environment firstly inland or closed basins in arid or semi arid areas and secondly strongly reducing aquifers often derived from alluvium both environments tend to contain geologically young sediments and to be in flat low lying areas where groundwater flow is sluggish historically these are poorly flushed aquifers and any as released from the sediments following burial has been able to accumulate in the groundwater arsenic rich groundwaters are also found in geothermal areas and on a more localised scale in areas of mining activity and where oxidation of sulphide minerals has occurred the as content of the aquifer materials in major problem aquifers does not appear to be exceptionally high being normally in the range 1 20 mg kg 1 there appear to be two distinct triggers that can lead to the release of as on a large scale the first is the development of high ph 8 5 conditions in semi arid or arid environments usually as a result of the combined effects of mineral weathering and high evaporation rates this ph change leads either to the desorption of adsorbed as especially as v species and a range of other anion forming elements v b f mo se and u from mineral oxides especially fe oxides or it prevents them from being adsorbed the second trigger is the development of strongly reducing conditions at near neutral ph values leading to the desorption of as from mineral oxides and to the reductive dissolution of fe and mn oxides also leading to as release iron ii and as iii are relatively abundant in these groundwaters and so4 concentrations are small typically 1 mg l 1 or less large concentrations of phosphate bicarbonate silicate and possibly organic matter can enhance the desorption of as because of competition for adsorption sites a characteristic feature of high groundwater as areas is the large degree of spatial variability in as concentrations in the groundwaters this means that it may be difficult or impossible to predict reliably the likely concentration of as in a particular well from the results of neighbouring wells and means that there is little alternative but to analyse each well arsenic affected aquifers are restricted to certain environments and appear to be the exception rather than the rule in most aquifers the majority of wells are likely to be unaffected even when for example they contain high concentrations of dissolved fe

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

dolomitization anhydrite cementation and porosity evolution in a reflux system insights from reactive transport models significant volumes of world hydrocarbon reserves occur in dolostones and the majority of these reservoirs are interpreted to be of reflux origin we used a two dimensional numerical reactive transport model to investigate systematically the temporal and spatial distribution of replacement dolomitization dolomite cementation anhydrite cementation and porosity evolution in a reflux system we tested the sensitivity of reflux dolomitization to brine concentration mesohaline to near halite saturated brines near surface temperature flow rate porosity permeability feedback relationships reactive surface area and the effect of initial porosity permeability heterogeneity simulations support the contention that hypersaline reflux is capable of extensive pervasive dolomitization and that mesohaline reflux dolomitization is viable reflux generated a tabular dolomite body that is thickest close to the brine source and thins basinward incorporation of initial porosity and permeability heterogeneity resulted in a dolomite body with pronounced lateral fingers replacement dolomitization increased porosity up to 8 but postreplacement reflux resulted in the precipitation of minor dolomite cements overdolomitization anhydrite cements that were spatially and temporally associated with replacement dolomitization caused a significant porosity reduction of up to 25 simulated rates of replacement dolomitization by reflux are fast up to three orders of magnitude faster than seawater dolomitization the rate of dolomitization and anhydrite mineralization proved to be critically sensitive to the flow rate and the brine chemistry temperature and reactive surface area were important controls on the rate of dolomitization whereas the feedback relationship between porosity and permeability was a relatively moderate control our reactive transport models predict the general spatial and temporal trends in dolomite porosity and anhydrite observed in some major dolomite reservoirs

morphology and isotope heterogeneity of late quaternary pedogenic carbonates implications for paleosol carbonates as paleoenvironmental proxies abstract stable isotope values and radiocarbon ages were determined for pedogenic carbonate microsamples from relict soils and palaeosols from the rio grande rift region of new mexico carbonate nodules and clusters were sampled from fluvial and piedmont soils and palaeosols with widely varying exposure durations 7 900 ky pedogenic carbonates from individual soils exhibited irregular relationships between age and depth ranging in radiocarbon age by 13 ky at individual depths 18 o values and to a lesser extent 13 c values likewise had wide ranges within soils however comparing the stable isotope values of carbonates with similar radiocarbon ages within and between soils revealed consistent trends in stable isotope values over time 18 o values of pedogenic carbonates tended to decrease with decreasing age 25 17 radiocarbon ka and increased with decreasing age 13 c values with either depth or age although the oldest palaeosol piedmont carbonates radiocarbon ages of 24 5 19 2 ka are 1 more negative than the younger piedmont palaeosol carbonates pedogenic carbonates in the relict fluvial soil which has by far the longest exposure period showed the greatest range in 13 c values comparing the 13 c values of samples of similar radiocarbon age from the relict fluvial soil indicates a transition from a mixed c 3 c 4 ecosystem at 11 ka to an effectively pure c 3 ecosystem at 9 ka followed by a return to mixed vegetation by 5 ka thus although c 4 vegetation persisted in southern new mexico through the last glaciation drought resistant c 3 vegetation became dominant at 9 ka prior to significant strengthening of the summer monsoon this study illustrates that the stable isotope values of carbonate nodules and clusters from relict soils and or slowly buried palaeosols can be used for palaeoenvironmental reconstructions in the context of a detailed chronologic framework

