taphonomy of ground squirrel remains in a late pleistocene ichnofabric nebraska usa abstract the burrows and skeletal remains of late pleistocene ground squirrels are present within the citellus zone a bioturbated interval that includes the base of the gilman canyon formation and the top of the loveland formation of the central great plains usa to determine the spatial relationship of the ground squirrel remains to the citellus zone ichnofabric the author screen washed 0 67 tonne of sediment sampled from burrow fill and from adjacent sediment matrix at 104 outcrops in 10 major canyons in the study area within the upper pedogenically altered portion of the zone 14 of the remains are in burrow fill and 86 are in adjacent matrix all of the remains in the lower portion of the zone are in burrow fill all of the weathered remains are found in the pedogenically altered upper portion of the zone published behavioral observations of spermophilus richardsonii explain this phenomenon upon emergence from hibernation the animals eject skeletal remains from burrows the bones are left on the surface in the vicinity of burrow entrances to be incorporated into the soil morphometric analysis of their postcranial remains confirms the conclusion of an earlier study of cranial remains that the s richardsonii represented in the citellus zone were intermediate between two modern subspecies this relationship is consistent with phylogenetic conclusions of genetic studies

an experimental study of the kinetics of decompression induced crystallization in silicic melt 1 experiments were conducted to study the temporal evolution of feldspar crystallization kinetics during isothermal decompression pinatubo dacite was held at 780 c 220 mpa fo2 nno 2 h2o saturated conditions for an equilibration period decompressed to final pressures pf ranging from 175 to 5 mpa and then held for 0 3 931 hours according to the plagioclase liquidus curve in ph2o t space for the relevant melt composition these decompressions impose effective undercoolings teff of 34 266 c growth of preexisting phenocrysts and newly formed sparse microlites dominate crystallization at 75 pf 150 mpa teff 34 93 c and equilibrium crystal modes are achieved in 168 hours microlite nucleation is the dominant transformation process for 10 pf 50 mpa teff 125 241 c and chemical equilibrium is not attained by 168 hours under these conditions slow steady decompressions typically produced normally zoned euhedral and planar faceted feldspar crystals although anhedral morphologies were produced at very low pf contrary to expectation slowly decompressed samples were usually further from chemical equilibrium than rapidly decompressed samples after similar durations below the initial pressure although counterintuitive these trends are consistent with new constraints on the relative rates of feldspar nucleation and growth controlled by teff and melt viscosity experienced during each decompression path analysis of liquid to solid transformation kinetics using ttt style diagrams shows that crystallization occurs most rapidly at 100 mpa by a crystal growth mechanism the next most efficient crystallization conditions are at 25 mpa in a crystal nucleation dominated regime

compositional gradients surrounding spherulites in obsidian and their relationship to spherulite growth and lava cooling spherical masses of crystal fibers spherulites crystalize from rhyolitic melt glass mainly in response to significant undercooling while lava cools spherulite growth should induce compositional gradients in the surrounding glass from expulsion of incompatible constituents and diffusion of those constituents away from the spherulite finite difference numerical modeling of one dimensional diffusion in which diffusivities are allowed to vary with temperature is used to investigate how compositional gradients reflect spherulite growth and lava cooling overall three forms of gradients are identified elements that diffuse quickly are expelled from the spherulite but then migrate away too quickly to become enriched at the boundary of the spherulite elements that diffuse slowly are trapped within the growing spherulite between those endmembers are elements that are not trapped yet diffuse slow enough that they become enriched at the contact their slow diffusion away then elevates their concentrations in the surrounding glass how enriched those elements are at the spherulite matrix interface and how far their enrichments extend outwards into the glass reflect how spherulites grow and thermal conditions during growth concentrations of h2o rb f li cl na k sr cs ba and be were measured in and around spherulites in obsidian from a 4 7 1 km3 rhyolite lava dome erupted from tequila volcano mexico measurable concentration gradients are found for h2o rb and f attributes of those gradients and the behaviors of the other elements are in accord with their experimentally constrained diffusivities spherulites appear to have grown following radial rather than volumetric growth the observed gradients and lack of others are more consistent with growth mainly below the glass transition which would necessitate the dome cooling at ca 10 5 to 10 7 c s 1 such slow cooling is consistent with the relatively large volume of the dome

equilibrium oxygen hydrogen and carbon isotope fractionation factors applicable to geologic systems as demonstrated by the chapters in this short course stable isotope techniques are an important tool in almost every branch of the earth sciences central to many of these applications is a quantitative understanding of equilibrium isotope partitioning between substances indeed it was harold urey s 1947 thermodynamically based estimate of the temperature dependence of 18o 16o fractionation between calcium carbonate and water and a recognition of how this information might be used to determine the temperatures of ancient oceans that launched the science of stable isotope geochemistry the approach pioneered by urey has since been used to estimate temperatures for a wide range of geological processes e g emiliani 1955 anderson et al 1971 clayton 1986 valley this volume in addition to their geothermometric applications equilibrium fractionation data are also important in the study of fluid rock interactions including those associated with diagenetic hydrothermal and metamorphic processes baumgartner and valley this volume shanks this volume finally a knowledge of equilibrium fractionation is a necessary first step in evaluating isotopic disequilibrium a widespread phenomenon that is increasingly being used to study temporal relationships in geological systems cole and chakraborty this volume in the fifty four years since the publication of urey s paper equilibrium fractionation data have been reported for many minerals and fluids of geological interest these data were derived from 1 theoretical calculations following the methods developed by urey 1947 and bigeleisen and mayer 1947 2 direct laboratory experiments 3 semi empirical bond strength models and 4 measurement of fractionations in natural samples each of these methods has its advantages and disadvantages however the availability of a variety of methods for calibrating fractionation factors has led to a plethora of calibrations not all of which are in agreement in this chapter we evaluate the major methods for determining fractionation factors

