geochemical variability in distal and proximal glass from the youngest toba tuff eruption the youngest toba tuff ytt erupted at ca 74 ka is a distinctive and widespread tephra marker across south and southeast asia the climatic human and environmental consequences of the ytt eruption are widely debated although a considerable body of geochemical data is available for this unit there has not been a systematic study of the variability of the ash geochemistry intrinsic magmatic and extrinsic post depositional chemical variations bring fundamental information regarding the petrogenesis of the magma the distribution of the tephra and the interaction between the ash and the receiving environment considering the importance of the geochemistry of the ytt for stratigraphic correlations and eruptive models it is central to the ytt debate to quantify and interpret such variations here we collate all published geochemical data on the ytt glass including analyses from 67 sites described in the literature and three new samples two principal sources of chemical variation are investigated i compositional zonation of the magma reservoir and ii post depositional alteration post depositional leaching is responsible for up to ca 11 differences in na2o k2o and ca 1 differences in sio2 al2o3 ratios in ytt glass from marine sites continental tephras are 2 higher in na2o k2o and 3 higher in sio2 al2o3 with respect to the marine tephra we interpret such post depositional glass alteration as related to seawater induced alkali migration in marine environments crystal fractionation and consequential magmatic differentiation which produced order of magnitude variations in trace element concentrations reported in the literature also produced major element differences in the ytt glass feo al2o3 ratios vary by about 50 which is analytically significant these variations represent magmatic fractionation involving fe bearing phases we also compared major element concentrations in ytt and oldest toba tuff ott ash samples to identify potential compositional differences that could constrain the stratigraphic identity of the morgaon ash western india no differences between the ott and ytt samples were observed

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

high resolution record of climate stability in france during the last interglacial period the last interglacial period 127 110 kyr ago has been considered to be an analogue to the present interglacial period the holocene which may help us to understand present climate evolution but whereas holocene climate has been essentially stable in europe variability in climate during the last interglacial period has remained unresolved because climate reconstructions from ice cores1 2 continental records3 4 and marine sediment cores5 6 give conflicting results for this period7 here we present a high resolution multi proxy lacustrine record of climate change during the last interglacial period based on oxygen isotopes in diatom silica diatom assemblages and pollen climate transfer functions from the ribains maar in france contrary to a previous study8 our data do not show a cold event interrupting the warm interglacial climate instead we find an early temperature maximum with a transition to a colder climate about halfway through the sequence the end of the interglacial period is clearly marked by an abrupt change in all proxy records our study confirms that in southwestern europe the last interglacial period was a time of climatic stability and is therefore still likely to represent a useful analogue for the present climate

pollen taphonomy of cave sediments what does the pollen record in caves tell us about external environments and how do we assess its reliability cave sediments may contain important long term records of past environments and human activity pollen provides key evidence since it disperses widely and is relatively durable we still know relatively little about the dispersal of pollen into caves and its preservation within cave sediments compared with our relatively detailed knowledge of pollen taphonomy in other sedimentary environments pollen taphonomy in caves is dependent on a variety of transport pathways and seems to be very contingent on local circumstance the airfall component of cave pollen assemblages often seems comparable with airfall spectra in the landscape outside the cave but bees birds and bats may transport considerable quantities of pollen into caves and the entrance flora may also be significant cave sediments are rarely waterlogged and pollen within them can be subject tomicrobial and chemical degradation sedimentation in caves is often episodic with episodes of storage and deposition sometimes redeposition of sediment which means that biostratinomic preservational factors become very significant comparison with sequences outside caves is difficult because few caves are found in landscapes where there are comparable pollen records from lakes and bogs here we review the factors affecting cave pollen taphonomy and hence the reliability of palynological analysis of sediments from caves with suggestions for future investigation