paleosol organic matter and pedogenic carbonates and paleontological δ13c records applied to the paleoecology of late pleistocene holocene in mexico abstract stable isotopes of carbon 13 c in terrestrial geological materials paleosol humus and carbonates as well as fossil bones collagen and tooth enamel are established as highly specific records on paleoenvironmental characteristics it was assumed that comparing the results of different types of materials on regional or local scales provides more accurate and reliable reconstructions and even opens new aspects of interpretation this was tested by the comparison of the data obtained from the late pleistocene paleosols and or remains of pleistocene megafauna in various locations in northwestern mexico sonora paleosols formed in mis3 mis2 and mis1 central northern mexico san luis potosi teeth corresponding to mis2 and mis1 and central southern mexico puebla paleosols corresponding to mis3 and mis2 and teeth associated with these paleosols and state of mexico teeth corresponding to mis2 the results of isotopic studies are complemented with other paleoenvironmental proxies the 13 c values of paleosols of sonora is 19 8 to 16 95 in organic matter and shows little difference between paleosols and holocene soils 13 c values of pedogenic carbonates are 6 4 to 4 52 in san luis potosi the 13 c values of paleosol are 12 16 in organic matter in puebla they vary from 24 6 in paleosols to 15 16 in the modern surface soil pointing to contrasting vegetation change the 13 c values in fossils range from 10 7 to 1 2 in slp of 2 73 and 2 93 in puebla and 6 5 to 1 3 in state of mexico the 13 c values of paleosols and analysis of megafauna in northwest and central northern mexico matched each other indicating mixed c3 c4 vegetation while for central southern mexico paleosols indicated predominance of c3 plants and megafauna indicated mixed c3 c4 composition in general the results indicate that in northern mexico environmental conditions were slightly wetter than at present while for the central area there was a large change in the environmental conditions of high humidity in mis3 and mis2 with a trend to drier climates in mis1

hydrogeochemistry of arsenic and other inorganic constituents in groundwaters from la pampa argentina groundwaters from quaternary loess aquifers in northern la pampa province of central argentina have significant quality problems due to high concentrations of potentially harmful elements such as as f no3 n b mo se and u and high salinity the extent of the problems is not well defined but is believed to cover large parts of the argentine chaco pampean plain over an area of perhaps 106 km2 groundwaters from la pampa have a very large range of chemical compositions and spatial variability is considerable over distances of a few km dissolved as spans over 4 orders of magnitude 4 5300 g l 1 and concentrations of f have a range of 0 03 29 mg l 1 b of 0 5 14 mg l l v of 0 02 5 4 mg l 1 no3 n of 0 2 140 mg l 1 mo of 2 7 990 g l 1 and u of 6 2 250 g l 1 of the groundwaters investigated 95 exceed 10 g as l 1 the who guideline value and 73 exceed 50 g as l 1 the argentine national standard in addition 83 exceed the who guideline value for f 1 5 mg l 1 99 for b 0 5 mg l 1 47 for no3 n 11 3 mg l 1 39 for mo 70 g l 1 32 for se 10 g l 1 and 100 for u 2 g l 1 total dissolved solids range between 730 and 11400 mg l 1 the high values resulting mainly from evaporation under ambient semi arid climatic conditions the groundwaters are universally oxidising with high dissolved o2 concentrations groundwater phs are neutral to alkaline 7 0 8 7 arsenic is present in solution predominantly as as v groundwater as correlates positively with ph alkalinity hco3 f and v weaker correlations are also observed with b mo u and be desorption of these elements from metal oxides especially fe and mn oxides under the high ph conditions is considered an important control on their mobilisation mutual competition between these elements for sorption sites on oxide minerals may also have enhanced their mobility weathering of primary silicate minerals and accessory minerals such as apatite in the loess and incorporated volcanic ash may also have contributed a proportion of the dissolved as and other trace elements concentrations of as and other anions and oxyanions appear to be particularly high in groundwaters close to low lying depressions which act as localised groundwater discharge zones concentrations up to 7500 g l 1 were found in saturated zone porewaters extracted from a cored borehole adjacent to one such depression concentrations are also relatively high where groundwater is abstracted from close to the water table presumably because this zone is a location of more active weathering reactions the development of groundwaters with high ph and alkalinity results from silicate and carbonate reactions facilitated by the arid climatic conditions these factors together with the young age of the loess sediments and slow groundwater flow have enabled the accumulation of the high concentrations of as and other elements in solution without significant opportunity for flushing of the aquifer to enable their removal

paleoecology of late pleistocene holocene faunas of eastern and central wyoming usa with implications for lgm climate models abstract oxygen and carbon isotope compositions of teeth were measured for a variety of fossil herbivores omnivores and carnivores from natural trap cave ntc and little box elder cave lbec central eastern wyoming usa these sites host some of the best preserved and most abundant late pleistocene to early holocene mammal fossils and provide key information about ecological and climatic change attending the pleistocene holocene transition average pleistocene compositions are consistent with c3 dominated diets but c4 grass consumption increased in bison from the late pleistocene to today a single sangamonian equus tooth also has elevated 13c suggesting that c4 biomass increased during interglacials in general tooth 18o values imply local water 18o values at ntc of 15 to 16 during the last glacial maximum lgm and 14 today consistent with modern regional studies and general circulation models gcm s for the lgm water 18o values at lbec were 12 although herbivore compositions are consistent with theoretical expectations carnivores exhibit lower 13c and higher 18o values relative to herbivores than anticipated these discrepancies could reflect poorly understood carnivore physiologies or diets and emphasize the need for further investigation of isotope systematics in carnivores isotope zoning in several herbivore teeth shows negative correlations between carbon and oxygen isotopes high and low 18o values representing summer and winter seasons occur with low and high 13c values respectively this trend could indicate seasonally changing diets e g consumption of drier foods or conifers during the winter or burning of stored fat during the winter increasing 18o values from the pleistocene to holocene in water dependent taxa are consistent with an increasing proportion of summer moisture derived from the gulf of mexico as predicted by isotope enabled gcm s mean annual precipitation during the late pleistocene is estimated at 350 mm yr similar to modern day c 200 mm yr indicating that dry conditions have prevailed for the last 25 ka in wyoming a revised analytical expression for c4 plant abundance in the western us is proposed that accounts for climate variables and pco2 combination of this expression with the climate predictions of the pmip2 ensemble average gcm explains lgm c4 plant abundances at ntc southern texas and florida changes to c4 plant abundances may provide sensitive tests of gcm accuracies