timescales of texture development in a cooling lava dome abstract crystal growth and crack development in cooling lava domes are both capable of redistributing and mobilizing water cracking and hydration decrease the stability of a dome which may lead to hazards including partial dome collapse and block and ash flows by examining the distribution of water around crystals and cracks we identify and confine temperature and timescales of texture development in glassy rocks of volcanic domes four generations of textures have been identified type a spherulites type b cracks associated with spherulite growth type c perlitic cracks and type d disparate cracks high resolution imaging using fourier transform infrared spectroscopy ftir performed on samples from the ngongotaha dome new zealand show an increase in h2o of up to 450 along gradients of around 100 m up to 300 m in length from perlitic cracks spherulitic cracks and in haloes around spherulites no gradients in water concentrations across the disparate cracks are present water diffusion models show potential timescale temperature couples that coincide with textural observations and previous studies and allow us to develop a conceptual model of spherulite growth and cracking in a cooling lava dome spherulite growth starts around the glass transition temperature t g when the viscous melt cools to a brittle solid and proceeds with cracking related to volume changes at slightly lower temperatures and shorter timescales days to weeks compared to spherulite growth perlitic cracking happens at t t g allowing hydration of a permeable network within weeks to months low temperature 50 c cracks could not be hydrated in the time since eruption 230 ka our data show that textures in cooling glass develop during cooling below t g within days producing cracks and crystals that create inhomogeneities in the spatial distribution of water the lengthscales of water diffusion away from spherulites spherulite cracks and perlite cracks suggest that most of the rehydration of melt glass occurs at relatively high temperatures 400 c lack of evidence for water diffusion around other cracks suggests minor low temperature meteoric water rehydration following emplacement

taphonomy and paleoecological implications of fossorial microvertebrates at the middle paleolithic open air site of nesher ramla israel variation in taphonomic modes which describe the characteristics of fossil depositional environments is an important but much understudied aspect of the formation of microvertebrate assemblages this study examined an assemblage of microvertebrate remains which was recovered from archaeological deposits in a deep karst depression at an open air setting a unique and so far undocumented type of depositional environment in the southern levant taxonomic and taphonomic characteristics of the assemblage reveal a striking difference from other known assemblages in the region from cave and fluvial depositional settings this includes especially low density taxonomic diversity and skeletal element survivorship three of the four taxa are fossorial or semi fossorial and their remains dominate the assemblage indicating strongly an accumulation history which involves underground burrow deaths of fossorial animals this is supported by additional evidence from skeletal modifications showing rare evidence of weathering extensive in situ fragmentation where the fragments remain fused together and abundant evidence for light abrasion these taphonomic patterns suggest extended underground protection of the remains followed by limited dispersal within a sedimentary matrix likely due to movement from the surrounding soil mantle into the karst depression through colluviation processes this taphonomic reconstruction has significant implications for understanding the long record of hominid occupation at the middle paleolithic site of nesher ramla phases of high density of the remains along the section correspond with glacial phases of marine isotope stages mis 6 and 5a 4 indicating an association between enhanced fossorial activity and environmental conditions during glacial stages intense deposition of cultural remains was recorded only during mis 6 however and this leads us to suggest that continued low intensity hominid presence in the upper layers of the site is related either to change in the usefulness of the site for hominid subsistence activities as it was being filled with sediments or to demographic changes linked to the arrival of new populations during mis 5a 4 detailed paleoenvironmental sequences which are recovered directly from hominid sites are critical for testing such hypotheses

widespread submarine tephras around japan petrographic and chemical properties abstract in deep sea sediments around the japanese islands tephra layers are frequently recognized and some tephras can be identified by petrographic and chemical features and correlated to source volcanoes of both japan and korea most tephras distributed over more than several hundred kilometers from the source volcanoes were presumably carried away by the dominant westerly wind six characteristic marker tephras in deep sea sediments can be identified and correlated according to their distribution and grain size petrography and chemistry they play an important role in compiling the late quaternary chronology of the deep sea sediments distributed around the japanese islands petrographic and geochemical studies reveal that the refractive index of volcanic glass shards in tephras is controlled by the amount of total transition metal oxides rather than the amount of sio 2 we propose a new equation relating refractive index to glass shard chemistry