properties weathering and classification of some soils formed in peralkaline volcanic ash in kenya abstract physical chemical and mineralogical properties were determined for six profiles in and west of the great rift valley in kenya data include morphology information on gross composition of horizons organic carbon cation exchange capacities extractable cations etc and detailed characterization of the clay fractions by means of transmission electron microscopy x ray diffraction infrared spectroscopy and additional techniques the three least weathered profiles nos 1 3 of table i have morphologies typical of andepts but lack certain other characteristics common to such soils their clay fractions were largely amorphous to x rays and consisted mainly of poorly ordered siliceous feoxides with virtually no allophane all of the clays contained halloysite the peralkaline nature of the ash parent material seems responsible for the clay mineralogy of the soils which differs from that generally found in andepts the high proportions of iron in the amorphous materials depart from the composition widely reported for such soils one distinctive feature was the presence of pantelleritic trachyte found in ash from a number of sites in addition to those of the profiles how the six profiles may best be classified is an open question none of the profiles qualifies as andept nor would they be included in the proposed order of andisols as presently defined modifications of the definition of andisols so as to include some of these soils would seem desirable

quantification of weathering processes in an acid brown soil developed from tuff beaujolais france part ii soil formation abstract mineralogy and chemical properties of the fine earth and particle size fractions were examined with total chemical analysis selective chemical analyses and x ray diffraction clay minerals were investigated using microprobe and transmission electron microscopy the chemical changes during soil formation were calculated from results of the chemical weathering mass balance the study soil is of the brown acid type unsaturated and poor in short range ordered products all soil fractions sized between 0 and 1 cm originate from transformation of the weathered rind developed around tuff stones where chemical weathering is intense the same weathering reactions which were initiated in the early stages of tuff weathered rind were continued in the soil with strong dissolution of plagioclases and transformation of biotite two chemical weathering reactions led to the formation of clay minerals in the soil the precipitation of kaolinite into biotite pseudomorphs and into the small white mica and the transformation of the biotite bi into hydroxy interlayered vermiculite hiv with intermediary stages shown in hiv bi interstratified minerals which were defined 95 75 of biotite layers pure vermiculite or v bi interstratified minerals were hydoxy interlayered even in the weathered rind of the tuff the chemical and mineralogical mass balance between the weathered rind and the soil shows a heavy dissolution of andesine 90 and to a lesser extent of albite 55 and of apatite 60 a precipitation of kaolinite and a transformation of biotite into hiv the plagioclase dissolution in weathered tuff was almost complete while there were only traces remaining in silt the biotite has almost disappeared in the fine earth fractions due to dissolution and transformation into hiv

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

palynological analysis of the late early pleistocene sediments from queque cave in guangxi south china abstract palynomorphs extracted from the sediments in queque cave of the late early pleistocene in chongzuo guangxi zhuang autonomous region were investigated to reconstruct the paleoenvironment in the study area while the sediments are pollen poor they are sufficiently productive to carry out a paleoenvironmental analysis the source vegetation reflected by the palynomorphs from the unfossiliferous layer was temperate to warm temperate deciduous and evergreen broadleaved forest while it was warm temperate to subtropical deciduous and evergreen broadleaved forest from the mammalian horizons climatic parameters obtained using the coexistence approach indicate that the unfossiliferous layer mat 11 3 15 4 c map 601 1 1076 1 mm was cooler and drier than that from the mammal bearing layers mat 12 6 18 6 c map 784 7 1523 1 mm

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

heat exchanges in the heterothermic zone of a karst system monlesi cave swiss jura mountains 1 subsurface ice accumulations in temperate karst environments are assumed to be highly sensitive to external climate forcing and therefore represent a favorable setting for studying processes controlling heat exchanges in the heterothermic zone of a karst system air rock water and ice temperatures were measured and complemented by airflow water discharge and cave air humidity data during a case study carried out between 2001 and 2006 at monlesi ice cave in the swiss jura mountains the energy balance of the system could be quantified for an annual cycle and results demonstrate that forced convection which is controlled by the temperature difference between the cave air and the external atmosphere is a driving force for the heat exchange between the cave and the surrounding environment therefore compared to the external mean annual conditions major thermal anomalies are to be expected in the entrance zone of a cave system since this heterothermic zone may extend over several hundreds of meters a better understanding of the mechanisms controlling the subsurface deposition environment represents a major prerequisite for high resolution paleoenvironmental reconstructions from cave deposits