geothermal convection in the tengiz carbonate platform kazakhstan reactive transport models of diagenesis and reservoir quality a fundamental challenge in carbonate reservoir characterization is predicting the spatial distribution of diagenesis we used a reactive transport model to investigate the viability of geothermal convection and associated patterns of diagenetic porosity modification in the tengiz isolated carbonate platform reservoir before burial forced convection generates significant calcite dissolution locally up to 45 toward the platform center minor calcite cementation up to 0 4 in the slope and moderate calcite dissolution and cementation up to 1 6 in serpukhovian boundstone convective cells the patterns and rates of diagenesis proved critically sensitive to specified vertical permeability after burial with 200 m 660 ft of salt modeled subsurface temperature contrasts drive platform scale free convection flow is hydraulically closed but significant dissolution up to 7 3 after 20 m y occurred in the serpukhovian and visean platform interior and minor cementation up to 0 7 occurred toward the margin a shale filled salt withdrawal basin 500 m 1640 ft deep significantly modifies the subsurface temperature distribution and free convective flow ascending groundwaters beneath the withdrawal basin created a zone of calcite dissolution up to 24 5 in 20 m y with a mushroom geometry and minor cementation up to 2 3 in 20 m y in the distal platform interior and margin rates of diagenesis are dramatically reduced with increasing overburden as compaction retards convective flow from a generic perspective free convection persists if the salt overburden is substituted with shale although flow is reversed resulting in a different distribution of diagenesis simulations of geothermal convection provide a physically viable model for the integration of direct diagenetic observations to augment predictions of reservoir quality in tengiz and other carbonate platform reservoirs

interactions between fluvial and eolian geomorphic systems and processes examples from the sahara and australia abstract the remains of once integrated drainage systems are still discernible in many of the hot deserts of the world some of these date back to the mesozoic as in arid western australia where they now form chains of salt lakes others were active in miocene times such as the sahabi rivers that once flowed from chad to the mediterranean a few remained active during quaternary interglacials as in the sahara all contributed sediments that were reworked by wind during drier phases to form desert dunes the desert dunes of australia and of the 9500 km long chain of deserts extending from the sahara through arabia to the thar desert of india originated from sediments eroded from the uplands and deposited in closed interior basins formed during the course of late mesozoic and cenozoic faulting rifting and epeirogenic movements it was the unconsolidated neogene sediments laid down in large subsiding sedimentary basins such as the kufra sirte basin in libya and the chad basin which provided the source material for the late pliocene and quaternary desert dunes of the sahara one effect of the progressive build up of high latitude ice sheets during the neogene was to steepen the temperature and pressure gradients between the equator and the poles resulting in increased trade wind velocities stronger winds were better able to mobilize the alluvial sands of the increasingly dry sahara and adjacent deserts and to fashion them into desert dunes a more subtle form of interaction between eolian and fluvial processes concerns the interplay between desert dust loess accumulation on hill slopes in arid regions and the onset of fine grained valley fill accumulation by sluggish low energy streams in mountain valleys some of these late pleistocene wetlands served as refuge areas for plants reptiles and invertebrates at a time when the surrounding desert plains were very cold and dry as in the flinders ranges of south australia in the arid flinders ranges such valley fills were built up between 35 kyr and 15 kyr ago after which the return of the summer monsoon led to stream channel incision and the formation of a network of gullies often erroneously attributed to human activities understanding the causes of such accelerated erosion can prevent unnecessary and expensive attempts at restoration since the latter are based on the incorrect assumption that overgrazing and present day land use are responsible

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

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

seasonal variation in kangaroo tooth enamel oxygen and carbon isotopes in southern australia abstract serial sampling of tooth enamel growth increments for carbon and oxygen isotopic analyses of macropus kangaroo teeth was performed to assess the potential for reconstructing paleoseasonality the carbon isotope composition of tooth enamel apatite carbonate reflects the proportional intake of c3 and c4 vegetation the oxygen isotopic composition of enamel reflects that of ingested and metabolic water tooth enamel forms sequentially from the tip of the crown to the base so dietary and environmental changes during the tooth s formation can be detected 13c and 18o values were determined for a series of enamel samples drilled from the 3rd and 4th molars of kangaroos that were collected along a 900 km north south transect in southern australia the serial sampling method did not yield pronounced seasonal isotopic variation patterns in macropus enamel the full extent of dietary isotopic variation may be obscured by attenuation of the isotopic signal during enamel mineralisation brachydont low crowned macropus teeth may be less sensitive to seasonal variation in isotopic composition due to time averaging during mineralisation however geographic variations observed suggest that there may be potential for tracking latitudinal shifts in vegetation zones and seasonal environmental patterns in response to climate change