groundmass crystallization of mount st helens dacite 1980 1986 a tool for interpreting shallow magmatic processes the 1980 1986 eruption of mount st helens volcano provides an unprecedented opportunity to observe the evolution of a silicic magma system over a short time scale groundmass plagioclase size measurements are coupled with measured changes in matrix glass plagioclase and fe ti oxide chemistry to document increasing groundmass crystallinity and thus to better constrain proposed physical models of the post may 18 1980 magmatic reservoir measurements of plagioclase microlite and microphenocryst sizes demonstrate that relatively rapid growth approximately 10 9 cm s of groundmass plagioclase occurred immediately subsequent to may 18 relatively rapid plagioclase growth continued through the end of 1980 at an average rate of 3x10 11 cm s plagioclase growth rates then decreased to 1x10 11 cm s through 1986 changes in groundmass crystallinity are reflected in changes in both matrix glass and plagioclase microphenocryst rim chemistry although the matrix glass composition appears to have remained approximately constant from 1981 1986 after a rapid compositional change from may 18 until the end of 1980 plagioclase microphenocrysts show increasingly more complex zoning patterns with time microphenocryst core compositions are commonly positively correlated with crystal size both of these observations indicate continuous groundmass plagioclase growth through 1986 magmatic temperatures estimated from fe ti oxide pairs are approximately constant through 1981 at eruption temperatures of 930 c and at log fo2 of 10 8 by 1985 1986 oxide temperatures decreased to 870 c chemical and textural changes can be explained by 1 rapid degassing and crystallization in response to the intrusion of magma into a shallow 4 5 km reservoir toward the end of the may 18 1980 eruption 2 continued crystallization at a much reduced rate through 1986 due to slow cooling of the shallow magma reservoir growth rates and consequent chemical changes appear to decrease at the end of 1980 this is coincident with the change in eruption style from explosive eruptions sometimes followed by dome growth to solely extrusive dome building events and can be explained by the expected viscosity increase of both degassing and increasing crystallinity the model of twostage crystallization of magma in a shallow reservoir is consistent with conclusions from gas studies casadevall et al 1983 gerlach and casadevall 1986 a b patterns of crater deformation chadwkck et al 1988 and post 1980 seismicity endo et al 1990 although it does not explain the experimental data of hill and rutherford 1989 on the growth rate of amphibole reaction rims textural measurements on mount st helens dacite can also be used to evaluate crystallization kinetics in silicic magmas systems for which experimental data is almost non existent plagioclase growth rates are 5 10 times slower than estimated plagioclase growth rates in basaltic systems a result consistent with the higher viscosity of a more silicic melt furthermore patterns of textural change both average crystal size and number density are similar to those observed during the 1984 mauna loa eruption by lipman and banks 1987 suggesting that the only modification to the crystallization behavior of plagioclase required in extrapolation from basaltic systems is a moderate decrease in rates such that the rate of crystallization scales with the melt viscosity

diffusion controlled spherulite growth in obsidian inferred from h2o concentration profiles spherulites are spherical clusters of radiating crystals that occur naturally in rhyolitic obsidian the growth of spherulites requires diffusion and uptake of crystal forming components from the host rhyolite melt or glass and rejection of non crystal forming components from the crystallizing region water concentration profiles measured by synchrotron source fourier transform spectroscopy reveal that water is expelled into the surrounding matrix during spherulite growth and that it diffuses outward ahead of the advancing crystalline front we compare these profiles to models of water diffusion in rhyolite to estimate timescales for spherulite growth using a diffusion controlled growth law we find that spherulites can grow on the order of days to months at temperatures above the glass transition the diffusion controlled growth law also accounts for spherulite size distribution spherulite growth below the glass transition and why spherulitic glasses are not completely devitrified

formation of low δ18o rhyolites after caldera collapse at yellowstone wyoming usa we present a new model for the genesis of low 18o rhyolites of the yellowstone caldera based on analyses of zircons and individual quartz phenocrysts low 18o rhyolites were erupted soon after the massive caldera forming lava creek tuff eruption 602 ka 1000 km3 and contain xenocrysts of quartz and zircon inherited from precaldera rhyolites these zircons are isotopically zoned and out of equilibrium with their host low 18o melts and quartz diffusion modeling predicts that magmatic disequilibria of oxygen isotopes persists for as much as tens of thousands of years following nearly total remelting of the hydrothermally altered igneous roots of the depressed cauldron in which the alteration resistant quartz and zircon initially retained their 18o values these results link melting to caldera collapse rule out rapid or catastrophic magma meteoric water interaction and indicate wholesale melting rather than assimilation or partial melting

oxygen isotope geothermometers for metamorphic rocks the chicago mineral carbonate oxygen isotope fractionation curves have been combined with mineral water fractionation data for jadeite zoisite and rutile and new data for grossular water to provide a set of self consistent mineral pair calibrations the a coefficients in the equation 1000 in a 106t 2 of the new mineral pair fractionations are jadeite zoisite grossular rutile quartz 1 69 2 00 3 03 5 02 jadeite 0 31 1 34 3 33 zoisite 1 03 3 02 grossular 1 99 the isotopic fractionation properties of natural pyralspite garnet ca fe mg mn 3al2si3o12 can be approximated by those of the grossular end member appropriate substitutions also yield coefficients for the solid solution minerals sodic pyroxene and epidote e g aquartz sodic pyroxene 2 75 1 06xjd aquartz epidote 2 00 0 75xps where xjd and xps are the mole fractions of the jadeite and pistacite components respectively the new data set is particularly suitable for the geothermometry of metamorphic rocks 18o data from minerals of the high pressure metamorphic rocks of the sesia zone of italy and cyclades complex of greece yield well constrained mean temperatures of 572 and 478d c respectively type iii blueschist metabasalts of the franciscan formation of california give mean quartz garnet temperatures of 354d c