lago grande di monticchio southern italy a long record of environmental change illustrated by sediment geochemistry abstract bulk geochemical analysis has been carried out on a 51 m sediment core from lago grande di monticchio in southern italy the record which may extend from the present back through more than one glacial cycle displays major variations in indicators of palaeoproductivity such as organic carbon and biogenic silica the most prominent change occurs at the holocene boundary lower in the sequence zones of moderately enhanced productivity highlight either interstadial or interglacial periods c n ratios and hydrogen indices provide possible indications of the sources and diagenetic state of the bulk organic matter but must be interpreted carefully as it is difficult to isolate the effects of these two factors changes in the clastic fraction e g na al ratio suggest that tephra deposition in the lake and its catchment has significantly altered the sedimentation this may also have influenced the biological productivity of the system

characterization functioning and classification of two volcanic soil profiles under different land uses in central mexico volcanic soils constitute an important resource for agriculture and forestry in central mexico as well as in various world regions they exhibit unique properties and high productive potential related to the amorphous materials they contain the relationship between amorphous materials soil characteristic and functioning has not been well studied the objectives of the present work were to assess the influence of land use agricultural and forest topography and other soil forming factors on physical chemical and mineralogical characteristics and pedological processes responsible for soil genesis and soil classification of two volcanic soil profiles derived from andesitic parent material located 150 m away from each other within the same toposequences the toposequence is located in the trans mexican volcanic belt tmvb a highly populated region of central mexico that provides part of the water for mexico city megapolis a series of field and laboratory techniques including physical chemical micromorphological x ray diffraction xrd transmission electron microscopy tem infra red analysis mossbauer spectroscopy were used the main factor affecting the present morphology of the soil profiles was the topography the mineralogical features of the upper layers of the maize profile pachic andosol indicate redistribution of soil material from the upper part of the toposequence the land use change favored this redistribution deeper horizons of this profile were developed from volcanic ashes deposited in situ hematite and ferrihydrite considered markers of evolution in redistributed soil material were observed in this profile associated with allophane the presence of hematite has been reported for the first time in mexican andosols the present characteristics of the forest profile dystric cambisol are mainly due to the pedological process of the volcanic ash layers remaining in situ after the redistribution and volcanic breccia it was concluded that the forest profile evolved from an andosol to an inceptisol which was evidenced by desaturation loss of silica and organic carbon in this profile the fe minerals were associated with the presence of gibbsite and halloysite the position in the toposequence and the physical and chemical characteristics of these profiles define their present functioning such as losses by erosion and c dynamics

quantification of weathering processes in an acid brown soil developed from tuff beaujolais france the petrographical and mineralogical composition of tuff in the studied area was determined by optical microscopy x ray analysis bulk chemical analysis and mean chemical composition of each mineral obtained from the electron microprobe the tuff stones sampled on the surface and in the pits of soil are usually surrounded by a bleached rind from the results of chemical weathering mass balance isovolumetric calculations the chemical and mineralogical transformation are quantified during the formation of this weathered rind this tuff from the upper visean was composed of about 45 5 phenocrysts quartz andesine albite and biotite and about 55 5 devitrified groundmass spherolites quartz k feldspar albite andesine and biotite this series was a broad monotonous series although some facies diversity occurred i e colour and density of plagioclase phenocrysts evidence of fluidality a local heterogeneity in the tuff mineralogy and a variation in its chemical composition k2o cao na2o and loss on ignition have been induced by devitrification of the groundmass and hydrothermal alteration the contact metamorphism seemed to have caused the groundmass devitrification and recrystallization of biotite phenocrysts as small biotite crystals 0 1 mm hydrothermal alteration has led to biotite chloritization transformation of plagioclase albite and andesine into white mica and k feldspar and a few veins quartz chlorite epidote in the montagne des aiguillettes tuff weathering appeared as a thin bleached rind around all stones the weathering gradient inside rinds corresponded to a progressive dissolution of tuff minerals quartz k feldspar white mica biotite albite apatite andesine the weathering processes were characterized by a strong dissolution of plagioclases and apatite increase of voids by about 12 and to a lesser extent by the transformation of micas biotite into hydroxy interlayered vermiculite hiv and mica hiv mixed layer minerals and by kaolinite ka precipitation the results of the petrographical study were consistent with the calculated mass balance the weight losses were about 18 and corresponded to a strong exportation of cao na2o sr p2o5 al2o3 and sio2 74 62 51 42 17 and 25 respectively and an increase in the water content eighty two percent of andesine 41 of apatite 40 of albite and biotite 3 were dissolved the increase in the total water content corresponded to the formation of hydrated weathered minerals 2 6 of hiv and 4 3 of ka