paleoenvironment of the folsom archaeological site new mexico usa approximately 10 500 14c yr b p as inferred from the stable isotope composition of fossil land snail shells abstract well preserved aragonitic land snail shells vallonia from late pleistocene eolian sediment in the folsom archaeological site in new mexico exhibit an overall decrease of 18opdb from maximum values of 2 7 more positive than modern to younger samples with lower average values of about 3 6 within the modern range the age of the samples approximately 10 500 14c yr b p suggests that the decrease in 18o may manifest climatic changes associated with the younger dryas some combination of increased relative humidity and cooler temperatures with decreased 18o of precipitation during the times of snail activity can explain the decrease in shell 18o a well known paleoindian bison kill occurred at the folsom site during this inferred environmental transition average 13c values of the aragonite shells of the fossil vallonia range from 7 3 to 6 0 among different archaeological levels and are not as negative as modern values this suggests that the proportion of c4 vegetation at the folsom site approximately 10 500 14c yr b p was greater than at present a result which is consistent with other evidence for higher proportions of c4 plants in the region at that time

the role of secondary minerals in controlling the migration of arsenic and metals from high sulfide wastes berikul gold mine siberia abstract the role of secondary minerals in controlling the migration of as cu zn pb and cd has been investigated in piles of high sulfide waste at the berikul au mine kemerovo region russia these wastes contain 40 45 wt sulfides and have been stored for approximately 50 a near the mokry berikul river sulfide oxidation generates acid pore solutions ph 1 7 with high concentrations of so42 190 g l fe 57 g l as 22 g l zn 2 g l cu 0 4 g l pb 0 04 g l and cd 0 03 g l from these solutions as is precipitated as amorphous non stoichiometric fe sulfoarsenates in the lower horizons of the waste piles during precipitation of the fe sulfoarsenates the concentration of fe in these phases decreases from 34 to 21 wt that of as increases from 11 to 22 wt while the s content remains approximately constant 5 4 5 8 wt arsenic is also accumulated in jarosite beudantite solid solutions up to 8 4 wt as which occur as inclusions in the amorphous fe sulfoarsenates in efflorescent crusts on the surface of the waste pile as co precipitates with the fe iii sulfates copiapite 0 27 wt as and rhomboclase 0 87 wt as zinc and cu are incorporated primarily into fe ii sulfates i e melanterite in the interior of the waste pile and rozenite in the efflorescent crust the zn mineral dietrichite is also formed at the surface of the waste pile as a result of evaporation of pore solutions and is the only fe ii sulfate containing detectable amounts of as 0 64 wt lead is mainly co precipitated with minerals of the jarosite group where the pb content may reach 4 3 wt co precipitation of toxic elements with sulfates and sulfoarsenates of fe is shown to be a significant mechanism in controlling the concentration of heavy metals in pore solutions of high sulfide mine wastes precipitation of secondary phases causes the formation of a hardpan layer with low permeability at a depth of 1 1 5 m below the surface of the waste pile rainwater accumulates above the hardpan horizons and slowly drains along these aquicludes to the bottom of the pile most of the rainwater evaporates during infiltration this leads to formation of the described efflorescent sulfate crusts dissolution of these crusts during the next rain storm produces highly acidic surface waters ph 1 1 rich in so42 30 g l fe 18 g l as 0 24 g l zn 0 12 g l cu 0 04 g l pb and cd 0 002 g l during the warm t 0 c period of the year which lasts about 7 months these surface waters transport a total of a few tens of kilograms of as and zn several kilograms of cu and a few hundred grams of pb and cd from the waste pile into the mokry berikul river as a result the concentrations of these metals in the river water increase by an order of magnitude thus reaching levels close to or exceeding the maximum values permissible for drinking water

spatial patterns of diagenesis during geothermal circulation in carbonate platforms geothermal convection of seawater deep in carbonate platforms could provide the necessary supply of magnesium for dolomitization at temperatures high enough to overcome kinetic limitations we used reactive transport simulations to predict the rates and spatial patterns of dolomitization during geothermal convection in a platform that was 40 km across and 2 km thick in the simulations porosity and permeability decrease with depth to account for sediment compaction dolomitization of a platform consisting of medium grained 0 0 5 mm sediments occurred in a broad band ranging from 2 5 km depth near the margin to 1 5 km depth near the platform center the area of dolomitization is deep enough that temperatures exceed 50 c but not so deep that low permeabilities restrict mass transport complete dolomitization in the center of this zone is estimated to require at least 60 my incorporation of permeability contrasts permeable beds and reactive beds focused dolomitization strongly and reduced the estimated time required for dolomitization by as much as 50 percent dolomitization created magnesium depleted calcium rich fluids in less than 10 ky and results support a link between dolomitization and anhydrite precipitation where adequate sulfate is available

the last pluvial climatic episodes in the deserts of southwestern north america long term variations in the effective moisture of deserts are linked both to glacial interglacial climatic cycles and through the milankovitch theory to orbitally induced changes in solar radiation intensity1 4 for southwestern north america comparison of palaeobotanical data with model predictions of palaeoclimate reveals two distinct pluvial regimes during the late wisconsin and early holocene 23 8 kyr bp southward displacement of the aleutian low pressure centre and strengthened westerlies from 40 to 30 n were important features of the full glacial 18 kyr bp pluvial maximum increased cyclonic storms and weakened monsoons led to a winter precipitation regime a feature seen both in the fossil record5 6 and climate models7 8 dominantly zonal flow during this period contrasts with the latest wisconsin and early holocene 12 8 kyr bp when meridional circulation transported maritime tropical air into the desert interior we now show that plant macrofossil assemblages from packrat neotoma spp middens9 in the mojave desert provide evidence for increased temperatures and summer rainfall during this period10 12 the anomalously late persistence to 8 kyr bp of woodland in low latitude low elevation deserts of the south west13 is attributed to enhanced monsoonal circulation3