low δ18o rhyolites from yellowstone magmatic evolution based on analyses of zircons and individual phenocrysts the yellowstone plateau volcanic field is one of the largest centers exchange time to form zoned zircons is between a few hundred and a few thousand years which reflects the residence time of lowo of rhyolitic magmatism on earth major caldera forming eruptions are followed by unusual lowo rhyolites new oxygen isotope magmas after formation and before eruption petrologic and geochemical data from rhyolites belonging to the 2 0 my eruptive history of yellowstone are presented with emphasis on the genesis of lowo magmas erupted after the huckleberry ridge tuff 2 0 ma 2500 km and lava creek tuff 0 6 ma

mid latitude interhemispheric hydrologic seesaw over the past 550 000 years an interhemispheric hydrologic seesaw in which latitudinal migrations of the intertropical convergence zone itcz produce simultaneous wetting increased precipitation in one hemisphere and drying in the other has been discovered in some tropical and subtropical regions for instance chinese and brazilian subtropical speleothem cave formations such as stalactites and stalagmites records show opposite trends in time series of oxygen isotopes a proxy for precipitation variability at millennial to orbital timescales suggesting that hydrologic cycles were antiphased in the northerly versus southerly subtropics this tropical to subtropical hydrologic phenomenon is likely to be an initial and important climatic response to orbital forcing the impacts of such an interhemispheric hydrologic seesaw on higher latitude regions and the global climate system however are unknown here we show that the antiphasing seen in the tropical records is also present in both hemispheres of the mid latitude western pacific ocean our results are based on a new 550 000 year record of the growth frequency of speleothems from the korean peninsula which we compare to southern hemisphere equivalents the korean data are discontinuous and derived from 24 separate speleothems but still allow the identification of periods of peak speleothem growth and thus precipitation the clear hemispheric antiphasing indicates that the sphere of influence of the interhemispheric hydrologic seesaw over the past 550 000 years extended at least to the mid latitudes such as northeast asia and that orbital timescale itcz shifts can have serious effects on temperate climate systems furthermore our result implies that insolation driven itcz dynamics may provoke water vapour and vegetation feedbacks in northern mid latitude regions and could have regulated global climate conditions throughout the late quaternary ice age cycles

quaternary geology and assessment of aggregate resources of korea for the national industrial resources exploration and development abstract demand for aggregates in korea fueled by construction has increased rapidly in recent years quaternary aggregate resources are associated with holocene alluvial deposits and shallow marine sands and with fluvial sequences developed during the late quaternary soil wedge structures developed in palaeosols on river terraces indicate that periglacial conditions prevailed during oxygen isotope stages 2 and 4 along the margins of the yellow sea sea level fluctuations involved a drop to 120 m a s l during the lgm ca 15 000 yr bp resulting in the formation of three seismosequences the uppermost sequence of which contains aggregate sediments repetitive episodes of sedimentation along the major river valleys have resulted in the production of fluvial aggregates preferred by construction engineers intensive exploitation of these resources however has forced korea to turn to other quaternary deposits for aggregate

describing krotovinas a contribution to methodology and interpretation abstract filled mammal tunnels krotovinas are the most common traces in modern grassland soils and trace fossils in loess paleosols krotovinas are still insufficiently used in paleogeographic reconstructions owing to the absence of a procedure for documenting their features when their tracemaker can be identified krotovinas complement body fossil evidence for past geographic ranges of fossorial mammals moreover local palaeoenvironments can be reconstructed more precisely based on the preferred habitat of the identified species however the morphology of krotovinas has rarely been reported in detail that would allow their identification in this article we suggest five groups of diagnostic features that should be recorded and assessed for taxonomic identification of krotovinas 1 ornamentation on the burrow walls which can be observed when there is sediment compaction contrast between infill and the host material provides the most taxonomically specific features 2 infill type distinguishes between subterranean forms and other burrowers 3 tunnel repair and reburrowing patterns 4 motifs representing distinctive architectural elements shafts spirals their connections to horizontal tunnels the shape of chambers and the predominant orientation of tunnels horizontal inclined vertical 5 diameter which has to be measured transverse to each tunnel or estimated from oblique sections the measurements and observations can be compared against a reference collection of burrow plaster casts synoptic diagrams are suggested as a method for condensing images of diagnostic features from several sections we suggest that the presence of krotovinas is one criterion for distinguishing grassland paleosols from humus rich colluvial deposits