the airfall pollen budget of archaeologically important caves creswell crags england this paper investigates fundamental taphonomic issues for palynologists working on archaeologically important cave deposits the extent to which the pollen and spores reaching the accumulating sediment surfaces reflect the vegetation in cave entrances or reflect the more regional environments beyond the caves the study sites were four adjacent caves at creswell crags near sheffield england church hole dog hole c7 and robin hood s cave the compositions of the pollen and spore assemblages caught in the caves over a one year period were shown to reflect the vegetation in the cave mouths and the wider area beyond the ap nap ratio in the assemblages trapped in the caves corresponded with the proportions of woodland and open ground within a 5 km radius of the site comparatively high representations of fern spores in caves were a persistent feature and were attributed to the interactions of habitat distribution and taphonomic processes i the abundance of ferns in cave mouths and ii the effects produced by a combination of diurnal micro climatological process interacting with diurnal variations in spore production in the cave entrance in two caves church hole cave and dog hole cave the numbers of grains caught appeared to decline with increasing distance into the cave in cave c7 the numbers of grains caught increased towards the back of the cave the number of grains caught appears to be a principal determinant of the number of plant taxa identified there were no clear relationships between the presence of a flue effect in the cave and the presence of an increase or a decrease in the number of grains caught with changing distance into the caves it is concluded that as long as account is taken of the particular topographic microclimatic and taphonomic conditions in these caves it is possible to infer the character of the vegetation beyond their confines from the airfall pollen and spores trapped with them at the cave sediment surface

evidence for a changing martian climate from the mineralogy at mawrth vallis abstract layered outcrops in the mawrth vallis region of mars contain the greatest diversity of aqueous alteration products on the planet and these materials are used to infer past aqueous environments orbital investigations indicate al si rich clay bearing units overly an fe mg smectite rich unit many different secondary minerals have been identified in the upper al si rich clay units but the presence of poorly crystalline phases has not been previously investigated identification of 10 30 allophane and imogolite in the clay bearing units resolves previous mineralogical discrepancies between tes and crism of clay bearing units on mars we demonstrate here that the poorly crystalline aluminosilicates allophane and imogolite comprise a significant portion of the uppermost stratum of the al si clay rich units these phases are unique to immature soils derived from volcanic ash in well drained mildly acidic environments on earth and we hypothesize that the deposits discovered here originate from supervolcanic activity in nearby arabia terra the transition through time from smectite bearing units to the uppermost allophane imogolite unit in mawrth vallis signifies a change in climate from a warm and wet environment to one where water was sporadic and likely depleted rapidly

human behavioral responses to the 8 2 ka bp climatic event archaeological evidence from the zhongshandong cave site in bubing basin guangxi southern china abstract as one of the most pronounced climatic episodes during the holocene the impact of the 8 2 ka bp cooling event was felt throughout the northern hemisphere however human behavioral responses to this climatic episode has only recently begun to be documented in different areas of the world southern china is one region where these human behavioral responses have yet to be clearly identified here we present a recent discovery of stone artifacts from the zhongshandong zsd cave site which is located in bubing basin guangxi zhuang autonomous region southern china the cultural deposits within zsd have been tentatively dated to the 8 2 ka bp cooling event the zsd cave is a narrow low ceiling cave about 60 m in length sixty one stone artifacts were surface collected in the extremely dark terminal chamber in the back of the cave one stone artifact was found in situ in the same area of the cave the overlying stalagmite was u series dated to 8130 430 years bp and charcoal found below the artifact was ams dated to 8242 54 years bp the stone artifact assemblage is comprised of cores flakes choppers and scrapers produced on locally available river cobbles an artifact collection normally assigned to the eastern asian early paleolithic charcoal fragments are abundant in the cultural layer implying that fire was possibly used for lighting and or warmth interestingly given the dimensions of the inner chamber and the fact that the cultural deposits sit about 60 m inside the cave this would not be considered a typical area that would be suitable for long term human occupation although other possibilities may exist one possible explanation may be that due to the cold winter and or harsh environment during the 8 2 ka bp climatic event these hunter gatherers were forced deeper inside the cave to set up their temporary campsite this is a hypothesis that needs further testing