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

paleoecology δ 13 c and δ 18 o stable isotopes analysis of a mammalian assemblage from the late pleistocene of hidalgo central mexico and implications for a better understanding of environmental conditions in temperate north america 18 36 n lat abstract paleoenvironmental interpretations inferred by the isotopic ecology of mammalian assemblages from the quaternary of mexico are scarce carbon 13 c and oxygen 18 o stable isotope analysis is performed on six late pleistocene localities from central mexico the objectives of the study are 1 to reconstruct the dietary traits and habitat of a mammalian community from the late pleistocene of southeastern hidalgo and 2 to characterize the paleoenvironments that existed in the region as well as placing them in the context of the paleoenvironmental conditions of temperate north america during the late pleistocene the carbon isotope composition shows a large diversity of dietary preferences including c3 intermediate c3 c4 and c4 feeders however c3 feeders are the most abundant in the assemblage the oxygen isotope composition also indicates a diversity of preferences for habitats including open habitats as well as humid and closed habitats the study reveals the presence of heterogeneous vegetation consisting of both woodland and grassland habitats during the late pleistocene the results obtained for the hidalgoan assemblage fit within the paleoenvironmental pattern known for other localities in temperate north america in particular those located in the western and central part between the coast of california the southern great plains and texas gulf coast i e grassland and mixed woodland grassland habitats

stable isotopes reflect the ecological stability of two high elevation mammals from the late quaternary of colorado abstract the vertebrate fossil record of cement creek cave colorado spans from 45 000 yr ago to the present and represents the richest stratified series of high elevation 2900 m mammal remains known from the late quaternary of north america stable carbon and oxygen isotope analyses of tooth enamel were used to assess potential ecological responses of two species found commonly throughout the cave yellow bellied marmots marmota flaviventris and bushy tailed woodrats neotoma cinerea to late quaternary climate and environmental changes of the southern rocky mountains results indicate that despite such perturbations the dietary ecologies of both species were maintained across this period neither taxon shifted to consuming c4 taxa or different c3 functional groups similarly no significant shifts in surface water use were detected variations in enamel 13c were observed however that represent the physiological responses of high elevation plants to changing levels of late quaternary atmospheric co2 while our findings extend both the geographic and elevational record of this plant co2 response they simultaneously highlight the ecological stability of high elevation m flaviventris and n cinerea during climate changes of late quaternary magnitude

was grass more prevalent in the pronghorn past an assessment of the dietary adaptations of miocene to recent antilocapridae mammalia artiodactyla abstract molar teeth of both tertiary and quaternary representatives of the family antilocapridae were examined using mesowear and light stereomicroscopy microwear taxa from the central and southern great plains and the northern and southern great basin were included in the analyses and results compared to those obtained on the modern pronghorn antilocapra americana species included spanned from the early miocene late hemingfordian to the late pleistocene rancholabrean results are concordant with well known trends toward increasing aridity and shifts in vegetational structure in the late miocene early pliocene of north america both mesowear and microwear results indicate a shift toward more abrasive diets beginning in the hemphillian late miocene pliocene and then a return to a less abrasive dietary regime for the duration of the pleistocene and into the recent the more derived antilocaprines more hypsodont relatively longer limbs apparently depended more on grass than the less advanced merycodontines but even the earliest of the latter seem to have relied more on grass as a dietary staple than the modern pronghorn seasonal grit encroachment on food items encountered by fossil antilocaprids coupled with a heavier reliance on grasses may provide a possible explanation for the extreme hypsodonty present in the modern pronghorn despite its mainly browsing dietary behavior

summer monsoon intensity controls c4 c3 plant abundance during the last 35 ka in the chinese loess plateau carbon isotope evidence from bulk organic matter and individual leaf waxes the natural abundance of c3 and c4 plants is affected by multiple environmental factors including temperature moisture balance and atmospheric pco2 the relative importance of these factors is a subject of considerable debate and may vary in different natural ecosystems previous studies generally focus on single loess sequences in the chinese loess plateau and conflicting conclusions on c4 c3 have been reached when studying carbon isotope ratios in carbonate and organic matter in this paper we report a comprehensive carbon isotopic characterization of total organic carbon toc and individual higher plant leaf waxes from five loess sequences spanning the last 35 ka from the chinese loess plateau clp the five coring sites encompass large gradients of annual mean temperature 9 2 13 9 c and precipitation 402 673 mm allowing us to assess the controlling mechanisms on c4 c3 plant ratios glacial interglacial sequences provide carbon isotope data for comparison with other climatic and environmental proxies such as lithology and magnetic susceptibility our results demonstrate that increased c4 c3 ratios are positively correlated with higher temperature and increased summer rainfall which characterize stronger summer monsoon in all five sites we conclude c4 abundance increases from the last glacial to the holocene in response to greater monsoon activity and that the c4 expression is suppressed in the cold and drier intervals

