holocene timberline and palaeoclimate of the northern uinta mountains northeastern utah usa clastic and organic sediments exposed in two stream cutbanks above modern timberline in the headwaters of the henrys fork drainage record multiple episodes of fluvial lacustrine and wetland deposition the location of the upper henrys fork at the boundary between modern summer wet winter dry and summer dry winter wet precipitation regimes suggests that changes in vegetation during the holocene were due primarily to variations in growing season temperature a radiocarbon date of 9310 6 70 bp on a salix fragment from the base of one exposure indicates that the upper reaches of the henrys fork were vegetated by riparian willows by the early holocene four other dates on wood and bulk organics ranging up to 4070 6 70 bp indicate that deposition continued through the middle holocene high picea pinus ratios and high percentages of artemisia pollen suggest that an open picea parkland was established at timberline by 9 5 ka cal bp in response to mean annual and july temperatures 1 0 c greater than at present

extinct mountain goat oreamnos harringtoni in southeastern utah the extinct harrington s mountain goat oreamnos harringtoni stock is predominantly known from dry cave localities in the grand canyon arizona in addition to two sites in the great basin nevada and from san josecito cave nuevo leon mexico a dry shelter in natural bridges national monument on the central colorado plateau southeastern utah preserves numerous remains of the extinct mountain goat in addition to pack rat middens remains from a 100 cm stratigraphic profile indicate that o harringtoni lived on the plateau 39 800 yr b p the oldest directly dated find of extinct mountain goat plant macrofossils indicate that engelmann s spruce picea engelmannii limber pine pinus flexilis rose rosa cf woodsii and douglas fir pseudotsuga menziesii grew during the late pleistocene where a riparian and a pinyon juniper pinus edulis juniperus osteosperma community now predominates douglas fir are found only in mesic protected north facing areas limber pine douglas fir bark and grasses were the major dietary components in the dung a springtime diet of birch betula is determined from pollen clumps in dung pellets

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

high salinity fluid inclusions formed from recycled seawater in deeply subducted alpine serpentinite abstract the origin of high pressure brines has been investigated in the erro tobbio peridotite western alps a mantle slice that was exposed to the seafloor of the mesozoic ligurian piedmontese tethys and was later involved in alpine subduction hydrothermal alteration by seawater derived fluids led to replacement of the mantle assemblage by cl bearing serpentine 0 35 wt cl brucite 0 2 wt cl and alkali bearing phyllosilicates 0 2 wt cl 0 2 0 55 wt na2o 1 5 wt k2o relics of these hydrous phases occur in olivine titanian clinohumite antigorite assemblages formed at 2 5 gpa and 550 600 c during partial devolatilization and veining of the hydrothermally altered peridotite the high pressure phases lack chlorine and alkalis and are coeval with fluid inclusions trapped in the syn eclogitic veins the inclusions are salt saturated and contain up to 50 wt cl na k mg and fe high fluid chlorinity was probably achieved during rehydration of relict mantle minerals and deposition of hydrous phases in the veins the data presented suggest that the seafloor hydrothermal signature was inherited by the eclogitic fluid due to partitioning of chlorine and alkalis into the fluid phase the presence of salty brines in eclogitized hydrous peridotites can indicate deep recycling of seawater derived fluids hydrous ultramafic systems can therefore act as large scale carriers of seawater into the mantle

sporormiella fungal spores a palynological means of detecting herbivore density during the historic period spores of the dung fungus sporormiella are abundant in lake and cave sediment where livestock are plentiful in the western united states sporormiella spores occasionally exceed 50 of the upland pollen sum in samples from corral ponds and bed grounds and routinely reach 4 in lake and marsh samples in pastoral areas sporormiella spores are comparatively rare in mid holocene sedimentary records but they reach values of 2 4 in pleistocene samples from lake sediments sporormiella spores are directly linked to extinct megaherbivores by their presence in mammoth dung from bechan cave utah in several sites in the western united states a precipitous decline of sporormiella percentages after ca 10 800 radiocarbon yr b p 12 900 years ago marks a decline of herbivore density probably associated with the north american megaherbivore extinction

deciphering the tectonic geodynamic context of the gem quality noble serpentine deposit formation combining microstructural chemical and micro raman analyses in palaeozoic olivine bearing marbles and serpentine hosting rocks pizzo tremogge margna unit austroalpine val malenco central alps italy abstract the gem quality noble serpentine of pizzo tremogge val malenco italy is included in palaeozoic olivine bearing marbles occurring in the margna unit central austroalpine domain a detailed inspection of serpentine samples reveals the presence of the three serpentine species lizardite chrysotile and antigorite occurring in different microstructural domains serpentine samples were investigated to obtain microstructural information preserved in the serpentine species by optical microscopy x ray powder diffraction electron microprobe spectrometry and micro raman spectroscopy the last of which is considered a reliable method for the identification of the different serpentine species two types of noble serpentine have been identified the yellow green type characterized by fine grained aggregates in marbles and the green type localized in fibrous veins in association with calcite and quartz the identification of the different serpentine types allowed us to recognize three stages of mineral crystallization characterized by i the formation of olivine bearing marbles stage 1 ii the growth of lizardite after olivine or within lizardite rich veins stage 2 and iii the replacement of lizardite by antigorite in marbles and by antigorite clinohumite in veins stage 3 these stages clarify the complex geodynamic tectonic evolution of the margna malenco system the paleozoic olivine bearing marbles margna protoliths stage 1 are subjected to extensional tectonics that brings the margna protoliths close to the malenco in a thinned extended type passive margin stage 2 finally an inversion of tectonics leads to the subduction and collision of the margna malenco system during alpine convergence stage 3 all this suggests that gem quality noble serpentine deposits may be related to different geological contexts

the selection of sites for paleovegetational studies the judicious selection of sites for paleovegetational and paleoclimatic studies permits paleoecologists to answer specific research questions that go beyond primary descriptions of past vegetation we present a model that describes the relationship between basin size and pollen source area and predicts the proportions of local extralocal and regional pollen sampled by lake basins of different size the distinctive sampling properties of lakes peats and small hollows can be exploited to provide details of pattern in paleovegetation so long as attention is given to the limitations and problems of these types of sites combinations of site types in a single study most fully exploit the information contained in sediments

evaluation of the potential of surface pollen spectra from caves in sw china for vegetation reconstruction abstract pollen analysis is rarely applied to cave sediments because of the complex range of processes influencing the origin transport and taphonomy of pollen grains in caves in order to evaluate the potential of pollen spectra from within caves for vegetation reconstruction we compared the modern pollen from the interior and exterior of four caves in guangxi and guizhou in southwestern china the results show that the pollen spectra from within the sack shaped caves and from the front and middle of a long narrow caves were similar to those outside the caves and therefore that the pollen spectra from these caves can reliably be used for palaeovegetation reconstruction wind is the major transport medium for the pollen entering caves but animals may be additional transport medium in addition cave geometry is likely to be responsible for the observed spatial distribution of pollen concentrations in caves in long narrow caves the entrance is the optimum sampling location for pollen analysis however in sack shaped caves an optimum sampling location cannot be specified due to the gradient in pollen concentration between the entrance and the rear together with its irregular distribution

holocene vegetation and climate in the puerto blanco mountains southwestern arizona abstract plant macrofossils from 21 pack rat neotoma sp middens at 535 605 m from the puerto blanco mountains southwestern arizona provide and excellent history of vegetation and climate for the last 14 120 yr b p in the sonoran desert a late wisconsin juniper joshua tree woodland gave way to a transitional early holocene desertscrub with sparse juniperus californica california juniper by 10 540 yr b p important sonoran desert plants including carnegiea gigantea saguaro and encelia farinosa brittle bush were dominants riparian trees such as acacia greggii catclaw acacia prosopis velutina velvet mesquite and cerdicium floridum blue palo verde grew on dry south facing slopes in a middle holocene sonoran desertscrub in a warm wet summer climate with frequent winter freezes modern subtropical sonoran desertscrub formed about 4000 yr b p as summer rainfall and winter freezes declined cercidium microphyllum foothills palo verde sapium biloculare mexican jumping bean olneya tesota ironwood and stenocereus thurberi organ pipe cactus became dominant as riparian trees retreated to wash habitats the inferences of a latest wisconsin early holocene summer monsoonal maximum by j e kutzbach 1983 modeling of holocene climates in late quaternary environments of the united states vol 2 the holocene h e wright ed pp 271 277 univ of minnesota press minneapolis are not supported for the southwest apparently the persistence of late wisconsin circulation patterns offset any increases in insolation