the weathering of basaltic rocks in burundi and vietnam abstract various stages of tropical weathering are described using a number of examples of red soil formation derived from rift basalts in burundi and laterite bauxites from plateau basalts of south vietnam the phenomena of decomposition of primary minerals are comparable in the two regions fine grained montmorillonites kaolinites halloysites and hematite were formed during an initial stage of weathering the two generations of kaolinites goethites and gibbsites are the main products of a more intense stage of weathering the gradients of chemical activities in the micro environment surfaces of grains pores microfissures seem to be the controlling factors of weathering

characterisation of andosols from laacher see tephra by wet chemical and spectroscopic techniques ftir 27al 29si nmr abstract at 12 900 a bp the eruption of the laacher see volcano generated a new parent material for holocene soil formation in parts of western germany weathering of these ashes commonly includes the formation of poorly crystalline minerals such as allophane imogolite and ferrihydrite detection of these minerals in soil is difficult yet an important task because they may govern soil functions and processes e g stabilisation of organic matter and nutrient availability therefore we characterised three forested andosols by a combination of wet chemical and spectroscopic techniques including infrared and 27 al 29 si nuclear magnetic resonance nmr spectroscopy together with x ray diffractometry deconvoluting the 29 si nmr spectra revealed that 1 6 to 10 4 of total si was present as allophanic compounds which coincided with the amounts of oxalate extractable si since extraction methods are not completely selective we observed a slight overestimation of allophanic si estimated from oxalate extraction although the sites under study are located close to each other in similar relief positions and with similar vegetation the combination of our results revealed varying amounts of loess in the parent materials and varying weathering intensity high weathering intensities correlate with the amounts of allophane

minerals formed and mineral formation from volcanic ash by weathering abstract weathering of volcanic ash and pumice is unique regarding minerals formed and mineral formation these minerals include allophane imogolite opaline silica and some halloysites and have distinctive structures and properties studies on the surface and subsurface weathering of various volcanic ashes in different settings are reviewed this review illustrates that relatively rapid weathering of finely comminuted volcanic ash well reflects the effects of climate vegetation and time and produces various combinations of weathering products the moisture regime the nature and amount of organic matter incorporated the deposition of volcanic ash as overburden and the chemical and mineralogical composition of parent ash are important in controlling the mineral formation in weathered volcanic ash

mineralogical and chemical composition of three tuffs from northern israel abstract the mineralogical and chemical composition of three types black yellow and red of tuffs from mt peres in northern israel that differ in terms of degree of weathering were determined in order to understand the weathering sequence under mediterranean or semi arid conditions the black tuff is very slightly weathered and contains 62 volcanic glass 15 primary minerals 12 titano magnetite 5 halloysite and 4 5 hydroxyapatite the yellow tuff considered to be the weathering product of the black tuff contains only 4 volcanic glass and 21 primary minerals 8 fe rich minerals 51 amorphous material identified as halloysite like allophane 15 halloysite and 5 hydroxyapatite a different mineralogical composition from that of red tuff indicates that this material was formed during a different eruption the red tuff consisted of 29 volcanic glass 26 primary minerals different from those of the black tuff 11 iron bearing minerals 10 halloysite 5 hydroxyapatite and 19 amorphous material the specific surface area and cation exchange capacity of the black red and yellow tuff 7 28 174 m2 g 1 and 107 285 601 mmolc kg 1 at ph 7 respectively were in accord with their amorphous material contents