geochemical controls on arsenic distribution in the baccu locci stream catchment sardinia italy affected by past mining abstract the baccu locci stream catchment sardinia italy is affected by serious as contamination as a consequence of past mining the presence of both point and widespread sources of contamination waste rock dumps and flotation tailings respectively strongly affects surface water chemistry and produces high as concentrations hundreds of g l 1 in stream waters water chemistry of the baccu locci stream changes considerably over a distance of about 10 km as a consequence of various locally concomitant processes acting along the stream course 1 mixing with metal rich so 4 waters 2 dissolution precipitation of metal bearing phases 3 mixing with hco 3 dominated lake waters 4 gypsum dissolution coupled with calcite precipitation 5 mixing with dilute surface and or ground waters in contrast to metals e g pb cu zn and cd whose dissolved concentrations rapidly decrease downstream of the mined area through co precipitation adsorption mechanisms as concentrations tend to gradually increase up to 0 9 mg l 1 along the stream course as far as the alluvial plain though significant variations are locally observed this behaviour is mainly due to the higher mobility of as than metals under the near neutral oxidative conditions occurring in the baccu locci stream waters results of a leaching test indicate that part of the as contained in the flotation tailings occurs as as iii which is more mobile and less strongly sorbed than as v the as released to the waters by various mechanisms i e release desorption from the fe iii hydroxides coatings of silicate grains oxidation of residual arsenopyrite decomposition of scorodite tends to remain in solution and to be transported long distances as a consequence of the widespread presence of highly as contaminated flotation tailings all over the medium lower baccu locci stream catchment long term as contamination is expected

rancho la brea stable isotope biogeochemistry and its implications for the palaeoecology of late pleistocene coastal southern california abstract we sampled 143 individuals from rancho la brea rlb large faunal collections for bone collagen stable carbon 13c and nitrogen 15n isotope ratios these collections were recovered from asphalt seeps in the los angeles basin california usa and date from 40 to 12 ka our findings indicate that despite a slight reduction in collagen nitrogen content rlb skeletal remains are relatively well preserved and most yield proteins diagnostic of diet herbivore 13c and 15n values covary with rumination and are consistent with changes in late pleistocene vegetation reconstructed from pollen profiles we find no evidence for reliance on c4 grasses at rlb despite low atmospheric co2 concentrations carnivore 15n values indicate canis dirus smilodon fatalis and panthera leo atrox competed for similar prey sets and were equally reliant on ruminant and nonruminant prey types the 15n values of mammut americanum indicate partial reliance on vegetation with lower 15n values such as nitrogen fixing taxa distinguishing them from the remainder of the study population a comparison of rlb and european faunal 15n values from the late pleistocene suggests that coastal southern california experienced greater aridity

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

fossil grass cuticles from lacustrine sediments a review of methods applicable to the analysis of tropical african lake cores the need for alternatives to fossil pollen for the reconstruction of vegetation dominated by grasses has prompted the use of grass cuticles which lack a described method of analysis methods used to analyse sediments for palaeoecological materials allied to grass cuticles including microscopic charcoal phytoliths and plant cuticles are reviewed a simple set of methods and protocols for extracting identifying and quantifying fossil grass cuticles are presented

inland california during the pleistocene megafaunal stable isotope records reveal new paleoecological and paleoenvironmental insights abstract we measured oxygen and carbon isotope compositions from teeth from three fossil localities in california the mckittrick tar seeps rancholabrean fairmead landfill and irvington both irvingtonian these sites have produced a variety of megafauna fossils and to date are relatively understudied previous ecological studies of pleistocene california megafauna have focused on the coastal rancho la brea tar seeps rlb neglecting inland faunas both fairmead landfill and mckittrick are located in california s san joaquin valley and provide the first isotopic data from the region we sampled a wide range of taxa equus camelops mammuthus mammut hemiauchenia odocoileus tetrameryx capromeryx platygonus canis dirus canis latrans arctodus simus smilodon homotherium miracinonyx panthera onca and panthera atrox stable carbon values from both middle pleistocene localities are consistent with a c3 dominated environment mean annual precipitation map estimates for the middle pleistocene localities are 340 mm year for fairmead landfill and 900 mm year for irvington while the inland map estimate is similar to modern levels irvington map estimates are significantly higher than the modern average in contrast the mckittrick tar seeps show clear evidence of c4 consumption among equus bison and camelops suggesting a mixture c4 grasses and halophytes similarly comparing between mckittrick and published data for rlb indicate a higher level of c4 resources inland serially sampled teeth from both inland localities reveal diet and resource partitioning between browsers and grazers

fluid expulsion from overpressured basins implications for pb zn mineralisation and dolomitisation of the east midlands platform northern england abstract our understanding of burial diagenesis within carbonates is often limited by poor constraints on available fluid volumes and geochemistry however regional stratigraphic and burial history data are often readily available using these data to develop numerical models which couple sedimentological and hydrological basin evolution we estimate the volumes and geochemistry of fluids that were available to drive dolomitisation and pb ore genesis within the carboniferous derbyshire platform of northern england current conceptual models of these processes invoke tectonic release of burial induced overpressure developed within adjacent dinantian basins as a drive for reactive fluid flow to the platform our simulations show that compaction driven flow may lead to a supply of fluids that is more complex in its temporal evolution than may be expected spatial variations in the rate of fluid expulsion from different sediments lead to a staggered delivery of fluids from different sources rapid fluid expulsion within deeper sediments leads to a downwards decreasing pressure gradient that subsequently draws down fluid from within overlying sediments thus early fluid supply to the platform is sourced from the deep basins while later fluid supply descends from above the platform as well as from the sides we suggest that such a flow development may have important implications for the relative timing and distribution of a sequence of diagenetic products within the platform this hypothesis is tested using volume estimates from our simulations we conclude that although this staggered fluid supply model may be applicable generically it appears that it is only valid for explaining mineralisation in the derbyshire platform fluid volumes supplied to the platform are insufficient to explain dolomitisation our simulations are supported by a sensitivity analysis that identifies that compaction driven flow in this system is strongly controlled by the rate of burial and sediment permeabilities within the compacting basins