ovi caprid dung as an indicator of paleovegetation and paleoclimate in northwestern china diverse palynomorphs and phytoliths recovered from coprolites of ovi caprids sheep goat collected from yang hai tomb at xinjiang province china have been used to elucidate the dietary pattern of ancient livestock and to reconstruct the paleovegetation and paleoclimate of this part of northwest china ca 2500 14 c yr bp palynological and phytolith data suggest that a rich dry temperate vegetation prevailed in the area

asbestos and other fibrous minerals contained in the serpentinites of the gimigliano mount reventino unit calabria s italy serpentinites are metamorphic rocks with good technological properties and valuable ornamental characteristics which have been exploited since ancient times actually their use is limited and monitored in several countries worldwide because they can contain fibrous asbestos minerals that may be carcinogenic furthermore certain types of fibrous minerals can be confused with asbestos and must therefore be carefully investigated we have investigated the possible presence of the asbestos and non asbestos fibrous phases contained in serpentinitic rocks in a meta ophiolitic sequence from the gimigliano mount reventino unit southern italy which had not been previously assessed the detection and quantification of asbestos and the correct distinction of the fibrous non asbestos minerals are very important not only from a scientific point of view but also from a legislative one this is especially the case for the administrative agencies that have to take decisions with regards to the implementation of public and occupational health protection measures e g in road yards and quarry excavations as a consequence of this serpentinitic rock samples have been characterized in detail through x ray powder diffraction scanning and transmission electron microscopy combined with energy dispersive spectrometry analytical electron microscopy sem eds and tem aem differential scanning calorimetry thermogravimetry and micro raman spectroscopy two kinds of asbestos and four kinds of non asbestos fibrous silicates have been detected in the examined samples in order of decreasing abundance these are polygonal serpentine chrysotile fibrous antigorite tremolite gedrite and magnesiohornblende the size morphology crystallinity and chemical composition of the fibres were also discussed in the light of the possible role these properties could play in the carcinogenic effect on human health

holocene fire occurrence and alluvial responses at the leading edge of pinyon juniper migration in the northern great basin usa abstract fire and vegetation records at the city of rocks national reserve ciro south central idaho display the interaction of changing climate fire and vegetation along the migrating front of single leaf pinyon pinus monophylla and utah juniper juniperus osteosperma radiocarbon dating of alluvial charcoal reconstructed local fire occurrence and geomorphic response and fossil woodrat neotoma middens revealed pinyon and juniper arrivals fire peaks occurred 10 700 9500 7200 6700 2400 2000 850 700 and 550 400 cal yr bp whereas 9500 7200 6700 4700 and 1500 1000 cal yr bp are fire free wetter climates and denser vegetation fueled episodic fires and debris flows during the early and late holocene whereas drier climates and reduced vegetation caused frequent sheetflooding during the mid holocene increased fires during the wetter and more variable late holocene suggest variable climate and adequate fuels augment fires at ciro utah juniper and single leaf pinyon colonized ciro by 3800 and 2800 cal yr bp respectively though pinyon did not expand broadly until 700 cal yr bp increased fire related deposition coincided with regional droughts and pinyon infilling 850 700 and 550 400 cal yr bp early and late holocene vegetation change probably played a major role in accelerated fire activity which may be sustained into the future due to pinyon juniper densification and cheatgrass invasion

reconstruction of annual temperature 1590 1979 for longmire washington derived from tree rings abstract annual growth records from trees at timberline in the cascade range of washington are correlated with variations in temperature and snow depth and used to reconstruct climatic variation in the past response surfaces indicate that growth of mountain hemlock tsuga mertensiana and subalpine larch larix lyallii is positively correlated with summer july to september temperature and negatively correlated with spring march snow depth when snow depth is at or below average during years of above average snow depth temperature has little effect on mountain hemlock but has a negative effect on growth in subalpine larch these interactions make it difficult to reconstruct these climatic variables separately using standard methods mean annual temperature values which combine information on both summer temperature and spring snow depth were estimated from a regression model that reconstructs past temperature at longmire washington as a function of larch and hemlock tree ring chronologies the reconstruction of mean annual temperature shows temperatures between 1590 and 1900 to be approximately 1 c lower than those of the 20th century only during a short period from 1650 to 1690 did temperatures approach 20th century values

transmission electron microscope observation of the high pressure form of magnesite retrieved from laser heated diamond anvil cell abstract we applied focused ion beam fib technique to make a thin foil for transmission electron microscope tem observations of mgco3 magnesite and its new high pressure form magnesite ii recovered from laser heated diamond anvil cell lhdac both of which should play fundamental roles in the circulation of carbon in the lower mantle heterogeneous microstructures due to significant temperature gradients were observed along the axial direction of the disk sample 100 m in diameter and 30 m thick in spite of double sided laser heating and the use of thermal insulators between the diamond anvil and the sample the central portion of the mgco3 sample was found amorphous while the peripheral part remained magnesite on the basis of electron diffraction measurements with tem this and our earlier results based on in situ x ray diffraction measurements suggest that magnesite transformed to magnesite ii only at the central part where the temperatures should have been significantly higher than those near the pressure medium magnesite ii was amorphisized on release of pressure in contrast to our interpretation that it was converted back to magnesite based solely on in situ x ray diffraction measurements the new method of combining the fib technique with tem observation thus provides important information on phase transitions under very high pressure using lhdac which may be overlooked by in situ optical and x ray diffraction measurements

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

reinterpretation of the exposed record of the last two cycles of lake bonneville western united states a substantially modified history of the last two cycles of lake bonneville is proposed the bonneville lake cycle began prior to 26 000 yr b p the lake reached the bonneville shoreline about 16 000 yr b p poor dating control limits our knowledge of the timing of subsequent events lake level was maintained at the bonneville shoreline until about 15 000 yr b p or somewhat later when catastrophic downcutting of the outlet caused a rapid drop of 100 m the provo shoreline was formed as rates of isostatic uplift due to this unloading slowed by 13 000 yr b p the lake had fallen below the provo level and reached one close to that of great salt lake by 11 000 yr b p deposits of the little valley lake cycle are identified by their position below a marked unconformity and by amino acid ratios of their fossil gastropods the maximum level of the little valley lake was well below the bonneville shoreline based on degree of soil development and other evidence the little valley lake cycle may be equivalent in age to marine oxygenisotope stage 6 the proposed lake history has climatic implications for the region first because the fluctuations of lake bonneville and lake lahontan during the last cycle of each were apparently out of phase there may have been significant local differences in the timing and character of late pleistocene climate changes in the great basin second although the bonneville and little valley lake cycles were broadly synchronous with maximum episodes of glaciation environmental conditions necessary to generate large lakes did not exist during early wisconsin time

phase transformations of ca3al2si3o12 grossular garnet to the depths of the earth s mantle transition zone abstract high pressure and high temperature phase transformations of ca 3 al 2 si 3 o 12 grossular garnet were examined at 19 26 gpa and 700 2000 k using kawai type multi anvil apparatus coupled with in situ x ray diffraction xrd recovered samples were analyzed by a combination of micro focused x ray diffraction xrd and transmission electron microscopy tem the results show that grossular garnet gradually transforms to an al rich casio 3 perovskite at 22 26 gpa and 1000 1400 k the transition boundary can be expressed as p gpa 0 0082 t k 33 05 when the garnet completely disappears we observed orthorhombic casio 3 perovskite with a grossular composition at 20 24 gpa and temperatures above 1500 k the cas phase with the composition caal 4 si 2 o 11 appears to accommodate excess al from the perovskite along with two distinct populations of al bearing casio 3 perovskites with al content of 3 7 and 10 0 wt al 2 o 3 respectively the pressure and temperature of these transitions correspond to the lowermost part of the transition zone and therefore it suggests that ca rich aluminosilicates could provide alternative candidates to explain multiple seismic reflections near the 660 km depth discontinuity