direct measurement of contact area and stress dependence of anisotropic flow through rock fracture with heterogeneous aperture distribution abstract direct measurement of a contact area using pressure sensitive film was performed for artificially generated granite tensile fractures with different shear displacements of 2 3 and 5 mm and at various normal stresses of up to approximately 100 mpa to clarify the relationship between anisotropic flow and normal stress in a rock fracture with shear displacement aperture distributions with contact areas were then numerically generated using fracture surface geometry data and anisotropic flow was evaluated through a bi directional flow simulation the directional distributions of contacting asperities in the fracture plane were clearly observed for every given condition and the contacting asperities tended to align in the direction perpendicular to shear displacement generally the contact area increased and the anisotropic distribution was enhanced with increasing normal stress however the contact areas for 3 mm shear displacement were less stress dependent anisotropic flow with higher permeability in the perpendicular direction was always observed for aperture distributions with an anisotropic distribution of the contacting asperities flow paths created in the aperture distributions seemed less tortuous in the perpendicular direction due to the distribution of the contacting asperities the anisotropic flow was enhanced with increasing normal stress to the fracture and was more evident for the smaller shear displacements of 2 mm due to the high sensitivity of the contact area to the normal stress the results suggested that the anisotropic flow was likely for a wide range of normal stresses and correspondingly at varying depths in the earth s crust at which anisotropic flow was enhanced with increasing normal stress based on the stress dependence of the contact area in addition the stress dependent anisotropic flow is expected for much higher normal stresses because complete fracture closure with 100 contact area may be unexpected under the crustal stress conditions at depths of several to ten thousand meters

permeability anisotropy induced by the shear displacement of rough fracture walls 1 the permeability anisotropy that results from a shear displacement between the complementary self affine walls of a rough fracture is investigated experiments in which a dyed fluid radially injected into a transparent fracture displaces a transparent one are presented a clear anisotropy is observed in the presence of shear displacements and allows us to estimate the ratio of the permeabilities for flows parallel and perpendicular to a simple model which accounts for the development of channels perpendicular to qualitatively explains these results and predicts a permeability decreasing increasing linearly with the variance of the aperture field for flow parallel perpendicular to the shear displacement these predictions are then compared to the results of numerical simulations performed using a lattice boltzmann technique and to the anisotropies measured in displacement experiments

pollen taphonomy and airfall sedimentation in a tropical cave the west mouth of the great cave of niah in sarawak malaysian borneo abstract this paper investigates the taphonomy of predominantly biogenic sediments and pollen in the key archaeological site in the west mouth of the great cave of niah sarawak strong spatial patterning of sediments and pollen were found with a zonation related to distance into the cave near the cave mouth sedimentation is silty and derived from waters running down the cliff outside the cave with leaves from external vegetation pollen assemblages are similar to forest floor samples outside the cave and thus are of airfall or wash origin in the interior of the west mouth sedimentation is highly organic and composed largely of bird droppings pollen assemblages in the interior are strongly but regularly biased with over representation of mangrove and riverine taxa resulting from the recruitment of pollen by bats and swiftlets foraging preferentially in these zones over 7 and over 2 km from the cave respectively the significance of these findings for the understanding of humid tropical cave sequences and particularly for the current reassessment of niah cave is discussed

a palaeoecological study in the western mediterranean area the upper pleistocene pollen record from cova beneito alicante spain abstract results are presented of palynological analyses of pleistocene deposits at cova beneito an archaeological site on the southern slopes of the sierra de benicadell alicante province se spain 650 m a s l with a wsw orientation the chronology is supported by radiocarbon dating archaeological evolution previous local sequences and recourse to several wider correlations for the first time in the region a warming event is defined in the mid last glacial stage during this event vegetation took on a mediterranean character with sclerophyllous elements such as quercus olea phillyrea rhamnus helianthemum etc the rest of the sequence shows a predominance of pinus within the ap phases of steppe like character and an aridity crisis immediately after the climate improvement due to local conditions forest cover was never very great