multiphase partial and selective dolomitization of carnian reef limestone transdanubian range hungary partially dolomitized carbonate successions provide a good opportunity to understand the commonly multistage process of dolomitization petrographic methods fluid inclusion microthermometry and stable isotope measurements were applied to reconstruct the diagenetic evolution and dolomitization of a partially dolomitized carnian reef limestone from the transdanubian range hungary the diagenetic history began with reef diagenesis and formation of dolomite micro aggregates in microbial fabric elements this was followed by the development of euhedral porphyrotopic dolomite crystals through overgrowths around the previously formed dolomite micro aggregates during the earliest burial stage increasing burial resulted in the extension of the dolomite patches via formation of finely crystalline replacement dolomite from the late norian when the carnian reef carbonates reached the depth of 1 0 to 1 8 km the diagenetic evolution continued in an intermediate to deep burial setting contemporaneously an extensional regime was established leading to fracturing the progressive burial resulted in the recrystallization of the pre existing dolomite with increasing temperature while saddle dolomite cement was precipitated in fractures in connection with the alpine orogeny intense denudation took place during the late cretaceous accompanied by fracturing similar tectonically controlled denudation and fracturing occurred in several stages during the cenozoic as a result of these processes the studied carnian carbonates were raised to a near surface position or became subaerially exposed leading to dedolomitization of the last dolomite phase and precipitation of calcite cement in cavities and fractures this study revealed that by investigating partially and selectively dolomitized rock types it is possible to document and understand those stages of the multiple dolomitization process which can barely be detected in the completely dolomitized rock bodies recognition of the dolomitization phases could provide the basis for the analysis of their relations with the depositional diagenetic and tectonic processes and stages of basin evolution

application of numerical modelling to a case of compaction driven dolomitization a jurassic palaeohigh in the po plain italy dolomitization of a carbonate platform can occur at different times and in different diagenetic environments from synsedimentary to deep burial settings numerical simulations are valuable tools to test and select the model that among different hypotheses compatible with field and geochemical data best honour mass balance kinetic and thermodynamic constraints moreover the simulation can predict the distribution of the dolomitized bodies in the subsurface and evaluate porosity changes valuable information for the oil industry this study is the first attempt to reproduce and investigate the compaction dolomitization model the diagenetic study of the jurassic carbonate basin and palaeohigh system of the po plain indicates that the carbonates of the palaeohighs were dolomitized by basin compaction fluids the main goal of the simulations is to evaluate the origin and evolution of the dolomitizing fluids and to provide insights regarding the distribution of the potential reservoir dolomitized bodies in the po plain the modelling process is subdivided into two steps basin modelling and reactive transport modelling the sebe3 basin simulator eni proprietary was used to create a three dimensional model of the compacting system the results include compaction fluid flow rate from the basin to the palaeohigh compaction duration and a determination of the total amount of fluid introduced into the palaeohigh these data are then used to perform reactive transport modelling with the toughreact code sensitivities on dolomite kinetic parameters suggest that dolomitization was an efficient process even at low temperatures with differences mainly related to the dynamics of the process fluid composition is one of the main constraints the sea water derived compaction fluid is proven to be efficient for dolomitization due to its relatively high mg content simulations also confirmed that permeability is the most important factor influencing fluid flow and consequently the dolomite distribution in the formation permeable fractured zones have a strong influence diverting the dolomitizing fluids from their normal path towards overlying or lateral zones moreover the simulations showed that after dolomite replacement is complete the dolomitizing fluids can precipitate dolomite cement causing over dolomitization with related localized plugging effects in the zone of influx mass balance calculations indicate that in the dolomitization compaction model the amount of compaction water fluxed from the basin to the carbonate is the main constraint on dolomitization efficiency this observation implies that the ratio between the volume of the basin undergoing compaction and the volume of the palaeohigh is a limiting factor on the final size of the dolomitized bodies an isolated palaeohigh could be an ideal site for pervasive replacement dolomitization due to the large volume of compaction fluids available compared with the carbonate rock volume in the case of large platforms the more permeable margin lithofacies are the most likely sites for compaction model dolomitization the combined use of a basin simulator and reactive transport modelling has proved to be a successful method to verify model reliability and it provides insights into the volumetric distribution of diagenetic products

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

evidence for geographic variation in the diets of late pleistocene and early holocene bison in north america and differences from the diets of recent bison abstract during the late pleistocene and early holocene bison was widely dispersed across north america and occupied most regions not covered by ice sheets a dietary study on bison paleopopulations from alaska new mexico florida and texas was performed using two methods that relate dental wear patterns to diet mesowear analysis and microwear analysis these data were compared to a mixed sample of extant bison from the north american central plains extant wood bison from alberta canada and a variety of other modern ungulates mesowear relates macroscopic molar facet shape to levels of dietary abrasion the mesowear signature observed on fossil bison differs significantly from the hyper abrasive grazing diet of extant bison tooth microwear examines wear on the surface of enamel at a microscopic scale the microwear signal of fossil samples resembles to modern bison but the fossil samples show a greater diversity of features suggesting that fossil bison populations regularly consumed food items that are texturally inconsistent with the short grass diet typical of modern plains bison mesowear and microwear signals of fossil bison samples most closely resemble a variety of typical mixed feeding ungulates all with diets that are substantially less abrasive than what is typical for modern plains bison furthermore statistical tests suggest significant differences between the microwear signatures of the fossil samples thus revealing geographic variability in pleistocene bison diets this study reveals that fossils are of value in developing an understanding of the dietary breadth and ecological versatility of species that in recent times are rare endangered and occupy only a small remnant of their former ranges