late glacial vegetation and climate at the manis mastodon site olympic peninsula washington abstract as the late wisconsin cordilleran ice sheet retreated sediment accumulated in shallow depressions at the manis mastodon archaeological site on the olympic peninsula near sequim washington pollen plant macrofossils and bones of mastodon caribou and bison occur within the lower 47 cm of these deposits the fossil pollen and seed assemblages indicate persistence for 1000 yr 11 000 12 000 yr b p of an herb and shrub dominated landscape at a time when forest species appear elsewhere in washington and in adjacent british columbia at present sequim is near the northern coastal limits of both cactaceae and ceratophyllum mean annual precipitation is 42 7 cm and summer temperatures average 15 16 c in july the absence of coniferous trees and the presence of cactus and ceratophyllum in late glacial sediments are explained by a regional climate that was drier and at least as warm as today these conditions persisted in the rain shadow of the olympic mountains until at least 11 000 yr b p

an experimental approach to the palynology of cave deposits surface sediment speleothems and bat guano from two adjacent topographically different cave sites in eastern spain have been studied palynologically to elucidate the potential of cave sediments for palaeoenvironmental reconstruction a cave opening with a large entrance and constant width presented far fewer problems of alteration in the pollen assemblages than a sac like cave opening with a constricted entrance pollen concentration is linked primarily to the amount of pollen input rather than to the result of post depositional alteration sampling should be undertaken away from parietal and rear areas and avoiding moisture zones lateral differences in the pollen spectra indicate that sampling should be on the basis of a multiple profile approach and selection of dry rather than wet sediments if these procedures are followed within cave sediments can realistically reflect not only local but also regional vegetation of the site copyright 2000 john wiley sons ltd

late wisconsin early holocene vegetation in the bonneville basin abstract woodrat middens from the northern bonneville basin allow a reconstruction of vegetation changes from 14 000 to 9000 yr ago cold montane steppe dominated by sagebrush covered much of the western bonneville basin prior to 13 000 yr ago from 13 000 10 800 yr ago the region was vegetated by limber pine woodlands in lower montane settings and a mosaic of limber pine and sagebrush steppe along basin flour margins these low elevation limber pine woodlands began to retreat upslope after about 11 000 yr ago due to increasingly drier climatic conditions and were replaced by relatively more xeric desert scrub dominated by sagebrush and shadscale the growth of limber pine at low elevations suggests that summer temperatures were as much as 6 c lower than at present this evidence is in apparent conflict with the currently accepted post provo lake bonneville chronology especially the magnitude of the postulated near dessication of lake bonneville from ca 13 000 12 200 yr ago

x ray microanalysis of high pressure high temperature phases synthesized from natural olivine in a diamond anvil cell the transformation products of natural mg0 83fe0 17 2sio4 olivine have been prepared at high pressures and high temperature in a laser heated diamond anvil cell dac the study of the quenched high pressure phases has been performed using analytical transmission electron microscopy the iron magnesium partition coefficient between perovskite pv and magnesiowustite mw defined as kmw pv fe mg mw fe mgpv was measured in samples synthesized at pressures from 25 to 75 gpa under various heating conditions in all cases iron goes preferentially into magnesiowustite it was observed however that the partition coefficient decreases strongly between 25 and 40 gpa at pressures higher than 40 gpa it is constant 3 5 within experimental error although there is a systematic increase in k as t decreases the effect of temperature is weak at high pressures from the values of the iron partition coefficient and previously existing thermodynamic values we obtain a consistent thermodynamic data set for the major constituents of the lower mantle the equilibrium compositions of mg fe 2sio4 spinel mg fe sio3 perovskite and mg fe o magnesiowustite phases have been measured and a new high pressure phase of composition mg fe si2o5 is shown to occur in very high temperature regions probably due to high temperature breakdown or non stoichiometry of mg fe sio3 perovskite

the stability of antigorite in the systems mgo sio2 h2o msh and mgo al2o3 sio2 h2o mash the effects of al3 substitution on high pressure stability the high pressure stability of antigorite in the systems msh and mash was investigated using two structurally and chemically well constrained natural samples careful sample selection and characterization ensured that the only significant difference between the samples was al content one sample being essentially al free and the other containing 3 06 2 wt al 2 o 3 in the system msh the reaction antigorite forsterite clinoenstatite water was bracketed under water saturated conditions between 630 and 650 c at 1 6 gpa between 620 and 660 c at 2 5 gpa between 620 and 660 c at 3 9 gpa and between 4 5 and 5 0 gpa at 520 c in the system mash the reaction antigorite forsterite clinoenstatite chlorite water was bracketed under water saturated conditions between 660 and 700 c at 2 0 gpa between 660 and 680 c at 2 9 gpa and between 5 0 and 5 5 gpa at 600 c at pressures above 5 8 gpa intersection of this reaction with the reaction chlorite clinoenstatite pyrope forsterite water leads to an additional reaction whereby the al component of the antigorite is transferred to pyrope upon antigorite breakdown the addition of a few weight percent al 2 o 3 into antigorite is shown to stabilize the antigorite structure to significantly higher temperatures and pressures possibly by minimizing structural misfit among the component octahedral and tetrahedral sheets this effect partially explains the considerable discrepancies noted between previous studies on the stability of antigorite at high pressure in addition antigorite breakdown in the system mash transfers a significant volume of water to chlorite bearing assemblages thereby greatly increasing the range of temperatures over which water is tied up in hydrous phases relative to the system msh

late quaternary vegetation and climate of the wind river range wyoming abstract sediments from rapid lake document glacial and vegetation history in the temple lake valley of the wind river range wyoming over the past 11 000 to 12 000 yr radiocarbon age determinations on basal detrital organic matter from rapid lake 11 770 710 yr b p and temple lake 11 400 630 yr b p bracket the age of the temple lake moraine suggesting that the moraine formed in the late pleistocene this terminal pleistocene readvance may be represented at lower elevations by the expansion of forest into intermontane basins 12 000 to 10 000 yr b p vegetation in the wind river range responded to changing environmental conditions at the end of the pleistocene following deglaciation alpine tundra in the temple lake valley was replaced by a pinus albicaulis parkland by about 11 300 14 c yr b p picea and abies established by 10 600 14c yr b p grew with pinus albicaulis in a mixed conifer forest at and up to 100 m above rapid lake for most of the holocene middle holocene summer temperatures were about 1 5 c warmer than today by about 5400 14 c yr b p pinus albicaulis and abies became less prominent at upper treeline because of decreased winter snowpack and higher maximum summer temperatures the position of the modern treeline was established by 3000 14 c yr b p when picea retreated downslope in response to neoglacial cooling

caves as sources of biotic remains in arid western north america caves have been a valuable source of paleoenvironmental information since the eighteenth century in arid portions of western north america caves have replaced small lakes as the primary source of biotic remains of quaternary age packrat middens dung of extinct animals pollen and archeological artifacts are excellently preserved aridity of the sediment which is influenced by the cave s topographic position internal morphology and the regional climate is the primary cause of good preservation for stratigraphic pollen analysis the best sites are those without internal moisture sources and without extensive bioturbation pollen samples should be taken near the center of the chamber where eolian deposition is most rapid pollen concentrations in cave sediment are lower 2000 355 000 grains g 1 than in lake sediment and pollen percentages in cave sediment differ from those in packrat middens due to additional transport mechanisms on plant tissue and on the packrats themselves for middens pollen diagrams for bechan cave utah and organ pipe cactus national monument arizona are presented as examples of cave sediment and packrat midden analysis