the effects of heterogeneity in magma water concentration on the development of flow banding and spherulites in rhyolitic lava abstract this study focuses on the origin of flow banded rhyolites that consist of compositionally similar darker and lighter flow bands of contrasting texture and color infrared radiation was used to obtain fourier transform infrared ftir spectra from which water concentrations were calculated and to map variations in water concentrations across zones of spherulites and glass from the 23 million year old sycamore canyon lava flow of southern arizona lighter colored thicker flow bands consist of gray glass fine grained quartz and large 1 0 to 1 5 mm spherulites darker colored thinner flow bands consist of orange glass and smaller 0 1 to 0 2 mm spherulites the centers of both large and small spherulites are occupied by either 1 a quartz or sanidine crystal 2 a granophyric intergrowth or 3 a vesicle mapping of water concentration dominantly oh in glass and oh and h2o in sanidine crystals illustrates fluctuating water availability during quenching of the host melt textures of large spherulites in the lighter gray bands in some cases indicate complex quenching histories that suggest that local water concentration controlled the generation of glass versus crystals small spherulites in darker orange bands have only one generation of radiating crystal growth both the glass surrounding spherulites and the crystals in the spherulites contain more water in the gray flow bands than in the orange flow bands flow banding in the sycamore canyon lava flow may have originated by the stretching of a magma that contained pre existing zones vesicles or proto vesicles of contrasting water concentration as the magma flowed in the conduit and on the surface variation in the original water concentration in the alternating layers is interpreted to have resulted in differences in undercooling textures in spherulites in the lighter compared to the darker flow bands

spherulites and lithophysae 200 years of investigation on high temperature crystallization domains in silica rich volcanic rocks high temperature crystallization domains htcds including spherulites and lithophysae form during cooling of silica rich lava and welded ignimbrites spherulites grow in silicate melts or hot glass and they display a radiating or microcrystalline texture typically consisting of cristobalite tridymite and sanidine lithophysae are htcds comprising one or more cavities this contribution reviews the research and discussions on htcds carried out over the last 200 years the emphasis here is on lithophysae and summarizes current knowledge of their formation a number of parameters influence the initiation and growth of lithophysae as well as their shapes and internal textures the most likely cause of cavity formation is transient tensional stress that produces a mechanical opening and widening at the interface between the crystallization front and the host melt e g where t tg cavity growth and expansion forced by rising vapor pressure is considered less important in some cases further growth of htcd cavities results from vapor phase corrosion and brecciation

the palaeoenvironment and deformation of beaconites like burrows in the old red sandstone at gortnabinna sw ireland the gortnabinna area contains a number of well preserved deformed burrows within the fluviatile old red sandstone of s ireland detailed logging of the local succession enables subdivision into four facies facies 1 represents sheet flood deposits facies 2 ephemeral stream channels facies 3 marginal sheet flood deposits and facies 4 low energy settling of fines the burrows occur in facies 1 and 4 the sediments are now folded into a large upright westward plunging anticline the fold has a well developed axial planar cleavage and is extended along strike by listric normal faults the burrows in facies 1 were originally circular and orthogonal to bedding and reveal a n s layer parallel shortening strain of 2 1 followed by a shear strain of 1 48 during folding these burrows have a bimodal distribution of diameters with peaks in the ranges 50 80 and 110 170 mm the burrows of facies 4 are sub parallel to the bedding plane and are generally curved with a maximum width of 180 mm and lengths of up to 2 3 m these burrows display passive infill following abandonment the burrows are morphologically similar though distinct from beaconites barratti which has been described from elsewhere in the old red sandstone and are tentatively interpreted as lungfish burrows

ichnology of a late pleistocene ichnofabric nebraska usa abstract the citellus zone is a regionally extensive biohorizon with abundant burrows and remains of ground squirrels spermophilus citellus and other rodents one hundred and four outcrops were evaluated to determine the stratigraphic relationship of the zone and to confirm its geographic extent citellus zone bioturbation exists over the entire 1700 km2 study area in south central nebraska and was synchronous with mid wisconsinan gilman canyon loess deposition altonian and farmdalian substages since burrow abundances are constant throughout its thickness calculations based upon maximum burrow abundance and the known digging rates of the burrowers confirm that the zone could have been produced during gilman canyon deposition in the lower part of the zone decline in burrow abundance with increasing depth in the loveland formation sangamonian and illinoian stages suggests that this unit predates burrowing thomomys sized geomyid trace fossils become proportionally less common with increasing depth consistent with the transition from fodinichnia to domichnia as spermophilus richardsonii sized spermophiline and prairie dog domichnia become more common

crystal size distribution csd in rocks and the kinetics and dynamics of crystallization ii makaopuhi lava lake crystal size distribution csd theory has been applied to drill core samples from makaopuhi lava lake kilauea volcano hawaii plagioclase and fe ti oxide size distribution spectra were measured and population densities n were calculated and analyzed using a steady state crystal population balance equation n n0 exp l g slopes on ln n versus crystal size l plots determine the parameter g a product of average crystal growth rate g and average crystal growth time the intercept is j g where j is nucleation rate known temperature depth distributions for the lava lake provide an estimate of effective growth time allowing nucleation and growth rates to be determined that are independent of any kinetic model plagioclase growth rates decrease with increasing crystallinity 9 9 5 4 10 11 cm s as do plagioclase nucleation rates 33 9 1 6 10 3 cm3 s ilmenite growth and nucleation rates also decrease with increasing crystallinity 4 9 3 4 10 10 cm s and 15 2 2 10 3 cm3 s respectively magnetite growth and nucleation rates are also estimated from the one sample collected below the magnetite liquidus g 2 9 10 10 cm s j 7 6 10 2 cm3 s moments of the population density function were used to examine the change in crystallization rates with time preliminary results suggest that total crystal volume increases approximately linearly with time after 50 crystallization a more complete set of samples is needed for material with 50 crystals to define the entire crystallization history comparisons of calculated crystallization rates with experimental data suggests that crystallization in the lava lake occurred at very small values of undercooling this interpretation is consistent with proposed thermal models of magmatic cooling where heat loss is balanced by latent heat production to maintain equilibrium cooling