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

reactive transport modeling of early burial dolomitization of carbonate platforms by geothermal convection reactive transport models rtms permit quantitative investigation of diagenesis and its effects on reservoir quality the rtm toughreact is used to investigate diagenesis in an isolated platform driven by geothermal kohout convection of seawater which has been invoked to explain dolomitization during early burial previous short 0 1 m y rtm simulations suggested that convection can drive dolomitization mostly at greater than 50c and anhydritization but complete dolomitization requires greater than 30 60 m y our more extended rtm simulations 30 m y indicate significant nonlinearities in the system consistent with high temperature experiments with parts of the platform completely dolomitized within 10 15 m y as dolomitization proceeds the process becomes predominantly flux controlled with development of a wedge shaped dolomite body which thins from the margin to the interior at considerably shallower depth and cooler temperatures 20 30c than suggested by short simulations dolomitization is relatively insensitive to boundary conditions such as relative sea level and platform geometry but is significantly slower in circular than elongate platforms sediment permeability and reactive surface area commonly inversely related are key controls dolomitization is limited to the margin of low permeability muddy platforms despite a high reactive surface area dolomitization of more permeable grainy platforms is limited by a lower reactive surface area occurring only in the platform core due to widespread cooling sedimentary layering produces a complex diagenetic stratigraphy dolomitization favoring more reactive beds at shallow depth where permeability is not limiting but switching to more permeable beds at depth bank marginal fracturing limits dolomitization of the platform interior whether the fractures are baffles or conduits for flow

lapse rates and other variables applied to estimating paleoaltitudes from fossil floras abstract a previous method for determining paleoaltitude from fossil floras has used the difference between sea level and upland paleotemperatures which is then multiplied by the reciprocal of a normal lapse rate the present study examines other variables that can significantly influence such results terrestrial lapse rates have been calculated for 39 areas of the world based upon mean annual temperature mat mean warm month temperature mat and mean cold month ttemperature cmt these show regional and seasonal variability that is explained by factors including continentality elevation of large massifs or high base levels cold air drainage fog mountain barrier effects and the location of the subtropical high pressure zone lapse rates and projected sea level temperatures based on data from the western united states show distinct regional patterns these indicate that within this region the highest lapse rate and temperature values are correlated with 1 continental climates in the subtropical high pressure zone and 2 areas having relief where the lowest elevation land surfaces base levels occur at high altitude the data are applied to evaluate and revise the methodology for estimating paleoaltitudes variables of climatic change sea level fluctuation and paleogeography are also considered limitations in application of the method are emphasized the method is exemplified by application to the latest eocene florissant flora of colorado u s a although the results are conjectural they strongly suggest that the late eocene erosion surface in the southern rocky mountains occurred at a much higher paleoaltitude than previously thought this high elevation may have resulted from earlier laramide crustal thickening

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

holocene environmental change in the eastern snake river plain of idaho usa as inferred from stable isotope analyses of small mammals abstract previous research on the small mammal population recovered from archeological excavations at the wasden site in southeastern idaho suggests that changing frequency distributions through time represent a shift in climate during the early holocene from a cooler wetter regime to a warmer drier one this conclusion was re evaluated using stable carbon and nitrogen isotope analyses of bone collagen from the three species of small mammals examined in the earlier studies pocket gophers thomomys talpoides pygmy rabbits brachylagus idahoensis and ground squirrels spermophilus townsendii resulting carbon and nitrogen isotopic values are consistent with known differences in feeding ecology suggesting high fidelity as proxies for past vegetation and thus climate regimes patterns of 15 n enrichment and increased representation of c 4 cam vegetation observed in the pocket gophers and to a lesser extent ground squirrels suggests increasing warmth and or aridity from the early holocene until 7000 cal yr bp thus supporting previous hypotheses of climate change on the eastern snake river plain the results highlight the potential contribution of such studies for archeological research by providing additional proxies for environmental conditions that bear on paleoecological adaptations to climatic change including past human use and occupation of the region

geothermal convection in south atlantic subsalt lacustrine carbonates developing diagenesis and reservoir quality predictive concepts with reactive transport models prolific hydrocarbon discoveries in the subsalt commonly known as the presalt section of brazil and the conjugate african margin have created a business imperative to predict reservoir quality in lacustrine carbonates geothermal convection is a style of groundwater flow known to occur in rift settings which is capable of diagenetic modification of reservoir quality we simulated variable density groundwater flow coupled with chemical reactions to evaluate the potential for diagenesis driven by convection in subsalt carbonates rates of calcite diagenesis are critically controlled by temperature gradient and fluid flux following the principles of retrograde solubility simulations predict that convection could operate in rift carbonates prior to salt deposition but with rates of dissolution in the reservoir interval only on the order of 0 01 vol m y which is too low to significantly modify reservoir quality the exception is around permeable fault zones and or unconformities where flow is focused and dissolution rates are amplified to 1 to 10 vol m y and could locally modify reservoir quality after salt deposition simulations also predict convection with a critical function for salt rugosity the greatest potential for dissolution at rates of 0 1 to 1 vol m y occurs where salt welds overlying permeable carbonates thin to 500 m 1640 ft or less with tens of million years residence times feasible convection under these conditions could locally result in reservoir sweet spots with porosity modification of 1 to 10 and potentially an order of magnitude or more in reservoir permeability integrating quantitative model derived predictive diagenetic concepts with traditional subsurface data sets refines exploration to production scale risking of carbonate reservoir presence and quality