fossil packrat middens and the tandem accelerator mass spectrometer analyses of well preserved plant remains from ancient packrat neotoma middens have yielded much information on the history of vegetation fauna and climate from the more arid portions of north america over the past 40 000 years1 2 in most of the modern deserts woodland or forest communities were present during the last glacial age the wisconsin radiocarbon dating of packrat midden assemblages from a single cave or from several nearby sites in a homogeneous local area can yield a detailed local vegetation chronology for many thousands of years from within 30 50 m on the rocky slopes in front of the dry rock shelters3 4 the development of radiocarbon dating using the tandem accelerator mass spectrometer tams allows direct dating of very small samples here we present 20 examples of tams radiocarbon dates on packrat midden materials to illustrate their usefulness in testing anomalous mixtures of species in ice age communities understanding the details of plant migrations and refining wisconsin and holocene time boundaries based on range changes of important plant species table 1 fig 1

petrogenetic grids for metacarbonate rocks pressure temperature phase diagram projection for mixed volatile systems isothermal or isobaric phase diagram sections as a function of fluid composition x f are widely used for interpreting the genetic history of metacarbonate rocks this approach has the disadvantages that 1 the influence of a key metamorphic variable either pressure p or temperature t is obscured 2 the diagrams are inappropriate for systems that are not fluid saturated these problems are avoided by constructing phase diagram projections in which the volatile composition of the system is projected onto a p t coordinate frame i e a petrogenetic grid the univariant curves of such p t projections trace the conditions of the invariant points of isothermal or isobaric phase diagram sections thereby defining the absolute stability of high variance mineral assemblages with and without a coexistent fluid phase petrogenetic grids for metacarbonate rocks are most useful for the study of regional metamorphism and for systems in which fluid composition has not been externally controlled a calculated example of a p t projection for the system cao mgo sio2 h2o co2 suggests that many assemblages e g calcite tale enstatite fluid magnesite tremolite antigorite diopside dolomite and calcite forsterite tremolite in mixed volatile systems have stability fields that make them useful as p t indicators consideration of the principles governing projection topology demonstrates that the univariant curves around a fluid present invariant point cannot be oriented independently with respect to the direction of compositional variation in the fluid phase this has the interesting predictive implication that if the direction of compositional variation along one univariant curve around an invariant point is known then the direction of compositional variation along the remaining curves can be determined solely from topologic constraints the same constraints can be applied to systems containing simple mineral solutions or melts in order to predict compositional variations

rapid climatic change in coastal southern california inferred from pollen analysis of san joaquin marsh pollen analysis and five radiocarbon dates of a 687 cm core provide a detailed chronology of environmental change in a marsh at the head of newport bay orange county california sediment deposition kept pace with sea level rise during the early history of the marsh from ca 7000 to 4500 yr b p the site was a freshwater marsh trees were more abundant than today and grassland was the regional vegetation as sea level rose salt marsh gradually invaded the site brief periods of freshwater marsh 3800 2800 2300 and after 560 yr b p correlate with episodes of global cooling during the neoglacial the historic period is marked by the appearance of exotic species particularly erodium cf cicutarium and eucalyptus and the spores of fungi sporormiella and thecaphora peak influx of pollen spores and charcoal probably reflect greater frequency of flooding and erosion ca 5000 yr b p and during the last 1000 yr

focused ion beam technique and transmission electron microscope studies of microdiamonds from the saxonian erzgebirge germany a focused ion beam of ga ions is a relatively new technique that has been developed for microelectronic industries now researchers of the earth sciences find it to be a promising tool for studying various geological materials using the fib technique and an fei strata db 235 dual beam system we have successfully prepared several electrontransparent foils which crossed wm sized diamonds included in host minerals such as zircon and garnet from quartzofeldspathic rocks of the saxonian erzgebirge germany scanning and transmission electron microscopy applied to these foils revealed that the diamonds contain crystalline nanometric inclusions these inclusions consist of minerals of known stoichiometries such as sio2 and al2sio5 whereas others are characterized by different combinations of si k p ti and fe in the presence of oxygen stoichiometries are not clear at this stage of research one suite of inclusions is assumed to be represented by archerite kh2po4 which is known to be stable at pressures of 4 22 gpa and one nanocrystal containing pb oxygen and carbon is interpreted to be pbxoy or pbco3 along with solid crystalline inclusions the diamonds contain cavities filled by liquid gas that escaped during sample preparation these are associated with dislocations of diamond growth our data are consistent with the concept of diamond crystallization from a coh rich multicomponent supercritical fluid and suggest that the composition of such a fluid is more consistent with a local crustal source rather than that of a mantle origin 2003 elsevier science b v all rights reserved

late quaternary vegetation and climatic history of the long valley area west central idaho u s a abstract paleoenvironmental data including pollen and sediment analyses radiocarbon ages and tephra identifications of a core recovered from a fen provide a ca 16 500 14c yr b p record of late quaternary vegetation and climate change in the long valley area of west central idaho the fen was deglaciated prior to ca 16 500 14c yr b p after which the pollen rain was dominated by artemisia suggesting that a cold dry climate prevailed until ca 12 200 14c yr b p from ca 12 200 to 9750 14c yr b p temperatures gradually increased and a cool moist climate similar to the present prevailed during this period a closed spruce pine forest surrounded the fen this cool moist climate was briefly interrupted by a dry and or cold interval between ca 10 800 and 10 400 14c yr b p that may be related to the younger dryas climatic oscillation from ca 9750 to 3200 14c yr b p the regional climate was significantly warmer and drier than at present and an open pine forest dominated the area around the fen maximum aridity occurred after the deposition of the mazama tephra ca 6730 14c yr b p after 3200 14c yr b p regional cooling brought cool moist conditions to the area the establishment of the modern montane forest around the fen and present day cool and moist climate began at ca 2000 14c yr b p

mgsio3 phase boundaries measured in the laser heated diamond cell abstract new data on phase equilibria in the mgsio3 system relevant to the stability of mg si perovskite perovskite are obtained in the laser heated diamond cell using improved techniques for accurate pressure measurement and novel heating techniques eliminating temperature gradients the data of the mgsio3 ilmenite akimotoite perovskite phase boundary measured in the range of 19 25 5 gpa and 1800 2350 k are consistent with the pressure and temperature conditions generally assumed at 660 km depth and agree within the experimental uncertainties with earlier multi anvil quench experiments the triple point wadsleyite stishovite akimotoite perovskite is at 21 gpa and 2300 k the slope of the akimotoite perovskite boundary is not well constrained by reversal experiments alone due to large hysteresis but results using glass starting materials yield a value of 0 004 0 002 gpa k the slopes of the phase transitions to mg si perovskite in both olivine and pyroxene systems are less negative than those required to cause layering in mantle convection at the pressure of the 660 km seismic discontinuity 23 8 gpa the phase boundary between akimotoite and perovskite yields a slightly lower temperature than that of the ringwoodite to perovskite periclase transition in the mg2sio4 system 1900 100 k garnet majorite is not observed above 21 gpa

the age of glacier peak tephra in west central montana at sheep mountain bog near missoula montana a late glacial tephra that probably fell in late summer is preserved as an 8 mm thick graded bed overlain by another 8 mm of redeposited ash mixed with lake deposits sediment surrounding the ash was 14c dated to about 11 200 yr b p electron microprobe analyses of the volcanic glass and hornblende phenocrysts from this ash layer indicate that they are similar in major element chemistry to those of glacier peak layer g previously considered to be about 12 000 yr old or older