engineering geomorphology of rock glaciers a partnership between geomorphology and engineering is facilitating human development in this harsh environment rock glaciers provide locations for urban water sources construction borrow sources drill sites shaft and tunnel portals ski tower supports and dam abutments rock glaciers as dynamic landforms necessitate proper identification in the field placing structures on in or adjacent to rock glaciers requires an appreciation and understanding of their temporal stability internal and surface characteristics provide important clues to the development and deformation of rock glaciers rock glaciers play a significant role in the alpine debris transport system active movement and mass wasting are perhaps the most obvious geologic hazards affecting engineered works the structure of the rock glacier is conducive to the production of a steady continuous supply of meltwater during summer months thus rock glaciers serve as alpine aquifers consideration of rock glaciers as potential aquifer sources requires caution because of the long term impact of climate change on the temporal nature of the landform from the rock glaciers that we have monitored for water quality characteristics it appears that they provide quality potable water this paper provides a foundation for appreciation and understanding of rock glaciers from an engineering geomorphologic point of view the approach taken in this paper provides practical important information to aid the engineer and engineering geologist in prudent evaluations of rock glaciers as potential sites for human development and uses the bottom line of our paper is rock glaciers must be avoided for essentially all structures

vertebrate burrows in late pleistocene paleosols at korean palaeolithic sites and their significance as a stratigraphic marker abstract a vertebrate burrow bearing layer of late pleistocene age is commonly found at many paleolithic archaeological sites in korea the burrows are straight to slightly curved in horizontal plan view and gently inclined in lateral sectional view they are interpreted as having been produced by rodent like mammals based on their size and architecture the significance of such burrow bearing layers as a characteristic stratigraphic marker unit is demonstrated by high burrow abundance consistent stratigraphic position lack of stratigraphic recurrence at these sites and widespread geographic extent three dating methods tephrochronology radiocarbon and osl dating were used to infer the age of these burrow bearing layers the dating results indicate that they were formed between ca 40 000 and 25 000 yr mis 3 2 and this suggests that this layer can be used as a stratigraphic time marker in late pleistocene paleosol sequences for this region

near liquidus growth of feldspar spherulites in trachytic melts 3d morphologies and implications in crystallization mechanisms the nucleation and growth processes of spherulitic alkali feldspar have been investigated in this study through x ray microtomography and electron backscatter diffraction ebsd data here we present the first data on shape preferred orientation spo and crystal preferred orientation cpo of alkali feldspar within spherulites the analysis of synchrotron x ray microtomography and ebsd datasets allowed us to study the morphometric characteristics of spherulites in trachytic melts in quantitative fashion highlighting the three dimensional shape preferred orientation branching of lamellae and crystal twinning providing insights about the nucleation mechanism involved in the crystallization of the spherulites the nucleation starts with a heterogeneous nucleus pre existing crystal or bubble and subsequently it evolves forming bow tie morphologies reaching radially spherulitic shapes in few hours since each lamella within spherulite is also twinned these synthetic spherulites cannot be considered as single nuclei but crystal aggregates originated by heterogeneous nucleation a twin boundary may have a lower energy than general crystal crystal boundaries and many of the twinned grains show evidence of strong local bending which combined with twin plane creates local sites for heterogeneous nucleation this study shows that the growth rates of the lamellae 10 6 10 7 cm s in spherulites are either similar or slightly higher than that for single crystals by up to one order of magnitude furthermore the highest volumetric growth rates 10 11 10 12 cm3 s show that the alkali feldspar within spherulites can grow fast reaching a volumetric size of 10 m3 in 1 s