towards a weathering model of mount lamington ash papua new guinea abstract the mount lamington ash halo has been studied at six sites both close to and distant from the volcano negligible alumina occurs in the seepage waters from the ash and so alumina is assumed constant during weathering in andesitic ashes weathering to allophane an approximation to a first order reaction was found in 1968 and is confirmed here with given infiltration and silica concentration the weathering rate constant decreases with increasing content of weathering minerals and increasing thickness of ash being weathered the rate constant also increased with increasing infiltration and decreasing median size of the ash the total weathering rate is the product of the thickness percentage of ash being weathered and the weathering rate constant the total weathering rate is the same for thick less weathered proximal ashes as it is for the thin more weathered distal ashes first order kinetics imply a high rate of leaching decreasing with time but continual burial under new ash at a nearly constant rate leads to linear leaching of the upper part of the profile the leaching rate decreases exponentially with depth and appears to ignore buried topsoil barriers it is possible to construct weathering models exploring the rate constant and to link it with leaching rates two thirds of the loss on weathering is silica and there is a total leaching rate of 3 4 mg sio 2 cm 2 year 1 as on basalt in hawaii and on andesite in st vincent water analyses show silica concentrations in the ash of 17 35 ppm and in draining streamlets of 9 20 ppm measured concentrations agree with calculated concentrations from the weathering data silica concentrations are similar in other humid tropical rivers

weathering sequence of soils from volcanic ash involving allophane and halloysite new zealand abstract the clay minerals in a series of soils from rhyolitic ash having the same stratigraphy but different leaching environments were estimated quantitatively by oxalate dissolution infrared spectroscopy differential thermal analysis electron microscopy and x ray diffraction three soils were studied in detail these were the kereone soil mean annual rainfall 1200 mm the ohaupo soil 1400 mm and the mairoa soil 2600 mm the kereone soil contained halloysite as the predominant clay mineral whereas the mairoa soil was mainly allophanic the ohaupo soil contained considerable amounts of both allophane and halloysite thus the allophane content of the soils increased as rainfall increased reflecting a sequence of increased l leaching the si concentration in soil solution decreased as rainfall increased also reflecting increasing leaching of the soils at mairoa si is rapidly removed and allophane al si 2 1 with monomeric silicate is formed whereas at kereone less leaching occurs si levels are higher and halloysite al si 1 1 with polymeric silicate is formed at intermediate sites either allophane or halloysite may form the often reported situation of younger allophanic beds overlying older 10 000 year halloysitic beds may not be due to allophane weathering to halloysite but may result from lower temperature and drier climate during the last glacial maximum between 10 000 and 26 000 years before present bp a new weathering scheme for volcanic ash in new zealand is presented

quantitative pollen based climate reconstruction in central japan application to surface and late quaternary spectra abstract climate reconstruction in japan by the best modern analogues method was tested with 285 surface pollen spectra and then applied to the 47 000 years pollen profile from lake mikata central japan both pollen taxa percentages and plant functional type affinity scores were used in the reconstruction of six climate variables the reconstructed values were compared with the estimated modern climate at each surface pollen site in order to evaluate the accuracy of the pollen based reconstruction the reconstruction of thermal parameters is very reliable correlation coefficient r between 0 86 and 0 89 the reconstruction of annual precipitation is less accurate r 0 7 we also proposed a new technique to calibrate reconstructed values into both probability distribution and or confidence regions of observed values the specialized programs for this calibration polcalib and polhist are available at qsr website http www elsevier nl locate quascirev the reconstruction of the late quaternary climate changes around lake mikata shows that the summer and winter temperatures were 5 c lower than present around 40 uncal kyr bp reached a minimum around 20 uncal kyr bp 10 c lower than present and became similar to present day at 8 uncal kyr bp the estimates for annual precipitation show that it was driest around 20 uncal kyr bp

mineralogy and weathering processes in recent and holocene tephra deposits of the pacific northwest usa abstract weathering and evolution of minerals in tephra deposits in the cascade range of washington state usa are influenced by climate vegetation time microtopography and in the vicinity of mt st helens naturally acidic precipitation we have observed the interaction of these factors in spodosols developed on holocene tephra in the central cascades and in entisols formed on the 1980 pyroclastic flow of mt st helens weathering regimens in these tephritic soils can be qualitatively characterized by the soil solution composition weathering reactions in the spodosol are driven by organic acids in the upper soil horizons and by carbonic acid in the lower b and c horizons the mineral assemblage in the spodosol reflects in part the chemical regimen dictated by each proton donor the presence of smectite in the highly acidic e horizon ph