pluvial climatic episodes in north america and north africa types and correlation with global climate abstract differences in late quaternary pluvial chronologies among the world s deserts can be related to fundamental differences in the climatology of those pluvial episodes paleoenvironmental records and climate model simulations for two northern hemisphere desert regions are used to illustrate two types of pluvial climatic regime in the higher latitude deserts of the american southwest pluvial conditions during the last glacial maximum were caused by the southward displacement of the westerly jet stream in turn caused by the blocking effect of laurentide ice sheet and a steepened arctic equator pressure gradient winter seasonality of precipitation and substantially lower mean annual temperatures are reflected in the paleoenvironmental record and simulated by models of 18 000 yr b p climate a second pluvial climate type which strongly influences the lower latitude deserts of north africa is characterized by enhanced summer monsoons and occurs during interglacials and perhaps interstadials the primary forcing mechanism of the last pluvial episode in the sahara and libyan deserts appears to have been increased solar radiation milankovitch forcing causing thermally enhanced ocean land pressure gradients and increased flow of maritime tropical air into the interior of the continent poleward displacement of the summer monsoon is consistent with floristic evidence for summer seasonality of precipitation and replicated by model simulations of 9000 and 6000 yr b p climate chronologies from some deserts such as the southern portion of the american southwest suggest the consecutive occurrence of both types of pluvial climatic regime pluvial conditions during the last glacial maximum were brought about by the equatorward displacement of the prevailing westerlies a subsequent more subdued pluvial period occurred later between 12 500 and 8000 yr b p caused by the poleward displacement of summer monsoons characterization of the climatology of pluvial episodes generates explanations for their temporal distribution and therefore this approach may be useful in assessing the quaternary chronology of pluvial episodes in other desert regions

late quaternary environments in ruby valley nevada abstract palynological data from sediment cores from the ruby marshes provide a record of environmental and climatic changes over the last 40 000 yr the modern marsh waters are fresh but no deeper than 3 m a shallow saline lake occupied this basin during the middle wisconsin followed by fresh and perhaps deep waters by 18 000 to 15 000 yr b p no sediments were recovered for the period between 15 000 and 11 000 yr b p possibly due to lake desiccation by 10 800 yr b p a fresh water lake was again present and deeper than modern conditions lasted until 6800 yr b p the middle holocene was characterized by very shallow water and perhaps complete desiccation the marsh system deepened after 4700 yr b p and fresh water conditions persisted until modern times vegetation changes in ruby valley were more gradual than those seen in the paleolimno logical record sagebrush steppe was more widespread than at present through the late pleistocene and early holocene giving way somewhat to expanded shadscale vegetation between 8500 and 6800 yr b p shadscale steppe contracted by 4000 yr b p but had greater than modern coverage until 1000 to 500 yr ago pinyon juniper woodland was established in the southern ruby mountains by 4700 yr b p

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

stability of holocene climate regimes in the yellowstone region abstract a 12 500 yr pollen record from loon lake wyoming provides information on the climate history of the southwestern margin of yellowstone national park the environmental reconstruction was used to evaluate hypotheses that address spatial variations in the holocene climate of mountainous regions loon lake lies within the summer dry winter wet climate regime an increase in xerophytic pollen taxa suggests drier than present conditions between ca 9500 and 5500 14 c yr b p this response is consistent with the hypothesis that increased summer radiation and the expansion of the east pacific subtropical high pressure system in the early holocene intensified summer drought at locations within the summer dry winter wet regime this climate history contrasts with that of nearby sites in the summer wet winter dry region which were under the influence of stronger summer monsoonal circulation in the early holocene the loon lake record implies that the location of contrasting climate regimes did not change in the yellowstone region during the holocene the amplitude of the regimes however was determined by the intensity of circulation features and these varied with temporal changes in the seasonal distribution of solar radiation

level of lake lahontan during deposition of the trego hot springs tephra about 23 400 years ago abstract the trego hot springs tephra bed is a silicic tephra about 23 400 yr old found at several localities in pluvial lake sediments in northern nevada southern oregon and northeastern california it has been characterized petrographically by the major and minor element chemistry of its glass and by its stratigraphic position with respect to other tephra layers at a newly described locality on squaw creek northwest of gerlach nevada at the north end of the smoke creek desert trego hot springs tephra has been found in sediments of the sehoo and indian lakes formations the depositional environments of these sediments show that when the tephra fell pluvial lake lahontan stood between 1256 and 1260 m and that immediately thereafter the lake rose to at least 1275 m these data corroborate earlier findings by benson quaternary research 9 300 318 from radiometric dating of calcareous tufa however the lake lahontan area has been affected by isostatic subsidence and rebound in response to changing water loads so that caution is required in the use of lakeshore elevations in correlation

antigorite high pressure stability in the system mgosio2h2o msh abstract the breakdown reactions of antigorite 1 forming talc forsterite water at low pressures and 2 forming forsterite clinoenstatite water at high pressures were determined in reversed equilibrium experiments results on reaction 1 were found to be in good agreement with former experimental determinations by both johannes johannes w 1975 zur synthese und thermischen stabilitat von antigorit fortschr mineral beih 53 36 and evans et al evans b w johannes w oterdoom h trommsdorff v 1976 stability of crysotile and antigorite in the serpentinite multisystem schweiz mineral petrogr mitt 56 79 93 from our experiments the invariant point i1 interconnecting the two reactions can be located at about 15 kbar 650 c this is consistent with the thermodynamic calculations using the dataset of berman berman r g 1988 internally consistent thermodynamic data for minerals in the system j petrol 29 445 522 however it is in contrast to recent experimental studies of ulmer and trommsdorff ulmer p trommsdorff v 1995a serpentine stability to mantle depths and subduction related magmatism science 268 858 861 who determined i1 at 21 kbar 730 c our pt conditions for i1 could be confirmed by equilibrium experiments on reaction 10 talc forsterite clinoenstatite water which is generated at i1 as well up to about 25 kbar the breakdown reaction 2 is nearly pressure independent towards still higher pressures the dp dt slope of reaction 2 bends and becomes negative schreinemakers analysis as well as thermodynamic calculations of the upper pressure stability of antigorite show that the possible antigorite breakdown reaction 3 antigorite clinoenstatite brucite water and reaction 4 brucite clinoenstatite forsterite water could originate at a new invariant point i2 provided that the reactions 2 and 11 brucite antigorite forsterite water intersect bracketing equilibrium 4 and combining these results with those on reaction 2 i2 was located at only about 51 kbar 490 c compared to 77 kbar 680 c according to berman s data however when taking into account the dense hydrous magnesium silicate dhms phase a mg7si2o8 oh 6 the phase relations of antigorite are changed resulting i in the metastability of i2 and reaction 3 and ii in a new invariant point i7 at about 44 kbar and 580 c generating the new antigorite breakdown reaction 16 antigorite phase a clinoenstatite water on the basis of these new data on the stability of antigorite earlier conclusions about dehydration depths in subducted serpentine bearing oceanic lithosphere have to be reconsidered the maximum pressure stability of antigorite according to reaction 16 extends between 44 and 55 kbar that is between about 130 and 160 km depths as opposed to about 75 kbar 220 km following ulmer and trommsdorff see above because many different thermal regimes are possible in subduction zones no specific dehydration depth can be expected but rather more continuous dehydration fronts in space and time

vegetation reconstruction on the basis of pollen in late pleistocene hyena coprolites from san teodoro cave sicily italy vegetation reconstruction based on pollen from coprolites of extinct spotted hyena crocuta crocuta spelaea goldfuss 1832 recovered from excavations carried out in 1998 at san teodoro cave sicily italy supports previous indications of pre late glacial conditions eight of the twelve coprolites analysed contained well preserved pollen grains there is a general similarity between the pollen contents from the coprolites but they show variability they suggest a main vegetation type dominated by steppic taxa poaceae artemisia ephedra chenopodiaceae and asteraceae but also including arboreal taxa pinus and cupressaceae low percentages of pollen of mesophilous woody taxa quercus betula abies alnus pistacia among others are noticeable suggesting the existence of nearby refugia for temperate and mediterranean vegetation a reconstruction of the landscape using the coprolite pollen record and other pollen records from sicily and south italy shows the predominance during the pre late glacial of a wooded steppe biome with elements representing a variety of local environmental conditions