holocene tephrochronology of the cold bay area southwest alaska peninsula abstract the major element glass geochemistry of 92 tephra samples from the southwest alaska peninsula provides the basis for establishing a holocene tephrochronology for the region electron microprobe analysis has been combined with field descriptions of samples stratigraphic relationships between tephra samples and sample localities and glass shard micro morphology to correlate these sampled distal tephra units throughout the area of cold bay and adjacent morzhovoi bay radiocarbon dating provides age constraints on correlated horizons previous research had clearly delineated only one horizon in the region the so called funk fisher ash dating to between 8425 350 and 9130 140 14 c yr bp in addition to constraining the bimodal andesitic and dacitic glass chemistry of that horizon this study has recognized six additional tephra layers in the area two horizons pre date the funk fisher ash and four are younger than it a tephra containing dacitic and andesitic components was identified in the vicinity of morzhovoi bay with a minimum age of 9300 80 14 c yr bp and a maximum age of 10 200 75 14 c yr bp a rhyolitic horizon composed of cm sized rounded pumice clasts was identified in the vicinity of cold bay it has been correlated to the ca 9500 bp eruption of roundtop volcano on unimak island the four younger tephra beds date to between 6070 340 and 3600 140 14 c yr bp the oldest of the four is rhyodacitic followed by a mixed rhyodacitic andesitic horizon another rhyodacitic horizon and finally an andesitic layer comparison of all the correlated horizons to proximal samples collected on unimak island provides conclusive geochemical evidence that the ca 9100 bp caldera forming eruption of fisher volcano is the source of the funk fisher ash correlation between the rhyodacitic tephra horizons and proximal samples from fisher volcano suggests that fisher caldera is the source of one of the rhyodacitic tephra horizons that post dates the funk fisher ash additional tephra samples from the southwest alaska peninsula and unimak island that were collected prior to this study correlate to the tephra horizons identified in the cold bay area and identify one additional horizon

crystallization kinetics of rhyolitic melts using oxygen isotope ratios crystals provide themeans to understand igneous systems but natural constraints on crystallization kinetics are rare because thermal conditions and crystallization timescales are typically unknown oxygen isotope ratios in quartz and alkali feldspar crystals in spherulites provide a natural record of the temperature interval of crystallization and crystal growth rates in rhyolitic melts oxygen isotope compositions in both phases change progressively with position from the spherulite core to rim quartz o increases from 5 0 0 3 in the core to 5 6 0 3 at the rims whereas alkali feldspar decreases from 3 7 0 4 in the core to 2 7 0 9 at the rims fractionation therefore increases from 1 3 0 7 in the cores to 2 9 1 1 at the rims oxygen isotope thermometry tracks crystallization temperature with position spherulites nucleate at 578 160 c and continue to grow until 301 88 c the in situ analyses demonstrate that spherulites self contain a record of their thermal history and that of the host lava

spherulite crystallization induces fe redox redistribution in silicic melt rhyolitic obsidians from krafla volcano iceland record the interaction between mobile hydrous species liberated during crystal growth and the reduction of ferric iron in the silicate melt we performed synchrotron ftir and xanes measurements along a transect extending from a spherulite into optically distinct colorless and brown glass zones measurements show that the colorless glass is enriched in oh groups and depleted in ferric iron while the brown glass shows the opposite relationship the color shift between brown and clear glass is sharp suggesting that the colorless glass zone was produced by a redox front that originated from the spherulite margin and moved through surrounding melt during crystallization we conclude that the most likely reducing agent is hydrogen produced by magnetite crystallization within the spherulite the krafla obsidians dramatically capture redox disequilibrium on the micoscale and highlight the importance of hydrous fluid liberation and late stage crystallization to the redox signature of glassy lavas

helical burrow casts of therapsid origin from the beaufort group permian of south africa abstract large helical burrow casts of vertebrate origin have been discovered at several localities in the lowermost strata of the teekloof formation of the beaufort group permian in the southwestern karoo basin south africa they are not only the oldest but also the first vertebrate burrows of helical geometry to be found in rocks of pre mammalian age the burrow casts are vertically disposed spiralling tubes filled with fine grained sandstone or siltstone often with a calcareous cement tube diameters gradually increase from 60 mm in the upper entrance decline through two non contacting dextral coils to about 160 mm at the base of the spiral whereupon the tube straightens and widens into a horizontal terminal chamber burrow depths range from 0 5 0 75 m and the ramp angle ranges from 10 to 32 although within any single spiral it is constant articulated skeletons of the small dicynodont diictodon have been found within the terminal chambers and spirals of three sand filled burrows linear ridges preserved on the outer walls and floor of some of the terminal chambers resemble scratch marks possibly made by the claws and beak of diictodon during burrow excavation the sedimentary sequences at two separate localities are interpreted as having been deposited by episodic sheet floods and distributary splay fans in the proximal floodbasin areas flanking an aggrading meanderbelt rise comparison is drawn between helical burrow casts in the lower beaufort and other recorded occurrences in particular daimonelix a beaver burrow from the miocene of nebraska fundamental similarities far outweigh differences to the extent that the beaufort helical burrows may be grouped with the daimonelices it is concluded that the excavation of large helical burrows an activity usually attributed to rodents was pre empted by mammal like reptiles some 50 million years before the first anatomical mammals evolved

bouldery slope landforms on mt biseul korea and implications for paleoclimate and slope evolution identification of bouldery landforms in mountains and correctly understanding their formative processes play an important role in reconstructing the geomorphic history of a region we propose that blocks were liberated by frost cracking and wedging of cliff walls during the last glacial period however we further suggest and test four hypotheses comprising different scenarios for preconditioning by chemical weathering and subsequent block transport using terrain analysis characterization of boulders and 10 be exposure dating frost shattering from the backing cliff produced the boulders since the beginning of the last glacial period 80 ka and gelifluction transported them downslope throughout the last glacial period their activity then entered a dormant phase at the beginning of the holocene distribution patterns of exposure ages of tors and block streams are similar to those of previous studies implying that bouldery landscapes in the southern korean peninsula were likely to be formed by similar processes under periglacial conditions the timing of active periods in transport of block streams corresponds well with the cold periods identified in regional and global climate proxy records interestingly the activity of block streams in the study area reached a maximum during marine oxygen isotope stage 3 to 2 when the growth rate of nearby speleothems was lowest