postglacial vegetation and climate in the northwestern great plains of montana abstract two pollen records from the northern great plains of montana portray vegetational and climatic changes during the last 12 200 yr in a region where few other data are available a 6 4 m core from guardipee lake east of the rocky mountains in the area formerly covered by the two medicine glacial lobe contains the glacier peak g and mt st helens jy volcanic ashes pollen percentage data are dominated by pinus poaceae artemisia and chenopodiaceae amaranthaceae high nonarboreal percentages and small amounts of juniperus alnus salix and populus pollen in sediments deposited between ca 12 200 and ca 9300 yr b p suggest a temperate grassland with shrubs growing locally in mesic settings after ca 9300 yr b p an increase in chenopodiaceae amaranthaceae pollen and a concomitant decline in artemisia indicate the development of more xerophytic grassland and the beginning of the altithermal period the lake probably was intermittently dry thoughout the holocene a high sedimentation rate and the presence of cereal taxa characterize the last ca 100 yr of euroamerican settlement lost lake at the northern margin of the highwood mountains yielded a 16 94 m core with no volcanic ashes that spans the last 9400 yr high amounts of chenopodiaceae amaranthaceae artemisia and poaceae pollen from ca 9400 to ca 6000 yr b p suggest the presence of xeric grassland and a climate drier than at present after ca 6000 yr b p chenopodiaceae amaranthaceae values declined and artemisia poaceae pinus picea salix alnus and betula increased the inferred spread of shrubs in wet habitats at this time and the expansion of forest in nearby mountain ranges indicate the end of the altithermal period and the onset of cooler moister conditions

vegetation responses to quaternary volcanic and hydrothermal disturbances in the northern rocky mountains and greater yellowstone ecosystem usa abstract volcanic and hydrothermal processes produce disturbances by diverse mechanisms and ecological responses are varied new and published pollen records from the northern rocky mountains and greater yellowstone ecosystem document the response of vegetation to three different types of volcanic and hydrothermal disturbances 1 pleistocene rhyolite lava flows in the central greater yellowstone ecosystem created infertile landscapes that have shaped vegetation since rhyolite emplacement nutrient poor well drained soils that developed on these flows supported low diversity grassland during late glacial time and pinus contorta forests in interglacial periods 2 ash layers from eruptions of pacific northwest stratovolcanoes are commonly preserved in lake sediment records in the northern rocky mountains and associated pollen records show enhancement of steppe vegetation for years to decades 3 local hydrothermal explosions have resulted in vegetation changes in hydrothermal areas that indicate tree mortality following deposition of explosion debris followed by recovery in years thus the type and duration of the vegetation response to volcanic and hydrothermal disturbances are highly contextual and governed by the antecedent plant communities and the magnitude and mechanism of the volcanic or hydrothermal disturbance vegetation resilience varied between disturbances ranging from enduring ecosystem parameter changes to short lived state changes in resilient plant communities

pressure temperature estimates of the lizardite antigorite transition in high pressure serpentinites serpentine minerals in natural samples are dominated by lizardite and antigorite in spite of numerous petrological experiments the stability fields of these species remain poorly constrained this paper presents the petrological observations and the raman spectroscopy and xrd analyses of natural serpentinites from the alpine paleo accretionary wedge serpentine varieties are identified from a range of metamorphic pressure and temperature conditions from sub greenschist p 20 kbar t 460 c along a subduction geothermal gradient we used the observed mineral assemblage in natural serpentinite along with the tmax estimated by raman spectroscopy of the carbonaceous matter of the associated metasediments to constrain the temperature of the lizardite to antigorite transition at high pressures we show that below 300 c lizardite and locally chrysotile are the dominant species in the mesh texture between 320 and 390 c lizardite is progressively replaced by antigorite at the grain boundaries through dissolution precipitation processes in the presence of sio2 enriched fluids and through a solid state transition in the cores of the lizardite mesh above 390 c under high grade blueschist to eclogite facies conditions antigorite is the sole stable serpentine mineral until the onset of secondary olivine crystallization at 460 c

a record of lateglacial holocene environmental change from a high elevation site in the intermountain west usa records of past vegetation and fire history can be complicated by changes in the depositional environment of a sampling location however these changes can alternatively be used as a measure of climate variability our study site ca 18 0 cal ka bp record from little brooklyn lake wyoming located near the crest of the snowy range records three moisture states initially the lake was likely a glacier fed pond indicated by the presence of pediastrum algae colonies around 13 0 cal ka bp this pond transitioned to a meadow environment suggested by the loss of pediastrum algae colonies and slow sedimentation rates meadow conditions were maintained until ca 5 0 cal ka bp when pediastrum algae colony abundance increased indicating the formation of a shallow lake from 18 0 to ca 5 0 cal ka bp the pollen record is suggestive of alpine vegetation conditions with relatively high spruce and herbaceous taxa low charcoal influx also characterizes the period between 18 0 and 5 0 cal ka bp after 5 0 cal ka bp the coincidence of the formation of shallow lake and pollen data indicating a shift to a spruce and fir forest suggests an increase in effective moisture fire remained rare in this basin over the entire record however once the lake established sedimentation rates and charcoal influx increased copyright 2013 john wiley sons ltd

contrasting climatic histories for the snake river plain idaho resulting from multiple thermal maxima abstract ten sites near the snake river plain have consistent differences in their climatic histories sites at low elevation reflect the early holocene xerothermic of the pacific northwest whereas most climatic chronologies at high elevation indicate maximum warmth or aridity somewhat later ca 6000 yr ago this elevational contrast in climatic histories is duplicated at three sites from the central snake river plain for sites in such close proximity the different chronologies cannot be explained by changes in atmospheric circulation during the late quaternary rather the differences are best explained by the autecology of the plants involved and the changing seasonal climate the seasonal climatic sequence predicted by multiple thermal maxima explains the high and low elevation chronologies during the early holocene maximum insolation and intensified summer drought in july forced low elevation vegetation upward however moisture was not a limiting factor at high elevation where vegetation moved upward in response to increased length of growing season coincident with maximum september insolation 6000 yr ago

a revised chronology for the last pleistocene lake cycle in the central lahontan basin radiocarbon dates of plant materials from packrat middens in caves below the elevation of the last high stand of pleistocene lake lahontan in conjunction with radiocarbon dates of ancient archaeological materials provide evidence that the last high stand terminated before 12 070 yr b p this new information suggests that the last major fluctuation in the level of lake lahontan was approximately synchronous with those of lakes bonneville and russell and that these three lakes probably responded contemporaneously to the same regional paleoclimatic changes

great salt lake and precursors utah the last 30 000 years sediment cores up to 6 5 m in length from the south arm of great salt lake utah have been correlated radiocarbon ages and volcanic tephra layers indicate a record of greater than 30 000 years a variety of approaches have been employed to collect data used in stratigraphic correlation and lake elevation interpretation these include acoustic stratigraphy sedimentologic analyses mineralogy geochemistry major element c o and s isotopes and organics paleontology and pollen the results indicate that prior to 32 000 year b p an ephemeral saline lake playa system was present in the basin the perennial lake which has occupied the basin since this time rose in a series of three major steps the freshest water conditions and presumably highest altitude was reached at about 17 000 year b p the lake remained fresh for a brief period followed by a rapid increase in salinity and sharp lowering in elevation to levels below that of the present great salt lake the lake remained at low elevations and divided at times into a north and south basin until about 8 000 year b p since that time with the exception of two short rises to about 1290 m the lake level has remained near the present elevation of 1280 m

an assessment of the contribution of fossil cave deposits to the quaternary paleontological record mammal bearing cave deposits are an important part of the quaternary fossil record but the exact nature of the contribution that caves make to the fossil record is a research area that is largely unexplored to explore this issue late pleistocene species representation in cave versuses non cave deposits was examined additionally this study examined how fossiliferous cave deposits influence perceptions of past biogeographic distributions and evaluated factors that impact the distribution of cave deposits across the united states cave deposits account for a high proportion of the individual species records known from the late pleistocene and caves provide the only late pleistocene records of 14 individual taxa calculated ratios of individual taxonomic records from caves relative to the total number of individual taxonomic records resulted in a value of 0 62 the impact of cave data on understanding of late pleistocene biogeographic distribution patterns vary among individual species of sciurid rodents geographic analyses comparing the distribution of cave and non cave sites in texas suggest a strong relationship between site distribution and specific geologic and hydrologic features ultimately understanding potential biases recorded in distinct depositional settings provides improved frameworks for interpreting the adequacy of the fossil record

paleoclimatic significance of lake level fluctuations in the lahontan basin abstract an energy flux balance model has been developed which treats evaporation as a function of air temperature surface water temperature precipitable water aloft the amount height and type of sky cover and the optical air mass the model has been used to estimate the mean historical evaporation rate for pyramid lake nevada using as input climatic data from the reno area averaged over the period 1950 1975 estimated and measured values of the mean annual evaporation rate were found to be in good agreement the model was used to simulate changes in the level the surface area and the volume of paleo lake lahontan in particular possible climatic states responsible for past high stands 1270 and 1330 m were investigated a conservative range of discharge values was used in the calculations results of the simulations indicate the fundamental importance of sky cover in the creation and destruction of large lake systems

spatial variations of holocene climatic change in the yellowstone region abstract the paleoecologic record of the northern rocky mountains shows considerable spatial variability which has been difficult to explain as a unified response to large scale changes in effective moisture or temperature through time comparison of past and present climatic patterns suggests that the spatial heterogeneity in the fossil record arises from a local response to the effects of greater summer solar radiation during the early holocene solar radiation directly determines evapotranspiration and indirectly controls the strength of the summer monsoon and the eastern pacific subtropical high pressure system the yellowstone region provides an example of an area where the indirect effects of solar radiation are manifest by the juxtaposition of two contrasting climatic regimes today and where these regimes were amplified during the early holocene fossil pollen data suggest that central and southern yellowstone the summer dry area became drier in the early holocene while northern yellowstone the summer wet area became wetter the boundary between regimes however is controlled by topography and has not changed significantly in the holocene the spatial variations of holocene vegetation and climatic changes in the northern rocky mountains may therefore be explained as a trade off between strengthened monsoonal circulation and a stronger subtropical high in the early holocene and the relative importance of these precipitation regimes on a topographically complex landscape

spores of the dung fungus sporormiella increased abundance in historic sediments and before pleistocene megafaunal extinction abstract spores of the dung fungus sporormiella become abundant following the historic introduction of grazing herbivores at seven sites in the western united states during the holocene they are generally rare but at six sites sporormiella spores are abundant before the extinction of pleistocene megaherbivores ca 11 000 yr b p sporormiella spores are directly linked to extinct megaherbivores by their presence in mammoth dung preserved in bechan cave southern utah their abundance in late glacial sediments may reflect the abundance of megaherbivores during quaternary thereby indicating the age of pleistocene extinctions where other indicators are absent

evaporite evidence of a mid holocene c 4550 4400 cal yr bp aridity crisis in southwestern europe and palaeoenvironmental consequences sedimentological evidence for an abrupt dry spell in south eastern spain during the middle holocene from c 4906 to 4384 cal yr bp is presented this phase was determined primarily from halite beds deposited between muddy slimes in a lagoon system of puerto de mazarron murcia province with a peak phase from c 4550 to 4400 cal yr bp a multi core multi proxy study of 20 geotechnical drills was made in the lagoon basin to identify the main sedimentary episodes and depositional environments the results suggest that this halite bed more than 80 cm thick was conditioned by climate change and was accompanied by a generalized drying out of the basin halite precipitation was linked with palaeoecological changes including forest and mesophyte depletions and increasing cover and diversity of xerophytic plant species archaeological evidence indicates a demise of the population at this period probably due to resource exhaustion an overall picture of the biostratigraphy and palaeoclimates of the region is given in a broader geographical context

evidence from north west canada for an early holocene milankovitch thermal maximum according to the milankovitch theory of global climatic change maximum summer solar radiation at high latitudes of the northern hemisphere occurred at 10 000 yr bp refs 1 2 in particular it predicts summer solstice radiation greater by 9 10 preliminary climate simulation experiments with these increased values of radiation confirm that high latitude land surfaces received maximal insolation at 10 000 yr refs 3 4 paradoxically however the large volume of fossil pollen and other evidence from north america indicates a maximum of holocene warmth at 7 000 6 000 yr ref 5 and a recent review of the evidence from new england suggests that the warming began at 9 000 and ended at 5 000 yr but also stresses the difficulties of interpretation in terms of climate change6 we summarize here data from sites in the north west corner of mainland canada fig 1 that directly support the milankovitch hypothesis

the fate of b cl and li in the subducted oceanic mantle and in the antigorite breakdown fluids we present an inventory of b cl and li concentrations in a key minerals from a set of ultramafic samples featuring the main evolutionary stages encountered by the subducted oceanic mantle and in b fluid inclusions produced during high pressure breakdown of antigorite serpentinite samples correspond to i nonsubducted serpentinites northern apennine and alpine ophiolites ii high pressure olivine bearing antigorite serpentinites western alps and betic cordillera iii high pressure olivine orthopyroxene rocks recording the subduction breakdown of antigorite serpentinites betic cordillera two main dehydration episodes are recorded by the sample suite partial serpentinite dewatering during formation of metamorphic olivine followed by full breakdown of antigorite serpentine to olivine orthopyroxene fluid ion probe and laser ablation icp ms la icp ms analyses of cl b and li in the rock forming minerals indicate that the hydrous mantle is an important carrier of light elements the estimated bulk rock b and cl concentrations progressively decrease from oceanic serpentinites 46 7 ppm b and 729 ppm cl to antigorite serpentinites 20 ppm b and 221 ppm cl to olivine orthopyroxene rocks 9 4 ppm b and 45 ppm cl this suggests release of oceanic cl and b in subduction fluids apparently without inputs from external sources lithium is less abundant in oceanic serpentinites 1 3 ppm and the initial concentrations are still preserved in high pressure antigorite serpentinites higher li contents in olivine ti clinohumite of the olivine orthopyroxene rocks 4 9 ppm bulk rock li as well as in the coexisting fluid inclusions suggest that their budget may not be uniquely related to recycling of oceanic li but may require input from external sources laser ablation icp ms analyses of fluid inclusions in the olivine orthopyroxene rocks enabled an estimate of the li and b concentrations in the antigorite breakdown fluid the inclusion compositions were quantified using a range of salinity values 0 4 2 wt naclequiv as internal standards yielding maximum average fluid rockdb 5 and fluid rockdli 3 5 we also performed model calculations to estimate the b and cl loss during the two dehydration episodes of serpentinite subduction the first event is characterized by high fluid rock partition coefficients for cl 100 and b 60 and by formation of a fluid with salinity of 4 8 wt naclequiv the antigorite breakdown produces less saline fluids 0 4 2 wt naclequiv and is characterized by lower partition coefficients for cl 25 60 and b 12 30 our calculations indicate that the salinity of the subduction fluids decreases with increasing depths fluid rockdb fluid rockdcl 1 0 5 indicates that cl preferentially partitions into the evolved fluids relative to b and that the b cl of fluids progressively increases with increasing depths and temperatures despite light element release in fluids appreciable b cl and li are still retained in chlorite olivine and ti clinohumite beyond the antigorite stability field this permits a bulk storage of about 10 ppm b 45 ppm cl and 5 ppm li i e concentrations much higher than in mantle reservoirs chlorite is the cl repository and its stability controls the cl and h2o budget beyond the antigorite stability b and li are bound in olivine and clinohumite the subducted oceanic mantle thus retains light elements beyond the depths of arc magma sources potentially introducing anomalies in the upper mantle