oxygen isotope fractionation in quartz albite anorthite and calcite laboratory measurements of equilibrium oxygen isotope fractionation in quartz albite anorthite and calcite have been carried out by anhydrous exchange between silicates and calcite at temperatures of 600 c and above exchange in these systems is as rapid as exchange between silicates and water fractionation factors can be summarized in the following equations qc 0 38 106t 2 abc 0 57 106t 2 anc 1 59 106t 2 from which the silicate pair fractionations are readily obtained these results are compared with published theoretical estimates as well as data derived from hydrothermal experiments some significant differences are found in particular it is difficult to reconcile all of the hydrothermal data either with theoretical calculations or with the present experimental data the new experiments provide an internally consistent set of fractionation factors suitable for isotopic thermometry and for test of disequilibrium in natural systems

crystal scale anatomy of a dying supervolcano an isotope and geochronology study of individual phenocrysts from voluminous rhyolites of the yellowstone caldera a voluminous 600 km3 and long lived 520 75 ka phase of rhyolitic eruptions followed collapse of the yellowstone caldera 640 ka whether these eruptions represent a dying cycle or the growth of a new magma chamber remains an important question we use new u th zircon ages and 18o values determined by ion microprobe and sanidine pb isotope ratios determined by laser ablation to investigate the genesis of voluminous post caldera rhyolites the oldest post caldera rhyolites erupted between 520 and 470 ka exhibit extreme age and oxygen isotopic heterogeneity requiring derivation from individual parcels of low 18o melts we find a progressive increase in zircon homogeneity for rhyolite eruptions from 260 to 75 ka with homogeneous low 18o zircon values of 2 7 2 8 that are in equilibrium with low 18o host melts for the majority of the youngest eruptions new sanidine pb isotope data define separate arrays for post caldera rhyolites and the caldera forming tuffs that preceded them indicating that they were not sourced from a mushy lava creek tuff batholith that remained after caldera collapse rather our new age and isotopic data indicate that the post caldera rhyolites were generated by remelting of a variety of intracaldera source rocks consisting of pre lava creek tuff volcanic and plutonic rocks and earlier erupted post lava creek tuff rhyolites batch assembly of low 18o melts starting at 260 ka resulted in progressive homogenization followed by differentiation and cooling up until the last rhyolite eruption 75 ka a trend that we interpret to be characteristic of a dying magma reservoir beneath the yellowstone caldera

timescales of spherulite crystallization in obsidian inferred from water concentration profiles we determined the kinetics of spherulite growth in obsidians from krafla volcano iceland we measured water concentration profiles around spherulites in obsidian by synchrotron fourier transform infrared spectroscopy the distribution of oh groups surrounding spherulites decreases exponentially away from the spherulite glass border reflecting expulsion of water during crystallization of an anhydrous paragenesis plagioclase sio2 clinopyroxene magnetite this pattern is controlled by a balance between the growth rate of the spherulites and the diffusivity of hydrous solute in the rhyolitic melt we modeled advective and diffusive transport of the water away from the growing spherulites by numerically solving the diffusion equation with a moving boundary numerical models fit the natural data best when a small amount of post growth diffusion is incorporated in the model comparisons between models and data constrain the average spherulite growth rates for different temperatures and highlight size dependent growth among a small population of spherulites

stable isotope thermometry at high temperatures determination of accurate temperatures for geological events has been the grail of stable isotope geochemistry since the seminal 1947 paper by urey in theory this should be simple calibrated mineral pairs are common analysis is rapid and there is no significant pressure correction however in spite of widespread application the promise of reliable thermometry has been elusive stable isotope temperatures in metamorphic and igneous rocks are often controversial is the fractionation between two phases a thermometer speedometer rate dependant hygrometer p h2o dependant or chimera a number of factors have contributed to this uncertainty including incomplete and sometimes conflicting calibration of isotope fractionation factors limited understanding of the kinetics of mineral exchange and the lack of microanalytical techniques this situation has improved dramatically over the past decade permitting reliable and detailed thermal histories to be inferred in a landmark paper bottinga and javoy 1975 empirically calibrated the oxygen isotope fractionation factors among ten rock forming minerals at t 500 c their compilation shows that 84 of analyzed samples contain at least three minerals meeting a concordance test for equilibrium they concluded the great majority of igneous and metamorphic rocks has conserved a state of oxygen isotope exchange equilibrium if correct this bodes well for thermometry however this conclusion was contested by deines 1977 who critically examined the existing data and concluded that less than half of the rocks analyzed to date would yield concordant 18o derived temperatures while seeming irreconcilable both conclusions are based on fact all rocks contain some degree of disequilibrium but many also preserve a thermometric record it is the purpose of this review to discuss the new strategies for reliable isotope thermometry and to explore disequilibrium processes so they may be recognized and properly interpreted the organization of this paper will be to discuss the assumptions