correlation of late quaternary tephra layers in a long pluvial sequence near summer lake oregon abstract near summer lake in southern oregon 54 tephra beds of late quaternary age are exposed in pluvial lake sediments of lake chewaucan seven of the tephra beds near the top can be correlated with tephra deposits younger than 117 000 yr at mount st helens washington at crater lake oregon and in northwestern nevada in the deposits of pluvial lake lahontan however most of the section at summer lake lies below the correlated units and contains 39 tephra beds older than 117 000 yr major element chemistry of tephra glasses was determined by electron microprobe analysis petrography supports the correlations made from chemical evidence compositions correlated range from 70 to 76 sio 2 the least silicic summer lake glass contained 57 extrapolation of depositional rate suggests that most of the sediments at summer lake are younger than about 335 000 yr but older lake beds containing tephra layers occur at one place the long lacustrine record suggests that lake chewaucan persisted through the last interpluvial stage and that the lake may have dried up at the end of the pleistocene due to diversion of the chewaucan river by relict shore features

using fire regimes to delineate zones in a high resolution lake sediment record from the western united states article i nfo article history received 20 february 2012 available online 10 november 2012 paleoenvironmental reconstructions are important for understanding the influence of long term climate variabil ity on ecosystems and landscape disturbance dynamics in this paper we explore the linkages among past climate vegetation and fire regimes using a high resolution pollen and charcoal reconstruction from morris pond located on the markagunt plateau in southwestern utah usa a regime shift detection algorithm was applied to back ground charcoal accumulation to define where statistically significant shifts in fire regimes occurred the early holocene was characterized by greater amounts of summer precipitation and less winter precipitation than mod ern ampleforest fuel and warm summer temperatures allowed for large firestooccur themiddleholocenewasa transitional period between vegetation conditions and fire disturbance the late holocene climate is characterized as cool and wet reflecting an increase in snow cover which reduced opportunities for fire despite increased avail ability of fuels similarities between modern forest fuel availability and those of the early holocene suggest that warmer summers projected for the 21st century may yield substantial increases in the recurrence and ecological impacts of fire when compared to the fire regime of the last millennium

a record of late quaternary vegetation from davis lake southern puget lowland washington abstract pollen and macrofossil analyses of a core spanning 26 000 yr from davis lake reveal late pleistocene and holocene vegetational patterns in the puget lowland the core ranges lithologically from a basal inorganic clay to a detritus gyttja to an upper fibrous peat and includes eight tephra units the late pleistocene pollen sequence records two intervals of tundra parkland vegetation the earlier of these has high percentages of picea gramineae and artemisia pollen and represents the vegetation during the evans creek stade fraser glaciation ca 25 000 17 000 yr b p the later parkland interval is dominated by picea tsuga mertensiana and gramineae it corresponds to the maximum ice advance in the puget lowland during the vashon stade fraser glaciation ca 14 000 yr b p an increase in pinus ontorta pollen between the two tundra parkland intervals suggests a temporary rise in treeline during an unnamed interstade after 13 500 yr b p a mixed woodland of subalpine and lowland conifers grew at davis lake during a period of rapid climatic amelioration in the early holocene the prolonged expansion of pseudotsuga and alnus woodland suggests dry temperate conditions similar to those of present rainshadow sites in the puget lowland more mesic forests of tsuga eterophylla thuja plicata and pseudotsuga similar to present lowland vegetation appeared in the late holocene ca 5500 yr b p

multiple thermal maxima during the holocene the astronomical theory of climatic change provides an alternative to the traditional chronology for holocene climatic change which calls for one thermal maximum about 6000 years ago the theory predicts a series of maxima during the holocene one for each season because the relation of the perihelion to the spring equinox changes with a 22 000 year period late summer insolation would have been greatest 5000 years ago whereas early summer insolation would have been greatest 13 000 years ago climatic reconstructions based on the response of ecosystems to late summer climate indicate a later holocene thermal maximum than paleoclimatic data sensitive to early summer climate in southern idaho three different vegetation types indicate thermal maxima at different times during the holocene depending on the climatic variable controlling each type

stratigraphic evidence of quaternary climatic change at echo cave transvaal and a paleoclimatic record for botswana and northeastern south africa summary changes in climate at echo cave during the last 35 000 years caused ground water levels to fluctuate by 29 m there was little speleothem deposition during dry climatic phases because of a lack of moisture and only localized deposition during very wet phases when water levels rose and most cave passages were flooded the most massive speleothems were laid down in transitional periods between very wet and dry conditions when water levels were low enough for many passages to be air filled and the climate wet enough for rapid deposition of travertine data from echo cave and from other sites in botswana and northeastern south africa suggest that there were three cooler and wetter phases during the holocene at 9 700 7 600 4 300 2 200 and 1 700 400 yr b p that the late glacial climate 12 000 10 000 yr b p was warm and dry and that the climate during the upper pleniglacial 18 000 13 000 yr b p and middle pleniglacial 38 000 30 000 yr b p was cooler and wetter than today but warmer and drier than the first 12 000 years 30 000 18 000 yr b p of the upper pleniglacial

formation of linear and parabolic dunes on the eastern snake river plain idaho in the nineteenth century abstract geomorphic and stratigraphic evidence show periods of distinct hydrologic excess and deficit sometime in the past 500 years on the eastern snake river plain natural exposures at the current shore of mud lake contain a lacustrine silty sand beneath eolian sands the latter deposit is expressed at the surface as hairpin parabolic and linear dunes these dunes can be traced into and across lakes a clear sign of recent aridity two shallow water gastropods and two wood fragments from the lacustrine silty sand yield the respective ams 14 c ages of ca 705 and 988 year bp and 195 and 305 year bp the offset in ages indicates a lake hard water effect of aquatic gastropods with the wood ages providing the closest age constraint optically stimulated luminescence single aliquot regeneration ages of 150 30 and 120 20 year bp on quartz grains from the overlying eolian sands further constrains a drop in lake level and subsequent aridity to the 19th century this lacustrine dune sequence is probably the geomorphic expression of a distinct wet period followed by a severe drought between ad 1845 and 1856 which has been documented in the dendroclimatic records for the rocky mountains and the western great plains lake fluctuations and dune formation is associated with greater subdecadal variability in spring precipitation than recorded in the past 100 years

speleothems travertines and paleoclimates abstract age data for about 660 speleothems and about 140 spring deposited travertines were collected including many unpublished results these data were plotted as histograms and also as error weighted frequency curves on a 350 000 yr scale these plots clearly show periods of increased speleothem travertine growth as well as times of cessation the periods of most frequent speleothem growth were between approximately 130 000 and 90 000 yr ago and since about 15 000 yr ago such periods before 150 000 yr ago however cannot be yet recognized because of a lack of sufficient data and the associated uncertainties of dates in this age range a comparison with the oxygen isotope record of deep sea core v28 238 shows a clear relationship indicating that terrestrial calcite formation is controlled by paleoclimatic fluctuations the evident climatic stimulation of quaternary calcite formation is readily explained geochemically and is substantiated by the obvious difference in speleothem travertine growth as a function of geographic position

analytical transmission electron microscopy study of a natural morb sample assemblage transformed at high pressure and high temperature natural mid ocean ridge basalt morb samples recovered from diamond anvil cell dac experiments performed between 33 to 89 gpa and 1700 to 2600 k were studied with a transmission electron microscope tem we used the focused ion beam fib lift out technique to prepare the recovered high pressure laser heated samples for tem study observations of tem sections show the presence of five phases for samples transformed at pressures ranging from 33 to 45 gpa al bearing mg perovskite ca silicate perovskite stishovite and two al rich phases the al rich phases were identified by selected area electron diffraction saed patterns and chemical composition analysis and include the new aluminous nal phase with hexagonal structure and the calcium ferrite cf type phase chemical analyses obtained by analytical transmission electron microscopy atem show that mg silicate perovskite is the major host for al with significant amounts also distributed between the cf type and nal phases and less than 1 wt in stishovite beyond pressures of 40 gpa 1100 km depth the al content of mg perovskite and cf type phase increases between 45 and 50 gpa the nal phase disappears this mineralogical change may explain reported seismic anomalies in subduction zones at mid mantle depths

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